Sensor System

Environmental monitoring system based on semi-conductor oxides thick film sensor

Development of an electronic nose for qualitycontrol in dairy products and other foods usingsemiconductor thin films

Research and development of an electronic nose,devoted to food analysis, based on mass and con-ductivity transduction of tetrapyrrolics macro-cycles: langmuir-blodgett deposition and sensorcharacterization

Devolopment of an artificial olfactory systemwith conducting polymer sensors for environ-mental applications

Electronics for sensor

Integrated electronics for sensor

Circuit architectures, design and characteriza-tion of integraded lock-in amplifiers foe sensorsapplications

Chemical sensor and biosensors

Oxygen sensors

Biosensors to monitor enzymatic activity pesti-cide and radical dependent

Solid state electrochemical sensor for indoor de-tection of CO (Icames)

Organometallic polyne polymers and relatedcomplexes for chemical sensors

Guided wave sensors for analysing liquids by meansof direct spectroscopy and for gas monitoring bymeans of chemically-assisted spectroscopy

Detection of ozone, nitrogen dioxide and clorineoxidizing gases by metal oxide sensors

Physico-chemical microsensors

Diagnostic microsensor by electrochemilumi-nescent detection

Screen-printed disposable sensors for heavy met-al detection

Physical sensors

Development of low cost pyroelectric matrix sen-sors for ir/uv measurements in production and en-viromental control

Design and development of a piezoresistive pres-sure sensor on micromachined silicon for hightemperature application and of the signal con-ditioning electronics

Ir smart sensor and automatically controlled rfapplicator for hyperthermia therapy

Development of an imaging system for the qual-ity control of materials/manufactures based up-on an array of x-ray detector

Interferormetric fringe relief in dental elements

Sensor for position measurements in industrialenvironment

A silicon microfabricated electrostatic transducer

Two-dimensional image sensor in amorphousand polycristalline silicon technology

Integrated photon counting modules

Microsensors for the detection of thermo-hy-grometric comfort conditions

All-silicon temperature microsensor with fiberoptic communication channel

Micromachined silicon gyroscope

Algorithm and digital electronics for high preci-sion load cell

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SUBPROJECT 6Sensors

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This subproject Sensors describes the first year researchactivity in the field of Sensors, Microsystems and InterfaceElectronics (SMIE), developed on behalf of about 29 Re-search Groups, spread all over Italy and related to Industries,Academic Institutions and National Research Council lab-oratories.

SMIE research responsibility is particularly felt in Italyeven if totally dedicated laboratories in this field are not yetpresent.This is due to the SMIE market growth, which in-dicates the success of innovative products and suggest theopportunity of a promising research in the field. The sci-entific validity of most of the research lines carried out inthis subproject concerns the following points:

a) the strong interdisciplinary character of the researchactivity based on the knowledge of Solid State Physics, Ma-terial sciences, Chemistry, Biology and Electronics;

b) the possibility to open new strategies in the field ofCAD tools;

c) the availability of technology induced by the huge de-velopment of the microelectronics, and of advanced diag-nostic tools.

On this basis a strong research effort was done in thelast year, and the following contributions represent the in-termediate results so far obtained, while they indicate in thesame time, the research directions of the next two years.

A look over the entire subproject allows the detection ofrather interesting results related to physical, chemical andbiochemical sensors, to sensors systems, to microsystems andalso to interface electronics. Examples, among others of sim-ilar value, are the integrated accelerometer sensors, the pres-sure sensors based on diamond, the room temperature in-frared sensor bolometer matrix, the electrostatic stansduc-ers, varieties of electronic noses, image sensors, polymer sen-sors, biosensors, integrated look-in amplifier and interfaceelectronics.

We are expecting from the subproject a varieties of newproducts even if not all of them will have chance to enterthe market and have the capability to meet scientific reso-nance.

Nevertheless the global effort in the SMIE field will cer-tainly generate new ideas for new products which could beutilized in the context of future needs.

Arnaldo D’AmicoSubproject 6 coordinator

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Introduction

Purpose of the work

The aim of the being proposed project is implementa-tion of a cheap and low-power-consuming air-monitoringsystem based on an array of sensors manufactured by thick-film printing technology [1].

The demonstrator is expected to detect gas concentra-tions of interest within the following ranges:

It must be highlighted that it is our purpose to evaluatethe thick -film printing technology onto silicon support af-ter micromachining treatment.

Outline of the work

The proposal is devoted to the development of an air-monitoring demonstrator based on an array of sensors man-ufactured by thick film printing technology. The activitiescan be summarised in the following steps:1. Preparation by several methods of nanosized powders from

semiconductor oxides like In2O3, WO3, MoO3, PdO bothpure and mixed to SnO2 and TiO2. Perovskite-type nano-sized powders of the series LnMO3, where Ln = RareEarths and M = Fe, Co will be prepared too.

2. Manufacturing of printable pastes.3. Physical-chemical characterisation of powders, pastes and

sensing layers.4. Preparation of miniaturised supports implemented with

heater, electrodes and a second resistor to keep constantthe operating temperature of the sensors.

5. Manufacturing of structurally-stable and reproduciblesensors by optimising the sintering process.

6. Electrical characterisation of the sensors at appropriate

temperature and humidity, in both the d.c. and a.c. op-erating voltage. The array as a whole will be characterisedtoo.

7. Development of an appropriate software to easily man-age the array outputs.

8. Calibration of each sensor and the array by convention-al equipment in the range of concentrations of interest.

9. Engineering development of the demonstrator.

Main results

We obtained SnO2 and MoOx-SnO2 powders showingnanosized and very regular shaped particles. The SnO2 pow-ders were prepared via a sol gel route [2]. By subsequent cal-cination up to 550 oC a micro-crystalline material was ob-tained, named SN(550). Two Mo-added materials (Mo:Sn-1.99 and MoSn-5.95) were prepared by impregnation of theSN(550) powder with acqueous solutions of ammoniumheptamolibdate and dried at 120 oC. Thick films of nanos-tructured TiO2 and tantalum-doped TiO2 have been fabri-cated by screen-printing technology starting from pure ti-tania and tantalum-doped titania powders prepared by sol-gel method [3]. The titania powders show crystalline anatasestructure and the particles are homogeneous and nanosized(30-50 nm). The sensors have been printed starting fromminiaturized laser pre-cut 96% alumina substrates (2.5 x2.5 mm2 and 0.25 mm thick for each device) provided witha heater element on the backside, a Pt-100 resistor for con-trolling the sensor operating temperature and a gold frontinterdigitated contacts. The thick films were prepared start-ing from pastes obtained by adding to the oxide powders anorganic vehicle together with a small percentage of glass frittfor improving the adhesion to substrates [4]. The films werethen fired for 1 h at the temperatures of 650 °C and 850°C.HRTEM and SEM observations have been pursued for struc-tural characterisation. Both these and electrical characteri-sations showed that the firing temperature strongly influ-ence the nanostructure [5] and the gas response of the puretitania samples. The addition of tantalum inhibits the grainsintering at the higher temperature. Moreover the electricaldata show that the tantalum addition (10 % at) doesn’t af-

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Environmental monitoring system based onsemiconductor oxides thick film sensors

Università di Ferrara, Universita` di Torino,Università Tor Vergata - Roma, C.N.R. - I.E.S.S., ORION s.r.l.

compound concentration range sensitivitySO2 0 - 200 ppb few ppbNO2 0 - 500 ppb few ppbCO 0 - 100 ppm 1 ppmO3 0 - 1 ppm few ppbC6H6 0 - 1 ppm few ppb

fect the conductance of the films in air while significantlyenhances the response towards CO and leaves almost unal-tered or enhances its ability to sense NO2 depending on thethermal treatments [6]. Ceramic thin film of TiO2-Al2O3

in different rating have been prepared, with and without al-kaline ions, for humidity sensor use. When K was added at10% at, during the sol-gel preparation, we observed a greatimprovement in the answer towards humidity, though thefilms were poreless. This improvement is attributed to a newmechanism of detection, which consists in the direct in-volvement of alkali ions in the charge carrying, exalted byhumidity [7].

Some results on SnO2 are reported in Fig.1,Fig.2 and Fig.3:

Some results about TiO2 structural and electrical char-acterisation are reported in Fig.4,5,6,7 and 8.

Future development

1. Individuation of the methodologies of screen printingpaste preparation and of the sensitive layers based on dif-ferent semiconductor oxides prepared by the OperationalUnits involved.

2. Individuation of the more suitable semiconductor oxidesfor each one of the gases in question.

3. Definition of a measurement protocol in co-operationwith the other Operational Units.

4. Deposition of the films through screen printing techniqueon micro-operated silicon bbsubstrates, to be preparedby the Operational Unit of IESS.

SUBPROJECT 6

Fig.1 HRTEM micrography of SnO2 sol gel powder

Fig.2 Pure and MO doped SnO2 answers to to different con-centration of NO

Fig 5 SEM micrography of TiO2 fired at 850 oC.

Fig.4 SEM micrography of TiO2 fired at 650

Fig.3 Pure and MO doped SnO2 answers bdifferent concen-tration of CO. to different concentration of NO2.

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Expected deliverables

a) Scientific results:

• nanosized powders of p and n type semiconductor oxides;• stable, reproducible and selective array of thick film sen-

sors;• coupling of thick film printing technology with micro-

machining treated silicon support

b) Deliverable items (technical products, prototypes, patents,etc.):

the final result is engineering development of a cheap andlow-power-consuming air-monitoring prototype based onthick film technology.

References

[1] M.C. Carotta, G. Martinelli, Y. Sadaoka, P. Nunziante,E. Traversa, Gas-sensitive electrical properties of per-ovskite-type SmFeO3 thick films, Sensors and ActuatorsB, 48 (1998) 270-276.

[2] A. Chiorino, G. Ghiotti, F. Prinetto, M.C. Carotta, D.Gnani, and G. Martinelli, Preparation and characteriza-tion of SnO2 and MoO3-SnO2 nanosized powders for thickfilm gas sensors, Sensors and Actuators B, in press.

[3] M.C. Carotta, M.A. Butturi, G. Martinelli, M.L. DiVona, S. Licoccia, and E. Traversa, Thick film microsen-sors based on nanosized Titania sol-gel powder ElectronTechnology, in press.

[4] G. Martinelli, M.C. Carotta, M. Ferroni, Y. Sadaoka,and E. Traversa, Screen-printed perovskite-type thick filmsas gas sensors for environmental monitoring, Sensors andActuators B, in press.

[5] G.Martinelli, M.C. Carotta, C.Malagù, Physics and tech-nology of thick film sensors and their applications for envi-ronmental gas monitoring, invited paper at SGS’98, Us-tron (Polonia) September 22-26,1998

[6] G. Martinelli, M.C. Carotta, G. Ghiotti, and E. Traver-sa, Thick Film Microsensors Based on Nanosized Semicon-ducting Oxides Powders, MRS Bulletin, invited, June 1999.

[7] A. Chiorino, G. Ghiotti, F. Prinetto, M.C. Carotta, M.Gallana, and G. Martinelli, Characterization of materi-als for gas sensors. Surface chemistry of SnO2 AND MoOX-SnO2 nano-sized powders and electrical responses of the re-lated thick films, Sensors and Actuators B, in press.

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Fig.6 Ta doped TiO2 fired at 650 oC.

Fig.7 Ta doped TiO2 fired at 850 oC.

Fig.8 Differences in the answers of pure and Ta doped TiO2.

SUBPROJECT 6

Project title: Environmental monitoring system based on semiconductor oxides thick film sensors.

Participants:

Universita` di FerraraDipartimento di Fisica Unit Responsible: Prof. Giuliano MartinelliVia Paradiso 12, 44100 Ferrrara Collaborators: M.C. Carotta, V.Guidi,Tel.: 0532/781853 Fax:0532/781810 D. Gnani, M.Ferroni, M.Merli, E.Angeli.Email: Martinelli@fe.infn.it

Dipartimento di Chimica IFM - Universita` di TORINO Unit Responsible: Prof. Ghiotti GiovannaVia Pietro Giuria, 7,10125 Torino Collaborators: F.Prinetto, A.Chiorino, G.Cerrato.Tel.: 011/6707539 Fax: 011/6707855Email: internet-silver-ghiotti@ch.unito.it

Dipartimento di Scienze Chimiche e Tecnologiche Unit Responsible: Prof. Gusmano GualtieroUniversita` TOR VERGATA Collaborators: E.Traversa, S.Licoccia,Via della Ricerca Scientifica, 00133 Roma M.L.DiVona, A.Bianco, P.Nunziante, E.DiBartolomeo.Tel.: 06 72594387 Fax: 06 72594328Email: gusmano@uniroma.it

I.E.S.S. - C.N.R. - ROMA Unit Responsible: Prof. De Gasperis PaoloVia Cineto Romano, 42 00156 Zona Centro Roma Collaborators: C.Freiegari, L.Scopa.Tel.: 06/415221 Fax:06/41522220Email: degasperis@violet.iess.rm.cnr.it

Ditta ORION s.r.l. Unit Responsible: Dr. Calore Michele Via Vernise Frascà n. 39, - 35030 - Rubano Padova Collaborators: F.Cercato, M.Bettella,Tel.: 049 8975839 Fax: 049 8975759 M. De Stefani, M.Mazzucato.Email: orion@asn.it

1. Purpose of the work

Project and realisation of a demonstrator of an ElectronicNose, which is in conformity with the needs of the food-stuff industry, namely a system devoted to the quality mon-itoring of foods, which are characterised by an aroma. Thissystem is capable to process samples without a particularpreparation in order to determine if a specific product iscomformable to the production characteristics or to classi-fy it without the intervention of a panel of professional tasterstrained for the sensory analysis.

In the frame of this project, the techniques of data analy-sis have been also applied to the processing of data obtainedwith commercial Electronic Noses.

2. Outline of the work

1) Preparation of the semiconducting layers,2) Identification of the chemical species characterizing the

aroma of foodstuffs.We have examined dairy products like cheeses belonging tothe Lombard-Emilian area or coffee blends used for the Ital-ian expresso and olive oil.3) Characterisation of the sampling methods of the aroma

based on the headspace technique operated both in stat-ic and in dynamic mode,

4) Development of a system for data acquisition based on aportable PC and of the electronics used for the controland the read-out of the electric signals supplied by thesensor matrix,,

5) Development of measurement protocols and soft com-puting models,

6) Functional tests.

3. Main results

- Depositions of SnO2 thin films with the well-establishedRGTO technique.

These layers were sensitised towards particular gaseous fam-ilies typical of the considered foodstuffs (milk, cheese, cof-

fee) by means of suitable bulk dopants or surface catalysts.The functional sensitization of the layers is made in ac-

cordance among the various U.O.s.- Beginning of the training phase of the sensor matrices with

the techniques of pattern recognition by means of repeat-ed measurements with the different matrices towards thedairy products, the coffea blends and the olive oils.

- Preparation of sensor layers based on innovative materi-als like MoO3 and TiO2-WO3 (U. O. Brescia).

- Development of the substrate, based on alumina and metal-lic layers, to be used for the deposition of the gas sensorsscheduled in the Project.

- Deposition of tin dioxide layers by the sol-gel technique(U. O. Lecce).

- Data analysis of the foodstuff headspace by means of GC-MS (U.O. Parma).

- Sensor data analysis by means of multivariate soft com-puting techniques (U. O. Genova).

- Investigation of the local structure of semiconducting lay-ers by means of TEM (U. O. Ferrara).

- Realization of the sampling system for the Volatile OrganicCompounds (VOC’s).

- Design and realization of the electronics for the controland data acquisition of the sensor matrix and PC interface(SARA srl, Brescia).

4. Future developments

Optimization of SnO2 thin films by means of the RGTOtechnique with particular reference to the degradation of theelectrical resistance in correspondence of a prolonged use ofthe sensors in presence of some gases typical of the aromaof dairy products and other foodstuffs.

Deposition of sensing layers of innovative materials likeMoO3 (Ti), TiO2 (W) and WO3 (Ti) deposited by sputter-ing and suitably doped and catalysed by means of sputter-ing and wet impregnation.

Functional characterizations of the sensor matrices to-wards particular gas families, in particular the gases typicalof the foods considered in this research.

Taining of the soft-computing techniques by means of

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Development of an electronic nose for quality controlin dairy products and other foods using

semiconductor thin films

CNR-IME, SARA, Università di Brescia, Universita` di Ferrara,Università di Genova, Università di Parma,

repeated measurements of the responses supplied by differ-ent sensor matrices in presence of particular foodstuffs whichwill be selected by the U.O.s.

The sensing layers will be deposited by sputtering on thealumina substrates, which have been developed during thefirst year of the Project.

The microstructure of the sensing layers will be exam-ined by U. O. Ferrara.

Some matrices will be realized with sensors supplied byall the U.O.s, these matrices will be characterized in the testsystem realized during the first year of the project and willbe formed with reference to the characteristics of the dif-ferent foodstuffs to be monitored.

The responses of the sensor matrices will be correlatedwith the properties of the considered foodstuffs (U.O. Par-ma), in particular, the volatile compounds will be deter-mined by using the quadrupole mass spectrometer connectedto the test chamber where the sensor matrix is operating atambient pressure.

The Demonstrator of this Project will be realized bySARA srl.

The results obtained in the frame of this Project can betransferred to Small and Medium Enterprises (SMEs) forthe industrial production.

5. Expected Results

Development of gas sensors with high response stabili-ty and capable to detect the major part of volatile organiccompounds typical of the tested foodstuffs.

Development, in collaboration with SARA srl, of a pro-totype of electronic nose for detecting the principal proper-ties of some dairy products..

6. References

[1] G. Sberveglieri, G. Benussi, E. Comini, G. Faglia, G.Niederjaufner, G. Contarini, and M. Povolo. A novel elec-tronic nose based on semi-conductor thin films gas sen-sor to distinguish different types of milk. In Proc. of theNinth European Conference on Food Chemistry (Euro FoodChem IX), pages 89–94, Interlaken, September 1997.

[2] G. Sberveglieri, G. Benussi, E. Comini, G. Faglia, G.Niederjaufner, G. Contarini, and M. Povolo. A novelelectronic nose based on semi-conductor thin films gassensor to distinguish different heat treatments of milk.In 4th International Symposium on Olfaction and Elec-tronic Nose, Nice, October 1997.

[3] G. Niederjaufner, G.P. Benussi, E. Comini, G. Faglia,and G. Sberveglieri. Sviluppo di un naso elettronicoper la discriminazione tra varie qualità di latte. In Abs.di Terza Conferenza Nazionale Associazione Italiana Sen-sori e Microsistemi, page 65, Genova, February 1998.

[4] G. Sberveglieri, E. Comini, G. Faglia, G. Niederjaufner,G. Benussi, G. Contarini, and M. Povolo. A novel elec-tronic nose based on semi-conductor thin films gas sen-

sor to distinguish different heat treatments of milk.Seminars in Food Analysis, 3, 67–76, 1998.

[5] M. Pardo, G. Faglia, G. Sberveglieri, M. Corte, F. Ma-sulli, and M. Riani. Estimation of gas concentrationsin a mixture using a neural dy-namical model. In Tech.Digest of the 7th International Meeting on Chemical Sen-sors IMCS, pages 770–772, Bejing, July 1998.

[6] G. Niederjaufner, E. Comini, G. Faglia, M. Pardo, andG. Sberveglieri. Use of an electronic nose to classify dif-ferent types of Italian cheeses. In Abs. 5th Symposiumon Olfaction and Electronic Nose, Hunt Valley, USA,September 1998.

[7] G. Sberveglieri, E. Comini, G. Faglia, G. Niederjaufner,M. Pardo, G.P. Benussi, G. Contarini, and M. Povolo.Distinguishing different heat treatments of milk by anelectronic nose based on ANN. In C. Di Natale, A.D’Amico, and G. Sberveglieri, editors, Proceeding of the3rd Italian Conference Sensors and Microsystems, pages205–210, Singapore, 1999. World Scientific.

[8] M. Pardo, G. Niederjaufner, E. Comini, G. Faglia, andG. Sberveglieri. Testing the resolving power of an elec-tronic nose by discriminating various types of cheeses.In Abs of the 4th Italian Conference Sensors and Mi-crosystems, pages 99–100, Rome, February 1999.

[9] M. Pardo, E. Comini, G. Faglia, and G. Sberveglieri.A systematic way of extracting features from the dy-namic response of a sensor array. In Abs of the 4th Ital-ian Conference Sensors and Microsystems, pages94–95,Rome, February 1999.

[10] M. Pardo, G. Niederjaufner, E. Comini, G. Faglia, andG. Sberveglieri. Electronic Nose for food and other ap-plications. In Abs. of the II Workshop on Chemical Sen-sors and Biosensors, Rome, March 1999.

[11] M. Pardo, G. Niederjaufner, L. Odello, E. Comini, G.Faglia, and G. Sberveglieri. Pattern recognition permitsclassification of coffee blends with a reduced numberof thin films sensors. In Proc. of the 6th InternationalSymposium Olfaction & Electronic Nose, pages 215–218,Tuebingen, Germany, 20-22 September 1999.

[12] M. Pardo, G. Sberveglieri, S. Gardini, E. Dalcanale. Se-quential classification of 14 olive oils types by an Elec-tronic Nose Proceedings of the 6th International Sympo-sium on Olfaction & Electronic Nose, Tuebingen, 1999.

[13] G. Niederjaufner, M. Pardo, E.Comini, G. Faglia andG. Sberveglieri. Use of an electronic nose to classifydifferent types of Italian cheeses In: Electronic Noses andSensor Array Based Systems: Design and Applications, (W.Jeffrey Hurst editor). Technomic Publishing, 1999.

[14] M. Pardo, G. Niederjaufner, E. Comini, G. Faglia, andG. Sberveglieri. Towards an Electronic Nose for Dem-ining Based on Semiconductor Thin Films. In Proc. Eu-roconference Mine99, pages 82–86, Florence, October1999.

[15] M. Pardo, E. Comini, G. Faglia, and G. Sberveglieri.A systematic way of extracting features from the dy-namic response of a sensor array. In C. Di Natale, A.D’Amico, and G. Sberveglieri, editors, Proceedings of

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the IV National Conference Sensors and Microsystems,Singapore, 2000. World Scientific.

[16] M. Pardo, G. Niederjaufner, E. Comini, G. Faglia, andG. Sberveglieri. Testing the resolving power of an elec-

tronic nose by discriminating various types of cheeses.In C. Di Natale, A. D’Amico, and G. Sberveg-lieri, ed-itors, Proceedings of the IV National Conference Sensorsand Microsystems, Singapore, 2000. World Scientific.

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Project title: Development of an electronic nose for quality control in dairy products and other foods using semiconductorthin films

Participants:

Università di Brescia Unit responsible: Giorgio SberveglieriDip Chimica Fisica per l’Ingegneria e i per i Materiali Collaborators: G. Faglia, M. Pardo, E. Comini, Via Valotti 9, 25133 Brescia P. NelliTel.: +39-030-3715771 Fax: +39-030-2091271Email: sbervegl@tflab.ing.unibs.it

SARA s.r.l. Unit responsible: Giampaolo BenussiVia S. Rocchino 52, 25133 Brescia Collaborators: Guido NiederjaufnerTel.: +39-030-303301 Fax: +39-030-3700041Email: jauf@tflab.ing.unibs.it

Università di Parma Unit responsible: Alessandro MangiaDip. di Chimica Generale e Inorganica Collaborators: M. Careri, M.Musci, P. Manini, Via dell'Università 12, 43100 Parma C. MucchinoTel.: +39-0521-905432 Fax: +39-0521-905557Email: mangia@ipruniv.cce.unipr.it

Università di Ferrara Unit responsible: Giuliano MartinelliDip. di Fisica Collaborators: C.Carotta , M. Ferroni; V. GuidiVia Paradiso 12, 44100 Ferrara Tel.: +39-0532-781811 Fax: +39-0532-781810Email: martinelli@fe.infn.it

Università di Genova Unit responsible: Francesco MasulliDip. di Fisica Collaborators: M. Riani, M. Corte, Via Dodecaneso 35, 16146 Genova Tel.: +39-010-3536604 Fax: +39-010-314218Email: masulli@ge.infm.it

CNR-Istituto per lo studio di nuovi Unit responsible: Pietro SicilianoMateriali per l'Elettronica (IME) Collaborators: R. Rella, F. Quaranta, M. EpifaniVia Arnesano, 73100 Lecce A. Taurino, F. CasinoTel.: +39-0832-320244 Fax: +39-0832-325299Email: pietro.siciliano@ime.le.cnr.it

Other collaborators:Lorenzo S. Caputi Università della CalabriaDip. di Fisica87030 Rende, Cosenza, Italy Tel.: +39 0984 839046 Fax: +39 0984 839046 493187Email caputi@fis.unical.it

thought as formed by three distinct components: the macro-cycle, the peripheral substituent and the metal ion coordinat-ed in the core of the molecule and each of this componentgives a contribution to the total selectivity. The number of vari-ables can increase considering also the deposition methods.

Two sets of metalloporphyrins have been prepared and test-ed. The compounds were deposited, by solvent casting, onto thesurface of quartz microbalances. Sensors responses have beenmeasured towards the following volatile organic compounds(VOC): n-pentane, pentanal, ethanol, dimethylsulphide, thio-phene and triethylamine. For each compound a number of mea-surements taken at different concentrations have been performed.

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Research and development of an electronic nose,devoted to food analysis, based on mass and

conductivity transduction of tetrapyrrolics macrocycles:Langmuir-BlOdgett Deposition and SENSORs

characterization

Technobiochip, Università di Roma “Tor Vergata”

1. Purpose of the work

This research was concerned with the development ofthe sensors to be utilized for an electronic nose application.In particular, the following purposes have been identified:• Development of chemical sensors based on quartz mi-

crobalances (QMB) for electronic nose applications. Thesesensors have to be characterized by a broad selectivity anda sensitivity towards compounds relevant in food analysis.

• Optimization of deposition methods of tetrapyrrolic macro-cycles on QMB sensors and SiO2 substrates. Investigationof Langmuir-Blodgett deposition of such compounds andoptimization of the deposition procedure.

2. Outline of the work

This unit worked in strict connection with the unit co-ordinated by Dr. Paolesse. From this unit we received syn-thesized tetrapyrrolic macrocycles. These molecules havebeen deposited onto solid-state sensors and successively thesesensors have been characterized. In particular the followingsteps have been considered:• Langmuir-Blodgett coated QMB sensors characterization;• Study of the effects on sensor sensitivity of the molecule

features.In order to study the relationships between coating mol-

ecule features and sensor performances, it has been neces-sary to assess a data analysis methodology. Chemometricsand neural networks have both been utilized for this scope.

3. Main results

Study of the effects on sensor sensitivity of the coating moleculestructure

Pyrrole-based macrocycles (such as metallo-porphyrins)have been used as sensitive layers for the fabrication of QMBsensors characterized by broad selectivity towards volatile or-ganic compounds. The main features of such sensors is thatthe selectivity spectrum can be changed varying the basic com-ponents of the molecules. Indeed these macrocycles can be

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n-Pentane Pentanal Ethanol Toluene Dimethylsulfide Thiophene Triethylamine

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CopBrTPP

CoTPP-CHO

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Fig. 2 Sensitivities of porphyrins with different laterals sub stitutents

Fig. 1 Sensitivity as a fuction of porphyrins with differentmetals

The QMB sensors behave as a mass transducer, namely,the response is proportional to the mass of the analyte. In or-der to remove this dependence and to compare the effectivecapability of adsorption of each coating, a coating responsehas been introduced dividing the sensor response (measuredin Hz) by the molecular weight of the testing compound.

The sensitivities of the different metal complexes of TPPare reported in Figure 1. It is quite evident that the metal co-ordinated to TPP strongly influences the sensitivity patternof the resulting sensors. When the VOC molecule containsa donor atom, such as oxygen or nitrogen, the most impor-tant effect of the central metal can be directly related to thecoordinative interactions between the VOC and the metalcenter. In this case the sensitivity properties can be predict-ed on the basis of the HSAB theory; for example chromiumshows higher sensitivities to oxygen ligands, such as ethanolor propanal, whereas cobalt, on the other hand, has good re-sponse to triethylamine. In particular it has to be remarkedthe opposite character of cobalt and chromium concerningthe polarizability and dipolarity interactions. It is also to notethe good sensitivity showed by NiTPP in the case of toluene;this particular behaviour can be ascribed to efficient π-π in-teractions between Ni porphyrins and aromatic compounds.

In the case of toluene and pentane, where coordinationto the metal can be excluded, a different approach must befollowed to explicate the behavior showed by the differentTPP complexes.

A different effect is given by the variation of the periph-eral substituents of the porphyrin ring. Figure 2 shows thereduced sensitivity for the second set of CoTPP, where dif-ferent peripheral groups have been introduced in the meso-phenyl groups or at the β-pyrrolic positions.

These substituents have been chosen among others be-cause they strongly influence the aromatic p-system of theporphyrin (β-pyrrolic substitution), or because they can en-hance non-specific interactions with VOC (such as hepty-loxy group).

In this case, the main character of the responses do notchange. The highest sensitivity is shown towards triethy-

lamine and the presence of the peripheral can induce onlylight variations.

This result confirms that the coordination to the metalcenter is the driving interaction to determine the selectivi-ty properties of the resulting sensor. In this case the coordi-nated cobalt induces the sensitivity pattern and the periph-eral substituents can only influence the intensity of the re-sponses.

The main interest in this paper was to study the affini-ty between a coating compound and the various analytes.The response of a generic chemical sensor can be thoughtas given by two aspects: qualitative and quantitative. Thequalitative aspect gives the strength of interaction betweenthe sensor and the analyte, while the quantitative term takesinto consideration the concentration of the analyte. It isclear that the simultaneous action of these two aspect maymask the real properties of the sensor. The quantitative partcan be removed assuming a linear relation between the sen-sor response and the analyte concentration. In this case asimple normalization procedure can be applied simply di-viding the response of one sensor by the sum of the responseof all the sensors.

This normalization works correctly in case of perfect lin-earity. Actually, for porphyrin based sensors the relation be-tween Df and the concentration is far to be linear; the canbe explained taking into consideration the kind of interac-tions, which take place in the adsorption of analytes into theporphyrin films. This process can occur in two differentmodalities: a specific adsorption onto the porphyrin and anon-specific sorption in the solid state matrix. The specificinteraction can occur in different ways depending on thefeatures of the analyte; as an example it can be the coordi-nation of the analyte to the metal center of the porphyrin(as expected in the case of amines) or a π-π interaction be-tween aromatic rings (as in the case of toluene). The specif-ic interaction can be modeled typically as a Langmuir-likeisotherm while the non-specific sorption follows the linearHenry law. The combination of both the isotherms gives anon-linear curve, which is characterized by a high sensitiv-ity at low concentration and a low sensitivity at high con-centrations. Nonetheless, the application of the linear nor-

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npent

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Fig. 4 Plot of the first two loadings of the data

malization helps to reject a large part of the quantitative in-formation contained in the data.

Data have been mostly analyzed by the Principal Com-ponent Analysis (PCA). As usual, the PCA has been appliedto the covariance matrix of the data, namely scaling the da-ta to zero mean and unitary variance.

Figure 3 shows the score plot of the data projected onto thefirst two principal components. A net separation between theamines (diethylamine, triethylamine and dipropylamine) andthe rest of analytes is evident, on the other hand, a second groupcontaining benzene and acetic acid is separated form the rest ofcompounds for which no specific interaction are supposed.

Figure 4 shows the loading plot of the PCA analysis, thesensors are labeled according to the added metal or peripher-al substituent. Sensors with different metals show a great vari-ability among them, while sensor with a modification of lat-eral part of porphrin molecules are rather more grouped. Thisindicates, as expected, that the metal coordinate at the centerof the metalloporphyrin molecule plays an important role indefining the sensitivity, while modification of the lateral groupgives alteration of the sensitivity of lesser importance.

Characterization of Langmuir-Blodgett coated QMBPorphyrin complexes have been prepared by the unit co-

ordinated by Dr. Paolesse.Films deposition were performed in a Class 100 clean

room. Pure water with a resistivity higher than 18 MΩ cm(after preparation) was used as a subphase. While in the caseof Mn(EMC)[14] and Cu(FP) it was possible to obtainmonocomponent films, deposition of films of satisfactoryquality has been possible for [H2T(HEO)PP] by using be-henic acid. Porphyrins and behenic acid were dissolved in amixture of hexane and CHCl3 (1:1 v/v, 0.25 mg/ml and 2:1v/v, 0.33 mg/ml, respectively). To obtain mixed working so-lutions, one volume of the solution of each porphyrin wasadded to two volumes of the behenic acid solution; this givesthe molar ratios of porphyrin/behenic acid in the mixturesof 1:8.3, 1:8.7 and 1:9 for [H2T(HEO)PP], Co[T(HEO)PP]and Mn[T(HEO)PP]Cl respectively. The surface pressure-area isotherms were recorded and the films were fabricatedby using KSV System 5000. The speed of monolayer com-pression was equal to 0.015 nm2 molecule-1 min-1. The filmdeposition was fulfilled at a speed of 5 mm min-1. The sur-face pressure during the deposition of the samples was main-tained at 17.0 mN m-1 for Mn(EMC) and 30.0 mN m-1 forporphyrin derivatives, while during working out the processitself the deposition was carried out also at higher values ofsurface pressure. The films composed of 40 monolayers havebeen deposited onto QMBs for sensor measurements.

Frequency variations have been measured exposing LBfilm coated quartzes at different concentrations of the fol-lowing volatile organic compounds: alkanes (n-pentane, do-decane), aldehydes (propanaldehyde, valeraldehyde,myristaldehyde), alcohols (methanol, ethanol, n-hexanol, n-octanol), aromatics (benzene, toluene) and amines (diethy-lamine, triethylamine, dipropylamine, ethylendiamine).These analytes have been chosen as models for compoundsof interest in food analysis and environmental control.

A 10*10 neurons SOM has been trained with the dataset considered for PCA analysis, before training data havebeen normalized and scaled to zero-mean and unitary vari-ance. The SOM results have been analyzed with a method-ology developed at the University of Rome “Tor Vergata”.

Figure 5 shows the arrangement of data onto the SOMgrid, being this display of the data a sort of curvilinear PCAit is expected to be a refinement of the PCA score plot.

SOM projection of the data preserves the same distrib-ution of compounds found in PCA score plot, namely aminestend to be grouped at the upright corner while light alco-hols lie at the down left corner of the map. This ordering ofcompounds according to their expected way of interactionwith metalloporphyrin is a clue of the influence of the met-al, of metalloporphyrin complex, in defining the perfor-mances of the sensor. A sure proof could be obtained demon-strating that those porphyrins which are expected to exhib-it a greater affinity towards certain compounds are domi-nant in the array when these compounds are sensed. Thiscan be obtained studying the component planes of the code-book vectors as outlined in the previous section.

