Conjugated Polymer Nanoparticles as Nano Floating Gate Electrets for High Performance Nonvolatile Organic Transistor Memory Devices

A molecular nano-floating gate (NFG) of pentacene-based transistor memory devices is developed using conjugated polymer nanoparticles (CPN) as the discrete trapping sites embedded in an insulating polymer, poly (methacrylic acid) (PMAA). The nanoparticles of polyfluorene (PF) and poly(fluorene-altbenzo[ 2,1,3] thiadiazole (PFBT) with average diameters of around 50-70 nm are used as charge-trapping sites, while hydrophilic PMAA serves as a matrix and a tunneling layer. By inserting PF nanoparticles as the floating gate, the transistor memory device reveals a controllable threshold voltage shift, indicating effectively electron-trapping by the PF CPN. The electron-storage capability can be further improved using the PFBT-based NFG since their lower unoccupied molecular orbital level is beneficial for stabilization of the trapped charges, leading a large memory window (35 V), retention time longer than 10(4) s with a high ON/OFF ratio of >10(4). In addition, the memory device performance using conjugated polymer nanoparticle NFG is much higher than that of the corresponding polymer blend thin films of PF/polystyrene. It suggests that the discrete polymer nanoparticles can be effectively covered by the tunneling layer, PMAA, to achieve the superior memory characteristics.