Abstract:
The present invention relates to a flat panel display, and more particularly, to a method of fabricating an organic light emitting display device so as to improve device characteristics by patterning a plurality of organic layers using a heat transfer method to optimize thicknesses according to R, G and B pixels. The method includes: forming lower electrodes of R, G and B pixels on an insulating substrate; forming an organic layer on the insulating substrate; and forming an upper electrode on the organic layer. Formation of the organic layer includes forming a hole injection layer and a hole transport layer of the R, G and B pixels on the entire surface of the substrate as a common layer. The R and G emission layers are patterned by a heat transfer method using a heat transfer device having a transfer layer such that an organic layer is patterned to a thickness obtained by subtracting a thickness of the B emission layer from the thicknesses of the R and G emission layers required in R and G colors.

Description:
CLAIM OF PRIORITY 
     This application makes reference to, incorporates the same herein, and clams all benefits accruing under U.S.C. §119 from an application for ORGANIC LIGHT EMITTING DISPLAY DEVICE AND METHOD OF FABRICATING THE SAME earlier filed in the Korean Intellectual Property Office on 19 Feb. 2004 and there duly assigned Serial No. 2004-11145. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a flat panel display and, more particularly, to a method of fabricating an organic light emitting display device capable of improving device characteristics by patterning a plurality of organic layers using a heat transfer method to optimize the thickness on the basis of each of R, G and B pixels. 
     2. Description of the Related Art 
     Generally, an organic light emitting display device (OLED) includes lower and upper electrodes formed on an insulating substrate, and a plurality of organic layers formed between the upper and lower electrodes. The organic layers are selected from a hole injection layer, a hole transport layer, an emission layer, a hole blocking layer, an electron transport layer and an electron injection layer according to functions of the respective layers. This display device has such a structure that the upper and lower electrodes are formed of transparent or non-transparent electrodes to emit light from the organic layer toward the insulating layer or in the reverse direction of the insulating layer, or toward the insulating layer and in the reverse direction of the insulating layer. 
     The full color OLED of the prior art has problems in that the optical thicknesses of the respective R, G and B pixels are different so that color coordinates and efficiency characteristics deteriorate. 
     SUMMARY OF THE INVENTION 
     The present invention solves the aforementioned problems by providing a method of fabricating an organic light emitting display device (OLED) using a heat transfer method capable of simplifying processes and improving device characteristics. 
     In an exemplary embodiment of the present invention, a method of fabricating an organic light emitting display device includes: forming lower electrodes of R, G and B pixels on a substrate; forming an organic layer on the substrate; and forming an upper electrode on the organic layer. Formation of the organic layer includes forming a hole injection layer and a hole transport layer of the R, G and B pixels on an entire surface of the substrate as a common layer, and patterning the R and G emission layers by a heat transfer method using a heat transfer device having a transfer layer such that an organic layer is patterned to a thickness obtained by subtracting a thickness of a B emission layer from thicknesses of the R and G emission layers required in R and G colors. 
     The organic layer is formed of a thin film, the R and G emission layers have thickness of about 300˜400 Å, the B emission layer has a thickness of about 100˜200 Å, the patterned R and G emission layers have thicknesses of about 100˜300 Å and 50˜250 Å, respectively, and each thickness has a tolerance of about 50˜200 Å. 
     In another exemplary embodiment of the present invention, a method of fabricating an organic light emitting display device includes: forming lower electrodes of R, G and B pixels on a substrate; forming an organic layer on the substrate; and forming an upper electrode on the organic layer. Formation of the organic layer includes forming a hole injection layer of the R, G and B pixels on an entire surface of the substrate, patterning a hole transport layer of the R and G pixels, patterning emission layers of the R and G pixels, and forming an emission layer of the B pixel on an entire surface of the substrate. The hole transport layers and the emission layers of the R, G and B pixels are simultaneously formed by a heat transfer method using a heat transfer device having an organic layer as a transfer layer, at which the hole transport layer and the emission layer are respectively patterned. Thicknesses of the hole transport layers of the R and G pixels are equal to the difference between a sum of the thicknesses of the hole injection layer and the hole transport layer of the R and G pixels and the value of the thickness of the hole injection layer of the B pixel. 
