Liquid crystal cells – elements and systems – Nominal manufacturing methods or post manufacturing...
Reexamination Certificate
2001-10-04
2004-01-13
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Nominal manufacturing methods or post manufacturing...
C349S128000, C349S134000, C349S136000
Reexamination Certificate
active
06678035
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a liquid crystal display and, more particularly, to a twisted nematic (TN) mode liquid crystal display.
(b) Description of the Related Art
Generally, a liquid crystal display has a structure where a liquid crystal layer is sandwiched between two substrates, and an electric field is applied to the liquid crystal to control light transmission. Of the two substrates, the bottom substrate is provided with thin film transistors and pixel electrode, and the top substrate with a common electrode and color filters.
The twisted nematic (TN) mode has been mainly employed for use in a large size and high definition liquid crystal display because it has the advantages of structural stability and simplified processing steps. In the TN mode liquid crystal displays, the substrates are rubbed for alignment such that the directors of the liquid crystal molecules at the top substrate are perpendicular to those of the liquid crystal molecules at the bottom substrate.
In order to enhance the viewing angle, a multi-domain technique has been developed for the TN mode liquid crystal displays. In the multi-domain liquid crystal display, a number of differently-structured liquid crystal domains are present at one pixel area. Assuming that a group of liquid crystal molecules with the same direction of twisting is referred to as the “domain,” the multi-domain liquid crystal display bears multiple groups of liquid crystal molecules at one pixel area.
FIG. 1
illustrates a sectional structure of a two-domain twisted nematic (TDTN) liquid crystal display at one pixel area according to a prior art.
As shown in
FIG. 1
, the liquid crystal panel
210
includes a bottom substrate
201
, a top substrate
202
, and a liquid crystal layer
209
sandwiched between the bottom and the top substrates
201
and
202
. A first liquid crystal domain A where the liquid crystal molecules are twisted in a first direction
1
is placed at the left side L of the pixel. A second liquid crystal domain B where the liquid crystal molecules are twisted in a second direction
2
is placed at the right side R of the pixel.
The two liquid crystal domains A and B may be formed through differentiating the pretilt angles of the liquid crystal molecules at the bottom substrate
201
or the top substrate
202
.
For instance, the liquid crystal molecules placed at a predetermined region of the bottom substrate are established to have a large pretilt angle, whereas those at the corresponding region of the top substrate to have a small pretilt angle. Furthermore, the liquid crystal molecules placed at another region of the bottom substrate are established to have a small pretilt angle, whereas those at the corresponding region of the top substrate to have a high pretilt angle. Even though the liquid crystal molecules placed close to the substrates are oriented depending upon the respective pretilt angles due to the condition of the substrate, the liquid crystal molecules within the liquid crystal layer are oriented pursuant to the higher pretilt angle, resulting in two or more liquid crystal domains.
In the drawing, the respective liquid crystal domains A and B bear different pretilt angles with respect to the bottom and the top substrates
201
and
202
. For instance, the liquid crystal molecules at the first liquid crystal domain A are tilted against the bottom substrate
201
at an angle of about 6-7°, while being tilted against the top substrate
202
at an angle of about 0-1°. By contrast, the liquid crystal molecules at the second liquid crystal domain B are tilted against the bottom substrate
201
at an angle of about 0-1°, while being tilted against the top substrate
202
at an angle of about 6-7°. The inclined lines at the bottom and the top substrates
201
and
202
indicate the pretilt angles of the liquid crystal molecules.
The pretilt angles of the liquid crystal molecules are determined depending upon the surface roughness of alignment films (not shown). The surface roughness of the alignment film varies depending upon the rubbing conditions, the amount of light exposure, and the surface roughness of the ITO-based layer. Conventionally, the ITO-based pixel electrode of the bottom substrate
201
and the ITO-based common electrode of the top substrate
202
have various surface roughness, thereby controlling the pretilt angles of the liquid crystal molecules close to the respective substrates. When the surface roughness of the pixel electrode is high, the pretilt angle of the liquid crystal molecules is reduced, whereas when the surface roughness of the pixel electrode is low, the pretilt angle of the liquid crystal molecules increases. Therefore, the pretilt angles of the liquid crystal molecules can be controlled based on the surface roughness of the pixel electrode.
In order to form such a pixel electrode, after the deposition of the pixel electrode layer, a photoresist pattern is formed on the pixel electrode layer while exposing the portion to be surface-treated, and the exposed portion of the pixel electrode layer is wet-etched using the photoresist pattern as a mask.
However, in the above technique, a separate mask should be provided to make surface treatment in addition to form the pixel electrode layer. This complicates the processing steps and lowers production efficiency.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for fabricating a multi-domain liquid crystal display bearing wide viewing angle characteristics without using an additional mask.
This and other objects may be achieved by a method for fabricating a liquid crystal display where a pixel electrode with different surface roughness is formed at each pixel area using one mask.
According to one aspect of the present invention, in a method of fabricating a liquid crystal display, a pixel electrode is formed on a bottom substrate at each pixel area using a first mask such that the pixel electrode has a first region with a smooth surface, and a second region with a rough surface, the bottom substrate having a gate wire, a data wire and a thin film transistor. And, a common electrode is formed on a top substrate using a second mask such that the common electrode has a first region with a smooth surface, and a second region with a rough surface, the top substrate having color filters; and the bottom substrate having the pixel electrode. And the top substrate is assembled with the bottom substrate, and liquid crystal is injected between the bottom substrate and the top substrate.
In order to form the bottom substrate, a gate wire is formed on a first insulating substrate. The gate wire includes gate line, and gate electrode. A gate insulating layer is formed on the substrate such that the gate insulating layer covers the gate wire. A semiconductor pattern and a data wire are formed on the gate insulating layer. The data wire includes data line, source electrode connected to the data line while being connected to the semiconductor pattern, and drain electrode facing the source electrode while being connected to the semiconductor pattern. A protective layer is formed on the substrate such that the protective layer covers the data wire. First contact holes are formed at the protective layer such that the first contact holes expose the drain electrode.
The first mask has a first region transmitting light with a first light transmissivity, and a second region transmitting the light with a second light transmissivity lower than the first transmissivity. The first and the second regions of the first mask define the shape of the pixel electrode. The first region has a semitransparent pattern, and the second region has an opaque pattern. Each of the first region and the second region consists of a plurality of sub-regions, and the sub-regions of the first region and the second region are alternately arranged.
In order to form the pixel electrode, a transparent conductive layer is deposited over the bottom substrate. A photoresist film is coat
Lee Jeong-Ho
Lee Jeong-Young
Park Young-Bae
Akkapeddi P. R.
Kim Robert H.
McGuireWoods LLP
Samsung Electronics Co,. Ltd.
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