P-122 / K.-S. Bae P-122: Fabrication of Single Substrate Flexible LCD by Laminating Functional Polymer Cover Film Kwang-Soo Bae 1 , Hak-Rin Kim 2 , Young Min Kim 3 , and Jae-Hoon Kim *1,4 1 Department of Information Display Engineering, Hanyang University, Seoul 133-791, Korea 2 School of Electrical Engineering and Computer Science, Kyungpook National University, Daegu 702-701, Korea 3 Department of Electronics and Electrical Engineering, Hongik University, Seoul 121-791, Korea 4 Department of Electronics and Computer Engineering, Hanyang University, Seoul 133-791, Korea Abstract We proposed a lamination process of a polymer film with a photo- curable polymer for fabricating flexible liquid crystal (LC) displays on single substrate. In our structure, a cover film layer was tightly attached to the polymer wall structure of a bottom plastic substrate after lamination, and LCs were uniformly aligned by grooves formed on the laminated cover film. 1. Introduction Flexible displays have attracted much attention due to their good portability such as light weight, thin packing, and flexibility. Among currently available competing technologies, flexible liquid crystal displays (LCDs) are considered to be the most promising ones, in that they have well-established techniques guaranteeing superior visibility with low power consumption. The serious obstacles to successful commercialization of flexible LCDs have been highly nonuniform electro-optic (EO) properties under external mechanical distortions on the plastic substrates, which originated from LC distortion or cell gap variation [1, 3, 4, 5]. Our recent results showed that such problems could be effectively solved by using pixel-isolated liquid crystal (PILC) mode [4, 5], where the stabilization of LC modes and the cell gap uniformity were provided by polymer wall structures. However, previous works required cumbersome anisotropic phase separation from LC/polymer mixtures to make polymer wall structures or to attach the polymer wall structures on one plastic substrate to the other plastic substrate [4, 6, 7]. Therefore, several efforts have been devoted to the development of a simple fabrication process for stable flexible LCDs. Among them, fabrication methods of flexible LCDs on single plastic substrate are regarded to be very suitable ones in applying cost- effective roll-to-roll process [8-10]. In this work, we demonstrate that the PILC mode can be simply obtained by laminating functional cover film, where the top cover film is tightly attached to the polymer wall structures of the bottom plastic film via photo-polymerization and the LCs are well-aligned by the patterned groove structure on the cover films. The proposed lamination method can be achieved by laminating a photo-curable polymer film layer from surface modified elastomeric buffer layers. With the method, it is expected that stable flexible LCDs can be simply fabricated via a cost-effective roll-to-roll mass production. 2. Experimental Figure 1 shows the schematic diagram of proposed single substrate LCD with laminating polymer cover film. Interdigital electrodes are patterned on a plastic substrate to produce in-plane field in the LC layer. The LCs in our structure are operated by in- plane electric field since the laminated cover film layer does not have electrode. Figure 1. The schematic diagram of proposed single substrate LCD with laminating polymer cover film The width and the spacing of the electrodes were 10 μm and 30 μm, respectively. Then, for isolating LC molecules and supporting the cell gap uniformity, patterned polymer wall structures are formed on the plastic substrate with electrodes, where the wall structure is formed so that the direction of the walls is 45 o with respect to the in-plane field direction. The width and the height of the wall structures were 30 μm and 8 μm, respectively. The spacing between the wall structures in a periodic line type was 100 μm. In our experiment, the polymer wall structure was fabricated by photolithographic method with photoresist, SU-8 (MicroChem. Co.), but the pixel-isolating wall structure can be made by the stamping method, as reported in our previous research [5]. On the plastic substrate, a LC alignment polyimide (PI) layer is spin-coated and cured. In our experiment, RN1199 (Nissan Chemical Ind., Ltd.) was used for a homogeneous LC alignment PI. The rubbing direction (R) of the PI surface was chosen along the wall direction to reduce LC distortion induced by the geometrical effect on LC anchoring of the polymer wall structure. The polymer cover film is laminated on the polymer wall structure of the bottom plastic film by roll pressing. And the film has groove structure for anchoring LC molecule, where the SID 07 DIGEST • 661 ISSN/007-0966X/07/3801-0661-$1.00 © 2007 SID