Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2000-04-07
2002-07-16
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S043000, C349S111000, C349S138000
Reexamination Certificate
active
06421101
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention disclosed in the present specification relates to a structure of a liquid crystal display or a fabrication method thereof.
DESCRIPTION OF RELATED ART
There has been known a flat panel display typified by a liquid crystal display. In a transmission type liquid crystal display having a mode of optically modulating light which has passed through a liquid crystal panel by the liquid crystal panel, light shielding means called a black matrix is required in order to clearly define a profile of pixels. In concrete, it is necessary to cover the peripheral portion of a pixel electrode by a light shielding frame. Such a black matrix plays an important role in displaying fine motion pictures in particular.
However, the black matrix has a demerit that it reduces an effective area of a pixel (this rate will be referred to as an aperture ratio) and darkens the screen.
It is being tried to utilize the flat panel display in low power consumption type portable equipments such as a portable video camera and a portable information terminal in recent years.
What comes into question here is the low power consumption characteristic which is required for such portable equipments. That is, it is necessary to reduce the power consumption used for displaying the screen.
In case of the transmission type liquid crystal display, a method how to reduce power consumed by a back-light for illuminating from the back of the liquid crystal panel comes into question. The power consumption of the back-light may be reduced by reducing brightness of the back-light by increasing the aperture ratio of the pixel.
Meanwhile, in case of the liquid crystal display, it is necessary to dispose a capacitor called an auxiliary capacitor in order to supplement a capacity which liquid crystal has in each pixel. This auxiliary capacitor has a function of holding information (which corresponds to a quantity of charge), which has been written to a pixel electrode and which is rewritten by a predetermined time interval, until it is rewritten in the next time. Flickers or nonuniformity of color (which is actualized specially in displaying in color) occurs in the display when the value of the auxiliary capacitor is small.
However, the provision of the auxiliary capacitor in each pixel also becomes a factor of dropping the aperture ratio of the pixel, similarly to the case of disposing the black matrix.
SUMMARY OF THE INVENTION
As described above, the disposition of the black matrix and the auxiliary capacitor for the purpose of increasing the image quality becomes the factor of dropping the aperture ratio of the pixel. The drop of the aperture ratio invites a drop of the image quality in another sense.
That is, it is contradictory to request a clear image to be displayed (by the effect of the black matrix) and to obtain a bright image (by increasing the aperture ratio).
It is also contradictory to suppress the flickers and nonuniformity of color in the display (by the effect of the auxiliary capacitor) and to obtain a bright image (by increasing the aperture ratio).
Accordingly, it is an object of the invention disclosed in the present specification to provide a technology for solving the above-mentioned contradictory requests.
According to one of the invention disclosed in the present specification, an active matrix type display device comprises an electrode pattern made of a conductive film disposed between source and gate lines and a pixel electrode; and an auxiliary capacitor formed between the electrode pattern and the pixel electrode.
According to another invention, an active matrix type display device comprises an electrode pattern made of a conductive film disposed between source and gate lines and a pixel electrode; an edge of the pixel electrode is disposed so as to overlap with the source and gate lines; and an auxiliary capacitor is formed between the electrode pattern made of the conductive film and the pixel electrode.
In the arrangements of the two inventions described above, the electrode pattern made of the conductive film functions as a shield film for electrically shielding the source and gate lines from the pixel electrode.
A structure of a still other invention is an active matrix type display device in which an electrode pattern made of a conductive film is disposed so as to cover source and gate lines.
In the structure described above, the electrode pattern made of the conductive film overlaps partially with the pixel electrode to form an auxiliary capacitor. Further, the electrode pattern made of the conductive film functions as a shield film for electrically shielding the source and gate lines from the pixel electrode.
One concrete example of the invention disclosed in the present specification is characterized in that an electrode pattern
106
made of the same material as a pixel electrode
107
is disposed between a source line
105
and a gate line
104
and the pixel electrode
107
to form an auxiliary capacitor between the electrode pattern
106
and the pixel electrode
107
as its pixel structure is shown in FIG.
1
.
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Teramoto Satoshi
Zhang Hongyong
Chowdhury Tarifur R.
Fish & Richardson P.C.
Semiconductor Energy Laboratory Co,. Ltd.
Sikes William L.
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