Graduate Thesis Or Dissertation
 

Synthesis and characterization of Pb(Zr,Ti)O₃ thin films for microelectromechanical systems

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/vm40xw93j

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  • Pb(Zr,Ti)O₃ (PZT) is a very attractive material for use in piezoelectric-based microelectromechanical systems (MEMS) due to its high piezoelectric coefficients and ability for large displacements with relatively low applied fields (as compared to electrostatic-based MEMS). The piezoelectric effect is strongly anisotropic, thus it is very desirable to control the crystallographic orientation of the active material. This study is designed to understand the effect of crystallographic texture on the long-term stability of piezoelectric-based MEMS devices. Utilizing (100)-oriented solution deposited LaNiO₃ (LNO) and PbTiO₃ (PT) seed layers, (001) fiber texture of rfmagnetron sputtered PZT films (ex situ annealed) with varying thickness was optimized. X-ray diffraction rocking curve data indicated good out-of-plane alignment, with full-width-at-half-maximum (FWHM) values of 3.8° - 4.5° and 2.5°- 3.1° for PZT on LNO and PT, respectively. This optimization of (001) orientation is paramount to maximizing the piezoelectric response of PZT thin films for MEMS applications, as this promotes the highest piezoelectric response. Dielectric and ferroelectric properties were obtained for films 120-1320 nm thick. Subsequently these films were subjected to lifetime (fatigue) tests similar to what is experienced in piezo- MEMS applications. Fatigue endurance is a critical factor in evaluating long-term device reliability in these devices. A study of fatigue dependence on film thickness, morphology, bottom electrode, and field strength was conducted. Results of these studies show film morphology contributes strongly to film fatigue and film failure prior to reaching 10⁸ fatigue cycles, with increased grain size leading to improved fatigue endurance. Film thickness was also shown to contribute significantly to fatigue, predominantly in PZT on PT films, with films over 1 μm in thickness showing large fatigue after 10⁸ cycles. Films with bottom LNO electrodes demonstrated improved performance over all thickness ranges studied when compared to PT bottom electrodes, exhibiting minimal fatigue after 10⁸ cycles.
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