Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-01-21
2001-01-30
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S073000, C349S158000
Reexamination Certificate
active
06181405
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a display device such as a liquid crystal display device, and more particularly to a display device allowing a large screen to be adopted by using a flat connected substrate composed of a plurality of small substrates connected to each other on the sides.
BACKGROUND OF THE INVENTION
Recently, a demand for a larger screen has been on the rise in a display device adopted in audio-visual (AV) equipment and office automation (OA) equipment, etc. In order to meet such a demand, the cathode ray tube (CRT) system, a liquid crystal display device (LCD), a plasma display device (PDP), an electroluminescence (EL) display device, and a light-emitting diode (LED) display device are under extensive research to realize an actual application of those devices.
Of those devices, the liquid crystal display device in particular has such an advantage in that (1) the thickness (depth) can be made significantly thinner compared with other display devices, (2) power consumption is low, and (3) a full-color image can be obtained with ease. For these reasons, the liquid crystal display device has been applied in a wide variety of fields, and is considered to be the best candidate for realizing a larger screen.
However, in the liquid crystal display device, when the screen is to be made larger, in the manufacturing process, the fraction defective induced by breakage of signal lines and a pixel failure is conspicuously increased. This presents a problem of a rise in cost.
The following will explain such a problem in detail using as an example an active-matrix-type liquid crystal display device which is most widely adopted. The active-matrix-type liquid crystal display device has an arrangement wherein liquid crystal is enclosed between a pair of substrates. One of the pair of substrates constitutes an active-matrix substrate on which a small active element such as a TFT (Thin Film Transistor) or an MIM (Metal-Insulator-Metal) is formed for each pixel. Thus, when the active matrix substrate is made larger, the active element and surrounding circuits become susceptible to breakage and failure. As a result, the fraction non-defective is conspicuously reduced.
As a method for solving this problem, a method for realizing a larger screen liquid crystal display device has been suggested in which a substrate is prepared by connecting to each other a plurality of small substrates on the sides, and the substrate thus prepared is faced with a large substrate sandwitching a liquid crystal layer therebetween.
For example, Japanese Publication for Unexamined Utility Model No. 191029/1985 (Jitsukaishou 60-191029) discloses a method for realizing a large screen liquid crystal display device in which, as shown in
FIG. 7
, (1) a large substrate
53
composed of small active matrix substrates (referred to as small substrates hereinafter)
53
a
provided in a 2×2 arrangement on which pixel electrodes
51
are formed in matrix, and (2) a large substrate (referred to as counter substrate hereinafter)
54
, on which counter electrodes (not shown) are formed, having a size substantially the same as the large substrate
53
are faced each other so as to be combined with a seal material
55
.
In this arrangement, as shown in
FIG. 8
, the small substrates
53
a
are connected to each other on the sides by a transparent bonding agent
56
so that the small substrates
53
a
thus connected to each other constitute the large substrate
53
, and between the large substrate
53
and the counter substrate
54
, a liquid crystal layer
57
is formed as liquid crystal is enclosed by the seal material
55
therebetween. Also, spacers
58
, which determine the thickness (cell gap) of the liquid crystal layer
57
, are spread over the region surrounded by the seal material
55
.
In the liquid crystal display device having the described arrangement, lowering of the fraction non-defective in response to a larger screen can be prevented, and therefore the productivity in the manufacturing process can be increased.
However, according to the method disclosed in Japanese Publication for Unexamined Utility Model No. 191029/1985 (Jitsukaihei 60-191029), as described above, in order to combine the counter substrate
54
and the large substrate
53
with each other, it is required beforehand to connect the small substrates
53
a
to each other on the sides so as to obtain the large substrate
53
. Generally, as the small substrates
53
a
, a glass substrate having a thickness of 0.7 mm or 1.1 mm is adopted. Thus, even when the small substrates
53
a
are connected to each other on the sides by the bonding agent
56
, because the bonding area is so small that the strength of the connecting portion connecting the small substrates
53
a
is extremely weak.
For example, in the case where two or four small substrates
53
a
each having an area of 300 mm×400 mm are connected, the small substrates
53
a
are connected to each other on the sides having a thickness of mere 0.7 mm or 1.1 mm. Thus, the strength of the connecting portion is extremely weak so that the connecting portion is destroyed by only a small amount of an external force. This presents a problem that the liquid crystal display device must be handled with great care not only in the manufacturing process but also as a product after the manufacturing process.
Further, on the large substrate
53
prepared by connecting to each other the small substrates
53
a
by the bonding agent
56
, only a 2 &mgr;m to 3 &mgr;m step-difference at the connecting portion on the side contacting with the liquid crystal layer
57
changes the cell gap at the connecting portion. The change in cell gap caused in this manner adversely affects the display image.
For example, when the thickness of the liquid crystal layer
57
is 5 &mgr;m, a step-difference of only 2 &mgr;m to 3 &mgr;m at the connecting portion makes the thickness of the liquid crystal layer
57
substantially in half. For this reason, a change in cell gap is significant at the connecting portion compared with other regions. This presents a problem of nonuniformity in displayed colors, and the display image being adversely affected.
In order to solve above-mentioned problems, Japanese Unexamined Patent publication No. 184849/1996 (Tokukaihei 8-184849) discloses a method for realizing a large screen liquid crystal display device wherein, as shown in FIG.
9
(
a
) and FIG.
9
(
b
), in a liquid crystal display device in which four small substrates
61
a
are connected to each other in a 2×2 arrangement so as to prepare a large substrate
61
, and in which the large substrate
61
thus prepared and a counter substrate
62
are combined with each other so as to enclose therebetween a liquid crystal layer
64
by a seal material
63
, a support base
66
is provided between the connecting portion of the small substrates
61
a
and a non-translucent patterning
65
formed on the counter substrate.
Specifically, in this method, as shown in FIG.
10
(
a
), the seal material
63
and the non-translucent patterning
65
are provided on a counter substrate
62
. Note that, the non-translucent patterning
65
is formed on a portion corresponding to the connecting portion of the small substrates
61
a
. On the non-translucent patterning
65
, the support base
66
made of the same material as that of the seal material
63
is provided. Also, on a region surrounded by the seal material
63
, gap materials
68
made of, for example, plastic beads are spread over. The gap materials
68
are also included in the seal material
63
and the support base
66
.
Then, as shown in FIG.
10
(
b
), the small substrates
61
a
are combined one by one with the counter substrate
62
, and as shown in FIG.
10
(
c
), the bonding agent
67
is injected into the connecting portion of the small substrates
61
a
so as to connect the small substrates
61
a
to each other, thereby obtaining a liquid crystal display device.
Thus, in the liquid crystal display device manufactured in this manner, the support base
Conlin David G.
Dike Bronstein, Roberts & Cushman LLP
Hartnell, III George W.
Sharp Kabushiki Kaisha
Sikes William L.
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