The next figure (fig.6) shows the component planes re-lated to each porphyrin as a 3D surface over the SOM grid.Three different behavior can be recognized.. The surfacesrelated to H2T(HEO)PP and Co[T(HEO)PP] have basi-cally the same shape, higher influence in amines detectionand low influence in short-chain alcohols detection, the sur-faces related to Mn[T(HEO)PP]Cl and Mn(EMC) behavesin the opposite direction (large response to alcohols and lowresponse to amines, while Cu(FP) has a completely differ-ent shape orthogonal to the others surfaces. These resultsare in agreement with those obtained by PCA with the dif-ference that here an evaluation of the sensor contributionto the array can be given for each experimental data point.

From these results it is possible to conclude that both weakand coordination interaction are important in determiningthe behavior of these sensors. It is worth mentioning that:

1. the metal ion can drastically influence the behavior ofthe sensor; indeed although the macrocycle is equal

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Fig. 5 Distribution of the data onto a grid of a trained som.

T(HEO)PP the addiction of manganese give raise to acomplementary component planes while, on the other sidethe presence of cobalt does not change the sensing proper-ties to respect the free base macrocycle;

2. manganese influence is stronger than the differenceinduced by the two different macrocycles T(HEO)PP andEMC: indeed surfaces related to Mn[T(HEO)PP]Cl andMn(EMC) are very similar and beside T(HEO)PP and EMCbased sensors have almost the same intensity towards thosespecies expected to weakly interact (those mapped at thecenter of the SOM grid);

3. Cu(FP) shows a completely different interaction withthe volatile compounds. This result suggests that also thepresence of different peripheral groups, on the porphyrin,can contribute to drastically change the sensing propertiesof the molecule. These results confirm the extreme interest in pursuing thisclass of materials for sensor applications due to the rich va-riety of sensing properties that can be obtained assemblingchemistry around a porphyrin macrocycle.

Future developments

• Manufacturing of a prototype of electronic nose based onQMB sensors and tetrapyrrolics macrocycles. The proto-

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H2T(HEO)PP

Cu(FP)

CoT(HEO)PP

CoT(HEO)PP

Mn(EMC)

type will be endowed with the electronics necessary forsensors conditioning, the management of the measure-ment fluids, the frequency measurement and the interfacewith the computer. The computer will be endowed witha software supervising the whole operations, the manage-ment of the measurements files and the data analysis pro-cedures.

• Study of feasibility of an hybrid electronic nose makinguse, at the same time, of QMB and conductivity changesbased sensors.

Expected Deliverables

Demonstrator, fully operative, of an electronic nose andits application on some food analysis application. Accord-ing to the current gained experience, a full operative elec-tronic nose based on QMB sensors will be given as deliver-able and its application in food quality assessment and spoilagetests in cases of fish and fruits will be investigated.

References:

1. R. Paolesse, R. G. Khoury, F. Della Sala, C. Di Natale, F.Sagone, K.M. Smith; Bis-vinylogous corrole: the first ex-panded corrole, Angewandte Chemie Int. Ed. Engl. 38(1999) 2577-2579

2. C. Goletti, A. Sgarlata, N. Motta, P. Chiaradia, R. Pao-lesse, A. Angelaccio, M. Drago, C. Di Natale, A. D’Am-ico, V.I. Troitsky, M. Cocco; Kelvin probe and scanningtunnelling microscope characterization of Langmuir-Blod-gett sapphyrin films, Applied Physics Letters 75 19991237-1239

3. R. Paolesse, C. Di Natale,A. Macagnano, F. Sagone, T.

Boschi, M. Scarselli, P. Chiaradia, V.I. Troitsky, T.S Berz-ina, A. D’Amico; Langmuir-Blodgett films of a manganesecorrole derivative, Langmuir 15 1999 1268

4. C. Di Natale, R. Paolesse, A. Macagnano, V.I. Troitsky,T.S. Berzina, A. D’Amico; Pattern recognition approachto the study of the interactions between metalloporphyrinLangmuir-Blodgett Films and volatile organic compounds,Analytica Chimica Acta 384 1999 249-259

5. R. Paolesse, C. Di Natale, A. Macagnano, A. D’Amico,C. Goletti, A. Sgarlata, R. Paradiso, M. Cocco; Study ofthe physical and sensing properties of Langmuir-Blodgettfilms of pyrrolic macrocycles Quarta conferenza nazionaleSensori e Microsistemi, Roma 3-5/2/1999

6. C; Di Natale; Application of artificial olfaction and tastesystem to the medical field, invited talk at the First USA-Italy conference on Neural Network and Cognitive Sci-ence Boston 4-5 Oct. 1999

7. D. Rutledge, C. Di Natale; ASTEQ: a concerted actionfor fruits quality assessment, Quarta conferenza nazionaleSensori e Microsistemi, Roma 3-5/2/1999

8. R. Paolesse, C. Di Natale, V. Campo dall’Orto, A.Macagnano, A. Angelaccio, A. Sgarlata, J. Hurst, I. Rez-zano, M. Mascini, A. D’Amico; Porphyrin thin films coat-ed quartz microbalances prepared by electropolymeriza-tion techniques, Thin solid films in print

9. C. Di Natale, C. Goletti, R. Paolesse, M. Drago, A.Macagnano, A. Mantini, V. Troitsky, T. Berzina, M. Coc-co, A. D’Amico; Kelvin probe investigation of the thick-ness effects in Langmuir-Blodgett films of pyrrolic macro-cycles sensitive to volatile compounds in gas phase, Sen-sors Actuators B in print

10. A. D’Amico, C. Di Natale, R. Paolesse, A. Mantini, A.Macagnano, F. Della Sala; Porphyrins: candidates forelectro-optical nose development, Sensors and Actua-tors B in print

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Participants:

Technobiochip s.c. a r.l. Unit responsible: Michele Cocco (Project Coord.)Via A. Moro 15, 57033 Marciana (LI) – Italy Collaborators: Antonella MacagnanoTel: +39 0565 904461 Fax: +39 0565 904447 Marco Zunini, Stefano Sinopoli, Daniele NardelliEmail: michele@technobiochip.com

Università di Roma “Tor Vergata” Unit responsible: Corrado Di NataleDipartimento di Ingegneria Elettronica Collaborators: Alessandro Mantini, Christian Falconi,Via di Tor Vergata 110, 00133 Roma – Italy Eugenio Martinelli, Sara NardisTel: +39 06 7259 7348 Fax: +39 06 2020 519Email: dinatale@eln.uniroma2.it

1. Purpose of the work

Many industrial and commercial plants are potentialsources of unpleasant odours, whose perception thresholdsare extremely varied. Effects of this kind of emission rangefrom nuisance to health damage; in any case they cause aloss of quality of life to people involved, the magnitude ofwhich is frequently determined by psychological factors. Infact, according to people’s feelings, unpleasant emissions arethe main and unmistakable sign of atmospheric pollution.Therefore, despite the lack of a specific law, a great interestexists from the environmental protection authority towardsthe development of an instrument capable of objectivelyquantifying odour annoyance. The goal of the present re-search is to try to fulfil this need, identifying the most wide-spread sources of unpleasant odours and developing aportable, cheap, user friendly instrument capable of char-acterizing several types of emission and producing an out-put made of simple lexical expressions.

2. Outline of the work

2.1) Collection of data relevant to different types of odoursources. Selection, following the indications of the en-vironmental protection authorities, of a restricted num-ber of sources existing in the environment.

2.2) Design of an experimental set-up composed of front-end electronic and an odour exposure system.

2.3) Design of monomers and polymers belonging to theclass of polyconjugated materials on the basis of thesubstances to be detected.

2.4) Synthesis of the polymers designed and polymerizationwith different techniques.

2.5) Study of the doping process and evaluation of the mostsuitable counterions.

2.6) Design and realization of new kinds of polypyrroleswith high chemical stability.

2.7) Study of the time stability of the materials produced.2.8) Design and realization of new conducting polymer sen-

sors based on materials supplied by the Polytechnic ofMilan and University of Parma.

3. Main results

Thanks to dialogues with the staff of the Regional Agencyfor the Environmental Protection of Tuscany (ARPAT) andof the Environmental Department of Province of Pisa andFlorence, the main sources of odorous emissions located inthe northern part of Tuscany were identified. In the districtof Pisa, major problems are met in the leather district, whereplants treating waste waters produced by leather tanneriesare often responsible for annoying emissions. Minor prob-lems are due to waste disposals. In the district of Florencethe situation is much more diversified. Activities accused forodour problems include waste treatment, animal by-prod-ucts processing, production of yeasts, medicines, mosquito-nets. Paper mills are often reported as odour polluting in thedistrict of Lucca. Substances involved in these emissions arenitrogen compounds like ammonia and amines, with thepungent odour of fish, or sulphur compounds like hydro-gen sulphide, mercaptans, indole, which have the odour ofthe rotten eggs or a faecal smell. Solvents like xylene, styrene,toluene, benzene and its derivatives are emitted by leathertanneries and paint producing plants.

Hence, three classes of compounds were selected to bedetected by sensors: aromatics, sulphur and nitrogen deriv-atives. Monomers in Figure 1 were designed and synthesizedby the staff of Polytechnic of Milan.

All the monomers were polymerised by oxidative poly-

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Development of an artificial olfactory system withconducting polymer sensors for environmental

applications

CNR-IEI, Politecnico di Milano, Università di Parma, Università di Pisa

S

R

S

RO

S

OR

S

OR

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DESIGNED MONOMERS

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Fig. 1 Monomers synthesized at the Polytechnic of Milan.

merisation methods using FeCl3 or Cu(ClO4)2 as oxidantsin chloroform or acetonitrile respectively. These crude poly-mers were washed with methanol and Soxhlet extracted withsolvents in order to separate the different molecular weightfractions.

All the neutral polymers were dissolved in chloroformand trichloroethylene (1:1 vol.) and doped with acetonitrilesolutions of selected salts (FeCl3·6H2O, Cu(ClO4)2·6H20,Fe(ClO4)3·9H20, CuCl2 ·2H2O) in molar ratios rangingfrom 15/1 to 3/1. We used these solutions of the doped poly-mers for casting films on sensors constituted of an aluminasubstrate with a gold interdigitated circuit.

The conductivity of the sensors was measured every dayfor the first weeks and then about every week for six months.The acceptable variation in the conductivity was less than10% monthly. All the sensors prepared with alkyl-substitut-ed thiophenes did not satisfy this requirement. On the con-trary, most of the sensors prepared with the alkoxy deriva-tives gave very good performances as reported in Figure 2.

Some of the stable sensors were tested in the presence ofsolvents such as benzene, acetone, butyl- and propyl-alco-hol etc. and a representative resistance variation is reportedin Figure 3.

Two additional types of sensors were produced by poly-merizing the pyrrol-3,4-dimetil carboxylate monomer withan excess (M/Ox = 4) of iron perchlorate or with copperperchlorate dissolved in acetonitrile. The resulting suspen-sion reacted for one hour, but the following deposition didnot originate a film of acceptable quality. Following testsunderlined the presence, in the final suspension, of highquantities of monomer and salt, thanks to a low efficiencyof reaction (about 50%). The salt is very hygroscopic andprolongs the evaporation of the drop and the formation ofthe film.

The purification of the final product from the reagentswas carried out by adding to the suspension the minimumquantity of chloroform necessary to obtain precipitation.The precipitate was washed with acetonitrile and precipi-tated again for three times. After this operations, acetoni-trile was added to it, and the result was a very dense sus-pension that was deposited. The resulting conductive film,despite all the efforts made, still contained some unreactedsalt. The sensors made in this way produced responses verydifferent from those obtained from sensors prepared withthe thiophene.

The treatment of the film with water removes all the salt,but in this case the conductivity of the polymer drops to val-ues close to zero. This seems to prove that conductivity wasdue exclusively to the presence of salt and that the polymerwas not doped, indicating the need of further studies for thistype of sensors.

4. Future developments

The Parma and Milan operating units will continue towork on new materials, in order to evaluate their propertiesand to solve the problems encountered. In particular,polypyrroles will be further studied, and the possibility ofintroducing molecular recognition elements to increase sen-sitivity to selected molecules will be investigated.

The conducting materials synthetized in Milan will bestudied by analysing the effect of odorants on their UV andIR spectra. Moreover, the development of an efficient odor-ant exposure system will enable the measurement of sensorresponses to single substances and mixtures which simulatepreviously identified malodorous emissions. These mea-surements will allow us to evaluate the stability, sensitivityand reproducibility of the sensors produced.

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Fig. 2 - Poly3,3’-dipentoxy-2,2’-bithiophene doped with Fe-Cl3 (M/OX=6). The data in a) and b) are referred to films ofdifferent thickness.

Fig. 3 - Poly3,3’-dipentoxy-2,2’-bithiophene doped with Fe-Cl3 (M/OX=6) in presence of Chlorobenzene (a saturation at-mosphere diluted 4 times with N2.

5. Expected deliverables

A number of sensors will be characterized with respect totheir relative calibration curves and temporal parameters. Chem-ical, morphological, structural and electrical parameters rele-vant to odour sensitivity in polymers will also be identified.

6. Bibliography

R. Stella, G. Serra, D. De Rossi: Artificial olfactory sys-tem: design, realisation and applications, Cell. Engineering, 2 161 (1998).

G. Casalbore-Miceli, N. Camaioni, G. Beggiato, A.M.Fichera, M.C. Gallazzi: Influence of the supporting elec-trolyte and of film thickness on the ratio between the crys-tal and amorphous structure in electrosynthesised poly(4,4’-dipentoxy-2,2’-bithiophene), Synth. Metals , 98 143 (1998).

D. Pede, R. Stella, D. De Rossi: Fabrication of conductingpolymer arrays of sensors by ink-jet printing, 3rd Nat. Conf.Sensors and Microsystems, Genova 11-13 February 1998.

R. Stella, D. De Rossi: Conducting polymer sensors forolive oil sniffing, , 3rd Workshop on Multifunctional and SmartPolymer Systems, Tirrenia 21-24 June 1998.

M.C. Gallazzi, F. Toscano, C. Bertarelli: From chemicaldesign to material properties, 3rd Workshop on Multifunc-tional and Smart Polymer Systems, Tirrenia 21-24 June 1998.

D. De Rossi, D. Pede, G. Serra, R. Stella: High sensi-tivity conducting polymer odour sensors made by ink-jetlithography, 5th Symp. Olfaction and Electronic Nose, HuntValley (Md) 27-30 September 1998.

F. Di Francesco, G. Pioggia, C. Ristori, G. Serra, D. DeRossi: Environmental applications for electronic noses, 4thNat. Conf. Sensors and Microsystems, Roma 3-5 February 1999.

L. Tassoni, M.C. Gallazzi: Polimeri Conduttori per NasiElettronici, Macrogiovani ’99, Gargnano 22 May 1999.

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Project title: Development of an artificial olfactory system with conducting polymer sensors for environmental applications

Participants:

Università di Pisa-Centro Piaggio Unit responsible: Danilo De Rossi(Project Coord.)Facoltà di IngegneriaVia Diotisalvi 2, 56126 Pisa Collaborators: M. S. GardiniTel.: +39-050-553639 - 554134 Fax: +39-050-550650Email: ramsete@piaggio.ccii.unipi.it

Università di Parma Unit responsible: Enrico DalcanaleDip. di Chimica Organica e Industriale Collaborators: F. di Francesco, Viale delle Scienze, 43100 Parma C. Domenici, G. PioggiaTel.: +39-0521-905414 Fax: +39-0521-905472 Email: dalcanal@unipr.it

Politecnico di Milano Unit responsible: Maria C. GallazziDip. di Chimica Industr. e Ing. Chimica Collaborators: L. TassoniPiazza L. da Vinci 32, 20133 MilanoTel.: +39-02-23993224 Fax: +39-02-70638173Email: maria.gallazzi@polimi.it

CNR-Istituto dell’Elaborazione delle Informazioni (IEI) Unit responsible: Anna VaccarelliVia Santa Maria 46, 56126 Pisa Collaborators: L. Azzarelli, A. Ribolini,Tel.: +39-050-593400 Fax: +39-050-550650 C. A. Giorgi, M. Chimenti, S. CerriEmail: vaccarelli@iei.pi.cnr.it

Purpose of the work

Development of a fully characterized library of CMOSanalog cells and A/D converters especially designed for in-terfacing microsensors, both single or in arrays. IC proto-types will be integrated by using either the IRST CI25 2mi-cron CMOS technology or the Silicon Foundries CMOSprocessing. These ICs will be designed and used to develophybrid packaged demonstrators. Two type of demonstratorsare planned:

a) an ISFET based battery operated chemical sensor forpH monitoring of aqueous solutions;

b) a thermal imager using 8×8 array of micromachinedvanadium oxide thermal sensor.

Outline of the work

A preliminary library of IC cells for A/D conversion andfor chemical and thermoresistive microsensor read-out hasbeen designed and fabricated by using the IRST CMOS2micron technology. The ICs designed for ISFET chemicalsensor read-out have been fully characterized and are nowbeing used for the development of the pH monitoring demon-strator. The ICs designed for A/C conversion and for bias-ing and reading resistive sensors are now under test.

Basically the efficient reading of a resistive type sensorrequires the sensor bias section (both voltage or current) fol-lowed by an impedance decoupling section and, if needed,by an amplifying section. The optimum choice of the readout strategy depends on:• the sensor resistance R at the reference temperature of300°K and its expected variation range DR in presence ofthe quantity to be sensed;• the Signal to Noise S/N or the NEP of the sensor;• the dynamic behavior of the sensor to be read out.

This requires a preliminary option on the type of resistivesensor to be considered. In our project it has been decided tofocus the reading IC electronics on the requirements of theVanadium Oxide VaO Infra Red thermal sensor now underdevelopment at CREO Laboratory. The VaO is particularlyattractive since it operates at room temperature and can be

fabricated into a 2D matrix suitable for IR imaging. The useof micromachining technology reduces the sensor thermalconductance towards the silicon substrate thus allowing thehighest thermal IR sensitivity. A close cooperation with CREOis therefore required in order to develop the intermediate sin-gle sensor and the final 8×8 array IR imager demonstratorsforeseen in this research project. Instead of pursuing the fullsensor with read out electronics integration on the same chip,we are planning to pursuing an hybrid approach which allowsthe sensor matrix and the read out electronics to be separate-ly optimized. In this approach the final thermal demonstra-tors will be mounted on custom designed packages.

Main results

a) ISFET read out IC electronics.The chip, fabricated by using the IRST 2micron CMOS

single polySi double metal technology, is shown in the mi-crograph.

A detailed description of the ISFET read-out IC is re-ported in ref. 1. The same circuits provides also the Elec-

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Integrated electronics for sensors

Università dell’Aquila, Università di Trento

Fig. 1 - Read-out I.C. for ISFET.

troStatic Discharge ESD protection for the ISFET. The per-formance of the read-out circuit coupled with the ISFETpH sensor is shown in the experimental diagram of fig.2.

To take fully advantage from these results, a completemicrosystem targeted to remote pH monitoring for waterpollution has been designed and is now being implement-ed as first demonstrator. The basic modules, to be packagedinto a stainless steel tube battery operated microsystem withexposed the pH sensitive area, are:a) the ISFET pH sensorb) the CMOS IC read-out electronicsc) the Ag(AgCl) reference electrode

The pH monitor microsystem target design are:• pH measuring range: 3÷11• sensitivity: >55mV/pH• resolution: <0.05pH• linearity within the measuring range: <0.1%• ElectroStatic Discharge (ESD) protection according to level 3CEI EN 61000-4-2 standard.

The overall microsystem schema is shown in fig.3.

b) 8bit A/D converterThe chip, fabricated by using the IRST 2micron CMOS

technology, is shown in the micrograph (fig. 4). Function-

al testing to fully characterize the A/D converter performanceis now being carried on. Based on these preliminary experi-ence, a more advanced version to be integrated by using the0.8micron CMOS technology will be designed and imple-mented by the end of year 1999.

c) resistive sensor bias/read out IC interfaceThe following options have been considered:

• direct methods, based on voltage partitioning and I/V con-verters.

• differential methods, based on Wheatstone bridges and cur-rent mirrors

These IC prototypes have been implemented in IRSTCMOS 2micron technology an are now under testing. The mi-crograph of the bias/read out IC interfaces is shown in fig 5.

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Fig. 2 - Measured performance of the ISFET pH sensor cou-pled with the read out IC electronics

Sensitivity 58mV/pH

Resolution < 0.05pH

Fig. 3 - Schematic of the pH monitoring microsystem.

Fig. 4 - A/D converter for sensor analog output conversion.

Fig 5 - Micrograph of the resistive sensor bias/read out IC in-terfaces.

Based on the critical analysis and performance compar-ison the same type of basic cells will be redesigned and willbe implemented in 0.8 CMOS technology by the end ofyear 1999. These ICs will be used for interfacing microma-chined vanadium oxide thermal sensors now under devel-opment at CREO. A dedicated 8×8 array of thermal sen-sors coupled with the to the purpose designed IC electron-ics to be mounted in an hybrid package will be designed anddeveloped as final demonstrator.

Future developments

The following activities are planned:

a) pH monitoring microsystemsFollowing the preliminary results and demonstrator, a

more advanced pH monitoring microsystem based on twoidentical ISFET devices to be read in differential mode inorder too reduce the ISFET shift and with a digital standardoutput, employing both the IC read out and the A/D con-verter chips mounted in a custom designed hybrid packageis foreseen. A temperature sensor will be added to the mi-crosystem final demonstrator.

b) Thermal imager The resistive sensor interfaces will be optimized to bias

and read the micromachined VaO sensors now under de-velopment at CREO. The different IC interfaces will becompared in order to define and validate the optimum op-tion. To this purpose preliminary test structures comprisinga single VaO thermistor coupled with a bias/read-out inter-face followed by an A to D converter will be developed. Fi-nally the development of a complete 8×8 thermal pixels ma-trix coupled with the IC electronics to form a complete ther-mal imager will be pursued. The schematic of the prototypedemonstrator is shown in fig. 6.

Expected deliverables

At the end of the first phase (three years) the followingdeliverables are to be expected:a) high performance battery operated hybrid packaged pH

monitoring microsystem comprising of the differentialISFET sensor section, interface IC read-out electronics,AtoD conversion, reference microelectrode and thermalsensor;

b) VaO thermal sensor (single) coupled with bias/read outelectronics and A to D conversion;

c) VaO thermal imager (8×8 pixel matrix) coupled with ICread out electronics, AtoD conversion and primary digi-tal preprocessing, mounted in hybrid packaging to forma stand alone battery operated complete microsystem.

References

• “Current mode A/D converter” L. Ravezzi, D. Stoppa,G.F. Dalla Betta Electronics Letters, Vol. 34, n. 7, p.615,1988.

• “A new current mode programmable cellular neural net-work” L. Ravezzi, G.F. Dalla Betta, G. Setti Proc. of theIEEE-CNNA’98, p.253, London, april 1998.

• “An ISFET based microsystem for pH measurements”,P. Conci, L. Ravezzi and G.Soncini. Sensors and Mi-crosystems, Proc. AISEM99 Conference (to be published)

• “An ISFET based chemical sensor for the food industry”,M. Corrà, G. U. Pignatel, P. Conci, B. Margesin, M. Zenand A. Maglione Sensors and Microsystems, Proc.AISEM99 Conference (to be published)

• “ISFET sensor coupled with CMOS read-out circuit mi-crosystem” L. Ravezzi, P. Conci. Electronics Letters, Vol.34, n. 23, p.313, 1988.

• “A CMOS monolithic optical head for high resolution op-tical encoders” D. Stoppa, L. Ravezzi, G. F. DallaBetta, M.Gottardi and G. Soncini, Proc. of the European Confer-ence on Circuit Theory and Design ECCTD’99, Stresa(Italy) Sept. 1999, pp. 487-490.

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S11 S12 S18

S81 S82 S88

Fig. 6.a – 8x8 thermosensor matrix.

Fig. 6 b - Schematic of the bias/read-out electronic.

Project title: Integrated electronics for sensors

Participants:

Università di Trento Unit responsible: Giovanni Soncini (Project Coord.)Dipt. Ingegneria dei Materiali Collaborators: Giorgio Umberto Pignatel, via Mesiano 77, I-38050 Trento – Italy Luca Ravezzi, Gian Franco Dalla Betta, Tel.: +39-0461-88.2451 Fax: +39-0461-881977 David Stoppa, Michele Corrà.Email: giovanni.soncini@ing.unitn.it

Università de L’Aquila Unit responsible: Marco FaccioDipt. Ingegneria Elettrica Collaborators:Mario Brandimarte, Loc. Monteluco di Roio Mauro Salpietro, Andrea Viscillo. I-67040 Poggio di Roio, L’Aquila – Italy.Tel.: +39-0362-434436 Fax: +39-0382-434403Email: faccio@ing.univaq.it

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Purpose of the work

The problems related with the integration on the samechip of a system composed of one or more sensing devicestogether with the conditioning and signal processing elec-tronic circuits are receiving increasing attention in the re-search activities, due to the obvious advantages in terms ofcost, size and flexibility over non integrated solutions. Acommon problem is the low level of the output signal gen-erated by the sensors, due to the poor sensitivity of sometypes of sensing elements, which calls for special amplifica-tion techniques, aimed at increasing the signal-to-noise ra-tio (S/N), prior to the A/D conversion and signal process-ing. One of such techniques is the lock-in amplification,which is known to be very effective when the sensor can bedriven by an AC stimulus. It works in the following way.The sensor modulates the amplitude of a carrier signal at asuitable frequency in a quiet part of the spectrum, and theresulting signal, of low level and covered by noise, is fed to

the input of the lock-in amplifier, as illustrated in Fig. 1.Here, it undergoes an AC amplification, followed by a co-herent demodulation and a low-pass filtering. The low-passfilter, with a very low cut-off frequency, suppresses most ofthe noise power, and determines the effective noise band-width of the amplifier and the required S/N.

Lock-in amplifiers for sensor applications have been builtusing discrete components, but, to our knowledge, no inte-grated implementation has been tried so far, which meets thecost and size requirements of a monolithic microsystem. Thegoal of this research project is to investigate the problems re-lated with the design, realization and testing of a totally inte-grated lock-in amplifier, suitable for being embedded as a macro-cell within a complete system, which includes both the sensingand the signal processing units. The project spans several issuespertaining the design and testing of analog integrated circuits:i) the definition of a suitable general-purpose architecture, witha large degree of flexibility, in order to fit a wide range of ap-plications, ii) the design and the implementation of several ana-

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308

Circuit architectures, design and characterization ofintegrated lock-in amplifiers for sensor applications

Università dell’Aquila, Università di Bologna, Università di Roma Tor Vergata

Fig. 1 Lock-in amplifier schematic

log building blocks (low-noise amplifier, filter, mixer, VCO,PLL), iii) the migration toward “scaled” technologies, and amethodology for efficiently scaling the previously designed cir-cuits, iv) the design of an architecture and of its circuit blockswith a special attention for the constraints imposed by the“scaled” low supply voltage, and by the low power consump-tion requirements, v) the set-up of a system for the completecharacterization and testing of the built prototypes.

As a main result of the three-years project activity, we ex-pect a well defined methodology for the development of ful-ly integrated lock-in amplifiers, both in a standard 5 V pow-er supply technology, and in a scaled technology. Prototypesof integrated lock-in amplifiers will be built and character-ized as a test vehicle of the proposed design methods.

Outline of the work

At the beginning of the project, a reference architectureof lock-in amplifier has been established to serve as the ba-sis for the successive developments. The block diagram is re-ported in Fig. 1, though variations can be found in the dif-ferent implementations that have been carried out.

In the signal channel, a variable-gain input stage pre-processes the signal, by amplifying it to a level suitable forthe demodulator. It is composed of a high performance lownoise amplifier (LNA), with high CMRR and PSRR, a band-pass filter, tuned at the signal frequency, which allows a firstout-of-band noise reduction, and a controlled-gain ampli-fier to increase the signal to the desired level.

Within the reference channel, the reference signal voltage,at the same frequency of the input signal, is phase-shifted andregenerated according to the demodulator requirements. Atthe output of the demodulator, a DC component, propor-tional to the amplitude of the input signal and also dependenton the phase difference between the input signal and the ref-erence signal, is thus present. By adjusting the phase-shift with-in the reference channel, such a phase difference can be broughtto zero (null shift procedure), and the amplifier sensitivity canbe maximized. So doing, it is possible to compensate for thephase response of the sensor, and to measure both the in-phaseand the quadrature components of the input signal.

The noise still present at the output of the demodulator,with a power that can be much larger than the signal pow-er, is reduced by the low pass filter, thus improving the S/N.A final DC amplifier sets the total amplification level.

During the first year of the project, the described archi-tecture has been independently implemented by the Oper-ating Units (O.U.) of Bologna and L’Aquila, introducingthe necessary variations oriented to the specific goals of de-signing and testing a general purpose integrated lock-in am-plifier in a standard 5 V CMOS technology for the O.U. ofBologna, and of investigating the design and implementa-tion issues related with the low-voltage and low-power op-eration for the O.U. of L’Aquila, respectively.

O.U. of BolognaBased on the test results of a previously developed pro-

totype of integrated lock-in amplifier, some critical blockshave been redesigned, and other blocks have been improved.The adopted technology is the 0.7 µm CMOS Mietec, en-hanced with analog features, such as low threshold p-chan-nel MOSFETs, high resistivity poly resistances, and linearpoly-n+ capacitors.

In particular, the reference channel for the regenerationand phase-shift of the reference voltage has been largely re-built, adopting a completely differential topology in order toincrease the noise immunity. Besides, the mixer has under-gone substantial changes. These blocks have been simulatedat circuit level, and the layout of the single components andof the complete amplifier has been prepared. The final designhas then been sent out for fabrication, and the returned pro-totypes have been successfully tested and characterized. Themain measured results are presented in the next section.

In the design process, any effort has been devoted to therealization of a flexible architecture, so as to fit a wide classof applications, in terms of i) operating frequency, ii) re-quired sensitivity (input signal level), iii) dynamic reserve(input noise level). For this reason several programmable el-ements have been introduced. Distinguishing features of theimplemented architecture are:a) phase-locked-loop (PLL) based reference channel, which

provides a sinusoidal output voltage, frequency-locked tothe reference voltage and with variable phase; the down-conversion of the noise at the harmonics of the input sig-nal is thus minimized, and the behavior of the amplifieris made independent of the duty-cycle of the referencesignal

b) linear four-quadrant demodulator with digitally pro-grammable conversion gain

c) digitally programmable gain of the input gain staged) final low-pass filter based on a switched-capacitor (SC)

implementation, with variable cut-off frequency down tothe sub-Hertz region

e) external components (RC) are required only in the PLLloop filter, and in the input coupling network.

O.U. of L’AquilaThe O.U. of L’Aquila has firstly studied the single blocks

which form a lock-in working at standard supply voltages.In order to guarantee the low voltage operation, most ofthese blocks have been topologically redesigned. In partic-ular, the reference channel block with the phase-shifters, andthe demodulator, which is essentially a wave rectifier whichrectifies the input signal even if the S/N ratio is less than 1,notably differ from the previous architecture. Moreover, inthe input gain stage, the operational amplifiers and the fil-ters have a suitable structure for low-voltage operation.

Next, the single blocks have been designed and simulat-ed with Spice using three different standard digital CMOStechnologies offered by two European silicon foundries (Mi-etec 0.7 µm, Mietec 0.5 µm, and AMS 0.6 µm), first sepa-rately and then altogether. This last part has been particu-larly delicate, because the coupling of the stages is very im-portant. The AMS technology has been considered the bestchoice for a first integrated prototype.

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Finally, the full custom layout of the single blocks andof the total amplifier has been drawn. This part has just beencompleted.

O.U. of Roma Tor VergataAt the O.U. of Tor Vergata, the research activity has been

developed along the following lines:a) set-up of a chip test chainb) simulation of some low voltage circuits as single compo-

nents for the integrated lock-in amplifier.A test line for integrated lock-in amplifiers has been de-

signed and set up. It is formed by an analog lock-in ampli-fier, characterized by a variable Q, in the frequency range10 Hz-200 KHz, by a spectrum analyzer, and by a calibrat-ed noise generator. This test line is ready to test the low volt-age prototype as soon as it will be fabricated.

Concerning the second research line, a low-voltage mix-er and a low-pass filter have been successfully simulated, inco-operation with the University of L’Aquila.

Main results

O.U. of BolognaAt the end of the first year, a prototype of a general pur-

pose integrated lock-in amplifier was available in a standardCMOS technology. The circuit has been functionally test-ed and the main characteristics have been measured. Table1 summarizes the results of the measurements.

As an indication of the amplifier behavior in a realisticenvironment, it has been verified that the circuit is able to

resolve an input sinusoidal signal with amplitude changingfrom 0 to 1 mV by steps of 100 nV, at the frequency of 20KHz, even in presence of a stronger sinusoidal interference,of tens of microvolt amplitude, at an offset frequency of on-ly 5 Hz from the useful signal. The test has been performedwith the variable cut-off frequency of the low-pass filter setto about 0.1 Hz, by adjusting the SC clock frequency.

O.U. of L’AquilaDuring the first year, a low-voltage (2 V) CMOS lock-

in amplifier has been completely designed and character-ized. Two different 1 KHz and 10 KHz signals, embeddedin noise, have been considered for the lock-in test, wherethe S/N has been taken less than 0.1. In this condition thesignal has been completely recovered. The equivalent inputnoise is 18 nV/(Hz)1/2 at 1 KHz and 15 nV/(Hz)1/2 at 10KHz. The theoretical dynamic reserve, a typical lock-in qual-ity factor which gives a direct measure of the worst-case S/N,has been demonstrated to be greater than 60 dB at 1 KHzinput frequency.

O.U. of Roma Tor VergataDuring the first year, the set-up of the chip test chain

has been designed and realized, so to characterize the inte-grated lock-in amplifiers.

Future developments

O.U. of BolognaBased on the test results of the fabricated amplifier, the

future activity will focus on the following improvements: i)automatic gain control system, ii) reduction of the outputDC offset voltage, iii) increase of the dynamic reserve.

O.U. of L’AquilaThe first future activity will be the realization (at AMS

foundry) and the testing of the first prototypes of the inte-grated low voltage lock-in amplifier. Optimization of thesingle blocks will follow chip test results.

O.U. of Roma Tor VergataThe testing and the characterization of some chip pro-

totypes of the lock-in amplifiers will be performed in thenext years.

Expected deliverables

1) prototypes of integrated lock-in amplifier in the 0.7 µmCMOS technology, enhanced with the aforementionedfeatures

2) characterization of the low-voltage test chips.

References

[1] Gnudi, L. Colalongo, and G. Baccarani: “Integrated Lock-In Amplifier for Sensor Applications”, to be presented atESSCIRC’99, September 21-23 1999, Germany.

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Table 1. Measured characteristics of the integratedlock-in amplifier.

