A Rotary Micromotor Supported on Microball Bearings

We report the successful development of the first operational bottom-drive, rotary, variable- capacitance micromotor supported on microball bearings. The rotor and stator of the micromotor were fabricated using a 9-level-mask process. Silicon carbide coating was used for reducing friction of silicon microball housing on the rotor. Top angular velocity of 517 rpm corresponding to the linear tip velocity of 324 mm/s was measured at 150 V and 800 Hz excitation. This is 44 times higher than the velocity previously measured for the linear micromotors supported on microball bearings. Characterization of two different designs showed a good agreement between predicted and measured velocities for the rotary machine. The rotary micromotor developed in this study is a platform technology for centrifugal micropumps for fuel delivery applications.