Multilevel Beam SOI-MEMS Fabrication and Applications

and demonstrated, which enhances the capabilities and applica-tions of high aspect ratio silicon-on-insulator microelectromechan-ical systems (SOI-MEMS) by enabling additional independent degrees of freedom of operation: both upward and downward vertical pistoning motion as well as bi-directional rotation. This is accomplished by applying multiple-mask high aspect ratio etches from both the front- and back-side of the SOI device layer, forming beams at different levels. The processes utilize four masks, two for front-side and two for back-side etching. As a re-sult, single-crystal silicon beams with four different cross-sections are fabricated, and can be combined to form many additional beam cross-sections. This provides a wide variety of possible mechanical designs that can be optimized for optical and other applications. By this methodology, unique high aspect ratio mi-cromirror devices were demonstrated with fully isolated and accurately self-aligned vertical combdrives in the SOI device layer, with initial combfinger overlap. Examples of fabricated devices are shown with performance summaries. [886] Index Terms—Deep reactive ion etch (DRIE), inductively cou-pled plasma (ICP) etch, microfabrication, micromirrors, optical MEMS, self-alignment, SOI-MEMS, vertical combdrives. I