Patent Publication Number: US-2006017379-A1

Title: Dual-sided display

Description:
BACKGROUND OF THE INVENTION  
      (1) Field of the Invention  
      The invention relates to an electro luminescence (EL) display, and more particularly to a dual-sided display of an organic light emitting diode (OLED) display.  
      (2) Description of the Prior Art  
      Since the first appearance of a multilayer OLED contributed by Tang and Van Slyke, potential applications of the OLEDs in flat panel displays have been widely acknowledged. Many approaches now have been devoted to constructing a full-color display of the OLEDs.  
      The OLED can also be called as an organic electro luminescence (OEL). A basic structure of the OLED is a multi-layer organic film laminating a hole-injection layer, a hole-transport layer, an emissive layer and an electron-transport layer. When a voltage is applied to the OLED cell, injected positive and negative charges recombine in the emissive layer and create electro luminescent light.  
      With advancement of electric appliances, display for the electric appliances is demanding reaction velocity, dots per inch, and pixel quality. Also, light weight and handy size are another trend. For example, the appearance of some dual-sided electric devices explains the urgent need upon a broader viewer to cooperate in the electric devices.  
      Presently, the dual-sided display is formed by composing two independent LCD displays. Such kind of dual-sided displays has a 8˜10 mm thickness, which is about twice to the thickness of a single display. Definitely, cost for constructing the conventional dual-sided display is also twice to that for constructing the single-sided display. Hence, this kind of the dual-sided displays is hard to be among the master stream of the displays.  
       FIG. 1  shows a cross-section view of a typical conventional dual-sided OLED display. The OLED display  1  is obtained by assembling two OLED sealing structures  11  and  12 . Each of the sealing structures  11 ,  12  comprises respectively an EL layer  111  or  121 , an upper substrate  112  or  122 , and an under plate  113  or  123 .  
      As shown, between the upper substrate  112  and the under plate  113 , an interior space  114  (exaggerated in thickness) is formed to accommodate the EL substrate  111  disposed under the upper substrate  112  and a desiccant layer  116  disposed above the under plate  113  but under the EL substrate  111 . The interior space  114  is mainly contributed by a shallow cavity formed at the under plate  113  by etching or any relevant machining. Also, it is noted that the upper substrate  112  is sealed on the under plate  113  via a sealing material  115 . The desiccant layer  116  positioned on the base  114   a  of the cavity of the under plate  113  is introduced to lower the humidity levels of the airtight space  114 .  
      Elements of the sealing structure  12  are basically the same as those of the sealing structure  11 , but presenting a mirror image arrangement with respect to the boarder line in between. The sealing structure  12  comprises an EL layer  121 , an upper substrate  122  and an under plate  123 . The EL substrate  121  is disposed on the upper substrate  122 , and an airtight interior space  124  is formed in the sealing structure  12  by shaping a respective cavity in the under plate  123 . The upper substrate  122  is sealed on the under plate  123  via a sealing material  125  so as to form the airtight space  124  for accommodating the EL layer  121  and the desiccant layer  126 .  
      In the art, the thickness of the dual-sided panel  1  is around 3 mm, which is a little too thick to be a so-called film structure. Also, the cost and weight of the dual-sided panel  1  may also make the panel  1  less competitive. Accordingly, an improvement upon the OLED dual-sided display which provides a thinner and larger screen but with a simple production process and a lower cost is definitely welcome to the skill in the art.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to provide a dual-sided display of an OLED display.  
      It is another object of the present invention to provide a dual-sided display with equal luminescent efficiency.  
      The dual-sided display panel in accordance with the present invention includes a first transparent substrate, a second transparent substrate, a first EL layer, and a second EL layer. Wherein the second transparent substrate is disposed under and sealed to the first transparent substrate, thereby forming an airtight space therebetween. The first EL layer and the second EL layer are both positioned between the first transparent substrate and the second transparent substrate. The first EL layer is disposed in the airtight space and positioned on a bottom surface of the first transparent substrate for displaying a first image through the first transparent substrate. The second EL layer is disposed in the airtight space and positioned on an upper surface of the second transparent substrate and displays a second image through the second transparent substrate. In particular, the area of the first EL layer is larger than the area of the second EL layer.  
