Patent Publication Number: US-7211944-B2

Title: Dual panel-type organic electroluminescent display device and method of fabricating the same

Description:
The present invention claims the benefit of Korean Patent Application No. 2002-79510, filed in Korea on Dec. 13, 2002, which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a flat panel display device, and more particularly, to an organic electroluminescent display (OELD) device and method of fabricating an OELD device. 
     2. Discussion of the Related Art 
     Liquid crystal display (LCD) devices have been commonly used in flat panel display devices because of their light weight and low power consumption. However, the liquid crystal display (LCD) devices are not light emitting elements, but are light receiving elements that require additional light sources to display images. Accordingly, there is a technical limit for improving brightness, contrast ratio, viewing angle, and enlarging a size of liquid crystal display panels. Thus, research has developed new flat panel display elements that can overcome the aforementioned problems. 
     Organic electroluminescent display (OELD) devices emit their own light and their viewing angles and contrast ratios are superior compared to the liquid crystal display (LCD) devices. In addition, since OELD device do not require a backlight device to function as a light source, the OELD devices are light weight, have small dimensions, and have low power consumption. Moreover, OELD devices can be driven with low DC (direct current) and have fast response times. Since the OELD devices use solid material instead of fluid material, such as liquid crystal, they are more stable under external impact and have wider operational temperature ranges than the liquid crystal display (LCD) devices. As compared to LCD devices, the OELD devices have relatively low production costs. For example, the OELD devices generally require deposition and encapsulation apparatus, whereas the LCD devices require many different types of fabrication apparatus. In addition, fabrication processes for manufacturing the OELD device are much simpler than the fabrication process for manufacturing the LCD devices. 
     The OELD devices may be classified into passive matrix-type and active matrix-type devices. In the passive matrix-type OELD devices, pixels are formed in a matrix configuration by crossings of scan and signal lines, wherein the scan lines must be sequentially driven to drive each pixel. Accordingly, a required average luminance depends on a total number of the scan lines. However, in the active matrix-type OELD devices, a thin film transistor (i.e., a switching element) is formed in each sub-pixel to switch the pixel ON and OFF, wherein a first electrode connected to the thin film transistor is turned ON and OFF by the pixel and a second electrode functions as a common electrode. 
     Moreover, in the active matrix-type OELD devices, a voltage that is supplied to the pixel is stored to a storage capacitor C St  and maintained until a signal for the next frame is applied. Accordingly, the pixel can retain the signal until the next frame regardless of the number of the scan lines. Since the active matrix-type OELD devices can obtain a same luminance with low direct current (DC), the active matrix-type OELD devices are advantageous due to their low power consumption, high resolution, and large size. 
       FIG. 1  is a schematic circuit diagram of a pixel of an active matrix OELD device according to the related art. In  FIG. 1 , a scan line  2  is formed along a first direction and signal and power supply lines  4  and  6  are formed along a second direction perpendicular to the first direction. The signal line  4  and the power supply line  6  are spaced apart from each other and define a sub-pixel by crossing the scan line  2 , wherein a switching thin film transistor  8  (i.e., an addressing element) is formed at a position near an intersection of the scan and signal lines  2  and  4  and a storage capacitor (C ST )  12  is electrically connected to the switching thin film transistor  8  and the power supply line  6 . A driving thin film transistor  10  (i.e., a current source element) is electrically connected to the storage capacitor (C ST )  12  and the power supply line  6 , and an organic electroluminescent diode  14  is electrically connected to the driving thin film transistor  10 . Accordingly, if current is supplied to organic light-emitting material of the OELD device along a positive direction, electrons and holes are recombined by passing through a P-N junction between an anode electrode for proving holes and a cathode electrode for proving electrons. The combined electron and the hole have a lower energy state than when the electron and the hole are not recombined and separated away. Accordingly, the OELD device makes use of energy states of the recombined electrons and holes to produce light. In addition, the OELD device can be classified into top emission-type and bottom emission-type OELD devices according to a light emission direction. 
       FIG. 2  is a cross sectional view of a bottom emission-type OELD device according to the related art. In  FIG. 2 , a pixel P includes sub-pixels SP for red (R), green (G), and blue (B) colors, wherein first and second substrates  10  and  30  are spaced apart from and oppose each other. A seal pattern  40  is formed on one of the first and second substrates  10  and  30  to attach the first and second substrates  10  and  30  and to prevent liquid crystal material injected between the first and second substrates  10  and  30  from leaking out. A plurality of thin film transistors T and a plurality of first electrodes  12  connected to the thin film transistor is formed within each sub-pixel SP on a transparent substrate  1  of the first substrate  10 . An organic light-emitting layer  14  connected to the thin film transistor T is formed on the thin film transistor T and the first electrode  12 , wherein the organic light-emitting layer  14  has portions for red (R), green (G), and blue (B) colors corresponding to the first electrode  12 . In addition, a second electrode  16  is formed on the organic light-emitting layer  14 , wherein the first and second electrodes  12  and  16  serve to supply an electric field to the organic light-emitting layer  14  and the second electrode  16  is spaced apart from the second substrate  30  by the aforementioned seal pattern  40 . Although not shown, a moisture absorbent desiccant is formed on an inner side of the second substrate  30  and a semitransparent tape is used to attach the moisture absorbent desiccant to the second substrate  30 . 
