Patent Publication Number: US-2006001675-A1

Title: Plasma display panel

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS  
      This application claims the benefit of Korean Patent Application No. 10-2004-0049722, filed on Jun. 29, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a plasma display panel, and more particularly, to a plasma display panel that can improve luminous efficiency.  
      2. Description of the Related Technology  
      Plasma display panels (PDPs) have drawn attention as devices which can replace conventional cathode ray tubes (CRT). PDPs are devices which obtain an image by exciting a fluorescent material formed in a predetermined pattern by ultraviolet rays generated from a discharge gas sealed in a space formed by two substrates on which a plurality of electrodes for applying a voltage are formed.  
       FIG. 1  is a plan view of barrier ribs  30  and sustaining electrodes  31  of a conventional PDP. Referring to  FIG. 1 , a plurality of discharge cells  80  in a matrix having a rectangular shaped cross-sectional surface are defined by the barrier ribs  30  which include horizontal units  30   a  and vertical units  30   b . Also, sustaining electrodes  31  disposed across the discharge cells  80  are formed in the PDP. Each of the sustaining electrodes  31  includes a bus electrode  41  and a transparent electrode  51 . Also, the transparent electrode  51  includes a main body unit  51   b  and connection units  51   a  that connect the main body unit  51   b  and the bus electrode  41 . The main body units  51   b , on which main discharges are generated, are disposed apart from each other in a direction toward the center of the discharge cells  80  and the connection units  51   a  are disposed on an upper part of the vertical units  30   b.    
      As shown in  FIG. 1 , each of the connection units  51   a  has a width (a) and each of the vertical units  30   b  has a width (b). If the width a of the connection units  51   a  is excessively small, the brightness of the PDP is reduced since the resistance of the PDP increases remarkably, thereby reducing the luminous efficiency. On the other hand, if the connection unit width (a) is excessively large relatively to the width (b) of the vertical units  30   b , the opening ratio of the PDP is reduced since the connection units  51   a  are protruded from sides of the vertical units  30   b , and the luminous efficiency of the PDP is reduced since the discharge current increases drastically.  
     SUMMARY OF CERTAIN INVENTIVE ASPECTS  
      One aspect of the present invention provides a plasma display panel that can improve the light emission efficiency.  
      Another aspect of the present invention provides a plasma display panel comprising a rear substrate; a front substrate disposed apart from the rear substrate; a plurality of barrier ribs that define discharge cells together with the rear substrate and the front substrate and disposed between the rear substrate and the front substrate; a plurality of sustaining electrode pairs extended across the discharge cells; a plurality of address electrodes extended across the discharge cells to cross the sustaining electrode pairs; a first dielectric layer that covers the address electrodes; a second dielectric layer that covers the sustaining electrode pairs; a fluorescent layer disposed in each discharge cell; and a discharge gas filled in the discharge cells, wherein the barrier ribs comprise vertical units formed in a direction in which the address electrodes are extended and horizontal units that cross the vertical units, each of the sustain electrodes comprises a bus electrode extending across the discharge cells and a discharge electrode, wherein the discharge electrode includes i) a main body unit disposed apart from the bus electrode toward the center of each discharge cell, and ii) connection units that connect the main body unit and the bus electrode, and wherein the relative width ratio of the connection units to the vertical units is in a range of about 3/7 to about 6/7.  
      In one embodiment, the connection units can be disposed on an upper part of the vertical units. In one embodiment, an imaginary axis of symmetry of the connection units in a width direction and an imaginary axis of symmetry of the vertical units in a width direction can be aligned in a vertical direction to the front substrate. In one embodiment, the connection units can be disposed in a shadow region of the vertical units in a vertical direction to the front substrate.  
      In one embodiment, the luminous efficiency can be maximized at the relative ratio of the width of the connection units to the width of the vertical units at a range of about 3/7 to about 6/7.  
      In one embodiment, the brightness of the PDP can be increased by the improved opening ratio since the connection units are disposed on an upper part of the vertical units. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Embodiments of the present invention will be described with reference to the attached drawings.  
       FIG. 1  is a plan view of barrier ribs and sustaining electrodes of a conventional PDP.  
       FIG. 2  is a partial cutaway exploded perspective view of a PDP according to one embodiment of the present invention.  
