Stress influences on the ultrasonic transducers

Arrayed ultrasonic transducers using the piezoelectric thin film (PZT) are fabricated with multilayer diaphragm structures. Due to the different thermal and elastic characteristics of each constitutive layer, residual stress is generated during high temperature deposition processes, and the resultant composite membrane is consequently bowing. We present the influences of residual stress on the resonant frequency (fr) and sensitivities of each sensor structure. Two type sensor devices are fabricated, and the frs of those are practically estimated. For the simulation of structural fr variations, the sensor structures having ideal and bended membrane are modeled, and the finite element analysis are carried out using ANSYS 7.1. The bended structures are represented almost same fr with practically measured ones, which is substantially higher than that of ideal ones meaning that the frequency deviations are mainly originated from the membrane deformations. The stiffness variations originated from the stress generations have important effects on the quality factors of vibrations, while those have not so large influences on the fr determinations. Sensitivities of each sensor structure are increased with increasing the membrane deflection intensities. These results are discussed relating to the stress generations and mechanical behaviors of composite membrane structures.