This article was downloaded by: [Hanyang University]On: 13 August 2012, At: 01:35Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,UK

Integrated Ferroelectrics: AnInternational JournalPublication details, including instructions forauthors and subscription information:http://www.tandfonline.com/loi/ginf20

Electrical Properties of PZT-PCW Thick Film on Pt/Sic/Si,and Structural Stability of SiCKi-Yong Choi a b , Tae-Song Kim a , Duck-Kyun Choi a b

, Ji-Yeun Park c & Dae-Sung Yoon aa Microsystem Research Center, KIST, 39-1Haweolgog-dong, Seongbuk-gu, Seoul, 136-791,Koreab Department of Ceramic Eng., Hanyang University,17 Hangdang-Dong, Seongdong-Gu, Seoul, 133-791,Koreac Department of Mater. Sci. and Eng., KAERI, 150Duckjin-dong, Yuseong-gu, Daejeon, 305-353, Korea

Version of record first published: 03 Sep 2006

To cite this article: Ki-Yong Choi, Tae-Song Kim, Duck-Kyun Choi, Ji-Yeun Park &Dae-Sung Yoon (2005): Electrical Properties of PZT-PCW Thick Film on Pt/Sic/Si, andStructural Stability of SiC, Integrated Ferroelectrics: An International Journal, 69:1,93-101

To link to this article: http://dx.doi.org/10.1080/10584580590897335

PLEASE SCROLL DOWN FOR ARTICLE

Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions

This article may be used for research, teaching, and private study purposes.Any substantial or systematic reproduction, redistribution, reselling, loan,

sub-licensing, systematic supply, or distribution in any form to anyone isexpressly forbidden.

The publisher does not give any warranty express or implied or make anyrepresentation that the contents will be complete or accurate or up todate. The accuracy of any instructions, formulae, and drug doses should beindependently verified with primary sources. The publisher shall not be liablefor any loss, actions, claims, proceedings, demand, or costs or damageswhatsoever or howsoever caused arising directly or indirectly in connectionwith or arising out of the use of this material.

Dow

nloa

ded

by [

Han

yang

Uni

vers

ity]

at 0

1:35

13

Aug

ust 2

012

Integrated Ferroelectrics, 69: 93–101, 2005

Copyright © Taylor & Francis Inc.

ISSN 1058-4587 print / 1607-8489 online

DOI: 10.1080/10584580590897335

Electrical Properties of PZT-PCW Thick Filmon Pt/Sic/Si, and Structural Stability of SiC

Ki-Yong Choi,1,2 Duck-Kyun Choi,1,2 Ji-Yeun Park,3 Dae-Sung Yoon,1

and Tae-Song Kim1,∗

1Microsystem Research Center, KIST, 39-1 Haweolgog-dong,Seongbuk-gu, Seoul 136-791, Korea, 2Department of Ceramic Eng., HanyangUniversity, 17 Hangdang-Dong, Seongdong-Gu, Seoul 133-791, Korea, and

3Department of Mater. Sci. and Eng., KAERI, 150 Duckjin-dong,Yuseong-gu, Daejeon 305-353, Korea

ABSTRACT

We have fabricated the PZT-PCW thick films on Pt/(Ti, Pt, and TiO2)/SiNx/SiC/Si sub-strates. SiC thick films were deposited on the Si substrate by thermal CVD method. SiNx

films with different film thickness as a diffusion barrier layer were deposited on SiC/Sisubstrates using plasma enhanced chemical vapor deposition. The bottom electrode usedwas double layers of Pt/(Ti, Ta, and TiO2). We used TiO2, Ti, and Ta as a buffer layerto improve the adhesion property of Pt film. PZT-PCW thick films were prepared onthe SiC thick films by screen printing. All samples were quickly introduced into thefurnace, kept at a temperature between 750 and 950◦ for 10 min, and then cooled inair. For application of cantilever based device, SiC thick film was used as a supportingmaterial in order to improve sensing sensitivity of cantilever based sensor. However, inorder to use SiC thick films, we needed to investigate interfacial properties between PZTand SiC thick films. We investigated the structural stability of the adhesion layer (Ti,TiO2, and Ta) and the diffusion barrier layer (SiNx) using the PZT-PCW thick films withdifferent layers. The PZT-PCW thick film with TiO2 as adhesion layer showed morestable interface than that with Ti and Ta below 900◦C. In the case of the PZT-PCW thickfilm with SiNx layer, SiNx films showed more stable interface at the thickness of 3000to 6000

