Patent Publication Number: US-2010109525-A1

Title: Plasma display panel

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2008-0108989, filed in the Korean Intellectual Property Office on Nov. 4, 2008, the entire content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a plasma display panel. More particularly, the present invention relates to a plasma display panel that can improve luminous efficiency. 
     2. Description of the Related Art 
     In general, an AC-type plasma display panel (PDP) includes a display electrode that forms a discharge gap to perform surface discharge, a dielectric layer that covers the display electrode and an inner surface of a front substrate, and a protective layer that covers the dielectric layer. 
     In gas discharge, a stronger electric field is concentrated on the discharge gap and a portion adjacent to the discharge gap than the outline of the discharge cell. Therefore, in order to protect the dielectric layer from sputtering that occurs due to the strong electric field, an exemplary protective layer has a relatively low secondary electron emission coefficient at the portion adjacent to the discharge gap. In this case, discharge firing voltage rises due to this low secondary electron emission coefficient. 
     In another example, the dielectric layer has a high dielectric constant at the portion adjacent to the discharge gap and a low dielectric constant at a portion away from the discharge gap. In this case, crosstalk, that is, wrong discharge is suppressed by the high dielectric constant, and the gas discharge is stabilized in the vicinity of the discharge gap. 
     However, the high dielectric constant causes the strong electric field, that is, high-density plasma to be formed at the portion adjacent to the discharge gap, thereby increasing energy loss and lowering luminous efficiency. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person having ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     An aspect of an embodiment of the present invention is directed toward a plasma display panel having an improved luminous efficiency. 
     An exemplary embodiment of the present invention provides a plasma display panel that includes a first substrate; a second substrate facing the first substrate; a plurality of barrier ribs partitioning a space between the first substrate and the second substrate to define a plurality of discharge cells; a plurality of address electrodes on the first substrate and extending in a first direction to correspond to the discharge cells; a first electrode and a second electrode extending in a second direction crossing the first direction on the second substrate to define a discharge gap at the center of a corresponding one of the discharge cells; a dielectric layer covering the first and second electrodes; and a protective layer covering the dielectric layer, wherein the dielectric layer includes a first dielectric constant section in the discharge gap and a portion adjacent to the discharge gap in the first direction and having a first dielectric constant, and a second dielectric constant section at either side of the first dielectric constant section in the first direction and having a second dielectric constant larger than the first dielectric constant. 
     The first dielectric constant section may include insulator particles that are not sintered. The insulator particles may have a property for not absorbing visible light. The insulator particles may include SiO 2  and/or Al 2 O 3 . 
     The second dielectric constant section may be sintered. The second dielectric constant section may be formed on a surface of each of the first and second electrodes facing the first substrate, and on a surface of the second substrate facing the first substrate and not covered with the first and second electrodes. 
     The first dielectric constant section may be formed on a surface of the second dielectric constant section facing the first substrate. 
     The first dielectric constant section may be sintered. Further, the second dielectric constant section may be sintered. The second dielectric constant section may be formed by a dispenser method (i.e., may be a dispensed dielectric constant section). 
     The first dielectric constant section may cover a surface of the second substrate facing the first substrate to correspond to the discharge gap, and may convert a surface of each of the first and second electrodes facing the first substrate at a portion adjacent to the discharge gap in the first direction. 
     The second dielectric constant section may cover a surface of each of the first and second electrodes facing the first substrate, and may cover a surface of the second substrate facing the first substrate at either side of the first dielectric constant section in the first direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective schematic view of a plasma display panel according to a first exemplary embodiment of the present invention. 
         FIG. 2  is a cross-sectional schematic view taken along line II-II of  FIG. 1 . 
         FIG. 3  is a plan schematic view of a disposition relationship of a display electrode, a first dielectric constant section, and a discharge cell. 
         FIG. 4  is a graph illustrating a relationship between luminance and luminous efficiency depending on sustain discharge voltage and a width of a first dielectric constant section. 
