A Single-Chip AlScN PMUTs-on-CMOS Hydrophone

This work presents a minute single-chip piezoelectric micromachined ultrasonic transducers (PMUTs)-on-complementary metal-oxide-semiconductor (CMOS)-based hydrophone with high receiving sensitivities and low noise. The system is based on three different Sc9.5%Al90.5%N PMUTs geometries: (a) square with an
$80 \, \mu $
m side, (b) rectangular with a dimension of
$60 \times 40 \, \mu $
m, and (c) annular with an outer diameter of
$80 \, \mu $
m which allows to carry out acoustic measurements at very close distances from the transducer under test. Each device is monolithically integrated with a CMOS low noise amplifier (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 1 V/
$\mu $
Pa (equivalent to 1.9 V/MPa), -234.6 dB re 1 V/
$\mu $
Pa (equivalent to 1.86 V/MPa), and -238.3 dB re 1 V/
$\mu $
Pa (equivalent to 1.22 V/MPa) for (a)–(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.