Research On Integrating Temperature-Magnetic Field In-situ Measurement Sensors On MEMS Accelerometer Chip

Accelerometers have been widely used in consumer electronics,automotive electronics,biomedicine and other fields,while gravity measurement,resource exploration,earthquake early warning,autonomous navigation have higher requirements for the accuracy of accelerometers.The accuracy is mainly refered to the stability of bias and scale factor which are susceptible to external environmental factors.Therefore,it is necessary to measure parameters such as pressure,temperature,and magnetic field variations as well as acceleration at the same time.However,it is difficult to achieve in-situ measurement of multiple environmental parameters for traditional sensors.MEMS（Micro-Electro-Mechanical Systems）technology can solve this problem,and make the fabrication of multiple different sensors on the same chip to detect different physical quantities,with small size and low unit cost,and has broad application prospects.In this thesis,in order to meet the requirements of ultra-high-precision accelerometer with a bias stability of less than 1μg and a scale factor stability of less than 1 ppm for precision gravity measurement,the on-chip integrated temperature sensor and magnetic sensor have been developed and fabricated on the accelerometer chip through the microfabrication process.Therefore,the high-precision in-situ measurement of temperature and magnetic induction intensity are implemented,which lays a technical foundation for system-level compensation.By analyzing the disturbance sources and influences of the accelerometer,and combining with the preliminary experimental results,the parameter requirements of the integrated temperature sensor and magnetic sensor are clarified.Through the design of the process of the overall fabrication scheme,the technical difficulties and compatibility issues are analyzed.In order to realize the in-situ temperature measurement of high-precision MEMS accelerometers,an integrated gold thin-film temperature sensor is proposed.The temperature sensor has an accuracy of 80 m K,the repeatability of 30 m K within 7 days,a noise floor of 0.1 m K/Hz^1/2@0.2～0.5 Hz.By compensation by using this temperature sensor,the stability of the MEMS accelerometer was improved to 0.6μg over 46 hours.In order to realize the in-situ magnetic field measurement of high-precision MEMS closed-loop electromagnetic feedback accelerometer,a resonant Lorentz-force magnetic sensor with structural topology based on double-ended tuning fork is proposed.By adding cavity-slots structure on the tine beam,the thermoelastic dissipation was reduced,and the quality factor of the device was improved by 5.9 times.Under a large bias magnetic field of the closed-loop feedback system,the proposed magnetic sensor has a sensitivity of 2500Hz/T,and a noise floor of 210 n T/Hz^1/2@0.1～10 Hz.In addition,the drift of the frequency output of the magnetic sensor with temperature was characterized as-2.9 Hz/℃,and the temperature coefficient was-28 ppm/℃.The simulation results show that the external acceleration will not interfere with its frequency output.The fabrication processing of the temperature sensor,magnetic sensor and accelerometer is completed by using SOI wafers.To solve the problems of process compatibility and stability,the metal etching method is proposed to eliminate the insulating film pinhole defects between two metal layers.The leakage current density of the samples treated by this method was on the same order of magnitude as the samples without pinholes,and was at least 6 orders of magnitude smaller than that of the untreated samples.The integrated gold thin film temperature sensor proposed in this thesis is expected to eliminate the main residual of traditional high-precision MEMS sensors temperature compensation due to temperature gradient,heat transfer,and low measurement resolution.The proposed resonant Lorentz-force magnetic sensor can be used in large bias magnetic field and complex magnetic field environment,it has outstanding measurement dynamic range,resolution,quality factor and universality,and is easy to be integrated.After fabricated on a monolithic chip with temperature and magnetic sensors,the environment disturbance of the high-precision accelerometer can in-situ measured.The compensated accelerometer can have a higher accuracy and has great application potential in many high-precision inertial measurement fields,such as gravity measurement,seismic measurement,and tilt measurement.