Parallel-plate electrostatic actuation with vertical hinges

A microactuating structure with vertical polyimide hinges has been designed, fabricated and tested. Unlike traditional microactuators, which are located on the substrate surface, this new actuation mechanism is capable of producing linear motion at a point far from the substrate. This advantage can make it possible to drive other out-of-plane folded structures for on-wafer or out-of-wafer applications such as optical alignment or precise manipulation. The unique design of the planar structure fabricated by surface micromachining makes use of elastic polyimide joints to bring a movable large silicon plate in front of another plate to form a parallel-plate capacitor. The area of the capacitive plate is 430 × 330 μm where the height of the structure is about 1 mm. At resonance frequency, flapping silicon plates can start very large oscillations leading to a deflection angle of 8◦ with a lateral displacement of more than 160 μm when applying a voltage of 174 V (p–p). The resonance frequency is measured to be 380 Hz. A two-dimensional simplified mechanical model of the structure has been built and has been used to estimate the mechanical behaviour of the structure by using a commercial finite element analysis program. (Some figures in this article are in colour only in the electronic version)