GENERAL CHARACTERISTICSarea (core) 6.5 mm2

supply voltage 5 Vpower dissipation 25 mWinput frequency 2 KHz – 50 KHzINPUT CHANNELCMRR > 60 dBnoise voltage @ 20 KHz 19 nV / rt(Hz)1/f noise corner frequency 2 KHzREFERENCE CHANNELduty cycle anyphase shift 0 – 180 o

amplitude (square) > 1.5 VGAINLNA gain 100 (fixed)input channel amplifier 1-2-5-10-20-50mixer conversion gain 1.2x(1-2-4-8-16)Final DC amplifier 3 (fixed)total max. nominal gain 109 dBSC LOW-PASS FILTERfilter order 2cut-off freq. @ 16 KHz clock freq. 1 Hz – 100 Hz

[2] G. Ferri, P. De Laurentiis, S. Sperandii: “A CMOS low-voltage shifter as an integrated resistive sensor front-end”,AISEM 99, The 4th Italian conference on Sensors andMicrosystems, Rome, 3-5 February 1999.

[3] G. Ferri, P. De Laurentiis, A. D’Amico, C. Di Natale,M. Ceccarelli: “A low-voltage fully integrated CMOSanalog lock-in amplifier”, Alta Frequenza (submittedfor publication).

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Project title: Circuit architectures, design and characterization of integrated lock-in amplifiers for sensor applications

Participants: Università di Bologna, Unit responsible: Antonio Gnudi (Project Coord.)Dip. Elettronica, Informatica e Sist. Collaborators: Giorgio Baccarani, Eleonora Franchi,Viale Risorgimento, 2, 40136 Bologna Luigi ColalongoTel.: 051-2093013 Fax: 051-2093073Email: agnudi@deis.unibo.it

Università di L’Aquila Unit responsible: Giuseppe Ferri Dipartimento di Ingegneria Elettrica Collaborators: Pierpaolo De Laurentiis, Francesco67040 Monteluco di Roio (L’Aquila) Alesii, Stefano Sperandii, Ernesto MassaTel.: 0862-434446 Fax: 0862-434403Email: ferri@ing.univaq.it

Università di Roma Tor Vergata Unit responsible: Giancarlo Bartolucci Dipartimento di Ingegneria Elettronica Collaborators: Arnaldo D’Amico, Corrado Di Natale,Via di Tor Vergata, 110 Mirko Ceccarelli, Alessandro MantiniTel.: 06-72597349 Fax: 06-2020519Email: bartolucci@eln.uniroma2.it

Purpose of the work

The presence of free oxygen (O2) in air, water and soilsvery important for biosphere, and technosphere. The knowl-edge of oxygen concentration (xO2)in the gaseous phase ofcomplex systems is necessary in many fields (Tab. 1); its val-ue may range from 21% to few ppm.

xO2 is object of determinations since the origin of ana-lytical chemistry; many methods have been developed (Tab.2). Nevertheless new ones are searched for: (a) xO2 at ppblevel; (b) xO2 variations in time interval less then 1s; (c) insitu monitoring of natural, biomedical,and technical com-plex systems and rapid processes.

Outline of the work

The O2 sensor is an electrochemical device; its use isbased on the measurement of the e.m.f. of a tensiometricgalvanic cell. The sensor develops an e.m.f. logarithmicallyrelated to xO2:

E=E0+k log(xO2) (1)

where E0 and k are calibration constants. The experi-mental k value is 10-15 mV about (close to theoretical val-ue). Eq. (1) was experimentally checked in the range from210 000 ppm to 400 ppm).

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Oxygen sensor

COSMED, CNR-PSM, Università di Roma “Tor Vergata”,Università di Roma “La Sapienza”

Table 2. Analytical methods

Method Principle NotesWinkler Titrimetric Largely applied for BOD determinations; off-line analysis; analysis time: 5-15 days.Clarke Amperometric Dangerous interactions between the invasive Clarke sensor and the system to be an-alyzed.Rankine Paramagnetic Highly dependent on temperature, vibrations and paramagnetic gases (such as NOx).O2 Sensor Potentiometric Non invasive method; in situ and in the field analysis; analysis time: few seconds.

Table 1. Outstanding processes which need xO2 monitoring

Field ProblemsAgriculture Air circulation in soilsBiology Respiration rateBiotechnology Maintenance of the best xO2 value in bioconversion (microaerophilia)Energy management Incondensable gas monitoringFoods O2 consumption of conserved vegetables (such as Potatoes);

Absence of O2 in bottled beverages and canned foodsMedicine Respiration rateMicrobiology Microbial growthToxicology Effects of toxic agents on O2 consumptionWaters Chemical and biological O2 demand (BOD)Waste-waters Pollution and biodegradation process monitoring

The block diagram of the measurement system is re-ported in Fig. 1.

The carrier gas (CG, pure nitrogen) is let to flow throughthe O2 sensor (O2-SS), at a constant flow rate, to obtain thereference signal E0. Then, analytical cycles are realized:1. For the analysis time (ta), CG flows trough the sampling

probe (SP) and the sensor. SP is a compact, non porous,plastic silicone or teflon tubing which is conveniently lo-cated into the analyzed system (AS). Because of the O2

chemical potential difference between the inside and theoutside of SP, O2 diffuses from AS into SP at a rate de-pendent on xO2 in AS.

2. For the sampling-recovery time (ts), CG flows only troughthe sensor, to return to the reference signal E0.Peak-shaped responses are obtained (Fig. 2); The peak-

signals depend on xO2 in AS, ts, fluidodynamic condi-tions, temperature, structural and compositional para-meters of SP.

Main results

In the current year a prototype of O2 sensor has been re-alized to verify the correct application of the principle. Fur-thermore, a data acquisition system for the sensor has beenprojected.

The main characteristics of the O2 sensor are:a) Low dependence of E0 from room temperature, atmos-

pheric pressure; low influence of E0 on peak-signals.b) Specificity: no interference from CO2, greenhouse and

IR gases, acid-base and redox volatile chemical species.

c) Amount of O2 for each determination: from mmol tonmol.

d) Life: unlimited.Fig 3 shows tidal xO2 variations in respiratory air; air was

continuously withdrawn by means of a peristaltic pump,from the mouth of a man; low response time of the sensorallows to follow the fast xO2 variations.

Future developments

For the next year we will study the mechanical, electronicand electrochemical optimization of the system.

A low cost, low noise, high impedance preamplifier sys-tem will be projected; furthermore a simplified, low cost,multichannel data acquisition board and the relative PC in-terface and analysis software will be realized. Thanks to thisboard we can control the entire system via computer (e.g.valve status, temperature monitoring…). Moreover we con-sider to do some experiments monitoring more gases si-multaneously (for the determination of human metabolismeither O2 decrease or CO2 increase are fundamental).

We will study the technological compatibility of the sen-sor with the silicon micromachining processes.

Expected deliverables

We will measure the respiration rate of some vegetablesto determinate the optimum CO2/O2 ratio. Controlled at-mosphere storage is used for some fruits, where the O2 lev-el in the storage room is lowered and the CO2 raised to in-hibit fruit respiration and subsequent breakdown.

We will measure the oxygen permeability of various plas-tic membrane used in canned foods.

Furthermore we will measure the human metabolism bymonitoring simultaneously CO2 and O2. We consider to de-velop a very low cost instrumentation for metabolic deter-mination.

References

[1] E. Scarano, “Advanced analytical systems”, in “Sensorsand microsystems”, pp.177-179 (1998)

[2] E. Scarano, “A non-invasive specific oxygen sensor: fun-damentals and application”, in “Sensors and microsys-tems”, pp.180-186 (1998)

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Figure 1. Block diagram of the measurement system.

Figure 2. O2 sensor peak-shaped responses and measurementsrepeatability.

Figure 3. Tidal xO2 variations in respiratory air

Participants: Oxygen sensor

COSMED s.r.l. Unit responsible: Paolo Brugnoli (Project Coord.)Via dei Piani di Monte Savello, 37 Collaborations: R. Aprile, F. Massussi, D. CelentanoC.P 3 00040 Pavona di AlbanoTel.: 069315492 Fax: 069314580Email: info@cosmed.it

Università di Roma II - Tor Vergata Unit responsible: Corrado Di NataleFac. Di Ingegneria - Dip. Di Ingegneria Collaborators: A. D’Amico, A. Mantini,elettronica Via di Tor Vergata - 00133 Roma E. Mazzone, F. Gobbi, R. CarboneTel.: 0672597349 Fax: 062020519

Università di Roma - La Sapienza Unit responsible: Elio Scarano,Fac. Di Chimica - Dip. Di Chimica Collaborators: Luca Lioce, Francesca SpinelliP.le Aldo Moro, 5 - 00185 Roma

CNR - Area di ricerca Roma - Tor Vergata Unit responsible: Andrea BearzottiIstituto del Progetto Sensori e Microsistemi Collaborators: S. Petrocco, C. Fraiegari, L. PalummoVia Fosso del Cavaliere, 100 - 00133 Roma

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Outline of the work

The electrochemical biosensors have become importantdevices very diffuse in the bioanalytical field; due to theircharacteristics by simple electrochemical measurements theyhave made possible analysis of compounds of particular in-terest in the chemical, biological, medical fields. The elec-trochemical biosensors are rapid, specific, easy to be han-dled devices. For their realization the couplement betweena thin layer of immobilized biological material such as en-zymes, antibodies, cells with an indicating transducer elec-trode able to convert the biochemical signal into an electricone, so being combined the specificity of the biocatalyticmaterial with the selectivity of the electrode.

The research in the field of the biosensors has turned itsattention during last years to the use of those enzymatic re-actions which can be performed in organic solvents. Reallyit has been recently shown that some enzymes can operatenot only in aqueous solutions, but also in anhydrous or al-most anhydrous organic solvents. This behaviour of certainenzymes can enlarge the field of research to hydrophobic orwater insoluble substrates. Really the use of the biosensorsof these devices operating in organic solvents extends thepossibility of the analytical application of these devices. Thesubstance contained in the hydrophobic matrices should re-quire costly and time wasting pretreatments to be dissolvedin aqueous solutions and then determined. The OPEEs (or-ganic phase enzyme electrodes) allow to avoid these pre-treatments and to analyze the substrate directly in the con-taining matrices, by dissolving them in the suitable organicsolvent.

The aim of this research is to build two biosensors ableto operate in organic solvents1) a biosensor based on the inhibiting effect of the

organophosforic and carbamminic pesticides, soluble inorganic solvents, on the cholinesterase enzymes;

2) a biosensors based on superoxidedismutase to determinefree radicalsIn both these cases the electrochemical transducer is an

amperometric gaseous diffusion electrode to determine oxy-gen, while the enzymes have been immobilized in K-car-raginean or cellulose triacetate membranes. Of both the

biosensors the responses have been recorded during the wholelifetime and parameters such as sensitivity, linearity rangeresponse time evaluated. The obtained results show that theaims of the research can be realized. The first proposed biosen-sors can be used to determine water insoluble pesticides inchloroform and chloroform-n-exane mixtures basing on thetwo reaction

where:

Buch = ButyrrylcholineBu Ch e = Butyrrylcholinesterase enzymeBu = Butirric acidCh = CholineChOe = Cholineoxidase enzyme

and on the reduced oxygen consumption in presence ofthe pesticides. On the other hand the adoption of bioenzy-matic biosensors, in place of monoenzymatic ones, even ifwith higher difficulties of development, presents the ad-vantage of increasing the specificity of the sensor’s responseand of lowering the interfering levels; to eliminate completelythese an help comes also from the replacement of potentio-metric and voltammetric detectors proposed in the existingliterature with an amperometric gaseous diffusion one. Theuse of these transducers has allowed not to introduce anyelectrolyte such as tetraebutylammonium p-toluenesulphonateor tetraethylammonium p-toluenesulphonate needed by theother two detectors to increase the conductivity of the medi-um. By the superoxidedismutase biosensor, superoxide rad-ical has been determined basing on the following reaction

2O2+2H+ superoxidedismutase >O2+H2O2 , so correlat-ing the substrate amount with the variation of the oxygenconcentration determined by the amperometric gaseous dif-fusion electrode. The enzyme has been immobilized in cel-

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Biosensors to monitor enzymatic activity pesticide and radical dependent

Università di Roma “La Sapienza”

Buch Bu ChBuche → +

Ch O Bet H OChOe+ → +2 2 2

lulose triacetate and placed between two gas permeable teflonmembranes in order to avoid its contact with an organic sol-vent.

The biosensor is the first meaning result of this not easyresearch, especially if compared with the low number ofbiosensor for radicals reported in literature, all anyway op-erating only in aqueous solution.

Even if this problem needs further studies, this proposedbiosensors to determine free radicals in organic solvent (di-methyl-sulphoxide) is the forst example of this kind report-ed in the scientific literature with potential applications ofenvironmental and medical natures. The only problem isconstituted by the presence of bacterial interference able toaffect the response of the oxygen detector, anyway is par-tially limited by the organic solvents where bacterial growthis slowed down.

Future developments

As hydrogen peroxide can negatively affect the enzymeactivity a couplement of the proposal systems with catalasewill be tempted in order to improve analytical characteris-tics. Application to real matrices even in flowing conditionwill be performed with particular attention to environmen-tal food and medical samples.

References

1. L.Campanella, G.Favero, F.Occhionero, M.Tomassetti,“Selective membrane sensors for free radical analysis basedon potentiometric and CHEMFET devices”, Analusis,26, 223-228, (1998).

2. L.Campanella, R.Roversi, M.P.Sammartino, M.Tomas-setti, “Hydrogen peroxide determination in pharmaceu-tical formulations and cosmetics using a new catalasebiosensor”, J.Pharm. Biomed. Anal, 18, 105-116, (1998).

3. L.Campanella, S.De Luca, M.P.Sammartino, M.Tomaset-ti, “A new organic phase for the analysis of organophos-phorus pesticides and carbamates”, Anal. Chim. Acta.,385, 59-71, (1999).

4. L.Campanella, F.Pacifici, M.P.Sammartino, M.Tomas-setti, “A new organic phase bienzymatic electrode forlecitin analysis in food products”, Bioelectrochemistryand Bioenergetics, 47, 25-38, (1998).

5. L.Campanella, G.Favero, M.P.Sammartino, M.Tomas-setti, “Further development of catalase, tyrosinase andglucose oxidase based organic phase enzyme electrode re-sponse as a function of organic solvent properties”, Ta-lanta, 46, 595-606, (1998).

6. L.Campanella, “Analysis of several real matrices using newmono-bi-enzymatic, or inhibition organic phase enzymeelectrodes”, Anal. Chim. Acta, 393, 109-120, (1999).

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Project title: Biosensors to monitor enzymatic activity pesticide and radical dependent

Participants: Università di Roma I Unit responsible: Luigi CampanellaDip. di Chimica Collaborators: Mauro Tomassetti P.le A. Moro 5, 00185 Roma Maria Pia Sammartino, Gabriele FaveroTel.: +39-06-4463828 Fax: +39-06-490631Email: campanella@axrma.uniromal.it

Purpose of the work

About twenty years ago, it was shown that a stabilizedzirconia-based electrochemical sensor operating in non-Nern-stian mode offered a new chance for determining low (<1000ppm) CO concentrations in air [1]. It was suggested thatthe deviation from the Nernstian behaviour arose from non-equilibrium conditions at the measuring electrode. The si-multaneous presence of an anodic and a catodic electro-chemical reaction was assumed taking place at the measur-ing electrode and the source of the anomalous e.m.f. valueswas associated with the presence of a mixed potential. Insuch a condition the driving force of this electrode poten-tial is kinetics instead of thermodynamics

Some investigation activities were focused to the catalyticproperties of materials to obtain, even at low temperatures,thermodynamic equilibrium conditions at one electrode inorder to avoid the need of two compartments cell [1,2].Meanwhile, more detailed electrochemical studies directly[3] and indirectly [4] substantiated the presence of the mixedpotential. In particular, it was demonstrated [4] that differ-ent electrode materials originated different e.m.f responses,at the same temperature and CO concentration. The possi-bility of using widespread microelectronic techniques to ob-tain a planar and miniaturized configuration of such a typeof sensor became a realistic perspective.

The aim of the research is directed at designing andrealising a solid state electrochemical device with non-Nern-stian behaviour for determining, in air, the CO concentra-tion (10-1000 ppm) with an accuracy of about 5-10% of theactual value. The screen printing technology is used to ob-tain the planar and small size (≤ 1 cm2) sensor as well as itsthe integrated heater (operating temperature 250-500 oC).

Outline of the work

The programme includes the choice of proper materialfor the measuring electrode and for the dielectric film as wellas the selection of the heater configuration and the sensorpackage.

Deposition process conditions are studied and the char-

acterisation of the layer and of their mutual interaction isperformed by means of adequate microscopies, electrical andanalytical spectroscopies.

E.m.f measurements are carried out as a function ofCO concentration and temperature. In order to have a widercharacterisation of the sensor its accuracy, sensitivity, re-sponse time and reliability are studied as well as the effectof interfering gases (CH4, CH3COH and water) on the e.m.f.output.

Main results

Preliminary results have been obtained with a sensitiveelement consisting in a small (10x10mm, 0.5 mm-thick) Yt-tria Stabilized Zirconia (YSZ) single crystal. A rutheniumdioxide and a platinum film were screen printed onto thesame face of the solid electrolyte. The sensitive element wasthen housed in a proper alumina package and the electrodesconnected to the platinum signals leads by means of ultra-sonic bonding.

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Solid State electrochemical sensor for indoordetection of CO (ICAMES)

Università di Modena e Reggio Emilia, Università di Milano-Bicocca

Fig. 1 E.m.f. vs temperature at costant CO concetration (48.2 ppm).

E.m.f. measurements were carried out in the 250-500°C temperature range, using synthetic air/CO (48.2, 204.0,407.0, and 818.0 ppm) gas mixtures.

The temperature dependence of the e.m.f signal mea-sured in dry plain air and in a air/CO (at constant concen-tration) mixture is reported in fig. 1; e.m.f values within ±1 mV are measured in dry air, while higher values are ob-

served in presence of the gas mixtures. The e.m.f. presentsa maximum at about 300°C. Increasing the CO concentra-tion this temperature shifts toward higher values. A system-atic analysis of this behaviour is in progress. In the 300-330oC temperature range a straight-line relationship betweene.m.f. values and CO concentrations was observed (fig.2).

Figure 3 reports a typical signal as a function (concen-tration 48.2 ppm). of the time. An e.m.f. is generated assoon as the flowing gas attains the sensing electrode sur-face; the relatively long delay time in reaching the steady-state e.m.f. value is probably due to the gas dynamics in thetesting cell. The values reported in fig. 2 pertain to the steady-state conditions.

It has been shown that an electrochemical planar COsensor can be produced with usual microelectronic tech-niques; from preliminary data the performances of such adevice appear to be quite interesting. Relatively large signalsare measured even without any amplification at low con-centrations of CO in air; this result offers the perspectivesfor a very sensitive sensor. Surely interesting is furthermorethe relatively low operating temperature; in fact, the devel-opment of a device in which the sensing element and itsheater are integrated might be relatively simple. These find-ings state the carrying on of the research until a whole de-velopment and characterization of the planar sensor.

Further work will be devoted to increase the number ofthe CO/air ratios, to define the actual resolution of the de-vice and to assess its accuracy and reliability (e.g. interfer-ing gasses, humidity). Moreover other electrode materialswill be prepared and tested. Finally the full integration ofthe sensing element and heater, in a proper package, will bedeveloped.

Expected deliverables

Papers and patent disclosing:- the possibility of detecting very low quantities (a few ppm

or less) of gaseous molecules on by planar solid state elec-trochemical sensors operating at low temperatures ;

- the quantitative evidence of the existence of a mixed po-tential also in solid state galvanic cells;

- results concerning interactions between solid electrolytesand thick film dielectric layers

Prototypes showing:- design and expertise in manufacturing a planar integrated

CO electrochemical sensor to be transferred to a compa-ny interested in production and commercialisation.

References

[1] H. Okamoto, H. Obayashi, T. Kudo, Carbon monox-ide gas sensor made of stabilized zirconia, Solid StateIonics, 1, 1980, pp. 319-326.

[2] N. Li, C. Tan, H.C. Zeng, High-temperature carbon

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Fig. 2 E.m.f. vs CO concentration at constant temperature (300°C)

Fig. 3. E.m.f. vs. time. The CO/air mixture was introduced inthe cell after 8 minutes.

monoxide potentiometric sensor, J. Electrochem. Soc. ,140, 4, 1993, pp.1068-1072.

[3] Z.Y. can, H. Narita, J. Mizusaky, H. Tagawa, Detectionof carbon monoxide by usind zirconia oxygen sensor,Solid State Ionics, 79, 1995, pp. 344-348.

[4] D. Narducci, A. Ornaghi, C.M. Mari, CO determina-

tion in air by YSZ-based sensors, Sensors and. ActuatorsB, 18/19, 1994, pp. 566-568.

[5] C.M. Mari, R. Ruffo, M. Prudenziati and B. Morten“Carbon Monoxide Electrochemical Planar Sensor ForIndoor Applications” Extended abstract for EurosensorsXIII , De Hague 12-15 Sep. 1999

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Project title: Solid State electrochemical sensor for indoor detection of CO (ICAMES)

Participants: Università degli Studi di Modena e Reggio Emilia, Unit responsible: M. Prudenziati (Project Coord.) Dipartimento di Fisica, Collaborators: B. Morten via G.Campi 213/A, 41100 ModenaTel: +39-059/586030 Fax: +39-059.367488Email: Prudenziati@imoax1.unimo.it

Università degli Studi Milano-Bicocca”, Unit responsible: C.M. Mari,. Dipartimento di Scienza dei Materiali, Collaborators: R. RuffoVia Cozzi 53, 20125 MilanoTel.: 02/64485122 Fax: 02/66174400Email: cmmari@icil64.cilea.it

Purpose of the work

The aim of the research has been focussed on the fol-lowing aspects:1) The search of a convenient synthetic access to highly

ethynylated organic and organometallic polymers.2) The use of these polymers as sensitive membranes in the

realization of sensors able to detect organic and inorgan-ic molecules in the vapour or gas phases.

3) The development of properly engineered electronic de-vices that, while supporting the polymeric film, are ca-pable to convert in a measurable electrical signal the phys-ical variations occurring upon absorption of the chemi-cal specie on the polymer surface.The sensors under study will be resistive type and SAW

(based on Surface Acoustic Wave propagation). The sensi-tive materials are prepared in the form of thin films whichare spin deposited on the electronic device. Upon exposureto the chemical environment under investigation (for ex-ample water vapour, alcohols, amines, carbon and nitrogenoxides), a measurable electric output is obtained by the sen-sor. A strict control of the chemical structure of the sensi-tive material is required in order to gain sensitivity and se-lectivity towards the different detectable chemicals. In par-ticular much attention is payed to the nature of the organ-ic repeating unit of the polymer and to the transition met-al that is eventually inserted in the polymer backbone.

Outline of the work

The three aspects of the project outlined in the previoussection are actively interacting toward the final goal of ob-taining gas sensors based on materials which are able to de-tect various chemicals with a reliable and reproducible re-sponse, without memory effects and drawbacks due to in-stability and degradation.

The initial efforts have mostly been dedicated to the syn-thesis and characterization of a series of polymers designedwith the aim of tuning the sensing properties trough thecontrol of the chemical structure. The materials are acetylenic

and metallaacetylenic polymers of different aromatic re-peating units and different side-chain lenght. They are airstable and processable in order to form thin membranes thatcan be deposited on the electronic devices.

Next step is the fabrication of a reliable sensor. Lookingfor the most advanced performances, it is necessary not on-ly to design the appropriate polymeric membranes, but al-so pay attention on the choice of the appropriate metal elec-trodes, which are expected to work with no problems at thepolymer/metal interface [XPS (X-ray Photoelectron Spec-troscopy) and NEXAFS (Near Edge X-ray Absorption Spec-troscopy) studies]. Then the electrical characterization of thesensor is performed and finally the tests in the presence ofrelative humidity, alcohol vapours, and other gas phase mol-ecules are carried out.

The parameters (temperature, applied voltage, shape andminiaturization of the devices, etc.), that are expected to beresponsible of the best performances of the sensors, will bealso investigated and optimized.

Main results

In the past few years our research group mainly focussedits efforts on the synthesis and characterization of poly-acetylenes and organometallic polyines [1-4], with a specialconcern to their applications as sensitive membranes in gassensors [5-7]. During the first year of this project we havededicated our efforts to find new procedures for the syn-thesis of novel polyines, organometallic complexes and poly-mers. The most interesting results are reported in the fol-lowing sections:

a) Synthesis of Organic and Organometallic Homopolymers andCopolymers

Pd catalyzed coupling reactions have been performed ei-ther by a modified Stille procedure and an innovative Pd-catalyzed metal-carbon coupling. Aromatic diiodides arecombined with tributyltinacetilene in a new “one pot” syn-thetic method, affording organostannanes which can be fur-ther reacted with a second organic diiodide or an organometal-lic dihalide to obtain organic or organometallic polymers re-

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Organometallic polyine polymers and related complexesfor chemical sensors

CNR-PSM, CNR-CSMDR, Università di Roma “La Sapienza”, Università di Roma Tre.

spectively [8,9]. These materials are soluble, processable andtheir electrical characteristics are probably modulated by thecombination of the different aromatic and metal units. Themolecular structure of the poly(arylene- ethynylene) poly-mers prepared are reported in Fig.1, while in Fig.2 are re-ported the organometallic polymers.

Particularly promising for the scope of the work seemsto be a class of iron containing polymers of peculiar chem-ical structure, prepared by the above cited “one pot” reac-tion. A representative example is depicted in Fig.3, [10].Such kind of molecules are expected to show electrical com-

munication between the Fe centers trough the organic spac-er and consequent charge delocalization througout the poly-mer backbone.

c) Synthesis of Model MoleculesWith the aim of getting a better insight into the chem-

ical properties of complicated polymers, a series of monoand polymetallic complexes with acetylenic ligands and therelated pure organic dimers, have been synthesized and char-acterized [11]. The organometallic molecules are asymmet-ric bis-acetylide complexes, i.e. [Pt(PBu3)2(C≡C-R)(C≡C-C6H4-C6H4-C≡CH)], (R= p-nitrophenyl, ferrocene), andsymmetric bi- and tetranuclear bridged complexes, i.e. [R-C≡C-PtL2-C≡C-C6H4-C6H4-C≡C-PtL2-C≡C-R], (L=Pbu3,R= phenyl, p-nitrophenyl, ferrocene). The pure organic mol-ecules are R-C≡C-C≡C-C6H4-C6H4-C≡C-C≡C-R, withR=phenyl, ferrocene. A modulation of the electron transfercapability between different metallic centers is expected tooccur for these model complexes.

Sensors

Among the variety of materials that have been prepared,we have selected two of them, as a starting point for the testof applications in chemical sensors. The molecules are a Pdbinuclear complex, that is Pd-TRI, and a Pt polymer, thatis Pt-TRI, drawn in Fig.4.

Pd-TRI and Pt-TRI have been deposited as thin filmsby spinnig ( at 2000 rpm) a CHCl3 solution of each mate-rial onto a silicon substrate (dimensions 5x5 mm) where 20pairs of interdigitated electrodes were previously photolith-ographically defined (Cr 100 nm thick and 20 µm wide).Theelectrical characterization was performed with a KeithleyQuasistatic CV Meter. The measurements of the responseto relative humidity (RH) were made by inserting the sen-sor into a testing cell (40 cm3 working volume, room tem-perature), where the RH variations (0-90%) were obtainedwith a MKS mass flow controller (at flow rate 200 SCCM)by introduction of a steam of dry or wet nitrogen, and record-ing the current intensity (I).

It is noteworthy that the two sensors show a quite dif-ferent behaviour, despite the similarity of chemical struc-ture. The I/V characteristics of Pd-TRI and Pt-TRI are re-ported in Fig.5 (A and B Pd-TRI and Pt-TRI respectively).

The linear shape of the Pd-TRI characteristic suggestsan intrinsec electronic conductivity, that is unusual for an

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Fig.1 Molecular structure of poly(arylene-ethynylene) polymers

Fig.2 Molecular structure of Pt and Pd organometallic poly-mers, oligomers and complexes

Fig.3 Poly[2,5-bis(h5-ethynylcyclopentadienyl-irondicar-bonyl)thiophene-2,5-bis(ethynyl)thiophene]

Fig.4 Chemical structure of molecules used in sensor devices

organometallic discrete molecule. Pt-TRI, a polymer withabout ten repeat units, shows a little hysteresis and a typicalsemiconductor I/V feature. The response to RH variationsof the two samples is reported in Fig.6 (A and B in the sameorder of the previous figures).

Future developments

The test of the synthesized molecules will continue andwill be performed in different experimental conditions inorder to find the best match between chemical structure andsensor response. The variety of materials should lead to therealization of selective and highly sensitive gas sensors.

Expected deliverables

New devices with well defined electronic characteriza-tion and multisensor systems capable to detect differentchemicals in the vapour or gas phase will be the final goalog the project.

References

11. M.V.Russo, A.Furlani, R.D’Amato, J.Polym.Sci., PartA: Polym.Chem., 36 (1998) 93

12. M.V.Russo, A.Furlani, P.Altamura, I.Fratoddi and G.Pol-zonetti, Polymer, 38 (1997) 3677

13. M.V.Russo, G.Infante, G.Polzonetti, G.Contini, G.Tuo-rillon, Ph.Parent, C.Laffon, J.Electr.Spectr.Relat.Phe-nom., 85 (1997) 53

14. M.V.Russo, G.Polzonetti, A.Furlani, A.Bearzotti, I.Fratod-di, and P.Altamura, J.Vac.Sci.Technol. A, 16 (1998) 35

15. P.Altamura, A.Bearzotti, A.D’Amico, V.Foglietti, I.Fratod-di, A.Furlani, G.Padeletti, M.V.Russo, G.Scavia,Mat.Sci.Engin. C, 5 (1998) 217

16. C.Caliendo, E.Verona, A.D’Amico, A.Furlani, G.In-fante, M.V.Russo, Sens.Actuat. B, 24 (1995) 670

17. E.Quartarone, P.Mustarelli, A.Magistris, A.Furlani,I.Fratoddi, and M.V.Russo, Solid State Ionics, (1999)in press

18. G.Giardina, P.Rosi, C.Lo Sterzo, A.Ricci, “An efficientOne Pot access to poly(arylene-ethynylene) homopoly-mers. Use of the Bu3Sn- moiety as recyclable carrier tointroduce the ethynyl Unit in the chain”, (1999) man-uscript submitted

19. C.Lo Sterzo, Synlett. (1999) in press10. E.Antonelli, P.Rosi, C.Lo Sterzo,E.Viola,

J.Organom.Chem., 578 (1999) 21011. M.V.Russo, C.Lo Sterzo, P.Franceschini, G.Biagini, and

A.Furlani, “Synthesis and characterization of mono anddinuclear Pt(II) acetylides with electron-donor and elec-tron-withdrawing ligands”, (1999) manuscript in prepa-ration

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Fig.5 A, I/V characteristic of Pd-TRI; B, I/V characteristicof Pt-TRI

Fig.6 A, response of Pd-TRI to RH variations; B, response ofPt-TRI to RH variations

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Project title: Chemical sensors based on polymeric membranes for detection of gases and vapours.

Participants:

P.S.M.-C.N.R. Unit responsible: Dr.Andrea Bearzotti (Project Coord.)Via Fosso del Cavaliere 100, Collaborators: Stefano Petrocco00133 Rome. Claudia Fraiegari, Lucrezia PalummoTel.: 06/49934537, Fax: 06/49934066Email: bearzotti@axrma.uniroma1.it

University of Rome "La Sapienza" Unit responsible: Prof. A.FurlaniDepartment of Chemistry, Collaborators: Maria Vittoria Russo,P.le A.Moro 5, 00185 Rome Ilaria Fratoddi, Patrizia Altamura,Tel.: 06/49913349 Fax: 06/490324 Rosaria D'AmatoEmail: furlani@axrma.uniroma1.it

CNR-Centro di Studio sui Meccanismi di Unit responsible: Claudio Lo SterzoReazione (CSMR) Collaborators: A. Stella,c-o Dip. di Chimica Univ. "La Sapienza"Piazzale Aldo Moro 5, 00185 RomaTel.: +39-06-4957808 Fax: +39-06-490421Email: losterzo@netmgr.ced.rm.cnr.it

ASSEL s.r.l. Unit responsible: Marco FlaminiVia Pontina Vecchia 189, Collaborators: A. Flamini, F. Flamini04011 Aprilia (LT) M. Flamini A. Pacchiarotti, P. PatellaTel.: 06/9255088, Fax: 06/9256707Email: info@assel.it

Purpose of the work

Spectroscopy in the visible and near infrared spectral re-gions is one of the most popular methods in conventionalanalytical chemistry. The intrinsic optical and mechanicalcharacteristics of optical fibers and integrated optical wave-guides, together with the wide availability of bright LEDsand portable spectrometers, further enhance the applicationareas of spectroscopy, and make possible the implementa-tion of compact instrumentation dedicated to the monitor-ing of specific parameters. Two measurement approaches arepossible:• Direct Spectroscopy, when the light intensity transmitted

through the analyte is measured and analyte characteris-tics such as concentration or molar absorptivity are ob-tained by applying the Lambert-Beer law. Direct spec-troscopy is mostly suitable for the colorimetry of non-tur-bid liquids or for analysing compounds with non inter-ferring spectra.

• Chemically-Assisted Spectroscopy, when the analyte underinvestigation interacts with a chemistry, and the status ofthe analyte is indirectly obtained by measuring the spec-tral properties of the chemistry itself.

The OptoSpec project involves the design, implementa-tion and testing of guided-wave sensors that address themonitoring of different parameters by means of direct andchemically-assisted spectroscopy.

Outline of the work

Guided-wave sensors proposed by the OptoSpec projectare intended for direct absorption spectroscopy of liquidsamples and chemically-assisted spectroscopy of gas samples.The work is planned according to the following develop-ment priorities:• a fiber optic sensor for the colorimetry of liquid samples

of interest for petrolchemical plants;• a fiber optic sensor for oxygen assessment that makes use

of luminescent metal complexes embedded in a polymer-ic matrix;

• an integrated optics probe, fiber-optic-compatible, for ni-

trogen oxide assessment that makes use of phthalocyaninLangmuir-Blodgett films.

The implementation of a custom instrumentation andsoftware is mandatory for each sensor type, as each moduleis PC compatible and interchangeable. A sketch of what theOptoSpec project resolves to achieve is shown in Figure 1.

Main results

1) Fiber optic sensor for colorimetry of liquid samples: on-linegasoline blending monitoring

The on-line near infrared spectrophotometry of raw andrefined hydrocarbon products is useful for the optimizationof refining and petrolchemical processes. The possibility ofinstalling a control unit in a non-classified area, while im-mersing a safe probe in inflammable and explosive envi-ronments, makes optical fiber probes extremely attactive.Another important application is colorimetry in gasolineblending control, especially when different blendings aresent sequentially along the same pipe and a final electrovalvemust decide on directing them to the relative tanks.