     The R, G and B emission layers, the hole injection layer and the hole transport layer are formed of thick organic films, and the B pixel has the hole transport layer having the smallest thickness of the R, G and B pixels. The hole injection layer of the B pixel has a thickness of about 1350 Å, and the hole transport layers of the R and G pixels have thicknesses of about 1350 Å and 350 Å, respectively. 
     In addition, the R and G emission layers are patterned to a thickness obtained by subtracting a thickness of the B emission layer from the thicknesses of the R and G emission layers. The R and G emission layers have thicknesses of about 300˜400 Å, the B emission layer has a thickness of about 100˜200 Å, the patterned R and G emission layers have thicknesses of about 100˜300 Å and 50˜250 Å, respectively, and each thickness has a tolerance of about 50˜200 Å. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: 
         FIG. 1  is a cross-sectional view of an OLED; 
         FIG. 2  is a cross-sectional view of an OLED in accordance with a first embodiment of the present invention; 
         FIG. 3  is a cross-sectional view of an OLED in accordance with a second embodiment of the present invention; and 
         FIGS. 4A and 4B  are views illustrating a method of fabricating an OLED using a heat transfer method in accordance with the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures, in which the length, the thickness, etc., of a layer and a region may be exaggerated for clarity. 
       FIG. 1  is a cross-sectional view illustrating the structure of a full color OLED. 
     Referring to  FIG. 1 , anode electrodes  111 ,  113  and  115  are patterned and formed on an insulating substrate  100  as lower electrodes according to the respective pixels, and then a hole injection layer  120  and a hole transport layer  130  are sequentially formed on the entire surface of the insulating substrate  100 . R, G and B organic emission layers  141 ,  143  and  145  are formed in correspondence to the anode electrodes,  111 ,  113  and  115 , respectively, of the pixels, and a hole blocking layer  150  and an electron transport layer  160  are sequentially formed over the entire surface of the insulating substrate  100 . A cathode electrode  170  is formed on the electron transport layer  160  as an upper electrode. 
     The emission layers (EML)  141 ,  143  and  145  of the R, G and B pixels are formed above the anode electrodes  111 ,  113  and  115  of the R, G and B pixels to an appropriate thickness according to R, G and B colors. In addition, a charge transport layer, such as the hole injection layer (HIL)  120  and the hole transport layer (HTL)  130 , and the hole blocking layer (HBL)  150  and the electron transport layer (ETL)  160  are formed on the entire surface of the substrate  100  as a common layer. 
     In the latter arrangement, the charge transport layer, such as the hole injection layer  120  and the hole transport layer  130 , is formed on the entire surface of the substrate  100 . That is, each of the R, G and B emission layers is formed using a shadow mask, and then the charge transport layer, such as the hole injection layer  120  and the hole transport layer  130 , is formed on the entire surface of the substrate  100 . 
       FIG. 2  is a cross-sectional view of an OLED in accordance with a first embodiment of the present invention. This embodiment employs a thin organic layer. 
     Referring to  FIG. 2 , anode electrodes  211 ,  213  and  215  of R, G and B pixels are formed so as to be isolated from each other on a substrate  200  as lower electrodes. An organic layer (described below) is formed on the substrate  200 , and a cathode electrode  270  is formed on the organic layer as an upper electrode. The upper electrode  270  comprises a transparent electrode or a semi-transparent electrode, and light emitted from the organic layer is emitted in a reverse direction relative to the substrate  200 . The organic layer includes emission layers  241  and  243  of the R and G pixels patterned in correspondence to the anode electrodes  211  and  213 , respectively, of the R and G pixels, an emission layer  250  of the B pixel formed as a common layer, and a charge transport layer (described below) formed on and under the emission layers  241 ,  243  and  250 . 
     The charge transport layer includes a hole injection layer  220  and a hole transport layer  230  formed between the anode electrodes  211 ,  213  and  215  of the R, G and B pixels and the emission layers  241 ,  243  and  250  of the R, G and B pixels. In addition, the charge transport layer includes an electron transport layer  260  formed between the R, G and B emission layers  241 ,  243  and  250  and the cathode electrode  270 . The R and G emission layers  241  and  243  are made of phosphorescent material, and the B emission layer  250  is made of fluorescent material so as to act as a hole blocking layer. 
     In accordance with a first embodiment of the present invention, a method of forming an organic layer using a heat transfer method will be described in conjunction with  FIG. 2  and Tables 1 and 2 as follows. 
     
