Microstructural evolution and piezoelectric properties of thick Pb(Zr,Ti)O 3 films deposited by the multi-sputtering met
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Jong-Jin Choi Department of Future Technology, Korea Institute of Machinery and Materials, Chang-Won, Gyeong-Nam 641-831, Korea (Received 19 September 2006; accepted 5 February 2007)
Highly dense and crack-free Pb(Zr,Ti)O3 (PZT) thick films with a controlled microstructure and orientation were deposited on a platinized silicon substrate by the radio frequency magnetron sputtering method using a single oxide target. The microstructure and orientation of the films were adjusted by applying a thin (100) PZT seed layer by the sol-gel method and subsequent repeated sputtering. When a thin layer was deposited on the seed layer, the film had small grains with a columnar structure. However, as the film became thicker, it developed a large and non-columnar grain structure. Therefore, reducing the thickness of the film per deposition allowed the columnar microstructure to be maintained. The (100) orientation of the film was able to be maintained by depositing it on a (100) oriented seed layer. PZT thick films with controlled orientations and microstructures were successfully deposited up to a thickness of about 5 m, and their ferroelectric and piezoelectric properties were characterized.
I. INTRODUCTION
Thick and crack-free lead zirconate titanate [Pb(Zr1–xTix)O3, PZT] films are required for a wide range of applications in microelectromechanical systems (MEMS) due to their excellent piezoelectric response.1,2 In our previous study,3 a crack-free 5-m-thick PZT film was successfully fabricated by controlling its microstructure using a seed layer and repeated deposition. However, PZT films deposited on (111) seed layers have limits in terms of their piezoelectric properties. According to theoretical expectations4,5 and previous experimental results,6,7 the piezoelectric properties of (100)-oriented rhombohedral PZT films near the morphotropic phase boundary (MPB) are superior to those of the corresponding (111) oriented films. Therefore, (100)-oriented PZT thick films with a Zr/Ti ratio of 60/40 would be expected to have excellent piezoelectric properties. The (100) orientation energetically favors the growth texture8–11 and has a positive effect on the piezoelectric properties.4–7 However, when it is deposited on Pt(111)/
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0177 J. Mater. Res., Vol. 22, No. 5, May 2007
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Ti/SiO2/Si, the film tends to have a (111) orientation at first to minimize the interfacial energy between the PZT and Pt(111).7–9 As the film gets thicker, the (100) orientation becomes dominant. As a result of this nucleation and growth behavior, thick PZT films have mixed orientations of (111) and (100) and, accordingly, their piezoelectric properties do not reach their full potential.4–7 Therefore, to optimize the piezoelectric properties of thick PZT films, it is necessary to deposit (100) oriented films from the beginning of the deposition process. Generally, it is not easy to ensure the (100) orientation
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