Cryogenic Behaviour Of Power MOSFET

The past few years has seen a surge in interest in the power devices for a cryogenic environment. As compared to room temperature, performance of most power devices improved markedly in 300K-77K because of an improvement in the material parameters of silicon. Power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) was thought to be especially suitable for cryogenic temperatures because Power MOSFET can be operated well in low temperature and the MOSFET on-resistance ,which reflects the switching losses,decreased remarkable at lower temperature. In this paper,from the point of view of semiconductor physics, the wide temperature range models of the important parameters of silicon were analysed and calculated , Based on those models ,the threshold voltage,the breakdown voltage,the specific on resistance and the transconductance of power MOSFET were calculated. Based on the Virtual Instruments Graphic Programming Language, the system for measuring the parameters of power MOSFET from 300K to 77K was set up. .Compared the calculated and measured results ,the breakdown voltage and on-resistance were found to decrease.whereas the threshold voltage and transconductance were found to increase with a decrease in operating temperature. Low temperature operation was expected to result in lower switching losses,higher frequency,and improvement in the safe-operating area (SOA). At last, a 25kHZ,50V/20V,200W BUCK converter was designed , the active and passive components used in the circuit and the conversion efficiency of the converter were both tested in 77K and 300K. It was found that the operated efficiency of the converter improved about 5% in 77K.