Patent Publication Number: US-7902753-B2

Title: Organic electroluminescent display device and fabricating method thereof

Description:
This application is a Divisional of application Ser. No. 11/107,875, filed Apr. 18, 2005 now U.S. Pat. No. 7,560,863 now allowed; which claims priority to Korean Patent Application No. 10-2004-0026571, filed Apr. 19, 2004, all of which are hereby incorporated by reference as if fully set forth herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a display device and a method of fabricating a display device, and more particularly, to an organic electroluminescent display (OELD) device and a method of fabricating an OELD device. 
     2. Discussion of the Related Art 
     In the past, many display devices have employed cathode-ray tubes (CRTs) to display images. However, various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, field emission display (FED) devices, and electro-luminescent display (ELD) devices, are currently being developed as substitutes for the CRTs. Among these various types of flat panel displays, the PDP devices have advantages of large display size, but have disadvantages of heaviness and high power consumption. Similarly, the LCD devices have advantages of thin profile and low power consumption, but have disadvantages of small display size. However, the OELD devices are luminescent displays having advantages of fast response time, high brightness, and wide viewing angles. 
       FIG. 1  is a cross-sectional view of an OELD device according to the related art. 
     As illustrated in  FIG. 1 , an OELD device includes first and second substrates  10  and  60  facing each other and bonded together with a sealant  70 . The first substrate  10  includes a thin film transistor T, an array layer AL and an organic emitting diode E including a first electrode  48  and an organic emitting layer  54  within a pixel region P, and a second electrode  56 . The second substrate  60  has a recessed portion  62  filled with a desiccant  64  for blocking entry of outer moisture. 
     In  FIG. 1 , when the first electrode  48  is formed of a transparent material, light emitted from the organic emitting layer  54  is transmitted toward the first substrate  10 . Thus, this OELD device is categorized as a bottom emission-type OELD device. 
       FIG. 2A  is a plan view of a pixel region of an OELD device according to the related art, and  FIG. 2B  is a cross-sectional view, which shows a driving thin film transistor, taken along a line IIb-IIb of  FIG. 2A . 
     As illustrated in  FIG. 2A , in a pixel region P of a first substrate  10 , a data line  42  and a gate line  22  crossing each other, a switching thin film transistor Ts, a driving thin film transistor Td, a power line  28  and an organic emitting diode E. 
     As illustrated in  FIG. 2B , a buffer layer  12  is disposed on a first substrate  10 . A semiconductor pattern  14  and a first capacitor electrode  16  is disposed on the buffer layer  12 . A gate insulating layer  18  and a gate electrode  20  is disposed on the semiconductor pattern  14 . The semiconductor pattern  14  includes an active region AR at a center portion, a drain region DR at a left portion and a source region at a right portion SR. 
     A first passivation layer  24  is disposed on the gate electrode  20 . A power electrode  26  as a second capacitor electrode extended from the power line  28  is disposed on the first passivation layer  24  corresponding to the first capacitor electrode  16 . The power electrode  26  as the second capacitor electrode and the first capacitor electrode  16  define a storage capacitor Cst. 
     A second passivation layer  30  is disposed on the power electrode  26 . The first and second passivation layers  24  and  30  have first and second contact holes  32  and  34  exposing the source and drain regions SR and DR. Furthermore, the second passivation layer  30  have a third contact hole  36  exposing the power electrode  26 . 
     Source and drain electrodes  38  and  40  are disposed on the second passivation layer  30 . The source and drain electrodes  38  and  40  contact the source and drain regions SR and DR through the first and second contact hole  32  and  34 , respectively. Furthermore, the source electrode  38  contacts the power electrode  26  through the third contact hole  36 . A third passivation layer  44  is disposed on the source and drain electrodes  38  and  40  and has a fourth contact hole  46  exposing the drain electrode  40 . 
     An organic emitting diode E including a first electrode  48 , an organic emitting layer  54  and a second electrode  56  is disposed on the third passivation layer  44 . The first electrode  48  is disposed on the third passivation layer  44  and contacts the drain electrode  40  through the fourth contact hole  46 . An inter layer  50  covers an end portion of the first electrode  48  and has an opening  51  exposing the first electrode  48 . The organic emitting layer  54  covers the opening  51  and a portion of the inter layer  50 . The second electrode  56  is disposed entirely on the substrate  10  having the organic emitting layer  54 . 
