Patent Publication Number: US-2022231114-A1

Title: Display device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese patent Application No. 2013-069663, filed on Mar. 28, 2013, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The present invention is related to an OLED (organic light-emitting diode) display panel and a manufacturing method of the OLED display panel. 
     BACKGROUND 
     In recent years, the development of OLED display panels is progressing with the goal of achieving thinness, high luminosity and high speed of the display panel. These OLED display panels are provided from at least three organic light emitting diodes (OLED element) in which each pixel emits light in three primary colors (red, green, blue) respectively, response speed is fast due to the lack of mechanical operations, and in addition to high luminosity display being possible due to each pixel itself emitting light, next generation display panels are being expected since thinness is possible due to backlights becoming unnecessary. 
     Although these OLED display panels generally include a structure in which a plurality of OLED elements corresponding to each pixel of an image to be displayed are provided in a matrix on one substrate (glass substrate), in a so called top emission type panel, a transparent opposing substrate for preventing external light from entering is further bonded on an OLED element. Each OLED element in a top emission type panel is comprised from a TFT (Thin Film Transistor) drive circuit layer, a reflectance electrode layer (anode), a hole injection layer, a hole transport layer, an organic EL (Electro Luminescence) light emitting layer, an electron transport layer, an electron injection layer and a transparent electrode layer (cathode) in sequence from the substrate side. Furthermore, because the transparent electrode layer (cathode) is one sheet of transparent conductive material common to all the OLED elements, the transparent electrode layer is provided across the entire region of the display area (area in which an OLED element is provided)  101  shown in  FIG. 12 . 
     Although the transparent electrode layer is provided on a different layer to the TFT drive circuit provided on a substrate in the stacked structure described above, because a drive circuit for driving each OLED element or an element for supplying external drive power or an external drive signal to the drive circuit or connecting to ground is provided on the substrate, it is necessary to form a cathode contact  100  at a plurality of locations passing from the wiring on the substrate through to the layer in which the transparent electrode is provided as is shown in  FIG. 12 , make an earth wire provided on the substrate to conduct with the cathode contact  100  and connect the transparent electrode to each cathode contact  100 . 
     Since the conducting material which forms the transparent electrode layer has a high resistance value, there is a larger drop in voltage from the wiring itself and a smaller potential difference with the cathode electrode the larger the gap between the transparent electrode and the cathode electrode  100  thereby a problem occurs wherein the amount of light emitted from an OLED element decreases (shedding). 
     Although arranging auxiliary wiring (bypass wiring) between the OLED element and each cathode contact in order to solve this shedding problem has been considered, this option is not suitable for a high definition display because auxiliary wiring must be arranged between each pixel. 
     Thus, the present invention attempts to provide an OLED display panel and manufacturing method thereof which can control shedding problems regardless of whether a panel is high definition or not. 
     SUMMARY 
     An OLED display panel according to the present invention arranged with an organic light-emitting element, the panel includes a substrate, a display area including a plurality of OLED elements arranged over the substrate, and a low resistance metal film provided along an exterior edge of the display area over the substrate, the low resistance metal film conducting with a transparent electrode of each OLED element forming the display area. 
