A High-Performance 9.5% Scandium-Doped Aluminum Nitride Piezoelectric MEMS Hydrophone With Honeycomb Structure

Abstract

This letter presents a high-performance scandium-doped aluminum nitride (Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-<i>x</i></sub> N, x = 9.5%) piezoelectric MEMS hydrophone. The doping of Sc increases the piezoelectric constants of the piezoelectric sensing layer and hence results in better receive sensitivity for the ScAlN-based piezoelectric MEMS hydrophone. The sensing cells of the MEMS hydrophone sensor are designed in a bioinspired honeycomb structure for achieving high fill-factor and thus a large receive sensitivity. The top electrodes of the sensing cells are split into the inner and outer sections with optimized size ratios for differential readout, which further enhances the sensor’s sensitivity. The receive sensitivity is improved even further by reducing the top oxide thickness on the sensing diaphragm. The best measured receive sensitivity of the reported MEMS hydrophone with differential readout is −164.5 dB (re: 1 V/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> Pa). An equivalent noise density as low as 44 dB (re: <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1 ~\mu $ </tex-math></inline-formula> Pa/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\surd $ </tex-math></inline-formula> Hz) at 1kHz is achieved. These metrics are much better than those of state-of-the-art bulk piezoceramic hydrophones as well as other reported piezoelectric MEMS hydrophones.