摘要
HfO2因高k值、热稳定性良好和相对Si导带偏移良好等特点,作为电荷俘获型存储器栅介质材料得到了广泛研究.为了明确高k俘获层提高CTM电荷俘获效率的原因,运用基于密度泛函理论的第一性原理计算,研究了氧空位引起HfO2的晶格变化及其影响计算结果显示优化后氧空位最近邻氧原子间距明显减小,次近邻O与Hf间距变化稍小.优化后氧空位明显改变局部晶格,而对较远晶格影响逐渐减弱,即引起了局部晶格变化深能级和导带电子态密度主要是Hf原子贡献,而价带则是O原子贡献.优化后各元素局部电子态密度和总电子态密度都明显大于未优化体系,局部电子态密度之和比总电子态密度小.优化后俘获电荷主要在氧空位周围和相邻氧原子上,而未优化时电荷遍布整个体系.优化后缺陷体系电荷局域能增大,电荷量增加时未优化体系电荷局域能明显减小,即晶格变化无饱和特性对电荷局域影响大.说明晶格变化对电荷的俘获能力较强,有利于改善存储器特性.
HfO2, as a gate dielectric material for the charge trapping memory, has been studied extensively due to its merits such as high k value, good thermal stability, and conduction band offset relative to Si, etc.. In order to understand the reason why the charge trapping efficiency is improved by high k capture layer with respect to charge trapping type memory, the variation of Hf O2 crystal texture induced by oxygen vacancy and the influences of it are investigated using the first principle calculation based on density functional theory. Results show that the distance of the nearest neighbor oxygen atom from oxygen vacancy is markedly reduced after optimization, whereas the decrease of distances between the next nearest neighbor oxygen atom from oxygen vacancy and hafnium is less. The change of local crystal lattice is caused by optimized oxygen vacancy for it significantly changes the local lattice, but rarely influences the far lattice.Deep energy level and density of electron states in conduction band are contributed by Hf atoms, while the density of electron states in valence band is contributed by O atoms. The local density of electron states in each element and the total density of electron states in the optimization system are all larger than those in the system without optimization,and the sum of the local densities of electron states is less than the total density of electron states. The trapped charges are moving mainly around the oxygen vacancy and the adjacent atoms of oxygen in the optimization system, but the charges are without optimization throughout the system. The local energy of charge is increased in optimized defect system, while the local energy of charge is conspicuously reduced in the system without optimization, i.e. lattice variation without saturation characteristic has a large effect on the local energy of charge. Results further prove that the change of crystal lattice induced by oxygen vacancy has strong ability to capture charge, which helps improve the features of memory.
出处
《物理学报》
SCIE
EI
CAS
CSCD
北大核心
2015年第3期248-254,共7页
Acta Physica Sinica
基金
国家自然科学基金面上项目(批准号:61376106)资助的课题~~
关键词
密度泛函理论
第一性原理
氧空位
电荷俘获
density function theory
the first-principle
oxygen vacancy
charge trapping
