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Show moreBackground of the invention: Flat panel liquid crystal displays are important components in display technology. Because of their relatively low cost and high definition, twisted nematic (TN) and supertwisted nematic (STN) cells, ferroelectric liquid crystals and liquid crystal-polymer dispersions have been used in a variety of display applications. Each of the foregoing technologies has drawbacks. Both TN and STN cells require complicated surface treatments which add to the difficulty and expense of their manufacture. Since TN cells inherently exhibit remnant birefringence near the cell surfaces, their dark state is not typically very dark. To obtain good contrast TN and STN cells may require an additional retardation or compensation layers which further adds to the difficulty and expense of their manufacture. Moreover, STN and TN cells are dark in their voltage-on state and bright in their voltage-off state, complicating the addressing scheme in multipixel displays. Ferroelectric liquid crystals also require delicate surface treatments and are susceptible to mechanical shock which limits their application. The polymer required for polymer-liquid crystal displays adds to their cost and complicates their manufacture. The instant invention provides an economical alternative to such technologies having the advantages of low cost, a very dark off-state, a bright on-state, excellent contrast, the possibility for inherent color transmission and, for certain applications, low threshold switching voltage. Disclosure of the invention: The invention is directed to new liquid crystal display technology employing chiral nematic liquid crystal having negative dielectric anisotropy. The invention provides an economical substitute for TN and STN cells and has a number of advantages thereover. First, the device relies on homeotropic surface alignment, which is much simpler to obtain than the homogeneous surface alignment required for TN cells. This reduces the number of processing steps, rendering the device both easier and cheaper to manufacture. Second, the dark or opaque "off" state of the inventive devices exhibits excellent extinction and has no remnant birefringence for normally incident light. Thus, the opaque state is much darker than that exhibited by TN cells and does not require a positive retardation layer. Third, the device can be adjusted to achieve vanishingly small threshold voltage and can exhibit grey scale. Fourth, the contrast ratio or collimated light, which is the ratio of transmitted intensity at a field on voltage to transmitted intensity in the absence of a field, can be over 3000:1 for normal incidence, which is far superior to most TN cells. Moreover, these contrast ratios are exhibited in a light on dark display. Light writing on a dark background is a significant advantage over dark on light displays, such as TN cells.
http://www.google.com/patents?vid=USPAT5477358
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Show moreBackground of the invention: Flat panel liquid crystal displays are important components in display technology. Because of their relatively low cost and high definition, twisted nematic (TN) and supertwisted nematic (STN) cells, ferroelectric liquid crystals and liquid crystal-polymer dispersions have been used in a variety of display applications. Each of the foregoing technologies has drawbacks. Both TN and STN cells require complicated surface treatments which add to the difficulty and expense of their manufacture. Since TN cells inherently exhibit remnant birefringence near the cell surfaces, their dark state is not typically very dark. To obtain good contrast TN and STN cells may require an additional retardation or compensation layer which further adds to the difficulty and expense of their manufacture. Ferroelectric liquid crystals also require delicate surface treatments and are susceptible to mechanical shock which limits their application. The polymer required for polymer-liquid crystal displays adds to their cost and complicates their manufacture. The instant invention provides an economical alternative to such technologies having the advantages of low cost, a very dark off-state, a bright on-state, excellent contrast, the possibility for inherent color transmission and, for certain applications, low threshold switching voltage. Disclosure of the invention: The invention is directed to new liquid crystal display technology employing chiral nematic liquid crystal having negative dielectric anisotropy. The invention provides an economical substitute for TN and STN cells and has a number of advantages thereover. First, the device relies on homeotropic surface alignment, which is much simpler to obtain than the homogeneous surface alignment required for TN cells. This reduces the number of processing steps, rendering the device both easier and cheaper to manufacture because no mechanical buffing is required. Second, the dark or opaque "off" state of the inventive devices exhibits excellent extinction and has no remnant birefringence for normally incident light. Thus, the opaque state is much darker than that exhibited by TN cells and does not require a positive retardation layer. Third, the device can be adjusted to achieve vanishingly small threshold voltage and can exhibit grey scale. Fourth, the contrast ratio of collimated light, which is the ratio of transmitted intensity at a field on voltage to transmitted intensity in the absence of a field, can be over 3000:1 for normal incidence, which is far superior to most TN cells. Moreover, these contrast ratios are exhibited in a light on dark display. Finally, in certain configurations, preferential transmission of color is possible where the color depends on the applied voltage. By adjusting the cell parameters the devices can be used in a number of display applications and be significantly more cost effective than currently existing technologies.
http://www.google.com/patents?vid=USPAT5602662
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