     In the related art OELD device, because the switching and driving thin film transistors and the organic emitting diode are both formed on the first (lower) substrate, the production efficiency of the OELD device is reduced. For example, when one of the switching and driving thin film transistors and the organic emitting diode is determined to have a defect after fabrication, then the first (lower) substrate is considered unacceptable, and thus the production efficiency of the OELD device is reduced. Furthermore, when the OELD device is a bottom emission-type OELD device in which the first electrode of the organic emitting diode is formed of a transparent material, the aperture ratio of the OELD device is reduced and high resolution is difficult to achieve, because the switching and driving thin film transistors and metal lines block bottom emission of the light. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to an OELD device and a method of fabricating an OELD device that substantially obviate one or more of problems due to limitations and disadvantages of the related art. 
     An advantage of the present invention is to provide an OELD device which can have an improved aperture ratio and high resolution. 
     Another advantage of the present invention is to provide a method of fabricating an OELD device which can have improved production efficiency. 
     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 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. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an electroluminescent display device includes first and second substrates facing each other and having a pixel region and a non-pixel region; a thin film transistor and an array layer on an inner surface of the first substrate; a first electrode on an inner surface of the second substrate; a buffer layer on the first electrode in the non-pixel region; a shielding pattern on the buffer layer; a separator on the shielding pattern; an emitting layer on the first electrode in the pixel region; a second electrode on the emitting layer; and a connection electrode between the first and second substrates. 
     In another aspect, a method of fabricating a substrate for an electroluminescent display device includes forming a first electrode on a substrate having a pixel region and a non-pixel region; forming a buffer layer on the first electrode in the non-pixel region; forming a shielding pattern on the buffer layer; forming a separator on the shielding pattern; forming an emitting layer on the first electrode in the pixel region; and forming a second electrode on the emitting layer. 
     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 
       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 principles of the invention. 
       In the drawings: 
         FIG. 1  is a cross-sectional view of an OELD device according to the related art; 
         FIG. 2A  is a plan view of a pixel region of an OELD device according to the related art; 
         FIG. 2B  is a cross-sectional view, which illustrates a driving thin film transistor, taken along a line IIb-IIb of  FIG. 2A ; 
         FIG. 3  is a cross sectional view of an OELD device according to a first embodiment of the present invention; 
         FIG. 4  is a plan view of an OELD device according to a second embodiment of the present invention; 
         FIG. 5  is a cross-sectional view taken along a line V-V of  FIG. 4 ; 
         FIG. 6  is a cross-sectional view of an OELD device according to a third embodiment of the present invention; 
         FIG. 7  is a cross-sectional view of an OELD device according to a fourth embodiment of the present invention; 
         FIG. 8  is a cross-sectional view of an OELD device according to a fifth embodiment of the present invention; 
         FIG. 9  is a cross-sectional view of an OELD device according to a sixth embodiment of the present invention; 
         FIG. 10  is a cross-sectional view of an OELD device according to a seventh embodiment of the present invention; 
         FIG. 11  is a plan view of an OELD device according to an eighth embodiment of the present invention; 
         FIG. 12  is a cross-sectional view taken along a line XII-XII of  FIG. 11 ; and 
         FIGS. 13A to 13E  are cross-sectional views of a method of fabricating an OELD device according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
       FIG. 3  is a cross-sectional view of an OELD device according to a first embodiment of the present invention. 
     As illustrated in  FIG. 3 , an OELD device includes first and second substrates  110  and  130  facing each other and bonded together by a sealant  180 . In the OELD device, a pixel region P displaying images and a non-pixel region NP disposed between adjacent pixel regions NP are defined. 
     The first substrate  110  includes a thin film transistor T and an array layer AL disposed on the inner surface of the first substrate  110 . The thin film transistor T is disposed in the pixel region P and connected to the array layer AL. Though not shown in drawings, the thin film transistor T may have a gate electrode, source and drain electrodes and a semiconductor pattern, as illustrated in  FIG. 2A . The thin film transistor T may correspond to switching and driving thin film transistors. Though not shown in the drawings, the array layer AL may include conductive patterns such as gate and data lines defining the pixel region P and a power line. 
     The second substrate  130  includes an organic emitting diode E, a buffer layer  148  and a separator  154  on the inner surface of the second substrate  130 . The organic emitting diode E includes a first electrode  144  on the second substrate  130 , and an organic emitting layer  156  and a second electrode  158  on the first electrode  144  in the pixel region P. The first electrode  144  as an anode may be formed of a transparent conductive material such as indium-tin-oxide (ITO), indium-zinc-oxide (IZO) or the like. The second electrode  144  as a cathode may be formed of an opaque conductive material (i.e., metal) or the like. The organic emitting layer  156  may include an emitting material layer (EML), a hole injection layer (HIL) disposed between the first electrode  144  and the emitting material layer, and an electron injection layer (EIL) disposed between the second electrode  158  and the emitting material layer. When the first electrode  144  is formed of a transparent material, light emitted from the organic emitting layer  156  can travel toward the second substrate  130 . Accordingly, the OELD device of  FIG. 3  may be categorized as a top-emission type OELD device due to the light emission direction. 
