1 Introduction

Surface micromachining and the intimately associated electrostatic actuation are two basic key technologies that have convinced a large number of researchers to push microsystems development ahead, resulting in the impact and results we recognise nowadays.

Surface micromachining is an efficient and relatively simple way to realise mobile microstructures on the surfaces of support wafers using processing steps that are compatible with silicon integrated circuits technology. These mobile microstructures are either sensor parts or microactuators that lead to microsystems, once associated with control electronic. The basic principle of surface micromachining and electrostatic actuation are depicted in Figure 1. Starting from a substrate, most commonly silicon, 2 layers are successively deposited, namely, the sacrificial layer and the structural layer, Figure 1(a). After a photolithography (resist coating, exposure and development), the resist is patterned according to the microstructure geometry. Then, the structural layer is etched and only the area protected by the resist remains, Figure 1(b). Finally, the resist is stripped away and the sacrificial layer is partially dissolved to release the microparts from the substrate. In the case of Figure 1, a cantilever is formed that is separated from the substrate by a gap corresponding to the thickness of the sacrificial layer. If a voltage is now applied to this cantilever, the substrate being grounded, attractive electrostatic forces pull the...