Abstract:
A top-emitting organic light-emitting device can prevent a voltage drop by electrically coupling a cathode bus line to a cathode electrode. A method for fabricating the same is also disclosed. The flat panel display device comprises an insulating substrate having a pixel region and a non-pixel region, a first electrode arranged in the pixel region. a second electrode arranged in the pixel region and the non-pixel region, an organic emission layer and a charge transporting layer formed between the first electrode and the second electrode of the pixel region, and an electrode line formed in the pixel region and the non-pixel region. The electrode line and the second electrode are electrically and directly coupled to each other in the non-pixel region.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional application of U.S. patent application Ser. No. 10/924,890, filed on Aug. 25, 2004, which claims the benefit of Korea Patent Application No. 2003-70338 filed on Oct. 9, 2003, the disclosure of which are incorporated herein by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an active matrix type flat panel display device and, more particularly, to a top-emitting organic light-emitting device (OLED) capable of reducing or preventing a voltage drop, with a cathode bus line and a cathode electrode being electrically coupled and method for fabricating the same. 
         [0004]    2. Description of Background 
         [0005]    In general, an organic light emitting device is an emissive display device which may be classified into a bottom-emitting structure type and a top-emitting structure type based on the direction of light emitted from an organic emission layer. The top-emitting organic light-emitting device emits light in a direction opposite to a substrate where pixels are arranged, and may increase an aperture ratio when compared to the bottom-emitting structure which emits light toward the substrate where the pixels are arranged. 
         [0006]    The light is emitted toward the substrate for encapsulation in the top-emitting structure, so that a transparent electrode is used for a cathode electrode. A transparent conductive layer, such as ITO or IZO, is used for the transparent electrode. However, the transparent conductive layer may have a higher work function, so that it is difficult to use it for the cathode electrode. 
         [0007]    To cope with this problem, a thin metal having a lower work function is deposited on an organic emission layer for the cathode electrode to form a semitransparent metal layer. A thick transparent conductive layer is then deposited on the semitransparent metal layer to form a transparent electrode having a stacked structure. 
         [0008]    However, in the cathode electrode of the stacked structure, since the transparent conductive layer, such as ITO or IZO, is deposited after an organic thin-film layer is formed, a low temperature deposition process minimizes degradation of an electroluminescence (EL) layer due to heat or plasma. When the ITO or IZO is deposited at a lower temperature, film quality may become worse and specific resistance may become higher. 
         [0009]    The cathode electrode is a common electrode, and the same voltage should be applied to all pixels arranged in a pixel portion. However, a voltage drop (namely, an IR drop) occurs due to the high specific resistance of the cathode electrode. This causes different voltage levels to be applied to the pixels in accordance with their arranged positions. Thus, when a cathode voltage is applied from an external terminal to the cathode electrode, pixels arranged near the external terminal and pixels spaced apart from the external terminal do not have the same voltage, which causes the voltage drop. This voltage difference per pixel position may cause non-uniformity of luminance and/or image quality. 
         [0010]    In particular, the voltage drop problems may become more serious in a top-emitting organic light-emitting device of medium and large size. Korea Patent Application No. 2002-0057336 discloses a technique that uses a cathode bus line in the top-emitting structure. The cathode bus line is connected to an external terminal and contacts a cathode electrode, so that the cathode electrode is connected to the external terminal through the cathode bus line. 
         [0011]    The method for connecting the cathode bus line to the cathode electrode may prevent the voltage drop of the cathode electrode with respect to the pixel position. However, when a carrier transporting layer, such as an organic layer, is formed on the entire surface of the substrate between the cathode bus line and the cathode electrode, the cathode bus line and the cathode electrode are not electrically coupled to with each other. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention provides an organic light emitting device capable of performing entire surface deposition of a carrier transporting layer by electrically coupling a cathode bus line to a cathode electrode in a non-pixel region and method for fabricating the same. 
         [0013]    The present invention further provides an organic light emitting device capable of connecting a cathode bus line to a cathode electrode per pixel in a pixel region by depositing a carrier transporting layer by means of a fine metal mask and method for fabricating the same. 
         [0014]    The present invention also provides an organic light emitting device having a structure for connecting a cathode bus line to a cathode electrode suitable for the organic light emitting device of medium and large size and method for fabricating the same. 
         [0015]    To achieve the above purpose, one aspect of the present invention provides a flat panel display, which comprises an insulating substrate having a pixel region and a non-pixel region, a first electrode arranged in the pixel region, a second electrode arranged in the pixel region and the non-pixel region, an organic emission layer and a charge transporting layer formed between the first electrode and the second electrode of the pixel region, and an electrode line formed over the pixel region and the non-pixel region of the insulating substrate, wherein the electrode line and the second electrode are electrically contacted with each other in the non-pixel region. 
