Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-01-28
2002-05-28
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S143000, C349S148000, C349S149000
Reexamination Certificate
active
06396554
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color liquid crystal display (LCD), and more particularly to a color LCD in which pixel electrodes of the same color located close to one another in a column direction are driven by a single data line.
2. Description of the Prior Art
Conventionally, an LCD having orientation control windows opened in a common electrode opposing pixel electrodes has been proposed in, for example, JPA H06-301036. An LCD having orientation control windows is a vertical orientation type LCD using liquid crystal having negative anisotropy of dielectric constant. The orientation of the liquid crystal is controlled by the curving of electric field caused between end portions of a pixel electrode and of an orientation control window. Accordingly, it is unnecessary to perform rubbing processing on orientation films to provide a pre-tilt angle.
3. Description of the Related Art
Liquid crystal located directly underneath an orientation control window is not subjected to any electric field and remains without being driven. The technique of placing a data line in such a region is proposed in Japanese Patent Application No. H10-337840 filed by the present applicant. An LCD having a data line overlapping an orientation window is described below. It is to be noted that this technique does not constitute the prior art of the present application.
FIG. 1
is a plan view showing a conventional LCD having a data line overlapping an orientation control window, and
FIG. 2
shows a cross-sectional view taken along line A—A of
FIG. 1. A
plurality of gate lines
51
made of metal such as chromium are formed extending along a row direction on a transparent insulator substrate
50
composed of materials such as glass or quartz. Over this layer, although not shown in
FIG. 2
, thin-film transistors (TFT)
53
are formed for each pixel, and an interlayer insulating film
52
is formed covering the TFT. Over the interlayer isolation film
52
, a plurality of data lines are formed extending in columns. A source region of a TFT
53
is connected to a data line
54
. A portion of a gate line
51
constitutes a gate electrode of a TFT. A pixel electrode
56
is formed over the TFT with a planarization film
55
disposed in between. A drain region of the TFT is connected to the pixel electrode via a contact hole. A vertical orientation control film
57
is formed further on top. Provided on a substrate arranged opposing the substrate
50
are color filters
61
each colored with a primary color for image display. The primary color may be one of the three colors of red (R), green (G), and blue (B), or alternatively, cyan, magenta, and yellow. The following explanation is made using the three colors of RGB. A protective film
62
is provided over the color filters
61
, and a common electrode
63
used commonly for all pixels and an orientation control film
64
are formed over the protective film
62
. Orientation control windows
65
where no electrode is present are formed in the common electrode
63
in regions opposing pixel electrodes
56
. Liquid crystal
70
is filled between these substrates
50
,
60
. The orientation of liquid crystal molecules is controlled in accordance with the strength of electric field generated by a voltage applied between pixel electrodes
56
and the common electrode
63
. In this way, the polarizing characteristic of the liquid crystal
70
is changed, controlling the transmittance of the light linearly polarized by the polarizers
41
,
42
.
The liquid crystal
70
has negative anisotropy of dielectric constant. That is, the liquid crystal has the property of orienting itself in a direction perpendicular to the direction of the electric field. The orientation control films
57
,
64
are vertical orientation control films which may be made of organic materials such as polyimide and polyamide or of inorganic silane materials. Liquid crystal molecules are controlled by the orientation control films such that their initial orientation when no voltage is applied is in the direction along the line normal to the substrates. When an electric field along the length of the Figure is generated by applying a voltage between a pixel electrode
56
and the common electrode
63
, the liquid crystal located between these electrodes are tilted in a direction perpendicular to the electric field, i.e., along the width of the Figure. At the end portions of the pixel electrode
56
and of the orientation control window
65
, the electric field becomes curved, and the direction in which the liquid crystal molecules are tilted is accordingly controlled towards the orientation control window
65
. No electric field is generated in a region directly underneath the orientation control window
65
because no voltage is applied. Liquid crystal molecules are therefore not tilted and remain without being driven in this region.
As shown in
FIG. 1
, the data line
54
is formed overlapping an orientation control window in each pixel. One data line
54
is connected to and overlapped on pixels of the same color. Specifically, a data line
54
g
driving green pixels overlaps green pixels indicated by G, a data line
54
r
driving red pixels overlaps red pixels indicated by R, and a data line
54
b
driving blue pixels overlaps blue pixels indicated by B.
The pixel electrodes
56
are arranged in a matrix, but the pixel electrodes in one column are shifted by half a pixel away from one, another in a row direction. In addition, pixels of the same color are not located adjacent to one another. This arrangement is the so-called delta arrangement. As a data line
54
drives pixels of the same color and overlaps those pixels of the same color in positions shifted by 1.5 pixels from one another, the data line is arranged meandering by an amplitude of 1.5 pixels.
FIG. 3
is a plan view of a liquid crystal display having orientation control windows
66
in the shape of two letter Y's connected at their bottoms. Pixel electrodes indicated by rectangles are disposed in a delta arrangement. Each TFT
53
which includes a gate constituted by a portion of a gate line
51
extending along a row direction is formed for each pixel. The TFT is connected to the pixel electrode
56
via a contact hole. As the cross-section along A—A is identical to the cross-section of FIG.
2
, the explanation will not be repeated.
The data line
54
is formed overlapping an orientation control window
65
in each pixel. One data line
54
is connected to and overlapped on pixels of the same color. Specifically, a data line
54
g
driving green pixels overlaps green pixels indicated by G, a data line
54
r
driving red pixels overlaps red pixels indicated by R, and a data line
54
b
driving blue pixels overlaps blue pixels indicated by B.
However, when a data line
54
is formed to overlap pixels that are shifted by 1.5 pixels as described above, the wiring of the data line
54
becomes long, possibly causing the following problems.
With the enlargement of an area in which the data line
54
and the common electrode
63
face one another, parasitic capacitance generated between the data line and the electrode becomes larger. Consequently, time required for applying a voltage to the data line
54
(referred to as the time constant) is increased. When the time constant is larger, it may not be possible to raise the voltage on the data line
54
within a predetermined time period. Accordingly, sufficient voltage may not be applied to the pixel electrodes
56
, resulting in degradation of display quality.
As data lines
54
are made of metal such as chromium, a region in which a data line
54
is formed does not let light pass through. When this region is enlarged, the aperture ratio is reduced, causing a decrease in display contrast and therefore degradation of display quality.
By having data lines
54
meandering by an amplitude of 1.5 pixels, regions are created where two data lines
54
overlap. Margins must therefore be reserved to accommodate widths of the data li
Hogan & Hartson L.L.P.
Qi Mike
Sanyo Electric Co,. Ltd.
Sikes William L.
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