Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-12-11
2004-04-20
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06724458
ABSTRACT:
This application claims the benefit of the Korean Application No. P2001-083218 filed on Dec. 22, 2001, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a display device, and more particularly, to a liquid crystal display device and a method of fabricating the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for providing a uniform cell gap in the liquid crystal display device.
2. Discussion of the Related Art
Generally, a liquid crystal display device has characteristics, such as low-voltage driving, low power consumption, full-color implementation, thin and compact size, and the like. Thus, it has been widely used for calculators, notebook computers, electronic watches, PC monitors, aircraft gauges, personal mobile terminals, mobile phones, etc.
Screens of liquid crystal display devices get wider and larger in size. In fabricating wide-screen liquid crystal display devices, a related art method for forming a liquid crystal layer by using vacuum injection takes too much time. Hence, a liquid crystal dropping method of dispensing liquid crystal droplets on a substrate under a vacuum condition has been widely used to resolve the problems in the conventional fabrication process.
When the liquid crystal layer is formed by the liquid crystal dropping method, a fabricating time can be reduced. The liquid crystal dropping method uses a UV-ray hardening sealant for bonding upper and lower substrates to each other.
The UV-ray hardening sealant is provided by mixing acrylate resin with a photo-hardener, which becomes a radical when a UV-ray is irradiated thereto at a predetermined ratio. The photo-hardener reacts with the acrylate to form polymer having strong adhesion to the glass substrate.
A spacer is used to maintain a uniform cell gap when the substrates are bonded to each other. The spacer types include a ball spacer scattered on the substrate and a column spacer formed on the substrate. The ball spacer may alter the cell gap when applied to a wide area. For this reason, the column spacer is mainly used.
When bonding the two substrates to each other by using a UV-ray hardening sealant, portions of the substrates with the sealant formed thereon are strongly bonded to each other. On the other hand, adhesion of the array portions of the substrates is weaker than that of the portions with the sealant. Thus, a stress is generated between the substrates.
A liquid crystal display device and a method of fabricating the same according to a related art are explained by referring to the attached drawings as follows.
FIG. 1
illustrates a layout of a liquid crystal display device by using a related art liquid crystal dropping method.
As shown in
FIG. 1
, a thin film transistor (TFT) array is formed in a liquid crystal display panel region on a first substrate
100
. A silver (Ag) pattern for applying voltage to a terminal Vcom is formed on the periphery of the liquid crystal display panel region. Liquid crystal droplets are then dispensed onto the liquid crystal display panel region. The liquid crystal display panel region has an active area
120
and a dummy area
130
.
Meanwhile, a color filter pattern is formed in the liquid crystal display panel region on a second substrate
150
. Column spacers
105
are formed in the active area
120
to correspond to a wiring part excluding a pixel region
112
of the first substrate
100
. The column spacers
105
formed on the second substrate
150
are then attached to the second substrate
150
. After forming the column spacers
105
, a UV-ray hardening sealant pattern
110
is formed on the periphery of the liquid crystal display panel region on the second substrate
150
.
Subsequently, a liquid crystal display panel is prepared by bonding the first and second substrates
100
and
150
to each other. A UV-ray is then applied to the UV-ray hardening sealant
110
to harden the UV-ray hardening sealant
110
.
The column spacers
105
maintain a uniform cell gap in the active area
120
on the entire surface of the liquid crystal display device. Meanwhile, due to its strong adhesion, the UV-ray hardening sealant pattern
110
pulls the first and second substrates
100
and
150
. Therefore, a portion where the sealant pattern
110
is formed generates a stress greater than that in the active area
120
. Moreover, since the UV-ray hardening sealant pattern
110
pulls the first and second substrates
100
and
150
, the cell gap around the sealant pattern
110
may vary in accordance with the amount of the sealant pattern
110
.
FIGS. 2A
to
2
G illustrate layouts and cross-sectional views illustrating a process of fabricating a liquid crystal display device using a related art liquid crystal dropping method.
A plurality of liquid crystal display panel regions are arranged on parent substrates (i.e., first and second substrates). As shown in
FIG. 2A
, a plurality of silver (Ag) patterns
201
are formed on the periphery of each liquid crystal display panel region on a first substrate
200
.
Referring to
FIG. 2B
, column spacers
205
are formed in an active area of each liquid crystal display panel region on a second substrate
250
to correspond to a wiring part of the first substrate
200
.
Referring to
FIG. 2C
, a UV-ray hardening sealant pattern
210
is formed on the periphery of each liquid crystal display panel region on the second substrate
250
.
As shown in
FIG. 2D
, a predetermined amount of liquid crystal droplets
203
are dispensed on each liquid crystal display panel region of the first substrate
200
. The second substrate
250
is disposed over the first substrate
200
to face into a bonding machine. The first and second substrates
200
and
250
are then bonded to each other. More specifically, the second substrate
250
is fixed to an upper stage
270
of the bonding machine, allowing movement in the Z-axis direction (i.e., vertical direction). Meanwhile, the silver (Ag) patterns
201
are disposed on the periphery of the UV-ray hardening sealant
210
on the second substrate
250
. And, the first substrate
200
is fixed to a lower stage
260
of the bonding machine, allowing movement in the X and Y axes directions (i.e., horizontal direction).
Referring to
FIG. 2E
, the upper and lower stages
270
and
260
are aligned to each other, thereby achieving a vacuum condition within the bonding machine. Hence, the first and second substrates
200
and
250
are bonded to each other. After bonding the substrates
200
and
250
in the bonding machine under a vacuum condition, a first cell gap is formed, and then the bonded substrates
200
and
250
are exposed to the atmospheric pressure.
As shown in
FIG. 2F
, after the bonded substrates
200
and
250
having the first gap are exposed to the atmospheric pressure, a pressure difference between inside the liquid crystal display panel and the atmospheric pressure generates a second cell gap between the bonded substrates
200
and
250
. In this case, the dispensed liquid crystal droplets become a liquid crystal layer
203
a
having a uniform thickness.
Referring to
FIG. 2G
, the bonded substrates
200
and
250
are placed on a quartz stage
280
. A UV-ray is then irradiated to the bonded substrates on a lower side of the first substrate
200
in order to harden the UV-ray hardening sealant pattern
210
.
The liquid crystal display device and the method of fabricating the same have the following problems or disadvantages.
The UV-ray hardening sealant pulls the bonded substrates while being hardened, thereby generating a stress between the active area part and the sealant pattern part. Since, the UV-ray hardening sealant pulls the bonded substrates while being hardened, the cell gap around the sealant pattern is altered in accordance with the quantity of the sealant pattern.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a liquid crystal display device and a method of fabricating the same that substantially
Ha Young Hun
Kang Sung Chun
Kim Jong Woo
Dudek James A.
LG.Philips LCD Co. , Ltd.
Morgan & Lewis & Bockius, LLP
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