Patent Publication Number: US-2009219228-A1

Title: Plasma display panel

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Example embodiments relate to a plasma display panel (PDP). More particularly, example embodiments relate to a PDP having reduced reactive power consumption. 
     2. Description of the Related Art 
     PDPs refer to display devices that may realize an image using gas discharge. That is, gas discharge in the PDP may generate plasma, thereby triggering emission of vacuum ultraviolet rays. The ultraviolet rays may excite phosphors to emit red, green, and blue visible light as the excited phosphors are stabilized. The PDPs may be self-emissive type display devices and, therefore, may have a quick response characteristic while overcoming a viewing angle limitation. Conventional PDPs, however, may have relatively high power consumption. 
     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 of ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     Example embodiments are therefore directed to a PDP, which substantially overcomes one or more of the disadvantages of the related art. 
     It is therefore a feature of an embodiment to provide a PDP having a dielectric layer structure with optimized dielectric constant with respect to thickness thereof capable of reducing reactive power consumption of the PDP. 
     At least one of the above and other features and advantages may be realized by providing a PDP, including rear and front substrates facing each other with a predetermined interval therebetween, barrier ribs between the rear and front substrates to define discharge cells, address electrodes on the rear substrate and extending in a first direction to correspond to the discharge cells, display electrodes on the front substrate and extending in a second direction intersecting the first direction to correspond to the discharge cells, and a dielectric layer that on the front substrate to cover the display electrodes, the dielectric layer having a dielectric constant of about 6 C 2 /N·m 2  to about 7 C 2 /N·m 2  and a thickness of about 16 μm to about 20 μm. A value of (the dielectric constant)×(the thickness) may be about 96×10 −6  C 2 /N·m to about 140×10 −6  C 2 /N·m. A value of (the dielectric constant)/(the thickness) may be about 0.3×10 6  C 2 /N·m 3  to about 0.437×10 6  C 2 /N·m 3 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments with reference to the attached drawings, in which: 
         FIG. 1  illustrates an exploded perspective view of a PDP according to an example embodiment; 
         FIG. 2  illustrates a cross-sectional view along line II-II of  FIG. 1 ; 
         FIG. 3  illustrates a top plan view of an arrangement of barrier ribs and electrodes in the PDP of  FIG. 1 ; and 
         FIG. 4  illustrates a graph of reactive power as a function of a dielectric layer structure in a 50-inch full-white PDP. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Korean Patent Application No. 10-2008-0018368, filed on Feb. 28, 2008, in the Korean Intellectual Property Office, and entitled: “Plasma Display Panel,” is incorporated by reference herein in its entirety. 
     Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings; however, they may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     In the drawing figures, the dimensions of layers and regions may be exaggerated for clarity of illustration. It will also be understood that when a layer or element is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. Further, it will be understood that when a layer is referred to as being “under” another layer, it can be directly under, and one or more intervening layers may also be present. In addition, it will also be understood that when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present. Like reference numerals refer to like elements throughout. 
     As used herein, the terms “a” and “an” are open terms that may be used in conjunction with singular items or with plural items. 
       FIG. 1  illustrates an exploded perspective view of a PDP according to an example embodiment, and  FIG. 2  illustrates a cross-sectional view along line II-II of  FIG. 1 . Referring to  FIGS. 1 and 2 , a PDP, e.g., an alternating current type PDP, of an example embodiment may include rear and front substrates  10  and  20  facing each other with a predetermined interval therebetween, barrier ribs  16  and a plurality of electrodes, i.e., address electrodes  11  and display electrodes  30 , between the rear and front substrates  10  and  20 , and at least one dielectric layer between the rear and front substrates  10  and  20  having optimized dielectric constant and thickness capable of reducing reactive power consumption of the PDP. In this respect, since the PDP may be driven by capacitance of the dielectric layer, it is noted that the driving power of the PDP may be classified into active power, i.e., power actively contributing to gas discharge by voltage application, and reactive power, i.e., power that does not contribute to the gas discharge but acts as a loss during switching operations. 
     The barrier ribs  16  of the PDP may be formed between the rear and front substrates  10  and  20 , and may define a plurality of discharge cells  17 . The discharge cells  17  may be filled with a discharge gas, e.g., neon (Ne) gas, xenon (Xe) gas, or a mixture thereof, and may include phosphor layers  19  on surfaces thereof. Accordingly, when the discharge gas generates vacuum ultraviolet rays in the discharge cells  17 , the phosphor layers  19  in the discharge cells  17  may be excited by the vacuum ultraviolet rays to emit visible light as the excited phosphor layers  19  are stabilized. The gas discharge may be induced in the discharge cells  17  via application of voltage to the address electrodes  11  and display electrodes  30 . 
