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In deep space missions, surface- and spacecraft are exposed to extreme low temperatures. For example, calculations indicate that temperatures of about 120 K (- 153degC) at the orbit of Jupiter and about 44 K (-229degC) at the orbit of Pluto. Even the moon, Mars, and asteroids can subject spacecraft to temperatures well below the conventional limit for electronic parts of -55degC. The utilization of electronics designed for and operated at low temperature is expected to increase efficiency and simplify thermal management of electronic systems. In this paper, the performance of engineering samples of silicon germanium (SiGe) power devices consisting of diodes and hetero-j unction bipolar transistors (HBT) were evaluated under low temperature and thermal cycling. The investigations were carried out to establish a baseline on the functionality and to determine suitability of such devices for use in space exploration missions under cryogenic temperatures. The power devices were evaluated in terms of their switching characteristics and DC current gain in the temperature range between -195degC and +85degC. The effects of thermal cycling and cold-restart capability were also investigated. All of the devices were able to maintain good operation between -195degC and +85degC. In addition, the limited thermal cycling had no effect on their switching performance or on their packaging, and they were able to cold start at -195degC.