      In the present invention, all the EL layers mentioned above can be composed of the organic light emitting diodes (OLED) or polymer light emitting diodes (PLED). The thickness of the dual-sided display of the invention can be reduced to range about 0.6-1.4 mm. By comparing to the conventional dual-sided OLED display, the manufacturing process to obtain the dual-sided display according to the present invention can be simplified, and the cost for producing the present dual-sided display can be thus reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention will now be specified with reference to its preferred embodiment illustrated in the drawings, in which  
       FIG. 1  is a cross-section view of a conventional OLED display;  
       FIG. 2  is a cross-section view of a first preferred embodiment of the dual-sided OLED display of the present invention;  
       FIG. 3  is a cross-section view of a second preferred embodiment of the OLED display of the present invention;  
       FIG. 4  is a cross-section view of a third preferred embodiment of the OLED display of the present invention; and  
       FIG. 5  is a cross-section view of a fourth preferred embodiment of the OLED display of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      As mentioned in the foregoing section, a need in improving the OLED dual-sided display to achieve a thinner and larger screen with a simple production process and a lower cost is obvious.  
       FIG. 2  shows a cross-section view of a first preferred embodiment of the dual-sided display of the present invention. As shown, the dual-sided display  2  comprises a first transparent substrate  21 , a second transparent substrate  22 , a first EL layer  23 , and a second EL layer  24 .  
      The second transparent substrate layer  22  is disposed under and sealed to the first transparent substrate, thereby forming an airtight space  26  therebetween. The first EL layer  23  is disposed on the bottom surface of the first transparent substrate  21 , for displaying a first image through the first transparent substrate  21 . The second EL layer  24  is disposed in the airtight space  26  and positioned on the upper surface of the second transparent substrate  22 , for displaying a second image through the second transparent substrate  22 . The first transparent substrate  21  is sealed in a perimeter wise to the second transparent substrate  22  with a sealing material  25  such that an internal airtight space  26  can be formed between the first transparent substrate  21  and the second transparent substrate  22  for accommodating the EL layers  23 , 24 .  
      In the present invention, the area of the first EL layer  23  and the area of the second EL layer  24  are not always the same. Basically, the sizes and the related positioning of these two EL layer  23 , 24  can be varied to comply with different kinds of electric devices. In the first preferred embodiment of the invention, the first EL layer  23  is larger in area than the second EL layer  24 .  
       FIG. 3  shows a cross-section view of a second preferred embodiment of the dual-sided OLED display of the present invention.  
      As shown, the dual-sided display  3  comprises a first transparent substrate  31 , a second transparent substrate  32 , a first EL layer  33 , a second EL layer  34 , and a-desiccant layer  35 .  
      The second transparent substrate layer  32  is disposed under and sealed to the first transparent substrate, thereby forming an airtight space  37  therebetween. The first EL layer  33  is disposed in the airtight space  37  and positioned on a bottom surface of the first transparent substrate  31  for displaying a first image through the first transparent substrate  31 . The second EL layer  34  is disposed n the airtight space  37  and positioned on an upper surface of the second transparent substrate  32  for displaying a second image on the second transparent substrate  32 . The first transparent substrate  31  is sealed on top of the second transparent substrate  32  with a circling sealing material  36  so as to obtain an airtight space  37  in between first transparent substrate for accommodating thereinside the EL layers  33 , 34 .  
      The first EL layer  23  is larger in area than the second EL layer  24 . The area of the substrate  31  or  32  which overlaps with the EL layer  33  or  34  is defined as a display area, and the rest area of the substrate is defined as a non-display area. As shown, the desiccant layer  35  is located in the airtight space and positioned on the non-display area of the upper surface of the second transparent substrate layer  32 .  
      The desiccant layer  35  can lower the humidity level of the airtight space  37  and thus prevent the EL layers  33 , 34  from possible moisture damage. The desiccant layer  35  on the non-display area of the second transparent substrate layer  32  can be formed by evaporating or sputtering. Upon such an arrangement, the existence of the desiccant layer  35  can show little effect to the thickness of the display  3 .  
      Except for positioning the desiccant layer  35  on the non-display area, the desiccant layer  35  can also be positioned on the display area or across the display area and the non-display area, especially to meet a high humidity environment.  