         FIG. 5  is a cross-sectional schematic view of a plasma display panel according to a second exemplary embodiment of the present invention. 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS INDICATING CERTAIN ELEMENTS IN THE DRAWINGS 
       100 : Plasma display panel  10 : First substrate (Rear substrate) 
       20 : Second substrate (Front substrate)  11 : Address electrode 
       13 ,  21 : First and second dielectric layer  16 : Barrier rib 
       16   a,    16   b:  First and second barrier rib member 
       17 : Discharge cell  19 : Phosphor layer 
       21   a,    121   a:  First dielectric constant section 
       21   b,    121   b:  Second dielectric constant section  23 : Protective layer 
       31 : Sustain electrode  32 : Scan electrode 
       31   a,    32   a:  Transparent electrode  31   b,    32   b:  Bus electrode 
     DG: Discharge gap F 1 , F 2 : First and second regions 
     T 1 , T 2 : Thickness of first and second dielectric constant section 
     W 1 : Width 
     ε 1 , ε 2 : Dielectric constants of first and second dielectric constant section 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. The drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. 
       FIG. 1  is an exploded perspective schematic view of a plasma display panel according to a first exemplary embodiment of the present invention.  FIG. 2  is a cross-sectional schematic view taken along line H-H of  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , the plasma display panel  100  according to the first exemplary embodiment includes a first substrate (hereinafter, “rear substrate”)  10  and a second substrate (hereinafter, “front substrate”)  20  that are attached to face each other with a space therebetween, and a barrier rib  16  disposed between the rear and front substrates  10  and  20 . 
     The barrier rib  16  partitions a space provided between the rear substrate  10  and the front substrate  20  to form a plurality of discharge cells  17 . Phosphor layers  19  are formed in the discharge cells  17  and are filled with discharge gas (i.e., mixed gas containing neon (Ne), xenon (Xe), etc.). 
     The discharge gas generates vacuum ultraviolet rays by gas discharge. While the phosphor layers  19  are excited by the vacuum ultraviolet rays, and then stabilized to emit visible light of red (R), green (G), and blue (B). To cause the gas discharge, address electrodes  11  and display electrodes are disposed in the discharge cells  17 . 
     In one example, the address electrodes  11  extend along an inner surface of the rear substrate  10  facing the front substrate  20  in a first direction (hereinafter, referred to as “y-axis direction”) and correspond to the discharge cells  17  adjacent in the y-axis direction. The plural address electrodes  11  are disposed parallel to the discharge cells  17  adjacent in a second direction (hereinafter, referred to as “x-axis direction”) crossing the y-axis direction. 
     A first dielectric layer  13  covers the inner surface of the rear substrate  10  and the address electrodes  11 . The first dielectric layer  13  protects the address electrodes  11  from the gas discharge by blocking (or preventing) positive ions or electrons from colliding directly with the address electrodes  11  in discharge. Further, the first dielectric layer  13  provides forming and accumulation spaces of wall charges to enable address discharge by low voltage. 
     The address electrodes  11  are disposed on the rear substrate  10  so as not to interrupt penetration of the visible light through the front substrate  20 . Therefore, the address electrodes  11  may be formed of an opaque electrode, that is, a metal electrode such as silver (Ag) having high electrical conductivity. 
     The barrier rib  16  is disposed on the first dielectric layer  13  and partitions a space between the first dielectric layer  13  and the front substrate  20 . For example, the barrier rib  16  includes first barrier rib members  16   a  that extend along the y-axis direction, and second barrier rib members  16   b  that connect the adjacent first barrier rib members  16   a  to each other in the x-axis direction and are disposed to be spaced apart from each other in the y-axis direction. 
     That is, the first barrier rib members  16   a  partition the discharge cells  17  adjacent in the x-axis direction, and the second barrier rib members  16   b  partition the discharge cells  17  adjacent in the y-axis direction. Therefore, in a quadrangular barrier rib structure, the discharge cells  17  are arranged in a matrix. 
     The phosphor layers  19  may be formed by applying a phosphor paste onto side surfaces of the first barrier rib  16   a  and the second barrier rib  16   b  and the surface of the first dielectric layer  13  defined (or surrounded) by the first barrier rib  16   a  and the second barrier rib  16   b,  and drying and sintering the applied phosphor paste. 
     The phosphor layers  19  are formed of phosphors that generate visible light of the same color in the discharge cells  17  in the y-axis direction. The phosphor layers  19  are formed of phosphors that generate visible light of red (R), green (G), and blue (B) in the discharge cells  17  in the x-axis direction. That is, the phosphor layers  19  that are formed of the phosphors generating the visible light of red (R), the phosphors generating the visible light of green (G), and the phosphors generating the visible light of blue (B) are repetitively and respectively disposed in the x-axis direction. 
