Patent Publication Number: US-9847486-B2

Title: Method of manufacturing organic light emitting display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a divisional application based on pending application Ser. No. 13/038,836, filed Mar. 2, 2011, the entire contents of which is hereby incorporated by reference. 
     This application claims the benefit of Korean Patent Application No. 10-2010-0021384, filed on Mar. 10, 2010, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     An aspect of the present invention relates to an organic light emitting display device, and more particularly, to a transparent organic light emitting display device and a method of manufacturing the same. 
     2. Description of the Related Art 
     As organic light emitting display devices have superior characteristics such as wide viewing angle, high contrast ratio, short response time, and low power consumption, they are widely used in personal portable devices such as MP3 players, mobile phones, television sets, etc. 
     Also, transparent organic light emitting display devices have been constructed using transparent thin film transistors and transparent organic light emitting devices. 
     However, since a cathode of the transparent organic light emitting display device is formed of a metal, there is a limit in increasing the transmittance of the transparent organic light emitting display device. 
     SUMMARY 
     An aspect of the present invention provides a transparent organic light emitting display device having high transmittance with respect to external light and a method of manufacturing the transparent organic light emitting display device. 
     According to another aspect of the present invention, there is also provided an organic light emitting display device including a cathode having transmission windows and that are formed in a simple way, and a method of manufacturing the organic light emitting display device. 
     According to an aspect of the present invention, there is provided an organic light emitting display device including a substrate; a plurality of pixels formed on the substrate, each of the pixels having a first region that emits light and a second region that transmits external light; a plurality of thin film transistors disposed in the first region of the pixel; a plurality of first electrodes disposed in the first region of the pixel and electrically connected to the thin film transistors, respectively; a second electrode formed opposite to the plurality of first electrodes and comprising a plurality of transmission windows corresponding to the second regions; and an organic layer formed between the first electrodes and the second electrode. 
     According to an aspect of the present invention, a decrease in the transmittance of the second region where external light is transmitted may be prevented as much as possible. Thus, a user may easily observe external images. 
     According to another aspect of the present invention, the transmission windows may be formed in the second electrode by using a simple method. 
     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a schematic cross-sectional view of an organic light emitting display device according to an embodiment of the present invention; 
         FIG. 2  is a schematic plan view of an organic light emitting display device according to an embodiment of the present invention; 
         FIG. 3  is a schematic plan view of an organic light emitting display device according to another embodiment of the present invention; 
         FIG. 4  is a cross-sectional view of a pixel of an organic light emitting display device according to an embodiment of the present invention; 
         FIG. 5  is a plan view of a mask for forming a second electrode having a transmission window, according to an embodiment of the present invention; 
         FIGS. 6A through 6D  are plan views illustrating an operation of forming a second electrode by using the mask illustrated in  FIG. 5 ; 
         FIG. 7  is a plan view of a mask for forming a second electrode having a transmission window, according to an embodiment of the present invention; 
         FIG. 8  is a plan view of a mask for forming a second electrode having a transmission window, according to another embodiment of the present invention; and 
         FIG. 9  is a cross-sectional view of a pixel of an organic light emitting display device according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present 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. 
     Here, it is to be understood that where is stated herein that one film or layer is “formed on” or “disposed on” a second layer or film, the first layer or film may be formed or disposed directly on the second layer or film or there may be intervening layers or films between the first layer or film and the second layer or film. Further, as used herein, the term “formed on” is used with the same meaning as “located on” or “disposed on” and is not meant to be limiting regarding any particular fabrication process. 
       FIG. 1  is a schematic cross-sectional view of an organic light emitting display device according to an embodiment of the present invention. Referring to  FIG. 1 , the organic light emitting display device according to an embodiment of the present invention includes a substrate  1  and a display unit  2  placed on the substrate  1 . External light enters the organic light emitting display device via the display unit  2  and the substrate  1 . 
     As will be described later, the display unit  2  transmits external light. Referring to  FIG. 1 , the display unit  2  allows a user positioned below the substrate  1  to view external images beyond the display unit  2 . Although a bottom-emission type organic light emitting display device in which images on the display unit  2  are displayed toward the substrate  1  as illustrated in  FIG. 1 , aspects of the present invention are not limited thereto, and may be equally applied to a top-emission type organic light emitting display device in which images on the display unit  2  are displayed in a direction opposite to the substrate  1 . 
