Patent Abstract:
An organic light emitting diode display comprises: an insulating substrate; common electrodes; a first electrode layer formed in a region adjacent to the common electrodes formed on the insulating substrate by electrically isolating from the common electrodes; an insulating layer which coats on the insulating substrate by respectively opening a first opening window exposing a part of the common electrodes and a second opening window exposing at least a part of the first electrode layer; ribs which form a cell area by crossing the common electrodes on the insulating substrate and surrounding each of the opening windows; a material layer formed on the first electrode layer exposed from the second opening window; and a second electrode layer which coats within the cell area surrounded by the ribs and electrically connected to the common electrodes through the first opening window.

Full Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method for removing luminance nonuniformity and crosstalk occurs on a display using organic electroluminescence and an organic electroluminescence display manufactured by this method.  
         [0003]     2. Description of Related Art  
         [0004]     Organic electroluminescent elements are configured by sandwiching a material layer between an anode and a cathode. The material layer may comprise a plurality of layers, such as an electron-injecting layer or a hole-injecting layer and an electron-transporting layer or a hole-transporting layer. Its emitting principle is similar to that of the emitting mechanism of light emitting diodes (LED). More specifically, a hole and an electron are fed into a light-emitting layer by the application of a direct current voltage between the anode and the cathode. The electronic state of organic molecules included in the light-emitting layer is changed to the excited state by energy generated by a recombination of the hole and electron in the light-emitting layer. Energy is emitted as light when this quite unstable electronic state falls to a ground state to emit organic light emitting diodes. Accordingly, organic electroluminescence is referred to also as organic light emitting device (OLED).  
         [0005]     In an OLED display, OLED elements are arranged on a substrate, such as a glass substrate as a matrix to be emitted to show information. OLED displays are expected as epoch-making displays because of superiority in electric power consumption, reaction speed, visual field, and luminance compared with other types of displays, such as liquid crystal displays.  
         [0006]     A method for driving OLED elements is roughly divided into two kinds of systems: passive matrix system and active matrix system. As shown in FIGS.  5 ( a ) and  5 ( b ), the passive matrix system is a driving method to intersect an anode  114  and a cathode  116  in a matrix state to selectively emit OLED elements sandwiched at an intersection. On the other hand, as shown in FIGS.  6 ( a ) and  6 ( b ), the active matrix system is a driving method to emit OLED elements by having switching and memory functions for each pixel  130  using a thin film transistor (TFT)  120 .  
         [0007]     Using the passive matrix system enables low production costs of displays because of its simple structure. However, large electric power consumption is required to keep the screen at high luminance because this system indicates information by sequentially emitting lines and using an after-image branded on the eyes. For this reason, the active matrix system for emitting the pixels  130  by aggressively using a TFT  120  has been adopting more despite its high production costs. Compared with the passive matrix system, the active matrix system enables high luminance at a low electric power consumption.  
         [0008]     On the other hand, a conventional method of taking out luminance of an OLED display  110  has two systems: bottom-emitting system and top-emitting system. As shown in  FIG. 7 ( a ), the bottom-emitting system takes out light from an insulating substrate side  118 . As shown in  FIG. 7 ( b ), the top-emitting system takes out light from a top surface layer side  115 .  
         [0009]     Japanese Patent Publication No. 8-227276 (Cited document 2) discloses embodiments of a method of manufacturing bottom-emitting and top-emitting OLED displays. According to these embodiments, an OLED display shown in  FIG. 10 ( a ) is manufactured by the processes shown in FIGS.  10 ( b ) to  10 ( d ). More particularly, as shown in  FIG. 10 ( b ), a plurality of parallel first display electrode lines  214  made of indium tin oxide (ITO) or the like are deposited as stripes on a glass substrate  218 . And ribs  222  of polyimides or the like are formed on the first display electrode lines  214 , so that the island shaped first display electrode portions  215  are defined and surrounded as shown in  FIG. 10 ( c ). An OLED light-emitting layer  213  is formed on each recess of the glass substrate  218  wherein the ribs  222  are formed. Next, a plurality of parallel stripe second display electrode lines  217  of low resistance metal are vacuum-deposited or sputtered with a shadow mask with parallel slits on the ribs  222  and the light-emitting layers  213  so that the second display electrode lines  217  extend perpendicular to the first display electrode lines  214 .  