     If the first electrode  12  functions as an anode electrode and the second electrode  16  functions as a cathode electrode, then the first electrode  12  is formed of transparent conductive material and the second electrode  16  is formed of material having a low work function. Accordingly, the organic light-emitting layer  14  has a sequential laminated structure of a hole injection layer  14   a , a hole transporting layer  14   b , an emission layer  14   c , and an electron transporting layer  14   d . The emission layer  14   c  has a structure in which light emitting materials for each of the red (R), green (G), and blue (B) colors are sequentially arranged corresponding to each of the sub-pixels SP. 
       FIG. 3  is an enlarged view of a sub-pixel region SP of  FIG. 2  according to the related art. In  FIG. 3 , the sub-pixel region SP (in  FIG. 2 ) includes a light emission region, a TFT region, and a storage capacitor region. In the TFT region, a semiconductor layer  62 , a gate electrode  68 , and source and drain electrodes  80  and  82  are sequentially formed on a transparent substrate  1 , thereby forming a thin film transistor T (in  FIG. 2 ). A power electrode  72  extending from a power supply line (not shown) and an organic electroluminescent diode E are connected to the source electrode  80  and the drain electrode  82 , respectively. In the storage capactor region, a capacitor electrode  64  is formed under the power electrode  72  using the same material as that of the semiconductor layer  62 , and an insulating layer is disposed between the power electrode  72  and the capacitor electrode  64 , wherein the capacitor electrode  64 , the insulating layer, and the power electrode  72  form a storage capacitor. In the light emission region, the organic electroluminescent diode E has first and second electrodes  12  and  16 , and an organic light-emitting layer  14  interposed between the first and second electrodes  12  and  16 . 
       FIG. 4  is a flow chart of a fabrication sequence of an OELD device according to the related art. In  FIG. 4 , a first step ST 1  includes forming array elements, such as scan lines, signal lines, power lines, switching thin film transistors and driving thin film transistors, on a first substrate. The scan lines are formed on a transparent substrate extending along a first direction and the signal and power lines are formed on the transparent substrate extending along a second direction perpendicular to the first direction, wherein the signal and power lines cross the scan lines and are spaced apart from each other. In addition, each of the switching thin film transistors are formed near intersections of the scan and signal lines, and each of the driving thin film transistors are formed near intersections of the scan and power lines. 
     A second step (ST 2 ) includes patterning a first electrode, which is a first component of an organic electroluminescent diode and is connected to the driving thin film transistor, within each sub-pixel region. 
     A third step (ST 3 ) includes forming an organic light-emitting layer, which is a second component of the organic electroluminescent diode, on the first electrode. If the first electrode functions as an anode electrode, the organic light-emitting layer may be formed in a sequence of a hole injection layer, a hole transporting layer, an emission layer, and an electron transporting layer from a top surface of the first electrode. 
     A fourth step (ST 4 ) includes forming a second electrode, which is a third component of the organic electroluminescent diode, on the light-emitting layer, wherein the second electrode is formed on an entire surface of the first substrate to function as a common electrode. 
     A fifth step (ST 5 ) includes encapsulating the first substrate with a second substrate to protect the first substrate from external impact and to protect the organic light-emitting layer from being damaged by an infiltration of exterior air. Thus, an absorbent desiccant is further formed in an inner surface of the second substrate. 
     The bottom emission-type OELD devices are completed by attaching the encapsulated substrate upon which the array element layer and the organic electroluminescent diode are formed to an additional encapsulating substrate. If the array element layer and the organic electroluminescent diode are formed on the same substrate, then panel yield is dependent upon the product of the individual yields of the array element layer and the organic electroluminescent diode. However, the panel yield is greatly affected by the yield of the organic electroluminescent diode. Accordingly, if a defective organic electroluminescent diode is fabricated, which usually is caused by formation of thin films having thicknesses of 1000 Å contaminated by impurities, the panel is classified as an inferior panel. Thus, production costs and materials are lost, thereby decreasing the panel yield. 