     The address electrodes  11  and display electrodes  30  of the PDP may be arranged between the rear and front substrates  10  and  20 , and may intersect each other at regions corresponding to the discharge cells  17 . Therefore, the PDP may have, e.g., millions or more unit discharge cells  17  arranged in a matrix pattern. For example, the address electrodes  11  may be formed on an inner surface of the rear substrate  10 , i.e., a surface of the rear substrate  10  facing the front substrate  20 , and may extend in a first direction, e.g., along the y-axis, so an array of discharge cells  17  may be arranged along an address electrode  11 , e.g., each address electrode  11  may extend along a center of a corresponding array of discharge cells  17 . The address electrodes  11  may be spaced apart from each other in a second direction, e.g., a space between two adjacent address electrodes  11  may extend along the y-axis. 
     The address electrodes  11  may be formed of metal having excellent electrical conductivity, e.g., silver (Ag). Since the address electrodes  11  are arranged on the rear substrate  10 , the address electrodes  11  may not interfere with the visible light emitted from the discharge cells  17  toward the front substrate  20 . The address electrodes  11  may be covered with a first dielectric layer  13 , i.e., the address electrodes  11  may be positioned between the first dielectric layer  13  and the inner surface of the rear substrate  10 . The first dielectric layer  13  may protect the address electrodes  11  from the discharge gas, and may generate and accumulate wall charges. That is, the first dielectric layer  13  may prevent charged particles, e.g., cations and electrons, from directly colliding with the address electrodes  11  during the gas discharge. 
     The barrier ribs  16  of the PDP may be formed on the first dielectric layer  13  of the rear surface  10  to define the discharge cells  17 . The barrier ribs  16  may include first barrier ribs  16   a  and second barrier ribs  16   b  arranged in any suitable pattern, e.g., a grid pattern, to define the discharge cells  17 , e.g., in a matrix pattern. The first barrier ribs  16   a  may extend in the first direction, e.g., along the y-axis, and may be spaced apart from each other in the second direction. The second barrier ribs  16   b  may extend in the second direction to cross the first barrier ribs  16   a , and may be spaced apart from each other in the first direction. It is noted, however, that other configurations of the barrier ribs  16 , e.g., the barrier ribs  16  may include only the first barrier ribs  16   a  along the y-axis in a stripe pattern corresponding to the address electrodes  11  to define discharge cells in a stripe pattern, are within the scope of the present invention. 
     The phosphor layers  19  of the PDP may be formed in the discharge cells  17 , e.g., on side surfaces of the barrier ribs  16 , and on a surface of the first dielectric layer  13  facing the discharge cells  17 . The phosphor layers  19  may be formed, e.g., by applying a phosphor paste on surfaces of the barrier ribs  16  and the first dielectric layer  13 , followed by drying and baking the applied phosphor paste. The phosphor layers  19  may be arranged in any suitable configuration in the discharge cells  17 . For example, phosphor layers  19  in discharge cells  17  along the y-direction may be formed of phosphors emitting a substantially same color of visible light, and phosphor layers  19  in discharge cells  17  along the x-axis may be alternately arranged of phosphors emitting red, green, and blue light. That is, the phosphor layers  19  that alternately emit the red, green, and blue visible light may be arranged in the x-direction. 
     The display electrodes  30  of the PDP may be disposed on the front substrate  20 , and may include pairs of first and second electrodes  31  and  32 , i.e., each pair of display electrodes  30  may include a first electrode  31 , e.g., a sustain electrode, and a second electrode  32 , e.g., a scan electrode. The sustain and scan electrodes  31  and  32  may be formed on an inner surface of the front substrate  20 , i.e., a surface facing the rear substrate  10 , to correspond to the discharge cells  17 . The sustain and scan electrodes  31  and  32  may be arranged in an alternating pattern, and may form surface discharge structures at centers of the discharge cells  17  to induce the gas discharge in the discharge cells  17 . An exemplary arrangement of the display electrode  30  will be described in more detail below with reference to  FIG. 3 . 
       FIG. 3  illustrates a top plan view of an arrangement of the barrier ribs  16  and the display electrodes  30  according to an example embodiment. Referring to  FIG. 3 , the sustain and scan electrodes  31  and  32  may extend in the x-direction, and may intersect the address electrodes  11 . Each of the sustain and scan electrodes  31  and  32  may include a transparent electrode  31   a  and  32   a , respectively, and a bus electrode  31   b  and  32   b , respectively, so voltage signals may be applied to the transparent electrodes  31   a  and  32   a  via the bus electrodes  31   b  and  32   b , respectively. 