      In the present invention, the desiccant layer  35  is made of a material selected from the group consisting of active metals, metallic oxides, and metallic sulfides. The ELs  33 , 34  can be OLEDs or PLEDs.  
      Additionally, the drive mode of the present invention can be a mode of passive matrix, a mode of active matrix, or a mixed mode of the passive matrix and the active matrix. The dual-sided display of the invention can be applied to a monochrome display, a polychrome display, or a full-colored display.  
       FIG. 4  shows a cross-section view of a third preferred embodiment of the dual-sided OLED display of the present invention. As shown, the dual-sided display  4  comprises a first transparent substrate  41 , a second transparent substrate  42 , a first EL layer  43 , a second EL layer  44 , a first protection layer  45 , and a second protection layer  46 .  
      The second transparent substrate layer  42  is disposed under and sealed to the first transparent substrate  41 , thereby forming an airtight space  48  therebetween. The first EL layer  43  is disposed in the airtight space  48  and positioned on a bottom surface of the first transparent substrate  41  for displaying a first image through the first transparent substrate  41 . The second EL layer  44  is disposed in the airtight space  48  and positioned on an upper surface of the second transparent substrate  42  for displaying a second image through the second transparent substrate  42 .  
      The first protection layer  45  is positioned on a bottom surface of the first EL layer  43 , and the second protection layer  46  is positioned on an upper surface of the second EL layer  44 . The first protection layer  45  is comprised of a first barrier layer  451  and a desiccant layer  452 , and the second protection layer  46  is comprised of another barrier layer. As shown, the first barrier layer  451  is laminated between the first EL  43  and the desiccant layer  452 . The desiccant layer  452  positioned on a bottom surface of the first barrier layer  451  can be formed by evaporating or sputtering.  
      The first transparent substrate  41  is sealed to the second transparent substrate  42  by a sealing material  47  and thus an airtight space  48  can be formed between the first transparent substrate  41  and the second transparent substrate  42  for accommodating the EL layers  43 , 44 .  
      The mentioned desiccant layer  452  can be a hydroscopic agent selected from the group of active metals, metallic oxides, and metallic sulfides.  
      The barrier layer,  451  or  46 , is used to provide the EL layer,  43  or  44  respectively, from possible damage of chemical materials which may come from the desiccant layer absorbing ambient mist. The material for the barrier layer  451  or  46  can be selected from the group consisting of nonconductors (such as SiN—SiO—SiC) and low activity metals (for example, Ag—Ti). By adding the desiccant layer  452 , the lifetime of the dual-sided display  4  can be substantially prolonged.  
      In this embodiment, the first EL layer  43  has a surface area the same as that of the second EL layer  44 , and the desiccant layer  452  extends to cover all over the barrier layer  451  that has an area about equal to that of the first EL  43 . In the case that the relative sizing of the first and the second ELs  43 , 44  is changed to leave a sufficient room for the desiccant layer  452  to surround either the first EL  43  or the second EL  44 , the desiccant layer  452  can be alternatively positioned on the non-display area as described in the foregoing second preferred embodiment.  
      In the present invention, the existence of the barrier layers  451 , 46  for protecting the EL layers  43 , 44  lessens the need of the desiccant layer  452 . Please refer to  FIG. 5 , which shows a cross-section view of a fourth preferred embodiment of the OLED display of the present invention.  
      Referring to  FIG. 5 , the dual-sided display  5  comprises a first transparent substrate  51 , a second transparent substrate  52 , a first EL layer  53 , a second EL layer  54 , a first barrier layer  55 , and a second barrier layer  56 . As shown, the arrangement of the dual-sided display  5  in  FIG. 5  is exact the same as that shown in  FIG. 4 , except that the desiccant layer is removed in this fourth embodiment  5 .  
      In the embodiment, either the first barrier layer  55  or the second barrier layer  56  can be a desiccant layer.  
      In the present invention, all the EL layers mentioned above can be composed of organic light emitting diodes (OLED) or polymer light emitting diodes (PLED). The thickness of the dual-sided display of the invention can be reduced to range about 0.6-1.4 mm, which is thinner than that mentioned in the prior art. Additionally, one more advantage of the invention is that the production cost can be lowered and the manufacturing process can be much simpler than the conventional process of composing two independent OLED displays.  
      While the present invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be without departing from the spirit and scope of the present invention.