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OptoSpecGuided wave sensors for analysing liquids by means ofdirect spectroscopy and for gas monitoring by means of

chemically-assisted spectroscopy

Centro Laser, CNR-IROE, CNR-IME, CNR-ITS, TRI-TECSA

Figure 1 OptoSpec modular instrumentation for direct andchemically-assisted guided-wave spectroscopy

The sensor implemented by the OptoSpec project was de-signed to recognise the difference between lead-free (green)and regular (red) gasoline and the blendings of these twotypes. The absorption spectra of green and red gasoline blend-ings are shown in Figure 2.

Direct absorption spectroscopy of gasoline blendings wasapproached by means of a twin-fiber connection, by mak-ing use of a multimode optical fiber for lighting and an iden-tical fiber for detection. The absorption probe coupled tothe fiber link permitted interaction between a collimatedlight beam and the analyte under test, over a prefixed path-length. Because of the fiber’s numerical aperture, opticalcomponents were used to convert the fiber’s divergent beaminto a collimated light brush and to refocus that beam intothe fiber link. Radially-graded refractive-index (GRIN) rodlenses were used as collimating-focussing optics: their cylin-drical shape made it possible to achieve compact, stable andrugged lens-to-fiber connections.

The microoptic probe coupled to the optical fiber linkis shown in Figure 3. The gap between the lenses, that rep-resents the path-length for absorption spectroscopy, can befixed according to the requirements of the application. Amodelling of the probe intrinsic loss as a function of thepath-length was performed by using the optical design soft-ware Solstis-Optis 3.22®, in order to identify the most suit-able fiber and lens types. The probe prototype used 50/125µm optical fibers and SLW-1.8-0.25p-0.63 GRIN lenses.

3) Modular instrumentationAn instrumentation for direct absorption spectroscopy

was set up. It consisted of an electrooptic module interfacedto a portable computer by means of an A/D board with in-put/output ports. The electrooptic module housed fourLEDs, to slice the 0.4-0.9 µm spectral range, and two PINs.LEDs and PINs were housed in ST-compatible receptacles,and were easily connectable to almost any fiber optic link.The LabView® software was used for electrooptic modulemanagement, which was programmed to perform automaticor semiautomatic measurements and data processing.

The module was set up to perform dual-wavelength dif-ferential absorption measurements by means of two LEDsat a time, or single-wavelength absorption measurements bymeans of a single LED. A temperature stabilization systemusing Peltier cells was added to guarantee temperature sta-bility of the module, so as to achieve LED spectral and in-tensity stability.

This instrumentation is compact and portable, and maybe battery-powered. Minor modifications to the sources andto the software make it possible to obtain a custom instru-mentation for dual-wavelength or single-wavelength ab-sorption measurements in the visible and near-infrared spec-tral regions for many other application areas.

2) Chemical indicators for oxygen detectionThe chemical indicator for the oxygen sensor was based

on the luminescencent of mononuclear and dinuclear Ir (III)cyclometalated complexes immobilized in a polymerizedpoly(ethyleneglycol) ethyl ether methacrylate (pPEGMA).

The interest in the luminescent properties of metal-polypyridine complexes, as far as their use as quenchiomet-ric oxygen sensors, was related to the nature of the excitedstate. The luminescence of such complexes usually origi-nated from triplet MLCT (metal-to-ligand charge-transfer)levels exhibiting long-lived lifetimes. The triplet-triplet en-ergy transfer process involving oxygen was quite efficient.In contrast to the results of many research groups, linearStern-Volmer plots were found; it was assumed that the na-ture of the polymeric matrices enabled the metal chro-mophores to experience similar environments. In addition,from the slopes of the Stern-Volmer plots, it seemed thatthese systems exhibited properties comparable with the moreused Ru(II) polypyridine complexes. This circumstanceseemed to confirm that the Ir (III) complexes consideredwere a valid alternative to the more extensively used Ru (II)

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Figure 2 Absorption spectra of lead-free (green) and regular(red)AGIP gasoline blendings

Agip 100% greengreen 90%-red 10%green 80%-red 20%green 70%-red 30%green 60%-red 40%green 50%-red 50%green 40%-red 60%green 30%-red 70%green 20%-red 80%green 10%-red 90%Agip 100% red

Figure 3 Fiber optic probe for direct absorption spectroscopy ofliquid samples

complexes as the active component of luminescent solid-state oxygen sensors. Furthermore, the results obtained sug-gested that, besides the lifetime of the chromophore and thepermeability of the matrices, the size and the charge of theluminophore could affect the sensitivity and the response ofthe sensor system.

Experiments are in progress to obtain a polymeric ma-trix with lower viscosity than the former; it is expected thatthe oxygen sensitivity of the system increases with decreas-ing the medium viscosity. Luminescent metalloporphyrincomplexes will also be considered for their excellent emis-sion quantum yields, very long lifetimes, and high absorp-tion in the visible range of radiation.

3) Integrated optical probes and Langmuir-Blodgett chemistryfor Nitrogen Oxide detection

Integrated optical waveguides were modelled and dif-ferent planar waveguide configurations were considered forperforming a simulation of the light guiding into opticalwaveguide structures in the presence of a gas-sensitive lay-er. Different simulation programs were implemented in or-der to consider both graded and step index waveguides, de-pending on the material to be used as a substrate.

The configurations tested considered four layers, the up-per one being the sensitive one. The increase or decrease inthe refractive index of this layer, depending on the gas con-centration, was responsible for the change in light propaga-tion.

In order to fabricate planar waveguides for Nitrogen Ox-ides (NOx) detection, the deposition process of thin filmsof phthalocyanine macromolecules was optimized, by usingthe Langmuir-Blodgett technique directly onto various sub-strates. The organic macromolecule investigated was a newmetal phthalocyanine containing copper as co-ordinatedmetal Cu(II)-tetrakis(3,3-dimethylbutoxycarbonyl)ph-thalocyanine [Cu(dmbc)Pc].

The substrates used were Corning glass, alumina, andsilicon; the corresponding adherence was evaluated.

Optical characterization was performed in the 200-800nm spectral range in order to evaluate the optical parame-ters (refractive index and extinction coefficient). Moreover,optical measurements performed in linearly-polarised lightdemonstrated the optical anisotropy induced onto the mul-tilayers using the LB deposition technique.

Preliminary tests were performed by using three mono-layers of copper-phthalocyanine Cu(dmbc)Pc as NO2 opti-cal gas sensors. The measurements were performed using asurface plasmon resonance apparatus as transducer method.In this case, a particular substrate was required, and a struc-ture Corning glass/Silver(50 nm)/LB layers was used. Testscarried out in a controlled atmosphere demonstrated thatCu(dmbc)Pc LB layers were potentially suitable for appli-cation in NO2 optical gas-sensor devices. In fact, a variationin the reflectance of the multilayers, near the plasmon res-onance angle, due to the presence of NO2 (50-100 ppm) indry-air, was obtained. The process was not completely re-versible; however, a study concerning the optimisation ofthe thickness, of deposition parameters of the sensing lay-

ers and a study of the interaction process that takes place be-tween NO2 and active layer are in progress.

Future developments

While the prototype system for monitoring gasolineblending is becoming available, the chemical transducers forthe realization of the other sensors will be optimized for theirfinal coupling to a fiber optic sensor link. The work will bedeveloped according to the following priorities:• realization of fiber optic bundles for optimized interroga-

tion of the oxygen-sensitive chemical indicators;• design and testing of modular instrumentation for inter-

rogation of oxygen-sensitive chemical indicators by meansof life time measurements;

• optical technologies for the practical implementation ofintegrated optics waveguides compatible with the deposi-tion of NOx-sensitive Langmuir-Blodgett films and thedesign of modular instrumentation for their interrogation.

Expected deliverables

The following deliverable items are expected from theOptoSpec project:• industrial prototypes of fiber optic sensors for direct ab-

sorption spectroscopy of liquid samples. The prototypeswill be tested in a petrolchemical plant for gasoline blend-ing monitoring;

• advanced prototype of fiber optic sensors for oxygen as-sessment in the 5-100% range woth 5% resolution;

• design and preliminary implementation of an integratedoptics sensor for NOx detection with minimum detectionlimit of 25 ppm.

References

1) A.G. Mignani, R. Falciai, “Direct and chemically-assistedabsorption spectroscopy using optical fiber instrumentation”,invited paper, SPIE Proc. Vol. 3666, 1998, pp. 561-565.

2) A.G. Mignani, R. Falciai, “Direct and chemically-assistedabsorption spectroscopy using optical fiber instrumentation”,invited paper, OSA Annual Meeting, 1999, Abstract Book.

3) Capone, R. Rella, P. Siciliano, L. Vasanelli, L. Valli, L.Troisi, “On the characterisation and gas sensing propertiesof Cu(II)tetra(Alkylamino Carbonyl)Phthalocyanine LBfilms”, Thin Solid Films (327-329)1-2 (1998) pp. 465-468.

4) 2. R. Rella, P. Siciliano, L. Valli, K. Spaeth, G. Gauglitz,“An ellipsometric study of LB films in a controlled atmos-phere”, Sensors and Actuators B, 48/1-3 (1998) 329-333.

5) R. Rella, P. Siciliano, F. Quaranta, L. Valli, “Effects of ni-trogen dioxide on surface plasmon resonance of copper ph-thalocyanine Langmuir-Blodgett films”, Proc. AISEM – 2nd

Italian Conference on Sensors and Microsystems, Editedby World Scientific Publ., Singapore, in press (1998).

6) S. Capone, S. Mongelli, R. Rella, P. Siciliano, L. Valli,

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“Gas sensitivity measurements on NO2 sensors based onCu(II) tetra(n-butylaminocarbonyl)phthalocyanine LB films”,Langmuir, vol. 15, 5 (1999) 1748-1762.

7) R. Rella, P. Siciliano, L. Valli, L. Vasanelli, “Ellipsomet-

ric and surface plasmon resonance effects on LB films oforganic materials in controlled atmosphere.”, Proc. IIWorkshop on Chemical Sensors and Biosensors –Marzo1999 - ENEA CASACCIA – ROMA.

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Project title: OPTOSPEC - Guided wave sensors for the analysiing liquids by means of direct spectroscopy and for gas mon-itoring by means of chemically-assisted spectroscopy

Participants:

CNR-Istituto di Ricerca sulle Onde Elettromagnetiche Unit responsible: Anna G. Mignani (Project Coord.)Via Panciatichi 64, I-50127 Firenze Collaborators: Franco Cosi, Riccardo FalciaiTel.: 055/42351 Fax: 055/410893email: mignani@iroe.fi.cnr.it

CNR-Istituto Tecniche Spettroscopiche Unit responsible: Gaetano Di MarcoVia la Farina 237, I-98123 Messina Collaborators: Francesco AliottaTel.: 090/2939522 Fax: 090/2939902 email: dimarco@hpits1.its.me.cnr.it

CNR-Istituto per lo Studio di Nuovi Materiali per l’Elettronica Unit responsible: Roberto RellaCampus Universitario, Via per Arnesano, I-73100 Lecce Collaborators: Pietro SicilianoTel.: 0832/320244 Fax: 0832/325299email: roberto.rella@ime.le.cnr.it

Centro Laser s.c.r.l. Unit responsible: Aurora Maria LosaccoS.P. per Casamassima km.3, I-70010 Valenzano (BA) Collaborators: Pasquale AntuofermoTel.: 080/4674314 Fax: 080/4674457email: aurora@centrolaser.it

T.R.I. TECSA Ricerca & Innovazione s.r.l. Unit responsible: Antonio LanciaVia Aldo Moro 1, I-24020 Scanzorosciate (BG) Collaborators: Leonetto Bordignon,Tel.: 035/657360 Fax: 035/656598 Sabrina Fumagalli, Stefano Locatelliemail: antonio.lancia@mediacom.it

Purpose of the work

Seven big companies, five in Japan and two in Europeshare the 90% of the world market of the metal-oxide gassensor manufacturer. Six of them still prepare the sensitiveelement, based on doped-SnO2 oxide, by thick film ceram-ic technology.

These first generation metal oxide sensors have shownmarket exploitation limits, because of their poor selectivityto certain target gas, as well as unsatisfactory reproducibili-ty and long term stability of the response.

Marked needs for the detection of new gases like Ozone,Nitrogen dioxide and Clorine have strongly pushed sensorcompanies and the scientific community for the release of asecond generation of metal oxide gas sensor. Key featuresof these new sensors comprises improved sensor Sensitivity,Selectivity and long term Stability (SSS).

Our research, in the frame of MADESS II project, is ba-sically focussed to R&D activities aimed at the preparationof new sensors with enhanced Selectivity and Stability. It isour believe that sensor Selectivity and Stability can be pur-sued addressing research activity efforts to:

• Testing of new class of metal-oxide materials • Validation of innovative preparations, based on thin film

technology

Regarding the first point, WO3, Ga2O3, In2O3, Nb2O5,MoO3 new materials have shown promising application forthe selective detection of certain toxic gases [1]. Amongthem WO3 is particularly indicated as a possible candidatematerial for selective detection of oxidizing gases like O3,NO2 and Cl2 [2].

Regarding the second point, physical preparation routeslike r.f. Sputtering (RFS) [3], Vacuum thermal evaporation(VTE) [4], and/or chemical ones like Sol-gel (SG) [5], canbe successfully utilized for the preparation of thin films.Physical deposition routes over suitable substrates like sap-phire, Si/SiO2 and Si/Si3N4, have shown high reproducibil-ity of the deposition process and improved long term sta-bility of the electrical response.

Purpose of this work is the investigation of the electrical

response to O3 (10 - 180 ppb) of WO3 thin films preparedby the SG, RFS and VTE techniques over alumina sub-strates.

This paper is the result of a joint research activity be-tween Prof. G. Sberveglieri’s group in Brescia, Prof. W. Wlo-darski’s one in Australia, and our research team in L’Aquila.

Outline of the work

• Deposition of WO3 thin films on alumina substrates bySol-Gel (SG), R.F. Sputtering (RFS), and Vacuum Ther-mal Evaporation (VTE) techniques and annealing at tem-peratures between 500°C and 600°C for 1 to 30 hours instatic air.

• Microstructural characterisation the films by SEM, glanc-ing XRD and XPS techniques

• Electrical characterisation by exposing the films to O3 (10- 180 ppb), NO2 (0.2 – 1 ppm) and Cl2 (0.4 –1 ppm) atoperating temperatures ranging between 200 and 400 °Cand humid air at 50 % R.H.

Main results

MicrostructureXRD diffraction investigation highlights the formation

of well crystallized microstructures after annealing at 600°C for all the prepared films. The VTE and SG are orient-ed with preferential growth along the [200] crystallograph-ic plane of monoclinic WO3 (JCPDS no. 43-1035). TheRFS thin film shows a crystallographic peak orientation closeto the tetragonal phase of WO3 (JCPDS no. 20-1324). Nodiffraction peaks belonging to any crystalline phase of TiO2

has been detected for the RFS film. XPS characterization of the SG film shows, the occur-

rence of negligible contamination of the surface due to in-complete organic carbon removal at high temperature. RFSand VTE films seem to be not contaminated since no peaks,than the characteristics W and O, with the only exceptionof Ti 2p peak for the RFS film, have been detected.

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Detection of Ozone, Nitrogen dioxide and Clorineoxidizing gases by metal oxide sensors

Università dell’Aquila

SEM investigations of the SG film reveal a uniform, con-tinuous and with an “orange skin” appearance micro-cracks freesurface. SEM of the VTE film shows, on the other hand, theoccurrence of extended surface cracks. These cracks are believednot to propagate through the whole thickness of the film, sinceno Al2p reflection coming from the substrate have been detect-ed by detailed XPS measurements. SEM of the RFS film showsa well compact structure of equiaxed grains, and relatively largeWO3 crystallites segregating along the grain boundaries.

Electrical Properties

Gas sensing characterisation has been carried out at 200°Cand 400 °C in wet air (50 % R.H. at 20 °C) and exposingthe films to three different atmospheres, namely: O3 (10-

200 ppb), NO2 (0.2-1 ppm) and Cl2 (0.4 –1 ppm).Figure 1 shows the electrical response of the films in 50%

R.H air carrier at 400 °C operating temperature when the O3

concentration is changed from 10 to 130 ppb. The responseto different ozone concentrations at 200 and 400 °C operat-ing temperatures, expressed as S = RG/RA, is reported in Fig.2.From this figure it turns out that SG film yields a higher re-sponse at 400 °C than at 200 °C operating temperature.

VTE and RFS films, considering the experimental error

and signal reproducibility, do not show significant variationof S with the working temperature. For a given operatingtemperature, here it is clearly evident how the chemical prepa-ration route enhances the O3 response as respect to the filmsprepared by physical methods.

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Fig.1 O3 response at 400 °C

Fig.2 O3 Sensitivity at 200 and 400 °C

Fig.3 NO2 response at 200 °C

Fig.4 O3 Sensitivity at 200 and 400 °C

Figure 3 shows the response of the films at 200 °C anddifferent NO2 concentrations. The test has been carried byexposing the film to the maximum gas concentration (1 ppmNO2), followed by a dynamic adsorption-desorption cycle,by increasing stepwise the NO2 gas concentration. SG filmyields higher resistance when exposed to 1 ppm NO2 for thefirst time, as compared to the resistance obtained at 1 ppmNO2 at the end of the dynamic conditioning. Arrows in thefigure highlight the difference of the measured resistance atsaturation and 1 ppm NO2.

Physical prepared films are highly reproducible through-out the experimental sequence and NO2 concentrations.The response to different NO2 concentrations and operat-ing temperatures is reported in Fig.4. NO2 response is forall the films at maximum at 200 °C.

Figure 5 shows the electrical response of the films in 50%R.H air carrier and 200 °C operating temperature when theCl2 concentration is changed stepwise from 0.4 to 1 ppm. RFSprepared has resulted to be the faster to respond and the morestable in terms of signal reproducibility. The response to dif-ferent Cl2 concentrations and operating temperatures, is re-ported in Fig.6. The Cl2 response is at maximum at 200 °C.

It may be concluded that SG prepared films have shownbigger responses (S = Rgas / RAir) as respect to VTE and RFSfor all the investigated gases and operating temperatures.RFS prepared has resulted to be less sensitive, but faster inthe response and more stable in terms of signal reproducibility.The response to O3 has been found to be at maximum at400 °C. At this temperature the response to 80 ppb of ozonehas been: S = 35 (SG), S = 18 (VTE) and S = 5 (RFS).

The NO2 and Cl2 responses are at the maximum at 200°C, while become negligible at 400 °C.

Future developments

Future developments will be focussed to the characteri-zation of the long term stability of the RFS, VTE, and SG

WO3 thin films prepared over high quality substrates. Thesesubstrates made of Si/Si3N4 and schematized in figure 7, willbe utilized to minimize all the possible thermo-mechanicaland microstructural mismatches between the films and thesubstrates. The objective is to improve the long term stabil-ity properties of the device.

Expected deliverables

A number of 4” wafers, each with 180 substrates, will beavailable for the deposition of metal oxide thin film sensorsby physical and chemical routes.

These substrates, will be manufactured by MICROSENSat Neuchatel (CH), according to our design.

It is our policy to promote the diffusion and the utiliza-tion of these substrates within the sensor community. Theaim is to provide a standard substrate, to whom referee thesensitive properties of different deposited metal oxide films.

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Fig.5 Cl2 response at 200 °C

Fig.6 Cl2 Sensitivity at 200 and 400 °C

Fig. 7 Schematic cross section of the substrate

References

[1] C. Cantalini et al., Thin Solid Films, 350 (1999) 276-282[2] C. Cantalini et al, Proc. Transducers 99, Vol 1, (1999)150-153[3] G. Sberveglieri et. al., Sensors and actuators B 44, (1997)

499 –502

[4] C. Cantalini et al., Sensors and Actuators. B35-36,(1996) 112-117

[5] W. Wlodarski et al., Journal Vacuum Science and Tech-nology, A 17 (1999) 1873-1879

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Project title: Detection of Ozone, Nitrogen dioxide and Clorine oxidizing gases by metal oxide sensors

Participants:

Università di L’Aquila Unit responsible: Carlo Cantalini (Project Coord.)Fac. di Ingegneria-Dip. di Chimica, Collaborators: M. Passacantando, P. RatnaIng. Chimica e dei MaterialiMonteluco di Roio, 67040 L’AquilaTel.: +39-0862/434233 - Fax: +39-0862/434203Email: canta@ing.univaq.it

Università di L’Aquila Unit responsible: Sandro SantucciFac. di Scienze-Dip. di Fisica Collaborators: M. Passacantando, P. Ratna, T. LepidiVia Vetoio 10, 67010 L’AquilaTel.: +39-0862/433037 Fax: +39-0862/433033Email: sandro.santucci@aquila.infn.it

Purpose of the work

Fabrication and functionalization of Silicon Nitride mi-crocantilevers. Fabrication of a miniaturized Kelvin probe.Characterization of the mechanical effects induced in func-tionalized microcantilevers.

Outline of the work

Following the invention of the atomic-force microscopein 1986 and recent advancements in micromechanics we havewitnessed a great deal of development of nano-scale microscopy.

Micro and sub-micro devices have been demonstratedenabling one to measure not only forces, but also heat [1],stress [2] and other physico-chemical parameters whose vari-ations are induced by bio-chemical reactions forcing a mi-crocantilever to bend. The cantilever deflection is usuallymeasured either by an atomic-force method (deviation of alight beam) or by a piezoresistor.

A crucial aspect in these devices is the so-called func-tionalization. The latter consists in covering the cantilevelsurface with gold on top of which a monolayer of a tio-alka-ne is chemisorbed. These molecules stick onto the gold sur-face by exposing a chemical group at their free end, therebyreacting with the environment.

In future, arrays of such sensors would conceivably beapplied to build an artificial “nose” and a complete “mi-crolaboratory”[3], of ultra-reduced size.

On the other hand, the work-function measurement bymeans of a Kelvin probe can be miniaturized as well. Thisis accomplished by using technologies similar to those of theSTM and AFM microscopes. In this field, lateral resolutionsbelow 10 microns [4] have been obtained, by using specialtungsten tips and a suitable electronics. With a cantileversimilar to that of an atomic-force microscope resolutionseven below 1 micron have been reported [5].

It should been emphasized that application of these Kelvinmicroprobes to gas sensors is at an infant stage. Therefore amultidisciplinary cultural effort to verify the possibility ofexciting achievements in this field seems very appropriate.

Main results

Functionalized microcantilevers.A setup has been developed for measuring surface stress

in functionalized microcantilevers. Commercial tips nor-

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Physico-chemical microsensors

CNR-IESS, CNR-ISM, Università di Genova, Università di Roma “Tor Vergata”

Fig.1 Experimental setup (schematic) showing the flow cell andthe AFM head

Fig.2 Cantilever deflection (nm) versus time during the inter-action antigene-antibody. The antigene (2,4-D) was stuck tothe cantilever by means of a series of crosslinkers, while the an-tibody (Monoclonal, Mab) was in the solution

mally used for atomic force microscopes have been used.They have been functionalized and inserted in a flow-throughcell suitable for measurement of the stress induced by a chem-ical reaction. Fig.1 shows a sketch of the experimental ap-paratus.

An antigene-antibody interaction (2,4-D / monoclonalantibody) has been monitored in order to test the appara-tus. Fig.2 shows the cantilever deflection as a function oftime during some environmental changes.

The results indicate that a specific reaction of the typeantigene-antibody can be monitored in this way by using ain functionalized microcantilever.

Fabrication of microcantileversMicrocantilevers made of silicon have been designed and

fabricated [6]. Since one of the goals of the project is to de-velop silicon nitride microcantilevers, films of this materialhas been grown by PECVD. SiH4, N2 and He have beenemployed. The method results in a low concentration of Si-H bonds, as witnessed by the trasmission curve in the IR re-gion, reported in Fig.3.

Fabrication of tips for non-contact AFMA commercial microcantilever has been mounted on a

piezoceramic. The resonance frequency was 11 KHz. By us-ing a standard optical method to detect the amplitude of thetip oscillation and a home-made electronic controller [7],AFM images of a test sample ( an old lithographic grating) have been recorded. They are reported in fig.4. After met-

allization these tips should be used for Kelvin-probe mea-surements with improved spatial resolution.

Kelvin-probe measurementsA study of Langmuir-Blodgett sapphyrin films with dif-

ferent thicknesses has been performed, by correlating con-tact-potential-difference measurements to scanning-tunnel-ing-microscope characterization of the surfaces. The results,obtained with a commercial Kelvin-probe tip, are an exam-ple of fruitful application of a surface science technique tostudy organic materials [7].

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Fig. 3. Trasmission coefficient of a of silicon nitride film, 4000Å thick, grown by PECVD.

Fig.4 Non-contact AFM images of a lithographic grating.

Future developments

Following a theoretical study and an experimental re-search on commercial microcantilevers and Kelvin probes,optimized prototypes of both the above devices will be fab-ricated and tested.

Expected deliverables

Two prototypes:1) a functionalized microcantilever, for heat and stress mea-

surements. An experimental set-up for measurements influx conditions.

2) a Kelvin microprobe, for work-function measurementswith lateral resolution of the order of 1 micron and scan-ning area of about 1 square mm.

References

[1] R.Berger, Ch. Gerber, e J.K.Gimzewski, “Thermal analy-sis using a micromechanical calorimeter”, Appl.Phys.Lett.69, 1 (1996)

[2] H.J.Butt, “A sensitive method to measure changes in thesurface stress of solids”, J. of Colloid and Interface Sci-

ence, 179, 103 (1996)[3] R.Berger, Ch. Gerber, H.P.Lang e J.K.Gimzewski, Mi-

cromechanics: a toolbox for femtoscale science, “Towards alaboratory on a tip”, Int.Conf.on Micro and Nanoengi-neering (MNE-96), Glasgow, Scotland, Sptember 23-25, 1996

[4] R.Mäckel, H.Baumgärtner e J.Ren, Rev.Sci.Instrum. 64,694 (1993)

[5] M.Nonnemacher et al., Appl.Phys.Lett. 58, 2921 (1991)[6] 1) V. Foglietti, A. D’ Amico, C. Di Natale, S. Petrocco,

“ Sensors and actuators: present developments in thefield of microsystems and MEMS”, Invited Proceedingsof world ceramics congress & forum on new materials,Florence, Italy 1998, “Advances in science and technol-ogy 25 : Smart meterials and systems” p.155-166, P. Vin-cenzini editor, 1999.

[7] A.Cricenti, R.Generosi, C.Barchesi, M.Luce, and M.Ri-naldi, “A multipurpose scanning near-field optical mi-croscope: reflectivity and photocurrent on semiconduc-tor and biological samples”, Rev.Sci.Instrum. 69, 3240(1998)

[8] C.Goletti, A.Sgarlata, N.Motta, P.Chiaradia, R.Paolesse,A.Angelaccio, M.Drago, C.Di Natale, A. D’Amico,M.Cocco, and V.I.Troitsky, “Kelvin probe and scanningtunneling microscope characterization of Langmuir-Blod-gett sapphyrin films”, Appl.Phys.Lett. 75, 1237 (1999)

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Project title: Physico-chemical microsensors

Participants

Universita’ di Roma Tor Vergata Unit Responsible: Piero Chiaradia (Project Coord.)Dipartimento di Fisica Collaborators: Claudio Goletti, Manuela ScarselliVia della Ricerca Scientifica, 00133, RomaTel.: 0672594546 Fax:062023507Email: chiaradia@roma2.infn.it

Universita’ di Genova Unit Responsible: Massimo Grattarola Dipartimento di Ingegneria Biofisica ed Elettronica Collaborators: Sergio Martinoia, Roberto Raiteri, Via Opera Pia 11a, 16145, Genova Davide RicciTel.: 0103532761 Fax:0103532133Email: gratta@dibe.unige.it

Istituto di Elettronica dello Stato Solido del CNR Unit Responsible: Vittorio Foglietti Via Cineto Romano 42, 00156 Roma Collaborators: Giovanni Saggio, Alessandro MontiniTel.: 06415221 Fax:0641522220Email: foglietti@iess.rm.cnr.it

Istituto di Struttura della Materia del Cnr Unit Responsible: Antonio CricentiVia del Fosso del Cavaliere Collaborators: Renato Generosi, Claudio (Area della Ricerca di Roma del CNR), 00133 Roma Barchesi, Marco, Luce, Massimiliano Rinaldi,Tel.: 0649934143 Fax: 0649934153 Carlo Giammichele, Paolo PerfettiEmail: antonio@www.ism.rm.cnr.it

1. Purpose of the work

The development of diagnostic methods for clinical, foodand environmental use represents a fast growing field. Themost recent tendencies are leading to a continuous reduc-tion of costs, higher sensitivity and easy-to-use systems, ob-tained through the integration and miniaturisation of thecomponents and the introduction of new detection methods.

Essential for all these methods is the design and develop-ment of low cost, sensitive detectors suitable for silicon fab-line processes. The most sensitive detectors commonly offe-red are either the optical type (measure of the fluorescence orof the chemiluminescence) or electrochemical (i.e. ampero-metric type). Both types of detectors are able to be miniatu-rised and integrated in micro-FIA (Flow Injection Analysis)systems. However there exists an alternative technique, a hy-brid type (optical and electrochemical), which offers remarkableadvantages according to the previous ones: the electrochemi-luminescence (ECL). It consists, in brief, of electrogeneratedchemiluminscence coming from some transition of metalcomplexes (for example Ru(bpy)2+

3 , where bpy is the 2,2-bipy-ridin). As, at the same time, this phenomena is rather efficientand unknown in nature (consequently it exhibits a very lowbackground noise), the acquired sensitivity is higher than theoptical or amperometric detectors.

Goal of the research is the realisation of an ECL micro-sensor, fully accessoried with the electronics and optoelec-tronics parts. The sensor is evaluated for its reliability aspects,for the manufacturing processes and costs. Intermediateobjectives are the functional characterisation and the defi-nition of the optimal chemical, opto-electronic and struc-tural parameters.

2. Outline of the work

• Design and evaluation of process steps• Design and implementation of a prototype micro-cell• Preparation of Ruthenium complexes• Set-up of detection subsystem: photodiode, preamplifier,

signal processing• Set-up of micro-cell FIA driving circuits

3. Main results

The system design has been split and developed accor-ding to the following parts: electrochemical cell, fluidicsand electrodes micromachining, opto-electronics subsystemand control and signal processing.

The electrochemical cell has been implemented both in in-tegrated (micro) and in non-integrated (macro) versions. Themacroscopic cell was intended for testing different chemistries,the set up was also useful in order to establish and optimisethe driving circuits and the opto-electronic detection part. Theintegrated versions will represent the final goal of the project,many test micro-cells with separated fluidics and electrodeshave been realised and tested using either standard (planar) si-licon processes or micromachining techniques. Examples ofcell and electrode prototypes are depicted in figures 1 and 2.

Figure 1 refers to the planar version and specifically showsthe first attempt in electrodes layout. The interdigitated areais exposed to the fluidics (off chip), while the pads are pro-tected by epoxy resin and bonded to external electrical con-nector. Several electrode patterns have been designed (cur-rently under investigation) both for tripropilamine (TPA)and direct ECL reactions.

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Diagnostical microsensorby electrochemiluminescent detection

Datamed, IRST ITC, Politecnico di Torino, Sorin Biomedica Cardio, Università di Pisa

Figure 1. Electrode test chip (first version)

The electrodes are realised in gold at ITC-IRST. Goldevaporation has been done on 4’’ Si wafers previously oxi-dised, obtaining electrical isolation of electrodes from bulk.Metal thickness varies from 100 to 300 nm. Deposition pro-blems were found and the adhesion was improved with anintermediate layer containing evaporated chromium. Opti-misation of the process was achieved with dedicated ther-mal cycles, determining the best solution with nitrogen an-nealing for 30 minutes at 300 oC. Ething was done in wetsolution with Na2S2O3/CS(NH2)2/K3[Fe(CN)6]:1/1/1, whe-re all compound were in solution at 10%, while Cr was in(NH4)2Ce(NO3)6 and acetic acid.

The intermediate layer in a first analysis seems to solve al-so bonding adhesion, but introduced problems coming fromchromium oxidation. The point was solved doing some chan-ges in the evaporation process, avoiding Cr oxidation.

Figure 2 refers to the first prototype of micromachinedcell realised by the Pisa unit. Anisotropic silicon etching is car-ried out with EDP on <100> Si wafers previously coveredwith a 5000Å thick oxide, different etching steps were carriedout in order to accommodate fluidic and electrodes channels.Borosilicate glass etching processes were experimented andtuned. Electrode and fluidic channels (3÷4µm and 50÷70µmin depth respectively) were etched starting from 500µm thickglass substrates with HF/HNO3/H2O:1/1/5 using chro-mium/resist mask. Silver evaporation and patterning has beenevaluated for the ECL reference electrode. Adhesion problemswere found, workaround activities and electroplating techni-ques are currently under investigation. Silver etching was do-ne in wet solution with NH4OH:H2O2:H2O:1/1/10. Ano-dic bonding process has been adopted and defined in orderto join the micromachined silicon and glass. Bonding of mul-tiple layers (glass-silicon-glass) and thermal bonding techni-ques are currently under evaluation.

Concerning the electronic tasks: opto-electronic circuits andthe electronic control, a PCB module and one lab test-equip-ment have been developed and set-up. The main sections ofelectronic module developed (block diagram in figure 3) are:• photodiode and low noise preamplifier: the circuit to de-

tect and amplify the luminescence signal• potentiostat: the circuit devoted to drive the ECL cell, ge-

nerating stimulus potentials• protection circuit: the circuit has been intended in order

to preserve the electrodes integrity specifically in the mi-niaturised implementations

• offset correction circuit: to automatically compensatethe output signal baseline.

Different circuit configurations for ECL potentiostat as

been implemented to reduce/compensate the capacitive cross-talk between the photodiode and the electrode/solution. Anintegrated test chip of a revisited opto-electronic conversiontechnique has been designed and recently submitted for fa-brication using EuroPractice IC manufacturing services (AMS0.8 µm CMOS technology).

Figure 4 depicts a typical output signal obtained fromtested detectors. The actual configuration presents a de-tection limit in water solutions down to 20 nM ofRu(bpy)

2+

3 , (using TPA, without flow injection), the adop-tion of low-cost photodiode and the luminescence quen-ching (due to water and oxygen) are the most relevant li-miting factors.

Measurements are done using an automatic test-set ba-sed on GPIB instrumentation bus, the software is develo-ped with C++ and runs on Window personal computers.

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Figure 2. SEM image of the first micromachined cell (w/o elec-trodes)

Figure 4. Typical sensor output.

Figure 3. System block diagram

4 Future developments

Different fluidic/electrode configurations and differentgeometric shapes of the cell are currently investigated in aseparated way, future developments will be the integrationof best solutions into a unique microdevice, devising amongthose solutions that demonstrate compatible processing ste-ps. Technological activities will continue on the adhe-sion/bonding of involved materials (glass, electrodes and si-licon substrate). Next developments for the electronic partswill be the test of the integrated O/E chip, the system levelintegration of the sensor. Concerning the next chemical de-velopments, Ru complexes coniugated with oligonucleoti-

des and new Ru chelates exhibiting a reduced quenching inwater solution are currently under the process.

