Patent Publication Number: US-7718281-B2

Title: Plasma display panel

Description:
TECHNICAL FIELD 
     The present invention relates to a plasma display panel for use in a display device and the like. 
     RELATED APPLICATIONS 
     This application is the U.S. National Phase under 35 U.S.C. §371 of International Application No. PCT/JP2006/319464, filed on Sep. 29, 2006, which in turn claims the benefit of Japanese Application No. 2005-289788, filed on Oct. 3, 2005, the disclosures of which Applications are incorporated by reference herein. 
     BACKGROUND ART 
     A plasma display panel (herein after referred to as a PDP) can achieve higher definition and have a larger screen. Thus, a television screen using a PDP approx. 65 inch in diagonal is commercially available. 
     A PDP is basically made of a front panel and a rear panel. The front panel includes a glass substrate made of sodium borosilicate glass by the float method, display electrodes that are made of stripe-like transparent electrodes and bus electrodes formed on the principle surface of the glass substrate on one side thereof, a dielectric layer covering the display electrodes and working as a capacitor, and a protective layer that is made of magnesium oxide (MgO) formed on the dielectric layer. On the other hand, the rear panel is made of a glass substrate, stripe-like address electrodes formed on the principle surface of the glass substrate on one side thereof, a primary dielectric layer covering the address electrodes, barrier ribs formed on the primary dielectric layer, and phosphor layers formed between the respective barrier ribs and emitting light in red, green, or blue. 
     The front panel and rear panel are hermetically sealed with the electrode-forming sides thereof faced with each other. A Ne—Xe discharge gas is charged in the discharge space partitioned by the barrier ribs, at a pressure ranging from 400 to 600 Torr. For a PDP, selective application of image signal voltage to the display electrodes makes the electrodes discharge. Then, the ultraviolet light generated by the discharge excites the respective phosphor layers so that they emit light in red, green, or blue to display color images. 
     Silver electrodes are used for the bus electrodes in the display electrodes to ensure electrical conductivity thereof. Low-melting glass essentially consisting of lead oxide is used for the dielectric layer. The examples of a lead-free dielectric layer addressing recent environmental issues are disclosed in Japanese Patent Unexamined Publication Nos. 2003-128430, 2002-053342, 2001-048577, and H09-050769. Further, an example of using binding glass that contains bismuth oxide and has a low softening point for the primary dielectric layer covering the address electrodes is disclosed in Japanese Patent Unexamined Publication No. H10-275564. 
     Because a PDP can achieve higher definition and have a larger screen, a television screen using a PDP approx. 65 inch in diagonal is commercially available. Recently, with advancement of application of PDPs to high definition televisions having scanning lines at least twice as many as conventional televisions compliant with the National Television System Committee (NTSC) system, PDPs containing no lead to address environmental issues have been required. 
     However, such compliance of a PDP with high definition increases the numbers of scanning lines and display electrodes, and decreases the spacing between the display electrodes. These changes decrease the pitch and width of the barrier ribs of the rear panel. Thus, defective shapes of the barrier ribs are likely to occur, and affect the display quality. 
     SUMMARY OF THE INVENTION 
     A plasma display panel (PDP) of the present invention is made of a front panel and a rear panel. The front panel includes display electrodes, a dielectric layer, and a protective layer that are formed on a glass substrate. The rear panel includes address electrodes, barrier ribs, and phosphor layers that are formed on a substrate. The front panel and the rear panel are faced with each other, and the peripheries thereof are sealed to form a discharge space therebetween. A primary dielectric layer is provided to cover the address electrodes, and the barrier ribs are formed on the primary dielectric layer. The primary dielectric layer is made of dielectric glass containing at least bismuth oxide and having a softening point exceeding 550° C. 
     Such a structure inhibits generation of bubbles in the interface between the address electrodes and the primary dielectric layer, and in the primary dielectric layer. This inhibition can maintain high accuracy of the shape of the barrier ribs formed on the primary dielectric layer, and provide an eco-friendly PDP with excellent display quality. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a structure of a plasma display panel (PDP) in accordance with an exemplary embodiment of the present invention. 
         FIG. 2  is a sectional view illustrating a structure of a front panel of the PDP in accordance with the exemplary embodiment of the present invention. 
     
