Large Vertical Displacement Electrostatic Zipper Microstage Actuators

An out-of-plane electrostatic microactuator delivering exceptionally high vertical displacements is described. The devices, based on an electrostatic zipper actuator design, employ composite Si/SiO₂ beams with engineered stress gradients that result in large and controllable beam curvatures. The microactuators are fabricated in a silicon-on-insulator/deep reactive-ion etching process, with an additional oxidized silicon wafer serving as a bonded ground electrode. Simple cantilever Si/SiO₂ zipper actuators are investigated and extended to a meander configuration with regions of variable curvature able to produce large tip deflections in a small on-chip footprint. An analytic model is presented and used to optimize deflection of the meander-shaped zipper actuators, followed by the implementation of a full microstage actuator employing parallel meanders connected to a moving silicon stage. Using this configuration, purely vertical actuation is realized. The static deflections of various actuator designs are characterized and shown to be in a good agreement with analytical predictions. Fabricated microstage actuators achieving deflections up to 60% of their in-plane dimensions are described, and reliable actuation over nearly 10⁶ Hz is demonstrated.