Patent Publication Number: US-7221097-B2

Title: Plasma display panel with controlled discharge driving voltage

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a Continuation-In-Part application of U.S. patent application Ser. No. 11/105,480 filed in the U.S. Patent &amp; Trademark Office on 14 Apr. 2005 now U.S. No. 7,015,643, and assigned to the assignee of the present invention. 

   CLAIM OF PRIORITY 
   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 May 7, 2004 and there, duly assigned Serial No. 10-2004-0032202. 
   BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The present invention relates to a plasma display panel (PDP), and more particularly, to a PDP used as a flat display panel in which electrodes are arranged on the opposed surfaces of substrates, discharge gas is filled in a discharge space between the substrates, and an image is displayed using light emitted by ultraviolet rays which are generated in the discharge space with application of a predetermined voltage. 
   2. Related Art 
   In recent years, display apparatuses employing a plasma display panel as a flat display panel have been widely used. Such display apparatuses have excellent characteristics such as high image quality, ultra thin thickness, small weight, and wide viewing angle, in addition to a large-sized screen. In addition, the display apparatuses can be easily manufactured and easily increased in size. Therefore, such display apparatuses have attracted attention as a next generation of large-sized flat display apparatuses. 
   PDPs are classified into a direct current (DC) type PDP, an alternating current (AC) type PDP, and a hybrid type PDP depending on the applied discharge voltages, and into an opposing discharge type and a surface discharge type depending on the discharge structures. 
   The DC type PDP has a structure in which all electrodes are exposed to discharge spaces and electric charges move directly between the corresponding electrodes. Conversely, the AC type PDP has a structure in which at least one electrode is covered with a dielectric layer and the electric charges do not move directly between the corresponding electrodes. The discharge of the AC type PDP is performed by an electric field of wall charges. 
   Since the electric charges move directly between the corresponding electrodes in the DC type PDP, there is a problem in that the electrodes are seriously damaged. Accordingly, an AC type PDP having a three-electrode surface-discharge structure has been recently adopted. 
   An AC type three-electrode surface-discharge PDP is disclosed in U.S. Pat. No. 6,753,645 to Haruki et al., entitled PLASMA DISPLAY PANEL, issued on Jun. 22, 2004. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a plasma display panel (PDP) in which aperture ratio and transmittance are greatly increased, the discharge area is significantly enlarged with significant enlargement of a discharge surface, and discharge is uniformly performed in the entire discharge area. 
   Furthermore, the present invention provides a PDP which can efficiently utilize space charges of plasma, improve light emission efficiency, and reduce permanent after-image phenomenon. 
   In addition, the present invention provides a PDP which can secure a large voltage margin by controlling a discharge driving voltage such that the discharge driving voltage is constant or similar in maximum amount in the discharge cells in which phosphor layers having different dielectric constants are formed. 
   According to an aspect of the present invention, there is provided a PDP including a front panel, a rear panel, side dielectric layers, front discharge electrodes, rear discharge electrodes, and phosphor layers. An electrode-burying depth corresponding to discharge cells differs according to magnitude of the dielectric constant of phosphor layers corresponding to the discharge cells. In this regard, an electrode-burying depth, corresponding to discharge cells in which phosphor layers having the lowest dielectric constant are formed, is smaller than an electrode-burying depth corresponding to discharge cells in which phosphor layers having a relatively high dielectric constant are formed. 
   In this case, the front panel and the rear panel are disposed parallel to each other and are spaced apart from each other. The side dielectric layers are formed of a dielectric substance and disposed between the front panel and the rear panel so as to define a plurality of discharge cells. The front discharge electrodes are disposed inside the side dielectric layers so as to surround the discharge cells, and are spaced from the side surfaces of the discharge cells toward the interiors of the side dielectric layers by an electrode-burying depth. The rear discharge electrodes are disposed inside the barrier ribs so as to surround the discharge cells, and are spaced from the side surface of the discharge cell toward the interiors of the side dielectric layers by an electrode-burying depth at the rear side of the first discharge electrodes. The phosphor layers having different dielectric constants are disposed inside the discharge cells, and receive ultraviolet rays and emit visible rays. Discharge gas fills the discharge cells. 
