Patent Publication Number: US-7595084-B2

Title: Organic light emitting device and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of prior U.S. patent application Ser. No. 11/020,671, filed on Dec. 27, 2004, and claims the benefit of Korean Patent Application No. 2003-98228, filed on Dec. 27, 2003, both of which are 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 device and a method of manufacturing the same. More particularly it relates to an organic light emitting device and a method of manufacturing the same. 
     2. Description of the Related Art 
     Top emitting light emitting devices may have superior light emitting efficiency compared to bottom emitting light emitting devices. Thus, the top emitting light emitting devices are more widely used for displays. 
     A conventional top emitting light emitting device, as illustrated in  FIG. 1 , can include a cathode layer  10 , a light emitting layer  12  that emits light L, a hole transport layer  14 , and an anode layer  16  formed sequentially. The anode layer  16  can be an indium tin oxide (ITO) layer, which is a conductive and transparent layer. 
     The ITO layer is deposited at a high temperature, and also subject to heat treatment to enhance conductivity. The deposition and heat treatment of the ITO layer are typically performed at a temperature of 400° C. or greater. However, light emitting material may not withstand such a the high temperature deposition process and the heat treatment process. 
     Thus, a method of depositing an ITO layer at a low temperature has been developed. However, when the ITO layer is deposited at a low temperature, the performance of the light emitting device degrades because the ITO layer breaks off. Accordingly, the desired result has not been obtained. 
     In addition, a conventional light emitting device has low out coupling efficiency. Out coupling efficiency is a measure of the amount of transmitted light compared to that amount plus the amount lost to total internal reflection. That is, light reflected from a boundary of elements having different reflective indices within an organic light emitting device can be reflected back inside the organic light emitting device. 
     This reflected light can be either substantially parallel to the substrate or substantially perpendicular to the substrate. Most of the light parallel to the substrate is emitted from the corners of the substrate. The light perpendicular to the substrate can be emitted to the desired direction by using a reflection layer on the opposite side from the substrate. The reflection layer can be formed separately from the anode layer. 
     However, of the initially reflected light from a boundary of elements, the light that is parallel to the substrate and leaks out of the organic light emitting device can be almost 50% of the total leakage light of the organic light emitting device. Therefore, the luminous efficiency is lower than desired. 
     SUMMARY OF THE INVENTION 
     The present invention relates, for example, to an organic light emitting device and a method of manufacturing the organic light emitting device that may help to alleviate the problems due to use of the ITO layer and may increase light emitting efficiency. 
     An organic light emitting device can include a substrate; first and second metal layers used as electrodes formed on the substrate; an electron transport layer formed on the first metal layer; a first partition wall that insulates the first metal layer from the second metal layer and extends onto the electron transport layer along the first metal layer; a second partition wall formed on the first metal layer around the electron transport layer; a third partition wall separated from the first partition wall and formed on the second metal layer; an organic light emitting layer formed on the electron transport layer; a hole transport layer formed on the organic light emitting layer, (covering the first partition wall and contacting an exposed portion of the second metal layer between the first and third partition walls); a protecting layer covering the hole transport layer and extending onto the first and second metal layers around the second and third partition walls; and a sealing material filling spaces between the protecting layer and the first and second metal layers. 
     A groove (which can be asymmetric) may be formed in the substrate. An inner surface of the groove may have a slight slope such that incident light parallel to the substrate is reflected upward. The first and second metal layers may extend toward the groove. 
     First and second steps may be formed in the groove. The second step may contact the bottom of the groove. The first step may be separated from the second step. 
     The first metal layer may extend to the second step across a portion of the inner surface of the groove where no steps are formed and across the bottom of the groove. 
     The second metal layer may cover the first step and the second metal layer extending to an upper surface of the substrate around the groove. Also, the second metal layer may extend to a flat surface of the substrate between the first and second steps. 
     A first coupling material may be formed on the first metal layer. A second coupling material combined with the first coupling material may be formed on the protecting layer. The first and second coupling materials may be a protruding portion and a groove respectively. The protruding portion may be designed to be inserted into the groove. 
     The electron transport layer may be a single layer or multiple layers having a work function between work functions of the organic light emitting layer and the first metal layer. 
     The substrate may comprise a base substrate forming the bottom of the groove and a glass substrate forming the inner surface of the groove. 
     An organic light emitting device according to the present invention does not require the inclusion of an ITO electrode layer. Therefore, the entire manufacturing process can be shorter and manufacturing costs can be lower. Moreover, the organic light emitting device of the present invention can be applied to flexible displays. 
     In addition, the organic light emitting device according to the present invention can improve luminance efficiency because it can include a reflecting material. Light emitted horizontally from an organic light emitting layer or reflected in a lateral direction can thus be reflected upward. 
     In an organic light emitting device manufactured according to the present invention, the surface state and thickness of the hole transport layer can have little effect on the performance of the organic light emitting device. That is, the organic light emitting device according to the present invention may have fewer factors that affect its performance. Moreover, the present invention may obviate the need for an indium-tin-oxide (ITO) or indium-zinc-oxide (IZO) layer. Accordingly the fabrication temperature of the device may be reduced, and the organic material may be more easily preserved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a conventional organic light emitting device. 
         FIG. 2  is a cross-sectional view of an organic light emitting device according to a first embodiment of the present invention. 
         FIG. 3  is a cross-sectional view of an organic light emitting device according to a second embodiment of the present invention. 
         FIG. 4  is a cross-sectional view of an organic light emitting device according to a third embodiment of the present invention. 
         FIG. 5  is a cross-sectional view illustrating an organic light emitting device according to a fourth embodiment of the present invention. 
         FIGS. 6 and 7  are flow charts illustrating methods of manufacturing organic light emitting devices according to the first and second embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Exemplary embodiments of an organic light emitting device according to the present invention and a method of manufacturing the same will now be described in detail with reference to the attached drawings. In the drawings, the thicknesses of layers and sizes of regions are exaggerated for clarity. 
     According to an embodiment of the present invention, an anode layer of a conventional multi-layered organic light emitting device can be divided into two layers, and one of the two layers may be used as an anode layer and the other of the two layers may be used as a cathode layer. A separating partition wall may be interposed between the cathode layer and the anode layer. An organic light emitting layer may be formed on the cathode layer. 
