Study Of Process In Memory Based On Electrical Control Of Magnetic Skyrmion

Since the first observation in 2009,magnetic skyrmions have received considerable attention and been widely studied.On the one hand,as topological,particle-like,and nonlinear localized spin structures,skyrmions show significant fundamental research value in physics and material fields.On the other hand,skyrmions are regarded as novel information carrier to develop high-density,low-power,multi-functional spintronic devices.Before the final application,it is the key to study the manipulation methods,the functional devices,and the system architectures of skyrmions.In this dissertation,by micromagnetic simulations and numerical calculations,the electric control of skyrmion dynamics is studied,based on which,the skyrmion-based memory and logic devices are optimized and designed to further used for constructing the architectures of process in memory(PIM).First,perpendicular current-induced skyrmion creation and annihilation is studied,and a kind of binary memory unit is further proposed based on the presence and absence of the skyrmion.Unidirectional current-induced spin transfer torque and Joule heating effect are used to induce the magnetization switching between uniform and skyrmion states in the free layer of magnetic tunnel junctions(MTJs)with thermal barriers.As compared to previous MRAM generations,thermally assisted skyrmion memory has potential improvement in terms of selector device option and operation temperature range.Then,voltage-modulated skyrmion size is studied,and the skyrmion memristive device is further proposed based on skyrmion scaling.Under voltage-controlled anisotropy via remnant strain in multiferroic heterostructure,continuously tunable resistance is obtained in MTJs.The relationships between dynamic resistance range and skyrmion polarity,device dimension and the number of skyrmion are studied.The performance evaluations indicate that the skyrmion memristor has ultra-low power consumption.In-plane current-driven skyrmion motion with skyrmion Hall effect in the magnetic nanowires is also studied.Nanotrack with composite magnetic anisotropy is used to improve the data stability in skyrmion-based racetrack memory.By adding an in-plane magnetized boundary region outside one side of the perpendicularly magnetized nanotrack,an enhanced repulsive edge force acts on the skyrmion to oppose the Magnus force,thus depressing the skyrmion Hall effect.The dependence of the transverse displacement on boundary region properties is studied,and the results are explained by calculations of edge force,Magnus force,and effective field.Furthermore,in-plane current-driven skyrmion motion in nanotrack with different shape is studied,based on which,several skyrmion logic units are proposed.Boolean logic functions including AND,OR,NOT,NAND,NOR,XOR,and XNOR are realized by virtue of various effects including skyrmion Hall effect and skyrmion-skyrmion collision.Within one device structure,different functions can be selected through voltage control terminals,thus implementing a reconfigurable skyrmion logic gate.Finally,based on the design and implementation of the skyrmion memory and logic units above,the skyrmion-based PIM architectures are constructed.Skyrmion memristor array is used to store matrix weight and performs multiply accumulation,thus implementing the artificial neural network-oriented PIM architecture.By using skyrmion-based binary memory unit array with skyrmion-based Boolean logic units included,another type of PIM architecture is realized.The results pave a way for developing skyrmion-based novel computing system.