Abstract:
Embodiments of the present invention provide an organic light emitting display device including: a plurality of light emitting elements on a first substrate, each of the plurality of light emitting elements including a first electrode and an organic light emitting layer, and a second electrode on the plurality of light emitting elements; a second substrate facing the first substrate with the plurality of light emitting elements therebetween; spacers on the second substrate corresponding to portions of the second electrode, the portions located on spaces between the plurality of light emitting elements; and an auxiliary electrode on the spacers and contacting the second electrode.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2008-0106359, filed on Oct. 29, 2008, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an organic light emitting display device having a front emitting structure, and more particularly to an organic light emitting display device having a cathode electrode shared by a plurality of light emitting devices in a display region. 
         [0004]    2. Description of Related Art 
         [0005]    An organic light emitting display device, which is a display device having self-light emitting characteristics, includes a substrate arranged with light emitting elements each including an organic light emitting layer, a sealing substrate disposed to facing the substrate, and a sealant sealing the light emitting elements between the substrate and the sealing substrate. 
         [0006]    The organic light emitting display device constituted as above is classified as a front emitting structure or a rear emitting structure according to the direction that light is emitted from the organic light emitting layer. The front emitting structure in which light is emitted in the direction of the sealing substrate has a larger aperture than that of the rear emitting structure in which light is emitted in the direction of the substrate on which the light emitting elements are arranged. 
         [0007]    The organic light emitting display device having the front emitting structure emits light in the direction of the sealing substrate so that a cathode electrode should be formed of a thin transparent electrode material such as indium tin oxide (ITO), indium zinc oxide (IZO) or the like. However, since the transparent electrode material has high resistivity, when the cathode electrode is formed as a common electrode over the display region, a voltage difference occurs between different locations across the cathode electrode, causing a problem that picture quality is not uniform. In other words, difference in brightness occurs due to the voltage difference between a position close to the power supply source and a position far from the power supply source, thereby causing the deterioration in the picture quality. The voltage difference increases as the size of the organic light emitting display device operated in a current driving manner is increased. The driving voltage can be increased in order to decrease the voltage difference. However, if the driving voltage is increased, it causes an increase in power consumption. Therefore, in order to implement a large-sized display device, there is demand for studies on material and a structure of the cathode electrode capable of implementing high definition without increasing power consumption. 
       SUMMARY OF THE INVENTION 
       [0008]    It is an aspect of the present invention to provide an organic light emitting display device capable of minimizing or reducing a voltage difference between different locations on a cathode electrode. 
         [0009]    It is another aspect of the present invention to provide an organic light emitting display device in which a cathode electrode can stably contact an auxiliary electrode for compensating for a voltage drop across the cathode electrode. 
         [0010]    According to a first embodiment of the present invention, there is provided an organic light emitting display device including: a first substrate; a plurality of light emitting elements on the first substrate, each of the plurality of light emitting elements including a first electrode and an organic light emitting layer, and a second electrode on the plurality of light emitting elements; a second substrate facing the first substrate with the plurality of light emitting elements therebetween; spacers on the second substrate corresponding to portions of the second electrode, the portions located on spaces between the plurality of light emitting elements; and an auxiliary electrode on the spacers and contacting the second electrode. 
         [0011]    According to another embodiment of the present invention, an organic light emitting display device includes: a first substrate having a plurality of light emitting elements; a common electrode on the plurality of light emitting elements; a second substrate facing the first substrate with the plurality of light emitting elements therebetween; and an auxiliary electrode substantially evenly distributed on non-light emitting regions of the common electrode. 
