Patent Publication Number: US-2006001365-A1

Title: Light emitting display device

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION  
      This application claims priority to and the benefit of Korean Patent Application No. 10-2004-0051524, filed on Jul. 2, 2004, which is hereby incorporated by reference for all purposes as if fully set forth herein.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a light emitting display device, and more particularly, to a light emitting display device having decreased contact resistance between an interconnecting line and a terminal.  
      2. Discussion of the Background  
      Generally, self-emissive light emitting display devices have many advantages. For example, they may have wide viewing angles, excellent contrast, and high response speed. Due to these advantages, self-emissive light emitting display devices are regarded as next generation display devices. Light emitting display devices may be inorganic or organic devices depending upon the material comprising their emission layer. Generally, organic light emitting display devices are brighter and they respond quicker than inorganic light emitting display devices. Additionally, organic light emitting display devices can form color images. Hence, active research is being conducted -into organic light emitting display devices.  
      A light emitting display device may include an anode, an emission layer, a cathode, and the like. The anode may be formed in a predetermined pattern on a transparent insulating substrate, such as a glass substrate. Then, an organic or inorganic layer may be disposed on the anode, thus forming the emission layer. The cathode may then be formed in a predetermined pattern on the emission layer. The cathode is disposed substantially perpendicular to the anode.  
      The emission layer may be interposed between a hole transport layer and an electron transport layer.  
      The light emitting display device forms an image as follows. Applying a voltage to the anode and the cathode injects holes from the anode to the emission layer through a hole transport layer and injects electrons from the cathode to the emission layer through an electron transport layer. The holes and electrons recombine in the emission layer, thus generating excitons. Then, the excitons drop from an exited state to a ground state, thereby causing luminous molecules of the emission layer to emit light, thus forming an image.  
      Hereinafter, organic light emitting display devices will be described.  
      The organic light emitting display device includes an organic emission unit, which forms an image and may be disposed on a transparent substrate. A cap covers and seals the organic emission unit and contacts the transparent substrate. In this case, an electrode terminal group, which applies a predetermined voltage or a signal to the organic emission unit, extends outside of the cap and may be connected to a flexible printed circuit board on which a circuit is mounted.  
      The organic emission unit may include a first electrode line, a second electrode line facing the first electrode line, and an organic layer, which includes at least an emission layer, disposed between the first electrode line and the second electrode line. With this structure, a portion of the organic layer formed above an edge of the first electrode line can be very thin, which may cause a short circuit between the first electrode line and the second electrode line. Additionally, the short-circuit can occur among the first electrode lines.  
      In order to prevent such short-circuits, an inner insulator may be formed among the first electrode lines, which is disclosed in U.S. Pat. Nos. 6,222,315 and 6,297,589. In particular, the inner insulator disclosed in U.S. Pat. No. 6,222,315 may gradually thin toward an adjacent electrode line. Therefore, short-circuits can be prevented at the boundary between adjacent electrode lines.  
      The first electrode line and the second electrode line may be connected to a first electrode terminal group and a second electrode terminal group, respectively, of an electrode terminal group. In this case, steps formed between the first and second electrode terminal groups and a surface of a substrate may cause an electric short at junctions of the first and second electrode lines and the first and second electrode terminal groups.  
      U.S. Patent Application Publication No. US 2004/0108809 A1 discloses an organic light emitting display device, as shown in  FIG. 1  and  FIG. 2 , to solve this problem.  
      Referring to  FIG. 1  and  FIG. 2 , first electrode lines  12  and second electrode lines  14  are disposed perpendicular to each other on a substrate  11 , and an organic layer  18  is interposed between the first electrode lines  12  and the second electrode lines  14 . The second electrode lines  14  are connected to second electrode terminals  24  of a second electrode pad portion  20 . Inter-insulating layers  16  are disposed between the first electrode lines  12 .  
      The second electrode terminals  24  include a first terminal  24   a,  which may be formed of a conducting oxide layer, and a second terminal  24   b,  which may be formed of a metal layer. An insulating layer  26 , which includes a contact hole  27 , may be formed on the second electrode terminal  24 .  