◦A. In the case of PZT-PCW thick film with the SiNx thickness of 6000

◦A, the

electrical properties were improved with the increase of sintering temperature. In caseof the PZT-PCW thick film with sintered at 950◦C, the remanent polarization (Pr) wasabout 13.0 µC/cm2 at the applied field of 150 kV/cm, and the dielectric permittivity (εr)was 551 at the frequency of 100 kHz.

Keywords: Piezoelectric; MEMS; SiC; PZT; thick film

Received May 1, 2004; In final form May 13, 2004.∗Corresponding author.

[1635]/93

Dow

nloa

ded

by [

Han

yang

Uni

vers

ity]

at 0

1:35

13

Aug

ust 2

012

94/[1636] K.-Y. Choi et al.

INTRODUCTION

The use of piezoelectric materials on micromachined silicon structure is of par-ticular interest in the field of microelectromechanical systems (MEMS). Leadzirconate titanate (PZT) thick films have been widely used for the actuation ofactive structures in MEMS. The piezoelectric properties of such films with thethickness range of 5–50 µm make them suited to integrated actuation applica-tion. For this application, a candidate method for fabricating thick films is thescreen printing method. However, the properties of screen printed thick films onSi-based substrate are poorer than those of bulk ceramics, due to some reactionbetween the PZT thick film and the Si-based substrate, and lower sinterabilityoriginated from the clamping effects of the substrate. The ability to producehigh-quality (especially high density) piezoelectric thick films at relatively lowtemperature is important in manufacturing of useful piezoelectric actuator onSi substrate.

Also, in recent years, silicon carbide has emerged as an important materialfor MEMS application [1–2]. SiC is a wide band-gap semiconductor materialwhich has high-temperature stability, high thermal conductivity, high break-down electric field, and high electron saturation velocity, making it suitable foruse in harsh environments [3–5]. Recently, the PZT-PCW thick films with SiCbuffer layer have been developed in our lab. In the case of piezoelectric micro-cantilever sensor, Si or SiNx have been used as supporting materials. However,in order to improve sensing sensitivity in sensor, it is necessary to use highlyelastic modulus material. Because SiC has higher elastic modulus than Si orSiNx, it is desirable that supporting material of cantilever.

In this work, SiC thick films are used as supporting material in piezoelectricmicro-cantilever sensor. However, in order to use SiC thick films, systematicresearch for interface between PZT and SiC thick film, and SiC thick film andbottom electrode is needed, because of the technical importance for successfulMEMS device application. Therefore, in this study, we focused on the prop-erty improvement of interface between PZT-PCW and SiC thick film throughadopting various adhesion layers (Ti, Ta, and TiO2) and a diffusion barrier layer(SiNx).

EXPERIMENTAL PROCEDURES

In a previous paper [6], the preparation and characterization of PZT (52/48) +0.12 mol% PCW thick films prepared by screen printing have been described.Figure 1 shows a schematic diagram of multilayer structure that consist offerroelectric thick film, electrode(Pt), adhesion layer(Ti, Ta, and TiO2), dif-fusion barrier layer(SiNx) and supporting material(SiC). SiC thick film wasdeposited on the Si substrate by thermal CVD method in the pressure of 10 torr

