Abstract:
An organic light emitting display (OLED) pixel structure and a method for manufacturing the same, which can be applied for improving the resolution of an OLED without significantly changing the current OLED manufacturing process. With a novel pixel arrangement and circuit layout, an organic light emitting material is evaporated onto a substrate through a mask and thus a plurality of sub-pixels are formed simultaneously while enabling each sub-pixel to correspond to different pixels. Thereby, the area of each sub-pixel is reduced and the resolution of a display is increased.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an organic light emitting display (OLED) pixel structure and a method for manufacturing the same and, more particularly, to an OLED pixel structure and a method for manufacturing the OLED pixel structure using a novel pixel arrangement so as to improve the resolution of an OLED panel. 
     2. Description of the Prior Art 
     In OLED manufacturing, full color displays implemented using red (R), green (G) and blue (B) organic electro-luminescent (EL) materials exhibit high brightness, high contrast, high color saturation but suffer from limited resolution because the opening areas on the shadow mask for EL material evaporation can not be effectively reduced. 
     Please refer to  FIG. 1 , which is a schematic diagram showing an evaporation process for an organic EL material. In mass production, the current EL evaporation process uses a single EL source in a vacuum chamber. As shown in  FIG. 1 , a shadow mask  10  is disposed between a substrate  12  and an EL source  14 , wherein the surface of the substrate  12  to be deposited thereon faces downwards to the EL source  14 . When the EL source  14  is heated up, the organic EL material is evaporated through a plurality of openings  102  in the shadow mask  10  onto a plurality of deposited regions  122  on the substrate  12 . By shifting the shadow mask  10  and the substrate  12 , the EL source  14  evaporates the organic EL material for one of the three colors onto the pre-determined deposited regions  122  and then evaporates the organic EL materials for each of the other two colors. Finally, the organic EL materials for R, G and B are formed on the deposited regions  122  on the substrate  12 , wherein each of the deposited regions  122  corresponds to a sub-pixel. 
     Please refer to  FIG. 2 , which is a schematic circuit diagram showing equivalent pixel circuits and driver circuits of an OLED panel. The OLED panel  20 , using two thin-film transistors (TFT&#39;s) for example, comprises data lines D 1 , D 2 , . . . , Dm and scanning lines G 1 , G 2 , . . . , Gn. Each data line and an intersecting scanning line are used to control a display unit  21 . For example, a switching transistor T S11  comprises the gate coupled to a scanning line G 1  and the source coupled to a data line D 1  for storage and addressing of an image data. A driving transistor T D11  comprises the gate coupled to the drain of the T S11  and the source coupled to a voltage source V DD  for controlling the driving current according to the storage capacitor C S11 . One end of the storage capacitor C S11  is coupled to the drain of the T S11  while the other end is coupled to a reference voltage VL. The anode of the OLED is coupled the drain of the T D11  and the cathode is coupled to the ground GND. 
     The schematic circuit diagram of  FIG. 2  comprises the switching transistors T S11 ˜T S1m , T S21 ˜T S2m , . . . , T Sn1 ˜T Snm , the driving transistors T D11 ˜T D1m , T D21 ˜T D2m , . . . , T Dn1 ˜T Dnm , the storage capacitors C S11 ˜C S1m , C S21 ˜C S2m , . . . , S Sn1 ˜C Snm , and the OLED&#39;s. Each display unit  21  corresponds to a sub-pixel. A pixel comprises three sub-pixels for R, G and B corresponding to three display units. In other words, in  FIG. 1 , when the organic EL material is evaporated through the plurality of openings  102  in the shadow mask  10  onto the plurality of deposited regions  122  on the substrate  12 , the area of one of the openings  102  corresponds to the area of a sub-pixel. Each sub-pixel corresponds to two TFT&#39;s and one storage capacitor. 
     Please refer to  FIG. 3A  and  FIG. 3B , which are schematic diagrams showing pixel arrangements of an OLED panel. In  FIG. 3A , there are a plurality of pixels  31  comprising a red sub-pixel  312 , a green sub-pixel  314  and a blue sub-pixel  316  on an OLED panel  30 . Each sub-pixel corresponds to two TFT&#39;s and one storage capacitor as shown in  FIG. 2 . Moreover, sub-pixels with different colors have different life-times. The sub-pixel with the shortest life-time limits the durability of whole display panel. If the red sub-pixel and the blue sub-pixel, which exhibit lower brightness, are designed to have larger areas, the driving currents for the red sub-pixel and the blue sub-pixel could be lowered so as to enhance the durability of whole display panel. In  FIG. 3B , there is a white (W) sub-pixel  368  in addition to a red sub-pixel  362 , a green sub-pixel  364  and a blue sub-pixel  366  in each of the pixels  36  on the OLED panel  35 . The red sub-pixel  362 , the green sub-pixel  364 , the blue sub-pixel  366  and the white sub-pixel  368  may have different areas. Since each of the sub-pixels corresponds to two TFT&#39;s and one storage capacitor as shown in  FIG. 2  and the area of each of the sub-pixels is determined by the opening  102  of the shadow mask  10 . In other words, the sub-pixel area formed by evaporating an organic EL material through the opening  102  of the shadow mask  10  onto the deposited region  122  can not be unlimitedly reduced. Therefore, the resolution of the OLED panel is limited by the evaporation process. 
