Ki-Yong Choi a b, Tae-Song Kim a, Duck-Kyun Choi a b, Ji-Yeun Park c & Dae-Sung Yoon a a Microsystem Research Center, KIST, 39-1

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1 This article was downloaded by: [Hanyang University] On: 13 August 2012, At: 01:35 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK Integrated Ferroelectrics: An International Journal Publication details, including instructions for authors and subscription information: Electrical Properties of PZT- PCW Thick Film on Pt/Sic/Si, and Structural Stability of SiC Ki-Yong Choi a b, Tae-Song Kim a, Duck-Kyun Choi a b, Ji-Yeun Park c & Dae-Sung Yoon a a Microsystem Research Center, KIST, 39-1 Haweolgog-dong, Seongbuk-gu, Seoul, , Korea b Department of Ceramic Eng., Hanyang University, 17 Hangdang-Dong, Seongdong-Gu, Seoul, , Korea c Department of Mater. Sci. and Eng., KAERI, 150 Duckjin-dong, Yuseong-gu, Daejeon, , 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, and Structural Stability of SiC, Integrated Ferroelectrics: An International Journal, 69:1, To link to this article: PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan,

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3 Integrated Ferroelectrics, 69: , 2005 Copyright Taylor & Francis Inc. ISSN print / online DOI: / Electrical Properties of PZT-PCW Thick Film on 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 Kim 1, 1 Microsystem Research Center, KIST, 39-1 Haweolgog-dong, Seongbuk-gu, Seoul , Korea, 2 Department of Ceramic Eng., Hanyang University, 17 Hangdang-Dong, Seongdong-Gu, Seoul , Korea, and 3 Department of Mater. Sci. and Eng., KAERI, 150 Duckjin-dong, Yuseong-gu, Daejeon , Korea ABSTRACT We have fabricated the PZT-PCW thick films on Pt/(Ti, Pt, and TiO 2 )/SiN x /SiC/Si substrates. SiC thick films were deposited on the Si substrate by thermal CVD method. SiN x films with different film thickness as a diffusion barrier layer were deposited on SiC/Si substrates using plasma enhanced chemical vapor deposition. The bottom electrode used was double layers of Pt/(Ti, Ta, and TiO 2 ). We used TiO 2,Ti, and Ta as a buffer layer to improve the adhesion property of Pt film. PZT-PCW thick films were prepared on the SiC thick films by screen printing. All samples were quickly introduced into the furnace, kept at a temperature between 750 and 950 for 10 min, and then cooled in air. For application of cantilever based device, SiC thick film was used as a supporting material in order to improve sensing sensitivity of cantilever based sensor. However, in order to use SiC thick films, we needed to investigate interfacial properties between PZT and SiC thick films. We investigated the structural stability of the adhesion layer (Ti, TiO 2, and Ta) and the diffusion barrier layer (SiN x ) using the PZT-PCW thick films with different layers. The PZT-PCW thick film with TiO 2 as adhesion layer showed more stable interface than that with Ti and Ta below 900 C. In the case of the PZT-PCW thick film with SiN x layer, SiN x films showed more stable interface at the thickness of 3000 to 6000 A. In the case of PZT-PCW thick film with the SiN x thickness of 6000 A, the electrical properties were improved with the increase of sintering temperature. In case of the PZT-PCW thick film with sintered at 950 C, the remanent polarization (P r )was about 13.0 µc/cm 2 at the applied field of 150 kv/cm, and the dielectric permittivity (ε r ) was 551 at the frequency of 100 khz. Keywords: Piezoelectric; MEMS; SiC; PZT; thick film Received May 1, 2004; In final form May 13, Corresponding author. [1635]/93

