Bistable electrical switching and write-once read-many-times memory effect in a donor-acceptor containing polyfluorene derivative and its carbon nanotube composites

A conjugated copolymer of 9,9-didodecylfluorene and 4-triphenylamino-2,6-bis(phenyl)pyridine (F12TPN), containing both electron donor and acceptor moieties, was synthesized via Suzuki coupling polymerization. Polymer memory devices, based on thin films of F12TPN and its carbon nanotube composites, were fabricated. The current density-voltage characteristics of the indium tin oxide (ITO)/F12TPN/Al sandwich structure could be switched from a low conductivity (off) state to a high conductivity (on) state, when operated under negative bias with ITO as the anode. The switch-on voltage of the as-fabricated device was around -2.3 V. The on/off state current ratio was about 10. The on/off state current ratio could be enhanced to 10(5) and the switch-on voltage reduced to about -1.7 V by doping the F12TPN layer with about 1 wt % of carbon nanotubes. Once the memory devices had been switched on, they could not be erased (switched off) with a reverse bias (positive bias). Thus the memory effect was characteristics of that of a write-once read-many-times memory. The memory mechanism was deduced from molecular simulation and modeling of the nature of currents in both states.