Patent Publication Number: US-6713958-B2

Title: Alternating current driven type plasma display device

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     The present invention relates to an alternating current driven type plasma display device having a characteristic feature in a discharge gas sealed in a discharge space where discharge takes place. 
     As an image display device that can be substituted for a currently mainstream cathode ray tube (CRT), flat-screen (flat-panel) display devices are studied in various ways. Such fat-panel display devices include a liquid crystal display (LCD), an electroluminescence display (ELD) and a plasma display device (PDP). Of these, the plasma display device has advantages that it is relatively easy to produce a larger screen and attain a wider viewing angle, that it has excellent durability against environmental factors such as temperatures, magnetism, vibrations, etc., and that it has a long lifetime. The plasma display device is therefore expected to be applicable not only to a home-use wall-hung television set but also to a large-sized public information terminal. 
     In the plasma display device, a voltage is applied to discharge cells formed by charging discharge spaces with a discharge gas composed of a rare gas, and a fluorescence layer in each discharge cell is excited with ultraviolet ray generated by glow discharge in the discharge gas, to give light emission. That is, each discharge cell is driven according to a principle similar to that of a fluorescent lamp, and generally, the discharge cells are put together on the order of hundreds of thousands to constitute a display screen. The plasma display device is largely classified into a direct current driven type (DC type) and an alternating current driven type (AC type) according to methods of applying a voltage to the discharge cells, and each type has advantages and disadvantages. The AC type plasma display device is suitable for attaining a higher fineness, since separation walls which work to separate the discharge cells within a display screen can be formed, for example, in the form of stripes. Further, it has an advantage that electrode is less worn out and has a long lifetime, since the surface of the electrode for discharge is covered with a dielectric material. 
     FIG. 1 shows a schematic exploded perspective view of typical constitution of the AC type plasma display device. This AC type plasma display device comes under a so-called tri-electrode type, and discharging takes place mainly between a pair of sustain electrodes  12 . In the AC type plasma display device shown in FIG. 1, a first panel  10  corresponding to a front panel and a second panel  20  corresponding to a rear panel are bonded to each other in their circumferential portions. Light emission from fluorescence layers  25  on the second panel  20  is viewed, for example, through the first panel  10 . 
     The first panel  10  comprises a transparent first substrate  11 ; pairs of sustain electrodes  12  composed of a transparent electrically conductive material and formed on the first substrate  11  in the form of stripes; bus electrodes  13  composed of a material having a lower electric resistivity than the sustain electrode  12  and formed on the sustain electrodes  12  for decreasing the impedance of the sustain electrode  12 ; a dielectric material layer  14  composed of a dielectric material and formed on the sustain electrodes  12 , the bus electrodes  13  and the first substrate  11 ; and a protective layer  15  composed of MgO and formed on the dielectric material layer  14 . 
     The second panel  20  comprises a second substrate  21 ; address electrodes (also called data electrodes)  22  formed on the second substrate  21  in the form of stripes; a dielectric film  23  formed on the second substrate  21  and on the address electrodes  22 ; insulating separation walls  24  which are formed in regions on the dielectric film  23  and between neighboring address electrodes  22  and which extend in parallel with the address electrodes  22 ; and fluorescence layers  25  which are formed on, and extend from, upper surfaces of the dielectric film  23  and which are also formed on side walls of the separation walls  24 . When the AC type plasma display device is used for display in colors, each fluorescence layer  25  is constituted of a red fluorescence layer  25 R, a green fluorescence layer  25 G and a blue fluorescence layer  25 B, and the fluorescence layers  25 R,  25 G and  25 B of these colors are formed in a predetermined order. FIG. 1 is an exploded perspective view, and in an actual embodiment, top portions of the separation walls  24  on the second panel side are in contact with the protective layer  15  on the first panel side. A region where a pair of the sustain electrodes  12  and the address electrode  22  positioned between two of the separation walls  25  overlap corresponds to a discharge cell. A discharge gas is sealed in each discharge space surrounded by neighboring two separation walls  24 , the fluorescence layer  25  and the protective layer  15 . The first panel  10  and the second panel  20  are bonded to each other with a frit glass in their circumferential portions. 
     The extending direction of a projection image of the sustain electrode  12  and the extending direction of a projection image of the address electrode  22  cross each other at right angles, and a region where a pair of the sustain electrodes  12  and one combination of the fluorescence layers  25 R,  25 G and  25 B for emitting light in three primary colors overlap corresponds to one pixel. Since glow discharge is caused between a pair of the sustain electrodes  12 , the AC type plasma display device of the above type is called “surface discharge type”. For example, a pulse voltage lower than the discharge initiating voltage of the discharge cell is applied to the address electrode  22  immediately before the application of a voltage between the pair of the sustain electrodes  12 . As a result, a wall charge is accumulated in the discharge cell (selection of a discharge cell for display), and the apparent discharge initiating voltage decreases. Then, the discharge initiated between the pair of the sustain electrodes  12  can be sustained at a voltage lower than the discharge initiating voltage. In the discharge cell, the fluorescence layer excited by irradiation with vacuum ultraviolet ray generated by glow discharge in the discharge gas emits light in a color characteristic of a fluorescence material. Vacuum ultraviolet ray having a wavelength according to a kind of the charged discharge gas is generated. 
     Generally, the discharge gas charged in the discharge space is composed of a mixture prepared by mixing approximately 4% by volume of a xenon gas with an inert gas such as neon (Ne) gas, helium (He) gas or argon (Ar) gas. The distance between a pair of the sustain electrodes  12  is approximately 100 μm, specifically 70 μm to 120 μm. 
     Currently commercialized AC type plasma display devices have a problem that the brightness thereof is low. For example, a 42-inch AC type plasma display device has a brightness of approximately 500 cd/m 2  at the highest. For practically commercializing an AC type plasma display device, further, it is required, for example, to attach a sheet or a film as a shield against electromagnetic waves or external light to the outer surface of the first panel  10 , and the AC type plasma display device comes to be dark on an actual screen. 
     When the discharge gas charged in the discharge space is pressure-increased for increasing the brightness, there is caused a problem that the discharge voltage increases, that the discharge comes to be unstable, or that the discharge is non-uniform. When the discharge gas charged in the discharge space is pressure-increased, the discharge gas exerts a force on the first panel  10  and the second panel  20  to separate them from each other. As a result, the reliability of the bonding of the first panel  10  and the second panel  20  with the frit glass may decrease. Further, when the discharge gas is expanded due to a temperature added to the AC type plasma display device, the discharge gas possibly leaks through the junction portion between the first panel  10  and the second panel  20 . In a conventional AC type plasma display device, therefore, it is therefore difficult to increase the pressure of the discharge gas sealed in the discharge space for increasing the brightness. 
     In the AC type plasma display device, further, there is the law of Paschen between a product (d·p) of a distance (d) between a pair of the sustain electrodes  12  and the total pressure (p) of the discharge gas and a discharge initiating voltage V bd , that is, the discharge initiating voltage V bd  can be expressed by the function of the product (d·p) of the distance (d) and the gas pressure (p). In the above expression, if the distance (d) between a pair of the sustain electrodes  12  is decreased for increasing discharge efficiency, it is required to increase the gas pressure (p), so that the reliability of the AC type plasma display device again decreases. 
     In addition to the above necessity to increase in brightness, it is also required to improve a contrast. It is known that visible light components generated by the light emission of the discharge gas cause the contract on the panel to decrease. When a neon (Ne) gas is used as a discharge gas, particularly, the visible light component generated by the light emission of the neon gas has orange color. When the neon gas concentration is high, image display on the screen of the AC type plasma display device has a color tone based mainly on orange color, and the contrast is decreased. 
     OBJECT AND SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an alternating current driven type plasma display device which has high reliability, can attain a high contrast, can give a high brightness even at a low discharge gas pressure, can decrease a discharge voltage and can decrease a driving power, i.e., consumption power. 
     An alternating current driven type plasma display device according to a first aspect of the present invention for achieving the above object is characterized in that a discharge gas charged in a discharge space where discharge takes place consists of a xenon (Xe) gas alone (i.e., 100% by volume of a xenon gas) and that the discharge gas has a pressure of 9.0×10 4  Pa or lower. When the pressure of the discharge gas exceeds 9.0×10 4  Pa, a frit seal of the alternating current driven type plasma display device may cause a decrease in reliability due to the pressure of the discharge gas. 
     An alternating current driven type plasma display device according to a second aspect of the present invention for achieving the above object is characterized in that a discharge gas charged in a discharge space where discharge takes place consists of a krypton (Kr) gas alone (i.e., 100% by volume of a krypton gas) and that the discharge gas has a pressure of 9.0×10 4  Pa or lower. When the pressure of the discharge gas exceeds 9.0×10 4  Pa, a frit seal of the alternating current driven type plasma display device may cause a decrease in reliability due to the pressure of the discharge gas. 
     An alternating current driven type plasma display device according to a third aspect of the present invention for achieving the above object is characterized in that a discharge gas charged in a discharge space where discharge takes place consists of a mixed gas of a xenon (Xe) gas and a krypton (Kr) gas alone and that the mixed gas have a total pressure of less than 6.6×10 4  Pa (500 Torr). In this case, essentially, the xenon gas/krypton gas mixing ratio in the above mixed gas may be any mixing ratio. 
     An alternating current driven type plasma display device according to a fourth aspect of the present invention for achieving the above object is characterized in that a discharge gas charged in a discharge space where discharge takes place consists of a mixed gas of at least one first gas selected from the group consisting of a xenon (Xe) gas and a krypton (Kr) gas and at least one second gas selected from the group consisting of a neon (Ne) gas, a helium (He) gas and an argon (Ar) gas, and that the first gas has a partial pressure of at least 1×10 3  Pa, preferably at least 4×10 3  Pa and a concentration of at least 10% by volume, preferably at least 30% by volume and that the discharge gas has a total pressure of less than 6.6×10 4  Pa (500 Torr). 
     The following Table 1 summarizes combinations of gases for the first gas and the second gas in the alternating current driven type plasma display device according to the fourth aspect of the present invention. Of the cases 1 to 21, it is practically the most preferred to select the case 1. In Table 1, symbol “+” means the use of two or three kinds of gases, and when two or three kinds of gases are used, the mixing ratio thereof is essentially determined to be any ratio. Other gas such as a hydrogen (H 2 ) gas of 1%, or less than 1% by volume may be included in the mixed gas. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Case 
                 First gas 
                 Second gas 
               
