Fabrication and Evaluation of the Low-Frequency Underwater Acoustic Arrayed Sensor Based on High-Quality VZO Film

This article presents a novel MEMS piezoelectric arrayed sensor based on vanadium-doped zinc oxide (VZO) thin films, specifically engineered to achieve heightened sensitivity in underwater acoustic measurements. The sensor design features a VZO-on-silicon-on-insulator (SOI) lamination process, culminating in a dimensions of $6\times 6$ mm with a $6\times 6$ element structure. The preparation of VZO films entails the meticulous optimization of magnetron sputtering parameters, a pressure of 0.8 Pa, a power setting of 80 W, and an argon-to-oxygen ratio of 40:15, resulting in reduced surface roughness of 2.4 nm and an optimized grain size of 15.9 nm. These optimizations facilitate the fabrication of high-performance films, enhancing the piezoelectric coefficient to 120.6 pm/V, with a significant increase in the figure of merit ( ${e}_{{31},{f}}$ / $\epsilon _{{0}}~\epsilon _{{33},{f}}$ ) to 66.2 GV/m. In addition, an underwater acoustic measurement system is established to assess the sensor’s efficacy. During system evaluations, the sensor consistently exhibits a stable sensitivity of $- 173~\pm ~2$ dB (ref. 1 V/ $\mu $ Pa), with a sensitivity variation of no more than ±0.8 dB from $10~^{\circ }$ C to $50~^{\circ }$ C, and a self-noise value of 56 dB (ref. $1~\mu $ Pa/ $\surd $ Hz) at the frequency range of 1 kHz. The investigation not only refines the design and manufacturing processes of MEMS piezoelectric sensors but also yields critical insights for the advancement of high-performance hydrophones.