표면 고정에너지가 Fringe Field Switching Mode의 동역학 특성에 미치는 영향

Abstract

Liquid crystal displays (LCDs) have been used for various display applications such as mobile phones, monitors, and televisions because of their excellent display performance. In general, LC modes which are organized by initial alignment of LC molecules and electrode structures govern display performance characteristics such as transmittance, response time, and viewing angle. Many kinds of LC mode devices have been developed. Of these types, the FFS mode has been favored because of their high transmittance and wide viewing angle qualities. However, response times of devices using this mode are not sufficiently fast for real moving pictures. Therefore, many researchers have worked to improve the response time of FFS mode devices by various approaches such as the optimization of rubbing angles, the optimization of LC material parameters, and the dynamic contrast compensation (DCC) driving. Recently, a polymer-stabilized IPS mode was proposed to allow fast response time by adopting a UV-curable reactive mesogen (RM) mixed in with the LCs. In their system, the polymer networks, formed by polymerized RMs, provide the volume stabilization of LC molecules and increase their surface anchoring energy. However, polymer network structures caused by increasing the operating voltage and rising time are very slow at low gray levels. In our previous works, we reported improvements in response time using a polymerized RM layer on top of a planar alignment layer, which increase the surface azimuthal anchoring energy. In this dissertation, theoretical and experimental researches to improve characteristics using the alignment layer mixed with reactive mesogen (RM) monomers were investigated from physical properties and applications in the FFS mode. At first, we showed several kinds of method for the improvement of the response time of the in-plane switching (IPS) mode and the fringe field switching (FFS) mode such as the optimization of rubbing direction, the optimization of LC material parameters, and the dynamic contrast compensation (DCC) driving. And their merits and demerits are introduced briefly. After that, we presented physical parameters of the response time, and the surface anchoring energy affected on the response time in the planar alignment was discussed. In particular, we analyzed the relationship between the response time and the azimuthal anchoring energy introduced the dielectric torque based on the LC order parameter in twist configuration like the IPS and the FFS mode. Next, we presented that the RM-mixed alignment layer was enhanced the azimuthal anchoring energy and decreased the pretilt angle. At first, we found that the azimuthal anchoring energy was enhanced and the pretilt angle was reduced by increasing RM concentrations in the planar alignment layer for rubbing method because directionally polymerized RMs on the surface induced strong interactions with LCs and increased the chain ordering of the alignment layer at rubbing direction. And we achieved fast response time of the FFS mode. In addition, we also found that the RM-mixed system in the planar alignment layer for photo alignment method also improved the response time by the enhancement of the azimuthal anchoring energy. Basis of experimental and phenomenological results, we studied the dependence of alignment materials on the azimuthal anchoring energy and the response time of the FFS mode; polyamic acid (PA) and polyimide(PI). The addition of RMs to the PI-type alignment layer was effective in enhancing the azimuthal anchoring energy, whereas the addition of RMs to the PA-type alignment layer had little effect. Continually, we made the 4.3 inch WVGA (480 _ RGB _ 800) FFS panel and measured electro-optic (EO) characteristics using the proposed system. We could achieve not only the improvement of the response time but also no gray inversion at all directions. In addition, we reported reliability characteristics using the measurement method of the voltage holding ratio (VHR) and the residual direct current voltage (VRD). From measured results, the RM-mixed alignment was satisfied with reliability characteristics which are commercially requested. It is obvious that the RM-mixed system is very useful method to improve the response time and the view angle characteristic without any severe degradation of the image quality and the reliability characteristic. In conclusion, throughout this dissertation, the relationship between the response time and the azimuthal anchoring energy in the FFS mode was theoretically derived from the viewpoints of the dielectric torque induced by the order parameter of LCs and successfully explained the improvement of the response time. And we experimentally confirmed that the LC order parameter in the RM-mixed alignment layer is superior to that in the bare alignment layer. And, we made real FFS panel and could achieved not only the improvement of the response time but also superior view angle characteristic without any severe degradation of the image quality and reliability characteristic. We believe that this method is very useful to improve LCDs performances such as the response time, the view angle characteristic and the stability in in-plane switching configurations. Theoretical and experimental results, reported in this dissertation, will be contributed to researches in the field of liquid crystal and display industry.