    
    
     
       
         
           
               
             
               
                   
               
               
                 REFERENCE MARKS IN THE DRAWINGS 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                  1 
                 Plasma display panel (PDP) 
               
               
                   
                  2 
                 Front panel 
               
               
                   
                  3 
                 Front glass substrate 
               
               
                   
                  4 
                 Scan electrode 
               
               
                   
                  4a, 5a 
                 Transparent electrode 
               
               
                   
                  4b, 5b 
                 Metal bus electrode 
               
               
                   
                  5 
                 Sustain electrode 
               
               
                   
                  6 
                 Display electrode 
               
               
                   
                  7 
                 Black stripe (lightproof layer) 
               
               
                   
                  8 
                 Dielectric layer 
               
               
                   
                  9 
                 Protective layer 
               
               
                   
                 10 
                 Rear panel 
               
               
                   
                 11 
                 Rear glass substrate 
               
               
                   
                 12 
                 Address electrode 
               
               
                   
                 13 
                 Primary dielectric layer 
               
               
                   
                 14 
                 Barrier rib 
               
               
                   
                 15 
                 Phosphor layer 
               
               
                   
                 16 
                 Discharge space 
               
               
                   
                 81 
                 First dielectric layer 
               
               
                   
                 82 
                 Second dielectric layer 
               
               
                   
                   
               
            
           
         
       
