Structure Design And Optimization Of A New Symmetric Fully Decoupled Dual-Mass Micro-Gyroscope

Inspired by the promising success of Microelectromechanical Systems (MEMS) technology, micro-gyroscopes are expected to lead to reliable, robust and high performance angular-rate sensors with miniaturization, low production costs and high yields, fitting into or enabling many applications in the consumer electronics, automotive and aerospace/defense markets. Over the past decades, micro-gyroscopes have experienced substantial improvement with the continuing research. However, being limited by the susceptibility to fabrication process variations and environmental fluctuations, the performance of micro-gyroscopes is still not sufficient for navigation and other high-precision required applications.Toward the goal of improving the performance of micro-gyroscopes, this dissertation investigates the operational principles and design algorithms for the silicon micro-gyroscope. Based on the analysis, the dual-mass scheme and fully decoupled proposal are employed to form the novel micromachined gyroscope. FEM simulations together with structure optimizations are implemented to verify the good properties of this micro-gyroscope. Simultaneously, fabrication process variations and environmental fluctuations that inevitably perturb the performance of the gyroscope are demonstrated. The specific achievements of this work are summarized below:(1) Analytical study of the working principles and resonance characteristicsThe operational principles of the silicon micro-gyroscope are illustrated, the basic architecture is outlined and the Coriolis effect is introduced. Afterwards, the dynamic scheme is modeled, followed by the theoretical analysis of traditional mass-spring-damper second order dynamic system. The dynamical formulas of the drive mode and sense mode are then derived. Ulteriorly, the resonant modes of the dual-mass are investigated. Additionally, the illustrations of electrostatic actuation and capacitive detection, as well as the damping related issues are provided.(2) Structure design and simulations of the new symmetric fully decoupled dual-mass micro-gyroscopeAfter investigation and comparison of the primary mechanical elements of the silicon micro-gyroscope, a complete symmetric fully decoupled dual-mass micro-gyroscope is proposed with the selections of proper mechanisms, including the structure of the drive and sense mechanisms, the scheme of decoupling, as well as the symmetric dual-mass concept. Afterwards, modal simulation, acceleration simulation, thermal stress simulation, harmonic simulation, and transient shock simulation are implemented by FEM software to verify the feasibility of this micro-gyroscope, based on which, structure and dimension optimizations are exploited to reach the optimal performance.(3) Error analyses of the micro-gyroscopeThe primary error sources of the silicon micro-gyroscope are illustrated and the induced impacts on the performance are presented. Design disciplines and optimization concepts are highlighted for each error. The structural error sources mainly incorporate the anisoelasticity and anisodamping which induce quadrature, the over-etching and side wall angle of suspension beams that result in drifts of modal frequencies, and the asymmetry of proof mass and stiffness which causes variation of resonant amplitudes. Moreover, electromechanical interfaces of the drive mode and sense mode are performed, and the disturbances caused by the stray capacitances are demonstrated. Finally, the temperature variations induced errors are addressed, of which, fluctuations of eigenfrequency, quality factor, time to stabilization, drive mode amplitude, mechanical sensitivity, as well as capacitive sensitivity are covered.(4) Fabrication and experiments of the micro-gyroscopeThe DDSOG based micromachining processes are introduced, and the packaging technology is discussed. Experiments are conducted using the finished sample. Experimental tests primarily include the resonance characteristics of the drive mode and sense mode, scale factor, bias, temperature dependent characteristics, etc. The experimental results obtained verify the good properties of the micro-gyroscope.