Sensitivity Enhancement Research Of Thin Film Magnetic Sensor

Thin film magnetic sensor is composed of soft magnetic films and planar coil.In the process of magnetization,the permeability of the soft magnetic film will change with the external magnetic field,resulting in the change of the coil inductance value,so as to sense and measure the magnetic field.Compared with magnetic sensors based on the magneto-resistance/impedance effect,the Hall effect,fluxgate and superconducting quantum interference technology,thin-film magnetic sensors have the advantages of small size,simple structure,easy processing integration and miniaturization,and have a broad application prospect in the fields of communication,exploration,navigation and industrial detection.The research object of this paper is the thin-filmed coil.The factors affecting the sensitivity of the thin-filmed coil and the method to improve the sensitivity of the thin-filmed coil are studied.The method is verified by finite element simulations and physical experiments.The main research and experimental contents are summarized as follows:(1)The sensing process of the thin-filmed coil is analyzed,that is,the inductance of the coil is changed by the permeability variation of the soft magnetic film during the magnetization.According to the sensing relationship,two ways to improve the sensitivity of the thin-filmed coil are studied: 1)Improving the permeability of the soft magnetic film to increase the film sensitivity to the external magnetic field;2)Improving the sensitivity of the inductance value of the thin-filmed coil to the permeability of the soft magnetic film.(2)A method to improve the sensitivity of film permeability to the external magnetic field is studied.The magnetic properties of several soft magnetic films have been tested.The results show that the effective permeability of the films is limited by the demagnetization effect.Two methods of restraining the demagnetization effect to improve the effective permeability of soft magnetic films are analyzed from the microscopic and macroscopic aspects: 1)Change the shape and volume fraction of magnetic particles in magnetic materials in microcosm;2)Adjust the size of the soft magnetic film in macrocosm.The method of designing groove gratings on the film surface to improve the permeability of the film is studied.This method has two advantages: 1)The demagnetization effect is improved and the effective permeability of the film is improved by reducing the local thickness;2)The effective permeability of the film is further enhanced by the stray magnetic field generated by the groove wall.The groove grating structure with depth and width up to micron on the film surface can be achieved by ultra-precision machining.The VSM test results show that in the length direction,the average effective permeability of the grooved film can be improved by 104.5% compared with that of the flat film,Within the range of 0?100Oe,the effective permeability variation rate increases by182.2% with the change of the external magnetic field.(3)The method of increasing the sensitivity of coil inductance to the film permeability is studied.The effects of the self-inductance,mutual-inductance and the size of the thin film on the coil inductance are studied.The coil inductance value expression with groove is derived.The theoretical analysis and simulation results show that the groove grating can improve the convergence effect of the film on the magnetic field excited by the coil to improve the inductance of the coil,and make the coil inductance variation rate higher when the film permeability changes.(4)Simulation analysis and physical experiment of the thin film magnetic sensor are carried out to verify the improvement of sensitivity.The enhancement of inductance sensitivity by groove gratings is simulated which become stronger with the increase of the groove depth and the density of the groove.The change rate of coil inductance can be effectively increased by machining groove gratings on the surface of the film which is deep and dense enough.A film magnetic sensor with grooves was obtained by combining the plane coil with the film after ultra-precision machining,and the inductance variation rate and sensitivity were tested.In the sinusoidal current excitation of 500 kHz and 10 mA,the improved magnetic sensor's maximum inductance value is 89.38?H,the inductance variation is 54.00?H,the inductance variation rate is 152.63%,which increase9.67%,26.37% and 42.42% respectively compared to the original thin film magnetic sensor without groove structure.The improved sensor sensitivity is 3.25 m V/Oe,12.85% better than the original structure.