      Outside an emission unit  10 , the second electrode line  14  may be formed on the insulating layer  26 , and it contacts the second electrode terminal  24  through the contact hole  27 .  
      The first terminal  24   a  and the first electrode line  12  may be made of indium tin oxide (ITO), and the second terminal  24   b  may be made of a highly conductive material, such as Cr or Ag, such that a decrease of a voltage due to a line resistance of the first terminal  24   a  can be prevented.  
      However, at a portion of the second terminal  24   b  exposed by the contact hole  27 , a contact resistance between the second electrode line  14  and the second terminal  24   b  may increase and be non-uniform. This is because the portion of the second terminal  24   b  exposed by the contact hole  27  may be contaminated by an organic or inorganic material used in the manufacturing process. The contamination of the second terminal  24   b  may not be completely prevented by UV washing or oxygen plasma cleansing.  
      The increase and non-uniformity of the contact resistance between the second electrode line  14  and the second terminal  24   b  may result in a high driving voltage in the corresponding line. Further, images may be formed with random black spots.  
     SUMMARY OF THE INVENTION  
      The present invention provides an electroluminescent device with a low contact resistance where an interconnecting line contacts a terminal, thus decreasing a driving voltage and obtaining more uniform signals.  
      Additional features 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 present invention discloses a light emitting display device including a substrate, an emission unit which forms an image and is disposed on the substrate, a first conductor which contacts a second conductor that is electrically connected to the emission unit, and a contact resistance controlling portion which decreases a contact resistance between the first conductor and the second conductor and is disposed where the first conductor contacts the second conductor.  
      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.  
       FIG. 1  is a plan view showing a portion of a conventional organic light emitting display device.  
       FIG. 2  is a sectional view taken along line I-I of  FIG. 1 .  
       FIG. 3  is an exploded perspective view showing an organic light emitting display device according to an exemplary embodiment of the present invention.  
       FIG. 4  is an enlarged plan view of a contact resistance controlling portion “A” of  FIG. 3  according to an exemplary embodiment of the present invention before forming a second electrode line.  
       FIG. 5  shows  FIG. 4  after forming the second electrode line.  
       FIG. 6  is a sectional view taken along line II-II of  FIG. 5 .  
       FIG. 7  is an enlarged plan view of a contact resistance controlling portion “A” of  FIG. 3  according to an exemplary embodiment of the present invention before forming a second electrode line.  
       FIG. 8  shows  FIG. 7  after forming the second electrode line.  
       FIG. 9  is a sectional view taken along line III-III of  FIG. 8 .  
       FIG. 10  an enlarged plan view of a contact resistance controlling portion “A” of  FIG. 3  according to an exemplary embodiment of the present invention before forming a second electrode line.  
       FIG. 11  shows  FIG. 10  after forming the second electrode line.  
       FIG. 12  is a sectional view taken along line IV-IV of  FIG. 11 . 
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS  
      The present invention will now be described more fully with reference to the accompanying drawings showing exemplary embodiments of the present invention. Exemplary embodiments of the present invention relate to organic light emitting display devices including an organic emission layer. However, techniques according to the present invention can also be used to form inorganic light emitting display devices including an inorganic emission layer.  
       FIG. 3  is an exploded perspective view showing an organic light emitting display device according to an exemplary embodiment of the present invention.  
      Referring to  FIG. 3 , the organic light emitting display device according to an exemplary embodiment of the present invention may include a substrate  31 , an emission unit  40 , which forms an image and may be disposed on an upper surface of the substrate  31 , a sealing element  32 , which seals the emission unit  40  with the substrate  31 , and terminals  50  applying a current to the emission unit  40  and extending outside the sealing element  32 . The terminals  50  exposed outside the sealing element  32  may be connected to a flexible printed circuit board  33  on which a circuit unit (not shown) is mounted to drive the emission unit  40 . This structure can be used in the following exemplary embodiments of the present invention.  
