| The micromachined MEMS devices offer a lot of advantages such as small size, low power dissipation, high reliability and high shock resistance, and have great potential applications. Especially in national defense and military, MEMS devices used in harsh environments have become one focus of study, such as high g accelerometers. The dynamic characteristic is one important factor which has determinant effect on the use of the devices, and the study of dynamic characteristic is an important aspect of MEMS study. Corresponding to the study of MEMS devices used in the harsh environments, its testing technology, especially dynamic testing technology falls behind relatively.In this thesis, in order to understand the effects of high g-force on the dynamic characteristics, with the beam and proof mass structure as typical MEMS microstructure, the dynamic equation and finite element simulation model of microstructure under high g-force have been formed. The testing technology under high g-force is systematically studied. The high g-force dynamic testing device has been set up and the dynamic testing experiments for microstructure under 0～10,000g accelerations have been performed.The effects of the external load on the dynamic characteristics of microstructure with different mechanical model are systematically studied. When the microstructure in in the linear state, the external high g-force has no effect on the dynamic characteristics of microstructure; while the microstructure is in the nonlinear behaviour, the external loads add an additional stiffness to the element stiffness matrix, thus enhance the structural stiffness and increase the microstrucutre natural frequency.The high g-force dynamic testing device has been developed. The high g acceleration environment is generated from the centrifugal acceleration produced by the centrifugal rotation plate and the 10,000g acceleration has been obtained. Because of the small size and high natural frequency of MEMS microstructure, the traditional dynamic excitation method can not be applied. The base excitation device which uses the piezoelectric ceramic as the driving source is established. The feasibility of the piezoelectric ceramic as the impulse excitation source is investigated, and the excitation device can implement the impulse excitation in 10,000g acceleration.The optic testing method used in MEMS dynamic testing can not be applied in high g-force testing device, so the microstructure with typical beam and proof mass structure which integrates the sensing element is designed and fabricated for dynamic testing under high g-force acceleration. By diffusing the piezoresistance in the micro-beam, the dynamic testing signal is acquired by the output change of the Wheatstone bridge formed by the piezoresistances. As a new fabrication procedure for the microstructure, the wet and dry combined bulk micromachining techniques are developed. The fabrication process is designed and the microstructures are successfully fabricated using the microfabrication processes reported in the thesis.The dynamic testing experiments for the microstructures under different high g-force accelerations from 0g to 10,000g are performed. Through the impulse excitation of the piezoelectric ceramic, the dynamic characteristics such as natural frequencies and damping ratios are obtained by analyzing the impulse response signals. The experimental results indicate that when the deflection of the micro-beam in microstructure is small and in linear state, the external transverse high g-force load has no effects on the dynamic characteristics of the microstructures. While the micro-beam in microstructure is in large deflection under external high g-force and thus in the geometrically nonlinear state, the natural frequency of the microstructure gets higher while the external high g-force acceleration increases. The finite element analysis with stress stiffness modal has been perfomed and the simulation results are in good agreement with the experimental results. |
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