Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-12-09
2002-08-27
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S138000
Reexamination Certificate
active
06441879
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an active matrix type liquid crystal display device incorporating switching elements, such as Thin Film Transistors (TFTs), and further relates to a manufacturing method of such a device.
BACKGROUND OF THE INVENTION
FIG.
5
(
a
) is a plan view showing a pixel region of an active matrix substrate incorporated in a conventional liquid crystal display device. As shown in FIG.
5
(
a
), the active matrix substrate has a plurality of pixel electrodes
54
provided in a matrix form. Gate wirings
51
and source wirings
52
are provided around the pixel electrodes
54
so as to orthogonally cross each other. A TFT
53
is provided in neighborhoods of crossing points of the gate and source wirings
51
and
52
as a switching element connected to the pixel electrode
54
through a contact hole.
FIG.
5
(
b
) is a cross-sectional view taken along line B—B of the active matrix substrate incorporated in the liquid crystal display device shown in FIG.
5
(
a
). As shown in FIG.
5
(
b
), a gate electrode
61
branching off from the gate wiring
51
shown in FIG.
5
(
a
) is provided on a transparent insulating substrate
60
. A gate insulating film
55
is provided to cover the gate electrode
61
. A semiconductor layer
64
is provided on the gate insulating film
55
above the gate electrode
61
. A channel protection layer
65
is provided on the center of the semiconductor layer
64
. Two n
+
layers
66
, respectively serving as a source area and a drain area, are provided so as to cover both ends of the semiconductor layer
64
and the channel protection layer
65
, and to be separated from each other on the channel protection layer
65
. The n
+
layers
66
are connected respectively to the source electrode
62
branching off from the source wiring
52
and the drain electrode
63
. An interlayer insulating film
59
is provided to cover the TFT
53
and the gate and source wirings
51
and
52
provided in this manner. The pixel electrode
54
is provided on the interlayer insulating film
59
. The pixel electrode
54
is connected to the drain electrode
63
of the TFT
53
through the contact hole in the interlayer insulating film
59
.
Finally, the manufacturing process of the conventional liquid crystal display device becomes complete with sealing liquid crystal
58
between a TFT substrate
70
configured in the above manner and an opposite substrate
71
equipped with an opposite electrode
56
. Here, spacers
57
are sandwiched between the TFT substrate
70
and the opposite substrate
71
to maintain a predetermined space therebetween (disclosed in Japanese Laid-Open Patent Application No. 61-156025/1986 Tokukaishou 61-156025).
Polyimide resin is used as the interlayer insulating film
59
in the conventional liquid crystal display device disclosed in the above laid-open patent application. However, other highly transparent materials, such as acrylic resin, polystyrene and polyester, are also generally used.
Although no disclosure is made about the spacers
57
, plastic beads and hard materials, such as glass, are usually used. The plastic bead spacer is generally made of polyimide, epoxy and polystyrene.
Nevertheless, if the above-mentioned acrylic resin is used as the interlayer insulating film
59
and the spacers
57
are made using epoxy resin, Newton rings are observed in a lighting test after injecting and sealing the liquid crystal (Newton rings are a series of circular bright and dark bands, which look like a wave pattern created on water surface by a stone dropping into the water). Especially the phenomenon frequently occurs in the sealing portion, and the rings were even more clearly observed with a liquid crystal display device incorporating an interlayer insulating film in an underlayer of the sealing portion. Consequently, such a liquid crystal display device has problems of a high defective ratio and low reliability.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a liquid crystal display device which does not cause Newton rings to occur and which has a low defective ratio and good reliability.
As a step toward achieving the above object, the inventors of the present invention conducted researches to pinpoint causes of Newton rings, and found out that if acrylic resin is used as an interlayer insulating film and epoxy resin is used as spacers as in a conventional liquid crystal display device, the spacers press a pixel electrode, sink into the interlayer insulating film, and thus change the space between a TFT substrate and an opposite substrate, thereby causing Newton rings to occur.
On the contrary, in order to achieve the above object, a liquid crystal display device in accordance with the present invention is configured in a preferred embodiment so that the spacers do not sink into the interlayer insulating film by optimizing materials of the interlayer insulating film and spacers. As a result, various problems with the liquid crystal display device using the resin-made interlayer insulating film are successfully solved.
Specifically, in a first preferred embodiment, the liquid crystal display device includes: a liquid crystal layer; a first substrate provided on one side of the liquid crystal layer; a second substrate provided on the other side of the liquid crystal layer; and a sealing member for sealing the liquid crystal layer between the first and second substrates. The liquid crystal layer has therein at least one first spacer for maintaining a thickness of the liquid crystal layer. The second substrate has: an interlayer insulating film of the same hardness with the first spacer or a greater hardness than the first spacer; a pixel electrode disposed on one side of the interlayer insulating film; at least one switching element disposed on the other side of the interlayer insulating film for controlling a display state of a pixel; and a base substrate facing the first substrate through the liquid crystal layer and the interlayer insulating film.
With the above configuration, the hardness of the interlayer insulating film is either the same as or greater than the hardness of the first spacer. Therefore, the first spacer can be prevented from sinking in the interlayer insulating film surface. Newton rings can be thus prevented from occurring, which improves reliability and defective ratio in manufacture of the liquid crystal display device. Moreover, even if pressure is applied by, for example, a user wiping the liquid crystal display device surface after the liquid crystal display device is manufactured, the space between the substrates are kept constant. The liquid crystal display device with high display quality is obtained for these reasons.
While the interlayer insulating film is formed to have a predetermined hardness in the above liquid crystal display device, an interlayer insulating film of a second preferred embodiment is made of elastic body. The second preferred embodiment is configured in the same manner as the first preferred embodiment, except that a different material is used for the interlayer insulating film. With this configuration, if pressure is applied to the display surface of the liquid crystal display device, the first spacer sinks in the interlayer insulating film surface and the space between the substrates changes temporarily. Nevertheless, as the pressure is removed, resilient power occurs and the space recovers to the predetermined space. Therefore, the space between the substrates of the liquid crystal display device are kept constant. The liquid crystal display device with good reliability, a low defective ratio and high display quality can be provided for these reasons in the same manner as in the first preferred embodiment.
In either of the liquid crystal display devices of the first and second preferred embodiments, the interlayer insulating film is preferably made of resin having a transmittance in the visible ray area of not less than 90%. With this configuration, especially if the interlayer insulating film is incorpora
Hiraishi Youichi
Shimada Takayuki
Tagusa Yasunobu
Nguyen Dung
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
Sikes William L.
LandOfFree
Liquid crystal display device 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 device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid crystal display device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2959099