Abstract:
An organic light emitting display apparatus including sub pixels, each of the sub pixels including: first and second electrodes, the second electrode extending over the first electrode; and an intermediate layer disposed between the first and second electrodes, the intermediate layer including an emission layer, wherein a first portion of the first electrode, the second electrode, and the intermediate layer extends within a weak resonance region, the weak resonance region being configured to induce a first resonance of light generated by the emission layer between the first and second electrodes, and a second portion of the first electrode, the second electrode, and the intermediate layer extends within a strong resonance region, the strong resonance region being configured to induce a second resonance of light generated by the emission layer between the first and second electrodes, the second resonance being stronger than the first resonance.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2011-0126274, filed on Nov. 29, 2011, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The embodiments relate to an organic light emitting display apparatus. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, an organic light emitting display apparatus displays colors by emitting light when holes and electrons that are injected from an anode and a cathode are recombined in an emission layer. The organic light emitting display has a stacked structure in which an emission layer is inserted between a pixel electrode that is an anode and a counter electrode that is a cathode. 
         [0006]    A unit pixel of an organic light emitting display apparatus includes red, green, and blue sub pixels which are combined to display a desired color. In more detail, each sub pixel has a structure in which an emission layer for emitting red, green, or blue light is disposed between two electrodes, and a unit pixel displays a color by appropriately combining the red, green, and blue light. 
         [0007]    Meanwhile, currently, in many cases, sub pixels are formed in a resonance structure in order to increase light extraction efficiency of an organic light emitting display apparatus. That is, the resonance structure induces constructive interference of light between two electrodes by forming one of an anode and a cathode for displaying an image as a translucent electrode, and forming the other as a total reflection electrode, and thus a quite enhanced light may be extracted from each sub pixel. 
         [0008]    However, if a strong resonance structure is used, although light extraction efficiency is increased, viewing angle characteristics may deteriorate. For example, if a strong resonance structure is used, a significant brightness reduction and color shift may occur, according to a viewing angle. 
         [0009]    Accordingly, in order to implement a product having high reliability, a new structure capable of improving light extraction efficiency and satisfactorily maintaining viewing angle characteristics is required. 
       SUMMARY 
       [0010]    One or more embodiments may provide an organic light emitting display apparatus including sub pixels, each of the sub pixels including: first and second electrodes, the second electrode extending over the first electrode; and an intermediate layer disposed between the first and second electrodes, the intermediate layer including an emission layer, wherein a first portion of the first electrode, a first portion of the second electrode, and a first portion of the intermediate layer extends within a weak resonance region, the weak resonance region being configured to induce a first resonance of light generated by the emission layer between the first and second electrodes, and a second portion of the first electrode, a second portion of the second electrode, and a second portion of the intermediate layer extends within a strong resonance region, the strong resonance region being configured to induce a second resonance of light generated by the emission layer between the first and second electrodes, the second resonance being stronger than the first resonance. 
         [0011]    The organic light emitting display apparatus may further include a mirror layer for resonating the light between the first and second electrodes, the mirror layer including a first portion in the weak resonance region and a second portion in the strong resonance region, the second portion of the mirror layer being thicker than the first portion of the mirror layer. The mirror layer may include a dielectric mirror layer, a first portion of the dielectric mirror layer extending in the weak resonance region, and a second portion of the dielectric mirror layer extending in the strong resonance region. The dielectric mirror layer may include alternately stacked layers of silicon oxide (SiOx) and silicon nitride (SiNx), and the second portion of the dielectric mirror layer may include a larger number of stacked layers than the first portion of the dielectric mirror layer. 
         [0012]    The mirror layer may include a dielectric mirror layer, a first portion of the dielectric mirror layer extending in the weak resonance region, and a second portion of the dielectric mirror layer extending in the strong resonance region, and a metal mirror layer extending only in the strong resonance region. The metal mirror layer may include a silver (Ag) layer, and the dielectric mirror layer may include alternately stacked layers of SiOx and SiNx. 