      The organic light emitting display device according to an embodiment of the present invention will now be described in detail with reference to  FIG. 4 ,  FIG. 5  and  FIG. 6 .  FIG. 4  is an enlarged plan view of a contact resistance controlling portion “A” of  FIG. 3  according to an embodiment of the present invention before forming a second electrode line.  FIG. 5  shows  FIG. 4  after forming the second electrode line, and  FIG. 6  is a sectional view taken along line II-II of  FIG. 5 .  
      Referring to  FIG. 3 ,  FIG. 4 ,  FIG. 5  and  FIG. 6 , the emission unit  40  may include a plurality of first electrode lines  42  arranged in a predetermined pattern and formed on the substrate  31 , an organic emission layer  48  formed on the first electrode lines  42 , and a plurality of second electrode lines  44  arranged in a predetermined pattern and formed on the organic emission layer  48 .  
      The substrate  31  may be made of glass, acryl, polyimid, polycarbonate, polyester, mylar, plastic, metal, or the like, but is not limited thereto. A buffer layer may be formed on the substrate  31  to prevent the diffusion of impurity ions, if needed. Additionally, a barrier layer may be formed on the substrate  31  to prevent leaking of water or air.  
      The first electrode lines  42  may be made of ITO, IZO, ZnO, or In 2 O 3 , but they are not limited thereto. The second electrode lines  44  may be made of Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, or a compound of these, but they are not limited thereto. A portion of the organic emission layer  48  between a first electrode line  42  and a second electrode line  44  emits light, thus forming a predetermined image.  
      Any organic layer that is commonly used in an organic light emitting display device can be used as the organic emission layer  48 . The organic emission layer  48  may be made of a low molecular weight material or a polymer material.  
      When the organic emission layer  48  is made of low molecular weight material, the organic emission layer  48  may comprise a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), an electron injection layer (EIL), a combination of these, or the like. An organic material comprising the organic layer may be copper phthalocyanine (CuPc), N,N′-Di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB), tris-8-hydroxyquinoline (Alq3), or the like. In this case, for example, a vacuum deposition method can be used to form the low molecular weight organic layer.  
      When the organic emission layer  48  is made of polymer material, the organic emission layer  48  may include the HTL and the EML. The HTL may be made of PEDOT, and the EML may be made of poly-phenylenevinylene (PPV), polyfluorene, or the like. In this case, for example, screen printing or inject printing may be used to form the polymer organic layer.  
      The organic emission layer  48  can be formed into various patterns, corresponding to the color of a pixel.  
      Descriptions of the first electrode lines  42 , the second electrode lines  44 , and the organic emission layer  48  are the same in the embodiments of the present invention.  
      The emission unit  40  may further include an inner insulating layer  46  formed below the organic emission layer  48 . The inner insulating layer  46  insulates the first electrode lines  42  from each other, and it also insulates the first electrode lines  42  from the second electrode lines  44  in a non-emission area. The inner insulating layer  46  may comprise an insulating material, such as a photosensitive polyimide, or the like, and it may be formed using photolithography. The inner insulating layer  46  may have a striped pattern, a lattice pattern, or the like.  
      Referring to  FIG. 3 , the terminals  50  include first electrode terminals  52  and second electrode terminals  54  that are disposed along edges of the substrate  31 . Specifically, the first electrode terminals  52  may be disposed on one edge of the substrate  31 , and the second electrode terminals  54  may be disposed on other, opposite edges of the substrate  31 . However, the configuration of the first and second electrode terminals  52  and  54  is not limited thereto. For example, the first electrode terminals  52  and the second electrode terminals  54  can be disposed on the same edge of the substrate  31 .  
      Referring to  FIG. 6 , the second electrode terminal  54  includes a lower first conducting layer  54   a  and an upper second conducting layer  54   b.  The first conducting layer  54   a  may be made of, for example, ITO, IZO, ZnO, or In 2 O 3 , which is similar to the first electrode line  42 . The second conducting layer  54   b  may be made of, for example, Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, or a compound of these. The second electrode line  44  extends from the emission unit  40  to the second electrode terminal  54 . Although not shown in the drawings, the first electrode terminal  52  may have the same configuration as the second electrode terminal  54 . In this case, a first conducting layer of the first electrode terminal  52  and the first electrode line  42  can be integrated in one body.  
