Dynamic behavior of perforated parallel-plate actuator under squeeze film damping effect

Dynamic performance is one of the most critical factors in many MEMS products, such as micro accelerometers, vibratory gyroscopes, micro deformable mirror, etc. Essentially, the dynamic behavior is totally determined by two factors: the internal factor, the stiffness of structure and the external factor, the damping of environment. In this paper both factors are analyzed accurately and a theoretical dynamic model of parallel-plate actuators is presented. The stiffness of the structure, i.e. the spring constant k of the suspension beam that supports the moving plate of the actuator, is achieved by many accurate experimental tests. The damping of environment, referring to the squeeze film damping coefficient c in parallel-plate actuators, is analyzed by calculation and FEA simulation. Further, we consider c a linear function of the actuator displacement, but not a constant value. This treatment greatly improves the accuracy of the dynamic model and could be applied in parallel-plate actuators with large displacement. Dynamic behaviors of the actuators under squeeze film damping, such as natural frequency, response time and bandwidth, are predicted based on the model. Three kinds of parallel-plate actuators are designed and fabricated using a surface micromachining process to verify the estimation of the presented theoretical model and experimental test results have showed good consistency with the theoretical analysis. The dynamic model proposed in this paper could be broadly applied in the MEMS/NEMS systems.