Thermopile infrared detector with detectivity greater than 10 ⁸ cmHz ^(1/2)/W

In this paper, the design, fabrication and experimental results of the thermopile infrared detector, with a single layer of low-stress SiN _x membrane, instead of thin sandwich layer membrane of SiO ₂-Si ₃N ₄ are presented. Thermal isolation is achieved by using back etching of bulk silicon. Thermopiles are consisted of serially interconnected p-poly-Si/Al thermocouples supported by the single layer of SiN _x membrane with low stress. Au/Ti reflective coating was evaporated on the surface of cold junctions of the thermopile to block incident radiation. In the measurement, we find that infrared absorbance of SiN _x membrane to different wavelength is diverse and less than 100%, which has great influence on calculating the actual absorbing power of the detector, so the infrared (IR) transmission spectrum is measured to calibrate the actual infrared absorbing amount of the detector. The analysis result shows that only 43.72% infrared radiation is absorbed by the detector. Based on the measurement of IR transmission spectrum and output voltage of the detector, the response sensitivity of the detector is calculated as 31.65 V/W, detectivity of the detector is 1.16∈×∈10 ⁸ cmHz ^(1/2)W ^-1, and response time of the detector is 126 ms.