Patent Publication Number: US-6982524-B2

Title: Dual panel-type organic electroluminescent display device and method of fabricating the same

Description:
The present invention claims the benefit of Korean Patent Application No. 2002-70299 filed in Korea on Nov. 13, 2002, which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an organic electroluminescent display device and a method of fabricating an organic electroluminescent display device, and more particularly, to a dual panel-type organic electroluminescent display device and a method of fabricating a dual panel-type organic electroluminescent display device. 
     2. Discussion of the Related Art 
     In general, organic electroluminescent display (OELD) devices have an electron-input electrode, which is commonly referred to as a cathode, and hole-input electrode, which is commonly referred to as an anode. The electrons and the holes are supplied to an electroluminescent layer from the cathode and anode, respectively, wherein the electron and hole together form an exciton. The OELD device emits light when the exciton is reduced from an excited state level to a ground state level. Accordingly, since the OELD devices do not require additional light sources, both volume and weight of the OELD devices may be reduced. In addition, the OELD devices are advantageous because of their low power consumption, high luminance, fast response time, and low weight. Presently, the OELD devices are commonly implemented in mobile telecommunication terminals, car navigation systems (CNSs), personal digital assistants (PDAs), camcorders, and palm computers. In addition, since manufacturing processes for the OELD devices are simple, manufacturing costs can be reduced as compared to liquid crystal display (LCD) devices. 
     The OELD devices may be classified into passive matrix-type and active matrix-type. Although the passive matrix-type OELD devices have simple structures and simplified manufacturing processes, they require high power consumption and are not suitable for large-sized display devices. In addition, aperture ratios decrease as the number of electro lines increase. On the other hand, the active matrix-type OELD devices have high light-emitting efficiency and high image display quality. 
       FIG. 1  is a cross sectional view of an OELD device according to the related art. In  FIG. 1 , the OELD device  10  has a transparent first substrate  12 , a thin film transistor array part  14 , a first electrode  16 , an organic electroluminescent layer  18 , and a second electrode  20 , wherein the thin film transistor array part  14  is formed on the transparent first substrate  12 . The first electrode  16 , organic electroluminescent layer  18 , and second electrode  20  are formed over the thin film transistor array part  14 . The electroluminescent layer  18  emits red (R), green (G), and blue (B) colored light, and it is commonly formed by patterning organic material separately in each pixel region “P” for the R, G, and B colored light. A second substrate  28  has a moisture absorbent desiccant  22 . The OELD device  10  is completed by bonding the first and second substrates  12  and  28  together by disposing a sealant  26  between the first and second substrates  12  and  28 . The moisture absorbent desiccant  22  removes moisture and oxygen that may be infiltrated into an interior of the organic ELD  10 . The moisture absorbent desiccant  22  is formed by etching away a portion of the second substrate  28 , filling the etched portion of the second substrate  28  with moisture absorbent desiccant material, and fixing the moisture absorbent desiccant material with a tape  25 . 
       FIG. 2  is a plan view of a thin film transistor array part of an OELD device according to the related art. In  FIG. 2 , each of a plurality of pixel regions “P” defined on a substrate  12  includes a switching element “T S ,” a driving element “T D ,” and a storage capacitor “C ST .” The switching element “T S ” and the driving element “T D ” may be formed with combinations of more than two thin film transistors (TFTs), and the substrate  12  is formed of a transparent material, such as glass and plastic. A gate line  32  is formed along a first direction, and a data line  34  is formed along a second direction perpendicular to the first direction, wherein the data line  34  crosses the gate line perpendicularly with an insulating layer between the gate and data lines  32  and  34 . In addition, a power line  35  is formed along the second direction, and is spaced apart from the data line  34 . 
     The TFT used for the switching element “T S ” has a switching gate electrode  36 , a switching active layer  40 , a switching source electrode  46 , and a switching drain electrode  50 . The TFT for the driving element “T D ” has a driving gate electrode  38 , a driving active layer  42 , a driving source electrode  48 , and a driving drain electrode  52 . The switching gate electrode  36  is electrically connected to the gate line  32 , and the switching source electrode  46  is electrically connected to the data line  34 . In addition, the switching drain electrode  50  is electrically connected to the driving gate electrode  38  through a contact hole  54 , and the driving source electrode  48  is electrically connected to the power line  35  through a contact hole  56 . Further, the driving drain electrode  52  is electrically connected to a first electrode  16  within the pixel region “P,” wherein the power line  35  and a first capacitor electrode  15  that is formed of polycrystalline silicon layer form a storage capacitor “C ST ”. 