     
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     Hereinafter, a description is provided of a plasma display panel (PDP) in accordance with the exemplary embodiment of the present invention, with reference to the accompanying drawings. 
     Exemplary Embodiment 
       FIG. 1  is a perspective view illustrating a structure of a PDP in accordance with the exemplary embodiment of the present invention. The PDP is similar to a general alternating-current surface-discharge PDP in basic structure. As shown in  FIG. 1 , for PDP  1 , front panel  2  including front glass substrate  3 , and rear panel  10  including rear glass substrate  11  are faced with each other, and the outer peripheries thereof are hermetically sealed with a sealing material including glass frits. Into discharge space  16  in sealed PDP  1 , a discharge gas including Ne and Xe is charged at a pressure ranging from 400 to 600 Torr. 
     On front glass substrate  3  of front panel  2 , a plurality of rows of display electrodes  6 , each made of a pair of stripe-like scan electrode  4  and sustain electrode  5 , and black stripes (lightproof layers)  7  are disposed in parallel with each other. Formed on front glass substrate  3  is dielectric layer  8  that covers display electrodes  6  and lightproof layers  7  and works as a capacitor. Further on the surface of the dielectric layer, protective layer  9  including magnesium oxide (MgO) is formed. 
     On rear glass substrate  11  of rear panel  10 , a plurality of stripe-like address electrodes  12  are disposed in parallel with each other in the direction orthogonal to scan electrodes  4  and sustain electrodes  5  of front panel  2 . Primary dielectric layer  13  coats the address electrodes. Further, on primary dielectric layer  13  between address electrodes  12 , barrier ribs  14  having a predetermined height are formed to partition discharge space  16 . Phosphor layers  15  are sequentially applied to the grooves between barrier ribs  14  so that ultraviolet light excites the phosphor layers to emit light in red, blue, or green for each address electrode  12 . Discharge cells are formed in the positions where scan electrodes  4  and sustain electrodes  5  intersect with address electrodes  12 . The discharge cells that include phosphor layers  15  in red, blue, and green, and are arranged in the direction of display electrodes  6  form pixels for color display. 
       FIG. 2  is a sectional view illustrating a structure of front panel  2  of the PDP in accordance with the exemplary embodiment of the present invention.  FIG. 2  shows a vertically inverted view of  FIG. 1 . As shown in  FIG. 2 , display electrodes  6 , each made of scan electrode  4  and sustain electrode  5 , and black stripes  7  are patterned on front glass substrate  3  made by the float method or the like. Scan electrodes  4  and sustain electrodes  5  include transparent electrodes  4   a  and  5   a  made of indium tin oxide (ITO) or tin oxide (SnO 2 ), and metal bus electrodes  4   b  and  5   b  formed on transparent electrodes  4   a  and  5   a , respectively. Metal bus electrodes  4   b  and  5   b  are used to impart electrical conductivity to transparent electrodes  4   a  and  5   a  in the longitudinal direction thereof, and made of a conductive material essentially consisting of silver (Ag) material. 
     Dielectric layer  8  is structured of at least two layers: first dielectric layer  81  that covers these transparent electrodes  4   a  and  5   a , metal bus electrodes  4   b  and  5   b , and black stripes  7  formed on front glass substrate  3 ; and second dielectric layer  82  formed on first dielectric layer  81 . Further, protective layer  9  is formed on second dielectric layer  82 . 
     Next, a description is provided of a method of manufacturing a PDP. First, scan electrodes  4 , sustain electrodes  5 , and lightproof layers  7  are formed on front glass substrate  3 . These transparent electrodes  4   a  and  5   a , and metal bus electrodes  4   b  and  5   b  are patterned by methods including the photolithography method. Transparent electrodes  4   a  and  5   a  are formed by the thin film process or the like. Metal bus electrodes  4   b  and  5   b  are solidified by firing a paste containing silver (Ag) material, at a predetermined temperature. Lightproof layers  7  are formed by the similar method. A paste containing a black pigment is silk-screened, or a black pigment is applied to the entire surface of the glass substrate and patterned by the photolithography method. Then, the paste or the pigment is fired. 
     Next, a dielectric paste is applied to front glass substrate  3  to cover scan electrodes  4 , sustain electrodes  5 , and lightproof layers  7  by the die coat method or the like, to form a dielectric paste layer (dielectric material layer). Leaving the dielectric paste for a predetermined period after application levels the surface of the applied dielectric paste and provides a flat surface. Thereafter, solidifying the dielectric paste layer by firing forms dielectric layer  8  covering scan electrodes  4 , sustain electrodes  5 , and lightproof layers  7 . The dielectric paste is a paint containing dielectric glass, such as glass powder, as well as a binder, and a solvent. Next, protective layer  9  made of magnesium oxide (MgO) is formed on dielectric layer  8  by vacuum deposition. With these steps, a predetermined structure (scan electrodes  4 , sustain electrodes  5 , lightproof layers  7 , dielectric layer  8 , and protective layer  9 ) is formed on front glass substrate  3 . Thus, front panel  2  is completed. 
     On the other hand, rear panel  10  is formed in the following process. First, a material layer to be a structure for address electrodes  12  is made by silk-screening a paste containing silver (Ag) material on rear glass substrate  11 , or forming a metal layer on the entire rear glass substrate followed by patterning the layer by the photolithography method. Then, the structure is fired at a predetermined temperature, to form address electrodes  12 . Next, on rear glass substrate  11  having address electrodes  12  formed thereon, a dielectric paste is applied to cover address electrodes  12  by the die coat method or the like, to form a dielectric paste layer. Thereafter, the dielectric paste layer is fired into primary dielectric layer  13 . The dielectric paste is a paint containing dielectric glass, such as glass powder, as well as a binder, and a solvent. 
