Contact Resistance Characteristics at Low Temperature

The application of cryogenics to the fields of electrical engineering has great possibility. However, performance of contacts used in the application may be estimated to deteriorate due to contaminant films. It is important subject to clarify the electrical conduction mechanisms of contacts covered with contamination films to obtain low contact resistance characteristics at the low temperature as well as at the normal temperature. From these standpoints, electrical conduction mechanism and contact resistance at low temperature were examined. Schottky current was observed in oxide film covered contacts over a range from 300 K to 77 K. The contact resistance at the low temperature increased by approximately 100 times or more over that of normal temperature due to Schottky conduction. For clean surface, the contact resistance passes through a minimum at low temperature due to thermal contraction of true contact area. In conclusion, Schottky conduction was found predominantly. Therefore, if the contaminant films exist at the contact surface, contact resistance increased remarkably at low temperature. Moreover, even for contacts of clean surfaces, contact resistance has a limiting value unlike resistance of metal conductors. These results give a serious problems in the performance of contacts for the cryogenic application.