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

Abstract

Abstract-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 complicated, also it is difficult to accurately observe and measure them, the characterization of the films is not well known. In the 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 model featured 'nanospots' is developed: multiple small conductive spots are scattered in a big mechanical contact asperity, and ultrathin oxide film is around the nano-spots. The size of electrical spots and mechanical asperity is calculated based on the measured electrical resistance and mechanical contact modeling respectively. The simulations results show a good match with the experimental results. This model allows us to determine some possible geometry configuration that leads to the measured contact resistance in real devices.

A review of micro-contact physics, materials, and failure mechanisms in direct-contact RF MEMS switches

“…In [51,60,61], Liu et al studied contact resistance using an asperity-based finite element model. They acquired AFMs of samples of several different contact materials including Au, Ru, and Au-Ni.…”