Low-Operating-Voltage Organic Field-Effect Transistors with Poly-p-Xylylene/High-k Polymer Bilayer Gate Dielectric

A novel bilayer gate dielectric system for organic field-effect transistors (OFETs) operating at a low voltage is investigated. This stacked gate dielectric system consists of cyanoethylpullulan (CyEPL; k =15.4) for a high- k polymer and chemical-vapor-deposited poly- p -xylylene (parylene-C) as a covering layer. Pentacene-based OFETs with this dielectric system show a field-effect mobility of 0.34 cm 2 /(V s), a maximum current on/off ratio of 9 × 10 4 , and a threshold voltage of -6 V. This threshold voltage is five times lower than that of a parylene-C monolayer dielectric. This dielectric system is also applicable to OFETs with polymer semiconductors fabricated by solution processes. Parylene-C coating deposited by chemical vapor deposition (CVD) is found to be an effective method of preparing a clean, solvent-tolerant and highly insulated surface. As another means of fabricating a polymer insulator with a high dielectric constant, embedding CyEPL with high- k BaTiO 3 nanoparticles is also reported.