     Next, a paste containing a barrier rib material for forming barrier ribs is applied to primary dielectric layer  13  and patterned into a predetermined shape to form a barrier rib material layer. Then, the material layer is fired to form barrier ribs  14 . The usable methods of patterning the barrier rib paste applied to primary dielectric layer  13  include the photolithography method and sandblast method. Next, a phosphor paste containing a phosphor material is applied to primary dielectric layer  13  between adjacent barrier ribs  14  and the side surfaces of barrier ribs  14  and fired, to form phosphor layers  15 . With these steps, rear panel  10  including predetermined structural members formed on rear glass substrate  11  is completed. 
     Front panel  2  and rear panel  10  including predetermined structural members manufactured as above are faced with each other so that scan electrodes  4  are orthogonal to address electrodes  12 . Then, the peripheries of the panels are sealed with glass frits, and a discharge gas including Ne and Xe is charged into discharge space  16 . Thus, PDP  1  is completed. 
     Next, a detailed description is provided of first dielectric layer  81  and second dielectric layer  82  constituting dielectric layer  8  of front panel  2 . The dielectric material of first dielectric layer  81  is composed of the following components: 20 to 40 wt % of bismuth oxide (Bi 2 O 3 ); 0.5 to 15 wt % of calcium oxide (CaO); and 0.1 to 7 wt % of at least one selected from molybdenum trioxide (MoO 3 ), tungstic trioxide (WO 3 ), cerium dioxide (CeO 2 ), and manganese dioxide (MnO 2 ). 
     Further, the dielectric material contains 0.5 to 12 wt % of at least one selected from strontium oxide (SrO) and barium oxide (BaO). 
     In place of molybdenum trioxide (MoO 3 ), tungstic trioxide (WO 3 ), cerium dioxide (CeO 2 ), and manganese dioxide (MnO 2 ), the dielectric material may contain 0.1 to 7 wt % of at least one selected from cupper oxide (CuO), chromium oxide (Cr 2 O 3 ), cobalt oxide (CO 2 O 3 ), vanadium oxide (V 2 O 7 ), and antimony oxide (Sb 2 O 3 ). 
     In addition to the above components, the dielectric material may contain components other than lead, such as 0 to 40 wt % of zinc oxide (ZnO), 0 to 35 wt % of boron oxide (B 2 O 3 ), 0 to 15 wt % of silicon dioxide (SiO 2 ), and 0 to 10 wt % of aluminum oxide (Al 2 O 3 ). The contents of these components are not specifically limited, and are within the range of the contents in the conventional arts. 
     The dielectric material having such composition is pulverized with a wet jet mill or ball mill to have an average particle diameter ranging from 0.5 to 2.5 to provide a dielectric material powder. Next, 55 to 70 wt % of this dielectric material powder and 30 to 45 wt % of binder components are sufficiently kneaded with a three-roll kneader, to provide a paste of the first dielectric layer for die coat or printing. The binder components include ethylcellulose, terpioneol containing 1 to 20 wt % of acrylate resin, or butyl carbitol acetate. As needed, the paste may additionally contain dioctyl phthalate, dibutyl phthalate, triphenyl phosphate, or tributyl phosphate, as a plasticizer, and glycerol monooleate, sorbitan sesquioleate, or alkyl aryl phosphate esters, as a dispersant, to improve printability. 
     Next, the paste of the first dielectric layer is applied to front glass substrate  3  to cover display electrodes  6  by the die coat or silk-screen printing method, and dried. Thereafter, the paste is fired at a temperature ranging from 575 to 590° C., slightly higher than the softening point of the dielectric material, to provide first dielectric layer  81 . 
     Next, a description is provided of second dielectric layer  82 . The dielectric material of second dielectric layer  82  is composed of the following components: 11 to 40 wt % of bismuth oxide (Bi 2 O 3 ); 6.0 to 28 wt % of barium oxide (BaO); and 0.1 to 7 wt % of at least one selected from molybdenum trioxide (MoO 3 ), tungstic trioxide (WO 3 ) cerium dioxide (CeO 2 ), and manganese dioxide (MnO 2 ). 
     The dielectric material further contains 0.8 to 17 wt % of at least one selected from calcium oxide (CaO) and strontium oxide (SrO). 
     In place of molybdenum trioxide (MoO 3 ), tungstic trioxide (WO 3 ), cerium dioxide (CeO 2 ), and manganese dioxide (MnO 2 ), the dielectric material may contain 0.1 to 7 wt % of at least one selected from cupper oxide (CuO), chromium oxide (Cr 2 O 3 ), cobalt oxide (Co 2 O 3 ), vanadium oxide (V 2 O 7 ), and antimony oxide (Sb 2 O 3 ). 
     In addition to the above components, the dielectric material may contain components other than lead, such as 0 to 40 wt % of zinc oxide (ZnO), 0 to 35 wt % of boron oxide (B 2 O 3 ), 0 to 15 wt % of silicon dioxide (SiO 2 ), and 0 to 10 wt % of aluminum oxide (Al 2 O 3 ). The contents of these components are not specifically limited, and are within the range of the contents in the conventional arts. 
     The dielectric material having such composition is pulverized with a wet jet mill or ball mill to have an average particle diameter ranging from 0.5 to 2.5 μm, so that a dielectric material powder is provided. Next, 55 to 70 wt % of this dielectric material powder and 30 to 45 wt % of binder components are sufficiently kneaded with a three-roll kneader, to provide a paste of the second dielectric layer for die coat or printing. The binder components include ethylcellulose, terpioneol containing 1 to 20 wt % of acrylate resin, or butyl carbitol acetate. As needed, the paste may additionally contain dioctyl phthalate, dibutyl phthalate, triphenyl phosphate, or tributyl phosphate, as a plasticizer, and glycerol monooleate, sorbitan sesquioleate, or alkyl aryl phosphate esters, as a dispersant, to improve printability. 
     Next, the paste of the second dielectric layer is applied to first dielectric layer  81  by the silk-screen printing method or the die coat method, and dried. Thereafter, the paste is fired at a temperature ranging from 550 to 590° C., slightly higher than the softening point of the dielectric material, to provide second dielectric layer  82 . Thus, dielectric layer  8  is formed. 