               
                   
               
             
            
               
                  1 
                 Xe 
                 Ne 
               
               
                  2 
                 Xe 
                 He 
               
               
                  3 
                 Xe 
                 Ar 
               
               
                  4 
                 Kr 
                 Ne 
               
               
                  5 
                 Kr 
                 He 
               
               
                  6 
                 Kr 
                 Ar 
               
               
                  7 
                 Xe 
                 (Ne + He) 
               
               
                  8 
                 Xe 
                 (Ne + Ar) 
               
               
                  9 
                 Xe 
                 (He + Ar) 
               
               
                 10 
                 Xe 
                 (Ne + He + Ar) 
               
               
                 11 
                 Kr 
                 (Ne + He) 
               
               
                 12 
                 Kr 
                 (Ne + Ar) 
               
               
                 13 
                 Kr 
                 (He + Ar) 
               
               
                 14 
                 Kr 
                 (Ne + He + Ar) 
               
               
                 15 
                 (Xe + Kr) 
                 Ne 
               
               
                 16 
                 (Xe + Kr) 
                 He 
               
               
                 17 
                 (Xe + Kr) 
                 Ar 
               
               
                 18 
                 (Xe + Kr) 
                 (Ne + He) 
               
               
                 19 
                 (Xe + Kr) 
                 (Ne + Ar) 
               
               
                 20 
                 (Xe + Kr) 
                 (He + Ar) 
               
               
                 21 
                 (Xe + Kr) 
                 (Ne + He + Ar) 
               
               
                   
               
            
           
         
       
     
