Abstract:
A Plasma Display Panel (PDP) having a structure capable of preventing a permanent afterimage generated by damage to a protective film during a sustain discharge includes: front and rear substrates arranged to face each other; barrier ribs arranged between the front and rear substrates to partition discharge cells in combination with the front and rear substrates; a plurality of electrodes adapted to generate a discharge in the discharge cells; a plurality of X electrodes each including a transparent X electrode arranged at a rear side of the front substrate in the discharge cell to extend in one direction; a plurality of Y electrodes each including a transparent Y electrode arranged at a rear side of the front substrate in the discharge cell to be spaced apart from the X electrode by a gap and to extend to and be aligned with the transparent X electrode; opaque X and Y shield layers respectively arranged on one end surface of the transparent X and Y electrodes, the one end surfaces neighboring the gap; a first dielectric layer arranged to cover a rear surface of the front substrate, the X and Y electrodes, and the opaque X and Y shield layers; a protective layer arranged to coat a rear surface of the first dielectric layer; a phosphor layer arranged in each discharge cell; and a discharge gas filling in an inner space of each discharge cell.

Description:
CLAIM OF PRIORITY  
       [0001]     This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for PLASMA DISPLAY PANEL earlier filed in the Korean Intellectual Property Office on 13 Oct. 2004 and there duly assigned Serial No. No. 10-2004-0081750.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a Plasma Display Panel (PDP), and more particularly, to a PDP in which electrodes are respectively formed on facing substrates, a discharge gas is injected into a discharge space between the facing substrates, UltraViolet (UV) light rays are radiated in the discharge space by a voltage supplied to the electrodes, and an image is produced by light emitted by the UV light rays.  
         [0004]     2. Description of the Related Art  
         [0005]     A PDP can be broadly classified into a Direct Current (DC) PDP and an Alternating Current (AC) PDP according to the type of discharge. In the DC PDP, corresponding electrodes are exposed to a discharge space, and a discharge is generated by a direct movement of charged particles between the corresponding electrodes. In the AC PDP, at least one electrode is covered with a dielectric layer, and a discharge is generated by an electric field induced by a wall charge, instead of by the direct movement of the charged particles.  
         [0006]     A unit PDP panel includes an upper plate for displaying an image to users and a lower plate arranged to face the upper plate.  
         [0007]     The upper plate includes a front substrate and sustain electrode pairs. The front substrate is made of glass, and the sustain electrode pairs are arranged on a rear surface of the front substrate. The sustain electrode pair includes an X electrode and a Y electrode. The X electrode includes a transparent X electrode and a bus X electrode formed on a partial rear surface of the transparent X electrode. The Y electrode includes a transparent Y electrode and a bus Y electrode formed on a partial rear surface of the transparent Y electrode.  
         [0008]     The lower plate includes a rear substrate and a plurality of address electrodes. The rear substrate is arranged to face the front substrate, and the address electrodes are arranged on a front surface of the rear substrate to intersect the sustain electrode of the front substrate.  
         [0009]     A front dielectric layer is formed on the rear surface of the front substrate to bury the sustain electrode pair, and a rear dielectric layer is formed on the front surface of the rear substrate to bury the address electrodes. A protective film is formed on the front dielectric layer, and barrier ribs are formed on the rear dielectric layer to main a discharge distance, to partition discharge cells and to prevent an electro-optical crosstalk between the discharge cells.  
         [0010]     Red, Green, and Blue (RGB) phosphors are coated on both side surfaces of the barrier ribs and a front surface of the rear dielectric layer on which the barrier ribs are not formed.  
         [0011]     When a sustain discharge is generated between the X electrode and the Y electrode in the PDP, a discharge amount at the right portion (that is, a portion near the Y electrode) of the X electrode becomes larger than that of the left portion thereof, and a discharge amount at the left portion (that is, a portion near the X electrode) of the Y electrode becomes larger than that of the right portion thereof.  
         [0012]     That is, a sustain discharge amount at a gap portion between the facing portions of the electrodes is relatively large. However, the sustain discharge amount at the gap portion becomes too large when the sustain discharge is sustained. Accordingly, a portion of the protective film corresponding to the gap portion is damaged more greatly than the other portions thereof.  
