Research Of Piezoresistive Micromachined Gyroscope

Micromachined gyroscopes, which can be used to sense angular veloity, have a variety of applications in auto electronics, inertial navigation and commercial electronics due to their small size, high reliability and low cost. Among the developed micromachined gyros, capacitive detection method is frequently used. Piezoresistive detection, however, is just used occasionally for its relatively low sensitivity and high temperature coefficient despite of its simple structure and interface circuits.In this paper, a novel tuning fork like micromachined gyroscope with electrostatic actuation and piezoresistive detection is designed, fabricated and tested. This gyro is designed to work under atmosphere. This gyro is proved to have high sensitivity and low temperature coefficient of sensitivity (TCS) by a piezoresistance on chip self-compensation feedback. This novel structure is superior to traditional cantilever-mass one in terms of sensitivity and resonant frequency. The central bending cantilever, which is rigid, can provide high resonance frequency. On another hand, two tiny beams are so slim that very large stress will occur when the proof mass moves slightly in sensing mode. By electrically connecting the two detectors, a full Wheatstone bridge achieved high performance Coriolis effect detection.In addition, a four-terminal piezoresistive element is used to monitor actuation amplitude by a feedback loop. With the same feedback loop, the four-terminal piezoresistive element is also used to compensate temperature drift of the gyro's piezoresistive output by modulating the actuation amplitude when temperature changes. The temperature coefficient of sensitivity (TCS) for gyro's output is improved dramatically from -0.235% to -0.028% by the compensation.DR1E is used in fabrication. Replacing formerly used SOI wafer with common wafer ina creative way, the process is simplified and the cost is reduced dramatically.Based on the signal-processing model, a simple interface circuit is developed. Test results showed that the angular-rate output of this gyro is with the sensitivity of 21.0V/°/s for ±300°/s measure range and 0.33 °/s noise limited angular-rate resolution. The two coriolis-detection accelerometers in sensing mode is with the sensitivity of 14.80mv/5V/g and 14.49mv/5V/g, Q value 58 and 42, resonance frequency 989Hz and 990Hz respectively.This piezoresistance-detection micromachined gyroscope is potential for much higher angular rate sensitivity. The TCS compensation feedback can improve the temperature characteristic remarkable. In additional to its relative simple interface circuits and high anti electro magnetic interference (EMI) characteristics, this piezoresistive micromachined gyroscope is promising in practical applications.