     The bottom emission-type organic OELD devices are advantageous because of their high image stability and variable fabrication processing. However, the bottom emission-type OELD devices are not adequate for implementation in devices that require high resolution due to limitations of increased aperture ratios. In addition, since top emission-type OELD devices emit light upward through the substrate, the light can be emitted without undue influence by the thin film transistor that is positioned under the light-emitting layer. Accordingly, design of the thin film transistor may be simplified. In addition, the aperture ratio can be increased, thereby increasing an operational life span of the OELD device. However, since a cathode is commonly formed over the organic light-emitting layer in the top emission-type OELD devices, material selection and light transmittance are limited such that light transmission efficiency is lowered. If a thin film-type passivation layer is formed to prevent a reduction of the light transmittance, the thin film passivation layer may fail to prevent infiltration of exterior air into the device. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to an organic electroluminescent display (OELD) device and method of fabricating an organic electroluminescent display (OELD) device that substantially obviates one or more of problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide an OELD device having an improved electrode structure. 
     Another object of the present invention is to provide an OELD device having improved contact electrodes. 
     An object of the present invention is to provide a method of fabricating an OELD device having an improved electrode structure. 
     Another object of the present invention is to provide a method of fabricating an OELD device having improved contact electrodes. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will 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 and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an organic electroluminescent display (ELD) device includes first and second substrates having a plurality of sub-pixels defined thereon, an array element layer on the first substrate having a plurality of thin film transistors corresponding to each of the sub-pixels, a connecting electrode on the array element layer connected to one of the thin film transistors, a first electrode on an inner surface of the second substrate, an insulating layer and an electrode separator formed within a boundary region of each of the sub-pixels, the insulating layer formed beneath the first electrode and the electrode separator formed beneath the insulating layer, and an organic light-emitting layer and a second electrode formed in each of the sub-pixels, wherein the electrode separator includes a first region having a pattern structure for separately forming the organic light-emitting layer and the second electrode within each of the sub-pixels, a second region having a pattern structure for directly contacting the connecting electrode with the second electrode under the electrode separator, and a third region having a pattern structure for preventing an electrical short between a second electrode portion in the first region and a second electrode portion in the second region, and wherein the second electrode formed within a space corresponding to the second region contacts the connecting electrode. 
     In another aspect, a method of fabricating an organic electroluminescent display (ELD) device having a first substrate including an array element layer comprising a thin film transistor, a second substrate having an organic electroluminescent diode, and a connecting electrode between the first and second substrates, the method includes forming a first electrode on the second substrate having a plurality of sub-pixels, forming an insulating layer and an electrode separator within a boundary of each of the sub-pixels, and forming an organic light-emitting layer and a second electrode within each of the sub-pixels separated by the electrode separator, wherein the electrode separator includes a first region having a trapezoidal shape with a width gradually increasing from a bottom surface and to a top surface, a second region having an asymmetrical shape with a first inverse-tapered lateral side and a second lateral side inclined toward the first lateral side, and a third region having a plurality of depressed portions spaced apart from each other and disposed between the first and second regions, and wherein the second electrode is formed within a space corresponding to the second region and contacts the connecting electrode. 
     In another aspect, a method for fabricating an organic electroluminescent display (ELD) device includes forming an array element layer having a plurality of thin film transistors on a first substrate upon which a first plurality of sub-pixels is defined, forming a connecting electrode connected to the thin film transistor on the array element layer, forming a first electrode on a second substrate upon which a second plurality of sub-pixels is defined that correspond to the first plurality of sub-pixels, forming an insulating layer and an electrode separator within a boundary of each of the first and second plurality of sub-pixels, forming an organic light-emitting layer and a second electrode within each of the first and second plurality of sub-pixels separated by the electrode separator, and attaching the first and second substrates together, wherein the electrode separator has a first region having a trapezoidal shape with a width gradually increasing from a bottom surface and to a top surface, a second region having an asymmetrical shape with a first inverse-tapered lateral side and a second lateral side inclined toward the first lateral side, and a third region having a plurality of depressed portions spaced apart from each other and disposed between the first and second regions, and wherein the second electrode is formed within a space corresponding to the second region and contacts the connecting electrode. 
