A front-side dry-etched thermopile detector with 3–5 μm infrared absorber and its application to novel NDIR CO2 gas sensors

We present a front-side micromachined thermopile with high sensitivity in the 3-5 mum window, and discuss its application to a novel non-dispersive infrared (NDIR) CO₂ gas sensor with a light source emitting collimated light. The micromachined thermopile shows a measured sensitivity of 30 mV/W and a D* of 0.3 times 10⁸ cmradicHz/W. Using this newly fabricated thermopile, we also have successfully developed a small, sensitive NDIR CO₂ detector module for accurate air quality monitoring systems in energy-saving building and automotive applications. The novel sample cavity comprising specular reflectors around the light bulb is configured to uniformly emit collimated light into the entrance aperture of the cavity in order to enhance the sensitivity of NDIR CO₂ detector.