Quantitative Evolution of Electrical Contact Resistance between Aluminum Thin Films

In the field of electrical contact, to explain the evolution of electrical resistance as a function of the applied load, it is necessary to take into account the fracture of the native oxide of a metal. This work investigates the role played by the native alumina present at the surface of Al thin film in the formation of micro-contacts as a function of the applied load and loading rate. Thin aluminum films (1μm) are sputtered on silica rods (curvature radii of 3 mm and 6 mm). Model crossed rods electrical contact experiments are performed for pressures ranging from 100 MPa up to 1.7 GPa. The following evolution of the electrical contact resistance is proposed. At low loads, the contact is first established without native oxide fracture leading to high levels of electrical resistance by tunneling effect (MOhm). Then fracture of native alumina is associated with the decreasing of the electrical contact resistance between kOhm to Ohm. Extrusion of aluminum through cracks is assumed to be responsible for good ohmic contact where cracks overlap. We show a strong influence of loading rate and contact geometry are investigated. At maximum load, the electrical contact resistance reaches a limit (<100 mOhm), which is controlled by experimental geometry and intrinsic resistivity of the thin film. Current line spreading is modeled for this geometry and non negligible correction is carried out.