Abstract:
An organic electroluminescent (EL) display device is provided which can reduce a level of power consumption. The organic EL display device includes a plurality of anode columns formed on a substrate, each anode column having first and second anodes disposed adjacent to each other, with emitting areas of the first and second anodes being arranged alternately in a line; a plurality of walls intersecting the anode columns. A plurality of cathodes are formed between walls which intersect the anode columns to form two sub pixels. A plurality of secondary walls are formed between two adjacent walls, between the light emitting areas of the first and second anodes of each anode column. Each secondary wall may include a plurality of unit walls corresponding to one pixel with first, second and third sub pixels which emit different colored lights. Alternatively, each subsidiary wall may include a plurality of unit walls, with each unit wall corresponding to one of the first, second or third sub pixels.

Description:
This application claims priority to Korean Patent Application Nos. 2004-100072 filed on Dec. 1, 2004 in Korea and 2004-107430 filed on Dec. 16, 2004 in Korea, the entirety of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an organic electroluminescent display device, and more particularly, to an organic electroluminescent display device which is capable of reducing power consumption. 
     2. Description of the Related Art 
     In order to overcome various shortcomings of the cathode ray tube (CRT), various types of flat panel display devices having a reduced weight and size compared to that of a CRT have been developed. These flat panel display devices include liquid crystal display (LCD) devices, field emission display (FED) devices, plasma display panels (PDP), and organic electroluminescent (EL) display device. 
     The structure and manufacturing process associated with a PDP are relatively simple, and so a PDP is often used when a large size display surface is required. However, the light emitting efficiency and brightness of a PDP tend to be low and an enormous amount of power is consumed by the PDP. 
     LCD devices are mainly used with laptop computers, and demand for LCD devices has increased. However, it is difficult to use an LCD device for a large display surface, and power consumption is high due to backlight requirements. Additionally, light loss in an LCD device is high due to optical members such as a polarized light filter, a prism sheet, a diffusion sheet and the like which may be included in the LCD device, and the viewing angle associated with an LCD device is narrow. 
     Electroluminescent devices (hereinafter, referred to as “EL devices”) can be either an organic EL device or an inorganic EL device based on the material which forms a light emitting layer of the device. As the EL device itself emits light, response time is short, light emitting efficiency and brightness are high, and viewing angle is wide when compared to other flat panel display devices. However, an inorganic EL device has a higher level of power consumption when compared to an organic EL device, high levels brightness cannot be obtained by the inorganic EL device, and various levels of R (red), G (green) and B (blue) light cannot be emitted. On the other hand, the organic EL device may be driven by a variety of levels of low direct current, has a rapid response time, and can obtain high brightness and emit various levels of R, G and B light, and so is well suited for the next generation of flat panel display devices. 
       FIG. 1  is a schematic view of a conventional organic EL display device. 
     The conventional organic EL display device includes an organic EL display panel  20  with anode columns DL 1 -DLm, cathodes SL 1 -SLn perpendicular to the anode columns DL 1 -DLm, and first and second organic EL diodes  10   a  and  10   b  formed at common sections of the anode columns DL 1 -DLm and the cathodes SL 1 -SLn. A non display area with a data pad  24  is connected to the anode columns DL 1 -DLm via data lines (not shown), and a scan pad  22  is connected to the cathodes SL 1 -SLn via scan lines (not shown). The data pad  24  and the scan pad  22  are connected to a tape carrier package (not shown) in which a data driving section (not shown) for generating a data signal and a scan driving section (not shown) for generating a scan signal are provided. A data signal transmitted from the data driving section is supplied to the anode columns DL 1 -DLm via the data pad  24  and the data lines, and a scan signal transmitted from the scan driving section is supplied to the cathodes SL 1 -SLn via the scan pad  22  and the scan lines. 
     Each anode column (for example, DL 1 ) comprises first and second anodes DL 1 - 1  and DL 1 - 2  adjacent to each other, and each cathode (for example, SL 1 ) is divided into first and second sub cathodes SL 1 - 1  and SL 1 - 2  spaced apart from each other as shown in  FIG. 1 . Accordingly, a scan signal supplied from the scan driving section to one of the cathodes (for example, SL 1 ) is supplied simultaneously to the first and second sub cathodes SL 1 - 1  and SL 1 - 2 . 
