Patent Publication Number: US-2011050083-A1

Title: Plasma display panel

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2009-0080700, filed Aug. 28, 2009, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     One or more embodiments relate to a plasma display panel (PDP). 
     2. Description of the Related Art 
     Plasma display panels (PDPs) are a type of flat display device that forms images of visible light produced from a phosphor material excited with ultraviolet (UV) rays generated by a plasma discharge. 
     In a general structure of the PDP, a front substrate, having discharge electrodes arranged thereon, and a rear substrate, having address electrodes arranged thereon, are attached to each other to face each other by interposing a plurality of barrier walls, which define a plurality of discharge cells, between the front and rear substrates. Then, a discharge gas is injected between the two substrates. A phosphor material coating the discharge cells, formed as a phosphor layer, is excited by applying a discharge voltage between the discharge electrodes resulting in images being formed of visible light generated as a result of the excitation. 
     In general, a large portion of the phosphor layer is attached to side surfaces of the barrier walls. However, the phosphor material may be a flowable paste such that the phosphor material sags and flows down from the side surfaces of the barrier walls resulting in the phosphor layer not being formed with a sufficiently large and uniform thickness. In addition, the visible light generated from the phosphor layer disposed on the side surfaces of the barrier walls is not emitted in an upward, display direction but rather in a direction orthogonal to the barrier walls. Consequently, visible light extraction efficiency therefrom is low. Furthermore, since bottom surfaces of the discharge cells on which the phosphor material is concentrated are relatively far from the front substrate where the discharge electrodes are arranged, a sufficient amount of UV light does not reach the phosphor layer and thus fails to effectively excite the phosphor layer. Since an address discharge occurs along a long discharge path corresponding to the height of a discharge cell, a high address driving voltage is required, and a sufficient voltage margin is not obtained. 
     SUMMARY 
     One or more embodiments includes a highly efficient plasma display panel (PDP) that can be driven with low power and obtain high luminous brightness. 
     According to one or more embodiments, a PDP includes a front substrate and a rear substrate that face each other; a pair of base portions disposed between the front substrate and the rear substrate and are concavely indented in directions away from each other; barrier walls disposed on the pair of base portions to define a discharge cell; a scan electrode and a sustain electrode that generate a mutual discharge in the discharge cell; an address electrode to cross the scan electrode and that generates an address discharge together with the scan electrode; a phosphor layer disposed in the discharge cell; and a discharge gas injected into the discharge cell. 
     According to one or more embodiments, the base portions may include maximally indented summits at portions of the base portions which face a center of the discharge cell. 
     According to one or more embodiments, the concave indentations of the base portions may be concave curves having the summits. 
     According to one or more embodiments, the concave indentations of the base portions may be concave V shapes having the summits. 
     According to one or more embodiments, a distance between the base portions facing each other may be at a maximum at the centers of the base portions. 
     According to one or more embodiments, the scan electrode and the address electrode may cross in an area aligned with the base portions or cross in an area adjacent to the base portions. 
     According to one or more embodiments, the address electrode may include discharge portions and connecting portions, the discharge portions each having a relatively large line width with respect to the connecting portions, and the connecting portions each having a relatively small line width with respect to the discharge portions. According to one or more embodiments, the discharge portions may be disposed on the rear substrate under at least one of the base portions. 
     According to one or more embodiments, a non-discharge space may be disposed between adjacent barrier walls. According to one or more embodiments, a light absorbing layer may be disposed in the non-discharge space. 
     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 an exploded perspective view of a plasma display panel (PDP) according to an embodiment; 
         FIG. 2  is a vertical cross-section taken along line II-II of  FIG. 1 ; 
         FIG. 3  is an exploded perspective view of a part of the PDP of  FIG. 1 ; 
         FIGS. 4 and 5  show a phosphor flow caused during baking and hardening of phosphor paste, wherein  FIG. 4  is a plan view of a discharge cell of the PDP of  FIG. 1  and  FIG. 5  is a vertical cross-section taken along line V-V of  FIG. 4 ; 
         FIG. 6  is a perspective view of a PDP according to another embodiment; 
         FIG. 7  is an exploded perspective view of a PDP according to another embodiment; and 
         FIG. 8  is an exploded perspective view of a PDP according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present embodiments, 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. 
       FIG. 1  is an exploded perspective view of a plasma display panel (PDP) according to an embodiment, and  FIG. 2  is a vertical cross-section taken along line II-II of  FIG. 1 . Referring to  FIGS. 1 and 2 , the PDP includes a front substrate  110  and a rear substrate  120  that face and are apart from each other, and a plurality of discharge cells S are interposed between the front substrate  110  and the rear substrate  120 . 
