Abstract:
Provided is a flat panel display apparatus including a sealant which has a small effective width and is able to effectively attach a substrate and an encapsulation substrate. The flat panel display apparatus includes the substrate, a display unit disposed on the substrate, the encapsulation substrate disposed facing the substrate so that the display unit is disposed on inner side of the encapsulation substrate, and the sealant attaching the substrate and the encapsulation substrate, wherein an end surface of the sealant facing the substrate contacts a silicon oxide layer disposed on the substrate.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2008-0114747, filed on Nov. 18, 2008, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present embodiments relate to a flat panel display apparatus, and more particularly, to a flat panel display apparatus including a sealant that has a small effective width and is able to effectively attach a substrate and an encapsulation substrate. 
     2. Description of the Related Art 
     In some flat panel display apparatuses, a substrate including a display unit and an encapsulation substrate covering the display unit are attached to each other by using a sealant. Such a sealant is generally disposed outside the display unit, covering the display unit. 
       FIG. 1  is a photograph showing bubbles A formed inside a sealant of a conventional flat panel display apparatus, and  FIG. 2  is another photograph showing bubbles formed inside the sealant of the conventional flat panel display apparatus. In detail,  FIGS. 1 and 2  are photographs when a silicon nitride layer is disposed on a substrate including a display unit and a sealant is disposed between the silicon nitride layer and a rear substrate. In such a conventional flat panel display apparatus, sizes of the bubbles A formed in the sealant reach up to 10 μm, and thus attachment of a substrate and the rear substrate may be weak. Strength of the sealant where the bubbles A are formed is weak, and thus the hardness of the sealant attaching the substrate and the rear substrate may deteriorate. Also, the bubbles A are generated in the sealant while coating and hardening the sealant, and thus a width of the hardened sealant is remarkably larger than a width of the sealant first coated due to the generation of the bubbles A. In  FIG. 2 , a width of the sealant that is hardened reaches up to approximately 600 μm due to the bubbles. 
     SUMMARY OF THE INVENTION 
     The present embodiments provide a flat panel display apparatus including a sealant that has a small effective width and is able to effectively attach a substrate and an encapsulation substrate. As one of skill in the art would realize, when an element is referred to as being “on” another element, it can be directly on the element or it can be indirectly on the element with one or more intervening elements interposed therebetween. Also, when an element is referred to as being “connected to” another element, it can be directly connected to the element or it can be indirectly connected to the element with one or more intervening elements interposed therebetween. 
     According to an aspect of the present embodiments, there is provided a flat panel display apparatus including: a substrate; a display unit disposed on the substrate; an encapsulation substrate disposed to face the substrate so that the display unit is interposed between the substrate and the encapsulation substrate; and a sealant attaching the substrate and the encapsulation substrate, wherein an end surface of the sealant facing the substrate contacts a silicon oxide layer disposed on the substrate. 
     An end surface of the sealant facing the encapsulation substrate may contact a surface of the encapsulation substrate facing the substrate. 
     The sealant may include bismuth. 
     The sealant may be melted by irradiating a laser beam and then hardened. 
     A bubble may not exist inside the sealant. 
     The silicon oxide layer may be extended from inside the display unit to outside the display unit. 
     A silicon nitride layer may be disposed between the silicon oxide layer and the substrate. 
     The sealant may not contact the silicon nitride layer. 
     A thickness of the silicon oxide layer may be 2000 Å or above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present embodiments will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a photograph showing bubbles formed inside a sealant of a conventional flat panel display apparatus; 
         FIG. 2  is another photograph showing bubbles formed inside a sealant of a conventional flat panel display apparatus; 
         FIG. 3  is a cross-sectional view schematically illustrating a flat panel display apparatus, according to an embodiment; 
         FIG. 4  is a cross-sectional view schematically illustrating an enlarged portion of the flat panel display apparatus of  FIG. 3 ; 
         FIG. 5  is a photograph illustrating bubbles formed inside a sealant of the flat panel display apparatus of  FIG. 3 ; 
         FIG. 6  is another photograph illustrating bubbles formed inside the sealant of the flat panel display apparatus of  FIG. 3 ; and 
         FIG. 7  is a photograph illustrating bubbles formed inside a sealant of a flat panel display apparatus according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, the present embodiments will be described more fully with reference to the accompanying drawings, in which exemplary embodiments are shown. 
