Characterization of composite piezoelectric thick film for MEMS application

Composite PZT films with thickness of 3 to 10 μm had been successfully integrated on platinum-coated silicon wafer using a composite process. In this sol–gel based process, submicron-sized PZT powder was uniformly dispersed into a xerogel precursor solution to obtain a suspension/slurry for spin-coating purpose. The properties of the resultant films are mainly determined by the property of the added PZT powder and the recipe of the slurry. Since the surface of the resultant film is nonreflecting, it is quite difficult to evaluate the piezoelectric properties of the film by double-beam interferometer. We have successfully measured the piezoelectric coefficient of the composite film by using scanning laser Doppler vibrometer (SLDV). Surface vibration in response to an applied electric filed was measured with SLDV, and thus, the dimension change of the activated part of the film was clearly separated from the passive bending of the substrate. The microstructure, ferroelectric properties and apparent longitudinal piezoelectric coefficient of the composite film have been investigated and reported.