Miniaturized two-chamber photoacoustic CO.sub.2 sensor with a wafer-bonded MEMS detector

• Published in: Journal of sensors and sensor systems Vol. 13; no. 2; pp. 219 - 437
• Main Authors: Gaßner, Simon, Essing, Simon, Tumpold, David, Schmitt, Katrin, Wöllenstein, Jürgen
• Format: Journal Article
• Language: English
• Published: Copernicus GmbH 02.08.2024
• Subjects: Air quality; Microelectromechanical systems; Sensors
• ISSN: 2194-8771; 2194-878X

The measurement of air quality, particularly the concentration of carbon dioxide (CO.sub.2 ), has gained significant interest due to increased public health awareness. Elevated concentrations of CO.sub.2 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 CO.sub.2 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 CO.sub.2 -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 CO.sub.2 molecules. The complete sensor module measures only 9x13x7.8 mm.sup.3 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 CO.sub.2 and exhibits a response time Ï.sub.63 of 53 s. The compact size and performance characteristics make the proposed sensor module suitable for applications in indoor air quality monitoring.