   According to another aspect of the present invention, there is provided a PDP including a front panel, a rear panel, side dielectric layers, front discharge electrodes, rear discharge electrodes, address electrodes, a dielectric layer, and phosphor layers. An electrode-burying depth corresponding to discharge cells differs according to a magnitude of the dielectric constant of phosphor layers corresponding to the discharge cells. In this regard, the electrode-burying depth, corresponding to the discharge cells in which the phosphor layers having the lowest dielectric constant are formed, is smaller than the electrode-burying depth corresponding to the discharge cells in which the phosphor layers having a relatively high dielectric constant are formed. 
   In this case, the front panel and the rear panel are disposed parallel to each other and are spaced from each other. The side dielectric layers are formed of a dielectric substance and are disposed between the front panel and the rear panel so as to define a plurality of discharge cells. The front discharge electrodes are disposed inside the side dielectric layers so as to surround the discharge cells, and are spaced from the side surfaces of the discharge cells toward the interiors of the side dielectric layers by the electrode-burying depth. The rear discharge electrodes are disposed inside the barrier ribs so as to surround the discharge cells, and are spaced from the side surfaces of the discharge cells toward the interiors of the side dielectric layers by the electrode-burying depth at the rear side of the first discharge electrodes. The address electrodes are disposed on the rear panel, and extend in a direction which intersects the front discharge electrodes and the rear discharge electrodes. The dielectric layer covers the address electrodes. The phosphor layers have different dielectric constants, are disposed at least on the dielectric layer inside the discharge cells, and receive ultraviolet rays and emit visible rays. Discharge gas fills the discharge cells. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same 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: 
       FIG. 1  is an exploded perspective view of an alternating current (AC) three-electrode surface-discharge plasma display panel (PDP); 
       FIG. 2  is an exploded perspective view of a PDP according to an embodiment of the present invention; 
       FIG. 3  is a sectional view taken along line III—III of  FIG. 2 ; 
       FIG. 4  is a sectional view taken along line IV—IV of  FIG. 3 ; 
       FIG. 5  is a perspective view illustrating an arrangement of a front discharge electrode, a rear discharge electrode, and an address electrode; 
       FIG. 6  is a sectional view illustrating a circuit equivalent to constituent elements of a green discharge cell; 
       FIG. 7A  is a cross-sectional view of a modification of the circuit illustrated in  FIG. 6 ; 
       FIG. 7B  is a cross-sectional view of another modification of the circuit illustrated in  FIG. 6 ; and 
       FIG. 8  is an exploded perspective view of a PDP according to another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is an exploded perspective view of an alternating current (AC) three-electrode surface-discharge plasma display panel (PDP). 
   Referring to  FIG. 1 , an AC type three-electrode surface-discharge PDP  10  includes a front panel  20  and a rear panel  30 . 
   The rear panel  30  is provided with address electrodes  33  generating address discharge, a rear dielectric layer  35  covering the address electrodes  33 , barrier ribs  37  defining discharge cells, and phosphor layers  39  coated on both side surfaces of the barrier ribs  37  and portions of the rear panel  30  in which the barrier ribs  37  are not formed. 
   The front panel  20  is disposed to oppose the rear panel  30 , and is provided with X and Y electrodes  22  and  23  generating sustain discharge, a front dielectric layer  25  covering the X and Y electrodes  22  and  23 , and a protective layer  29 . In this case, each X electrode  22  includes a transparent X electrode  22   a , and a bus X electrode  22   b  which is disposed at a side of the transparent X electrode  22   a  and which compensates for voltage loss of the transparent X electrode  22   a . Each Y electrode  23  includes a transparent Y electrode  23   a , and a bus Y electrode  23   b  which is disposed at a side of the transparent Y electrode  23   a  and which compensates for voltage loss of the transparent Y electrode  23   a.    
   However, in the PDP  10 , the transparent X electrodes  22   a , the bus X electrodes  22   b , the transparent Y electrodes  23   a , the bus Y electrodes  23   b , the front dielectric layer  25 , and the protective layer  29  exist on the portion of the front panel  20  through which visible rays emitted from the phosphor layers  39  in the discharge spaces are transmitted. The PDP  10  has a serious problem in that the transmittance of the visible rays decreases to about 60% due to such factors. 