     It is to be understood that both the foregoing general description and the following detailed description 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 specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a schematic circuit diagram of a pixel of an active matrix OELD device according to the related art; 
         FIG. 2  is a cross sectional view of a bottom emission-type OELD device according to the related art; 
         FIG. 3  is an enlarged view of a sub-pixel SP region of  FIG. 2  according to the related art; 
         FIG. 4  is a flow chart of a fabrication sequence of an OELD device according to the related art; 
         FIG. 5  is a cross sectional view of an exemplary dual panel-type OELD device according to the present invention; 
         FIG. 6  is a plan view of an exemplary dual panel-type OELD device according to the present invention; 
         FIG. 7A  is a cross sectional view along I—I of  FIG. 6  according to the present invention; 
         FIG. 7B  is a cross sectional view along II—II of  FIG. 6  according to the present invention; 
         FIG. 7C  is a cross sectional view along III—III of  FIG. 6  according to the present invention; 
         FIG. 8  is a flow chart of an exemplary fabrication sequence for an organic electroluminescent diode of a dual panel-type OELD device according to the present invention; 
         FIG. 9  is a cross sectional view of an exemplary array substrate for a dual panel-type OELD device according to the present invention; 
         FIG. 10  is a cross sectional view of another exemplary array substrate for a dual panel-type OELD device according to the present invention; and 
         FIG. 11  is a flow chart of another exemplary fabrication sequence for a dual panel-type OELD device according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, which are illustrated in the accompanying drawings. 
       FIG. 5  is a cross sectional view of an exemplary dual panel-type OELD device according to the present invention. For sake of brevity, a portion of the dual panel-type OELD device near a driving thin film transistor is shown, and a storage capacitor and a switching thin film transistor are excluded from being shown. In  FIG. 5 , first and second substrates  110  and  150  may be spaced apart from and oppose each other, wherein a plurality of sub-pixels SP may be defined on the first and second substrates  110  and  150 . An array element layer  140  having a plurality of thin film transistors TFT corresponding to each the sub-pixels SP may be formed on the first substrate  110 , and a connecting electrode  132  connected to the thin film transistor T may be formed on the array element layer  140 . A first electrode  152  may be formed on an inner surface of the second substrate  150 , and an insulating layer  154  and an electrode separator  156  may be formed near a boundary of each of the sub-pixels SP. An organic light-emitting layer  158  and a second electrode  160  may be formed within each of the sub-pixels SP in space between the electrode separators  156  without using an additional patterning process. The first and second electrodes  152  and  160  and the light-emitting layer  158  form an organic electroluminescent diode E. 
     Although not shown, the electrode separator  156  may have a frame structure formed along boundaries of the sub-pixels SP, and may include first, second, and third regions. The first region may separate the second electrode within one of the sub-pixels SP from the second electrode in an adjacent one of the sub-pixels SP. The second region may include a region where the connecting electrode  132  is connected to the second electrode  160 . The third region disposed between the first and second regions may prevent an electrical short of the second electrodes in the adjacent ones of the sub-pixels SP. The electrode separator  156  may correspond to the second region, and the connecting electrode  132  may be electrically connected to a bottom surface of the second electrode  160  formed within each of the sub-pixels SP. 
     The first and second substrates  110  and  150  may be attached together by a seal pattern  170  formed on one of the first and second substrates  110  and  150 . An inert gas or a liquid may be injected into a space between the attached first and second substrates  110  and  150  to prevent exposure of a laminated structure of the OELD device to moisture and ambient air. A buffer layer  112  may be formed along an entire surface of the first substrate  110 , and a semiconductor layer  114  having an active region I, a source region II, and a drain region III within each of the sub-pixels SP may be formed on the buffer layer  112 . The source and drain regions II and III may be disposed on both sides of the active region I, and a gate insulating layer  116  and the gate electrode  118  may be sequentially formed on the active region I. 
     A first passivation layer  124  having a first and second contact holes  120  and  122  for exposing portions of the source and drain regions II and III, respectively, may be formed on an entire surface of the first substrate  110  upon which the gate insulating layer  116  and the gate electrode  118  may be formed. Source and drain electrodes  126  and  128  may be formed on the first passivation layer  124 , and may be electrically connected to the source and drain regions II and III via the first and second contact holes  120  and  122 , respectively. In addition, a second passivation layer  131  having a third contact hole  130  for exposing a portion of the drain electrode  128  may be formed on an entire surface of the first substrate  110  upon which the source and drain electrodes  126  and  128  may be formed. A connecting electrode  132  may be formed on the second passivation layer  132 , and may be electrically connected to the drain electrode  128  via the third contact hole  130 . The connecting electrode  132  may contact a bottom surface of the second electrode  160  that is formed under the electrode separator  156 , whereby current may flow from the drain electrode  128  to the second electrode  160 . The semiconductor layer  114 , the gate electrode  118 , and the source and drain electrodes  126  and  128  form a driving thin film transistor T. Although not shown, a storage capacitor connected to the driving thin film transistor T and a switching thin film transistor connected to the gate electrode  118  of the driving thin film transistor T may be further formed in each of the sub-pixels SP. 