     A pair of base portions  123  is arranged in each discharge cell S on the rear substrate  120 , and barrier walls  124 , having smaller widths than the base portions  123 , are arranged on the base portions  123 . The barrier walls  124  and the base portions  123  may be integrally or separately formed. The barrier walls  124  include first barrier walls  124   a  that extend in a first direction (i.e., a Z 2  direction as shown in  FIG. 1 ) and second barrier walls  124   b  that extend in a second direction (i.e., a Z 1  direction as shown in  FIG. 1 ). However, aspects are not limited thereto such that the second barrier walls  124   b  need not be included. The first and second barrier walls  124   a  and  124   b  may have widths in the first and second directions, respectively, that are smaller than the widths of the base portions  123  in the first and second directions, respectively. The barrier walls  124  (i.e., first and second barrier walls  124   a  and  124   b ) define a discharge cell S that corresponds to or aligns with a scan electrode Y and a sustain electrode X, which generate a mutual display discharge, and each discharge cell S constitutes an independent light-emission unit. The base portions  123  form steps within the discharge cells S that extend from the first barrier walls  124   a  in the first direction (the Z 2  direction) toward centers of the discharge cells S. 
     A non-discharge space  130  may be defined between barrier walls  124  which define different discharge cells S. As shown in  FIGS. 1 and 2 , the non-discharge spaces  130  may be disposed between first barrier walls  124   a  that define adjacent discharge cells S in the first direction (i.e., the Z 1  direction), but aspects are not limited thereto such that the non-discharge spaces  130  may be disposed between the second barrier walls  124   b  that define adjacent discharge cells S in the second direction (i.e., the Z 2  direction). The non-discharge space  130  provides a passage for impurity gas to flow so that a flow resistance in a process of exhausting impurity gas remaining in a panel may be reduced. A light absorption layer  140  may be disposed in, on, or to align with the non-discharge space  130 . The light absorption layer  140  may be an external light absorption layer. The light absorption layer  140  may include a dark-colored pigment or a dark-colored material and improves a contrast characteristic and visibility of an image. However, the light absorption layer  140  is optional and need not be included in all aspects. 
     The sustain electrode X and the scan electrode Y, which generate a mutual display discharge, are arranged on the front substrate  110 . The sustain electrodes X and the scan electrodes Y, are paired such that the sustain electrodes X and the scan electrodes Y generate a display discharge in discharge cells S corresponding to the pair. The sustain electrode X and the scan electrode Y include transparent electrodes Xa and Ya, respectively, which are formed of a phototransparent conductive material, and bus electrodes Xb and Yb, respectively, which electrically contact the transparent electrodes Xa and Ya and form power supply lines. As shown in  FIGS. 1 and 2 , the light absorption layer  140  is disposed on an internal surface of the front substrate  110  to align with the non-discharge space  130 . The light absorption layer  140  may be further disposed on the transparent electrodes Xa and Ya of adjacent sustain electrodes X and the scan electrodes Y of adjacent discharge cells S, i.e., adjacent sustain electrodes X and the scan electrodes Y that are not paired as further described below. Further, the bus electrodes Xb and Yb may be disposed on the light absorption layer  140  so as to be electrically connected to the transparent electrodes Xa and Ya, respectively. 
     The sustain electrode X and the scan electrode Y are buried in a dielectric layer  114  disposed on the front substrate  110  so as not to be exposed to a discharge environment of the discharge cells S, thereby being protected from direct collision of charged particles participating in the discharge. The dielectric layer  114  may be protected by being covered with a protection layer  115  which is formed of, for example, an MgO thin layer. 
     Address electrodes  122  are arranged on the rear substrate  120 . The address electrodes  122  perform address discharges with the scan electrodes Y. The scan electrodes Y and the address electrodes  122  may cross each other in areas of the discharge cells S corresponding to or aligning with the base portions  123  or areas of the discharge cells S adjacent to the base portions  123 . A voltage applied between one the scan electrodes Y and one of the address electrode  122  forms a high electric field sufficient for discharge firing in the discharge cell S in which the scan electrode Y and the address electrode  122  cross via the dielectric layer  114  (or the protection layer  115 ) covering the scan electrodes Y and via the base portions  123  on the address electrodes  122 . At this time, the dielectric layer  114  (or the protection layer  115 ) covering the scan electrodes Y and the base portions  123  on the address electrodes  122  form discharge surfaces that face each other, thereby generating the address discharge. 
     In a conventional structure, a discharge is generated between scan electrodes and address electrodes via a long discharge path between the front substrate and the rear substrate. In contrast, according to aspects, since the address discharge is performed via the base portions  123  protruding from the rear substrate  120  toward the scan electrodes Y by a height h, the address discharge path is reduced to the size of a discharge gap g (see  FIG. 2 ) above the base portions  123  so that a driving efficiency may be improved compared to the conventional structure. Further, a dielectric layer  121  may be disposed on the rear substrate  120  to cover the address electrodes  122  such that the address electrodes  122  may be buried in the dielectric layer  121  disposed above the rear substrate  120 . In such case, the base portions  123  may be disposed on a flat surface provided by the dielectric layer  121 . 