Dow

nloa

ded

by [

Han

yang

Uni

vers

ity]

at 0

1:35

13

Aug

ust 2

012

Electrical Properties of PZT-PCW Thick Film [1637]/95

Figure 1. A schematic diagram of the multilayer structures with (a) no diffusion barrierlayer and (b) diffusion barrier layer (SiNx). (See color plate I)

at 1000◦C. MTS(methyltrichlorosilane; CH3SiCl3) and H2 were used as precur-sor materials. Ti, Ta, and TiO2 thin films of 300

◦A as an adhesion layer between

SiC and Pt were deposited by rf magnetron sputter. Pt film of 3000◦A as a bot-

tom electrode was deposited by rf magnetron sputter. Also, in order to preventreaction between PZT and SiC thick film, we used SiNx as a diffusion barrierlayer between the adhesion layer and the SiC thick film. The SiNx films withdifferent thickness (3000, 6000, 9000, and 12000

◦A) were deposited on SiC

thick films using PECVD. After the bottom electrode deposition, PZT-PCWpaste was printed on the substrate using screen printing. Multiple printingsand dryings were carried out up to 20∼40 µm in final film thickness. Organicbinder was burned out at 400◦ for 10–20 min. Finally, all samples were directlyinserted into the furnace, and sintered at a temperature between 750 and 950◦

for 10 min. Pt film of 1500◦A as a top electrode was deposited by rf magnetron

sputter.The electrical properties such as remanent polarization (Pr), dielectric

constant (εr), and tan δ were measured as a function of heat treatment tem-perature. The dielectric constant and the loss tangent were measured by aHP 4924A LF impedance analyzer at 100 kHz. The ferroelectric hysteresisbehavior of the thick film can also obtained using RT66A ferroelectric tester—high voltage system (Radient technology Inc) with a virtual ground at appliedfields of 100 kV/cm and 150 kV/cm. In addition, the structural stabilities ofinterface between the PZT-PCW thick film and the SiC thick film were inves-tigated using field emission scanning electron microscope (FE-SEM, HitachiCo.) and electron probe micro analyzer(EPMA, JEOL, JXA-8900R).

Dow

nloa

ded

by [

Han

yang

Uni

vers

ity]

at 0

1:35

13

Aug

ust 2

012

96/[1638] K.-Y. Choi et al.

Figure 2. XRD pattern of SiC film deposited by a thermal CVD on Si substrate.

RESULTS AND DISCUSSION

In order to analyze the crystallographic orientation of the fabricated SiC thickfilm, x-ray diffraction(XRD) analysis was conducted. Figure 2 shows the XRDpattern of the SiC film deposited by a thermal CVD on Si substrate. Two peaksat 2θ = 35.68◦ and 69.2◦ were observed. The peak at 2θ = 69.2◦ is Si substratediffraction peak [7]. The peak at 2θ = 35.68◦ corresponds to the 3C-SiC (111)orientation, indicating that the SiC thick film has (111) preferred alignment.

Figure 3 shows SEM images of the cross-section and the surface of the SiCthick films deposited on the Si substrates for (a) 1 and (b) 4 hours. The SiC thickfilm deposited for 1 hour exhibited island structure at the surface. However, theSiC thick film deposited for 4 hours showed that the island structure becamesmooth and relatively uniform film thickness was acquired. From this result, itmay be speculated that surface roughness of the SiC thick films decreased withthe increase of deposition time.

Figure 4(a), (b), and (c) show SEM images of the cross-section of theinterfaces between PZT-PCW and SiC thick films with various adhesion layers(TiO2, Ti, and Ta) at 800, 850, and 900◦. The substrates with Ti and Ta asan adhesion layer were severely damaged at all temperatures, indicating thatthe electrode and the adhesion layer (Pt/Ti and Pt/Ta) could not prevent theinter-diffusion of Pb (PZT-PCW) and Si (SiC). A part of PZT-PCW thick filmand a part of SiC near the electrode transformed to glass phases. Because ofthe formation of glass phases, the electrode was easy to be destroyed and anytrace is not observed in Fig. 4(a) and (b). However, the substrate with TiO2 asadhesion layer, as shown in Fig. 4(c), showed more stable interface than thatwith Ti and Ta below 900◦C, indicating that TiO2 was suitable for the adhesionlayer. In order to investigate main causes of the glass formation, systematic

Dow

nloa

ded

by [

Han

yang

Uni

vers

ity]

at 0

1:35

13

Aug

ust 2

012

Electrical Properties of PZT-PCW Thick Film [1639]/97

Figure 3. SEM images of the cross-section and the surface of the SiC thick filmsdeposited on Si substrates for (a) 1 hour and (b) 4 hours.

