面向信息存储应用的非晶硅与非晶碲化锑界面特性第一性原理研究

发布时间：2018-04-14 16:40

本文选题：相变存储器 + 硅锑碲　；参考：《吉林大学》2015年硕士论文

【摘要】：相变存储器是一种新型的非易失性半导体存储器。相变存储器中存储信息的载体是相变材料，相变材料在一定外界条件的作用下可以发生晶相和非晶相之间的快速可逆相变，同时两相之间存在明显的光学或者电学性质的差异。目前的相变材料中研究最广泛的是Ge2Sb2Te5，但是Ge2Sb2Te5的非晶稳定性还不够好，在制作器件中难以承受高温工艺，同时功耗较高。为了解决这些问题，人们又构建了其他非晶稳定性更好的相变材料组分，硅锑碲材料就是其中之一。实验上得到的硅锑碲材料最佳配比为SixSb2Te3(3x3.5)，其中Sb2Te3的非晶相不稳定，加入硅元素之后得到的硅锑碲材料表现出了良好非晶稳定性。实验上发现，硅锑碲材料相变过程中会发生相分离，硅始终保持非晶状态，非晶硅与碲化锑形成纳米尺度下互相包裹的网状结构，这些网状结构中存在大量的硅和碲化锑的界面。一般来说，界面处会表现出不同于体材料性质，我们认为这些硅和碲化锑界面结构对稳定非晶相方面起着非常重要的作用，本文利用第一性原理分子动力学模拟，建立非晶硅和非晶碲化锑界面的原子结构模型，通过研究界面成键特性与电子结构探究硅提高碲化锑非晶稳定性的内在原因。本文共分为四章，第一章对相变存储器和相变材料的研究背景进行介绍，同时介绍一些国内外科研工作者的研究进展。第二章，介绍研究方法。对第一性原理、密度泛函理论、分子动力学模拟进行简单的介绍。第三章，利用分子动力学模拟建立非晶硅和非晶碲化锑的界面结构，从成键结构和电子结构两方面进行分析，并与体相非晶碲化锑进行对比，结果表明，在界面结构中，碲元素的成键结构从原来p电子成键结构转变成sp3杂化成键与p电子键共存的结构，同时碲化锑部分的电子局域程度明显升高，这两种变化使得碲化锑非晶和晶相结构上的相似性被破坏，并且不利于形成晶相中共振键，这就是非晶硅提高碲化锑非晶稳定性的内在原因。第四章，介绍对三种相变材料Ge15Sb85、Sb2Te、Sb2Te3相变特性的研究。在对非晶的Ge15Sb85研究中，，我们发现Ge在非晶Ge15Sb85中就存在聚集的现象，这也是这种材料容易相分离的原因。另外我们发现利用分子动力学模拟得到的Sb2Te，Sb2Te3晶相呈现出结构上有序，但成分上无序的特点，我们认为相变材料实际相变过程中的晶相可能呈现这种结构有序而成分无序的结构，这也可能是相变材料能够快速相变的原因。
[Abstract]:Phase change memory (PCM) is a new type of non-volatile semiconductor memory.The carrier of information stored in phase change memory is phase change material. Under certain external conditions, phase change can occur rapidly and reversible between crystalline phase and amorphous phase, and there are obvious differences in optical or electrical properties between the two phases.Ge2Sb2Te5 is the most widely studied phase change material at present, but the amorphous stability of Ge2Sb2Te5 is not good enough, and it is difficult to withstand high temperature process and high power consumption in fabricating devices.In order to solve these problems, other phase change materials with better amorphous stability have been constructed, among which the silicon antimony tellurium material is one of them.The optimum ratio of SiSb _ 2TE _ 3N _ 3x 3.5N is obtained by experiments. The amorphous phase of Sb2Te3 is unstable, and the Si-antimony-tellurium material with silicon element exhibits good amorphous stability.It is found that phase separation occurs in the process of phase transformation of antimony tellurium and the amorphous state of silicon remains. The amorphous silicon and antimony telluride form a netted structure wrapped in each other at nanoscale.There are a large number of interfaces between silicon and antimony telluride in these network structures.Generally speaking, the interfacial properties are different from those of bulk materials. We think that these interfacial structures of silicon and antimony telluride play a very important role in stabilizing the amorphous phase.The atomic structure model of the interface between amorphous silicon and amorphous antimony telluride was established. The intrinsic reasons for improving the amorphous stability of antimony telluride were investigated by studying the bonding characteristics and electronic structure of the interface.This paper is divided into four chapters. In the first chapter, the research background of phase change memory and phase change material is introduced, and the research progress of some researchers at home and abroad is also introduced.The second chapter introduces the research methods.The first principle, density functional theory and molecular dynamics simulation are briefly introduced.In chapter 3, the interfacial structure of amorphous silicon and amorphous antimony telluride is established by molecular dynamics simulation. The bonding structure and electronic structure are analyzed, and compared with bulk amorphous antimony telluride. The results show that, in the interfacial structure,The bonding structure of tellurium changed from the original p-electron bonding structure to the coexistence of sp3 heterogenetic bond and p-electron bond, and the electronic localization of antimony telluride part increased obviously.These two changes destroy the similarity between amorphous and crystalline structure of antimony telluride and are not conducive to the formation of resonance bonds in the crystalline phase, which is the intrinsic reason why amorphous silicon improves the stability of amorphous antimony telluride.In chapter 4, the phase transition characteristics of three kinds of phase change materials Ge15Sb85Sb2TeSb2Te3 are introduced.In the study of amorphous Ge15Sb85, we found that GE aggregates in amorphous Ge15Sb85, which is the reason for the easy phase separation of this material.In addition, we find that the crystal phase of SB _ 2TeN _ (SB _ 2TE _ 3) obtained by molecular dynamics simulation has the characteristics of ordered structure, but disordered composition. We think that the crystal phase of phase change material in the actual phase transition process may present this kind of ordered structure and disordered composition structure.This may also be the reason for the rapid phase transition of phase change materials.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TP333

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