     In a first organic EL diode  10   a , an anode electrode is connected to the first anode DL 1 - 1  of the anode column DL 1 , and a cathode electrode is connected to the first sub cathode SL 1 - 1  of the cathode SL 1 . In the second organic electroluminescent diode  10   b,  an anode electrode is connected to the second anode DL 1 - 2  of the anode column DL 1 , and a cathode electrode is connected to the second sub cathode SL 1 - 2  of the cathode SL 1 . Therefore, though the scan signal is supplied to the cathode SL 1  from the scan driving section, the data driving section can drive the first and second organic EL diodes  10   a  and  10   b  independently. This operation is performed in all anode columns DL 1 -DLm and cathodes SL 1 -SLn. 
     When a negative scan signal is supplied to the cathodes SL 1 -SLn to which the cathode electrodes of the first and second organic electroluminescent diodes  10   a  and  10   b  are connected, and a positive data signal is supplied to the first anode (for example, DL 1 - 1 ) of each anode column (for example, DL 1 ) to which the anode electrode of the first organic EL diode  10   a  is connected and the second anode DL 1 - 2  of each anode column to which the anode electrode of the second organic EL diode  10   b  is connected, the current flows based on a forward bias, and so the first and second organic EL diodes  10   a  and  10   b  emit light. 
     Each of the first and second organic EL diodes  10   a  and  10   b  is formed with a first EL cell R having red fluorescent material, a second EL cell G having green fluorescent material, and a third EL cell B having blue fluorescent material. Each organic EL diode corresponding to one pixel of the organic EL display device emits a color image for that pixel by combining the first EL cell R, the second EL cell G and the third EL cell B. 
       FIG. 2  is a detailed view of section “A” of  FIG. 1 . Simply for ease of discussion and illustration, only three (3) anode columns and one (1) cathode are shown in  FIG. 2 . As shown in  FIG. 2 , the cathode SL 1  is positioned substantially perpendicular to the anode columns DL 1 , DL 2 , DL 3 , with a first EL cell R, a second cell G, and a third EL cell B formed at areas of the anode columns DL 1 , DL 2 , DL 3  which correspond to the cathode SL 1 . Primary walls  8   a  and a secondary wall  8   b  are positioned parallel to the cathode SL 1 . 
     Each anode column (for example, DL 1 ) adjacent first and second anodes DL 1 - 1  and DL 1 - 2 , and a section of the cathode SL 1  (that is, a section corresponding to the emitting area) is divided into first and second sub cathodes SL 1 - 1  and SL 1 - 2  separated from each other by the secondary wall  8   b . Accordingly, two emitting light areas are formed at each area where an anode column (for example, DL 1 ) and the cathode SL 1  meet. 
     The primary walls  8   a  extend to a non-display, or non-emitting area, but the secondary wall  8   b  is formed only in the EL cell array area, or active region. After forming the walls  8   a  and  8   b , organic emitting material is deposited through a mask on the EL cell array area of the substrate on which the walls  8   a  and  8   b  are formed, and so the first EL cell R, the second cell G and the third EL cell B are formed. Thereafter, the cathode SL 1  is formed by depositing conductive material on an entire structure. 
     When a negative scan signal is supplied to the cathode SL 1 , i.e., the first and second sub cathodes SL 1 - 1  and SL 1 - 2 , and a positive data signal is supplied to one anode (for example, DL 1 - 1 ) of the anode column DL 1  at the same time, the current flows to the cathode SL 1  via the current path shown in  FIG. 3  so as to emit light through a corresponding cell. In this type of organic EL display device, if the data current for driving the pixels in full white is applied to the first and second sub cathodes SL 1  and SL 1 - 2  through the anodes or if a relatively large data current is applied, the first and second sub cathodes SL 1  and SL 1 - 2  may not be able to withstand the load resulting from the supplied the current. 
     Since the scan signal is supplied to two sub cathodes SL 1 - 1  and SL 1 - 2  through the cathode SL 1  formed at the non-emitting area, the number of cathodes formed may be half the number of sub cathodes so that each cathode has a larger width in the non-emitting area. This will decrease line resistance of each cathode SL 1 -SLn in the non-emitting area, thus decreasing power accordingly. 