Figure 4. SEM images of the cross-section of the interfaces between PZT-PCW andSiC thick films as function of adhesion layers ((a) Ti, (b) Ta, and (c) TiO2) at 800, 850,and 900◦C.

Dow

nloa

ded

by [

Han

yang

Uni

vers

ity]

at 0

1:35

13

Aug

ust 2

012

98/[1640] K.-Y. Choi et al.

Figure 5. (a) A SEM image and (b) EPMA line profiles of the cross-section of theinterface between the PZT-PCW and the SiC thick film with TiO2 as an adhesion layer,it was sintered at 950◦C for 10 min.

composition analysis of the interface between the PZT-PCW and the SiC thickfilm was needed.

A SEM image and EPMA line profiles of the cross section of the inter-face between PZT-PCW and SiC thick film are shown in Fig. 5. The PZT-PCW thick film with Pt/TiO2/SiC/Si was sintered at 950◦ for 10 min. InFig. 5(a), it was found that a part of the SiC thick film was partially changed.And, as shown in Fig. 5(b), EPMA line profiles indicate that Pb and O com-ponents in the PZT-PCW thick film diffused into the SiC thick film. Theupper layer of SiC thick film was partially reacted with Pb and O compo-nent. From this result, it was revealed that for the fabrication of good PZT-PCW thick film, the prevention of inter-diffusion was critical. SiNx films asa diffusion barrier layer were deposited on the SiC/Si substrates in order toprevent the structural degradation of SiC due to the inter-diffusion and thereaction.

The dependence of SiNx film thickness on the electrical properties of thePZT-PCW thick film was investigated. The dielectric constants and loss tangentsof the PZT-PCW thick films were shown in Table? The dielectric constant of thethick film increased with the thickness increase of diffusion barrier layer up to6000

◦A. However, above the SiNx thickness of 6000

◦A, the dielectric constant

decreased with the increase of SiNx thickness. The loss tangent of PZT thickfilm was improved with the thickness increase of SiNx diffusion barrier layer.From the result, it was found that the SiNx with a thickness range of 3000–6000

◦A was more effective for the improvement of interfacial and electrical

properties of the PZT-PCW thick film.Figure 6(a) and (b) show the remanent polarization values and the P-E

hysteresis loops of PZT-PCW thick films with the SiNx thickness of (a) 3000

Dow

nloa

ded

by [

Han

yang

Uni

vers

ity]

at 0

1:35

13

Aug

ust 2

012

Electrical Properties of PZT-PCW Thick Film [1641]/99

Table 1The dielectric constants and the loss tangents of the PZT-PCW thick films with differentSiNx thickness at various sintering temperatures

SiC wafer Pt/TiO2/ SiNx/SiC

0◦A 3000

◦A 6000

◦A 9000

◦A 12000

◦A

Temp. (◦) εr tan δ εr tan δ εr tan δ εr tan δ εr tan δ

750 274 0.029 208 0.028 242 0.024 88 0.021 50 0.021800 317 0.031 312 0.03 317 0.026 207 0.024 73 0.022850 358 0.032 330 0.033 412 0.031 230 0.025 174 0.024900 408 0.036 429 0.033 456 0.033 358 0.027 158 0.024950 308 0.025 572 0.035 551 0.044 63 0.027 49 0.025

and (b) 6000◦A. The remanent polarization (Pr) increased with the increase

of sintering temperature in both cases. In case of the PZT-PCW thick filmssintered at 950◦C, the remanent polarization (Pr) at the sweep electric field of±150 kV/cm was 13.0 µC/cm2. All samples showed well-saturated hysteresis

Figure 6. The remanent polarization and the P-E hysteresis loops of the PZT-PCWthick films with various sintering temperature at a thickness of (a) 3000 and (b) 6000

◦A.

