Abstract:
An organic electroluminescent device, adapted to enhance device reliability while allowing simplification of a manufacturing process, and a method for manufacturing the same are disclosed. The organic electroluminescent (EL) device, comprising a substrate, TFTs located in respective unit pixel regions on the substrate, a first insulation layer to insulate the TFTs, first electrodes formed on the first insulation layer while contacting the TFTs, respectively, a partition wall positioned between the unit pixel regions on the first insulation layer, a subsidiary electrode formed on the partition wall, an organic light emitting layer positioned on the first electrodes, an insulation part to insulate each first electrode from an associated subsidiary electrode, and a second electrode positioned on the organic light emitting layer and connected with the subsidiary electrode.

Description:
This application claims the benefit of Korean Patent Application No. P2005-0041203, filed on May 17, 2005, which is hereby incorporated by reference as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a flat panel display device, and more particular to, an organic electroluminescent device, which can enhance device reliability while allowing simplification of a manufacturing process, and a method for manufacturing the same. 
     2. Discussion of the Related Art 
     In recent years, there is an increasing demand for providing flat panel display devices occupying a small space according to an increase in size of a display device. As one of such flat panel display devices, an organic electroluminescent device also referred to as an organic light emitting diode (OLED) has been rapidly advanced in its manufacturing technique, and widened in application thereof. 
     The organic electroluminescent device is a device that comprises a first electrode as an electron injection electrode (cathode), a second electrode as a hole injection electrode (anode) and an organic light emitting layer formed between the first and second electrodes in which electrons and holes injected through the first and second electrodes are recombined to form pairs of exitons, so that the pairs of exitons release light when they are extinguished as a result of energy transition from an exited state to a ground state. 
     Since the organic electroluminescent device has a merit in terms of its driving voltage of 5˜10 V which is lower than that of a plasma display panel (PDP) or an inorganic electroluminescent display device, it has been actively investigated. 
     In addition, since the organic electroluminescent device has excellent characteristics such as wide viewing angle, high response speed, high contrast and the like, it can be applied to pixels of a graphic display, and pixels of a TV screen or a surface light source. In addition, the organic electroluminescent device can be formed on a flexible transparent substrate like a plastic substrate, and formed in a very compact and light structure. Furthermore, since the organic electroluminescent device exhibits good color reproduction, it is appropriate for a next generation flat panel display. 
     Furthermore, since the organic electroluminescent device does not require a backlight member generally used in a well-known liquid crystal display (LCD), it has low power consumption, and provides excellent color sensation. 
     Generally, the organic electroluminescent device is generally classified into a passive matrix type and an active matrix type according to its structure and driving method. 
     Unlike the passive matrix type, in the case where the active matrix type is adapted to emit light through a glass surface of a substrate (typically, known as a bottom emission manner), an increase in the size or the number of thin film transistors (TFT) causes a rapid reduction in aperture ratio, thereby making it difficult to use the organic electroluminescent device as the display device. 
     In order to solve the problem, a top emission manner has been suggested, in which light is emitted through a side opposite to the glass surface so as to allow the aperture ratio to be independent of the size or the number of TFTs. 
     The top emission type organic electroluminescent device comprises a reflection layer, an organic light emitting layer, and a transparent electrode layer sequentially formed in this order on a substrate having TFTs and a storage capacitor formed therein, such that, when light is emitted from the organic light emitting layer, it is reflected by the reflection layer, and then emitted to an outside through an opposite side of the substrate. As a result, the organic electroluminescent device of this type is prevented from having its aperture ratio lowered due to the TFTs. 
     A conventional method for manufacturing a top emission type active matrix organic EL device will be described with reference to the drawings. 
       FIGS. 1A to 1F  are cross-sectional views illustrating manufacturing steps of the conventional top emission type active matrix organic EL device. 
     At first, referring to  FIG. 1A , a thin film transistor (TFT)  12  is formed in pixel unit on a transparent substrate  11 . 
     Specifically, after forming an amorphous silicon layer on the transparent substrate  11 , laser is illuminated on the surface of the amorphous silicon layer to form a poly-silicon layer through melting and recrystallization of the amorphous silicon layer. Then, the poly-silicon layer is patterned to form an island shape via a photolithography and etching process to form a semiconductor layer  12   a.    
     Next, a gate insulation layer  12   b  is formed on the overall surface including the semiconductor layer  12   a , and a metallic layer comprising, for example, chrome (Cr) is formed thereon, followed by forming a gate electrode  12   c  at a location corresponding to a central portion of the semiconductor layer  12   a  on the gate insulation layer  12   b  via the photolithography and etching process. 
