m icrofluidic s cintillation d etectors 25.06.2015 // pietro maoddi dt seminar: microfluidic...

DT Seminar: Microfluidic Scintillation Detectors 1

MICROFLUIDIC SCINTILLATION DETECTORS

25.06.2015 // Pietro Maoddi

Pietro Maoddi

Detector Technologies group, CERNMicrosystems Laboratory 4, EPFL

June 25th 2015


OUTLINE

Introduction

Main results

Conclusions


• Scintillation detectors

• Project goals

• Intro to microfabrication

• Conclusions

• Outlook

• Detectors based on SU-8

• Detectors based on Silicon

• Radiation damage studies


SCINTILLATION DETECTORS

• Scintillator + Photodetector = Scintillation detector


Photodetector

Electrical signal

Particle

Scintillator

Light

1

23

4

5

6

x

How to track the particle position?

Segment the detection volume

The particle passed in position x=4


FIBRE DETECTORS

• Principle


Scintillatingcore (n1)Cladding(n2 < n1)

Photons emitted above critical angle are guided

Air (n = 1)

Water (n = 1.33)


FIBRE DETECTORS

• Principle

• Example: LHCb SciFi• Large active area• ~36 µm RMS spatial resolution• ~2 p.e. per MIP per fibre




2 ×

2.5

m

2 × 3 m

Module section:5 layers of Ø250 µm fibres

Pictures: C. Joram, “LHCb SciFi, the new Fibre Tracker for LHCb”, ECFA High Luminosity LHC ExperimentsWorkshop. Aix-Les-Bains, France, 2014. url: http://goo.gl/xF8sL6

xu v

http://goo.gl/xF8sL6


FIBRE DETECTORS

• Principle

• Example: LHCb SciFi• Large active area• ~36 µm RMS spatial resolution• ~2 p.e. per MIP per fibre• Defects may appear in fabrication• Fibres need to be replaced

upon damage25.06.2015 // Pietro Maoddi



2 ×

2.5

m

2 × 3 m

Module section:5 layers of Ø250 µm fibres

Pictures: C. Joram, “LHCb SciFi, the new Fibre Tracker for LHCb”, ECFA High Luminosity LHC ExperimentsWorkshop. Aix-Les-Bains, France, 2014. url: http://goo.gl/xF8sL6

http://goo.gl/xF8sL6


CAPILLARY DETECTORS

• CERN RD46 collaboration (1990s)• Glass capillaries filled with liquid scintillator “Liquid core” scintillating fibres


Pictures: RD46 Status Report, CERN/LHCC 97-38, 1997

nglass ~ 1.49nliquid ~ 1.62


CAPILLARY DETECTORS

• CERN RD46 collaboration (1990s)• Glass capillaries filled with liquid scintillator“Liquid core” scintillating fibres

• Defects may appear in fabrication• Complex filling system


Pictures: RD46 Status Report, CERN/LHCC 97-38, 1997

nglass ~ 1.49nliquid ~ 1.62




• Microfluidic channel filled with liquid scintillator defining an array of waveguides• Photodetector pixel coupled to each channel end• Scintillation light guided along microchannel and detected

Photodetector array

Microchannel

Scintillation

particle(e-, p+, n, γ, …)

electrical signal




DAQ syste

m

Photo: J. Daguin

20 mm

15 mm

First MSD prototype (A. Mapelli)• Microchannels made by SU-8

photolithography filled with liquid scintillator

• Gold reflective coating

𝑁 𝑝𝑒=1.6(200 µm deep channel)

MAPMT

A. Mapelli PhD thesisScintillation Particle Detectors Based on Plastic Optical Fibres and Microfluidics, 2011



Main advantages of MSDs• Radiation resistance• Liquid scintillator intrinsically radiation resistant…• …and recirculation (substitution) easily possible

• Dimensional control• Precise/reproducible geometries wrt traditional assembly higher

resolution• Very thin detectors, minimal material budget new applications



HADRON THERAPY

• Cancer treatment using particle beams(protons, heavy ions, neutrons, pions, …)

• More selective than radiotherapy Less damage to healthy tissues

• 39 facilities worldwide~100’000 patients treated as of 2012Most facilities in US and JapanMany new centers in Europe, e.g. HIT (Germany), CNAO (Italy), ETOILE (France)


Radiotherapy Hadrontherapy


ON-LINE BEAM MONITORING

Microfluidic detectors• Thin, very «light» devices• Excellent radiation hardness


Extremely thinmicrofluidic detector

Real-time monitoring of the beamduring patient irradiation possible• Safer treatment• Optimized beam time use• Cost reductionBeam line end

A. Mapelli, P. Maoddi, P. Renaud, WIPO Patent 2013167151 A1, 2013

Project funded for 1/3 by CERN’s Knowledge Transfer office for this application


DOUBLE LAYER MSDS

• 1 microchannel layer 1D spatial resolution• 2 microchannel layers 2D spatial resolution

• Analogous to scintillating fiber detectors• Needed in many applications

• Keeps advantages of single layer MSD(… but fabrication more complex)


