Abstract
Semiconductor and micro-electromechanical system (MEMS) technologies have been already proved as strong solutions for producing miniaturized optical spectrometers, light sources and photodetectors. However, the implementation of optical absorption spectroscopy for in-situ gas analysis requires further integration of a gas cell using the same technologies towards full integration of a complete gas analysis system-on-chip. Here, we propose design guidelines and experimental validation of a gas cell fabricated using MEMS technology. The architecture is based on a circular multi-pass gas cell in a miniaturized form. Simulation results based on the proposed modeling scheme helps in determining the optimum dimensions of the gas cell, given the constraints of micro-fabrication. The carbon dioxide spectral signature is successfully measured using the proposed integrated multi-pass gas cell coupled with a MEMS-based spectrometer.
Highlights
Gas sensing is gaining increased interest mainly for air pollution monitoring and to trigger air purification systems when needed
Sensor miniaturization is dominated nowadays by semiconductor technologies, including micro-electromechanical system (MEMS) mainly due to their potential for volume manufacturing at low cost
While chromatography requires collection and injection of a sample of the analyte into a chromatographic column, optical spectroscopy offers the great advantage of allowing non-invasive analysis thanks to light–matter interaction
Summary
Gas sensing is gaining increased interest mainly for air pollution monitoring and to trigger air purification systems when needed. Efficient gas absorption of light requires a long-enough interaction length L, according to the Beer–Lambert law: Ap = P0(1 − exp[c.ε(λ).L]), where Ap is the amount of absorbed light, P0 is the incident light, c the gas concentration and ε(λ) its wavelength-dependent absorptivity This light–matter interaction occurs inside dedicated gas cells, which are key components, enabling good control of both the sample being measured and the optical path L. The use of the lithographic process offers the great advantage of high-quality self-alignment of the micro-fabricated optical parts according to a given computer-aided design (CAD) mask design This can lead to high mechanical stability as well since all components are micromachined in the same substrate. Carbon dioxide gas is measured using the proposed cell together with a MEMS-based Fourier Transform Infra-Red Spectrometer (FTIR) as a proof of concept
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