     In addition, the organic light emitting layer and the anode layer may be interconnected by a hole transport layer that is transparent and conductive. As the partition wall extends on a slanted surface, out coupling efficiency of the organic light emitting device can be improved using the cathode layer. Detail constitutions of organic light emitting devices according to the present invention may differ as explained in the embodiments described below. 
     First Embodiment 
     As shown in  FIG. 2 , a groove  22  having a predetermined depth may be formed in a substrate  20  of an organic light emitting device according to a first embodiment of the present invention (first organic light emitting device). The substrate  20  may be glass. A side surface of the groove  22  may have a slight slope. 
     First and second steps S 1  and S 2  may be formed on a portion of the side surface between a surface  20   a  of the substrate  20  and a bottom  22   a  of the groove  22 . The first and second steps S 1  and S 2  may be horizontally separated from each other, have the same slopes, and may be vertically disposed at different heights. A horizontal surface  22   b  may lie between the first and second steps S 1  and S 2 . The horizontal surface  22   b  may be lower than the surface  20   a  of the substrate  20 , and may be disposed at approximately the midpoint between the surface  20   a  of the substrate  20  and the bottom  22   a  of the groove  22 . 
     To increase the out coupling efficiency, the first and second steps S 1  and S 2  may have a slight slope like a portion of the groove  22  where steps are not formed. A first metal layer  24   a  and a second metal layer  24   b  may be formed on the substrate  20 . The first and second metal layers  24   a  and  24   b  may be used as a cathode layer and an anode layer respectively. The first and second metal layers  24   a  and  24   b  may be composed of the same metal, for example, Al. Alternatively, the first and second metal layers  24   a  and  24   b  may be composed of other metals and may differ from one another in metal content. 
     The first and second metal layers  24   a  and  24   b  may extend on the surface of the groove  22 . Specifically, the first metal layer  24   a  may extend from a top of the substrate  20  facing the first and second steps S 1  and S 2  to the horizontal surface  22   b  across the side surface (inner surface) of the groove  22 , the bottom  22   a  of the groove  22 , and the second step S 2 . The second metal layer  24   b  may extend from the top of the substrate  20  adjacent to the first step S 1  to the horizontal surface  22   b  between the first and second steps S 1  and S 2  across the first step S 1 . 
     Even though both the first and second metal layers  24   a  and  24   b  extend to the horizontal surface  22   b  between the first and second steps S 1  and S 2 , the first and second metal layers  24   a  and  24   b  may not contact each other. This may be because they are to be used as different electrodes. Therefore, a first partition wall  26  can be formed on the horizontal surface  22   b  between the first and second steps S 1  and S 2  to separate and insulate the first and second metal layers  24   a  and  24   b.    
     The first partition wall  26  may be composed of an insulating film, for example a silicon oxide film. The first partition wall  26  may fill a gap g between the first and second metal layers  24   a  and  24   b.  The first partition wall  26  may extend on parts of the first and second metal layers  24   a  and  24   b.  Specifically, in the direction of the second metal layer, the first partition wall  26  may extend onto only a portion of the second metal layer  24   b,  but in the direction of the first metal layer extends on an edge of the bottom  22   a  of the groove  22  across the second step S 2 . An electron transport layer  31  may be formed on the first metal layer  24   a  formed on the bottom  22   a  of the groove  22 . The thickness of the electron transport layer  31  may be equal to that of a portion of the first partition wall  26  extending onto the first metal layer  24   a.    
     The electron transport layer  31  may be a single or multiple layer structure having an appropriate work function so that electrons can easily migrate from the first metal layer  24   a  to a light emitting layer  36  provided on the electron transport layer  31 . When the electron transport layer  31  is a single layer, the electron transport layer  31  may be, for example, a Ba layer. When the electron transport layer  31  is a multiple layer, the electron transport layer  31  may include first and second electron transport layers  32  and  34  stacked sequentially. The first electron transport layer  32  may be, for example, a Ca layer, and the second electron transport layer  34  may be, for example, a Ba 2 F layer. A second partition wall  28  may be formed on the first metal layer  24   a.  The second partition wall  28  may contact the electron transport layer  31  across a slanted surface of the first metal layer  24   a.  The second partition wall  28  may be composed of the same material as the first partition wall  26 . 
     The first and second partition wall  26  and  28  may be formed simultaneously during the manufacturing process. Accordingly, the thickness of the second partition wall  28  may be equal to the thickness of a portion of the first partition wall  26  extending onto the first metal layer  24   a.    
     A portion of the second metal layer  24   b  corresponding to the first step S 1  may be covered by a third partition wall  30 . The third partition wall  30  is composed of the same material as the first partition wall  26 . The third partition wall  30  and the first partition wall  26  are separated on the second metal layer  24   b.  The third partition wall  30  is simultaneously formed together with the first and second partition walls  26  and  28 . 
     Accordingly, the thickness of the third partition wall  30  may be equal to the thickness of the second partition wall  28 . A light emitting layer  36 , from which light is generated by the recombination of carriers provided from the first and second metal layer  24   a  and  24   b,  may be formed on the electron transport layer  31 . The light emitting layer  36  may contact extended portions of the second partition wall  28  and the first partition wall  26 . The light emitting layer  36  may be a low molecular fluorescent layer, a high molecular fluorescent layer, or a phosphor layer. 
     An upper surface of the light emitting layer  36  may be disposed lower than an upper surface of the first partition wall  26 . A hole transport layer  38  may be formed on the light emitting layer  36 . One side of the hole transport layer  38  may contact the second partition wall  28 , and the other side of the hole transport layer  38  may cover the first partition wall  26  and may contact the third partition wall  30  and a portion of the second metal layer  24   b  exposed between the first and third partition walls  26  and  30 . 
     An upper surface of the hole transport layer  38  may be disposed lower than upper surfaces of the first and second metal layers  24   a  and  24   b.  The hole transport layer  38  may transport holes from the second metal layer  24   b  that is an anode layer to the light emitting layer  36 . The work function of the hole transport layer  38  may be like that of the second metal layer  24   b  so that holes can be easily injected into the hole transport layer  38 . 
