Out-of-plane electrostatic actuation of microcantilevers

An electrostatic actuation method to generate useful out-of-plane motion of a cantilever structure is described. The critical design feature is to create an asymmetric electric field such that an electrostatic force is generated in a direction perpendicular to the wafer surface. The technical application of the actuation method is to large arrays of microfabricated sensors such as cantilevers and in particular to resonator type sensors. The design approach also overcomes several problems associated with exposure of microfabricated cantilever structures to fluid environments, either during processing or during application of such devices as bio-sensors, e.g. stiction, condensation, squeeze damping, exposure to a biological sample, cleaning and biological activation treatments of the cantilever surfaces. The viability of the technique is demonstrated using microfabricated silicon cantilevers utilizing both optical and piezoresistive detection of the cantilever displacement.