“CoFeB-MgO”基磁隧道结的自旋轨道矩效应超快翻转动态研究

The Spin Orbit Torque (SOT) Magnetic Random Access Memory (MRAM) based on Perpendicular Magnetic Anisotropy (PMA) presents non-volatile and ultra-high-speed data storage, which has a wide potential application in the Last Level Cache (LLC) and becomes a research focus in “Beyond Moore” integrated circuit (IC). However, the physical fundamentals of the SOT magnetization reversal in PMA Magnetic Tunnel Junctions (MTJs) are unclear. Especially, there are still lack of research woks on dynamic properties of sub-ns ultrafast magnetization reversal. Therefore, first of all in this project, we will deeply analyze the mechanism of dynamic ultrafast magnetization reversal (down to ps-level) within the in-plane magnetic fields in “CoFeB-MgO” based SOT-MTJs. Then, by introducing the coupling effect of the SOT and the Spin Transfer Torque (STT), we will design the MTJ devices and measurement methods which satisfy both the SOT and STT effects at the same time. The dynamic magnetization reversal under the coupling effects will be studied and the field-free ultrafast switching will also be revealed as well. Finally, by analyzing the effects of different SOT metals or inset layers on perpendicular anisotropy, spin injection efficiency and damping coefficient of free layers, we will deeply understand the initial law and nature of the dynamic ultrafast magnetization switching and coupling effects in the SOT or SOT+STT-MTJs. We believe that this project would provide theoretical and experimental basis for further research and development of new high-speed storage spintronic devices in IC design and information industry.

基于垂直磁各向异性（PMA）的自旋轨道矩（SOT）磁随机存储器具有非易失、超高速的数据存储特点，在末级缓存中具有广泛的应用前景，目前逐步成为“后摩尔时代”集成电路的一个研究热点。然而PMA磁隧道结（MTJs）中SOT引起磁矩翻转的物理机理仍不够清楚，尤其是sub-ns级超快磁矩翻转的动态研究非常匮乏。因此，本项目基于“CoFeB-MgO”基MTJs，首先拟在SOT-MTJs中，研究面内磁场辅助下的ps级超快翻转动态过程和机制；然后引入SOT与自旋转移矩（STT）的协同效应，设计同时满足两种效应的MTJ器件和测试方法，研究协同作用下的磁矩翻转动态过程，实现无磁场的超高速磁矩翻转。最后，研究不同SOT金属层或内插层对垂直各向异性、自旋注入效率以及自由层的阻尼系数的影响，深入探索SOT以及SOT+STT协同效应磁矩动态翻转规律和耦合机制，为进一步新型高速存储自旋电子器件的研发提供理论和实验依据。

基于垂直磁各向异性（PMA）的自旋轨道矩（SOT）磁随机存储器（MRAM）具有低功耗、超高速的数据存储特点，在新型非易失存储器中具有广泛的应用前景。然而PMA磁隧道结（MTJs）中SOT引起磁矩超快翻转的物理机理和动态过程仍不够清楚。因此，本课题针对“CoFeB-MgO”基SOT-MTJs开展超快翻转研究，通过自主搭建的双通道超快电学测试系统，对制备的纳米结高频器件开展时域分析，揭示磁矩翻转的动态过程，不仅加强了对SOT以及SOT+STT协同效应磁矩动态翻转机制的认识，也为进一步新型高速存储自旋电子器件的研发提供理论和实验依据。.在该项目资助下，我们在Fundamental Research, Proceedings of the IEEE, IEEE Electron Device Lett., Sci. China-Phys. Mech. Astron.等杂志发表文章6 篇，其中SCI 收录5 篇；申请国家发明专利1项。主要研究成果包括：首先在SOT-MTJs中，研究了面内磁场辅助下的超快翻转动态过程，揭示了类场矩效应影响SOT翻转的物理图像，阐明了SOT翻转弛豫时间的产生机制；然后引入SOT与自旋转移矩（STT）的协同效应，研究协同作用下的磁矩翻转动态过程，实现800 ps无磁场的超高速磁矩翻转，探究了时序调控对SOT+STT协同效应磁矩动态翻转的影响规律，为实现低功耗超快写入奠定了基础。最后，设计制备了NAND-SPIN型SOT+STT写入的磁存储器结构，实现一次擦出和选择写入功能，为实现高密度SOT-MRAM提供解决方案之一；此外，还揭示了自旋矩翻转过程中出现的瞬态中间态行为和稳定的磁滴孤子行为，为进一步研究磁矩动力学行为提供研究基础。