Nanoparticle Liquids for Surface Modification and Lubrication of MEMS Switch Contacts

Contact failures in microelectromechanical system (MEMS) switches, particularly during hot switching, prevent their widespread use. In this paper, a nanoparticle liquid (NPL) lubricant is synthesized and deposited on MEMS switch contacts as a nanotechnology-based lubricant. NPLs are monolithic hybrid materials comprised of an inorganic nanosized metallic core and an organic low viscosity corona. The NPL used here utilizes either Au or Pt nanoparticles as the core and a mercaptoethanesulfonate ionic liquid as the corona. Performance, reliability, and chemical/physical processes on hot-switched NPL-lubricated contact surfaces were investigated at high (1 mA) and low (10 ) currents using a micro/nanoadhesion apparatus as a MEMS switch simulator with in situ monitoring of contact resistance and adhesion force. This was coupled with ex-situ analyses of the contacts using scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and scanning Auger spectroscopy. NPLs exhibited improved electrical performance and durability (orders of magnitude improvement) as compared to uncoated and self-assembled monolayer-coated switch contacts. Improved performance and reliability results from the following: 1) controlled nanoscale surface roughness that spreads current through multiple nanocontacts; 2) restricted size melting regions and termination of nanowire growth (prevents shorting) during contact opening; 3) enhanced thermal and electrical conductivity that reduces lubricant degradation; and 4) lubricant self-healing (flow to damaged areas) as confirmed with physical and chemical analyses. Based on these results, NPLs show excellent potential as surface modifiers/lubricants for MEMS switch contacts.