Patent Publication Number: US-2006012303-A1

Title: Plasma display panel

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates to a panel structure for a surface-discharge-type alternating-current plasma display panel.  
      The present application claims priority from Japanese Application No. 2004-207655, the disclosure of which is incorporated herein by reference.  
      2. Description of the Related Art  
       FIG. 1  is a sectional view of a conventional plasma display panel (hereinafter referred to as “PDP”) taken along the column direction (the vertical direction of the panel) to show the structure.  
      The conventional PDP in  FIG. 1  has a front glass substrate  1  provided on a face thereof which faces toward the back of the panel (hereinafter referred to as “back-facing face”) with a plurality of row electrode pairs (X, Y) each constituted of a pair of row electrodes X, Y facing each other across a discharge gap g, and a dielectric layer  2  covering the row electrode pairs. The front glass substrate  1  is opposite a back glass substrate  3  with a discharge space in between. The back glass substrate  3  is provided on a face thereof which faces toward the display surface (hereinafter referred to as “front-facing face”) with a plurality of column electrodes D that form discharge cells C in the display space at the intersections with the row electrode pairs (X, Y), a column-electrode protective layer  4  that covers the column electrodes D, a partition wall unit  5  that is formed on the column-electrode protective layer  4  to partition the discharge space into the discharge cells C, and phosphor layers  6  to which the three primary colors, red, green and blue, are applied for each display cell C.  
      Further, the PDP has dielectric projections  7  each projecting into the discharge cell C from a portion of the back-facing face of the dielectric layer  2  opposite the discharge gap g between the opposing transparent electrodes Xa and Ya of the row electrodes X and Y.  
      Such a conventional PDP is disclosed in Japanese unexamined patent publication 2003-257320, for example.  
      The conventional PDP produces an address discharge between the row electrode Y and the column electrode D, and uses the surface discharge to initiate a sustaining discharge d between the transparent electrodes Xb and Yb of the row electrodes X and Y facing each other across the discharge gap g in each of the discharge cells C which have been selected through the address discharge. At the time when the sustaining discharge induces light emission from the phosphor layer  6 , as shown in  FIG. 1 , the sustaining discharge d is initiated along the surface of the dielectric projection  7  projecting from the dielectric layer  2  into the discharge cell C so as to be diverted in the direction of the center of the discharge cell C.  
      Accordingly, in this PDP the sustaining discharge is initiated near the central portion of the discharge cell C. This gives rise to an increase in the amount of vacuum ultraviolet light traveling toward the phosphor layer  6  out of the total amount of vacuum ultraviolet light generated from the discharge gas filling the discharge space, as compared with that in previous PDPs. This results in the exertion of the technical effect of improving the luminous efficiency of the PDP because of the increase in the efficiency of use of the available amount of vacuum ultraviolet light.  
      However, this PDP has an increase in the discharge path of the sustaining discharge d as a result of the provision of the dielectric projection  7 , as compared with previous PDPs. In consequence, a further problem arises of an increase in the discharge voltage for the sustaining discharge, leading to an increase in the electric power consumption.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to solve the problems associated with the conventional PDPs as described above.  
      To attain this object, a plasma display panel according to the present invention has a pair of substrates placed opposite each other across a discharge space, one of the pair of substrates being provided on its inner surface with a plurality of row electrode pairs each extending in the row direction and arranged in the column direction and a dielectric layer covering the row electrode pairs, the discharge space being partitioned into areas to form unit light emitting areas each corresponding to paired discharge portions that are opposite each other across a discharge gap constituted by parts of row electrodes constituting each of the row electrode pairs, and the other substrate being provided on its inner face with phosphor layers for the respective unit light emitting areas. The plasma display panel is characterized in that dielectric protuberances each extend out from a portion of the dielectric layer opposite the discharge gap between the row electrode pair toward the other substrate into the unit light emitting area and floating electrodes are provided in the dielectric protuberances and out of electric connection with the others.  
