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An overview of surface micromachining techniques is given and major applications are described. The sacrificial layer technology for the fabrication of free-standing thin-film structures (e.g. polysilicon) by lateral underetching of an underlying sacrificial layer (e.g. silicon dioxide) is discussed in detail. Another technological approach uses the combination of standard IC processing steps with crystal-orientation-dependent etching of the silicon substrate surface for the construction of free-standing multilayer microstructures. A third surface micromachining technique is based on isotropic plasma etching of the silicon substrate for the realization of micromechanical structures at the wafer surface. The state of the art of microstructures realized by the sacrificial layer technology is illustrated by several examples such as comb actuators, micromotors, switches, resonators and microcavities.

We report on recent advances in micro fabrication technology using micromoulding and high-aspect ratio structuring of photopolymer. The direct application is the realization of components for millimeter-size, ultrasonic piezoelectric motors. A new fabrication process using a thick epoxy-based material (SU-8) and the electroplating of nickel is demonstrated. Photopolymer structures have also been realized and released using a positive tone resist as sacrificial layer. The main advantages over past fabrication methods are better design flexibility, simplicity of the fabrication process, the capability to combine metallic materials (Ni) with polymeric materials (SU-8), and the use of positive tone resist as a sacrificial layer.

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This work illustrates and explores one possibility to link watch fine mechanics to silicon-based actuators. A small scale microreduction module, a pinion-gear train, coupled to an electrostatic wobble motor (calculated power figure about 1 pW), is described. The motor parts are fabricated on silicon. Electrodeposition of nickel in a positive photoresist mould is used for the fabrication of the rotor (a 2").This last is flexible to permit verticallywobbling and is directly connected to a n output shaft. Functional operation of this microreduction unit was successful and demonstrated the possibility to output torque from a n electrostatic wobble motor. Measurements and observations of rotor elasticity and geardaxle characteristics are presented and discussed in view of a possibly improved design.