       FIG. 3  is a cross sectional view along III—III of  FIG. 2  according to the related art. In  FIG. 3 , a first insulating layer (i.e., a buffer layer)  14  is formed on a substrate  12 , and a driving element, (i.e., a driving thin film transistor TFT) “T D ” including an active layer  42 , a gate electrode  38 , and source and drain electrodes  48  and  52  is formed on the first insulating layer  14 . The active layer  42  is formed on the first insulating layer  14  and a second insulating layer (a gate insulating layer)  37  is interposed between the active layer  42  and the gate electrode  38 . In addition, third and fourth insulating layers  39  and  41  are interposed between the gate electrode  38  and the source and drain electrodes  48  and  52 . Further, a power line  35  is formed between the third and fourth insulating layers  39  and  41 , and connected to the source electrode  48 . 
     A first electrode  16  is formed over the driving TFT “T D ” and is connected to the drain electrode  52  of the driving TFT “T D ” with a fifth insulating layer  57  between the first electrode  16  and the driving TFT “T D .” An organic electroluminescent (EL) layer  18  is formed on the first electrode  16  for emitting light of a particular color wavelength, and a second electrode  20  is formed on the organic EL layer  18 . Accordingly, after forming a sixth insulating layer  58  on the first electrode  16 , the sixth insulating layer  58  is patterned to expose the first electrode  16 . Then, the organic EL layer  18  and the second electrode  20  are sequentially formed on the exposed first electrode  16 , and a storage capacitor “C ST ” is connected in parallel to the driving TFT “T D ,” and includes first and second capacitor electrodes  15  and  35 . The source electrode  48  contacts the second capacitor electrode  35  (i.e., a power line), and the first capacitor electrode  15  is formed of polycrystalline silicon material under the second capacitor electrode  35 . Moreover, the second electrode  20  is formed on an entire surface of the substrate  12  on which the driving TFT “T D ,” the storage capacitor “C ST ,” and the organic electroluminescent layer  18  are formed. 
     In the OELD device, a TFT array part and an organic electroluminescent diode are formed over a first substrate, and an additional second substrate is attached with the first substrate for encapsulation. However, when the array part and the organic EL diode are formed on one substrate, a production yield of the organic ELD is determined by a multiplication of TFT&#39;s yield and organic emission layer&#39;s yield. Since the yield of the organic emission layer is relatively low, the production yield of an ELD is limited by the yield of the organic layer. For example, even when a TFT is properly fabricated, an OELD device using a thin film of about 1000 Å thickness can be determined to be unacceptable due to defects of the organic emission layer. Accordingly, the loss of materials causes an increase in production costs. 
     In general, OELD device are classified into bottom emission-type and top emission-type according to an emission direction of light used for displaying images. Bottom emission-type OELD devices have the advantages of high encapsulation stability and high process flexibility. However, the bottom emission-type OELD devices are ineffective for high resolution devices because they have poor aperture ratios. In contrast, the top emission-type OELD devices have a higher expected life span because they are easily designed and have a high aperture ratio. However, in the top emission-type OELD devices, the cathode is generally formed on an organic emission layer. As a result, transmittance and optical efficiency of the top emission-type OELD devices are reduced because of a limited number of materials that may be selected. If a thin film-type passivation layer is formed to prevent a reduction of the light transmittance, the thin film-type passivation layer may fail to prevent infiltration of exterior air into the device. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to an OELD device and a method of fabricating an OELD that substantially obviate one or more of the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a dual panel-type OELD device that is fabricated through forming array elements and organic electroluminescent diodes on respective substrates and attaching the respective substrates. 
     Another object of the present invention is to provide a method of fabricating a dual panel-type OELD device that is fabricated through forming array elements and organic electroluminescent diodes on respective substrates and attaching the respective substrates. 
     Another object of the present invention is to provide an OELD device having improved production yield, high brightness, and high aperture ratio. 
     Another object of the present invention is to provide a method of fabricating an OELD device having improved production yield, high brightness, and high aperture ratio. 
     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. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an organic electroluminescent display device includes first and second substrates bonded together, the first and second substrates having a plurality of pixel regions, each pixel region includes a central portion and first and second portions at both sides of the central portion, a driving element on an inner surface of the first substrate within each of the plurality of pixel regions, the driving element being disposed in the central portion, first and second connection electrodes contacting the driving element and disposed in the first and second portions, a first electrode on an inner surface of the second substrate, an organic electroluminescent layer on the first electrode, and a second electrode on the organic electroluminescent layer, the second electrode contacting the first and second connection electrodes. 