       FIG. 3  is a plan view of barrier ribs and sustaining electrodes of  FIG. 2 .  
       FIG. 4  is a graph showing the measurement result of the luminous efficiency by varying the relative ratio of the width of the vertical units to the width of the connection units of the PDP of  FIG. 2 . 
    
    
     DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS  
      Embodiments of the present invention will now be described with reference to  FIGS. 2 and 4 . Like reference numerals refer to like elements throughout the drawings and the specification.  
       FIG. 2  is a partial cutaway exploded perspective view of a PDP  100  according to one embodiment of the present invention.  
      Referring to  FIG. 2 , the PDP  100  comprises a rear substrate  121 , a front substrate  111  disposed apart from the rear substrate  121 , a plurality of barrier ribs  130  that define discharge cells  180  together with the front substrate  111  and the rear substrate  121  and disposed between the front substrate  111  and the rear substrate  121 . The PDP  100  also includes a plurality of sustaining electrode pairs  112  extended across the discharge cells  180 , a plurality of address electrodes  122  extended across the discharge cells  180  to cross the sustaining electrode pairs  112  in each discharge cell  180 . The PDP  100  further includes a first dielectric layer  125  that covers the address electrodes  122 , a second dielectric layer  115  that covers the sustaining electrode pairs  112 , a fluorescent layer  126  disposed in each discharge cell  180 , and a discharge gas filled in each of the discharge cells  180 .  
      The sustaining electrode pairs  112  are disposed on the front substrate  111 . In one embodiment, the front substrate  111  can be formed of a transparent material in which glass is a typical substance.  
      The sustaining electrode pairs  112  represent a pair of sustaining electrodes  131  and  132 , formed on a rear surface of the front substrate  111 , configured to generate a discharge. The sustaining electrode pairs  112  are generally arranged in parallel at a predetermined distance from each other on the front substrate  111 . Each of the sustaining electrode pairs  112  includes an X electrode  131  and a Y electrode  132 .  
      The X and Y electrodes  131  and  132 , respectively, include discharge electrodes  151  and  152  and bus electrodes  141  and  142 . In one embodiment, the discharge electrodes  151  and  152  can be formed of a conductive transparent material that can generate discharges and that does not interrupt the progress of light generated from a fluorescent layer  126  toward the front substrate  111 . In one embodiment, the transparent conductive material can be indium tin oxide (ITO). The transparent conductive material such as the ITO generally has a large resistance. Therefore, if the discharge electrodes  151  and  152  are formed using only transparent electrodes, a driving power can be increased due to a large voltage drop in a length direction of the transparent electrodes and a response time is delayed. To solve this problem, the bus electrodes  141  and  142  formed of a metal having a narrow width are provided on the transparent electrodes.  
      The address electrodes  122  are formed, to cross the X electrode  131  and the Y electrode  132  of the front substrate  111 , on the rear substrate  121  facing the front substrate  111 .  
      The address electrodes  122  are formed to generate an address discharge which facilitates a sustain discharge between the X electrode  131  and the Y electrode  132 . More specifically, the address electrodes  122  reduce a discharge voltage for generating a sustaining discharge. The address discharge occurs between the Y electrode  132  and the address electrode  122 . When the address discharge is completed, positive ions are accumulated on the Y electrode  132  and electrons are accumulated on the X electrode  131 , thereby facilitating the sustaining discharge between the X electrode  131  and the Y electrode  132 .  
      A space formed by a pair of the X electrode  131  and the Y electrode  132  and the address electrodes  122  crossing the X and Y electrodes  131  and  132  is a unit discharge cell  180  that forms a discharge unit.  
      A first dielectric layer  125  covering the address electrodes  122  is formed on the rear substrate  121 . In one embodiment, the first dielectric layer  125  is formed of a dielectric that can prevent the address electrodes  122  from being damaged by colliding with positive ions or electrons during discharging, and can induce electrons. In one embodiment, the dielectric can be PbO, B 2 O 3 , or SiO 2 , etc.  
