Research On Multi-spring Sensitive Suspension Of Low Frequency MEMS Acceleration Sensor

Seismic exploration technology is the main method for exploration of energy minerals.Acceleration sensor is the main equipment for seismic exploration.With the development of exploration requirements and the influence of deep geological structure,traditional acceleration sensors for seismic exploration can not meet the application requirements.The Micro Electro Mechanical System(MEMS)acceleration sensor provides a new solution for seismic exploration.However,the key technology of high-precision and low-frequency MEMS acceleration sensor is still monopolized by foreign technologies.Moreover,due to the high fundamental frequency and lack of sensitivity,domestic MEMS accelerometer with property rights cannot effectively collect and monitor low-frequency micro-seismic signals.In this dissertation,to overcome the disadvantage of domestic micro-seismic monitoring,a silicon-based low-frequency multi-spring suspension is designed as the sensitive element of the MEMS acceleration sensor.The main works of this dissertation are given as follows:Firstly,a multi-spring sensitive suspension with inner frame and seven springs connected in series was proposed.Based on available multi-spring suspension structures and the theoretical analysis of the spring-mass damping system in traditional accelerometers,the multi-spring suspension structure with overall size of 25 mm × 25 mm was designed.By calculating mechanical structures of the multi-spring,combined with the finite element analysis(static simulation analysis and modal simulation analysis based on ANSYS Workbench)of multi-spring suspension of different sizes,the multi-spring suspension were studies.Based on simulation results,the shape and number of springs,critical geometric parameters of the multi-spring sensitive suspension were optimized.Based on the above analysis,the size of center mass of multi-spring sensitive suspension,structure with seven sets of series springs arranged symmetrically at both ends of the mass and the inner frame structure were determined.Modal analysis and harmonic response analysis showed that the resonant frequencies of the multi-spring sensitive suspension were respectively 9.9666 Hz and 10.5 Hz.Secondly,the multi-spring sensitive suspension processing based on Deep Reactive Ion Etching(DRIE)was achieved.The process of DRIE was designed,and the parameters such as cycle time,chamber pressure,gas flow rate,gas ratio,the number of etching and passivation steps were optimized.A total of 196 DRIE cycles were performed to achieve the penetrating etching of the designed structure.Thirdly,the resonant frequency of multi-spring sensitive suspension wasmeasured by scanning electron microscope(SEM).A resonant frequency test platform was built.An exciter was used to stimulate the SEM.The SEM scanned the vibration patterns of the multi-spring suspension under different excitations.By analyzing the SEM scanning waveform,the resonant frequency of the multi-spring sensitive suspension was about 11.13 Hz.In a word,in this dissertation,the multi-spring suspension was designed by theoretical calculation and finite element simulation,the structure was obtained by DRIE,and the suspension's resonant frequency about 11.13 Hz was verified by experiment.