Faculty of Information Science and Technology, Hokkaido University, Sapporo 060-0814, Japan.
Laboratory for Materials and Structures, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8503, Japan.
ACS Appl Mater Interfaces. 2023 Apr 5;15(13):16842-16852. doi: 10.1021/acsami.2c21568. Epub 2023 Mar 23.
Amorphous metal oxides with analog resistive switching functions (i.e., continuous controllability of the electrical resistance) are gaining emerging interest due to their neuromorphic functionalities promising for energy efficient electronics. The mechanisms are currently attributed to field-driven migration of the constituent ions, but the applications are being hindered by the limited understanding of the physical mechanisms due to the difficulty in analyzing the causal ion migration, which occurs on a nanometer or even atomic scale. Here, the direct electrical transport measurement of analog resistive switching and ångström scale imaging of the causal ion migration is demonstrated in amorphous TaO (a-TaO) by conductive atomic force microscopy. Atomically flat thin films of a-TaO, which is a practical material for commercial resistive random access memory, are fabricated in this study, and the mechanisms of the three known types of analog resistive switching phenomena (current-dependent set, voltage-dependent reset, and time-dependent switching) are directly visualized on the surfaces. The observations indicate that highly analog type of resistive switching can be induced in a-TaO by inducing the continuous redox reactions for 2.0 < < 2.5, which are characteristic of a-TaO. The measurements also demonstrate drastic control of the switching stochasticity, which is attributable to controlled segregation of a metastable a-TaO phase. The findings provide direct clues for tuning the analog resistive switching characteristics of amorphous metal oxides and developing new functions for future neuromorphic computing.
具有类似电阻开关功能（即电阻的连续可控性）的非晶态金属氧化物由于具有神经形态功能，有望用于节能电子设备，因此越来越受到关注。目前，这些功能归因于构成离子的电场驱动迁移，但由于难以分析导致电阻开关的因果离子迁移（发生在纳米甚至原子尺度上），对物理机制的理解有限，因此限制了其应用。在这里，通过导电原子力显微镜在非晶态 TaO（a-TaO）中演示了模拟电阻开关的直接电传输测量和因果离子迁移的埃尺度成像。本研究中制备了原子级平坦的 a-TaO 薄膜，这是商用电阻随机存取存储器的实用材料，并且可以直接在表面上观察到三种已知类型的模拟电阻开关现象（电流相关置位、电压相关复位和时间相关开关）的机制。观察结果表明，通过诱导 2.0 < < 2.5 的连续氧化还原反应，可以在 a-TaO 中诱导出高度模拟类型的电阻开关，这是非晶态 TaO 的特征。该测量还证明了对开关随机性的剧烈控制，这归因于亚稳 a-TaO 相的受控分凝。这些发现为调整非晶态金属氧化物的模拟电阻开关特性和开发未来神经形态计算的新功能提供了直接线索。