     Phosphor layers  125  are disposed on the dielectric layers  121  between the base portions  123 . The phosphor layers  125  generate visible rays of different colors, for example, red (R), green (G), and blue (B), by interacting with ultraviolet rays generated as a result of the display discharge. The position of the phosphor layers  125  is not limited to the position between the base portions  123  in the discharge cells S, and may extend to a neighboring position so as to cover parts of the base portions  123 . For example, the phosphor layers  125  may continuously extend to upper surfaces  123 U of the base portions  123 , and further to the side surfaces of the barrier walls  124 . Further, the phosphor layers  125  may be continuously extended up sides of the first and second barrier walls  124   a  and  124   b.    
     Portions of the phosphor layers  125  disposed on the upper surfaces  123 U of the base portions  123  are close to the scan electrode Y and the sustain electrode X and thus may be effectively excited. Also, the upper surfaces  123 U of the base portions  123  are arranged close to the front substrate  110 , which includes a display surface  110   a , so as to face in a display direction (i.e., a Z 3  direction of  FIG. 1 ). Thus, visible rays VL of  FIG. 2  emitted from the phosphor layers  125  on the base portions  123  may comparatively more quickly exit the display surface  110   a , and an extraction efficiency of the visible ray VL may be improved. 
       FIG. 3  is an exploded perspective view of a part of the PDP of  FIG. 1 . Referring to  FIG. 3 , side surfaces  123 S of the base portions  123  are indented so as to be concave with respect to the center of the discharge cell S. In detail, the side surfaces  123 S of a pair of base portions  123  have concave shapes that are indented in directions farther from the respective other parts of the base portions  123  (directions ±Z 2 ). The side surfaces  123 S of the base portions  123  have V shapes in which summits P are disposed at the centers of the base portions  123  in the Z 1  direction, which face the center of each discharge cell S. A distance between the side surfaces  123 S of the base portions  123  facing each other is a maximum Lmax at the summits P among the entire side surfaces  123 S of the base portions  123 . Accordingly, a sufficient distance of Lmax that enables a display discharge to occur without interference of the base portions  123  is secured, whereby charge loss, in which charged particles participating in the display discharge are lost due to collision with the base portions  123 , may be reduced. 
       FIGS. 4 and 5  show a phosphor flow caused during baking and hardening of phosphor paste  125 ′.  FIG. 4  is a plan view of a discharge cell S, and  FIG. 5  is a vertical cross-section taken along line V-V of  FIG. 4 . Referring to  FIG. 4 , when the base portions  123  have flat side surfaces  123 S′, the phosphor paste  125 ′ coated on edges e of the base portions  123  are subject to left and right surface tensions. Referring to  FIG. 5 , the phosphor paste  125 ′ coated on the edges e of the base portions  123  are also subject to surface tension in upward and downward sides where a relatively large amount of phosphor paste  125 ′ has been coated. Consequently, a small amount or none of the phosphor paste  125 ′ remains on the edges e of the base portions  123 , so that the luminous brightness degrades. As indicated by dotted lines of  FIG. 4 , when the base portions  123  have concave side surfaces  123 S, the side surfaces  123 S of the base portions  123  are relatively farther away from a center of the discharge cells S compared to the flat side surfaces  123 S′ (see  FIG. 5 ). Thus, phosphor paste  125 ′ may more thickly accumulate in the center of the discharge cell S when the base portions  123  have the concave side surfaces  123 S than in the case where the base portions  123  have the flat side surfaces  123 S′ by reducing phosphor paste detachment caused due to surface tension. 
     The shape of the base portions  123  is not limited to the above example, and the base portions  123  may be modified into other various shapes as long as they are indented concavely.  FIG. 6  illustrates a PDP including base portions  223  according to another embodiment. Side surfaces  223 S of the base portions  223  may be formed along concave curves that have summits P′ at the centers, in the Z 1  direction, of the base portions  223 , which face the center of each discharge cell S. Accordingly, the side surfaces  223 S of the base portions  223  may be formed along concave curves having an arbitrary curvature, including semicircular or oval lines. The barrier walls  124  and the base portions  223  may be integrally or separately formed. 
     A discharge gas (not shown) is injected into the discharge cells S. The discharge gas may be a multi-element gas in which xenon (Xe), krypton (Kr), helium (He), neon (Ne), and the like, capable of providing UV light through discharge excitation, are mixed at a determined volumetric ratio. 
     Table 1 shows the result of an experiment for showing effects achieved by forming a base portion having a concave side surface. A base portion according to an embodiment had a concave V shape, while a base portion according to a comparative example had a flat plane, i.e., the side surfaces of the base portions had a concave V shape and flat shape, respectively. The Experimental Example had the same structure as the Comparative Example except for the shape of a base portion. In the experiment, a discharge gas of Xe 15%-He 61% was used, and the driving efficiency represents brightness per consumed unit power. The driving efficiency was measured when 30% of all effective cells were lit. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Experimental 
                 Comparative 
               