      A second dielectric layer  115  covering the sustain electrode pairs  112  is formed on the front substrate  111 . In one embodiment, the second dielectric layer  115  is formed of a dielectric that can prevent a direct communication between the X electrode  131  and the adjacent Y electrode  132  during the sustaining discharge. The second dielectric layer  115  can prevent the X electrode  131  and the Y electrode  132  from being damaged by the direct collision between positive ions or electrons with the sustain electrodes  131  and  132 . Furthermore, the second dielectric layer  115  can accumulate wall charge by inducing the charges. In one embodiment, the dielectric can be PbO, B 2 O 3 , or SiO 2 , etc.  
      Also, a protection layer  116 , conventionally formed of MgO, for example, is formed on the second dielectric layer  115 . The protection layer  116  prevents the second dielectric layer  115  from being damaged by collisions from positive ions or electrons during discharging, has high light transmittance, and generates a lot of secondary electrons.  
      Barrier ribs  130  are formed between the first dielectric layer  125  and the second dielectric layer  115 . The barrier ribs  130  maintain a discharge distance, define discharge cells of red  180 R, green  180 G, and blue  180 B light, and prevent electrical and optical cross talk between the adjacent discharge cells  180 . As depicted in  FIGS. 2 and 3 , the barrier ribs  130  include vertical units  130   b  formed in a direction (y direction) in which the address electrodes  122  are extended, and horizontal units  130   a  formed to cross the vertical units  130   b . In one embodiment, a non-discharge region  190  is formed between the horizontal units  130   a  adjacent to each other in a direction (y direction) in which the address electrodes  122  are extended since the horizontal units  130   a  are formed in a double barrier rib. The non-discharge region  190  increases the contrast of the PDP and also can be used as a passage to exhaust an impure gas.  
      The fluorescent layers  126  of red, green, and blue emitting colors are coated on side surfaces of the barrier ribs  130  and on the entire surface of the first dielectric layer  125  on which the barrier ribs  130  are not formed.  
      In one embodiment, the fluorescent layer  126  contains a substance that generates visible light by receiving ultraviolet rays. The fluorescent layer  126  formed in a sub-pixel that generates red light includes a fluorescent material such as Y(V,P)O 4 :Eu. The fluorescent layer  126  formed in a sub-pixel that generates green light includes a fluorescent material such as Zn 2 SiO 4 :Mn, or YBO 3 :Tb. The fluorescent layer  126  formed in a sub-pixel that generates blue light includes a fluorescent material such as BAM:Eu.  
      Discharge gases are filled in the discharge cells  180  and sealed. In one embodiment, the discharge gases include a gas selected from Ne, He, Xe, and a gas mixture of these gases.  
      In one embodiment, the discharge electrodes  151  and  152 , respectively, include main body units  151   b  and  152   b  and connection units  151   a  and  152   a . Each of the main body units  151   b  and  152   b  are disposed toward the center of the discharge cells  180  from the bus electrodes  141  and  142 . Each of the connection units  151   a  and  152   a  connects the bus electrodes  141  and  142  and the main body units  151   b  and  152   b . Also, each of the connection units  151   a  and  152   a  can be disposed on each upper part of the vertical units  130   b  of the barrier ribs  130  so as to make the voltage uniform applied to the main body units  151   b  and  152   b  connected to the bus electrodes  141  and  142  and for structural stability. Also, the bus electrodes  141  and  142  are formed on an upper part of the horizontal units  130   a  to increase the opening ratio. In one embodiment, the main body units  151   b  and  152   b  and the connection units  151   a  and  152   a  can be integrally formed to simplify the manufacturing process.  
      The connection units  151   a  and  152   a  are generally disposed in shadow regions of the vertical units  130   b  in a vertical direction (z direction) to the front substrate  111  as shown in  FIG. 3 . In one embodiment, the connection units  151   a  and  152   a  are narrower than and aligned with the vertical units  130   b  so as not to block the visible light emitting path as shown in  FIG. 3 . Otherwise, the connection units  151   a  and  152   a , although formed of a transparent material, can not transmit 100% of the visible light resulting in the reduction of the opening ratio of the PDP  100 , thereby reducing the brightness of the PDP.  
      In one embodiment, an imaginary axis of symmetry C-C of the connection units  151   a  and  152   a  in a width direction and an imaginary axis of symmetry C′-C′ of the vertical units  130   b  in a width direction are aligned in a vertical direction (z direction) to the front substrate  111  as shown in  FIG. 3 . Generally, the sustain electrodes  131  and  132  are formed when the upper plate  150  is manufactured and the barrier ribs  130  are formed when the lower plate  160  is manufactured. By aligning the C-C axis with the C′-C′, the connection units  151   a  and  152   a  and the vertical units  130   b  can be aligned correctly when the upper plate  150  and the lower plate  160  are coupled after separate manufacturing.  
