Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-02-12
2003-04-15
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S155000, C349S043000
Reexamination Certificate
active
06549259
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display panel and a fabrication method of the same, and more particularly to an active matrix type liquid crystal display panel having a sealing member mixed with spacers.
2. Description of the Prior Art
In the active matrix type liquid crystal display panel, liquid crystal is sandwiched between an array substrate and an opposing substrate. The array substrate is provided with pixel electrodes connected to switching element, respectively. The opposing substrate is provided with an opposing electrode. The liquid crystal is sealed within a display area of the panel by using a sealing member provided at peripheral area of the panel. display area
On the array substrate, a plurality of scan lines and a plurality of signal lines, which are crossing mutually, a plurality of pixel electrodes each provided in a different one of cross points of the scan lines and the signal lines, for applying voltages to the respective cross points and a plurality of switching elements such as TFT's (thin film transistors) for selectively driving the pixel electrodes are provided in matrices through patterning processes. Therefore, there may be some irregularity of an upper surface of the array substrate by the patterning processes.
On the other hand, liquid crystal filling the gap between the array substrate and the opposing substrate constitutes pixel capacitors each having the liquid crystal as a dielectric layer. The liquid crystal display is performed by controlling transmittivity of light correspondingly to electric field intensity of the pixel capacitor, to which a voltage selected by the switching element is applied, by utilizing electro-optical anisotropic property of the liquid crystal.
Therefore, the pixel capacity is varied with variation of thickness (cell gap) of the liquid crystal layer, so that intensity of display is varied. In order to obtain a uniform display quality throughout the display area, it is necessary to improve uniformity of the cell gap throughout the display area. Under the circumstance, various endeavors to uniform the cell gap have been continuing in the technical field to which the present invention belongs.
It has been usual, in order to uniform the cell gap, to use gap maintaining members (spacers) for maintaining the gap between the array substrate and the opposing substrate. As a method for providing the spacers between the array substrate and the opposing substrate, it is usual to arrange them in the liquid crystal in the display area and/or mix them in the seal provided around the display area.
In the case where the spacers are provided in the display area, the spacers may adversely affect the display characteristics. Therefore, this method is not preferable when high display quality is required. That is, in order to constitute a liquid crystal display panel having high display quality, it is effective to maintain the gap between the substrates by removing the spacers arranged in the display area or reducing the number of the spacers.
Furthermore, the variation of the cell gap, which is caused by the surface irregularity of the array substrate resulting from the patterning process, is improved by coating the patterned surface of the array substrate with a soft leveling layer.
FIG. 10
is a partial cross section of a conventional liquid crystal display panel
101
of the type in which a leveling layer is formed on an array substrate and gap retaining members (spacers) are provided in a seal in a mixed relation thereto.
The liquid crystal display panel
101
includes the array substrate
102
as shown in FIG.
10
. The array substrate
102
includes a transparent glass substrate
10
and a gate line
11
and a switching element
12
are formed on the transparent glass substrate
10
by patterning. An oxide layer
13
, a metal wiring layer
14
, the first interlayer insulating layer
15
, a light shielding layer
16
and the second interlayer insulating layer
18
are formed on the wafer in the order to constitute a laminated structure including predetermined lamination patterns on the transparent glass substrate
10
. A portion of the metal wiring layer
14
constitutes lead wiring lines
14
a.
As shown in
FIG. 10
, the patterned surface of the array substrate
102
, which is the surface of the second interlayer insulating layer
18
in the shown case, becomes irregular. Forming a leveling layer
19
thereon by using spin coating method flattens the patterned, irregular surface of the array substrate
102
. On an upper surface of the leveling layer
19
, a pixel electrode
20
of ITO (Indium Tin Oxide) is formed. That is, the pixel electrode
20
is an electrically conductive transparent thin layer discretely provided every pixel. The pixel electrode
20
is connected to the metal wiring layer
14
through a contact hole
21
so that the pixel electrode is connectable to the switching element
12
.
On the other hand, the liquid crystal display panel
101
includes an opposing substrate
3
as shown in FIG.
10
. The opposing substrate
3
is constituted with a transparent glass substrate
30
and at least an opposing electrode
31
formed thereon. It is usual that a light shielding layer and, in a case of a color liquid crystal display device, R, G and B color layers are additionally formed on the transparent glass substrate
30
.
After the array substrate
102
and the opposing substrate
3
are completed, respectively, the liquid crystal display panel
101
is assembled. First, a sealing agent
22
is printed on an outer peripheral portion of a display area of either the array substrate
102
or the opposing substrate
3
to seal liquid crystal
130
within a display area. The printing of the sealing agent is performed by the drawing printing in which it is drawn with a single stroke of a seal dispenser or the screen printing. Spacers
23
of a glass material are preliminarily mixed in the sealing agent
22
. The sealing agent
22
may be formed of ultraviolet ray setting resin or thermosetting resin.
After the sealing agent printing step, the substrates are stuck together. First, one of the substrates is laid on top of the other and the substrates are positioned such that corresponding cells of the substrates become in opposing relations, respectively. Thereafter, the substrates are pressed by pressing plates to exert pressure on the sealing agent
22
and the spacers
23
to thereby regulate the gap between the substrates to a predetermined value. During this pressing state, the seal agent
22
is hardened. In a case where a ultraviolet setting resin is used as the material of the sealing agent
22
, the pressing plates are formed of a material which is transparent for ultraviolet ray and the seal agent
22
is hardened by irradiating the sealing agent
22
with ultraviolet ray through the pressing plates. In a case where a thermosetting resin is used as the material of the sealing agent
22
, the seal agent
22
is hardened by heating the sealing agent
22
by a heater provided in the pressing plate or by disposing the liquid crystal display panel in an oven and heating air within the oven.
The liquid crystal display panel
101
which includes the array substrate
102
and the opposing substrate
3
piled on the array substrate and adhered to the array substrate
102
by the seal
4
, which contains the spacers
23
and is provided on the outer periphery of the display area A of either one of the array substrate
102
and the opposing substrate
3
, is constituted as shown in FIG.
10
. The seal
4
is formed of the sealing agent
22
and the spacers
23
mixed therein. The gap between the array substrate
102
and the opposing substrate
3
is maintained uniform owing to the spacers
23
. It should be noted that a seal area B is also shown in FIG.
10
. The seal area B indicates a common area of the substrates and a space of the gap therebetween, which is covered by the seal
4
provided on either one of the substrates.
There are problems in the ab
Sato Yuko
Sugimoto Mitsuhiro
Qi Mike
Sughrue & Mion, PLLC
Ton Toan
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