     In another aspect, a method of fabricating an organic electroluminescent display device includes forming a driving element on a first substrate having a plurality of pixel regions, each pixel region including a central portion and first and second portions at both sides of the central portion, the driving element being disposed in the central portion, forming first and second connection electrodes contacting the driving element, the first and second connection electrodes being respectively disposed in the first and second portions, forming a first electrode on a second substrate, forming an organic electroluminescent layer on the first electrode, forming a second electrode on the organic electroluminescent layer, and bonding the first and second substrates together such that the second electrode contacts the first and second connection electrodes. 
     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 principle of the invention. In the drawings: 
         FIG. 1  is a cross sectional view of an OELD device according to the related art; 
         FIG. 2  is a plan view of a thin film transistor array part of an OELD device according to the related art; 
         FIG. 3  is a cross sectional view along III—III of  FIG. 2  according to the related art; 
         FIG. 4  is a schematic cross-sectional view of an exemplary OELD device according to the present invention; 
         FIG. 5  is a schematic plan view of an exemplary thin film transistor array part of an OELD device according to the present invention; 
         FIGS. 6A to 6D  are schematic cross sectional views along VI—VI of  FIG. 5  of an exemplary method of fabricating a thin film transistor array part of an organic electroluminescent device according to the present invention; 
         FIGS. 7A to 7D  are schematic cross sectional views along VII—VII of  FIG. 5  of another exemplary method of fabricating a thin film transistor array part of an organic electroluminescent device according to the present invention; and 
         FIGS. 8A to 8C  are schematic cross sectional views of another exemplary method of fabricating an organic electroluminescent diode of an organic electroluminescent device according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
       FIG. 4  is a schematic cross-sectional view of an exemplary OELD device according to the present invention. In  FIG. 4 , an OELD device  99  may include first and second substrates  100  and  200  facing each other, and bonded together with a sealant  300 . The first and second substrates  100  and  200  may include a plurality of pixel regions “P,” switching and driving thin film transistors (TFTs) “T,” and array lines (not shown) formed on an inner surface of the first substrate  100  within each of the pixel regions “P.” Although not shown, the array lines may include a gate line, a data line, a power line, and a common line. 
     In  FIG. 4 , a first electrode  202  may be formed on an inner surface of the second substrate  200 , and an organic electroluminescent (EL) layer  208  emitting one of red, green, and blue colored lights may be formed on the first electrode  202  within each of the pixel regions “P.” In addition, a second electrode  210  may be formed on the organic EL layer  208  within each of the pixel regions “P.” The organic EL layer  208  may include a single layer structure or may include a multiple layer structure. The multiple layer structure may include the organic EL layer  208  having a hole-transporting layer  208   b  on the first electrode  202 , an emission layer  208   a  on the hole-transporting layer  208   b , and an electron-transporting layer  208   c  on the emission layer  208   a.    
     The pixel regions “P” may each include a central portion “C” and first and second portions “D1” and “D2” surrounding the central portion “C,” wherein the driving TFT “T” may be formed in the central portion “C.” In addition, first and second connection electrodes  128   a  and  128   b  may be formed in the first and second portions “D1” and “D2,” respectively, wherein the first and second connection electrodes  128   a  and  128   b  may be connected to the second electrode  210 . The first and second connection electrodes  128   a  and  128   b  may be formed on the driving TFT “T” during a fabricating process of the first substrate  100 , or the first and second connection electrodes  128   a  and  128   b  may be formed on the second electrode  210  during a fabricating process of the second substrate  200 . After bonding the first and second substrates  100  and  200  together, the driving TFT “T” and the second electrode  210  may be connected to each other through the first and second connection electrodes  128   a  and  128   b.    
       FIG. 5  is a schematic plan view of an exemplary thin film transistor array part of an OELD device according to the present invention. In  FIG. 5 , a gate line  103 , a data line  115 , and a power line  114  may be formed on a first substrate  100 , wherein the data line  115  and the power line  114  may cross the gate line  103  to define a pixel region “P.” A driving thin film transistor (TFT) “T D ,” a switching thin film transistor (TFT) “T ST ,” and a storage capacitor “C ST ” may be formed within the pixel region “P.” The driving TFT “T D ” may include a driving active layer  104 , a driving gate electrode  110 , and driving source and drain electrodes  126  and  125 , and the switching TFT “T ST ” may include a switching active layer  106 , a switching gate electrode  111 , and switching source and drain electrodes  121  and  123 . The storage capacitor “C ST ” may be connected in parallel to the driving TFT “T D ,” and may use an active pattern  107  of polycrystalline silicon as a first capacitor electrode and the power line  114  as a second capacitor electrode. The switching source electrode  121  may be connected to the data line  115 , and the switching drain electrode  123  may be connected to the driving gate electrode  110 . 
