26 October 1998 Infrared sensor with precisely patterned Au black absorption layer
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Thermoelectric infrared sensors has been fabricated by adding to the CMOS process a surface micromachining technique and a highly accurate process for forming an infrared radiation absorbing layer. The sensor, or thermopile, consists of alternating areas of p-type and n-type polysilicon connected in series on a Si3N4 layer. An anisotropic etching technique using hydrazine is employed to form a thermally isolated membrane. While a Au-black layer for infrared radiation absorption provides the best absorption efficiency over a broad infrared wavelength region, it has been difficult to pattern the layer precisely. Patterning is accomplished by forming the Au-black layer by a low-pressure vapor deposition technique on amorphous Si and a PSG sacrificial layer and then removing it on PSG by the lift-off technique or wet etching PSG. This technique makes it possible to obtain a Au-black pattern with the same degree of accuracy as with the CMOS process. As a result, sensor performance has been improved and a device array has also been achieved. A simple sensor design method has been established by which simulations are easily conducted using a thermal equivalent circuit based on the CMOS process. Prototype sensors, having external dimensions of 160 micrometer X 160 micrometer, achieved responsivity of 300, 149 and 60 V/W and a time constant of 2.0, 0.46 and 0.27 msec in the air, respectively. These performance figures surpass the performance reported to date for thermoelectric infrared sensors.
© (1998) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Masaki Hirota, Masaki Hirota, Shinichi Morita, Shinichi Morita, } "Infrared sensor with precisely patterned Au black absorption layer", Proc. SPIE 3436, Infrared Technology and Applications XXIV, (26 October 1998); doi: 10.1117/12.328062; https://doi.org/10.1117/12.328062

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