Preparation of PZT(53/47) thick films deposited by a dip-coating process

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1 Microelectronic Engineering 66 (003) locate/ mee Preparation of PZT(53/47) thick s deposited by a dip-coating process * Xi-Yun He, Ai-Li Ding, Xin-Sen Zheng, Ping-Sun Qiu, Wei-Gen Luo State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 195 Ding Xi Rd., Shanghai 00050, China Abstract Crack-free polycrystalline PZT (PbZrTiO 3) thick s up to 15 mm with perovskite structure have been prepared from a dip-coating process. The influence of substrate characteristics, withdrawal speed and ionic concentration of precursor solution on the morphology and microstructure of PZT was examined. The dielectric, ferroelectric and piezoelectric properties of PZT thick s on Pt/ Ti substrate were measured and evaluated. PZT(53/ 47) thick s on Pt/ Ti substrate exhibits a excellent electric properties, e.g. P r: 35 mc/cm ; E c: 3 kv/cm; e r: 830; tan d : ; d 33: Elsevier Science B.V. All rights reserved. Keywords: PZT thick s; Substrate characteristics; Dip-coating process 1. Introduction PZT thick s (1 30 mm) are promising candidates for numerous device applications such as piezoelectric actuators and ultrasound transducers [1]. Many fabrication processes are devised for the fabrication of PZT thick s including various chemical methods, screen-printing process, etc. [,3]. Among the chemical methods, dip-coating is a very simple process used to deposit the from a chemical precursor solution. It can be applied to prepare large and irregular shaped objects. In this process, a specified substrate is dipped in a uniform solution, and then it is withdrawn from the solution, dried and heat-treated. So the morphology, microstructure and properties are influenced *Corresponding author. Fax: address: alding8@yahoo.com (A.-L. Ding) /0/$ see front matter 00 Elsevier Science B.V. All rights reserved. doi: /s (0)

2 866 X.-Y. He et al. / Microelectronic Engineering 66 (003) by the process parameters such as solution characteristics, substrate feature and withdrawal speed, etc. Moreover, it is well known that the substrate characteristics make a considerable influence on the preparation of the s [4]. So in this study, several different substrates were selected for investigation. The morphology and phase structure of the s on different substrates were examined and evaluated. The influence of withdrawal speed and the ionic concentration of the precursor solution on the morphology were also investigated. PZT(53/47) thick s up to 15 mm in thickness on Pt/ Ti substrate with excellent electric properties were obtained.. Experimental Lead acetate trihydrate, zirconium n-propoxide and titanium i-propoxide were selected as starting reagents. Acetic acid was employed as solvent. The precursor solution of zirconium, titanium, and lead was prepared by adding the raw materials to acetic acid with heating and stirring. Amorphous fused quartz (SiO ), platinum-coated titanium foil ((111)Pt/ Ti) and platinum-coated silicon ((111)Pt/ Ti/ SiO / Si) were chosen as substrates. The precursor solution was then deposited on the selected substrate via semi-automatically controlled dipping and sintering operation as shown in Fig. 1. Drying occurred in a matter of a few seconds, immediately followed by the introduction of the coated substrate into a furnace preheated to the sintering temperature of 700 8C. Multiple dipping, drying, sintering and cooling cycles were semi-automatically performed, and finally the was annealed at 700 8C for 0.5 h. Film phase structure was evaluated by X-ray diffraction (XRD). Film thickness was examined by surface profile measuring system. Film morphology and microstructure were investigated by scanning electron microscopy (SEM). Dielectric constant er and dissipation factor tan d were measured by HP419 impedance analyzer. Ferroelectric hysteresis loops were examined using RT-66A ferroelectric tester. Piezoelectric coefficient (d ) was measured by the Berlin-cord method. 33 Fig. 1. Thick semi-automated dipping apparatus.

