Experimental Study of Electrical Contact Nonlinearity and its Passive Intermodulation Effect

In this article, the single-point electrical contact nonlinearity of the oxidation enhanced copper and its induced passive intermodulation (PIM) effect were systematically investigated. First, based on the composition analysis of the intentionally oxidized copper samples and the pristine ones, the electron potential barrier model across the contact interface was built. Then, based on an equivalent circuit model concluding a linear and nonlinear resistance, a total current equation based on the thermal emission mechanism was deduced and verified by performing a series of I-V measurements. When an oxide film is integrated, the linear current and the nonlinear current are comparable; when the oxide film was broken under an external force, the nonlinear current changes lightly, while the linear current increases sharply by more than two orders of magnitude. Therefore, we observed the transition process from the obvious nonlinear I-V characteristics to the dominant linear curves. Finally, the induced PIM behavior of the pristine and thermal oxidized single-point copper joints was investigated utilizing a specially designed near-field coupling PIM test system. As the pressure increases, the PIM level decrease with the joint pressure increases because both the contact resistance and the nonlinear current decrease. The measured PIM results are consistent with the obtained linear-nonlinear relation from the contact characteristics experiments. Experimentally, the total nonlinear current as the function of voltage drop across the contact interface, which is caused by the linear current, determines the induced PIM level.