Outer-rotor polysilicon wobble micromotors

This paper reports the development of a new class of polysilicon surface micromachined wobble micromotors in which the rotor outer radius is exposed for mechanical coupling. These motors are fabricated in a three-mask process which results in a flange bearing. The rotor and seater are fabricated from phosphorus-doped polysilicon, while the bearing is made of an insulating material such as polyimide or silicon-rich silicon nitride. Rotor radii of 75 to 125 μm and rotor/stator thicknesses of 3 to 5 μm are typical. The 5 μm-thick micromotors with silicon nitride bearings operate smoothly and reproducibly in room air for at least several months after release. Minimum operating voltages can be as low as 14 V, while maximum rotor speeds have been limited by the power supply to 35 rpm. These micromotors have gear ratios over 300 and motive torques over two orders of magnitude larger than previously reported polysilicon micromotors