     The driving TFT “T D ” may be formed at a central portion of the pixel region “P.” Accordingly, the driving gate electrode  110  may extend to the switching TFT “T ST ” and may contact the switching drain electrode  123 . The driving drain electrode  125  may include first and second extensions  125   a  and  125   b , and the pixel region “P” may be divided into first and second portions with the central portion having the driving TFT “T D ” as a center. The first and second extensions  125   a  and  125   b  may be formed in the first and second portions, respectively. Although not shown, the first and second extensions  125   a  and  125   b  may contact the first and second connection electrodes  128   a  and  128   b  (in  FIG. 4 ), respectively. 
       FIGS. 6A to 6D  and are schematic cross sectional views along VI—VI of  FIG. 5  of an exemplary method of fabricating a thin film transistor array part of an organic electroluminescent device according to the present invention, and  FIGS. 7A to 7D  are schematic cross sectional views along VII—VII of  FIG. 5  of another exemplary method of fabricating a thin film transistor array part of an organic electroluminescent device according to the present invention. 
     In  FIGS. 6A and 7A , a first insulating layer (i.e., a buffer layer)  102  may be formed on a first substrate  100  having a pixel region “P” by depositing one of inorganic insulating material(s), such as silicon nitride (SiN x ) and silicon oxide (SiO 2 ). The pixel region “P” may be divided into a central portion “C,” and first and second portions “D1” and “D2” at both sides of the central portion “C,” wherein a driving thin film transistor “T D ” and a storage capacitor “C ST ” may be disposed in the central portion “C.” 
     Then, an amorphous silicon (a-Si:H) layer (not shown) may be formed on the first insulating layer  102 , and crystallized to form a polycrystalline silicon layer (not shown). Next, a driving active layer  104  including a channel region  104   a , and source and drain regions  104   b  and  104   c  at both sides of the channel region  104   a  may be formed by patterning the polycrystalline silicon layer. At the same time, an active pattern  107  used as a first capacitor electrode may be formed on the first insulating layer  102 . Alternatively, a dehydrogenation process may be performed before the crystallization process, and the crystallization process can be performed by using heat or light. 
     Next, a second insulating layer (i.e., a gate insulating layer)  108  may be formed on the driving active layer  104  by depositing inorganic insulating material(s), such as silicon nitride (SiN x ) and silicon oxide (SiO 2 ). The second insulating layer  108  may be formed on an entire surface of the first substrate  100  without any subsequent etch process, or may be etched to have the same shape as a driving gate electrode  110  after forming the driving gate electrode  110 . 
     Next, a driving gate electrode  110  may be formed on the second insulating layer  108  over the channel region  104   a , and as shown in  FIG. 5 , the driving gate electrode  110  may extend to a switching TFT “T ST .” Then, the source and drain regions  104   b  and  104   c  of the active layer  104  may be doped with impurities, such as boron (B) or phosphorous (P). The driving gate electrode  110  may include conductive metallic material(s), such as aluminum (Al), an aluminum (Al) alloy, copper (Cu), tungsten (W), tantalum (Ta), and molybdenum (Mo). 
     Next, a third insulating layer (i.e., an interlayer insulating layer)  112  may be formed on the driving gate electrode  110 , and a power line  114  may be formed on the third insulating layer  112 . The power line  114  may supply signals to a driving drain electrode (not shown) and may be used as a second capacitor electrode. 
     In  FIGS. 6B and 7B , a fourth insulating layer (i.e., a passivation layer)  116  may be formed on the power line  114  by depositing inorganic insulating material(s), such as silicon nitride (SiN x ) and silicon oxide (SiO 2 ), or organic insulating material(s), such as benzocyclobutene (BCB) and acrylic resin. The fourth insulating layer  116  may include first, second, and third contact holes  120 ,  118 , and  122  to expose the source region  104   b , the drain region  104   c , and the power line  114 , respectively. Although not shown, a switching active layer may be simultaneously exposed. 
