A high fill-factor uncooled infrared detector with low noise characteristic

摘要

An uncooled capacitive type bimaterial infrared detector with high fill-factor and improved noise characteristic is investigated. Top electrode is insulated from the substrate thermally as well as electrically. Only small dimension (10μm×2μm×0.2μm) of SiO_2 only layer (thermal insulation leg) assures thermal conductance of 1.06×10~(-7)W/K, while keeping the infrared absorber (top electrode) separated from the bias signal. Due to the decreased thermal isolation leg length, high fill-factor of 0.77 is achieved. The bimaterial leg that connects the infrared absorber to the thermal insulation leg is a 38μm long cantilever structure composed of Al and SiO_2 bi-layer, which has large difference in the thermal expansion coefficient (Al:25ppm/K and SiO2:0.35ppm/K). Bimaterial leg length (38μm) is quite shorter than the previously designed device, resulting in the decreased bending of the bimaterial leg. However, the increased fill-factor reduces temperature fluctuation noise term that is inversely proportional to the absorber area, and it is found by FEM simulation that the enhanced mechanical properties such as spring constant reduce the thermo-mechanical noise term of the proposed device.