Perpendicular magnetic tunnel junction and its application in magnetic random access memory

Recent progresses in magnetic tunnel junctions with perpendicular magnetic anisotropy(PMA) are reviewed and summarized. At first, the concept and source of perpendicular magnetic anisotropy(PMA) are introduced. Next, a historical overview of PMA materials as magnetic electrodes, such as the RE–TM alloys TbFeCo and GdFeCo, novel tetragonal manganese alloys Mn–Ga, L10-ordered(Co, Fe)/Pt alloy, multilayer film [Co, Fe, CoFe/Pt, Pd, Ni, Au]N, and ultra-thin magnetic metal/oxidized barrier is offered. The other part of the article focuses on the optimization and fabrication of CoFeB/MgO/CoFeB p-MTJs, which is thought to have high potential to meet the main demands for non-volatile magnetic random access memory.     

Magnetic non‐volatile flip‐flop with spin‐Hall assistance

A novel multi‐bit non‐volatile flip‐flop (NVFF) written by spin‐Hall‐assisted spin‐transfer torque (STT) is proposed. This NVFF employs perpendicular‐anisotropy MTJs and requires an STT current combined with a spin‐Hall current to write the data. Thanks to the assistance of spin‐Hall effect (SHE), the incubation delay required by the conventional STT switching can be eliminated to achieve fast operation. Our proposed NVFF uses multi‐bit architecture and shows high‐density and low‐energy advantages over hybrid NV/volatile FFs in the application of the NV register file. Sim‐ulation results show that the proposed spin‐Hall‐assisted NVFF saves ～31% storage density and ～32% energy dissipation compared with the conventional STT‐NVFF. Moreover, the reliability of MTJ barrier is enhanced due to the reduction of the write voltage. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

CoFeB/AlOx/Ta及AlOx/CoFeB/Ta结构中垂直易磁化效应的研究

本文详细研究了在不同氧化层和铁磁层厚度情况下, 底层CoFeB/AlO_x/Ta结构和 顶层AlO_x/CoFeB/Ta结构中的垂直磁各向异性. 在底层CoFeB/AlO_x/Ta结构中观察到了垂直磁化的磁滞回线, 证明了其垂直易磁化效应的存在; 而在顶层AlO_x/CoFeB/Ta结构中却没有观察到类似的磁滞回线. 对这种对称结构中的非对称现象进行了分析. 研究还发现不同的氧化层和铁磁层厚度均会影响层间界面相互作用的强度, 从而导致结构的垂直磁化曲线矫顽力大小发生改变. 这项研究将对基于AlO_x氧化层垂直磁隧道结的研制具有重要的意义. 关键词： 垂直磁各向异性 磁隧道结 随机存储器     

磁性随机存储器的研究进展

通过分析磁性随机存储器(MRAM)的基本原理,及其与现有的静态存储器(SRAM)、动态存储器(DRAM)和快闪存储器(Flash)的性能比较,探讨了MRAM作为下一代新型存储器的应用前景.     

Application of magnetic Compton scattering for spin‐specific magnetic hysteresis measurement

An application of magnetic Compton scattering as a new tool to measure a spin‐specific magnetic hysteresis (SSMH) loop is introduced and its validity demonstrated. The applied magnetic field dependence of the integrated intensity of magnetic Compton scattering spectra, which reflect only the spin‐dependent magnetic properties of magnetically active electrons, was interpreted as the spin‐specific hysteresis. The spin magnetization of amorphous Tb₃₃Co₆₇ film was observed and its SSMH loop exhibited qualitative agreement with the ordinal magnetic hysteresis loop measured using a conventional vibrating sample magnetometer.     

Interface‐engineered resistive memory using plasma‐modified electrode on polyimide substrate

In this study, we report a low power Ni/GeO_x /TiO_y /TaN resistive random access memory (RRAM) using plasma‐modified electrode. The low sub‐mA switching current, highly uniform switching cycles (only 4% variation for the set) and good high‐temperature current distribution at 125 °C are simultaneously achieved in this RRAM device. Such good performance can be ascribed to interface plasma treatment on TaN electrode where the resulting Ta–N ionic bond increases the oxidation resistance and reduces the oxygen vacancy concentration near TaN interface that is favorable to lower switching power and improve high‐temperature current distribution.

     

Characterization of high‐density bit‐patterned media using ultra‐high resolution magnetic force microscopy

Bit‐patterned media at one terabit‐per‐square‐inch (Tb/in²) recording density require a feature size of about 12 nm. The fabrication and characterization of such magnetic nanostructures is still a challenge. In this Letter, we show that magnetic dots can be resolved at 10 nm spacing using magnetic force microscopy (MFM) tips coated with a magnetic film possessing a perpendicular magnetic anisotropy (PMA). Compared to MFM tips with no special magnetic anisotropy, MFM tips with PMA can resolve the bits clearly, because of a smaller magnetic interaction volume, enabling a simple technique for characterizing fine magnetic nanostructures. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Sixteen-state magnetic memory based on the extraordinary Hall effect

We report on a proof-of-concept study of split-cell magnetic storage in which multi-bit magnetic memory cells are composed of several multilevel ferromagnetic dots with perpendicular magnetic anisotropy. Extraordinary Hall effect is used for reading the data. Feasibility of the approach is supported by realization of four-, eight- and sixteen- state cells.     

