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.