Expected deliverables

a) Scientific results:• Documentation about the project results• Technical report on ECL microsensor characterisationb) Deliverable items:• Technology test patterns and prototypes• ECL chemistry of Ru complexes • Final version of the sensor including the electronics.

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Project title: Diagnostical microsensor by electrochemiluminescent detection.

Participants:

Politecnico di Torino. Unit responsible: Pierluigi Civera (Project Coord.)Dipartimento di Elettronica Collaborators: Danilo DemarchiC.so Duca degli Abruzzi, 24, 10129 TorinoTel.: +39 011 5644080 - Fax: +39 011 564 4099Email: civera@polito.it

Istituto Trentino di Cultura. Unit responsible: Mario ZenVia Sommarive 18, 38050 Povo di Trento (TN) Collaborators: Pierluigi BelluttiTel.: +39 0461 314484 Fax: +39 0461 810851Email: zen@itc.it

Sorin Biomedica Cardio SpA. Unit responsible: Leopoldo Della CianaStrada Crescentino, Saluggia (VC) Collaborators: Giuseppe CaputoTel.: +39 0161 4871 - Fax: +39 0161 487524Email: capsorin@tin.it

Università di Pisa. Unit responsible: Andrea NanniniDipartimento di Ingegneria dell’Informazione Collaborators: Alessandro DiligentiVia Diotisalvi, 2, 56126 PisaTel.: +39 050 568511 Fax: +39 050 568522Email: nannini@iet.unipi.it

Datamed srl. Unit responsible: Roberto PozziVia Pordenone 15, 20132 Milano Collaborators: Gianpiero PorroTel.: +39 02 95327090, 02 26417178Fax: +39 02 26410198

1. Purpose of the work

Heavy metals are very toxic environmental pollutants;thus the knowledge of their real content in various matricesis very important. Over the last few years, decentralised mo-nitoring equipment for heavy metal detection has been mo-re and more requested.

In this work screen-printed electrodes were realised forheavy metal detection by stripping analysis. The purposewas to prepare a disposable sensor for decentralised measu-rements. First the carbon strips were used as a substrate fora thin mercury film, and an electrochemical characterisationof these devices was performed. Different electroanalyticaltechniques were tested. The performance of the screen-prin-ted strips was compared to classical electrodes and real sam-ples were tested in field analysis. To eliminate the problemof the use of mercury (a highly toxic metal), mercury-freemetal sensors were obtained, modifying the electrode surfa-ce with synthetical and/or biological compounds able to ac-cumulate heavy metal ions.

2. Outline of the work

2.1) Development, production and general electrochemicalevaluation of disposable screen-printed electrodes (SPE):single carbon working electrodes and three electrodesdevice.

2.2) Mercury thin-film carbon screen-printed electrodes:optimisation of mercury deposition step and of squarewave anodic stripping voltammetry (SWASV) and po-tentiometric stripping analysis (PSA) instrumental pa-rameters for heavy metals detection.

2.3) Comparison between the mercury thin-film SPE anda classical hanging mercury drop electrode (HMDE).

2.4) Analysis of real samples: river water samples and indu-strial waste water samples.

2.5) Modification of screen-printed working electrode sur-face with mercury salts.

2.6) Modification of SPE working surface with a chemicalmodifiers.

3. Main Results

The first step of this work was to prepare screen-printed elec-trodes and evaluate the influence of different electrochemicalparameters for stripping analysis. Two kinds of disposable sy-stems were used: a strip with a single carbon working electrode,and a strip with three electrodes, a carbon working electrode, asilver counter electrode, and a silver reference electrode. Figure1 shows the three electrodes strip produced in our lab.

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Screen-Printed Disposable Sensors for Heavy Metal Detection

Università di Firenze

Fig. 1

1.5 cm

3 cm

Experimental results are shown using different voltam-metric procedures such as square wave anodic stripping vol-tammetry (SWASV) and potentiometric stripping analysis(PSA). The square wave form is reported to facilitate strip-ping measurements in the presence of dissolved oxygen [1].Such capability can be attributed to the electrolytic deple-tion of oxygen at the surface prior to the fast scan. Reduc-tion of oxygen takes place during metal reduction at the elec-trode surface, by holding the potential of the electrode suf-ficiently negative during the deposition. This should mini-mise, in the second step, the extent of chemical stripping ofthe reduced metal by oxygen. If the scan is completed befo-re significant amounts of oxygen diffuse to electrode surfa-ce the resulting voltammogram should be similar to that ob-tained from a de-areated solution [2]. Thus a substantial re-duction in analysis time can be achieved by eliminating theneed for de-aeration. Even with the use of PSA [3] the de-aeration of samples is, generally, unnecessary since dissolvedoxygen can be used as oxidant. This technique is based onpotentiostatic preconcentration and on potentiometric re-cording. The analysis comprised two phases: an electrolysisstep and a stripping step. During the electrolysis, the metalswere accumulated in a mercury film on the surface of aworking electrode to which a reducing potential had beenapplied. During the stripping step, the applied electrolysispotential was removed. The oxidising agent, in this work aconstant current of 1 microA, strips the amalgamated me-tals off the electrode, and the metals diffuse, in ionic form,back into the solution. Measurement of the electrode po-tential as a function of time provides quantitative as well asqualitative information about the metals present in the so-lution.

In fig. 2 is shownSWASV calibration cur-ves of lead(II), cad-mium(II) with a 3 min.of deposition time. In fi-gure 3 is shown a PSAcalibration curve oflead(II) and cadmium(II)with 1 min. of deposi-tion time [4].

Under our condi-tions the PSA techniqueis more sensitive andmore rapid then SWA-SV. The relative standarddeviation after 9 repeti-tions was 7%, with 5ppb of lead(II). The de-tection limit, calculatedas three times the signalto noise ratio at 5 ppb ofthe three metals, was 0.6ppb for lead(II) and 0.4ppb for cadmium (II).

Figure 4 shows acomparison between theperformance of the thin-film mercury strip anda classical bulky HM-DE. The strip was em-ployed in the PSA (60 spreconcentration time)and the HMDE in thedifferential pulse vol-tammetry (DPV) mode(120 s preconcentrationmode and 10 min dea-reation). This compari-son was realised spikingknown amounts of leadin tap water samples.The correlation coeffi-cient r=0.97 (n=23),shows a significant cor-relation between thetwo methods.

Using these devicesdifferent water sampleswere tested. Figure 5shows an industrial wa-ste water sample analy-sed with the optimisedprocedure.

These results showthat screen-printed elec-trodes are interestingdevices for determina-tion of heavy metals.

SUBPROJECT 6

340

F ig u re 2

Pot en tia l, mV

-9 00 - 75 0 -6 0 0 - 4 50

Current, nA

0

3 0 00 0

6 0 00 0

p pb

0 2 0 40 6 0

Current,

A 0

2 0

4 0

6 0

pp b

0 2 0 40 6 0

Current,

A 0

2 0

4 0

6 0

Cd 2+P b 2+

Fig. 2

Figure 3

potential, V-0.8 -0.6

dt/dE, s/V

0

4

8

12

ppb

0 6 12 18 24 30

dt/dE, s/V

0

2

4

6

8

Fig. 3

ppb Pb(II), DPV method with HMDE

0 10 20 30 40 50 60 70 80

ppb Pb(II), P

SA

method

0

10

20

30

40

50

60

70

80

Fig. 4

E, V-0.7 -0.6 -0.5

dt/dE, s/V

0.0

0.5

1.0

1.5

2.0

lead, g/l

-6 0 6 12

dt/dE, s/V

0.2

0.6

1.0

Fig. 5

In order to eliminate the use of mercury solution for thefilm deposition step (that could be a great problem espe-cially during in filed analysis), the screen-printed workingelectrode surface was modified with different kind of mer-cury membrane. Moreover in order to eliminate completelythe use of mercury, preliminary experiments were realisedchemically modifying the electrode surface with ligands(dithizone) and ion exchangers (nafion, dowex).

4. Future Development and expected deliverables

Different modification strategies will be tested such as ad-sorption, covalent coupling, copolymerisation, electrochemi-cal polymerisation of commercially available ligands (ionophoreor other molecules). The expected results are to develop a se-ries of procedures based on chemically modified disposable

screen-printed electrodes capable of analysing heavy metalssuch as lead, copper, cadmium in the 1-100 ppb range. Par-ticular attention will be devoted on the optimisation of theprinting procedures of the modified carbon ink and in thecharacterisation of the modified electrode surface.

5. References

[1] Wojciechowski M., Balcerak J., Anal. Chem., 1990, 62,1325

[2] Wojciechowski M., Go W., Osteryoung J., Anal. Chem.,1985, 57, 155-158

[3] Kissinger P.T., Heineman W.R., Laboratory Techniquesin Elettroanal. Chem., 1984. M. Dekker, INC., New York

[4] Palchetti I, Cagnini A., Mascini M., Turner A.P.F., Mik-rochim. Acta, 131, 65-73, 1999

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Project title: Screen-Printed Disposable Sensors for Heavy Metal Detection

Participants:

Università degli studi di Firenze Unit responsible: Marco Mascini (Project Coord.)Dipartimento di Sanità Pubblica, Collaborators: Ilaria Palchetti Enrico Epidemiologia e Chimica Analitica Ambientale, Malavolti, Silvia HernandezSez. di Chimica Analitica,Via G. Capponi 9, 50121 Firenze, Tel.: 0552757274 Fax: 0552476972Email: mascini@cesit1.unifi.it, Internet site: http://www.igiene.unifi.it/Chimica/sensori

1. Purpose of the work

The development of low cost pyroelectric sensors is afundamental task for many applications requiring infrareddetection, like intruder alarms, environmental monitoringand industrial production control. Our research was focusedon the development of square matrices with 2x2 and 4x4 el-ements and 10-14 elements linear arrays for the fabricationof sensors not currently available using PVDF films. Thefabrication of the detectors was performed with differenttechnologies and different electronic configurations aimedto the optimisation of the sensor performances both in lowpower and high power applications. Particular attention wasdedicated to the development of relatively fast sensors, atmost suitable for real-time data acquisition and visualisationwas addressed. In each specific application, the characteri-sation of the environmental conditions limiting the sensorperformances was faced and given in terms of sensor noiseequivalent power or damage threshold.

2. Outline of the work

2.1) Development of computer programs for the simulationof the pyroelectric response of thick film multilayer sen-sors to sine wave and square wave modulated sources.

2.2) Design of transimpedance amplifiers with high gain-bandwidth product.

2.3) Design and realisation of amplification electronic chainsincluding ac coupled low pass or resonant filters fornoise reduction.

2.4) Fabrication of linear and matrix array of sensors.2.5) Characterisation and comparison of array of sensors for

low and high power laser sources.2.6) Characterisation of sensors and electronics.2.7) Design and development of PC based data acquisition

and visualisation system.

3. Main Results

Four quadrant sensors with total surface area of 16 mm2

suitable for working with diode beam spot were designedand built using PVDF bonded to a common copper elec-trode on a glass-epoxy substrate. PVDF foils coated withconductive ink or sputtered gold were mechanically cut witha 50 µm thick dice saw into four equal size square pixels.The cut depth of about 0.5 mm in order to separate also thebottom copper electrodes on the glass epoxy substrate. Thefabrication method allows separation between the elementsof about 50 µm, and a very small thermal cross-talk (betterthan -50 dB at 100 Hz), as the material is removed com-pletely for all the layers. The connections with top electrodeson PVDF are made by a PCB frame mounted over the sub-strate sustaining the sensor. The top PCB frame has fourmetallised vias with pads on the bottom layer. The contactswith electrodes are made by depositing a drop of conduc-tive epoxy in the cavities of the vias. Before curing at roomtemperature, a small pressure between the top and substratePCB is sufficient to obtain reliable and stable contacts. Thiselectrodes arrangement allows a differential connection ofeach element to a transimpedance amplifier suitable in ap-plications requiring high sensitivity and high common moderejection. The sensor performances reduction next to themechanical cut was controlled and balanced via software ineach specific application. The assembly is completed by tinsoldering of standard 2.54 mm copper pins to the four cop-per pads on the PCB frame.

High responsivity associated to relatively large band-widths were obtained with matrices built using commercialPVDF foils, 25 µm thick, coated with conductive silver ink.The current responsivities to the average power of modu-lated radiation sources resulted of about 50 nARMS/W

—in a

–3dB bandwidth of about 400 Hz. In the low power appli-cations (2.5 µW – 250 µW), a black paint (Supertherm, byDupli-Color, Germany) was deposited with a spray systemon the front electrode of the multilayer to further improvethe sensor absorbance.

An electronic board with a four channel transimpedanceamplifier in a differential configuration with high gain andlarge bandwidth was designed. A second stage with a band-pass filter bank provides an output voltage with low im-pedance for the board connection to external measurementinstruments through a coaxial cable. The sensor is mount-

SUBPROJECT 6

342

Development of low cost pyroelectric matrix sensorsfor IR/UV measurements in production and

environmental control

CNR-IEQ, El-En, Università di Firenze

ed on a standard socket placed in proximity of a quad am-plifier. This is essential for achieving low parasitic capaci-tance and low pick up of environmental noise. The char-acterisation of transimpedance amplifier frequency responserevealed good performances, comparable to the highest com-mercial standard. With a maximum transimpedance gainof RG=2.3 GW, we obtained bandwidths of about 840 Hzat –3dB that largely satisfy the requirements of the fabri-cated PVDF pyroelectric sensor (see Fig.1).

The blackened four quadrant sensor with an on boardresonant filter centered at 85 Hz was used for the beam cen-troid determination of an IR diode laser diode emitting atλ= 5.8 µm. The overall maximum voltage responsivity to theaverage power of the square wave modulated laser was about3600 VRMS/W

—. In this application, the four analog signals

were equalized at the source modulation frequency at 85 Hzand then sampled with a 12 bit Microstar Data AcquisitionProcessor (DAP 2400e). The DAP adjustable gain was set tomatch the weak signal amplitudes to the ADC dynamic rangeand reduced the digitizing error. The noise deriving from allthe sources external to the sensor, including the high fre-quency signals deriving from PC is decreased by a numeri-cal convolution bandpass filter (Blackman) centered at thesource modulation frequency. The resulting waveforms arethen averaged (typically over 10 acquisitions, each one 99samples long). The rms amplitude of the averaged waveformsis then calculated and transferred to the host PC, at a rate of0.1 s/data. LabVIEW was used for data logging and visual-ization, in particular to calculate and graphically display inreal time the difference signals between two diagonal ele-ments. The beam spot centroid is found minimizing the dif-ference signals in two orthogonal directions (see Fig.2). Weworked with an rms dark voltage higher than the digitizinguncertainty (16 counts) corresponding to a minimum de-tectable peak power of about 10% the diode laser peak pow-er (25 µW). The cross-talk between adjacent pixels resultedlower than 3 %. The centroid can be determined with a beamposition uncertainty of 20 µm at this power. The uncertain-ty reduces to 0.5 % with laser diode powers ten times high-

er. For the spatial characterisation of the laser beam a 4x4

elements matrix was developed with screen printed elec-

trodeson aPVDFfilm.

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Fig. 1. Photograph of a four quadrant sensor and the four chan-nels transimpedance amplifier board (dimensions 98.5x55 mm)with pass band filters.

Fig. 2. Results (+) of the scans along vertical (z) and horizon-tal (y) directions with a four quadrant PVDF pyroelectric sen-sor. The solid line is the gaussian function computed with thefitting parameters derived from the laser spot profiling.

Fig. 3 Assembly (above) and photograph (below) of a 4x4 pix-el matrix with screen printed electrodes on non metallized 25µm thick PVDF layer. Pixel area 1mm2, pitch 0.5 mm.

However this electrodes patterning technique suffers fromthickness irregularities and aging that penalize bandwidthand responsivity. The assembly techniques used is similar tothat described for 2x2 matrices. The two PCBs intercon-nection system allows both single-ended and differentialconnection to each element.

PVDF foils with gold sputtered or evaporated electrodesprovide lower responsivities and comparable (generally high-er) bandwidths (about 550 Hz at –3dB). They proved suit-able to high power application owing to the high reflectiv-ity of the front layer that greatly enhances the power dam-age threshold evaluated to be about 3.5 W/ cm2 in a test per-formed with a CO2 laser. We demonstrated the possibilityto fabricate linear and matrix array sensors by evaporationof gold electrodes on PVDF foils with the use of masks [2].Even if PVDF is a limited temperature range material, theevaporation of metals in still possible with samples of smallarea. The separation between adjacent elements cannot bebetter than 0.3 mm in this case. A low cost solution for arobust linear array was constructed with connections be-tween electrodes and pins soldered on a printed circuit board(PCB) (see Fig.4) for diagnostics of CO2 laser beams in re-

al-time. The 14 elements linear array with element pitch of2.54 mm separated by 0.3 mm.

The low manufacturing cost of the array allows the in-sertion of such kind of device as permanent internal diag-nostic tool inside the laser or laser system, eventually in aclosed loop beam quality control system.

For the temporal control of CO2 pulsed lasers a devicewas built with a bandwidth of 10 kHz [3].

All the multilayer sensors were designed and optimisedwith computer simulations taking into account the ther-moelectric properties and thickness of the different layersfor maximum responsivity and bandwidth. An original de-velopment of the existing theory was performed to extendthe temporal and frequency response analysis to arbitrarilymodulated sources. Both the voltage (current) temporal re-sponse and the voltage (current) responsivity were simulat-ed. Best fits were also performed for the determination ofunknown thermoelectric properties of some of the materi-als used in the multilayer sensors (see Figs. 5 and 6).

SUBPROJECT 6

10 mm

36 m

m

5 mm

2.54

mm

8 mm

Fig.4. (above) Assembly of a 14 elements linear array withdifferential connection to each pixel and (below) photographof a prototype with evaporated gold electrodes.

Fig. 5. Measured temporal voltage response (solid line) to rec-tangular light pulses with duty cycle 0.5. Initial guess (dottedline), best fit (dashed line).

Fig.6. Measured voltage responsivity (solid line) and simula-ted (dashed line) using the values of the parameters deducedin the voltage response best fit of Fig. 5.

344

Future developments

Works are in progress for producing linear and matrixarrays with pixel size 1mm and separation 0.1mm for highand low power applications.

A portable instrument is being designed with a display fordata visualisation (temporal and spatial intensity distribution).

Expected deliverables

• Four quadrant sensors for high and low power laser alignment.• Matrices with 4x4 elements 5.5x5.5 µm2 for laser beam

mapping.• Linear array with 10-14 elements, 2.54 mm pitch, for high

power laser spot dimension control. • Fast pyroelectric sensors for CO2 laser pulse evolution mon-

itoring.

References

[1] L. Capineri, L. Masotti, M. Mazzoni, G. Toci , P. Mazz-inghi, “A beam position sensor for low power infraredlaser diodes,” Review of Scientific Instruments, Volume70, N.2, pp 1-8, 1999,

[2] G. Bozzi, L. Capineri, L. Masotti, P. Mazzinghi, M. Maz-zoni, “Low-cost fabrication technologies for PVDF trans-ducer arrays: application for pyroelectric sensors”, sub-mitted for the Special Issue on The 30th Anniversary ofPiezoelectric PVDF on IEEE Transactions on UFFC,June 1999

[3] L. Panerai, L. Capineri, P. Mazzinghi, M. Mazzoni, L.Masotti, “A low cost matrix of pyroelectric transducersfor real-time control of CO2 laser”, Conference EU-ROSENSOR X, September 8-11, 1996, Leuven, Bel-gium, pp. 1429-1432

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Project title: Development of low cost pyroelectric matrix sensors for IR/UV measurements in production and environmentalcontrol

Participants:

Universita’ di Firenze Unit responsible: Leonardo Masotti (Project Coord.)Dipartimento di Ingegneria Elettronica, Collaborators: Lorenzo Capineri, MarcoVia S. Marta 3, 50139 Firenze Calzolai, Andrea Giombetti, Gianluca Bozzi,Tel.: +39-055 4796277 Fax: +39-055 4796517 Lorenzo Capecchi, Massimo Messeri,Email masotti@ingfi1.ing.unifi.it Piero Mazzinghi

CNR-IEQIstituto di Elettronica Quantistica Unit responsible: Marina MazzoniVia Panciatichi 56/30, 50127 Firenze Collaborators: Guido TociTel.: +39-055 416128 Fax +39-055 414612Email mazzoni@ieq.fi.cnr.it

El. En. S.P.A. Unit responsible: Giovanni MasottiVia Baldanzese, 17, 50041 Calenzano Firenze Collaborators: Daniele Bigazzi, Tel.: +39-055 8826807 Fax: +39-055 8832884 Monica ScioniEmail elen@flashnet.it

1. Purpose of the work

Silicon piezoresistors are unsuitable for use in high-temperature applications due to the significant decreaseof the piezoresistive effect in this material with rising tem-perature.

On the contrary, high gauge factors have been recen-tly reported for p-type diamond films obtained by CVDtechnique , which suggest their possible use as high-performance piezoresistors in a thermally aggressive envi-ronment.

As far as the signal conditioning electronics is concer-ned, the current trend is toward its integration on a siliconchip in close contact with the sensors.

However, in the present application, this is impeded bythe temperature constraints and, therefore, a different ap-proach needs to be followed in order to individuate an al-ternative solution.

Diamond has been recently investigated as a materialexhibiting piezoresistive effect which appears to be exploi-table at high temperature.

However , the gauge factor of diamond-on-silicon pie-zoresistors is highly dependent on the doping characteri-stic and the microstructure of the material as well as on themanufacturing process.

The influence of these parameters on the stress-inducedresistive variation needs further investigations.

This is a necessary first step toward the fabrication of relia-ble devices having controlled and reproducible characteristics.

The signal conditioning electronics will be purposely de-signed to provide high accuracy when operated remotelyfrom the sensor and , as a final goal, it will be integrated ona stand-alone silicon chip.

The research goals are listed in the following:- design and development of a piezoresistive sensing struc-

ture based on elastic deformations of a silicon microma-chined diaphragm for operation at high temperature (inthe order of 500 - 600 °C), with the following specifica-tions:

• input pressure range 0 - 1000 bar• bridge resistance 5 kΩ

• temperature working range 0 - 500 °C• TCR < 1000 ppm / °C

- design and development of the signal conditioning elec-tronics optimized to operate remotely from both the sen-sing head and the acquisition unit.

As a practical result, at the end of the third year, severalworking prototypes are expected to be completed accor-ding to the project specifications.

The following milestones toward the overall projectgoal can be individuated on a yearly basis:

- development of a silicon cantilever with built-in piezore-sistors suitable for the functional characterization ( 1st

year )- development of a silicon micromachined diaphragm with

built-in piezoresistors in a bridge arrangement suitable forthe functional characterization and the interfacing to thesignal conditioning electronics. ( 2nd year )

General Objectives:- Production of working prototypes- Device optimization toward the maximization of overall

performances- Engineering of the device with particular care to the packa-

ging requirements posed by the most attractive industrialapplications

Forecast results:- An increase of the knowledge is expected on the basic phe-

nomena that influence piezoresistivity in silicon-compati-ble polycrystalline materials.

- The correlation between device parameters, such as a gau-ge factor and TCR, and material microstructural proper-ties, such as grain dimension and orientation, will be in-vestigated.

- Deliverable items (technical products, prototype , patents,etc.) . Prototypes satisfying the specified requirements willbe available at the end of the project.

SUBPROJECT 6

Design ad development of a piezoresistive pressuresensor on micromachined silicon for high-temperatureapplication and of the signal conditioning electronics

Gefran Sensori, Università di Brescia, Università di Trento, Università di Roma “Tor Vergata”

346

2. Outline of the work

The first year of activity within the joined research projecthas involved four Operating Units, namely three AcademicUnits and one Industrial Unit, the latter acting as the pro-posing and coordinating partner.

Gefran Sensori (Industrial Unit):

- study and definition of the sensor specifications and ge-neral coordination of the research activity.

Facoltà di Ingegneria dell’Università di Trento:

- study, design and modelling of the silicon micromachinedsensor from the point of view of its mechanical structure

Facoltà di Ingegneria dell’Università di Brescia - Dip. di Elet-tronica:

- study and experimental characterization of the developeddevices from the point of view of their sensing properties

- design, development and experimental characterization ofa proposed topology for the sensor signal conditioning elec-tronics

Facoltà di Ingegneria dell’Università di Roma “Tor Vergata”- Dip. di Scienze e Tecnologie Fisiche ed Energetiche:

- study, development and microstructural and electronic cha-racterization of the materials involved in the primary sen-sing elements

The research results have led to the definition of the geo-metrical parameters of the sensor elastic structure as a ne-cessary prerequisite for optimizing the forthcoming experi-mental tests at different operating temperatures.

To this purpose, a dedicated experimental setup has beendesigned and built as shown in the block diagram of Figu-re 1, which enables the determination of the metrologicalcharacteristics of piezoresistive films at temperatures up to300°C [1]. In particular, the parameters of interest that ha-ve to be measured are: the gauge factor (GF), the tempera-ture coefficient of resistance (TCR), the creep at differenttemperatures and the dynamic response.

A linear displacement actuator is used to generate a givenstrain on the film being tested. A piezoelectric stack was cho-sen (Å in Figure 1) with an internal feedback position sensormade by an estensimetric bridge. The actuator ends with aceramic plate that impinges on the substrate supporting thepiezoresistive film (1 in Figure 1) thereby generating a stresswithin the substrates. The stress induces a strain state on thefilm and, consequently, a resistance variation. The clampingmethod of the mechanical structure is based on a two pointsimply supported system. This solution ensures the most ac-curate measurement of the metrological parameters withoutany undesirable effect due to the changing in the clampingcondition due to the temperature changes. For the heating of

the sample two infrared heaters are used (2 in Figure 1). Thetemperature of the substrate under test has to be measured bya contactless method. To this purpose, a second supportingstructure is used which is exactly equal to the first one exceptthat it includes a sample that is not mechanically loaded (8 inFigure 1). During the measurement process, both structuresare heated by direct conduction and therefore they both irra-diate in the back side towards two equal receivers (4 in Figu-re1) instrumented with two resistive temperature detectors(RTD). When the temperature of RTD1 is equal to that ofRTD2, the temperatures of the substrate under test and ofthe duplicated substrate are the same. Since the duplicatedsubstrate temperature is taken by conduction, it is possible toknow the temperature of the film tested. The system is con-nected to a power amplifier (7 in Figure 1) which in turn com-municates to an acquisition system and PC that make it pos-sible to register the data for up to 48 hours.

In order to evaluate the functionality of the whole appa-ratus a series of measurements were taken on piezoresistivefilms prepared by screen printing on alumina substrate accor-ding to the methods of thick-film technology. The size of thesamples which are shown in Figure 2 was 0.38 mm X 10 mm.

At the same time, the Operating Unit at the Universitàdi Roma Tor Vergata has ultimated the development of anew chamber for the PECVD deposition of piezoresistivefilms of boron-doped diamond.

3. Main results

As far as the GF measurement at ambient temperatureis concerned, the measurements taken have shown values

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347

Å

Ç

É

ÑRTD 1

ÑTD 2

Ç

Ö

Üá

direct thermal direct thermalonduction

Piezoelectric actuators with position sensor

Infrared heaters

Sample under test in thick-film technology

Receivers with temperature detectors

Heater (by direct thermal contact)

Acquisition system

Power controller

Sample duplicated

à

Figure 1 - Block diagram of the measuring system.

Figure 2 - Photograph of the thick-film sample.

equal to 21.4. The measured data show non-linearity in-cluding 1% FS while the hysteresis values were kept to lessthan 2%. TCR measurements (up to 300°) were taken withvalues between 60 and 80 ppm/C°. The gauge factor varia-tion in temperature (see figure 3) demonstrated a decreasingtrend up to 100°C (as found in literature for low tempera-ture) while for higher temperature there was an increase up

to an overall variation (at 300°C) of 3-4% with respect tothe value of 25°C.

Regarding the signal conditioning electronics, a circuittopology has been preliminary designed and experimentallyevaluated in which both the sensor pressure and temperatu-re are simultaneously measured and transmitted as, respecti-vely, the frequency and duty-cycle of the output signal [2].

From the film preparation point of view, the optimiza-tion of the deposition apparatus has produced remarkableimprovements on the film crystalline quality, as evidencedby the almost total absence of any significant luminescencebackground in the measured Raman spectra. (fig. 4)

SUBPROJECT 6

Figure 3 - Gauge factor versus temperature for the thick-filmsamples.

Fig. 5 Microscope Scanning Electron image of diamond films

Fig. 4 Raman Spectra Fig. 6 Measuring system

348

4. Future developments

Given the results obtained so far, the main goals of thesecond year of activity are the following:- development and optimization of the technique for the se-

lective growth and doping of the diamond films- definition of the design specifications for the micromecha-

nical structure in silicon and manufacturing of the same- lay-out design, fabrication of the masks for the piezoresi-

stive elements and completion of the experimental setupfor the electronic and microstructural characterization ofthe boron-doped diamond piezoresistive films on the sili-con elastic microstructures

- completion of the experimental setup for the in vacuumtesting of the silicon elastic microstructures

- start of the design and simulation of the integrated signalconditioning electronics

5. Expected deliverables

As already stated, the main goal of the present researchis the development of a demonstrator whose characteristicsare basically those described at point 1.

However, the development of the demonstrator is not apurely technological achievement, as it contextually requires

to gain a deeper insight and increase the available knowled-ge on the basic phenomena governing the piezoresistive ef-fect in polycrystalline materials and diamond in particular.

Therefore, it is hopefully expected to correlate the gau-ge factor of the piezoresistor with its microstructural cha-racteristics, such as grain dimensions and orientation, pre-sence of residual stress.

Moreover, given the wide temperature range that will beexplored in order to characterize the devices in operatingconditions, the experimental results will most likely provi-de important indications on the mechanical and thermalphenomena occurring at the interface between different ma-terials and deposition layers.

6. References

[1] D. Crescini, D. Marioli, E. Sardini and A. Taroni, “High tem-perature characterization of piezoresistive elements in thickfilm technology”, submitted for presentation at IMEKO 2000XVI World Congress in Vienna, September 25-28, 2000.

[2] V. Ferrari, D. Marioli, A. Taroni, Oscillator-based in-terface for measurand-plus-temperature readout from re-sistive bridge sensors, Proceedings of the IEEE Instru-mentation and Measurement Technology Conference(IMTC99), Venice, 24-26 May 1999, 1233-1238.

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Project title: Design and development of a piezoresistive pressure sensor on micromachined silicon for high-temperature ap-plication and of the signal conditioning electronics

Participants:

Gefran Sensori Scientific responsible: Angelo Borgese (Project Coord.)Via Statale Sebina 74 Unit responsible: Francesco Simonelli25050 Provaglio d'Iseo (Brescia) Collaborators: Sergio Doneda, Giosuè Iseni,Tel.: +39-030-983786 Fax: +39-030-9823201 Giambattista Preve, Cesare ZubaniEmail: inntec@onion.it

Università degli Studi di Brescia Unit responsible: Andrea TaroniFac. Ingegneria -Dipartimento di Elettronica Collaborators: Daniele Marioli, Zsolt Kovacs Vajna, Via Branze 38 Emilio Sardini, Damiano Crescini, Vittorio Ferrari,25129 Brescia Alessandra Flammini, Danilo Febbrari, Alberto TiburziTel.: +39-030-3715430 Fax: +39-030-380014Email: taroni@bsing.ing.unibs.it

Università degli Studi di Trento Unit responsible: Giovanni SonciniFacoltà di Ingegneria Collaborators: G. Verzellesi, D. Stoppa, M. BrandimarteVai Mesiano 77 G.U. Pignatel, G. Dalla Betta, M. Faccio, M. Salpietro38100 TrentoDipartimento di Ingegneria dei MaterialiTel.: +39-0461-881915 Fax: +39-0461-881977Email: soncini@ing.unitn.it

Università di Roma - Tor Vergata Unit responsible: Aldo TucciaroneFacoltà di Ingegneria Collaborators: Marco Marinelli, Enrico Milani, Dip. di Scienze e Tecnologie Fis. Ed Energ. Antonio PaolettiVia di Tor Vergata 110, 00133 RomaTel.: +39-06-72597219 Fax: +39-06-72597145Email: tucciarone@uniroma2.it

Purpose of the work

A non invasive thermal monitoring system to control ra-diofrequency (RF) applicators for hyperthermia is under de-velopment. The technique is based on the use of mi-crobolometric IRFPA sensors.

Hyperthermia (HT) is used for the treatment of severalpathologies, also tumoral ones. Generally it makes use of aelectromagnetic (HT) applicators to warm up the humantissues to therapeutic temperatures. The monitoring of thesurface thermal pattern of the tissue allows to control theposition and the energy density distribution of the RF beam.Today, invasive-probes such as thermocouples are used forthis scope with problems of EM compatibility. IR sensorsare completely non-invasive, moreover they can detect withgood spatial resolution the thermal pattern distribution. Infact in HT treatments the tissues are heated up to about42°C, therefore the radiation emitted at such temperaturesis peaked in the thermal infrared region (8÷12 micron). TheEM applicators of most current HT machines usually de-liver a quasi-uniform beam that cannot be optimized ac-cording to dielectric and morphological non uniformity ofthe great variety of anatomic sites to be exposed.

Outline of the work

The microbolometer

The sensor that is specifically developed for this appli-cation has the following characteristics: non-invasive; de-tection capability of the superficial thermal pattern distrib-ution of heated tissues; small size to allow installation intoradio-frequency applicators; embedded processing of thethermal pattern. The sensor will be a staring type mi-crobolometer IRFPA with spatial resolution better than 1cm2 and sensitivity better than 0.2°C. Conventional pho-tonic sensor operates at cryogenic temperatures, mi-crobolometer IRFPAs can work at room temperature, thusno cryogenic system is needed. Consequently a considerablereductions of the size and cost is achievable.

Description of the apparatus

The principles of operation of the non invasive moni-toring and control system is showed in fig.1. One RF ap-plicator generates the electromagnetic field that warms upthe region of interest of the human tissue. The temperatureincrease of the inner part of the body is evaluated throughthe analysis of the superficial thermal pattern distributionobserved by the IR smart sensor.

The smart architecture and processing of the sensor mea-sures the thermal radiation emitted by the heated surfaceand also elaborates the useful information to control the ap-plicator for a correct distribution of the thermal treatment.

The IRFPA microbolometers can detect the incident IRradiation at room temperature because it is made of mi-crobolometers with high TCR values. The radiation emit-ted from the zone previously heated by EM irradiation iscollected by an IR lens system and focalized on the IRFPAsensor surface. The thermal pattern detected is acquired andprocessed by the electronics embedded into the sensor thatboth equalizes the signal and can compare the thermal pat-tern acquired and can equalized it to a reference pattern. Thecomparison will be performed both for the pattern behav-ior and intensity, then the processing electronics will gener-ate the control signal to adjust the conformation of the pow-er emission of the applicator antenna.

