High-Pressure Output 40 kHz Air-Coupled Piezoelectric Micromachined Ultrasonic Transducers

Abstract

This paper presents air-coupled piezoelectric micromachined ultrasonic transducers (PMUTs) fabricated from single-crystal PZT, enabling very high sound pressure level (SPL) output of 100.3 dB at 33 cm distance. The single-crystal PZT deposited via PVD has low permittivity, enabling the highest figure of merit (FOM, e31j <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /εrε0) PMUTs to date. The PMUTs operate at a low resonant frequency of 40 kHz, which results in lower acoustic absorption loss and therefore longer operating distance, and have 10X greater mechanical displacement and SPL output compared to prior-art AlN PMUTs. Comparing to prior PZT PMUTs, the single-crystal PZT used here has low permittivity ( εr=308) and high piezoelectric coefficients ( e31, f ~ 24.5), resulting in low insertion loss. Acoustic experiments conducted with commercial ultrasonic transducers and reference microphones show that a 2×2 array PMUTs has 1.91mV/Pa (-74.3dB) receive sensitivity, demonstrating much higher efficiency per unit transducer volume compared to conventional transducers.