Design and Implementation of PZT Piezoelectric Micromachined Ultrasonic Transducers for Distance Sensing

This paper presents two PZT piezoelectric micromachined ultrasonic transducer (PMUT) designs for distance sensing applications, fabricated using a foundry-compatible multi-project wafer (MPW) process. By leveraging distinct PZT mode shapes within identical suspended membrane areas, the PMUTs achieve enhanced operating frequencies and sensitivity. The single-mode and differential-mode PMUTs operate at resonant frequencies of 849 kHz and 2.39 MHz, which correspond to maximum sensing distances of 2.5 cm and 2 cm, respectively. The measured sensitivities are 226.7 nm/V and 9.6 nm/V for actuation and 0.18 mV/nm and 1.07 mV/nm for sensing. At ~0.5 cm, the differential-mode PMUT offers 1.78 times the sensitivity of the single-mode. Furthermore, at ~ 1.5 cm, ultrasonic signal attenuation caused by biological obstacle (e.g., a finger) remains minimal at approximately 5%.