Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Patent
1997-03-17
2000-11-14
Sikes, William L.
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
349113, 349112, 349 97, 430 7, G02F 11335, G03F 900
Patent
active
061477281
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention concerns a reflective type color liquid crystal device and an electronic apparatus using this.
PRIOR ART
The display mounted on a portable information terminal first must be low in power consumption. Consequently, reflective type liquid crystal devices not requiring backlights are optimal for this purpose. Nevertheless, the conventional reflective type liquid crystal device was mainly a monochrome display, and a good reflective type color liquid crystal device is yet to be obtained.
The development of the reflective type color liquid crystal device appears to have been started in earnest from the middle of the 1980s. Before that, for example, as in the publication of Japanese Laid-open Pat. No. 50-80799, it was not recognized that if the backlights of a transmissive type color liquid crystal device were replaced with a reflection plate, that was equivalent to saying a reflective type color liquid crystal device may be possible. Nevertheless, it is clear if actually test created, but with such a configuration it is dark and unusable. There are three causes: (1) 1/2 or more of the light is lost with the filter, (2) 2/3 or more of the light is further lost due to the color filter, and (3) the problems of parallax. The problems of parallax cannot be avoided with the TN (twisted nematic) mode and STN (super twisted nematic) mode in a transmissive liquid crystal device. The reason is because, since these modes necessarily use two polarizing plates, as long as the polarizing plates cannot be built into the cell, there occurs a gap that cannot be ignored between the reflective plate and the liquid crystal layer. The problems of parallax mentioned here are not only the problem of double reflection of the display as was the case with the conventional reflective type monochrome liquid crystal device, but it indicates a problem inherent in the reflective type color liquid crystal device.
The problems of parallax are explained using drawings. FIGS. 77(a) and (b) are cross section drawings of a reflective type color liquid crystal device using either the TN mode or the STN mode. This liquid crystal device is composed of an upper polarizing plate 7701, an upper glass substrate 7702, a liquid crystal layer 7703, a lower glass substrate 7704, a lower polarizing plate 7705, a light reflecting plate 7706, and a red-green-blue (RGB) tricolor filter 7707. Between the upper and lower glass substrates are additionally present a transparent electrode, an orientation film, and an insulating film, but they are omitted as they are not needed in explaining the problems of parallax. There are two problems of parallax. One of these is the mutual cancellation of the colors. In FIG. 77(a), the observer 7712 sees the reflected light 7711 emanating through the green filter, but this light is a blend of the introduced light 7713 passing through the red, green, and blue filters, and being scattered and reflected by the light reflecting plate. If the thickness of the lower glass substrate is sufficiently thick in comparison to the pitch of the color filters, the light passing through any colored filters will blend at equal probabilities. As a matter of fact, the light passing a course of red.fwdarw.green.fwdarw.blue, regardless of the wavelength of the light, is absorbed and becomes pitch black with any color filter, and only the light passing the course of green.fwdarw.green remains. Since the same can be said about the reflected light passing through a blue and a red filter, it becomes a problem that the brightness finally ends up 1/3 of that of a white display having no parallax. Another problem is that the color display becomes dark. FIG. 77(b) shows the status of a green display. Also, the part having applied a matrix-like hatching on the liquid crystal layer 7703 indicates that it is in the unlit status (dark status). The introduced light 7713 passes through red, green, and blue dots at equal probabilities, and 2/3 is absorbed by the red and blue dots being in the off status. Furthermore,
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patent: 4560241 (1985-12-01), Stolov et al.
patent: 5122887 (1992-06-01), Mathewson
patent: 5124818 (1992-06-01), Conner et al.
patent: 5508831 (1996-04-01), Nakamura et al.
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Maeda Tsuyoshi
Matsushima Toshiharu
Okamoto Eiji
Okumura Osamu
Seiko Epson Corporation
Sikes William L.
Ton Toan
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