Analysis of thin film piezoelectric microaccelerometer using analytical and finite element modeling

Microaccelerometers using piezoelectric lead zirconate titanate (PZT) thin films have attracted much interest due to their simple structure and potentially high sensitivity. In this paper, we present a theoretical model for a microaccelerometer with four suspended flexural PZT-on-silicon beams and a central proof mass configuration. The model takes into account the effect of device geometry and elastic properties of the piezoelectric film, and agrees well with the results obtained by the finite element analysis. This study shows that the accelerometer sensitivity decreases with increases in the beam width, in the thickness of the bilayer beams, and in the elastic modulus of the mechanical microstructure. Increases in the beam length increase sensitivity. For a fixed beam thickness, a maximum sensitivity exists for appropriate PZT/Si thickness ratio. In addition, it is found that with appropriate geometrical dimensions, both high sensitivity and broad frequency bandwidth can be achieved. The calculation of the stress distribution in the suspended PZT/Si beam structure when the device is subjected to large vibrational acceleration indicates that the thin film microaccelerometer can stand extremely large g conditions with very good mechanical reliability. In the dynamic analysis, it is found that both analytical model and finite element modeling give very close results of the resonance frequency of the device. The results of this study can be readily applied to on-chip piezoelectric microaccelerometer design and its structural optimization.

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