     Then, p-type or n-type impurities are implanted into the semiconductor layer  12   a  using the gate electrode  12   c  as a mask, after which heating is performed for the purpose of activating the implanted impurities, thereby forming a source electrode  12   d  and a drain electrode  12   e  in the semiconductor layer  12   a . As a result, each of the TFTs  12  is completely formed. 
     After a first insulation layer  13  is formed on the overall surface including the TFTs  12 , a contact  14  is formed so as to be connected with the source electrode  12   d  and the drain electrode  12   e  of each TFT  12  through the first insulation layer  13  and the gate insulation layer  12   b , and a second insulation layer  15  is formed on the overall surface thereof. 
     Then, a flattening insulation layer  16  is formed on the second insulation layer  15  as shown in  FIG. 1B , and selectively removed along with the second insulation layer  15  so as to expose the surface of the contact  14  connected with the drain electrode  12   e  via the photolithography and etching process, thereby forming a first contact hole  17 . 
     Then, an anode electrode material  18  is deposited on the flattening insulation layer  16  and into the first contact hole  17  such that the first contact hole  17  is filled with the anode electrode material, as shown in  FIG. 1C . 
     Next, as shown in  FIG. 1D , an anode electrode  18   a  is divided in pixel unit by selectively removing the anode electrode material  18  via the photolithography and etching process, and then an insulation layer  21  is formed on a portion excluding a light emitting part. 
     Next, an organic EL layer  22  is formed on the overall surface, as shown in  FIG. 1E , and a cathode electrode  23  is formed on the organic EL layer  22 , as shown in  FIG. 1F . 
     As a result, the conventional top emission type active matrix organic EL device is completed. 
     Meanwhile, adhesion between the anode electrodes  18   a  and the flattening insulation layer  16  is low. Accordingly, when removing the photoresist film used for the photolithography and etching process for dividing the anode electrodes, there is high possibility that the anode electrodes  18   a  are also separated from the flattening insulation layer  16 . 
     The problems of the prior art described above will be set forth in detail with reference to the drawings hereinafter. 
       FIGS. 2A to 2D  illustrate the problems which can arise when manufacturing the conventional organic EL device. 
     As shown in  FIG. 1C  described above, after depositing the anode electrode material  18 , the photolithography and etching process is performed to allow the anode electrodes to be divided from each other in pixel units. 
     Specifically, as shown in  FIG. 2A , after a photo-resist  19  is applied to the anode electrode material  18 , a mask  20  having patterns to expose edges of each pixel is aligned on the transparent substrate  11 , and the photo-resist  19  is exposed to light by illuminating the light towards the transparent substrate  11  from above the mask  20 . 
     Then, the exposed portions of the photo-resist  19  are removed by stripping off the mask  20  and developing the photo-resist  19 , as shown in  FIG. 2B . 
     Next, as shown in  FIG. 2C , after forming the anode electrodes  18   a  in pixel units by removing the anode electrode material  18  using the photo-resist  19  as a mask, the transparent substrate  11  is input to a stripper to remove the photo-resist  19 , as shown in  FIG. 2D . 
     At this time, separation of the anode electrodes  18   a  from the flattening insulation layer  16  occurs due to low adhesion between the anode electrodes  18   a  and the flattening insulation layer  16 . As a result, device reliability is significantly deteriorated. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to an organic electroluminescent device, and a method for manufacturing the same that substantially obviate one or more problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide an organic EL device, which can prevent anode electrodes from being peeling off, and a method for manufacturing the same. 
     It is another object of the present invention to provide the organic EL device, which solves the problem of resistance increase of a transparent cathode electrode in the top emission type device, thereby enhancing efficiency and reliability of the device, and the method for manufacturing the same. 
     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided an organic electroluminescent device, comprising: a substrate; TFTs located in respective unit pixel regions on the substrate; a first insulation layer on the TFTs to insulate the TFTs; first electrodes formed on the first insulation layer while contacting the TFTs, respectively; a partition wall positioned between the respective unit pixel regions on the first insulation layer; a subsidiary electrode formed on the partition wall; an organic light emitting layer positioned on the first electrodes; an insulation part to insulate each of the first electrodes from an associated subsidiary electrode; and a second electrode positioned on the organic light emitting layer and connected with the subsidiary electrode. 
