Variable Reluctance Magnetic Integrated Mini-Motor Fabrication And Test Results

Infroducfion: Small-size, highefficiency motors, fabricated by low cost batch fabrication techniques, are expected to have application in storage, automotive, medical and other fields. We describe a new approach to fabrication of an integrated experimental variable reluctance magnetic mini-motor, based on lithography and electroplating techniques, similar to those used in inductive head fabrication. Strumre Fabrication: The mini-motor consists of six, nearly planar, horseshoe-shaped electromagnets which surround a rotor. The stator diameter is 17 mm, rotor radius 2.976 mm, core width 0.7 mm, coil width 60 pm, and there are 120 turns per core., The motor thickness is -5OOpm, with a substrate approximately 1.0 mm. The fabrication sequence consists of a series of lithography, electroplating, seed layer removal, dielectric fill, and planarization steps. The process for the stator begins by sputterdepositing a Cu seed layer on an oxidized Si wafer, lithographically forming the plate-thru mask for the bottom part of the windings, and electroplating Cu through the mask. After removing the seed layer, a dielectric is applied across the entire structure, which is then planarized, and a pattemed dielectric is formed on top of the Cu to insulate the windings from the magnetic core. The Permalloy core is plated, and the top of the windings are formed by similar process steps. This simplifies the fabrication process. The vias that complete each tun of the coil are formed of PennaIloy during the core plating step. The rotor is fabricated by thru-mask plating of Permalloy on a separate substrate, detaching it, using a sacrificial layer, and then slipping it onto the pin. 'The pin is formed during the same lithography and plating steps thar created the core and the winding. Seed Layers: The seed layers for Cu and Permalloy plating respectively are of sputtered Ti/Cu (I 000-3000A) and of 1000-2OOOA sputtered Permalloy (80120) NiFe).