Perspectives on field-free spin–orbit torque devices for memory and computing applications
Perspectives on field-free spin–orbit torque devices for memory and computing applications
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DOI：
10.1063/5.0135185
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发表时间：
2023-01
影响因子：
3.2
通讯作者：
V. Lopez-Dominguez;Yixin Shao;P. Khalili Amiri
中科院分区：
文献类型：
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作者：
V. Lopez-Dominguez;Yixin Shao;P. Khalili Amiri
嵌入式磁性随机存取存储器（MRAM）的出现及其在主流半导体制造技术中的集成为工程计算系统创造了前所未有的机会，这些系统具有更高的性能、能效、更低的成本和非常规的计算能力。虽然最初对现有一代MRAM（基于铁磁隧道结中的自旋传递扭矩（STT）效应）的兴趣是由其非易失性数据保留和与嵌入式闪存（eFlash）相比更低的集成成本驱动的，但MRAM研究和开发工作的重点近年来越来越多地转向替代写入机制（超越STT）和新材料（超越铁磁）。这是由于需要更好的速度与密度、速度与耐用性之间的权衡，使MRAM适用于更广泛的内存市场，以及利用MRAM在利用纳米级磁铁物理的各种非常规计算架构中的潜力。从这个角度来看，我们概述了自旋轨道扭矩（SOT）作为MRAM器件的超stt写入机制之一。我们特别讨论了垂直磁化的SOT-MRAM器件的研究进展。从基本的对称性考虑出发，我们讨论了阻碍实际SOT-MRAM器件发展的面内偏置磁场的要求。然后，我们讨论了几种基于结构、磁性和手性对称性破断的方法，这些方法已经被探索来克服这一限制，并实现具有垂直磁化的无偏场SOT-MRAM器件。我们还回顾了每种情况下相应的材料级和设备级挑战。然后，我们展示了这些设备在计算和安全应用方面的潜力，超出了它们在传统内存层次结构中的使用。
The emergence of embedded magnetic random-access memory (MRAM) and its integration in mainstream semiconductor manufacturing technology have created an unprecedented opportunity for engineering computing systems with improved performance, energy efficiency, lower cost, and unconventional computing capabilities. While the initial interest in the existing generation of MRAM—which is based on the spin-transfer torque (STT) effect in ferromagnetic tunnel junctions—was driven by its nonvolatile data retention and lower cost of integration compared to embedded Flash (eFlash), the focus of MRAM research and development efforts is increasingly shifting toward alternative write mechanisms (beyond STT) and new materials (beyond ferromagnets) in recent years. This has been driven by the need for better speed vs density and speed vs endurance trade-offs to make MRAM applicable to a wider range of memory markets, as well as to utilize the potential of MRAM in various unconventional computing architectures that utilize the physics of nanoscale magnets. In this Perspective, we offer an overview of spin–orbit torque (SOT) as one of these beyond-STT write mechanisms for the MRAM devices. We discuss, specifically, the progress in developing SOT-MRAM devices with perpendicular magnetization. Starting from basic symmetry considerations, we discuss the requirement for an in-plane bias magnetic field which has hindered progress in developing practical SOT-MRAM devices. We then discuss several approaches based on structural, magnetic, and chiral symmetry-breaking that have been explored to overcome this limitation and realize bias-field-free SOT-MRAM devices with perpendicular magnetization. We also review the corresponding material- and device-level challenges in each case. We then present a perspective of the potential of these devices for computing and security applications beyond their use in the conventional memory hierarchy.