         [0010]     In the area surrounded by the ribs  222 , a TFT connected to the first display electrode portions  215  is formed on the glass substrate  218 , where data signal lines and scan signal lines or the like are arranged. As shown in  FIG. 10 ( a ), in this embodiment, the OLED display takes out light from the glass substrate side  218 .  
         [0011]     In the active matrix system, however, the aperture ratio is reduced due to TFT, capacitors, and wiring or the like after taking out luminescence from the glass substrate side  218  like the bottom-emitting system. Consequently, when the active matrix system is adopted, the top-emitting system is advantageous. Light is not shielded by the TFT, which results in an increase of the aperture ratio and high luminance when adopting the top-emitting system.  
         [0012]      FIG. 11  shows a cross sectional view of the structure of a top-emitting active matrix OLED display. In  FIG. 11 , an OLED display  310  comprises: an insulating substrate  318 ; a thin film transistor (TFT)  320  formed on the insulating substrate  318 ; an insulating layer  319 ; a first electrode  314 ; a material layer  313 ; a second electrode  317 ; and a via hole  326  for connecting the first electrode  314  and the TFT  320  through the insulating layer  319  (For examples, see cited document 1).  
         [0013]     Unlike the bottom-emitting system, the second electrode  317  is required to be made from a transparent material because the OLED display  310  takes out luminescence from the second electrode side  317 . Further, to increase optical transmittance, the second electrode  317  needs to be as thin as possible. Moreover, the second electrode  317  may be laminated covering the entire surface of the OLED display.  
         [0014]     A light-emitting layer included in the material layer  313  of the OLED display  310  emits light to take out the luminescence from the second electrode side  317 .  
         [0015]     Since the structure of such top-emitting active matrix OLED displays is various, the second electrode  317  covering the entire surface of the above-mentioned OLED display may be divided in stripe like the passive matrix system. Further, the via hole  326  in  FIG. 11  connects the first electrode  314  to the TFT  320 , but may be used to connect, for examples, the second electrode and the common electrodes.  
         [0016]     One example of a top-emitting active matrix OLED display having ribs will be now described by using FIGS.  8 ( a ) and  8 ( b ).  
         [0017]     AS shown in  FIG. 8 ( b ), in an OLED display  110 , ribs  122  are arranged on an insulating substrate  118  in parallel. As shown in  FIG. 8 ( a ), OLED elements  112  are sandwiched between ribs  122 . The area of one unit of matrix divided by the ribs  122  and OLED elements  112  are referred to as a cell area  132 . The cells completed by equipping the cell area  132  with the TFT  120  and the OLED elements  112  are referred to as pixels  130 .  
         [0018]     The pixels  130  in each cell area  132  are so configured that an anode  114  and the ribs  122  are formed on the insulating substrate  118  by sandwiching the anode  114  in the column direction of the matrix in parallel as shown in  FIG. 8 ( a ). Further, in parallel with the ribs  122 , common electrodes  124  isolated from the anode  114  and the ribs  122  are formed on the insulating substrate  118 . Furthermore, the OLED elements  112  are formed by the lamination of at least a light-emitting layer and a thin film cathode  117  on the upper part of the anode  114 . Moreover, the thin film cathode  117  is laminated on the pixels  130 . And the via holes  126  for conducting the thin film cathode  117  and the common electrodes  124  may be formed in each cell area  132 .  
         [0019]     The thin film cathode  117  is laminated on the entire surface of the OLED display  110 . The thin film cathode  117  is partitioned by the ribs  122  formed among the adjacent cell areas  132  in a column direction when laminating the thin film cathode. The anode  114  is not needed to be optical transparent due to the-top emitting system but may be made from a metal, such as Al.  
         [0020]     Additionally, the cell areas  132  are in a rectangle shape. Each cell area  132  includes OLED elements  112 . The common electrodes  124  are formed on the insulating substrate  118  in parallel with the ribs  122  to be isolated from the anode  114 . The common electrodes  124  may conduct with the thin film cathode  117  through the via holes  126  formed within each cell area. Accordingly, the thin film cathode  117  laminated on the surface of the OLED display  110  is equipotential through the common electrodes  124 .  