     An alternating current driven type plasma display device according to a fifth aspect of the present invention for achieving the above object is characterized in that a discharge gas charged in a discharge space where discharge takes place consists of a mixed gas containing a xenon (Xe) gas, 
     that the xenon (Xe) gas has a concentration of at least 10% by volume, preferably at least 30% by volume, but less than 100% by volume and that the mixed gas has a total pressure of less than 6.6×10 4  Pa (500 Torr). 
     In the alternating current driven type plasma display device according to the fifth aspect of the present invention, the partial pressure of the xenon (Xe) gas is preferably at least 1×10 3  Pa, more preferably at least 4×10 3  Pa. The other gas for the mixed gas includes a krypton (Kr) gas, a neon (Ne) gas, a helium (He) gas and an argon (Ar) gas. 
     Each of the alternating current driven type plasma display devices according to the first to fifth aspects of the present invention (to be sometimes generally and simply referred to as “plasma display device” hereinafter) has a plurality of pairs of sustain electrodes, and discharge takes place between each pair of the sustain electrodes. The distance between a pair of the sustain electrodes may be arbitrary so long as necessary glow discharge can take place at a predetermined discharge voltage. For decreasing a discharge voltage, however, the above distance is less than 5×10 −5  m, preferably less than 5.0×10 −5  m, more preferably equal to, or less than, 2×10 −5  m. There may be employed a constitution in which one sustain electrode between a pair of the sustain electrodes is formed on the first substrate and the other sustain electrode is formed on the second substrate. The thus-constituted plasma display device will be referred to as bi-electrode type for the convenience. In this case, the projection image of one sustain electrode extends in a first direction, the projection image of the other sustain electrode extends in a second direction different from the first direction, and a pair of the sustain electrodes are arranged such that one sustain electrode faces the other. Otherwise, there may be employed a constitution in which a pair of the sustain electrodes are formed on the first substrate and a so-called address electrode is formed on the second substrate. The thus-constituted plasma display device will be referred to as tri-electrode type for the convenience. In this case, there may be employed a constitution in which the projection image of a pair of the sustain electrodes extends in a first direction such that the projection image of one sustain electrode extends in parallel with the projection image of the other, the projection image of the address electrode extends in a second direction, and a pair of the sustain electrodes and the address electrode are arranged such that a pair of the sustain electrodes face the address electrode, but the constitution shall not be limited to the above constitution. In these cases, in view of the structural simplification of the plasma display device, preferably, the first direction and the second direction cross each other at right angles. Further, there may be also employed a constitution in which a pair of the sustain electrodes and the address electrode are formed on the first substrate. 
     In the plasma display device according to any one of the first to fifth aspects of the present invention, the form of a gap between the edge portions of a pair of the sustain electrodes may be linear. Otherwise, the form of the above gap may have a pattern bent or curved in the width direction of the sustain electrode. In this case, the area of portions of the sustain electrodes which portions contribute to discharging can be increased. 
     The plasma display device of the present invention will be explained with reference to the tri-electrode type plasma display device hereinafter. For the bi-electrode type plasma display device, “address electrode” in the following explanation can be taken as “the other sustain electrode” as required. 
     The electrically conductive material constituting the sustain electrode differs depending upon whether the plasma display device is a transmissiton type or a reflection type. In the transmission type plasma display device, light emission from the fluorescence layers is observed through the second substrate, so that it is not any problem whether the electrically conductive material constituting the sustain electrode is transparent or non-transparent. However, since the address electrode is formed on the second substrate, the address electrode is required to be transparent. In the reflection type plasma display device, light emission from the fluorescence layers is observed trough the first substrate, so that it is not any problem whether the electrically conductive material constituting the address electrode is transparent or non-transparent. However, the electrically conductive material constituting the sustain electrode is required to be transparent. The term “transparent or non-transparent” is based on the transmissivity of the electrically conductive material to light at a wavelength of emitted light (in visible light region) inhererent to fluorescence materials. That is, when an electrically conductive material constituting the sustain electrode or the address electrode is transparent to light emitted from the fluorescence layers, it can be said that the electrically conductive material is transparent. The non-transparent electrically conductive material includes Ni, Al, Au, Ag, Pd/Ag, Cr, Ta, Cu, Ba, LaB 6 , Ca 0.2 La 0.8 CrO 3 , etc., and these materials may be used alone or in combination. The transparent electrically conductive material includes ITO (indium-tin oxide) and SnO 2 . The sustain electrode and the address electrode can be formed by a sputtering method, a deposition method, a screen printing method, a sand blasting method, a plating method or a lift-off method. 
     There may be employed a constitution in which, in addition to the sustain electrode, a bus electrode composed of a material having a lower electric resistivity than the sustain electrode is formed in contact with the sustain electrode for decreasing the impedance of the sustain electrode as a whole. The bus electrode can be composed, typically, of a metal material such as Ag, Au, Al, Ni, Cu, Mo, Cr or a Cr/Cu/Cr stacked film. In the reflection type plasma display device, the bus electrode composed of the above metal material can be a factor to decrease a transmission quantity of visible light which is emitted from the fluorescence layers and passes through the first substrate, so that the brightness of a display screen is decreased. It is therefore preferred to form the bus electrode so as to be as narrow as possible so long as an electric resistance value necessary for the sustain electrode as a whole can be obtained. The bus electrode can be formed by a sputtering method, a deposition method, a screen printing method, a sand blasting method, a plating method or a lift-off method. 
     Preferably, a dielectric material layer is formed on the surface of the sustain electrode, for example, by an electron beam deposition method, a sputtering method, a deposition method or a screen printing method. When the dielectric material layer is formed, the direct contact of ions or electrons to the sustain electrode can be prevented, and as a result, the wearing of the sustain electrode can be prevented. The dielectric material layer works to accumulate a wall charge, works as a resistor to limit an excess discharge current and works as a memory to sustain a discharge state. The dielectric material layer can be composed, typically, of a low-melting glass or silicon oxide, or it can be also formed from other dielectric material. 
