We have fabricated pentacene organic thin film transistors with spin-coated polymer gate dielectric layers, including cross-linked polyvinylphenol and a polyvinylphenol-based copolymer, and obtained devices with excellent electrical characteristics, including carrier mobility as large as 3 cm2/V s, subthreshold swing as low as 1.2 V/decade, and on/off current ratio of 105. For comparison, we have also fabricated pentacene transistors using thermally grown silicon dioxide as the gate dielectric and obtained carrier mobilities as large as 1 cm2/V s and subthreshold swing as low as 0.5 V/decade.

Organic thin‐film transistors and circuits have been fabricated on glass and on flexible substrates, achieving carrier mobilities of 0.3 cm2 V–1 s–1 on glass. In particular, the authors investigate how the substitution of inorganic gate dielectrics and metals with solution‐processed polymers affects the performance of the transistors. Two pentacene inverters on glass are shown in the Figure (see also cover).

We have fabricated fully patterned all-organic thin film transistors on glass substrates using the conducting polymer poly(3,4-ethylenedioxythiophene) for the gate electrodes and the source and drain contacts, poly-4-vinylphenol for the gate dielectric layer, and pentacene or poly-3-hexylthiophene for the organic active layer. All-organic pentacene transistors have carrier mobility as large as 0.1 cm2/V s and threshold voltage of 1 V, similar to pentacene transistors fabricated with high-quality inorganic gate dielectrics and noble-metal contacts. The carrier mobility of all-polymer poly-3-hexylthiophene transistors is somewhat lower compared with that of pentacene transistors, but similar to that of poly-3-hexylthiophene devices made with inorganic metals and dielectrics.

We have fabricated organic thin-film transistors and integrated circuits based on the small-molecule organic semiconductors α,α′-didecylquaterthiophene, α,α′-didecylquinquethiophene, and α,α′-didecylsexithiophene. The organic semiconductors were deposited by thermal evaporation, with solution-processed and cross linked poly-4-vinylphenol serving as the gate dielectric layer. We have found that bottom-contact devices based on these materials have better electrical performance than top-contact devices, presumably due to more efficient carrier injection from bottom contacts due to the presence of the relatively long alkyl chains substituted at the α- and ω-positions of the oligothiophene molecules. Bottom-contact transistors have carrier mobility as large as 0.5 cm2/V s and on/off current ratio as large as 105, and ring oscillators fabricated using bottom-contact transistors and α,α′-didecylsexithiophene as the organic active layer have signal propagation delay as low as 30 μs per stage.

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