Bistable Snap-Through Nonlinear Mode PMUT with Remarkable Bandwidth and Mid-Air Transmission

Lead-free Aluminum Nitride (AIN) piezoelectric micromachined ultrasonic transducer (PMUT) is a promising candidate for miniaturized bio-compatible ultrasonic systems and consumer electronics. However, it suffers from material-associated poor transmitting performance and a narrow mid-air bandwidth. Here, by harnessing the nonlinearity-triggered “snap-through” effect of the PMUT diaphragm, we developed a novel bistable mode 30 % Sc-doped AlN PMUT with an enhanced mid-air bandwidth and a significant vibration amplitude beyond the inherent piezoelectricity. The proposed bistable snap-through$\text{Sc}_{0.3} \text{Al}_{0.7} \mathrm{N}$PMUT demonstrated remarkable mid-air transmission with a displacement over$6.2 \mu \mathrm{m}$, a sensitivity greater than 3$\mu \mathrm{m} / \mathrm{V}$, a vibration velocity up to$6.74 \mathrm{m} / \mathrm{s}$, and an impressive 35 -fold velocity improvement over monostable vibration at a specific excitation frequency. Additionally, it has an exceptional bandwidth of 84.5 kHz, spanning the range from 121.5 kHz to 206 kHz in air.