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| 基于MnGa/Co2MnSi双层膜的垂直易磁化隧道结设计及制备 | |
| 毛思玮 | |
| 学位类型 | 硕士 |
| 导师 | 刘剑 |
| 2017-05-24 | |
| 学位授予单位 | 中国科学院研究生院 |
| 学位授予地点 | 北京 |
| 学位专业 | 电子与通信工程 |
| 关键词 | 分子束外延 垂直磁性隧道结 Mnga Co2mnsi 反铁磁耦合 |
| 其他摘要 | 垂直易磁化隧道结是新一代磁随机存储器件的核心单元，具有十分重要的研究和应用究价值。近年来，人们发现四方相MnGa合金拥有本征的高垂直磁各向异性、高自旋极化率和超低的磁阻尼因子，非常适宜用作垂直磁隧道结的磁性电极材料。然而，由于材料制备过程中的困难，目前钉扎层与自由层全部基于MnGa的垂直易磁化隧道结器件尚未实现，使得MnGa材料的本征优势不能得到充分发挥。为解决这一问题，本文对相关器件提出了新的设计方案，将半金属Heusler合金Co2MnSi薄膜引进到MnGa基磁隧道结的结构中，制备出了基于MnGa/Co2MnSi双层膜结构的垂直易磁化隧道结。具体研究内容如下：（1）利用分子束外延技术对半金属全Heusler合金Co2MnSi薄膜的生长进行了探索。通过合理选取衬底种类、生长温度以及元素束流比等实验参数，得到了理想的Co2MnSi薄膜样品。X射线衍射和波谱仪测试结果表明上述Co2MnSi薄膜具有很好的单晶质量以及接近2:1:1的原子组分比。在此基础上，我们制备了MnGa/Co2MnSi双层膜异质结构并对其磁性质进行了研究。微磁学模拟软件OOMMF对样品磁滞回线的拟合结果表明MnGa/Co2MnSi双层膜之间存在很强的界面反铁磁交换耦合作用，交换耦合常数高达-5mJ/m2。进一步，我们制备出[MnGa/Co2MnSi]n多层堆叠的超晶格结构，证明了超薄的Co2MnSi能够在MnGa的诱导下实现完全垂直磁化。通过改变环境温度或MnGa/Co2MnSi的相对厚度，可以对二者之间的反铁磁磁矩补偿效果进行调节，从而可以在很大范围内调控MnGa/Co2MnSi体系的饱和磁化强度、矫顽力等宏观特性。（2）设计加工出基于MnGa/Co2MnSi双层膜的垂直易磁化隧道结。利用分子束外延技术将超薄的Co2MnSi作为插层材料植入到上、下层MnGa和MgO势垒层之间，并通过MnGa/Co2MnSi间的反铁磁耦合作用对插层的磁矩方向进行调控，最终制备出以Co2MnSi/Mn3.1Ga(23nm)/Co2MnSi(0.6nm)/MgO(1.8nm)/ Co2MnSi(0.6nm)/Mn2.9Ga (12nm)为核心结构的复合电极垂直磁隧道结器件。截面高分辨透射电镜测试结果说明样品具有良好的晶体质量和界面质量。样品的面外磁滞回线也表明上、下复合电极都具有明显的垂直易磁化特性，能够满足全垂直磁性隧道结的要求。此外，上述复合电极隧道结表现出明显的隧穿磁阻效应，隧穿磁电阻率在室温时约10%，低温时（10K）达到65%。最后，我们通过I-V曲线拟合以及微分电导测试的方法对隧道结的质量作了进一步评估，指出了现阶段存在的问题及其可能原因。; Perpendicular magnetic tunnel junctions (p-MTJs) have attracted great interests because it’s the core structure of new generation magnetic random access memory (MRAM). Recently, researchers found that tetragonal structured MnGa alloys have intriguing properties such as intrinsic high perpendicular magnetic anisotropy (PMA), high spin polarization and small Gilbert damping constant, which are very suitable for the magnetic electrodes used in p-MTJs. However, due to some difficulties of the sample preparation, p-MTJs with both MnGa pinning layers and MnGa free layers have not been realized experimentally yet. To solve this problem, novel MTJ structures should be exploited. In this dissertation, we have introduced Heusler alloy Co2MnSi with half-metallic property into the design of MnGa-based MTJs, and successfully fabricated the fully p-MTJs based on MnGa/Co2MnSi bilayers. The main research results can be summarized as follows:(1) Fully Heusler alloy Co2MnSi films have been epitaxially grown on GaAs (001) and MgO (001) substrates by molecular-beam epitaxy (MBE) system. By optimizing the experimental parameters, we obtained Co2MnSi samples with high crystalline quality and appropriate components (indicated by XRD and WDS measurements). In addition, MnGa/Co2MnSi bilayer structures have been fabricated and their out-plane hysteresis loops were fitted by micro-magnetic simulation software OOMMF. The fitting results show a very strong antiferromagnetic exchange coupling between MnGa and Co2MnSi layers with the interfacial coupling constant of -5mJ/m2. Due to the antiferromagnetic coupling, the perpendicular magnetization of ultra-thin Co2MnSi films has been realized in an artificial superlattice structured by [MnGa/Co2MnSi]n. Interestingly, we can modulate the coercivity and net magnetic moment of the superlattice in a long range by changing the film thickness or environment temperature, which can be explained by the magnetic moment compensation mechanism between MnGa and Co2MnSi layers.(2) Fully perpendicular magnetic tunnel junctions based on MnGa/Co2MnSi bilayers have been designed and fabricated. Ultra-thin Co2MnSi interlayers were introduced to fabricate fully p-MTJs with the core structure of Co2MnSi/ Mn3.1Ga(23nm)/Co2MnSi(0.6nm)/MgO(1.8nm)/Co2MnSi(0.6nm)/Mn2.9Ga(12nm). As a result, the p-MTJ is with high crystalline quality, and both the top and bottom MnGa layers show strong PMA, as shown by HRTEM and SQUID measurements, respectively. Meanwhile, a distinct tunneling magnetoresistance (TMR) ratio of 65% at 10 K is achieved. To further assess the electronic transport properties of our p-MTJ samples, I-V curve and differential conductance measurement were taken. |
| 学科领域 | 微电子学 |
| 语种 | 中文 |
| 公开日期 | 2017-05-31 |
| 文献类型 | 学位论文 |
| 条目标识符 | http://ir.semi.ac.cn/handle/172111/28144 |
| 专题 | 半导体超晶格国家重点实验室 |
| 推荐引用方式 GB/T 7714 | 毛思玮. 基于MnGa/Co2MnSi双层膜的垂直易磁化隧道结设计及制备[D]. 北京. 中国科学院研究生院,2017. |
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