       FIG. 1  illustrates two adjacent pixels, namely, a first pixel P 1  and a second pixel P 2 , of the organic light emitting display device according to an aspect of the present invention. 
     Each of the first and second pixels P 1  and P 2  includes a first region  31  and a second region  32 . 
     An image is displayed on the display unit  2  in the first region  31 , and external light passes through the display unit  2  in the second region  32 . 
     In other words, since each of the first and second pixels P 1  and P 2  includes the first region  31  where images are displayed and the second region  32  which transmits external light, a user can see an external image through the second region  32  when the user does not see the image displayed through the first region  31 . 
     Thus, the second region  32  does not include devices such as a thin film transistor, a capacitor, and an organic light emitting device, and thus external light transmittance may be maximized and distortion of a transmitted image due to interference of the devices such as a thin film transistor, a capacitor, and an organic light emitting device may be prevented as much as possible. 
       FIG. 2  is a schematic plan view of a red pixel P r , a green pixel P g , and a blue pixel P b  that are adjacent to one another. 
     Each of the red, green, and blue pixels P r , P g , and P b  includes a circuit region  311  and an emission region  312  in the first region  31 . The circuit region  311  and the emission region  312  are adjacent to each other. 
     The second region  32  that transmits external light is adjacent to the first region  31 . 
     As illustrated in  FIG. 2 , independent second regions  32  may be included in the red, green, and blue pixels P r , P g , and P b , respectively. Alternatively, as illustrated in  FIG. 3 , second regions  32  may be connected to one another across the red, green, and blue pixels P r , P g , and P b . In the embodiment of  FIG. 3 , an area of the second region  32  through which external light passes is increased, and thus the transmittance of the entire display unit  2  may be increased. 
     Although the second regions  32  of the red, green, and blue pixels P r , P g , and P b  are integrally connected to one another in  FIG. 3 , the aspects of the present invention are not limited thereto, and the second regions of only two adjacent pixels from among the red, green, and blue pixels P r , P g , and P b  may be connected to each other. 
       FIG. 4  illustrates a cross-section of the red, green, or blue pixel Pr, Pg, or Pb illustrated in  FIGS. 2 and 3 . 
     As illustrated in  FIG. 4 , a thin film transistor TR is arranged in the circuit region  311 . However, a pixel circuit including the thin film transistor TR may be also included in the circuit region  311 . Alternatively, the circuit region  311  may further include a plurality of thin film transistors TR and a storage capacitor. In this case, wires such as scan lines, data lines, and Vdd lines connected to the thin film transistors TR and the storage capacitor may be further included in the circuit region  311 . 
     An organic light emitting diode EL may be disposed in the emission region  312 . The organic light emitting diode EL is electrically connected to the thin film transistor TR of the circuit region  311 . 
     A buffer layer  211  is formed on the substrate  1 , and a pixel circuit including the thin film transistor TR is formed on the buffer layer  211 . 
     First, a semiconductor active layer  212  is formed on the buffer layer  211 . 
     The buffer layer  211  is formed of a transparent insulation material and prevents impurity elements from penetrating into the substrate  1  and planarizes a surface of the substrate  1 . The buffer layer  211  may be formed of any of various materials that can perform the functions described above. For example, the buffer layer  211  may be formed of an inorganic material such as silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide, aluminum nitride, titanium oxide, or titanium nitride, an organic material such as polyimide, polyester, or acryl, or stacks of these materials. The buffer layer  211  is not an essential element and may not be formed at all. 
     The semiconductor active layer  212  may be formed of polycrystal silicon, but is not limited thereto and may be formed of a semiconductor oxide. For example, the semiconductor active layer  212  may be a G-I-Z—O layer [a(In 2 O 3 )b(Ga 2 O 3 )c(ZnO) layer] (where a, b, and c are natural numbers that respectively satisfy a≧0, b≧0, and c≧0). When the semiconductor active layer  212  is formed of a semiconductor oxide, light transmittance in the circuit region  311  of the first region  31  may be increased, and thus external light transmittance of the entire display unit  2  may be increased. 
