Piezoelectric MEMS-Based Underwater Acoustic Vector Sensor: Design and Characterization

Abstract

This study introduces a novel microfabrication approach for developing a directional hydrophone with a distinctive design incorporating cross-shaped piezoelectric cantilevers. In the microfabrication process, a thin layer of aluminum nitride (AlN), featuring Molybdenum (Mo) thin film electrodes, is utilized as the piezoelectric functional layer for a cantilever-based underwater ultrasonic microelectromechanical system (MEMS) hydrophone. Through parameterized simulation, the length of the cantilevers is systematically adjusted within the range of 100 to 1000 μm to achieve the first resonant mode within the 20 kHz to 200 kHz frequency spectrum, aligning with the targeted underwater ultrasonic acoustic frequencies. The microsystem design incorporates cantilevers arranged in a cross configuration, aiming to realize a unique MEMS hydrophone with omnidirectional response capabilities. To investigate the first resonance frequency mode and displacement measurements, a Laser Doppler Vibrometer is employed, demonstrating a robust correlation between simulation predictions and experimental data. In-water responsivity and directionality assessments of the piezoelectric MEMS cantilevers reveal a maximum sensitivity of up to -153 dB, accompanied by an omnidirectional directivity pattern achieved by the fabricated MEMS sensor.