Controllable field hyperthermia applicatorsThe hyperthermia EM energy delivery device is an ap-

plicator that can be EM matched to the body tissues with-out a direct contact in order not to modify the exposed bodysurface temperature distribution and with a radiation dia-gram exhibiting a multiplicity of split radiation lobes whichmay independently be controlled in shape, size, intensityand phase to constitute specifically conformed and sub-stantially time-controlled radiation beams.

Anatomic phantomsIn effective treatments, case the applicator beam has first

to be shaped by the operator in the preliminary planning phaseaccording to the dielectric and morphological heterogeneityof the anatomic site, whilst will be timely modified during the

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350

IR Smart Sensor and Automatically Controlled RF Ap-plicator for Hyperthermia Therapy

Consorzio CREO, Gelco, Università di Roma “Tor Vergata”

course of the treatment with the help of a specific adaptivecontrol algorithm following the tissue modifications broughtabout by the treatment itself and detected by the exposed bodysurface temperatures changes. These applicators are to be de-signed specifically for each anatomic site and the design of theirsplit and controllable radiators and of the multichannel con-trol system requires the development of anatomic phantomsfor their specific development and optimization.

Main results

An experimental test bed (fig.2) has been set up to evaluatethe possibility of superficial thermal distribution pattern recog-nition using microbolometric IRFPA sensors. For this purposea thermal imaging system with such sensor type has been uti-lized to acquire thermal path generated by a hypertermia RFapplicator for several intensity values and exposure times. Ther-mal blackbody references are used to recover the absolute val-ues of the thermal distribution of the heated surface.

Fig. 3 shows one example of the image acquired from asample tissue after five minutes exposure to a 200 W RF ap-plicator and a plot of the absolute thermal distribution pat-tern reconstructed.

Conformable field applicatorA RF inductive and non-contact power hyperthermia

applicator has been designed and developed to test the ad-equacy of the flexible heating technology selected. Fig. 4shows the water cooled applicator with the two opposedC-shaped radiators each of which can independently be fedwith a RF current of variable intensity and relative phase froma dedicated hyperthermia apparatus (not shown). The heat-ing field of the applicator was tested in a standard fat-mus-cle bi-layered EM phantom simulating a flat anatomic site(not shown). Fig.5 (top) shows the resulting heating patternwith the two opposed “C” radiators fed with equiphase RFcurrents and delivering an almost uniform treatment volumein the deeper muscle-like tissue the volume of which is cir-cumscribed by the radiators quasi-circular pattern. Fig. 5(bottom) shows instead the split heating pattern obtainedwith the same “C” radiators fed with opposed phase RF cur-rents, which generate two distinct treatment volumes close-ly following the respective radiator layout.

Anatomic phantomsFig. 6 (above) is a photo of a trunk EM bi-layer (fat-mus-

cle) EM phantom during the development process, in whichthe pulmonary bony cage and the first layer of thermomet-ric sensor channels - that are going to be embedded within

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Figure 2

Figure 3a

Figure 3b

the inner muscle-like tissue layer - are visible. FIG. 6 (right)shows instead the finished phantom after the encapsulationof the array of invasive measuring channels in both mus-cle-like and fat-like tissue layers to monitor the efficiencyand specificity of the applicators heating fields. The tissue-like materials employed are compounds developed in houseto accomplish the complex dielectric constant of the re-spective biological tissues.

Future developments and expected deliverables

Investigations supported by laboratory tests have sug-gested the real possibility of performing an automatic con-

trol of RF applicator for hypertermia treatment by means ofan IR smart sensor. Further investigations are in progress todefine the best sensor architecture, especially array and pix-els pich and size, optics and optoelectronic integration of thesmart processing unit with the sensor and the actuator.

Moreover, further research are under way to define thesplit-field and in-field adjustable EM architecture for a stan-dard multiuse hyperthermia EM applicator for controllableEM and associated multi-channel control algorithm, to-

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Figure 4 – The split-field RF hyperthermia applicator with twoopposed “C” shaped RF strip-inductor split radiators

Figure 5 - Transverse SAR (W/kg) heating patterns inside thedeeper muscle-like layer of a flat bi-layer (fat-muscle) EM phan-tom for the applicator of Figure 4.(above) split strip-inductors fed with equiphase and same in-tensity RF currents, (below) id. fed with opposed phase and sameintensity RF currents.

Figure 6 – The trunk hyperthermia EM bi-layer (fat-muscle)RF phantom: (above) under development, with the bony cageand measuring catheters but without muscle-like and fat-likelayers; (below) the completed phantom.

gether with a number of EM anthropomorphic phantomssimulating selected anatomic sites for establishing the es-sential guidelines for site-specific treatment protocols.

References:

D. Zintu, M. Di Loreto, G. Tosone, C. Corsi - CREO,Vanadium Oxides Films for Microbolometric Applications, AI-TA Venice 1999.

K.C. Liddiard, Status of Uncooled Focal Plane Detector Ar-ray for Smart IR Sensor, Proc. SPIE vol. 2746, pp. 72-79, 1996.

J.L. Tissot, F. Rothan, C. Vedel, M. Vilain, J.J. Yon -LETI (CEA), LETI/LIR’s Amorphous Silicon Uncooled Mi-crobolometer Development, Orlando 1998.

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Project title: IR Smart Sensor and Automatically Controlled RF Applicator for Hyperthermia Therapy

Participants:

University of Rome II Unit responsible: Cafiero Franconi (Project Coord.)Department of Diagnostic Imaging Collaborators: Enrico M. Staderini, OndrejMedical Physics Center Voles, Antonio Canichella, Paolo NecciVia di Tor Vergata 135, 00133 Roma, ItalyTel.: +39 06 7259 2820 Fax: +39 06 7259 2821Email: cafiero.franconi@uniroma2.it

Consorzio Centro Ricerche Elettro Ottiche – CREO Unit responsible: Sergio BernardiVia Pile 60, 67100 L’Aquila, Italy Collaborators: D. Zintu, N. Liberatore, R. Viola, S. GalliTel.: +39 0862 346 202Fax: +39 0862 346 201 Email: creoit@tin.it

General Electronic Company - GELCO srl Unit responsible: Enzo ManciniViale Industria 21/23, 01100 Viterbo, Italy Collaborators: Alessandro MattioliTel.: +39 0761 354357 Fax: +39 0761 35 44 82 Angelo Torroni, Michele De SantisEmail: enzomanc@tin.it

Purpose of the work

X-ray imaging is a technique of primary importance inthe quality control of materials and/or manufactures whichare not directly accessible to optical inspection systems. Forinstance, large X-ray vision system are available on the mar-ket for the inspection of pin-grid ball arrays in ICs bondedto PC boards. Our work is aimed to the development of alow cost X-ray inspection system based on arrays of siliconpin X-ray detectors coupled with Cs-I scintillators and withan appropriated read-out electronics. The problem of inte-grating mixed-mode analog-digital signals onto one singlesilicon chip will be addressed. The study of an innovativeelectronic architecture based upon chip-on-board bondingon hybrid low-temperature ceramic substrates will also bepart of the research. Packaging techniques for the realizationof modular interfaces with the aim to form linear arrays fewmeters long will be developed. The targeted application isthe quality control of wood for the industry which produceswooden boards from trees. However, because of the generalsystematic approach to the problem, other applications inthe inspection of materials / manufactures are foreseeable.

Outline of the work

1. The University of Trento (Uni-TN) will be responsibleof the design and realization of linear matrixes of pin X-ray detectors integrated on high-resistivity float-zone (FZ)silicon. A dedicated technology will be implemented atIRST - an independent Institute for Research, Science,and Technology - founded by the local government of‘Provincia Autonoma di Trento’. Coupling of the detec-tors with Cs-I scintillators and mounting of them on mod-ular packages with the aim to realize large area inspectionsystems will be carried out at Opto-I, a small enterprisewith competence in die assembly and packaging.

2. The University of Bari (Uni-BA) will be responsible ofthe design and validation of the read-out electronics. First,a feasibility study of the integration in CMOS technolo-gy of a front-electronic circuit with mixed-mode analog-

digital signals will be performed. Secondly, a hybrid so-lution with chip-on-board bonding of rough chips on lowtemperature ceramic carriers (LTCC) will be investigat-ed. The latter is an innovative and emerging technologywhich seems very promising as replacement of multi-chip-modules (MCM). Definition of the final system impliesthe study and evaluation of several architectures whichincludes one or more trans-impedance amplifiers, analogmultiplexing, analog-to-digital converters, control logic.In particular, as far as the control logic is concerned, theuse of DSPs, FPGAs or other innovative devices recent-ly appeared on the marked, as for instance the LM9830from National Semiconductors, will be evaluated.

3. Ital-Structures s.r.l. (I-S) of Riva del Garda TN, will beresponsible of the realization of the demonstrator system.I-S is a small enterprise with competence in X-ray sourcesand diffracto-meters who is potentially interested in theexploitation of the results of the research. The targetedapplication is the detection of the presence of nodes in-side wooden boards, which are produced from cut trees.

Main results

1. PIN arrays with spatial resolution of 0.7 and 0.35mmhave been designed at Uni-TN in modules of 16 and 32diodes, in such a way that linear arrays up to 1024 pixel canbe realized. Each module is one inch wide, and it is designed

SUBPROJECT 6

354

Development of an imaging system for the qualitycontrol of materials / manufactures based upon an array

of X-ray detectors

Ital-Structures, Politecnico di Bari, Università di Trento

in such a way that it can be put next to one another. Thesame rule should apply to the associated read-out electron-ics (one module every 32 channels). The following figurereports a schematic representation of the diode layout, alongwith a cross section of the device, which shows some detailson the technology used to realize the anti-reflecting coatingoptimized for the peak wavelength of 540nm emitted by theCs-I scintillator. The first run of PIN diodes has beenprocessed at IRST. The table shows preliminary results con-cerning the electrical characterization of a few devices onwafer (before cutting).

2. A front-end chip has been designed at Uni-BA in 0.8µmCMOS-AMS (Austria Micro Systems) technology. Thechip includes 16 or 32 trans-impedance amplifiers withanalog multiplexing. Design validation of the chip hasbeen carried out with SPICE circuit simulation. In paral-lel, two prototypes of the read-out electronics, one at Uni-BA and one at Uni-TN, have been realized on printed cir-cuit boards (PCB) with commercially available devices, inorder to define and verify the optimum architecture. Test-ing of the PCBs is currently under way. The present ar-chitecture foresees the use of either a DSP (Texas) or anLM9801-30 from National Semiconductor. This latter de-vice is interesting because it is able to perform offset cor-rection and gain compensation pixel-by-pixel during theanalog-to-digital conversion (on-fly correction).

3. Ital-Structures has provided a Molibdenum X-ray tube asradiation source along with the software necessary to an-alyze X-ray spectra. Some preliminary tests on PIN diodedetectors exposed to a radiation of 140 keV have shownthat the photo-generated current is of about 300nA. Asa consequence, the dynamic current resolution of the sys-tem has been established to be 30nA. Other specificationof the system have been defined as: spatial resolution of0.3mm with an object velocity under the X-ray beam of4m/s; electronic scan rate of 2MHz per line (1 line=1024pixels); digital resolution = 8bit (256 gray scale).

Future developments

According with the results obtained from testing thePCBoards - currently under evaluation - a decision will betaken as to continue with the integration of the front-endelectronics on a single chip, or with the realization of a mul-ti-chip architecture. The latter solution should be based onchip-on-board bonding of commercially available chips overlow temperature ceramic carriers (LTCC). This substratesare able to withstand six level of interconnections. This tech-nology is emerging as replacement of multi-chip-modules

(MCM) because it allows to shrink the dimensions of actu-al surface-mounted PCBs to a factor of 10, without the prob-lems associated with MCM testing and repair. A small ital-ian enterprise (MicroTel) with expertise in this field has beenalready contacted.

Expected deliverables

1. Year: i) first run of pin photo-diodes processed and tested;ii) sample arrays encapsulated in standard package for

preliminary test;iii) one CMOS chip designed and modeled;

iv) two PCB prototypes for system architecture eval-uation.

2. Year: i) second optimized run of pin photo-diodes processed

and tested;ii sample arrays coupled with Cs-I scintillator and en-

capsulated in a dedicated package;iii) first prototype of the read-out electronics.

3.Year:i) full characterization of the pin diode arrays;ii) second prototype of the read-out electronics;iii) demonstrator system assembled by I-S.

References

[1] “Silicon PIN radiation detectors with on-chip front-endjunction field effect transistors” G.F.Dalla Betta,G.Verzellesi, M.Boscardin, L.Bosisio, G.U.Pignatel, L.Fer-rario, M.Zen, G.Soncini, NUCLEAR INSTRUMENTSAND METHODS IN PHYSICS RESEARCH, NIM-A 417 (1998) pp. 325-331.

[2] “On the accuracy of generation lifetime measurementsin high-resistivity silicon using PN gated diodes”,G.Verzellesi, G.F.Dalla Betta, L.Bosisio, M.Boscardin,G.U.Pignatel, and G.Soncini. IEEE TRANSACTIONSON ELECTRON DEVICES, TED 46-4 (1999) pp.817-820.

[3] “Ultra Low Noise CMOS Preamplifier-Shaper for X-Ray Spectroscopy”, P.O’Connor, P. Rehak, G. Grameg-na, F. Corsi, C. Marzocca, NUCLEAR INSTRUMENTSAND METHODS IN PHYSICS RESEARCH, NIM-A 409 (1998) pp.315-321.

[4] “DC Characterization of Lateral Bipolar Devices in Stan-dard CMOS Technology: a New Model for Base Currentpartitioning”, F. Corsi, M. Di Ciano, C. Marzocca, SOL-ID STATE ELECTRONICS, SSE-43 (1999) pp. 883-889.

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SUBPROJECT 6

Project title: Development of an imaging system for the quality control of materials / manufactures based upon an array ofX-ray detectors

Participants:

Università di Trento Unit responsible: Giorgio U. Pignatel (Project Coord.)Dipt. Ingegneria dei Materiali Collaborators: Giovanni Soncini, Giovanni Verzellesi, via Mesiano 77, I-38050 Trento – Italy Franco Andreis, Gian Franco Dalla Betta, Michele Tel: +39-0461-88.2451 Fax: +39-0461-881977 Corrà.Email: Giorgio.Pignatel@ing.unitn.it

Politecnico di Bari Unit responsible: Francesco Corsi Dipt. Elettrotecnica ed Elettronica (DEE) Collaborators: Cristoforo Marzocca, Daniela DeVia Orabona 4, I-70125 Bari – Italy ,Venuto, Gianvito Matarrese, Domenico Minervini, Tel: +39-080-5460.265 Fax: +39-080-5460.410 Andrea Viscillo.Email: corsi@poliba.it

Ital-Structures Unit responsible: Manuel Valdes Via M.Misone 11/d – Z.I. Baltera Collaborators: Ezio Petricci.I-38066 Riva del Garda TN – Italy.Tel.: +39-0464-553426 Fax: +39-0464-555270Email: isinfo@italstructures.com

Purpose of the work

This research is aimed to create a system of automaticacquisition of the three-dimensional data of one or moreteeth and the oral cavity for being able to reconstruct themore accurate substitutive prosthesis. It’s purpose is: Ref.[1], to reduce the disturbance to the patient in the phase ofsurvey of the data; Ref. [2] to provide a greater precision inthe phase of production and Ref. [3] to give therein a greaterreliability in the time.

In the classic construction of a dental prosthesis the low ac-curacy modeling gives am imperfect matching between the pros-thesis and the oral cavity which in turn causes the lasting dis-turbance to the patient. Moreover, the creation of a solid mod-el from the impression or mold taken of patient’s teeth requirescontact between the model material and the dental mold andmay result in contamination if either is not properly sterilized.Therefore, a non-contact measuring system is essentially required.

Outline of the work and main results

Two techniques have been analyzed in order to chose themost suitable one for our research: a) Conoscopic hologra-phy; b) Phase-shift Grating Projection.

During the past years the optic interferometric methodshave played a more and more important role in the mea-surement of various scientific disciplines like engineeringand the medicine. In this work, a comparison of two ad-vanced interferometric techniques of high accuracy for the3D reconstruction of whole field has been made in variousaspects: the conoscopic holography and moiré projectiontechnique.

Conoscopic holography

The conoscopic holography is based on the property ofthe anisotropy uniaxial crystal to divide the incident light[spatially incoherent] into an ordinary beam, propagatingin the crystal with constant speed, and an extraordinarybeam that propagates with a variable speed depending on

the angle of incidence. The interference of the two beamsof a single point source gives a Fresnel Zone Plate [FZP] bywhose intensity profile the distance between the source andthe observation screen can be determined. The use of in-coherent light gives a good intrinsic stability and a greatflexibility to fit wide measuring range. The set-up realizedhas the ability of high resolution (up to 0.5 µm), wide work-ing range (10 – 300 mm) and is able to work on difficultgeometry as in a steep slope (up to 85°). An example of set-up is given in Fig. 1a, while in Fig. 1b, a 3D reconstruction

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Interferometric fringe relief in dental elements

Tecnopolis-CSATA, Politecnico di Bari

Fig. 1 Conoscopic holography in 3D reconstruction(a) set-up; [b] 3D reconstruction of tooth remaining

[a]

[b]

of a model of a tooth remaining is shown. The main dis-advantage of this method is the method of scanning whichrequires a significant measuring time for a 3D reconstruc-tion of a tooth with required accuracy (30 µm for scanningresolution). For the case in Fig. 1b the acquisition time was20 minutes.

Phase-shift Grating Projection

The Phase-shift Grating Projection technique is based onthe use of sinusoidal grating projection and digital phase shift-ing techniques to obtain 3D reconstruction. It permits the ac-

quisition and processing of large amount of data points withhigh accuracy and high speed. The superposition of projectedreference grating and the deformed object grating, due to theobject depth and the different direction between the projectionand observation, gives the contour fringes. The phase shiftingmethod provides a whole filed and accuracy contour determi-nation. The accuracy of such method depends on mainly theerror of phase shifter which could be a high accuracy piezo-electric position controlling as widely used or a photoelasticcompensator as in our case. Its main disadvantage lies on thedifficulty to deal with the geometry as discontinuity, valley, hill,and so on, in particularly in the so-called “unwrapping” stageof data processing Ref. [4, 5]. Various unwrapping method havebeen proposed. In this work, it has been applied an unique un-wrapping method originated by Prof. C. Sciammarella whichgives a flexibility and feasibility to handle.

Future developments and expected deliverables

The results obtained show the good applicability of boththe applied techniques.

They provide a measuring precision in terms of mi-crometer and whole field data which can be processed au-tomatically by specific software for different use.

In the future we will concentrate our research in devel-oping a optoeletronic sensor in order to obtain tridimen-sional shape information of teeth in live.

The optical data will be detected by means of an highresolution optical system connected to a smart sensor andan image processing system. After a further analysis it willbe possible to compute the data for a numerical control ma-chine for master production.

References:

[1] Sirat G.; Psaltis D.: “Conoscopic Holography”; Optics Let-ters; vol 10 [1985].

[2] G. Y. Sirat: “Conoscopic Holograpy Application: Multi-purpose Rangefinders”; Optimet 1994.

[3] Maurice Halioua, Hsin-Chu Liu, Optical Three-Di-mensional Sensing by Phase Measuring Profilometry,Optics and Lasers in Engineering, 11[1989].

[4] Ming Chang, On-Line Phase-Measuring Profilometry,Optics and Lasers in Engineering, 15[1991].

[5] T.R. Judge, P.J. Bryanston-Cross, A review of phase un-wrapping techniques in fringe analysis, Optics and Lasersin Engineering, 21[1994].

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Fig. 2 Projection Moiré in 3D reconstruction [a] set-up; [b] 3Dreconstruction of tooth remaining

[a]

[b]

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Project title: Interferometric fringe relief in dental elements

Participants: Politecnico di Bari Unit responsible: Carmine PappalettereDip. di Progettazione e Produzione Industriale Collaborators: W.M. Sun, B. TrentadueVia Japigia 182, 70126 Bari Tel.: +39-080-5460517 Fax: +39-080-5460520email: carpa@poliba.it

Tecnopolis-Csata Novus Ortus Unit responsible: Antonio ScaramuzziStrada Prov. per Casamassima Km 3, Collaborators: G. Grasso70010 Valenzano BATel.: +39-080-4670333 Fax: +39-080-4670372email: scaramuz@tno.it

Other Collaborators:R. AciernoUniversità di LecceDip. di BiologiaVia per Monteroni73100 Lecce

1. Purpose of the work

An optical rotary encoder is an angular rotation/positiontransducer, which is used in processes where the position of me-chanical parts, moved automatically, must be monitored andcontrolled. An optical rotary encoder includes a glass disc witha suitable number of concentric traces, each having alternatedtransparent and opaque zones [1]. The pattern of these zonesprovides the information of the angular position according toa predetermined code (typically, a Gray code). All disc tracesare illuminated by a LED from one side of the disc. On the op-posite side, the light beam turns out to be modulated by thedisc traces and, after passing through a collimating slit, is col-lected by a photodiode array. The information correspondingto the angular position is extracted from the photogeneratedcurrent signals. An absolute rotary encoder provides direct andabsolute information of the angular position of the mobile sys-tem (typically, a drive-shaft) mechanically connected to the en-coder disc. The number of disc traces is equal to the numberof resolution bits.

The objective of the Project is to develop and realise a pro-totype of an absolute rotary encoder able to implement a num-ber of functions required to overcome production problemspresently encountered. In particular, a specific goal is to de-velop an integrated circuit including a photodiode array, whichtransduces light pulses into current signals, and the corre-sponding readout electronics, which produces the digital out-put related to the angular position information. The devel-oped system is intended to replace presently-used optical ro-tary encoders, providing advantages as far as performance(speed, sensitivity, power consumption) and production andcalibration costs are concerned.

2. Outline of the work

2.1 Definition of electrical, optical and mechanical specifica-tions of the angular position measurement system.

2.2 Definition of electro-optical device (chip) specifications.2.3 Definition of the electro-optical device architecture.2.4 Design, computer simulations and layout of a first version

of the encoder channel, including one photodiode and the

corresponding read-out electronics.2.5 Preparation of a test bench for the experimental evaluation

of the prototypes to be developed within the Project.2.6 Definition of additional features (“on-line calibration”).

3. Main Results

All the expected results has been fully achieved.3.1) The electrical, optical and mechanical specifications of the

angular position measurement system were defined [2].3.2) A test system was realised to reproduce real operating con-

ditions similar to those of the final system. The performanceand specifications required of the electro-optical device couldtherefore be analysed, which allowed the electro-optical de-vice specifications to be precisely defined [3]. The main elec-tro-optical specifications are the following:• Angular resolution: 13 bits. This entails the need for 13

traces on the glass disc and, hence, for an integrated ar-ray of 13 photodiodes and the corresponding read-outchannels.

• Maximum signal frequency: 500 kHz. This is the maxi-mum frequency of the signal from the outmost disc trace,where the largest number of transparent/opaque zones isprovided, and corresponds to a rotation frequency of thedrive-shaft in excess of 5000 rpm.

• Photodiode size: 200 µm x 300 µm, with a pitch equalto 600 µm. The photodiode size and pitch depend on thegeometrical characteristics of the glass disc chosen for thefinal encoder system.

• Minimum detectable light power density: ~90 W/m2.The corresponding light power impinging onto the 13thphotodiode in the array (outmost trace) is equal to 800nW, since the useful area in this photodiode is 31 µm(width of the transparent zone in the relevant trace) ¥ 300µm (photodiode height). Considering a measured pho-todiode responsivity of 0.125 A/W (at λ = 680 nm), thismeans a photogenerated current of ~100 nA.

• Maximum allowed light power density: ~600 W/m2. Thiscorresponds to a light power impinging onto the centralphotodiode in the array (element 7) equal to 8 µW, sincethe useful area in the latter is 45 µm (width of the colli-

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360

Sensors for position measurements in industrialenvironment

Istituto Trentino di Cultura, LIKA Electronic, Università di Pavia

mating slit) x 300 µm (photodiode height). The ensuingphotogenerated current is ~1 µA.

• Dedicated digital outputs from read-out channels. Anydigital output (including those from read-out channelsand digital interface) will have external standard CMOSload drive capability.

• Integration technology: double-poly double-metal 0.8-µm CMOS process. In case, a post-processing step willbe added to provide anti-reflecting coating.

• Calibration facility for each channel through a digital in-terface. Any channel will be independently calibrated un-der the control of a personal computer by adjusting itsoperating point as a function of the impinging light pow-er. This feature will greatly improve the encoder calibra-tion procedure.

• Temperature range from 0 to 70 °C. • Supply voltage (both digital and analog): 5 V.

3.3) The electro-optical device architecture has been defined, al-so taking into account sensor read-out techniques present-ed in the literature for similar applications. The functionalblocks of the device have then been precisely specified [3].

3.4) A chip including one photodiode and one read-out chan-nel (hereinafter referred to a sensor chip) has been designedand simulated. Its layout has been completed and released.

Fig. 1 and Fig. 2 show the simplified block diagram andthe microphotograph of the designed sensor chip, respective-ly. The chip includes a photodiode which converts the in-coming light beam into a current, a readout channel whichprocesses this current signal and produces a digital output wave-form, a thermal stabilization block which ensures the correctoperation of the readout channel even in the presence of tem-perature drifts, a bias generator which provides the requiredbias levels to the chip and a calibration block which allows dig-ital calibration of the readout channel under the control of anexternal microprocessor.

The photodiode is realised with an n+/p-substrate junctionhaving a photo-sensitive area of 200 x 300 µm_ and a capaci-tance Cd = 12 pF at a reverse bias voltage Vbias = 1.2 V. The pho-to-active region is surrounded by a triple guard-ring, that pro-vides adequate protection from the noise injected by the digitalsections and pads into the substrate. As from above specifica-tions, the light pulses are converted into current pulses whoseamplitude ranges from 100 nA to 1 µA.

The readout channel processes the current pulses comingfrom the photodiode and performs waveform shaping througha comparison between the analog input signal and a suitablethreshold level, thus providing the required digital output sig-nal. Waveform shaping is a crucial process, as a precise phase re-lationship is required between the digital signals correspondingto different channels to extract correct angular position infor-mation in spite of variations due to causes such as spreads inLED and photodiode characteristics, LED aging, temperaturedrifts, etc.

Fig. 3 shows the block diagram of the readout channel. Atransimpedance preamplifier converts the photo-generated cur-rent, Isig, into a voltage signal, Vop (a single-input-transistor am-plifier is used to minimise noise contributions). The voltage sig-nal Vop is fed to a filter-and-buffer circuit, which limits thenoise bandwidth. The filter output, Vof, is compared with athreshold voltage, Vofth, thereby providing the required wave-form shaping. As, for any fixed comparator input differentialsignal, a readout channel with tunable gain is necessary, whichis obtained by adjusting the value of the feedback resistor Rf. Asuitable control of Rf allows the signal amplitude at the ampli-fier output to be kept at a predetermined value Vof, pp for anyinput current signal amplitude in the specified range. In ourdesign, we set Vof, pp = 500 mV to guarantee adequate signalamplitude while still avoiding saturation problems. The pre-amplifier was designed according to the four main requirementspointed out in [5].

For signal frequencies from dc up to 500 kHz, the mini-mum bandwidth B sufficient to ensure no degradation in riseand fall times of the trapezoidal waveform at the preamplifieroutput was calculated to be around 2 MHz.

With an input device width W = 30 µm, the calculated equiv-alent input current noise is about 1 nARMS, corresponding toa S/N ratio of 40 dB in the presence of the minimum signal am-plitude, which is more than adequate for the specific applica-tion.

The filter-and-buffer circuit was designed so as to limit thenoise bandwidth and provide an output signal Vof compatiblewith the comparator input. A low-offset voltage comparator with

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Fig. 1 Functional block diagram of the sensor chip

Fig. 2 Die microphotograph of the sensor chip.

a PMOS input stage and without hysteresis was used. The com-parator output Ocv represents the output digital signal of thereadout channel.

The threshold voltage Vofth is generated on-chip by a ded-icated circuitry, which makes it to have the same thermal be-havior as that exhibited by the zero-signal level of Vof. In thisway, the overall thermal independence of the output duty-cycleis achieved by thermal stabilization of the filter output ampli-tude.

As mentioned above, a highly variable resistor is necessary

to obtain a transimpedance amplifier able to maintain a 500-mV output amplitude for any input current signal whose am-plitude is in the range from 100 nA to 1 µA. In the proposedsolution, shown in Fig. 4, the feedback resistor is realised witha T-network made up of two polysilicon resistors (R1 and R2)and an NMOS transistor (Rmos) working in its triode re-gion: Rf = (1 + R2/ R1)Rmos.

Thermal stabilization of the feedback network is needed toobtain a temperature-independent amplitude of the preampli-fier output signal Vop and, hence, of the comparator input sig-nal. While the voltage divider R2-R1 in the T-network does notgive rise to any thermal dependence, the equivalent NMOS tran-sistor resistance, Rmos, requires thermal stabilization. The lat-ter is obtained as shown in Fig. 5 [6], where Mf1 and Mf2 arematched transistors, and VBGAP and Ic represent a stabilizedvoltage and current reference, respectively. The drain-to-sourcevoltage of Mf2 and, hence, that of Mf1, are set to a constant val-ue proportional to Ic. Therefore, they turn out to be substan-

tially independent of temperature. Moreover, this scheme alsoallows calibration: the gain control required to maintain a con-stant peak-to-peak voltage Vop, pp = 500 mV over the wholeamplitude range of Isig, is achieved by adequately setting the cal-ibration current Ic. This changes the gate voltage of Mf1 and,hence, adjusts the transimpedance amplifier gain as desired. Cal-ibration is carried out during a dedicated (no-operation) phaseunder the control of a personal computer. The calibration cur-rent Ic is provided by an array of digitally programmable currentsources covering the range from 0 to 3 µA with a resolution of1 nA. These current sources, as well as all the bias current gen-erators in the chip, are derived from a temperature-stable mi-cro-power CMOS current reference [7], which ensures stabili-ty against thermal drifts .3.5) A test bench for the experimental evaluation of the devices

developed within the Project has been designed and im-plemented. This bench allows the required test-board to beallocated and several signals from the board to be accessedduring the device evaluation phase. Moreover, the lightsource can be moved in the three directions with respect tothe test board and, hence, to the photodetectors, therebyallowing the prototypes to be tested out under differentlight conditions (Fig. 6).

3.6) A signal processing architecture for automatic system cali-bration during operation has been conceived. This scheme,which is based on digital signal processing techniques, de-tects positive and negative peaks of the analog signals com-ing from each photodiode during normal operation, andcomputes the corresponding threshold voltages. The valueof the latter is therefore up-dated continuously for eachchannel (“on-line calibration”), which allows environmentand operating variations to be automatically taken into ac-count. The proposed technique is intended to provide theencoder system with a longer life without resorting to re-calibration procedures involving reprogramming of the cur-rent Ic during a dedicated phase.

3.7) A study has also been carried out to increase resolutionin rotary encoder systems by suitable processing of thesignals generated by the photodiode array. This allowsincreased resolution with no need for increasing glassdisc size. The proposed approach uses an encoder discof mixed absolute/incremental type (11 absolute, 2 in-cremental traces), and increases maximum resolutionfrom 13 to 16 bits by interpolating the signals coming

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Fig. 3 Block diagram of the read-out channel.

Fig. 5 Circuit for read-out channel thermal stabilization.

Fig. 4 Implementing the feedback resistor Rf with a T-network.

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from the incremental section. Moreover, the developeddesign allows the unit of measure and the resolution ofoutput data to be selected by the user, which increasessystem flexibility. The system has been designed usingVHDL [8], [9].

4. Future developments

• Experimental evaluation of the sensor chip (first version) andpossible refinements.

• Design and experimental evaluation of a prototype chip foron-line calibration.

• Second version of the sensor chip, including the on-line cali-bration circuit.

• Experimental evaluation of the second version of the sensorchip.

• Integration of the final sensor chip (13 photodiodes and read-out channels).

• Assembly of the rotary encoder system.• Experimental evaluation of the rotary encoder prototype.

5. Expected deliverables

• The final expected deliverable is a prototype of optical mea-surement system based on the integrated electro-optical devicedeveloped during the research activity.

• Intermediate deliverables will be prototypes of the sensor chipsand corresponding reports.

References

[1] R. Ohba, Intelligent Sensor Technology, John Wiley & Sons,Chichester, U.K., 1992.

[2] Document 1, Project “Sensors for Position Measurementsin Industrial Environments”: “Descrizione del sistema en-coder rotativo”, Nov 1998.

[3] Document 2, Project “Sensors for Position Measurementsin Industrial Environments”: “Specifiche del dispositivo elet-tro-ottico”, Nov. 1998.

[4] Document 3, Project “Sensors for Position Measurementsin Industrial Environments”: “Progetto del dispositivo elet-tro-ottico”, Feb. 1999.

[5] A. A. Abidi, "Gigahertz transresistance amplifiers in fine lineNMOS", IEEE J. Solid-State Circuits, vol. 19, pp. 986-994,Dec. 1984.

[6] D. M. Pietruszynski, J. M. Steininger, and E. J. Swanson,"A 50-M-bit/s CMOS monolithic optical receiver", IEEEJ. Solid-State Circuits, vol. 23, pp. 1426-1432, Dec. 1988.

[7] H. J. Oguey and D. Aebischer, "CMOS current referencewithout resistance", IEEE J. Solid-State Circuits, vol. 32, pp.1132-1135, July 1997.

[8] F. Cherchi, V. Liberali, G. Torelli, A. Simoni, "A rotary en-coder system with digitally increased resolution", Proc. 2ndMeeting on Optoelectronic Distance/Displacement Mea-surements and Applications (ODIMAP II), Pavia, Italy, May1999, pp. 313-318.

[9] F. Cherchi, L. Gonzo, V. Liberali, G. Torelli, Proc. Euro-pean Conference on Circuit Theory and Design (ECCTD’99), Stresa, Italy, Aug./Sept. 1999, pp. 483-486.

Fig. 6 Test bench for the experimental evaluation of the pro-totypes

Project title: Sensors for position measurements in industrial environment

Participants

Istituto Trentino di Cultura, Microsystem Division Unit responsible: Andrea Simoni (Project Coord.)Via Sommarive 18, 38050 Povo di Trento (TN) Collaborators: Lorenzo Gonzo,Tel.: 0461/314532 Fax: 0461/314591 Massimo Gottardi, Davide MascheraEmail: Simoni@itc.it

Università di Pavia, Dipartimento di Elettronica Unit responsible: Guido TorelliVia Ferrata, 1, 27100 Pavia. Collaborators: Ortensia Fedeli,Tel.: 0382/505215 (0382/505598) Fax: 0382/422583 Stefano Gregori, Valentino Liberali,email: torelli@ele.unipv.it Piero Malcovati, Franco Maloberti

LIKA Electronic S.N.C. Unit responsible: Mauro StefaniVia San Lorenzo 25, 36010 Carrè (VI) Collaborators: Lorenzo NeffariTel.: 0445/367186 Fax: 0445/383877Email: lika@likasiko.com

Purpose of the work

Broadband transmission of ultrasound in air and in wa-ter using capacitive, microfabricated electrostatic transduc-ers is reported. Using a pair of these devices, transmission isobserved from 0.2 to 1 MHz. The transducers are made us-ing silicon surface micromachining techniques and metal-lized Mylar membrane. A complete set of experimental re-sults has been performed, both in air and in water. Wave-forms with a bandwidth of approximately 700 kHz can begenerated and detected in air, whereas in water the band-width is in excess of 1 MHz. Finally, a pair of air-coupledtransducers have been used to test an aluminium plate (3.5mm thick) using broadband pulses in non-contact through-transmission.

