Comb actuators with submicrometer-wide suspensions have been fabricated and tested. Measurements proved that they are reliable devices for displacements in the range of several micrometers with a precision in the tens of nanometers. Due to the very flexible suspensions (10 mN m-1) only low voltages-around 20 V- were required for the actuation. As an application, the author have fabricated and characterized an xy microstage which allows precise two-dimensional positioning. The limits of the devices were also tested. A main source of problems is the sticking phenomenon. Depending on the design of the actuator, the movable comb will, at a critical voltage, either stick on the sides of the fixed fingers (side sticking) or on the front ends of the fixed finger (front sticking). Analytical calculations, simulation and measurements are compared.

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This paper presents a microsystem consisting of an overhanging xy-microstage with integrated tip and comb actuators for scanning surface profiling. The design is optimized with respect to precise xy positioning at low drive voltages and accurate detection of vertical deflection. The structure is micromachined in monocrystalline silicon, requiring only three masks and combining various techniques such as KOH and sacrificial layer etching, silicon fusion bonding and wet isotropic and dry anisotropic etching.

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.