CoFeB/MgO磁性多层膜中自旋轨道矩与自旋转移矩耦合效应研究

Spintronics becomes a key technology to construct ultra low-power integrated circuit in "Post-Moore" law era. Based on magnetoelectric effects, non-volatile memory devices with Perpendicular Magnetic Anisotropy (PMA) attract much research attention from both the academics and industries. Particularly, the discovery of Spin Orbit Torque (SOT) effect, which accelerate the operating speed and reliability of non-volatile memory devices, has shown its bright potential. The SOT effect may arise from the Spin Hall Effect (SHE) and thin film interfacial effects, their relative contributions to spin orbit coupling are currently under argument. Besides, the SOT magnetization reversal of PMA device suffers from high current density and the dependence of external magnetic field. Regarding these issues, the applicant has demonstrated through macro-magnetic simulation that the SHE effect is able to assist the Spin Transfer Torque (STT) switching in perpendicular Magnetic Tunnel Junction (MTJ) while improving its speed and power performance. This project plans to study the coupling mechanisms of STT and SOT effect in CoFeB/MgO interfacial PMA devices by experiment, aimed at realizing low-power magnetization reversal in absence of magnetic field. In this project, a new multilayer structure will be proposed by integrating an ultra-thin metallic film between heavy metal and ferromagnetic layer to enhance both the spin current injection efficiency and interfacial PMA ; the interfaces between the added ultra-thin metallic film and ferromagnetic layer and the heavy metal will be adjusted to reinforce the SOT effect; Furthermore, nano-device will be fabricated to study the mechanism and control of the coupling between STT and SOT effects. This project will validate a new way for non-volatile magnetic memory switching from both the theory and experiments, which combines fast and low-energy operation with high reliability.

自旋电子学是构建“后摩尔时代”超低功耗集成电路的关键技术，基于磁电效应的垂直磁各向异性非易失存储器件成为研究热点，特别是自旋轨道矩的发现可以实现高速及高可靠性数据存储，具有广泛应用前景。然而垂直磁各向异性器件中的自旋轨道矩效应机理尚未明确，存在电流密度高及需要外界磁场辅助等问题，针对自旋霍尔、界面自旋相关效应等自旋轨道耦合现象的研究有待于进一步深入。申请者已经通过仿真验证了自旋霍尔效应对自旋转移矩的辅助作用，本课题拟针对界面垂直磁各向异性多层膜开展自旋轨道矩－自旋转移矩耦合效应研究，实现无磁场、低电流密度磁矩翻转。我们将设计新型超薄膜结构可同时增强自旋注入效率及界面垂直磁各向异性；通过调节铁磁／非铁磁金属薄膜的界面自旋相关效应调节自旋轨道矩；制备纳米级器件探索自旋轨道矩－自旋转移矩的耦合机制及调控。本课题将实现一种新的自旋电子器件写入方法，为超低功耗存储器研发提供理论与实验依据。

自旋电子学是构建“后摩尔时代”超低功耗集成电路的关键技术，基于磁电效应的垂直磁各向异性非易失信息存储器件成为研究热点，特别是自旋轨道矩效应的发现可以实现高速及高可靠性数据存储，具有广泛应用前景。然而垂直磁各向异性器件中的自旋轨道矩效应机理尚未明确，存在电流密度高及需要外界磁场辅助等问题，针对自旋霍尔效应、Rashba界面效应等自旋轨道耦合现象的研究有待于进一步深入。本项目针对界面垂直磁各向异性的薄膜开展自旋轨道矩效应研究，最终实现无磁场、低电流密度磁矩翻转。本项目主要包括以下研究内容：探究非磁重金属导线及其与铁磁金属薄膜界面，提高薄膜自旋霍尔角，增强自旋轨道效应；确定磁隧道结全结构，优化制备工艺；制备三端口纳米垂直磁隧道结器件，验证通过自旋轨道矩和自旋转移矩效应协同作用实现磁隧道结器件无磁场翻转；研究自旋轨道矩辅助自旋转移矩效应的物理机制。最终，本项目使用以Ta作为底电极的垂直磁各向异性磁隧道结三端器件，验证了无场条件下利用自旋转移矩和自旋轨道的矩协同作用能够实现垂直磁隧道结翻转，即在零磁场条件下向该器件的底电极注入面内方向自旋轨道矩电流，同时由磁隧道结注入垂直方向自旋转移矩电流，能够翻转磁隧道结自由层的磁化方向。自旋轨道矩的临界电流密度随自旋转移矩矩电流密度的增加而降低，因此可以通过调整两个电流实现垂直磁各向异性磁隧道结的超低功耗翻转。本项目表明自旋转移矩辅助自旋轨道矩翻转可用于改善纳米垂直磁隧道结器件的功耗和寿命，给出了一种无场高密度低功耗磁存储器的潜在途径。该成果已被格罗方德半导体股份有限公司收入其发展技术路线图中，基于该成果的新型双势垒垂直磁隧道结专利也已转让华为技术有限公司。