Outline of the work

Although low frequency capacitive ultracoustic trans-ducers have been around for several years, recent develop-ments in microfabrication technology have spurred noveldesigns for these transducers in the high ultrasonic range.As it is well known, ultrasonic transducers are generally basedon piezoelectric effect and they are used in a wide variety ofapplications, including medical imaging, non-destructiveevaluation (NDT), underwater imaging, ranging, etc. Someof the main reasons for choosing alternative microfabricat-ed transducers, based on electrostatic effect, are energy den-sity, efficiency, cost, and integration with control electron-ics. Moreover, electrostatic devices have relatively high effi-ciency because they do not require large current densities.In principle they consist in a parallel plate capacitor withone fixed and one free electrode. If a voltage V is applied tothe capacitor, the free electrode will experience an attractiveelectrostatic force. Since the electrostatic force is propor-tional to the square of the electric field, a single order ofmagnitude closer spacing of the electrodes results in two or-ders of magnitude greater electrostatic force for the samevoltage. Because the force depends on the square of the volt-age, the second harmonic of the applied voltage will be gen-erated. For operation at the first harmonic, a DC bias volt-

age is applied to the capacitor along with the RF signal. Agood design requires a large linear displacement of the freeelectrode due to the applied voltage so that a large amountof ultrasonic energy is coupled into the air (or in the water).Capacitive transducer [1] can be microfabricated onto thesilicon wafers and they work as an array of condenser mi-crophones where a thin membrane (free electrode) is posi-tioned few micrometers above a fixed electrode (the sub-strate or backplate, fig. 1). The present work reports exper-imental results with an air gap micromachined ultrasonictransducer, well suited both in air and in water. The trans-ducers use various types of membranes, like Mylar and Kap-ton, metallized on one side whose thickness is ranging from1.2 to 10 µm.

Capacitive ultrasonic transducers are expected to be usedin many applications [2], especially in air, i.e. surface pro-filing, ultrasound testing of metals [3], as well as in hightemperature ambient [4], etc.

Three fundamental parts compose the realized device:the case, the backplate, and the membrane. The case is asupport for the other structures and its design is optimizedfor use of the transducer in water. The backplate (fig. 2) isfabricated from a polished (100) silicon wafer, with con-ventional contact UV lithography with mastering layers ofsilicon nitride (5000 Å thick) deposited by PECVD. Thewafer is coated with a photoresist and the pattern (a uni-form array of rectangular shape, from 40 to 150 mm) istransferred using contact UV mask aligner. The silicon ni-tride will be the mask for the next anisotropic silicon etch-ing. The silicon nitride is etched using a Reactive Ion etch-ing based on fluorine chemistry (CHF3); the photoresist isremoved using acetone. The wafer is dipped in a 5% HF so-lution to remove oxide on the silicon surface and to let thesubsequent etching start immediately. The silicon is etchedusing a wet anisotropic etching based on an aqueous solu-tion of KOH (33 wt%) at a temperature of 70°C. The etch-ing rate is carefully calibrated on a dummy wafer immedi-ately before starting the etching process. The etch rate is ap-proximately 1 µm per minute. After the etching, the waferis cleaned using RCA cleaning procedure. The silicon ni-tride mask is removed by dip in 50% HF solution. The waferis finally cut using a precision dicing system.

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A silicon microfabricated electrostatic transducer

ATEL, Università di Roma Tre

The membrane is fabricated from a Mylar folio, evaporat-ing a thin layer of aluminum (1000 Å thick) on one surface.

The next operation is to superimpose the thin membraneupon the backplate so as to trap resonating air pockets with-in the small holes of the backplate. Applying a transient volt-age between the backplate and the grounded front metal-lized surface of the membrane forces the membrane intomotion via electrostatic forces, thus generating acoustic sig-nals. In detection, an arriving acoustic wave compresses thecapacitive structure in the presence of a DC bias so that ameasurable charge variation is produced. This design leadsto devices with good frequency response (into MHz region),excellent sensitivity, and it does not show the signal ringingwhich normally is a negative characteristic for piezoelectricdevices.

The equipment used for the air-coupled (and water-cou-pled) transducers is shown in fig. 3. A pair of capacitancetransducers was separated by a 30 mm air gap (water gap).The source transducer was driven by a Panametrics 5052PRpulse-receiver, which delivered a - 300 V into 250 Ω tran-sient with a rise time < 10 ns (50 Ω damping and #1 ener-gy setting). A DC bias voltage of 100 V was also applied tothe transducer, using a simple capacitive decoupling circuit.The receiver was attached to a Cooknell CA6/C charge am-plifier, which had a sensitivity of 250 mVpC-1 and applieda well-regulated DC bias voltage of 100 V to the transduc-er. An additional 40 dB of gain was obtained by passing thesignal through the amplifier stage of the Panametrics unit.Finally, the received signal was acquired on a TektronixTDS620 digital oscilloscope and then transferred to a PCvia an IEEE488 interface. A software written under LAB-VIEW National Inst. controlled the acquisition and per-formed the analysis.

Main Results

Fig. 4 shows the water coupled waveform measured atthe receiver transducer. The pulse width is about 3.2 ms andthe residual ringing is very small. The spectrum of the re-ceived waveform is shown in Fig. 5. In the Fig. 5 the spec-trum in air (dotted) and in water is reported. In air, thebandwidth is from 0.4 to 1.1 MHz (@ 6 dB) while in wa-ter the bandwidth increases, from 0.2 to 1.2 MHz (@ 6 dB).This is a well-known behavior [7], which occurs when thedevices are subject to water loading. There are at least threereasons to explain the difference in response. The first is thatthe acoustic impedance of water is very much higher thanthe one in air, yet it is closer to the bulk membrane mater-ial (Mylar). Secondly, the increased pressure exerted on themembrane through water loading can change both band-widths and sensitivities. Finally, the attenuation in air is aserious limitation in air-coupled systems, while the attenu-ation is not a problem when the transducers work in water.

Ultrasonic NDT of materials using air-coupled trans-ducers has been studied for many years, but the frequencyrange was restricted to low frequencies. With the recentprogress in capacitive transducers, bulk wave modes have

been successfully used by many of authors to test polymer-ic materials and metals [3, 5, and 6]. This type of measure-ment is normally very difficult to obtain, because the largeimpedance mismatch between air and solid causes a largeattenuation of the signal, at the receiver. As it is easily cal-culated, the total loss between the transmitter and the re-ceiver, with an aluminum plate (3.5 mm thin) in the mid-dle of the path (totally ca. 5 mm) is almost 80 dB. Howev-er, this is based on the assumption that both air-aluminuminterfaces are acting independently (e.g. the thickness of thesample is large when compared to the longitudinal wave-length). In the case of our interest, the wavelength of lon-gitudinal waves in aluminum is in the order of mm, that iscomparable with the thickness of the layer, so this assump-tion is not valid. As it is well known [8], the thin layer be-haves as a half-wavelength resonator, and the half-wavelengthresonance can be measured more accurately in the frequen-cy domain, operating the FFT of the received signal. Weused an aluminum plate, 3.5 mm thick with a theoretic res-onant frequency of about 917 kHz (assuming v = 6420 ms-1,λ=2⋅thickness). Fig. 6 shows the FFT of the measured sig-nal: the frequency peak is very evident and located at 900kHz, which is in good agreement with the expected fre-quency.

Conclusions and Future developments

We have developed an inexpensive, non-resonant, mi-cromachined capacitance transducer with a wide bandwidth,for application in air and in water. While the use of thistransducer, in air, will perform an important leap forwardin NDT (due to the large bandwidth), the possible appli-cation in water will be even more important. The well-matched impedance, the large bandwidth, the good sensi-tivity and the expected very low cost (due to the use of stan-dard microelectronic technology) will be an important im-provement for medical diagnostic use. In the near future wehope to extend this work, by using a nitride membrane, self-fabricated in planar technology, in order to realize a 4-5 MHztransducer, well suited for medical echographic applications.

References

[1] W. Kuhl, G.R. Schoder, F.K. Schröder, Condenser trans-mitters and microphones with solid dielectric for air-borne ultrasonics, Acustica, 4 (5) (1954), 519-532

[2] D.W.Schindel, D.A. Hutchins, Applications of micro-machined capacitance transducers in air-coupled ultra-sonics and nondestructive evaluation, IEEE UFFC, 42(1) (1995), 51-58

[3] W.M.D. Wright, D.A. Hutchins, Air -coupled ultrasonictesting of metals using broadband pulses in through trans-mission, Ultrasonics, 37 (1999), 19-22

[4] W.M.D. Wright, D.A. Hutchins, Monitoring of binderremoval from injection molded ceramics using air-cou-pled ultrasound at high temperature, IEEE UFFC, 46

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(3) (1999), 647-653[5] D.A. Hutchins, W.M.D. Wright, D.W. Schindel, Ul-

trasonic measurement in polymeric materials using air-coupled capacitance transducers, JASA, 96 (3) (1994),1634

[6] D.W. Schindel, Air-coupled generation and detection ofultrasonic bulk waves in metals using micromachined

capacitance transducers, Ultrasonics, 35 (2) (1997), 179[7] A.G. Bashford, D.W. Schindel, D.A. Hutchins, Micro-

machined ultrasonic capacitance transducers for im-mersion application, IEEE UFFC, 45 (2) (1998), 367-375

[8] J.Krautkrämer, H. Krautkrämer, Ultrasonic testing ofmaterials, Springer-Verlag, Berlin, 1990

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Silicon (p++)(back plate)

Air-gap

Membrane(Mylar)

Al or Au

Water

GPIB

Chargeamplifier

100V DCbias

AC/DCdecoupling

100V DCbias

Ultrasonicp ulser

Digitalo scilloscopeC + LabView 5.0

RX X

0.0E+0 1.0E+6 2.0E+6Freq. [Hz]

-60.00

-50.00

-40.00

-30.00

-20.00

-10.00

0.00

Spe

ctru

m [dB ]

In air (0.4 - 1.1 MHz @ -6 dB)

In water (0.2 - 1.2 MHz @ -6 dB)

Pulse width - 3.2 us

Fig 1 Schematic of micromachined transducer Fig. 4 Waveform measured at receiver transducer.

Fig. 2 SEM picture of a part of the back plate Fig. 5 Spectrum of received waveform in air (dotted)and water (solid) for the same driving pulse

Fig. 3 Arrangement used for transmitter-receiver mode

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Project title: A silicon microfabricated electrostatic transducer

Participants:

ATEL s.r.l. Unit responsible: Lucio Giuliani (Project Coordinator)Via di Valle Caia s.n.c. Collaborators: P. Pieretti, D. Centomini00040 Pomezia RM M. ZucchettiTel.: +39-06-9146053 Fax: +39-06-9145963Email: atel.info@flashnet.it

Università di Roma III Unit responsible: Massimo PappalardoDip. di Ing. Elettronica Collaborators: R. Carotenuto P. Di Rosa, Via della Vasca Navale 84, 00146 Roma G. Cincotti ,A. Iula, N. Lamberti. L. AcciariniTel.: +39-06-55177010 Fax: +39-06-5579078 G. GuidarelliEmail: pappalar@uniroma3.it

Fig. 6 Spectrum of received waveform through a 3.5-mm thin aluminum plate

3. Main results

3.1 Development of the technology for large area integrationThe importance of amorphous silicon relay on the pos-

sibility of developing a large area electronics, in particular

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Two-dimensional image sensor in amorphous andpolycrystalline silicon technology

CNR-IESS, Università di Bologna, Università di Roma “La Sapienza”

Fig. 1 Schematics of array layout for a four cell structure.

Fig.2 Single pixel structure with TFT drivers and photodetector.

1. Purpose of the work

Amorphous silicon (a-Si:H) can be deposited on largearea by chemical vapor deposition, inexpensive substrates asglass or plastics can be used due to the low deposition tem-perature. This fact together with peculiar optical and elec-tronic properties allows the use of this material in large areaelectronics and in particular large area image detector.

In particular there is the possibility to obtain a red, greenand blue colors (RGB) signal directly from one two termi-nal detector. In fact, the detector structure itself behaves likea filter, while color information are obtained by applyingdifferent bias voltage to the device.

The main purpose of the present project is to develop anumber of technologies necessary to reach large area amor-phous silicon electronics and to achieve all the steps neces-sary to the integration of driving a-Si:H thin film Transistors(TFT) together with three color photodetectors on a singlesubstrate. A complete design of the driving process for theseparate detection of the three main colors is also carried out.

In addition research on high speed Polycrystalline (poly-silicon) silicon TFT, necessary for external multiplexing elec-tronics will be carried out. Recently, excimer laser crystal-lized polysilicon TFTs with high field-effect mobility (>100cm2/Vs) have been reported, leading to the possibility offabrication of complex CMOS circuits based on such de-vices. In the present project, polysilicon TFTs will be fabri-cated and the electrical characteristics will be analyzed byusing both experimental measurement and numerical sim-ulations. Finally, the device performance will be tested byusing a ring oscillator circuit.

2. Outline of the work

2.1 Development of the technology for large area integration2.2 Modellization transient phenomena and of the self-bi-

asing process in three color photodetectors2.3 Optimization of three color a-Si:H detectors2.4 Realization of driving electronics by discrete components2.5 Development of a-Si:H TFT with high field mobility2.6 Parameter extraction for TFT and photodetectors

in the possibility to achieve a large area image detector. Tothis aim the technology of deposition of TFT and of detec-tors must be integrated in order to obtain a single device,containing either the detector and the electronic switch ca-pable to drive the periodic reading pulse of the structure ac-cording with the schematic reported in fig. 2. Both the com-ponents can be obtained by the use of a-Si:H technology. Inparticular in this project plans to achieve to following steps:

1) Lithography of the transparent conductive oxide (TCO)for the photodetectors back electrode conformation;

2) realization of a-Si:H TFT with connection of gate to col-umn line and of the drain to the row line;

3) passivation of TFT 4) windowing of passivation and exposure of TCO contacts5) deposition and photolitographic patterning of a-Si:H pho-

todetectors6) passivation of photodetectors7) windowing of passivation and exposure of photodetector

back contacts8) final ground metallization

The integrated structure has been designed, masks hasbeen prepared for a 40x40 matrix, following the schematicspresented in fig. 1, relative for the sake of simplicity to a 2x2pixels structure. Several steps of the technology have beenindependently proven and optimized, in particular the re-active ion etching recipe of photodetector structure has beendetermined in order to avoid junction shunting, Fig. 3 re-port comparison of I-V characteristics of a p-i-n structurebefore and after etching. A new metallization structure con-stituted by chromium aluminum sandwich in order to avoidinterdiffusion has been developed, finally the TCO etchingprocess has been optimized.

3.2 Modeling of transient phenomena and of the self-bias-ing process in three color photodetectors.

Practical use of color sensors in large area arrays requiresperiodic readout of the photo-charge stored in the parasiticcapacitance of the device by a transient technique of sens-ing [1]. The duration of charge integration and data ex-

traction from columns determines the frame rate. This read-ing technique is referred to as “charge integration regime”.Both integration and readout times are strictly dependenton the electronic characteristics of photodetectors.

At a given value of the external bias Vbias, photo chargegenerated by radiation absorbed on any one of the threejunctions, can be extracted repeating the sensing cycle con-stituted by an integration time in open circuit condition fol-lowed by a reading time in which the device is connected tothe bias voltage [2].

We used a well-known 2D simulator (DESSIS) in orderto investigate the effect of material properties on the self-biasprocess. The goal is to get indications about the possibilityto reduce the number of readout/integration cycles for theequilibrium starting from the technology, once the illumi-nation conditions are fixed.

An example is reported in Fig. 2, where a p-i-n-i-p struc-ture of a two-color detector and only red light illumination(at 0.1mW/cm2) have been considered for simplicity. Thedevice is biased with 4V, so that D2 is reverse biased and D1forward biased. We reproduced the self-bias process usingreading pulses of 8 ms, and 2 ms integration times. Wedemonstrated the rule the density of defects in the intrinsicmaterials in the time necessary to reach equilibrium[3].

The charge exchanged contains information on the ab-sorbed radiation at different colors, it depends on a complexway on either the changes on charge accumulated at the junc-tions and on their differential capacitance. In fig. 4 the sim-ulated total carriers distribution is presented (dashed line) to-gether with the charge on carriers density (full) line duringone integration time cycle. One can notice how the forwardbiased junction loses excess carriers in the intrinsic zone whileincrease the charge in the depleted zones. On the contraryin the reverse biased junction the main effect is a reductionof the charge in the depleted zone. One can notice how thecharge changes in the forward bias junction is comparable orgreater than the charge changes in the reverse biased junc-tion according with the picture of a self-biasing process. Inthe figure the density of photocurrent and the density of cur-rent due to excess carrier recombination are also depicted.These considerations allowed to seek optimization of threecolor a-Si:H detector by reducing the defect density in the

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Fig.3. Simulation of self-bias process obtained decreasing theslope of the, deep defect profile to the value 1017 cm-3.

Fig. 4 Total density of carrier, trapped and free, in the struc-ture and change of total density of carrier during the integra-tion time (continuos line).

intrinsic layer and by choosing the thickness of the internaljunction, which detects the green radiation, thicker than thefront junction which detects the blue one. The effect of di-mensions of TFT and detector capacitance will be studied.

3.3 Development of Polycrystalline silicon TFT with high fieldmobility

Amorphous silicon films (50 nm thick) were depositedby PECVD at 300 °C on thermally oxidized silicon wafersand crystallized by Excimer Laser Annealing (ELA) tech-nique. The samples were irradiated at different energy den-sities (El) by using a XeCl Lambda Physik excimer laser withapproximately 30 ns pulse duration (FWHM). Before ELAtreatment amorphous silicon films were dehydrogenated at450 °C for 3 h. During laser irradiation, the samples werekept in vacuum at RT and a beam homogenizer was usedto produce a 7x7 mm2 laser spot onto the sample. After ir-radiation the samples were analyzed by SEM (after Secco-etching) and atomic force microscopy (AFM). We have in-vestigated the grain size and surface roughness variation withlaser energy density to optimized ELA polycrystalline sili-con (polysilicon) for device applications. In fact, it is foundthat by increasing the grain size the electrical characteristicsare improved and, in particular, an increase in field effectmobility and subthreshold slope is observed, accompaniedby a decrease in of threshold voltage [4]. As can be seen inFig. 5 a-c, grain size increases with the energy density up toabout 1 µm, where the so call Super Lateral

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Fig. 5 SEM micrograph of Secco-etched polysilicon film crys-tallized energy laser densities: 180 mJ/cm2 (a), 200 mJ/cm2 (b)and 240 mJ/cm2 (c).

Fig. 7 Layout of the lithographic masks for polysilicon TFTs fab-rication (device with channel length=10 mm and channelwidth = 40 mm). Different lines correspond to different processsteps: - green: via-holes for ion doping;- purple: silicon islands;- black: via-holes for source and drain contacts;- red: source, drain and gate contact metallization.

Fig.6. Surface roughness of polysilicon films crystallized at dif-ferent laser energy densities.

Growth (SLG) regime [5] is triggered (fig.5c). However,due to its peculiar mechanism, the SLG regime correspondsto a narrow processing window and large non-uniformities inthe grain size distribution are observed (fig.5c). On the oth-er hand, irradiations performed at lower energies produce poly-silicon films with smaller grains (~ 300 nm) but better grainsize distribution uniformity (fig 5b). The AFM analyses showthat the surface roughness increases with laser energy densitywith a maximum value corresponding to SLG regime (fig.6)Surface roughness influences the characteristics of gate ox-ide/silicon interface as well as the electric field intensity at theinterface. High roughness produces high electric field regionsat the interface, increasing leakage current through the gateoxide. These results suggest that the use of laser energy densi-ty lower than SLG regime for polysilicon crystallization, i.e.El < 240 mJ/cm2 for films 50 nm thick irradiated at roomtemperature, can be more effective to obtain polysilicon TFTswith good and uniform electrical characteristics.

Photolithographic masks (see fig.7) have been designedand fabricated by electron been lithography (EBL). TFTs willbe fabricated in non-self-aligned configuration, i.e. with thegate contact overlapping the source and drain contacts. Thisconfiguration required only one laser irradiation, performedafter the ion implantation of the source and drain regions. In-deed, the ELA treatment results in the silicon crystallizationas well as the doping activation. In addition, the diffusion ofdoping atoms during laser irradiation produces lightly dopedregions near the source and drain contacts, reducing the elec-tric field at the drain contact during the device operation.

4. Future developments

The final goal of the three years project consist in thecomplete realization of a 40x40 matrix of three color de-

tectors, switched by a-Si:H TFT. Combined simulation ofTFT and sensor will allow correct dimensioning of transis-tors. At this stage of the project multiplexing and signal tim-ing will be demanded to external electronics. Polycrystallinetransistor for high speed switching will also be developed.In a future development multiplexing will be realized on thesubstrate by combination of amorphous and polycrystallinedevices. In this second stage also signal processing and im-age formation will be considered.

5. expected deliverables

The expected deliverables are:1) a 40x40 matrix of three color detectors driven by a-Si:H

TFT;2) a ring oscillator obtained by polycrystalline transistors.

6. References

[1] R. L. Weisfield, Mat. Res. Soc. Symp. Proc. Vol. 258(1992), p. 1105.

[2] F. Irrera, F. Lemmi, F. Palma, "Transient behaviour ofAdjustable Threshold a-Si:H/a-SiC:H Three-Color De-tector", IEEE Transaction on Electron Devices, 44 N.9, (1997), p. 1410

[ 3] L. Colalongo, F. Irrera, F. Lemmi, F. Palma, "Effects ofmaterial properties in three color amorphous silicon de-tectors", Proceedings of the 1999 MRS Sring meeting,to be published

[4] G. Fortunato, L. Mariucci, R. Carluccio, A. Pecora, V.Foglietti, to be published on Applied Surface Science

[5] J. S. Im, H. J. Kim, Appl. Phys. Lett. vol. 64, (1994) P.2303

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Project title: Two-dimensional image sensor in amorphous and polycrystalline silicon technology.

Participants:

Università di Roma I Unit responsible: Fabrizio Palma (Project Coordinator)Dip. di Ing Elettronica Collaborators: D. Caputo, G. de CesareVia Eudossiana 18, 00184 Roma F. Irrera, A. NascettiTel.: +39-06-44585418 - 44585835 Fax: +39-06-4742647email: palma@die.ing.uniroma1.it

CNR-Istituto di Elettronica dello Stato Solido (IESS) Unit responsible: Luigi MariucciVia Cineto Romano 42, 00156 Roma Collaborators: G. Fortunato, L. PecoraTel.: +39-06-415221 Fax: +39-06-41522220Email: luigi@iess.rm.cnr.it

Università di Bologna Unit responsible: Massimo RudanDipartimento di Elettronica Informatica e Sistemistica (DEIS) Collaborators: L. Colalongo, M. ValdinociViale Risorgimento 2, 40136 Bologna Tel.: +39-051-2093001-016 Fax: +39-051-2093073email: mrudan@deis.unibo.it

Purpose of the work

Special avalanche photodiodes operated in the Geiger-mode, i.e. at voltage higher than the breakdown level, canbe used to detect single photons. These Single PhotonAvalanche Diodes (SPADs) are emerging as a convenient al-ternative to photomultiplier tubes (PMTs) in photon count-ing and timing applications, thanks to their ruggedness,small size, low bias voltage, and high photon detection effi-ciency also in the red and near-infrared (NIR) range. In re-cent years, significant experimental results have been ob-tained with SPADs in various fields, such as criptography,astronomy, single molecule detection, fluorescent decayanalysis, laser diode characterization, optical fiber testing,laser ranging in space applications and telemetry, photoncorrelation techniques in laser velocimetry and dynamic lightscattering, basic quantum mechanics, etc.. SPAD devices forpicosecond photon timing have been developed at Politec-nico di Milano, along with a special driving circuit (AQC-active quenching circuit) suitable for operating the SPADin Geiger mode.

The aim of this work is the development of compact op-toelectronic modules including the SPAD detector and theassociate AQC, which can be easily employed in the afore-mentioned photon counting and timing applications. Thesemodules must feature low power dissipation, low fabrica-tion cost and small physical size, along with plug-and-playcapability. In order to attain the basic objective, the first nec-essary goal was the design and fabrication of dedicated mono-lithic silicon circuits (ASIC Application Specific IntegratedCircuits) for driving the SPADs.

Outline of the work

An active quenching circuit can be generally divided intwo parts: i) the comparator and logic block, that senses theavalanche onset and generates the logic commands forquenching and resetting the SPAD, and ii) the driver block,that generates the actual voltage signal applied to the SPAD.The first step toward a monolithic AQC was the integrationof the comparator and logic block into one chip, named

AQC-ASIC1, by using a CMOS technology. A completeAQC is obtained by adding only a few discrete componentsto the AQ-ASIC1, with a remarkable reduction of the print-ed circuit board (PCB) size. In comparison to previous cir-cuits, power dissipation can be minimizeed by proper cir-cuit design.

The Milano unit carried out the design, fabrication andcharacterization of the AQ-ASIC1 by exploiting the Euro-practice facilities.

The Bolzano unit was involved in the electrical and me-chanical design of the module, PCB layout design and op-timisation, and auxiliary electronic design (Peltier cell con-troller, input/output interface, dedicated power supply).

A basic version of the photon counting/timing moduleand a more sophisticated four-quadrant module have beenassembled and characterized.

Main results

A simplified schematic of the active quenching circuitbased on the AQ-ASIC1 is sketched in Fig. 1.The SPAD isbiased at the voltage Va, higher than the breakdown volt-age, Vb. In stand-by condition, switches Squench and Sreset areopen. When a photon is detected, a fairly high passive load(Rb+Rs) provides prompt passive quenching by reducingthe avalanche current to a very low value. After a short de-

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Integrated photon counting modules

Microgate, Politecnico di Milano

Fig.1: Basic block diagram of the AQC. The integrated logiccircuit is shown within the dased box .

lay (typically 10 - 15 ns), quenching is confirmed or com-pleted by the active loop formed by the comparator Comp,the monostable Mhold-off and the quenching switch Squench.The active loop drives the voltage across the SPAD downto Va - Vquench , a level lower than the breakdown voltageVb by a few volts, thus avoiding reignition due to nonuni-formity of Vb over the detector active area [1]. The quench-ing pulse duration (hold-off time) is accurately controlledby the monostable Mhold-off. As soon as the quenching pulseis terminated, the bias voltage across the photodetector isswiftly restored to Va by means of switch Sreset. The dura-tion of the reset pulse is determined by the monostable Mre-

set, which is triggered by the negative transition of Mhold-off.The output TTL signal, that marks the detection of a pho-ton, is generated by the monostable Mout. The AQC-ASIC1includes a fast gating option by means of an external TTLsignal. Gate-off pulses with duration ranging from 15 ns tominutes can be employed.

The external quenching and reset switches are fast DMOStransistors (Siliconix SST215). The ASIC has been fabricat-ed with a standard digital 1µm-CMOS single-polysilicon,double-metal process. The chip area (1.1mm x 1.4mm) ismostly ocwcupied by the pads and the three 3pF-capacitorsassociated to each monostable. The chip was not optimizedfor a reduced area occupation, because at this stage the size ofthe detection module is limited by the external components.

The AQC-ASIC1 and the discrete components were mount-ed on a multiylayer PCB by means of surface mounting tech-nology and assembled with the SPAD detector. Tests have beenperformed with thick-junction avalanche photodiodes, devel-oped by EG&G Optoelectronics, Canada and with thin-junc-tion SPAD devices, developed by Politecnico di Milano.

The AQC can operate SPAD detectors with excess biasvoltage up to 25V. Power dissipation is 60mW in quies-cent conditions. As shown in Fig. 2, the circuit features aminimum deadtime of less than 40 ns, corresponding to asaturated counting rate exceeding 25 Mcounts/s. The min-imum duration of the gate-off TTL signal is about 15 ns.The maximum duration of the gate-off signal is 2.5 min-utes. The linearity between photon flux and counting rateis excellent with thin-junction SPADs; with thick-junctionSPADs operated at at high counting rate, the linearity is in-herently limited by self-heating effects [1]. The measuredperformance are equivalent to that of the previous AQCsassembled with discrete-component, but with with remark-ably reduced size, complexity and dissipated power.

The timing performance of the module was assessed byusing a conventional photon timing set-up [1]. We mea-sured a moderately good timing resolution of 300 ps FullWidth at Half Maximum with thin-junction SPAD. Thisperformance is remarkably inferior to the intrinsic timingresolution of the SPAD device, due to the integration of theavalanche current signal by the parasitic capacitance betweenground and the SPAD anode [2]. This effect will be elimi-nated in a future circuit release, by picking up the avalanchesignal in a more appropriate way.

A complete photon counting module, including theSPAD detector and the associate AQC and interface cir-

cuits was assembled in the small box shown in Fig. 3,. Thebox dimensions are 4.5 cm x 10 cm x 3 cm.

The input/output interface has been designed in orderto guarantee the signal integrity even with relatively long

transmission lines (up to 20 m). In particular, the “count”output pulse and the gating input signal have high speed re-quirements. These signals are translated TTL level to RS485level and transferred over twisted cable pairs. This choice re-duces crosstalk and increases noise immunity.

The first prototype module works with a low voltage,low dark counting rate SPAD, that can be operated at room

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Fig. 2: Output pulses corresponding to the detection of singlephoton

Fig. 3 Photon counting module prototype (left) Printed circuitboard containing the AQC and the interface circuits (right)

temperatutre with no need of thermal stabilization. Never-theless, sufficient room has been left in the box to accom-modate a Peltier cooler with the associate control circuit.

A more sophisticated photon counting sensor wasassembled by the unit of Bolzano, including four SPAD de-vices, the associate AQCs, protection and interface circuits.The SPADs (EG&G “Slik”) were mounted on a double-stage Peltier cooler and enclosed in a dedicated package inorder to obtain a four-quadrant detector. The operating tem-perature of the SPAD can be set betweeen -30 °C and 0 °C.Regulation is performed by a conventional PID controller,that ensures fast response and zero steady state error perfor-mances along with an accuracy better than 0.2 °C.

As shown in Fig. 4, the quad-cell and the associate cir-cuits are tightly packed in a cilinder with a diameter of 6cm and a length of 16 cm. This sensor has been specifi-cally designed to implement a high-sensitivity “image track-er” for advanced adaptive optic applications. The first pro-totype will be the key component of the tip-tilt correctionsystem designed for the European VLT (Very Large Tele-scope), located at Cerro Paranal (Chile).

Future developments

The second stage of the program will be to design andfabrication of a fully monolithic AQC (AQ-ASIC2), in-cluding both the logic section and the driver section. Re-markable problems have to be solved, mainly concerningthe technological compatibility between high-voltage com-ponents and low-voltage logic circuitry. Starting from thethe results achieved in the this phase of the project, it willbe possible to investigate the feasibility of a new AQ-ASICfor driving a multielement SPAD detector and the feasibil-ity of a fully integrated photon counting module, includingthe SPAD detector and the AQC in a single silicon chip.

Work will be done in order to include the circuits forcontrolling the bias voltage and temperature of the SPADphotodetector in the module. Electronics for signal condi-tioning and data preprocessing will also be included for ob-taining a smart sensor head, that can be direcly interfacedto a PC.

Expected deliverables

• Fully integrated active quenching circuit (AQ-ASIC2) fordriving SPAD detectors

• Smart and compact photon counting modules• Analysis of the feasibility of a complex AQ-ASIC for dri-

vig multielement SPAD detectors• Analysis of the feasibility of a fully integrated photon count-

ing module including the SPAD detector and the AQCon a single chip.

References

1. S.Cova, M.Ghioni, A.Lacaita, C.Samori, F.Zappa“Avalanche photodiodes and quenching circuits for siglephoton detection” Appl. Opt., 35, 1956-1976 (1996)

2. A. Spinelli, A. L. Lacaita, “Physics and Numerical Simu-lation of Single Photon Avalanche Diodes”, IEEE Trans-actions on Electron Devices, 44, 1931-1943 (1997)

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Fig. 4 Four-quadrant photon counting module

Project title: Integrated photon counting modules

Participants: Politecnico di Milano Unit responsible: Sergio Cova (Project Coord.)Dipartimento di Elettronica e Informazione Collaborators: Massimo Ghioni, Piazza Leonardo da Vinci, 32 – 20133 Milano Franco ZappaTel.: 02/23996103 Fax: 02/2367604Email: cova@elet.polimi.it

Microgate s.r.l. Unit responsible: Roberto Biasi Via Valdagno, 4 – 39100 Bolzano Collaborators: Federico GoriTel.: 0471/288545 Fax: 0471/281760 Email: rbiasi@microgate.it

Abstract

In the framework of a tri-annual research activity focusedon the development of a microsystem able to assess the ther-mo-hygrometric comfort level in a mean of transport, a fea-sibility study on the measurement principle, based on theskin thermo-regulation simulation, has been carried out.

The study is based on the evolution of a sensor conceivedto measure the dry equivalent temperature. A prototypesensor has been developed and tested preliminarily on fab-rics and seats to measure the thermal parameters needed forseat comfort evaluation.

A suitable algorithm makes it possible to identify thethermal parameters needed for the seat comfort evaluation:the thermal resistance and the water vapour resistance.

Purpose of the work

The increasing market demand for highly effective andefficient HVAC systems for mobile applications has deter-mined a great impulse in the research and development ofinnovative methods and instruments to predict passengersthermal sensation. This trend is particularly evident in theautomotive compartment.

The thermal conditions in cars are very often differentfrom the typical indoor climate in buildings due to asym-metries and non-uniformity in the temperature and air ve-locity fields and in the dynamic behavior. This fact dramat-ically increases the complexity of the comfort evaluationcompared to the already defined methodologies used inbuilding applications. The need of standard procedures andinstruments is a crucial point that has to be faced. The avail-ability of specific instruments and devices may allow a sig-nificant enhancement of the comfort level in the means oftransport.

The ultimate objective of the activity is the developmentof a Smart micro-system able to assess the thermal comfortlevel in indoor environment. To reach these ambitious ob-jectives the emerging technologies of micromachining willbe used together with the modern signal analysis techniquesas fuzzy logic, neural netwotk , etc..

