Real-time gas analysis using mid-infrared microcavities

In-situ gas analysis was demonstrated using a mid-infrared (mid-IR) microcavity. Optical apertures were made of ultrathin silicate membranes using the complementary metal-oxide-semiconductor (CMOS) process. Fourier transform infrared spectroscopy (FTIR) shows that the silicate membrane is transparent in the range 2.5 - 6.0 μm, overlapping with gas absorption lines and therefore enables gas detection applications. CH4, CO2, and N2O were selected as analytes due to their strong absorption bands corresponding to functional group stretching: C-H, C-O, and O-N, respectively. A short response time of subsecond and high accuracy of gas identification were achieved. The chip-scale mid-IR sensor is a new platform for an in-situ, remote, and embedded gas monitoring system.