      The operation of the PDP  100  according to one embodiment will now be described.  
      An address discharge is generated by applying an address voltage between the address electrodes  122  and the Y electrode  132 . As a result of the address discharge, a discharge cell  180 , in which a sustain discharge will be generated, is selected.  
      Afterward, when a sustain discharge voltage is applied between the X electrode  131  and the Y electrode  132  of the selected discharge cell  180 , a sustain discharge is generated by colliding the positive ions accumulated on the Y electrode  132  with the electrons accumulated on the X electrode  131 . Ultraviolet rays are emitted by reducing the energy level of the discharge gas excited during the main discharge. The ultraviolet rays excite the fluorescent layer  126  coated in the discharge cell  180 , and visible light is generated by reducing the energy level of the fluorescent layer  126 , thereby displaying an image.  
      As described above, the width “w” of the connection units  151   a  and  152   a  of the discharge electrodes affect the luminous efficiency of the PDP  100 . That is, if the width “w” of the connection units  151   a  and  152   a  is excessively small, the resistance of the PDP remarkably increases resulting in the reduction of the brightness and eventually the luminous efficiency of the PDP  100 . Furthermore, if the width “w” is excessively great, the opening ratio of the PDP is reduced and the discharge current increases, resulting in reducing the luminous efficiency of the PDP  100 . In one embodiment, the opening ratio and the discharge current of the PDP  100  are affected not only by the width “w” of the connection units  151   a  and  152   a  but also by the width “h” of the vertical units  130   b  of the barrier ribs  130 . For example, if the width “h” of the vertical units  130   b  is large, the width “w” of the connection units  151   a  and  152   a  does not affect the opening ratio of the PDP since the connection units  151   a  and  152   a  can be disposed in a shadow region of the vertical units  130   b . One embodiment of the invention provides a ratio, which can maximize the luminous efficiency of the PDP, of the width “h” of the vertical units  130   b  to the width “w” of the connection units  151   a  and  152   a.    
       FIG. 4  is a graph showing the measurement results of the luminous efficiency of the PDP  100  by varying the width “w” of the connection units from 10 μm to 170 μm after fixing the width “h” of the vertical units  130   b  at 70 μm. The Equation 1 defines the luminous efficiency of the PDP. Here, the power consumption on is a measured power consumption of the PDP when a power is applied to the sustain electrodes and the address electrodes. Also, the power consumption off is a measured power consumption when a power is applied to only the sustain electrodes. In the case of the power consumption off, the value remains almost constant at 77 W. Also, the display area is 0.50 m 2 .  
             η   =       π   ×   Area   ×   brightness         power   ⁢           ⁢   consumtion   ⁢           ⁢     (   on   )       -     power   ⁢           ⁢   consumtion   ⁢           ⁢     (   off   )                   Equation   ⁢           ⁢   1               
 where η is luminous efficiency, and the Area is a display area. 
 
      Referring to  FIG. 4 , in case of the relative ratio w/h being less than about 3/7, the luminous efficiency is small. This denotes that the brightness of the PDP is reduced due to the increase in the resistance between the bus electrodes  141  and  142  and the connection units  151   a  and  152   a  when the width “w” of the connection units  151   a  and  152   a  is excessively small. Also, when the relative ratio w/h is greater than about 6/7, the luminous efficiency is reduced since the opening ratio is reduced by the connection units  151   a  and  152   a  and the discharge current is increased. In one embodiment, the relative ratio w/h in a range of about 3/7 to about 6/7 can maximize the luminous efficiency of the PDP. In this embodiment, the width w of the connection units  151   a  and  152   a  may be in a range of about 30 μm to about 60 μm and the width h of the vertical units  130   b  is in a range of about 100 μm to about 350 μm.  
      While the above description has pointed out novel features of the invention as applied to various embodiments, the skilled person will understand that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made without departing from the scope of the invention. Therefore, the scope of the invention is defined by the appended claims rather than by the foregoing description. All variations coming within the meaning and range of equivalency of the claims are embraced within their scope.