     The display electrodes include a first electrode (hereinafter, referred to as “sustain electrode”)  31  and a second electrode (hereinafter, referred to as “scan electrode”)  32  formed on the inner surface of the front substrate  20  facing the rear substrate  10 , which correspond to the discharge cells  17 . The sustain electrode  31  and the scan electrode  32  form a surface discharge structure in correspondence with each of the discharge cells  17 . 
     The sustain electrode  31  and the scan electrode  32  are paired in the x-axis direction crossing the address electrode  11 . A discharge gap DG is formed between the sustain electrode  31  and the scan electrode  32 . The discharge gap DG corresponds to the center of the discharge cell  17 . 
     For example, the sustain electrode  31  and the scan electrode  32  include the discharge gap DG, transparent electrodes  31   a  and  32   a  that form a surface discharge region, and bus electrodes  31   b  and  32   b  that apply voltage signals to the transparent electrodes  31   a  and  32   a.    
     The transparent electrodes  31   a  and  32   a  are made of a transparent material (i.e., indium tin oxide (ITO)) to secure an aperture ratio of the discharge cell  17 . Further, the bus electrodes  31   b  and  32   b  are disposed on the transparent electrodes  31   a  and  32   a  at a position separate (or away) from the discharge gap and made of a metallic material having high electrical conductivity so as to apply the voltage signals to the transparent electrodes  31   a  and  32   a.    
     The transparent electrodes  31   a  and  32   a  may be formed of a protruding electrode that protrudes toward the discharge gap DG from each of the bus electrodes  31   b  and  32   b  to correspond to each of the discharge cells  17 . 
     A second dielectric layer  21  covers the inner surface of the front substrate  20 , the sustain electrode  31 , and the scan electrode  32 . The second dielectric layer  21  protects the sustain electrode  31  and the scan electrode  32  from the gas discharge by protecting (or preventing) the positive ions or electrons from colliding directly with the sustain electrode  31  and the scan electrode  32  in discharge. Further, the second dielectric layer  21  provides the forming and accumulation spaces of the wall charges to enable the sustain discharge by the low voltage. 
     In addition, the second dielectric layer  21  induces weak discharge by lowering density of discharge current in the discharge gap DG and at a portion adjacent to the discharge gap DG on which an electric field is concentrated to reduce energy loss, thereby improving luminous efficiency. As one example, the second dielectric layer  21  includes a first dielectric constant section  21   a  and a second dielectric constant section  21   b  that have different dielectric constants so as to reduce a capacitance in the discharge gap DG and at the portion adjacent to the discharge gap DG. 
       FIG. 3  is a plan schematic view of a disposition relationship of a display electrode, a first dielectric constant section, and a discharge cell. Referring to  FIG. 3 , the first dielectric constant section  21   a,  having a width W 1 , is formed in the discharge gap DG and at the portion adjacent to the discharge gap DG and has a first dielectric constant ε 1 . The second dielectric constant section  21   b  is formed on the inner surface of the front substrate  20  over the scan electrodes  32  and the sustain electrodes  31 , and has a second dielectric constant ε 2  larger than the first dielectric constant ε 1  (ε 1 &lt;ε 2 ). 
     That is, in the discharge gap DG, end portions of the transparent electrodes  31   a  and  32   a  and the first dielectric constant section  21   a  have first and second regions F 1  and F 2  that are overlapped with each other. Therefore, the first dielectric constant section  21   a  induces the weak discharge by lowering the capacitance and the density of the discharge current in the discharge gap DG and the first and second regions F 1  and F 2 . 
     Therefore, the first dielectric constant section  21   a  reduces the energy loss by lowering the capacitance and the density of the discharge current in the discharge gap DG on which the electric field is concentrated and at the portion adjacent to the discharge gap DG on which the electric field is concentrated. 
     As the first and second regions F 1  and F 2  are large, weaker discharge may be induced by lowering the capacitance and the discharge current by the first dielectric constant section  21   a,  but when the first and second regions F 1  and F 2  are too large, the weak discharge is induced even at a position away (or distant) from the discharge gap DG, such that desired luminance may not be achieved. Therefore, the first and second regions F 1  and F 2  are limited to a size range to lower the capacitance and the density of the discharge current without interrupting display of an image by sustain discharge. 
     In one example, the first dielectric constant section  21   a  is not sintered, and the second dielectric constant section  21   b  is sintered. The first dielectric constant section  21   a  includes insulator particles that are not sintered, and the insulator particles have a property that does not absorb visible light. In one example, the insulator particles include SiO 2  and/or Al 2 O 3 . 
