Breakdown and Healing of Tungsten-Oxide Films on Microelectromechanical Relay Contacts

Abstract

This work discusses the electrical break down of tungsten oxide films that form on contacting surfaces of tungsten electrodes in micro-electro-mechanical (MEM) relays. Electrical tests were applied to the contacts of 27 devices to measure the voltage, current and charge required to break down the oxide films, and also to measure the change in current through the contacts as the film healed. The oxide breaks down when an average of 58 <inline-formula> <tex-math notation="LaTeX">$\mu \text{C}$ </tex-math></inline-formula> of electronic charge passes through the oxide, which usually requires applying 1&#x2013;2 V to drive 100 nA-<inline-formula> <tex-math notation="LaTeX">$10~\mu \text{A}$ </tex-math></inline-formula> of current through the contact. The tungsten oxide heals quickly in laboratory ambient conditions: applying 0.5 V to a contact immediately after breaking down an oxide results in a contact current greater than <inline-formula> <tex-math notation="LaTeX">$5~\mu \text{A}$ </tex-math></inline-formula>, but the same test only induces 1 nA of current 1&#x2013;5 minutes later. The reduction in contact current with time follows a power law, which is characteristic of charge relaxation in oxides. Additionally, Holm&#x2019;s experiment shows that current conduction through the contacts is dominated by tunneling through an oxide. These facts together suggest that the break down and healing are electrical processes related to trap accumulation and relaxation in the tungsten oxide. [2021-0161]