EP1627408B1 - Plasma display panel comprising a reduced-section discharge expansion zone - Google Patents

Description

With reference to Figures 1A and 1B , the invention as defined in claim 1 relates to a plasma display panel comprising a first slab 11 and a second slab 12 between them a space filled with partitioned waste gas, in particular using a network of barriers, in a plurality of discharge cells 17 arranged in rows and columns.

The first slab 11 comprises at least two networks of electrodes Y, Y 'coplanar said maintenance, which are oriented in general directions parallel to each other and to the cell lines, and which are coated with a dielectric layer 13 and a protective layer and secondary electron emission 14 (dashed in the figure).

The second slab 12 comprises at least one array of so-called addressing electrodes X, which are oriented in general directions parallel to one another and to the columns of cells, and which are coated with a dielectric layer 16.

The electrodes Y, Y ', X of the different networks are arranged in such a way that each discharge cell is traversed by an electrode of each network.

The network of insulating barriers comprises inter-cell separating elements 15 each separating two adjacent columns of cells.

Finally, the slopes of the barriers and the second slab are covered with a phosphor layer (not shown) capable of emitting visible light under the excitation of the discharges in the cells.

• pour générer des opérations d'adressage pour activer sélectivement des cellules et pour générer des opérations d'entretien pour obtenir des décharges de plasma uniquement dans les cellules préalablement activées,
• pour que, lors des phases d'entretien, les décharges coplanaires d'entretien soient déclenchées par des décharges matricielles.

The invention as defined in claim 1 relates to an image display device comprising such a plasma panel and means for controlling and feeding the electrodes of this panel which are adapted:

• to generate addressing operations to selectively activate cells and to generate maintenance operations to obtain plasma discharges only in previously activated cells,
• so that, during the maintenance phases, the coplanar maintenance discharges are triggered by matrix discharges.

• pour appliquer, entre l'électrode d'adressage X et l'une des électrodes d'entretien Y ou Y' qui traversent chaque cellule 17, un signal de tension d'adressage adapté pour déposer des charges électriques d'activation sur la couche diélectrique recouvrant ladite électrode d'entretien,
• pour appliquer, entre les électrodes d'entretien Y, Y' qui traversent chaque ligne de cellules, une succession de signaux de tension d'entretien adaptés pour générer des décharges de plasma uniquement dans les cellules de cette ligne qui ont été préalablement activées, et pour générer, juste avant ou pendant chaque signal d'entretien, entre les électrodes d'adressage X et l'une ou l'autre des électrodes d'entretien Y ou Y' qui traversent les cellules de cette ligne, un signal de tension de déclenchement adapté pour déclencher lesdites décharges.

For this purpose, these control and feeding means are adapted:

• for applying, between the X address electrode and one of the Y or Y 'maintenance electrodes which pass through each cell 17, an address voltage signal adapted to deposit electrical activation charges on the dielectric layer covering said maintenance electrode,
• for applying, between the maintenance electrodes Y, Y 'which pass through each line of cells, a succession of maintenance voltage signals adapted to generate plasma discharges only in the cells of this line which have been previously activated, and to generate, just before or during each maintenance signal, between the addressing electrodes X and one or the other of the maintenance electrodes Y or Y 'which pass through the cells of this line, a voltage signal of trigger adapted to trigger said discharges.

The triggering signals can be induced automatically or applied voluntarily using a suitable generator; these signals induce matrix discharges in the thickness of the gas space separating the slabs, in order to facilitate the start of maintenance discharges between the coplanar electrodes.

The document US6184848 discloses an image display device of this type, adapted for controlling coplanar discharges by matrix triggering.

One objective pursued by the invention is to improve the luminous efficiency of this type of panel.

