Design techniques for surface-micromachining MEMS processes

This paper describes design techniques and structural components for building surface- micromachined polycrystalline silicon microelectromechanical systems (MEMS). The devices presented in this paper were fabricated thorugh the ARPA-sponsored multi-user MEMS process (MUMPS), but the ideas are applicable to other surface-micromachining polycrystalline silicon (polysilicon) processes. Specific devices are not discussed; instead, generic design and assembly techniques are presented to give novice or experienced MEMS designers new tools and ideas to improve their own designs. The topological effects which result from the fabrication of surface-micromachined polysilicon structures can be detrimental to many designs. However, these same effects can be turned into an advantage for the MEMS designer. Design techniques are presented for using conformal layer topologies to shape structures for guide rails, bossing, or to obtain closer tolerances than the design rules would seen to imply. Methods are also described for wiring hinged devices and large systems. These techniques were developed from the experience gained by the faculty and students at the Air Force Institute of Technology from the design of over 200 different devices and test structures on over 25 MUMPS die in the past two years.