3 3. Results and discussion 3.1. Effect of the withdrawal speed X.-Y. He et al. / Microelectronic Engineering 66 (003) A 1-M precursor solution was chosen to determine the suitable withdrawal speed in preparing PZT thick s. To justify the best withdrawal speed, speeds of 5, 10 and 15 mm/min were used to prepare the s with single layer on the fused quartz substrate. The SEM images of the surface morphology of the s made from different withdrawal speeds are shown in Fig.. The from 5 mm/ min withdrawal speed displays a dense, homogenous morphology with fine grains, no obvious crack can be found (Fig. a). On the other hand, there are many large cracks appeared in the s obtained from 10 and 15 mm/min withdrawal speed, as shown in Fig. b,c. The thickness of the single layer prepared from 5, 10 and 15 mm/min withdrawal speed are 1500, 000, and 300A, respectively, as shown in Table 1. In the chemical solution decomposition method, the stress, produced from the shrinkage of the green during thermal treatment, develops as the thickness increasing. When the thickness reaches a critical value, the huge stress in the always leads to the cracking. In this study, the suitable withdrawal speed is 5 mm/min. Fig.. SEM images of the surface morphology of PZT s with different withdrawal speed: (a) 5, (b) 10, and (c) 15 mm/ min.

4 868 X.-Y. He et al. / Microelectronic Engineering 66 (003) Table 1 Thickness of single layer s Substrate Ionic Withdrawal speed Thickness of concentration (M) (mm/ min) single layer (A) Pt/ Ti/ SiO / Si (smooth) Fused quartz (SiO ) (smooth) Pt/ Ti (rough) Effect of the ionic concentration PZT s were prepared from the solution with different ionic concentration on the Pt/Ti/SiO /Si substrate by 5 mm/min withdrawal speed. The single layer thickness of the increases from 300 to 1500 A as the ionic concentration increasing from 0.5 to 1 M (Table 1). The reason is that the higher solution concentration leads to a higher solution viscosity and further makes more material adhere to the substrate during the withdrawal process. However, the single layer s prepared on the Pt/Ti/SiO /Si substrate from different ionic concentration solution are all smooth and crack free. The main reason is that the single layer on the Pt/Ti/SiO /Si substrate is thinner( # 1500 A). On the other hand, the fact, that the silicon has a closer thermal expansion coefficient ( C) to PZT 6 6 ( C) than in the case for fused quartz ( C), makes the on Pt/Ti/SiO /Si substrate not easy to crack. It can be seen that the thickness of the crack free PZT on silicon substrate can be reached a higher value than that of the on fused quartz substrate Effect of the substrate characteristics Platinum-coated silicon ((111)Pt/ Ti/ SiO / Si) and fused quartz (amorphous SiO ) with smooth surface, platinum-coated titanium foil ((111)Pt/ Ti) with rough surface were selected as the substrates to investigated the effects of the substrate characteristics on the fabrication. In the same condition, the deposited on the different substrate has a various thickness. As shown in Table 1, the thicknesses of the s made on Pt/ Ti/ SiO / Si and SiO substrates are 950 and 1500 A, respectively (from 0.5 M precursor solution with 5 mm/ min withdrawal speed). To the different substrate, the surface characteristics such as surface wettability is different, this will influence the adhesion of the solution to the substrate surface and then result to the changes in thickness. Also it has been demonstrated that the surface roughness makes a great effect on surface wettability and further influence the solution adhesion behavior. To the wettable surface, roughing the surface is useful to improve the surface wettability, and then is benefit to the adhesion of solution on the surface. Therefore, on the Pt/Ti substrate with a rough surface, the thickness of single layer of the prepared from the same condition is about 4000 A, larger than that of the two others. X-ray diffraction patterns of the s on different substrates are shown in Fig. 3. The (3000 A)