     The buffer layer  148  and the separator  154  are disposed sequentially on the first electrode  144  in the non-pixel region NP. Since the separator  154  is disposed between adjacent pixel regions P, the separator  120  separates the organic emitting layer  156  and the second electrode  158 . The buffer layer  148  acts as a means for preventing the first and second electrodes  144  and  158  from contacting each other. 
     A connection pattern  120  is disposed between the first and second substrates  110  and  130 , and thus connects the thin film transistor T and the second electrode  158 . 
     In the OELD device of the first embodiment, the thin film transistor T and the organic emitting diode E are respectively formed on the different substrates  110  and  130 . Therefore, the production efficiency of the OELD device can increase. Further, in the top emission type OELD, the light emitted from the organic emitting layer  156  can travel toward the second substrate  130  facing the first substrate  110 , where the thin film transistor T and metal lines blocking light emission are disposed. Therefore, the aperture ratio of the OELD device can increase, thereby achieving a high resolution. 
     As above explained, the light emitted from the organic emitting layer  156  travels toward the second substrate  130 . However, portions of the emitted light may travel toward the first substrate  110  through the transparent separator  154 , as shown with a dashed arrow of  FIG. 3 . This abnormal light traveling toward the first substrate  110  may cause a current leakage of the thin film transistor T when amorphous silicon is used for the semiconductor pattern of the thin film transistor T. 
     Next, a second embodiment of the present invention will be described as an improvement of the first embodiment as shown in  FIG. 3 . 
       FIG. 4  is a plan view of an OELD device according to a second embodiment of the present invention, and  FIG. 5  is a cross-sectional view taken along a line V-V of  FIG. 4 . Detailed explanation of the similar parts to the first embodiment will be omitted. 
     As illustrated in  FIGS. 4 and 5 , an OELD device further includes a shielding pattern  252  disposed between a buffer layer  248  and a separator  254 . The shielding pattern  252  shields the abnormal light emitted from an organic emitting layer  256  and traveling toward the first substrate (not shown) through the separator  254 , which is shown with a dashed arrow of  FIG. 5 . The shielding pattern  252  may be formed of a light shielding insulating material such as a black resin. 
     The buffer layer  248  has a first width W 1 , the shielding pattern  252  has a second width W 2 , and the separator  254  has a third width W 3  at a contacting portion between the separator  254  and the shielding pattern  252 . The first width W 1  may be greater than the second width W 2 , and the second width W 2  may be greater than the third width W 3 . 
     First and second dummy layers  257  and  259  are disposed sequentially on the separator  254 . The first dummy layer  257  is formed of the same material as the organic emitting layer  256 , and the second dummy layer  259  is formed of the same material as the second electrode  258 . The organic emitting layer  256  and the second electrode  258  are formed after forming the separator  254 . Accordingly, the first and second dummy layers  257  and  259  are formed on the separator  254  when the organic emitting layer  256  and the second electrode  258  are formed. The OELD device of the second embodiment can be effectively applied to an OELD device having a size under fifteen inches. 
       FIG. 6  is a cross-sectional view of an OELD device according to a third embodiment of the present invention. The third embodiment relates to an OELD device capable of displaying colors. Detailed explanation of the similar parts to the first and second embodiments will be omitted. The OELD device of the third embodiment is similar to that of the second embodiment, except for a color displaying means. 
     As illustrated in  FIG. 6 , the OELD device includes a color filter pattern  334  as well as a shielding pattern  352 . The color filter pattern  334  as a color displaying means is disposed on a second substrate  330 . The color filter pattern  334  may further include red (R), green (G) and blue (B) color filter patterns  334   a ,  334   b  and  334   c  in respective pixel regions P. The red (R), green (G) and blue (B) color filter patterns  334   a ,  334   b  and  334   c  may be formed of red, green and blue color resins, respectively. 
     A black matrix  336  is disposed in a non-pixel region NP between adjacent pixel regions P. The black matrix  336  may correspond to metal lines such as gate and data lines. A planarization layer  340  and a barrier layer  342  are disposed between the color filter pattern  334  and a first electrode  344 . The planarization layer  340  planarizes the second substrate  330  having the color filter patterns  334 . The barrier layer  342  prevents the color filter pattern  334  from outgassing and stabilizes elements deposited thereon. The shielding pattern  352  may be disposed between a buffer layer  348  and a separator  354 , similarly to that of the second embodiment. 
