Research On Z-Oriented MEMS Orthogonal Fluxgate Sensor

Fluxgate sensors have advantages of high accuracy,high sensitivity,and relatively simple preparation processes.They are widely applied in space exploration,geological exploration,and geomagnetic detection.Existing research shows that technical methods for preparing two-dimensional planar fluxgate sensors by MEMS technology are relatively mature.However,the problem on how to realize the miniaturization and integration of three-axis fluxgate sensor is to be solved.Based on the problem,the paper studies the MEMS preparation process and performance improvement methods of Z-oriented orthogonal fluxgate sensor.It will provide a sufficient research basis for the realization of fully integrated miniaturized triaxial fluxgate sensors.In the paper,the optimal core turns of the Z-orientation miniature orthogonal fluxgate sensor were determined by finite element simulation.The simulation results showed that when the number of the magnetic core turns was three,the comprehensive performance of the miniature orthogonal fluxgate sensor was best.The linear range of the emulated device was 0-800 ?T,the sensitivity 53 V/T,the power consumption growth rate small as well.Then the Z-orientation planar fluxgate sensor is fabricated by MEMS technology.In order to improve the feasibility of the experiment,the induction coil was changed from three-dimensional spiral coil to planar spiral coil.Subsequently,a fluxgate test system was set up to test orthogonal miniature fluxgate sensors with the same number of core turns but different structures to obtain the optimal shape of the core.Three-turn zigzag,three-turn parallel,and three-turn vertical fluxgate sensors were tested.The results showed that the three-turn zigzag fluxgate sensors had excellent performance,whose linear measurement range was 0-100 ?T,the highest sensitivity 109.78 V/T,and noise at 1Hz was 41.566 n T/?Hz.Compared with the planar X-Y miniature orthogonal fluxgate sensor,the performance parameters of the sensor in this paper still need to be improved.Part of the reason was that the planner spiral induction coil had a higher magnetic leakage than the three-dimensional spiral induction coil,which reduces the sensitivity of the sensor.To solve the problem,the planar spiral induction coil was to be improved in two aspects :(1)the multi-turn planar spiral coil should be connected in multiple layers in series,and the sensitivity of the device would be greatly improved;(2)ultra-thin graphene film could be electrophoresis deposited,and then patterned by MEMS process.Planar spiral coil based on a graphene/copper composite film may improve the electrical performance of the copper spiral coil.Experiments found that when multi-turn planar spiral induction coils were connected in series,the sensitivity of the fluxgate sensor increased a lot:when the number of layers of the planar spiral induction coil was doubled,the sensitivity of the fluxgate sensor increased 13 times.The optimal working conditions for the preparation of graphene films by electrophoresis were determined as: voltage 10 V and electrophoresis time 30 s.The best drying environment for the graphene film was: 45 °C in vacuum drying box.Testing of micro-inductive devices based on graphene/copper composite films showed a big change in inductance:compared to micro-inductive devices made of copper,the inductance of graphene/copper-based composite film micro-inductive devices increased as high as 48.64% at frequency f = 1 MHz.