Lateral motion control of electrostatic comb drive: New methods in modeling and sensing

A new sensing method is presented for control of lateral instability in micro-electromechanical (MEMS) electrostatic comb drives. Two degrees-of-freedom modeling of a tiny (2mm × 2mm) comb drive is given. A structure of the dynamical model in both axial and lateral direction has been developed analytically for the purpose of confronting the problem of lateral instability. The mechanical part of the model is given and an emphasis is placed on its input and output parts, e.g. generation and distribution of both actuating and parasitic forces, and the sensitivity of the displacement sensors. The optimal sensitivity of a special capacitive position sensor is calculated with respect to limited area available for the sensor. Finally, the influence of the measurement electronics on sensitivity of the sensor and the influence of a finite aspect ratio of the Deep-Reactive-Ion-Etching (DRIE) fabrication on the capacitive structures are analyzed. This analysis lays the foundation for more effective control of future comb drive actuators.