     In  FIGS. 6C and 7C , driving source and drain electrode  126  and  125  may be formed on the fourth insulating layer  116  by depositing and patterning conductive metallic material(s), such as aluminum (Al), an aluminum (Al) alloy, chromium (Cr), tungsten (W), and molybdenum (Mo). The driving drain electrode  125  may be connected to the drain region  104   c  through the first contact hole  118  and may extend to the first and second portions “D1” and “D2.” The source electrode  126  may be connected to the source region  104   b  through the second contact hole  120  and may be connected to the power line  114  through the third contact hole  122 . Although not shown, switching source and drain electrodes and a data line  115  (in  FIG. 5 ) may be simultaneously formed over the switching active layer. The switching source electrode may be connected to the data line  115  (in  FIG. 5 ) parallel to the power line  114 , and the switching drain electrode may be connected to the driving gate electrode  110 . In addition, the driving drain electrode  125  may include first and second extensions  125   a  and  125   b  disposed in the first and second portions “D1” and “D2” of the pixel regions “P,” respectively, wherein the first and second extensions  125   a  and  125   b  may be formed to have various shapes. 
     In  FIGS. 6D and 7D , a fifth insulating layer  130  having first and second open portions  132   a  and  132   b  may be formed on the driving source and drain electrodes  126  and  125  by depositing organic insulating material(s), such as benzocyclobutene (BCB) and acrylic resin. The first and second open portions  132   a  and  132   b  may expose the first and second extensions  125   a  and  125   b  of the driving drain electrode  125 , respectively. In addition, first and second connection electrodes  128   a  and  128   b  may be formed on the first and second extensions  125   a  and  125   b , respectively, wherein the first and second connection electrodes  128   a  and  128   b  may contact a second electrode  210  (in  FIG. 4 ) after bonding the first and second substrates  100  and  200  (in  FIG. 4 ) together. Accordingly, the first and second connection electrodes  128   a  and  128   b  may include the same material as the second electrode  210  (in  FIG. 4 ). Alternatively, the fifth insulating layer  130  may be omitted. 
     In the present invention, a driving TFT may be disposed in a central portion of a pixel region. In addition, first and second connection electrodes may be disposed in first and second portions at both sides of the central portion, respectively. Accordingly, a connection portion between a second electrode and a driving drain electrode may be enlarged. Moreover, since the connection portion may include two parts (first and second connection electrodes), connection inferiority due to a substrate warpage may be prevented. 
       FIGS. 8A to 8C  are schematic cross sectional views of another exemplary method of fabricating an organic electroluminescent diode of an organic electroluminescent device according to the present invention. In  FIG. 8A , a first electrode  202  may be formed on a second substrate  200  having a plurality of pixel regions “P.” The first electrode  202  may include transparent conductive metallic material(s), such as indium-tin-oxide (ITO) and indium-zinc-oxide (IZO). 
     In  FIG. 8B , an organic electroluminescent (EL) layer  204  emitting one of red (R), green (G), and blue (B) colored lights may be formed on the first electrode  202  within each of the pixel regions “P.” The organic EL layer  204  may have a single layer structure or a multiple layer structure. In the multiple layer structure, the organic EL layer  204  may having a hole-transporting layer  204   b  on the first electrode  202 , an emission layer  204   a  on the hole-transporting layer  204   b , and an electron-transporting layer  204   c  on the emission layer  204   a.    
     In  FIG. 8C , a second electrode  210  may be formed on the organic EL layer  204  within each of the pixel regions “P.” The second electrode  210  may include a single layer structure including at least one of aluminum (Al), calcium (Ca), and magnesium (Mg), for example, or may have a multiple layer structure including lithium fluorine/aluminum (LiF/Al), for example. 
     Next, an OELD device may be obtained by bonding the first and second substrates  100  and  200  fabricated through processes of  FIGS. 6A to 8C  together. 
     An OELD device according to the present invention is advantageous since a connection portion may include two parts (first and second connection electrodes) disposed in first and second portions at both sides of a central portion of a pixel region. Accordingly, the connection portion may be enlarged and a connection inferiority due to a substrate warpage may be prevented, thereby obtaining a highly reliable device. 
     In addition, since the OELD device is a top emission-type OELD device, a thin film transistor may be easily designed, and high resolution and high aperture ratio may be obtained regardless of lower array patterns. Furthermore, since array patterns and an organic EL diode may be formed on respective substrates, production yield and production management efficiency are improved, and a lifetime of an organic EL device is lengthened. 
     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.