     However, though the line resistance of the cathodes SL 1 -SLn is decreased, the line resistance of the first and second sub cathodes SL n-1 -SL n-2  formed on the EL cell array area is not decreased, and so this method is limited in its ability to decrease power consumption of the organic EL device. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described hereinafter. 
     An object of the invention is to provide an organic electroluminescence display device which can reduce the power consumption. 
     To achieve these objects, in whole or in part, as embodied and broadly described herein, an organic electroluminescent display device in accordance with an embodiment of the invention includes a plurality of anode columns formed on a substrate, each anode column including first and second anodes to which each driving signal is supplied, the first and second anodes being disposed adjacent to each other, and emitting areas of the first and second anodes of each anode column being arranged alternatively in one line, a plurality of walls intersecting the anode columns, a plurality of cathodes, each cathode being formed between the walls and intersecting the light emitting areas of the first and second anodes of each anode column to form two sub pixels, and a plurality of subsidiary walls, each subsidiary wall being formed between two adjacent walls and placed between the light emitting areas of the first and second anodes of each anode column. 
     Each subsidiary wall may include a plurality of unit walls, each unit wall corresponds to one pixel consisted of first to third sub pixels which emit different colored lights. Each subsidiary wall may also include a plurality of unit walls, each unit wall corresponds to one of first to third sub pixels which emit different colored lights. 
     Additionally, each unit wall of each subsidiary wall may include an extension portion formed on at least one end thereof, and the extension portion of each unit wall is extended in parallel with the anode. 
     Further, the extension portion of each unit wall may be divided into first and second extension portions which are extended with a certain angle to the anode columns. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in detail with reference to the following drawings in which like reference numerals refer to like elements, wherein: 
         FIG. 1  is a schematic view of a conventional organic electroluminescent (EL) display device; 
         FIG. 2  is a detailed view of section “A” of  FIG. 1 ; 
         FIG. 3  illustrates a current path formed in the conventional organic EL display device shown in  FIG. 1 ; 
         FIG. 4  is a schematic view of an organic EL display device, in accordance with an embodiment of the invention; 
         FIG. 5   a  is a detailed view of section “B” of  FIG. 4 , in accordance with an embodiment of the invention; 
         FIG. 5   b  is a partial sectional view taken along line B-B in  FIG. 5   a;    
         FIG. 5   c  is a partial sectional view taken along line C-C in  FIG. 5   a;    
         FIG. 6  illustrates a current path formed in the organic EL display device, in accordance with an embodiment of the invention; 
         FIG. 7   a  is a detailed view of section “B” of  FIG. 4 , in accordance with another embodiment of the invention; 
         FIG. 7   b  is a partial sectional view taken along line B-B in  FIG. 7   a;    
         FIG. 8  is a detailed view of section “B” of  FIG. 4 , in accordance with another embodiment of the invention; 
         FIG. 9  illustrates a current path formed in the organic EL display device, in accordance with embodiments of the invention; 
         FIG. 10  is a detailed view of section “B” of  FIG. 4 , in accordance with another embodiment of the invention; 
         FIG. 11  illustrates a current path formed in the organic EL display device, in accordance with an embodiment of the invention; 
         FIG. 12  is a detailed view of section “B” of  FIG. 4 , in accordance with another embodiment of the invention; 
         FIG. 13  is a detailed view of section “B” of  FIG. 4 , in accordance with another embodiment of the invention; and 
         FIG. 14  illustrates a current path formed in the organic electroluminescent display device, in accordance with embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 4  is a schematic view of an organic electroluminescent (EL) display device in accordance with the embodiments of the invention. The structure of the organic EL display device shown in  FIG. 4  is similar to that of the organic EL display device shown in  FIG. 1 , and thus a description of the similar sections of the two devices is omitted. Further, simply for ease of discussion and illustration, only three (3) anode columns and one (1) cathode are described and shown. However, it is well understood that a number of anode columns and cathodes in a particular display device are dependent on a number of different parameters, including, but not limited to, a size and quality of the display device. 
