基于GeSbTe纳米线无序度调控的非熔融相变存储机理及性能研究

Phase change memory is the most promising candidate for the next generation memory technology. However, a desperately high RESET or SET current is needed for joule-heating induced typical melt-amorphization-crystalization switching cycling, and results in serious thermal crosstalk among adjacent memory cells. Thus, power consumption and thermal stability become the bottleneck of the phase change memory commercialization. In order to solve the above mentioned problem, we propose a disorder induced non-melting solid-to-solid phase change mechanism to realize the dramatic resistance switching. It is based on the short period atomic arrangement of textured GeSbTe nanowires which makes the atom moving along one direction instead of three directions, resulting in a decrease of configurational entropy and presence of a non-melting switching. This project is firstly focused on the preparation method of highly textured GeSbTe nanowires by electrochemical deposition and then the ground state structure of the GeSbTe nanowires is deduced for realizing the non-melting phase change memory. The absence of melting state is confirmed as well disorder evolution during the switching, contributing to an in-depth understanding of the non-melting phase change storage mechanism. At last, we verify the great improved performance of memory cells such as the power consumption, read/wirte speed and thermal stability with the explanation of non-melting phase change mechanism. This progress is of great significant for promoting the further commercial development of newly designed low-power and high density memory device with proprietary intellectual property rights.

相变存储器被认为是最有潜力的下一代半导体存储技术之一，但是其热致熔融相变机制往往需要较大的操作电流，并导致邻近单元之间严重的热串扰问题，使得器件功耗及热稳定性成为制约相变存储器大规模商用化的重要瓶颈。为了从根本上解决这一问题，本项目提出了一种基于无序调控的非熔融固-固相变来实现高低阻变化，主要利用GeSbTe纳米线高度择优取向的短周期原子排列结构，使其在势垒较低的方向上优先发生位移而不需历经三维方向的结构调整，体系熵变大为降低，无需经过高能耗的熔融过程。项目主要研究高度择优取向GeSbTe纳米线的电化学沉积方法，建立非熔融相变纳米线基态结构模型，判断纳米线相变前后是否经历熔融过程，分析其无序度演变规律，并探寻非熔融无序相变存储机理，最后验证非熔融无序相变单元在器件功耗、读写速度以及热稳定性方面的改善作用。这对推动具有自主知识产权的新型低功耗、高密度相变存储器技术逐步走向市场具有重要意义。

RESET电流过大是导致相变存储器热串扰的重要因素，本项目提出了非熔融相变机制来降低RESET电流，并基于电化学沉积方法制备实现超低功耗的Ge-Sb-Te纳米线相变存储器件，取得的主要成果如下：.（1）优化了电解液以及沉积参数，解决了业界普遍面临的Ge与Sb/Te共沉积的难题，首次基于电化学法制备出直径低至31.39nm且取向良好的Ge-Sb-Te纳米线；.（2）基于第一性原理计算，提出了Ge-Sb-Te体系基于无序度调控的相转变模型，并在TEM微观表征等实验基础上提出了Ge-Sb-Te纳米线特有的局域非晶网络结构导致的低功耗相变机制；.（3）基于双束电镜法、电泳法和抛洒法等优化了小尺寸纳米线相变存储器件的制备方法，有效改善了纳米线的接触问题，测得Ge-Sb-Te纳米线器件的主要电学性能如下：阈值电流为0.54µA（比传统GeSbTe器件低2个量级，具有非常低的功耗），写电压为1.4V，擦写速度为30ns，并表现出较好的多值特性。. 该项目研究为降低相变存储器的RESET电流、解决热串扰问题提供了一种新的思路。并且项目采用的电化学制备方法相较于传统PVD制备方法有更好的小孔填充能力，更适用于垂直三维集成器件的制备，这对开发新型低功耗、高密度三维相变存储器具有重要指导意义。

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