     More preferably, a protective layer is formed on the dielectric material layer. When the protective layer is formed, the direct contact of ions or electrons to the sustain electrode can be prevented, and as a result, the wearing of the sustain electrode can be prevented. The protective layer also works to emit secondary electrons necessary for discharge. The material constituting the protective layer includes magnesium oxide (MgO), magnesium fluoride (MgF 2 ) and calcium fluoride (CaF 2 ). Of these, magnesium oxide is a suitable material having properties such as a high emission ratio of secondary electrons, a low sputtering ratio, a high light transmissivity at a wavelength of light emitted from the fluorescence layers and a low discharge intiating voltage. The protective layer may be constituted of a stacked structure composed of at least two materials selected from the group consisting of these materials. 
     In the plasma display device of the present invention, examples of the material constituting the first substrate for the first panel and the second substrate for the second panel include high-distortion-point glass, soda glass (Na 2 O·CaO·SiO 2 ), borosilicate glass (Na 2 O·B 2 O 3 ·SiO 2 ), forsterite (2MgO·SiO 2 ) and lead glass (Na 2 O·PbO·SiO 2 ). The material for the first substrate and the material for the second substrate may be the same as, or different from, each other. 
     The fluorescence layer is composed of a fluorescence material selected from the group consisting of a fluorescence material which emits light in red, a fluorescence material which emits light in green and a fluorescence material which emits light in blue. The fluorescence layer is formed on or above the address electrode. When the plasma display device is for displaying in colors, specifically, the fluorescence layer composed of a fluorescence material which emits light, for example, of a red color (red fluorescence layer) is formed on or above the address electrode, the fluorescence layer composed of a fluorescence material which emits light, for example, of a green color (green fluorescence layer) is formed on or above another address electrode, and the fluorescence layer composed of a fluorescence material which emits light, for example, of a blue color (blue fluorescence layer) is formed on or above still another address electrode. These three fluorescence layers for emitting light of three primary colors form one set, and such sets are formed in a predetermined order. A region where a pair of the sustain electrodes and one set of the fluorescence layers which emit light of three primary colors overlap corresponds to one pixel. Each of the red fluorescence layer, the green fluorescence layer and the blue fluorescence layer may be formed in the form of a stripe, or may be formed in the form of a dot. Further, the fluorescence layers may be formed only on regions where the sustain electrodes and the address electrodes overlap. 
     As the fluorescence material for constituting the fluorescence layers, fluorescence materials which have high quantum efficiency and causes less saturation to vacuum ultraviolet ray can be selected from known fluorescence materials as required. When the plasma display device is assumed to be used as a color display, it is preferred to combine those fluorescence materials which have color purities close to three primary colors defined in NTSC, which give excellent white balance when three primary colors are mixed, which show a small afterglow time period and which can secure that the afterglow time periods of three primary colors are nearly equal. Examples of the fluorescence material which emits light in red when irradiated with vacuum ultraviolet ray include (Y 2 O 3 :Eu), (YBO 3 Eu), (YVO 4 :Eu), (Y 0.96 P 0.60 V 0.40 O 4 :Eu 0.04 ), [(Y,Gd)BO 3 :Eu], (GdBO 3 :Eu), (ScBO 3 :Eu) and (3.5MgO·0.5MgF 2 ·GeO 2 :Mn). Examples of the fluorescence material which emits light in green when irradiated with vacuum ultraviolet light include (ZnSiO 2 :Mn), (BaAl 12 O 19 :Mn), (BaMg 2 Al 16 O 27 :Mn), (MgGa 2 O 4 :Mn), (YBO 3 :Tb), (LuBO 3 :Tb) and (Sr 4 Si 3 O 8 Cl 4 :Eu). Examples of the fluorescence material which emits light in blue when irradiated with vacuum ultraviolet ray include (Y 2 SiO 5 :Ce), (CaWO 4 :Pb), CaWO 4 , YP 0.85 V 0.15 O 4 , (BaMgAl 14 O 23 :Eu), (Sr 2 P 2 O 7 :Eu) and (Sr 2 P 2 O 7 :Sn). The method for forming the fluorescence layers includes a thick film printing method, a method in which fluorescence particles are sprayed, a method in which an adhesive substance is pre-applied to a region where the fluorescence layers are to be formed and fluorescence particles are allowed to adhere, a method in which a photosensitive fluorescence paste (slurry) is provided and a fluorescence layer is patterned by exposure and development, and a method in which a fluorescence layer is formed on the entire surface and unnecessary portions are removed by a sand blasting method. 
     The fluorescence layer may be formed directly on the address electrode or may be formed on the address electrode and on the side walls of the separation wall. Otherwise, the fluorescence layer may be formed on the dielectric film formed on the address electrode or may be formed on the dielectric film formed on the address electrode and on the side walls of the separation wall. Further, the fluorescence layer may be formed only on the side walls of the separation wall. The material constituting the dielectric film includes a low-melting glass and silicon oxide, and it can be formed by a screen printing method, a sputtering method or a vacuum deposition method. In some cases, a protective layer composed of magnesium oxide (MgO), magnesium fluoride (MgF 2 ) or calcium fluoride (CaF 2 ) may be formed on the fluorescence layer and the separation wall. 
     Preferably, the separation walls (ribs) extending in parallel with the address electrodes are formed on the second substrate. The separation wall (rib) may have a meander structure. When the dielectric film is formed on the second substrate and on the address electrode, the separation wall may be formed on the dielectric film in some cases. The material constituting the separation wall can be selected from a known insulating material. For example, a mixture of a widely used low-melting glass with a metal oxide such as alumina can be used. The separation wall can be formed by a screen printing method, a sand blasting method, a dry filming method and a photosensitive method. The above screen printing method refers to a method in which opening portions are formed in those portions of a screen which correspond to portions where the separation walls are to be formed, a separation-wall-forming material on the screen is passed through the opening portion with a squeeze to form a separation-wall-forming material layer on the second substrate or the dielectric film (these will be generically referred to as “second substrate or the like” hereinafter), and then the separation-wall-forming material layer is calcined or sintered. The above dry filming method refers to a method in which a photosensitive film is laminated on the second substrate or the like, the photosensitive film on regions where the separation walls are to be formed is removed by exposure and development, opening portions formed by the removal are filled with a separation-wall-forming material and the separation-wall-forming material is calcined or sintered. The photosensitive film is combusted and removed by the calcining or sintering and the separation-wall-forming material filled in the opening portions remains to constitute the separation walls. The above photosensitive method refers to a method in which a photosensitive material layer for forming the separation walls is formed on the second substrate or the like, the photosensitive material layer is patterned by exposure and development and then the patterned photosensitive material layer is calcined or sintered. The above sand blasting method refers to a method in which a separation-wall-forming material layer is formed on the second substrate or the like, for example, by screen printing or with a roll coater, a doctor blade or a nozzle-ejecting coater and is dried, then, those portions where the separation walls are to be formed in the separation-wall-forming material layer are masked with a mask layer and exposed portions of the separation-wall-forming material layer are removed by a sand blasting method. The separation walls may be formed in black to form a so-called black matrix. In this case, a high contrast of the display screen can be attained. The method of forming the black separation walls includes a method in which the separation walls are formed from a color resist material colored in black. 
