[Paper] Design of VA-LCD System with Microstructure Film for Wide Viewing

Abstract

122 BackgroundVertical alignment (VA) mode liquid crystal display (LCD) is widely used especially in large size display market because it shows very high contrast ratio in the normal direction and wide viewing characteristics, achieved by many efforts 1)-7) . However, much wider viewing angle is required in the movement of high definition from Full-High Definition (FHD) to UltraHigh Definition (UHD) because of its short preferred viewing distance 8)9) . As a reasonable method to measure viewing angle of display, the color viewing angle has been suggested 10) . This is angular range of low color shift from the normal direction. In particular, the color viewing angle is defined as the angle range within the noticeable threshold of ∆u'v' = 0.015, where u'v' is average value of 9 colors (dark skin, light skin, blue, green, red, yellow, magenta, cyan and gray in the Macbeth Chart). UHD display should require the color viewing angle above 100°, which is horizontal viewing angle at the preferred viewing distance.Some approaches such as the capacitive coupled method and the two-TFT method have been proposed to improve the gamma curve of VA-LCDs 4)6) . However, the color viewing angle did not reach 100°and also these methods require complex electronic circuits. In addition, the manufacturing cost and device power consumption increase when two TFTs are used in each unit pixel.To overcome these drawbacks, we achieved outstanding wide viewing angle characteristics by applying the microstructure film without these complex circuit technologies. This film can control the scattering characteristics with the shapes of the internal air-micro cavities capped by black dots. In the case of TN-LCD, we could drastically improve the viewing angle characteristics by just attaching the film to the surface 11)-16) . However, in the case of 4-domain VA-LCD, improvement effects by attaching the film were limited 15) . Therefore, for VA-LCD, we optimized the backlight (BL) distribution and the LC alignment direction as well as the scattering profile of the microstructure film. Feature of the Microstructure FilmThe microstructure film is attached to the surface of LCD. It is composed of a transparent polymer layer, airmicro cavities, black dots and a base film, as shown in Abstract We have developed a wide viewing VA-LCD system with the microstructure film. This film is attached on LC panel and scatters incident lights from LC panel by reflection at internal air cavities to improve the viewing angle characteristics. In this system, we have optimized LC alignment directions and BL distribution as well as the scattering profile of the film. LC panel has two-domain LC aligned pixel (each LC director is antiparallel in vertical direction) and wide viewing angle in horizontal direction. Backlight distribution is collimated to horizontal direction. To distribute lights in horizontal direction to vertical direction, we designed and fabricated the microstructure film which had rhombus shaped air cavities. This display system indicated smaller color s...

Effect of propionyl group on birefringence and wavelength dispersion of propionylated cellulose acetate optical compensation films

“…According to the panel type, LCD can be divided into traditional twisted column LCD (TN-LCD), in-plane switching LCD (IPS-LCD) and vertically aligned LCD (VA-LCD), while IPS-LCD and VA-LCD occupy most of the current LCDs (Kim et al 2011). Due to the vertical arrangement of liquid crystal molecules, the VA-LCD has a higher contrast ratio than IPS-LCD and TN-LCD and has been widely applied in the eld of large size televisions (Kim et al 2015;Ochi et al 2017).…”