         [0013]    The intermediate layer may further include a hole injection layer, a hole transporting layer, an electron injection layer, and an electron transporting layer for respectively injecting and transporting holes and electrons into the emission layer. A thickness of a portion of the hole transporting layer in the weak resonance region may be different from a thickness of a portion of the hole transporting layer in the strong resonance region, to facilitate adjusting resonance of light between the first and second electrodes. 
         [0014]    One or more embodiments may provide an organic light emitting display apparatus including a plurality of unit pixels, each of the unit pixels including sub pixels for emitting light of different colors, the plurality of unit pixels including weak resonance unit pixels for inducing a first resonance, and strong resonance unit pixels for inducing a second resonance, the second resonance being stronger than the first resonance. Each of the sub pixels may include first and second electrodes, the second electrode extending over the first electrode, an intermediate layer disposed between the first and second electrodes, the intermediate layer including an emission layer and a mirror layer for resonating light generated by the emission layer between the first and second electrodes, the mirror layer including a first portion in the weak resonance unit pixels and a second portion in the strong resonance unit pixels, wherein the second portion of the mirror layer is thicker than the first portion of the mirror layer. 
         [0015]    The mirror layer may include a dielectric mirror layer, a first portion of the dielectric mirror layer in the weak resonance unit pixels, and a second portion of the dielectric mirror layer in the strong resonance unit pixels. The dielectric mirror layer may include alternately stacked layers of silicon oxide (SiOx) and silicon nitride (SiNx), and the second portion of the dielectric mirror layer includes a larger number of stacked layers than the first portion of the dielectric mirror layer. The mirror layer may include a dielectric mirror layer, a first portion of the dielectric mirror layer in the sub pixels of the weak resonance unit pixels, and a second portion of the dielectric mirror layer in the sub pixels of the strong resonance unit pixels; and a metal mirror layer formed in the sub pixels of only the strong resonance unit pixels. The metal mirror layer may include a silver (Ag) layer, and the dielectric mirror layer may include alternately stacked layers of SiOx and SiNx. The intermediate layer may further include a hole injection layer, a hole transporting layer, an electron injection layer, and an electron transporting layer for respectively injecting and transporting holes and electrons into the emission layer. A thickness of a portion of the hole transporting layer in the sub pixels of the weak resonance unit pixels is different from a thickness of a portion of the hole transportion layer in the sub pixels of the strong resonance unit pixels, to facilitate adjusting resonance of light between the first and second electrodes. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The above and other features and advantages of the embodiments will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
           [0017]      FIG. 1  illustrates a cross-sectional view of a sub pixel of an organic light emitting display apparatus, according to an embodiment; 
           [0018]      FIG. 2  illustrates an equivalent circuit diagram of the sub pixel illustrated in  FIG. 1 ; 
           [0019]      FIG. 3  illustrates a cross-sectional view of a sub pixel modified from  FIG. 1 , according to another embodiment; 
           [0020]      FIG. 4  illustrates a cross-sectional view of unit pixels of an organic light emitting display apparatus, according to an embodiment; and 
           [0021]      FIG. 5  illustrates a cross-sectional view of unit pixels modified from  FIG. 4 , according to another embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Hereinafter, the embodiments will be described in detail by explaining embodiments with reference to the attached drawings. 
         [0023]      FIG. 1  illustrates a cross-sectional view of a sub pixel for forming a unit pixel of an organic light emitting display apparatus, according to an embodiment.  FIG. 2  illustrates an equivalent circuit diagram of the sub pixel illustrated in  FIG. 1 . The unit pixel may include three-color sub pixels such as a red sub pixel R, a green sub pixel G, and a blue sub pixel B.  FIG. 1  illustrates one sub pixel. The green and blue sub pixels G and B, may also have the structure illustrated in  FIG. 1 . Also, in the organic light emitting display apparatus, unit pixels each having the three-color sub pixels may be repeatedly aligned in row and column directions. 
