FATIGUE AND WEAR IN SILICON STRUCTURAL FILMS FOR MICROELECTROMECHANICAL SYSTEMS APPLICATIONS

Silicon is the most widely used material in microelectromechanical systems (MEMS) sensors and actuators. This is largely a result of the ease with which silicon can be microfabricated to produce complex mechanical structures in thin film form, because of highly developed processing methods directly related to semiconductor electronics processing.

However, silicon is in not an ideal structural material. It is quite brittle and subject to several reliability concerns – most importantly stiction, wear and fatigue – that strongly limits the utility of silicon MEMS devices in commercial and defense applications. Additionally, because the surface-to-volume ratio in these structural films is very large, models that have been developed for bulk materials cannot always be applied and inherently new physical mechanisms may be operative.

While the reliability of MEMS has received extensive attention, the mechanisms responsible for the various failure modes have yet to be conclusively determined. This is particularly true for fatigue, a research area that has been the subject of intense debate, and wear, the most important failure mechanism in MEMS actuators.

In our work we have used on-chip testing and a suite of electron microscopy techniques to investigate the mechanisms causing both fatigue and wear in micro-scale polycrystalline silicon structural films.

Earlier work on fatigue of structural films in the Ritchie group

Last updated 03/05/08 by Daan Hein Alsem (dhalsem@lbl.gov)