         [0016]    In addition, the present invention provides a method for fabricating a flat panel display, which comprises providing an insulating substrate having a pixel region and a non-pixel region, forming a first electrode on the pixel region of the insulating substrate, forming an organic emission layer and a charge transporting layer on the first electrode, forming an electrode line in the pixel region and the non-pixel region, forming a second electrode in the pixel region and the non-pixel region, wherein the electrode line and the second electrode are electrically contacted in the non-pixel region. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail preferred embodiments thereof with reference to the attached drawings. 
           [0018]      FIGS. 1A and 1B  illustrate plan views of an organic light emitting device in accordance with an embodiment of the present invention. 
           [0019]      FIG. 2  illustrates a cross-sectional view of an organic light emitting device in accordance with an embodiment of the present invention. 
           [0020]      FIGS. 3A and 3B  illustrate plan views of an organic light emitting device in accordance with an embodiment of the present invention. 
           [0021]      FIG. 4  illustrates a cross-sectional view of an organic light emitting device in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will more fully convey the scope of the invention to those skilled in the art. In the drawings, the thickness of layers and regions are exaggerated for clarity. Like numbers refer to like elements throughout the specification. 
         [0023]      FIG. 1A  illustrates a plan view of an organic light emitting device in accordance with an embodiment of the present invention. 
         [0024]    Referring to  FIG. 1A , a substrate has a pixel region  100 , where pixels are arranged, and a non-pixel region  101 . A cathode bus line  170  is formed at a peripheral portion of the pixel region  100 , namely, the non-pixel region  101 , so that the cathode bus line  170  and a cathode electrode  190  are electrically coupled to each other at a contact region  103  of the peripheral portion of the pixel region  100 . 
         [0025]    While  FIG. 1A  illustrates the cathode bus line  170  formed only in the non-pixel region  101 , the cathode bus line  170  also may be formed to have a matrix or stripe shape in the pixel region  100  as illustrated in  FIGS. 3A and 3B , or to have other shapes which allow the voltage drop to be prevented by supplying voltage to the pixels arranged in the pixel region  100 . 
         [0026]      FIG. 2  illustrates a cross-sectional view of an organic light emitting device taken along line II-II′ of  FIG. 1A , and, in particular, illustrates pixels arranged in the middle and edges of the pixel region  100 . 
         [0027]    Referring to  FIG. 2 , a buffer layer  110  is formed on an insulating substrate  105  comprised of the pixel region  100  and the non-pixel regions  101 . Thin film transistors  121 ,  123 ,  125  are formed in the pixel region  100  of the insulating substrate  105 . The thin film transistor  121  is arranged in the left most position of the pixel region  100 , the thin film transistor  125  is arranged in the right most position of the pixel region  100 , and the thin film transistor  123  is arranged for the pixel between the thin film transistor  121 ,  125  in the pixel region  100 . 
         [0028]    Anode electrodes  141 ,  143 ,  145  are formed on a passivation layer  130  and act as lower electrodes to be coupled to the thin film transistors  121 ,  123 ,  125  through via holes  131 ,  133 ,  135 . The anode electrode  141  is arranged for the pixel in the left most position of the pixel region  100 , the anode electrode  145  is arranged for the pixel in the right most position of the pixel region  100 , and the anode electrode  143  is arranged for the pixel between the anode electrode  141  and anode electrode  145 . 
         [0029]    A pixel defining layer  150  is formed to expose some portions of the anode electrodes  141 ,  143 ,  145 . Cathode bus lines  171 ,  173 ,  175  are formed on the pixel defining layer  150 , and an organic thin-film layer is formed to include organic emission layers  161 ,  163 ,  165 , for R, G, B, respectively, and a charge transporting layer  180 . A cathode electrode  190 , as an upper electrode, is deposited on the entire surface of the substrate, including the pixel region  100  and the non-pixel region  101 . 
         [0030]    The charge transporting layer  180  is a common layer for R, G, B, and is deposited on the entire surface of the pixel region  100  using, for example, an open mask. The charge transporting layer  180  may include at least one of a hole injecting layer, a hole transporting layer, a hole blocking layer, an electron transporting layer, or an electron injecting layer, which are not shown in the same figure. 
         [0031]    R, G, B organic emission layers  161 ,  163 ,  165  are deposited on the exposed portions of the anode electrodes  141 ,  143 ,  145 , respectively, using, for example, a fine metal mask. The organic emission layer  161  is arranged for the pixel in the left most position of the pixel region  100 , the organic emission layer  165  is arranged for the pixel in the right most position of the pixel region  100 , and the organic emission layer  163  is arranged for the pixel between organic emission layer  161  and organic emission layer  165 . 
