Flat panel display device with first electrode having concentration gradient and fabrication method thereof

A method of fabricating a flat panel display comprises forming a first electrode, forming at least one organic electroluminescent layer on the first electrode, forming an second electrode, wherein the first electrode comprises a first component of a transparent material and a second component of a metallic material, and the forming of the first electrode comprises depositing the first and second components so as to have a gradual concentration gradient in which the first component is decreased while the second component is increased at a part in contact with the exposed electrode, according to a thickness of the first electrode. The first electrode functions as a pixel electrode and a black matrix of the flat panel display.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a flat panel display device, and more particularly, to a front light emitting type organic electroluminescent display device with a first electrode having a concentration gradient which functions as a pixel electrode and a black matrix at the same time, and a method of fabricating the front light emitting type organic electroluminescent display device.

2. Description of the Related Art

FIG. 1Aillustrates the cross-sectional structure of a conventional front light emitting type organic electroluminescent (EL) display device.FIG. 1Billustrates the plan structure of a conventional organic electroluminescent display device.FIG. 1Aillustrates the cross-sectional structure taken along the line I—I ofFIG. 1B.

Referring toFIG. 1AandFIG. 1B, a transparent insulation substrate10is divided into a first region11in which a pixel electrode is formed, and a second region12in which a thin film transistor (TFT) and a capacitor are formed. The second region12includes a semiconductor layer20in which source/drain regions21and22are formed, a thin film transistor equipped with a gate electrode31and source/drain electrodes51and52, and a capacitor equipped with a first electrode32, and a second electrode53connected to the source electrode51of the thin film transistor.

A gate insulating layer30is formed in a space between the semiconductor layer20and the gate electrode31.

An interlayer insulating layer40is formed in a space between the gate electrode31and the source/drain electrodes51and52.

A pixel electrode70connected to one of the source/drain electrodes51and52, e.g., the drain electrode52through a via hole61, is formed on a passivation layer60of the first region11as an anode electrode. A planarization layer80equipped with an opening part81which exposes a portion of the pixel electrode70is formed on the pixel electrode70. An organic EL layer90is formed in the opening part81, and a transparent electrode95is formed on the organic EL layer90as a cathode electrode.

References35,55and56ofFIG. 1Brepresent gate lines, data lines and power supply lines, respectively.

In the above described conventional front light emitting type organic electroluminescent display device, contrast deteriorates because a material having a high reflection ratio is used, thereby reflecting an external light through a metal wiring material, particularly a metallic material for source/drain electrodes.

Although the external light can be prevented from being reflected by adhering a polarizer onto a front of the conventional organic electroluminescent display device, using the polarizer is expensive, and a luminance of the organic electroluminescent display device is lowered because a transmittancy of light emitted from an organic electroluminescent (EL) layer of the organic electroluminescent display device is lowered by the polarizer. Furthermore, a life cycle of the organic EL layer is shortened where a current flowing through the conventional organic electroluminescent display device is increased to improve the luminance of the organic electroluminescent display device.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a flat panel display device having a black matrix which prevents reflection of an external light.

Another object of the present invention is to provide a simplified method of fabricating a flat panel display device where a black matrix and a pixel electrode of the flat panel display device are simultaneously formed by using a conductive layer having a predetermined concentration gradient of a transparent conductive material and a metallic material.

Yet another object of the present invention is to provide a flat panel display device which prevents formation of a surface profile due to a use of a black matrix, and a method of fabricating the flat panel display device thereof.

Still another object of the present invention is to provide a flat panel display device which reduces a surface resistance and a contact resistance of source/drain electrodes by using an Al series material as the source/drain electrodes, and a method of fabricating the flat panel display device thereof.

To achieve the above and other objects of the present invention, there is provided a method of fabricating a flat panel display, the method comprising forming a first electrode; forming at least one organic electroluminescent layer on the first electrode; forming a second electrode; wherein the first electrode comprises a first component of a transparent material and a second component of a metallic material, and the forming of the first electrode comprises depositing the first and second components so as to have a gradual concentration gradient in which the first component is decreased while the second component is increased at a part in contact with the exposed electrode, according to a thickness of the first electrode.

According to an aspect of the present invention, the first electrode functions as a black matrix as well as a pixel electrode of the display device.

The first component of the first electrode may be one of ITO, IZO and ZnO, and the second component thereof may be one of Al, Cr, Mo, Ti, Ag, Au and W. The first electrode may be deposited by one of co-sputtering and co-evaporating the transparent first material and the metallic second material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2Ashows a cross-sectional view of an organic electroluminescent display device according to an embodiment of the present invention, andFIG. 2Bshows a plan view of the organic electroluminescent display device, wherein theFIG. 2Aillustrates a cross-sectional structure taken along the line II—II ofFIG. 2B.

Referring toFIG. 2AandFIG. 2B, the display device includes an insulation substrate100having a first region101to form a pixel electrode, and a second region102to form a thin film transistor (TFT) and a capacitor. A buffer layer115is formed on the insulation substrate100. The thin film transistor (TFT) is formed in a second region102of the insulation substrate100. The TFT comprises a semiconductor layer120equipped with n or p type source/drain regions121and122, a gate electrode131, and source/drain electrodes141and142, each of which is connected to the source/drain regions121and122through contact holes136and137, respectively.

A capacitor having a first electrode132and a second electrode143connected to the source electrode141are formed in the second region102. Each of insulation layers, e.g., a gate insulation layer135and an interlayer insulation layer145, are formed in a space surrounded by the semiconductor layer120, gate electrode131and first electrode132, and a space surrounded by the gate electrode131, first electrode132and source/drain electrodes141and142, respectively. A part between the first electrode132and the second electrode143in the interlayer insulation layer145functions as a capacitor dielectric layer.