      The organic light emitting display device may further include an outer insulating layer  56  comprising an insulating material interposed between the emission unit  40  and at least the second electrode terminal  54 . The outer insulating layer  56  may be formed by extending a portion of the inner insulating layer  46  from the first electrode line  42   a,  which is disposed at an edge of the emission unit  40 , to the second electrode terminal  54 . In this case, the outer insulating layer  56  may contact an edge of the second electrode terminal  54  disposed toward the emission unit  40 . In other words, the emission unit  40  may be connected to the second electrode terminal  54 . According to an exemplary embodiment of the present invention, as illustrated in  FIG. 6 , the outer insulating layer  56  may overlap the edge of the second electrode terminal  54  that is disposed toward the emission unit  40 . The outer insulating layer  56  may decrease a step difference between the second electrode terminal  54  and the upper surface of the substrate  31 . Therefore, when a second electrode interconnecting line  45 , which is electrically connected to the second electrode line  44 , extends to an upper surface of the second electrode terminal  54 , a short-circuit due to the step difference may be prevented.  
      A portion of the outer insulating layer  56  covering the edge of the second electrode terminal  54  has a contact hole  57 . The second electrode interconnecting line  45  may be coupled to the second electrode terminal  54  through the contact hole  57 .  
      The contact hole  57  may expose the second conducting layer  54   b  of the second electrode terminal  54 .  
      The contact hole  57  includes a contact resistance controlling portion  58  to decrease a contact resistance between the second electrode terminal  54  and the second electrode interconnecting line  45  and maintain it at a predetermined level.  
      As  FIG. 4  shows, the contact resistance controlling portion  58  may include an inlet portion  58   a  formed in the second conducting layer  54   b.    
      The inlet portion  58   a  may be formed in the second conducting layer  54   b  such that a portion of the first conducting layer  54   a  is exposed by the contact hole  57  and the inlet portion  58   a.  Therefore, currents flowing in the second electrode interconnecting line  45  and the second electrode terminal  54  may be focused in the inlet portion  58   a,  thus decreasing the contact resistance.  
      As illustrated in  FIG. 4 , the inlet portion  58   a  may comprise a recess in at least a part of the second conducting layer  54   b  exposed by the contact hole  57 . The inlet portion  58   a  can be formed with other shapes than that shown. For example, the inlet portion  58   a  can be formed with a wavelike shape.  
      The inlet portion  58   a  can be formed even when the second electrode interconnecting line  45  contacts the second electrode terminal  54  without the outer insulating layer  56 . That is, the inlet portion  58   a  may be formed at a point of contact between the second electrode interconnecting line  45  and the second electrode terminal  54  so that currents may be focused in the inlet portion  58   a,  thus decreasing the contact resistance.  
       FIG. 7 ,  FIG. 8  and  FIG. 9  illustrate a contact resistance controlling portion  58  according to another exemplary embodiment of the present invention.  FIG. 7  is an enlarged plan view of a contact resistance controlling portion “A” of  FIG. 3  according to an exemplary embodiment of the present invention before forming a second electrode line.  FIG. 8  shows  FIG. 7  after forming the second electrode line, and  FIG. 9  is a sectional view taken along line III-III of  FIG. 8 . Referring to  FIG. 7 ,  FIG. 8  and  FIG. 9 , the contact resistance controlling portion  58  may include a structure  58   b  with a predetermined shape formed on a portion of the second electrode terminal  54  where it overlaps with the second electrode interconnecting line  45 . The contact hole  57  may expose the structure  58   b,  and the second electrode interconnecting line  45  may cover the structure  58   b  while contacting the second electrode terminal  54 .  
      The structure  58   b  may comprise various materials. For example, the structure  58   b  and the outer insulating layer  56  may be made of the same materials, and the structure  58   b  and the contact hole  57  can be patterned at the same time.  