   Furthermore, in the surface-discharge PDP  10 , the discharge electrodes are formed on the upper side of the discharge space, that is, on the inner surface of the front panel  20  transmitting the visible rays. As a result, since the discharge occurs from the inner surface of the front panel  20  and diffuses into the discharge space, the surface-discharge PDP  10  has a basic problem in that the light emission efficiency decreases. 
   In addition, in the surface-discharge PDP  10 , when it works for a long period of time, charged particles of the discharge gas cause an ion sputtering phenomenon in the fluorescent substance, whereby undesirable permanent after-images are generated. 
     FIG. 2  is an exploded perspective view of a PDP according to an embodiment of the present invention, while  FIG. 3  is a sectional view taken along line III—III of  FIG. 2 ,  FIG. 4  is a sectional view taken along line IV—IV of  FIG. 3 ,  FIG. 5  is a perspective view illustrating an arrangement of a front discharge electrode, a rear discharge electrode, and an address electrode, and  FIG. 6  is a sectional view illustrating a circuit equivalent to constituent elements of a green discharge cell. 
   Referring to  FIGS. 2  thru  4 , a plasma display panel (PDP)  100  according to an embodiment of the present invention includes a front panel  120 , a rear panel  130 , side dielectric layers  127 , front discharge electrodes  122 , rear discharge electrodes  123 , phosphor layers  139 R,  139 G and  139 B, address electrodes  133 , and discharge gas  140  (see  FIG. 6 ). 
   The front panel  120 , through which visible rays of light can pass so as to project an image, is disposed at a front side (z-direction) parallel to the rear panel  130 . 
   The side dielectric layers  127  are formed between the front panel  120  and the rear panel  130 . The side dielectric layers  127  are disposed at non-discharge portions and define discharge cells  150 R,  150 G, and  150 B. The front electrodes  122  and the rear electrodes  123  are spaced apart from each other in the side dielectric layers  127 . In this regard, the side dielectric layers  127  are disposed in a single body between neighboring discharge cells to serve as barrier ribs as illustrated in  FIG. 2 . To the contrary, barrier ribs are formed between the side dielectric layers  127  formed between the neighboring discharge cells, and define the discharge cells  150 R,  150 G and  150 B to form a basic unit of an image, and to prevent crosstalk between discharge cells. 
   The phosphor layers  139 R,  139 G, and  139 B are disposed at spaces defined by the side dielectric layers  127 , the front panel  120 , and the rear panel  130 . The phosphor layers are composed of the red phosphor layers  139 R emitting red visible rays, the green phosphor layers  139 G emitting green visible rays, and the blue phosphor layers  139 B emitting blue visible rays. 
   The discharge gas  140  (see  FIG. 6 ) fills the discharge cells  150 R,  150 G, and  150 B. 
   The front panel  120  is formed of a material, such as glass, which has an excellent optical transmittance, and through which visible rays of light are emitted to the outside. 
   The side dielectric layers  127  are formed of a dielectric substance and define adjacent discharge cells  150 R,  150 G, and  150 B. The side dielectric layers  127  prevent the rear discharge electrodes  123  and the front discharge electrodes  122  from being electrically connected to each other during sustain discharge, and prevent the front discharge electrodes and the rear discharge electrodes  122  and  123  from being damaged due to the direct collision of charged particles. Further, the side dielectric layers  127  function to store wall charge by inducing the charged particles. 
   In this regard, as illustrated in  FIG. 2 , a cross section of the side dielectric layers  127  has a circular shape, so that the first and second electrodes  122  and  123  have a circular shape. In this case, corners of the side dielectric layers  127  are not supported, which does not cause an edge. Therefore, a sustain discharge is not partly performed, thereby increasing the lifetime of the PDP and causing no permanent afterimage. However, the present invention is not necessarily restricted thereto, and the side dielectric layers  127  and the first and second electrodes  122  and  123  may have a polygon shape such as that of a tetragon, an octagon, etc., or any other shape. 
   The front discharge electrodes  122  and the rear discharge electrode  123  are disposed inside the side dielectric layers  127 . The front discharge electrodes  122  and the rear discharge electrode  123  may be formed of a conductive metal, such as aluminum, copper or silver. 
