Organic field-effect transistors with cross-linked high-k cyanoethylated pullulan polymer as a gate insulator

Low-voltage operable organic field-effect transistors (OFETs) were fabricated with a high-k polymer gate insulator, consisting of cyanoethylated pullulan (CEP) and poly(methylated melamine-co-formaldehyde) (PMMF) as a cross-linker. Effect of the cross-linker amount on the dielectric properties of the film was studied and transistor performance was evaluated. At the optimum PMMF contents, field-effect mobility as high as 2.16 cm2/V s, on/off current ratio of ∼3 × 105, low hysteresis (ΔVth ∼ 0.01 V) and a steep inverse subthreshold slope of 0.066 V/dec were obtained. A utilization of stainless steel as a gate metal and substrate markedly improved the device performance under a low-voltage operation (∼1 V) due to the positively shifted threshold voltage from the work function change. The devices showed very little degradation in electrical properties with bending.