Abstract:
An encapsulation of an organic electro-luminescence element is provided. A luminescent body is formed on the inner surface of a first substrate. A second substrate serves as a planar sealing case. A sealing agent is formed on the rims of the first substrate and the second substrate to bond the first substrate and the second substrate and form an airtight space. A first drying layer is formed on the inner surface of the second substrate within the airtight space.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an organic electro-luminescence (EL) element for a display device and, more particularly, to an encapsulation of an organic EL element for a display device.  
           [0003]    2. Description of the Related Art  
           [0004]    In an electro-luminescence (EL) element used for a display device, electric current applied to specific fluorescence or phosphorus transforms electricity into luminosity. Based on the materials utilized in a luminescent layer, EL elements are classified into organic and inorganic, wherein the organic EL element employs laminated organic layers having advantages such as thin profile, light-weight, high luminescent efficiency, and low driving voltage. Moreover, based on the materials utilized in an organic luminescent layer, the organic EL elements are classified into molecule-based devices and polymer-based devices. The molecule-based device employs dyes or pigments to form an organic luminescent layer called an organic light emitting display (OLED) The polymer-based device employs conjugate macromolecule to form an organic luminescent layer called a polymer light emitting display (PLED).  
           [0005]    In order to prevent the internal space of an organic EL element from developing high humidity, a sealing case is commonly used to package a glass substrate on which metal electrodes and one or more organic luminescent layers are formed. Also, in order to prolong the active lifetime, a desiccant is provided-to absorb moisture and impurities generated in the interior space, the water and oxygen permeating from the atmosphere, and the moisture generated from the outgassing effect caused by the bonding agent on the rim of the sealing case. Furthermore, various technologies for reducing interior humidity have been developed to eliminate dark spots, such as forming photo-hardened resin on the glass substrate, plating a metal oxide, fluoride or sulfide on the glass substrate, forming a water-resistant film on the glass substrate, and using an airtight case to package the organic EL element. Nevertheless, other problems, such as leakage current, crosstalk and oxide dissolution, remain to be solved.  
           [0006]    As shown in FIG. 1, U.S. Pat. No. 5,882,761 discloses an encapsulation  1  of an organic EL element, which comprises a glass substrate  10 , a sealing agent  9  composed of a UV-cured resin formed on the rim of the glass substrate  10 , and a sealing case  7  bonded to the glass substrate  10  by the sealing agent  9 . Thus, an internal space  11  formed by the glass substrate  10  and the sealing case  7  becomes an airtight space. In the airtight space, a lamination body  6  formed on the glass substrate  10  comprises an anode layer  3 , an organic luminescent material layer  4 , and a cathode layer  5 . A drying substance  8  may be disposed on the bottom of the sealing case  7  and separated from the lamination body  6  by an internal space  11  filled with dried inert gas. The drying substance  8  comprises a solid compound, such as BaO, CaO, CaSO 4 , and CaCl 2 , which chemically absorbs moisture and remains in solid state. The drying substance  8  is a sheet body fixed on the concave of the sealing case  7  via bonding.  
           [0007]    To provide an attachment area for the drying substance  8 , however, the fabrication of the sealing case  7  having a concave bottom necessitates an all-in-one technology, which may encounter problems, such as shaping difficulties, high process costs, and a difficult in applying to glass materials. Also, as the depth of the concave of the sealing case  7  increases, the volume of the internal space  11  increases to provide a larger space for accommodating moisture and oxygen, resulting in an uncertainty of the moisture-absorbing effectiveness provided by the drying substance  8 . Moreover, the design of the sealing case  7  having a concave will unfavorably increase the thickness of the encapsulation structure, which does not conform to the development trend toward light-weight, thin profile and small size characteristics of the panel display.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention provides an encapsulation of an organic electro-luminescence element for a display device and a method for encapsulating the same to solve the problems accompanied by the prior art.  
           [0009]    In an encapsulation of an organic electro-luminescence element for a display device, a luminescent body is formed on the inner surface of a first substrate. A second substrate serves as a planar sealing case. A sealing agent is formed on the rims of the first substrate and the second substrate to bond the first substrate and the second substrate and form an airtight space. A first drying layer is formed on the inner surface of the second substrate within the airtight space.  
           [0010]    Accordingly, it is an object of the invention to form the drying layer on the planar sealing case by sputtering to simplify the encapsulating process.  
           [0011]    It is another object of the invention to form the drying layer on the planar sealing case by sputtering to reduce process cost of the sealing case.  
           [0012]    Yet another object of the invention is to form the drying layer on the planar sealing case by sputtering to increase material selectivity of the sealing case.  
           [0013]    It is a further object of the invention to provide a combination of the sealing case having a planar profile and the drying layer with an extremely thin deposition, resulting in a smaller volume of the internal space  32  as compared with the prior art.  