   At least one, corresponding to one discharge cell, of the front discharge electrodes  122  and the rear discharge electrodes  123  partly surrounds the discharge cells  150 R,  150 G and  150 B. Conversely, at least one, corresponding to one discharge cell, of the front discharge electrodes  122  and the rear discharge electrodes  123  entirely surrounds the discharge cells  150 . 
   The front discharge electrodes  122  and the rear discharge electrodes  123  may be disposed in directions which intersect each other. Specifically, the front discharge electrode  122  may extend along discharge cells  150 R,  150 G, and  150 B, which are oriented in a first direction, and the rear discharge electrode  123  may extend along discharge cells  150 R,  150 G, and  150 B, which are oriented in a second direction which intersects the first direction. In this case, either the front discharge electrode  122  or the rear discharge electrode  123  can serve as both an address electrode generating an address discharge and a sustain electrode generating a sustain discharge. To the contrary, one of the first electrode  122  and the second electrode  123  serves as an address electrode, and the other is divided into two electrodes to serve as an X electrode and a Y electrode. 
   Conversely, as shown in  FIGS. 2 and 5 , the front discharge electrodes  122  and the rear discharge electrode  123  may extend in one direction (an x-direction) parallel to each other and the address electrodes  133  may extend in another direction (a y-direction) intersecting the front discharge electrodes  122  and the rear discharge electrodes  123 . The front discharge electrodes  122  and the rear discharge electrodes  123  intersect the address electrodes, which means that a line of the discharge cells  150 R,  150 G, and  150 B, through which the address electrodes passes, and a line of the discharge cells  150 R,  150 G, and  150 B, through which the front discharge electrodes and the rear discharge electrodes pass, intersect each other. Furthermore, the front discharge electrodes  122  extend in a direction parallel to that of the rear discharge electrodes  123 , which means that the front discharge electrodes  122  and the rear discharge electrodes  123  are spaced from each other by a predetermined constant distance. 
   In this case, the rear discharge electrodes  123  and the front discharge electrodes  122  are electrodes for a sustain discharge (ks), and the sustain discharge for realizing an image of the plasma display panel occurs between the sustain discharge electrodes. 
   The address electrodes  133  are electrodes generating address discharge (ka) for facilitating the sustain discharge between the rear discharge electrodes  123  and the front discharge electrodes  122 . More specifically, the address electrodes  133  have a function of lowering a starting voltage of the sustain discharge. 
   In this case, it is preferable that the address electrodes  133  be disposed between the rear panels  130  and the phosphor layers  139 R,  139 G, and  139 B, and a dielectric layer  135  be formed between the address electrodes  133  and the phosphor layers  139 R,  139 G, and  139 B. In this case, the rear panel  130  supports the address electrodes  133  and the dielectric layer  135 . 
   Assuming that the rear discharge electrodes  123  serve as Y electrodes and the front discharge electrodes  122  serve as X electrodes, the address discharge (ka) occurs between the rear discharge electrode  123  and the address electrode  133 . When the address discharge is terminated, positive ions are accumulated at the side of the rear discharge electrodes  123 , and electrons are accumulated at the side of the front discharge electrodes  122 . As a result, the sustain discharge easily occurs between the rear discharge electrodes  123  and the front discharge electrodes  122 . 
   In  FIG. 2 , each the rear discharge electrodes  123  and the front discharge electrodes  122  is formed as a single electrode. However, each of the rear discharge electrodes  123  and the front discharge electrodes  122  may include two or more sub-electrodes. 
   As described above, the address electrodes  133  may be covered by the dielectric layer  135 . The dielectric layer  135  is made of a dielectric substance, such as PbO, B2O3, SiO2, etc., which can prevent the address electrodes  133  from being damaged due to the collision of positive ions or electrons therewith, and can induce electric charges during discharge. 
   The side dielectric layers  127  are, preferably, covered by a protective layer  129 . The protective layer  129  is not an essential component, but it functions to prevent the side dielectric layers  127  from being damaged due to the collision of the charged particles therewith, and to emit a lot of secondary electrons during discharge, so that it is preferable to form the protective layer  129 . 
