Surface Modification of Solution-Processed ZrO₂ Films through Double Coating for Pentacene Thin-Film Transistors

Abstract

We report the modification of surface properties of solution-processed zirconium oxide (ZrO₂) dielectric films achieved by using double-coating process. It is proven that the surface properties of the ZrO₂ film are modified through the double-coating process; the surface roughness decreases and the surface energy increases. The present surface modification of the ZrO₂ film contributes to an increase in grain size of the pentacene film, thereby increasing the field-effect mobility and decreasing the threshold voltage of the pentacene thin-film transistors (TFTs) having the ZrO₂ gate dielectric. Herein, the molecular orientation of pentacene film is also studied based on the results of contact angle and X-ray diffraction measurements. Pentacene molecules on the double-coated ZrO₂ film are found to be more tilted than those on the single-coated ZrO₂ film, which is attributed to the surface modification of the ZrO₂ film. However, no significant differences are observed in insulating properties between the single-and the double-coated ZrO₂ dielectric films. Consequently, the characteristic improvements of the pentacene TFTs with the double-coated ZrO₂ gate dielectric film can be understood through the increase in pentacene grain size and the reduction in grain boundary density.