Modeling and simulation of the comb structure in the presence of imperfections

Comb structures are widely used in MEMS (Micro-Electro-Mechanical-System) devices, especially in MEMS gyroscope, which is used for electrostatic actuation or capacitive detection. This paper has studied the behavior of non-ideal comb structures. As the presence of fabrication imperfections, the defects like tilting and inclination of the finger are generated due to ICP etching. In this research, FEM (finite element method) model is built to simulate the behavior of comb structures. Impact of tilting of the comb finger is analyzed. For ideal comb structure, the electrostatic force should be applied exactly in drive direction (x-direction) and be independent of the displacement in this direction. When the comb finger has a tilting angle, the simulation result shows the electrostatic force will deflect the drive direction and be coupled to the displacement in drive direction. In addition, tilting of fingers results in large electrostatic forces in y-direction. The impact of inclination of comb finger is analyzed both in theory and simulation. The results indicate that the comb structure also provides displacement-independent electrostatic forces in drive direction under fingers inclination condition. However, the inclination result in fluctuation of drive force. The simulation results also indicate that with the increase of inclination angles, the fluctuation of drive force will become more serious and the out-of-plane forces will be larger, which may cause failure of MEMS devices.