2016 Volume 65 Issue 9 Pages 652-655
We improved the carrier mobility of the pentacene thin film transistors (TFT), which were fabricated with polysilsesquioxane (PSQ) gate dielectric layers, from 0.082 to 0.31 cm2V-1s-1 by treating the PSQ surface with ultra-violet irradiation (UV)/O3 and 1,1,1,3,3,3-hexamethyldisilazane (HMDS). It was found that the PSQ layers were flattened by the UV/O3 treatment, and the PSQ surface became hydrophilic at the same time because the organic functional groups on the PSQ surface were changed to hydroxyl groups. The grains of the pentacene films deposited on the UV/O3-treated PSQ surfaces were found to be as large as a few microns. However, the carrier mobility of the pentacene TFTs was not so much improved as expected from the largely grown pentacene grains probably because the hydroxyl groups scattered the charged carriers. In addition, the off-current of the pentacene TFTs increased by 4 orders of magnitude. It is thus considered that the hydroxyl groups also worked as hopping sites for the increased off-current which flew without the gate voltage. On the other hand, the carrier mobility of the pentacene TFTs fabricated with the PSQ dielectric layers of which surfaces were treated with UV/O3 and HMDS became ~4 times larger than that without any surface treatment of the PSQ layers, and also the off-current decreased by 3 orders of magnitude because the hydroxyl groups were changed with silyl groups by the HMDS treatment.
