Patent Publication Number: US-7898178-B2

Title: Plasma display device with auxiliary electrodes

Description:
This application claims priority from Korean Patent Application No. 10-2006-0117110 filed on Nov. 24, 2006 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a plasma display device, and more particularly, to a plasma display device in which the amount of invalid power generated during the operation of a plasma display panel (PDP) can be reduced by forming auxiliary electrodes on an upper substrate so that the auxiliary electrodes can overlap respective corresponding horizontal barrier ribs. 
     2. Description of the Related Art 
     Plasma display panels (PDPs) are display devices which display an image, including text data and graphic data, by applying a predetermined voltage to a number of electrodes installed in a discharge space to cause a gas discharge and then exciting phosphors with the aid of plasma that is generated as a result of the gas discharge. PDPs are easy to manufacture as large-dimension thin flat displays. In addition, PDPs can provide wide viewing angles, full colors and high luminance. 
     In order to improve the luminance and brightness of an image displayed on a PDP, a PDP architecture has been developed in which the height of horizontal barrier ribs is lower than the height of vertical barrier ribs. This PDP architecture, however, results in crosstalk between sustain electrodes. 
     SUMMARY OF THE INVENTION 
     The present invention provides a plasma display device in which auxiliary electrodes are disposed in parallel with sustain electrodes and overlap respective corresponding horizontal barrier ribs so that crosstalk can be prevented from being generated regardless of a low height of the horizontal barrier ribs, and that the amount of invalid power can be minimized. 
     According to an aspect of the present invention, there is provided a plasma display device including a plasma display panel (PDP); an upper substrate and a lower substrate which face each other; a plurality of scan electrodes and a plurality of sustain electrodes which are disposed on the upper substrate; a plurality of first barrier ribs which are disposed on the lower substrate in parallel with the scan electrodes and the sustain electrodes; a plurality of second barrier ribs which are disposed on the lower substrate, intersect the first barrier ribs, and are higher than the first barrier ribs; and a plurality of auxiliary electrodes which are disposed on the upper substrate and overlap the first barrier ribs. 
     The auxiliary electrodes may be spaced apart from the respective scan electrodes and from the respective sustain electrodes. 
     A width of the auxiliary electrodes may be greater than at least one of a distance between the auxiliary electrodes and the respective scan electrodes and a distance between the auxiliary electrodes and the respective sustain electrodes. 
     The auxiliary electrodes may include floating electrodes which are disconnected from a power supply. 
     The auxiliary electrodes may be connected to a ground. 
     A predetermined voltage may be applied to the auxiliary electrodes. 
     The auxiliary electrodes may include indium tin oxide (ITO). 
     The auxiliary electrodes may be darker than phosphors that emit light upon receiving ultraviolet rays generated during a discharge. 
     The auxiliary electrodes may include black matrices. 
     The auxiliary electrodes may be adjacent to the respective scan electrodes and to the respective sustain electrodes. 
     The auxiliary electrodes may be discontinuous. 
     The auxiliary electrodes may be discontinuous at intersections between the first barrier ribs and the second barrier ribs. 
     A width of the auxiliary electrodes may be 0.7-1.3 times greater than an upper width of the first barrier ribs. 
     A width of the auxiliary electrodes may be 0.9-1.1 times greater than an upper width of the first barrier ribs. 
     Some of the first barrier ribs may have concave top surfaces. 
     The first barrier ribs may be 5-32 μm lower than the second barrier ribs. 
