Singularity of Contact Resistance at Very Low Temperature

For low-temperature applications of electrical contacts such ´ as cryogenic semiconductor devices and superconduction coils, contact resistance properties must be studied. Moreover, the cryogenical properties of contact resistance are important in clarifying basic contact mechanisms and controlling the contact resistance. From these standpoints, low-temperature dependences of the contact resistance of clean surfaces were examined over a range from room temperature to liquid helium temperature. As results, singular phenomena of increasing contact resistance with decreasing temperature and hysteresis of the contact resistance at low temperature were found. The causes of these phenomena were clarified from thermal properties of the contacts. Namely, as constriction resistance is generally given by resistivity of the contact metal and true contact area, temperature dependence of those was examined. The constriction resistance as a function of the temperature, which explained the measured singular phenomena of the constriction resistance was deduced.