         [0032]    The cathode bus line  171  is formed in the pixel region  100  and the non-pixel region  101 , and is arranged in the left most position of the pixel region  100 . The cathode bus line  175  is formed in the pixel region  100  and the non-pixel region  101 , and is arranged in the right most position of the pixel region  100 , and the cathode bus line  173  is arranged between the right most and left most positions of the pixel region  100 . 
         [0033]    The cathode bus lines  171  and  175 , of the cathode bus line  170  arranged in the right most and left most positions of the pixel region, are extended to the contact region  103  of the non-pixel region  101 , as well as to the pixel region  100 . The cathode bus line  170  is formed along the peripheral portion of the pixel region  100  in the non-pixel region  101  to be electrically and directly coupled. The pixel region  100  has an emission region and a non-emission region. The emission region corresponds to the region where light is emitted from the organic emission layers  161 ,  163 ,  165 , and the non-emission region corresponds to the pixel defining layer  150 , namely the region except the emission region. Some portions of the cathode bus line  170  in the pixel region  100  are formed on the pixel defining layer  150 , so that these portions of the cathode bus line are not electrically coupled with the cathode electrode  190  in the pixel region by the charge transporting layer  180  interposed therebetween. 
         [0034]    The cathode bus line  170  may use a conductive material that absorbs light, such as, for example, a MIHL (metal insulator hybrid layer) thin-film layer having a concentration gradient of a transparent conductive layer and a metal layer, to act as an electrode as well as a black matrix for blocking light. The cathode bus line  170  may be a supplementary electrode of the cathode electrode, wherein a voltage, having the same polarity and the same level as that applied to the cathode electrode  190 , is applied to the cathode bus line  170  to prevent the voltage drop through the cathode electrode. 
         [0035]      FIG. 1B  illustrates another plan view of an organic light emitting device in accordance with an embodiment of the present invention, wherein a cathode bus line  271  is formed only at one outer portion of a pixel region  200  in a non-pixel region  201 . The cathode bus line  271  and a cathode electrode  290  are electrically and directly coupled to each other only at the outer portion of the pixel region  200 . This differs from  FIG. 1A  in that the cathode bus line  170  is formed along the pixel region  100  in the non-pixel region  101 , so that the cathode bus line  170  and the cathode electrode  190  are electrically and directly coupled to each other in all directions of the non-pixel region  100 . 
         [0036]    In accordance with an embodiment of the present invention, the cathode bus line is formed in at least one portion of the non-pixel region, so that the cathode bus line and the cathode electrode are electrically and directly coupled to each other through the contact region of the non-pixel region, even when the charge transporting layer is deposited on the entire surface of the pixel region using an open mask. 
         [0037]    In addition to the structure connecting the cathode bus line to the cathode electrode, as shown in an embodiment of the present invention, the cathode bus line and the cathode electrode may be connected in the non-pixel region, which is the outer portion of the pixel region. 
         [0038]      FIG. 3A  illustrates a plan view of an organic light emitting device in accordance with an embodiment of the present invention. 
         [0039]    Referring to  FIG. 3A , a cathode bus line  370  is formed in a grid or matrix shape only in the pixel region  100 , so that the cathode bus line  370  and a cathode electrode  390  are electrically and directly coupled to each other through a contact region  303  per each pixel. 
         [0040]      FIG. 4  illustrates a cross-sectional view of the organic light emitting device taken along line IV-IV′ of  FIG. 3A , and, in particular, illustrates pixels arranged in the middle and edge portions of the pixel region  300 . 
         [0041]    Referring to  FIG. 4 , a buffer layer  310  is formed on an insulating substrate  305  comprised of a pixel region  300  and a non-pixel region  301 . Thin film transistors  321 ,  323 ,  325  are formed in the pixel region  300  of the insulating substrate  305 . The thin film transistor  321  is arranged for the pixel in the left most position of the pixel region  300 , and the thin film transistor  325  is arranged in the right most position of the pixel region  300 . The thin film transistor  323  is arranged, for the pixel between thin film transistor  321  and thin film transistor  325 . 
         [0042]    Anode electrodes  341 ,  343 ,  345  are formed on a passivation layer  330 , and act as lower electrodes to be connected to the thin film transistors  321 ,  323 ,  325  through via holes  331 ,  333 ,  335 , respectively. The anode electrode  341  is arranged for the pixel in the left most position of the pixel region  300 , and the anode electrode  345  is arranged for the pixel in the right most position of the pixel region  300 . The anode electrode  343  is arranged, for the pixel between the anode electrode  341  and the anode electrode  345 . 
