Carbon-based OTFT devices were fabricated using a plasma process for the gate electrode and gate insulators. A nanocrystalline carbon (nc-C) film was used as the gate electrode, and three different layers, cyclohexene, diamond-like carbon (DLC), and cyclohexene/DLC (hybrid insulator), were used as the gate insulator. The surface and electrical properties of the three different gate insulators on the nc-C gate electrode were investigated using the SPM method, and the leakage current density and dielectric constant of the metal-insulator-metal (MIM) structures with three different insulator layers were evaluated. The hybrid insulator layer had a very smooth surface, approximately 0.2 nm, a uniform surface without defects, and good adhesion between the layers. Overall, it is believed that the hybrid insulator lead to a decrease in the electrical leakage current and an improvement in the device performance. (C) 2009 Elsevier B.V. All rights reserved.