     One discharge cell is constituted of a pair of the separation walls formed on or above the second substrate, and the sustain electrodes, the address electrode and the fluorescence layer (one fluorescence layer of a red fluorescence layer, a green fluorescence layer or a blue fluorescence layer) which occupy a region surrounded by the pair of the separation walls. The discharge gas is sealed in the above discharge cell, more specifically, the discharge space surrounded by the separation walls, and the fluorescence layer emits light when irradiated with vacuum ultraviolet ray generated by AC glow discharge which takes place in the discharge gas in the discharge space. 
     In the alternating current driven type plasma display device according to the first aspect of the present invention, the discharge gas composed of a xenon (Xe) gas alone is used. In the alternating current driven type plasma display device according to the second aspect of the present invention, the discharge gas composed of a krypton (Kr) gas alone is used. In the alternating current driven type plasma display device according to the third aspect of the present invention, the discharge gas consisting of a mixture of a xenon (Xe) gas and a krypton (Kr) gas alone is used. Therefore, the pressure of the xenon or krypton gas which contributes to light emission can be relatively remarkably increased as compared with the counterpart in a conventional alternating current driven type plasma display device. As a result, the light emission efficiency is improved, and the stability of discharge can be maintained even if the total pressure of the discharge gas is maintained at a lower level. At the same time, a brightness higher than the counterpart obtained by increasing the discharge gas pressure can be achieved. 
     In the alternating current driven type plasma display device according to the fourth aspect of the present invention, mainly, the first gas contributes to the light emission of the fluorescence layers. And, since the discharge gas consists of a mixture of the first gas with the second gas, the discharge initiating voltage V bd  can be decreased due to a Penning effect. Further, the partial pressure and the concentration of the first gas are defined, and the volume ratio of, for example, a xenon (Xe) gas in the mixed gas is increased, so that the brightness of the alternating current driven type plasma display device can be increased. 
     In the alternating current driven type plasma display device according to the fifth aspect of the present invention, mainly, a xenon gas contributes to the light emission of the fluorescence layers. And, since the discharge gas consists of the mixed gas of a xenon gas, the brightness of the alternating current driven type plasma display device can be increased. Further, the concentration of the xenon gas in the mixed gas is defined, so that the discharge initiating voltage V bd  relative to the value of brightness can be decreased and that the light emission efficiency can be accordingly improved. 
     Meanwhile, the plasma display device is with the law of Paschen as explained already, that is, the discharge initiating voltage V bd  can be expressed by the function of the product (d·p) of the distance (d) and the gas pressure (p). In the plasma display device of the present invention, the distance (d) of a pair of the sustain electrodes is defined to be less than 5×10 −5  m, preferably, less than 5.0×10 −5  m, more preferably, 2×10 −5  m or less. In this case, not only the discharge initiating voltage V bd  can be decreased, but also the pressure or partial pressure of the gas which contributes to light emission (a xenon gas, a krypton gas or the first gas) can be further increased, so that the brightness of the plasma display device can be further increased. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be explained on the basis of Examples with reference to drawings. 
     FIG. 1 is a schematic partial exploded perspective view of a general constitution example of a tri-electrode type alternating current driven type plasma display device. 
     FIG. 2 is a graph showing relationships between Xe gas concentrations and brightness measurement results with regard to total gas pressures in the plasma display devices of Example 1. 
     FIG. 3 is a graph showing relationships between Xe gas concentrations and brightness measurement results with regard to Xe gas partial pressures in the plasma display devices of Example 1. 
     FIG. 4 is a graph showing relationships between Xe gas concentrations and optimum discharge voltages with regard to total gas pressures in the plasma display devices of Example 1. 
     FIG. 5 is a graph showing a relationship between a distance between a pair of sustain electrodes and a brightness measurement result in the plasma display devices of Example 2. 
     FIG. 6 is a graph showing a relationship between a Kr gas concentration in a mixed gas of Xe gas and Kr gas and a brightness measurement result in the plasma display devices of Example 3. 
     FIG. 7 is a graph showing relationships between Kr gas concentrations and brightness measurement results with regard to total gas pressures in the plasma display devices of Example 4. 
     FIG. 8 is a graph showing relationships between Kr gas concentrations and brightness measurement results with regard to Kr gas partial pressures in the plasma display devices of Example 4. 
     FIG. 9 is a graph showing relationships between Kr gas concentrations and optimum discharge voltages with regard to total gas pressures in the plasma display devices of Example 4. 
     FIG. 10 is a graph showing a relationship between the brightness of light emitted from a discharge gas alone and a color of the emitted light. 
     FIGS. 11A,  11 B and  11 C are schematic partial plan views of two sets of a pair of sustain electrodes when the gap formed by edge portions of a pair of the facing sustain electrodes has the form of a pattern bent or curved in the width direction of the sustain electrodes. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A tri-electrode type plasma display device having a structure shown in FIG. 1 was fabricated by the following method. Plasma display devices to be explained below are plasma display devices for various tests and differ from plasma display devices to be mass-produced practically. Therefore, evaluation of brightness values obtained by a brightness measurement is not any absolute evaluation and is relative evaluation. 
