Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-04-12
2004-02-03
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S106000
Reexamination Certificate
active
06686982
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device and, in particular, to a reflection type liquid crystal display device which effects display by using external light.
2. Description of the Related Art
Recently, the demand for longer operational life in portable information apparatuses such as notebook PCs and electronic notebooks when connected to a portable power supply (e.g. a battery) has increased. Mechanisms that lead to this longer operational life include an increase in battery capacity and a decrease in power consumption of the apparatus. The display in a portable information apparatus is one of the devices that uses a large amount of power. Thus, to lower the amount of power used, it is useful to decrease the amount of power consumed in displaying information to the user. For this reason, devices using liquid crystal displays (or liquid crystal display devices) are widely used as low power consumption displays. In general, conventional liquid crystal display devices use backlighting to aid in displaying data. However, the use of backlighting consumes power. Thus, a reflection type liquid crystal display device, which does not use a backlight is effective in achieving a reduction in power consumption.
As shown in
FIG. 10
, a conventional reflection type display device
100
comprises a pair of glass substrates
113
and
114
, transparent electrode layers
120
and
121
respectfully provided on the opposing (inside) surfaces of the glass substrates
113
and
114
, liquid crystal orientation films
122
and
123
respectively provided on the transparent electrode layers
120
and
121
, and a liquid crystal layer
115
provided between the orientation films
122
and
123
. First and second polarizing plates
117
and
118
are respectfully provided on the other surfaces (outside) of the glass substrates
113
and
114
. A reflection plate
101
is provided on the outside of the second polarizing plate
118
. The surface of a reflection film
105
on the reflection plate
101
is disposed between the reflection plate
101
and the second polarizing plate
118
. Note that the terms inside (or inner side) and outside (or outer side) have been used here to denote sides of layers more proximate and more distal, respectfully, to the liquid crystal layer
115
.
In the reflection type liquid crystal display device
100
described above, light impinging upon the first polarizing plate
117
undergoes linear polarization, and is further transmitted through the liquid crystal layer
115
to become elliptically polarized. The second polarizing plate
118
changes the elliptically polarized light into linearly polarized light, the reflection plate
101
reflects the linearly polarized light, which is subsequently transmitted through the second polarizing plate
118
and the liquid crystal layer
115
and emitted from the first polarizing plate
117
.
In the conventional reflection type liquid crystal display device described above, the reflection plate
101
is endowed with scattering reflection characteristics by, for example, forming a reflection layer consisting of aluminum or the like on the rough surface of a metal film, synthetic paper or the like.
One problem with the typical reflection plate described above is that it has wide scattering angle characteristics, which is to say that it is difficult to enhance the brightness in a particular, frequently viewed direction (as in the case of the front of the display surface as viewed by the user). As a result, although the angle of sight is wide, the display is rather dark.
Alternatively, a flat, mirror-like surface may be used as the reflection surface rather than the rough reflection surface described above. When a mirror surface is used as the reflection surface, it is possible to obtain very bright characteristics in the specular direction with respect to the incident light. However, a disadvantage of using a mirror surface as the reflection surface is that when viewing the display from a direction that deviates slightly from the specular direction, the display is dark.
Thus, ideal reflection plate characteristics include both a wide viewing angle and high brightness. In view of this, effective scattering reflection in the viewing direction is desirable. A mechanism for achieving these characteristics is using a reflection plate having an intentionally controlled reflection scattering angle. It is also desirable for the arrangement to be random to avoid coloring due to the interference of the reflection light.
To control the reflection scattering angle, it may be possible to use machining or the like to form controlled, minute protrusions and recesses. However, when a completely random arrangement is adopted, the coordinate data on the work points is enormous and is impractical to create this type of reflection plate. Alternatively, it may be possible to generate random coordinates each time machining is conducted. In this case, however, it would be difficult to control the reflection scattering angle.
In addition, as a practical matter, it is easier from the viewpoint of designing and machining to form a random arrangement in a small-scale region and repeat the arrangement. In a possible example, recesses (or protrusions) are sequentially mechanically formed on the surface. It is convenient to form either one shape or a plurality of shapes at one time in a certain place on the surface and subsequently feed the surface sequentially in the X-direction in a fixed pitch, feed the machining position in the Y-direction after machining for a predetermined length, and perform surface processing while again feeding in the X-direction. This machining method results in a structure having a repeated arrangement in the machining feeding direction.
Using a reflection plate having a repeated arrangement (either formed by this or other methods) and combining with a stripe-shaped electrode as a display electrode may result in periodic overlapping between the patterns if the directions of the repeated structures do not completely coincide but are slightly angled with respect to each other. This periodical overlapping creates a fringe-like pattern, which is oblique with respect to the pattern direction, and results in a so-called moiré fringe being viewed. Even if a reflection type liquid crystal display device of this type is combined with color filters to perform color display, a moiré fringe is viewed due to the repeated structure of the protrusions and recesses of the reflection plate and the repeated alignment structure of the colored pixels of the color filters. The moiré fringe created impairs the display quality.
SUMMARY OF THE INVENTION
The present invention has been made with a view toward solving the above problem. It is an object of the present invention to provide a liquid crystal display device having a decreased viewable oblique moiré fringe while using a reflection plate having satisfactory reflection characteristics with a repeated recess arrangement and which is superior in display quality.
In accordance with the present invention, there is provided a reflection type liquid crystal display device comprising upper and lower substrates, a liquid crystal layer provided between the upper and lower substrates, a plurality of transparent electrodes formed on the side of at least one of the opposed surfaces of the upper and lower substrates so as to extend in a predetermined direction, and a reflection member on the opposed surface side or outside of the lower substrate, the reflection member having a plurality of recesses arranged in a direction, wherein the direction in which the recesses are arranged is deviated about 2.5 to about 40 degrees from the direction in which the transparent electrodes extend, thereby decreasing the viewable moiré fringe and improving the display quality of the liquid crystal display device.
Further, in accordance with the present invention, there is provided a reflection type liquid crystal display device, wherein the reflection m
Chowdhury Tarifur R.
Nguyen Dung
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