(See color plate II)

Dow

nloa

ded

by [

Han

yang

Uni

vers

ity]

at 0

1:35

13

Aug

ust 2

012

100/[1642] K.-Y. Choi et al.

curves except for the thick film with SiNx thickness of 3000◦A (sintered at

900◦). From the structural and the electrical evaluation, it was known that theoptimal substrate condition for the fabrication of the PZT-PCW thick film wasthe substrate structure of Pt/TiO2(300

◦A)/SiNx(3000–6000

◦A)/SiC/Si.

CONCLUSIONS

We have fabricated the PZT-PCW thick films on Pt/(Ti, Ta, andTiO2)/SiNx/SiC/Si substrates. In this study, to improve the interface of be-tween PZT-PCW and SiC thick films, we used adhesion layers (Ti, Ta, andTiO2) and a diffusion barrier layer (SiNx). The substrate with TiO2 as ad-hesion layer showed more stable interface than that with Ti and Ta below900◦C. The SiNx with a thickness range of 3000–6000

◦A was more effective

for the improvement of interfacial and electrical properties of the PZT-PCWthick film. The electrical properties of PZT-PCW thick films with the SiNx

thickness of 3000 and 6000◦A were improved with the increase of sintering

temperature. The maximum dielectric permittivity (εr) of PZT-PCW thick filmsmeasured at the frequency of 100 kHz, shows 551 at the SiNx thickness of6000

◦A. The PZT-PCW thick films with the SiNx thickness of 3000–6000

◦A

exhibited well-saturated hysteresis curves. The remanent polarization (Pr) ofPZT-PCW thick film with 6000

◦A SiNx was 13.0 µC/cm2 at the sweep electric

field of ±150 kV/cm. From the structural and electrical evaluation, we foundthat the optimal substrate condition for the fabrication of the PZT-PCW thickfilm was the substrate structure of Pt/TiO2(300

◦A)/SiNx(3000–6000

◦A)/SiC/Si.

ACKNOWLEDGEMENTS

This research, under the contract project code MS-04-133-01, has been sup-ported by the Intelligent Microsystem Center(IMC; http://www.microsystem.re.kr), which carries out one of the 21st century’s Frontier R&D Projects spon-sored by the Korea Ministry of Science & Technology.

REFERENCES

1. M. Meregany and C. A. Zorman, Thin Solid Films 355/356, 518 (1999).2. P. M. Sarro, Sen. Actuators A 82, 210 (2000).3. S. Sriram, R. C. Clarke, A. A. Burk, Jr., H. M. Hobgood, P. G. McMullin, P.

A. Orphanos, R. R. Siergiej, T.J. Smit, C. D. Brandt, M. C. Driver, and R.H. Hopkins, IEEE Electron Device Lett. EDL-15, 458 (1994).

4. N. Susumu, A. Sadao, Jpn. J. Appl. Phys. 33, 1833 (1994).

Dow

nloa

ded

by [

Han

yang

Uni

vers

ity]

at 0

1:35

13

Aug

ust 2

012

Electrical Properties of PZT-PCW Thick Film [1643]/101

5. H. S. Kong, J. W. Palmour, J. T. Glass, and R. F. Davis, Appl. Phys. Lett. 51,442 (1987).

6. Y. B. Kim, H. J. Kim, C. I. Cheon, D. J. Choi, and T. S. Kim, IntegratedFerroelectric 41, 107–116 (2001).

7. R. J. Iwanowski, K. Fronc, W. Paszkowicz, and M. Heinonen, J. Alloys &Compounds 286, 143 (1999).

Dow

nloa

ded

by [

Han

yang

Uni

vers

ity]

at 0

1:35

13

Aug

ust 2

012