Paper EM-ThP18
Flexible Organic Thin Film Transistor using Al₂O₃-PVP Nano-Composite Gate Dielectrics

Thursday, October 18, 2007, 5:30 pm, Room 4C

Organic TFTs with low threshold voltage (V_T), low-leakage current, and high current on-off ratio are needed for various applications in flexible electronics. Employment of organic/inorganic nano-composite gate dielectrics may provide a low V_T and flexibility improvement in OTFT devices. For this purpose, the nano-composite gate dielectric layers composed of the PVP polymer matrix and alumina nano-particle filler were investigated in this work. Treatment of alumina nano-particles by a coupling agent was carried out for improved dispersion of the nano-particles and their chemical binding with the PVP matrix. Flexible organic thin film transistors were fabricated using pentacene semiconducting layer and electroplated nickel (Ni) gate electrode on flexible polyimide substrate. Electroplated gate electrode fabricated on the plasma-treated polyimide substrate also provides a good adhesion. PVP/Al₂O₃ nano-composite layer with different volume fractions was spin-coated. Pentacene and gold source-drain electrodes were thermally evaporated on the gate dielectric layer using a shadow mask in vacuum chamber. Leakage current of the nano-composite gate dielectric was reduced by two order magnitude compared to that of pure PVP layer for the same film thickness. Electrical measurements of the OTFT devices showed the electrical performance of a field-effect channel mobility of 0.94 cm² V^-1s^-1, an on/off current ratio of 10⁵, a threshold voltage of -11.5V. Flexible tests indicated that the device with the nano-composite gate dielectric has the electrical performance superior to the device with pure PVP gate dielectric with repetitive cyclic bending.