     The transparent electrodes  31   a  and  32   a  may be arranged above the discharge cells  17 , and may be formed of a transparent material, e.g., indium tin oxide (ITO), to secure a sufficient aperture ratio. The transparent electrodes  31   a  and  32   a  may extend from respective bus electrodes  31   b  and  32   b , i.e., peripheral portions of the discharge cells  17 , toward centers of respective discharge cells  17 . That is, as illustrated in  FIG. 3 , the transparent electrodes  31   a  and  32   a  may have respective widths W 31  and W 32 , such that a discharge gap DG may be defined between the transparent electrodes  31   a  and  32   a , e.g., in a center of each discharge cell  17 . 
     The bus electrodes  31   b  and  32   b  may extend along the x-axis, and may be formed of a material having excellent electric conductivity, e.g., metal, to effectively apply the voltage signals to the transparent electrodes  31   a  and  32   a . The bus electrodes  31   b  and  32   b  may be arranged along opposite ends of the discharge cells  17 , so a center of a discharge cell  17  may be between bus electrodes  31   b  and  32   b . Therefore, the voltage signals applied to the bus electrodes  31   b  and  32   b  may be transferred to the transparent electrodes  31   a  and  32   a  that are connected to the bus electrodes  31   b  and  32   b  and correspond to the discharge cells  17 . 
     Referring again to  FIGS. 1 and 2 , a second dielectric layer  21  may be formed on the front substrate  20  to cover the display electrodes  30 , so the display electrodes  30  may be between the front substrate  20  and the second dielectric layer  21 . The second dielectric layer  21  may protect the sustain and scan electrodes  31  and  32  during the gas discharge. The second dielectric layer  21  may generate and accumulates wall charges during the gas discharge. The second dielectric layer  21  may be formed of any suitable dielectric material, e.g., the second dielectric layer  21  may include silicon (Si) due to its insulating properties and relatively high strength. 
     The second dielectric layer  21  may have a dielectric constant (∈) of about 6 C 2 /N·m 2  to about 7 C 2 /N·m 2 , and may have a thickness t of about 16 μm to about 20 μm. The dielectric constant (∈) may be determined, e.g., by capacitance-voltage measurement of a thin film of the dielectric layer and calculating the k value based on the film thickness. As illustrated in  FIG. 2 , the thickness t of the second dielectric layer  21  may be measured from a lower surface of the second dielectric layer  21  to an upper surface of the second dielectric layer  21  along the z-axis. It is noted that the upper surface of the second dielectric layer  21  may face the front substrate  20 , e.g., may be directly on the front substrate  20 , and the lower surface of the second dielectric layer  21  may be opposite the upper surface of the second dielectric layer  21  to face away from the front substrate  20 . 
     When the dielectric constant (∈) is greater than about 7 C 2 /N·m 2 , the reactive power of the PDP may increase. When the dielectric constant (∈) of the second dielectric layer  21  is less than about 6 C 2 /N·m 2 , the second dielectric layer  21  may require a high baking temperature, e.g., above the transition temperature of glass, thereby making it difficult to apply the second dielectric layer  21  to the PDP. 
     In particular, a low dielectric constant (∈) of the second dielectric layer  21 , e.g., lower than about 6 C 2 /N·m 2 , may indicate an increased content of silicon therein, thereby requiring a baking temperature of about 1400° C. Since the transition temperature of glass, e.g., a material used to form the front substrate  20 , is about 600° C., a temperature of about 1400° C. for baking a high silicon content second dielectric layer  21  may be too high for applying the second dielectric layer  21  to the front substrate  20 . 
     It is noted that although the baking temperature of a dielectric layer may be reduced by adding an alkali material thereto, there is a limit of an amount of the alkali material that may be added to the silicon (Si) in the second dielectric layer  21  while maintaining the physical characteristics of the second dielectric layer  21 . Further, when the content of the alkali material is high in the second dielectric layer  21 , the second dielectric layer  21  may yellow, thereby reducing light transmittance through the second dielectric layer  21 . 
