Noise in Refrigerating Tunnel Junctions and in Micorobolometers
The high sensitivity required for the astronomical observations of cosmic sources in the far-infrared (IR) or X-ray bands imposes very serious constraints on the construction of detectors. To minimize the noise and increase the response of the detectors, these experiments have to be carried out in space, at very low temperatures. A typical device, such as a bolometer or a calorimeter, consists of a thermal sensing element (TSE), connected to a heat sink (see Fig. 1). The TSE is formed of an absorber and a thermometer and can absorb directly high frequency electromagnetic radiation (X-rays) or can be coupled to an antenna that absorbs infra-red radiation (IR). The temperature of the detector usually has to be lowered to 100 mK or below to meet the sensitivity requirements. The last stage of cooling (from 300 to 100 mK) often poses significant difficulties in space-borne experiments both in system complexity and reliability.
KeywordsHeat Sink Shot Noise Tunnel Junction Heat Bath Normal Metal
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