       FIG. 3  is a cross-sectional view schematically illustrating a flat panel display apparatus, according to an embodiment. 
     Referring to  FIG. 3 , the flat panel display apparatus includes a substrate  110 , a display unit  100 , an encapsulation substrate  600 , and a sealant  700 . The substrate  110  may be formed of various materials, such as a glass material, a metal material, or a plastic material etc. The display unit  100  is disposed on the substrate  110 , and may include various display devices. For example, when the flat panel display apparatus of  FIG. 3  is an organic light emitting display apparatus, the display unit  100  may include an organic light emitting device as a display device. The encapsulation substrate  600  is disposed to face the substrate  110 , and, the encapsulation substrate  600  is disposed to face the substrate  110  so that the display unit  100  is interposed between the substrate  110  and the encapsulation substrate  600 . The encapsulation substrate  600  may also be formed of various materials, such as a glass material, a metal material, and a plastic material etc. The sealant  700  attaches the substrate  110  and the encapsulation substrate  600  disposed as above. Here, an end surface of the sealant  700  facing the substrate  110  contacts a silicon oxide layer  182  disposed on the substrate  110 . An end surface of the sealant  700  facing the encapsulation substrate  600  contacts a surface of the encapsulation substrate  600  facing the substrate  110 . The silicon oxide layer  182  may be extended from inside the display unit  100  to outside the display unit  100 . Details thereof will be described later. 
     As described above, a sealant is disposed between a silicon nitride layer and a rear substrate, and thus an end surface of the sealant facing a substrate contacts the silicon nitride layer disposed on the substrate. Here, while hardening the sealant, sizes of bubbles formed in the sealant reach up to 10 μm, and thus attachment between the substrate and the rear substrate by using the sealant may be weak. Also, a plurality of bubbles are generated in the sealant while coating and hardening the sealant. Due to the generation of the bubbles, a width of the sealant that is finally hardened is remarkably bigger than a width of the sealant that is first coated. 
     While not wishing to be bound to a particular theory, one reason that the bubbles are generated in the sealant is related to a process of manufacturing the silicon nitride layer below the sealant. The silicon nitride layer is formed by synthesizing SiH 4  and NH 3  in gas statuses, and here, SiN 2  and/or SiNH is formed. The sealant is melted and then hardened with a laser beam, and thus when the laser beam is directed to the sealant so as to harden the sealant, H 2  is evaporated thereby forming the bubbles in the sealant. This is because the evaporated H 2  may penetrate into the sealant that has fluidity, while the sealant is melted. 
     Accordingly unlike a conventional flat panel display apparatus, in the flat panel display apparatus according to the current embodiment, the end surface of the sealant  700  facing the substrate  110  contacts the silicon oxide layer  182  instead of the silicon nitride layer. Here, a reaction like the silicon nitride layer is not generated while using a laser beam to harden the sealant  700  after coating the sealant  700 . Accordingly, bubbles are prevented from being generated in the sealant  700 , and the final width of the sealant  700  is thinner than that of a conventional sealant. 
       FIG. 4  is a cross-sectional view schematically illustrating an enlarged portion of the flat panel display apparatus of  FIG. 3 , a cross-sectional view of an edge of an organic light emitting display apparatus. Referring to  FIG. 4 , the display unit  100  includes an organic light emitting device  200 , which includes a pixel electrode  210 , a facing electrode  230  facing the pixel electrode  210 , and an intermediate layer  220  including at least a light emitting layer disposed between the pixel electrode  210  and the facing electrode  230 . Various circuit units, for example, a circuit unit including a thin film transistor TFT 2 , may be disposed outside the display unit  100  on the substrate  110 , beside the organic light emitting device  200  of the display unit  100 . Also, the sealant  700  is disposed on the edge of the substrate  110 , so that the encapsulation substrate  600  covers the display unit  100 . 
     Structures of the display unit  100  and the organic light emitting device  200  will now be described in detail. 
