A high-aspect-ratio two-axis electrostatic microactuator with extended travel range

Abstract

The design, fabrication, modelling, and control of a two-axis electrostatic microactuator for precision manipulation tasks is described. A high-yield fabrication process using deep reactive ion etching (DRIE) on silicon-on-insulator (SOI) wafers forms the 3-D high aspect ratio transverse comb drives that produce a relatively large electrostatic force. The structure is suspended by removing the substrate beneath the comb drives, therefore, a ground plane is not needed in order to compensate for electrostatic levitation. Among other advantages of the developed process is a dice-free release of wafer structures, allowing fragile structures to be individually packaged. Notching or footing effects and bowing effects are well-known problems in DRIE on SOI wafers. Techniques to overcome notching and bowing effects using a PlasmaTherm SLR-770 etcher are presented that do not require hardware modifications. A capacitive position sensing mechanism, capable of measuring displacements up to 4.5 μm with a resolution of 0.01 μm in both X and Y is integrated to provide position feedback. A nonlinear model inversion technique is proposed for nonlinear electrostatic microactuation system identification and improving system linearity and response. Pull-in instability limits the travel distance of transverse comb drive actuators. Using a nonlinear model inversion technique, a stable travel distance of 3.7 μm with a 4.5 μm gap has been achieved.