         [0013]     However, since the transparent X electrode and the transparent Y electrode are arranged on the front substrate corresponding to a center portion of a discharge cell so as to increase luminance, the greatly-damaged portion of the protective film  19  is undesirably observed by the naked eye through the transparent electrodes.  
         [0014]     The protective film protects the front dielectric layer from ion sputtering and lowers a sustain voltage and a driving voltage due to its high Secondary Electron Emission (SEE) coefficient. However, radiation efficiency greatly decreases especially at the greatly-damaged portion of the protective film, whereby a permanent afterimage (image sticking) is undesirably generated on the PDP.  
         [0015]     In addition, visible light rays generated by the RGB phosphors have different luminance ratios. Accordingly, an optimum color temperature cannot be obtained when sustain discharge frequencies for the RGB phosphors in each discharge cell coated with RGB phosphors are the same.  
         [0016]     A method that changes the thickness of the front or rear dielectric layer or an interval therebetween can be used to make the sustain discharge frequencies for the RGB phosphors different. However, such a method has a limitation in changing the thickness of the front or rear dielectric layer or the interval therebetween. Furthermore, the effect of such a structural modification becomes more reduced with a recent trend toward the size and thickness reduction of a PDP.  
       SUMMARY OF THE INVENTION  
       [0017]     The present invention provides a Plasma Display Panel (PDP) having a structure capable of preventing a permanent afterimage generated by damage to a protective film during a sustain discharge.  
         [0018]     The present invention also provides a PDP having a structure capable of adjusting a color temperature in each discharge cell equipped with phosphor layers generating visible light rays of different colors.  
         [0019]     According to one aspect of the present invention, a PDP is provided comprising: front and rear substrates arranged to face each other; barrier ribs arranged between the front and rear substrates to partition discharge cells in combination with the front and rear substrates; a plurality of electrodes adapted to generate a discharge in the discharge cells; a plurality of X electrodes each including a transparent X electrode arranged at a rear side of the front substrate in the discharge cell to extend in one direction; a plurality of Y electrodes each including a transparent Y electrode arranged at a rear side of the front substrate in the discharge cell to be spaced apart from the X electrode by a gap and to extend to and be aligned with the transparent X electrode; opaque X and Y shield layers respectively arranged on one end surface of the transparent X and Y electrodes, the one end surfaces neighboring the gap; a first dielectric layer arranged to cover a rear surface of the front substrate, the X and Y electrodes, and the opaque X and Y shield layers; a protective layer arranged to coat a rear surface of the first dielectric layer; a phosphor layer arranged in each discharge cell; and a discharge gas filling in an inner space of each discharge cell.  
         [0020]     The X electrode preferably includes a bus X electrode arranged on a rear end surface of the transparent X electrode and adapted to reduce line resistance of the transparent X electrode, and the Y electrode preferably includes a bus Y electrode arranged on a rear end surface of the transparent Y electrode and adapted to reduce line resistance of the transparent Y electrode.  
         [0021]     The opaque X and Y shield layers are preferably electrically conductive.  
         [0022]     The X and Y shield layers are preferably respectively of the same materials as those of the X and Y electrodes.  
         [0023]     The opaque X shield layer is preferably electrically conductive and is arranged on one end surface of the transparent X electrode neighboring the gap, and the opaque Y shield layer is preferably electrically conductive and is arranged on one end surface of the transparent Y electrode neighboring the gap.  
         [0024]     Each discharge cell is preferably one of RGB discharge cells having one of RGB phosphor layers adapted to generate one of the RGB visible light rays, and widths of X and Y shield layers disposed in the RGB discharge cells are preferably varied according to color types of the discharge cells.  
         [0025]     Widths of X and Y shield layers arranged in the R discharge cells are preferably greater than widths of X and Y shield layers arranged in the G discharge cells and widths of X and Y shield layers arranged in the G discharge cells are preferably greater than widths of X and Y shield layers arranged in the B discharge cells.  
         [0026]     Widths of X and Y shield layers arranged in the B discharge cells are preferably less than 50 μm, and widths of X and Y shield layers arranged in the R discharge cells are preferably less than 120 μm.  
         [0027]     The PDP preferably further comprises: an address electrode arranged on a front surface of the rear substrate; and a second dielectric layer arranged on a front side of the rear substrate to cover the rear substrate and the address electrode.  