         [0012]    With the organic light emitting display device according to the embodiments of the present invention, the spacers and the auxiliary electrode in a stacked structure may be formed on the sealing substrate, and the auxiliary electrode may be closely adhered to the cathode electrode by the spacers. The voltage across the cathode electrode may be substantially constantly maintained by the auxiliary electrode having lower resistance than that of the cathode electrode irrespective of its location, such that power consumption may be decreased, and difference in brightness between pixels may be reduced. The auxiliary electrode may contact the cathode electrode stably by using the spacers, making it possible to implement high definition picture quality. Also, the auxiliary electrode of the embodiments of the present invention may be formed of metal having low transmittance to function as a black matrix for suppressing reflection of external light, thereby decreasing black brightness and improving contrast. As such, a separate black matrix or polarizing plate may not be required, thereby simplifying a structure of a display device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    These and/or other aspects of the present invention will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings of which: 
           [0014]      FIG. 1  is a schematic drawing illustrating a plan view of an organic light emitting display device according to an embodiment of the present invention; 
           [0015]      FIG. 2  is a schematic drawing illustrating a cross-sectional view of a light emitting element of the organic light emitting display device of  FIG. 1 ; 
           [0016]      FIG. 3  is a schematic drawing illustrating an enlarged plan view of a portion of a sealing substrate for sealing a display region on which a plurality of light emitting elements are formed; 
           [0017]      FIG. 4  is a schematic drawing illustrating a cross-sectional view taken along the line I 1 -I 2  of  FIG. 3 ; 
           [0018]      FIG. 5  is a schematic drawing illustrating a cross-sectional view of an organic light emitting display device according to an embodiment of the present invention; and 
           [0019]      FIG. 6  is a schematic drawing illustrating an enlarged cross-sectional view of portion “B” of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0020]    In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. In addition, when an element is referred to as being “on” another element, it can be directly on another element or be indirectly on another element with one or more intervening elements interposed therebetween. Also, when an element is referred to as being “connected to” another element, it can be directly connected to another element or be indirectly connected to another element with one or more intervening elements interposed therebetween. Hereinafter, like reference numerals refer to like elements. 
         [0021]      FIG. 1  is a schematic drawing illustrating a plan view of an organic light emitting display device according to an embodiment of the present invention, and  FIG. 2  is a schematic drawing illustrating a cross-sectional view of a light emitting element of the organic light emitting display device of  FIG. 1 . 
         [0022]    Referring to  FIG. 1 , a substrate  100  includes a display region  120  and a non-display region  140  located around the display region  120 . Scan lines  150  and data lines  160  extend on the substrate  100 , and a plurality of light emitting elements  130  arranged in a matrix form in the display region  120  are connected between the scan lines  150  and the data lines  160 . The scan lines  150  and the data lines  160  extend from the non-display region  140  to the display region  120 . Power supply lines (not shown) supply power to operate the light emitting elements  130 , and a scan driver  170  and a data driver  180  are provided to process signals provided from the outside through a pad  190  and supply them to the scan lines  150  and data lines  160 . The scan driver  170  and the data driver  180  each include driving circuits for converting signals provided from the outside into scan signals and data signals, respectively, to drive the light emitting elements  130  selectively. 
         [0023]    Referring to  FIG. 2 , each of the light emitting elements  130  includes an anode electrode  131 , a cathode electrode  134  and an organic light emitting layer  133  between the anode electrode  131  and the cathode electrode  134 . A plurality of the anode electrodes  131  are formed on the substrate  100 . The organic light emitting layer  133 , which is formed on a light emitting region (a region on which the anode electrode is exposed) defined by a pixel defining film  132 , may include a hole injection layer, a hole transporting layer, an electron transporting layer and an electron injection layer. Also, the cathode electrode  134  is disposed over the display region  120  to be used as a common electrode of the plurality of light emitting devices  130 . 
         [0024]    Also, the light emitting element  130  is coupled to a thin film transistor  110  for controlling the operation of the light emitting element  130 , and a capacitor (not shown) is coupled to the thin film transistor  110  for maintaining a signal (e.g., a gate voltage). The thin film transistor  110  includes a semiconductor layer  112 , a gate electrode  114  and source/drain electrodes  116 . The semiconductor layer  112  provides a source and drain region and a channel region. The gate electrode  114  is insulated from the semiconductor layer  112  by a gate insulating layer  113 . Also, the source/drain electrodes  116  are connected to the semiconductor layer  112  at the source and drain regions through contact holes formed on the insulating layer  115  and the gate insulating layer  113 . Further, a buffer layer  111  is located on the substrate  100 , and another insulating layer  117  is located on the insulating layer  115 . 
