Pentacene Thin-Film Transistors with Hydrophobic Nanostructures on a Polymeric Gate Insulator

Abstract

The effects of hydrophobic nanostructures on the growth of pentacene molecules and the electrical characteristics of pentacene thin-film transistors (TFTs) are investigated. X-ray diffraction results show that hydrophobic nanostructures are conducive to the upright growth of pentacene molecules to the substrate. Pentacene TFTs, in which hydrophobic nanostructures with a cowl shape were introduced at the interface between the pentacene layer and the gate insulator, thus exhibit a pronounced enhancement in the field-effect mobility, up to approximately 2.94 cm 2 /Vs. These results suggest that hydrophobic nanostructures are effective to the ordered growth of pentacene molecules for high-performance organic TFTs. Pentacene Thin-Film Transistors with Hydrophobic Nanostructures on a Polymeric Gate Insulator Keywords:Organic semiconductor, Thin-film transistor, Molecular ordering Research ArticleOpen Access IntroductionOrganic thin-film transistors (TFTs) are attracting much interest because of their simple and low-temperature process ability. It is envisaged that they will have enormous market in a wide range of applications, for example as the driving elements for flexible displays, radio-frequency identification tags and large area sensors [1][2][3]. Previous investigations on organic TFTs have focused on materials [4], interfacial properties [5], source/drain contact engineering [6] and processing techniques [7], to enhance the TFT performance. Among the characteristic parameters, the field-effect mobility is known to be greatly influenced by the deposition conditions and consequent crystallinity of organic semiconductors. Likewise, the chemical and morphological properties of a gate insulator are deemed decisive to the field-effect mobility in bottom-gate organic TFTs by influencing the crystalline growth of an organic semiconductor. Several works have shown that the rough surface of a gate insulator causes a reduction in the field-effect mobility [5,8]. In contrast, recent studies reported that the crystalline growth of organic semiconductors and the performance of organic TFTs can be improved by introducing structured morphologies on the surface of a gate insulator [9,10], which motivates our research into cowl-shaped nanostructures for application in organic TFTs.In this study, we show that hydrophobic nanostructures with a cowl shape facilitate the upright growth of pentacene molecules to the substrate. The influence of hydrophobic cowl-shaped nanostructures on the morphological and structural characteristics of pentacene films are investigated. The enhancement in the field-effect mobility of pentacene-based TFTs fabricated with these nanostructures is reported. Experimental ProcedureTo fabricate pentacene TFTs, a 150-nm-thick Al gate was deposited on a glass substrate using the first shadow mask. Poly (4-vinylphenol) (PVP) with a cross-linking agent was spin-coated on the gate-patterned substrates and baked consecutively at 175°C for 1 h in a vacuum oven. A 480-nm-thick layer of cross-linked PVP (cP...