Modeling a Monolithic Comb Drive for Large-Deflection Multi-DOF Microtransduction

To help extend the investigation and exploitation of nanoscale phenomena, there is a need for high precision, large deflection microtransducers with multiple degrees of freedom (DOF). In this paper, we investigate the predicted performance of such a large deflection microtransducer using finite element analysis. To sense and actuate in three dimensions, we use three types of comb drives: a vertical comb drive, a planar comb drive, and a novel planar monolithic comb drive, which operates as an in-situ RC circuit. The two planar comb drives are used to translate a proof mass with independent in-plane x- and y- directions, and the vertical comb drive translates the proof mass in the out-of-plane z-direction. The device resists rotation about the z axis. We address precise sensing and actuation by using high-precision capacitance and voltage to detect position and to apply force, respectively. We explore design issues such as geometry and material properties, and we characterize the monolithic comb drive. We limit the geometry of the transducer to one structural layer, which is amenable to a simple one-mask fabrication process such as silicon-on-insulator (SOI).