Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2002-12-11
2004-06-29
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
Reexamination Certificate
active
06757033
ABSTRACT:
This application claims the benefit of the Korean Application No. P2001-86764 filed in Korea on Dec. 28, 2001, which is hereby incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a method of manufacturing the same having a storage-on-gate system.
2. Discussion of the Related Art
As an information society develops, so does the demand for various types of displays. Recently, efforts have been made to research and develop various types of flat display panels, such as Liquid Crystal Display (LCD), Plasma Display Panel (PDP), Electroluminescent Display (ELD), Vacuum Fluorescent Display (VFD), and the like. An LCD is widely used as a substitution for a Cathode Ray Tube (CRT) because of the characteristics or advantages of a high quality image, light weight, shallow depth, compact size, and low power consumption. An LCD is applicable to devices that receive display signals, such as a television, computer monitor, and the like. Various technical developments for different types of LCD have been made such that LCDs play a role as an image display in various fields. However, in order for an LCD to be used as a general display device for a variety of various fields, the LCD needs to realize a high quality image with high resolution, a high brightness, a wide screen and the like, as well as, maintain the characteristics of light weight, shallow depth, compact size, and low power consumption
In general, a liquid crystal display includes two substrates in which electrodes on one substrate confront an electrode on the other substrate. A liquid crystal is injected between the confronting electrodes of the substrates. If a voltage is applied across the confronting electrodes, which generate an electric field, liquid crystals molecules are driven in accordance with the electric field and thus light transmittance through the substrates is varied. There are various types of liquid crystal displays. In particular, an Active Matrix Liquid Crystal Display (AM-LCD) contains thin film transistors that are respectively connected to pixel electrodes. The pixel electrodes, which are on one substrate, are arranged in a matrix and confront a common electrode, which is on the other substrate. The pixel electrodes and common electrode drive liquid crystal molecules by applying an electric field between the substrates in a direction vertical to the substrates. The AM-LCD provides excellent resolution for displaying moving images.
A liquid crystal display according to the related art is explained by referring to the attached drawings of FIG.
1
and FIG.
2
. As shown in
FIG. 1
, a plurality of gate lines
11
is formed in one direction on a lower array substrate
10
of a liquid crystal display. A gate
12
protrudes from one side of each of the gate lines
11
. A plurality of data lines
14
is formed perpendicularly to the gate lines
11
that cross over the gate lines
11
. Pixel areas are defined between pairs of data lines and gate lines adjacent to where they cross over each other. Source electrodes
15
protrude from one side of each of the data lines
14
. A drain electrode
16
is separated from the source electrode
15
by a predetermined interval. The drain electrode connects to a pixel electrode
18
through a contact hole
17
a
. Moreover, the source electrode
15
, drain electrode
16
, and gate electrode
12
are parts of a thin film transistor T.
FIG. 2
is a cross-sectional view along line II-II′ in
FIG. 1
showing that the thin film transistor includes an active layer
13
′ of amorphous silicon over the gate electrode
12
. A gate insulator
22
insulates amorphous silicon layer
13
from the gate electrode
12
. The source electrode
15
and drain electrode
16
respectively overlap separate sides of the gate electrode
12
. The amorphous silicon layer
13
includes a pair of ohmic contact layers
13
″ that respectively connect the source electrode
15
and drain electrode
16
to the active layer
13
′.
An upper electrode
19
a
, as shown in
FIG. 1
, is formed for a storage capacitor Cst that maintains a pixel voltage on the pixel electrode
18
. The upper electrode
19
a
of the storage capacitor Cst is formed of an opaque metal layer having a predetermined pattern. The lower electrode of the storage capacitor Cst is the gate line
11
b
for an adjacent cell, as shown in FIG.
1
. The upper electrode
19
a
is formed to overlap the gate line
11
b
when the data line
14
and/or source electrode
15
is formed. The upper electrode
19
a
is insulated from the gate line
11
b
by the gate insulator
22
. Hence, the gate line
11
b
, upper electrode
19
a
and gate insulating layer
22
construct the storage capacitor Cst of a storage-on-gate system.
A passivation layer
24
is formed to cover the source electrode
15
, drain electrode
16
, the first semiconductor layer
13
and the upper electrode
19
a
. The passivation layer
24
can be formed of silicon oxide, silicon nitride or other types of insulating materials. A pixel electrode
18
made of a transparent conductive material, such as indium-tin-oxide, is formed in each of the pixel areas on the passivation layer
24
such that it overlaps the upper electrode
19
a
and the drain electrode
16
in part. A contact hole
17
a
is formed in the passivation layer
24
at a portion where the pixel electrode
18
and drain electrode
16
overlap each other. In addition, another contact hole
17
b
is formed in the passivation
24
to expose a predetermined portion of the upper electrode
19
a
, as shown in FIG.
2
. The pixel electrode
18
connects to the drain electrode
16
and upper electrode
19
a
through the contact holes
17
a
and
17
b
, respectively.
The cross-sectional view shown in
FIG. 2
illustrates a storage-on gate part A and a thin film transistor part B of a cell for explaining the method of making the related art device. Referring to
FIG. 2
, a gate line
11
b
of an adjacent cell is formed on a lower array substrate
10
in the storage-on-gate part A. A gate line
11
a
of the cell is formed on the lower substrate
10
in the thin film transistor part B. A gate electrode
12
extending from the gate line
11
a
of the cell is formed in the thin film transistor part B. A gate insulating layer
22
is formed on the gate lines
11
a
and
11
b
and over entire surface of both the storage-on-gate part A and thin film transistor part B. A semiconductor layer
13
is formed in a thin film transistor forming area on the gate insulating layer
22
of the thin film transistor part B. The first semiconductor layer
13
includes, for example, an active layer
13
′ of amorphous silicon and a pair of ohmic contact layers
13
″ of doped amorphous silicon on the active layer
13
′. The doped semiconductor layers or ohmic contact layers
13
″ are for ohmic contact and over-etch prevention. A source electrode
15
and a drain electrode
16
are formed to respectively overlap and connect to an ohmic contact layer
13
″. In this case, the source electrode
15
is an electrode extending from the data line
14
. In addition, an upper electrode
19
a
that overlaps an adjacent gate line
11
b
is formed in the storage electrode part A simultaneously when the source and drain electrodes
15
and
16
are formed. A passivation layer
24
is formed over the upper electrode
19
a
, source electrodes
15
, drain electrodes
16
and the semiconductor layer
13
. Contact holes
17
a
and
17
b
exposing predetermined portions of the drain electrode
16
and opaque metal layer
19
a
respectively are formed in the passivation layer
24
. A pixel electrode
18
made of a transparent material is formed on the passivation layer
24
and connected to the drain electrode
16
and upper electrode
19
a
through contact holes
17
a
and
17
b
, respectively.
However, the fabrication of the above-constituted liquid crystal dis
Cho Young Woo
Song In Duk
Dudek James A.
LG. Philips LCD Co. Ltd.
Morgan & Lewis & Bockius, LLP
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