Transmitting Sensitivity Enhancement of Piezoelectric Micromachined Ultrasonic Transducers via Residual Stress Localization by Stiffness Modification

Residual stress dramatically affects the performance of piezoelectric micromachined ultrasonic transducers (pMUTs), in particular, the transmitting sensitivity. This letter presents a novel architecture for pMUTs with V-shaped springs. Stiffness modification achieved by the V-shaped springs contributes to localize the residual stress, resulting in a flat vibrating membrane rather than a curved one. The experimental results show that the initial deflection of the vibration membrane is less than 10 nm or 0.004% (deflection/membrane size) for the enhanced pMUT. Leveraging on the flat vibrating membrane, the transmitting sensitivity of the enhanced pMUT is 50.9 nm/V, which is 203% higher than the pMUT without springs. Combining with the piston-like mode shape, the output sound pressure of the pMUT can be improved by around 23 dB.