Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-03-07
2004-04-27
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S106000, C349S038000
Reexamination Certificate
active
06727965
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a semitransparent liquid crystal display device with high intensity and low power consumption.
BACKGROUND ART
With the widespread use of mobile terminals and other similar equipment, the reflective liquid crystal panel has been drawn attention. This type of panel reflecting outer light for display shows sufficient display performance in bright conditions like outdoors; however, its visibility remarkably decreases in dark conditions.
In order to overcome this problem, a semitransparent liquid crystal panel capable of being used both indoors and outdoors has been developed by applying the technique of the reflective liquid crystal panel. In such a semitransparent liquid crystal panel, when a backlight is employed, each transparent portion in the form of a square is arranged at the center of a pixel in reflective layers which have a projections and depressions structure. In order to simplify manufacturing requirements, the projections and depressions structure is identical in all pixels (Refer to Japanese Laid-open Patent Application No. 10-319422).
However, in the case where such a large transparent portion is provided at the center of each pixel in the reflective layers, as in the above prior art case, the large total area of the transparent portions are irrelevant to reflection; intensity is insufficient when the panel is used as reflective type. As another problem, since the intensity in the reflective type is determined by the area of the transparent portions, providing transparent portions without regard to the projections and depressions structure makes reflectivity during reflection and permeability during permeation incompatible.
If the color filter layer has the same degree of thickness during permeation and during reflection, there is a problem that light has different degrees of absorption between during reflection and during permeation, thereby making color phases differ between during reflection and during permeation. The reason for this is considered that during reflection, light goes through the color filter layer and then returns through it, substantially making the color filter layer twice as thick as it is during permeation. As a result, for example, when a color filter for reflection with high permeability is used by giving reflectivity priority, there is a problem that the color is lightened during permeation
Further the pixels having the same projections and depressions structure also have the same capacity within the screen. Therefore, when the screen is larger, there is a problem that a decrease in gate voltage due to the line resistance of the gate and the source makes the punch-through voltage show different values within the screen, thereby causing flicker.
DISCLOSURE OF THE INVENTION
In order to solve the above-described problems, the inventors of the present invention have achieved a semitransparent liquid crystal display device with backlighting comprising semitransparent reflective layers having a projections and depressions structure as follows.
A first aspect of the invention is a semitransparent liquid crystal display device comprising semitransparent layers having a projections and depressions structure including reflective portions and transparent portions, wherein said transparent portions are so formed as to include nearly flat regions of said projections and depressions structure.
The nearly flat regions (regions of extremely small angles of inclination) in the projections and depressions structure do not contribute to an increase in panel reflectivity, and what is worse, deteriorate display performance because they cause specular reflection. Therefore, by so forming transparent portions as to include the nearly flat regions of the projections and depressions structure, the specular reflection can be prevented. In addition, the presence of the transparent portions can improve the permeability of light emitted from the backlight. The specific effects of the transparent portions will be described in the effects for a second aspect of the invention.
A second aspect of the invention is characterized in the first aspect of the invention, wherein the projections and depressions structure in the nearly flat regions has the angle of inclination of not less than 0 degree nor more than 2 degrees.
The reflection performance of the semitransparent layers having the projections and depressions structure is determined by the angle of inclination of the projections and depressions structure in the reflective portions. In order to efficiently gather ambient light in the viewer's direction, it is necessary to arrange the angle of inclination of 2 to 10 degrees degrees in a specific distribution. Asperities having the angle of inclination of less than 2 degrees are likely to cause specular reflection and are not effective in light-gathering. The specular reflection causes degradation reverse, which remarkably lowers visibility. Thus, regions having the angle of inclination less than 2 degrees do not contribute to an increase in the panel reflectivity, and what is worse, may deteriorate the display performance due to the specular reflection. For this reason, in prior art devices, the reflective layers have been so arranged as not to create regions with small angles of inclination. However, the inventors of the present inventions have found that in a semitransparent display with backlighting, devoting the regions with small angles of inclination to transparent portions not only prevents the occurrence of specular reflection but also improves the panel reflectivity.
The specific effects of the present invention will be described as follows in comparison with a prior art device.
FIGS. 1 and 2
respectively show the top view and a cross sectional view of the array substrate of the liquid crystal panel in the prior art semitransparent liquid crystal display device. In the prior art device, the projections and depressions structure
204
is made from a resist in such a manner that as small flat regions as possible are created so as to prevent the reflective layers
202
from having small angles of inclination. However, no manner how the structure
204
is arranged, the peaks of the projective portions must be nearly flat, so that the reflective layers
202
are formed even in the nearly flat regions. On the other hand, since a large transparent portion
205
not provided with the reflective layers
202
is arranged at the center of a pixel so as to realize the semitransparent type, the projections and depressions structure
204
in the transparent portion
205
does not contribute to an increase in the reflectivity at all.
FIG.
3
(
a
) shows an example of light trails on the reflective layers of the prior art semitransparent liquid crystal display panel. Light
210
reflected on an inclined surface in the projections and depressions structure
204
contributes to an increase in intensity, while light
211
regularly reflected near the peak of a projective portion is one cause of degradation reverse. Furthermore, the inclined surfaces of the projective portions in the transparent portions
213
are provided with transparent electrodes
214
only so that transparent light
215
can be generated without regard to the projections and depressions structure
204
. Therefore, the inclined surfaces of the projective portions in the transparent portion
213
do not contribute to an increase in the panel reflectivity at all.
In contrast, the semitransparent liquid crystal display device of the present invention devotes the nearly flat regions of the projections and depressions structure in the reflective layers to transparent portions, which prevents a decrease in panel reflectivity and improves intensity during permeation. Thus devoting the regions not contributing to an increase in the panel reflectivity to transparent portions, both the reflectivity and the permeability can be improved.
FIG.
3
(
b
) shows an example of light trails on the reflective layers of a semitransparent liquid crystal display panel of the pres
Duong Thoi V.
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
Ton Toan
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