         [0024]    Referring to  FIG. 2 , a plurality of signal lines ( 121 ,  171 , and  172 ) may be connected to a sub pixel PX. 
         [0025]    The signal lines may include a scanning signal line  121  for transmitting a gate signal (or a scanning signal), a data line  171  for transmitting a data signal, and a driving voltage line  172  for transmitting a driving voltage. 
         [0026]    The sub pixel PX may include a switching transistor Qs, a driving transistor Qd, a storage capacitor Cst, and an organic light emitting element LD. 
         [0027]    The switching transistor Qs may include a control terminal T 1 , an input terminal T 2 , and an output terminal T 3 , wherein the control terminal T 1  is connected to the scanning signal line  121 , the input terminal T 2  is connected to the data line  171 , and the output terminal T 3  is connected to the driving transistor Qd. The switching transistor Qs may transmit the data signal received from the data line  171  to the driving transistor Qd in response to the scanning signal received from the scanning signal line  121 . 
         [0028]    The driving transistor Qd may include a control terminal T 3 , an input terminal T 4 , and an output terminal T 5 , wherein the control terminal T 3  is connected to the switching transistor Qs, the input terminal T 4  is connected to the driving voltage line  172 , and the output terminal T 5  is connected to the organic light emitting element LD. The output terminal T 3  of the switching transistor Qs may function as the control terminal T 3  of the driving transistor Qd. The driving transistor Qd may provide an output current ILD having a variable size according to a voltage applied between the control terminal T 3  and the output terminal T 5 . 
         [0029]    The storage capacitor Cst may be connected between the control terminal T 3  and the input terminal T 4  of the driving transistor Qd. The storage capacitor Cst may charge the data signal applied to the control terminal T 3  of the driving transistor Qd and retain the data signal even after the switching transistor Qs is turned off. 
         [0030]    The organic light emitting element LD may include a pixel electrode connected to the output terminal T 5  of the driving transistor Qd (hereinafter referred to as a first electrode), a counter electrode connected to a common voltage line Vss (hereinafter referred to as a second electrode), and an emission layer disposed between the first and second electrodes and for emitting light due to a voltage applied between the first and second electrodes. 
         [0031]    The detailed structure of the organic light emitting element LD will be described with reference to  FIG. 1 . 
         [0032]    Referring to  FIG. 1 , initially, the driving transistor Qd may be formed on an insulating substrate  110  formed of transparent glass or plastic. Although not shown in  FIG. 1 , the switching transistor Qs and the signal lines ( 121 ,  171 , and  172 ) illustrated in  FIG. 2  may also be formed on the insulating substrate  110 . 
         [0033]    A mirror layer  120  may be a dielectric mirror layer formed on the driving transistor Qd. A first electrode  130  may be connected to the driving transistor Qd via a contact hole  127  formed on the mirror layer  120 . 
         [0034]    An intermediate layer  140 , including an emission layer  143 , and a second electrode  150  may be sequentially stacked on the first electrode  130 , and a sealing layer (not shown) for preventing penetration of moisture and oxygen may be further formed on the second electrode  150 . For example, the second electrode  150  may extend over the first electrode  130 . A reference numeral  160  indicates a pixel defining layer. 
         [0035]    The mirror layer  120  may reflect light generated by the emission layer  143  to be resonated between the first and second electrodes  130  and  150 . The mirror layer  120  may divide each sub pixel into weak and strong resonance regions  101  and  102 . For example, in  FIG. 1 , a left region of the sub pixel may be the weak resonance region  101 , and a right region of the sub pixel may be the strong resonance region  102 . A first portion of the mirror layer may be in the weak resonance region  101  and a second portion of the mirror layer may be in the strong resonance regions  102 . The first portion of the mirror layer  120  may have a two-layered structure in which a silicon oxide (SiOx) layer  125  and a silicon nitride (SiNx) layer  126  are stacked, e.g., the silicon nitride (SiNx) layer  126  may be stacked on the silicon oxide (SiOx) layer  125 . The second portion of the mirror layer  120  may have a four-layered structure in which SiNx layers  121  and  123  and SiOx layers  122  and  124  are stacked. Furthermore, the SiOx layer  125  and the SiNx layer  126  of the weak resonance region  101  may extend to the strong resonance region  102 . As such, the second portion of the mirror layer  120  (in the strong resonance region  102 ) may have a six-layered structure. For example, the second portion of the mirror layer  120  (in the strong resonance region  102 ) may include a larger number of stacked layers than the first portion of the mirror layer  120  (in the weak resonance region  101 ). 
