Study On Key Technologies Of A Novel Micromachined Gyroscope Based On Shear Stress Detection

A great amount of micromachined gyroscopes are direly needed in the miniaturization and precision of weapons and equipments. However, domestic micromachined gyroscopes couldn't achieve the same performances as foreign ones; and exporting of high performance micromachined gyroscopes is forbidden by foreign governments. Therefore, researching the micromachined gyroscope technologies to improve the ability of independent innovation are of great importance.Normally, one or two ended tuning fork is employed as quartz micromachined gyroscopes'structure. The drive mode is the turning fork's vibration in width direction and the sense mode is the vibration in thickness direction. Detecting sense mode is achieved by sensing the normal stress in the fork. However, the piezoelectric coefficient corresponding to the normal stress is not the largest one for quartz. A pair of parallel and divided electrodes is needed to be fabricated on each sidewall of the structure. For the two-dimension process of MEMS technologies, it is impossible to form the electrode patterns on sidewalls. Furthermore, the inaccuracy electrodes affect the gyroscope's sensitivity seriously. Therefore, a novel quartz micromachined gyroscope based on shear stress detection is designed in this dissertation. The electromechanical coupling coefficient used is the largest one of the quartz's piezoelectric coefficients, and a high performance micromachined gyroscope is easy to be achieved. Moreover, only a single electrode on each sidewall is needed by using the shear stress detection method.This dissertation focuses on the structure design, fabrication, readout techniques and characterization of the novel quartz micromachined gyroscope. Subsequent research contents are included in this dissertation.1. A novel quartz micromachined gyroscope base on shear stress detection is demonstrated. The mechanical characteristic and the vibration mode are studied. The dimensions of this gyroscope are worked out according to the analysis. The gyroscope structure has a feature of differential vibration in two directions, which can make the structure immune to environment vibration. Especially accelerations are restrained. The structure's vibration damping is slide-film damping; this can help to enhance the quality factor. The drive mode quality factor measured is 7600 and the sense mode quality factor is 600 in air.2. The dynamic response mode of the gyroscope structure is established and the dynamic behavior is characterized. The most important damping effecting the vibration is derived, by calculating the structure damping. And the structure vibration is analyzed by using modal superposition. The structure sensitivity is achieved. The equivalent circuit model of the quartz micromachined gyroscope is presented by using admittance circle, and the parameter relations between mechanical domain and electric domain are analyzed. The equivalent circuit model parameters are identified according to the admittance circles.3. Several quartz micromachined gyroscope samples are fabricated based on anisotropic wet etching. A method forecasting the structure shape after etching is demonstrated according to the crystal planes'etching rates. A shape trimming technique is demonstrated to remove the crystal facets on sidewalls. A fabrication of three-dimension surface electrodes is demonstrated by using mechanical masks, Based on the techniques above, The fabricated structure's volume is 13.0mm×12.2mm×0.5mm, and the smallest structure dimension is 0.3mm.4. A readout circuit is designed according to the electromechanical coupling feature of the micromachined gyroscope. Based on the phase controller, a resonant loop is designed to excite the drive beam vibrating. A canceling static capacity method is presented to make the resonant loop immune to the variety of mode frequency. A closed-loop controller is designed to maintain a stable drive mode oscillation. Based on the correlation demodulator, the rate signal is demodulated from the weak Coriolis'force signal.5. A fabricated quartz micromachined gyroscope is characterized. The scale factor at room temperature is measured as 23.9mV/(?/s) with a nonlinearity better than 1.1% in a range of±150?/s. The output noise floor is measured as 0.1(?/s)/√Hz. The bias stability is 0.37?/s. And the frequency temperature coefficient is -6.5 ppm/?C.