| With the development of science and technology,spin electronic devices have made great progress.STT-MRAM and SOT-MRAM,as new generation magnetic memories,have been used for commercialization.However,STT-MRAM has the problem of thermal noise,and the read and write terminals are shared.SOT-MRAM also has the problem of in-plane magnetic field.Therefore,it is particularly necessary to find a suitable switching scheme.MTJ,as the core device of magnetic memory,The research on vertical magnetization switching of MTJ is helpful to improve the performance of magnetic random access memory.This paper constructs the micromagnetics models of STT-MTJ,SOT-MTJ,VCMA-MTJ,TI/FM structured SOT-MTJ,and studies the switching mechanisms under the four models.The main work includes the following aspects:(1)The P-MTJ and I-MTJ models of multilayer magnetic films based on the STT effect are constructed.The switching characteristics,magnetization of the free layer and system energy changes under P-AP and AP-P switching modes are analyzed by using micromagnetics software.The results show that the current density and switching time achieved by P-MTJ are smaller compared to I-MTJ,and the limit switching time reached by P-MTJ is also smaller as the current density increases;In the process of P-MTJ switching,the magnetization of the free layer presents a periodic change of magnetic vortex state,while in the process of I-MTJ switching,the magnetization presents a complex and time-consuming multi domain change,which makes the switching time of I-MTJ longer;In terms of energy change,the trend of energy change of P-MTJ and I-MTJ is to increase first and then decrease,but the fluctuation of energy change of I-MTJ is greater.In addition,because the demagnetization field energy in P-MTJ decreases first and then increases,the demagnetization field makes positive work on magnetization first during switch switching,reducing the difficulty of turning over,thus shortening the switching time of P-MTJ.(2)The micromagnetics model of SOT-MTJ is constructed,and the micromagnetics software is used for simulation.The switching mechanism of magnetic field assisted switching scheme and DMI induced field-free switching scheme is analyzed.In the magnetic field assistance scheme,the magnitude of the magnetic field,damping constant,and field like moment will affect the deterministic switching of SOT.A magnetic field intensity higher than 17.5 m T will cause interference from the magnetic field,leading to SOT switching failure.When the damping constant is less than 0.1,the switching will have randomness.When the efficiency value of field-like torque moment is between-0.12 and-0.03,SOT switching shows a significant improvement effect,and the switching time can be increased by up to 1.86 ns;In the DMI induced switching scheme,the constant value of DMI is negatively correlated with the switching current density value.The combination of SOT and DMI drives the rapid movement of Néel type domain walls,thus achieving field-free switching.This indicates that the DMI effect has a significant improvement on the performance of SOT-MTJ.DMI effect can be used to achieve monopole/bipolar switching of magnetization vectors.In addition,introducing field-like torque moments under the DMI effect actually hinders the trend of magnetic moment flipping.(3)The micromagnetics model of VCMA-MTJ is constructed,and the switching mechanism of VCMA-MTJ is studied by using the micromagnetics software for simulation.The results show that when the voltage pulse is in the proper range,VCMA can achieve fast switching of hundreds of ps with the help of magnetic field,but this scheme requires in-plane magnetic field and precise control of voltage pulse.Based on this,we propose a field-free switching scheme of SOT-MTJ based on TI/FM heterostructure,Compared to the traditional HM/FM magnetic field assisted scheme and DMI induced field-free switching scheme,this scheme can achieve a critical switching current density reduction of 80.3% and 90.9%-91.2%,respectively.Additionally,the TI/FM heterostructure exhibits significant DMI effect,enabling field-free perpendicular magnetization switching. |
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