     In accordance with another aspect of the present invention, there is provided a method for manufacturing the organic electroluminescent device, comprising the steps of: forming a first insulation layer on a substrate having TFTs formed thereon; forming a contact connected with a source electrode and a drain electrode of each TFT through the first insulation layer; forming a second insulation layer on the first insulation layer and the contact; forming a first contact hole on the second insulation layer so as to expose the surface of the contact connected with the drain electrode; forming a partition wall at a portion separating respective unit pixel regions on the second insulation layer; depositing a first electrode material on the second insulation layer and the partition wall; forming an insulation part at a side of the partition wall; forming a second contact hole in the insulation part so as to expose a subsidiary electrode formed on the partition wall; forming an organic light emitting layer on each unit pixel region; and depositing a second electrode on an overall surface including the organic light emitting layer and the second contact hole. 
     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
         FIGS. 1   a  to  1   f  are cross-sectional views illustrating manufacturing steps of a conventional organic EL device; 
         FIGS. 2A to 2D  illustrate the problems which can arise when manufacturing the conventional organic EL device; 
         FIGS. 3A to 3E  are plan views illustrating manufacturing steps of an organic EL device in accordance with one embodiment of the present invention; 
         FIGS. 4A to 4E  are cross-sectional views taken along line A-A shown in  FIGS. 3A to 3E ; 
         FIGS. 5A to 5E  are views illustrating examples of a partition wall in accordance with the present invention; 
         FIG. 6A  is a plan view illustrating an organic EL device in accordance with another embodiment of the present invention; 
         FIG. 6B  is a cross-sectional view taken along line A-A shown in  FIG. 6A ; 
         FIGS. 7A to 7F  are plan views illustrating manufacturing steps of an organic EL device in accordance with another embodiment of the present invention; and 
         FIGS. 8 and 9  are cross-sectional views taken along line A-A′ shown in  FIGS. 7A to 7F . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
       FIGS. 3A to 3E  are plan views illustrating manufacturing steps of an organic EL device according to one embodiment of the present invention, and  FIGS. 4A to 4E  are cross-sectional views taken along line A-A shown in  FIGS. 3A to 3E , respectively. 
     In a method for manufacturing the organic EL device according to the present invention, a thin film transistor (TFT)  32  is formed in pixel unit on a transparent substrate  31 , as shown in  FIGS. 3A and 4A . 
     Specifically, after forming an amorphous silicon layer on the transparent substrate  31 , laser is illuminated on the surface of the amorphous silicon layer to form a poly-silicon layer through melting and recrystallization of the amorphous silicon layer. Then, the poly-silicon layer is patterned to form an island shape via a photolithography and etching process to form a semiconductor layer  32   a.    
     Next, a gate insulation layer  32   b  is formed on the overall surface including the semiconductor layer  32   a , and a metallic layer comprising, for example, chrome (Cr) is formed thereon and patterned to form a gate electrode  32   c  at a location corresponding to a central portion of the semiconductor layer  32   a  on the gate insulation layer  32   b  via the photolithography and etching process. 
     Then, p-type or n-type impurities are implanted to the semiconductor layer  32   a  using the gate electrode  32   c  as a mask, after which heating is performed for the purpose of activating the implanted impurities, thereby forming a source electrode  32   d  and a drain electrode  32   e  on the semiconductor layer  32   a . As a result, each of the TFTs  32  is formed. 
     After a first insulation layer  33  is formed on the overall surface including the TFTs  32 , a contact  34  is formed so as to be connected with the source electrode  32   d  and the drain electrode  32   e  of each TFT  32  through the first insulation layer  33  and the gate insulation layer  32   b , and a second insulation layer  35  is formed on the overall surface thereof. 
     Then, as shown in  FIGS. 3B and 4B , a flattening insulation layer  36  is formed on the second insulation layer  35 , and selectively removed along with the second insulation layer  35  so as to expose the surface of the contact  14  connected with the drain electrode  32   e , thereby forming a first contact hole  37 . 
     Then, as shown in  FIGS. 3C and 4C , a partition wall  38  is formed at a portion (boundary between unit pixel regions) designed to divide anode electrodes (first electrodes) from each other. 
     At this time, the partition wall  38  is formed to an overhang structure wherein an upper portion of the partition wall is wider than a lower portion. 
     For example, the partition wall  38  may have an inversed trapezoidal-shape as shown in  FIG. 5A  or an eave shape as shown in  FIGS. 5B and 5C . Alternatively, the partition wall may have a multiple-layer shape as shown in  FIGS. 5D and 5E , and be made of organic material, inorganic material, metal or a combination thereof. 
     At this time, when manufacturing the device by forming the anode electrodes directly on the second insulation layer  35  which is used to manufacture the TFT substrate without using a flattening insulation layer  36 , the step shown in  FIGS. 3B and 4B  is omitted. 
     In other words, the partition wall  38  is formed directly on the flattening insulation layer  36 . 
     Herein, the structure having the flattening insulation layer  36  will be described. 
