Comprehensive parametric study of curved piezoelectric micromachined ultrasonic transducers

Piezoelectric micromachined ultrasonic transducers (PMUTs) hold strong promise for miniaturized, energy-efficient ultrasound devices; however, conventional designs exhibit limited electromechanical coupling and biocompatibility. Here we present a comprehensive parametric study investigating the effects of electrode coverage, curvature, and passive layer thickness on the performance of lead-free scandium aluminum nitride (ScAlN)-based curved PMUTs (cPMUTs). Combining finite element modeling with experimental measurements of laser Doppler vibrometry and impedance spectroscopy, we identify design strategies to maximize displacement and electromechanical coupling of cPMUTs. Passive-layer-free cPMUTs achieve low-frequency displacements up to 8 nm V⁻¹ and effective coupling coefficients of 6.5%. A 20-element linear cPMUT array, under low voltage operation enables focused and electronically steerable beams with peak-to-peak pressures of approximately 300 kPa, and a 6 dB fractional bandwidth of 73%. Phantom experiments demonsrate dual-modality B-mode ultrasound and photoacoustic imaging in real-time. Together, this work provides the first systematic design framework for optimizing ScAlN cPMUTs for multimodal imaging and therapeutic applications.