HIGH PRESSURE OUTPUT 40 kHz AIR COUPLED PIEZOELECTRIC MICROMACHINED ULTRASONIC TRANSDUCERS

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, e(31,f2)/epsilon(r)epsilon(o)) 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 A1N PMUTs. Comparing to prior PZT PMUTs, the single-crystal PZT used here has low permittivity (epsilon(r) = 308) and high piezoelectric coefficients (e(31, f) similar to 24.5), resulting in low insertion loss. Acoustic experiments conducted with commercial ultrasonic transducers and reference microphones show that a 2x2 array PMUTs has 1.91mV/Pa (-74.3dB) receive sensitivity, demonstrating much higher efficiency per unit transducer volume compared to conventional transducers.