Abstract:
An organic electroluminescent device includes a substrate, a plurality of gate lines on the substrate, a plurality of data lines on the substrate, each of the plurality of data lines crossing the gate lines, a plurality of switching elements and driving elements interconnected on the substrate, and a power line disposed in parallel to the data lines on the substrate, wherein the power line is electrically connected to at least two of the plurality of driving elements.

Description:
[0001]    The present invention claims the benefit of the Korean Patent Application No. 2002-24551 filed in Korea on May 3, 2002, which is hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field Of The Invention  
           [0003]    The present invention relates to a semiconductor device, and more particularly, to an organic electroluminescent device and a fabricating method thereof.  
           [0004]    2. Discussion Of The Related Art  
           [0005]    In general, an organic electroluminescent device (ELD) emits light by injecting electrons from a cathode and holes from an anode into an emission layer, combining the electrons with the holes, generating an exciton, and transitioning the exciton from an excited state to a ground state. Contrary to a liquid crystal display (LCD) device, an additional light source is not necessary for the organic ELD to emit light because the transition of the exciton between states causes light to be emitted. Accordingly, the size and weight of the organic ELD can be reduced. The organic ELD has other excellent characteristics such as low power consumption, superior brightness, and fast response time. Because of these characteristics, the organic ELD is regarded as a promising candidate for next-generation consumer electronic applications, such as cellular phones, car navigation systems (CNS), personal digital assistants (PDA), camcorders, and palmtop computers. Moreover, since fabricating the organic ELD is a simple process with few processing steps, it is much cheaper to produce an organic ELD than an LCD device.  
           [0006]    Two different types of organic ELDs exist: passive matrix and active matrix. While both the passive matrix organic ELD and the active matrix organic ELD have a simple structure and are formed by a simple fabrication process, the passive matrix organic ELD requires a relatively high amount of power to operate. In addition, the display size of a passive matrix organic ELD is limited by its structure. Furthermore, as the number of conductive lines increases, the aperture ratio of a passive matrix organic ELD decreases. In contrast, active matrix organic ELDs are highly efficient and can produce a high-quality image for a larger display with relatively low power.  
           [0007]    [0007]FIG. 1 is a cross-sectional view of an organic ELD according to the related art. In FIG. 1, an array element  14  including a thin film transistor (TFT) “T” is formed on a first substrate  12 . A first electrode  16 , an organic electroluminescent layer  18 , and a second electrode  20  are formed over the array element  14 . The organic electroluminescent layer  18  may separately display red, green, and blue colors for each pixel region. Generally, separate organic materials are used to emit light of each color for the organic electroluminescent layer  18  in each pixel region. An organic ELD is encapsulated by attaching the first substrate  12  and a second substrate  28 , which includes a moisture absorbent material  22 , with a sealant  26 . The moisture absorbent material  22  eliminates moisture and oxygen that may penetrate into a capsule of the organic electroluminescent layer  18 . After etching a portion of the second substrate  28 , the etched portion is filled with the moisture absorbent material  22 , and the filled moisture absorbent material is fixed by a holding element  25 .  
           [0008]    [0008]FIG. 2 is a plan view of an organic ELD according to the related art. In FIG. 2, a switching element T s , a driving element T D , and a storage capacitor C ST  are formed in each pixel region on a substrate  12 . The switching element T s  and the driving element T D  can be a combination of at least two thin film transistors (TFTs) according to the operating requirements of the organic ELD. The substrate  12  is made of a transparent insulating material, such as glass or plastic. Moreover, a gate line  32  and a data line  34  cross each other with an insulating layer (not shown) in between the gate line  32  and the data line  34 . A power line  35  is placed in parallel to and separated from the data line  34 . Two TFTs are used as the switching element T s  and the driving element T D . The switching element T s  includes a gate electrode  36 , an active layer  40 , a source electrode  46 , and a drain electrode  50 . The driving element T D  includes a gate electrode  38 , an active layer  42 , a source electrode  48 , and a drain electrode  52 . The gate electrode  36  and the source electrode  46  of the switching element T s  are connected to the gate line  32  and the data line  34 , respectively. The drain electrode  50  of the switching element T s  is connected to the gate electrode  38  of the driving element T D  through a first contact  54 . The source electrode  48  of the driving element T D  is connected to the power line  35  through a second contact  56 . The drain electrode  52  of the driving element T D  contacts a first electrode  16  in a pixel region P. The power line  35  overlaps the first electrode  16 , which is composed of polycrystalline silicon, with an insulating layer interposed between the power line  35  and the first electrode  16  to form a storage capacitor C ST .  
