Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-07-08
2003-03-18
Parker, Kenneth (Department: 2871)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C349S106000, C349S156000
Reexamination Certificate
active
06535188
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to a liquid crystal display device in which light emission from viewer's side (display side) of a liquid crystal layer is turned ON/OFF or controlled to be increased/decreased on the basis of a birefringence (double refraction) effect of the liquid crystal material.
2. Description of the Related Art
Liquid crystal display devices have excellent features such as thin and light weight, low power consumption and mild fatigue in eyes. For this reason, the liquid crystal display devices have come to be used in various fields such as displays for notebook-size personal computers and for portable wordprocessor-dedicated machines, and is expanding their fields of use and markets more and more.
In recent years, not only the market of medium/small screen-sized liquid crystal display devices expands continuously, but also the market of large screen-sized (larger than, or equal to 13 inches) liquid crystal display devices expands rapidly. As for the large screen sized liquid crystal display devices, reduction of viewing-angle-dependency in a color tone and contrast is a requirement to meet. Particularly for large screen-sized computer displays for CAD system and the like, and for displays for conference or interview purposes, reduction of the viewing-angle-dependency is an important requirement.
As one of the methods for reducing the viewing-angle-dependency, liquid crystal display devices utilizing the birefringence effect of liquid crystal materials, in particular, IPS (In-Plane Switching) type liquid crystal display devices are researched and developed eagerly.
Referring now to a schematic diagram of
FIG. 5
, a basic displaying mechanism in an IPS type liquid crystal display device will be explained. In following, an IPS type liquid crystal display device operated in a normally black mode is exemplified.
Liquid crystal molecules are oriented to be substantially horizontally with respect to a plane of the substrate, and to be in substantially parallel to each other. A polarizing plate
15
is arranged on an outer surface of an array substrate
2
(namely, on lower surface of lower board in FIG.
5
), while another polarizing plate
28
is arranged on an outer surface of a counter substrate (namely, on upper surface of upper board in
FIG. 5
) which is provided on a screen side or viewer's side. The arrangement is made in such a manner that polarizing directions of these polarizing plates
15
and
28
are intersected substantially perpendicular to each other.
At an initial stage (non-voltage-applied state), as represented in a left half portion of
FIG. 5
, the liquid crystal molecules are arranged to be substantially parallel to the polarizing direction of the lower polarizing plate
28
. As a result, light from a light source at underneath is not transmitted to viewer's side, that is upper side in the figure.
On the other hand, as shown in a right half portion of
FIG. 5
, in a domain of each of pixels (minimum display unit) on the array substrate
2
, when a voltage is applied between a pixel electrode
21
and a counter electrode
22
, on orientation (director direction)
5
of liquid crystal molecules are controlled to be aligned along lines of electric force, so that the light is transmitted on basis of the birefringence effect.
Ordinarily, to perform a color representation, colored patterns constituted by fine patches of red (R), blue (B), and green (G), which are three primary colors of light, are formed on the counter substrate
1
. This colored pattern called as a color filter is formed in such a manner that colored films of the three primary colors are allocated every three pixels located adjacent to each other. Then, relative ratios of light intensities as to these three pixels located adjacent to each other are adjusted, so that color tone representation can be realised. There are frequent occasions when a set of 3 minimum display units, i.e., R, G, D is counted as a 1 pixel in color display devices. However, in this specification, a minimum display unit is referring to as a “pixel”.
The color patterns of three primary colors are formed in the following manner. A coating material in which any one of primary color pigments has been dispersed is coated on a whole surface of the substrate by way of either a spin coater or a curtain coater. Subsequently, a patterning process in use of photolithography technique is carried out so as to form colored films only over pixels that are allocated to this selected color of the three primary colors. A similar patterning process is carried out with respect to other primary colors. In this way, colored patterns of the three primary colors are obtained by 3 times of the coating and patterning processes.
On the other hand, in order to make a uniform thickness of liquid crystal layer, spherical resin bodies having uniform diameters are dispersed on any one of the substrate boards before the array substrate is attached to the counter substrate. This spherical resin body is called as a “spacer”.
However, these spherical spacers are partially aggregated, in the worst case, a bright-point defect is produced on the screen of the liquid crystal display device. Further, when fluctuation and deviation in dispersing density give rise a region of substantially no spherical spacer, the thickness of the liquid crystal layer in this region becomes thinner than that of another region. Thus, the resulting contrast ratio on the display screen would become unequal, to deteriorate the picture representation on the screen. Additionally, since the spherical spacers are distributed also to the display areas within the pixels, light leakage will occur by these spherical spacers themselves, and by the orientation failures of the liquid crystal molecules at around the spherical spacers. Such light leakage deteriorate the contrast ratio.
Usually, each of these colored films of three primary colors, which constitute colored patterns, is formed separately in respective process step. As a result, it is difficult to achieve sufficiently uniform thickness. In most cases, a stepped portion is produced between a color-film region of a certain primary color and an adjacent color-film region of another primary color. That is, a height difference in respect of a surface of the substrate is produced between these regions.
More specifically, in order that a color representation characteristic of a liquid crystal display device may be improved so as to substantially represent a natural color, a thickness of a colored film used to form a colored pattern must be made thick, so that color density of the colored pattern is increased. However, when the thicknesses of the respective colored films of the three primary colors are increased as a whole, the differences in the thicknesses among the regions of the colored films are also increased. Usually, a thickness of a colored film is required to be about 1 &mgr;m. In this case, fluctuations in thickness is up to about 0.2 &mgr;m.
In the case that a thickness of a colored film is made thicker than 1 &mgr;m, fluctuations in thickness would be further increased. This is because in such a coating apparatus as a spin coater and a curtain coater, a coating materials for colored film having a high content of pigment and having a high viscosity cannot be sufficiently uniformly distributed on a substrate board.
The larger, the size of the substrate board on which the colored patterns are formed is, the bigger the fluctuation in the thickness of such colored films becomes.
Deterioration of the display performance due to uneven thickness of the liquid crystal layer is especially intense in the liquid crystal display devices which utilizes the birefringence effect of the liquid material as a display mode. As mentioned previously, the thicknesses of the liquid crystal layer has been made uneven because of the fluctuation and deviation in the distribution of the spherical spacers and because of the fluctuation in the thickness of the colored films.
Chung David Y
Parker Kenneth
Pillsbury & Winthrop LLP
LandOfFree
Liquid crystal display device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Liquid crystal display device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid crystal display device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3082606