   The phosphor layers  139 R,  139 G, and  139 B are disposed in the discharge cells. Specifically, when the plasma display panel  100  includes the partition walls  137 , the phosphor layers  139 R,  139 G, and  139 B are formed in spaces defined by the partition walls  137 . In this case, it is preferable that the phosphor layers  139 R,  139 G, and  139 B be disposed at the same level as the partition walls  137 . Specifically, it is preferable that the side dielectric layers be made of a dielectric substance so as to cause the sustain discharge to easily occur and to exhibit an excellent memory characteristic. It is also preferable that the phosphor layers  139 R,  139 G, and  139 B be formed on the partition walls  137  disposed below the side dielectric layers  127  so as to generate the visible rays in a wide area. 
   In this case, it is possible that the front discharge electrodes  122  and the rear discharge electrodes  123  be disposed to surround the upper side of the discharge cells  150 R,  150 G, and  150 B. In the latter regard, the upper side of the discharge cells means a portion which is located above the phosphor layer  139 R,  139 G, and  139 B. Conversely, the first and second electrode  122  and  123  surround bottom surfaces of the discharge cells  150 R,  150 G, and  150 B in which the phosphor layers  139 R,  139 G, and  139 B are disposed on the front panel  120 . 
   Referring to  FIG. 7A , a groove  130   a  is formed in the rear panel  130  of every discharge cell, and the phosphor layers  139 R,  139 G, and  139 B are formed in the groove  130   a . In this case, address electrodes are preferably not disposed on the rear panel  130 , such that the shape of the rear panel  130  has no restriction. If the groove  130   a  is formed in the rear panel  130 , the surface cross-sectional area of the rear panel  130  is increased by the groove  13   a . If the phosphor layer  139  is coated on the rear panel  130  having the groove  130   a , the surface cross-sectional area of the phosphor layer  139  is increased. 
   Referring to  FIG. 7B , a groove  120   a  is formed in the front panel  120  of every discharge cell, and the phosphor layers  139 R,  139 G, and  139 B are formed in the groove  120   a . In this case, the PDP is a transmission type PDP. Since it is not necessary to form electrodes in the front panel  120 , the groove  120   a  can be formed in the front panel  120 . If the phosphor layer  139  is coated on the front panel  120  having the groove  120   a , the surface cross-sectional area of the phosphor layer  139  is increased. 
   The phosphor layers  139 R,  139 G, and  139 B include a component which receives ultraviolet rays emitted by the sustain discharge and which emits visible rays. The phosphor layers  139 R disposed in sub-pixels emitting red light beams include a phosphor substance, such as Y(V, P)O 4 :Eu, etc. The phosphor layers  139 G disposed in sub-pixels emitting green light beams include a phosphor substance, such as Zn 2 SiO 4 :Mn, YBO 3 :Tb, etc. The phosphor layers  139 B disposed in sub-pixels emitting blue light beams include a phosphor substance, such as BAM:Eu, etc. 
   The discharge gas  140  filling the discharge cells  150 R,  150 G, and  150 B is composed of a penning mixture, such as Xe—Ne, Xe—He, and Xe—Ne—He. The reason that Xe is used as the main discharge gas is described below. Since Xe is an inert gas, which is chemically stable, Xe is not dissociated by the discharge. Further, since the atomic number thereof is large, the excitation voltage is low and the wavelength of emitted light is large. The reason why He or Ne is used a buffer gas is that a voltage-decreasing effect caused by a penning effect due to Xe, and a sputtering effect caused by a high pressure, can be reduced. 
   The front panel  120  employed by the present invention is not provided with the transparent Y electrodes  23   a , the transparent X electrodes  22   a , the bus X electrodes  22   b , the bus Y electrodes  23   b , the front dielectric layer  25 , and the protective layer  29 , as shown in  FIG. 1 . As a result, the transmittance of the visible rays toward the front side largely increases to about 90%. Assuming that an image is realized with a conventional brightness level, the electrodes  122  and  123  can be driven with a relatively low voltage, whereby the light emission efficiency increases. 
   In this case, since the front discharge electrodes  122  and the rear discharge electrodes  123  are disposed at the side of the discharge spaces, and not on the front panel  120  transmitting visible rays, there is no need to use a transparent electrode with high resistance as the discharge electrode. Therefore, an electrode with low resistance (for example, a metal electrode) can be used as the discharge electrode. As a result, the discharge-response speed becomes fast, and it is possible to perform low-voltage driving without distorting the waveform. 
