High aspect-ratio dry-release poly-silicon MEMS technology for inertial-grade microgyroscopes

This paper presents an all-silicon, single wafer high aspect-ratio dry-release MEMS technology capable of producing 10-100´s of microns thick, electrically isolated 3-D silicon microstructures. This process utilizes polysilicon as the structural material and is capable of producing very thick polysilicon and silicon electrodes using deep reactive ion etching of silicon. Various size capacitive air-gaps ranging from sub-micron to tens of microns can be realized in this technology. Using a bent-beam strain gauge, residual stress in 80 μm thick, 4 μm wide trench-refilled vertical polysilicon beams fabricated through this technology have been measured to be zero. 300 μm long clamped-clamped beam resonators have shown quality factors as high as 85,000 in 1m Torr vacuum. This technology provides features required for high performance vibratory gyroscopes. The all-silicon feature of the technology improves long-term stability and temperature sensitivity; fabrication of large area, vertical electrodes with sub-micron gap will increase the sensitivity by orders of magnitude. Larger air-gaps can accommodate large drive amplitudes for increased Coriolis acceleration