This thesis reports the development of high-performance symmetric and decoupled micromachined gyroscopes for tactical-grade inertial measurement applications. The symmetric structure allows easy matching of the resonance frequencies of the drive and sense modes of the gyroscopes for achieving high angular rate sensitivity / while the decoupled drive and sense modes minimizes mechanical cross-coupling for low-noise and stable operation. Three different and new symmetric and decoupled gyroscope structures with unique features are presented. These structures are fabricated in four different micromachining processes: nickel electroforming (NE), dissolved-wafer silicon micromachining (DWSM), silicon-on-insulator (SOI) micromachining, and silicon-on-glass (SOG) micromachining. The fabricated
gyroscopes have capacitive gaps from 1.5µ / m to 5.5µ / m and structural layer thicknesses from 12µ / m to 100µ / m, yielding aspect ratios up to 20 depending on the fabrication process. The size of fabricated gyroscope chips varies from 1x1mm2 up
to 4.2x4.6mm2.
Fabricated gyroscopes are hybrid-connected to a designed capacitive interface circuit, fabricated in a standard 0.6µ / m CMOS process. They have resonance frequencies as small as 2kHz and as large as 40kHz / sense-mode resonance
frequencies can be electrostatically tuned to the drive-mode frequency by DC voltages less than 16V. The quality factors reach to 500 at atmospheric pressure and exceed 10,000 for the silicon gyroscopes at vacuum. The parasitic capacitance of the gyroscopes on glass substrates is measured to be as small as 120fF.
The gyroscope and interface assemblies are then combined with electronic control and feedback circuits constructed with off-the-shelf IC components to perform angular rate measurements. Measured angular rate sensitivities are in the range from 12µ / V/(deg/sec) to 180µ / V/(deg/sec), at atmospheric pressure. The SOI gyroscope demonstrates the best performance at atmospheric pressure, with noise equivalent rate (NER) of 0.025(deg/sec)/Hz1/2, whereas the remaining gyroscopes has an NER better than 0.1(deg/sec)/Hz1/2, limited by either the small sensor size or by small quality factors. Gyroscopes have scale-factor nonlinearities better than 1.1% with the best value of 0.06%, and their bias drifts are dominated by the phase errors in the
demodulation electronics and are over 1deg/sec. The characterization of the SOI and SOG gyroscopes at below 50mTorr vacuum ambient yield angular rate sensitivities as high as 1.6mV/(deg/sec) and 0.9mV/(deg/sec), respectively. The NER values of these gyroscopes at vacuum are smaller than 50(deg/hr)/Hz1/2 and 36(deg/hr)/Hz1/2, respectively, being close to the tactical-grade application limits.
Gyroscope structures are expected to provide a performance better than 10 deg/hr in a practical measurement bandwidth such as 50Hz, provided that capacitive gaps are
minimized while preserving the aspect ratio, and the demodulation electronics are improved.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/12606483/index.pdf |
| Date | 01 September 2005 |
| Creators | Alper, Said Emre |
| Contributors | Akin, Tayfun |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | Ph.D. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
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