Combined AFM and ToF-SIMS analyses for the study of filaments in organic resistive switching memories

The resistive switching mechanism in organic and hybrid resistive memories has been intensively studied in the last years. A particular interest have been directed to solution processed resistive layers based on an organic or polymer compounds for which convincing direct and indirect evidences indicated that the switching mechanism is based on the formation of conductive filaments (CFs) bridging the two metal electrodes. However, the CF composition, formation and rupture dynamics and evolution during the prolonged cycling are still poorly explored. Experiments are rare because of the well-known challenges in characterizing nanoscale filaments. In this work, we combine time-of-flight secondary ion mass spectrometry (ToF-SIMS) 3D imaging and in-situ atomic force microscopy (AFM), acquired at different profile depths, to characterize the CF composition and dynamics in high-performance and environmental stable crossbar Ag/parylene C/Ag printed memories. The results allow characterizing the filaments composition, their formation mechanism by electrochemical metallization and their evolution upon cycling. Moreover, the AFM images allow for a more clear interpretation of ToF-SIMS 3D reconstructions of molecular ions and to highlight artifacts arising from the different sputtering rate of metals as compared to the organic material.