Abstract
Downsizing and compatibility with MEMS silicon foundries is an attractive path towards a large diffusion of photoacoustic trace gas sensors. As the photoacoustic signal scales inversely with the chamber volume, a trend to miniaturization has been followed by several teams. We review in this article the approach initiated several years ago in our laboratory. Three generations of components, namely a 40 mm3 3D-printed cell, a 3.7 mm3 silicon cell, and a 2.3 mm3 silicon cell with a built-in piezoresistive pressure sensor, have been designed. The models used take into account the viscous and thermal losses, which cannot be neglected for such small-sized resonators. The components have been fabricated either by additive manufacturing or microfabrication and characterized. Based on a compilation of experimental data, a similar sub-ppm limit of detection is demonstrated. All three versions of photoacoustic cells have their own domain of operation as each one has benefits and drawbacks, regarding fabrication, implementation, and ease of use.
Highlights
Integration on silicon platform led in the recent years to major successes in the domain of micro-electromechanical systems (MEMS)
As the photoacoustic signal is inversely proportional to the chamber volume [2], a straightforward way to improve the sensor resolution consists in reducing its size
We review hereunder the existing literature on miniaturized sensors from two different perspectives towards cost reduction: (i) additive manufacturing, nowadays limited to small-scale production, and (ii) silicon microfabrication in MEMS foundries, well adapted to high-volume production
Summary
Integration on silicon platform led in the recent years to major successes in the domain of micro-electromechanical systems (MEMS). At the University of Freiburg, Palzer et al intend to build an entire sensor, including a mid-infrared LED source, compatible with integration in a smartphone, at the expense of reduced performances [7] Their measurement principle relies on a combination of absorption spectroscopy and photoacoustics. On the other hand, relying on silicon microfabrication techniques has first been considered, more than 20 years ago, by Weber et al [8] They imagined, but apparently never realized, a complete sensor composed of a filtered blackbody infrared source, a PA chamber, and a suspended membrane, detecting the pressure fluctuations by capacitive or piezoelectric means. A few years later, the same principle was successfully implemented by Ledermann et al [9] They combined a commercial micromachined infrared light source, filtered to match the 4.2 μm absorption band of CO2, and a piezoelectric thin film deposited on a silicon suspended cantilever. A concise presentation of the different PA set-ups is presented in Table 1, in the concluding section
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