         [0021]     When an OLED display  110  having such configuration is driven employing the active matrix and top-emitting systems, a circuit formed by circuit elements, such as the OLED elements  112  and common electrodes  124  are shown in a schematic diagram  4 ( a ) or  4 ( b ) as an ideal example. More specifically, the OLED elements  112  emit light by the application of a forward voltage between the OLED elements  112  through the TFT because of this mechanism. For example, in  FIG. 4 ( a ), a current passing via the OLED elements passes into the common electrodes  124  from the surface of the thin film cathode  117 . Following explanation is given using the schematic diagram  4 ( a ) for convenience sake.  
         [0022]     Considering a circuit as shown in  FIG. 4 ( a ), a predetermined amount of current always passes through the OLED elements  112  selectively applied by a certain voltage. And a current does not always pass through the OLED elements  112  which are not selected. On the other hand, it is known that the luminance of the OLED elements  112  are virtually in proportional to the current passing through the OLED elements  112 . It follows that the light emission of the selected OLED elements  112  is performed at predetermined luminance and the light emission of the unselected OLED elements  112  is never performed, which results in no unexpected luminance nonuniformity.  
         [0023]     Upon driving the OLED display  110  having the above-mentioned configuration, however, as shown in  FIG. 9 , it has turned out that an apparent linear luminance nonuniformity appears on the surface of the display. Especially, such linear luminance nonuniformity distinctly appears on top-emitting active matrix OLED displays wherein ribs  122  are arranged in parallel like the above-mentioned systems. Further, luminance nonuniformity in a spot state easily occurs on the kind of OLED displays without ribs  122 , wherein the entire surface is covered with a thin film electrode.  
         [0024]     (Cited Document 1)  
         [0025]     Japanese Patent Publication No. 2003-22035 (Page 2,  FIG. 1 )  
         [0026]     (Cited Document 2)  
         [0027]     Japanese Patent Publication No. 08-227276 (Pages 4 and 5,  FIGS. 13 and 14 )  
       SUMMARY OF THE INVENTION  
       [0028]     An OLED display according to the present invention comprises: an insulating substrate; common electrodes formed on the insulating substrate; a first electrode layer formed in a region adjacent to the common electrodes formed on the insulating substrate by electrically isolating from the common electrodes; an insulating layer which coats on the insulating substrate by respectively opening a first opening window exposing a part of the common electrodes and a second opening window exposing at least a part of the first electrode layer; ribs which form a cell area by crossing the common electrodes on the insulating substrate and surrounding each of the opening windows; a material layer formed on the first electrode layer exposed from the second opening window; and a second electrode layer which coats within the cell area surrounded by the rib and electrically connected to the common electrodes through the first opening window. The crossing walls of these ribs include a reserve tapered shape.  
         [0029]     A method for manufacturing an OLED display according to the present invention comprises: preparing an insulating substrate; forming common electrodes on the insulating substrate; forming a first electrode layer in a region adjacent to the common electrodes formed on the insulating substrate by electrically isolating from the common electrodes; coating on the insulating substrate with an insulating layer by respectively opening a first opening window exposing a part of the common electrodes and a second opening window exposing at least a part of the first electrode layer; forming a cell area on the insulating substrate by surrounding each of the opening windows with ribs across the common electrodes; forming a material layer on the first electrode layer exposed from the second opening window; and forming a second electrode layer electrically connected to the common electrodes through the first opening window by coating within the cell area.  
