Equidimensional Piezoelectric Micromachined Ultrasonic Transducer Array With Synchronously Improved Bandwidth and Sensitivity

Abstract

Common methods to enhance PMUT arrays’ Bandwidth (BW) may compromise the sensitivity and fill factor. This study introduces a novel PMUT array with circular suspended plate structure and variable mass load atop the membranes to establish identical cell size but different resonant frequencies, and finally achieves a broad BW, improved sensitivity and augmented fill factor. Four such kinds PMUT arrays (20 element $\times 25$ cells) with different mass loads are studied and compared to traditional one with clamped boundary. In each design, 13 variations of cells equipped with varying-diameter mass load are integrated in one element (25 cells), resulting in a notable large BW. This design features PMUTs with an equidimensional cell size, leading a heightened filling factor compared to current wideband PMUTs with multi-size cells. Prototyped devices are fabricated and show a 1.7X improvement in membrane volume displacement, 1.5X higher ultrasound pulse-echo sensitivity and 5.2X increase in BW, from 17% to 89% @ 5.5 MHz center frequency, comparing to the traditional one. This innovative design suggests a promising solution for high sensitivity and wideband PMUT arrays, benefiting high-quality ultrasound imaging. [2024-0055]