Soft lithography fabrication of all-organic bottom-contact and top-contact field effect transistors

All-organic field effect transistors on flexible plastic substrates have been fabricated. A thin Mylar (R) foil acts both as substrate and gate dielectric. The contacts have been fabricated with poly(ethylene-dioxythiophene)/polystyrene sulfonate (PEDT/PSS) by means of soft lithography. The active layer (pentacene) is vacuum sublimed on the prepatterned film in case of bottom-contact devices or, in case of top-contact devices, the active layer sublimation is made in advance. On the opposite side of the foil, a thin PEDT/PSS film, acting as gate electrode, is spin coated. The comparison between top-contact and bottom-contact devices shows interesting characteristics as a marked difference in the I-D versus V-D curve that can be mainly attributed to a different quality of PEDT/PSS-semiconductor contact. The flexibility of the obtained structure and the easy scalability of the technological process open the way for economic production of high resolution organic devices.