     Therefore, there exists a need in providing an OLED pixel structure and a method for manufacturing the OLED pixel structure using a novel pixel arrangement so as to improve the resolution of an OLED panel. 
     SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to provide an OLED pixel structure and a method for manufacturing the OLED pixel structure using a novel pixel arrangement so as to improve the resolution of an OLED panel. The organic EL material for R, G, B or W is heated up and evaporated through an opening of a shadow mask onto a plurality of deposited regions on a substrate. The deposited regions with the evaporated organic EL material are categorized into a plurality of groups of sub-pixels with the same color, wherein each of the sub-pixels corresponds to different pixels. Therefore, the organic EL material evaporated through one single opening onto one deposited region can be used for multiple sub-pixels so as to effectively reduce the sub-pixel area and hence improve the resolution of an OLED panel. 
     It is a secondary object of the present invention to provide an OLED pixel structure and a method for manufacturing the OLED pixel structure using a novel pixel arrangement so as to improve the resolution of an OLED panel without significantly changing the current OLED manufacturing process. The present invention can be used in both bottom-emission and top-emission OLED&#39;s. 
     In order to achieve the foregoing objects, the present invention provides a method for manufacturing an organic light-emitting device (OLED) pixel structure, comprising steps of: providing a substrate; forming a plurality of thin-film transistors on the substrate; defining a plurality of deposited regions on the plurality of thin-film transistors; and evaporating an organic electro-luminescent (EL) material through an opening of a shadow mask onto at least two of the deposited regions, wherein each of the deposited regions with the evaporated organic electro-luminescent material is a sub-pixel corresponding to different pixels. 
     The present invention further provides a substrate; a plurality of thin-film transistors formed on the substrate; a plurality of deposited regions defined on the plurality of thin-film transistors; and an organic electro-luminescent (EL) layer formed on the deposited regions, wherein each of the deposited regions coated with the organic electro-luminescent material is a sub-pixel corresponding to different pixels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects, spirits and advantages of the preferred embodiments of the present invention will be readily understood by the accompanying drawings and detailed descriptions, wherein: 
         FIG. 1  is a schematic diagram showing an evaporation process for an organic EL material; 
         FIG. 2  is a schematic circuit diagram showing equivalent pixel circuits and driver circuits of an OLED panel; 
         FIG. 3A  and  FIG. 3B  are schematic diagrams showing pixel arrangements of an OLED panel; 
         FIG. 4A  to  FIG. 4E  are cross-sectional views showing an OLED pixel structure according to the present invention; 
         FIG. 5A  is a schematic diagram showing a pixel arrangement of an OLED panel according to a first embodiment of the present invention; 
         FIG. 5B  is a schematic diagram showing a pixel arrangement of an OLED panel according to a second embodiment of the present invention; and 
         FIG. 6  is a schematic diagram showing a pixel arrangement of an OLED panel according to a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention providing an OLED pixel structure and a method for manufacturing the same can be exemplified by the preferred embodiments as described hereinafter. 
     Please refer to  FIG. 4A  to  FIG. 4E  for the cross-sectional views showing an OLED pixel structure according to the present invention. In  FIG. 4A , a substrate  401  is provided. On the substrate  401 , in addition to thin-film transistors  41 , there are formed a buffer layer  402 , a gate dielectric layer  403 , a first protective layer  404 , an isolating layer  405  and a second protective layer  406 . One of the source/drain regions of each of the thin-film transistors  41  is coupled to a pixel electrode (anode)  42 . Deposited regions  43  are formed on the pixel electrode  42 . Moreover, an insulating layer  407  is formed on the isolating layer  405  so as to distinguish the sub-pixels R, G, B. In  FIG. 4B , an organic electro-luminescent (EL) material for red is evaporated through an opening  445  of a shadow mask  44  onto the deposited region  43  for a sub-pixel R. Therefore, an organic electro-luminescent layer  45  for red is formed. As shown in  FIG. 4C , an organic electro-luminescent material for green is evaporated through the opening  445  of the shadow mask  44  onto the deposited region  43  for a sub-pixel G. Therefore, an organic electro-luminescent layer  46  for green is formed. As shown in  FIG. 4D , an organic electro-luminescent material for blue is evaporated through the opening  445  of the shadow mask  44  onto the deposited region  43  for a sub-pixel B. Therefore, an organic electro-luminescent layer  46  for blue is formed. Finally in  FIG. 4E , a pixel electrode (anode)  48  is formed on the organic electro-luminescent layers  45 ,  46 ,  47  so that a pixel structure is formed to comprise an R sub-pixel, a G sub-pixel and a B sub-pixel. Each sub-pixel comprises a thin-film transistor  41  as its driving transistor. 
