Operando Direct Observation of Filament Formation in Resistive Switching Devices Enabled by a Phase Transformation Molecule

Conductive filaments (CFs) play a critical role in the mechanism of resistive random-access memory (ReRAM) devices. However, in situ detection and visualization of the precise location of CFs are still key challenges. Herein, we demonstrate for the first time, the use of an organic π-conjugated molecule with phase transformation behavior for the positioning and visualizing of the CFs in the ReRAM devices. The π- conjugated molecule (called TT molecule) has the capacity to transform its molecular shape between twisted and planner states under varying temperatures, which can be translated into corresponding adaptations in crystallization, aggregation behavior, and optical properties. Hence, based on localized Joule heating generated within filament regions, the π- conjugated molecule exhibited reversible optical transformation and thus reflecting the location of the underlying CF. Customized patterns of CFs were induced and observed by the π-conjugated molecule layer, which confirmed the hypothesis. Additionally, statistical studies on filaments distribution were conducted to study the effect of device sizes and bottom electrode heights, which serves to enhance the understanding of switching behavior and their variability at device level. Therefore, this phase transformation molecule and such approach have great potential in aiding the development of ReRAM technology.<br/>Keywords: phase transformation, π-conjugated molecule, conductive filament, ReRAM, spatial filament mapping