A Nano-Scale Investigation of Material Transfer Phenomena at Make in a MEMS Switch

MEMS switches have considerably improved over the last decade, however their lack of reliability remains a weak point for a large scale production. The main limiting factor comes from the electrical contacts. In particular, material transfer at the nano-scale is of significant importance in terms of performance and lifetime, however the existing literature remains rather limited. In this paper we present original experiments carried out in air using a modified atomic force microscope (AFM) equipped with a tipless conductive cantilever representing the mobile contact. The fixed contact is composed of a Si substrate covered with the metal of interest (Au, Ru or Pt). The experimental setup is configured to perform successive commutations at extremely low closing/opening speeds of about 10nm/s. This study focuses on the closing sequence under 5V DC, the current being limited to 1mA. The results show a sudden current increase when the contact gap becomes smaller than a few tens of nanometers. This emission of electrons from the cathode tends to follow the Fowler-Nordheim theory and leads to the damage of the opposite contact member (anode) thus causing, by impact heating, the evaporation of the anode material and its deposition on the opposite contact member (cathode). A material transfer from anode to cathode can then be observed and explained.