For this purpose, the invention as defined in claim 1 relates to a plasma display panel comprising a first slab and a second slab between them a space filled with partitioned discharge gas, using a network of barriers, in a plurality of discharge cells disposed in rows and columns,
said first slab comprising at least two coplanar electrode networks called maintenance networks, which are oriented in general directions parallel to each other and to said lines,
said second slab comprising at least one array of so-called addressing electrodes, which are oriented in general directions parallel to each other and to said columns,
said electrodes being arranged so that, at each cell, an addressing electrode crosses an electrode of each maintenance network,
said barrier network comprising inter-column separating elements separating, each, two adjacent columns of cells,
each cell being subdivided into a trip zone at each of the crossings of the addressing electrode with a maintenance electrode, and at least one coplanar discharge expansion zone extending between the trip zones, said barrier network is adapted so that, at each cell, that is to say in each cell, each coplanar expansion zone has, in an interval situated between the triggering zones which delimit it along the columns, a width which, when measured between two adjacent separating elements which delimit it along the lines, is less than the width of all the triggering zones measured between two adjacent separating elements delimiting these zones also along the lines.

All widths are evaluated along the lines.

Since there are at least two coplanar electrode arrays and as, at each cell, an addressing electrode crosses an electrode of each maintenance network, there must be in each cell several crossings of the electrode. addressing with a maintenance electrode, and therefore several triggering areas, more precisely at least two; thus, each cell comprises at least two trigger zones, each located at a crossing of the addressing electrode with a maintenance electrode.

Each expansion zone forms a channel for containing the positive pseudo-column of the coplanar plasma discharge. According to the invention, this channel has at least a narrower constriction part of the positive pseudo-column; this narrower part corresponds to the said interval situated between the trigger zones; the expansion zone may be narrow all along the channel, in which case said gap corresponds to the distance between the triggering zones.

It will be noted that the plasma panel described in the document WO03 / 060864 (not published on the priority date of this document, but benefiting in principle from an earlier priority date) has, at the level of each cell, one or more cavities; when these cavities are curved or elliptical as in Figures 10C and 10D of this document, these cavities provide zones of coplanar expansion whose width, measured along the lines, is not constant; nevertheless, nothing indicates in this document that there exists in each cell at least two trigger zones at the intersection of an addressing electrode carried by a slab and a coplanar electrode carried by another slab; nor, a fortiori, that there is a gap between these trigger zones; nor, a fortiori, that the width of the expansion zone measured along the lines in this range is less than the width of the triggering zones also measured along the lines.

• dans le cas où il n'existerait qu'une seule zone de déclenchement dans chaque cellule, la zone d'expansion coplanaire entre les électrodes X et Y ne présente pas, contrairement à l'invention, d'intervalle situé entre les zones de déclenchement ;
• dans le cas où il existerait, comme dans l'invention, deux zones de déclenchement dans chaque cellule (au croisement de X' et A, et au croisement de Y' et A), alors, dans l'intervalle situé entre ces zones, la largeur de la zone d'expansion n'est, en aucun point de cet intervalle, inférieure à la largeur de l'une ou de l'autre zone de déclenchement, contrairement à l'invention ; en effet, dans cet intervalle comme au niveau de chaque zone de déclenchement, la barrière séparant les colonnes ne s'étend qu'à mi-hauteur, de sorte que la largeur est identique en tous points.

It will be noted that the plasma panel described in the document US2003 / 0080683 is provided with an array of addressing electrodes and four (or only three) coplanar electrode arrays; as in the invention, at each cell, an addressing electrode crosses an electrode of each coplanar network; as indicated in §30 of this document (and in more detail below), it is one of the coplanar electrodes X 'or Y' positioned at the center of each cell which serves to trigger each coplanar discharge, and not the addressing electrode as in the invention; at the level of the trigger zone of each cell, in this case here in the center of this cell, the barrier separating the columns extends only halfway up so that the cells appear wider at this location, at least on the side of the slab carrying the coplanar electrodes (see figure 1 of the document) ; however:

• in the case where there is only one trigger zone in each cell, the coplanar expansion zone between the electrodes X and Y does not have, contrary to the invention, an interval situated between the triggering zones ;
• in the case where there exist, as in the invention, two trigger zones in each cell (at the intersection of X 'and A, and at the intersection of Y' and A), then, in the interval between these zones, the width of the area at no point in this range is less than the width of one or the other trigger zone, contrary to the invention; indeed, in this interval as in each trip zone, the barrier separating the columns extends only halfway up, so that the width is identical in all respects.

