Thermopile-Integrated Mid-Infrared Metasurface Photodetector

This study presents a filterless mid-infrared (MIR) photodetector that integrates the wavelength-selective photo-thermal conversion properties of a Metal/Insulator/Metal (MIM) nanostructure metasurface with the high-sensitivity thermoelectric conversion of a thermopile (series-connected thermocouples). We overcame the low output electromotive force (EMF) of a single thermocouple by connecting multiple thermocouples in series. The proposed device was fabricated using a semiconductor manufacturing process, employing the polymer dielectric PBI (Polybenzimidazole) for its high insulation and film stability, and Ti-Cr as the thermoelectric pair. Electromagnetic field simulations optimized the Localized Surface Plasmon Resonance (LSPR) in the desired wavelength band. The device was designed by parameterizing the number of thermocouples in the thermopile ($N=10,20,40$). Evaluation of the fabricated devices confirmed a linear increase in EMF proportional to the number of thermocouples $N$. Under a narrow-band infrared illumination at a specific wavelength of 5 μm, the device demonstrated an EMF level comparable to an ideal black body (perfect light absorber) at the resonant wavelength, successfully achieving a significant improvement in detection sensitivity.