All-organic thin-film transistors made of alpha-sexithienyl semiconducting and various polymeric insulating layers

Thin-film transistors (TFTs) were fabricated with a variety of organic polymer insulators topped with a vacuum evaporated organic semiconductor, α-sexithienyl (α6T). No field-enhanced source-drain current was obtained with polystyrene (PSt) and polymethylmethacrylate (PMMA). The field-enhanced current is weak with polyvinyl chloride (PVC), but much stronger with polyvinyl alcohol (PVA) and cyanoethylpullulan (CYEPL), a cyanoethylated polysaccharide which possesses a high dielectric constant (εr=18.5 at 10 kHz). In these last two instances, the field-effect mobility surpasses the one measured on TFTs made on a SiO2 insulating layer. A strong correlation is found between the dielectric constant of the insulator and the field-effect mobility.