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设备来存储和访问信息。对这些存储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优异性能的存储器件的新材料，以满足日益增长的信息技术需求。在众多类型的材料中，相变材料是一种非常有前途的系统，因为当施加电流脉冲时，它们可以非常快速且可逆地在高和低电阻状态之间切换。然而，为了使这项技术在商业上可行，仍有许多挑战需要克服。一个主要的问题是需要很大的电流来改变电阻状态。大电流降低了电源效率，导致材料劣化。这项研究项目解决了材料科学的挑战，并通过先进的显微技术研究了降解机理。研究成果可用于为未来的电子存储设备设计更好的材料。在这个项目中，研究、培训和教育活动紧密结合在一起。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，以及(3)在少数族裔人口较多的费城地区对高中和大学教师进行培训。技术描述：本研究项目研究电场对锗-锑-碲(Ge-Sb-Te)合金相变纳米线结构和化学变化的影响。该研究小组利用纳米线器件独特的横向配置，通过原位电子显微镜测量，在偏压下操作器件时，直接研究Ge-Sb-Te纳米线结构、形貌和化学成分的变化。其目的是了解相变材料功能背后的基本机制，特别是电场和电流对原子迁移和再结晶的影响。这项研究提供了对负责相变存储器件功能的原子过程及其故障机制的洞察。所获得的见解将影响用于非易失性、超高密度、超快和节能存储设备的新材料的发展。

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 .