Square-patterned narrow-band infrared emitter for filter less infrared gas sensor

In this study, we proposed a square-patterned narrow-band infrared (IR) emitter for a filterless IR gas sensor. As a new method of infrared gas sensing compared with previous research, it is proposed that a narrow-band IR emitter fabricated by micro-electro-mechanical-systems (MEMS) technology be applied to analyze dimethyl ether [(CH ₃) ₂O] gas. The proposed IR emitter consists of a TiN/SiO ₂/TiN trilayer, where the top TiN layer is square-patterned. The IR emitter radiates emissions at wavelengths of 7.68 and 7.88 μm in accordance with the type of sample. The wavelength can be adjusted by changing the period of the surface pattern. The proposed IR emitter shows a narrow peak width (Δλ=λ) of 0.16-0.23. The apparatus for gas detection consists of the proposed IR emitter, a gas cell and a bolometric IR sensor based on amorphous SiGe:H. The change in electrical resistance of the gas detector during inflow of (CH ₃) ₂O gas, which has a fingerprint wavelength in the range of 7.6-10 μm, was much smaller than that during inflow of CO ₂ gas, because (CH ₃) ₂O absorbed its corresponding wavelength in the range of 7.6-10 μm. Because of the concentrated radiation of the IR emitter at the wavelength of 7.88 μm, (CH ₃) ₂O absorbs relatively large amounts of infrared energy. The electrical resistance of the gas detector changed linearly as the concentration of (CH ₃) ₂O gas increased in the range of 0 to 500 ppm.