접착 구조물을 이용한 플렉서블 액정 디스플레이의 합착 특성 연구

Abstract

In recent years, the flexible displays have been expected to become next generation of the information displays because they have potential advantages such as light weight, thin pack-aging and ability to flexibility. Besides, developing of flexible displays is the attractive thing for application in wearable computer screens, electronic newspapers, and smart identity cards. In this respect, various candidates for realizing these valuable displays have been proposed such as electrophoresis displays, organic light emitting diodes (OLEDs), in addition to polymer dispersed liquid crystals (PDLCs) and cholesteric liquid crystals which is utilized the technologies of liquid crystal displays (LCDs) with plastic substrates. Among the diverse competing technologies for actualizing and commercializing the flexible displays, LCDs based on plastic substrates are considered to be the most promising candidate due to their well-established techniques guaranteeing superior visibility. However, flexible LCDs have the serious obstacle to conflict for seizing the initiative of the competitive display market. The primary problem is the quite nonuniform electro-optic (EO) characteristics under the external mechanical distortions on the plastic substrates, which originated from the distortion of LC alignment or cell gap variation. The key issue in fabricating LCDs on a plastic substrate is how to retain the mechanical stability under the various external conditions. To solve these problems effectively, several solutions have been suggested such as pixel-isolated liquid crystals (PILCs) and micro-contact printing (μCP) with UV or thermal curable adhesive resin as the bonding material. These recent effortful developments have shown the enhanced mechanical stabilities. However, although PILC structure has the rein-forced durability against the external force, it has the drawback to solve the limits such as the complex fabrication and decline the video quality induced from the residual monomers. For overcoming the demerits of the PILC technology, μCP technologies with UV or thermal cur-able resin was demonstrated for obtaining the flexible LCD with the stable structure. These methods could improve the adhesion properties between the rigid spacers and the substrate spin-coated alignment layer and maintain the stable uniformity of the cell gap against the external distortions. However, even these successful solutions have some issues such as the overflow of adhesive material and an LC alignment distortion by the reaction between LCs and adhesive resins. In this paper, we proposed a flexible LCD with the patterned ARS structure by the thermo-pressure fabrication procedures. ARS structure manufactured in this work acts as a role of the pillars to maintain the constant cell thickness as well as the glues to attach the rigid spacers on the bottom substrate to the alignment layer on the top substrate. By the field emission scanning electron microscopy (FESEM; JSM6330F from JEOL Ltd.) and the Raman spectroscopy (Jobin-Yvon T64000 from Horiba Ltd.), we could confirm the phenomenological results in the enhanced adhesive properties of the ARS structure and investigate the origin of the adhesion strength between rigid spacers and the substrate spin-coated the alignment layer. Subsequently, through the measurement of the EO characteristics of the flexible LC device in a twisted nematic (TN) mode manufactured in this work, we demonstrated the application of practical process of flexible LCDs directly.