Conjugated Fluorene Based Rod-Coil Block Copolymers and Their PCBM Composites for Resistive Memory Switching Devices

We report the fabrication and characterization of polymer resistive switching memory devices fabricated from conjugated rod coil poly[2,7-(9,9-dihexylfluorene)]-block-poly-(2-vinylpyridine) diblock copolymers (PF-b-P2VP) and their hybrids with [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM). PF10-b-P2VP(37) and PF10-b-P2VP(68)-based devices exhibited the volatile static random access memory (SRAM) characteristic with an ON/OFF current ratio up to 1 x 10(7), which was explained by the trapping/back transferring of charge carrier. PF10-b-P2VP(68) had a longer holding time in the ON state than PF10-b-P2VP(37) because of the delayed back transfer of trapping carriers originally from the longer P2VP blocks. The PCBM aggregated size in the composite thin films were effectively reduced by PF-b-P2VP compared to the homopolymer of PF or P2VP, because of the supramolecular charge transfer interaction, as evidenced by absorption and photoluminescence spectra. Their PCBM/PF-b-P2VP composite devices changed from the nonvolatile write-once-read-manytimes (WORM) memory to the conductor behavior as the PCBM composition was increased. The electric-field induced charge transfer effect enabled the electrical bistable states for the applications in digital WORM memory device. The tunable memory characteristics through the block length ratio of block copolymers or PCBM composition provided the solution-processable charge storage nanomaterials for programmable high density memory device with a reducing bit cell size.