Highly-multiplexed Large-area Achromatic Liquid Crystal Display

Influences of retardation and polarizer configuration on background color, background brightness and contrast ratio have been studied for a ST LCD with a twist angle of 240 degrees. There exists an optimum polarizer configuration which gives an achromatic background color and the highest contrast ratio for each retardation. When the optimum polarizer configuration is used for each retardation, a bright background and a high contrast ratio are obtained as the retardation is larger. On the other hand, the background color becomes more achromatic as the retardation is smaller. Therefore, it is necessary to optimize cell conditions taking account of a balance of the background brightness, contrast ratio and background color. It is concluded that the optimum retardation ranges from 0.59 to 0.60 μm. On the basis of the optimization of a LC material as well as the retardation and polarizer configuration, an achromatic ST LCD with 640 × 400 pixels in an A4 page size and a twist angle of 240 degrees which operates under a 1/200 duty multiplexing drive has been successfully developed. The achromatic ST LCD has an excellent display performances such as not only almost the same achromatic background color as that of a conventional TN LCD but also a high contrast ratio and a wide viewing angle.