     A first panel  10  was produced by the following method. First, an ITO layer was formed on the entire surface of a first substrate  11  made of a high-distortion-point glass or a soda glass, for example, by a sputtering method, and the ITO layer was patterned in the form of stripes by photolithography and etching, to form a plurality of pairs of sustain electrodes  12 . The sustain electrodes  12  extend in a first direction. Then, an aluminum layer was formed on the entire surface, for example, by a deposition method, and the aluminum layer was patterned by photolithography and etching to form bus electrodes  13  along the edge portions of the sustain electrodes  12 . Then, a dielectric material layer  14  which, for example, had a thickness of 3 μm and was composed of silicon oxide (SiO 2 ) was formed on the entire surface, and a 0.6 μm thick protective layer  15  composed of magnesium oxide (Mgo) was formed thereon by an electron beam deposition method. By the above steps, the first panel  10  can be completed. 
     A second panel  20  was produced by the following method. First, a silver paste was printed on a second substrate  21  made of a high-distortion-point glass or a soda glass by a screen printing method such that the silver paste had the form of stripes, and then the silver paste was calcined or sintered to form address electrode  22 . The address electrode  22  extends in a second direction which crosses the first direction at right angles. Then, a low-melting glass paste layer was formed on the entire surface by a screen printing method, and the low-melting glass paste layer was calcined or sintered to form a dielectric film  23 . Then, a low-melting glass paste was printed on the dielectric film  23  above a region between one address electrode  22  and another address electrode  22 , for example, by a screen printing method, and calcined or sintered to form separation walls  24 . The separation wall had an average height of 130 μm. Fluorescence material slurries of three primary colors were consecutively printed and calcined or sintered to form each of fluorescence layers  25 R,  25 G and  25 B on the dielectric film  23  between one separation wall  24  and another separation wall  24  and on the side walls of each separation wall  24 . By the above steps, the second panel  20  can be completed. 
     Then, a plasma display device was assembled. That is, a seal layer made of a frit glass was formed on a circumferential portion of the second panel  20 . Then, the first panel  10  and the second panel  20  were attached to each other and then calcined or sintered to cure the seal layer. Then, a space formed between the first panel  10  and the second panel  20  was vacuumed, charged with a discharge gas and sealed to complete the plasma display device. 
     For a testing purpose, the sustain electrodes  12  was determined to have a width of 0.2 mm and a thickness of approximately 0.3 μm. There were prepared plasma display devices for testing, in which the distance (d) between a pair of the sustain electrodes  12  was 10 μm, 20 μm, 40 μm or 70 μm. 
     One example of glow discharge operation of the thus-constituted plasma display device will be explained below. First, for example, a pulse voltage higher than a discharge initiating voltage V bd  is applied to all of one sustain electrodes between pairs of the sustain electrodes  12  for a short time of period, whereby glow discharge takes place, and a wall charge is generated and accumulated on the surface of the dielectric material layer  14  near the one sustain electrode between a pair of the sustain electrodes  12  due to dielectric polarization, so that an apparent discharge initiating voltage decreases. Then, while a voltage is applied to the address electrode  22 , a voltage is applied to the one sustain electrode between a pair of the sustain electrodes  12  included in the discharge cell which is not driven for display, whereby glow discharge is allowed to take place between the address electrode  22  and the one sustain electrode between a pair of the sustain electrodes  12  to erase the accumulated wall charge. The above discharge for erasing is carried out consecutively in the address electrodes  22 . On the other hand, no voltage is applied to the one sustain electrode between a pair of the sustain electrodes included in the discharge cell which is driven for display, whereby the accumulation of the wall charge is sustained. Then, a predetermined pulse voltage is applied between all of pairs of the sustain electrodes  12 . As a result, in the cell where the wall charge is accumulated, glow discharge starts between each pair of the sustain electrodes  12 , and in the discharge cell, the fluorescence layer excited by irradiation with vacuum ultraviolet ray generated on the basis of the glow discharge in the discharge gas in the discharge space emits light in color inherent to the fluorescence material. The phase of the discharge sustain voltage applied to one sustain electrode between a pair of the sustain electrodes and the phase of the discharge sustain voltage applied to the other sustain electrode between a pair of the sustain electrodes deviate by half a cycle, and the polarity of the sustain electrodes is reversed depending upon the frequency of alternating current. 
     EXAMPLE 1 
     Example 1 is concerned with the plasma display devices according to the first, fourth and fifth aspects of the present invention. Example 1 used the plasma display devices for testing in which the distance between a pair of the sustain electrodes  12  was constant or 20 μm. Example 1 used a mixed gas of a xenon (Xe) gas as a first gas and a neon (Ne) gas as a second gas. While the Xe gas concentration was varied between 4% by volume and 100% by volume, the total pressure of the mixed gas was set at 5×10 3  Pa (indicated by hollow squares in FIGS.  2  and  4 ), 1×10 4  Pa (indicated by hollow triangles in FIGS.  2  and  4 ), 3×10 4  Pa (indicated by solid circles in FIGS. 2 and 4) or 6.6×10 4  Pa (indicated by hollow circles in FIGS.  2  and  4 ). The plasma display devices for testing under such conditions were measured for brightness. The voltage to be applied was set at an optimum level depending upon the total pressure in each gas mixture, and FIG. 4 shows the optimum discharge voltages with regard to the total pressures. In the drawings, the pressure is shown in the unit of “kPa”, and the distance between a pair of the sustain electrodes is shown as “Discharge gap”. 
     FIGS. 2 and 3 show results of brightness measurement of the prepared plasma display devices. FIG. 2 is a graph showing the relationships between the Xe gas concentrations and the brightness measurement results with regard to the total gas pressures. FIG. 3 is a graph showing the relationships between the Xe gas concentrations and the brightness measurement results with regard to the Xe gas partial pressures on the basis of data shown in FIG.  2 . FIG. 2 clearly shows that with an increase in the Xe gas concentration, the brightness increases. Further, FIG. 3 clearly shows that with an increase in the partial pressure of a Xe gas, the brightness increases. When the Xe gas pressure is particularly 30% by volume or higher, a high brightness can be attained. Further, with an increase in the Xe gas concentration, the brightness increases. In this case, the partial pressure of the Xe gas is required to be at least 1×10 3  Pa. When the partial pressure of the Xe gas is lower than the above level, the discharge initiating voltage comes to be extremely high due to the law of Paschen. Further, as shown in FIGS. 2 and 4, when the total pressure of the mixed gas is less than 6.6×10 4  Pa, the discharge voltage can be maintained at approximately 200 volts or lower, and a high brightness can be also attained. When the Xe gas concentration is particularly 100% by volume, that is, when the discharge gas consists of a xenon gas alone, a very high brightness can be attained even if the xenon gas concentration is 6.6×10 4  Pa or higher, which sufficiently offsets an increase in the discharge voltage. Therefore, the total pressure of the discharge gas can be decreased, and a high brightness can be attained without incurring a decrease in reliability caused, for example, by a frit seal. 