     A thin film transistor TFT 1  is disposed in the display unit  100  on the substrate  110 . The thin film transistor TFT 1  includes source/drain electrodes  170 , a semiconductor layer  130 , and a gate electrode  150 . A gate dielectric layer  140  is disposed between the gate electrode  150  and the semiconductor layer  130  so as to isolate the semiconductor later  130  from the gate electrode  150 , and an interlayer dielectric layer  160  is disposed between the gate electrode  150  and the source/drain electrodes  170  so as to isolate the source/drain electrodes  170  from the gate electrode  150 . A buffer layer  120 , formed of such as SiO 2 , may be disposed between the thin film transistor TFT 1  and the substrate  110 . 
     A first dielectric layer  181 , which is a passivation layer, is disposed on the thin film transistor TFT 1  so as to protect the thin film transistor TFT 1 . The first dielectric layer  181  may be formed of various materials, such as an inorganic matter like silicon nitride or silicon oxynitride, which has excellent performance of protecting the thin film transistor TFT 1 . As illustrated in  FIG. 4 , such a first dielectric layer  181  may not only be formed on the display unit  100  but may also be extended to outside the display unit  100 . Accordingly, when the sealant  700  contacts the first dielectric layer  181 , bubbles may be formed in the sealant  700  as described above while hardening the sealant  700 . Consequently, in the organic light emitting display apparatus according to the current embodiment, a second dielectric layer  182  formed of silicon oxide is formed on the first dielectric layer  181 . Ultimately, a silicon nitride layer (the first dielectric layer  181 ) is disposed below a silicon oxide layer (the second dielectric layer  182 ) facing the substrate  110 . Accordingly, the sealant  700  contacts the second dielectric layer  182  formed of silicon oxide instead of the first dielectric layer  181  formed of silicon nitride, and thus a plurality of big bubbles are effectively prevented from being generated in the sealant  700 . In the structure as illustrated in  FIG. 4 , when a laser beam is used to harden the sealant  700 , the laser beam may be used on the first dielectric layer  181  besides the sealant  700  and the second dielectric layer  181 . In this case, H 2  may be evaporated in the first dielectric layer  181 , and thus a thickness of the second dielectric layer  182  may be formed to at least about 2000 Å, so that the evaporated H 2  does not move to the sealant  700 . When the thickness of the second dielectric layer  182  is at least about 2000 Å,  112  that is evaporated in the first dielectric layer  181  due to the laser beam does not pass through the second dielectric layer  182 . 
     The organic light emitting device  200  including the pixel electrode  210 , the intermediate layer  220 , and the facing electrode  230 , which are sequentially stacked, is disposed on the second dielectric layer  182 . This will now be described in detail. 
     An opening exposing at least one of the source/drain electrodes  170  of the thin film transistor TFT 1  is formed in the first dielectric layer  181  and the second dielectric layer  182 , and the pixel electrode, which is electrically connected to the thin film transistor TFT 1  by contacting any one of the source/drain electrodes  170  via the opening, is disposed on the display unit  100  of the substrate  110  such as on the second dielectric layer  182 . The pixel electrode  210  may be a transparent electrode or a reflective electrode. When the pixel electrode  210  is a transparent electrode, the pixel electrode  210  may be formed of ITO, IZO, ZnO, or In 2 O 3 , for example. When the pixel electrode  210  is a reflective electrode, the pixel electrode  210  may include a reflective layer formed of Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, or a mixture thereof for example and a layer formed of ITO, IZO, ZnO, or In 2 O 3 , for example. However, a material of the pixel electrode  210  is not limited thereto, and a structure of the pixel electrode  210  is not limited thereto, and may be a single layer or multi layer. 
     A third dielectric layer  183  is disposed on the second dielectric layer  182 . In some embodiments, the third dielectric layer  183  is formed to cover the second dielectric layer  182 . The third dielectric layer  183  is a pixel defining layer that defines a pixel by including an opening corresponding to each sub-pixel, such as an opening that exposes at least a portion, for example, a center portion, of the pixel electrode  210  or the entire pixel electrode  210 . Also as illustrated in  FIG. 4 , the third dielectric layer  183  increases a distance between an end portion of the pixel electrode  210  and the facing electrode  230 , thereby preventing an arc, or the like, from generated in the end portion of the pixel electrode  210 . 
     The intermediate layer  220  of the organic light emitting device  200  may be formed of a low molecular or high molecular material. When the intermediate layer  220  is formed of a low molecular material, a hole injection layer, a hole transport layer, an emission layer, an electron transport layer, and an electron injection layer may be stacked in a single or multi structure. Also, the intermediate layer  220  may be formed of various materials including, for example, copper phthalocyanine (CuPc), (N,N′-Di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB), and tris-8-hydroxyquinoline aluminum (Alq3). The intermediate layer  220  may be formed via a vacuum deposition method, for example. 
