Comparative measurements of piezoelectric coefficient of PZT films by Berlincourt, interferometer, and vibrometer methods.

Chemical solution deposition (CSD) techniques were used to prepare lead zirconate (Zr) titanate (Ti) (PZT) thin films with Zr/Ti ratios of 30/70 and 52/48. Usually CSD processing is restricted to making crack-free, single-layer films of 70-nm thick, but modifications to the sol-gel process have permitted the fabrication of dense, crack-free, single layers up to 200 to 300 nm thick, which can be built-up into layers up to 3-microm thick. Thicker PZT films (> 2-microm single layer) can be produced by using a composite sol-gel/ceramic process. Knowledge of the electroactive properties of these materials is essential for modeling and design of novel micro-electromechanical systems (MEMS) devices, but accurate measurement of these properties is by no means straightforward. A novel, double-beam, common-path laser interferometer has been developed to measure the longitudinal (d33) piezoelectric coefficient in films; the results were compared with the values obtained by Berlin-court and laser scanning vibrometer methods. It was found that, for thin-film samples, the d(33,f) values obtained from the Berlincourt method are usually larger: than those obtained from the interferometer and the vibrometer methods; the reasons for this are discussed.