         [0028]     According to another aspect of the present invention, a PDP is provided comprising: front and rear substrates arranged to face each other; barrier ribs arranged between the front and rear substrates and partitioning discharges cells in combination with the front and rear substrates; a plurality of electrodes adapted to generate a discharge in the discharge cells; a plurality of X electrodes each including a transparent X electrode arranged on a rear side of the front substrate in the discharge cell to extend in one direction; a plurality of Y electrodes each including a transparent Y electrode arranged on a rear side of the front substrate in the discharge cell to be spaced apart from the X electrode by a gap and to extend and be aligned with the transparent X electrode; opaque X and Y shield layers respectively arranged on one end surface of the transparent X and Y electrodes, the one end surfaces neighboring the gap; a first dielectric layer arranged to cover a rear surface of the front substrate, the X and Y electrodes, and the opaque X and Y shield layers; RGB phosphor layers adapted to respectively generate one of RGB visible light rays in each discharge cell; and a discharge gas filling in an inner space of each discharge cell; wherein widths of X and Y shield layers arranged in RGB discharge cells are varied according to required color types of the discharge cells.  
         [0029]     Widths of X and Y shield layers arranged in the R discharge cells are preferably greater than widths of X and Y shield layers arranged in the G discharge cells and widths of X and Y shield layers arranged in the G discharge cells are preferably greater than widths of X and Y shield layers arranged in the B discharge cells.  
         [0030]     The widths of X and Y shield layers arranged in the B discharge cells are preferably less than 50 μm, and the widths of X and Y shield layers arranged in the R discharge cells are preferably less than 120 μm.  
         [0031]     The opaque X and Y shield layers are preferably electrically conductive.  
         [0032]     The X electrode preferably includes a bus X electrode arranged on a rear end surface of the transparent X electrode and adapted to reduce line resistance of the transparent X electrode, and the Y electrode preferably includes a bus Y electrode arranged on a rear end surface of the transparent Y electrode and adapted to reduce line resistance of the transparent Y electrode.  
         [0033]     The X and Y shield layers are preferably respectively of the same materials as those of the bus X and Y electrodes.  
         [0034]     The PDP preferably further comprises: an address electrode arranged on a front surface of the rear substrate; and a second dielectric layer arranged on a front side of the rear substrate to cover the rear substrate and the address electrode.  
         [0035]     A protective layer is preferably arranged to coat a rear surface of the first dielectric layer. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0036]     A more complete appreciation of the present invention, and many of the attendant advantages thereof, will be readily apparent as the present invention becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:  
         [0037]      FIG. 1  is a sectional view of a unit discharge cell of a PDP;  
         [0038]      FIG. 2  is an exploded perspective view of a PDP according to an embodiment of the present invention;  
         [0039]      FIG. 3  is a cross-sectional view of a side of the PDP taken along line III-III of  FIG. 2 ;  
         [0040]      FIG. 4  is a sectional view of a blue discharge cell of  FIG. 2 ;  
         [0041]      FIG. 5  is a sectional view of a green discharge cell of  FIG. 2 ;  
         [0042]      FIG. 6  is a sectional view of a red discharge cell of  FIG. 2 ; and  
         [0043]      FIG. 7  is a rear plan view of a sustain discharge cell and X and Y light shielding layers of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0044]      FIG. 1  is a sectional view of a unit discharge cell (pixel) of a PDP. Referring to  FIG. 1 , a unit PDP panel  10  includes an upper plate  11  for displaying an image to users and a lower plate  21  arranged to face the upper plate  11 .  
         [0045]     The upper plate  11  includes a front substrate  12  and sustain electrode pairs  13 . The front substrate  12  is made of glass, and the sustain electrode pairs  13  are arranged on a rear surface of the front substrate  12 . The sustain electrode pair  13  includes an X electrode  14  and a Y electrode  15 . The X electrode  14  includes a transparent X electrode  14   a  and a bus X electrode  14   b  formed on a partial rear surface of the transparent X electrode  14   a . The Y electrode  15  includes a transparent Y electrode  15   a  and a bus Y electrode  15   b  formed on a partial rear surface of the transparent Y electrode  15   a.    