      In the best mode for carrying out the present invention, a PDP has a dielectric layer covering row electrode pairs formed on the back-facing face of a front glass substrate, and dielectric-formed protuberances each formed on a portion of the dielectric layer that is positioned opposite a discharge gap between paired and opposing transparent electrodes of the row electrodes and extending out from a dielectric layer into a discharge cell. Further, floating electrodes are provided in the protuberances without electric connection with the others of the PDP.  
      In the PDP in the best mode, because each of the dielectric protuberances is formed in such a manner as to each extend out from the back-facing face of the dielectric layer into the discharge cell, the sustaining discharge caused between the transparent electrodes of the row electrodes opposing each other across the discharge gap is initiated in an area close to the center of the discharge cell along the surface of the protuberance, namely, an area near the phosphor layer formed on the back glass substrate which is placed opposite the front glass substrate with the discharge space in between. In consequence, the efficiency of use of the available amount of vacuum ultraviolet light generated from the discharge gas in the discharge cell as a result of the sustaining discharge is increased, leading to an improvement of the efficiency of light emission from the phosphor layers.  
      Further, by forming the floating electrode in the protuberance, the discharge voltage will not build up even though the discharge path of the sustaining discharge is increased by the formation of the protuberance. Further, room is allowed for discharges between the floating electrode and the transparent electrodes between which the sustaining discharge is initiated. This increases the electric filed strength in the site of occurrence of the discharge, which in turn reduces the discharge voltage.  
      These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a sectional view illustrating the structure of a conventional PDP.  
       FIG. 2  is a schematic front view of a first embodiment according to the present invention.  
       FIG. 3  is a sectional view taken along the V 1 -V 1  line in  FIG. 2 .  
       FIG. 4  is a schematic front view of a second embodiment according to the present invention.  
       FIG. 5  is a schematic front view of a third embodiment according to the present invention.  
       FIG. 6  is a sectional view taken along the V 2 -V 2  line in  FIG. 5 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       FIGS. 2 and 3  illustrate a first embodiment of a PDP according to the present invention.  FIG. 2  is a schematic front view of the PDP in the first embodiment.  FIG. 3  is a sectional view taken along the V 1 -V 1  line in  FIG. 2 .  
      The PDP shown in  FIGS. 2 and 3  has a front glass substrate  10  serving as the display surface which is provided on its back-facing face with a plurality of row electrode pairs (X 1 , Y 1 ) each extending in the row direction (the right-left direction in  FIG. 2 ) of the front glass substrate  10  and arranged parallel to each other.  
      The row electrode X 1  constituting part of a row electrode pair (X 1 , Y 1 ) is composed of a strip-shaped bus electrode X 1   a  formed of a metal film extending in the row direction, and T-shaped transparent electrodes X 1   b  that are formed of a transparent conductive film made of ITO or the like and respectively connected to the bus electrode X 1   a  at regularly spaced intervals to extend outward therefrom toward their counterpart row electrode Y 1  in the column direction (the vertical direction in  FIG. 2 ).  
      Likewise, the row electrode Y 1  is composed of a strip-shaped bus electrode Y 1   a  formed of a metal film extending in the row direction, and T-shaped transparent electrodes Y 1   b  that are formed of a transparent conductive film made of ITO or the like and respectively connected to the bus electrode Y 1   a  at regularly spaced intervals to extend outward therefrom toward their counterpart row electrode X 1  in the column direction (the vertical direction in  FIG. 2 ).  
      The row electrodes X 1  and Y 1  are arranged in alternate positions in the column direction of the front glass substrate  10 . In each row electrode pair (X 1 , Y 1 ), the broad top ends (corresponding to the head of the “T”) of the paired transparent electrodes X 1   b  and Y 1   b  disposed along the associated bus electrodes X 1   a  and Y 1   a  face each other across a discharge gap g 1  of a required width.  
      A dielectric layer  11  is formed on the back-facing face of the front glass substrate  10  and covers the row electrode pairs (X 1 , Y 1 ).  
      An additional dielectric layer  12  is further formed on the back-facing face of the dielectric layer  11 .  
      The additional dielectric layer  12  extends outward from the dielectric layer  11  in a direction opposite to the front glass substrate  10  in the whole of the area except quadrangular areas h 1 , h 2  corresponding to the transparent electrodes X 1   b , Y 1   b  of the row electrodes X 1 , Y 1  on the back-facing face of the dielectric layer  11 .  
