Structural and Chemical Changes due to Electrical Stress in Phase-Change Nanowires: An In-Situ Electron Microscopy Study

非技术描述：几乎所有的电子产品都使用存储器设备来存储和访问信息。对这些存储器设备的要求包括高密度信息存储容量、快速读/写速度和低功耗。需要不断地发现具有上级性能的用于存储器件的新材料以满足信息技术日益增长的需求。在许多类型的材料中，相变材料是非常有前途的系统，因为当施加电流脉冲时，它们可以在高电阻状态和低电阻状态之间非常快速且可逆地切换。然而，为了使这项技术在商业上可行，仍有许多挑战有待克服。一个主要的问题是需要大电流来改变电阻状态。大电流降低了功率效率，并导致材料的退化。该研究项目解决了这一材料科学挑战，并通过先进的显微镜技术研究了降解机制。研究结果可用于设计未来电子存储器件的更好材料。在这个项目中，研究、培训和教育活动紧密结合。后者包括（1）本科生参与研究实验室，（2）将最新研究成果纳入教学模块，（3）在少数民族学生人数较多的费城地区培训高中和大学教师。技术说明：本研究计画主要研究电场对锗锑碲材料所制成之相变化奈米线之结构与化学变化之影响（Ge-Sb-Te）合金。研究小组利用纳米线器件的独特横向配置，通过原位电子显微镜测量直接研究Ge-Sb-Te纳米线结构，形态和化学成分的变化，同时在电偏压下操作器件。目的是了解相变材料运作背后的基本机制，特别是电场和电流对原子迁移和再结晶的影响。该研究提供了对负责相变存储器设备及其故障机制的原子过程的见解。所获得的见解将影响非易失性，超密度，超快和节能存储设备的新型材料的开发。

Nontechnical Description: Almost all electronic products utilize memory devices to store and access information. The requirements for these memory devices include high-density information storage capacity, fast read/write speed and low power consumption. There is a need to continuously discover new materials for memory devices with superior properties to meet the increasing demand of the information technology. Amongst many types of materials, phase change materials are a very promising system as they can switch very rapidly and reversibly between high and low resistance states when electrical current pulses are applied. However, many challenges remain to be overcome in order to make the technology commercially viable. A major one is that a large electrical current is required to change the resistance states. The large current reduces power efficiency and leads to material's degradation. This research project tackles this materials science challenge and studies the degradation mechanisms via advanced microscopy techniques. The research findings can be used to design better materials for future electronic memory devices. In this project, research, training and educational activities are tightly integrated. The latters include (1) the involvement of undergraduates in the research laboratory, (2) incorporation of the latest research results in the teaching module, and (3) training of high-school and college teachers in the Philadelphia district with a high minority student population.Technical Description: This research project studies the effect of electric field on the structural and chemical changes in phase change nanowires made of germanium-antimony-tellurium (Ge-Sb-Te) alloys. The research team utilizes a unique lateral configuration of nanowire devices to directly investigate the changes in Ge-Sb-Te nanowire structure, morphology and chemical composition via in-situ electron microscopy measurements while operating the device under an electrical bias. The goal is to understand the fundamental mechanisms operative behind the functioning of phase change materials, especially the effect of electric field and current on atomic migration and recrystallization. The research provides insights into the atomic processes that are responsible for the functioning of phase change memory devices and their failure mechanisms. The insights obtained will impact the development of novel materials for non-volatile, ultra-dense, ultrafast and energy efficient memory devices .