Abstract:
There are disclosed an organic electro luminescence display device that is adaptive for improving its contrast ratio, and a fabricating method thereof. 
     An organic electro luminescence display device according to an embodiment of the present invention includes an anode electrode formed on a substrate; and a concavo-convex area formed on the substrate in an area except for an area where the anode electrode is formed.

Description:
This application claims the benefit of the Korean Patent Application No. P2004-92140 filed on Nov. 11, 2004, which is hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an organic electro luminescence display device, and more particularly to an organic electro luminescence display device that is adaptive for improving its contrast ratio, and a fabricating method thereof. 
   2. Description of the Related Art 
   Recently, there have been developed a variety of flat panel display devices that can reduce their weight and size, which are a disadvantage of a cathode ray tube CRT. The flat panel display device includes a liquid crystal display LCD, a field emission display FED, a plasma display panel PDP and an electro luminescence EL display device. 
   Especially, the EL display device basically has a shape of sticking an electrode to both side surfaces of an organic light emitting layer which is made up of a hole transport layer, a light emitting layer and an electron transport layer, and the EL display device attracts attention as a next generation flat panel display because of its wide viewing angle, high aperture ratio, high color sense and so on. 
   The EL display device is largely divided into an inorganic EL display device and an organic EL display device in accordance with a material used. The organic EL display device among these has an advantage of being driven with lower voltage than an inorganic EL display device because electrons and holes form pairs and then they become extinct to emit light when electric charges are injected into an organic EL layer which is formed between a hole injection electrode and an electron injection electrode. Further, the organic EL display device can form elements even on a transparent substrate which is flexible like plastics, and the organic EL display device can be driven at a low voltage of below 10V, has relatively low power consumption and has excellent color sense in comparison with the PDP or the inorganic EL display device. 
     FIG. 1  is a perspective view representing a related art organic EL display device, and  FIG. 2  is a diagram representing the organic EL display device shown in  FIG. 1 , taken along the line I-I′. 
   The organic EL display device shown in  FIG. 1  has a first electrode (or an anode electrode)  4  and a second electrode (or a cathode electrode)  12  formed on a substrate  2  in a direction of crossing each other. 
   A plurality of anode electrodes  4  are formed on the substrate  2  to be separated from each other with a designated gap. An insulating film  6  having an aperture part for each EL cell area is formed on the substrate  2  where the anode electrode  4  is formed. Barrier ribs  8  are located on the insulating film  6  for separating an organic light emitting layer  10  and the cathode electrode  12  which are to be formed thereon. The barrier ribs  8  are formed in a direction of crossing the anode electrode  4  and have a reverse taper structure where an upper end part has a wider width than a lower end part. The organic light emitting layer  10  and the cathode electrode  12  formed of an organic compound are sequentially deposited over the entire surface of the insulating film  6  where the barrier ribs  8  are formed. The organic light emitting layer  10  has a hole transport layer, a light emitting layer and an electron transport layer deposited and formed on the insulating film. The organic EL display device has electrons and holes emitted if a driving signal is applied to the anode electrode  4  and the cathode electrode  12 , and the electrons and holes emitted from the anode electrode  4  and the cathode electrode  12  are recombined within the organic light emitting layer  10  to generate a visible ray. At this moment, the generated visible ray exits to the outside through the anode electrode  4  to display a designated picture or image. 
   On the other hand, in the related art organic EL display device, the light incident from the outside almost completely transmits the anode electrode  4 , the barrier rib  8  and the organic light emitting layer  10 . As a result, when the light is not emitted from the organic light emitting layer  10 , as shown in  FIG. 3 , an external light  40  being incident from the surface of the substrate  2  transmits the organic light emitting layer  10  and the anode electrode  4  of a transparent conductive material, and is reflected by the cathode electrode  12  of metal electrode to exit to the outside of the device. Accordingly, there is a problem in that its contrast ratio is deteriorated. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide an organic electro luminescence display device that is adaptive for improving its contrast ratio by intercepting an external light, and a fabricating method thereof. 
   In order to achieve these and other objects of the invention, an organic electro luminescence display device according to an aspect of the present invention includes an anode electrode formed on a substrate; and a concavo-convex area formed on the substrate in an area except for an area where the anode electrode is formed. 
   In the organic electro luminescence display device further includes an insulating film which partially exposes the anode electrode to define a light emitting area; an organic light emitting layer formed on the light emitting area; and a cathode electrode which crosses the anode electrode with the organic light emitting layer therebetween, and wherein the concavo-convex area intercepts a progress path of an external light which is incident to the anode electrode and reflected in the cathode electrode. 
   A fabricating method of an organic electro luminescence display device according to another aspect of the present invention includes the steps of forming a concavo-convex area in an area except for an area where an anode electrode is formed on a substrate; forming the anode electrode in an area except for the concavo-convex area; forming an insulating film which partially exposes the anode electrode to define a light emitting area; forming an organic light emitting layer on the light emitting area; and forming a cathode electrode which crosses the anode electrode with the organic light emitting layer therebetween. 
   In the fabricating method, the concavo-convex area which is formed on the substrate is formed by use of at least any one of a laser, a photolithography process and a sand blast process. 
