Annealing effects on the electrical characteristics of pentacene thin filmtransistors

There is currently considerable interest in the applications of conjugated polymers, oligomers, and small molecules for thin-film electronic devices. Organic materials have potential advantages as semiconductors in field effe ct transistors and light-emitting didoes. In this study, pentacene thin fil m transistors (TFTs) were fabricated on glass substrates. Aluminum and gold were used for the gate and the source/drain electrodes, respectively. Sili con dioxide was deposited as the gate insulator by plasma enhancement chemi cal vapor deposition (PECVD) and was patterned by reactive ion etching (RIE ). The semiconductor layer of pentacene was thermally evaporated in vacuum at a pressure of about 10(-8) Torr and at a deposition rate of 0.3 Angstrom /sec. The gate electrodes were annealed before the gate insulator layer wa s formed. Another annealing process was performed after the source/drain el ectrodes were formed. The effects of the gate metal annealing were observed through atomic force microscopy (AFM) images of the thin films and the tra nsfer characteristics of the TFTs. The TFTs with the annealed gate electrod e provided better characteristics than TFTs with the unannealed gate electr ode. The TFTs with the annealed gate electrode exhibited field-effect mobil ities as large as 0.07 cm(2)/Vs and on/off current ratios larger than 10(7) . The adverse effects of the closing annealing process on the fabricated TF Ts are clearly revealed.