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Unformatted text preview: Surface Micromachining for Microelectromechanical Systems JAMES M. BUSTILLO, ROGER T. HOWE, FELLOW, IEEE, AND RICHARD S. MULLER, LIFE FELLOW, IEEE Invited Paper Surface micromachining is characterized by the fabrication of micromechanical structures from deposited thin films. Originally employed for integrated circuits, films composed of materials such as low-pressure chemical-vapor-deposition polycrystalline silicon, silicon nitride, and silicon dioxides can be sequentially deposited and selectively removed to build or machine three-dimensional structures whose functionality typically requires that they be freed from the planar substrate. Although the process to accomplish this fabrication dates from the 1960s, its rapid extension over the past few years and its application to batch fabrication of micromecha- nisms and of monolithic microelectromechanical systems (MEMS) make a thorough review of surface micromachining appropriate at this time. Four central issues of consequence to the MEMS technologist are: i) the understanding and control of the material properties of microstructural films, such as polycrystalline silicon, ii) the release of the microstructure, for example, by wet etching silicon dioxide sacrificial films, followed by its drying and surface passivation, iii) the constraints defined by the combination of mi- cromachining and integrated-circuit technologies when fabricating monolithic sensor devices, and iv) the methods, materials, and practices used when packaging the completed device. Last, recent developments of hinged structures for postrelease assembly, high- aspect-ratio fabrication of molded parts from deposited thin films, and the advent of deep anisotropic silicon etching hold promise to extend markedly the capabilities of surface-micromachining technologies. Keywords Integrated MEMS, MEMS, microelectromechanical systems, micropackaging, polysilicon micromachining, sacrificial release layer, stiction, surface micromachining. I. INTRODUCTION A. Historical Perspective There has been activity in silicon-based micromachining since the early 1960s, when the integrated circuit (IC) tech- Manuscript received February 1, 1998; revised April 16, 1998. This work was supported by the Berkeley Sensor &amp; Actuator Center, an NSF/Industry/University Cooperative Research Center. The authors are with the Berkeley Sensor &amp; Actuator Center, Department of Electrical Engineering and Computer Science, Uni- versity of California at Berkeley, Berkeley, CA 94720 USA (e-mail: [email protected]). Publisher Item Identifier S 0018-9219(98)05087-7. nology was developed. During the 1960s1970s, much of the research centered on anisotropic single-crystalline silicon etching. This technology demonstrated simple struc- tures, with initial commercial products being pressure trans- ducers. By the 1980s, improvements in thin-film deposition and increased understanding of the micromechanical prop- erties of such films allowed thin-film microstructures to be...
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This note was uploaded on 10/31/2010 for the course C 218 taught by Professor Clarknguyen during the Fall '09 term at Berkeley.
- Fall '09