A. Mapelli, P. Maoddi, P. Renaud, WIPO Patent 2013167151 A1, 2013


DESIGN CONSIDERATIONS

• Materials environmental requirements• High radiation levels radiation resistance• Liquid scintillators chemical compatibility• High vacuum (in some applications) mechanical resistance

• Materials technological requirements• Compatibility with microfabrication techniques• Optical quality: refractive index, reflectivity, transparency, smoothness…

• Dimensions• Thinness vs. light yield trade-off• Area: control of micropatterning over relatively large areas (several cm2)



MICROFABRICATION

• Fabrication performed at EPFL Micro and Nano Technology (CMi)

• Class 100 cleanroom(Maximum 100 particles of size 0.5 µm or larger permitted per cubic foot of air)

• Standard working substrate:silicon wafersØ100 mm, 0.5 mm thick



MICROFABRICATION

Additive approach Subtractive approach



OUTLINE

Introduction

Main results

Conclusions


• Conclusions

• Outlook





• Project goals



SU-8 FOR MSDS

• Radiation resistant• Compatible with liquid

scintillators• Mechanically resistant

• Relatively “light” (X0~350 mm)• Optically smooth and

transparent(but high refractive index n~1.6)• Used in other detector

technologies25.06.2015 // Pietro Maoddi

Pictures from P. Maoddi, A. Mapelli, S. Jiguet and P. Renaud. SU-8 as a Material for Microfabricated Particle Physics Detectors, Micromachines, vol. 5, num. 3, p. 594-606, 2014


SINGLE LAYER SU-8 DEVICES

• SU-8 lithography over a sacrificial layer on 2 wafers• Mylar film• Aluminum layer*

• Bonding of the devices• SU-8/SU-8 bonding

• Release of the devices• Mechanical• Wet etching• Anodic dissolution*


«Bottom» wafer «Top» wafer

Deposition of a sacrificial layer Deposition of a sacrificial layerPatterning of SU-8 device bottom Patterning of SU-8 device topPatterning of SU-8 microchannelsWafer bondingSacrificial layer removal

Free-standing thin SU-8 device

110 µm total thickness(30 + 50 + 30)

200 µm

* Preferred process

¿0.03% 𝑋 0


SINGLE LAYER SU-8 DEVICES

• SU-8 lithography over a sacrificial layer on 2 wafers• Mylar film• Aluminum layer*

• Bonding of the devices• SU-8/SU-8 bonding

• Release of the devices• Mechanical• Wet etching• Anodic dissolution*


Free-standing thin SU-8 device

110 µm total thickness(30 + 50 + 30)

200 µm

* Preferred process

¿0.03% 𝑋 0

Al-coated Mylar (clamped)

Silicon

Previous device:

For comparison:one CMS tracker layer,Si only:


DOUBLE LAYER SU-8 DEVICES

• Extension to two microchannel layers• Cr and Al sacrificial films• Selective dissolution (HCl, KOH)• Bonding optimization


Pictures: P. Maoddi, A. Mapelli, S. Jiguet and P. Renaud. SU-8 as a Material for Microfabricated Particle Physics Detectors, Micromachines, vol. 5, num. 3, p. 594-606, 2014

𝑡=200 µm(¿0.06% 𝑋 0)


CHALLENGES IN SU-8 MSDS

• SU-8 R.I. higher than that of commercial LS optical coating needed

• Alternative solution: high R.I. liquid scintillator


Internal coating by injection of low R.I polymer (e.g. Teflon AF n=1.3)Semester projects• Dara Haftgoli Bakhtiari• David McMeekin Results not suitable for optics (thickness < 5µm, low uniformity)

SU-8 (n=1.6) microchannels filledwith methylene diiodide (n=1.8)+ rhodamine 6G fluorescent dye Light spot Ø

~ 4 mm

Filled chip

Empty chip

Photodetector pixel numberTim

e-i

nte

gra

ted inte

nsi

ty (

a.u

.)

Proof of concept in collaboration with INFN Rome group:P. Bagiacchi, G. Gemignani, F. Safai Tehrani, S. Veneziano Photodiode array

5 µm

~ 200 nm

SU-8

Teflon AFcoating

Post-bondingoptical coating

Pre-bondingoptical coating

e.g. Al coating after µchannel patterning

No suitable method found for bonding


SU-8 MSDS: CONCLUSIONS

• Novel fabrication approach based on wafer bonding and selective release developed

• Both single and double layer thin devices made

• Experimental validation with high-n fluorescent liquid

• To do: integrate optical coating (or use high-n scintillator)



OUTLINE

Introduction

Main results

Conclusions


• Conclusions

• Outlook





• Project goals



SILICON AS A MATERIAL FOR MSDS

• Radiation resistant• Compatible with liquid scintillators• Mechanically and thermally resistant• Can be optically smooth

(but it’s not transparent)• Used in other detector technologies• Offers new integration possibilities

