Design and Implementation of 6 × 6 Array Piezoelectric AlN Hydrophone With High Sensitivity

This paper presents the design, fabrication and characterization of a MEMS piezoelectric hydrophone based on Silicon-On-Insulator (SOI), using Aluminum Nitride (AlN) as the functional piezoelectrical material. The hydrophone has a
${6}\times {6}$
array and a sandwich structure composed of Molybdenum-Aluminum-Molybdenum (Mo-AlN-Mo) films. The three-layered films adhere back cavities that have a radius of
$200~ \boldsymbol {\mu }\text{m}$
and a pitch of
$400~ \boldsymbol {\mu }\text{m}$
. The hydrophone shows proximal resonance frequencies of 479 kHz and 476 kHz under Impedance and Doppler tests, respectively. The initial deformation of the diaphragm is avoided by using a hollow PCB in the packaging to keep the hydrophone in a pressure-equalizing environment. The hydrophone is characterized in both water and air platforms. In water, the hydrophone has a sensitivity of −172.6 dB in the range of 100-2000 Hz, and a linearity of 99% at 1000 Hz, whereas in air it has a linearity of 98% at 1000 Hz. These results demonstrate the potential of high performance miniaturized hydrophone systems for wide-band and low-frequency applications.