     In order to use the silicon (Si) as a dielectric material for forming the second dielectric layer  21 , the silicon (Si) may be in a form of particles having a diameter of about 2 μm or less formed by, e.g., wet milling. When using the wet milling, a cost for forming silicon particles is high. It is noted that if dry milling is used for forming small silicon particles, the silicon particles may be blown by a jet mill to collide with each other to be further reduced in size, thereby deteriorating yield. For example, when the dielectric constant (∈) is about 12 C 2 /N·m 2 , the material yield in dry milling may be about 100 kg/hour, and when the dielectric constant (∈) is about 6 C 2 /N·m 2 , the material yield in dry milling may be reduced to about 20 kg/hour. The material yield may directly affect the manufacturing cost of the second dielectric layer  21 . 
     When the thickness of the second dielectric layer  21  is more than about 20 μm, the reactive power of the PDP may increase and the discharge efficiency of the PDP may deteriorate. When the thickness of the second dielectric layer  21  is less than about 16 μm, thickness uniformity of the second dielectric layer  21  may be reduced, thereby deteriorating mechanical strength and voltage withstanding property of the second dielectric layer  21  against the gas discharge, which may damage the second dielectric layer  21  during the gas discharge. 
     In particular, when the thickness of the second dielectric layer  21  is below about 16 μm, the thickness of the second dielectric layer  21  may be insufficient to properly cover a total sum of thicknesses of the bus electrodes  31   b  and  32   b  with a corresponding black stripe (not shown), i.e., a dark opaque layer on the bus electrodes  31   b  and  32   b , so a resultant portion of the second dielectric layer  21  measured between the bus electrodes  31   b  and  32   b  and the lower surface of the second dielectric layer  21  may be thin and may exhibit non-uniform thickness. For example, when the thickness of the bus electrodes  31   b  and  32   b  on the transparent electrodes  31   a  and  32   a  is about 5 μm or more, a total thickness of the bus electrodes  31   b  and  32   b  with the corresponding black stripes may be 10 μm. Since the thickness of the second dielectric layer  21  coated on the sustain and scan electrodes  31  and  32  may be reduced during the baking process, a dielectric layer having a thickness of less than about 16 μm may be too thin, thereby deteriorating mechanical strength and voltage withstanding property of the second dielectric layer  21 , which may damage the second dielectric layer  21  and the PDP. 
     If the second dielectric layer  21  has a dielectric constant (∈) of about 6 C 2 /N·m 2  to about 7 C 2 /N·m 2 , and a thickness t of about 16 μm to about 20 μm, a product value (∈×t), i.e., value of (the dielectric constant)×(the thickness), may be about 96×10 −6  C 2 /N·m to about 140×10 −6  C 2 /N·m. The value of (the dielectric constant)×(the thickness) may correspond to a value of the reactive power consumed by switching elements during driving of the PDP. When the value of (the dielectric constant)×(the thickness) increases, the reactive power consumption may increase. 
     When the value of (the dielectric constant)×(the thickness) (∈×t) is less than about 96×10 −6  C 2 /N·m, the dielectric constant (∈) may be less than about 6 C 2 /N·m 2  and/or the thickness t of the second dielectric layer  21  may be less than about 16 μm, thereby making application of the second dielectric layer  21  to the PDP impossible or damaging the second dielectric layer  21  as discussed previously. When the value of (the dielectric constant)×(the thickness) (∈×t) is more than about 140×10 −6  C 2 /N·m, the dielectric constant (∈) may be more than about 7 C 2 /N·m 2  and/or the thickness t of the second dielectric layer  21  may be more than about 20 μm, thereby increasing the reactive power of the PDP as discussed previously. For example, as illustrated in  FIG. 4 , when the dielectric constant (∈) is greater than about 7 C 2 /N·m 2  and/or the thickness t of the second dielectric layer  21  is greater than about 20 μm, the reactive power of the PDP may increase in proportion to an excess value of the dielectric constant (∈) or the thickness t. In addition, bismuth (Bi) may be added to the PDP, thereby increasing the manufacturing costs thereof. 
     It is noted that the graph in  FIG. 4  illustrates reactive power consumption of a 50-inch full-white PDP with respect to varying dielectric constants and thickness of a second dielectric layer therein. In  FIG. 4 , the first point on the graph indicates a second dielectric layer  21  according to an example embodiment, i.e., a second dielectric layer  21  having a dielectric constant of 7 C 2 /N·m 2  and thickness of 18 μm, so a corresponding PDP is exhibiting a reactive power consumption of about 75 W. The remaining points on the graph of  FIG. 4  indicate dielectric layers having dielectric constant greater than about 7 C 2 /N·m 2 , i.e., gradually increasing dielectric constants, and thicknesses greater than about 20 μm, so corresponding PDP are exhibiting reactive power consumption substantially higher than about 75 W. The PDPs used to illustrate the graph of  FIG. 4  were realized by currently-used processes and/or materials. 
