Integrated, variable-reluctance magnetic minimotor

The use of lithography and electroplating to fabricate variable-reluctance, nearly planar, integrated minimotors with 6-mm-diameter rotors on silicon wafers is described. The motors consist of six electroplated Permalloy(R) horseshoe-shaped cores that surround the rotor. Copper coils are formed around each core. The Permalloy and copper electroplating baths, electroplating seed layers, and through-mask plating techniques are similar to those used to fabricate inductive thin-film heads. High-aspect-ratio optical lithography or X-ray lithography was used to form the various resist layers. The rotors were fabricated separately, released from the substrate, and then slipped onto the shaft, which was plated as part of the stator fabrication process. The fabrication processes for stator and rotor are described in this paper, and initial minimotor operation data are presented.