Electrical conduction through Cu2S corrosion films on copper contacts

It is noted that contact resistance increase in a contaminated atmosphere is generally attributed to corrosion film growth. However, its usual measurement does not reveal the basic conduction phenomena which occur at the contact point. Results on electrical conduction through Cu₂S films from 430 to 4500 Å thick grown on copper samples in a controlled atmosphere were reported. The study is based on the analysis of the current-voltage characteristics of the contact point using a fully automatic device which avoids electrical or mechanical breakdowns. It is shown that the contact point has an equivalent circuit composed of serial elements: diode, thermoelectric voltage, and contact resistance. The diode parameters resulting from the junction between Cu₂S (semiconductor) and copper (metal) are determined. The main result is a relationship between reverse current density and the thickness of the film that can explain and predict film breakdown. Furthermore, dynamic contact resistance is shown to depend on current level and direction; its limit (static resistance) is reached with a higher current level value or with gold-flashed film