       FIG. 6  is a plan view of an exemplary dual panel-type OELD device according to the present invention. In  FIG. 6 , an electrode separator  210  may be formed along boundaries of the sub-pixels SP for red (R), green (G), and blue (B) colors, and a second electrode  212  may be separately formed within each of the sub-pixels SP by the electrode separator  210 . The electrode separator  210  may include a first region IV, a second region V, and a third region VI. The first region IV may function to separate the second electrode  212  for each of the sub-pixels SP. The second region V may function to directly connect the connecting electrode (not shown) to the second electrode  212  under the electrode separator  210 . The third region VI may be disposed between the first and second regions IV and V, and may function to prevent electrical shorting of the second electrodes  212  between the first region IV and the second region V. The electrode separator  210  having the first, second, and third regions IV, V, and VI may be formed in a body, as shown in  FIG. 6 , but each region of the first, second, and third regions IV, V, and VI may have a different pattern structure. 
       FIG. 7A  is a cross sectional view along I—I of  FIG. 6  according to the present invention,  FIG. 7B  is a cross sectional view along II—II of  FIG. 6  according to the present invention, and  FIG. 7C  is a cross sectional view along III—III of  FIG. 6  according to the present invention.  FIGS. 7A ,  7 B, and  7 C correspond to the first, second, and third regions IV, V and VI in  FIG. 6 . In  FIG. 7A , a first electrode  252  may be formed on a substrate  250  upon which a plurality of sub-pixels SP may be defined. An insulating layer  254  and an electrode separator  256  may be sequentially formed on the first electrode  252  within space corresponding to a boundary region of adjacent ones of the sub-pixels SP. An organic light-emitting layer  258  and a second electrode  260  may be separately formed within each of the sub-pixels SP by the electrode separator  256 . 
     In  FIG. 7A , a pattern structure of the electrode separator  256  corresponding to the first region IV and the electrode separator corresponding to the first region IV may have a trapezoidal pattern whose width increases from a bottom surface to a top surface of the electrode separator  256 . The organic light-emitting layer  258  and the second electrode  260  may be sequentially formed within the sub-pixels SP at both sides of the electrode separator  256 , and may be separated by the electrode separator  256 . Accordingly, if organic light-emitting material  257  and second electrode material  259  are sequentially formed on the substrate  250  upon which the electrode separator  256  may be formed, the electrode separator  256  may function as a mask to prevent residues of the organic light-emitting material  257  and the second electrode material  259  from contacting the organic light-emitting layer  258  and the second electrode  260 . Thus, organic light-emitting material  257  and second electrode material  259  may remain on a top surface of the electrode separator  256 . 
     In  FIG. 7B , the electrode separator  256  may have an asymmetrical structure with respect to a centerline of the insulating layer  254  under the electrode separator  256 . The second electrode  260  may directly contact the connecting electrode (not shown) within an electrode separator-forming region. Accordingly, since a first side of the electrode separator  256  may have a tapered shape, which may be similar to the electrode separator  256  (in  FIG. 7A ), and a second side of the electrode separator  256  may have a tapered shape as an opposing sides of the electrode separator  256 , the organic light-emitting layer  258  and the second electrode  260  on the left side of the electrode separator  256  are electrically separated from the organic light-emitting layer  258  and the second electrode  260  in an adjacent one of the sub-pixels SP on the right side of the electrode separator  256 . In addition, the organic light-emitting layer  258  and the second electrode  260  are formed along a tapered lateral side and along the top surface of the electrode separator  256 , Furthermore, the electrode separator  256  may be formed within a non-light emission region and the second electrode  260  may be formed on the top surface of the electrode separator  256  and may directly contact the connecting electrode (not shown). Thus, the connecting electrode (not shown) may be electrically connected to the second electrode  260  without forming an additional connecting pattern between the connecting electrode (not shown) and the second electrode  260  due to the electrode separator  256  being formed within the non-light emission region. 
     In  FIG. 7C , the electrode separator  256  may include a plurality of depressed portions  262  spaced apart from each other. Accordingly, the organic light-emitting material  257  and the second electrode material  259  may be sequentially formed on the electrode separator  256  and on bottom portions of the depressed portions  262  within the third region VI. The organic light-emitting material  257  and the second electrode material  259  formed on the electrode separator  256  within the second region V may function as the organic light-emitting layer  258  and the second electrode  260 , respectively. In addition, the depressed portion  262  may be formed to have a depth so as not to expose the insulating layer  254 , and may be patterned using photolithographic processes, such as diffraction exposure processes. 
       FIG. 8  is a flow chart of an exemplary fabrication sequence for an organic electroluminescent diode of a dual panel-type OELD device according to the present invention. In  FIG. 8 , a first step ST 1  may include forming a first electrode on a substrate upon which a plurality sub-pixels may be defined. The first electrode may be formed of transparent conductive material, such as indium tin oxide (ITO). 
