Piezoelectric and ferroelectric properties of lead zirconate titanate thin films

The purpose of this research has been to characterize piezoelectric and ferroelectric properties of lead zirconate titanate (PZT) thin films for microelectromechanical systems (MEMS) applications. For systematic and comprehensive analysis of the electromechanical properties, a highly sensitive double beam laser interferometer system and a robust chemical solution deposition (CSD) process have been developed. The piezoelectric, ferroelectric and dielectric properties have been examined in context with microstructural and texture analysis.; The piezoelectric, dielectric, and ferroelectric properties of highly textured polycrystalline PZT films with Zr/Ti composition have been investigated. Distinct peak of piezoelectric coefficient at the morphotropic phase boundary (MPB) observed in bulk PZT ceramics has not been found in thin film PZTs. From the result of nonlinear behavior between piezoelectric response and ac amplitude, extrinsic contribution (non-180° domain wall motion) in these films has been found to be negligible, indicating that extrinsic contribution in room temperature dielectric constant is dominated by only 180° domain wall motion.; The semi-empirical phenomenological equation for piezoelectric coefficient has been demonstrated to account very well for the quantitative estimation in these PZT thin films when extrinsic contribution is negligible. Small deviation between calculated and measured piezoelectric coefficients as well as the dependence of piezoelectric and polarization behavior on the external dc field, i.e., hysteresis loop, have been suggested, primarily due to backswitching of 180° domains. Temperature dependence of polarization behavior as well as poling effects on the dielectric and piezoelectric behavior have been examined to support this hypothesis. The results of orientation and thickness effect have shown that the effect of polydomain structure could be explained in terms of a tilted polarization axis (misfit grains), interfacial layers, internal bias, defects, microstructure, crystallinity, and residual stress. These parameters have been found to affect both intrinsic and extrinsic contributions.; Engineering implication for successful incorporation PZT thin films into an electromechanical device is that designing PZT systems for maximization of intrinsic contribution is more important than controlling non-180° domain wall activity like bulk ceramics.