Date

2022-2-08

Author

Ersoy, Emre

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This thesis reports development of a novel capacitive enhancement approach for MEMS gyroscopes with in-plane drive motion. The study includes design, fabrication, post-processing, and test steps of the MEMS device and enhancement setup. The gyroscope consists of two identical masses which were connected by a diamond shape coupling mechanism. This coupling mechanism provides mode ordering in drive mode. The gyroscope is designed to be mode-matched in order to achieve higher displacements in the sense mode. Therefore, the sense mode resonance frequency is selected higher than drive mode so that the dedicated frequency tuning electrodes can adjust the frequencies to match them. Beside from that, to decrease the mechanical noise the structure is designed to be larger and thicker than the conventional gyroscopes with a boosted proof mass. Despite the thicker structure providing larger capacitive area, the aspect ratio in the silicon etching limits the minimum capacitive gap and obstruct reaching higher signal-to-noise ratio (SNR) values. Therefore, a post-processing approach is developed to eliminate the minimum achievable gap limitation. Both drive and sense electrodes are designed to be within the limits of the aspect ratio and both drive and sense electrodes are post-processed after the fabrication. The designed structure is verified by performing simulations in the COMSOL environment. The fabrication of the gyroscope is conducted in the METU MEMS Center. The device layer of an SOI wafer is micromachined and bonded to a substrate wafer which provides bonding regions (anchors) and electrode wiring. The fabricated devices have a footprint of 48 mm x 21 mm with a 400 μm thickness. The drive capacitive gaps of the gyroscopes are tested before the post-processing in a vacuum environment with the constructed read-out electronics. The quality factors are between 700-800 under 0.075 mTorr for the drive mode. After the capacitive enhancement, the 25 μm capacitive gaps of the sense electrodes are enhanced to 1.4 μm and drive fingers are engaged with an average gap of 5.5 μm. As a result of the capacitive enhancement process, the achieved capacitance increase in the sense mode is approximately 11.5 times with respect to the initial value.

Subject Keywords

Gyroscope, Post-processing, Capacitive enhancement

URI

https://hdl.handle.net/11511/96704

Collections

Graduate School of Natural and Applied Sciences, Thesis