     The advantage of increasing the brightness of the panel and decreasing the discharge voltage is more distinct at the smaller thickness of dielectric layer  8 . For this reason, preferably, the thickness is as small as possible within the range in which the dielectric voltage does not decrease. From the viewpoints of these conditions and visible-light transmittance, in this exemplary embodiment of the present invention, the thickness of dielectric layer  8  is up to 41 μm, with that of first dielectric layer  81  ranging from 5 to 15 μm and that of second dielectric layer  82  ranging from 20 to 36 μm. 
     For second dielectric layer  82  with a content of bismuth oxide (Bi 2 O 3 ) up to 11 wt %, coloring is unlikely to occur, but bubbles are likely to foam in second dielectric layer  82 . Thus, such a content is not preferable. With a content of bismuth oxide (Bi 2 O 3 ) exceeding 40 wt %, coloring is likely to occur. For this reason, such a content is not preferable to increase the transmittance. 
     Further, it is necessary that there should be a difference in the content of bismuth oxide (Bi 2 O 3 ) between first dielectric layer  81  and second dielectric layer  82 . This is confirmed by the following phenomenon. When the content of bismuth oxide (Bi 2 O 3 ) is the same in first dielectric layer  81  and second dielectric layer  82 , the bubbles generated in first dielectric layer  81  also generates bubbles in second dielectric layer  82  during the step of firing second dielectric layer  82 . 
     When the content of bismuth oxide (Bi 2 O 3 ) in second dielectric layer  82  is smaller than that of bismuth oxide (Bi 2 O 3 ) in first dielectric layer  81 , the following advantage is given. Because second dielectric layer  82  accounts for at least approx. 50% of the total thickness of dielectric layer  8 , an yellowing phenomenon of coloring is unlikely to occur and thus the transmittance can be increased. Further, because the Bi-based materials are expensive, the cost of the raw materials to be used can be reduced. 
     On the other hand, when the content of bismuth oxide (Bi 2 O 3 ) in second dielectric layer  82  is larger than the content of bismuth oxide (Bi 2 O 3 ) in the first dielectric layer, the softening point of second dielectric layer  82  can be lowered and thus removal of bubbles in the firing step can be promoted. 
     It is confirmed that a PDP manufactured in this manner can provide front glass substrate  3  having a minimized coloring (yellowing) phenomenon, and dielectric layer  8  having no bubbles generated therein and an excellent dielectric strength, even with the use of a silver (Ag) material for display electrodes  6 . 
     Next, consideration is given to the reasons why these dielectric materials inhibit yellowing or foaming in first dielectric layer  81 , in a PDP in accordance with the exemplary embodiment of the present invention. It is known that addition of molybdenum trioxide (MoO 3 ) or tungstic trioxide (WO 3 ) to dielectric glass containing bismuth oxide (Bi 2 O 3 ) is likely to generate compounds, such as Ag 2 MoO 4 , Ag 2 Mo 2 O 7 , Ag 2 Mo 4 O 13 , Ag 2 WO 4 , Ag 2 W 2 O 7 , and Ag 2 W 4 O 13 , at low temperatures up to 580° C. In the exemplary embodiment of the present invention, the firing temperature of dielectric layer  8  ranges from 550 to 590° C. Thus, silver ions (Ag + ) diffused in dielectric layer  8  during firing react with molybdenum trioxide (MoO 3 ), tungstic trioxide (WO 3 ), cerium dioxide (CeO 2 ), or manganese dioxide (MnO 2 ) in dielectric layer  8 , generate stable compounds, and stabilize. In other words, because the silver ions (Ag + ) are not reduced and are stabilized, the ions do not coagulate into colloids. Consequently, the stabilization of the silver ions (Ag + ) decreases oxygen generated by colloidization of silver (Ag), thus reducing the bubbles generated in dielectric layer  8 . 
     On the other hand, preferably, the content of molybdenum trioxide (MoO 3 ), tungstic trioxide (WO 3 ), cerium dioxide (CeO 2 ), or manganese dioxide (MnO 2 ) in the dielectric glass containing bismuth oxide (Bi 2 O 3 ) is at least 0.1 wt %, to offer these advantages. More preferably, the content ranges from 0.1 to 7 wt %. Particularly with a content up to 0.1 wt %, the advantage of inhibiting yellowing is smaller. With a content of at least 7 wt %, yellowing occurs in the glass, and thus is not preferable. 
     Calcium oxide (CaO) contained in the first dielectric layer works as an oxidizer in the firing step of first dielectric layer  81 , and has an effect of promoting removal of binder components remaining in the electrodes. On the other hand, barium oxide (BaO) contained in second dielectric layer  82  has an effect of increasing the transmittance of second dielectric layer  82 . 
     In other words, for dielectric layer  8  of the PDP in accordance with the exemplary embodiment of the present invention, first dielectric layer  81  in contact with metal bus electrodes  4   b  and  5   b  made of a silver (Ag) material inhibits the yellowing phenomenon and foaming therein, and second dielectric layer  82  provided on first dielectric layer  81  achieves high light transmittance. This structure can provide a PDP that has extremely minimized foaming and yellowing, and high transmittance in the entire dielectric layer  8 . 
     Next, a detailed description is provided of the compositions of address electrodes  12 , primary dielectric layer  13 , and barrier ribs  14  of rear panel  10  of the PDP in accordance with the exemplary embodiment of the present invention. 
     A photosensitive paste is applied to rear glass substrate  11  by printing or other methods, to form an electrode paste layer. The photosensitive paste is composed of the following components: 70 to 90 wt % of at least silver (Ag) particles; 1 to 15 wt % of binding glass; and 8 to 15 wt % of photosensitive organic binder components including a photosensitive polymer, a photosensitive monomer, a photo-polymerization initiator, and a solvent. The binding glass of the electrode paste contains at least 20 to 50 wt % of bismuth oxide (Bi 2 O 3 ) and has a softening point exceeding 550° C. The electrode paste layer is patterned into 100-μm-wide silver (Ag) electrodes by the photolithography method. Then, the electrodes are fired at a temperature ranging from 550 to 570° C. to provide address electrodes  12 . 
