Liquid crystal display and fabricating method thereof

Details Liquid crystal display and fabricating method thereof Liquid crystal display and fabricating method thereof

2000-12-20

2003-01-21

Sikes, William L. (Department: 2871)

Liquid crystal cells, elements and systems

Particular excitation of liquid crystal

Electrical excitation of liquid crystal

C349S042000, C257S059000, C257S072000

Reexamination Certificate

active

06509940

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a liquid crystal display, and more particularly to a liquid crystal display and a fabricating method thereof wherein four masks are used so as to reduce a process.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) includes switching devices consisting of thin film transistors having gate electrodes, a gate insulating film, an active layer, an ohmic contact layer and source and drain electrodes, and a liquid crystal injected between a lower plate provided with pixel electrodes and an upper plate provided with color filters.
FIG. 1
is a plan view showing a structure of a conventional LCD, and
FIG. 2
is a section view of the conventional LCD taken along the A—A′ line in FIG.
1
. Referring to FIG.
1
and
FIG. 2
, in the conventional LCD, a gate electrode
13
is formed on a transparent substrate
11
from a metal such as aluminum (Al) or copper (Cu) in such a manner to be connected to a gate line
14
. A gate insulating film
15
is formed on the transparent substrate
11
to cover the gate electrode
13
and the gate line
14
. The gate insulating film is made from silicon nitride or silicon oxide.
An active layer
17
and an ohmic contact layer
19
are provided at a portion corresponding to the gate electrode
13
on the gate insulating film
15
. The active layer
17
is formed from amorphous silicon or polycrystalline silicon being not doped with an impurity. The ohmic contact layer
19
is made from amorphous silicon or polycrystalline silicon doped with an n-type or p-type impurity at a high concentration.
Source and drain electrodes
21
and
23
are formed at each side of the active layer
17
on the gate insulating film
15
in such a manner to contact the ohmic contact layer
19
. The source and drain electrodes
21
and
23
is made from a metal such as molybdenum (Mo), chrome (Cr), titanium (Ti) or tantalum (Ta), etc., or a molybdenum alloy such as MoW, MoTa or MoNb, etc. The source electrode
21
is connected to a data line
24
while the drain electrode
23
is opposed to the source electrode
21
with having the gate electrode
13
therebetween.
A thin film transistor is constituted by the gate electrode
13
, the gate insulating film
15
, the active layer
17
and the source and drain electrodes
21
and
23
as described above. A passivation layer
25
is formed on the gate insulating film
15
to cover the thin film transistor. The passivation layer
25
is made from an inorganic insulating material such as silicon nitride or silicon oxide, etc., or an organic insulating material such as acrylic compound, BCB (&bgr;-stagged-divinyl-siloxane-benzocyclobutene) or PFCB (perfluorocyclobutane).
A contact hole
27
for exposing the drain electrode
23
is defined at the passivation layer
25
. A pixel electrode
29
contacting the drain electrode
23
via the contact hole
27
is formed on the passivation layer
25
. The pixel electrode
29
is formed from a transparent conductive material such as indium tin oxide (ITO), tin oxide (TO) or indium zinc oxide (IZO) at an area excluding a portion corresponding to the thin film transistor on the passivation layer
25
.
However, the conventional LCD has a problem in that, since a contact hole must be defined so as to connect the drain electrode to the pixel electrode, an aperture ratio is reduced and a process is complicated.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a liquid crystal display and a fabricating method thereof wherein a drain electrode and a pixel electrode are connected to each other with no contact hole, thereby increasing an aperture ratio.
In order to achieve these and other objects of the invention, a liquid crystal display device according to one aspect of the present invention includes a transparent substrate; a gate electrode formed on the transparent substrate; a gate insulating film formed on the transparent substrate to cover the gate electrode; an active layer provided at a portion corresponding to the gate electrode on the gate insulating film; source and drain electrodes intervened by an ohmic contact layer on the active layer; a contact portion connected to and extended from a portion of the drain electrode opposed to the source electrode and having an exposed side surface; a passivation layer formed on the active layer in such a manner to cover the source and drain electrodes, but to expose the side surface of the contact portion; and a pixel electrode formed on the gate insulating film in such a manner to contact the exposed side surface of the contact portion.
A liquid crystal display device according to another aspect of the present invention includes a transparent substrate; a gate electrode formed on the transparent substrate; a gate insulating film formed on the transparent substrate to cover the gate electrode; an active layer provided at a portion corresponding to the gate electrode on the gate insulating film; source and drain electrodes intervened by an ohmic contact layer on the active layer; at least one of come-shaped contact portion connected to and extended from a portion of the drain electrode opposed to the source electrode and having an exposed side surface; a passivation layer formed on the active layer in such a manner to cover the source and drain electrodes and the upper portion of the contact portion, but to expose the side surface of the contact portion; and a pixel electrode formed on the gate insulating film in such a manner to contact the exposed side surface of the contact portion.
A method of fabricating a liquid crystal display device according to still another aspect of the present invention includes the steps of forming a gate electrode on a transparent substrate; sequentially forming a gate insulating film, an active layer and an ohmic contact layer on the transparent substrate in such a manner to cover the gate electrode; forming a metal thin film on the ohmic contact layer and then patterning the metal thin film to expose the active layer, thereby forming source and drain electrodes; forming a passivation layer covering the source and drain electrodes on the active layer and then patterning the passivation layer and the active layer to expose the gate insulating film and also a portion of the drain electrode opposed to the source electrode and formed to have more than a desired size, thereby providing a contact portion connected to and extended from the drain electrode to have an exposed side surface; and forming a pixel electrode on the gate insulating film in such a manner to contact the side surface of the contact portion.


REFERENCES:
patent: 5949507 (1999-09-01), Shimada et al.
patent: 6207970 (2001-03-01), Kim
patent: 6310669 (2001-10-01), Kobayashi et al.

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