Research On Magnetic Sensors With Tunable Sensitivity

CoFeB magnetic material exhibits an obvious abnormal Hall effect due to the spin-orbit coupling effect,and it holds great potential in the magnetic field sensing field.Meanwhile,CoFeB film materials and oxides such as MgO will form a strong interface anisotropy,and the interface anisotropy is sensitive to the voltage along the perpendicular direction of the film.Therefore,we choose to study magnetic field sensor with adjustable sensitivity based on the anomalous Hall effect with the principle of voltage regulation anisotropy.This paper contains four parts:film performance test,device processing technology,device performance test and sensitivity adjustment.The main research contents are as follows:Firstly,the structure of the CoFeB multilayer film was designed,and the Ta/CoFeB/MgO/Ta structured film was prepared by magnetron sputtering,and the relationship between the thickness of different CoFeB layers and the magnetic anisotropy of the film was explored.When the thickness of the CoFeB layer was 0.85 to 1.1nm,it was found that the film exhibited perpendicular anisotropy;when the thickness was 1.15 to 1.25nm,it exhibited in-plane anisotropy.Besides,photolithography process and magnetron sputtering were utilized to prepare Ta/CoFeB/MgO/Ta/Pt/Si₃N₄/Ta magnetic field sensor.For magnetic field sensor device with perpendicular anisotropy,the relationship between external voltage and vertical anisotropy were analyzed and the results showed that external voltage be used to adjust the perpendicular anisotropy of the device,therefore,the sensitivity can be adjusted by the external voltage.Further testing show that the sensitivity of the magnetic field sensor with vertical anisotropy decreased with the increased external voltage;when the thickness of the CoFeB layer was set to be 1.05nm,and the external voltage increased from-8V to 6V,then,the sensitivity variation would be 0.013m V/k Oe.For the magnetic field sensor device with in-plane anisotropy,it’s the corresponding sensitivity would decrease with the increased external voltage.If the thickness of the CoFeB layer was set to be1.15nm,the charge in sensitivity get larger.When the voltage increased from-8V to 8V,the sensitivity variationΔS could achieve 0.203m V/k Oe.Therefore,the sensitivity of the sensing device can be adjusted by applying different external voltages,and the sensitivity variation is related to the polarity and magnitude of the external voltage.