           [0009]    [0009]FIG. 3 is a cross-sectional view of the organic ELD shown of FIG. 2 taken along III-III according to the related art. In FIG. 3, a driving element T D  including a gate electrode  38 , an active layer  42 , a source electrode  56 , and a drain electrode  52  is formed on a substrate  12 . A first electrode  16  contacting the drain electrode  52  of the driving element T D  with an insulating layer interposed between the first electrode  16  and the drain electrode  52  is formed over the driving element T D . An organic electroluminescent layer  18  emitting light of one color is formed on the first electrode  16 , and a second electrode  20  is formed on the organic electroluminescent layer  18 . The organic electroluminescent layer  18 , the first electrode  16 , and the second electrode  20  constitute an organic electroluminescent diode D EL . A storage capacitor C ST  including first capacitor electrode  15  and second capacitor electrode  35  and the driving element T D  are electrically connected in parallel to the switching element T s  (as shown in FIG. 2). The second capacitor electrode  35  is connected to a power line. The source electrode  56  of the driving element T D  is connected to the second capacitor electrode  35 . The second electrode  20  covers the driving element T D , the storage capacitor C ST , and the organic electroluminescent layer  18 .  
           [0010]    [0010]FIG. 4 is an equivalent circuit diagram of an organic ELD according to the related art. In FIG. 4, a data line  34  is in parallel to and separated from a power line  35 . A gate line  32  crosses the data line  34  and the power line  35  to define a pixel region P. A switching element T s , a driving element T D , and a storage capacitor C ST  are disposed in the pixel region.  
           [0011]    In the organic electroluminescent device according to the related art, the power line  35  limits the area of the organic electroluminescent layer. As the area of the electroluminescent layer decreases, the current density required to obtain the same brightness increases. Increasing the current density shortens the expected life span of an organic ELD. An increased current density is required to obtain sufficient brightness in a bottom emission organic ELD because the use of at least three lines causes a reduction in the aperture ratio. Moreover, as the number of conductive lines increases, the probability of defects in the conductive lines increases resulting in a decrease in the production yield.  
         SUMMARY OF THE INVENTION  
         [0012]    Accordingly, the present invention is directed to an organic electroluminescent device and a fabricating method thereof that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.  
           [0013]    An object of the present invention is to provide an organic electroluminescent device where one power line is used for two adjacent pixel regions and a fabricating method thereof.  
           [0014]    Another object of the present invention is to provide an organic electroluminescent device where an aperture ratio is improved and the expected lifetime of the device is increased, and a fabricating method thereof.  
           [0015]    Another object of the present invention is to provide an organic electroluminescent device with a reduced probability of line defects and a fabricating method thereof.  
           [0016]    Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
           [0017]    To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an organic electroluminescent device includes a substrate, a plurality of gate lines on the substrate, a plurality of data lines on the substrate, each of the plurality of data lines crossing the gate lines, a plurality of switching elements and driving elements interconnected on the substrate, and a power line disposed in parallel to the data lines on the substrate, wherein the power line is electrically connected to at least two of the plurality of driving elements.  
