Research Area: Micro-electro-optical-mechanical System; MEMS Mechanics; Micro Scraping Machining; Non-silicon-based  Micromachining Optical Devices

Title: Some bifurcation phenomena in MEMS

Abstract: It is known most theorems of classic physic are well applied in MEMS. However, some effects ignored in macro world become important in micro meter scale. Due to the increasing significant effect of such effects, there are bifurcation phenomena happening in MEMS. The bifurcation phenomena would be troublesome in MEMS. Sticking in wet etching and pull-in in electrostatically actuated MEMS are widely known. And they will damage the MEMS devices. For sticking problems, the mechanical stability and adhesion of microstructures under capillary forces are investigated. And a nondimensional elastocapillary number in terms of structure sizes and material properties is derived for center anchored circular plate. For pull-in phenomena, as applying enough voltage is on the structure, the structure will cause electrostatic adhesion due to the electrostatic force larger than the elastic recovery force. If the displacements are greater than 1/3 of the gap, unstable collapse will occur. However, bifurcation phenomena would have advantages for used in some MEMS structures. The well known bistable mechanism for exhibiting stable states in two distinct positions have advantages for their unique mechanical behaviors used in MEMS devices to achieve a high response, reduce power consumption and prevent external disturbances. A bistable criterion for double V-beam mechanisms is derived. This theoretical derivation of the criterion in terms of structure sizes and material properties is able to determining whether bistability can occur in micromechanically bistable mechanisms. It would help in MEMS device designs.