Micro-/nanohoneycomb-like porous silicon loaded with Ag particles leads to synergistic enhancement of photothermal and thermoelectric conversions for MEMS thermopile chip application

Infrared detection technology has extensive and important applications in both military and civilian fields. Due to the advantages including no refrigeration, wide spectral response range, no chopping, low cost, and simple output circuit, MEMS thermopile chip has become one of the research hotspots in the field of infrared detection. The working mode of the thermopile chip is based on the photothermal and thermoelectric conversions, which are achieved by the infrared absorber and thermocouples, respectively. Actually, the resulting complex multilayer structure brings about the shortcomings of thermopile chips, such as large heat capacity, large loss of heat transfer, low stacking efficiency and long response time, which has become the bottleneck of performance improvement. This work proposes a new concept for achieving high-efficiency photothermal and thermoelectric conversions of the thermopile chip simultaneously by a monolayer of multi-functional material. Herein, a micro-/nanohoneycomb-like porous Si loaded with Ag particles was constructed by metal-assisted chemical etching. The etched Si/Ag was endowed with high-efficiency light absorption in a wide spectral range (2-20 mu m) and thermoelectric conversion, with the help of synergistic effect of light trapping, phonon scattering, energy filtering, and plasmon resonance. Replacing the infrared absorption layer, thermocouple layer, and insulation layer of the thermopile chip by the as-constructed porous Si/Ag composite can significantly reduce the heat capacity and energy transfer loss of the chip. It is expected to acquire a leap in the performance of the thermopile infrared detectors, providing a new technical approach for breaking through the bottleneck of small-scale and high-performance thermopile chips.