     The hole transport layer  38  may be a material layer having good conductivity. This may be because it may be used to transport holes to a light emitting area. A protecting layer  40  may be separated from the hole transport layer  38  by a predetermined distance. The protecting layer  40  may be a glass layer or a thin film, for example an Au film. 
     The protecting layer  40  may extend onto the first and second metal layers  24   a  and  24   b  formed on the substrate  20  outside of the groove  22 , and may contact the second and third partition walls  28  and  30  at the border of the groove  22 . Spaces between portions of the protecting layer  40  extending beyond the second and third partition walls  28  and  30  and the first and second metal layers  24   a  and  24   b  may be filled with a sealing material  44  such as a UV resin. 
     For virtually perfect sealing, a comb-like protruding portion  42  may be formed on a predetermined region of the first metal layer  24   a  and/or the second metal layer  24   b  facing the protecting layer  40 , such as a region outside the groove  22  of the first metal layer  24   a.  In addition, the protecting layer  40  may have a groove  40   a,  in which the protruding portion  42  is inserted. In this case, the sealing material  44  may lie between the protruding portion  42  and the groove  40   a.    
     The sealing may be completed as follows. The sealing material  44  may be dropped onto a region where the protruding portion  42  of the first metal layer  24   a  is formed, the protecting layer  40  may be arranged such that the protruding portion  42  is inserted into the groove  40   a,  and then the protecting layer  40  may be pressed. 
     In  FIG. 2 , an arrow L 1  represents light emitted upward from the organic light emitting layer  36 , or light reflected upward by the first metal layer  24   a  below the organic light emitting layer  36 . An arrow L 2  represents light reflected upward by the slanted surface of the first metal layer  24   a.  Light approximately parallel to the upper surface of the organic light emitting layer  36  (whether emitted from the organic light emitting layer  36  or reflected from the upper surface of the organic light emitting layer  36  into the organic light emitting layer  36 ) may be incident to the slanted surface of the first metal layer  24   a.    
     Second Embodiment 
     An organic light emitting device according to a second embodiment of the present invention (second organic light emitting device) may have an embossed form. 
     As shown in  FIG. 3 , the second organic light emitting device can include a glass substrate  48  on a base substrate  18 . A penetrating hole  50  exposing the base substrate may be formed in the glass substrate  48 . The inner surface of the penetrating hole  50  may have the same form as the side surface of the groove  22  formed in the substrate  20  of the first organic light emitting device (see  FIG. 2 ). Also, the base substrate  18  may lie beneath the penetrating hole  50 . 
     Accordingly, the penetrating hole  50  may become functionally the same as the groove  22  formed in the substrate  20  of the first organic light emitting device. A portion  18   a  of the base substrate  18  exposed through the penetrating hole  50  may have the same form as the bottom  22   a  of the groove  22 . The penetrating hole  50  may have third and fourth steps S 3  and S 4  in a portion of the inner surface between the exposed portion  18   a  of the base substrate  18  and a surface  48   a  of the glass substrate  48 . 
     A flat surface  50   b  may be in between the third and fourth steps S 3  and S 4 . The inner surfaces of the penetrating hole  50  and the third and fourth steps S 3  and S 4  may have slight slopes. The third and fourth steps S 3  and S 4  may be the same as the first and second steps S 1  and S 2  formed in the groove  22  of the first organic light emitting device. 
     Third and fourth metal layers  52   a  and  52   b  may be formed on the glass substrate  48 . The third and fourth metal layers  52   a  and  52   b  may be like the first and second metal layers  24   a  and  24   b  of the first organic light emitting device. The third metal layer  52   a  may extend from the top of the glass substrate  48  facing the third and fourth steps S 3  and S 4  to the flat surface  50   b  between the third and fourth steps S 3  and S 4  across the inner surface of the penetrating hole  50 , the exposed surface  18   a  of the base substrate  18 , and the slanted surface of the fourth step S 4 . 
     The fourth metal layer  52   b  may be formed on a portion of the glass substrate  18  in which the third and fourth steps S 3  and S 4  are formed. The fourth metal layer  52   b  may extend to the flat surface  50   b  formed between the third and fourth steps S 3  and S 4  across the third step S 3 . The third and fourth metal layers  52   a  and  52   b  may be separated on the flat surface  50   b.    
     A fourth partition wall  58  filling a gap g 1  between the third and fourth metal layers  52   a  and  52   b  may be formed on the flat surface  50   b.  The fourth partition wall  58  may be like the first partition wall  26  of the first organic light emitting device. 
     An electron transport layer  53  may be formed on a portion of the third metal layer  52   a  extending onto the base substrate  18 . The electron transport layer  53  may include third and fourth electron transport layers  54  and  56  stacked sequentially. The third and fourth electron transport layers  54  and  56  may be the same as the first and second electron transport layers  32  and  34  of the first organic light emitting device. 
     The electron transport layer  53  may be a single layer. A fifth partition wall  60  may be formed on the slanted portion of the penetrating hole  50  where no steps are formed. One end of the fifth partition wall  60  may extend toward the base substrate  18 , contacting the electron transport layer  53 , and the other end of the fifth partition wall  60  may extend on the third metal layer  52   a  around the penetrating hole  50 . 
     The third step S 3  of the fourth metal layer  52   b  may be covered by a sixth partition wall  62 . The sixth partition wall  62  may extend on the fourth metal layer  52   b  around the penetrating hole  50 . The fourth partition wall  58  and the sixth partition wall  62  may be separated by a predetermined distance, and a portion of the fourth metal layer  52   b  may be exposed through the distance between the fourth and sixth partition wall  58  and  63 . 
     The electron transport layer  53  may be covered by an organic light emitting layer  64 . The organic light emitting layer  64  may contact a portion of the fourth partition wall  58  extending onto the fourth step S 4  and the fifth partition wall  60 . An upper surface of the organic light emitting layer  64  may be disposed lower than an upper surface of the fourth partition wall  58 . 
     A hole transport layer  66  may lie on the organic light emitting layer  64 . An upper surface of the hole transport layer  66  may be disposed lower than upper surfaces of the third and fourth metal layers  52   a  and  52   b.  The hole transport layer  66  may be like the hole transport layer  38  of the first organic light emitting device. 
