In-situ Electron Microscopy of Memristive Devices

本项目由材料研究部电子与光子材料项目和陶瓷项目共同资助。非技术描述：该项目解决了用于新型高密度计算机存储器的电阻开关器件中电阻率可逆和非易失性变化的基本材料科学机制。研究活动在很大程度上依赖于先进的电子显微镜技术。更好地理解这种机制可以提高电阻开关的质量和可靠性，从而导致更强大的计算机。该项目涉及卡内基梅隆大学的研究生和本科生。每年，两名大一新生通过大学资助的项目进行为期一个学期的涉及忆阻器的研究项目。其中一人有望获得半导体研究公司（Semiconductor research Corporation）的奖学金，继续研究到大四。主要研究人员积极与半导体公司合作，如GlobalFoundries，应用材料和英特尔。此次合作为研究生和本科生提供了暑期实习的机会。技术描述：本项目探索金属/氧化物/金属系统中双极电阻开关现象的基本机制。众所周知，在称为电铸的调节过程中，在高电阻功能氧化膜中形成小直径导电丝。在PI之前的NSF项目中开发的电铸和电阻开关模型断言，这些过程中的任何一个都有两个阶段。在第一阶段，电子输运不稳定导致器件特性中出现负差分电阻，从而导致高电流密度灯丝的形成。灯丝形成的这个阶段是完全可逆的，也就是说，如果电压降低，灯丝就会溶解。如果电流密度超过临界值，在第二阶段，局部焦耳加热导致氧化物结构发生非挥发性变化。本项目着重于利用先进的电子显微镜技术研究灯丝形成的两个阶段的基本机制，即在偏压下对纳米级金属-绝缘体-金属器件进行原位成像。成像技术包括电子能量损失光谱，微分衍射，高角度环形暗场和电子全息，与亚利桑那州立大学合作。实验结果用于描述几种可能的电子不稳定性机制，并评估氧化层中非挥发性变化的性质。

This project is jointly funded by the Electronic and Photonic Materials Program and the Ceramics Program, both in the Division of Materials Research.Non-technical Description: This project addresses fundamental materials science mechanisms responsible for the reversible and nonvolatile changes of resistivity in resistive switching devices used in novel high-density computer memories. The research activities rely to large extent on advanced electron microscopy techniques. Better understanding of such mechanisms allows for improved quality and reliability of resistive switches and thus leads to more powerful computers. The project involves graduate and undergraduate students at Carnegie Mellon University. Each year, two freshmen work on semester-long research projects involving memristors, through a university-funded program. One of them is expected to continue the research to senior year with a fellowship from the Semiconductor Research Corporation. Principal Investigators actively collaborate with semiconductor companies such as GlobalFoundries, Applied Materials, and Intel. The collaboration brings summer internship opportunities for graduate and undergraduate students in the project. Technical Description: This project explores the fundamental mechanisms of bipolar resistive switching phenomena in metal/oxide/metal systems. It is known that the small diameter conducting filament forms in the high resistance functional oxide film during a conditioning process referred to as electroforming. The model of electroforming and resistive switching developed during the PI's prior NSF project asserts that either one of these processes has two stages. In the first stage, the electron transport instability leads to appearance of negative differential resistance in the device characteristics, which in turn causes formation of the high current density filament. This stage of the filament formation is fully reversible, i.e., the filament dissolves if the voltage is reduced. If the current density exceeds a critical value, in the second stage the localized Joule heating leads to nonvolatile changes in the oxide structure. This project focuses on the fundamental mechanisms in both stages of filament formation using advanced electron microscopy techniques, i.e., in-situ imaging of the nanoscale metal-insulator-metal devices under bias. The imaging techniques include electron energy loss spectroscopy, differential diffraction, high-angle annular dark field, and electron holography, in collaboration with Arizona State University. The experimental findings are used to delineate several possible mechanisms of electronic instability and to assess the nature of the nonvolatile changes in the oxide layer.