Micromotor Fabrication

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Micromotor Fabrication
Mehran Mehregany, Stephen D. Senturia, Member, IEEE, Jeffrey H. Lang, Member, IEEE, and Pradnya Nagarkar

Abstract-This paper presents a detailed discussion of micromotor fabrication and related critical issues. The micromotors under study are of the variable-capacitance side-drive type with salient-pole and wobble (harmonic) designs. Polysilicon surface micromachining forms the basis of the micromotor fabrication process. In this process, LPCVD heavily phosphorus-doped polysilicon is used for the structural parts. LPCVD silicon nik d e is used for electrical isolation, and CVD low-temperature oxide is used as the sacrificial material. The fabrication process impacts the performance characteristics of the micromotor through the reproduction accuracy of the design geometry and through the modification of the characteristics of contacting surfaces. Pattern definition and delineation are among the most critical steps of the micromotor fabrication process because of the increasing surface topography during fabrication and the large film thicknesses utilized. The release and testing process can affect the frictional characteristics of the micromotor significantly, determining success or failure of operation by dielectric excitation.

have been fabricated in our work and by outlining the impact of the fabrication process on micromotor perfor-

I. INTRODUCTION ICROFABRICATION provides a powerful tool for batch processing and miniaturization of mechanical systems into a dimensional domain not accessible by conventional machining. Additionally, microfabrication provides the potential for integration of mechanical systems with the electronics required for closed-loop control. To realize these potentials, a number of recent studies have concentrated on the development of microfabricated silicon passive mechanisms and electric microactuators [ 13. Electric micromotors are an integral part of this emerging silicon microactuator technology [2]-[6]; they can provide unrestrained motion in at least one degree of freedom. An important aspect of the electric micromotor technology is fabrication. This paper provides a detailed documentation of our studies on micromotor fabrication and critical related issues. To illustrate the points under discussion, we start by describing the micromotors that


Manuscript received April 26, 1991; revised December 2, 1991. This work was supported in part by the National Science Foundation under Grant ECS-8614328 and an IBM Fellowship (to M. Mehregany). The review of this paper was arranged by Associate Editor S. D. Senturia. M. Mehregany was with Microsystems Technology Laboratories, Laboratoly for Electromagnetic and Electronic Systems, Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02130. He is now with the Electronics Design Center, Department of Electrical Engineering and Applied Physics, Case Western Reserve University, Cleveland, OH 44106. S. D. Senturia, J . H. Lang, and P. Nagarkar are with Microsystems Technology Laboratories, Laboratory for Electromagnetic and Electronic Systems, Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02 130. IEEE Log Number 9202266.

11. VARIABLE-CAPACITANCE SIDE-DRIVE M I c R o M o T o R s Electric, as opposed to magnetic, drive has been argued as the preferable actuator drive in the microscopic scale [ 13, [5]. In general, in an electric actuator, the attractive and repulsive forces generated by electric charge distributions are used to convert electrical to mechanical energy. By proper commutation of these charge distributions on a set of stationary electrodes, known as the stator, and a set of moving electrodes, known as the rotor, continuous motion of the rotor can be achieved. Our work has focused on the development of...
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