     A second step ST 2  may include forming an insulating layer and an electrode separator on the first electrode within a boundary region between a first one of the sub-pixels and an adjacent one of the sub-pixels. The insulating layer may improve contact properties between the first electrode and the electrode separator, and may include insulating materials, such as silicon. For example, the insulating layer may be formed of inorganic insulating materials, such as silicon nitride (SiNx) and silicon oxide (SiO 2 ). 
     The electrode separator may include first, second, and third regions, wherein the electrode separator corresponding to the first region may have an inverse-tapered structure to separately form the organic light-emitting layer and the second electrode within each of the sub-pixels. The electrode separator corresponding to the second region may have an asymmetrically shape structure to cause the connecting electrode to directly contact the second electrode at an electrode separator forming region. The electrode separator corresponding to the third region may have a plurality of depressed portions to prevent an electrical short between the second electrodes within the first and second regions. 
     The electrode separator may be patterned using photolithographic processes using exposure developing processes of a photoresist material. The electrode separator corresponding to the third region and having a plurality of depressed portions may be formed by using a diffraction exposure method in which only desired portions are selectively exposed to light during the exposure process of the photolithographic processes. More specifically, if a positive-type photoresist material, which has portions that are exposed to light removed after the developing process, is used for forming the electrode separator, the electrode separator corresponding to the third region may be formed by disposing a mask having a slit-pattern corresponding to the depressed portions over the photoresist and then exposing the photoresist material to light. The slit-pattern corresponding to the depressed portions may reduce the light intensity within regions corresponding to the depressed portions of the electrode separator. 
     The electrode separator corresponding to the second region may have an asymmetrical shape structure with respect to a centerline thereof. That is, a first lateral side of the electrode separator may have an inverse-tapered structure so that the second electrode corresponding to the inverse-tapered side may be severed near the inverse-tapered side of the electrode separator. A second lateral side of the electrode separator may have a slope so that the second electrode corresponding to the sloped side is continuously formed within the sub-pixel and is disposed on the sloped side and on a top surface of the electrode separator. Accordingly, a connecting electrode may be electrically connected to the second electrode by directly contacting the second electrode. 
     The tapered side structure of the electrode separator may be formed by controlling a width of a light transmission portion and an interval between the light transmission portions formed in the mask used during the photolithographic processes. For example, if a positive-type photoresist material is used for forming the electrode separator, the electrode separator having a sloped lateral side may be formed by gradually narrowing the width of the light transmission portion and the interval between the light transmission portions from a middle portion to a side portion of the electrode separator. 
     A third step (ST 3 ) may include sequentially forming an organic light-emitting layer material and second electrode material onto the substrate upon which the electrode separator may be formed, thereby forming an organic light-emitting layer and a second electrode within each of the sub-pixels. The organic light-emitting layer and the second electrode may be separately formed within each of the sub-pixels by the electrode separator formed within a boundary region between adjacent ones of the sub-pixels. The organic light-emitting layer and the second electrode corresponding to the second region of the electrode separator may be further formed along the sloped lateral side and on top surface of the electrode separator having the asymmetrical shape structure so that the connecting electrode may directly contact the second electrode. While portions of the organic light-emitting layer material and the second electrode material on top of the electrode separators corresponding to the first and third regions may not function as the organic light-emitting layer and the second electrode, respectively, the organic light-emitting layer material and the second electrode material on the electrode separator corresponding to the second region may function as the organic light-emitting layer and the second electrode. If the first electrode is an anode electrode and the second electrode is a cathode electrode, then the organic light-emitting layer may have a laminated structure including a sequence of a hole injection layer, a hole transporting layer, an emission layer, and an electron transporting layer. 
       FIG. 9  is a cross sectional view of an exemplary array substrate for a dual panel-type OELD device according to the present invention. In  FIG. 9 , a gate electrode  312  and a first pattern  314 , which may be spaced apart from the gate electrode  312 , may be formed on a substrate  310  using a first metal material. A gate insulating layer  316  may be formed along an entire surface of the substrate  310  upon which the gate electrode  312  and the first pattern  314  may be formed. A first semiconductor pattern  318  may cover the gate electrode  312  and a second semiconductor pattern  320  may cover the first pattern  314  using first and second semiconductor materials. For example, the first semiconductor pattern  318  may include a laminated structure of an active layer  318   a  and an ohmic contact layer  318   b , and the second semiconductor pattern  320  may include a laminated structure of first and second layers  320   a  and  320   b . The active layer  318   a  and the first layer  320   a  may include amorphous silicon, and the ohmic contact layer  318   b  and the second layer  320   b  may include impurity-doped amorphous silicon. Source and drain electrodes  322  and  324  may be spaced apart from each other, and may be formed on the ohmic contact layer  318   b . In addition, a third pattern  326  is formed on the second semiconductor pattern  320 , wherein the source and drain electrodes  322  and  324  and the third pattern  326  may be formed of the same conductive materials. Accordingly, the gate electrode  312 , the first semiconductor pattern  318 , and the source and drain electrodes  322  and  324  form a thin film transistor T. 
