An Infrared Sensor for NDIR Applications Integrating a Metal-Polymer Layered Wavelength-Selective Absorber and a Thermopile

In this study, a compact infrared sensor for non-dispersive infrared (NDIR) gas sensing is developed by integrating a thermopile with a metal-polymer layered wavelength-selective infrared absorber. The absorber consists of a metal hole array (MHA), which acts as a plasmonic wavelength selector, and an infrared-absorbing polymer layer. The absorber structure is designed using finite element method simulations and fabricated on a thermopile wafer through a low-temperature process operated below 200°C. Fourier transform infrared spectroscopy (FTIR) confirms that the fabricated absorber exhibits a clear absorption peak near 4.3 µm, corresponding to the CO2 absorption band. Gas sensing experiments demonstrate stable detection of CO2 concentrations ranging from 2% to 20% vol., and the sensor response follows the Lambert-Beer law over a wide concentration range. These results indicate that the proposed integration approach is effective for compact NDIR sensors with multi-band wavelength-selective characteristics.