4 94/[1636] K.-Y. Choi et al. INTRODUCTION The use of piezoelectric materials on micromachined silicon structure is of particular interest in the field of microelectromechanical systems (MEMS). Lead zirconate titanate (PZT) thick films have been widely used for the actuation of active structures in MEMS. The piezoelectric properties of such films with the thickness range of 5 50 µm make them suited to integrated actuation application. For this application, a candidate method for fabricating thick films is the screen printing method. However, the properties of screen printed thick films on Si-based substrate are poorer than those of bulk ceramics, due to some reaction between the PZT thick film and the Si-based substrate, and lower sinterability originated from the clamping effects of the substrate. The ability to produce high-quality (especially high density) piezoelectric thick films at relatively low temperature is important in manufacturing of useful piezoelectric actuator on Si substrate. Also, in recent years, silicon carbide has emerged as an important material for MEMS application [1 2]. SiC is a wide band-gap semiconductor material which has high-temperature stability, high thermal conductivity, high breakdown electric field, and high electron saturation velocity, making it suitable for use in harsh environments [3 5]. Recently, the PZT-PCW thick films with SiC buffer layer have been developed in our lab. In the case of piezoelectric microcantilever sensor, Si or SiN x have been used as supporting materials. However, in order to improve sensing sensitivity in sensor, it is necessary to use highly elastic modulus material. Because SiC has higher elastic modulus than Si or SiN x,itisdesirable that supporting material of cantilever. In this work, SiC thick films are used as supporting material in piezoelectric micro-cantilever sensor. However, in order to use SiC thick films, systematic research for interface between PZT and SiC thick film, and SiC thick film and bottom electrode is needed, because of the technical importance for successful MEMS device application. Therefore, in this study, we focused on the property improvement of interface between PZT-PCW and SiC thick film through adopting various adhesion layers (Ti, Ta, and TiO 2 ) and a diffusion barrier layer (SiN x ). EXPERIMENTAL PROCEDURES In a previous paper [6], the preparation and characterization of PZT (52/48) mol% PCW thick films prepared by screen printing have been described. Figure 1 shows a schematic diagram of multilayer structure that consist of ferroelectric thick film, electrode(pt), adhesion layer(ti, Ta, and TiO 2 ), diffusion barrier layer(sin x ) and supporting material(sic). SiC thick film was deposited on the Si substrate by thermal CVD method in the pressure of 10 torr

5 Electrical Properties of PZT-PCW Thick Film [1637]/95 Figure 1. A schematic diagram of the multilayer structures with (a) no diffusion barrier layer and (b) diffusion barrier layer (SiN x ). (See color plate I) at 1000 C. MTS(methyltrichlorosilane; CH 3 SiCl 3 ) and H 2 were used as precursor materials. Ti, Ta, and TiO 2 thin films of 300 Aasanadhesion layer between SiC and Pt were deposited by rf magnetron sputter. Pt film of 3000 Aasabottom electrode was deposited by rf magnetron sputter. Also, in order to prevent reaction between PZT and SiC thick film, we used SiN x as a diffusion barrier layer between the adhesion layer and the SiC thick film. The SiN x films with different thickness (3000, 6000, 9000, and A) were deposited on SiC thick films using PECVD. After the bottom electrode deposition, PZT-PCW paste was printed on the substrate using screen printing. Multiple printings and dryings were carried out up to µm infinal film thickness. Organic binder was burned out at 400 for min. Finally, all samples were directly inserted into the furnace, and sintered at a temperature between 750 and 950 for 10 min. Pt film of 1500 Aasatop electrode was deposited by rf magnetron sputter. The electrical properties such as remanent polarization (P r ), dielectric constant (ε r ), and tan δ were measured as a function of heat treatment temperature. The dielectric constant and the loss tangent were measured by a HP 4924A LF impedance analyzer at 100 khz. The ferroelectric hysteresis behavior of the thick film can also obtained using RT66A ferroelectric tester high voltage system (Radient technology Inc) with a virtual ground at applied fields of 100 kv/cm and 150 kv/cm. In addition, the structural stabilities of interface between the PZT-PCW thick film and the SiC thick film were investigated using field emission scanning electron microscope (FE-SEM, Hitachi Co.) and electron probe micro analyzer(epma, JEOL, JXA-8900R).

6 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 thick film, x-ray diffraction(xrd) analysis was conducted. Figure 2 shows the XRD pattern of the SiC film deposited by a thermal CVD on Si substrate. Two peaks at 2θ = and 69.2 were observed. The peak at 2θ = 69.2 is Si substrate diffraction peak [7]. The peak at 2θ = 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 SiC thick films deposited on the Si substrates for (a) 1 and (b) 4 hours. The SiC thick film deposited for 1 hour exhibited island structure at the surface. However, the SiC thick film deposited for 4 hours showed that the island structure became smooth and relatively uniform film thickness was acquired. From this result, it may be speculated that surface roughness of the SiC thick films decreased with the increase of deposition time. Figure 4(a), (b), and (c) show SEM images of the cross-section of the interfaces between PZT-PCW and SiC thick films with various adhesion layers (TiO 2,Ti, and Ta) at 800, 850, and 900. The substrates with Ti and Ta as an adhesion layer were severely damaged at all temperatures, indicating that the electrode and the adhesion layer (Pt/Ti and Pt/Ta) could not prevent the inter-diffusion of Pb (PZT-PCW) and Si (SiC). A part of PZT-PCW thick film and a part of SiC near the electrode transformed to glass phases. Because of the formation of glass phases, the electrode was easy to be destroyed and any trace is not observed in Fig. 4(a) and (b). However, the substrate with TiO 2 as adhesion layer, as shown in Fig. 4(c), showed more stable interface than that with Ti and Ta below 900 C, indicating that TiO 2 was suitable for the adhesion layer. In order to investigate main causes of the glass formation, systematic

7 Electrical Properties of PZT-PCW Thick Film [1639]/97 Figure 3. SEM images of the cross-section and the surface of the SiC thick films deposited 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 and SiC thick films as function of adhesion layers ((a) Ti, (b) Ta, and (c) TiO2 ) at 800, 850, and 900 C.

