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Publication
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Flexible bearings are advantageous for microelectromechanical systems as they enable precise, accurate, repeatable, and reliable motion without frictional contact. Based on the principle of a rotary folded-beam suspension, we have designed, fabricated, modeled, and characterized an electrostatic rotary stepper micromotor in silicon. Using 3-D finite-element analysis simulations that were corroborated by extensive characterizations performed in quasi-static, transient, and dynamic regimes, we could establish a consistent electromechanical model of the motor. In particular, dynamic nonlinearities such as superharmonic and subharmonic resonances are well described by the proposed model. Two prototypes of monolithic three-phase stepper motors have been fabricated with standard silicon-on-insulator (SOI) technology, using either a two-mask or a single-mask process. The two-mask SOI motor has a rotor diameter of 1.4 mm and has an angular range of 30°(+/- 15°) for a 65-V (130 Vpp) sinusoidal actuation. The single-mask SOI motor has a rotor diameter of 1.8 mm and incorporates a differential capacitive sensor for angular position measurement. It reaches a maximum angular speed of 1°/ms and has an angular range of 30° for a 23-V (46 Vpp) sinusoidal actuation. The exceptional performance of the motor and the demonstration of successful capacitive sensing make it suitable for use as an active joint module in future microrobotic applications