     Primary dielectric layer  13  formed on address electrodes  12  is made of dielectric glass powders containing the following components: 23 to 50 wt % of bismuth oxide ((Bi 2 O 3 ); 1.5 to 8.1 wt % of at least one selected from calcium oxide (CaO), strontium oxide (SrO), and barium oxide (BaO); and 0.2 to 1.0 wt % of at least one selected from molybdenum trioxide (MoO 3 ) and tungstic trioxide (WO 3 ). Titanium oxide (TiO 2 ) or alumina (Al 2 O 3 ) having an average particle diameter ranging from 0.1 to 0.5 μm is added to the above dielectric glass power. Particles of titanium oxide (TiO 2 ) or alumina (Al 2 O 3 ) are added to improve the function of the primary dielectric layer as a reflecting layer. For these glass powders, the softening point is at least 550° C., the firing temperature ranges from 570 to 590° C., and the thickness ranges from 8 to 15 μm. 
     In place of molybdenum trioxide (MoO 3 ) and tungstic trioxide (WO 3 ), the dielectric glass may contain 0.1 to 7 wt % of at least one selected from cerium dioxide (CeO 2 ), manganese dioxide (MnO 2 ), cupper oxide (CuO), chromium oxide (Cr 2 O 3 ), cobalt oxide (CO 2 O 3 ), vanadium oxide (V 2 O 7 ), and antimony oxide (Sb 2 O 3 ). 
     In addition to the above components, the dielectric glass may contain components other than lead, such as 0 to 40 wt % of zinc oxide (ZnO), 0 to 35 wt % of boron oxide (B 2 O 3 ), 0 to 15 wt % of silicon dioxide (SiO 2 ), and 0 to 10 wt % of aluminum oxide (Al 2 O 3 ). The contents of these components are not specifically limited, and are within the range of the contents in the conventional arts. 
     Barrier ribs  14  provided on primary dielectric layer  13  are made by applying a photosensitive paste to primary dielectric layer  13  by printing and other methods, and formed by the photolithography method. The photosensitive paste contains the following components: 50 to 70 wt % of a glass powder based on silicon oxide (SiO 2 )-boron oxide (B 2 O 3 )-barium oxide (BaO)-alumina (Al 2 O 3 )-lithium oxide (LiO 2 ); 10 to 25 wt % of at least one of alumina (Al 2 O 3 ), zinc oxide (ZnO), and barium oxide (BaO), as a filler; and 8 to 15 wt % of photosensitive organic binder components including a photosensitive polymer, a photosensitive monomer, a photo-polymerization initiator, and a solvent. The paste is fired at a temperature ranging from 570 to 590° C. 
     In other words, in the PDP in accordance with the exemplary embodiment of the present invention, when address electrodes  12  are formed on rear glass substrate  11  of rear panel  10 , address electrodes  12  contain at least silver (Ag) and binding glass, and the binding glass contains at least bismuth oxide (Bi 2 O 3 ) and has a softening point exceeding 550° C. For conventional binding glass having a low softening point ranging from 450 to 550° C., highly-reactive bismuth oxide (Bi 2 O 3 ) intensely reacts with silver (Ag), or organic binder components in the paste, at a firing temperature almost 100° C. higher than the softening point. This reaction generates bubbles in address electrodes  12  and primary dielectric layer  13  thereon, thus degrading the dielectric strength and the accuracy of the shape of primary dielectric layer  13 . Further, this reaction degrades adhesion of primary dielectric layer  13  to barrier ribs  14  formed thereon and causes inclination or chipping of the barrier ribs. In contrast, the binding glass having a softening point of at least 550° C. in accordance with the present invention has less reactivity of silver (Ag) or organic binder components with bismuth oxide (Bi 2 O 3 ) and causes less foaming. On the other hand, at a softening point of the binding glass of at least 600° C., adhesion of address electrodes  12  to rear glass substrate  11  or primary dielectric layer  13  deteriorates. Thus, this softening point is not preferable. 
     In this embodiment, primary dielectric layer  13  is made of dielectric glass including at least bismuth oxide (Bi 2 O 3 ) and having a softening point exceeding 550° C. The content of bismuth oxide (Bi 2 O 3 ) ranges from 20 to 50 wt %. Such a structure inhibits generation of bubbles in the interface between address electrodes  12  and primary dielectric layer  13 , and in primary dielectric layer  13 . This inhibition can maintain high accuracy of the shape of barrier ribs  14  formed on the primary dielectric layer, and provide an eco-friendly PDP with excellent display quality. 
     Additionally, the compositions of address electrodes  12 , primary dielectric layer  13 , and barrier ribs  14  described above allow the entire rear panel  10  to be made by lead (Pb)-free, eco-friendly materials. 
     EXAMPLES 
     As PDPs in accordance with this exemplary embodiment of the present invention, PDPs suitable for a high definition television screen approx. 42 inch in diagonal are fabricated and their performances are evaluated. Each of the PDPs includes discharge cells having 0.15-mm-high barrier ribs at a regular spacing (cell pitch) of 0.15 mm, display electrodes at a regular spacing of 0.06 mm, and a Ne—Xe mixed gas containing 15 vol % of Xe charged at a pressure of 60 kPa. 
     Table 1 shows samples of the binding glass constituting address electrodes  12  that have different compositions. Table 2 shows samples of the dielectric glass constituting primary dielectric layer  13  that have different compositions. Table 3 shows PDPs fabricated by combination of the samples of address electrodes  12  and the samples of primary dielectric layer  13 , and the evaluation results thereof. In this exemplary embodiment, the binding glass and the dielectric glass have the same composition. Sample Nos. 6 and 7 in Tables 1 and 2 have compositions outside the preferable composition range of the present invention. 
     “Other components” in the columns of Tables 1 and 2 show the components other than lead, such as zinc oxide (ZnO), boron oxide (B 2 O 3 ), silicon dioxide (SiO 2 ), and aluminum oxide (Al 2 O 3 ), as described above. The contents of these components are not specifically limited, and are within the range of the contents in the conventional arts. 
     Dielectric layer  8  of front panel  2  has at least two layers and made of the above-mentioned compositions of first dielectric layer  81  and second dielectric layer  82 . 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Composition and 
               