8 98/[1640] K.-Y. Choi et al. Figure 5. (a) A SEM image and (b) EPMA line profiles of the cross-section of the interface between the PZT-PCW and the SiC thick film with TiO 2 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 thick film was needed. A SEM image and EPMA line profiles of the cross section of the interface between PZT-PCW and SiC thick film are shown in Fig. 5. The PZT- PCW thick film with Pt/TiO 2 /SiC/Si was sintered at 950 for 10 min. In Fig. 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 components in the PZT-PCW thick film diffused into the SiC thick film. The upper layer of SiC thick film was partially reacted with Pb and O component. From this result, it was revealed that for the fabrication of good PZT- PCW thick film, the prevention of inter-diffusion was critical. SiN x films as a diffusion barrier layer were deposited on the SiC/Si substrates in order to prevent the structural degradation of SiC due to the inter-diffusion and the reaction. The dependence of SiN x film thickness on the electrical properties of the PZT-PCW thick film was investigated. The dielectric constants and loss tangents of the PZT-PCW thick films were shown in Table? The dielectric constant of the thick film increased with the thickness increase of diffusion barrier layer up to 6000 A. However, above the SiN x thickness of 6000 A, the dielectric constant decreased with the increase of SiN x thickness. The loss tangent of PZT thick film was improved with the thickness increase of SiN x diffusion barrier layer. From the result, it was found that the SiN x with a thickness range of Awas 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 SiN x thickness of (a) 3000

9 Electrical Properties of PZT-PCW Thick Film [1641]/99 Table 1 The dielectric constants and the loss tangents of the PZT-PCW thick films with different SiN x thickness at various sintering temperatures SiC wafer Pt/TiO 2 / SiN x /SiC 0 A 3000 A 6000 A 9000 A A Temp. ( ) ε r tan δ ε r tan δ ε r tan δ ε r tan δ ε r tan δ and (b) 6000 A. The remanent polarization (P r ) increased with the increase of sintering temperature in both cases. In case of the PZT-PCW thick films sintered at 950 C, the remanent polarization (P r )atthe sweep electric field of ±150 kv/cm was 13.0 µc/cm 2. All samples showed well-saturated hysteresis Figure 6. The remanent polarization and the P-E hysteresis loops of the PZT-PCW thick films with various sintering temperature at a thickness of (a) 3000 and (b) 6000 A. (See color plate II)

10 100/[1642] K.-Y. Choi et al. curves except for the thick film with SiN x thickness of 3000 A (sintered at 900 ). From the structural and the electrical evaluation, it was known that the optimal substrate condition for the fabrication of the PZT-PCW thick film was the substrate structure of Pt/TiO2(300 A)/SiN x ( A)/SiC/Si. CONCLUSIONS We have fabricated the PZT-PCW thick films on Pt/(Ti, Ta, and TiO2)/SiN x /SiC/Si substrates. In this study, to improve the interface of between PZT-PCW and SiC thick films, we used adhesion layers (Ti, Ta, and TiO 2 ) and a diffusion barrier layer (SiN x ). The substrate with TiO 2 as adhesion layer showed more stable interface than that with Ti and Ta below 900 C. The SiN x with a thickness range of Awas more effective for the improvement of interfacial and electrical properties of the PZT-PCW thick film. The electrical properties of PZT-PCW thick films with the SiN x thickness of 3000 and 6000 A were improved with the increase of sintering temperature. The maximum dielectric permittivity (ε r )ofpzt-pcw thick films measured at the frequency of 100 khz, shows 551 at the SiN x thickness of 6000 A. The PZT-PCW thick films with the SiN x thickness of A exhibited well-saturated hysteresis curves. The remanent polarization (P r )of PZT-PCW thick film with 6000 A SiN x was 13.0 µc/cm 2 at the sweep electric field of ±150 kv/cm. From the structural and electrical evaluation, we found that the optimal substrate condition for the fabrication of the PZT-PCW thick film was the substrate structure of Pt/TiO 2 (300 A)/SiN x ( A)/SiC/Si. ACKNOWLEDGEMENTS This research, under the contract project code MS , has been supported by the Intelligent Microsystem Center(IMC; re.kr), which carries out one of the 21st century s Frontier R&D Projects sponsored 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).

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