     The hole transport layer  66  may contact the fifth and sixth partition walls  60  and  62 , cover the fourth partition wall  58 , and contact a portion of the fourth metal layer  52   b  exposed between the fourth and sixth partition walls  58  and  62 . 
     By the above contacts, holes can be transported from the fourth metal layer  52   b  to the organic light emitting layer  64  through the hole transport layer  66 . Electrons can be transported from the third metal layer  52   a  to the organic light emitting layer  64  through the electron transport layer  53 . The electron transport layer  53  can have a predetermined work function between work functions of the third metal layer  52   a  and the organic light emitting layer  64 . The holes and the electrons transported in this way may be combined in the organic light emitting layer  64  to emit light. 
     The light emitted from the organic light emitting layer  64  approximately parallel to the upper surface of the organic light emitting layer  64  may be reflected upward at slanted portions of the third and fourth metal layers  52   a  and  52   b.  Thus, such light may contribute to the overall emitted light. 
     In addition, emitted light that is obliquely incident to the upper surface of the organic light emitting layer  64  may be reflected into the organic light emitting layer  64 . Emitted light toward the base substrate  18  that is almost perpendicular to an upper surface of the organic light emitting layer  64  may be reflected at the base substrate  18 , and then emitted upward. On the other hand, light parallel or almost parallel to the upper surface of the organic light emitting layer  64  may be reflected upward at the slanted portions of the third and fourth metal layers  52   a  and  52   b.    
     Therefore, the light emitted parallel to the upper surface of the organic light emitting layer  64 , and the light emitted from the border of the organic light emitting layer  64  to the inside of the organic light emitting layer  64  contribute to the total emitted light. Thus, the out coupling efficiency of the second organic light emitting device (the luminescent efficiency) may be much better than that of a conventional organic light emitting device. 
     As shown in  FIG. 3 , a protecting layer  68  may be formed above the hole transport layer  66 , and they may be separated by a predetermined space. The protecting layer  68  may prevent external harmful materials such as dust and humidity from entering the second organic light emitting device. The protecting layer  68  may cover the entire surface of the hole transport layer  66 , contacts the fifth and sixth partition walls  60  and  62  around the hole transport layer  66 , and may cover portions of the third and fourth metal layers  52   a  and  52   b  beyond the fifth and sixth partition walls  60  and  62 . A space may exist between the hole transport layer  66  and the protecting layer  68 . The space may be filled with an inert gas such as nitrogen. 
     However, because of the fifth and sixth partition walls  60  and  62 , spaces may be formed between the protecting layer  68  and the third and fourth metal layers  52   a  and  52   b.  The spaces may be completely filled with a sealing material  70  between the protecting layer  68  and the third and fourth metal layers  52   a  and  52   b.  For perfect sealing, a protruding portion and a groove into which the protruding portion is inserted may be formed in a predetermined region BP of the protecting layer  68  and the third metal layer  52   a.  The protruding portion and the groove may be like the protruding portion  42  and the groove  40   a  of the first organic light emitting device. 
     Third Embodiment 
     An organic light emitting device engraved in a substrate such as the first organic light emitting device is described below. The organic light emitting device can have a doped area instead of a metal layer as a cathode layer. 
     As shown in  FIG. 4 , the organic light emitting device according to the third embodiment of the present invention (third organic light emitting device) can include a substrate  80 . A groove  82  may be formed in the substrate  80 . The groove  82  may have a depth. The substrate  80  may be a silicon substrate doped with a conductive impurity such as a p-type silicon substrate. 
     An inner surface of the groove  82  may have a slight slope. A slight slope may improve the out coupling efficiency of light reflected approximately parallel to the substrate  80 . A portion of the inner surface of the groove  82  may include fifth and sixth steps S 5  and S 6 . The fifth step S 5  may be separated by a predetermined space apart from the sixth step S 6 . The fifth step S 5  may be disposed higher than the sixth step S 6 . 
     The flat surface  82   b  may be formed between the fifth and sixth steps S 5  and S 6 . The flat surface  82   b  may be disposed lower than a top surface of the substrate  80  and higher than the bottom  82   a  of the groove  82 . An inner surface S 5   a  of the fifth step S 5  and an inner surface S 6   a  of the sixth step S 6  may have the same slant as an inner surface of a portion of the groove  82  where steps are not formed. 
     A region  84  in which conductive impurities are doped to a predetermined depth may be formed in the bottom  82   a  of the groove  82 . The doped region  84 , which is injected with an n-type impurity, may be used as a cathode layer such as the first metal layer  24   a  of the first organic light emitting device or the third metal layer  52   a  of the second organic light emitting device. 
     A negative voltage may be applied to the doped region  84  through the substrate  80 . The entire surface of the doped region  84  may be covered by an electron transport layer  86 . The electron transport layer  86  may extend on the bottom  82   a  of the groove around the doped region  84 . 
     The electron transport layer  86  may include fifth and sixth electron transport layers  88  and  90  stacked sequentially. The fifth and sixth electron transport layers  88  and  90  may be like the first and second electron transport layers  32  and  34  of the first organic light emitting device respectively. 
     The electron transport layer  86  may be a single layer. A portion of the inner surface of the groove  82  where steps are not formed may be covered by a fifth metal layer  92   a . The fifth metal layer  92   a  may be, for example, an Al layer. The fifth metal layer  92   a  may cover the inner surface between the substrate  80  and the electron transport layer  86 , and may contact the electron transport layer  86 . 
     The sixth step S 6 , which may be sloped and face the inner surface of the groove  82  where steps are not formed, may be covered by a sixth metal layer  92   b.  The sixth metal layer  92   b  may be like the fifth metal layer  92   a,  and may likewise be an Al layer. The sixth metal layer  92   b  may extend to the flat surface  82   b,  and contact the electron transport layer  86 . 
     The fifth step S 5  may be covered by a seventh metal layer  92   c.  The seventh metal layer  92   c  may be used as an anode layer. The seventh metal layer  92   c  may extend onto an upper surface  80   a  of the substrate  80 , and may cover a portion of the flat surface  82   b  between the fifth and sixth steps S 5  and S 6 . 