     A thickness of the auxiliary electrodes may be substantially the same as at least one of a thickness of the scan electrodes and a thickness of the sustain electrodes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  illustrates a perspective view of a plasma display panel (PDP) according to an embodiment of the present invention; 
         FIG. 2  illustrates a perspective view of a PDP according to another embodiment of the present invention; 
         FIGS. 3A and 3B  illustrate plan views of the patterns of the arrangement of barrier ribs and sustain electrode pairs of a PDP, according to embodiments of the present invention; 
         FIG. 3C  illustrates cross-sectional views of a horizontal barrier rib and an auxiliary electrode, according to an embodiment of the present invention; 
         FIG. 3D  illustrates graphs of the relationships between luminance and the ratio of the upper width of horizontal barrier ribs and the width of auxiliary electrodes and between crosstalk and the ratio of the upper width of horizontal barrier ribs and the width of auxiliary electrodes; 
         FIGS. 4A and 4B  illustrate plan views of the patterns of the arrangement of electrodes of a PDP, according to embodiments of the present invention; 
         FIG. 5  illustrates a plan view of the pattern of the arrangement of electrodes of a PDP, according to another embodiment of the present invention; 
         FIGS. 6(   a ) through  6 ( c ) illustrate cross-sectional views of barrier rib structures according to embodiments of the present invention; 
         FIG. 7  illustrates a plan view of the pattern of the arrangement of electrodes of a PDP, according to another embodiment of the present invention; 
         FIG. 8  illustrates a timing diagram of a time-division method of driving a PDP according to an embodiment of the present invention, in which a frame is divided into a plurality of sub-fields; 
         FIG. 9  illustrates a graph of the relationship between luminance and the height of horizontal barrier ribs and the height of vertical barrier ribs; 
         FIG. 10  illustrates a graph of the relationship between gas pollution and the difference between the height of horizontal barrier ribs and the height of vertical barrier ribs; and 
         FIG. 11  illustrates a graph of the relationship between a voltage applied to auxiliary electrodes and crosstalk. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will hereinafter be described in detail with reference to the accompanying drawings in which exemplary embodiments of the invention are shown. 
       FIG. 1  is a perspective view of a plasma display panel (PDP). Referring to  FIG. 1 , the PDP includes an upper substrate  10 , a plurality of sustain electrode pairs which are formed on the upper substrate  10  and consist of a scan electrode  11  and a sustain electrode  12  each; a lower substrate  20 ; and a plurality of address electrodes  22  which are formed on the lower substrate  20 . 
     Each of the sustain electrode pairs includes transparent electrodes  11   a  and  12   a  and bus electrodes  11   b  and  12   b . The transparent electrodes  11   a  and  12   a  may be formed of indium-tin-oxide (ITO). The bus electrodes  11   b  and  12   b  may be formed of a metal such as silver (Ag) or chromium (Cr) or may be comprised of a stack of chromium/copper/chromium (Cr/Cu/Cr) or a stack of chromium/aluminium/chromium (Cr/Al/Cr). The bus electrodes  11   b  and  12   b  are respectively formed on the transparent electrodes  11   a  and  12   a  and reduce a voltage drop caused by the transparent electrodes  11   a  and  12   a  which have a high resistance. 
     According to an embodiment of the present invention, each of the sustain electrode pairs may be comprised of the bus electrodes  11   b  and  12   b  only. In this case, the manufacturing cost of the PDP can be reduced by not using the transparent electrodes  11   a  and  12   a . The bus electrodes  11   b  and  12   b  may be formed of various materials other than those set forth herein, e.g., a photosensitive material. 
     An upper dielectric layer  13  and a passivation layer  14  are deposited on the upper substrate  10  on which the scan electrodes  11  and the sustain electrodes  12  are formed. Charged particles generated as a result of a discharge accumulate in the upper dielectric layer  13 . The upper dielectric layer  13  may protect the sustain electrode pairs. The passivation layer  14  protects the upper dielectric layer  13  from sputtering of the charged particles and enhances the discharge of secondary electrons. 
     The address electrodes  22  are formed and intersects the scan electrode  11  and the sustain electrodes  12 . A lower dielectric layer  24  and the barrier ribs  21  are formed on the lower substrate  20  on which the address electrodes  22  are formed. A phosphor layer  23  is formed on the lower dielectric layer  24  and the barrier ribs  21 . 
     The phosphor layer  23  is excited by UV rays that are generated upon a gas discharge. As a result, the phosphor layer  23  generates one of R, G, and B rays. A discharge space is provided between the upper and lower substrates  10  and  20  and the barrier ribs  21 . A mixture of inert gases, e.g., a mixture of helium (He) and xenon (Xe), a mixture of neon (Ne) and Xe, or a mixture of He, Ne, and Xe is injected into the discharge space. 
     The barrier ribs  21  include vertical barrier ribs  21   a  which are formed in parallel with the address electrodes  22  and horizontal barrier ribs  21   b  which intersect the address electrodes  22 . The barrier ribs  21  define a plurality of discharge cells and prevent ultraviolet (UV) rays and visible rays generated in one discharge cell due to a gas discharge from penetrating other discharge cells. 
     In this embodiment, red (R), green (G), and blue (B) discharge cells are arranged in a straight line. However, the present invention is not restricted to this. For example, R, G, and B discharge cells may be arranged as a triangle or a delta. Alternatively, R, G, and B discharge cells may be arranged as a polygon such as a rectangle, a pentagon, or a hexagon. 