           [0018]    In another aspect, an organic electroluminescent device includes a first substrate, a second substrate facing and spaced apart from the first substrate, a plurality of gate lines on an inner surface of the first substrate, a plurality of data lines on an inner surface of the first substrate, each of the plurality of data lines crossing the gate lines, a plurality of switching elements and driving elements interconnected on the first substrate, a power line disposed in parallel to the data lines on the substrate and electrically connected to at least two of the plurality of driving elements, a plurality of connection electrodes connected to the plurality of driving elements, a plurality of first electrodes on an inner surface of the second substrate, an organic electroluminescent layer on the plurality of first electrodes; and a plurality of second electrodes on the organic electroluminescent layer, each of the plurality of second electrodes contacting one of the plurality of connection electrodes.  
           [0019]    In another aspect, a method of fabricating an organic electroluminescent device includes steps of forming a plurality of switching active layers, a plurality of driving active layers, and a plurality of active patterns on a first substrate, the plurality of active patterns including polycrystalline silicon, forming a first insulating layer on the plurality of switching active layers, the plurality of driving active layers, and the plurality of active patterns, forming a plurality of switching gate electrodes on the first insulating layer to extend over the plurality of switching active layers, forming a plurality of driving gate electrodes on the first insulating layer to extend over the plurality of driving active layers, doping the plurality of switching active layers, the plurality of driving active layers, and the plurality of active patterns with impurities to form a switching source region and a switching drain region in each of the plurality of switching active layers and a driving source region and a driving drain region in each of the plurality of driving active layers, forming a second insulating layer on the plurality of switching gate electrodes and the plurality of driving gate electrodes, forming a power line on the second insulating layer, forming a third insulating layer on the power line, forming a plurality of switching source electrodes on the third insulating layer to contact the switching source region, forming a plurality of switching drain electrodes on the third insulating layer to contact the switching drain region, forming a plurality of driving source electrodes on the third insulating layer to contact the driving source region, and forming a plurality of driving drain electrodes on the third insulating layer to contact the driving drain region, wherein at least two of the plurality of driving drain electrodes are connected to the power line.  
           [0020]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention. In the drawings:  
         [0022]    [0022]FIG. 1 is a cross-sectional view of an organic electroluminescent device according to the related art;  
         [0023]    [0023]FIG. 2 is a plan view of an organic electroluminescent device according to the related art;  
         [0024]    [0024]FIG. 3 is a cross-sectional view of the organic electroluminescent device of FIG. 2 taken along III-III according to the related art;  
         [0025]    [0025]FIG. 4 is an equivalent circuit diagram of an organic electroluminescent device according to the related art;  
         [0026]    [0026]FIG. 5 is an equivalent circuit diagram of an exemplary organic electroluminescent device according to the present invention;  
         [0027]    [0027]FIG. 6 is a plan view of an exemplary organic electroluminescent device according to the present invention;  
         [0028]    [0028]FIGS. 7A to  7 E are cross-sectional views of the exemplary organic electroluminescent device of FIG. 6 taken along VII-VII, showing an exemplary fabricating method of an organic electroluminescent device according to the present invention;  
         [0029]    [0029]FIG. 8 is a cross-sectional view of an another exemplary organic electroluminescent device according to the present invention; and  
         [0030]    [0030]FIGS. 9A to  9 C are cross-sectional views of another exemplary fabricating process of an organic electroluminescent diode according to the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0032]    [0032]FIG. 5 is an equivalent circuit diagram of an exemplary organic electroluminescent device according to the present invention. In FIG. 5, a data line  111  may be in parallel to and separated from a power line  112 . A gate line  101  may cross the data line  111  to define a pixel region P. A switching element T s , a driving element T D1 , a storage capacitor C ST , and an organic electroluminescent diode D EL  may be formed in the pixel region P. The adjacent driving elements T D1  and T D2  of adjacent pixel regions P may be connected to the same power line  112 . Since the number of the power lines  112  may be reduced by a factor of 2, the aperture ratio may increase, and the resulting device may have a resulting reduction in material cost.  