     A method of manufacturing an OLED display panel according to the present invention arranged with an organic light-emitting element, the method includes forming a rectangular display area including a plurality of OLED elements and a layer of an insulation material surrounding the display area on a substrate, forming a low resistance metal film overlapping a plate shaped mask arranged with a slit along four edges of the display area over the substrate, on a surface of the layer of the insulation material, and forming a transparent electrode layer conducting with an OLED element forming the display area and each low resistance metal film. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a planar diagram of an OLED display panel according to a first embodiment; 
         FIG. 2  is an exploded vertical cross sectional diagram of the vicinity of a cathode contact and a low resistance metal film; 
         FIG. 3  is a planar diagram of a mask for forming the low resistance metal film according to the first embodiment; 
         FIG. 4  is an exploded vertical cross sectional diagram showing a formation process of the low resistance metal film; 
         FIG. 5  is a planar diagram showing a connection position of a flexible printed substrate to an OLED display panel; 
         FIG. 6  is a planar diagram of an OLED display panel according to a second embodiment; 
         FIG. 7  is a planar diagram of a mask for forming the low resistance metal film according to the second embodiment; 
         FIG. 8  is a modified example of a mask; 
         FIG. 9  is a planar diagram of an OLED display panel according to a third embodiment; 
         FIG. 10  is a planar diagram of an OLED display panel according to a fourth embodiment; 
         FIG. 11  is an exploded vertical cross sectional diagram showing a modified example of a layer structure of a cathode electrode and low resistance metal film; and 
         FIG. 12  is a planar diagram of a conventional OLED display panel. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       FIG. 1  is a planar diagram of an OLED display panel  1 .  FIG. 2  is an exploded vertical cross sectional diagram along the line II-II shown in  FIG. 1 . Furthermore, the dotted line in  FIG. 2  indicates that although the structure to the left side of the dotted line is also connected, this illustration omitted. 
     As is shown in  FIG. 1 , in a planar view, a display area  2  is provided at the center of the OLED display panel  1  by arranging a plurality of OLED elements aligned in a matrix shape and displays an image by selectively driving each OLED element. In addition, a long low resistance metal film  3  comprised from a metal such as aluminum or silver or the like is provided at four sections of a periphery area (referred to in the present specification below as [frame area]) which are each connected to four sides of the display area  2  over the upper surface of the OLED display panel  1 . The length in the long direction of each low resistance metal film  3  is the same as the length of an adjacent side in the display area. In addition, a connector  4  which includes an earth terminal which conducts with each low resistance metal film  3  via an earth wire and a terminal for supplying drive power and a drive signal to a drive circuit (not shown in the diagram) for selectively driving each OLED light emitting element within the display area  2  is arranged on one side of the frame area. 
     As is shown in  FIG. 2 , each OLED element  2   a  within the display area  2  is provided by a reflectance electrode layer (anode)  17 , a hole injection layer  18 , a hole transport layer  19 , an organic EL (Electro Luminescence) light emitting layer  21 , an electron transport layer  22 , an electron injection layer  23  and a transparent electrode layer (cathode)  9  on a substrate  1 . A transparent metal compound with a low work function is required for the material of the transparent electrode layer (cathode)  9 . Thus, for example, it is possible to use IZO (In 2 O 3 —ZnO) as the material of the transparent electrode layer (cathode)  9 . In addition, after forming a silver thin film on the electron injection layer  23 , a compound structured transparent electrode layer (cathode)  9  may be provided by forming an ITO (In 2 O 3 —SnO 2 ) thin film. 
     A metal wire  5  comprised from a low resistance metal (aluminum, silver or the like) thin film which conducts with an earth terminal of the connector  4  is provided over the frame area over the substrate  1 . The metal wire  5  is covered by a planarized layer  6  comprised from an insulation material the same as the TFT (Thin Film Transistor) drive circuit layer  16  which forms the OLED element  2   a  within the display area  2 . In addition, a contact hole  6   a  is provided at one part of the planarized layer  6 . An ITO (Indium Tin Oxide) layer  7  is provided on the interior surface of the contact hole  6   a  and the periphery of the contact hole  6   a  on the surface of the planarized layer  6  and this ITO layer  7  conducts with the metal wire  5  via the contact hole  6   a . The planarized layer  6  and ITO layer  7  are further covered by a rib layer  8  which is a layer of an insulation material for sectioning each OLED element  2   a  (except the transparent electrode layer (cathode)  9 ) within the display area  2 . A contact hole  8   a  is arranged at one section (a position overlapping the left end of the low resistance metal film  3  on the bottom side of  FIG. 1 ) of the rib layer  8 . 
     Each low resistance metal film  3  described above is provided on the surface of the rib layer  8 . In addition, one part (contact  3   a ) of the low resistance metal film  3  overlapping the contact hole  8   a  described above enters the interior of the contact hole  8   a  and conducts with the ITO layer  7 . Furthermore, if the thickness of each low resistance metal film  3  is for example about 100 nm or above, it is possible to maintain a low resistance value of the low resistance metal film  3  itself. 
