Subthreshold characteristics of field effect transistors based on poly(3-dodecylthiophene) and an organic insulator

The properties of field effect transistors with organic insulator and semiconducting regions, fabricated with a top-gate architecture, have been investigated. Thin films (d≈30 nm) of regioregular poly(3-dodecylthiophene) were employed as the active semiconductor and the gate insulator was formed by a 500-nm-thick layer of poly(4-vinylphenol). Both were solution-processed on top of poly(ethylenetherephthalate) films, which were used as substrates. The output characteristics show a pronounced saturation behavior with an unconventional nonquadratic saturation current dependence on the gate voltage. Hence the (hole) mobility of 0.002–0.005 cm2/Vs has been estimated from the linear region of the transfer characteristics. The transistor turn-on occurs at a threshold voltage of approximately Vth=0 V, and the device can be operated with a supply voltage of between 15 and 20 V. As is usually observed for organic transistors, the inverse subthreshold slope (S) is very high, in our case S≈7 V/dec, by contrast with S...