Epitaxial piezoelectric MEMS on silicon
This paper reports on the microfabrication and characterization of piezoelectric MEMS structures based on epitaxial Pb(Zr0.2Ti0.8)O-3 (PZT) thin films grown on silicon wafers. Membranes and cantilevers are realized using a sequence of microfabrication processes optimized for epitaxial oxide layers. Different issues related to the choice of materials and to the influence of the fabrication processes on the properties of the piezoelectric films are addressed. These epitaxial PZT transducers can generate relatively large deflections at low bias voltages in the static mode. Estimations of the piezoelectric coefficient d(31) of the epitaxial PZT thin film (100 nm) yield 130 pm V-1. In the dynamic mode, the performance of the epitaxial PZT transducers in terms of the resonant frequency, modal shape and quality factor are examined. An epitaxial PZT/Si cantilever (1000 x 2500 x 40 mu m(3)) resonating in air and in vacuum exhibits a deflection of several microns with quality factors of 169 and 284, respectively. For a 1500 mu m diameter membrane, the quality factor is 50 at atmospheric pressure, and this rises to 323 at a pressure of 0.1 mbar. These results indicate the high potential of epitaxial piezoelectric MEMS, which can impact a variety of technological applications.