     As above explained, the color filter patterns  334  are disposed on the inner surface of the second substrate  330 . However, it should be understood that the arrangement of the color filter patterns  334  in the OELD device is not limited to, and that various modifications are feasible according to the principles of the present invention. 
     In the third embodiment, the OELD device can display color images through the color filter patterns  334 . Accordingly, an organic emitting layer  356  may emit a single color, for example, a white color. 
     In the third embodiment, the OELD device includes the color filter patterns as a color displaying means. However, it should be understood that a color changing medium (CCM) disposed between the second substrate and the color filter patterns can be further used as a color displaying means. 
       FIG. 7  is a cross-sectional view of an OELD device according to a fourth embodiment of the present invention. The fourth embodiment relates to an OELD device displaying colors as in the third embodiment. Detailed explanation of the similar parts to the first to third embodiments will be omitted. 
     As illustrated in  FIG. 7 , the OELD device includes organic emitting layers  357  as a color displaying means including red (R), green (G) and blue (B) emitting layers  357   a ,  357   b  and  357   c  in respective pixel regions P between adjacent separators  354 . The red (R), green (G) and blue (B) emitting layers  357   a ,  357   b  and  357   c  are used as a color display means instead of the color filter patterns  334  of the third embodiment. 
       FIG. 8  is a cross-sectional view of an OELD device according to a fifth embodiment of the present invention. Detailed explanation of the similar parts to the first to fourth embodiments will be omitted. The OELD device of the fifth embodiment is similar to that of the second embodiment, except for a resistance reducing means. 
     As illustrated in  FIG. 8 , the OELD device includes an auxiliary electrode  446  as a resistance reducing means in a non-pixel region P. The auxiliary electrode  446  contacts a first electrode  444  and is disposed between the first electrode  444  and a buffer layer  448  in a non-pixel region NP. Since the first electrode  444  is formed of a transparent conductive material such as indium-tin-oxide (ITO), the first electrode  444  has a high resistance compared with metal. In particular, when the OELD device has a large size more than fifteen inches, the high resistance of the first electrode  444  causes electrical problems. Accordingly, to reduce the resistance of the first electrode  444 , the auxiliary electrode  446  having a resistance lower than the first electrode  444  is used. The auxiliary electrode  446  may be formed of a material that can prevent galvanic corrosion with the first electrode  444 . In other words, the auxiliary electrode  446  may not be formed of a material including aluminum (Al), because a material including aluminum may create a galvanic corrosion problem when used in association with the first electrode  444  formed of ITO. Instead, molybdenum (Mo) may be used for the material of the auxiliary electrode  446 . 
     On the buffer layer  448 , a shielding pattern  452  and a separator  454  are disposed. Between adjacent separators  454 , an organic emitting layer  456  and a second electrode  458  are disposed. 
       FIG. 9  is a cross-sectional view of an OELD device according to a sixth embodiment of the present invention. Detailed explanation of the similar parts to the first to fifth embodiments will be omitted. The OELD device of the sixth embodiment is similar to that of the fifth embodiment, except for structures of a resistance reducing means and a shielding pattern. 
     As illustrated in  FIG. 9 , the OELD device includes a shielding pattern  552  acting as both a light shielding means and a resistance reducing means in a non-pixel region NP. The shielding pattern  552  is disposed between a buffer layer  548  and a separator  554  to shield light, similarly to that of the second embodiment. Furthermore, the shielding pattern  552  having a resistance lower than the first electrode  544  contacts a first electrode  544  to reduce a resistance of the first electrode  544 , similarly to the auxiliary electrode of the fifth embodiment. 
     The buffer layer  548  has a contact hole  550  to contact the shielding pattern  552  and the first electrode  544 . Since the shielding pattern  522  acts as a resistance reducing means, the shielding pattern  552  may be formed of a conductive material. In particular, the shielding pattern  552  may be formed of a material that can prevent galvanic corrosion with the first electrode  544 , for example, molybdenum (Mo), as explained in the fifth embodiment. Between adjacent separators  554 , an organic emitting layer  556  is disposed. 
       FIG. 10  is a cross-sectional view of an OELD device according to a seventh embodiment of the present invention. Detailed explanation of the similar parts to the first to sixth embodiments will be omitted. The OELD device of the seventh embodiment is similar to that of the fifth and sixth embodiments, except for structures of a resistance reducing means and a shielding pattern. 