     The seventh metal layer  92   c  may be like the fifth and sixth metal layers  92   a  and  92   b.  The sixth metal layer  92   b  and the seventh metal layer  92   c  may be separated by a gap g 2  on the flat surface  82   b.  The gap g 2  may be completely filled by a seventh partition wall  94 . The seventh partition wall  94  may extend onto a portion of the seventh metal layer  92   c,  and onto the sixth metal layer  92   b.    
     The seventh partition wall  94  may cover the entire upper surface of the sixth metal layer  92   b.  An eighth partition wall  96  may be formed on the entire upper surface of the fifth metal layer  92   a.  A slanted surface of the seventh metal layer  92   c  corresponding to the slanted surface S 5   a  of the fifth step S 5  may be covered by a ninth partition wall  98 . The ninth partition wall  98  may be formed along a surface of the seventh metal layer  92   c.    
     The seventh partition wall  94  and the ninth partition wall  98  may be separated by a predetermined distance on the seventh metal layer  92   c,  and a portion of the seventh metal layer  92   c  may be exposed through the distance between the ninth partition wall  98  and the seventh metal layer  92   c.  The electron transport layer  86  may be covered by an organic light emitting layer  100  having a predetermined thickness. 
     The organic light emitting layer  100  may contact the fifth metal layer  92   a,  the eighth partition wall  96  around the electron transport layer  86 , the sixth metal layer  92   b,  and the seventh partition wall  94 . An upper surface of the organic light emitting layer  100  may be disposed lower than the upper surface of the seventh metal layer  92   c.    
     A hole transport layer  102  is formed on the organic light emitting layer  100 . The hole transport layer  102  may act like the hole transport layer  38  of the first organic light emitting device, and may be composed of the same material as the hole transport layer  38  of the first organic light emitting device. 
     The hole transport layer  102  may contact the eighth partition wall  96 , cover an exposed portion of the upper surface of the seventh partition wall  94 , and contact the ninth partition wall  98  and a portion of the seventh metal layer  92   c  exposed between the seventh and ninth partition walls  94  and  98 . An upper surface of the hole transport layer  102  may be disposed lower than an upper surface of an upper portion of the seventh metal layer  92   c  around the fifth step S 5 . 
     A protecting layer  104  may be formed over the hole transport layer  102 , with a predetermined space between them. The protection layer  104  may cover the entire surface of the hole transport layer  102 , contact the eighth and ninth partition walls  96  and  98 , and extend beyond the eighth and ninth partition walls  96  and  98 . 
     Spaces between a portion of the protecting layer  104  around the eighth partition wall  96 , and between a portion of the protecting layer  104  around the ninth partition wall  98  and the seventh metal layer  92   c  may be completely sealed with a sealing material  106 . That is, the circumference of the protecting layer  104  may be completely sealed by the sealing material  106 . A space may exist between the hole transport layer  102  and the protecting layer  104 . The space may be filled with an inert gas such as nitrogen. 
     The protection layer  104  may act like the protecting layer  40  of the first organic light emitting device. 
     Fourth Embodiment 
     As shown in  FIG. 5 , an organic light emitting device (fourth organic light emitting device) according to a fourth embodiment of the present invention may include a substrate  110  having a groove  112  formed to a predetermined depth. The substrate  110  may be a flexible substrate such as a plastic substrate. 
     The inner surface of the groove  112  may be a slanted surface by which light incident to the slanted surface substantially parallel to the bottom of the groove  112  may be reflected almost straight upward. The groove  112  may be asymmetrical with respect to the bottom  112   a.  That is, with respect to the bottom  112   a,  a portion of the inner surface of the groove  112  may have a slight slope connecting the bottom  112   a  and an upper surface  10   a  of the substrate  110 . The other portion of the inner surface of the groove  112  facing the portion may include a seventh and eighth steps S 7  and S 8 . 
     The eighth step S 8  may start at the bottom  112   a  of the groove  112 . The seventh step S 7  may be horizontally separated from the eighth step S 8  by a predetermined distance. The seventh step S 7  may be disposed higher than the eighth step S 8 . A flat surface  112   b  may be formed between the seventh and eighth steps S 7  and S 8 . The flat surface  112   b  may be disposed higher than the bottom  112   a  of the groove  112  and lower than the upper surface  110   a  of the substrate  110 . 
     The seventh step S 7  may start at the flat surface  112   b.  The eighth step S 8  may end at the flat surface  112   b.  An eighth metal layer  114   a  that may be used as a cathode layer and a ninth metal layer  114   b  that may be used as an anode layer may be formed on the substrate  110 . A predetermined gap g 3  may lie between the eighth and ninth metal layers  114   a  and  114   b.  The eighth metal layer  114   a  may extend to the flat surface  112   b  and across the inner surface of the groove  112  where steps are not formed, the bottom  112   a  of the groove  112 , and the eighth step S 8 . 
     The ninth metal layer  114   b  may cover the seventh step S 7 . The ninth metal layer  114   b  may extend to the upper surface  110   a  of the substrate  110 , and may extend to the flat surface  112   b.  The gap g 3  between the eighth and ninth metal layers  114   a  and  114   b  may be filled by a tenth partition wall  126 . 
     The tenth partition wall  126  may act like the first partition wall  26  of the first organic light emitting device and may extend to the bottom  112   a  of the groove  112  along the surface of the eighth metal layer  114   a.  An electron transport layer  120  may be formed on a portion of the eighth metal layer  114   a  disposed on the bottom  112   a  of the groove  112 . The electron transport layer  120  may include seventh and eighth electron transport layers  122  and  124 . The electron transport layer  120  may be like the electron transport layer  31  of the first organic light emitting device. 
     An eleventh partition wall  128  may be formed on a slanted portion of the eighth metal layer  114   a.  The eleventh partition wall  128  may extend onto the upper surface of the eighth metal layer  114   a.  The eleventh partition wall  128  may contact the electron transport layer  120 . 
     A twelfth partition wall  130  may be formed on a slanted portion of the ninth metal layer  114   b.  The twelfth partition wall  130  may extend onto the upper surface of the ninth metal layer  114   b  formed on the upper surface of the substrate  110 . The twelfth partition wall  130  may extend toward the tenth partition wall  126  with a predetermined distance between the tenth and twelfth partition walls  126  and  130 . 
