Morphology optimization of side-chain copolymers yields a ternary memory device with high stability and reproducibility†
Abstract
Side-chain polymers have been widely used in data-storage devices owing to their specific merits such as easy synthesis and post-treatment, which is helpful for their large-scale application in future multilevel data-storage fields. However, recently designed side-chain polymers still have some deficiencies concerning undulating surface morphologies, poor device stability/reproducibility and ambiguous switching mechanisms. Herein, through rationally introducing a flexible OC–O–C–C spacer, tuning the pendent D/A ratio and using a random copolymerization method, three polymers, PMCz1-co-PMNCz1, PMCz2-co-PMNCz1 and PMCz4-co-PMNCz1, were designed and synthesized to optimize the surface morphology. The AFM test showed the smoothest surface morphology of PMCz4-co-PMNCz1 based films, the threshold voltage of which was superior to that of PMCz1-co-PMNCz1 and PMCz2-co-PMNCz1 based devices. Furthermore, PMCz4-co-PMNCz1 based memory devices showed the best device reproducibility and long-term stability. XRD and UV-vis measurements before and after voltage-sweeping confirmed that the ternary memory properties were attributed to the cooperation between conformational change and intramolecular charge transfer mechanisms. Therefore, this paper provides theoretical and experimental guidance for designing novel side-chain polymeric materials with optimized morphology, clear switching mechanisms and stable ternary storage performance in the future.