Research On Frequency Response Characteristics Of Tunnel Junction Magnetosensitive Devices

Magnetic tunnel junctions(MTJs)have been widely applied in the fields closely linked with human life.And it is one of the ideal sensitive elements of micro magnetic sensors.In order to reduce 1/f noise and improve sensor resolution,AC modulation methods have been proposed.At this time,the tunnel junction magneto-sensitive device will work in an AC state,and its frequency response characteristics will affect the sensor bandwidth and AC modulation efficiency.The frequency response characteristics of the device are affected by the impedance characteristics of a single magnetic tunnel junction and the internal electromagnetic coupling.Nevertheless,at present,the research on the impedance characteristics and its intrinsic mechanism of MTJs is insufficient.Meanwhile,the research of frequency response characteristics of tunnel junction magnetosensitive devices are mainly based on experiment and the method is single,and there is no efficient simulation approach.Therefore,based on the premise of designing and building an impedance test system,this paper establishes a single MTJ impedance model based on the impedance characteristic test and mechanism analysis of a single MTJ.On this basis,researches on the simulation methods and influence laws of the frequency response of the devices based on multiple MTJs have been carried out.The main contents are as follows:Aiming at the needs of impedance characteristic test,a multi-parameter and high-precision automatic impedance test system of MTJs was designed and established.Based on impedance test theory analysis,a multi-parameter MTJ impedance test system was designed and built based on the self-balancing bridge method under the support of impedance analyzer,two-dimensional vector electromagnet,and Lab VIEW software,which realized the automatic test of MTJ impedance under different magnetic fields with variable magnitudes & directions and different excitation voltages with variable frequencies & amplitudes;Through the batch processing of test data,a complete set of processes of data preprocessing,fitting and display were realized,and the analysis method of impedance characteristics was formed;After calibration and high-frequency compensation,the test accuracy for resistance can reach 1%,and the test accuracy for capacitance can reach 5% in the frequency range of 20 Hz-500 k Hz.An improved MTJ impedance Debye-Fr?hlich(D-F)model based on spindependent tunneling was proposed,which revealed the anisotropy of magnetic capacitance.(1)The impedance behavior of MTJs was systematically studied: tunneling magnetoresistance,tunneling magnetocapacitance effect,and the variation rule of impedance with frequency were observed,and the frequency dependence was explained based on the D-F model;(2)The influence of magnetic field direction on the impedance was studied: the significant anisotropic behavior of magnetocapacitance was observed,and by combining the spin-dependent tunneling mechanism of MTJs,the D-F model was improved and the theoretical formula of relaxation time versus magnetic field direction was deduced.The theoretical fitting was consistent with the experimental results,which verified the accuracy of the proposed model.The finite element simulation method of frequency response characteristics for tunnel junction magnetosensitive devices based on “MTJ circuit model + distributed parasitic capacitance” was proposed,and the influence law of the frequency response characteristics of the device was studied.The MTJ parametric model was established by analyzing the electromagnetic coupling problem in tunnel junction magnetosensitive devices.Based on the circuit and current interface in COMSOL software,the finite element simulation method of frequency response characteristics of MTJ magnetic sensor was established.The effectiveness of the simulation method was verified through the comparative analysis of simulation and experimental results of typical devices;Based on this method,the effects of the electrode structure,insulating layer material,and fabrication process,and MTJ topology on the frequency response characteristics of magnetic sensors were systematically simulated,and the influence laws were obtained.