Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
2001-02-08
2003-02-18
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C349S126000
Reexamination Certificate
active
06521472
ABSTRACT:
This application claims the benefit of Korean Paten Application No. 2000-5836 filed on Feb. 8, 2000, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD), and more particularly to a method of fabricating a liquid crystal display device for eliminating a rubbing error.
2. Discussion of the Relate Art
An LCD device consumes a low power and weighs light. Due to such characteristics, it is well suited for use in word processors, personal computers, and navigational systems. The LCD conventionally includes an upper substrate having a transparent electrode, a lower substrate having a switching device and a pixel electrode, and a liquid crystal interposed between the upper and lower substrates. Various types of liquid crystals have been used in the LCD, such as a twisted nematic (TN) liquid crystal, a super twisted nematic (STN) liquid crystal, and a cholesteric liquid crystal.
FIG. 1
illustrates a cross-sectional view of a conventional LCD. As shown in
FIG. 1
, the conventional LCD
11
includes an upper substrate
5
having a color filter
7
, a black matrix
6
, and a common electrode
18
. The LCD also has a lower substrate
21
spaced apart from the upper substrate
5
. The lower substrate
21
has a pixel electrode
8
and a switching device (not shown) that are formed in a pixel area of the lower substrate
21
. Orientation films
23
are formed on the upper and lower substrates
5
and
21
. After the upper and lower substrates
5
and
21
are attached to each other using a sealant
35
, a liquid crystal
33
is injected between the upper and lower substrates
5
and
21
. Finally, upper and lower polarizers
25
and
27
are respectively formed on the outer surfaces of the upper and lower substrates
5
and
21
.
The LCD
11
controls incident light by absorbing or transmitting from backlight
31
. The control is based on an alignment of the molecules of the liquid crystal
33
, which has an optical anisotropy. By properly controlling the transmission of the light from the back light
31
, desired images can be displayed. Since the alignment of the molecules of the liquid crystal
33
affects an optical property of the LCD
11
, it is very important to accurately control the alignment of those molecules. The orientation films
23
are critical elements in controlling the alignment of the liquid crystal molecules.
Conventionally, orientation films
23
are rubbed to have a plurality of minute grooves on their surface. Using a rubbing fabric rolled onto a roller, the surface of the orientation film is rubbed in a uniform direction. After rubbing, the orientation film has a plurality of minute grooves on its surface and an alignment angle due to the grooves such that the liquid crystal molecules align according to the alignment angle. In this process, a smooth fabric is used for the rubbing fabric. A rubbing apparatus includes a roller and has a relatively simple configuration. In a rubbing process, it is important to apply an appropriate rubbing force in a uniform direction. Unless the rubbing is uniform, localized variations of optical properties occur.
As previously explained the orientation films
23
on the upped and lower substrates
5
and
21
provide conditions such that a uniform liquid crystal molecule alignment is achieved. A relative orientation of the liquid crystal molecules is often indicated by an angle formed between the longitudinal axes of the liquid crystal molecules and the substrates. The alignment stability of a liquid crystal is greatly affected by an anchoring force that is produced between the substrate and the liquid crystal molecules. The anchoring force is dependent upon the surface area of the liquid crystal molecules and the orientation film. In other words, the anchoring force serves to stabilize an alignment state of the liquid crystal molecules.
Orientation films
23
can be inorganic, organic, or both inorganic and organic. For example, an inorganic orientation film may be formed by a silicon oxide (SiO
2
) deposition method. In the SiO
2
deposition method, an inorganic material (such as a metal) or an oxide is deposited on the substrate such that a slope is formed between the inorganic material and the substrate. Silicon oxide (SiO
2
) is conventionally used for the inorganic material. The molecular alignment of a liquid crystal varies with the deposited material, the liquid crystal itself, and deposition conditions including a deposition angle, speed, a vacuum rate, a substrate temperature, and a film thickness.
To achieve a uniform alignment, the orientation film formed on the substrate is repeatedly rubbed in one direction using a diamond paste. Due to the minute grooves formed on the orientation film along the rubbing direction, a desired alignment of the liquid crystal molecules is achieved. In practice, a tilt angle of the rubbing process is almost 0 degree, resulting in the liquid crystal molecules to be homogeneously aligned. Physical properties of the liquid crystal
33
vary with the molecular alignment. The alignment nay vary by external forces, such as an electric field. A technology for controlling the molecular alignment of the liquid crystal molecules
33
is of interest in fabricating an LCD.
The process of fabricating the above-mentioned orientation film is explained with reference to FIG.
2
. As shown in
FIG. 2
, an orientation film
53
of polyimide or the like is formed on a substrate
51
. Thereafter, the surface of the orientation film
53
is rubbed using a rubbing fabric
57
wound around a roller
55
. The orientation film
53
has a plurality of minute grooves
53
a
. Since the rubbing fabric
57
has a plurality of woof and warp threads that are crossed with each other, a pattern of the minute grooves
53
a
are formed on the orientation film
53
during the above-mentioned rubbing process. However, when the rubbing process is repeated, defects may occur on the surface of the rubbing fabric
57
The defects of the rubbing fabric
57
result from either an extraneous matter on the orientation film
53
or patterns formed on the substrate
51
. These defects of the rubbing fabric
57
cause rubbing defects such as an irregular surface of the orientation film
53
(a scratch error) or a wave of the polyimide.
FIG. 3
is a photograph showing a surface of an orientation film where the above-mentioned scratch error occurs. As shown in the drawing, the surface of the orientation film is very irregular. The above-mentioned irregular surface of the orientation film negatively affects a first alignment state of the liquid crystal. Thus, uniformity in aligning the liquid crystal molecules decreases. Therefore, a display quality of the liquid crystal display is deteriorated.
In another aspect, many complicate processes were already proceeded for the substrate having a defective orientation film. Nevertheless, since the substrate having a defective orientation film should be disposed, it causes a lot of losses in the Fabrication process.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a method of fabricating a liquid crystal display for eliminating an rubbing error that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method of repairing a rubbing defect of a LCD device having orientation films.
Additional features and advantages of the invention will be set forth in the description, which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a method of rubbing for a liquid crystal display includ
LG.Philips LCD Co. , Ltd.
Lytle Craig P.
Morgan & Lewis & Bockius, LLP
Smith Matthew
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