Optimal materials and process conditions of functional layers for piezoelectric MEMS process at high temperature

Pb(Zr_0.52Ti_0.48)O₃ (PZT) thick film-based micro-transducers demonstrate excellent piezoelectric performances. However, its powder-based film requires very high sintering temperature to obtain high density and good electromechanical properties of the active film. High processing temperature enables inter-diffusion or reaction between PZT active materials and Si-based substrate to result in device failure via volatilisation of PbO especially over 800°C. Therefore the preventive solution to this problem should be considered in fabricating silicon-based piezoelectric microdevices for the better performance. In this research, compatibility in the interface stability and adhesion between the layers of the overall integrated piezoelectric thick-film devices were thoroughly investigated for the successful application of the process at high temperature. The Pt (or PtO_x)/TiO_2/SiN_x/Si substrate represented the best interfacial properties among various combinations of structural substrates, so this structure is highly recommended to integrated piezoelectric thick-film microelectromechanical system devices.