标题： 二维纳米变阻器在晶界处负责多晶BiFeO3中的忆阻开关 显示英文标题

标题： Two-dimensional nanovaristors at grain boundaries account for memristive switching in polycrystalline BiFeO3

摘要： 忆阻器在多晶材料中的开关行为通常归因于导电丝的形成和断裂，这被认为是由氧空位再分布介导的。 然而，基本的原子尺度过程仍然未知，这限制了器件建模和设计。 在这里，我们将实验数据与多尺度计算相结合，阐明未掺杂多晶BiFeO3中的整个原子尺度循环。 导电原子力显微镜显示，晶界表现得像二维纳米变阻器，而在循环的返回部分，电流的减少是通过晶粒的。 使用密度泛函理论和蒙特卡洛计算，我们推断出所观察现象的原子尺度机制。 非平衡浓度的氧空位最初相对均匀分布，但它们被逐渐增加的电压带入晶界。 临界电压，即SET电压，随后消除了通过晶界中空位能级跳跃传导的障碍。 在循环的返回部分，晶界再次不导电，但晶粒由于氧空位的远程掺杂而表现出非零导电性。 RESET电压相当于一个热脉冲，重新分布空位。 认识到纳米变阻器是多晶材料中忆阻器开关的核心，可能会为新型器件和电路开辟可能性。 显示英文摘要

摘要： Memristive switching in polycrystalline materials is widely attributed to the formation and rupture of conducting filaments, believed to be mediated by oxygen-vacancy redistribution. The underlying atomic-scale processes are still unknown, however, which limits device modeling and design. Here we combine experimental data with multi-scale calculations to elucidate the entire atomic-scale cycle in undoped polycrystalline BiFeO3. Conductive atomic force microscopy reveals that the grain boundaries behave like two-dimensional nanovaristors while, on the return part of the cycle, the decreasing current is through the grains. Using density-functional-theory and Monte-Carlo calculations we deduce the atomic-scale mechanism of the observed phenomena. Oxygen vacancies in non-equilibrium concentrations are initially distributed relatively uniformly, but they are swept into the grain boundaries by an increasing voltage. A critical voltage, the SET voltage, then eliminates the barrier for hopping conduction through vacancy energy levels in grain boundaries. On the return part of the cycle, the grain boundaries are again non-conductive, but the grains show nonzero conductivity by virtue of remote doping by oxygen vacancies. The RESET voltage amounts to a heat pulse that redistributes the vacancies. The realization that nanovaristors are at the heart of memristive switching in polycrystalline materials may open possibilities for novel devices and circuits.