         [0033]    [0033]FIG. 6 is a plan view of an exemplary organic electroluminescent device according to the present invention. In FIG. 6, a gate line  101  may cross a first and second data line  111  and  111 ′ and a power line  112 . The data lines  111  and  111 ′ and the power line  112  may be in parallel to and separated from each other. The gate line  101  and the data lines  111  and  111 ′ may define a first pixel region and a second pixel region P1 and P2, respectively, that are adjacent to each other. First and second switching elements T s1 , and T S2 , respectively, first and second driving elements T D1  and T D2 , respectively, and first and second storage capacitors C ST1  and C ST2 , respectively, may be formed in the respective adjacent first and second pixel regions P1 and P2. The power line  112  may be used as a common first capacitor electrode for the first storage capacitor C ST1  and the second storage capacitor C ST2 . The first and second active patterns  105  and  105 ′, each positioned under the power line  112 , may be used as second capacitor electrodes of the first and second storage capacitors C ST1  and C ST2 , respectively.  
         [0034]    The first switching element T s , may include a switching active layer  103 , a switching gate electrode  107 , a switching source electrode  117  and a switching drain electrode  119 . The driving element T D1  may include a driving active layer  104 , a driving gate electrode  108 , a driving source electrode  116 , and a driving drain electrode  118 . The switching drain electrode  119  may be electrically connected to the driving gate electrode  108 . Since the switching source electrode  117  is connected to the data line  111 , an image signal may be applied to the switching source electrode  117  from the data line  111 . The driving drain electrode  118  may be connected to a first electrode  122  of the organic electroluminescent diode (not shown). The driving source electrode  116  may be connected to the power line  112 . Structures of the second switching element T S2  and the second driving element T D2  may be similar to structures of the first switching element T S1  and the first driving element T D1 , respectively. The adjacent first and second driving source electrodes  116  and  116 ′ of the adjacent first and second pixel regions P1 and P2 may be connected to the same power line  112 . Accordingly, the first and second driving elements T D1  and T D2  may be symmetrically disposed with respect to the power line  112  in the adjacent first and second pixel regions P1 and P2. The adjacent first and second active patterns  105  and  105 ′, which are made of polycrystalline silicon, may extend from the respective first and second switching active layers  103  and  103 ′ of the adjacent first and second pixel regions P1 and P2. Since the number of power lines  112  may be reduced by a factor of two, the aperture ratio of the organic electroluminescent device may be improved and line defects may be prevented. Indeed, the increased aperture ratio may be particularly beneficial to a bottom emission organic electroluminescent device because the aperture ratio of such a device is generally limited.  
         [0035]    [0035]FIGS. 7A to  7 E are cross-sectional views of the exemplary organic electroluminescent device of FIG. 6 taken along VII-VII, showing an exemplary fabricating method of an organic electroluminescent device according to the present invention. In FIG. 7A, a buffer layer  102  (i.e., a first insulating layer) of an insulating material may be formed on a substrate  100  including adjacent first and second pixel regions P1 and P2 and adjacent first and second capacitor regions C1 and C2. Each pixel region P1 and P2 may include a switching region (not shown) and a driving region D. A first switching active layer (not shown), a first driving active layer  104 , and a first active pattern  105 , which is made of polycrystalline silicon, may be formed on the buffer layer  102  in the switching region, driving region D and capacitor region C1. Similarly, a second switching active layer (not shown), a second driving active layer  104 ′, and a second active pattern  105 ′, which is made of polycrystalline silicon, may be formed on the buffer layer  102  in the switching region, driving region D and capacitor region C2. The first and second active patterns  105  and  105 ′ of the adjacent capacitor regions C1 and C2 may extend from the first and second switching active layers of the switching regions of the adjacent pixel regions P1 and P2, respectively. After a gate insulating layer  106  (i.e., a second insulating layer) is formed on an entire surface of the substrate  100 , first and second switching gate electrodes (not shown) and first and second driving gate electrode  108  and  108 ′ may be formed on the gate insulating layer  106  over the respective first and second switching active layers and first and second driving active layers  104  and  104 ′. The gate insulating layer  104  may include an inorganic insulating material, such as silicon nitride (SiN x ) or silicon oxide (SiO 2 ). The first and second switching gate electrodes and the first and second driving gate electrodes  108  and  108 ′ may include a conductive metallic material, such as aluminum (Al), aluminum alloy, copper (Cu), tungsten (W), tantalum (Ta), or molybdenum (Mo). The gate insulating layer  106  may be etched to have the same patterns as the first and second switching gate electrodes and the first and second driving gate electrodes  108  and  108 ′.  