         [0036]    In comparison to the mirror layer  120  having a relatively small number of stacked layers, the mirror layer  120  having a relatively large number of stacked layers may resonate light generated by the emission layer  143  between the first and second electrodes  130  and  150  more strongly. Accordingly, the strong resonance region  102 , in which the mirror layer  120  includes a larger number of stacked layers, may induce a strong resonance in comparison to the weak resonance region  101 . Thus, the strong resonance region  102  may have a higher light extraction efficiency than the weak resonance region  101 . The weak resonance region  101 , inducing a relatively weak resonance, may have a relatively low light extraction efficiency, but a relatively large viewing angle in comparison to the strong resonance region  102 . For example, the strong resonance region  102  may increase light extraction efficiency and the weak resonance region  101  may ensure a sufficient viewing angle. 
         [0037]    Also, according to the current embodiment, in addition to the mirror layer  120 , the intermediate layer  140  (including the emission layer  143 ) may also be structured to divide the sub pixel into the weak and strong resonance regions  101  and  102 . In the intermediate layer  140 , a hole injection layer  141  and a hole transporting layer  142  (for respectively injecting and transporting holes into the emission layer  143 ), the emission layer  143 , an electron injection layer  144  and an electron transporting layer  145  (for respectively injecting and transporting electrons into the emission layer  143 ), have different thicknesses according to the weak and strong resonance regions  101  and  102 . The thickness of the hole transporting layer  142 , in particular, may vary significantly between the weak and strong resonance regions  101  and  102 . For example, the hole transporting layer  142  may have a significantly greater thickness in the weak resonance region  101  than in the strong resonance region  102 . In general, resonance may induce constructive interference of light. Light generated by the emission layer  143  may efficiently cause constructive interference at a certain gap between the first and second electrodes  130  and  150 . Accordingly, if the gap is adjusted, resonance may be induced strongly or weakly. In the current embodiment, the sub pixel may also be divided into the weak and strong resonance regions  101  and  102  by varying the thickness of the hole transporting layer  142  according to the weak and strong resonance regions  101  and  102 . 
         [0038]    Light generated by the emission layer  143  of one sub pixel may be emitted at different intensities according to the weak and strong resonance regions  101  and  102 . For example, the strong resonance region  102  may emit light having a relatively high light extraction efficiency, and the weak resonance region  101  may emit light having a relatively low light extraction efficiency but ensuring a sufficient viewing angle. Consequently, light emitted from the weak resonance region  101  and light emitted from the strong resonance region  102  may be mixed in one sub pixel. An effect of improving both light extraction efficiency and viewing angle characteristics may be achieved by mixing weakly resonated light and strongly resonated light. 
         [0039]    Light emitted from the strong resonance region  102  has increased intensity and directionality due to strong resonance. Accordingly, light extraction efficiency may be increased. However, due to a high directionality, a brightness level or a color coordinate of light may greatly vary even when a viewing angle is slightly out of the center of a screen. On the other hand, the weak resonance region  101  may not increase light extraction efficiency but may have better viewing angle characteristics than the strong resonance region  102 . Therefore, an effect of improving light extraction efficiency may be achieved in comparison to a sub pixel including only the weak resonance region  101 , while better viewing angle characteristics may be achieved in comparison to a sub pixel including only the strong resonance region  102 . 
         [0040]    Accordingly, if the organic light emitting display apparatus according to the current embodiment is used, both light extraction efficiency and viewing angle characteristics may be improved. 
