Stable TiO₂/Pt electrode structure for lead containing ferroelectric thick films on silicon MEMS structures

A thermally stable electrode structure for lead zirconate titanate (PZT) thick films was developed for silicon/silicon nitride substrates by incorporating titanium oxide (TiO₂) as a diffusion barrier layer between a Pt electrode and the underlying Si₃N₄ layer. The titanium oxide was prepared by thermal oxidation of the titanium in air. Wet etching of the PZT was used as a low cost technique to make contact with the back electrode and assess its robustness. Initial results revealed bubbling in the PZT and platinum. This was found to be due to incomplete oxidation of the titanium and high compressive stresses within the Pt layer at the maximum processing temperature of 710 °C. It was found that titanium was optimally oxidised at 700 °C. Work on post-annealing showed that the stress within the platinum, at the processing temperature, could be reduced by annealing at 300 °C. A clear and non-delaminated interface was then obtained using 350 nm of titania oxidised at 700 °C and 200 nm of platinum post-annealed at 300 °C.