       
         
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Sum of thicknesses 
                   
                 Sum of thicknesses 
               
               
                   
                 of HIL and HTL 
                 Thickness of EML 
                 of HBL and ETL 
               
               
                   
               
             
             
               
                 R 
                 350 Å 
                 300~400 Å 
                 300 Å 
               
               
                 G 
                 350 Å 
                 250~350 Å 
                 300 Å 
               
               
                 B 
                 350 Å 
                 100~200 Å 
                 300 Å 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Sum of 
                   
                   
                   
               
               
                   
                 thicknesses of 
                 Thickness of 
                 Thickness of B 
                 Sum of thicknesses 
               
               
                   
                 HIL and HTL 
                 EML 
                 common layer 
                 of HBL and ETL 
               
               
                   
               
             
             
               
                 R 
                 350 Å 
                 100~300 Å 
                 100~200 Å 
                 300 Å 
               
               
                 G 
                 350 Å 
                  50~250 Å 
                 100~200 Å 
                 300 Å 
               
             
          
           
               
                 B 
                 350 Å 
                 100~200 Å 
                 300 Å 
               
               
                   
               
             
          
         
       
     
     Tables 1 and 2 represent thicknesses optically optimized according to R, G and B pixels, when indium tin oxide (ITO) having a thickness of 125 Å is used as an upper electrode and the organic layer is formed of a thin film. In the latter regard, the thicknesses of the respective layers have a tolerance of about 50˜200 Å. Table 1 represents optically optimized thicknesses of the respective layers when each of the R, G and B emission layers is patterned and then formed, and Table 2 represents optically optimized thicknesses of the respective layers, as described in the first embodiment, when the R and G emission layers  241  and  243  are patterned and the B emission layer  250  is formed as a common layer so as to act as a hole blocking layer. 
     In accordance with the first embodiment of the present invention, the anode electrodes  211 ,  213  and  215  of the R, G and B pixels are formed so as to be isolated from each other on the substrate  200 , and the hole injection layer  220  and the hole transport layer  230  are deposited on the entire surface of the substrate as a charge transport layer. The R and G emission layers  241  and  243  are then formed on the hole transport layer  230  in correspondence to the anode electrodes  211  and  213  of the R and G pixels. That is, the R emission layer  241  is patterned so as to correspond to the anode electrode  211  of the R pixel through a heat transfer method using a heat transfer device (not shown) having only an organic layer for the R emission layer as a transfer layer. Then, the G emission layer  243  is patterned so as to correspond to the anode electrode  213  of the G pixel through a heat transfer method using a heat transfer device (not shown) having only an organic layer for the G emission layer as a transfer layer. 
     Subsequently, the B emission layer  250  is formed on the entire surface of the substrate  200  as a common layer so as to act as the B emission layer of the B pixel and a hole blocking layer. The electron transport layer  260  is formed on the entire surface of the B emission layer  250  as a common layer, and the cathode electrode  270  is formed on the electron transport layer  260  as the upper electrode. 
     When the R and G emission layers  241  and  243  are formed, as shown in Table 1, it is preferable that the layers be formed to an optically optimized thickness. Therefore, since the B emission layer  250  is formed over the entire surface of the substrate  200  as a common layer in the first embodiment, when the R and G emission layers  241  and  243  are patterned by the heat transfer method, the R and G emission layers  241  and  243  are patterned to have a thickness such that the thickness of the commonly used B emission layer  250  is subtracted from the thicknesses of the R and G emission layers  241  and  243  described in Table 1. 
     That is, the sum of the thicknesses of the R and G emission layers  241  and  243  patterned in the first embodiment and the thickness of the B emission layer formed as a common layer is equal to the thicknesses of the R and G emission layers in Table 1 required in the R and G colors. Specifically, referring to Tables 1 and 2, the B emission layer  250  is formed so as to have a thickness of about 100˜200 Å required in the B color, and the R and G emission layers  241  and  243  are patterned by the heat transfer method so that the R and G emission layers  241  and  243  have thicknesses of about 100˜300 Å and 50˜250 Å, respectively, which are the thicknesses obtained by subtracting the thickness of the B emission layer  250  from the thicknesses required in the R and G emission layers  241  and  243 . 
       FIG. 3  is a cross-sectional view of an OLED in accordance with second embodiment of the present invention. This embodiment employs a thick organic layer. 
     Referring to  FIG. 3 , anode electrodes  411 ,  413  and  415  of R, G and B pixels are formed so as to be isolated from each other on a substrate  400  as lower electrodes, an organic layer (described below) is formed on the substrate  400 , and a cathode electrode  470  is formed on the organic layer as an upper electrode. The cathode electrode  470  comprises a transparent electrode or a semi-transparent electrode, and light emitted from the organic layer is emitted in the reverse direction relative to the substrate  400 . The organic layer includes R and G emission layers  441  and  443  patterned in correspondence to the anode electrodes  411  and  413  of the R and G pixels, a B emission layer  450  of the B pixel formed as a common layer, and a charge transport layer (described below) formed on and under the emission layers  441 ,  443  and  450 . 
     The charge transport layer includes a hole injection layer  420  and hole transport layers  431  and  433  of the R and G pixels formed between the anode electrodes  411 ,  413  and  415  of the R, G and B pixels and the emission layers  441 ,  443  and  450  of the R, G and B pixels. The hole transport layer  435  of the B pixel is not formed, and thus has a thickness of zero, as indicated in Table 4. The hole injection layer  420  is formed on the entire surface of the substrate  400 , and the hole transport layers  431  and  433  having different thicknesses relative to each other according to the pixels are patterned in correspondence to the R and G anode electrodes  411  and  413 . In addition, the charge transport layer further includes an electron transport layer  460  formed between the R, G and B emission layers  441 ,  443  and  450  and the cathode electrode  470 . The R and G emission layers  441  and  443  are made of phosphorescent material, and the B emission layer  450  is made of fluorescent material so as to act as a hole blocking layer. 
     A method of fabricating an organic layer in accordance with the second embodiment of the present invention will be described in conjunction with Tables 3 and 4, and  FIGS. 4A and 4B . 
     
