Co3O4-graphene core-shell QDs-PMMA insulating polymer composites structured nonvolatile bistable memory devices

Nonvolatile hybrid inorganic/organic bistable memory devices fabricated utilizing Co₃O₄-graphene core-shell quantum dots (QDs) embedded in an insulating poly (methyl methacrylate) (PMMA) polymer matrix as active layer which were fabricated using a spin-coating technique. To improve the quantum confinement of Co₃O₄ QD, graphene, which has high electron affinity, was synthesized with Co₃O₄ QD core as a shell to form a core-shell structure that serves as an excellent trap site. Transmission electron microscopy (TEM) images revealed that Co₃O₄-graphene core-shell QDs with a diameter of approximately 5 nm were formed among the PMMA polymer matrix. Current-voltage (I-V) measurements on Al/ Co₃O₄-graphene core-shell QDs embedded in PMMA polymer matrix/indium-tin-oxide (ITO) devices at 300 K showed electrical bistability. The maximum ON/OFF ratio of the current bistability for the OBMDs was as large as 1.8 × 10⁴, the cycling endurance for the devices was above 2.5 × 10³ cycles, and retention times for the devices were larger than 5.8 × 10⁴ s. The carrier transport mechanisms for the devices were described by fitting the experimental I-V data using several models.