新型核壳结构相变纳米线的构筑及其多态存储特性研究

In this project, mass-selected Au nanoclusters with uniform size will be prepared by a magnetron-sputtering gas-condensation cluster-beam source. Then, by controlling the size and density distribution of Au nanocluster catalysts on Si substrates, and the growth parameters such as temperature and pressure of the gas-phase method, uniform phase-change nanowires (Ge2Sb2Te5 and GeTe) with controlled diameters will be prepared via the gas-phase vapor-liquid-solid mechanism. The effect of the diameter of nanowires on the data storage characteristics of nanowire-based memory will be deeply studied. Moreover, the effect of controllable N/Zn/Ni doping on the storage characteristics of Ge2Sb2Te5 nanowire-based memory including threshold voltage, power consumption, crystalline and amorphous resistance, will be researched based on experimental and theoretical investigations. Furthermore, composition- and lattice-matched N-Ge2Sb2Te5/Ge2Sb2Te5 and Zn-Ge2Sb2Te5/Ge2Sb2Te5 core-shell structured nanowires with stable multi-state switching characteristics will be constructed by pulsed laser deposition using doped Ge2Sb2Te5 nanowires as templates. Structure, composition and interface of the core-shell nanowires will be analyzed during phase transformation. The mechanism of multi-state data storage characteristics, as well as the influences of the nanowire configuration (such as N/Zn content and diameter of the core, shell thickness) on the multi-state data storage characteristics and device reliability will be revealed. The achievements of the project will provide experimental and theoretical basis for development of new materials with multi-state data storage characteristics, and manufacture of the new generation phase-change memory with low power consumption and high density.

本项目拟采用先进的“质量选择团簇束流源技术”制备尺寸高度均一的金纳米团簇，通过控制硅衬底上金团簇催化剂的尺寸与密度分布，并结合对气相法中温度、气压等参数的调控，可控地合成尺寸均一的硫系化合物相变纳米线；深入研究纳米线直径对其相变存储器件存储性能的影响；结合实验与第一性原理计算，研究N/Zn/Ni可控掺杂对Ge2Sb2Te5（GST）纳米线存储单元阈值电压、功耗、晶态/非晶态电阻等性能的影响；在此基础上，构筑核层与壳层成分差别小、晶格失配低的具有稳定多态存储性能的核壳结构纳米线（如N-GST/GST、Zn-GST/GST），研究相变过程中核壳结构纳米线的晶相、成分和界面的具体变化信息，阐明其多态存储机理，揭示核壳纳米线的微观构造（如：核层N/Zn含量、核层直径，壳层厚度）与其宏观多态存储性能和器件可靠性的内在联系，为新型多态存储材料的研发及低功耗、高密度相变存储器的研制提供实验和理论依据。

探索了“质量选择团簇束流源”设备的工艺参数，可控地制备了多种贵金属纳米团簇。所制备的团簇具有较小的尺寸和较好的单一性和分散性，这些贵金属团簇在相变纳米线制备及材料改性领域具有重要应用。采用Au催化的化学气相沉积法，在Si基片上可控生长了GeTe硫系化合物相变纳米线。GeTe纳米线直径随着Au催化剂颗粒尺寸和GeTe粉末量的增加而增加。通过调控Au催化剂颗粒尺寸和GeTe粉末量，得到了直径可调的GeTe纳米线。基于吉布斯-¬汤姆逊效应过饱和度的理论，分析了Au催化剂颗粒尺寸和GeTe粉末量对GeTe硫系化合物纳米线直径的影响机制。采用热退火触发了Ge2Sb2Te5材料非晶到晶态的相变。研究了退火温度对Ge2Sb2Te5材料结构和晶粒尺寸的影响。随着退火温度的增加，薄膜颗粒尺寸逐渐增加；进一步增加退火温度至400 °C，Te原子会扩散至薄膜表面并蒸发。采用纳秒激光照射触发了Ge2Sb2Te5材料非晶到晶态的相变，40 mJ/cm2的单脉冲纳秒激光（20 ns）即可触发Ge2Sb2Te5由非晶态向FCC态转变。采用热退火触发了GeTe材料非晶到晶态的相变，研究了热退火温度对GeTe材料结构和光学反射率的影响。随着退火温度的增加，d(202)面间距逐渐增加，这可能与退火薄膜中存在大的压应力有关。GeTe薄膜的晶态和非晶态具有高的反射率对比度，表明我们制备的GeTe材料在光学相变存储领域具有较好的应用潜能。将“质量选择团簇束流源技术”制备的小尺寸的Ag纳米团簇应用到气敏领域，获得了显著增强的气敏性能。上述相关研究为相变纳米线的可控制备及低功耗、高密度相变存储器的研制提供了有益的参考。上述相关研究共发表科研论文10篇。