Stability of point defects near MgO grain boundaries in FeCoB/MgO/FeCoB magnetic tunnel junctions
Stability of point defects near MgO grain boundaries in FeCoB/MgO/FeCoB magnetic tunnel junctions
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DOI：
10.1103/physrevmaterials.2.125002
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发表时间：
2018-12-14
影响因子：
3.4
通讯作者：
McKenna, Keith P.
中科院分区：
文献类型：
--
作者：
Bean, Jonathan J.;McKenna, Keith P.
采用FeCoB作为铁磁体和MgO作为间隔层的磁性隧道结表现出高性能，并且对于磁性随机存取存储器应用是有吸引力的。在沉积后退火时，观察到B扩散出FeCo B层，从而诱导FeCo的结晶。已知大比例的B逃逸到相邻的钽底层中。虽然已知B扩散到块体MgO中是不利的，但是B可能扩散到多晶MgO层中的晶界（GB）中，从而影响其电子性质。本文采用密度泛函理论研究了MgO晶界中氧空位和B间隙缺陷的稳定性和电子性质。我们发现，这两种类型的缺陷表现出增加的稳定性在GB，我们引入电子状态的差距，可能会产生负面影响的性能。这些预测与最近的实验结果是一致的，我们讨论了进一步的手段，以确认实验结果使用的技术，如X射线或紫外光电子能谱。
Magnetic tunnel junctions employing FeCoB as the ferromagnet and MgO as a spacer layer exhibit high performance and are attractive for magnetic random access memory applications. Upon postdeposition annealing, B is observed to diffuse out of the FeCoB layers inducing crystallization of FeCo. It is known that a large proportion of B escapes into the adjacent tantalum underlayer. While diffusion of B into bulk MgO is known to be unfavorable, it is possible that B could diffuse into grain boundaries (GBs) in the polycrystalline MgO layer, affecting its electronic properties. In this paper, density functional theory is used to investigate the stability and electronic properties of oxygen vacancy and B interstitial defects at MgO GBs. We show that both types of defects exhibit increased stability at the GBs, and we introduce electronic states in the gap that could negatively impact performance. These predictions are consistent with recent experimental results, and we discuss further means to confirm the results experimentally using techniques such as x-ray or ultraviolet photoelectron spectroscopy.