     Referring back to  FIG. 2 , the second dielectric constant section  21   b  covers a top surface of each of the sustain electrode  31  and the scan electrode  32  and the inner surface of the front substrate  20  that is not covered with the sustain electrode  31  and the scan electrode  32 . The first dielectric constant section  21   a  is formed on the surface of the second dielectric constant section  21   b  that corresponds to the discharge gap DG and the portion adjacent to the discharge gap DG. Therefore, the first dielectric constant section  21   a  may protrude toward the inner surface of the rear substrate  10  further than the second dielectric constant section  21   b.    
     The protective layer  23  covers the second dielectric layer  21 , and more particularly, covers the first dielectric constant section  21   a  and the second dielectric constant section  21   b  where the first dielectric constant section  21   a  is not formed. For example, the protective layer  23  is made of transparent MgO that protects the first dielectric constant section  21   a  and the second dielectric constant section  21   b  in gas discharge and increases secondary electron emission coefficient in discharge. 
     In addition, the first and second dielectric constant sections  21   a  and  21   b  will be described in more detail. A thickness T 1  of the first dielectric constant section  21   a  that is not sintered is about 1/10 of a thickness T 2  of the second dielectric constant section  21   b  that is sintered (T 1 =T 2 /10). For example, the thickness T 1  of the first dielectric constant section  21   a  is about 2 μm. When the protective layer  23  is formed on the first dielectric constant section  21   a,  a gap of about 2 μm is formed between the protective layer  23  and the first barrier rib  16   a,  but crosstalk does not occur. 
     Since the first dielectric constant section  21   a  is not sintered, the first dielectric constant section  21   a  has a space that is formed between dielectric particles and has a very low first dielectric constant ε 1 . In the case of the dielectric particles completed from a compound containing SiO 2  having a low dielectric constant, the first dielectric constant ε 1  of the first dielectric constant section  21   a  may decrease to about 1. 
     The sintered second dielectric constant section  21   b  has a second dielectric constant a of between 7 and 20. Therefore, the capacitance formed in the discharge gap DG and the capacitance formed between the sustain electrode  31  or the scan electrode  32  and the protective layer  23  at the portion (that is, first and second regions F 1  and F 2 ) adjacent to the discharge gap DG may decrease. 
     As the capacitance decreases, the density of the discharge current in the discharge gap DG and at the portion adjacent to the discharge gap DG is lowered, and the weak discharge is induced, such that the energy loss in the discharge gap DG and at the portion adjacent to the discharge gap DG on which the electric field is concentrated is reduced in discharge. That is, the luminous efficiency is improved. 
     For example, when the second dielectric constant ε 2  is 13, the thickness T 2  is 20 μm in the second dielectric constant section  21   b,  the first dielectric constant ε 1  is 1.3 and the thickness T 2  is 2 μm in the first dielectric constant section  21   a,  the capacitance C in the discharge gap DG and at the portion adjacent to the discharge gap DG where the first dielectric constant section  21   a  is provided is reduced by half. 
     
       
         
           
             
               
                 
                   C 
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                      
                     
                       A 
                       d 
                     
                   
                 
               
               
                 
                   Equation 
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     In Equation 1, ε represents dielectric constant ε 1  or ε 2  of a dielectric, A represents an area of the dielectric, and d represents thickness T 1  or T 2  of the dielectric. 
     That is, referring to Equation  1 , since the area A is constant, the capacitance C is calculated as (1/(T2/ε2+T1/ε1))/(ε2/T2)=(1/(20/13+2/1.3))/(13/20)=0.5. 
     In addition, since the portion distant from (i.e., the portion of the second dielectric layer  21  that is away from) the discharge gap DG includes only the second dielectric constant section  21   b  without the unsintered first dielectric constant portion  21   a,  the capacitance at the portion distant from the discharge gap DG is equal to the capacitance in related art. 
     Further, even though the unsintered first dielectric constant section  21   a  is inserted into the discharge gap DG and the portion adjacent to (i.e., the portion of the second dielectric layer  21  that is adjacent to) the discharge gap DG, sustain voltage applied to the sustain electrode  31  and the scan electrode  32 , which should be utilized for sustain discharge does not substantially increase. 