     As illustrated in  FIG. 10 , the OELD device includes a shielding pattern  652  and an auxiliary electrode  646  contacting each other in a non-pixel region NP. The auxiliary electrode  646  contacts a first electrode  644  and is disposed between the first electrode  644  and a buffer layer  648 , similarly to that of the fifth embodiment. Thus, the auxiliary electrode  646  reduces a resistance of the first electrode  644 . The shielding pattern  652  is disposed between the buffer layer  648  and a separator  654  to shield light and contacts the auxiliary electrode  646 , similarly to that of the sixth embodiment. 
     The buffer layer  648  has a contact hole  650  to contact the shielding pattern  652  and the auxiliary electrode  646 , similarly to that of the sixth embodiment. As explained in the fifth and sixth embodiments, the shielding pattern  652  may be formed of a conductive material that can prevent galvanic corrosion with the first electrode  644 , for example, molybdenum (Mo). Between adjacent separators  654 , an organic emitting layer  656  is disposed. 
       FIG. 11  is a plan view of an OELD device according to an eighth embodiment of the present invention, and  FIG. 12  is a cross-sectional view taken along a line XII-XII of  FIG. 11 . Detailed explanation of the similar parts to the first to seventh embodiments will be omitted. The OELD device of the eighth embodiment is similar to that of the second embodiment, except for structures of a shielding pattern and a separator. 
     As illustrated in  FIGS. 11 and 12 , the OELD device includes a shielding pattern  752  and a separator  754  having double-patterned structures. In other words, the shielding pattern  752  includes a first pattern  752   a  and a second pattern  752   b  on both side portions of a buffer layer  748 , and the separator  754  includes a first sub-separator  754   a  and a second sub-separator  754   b  on the first pattern  752   a  and the second pattern  752   b , respectively. 
     Width relations of the buffer layer  748 , the shielding pattern  752  and the separator  754  are similar to those of the second embodiment. In other words, a width of a portion of the buffer layer  748  corresponding to the first pattern  752   a  is greater than that of the first pattern  752   a , and the width of the first pattern  752   a  is greater than that of the first sub-separator  754   a  at a contacting portion between the first sub-separator  754   a  and the first pattern  752   a . Furthermore, a width of a portion of the buffer layer  748  corresponding to the second pattern  752   b  is greater than that of the second pattern  752   b , and the width of the second pattern  752   b  is greater than that of the second sub-separator  754   b  at a contacting portion between the second sub-separator  754   b  and the second pattern  752   b.    
     In the eighth embodiment, since the separator  754  includes the first and second sub-separators  754   a  and  754   b  in a non-pixel region NP, the separator  754  can effectively separate adjacent pixel regions P. 
       FIGS. 13A to 13E  are cross-sectional views of a method of fabricating an OELD device according to the present invention. Although a method of fabricating the OELD device of the second embodiment will be explained, it should be understood that a fabricating method according to the present invention can vary and it can be applied to fabricating methods of the OELD devices of the first embodiment and the third to eighth embodiments with minor variations. 
     As illustrated in  FIG. 13A , a first electrode  844  is formed on a substrate  830  having pixel and non-pixel regions P and NP. The first electrode  844  may be formed of a transparent conductive material such as indium-tin-oxide (ITO) and indium-zinc-oxide (IZO). 
     As illustrated in  FIG. 13B , a buffer layer  848  is formed on the first electrode  844  in the non-pixel region NP. 
     As illustrated in  FIG. 13C , a shielding pattern  852  is formed on the buffer layer  848 . A width of the buffer layer  848  may be greater than a width of the shielding pattern  852 . As explained in the second to eighth embodiments, the shielding pattern  852  may be formed of a light shielding material. In particular, when the OELD device has a large size, the light shielding material can be selected from conductive materials such as metal, especially when the shielding pattern contacts the first electrode or the auxiliary electrode, as shown in  FIG. 9  or  10 . However, when the shielding pattern does not connected to the first electrode as shown in  FIG. 8 , the light shielding material may not be a conductor. In such a case, a black resin can also be used for the light shielding material. 
     As illustrated in  FIG. 13D , a separator  854  is formed on the shielding pattern  852 . A width of the shielding pattern  852  may be greater than a width of the separator  854  at a contacting portion between the shielding pattern  852  and the separator  854 . 
     As illustrated in  FIG. 13E , first and second dummy layers  857  and  859  are formed on the separator  854 , and an organic emitting layer  856  and a second electrode  858  are formed sequentially on the first electrode  844  in the pixel region P. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the OELD device and method fabricating an OELD device 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.