Three-Dimensional Microelectromechanical Systems (MEMS) Structures Assembled from Polysilicon Surface Micromachined Elements Containing Continuous Hinges and Microrivets

Abstract

A new polysilicon surface micromachining technique for fabricating and assembling three-dimensional MEMS 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 microrivets with flexible barbs that readily flex to facilitate their joining and assembly. Because the 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. A mechanical gripper has been developed with this technology that will be used to interface with and change the focal point of a polymeric lens that has the potential for human implant. The seamless integration of conventional microelectronics with three-dimensional, microdynamic, mechanical components is one of the prominent goals of microelectromechanical systems (MEMS) technology. 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. 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. Most of the common IC fabrication processes either sacrifice planar resolution The authors have adapted this popular MEMS fabrication technology to produce robust, three-dimensional structures whose components are fabricated as planar entities. The planar entities are then rotated out of the plane of the silicon substrate on integrally fabricated hinges, whereby they are assembled and joined using arrays of open windows and microrivets. The resulting three-dimensional structures not only manifest IC quality resolution in both the planar and vertical dimensions, but now the vertical feature sizes that are realizable span from 1 µm to nearly a millimeter. The fabrication process for producing three-dimensional structures from microhinged and latachable polysilicon panels was developed using the popular Multi-User Microelectromechanical Systems (MEMS) Process (MUMPs) foundry and material system. It is reasonable to project that the continuous microhinge concept could also be adapted to elements not attached to the substrate, thus affording an even higher degree of freedom for realizing more complex three-dimensional MEMS structure. microsensors, micromachining to multi-chip packaging solid-state chromatography microelectromechanical