Ultrathin Diaphragm Curved Piezoelectric Micromachined Ultrasound Transducers Enabling 2.5V Low Voltage Artery Monitoring

Current ultrasound sensors used for wearable blood pressure monitoring typically require driving voltages above 15 V. This study aims to enhance device sensitivity to enable low-voltage operation, thereby reducing power consumption and improving user safety. We propose an ultrathin curved piezoelectric micromachined ultrasonic transducer (PMUT) featuring a 0.5 $\mu$m aluminum nitride (AlN) film, which exhibits a resonance frequency of 7.5 MHz in water. The curved PMUT array exhibits a 1.8× improvement in unit-area transmitting sensitivity and a 2.6× enhancement in unit-area echo sensitivity compared to a planar PMUT array fabricated with the same piezoelectric material. Continuous in vivo monitoring of radial artery diameter was performed using a 2.5V driving voltage, validating its feasibility for noninvasive blood pressure measurement. The proposed curved PMUT offers an innovative solution for wearable ultrasonic sensing, featuring high sensitivity, low power consumption, and enhanced circuit integration, positioning it as a promising candidate for next-generation physiological monitoring devices.