       
         
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Sum of thicknesses 
                   
                 Sum of thicknesses 
               
               
                   
                 of HIL and HTL 
                 Thickness of EML 
                 of HBL and ETL 
               
               
                   
               
             
             
               
                 R 
                 2350 Å 
                 300~400 Å 
                 350 Å 
               
               
                 G 
                 1700 Å 
                 250~350 Å 
                 350 Å 
               
               
                 B 
                 1350 Å 
                 100~200 Å 
                 350 Å 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                 Sum of 
               
               
                   
                 Thickness 
                 Thickness 
                   
                   
                 thicknesses 
               
               
                   
                 of 
                 of 
                 Thickness of 
                 Thickness of B 
                 of HBL 
               
               
                   
                 HIL 
                 HTL 
                 EML 
                 common layer 
                 and ETL 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 R 
                 1350 Å 
                 1000 Å 
                 100~300 Å 
                 100~200 Å 
                 350 Å 
               
               
                 G 
                 1350 Å 
                  350 Å 
                  50~250 Å 
                 100~200 Å 
                 350 Å 
               
             
          
           
               
                 B 
                 1350 Å 
                 0 
                 100~200 Å 
                 350 Å 
               
               
                   
               
             
          
         
       
     
     Tables 3 and 4 represent thicknesses optically optimized according to the R, G and B pixels when ITO having a thickness of 125 Å is used as an upper electrode and the organic layer is formed of a thick film. In the latter regard, the thicknesses of the respective layers have a tolerance of about 50˜200 Å. Table 3 represents optically optimized thicknesses of the respective layers when the hole transport layer and the hole injection layer are formed as a common layer, and Table 4 represents optically optimized thicknesses of the respective layers when the hole transport layer is formed by patterning simultaneously with the emission layer using the heat transfer method. 
     The anode electrodes  411 ,  413  and  415  of the R, G and B pixels are formed so as to be isolated from each other on the insulating substrate  400 , and the hole injection layer  420  is formed on the entire surface of the substrate  400  as a charge transport layer. In that regard, the hole injection layer  420  is formed to have thicknesses of a hole transport layer and a hole injection layer of a pixel having the minimum value among the sums of the thicknesses of the hole transport layer and the hole injection layer of the R, G and B pixels. That is, as shown in Table 3, since the thicknesses of the hole transport layer and the hole injection layer of the B pixel are the smallest, the hole injection layer  420 , formed as a common layer, has a thickness of about 1350 Å, which is equal to the sum of the thicknesses of the hole transport layer and the hole injection layer of the B pixel. 
     Subsequently, as shown in  FIG. 4A , a heat transfer device  610  for patterning an R hole transport layer  431  and an R emission layer  441  is prepared. The heat transfer device  610  includes a light conversion layer  621 , an organic layer  631  for the R hole transport layer  431 , and an organic layer  641  for the R emission layer  441  as a transfer layer, disposed on a base substrate  611 . A laser  500  is irradiated onto the heat transfer device  610  to form the R hole transport layer  431  and the R emission layer  441  on the hole injection layer  420  above the R anode electrode  411  by simultaneously patterning the layers  431  and  441 . 
     Next, as shown in  FIG. 4B , a heat transfer device  630  for patterning a G hole transport layer  433  and a G emission layer  443  is prepared. The heat transfer device  630  includes a light conversion layer  623 , an organic layer  633  for the G hole transport layer  433 , and an organic layer  643  for the G emission layer  443  as a transfer layer, disposed on a base substrate  613 . A laser  500  is irradiated onto the heat transfer device  630  to form the G hole transport layer  433  and the G emission layer  443  on the hole injection layer  420  above the G anode electrode  413  by simultaneously patterning the layers  433  and  443 . 