     The ninth metal layer  114   b  may be exposed through the space between the tenth and twelfth partition walls  126  and  130 . During the manufacturing process, the tenth through twelfth partition walls  126 ,  128 , and  130  may be formed simultaneously. Thus, the thicknesses of the eleventh and twelfth partition walls  128  and  130  may be equal to that of a portion of the tenth partition wall  126  extending onto the eighth metal layer  114   a.    
     The electron transport layer  120  may be covered by an organic light emitting layer  132  having a predetermined thickness. The organic light emitting layer  132  may be like the organic light emitting layer  36  of the first organic light emitting device. One end of the organic light emitting layer  132  may contact the eleventh partition wall  128 , and the other end of the organic light emitting layer  132  may contact the extended portion of the tenth partition wall  126 . 
     An upper surface of the light emitting layer  132  may be disposed lower than the upper surface of a portion of the ninth metal layer  114   b  exposed between the tenth and twelfth partition walls  126  and  130 . A hole transport layer  134  having a predetermined thickness may be formed on the organic light emitting layer  132 . The hole transport layer  134  may act like the hole transport layer  66  of the first organic light emitting device. 
     One end of the hole transport layer  134  may contact the eleventh partition wall  128 , and the other end of the hole transport layer  134  may contact the twelfth partition wall  130 . In addition, the hole transport layer  134  may contact an exposed portion of the ninth metal layer  11   b  between the tenth and twelfth partition walls  126  and  130 , and may cover the tenth partition wall  126 . Therefore, when a voltage is applied to the ninth metal layer  114   b  used as an anode layer, carriers (that is, holes) may be transported to the organic light emitting layer  132  through the hole transport layer  134 . 
     Because the holes flow on the surface of the tenth partition wall  126 , the surface state of the hole transport layer  134  may not substantially affect the transportation of the hole. Thus, the surface state of the hole transport layer  134  may not be very important in the design considerations for the hole transport layer  134 . 
     An upper surface of the hole transport layer  134  may be disposed lower than upper surfaces of the eighth and ninth metal layers  114   a  and  114   b  around the eleventh an twelfth partition walls  128  and  130 . This arrangement of layers may ease the sealing process. 
     A protecting transport layer  136  may be formed above the hole transport layer  134 . The protecting layer  136  may cover the entire surface of the hole transport layer  134  and the eleventh and twelfth partition walls  128  and  130  and may extend over the eighth and ninth metal layers  114   a  and  114   b.  The protecting layer  136  may closely contact the eighth and ninth metal layers  114   a  and  114   b.  This close contact may help to prevent external impurities and humidity from penetrating under the protecting layer  136 . 
     The first through fourth organic light emitting devices described above may include a reflecting means: metal layers having slight slopes around organic light emitting layers  36 ,  64 ,  100 , and  132 . The metal layers may reflect incident light upward. 
     Accordingly, lateral light emitted from the organic light emitting layers  36 ,  64 ,  100 , and  132  and the light emitted from the upper surfaces of the organic light emitting layers  36 ,  64 ,  100 , and  132  to the insides of the first through fourth organic light emitting devices in a lateral direction may be reflected upward. As a result, the out coupling efficiencies of the first through fourth organic light emitting devices of the present invention may be higher than the out coupling efficiency of the prior art. 
     In addition, the anode layer and the cathode layer may be formed horizontally instead of vertically. Thus, the organic light emitting device may be thinner. 
     A method of manufacturing an organic light emitting device according to exemplary embodiments of the present invention will now be described. 
     Even though some of the substrates of the first, second, and fourth organic light emitting devices may be embossed and others may be engraved, methods of manufacturing the first, second, and fourth organic light emitting devices may not substantially differ from each other. By way of illustration, therefore, only methods of manufacturing the first and third organic light emitting devices will now be described. The method of manufacturing the first organic light emitting device can be readily applied to the second and fourth organic light emitting devices. 
     &lt;Manufacturing of First Embodiment&gt; 
     As shown in  FIG. 2 , a groove  22  having a predetermined depth may be formed in a substrate  20 . The substrate  20  may be a glass substrate or a flexible substrate such as a plastic substrate. When forming the groove  22 , a mask engraved with the same pattern as the groove  22  may be used. 
     The groove  22  may be formed wide enough to be able to include important elements of the first organic light emitting device. The width of the groove  22  may increase toward the inlet of the groove  22 , and an inner surface of the groove  22  may have a slight slope. The groove  22  may be asymmetrically formed centering on the bottom  220  of the groove  22 . 
     To form anode and cathode layers horizontally, a portion (in  FIG. 2 , a portion of the inner surface of the groove  22  disposed to the left side of the bottom  22   a ) of the inner surface of the groove  22  on which a cathode layer is to be formed, may be given a slight slope, and first and second steps S 1  and S 2  may be formed in a portion (in  FIG. 2 , a portion of the inner surface disposed to the right side of the bottom  22   a ) of the groove  22  where an anode layer is to be formed. 
     The first and second steps S 1  and S 2  may be horizontally separated by a predetermined distance, and the first step S 1  may be disposed higher than the second step S 2 . The second step S 2  may begin at an edge of the bottom  22   a  of the groove  22 , and a flat surface  22   b  may be formed between the first and second steps S 1  and S 2 . The flat surface  22   b  may be disposed lower than a top surface  20   a  of the substrate  20  and higher than the bottom  22   a  of the groove  22 . 
     When the first and second steps S 1  and S 2  are formed, a surface S 1   a  of the first step S 1  and a surface S 2   a  of the second step S 2  may have the same gradient as the inner surface of the groove  22 . 
     After the groove  22  is formed, a portion of the flat surface  22   b  of the groove  22  may be covered using a mask (not shown). A metal layer (not shown) may be formed to a predetermined thickness on the substrate  20 . The metal layer may be, for example, an aluminum layer. 
