Contact Bounce Phenomena in a MEM Switch

Contact bounces are usually erratic and undesirable phenomena that greatly affect the lifetime and reliability of electrical contacts. This paper deals with bounce phenomena that are experimentally observed during DC contact make and break in a MEM switch. In such a device, the bouncing behavior cannot be explained by inertia forces that are far lower from those existing in macroscopic relays. Therefore this study aims at providing a better understanding of bounce phenomena at the nanometer scale. Experiments have been performed with a nano-indenter and an Atomic Force Microscope (AFM), both used to actuate a contact with a well controlled electrode velocity. Multiple voltage transients of several tens of ms are observed when make/break operations are performed at an extremely low velocity (few tens of nm/s). This occurs when the distance between contact electrodes is of the order of 10nm. A simple analysis of the static balance of forces shows that the electrostatic force becomes predominant at this scale, and that bounces result from a competition between the electrostatic force and the restoring force of the mobile contact. This paper highlights that in a MEMS switch a minimal actuation velocity (here 1μm/s) is required to prevent contacts from bouncing.