   On the other hand, assuming that ‘A’ is the surface area of a pole plate of a condenser, ‘d’ is the interval between the pole plates, and ‘e’ is the electric capacitance of an insulator interposed between the pole plates, ‘C’ is proportional to the dielectric constant e and the surface area ‘A’, and is inversely proportional to the interval ‘d’, that is, C=εA/d. In this case, when the sizes of the address electrodes  133 , the rear discharge electrodes  123 , and the front discharge electrodes  122  are equal to each other in the entirety of the discharge cells, the surface areas A of the pole plates are equal to each other in discharge cells  150 R,  150 G, and  150 B. Furthermore, the distance from the address electrode  133  to the rear discharge electrode  123 , or to the front discharge electrode  122 , is also constant in each discharge cell. Therefore, the distances d between the pole plates are also the same in each discharge cell. The formed discharge cells have phosphor layers having a low dielectric constant e and a lower electric capacitance C than discharge cells in which the phosphor layers have a relatively high dielectric constant ?. 
   In addition, assuming that ‘Q’ is an amount of electric charge and ‘V’ is a voltage, the electric capacitance C is proportional to the amount of electric charge, that is, C=Q/V. Therefore, there is need to increase voltage to equalize the amount of electric charge, Q, of discharge cells in which the phosphor layers have a relatively low electric capacitance C to the amount of electric charge, Q, of the other discharge cells. In this case, the degree of voltage drop is not negligible in discharge cells in which the phosphor layers having a relatively low dielectric constant e are formed. Therefore, to compensate for the voltage drop, the voltage needs to be increased in the discharge cells in which the phosphor layers having a relatively low dielectric constant e are formed. 
   From this standpoint, if the distance d between the pole plates and the surface area A of the pole plates is the same in all discharge cells  150 R,  150 G, and  150 B, there is a need to control the discharge starting voltage in conformity with the discharge cells having a relatively high discharge starting voltage. As a result, the efficiency of the driving voltage decreases, thereby deteriorating driving performance of the plasma display panel. 
   According to the present invention, as shown in  FIG. 3 , to overcome such a problem, the electrode-burying depths are differently formed in correspondence to red, green, and blue discharging cells in which the phosphor layers  139 R,  139 G, and  139 B are disposed, each of which emits visible rays of red, green, and blue. 
   In this case, the electrode-burying depth corresponding to discharge cells differs according to a dielectric constant size of phosphor layers corresponding to the discharge cells. The electrode-burying depth corresponding to the discharge cells in which the phosphor layers having the lowest dielectric constant e are disposed is smaller than the electrode-burying depth corresponding to the discharge cells in which the phosphor layers having a relatively high dielectric constant e are disposed. Here, the electrode-burying depths (Wr, Wg, Wb) mean the depths or distances from the side surfaces of the first partition wall of each discharge cell to the front discharge electrode  122  or the rear discharge electrode  123  which is disposed inside the side dielectric layer and which corresponds to the discharge cell. 
   In this case, the phosphor layers having the lowest dielectric constant e are the green phosphor layers emitting visible rays of green. It is preferable that the electrode-burying depth (Wg) corresponding to the green discharging cells  150 G, in which the phosphor layers  139 G are formed, be smaller than electrode-burying depths Wr and Wb corresponding to the red and blue discharge cells  150 R and  150 B, in which the red phosphor layers and blue phosphor layers  139 G and  139 B are formed. 
   More specifically, a fluorescent substance, which is used in general phosphor layers  139 R,  139 G, and  139 B employed in the plasma display panel, has a particle size of about 2 to 4 μm and a thickness of 15 to 20 μm. 
   The green phosphor layers  139 G emitting visible rays of green are made of Zn 2 SiO 4 :Mn, YBO 3 :Tb, and the charged amount of the green phosphor layers  139 G is less than that of the red and blue phosphor layers  139 R and  139 B emitting visible rays of red and blue. Therefore, when the electrode-burying depths Wr, Wg, and Wb are equal in all discharge cells  150 R,  150 G, and  150 B, the discharge starting voltage of the green discharge cells  150 G increases. Specifically, assuming that the discharge starting voltages of the red and blue discharge cells  150 R and  150 B are about 165 to 183V, in discharge cells in which the phosphor layers having same thickness, the discharge starting voltage of the green discharge cells  150 G is about 169 to 184V, which is relatively higher than that of the red and blue discharge cells  150 R and  150 B. 