     Here, unsintered insulator particles are collected to form the first dielectric constant section  21   a.  A paste is prepared by mixing the insulator particles with an organic dispersion material, the paste is applied onto the surface of the sintered second dielectric constant section  21   b  in patterns by a screen printing method and/or a dispenser method, and an organic component is removed by heat-treating the pattern to form the first dielectric constant section  21   a.    
     The heat-treatment of the paste pattern for forming the first dielectric constant section  21   a  is performed at a temperature at which the insulator particles maintain an unsintered state. For example, the insulator particles that are made of a high-melting-point oxide, such as SiO 2  or Al 2 O 3 , are heat-treated at a heat-treatment temperature (i.e., 600° C. or lower) that is suitably used in a PDP manufacturing process. 
     When heat-treatment of the first dielectric constant section  21   a  and heat-treatment for sintering the second dielectric constant section  21   b  are performed at the same (or substantially the same) time, a separate heat-treatment of the pattern for forming the first dielectric constant section  21   a  need not be added. 
     The first dielectric constant section  21   a  is transparent and transmits visible light (i.e., light having a wavelength between 400 and 700 nm) generated from the phosphor layer  19  toward the front substrate  20  without interrupting the visible light. Further, the insulator particles of the first dielectric constant section  21   a  have an average grain size that is still smaller than the wavelength of the visible light, thereby reducing (or minimizing) dispersion of the visible light. For example, the insulator particles of the first dielectric constant section  21   a  may be smaller than 100 nm. When the insulator particles of the first dielectric constant section  21   a  are formed of a material having a low refractive index such as SiO 2 , the insulator particles can effectively suppress the dispersion of the visible light. 
     In the first exemplary embodiment, the pattern of the first dielectric constant section  21   a  is plated on the second dielectric constant section  21   b,  but the pattern may be inserted into the second dielectric constant section  21   b  or inserted between the second dielectric constant section  21   b  and the sustain and scan electrodes  31  and  32 . 
     Reset discharge occurs by a reset pulse applied to the scan electrode  32  during a reset period while driving the plasma display panel  100 . Address discharge occurs by a scan pulse applied to the scan electrode  32  and an address pulse applied to the address electrode  11  during an addressing period subsequent to the reset period. Thereafter, the sustain discharge occurs by a sustain pulse applied to the sustain electrode  31  and the scan electrode  32  during a sustain period. 
     The sustain electrode  31  and the scan electrode  32  serve as an electrode that applies the sustain pulse required for the sustain discharge. The scan electrode  32  serves as an electrode that applies the reset pulse and the scan pulse, and the address electrode  11  serves as an electrode that applies the address pulse. 
     The sustain electrode  31 , the scan electrode  32 , and the address electrode  11  may play different roles depending on the waveform of voltage applied to the electrodes. Therefore, the electrodes may play different roles. 
     The plasma display panel  100  selects a discharge cell  17  to be turned on by the address discharge that occurs by an interaction between the address electrode  11  and the scan electrode  32  and drives the selected discharge cell  17  by the sustain discharge that occurs by an interaction between the sustain electrode  31  and the scan electrode  32  to display the image. 
       FIG. 4  is a graph illustrating a relationship between luminance and luminous efficiency depending on sustain discharge voltage and a width of a first dielectric constant section. Referring to  FIG. 4 , 6-inch test plasma display panels having widths 
     W 1  of the first dielectric constant section  21   a  of 275 micrometers and 385 micrometers are fabricated. Herein, the second barrier rib members  16   b  are spaced apart from each other with a period of 675 micrometers in the y-axis direction. 
     The graph of  FIG. 4  illustrates luminance and luminous efficiency in the related art without the first dielectric constant section  21   a  and luminance and luminous efficiency when the same sustain voltage is variously applied to the sustain electrode  31  and the scan electrode  32  of the plasma display panels of Experimental Examples 1 and 2, which have widths W 1  of the first dielectric constant section  21   a  of 275 micrometers and 385 micrometers, respectively, under the same (or substantially the same) condition. 
     When the sustain voltage is the same (or substantially the same), the luminance and luminous efficiency of Experimental Example 1 are improved in comparison with the related art and the luminance and luminous efficiency of Experimental Example 2 is improved in comparison with Experimental Example 1, in general. Further, when the width W 1  of the first dielectric constant section  21   a  increases as the discharge gap DG is constant, the capacitance and current decrease while the first and second regions F 1  and F 2  increase, such that the luminous efficiency is further improved. 