5 X.-Y. He et al. / Microelectronic Engineering 66 (003) Fig. 3. XRD pattern of PZT s on different substrates: (a) fused quartz (d A), (b) Pt/Ti/SiO /Si (d Å), and (c) Pt/Ti (d 5 15 mm). prepared on the amorphous fused quartz is almost amorphous after annealing at 700 8C for 30 min (Fig. 3a). On the other hand, the (3000 A) prepared on the (111) Pt/Ti/SiO /Si substrate displays a excellent (111) preferred orientation (Fig. 3b). This occurs because of close lattice matching between PZT(53/47) and Pt, PbPtx or Pt3Ti [5]. This reduces the nucleation energy of (111) planes at the electrode interface and so promotes (111) preferred orientation during the early stages of crystallization. But it has been demonstrated that the effect of the heterogenous nucleation and growth from the bottom heteroepitaxial (111) Pt/ TiSiO / Si electrode will be diminished toward the surface [6]. In this study, PZT thick s up to 15 mm prepared on the Pt/Ti substrate displays a (110) preferred random pattern, as shown in Fig. 3c. This result is consistent with the reports Properties and microstructure of PZT thick s PZT(53/47) thick s up to 15 mm were fabricated from 1 M precursor solution with withdrawal speed of 5 mm/min on the Pt/Ti substrate (thickness of the foil is about 0 mm). The microstructure of the surface and cross section of the were investigated by SEM, as shown in Fig. 4a,b. It can be found that the thick displays a dense, homogenous and crack free microstructure with smooth surface. Dielectric, ferroelectric and piezoelectric properties of the s were examined and evaluated. Fig. 5 shows the dielectric constant (e r) and dissipation factor (tan d ) as a function of frequency. As the frequency increasing, the dielectric constant inclined slightly. The average value of er is about 830. The tan d value of the thick is scattered in the range of at the examined frequency. The obtained thick exhibits a excellent hysteresis loop with a remnant polarization value of Pr5 35 mc/ cm and coercive field value of Ec5 3 kv/ cm (see Fig. 6). Piezoelectric coefficient (d 33) of the PZT thick was approximately measured by the Berlin-cord 10 method by applying 0. N on the. For the Young s modulus of titanium foil ( N/m ) is 10 similar to that of the PZT ( N/ m ), the restraint composed on the from the substrate during the measurement can be diminished to ensure the examined d33 value close to the real one. The examined d33 value is about 14.

6 870 X.-Y. He et al. / Microelectronic Engineering 66 (003) Fig. 4. SEM images of the surface morphology (a) and cross section (b) of PZT thick s on Pt/Ti substrate (d 5 15 mm). 4. Conclusion Homogenous and crack free PZT(53/47) thick s up to 15 mm can be prepared by dip-coating process on Pt/ Ti substrate. The effects of withdrawal speed, ionic concentration of solution and substrate characteristics on the preparation were investigated and analyzed. The surface wettability and roughness make a great effect on the morphology of the. The withdrawal speed of 5 mm/min, ionic concentration of 1 M and the Pt/Ti substrate are suitable to fabricate crack free PZT thick. In these conditions, PZT(53/47) thick of 15 mm in thickness with good electric properties have been obtained: Pr5 35 mc/ cm ; Ec5 3 kv/ cm, er 5 830; tan d ; d 5 14 pc/n. 33 Fig. 5. Dielectric constant e and dissipation factor tan d of PZT thick as a function of frequency. r

7 X.-Y. He et al. / Microelectronic Engineering 66 (003) Fig. 6. The ferroelectric hysteresis loops of PZT(53/ 47) thick s. Acknowledgements The authors thank Natural Science Foundation of China (no: ) for financial support. References [1] M. Lukacs, M. Sayer, IEEE Trans. Ultrasonic Ferroelectr. Freq. Control 47 (1) (1999) [] X.H. Pu, W.L. Luo, A.L. Ding, Phys. Status Solidi (a) 18 (000) R10 1. [3] Y. Jeon, J. Chung, K. No, J. Electroceram. 4 (000) [4] G.H. Haertling, Integrated Thin Films and Applications, Ceramic Trans. 86 (1998) [5] S.Y. Chen, I.W. Chen, J. Am. Ceram. Soc. 77 (1994) [6] R. Kurchania, S.J. Milne, J. Mater. Res. 14 (5) (1999)