         [0030]     The method for manufacturing an OLED display according to the present invention comprises: preparing an insulating substrate; forming band-like common electrodes on the insulating substrate; forming a first electrode layer in an region adjacent to the common electrodes formed on the insulating substrate; coating the insulating substrate with an insulating layer; forming ribs wherein the walls are in a reverse tapered shape and a thin insulating layer in a cell area surrounded with the ribs by etching the insulating layer across the common electrodes; forming a first opening window exposing a part of the common electrodes and a second opening window exposing a part of the first electrode layer on the insulating layer within the cell area; forming a material layer on the first electrode layer exposed from the second opening window; and electrically connecting the second electrode layer which coats the material layer to the common electrodes through the first opening window by coating the ribs with the second electrode layer as a mask within the cell area. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0031]      FIG. 1 ( a ) is a plan view of an OLED display,  FIG. 1 ( b ) is a cross sectional view taken on line A-A of  FIG. 1 ( a ),  FIG. 1 ( c ) is a cross sectional view taken on line B-B of  FIG. 1 ( a ),  FIG. 1 ( d ) is a cross sectional view taken on line of C-C of  FIG. 1 ( a ),  FIG. 1 ( e ) is a cross sectional view taken on line D-D of  FIG. 1 ( a ), and  FIG. 1 ( f ) is a cross sectional view taken on line E-E of  FIG. 1 ( a ) according to the present invention.  
         [0032]      FIG. 2 ( a ) is a cross sectional view of another embodiment of the OLED display of the present invention, and  FIG. 2 ( b ) is a cross sectional view of further another embodiment of the OLED display of the present invention.  
         [0033]      FIG. 3  is an equivalent circuit diagram of an OLED display of the present invention.  
         [0034]      FIG. 4 ( a ) is an ideal equivalent circuit diagram of a conventional top-emitting OLED display, and  FIG. 4 ( b ) is another ideal equivalent circuit diagram of a conventional top-emitting OLED display.  
         [0035]      FIG. 5 ( a ) is a perspective view of a passive matrix OLED display, and  FIG. 5 ( b ) is a plan view of a passive matrix OLED display.  
         [0036]      FIG. 6 ( a ) is a perspective view of an active matrix OLED display, and  FIG. 6 ( b ) is a plan view of an active matrix OLED display.  
         [0037]      FIG. 7 ( a ) is a cross sectional view of a bottom-emitting OLED display, and  FIG. 7 ( b ) is a cross sectional view of a top-emitting OLED display.  
         [0038]      FIG. 8 ( a ) is a plan view of a conventional OLED display, and  FIG. 8 ( b ) is a cross sectional view of  FIG. 8 ( a ).  
         [0039]      FIG. 9  shows a top-emitting OLED display having linear luminance nonuniformity.  
         [0040]      FIG. 10 ( a ) is a cross sectional view of a bottom-emitting active matrix OLED display,  FIG. 10 ( b ) is a perspective view of an OLED display wherein first display electrode lines,  FIG. 10 ( c ) is a perspective view of an OLED display wherein ribs are arranged, and  FIG. 10 ( d ) is a perspective view of an OLED display wherein second display electrode lines are formed.  
         [0041]      FIG. 11  is a cross sectional view of a top-emitting active matrix OLED display. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0042]     The present invention will now be described in detail. For the sake of convenience, a first electrode refers to an anode and a second electrode refers to a cathode. Further, a first opening window opened in an insulating layer for coating on an insulating substrate refers to a via hole reaching from the surface of the cathode of OLED to common electrodes. An anode is exposed to the inside of a second opening window.  
         [0043]     FIGS.  1 ( a ) to  1 ( f ) are a plan view and cross sectional views per each cut section of an OLED display in an embodiment of the present invention. In this embodiment, as shown in a shaded area of  FIG. 1 ( a ), an OLED display  10  is divided into cell areas  32  in matrix state by ribs  22  arranged on an insulating substrate  18  or an insulating layer  19  covering the insulating substrate  18 . Inside the cell area  32 , an anode  14  is formed on the insulating substrate  18 , where common electrodes  24  are formed by being isolated from the anode  14  in parallel with the ribs  22 . In addition, OLED elements  12  formed on the anode  14  by laminating a material layer  13  and a thin film cathode  17 , and via holes  26  conducting the thin film cathodes  17  and the common electrodes  24  are formed within the cell areas  32 .  
         [0044]     The insulating substrate  18  herein may be, for example, a glass substrate. The ribs  22  are ribs made from an insulator, such as polymer and ribs in a reverse tapered shape. The anode  14  may be an electrode made from a metal, such as Al or an electrode made from other materials. Although the common electrodes  24  are preferably made from a metal having superior conductivity and the shape is not limited, as shown in  FIG. 1 ( a ), they may be common electrodes  24 . Further, the thin film cathode  17  is prepared by utilizing a transparent electrode material itself or by laminating ordinary metals to be formed with the surface of the cell areas  32  covered. Furthermore, the material layer  13  sandwiched between the anode  14  and thin film cathode  17  may include a plurality of layers, such as an electron or a hole-injecting layer, an electron or a hole-transporting layer other than a light-emitting layer.  
