Research On Self-calibration Technology Of High Precision MEMS Capacitive Accelerometer

The capacitive accelerometer has many merits,such as small temperature coefficient,high sensitivity and good stability.It can be used in the field of automobile electronics,oil exploration and bridge vibration monitoring.The calibration of the acceleration sensor is very important for its accurate application.Conventional acceleration sensor commonly uses mechanical vibration table calibration method,but the equipment is expensive,complex and inconvenient for on-site calibration.In this thesis,the inertia force of the mechanical vibration table is simulated by using the electromagnetic force and electrostatic force to realize the on-site self-calibration of acceleration sensor.In this thesis,the principles of variable spacing and variable area in MEMS capacitive accelerometer are introduced.Several common micro-drive methods and their respective advantages and disadvantages are described.Then,the mathematic model of the acceleration sensor is analyzed and the transfer function and response characteristics are obtained.Then,based on the second theorem of Cartesian,the relationship between the elastic coefficient of the U-shaped support beam and the beam size parameter is deduced empirically.It is shown that the influence of the axial deformation of the vertical part of the elastic beam structure is only 13.1ppm.Secondly,a MEMS accelerometer with on-site calibration function is designed.The principle of electromagnetic drive is used to simulate the inertia force of traditional mechanical vibration table with the ampere force generated on the conducting wire.The structure of the acceleration sensor and the bulk silicon micromachining process for manufacturing the sensor are given.The motion mode and sensitivity of the sensor are analyzed with the finite element simulation software ANSYS,and the verification of the calibration characteristic is realized.The results show that the resonant frequency of the designed acceleration sensor is 1528.84 Hz,the static displacement sensitivity is 0.109?m / g,and the influence of electromagnetic induction current on the calibration current is only 1.5ppt.And when the DRIE process error caused by the sensor structure is 1 ° tilt,the calibration current changes less than 0.16%.In addition,the electrostatic drive and calibration technique are combined to simulate the dynamic acceleration signal with varying electrostatic force,and the drive voltage formula at fixed comb is given.It also shows the existence of the fringe effect and corrects the calibration voltage.It is shown that the increase of the plate spacing does exacerbate the fringe effect,but after adding the correction factor,the error at the amplitude decreases from 9.34% before compensation to 0.27% after compensation.The correction effect is obvious.The error conditions show that this idea can be applied to the calibration of high-precision MEMS capacitive acceleration sensor.Finally,a new type of capacitive acceleration sensor with self-calibrating vibration table is designed.The calibration shaker is miniaturized and integrated with the capacitive acceleration sensor itself.The new structure uses the principle of electrostatic drive,and it can calibrate sensor in the sensitive direction as well as realize the real-time test of the cross-axis characteristic.It can overcome the shortcomings that the sensor cannot be calibrated after it is sold or the sensor characteristics change.