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.

Halik, M., Klauk, H., Zschieschang, U., Schmid, G., Radlik, W., Ponomarenko, S., Kirchmeyer, S., & Weber, W. (2003). High-mobility organic thin-film transistors based on α,α′-didecyloligothiophenes. Journal of Applied Physics, 93(5), 2977–2981.