Effects of molecular weights of a polymeric insulator on the electrical properties of pentacene thin-film transistors

This paper reports the effects of the molecular weights (MWs) of a polymeric insulator on the electrical properties of a pentacene thin-film transistor. The MWs of polystyrene used as a polymeric insulator were varied from 13,000 to 980,000. The mobility and current on/off ratio in a pentacene thin-film transistor were improved considerably (more than twofold and by a factor of 2, respectively) with increasing MW of polystyrene. In addition, the magnitude of the subthreshold slope was reduced significantly. Both the thickness and dielectric constant remained the same regardless of the MWs of polystyrene. The improved electrical properties could be explained because the higher MW of polystyrene results in the pentacene film with enhanced grain and crystalline intensity. This suggests that a higher MW is important for obtaining better electrical characteristics in organic transistors with polymeric insulators.