Aln Based Piezoelectric Micromachined Ultrasonic Transducers for Continuous Monitoring of the Mechano-Acoustic Cardiopulmonary Signals

Abstract

This paper presents, for the first time, Aluminum Nitride (AlN) based Piezoelectric Micromachined Ultrasonic Transducers (PMUTs) with high fill-factor and high acoustic sensitivity for continuous monitoring of the mechano-acoustic cardiopulmonary signals. The sensing cells of the reported PMUTs are designed and arranged as honeycomb architecture. The honeycombs innovative structural system not only achieves high fill-factor, but also enhances the acoustic sensitivity of the PMUTs. An 8 × 9 array of 180 μm side-length, 1.08 MHz PMUTs is fabricated based on an AlN-on-Cavity Silicon-on-Insulator (CSOI) platform. The fabricated PMUTs array achieves an acoustic pressure sensitivity of -178 dB (re: 1 V/μPa) and a signal-to-noise ratio of around 52 dB at 500 Hz. The PMUTs array is die-attached on their condition circuit and packaged with medical ultrasonic couplants to acquire wideband mechano-acoustic physiological signals, which achieves continuous monitoring of varieties of health factors associated with the cardiopulmonary system, such as heart rate, heart sound, respiratory rate and lung sound.