Liquid crystal cells – elements and systems – Nominal manufacturing methods or post manufacturing... – Defect correction or compensation
Reexamination Certificate
2001-02-12
2004-04-06
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Nominal manufacturing methods or post manufacturing...
Defect correction or compensation
Reexamination Certificate
active
06717648
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a defect correcting method for a liquid crystal panel, which is designed to correct a defect occurring in a manufacturing process of a liquid crystal panel.
2. Description of the Prior Art
Nowadays, the use of a liquid crystal panel is not limited to a display of a portable computer, but has become widespread to various electronic devices including the display of a desktop computer, a television set, the display of a portable terminal, and so on.
A typical Twisted Nematic (TN) liquid crystal panel has a structure where liquid crystal is sealed in between two transparent substrates. On one of the two opposing surfaces of the transparent substrates, a common electrode, color filters, an alignment film and the like are formed. On the other surface, Thin Film Transistors (TFTs), pixel electrodes, an alignment film and the like are formed. Also, polarizing plates are respectively stuck to surfaces opposite the opposing surfaces of the transparent substrates. These two polarizing plates are disposed, for example, so that polarization axes thereof can intersect perpendicularly to each other. When no voltages are applied between the pixel electrode and the common electrode, a light is transmitted to make displaying bright. When a voltage is applied therebetween, a light is shielded to make the displaying dark. When the polarization axes of the two polarizing plates are disposed in parallel to each other, the displaying becomes dark with no voltages applied between the pixel electrode and the common electrode. The displaying becomes bright with a voltage applied therebetween. Hereinafter, the substrate having TFTs and pixel electrodes formed thereon will be referred to as a TFT substrate; and the substrate having color filters and a common electrode formed thereon as a CF substrate.
FIG. 1
is a sectional view showing the structure of a typical TN liquid crystal panel; and
FIG. 2
a plan view showing the TFT substrate of the same.
FIG. 1
specifically shows a section taken on line I—I of FIG.
2
.
The TN liquid crystal panel comprises: a TFT substrate
10
; a CF substrate
20
; and liquid crystal
29
sealed in between these TFT and CF substrates
10
and
20
.
The TFT substrate
10
is formed in the following process. That is, on a glass substrate
11
, a plurality of gate bus lines
12
a
and a plurality of auxiliary capacitor bus lines
12
b
are formed to constitute a first wiring layer. Each gate bus line
12
a
is formed in parallel to another. Between the gate bus lines
12
a
, an auxiliary capacitor bus line
12
b
is disposed in parallel thereto.
A first insulating film (gate insulating film, not shown) is formed on these gate and auxiliary capacitor bus lines
12
a
and
12
b
. On the first insulating film on the gate bus line
12
a
, an amorphous silicon film
13
is formed to become a channel of a TFT
15
. To constitute a second wiring layer on the first insulating film, a data bus line
14
a
, and source and drain electrodes
14
b
and
14
c
of the TFT
15
are formed. The data bus line
14
a
is formed to perpendicularly intersect the gate bus line
12
a
, and the source and drain electrodes
14
b
and
14
c
are formed to be separated from each other in both sides of the width direction of the amorphous silicon film
13
. The drain electrode
14
c
is connected to the data bus line
14
a
. A rectangular region partitioned by the gate bus lines
12
a
and the data bus lines
14
a
is a pixel region.
A second insulating film
16
is formed on the data bus line
14
a
and the source and drain electrodes
14
b
and
14
c
. On the second insulating film
16
, a transparent pixel electrode
17
made of Indium-Tin Oxide (ITO) is formed. This pixel electrode
17
is electrically connected to the source electrode
14
b
through a contact hole
16
a
formed in the second insulating film
16
.
On the pixel electrode
17
, an alignment film
18
is formed to decide the alignment of liquid crystal molecules. This alignment film
18
made of, e.g., polyimide, has been subjected to alignment treatment by rubbing or the like.
On the other hand, the CF substrate
20
is formed in the following process. That is, on one surface (lower surface in the drawing) of the glass substrate
21
, a black matrix
22
made of a light shielding material such as chromium (Cr) is formed to shield a region between pixels and TFTs forming region from lights. In a position opposite to each pixel electrode
17
of the TFT substrate
10
, a color filter
23
of one selected from red (R), green (G) and blue (B) is formed. In the described example, color filters
23
of green (G), blue (B) and red (R) are alternately disposed in pixels arrayed in a lateral direction, while color filters of identical colors are disposed in pixels arrayed in a longitudinal direction.
Under the color filters
23
, a common electrode
24
made of ITO is formed, and there is an alignment film
25
made of, e.g., polyimide, under this common electrode
24
. This alignment film
25
has also been subjected to alignment treatment by rubbing or the like.
Between the TFT substrate
10
and the CF substrate
20
, for example spherical or columnar spacers (not shown) uniform in diameter are disposed such that a spacing between these substrates can be kept constant. In addition, polarizing plates (not shown) are respectively disposed on the lower side of the TFT substrate
10
and on the upper side of the CF substrate
20
.
In the liquid crystal panel constructed in the foregoing manner, a desired image can be displayed by supplying scanning and video signals from a driving circuit to the gate and data bus lines
12
a
and
14
a
at a predetermined timing, and by controlling a voltage between the pixel electrode
17
and the common electrode
24
for each pixel.
In the manufacturing process of a liquid crystal panel, patterning may not be executed correctly because of the sticking of dust or the like, causing short-circuiting or disconnection. Consequently, a pixel may be placed in a constantly lit or unlit state. Usually, in the liquid crystal panel, the presence of dot defects amounting to a predetermined number or smaller is permitted. But when the number is too large, the liquid crystal panel becomes a defective product. In addition, when a plurality of pixel electrodes are connected together, a so-called killer defect occurs, making the liquid crystal panel defective alone.
As regards a method for correcting a dot defect, the prior art has presented a method for welding and joining the electrode of a defective pixel to the gate bus line, the auxiliary capacitor bus line or the data bus line by laser irradiation. When the electrode of the defective pixel is connected to the gate bus line or the auxiliary capacitor bus line, the defective pixel is constantly unlit. Consequently, for example, for white displaying or half-tone displaying, the defective pixel becomes a dark spot to be conspicuous. When the electrode of the defective pixel and the data bus line are connected to each other, any defects cannot be recognized if the same color is displayed on the full surface of a screen. However, when displaying is carried out with the upper half of the screen set white and the lower half thereof set black, if there is a defective pixel in the black portion, it becomes a bright luminescent spot, making a defect conspicuous.
As another method for correcting a dot defect, the prior art has presented a method for disturbing the alignment of liquid crystal molecules by irradiating the entire region of the defective pixel with a laser beam. In this case, a pixel, of which alignment has been disturbed by laser irradiation, is fixed to be black. Thus, as in the case of the connection of the defective pixel electrode to the gate bus line or the auxiliary capacitor bus line, a drawback is inherent, that is, the defective pixel becomes a dark spot in white displaying or half-tone displaying to be conspicuous.
SUMMARY OF THE INVENTION
It is an object of the present
Chowdhury Tarifur R.
Fujitsu Display Technologies Corporation
Greer Burns & Crain Ltd.
Kim Richard
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