         [0046]     The lower plate  21  includes a rear substrate  22  and a plurality of address electrodes  23 . The rear substrate  22  is arranged to face the front substrate  12 , and the address electrodes  23  are arranged on a front surface of the rear substrate  22  to intersect the sustain electrode  13  of the front substrate  12 .  
         [0047]     A front dielectric layer  18  is formed on the rear surface of the front substrate  12  to bury the sustain electrode pair  13 , and a rear dielectric layer  28  is formed on the front surface of the rear substrate  22  to bury the address electrodes  23 . A protective film  19  made of MgO (magnesium oxide) is formed on the front dielectric layer  18 , and barrier ribs  31  are formed on the rear dielectric layer  28  to main a discharge distance, to partition discharge cells and to prevent an electro-optical crosstalk between the discharge cells.  
         [0048]     Red, Green, and Blue (RGB) phosphors  35  are coated on both side surfaces of the barrier ribs  31  and a front surface of the rear dielectric layer  28  on which the barrier ribs  31  are not formed.  
         [0049]     When a sustain discharge is generated between the X electrode  14  and the Y electrode  15  in the PDP  10 , a discharge amount at the right portion (that is, a portion near the Y electrode  15 ) of the X electrode  14  becomes larger than that of the left portion thereof, and a discharge amount at the left portion (that is, a portion near the X electrode  14 ) of the Y electrode  15  becomes larger than that of the right portion thereof.  
         [0050]     That is, a sustain discharge amount at a gap portion between the facing portions of the electrodes  14  and  15  is relatively large. However, the sustain discharge amount at the gap portion becomes too large when the sustain discharge is sustained. Accordingly, a portion of the protective film  19  corresponding to the gap portion is damaged more greatly than the other portions thereof.  
         [0051]     However, since the transparent X electrode  14   a  and the transparent Y electrode  15   a  generally made of Indium Tin Oxide (ITO) are arranged on the front substrate  12  corresponding to a center portion of a discharge cell so as to increase luminance, the greatly-damaged portion of the protective film  19  is undesirably observed by the naked eye through the transparent electrodes  14   a  and  15   a.    
         [0052]     The protective film  19  protects the front dielectric layer  18  from ion sputtering and lowers a sustain voltage and a driving voltage due to its high Secondary Electron Emission (SEE) coefficient. However, radiation efficiency greatly decreases especially at the greatly-damaged portion of the protective film  19 , whereby a permanent afterimage (image sticking) is undesirably generated on the PDP  10 .  
         [0053]     In addition, visible light rays generated by the RGB phosphors  35  have different luminance ratios. Accordingly, an optimum color temperature cannot be obtained when sustain discharge frequencies for the RGB phosphors in each discharge cell coated with RGB phosphors are the same.  
         [0054]     A method that changes the thickness of the front or rear dielectric layer ( 18  or  28 ) or an interval therebetween can be used to make the sustain discharge frequencies for the RGB phosphors different. However, such a method has a limitation in changing the thickness of the front or rear dielectric layer or the interval therebetween. Furthermore, the effect of such a structural modification becomes more reduced with a recent trend toward the size and thickness reduction of a PDP.  
         [0055]     The present invention is described more fully below with reference to the accompanying drawings, in which exemplary embodiments of the present invention are shown.  
         [0056]      FIG. 2  is an exploded perspective view of a PDP according to an embodiment of the present invention, and  FIG. 3  is a cross-sectional view of a side of the PDP taken along line III-III of  FIG. 2 .  
         [0057]     Referring to  FIGS. 2 and 3 , a PDP  100  includes a front substrate  112 , a rear substrate  122 , sustain electrode pairs  113 , a first dielectric layer  118 , a phosphor layer  135 , address electrodes  123 , a barrier rib  131 , and discharge gas (not shown).  
         [0058]     The front substrate  112  is transparent and is arranged parallel to the rear substrate  122  at a front side (z direction) of the rear substrate  122  so that visible rays in a discharge cell can passes therethrough and an image can be projected. The front substrate  112  is made of a material having good light permeability, such as glass, whereby visible light rays are emitted therethrough. The rear substrate  122  can also be made of material having glass as a main constituent.  
         [0059]     The sustain electrode pair  113  is formed of an X electrode  114  and a Y electrode  115 , and the plural sustain electrode pairs  113  are formed at a rear side (−z direction) of the front substrate  112 .  