     Please refer to  FIG. 5A , which is a schematic diagram showing a pixel arrangement of an OLED panel according to a first embodiment of the present invention. An OLED panel  50  comprises a plurality of pixels  51 . Using evaporation, a rectangular region for red  52  comprising four red rectangular sub-pixels  521  is formed. Each of the red rectangular sub-pixels  521  corresponds to different pixels  51 . Similarly, a rectangular region for green  53 , a rectangular region for blue  54  and a rectangular region for white  55  are formed using evaporation. Each of four green rectangular sub-pixels  531  in the rectangular region for green  53  corresponds to different pixels  51 . Each of four blue rectangular sub-pixels  541  in the rectangular region for blue  54  corresponds to different pixels  51 . Each of four white rectangular sub-pixels  551  in the rectangular region for white  55  corresponds to different pixels  51 . In other words, each pixel  51  is composed of a red rectangular sub-pixel  521 , a green rectangular sub-pixel  531 , a blue rectangular sub-pixel  541  and a white rectangular sub-pixel  551 . In the prior art, the opening has a certain area, which limits the sub-pixel area. However, with the pixel arrangement of the present invention, multiple sub-pixels of the same color can be formed in one evaporation process for different pixels. Therefore, the sub-pixel for one pixel is down-sized and thus the resolution of an OLED panel can be effectively improved. 
     Please refer to  FIG. 5B , which is a schematic diagram showing a pixel arrangement of an OLED panel according to a second embodiment of the present invention. Since the durability of an OLED panel depends on the sub-pixel with the shortest life-time, the sub-pixel with the shortest life-time can be designed to have the largest area without changing the evaporation process so as to improve the durability of the OLED panel according to the present invention. For example, the rectangular region for white  55  in  FIG. 5A  can be used to deposit the organic EL material for red so that all the rectangular regions for white  55  in  FIG. 5A  are replaced by the rectangular regions for red  52 . Accordingly, the organic EL material for red occupies twice the area and thus the red sub-pixels share a larger luminescent area. Under the same luminescent intensity, the driving current for the red sub-pixels can be lowered so as to improve the durability of the OLED panel. 
     Please refer to  FIG. 6 , which is a schematic diagram showing a pixel arrangement of an OLED panel according to a third embodiment of the present invention. An OLED panel  60  comprises a plurality of pixels  61 . In the first embodiment as shown in  FIG. 5A , the rectangular region for red  52 , the rectangular region for green  53 , the rectangular region for blue  54  and the rectangular region for white  55  are formed by evaporating organic EL materials through the opening with the identically small area for all the sub-pixels. Therefore, a highest resolution is obtained using the identically small area for the red rectangular sub-pixels  521 , the green rectangular sub-pixels  531 , the blue rectangular sub-pixels  541  and the white rectangular sub-pixels  551  because the opening area of the shadow mask can not be unlimitedly down-sized. However in the third embodiment as shown in  FIG. 6 , the areas for the red rectangular sub-pixels  621 , the green rectangular sub-pixels  631 , the blue rectangular sub-pixels  641  and the white rectangular sub-pixels  651  can be different according to practical use. Different opening areas can be selected when evaporating the organic EL materials onto the rectangular regions for red  62 , the rectangular regions for green  63 , the rectangular regions for blue  64  and the rectangular regions for white  65 . For example, the rectangular regions for red  62  require the largest area and therefore a shadow mask with a largest opening area is selected when evaporating the EL material onto the rectangular regions for red  62 . On the contrary, the rectangular regions for green  63  require the smallest area and therefore a shadow mask with a smallest opening area is selected when evaporating the EL material onto the rectangular regions for green  63 . After the rectangular regions for red  62 , the rectangular regions for green  63 , the rectangular regions for blue  64  and the rectangular regions for white  65  are formed using evaporation, each of the pixels  61  comprises a red rectangular sub-pixel  621 , a green rectangular sub-pixel  631 , a blue rectangular sub-pixel  641  and a white rectangular sub-pixel  651 . Each sub-pixel area is different. Even though the resolution of the OLED panel  60  in  FIG. 6  is superior to the resolution of the OLED panel  50  in  FIG. 5A , the resolution of the OLED panel  60  is still higher than the resolution of conventionally manufactured OLED panel. The third embodiment of the present invention provides OLED panel designers with greater flexibility since the areas of sub-pixels for different colors are not identical. 
     It is to be noted that the cross-sectional views in  FIG. 4A  to  FIG. 4E  are only exemplary. The present invention can be used in both bottom-emitting and top-emitting pixel structures. The substrate used in the present invention can be a flexible substrate, a glass substrate or a metal substrate. The transistors of the present invention are not limited to a certain type of transistors. The transistors of the present invention can be implemented using a bottom gate or a top gate, amorphous silicon, poly-silicon or an organic material so as to be adapted in the OLED pixel structure and the method for manufacturing the same. 
     According to the above discussion, it is apparent that the present invention discloses an OLED pixel structure and a method for manufacturing the OLED pixel structure using a novel pixel arrangement so as to improve the resolution of an OLED panel without significantly changing the current OLED manufacturing process. Therefore, the present invention is novel, useful and non-obvious. 
     Although this invention has been disclosed and illustrated with reference to particular embodiments, the principles involved are susceptible for use in numerous other embodiments that will be apparent to persons skilled in the art. This invention is, therefore, to be limited only as indicated by the scope of the appended claims.