Effects of thickness on the piezoelectric and dielectric properties of lead zirconate titanate thin films

Lead zirconate titanate (PZT) thin films with a Zr/Ti ratio of 52/48 were deposited on platinized silicon substrates by a sol-gel method and crystallized with preferred (111) or (100) orientation. Both the piezoelectric properties (d₃₃) and the field-induced strains of the films with different thickness and preferred orientation were measured by a laser Doppler heterodyne interferometer. The weak-field dielectric constants and dissipation factors were also measured as a function of film thickness for comparison with other work reported in the literature. The field-forced polarization switching (P-E) behavior was examined by Sawyer-Tower measurement. Both the piezoelectric properties and the dielectric constants of the PZT thin films were found to be strongly dependent on the film thickness. An increase in the piezoelectric constants and dielectric constants with increasing film thickness was observed for both films with preferred (111) and (100) orientations. Films with (100) preferred orientation were found to have higher piezoelectric constants and lower dielectric dissipation factors than films with (111) preferred orientation. A finite element analysis was carried out to evaluate the existing methods for determination of the d₃₃ coefficient of ferroelectric thin films. The measured changes in properties with thickness were correlated with the residual stress state in the films.