         [0041]    Although the weak and strong resonance regions  101  and  102  of the sub pixel have similar sizes in the above embodiment, in some cases, the weak and strong resonance regions  101  and  102  may be asymmetrically formed to emphasize one effect. According to some embodiments, the strong resonance region  102  may have a larger size than the weak resonance region  101  in order to maximize light extraction efficiency. According to some embodiments, the weak resonance region  101  may have a larger size than the strong resonance region  102  in order to maximize viewing angle characteristics. 
         [0042]      FIG. 3  illustrates a cross-sectional view of a sub pixel modified from  FIG. 1 , according to another embodiment. 
         [0043]    The sub pixel according to the current embodiment (illustrated in  FIG. 3 ) also includes weak and strong resonance regions  201  and  202 . 
         [0044]    For example, like the sub pixel illustrated in  FIG. 1 , the sub pixel illustrated in  FIG. 3  has a structure in which a mirror layer  220 , a first electrode  230 , an intermediate layer  240 , and a second electrode  250  are sequentially stacked on a substrate  210 , and the mirror layer  220  of the strong resonance region  202  is relatively thicker than that of the weak resonance region  201 . 
         [0045]    However, in the current embodiment, the mirror layer  220  of the strong resonance region  202  may further include a metal mirror layer ( 223  and  224 ), while the mirror layer  220  of the weak resonance region  201  may not. The mirror layer  220  of the weak resonance region  201  may be formed as a dielectric mirror layer having a two-layered structure in which a SiNx layer  221  and a SiOx layer  222  are stacked. The mirror layer  220  of the strong resonance region  202  may further include a metal mirror layer including a silver (Ag) layer  223  and an indium tin oxide (ITO) layer  224  sequentially stacked on the first electrode  230  (formed on the dielectric mirror layer). Due to the above enhanced structure, the strong resonance region  202  may induce a more enhanced resonance in comparison to the weak resonance region  201 , and thus light extraction efficiency may be improved. A problem of narrowing a viewing angle may be compensated by the weak resonance region  201 , as described above in relation to  FIG. 1 . 
         [0046]    The intermediate layer  240  may also be structured as described above for the previous embodiment (illustrated in  FIG. 1 ). For example, in the intermediate layer  240 , a hole injection layer  241 , a hole transporting layer  242 , an emission layer  243 , an electron transporting layer  244 , and an electron injection layer  245 , may have different thicknesses according to the weak and strong resonance regions  201  and  202 , such that the strong resonance region  202  induces a stronger resonance. The thickness of the hole transporting layer  242 , in particular, may vary significantly between the weak and strong resonance regions  201  and  202 . For example, the hole transporting layer  242  may have a significantly greater thickness in the weak resonance region  201  than in the strong resonance region  202 . The organic light emitting display apparatus may further include a pixel defining layer  260   
         [0047]    The organic light emitting display apparatus according to the current embodiment may achieve an effect of improving both light extraction efficiency and viewing angle characteristics. 
         [0048]    Although one sub pixel may be divided into a strong resonance region and a weak resonance region, as described above, the principles described above may be applied to units of pixels as described below. 
         [0049]      FIG. 4  illustrates a cross-sectional view of unit pixels of an organic light emitting display apparatus, according to an embodiment. The sub pixel structure illustrated in  FIG. 1  is incorporated in the units of pixels of  FIG. 4 . 
         [0050]    In general, a pixel, i.e., a unit pixel, includes three-color (red, green, and blue) sub pixels. In  FIG. 4 , weak and strong resonance unit pixels  301  and  302  may be alternately aligned. On a plane, the weak and strong resonance unit pixels  301  and  302  may be alternately aligned in row and column directions. 
