LEAD ZIRCONATE TITANATE THIN FILMS FOR PIEZOELECTRIC ACTUATION AND SENSING OF MEMS RESONATORS
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This research is focused on examining the potential benefits and limitations of applying sol-gel lead zirconate titanate (PZT) piezoelectric thin films to on-chip piezoelectrically driven RF microelectromechanical system (MEMS) resonators in the low frequency (LF) to very high frequency (VHF) frequency range. MEMS fabrication methods are presented for fabricating PZT-based MEMS resonator structures along with investigations into the resultant thin film residual stresses and material properties, and their impact on resonator frequency, beam curvature, and resonant mode shape. The PZT, silicon dioxide (SiO2), platinum (Pt), and silicon nitride (Si3N4) thin film material properties are characterized and validated by wafer bow, cantilever resonance, cantilever thermal-induced tip deflection and finite element modeling (FEM) techniques. The performance of the fabricated PZT-based MEMS resonators are presented and compared to previously demonstrated zinc oxide (ZnO) based resonators as well as to electrostatically based MEMS resonator designs. Resonators with frequency response peaks of greater than 25 dB, quality factors up to 4700, and resonant frequencies up to 10 MHz are demonstrated along with a discussion of their advantages and disadvantages for use as MEMS resonators. Nonlinear resonator response is also investigated in relation to the onset of classic Duffing behavior, beam buckling and mode coupling. Fabrication techniques, operating conditions, and design rules are presented to minimize or eliminate nonlinear resonator response.