     EXAMPLE 2 
     Example 2 used plasma display devices for testing in which the distance between a pair of the sustain electrodes  12  was 10 μm, 20 μm, 40 μm or 70 μm. And, the plasma display devices having a xenon gas pressure of 1.0×10 4  Pa and a xenon gas concentration of 100% by volume were measured for brightness. 
     FIG. 5 shows results of the brightness measurement of the prepared plasma display devices. FIG. 5 clearly shows that the brightness tends to increase with a decrease in the distance between a pair of the sustain electrodes  12 . That is, it is seen that when the distance between a pair of the sustain electrodes is less than 5×10 −5  m, preferably less than 5.0×10 −5  m, more preferably 2×10 −5  m or less, higher brightness can be obtained. 
     Further, in cases using other discharge gases, that is, in the plasma display devices according to the second to fifth aspects of the present invention, similarly, the brightness tends to increase with a decrease in the distance between a pair of the sustain electrodes  12 . 
     EXAMPLE 3 
     Example 3 is concerned with the plasma display devices according to the first, second and third aspects of the present invention. Example 3 used plasma display devices in which the distance between a pair of the sustain electrodes  12  was constant or 20 μm, and the discharge gas consisted of a xenon gas and a krypton gas alone. 
     FIG. 6 shows results of the brightness measurement of the prepared plasma display devices. The results shown in FIG. 6 are results of brightness measurements when the total pressure of the mixed gas of a xenon gas and a krypton gas alone was constant or 1×10 4  Pa (10 kPa) and the concentration ratio of the Kr gas was varied between 0% and 100%. FIG. 6 clearly shows that the use of the mixed gas of a Xe gas and a Kr gas as a discharge gas gives a higher brightness than the use of a Xe gas alone or a Kr gas alone. Like the results shown in Example 1, further, the mixed gas of a Xe gas and a Kr gas give a higher brightness even when the total pressure of the mixed gas is less than 6.6×10 4  Pa (500 Torr). Therefore, the total pressure of the discharge gas can be decreased, and a high brightness can be attained without incurring a decrease in reliability caused, for example, by a frit seal. 
     EXAMPLE 4 
     Example 4 is concerned with the plasma display devices according to the second and fourth aspects of the present invention. Example 4 used the plasma display devices for testing in which the distance between a pair of the sustain electrodes  12  was constant or 20 μm. Further, the mixed gas of a krypton (Kr) gas as the first gas and a neon (Ne) gas as the second gas were used. While the Kr gas concentration was varied between 4% by volume and 100% by volume, the total pressure of the mixed gas was set at 5×10 3  Pa (indicated by hollow squares in FIGS.  7  and  9 ), 1×10 4  Pa (indicated by hollow triangles in FIGS.  7  and  9 ), 3×10 4  Pa (indicated by solid circles in FIGS. 7 and 9) or 6.6×10 4  Pa (indicated by hollow circles in FIGS.  7  and  9 ). The plasma display devices for testing under such conditions were measured for brightness. The voltage to be applied was set at an optimum level depending upon the total pressure in each gas mixture, and FIG. 9 shows the optimum discharge voltages with regard to the total pressures. 
     FIGS. 7 and 8 show the results of the brightness measurements of the prepared plasma display devices. FIG. 7 shows a graph of the relationships between the Kr gas concentrations and the brightness measurement results with regard to the total gas pressures. FIG. 8 shows a graph of the relationships between the Kr gas concentrations and the brightness measurement results with regard to the Kr gas partial pressures on the basis of data shown in FIG.  7 . FIG. 7 clearly shows that with an increase in the Kr gas concentration, the brightness increases. Further, FIG. 8 clearly shows that with an increase in the partial pressure of a Kr gas, the brightness increases. When the Kr gas pressure is particularly 30% by volume or higher, a high brightness can be attained. Further, with an increase in the Kr gas concentration, the brightness increases. In this case, the partial pressure of the Kr gas is required to be at least 1×10 3  Pa. When the partial pressure of the Kr gas is lower than the above level, the discharge initiating voltage comes to be extremely high due to the law of Paschen. Further, as shown in FIGS. 7 and 9, when the total pressure of the mixed gas is less than 6.6×10 4  Pa, the discharge voltage can be maintained at approximately 200 volts or lower, and a high brightness can be also attained. When the Kr gas concentration is particularly 100% by volume, that is, when the discharge gas consists of a krypton gas alone, a very high brightness can be attained even if the krypton gas concentration is 6.6×10 4  Pa or higher, which sufficiently offsets an increase in the discharge voltage. Therefore, the total pressure of the discharge gas can be decreased, and a high brightness can be attained without incurring a decrease in reliability caused, for example, by a frit seal. 
     EXAMPLE 5 
     Example 5 used a plasma display device having no fluorescence layers formed, and the plasma display device was tested for discharge and measured for brightness. In the test, the distance between a pair of the sustain electrodes  12  was 20 μm, the discharge gas consisted of 100% by volume of a Xe gas and the applied voltage was set at 150 volts. For comparison, there was prepared a plasma display device in which the distance between a pair of the sustain electrodes  12  was 20 μm and the discharge gas consisted of 4% by volume of a Xe gas and 96% by volume of a Ne gas, and the plasma display device was allowed to discharge at an applied voltage of 150 volts. These plasma display devices were measured for brightness. 
     Since the plasma display devices having no fluorescence materials were used, each of the brightness obtained by the measurement was data based on the light emission (visible light) of the discharge gas. FIG. 10 shows a chromaticity diagram of a relationship between a measured brightness and color of emitted light. Generally, the light emission of the discharge gas is an undesirable phenomenon since it decreases a contrast of the plasma display device. In Comparative Example (4% by volume of a Xe gas and 96% by volume of a Ne gas) shown in FIG. 10, the discharge gas showed a brightness of 24.11 (lm/m 2 ), which is not negligible. In Example 5, consisting of 100% by volume of a Xe gas, the discharge gas showed a brightness of 2.93 (lm/m 2 ), which is approximately ⅛ of the data in Comparative Example. Therefore, the contrast in the image display of the plasma display device can be maintained in an excellent state. 
     Further, as shown in the chromaticity diagram in FIG. 10, the color of emitted light in Comparative Example is orange, and this is caused by the main light emission of a Ne gas which emits light in orange. In Example 5, the color of emitted light is close to blue, and it is seen that the influence of the discharge gas in Example 5 on the color tone in image display of the plasma display device is smaller than the counterpart in Comparative Example. 
     The results of the above Examples 1 to 5 are summarized as follows. 
     (1) With an increase in the partial pressure of the first gas, the brightness increases, and when the partial pressure of the first gas is particularly 4×10 3  Pa or higher, a high brightness can be attained. 
