Effects of lanthanum nitrate buffer layer on the orientation and piezoelectric property of Pb(Zr,Ti)O 3 thick film
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Highly oriented Pb(Zr,Ti)O3 (PZT) films were deposited on Pt/Ti/SiO2/Si substrates by the sol-gel method using lanthanum nitrate as a buffer layer. When the lanthanum nitrate buffer layer was heat treated at temperatures between 450 and 550 °C, the PZT layer coated onto this buffer layer showed a strong (100) preferred orientation. Regardless of the other deposition conditions, such as the pyrolysis temperature, pyrolysis time, annealing temperature and heating rate, the film deposited on the buffer layer had this orientation. Thick films were also fabricated using the sol-gel multi-coating method, and the (100) texture was found to be maintained up to a thickness of 10 m. The ferroelectric hysteresis and piezoelectric coefficient (d33) of highly oriented PZT thick films were characterized, and the (100) oriented PZT film showed higher piezoelectric property than the (111) oriented film.
I. INTRODUCTION
The lead zirconate titanate [Pb(Zr,Ti)O3, PZT] solid solution system is a well known and widely used piezoelectric material. In many micro-electro-mechanical system (MEMS) applications, such as pyroelectric infrared detectors, piezoelectric actuators, and bulk acoustic wave bandpass filters, PZT films with a thickness of 1–10 m are necessary.1 The piezoelectric properties of PZT film are strongly dependent on its crystallographic orientation. Du et al.2 calculated the dependence of the piezoelectric properties on the crystallographic direction phenomenologically for tetragonal and rhombohedral PZT in three-dimensional space. They concluded that for rhombohedral PZT, the d33 value along the perovskite (100) is much larger than that along the spontaneous polarization direction (111). This suggests that PZT film having a rhombohedral composition with the perovskite (100) epitaxially oriented configuration is the best candidate for piezoelectric applications. In previous studies, attempts were made to grow highly oriented PZT films on a platinized silicon substrate using the sol-gel method, by precisely controlling the pyrolysis and annealing temperatures and the heating rate or using buffer layers such as TiO2 and PbTiO3 single-crystal seeds.3–11 These studies mainly focused on the nucleation mechanism and growth kinetics of PZT film on Pt/Ti/SiO2/Si substrates. Brooks et al.3 reported
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0470 J. Mater. Res., Vol. 19, No. 12, Dec 2004
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that the stability of the pyrochlore phase determines the growth kinetics of PZT film, and Chen et al.4,5 reported that the nucleation mechanism and growth kinetics were controlled by formation of intermediate phase such as PbO [001] microcrystal and Pb5–7Pt intermetallic phase. However, most of these methods are sensitive to temperature or other conditions. There were some studies of fabricating textured PZT film using a perovskitestructure buffer layer such as LaNiO3; however the controlling of the texture of LaNiO3 buffer layer is also
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