A passivation layer150is formed on the interlayer insulation layer145equipped with the TFT and the capacitor. A via hole155, which exposes a part of one electrode out of the source/drain electrodes141and142, e.g., the drain electrode142, is formed by etching the passivation layer150.

A first electrode160connected to the drain electrode142through the via hole155is formed on the passivation layer150. An opening part175which exposes a part corresponding to a first region in the first electrode160is formed after forming an insulation layer170on a front face of the insulation substrate100. An organic EL layer180is formed on the first electrode160exposed by the opening part175, and a cathode electrode is formed on the organic EL layer180as a transparent electrode190.

The insulation layer170formed on the passivation layer separation wall which prevents a short, and separates each of pixels of a pixel electrode (described herein below) under the insulation layer170.

The first electrode160functions as an anode electrode which is a pixel electrode of the organic electroluminescent display device, as well as a black matrix which prevents reflection of an external incident light. Since the transparent electrode190is used as a cathode electrode, a material having a smaller work function from that of the first electrode160, which functions as a pixel electrode, is used as a material for the transparent electrode190.

FIG. 3shows concentration gradients of a transparent conductive material and a metallic material of the first electrode160. The first electrode160includes a first component of a transparent conductive material and a second component of a metallic material, and has a gradual concentration gradient corresponding to a deposition thickness of the first electrode160.

That is, as illustrated inFIG. 3, the first electrode160is deposited in such a manner that the deeper an incidence depth “r” of external light is in an incidence direction, a concentration gradient of the first component of the transparent conductive material is gradually decreased while a concentration gradient of the second component of the metallic material is gradually increased. The rate of decrease/increase and the arrangement of the concentration gradients depend on a deposition thickness “d” of the first electrode160, wherein the transparent conductive material and the metallic material exist in an almost equal ratio at about a half deposition thickness of the first electrode160.

As described in the above, absorption rather than reflection of the external incident light occurs in the first electrode160since a composition ratio of the transparent conductive material and the metallic material is gradually and slowly changed by the gradual concentration gradients of the transparent conductive material and the metallic material. Therefore, the first electrode160functions as a black matrix which prevents reflection of the external light as reflection of the external light is inhibited by the first electrode160.

Indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), etc., can used as a first component of a transparent conductive material of the first electrode160, while Al, Cr, Mo, Ti, Ag, Au, W, etc., can used as a second component of a metallic material of the first electrode160. The first electrode160is deposited by, for example, simultaneously cosputtering or coevaporating the metallic material and the transparent conductive material.

The first electrode160is deposited in such a manner that the deeper an incidence depth “e” of external light is, a transparent conductive material is gradually decreased while a metallic material is gradually increased, depending on a deposition thickness “d” of the first electrode160. Accordingly, a part which contacts the drain electrode142through the via hole155, that is, a bottom of the first electrode160, is formed with a relatively high composition of the metallic material while a part which contacts the organic EL layer180, that is, an upper surface of the first electrode160, is formed with a relatively high composition of the transparent conductive material.

Therefore, although it has conventionally been difficult to use Al having a low resistivity as source/drain electrodes, due to diffusion problems between Al and ITO (which is used as a transparent conductive layer or a pixel electrode), an organic electroluminescent display device of the present invention is capable of using Al as the source/drain electrode material by using the first electrode160, which has gradual concentration gradients of the transparent conductive material and the metallic material, as a pixel electrode.

That is, diffusion problems between Al and the pixel electrode do not occur, although Al is used as the source/drain electrodes, since a composition of the transparent conductive material is relatively low, and a composition of the metallic material is relatively high at a part where the first electrode160is in contact with the drain electrode142. Therefore, since Al can be used as the source/drain electrodes in an organic electroluminescent display device of the present invention, a surface resistance of the source/drain electrodes as well as a contact resistance between the pixel electrode and the source/drain electrodes can be reduced.

The first electrode160is conductive since it functions as the pixel electrode and the black matrix at the same time. Therefore, the first electrode160should be separately formed per each pixel electrode of an organic electroluminescent display device. An organic electroluminescent display device according to the present invention has a structure in which a first electrode160is formed on a front surface of a pixel region defined by gate lines130, data lines140and power supply lines147, as illustrated in the planar structure ofFIG. 2B. However, the structure is not limited thereto, and it is understood that other arrangements can be made so as to have the first electrode be electrically separated between each of the pixels.

Although a first electrode160having gradual concentration gradients of first and second materials is illustrated as both a pixel electrode and a black matrix with respect to a front light emitting type organic electroluminescent display device, it is understood that the present invention can be applied to other display devices including a reflection type liquid crystal display device.

Additionally, a display device of the present invention can be an all organic electroluminescent display device having an electrode layer, which does not transmit light from an organic thin layer formed between two electrodes, that functions as a first electrode.

A formation of an organic electroluminescent (EL) display device of the present invention is simple because a pixel electrode and a black matrix of the organic EL display device are formed at the same time using a conductive layer having gradual concentration gradients of a transparent conductive material and a metallic material.

In an organic EL display device of the present invention, a luminance is improved by preventing reflection of external light without the use of an expensive polarizer. Additionally shorts between wirings are prevented by preventing the formation of a surface profile due to the formation of a black matrix.

Furthermore, an organic EL display device of the present invention is capable of using Al having a low resistance as source/drain electrodes. A conductive layer, in which a part which contacts the source/drain electrodes has a low composition of an ITO and a high composition of a metallic material, is used as a pixel electrode. Accordingly, an Al-series material can be used as the source/drain electrodes, and a contact resistance between the source/drain electrodes and the pixel electrode is reduced.