         [0025]      FIG. 3  is a schematic drawing illustrating an enlarged plan view of a portion of the sealing substrate  300  for sealing the display region  120  on which a plurality of light emitting elements  130  are formed, and  FIG. 4  is a schematic drawing illustrating a cross-sectional view taken along the line I 1 -I 2  of  FIG. 3 . 
         [0026]    Referring to  FIGS. 3 and 4 , spacers  320  and an auxiliary electrode  340  are formed in a stacked structure on the sealing substrate  300  so as to correspond to the cathode electrode  134 , and are located between the plurality of light emitting elements  130 . The auxiliary electrode  340  may also be described as a plurality of electrically interconnected electrodes. For example, the auxiliary electrode  340  is shown as a plurality of electrodes connected in a mesh shape. The “A” portion of  FIG. 3  shown using dotted lines is a portion corresponding to a light emitting region  136  (shown in  FIG. 2 ) so as to show a portion corresponding to the cathode electrode  134  between the plurality of light emitting elements  130 . 
         [0027]    The spacers  320  are formed so as to maintain a spacing between the light emitting elements  130  and the sealing substrate  300 , and to closely adhere the auxiliary electrode  340  to the cathode electrode  134 . Thereby, the heights of the spacers  320  may be controlled by the spacing between the light emitting elements  130  and the sealing substrate  300  and the thickness of the auxiliary electrode  340 . The spacers  320  may be formed of an organic material or inorganic material. Also, the auxiliary electrode  340  is formed so as to contact the cathode electrode  134  to decrease its resistivity, and at the same time, to decrease voltage difference between locations across the cathode electrode  134  through the evenly distributed contact parts formed by the auxiliary electrode  340 . Further, the auxiliary electrode  340  is formed of a conductive material or metal having lower resistivity than that of the cathode electrode  134 . For example, when the cathode electrode  134  is formed of ITO, IZO or the like, the auxiliary electrode  340  may be formed of metal having lower resistivity, for example, Al, Mo, Cr, Pt, W, Cu, Ag, Au or the like. 
         [0028]      FIG. 3  shows an embodiment where the spacers  320  and the auxiliary electrode  340  are formed in a mesh shape, but they may also be formed in a stripe shape where the contact parts of the auxiliary electrode  340  and the cathode electrode  134  are evenly distributed and electrically connected. 
         [0029]      FIG. 5  is a schematic drawing illustrating a cross-sectional view of an organic light emitting display device according to an embodiment of the present invention, and  FIG. 6  is a schematic drawing illustrating an enlarged cross-sectional view of portion “B” of  FIG. 5 . 
         [0030]    Referring to  FIGS. 5 and 6 , the sealing substrate  300  for sealing the display region  120  is disposed on the top of the substrate  100  including the plurality of light emitting elements  130 , and the sealing substrate  300  is bonded or attached to the substrate  100  by a suitable sealant  400 . As the sealing substrate  300  is bonded to the substrate  100 , the auxiliary electrode  340  of the sealing substrate  300  contacts the cathode electrode  134 . The contact parts of the auxiliary electrodes  340  and the cathode electrode  134  can be maintained stably by the spacers  320 . 
         [0031]    In another embodiment of the present invention, the auxiliary electrode  340  may be formed of metal having low transmittance such as chrome (Cr), an oxide including metal having such low transmittance (for example, Cr 2 O 3  or the like) or a conductive material having an inverse proportion of inorganic material and metal according to a thickness, such as metal insulator hybrid layer (MIHL) or the like. Therefore, the auxiliary electrode  340  can function as a black matrix for suppressing reflection of external light, thereby decreasing black brightness and improving contrast. In this case, a separate black matrix or polarizing plate is not required, thereby simplifying a structure of a display device. In order words, the auxiliary electrode  340  may be formed on the non-light emitting regions of the cathode electrode  134 . 
         [0032]    Also, if spacers (not shown) are formed on the pixel defining film  132  corresponding to the spacers  320  in the structure shown in  FIG. 6 , the contacts between the auxiliary electrode  340  and the cathode electrode  134  can be maintained more stably. 
         [0033]    While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the present invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.