Structure Design And Optimization Of Micromechanical Silicon Resonant Accelerometer

Silicon-based micro-machined resonant accelerometer is a Micro-Electro-Mechanical Systems(MEMS)inertial sensor which uses the Newton’s second law to convert the measured acceleration into the vibration frequency change of the resonator.Compared with traditional accelerometers,silicon-based micro-machined resonant accelerometers have become one of the research hotspots of high-performance MEMS accelerometers at home and abroad because of their small size,low power consumption,high precision and the ability to provide quasi-digital output.This paper focuses on the structural design and optimization of the silicon-based micro-machined resonant accelerometer.Through theoretical analysis,finite element simulation,prototype test to present the influence factors of the structure for high sensitivity accelerometer,the key modal characteristics and the identification and compensation of the static error model.The main work of this thesis are as follows:By analyzing the operating principle of silicon-based micro-machined resonator acceleration,two structural design schemes are introduced and their characteristics were described and compared in detail.Based on the research goal of a high sensitivity accelerometer,the main design indexes of high-sensitivity micro-machined resonance accelerometer structure are established.Through the derivation and analysis of the key design parameters and model,the design and optimization direction towards the high sensitivity accelerometer structure is determined.The improvement of sensitivity is mainly achieved by increasing the scale factor and reducing the structure temperature drift coefficient.At the same time,in order to reduce the cross-axis coupling sensitivity of the accelerometer and improve the stability of the designed structure,the key parts which affect the cross-axis coupling error are analyzed and determined while,the ANSYS finite element simulation is further used to optimize the structure parameters.Finally,four kinds of high sensitivity structures are designed and fabricated successfully.The result shows that the scale factor of all accelerometer is above 500 Hz / g,and the temperature drift coefficient of single side structure is about 0.58 Hz /℃.In order to guide the designers to choose the working modes of the accelerometer structure properly,the stiffness method is used to analyze the vibration characteristics of the resonator where two modes can reflect the vibration state of the resonator.The linear relationship between the resonant frequency difference and scale factor difference in two modes is presented by theoretical analysis and simulation results.By analyzing the energy distribution of a micro-machined resonant accelerometer operating at two vibration modes,the relationship between the quality factor of resonators and amplitude of the vibration beams is obtained and a quantitative comparison of the associated energy consumption is also presented.By evaluating the noise of the silicon micro resonant accelerometer,the reason of the discrepancy for noise contribuation in two modes is explained and further verified by experiments.The static error model of such silicon-based micro-machined resonant accelerometer is analyzed and provided.The main factors of each parameter in model are analyzed in detail.The main parameters of the acceleration structure in the two design schemes are substituted into the conclusion to calculate the main items in model to obtain the theoretical calculation results.Besides,the experimental scheme is designed to test a prototype of micro-machined resonance accelerometers used in theoretical calculation,and coefficients in the static error model are identified.Finally,the output data of the prototype is compensated by the identified static error model,and the difficulties of compensation are discussed.Results show that,with the increase of an input acceleration along the sensitive axis,the compensation effect is gradually obvious and the maximum output deviation is reduced by 84%.The associated equipment and parts for the test setup are designed and assembled carefully.Then the performance tests of four high sensitivity prototypes are performed.The sensitivity of a prototype is increased up to 832 Hz/g where the optimal temperature drift coefficient is-1.93 μg/℃ and the bias stability is 0.82 μg.The test results show that the sensitivity is greatly improved along with excellent temperature drift performance.It has the potential to be used for high-precision inertial navigation and gravity measurement.