   Therefore, the dielectric constants e of the phosphor layers  139 R,  139 B are equal to or similar to each other, but the dielectric constant e of the green phosphor layers  139 G is relatively lower than that of the red and blue phosphor layer  139 R and  139 B. 
   Thus, it is preferable that the electrode-burying depth Wg corresponding to the green discharge cells  150 G be smaller than that of the electrode-burying depths Wr and Wb corresponding to the red discharge cells  150 R and the blue discharge cell  150 B. 
   This will be apparent from an equivalent circuit of the green discharge cells  150 B shown in  FIG. 6 , which is a sectional view illustrating a circuit equivalent to constituent elements of a green discharge cell. 
   Referring to  FIG. 6 , assuming that the side dielectric layers  127 , the protective layer  129 , the discharge gas  140 , and the dielectric layer  135  are serially connected to each other, and capacitors have constant electric capacitance, it is possible to obtain the entire electric capacitance of the green discharge cells  150 G using the equivalent circuit. 
   Specifically, assuming that C 1  is the electric capacitance of the side dielectric layers, C 2  is the electric capacitance of the protective layer, C 3  is the electric capacitance of the discharge gas, C 4  is the electric capacitance of the phosphor layer, and C 5  is the electric capacitance of the dielectric layer, the total electric capacitance of the green discharge cell  150 G can be expressed as follows: 1/C=1/C 1 +1/C 2 +1/C 3 +1/C 4 +1/C 5 . Specifically, if the electric capacitance of the first partition wall in a discharge cell, the phosphor layer of which has a low dielectric constant, can be increased, the electric capacitance of the entire discharge cell can be increased. 
   In this case, the electric capacitance C 1  of the side dielectric layers is inversely proportional to the electrode-burying depth, that is, C=εA/d. Therefore, when the electrode-burying depth Wg corresponding to the green discharge cell  150 G decreases, the total electric capacitance C thereof increases. 
   Accordingly, when the electrode-burying depth Wg has an appropriately small thickness relative to the electrode-burying depth Wr of the red discharge cell and the electrode-burying depth Wb of the blue discharge cell, each the discharge cells  150 R,  15 G and  150 B can have an equal or similar electric capacitance. 
   As a result, even though the same discharge starting voltage is applied to the respective discharge cells  150 R,  150 G, and  150 B, uniform discharge can be generated and stable discharge can be maintained. In addition, since the discharge starting voltage can be lowered to the discharge starting voltage of the discharge cells in which the phosphor layers having the smallest dielectric constant are formed, the voltage margin is increased. 
   Hereinafter, the operation of the plasma display panel  100  having the above-described structure will be described. In this case, it is assumed that the rear discharge electrodes  123  serve as the Y electrodes, which generate the address discharge Ka in cooperation with the address electrodes  133 , and the front discharge electrodes  122  serve as the X electrodes, which generate the sustain discharge in cooperation with the rear discharge electrode  123 , as shown in  FIG. 3 . 
   First, the address voltage is applied between the address electrodes  133  and the rear discharge electrodes  123 , and thus the address discharge occurs. Depending on the result of the address discharge, discharge cells  150 R,  150 G, and  150 B, in which the sustain discharge will occur, are selected. 
   Then, when an alternative sustain discharge voltage is applied between the rear discharge electrodes  123  and the front discharge electrodes  122  of the selected discharge cells, the sustain discharge occurs between the discharge electrodes, and ultraviolet rays are emitted while the energy level of discharge gas is lowered, which is excited due to the sustain discharge. Furthermore, the ultraviolet rays excite the phosphor layers  139  coated inside the discharge cells, and thus visible rays are emitted while the energy level of the excited phosphor layers is lowered, whereby the emitted visible rays realize an image. 
