Enhanced Transmission and Low-Voltage Performance of Sealed-Silicon-Cavities PMUTs

This work presents sealed-silicon-cavity piezoelectric micromachined ultrasonic transducers (SSC-PMUTs) fabricated via high-temperature silicon surface migration, eliminating fragile release steps and complex cavity bonding while maintaining array design flexibility. Two device configurations demonstrate displacement sensitivities of$95 ~\text{nm} / \mathrm{V}$at 3.89 MHz and$42 ~\text{nm} / \mathrm{V}$at 7.09 MHz, with electromechanical coupling coefficients of 2.53 % and 2.0 %, respectively. Pulse-echo measurements reveal transmit sensitivities of$2.0-2.78 \text{MPa} / \mathrm{V}$at 2 Vpp. The migration-sealed architecture exhibits fractional bandwidths of 22.6 % and 24.9 %, and beamwidths of$5-13^{\circ}$depending on pitch, confirming excellent directivity control. These results establish SSC-PMUTs as a robust, power-efficient platform for biomedical imaging and industrial sensing, achieving superior pressure-per-volt efficiency through simplified wafer-level manufacturing and enhanced device reliability.