     After the metal layer is formed, the mask may be removed. As a result, a first metal layer  24   a  used as a cathode layer and a second metal layer  24   b  used as an anode layer may be formed on the substrate  20 . The first metal layer  24   a  may extend to the flat surface  22   b  of the groove  22  across the inner surface of the groove  22  where steps are not formed, the bottom  22   a  of the groove  22 , and the second step S 2 . The second metal layer  24   b  may extend to the flat layer  22   b  across the first step S 1 . 
     Even though both the first and second metal layers  24   a  and  24   b  may extend onto the flat surface  22   b  of the groove, they may be separated by a gap g formed on the flat layer  22   b  of the groove  22  using the mask. The gap g may be sufficient to prevent a carrier provided to the first and second metal layers  24   a  and  24   b  from tunneling between the first and second metal layers  24   a  and  24 . 
     Next, a mask (not shown) is formed to cover a region of the bottom  22   a  of the groove  22  in which an electron transport layer  31  is to be formed, a portion of the second metal layer  24   b  formed on the flat surface  22   b  of the groove  22 , and the first and second metal layers  24   a  and  24   b  formed around the groove  22 . An insulating layer (not shown), such as a silicon oxide film, filling the gap g between the first and second metal layers  24   a  and  24   b  may be formed on the substrate  20  where the mask is formed. Next, the mask is then removed. 
     As a result, a first partition wall  26  filling the gap g between the first and second metal layers  24   a  and  24   b  may be formed. The first partition wall  26  may extend to the bottom  22   a  of the groove  22  across the second step S 2 . A second partition wall  28  covering the sloped surface of the groove  22  without steps may be formed. A third partition wall  30  may be formed covering the second step S 2 . The thickness of a portion of the first partition wall  26  extending to the bottom  22   b  of the groove  22  may equal that of the second and third partition walls  28  and  30 . 
     An electron transport layer  31  may be formed on the bottom  22   a  of the groove  22  between the first and second partition walls  26  and  28 . The electron transport layer  31  may be formed with a material layer capable of matching work functions of both the metal layer  24   a  and an organic light emitting layer  36  to be formed in a subsequent process. The electron transport layer  31  may be a formed of a single layer or multiple layers. 
     If the electron transport layer  31  is formed with a single layer, it may be formed of a Ba layer. If the electron transport layer  31  is formed with multiple layers, it may be formed with first and second electron transport layers  32  and  34 . The first electron transport layer  32  may be formed of a Ca layer, and the second electron transport  34  may be formed of a BaF 2  layer. 
     A mask (not shown), which exposes the electron transport layer  31  and portions of the first and second partition walls  26  and  28  around the electron transport layer  31  and covers the rest area is formed. The organic light emitting layer  36  is formed on the electron transport layers  31  and portions of the first and second partition walls  26  and  28 , and then the mask is removed. The organic light emitting layer may be formed with a low or high molecular weight fluorescent layer or a phosphor layer. 
     After the organic light emitting layer  36  is formed, a mask that exposes the organic light emitting layer  36 , the first partition wall  26 , the exposed portion of the second metal layer  24   b  between the first and third partition walls  26  and  30 , and portions of the second and third partition walls  28  and  30  adjacent to the organic light emitting layer  36  may be formed. A hole transport layer  38  having a predetermined thickness may be formed on the entire exposed region using the mask. While the hole transport layer  38  is formed, an upper surface of the hole transport layer  38  may be formed lower than upper surfaces of the first and second metal layers  24   a  and  24   b  for convenience in subsequently sealing the device. 
     During the operation of the organic light emitting device, holes provided by the second metal layer  24   b  (which may be an anode layer) may be transported through a portion of the hole transport layer  38  that is close to a material layer formed below the hole transport layer  38 . Therefore, the surface of the hole transport layer  38  may be formed by planarization or by any other suitable method. 
     A protecting layer  40  is formed to protect the hole transport layer  38  and components formed therebelow from impurities and humidity. The protecting layer  40  may be formed with a glass layer or a gold layer. The protecting layer  40  extends beyond the second and third partition walls  28  and  30 . The second and third partition walls  28  and  30  formed on the upper surfaces of the first and second metal layers  24   a  and  24   b  may support and contact the protecting layer  40 . A gap may be formed in between the protecting layer  40  and the hole transport layer  38 . 
     After the protecting layer  40  is formed, a space between the protecting layer  40  and the first and second metal layer  24   a  and  24   b  may be filled with a sealing material  44 . The sealing material  44  may be a material that prevents external impurities such as moisture and air from penetrating. For example, the sealing material  44  may be a UV resin. For the sealing process, the sealing material  44  may be first prepared where the sealing is to be performed, and then the protecting layer  40  may be contacted with the sealing material  44  and pressure may be applied to the protecting layer  40  to complete the sealing process. 
     To improve sealing where the sealing material  44  is formed between the first and second metal layers  24   a  and  24   b  and the protecting layer  40 , a protruding portion  42  (a first coupling material) may be formed in the first metal layer  24   a,  and a groove  40   a  (a second coupling material matched with the first coupling material) may be formed in the protecting layer  40 . The first coupling material may be formed in the second metal layer  24   b.    
     If the first and second coupling materials are formed in the first and second metal layers  24   a  and  24   b  and the protecting layer  40 , the first and second metal layers  24   a  and  24   b  and the protecting layer  40  may be sealed in a manner described below. 
     A portion where the first coupling material is formed may be covered with the sealing material  44 . The protecting layer  40  may be arranged so that the first and second coupling materials are exactly combined, and then the protecting layer  40  may be pressed. 
     In the sealing process, it may be preferable that spaces between portions of the protecting layer  40  extending beyond the second and third partition walls  28  and  30  and the first and second metal layers  24   a  and  24   b  may be completely filled. 
     As shown in  FIG. 3 , a method of manufacturing the second organic light emitting device can include forming a glass substrate  48  on a base substrate  18  and forming a penetrating hole  50  in the glass substrate  48  that exposes the base substrate  18 . The inner surface of the penetrating hole  50  may be the same as the inner surface of the groove  22 . Since the bottom of the penetrating hole  50  is blocked by the base substrate  18 , the penetrating hole  50  may be like the groove  22  formed according to the manufacturing method according to the first embodiment of the present invention. 
     After forming the penetrating hole  50 , the manufacturing process is identical to the manufacturing process according to the first embodiment by the present invention described above. 