   Meanwhile, referring to  FIG. 8 , partition walls  137  may be formed between the side dielectric layers  127  and the rear panel  130 . In this case, the partition walls  137  are disposed between the side dielectric layers  127  and the rear panel  130 , and define the discharge cells  150 R,  150 G, and  150 B in cooperation with the side dielectric layers  127 . The partition walls  137  prevent the occurrence of undesirable discharge among the discharge cells  150 R,  150 G, and  150 B.  FIG. 8  shows that the partition walls  137  define the discharge cells  150 R,  150 G, and  150 B in a circular shape, but the invention is not limited thereto, and the discharge cells  150 R,  150 G, and  150 B may be defined in other shapes, such as a honeycomb shape. Furthermore,  FIG. 8  shows that the discharge cells  150 R,  150 G, and  150 B defined by the partition walls  137  have a circular cross-section, but the invention is not limited thereto, and the cross-section thereof may be formed in a polygonal shape, such as that of a triangle and a pentagon, or may be formed as a circle or an ellipse. 
   Conversely Partition walls  137  may be formed between the side dielectric layers  127  and the front panel  120 . 
   The plasma display panel having the above-describe construction has the following advantages. 
   First, since no element is formed in the portion of the front panel through which the visible rays are transmitted, the aperture ratio can be largely increased, and the transmittance can be increased to about 90%. 
   Second, since the sizes of the discharge cells in the horizontal and vertical directions are similar to each other, the discharge area can be uniformly enlarged, the electric field can be concentrated on the center, and abnormal discharge does not occur. Therefore, the light emission efficiency increases. Furthermore, the discharge occurs from the side surfaces forming a discharge space and diffuses into the center of the discharge space, and thus plasma is also concentrated on the center of the discharge space. In addition, plasma tends to be concentrated at the center of the discharge space due to the electric field generated by the voltage applied to the discharge electrodes formed on the side surfaces. Therefore, it is possible to utilize the space charges for the discharge. 
   Third, the volume and the amount of plasma can be significantly increased. In the plasma display panel according to the present invention, the discharge occurs at the side surfaces forming the discharge space, and diffuses into the center portion, so that the volume of the plasma due to the discharge can be significantly increased, and the amount of the plasma can be significantly increased. Thus, it is possible to emit visible rays to large extent due to the increased amount of plasma. 
   Fourth, it is possible to significantly enhance the light emission efficiency. The present plasma display panel having the above-described effect can be driven at a low voltage. Thus, the light emission efficiency can be largely enhanced. 
   Fifth, even though a highly-concentrated Xe gas is used as the discharge gas, it is possible to enhance the light emission efficiency. When the highly-concentrated Xe gas is used as the discharge gas, it is generally difficult to operate the plasma display panel at a low voltage. However, in the plasma display panel according to the present invention, low-voltage driving becomes possible, as described above. As a result, even though a highly-concentrated Xe gas is used as the discharge gas, the low-voltage driving becomes possible, thereby enhancing the light emission efficiency. 
   Sixth, the discharge-response speed is fast and the low-voltage driving becomes possible. In the plasma display panel according to the present invention, discharge electrodes are disposed at the side of the discharge space, not on the portion of the front panel through which the visible rays can transmit, so that it is possible to use an electrode having low resistance, such as a metal electrode, as the discharge electrode, and not use a transparent electrode with high resistance. Thus, the response speed becomes fast and low-voltage driving becomes possible without distorting the waveform. 
   Seventh, it is possible to basically prevent a permanent after-image. In the plasma display panel according to the present invention, the plasma is concentrated at the center of the discharge space by the electric field which is generated by the voltage applied to the discharge electrodes disposed at the side of the discharge cells, thereby preventing ions generated by the discharge from colliding with the phosphor layers due to the electric field, even though the discharge is performed for a long period of time. Thus, it is possible to basically prevent the problem of a permanent after-image remaining due to damage to the phosphor layers caused by ion sputtering. Specifically, when a highly-concentrated Xe gas is used as the discharge gas, the permanent after-images cause a serious problem. However, according to the present invention, it is possible to basically prevent the permanent after-images. 
   Eighth, the electrode-burying depth is different in each discharge cell depending on the dielectric constants of the phosphor layers, so that the discharge drive voltages in the discharge cells are controlled so that they are equal or similar to each other, thereby securing a wide range of voltage margin. Thus, it is possible to secure a large voltage margin. 
   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 changes in form and detail may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.