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Proceedings Paper

Infrared sensor with precisely patterned Au black absorption layer
Author(s): Masaki Hirota; Shinichi Morita
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Paper Abstract

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.

Paper Details

Date Published: 26 October 1998
PDF: 12 pages
Proc. SPIE 3436, Infrared Technology and Applications XXIV, (26 October 1998); doi: 10.1117/12.328062
Show Author Affiliations
Masaki Hirota, Nissan Motor Co., Ltd. (Japan)
Shinichi Morita, Nissan Motor Co., Ltd. (Japan)


Published in SPIE Proceedings Vol. 3436:
Infrared Technology and Applications XXIV
Bjorn F. Andresen; Marija Strojnik, Editor(s)

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