Aln Based Piezoelectric Micromachined Ultrasonic Transducers for Continuous Monitoring of the Mechano-Acoustic Cardiopulmonary Signals
Licheng Jia, Lei Shi, Chengliang Sun, Sheng Liu, Guoqiang Wu
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.