Al掺杂对HfO2俘获层可靠性影响第一性原理研究

采用基于MS(Materials Studio)软件和密度泛函理论的第一性原理方法, 研究了HfO₂ 俘获层的电荷俘获式存储器(Charge Trapping Memory, CTM)中电荷的保持特性以及耐擦写性. 在对单斜晶HfO₂中四配位氧空位(V_O4) 缺陷和V_O4 与Al替位Hf掺杂的共存缺陷体(Al+V_O4)两种超晶胞模型进行优化之后, 分别计算了其相互作用能、形成能、Bader电荷、态密度以及缺陷俘获能. 相互作用能和形成能的计算结果表明共存缺陷体中当两种缺陷之间的距离为2.216 Å时, 结构最稳定、缺陷最容易形成; 俘获能计算结果表明, 共存缺陷体为双性俘获, 且与V_O4缺陷相比, 俘获能显著增大; Bader电荷分析表明共存缺陷体更有利于电荷保持; 态密度的结果说明共存缺陷体对空穴的局域能影响较强; 计算两种模型擦写电子前后的能量变化表明共存缺陷体的耐擦写性明显得到了改善. 因此在HfO₂俘获层中可以通过加入Al杂质来改善存储器的保持特性和耐擦写性. 本文的研究可为改善CTM数据保持特性和耐擦写性提供一定的理论指导.

Effect of Al doping on the reliability of HfO2 as a trapping layer: First-principles study

In this work, the first-principles method based on materials studio(a soft ware) and the density functional theory is used to invesigate the properties of charge reflention and charge endurance in HfO₂ as a trapping layer in charge trapping memory (CTM). Two supercell models are optimized for the monoclinic HfO₂, separately. One contains a four-fold-coordinated O vacancy defect (V_O4), and the other is a co-doped composite defect consisting of a V_O4 and an Al atom. Interaction energies, formation energies, Bader charge, density of states and trapping energy are calculated for the two models. According to the calculated results of interaction energies and formation energies, it is found that the structure is the most stable and the defect is the most easily formed when the distance between the two kinds of defects is of 2.216 Å in the co-doped composite defect system. The trapping energy results show that the co-doped composite defect system can trap both electrons and holes. Moreover, the trapping ability of the co-doped composite defect is enhanced significantly as compared with the V_O4 defect. Bader charge analysis shows that the co-doped composite defect system provides a more preflerable site for the charge reflention. Calculations of the density of states show that the co-doped composite defect system has a strong effect on the trapping energy of holes. Calculated energy changes after program/erase cycles show that the endurance is improved obviously in the co-doped composite defect system. In conclusion, the date reflention and endurance in the trapping layer of monoclinic HfO₂ can be improved by doping of the substitutional impurity Al. This work may provide a theoretical guidance for performance improvement with respect to the date reflention and endurance of CTM.