         [0045]     To solve the above-mentioned problems,  FIG. 4 ( a ) assumed as equivalent circuit is amended to assume the circuit of  FIG. 4 ( c ) as equivalent circuit of a realistic OLED display. The presence of a leakage current passing through the surface of the thin film cathode  17  uniformly laminated on the OLED display needs to be considered in  FIG. 4 ( c ).  
         [0046]     Referring to the circuit represented in  FIG. 4 ( c ), OLED  1  to OLED  4  are assumed as OLED elements  12 . The OLED elements  12  are respectively connected to TFT  20  within the cell areas  32  and similarly connected to the common electrodes  24  through via holes  26  in the cell areas  32 . Rg shows resistance of the common electrodes  24 . Rc shows resistance among the cell areas  32 . Rvia1 shows average resistance of the via holes  26 . Rvia2 shows resistance of the via holes  26  having resistance different from Rvia1.  
         [0047]     As described in the above-mentioned conventional examples, the thin film cathode of the surface of the OLED display is unidirectionally isolated by the ribs  22  arranged in stripe. However, no isolation is provided among OLED elements formed along the ribs  22 , so that a leakage current may unidimensionally pass among the cell areas through the surface of the thin film cathode. Accordingly, in an equivalent circuit shown in  FIG. 4 ( c ), the presence of resistance Rc among the cell areas  32  needs to be considered.  
         [0048]     Further, the via holes  26  are holes to reach from the surface of the thin film cathode  22  to the common electrodes  24  and seems to have large resistance Rvia1 comparing with the thin film cathode  22  in a planar state. Furthermore, the via holes  26  often have nonuniform resistance because it is difficult to keep uniform resistance. Consequently, resistance Rvia2 of via holes  26  different from that of the average via holes  26  has to be taken into consideration in the equivalent circuit diagram of  FIG. 3 . The equation of Rvia1&gt;Rvia2&gt;&gt;Rc&gt;&gt;Rg is assumed to be established in the equivalent circuit diagram of  FIG. 4 ( c ).  
         [0049]     In the equivalent circuit diagram of  FIG. 4 ( c ), such as the above-mentioned figure, current is passed into Rvia2 by passing a leakage current through Rc because Rvia2 is smaller than Rvia1. The effects of the presence of voltage depending on a path reaching Rvia2 enable the current value passing through each of the cell areas  32  to make difference from the estimated current value. As mentioned above, emitting luminance of the OLED elements  12  depends on the current value. As a result, luminance nonuniformity is observed around Rvia2 in the cell areas  32  due to different luminance from other places of the display. Further, the leakage current gives impact on the current passing through the OLED elements in the cell areas  32  near Rvia2, so that luminance nonuniformity easily appears as linear luminance nonuniformity in the direction of the ribs because the thin film cathode  17  which is used as a flowing path is unidirectionally isolated.  
         [0050]     To avoid such luminance nonuniformity, a method for closing off a path where a leakage current passes through by separating an anode and a cathode for each adjacent cell area is adopted. More particularly, a wide range of luminance nonuniformity is replaced with luminance nonuniformity in the cell areas  32  by arranging ribs among the cell areas  32  to interrupt the leakage current passing through the cell areas  32  in  FIG. 3 .  
         [0051]     In this embodiment, an OLED display  10  is formed as mentioned below. As shown in FIGS.  1 ( a ) to  1 ( f ), common electrodes  24  are formed on an insulating substrate  18  and then ribs  22  for dividing the insulating substrate into a plurality of cell areas  32  to electrically isolate among each cell area are formed on the insulating substrate  18  and the common electrodes  24 . Next, the anode  14  is formed within the plurality of cell areas  32  and OLED elements  12  are formed by laminating in the order of a material layer  13  and a thin film cathode  17 . Additionally, via holes  26  for electrically conducting the thin film cathode  17  and the common electrodes  24  are formed.  
