Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1999-11-18
2001-08-28
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S187000, C257S059000
Reexamination Certificate
active
06281954
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a structure and manufacturing method of a TFT type liquid crystal display, and particularly, to a TFT designed to prevent a drain electrode from being disconnected from a pixel electrode.
2. Description of Related Art
In general, a TFT type LCD comprises a bottom plate, an upper plate and a liquid crystal which is filled in between the two plates. A polarizing plate which polarizes a visible ray so that only one aspect of the ray could be seen is attached at both sides of the two plates. A polarizing plate is attached at one side, and a color filter and a common electrode are formed on the other side of the upper plate. A plurality of gate bus lines
10
and a data bus line
20
are in a matrix form and on a certain space formed by the crossing of a plurality of gate bus lines
10
and a data bus line. A pixel electrode
40
is located in the structure of the bottom plate. Structure of the bottom plate of the active matrix type LCD is illustrated hereafter with reference to
FIGS. 1
a
and
1
b.
A plurality of gate bus lines
10
is formed horizontally on the bottom plate of the LCD, and a gate electrode
11
is formed by deriving from the gate bus line
10
. A plurality of data bus lines
20
is formed perpendicularly to each of the gate bus line
10
, and a source electrode
21
is formed by deriving from the data bus line
20
. The switching element of the TFT structure comprises a gate electrode
11
, a source electrode
21
and a drain electrode
31
by forming the drain electrode
31
opposite to the source electrode
21
. The manufacturing step of the bottom plate of the active matrix type LCD is illustrated below with reference to
FIGS. 2
a
to
2
f
.
Bottom plate or substrate
1
is formed with a glass substrate. A gate electrode
11
, which is derived from the gate bus line, is formed through patterning on the bottom plate
1
. A gate anodizing layer
12
is formed on the gate electrode
11
. A gate insulating layer
13
is deposited on the bottom plate
1
where the gate anodizing layer
13
is formed. A gate insulating layer
13
is then formed with SiNx, SiOx and the like which have good interfacial property with a-Si, good adhesiveness with the gate electrode
11
and the bottom plate
1
and a high insulating characteristic. A semiconductor layer
14
is formed by depositing a-Si which has a high moving density of carrier on the gate insulating layer
13
. An ohmic contact layer
15
is formed on the semiconductor layer
14
for satisfactory ohmic contact between source electrode
21
and drain electrode
31
. A Ti metal layer is applied on the entire surface of the bottom plate
1
by a sputtering method and then the data bus line
20
which acts as a signal line, source electrode
21
which is derived from data bus line
20
and drain electrode
31
which acts as an output terminal located opposite to the source electrode
21
are formed by patterning the Ti metal layer. The switching element of TFT structure comprising gate electrode
11
, semiconductor layer
14
, source electrode
21
and drain electrode
31
is formed through the sequential steps mentioned above.
A protection layer
23
is formed by applying an organic insulating layer, such as BCB and the like, on the switching element. Referring to
FIG. 2
a
, photo resister
60
is developed into a certain pattern by exposing with mask after applying photo resister
60
on the protection layer
23
using a spin coating method.
The bottom plate
1
, including photo resister
60
which is developed into a certain pattern, is etched by plasma gas like SF
6
/O
2
or CF
4
/O
2
inside the etching chamber and, through this process, a part of the protection layer
23
is eliminated. The photo resister
60
on the protection layer
23
is concurrently eliminated by ashing with 0
2
gas. Therefore, a contact hole
50
, which is exposed through the place where drain electrode
31
and protection layer
23
, are partly eliminated as shown in
FIG. 2
b.
An ITO layer
42
is deposited on the entire surface of the protection layer
23
where the contact hole is formed by a sputtering method as shown in
FIG. 2
c.
Another photo resister
60
is applied on the ITO layer
42
by a spin coating method. By exposing the spin coated photo resister
60
using a mask, it is developed into a certain pattern as shown in
FIG. 2
d.
The pixel electrode
40
is then formed by etching the bottom plate
1
which includes photo resister
60
developed into a certain pattern with etching solution like HCI. The photo resister
60
remaining on the pixel electrode
40
is eliminated by using an organic solution which is a mixture of NMP{N-Methyl-Pyrrolidone), alcohol and amine. The pixel electrode
40
which is in contact with drain electrode
31
through contact hole
50
is formed as a result as shown in
FIG. 2
e.
An orientation layer with a polyimide layer and the like is applied on the entire surface of the bottom plate of the LCD which includes a plurality of switching elements and pixel electrodes
40
that are formed through sequential steps illustrated in
FIGS. 2
a
-
2
f
and described above. The manufacturing step of the bottom plate
1
of the LCD is carried out by using a baking method which is a heat treatment of high temperature approximately 150~200° C. at the bottom plate of the LCD where the orientation layer is applied.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a liquid crystal device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
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.
Pixel electrode
40
is formed by developing photo resister
60
into a certain pattern on an ITO layer and etching the ITO layer with etching solution like HCI along the developed pattern at the stage where the ITO layer is applied on the switching element which is covered with a protection layer
23
including a contact hole
50
and the ITO layer is etched according to a conventional manufacturing method and structure of the bottom plate of an LCD. Furthermore, organic solution which is a mixture of NMP, alcohol and amine is used to eliminate photo resister
60
in which an ITO layer is applied and in order to form an orientation layer on the bottom plate of the LCD, a baking process of high temperature is carried out after polyimide layer is applied.
During this process, an etching solution like HCI is used in the etching process of the ITO layer and an organic solution which is a mixture of NMP, alcohol and amine is used in the process of eliminating photo resister
60
remaining at the edge part S
1
of pixel electrode
40
during the etching process or etching solution which penetrates between pixel electrode
40
and protection layer
23
through the edge part Si as shown in
FIG. 2
e
. So, if a hard baking process of high temperature is carried out after applying polyimide layer on the entire surface of the bottom plate in which pixel electrode
40
is formed, swelling occurs due to thermal expansion of protection layer
23
of the bottom plate. In addition, cracking occurs at the edge of pixel electrode
40
as an area where pixel electrode
40
is on protection layer
23
; the area where there is no pixel electrode
40
on protection layer
23
receives a different pressure due to swelling of protection layer
23
. swelling of protection layer
23
and cracking of pixel electrode
40
obstructs contact between drain electrode
31
and pixel electrode
40
through the contact hole
50
of protection layer
23
and this leads to the problem of contact between drain electrode
31
and pixel
Kim Jeong Hyun
Lim Kyoung Nam
Park Sung Il
LG. Philips LCD Co. Ltd.
Long Aldridge & Norman LLP
Ton Toan
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