Integration of an interferometric IR absorber into an epoxy membrane based CO2 detector

Measurements of carbon dioxide levels in the environment are commonly performed by using non-dispersive infrared technology (NDIR). Thermopile detectors are often used in NDIR systems because of their non-cooling advantages. The infrared absorber has a major influence on the detector responsivity. In this paper, the fabrication of a SU-8 epoxy membrane based Al/Bi thermopile detector and the integration of an interferometric infrared absorber structure of wavelength around 4 m m into the detector is reported. The membrane of thermopile detector has been utilized as a dielectric medium in an interferometric absorption structure. By doing so, a reduction in both thermal conductance and capacitance is achieved. In the fabrication of the thermopile, metal evaporation and lift off process had been used for the deposition of serially interconnected Al/Bi thermocouples. Serial resistance of fabricated thermopile was measured as 220 k Omega. The response of fabricated thermopile detector was measured using a visible to infrared source of radiation flux 3.23mWmm(-2). The radiation incident on the detector was limited using a band pass filter of wavelength 4.26 mu m in front of the detector. A responsivity of 27.86Vmm(2)W(-1) at room temperature was achieved using this setup. The fabricated detector was compared to a reference detector with a broad band absorber. From the comparison it was concluded that the integrated interferometric absorber is functioning correctly.