†Department of Physics and Astronomy, University of California, Los Angeles, California 90095, United States.
‡California NanoSystems Institute, University of California, Los Angeles, California 90095, United States.
Nano Lett. 2015 Jun 10;15(6):3983-7. doi: 10.1021/acs.nanolett.5b00901. Epub 2015 May 5.
Conductive bridge random access memory (CBRAM) is a leading candidate to supersede flash memory, but poor understanding of its switching process impedes widespread implementation. The underlying physics and basic, unresolved issues such as the connecting filament's growth direction can be revealed with direct imaging, but the nanoscale target region is completely encased and thus difficult to access with real-time, high-resolution probes. In Pt/Al2O3/Cu CBRAM devices with a realistic topology, we find that the filament grows backward toward the source metal electrode. This observation, consistent over many cycles in different devices, corroborates the standard electrochemical metallization model of CBRAM operation. Time-resolved scanning transmission electron microscopy (STEM) reveals distinct nucleation-limited and potential-limited no-growth periods occurring before and after a connection is made, respectively. The subfemtoampere ionic currents visualized move some thousands of atoms during a switch and lag the nanoampere electronic currents.
导电阻变随机存取存储器（CBRAM）是一种有望取代闪存的技术，但对其开关过程的理解不足阻碍了其广泛应用。直接成像可以揭示其潜在物理机制和基本的未解决问题，如连接细丝的生长方向，但纳米级目标区域完全被包裹，因此难以使用实时、高分辨率探头进行访问。在具有实际拓扑结构的 Pt/Al2O3/Cu CBRAM 器件中，我们发现细丝朝着源金属电极反向生长。这一观察结果在不同器件的多个循环中都是一致的，证实了 CBRAM 操作的标准电化学金属化模型。时间分辨扫描透射电子显微镜（STEM）揭示了在连接前后分别存在明显的以成核为主和以势垒为主的无生长阶段。可视化的亚微微安离子电流在开关过程中移动了数千个原子，滞后于纳安电子电流。