       FIG. 5   a  is a detailed view of section “B” in  FIG. 4 , in accordance with a first embodiment of the invention. Section “B” of the organic EL display device includes anode columns DL 1 , DL 2  and DL 3 , a cathode SL 1  which crosses the anode columns DL 1 , DL 2  and DL 3 , and primary walls  18   a  and a secondary wall  18   b  which cross the anode columns DL 1 , DL 2  and DL 3  and are positioned parallel to the cathode SL 1 . 
     A section of the cathode SL 1  such as, for example, a section corresponding to the active region, is divided into first and second sub cathodes SL 1 - 1  and SL 1 - 2  by the secondary wall  18   b , forming two individual cells at an area common to one anode column DL 1  and one cathode SL 1 . Also, although the primary walls  18   a  may extend to a non-display, or non-emitting area, the secondary wall  18   b  may be formed on only a cell array area, or active region. 
     The secondary wall  18   b  which divides the cathode SL 1  may actually be a plurality of unit secondary walls  18   b , each unit secondary wall  18   b  corresponding to the first, second and third sub-pixels (EL cells) R, G and B, respectively, which make up one pixel. When constructed in this manner, the first and second sub cathodes SL 1 - 1  and SL 1 - 2  may be connected to each other, for example, at an area between adjacent unit secondary walls  18   b . These areas which connect the first and second sub cathodes SL 1 - 1  and SL 1 - 2  cause the first and second sub cathodes SL 1 - 1  and SL 1 - 2  to have a larger surface area, thus reducing the resistance of the sub cathodes SL 1 - 1  and SL 1 - 2 . Accordingly, the current supplied to the first and second sub cathodes SL 1 - 1  and SL 1 - 2  flows easily to the cathode SL 1  by following the current path shown in  FIG. 6  so that power consumption of the organic EL display device may be decreased. 
       FIGS. 5   b  and  5   c  are partial sectional views taken along lines B-B and C-C, respectively, shown in  FIG. 5   a .  FIGS. 5   b  and  5   c  provide an exemplary illustration of a relationship between an anode column DL 1  with first and second anodes DL 1 - 1  and DL 1 - 2  formed on a substrate  100 , and a first subcathode SL 1 - 1  which crosses the anode column DL 1 . As shown in  FIGS. 5   b  and  5   c , an insulating layer  110  may be formed on the substrate  100  and portions of the anode column DL 1 , leaving at least a portion of the first anode DL 1 - 1  exposed. An electroluminescent layer  120  may be formed on the exposed portion of the first anode DL 1 - 1 , and the cathode SL 1 - 1  may be formed on the surface of the insulating layer  110  and the electroluminescent layer  120 . 
       FIG. 7   a  is a detailed view of section “B” of  FIG. 4 , in accordance with a second embodiment of the invention. Section “B” of the organic EL display device includes anode columns DL 1 , DL 2  and DL 3 , a cathode SL 1  which crosses the anode columns DL 1 , DL 2  and DL 3 , and primary walls  18   a  and a secondary wall  28   b  which cross the anode columns DL 1 , DL 2  and DL 3  and are positioned parallel to the cathode SL 1 . 
     A section of the cathode SL 1 , such as, for example, a section corresponding to an active region, may be divided into first and second sub cathodes SL 1 - 1  and SL 1 - 2  by the secondary wall  28   b , forming two individual cells at an area common to one anode column (for example, DL 1 ) and one cathode SL 1 . Also, although the primary walls  18   a  may extend to the non display region, the secondary wall  28   b  may be positioned only in a cell array area. 
     The secondary wall  28   b  which divides the cathode SL 1  may actually be a plurality of unit secondary walls  28   b , each unit secondary wall  28   b  corresponding to the first, second and third sub-pixels (EL cells) R, G and B, respectively, which make up one pixel. Each unit of the secondary walls  28   b  shown in  FIG. 7  may also include at least one extension portion  28   c  formed on at least one end thereof which may be positioned parallel to the anode columns DL 1 -DL 3 , or may include an extension portion  28   c  formed at each end of each unit secondary wall  28   b , as shown in  FIG. 7   a .  FIG. 7   b  provides a partial sectional view of the extension portion  28   c  taken along line B-B of  FIG. 7   a.    