         [0060]     The address electrodes  123  can be arranged at a front side of the rear substrate  122 , which faces a surface of the front substrate  112  on which the sustain electrode pairs  113 . The address electrodes  123  generate an address discharge in combination with the Y electrodes  115 .  
         [0061]     The sustain electrode pairs  113  can be extended across a sub-pixel, that is, in a y-direction in  FIG. 2 , and the address electrodes  123  can be extended across the sub-pixel in another direction intersecting the sustain electrode pairs  113 , that is, along a x-direction in  FIG. 2 .  
         [0062]     The X electrode  114  is formed of a transparent X electrode  114   a  and a bus X electrode  114   b , and the Y electrode  115  is formed of a transparent Y electrode  115   a  and a bus Y electrode  115   b . The transparent X electrode  114   a  and the transparent Y electrode  115   a  are made of ITO. The bus X electrode  114   b  and the bus Y electrode  115   b  are made of a metallic material, for example, and are respectively formed on the rear surfaces of the transparent X and Y electrodes  114   a  and  115   a  to reduce the electrode line resistance of the transparent X and Y electrodes  114   a  and  115   a . However, the present invention is not limited to this construction. For example, the X electrode  114  and the Y electrode can be respectively formed of only the transparent X electrode  114   a  and the transparent Y electrode  115   a.    
         [0063]     The first dielectric layer  118  is arranged at a rear side of the front substrate having the sustain electrode pairs  113  to bury the X electrode  114 , the Y electrode  115  and the front substrate  112 . Also, the address electrodes  123  and the rear substrate  122  are preferably covered by the second dielectric layer  128 .  
         [0064]     The first and second dielectric layers  118  and  128  are formed of a dielectric material that can not only induce an electric charge but also prevent the sustain electrode pairs  113  and the address electrodes  123  from being damaged by the collision of positive ions and electrons thereagainst during discharge.  
         [0065]     A protective film  119  is preferably formed on a rear surface of the first dielectric layer  118 . The protective film  119 , formed of an MgO film through evaporation, for example, prevents the damage of the protective film caused by the sputtering of plasma particles, and lowers a discharge voltage and a sustain voltage through the emission of secondary electrons.  
         [0066]     The barrier ribs  131  are formed between the front and substrates  112  and  122 , partition a discharge cell “C” in combination with the front and rear substrates, and prevent erroneous discharge between the discharge cells.  
         [0067]     An inside of the discharge cell “C” is coated with the phosphor layer  135 . The UV light rays generated by the sustain discharge impinge upon the phosphor layer  135  to thereby excite visible light rays and emit the visible light rays outside.  
         [0068]     The discharge gas contained within the discharge cell “C” is formed of a penning mixture, such as Xe—Ne, Xe—He, Xe—Ne—He or so on. Xe is used as main discharge gas because Xe is not dissociated by a discharge because it is a chemically stable inert gas, and because Xe has a low excitation voltage and a long emission wavelength because it has a high atomic number. He or Ne is used as a buffer gas because it can reduce a voltage decrease effect due to a panning effect by Xe and a sputtering effect in a high pressure state. An inert gas, such as Kr, can also be used as the main gas.  
         [0069]     In the PDP  100 , when a given voltage is supplied to the address electrode  123  and the Y electrode  115 , a discharge cell for radiation is selected, an address discharge is generated between the two electrodes  115  and  123 , and then a wall charge is charged on the first dielectric layer  118 . Thereafter, when a given voltage is alternately supplied to the X electrode  114  and the Y electrode  115 , the wall charge is moved between the two electrodes  114  and the  115 , thereby causing the discharge gas to generate a sustain discharge. Accordingly, the discharge gas generates UV light rays, and the UV light rays excite the phosphor of the phosphor layer  135 , thereby forming an image.  
         [0070]     In more detail, when a discharge initiating voltage of 150V to 300V is supplied to the sustain electrode pair  113  and the address electrode  115 , a wall charge is formed on an inner surface of a corresponding discharge cell.  
