Electrostatically actuated and bi-stable MEMS structures

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Bistable compliant micro-structures offer a tremendous advantage in the industry today, as these structures have an ability to maintain their shape even in power-off condition. Bistable mechanisms implemented in MEMS devices are categorized as electrostatically and mechanically bistable elements. Electrostatically bistable devices exhibit pull-in behavior whereas mechanically bistable devices utilize snap-through phenomenon. A general approach is presented to develop a pin-jointed bistable compliant mechanism utilizing snap-through behavior. Exploiting the snap-through and the pull-in characteristics, the device operating voltages can be reduced drastically since the required switch-over voltage in MEMS devices is often too high. We also investigate the effect of non-critical forces on the structure which might lead to an operational failure of such mechanisms. The most general bistable mechanism consists of two constrained micro flexures (arch). These structures have a tendency to undergo large displacements/ rotations without exceeding the structural elastic limit. MATLAB based Finite Element Analysis package GESA is used to simulate the static and transient behavior of the micro structure as it completely accounts for the geometric nonlinearities. A fully nonlinear beam element is used in the analysis and the results are compared to a beam element with Von-Karman nonlinearity. The study also includes stability and bifurcation analysis and therefore buckling and post-buckling characteristics of the arch are studied thoroughly.