Ti-Sb-Te相变材料的结晶行为以及相变机理研究

Phase Change Random Access Memory (PCRAM), owing to its non-volatility, scalability, compatibility with CMOS technology, has been successfully used in Mobile replacing FLASH memory. However, there are still many problems needed to be overcome for further replacing DRAM. Ti-Sb-Te alloy has been proved to be capable of rapid phase transition at low power consumption, which seems to be a highly promising candidate for high-speed PCRAM applications. But the crystallization behavior and phase change mechanism of Ti-Sb-Te are still unclear. In this project, real-time Radial Distribution Function (RDF), extracted from the electron diffraction image, is proposed as a powerful structural probe to investigate the crystal-growth behavior of Ti-Sb-Te, including the nucleation stage, growth stage and size of the critical nuclei. In addition, combined with Reverse Monte Carlos Simulation and Molecular Dynamics Calculation, the structure evolution of Ti-Sb-Te during the crystalline process can be obtained, from which its inherent phase change mechanism would be summarized.

相变存储器(Phase Change Random Access Memory, PCRAM)由于具有非挥发性、可微缩性、与CMOS工艺兼容等优点，已经替代部分手机中的FLASH存储芯片而实现应用，然而要想进一步替代DRAM则依然面临诸多挑战。自主新型的Ti-Sb-Te(TST)材料能够在很低操作功耗下快速相变，很有潜力在高速PCRAM中实现应用，但其结晶行为以及相变机理仍未清楚。本项目通过对Ti-Sb-Te相变材料进行原位加热结晶，从获得的实时电子衍射信息中提取出实时径向分布函数的方法来研究Ti-Sb-Te的结晶行为，包括成核阶段、生长阶段以及临界晶核大小；将实时径向分布函数与逆蒙特卡洛模拟、分子动力学计算相结合，得到Ti-Sb-Te晶化过程中的微观结构演化信息，从而概括出Ti-Sb-Te的快速相变机理。

自主新型Ti-Sb-Te (TST)相变材料由于速度快、功耗低、疲劳性能好等优点，很有潜力在高速相变存储中实现应用，但其结晶行为以及相变机理仍不清楚。本项目通过实时径向分布函数来研究Ti-Sb-Te的结晶行为；将球差电镜获得的晶态结构与分子动力学模拟相结合，概况出Ti-Sb-Te的快速相变机理。本项目主要取得的结果如下：1）研究了自主Ti-Sb-Te相变材料的结晶行为，发现Ti-Sb-Te的临界晶核在2.2nm左右，且随着Ti含量的增加而减小；同时发现未掺杂Sb2Te3的结晶机制为生长型，当掺杂Ti含量超过8 at.%时，Ti-Sb-Te的结晶机制变成成核型。2）研究了非晶态和晶态Ti-Sb-Te的微观结构，证实Ti原子一直处于八面体结构中，其结构稍微调整完成成核过程，因而能够实现高速相变；同时发现过量的Ti以TiTe2纳米晶的形式在晶界析出，起到降低功耗的作用。3）研究Ti-Sb-Te的过程中发现，过量的Ti以TiTe2纳米晶的形式在晶界析出，起到降低功耗的作用。因而人为的构造TiTe2/Sb2Te3多层相变材料，其相变器件的Reset电流只需0.5 mA，操作速度为10 ns, 疲劳超过2E7次。这些研究工作为自主Ti-Sb-Te相变存储器的材料优化以及工程化提供了理论依据。