Universal memory based on phase-change materials: From phase-change random access memory to optoelectronic hybrid storage

The era of information explosion is coming and information need to be continuously stored and randomly accessed over long-term periods, which constitute an insurmountable challenge for existing data centers. At present, computing devices use the von Neumann architecture with separate computing and memory units, which exposes the shortcomings of “memory bottleneck”. Nonvolatile memristor can realize data storage and in-memory computing at the same time and promises to overcome this bottleneck. Phase-change random access memory (PCRAM) is called one of the best solutions for next generation non-volatile memory. Due to its high speed, good data retention, high density, low power consumption, PCRAM has the broad commercial prospects in the in-memory computing application. In this review, the research progress of phase-change materials and device structures for PCRAM, as well as the most critical performances for a universal memory, such as speed, capacity, and power consumption, are reviewed. By comparing the advantages and disadvantages of phase-change optical disk and PCRAM, a new concept of optoelectronic hybrid storage based on phase-change material is proposed. Furthermore, its feasibility to replace existing memory technologies as a universal memory is also discussed as well.     

微纳尺度多铁异质结中电驱动磁反转

近年来,多铁异质结中电控磁性研究引起了广泛关注,已成为多铁领域的热点.现代自旋电子学器件(如磁内存)通常利用电流产生的磁场或自旋转移扭矩效应驱动磁反转来实现数据擦写,但这带来高额能耗和热量,成为亟待解决的关键难题.而利用多铁异质结实施电场驱动磁反转则有望大幅降低能耗,从而实现高速、低能耗、高稳定性新型高密度磁存储、逻辑及其他自旋电子学器件.在当前器件发展的微型化趋势下,探索可集成化的微纳尺度电场驱动磁反转方案显得越发重要.本文针对发展新型磁电器件所面临的微型化关键问题,回顾了微纳尺度电场驱动磁反转研究的新进展,主要关注小尺度多铁异质结中电控磁的新特点、新方法及相关物理机理的实验和理论成果,讨论了进入纳米尺度将面临的挑战,并对未来研究工作提出一些展望.     

Magnetization switching modes in nanopillar spin valve under the external field

The current-induced magnetic switching is studied in Co/Cu/Co nanopillar with an in-plane magnetization traversed under the perpendicular-to-plane external field.Magnetization switching is found to take place when the current density exceeds a threshold.By analyzing precessional trajectories,evolutions of domain walls and magnetization switching times under the perpendicular magnetic field,there are two different magnetization switching modes:nucleation and domain wall motion reversal;uniform magnetization ...     

Thermally activated magnetization reversal in magnetic tunnel junctions

In this paper, the magnetization reversal of the ferromagnetic layers in the IrMn/CoFe/AlO_x/CoFe magnetic tunnel junction has been investigated using bulk magnetometry. The films exhibit very complex magnetization processes and reversal mechanism. Thermal activation phenomena such as the training effect, the asymmetry of reversal, the loop broadening and the decrease of exchange field while holding the film at negative saturation have been observed on the hysteresis loops of the pinned ferromagnetic layer while not on those of the free ferromagnetic layer. The thermal activation phenomena observed can be explained by the model of two energy barrier distributions with different time constants.     

Imaging the Magnetic Reversal of Isolated and Organized Molecular‐Based Nanoparticles using Magnetic Force Microscopy

In the race towards miniaturization in nanoelectronics, magnetic nanoparticles (MNPs) have emerged as potential candidates for their integration in ultrahigh‐density recording media. Molecular‐based materials open the possibility to design new tailor‐made MNPs with variable composition and sizes, which benefit from the intrinsic properties of these materials. Before their implementation in real devices is reached, a precise organization on surfaces and a reliable characterization and manipulation of their individual magnetic behavior are required. In this paper, it is demonstrated how molecular‐based MNPs are accurately organized on surfaces and how the magnetic properties of the individual MNPs are detected and tuned by means of low‐temperature magnetic force microscopy (LT‐MFM) with variable magnetic field. The magnetization reversal on isolated and organized MNPs is investigated; in addition, the temperature dependence of their magnetic response is evaluated.     

磁存储器环形带切口结构自由层磁化反转的微磁模拟

针对基于磁性隧道结的赝自旋阀磁随机存储器, 使用带斜面切口环形结构自由层, 抛弃采用厚度改变矫顽力的方式, 降低了磁性隧道结的面积电阻, 改进了垂直电流磁随机存储器. 通过集成工艺中淀积的二次效应生成磁环的切口, 利用微磁学方法计算分析了自由层的磁化反转特性, 结果表明该模型具有低串扰、低面积电阻、高磁阻率以及较强的抗干扰性能. 关键词： 自由层结构 磁化翻转 微磁 VMRAM     

静态随机访问存储器型现场可编程门阵列辐照效应测试系统研制

 在调研静态随机访问存储器型现场可编程门阵列(FPGA)器件空间辐照效应失效机理的基础上,详细论述FPGA辐照效应测试系统内部存储器测试、功能测试及功耗测试的实现原理,给出了系统的软硬件实现方法。所建立的系统可以测试FPGA器件的配置存储器翻转截面、块存储器翻转截面、功能失效截面、闭锁截面等多个参数,其长线传输距离达到50 m以上,最大可测门数达到了100万门,为FPGA辐照效应研究提供了测试平台。     

Effect of a planar magnetic field on the domain wall dynamics in a double-layer uniaxial magnetic film

Motion of an isolated domain wall in a double-layer uniaxial magnetic film, where the film layers differ in characteristic length, saturation magnetization and damping parameter, is investigated by solving the Slonczewski equation. A planar magnetic field is applied normal to the domain-wall plane. The dependences of the threshold field and limiting velocity of disruption of the steady-state motion of the domain wall on the planar magnetic field value are obtained. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 60–63, December, 2008.