Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-01-11
2001-05-29
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S153000, C349S152000
Reexamination Certificate
active
06239854
ABSTRACT:
The present invention related to a structure of a liquid crystal display device integral with peripheral circuits in which an active matrix display circuit and peripheral driving circuits are provided on the same substrate.
More particularly, the present invention related to a configuration in which peripheral driving circuits are provided inside a region enclosed by a sealant for sealing a liquid crystal material.
There are configurations of liquid crystal display devices integral with peripheral circuits having an active matrix circuit and peripheral driving circuits provided on the same substrate in which peripheral driving circuits are provided inside a region enclosed by a sealant for sealing the liquid crystal material. A CPU, a memory, a control circuit and the like may be provided in addition to peripheral driving circuits.
In such a device, lines are provided under the region where the sealant is provided (hereinafter referred to as “sealant region”). For example, such lines include external connection lines for transmitting signals between the outside and inside of the sealant and short rings formed by extending scanning lines and signal lines and shorting them outside the sealant region in order to prevent electrostatic breakdown of TFTs (thin film transistors) forming an active matrix display circuit during manufacturing.
The lines provided under the sealant region results in different heights in the sealant. Such a height difference is primarily caused by two reasons.
One reason is that the lines under the sealant region are localized and are not present in some locations.
The other reason is that the line width and line intervals of the lines under the sealant region vary.
FIG. 13
shows an example of a liquid crystal display device integral with peripheral driving circuits. Referring to
FIG. 13
, a substrate
1501
and a counter substrate
1502
are disposed in a face-to-face relationship with a sealant
1505
having an injection hole
1510
interposed therebetween to form a panel. On the substrate
1501
, there is provided an active matrix display circuit
1503
, peripheral driving circuits such as shift registers and decoders for driving the circuit
1503
, and external connection lines
1508
for electrically connecting those circuits and circuits outside the sealant to transmit signals therebetween.
The external connection lines
1508
are connected to the external circuits through a FPC (flexible printed circuit).
There is further provided short rings
1509
which are formed by extending scanning lines and signal lines. The short rings
1509
are formed to short those lines with each other outside the sealant region to prevent electrostatic breakdown of TFTs (thin film transistors) forming the active matrix display circuit during manufacturing. The configuration of the short rings
1509
shown in
FIG. 13
is a configuration for multi-shot manufacture in which a plurality of panels are obtained from a single substrate. Although not shown in
FIG. 13
, the short rings are electrically connected to the short rings of an adjacent panel to short the scanning lines and signal lines, and the short rings are separated when the substrate is separated into independent panels, as shown in FIG.
13
.
FIG. 14A
shows sections of a region under the sealant
1505
where the external connection lines
1508
and a region with no line are provided. Referring to
FIG. 14A
, provided on the substrate
1501
are the following an underlying film
1511
such as a silicon oxide film, a first inter-layer film
1512
formed by a silicon oxide film, a silicon nitride film or a multi-layer film consisting of these films, external connection lines
1508
, and a resin inter-layer film
1513
made of resin such as polyimide or acrylic.
The external connection, lines
1508
are formed by a metal film, e.g., an aluminum film, in the range from about 200 nm to 700 nm. Although dependent on the application, the external connection lines
1508
are formed by a plurality of lines each having a width in the range from 50 &mgr;m to 300 &mgr;m provided as a group at intervals in the range from 30 &mgr;m to 100 &mgr;m.
In such a configuration, the resin inter-layer film
1513
has a thickness of about 1 &mgr;m and is provided to achieve flatness.
However, regions of the resin inter-layer film
1513
slaving the external connection lines
1508
are higher than regions having no lines by a height difference d. Such a step can be in the range from a few hundred nm to 500 nm, although it is smaller than the height (thickness) of the external connection lines
1508
.
FIG. 14B
shows a sectional view of a region under the sealant
1505
where the short rings
1509
are provided in the same layer and having the same material as those of the external connection lines
1508
.
Therefore, the thickness (height) of the short rings
1509
is the same as that of the external connection lines
1508
. The short rings are extensions of signal lines and scanning lines. They are a plurality of lines each having a width in the range from 2 &mgr;m to 10 &mgr;m provided as a group at intervals in the range from 20 &mgr;m to 100 &mgr;m.
There is a height difference d2 between the region where the short rings
1509
are provided and the region where the external connection lines
1508
are provided. This height difference can also be in an approximate range from a few hundred nm to 500 nm. The height difference is especially increased when a plurality of the resin inter-layer films are formed. A step on the order of 1000 nm may be formed when the films are stacked to a thickness on the order of 2 &mgr;m.
A step can also be formed on the resin inter-layer film between the region having the short rings
1509
and the region having no lines.
The substrate having the active matrix display circuit provided thereon and the counter circuit are provided in a face-to-face relationship with a sealant including spacers (spherical or cylindrical microscopic particles for maintaining an interval between the substrates) interposed therebetween. Therefore, any uneven height difference in, the sealant region where the sealant is provided causes distortion such as flexing and twisting of the counter substrate to making the substrate interval uneven. As a result, a uniform state of display can not be achieved in a single screen, and there will be unevenness in color and brightness.
The problem of the distortion of the substrate does not occur, even in the presence of a height difference under the sealant, if the height difference is uniformly distributed under the sealant region. However, since the lines extending across the sealant region are provided as a group of lines which are locally concentrated, in general, such a height difference is not uniformly distributed under the sealant region. This results in distortion of the substrate as described above.
The allowance (the range in which no uneven display occurs.) for the height difference under the sealant region is on the order of only 1000 nm for a TN (twisted nematic) type liquid crystal display. For an ECB (electrically controlled multi-reflectivity) mode utilizing nematic liquid crystal, a height difference of only 200 nm causes distortion of the substrate and leads to uneven display and color variation. For example, a height difference of 200 nm between the external connection lines and the short rings makes the substrate interval in the vicinity of the short rings smaller than that in the vicinity of the external connection, lines, thereby causing distortion of the substrate and uneven display. Therefore, it is quite important for a liquid crystal display device to have a small height difference under the sealant region in order to provide uniform display in one screen.
It is an object of the present invention too reduce the height difference under a sealant region where wiring is provided under the sealant region (sealant).
It is an especial object of the present invention to reduce the height difference under a sealant region in a configuration wherein wiring is provided un
Hirakata Yoshiharu
Yamazaki Shunpei
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
Qi Mike
Semiconductor Energy Laboratory Co,. Ltd.
Sikes William L.
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