Electrical Contact Resistance Presumption about Tin-Coated Copper-Alloy Contacts Using RF Sputtered SnOx Thin Films

The general theory of electrical contact resistance is essentially described with constriction resistance and film resistance. On the basis of this theory, even a simplified macroscopic model can be applied to most contacts as industrial products with plain surfaces. However, the surface gets degraded during operation. Thus, the authors constructed a resistor network model for complicated surface structures, as reported in the 56th Holm conference. In this case, accurate material properties are required for proper simulation. This paper focuses on tin-plated contacts and investigates material properties of several tin dioxide films. In general, electrical resistivity of tin dioxide shows significant variation with change in carrier density and mobility. In addition, carrier density and mobility of tin dioxide depend on reaction process conditions. The samples evaluated in this study are prepared by RF magnetron sputtering with a tin dioxide target, and this illustrates the variation in electrical resistivity. Lower amount of oxygen leads to lower resistivity while the deviation of atomic ratio from stoichiometry is not too large. On the other hand, the samples made without oxygen gas become insulators. Finally, a presumption regarding the amount of oxygen vacancy in the oxidized surface layer of actual tin-plated contacts is made.