High aspect-ratio polysilicon micromachining technology

This paper presents a single wafer, all-silicon, high aspect-ratio multi-la yer polysilicon micromachining technology that combines deep dry etching of silicon with conventional surface micromachining to realize tens to hundre ds of microns thick, high aspect-ratio, electrically isolated polysilicon s tructures with sub-micron air-gaps. Vertical polysilicon sense electrodes a s tall as the main body polysilicon structure can be realized in this techn ology. A 70-mum-tall, 2.5-mum-wide polysilicon vibrating ring gyroscope wit h 1.2 mum capacitive air-gaps and electrodes as tall as the ring structure has been fabricated using this technology. Vertical polysilicon beams that are 220 mum tall with a 100:1 aspect-ratio have been also fabricated. The a ll-silicon feature of such a technology improves long ten stability and tem perature sensitivity, while fabrication of large area, vertical pick-off el ectrodes with sub-micron gap spacing will increase the sensitivity of MEMS devices by orders of magnitude. This technology is also capable of simultan eously producing electrically isolated 2-D (planar) and 3-D (vertical) poly silicon structures on the same silicon substrate. (C) 2000 Elsevier Science B.V. All rights reserved.