         [0071]     Thereafter, when an address discharge voltage is supplied to the Y electrode  115  and the corresponding address electrode  123  in the selected discharge cell, an address discharge is generated between the two electrodes  115  and  123 . Thereafter, when a sustain discharge voltage of 150V or more is alternately supplied to the corresponding Y and X electrodes  115  and  114 , a sustain discharge is generated, whereby the radiation of a corresponding discharge cell is sustained during a given time. That is, an electric field is generated in the discharge cell, and a very small amount of electrons of discharge gas is accelerated. The accelerated electrons collide with neutral particles of the discharge gas, thereby causing the neutral particles to be ionized into electrons and ions. The neutral particles are more rapidly ionized into electrons and ions by another collision of the ionized electrons and neutral particles, whereby the discharge gas changes to a plasma state and simultaneously vacuum UV light rays are generated.  
         [0072]     The generated UV light rays excite the phosphor of the phosphor layer  135  to thereby generate visible light rays, and the generated visible light rays are projected externally through the front substrate  112 , whereby the radiation of the discharge cell, that is, an image display can be perceived.  
         [0073]     However, a sustain discharge is strongly generated at a gap portion “G” between the transparent X and Y electrodes  114   a  and  115   a , whereby the failure “F” of the protective film  119  is generated at a center portion of the discharge cell. Consequently, the radiation efficiency of the center portion of the discharge cell is reduced, whereby a permanent afterimage can be generated at the center portion of the discharge cell.  
         [0074]     Accordingly, in the present invention, an X shield layer  116  is arranged on a left end portion of the transparent X electrode  114   a  (that is, an end portion thereof positioned near the gap portion “G”), and a Y shield layer  117  is arranged on a right end portion of the transparent Y electrode  115   a  (that is, an end portion thereof positioned near the gap portion “G”). The X and Y shield layers  116  and  117  are formed of an opaque material, whereby the failure “F” of the protective film  119  is prevented from being observed externally. Consequently, the X and Y shield layers  116  and  117  prevent the permanent afterimage that can be generated at the center portion of the discharge cell.  
         [0075]     The X and Y shield layers  116  and  117  are preferably made of conductive a material because they are respectively formed on the transparent X and Y electrodes  114   a  and  115   a . That is, when the X and Y shield layers  116  and  117  are made of a non-conductive material, a sustain discharge between the transparent X and Y electrodes  114   a  and  115   a  is obstructed and thus insufficiently generated. The insufficient sustain discharge can be compensated for by a high sustain voltage, but such a high sustain voltage reduces the efficiency of the PDP.  
         [0076]     The X electrode  114  can include the bus X electrode  114   b  arranged on a rear right end surface of the transparent X electrode  114   a , and the Y electrode  115  can include the bus Y electrode  115   b  arranged on a rear left end surface of the transparent Y electrode  115   a . The X shield layer  116  is preferably formed on a rear left end surface of the transparent X electrode  114   a , and the Y shield layer  117  is preferably formed on a rear left end surface of the transparent Y electrode  115   a.    
         [0077]     The X and Y shield layers  116  and  117  are preferably made of the same material as that of the bus X and Y electrodes  114   b  and  115   b , whereby the X and Y shield layers  116  and  117  can be formed at the same time that the bus X and Y electrodes  114   b  and  115   b  are formed. That is, if the bus X and Y electrodes  114   b  and  115   b  are preferably made of a conductive material so as to compensate for the line resistance of the transparent X and Y electrodes  114   a  and  115   a , such a conductive material is preferably used as the material of the X and Y shield layers  116  and  117 . Also, if the bus X and Y electrodes  114   b  and  115   b  are respectively formed on the X and Y electrodes  114  and  115  using a mask, the X and Y shield layer  116  and  117  can be easily respectively formed on the X and Y electrodes  114  and  115  by forming openings for not only the bus X and Y electrodes but also for the X and Y shield layers on the mask, disposing the resulting mask between the front substrate  112  and a spray nozzle and then spraying the material of the bus X and Y electrodes on the disposed mask.  
         [0078]     Unlike this structure, the X electrode  114  can not be equipped with the bus X electrode  114   b , and the conductive X shield layer  116 , instead of the bus X electrode  114   b , can be connected to an X electrode driving unit. Also, the Y electrode  115  can not be equipped with the bus Y electrode  115   b , and the conductive Y shield layer  116 , instead of the bus Y electrode  115   b , can be connected to a Y electrode driving unit.  
