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We present a concept for a wafer-level manufactured photoacoustic transducer, suitable to be used in consumer-grade gas sensors. The transducer consists of an anodically bonded two-layer stack of a blank silicon wafer and an 11 µm membrane, which was wet-etched from a borosilicate wafer. The membrane separates two cavities; one of which was hermetically sealed and filled with CO2 during the anodic bonding and acts as an infrared absorber. The second cavity was designed to be connected to a standard MEMS microphone on PCB-level forming an infrared-sensitive photoacoustic detector. CO2 sensors consisting of the detector and a MEMS infrared emitter were built up and characterized towards their sensitivity and noise levels at six different component distance ranging from 3.0 mm to 15.5 mm. The signal response for the sample with the longest absorption path ranged from a decrease of 8.3% at a CO2 concentration of 9400 ppm to a decrease of 0.8% at a concentration of 560 ppm. A standard deviation of the measured values of 18 ppm was determined when the sensor was exposed to 1000 ppm CO2.

We present a sophisticated method to improve the sensitivity of CO2-detecting non-resonant MEMSbased photoacoustic gas spectroscopy systems by more than 50 % compared to state-of-the-art approaches. The method based on signal demodulation can also be used to linearize the measured system's response in order to reduce the calibration effort for future sensors. Tuning the filter transmission spectra accordingly is utilized to further increase the linearity of the system response and enhancing the sensitivity by more than 200 %.

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The increasing interest in monitoring indoor air quality has led to a growing demand for simple and smallscale gas sensors. We present a miniaturized photoacoustic dual chamber sensor module that includes an infrared hotplate emitter and a wafer-level manufactured photoacoustic detector. The sensor module was controlled by a PSoC 4200M microcontroller and is capable of being soldered in a SMD reflow soldering process. The sensor prototype achieves a 3-sigma noise level of 138 ppm CO2, which is suitable for most consumer applications.