Ink printing cliché and fabrication method thereof

Details Ink printing cliché and fabrication method thereof Ink printing cliché and fabrication method thereof

2002-10-03

2004-04-20

Gordon, Raquel Yvette (Department: 2853)

Incremental printing of symbolic information

Ink jet

Ejector mechanism

Reexamination Certificate

active

06722760

ABSTRACT:

This nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 88553/2001 filed in Korea on Dec. 29, 2001, which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an ink printing device for pattern formation, and more particularly, to an ink printing cliché capable of forming a fine pattern and lengthening the life span of a printing device by forming a cliché with an organic material or an organic/metal.
2. Description of the Related Art
Display devices, especially a flat panel display such as a liquid crystal display (LCD) device, include an active device such as a thin film transistor (TFT) in each pixel to drive the display device. This display device driving method is called an active matrix driving method. In an active matrix method, the active driving device is disposed in each pixel. The pixels are arranged in a matrix.
FIG. 1
illustrates an active matrix liquid crystal display device, in which the liquid crystal display device is a TFT LCD using a thin film transistor as the active device.
As shown in
FIG. 1
, the TFT LCD has N×M pixels vertically and horizontally arranged. Each pixel has a gate line
4
to which a scan signal is applied from an external driving circuit, a data line
6
to which an image signal is applied, and a TFT formed at the intersection of the gate line
4
and the data line
6
.
The TFT includes a gate electrode
3
connected to the gate line
4
. A semiconductor layer
8
is formed on the gate electrode
3
, and the semiconductor layer
8
activates when a scan signal is applied to the gate electrode
3
. A source/drain electrode
5
is formed on the semiconductor layer
8
.
A pixel electrode
10
is formed at a display region of the pixel
1
, and the pixel electrode
10
connects to the source/drain electrode
5
. An image signal is applied through the source/drain electrode
5
as the semiconductor layer
8
is activated, to thereby activate a liquid crystal (not shown).
The source/drain electrode
5
of the TFT is electrically connected to the pixel electrode
10
formed in the pixel
1
, so that as a signal is applied to the pixel electrode
10
through the source/drain electrode
5
, the source/drain electrode
5
drives the liquid crystal and displays an image.
In the active matrix type display device such as the liquid crystal display device, each pixel has a size of scores of &mgr;m. Thus, the active device such as the TFT disposed in the pixel should have a fine size, i.e., a few &mgr;m.
In addition, high picture quality display devices such as the high definition (HD) TV have been in increasing demand. These devices require a greater concentration of pixels occupying a screen of the same area. As a result, the active device pattern (including gate line and data line patterns) disposed on the pixel also becomes more dense and requires a finer structure.
In the conventional art, fabrication of an active device, such as a TFT, utilizes a pattern or a line of the active device formed by a photolithography method using an exposure device.
However, this photolithography method uses a high-priced exposing device. The steps of photolithography can include vapor prime, spin coat, soft bake, alignment and exposure through a mask, post-exposure bake, development, hard bake and inspection. The result is increased fabrication cost and a complicated fabrication process.
Additionally, the exposure region of the exposing device is limited in the photolithographic production of a display device. In order to fabricate a large-scale display device, the screen is divided to accommodate the photolithographic process. This degrades productivity because it is difficult to accurately match the positions when processing the divided regions, and the photolithographic process has to be repeated several times.
In order to solve this problem, pattern forming by gravure offset printing has been recently proposed.
Gravure offset printing is a printing method in which ink is put on a concave plate. Redundant ink is removed by scraping or doctoring, and then printing is performed. This printing method has been adopted in various applications such as printing wrappings of cellophane, vinyl or polyethylene.
Recently, efforts have been made to adapt gravure printing to produce an active device used for the display device or to produce a circuit pattern.
Gravure offset printing transfers ink to a substrate by using a transfer roll, and a pattern can be formed by a single printing step. Even a large-scale display device can be produced by using a transfer roll corresponding to the area of the desired display device.
Gravure offset printing can be used to pattern various configurations and sub-assemblies of the display device. These can include, for example, a metal pattern for a capacitor, a pixel electrode, the gate line and the data line connected to the TFT, and the TFT, which are all structures necessary for a liquid crystal display device.
FIGS. 2A through 2C
illustrate pattern forming by a conventional gravure offset printing method.
As shown in
FIG. 2A
, the conventional gravure offset printing method forms a groove
22
at a specific position of a cliché
20
or a concave plate. The groove
22
corresponds to a pattern that is desired to form on a substrate. The groove
22
is filled with ink
24
.
The ink
24
in the groove
22
results in pattern forming ink
24
being coated at an upper portion of the cliché
20
, and then a doctor blade
28
proceeds while in contact with the cliché
20
. A doctor blade
28
proceeds to impress the ink
24
filled into the groove
22
. The doctor blade simultaneously removes the excess ink
24
remaining on the surface of the cliché
20
. Alternatively, a Meyer rod can be used instead of a doctor blade.
As shown in
FIG. 2B
, the ink
24
filling in the groove
22
of the cliché
20
contacts and transfers to the surface of the transfer role
30
.
The transfer roll
30
is formed with a circumference having the same length as that of the panel of a display device to be fabricated. That is, the transfer roll
30
has the circumferential length equal to the length of the desired panel. Accordingly, the ink
24
filled in the groove
22
of the cliché
20
can be wholly transferred on the surface of the circumference of the transfer roll
30
by a single rotation.
Thereafter, as shown in
FIG. 2C
, the transfer roll
30
contacts the surface of a process-object layer
41
formed on the substrate
40
, and the transfer roll
30
is rotated. Then, the ink
24
transferred on the transfer roll
30
is re-transferred on the process-object layer
41
. By applying heat to the re-transferred ink
24
and drying it, an ink pattern
42
is formed. At this time, the desired ink pattern
42
can be formed on the entire substrate
40
of the display device by a single rotation of the transfer roll
30
.
In the gravure offset printing method discussed above, since the ink pattern
42
is mechanically formed by using the cliché
20
, and the transfer roll
30
and the process-object layer
41
is etched by the ink pattern
42
to form a desired pattern, the pattern forming process is simplified compared to the conventional photolithographic exposure process.
However, the conventional art gravure offset method has shortcomings. Generally, since the cliché
20
is made of a metal such as ferrite and nickel, it is difficult to form a fine groove.
Usually, the groove
22
of the cliché
20
is formed by a mechanical process. In this respect, it is not substantially possible to mechanically process a groove of below a few &mgr;m. Thus, it is difficult to form a fine ink pattern, and this process can scarcely be adopted to fabricate a display device.
In addition, the surface of the metal cliché
20
becomes damaged due to abrasion by the doctor blade
28
, and particles are generated. These particles are a critical factor leading to pattern defects during formation of an ink pattern. Moreover, since the grain is large, a rough edge regi

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