Tensile and compressive stress dependency of the transverse (e31,f) piezoelectric coefficient of PZT thin films for MEMS devices

Two measurement methods are presented to determine precisely and reliable the electrical and electromechanical response of piezoelectric thin film structures. A double beam laser interferometer (DBLI) was used to measure large signal polarization, displacement, dielectric constant and the effective longitudinal piezoelectric coefficient d_33,f in out of plane direction of the film. Secondly, a unique and newly developed measurement setup based on a 4-point bending sample holder for cantilever devices was used to determine the transverse effective piezoelectric coefficient e_31,f. This setup allows the application of precisely defined and homogeneous in plain mechanical strains to the piezoelectric film. The homogeneous stress and strain distributions were proved by Finite Element Simulations. Additional measurements have been performed to investigate the influence of in plane mechanical preloads on the transverse coefficient. Measurements are shown on Pb(Zr₅₃,Ti₄₇)O₃ (PZT) thin film samples deposited by a sol-gel based chemical solution deposition process which was optimized to maximize the e_31,f coefficient. Exceptional high e_31,f coefficients demonstrate the quality of the processed films.