A micromachined vibrating ring gyroscope.

Abstract

A new micromachined gyroscope based on a vibrating ring is described. The device measures rotation rate or whole angle inertial rotation by monitoring the position of node lines in a vibrating ring. To sense rotation, the ring is electrostatically forced into an elliptically shaped vibration mode and the position of the node lines are capacitively monitored. When the device is rotated about the ring center, the node lines lag behind the rotation due to the Coriolis force. The control and readout circuitry monitors this lag and develops a corrective voltage, that is proportional to the rotation rate, to hold the position of the node lines fixed. In the dissertation a detailed mathematical model of the sensor is developed. This model is used to understand and discuss the operation of the sensor and in the design of the control and readout circuitry. Experimental measurements of the model parameters show good agreement with the theoretical predictions of the device model. To fabricate the sensor, a low-cost process based on metal electroforming techniques was developed that allows large amounts of circuitry to be included with the sensor for signal readout, compensation, autocalibration, and self-test. Using this process sensors, including 3$\mu$m CMOS on-chip buffer amplifiers, have been fabricated. A resolution of approximately 0.5$\sp\circ$/sec in a 10 Hz bandwidth, limited by the on-chip electronics, has been obtained with this new sensor. The zero bias drift of the device was less than 1.5$\sp\circ$/sec over the automotive temperature range while the sensitivity of the device varied by approximately 30% over this same temperature range. Further improvements in the on-chip electronics, the sensor materials, and the sensor design are expected to push the resolution to below 0.1$\sp\circ$/sec in a 50 Hz bandwidth and to improve the temperature performance of the sensor. Recommendations for improving the sensor to meet the requirements for low to medium performance applications are discussed.