               
                 softening point 
               
            
           
           
               
               
            
               
                 of binding 
                 Sample No. of address electrode 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 glass (° C.) 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Bi 2 O 3   
                 23 
                 30 
                 28 
                 40 
                 50 
                 15 
                 72 
               
               
                 CaO 
                 — 
                 3.1 
                 — 
                 8.1 
                 — 
                 — 
                 — 
               
               
                 SrO 
                 — 
                 1.8 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 BaO 
                 6.4 
                 1.5 
                 4.8 
                 — 
                 — 
                 — 
                 4.0 
               
               
                 MoO 3   
                 0.8 
                 0.2 
                 0.3 
                 0.5 
                 — 
                 1.0 
                 — 
               
               
                 WO 3   
                 — 
                 — 
                 — 
                 1.0 
                 — 
                 — 
                 — 
               
               
                 Other 
                 70 
                 63 
                 67 
                 50 
                 50 
                 84 
                 24 
               
               
                 components** 
               
               
                 Softening 
                 597 
                 566 
                 560 
                 565 
                 551 
                 610 
                 460 
               
               
                 point(° C.) 
               
               
                   
               
               
                 **“Other components” include no lead. 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Composition and 
               
               
                 softening point 
               
            
           
           
               
               
            
               
                 of dielectric 
                 Sample No. of primary dielectric layer 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 glass(° C.) 
                 1 
                 2 
                 3 
                 4 
                 5 
                 6 
                 7 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Bi 2 O 3   
                 23 
                 30 
                 28 
                 40 
                 50 
                 15 
                 72 
               
               
                 CaO 
                 — 
                 3.1 
                 — 
                 8.1 
                 — 
                 — 
                 — 
               
               
                 SrO 
                 — 
                 1.8 
                 — 
                 — 
                 — 
                 — 
                 — 
               
               
                 BaO 
                 6.4 
                 1.5 
                 4.8 
                 — 
                 — 
                 — 
                 4.0 
               
               
                 MoO 3   
                 0.8 
                 0.2 
                 0.3 
                 0.5 
                 — 
                 1.0 
                 — 
               
               
                 WO 3   
                 — 
                 — 
                 — 
                 1.0 
                 — 
                 — 
                 — 
               
               
                 Other 
                 70 
                 63 
                 67 
                 50 
                 50 
                 84 
                 24 
               
               
                 components** 
               
               
                 Softening 
                 597 
                 566 
                 560 
                 565 
                 551 
                 610 
                 460 
               
               
                 point(° C.) 
               
