The Nonlinear Dynamics Combined With Temperature Research And Optimal Design On Sensitive Structure Of Silicon Micro Resonant Accelerometer

Compared with traditional high-precision accelerometers,silicon resonant accelerom-eter(SRA)has the advantages of small size,light weight and low power consumption.Compared with other micro-electromechanical(MEMS)accelerometers such as capacitive accelerometer,it also has the advantages of large dynamic range and high sensitivity.This kind of accelerometer has a wide application prospect in the field of miniaturization and high-precision navigation.It has developed rapidly in the past 20 years and has became one of the research hotspots in major academic institutions.Although the circuit of the resonant accelerometer has been greatly improved in terms of medium and high fre-quency noise and power consumption,its frequency drift and low frequency noise affect the navigation accuracy greatly,which exists a big gap compared to the conventional accelerometer.The accelerometer resonator's temperature characteristics and nonlinear vibration arc the two non-ideal factors of the frequency drift and low frequency 1/f noise.A struc-tural design scheme that,suppresses the influence of nonlinear stiffness and thermal stress from the perspective of structural design have been studied and proposed in this thesis.According to the design goal,the optimized design and the prototype were completed,which helped improve several key performances of the silicon micro-resonant accelerom-eter.Firstly,as resonator is the key component of SRA,the dynamic response of the resonator for nonlinear vibration coupling temperature has been studied.After modeling the dynamic equation of the resonator,the nonlinear dynamic response of SRA vibrating beam resonator in the varying temperature environment was proved to be described and predicted through numerical method.The mechanism of coupling between nonlinear vibration and temperature could be revealed by analyzing the regulation of the system response.This built a foundation for the follow-up theoretical analysis and structural design.Secondly,by analyzing the factors affecting the nonlinear vibration of the resonator,the nonlinear stiffness was studied and calculated,which helped quantify the amplitude-frequency effect of the resonator vibration in the typical SRA sensitive structure.Fur-thermore,an improved "C-beam" design of the resonator structure was proposed.This kind of design reduced the nonlinear stiffness to the original 41%,and increased the linear vibration range of the resonator by 66%,which helped to reduce the effect of amplitude noise on the output signal.Finally,the theoretical analysis and design scheme were verified by experimental methods.Thirdly,the frequency drift of resonator caused by varying temperature was sys-tematically studied in this paper.The relationship between the characteristics of silicon material and the temperature-dependent stress distribution on the sensitive structure and the frequency drift of the resonator were analyzed,which had been verified by fi-nite element simulation.However,thermal stress resulting from the anchors was random and uncontrollable,which became too difficult to compensate the drift caused by ther-mal stress.Therefore,a stress isolated structure compatible with MEMS technology was proposed.It took advantage of the combination of planar flexible structure and rigid structure which could restrain the thermal stress significantly,reducing temperature co-efficient of the resonator frequency effectively.This kind of stress relief structure design could also be applicable to all other MEMS sensors that are sensitive to thermal stress.Fourthly,constrainted by the layout and process,the relationship between each part of the SRA structure has been analyzed.The theoretical model of the scale factor of the improved SRA sensitive structure was established,which provided a theoretical basis for optimization.At the same time,a coordinated optimization design method was proposed for the improved SRA sensitive structure to enhance the scale factor.According to the optimization results,a new generation of SRA prototype was designed and implemented.The MEMS structure was fabricated under the process of 80?m SOI,and the PCB circuit composed of discrete devices was encapsulated and welded by LCC ceramic shell.Finally,all the experiments showed that the prototype had been improved in terms of temperature performance,scale factor and zero-bias instability associated with flash noise.The temperature coefficient of the resonator frequency could be reduced from the original near-1000ppm/? to the level of the silicon material(about-32ppm/?).At the same time,the accelerometer prototype achieved a scale factor of 124.2 Hz/g in the range of ±50g,zero offset stability of 9.6?g,1.3?g of zero offset instability,1.2 ?g/(?)acceleration noise density and 34.9?g of threshold.