Switching Mechanism And Optimization Of Spin-transfer-torque Magnetoresistance Random Access Memory

Since the first generation of magnetic random access memory(MRAM)came out,more and more researchers have begun to study MRAM.As the core structure of MRAM,magnetic tunnel junction(MTJ)has been the focus of research.For the first generation MRAM,the magnetization direction and the magnetic resistance state of MTJ is changed by the magnetic field generated by the current,thus the data reading and writing are realized.But its disadvantages are also obvious.Because the magnetic field needs strong current to support,the system would bring serious energy consumption problems,and would reduce the overall thermal stability.Spin-transfer torque(STT)effect can solves these problems well,so the second generation MRAM is also called STT-MRAM.Compared with MRAM,STT-MRAM has such advantages as high integration,fast reading and writing,good thermal stability,so it is the next generation MRAM with great application prospect.On the basis of STT-MRAM,the relevant experimental and theoretical models,several optimization schemes of STT-MRAM are analyzed in this paper for the purpose of further enhancing the STT effect.The main research contents are as follows:1.The origin and development of the STT-MRAM are described in detail.Using the Landau-Lifshitz-Gilbert-Slonczewski(LLGS)equation and the macro spin model,the magnetization reversal is discussed without any assistance.2.the external electrical field is exerted to assist the magnetization reversal of MTJ.The results show that the external field can effectively improve the magnetization reversal speed,but it will increase the energy consumption of the system.Therefore,exerting external field is generally chosen as the auxiliary scheme for STT-MRAM optimization.3.In the paper,we study the perpendicular MTJ with perpendicular anisotropy using micromagnetism simulation.The results show that,compared with the trilayered structure,the perpendicular structure can effectively improve the STT effect,reduce the critical current and accelerate the magnetization reversal speed.4.By adding the buffer layer into the MTJ,the vertical magnetic anisotropy of MTJ can be adjusted and form an easy-cone structure.In this paper,we analyzes the influence of cone angle on the switching mechanism of the structure.The results show that the switching time is the shortest,6.201 ns,and the switching efficiency is improved by about 48.28% when the cone angle is about 23°.