     A gate insulating layer  213  is formed on the buffer layer  211  so as to cover the semiconductor active layer  212 , and a gate electrode  214  is formed on the gate insulating layer  213 . 
     An interlayer insulating layer  215  is formed on the gate insulating layer  213  so as to cover the gate electrode  214 . A source electrode  216  and a drain electrode  217  are formed on the interlayer insulating layer  215  so as to contact the semiconductor active layer  212  via contact holes. 
     The structure of the thin film transistor TR is not limited to the above-described structure, and the thin film transistor TR may have various other structures. 
     A passivation layer  218  is formed to cover the thin film transistor TR. The passivation layer  218  may be a single-layered or multi-layered insulating layer, an upper surface of which is planarized. The passivation layer  218  may be formed of an inorganic material and/or an organic material. 
     As illustrated in  FIG. 4 , a first electrode  221  of an organic light emitting diode EL electrically connected to the thin film transistor TR is formed on the passivation layer  218 . The first electrode  221  corresponds to each pixel. 
     An insulating layer  219  is formed of an organic and/or inorganic insulating material on the passivation layer  218  to cover at least an edge portion of the first electrode  221 . 
     The insulating layer  219  exposes only a central portion of the first electrode  221 . Although the insulating layer  219  may be included to cover the first region  31 , the first insulating layer  219  does not necessarily cover the entire first region  31 , and it is sufficient for the insulating layer  219  to cover only a part of the first region  31 , particularly, an edge of the first electrode  221 . 
     An organic layer  223  and a second electrode  222  are sequentially stacked on the first electrode  221 . The second electrode  222  covers the organic layer  223  and the insulating layer  219 , and second electrodes  222  corresponding to all of the pixels are electrically connected to one another. 
     The organic layer  223  may be a low molecular weight organic layer or a polymer organic layer. When the organic layer  223  is a low molecular weight organic layer, the organic layer  223  may be formed by stacking a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and an electron injection layer (EIL) in a single structure or a composite structure, and may be formed of any of various materials such as copper phthalocyanine (CuPc), N,N′-Di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB), or tris-8-hydroxyquinoline aluminum (Alq3). The low-molecular weight organic layer may be formed by vacuum deposition. Herein, the HIL, the HTL, the ETL, and the EIL are common layers and may be commonly applied to red, green, and blue pixels. 
     The first electrode  221  may function as an anode, and the second electrode  222  may function as a cathode. Alternatively, the first electrode  221  may function as a cathode, and the second electrode  222  may function as an anode. 
     According to an embodiment of the present invention, the first electrode  221  may be a transparent electrode, and the second electrode  222  may be a reflection electrode. The first electrode  221  may include ITO, IZO, ZnO, In 2 O 3 , or the like each having a high work function. The second electrode  222  may be formed of a metal having a low work function, such as Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, or Ca. Accordingly, the organic light emitting diode EL is a bottom emission type in which light is emitted towards the first electrode  221 . 
     However, the aspects of the present invention are not limited thereto, and the second electrode  222  may also be a transparent type electrode. 
     The passivation layer  218 , the gate insulating layer  213 , the interlayer insulating layer  215 , and the insulating layer  219  may be transparent insulating layers. 
     A sealing substrate  4  may be installed over the second electrode  222 . The sealing substrate  4  is located outside the display unit  2  and bonded with the substrate  1  by a sealant (not shown) so as to protect the second electrode  222  from external air. A filler (not shown) may be filled between the sealing substrate  4  and the second electrode  222 , and a moisture absorbent may also be interposed therebetween. A sealing structure for the display unit  2  is not limited to the use of the sealing substrate  4 , and a film-shaped sealing structure may be used. 
     Transmission windows  224  are further formed in the second electrode  222  and the insulating layer  219 . The transmission windows  224  may be formed only in the second electrode  222 , or may be formed in at least one selected from the group consisting of the passivation layer  218 , the interlayer insulating layer  215 , the gate insulating layer  213 , and the buffer layer  211 . 
