Computational simulation for MEMS combdrive levitation using FEM

Generally the levitation value is a very important design parameter for a comb drive, because the levitation effect will seriously downgrade the performance and reliability of electrostatic MEMS devices. Thus an accurate electrostatic and structural analysis is essential. Besides the distance traveled by the movable finger of MEMS comb drive, studies of the effect of gap sizes between comb drive fingers and ground plane and between movable and fixed fingers for levitation are also needed. By way of the finite element method, an accurate electrostatic field under diverse gap sizes considering the fringing electric field around the edges of the fixed and movable fingers of comb drive can be obtained. The subsequent levitation and strain analyses for an MEMS comb drive can be also implemented more precisely. Results show that the levitating displacement and strain of the movable finger are dependent on the distance traveled. The smaller the gap between comb drive fingers and ground plane, the larger the structural response of the movable finger. In addition, the levitation also becomes more predominant as the gap between the movable and fixed fingers decreases.