Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-08-29
2004-09-07
Flynn, Nathan J. (Department: 2826)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S096000, C349S119000, C349S143000, C349S147000, C257S059000
Reexamination Certificate
active
06788370
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display apparatus, and more particularly to a liquid crystal display apparatus including a reflection display unit and a transmission display unit within one pixel.
2. Description of the Prior Art
One type of the reflection-type liquid crystal display apparatuses has a reflection display unit and a transmission display unit within one pixel. The reflection display unit performs the display by reflecting, using a reflection plate, the light incoming from the surroundings. Since the reflection display unit has a fixed contrast ratio independently of the brightness of the surroundings, it offers an advantage of making it possible to obtain an excellent display under an environment ranging from outdoors to indoors at the time of sunny weather. The reflection display unit, however, becomes incapable of recognizing the display in a dark environment such as a dark room.
Meanwhile, the transmission display unit performs the display by taking advantage of the light from a backlight light-source located at the rear thereof. The transmission display unit offers an advantage of making it possible to recognize the display even in the dark environment such as the dark room. The transmission display unit, however, becomes incapable of recognizing the display under a bright environment where, e.g., the intensity of the interfacial reflection light is stronger than that of the backlight light.
In this way, the reflection display unit and the transmission display unit are in a relationship of complementing the respective disadvantages to each other. As a result, the reflection-type liquid crystal display apparatus including both of them is usable under a wider condition including the outdoors at the time of sunny weather to the dark room. The reflection-type liquid crystal display apparatus including the reflection display unit and the transmission display unit within one pixel has been described in, e.g., JP-A-11-242226.
In the reflection-type liquid crystal display apparatus including the reflection display unit and the transmission display unit (hereinafter, referred to as simply “the reflection-type liquid crystal display apparatus”), the reflection display unit has built the reflection plate in a liquid crystal cell, and includes one sheet of polarizer and one sheet or two sheets of phase plates. Meanwhile, the transmission display unit in the reflection-type liquid crystal display apparatus uses one sheet of polarizer over and under a liquid crystal cell, and includes one sheet or two sheets of phase plates between the liquid crystal cell and the polarizers.
The display characteristics of the reflection display unit are determined by the respective optical parameters of the liquid crystal layer, the phase plates, and the polarizers. The optical parameters of the liquid crystal layer are a twist angle and a retardation. The optical parameters of the phase plates are the azimuthal angle of a slow axis and a retardation. The optical parameter of the polarizers is the azimuth-angle of an absorption axis.
Similarly, the display characteristics of the transmission display unit are also determined by the optical parameters of the liquid crystal layer, the phase plates, and the polarization plates.
On the upper side of the reflection-type liquid crystal display apparatus (i.e., on an observation-plane side of the liquid crystal display apparatus), the phase plate and the polarizer located thereon can be used in common to the reflection display unit and the transmission display unit. On the other hand, on the lower side of the reflection-type liquid crystal display apparatus, it is difficult to form, as one and the same layer, a reflection electrode for applying a voltage to the reflection display unit and a transparent electrode for applying a voltage to the transmission display unit. Accordingly, both of the electrodes are usually formed as different layers. This condition results in a difference in the liquid crystal layer thickness between the reflection display unit and the transmission display unit, thereby making it impossible to obtain excellent displays on both the reflection display and the transmission display.
On account of this, in a reflection-type liquid crystal display apparatus using, e.g., a super-twisted nematic liquid crystal, the margin for a variation in the liquid crystal layer thickness is extremely narrow. Consequently, a configuration has been employed where layer-gap between the reflection display unit and the transmission display unit is eliminated. In this apparatus, however, the combination of a lower-side phase plate and a lower-side polarizer has been formed into an elliptical polarizer in order to increase the transmission of the transmission display unit. In this case, in spite of the condition that there exists no layer-gap between the reflection display unit and the transmission display unit, the combination has been formed into the elliptical polarization plate. This reduces the contrast ratio on the transmission display down to an order of 10:1.
SUMMARY OF THE INVENTION
The present invention has been made in view of these problems, and provides a reflection-type liquid crystal display apparatus that allows the excellent displays to be obtained on both the reflection display and the transmission display.
In order to solve the above-described problems, the present invention has employed the following method:
In a liquid crystal display apparatus including a pair of facing substrates, a liquid crystal layer and a liquid crystal driving unit which are held in being sandwiched between the facing substrates, and polarization plates and phase plates which are located on the upper side and on the lower side of the facing substrates, respectively, wherein a pixel of the liquid crystal display apparatus includes a reflection display unit whose reflectivity's applied voltage dependance of reflection is the normally-closed type and a transmission display unit whose layer thickness is thicker than that of a liquid crystal layer constituting the reflection display unit. Moreover, the polarization plate and the phase plate which are located on the lower side of the facing substrates form an elliptical polarizer, thereby converting, into a circularly-polarized light, a backlight light at a point-in-time of having passed through a liquid crystal layer's portion corresponding to a difference in the layer thickness between the liquid crystal layers.
An optical parameter setting method for the liquid crystal layer, the phase plates, and the polarizer of the reflection-type liquid crystal display apparatus has been described in, e.g., a presentation given by O. Itou, S. Komura, K. Kuwabara, K. Funahata, K. Kondo, K. Kubo et al. (SID '98 DIGEST (1998), pp. 766-769). In the reflection-type liquid crystal display apparatus, a light is incident into the polarizer, and passes through the phase plate and the liquid crystal layer, then being reflected by the reflection plate. Moreover, the light passes through the liquid crystal layer and the phase plate again, then being incident into the polarizer. At the time of the dark display, if, in this process, a phase difference equivalent to a half wavelength is added to the light, the light is completely absorbed at a point-in-time of being incident into the polarizer at the second time, which, accordingly, is ideal. Namely, this is because the oscillation plane of the light that has become a linearly-polarized light by passing through the polarizer at the first time rotates by 90° in this process, and thus the oscillation direction becomes parallel to an absorption axis of the polarizer at the point-in-time of being incident into the polarizer at the second time. When performing the conversion into the one-way light path, the phase difference added to the transmission light is equal to a quarter wavelength. Accordingly, at a point-in-time of having reached the reflection plate, the polarization state of the transmission lig
Itou Osamu
Komura Shinichi
Flynn Nathan J.
Sefer Ahmed N.
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