     The PDP illustrated in  FIG. 1  has a differential barrier structure in which the height of the vertical barrier ribs  21   a  is different from the height of the horizontal barrier ribs  21   b . More specifically, the height of the horizontal barrier ribs  21   b  is lower than the height of the vertical barrier ribs  21   a . Thus, according to the embodiment of  FIG. 1 , it is possible to improve the luminance and brightness of a PDP and effectively exhaust air during the manufacture of a PDP. 
     The height of the horizontal barrier ribs  21   b  may be 5-32 μm lower than the height of the vertical barrier ribs  21   a . In this case, a phosphor material, if any, stuck onto a barrier rib can be easily removed and can be prevented from reducing the luminance and brightness of a PDP. In order to facilitate the exhaustion of air, the difference between the height of the vertical barrier ribs  21   a  and the height of the horizontal barrier ribs  21   b  must be 5 μm or more. In order to prevent a reduction in the luminance of a PDP, the difference between the height of the vertical barrier ribs  21   a  and the height of the horizontal barrier ribs  21   b  must be less than 32 μm. 
       FIG. 9  illustrates a graph of the relationship between luminance and the height of the horizontal barrier ribs  21   b  and the height of vertical barrier ribs  21   a , and  FIG. 10  illustrates a graph of the relationship between gas pollution and the difference between the height of the horizontal barrier ribs  21   b  and the height of vertical barrier ribs  21   a.    
     Referring to  FIG. 9 , a vertical axis represents luminance, and a horizontal axis represents the difference between the height of the horizontal barrier ribs  21   b  and the height of the vertical barrier ribs  21   a . As the difference between the height of the horizontal barrier ribs  21   b  and the height of the vertical barrier ribs  21   a  increases within the range of 5-32 μm, luminance linearly decreases. However, once the difference between the height of the horizontal barrier ribs  21   b  and the height of the vertical barrier ribs  21   a  exceeds about 32 μm, luminance drastically decreases for the following reasons: the lower the height of the horizontal barrier ribs  21   b , the smaller the surface area of discharge cells; the smaller the surface area of discharge cells, the smaller the surface area of phosphor layers; and a reduction in the surface area of phosphor layers may result in a reduction in the luminance of a PDP. 
     The greater the difference between the height of the horizontal barrier ribs  21   b  and the height of vertical barrier ribs  21   a , the easier it becomes to exhaust air. Referring to  FIG. 10 , a vertical axis represents the remaining amount of oxygen and nitrogen, which is an indicator of the degree of gas pollution, and a horizontal axis represents the difference between the height of the horizontal barrier ribs  21   b  and the height of vertical barrier ribs  21   a . Once the difference between the height of the horizontal barrier ribs  21   b  and the height of vertical barrier ribs  21   a  exceeds about 5 μm, the remaining amount of oxygen and nitrogen considerably decreases. Referring to  FIGS. 9 and 10 , the difference between the height of the horizontal barrier ribs  21   b  and the height of vertical barrier ribs  21   a  may be determined to be within the range of 5-32 μm, thereby maintaining appropriate luminance and facilitating the exhaustion of air. 
     Referring to  FIG. 1 , a plurality of auxiliary electrodes  30  are formed in parallel with the sustain electrode pairs and overlap the horizontal barrier ribs  21   b . The auxiliary electrodes  30  include a conductive material and are formed as bars. The thickness of the auxiliary electrodes  30  may be substantially the same as the thickness of the sustain electrode pairs, thereby facilitating the manufacture of PDPs and increasing the yield of PDPs. 
     The auxiliary electrodes  30  may be floating electrodes which are disconnected from a power source. Floating electrodes block an electric field and can thus prevent crosstalk. In other words, floating electrodes can prevent the occurrence of unnecessary misdischarge by preventing the electric potentials of a scan electrode and a sustain electrode between a pair of adjacent discharge cells from being significantly discrepant from each other. The auxiliary electrodes  30  may be disconnected from a power source and connected to a ground. In this case, the auxiliary electrodes  30  may maintain a ground voltage and may thus be less affected by a voltage applied to a scan electrode and a sustain electrode belonging to different discharge cells. This effect can also be obtained by applying a predetermined voltage to the auxiliary electrodes  30 .  FIG. 11  illustrates a graph of the relationship between a voltage applied to the auxiliary electrodes  30  and crosstalk. Referring to  FIG. 11 , a horizontal axis represents a voltage applied to the auxiliary electrodes  30 , and a vertical axis represents crosstalk. Only a small amount of crosstalk is generated until the electric potential of the auxiliary electrodes  30  exceeds 30 V. However, once the electric potential of the auxiliary electrodes  30  exceeds 30 V, the amount of crosstalk considerably increases, partly because the electric potential of the auxiliary electrodes  30  becomes too much discrepant from the electric potential of the scan electrodes  11  or the electric potential of the sustain electrodes  12 . Therefore, a voltage of −30 V-30 V may be applied to the auxiliary electrodes  30 . 
