A Hybrid MEMS Microphone Combining Piezoelectric and Capacitive Transduction Mechanisms

This work describes a hybrid micro-electro-mechanical-systems (MEMS) microphone based on combined piezoelectric and capacitive transduction mechanisms to enhance the sensitivity. The fabrication process for the proposed hybrid MEMS microphone is presented. A lumped element model of the prototype is derived and employed for device design. The microphone is fabricated on a silicon-on-insulator (SOI) wafer. Piezoelectric transduction is realized by a piezoelectric diaphragm consisting of a stack of Si/SiO2/Pt/PZT/Pt layers. Capacitive transduction is realized by a variable capacitor composed of a silicon device layer and a silicon handle layer. The measured sensitivities of the piezoelectric and capacitive parts of the hybrid MEMS microphone are −51.18 dB (re: 1 V/Pa) and −57.59 dB at 1 kHz, respectively. The signal-to-noise ratios (SNR) of the piezoelectric and capacitive parts of the microphone are 49.21 dB (re: 1 V/Pa) and 60.71 dB at 1 kHz, respectively. By combining dual output signals from piezoelectric and capacitive transduction mechanisms, the measured sensitivities and SNR are −47.63 dB (re: 1 V/Pa) and 52.57 dB at 1 kHz, respectively. The experimental results demonstrate that the sensitivity of the hybrid transduction microphone is improved by 3.55 dB and 9.96 dB compared to individual piezoelectric and capacitive transduction modes, respectively.[2024-0218]