         [0052]     The ribs  22  are made from an insulator and separate the anode  14  and thin film cathode  17  for each cell area  32 . The thin film cathode  17  and common electrodes  24  in each cell area  32  are ordinarily equal potential because of being connected to each other through the via holes  26 . Even when a potential difference occurs among the cell areas  32  for a particular reason, there is no possibility of the current passing among the cell areas  32  via the surface of the thin film cathode  17  because of isolating each of the cell areas  32  from the other cell areas by the formation of the ribs  22 .  
         [0053]     The ribs  22  are formed by applying a negative typed photo resist onto the insulating substrate  18  employing the spin coat method and being developed after exposure using a photo mask. These ribs are in a reverse tapered shape in 10 μm order previously arranged on the insulating substrate  18 . These ribs in a reverse tapered shape are formed, for example, with a negative-type photo polymer by utilizing the difference of developing speed caused by the difference in amount exposed in the thickness direction.  
         [0054]     Such configuration of an OLED display  10  makes it possible to avoid the above-mentioned leakage current from occurring by electrically isolating each of the cell areas  32  from the thin film cathode  17  on the surface of the thin film cathode  17 . That is, the ribs  22  isolate among OLED elements  12  in cell state, which leads to prevent the current from passing among the cell areas  32  via the surface of the thin film cathode  17 .  
         [0055]     Further, the impact of the ribs  22  made on luminance nonuniformity will be now described using  FIG. 3 . Since an anode and a cathode are separated for each cell area  32  by the ribs  22  to close off the path for the leakage current, the current passing through the OLED elements  12 , such as OLED  1 , OLED  2 , and OLED  4  reaches the common electrodes  25  through resistance Rvia1. Accordingly, the current passing through three OLED elements  12  is uniform and the luminance is also uniform.  
         [0056]     However, the current passing through the OLED elements  12  indicated as OLED  3  reaches the common electrodes  24  via resistance Rvia2. From the above-mentioned conditions, Rvia1 is larger than Rvia2, so that the current passing through the OLED elements  12  indicated as OLED  3  becomes larger than the current passing through other OLED elements  12  indicated as OLED  1 , OLED  2 , and OLED  4 . As a result, the luminance of OLED  3  is unexpectedly larger than other 3 OLEDs, which leads to luminance nonuniformity.  
         [0057]     Unlike conventional OLED displays, the OLED display of the present invention is capable of removing the whole linear luminance nonuniformity. More particularly, in  FIG. 3 , a wide range of luminance nonuniformity is replaceable with luminance nonuniformity in each of the cell areas  32 .  
         [0058]     The structure of the OLED display according to the present invention is not limited to the above-mentioned embodiments. For example, common electrodes may be formed on the entire surface of the insulating substrate  18  to laminate an insulating layer  19  on the entire surface of the common electrodes  24 , and on the insulating layer  19 , the cell areas  32  may be formed by the ribs  22 .  
         [0059]     An anode  14  is formed within each cell area  32 , and a material layer  13  and a thin film cathode  17  are laminated on the anode  14  in order to form the OLED elements  12 . The ribs  22  are high enough to divide the thin film cathode  17  into each cell area  32 . The via holes  26  for electrically conducting the thin film cathode  17  and the common electrodes  24  are formed by penetrating the anode  14  and insulating layer  19  in this embodiment.  
         [0060]     The OLED display of this embodiment is capable of interrupting the leakage current passing via the surface of the thin film cathode  17  in the cell areas  32  by the arrangement of the ribs among the cell areas  32 . Accordingly, the OLED display of this embodiment is capable of removing a wide range of luminance nonuniformity easily discovered as well as the above-mentioned embodiments.  
         [0061]     Alternatively, as shown in  FIG. 2 ( a ), common electrodes  24  may be formed on the entire surface of an insulating substrate  18 , and ribs  22  are arranged on the common electrodes  24  so that cell areas  32  may be formed, and then an insulating layer  19  may be laminated. After that, OLED elements  12  and via holes  26  are formed within each cell area in the same manner as the above-mentioned embodiments. The common electrodes  24  and an anode not shown in figures are isolated by the insulating layer  19  and the thin film cathodes  17  located adjacent to each other are isolated by the ribs  22  in this embodiment as well as the above-mentioned embodiments.  