         [0036]    Next, the first and second switching active layers, the first and second driving active layers  104  and  104 ′, and the first and second active patterns  105  and  105 ′ may be doped with impurities. Since the first driving gate electrode  108  may be used as a doping mask, the first driving active layer  104  may be divided into a first driving channel region  104   a , a first driving source region  104   b , and a first driving drain region  104   c . Similarly, the second driving active layer  104 ′ may be divided into a second driving channel region  104   a ′, a second driving source region  104   b ′, and a second driving drain region  104   c ′. Even though not shown in FIG. 7A, the first and second switching active layers may also be divided into first and second switching channel regions, first and second switching source regions, and first and second switching drain regions.  
         [0037]    Subsequently, an interlayer insulating layer  110  (i.e., a third insulating layer) may be formed on the entire surface of the substrate  100 . The interlayer insulating layer  110  may include an inorganic insulating material, such as silicon nitride (SiN x ) or silicon oxide (SiO 2 ). A power line  112  may be formed on the interlayer insulating layer  110  between the adjacent pixel regions P1 and P2. The power line  112  may include a conductive metallic material, such as aluminum (Al), aluminum alloy, copper (Cu), tungsten (W), tantalum (Ta), or molybdenum (Mo).  
         [0038]    In FIG. 7B, a fourth insulating layer  113  having first and second switching source contact holes (not shown), first and second switching drain contact holes (not shown), first and second driving source contact holes  114   a  and  114   a ′, first and second driving drain contact holes  114   b  and  114   b ′, and first and second power contact holes  115  and  115 ′ may be formed on the entire surface of the substrate  100 . The first driving source contact hole  114   a  and the first driving drain contact hole  114   b  may expose the first driving source region  104   b  and the first driving drain region  104   c , respectively. Similarly, the first switching source contact hole and the first switching drain contact hole may expose the first switching source region and the first switching drain region, respectively (not shown in FIG. 7B). The first and second power contact holes  115  and  115 ′ exposing the power line  112  may be disposed adjacent to the respective driving regions D of the adjacent pixel regions P1 and P2.  
         [0039]    In FIG. 7C, first and second switching source electrodes (not shown), first and second switching drain electrodes (not shown), first and second driving source electrodes  116  and  116 ′, and first and second driving drain electrodes  118  and  118 ′ may be formed on the fourth insulating layer  113  by depositing and patterning a conductive metallic material, such as aluminum (Al), aluminum alloy, copper (Cu), tungsten (W), tantalum (Ta), or molybdenum (Mo). The first driving source electrode  116  and the first driving drain electrode  118  may be connected to the first driving source region  104   b  and the first driving drain region  104   c , respectively. Similarly, the first switching source electrode and the first switching drain electrode may be connected to the first switching source region and the first switching drain region, respectively (not shown in FIG. 7C). The first and second driving source electrodes  116  and  116 ′ may be connected to the same power line  112  through the first and second power contact holes  115  and  115 ′. As a result, the same source voltage may be applied to first and second driving elements T D1 , and T D2  of the adjacent pixel regions P1 and P2 through the same power line  112 . The first and second driving elements T D1  and T D2  may be symmetrically disposed with respect to the power line  112 . The first and second driving gate electrodes  108  and  108 ′ may be connected to the first and second switching drain electrodes (not shown), respectively.  
         [0040]    In FIG. 7D, after a fifth insulating layer  120  is formed on an entire surface of the substrate  100 , the first and second driving drain electrodes  118  and  118 ′ may be exposed. First and second lower electrodes  122  and  122 ′ may be formed on the fifth insulating layer  120 . The first and second lower electrodes  122  and  122 ′ may be connected to the first and second driving drain electrodes  118  and  118 ′, respectively. Moreover, the first and second lower electrodes  122  and  122 ′ may extend to the first and second pixel regions P1 and P2, respectively. The first and second lower electrodes  122  and  122 ′ may function as an anode that injects holes. The first and second lower electrodes  122  and  122 ′ may include a material of a high work function, such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO).  
