Spin torque MRAM — Challenges and prospects
Spin torque MRAM — Challenges and prospects
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自旋力矩 MRAM — 挑战与前景
DOI：
10.1109/drc.2009.5354906
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
R. Buhrman
中科院分区：
文献类型：
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作者：
R. Buhrman
自旋极化电流能够可逆地切换纳米磁体磁矩的方向，和/或通过入射传导电子的自旋角动量转移所施加的扭矩将其激发为微波进动，这已经催化了目前自旋扭矩研究的一个相当广泛和非常活跃的领域。在推进对这种新的自旋电子学现象的基本理解，以及成功地将其推向技术实现方面，特别是自旋扭矩磁性随机存取存储器（ST-MRAM）和可能的自旋扭矩激励纳米级微波振荡器方面，已经取得了非常实质性的进展。这些研究工作的主要目标是降低可靠开关薄膜纳米磁体所需的电流幅度和脉冲宽度，并开发自旋扭矩器件，其中有源元件被合并在可靠且高性能的磁隧道结中，该磁隧道结与高度缩放的 CMOS 晶体管阻抗匹配。在本次演讲中，我将讨论一些最近的工作，这些工作旨在通过推进对现象细节的定量理解，以及开发提高该效应的效率和适用性的材料系统和磁性纳米结构，为快速推进的自旋扭矩研究工作做出贡献。后者包括调整纳米磁体的磁各向异性，这可以将反转的起始电流降低到 100 微安范围内，并使用垂直各向异性参考层来产生在与纳米磁体平面正交的方向上极化的自旋电流，这对于小于 0.2 pJ 的能量脉冲，在短至 100 皮秒的脉冲宽度下产生了可靠的反转行为。我还将报告三端子自旋阀器件的初步结果，其中采用低阻抗自旋阀触点来驱动纳米磁体反转，同时高阻抗隧道结触点感测纳米磁体的磁性方向。最后，我将简要讨论基于自旋转矩的技术（特别是 ST-MRAM）成功实施之前仍需克服的一些挑战。
The ability of a spin-polarized current to reversibly switch the orientation of the magnetic moment of a nanomagnet, and/or to excite it into microwave precession, by the torque exerted through the transfer of spin angular momentum from the incident conduction electrons, have catalyzed what is now a quite broad and very active area of spin torque research. There has been very substantial progress in advancing the fundamental understanding of this new spintronics phenomenon, and in successfully moving it towards technological implementations, particularly spin-torque magnetic random access memory (ST-MRAM) and possibly spin-torque excited, nanoscale microwave oscillators. Major objectives of these research efforts are to reduce the current amplitude and the pulse width required to reliably switch a thin film nanomagnet, and to develop spin torque devices where the active element is incorporated in a reliable and high performance magnetic tunnel junction that is impedance matched to highly scaled CMOS transistors. In this presentation I will discuss some recent work that has sought to contribute to the rapidly advancing spin-torque research effort, by advancing the quantitative understanding of the details of the phenomenon, and by developing materials systems and magnetic nanostructures that enhance the efficiency and applicability of the effect. The latter includes tuning the magnetic anisotropy of the nanomagnet, which can reduce the onset current for reversal into the 100 microamp range, and the use of a perpendicular anisotropy reference layer to produce a spin current that is polarized in the direction orthogonal to the plane of the nanomagnet which has yielded reliable reversal behavior for pulse widths as short as 100 psec for an energy pulse of less than 0.2 pJ. I will also report on initial results with a three terminal spin valve device where a low impedance spin-valve contact is employed to drive the nanomagnet reversal while a high impedance tunnel junction contact senses the nanomagnet's magnetic orientation. I will conclude by briefly discussing some of challenges that remain to be overcome before spin-torque based technologies, particularly ST-MRAM, can be successfully implemented.