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The low-temperature processed organic FETs have attracted considerable attention owing to their potential application to low-cost, large-area, and flexible electronics. A use of double-layered gate insulators consisting of high-k material and polymer dielectrics is considered as effective techniques to reduce the operating voltage and interfacial trap densities. Especially, the self-assembled vertical phase separation of polymer dielectrics and organic semiconductors is easy but effective way to obtain the high-quality interface and higher FET performance. We have investigated the electrical properties and interfacial phenomena of the metal-insulator-semiconductor (MIS) diodes and the organic field effect transistors consisting of Ta/Ta2O5 (anodic oxidation)/ polystylene (PS)/ TIPS-pentacene/ MoO3/ Ag multilayers. A clear vertical phase separation of TIPS pentacene and PS layers were successfully obtained by controlling the ratio of TIPS-pentacene/PS blend and the sweep rate of meniscus coating of their solution dissolved in toluene, and it was confirmed by TOF-SIMS and cross-sectional TEM images. The operating voltage and sub-threshold swing values were successfully reduced by the high-k oxide (~50 nm-thick)/ PS (10-100 nm) double layered gate insulator. Optimized meniscus coating of TIPS-pentacene/ PS blends also contributed to the in-plane crystal-growth (pi-pi stacking) of TIPS-pentacene layers parallel to the sweep direction. The crystal size, thickness, and the field effect mobilities gradually increased with the decrement of sweep rate, and we obtained the field effect mobilities of higher than 0.3 cm2/Vs and low-operation voltages below 5 V. The interfacial electrical properties of MIS diodes were also investigated by the capacitance-voltage measurement and the displacement current measurement.
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