         [0062]     On the other hand, the ribs  22  may be directly arranged on the insulating substrate  18  in another embodiment shown in  FIG. 4 ( b ). Common electrodes  24 , an insulating layer  19 , an anode (not shown in figures), OLED elements (not shown in figures), and a thin film cathode  17  are laminated in order. In this case, a wide range of luminance nonuniformity is removable in the same manner as the OLED display of the above-mentioned embodiments.  
         [0063]     Although a thin film cathode is used in the embodiments of the OLED display according to the present invention described above, a cathode with thicker thickness may be laminated on a material layer  13 . In this case, problems with luminance nonuniformity caused by a leakage current do not become evident so often because resistance of the thick cathode is smaller than that of the thin film cathode  17  and is sufficiently close to resistance of the common electrodes  24 . In addition, it is not so common that such problems of a wide range of luminance nonuniformity become evident when employing the bottom-emitting system for the similar reason.  
         [0064]     Even when resistance of the thick cathode is small, luminance nonuniformity is presumed to appear not in a wide range but locally due to the mechanism of the above-mentioned description. Consequently, a method for removing luminance nonuniformity using the ribs  22  of the present invention is effective regardless of whether using the top-emitting system or the bottom-emitting system. The method for removing luminance nonuniformity using the ribs  22  of the present invention is effective to all OLED displays wherein OLED elements  12  are not electrically insulated from each other on the surface electrode.  
         [0065]     Furthermore, the anode  14  and the thin film cathode  17  may be interchangeable in the above-mentioned embodiments of the present invention. More specifically, similar effects of removing luminance nonuniformity can be obtained in OLED displays wherein OLED elements  12  are formed by forming a cathode on the insulating substrate  18  and laminating the material layer  13  and an anode. In this case, partitioning among the OLED elements by the ribs  22  enables to remove luminance nonuniformity which occurs on OLED displays each having a structure in which the common electrodes are connected to the anode as shown in  FIG. 4 ( b ) In each embodiment of the present invention described so far, an insulating substrate  18  is made of glass and the like, but it is not limited to a transparent material as far as the top-emitting system is used for the OLED display. More particularly, the insulating substrate  18  is not particularly limited as far as it is an insulator and may be made of plastic and the like.  
         [0066]     Similarly, the anode is not limited to a transparent material but may be made from a metal, such as Al and a thin plate made of stainless or the like. Further, the above-mentioned first opening window is not limited to be called as via holes and through holes or the like and includes all opening windows for electrically conducting the cathode surface of the OLED elements and common electrodes.  
         [0067]     The ribs  22  preferably include a reverse tapered shape crossing upwardly on a second electrode layer and may be so-called cathode ribs. In this case, the ribs  22  also act as a role of a shadow mask at the time of laminating the cathode. Alternatively, the ribs  22  may be exclusively used for shutting down the continuity among the cell areas  32 . In this case, the ribs  22  are not limited to particular shape and material or the like as long as isolation among the cell areas  32  can be obtained.  
         [0068]     Additionally, the cell areas  32  surrounded by the ribs  22  are in a rectangle shape partitioned in a row direction and a column direction, but the shape of the cell areas  32  are not particularly limited. The shape may be in other polygonal shape, such as triangle shape and the like. Alternatively, the shape of the cell area  32  may be a round shape or an oval shape. The shape and size of each of the cell areas  32  may be arbitrary.  
         [0069]     The cell areas  32  in such shape are disposed on the row and column in matrix state. Alternatively, these cell areas  32  are aligned in such a manner to form a polygonal grating, such as a triangle grating and a hexagonal grating. These cell areas  32  may be arbitrarily disposed.  
         [0070]     There have thus been shown and described a novel OLED display and a method for manufacturing thereof which fulfill all the objects and advantages sought therefor. Many changes, modifications, variations, combinations, and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, Which is to be limited only by the claims which follow. This application claims priority from Japanese Patent Application No. 2003-209273, which is incorporated herein by reference.

Technology Classification (CPC): 7