      Similar as above, currents may be focused at the structure  58   b,  thus decreasing a contact resistance between the second electrode interconnecting line  45  and the second electrode terminal  54 .  
      The shape of the structure  58   b  is not limited to the shape shown in  FIG. 7  and  FIG. 9 . In other words, the structure  58   b  can have various shapes. For example, the structure  58   b  may have a cylindrical shape.  
      Additionally, as described above, the structure  58   b  can be formed where the second electrode interconnecting line  45  overlaps the second electrode terminal  54  even when the second electrode interconnecting line  45  contacts the second electrode terminal  54  without the outer insulating layer  56 . Therefore, currents may be focused at the structure  58   a,  thus decreasing the contact resistance.  
       FIG. 10 ,  FIG. 11  and  FIG. 12  illustrate a contact resistance controlling portion  58  according to another exemplary embodiment of the present invention.  FIG. 10  is an enlarged plan view of a contact resistance controlling portion “A” of  FIG. 3  according to an exemplary embodiment of the present invention before forming a second electrode line.  FIG. 11  shows  FIG. 10  after forming the second electrode line, and  FIG. 12  is a sectional view taken along line IV-IV of  FIG. 11 . Referring to  FIG. 10 ,  FIG. 11  and  FIG. 12 , the contact resistance controlling portion  58  may be formed such that the contact hole  57  exposes a portion of the first conducting layer  54   a.  In this case, the first conducting layer  54   a  of the second electrode terminal  54  may have better cleaning characteristics than the second conducting layer  54   b  of the second electrode terminal  54 .  
      The first conducting layer  54   a  may be made of a conducting oxide, such as, for example, ITO, IZO, ZnO, or In 2 O 3 , and the second conducting layer  54   b  may be made of a metal, such as, for example, Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, or Cr. Here, the first conducting layer  54   a  may have better cleansing characteristics than the second conducting layer  54   b  during a cleansing process, such as cleansing with oxygen plasma, or a UV cleansing. In other words, impurities existing on the first conducting layer  54   a,  which comprises an oxide, may be more easily removed than impurities existing on the metallic second conducting layer  54   b.    
      Therefore, as illustrated in  FIG. 10 ,  FIG. 11  and  FIG. 12 , the second electrode interconnecting line  45  contacts the first conducting layer  54   a  such that the contact resistance between the second electrode interconnecting line  45  and the second electrode terminal  54  may decrease.  
      As described above, the contact resistance controlling portion  58  may decrease the contact resistance between the second electrode interconnecting line  45  and the second electrode terminal  54 . However, embodiments of the present invention can also be used for any interconnecting line that extends from the emission unit  40  to contact a terminal outside the emission unit  40 .  
      Additionally, although the organic light emitting display devices shown are passive matrix types, embodiments of the present invention may also be used to form active matrix-type organic light emitting display devices.  
      In an active matrix-type organic light emitting display device, a pixel electrode may be formed in each pixel and a counter electrode may be commonly patterned for all pixels instead of first and second electrodes of an emission unit, respectively.  
      In this case, a contact resistance controlling portion can be used between the counter electrode and a terminal thereof. Further, the contact resistance controlling portion can be used between scan, data, VDD interconnecting lines and terminals thereof.  
      The exemplary embodiments of the present invention may provide the following effects.  
      First, an inlet portion may formed where an interconnecting line contacts a terminal such that currents may be focused in the inlet portion, thereby decreasing a contact resistance.  
      Second, a structure may be formed where the interconnecting line contacts the terminal such that currents may be focused at the structure, thereby decreasing the contact resistance.  
      Third, the portion where the interconnecting line contacts the terminal may have excellent cleansing characteristics, thereby permitting decreased contact resistance.  
      Fourth, lower contact resistance between the electrode interconnecting line and the terminal may result in a lower driving voltage. Therefore, signals may become more uniform.  
      It will be apparent to those skilled in the art that various modifications and variation can be made in 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.