     The transparent electrode  9  is a common electrode with respect to each OLED element and is provided over the entire surface of the display area  2 . The transparent electrode  9  spreads to the periphery portion of the display area  2 . The transparent electrode  9  overlaps the low resistance metal film  3  at the periphery portion of the display area  2  and conducts with the low resistance metal film  3 . The surfaces of the transparent electrode layer  9 , rib layer  8  and substrate  1  are covered by a sealing film  10  across the entire area except the formation sections of the connector  4 . 
     A transparent opposing substrate  13  is covered in the area except the formation sections of the connector  4  over the substrate  1  while a gap is maintained with the substrate  1  by a seal  11 . A filler  12  comprised from a transparent epoxy resin is filled into a space enclosed by the opposing substrate  13 , seal  11  and sealing film  10 . 
     Using the OLED display panel  1  of the present embodiment configured as described above, all of the low resistance metal films  3  provided along the four sides of the display area  2  mutually conduct with each other via an interposing transparent electrode layer  9  and also conducts with the contact  3   a  using this conduction. At this time, although a slight drop in voltage occurs when a current crosses a transparent electrode  9  between a pair of adjacent low resistance metal films  3 , a slight amount of voltage drop is acceptable since the gap between pairs of low resistance metal films  3  is narrow and consequently a conducting potential is maintained across almost the entire area of all the low resistance metal films  3 . 
     In addition, because the low resistance metal film  3  is provided near the four sides of the display area  2 , the distance up to the nearest low resistance metal film  3  at any position within the display area  2  is shorter than the distance up to the vicinity of the four corners of the display area  2  provided with a contact  100  in the conventional OLED display shown in  FIG. 12 . Therefore, even if a drop in voltage occurs due to the resistance distribution of the transparent electrode layer  9  itself, because the amount of the drop in voltage is proportional to the distance up to a low resistance metal film (low resistance metal film  3 , contact  100 ), the amount of the drop in voltage according to the present embodiment is smaller than in a conventional display. Therefore, according to the present embodiment, shedding which accompanies a cathode resistance distribution is deleted and high image quality is achieved even in high definition panels. 
     In addition, according to the present embodiment, since a sufficient number of sections of the contact  3   a  is kept to a necessary minimum, it is possible to narrow the width of the frame area for securing formation of the contact  3   a  and consequently it is possible to realized a narrow frame area width. 
     A manufacturing process of the low resistance metal film  3  is explained below. Metal wiring  5 , planarized layer  6 , ITO layer  7  and rib layer  8  are provided over the substrate  1  at the same time as forming the display area  2  comprised from a plurality of OLED elements  2   a  (except the transparent electrode layer (cathode)  9 ). In this state, a mask  14  which shows this planar shape in  FIG. 3  is overlaps the rib layer  8 . The mask  14  is a plate with the same area as the substrate  1  and four slits  14   a  with the same shape as each low resistance metal film  3  are arranged aligned in a rectangle. In this way, because a slit arranged in the mask  14  is divided into four slits  14   a  corresponding to the low resistance metal film  3  which is also divided into four, a part (part which sections the inner edge of the low resistance metal film  3 ) further to the interior than the slit  14   a  in the mask  14  is supported in the interior of a part (part which sections the outer edge of the low resistance metal film  3 ) further to the exterior than the slit  14   a  near the four corners. Therefore, since one entire mask  14  is sufficient, it is possible to form the four low resistance metal films  3  by just one film formation process (deposition or sputtering) using this single mask  14 . 
     Thus, the low resistance metal film  3  is provided at a position overlapping the slit  14   a  of the mask  14  by inserting the substrate  1  overlapping the mask  14  into a chamber and depositing or sputtering a low resistance metal. Following this, the mask  13  is removed from the substrate  1 , the transparent electrode layer  9  and sealing film  10  are provided and the opposing substrate  13  is applied via the seal  11  and filler  12 . Furthermore, it is desirable that aluminum (Al) or silver (Ag) is used as the low resistance metal film  3 . 