     Finally, the B emission layer  450  ( FIG. 3 ) is formed on the entire surface of the hole injection layer  420  to cover upper surfaces of the R and G emission layers  441  and  443 . At this point, referring to Tables 3 and 4, since the sums of the thicknesses of the hole injection layer and the hole transport layer of the R, G and B pixels are different from one another, the thicknesses of the patterned hole transport layers  431  and  433  of the R and G pixels are different from each other. 
     That is, since the hole transport layer is formed in correspondence to the R and G anode electrodes  411  and  413  according to the R and G pixels, the hole injection layer  420  is formed to have a thickness of the hole transport layer of the B pixel having the smallest thickness of the R, G and B pixels. Therefore, as shown in Table 4, the hole transport layer  431  of the R pixel is formed to have a thickness of about 1000 Å, i.e., a value formed by subtracting the sum of the thicknesses of the hole injection layer and the hole transport layer of the B pixel from the sum of the thicknesses of the hole injection layer and the hole transport layer of the R pixel as shown in Table 3. In addition, the hole transport layer  433  of the G pixel is formed to have a thickness of about 350 Å, i.e., a value formed by subtracting the sum of the thicknesses of the hole injection layer and the hole transport layer of the B pixel from the sum of the thicknesses of the hole transport layer and the hole injection layer of the G pixel. 
     In addition, in a manner similar to the first embodiment, when the R and G emission layers  441  and  443  are formed in the second embodiment, it is preferable that the layers be formed with optically optimized thicknesses as shown in Table 3. Therefore, since the B emission layer  450  is formed on the entire surface as a common layer in the second embodiment, when the R and G emission layers  441  and  443  are patterned by a heat transfer method, the R and G emission layers  441  and  443  are simultaneously formed by patterning the R and G hole transport layers  431  and  433  so that they have thicknesses formed by subtracting the thickness of the B emission layer  450  used as a common layer from the thicknesses of the R and G emission layers  441  and  443  as described in Table 3. 
     Thus, the sum of the thicknesses of the R and G emission layers  441  and  443  patterned in the second embodiment and the thickness of the B emission layer  450  formed as a common layer becomes the thicknesses of the R and G emission layers in Table 3 as required in the R and G colors, respectively. That is, referring to Tables 3 and 4, the B emission layer  450  is formed to have a thickness of about 100˜200 Å, required in the B color, and the R and G emission layers  441  and  443  are patterned by a heat transfer method so that they have thicknesses of about 100˜300 Å and 50˜250 Å, subtracting the thickness of the B emission layer  450  from the thicknesses required in the R and G emission layers  441  and  443 , respectively. 
     When the emission layers and the hole injection layer are simultaneously patterned using a laser heat transfer method as described above, processes are simplified, and device characteristics are also improved by optimally forming the thicknesses of the organic layers according to the R, G and B pixels. 
     While the embodiments of the present invention illustrate the heat transfer device having a structure such that the light conversion layer and the transfer layer are deposited on the base substrate, a layer for improving heat transfer characteristics, (i.e., an intermediate layer) may be inserted. In addition, the thicknesses of the respective layers described in Tables 1 to 4 may be varied according to changes in process conditions and device characteristics. 
     As can be seen from the foregoing, the present invention is capable of simplifying the processes and improving yield and characteristics by forming the B emission layer as a common layer to act as a hole blocking layer. In addition, the number of processes is reduced so as to save manufacturing cost, and precision of the pattern is improved. 
     Further, the present invention uses a laser heat transfer method to simultaneously form emission layers and charge transport layer having optically optimized thicknesses, thereby improving color coordinates and efficiency characteristics, and improving display quality, thus rendering the invention applicable to high resolution OLEDs. 
     Although the present invention has been described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that a variety of modifications and variations may be made to the present invention without departing from the spirit or scope of the present invention as defined in the appended claims, and their equivalents.