     In  FIG. 9 , an interlayer  330  having a first contact hole  328  for exposing a portion of the source electrode  322  may formed along an entire surface of the substrate  310  upon which the source and drain electrodes  322  and  324  and the third pattern  326  may be formed. A power supply line  332  contacting a portion of the source electrode  322  via the first contact hole  328  may be formed on the interlayer  330 , and a fourth pattern  336  may be formed on the interlayer  330  within a space corresponding to the third pattern  326  using the same materials as the power supply line  332 . A passivation layer  340  having a drain contact hole  338  for exposing a portion of the drain electrode  324  may be formed along an entire surface of the substrate  310  upon which the power supply line  332  and the fourth pattern  336  may be formed. A connecting electrode  342  that contacts a portion of the drain electrode  324  via the drain contact hole  338  may be formed on the passivation layer  340 . Although not shown, the power supply line  332  may serve to provide a signal for power supplying to the thin film transistor T. 
     In  FIG. 9 , a connecting electrode  342  may be further formed to cover the fourth pattern  336 . An area on the substrate  310  where the first, second, third, and fourth patterns  314 ,  320 ,  326 , and  336  and the connecting electrode  342  overlap may form a projected region VII. A first height H 1  of the projected region VII may be larger than a second height H 2  of a thin film transistor region TR. 
     Accordingly, a second electrode  160  (in  FIG. 5 ) that may be formed beneath the electrode separator  156  (in  FIG. 5 ) may directly contact the connecting electrode  342 . In addition, the second electrode  160  (in  FIG. 5 ) may be connected to the connecting electrode  342  within space corresponding to the projected region VII. Thus, if the first height H 1  of the projected region VII having a laminated structure of first, second, third, and fourth patterns  314 ,  320 ,  326 , and  336  and the connecting electrode  342  is lower than the second height H 2  of the thin film transistor region TR, then the electrode separator  156  (in  FIG. 5 ) having a certain height may fail to contact the connecting electrode  342  due to a distance between the connecting electrode  342  and an upper substrate (not shown). In addition, there is a limit in forming the electrode separator  156  (in  FIG. 5 ) to have a certain height. If the electrode separator  156  (in  FIG. 5 ) fails to properly contact the connecting electrode  342 , it may cause poor electrical connection properties between a sub-pixel and an adjacent sub-pixel, thereby causing a defective array element. 
     To overcome aforementioned problems, the first height H 1  of the laminated structure corresponding to the projected region VII may be formed higher than the second height H 2  of the laminated structure corresponding to the thin film transistor region TR. The first, second, third, and fourth patterns  314 ,  320 ,  326  and  336  may not be electrically connected to any component of the array elements and may be simultaneously formed with the gate electrode  312 , the semiconductor layer  318 , the source and drain electrodes  322  and  324 , and the power supply line without any additional fabrication processes. 
     In  FIG. 5 , the thin film transistor T may be a driving thin film transistor connected to the organic electroluminescent diode E. Although the thin film transistor T having the inverted staggered-type gate structure is shown in  FIG. 5 , the present invention may be applied to other OELD devices having different types of thin film transistors, for example, a thin film transistor having a top gate structure. 
       FIG. 10  is a cross sectional view of another exemplary array substrate for a dual panel-type OELD device according to the present invention. In  FIG. 10 , an OELD device may include a thin film transistor region TR, which may having a thin film transistor T, and a projected region VIII, which may have an additional projected pattern  442  formed to increase a height of a laminated structure corresponding to the projected region VIII. While many laminated layers such as the first, second, third, and fourth patterns  314 ,  320 ,  326 , and  336  (in  FIG. 9 ) may be formed within the projected region VII (in  FIG. 9 ) to raise the first height H 1  of the laminated structure corresponding to the projected region VII, the additional projected pattern  442  may be formed to raise a first height H 11  of a laminated structure corresponding to the projected region VIII. 
