Enhanced-Performance ScAlN MEMS Piezoelectric Hydrophones Enabled by Cross-Array Architecture

This work focuses on the structural design of a ScAlN-based piezoelectric hydrophone for microelectromechanical systems (MEMS), with particular emphasis on analyzing the impact of the fill factor on the device's acoustic and electromechanical performance. Two hydrophone arrays with distinct configurations were designed and fabricated: a matrix arrangement and a cross arrangement. Both arrays employ identical cell structure dimensions and functional layer thicknesses, and are fabricated on the same 4-inch Silicon-On-Insulator (SOI) wafer to ensure process consistency. Among these, the cross-arranged (CA) chip achieves a 45.45% higher fill factor than the matrix-arranged (MA) chip through a more compact arrangement design. Performance test results indicate that the CA chip demonstrates significantly enhanced performance. During air testing, its electromechanical coupling coefficient reached 13.70%, representing a 106.9% improvement over the 6.62% achieved by the MA chip. During underwater testing, the sensitivity of the CA chip in the 100 kHz-200 kHz frequency band was -175.7 ± 4.3 dB (re:1V/μPa). In contrast, the MA chip's sensitivity was -179.7 ± 2.5 dB (re:1V/μPa), resulting in an average improvement of approximately 2.7%. This study clearly demonstrates that a higher fill factor can effectively enhance the key acoustic performance of hydrophones. This finding provides essential guidance for the optimized design of future high-performance MEMS hydrophones.