         [0051]    In the weak resonance unit pixel  301 , a mirror layer  320  on a substrate  310  has a two-layered structure in which a SiOx layer  325  and a SiNx layer  326  are stacked. However, in the strong resonance unit pixel  302 , the mirror layer  320  has a six-layered structure including the two-layered structure ( 325  and  326 ) and a four-layered structure in which SiNx layers  321  and  323  and SiOx layers  322  and  324  are stacked. A pixel defining layer  360  and a gap adjusting electrode  370  may further be provided. The gap adjusting electrode may adjust a gap between the first and second electrodes  330  and  350  to be appropriate for a resonance condition of each sub pixel. 
         [0052]    An intermediate layer  340  between first and second electrodes  330  and  350  may have slightly different structures when same-color sub pixels of the weak and strong resonance unit pixels  301  and  302  are compared. In the intermediate layer  340 , a hole injection layer  341 , a hole transporting layer  342 , an emission layer  343 , an electron transporting layer  344 , and an electron injection layer  345 , particularly, the hole transporting layer  342  may have different thicknesses when same-color sub pixels of the weak and strong resonance unit pixels  301  and  302  are compared. Thus, as described above in relation to  FIG. 1 , the strong resonance unit pixel  302  may induce a stronger resonance. 
         [0053]    Accordingly, light emitted from the weak resonance unit pixel  301  and light emitted from the strong resonance unit pixel  302  may be mixed. An effect of improving both light extraction efficiency and viewing angle characteristics may be achieved by mixing weakly resonated light and strongly resonated light. 
         [0054]      FIG. 5  illustrates a cross-sectional view of unit pixels according to another embodiment. The sub pixel structure illustrated in  FIG. 3  is incorporated in the units of pixels of  FIG. 5 . 
         [0055]    Weak and strong resonance unit pixels  401  and  402  each including three-color (red, green, and blue) sub pixels may be alternately aligned. On a plane, the weak and strong resonance unit pixels  401  and  402  may be alternately aligned in row and column directions. 
         [0056]    A mirror layer  420  of the weak resonance unit pixel  401  may be formed as a dielectric mirror layer having a two-layered structure in which a SiNx layer  421  and a SiOx layer  422  are stacked. The mirror layer  420  of the strong resonance unit pixel  402  may further include a metal mirror layer including an Ag layer  423  and an ITO layer  424  sequentially stacked on a first electrode  430  (formed on the dielectric mirror layer). Due to the above enhanced structure, the strong resonance unit pixel  402  may induce a much enhanced resonance in comparison to the weak resonance unit pixel  401 . Thus, light extraction efficiency may be improved. A problem of narrowing a viewing angle may be compensated by the weak resonance unit pixel  401 , as described above in relation to  FIG. 1 . 
         [0057]    An intermediate layer  440  between first and second electrodes  430  and  450  may have slightly different structures when same-color sub pixels of the weak and strong resonance unit pixels  401  and  402  are compared. In the intermediate layer  440 , a hole injection layer  441 , a hole transporting layer  442 , an emission layer  443 , an electron transporting layer  444 , and an electron injection layer  445 , particularly, the hole transporting layer  442  may have different thicknesses when same-color sub pixels of the weak and strong resonance unit pixels  401  and  402  are compared. Thus, as described above in relation to  FIG. 3 , the strong resonance unit pixel  402  may induce a stronger resonance. 
         [0058]    A pixel defining layer  460 , a gap adjusting electrode  470  may also be provided. The gap adjusting electrode  470  may adjust a gap between the first and second electrodes  430  and  450  to be appropriate for a resonance condition of each sub pixel. 
         [0059]    Accordingly, light emitted from the weak resonance unit pixel  401  and light emitted from the strong resonance unit pixel  402  may be mixed. An effect of improving both light extraction efficiency and viewing angle characteristics may be achieved by mixing weakly resonated light and strongly resonated light. 
         [0060]    As described above, since an organic light emitting display apparatus according to an embodiment may include strong and weak resonance structures, both light extraction efficiency and viewing angle characteristics may be improved. Thus, a product having a high reliability may be implemented by using the organic light emitting display apparatus. 
         [0061]    While the embodiments have been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.