     The transmission windows  224  are formed at locations corresponding to the second regions  32 . The transmission windows  224  may be formed in any pattern such as the one shown in  FIGS. 2 and 3 . However, it is understood that the transmission windows can have a different pattern than those illustrated in  FIGS. 2 and 3 . 
     However, it is difficult to form the transmission windows  224  in the second electrode  222 , because a metal for the second electrode  222  should be deposited using a mask having a shield portion corresponding to the pattern of the transmission windows  224  in order to form the transmission windows  224  in the pattern and manufacturing the mask having the shield portion corresponding to the pattern is very difficult. 
     A mask  5  illustrated in  FIG. 5  is used to form the second electrode  222  having the transmission windows  224  arranged in such pattern. 
     The mask  5  has an aperture  51  corresponding to a first region  31  of a specific pixel. A pattern of the apertures  51  shown in  FIG. 5  is used to form the transmission windows  224  having the pattern illustrated in  FIG. 3 . The mask  5  has an aperture  51  corresponding to the first regions  31  of three adjacent pixels, namely, a red pixel, a green pixel, and a blue pixel. The size of the aperture  51  is generally slightly greater than the overall size of the three pixels so that patterns obtained when a material used to form the second electrode  222  is deposited via the apertures  51  overlap each other. Thus, the second electrode  222  may act as a common electrode. 
     When the three pixels constitute a unit pixel, the apertures  51  are separated from one another by a distance corresponding to the unit pixel in a horizontal direction and a vertical direction. 
     When a metal used to form the second electrode  222  is deposited on the organic layer  223  by using the mask  5 , a pattern illustrated in  FIG. 6A  is obtained. 
     When the mask  5  is shifted by one unit pixel horizontally and then metal is deposited, a pattern as illustrated in  FIG. 6B  is obtained. When the mask  5  is shifted again by one unit pixel downward and then metal is deposited, a pattern as illustrated in  FIG. 6C  is obtained. Thereafter, when the mask  5  is shifted again by one unit pixel horizontally and then metal is deposited, a pattern as illustrated in  FIG. 6D  is obtained. Thus, as illustrated in  FIG. 6D , the second electrode  222  having the transmission windows  224  in the pattern of  FIG. 3  is obtained. 
     The pattern of the apertures  51  of the mask  5  is not limited to the pattern illustrated in  FIG. 5 . In other words, if an aperture  51  is formed at the center of the four adjacent apertures  51  illustrated in  FIG. 5  and the aperture  51  at the center is the same as each of the four adjacent apertures  51 , the second electrode  222  having the pattern illustrated in  FIG. 6D  may be obtained by shifting the mask  5  horizontally only once. 
       FIGS. 7 and 8  illustrate masks  5  having other shapes than the mask  5  of  FIG. 5 . 
     An aperture  51  corresponding to a first region  31  corresponding to three pixels is formed around a region corresponding to a transmission window  224 . The pattern of the apertures  51  illustrated in  FIG. 7  may allow the second electrode  222  having the pattern illustrated in  FIG. 6D  to be obtained by shifting the mask  5  horizontally only once. In this case, since an interval between apertures  51  is sufficient, the mask  5  is not destroyed by a tensile force but may be stable. 
       FIG. 8  illustrates a modified example of  FIG. 7 . A center of an aperture  51  protrudes upward and downward, and thus when a mask  5  of  FIG. 7  is shifted horizontally by one unit pixel and deposition is performed, deposition occurs redundantly on the upward and downward protrusions of the aperture  51 . Thus, the second electrode  222  may be stably formed through the entire display unit without any discontinuity. 
     The above embodiment applies not only to a structure in which a circuit part including the thin film transistor TR is not overlapped by the first electrode  221  as illustrated in  FIG. 4  but also to a structure in which a circuit part including the thin film transistor TR is overlapped by the first electrode  221  as illustrated in  FIG. 9 . 
     In the case of the structure illustrated in  FIG. 9 , when the first electrode  221  is formed as a reflection electrode, an effect where a conductive pattern of a circuit part is shielded by the first electrode  221  may be obtained. Thus, distortion of a penetrated image due to external light scattered by the conductive pattern of the circuit part may be suppressed. 
     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.