         [0079]      FIG. 4  is a sectional view of a blue discharge cell of  FIG. 2 ,  FIG. 5  is a sectional view of a green discharge cell of  FIG. 2 ,  FIG. 6  is a sectional view of a red discharge cell of  FIG. 2 , and  FIG. 7  is a rear plan view of a sustain discharge cell and X and Y light shielding layers of  FIG. 2 .  
         [0080]     As shown in  FIGS. 4 through 6 , the phosphor layer  135  can be classified into a Red (R) phosphor layer  135   r , a Green (G) phosphor layer  135   g  and a Blue (B) phosphor layer  135   b . The R phosphor layer  135   r  can include a phosphor such as Y(V,P)O 4 :Eu, the G phosphor layer  135   g  can include phosphors such as Zn 2 SiO 4 :Mn, YBO 3 :Tb, and the B phosphor layer  135   b  can include a phosphor such as BAM:Eu.  
         [0081]     An R discharge cell Cr including the R phosphor layer  135   r , a G discharge cell Cg including the G phosphor layer  135   g , and a B discharge cell Cb including the B phosphor layer  135   b  respectively function as an R sub-pixel, a G sub-pixel and a B sub-pixel. The R, G and B sub-pixels together constitute a unit pixel to produce colors according to combinations of the three primary colors.  
         [0082]     In more detail, when the luminance of R, G and B light from the R, G and B phosphor layers  135   r ,  135   g  and  135   b  each is subdivided into many levels (for example, 256 levels) and the subdivided R, G and B light are mixed in many combinations, 16.77-million colors can be produce from the unit pixel. For example, when the R, G and B lights each has 256 gradations, a black color is displayed if the R, G and B gradations are all “0”, and a white color is displayed if the R, G and B gradations are all “1”. Also, when the R, G and B gradations are below 256 but are identical to one another, a low-luminance white color (that is, a gray color) is displayed.  
         [0083]     When a white color temperature is formed by three primary colors, it is generally estimated that a white color temperature of 9000K through 10000K (Kelvin) is suitable for Asia. It is preferable that an optimal color temperature is set according respective conditions.  
         [0084]     In general, a color temperature of an object is defined as a temperature of a black-body that radiates light of a color identical to that of light radiated by the object.  
         [0085]     Accordingly, when the luminance of each discharge cell is changed, a white color temperature is accordingly changed. In the present invention, widths of the X and Y shield layers  116  and  117  are varied according to the R, G and B discharge cells Cr, Cg and Cb so as to adjust an optical color temperature while making sustain discharge frequencies of the cells Cr, Cg and Cb identical.  
         [0086]     This is because the amount of light emitted from the discharge cell C to the outside is decreased due to the X and Y shield layer  116  and  117  formed therein, thereby reducing the luminance of the discharge cell C.  
         [0087]     Accordingly, the luminance of the discharge cell C is varied according to the widths of the X and Y shield layers  116  and  117 , whereby the color temperature can be easily adjusted.  
         [0088]     A conventional white color temperature is about 6500K. Accordingly, in order to embody an white color temperature of 9000K suitable for Asia, it is necessary to raise the luminance of the B discharge cell Cb the most and to lower the luminance of the R discharge cell Cr the most.  
         [0089]     Accordingly, as shown in  FIGS. 4 through 7 , the X and Y shield layers  116  and  117  are preferably formed such that the width “Wr” of X and Y shield layers arranged in the cell Cr is greater than the width “Wg” of X and Y shield layers arranged in the cell Cg greater than the width “Wb” of X and Y shield layers arranged in the cell Cb.  
         [0090]     When the width of the X and Y shield layers  116  and  117  are excessively increased, the luminance is undesirably reduced. Accordingly, it is preferable that the width “Wb” is below 50 μm and the width “Wr” is below 120 μm.  
         [0091]     As stated above, the inventive X and Y shield layers  116  and  117  prevents the permanent afterimage by making the failure of the protective film be invisible to the naked eye, thereby improving an image quality of the PDP.  
         [0092]     Also, the luminance in the discharge cell is adjusted by varying the width of the X and Y shield layers, whereby the white color temperature can be easily adjusted without adjusting the sustain discharge frequency.  
         [0093]     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various modifications in form and detail can be made therein without departing from the spirit and scope of the present invention as defined by the following claims.