      Strip-shaped protuberances  12 A are formed integrally with the additional dielectric layer  12 . Each of the protuberances  12 A extends in the row direction in an area opposing the discharge gap g 1  between the paired transparent electrodes X 1   b  and Y 1   b.    
      A floating electrode Z 1  extends in each of protuberances  12 A along the tops of the broad ends of the transparent electrodes X 1   b , Y 1   b , while being opposite the mid-position of the discharge gap g 1 .  
      The floating electrode Z 1  is out of connection with other electrodes and so on, and formed in an isolated-island form in each area opposing the discharge gap g 1 .  
      An MgO protective layer (not shown) is formed on and covers the back-facing face of the dielectric layer  11  and the additional dielectric layer  12 .  
      The front glass substrate  10  is placed parallel to a back glass substrate  13  with a discharge space in between. The back glass substrate  13  is provided on its front-facing face with column electrodes D 1  that each extend in a direction at right angles to the row electrode pairs (X 1 , Y 1 ) (i.e. the column direction) along an area opposite the paired transparent electrodes X 1   a  and Y 1   a  of the row electrode pairs (X 1 , Y 1 ), and are arranged parallel to each other at predetermined intervals.  
      A white-colored column-electrode protective layer  14  is further formed on the back glass substrate  13  and covers the column electrodes D 1 .  
      Partition wall units  15  are formed on the column-electrode protective layer  14 .  
      Each of the partition wall units  15  is formed in an approximate ladder shape made up of a pair of lateral walls  15 A extending in the row direction in the respective areas opposite the bus electrodes X 1   a  and Y 1   a  of the row electrode pair (X 1 , Y 1 ), and vertical walls  15 B each extending between the pair of lateral walls  15 A in the column direction in a mid-area between the adjacent column electrodes D 1 . The partition wall units  15  are regularly arranged in the column direction with interstices SL each interposed between back-to-back lateral walls  15 A of adjacent partition wall units  15 .  
      The ladder-shaped partition wall units  15  partition the discharge space defined between the front glass substrate  10  and the back glass substrate  13  into quadrangular discharge cells C 1  in correspondence with the paired transparent electrodes X 1   b , Y 1   b  in each row electrode pair (X 1 , Y 1 ).  
      Phosphor layers  16  are respectively formed in the discharge cells C 1  so as to cover all the five faces facing each discharge cell C 1 : the side faces of the lateral walls  15 A and the vertical walls  15 B of the partition wall unit  15  and the front-facing face of the column-electrode protective layer  14 . The phosphor layers  16  are individually colored such that the three primary colors, red, green and blue, for each discharge cell C 1  are arranged in order in the row direction.  
      A portion of the protective layer covering the additional dielectric layer  12  is in contact with the front-facing faces of the lateral walls  15 A and the vertical walls  15 B of each partition wall unit  15  (see  FIG. 3 ) to block each discharge cell C 1  from the discharge cells C 1  adjacent thereto in the row direction and from the interstices SL.  
      Each of the discharge cells C 1  is filled with a discharge gas including xenon.  
      The above PDP produces reset discharges simultaneously between all the paired transparent electrodes X 1   b  and Y 1   b  of the row electrode pairs (X 1 , Y 1 ) in a reset period for the generation of an image. The reset discharge results in complete erasure of the wall charge on the portion of the dielectric layer  11  adjoining each discharge cell C 1  (alternatively, deposition of wall charge on the portion of the dielectric layer  11  adjoining each discharge cell C 1 ).  
      In the following address discharge period, an address discharge is produced selectively between the transparent electrode Y 1   b  of the row electrode Y 1  to which a scan pulse is applied and the column electrode D 1  to which a data pulse is applied. The address discharge results in the distribution of the light-emitting cells with the deposition of wall charge on the dielectric layer  11  and the non-light-emitting cells which have had the wall charge erased from the dielectric layer  11 , over the panel surface in accordance with the image data of the video signal.  
