Finite element modeling of nickel oxide film for Au-Ni contact of MEMS switches

Contamination and oxidation are inevitable in contact surfaces, especially for micro contact under low load (μN-mN). They are considered as major causes for a high contact resistance, and can lead to the failure of a contact. However, as the film formation is a complex phenomenon, it is difficult to accurately observe and characterize the film properties. In this paper, a finite element model of nickel oxide film is developed for Au-Ni contact of MEMS switches. Considering the fact that the electrical contact area is only a portion of the mechanical contact area, a so-called `nano-spots´ model is developed: multiple small conductive spots are scattered on a large mechanical contact asperity, and ultrathin oxide film is located around the nano-spots. The sizes of the electrical spots and the mechanical asperity are deduced from the measured electrical resistance and a mechanical contact modeling, respectively. The simulations results show a good agreement with the experimental results. This model allows us to determine some possible geometrical configurations of contact surfaces that lead to the measured contact resistance in real devices.