AVS 50th International Symposium
    Microelectromechanical Systems (MEMS) Tuesday Sessions
       Session MM-TuA

Invited Paper MM-TuA3
Design and Process Integration of an Electric Induction Micromotor

Tuesday, November 4, 2003, 2:40 pm, Room 320

Session: Fabrication and Characterization of MEMS Devices
Presenter: C. Livermore, Massachusetts Institute of Technology
Authors: C. Livermore, Massachusetts Institute of Technology
J.L. Steyn, Massachusetts Institute of Technology
J.U. Yoon, MIT Lincoln Laboratory
A. Forte, MIT Lincoln Laboratory
R. Khanna, Massachusetts Institute of Technology
T. Lyszczarz, MIT Lincoln Laboratory
S.D. Umans, Massachusetts Institute of Technology
J.H. Lang, Massachusetts Institute of Technology
Correspondent: Click to Email
We present the development of a millimeter-scale electric induction machine designed to output Watt-level power for portable power applications. The micromotor comprises a stack of five micromachined silicon wafers. A 4 mm spinning silicon rotor disk is encapsulated within the stack; facing the spinning rotor is a six-phase electric stator. Mechanical-electrical power conversion is accomplished by the interaction of the stator potential with induced charges on the rotor. To operate at high power levels, the micromotor must operate under extreme conditions: high speed rotation (near one million rpm), high voltages (300 V across 3 µm to 4 µm gaps), and high electric frequencies (about 1.5 MHz). These requirements in turn place stringent requirements on the device design and fabrication flow: low electric losses, excellent resistance to electric breakdown, and essentially leak-free wafer bonds among the five silicon wafers. This presentation describes the approaches that are used to meet these requirements simultaneously in a complete, functional device. A thick oxide liftoff process is used to embed islands of oxide in the silicon substrate under the electric elements to reduce stray capacitance and electric losses. The island structure also minimizes overall bow from the stressed films, making wafer bonding possible. The stator's two-level interconnected electric elements are made of platinum and fabricated by a liftoff process. The platinum electrodes and interconnects reduce line resistance, minimize ohmic losses, and provide a smooth, break-down resistant line shape.@footnote 1@ @FootnoteText@ @footnote 1@ The Lincoln Laboratory portion of this work was sponsored by the Defense Advanced Research Projects Agency. Opinions, interpretations, conclusions, and recommendations are those of the authors and are not necessarily endorsed by the Department of Defense.