Residual Stress and Membrane Deflection Influences on the Ultrasonic Sensor Device

The influences of residual stress on the piezoelectric ultrasonic sensors having composite membrane structure included PZT (Pb(Zr_0.52Ti_0.48)O₃) thin film are presented. Due to the different thermal and elastic characteristics of each constitutive layer, a subsequent residual stress and deflection is usually generated on the composite membrane. We discuss the influences of residual stress on the Si-based integrated sensor device in the two point of view; the mechanical behaviors and piezoelectric thin film properties. The composite layer structure and fabrication process especially related to thermal process have significant effects on the stress state of the composite membrane. The relationships among the stress states, deflections of composite membrane and sensitivities of sensor devices are considered.