Viscoelastic and Viscoplastic Behavior of Thin Metal Films for MEMS

Lehigh University, Bethlehem PA

Investigators

Abstract

This research is about the basic mechanisms that underlie a problem that often exists with the metals in micro-electromechanical devices used for applications like cell phones. Although the behavior of these tiny metal components may be fine immediately after fabrication, over time the behavior can change and the device may fail. In particular, the required tension that exists in certain metallic components can gradually relax, much like a guitar string relaxes over time. Unlike a guitar string, however, it is not possible to periodically tighten a metallic micro-electromechanical component to regain optimum functionality. A number of workaround solutions have been found, but the lack of basic understanding leads to greater device complexity, greater cost, and less capability than would otherwise be possible. The approach of this research is to systematically explore the root cause of the undesirable behavior by altering aspects of metal structure one at a time while holding the other aspects constant. Gold films approximately one micrometer thick will serve as a model system that can be modified on the surface and in the interior in order to simulate conditions that are common to other metals used in micro-electromechanical devices, including aluminum, copper, and platinum. If successful, the benefits of this research will include a greatly improved understanding of the undesirable time-dependent changes in metals used for micro-electromechanical devices. This will guide future development of metallic alloys and surface treatments to reduce or eliminate time-dependent changes. Mathematical descriptions of the trends observed in this research will provide device designers with the modeling tools needed to accelerate device development and reduce cost while doing so. With a micro-electromechanical devices market of approximately $12 billion US dollars in 2012, influencing even a fraction of devices can have a significant economic effect. In particular, micro-electromechanical devices for cell phones, small displays, and automotive radars will benefit. Concepts related to micro-electromechanical devices and the methods used in this research will be shared with children in grades K-12 through an annual outreach event, stimulating their interest in science and engineering.