         [0043]    A pixel defining layer  350  is formed to expose some portions of the anode electrodes  341 ,  343 ,  345 , and cathode bus lines  371 ,  373 ,  375  are formed on the pixel defining layer  350 . Organic thin-film layers, including organic emission layers  361 ,  363 ,  365  for R, G, B and charge transporting layers  381 ,  383 ,  385  as an organic EL common layer, are selectively formed on the exposed portions of the anode electrodes  341 ,  343 ,  345 , respectively, using, for example, a fine metal mask (not shown in the same figure), which correspond to an emission regions of the pixel region  300 . The cathode electrode  390  is deposited on the entire surface of the substrate, including the pixel region  300  and the non-pixel region  301 . 
         [0044]    The organic emission layer  361  corresponds to the pixel arranged in the left most position of the pixel region  300 , the organic emission layer  365  corresponds to the pixel arranged in the right most position of the pixel region  300 , and the organic emission layer  363  corresponds to the pixel arranged between the right most and left most positions. The charge transporting layer  380  as a common layer for R, G, B, is deposited on only the organic emission layers using, for example a fine metal mask (not shown). In this case, the charge transporting layer  380  may include at least one of a hole injecting layer, a hole transporting layer, a hole blocking layer, an electron transporting layer and/or an electron injecting layer, which are not shown in the figure. 
         [0045]    The cathode bus lines  371 ,  373 ,  375  are formed only in the pixel region  300 . The cathode bus line  371  corresponds to the pixel arranged in the left most position of the pixel region  300 , the cathode bus line  375  corresponds to the pixel arranged in the right most position of the pixel region  300 , and the cathode bus line  373  corresponds to the pixel arranged between the right most and left most positions of the pixel region  300 . 
         [0046]    The cathode bus line  370  is formed to have a grid or matrix shape on the pixel defining layer  350  in the pixel region  300  as shown in  FIG. 3A . The cathode bus line  370  may use a material that absorbs light and has conductivity, such as, for example, an MIHL thin-film layer having a concentration gradient of a transparent conductive layer and a metal layer to act as an electrode as well as a black matrix for blocking light. The cathode bus line  370  may act as a supplementary electrode of the cathode electrode  390 , wherein a voltage having the same polarity and the same level as that applied to the cathode electrode  390  is applied to the cathode bus line  370  to prevent the voltage drop through the cathode electrode. 
         [0047]      FIG. 3B  illustrates a cross-sectional view of an organic light emitting device in accordance with an embodiment of the present invention. The cathode bus line  470  is a stripe shape, so that the cathode bus line  470  and the cathode electrode  490  are electrically and directly coupled to each other on a line basis in the pixel region  400 . This is different from  FIG. 3A  in that the cathode bus line  370  is formed to have a grid shape in the pixel region  300  so that the cathode bus line  370  and the cathode electrode  390  are electrically and directly coupled in the pixel region  310  per each pixel. 
         [0048]    According to an embodiment of the present invention, the cathode bus line  370  is a grid shape only in the pixel region  300 , so that the charge transporting layers  381 ,  383 ,  385  are formed only on each of the anode electrodes  341 ,  343 ,  345  per each pixel. This may be formed using a fine metal mask, for example, and the cathode electrode  390  is formed on the entire surface of the substrate. The charge transporting layers  381 ,  383 ,  385  are partially formed only on the organic emission layers  361 ,  363 ,  365 , so that the cathode bus line  370  and the cathode electrode  390  are electrically coupled to each other per each pixel in the pixel region  300 . 
         [0049]    In addition to the structure of the cathode bus line described in other embodiments of the present invention, other structures may be applied such that the cathode bus line is connected to the cathode electrode in the pixel region. 
         [0050]    As mentioned above, the organic light emitting device in accordance with an exemplary embodiment of the present invention allow the cathode bus line to be formed only in the pixel region and, concurrently, charge transporting layers to be separated from one another for each pixel, so that the cathode bus line and the cathode electrode may be electrically coupled to each other in the pixel region. Further exemplary embodiments of the present invention allow the cathode bus line to be formed in the non-pixel region so that the cathode bus line and the cathode electrode may be electrically and directly coupled to each other at the outer portion of the pixel region. Therefore, the cathode electrode and the cathode bus line may be easily coupled to each other and, at the same time, the voltage drop of the cathode electrode per each pixel may be prevented. 
         [0051]    While the present invention has been described with reference to particular embodiments, it is understood that the disclosure has been made for purpose of illustrating the invention by way of examples and is not limited to limit the scope of the invention. And one skilled in the art can make amend and change the present invention without departing from the scope and spirit of the invention.