     When constructed in this manner, the first and second sub cathodes SL 1 - 1  and SL 1 - 2  may be connected to each other, for example, at an area between adjacent unit secondary walls  28   b . These areas which connect the first and second sub cathodes SL 1 - 1  and SL 1 - 2  cause the first and second sub cathodes SL 1 - 1  and SL 1 - 2  to have a larger surface area, thus reducing the resistance of the sub cathodes SL 1 - 1  and SL 1 - 2 . Also, the extension portions  28   c  which extend from each unit secondary wall  28   b  reduces interference generated between adjacent pixels when the EL cells emit light, thus enhancing an image displayed on the organic EL display panel. 
       FIG. 8  is a detailed view of section “B” of  FIG. 4 , in accordance with a third embodiment of the invention. 
     The structure of the organic EL display device shown in  FIG. 8  is similar to that shown in  FIG. 6 . However, the secondary wall  38   b  shown in  FIG. 8  includes a first extension portion  38   c  and a second extension portion  38   d  formed on at least one end of each unit secondary wall  38   b , oriented at a predetermined angle relative to the anode columns DL 1  and DL 2 . In certain embodiments of the invention, the first extension portion  38   c  may be longer than the second extension portion  38   d , and the first extension portion  38   c  of each unit secondary wall  38   b  may be adjacent to the second extension portion  38   d , and parallel to a first extension portion  38   c  of an adjacent unit secondary wall  38   b . Likewise, the second extension portion  38   d  of each unit secondary wall  38   b  may be adjacent to the first extension portion  38   c , and parallel to a the second extension portion  38   d  of an adjacent unit secondary wall  38   b . 
     When constructed as described above, the first and second sub cathodes SL 1 - 1  and SL 1 - 2  may be coupled to each other, for example, at a region between adjacent unit secondary walls  38   b . These areas which connect the first and second sub cathodes SL 1 - 1  and SL 1 - 2  cause the first and second sub cathodes SL 1 - 1  and SL 1 - 2  to have a larger surface area, thus reducing the resistance of the first and second sub cathodes SL 1 - 1  and SL 1 - 2 . Also, the extension portions  38   c  and  38   d  formed at one end or both ends thereof may reduce interference generated between adjacent pixels when the EL cells emit light, thus producing an enhanced image on the organic EL display panel 
     In the organic EL device in accordance with the second and third embodiments of the invention, current supplied to the first and second sub cathodes SL 1 - 1  and SL 1 - 2  through the anode may flow to the cathode SL 1  via the current path shown in  FIG. 9  so that power consumption of the organic EL display device may be decreased. 
       FIG. 10  is a detailed view of section “B” of  FIG. 4 , in accordance with a fourth embodiment of the invention. Section “B” of the organic EL display device includes anode columns D 1 , D 2  and D 3 , a cathode SL 1  which crosses the anode columns D 1 , D 2  and D 3 , and primary walls  18   a  and a secondary wall  48   b  which cross the anode columns D 1 , D 2  and D 3  and are positioned parallel to the cathode SL 1 . 
     A section of the cathode SL 1  such as, for example, a section corresponding to an active region may be divided into first and second sub cathodes SL 1 - 1  and SL 1 - 2  by the secondary wall  48   b , forming two individual cells at an area common to one anode column, such as, for example, DL 1  and one cathode, such as, for example, SL 1 . Also, although the primary walls  18   a  may extend to a non display region, the secondary wall  48   b  may be positioned only in a cell array region. The secondary wall  48   b , which divides the cathode SL 1  may actually be a plurality of unit secondary walls  48   b , each unit secondary wall  48   b  corresponding to each of the first, second and third sub-pixels (EL cells) R, G and B, respectively, which make up one pixel. 
     When constructed in this manner, the first and second sub cathodes SL 1 - 1  and SL 1 - 2  may be coupled to each other, for example, at an area between adjacent unit secondary walls  48   b . These areas which connect the first and second sub cathodes SL 1 - 1  and SL 1 - 2  cause the first and second sub cathodes SL 1 - 1  and SL 1 - 2  have a larger surface area, thus reducing the resistance of the sub cathodes SL 1 - 1  and SL 1 - 2 . The current supplied to the first and second sub cathodes SL 1 - 1  and SL 1 - 2  through the anode flows easily to the cathode SL 1  via the current path shown in  FIG. 11  so that power consumption of the organic EL display device may be decreased. 
