IMPROVED PERFORMANCE OF PASSIVE LAYER-FREE CURVED PMUT ARRAY

We have successfully demonstrated a novel, passive layer-free, curved piezoelectric micromachined ultrasound transducer (PMUT) array using a sacrificial curved glass template and 30% scandium-doped aluminum nitride (Sc-AlN) as the active layer. The PMUTs were fabricated using a curved, suspended borosilicate glass template created via a chip-scale glass-blowing technique, onto which electrodes and the piezoelectric layer were deposited. The glass layer was thereafter selectively removed. We characterized the performance of a 13 ×13 curved PMUT (cPMUT) array using an electrical impedance analyzer, a Laser Doppler Vibrometer (LDV), and hydrophone pressure measurements. Our results reveal a device resonance frequency of approximately 1.8 MHz in air, with LDV analysis indicating a significantly enhanced low-frequency response of 1.68 nm/V—a fivefold improvement over conventional curved PMUTs with a passive layer. Additionally, acoustic characterization in water showed that this array generates an acoustic pressure of approximately 80 kPa at a 4.4 mm focal distance, with a beam width of 5 mm, and achieves a spatial peak pulse average intensity (ISPPA) of 216 mW/cm² when driven off-resonance. Furthermore, we demonstrate 20-degree steering capability using our data acquisition system. These advancements highlight significant potential for enhancing the precision and efficacy of medical imaging and therapeutic applications, particularly in ultrasonic diagnostics and treatments.