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基于密度泛函理论的第一性原理平面波超软赝势方法和VASP软件对电荷俘获存储器过擦现象进行了分析研究.通过形成能的计算,确定了含有氮空位缺陷的Si3N4和含有间隙氧缺陷的Hf O2作为研究的对象;俘获能的计算结果表明两种体系对电子的俘获能力比对空穴的大,因而对两体系擦写载流子确定为电子.分别计算了Hf O2和Si3N4擦写前后的能量、擦写前后电荷分布变化、吸附能和态密度,以说明过擦的微观机理.对能量和擦写电荷变化的研究,表明Si3N4相比于Hf O2,其可靠性较差,且Si3N4作为俘获层,在一个擦写周期后,晶胞中电子出现减少现象;界面吸附能的研究表明,Si3N4相比于Hf O2在缺陷处更容易与氧进行电子交换;最后,通过对态密度的分析表明Si3N4和Hf O2在对应的缺陷中均有缺陷能级俘获电子,前者为浅能级俘获,后者为深能级俘获.综上分析表明,Si3N4在氮空位的作用下,缺陷附近原子对电子的局域作用变弱,使得Si3N4作为俘获层时,材料本身的电子被擦出,使得擦操作时的平带偏移电压增大,导致存储器发生过擦.本文的研究结果揭示了过擦的本质,对提高电荷俘获存储器的可靠性以及存储特性有着重要的指导意义.
Based on density functional theory (FIR) first-principles plane-wave ultra-soft pseudopotential method and VASP software, the phenomenon of over-wiping of charge-trapping memory has been studied.According to formation energy calculations, Si3N4 containing nitrogen vacancy defects and interstitial oxygen defects Of the Hf O2 as the object of study; capture energy calculation results show that the two systems of electron capture ability than holes, so the two system erase carriers identified as electrons were calculated Hf O2 and Si3N4 wipe The energy before and after writing, the change of charge distribution before and after erase, the adsorption energy and density of states, to illustrate the micro-mechanism of over-erase.The research on the change of energy and erase charge shows that Si3N4 is less reliable than Hf O2, And Si3N4 as a trapping layer, after a write-erase cycle, the reduction of electrons in the unit cell; interface adsorption energy studies show that Si3N4 compared with Hf O2 at defect more easily with oxygen electron exchange; and finally, by the state Density analysis shows that both Si3N4 and Hf O2 have defect level electron trapping in the corresponding defects, the former is a shallow energy level trap and the latter is a deep level trap.In summary, the results show that Si3N4 and nitrogen vacancy When the trapped layer of Si3N4 is trapped, the electron of the material itself is rubbed out, which causes the flat band offset voltage of the rubbing operation to increase, resulting in over-rubbing of the memory. The findings in this paper Reveals the nature of over-wiping, which has important guiding significance for improving the reliability and storage characteristics of charge-trapping memory.