Development And Test Of MEMS Planetary Seismometer

Planetary microseismometers can be used for resource exploration,planetary seismic monitoring,and internal geological structure study of planets.These applications have higher environmental adaptability requirements for microseismometers,including shocks,vibrations,temperature alternating and other harsh environments during launch and landing.This thesis has performed structure design,optimization and fabrication process development with the target of planetary seismic monitoring applications.The target noise level of the MEMS microseismometer is lower than 1 ng/?Hz @ 0.1-10 Hz.Meanwhile,the MEMS microseismometer should endure random vibrations of greater than 10 g and shocks of greater than 500 g.The total weight of the triaxial seismometer should be less than 2 kg.First of all,the overall scenario design of the MEMS microseismometer has carried out according to application requirement.The structural design uses springs in series to reduce the stiffness in the sensitive direction and through the high aspect ratio deep reactive ion etching process to increase the proof mass so that reduce the mechanical thermal noise of the structure.In order to improve the capacitance-to-displacement sensitivity of the MEMS microseismometer,the main affecting factors have been studied.Then,a novel array capacitance displacement transducers based on fringe effect has been proposed.It ultizes the nonlinear effect to obtaina a higher capacitance-displacement sensitivity within a smaller range.The experiments have been carried out to evaluate the MEMS microseismometer.Secondly,the research and exploration on processing and packaging of the MEMS microseismometer has been carried out,including the metal layer deposition process,the insulation layer deposition process,the metal layer electroplating process and the deep silicon etching process.For the small linewidth of the metal patterns,the metal lift-off method has been found to be suitable for the photolithography process.For the pinhole problem in the insulation layer,the gold etching solution has been used to detect the pinhole defects and also prevent shorts between the upper and lower metal layers through pinholes.In terms of the deep silicon etching process,process exploration and testing have been carried.For the electrical connection problems in the packaging process,process adjustments have been made to have suitable packaging conditions.Then,the overall performance evaluation of the MEMS microseismometer has been carried out,including electrical performance test,static self noise test,seismic monitoring and environmental adaptability test.The best result of the static noise floor is 0.25 ng/?Hz@1 Hz.The MEMS microseismometer prototype has successfully monitored the earthquake(M 4.9)occurred in Xiaogan,Hubei at 18:36 on December 26,2019.The environmental adaptability test includes the random vibration with the maximum root mean square acceleration of 12.45 g(20-2000 Hz),the sinusoidal vibration acceleration with the amplitude of 14 g(4-100 Hz),the shock response with the amplitude of 750 g(100-3000 Hz))and the steady acceleration test with the amplitude of 15 g.Finally,in order to verify some key technologies of the MEMS microseismometer and the adaptability of the space application environment,a three-component MEMS seismic measurement module has been designed.The ground performance tests,environment adaptability tests,and on-orbit tests have been carried out.The resolution,scale factor,zero offset and other parameters of the MEMS seismic measurement module have been evaluated.The environmental adaptability tests include random vibration,sinusoidal vibration,shock response tests,and high-low temperature cycling tests.The three-component MEMS seismic measurement module carried by CZ-5B rocket has been launched at 18:00 on May 5,2020,and 11 hours of on-orbit data has been recorded.Through the comparison with the reference sensor STIM300,the acceleration measurement function of the MEMS microseismometer has been verified,which provides technical reserves for the future lunar and planetary geological exploration in our country.This thesis has implemented the structural design and optimization,process research and exploration,overall performance testing,environmental adaptability testing and flight verification of key technologies of the MEMS microseismometer.The proposed MEMS microseismometer can not only be used for active vibration isolation systems of space stations,satellite drag-free control,and high-microgravity space scientific experiments,but also for monitoring Lunar and Mars earthquakes to provide information for internal structure and evolution study of planets.It also lays the technical foundation for the upcoming "Chang'E-7" lunar earthquake monitoring experiments.