Outline of the work

Since about 25% of the body’s surface is in contact withthe car seat acting like an extra layer of clothing, it becomesclear the importance of the seat to the global thermal com-fort perceived. A good thermal comfort of the seat is main-ly related to its characteristics of permeability to evaporativeand sweat losses. So the study on seats and fabrics charac-terisation in terms of effect on thermal sensation has beenchosen as starting point and on this subject the first part ofthe research activity has been addressed.

Main results

The principal difference in the evaluation of the seat ther-mal comfort compared to dry thermal comfort, consists inthe measurement of the heat flux produced by the sweatingand lost through the seat. This heat flux is simulated withthe evaporation of a controlled quantity of distilled waterfrom an heated surface in contact with the seat.

The total heat transfer from a constant temperature wa-ter-wetted flat plate is [7]:

where:A = area of the plate; m2

Rc = thermal resistance; m2K/WRe = water vapour resistance; m2kPa/Ww = wetted area ratio from 0 to 1; dimensionless TS = superficial temperature; OCTA = ambient temperature; OCPS = saturated water vapour pressure at superficial temper-

ature TS; kPaPa = saturated water vapour pressure at ambient tempera-

ture TA; kPaf = relative humidity; dimensionless

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Microsensors for the detection ofthermo-hygrometric comfort conditions

Centro Ricerche Fiat, Università di Roma “Tor Vergata”

WR

A T TwR

A p pc

S Ae

S a= − + −1( ) ( )Φ

Measuring the surface temperature of the sensor, the elec-tric power supplied to the sensor to keep its superficial tem-perature constant, the humidity and the ambient tempera-ture, it is possible to identify the two parameters Re and Rc

that characterise the thermal exchange through the seat.The sensor is based on a hot film element heated via Joule

effect. To establish the heat lost by evaporation heat the sen-sor is covered with a polyethylene membrane and a single

sweat impulse is generated by wetting this fabric with a con-trolled quantity of demineralised water (0.005 ml). To sim-ulate the human skin, the sensor temperature is set on 34 °Cwith an integrated heater. This temperature is kept constantand controlled by an electronic circuit that supplies the pow-er in function of the temperature measured by the sensor. Toreduce the heat flux lost in others directions than that flowsthrough the seat, the sensor is contained in a polipan case.

The value of the thermal resistance and the water vapourresistance relative to the polyethylene membrane are calcu-lated using the previous equation. The value of the thermalresistance and the water vapour resistance relative to a sam-ple fabric and relative to the same fabric covered with a filmof nylon has been measured. To allow a complete tran-spirability of the analysed fabric the sensor is placed on asupport with a wire-netting. The fabric to analyse is put be-tween the wire-netting and the sensor. Because the pressureplays an important role for the transpirability of the seat,

the static pressure exerted by the human body on the seat issimulated by a standardised weight placed over the sensor.

The values of the thermal resistance and water vapour re-sistance calculated during the three tests are reported in fig. 3.

Then the cushions of three different seats have beenanalysed. The human body pressure has been simulated witha standardised weight that exerts a pressure of 21 mbar.

For each seat there have been carried out three tests; the val-ues of Rc and Re are reported in fig. 3. These preliminary testsdemonstrate that the device presents a good repeatability (5%)and a sensibility adequate to characterise the different fabrics/seats.

These tests have demonstrated that the selected methodcould be considered promising and adequate for an auto-motive use.

Future developments

The results of the illustrated activity will constitute the ba-sis for the evolution of the sensor to a more sophisticated andeffective structure. The next step of the activity is the feasibil-ity demonstration of an integrated microsystem where all thethermal function here described are performed automatically.So the surface temperature of the sensor will be kept constantregulating the dissipated heat and the evaporation processes.

The thermal regulation processes will be simulated withspecific mathematical model that will be used in a secondphase to develop the control algorithm of the microsystem.Then a “macrosystem” will be realised with hybrid tech-nologies to demonstrated the effectiveness of the workingprinciple and to allow starting the control strategies devel-opment.

Expected deliverables

The activity will demonstrate the feasibility of a new sen-sor to assess the thermo-hygrometric comfort level. Duringthe development some intermediate results will be produced.In the first phase a preliminary sensor prototype able to qual-ify the effect on thermal sensation of fabrics and seats. Thena mathematical model of the thermal sensation and thermal

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Fig. 1 – Sensor prototype. The polyethylene film keep the humidthe heated surface. The polipan avoids the side thermal losses

Fig. 2 Water vapour and thermal resistance of the three tests

Fig.3 Water vapour and thermal resistance of the three differentseats. The values are the mean and the standard deviation of th-ree tests.

376

0

50100150200250

300350400

Blank Fabric Nylon film

Rc (Km2/kW)

Re (Pam2/W)

91.5–1.6497.6–0.87

90.5–0.39

45–1.239.2–1.87

36.2–1.2

0.0

20.0

40.0

60.0

80.0

100.0

B class car seat (fabric) E class car seat (velvet) E in alcantaraE class car seat(alcantara)

Rc (Km2/kW)

Re (Pam2/W)

regulation of the human body will be released and in paral-lel an hybrid system to qualify an environment in terms ofthermal sensation will be produced. Finally a feasibility studyfor a micro-system able to simulate the thermo-regulationprocess of the human skin will be carried out.

References

[1] ASHRAE, 1993, “Physiological Principles and Ther-mal Comfort”. In Handbook of Fundamentals,(ASHRAE, Atlanta), 8.1-8.29.

[2] Nishi, Y., R. R. Gonzalez and A. P. Gagge, “Direct Mea-surement of Clothing Heat Transfer Properties DuringSensible and Insensible Heat Exchange with ThermalEnvironment”, ASHRAE TRANSACTIONS, Vol 81(2), 183 - 199, 1975.

[3] J. Temming Volkswagen AG, “A New Method to As-sess the Summer Suitability of Car Seats”, SAE paper930106.

[4] B. Kurz, “Measuring Thermal Aspects of Seating”, Seat-ing Workshop, IESC 1996.

[5] S.-E. Hänel, T. Dartman, R. Shishoo, “Measuring Meth-ods for Comfort Rating of Seats and Beds”, Interna-tional Journal of Industrial Ergonomics 1997.

[6] K:H: Umbach “Physiological Aspects of Seat Comfort”.[7] ASHRAE, 1993, “Mass Transfer”. In Handbook of Fun-

damentals, (ASHRAE, Atlanta), 5.1-5.16.[8] ASHRAE Standard 55 - 1981 “Thermal Environmen-

tal Conditions for Human Occupancy”. [9] G. Alfano, F.R. d’Ambrosio e F. de’Rossi, “Fondamen-

ti di Benessere Termoigrometrico”, CUEN 1987.[10] INTERNATIONAL STANDARD ISO 11092 1993

“Textiles-Physiological effects-Measurement of thermaland water-vapour resistance under steady-state condi-tions (sweating guarded-hotplate test)”.

[11] INTERNATIONAL STANDARD ISO 7730 1984“Moderate thermal environments - Determination ofthe PMV and PPD indices and specification of the con-ditions for thermal comfort”.

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Project title:Microsensors for the detection of thermo-hygrometric and vibrational comfort conditions

Participants: Centro Ricerche Fiat Strada Torino 50, 10043 Orbassano Unit responsible: Carloandrea Malvicino (Project Coord.)Tel.: 011/9083260 Fax 011/9083672 Collaborators: Maurizio Cisternino, Andrea Zussinoemail: d.malvicino@crf.it

UniRoma Tor Vergata Unit responsible: Massimiliano PetternellaDip. Ing. Elettronica Collaborators: Paolo Coppa, Marco TibertiVia di Tor Vergata 00133 Roma Tel.: 06/72597411 Fax: 06/72597410 email: petternella@eln.uniroma2.it

Purpose of the work

The growing technology of silicon-based photonic mi-crosystems requires the development of new classes of pla-nar micro-optical devices suitable for integration with stan-dard microelectronic circuitry.

The purpose of this project is the design of an all-siliconoptical temperature microsensor whose fabrication involvestechnological steps common to a VLSI chip fabrication se-quence. The device consists of a Fabry-Perot cavity whichexperiences a temperature induced frequency shift of itstransmittivity spectrum. Due to the strong thermo-optic ef-fect and thermal conductivity of silicon, and taking advan-tage of the high sensitivity typical of interferometric mea-surement technique, the sensor is predicted to perform highresolution and fast response.

The design of such a device on a silicon chip prelimi-nary requires the knowledge of the fundamental parameterdetermining its operation, namely the thermo-optic coeffi-cient of silicon. In particular, the few data available in theliterature on this important parameter are widely spread,usually not centered in the region of transparency of silicon,especially at those infrared wavelengths where there is plen-ty of solid state laser sources, as at 1.3 and 1.55 µm. There-fore, after presenting the working principle of the proposedtemperature sensor, in the following we describe our recentresults in the characterisation of the thermo-optic effect insilicon in the temperature range of interest for us, namelyfrom room temperature to 550 °K.

Outline of the work

Silicon is a key material for the sensor’s industry. Besidethe degree of development reached by its technology, thereason of this success lays in its fundamental properties,among which photoconductivity, piezoresistivity, magne-toresistivity and thermoelectric effect; all of them have beenwidely used for realizing sensors. In recent times, however,the thermo-optic effect (TOE), which consists in the varia-tion of the complex refractive index of a material inducedby temperature changes, has received increasing attention

in silicon as well as in other materials. Crystalline silicon (c-Si), with its ∂n/∂T= 1.86⋅10-4 K-1 at λ=1.5 µm, possesses avery high thermo-optic coefficient compared to the mostcommonly used semiconductors and optical materials, suchas LiNbO3 (5.3◊10-5, relative to the extraordinary refractiveindex), Soda-Lime glass (1÷1.5⋅10-5), and fiber-grade silica(1.26⋅10-5). This fact has suggested the present applicationsof silicon for temperature sensing. In particular The prin-ciple of operation of a Fabry-Perot temperature sensor is thefollowing: if a monochromatic light beam impinges on thefront mirror of the cavity with an intensity Io , the intensi-ty of the light transmitted through the back mirror is givenby the Airy’s formula:

In this formula φ is a phase factor related to the length lof the cavity, the wavelength λ of the radiation, the internalrefraction angle θ to the front mirror, and finally to the re-fractive index n of the medium, by: φ=(2πn/cosθ)/λ; a is aneffective absorption coefficient taking into account the intra-cavity optical losses, and R is the reflectance of the mirrors

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All-silicon temperature microsensor with fiber optic communication channel

CNR-IRECE

(1)

Fig. 1 Experimental fringe pattern generated by a 2-mm-longsilicon Fabry-Perot interferometer.

forming the cavity. Finally, FR is called reflecting finesse andis given by: Fr=π√R/(1-R). Due to the TOE, any variationin the temperature of the medium will cause an alterationof its refractive index and consequently a shift in the valueof φ, which will in turn induce an amplitude modulation ofthe transmitted light. For ∆φ exceeding π, the intensity ofthe transmitted radiation, collected for instance by a pho-todiode, will exhibit a periodical pattern (fringe pattern inFig. 1) and maxima and minima in It will be observed forφ=mπ respectively φ=(m+1/2)π, with m integer. Referringto Fig. 1, the linear region between a maximum and a min-imum of It, which corresponds to almost 40% of the dy-namic of the curves shown, can be exploited to deduce theabsolute temperature value; alternatively the full dynamiccan be used if an appropriate calibration curve is provided.

As an alternative approach one could make use of a muchlonger interferometer, which will show many more fringesin the same ∆Τ range. In such a scheme the temperaturevariation is measured simply by counting the fringes. In thiscase the optical losses introduced by an undesired fiber bentwould now only produce a variation of the amplitude of thetransmitted signal, but not of the phase. Of course, due tothe periodicity of the monitored signal, this fringe-count-ing scheme only allows the measurement of the modulus ofthe temperature variation. A mean to overcome this seriouslimitation consists in the realization, on the same chip, ofan array of interferometers of different lengths. Dependingon the expected temperature range and the desired resolu-tion, a proper couple of cavities can be selected and moni-tored at the same time. In this way, in fact, the modulus of∆Τ is measured by counting the fringes produced by thelonger sensor, while the information on its sign is derivedby monitoring the output of the shorter one, chosen so thatfor it the maximum ∆φ produced within the temperaturerange of interest is less than π/2, the phase distance betweena transmission maximum and a minimum.

In either of the proposed temperature measurementschemes, however, the precise knowledge of the thermo-op-tic coefficient is essential. In spite of its importance, poordata is available to date, especially at the two important in-frared wavelengths of 1.3 and 1.55 µm. For this reason webelieved necessary a preliminary careful characterisation ofthis effect in silicon.

Many different techniques have been used in the past tomeasure ∂n/∂T, most of which require the fabrication of adhoc samples, like those based on prism-shaped specimens[1,2], or on diffraction grating based photonic devices [3,4].However, the complexity of these techniques has in fact pre-vented the acquisition of data on a real large scale.

A much simpler technique, applied to a bulk crystal sil-icon sample, was recently introduced by our group to mea-sure ∂n/∂T at a given temperature [5], and is adopted in thiswork, extending the data acquisition in a wide temperaturerange. The technique is direct, and is based on the measureof the temperature variation necessary to cause a completeoptical detuning of a Fabry-Perot filter. The test structure isa one-dimension device, actually an étalon, obtained by op-tical polishing both sides of a chip made of the material un-

der test. The experimental setup we used for our measure-ments is sketched in Fig.2. In brief, the monochromaticbeam at λ=1.523 µm, produced by a 1 mW HeNe laser, islaunched across the Fabry-Perot étalon made of silicon, nor-mally to the two parallel planes defining it, and the trans-mitted radiation is collected by an InGaAs photodiode, whichconverts it into an electrical signal. The sample is containedin a windowed oven, whose temperature can be controlledwith a precision of 0.1°C. The sample temperature is mea-sured by monitoring the resistance of a thin film Pt100 cal-ibrated thermistor glued on it. As already discussed, the trans-mitted light intensity It has a periodic dependence on tem-perature described by Eq. 1, caused by the variation of boththe refractive index n and the cavity length l, the latter dueto thermal expansion. Therefore f has in fact a double tem-perature dependence, which can be synthetized in the dif-ferential equation:

where the term α=∂l (l∂T) is the thermal expansion coeffi-cient. By measuring the distance in temperature betweentwo transmission peeks, DTπ, corresponding to a phase shift∆φ=π, the value of ∂n/∂T can be obtained from Eq. 2 [6].It should be noted that, provided a modulation pattern isstill distinguishable in the noise, the extraction of the ther-mo-optic coefficient can be performed independently of themodulation depth of the periodic pattern, and therefore al-so in cavities affected by poor internal interference due tolow mirror reflectivity or made of materials showing highoptical absorption.

Main results

Measurements were carried out on c-Si samples with dif-ferent crystal plane orientations and thicknesses. In partic-ular the samples were taken from several <111>, <100> or<110> wafers, with resistivities in the range of 10 to 100Ω⋅cm, indifferently P-type or N-type. The wafers were pre-viously lapped for thinning and then polished on both sides

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Fig. 2 Experimental set-up used for the measurement of thethermo-optic coefficient in Si from R.T. to 550 K.

(2)

to an optical degree with a colloidal silica polishing suspen-sion. The samples, usually 4×3 mm2 sized, were obtainedby wafer cleaving. Their measured final thicknesses were 97µm and 2000 µm for the <100> samples (N-type), 375 mmfor the <110> samples (P-type), and 495 µm for the <111>samples (N-type). The uncertainty in the measurement ofthe sample thickness was 3 µm.

Each sample underwent several temperature excursions,during which the transmitted light intensity was tracked bya computer controlled data acquisition setup. The maximumtemperature step between acquisitions was 0.2°C, depend-ing on the sample thickness, and then on the fringe patternperiod ∆Τp.

The values of ∂n/∂T, obtained from the previously de-scribed calculations, are plotted in Fig. 3 from room tem-perature to 550 °K, distinguished for sample type. We esti-mate that the reported data can be affected by a 8% errordue to uncertainties in the sample thickness, experimentalsetup alignment procedure, and in the actual sample tem-perature at each measurement step. It is worthwhile notingthat, given this experimental error, no difference seems tohold for ∂n/∂T among the considered sample types.

The polynomial interpolation of the data gives a weakquadratic dependence of ∂n/∂T from T (in K), described bythe polynomial fit:

The ∂n/∂T relation of Eq. 3, can be used to extract thetemperature dependence of the excitonic band gap Eeg of sil-icon. In the model described by Ghosh [7] in fact, the ther-mo-optic effect is attributed to a thermal expansion compo-nent and to a variation of Eeg. This relation is expressed as:

where α is again the thermal expansion coefficient, andR=λ2/(λ2-λ ig

2), with λ ig=0.333 µm, the wavelength corre-sponding to the isentropic band gap.

By assuming α constant in the given temperature range,and ∂n/∂T as Eq. 3, Eq. 4 can be integrated to give:

Eeg(T)=A×exp[p(T)] [eV], with A=3.47 and:

Factor A has been calculated by assuming Eeg=3.38 eVat T=300 K. At the same temperature we find dEeg/dT= -3.91×10-4 eV⋅K-1.

Future developments

The knowledge of the refractive index and its tempera-ture dependence in silicon has recently allowed to start thestudy of the guided wave propagation in planar structuresmade on a chip [8]. These structures are necessary for thedesign of a planar Fabry-Perot interferometer to be realisedwith the standard microelectronic processes. Although thisstudy is still at a preliminary stage, first results indicate thatthe design of all-silicon, single-mode waveguides with prop-agation losses lower than 4 db/cm is possible.

On the technological side, in order to improve the verticalconfinement of the radiation, necessary to reduce the propaga-tion losses, it is planned to recur to ion implantation for the for-mation of the heavily doped silicon undercladding, while thecore of the waveguide will be made of undoped epitaxial silicon.

In order to allow the highest the compatibility with sub-sequent planar processes, the basic waveguide is expected tobe of the rib type, and therefore it will require only a shal-low etching (<0.5 µm) of the epitaxial layer.

Expected deliverables

The already started propagation modeling efforts willlead to the definition of optimal design criteria for all-Siwaveguides to be realised on a silicon chip with technolo-gies common to the VLSI industry. Details of the techno-logical steps required for the fabrication of such waveguideswill be described.

Moreover, the experimental set-up used for the charac-terisation of the thermo-optic effect in silicon will allow tocontribute to the few available data in the literature on thesame effect in other common optoelectronic semiconduc-tors, like GaAs and InP.

References

[1]M. Bertolotti, V. Bogdanov, A. Ferrari, A. Jascow, N.Nazarova, A. Pikhtin, L. Schirone, J. Opt. Soc. Am. B 7,918 (1990)

[2] S. Walder, K. Razi Naqvi, Opt. Phot. News 7, S1 (1996)[3] P. Martin, El M. Skouri, L. Chusseau, C. Alibert, H.

Bissessur, Appl. Phys. Lett. 67, 881 (1995)[4] E. Gini, H. Melchior, J. Appl. Phys. 79, 4335 (1996)

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Fig. 3 Mesured thermo-optic coefficient in various Si samples.

(3)

(4)

TTTTp ??−??−??= −−− 5273111027.61001.11090.2)( (5)•• • •• •

[5] G. Cocorullo, I. Rendina, El. Lett., 28, 83 (1992)[6] G. Cocorullo, F.G. Della Corte, I. Rendina, Appl. Phys.

Lett.74, 3338 (1999)

[7] G. Ghosh, Appl. Phys. Lett. 66, 3570 (1995)[8] G. Cocorullo, F. G. Della Corte, M. Iodice, I. Rendina, P. M.

Sarro, J. Sel. Topics in Quantum Electronics, 4, 983 (1998)

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Project title: All-silicon temperature microsensor with fiber optic communication channel

Istituto di Ricerca per l’Elettromagnetismo Unit responsible: Francesco G. Della Corte (Project Coord.)ed i Componenti Elettronici Collaborators: Giuseppe Cocorullo,Via Diocleziano 328, 80124 Napoli Mario Iodice, Maurizio Indolfi, Ivo RendinaTel.: 081 5707999 - fax: 081 5705734Email: dellacor@irece1.irece.na.cnr.it

1. Purpose of the work

Recently, a large interest has arisen on rotation sensorsfor robotics, for the automotive field, and for the consumermarket. Though high performance mechanical and elec-trooptical gyroscopes are available, which are suitable for in-ertial navigation and other critical applications, they are toobig and expensive for the new market.

For this reason, alternative approaches have been considered.Presently, the most promising technology, especially for the au-tomotive navigation, is silicon micromachining, which exploitsthe know-how and facilities typical of the microelectronics in-dustry to produce micromechanical systems in volumes.

The purpose of this research is the development of a low-cost micromachined gyro for automotive applications based onthe Coriolis force acting on a small silicon mass upon rotation.Expected performances are: dynamic range: +/- 100 °/s, zerodrift error: 0.01 °/s, linearity error: 1%, bandwidth: 100 Hz.

ST-Microelectronics has designed and built microma-chined structures, such as accelerometers, based on propri-etary technologies, which offer a basic set of simple but re-liable and reproducible elements. This technology representsa suitable starting point for the design of a low cost gyro.

2. Outline of the work

- Measurement of relevant mechanical constants of silicon.

- Definition of gyro structures suitable for the implementa-tion by surface micromachining.

- Optimization of design parameters.

- Theoretical signal and noise analysis of the sensor.

- Design and building of a suitable setup for the character-ization of the sensors.

- Production of gyro prototypes.

- Characterization of prototypes.

3. Main results

The typical geometry (layout) of the sensors which havebeen produced in the first year is reported in Fig.1. A pla-nar mass m (100x100x10µm) of 2.8µg, is suspended to anexternal frame by four laminar springs, and is forced to vi-brate along the x-axis by applying a sinusoidal driving volt-age (10-20 KHz, maximum speed v ) to a suitable combstructure. When the gyro is still, the mass does not movealong the y-axis; however, when the gyro rotates at angularspeed Ω around an axis perpendicular to the mass, the aris-ing Coriolis force: Fc=-2m v Ω couples the vibration fromthe x-axis to the y-axis.

The vibration amplitude along the y-axis is also pro-portional to the rotation speed, and it is capacitively detectedby using another comb structure (Cdrive = Csensor = 0.4pF),which is designed to give a differential output signal, for abetter S/N ratio.

The technology steps used to build the integrated gy-roscope are shown in fig.2.

On a standard silicon substrate, islands of silicon dioxideare formed and covered with polysilicon layer which acts as a

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Micromachined silicon gyroscope

ST-Microelectronics, Universita’ di Pavia

x

y

springsensingcomb

massdrivingcomb

case

Fig. 1 Gyro geometry

nucleation seed during the following epitaxial growth. A stan-dard epilayer growth will then form epi - poly (10µm) on theseed and single crystal where the substrate is bare (fig.2a).

The growths were carried out in a single - wafer epitax-ial reactor (ASM Epsilon One) using trichlorosilane (TCS)gas at T = 1190°C (growth rate = 3.5µm/min.)

After this epitaxial growth the process continues with thestandard integrate circuit steps until the final passivation in-cluded. At this point deep trenches are performed (fig.2b)allowing the release of the micromechanical structures (ac-celerometers and gyroscopes) by a wet removal of the buriedoxide (fig.2c)

This specific process flows have been set with the pur-pose to overcome the disadvantages of surface and bulk mi-cromachining and to obtain on the same silicon chip thesensor and the electronic integrated circuit for the signaltreatment and the appropriate electrical output interface forthe actuator.

In with fact in respect to conventional surface micro-machining, where structures present some drawbacks causedby the limited thickness of the constructional layer (2µm),these epipoly microelectromechanical devices are counter-sunk in the epitaxial layer, yielding a highly planar structure,and are rather stiff in the vertical direction due to their largeepipoly thickness (10µm). This lowers the probability of stic-tion of these devices to the underlying substrate.

Two different ap-proaches have beenused to characterizethe gyroscopes.

Basic electricalmeasurements havebeen made by detect-ing the capacitancevariation of the outputcomb by using a ca-pacitive voltage dividerscheme. More sophis-ticated electrical mea-surements, by using asupplementary signalas a carrier, have been

also used. These methods have allowed to find the structuremechanical resonances along both the x- and the y-axis. Ithas been found that the quality factor of both resonancesare strongly influenced by pressure, and we have concludedthat a vacuum level of at least 0.1 mbar will be required inthe package for correct operation. In addition to electricalmeasurements, an alternative optical method has been alsodeveloped, which provides an independent, non-invasivemeans to detect the mass movement. This approach is basedon feedback inteferometry, and is shown in Fig.3 . Here, theoutput beam of a semiconductor laser is focussed on the sen-sor mass. The light scattered back into the laser by the masssurface perturbates the laser oscillation. By analizing the laserradiation at the second mirror, it has been possible to accu-rately determine the mass movement [1,2].

Differently from traditional interferometric schemes,which require a flat optical surface on the target, feedbackinterferometry works well even on a holed rough surface asthe gyro mass. Thus, the setup of Fig.3 represents an effec-tive alternative to the electrical methods, which are some-what critical, due to parasitic capacitances which often re-sult in spurious resonances.

In Fig.4, we show typical resonance curves for differentvalues of the driving voltage at atmosferic pressure. Hys-teresis due to nonlinear effects is evident in the higher curve.

A theoretical analysis of mechanical thermal noise in thegyro structure has also been developed [3]. This noise source,which is not present in electronic devices, arises from theminute vibrations of the small mechanical elements of thesensor at non - zero temperature.

4. Future developments

- Improving the gyrosope design, after the results of the char-acterization of the first samples. New samples will includeprovisions to reduce parasitic capacitances and spurius me-chanical oscillations mode.

- Design of the processing and control electronic circuitryto be implemented on the same or on a different chip.

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PD1

Lens

OpticalSpectrumAnalyser

Laser

PD2

Gyroscope

Vacuumchamber

DigitalOscilloscope

Amplif.

α

Fig.2 EpitaxialMicromachining

Fig.3 Optical measurement setup

Fig. 4 Typical sensor resonance curve.

- Make up of the precision rotating table (presently underconstruction) for the gyro characterization.

- More detailed investigation of the noise limit of the struc-ture. The practical sensor sensitivity is expected to dependon the combination of the electronic noise and of the me-chanical-thermal noise.

5. Expected deliverables

-Gyro design know-how.-Gyro characterization know-how.-Gyro prototypes suitable for automotive applications.-Gyro characterization setup.-Patents.

6. References

[1] V. Annovazzi-Lodi, S. Merlo, M. Norgia: “Interfero-metric Characterization of a Micromachined Gyroscope”,Proceedings of ‘ODIMAP II Optoelectronic Distance/Dis-placement Measurement and Applications’, Pavia, 20-22mag. 1999, pp. 307-312.[2] V. Annovazzi Lodi, S. Merlo, M. Norgia: “ Measure-

ments on a Micromachined Silicon Gyroscope by Feed-back Interferometry”, submitted to IEEE Transactionson Mechatronics.

[3] V. Annovazzi Lodi, S. Merlo: “ Mechanical ThermalNoise in Micromachined Gyros “, to be published onMicroelectronics Journal.

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Project title: Micromachined silicon gyroscope.

Participants:

ST-Microelectronics S.r.l. Unit responsible: Flavio Villa - TPA groups (Project Coord.)Via Tolomeo 1, 20010 Cornaredo - Mi Collaborators: Roberto Civeriati, Massimiliano De Pisapia,Tel. 02-93519395 , Fax: 02-93519355 Paolo Ferrari, Marco Ferrera, Email: flavio.villa@st.com Benedetto Vigna, Sarah Zerbini.

Universita' di Pavia. Unit responsible: Valerio Annovazzi-Lodi,Via Ferrata 1, 27100 Pavia Facolta' di Ingegneria, Dipartimento di Elettronica.Tel.: 0382/505200 Fax:0382 422583 Collaborators: Silvano Donati, Sabina Merlo,Email: v.annovazzi@ele.unipv.it M. Norgia, G. Giuliani, A. Scire', A. Fanzio.

Purpose of the work

The general goal of the research is the design of a loadcell with digital electronics on board for automatic auto-tuning, for correction of all the measurement errors and witha digital output in order to increase the class of precision ofthe cell and decrease the cost of production. The precisionshould pass from the actual 1/3.000-1/4.000 (classes C3-C4) to 1/10.000 (class C10) in the range of temperature [-10, +40] °C.

Outline of the work

Nowadays, the load cells are largely used for industrialmeasurement of masses and forces. They are analogic, usu-ally realised with strain-gauges bride-connected, and theirstypical precision class is 1/3.000-1/4.000 (classes C3-C4).The errors which affect the analogic output of the load cellsare: nonlinearity, hysteresis, creep, zero drift, temperaturedependence, etc. Nowadays, only the nonlinearity and thezero drift errors are corrected. The correction is done byhand adding passive elements (i.e. resistences, thermo-re-sistences, etc.) to the electric circuit of the load cell.

The introduction of a digital electronics on board of theload cells would allow the “digital” correction of all theseerrors (by means of proper correction algorithms), wouldlargely improve the precision of the cell and would decreasethe production costs. The outline of the work is the fol-lowing: 1) Study of the physical system, that is, the active element

and bridge-connected strain-gauges;2) Obtain algorithms suitable for describing the physical sys-

tem for different types of load cells;3) Identification of the simplest and most robust models to

be used for the compensation of all the measurement er-rors (nonlinearity, hysteresis, creep, dependence from thetemperature, etc.);

4) Design and realisation of an electronic breadboard whichimplements the correction algorithms characterised bythe minimum number and minimum complexity of theelectronic components;

5) Validation in field of the obtained improvements with re-spect to the traditional cells. The goal is to increase the precision of the load cell of at

least a factor 3 with the same realisation costs.The final goal will be validated by the realisation of a

demonstrator. The fact that this proposal is done jointlywith the Soc. Coop. Balanciai Campogalliano guaranteesthat the results of the research will be directly transferredon the product.

Main results

The physical system is composed by the active elementand the bridge-connected strain-gauges. The study of thissystem has shown the presence of the following non linearphenomena: 1. Nonlinearity: this phenomenon is shown in Fig.1 for a

column load cell (code P96043) at the temperature of 22°C. On the same figure it also reported the admissible re-gion corresponding to the desired precision C10.

2. Hysteresis: this phenomenon is shown in Fig.2 for a cutload cell at the temperature of 21.9 °C. The main causefor the hysteresis is the presence of nonlinear friction inthe mechanical and electrical parts of the system.

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Algorithms and digital electronicsfor high precision load cells

Soc. Coop. Bilanciai, Università di Modena e Reggio Emilia

Fig.1 Nonlinearity phenomenon

3. Creep: this phenomenon is shown in Fig.3 for a cut loadcell when the input is constant at the maximum load(10.000 N).

4. Output voltage at zero load. This voltage is a specific char-acteristic of each load cell and it mainly depends on howthe strain gauges has been glued on the mechanical support.

5. Dependence from the temperature. All the main parame-ters of the load cell are functions of the temperature. Forexample, in Fig. 4 it is shown how the dependence from thetemperature of the linear gain in the range [–10 to 40 ∞C].

From the analysis of the measured data it came out that thedesired precision (class C10) can be obtained only if all thesenon linear phenomena are properly compensated. For thispurpose, a digital correction algorithm has been designed.Within the algorithm the previous undesired phenomenahave been modelled as follows:

1. The nonlinearities have been modelled with a static thirdorder polynomial with coefficients which are functionsof the temperature.

2. The hysteresis has been modelled with a second order nonlinear discrete dynamic system. The amplitude of the hys-teresis has been made a function of the temperature;

3. The creep has been modelled with a first order linear dy-namic system;

4. The output voltage at zero load has been modelled withstatic third order polynomial with coefficients which arefunctions of the temperature. For each load cell the following measures are available:

a) three load-unload cycles at the maximum load and at thetemperature T=20 °C; b) the output voltages at zero loadat the temperatures T=-10 °C, T=20 °C and T=40 °C. Onthe basis of these data it is possible to identify the main partof the model coefficients of the undesired phenomena. Theremaining coefficients are identified on the basis of statis-tical information coming from specific measures obtainedfrom a small group of load cells.

The basic structure of the algorithm which corrects thenon linearities, the output voltage at zero load, the hysteresisand the dependence from the temperature is the following:

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Fig.2 Hysteresis phenomenon Fig.4 Dependence from the temperature

Fig.3 Creep phenomenon

Fig. 5 Corrected characteristics obtained for a column loadcell at different temperatures

The results obtained “off-line” with this type of cor-rection algorithm are encouraging. In Fig. 5 as shown, forexample, the results obtained for a column load cell at dif-ferent temperatures. How it can be seen from the figure,the corrected characteristics are almost all “within” theadmissible region corresponding to the desired precisionC10.

The correction algorithm is still under development es-pecially for the modelling and the correction of the creepphenomenon.

Future developments

Design and realisation of an electronic breadboard whichimplements the correction algorithms characterised by theminimum number and minimum complexity of the elec-tronic components; Validation in field of the obtained im-provements with respect to the traditional cells.

Expected Deliverables

a) Scientific results: identification of simple and robust mod-els to be used for the compensation of measurement er-

rors such as nonlinearity, hysteresis, creep, dependencefrom the temperature, etc.

b) Deliverable items (technical products, prototypes, patents,etc.): the final goal is the realisation of a demonstrator,composed by a load cell and a digital electronic bread-board, which is able to compensate all the measurementerrors and improve the precision of the load cell up to1/10.000.

References

[1] R.Zanasi, “Sliding Mode Using Discontinuous ControlAlgorithms of Integral Type”, Int. Journal of Control,Special Issue on Sliding Mode Control, V. I. Utkin, GuestEd., vol.57, no.5, pp.1079-1099, 1993.

[2] F. Magistrali, C. Tedesco, E. Zanoni, C. Canali: “Relia-bility issues of discrete FETs and HEMTs” Chapt. 5, pp.101-189 in “Reliability of Gallium Arsenide MMICs”,A. Christou Ed., J. Wiley & Sons, 1992

[3] P.Cremonesi, M.Pugassi, N.Scarabottolo: Motion De-tection on Distributed-Memory Machines: a Case Study,Proceedings of the 1st IEEE International Conference onAlgorithms And Architectures for Parallel Processing:ICA3PP95, pp.404-413, Brisbane, Australia, aprile 1995.

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Project title: Algorithms and digital electronics for high precision load cells

Participants:

Soc. Coop. Bilanciai Campogalliano a r.l. Unit responsible: Luciano Diacci (Project Coord).Via S. Ferrari 16, 41011 Campogalliano (MO) Collaborators: Luciano Secchi, Stefano Tel.: 059 893611 Fax: 059 527079 Rinaldi, Franco Brighenti, Luca Massarenti,Email: cb@coopbilanciai.it Morena Casali, Germano Anderlini,

Massimo Zanetti.

Università di Modena e Reggio Emilia. Unit responsible: Roberto Zanasi.Dipartimento di Scienze dell’Ingegneria, Collaborators: Claudio Canali, Nello Via Vivaldi 70, Scarabottolo, Roberto Fromentini.41100 Modena;Tel.: 059 374057 Fax. 059 364132Email: roberto.zanasi@unimo.it

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