The effect of contact capacitance on current-voltage characteristics of stationary metal contacts

This paper investigates experimentally the significance of the effective contact capacitance, i.e., the interfacial capacitance during the current flow, for a wide range of stationary metal contacts operating under high charge injection rates. The effective capacitance of metallic interfaces depends on the ratio between the apparent contact area (which is optically determined) and the effective contact area (which injects the electronic charges). Silver contacts having series resistance values significantly less than the contact resistance were subjected to ac high current densities (up to 500 A/mm²). The obtained i(t) and v(t) profiles were further analyzed to obtain I-V curves. Due to the phase shift between i(t) & v(t) profiles the I-V curve within a single period of the stimulating current will produce a closed loop. The area of the loop determines the interfacial electrical energy. According to the obtained results the electrical energy storage at a given metal contact, increases at: 1) higher ampacity values; 2) lower operating temperatures; 3) higher clamping forces between the joints (elastic deformation regime) each of the above parameters acting independently. The experimental results were obtained for AgSnO2 and OFHC contacts operated in a wide temperature range, varying between −130 °C and +40 °C. The observed response of the electrical contacts is mainly characterized by the implications of the asperity contact model and dominating charge transport processes across the metallic interfaces. When standard simple equivalent circuits are used to determine contact impedance, the effective capacitance of current carrying metal contacts acquires exceptionally high values.