Sc₀.₁Al₀.₉N-Based Bimorph Piezoelectric MEMS Microphones With Tractive Structures

Scandium-doped aluminum nitride (ScAlN) can effectively improve the piezoelectric coefficient; meanwhile, the bimorph obtains a higher sensitivity per unit area than a unimorph structure, thereby greatly improving the sensitivity of MEMS sensors. This article proposes Sc0.1Al0.9N-based bimorph piezoelectric MEMS microphones with tractive structures, which generate a larger high-stress area during operation compared with conventional cantilevers based on finite element method (FEM) simulation and analytical methods. Four electrical connections are designed as components with the tractive structure on the same area of only 0.4679 mm2. The devices are fabricated on a thermal oxide silicon wafer using a nine-mask process. Acoustic measurements show that the maximum unamplified sensitivity is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$353.79~\mu $ </tex-math></inline-formula>V/Pa from the combined series-parallel electrical connection, which is 75% higher than the full series electrical connection of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$208.27~\mu $ </tex-math></inline-formula>V/Pa. Furthermore, the combined series-parallel electrical connection exhibits grateful performance, where both unamplified and amplified minimum detectable pressure (MDP) are 2 mPa, the signal-to-noise ratio (SNR) is 48.3 dB, and the total harmonic distortion (THD) is only 0.96% at 1 kHz. This work demonstrates a small-size, high-sensitivity piezoelectric MEMS microphone with combined series-parallel connection, which has great commercial value for future scenarios.