Fully-Symmetrical And Doublly-Decoupled Micromachined Gyroscope

Based on the theoretical model of the fully-symmetrical and doubly-decoupled micromachined gyroscope, the dynamic characteristics of the device was researched systematically. A novel fully-symmetrical and doubly-decoupled micromachined gyroscope was presented and fabricated by bulk silicon micromachining technology. Further, corresponding experiments were performed to validate the research.Firstly, the working bandwidth is an important parameter for the application of MEMS gyroscopes. It was simply defined as the difference between the esonant frequencies of the drive mode and that of the sense mode, or the bandwidth and sensitivity of MEMS gyroscopes were regarded as a conflict qualitatively. Based on the systematical research of the dynamic characteristics of the presented gyroscope model, several conclusions were obtained. When the frequency of the input angular rate is equal to the difference of resonant frequencies between the drive mode and sense mode, the sensitivity reaches maximum. In the condition that the quality factor of the drive mode keeps constant, there is a critical value with the decrease of the quality factor of the sense mode, at which the peak sensitivity satisfies the 3dB bandwidth theory. Thus, the bandwidth is widened significantly.Secondly, a novel fully-symmetrical and doubly-decoupled micromachined gyroscope, fabricated by bulk micromaching technology, was presented. The fully-symmetrical structure enables the precisely matched frequency for the drive mode and sense mode. The doubly-decoupled structure reduces the cross coupling between the drive mode and sense mode. The free vibrating model without damping of the device was established and solved considering the couple elastic coefficient. The solution indicates that the model couple of the presented gyroscope is 1.56%, and the resonant frequencies of the drive and sense modes are 2966.9Hz. Also, the theoretical model was validated by the finite element model with the software package of ANSYS.At last, based upon the analysis of dynamic characteristic of micro gyroscope, an open-loop detecting circuit of micro-gyroscope was designed. This circuit was composed of C-V converting circuit, high/low pass filter, phase shifter and phase-sensitive demodulation circuit. The mode characteristic, temperature characteristic and sensitivity of micro gyroscope were tested with this testing board. The nonlinear vibration was tested by the established microscope experimental platform. The test results indicate that the resonant frequency increases with the vibration amplitude. The mode parameters tests prove that the two modes'resonant frequencies are well matched. The resonant frequencies distribute from 2300Hz to 2500Hz, which are in good accordance with the theoretical solution of the fabricated chip. The temperature characteristics tests indicate that resonant frequency and the quality factor decrease with the increasing of temperature, while the frequencies of the two modes match well. The measured sensitivity at atmospheric pressure is 5.61mV/°/s.The research presents a solution scheme for the frequency match, doubly-decouple, and capable of working at atmospheric pressure of MEMS gyroscopes. The work has some significance to the design of the fully-symmetrical and doubly-decoupled micromachined gyroscope.