Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2001-02-22
2004-06-22
Ngo, Julie-Huyen L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S139000, C345S093000
Reexamination Certificate
active
06753935
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a liquid crystal display (LCD) element and, in particular, to an LCD element with a defect repairing function. The invention also discloses a defect repairing method.
2. Related Art
With the merits of small volume and light weight, liquid crystal display (LCD) holds the edge in the market of portable display devices and smallspace application displays. Among all, the thin film transistor liquid crystal display (TFT-LCD) is the most favorable device. The device is using the field effect transistors to control the voltage applied to the liquid crystal film layer so as to control the orientation of liquid crystal molecules, thus adjusting the penetration of light through the liquid crystal layer. With the utilization of filters, a screen is able to display various colors and brightness.
FIG. 1A
shows a standard circuit layout of a thin film transistor liquid crystal display (TFT-LCD) panel. A series of parallel scan lines
10
and a series of parallel data lines
20
are orthogonal to each other and not connected. They connect to a control electrode
12
and a control electrode
22
, respectively, and separate the display panel into an array composed of pixels. Each pixel in the array has a field effect transistor (FET)
30
, a liquid crystal capacitor
40
and a storage capacitor
50
. Each FET has a gate, a drain and a source, wherein the gate connects to the corresponding scan line, and the drain connects to the corresponding data line. The liquid crystal capacitor
40
and the storage capacitor
50
are connected in parallel between the drain of the FET
30
and the ground.
In the conventional LCD elements, a detailed standard layout of each pixel is shown in FIG.
1
B. The conduction areas
32
,
34
,
36
are the gate, source, and drain of the FET
30
, respectively. The area
38
is the semiconductor channel of the transistor
30
. The FET drain
36
connects to a transparent electrode plate
45
, which functions simultaneously as the electrodes for the liquid crystal capacitor
40
and the storage capacitor
50
. The transparent electrode plate
45
is usually made of indium tin oxide (ITO). A storage electrode plate
52
is installed underneath the transparent electrode plate
45
with a dielectric layer inserted between (not shown) so as to form a storage capacitor
50
. The liquid crystal capacitor
40
is formed above the transparent electrode plate
45
.
With the technology development of displays heading toward high screen quality and large sizes, manufacturers have to use narrower line width and smaller pixel sizes to make longer signal transmission lines (including scan lines and data lines) on the large-scale panels. Under this situation, such problems as uneven line width distribution and broken lines are likely to happen. It is also likely to have short circuits because of holes between separated electrodes, e.g., between the upper and lower electrode plates of the storage capacitor
50
(the transparent electrode plate
45
and the storage electrode plate
52
), between the FET gate
32
and the source and drain
34
,
36
, or between channels
38
. Broken signal lines will result in line defects since an entire row of pixels cannot receive control signals. Short circuits of electrode plates will cause point defects as the pixels cannot react to the voltage. Both of them have bad influence on the quality and the production yield of the display panels.
FIG. 2A
shows a pixel array circuit for repairing line defects in the prior art. The basic circuit layout is the same as in
FIG. 1A
, except that the array border is surrounded with a spare line
80
over three sides. The spare line
80
is floating and striding over the data lines and scan lines, with a dielectric layer between. Its cross-sectional view is shown in FIG.
2
B. The conduction layer
210
on the substrate
200
representing the signal lines
10
on the lower layer, and the conduction layer
230
representing the spare line
80
on the upper layer are segregated by a dielectric layer
220
inserted between. When no defect is detected in the display panel, the spare line is maintained in the default configuration. However, when one of the data lines is detected to have a line defect, i.e., the data line is broken because of discontinuity, then the spare line overlapping on the defective data line is melted (usually using a high energy laser) so that the conductive material can pass through the dielectric isolation layer to form a contact window
240
with the conductive wire on the lower layer. When both ends of the defective data line are connected to the conduction layer
210
by melting, the spare line
80
can replace the broken data line and transmit control signals to transistors.
Nevertheless, this line defect repairing design still has its drawbacks. The spare line is so long and strides over so many data lines and scan lines that parasitic capacitance effect occurs during the control signal transmission. The signal received by the transistors will be decreased and seriously distorted, resulting in bad screen images. In addition, this surrounding spare line design cannot repair multiple defects, such as line defects indicated above. To further increase the product quality and manufacturing yield and to control production costs, it is crucial to develop a better defect repairing method.
SUMMARY OF THE INVENTION
In view of the foregoing bad defect repairing ability in conventional liquid crystal display (LCD) panel, it is an object of the invention to provide an LCD element with good defect repairing ability and the corresponding defect repairing method capable of repairing line defects and point defects due to broken circuits and short circuits, respectively.
To repair the line defects, the invention provides a circuit design of a single pixel having multiple scan lines and multiple data lines, with separate spare lines installed between. When a broken circuit occurs to any data line or scan line, the spare line is electrically welded to connect to the broken circuit, thereby forming the shortest connection path. This can minimize the signal attenuation due to long wiring and is suitable for multiple line defect repairs.
To repair point defects, the invention provides a circuit design of a single pixel having multiple subpixel electrodes, with spare conduction ports installed between. With the application of welding and connecting joints, the defective electrode can be readily separated once any subpixel has a defect. The spare conduction port for connection is melted for connection, and the resource of other subpixels will be used to support and compensate for the defective subpixel in an attempt to decrease the loss in screen image signals.
REFERENCES:
patent: 5298891 (1994-03-01), Plus et al.
patent: 5825438 (1998-10-01), Song et al.
patent: 6191832 (2001-02-01), Nakakura
patent: 2002/0024493 (2002-02-01), Ozawa et al.
Chi Mei Optoelectronics Corp.
Ngo Julie-Huyen L.
LandOfFree
Liquid crystal display element with a defect repairing function does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Liquid crystal display element with a defect repairing function, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid crystal display element with a defect repairing function will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3347659