Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-04-14
2004-01-20
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S043000, C349S192000
Reexamination Certificate
active
06680770
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device and a repair process for the same, more specifically to a liquid crystal display device disconnection of the bus lines of which can be repaired and a repair process for the same.
Recently, active matrix-type liquid crystal display devices are widely used in OA machines and tools, typically personal computers, and are larger-sized and more fined for the purpose of their application to EWS (Engineering WorkStations), etc.
However, there is a tendency that the bus lines for driving the TFTs (Thin-Film Transistors) of the picture elements are made longer for larger sizes of the liquid crystal display devices, and for further fineness of the liquid crystal display devices the bus lines are made thinner. Accordingly, the bus lines have higher possibility of being disconnected in the process of fabricating the bus lines.
A conventional liquid crystal display device, and a conventional repair process for repairing disconnected bus lines of the liquid crystal device will be explained with reference to FIG.
27
.
FIG. 27
is a plan view of the conventional liquid crystal display device.
As shown in
FIG. 27
, gate bus lines
112
are formed on a glass substrate
110
, extended horizontally as viewed in the drawing, and data bus lines
120
are formed, crossing the gate bus lines
112
.
A plurality of TABs (Tape Automated Bondings)
116
a
,
116
b
are adhered to the left margin of the glass substrate
110
as viewed in the drawing. Gate drivers
114
a
,
114
b
are formed respectively on the gate TABs
116
a
,
116
b
. The respective gate lines
112
are connected to the outputs of the gate drivers
114
a
,
114
b
. The gate TABs
116
a
,
116
b
are adhered to a print substrate
118
.
On the other hand, a plurality of data TABs
124
a
to
124
c
are adhered to the lower margin of the glass substrate
110
as viewed in the drawing. Respective data drivers
122
a
to
122
c
are formed in the data TABs
124
a
to
124
c
. The respective data bus lines
120
are connected to the outputs of the data drivers
122
a
to
122
c
. The data TABs
124
a
to
124
c
are adhered to the print substrate
126
.
Repair lines
134
a
to
134
c
are formed, crossing the data bus lines
120
below a display region
130
of the liquid crystal display device. The repair lines
134
a
to
134
c
are associated respectively with the data TABs
124
a
to
124
c
and are connected to lines (not shown) of the print substrate
126
via the data TABs
124
a
to
124
c.
On the other hand, repair lines
132
a
to
132
c
are formed, crossing the data bus lines
120
upper of the display region
130
of the liquid crystal display device. The repair lines
132
a
to
132
c
are extended to the right as viewed in the drawing corresponding respectively to the repair lines
134
a
to
134
c
. The repair lines
132
a
to
132
c
are connected to lines (not shown) of a print substrate
118
via the gate TAB
116
a.
The repair line
132
a
is connected to the repair line
134
a
via the print substrate
118
, the connection cable
128
and the print substrate
126
. Similarly therewith, the repair line
132
b
is connected to the repair line
134
b
, and the repair line
132
c
is connected to the repair line
134
c.
In the liquid crystal display device having such structure, when the data bus line
120
is disconnected at a line disconnected part
121
, for example, the line disconnection has been repaired by the following process.
First, a laser beam is applied to a region where the data bus line
120
a
, which is upper of the line disconnected part
121
as viewed in the drawing, crosses the repair line
132
c
from the side of the glass substrate
110
to electrically connect the data bus line
120
a
to the repair line
132
c
. Thus, the data bus line
120
a
and the repair line
132
c
are connected to each other in a connection region
133
a.
Similarly therewith, the data bus line
120
b
, which is below the line disconnected part
121
as viewed in the drawing, and the repair line
134
c
are connected to each other, and the data bus line
120
b
and the repair line
134
c
are connected to each other in a connection region
133
b.
The data bus line
120
a
, which is upper of the line disconnected part
121
as viewed in the drawing, is brought into connection with the output of the data driver
122
c
because the repair line
132
c
and the repair line
134
c
are connected to each other in advance by the print substrate
118
, the connection cable
128
and the print substrate
126
, etc.
However, the above-described line disconnection repair is only for disconnection of the data bus lines
120
and cannot repair disconnection of the gate bus lines
112
.
That is, in the normal gate bus line
112
without disconnection a gate signal has a time constant which increases away from the output of the gate drivers
114
as shown in
FIG. 28A
, and has waveforms of blunter rises and falls.
In contrast to this, in the above-described case that the disconnection of the gate bus line
112
is repaired, the gate bus line
112
a
and the gate driver
114
are connected to each other by the repair line
135
in a remotest region from the gate driver
114
without the intermediary of capacitance components, etc. in the display region
130
. Accordingly, a signal waveform of the gate bus line
112
a
is adversely substantially the same as that of an output waveform of the gate driver
114
.
Furthermore, as a gate signal comes nearer the disconnected line part
113
from the remotest region from the gate driver
114
, the gate signal has a time constant increased and has waveforms of blunt rises and falls.
As a result, a signal waveform of the gate bus line
112
a
(see
FIG. 28B
) and a signal waveform (see
FIG. 28A
) of the normal gate bus line
112
adjacent to the gate bus line
112
a
are shifted with respect to each other. The shift between the signal waveforms of the gate bus line
112
and that of the gate bus line
112
a
causes the following potential shift between picture element electrodes. A mechanism for causing the potential shift between picture element electrodes adjacent to each other will be explained with reference to
FIG. 29A and 29B
.
As shown in
FIG. 29B
, when a gate signal Vg falls, a potential Vp of a picture element electrode
136
lowers by a potential difference &Dgr;Vs than a potential Vd of the data bus line
144
.
A potential difference AVs is expressed by
&Dgr;
Vs=C
gs
/(
C
gs
+C
s
+C
1c
)×(
Vg
on
−Vg
off
)
when a potential Vg
on
of the gate bus line
112
at the time that a gate signal is ON; a potential Vg
off
of the gate bus line
112
at the time that a gate signal is OFF; a capacitance C
gs
between the gate bus line
112
and the picture element electrode
136
; a capacitance between the picture element electrode
136
and a Cs bus line
115
is C
s
; and a capacitance between the picture element electrode
136
and an opposed electrode
117
is C
1c
.
Accordingly, when a potential Vg changes as indicated by the dot line in the gate bus line
112
a
having the disconnection repaired, and a potential Vg changes as indicated by the solid line in the normal gate bus line
112
adjacent to the gate bus line
112
a
, an effective value of Vg
on
−Vg
off
differs between the gate bus line
112
a
having the disconnection repaired and the normal gate bus line
112
adjacent thereto. When an effective value of Vg
on
−Vg
off
thus differs, a potential difference Vs differs, whereby the picture element electrode
136
connected to the gate bus line
112
a
having the disconnection repaired and the normal gate bus line
112
adjacent thereto have different potential Vp from each other. A potential Vp of the picture element electrode
136
influences luminance of display of the liquid crystal display device, with a result that a line defect is caused in display on the gate bus line
112
a
having the line disconnection repaired.
When a data bus line
120
has
Chowdhury Tarifur R.
Fujitsu Display Technologies Corporation
Greer Burns & Crain Ltd.
Qi Mike
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