A Planar Variable Reluctance Magnetic Micromotor with Fully Integrated Stator and Coils

A fully functional electrically excited planar variable reluctance magnetic micromotor has been demonstrated on a silicon wafer. The motor uses a micromachined nickel-iron rotor and a fully integrated stator, in which a toroidal-meander type integrated inductive component is used for flux generations. To reduce the magnetic reluctance in the stator, a modified stator geometry was adopted which removes the yoke used in a conventional magnetic variable reluctance motor. Using polyimide as both an integral structural material as well as an electroplating mold, a 40-μm-thick nickel-iron rotor 500 μm in diameter was microassembled onto a fully integrated nickel-iron stator 120 μm in thickness. When 500 mA of current was applied to each stator, 12° of rotation (1 stroke in this motor) was observed. By applying three phase 200-mA current pulses to the stators, rotation of the rotor was observed. The speed and direction of the rotation could be adjusted by changing the frequency and phase firing order of the power supply, respectively. Continuous rotor rotation was observed at speeds up to 500 rpm; this speed limitation was solely due to the limitation of the maximum frequency of the controller used. The micromotor could be reproducibly started, stopped, reversed, and continuously rotated. The predicted torque for the fabricated micromotor at 500-mA driving current was calculated to be 3.3 nN-m.