Title: High-Resolution Full-field Structural Microscopy of the Voltage Induced Filament Formation in Neuromorphic Devices Show Chinese title

Title: 神经形态器件中电压诱导丝状结构形成的高分辨率全场结构显微镜

Abstract: Neuromorphic functionalities in memristive devices are commonly associated with the ability to electrically create local conductive pathways by resistive switching. The archetypal correlated material, VO2, has been intensively studied for its complex electronic and structural phase transition as well as its filament formation under applied voltages. Local structural studies of the filament behavior are often limited due to time-consuming rastering which makes impractical many experiments aimed at investigating large spatial areas or temporal dynamics associated with the electrical triggering of the phase transition. Utilizing Dark Field X-ray Microscopy (DFXM), a novel full-field x-ray imaging technique, we study this complex filament formation process in-operando in VO2 devices from a structural perspective. We show that prior to filament formation, there is a significant gain of the metallic rutile phase beneath the metal electrodes that define the device. We observed that the filament formation follows a preferential path determined by the nucleation sites within the device. These nucleation sites are predisposed to the phase transition and can persistently maintain the high-temperature rutile phase even after returning to room temperature, which can enable a novel training/learning mechanism. Filament formation also appears to follow a preferential path determined by a nucleation site within the device which is predisposed to the rutile transition even after returning to room temperature. Finally, we found that small isolated low-temperature phase clusters can be present inside the high-temperature filaments indicating that the filament structure is not uniform. Our results provide a unique perspective on the electrically induced filament formation in metal-insulator transition materials, which further the basic understanding of this resistive switching. Show Chinese abstract

Abstract: 神经形态功能在忆阻器件中通常与通过电阻开关电学创建局部导电路径的能力有关。典型的关联材料VO2因其复杂的电子和结构相变以及在施加电压下的丝状物形成而被深入研究。由于扫描耗时，局部结构研究常受到限制，这使得许多旨在研究与相变电触发相关的较大空间区域或时间动态的实验变得不切实际。利用暗场X射线显微镜（DFXM），一种新颖的全视场X射线成像技术，我们从结构角度对VO2器件中的复杂丝状物形成过程进行了原位研究。我们表明，在丝状物形成之前，在定义器件的金属电极下方有显著的金属金红石相增加。我们观察到，丝状物形成遵循由器件内部的成核位点决定的优先路径。这些成核位点倾向于发生相变，并且即使在回到室温后仍能持续保持高温金红石相，这可以实现一种新的训练/学习机制。丝状物形成似乎也遵循由器件内部的成核位点决定的优先路径，该成核位点即使在回到室温后仍倾向于金红石转变。最后，我们发现小的孤立低温相簇可能存在于高温丝状物内部，表明丝状物结构并不均匀。我们的结果为金属-绝缘体转变材料中电诱导的丝状物形成提供了独特的视角，进一步加深了对这种电阻开关的基本理解。