ECCS-EPSRC: Collaborative Research: Acoustically induced Ferromagnetic Resonance (FMR) assisted Energy Efficient Spin Torque memory devices

基于纳米级磁体的磁随机存取存储器（MRAM）可以在断电时保留信息；这种非易失性存储器不能单独使用互补金属氧化物硅（CMOS）技术来实现。然而，切换最先进的MRAM设备所需的能量和电流很大，这限制了它们在小众应用中的使用。应变和声波可以用来显著降低在这种设备中写入信息所需的电流，但不幸的是，它们缺乏能量密度，使得它们对于纳米级磁铁缩放到非常小的横向尺寸（远低于100纳米）无效。在这个项目中提出的关键创新是使用表面声波（SAW）诱导铁磁共振（FMR），通过这种现象，施加在纳米磁铁上的能量在几十个循环中积累，在几纳秒内产生很大的磁化偏转，从而显著降低切换极小纳米磁铁的磁性状态所需的电流。这项研究可能会导致致密、节能和非易失性的磁存储器。弗吉尼亚联邦大学（VCU）和麻省理工学院（MIT）的pi将与工业界合作，转移相关的研究进展，将磁存储模块纳入研究生或本科生课程，为高中生举办纳米磁学研讨会，并通过研讨会和/或作为暑期研究实习生接待代表性不足的K-12学生。该项目工作将包括互补材料生长和表征（MIT）、纳米制造（MIT和VCU）、器件表征（VCU）、先进的时间分辨磁化可视化（英国埃克塞特大学）、建模和仿真（VCU）。任务包括：(i)纳米级磁体的生长和图像化，以及在铌酸锂压电薄膜上沉积互指换能器（IDT）以产生SAW。（ii）利用磁力显微镜（MFM）表征上述纳米结构的磁化反转，以找到最佳的SAW和自旋电流条件。这样确定的样品将被送到埃克塞特大学，用时间分辨扫描克尔显微镜（TRSKM）在(a) SAW诱导FMR (b)自旋扭矩和(c)“a”和“b”的组合下研究详细的时间分辨磁化动力学。（iii）对磁化动力学进行微磁建模，以解释TRSKM研究，并了解SAW诱导FMR和SOT/STT相结合时存在实际热噪声、缺陷、边缘粗糙度等情况下的动态误差。这一密切协调的研究项目将推进SAW诱导FMR、自旋扭矩和两者结合下丰富的非线性磁化动力学的知识，并为这种节能、可扩展的非易失性存储器概念提供概念验证演示。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Magnetic Random-Access Memory (MRAM) based on nanoscale magnets can retain information when power is turned off; such non-volatile memory cannot be implemented with Complementary Metal Oxide Silicon (CMOS) technology alone. However, the energy and current required to switch a state-of-the-art MRAM device is large, which limits their use to niche applications. Strain and acoustic waves can be used to significantly lower the current required to write information in such devices, but unfortunately which lacks energy density making them ineffective for nanoscale magnets scaled to very small lateral dimensions (well below 100 nanometers). The key innovation proposed in this project is to use surface acoustic waves (SAW) induced ferromagnetic resonance (FMR), a phenomenon by which energy applied to the nanomagnets is accumulated over tens of cycles to produce a large magnetization deflection in a few nanoseconds to significantly lower the current needed to switch the magnetic state of extremely small nanomagnets. This research could lead to dense, energy efficient, and non-volatile magnetic memory. The Virginia Commonwealth University (VCU) and Massachusetts institute of Technology (MIT) PIs will work with industry to transfer relevant research developments, incorporate magnetic memory modules in graduate or undergraduate classes, hold nanomagnetism workshops for high school students and engage in outreach to under-represented K-12 students through workshops and/or hosting them as summer research interns. The project work will consist of complementary materials growth and characterization (MIT), nanofabrication (MIT and VCU), device characterization (VCU), advanced time-resolved magnetization visualization (Univ. of Exeter, UK), modeling and simulation (VCU). The tasks include: (i) Growth and patterning of nanoscale magnets and deposition of interdigitated transducers (IDT) to generate SAW on piezoelectric Lithium Niobate films. (ii) Characterization of magnetization reversal in the above nanostructures with magnetic force microscopy (MFM) to find optimum SAW and spin current conditions. Samples thus identified will be sent to Exeter Univ. for study of detailed time resolved magnetization dynamics with time resolved scanning Kerr microscopy (TRSKM) under (a) SAW induced FMR (b) spin torque and (c) combination of both “a” and “b”. (iii) Performing micromagnetic modeling of the magnetization dynamics to explain the TRSKM studies and understand the dynamic error in the presence of realistic thermal noise, defects, edge roughness, etc. under combination of SAW induced FMR and SOT/STT. This closely coordinated research project would advance knowledge of rich non-linear magnetization dynamics under SAW induced FMR, spin torque and a combination of both as well as provide a proof-of-concept demonstration of this energy efficient and scalable non-volatile memory concept.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.