     In this embodiment, the auxiliary electrodes  30  are spaced apart from the respective sustain electrode pairs. If the auxiliary electrodes  30  are not spaced apart from the respective sustain electrode pairs, the resistance between the scan electrodes  11  and the respective sustain electrodes  12  may become zero. Thus, a short circuit may occur, and a driving circuit may not operate at all. The width of the auxiliary electrodes  30  may be greater than the width of the scan electrodes  11  or the sustain electrodes  12 . In this case, it is possible to reduce the probability of the occurrence of crosstalk. 
       FIG. 2  illustrates a perspective view of a PDP according to another embodiment of the present invention. Referring to  FIG. 2 , the PDP may include black matrices  15 . The black matrices  15  perform a light shield function by absorbing external light and reducing the amount of light reflected from an upper substrate  10 . The black matrices  15  improve the contrast of the PDP. 
     The black matrices  15  include first black matrices  15   a  which are disposed between the transparent electrodes  11   a  and the respective bus electrodes  11   b , first black matrices  15   b  which are disposed between the transparent electrodes  12   a  and the respective bus electrodes  12   b , and second black matrices  15   c  which are disposed on the first black matrices  15   a  and  15   b  and on the auxiliary electrodes  30 . 
     The second black matrices  15   c  may be referred to as black layers or black electrode layers. The first black matrices  15   a  and  15   b  and the second black matrices  15   c  may be formed at the same time and may thus be physically connected to one another. Alternatively, the first black matrices  15   a  and  15   b  and the second black matrices  15   c  may not be formed at the same time and thus may not be physically connected to one another. 
     If the first black matrices  15   a  and  15   b  and the second black matrices  15   c  are physically connected to one another, the first black matrices  15   a  and  15   b  and the second black matrices  15   c  may be formed of the same material. However, if the first black matrices  15   a  and  15   b  and the second black matrices  15  are physically separated from one another, the first black matrices  15   a  and  15   b  and the second black matrices  15   c  may be formed of different materials. The second black matrices  15   c  may be optional. 
     The auxiliary electrodes  30  may be formed of the same material as the transparent electrodes  11   a  and  12   a , i.e., may be formed of ITO. Alternatively, the auxiliary electrodes  30  may be formed of the same material as the bus electrodes  11   b  and  12   b , i.e., may be formed of a metal. In this manner, it is possible to facilitate the fabrication of the auxiliary electrodes  30  without a requirement of additional materials or processes. 
     If the auxiliary electrodes  30  are formed of a dark metal, the contrast of the PDP may be improved. In this case, the first black matrices  15   a  and  15   b  and the second black matrices  15   c  may be replaced with the auxiliary electrodes  30 . That is, the auxiliary electrodes  30  may be darker than phosphors and may thus be able to absorb external light and reduce glare. If the first black matrices  15   a  and  15   b  and the second black matrices  15   c  are replaced with the auxiliary electrodes  30  and the auxiliary electrodes  30  are darker than phosphor layer  23 , only the first black matrices  15   a  and  15   b  may be formed without forming the second black matrices  15   c.    
     The auxiliary electrodes  30  may be formed together with the sustain electrode pairs, thereby facilitating the fabrication of PDPs and increasing the yield of PDPs. 
       FIGS. 3A and 3B  illustrate plan views of the patterns of the arrangement of barrier ribs  121   b  and sustain electrode pairs ( 111  and  112 ) of a PDP, according to embodiments of the present invention. Referring to  FIGS. 3A and 3B , the width of auxiliary electrodes  130  may be slightly greater than or slightly less than the upper width of horizontal barrier ribs  121   b .  FIG. 3A  illustrates the situation when the width of the auxiliary electrodes  130  is slightly greater than the upper width of the horizontal barrier ribs  121   b , and  FIG. 3B  illustrates the situation when the width of the auxiliary electrodes  130  is slightly less than the upper width of the horizontal barrier ribs  121   b.    