     In addition, the second dielectric layer  21  may exhibit a quotient value (∈/t), i.e., value of (the dielectric constant)/(the thickness), of about 0.3×10 −6  C 2 /N·m 3  to about 0.437×10 −6  C 2 /N·m 3 . The value of (the dielectric constant)/(the thickness) may correspond to active power consumption of the PDP. That is, since an external voltage is applied to the discharge cells  17  of the PDP in order to induce gas discharge therein, an actual voltage applied to the discharge cells  17  may be determined by the value of (the dielectric constant)/(the thickness). 
     When the value of (the dielectric constant)/(the thickness) (∈/t) is less than about 0.3×10 −6  C 2 /N·m 3 , capacitance of the PDP may be reduced, i.e., the dielectric constant (∈) may be less than about 6 C 2 /N·m 2  and/or the thickness t of the second dielectric layer  21  may be greater than about 20 μm. As discussed previously, an increased thickness t of the second dielectric layer  21  may increase reactive power consumption of the PDP, and a reduced dielectric constant (∈) of the second dielectric layer  21  may cause damage thereto. Even though reduced capacitance of the second dielectric layer  21  may improve discharge efficiency of the PDP, the discharge voltage of the PDP may increase, e.g., because sustain voltage may vary with respect to the dielectric constant and thickness of the second dielectric layer  21 , thereby increasing the reactive power consumption of the PDP. 
     For example, when the value of (the dielectric constant)/(the thickness) (∈/t) is less than about 0.3 and the dielectric constant (∈) is about 12, the sustain voltage may increase by about 2.5 V as a thickness of a dielectric layer increases by about 1 μm from about 35 μm. When the dielectric constant (∈) is about 6, the sustain voltage may increases by about 2.5 V as the thickness t of the second dielectric layer  21  increase by about 0.5 μm from about 16 μm. That is, a driving voltage of the PDP having the second dielectric layer  21  with the thickness of about 16 μm may be higher than that of the PDP having a dielectric layer with the thickness of about 35 μm by about 20 V. As a result, as the sustain voltage increases, the manufacturing cost of a driving circuit and the power consumption of the PDP may increase. 
     When the value of (the dielectric constant)/(the thickness) (∈/t) is greater than about 0.437×10 −6  C 2 /N·m 3 , the capacitance of the PDP may significantly increase, i.e., the dielectric constant (∈) may be greater than about 7 C 2 /N·m 2  and/or the thickness t of the second dielectric layer  21  may be less than about 16 μm. As discussed previously, a reduced thickness t of the second dielectric layer  21  may reduce thickness uniformity of the second dielectric layer  21 , thereby requiring a new dielectric material coating process and deteriorating mechanical strength and a voltage withstanding property of the second dielectric layer  21 . Further, the reactive power consumption may increase and the luminance efficiency of the PDP may decrease. For example, when the value of (the dielectric constant)/(the thickness) (∈/t) is greater than about 0.437 C 2 /N·m 3 , the capacitance of the PDP may increase by about 46%, as compared to the capacitance of the PDP when the value of (the dielectric constant)/(the thickness) (∈/t) is about 0.3 C 2 /N·m 3 , so the corresponding reactive power consumption of the PDP may increase by about 46% as well. 
     As illustrated in  FIGS. 1-2 , the PDP may further include a protective layer  23  to cover the second dielectric layer  21 . For example, the protective layer  23  may be formed of a transparent material, e.g., MgO, for transmitting visible light. The protective layer  23  may protect the second dielectric layer  21  and may increase a secondary electron emission coefficient. 
     The PDP may operate as follows. Discharge cells  17  of the PDP to be operated may be selected, i.e., turned on, by address discharge induced by voltage signals applied to the address and scan electrodes  11  and  32 . The selected discharge cells  17  may be driven using sustain discharge induced by application of voltage signals to the sustain and scan electrodes  31  and  32  that correspond to the selected discharged cells  17 . Inducing the sustain discharge may cause gas discharge as discussed previously, thereby emitting visible light toward the front substrate  20  to realize an image. 
     A PDP according to an example embodiment may include a dielectric layer covering the display electrodes and designed to have a dielectric constant (∈) of about 6 C 2 /N·m 2  to about 7 C 2 /N·m 2  and a thickness t of about 16 μm to about 20 μm, thereby improving the luminance efficiency of the PDP by reducing power consumption, e.g., reactive power consumption, during driving of the PDP. 
     Example embodiments of the present invention have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.