       FIG. 12  is a detailed view of section “B” of  FIG. 4 , in accordance with a fifth embodiment of the invention. The structure of the organic EL display device shown in  FIG. 12  is similar to that shown in  FIG. 10 . However, each unit secondary wall  58   b  shown in  FIG. 12  includes an extension portion  58   c  formed on at least one end thereof, and each unit secondary wall  58   b  corresponds to one sub-pixel. The extension portion  58   c  may extend parallel to the anode columns DL 1 , DL 2  and DL 3  on just one end of each unit secondary wall  58   b , or alternatively, an extension portion  58   c  may be formed on each end of each unit secondary wall  58   b , as shown in  FIG. 12 . 
     When constructed in this manner, the first and second sub cathodes SL 1 - 1  and SL 1 - 2  may be coupled to each other, for example, at an area between adjacent unit secondary walls  58   b . These areas which connect the first and second sub cathodes SL 1 - 1  and SL 1 - 2  cause the first and second sub cathodes SL 1 - 1  and SL 1 - 2  to have a larger surface area, thus reducing the resistance of the sub cathodes. Also, the extension portions  58   c  formed at one end or both ends thereof may reduce interference generated between adjacent sub-pixels (such as, for example, R and G, G and B) when the EL cells emit light, thus producing an enhanced image on the organic EL display panel. 
       FIG. 13  is a detailed view of section “B” of  FIG. 4 , in accordance with a sixth embodiment of the invention. The structure of the organic EL display device shown in  FIG. 13  is similar to that of the organic EL device shown in  FIG. 10 . However, each unit secondary wall  68   b  includes extension portions  68   c  and  68   d  are formed on at least one end thereof, and each unit secondary wall  68   b  corresponds to a single sub-pixel. The first and second extension portions  68   c  and  68   d  may extend at a predetermined angle relative to the anode columns DL 1  and DL 2 , as shown in  FIG. 13 . 
     The first extension portion  68   c  may be longer than the second extension portion  68   d . Also, the first extension portion  68   c  of each unit secondary wall  68   b  may be adjacent to the second extension portion  68   d , and parallel to a first extension portion  68   c  of an adjacent unit secondary wall  68   b . 
     Likewise, the second extension portion  68   d  of each unit secondary wall  68   b  may be adjacent to the first extension portion  68   c , and parallel to a second extension portion  68   d  of an adjacent unit secondary wall  68   b . 
     When constructed as described above, the first and second sub cathodes SL 1 - 1  and SL 1 - 2  may be coupled to each other, for example, at an area between adjacent unit secondary walls  68   b . These areas which connect the first and second sub cathodes SL 1 - 1  and SL 1 - 2  cause the first and second sub cathodes SL 1 - 1  and SL 1 - 2  to have a larger surface area, thus reducing the resistance of the sub cathodes. Also, the extension portions  68   c  and  68   d  at one end or both ends thereof may reduce interference generated between adjacent sub-pixels when the EL cells emit light, thus producing an enhanced image on the organic EL display panel. 
     In the organic EL devices in accordance with the fifth and sixth embodiments of the invention, current supplied to the first and second sub cathodes SL 1 - 1  and SL 1 - 2  through the anode can flow to the cathode SL 1  via the current path shown in  FIG. 14  so that power consumption of the organic EL display device may be decreased. 
     The electroluminescent device of the present invention may be used in or formed as a flexible display for numerous devices, such as, for example, electronic books, newspapers, magazines, and the like, different types of portable devices, such as, for example, handsets, MP3 players, notebook computers, and the like, audio applications, navigation applications, televisions, monitors, or other types of devices using a display, either monochrome or color. 
     In an organic EL device as embodied and broadly described herein, each cathode may be divided in an active region by a secondary wall into two sub cathodes, and the two sub cathodes may be connected to each other at an area between adjacent unit secondary walls so increase surface area of the cathode formed on the emitting area. In this manner, resistance of the cathode may be reduced so that power consumption of the organic EL device may be decreased. 
     Additionally, extensions formed at the end(s) of each unit secondary wall and extending parallel to or at a predetermined angle to the anodes may reduce interference between adjacent pixels or sub-pixels so that image quality of the organic EL device may be enhanced. 
     The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not limit the scope of the claims. Many alternatives, modifications and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.