      In the following sustaining discharge period, a sustaining pulse is applied alternately to the row electrode X 1  and Y 1  in order to produce a sustaining discharge d 1  between paired transparent electrodes X 1   b  and Y 1   b  of the row electrode pair (X 1 , Y 1 ) in each of the light-emitting cells. The sustaining discharge d 1  causes radiation of vacuum ultraviolet light from the xenon included in the discharge gas. The vacuum ultraviolet light excites the red-, green- and blue-colored phosphor layers  16  to permit them to emit light for the generation of an image on the panel surface.  
      When this sustaining discharge D 1  occurs, a potential difference is caused between the floating electrode Z 1  placed in isolated-island form in each protuberance  12 A of the additional dielectric layer  12  and having a floating potential, and the transparent electrode X 1   b  or Y 1   b  to which the sustaining pulse is applied. Therefore, the sustaining discharge D 1  occurring along the surface of the protuberance  12 A in such a way as to be diverted in the direction of the center of the discharge cell C 1  passes through the floating electrode Z 1 . For this reason, the discharge path of the sustaining discharge D 1  is shortened as compared with that in the conventional PDP described in  FIG. 1 .  
      Further, the location of the floating electrode Z 1  in the protuberance  12 A extending out toward the center of the discharge cell C 1  allows room for generating discharges between the transparent electrodes X 1   b , Y 1   b  and the floating electrode Z 1 . This increases the electric field strength in the site of occurrence of the discharge, which in turn reduces the discharge voltage for the sustaining discharge D 1 .  
      As described above, in the structure of the PDP, the dielectric-formed protuberance  12 A extending out from the back-facing face of the dielectric layer  11  toward the interior of the discharge cell C 1  allows the sustaining discharge D 1  to develop in an area along the surface of the protuberance  12 A close to the phosphor layer  16 . As a result, the efficiency of use of the vacuum ultraviolet light generated from the discharge gas is increased, and this increase enables an improvement in the luminous efficiency from the phosphor layers  16 .  
      Because of the location of the floating electrode Z 1  in the protuberance  12 A, although the discharge path of the sustaining discharge D 1  is increased by the provision of the protuberance  12 A, the discharge voltage will not build up. Further, because room is allowed for initiating discharges between the transparent electrodes X 1   b , Y 1   b  and the floating electrodes Z 1 , the electric field strength in the site of occurrence of the discharge is increased, leading to a reduction in the discharge voltage.  
      The PDP has the transparent electrodes X 1   b , Y 1   b  of the row electrodes X 1 , Y 1  each formed in a T shape and disposed in such a way as to make their broad ends face each other across a discharge gap g 1 . This design produces the sustaining discharge intensively from around the broad ends of the transparent electrodes X 1   b , Y 1   b , and thus inhibits the dispersion of discharge current into the surrounding areas, which in turn also improves the luminous efficiency.  
      The additional dielectric layer  12  extends out from the back-facing face of the dielectric layer  11 , except for the portions thereof each opposing the paired transparent electrodes X 1   b , Y 1   b , into each discharge cell C 1  so as to surround the opposing portions of these transparent electrodes X 1   b , Y 1   b . Thereby, the occurrence of a so-called “shifting-aside” or a false discharge of the sustaining discharge produced between the transparent electrodes X 1   b , Y 1   b  is prevented. Further, the electric field strength of the surface discharge (sustaining discharge) produced between the transparent electrodes X 1   b , Y 1   b  is increased to reduce the discharge voltage.  
      The following is the procedure for manufacturing the foregoing PDP.  
      In the manufacturing process for the front glass substrate  10 , first, the bus electrodes X 1   a , Y 1   a  and the transparent electrodes X 1   b , Y 1   b  are formed on the back-facing face of the front glass substrate  10  by means of patterning to form row electrodes X 1 , Y 1 .  
      After that, the dielectric layer  11  is further formed on the back-facing face of the front glass substrate  10  so as to cover the row electrodes X 1 , Y 1 .  
      After the formation of the dielectric layer  11 , the additional dielectric layer  12  is formed on the back-facing face of the dielectric layer  11 . At this point, the floating electrodes Z 1  are formed in the protuberances  12 A of the additional dielectric layer  12 .  
