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, 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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