       FIG. 3C  illustrates cross-sectional views of a horizontal barrier rib  121   b  and an auxiliary electrode  130 , according to an embodiment of the present invention, and  FIG. 3D  illustrates graphs of the relationships between luminance and the ratio of an upper width d 1  of horizontal barrier ribs  130  and a width d 2  of auxiliary electrodes  130  and between crosstalk and the ratio of the upper width of horizontal barrier ribs and the width of auxiliary electrodes. Referring to  FIG. 3D , once the ratio of the upper width d 1  and the width d 2  exceeds about 0.7, the amount of crosstalk considerably decreases. When the ratio of the upper width d 1  and the width d 2  exceeds about 1.3, the level of luminance considerably decreases. Therefore, the ratio of the upper width d 1  and the width d 2  may be 0.7-1.3. More specifically, the ratio of the upper width d 1  and the width d 2  may be determined to be 0.9-1.1 given that the level of luminance does not much decrease unless the ratio of the upper width d 1  and the width d 2  exceeds 1.1, and that the probability of the occurrence of crosstalk is maintained to be very low as long as the ratio of the upper width d 1  and the width d 2  is 0.9 or greater. 
       FIGS. 4A and 4B  illustrate plan views of the patterns of the arrangement of electrodes of a PDP, according to embodiments of the present invention. Referring to  FIGS. 4A and 4B , a plurality of auxiliary electrodes  230  may be interposed between respective corresponding sustain electrode pairs, each comprising a scan electrode  210  and a sustain electrode  220 . Thus, the auxiliary electrodes  230  are adjacent not only to the respective scan electrodes  210  but also to the respective sustain electrodes  220 . In this case, it is possible to stabilize a sustain discharge and reduce the power consumption of a PDP compared to the situation when the auxiliary electrodes  230  are adjacent only to the respective scan electrodes  210  or to the respective sustain electrodes  220 . However, since a voltage is alternately applied to the scan electrodes  210  and the sustain electrodes  220 , the difference between the electric potential of the scan electrodes  210  and the electric potential of the respective sustain electrodes  220  increases, and thus, the probability of the occurrence of crosstalk increases. 
     According to the embodiment of  FIGS. 4A and 4B , the auxiliary electrodes  230  may overlap respective corresponding horizontal barrier ribs  221   b , thereby preventing the occurrence of crosstalk. 
       FIG. 5  illustrates a plan view of the pattern of the arrangement of auxiliary electrodes  330  of a PDP according to an embodiment of the present invention. Referring to  FIG. 5 , the auxiliary electrodes  330  may be discontinuous at the intersections between the horizontal barrier ribs  321   b  are a plurality of vertical barrier ribs  321   a . In this case, it is possible to reduce the manufacturing cost of a PDP. 
       FIGS. 6(   a ) through  6 ( c ) illustrate cross-sectional views of barrier rib structures according to embodiments of the present invention. Referring to  FIGS. 6(   a ) through  6 ( c ), the height of horizontal barrier ribs  420 ,  430  and  440  is lower than the height of a vertical barrier rib  410 , and thus, the horizontal barrier ribs  420 ,  430  and  440  may serve as a passage of ventilation. Referring to  FIG. 6(   a ), the horizontal barrier rib  420  has a flat top surface. Referring to  FIG. 6(   b ), the horizontal barrier rib  430  has a concave top surface. The referring to  FIG. 6(   c ), the horizontal barrier rib  440  has a convex top surface. The amount of crosstalk can be reduced further when horizontal barrier ribs have concave top surfaces than when horizontal barrier ribs have convex top surfaces. 
       FIG. 7  illustrates a plan view of the pattern of the arrangement of electrodes of a PDP, according to another embodiment of the present invention. Referring to  FIG. 7 , a plurality of discharge cells may be arranged in a matrix. The discharge cells are respectively disposed at the intersections between a plurality of address electrodes X 1  through Xn and a plurality of scan electrode lines Y 1  through Ym or a plurality of sustain electrode lines Z 1  through Xm. The scan electrode lines Y 1  through Ym may be driven sequentially or simultaneously. The address electrode lines X 1  through Xn may be divided into two groups, i.e., one group including odd-numbered address electrode lines and the other group including even-numbered address electrode lines, and may be driven in units of the groups. 
