Design and Test of a High-Sensitivity MEMS Capacitive Resonator for Photoacoustic Gas Detection

This article presents the design, fabrication, and test of a high-sensitivity micro-electromechanical systems (MEMS) capacitive resonator specifically designed for photoacoustic gas detection. The sensor employs area-variable capacitive detection by surrounding the silicon resonator with dense comb teeth. To mitigate the effects of gas damping on the resonator motion, the gap between the movable structure and the substrate was increased to $260 \mu \text{m}$ . This approach effectively resolves the capacitance detection sensitivity and motion damping trade off typically encountered in acoustic detection. Under the excitation of sound waves, the resonator demonstrated a maximum sensitivity of 3749 mV/Pa at its resonant frequency of 1870 Hz when subjected to a bias voltage of 15 V. The equivalent noise exhibited a peak value of $7.9 \mu $ Pa/Hz1/2. Subsequently, the resonator was integrated into a carbon dioxide gas detection system based on photoacoustic spectroscopy (PAS). A sensitive measurement of gas concentrations was performed successfully. The minimum detection limit (MDL) estimated by noise equivalent concentration was determined to be 0.58 ppb at an average time of 49 s. The normalized noise equivalent absorption (NNEA) was calculated to be $8.45\times 10^{-{9}}$ cm $^{-{1}}\cdot \text{W}\cdot $ Hz−1/2. The experimental results demonstrate the exceptional performance among photoacoustic gas detection systems utilizing capacitive sensors.