           [0014]    These and other objects and advantages of the present invention will become readily apparent upon further reference to the following detailed description and the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a sectional diagram showing an encapsulation of an organic EL element according to the prior art;  
         [0016]    [0016]FIG. 2 is a sectional diagram showing an encapsulation of an organic EL element according to the first embodiment of the present invention; and  
         [0017]    [0017]FIG. 3 is a sectional diagram showing an encapsulation of an organic EL element according to the second embodiment of the present invention. 
     
    
       [0018]    Similar reference numerals denote corresponding features consistently throughout the attached drawings.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    [First Embodiment] 
         [0020]    [0020]FIG. 2 is a sectional diagram showing an encapsulation of an organic EL element according to the first embodiment of the present invention. The encapsulation  20  of an organic EL element comprises a substrate  22 , a sealing agent  24  formed on the rim of the substrate  22 , and a sealing case  26  bonded to the substrate  22  by the sealing agent  24 . Thus, the substrate  22  and the sealing case  26  form an airtight space. Preferably, the substrate  22  is a transparent insulating material such as glass, polymer, or ceramic. The sealing agent  24  may be composed of a UV-cured resin, and the sealing case  26  is preferably a plane substrate made of glass, polymer, ceramic, or metal.  
         [0021]    Also, on the inner surface of the substrate  22 , a lamination body  28  is formed by an anode layer  25 , an organic luminescent material layer  27  and a cathode layer  29 . A drying layer  30  is deposited on the inner surface of the sealing case  26  by sputtering and separated from the lamination body  28  by an internal space  32 . In this preferred embodiment of the present invention, the drying layer  30  is a metal oxide (e.g. alkaline metal oxide and alkaline-earth metal oxide), metal sulfide, metal halide, metal perchlorate, or a highly active metal (e.g. alkaline metal and alkaline-earth metal). Preferably, the thickness of the drying layer  30  is less than 10 μm.  
         [0022]    The drying layer  30  is sputtered on the inner surface of the sealing case  26  so that it is not necessary to form a concave on the sealing case  26  by an additional shaping process, or fill the internal space  32  with other drying substances. This not only simplifies the encapsulating process and therefore reduces process cost of the sealing case  26 , but also increases material selectivity of the sealing case  26 . Moreover, since sputtering can easily control the quality and thickness of the drying layer  30 , a combination of the sealing case  26  having a planar profile and the drying layer  30  with an extremely thin deposition can result in a smaller volume of the internal space  32  as compared to the prior-art. This feature also conforms to the development trend toward light-weight, thin profile, and small size characteristics of the panel display.  
         [0023]    [Second Embodiment] 
         [0024]    [0024]FIG. 3 is a sectional diagram showing an encapsulation of an organic EL element according to the second embodiment of the present invention. An encapsulation  40  of an organic EL element comprises a substrate  42 , a sealing agent  44  formed on the rim of the substrate  42 , and a sealing case  46  bonded to the substrate  42  by the sealing agent  44 . Thus, the substrate  42  and the sealing case  46  form an airtight space. Preferably, the substrate  42  is a transparent insulating material such as glass, polymer, or ceramic. The sealing agent  44  may be composed of a UV-cured resin, and the sealing case  46  is a plane substrate made of glass, polymer, ceramics, or metal.  
         [0025]    Also, a lamination body  48  including an anode layer  45 , an organic luminescent material layer  47  and a cathode layer  49  is formed on the inner surface of the substrate  42 . In this preferred embodiment of the present invention, a buffering layer  54  is deposited on the substrate  42  to cover the lamination body  48 , and a second drying layer  50 II is deposited on the substrate  42  to cover the buffering layer  54 . Furthermore, a first drying layer  50 I is deposited on the inner surface of the sealing case  46 , and separated from the second drying layer  50 II by an internal space  52 . Preferably, the buffering layer  54  is a high dielectric constant material, or a polymer material with a high dielectric constant. In this preferred embodiment of the present invention, the first drying layer  50 I and the second drying layer  50 II are both formed by sputtering. Preferably, the drying layers  50 I and  50 II are metal oxides (e.g. alkaline metal oxide and alkaline-earth metal oxide), metal sulfide, metal halide, metal perchlorate, or a highly active metal (e.g. alkaline metal and alkaline-earth metal). Preferably, the thicknesses of both drying layers  50 I and  50 II are less than 10 μm.  
         [0026]    As compared with the first embodiment of the present invention, the second embodiment advantageously forms a protection structure including the buffering layer  54  and the second drying layer  50 II on the lamination body  48  to provide a better drying effect and a longer lifetime for the organic EL element. Also, the combination of the first drying layer  50 I, the second drying layer  50 II and the buffering layer  54  can further reduce the volume of the internal space  52 .  
         [0027]    While the present invention has been described with reference to specific embodiments thereof, it is to be understood that the present invention is not limited to the embodiments described above, but rather encompasses any and all embodiments within the spirit and scope of the present invention as set forth in the claims.