Miniaturized two-chamber photoacoustic CO2 sensor with a wafer-bonded MEMS (micro-electro-mechanical systems) detector

The measurement of air quality, particularly the concentration of carbon dioxide (CO2), has gained significant interest due to increased public health awareness. Elevated concentrations of CO2 in the air have been linked to negative effects on cognitive functions and directly correlate with the quality of indoor air. This work presents the prototype of a miniaturized sensor module designed for sensing CO2 concentrations in the air. The sensor module utilizes the two-chamber photoacoustic concept and features a compact design combining an absorption cell with a wafer-bonded detector based on silicon MEMS (micro-electro-mechanical systems) microphone technology. The CO2-filled detector chip uses the photoacoustic effect and is able to detect pressure oscillations within an enclosed volume generated by the absorption of modulated infrared (IR) light by CO2 molecules. The complete sensor module measures only 9×13×7.8 mm3 and the used detector chip is the smallest detector for two-chamber photoacoustic sensors reported to date. Experimental characterization showed that the prototype achieves a detection limit of 81 ppm CO2 and exhibits a response time τ63 of 53 s. The compact size and performance characteristics make the proposed sensor module suitable for applications in indoor air quality monitoring.