   In the fabricating method, the concavo-convex area intercepts an external light. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects of the invention will be apparent from the following detailed description of the embodiments of the present invention with reference to the accompanying drawings, in which: 
       FIG. 1  a perspective view briefly illustrating a related art organic electro luminescence display device; 
       FIG. 2  is a sectional diagram representing the organic electro luminescence display device shown in  FIG. 1 , taken along the line I-I′; 
       FIG. 3  is a diagram representing that an incident external light is reflected in a cathode electrode of an organic electro luminescence display device; 
       FIG. 4  is a perspective view representing an organic electro luminescence display device according to an embodiment of the present invention; 
       FIG. 5  is a sectional diagram representing the organic electro luminescence display device shown in  FIG. 4 , taken along the line II-II′; 
       FIG. 6  is a diagram representing a light shielding role of a concavo-convex area shown in  FIG. 5 ; and 
       FIGS. 7A to 7F  are diagrams representing a fabricating method of a related art organic electro luminescence display device. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
   With reference to  FIGS. 4 to 7F , embodiments of the present invention will be explained as follows. 
     FIG. 4  is a perspective view representing an organic EL display device according to an embodiment of the present invention, and  FIG. 5  is a sectional diagram illustrating the organic EL display device, taken along the line II-II′ shown in  FIG. 4 . 
   An organic EL display device shown in  FIGS. 4 and 5  has a first electrode (or an anode electrode)  104  and a second electrode (or a cathode electrode)  112  formed on a display area P 1  of a substrate  102  in a direction of crossing each other, and includes a concavo-convex area (A) formed in an area except for an area where the first electrode  104  is located in the display area P 1  of the substrate  102 . 
   A plurality of anode electrodes  104  are formed on the substrate  102  to be separated from each other with a designated gap. An insulating film  106  having an aperture part for each EL cell area is formed on the substrate  102  where the anode electrode  104  is formed. Barrier ribs  108  are located on the insulating film  106  for separating an organic light emitting layer  110  and the cathode electrode  112  which are to be formed thereon. The barrier ribs  108  are formed in a direction of crossing the anode electrode  104  and have a reverse taper structure where an upper end part has a wider width than a lower end part. The organic light emitting layer  110  and the cathode electrode  112  formed of an organic compound are sequentially deposited over the entire surface of the insulating film  106  where the barrier ribs  108  are formed. The organic light emitting layer  110  has a hole transport layer, a light emitting layer and an electron transport layer deposited and formed on the insulating film  106 . 
   The concavo-convex area (A) plays the role of shielding or absorbing an external light. That is, the concavo-convex area (A) is a uneven area which is damaged by irradiating a laser to the substrate  102  or formed by use of a photo resist process and an etching process, so that the concavo-convex area (A) plays the role of shielding the external light. 
   In other words, the external light  140  being incident to the substrate  102 , as shown in  FIG. 6 , becomes extinct by a plurality of reflection within the concavo-convex area (A), and the external light  140  being incident through an area except for the concavo-convex area (A) is reflected by the cathode electrode  112 , and then the external light  140  almost cannot exit to the outside and becomes extinct by the concavo-convex area (A). In this way, the concavo-convex area (A) intercepts a progress path of the external light, thereby enabling to improve its contrast ratio. 
   In this way, in the organic EL display device according to the present invention, the concavo-convex area (A) is formed in an area except for the anode electrode  104  on the display area P 1 . The concavo-convex area (A) intercepts a considerable amount of the external light which is incident to the inside of the device from the outside, and plays the role of also intercepting the external light which is partially transmitted and reflected in the cathode electrode  112 . Accordingly, the contrast ratio is improved. 
   Hereinafter, in reference to  FIGS. 7A to 7F , a fabricating method of the related art organic EL display device is described as follows. 
   Firstly, after providing a substrate  102  which is formed by use of sodalime or hard glass, a laser is irradiated to an area except for an area where the anode electrode  104  is to be formed in the display area P 1  of the substrate  102  so as to give damage to the surface of the substrate  102 , or a photolithography process and an etching process are performed, thereby forming the concavo-convex area (A) on the substrate  102 , as shown in  FIG. 7A . On the other hand, the concavo-convex area (A) can be formed by use of a sand blast method using a dry film resist DFR instead of the photolithography process and the dry etching process. 
   After depositing a transparent conductive metal material on the substrate  102  where the concavo-convex area (A) is formed, the transparent conductive metal material is patterned by the photolithography process and the etching process, thereby forming the anode electrode  104 , as shown in  FIG. 7B . Herein, the metal material is indium tin oxide or SnO2. 
   After forming a photo sensitive insulating material on the substrate  102  where the anode electrode  104  is formed, the photo sensitive insulating material is patterned by the photolithography process, thereby partially exposing the anode electrode  104  to form the insulating film  106  which defines a light emitting area, as shown in  FIG. 7C . 
   After a photo sensitive organic material is deposited on the substrate  102  where the insulating film  106  is formed, the photo sensitive organic material is patterned by the photolithography process, thereby forming the barrier rib  108 , as shown in  FIG. 7D . The barrier rib  108  is formed in a non light emitting area to cross a plurality of anode electrodes  104  for dividing pixels. 
   An organic material is deposited on the substrate  102  where the barrier rib  108  is formed by use of a thermal deposition method and a vacuum deposition method, thereby forming the organic Light emitting layer  110 , as shown in  FIG. 7E . 
   A metal material is deposited on the substrate  102  where the organic light emitting layer  110  is formed, thereby forming the cathode electrode  112 , as shown in  FIG. 7F . 
   As described above, the organic EL display device and the fabricating method thereof according to the present invention has the concavo-convex area formed in the area except for the anode electrode on the display area. The concavo-convex area intercepts a considerable amount of the external light which is incident to the inside of the device from the outside, and plays the role of also intercepting the external light which is partially transmitted and reflected in the cathode electrode. Accordingly, the contrast ratio is improved. 
   Although the present invention has been explained by the embodiments shown in the drawings described above, it should be understood to the ordinary skilled person in the art that the invention is not limited to the embodiments, but rather that various changes or modifications thereof are possible without departing from the spirit of the invention. Accordingly, the scope of the invention shall be determined only by the appended claims and their equivalents.