     As shown in  FIG. 6 , the manufacturing method according to the first embodiment of the present invention can be summarized as follows. The method of manufacturing an organic light emitting device according to the first embodiment may include forming a groove in a substrate (SS 1 ); forming first and second metal layers on the substrate extending to the groove and leaving a gap between the first and second metal layers (SS 2 ); forming a plurality of partition walls that fill the gap while a portion of the first metal layer formed on a bottom of the groove and a portion of the second metal layer adjacent to the gap are exposed, on the first and second metal layers (SS 3 ); forming an electron transport layer on a predetermined portion of the first metal layer formed on the bottom of the groove (SS 4 ); forming an organic light emitting layer on the electron transport layer (SS 5 ); forming a hole transport layer on the organic light emitting layer (SS 6 ) and in contact with an exposed portion of the second metal layer between the partition walls; and (SS 7 ) forming and sealing a protecting layer that covers the elements formed on the groove. 
     &lt;Manufacturing of Second Embodiment&gt; 
     As shown in  FIG. 4 , a groove  82  may be formed in a substrate  80 . The substrate  80  may be a p-type silicon substrate. The groove  82  may be formed like the groove  22  formed in the manufacturing method of the previous embodiment. A conductive impurity, such as an n-type impurity, may be injected into the bottom  82   a  of the groove  82 , thereby forming a doped region  84 . Like the first metal layer  24   a  of the first embodiment, the doped region  84  may be used as a cathode layer. 
     A mask (not shown) exposing the bottom  82   a  of the groove  82  and a flat surface  82   b  of the groove  82  and covering the rest porton may be used to form fifth, sixth, and seventh metal layers  92   a,    92   b,  and  92   c  on the inner surface of the groove  82  where steps are not formed and on the fifth and sixth steps S 5  and S 6 , respectively. The mask may then be removed. 
     The fifth and sixth metal layers  92   a  and  92   b  are used as reflecting layers that reflect light that is incident in a lateral direction upward. The seventh metal layer  92   c  is used as an anode layer. The sixth and seventh metal layers  92   b  and  92   c  may extend onto the flat surface  82   b  of the groove  82 , but it is preferable that a gap g 2  be formed between the sixth and seventh metal layers  92   b  and  92   c  on the flat surface  82   b.    
     An insulating layer (not shown) may be formed on the substrate  80  using a mask (not shown) covering a portion of the seventh metal layer  92   c  extending onto the flat surface  82   b  of the groove  82 , the bottom  82   a  of the groove  82 , and a portion around the groove  82 . The insulating layer may be a silicon oxide layer. 
     After the insulating layer is formed, the mask is removed, thereby forming a seventh partition wall  94  that completely fills a space between the sixth and seventh metal layers  92   b  and  92   c.  Also, an eighth partition wall  96  may be formed on the inner surface of the groove  82  where no steps are formed. Additionally, a ninth partition wall  98  may be formed on the fifth step S 5 . 
     The seventh partition wall  94  may extend downward to the bottom  82   a  of the groove  82  across the sixth step S 6 . A portion of the seventh partition wall  94  may extend onto the seventh metal layer  92   c.  The seventh partition wall  94  and the ninth partition wall  98  may be separated a predetermined distance on the seventh metal layer  92   c  due to the mask. 
     Processes forming an organic light emitting layer  100  and a hole transport layer  102  (on which the seventh through ninth partition wall  94 ,  96 , and  98  may be formed) may be performed according to the method of manufacturing an organic light emitting device by the first embodiment. After the hole transport layer  102  is formed, a protecting layer  104  may be formed to protect elements inside the eighth and ninth partition walls  96  and  98 . The protecting layer  104  may be formed like the protecting layer  40  ( FIG. 2 ) formed in the previous embodiment. 
     Spaces between the protecting layer  104  and the seventh metal layer  92   c  and between the protecting layer  104  and the substrate  80  may be sealed with a sealing material  106 . 
     As shown in  FIG. 7 , the manufacturing method according to the second embodiment of the present invention can be summarized as follows. The manufacturing method can include forming a doped region as a cathode layer in a substrate (ST 1 ); forming first and second metal layers separated by a gap on the substrate around the doped region (ST 2 ) (the second metal layer may be used as an anode layer); forming a plurality of the partition walls filling the gap and exposing a predetermined portion of the second metal layer contacting the gap on the first and second metal layers (ST 3 ); forming an electron transport layer on the doped region (ST 4 ); forming an organic light emitting layer contacting the partition walls formed on the first metal layer on the electron transport layer (ST 5 ); forming a hole transport layer contacting the partition walls and the second metal layer on the organic light emitting layer (ST 6 ); and forming and sealing a protecting layer to protect at least the hole transport layer and elements formed below the hole transport layer (ST 7 ). In this summary, the first metal layer may correspond to the fifth and sixth metal layers  92   a  and  92   b  illustrated in  FIG. 4 , and the second metal layer may correspond to the seventh metal layer  92   c  illustrated in  FIG. 4 . 
     An organic light emitting device according to the present invention may not include an ITO electrode layer. Therefore, the entire manufacturing process may be shorter and less costly. Moreover, the organic light emitting device of the present invention can be applied to flexible displays. 
     In addition, the organic light emitting device according to the present invention can improve luminance efficiency because it includes a reflecting material, by which light emitted horizontally from an organic light emitting layer or reflected in a lateral direction is reflected upward. 
     In an organic light emitting device manufactured according to the present invention, the surface state and thickness of the hole transport layer may have little effect on the performance of the organic light emitting device. In general, the organic light emitting device according to the present invention may have fewer factors affecting performance. Moreover, the present invention may obviate the need for an indium-tin-oxide (ITO) or indium-zinc-oxide (IZO) layer. Accordingly the fabrication temperature of the device may be reduced, and the organic material may be more easily preserved. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, various changes may be made to the described embodiments without departing from the scope of the invention. 
     For example, coupling materials equivalent in function to the coupling materials  42  and  40   a  illustrated in  FIG. 2  may be formed in a portion of the protecting layer  104  extending beyond the groove  82  and in a predetermined portion of the substrate  80  facing the portion of the protecting layer  104 , but this is still within the scope of the invention.