      For forming the floating electrodes Z 1 , for example, each of the protuberances  12 A of the additional dielectric layer  12  is divided into two layers in order to be formed in stages. After the first layer has been formed, the floating electrode Z 1  is formed, and then the second layer is formed so as to cover the floating electrode Z 1 .  
      The floating electrode Z 1  is formed by use of methods such as lamination of a silver film, solid printing of a photosensitive silver paste, pattern printing of a silver paste, Cr—Al—Cr evaporation, Al evaporation, or forming an ITO film.  
      After the formation of the additional dielectric layer  12  and the floating electrodes Z 1 , the MgO protective layer is formed to cover the surfaces of the dielectric layer  11  and the additional dielectric layer  12 .  
      In the manufacturing process for the back glass substrate  13 , the column electrodes D 1  are formed on the front-facing face of the back glass substrate  13 , then the column-electrode protective layer  14  is formed to cover the column electrodes D 1 .  
      After that, the partition wall units  15  are formed on the column-electrode protective layer  14 , and then the red-, green- and blue-colored phosphor layers  16  are formed individually in the blank spaces created in each of the partition wall units  15 .  
      Then, a sealing layer is formed on the periphery end of the front-facing face of the back glass substrate  13 .  
      The front glass substrate  10  on which the components have been thus formed in the front-glass-substrate manufacturing process and the back glass substrate  13  on which the components have been thus formed in the back-glass-substrate manufacturing process are placed on and aligned with each other with the discharge space in between. Then, various processes, such as the sealing process for the discharge space and the process of removing gases from the interior of the discharge space and of baking, the process of introducing a discharge gas into the discharge space, and the chip-off process for the discharge gas, are performed in order to complete the PDP.  
      Second Embodiment  
       FIG. 4  is a front view illustrating a second embodiment of a PDP according to the present invention.  
      The first embodiment has described a PDP having the floating electrodes Z 1  each formed in an isolated-island form independently in each discharge cell C 1 , whereas the PDP described in the second embodiment has floating electrodes Z 2  each formed in the additional dielectric layer  12  in a strip shape extending in the row direction through the protuberances  12 A each formed in the portion opposite the discharge gap g 1  between the transparent electrodes X 1   b , Y 1   b.    
      The structure of the other components in this PDP is approximately the same as that in the first embodiment, and in  FIG. 4  the same components are designated with the same reference numerals as those in the first embodiment.  
      As in the case of the PDP in the first embodiment, in the PDP in the second embodiment the dielectric-formed protuberance  12 A extending out into the interior of the discharge cell C 1  in the portion opposite the discharge gap g 1  allows the sustaining discharge between the transparent electrodes X 1   b , Y 1   b  to develop in an area close to the central portion of the discharge cell C 1 . As a result, the efficiency of use of the vacuum ultraviolet light generated from the discharge gas is increased, and this increase enables an improvement in the luminous efficiency from the phosphor layers. Further, because of the location of the floating electrode Z 2  in the protuberances  12 A, although the discharge path of the sustaining discharge is increased by the provision of the protuberance  12 A, the discharge voltage will not build up. Further, because room is allowed for initiating discharges between the transparent electrodes X 1   b , Y 1   b  and the floating electrodes Z 2 , the electric field strength in the discharge occurring site is increased, leading to a reduction in discharge voltage.  
      Third Embodiment  
       FIGS. 5 and 6  illustrate a third embodiment of the PDP according to the present invention.  FIG. 5  is a schematic front view of the PDP in the third embodiment.  FIG. 6  is a sectional view taken along the V 2 -V 2  line in  FIG. 5 .  
      The first and second embodiments have described a PDP having the column electrodes D 1  formed on the back glass substrate  13 , whereas the PDP in the third embodiment as shown in FIGS.  5  and  6  has column electrodes D 2  formed on the back-facing face of the front glass substrate  10 .  
