Annealing effects on the electrical characteristics of pentacene thin film transistors

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 effect transistors and light-emitting didoes. In this study, pentacene thin film transistors (TFTs) were fabricated on glass substrates. Aluminum and gold were used for the gate and the source/drain electrodes, respectively. Silicon dioxide was deposited as the gate insulator by plasma enhancement chemical 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 was formed. Another annealing process was performed after the source/drain electrodes were formed. The effects of the gate metal annealing were observed through atomic force microscopy (AFM) images of the thin films and the transfer characteristics of the TFTs. The TFTs with the annealed gate electrode provided better characteristics than TFTs with the unannealed gate electrode. The TFTs with the annealed gate electrode exhibited field-effect mobilities 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 TFTs are clearly revealed.