Solution Processed Donor–Acceptor Polymer Based Electrical Memory Device with High On/Off Ratio and Tunable Properties

A nonvolatile “resistive random access memory” (ReRAM) device is reported with a series of four conjugated polymers (CPs) containing poly[2,7-(9,9′-dioctylfluorene)-co-N-phenyl-1,8-naphthalimide (PFO–NPN) as donor and acceptor, respectively. A single layer, thin film of PFO–NPN copolymer that is sandwiched between indium tin oxide (ITO) and aluminum shows bistable property with a remarkably high Ion/Ioff ratio of 108. The charge transport of the polymer is studied by fitting I–V curves with various conduction models to realize that the trap charge limited current (TCLC) assists in switching and exhibiting bistable property of the memory device. Theoretical calculations were also performed on the polymer to elucidate the presence of traps on the carbonyl oxygen atoms of NPN moiety. In addition, ReRAM properties like Ion/Ioff ratio and write voltage were also tuned by changing the concentration of the acceptor moiety. Four different copolymers of acceptor concentrations (5%, 10%, 35%, and 50%) with respect to donor concentrations were characterized as a memory device. The device with high acceptor concentration (50%) showed the lowest Ion/Ioff ratio (103) and write voltage (0.8 V). It was also observed experimentally that the Ion/Ioff ratio and write voltage decrease sequentially with an increase in the acceptor concentration, thereby providing flexibility in tuning the memory parameters by allowing a molecular level change in the active material. The optical studies were performed to elucidate the mechanism of the tunable memory characteristic of the polymer, and the results reveal that the tunability is achieved due to the variation in the injection barrier and the strength of ICT for the different polymers.