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-SOI lamination process, culminating in a dimension of 6 mm x 6 mm with a 6x6 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 (e31,f / ϵ0ϵ33,f) to 66.2 GV/m. Additionally, 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 ±2 dB (ref. 1 V /μPa), with a sensitivity variation of no more than ±0.8 dB from 10 ℃ to 50 ℃, and a self-noise value of 56 dB (ref. 1 μPa/√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.