Printable organic TFT technologies for FPD applications

Abstract

In this paper, we introduce our recent results on organic thin-film transistor (TFT) technologies; self-aligned self-assembly process and a high-resolution color active-matrix LCD panel driven by organic TFT. First, a novel process for fabricating alignment-free, printable, organic thin-film transistors is presented. This process exploits a self-assembly phenomenon in which soluble nanomaterials such as metal nanoparticles and organic molecules are self-assembled into a device structure. Solution-processed source and drain electrodes were self-aligned to a gate electrode by using a hydrophobic self-assembled monolayer optically patterned onto the gate electrode with a back-substrate exposure technique. An organic semiconductor film deposited on the patterned SAM was selectively ordered and substantially self-aligned to the gate electrode. A field-effect mobility of 0.15 cm²/Vs and on/off current ratio of 10⁵ were experimentally demonstrated when pentacene molecules were used as the semiconductor and silver nanoparticles were used as electrode materials. Second, a full-color twisted-nematic type liquid crystal display (TN-LCD) of 1.4-inch diagonal size driven by organic TFT has been fabricated. This TN-LCD has 80 x 80 x 3 (RGB) pixel arrays addressed by pentacene TFT with a channel width of 50 μm. The contact resistance between the pentacene film and the source/drain electrodes has been reduced by steepening the side slope of the electrodes. In addition, a solution-processed passivation film with a novel structure, consisting of organic and inorganic stacked layers, has been developed to protect the TFT against degradation induced by integration with TN-LCD devices. Consequently, the organic-TFT-driven TN-LCD is capable of displaying full-color moving images at a resolution of 80 pixels per inch.