               
                   
               
               
                 **“Other components” include no lead. 
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                   
                   
                 Inclination 
               
               
                   
                 Sample 
                 Sample No. 
                 Number of 
                 and 
               
               
                   
                 No. of 
                 of primary 
                 bubbles in 
                 chipping 
               
               
                 Panel 
                 address 
                 dielectric 
                 primary 
                 of barrier 
               
               
                 No. 
                 electrode 
                 layer 
                 dielectric layer 
                 ribs 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 No. 1 
                 No. 1 
                 3 
                 None 
               
               
                 2 
                 No. 1 
                 No. 5 
                 8 
                 Exist 
               
               
                 3 
                 No. 1 
                 No. 6 
                 20 
                 Exist 
               
               
                 4 
                 No. 1 
                 No. 7 
                 5 
                 None 
               
               
                 5 
                 No. 2 
                 No. 2 
                 2 
                 None 
               
               
                 6 
                 No. 2 
                 No. 6 
                 10 
                 Exist 
               
               
                 7 
                 No. 2 
                 No. 7 
                 18 
                 Exist 
               
               
                 8 
                 No. 3 
                 No. 3 
                 0 
                 None 
               
               
                 9 
                 No. 3 
                 No. 6 
                 11 
                 Exist 
               
               
                 10 
                 No. 3 
                 No. 7 
                 22 
                 Exist 
               
               
                 11 
                 No. 4 
                 No. 4 
                 1 
                 None 
               
               
                 12 
                 No. 4 
                 No. 6 
                 8 
                 Exist 
               
               
                 13 
                 No. 4 
                 No. 7 
                 17 
                 Exist 
               
               
                 14 
                 No. 5 
                 No. 5 
                 2 
                 None 
               
               
                 15 
                 No. 5 
                 No. 6 
                 10 
                 Exist 
               
               
                 16 
                 No. 5 
                 No. 7 
                 12 
                 Exist 
               
               
                 17 
                 No. 6 
                 No. 6 
                 25 
                 Many 
               
               
                 18 
                 No. 6 
                 No. 7 
                 30 
                 Many 
               
               
                 19 
                 No. 7 
                 No. 7 
                 28 
                 Many 
               
               
                   
               
            
           
         
       
     
     These PDPs of panel Nos. 1 through 19 are fabricated using these materials, and evaluated for the following items: the number of bubbles generated in primary dielectric layer  13  after the completion of rear panel  10 ; and inclination and chipping of barrier ribs  14  on primary dielectric layer  13 . Table 3 shows the evaluation results. 
     The results of Table 3 show, when one of the composition of the binding glass of address electrodes  12  and the composition of the dielectric glass of primary dielectric layer  13  is outside the composition range of the present invention, the number of bubbles in primary dielectric layer  13  has increased and inclination or chipping of barrier ribs  14  is seen. Further, when the composition of address electrodes  12  and the composition of primary dielectric layer  13  are both outside the composition range of the present invention, like panel Nos. 17 through 19, the number of bubbles and inclined barrier ribs abnormally increases. Naturally, less foaming increases the dielectric strength of primary dielectric layer  13 , and thus achieves a reliable PDP. 
     The reasons for these results are considered as follows. When the binding glass of address electrodes  12  or the dielectric glass of primary dielectric layer  13  has a low softening point, bubbles are likely to be generated by the reaction of silver (Ag) material or organic binder components with bismuth oxide (Bi 2 O 3 ), during firing. On the other hand, when the binding glass or the dielectric glass has a high softening point, the weak adhesion between rear glass substrate  11 , address electrodes  12 , and primary dielectric layer  13  increases peeling or foaming in the interfaces thereof. In either case, these phenomena induce the defective shapes of primary dielectric layer  13  and barrier ribs  14  formed thereon, thereby causing inclination and chipping of barrier ribs  14 . 
     For the binding glass of the address electrodes and the dielectric glass of the primary dielectric layer, the content of each component described above has a measurement error in the range of approx. ±0.5 wt %. For the address electrodes and primary dielectric layer after firing, the content has a measurement error in the range of approx. ±2 wt %. The contents of the components in the range of the values including these errors can provide the similar advantages of the present invention. 
     As described above, a PDP in accordance with the exemplary embodiment of the present invention can ensure the accuracy of the shape of the rear panel and provide a lead (Pb)-free, eco-friendly PDP having a high dielectric strength. 
     INDUSTRIAL APPLICABILITY 
     As described above, the PDP of the present invention increases the reliability of the rear panel and achieves an eco-friendly PDP with excellent display quality. Thus, the PDP is useful for a large-screen display device and the like.