Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
2002-12-27
2004-02-10
Picardát, Kevin M. (Department: 2822)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C438S026000, C438S034000, C438S082000
Reexamination Certificate
active
06689632
ABSTRACT:
This application claims the benefit of the Korean Patent Application No. P2002-029946 filed on May 29, 2002, which is hereby incorporated by reference for all purposes as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electroluminescence display device, and more particularly, to an organic electroluminescence display device and a fabricating method of the same.
2. Discussion of the Related Art
Recently, flat panel displays have been proposed as a display device due to their characteristics of being thin, light weight, and low in power consumption. The flat panel displays include a liquid crystal display, a plasma display panel, a field emission display, and an electroluminescence display.
Among these displays, the electroluminescence display may be categorized into an inorganic electroluminescence display device and an organic electroluminescence display device depending upon a source material for exciting carriers. The organic electroluminescence display (OELD) device has drawn a considerable attention due to its high brightness, low driving voltage, and natural color images from the entire visible light range. Additionally, the OELD device has a wide viewing angle and a great contrast ratio because of self-luminescence. Since the OELD device does not require an additional light source such as a backlight, the OELD device has small size and light weight and low power consumption as compared with the liquid crystal display. Furthermore, the OELD device can be driven by a low voltage of direct current (DC), and has a short response time of several microseconds. Since the OELD device is totally solid phase, it is sufficiently strong to withstand external impacts and has a greater operational temperature range. Additionally, the OELD device can be manufactured at a low cost. Particularly, only deposition and encapsulation apparatuses are necessary for manufacturing the organic EL devices, and thus a manufacturing process of the OELD device is very simple in contrast with the liquid crystal display or plasma display panel.
The organic electroluminescence display device may be classified into a passive matrix type and an active matrix type depending upon a driving method.
The passive matrix type, which does not have additional thin film transistors (TFTs), has been conventionally used. In the passive matrix OELD device, scanning lines and signal lines perpendicularly cross each other to be arranged in a matrix shape. Since a scanning voltage is sequentially applied to the scanning lines to operate each pixel, an instantaneous brightness of each pixel during a selection period should reach a value resulting from multiplying the average brightness by the number of the scanning lines to obtain a required average brightness. Accordingly, as the number of the scanning lines increases, applied voltage and current also increase. Therefore, the passive matrix OELD device is not adequate to a display of high resolution and large area because the device is easily deteriorated and the power consumption is high.
Since the passive matrix OELD device has many limitations in resolution, power consumption and lifetime, an active matrix OELD device has been researched and developed as a next generation display device requiring high resolution and large display area. In the active matrix OELD device, a thin film transistor (TFT) is disposed at each sub-pixel as a switching element for turning on/off each sub-pixel. A first electrode connected to the TFT is turned on/off by the sub-pixel and a second electrode facing the first electrode functions as a common electrode. Moreover, a voltage applied to the pixel is stored in a storage capacitor, thereby maintaining the voltage and driving the device until a voltage of next frame is applied, regardless of the number of the scanning lines. As a result, since an equivalent brightness is obtained with a low applied current, an active matrix OELD device of low power consumption, high resolution and large area may be made.
FIG. 1
shows a band diagram of a related art organic electroluminescence display. As shown in
FIG. 1
, the related art organic electroluminescence display includes an anode electrode
1
, a cathode electrode
7
, a hole transporting layer
3
, an emissive layer
4
, and an electron transporting layer
5
between the anode electrode
1
and the cathode electrode
7
. The related art organic electroluminescence display device further includes a hole injection layer
2
, which is disposed between the anode electrode
1
and the hole transporting layer
3
, and an electron injection layer
6
, which is disposed between the cathode electrode
7
and the electron transporting layer
5
, to efficiently inject holes and electrons.
The holes and the electrons are injected into the emissive layer
4
through the hole injection layer
2
and the hole transporting layer
3
from the anode electrode and through the electron injection layer
7
and the electron transporting layer
5
from the cathode electrode
7
, respectively, thereby generating an exciton
8
in the emissive layer
4
. Then, light corresponding to energy between the hole and the electron is emitted from the exciton
8
.
The anode electrode
1
is formed of a transparent conductive material having a relatively high work function such as indium-tin-oxide and indium-zinc-oxide. Light is observed at the anode electrode
1
. On the other hand, the cathode electrode
7
is formed of an opaque conductive material having a relatively low work function, such as aluminum, calcium, and aluminum alloy.
In the OELD device, in order to display full color images, the organic emissive layers of red, green and blue are formed by sub-pixels, respectively, and an insulating material is used as a partition wall. The partition wall can separate adjacent organic emissive layers and adjacent cathode electrodes to be formed thereon by sub-pixels without a patterning process.
In the OELD device having the partition wall, a printing method is widely used by dropping an organic emissive material solution of an ink type at a portion between the adjacent partition walls.
FIGS. 2A
to
2
D illustrate a fabricating method of a related art organic electroluminescence display device using an inkjet method.
In
FIG. 2A
, an anode electrode
12
is formed on a substrate
10
, which has an emission region “A” and a non-emission region “B” defined thereon. A buffer layer
14
is formed on the anode electrode
12
in the non-emission region “B”, and a partition wall
16
is formed on the buffer layer
14
. The buffer layer
14
is widely made of silicon oxide (SiO2).
The partition wall
16
includes a polyimide and makes it possible that an organic emissive layer (not shown) and a cathode electrode (not shown) will be formed without a patterning process in the next step, wherein the organic emissive layer is formed by using an inkjet method. Although not shown in the figure, the partition wall
16
may have an inverse taper, that is, an inverse trapezoid having the top side longer than the bottom side depending on exposing extents.
In the inkjet printing method, a solution of an ink type is used, and the solution includes a water-soluble organic emissive material. Therefore, the anode electrode
12
and the buffer layer
14
, which are disposed in the emission region “A”, should be hydrophilic in order to attach the solution thereto, while the partition wall
16
, which is disposed in the non-emission region “B”, should be hydrophobic in order to prevent the partition wall
16
from being stained with the solution.
That is, in a high definition OELD fabricated by the inkjet printing method, before forming the organic emissive layer, a step to differ wettability of the elements in the emission region “A” from that in the non-emission region “B” is required.
In
FIG. 2B
, the substrate
10
including the partition wall
16
is disposed in a vacuum chamber (not shown), and a first plasma treatment using an oxygen (O
2
) gas is carried out to have the an
Kim Jin-Ook
Kim Kyung-Man
LG.Philips LCD Co. , Ltd.
McKenna Long & Aldridge LLP
Picardát Kevin M.
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