AVS 49th International Symposium
    Microelectromechanical Systems (MEMS) Thursday Sessions
       Session MM+TF-ThM

Paper MM+TF-ThM9
Physics of Metal Micro-contact Events in Micro-Electro-Mechanical (MEM) Relays

Thursday, November 7, 2002, 11:00 am, Room C-210

Session: Development and Characterization of MEMS Materials
Presenter: J.W. Tringe, Air Force Research Laboratory
Authors: J.W. Tringe, Air Force Research Laboratory
T.A. Uhlman, Air Force Research Laboratory
A.C. Oliver, Sandia National Laboratories
J.E. Houston, Sandia National Laboratories
Correspondent: Click to Email
Much research has been previously performed on the physics of electrical contacts, but this has mostly focused on larger contact areas, force and current levels than are relevant for typical MEM switches. Recent work using interface force microscopy (IFM) has experimentally approximated single-asperity gold-gold electrical contact events under conditions appropriate to MEM relay materials. The contact force and resistance were measured simultaneously under constant-current conditions as a function of relative probe-surface separation using parabolic gold probes a few microns in diameter on an electroplated gold surface, typical of the contact surface found in MEM relays. Results will be presented which demonstrate that a very small number of asperities define the electrical behavior of gold-gold MEM switches. Further, the existence of a non-metallic contamination layer on the gold surfaces, up to many tens of angstroms thick, will be shown to critically determine the force and current levels necessary for low contact resistance (on the order of a few ohms or lower). Contact resistance decreases precipitously upon break-down or thinning of the contamination layer, then more slowly and linearly as the probe-surface contact area increases. The contamination layer deforms plastically upon initial contact, then maintains physical and electrical contact with the tip to distances over 5 nm from the point of initial contact. Due to the topography of the electroplated gold surface and the mechanical, electrical and chemical nature of the contamination layer, contact events in gold-gold microsystem relays involve relative contact areas on the order of 0.1%. @FootnoteText@ Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin company, for the DOE under Contract DE-AC04-94AL85000.