     In  FIG. 4 , in the case of points having sustain voltage of 205 V, when Experimental Examples 1 and 2 have the same luminance of about 1.02, Experimental Example 1 has luminous efficiency of 1.04 and Experimental Example 2 has luminous efficiency of 1.15. Therefore, Experimental Example 2 at the same luminance as that of Experimental Example 1 has luminous efficiency higher than that of Experimental Example 1. By contrast, the related art having the sustain voltage of 205 V has luminance of 1 and luminous efficiency of 1. That is, Experimental Examples 1 and 2 have relatively high luminance and luminous efficiency as compared to the related art. 
       FIG. 5  is a cross-sectional schematic view of a plasma display panel according to a second exemplary embodiment of the present invention. Since the first and second exemplary embodiments include similar components, in the following description of the second exemplary embodiment, the description of the same components will not be provided again, and the description of different components will be described in comparison with the first exemplary embodiment. 
     Referring to  FIG. 5 , in the plasma display panel  200 , first and second dielectric constant sections  221   a  and  221   b  are formed on the inner surface of the front substrate  20  which is generally on the same plane. That is, the first dielectric constant section  221   a  is formed on the inner surface of the front substrate  20  that corresponds to the discharge gap DG and the surface of each of the sustain electrode  31  and the scan electrode  32  at the portion adjacent to the discharge gap DG. 
     The second dielectric constant section  221   b  is formed at either side (or both sides) of the first dielectric constant section  221   a  in the y-axis direction. That is, the second dielectric constant section  221   b  is formed on the surface of each of the sustain electrode  31  and the scan electrode  32  and the inner surface of the front substrate  20 . 
     The capacitance formed in the discharge gap DG and at the portion adjacent to the discharge gap DG by the first dielectric constant section  221   a  is smaller than the capacitance at the portion distant from the discharge gap DG. As the capacitance decreases, the density of the discharge current in the discharge gap DG and at the portion adjacent to the discharge gap DG is lowered, thus, the weak discharge is induced, such that the energy loss in the discharge gap DG and at the portion adjacent to the discharge gap DG on which the electric field is concentrated is reduced. That is, the luminous efficiency is improved. 
     At this time, the first and second dielectric constant sections  221   a  and  221   b  are sintered. The second dielectric constant section  221   b  may be formed by a suitable dispenser method (i.e., may be a dispensed constant section). 
     A dielectric paste having a first dielectric constant ε 1  and a dielectric paste having a second dielectric constant E 2  are separately provided. That is, the dielectric paste having the first dielectric constant ε 1  is dispensed and applied to correspond to the discharge gap DG and the portion adjacent to the discharge gap DG, and the dielectric paste having the second dielectric constant ε 2  is dispensed and applied to a space between dielectric stripe patterns of the first dielectric constant ε 1  to form the first and second dielectric constant sections  221   a  and  221   b.    
     Stripe patterns of the both pastes are naturally leveled in contact with each other by flowability of the dielectric pastes having the first and second dielectric constants ε 1  and ε 2 . Here, the pastes are dispersed therebetween on a contact interface, but the pastes have viscosity, such that the pastes are not rapidly dispersed, thus, the pastes are not deeply dispersed. 
     When the both paste patterns are dried during the dispersion, the first and second dielectric constant sections  221   a  and  221   b  are fixed while being applied with the dielectric pastes and when the first and second dielectric constant sections  221   a  and  221   b  are heat-treated for sintering, the first and second dielectric constant sections  221   a  and  221   b  are sintered. In order to block (or prevent) the both pastes from being dispersed on the interface, the dielectric paste having the second dielectric constant ε 2  is applied after the dielectric paste having the first dielectric constant ε 1  is applied, and the first dielectric pattern having the first dielectric constant ε 1  is dried before the second dielectric pattern having the second dielectric constant ε 2 . 
     As described above, according to an exemplary embodiment of the present invention, an electric field is concentrated on a portion adjacent to a discharge gap such that plasma density and energy loss may increase. However, in an exemplary embodiment of the present invention, comparatively weaker discharge can be induced at the portion adjacent to the discharge gap by decreasing the density of discharge current at the portion adjacent to the discharge gap and increasing the density of the discharge current at a portion distant from the discharge gap. As such, the weak discharge at the portion adjacent to the discharge gap reduces the possible energy loss, thereby improving luminous efficiency. 
     While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.