A Single-chip AlScN PMUTs-on-CMOS hydrophone

This work presents a minute single chip PMUTs-on-CMOS-based hydrophone with high receiving sensitivities and low noise. The system is based on three different Sc 9.5% Al 90.5% N PMUTs geometries, (a) square with an 80 μm side, (b) rectangular with a dimension of 60 μm x 40 μm, and (c) annular with an outer diameter of 80 μm which allows to carry out acoustic measurements at very close distances from the transducer under test. Each device is monolithically integrated with a CMOS LNA amplifier with a gain of 25 dB. The first hydrophone prototype was validated in water where two commercial hydrophones from ONDA (HGL-0085 and HNC-0200) were used as references. The experimental results give mean receiving sensitivities of -234 dB re 1V/μPa (equivalent to 1.9 V/MPa), -234.6 dB re 1V/μPa (equivalent to 1.86 V/MPa) and -238.3 dB re 1V/μPa (equivalent to 1.22 V/MPa) for (a), (b) and (c), respectively. These results demonstrate the high performance of the presented PMUTs-on-CMOS to be used in a miniaturized hydrophone for characterizing high-frequency ultrasound transducers.