Multilevel beam SOI-MEMS fabrication and applications

A microfabrication technology has been developed and demonstrated, which enhances the capabilities and applications of high aspect ratio silicon-on-insulator microelectromechanical 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 result, 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 micromirror 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.