Bulk silicon micro electro mechanical devices fabricated from commercial BESOI substrates

A great number of micro electro mechanical (MEM) devices have been developed during the last decade. The fabrication of such devices is usually based in some kuid of surface micromachining technology, in which supporting sacrificial layers are removed to free the niicromechanical structures. Due to its technological compatibility with standard IC processing, polycrystalline silicon has been used as the device material for MEM devices such as beams [ 11, pin joints, cranks and sliders (21, gears [3], electrostatic micromotors [4] and electrostatic combdriven structures [SI. The standard chemical vapor deposition method for polysilicon limits the thickness of the microstructures to a few microns. However, for many kinds of microstructures a greater thickness is beneficial. These would include devices with its motion constrained to the plane parallel to the substrate. In that case the increased thickness increases the stiffness of the device in the direction perpendicular to the plane of motion. Also, for devices that use electrostatic attraction between sidewalls as the driving force, such as comb actuators aid micromotors, the increased thickness allows a greater driving power for a given voltage.