(photodetectors, electronics, …)• Many reliable processing techniques

available



DRY ETCHING AND SMOOTHING

• RF plasma reactor alternating SF6 (etching) and C4F8 (polymer coating) plasmas

• Vertical etching profile but resulting in «scalloping»

• Wet oxidation SiO2 has larger volume than Si surface features loss

• SiO2 removal with hydrofluoric acid smooth silicon


2 µm 5 µm


SI MSDS: FABRICATION BY DRY ETCHING

• Two level DRIE (µchannels + inlets)• Smoothing by thick wet oxidation• Optical coating (Al deposition)• Bonding and «packaging»


20 m

m

15 mm

Etching Smoothing

Al coatingPyrex w/ stripes

Bonding Dicing & packaging

(top view)

2 µm

5 µm


SI MSDS: FABRICATION BY WET ETCHING

• Double side wet etching 2 µchannel layers• Alignment to {100} silicon planes to obtain

vertical sidewalls


Oxide mask etch

Wet etching

Aluminum coating

Three wafer stack bonding

Dry etching (fluidic via)

… then dicing & packaging

90°

20 µm

Internship• L. Serex


SI MSDS: PHOTODETECTOR INTEGRATION

• Si process compatibility integration of photodiodes to µ-channels


Master projects• L. Batooli• E. Cuenot• C. Wiese• R. Moreddu (ongoing)Internship• L. SerexCollaborators• N. Wyrsch• M. Moridi• D. Bouvet

Picture: C. Wiese

• Experimental validation by detecting light from micromirrors with PMTs

• Integration of a-Si:H photodiodes still ongoing

planar integration:

PD

wire bond

PCB


SI MSDS: CHARACTERIZATION WITH SIPMS

• Silicon photomultipliers (SiPMs): new high gain photodetectors


Readout electronics development at INFN Rome• S. Veneziano, F. Safai Tehrani

et al.

Custom electronics and DAQ systemMaster project• M. Asiatici

• Sensitive to single photon (~50% PDE)

• Custom readout electronics and DAQ

Single photon peaks


CHARACTERIZATION WITH SIPMS


Measurements at CERN with:• C. Joram• E. Van Der

Kraji

𝑘𝑝

𝜎0√2𝜋exp(− (𝑥−𝜇0 )2

2𝜎02 )+ 𝑘𝜋 ∑

𝑖=1

∞ { 1

√2𝜋 (𝜎02+𝑖 ∙𝜎𝑀

2 )exp(− (𝑥− (𝜇0+𝑖 ∙𝐺 ))2

2 (𝜎02+𝑖 ∙𝜎𝑀

2 ) ) ∙∫0∞

exp(−𝑡 log 𝑡−𝐺 𝑖−𝑁 𝑝𝑒∗

𝜎∗ 𝑡)sin (𝜋𝑡 )𝑑𝑡}Landau distrubutionith photoelectron peakPedestal


CHARACTERIZATION WITH SIPMS


Average: MPV Attenuation length:

(700×190 µm2 microchannel cross section)


OUTLINE

Introduction

Main results

Conclusions


• Conclusions

• Outlook





• Project goals



INCREASED RADIATION RESISTANCE


• Device irradiation necessary to validate radiation resistance concept

• Heavy irradiation tests with protons possible, but complex (safety, logistics, …)

• Lab surrogate: UV irradiation• Indirect damage of the liquid scintillator in the microchannels by destruction of

the fluors

Master project• D. Brouzet

Base Fluor

UV photons / Forster transfer Blue photons

Ionising particles

Liquid scintillator

Damage by intense UV irradiation

(photobleaching)


INCREASED RADIATION RESISTANCE


Proof of concept of increased radiation resistance by scintillator recirculation

Experiment 1• Continuous UV irradiation• Periodic replacement of LS

Experiment 2• Continuous UV irradiation• Constant circulation of LS


SI MSDS: CONCLUSIONS

• Several fabrication approaches proposed

• Both single and double layer devices made

• Experimental characterizations with SiPMs (and PMTs)

• Principle of scintillator recirculation validated



OUTLINE

Introduction

Main results

Conclusions


• Conclusions

• Outlook





• Project goals



CONCLUSIONS

• Different technologies for the fabrication of MSDs explored

• Very thin and double layer devices

• Increased radiation resistance by scintillator recirculation

• New open development lines for the future• Wafer-level photodetector integration• Large devices operating by TIR microchannels in low R.I. material


SU-8

Single layer Double layer

Silicon

Dry etched Wet etchedDouble layer

With mirrors


THANK YOU


Acknowledgements: C. Bault, M. Capeans, A. Catinaccio, B. Gorini, M. Haguenauer, S. Jiguet, C. Joram, G. Lehmann Miotto, A. Mapelli, F. Perez Gomez, P. Petagna, P. Renaud, F. Safai Tehrani, S.Veneziano

CERN Contact:Alessandro Mapelli (PH-DT-EO)

CERN-THESIS-2015-078https://cds.cern.ch/record/2027620

https://cds.cern.ch/record/2027620

m icrofluidic s cintillation d etectors 25.06.2015 // pietro maoddi dt seminar: microfluidic...

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