     In  FIG. 10 , the thin film transistor T may include a gate electrode  412 , a semiconductor layer  418 , and source and drain electrodes  422  and  424  formed on a substrate  410 . An interlayer  430  having a first contact hole  428  for exposing a portion of the source electrode  422  may be formed along an entire surface of the substrate  410  upon which the source and drain electrodes  422  and  424  may be formed. A power supply line  432  connected to the source electrode  422  via the first contact hole  428  may be formed on the interlayer  430 . A passivation layer  440  having a drain contact hole  438  for exposing a portion of the drain electrode  424  may be formed along an entire surface of the substrate  410  upon which the power supply line  432  may be formed. The projected pattern  442  spaced apart from the thin film transistor T may be formed on the passivation layer  440  within space corresponding to the projected region VIII. A connecting electrode  444  connected to the drain electrode  424  via the drain contact hole  438  may be formed on the projected pattern  442  and a portion of the passivation layer  440 . 
     The projected pattern  442  corresponding to the projected region VIII and a first height H 11  of a laminated structure corresponding to the projected region VIII may be higher than a second height H 22  of a laminated structure corresponding to the thin film transistor region TR. The projected pattern  442  may be formed of insulating material, such as an organic insulating material, in order to form the projected pattern  442  to have a relatively large thickness. 
       FIG. 11  is a flow chart of another exemplary fabrication sequence for a dual panel-type OELD device according to the present invention. A first step ST 1  may include forming an organic electroluminescent diode having a plurality of electrode separators having first, second, and third regions on a second substrate. For example, the first step ST 1  may comprise steps of defining a plurality of sub-pixels on first and second substrates, forming a first electrode on the second substrate, forming an insulating layer and an electrode separator on the first electrode in a boundary of sub-pixel, and forming an organic light-emitting layer and a second electrode in each pixel. 
     The electrode separator may include first, second, and third regions. The first region of the electrode separator may have a trapezoidal shape whose opposing lateral sides have inverse-tapered surfaces. The second region of the electrode separator may have an asymmetrical shape whose first lateral side is inversely tapered and a second lateral side is inclined. The third region disposed between the first and second regions may have a plurality of depressed portions. The electrode separator having the first, second, and third regions may be patterned by a diffraction exposure method in which light intensity is selectively controlled by a mask according to a width of a light transmission portion and an interval between the light transmission portions. 
     A second step ST 2  includes forming a thin film transistor within a thin film transistor region and forming a laminated structure having a height higher than that of the thin film transistor region within a projected region. For example, a gate electrode, a semiconductor layer, a source electrode, a drain electrode, and a power supply line may be formed during the forming of the thin film transistor within the thin film transistor region. The laminated structure of the projected region may have a height larger than the laminated structure of the thin film transistor region and may provide an area for contacting the second region of the electrode separator and a connecting electrode. The height of the laminated structure of the projected region may be increased by forming first, second, third, and fourth patterns within the projected region simultaneously with formation of the gate electrode, the semiconductor layer, the source electrode, the drain electrode, and the power supply line, respectively. Alternatively, the height of the laminated structure of the projected region may be increased by forming an additional projected pattern after forming a passivation layer over the thin film transistor. The projected pattern may be formed of organic insulating material. 
     A third step (ST 3 ) may include attaching the first and second substrates together. Accordingly, an array element layer on the first substrate may be electrically connected to an organic electroluminescent diode on the second substrate by contacting a portion of the second electrode formed within the second region of the electrode separator with the connecting electrode formed over the projected region. 
     According to the present invention, the OELD device has the following advantages. First, since the array element layer and the organic electroluminescent diode may be formed on a different substrate, production yield, production management efficiency, and life cycle of the device may be improved. Second, since the dual panel-type OELD device may function as a top emission-type OELD device, design of the thin film transistor may be simplified and high aperture ratio and high resolution may be achieved. Third, since the connecting electrode may directly contact the second electrode formed on the electrode separator, additional connecting patterns for connecting the connecting electrode to the second electrode may not be necessary. Fourth, since the connecting electrode may be connected to the second electrode at the electrode separator forming region within the non-light emitting region, damage to the light-emitting region may be avoided. Fifth, since laminated structures within the projected region having first, second, third, and fourth patterns may be formed simultaneously with the gate electrode, the semiconductor layer, the source and drain electrodes, and the power supply line, respectively, a height of the laminated structure within the thin film transistor region may be increased. Thus, electrical connection properties between the connecting electrode and the second electrode and between the array elements within a sub-pixel and the array element in an adjacent sub-pixel may be improved, thereby increasing production yield. Sixth, since the height of the projected region may be increased by forming a projected pattern on the passivation layer within space corresponding to the projected region instead of forming laminated patterns within the projected region, contact properties between the connecting electrode and the second electrode and between the array elements in a sub-pixel and the array element in an adjacent sub-pixel may be improved, thereby increasing production yield. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the dual panel-type organic electroluminescent display device and the method of fabricating dual panel-type organic electroluminescent display device of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.