     When the intermediate layer  220  is formed of a high molecular material, the intermediate layer  220  can include a hole transport layer and an emission layer. Here, PEDOT (Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) can be used as the hole transport layer and a poly-phenylenevinylene (PPV) based or polyfluorene based high molecular material is used as the emission layer. The intermediate layer  220  may be formed via a screen printing or inkjet printing method. However, a structure of the intermediate layer  220  is not limited thereto. 
     The facing electrode  230  is disposed on the intermediate layer  220 , i.e. on the display unit  100 . As illustrated in  FIG. 4 , the facing electrode  230  may be disposed to cover the display unit  100 . The facing electrode  230  may be a transparent electrode or a reflective electrode. When the facing electrode  230  is a transparent electrode, the facing electrode  230  may include a layer formed of a metal having a low work function, such as, for example, Li, Ca, LiF/Ca, LiF/Al, Al, Ag, Mg, or a mixture thereof, and a transparent conductive layer formed of, for example, ITO, IZO, ZnO, or In 2 O 3 . When the facing electrode  230  is a reflective electrode, the facing electrode  230  may be formed of, for example, Li, Ca, LiF/Ca, LiF/Al, Al, Ag, Mg, or a mixture thereof However, a structure and a material of the facing electrode  230  are not limited thereto. 
       FIG. 5  is a photograph illustrating bubbles formed inside a sealant of the flat panel display apparatus of  FIG. 3 , and  FIG. 6  is another photograph illustrating bubbles formed inside the sealant of the flat panel display apparatus of  FIG. 3 . Comparing  FIG. 5  and  FIG. 1  that shows the bubbles formed in the sealant of the conventional flat panel display apparatus, the diameters of the bubbles formed in  FIG. 1  reach up to about 10 μm, but diameters of the bubbles formed in  FIG. 5  reach up to about 3 μm or lower. Accordingly, attachment between a substrate and a rear substrate is effectively increased. 
     Comparing  FIG. 6  and  FIG. 2  that shows the bubbles formed in the sealant of the conventional flat panel display apparatus, not only the diameter but also the number of bubbles formed in the sealant of the flat panel display apparatus according to the current embodiment are remarkably reduced. Accordingly, even when a width of the sealant first applied while manufacturing the conventional flat panel display apparatus and a width of the sealant first applied while manufacturing the flat panel display apparatus according to the current embodiment are the same, a width of the sealant hardened on the conventional flat panel display apparatus reaches up to 600 μm, whereas a width of the sealant hardened on the flat panel display apparatus according to the current embodiment is below 500 μm. Accordingly, the width of the sealant on the flat panel display apparatus according to the current embodiment is smaller than that of the sealant on the conventional flat panel display apparatus, and the sealant is effectively prevented from being flowing into a display unit while hardening the sealant. 
       FIG. 7  is a photograph illustrating bubbles formed inside a sealant of a flat panel display apparatus according to another embodiment. 
     In  FIG. 5 , which shows the sealant in the flat panel display apparatus according to the previous embodiment, the sealant includes V 2 O 5 . In the flat panel display apparatus according to the previous embodiment, the sealant contacts a silicon oxide layer, but does not directly contact a silicon nitride layer, and thus bubbles are effectively prevented from being formed in the sealant by the silicon nitride layer. However even in this case, small bubbles may be generated as O 2  is evaporated from V 2 O 5  included in the sealant. 
     In order to maximize attachment between a substrate and an encapsulation substrate by using a sealant, bubbles should be prevented from being formed. Accordingly, the sealant may include bismuth instead of V 2 O 5 . Here, as illustrated in  FIG. 7 , bubbles are not formed in the sealant. Of course, the sealant including bismuth contacts the silicon oxide layer but does not directly contact the silicon nitride layer. Accordingly, the attachment between the substrate and the encapsulation substrate is maximized. 
     As described above, the flat panel display apparatus including the sealant, which has a small effective width and effectively attaches the substrate and the encapsulation substrate, can be realized. 
     While the present 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 embodiments as defined by the following claims.