Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1999-02-25
2001-12-18
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C257S072000
Reexamination Certificate
active
06331880
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD), and more particularly, to an LCD and its fabrication method with enhanced reliability.
2. Discussion of the Related Art
Generally, an LCD has a lower substrate having a thin film transistor (TFT) and a pixel electrode, an upper substrate having a color filter for displaying color and a common electrode, and a liquid crystal filled between the lower and upper substrates. Here, glass or crystalline is generally used as the material for the substrates.
A crystal substrate facilitates the use of a high temperature process, but is rarely used to fabricate a large-sized display. Also, a crystal substrate is too expensive.
A glass substrate, however, is relatively inexpensive, but cannot be used in a high temperature process, and has a reduced reliability from stress. That is, the stress on the glass substrate is different when depositing a chrome layer on the glass substrate as opposed to depositing an amorphous silicon layer on the glass substrate.
FIGS. 1A and 1B
illustrate a stress characteristics when chrome is generally deposited on a glass substrate.
FIGS. 2A and 2B
illustrate stress characteristics when amorphous silicon is generally deposited on the glass substrate.
Referring to
FIG. 1A
, when a chrome layer
2
is deposited on the glass substrate
1
, the substrate takes on a tensile stress. Thus, the glass substrate
1
is bent upward, as shown in FIG.
1
B.
Referring to
FIG. 2A
, when an amorphous silicon layer
3
is deposited on the glass substrate
1
, the glass substrate
1
is bent downward, as shown in FIG.
2
B.
Accordingly, when a data line is formed of chrome in the LCD, the glass substrate is bent by the tensile stress as shown in
FIG. 1B
, but tends to return to its original state. Hence, a weak portion in the data line may become open.
The conventional LCD is described below with reference to the attached drawings.
Generally, an upper substrate of the LCD includes an active display area where a TFT and pixel electrode are arranged, a gate line pad for applying a driving signal to a TFT gate electrode of the active display area, and a data line pad for applying a data signal to a TFT source electrode. The TFT and pixel electrode of the active display area is illustrated in FIG.
3
. In particular, the TFT is formed at the intersection of the gate line and data line, where the gate line is connected to a gate electrode, the data line is connected to a source electrode, and the drain electrode is formed to be connected to an ITO pixel electrode.
Here, for the active area of the TFT, the amorphous silicon layer is deposited between the gate electrode and source/drain electrode, and the active area is formed under the data line and is wider than the data line.
A method for forming the conventional LCD is described below with reference to
FIGS. 4A-4E
, which are cross-sectional views taken along the line I-I′ in FIG.
3
.
As illustrated in
FIG. 4A
, a metal such as aluminum (Al) is deposited on a glass substrate
1
, and then selectively etched to form a gate line including a gate electrode
4
. As illustrated in
FIG. 4B
, a gate insulating layer
6
(such as a silicon nitride layer), an amorphous silicon layer
7
, and a high concentration n-type amorphous silicon layer
8
are sequentially deposited on the overall surface of the glass substrate
1
including the gate line. As illustrated in
FIG. 4C
, the amorphous silicon layer
7
and high concentration n-type amorphous silicon layer
8
are selectively removed except on the active area and the data line region of TFT.
As illustrated in
FIG. 4D
, a chrome layer
9
is deposited on the overall surface of the substrate, and then selectively removed except on the high concentration n-type amorphous silicon layer
8
of the data line region and on both sides of the amorphous silicon layer
7
and high concentration n-type amorphous silicon layer
8
of the active area to form the data line and source/drain electrode of the TFT. The exposed center portion of the high concentration n-type amorphous silicon layer
8
is removed using the chrome layer of the source/drain electrode as a mask. Here, the data line and source electrode are integrally formed (not shown).
As illustrated in
FIG. 4E
, a passivation layer
10
is formed on the overall surface of the substrate having the chrome layer
9
. Then, the passivation layer on the chrome layer
9
of the drain electrode is selectively removed to form a contact hole. A transparent conductive layer is deposited on the overall surface and then selectively etched to remain only on the pixel area to form a transparent electrode
11
. The transparent electrode
11
of the pixel area is electrically connected to the chrome layer
9
of the drain electrode through the contact hole.
However, the conventional LCD has problems as follows.
As the chrome layer is deposited in a state where the amorphous silicon layer and high concentration n-type amorphous silicon layer are formed on the active area and data line area, (with the remaining portion removed) the glass substrate takes on a tensile stress and becomes bent. Moreover, because the glass substrate also has a tendency to return to its original (unbent) state, the data line becomes open. Therefore, the reliability of the LCD is decreased.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a liquid crystal display and method for forming the same that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
A feature of the invention is to provide an LCD and fabrication method for preventing the data line from becoming open.
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, the liquid crystal display includes a substrate; a gate line formed on the substrate, and having a gate electrode; a gate insulating layer formed on the overall surface of the substrate including the gate line; a data line formed on the gate insulating layer and having source/drain electrode; an intrinsic semiconductor layer and high concentration n-type semiconductor layer formed between the data line and gate insulating layer and wider than the width of the data line; a passivation layer formed on the overall surface of the substrate including the semiconductor layer, and having a contact hole on the drain electrode; and a pixel electrode formed on a pixel area and connected to the drain electrode.
In another aspect, the present invention provides a method for forming a liquid crystal display including the steps of forming a gate line having a gate electrode on a substrate; sequentially depositing a gate insulating layer, semiconductor layer and high concentration n-type semiconductor layer on the overall surface of the substrate including the gate line; forming a data line and source/drain electrode on the respective portions of the high concentration n-type semiconductor layer; selectively removing the high concentration n-type semiconductor layer and semiconductor layer to remain only under the data line and on the active area of a thin film transistor; and forming a passivation layer on the overall surface of the substrate where the data line and source/drain electrode are formed, forming a contact hole on the pad and the drain electrode, and then forming a transparent electrode on the pad and pixel.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide fur
LG Electronics Inc.
Morgan & Lewis & Bockius, LLP
Nguyen Dung
Sikes William L.
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