A ScAlN Piezoelectric High-Frequency Acoustic Pressure-Gradient MEMS Vector Hydrophone With Large Bandwidth

In this letter, a scandium-doped aluminum nitride (Sc _x ${\mathrm {Al}}_{1-x}\text{N}$ , x = 9.5%) piezoelectric high-frequency MEMS vector hydrophone with large operation bandwidth is presented, which measures acoustic pressure gradient underwater. The hydrophone sensor consists of four groups of sensing cell arrays. Each sensing cell is composed of a hexagonal sensing diaphragm made up of a piezoelectric stack of ScAlN piezoelectric thin-film sandwiched by Mo and highly doped single-crystal silicon, with a top and a bottom oxide film surrounding the piezoelectric stack. The hydrophone sensor can operate in not only omnidirectional receive mode, but also dipole receive mode, depending on the signal processing algorithm used for the four array groups. The vector hydrophone operates in the frequency range of 20 kHz to 160 kHz, which is specially designed to monitor the dolphin calls. The measured maximum receive sensitivity is -175 dB (re: 1 V/ $\mu $ Pa) in the dipole receive mode at 160 kHz and −169±2 dB (re: 1 V/ $\mu $ Pa) in the omnidirectional receive mode in the operation bandwidth, respectively. The reported vector hydrophone also presents a smooth directivity pattern at 100 kHz. The experiments show the reported MEMS vector hydrophone has good potential in conservation of dolphins and other underwater detection at high frequency between 20 kHz to 160 kHz.