Nanospot welding and contact evolution during cycling of a model microswitch

Abstract

The useful lifetime of microelectromechanical system switches is shortened during repetitive contact when the continual making and breaking of an electrical circuit accelerates damage done to the metallic contact points in the switch. In this study the interfacial force microscope is used as a model switch, and we explore the fundamental processes involved in switch failure. We find that repeated indentation (cyclic contact) causes protective coatings (in the form of self-assembled monolayers) to fail allowing metal-metal intimacy and formation of a malleable "nanospot weld." The weld is stretched during separation of the contacting surfaces, leading to the development of nanoasperities. With the help of atomistic simulations, which provide insight into material transfer and consequential roughening of the surfaces, we show that asperity length grows with continued repetition, drastically changing the resistance of the contact over the lifetime of the switch. Controlling the amount of current passed through the contact influences the extent of weld stretching and arcing observed during contact separation. © 2007 American Institute of Physics.