A polyhedral oligomeric silsesquioxane derivative (POSS-OXT) containing photo-curable 4-membered cyclic oxetane functional groups was used as a gate dielectric of organic field effect transistor. The POSS-OXT was cross-linked and completely solidified by UV irradiation in the presence
of a selected photo acid generator, and pinhole free uniform thin film was obtained. We fabricated a metal/insulator/metal device of Au/POSS-OXT (300 nm)/Au with area of 0.7 mm2 and the measured leakage current and capacitance of the device to evaluate the insulating properties
of the POSS-OXT thin film. The maximum current was about 0.25 nA when 40 V was applied to the device. The observed values of the capacitance per unit area and dissipation factor were 11.4 nF/cm2 and 0.025, respectively. We fabricated an organic thin film transistor with pentacene
as the active semiconductor and the photo-cross-linked POSS-OXT as an insulator. A field effect carrier mobility of 0.03 cm2/V·s was obtained with the device.