     Next, as shown in  FIGS. 3D and 4D , an anode electrode material  39  is deposited on the overall surface so as to allow the first contact hole  37  to be filled therewith. 
     As for the anode electrode material  39 , a conductive material having good reflectance, in particular, metallic materials including Cr, Cu, W, Au, Ni, Al, AlNd, Ag, Ti, Ta, etc., alloys thereof or a lamination thereof can be used. 
     Since the partition wall  38  is formed at the portion which will divide the anode electrodes from each other, the anode electrodes  39  are automatically divided from each other when depositing the anode electrode material  39 . 
     In other words, the anode electrode material  39  is formed on the partition wall  38  as well as the flattening insulation layer  36 , at which the anode electrode material  39  on the partition wall  38  is automatically divided from the anode electrode material  39  on the flattening insulation layer  36 , thereby allowing the anode electrodes  39  to be formed on the flattening insulation layer  36 . 
     The anode electrode material  39  on the partition wall  38  may be formed to have a thickness in a range of about 500-2000 Å. Also, the anode electrode material  39  on the flattening insulating layer  36  may be formed to have a thickness in a range of about 500-2000 Å. 
     Next, as shown in  FIGS. 3E and 4E , an insulation part  40  is formed on the overall surface other than a light emitting region (unit pixel region). At this time, the portion where the insulation part  40  is not formed will become a light emitting pixel. 
     As for the insulation part  40 , an organic insulator or an inorganic insulator is used. 
     At this time, when the insulation part  40  comprises the organic insulator, the insulation part  40  preferably comprises SiN x  or SiO x , and when the insulation part  40  comprises the inorganic insulator, the insulation part  40  preferably comprises polyimide, poly-acryl, or novolac-based material. 
     Finally, an organic EL layer is formed on the overall surface including the insulation part  40 , and a cathode electrode (second electrode) is formed on the organic EL layer, thereby completing the organic EL device of the present invention. 
     However, with the top-emission type organic EL device constructed as described above does, the problem of the prior art is not completely solved. The most important problem of the top-emission type organic EL device constructed as described above is in its structure. 
     In other words, since light advances upwardly towards each cathode electrodes, the cathode electrode must be transparent, and thus suffers from high resistance. 
     Thus, even though it is necessary to form a subsidiary electrode for each cathode electrode, a satisfactory method has not been yet developed due to weakness of the organic EL layer against moisture and oxygen. 
     According to the present invention, such a problem can be solved by constituting the anode electrode material formed on the partition wall so as to be used as a subsidiary electrode  39  when the anode electrode material  39  is deposited on the overall surface such that the first contact hole  37  is filled with the anode electrode material, as shown in  FIGS. 3D and 4D . 
     To this end, when forming the insulation part  40  at the portion excluding the light emitting region, as shown in  FIGS. 3E and 4E , a second contact hole  41  is formed on the insulation part  40  so as to expose the anode electrode material (subsidiary material  39 ) on the partition wall  38 , as shown in  FIGS. 6A and 6B . 
     At this time, the shape or the number of the second contact holes  41  is not important. 
     Then, an organic EL layer is formed on the substrate constructed as shown in  FIG. 7A  by depositing an organic layer on each of R, G and B pixels in the pixel regions for light emission using a shadow mask having openings corresponding to the pixel regions as shown in  FIG. 7B  while moving the shadow mask as shown in  FIGS. 7C and 7E . 
     At this time, as shown in  FIG. 8 , the shadow mask is structured such that the second contact holes  41  formed to expose the subsidiary electrodes  39  on the partition walls  38  are shielded by the shadow mask  42  when depositing the RGB organic layer  43  while allowing the openings of the shadow mask to correspond only to the pixel regions. 
     Finally, as shown in  FIG. 7F , the cathode electrode  44  is formed on the overall surface including the organic EL layer and the second contact holes  41 , thereby completing the organic EL device according to the present invention. 
     At this time, as shown in  FIG. 9 , RGB organic EL layers  43   a ,  43   b  and  43   c  are not formed on the anode electrode material  39  exposed through the second contact holes  41  on the partition wall  38 . Instead, the cathode electrode  44  is directly deposited on the anode electrode material  39 , and connected with a connection part  45  so that the anode electrode material  39  naturally serves as the subsidiary electrode  39  for the cathode electrode. 
     The cathode electrode  44  may be composed of a metal and ITO (indium tin oxide), or metal only. The thickness range of the ITO may be 500-2000 Å and the thickness range of the metal may be 50-250 Å. Accordingly, the entire thickness of the cathode electrode may be in a range of 50-2250 Å. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.