Surface Micromachined Polysilicon Components Containing Continuous Hinges and Microrivets Used to Realize Three-Dimensio
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Surface Micromachined Polysilicon Components Containing Continuous Hinges and Microrivets Used to Realize Three-Dimensional MEMS Structures Edward S. Kolesar, Matthew D. Ruff, William E. Odom, Simon Y. Ko, Jeffery T. Howard, Peter B. Allen, Richard J. Wilks, Josh M. Wilken, Jorge E. Bosch and Noah C. Boydston Texas Christian University, Department of Engineering, Box 298640, 2800 S. University Drive Fort Worth, TX 76129 ABSTRACT A new polysilicon surface micromachining technique for fabricating and assembling threedimensional structures has been developed. Single-layer polysilicon elements and laminated polysilicon panels incorporating trapped-glass reinforcement ribs have been successfully fabricated on a silicon substrate with robust and continuous hinges that facilitate out-of-plane rotation and assembly. To realize a stable three-dimensional structure, one of the device’s elevatable panel components is terminated with an array of open windows, and the mating rotatable element has a matched set of protruding arrowheads/microrivets with flexible barbs that readily flex to facilitate their joining and assembly. Because the arrowhead/microrivet barb tip-to-barb tip separation is larger than the opening in the mating window, the barbs flex inward as they pass through the open window and then expand to their original shape upon exiting the window, resulting in a permanently latched joint and a three-dimensional structure. Three novel arrowhead/microrivet designs have been micromachined to facilitate the latching process, including a simple arrowhead, a high-aspect ratio arrowhead, and a rivet-like structure with a hemispherical shaped cap and a flexible split shank. INTRODUCTION The seamless integration of conventional microelectronics with three-dimensional, microdynamic, mechanical components is one of the prominent goals of microelectromechanical systems (MEMS) technology [1]. Conventional microelectronic integrated circuit (IC) processing is predominantly a two-dimensional fabrication technique. On the other hand, many MEMS microsensor and microactuator applications require three-dimensional components [2]. Since MEMS technology is an extension of IC processing, the primary challenge is to realize mechanical components with physically large and high-resolution features in all three dimensions [3]. Conventional surface micromachining manifests high planar resolution, low vertical resolution, and limited vertical range (typically less than 5 µm) [4]. These characteristics are indicative of an excellent planar (two-dimensional) process, but would otherwise imply limited utility for three-dimensional MEMS applications. Nevertheless, the authors have adapted this popular MEMS fabrication technology to produce robust three-dimensional structures whose components are fabricated as planar entities and are then rotated out of the plane of the silicon substrate on integrally fabricated hinges and assembled/joined with arrowheads/microrivets [5]. The resulting three-dimensional structures not only manifest IC quality resolut
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