缺陷对RRAM材料阻变机理的影响

Influence of defects on the resistive switching mechanism of RRAM

基于密度泛函理论(DFT)的第一性原理和VASP仿真软件,分析了阻变随机存储器(RRAM)阻变效应的物理机制。对比计算了单斜晶相HfO2中Ag掺杂体系、氧空位缺陷体系和Ag及氧空位缺陷共掺杂复合缺陷体系的能带、态密度、分波电荷态密度面和形成能,结果表明在相同浓度下Ag掺杂体系能形成导电通道,而氧空位缺陷体系不能形成导电通道;共掺杂体系中其阻变机制以Ag传导为主,氧空位缺陷为辅,且其形成能变小,体系更加稳定。计算共掺杂体系的布居数和迁移势垒,得出在氧空位缺陷存在的前提下,Ag—O键长明显增加,Ag离子的迁移势垒变小,电化学性能增强。进一步计算了缺陷间的相互作用能,其值为负,表明缺陷间具有相互缔合作用,体系更加稳定。

The resistance switching effect physical mechanisms of resistance random accessory memory was stud- ied with the first-principles based on the density functional theory and the VASP software. The comparison cal culation of the energy band, density of states, isosurface of partial charge density and formation energies of Ag doped system, oxygen vacancy defect system and the co-doped composited defect system of the Ag and oxygen vacancy in the monoclinic Hf02 are performed. The calculated results reveal that the conductive path of Ag doped system can be established, but the oxygen vacancy defect system cannot be established under the same concentration. The calculated results also reveal that the conductivity of the resistance switching mechanisms in co-doped system was mainly dependent on the Ag and was auxiliary dependent on the oxygen vacancy defects, the formation energy becomes smaller and the system was more stable. The mulliken population and migration barrier of the co-doped system was calculated. The calculated results indicate that when the oxygen vacancy de fects exist, the Ag--O bond was enhanced obviously, the migration barrier of the Ag ions becomes smaller and the electrochemical performance was also enhanced. In addition, the calculated results of the interaction energy among the defects of the co-doped system are negative, which show that the associative ability exists among the defects and the system becomes more stable.