Modeling and experimental characterization of the chevron-type bi-stable microactuator

A compliant bi-stable micromechanism allows two stable states within its operation range to remain at one of the local minimum states of potential energy. Bi-stable energy characteristics offer two distinct and repeatable stable states that require no power input to maintain. In this paper we suggest a new theoretical model of the chevron-type bi-stable microactuator using equivalent stiffness in the rectilinear and rotational directions. From this model, the range of the spring stiffness in which the bi-stable mechanism can be operated is analyzed and compared with the results of finite element analysis (FEA) for buckling analysis. The analysis of the equivalent stiffness model shows that the forces necessary for the forward and backward actuation are almost linearly proportional to the equivalent stiffness, also in agreement with that of FEA. Based on the analysis, a novel chevron-type bi-stable microelectromechanical systems (MEMS) actuator with hinges and coupling bars is proposed for the improvement of a stable latch-up operation. The thickness and orientation of the hinge is determined through FEA in the light of reliable operation, stroke requirement, mechanical stress, and process constraint. The change in the cross-sectional area during the fabrication process is also considered to take into account its effects on the reduction of equivalent stiffness of the bi-stable MEMS actuator. The fabricated chevron-type microactuator showed a reliable bi-stable operation with a 60 µm stroke at 36 V input voltage, in agreement with the results of the equivalent stiffness model. Therefore, these results confirm that the chevron-type bi-stable MEMS actuator using hinges with coupling bars is applicable to optical switches.