     The OLED display panel completed as described above is incorporated into a casing of an electronic device not shown in the diagram by connecting the end of a flexible printed substrate  15  which includes a wire for supplying drive power or a drive signal and an earth wire to the terminal  4  as is shown in  FIG. 5 . 
     Second Embodiment 
       FIG. 6  is a planar diagram of an OLED display panel  20  according to a second embodiment of the present invention. As is shown in the low resistance metal film  3  of the OLED display panel  20  according to the second embodiment is provided from four long low resistance metal films  3   b  each provided parallel to the four sides of the display area  2  and four hook shaped low resistance metal films  3   c  each provided near the four corners of the display area  2 . Because the remaining structure of the OLED display panel  20  according to the second embodiment of the present invention is exactly the same as the structure described in the first embodiment, an explanation is omitted here. 
       FIG. 7  is a planar diagram of the mask  14  used for forming the low resistance metal films  3   b ,  3   c  according to the second embodiment. As is shown in  FIG. 7 , six slits  14   b ,  1   c  with the same shape as the low resistance metal film  2  shown in  FIG. 6  are arranged in the mask  14  of the second embodiment. 
     As is shown in the second embodiment explained above, it is not an essential requirement that the low resistance metal film  3  be divided at the four corners of the display area  2 . Therefore, for example, as is shown in  FIG. 8 , the mask  14  provided with a hole  14   d  for forming a dot shaped low resistance metal film at the four corners of the display area  2  may also be used. 
     Third Embodiment 
       FIG. 9  is a planar diagram of an OLED display panel  40  according to a third embodiment of the present invention. As is shown in  FIG. 9 , compared to the first embodiment shown in  FIG. 1 , the low resistance metal film  3  between the connector  4  and the display area  2  is omitted from the OLED display panel  40  according to the third embodiment. Because the remaining structure of the OLED display panel  40  according to the third embodiment of the present invention is exactly the same as the structure described in the first embodiment, an explanation is omitted here. 
     In this way, if the low resistance metal film  3  is provided at least along the pair of long sides and one short side of the rectangular display area, because the distance from an OLED element positioned at the center of the other short side up to another low resistance metal film  3  is equal to the distance from an OLED element positioned at the center of the display area  2  up to the low resistance metal film  3  provided adjacent to a long side, it is possible to sufficiently obtain the effect of shedding prevention. 
     Fourth Embodiment 
       FIG. 10  is a planar diagram of an OLED display panel  50  according to a fourth embodiment of the present invention. As is shown in  FIG. 10 , compared to the first embodiment shown in  FIG. 1 , only the point where the connector  4  is provided between the display area  2  and the low resistance metal film  3  is different. Because the remaining structure of the OLED display panel  50  according to the fourth embodiment of the present invention is exactly the same as the structure described in the first embodiment, an explanation is omitted here. 
     MODIFIED EXAMPLE 
       FIG. 11  is an exploded vertical cross sectional diagram which shows a modified example of an OLED display panel according to the present invention and is equivalent to  FIG. 2 . As is shown in  FIG. 11 , the transparent electrode layer  9  may be provided below the low resistance metal film  3 , inserted into the contact hole  8   a  and connected and conducting with the ITO layer  7 . That is, the transparent electrode layer  9  may also be provided before the low resistance metal film  3 . Even in this case, a current from each OLED element flows once to the nearest low resistance metal film  3  via the transparent electrode  9 , reaches the interior of the contact hole  8   a  via each low resistance metal film  3 , flows through the transparent electrode layer  9  and to the ITO layer  7 . Therefore, even when a structure according to this modified example is adopted, it is possible to achieve the same shedding prevention effects as those explained in the first embodiment. 
     As described above, according to the OLED display panel disclosed in the first to fourth embodiments, it is possible to control the problem of shedding even in a high definition panel. In addition, according to the manufacturing method of an OLED display panel of the present invention, it is possible to form a low resistance metal film of this OLED display panel in one formation process using a single mask.