Date

2021-12-7

Author

Beşcan, Batuhan

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This thesis presents the design, fabrication, and test steps of a gyroscope that can perform the maytagging and carouseling without the need for a rotary platform. The sensor has two orthogonal, decoupled, and identical drive axes connected to the same proof mass, and there is a sense axis orthogonal to both of these drive axes. The drive axes can be driven independently; hence, the motion path of the proof mass can be adjusted by adjusting the frequencies, amplitudes and phases of the driving signals. Thus, carouseling and maytagging methods can be applied by changing the direction of the sensitive axis, which is in the same plane with the drive axes. The gyroscope is designed to minimize measurement uncertainty, which is the most limiting factor in north-finding applications. To achieve this, the structure is scaled up compared to the reported studies in the literature, and frequency tuning electrodes are placed to match the frequencies of the sense and the drive axes to reduce the signal-to-noise ratio. The footprint of the sensor is 20 x 20 mm with a thickness of 400 µm. In addition to theoretical design, finite element analyses were performed to verify the frequencies of the driving and sensing modes to determine the amount of the frequency split between the drive and the sense modes. Different fabrication methods have been studied, and optimization studies for DRIE and wafer bonding have been carried out to fabricate a gyroscope of this size and thickness. In the fabrication steps, SOI wafers were used to form the device layer, whereas for the substrate layer both glass and SOI wafer options are tried. The DRIE process parameters were optimized for 400 µm device thickness with a minimum gap of 12 µm. In the optimization studies, ramped process parameters were fine tuned to solve etch termination and grassing problems. Then, the fabricated device and substrate wafers were bonded with Si-Au eutectic formation. After fabrication was completed, sensor characterization had been performed for the two different substrates in both vacuum and atmosphere conditions. Due to the size of the proof mass, these trials suffered from stiction of proof mass to the thin film Au substrate electrodes. Since the SOI substrates allow conductive Si electrodes, only devices with SOI substrates survived the proposed fabrication process. Resonance frequencies of the fabricated device were found as 11762.5 Hz and 11599.2 Hz for the two drive axes. Sense mode resonance frequency was found to be 12545.4 Hz. Finally, the scale factor for the fabricated gyroscope was measured for orthogonal sensitive axes as 10.4 µV/(deg/sec) and 12.82 µV/(deg/sec) under atmospheric conditions.

Subject Keywords

MEMS Gyroscope, Quad Mass Gyroscope, North-Finding, MEMS Fabrication, DRIE Optimization

URI

https://hdl.handle.net/11511/95225

Collections

Graduate School of Natural and Applied Sciences, Thesis