Design And Optimization Of The Subwavelength Gratings And Compliant Beams For High Precision MEMS Accelerometers

As the critical part of inertial navigation system,MEMS(Micro-electromechanical Systems)accelerometers,especially those of large dynamic range and high precision(10-6-10-9g),are the focus of advanced military and defense researches.In recent years,accelerometers aborad has developed rapidly while there has not been a significant technological breakthrough in China.Traditional piezoelectric accelerometers and capacitive accelerometers are still the main type of accelerometers in our country and their precison level are only around 10-4-10-5g.The precision and dynamic range of those types of accelerometers are quite small.Therefore,it is of great importance to develop accelerometers of high precision and large dynamic range in order to improve the inertial navigation technology in China.Recently,in order to further improve the sensitivity of the accelerometer,new types of MEMS accelerometers have become an important research topic.This paper focused on the design and optimization of three new types of MEMS accelerometers and proposed an optimized design method for the flexible free form beams of MEMS accelerometers.In addition,in terms of the dynamic range,we studied the closed-loop control system of the MEMS accelerometer and developed a joint mechanical and electronic optimization method for the closed-loop system of MEMS accelerometer.The main work of this article is summarized as follows:This paper studied how to improve the sensitivity by using new detection method and conducted the analysis and design method of a sub-wavelength optical MEMS accelerometer based on Wood's anomaly.The proposed design method made up for the shortagae of the theoretical study in this type of structural design.The sensitivity of the MEMS accelerometer has been increased by 41%after optimization.In this paper,the optimal parameter values of the structure under different common wavelengthes were given and the influence of each parameter on the device performance was analyzed in detail.A Monte Carlo analysis has been conducted to predict the yield of such accelerometer and laid a theoretical foundation for the fabricationin the future.Based on the work mentioned above,we innovatively discovered a "pulsed" special Wood's anomaly phenomenon and designed a sub-wavelength optical MEMS accelerometer based on this new phenomenon.In this phenomenon,the change rate of the optical signal with respect to the displacement is increased by 8 times and thus the sensitivity of the MEMS accelerometer based on this phenomenon has also been improved by 8 times.We named it as a "pulsed" special Wood's anomaly phenomenon.Two kinds of calculation methods,finite-difference time-domain method and rigorous coupled-wave analysis theory,are used to verify this phenomenon.Two methods of design and optimization are proposed.The parameter analysis of the MEMS accelerometer based on this phenomenon was conducted and the optimal parameter values of the device in terms of different common wavelengths were given.Through Monte Carlo analysis,the effects of processing errors on the performance of the device were studied.In addition to improving the sensitivity by using new detection method,this paper studied how to increase the sensitivity by optimizing the mechanical structure and innovatively introduced the flexible free form beam structure into a mechanically amplified MEMS accelerometer.The flexible free form beam has greatly improved the bandwidth and sensitivity of the accelerometer and solved the contradiction between the mechanical magnification and the stiffness of the beam.And we developed an optimization software for MEMS flexible free beam structure.It is a new method to design MEMS flexible free beam structure and reliefed the designer from the complex theoretical calculations.As for the design requirements for large dynamic range,this paper innovatively studied the mechanical and electronic co-optimization techniques for MEMS sensors.This technology increased the sensitivity and dynamic range of the device.It solved the problem in which the mechanical design and electrical designa are separated from each other.It allows mechanical part and electronic part to complement each other and greatly shortens the MEMS design cycle.Based on this technology,a set of optimization software was developed and we designed the EM ??M(Electronic Mechanical Sigma Delta Modulator)of the mechanically-magnified MEMS accelerometer with flexible free form beam.