      More specifically, the dielectric layer  11  covers the row electrode pairs (X 1 , Y 1 ), and each of the column electrodes D 2  extends in the column direction on a portion of the back-facing face of the dielectric layer  11  opposite a mid-area between adjacent transparent electrodes X 1   b  (Y 1   b ) arranged at regular intervals along the associated bus electrodes X 1   a  (Y 1   a ) of the row electrode pairs (X 1 , Y 1 ). The column electrodes D 2  are covered by the additional dielectric layer  12  formed on the back-facing face of the dielectric layer  11 .  
      The structure of the other components in this PDP is approximately the same as that in the first embodiment, and in  FIGS. 5 and 6  the same components are designated with the same reference numerals as those in the first embodiment.  
      As in the case of the PDP in the first and second embodiments, in the PDP in the third embodiment the dielectric-formed protuberance  12 A extending out into the interior of the discharge cell C 1  in the portion opposite the discharge gap g 1  allows the sustaining discharge between the transparent electrodes X 1   b , Y 1   b  to develop in an area close to the central portion of the discharge cell C 1 . As a result, the efficiency of use of the vacuum ultraviolet light generated from the discharge gas is increased, and this increase enables an improvement in the luminous efficiency from the phosphor layers. Further, because of the location of the floating electrode Z 1  in the protuberances  12 A, although the discharge path of the sustaining discharge is increased by the provision of the protuberance  12 A, the discharge voltage may not build up. Further, because room is allowed for initiating discharges between the transparent electrodes X 1   b , Y 1   b  and the floating electrodes Z 1 , the electric field strength in the discharge occurring site is increased, leading to a reduction in discharge voltage.  
      The following is the procedure for manufacturing the foregoing PDP.  
      In the manufacturing process for the front glass substrate  10 , first, the bus electrodes X 1   a , Y 1   a  and the transparent electrodes X 1   b , Y 1   b  are formed on the back-facing face of the front glass substrate  10  by means of patterning to form row electrodes X 1 , Y 1 .  
      After that, the dielectric layer  11  is further formed on the back-facing face of the front glass substrate  10  so as to cover the row electrodes X 1 , Y 1 .  
      After the formation of the dielectric layer  11 , the column electrodes D 2  are formed in predetermined positions on the back-facing face of the dielectric layer  11 .  
      Then, the additional dielectric layer  12  is formed on the back-facing face of the dielectric layer  11 . The column electrodes D 2  are covered by the additional dielectric layer  12 . The floating electrodes Z 1  are formed in the protuberances  12 A of the additional dielectric layer  12 .  
      For forming the floating electrodes Z 1 , for example, each of the protuberances  12 A of the additional dielectric layer  12  may be divided into two layers in order to be formed in stages. After the first layer has been formed, the floating electrode Z 1  can be formed, and then the second layer can be formed so as to cover the floating electrode Z 1 .  
      The floating electrode Z 1  is formed by use of methods such as the lamination of a silver film, solid printing of a photosensitive silver paste, pattern printing of a silver paste, Cr—Al—Cr evaporation, Al evaporation, or forming an ITO film.  
      After the formation of the additional dielectric layer  12  and the floating electrodes Z 1 , the MgO protective layer is formed to cover the surfaces of the dielectric layer  11  and the additional dielectric layer  12 .  
      In the manufacturing process for the back glass substrate  13 , the column-electrode protective layer  14  is formed on the front-facing face of the back glass substrate  13 . Then, the partition wall units  15  are formed on the column-electrode protective layer  14 , and then the red-, green- and blue-colored phosphor layers  16  are formed individually in the blank spaces created in each of the partition wall units  15 .  
      Then, a sealing layer is formed on the periphery end of the front-facing face of the back glass substrate  13 .  
      The front glass substrate  10  on which the components have been thus formed in the front-glass-substrate manufacturing process and the back glass substrate  13  on which the components have been thus formed in the back-glass-substrate manufacturing process are placed on and aligned with each other with the discharge space in between. Then, various processes, such as the sealing process for the discharge space and the process of removing gases from the interior of the discharge space and of baking, the process of introducing a discharge gas into the discharge space, and the chip-off process for the discharge gas, are performed in order to complete the PDP.  
      The terms and description used herein are set forth by way of illustration only and are not meant as limitations. Those skilled in the art will recognize that numerous variations are possible within the spirit and scope of the invention as defined in the following claims.