Nanostructural tuning of the texture of PZT pervoskite thin films grown by RF sputtering for piezoelectric MEMS

Abstract

ABSTRACTCurrently, large efforts are going on to scale up PZT thin film processes for large volume MEMS fabrication. It is critical to complete the scaling up with optimized film properties. In this work we report about microstructural control and piezoelectric properties of RF magnetron sputtered PZT (Pb(Zrx,Ti1−x)O3) thin films. The former is a prerequisite to achieve good properties homogeneously on the entire wafer, and with a good repeatability. We focus on the use of a commercial tool capable to reach a deposition rate of 1nm/sec with a thickness uniformity better than +/-3%. We show particularly how the texture can be chosen between (100) and (111) orientation upon tuning the thickness of a very thin TiO2 seed layer on fully passivated Pt electrodes. The surface morphology as resulting from the various grain shapes is strongly influenced by the self-bias established on the substrate, and by the growth temperature. PZT films with compact grain structure and flat surface reached a transverse piezoelectric coefficient e31,f of -23±1 C/m2 in the actuator mode (converse piezoelectric effect) and a dielectric strength of 0.5MV/cm. Both are remarkable values for un-doped, pure PZT thin films.