Adhesion-related failure mechanisms in micromechanical devices

Adhesion-related failures occur in microelectromechanical systems (MEMS) when suspended elastic members unexpectedly stick to their substrates. This type of device failure is one of the dominant sources of yield loss in MEMS. This paper reviews the physical mechanisms responsible for the failure from both the theoretical and practical stand point. In general, the failure requires two different phenomena. First (a) the device must be subject to a force sufficiently strong to collapse the elastic member thus bringing it in contact with the substrate. (b) After contact is established and the force removed, the intersolid adhesion must exceed the elastic member restoring force hence keeping the device permanently pinned to the substrate. Both of these problems develop during the device fabrication as well as during the device operation. Normalized elastic member dimension bounds for prevention of collapse and pinning are presented. The failure rate can also be reduced using a wide variety of processing, surface treatment, and physical schemes. These are discussed in regard to their practical applicability.