     (2) When the concentration of the first gas is at least 10% by volume, particularly, at least 30% by volume, the brightness increases. The partial pressure of the first gas is required to be at least 1×10 3  Pa or higher. 
     (3) When the total gas pressure is less than 6.6×10 4  Pa, the discharge sustain voltage can be retained at a low level sufficient for driving. 
     (4) When the discharge gas is selected from a xenon (Xe) gas alone, a krypton (Kr) gas alone or a mixture of these, the brightness can be further improved. 
     (5) With a decrease in the distance between a pair of the sustain electrodes, the brightness tends to increase. Particularly, when the distance between a pair of the sustain electrodes is less than 5×10 −5  m particularly equal to, or less than, 2×10 −5  m, and when the concentration of the first gas is at least 10% by volume, particularly at least 30% by volume, the brightness remarkably increases. 
     While the present invention has been explained on the basis of preferred embodiments hereinabove, the present invention shall not be limited thereto. The structures or constitutions of the plasma display device explained in Examples and the materials, dimensions and production methods employed in Examples are all for illustrative purposes and can be modified or altered as required. The present invention can be applied to a transmission type plasma display device which permits observation of light emission of the fluorescence layers through the second substrate. In Examples, plasma display devices are constituted of a pair of the sustain electrodes extending in parallel with each other. Instead of such a constitution, there may be employed a constitution in which a pair of the bus electrodes extend in a first direction, one sustain electrode between a pair of the sustain electrodes extends in a second direction from one bus electrode between a pair of the bus electrodes toward and near the other bus electrode between a pair of the bus electrodes, and the other sustain electrode between a pair of the sustain electrodes extends in the second direction from the other bus electrode between a pair of the bus electrodes toward and near the one bus electrode between a pair of the bus electrodes. There may be employed a constitution in which one sustain electrode between a pair of the sustain electrodes extending in the first direction is formed on the first substrate and the other sustain electrode between a pair of the sustain electrodes is formed on an upper portion of the side wall of the separation wall in parallel with the address electrode. Further, the plasma display device of the present invention may be a bi-electrode type plasma display device. Furthermore, the address electrode can be formed on the first substrate. The thus-structured plasma display device can be constituted, for example, of a pair of the sustain electrodes extending in a first direction and an address electrode along one sustain electrode between a pair of the sustain electrodes in the vicinity of the one sustain electrode between a pair of the sustain electrodes (provided that the length of the address electrode along one sustain electrode between a pair of the sustain electrodes is equal to, or smaller than, the length of a discharge cell along the first direction). In addition, there is employed a structure in which a wiring for the address electrode which wiring extends in a second direction is formed through an insulating layer for preventing the short-circuiting thereof to the sustain electrodes, the wiring for the address electrode and the address electrode are electrically connected to each other, or the address electrode extends from the wiring for the address electrode. 
     In Examples, the gap formed by the edge portions of a pair of the facing sustain electrodes has the form of a straight line. However, the gap formed by the edge portions of a pair of the facing sustain electrodes may have the form of a pattern bent or curved in the width direction of the sustain electrodes (for example, a combination of any forms such as the forms of a “dogleg”, “S-letter” or arc). In such a constitution, the length of each of facing edge portions of a pair of the facing sustain electrodes can be increased, so that the discharge efficiency can be expected to improve. FIGS. 11A,  11 B and  11 C show schematic partial plan views of two sets of a pair of sustain electrodes having the above structures. 
     Alternatively, the plasma display device can be operated in the following AC glow discharge. First, erasing discharge is carried out with regard to all the pixels for initializing all the pixels. Then, discharge operation is carried out. The discharge operation is divided into an address period for which a wall charge is generated in the surface of the dielectric material layer by an initial discharge and a discharge sustain period for which the glow discharge is sustained. In the address period, a pulse voltage lower than the discharge initiating voltage V bd  is applied to selected one sustain electrode between a pair of the sustain electrodes and to a selected address electrode. A region where the pulse-applied one sustain electrode between a pair of the sustain electrodes and the pulse-applied address electrode overlap is selected as a display pixel, and in the overlap region, the wall cahrge is generated in the surface of the dielectric material layer due to dielectric polarization, whereby the wall charge is accumulated. In the succeeding discharge sustain period, a discharge sustain voltage V sus  lower than V bd  is applied to a pair of the sustain electrodes. When the sum of the wall voltage V W  induced by the wall charge and the discharge sustain voltage V sus  comes to be greater than the discharge initiating voltage V bd , (i.e., V W +V sus &gt;V bd ), glow discharge is initiated. The phases of the discharge sustain voltages V sus  applied to one sustain electrode between a pair of the sustain electrodes and the phase of the discharge sustain voltage V sus  applied to the other sustain electrode between a pair of the sustain electrodes deviate from each other by half a cycle, and the polarity of each electrode is reversed according to the frequency of alternate current. 
     In the alternating current driven type plasma display devices according to the first to third aspects of the present invention, since the discharge gas consists of a xenon (Xe) gas alone or a krypton (Kr) gas alone, or the discharge gas consists of a mixed gas of a xenon (Xe) gas and a krypton (Kr) gas, a high brightness can be achieved, the discharge voltage can be decreased, the total pressure of the discharge gas can be decreased, and the reliability of the alternating current driven type plasma display device can be improved. Otherwise, in the alternating current driven type plasma display devices according to the fourth and fifth aspects of the present invention, since the discharge gas consists of a mixed gas and the partial pressure and the concentration of the first gas or a xenon gas which mainly contributes to discharging are defined, a high brightness can be achieved and the discharge voltage can be decreased. The concentration of the first gas or the xenon gas is increased, in other words, the concentration of the second gas or the other gas is decreased, and when the partial pressure of the first gas or the xenon gas is constant, the total pressure of the discharge gas can be decreased, so that the reliability of the alternating current driven type plasma display device can be improved. Further, since the discharge voltage can be decreased, a load on a driving circuit of the alternating current driven type plasma display device can be decreased, and further, the discharge is improved in stability.