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

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]