Pb(Zr,Ti)O3 thin films by in-situ reactive sputtering on micromachined membranes for micromechanical applications

For micromechanical applications, piezoelectric PbZrTO3 (PZT) thin films have been deposited on metallised Si3N4/SiO2 layers on Si wafers. Films with compositions near the morphotropic phase boundary (x=0.53) were prepared at 600°C using a multitarget, in-situ, reactive deposition process. The PZT films were optimised with respect to Pb/(Zr+Ti) flux and Zr content. Within certain processing limits, the lead content was found to be self-stabilising, e.g. any excess lead re-evaporated from the substrate, resulting in essentially single phase films. The crystallisation and orientation were improved by the presence of a PbTiO3 - rich seed layer, which allowed the deposition of films with >95% / orientation. Membranes with piezoelectric films were micromachined by chemically etching the Si substrate. The piezoelectric response, i.e. the deflections, of the resulting membranes were measured as a function of applied voltage and frequency using an interferometer.