         [0041]    In FIG. 7E, after a sixth insulating layer  124  is formed on an entire surface of the substrate  100 , the first and second lower electrodes  122  and  122 ′ may be exposed. First and second organic electroluminescent layers  126  and  126 ′ may be formed on the first and second lower electrodes  122  and  122 ′, respectively. An upper electrode  128  may be formed on the entire surface of the substrate  100 . The upper electrode  128  may function as a cathode injecting electrons. The upper electrode  128  may include a metallic material, such as calcium (Ca), aluminum (Al), or magnesium (Mg).  
         [0042]    In another embodiment, array elements and organic electroluminescent diodes may be formed on individual substrates. Subsequently, the individual substrates may be attached.  
         [0043]    [0043]FIG. 8 is a cross-sectional view of another exemplary organic electroluminescent device according to the present invention. In FIG. 8, a first substrate  100  may face and be separated from a second substrate  200 . An array element including a TFT “T” may be formed on an inner surface of the first substrate  100 , and a first electrode  202  that inject electrons, an organic electroluminescent layer  208 , and a second electrode  210  that inject holes may be formed on an inner surface of the second substrate  200 . The first and second substrates  100  and  200  may be bonded together with a sealant  300 . A connection pattern  140 , which is connected to the TFT “T,” may contact the second electrode  210  during the process of attaching the first substrate  100  to the second substrate  200 . The array element may be fabricated through the process described in reference to FIGS. 7A to  7 C except that a forming step for the connection pattern  140  may be added.  
         [0044]    [0044]FIGS. 9A to  9 C are cross-sectional views of an exemplary fabricating process of an organic electroluminescent diode according to the present invention. In FIG. 9A, a first electrode  202  may be formed on a substrate  200 . The first electrode  202  may function as a cathode injecting electrons into an organic electroluminescent layer (not shown). The first electrode  202  may include aluminum (Al), calcium (Ca), magnesium (Mg), or two layers of lithium fluoride/aluminum (LiF/Al), for example.  
         [0045]    In FIG. 9B, an organic electroluminescent layer  204  may be formed on the first electrode  202 . The organic electroluminescent layer  204  may emit red, green, or blue light and may correspond to a pixel region P. The organic electroluminescent layer  204  may have a single layer structure or a multi layer structure. The organic electroluminescent layer  204  with a multi layer structure may include an emission layer  204   a , a hole transporting layer  204   b , and an electron transporting layer  204   c.    
         [0046]    In FIG. 9C, a second electrode  206  may be formed on the organic electroluminescent layer  204 . The second electrode  206  may function as an anode that injects holes into the organic electroluminescent layer  204  and may correspond to the pixel region P. The second electrode  206  may include a conductive material having a high work function, such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO).  
         [0047]    After the organic electroluminescent diode is formed on the second substrate, the second substrate may be bonded to the first substrate that has the array element such that the second electrode of the second substrate contacts the connection pattern of the first substrate.  
         [0048]    Since the disclosed organic electroluminescent device has one power line for two adjacent driving elements of two adjacent pixel regions, the number of power lines is reduced by a factor of two. As a result, the aperture ratio of the disclosed organic electroluminescent device is improved. Moreover, since the disclosed organic electroluminescent device reduces line defects and decreases material cost, the production yield for organic electroluminescent devices is improved. Indeed, the increased aperture ratio resulting from the disclosed organic electroluminescent device may be particularly beneficial to a bottom emission organic electroluminescent device because the aperture ratio of a bottom emission organic electroluminescent device is generally limited.  
         [0049]    It will be apparent to those skilled in the art that various modifications and variations can be made in the organic electroluminescent device and fabricating method thereof of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.