Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-05-13
2001-01-09
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S196000, C349S039000
Reexamination Certificate
active
06172729
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device and more particularly, to a liquid crystal display device of a delta type pixel arrangement.
2. Description of the Prior Art
The liquid crystal display device is remarked as a thin and low power consuming display device replacing the conventional cathode ray tube. Particularly, the so-called active matrix type liquid crystal display device which employs as a driving element a non-linear element such as a TFT (Thin Film Transistor) and a MIM (Metal Insulator Metal) is specially remarked because of the beautiful display thereof.
In the liquid crystal display device, a stripe type and a delta type (or triangular type) are mainly employed as pixel arrangements. The pixel arrangements of the both types will be explained with reference to
FIGS. 9 and 10
.
FIG. 9
is a diagram showing the stripe type pixel arrangement and
FIG. 10
is a diagram showing the delta type pixel arrangement.
First, in the stripe type pixel arrangement as shown in
FIG. 9
, there is a configuration in which pixels
53
of R, G and B corresponding to colors of red, green and blue in color layers applied to the opposed substrate are arranged linearly in the horizontal and vertical directions. A set of three colors of R, G and B forms a dot
54
.
Next, in the delta type pixel arrangement as shown in
FIG. 10
, there is a configuration in which pixels
53
of R, G and B corresponding to red, green and blue on the opposed substrate are arranged linearly in the horizontal direction (row direction) in the figure the as same as those in the stripe type, but in the vertical direction (column direction) in the figure, pixels
53
are shifted by a half pitch. Therefore, dot
54
consisting of the set of three colors of R, G and B is arranged in the form of a nest for the row direction. Therefore, the delta type pixel arrangement enables to provide a beautiful display without a remarkable zigzag in inclined lines and curves and is employed widely for the use of displaying particularly a natural image and the like.
Further, in the liquid crystal display device, it is important to prepare a sufficient auxiliary capacitance for sustaining an electric field applied across the liquid crystal layer in order to realize a high contrast and beautiful display.
Auxiliary capacitance is classified into two types in accordance with circuit configurations. Referring to
FIGS. 3 and 4
which show equivalent circuits of one pixel, auxiliary capacitance
39
is formed between pixel electrode
13
and pre-stage scan line
12
in a case shown in
FIG. 3
(this is referred to as a gate storage type). Alternatively, auxiliary capacitance
39
is also formed between pixel electrode
13
and auxiliary capacitance electrode
15
connected electrically with the opposed electrode in another case shown in
FIG. 4
(this is referred to as a common storage type). The both cases have the following features. Auxiliary capacitance
39
is formed in parallel with liquid crystal capacitance
37
in any of the types.
FIGS. 5A and 5B
are a diagram for explaining a conventional gate storage type liquid crystal display device of the delta type arrangement.
FIG. 5A
is a diagram showing a plan view of a substrate, and
FIG. 5B
is a diagram showing a shape of an opening.
The operation of the liquid crystal display device will be explained with reference to
FIGS. 5A and 5B
. The present device obtains a display by turning on a TFT with a scan signal given to scan line
12
, that is, making conduction between drain electrode
14
a
and source electrode
14
b
of TFT
14
through channel
14
c
disposed between the both electrodes, at the moment charging up a liquid crystal capacitance between pixel electrode
13
and an opposed electrode (not depicted) and an auxiliary capacitance formed at a part between pixel electrode
13
and pre-scan line
12
with a display signal given to signal line
11
, and sustaining the charges after turning off TFT
14
.
Signal line
11
is bent at right angles in order to detour pixel electrode
13
, and a portion shown by detour
11
a
of the signal line is disposed in parallel with scan line
12
. Thus, a length of a region for forming the auxiliary capacitance, that is, an adjacent region
51
between pixel electrode
13
mR and pre-stage scan line
121
is extremely shortened relative to a transverse width of pixel
13
mR by affection of detour
11
a
of the signal line. Therefore, in order to form a sufficient auxiliary capacitance at auxiliary capacitance section
12
a
, it is necessary to extend scan line
121
toward scan line
12
m
in the next stage so as to invade an opening (transparent region).
Next, a conventional liquid crystal display device of the common storage type will be explained.
FIGS. 6A and 6B
are diagrams for explaining the conventional common storage type liquid crystal display device of the delta type arrangement.
FIG. 6A
is a diagram showing a plan view of a substrate, and
FIG. 6B
is a diagram showing a shape of an opening.
The operation of the liquid crystal display device will be explained with reference to
FIGS. 6A and 6B
. The mechanism of the operation is the same as that of the gate storage type liquid crystal display device, but the common storage type liquid crystal display device includes an auxiliary capacitance section
15
a
formed between pixel electrode
13
and auxiliary capacitance line
15
. Auxiliary capacitance line
15
is formed simultaneously with scan line
12
, and is connected electrically to the opposed substrate (not depicted). In the common storage type, there is no limitation to the region for forming the auxiliary capacitance by the bending of the signal line as practiced in the gate storage type.
However, auxiliary capacitance line
15
is formed on the same layer as that of the scan line. Therefore, in order to avoid a short circuit defect, it is desirable to extend a distance between scan line
11
and auxiliary capacitance line
15
as long as possible. From this reason, auxiliary capacitance line
15
n
is usually formed close to the medium portion between pre-stage scan line
12
m
and scan line
12
n
as shown in FIG.
6
A.
In the liquid crystal display device of which pixel arrangement forms the delta type, there are the following disadvantages with respect to each of the gate storage type and common storage type.
Namely, with respect the gate storage type, as shown in
FIG. 5A
, signal line
11
is bent at right angles in order to go round pixel electrode
13
, and the part shown by detour
11
a
of the signal line is arranged in parallel to scan line
12
. Therefore, in order to form a sufficient auxiliary capacitance at auxiliary capacitance section
12
a
, it is necessary to extend scan line
121
toward scan line
12
m
in the next stage so as to invade opening
52
(transparent region). As the result, there is a disadvantage that a pixel opening shape is extremely disturbed, whereby the beautiful display quality which is a feature of the delta type arrangement is deteriorated. The disturbance to the shape of opening
52
is remarkable particularly in a fine liquid crystal display device in which the width of the line is larger relatively to the size of pixel
53
and opening
52
is shortened as the result.
In addition, as signal line
11
is arranged to bend at right angles, a total wiring length increases relative to that in the case where signal line
11
is disposed linearly, and a wiring resistance increases. The increase of the wiring resistance causes a disadvantage to delay the display signal.
In the gate storage type, a part of the auxiliary capacitance is formed on the scan line which is originally an opaque section. To the contrary, in the common storage type, because the whole auxiliary capacitance is formed on the region which has original opening
52
, there is a disadvantage that the opening is extremely reduced. Further, in the common storage type, auxiliary capacitance line
15
is formed on the same layer as th
Foley & Lardner
NEC Corporation
Sikes William L.
Ton Toan
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