               
                 Remarks 
                 Example 
                 Example 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Discharge voltage 
                 sustain voltage (V) 
                 228 
                 237 
               
               
                   
                 address voltage (V) 
                 194 
                 197 
               
               
                 Driving efficiency 
                 driving efficiency 
                 1.59 
                 1.5 
               
               
                 (30% Load) 
                 (cd/W) 
               
               
                   
                 luminous brightness 
                 650 
                 590 
               
               
                   
                 (cd) 
               
               
                   
                 Consumed power 
                 409 
                 393 
               
               
                   
                 (W) 
               
               
                 Discharge delay 
                 Delay time (nsec) 
                 946 
                 1014 
               
               
                   
               
            
           
         
       
     
     According to the results of the experiment, the sustain voltage and the address voltage in the Experimental Example were smaller than those in the Comparative Example, and the driving efficiency in the Experimental Example was higher than that in the Comparative Example. In addition, a delay time between the moment when a discharge firing signal was applied and the moment when actual discharge occurred was reduced in the Experimental Example with respect to the Comparative Example. 
       FIG. 7  is an exploded perspective view of a PDP according to another embodiment. As described above with reference to  FIGS. 1 through 5 , the scan electrodes Y and address electrodes  222  generate an address discharge through the base portions  123  each having the height h, thereby reducing a discharge gap and accelerating the address discharge. 
     In the present embodiment, the line width of each of the address electrodes  222  varies along the length direction thereof, i.e, the Z 2  direction. In detail, each of the address electrodes  222  includes discharge portions  222   a , having large line widths Wa, and connecting portions  222   b , having small line widths Wb, between the discharge portions  222   a . The discharge portions  222   a  are disposed directly under the base portions  123  and are arranged to face the scan electrodes Y. Since the discharge portions  222   a  are formed to have the large line widths Wa, a high electric field may be formed through the base portions  123 , and the address discharge by the discharge portions  222   a  and the scan electrodes Y may be accelerated. The connecting portions  222   b  connect the discharge portions  222   a  together so as to form a single electrode unit and transmit a driving signal to each of the discharge portions  222   a.    
       FIG. 8  is an exploded perspective view of a PDP according to another embodiment. In the present embodiment, a non-discharge space is not disposed between adjacent discharge cells S. In detail, a barrier wall  324  is disposed at an almost-center position of a base portion  323 , and the barrier wall  324  defines two adjacent discharge cells S. The barrier walls  324  and the base portions  323  may be integrally or separately formed. 
     As described above, in a PDP according to the one or more of the above embodiments, phosphor layers are disposed on planes that are close to discharge electrodes that generate a mutual display discharge and to a display plane, so that phosphor may be more effectively excited and the visible light extraction efficiency may increase. In particular, the shape of a base portion is suitably designed by analyzing the flow of flowable phosphor paste so that the paste is securely attached, thereby increasing overall display light emission. The shape of a base portion is also designed in consideration of a discharge path, thereby decreasing charge loss that occurs when charged particles participating in discharge are uselessly lost due to collisions with the base portions or other interferences. Due to shortening of an address discharge path, low-voltage addressing is possible, and a sufficient voltage margin may be secured. 
     Although a few embodiments 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.