The basic study on improved picture quality and reduced power consumption of reflective color liquid crystal displays

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High-quality, lightweight, reflective color LCDs with low power consumption are important devices for highly functional and portable information terminals. Although various types of reflective LCDs have been proposed, only reflective color LCDs using single-polarizer TN-LCDs and STN-LCDs are presently being used for practical applications. However, the power consumption of a reflective color TN-LCD is several times greater than that of a reflective color STN-LCD. Clearly, it would be advantageous to reduce the TN-LCD's power consumption while maintaimng its superior image quality.To achieve this, we analyzed the numerical relationship between the electro-optical properties and the on-voltage of a TFT-LCD in the following single-polarizer reflective TN-LCDs.(1)Single-polarizer DTN-LCD and FDTN-LCD with a retardation fun(2)Single-polarizer DTN-LCD and FDTN-LCD with a quarter waveplat(3)Single-polarizer TN-LCD with two retardation filmsOur results showed that the LCD exhibited an achromat … More ic image with a high luminous reflectance (about 50%) and a very high contrast ratio, even when the on-voltage was reduced to 2V. The power consumption of the panel could potentially be decreased to about 1/3 of that presently needed for reflective TETLCDs operating at 3.2V in the on-stateIn addition, we found that a single-polarizer reflective TN-LCD with a retardation film exhibited a NB and/or NW-mode achromatic image of high luminous reflectance and high contrast ratio, even when the on-voltage of TFT-LCD was reduced to 2V, if we optimized the birefringence dispersion of the retardation film Δ_<nR>(λ).To further test the possibility of reducing power consumption, we analyzed the influence of the material parameters of an LC on the electro-optical properties of the TN-LCD. Our results demonstrated that an ultra-low-power reflective TFT-LCD with a high-quality image can be obtained if a liquid-crystal material with a low threshold voltage (i.e., a small value for K_<11> and a large value of Δ_ε) can be developed. Less