     The electrode arrangement pattern illustrated in  FIG. 7  is exemplary. Thus, the present invention is not restricted to the pattern of the arrangement of electrode lines and the method of driving electrode lines set forth herein. For example, the present invention may be applied to a dual scan method by which two of the scan electrode lines Y 1  through Ym may be scanned at a time. Also, the address electrode lines X 1  through Xn may be divided into two groups, i.e., one group including one half of the address electrode lines X 1  through Xn and the other group including the other half of the address electrode lines X 1  through Xn, and may be drive in units of the groups. 
       FIG. 8  illustrates a timing diagram of a time-division method of driving a PDP according to an embodiment of the present invention, in which a frame is divided into a plurality of sub-fields. Referring to  FIG. 8 , a unit frame may be divided into a predefined number of sub-fields, e.g., eight sub-fields SF 1  through SF 8 , in order to represent grayscale values in a time-division manner. Each of the sub-fields SF 1  through SF 8  includes a reset period (not shown), an address period (A 1 , A 2 , A 3 , A 4 , A 5 , A 6 , A 7  or A 8 ), and a sustain period (S 1 , S 2 , S 3 , S 4 , S 5 , S 6 , S 7 , or S 8 ). 
     At least one of the sub-fields SF 1  through SF 8  may not include a reset period. For example, only the first sub-field SF 1  or a sub-field in the middle of a unit frame may include a reset period. 
     During the address period A 1 , A 2 , A 3 , A 4 , A 5 , A 6 , A 7  or A 8 , an address signal is applied to an address electrode, and a plurality of scan signals respectively corresponding to a plurality of scan electrodes are sequentially applied. During the sustain period S 1 , S 2 , S 3 , S 4 , S 5 , S 6 , S 7 , or S 8 , a sustain signal is alternately applied to a scan electrode and a sustain electrode so that a plurality of discharge cells including wall charges generated during the address period A 1 , A 2 , A 3 , A 4 , A 5 , A 6 , A 7  or A 8  can cause a sustain discharge. 
     The luminance of a PDP is proportional to the number of sustain discharge pulses generated during the sustain period S 1 , S 2 , S 3 , S 4 , S 5 , S 6 , S 7 , or S 8 . If a frame for forming an image is represented by eight sub-fields and 256 grayscale values, 1 sustain signal, 2 sustain signals, 4 sustain signals, 8 sustain signals, 16 sustain signals, 32 sustain signals, 64 sustain signals and 128 sustain signals may be applied to first, second, third, fourth, fifth, sixth, seventh and eighth sub-fields, respectively, of a frame. In order to obtain a grayscale value of 133, discharge cells may be addressed during first, third sub-field, and eighth sub-fields of a frame so that the discharge cells can cause a sustain discharge. 
     The number of sustain discharges allocated to each of a plurality of sub-fields of a frame may vary according to the weights respectively allocated to the plurality of sub-fields during an automatic power control (APC) operation. That is, a frame is illustrated in  FIG. 8  as being divided into eight sub-fields, but the present invention is not restricted to this. The number of sub-frames of a frame may vary according to design specification. For example, a frame may be divided into more than eight sub-frames, e.g., twelve or sixteen sub-fields. Also, the number of sustain discharges allocated to each of a plurality of sub-fields of a frame may vary according to the gamma characteristics and other physical characteristics of a PDP. For example, a gray scale of 6, instead of a grayscale of 8, may be allocated to a fourth sub-field of a frame, and a grayscale value of 34, instead of a grayscale value of 32, may be allocated to a sixth sub-field of a frame. 
     In the case of driving a PDP in the above-mentioned manner, a number of sustain discharges are required to occur during each of a plurality of a frame in order to continuously display a still image or to display more than one image with the same grayscale. Thus, phosphors may have to be continuously turned on in order to display even the same image or even the same grayscale and may thus deteriorate. Therefore, various problems such as grayscale fluctuations, afterimages, or luminance reductions may arise. In this embodiment, in order to address these problems, an image sticking minimization (ISM) mode in which the number of sustain pulses is reduced for the situations when the same image is displayed over and over may be adopted. 
     As described above, according to the present invention, it is possible to improve the luminance and brightness of a PDP using horizontal barrier ribs that are lower than vertical barrier ribs. In addition, it is possible to prevent the occurrence of crosstalk and thus to prevent the occurrence of invalid power by forming floating electrodes to overlap respective corresponding horizontal barrier ribs. 
     Moreover, it is possible to improve the contrast of a PDP by forming floating electrodes of a dark metal. Furthermore, it is possible to facilitate the fabricate of a PDP by forming floating electrodes of a transparent conductive material such as ITO. 
     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 details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.