Preferably, the barrier network is adapted so that, at each cell, the width of each coplanar expansion zone measured in the direction of the lines between two adjacent separating elements delimiting it is at least 15% less than the width of all the trigger zones measured in the direction of the lines between two adjacent separating elements delimiting them.

Preferably, the first slab comprises only two networks of coplanar maintenance electrodes, unlike the panel described in the document US2003 / 0080683 ; alternatively, each maintenance electrode serves the cells of two consecutive rows of cells; thus simplifying the manufacture of the panel.

Preferably, said inter-column separating elements extend continuously over approximately the entire height of said space between the slabs, unlike the barriers described in the document US2003 / 0080683 .

Preferably, the second slab comprises a single array of addressing electrodes, so that each cell is traversed only by a single addressing electrode; thus simplifying the manufacture of the panel.

The ignition voltage of a maintenance discharge between two coplanar maintenance electrodes obviously depends on the electrical charges previously stored on the dielectric layer covering these electrodes in the vicinity of the ignition zone; these charges may have been previously stored during a previous maintenance discharge or during an addressing operation; thus, before a maintenance discharge in a cell, positive charges are generally stored on the maintenance electrode which will serve as anode and negative charges on the maintenance electrode which will serve as a cathode; these stored charges create what's called a voltage of memory ; the ignition voltage corresponds to the voltage of a maintenance signal applied between the electrodes, to which the memory voltage is added.

Upon the ignition of a maintenance discharge in a cell, the electronic avalanche that occurs in the discharge gas between the electrodes passing through this cell creates a positive space charge which concentrates towards the cathode to form what is called a cathodic sheath; the plasma zone, called the positive pseudo-column, which is situated between the cathode cladding and the anode end of the discharge, contains, in an identical proportion, positive and negative charges; this zone is therefore conductive of the current and the electric field is weak there; the electrons present in the pseudo-positive column area have a relatively low energy, which promotes the excitation of the discharge gas and the production of ultraviolet photons with high energy efficiency.

During this discharge, along the electric field lines between the electrodes passing through this cell, the largest potential drop portion corresponds to the cathode cladding zone; the impact of the ions which are accelerated in the intense field of the cathodic sheath and which are sprayed on the protective layer and secondary electron emission, which coat the dielectric layer and the maintenance electrodes, causes a significant emission secondary electrons in the vicinity of the cathode; under the effect of this intense electronic multiplication, the density of the conductive plasma then strongly increases between the electrodes, both in ions and in electrons, which causes a contraction of the cathodic sheath in the vicinity of the cathode and the positioning of this sheath at the level where the plasma ions are deposited, on the dielectric surface portion covering the coplanar electrode serving as a cathode; on the side of the anode or anodes, the electrons of the plasma, which are much more mobile than the ions, are deposited on the portion of dielectric surface covering the coplanar electrode serving as anode, to neutralize progressively, from the front backwards, the layer of positive charges "memory" previously stored; when all of this stored positive charge is neutralized, the potential between the anode and the cathode then begins to decrease; the electric field in the cathode sheath then reaches a maximum, corresponding to the maximum contraction of the sheath, and the electric current between the electrodes is then also maximum.

The luminous efficiency of the plasma panels is generally low because a large amount of electrical power supply and maintenance of the panel is dissipated in the acceleration of ions and in the heating of the walls under the effect of the spraying of ions. The document US6184848 describes a method of piloting maintenance discharges which allows a first improvement of the light output of the discharges. As illustrated on Figures 1A and 1B the distance, or "gap", separating the maintenance electrodes Y, Y 'is substantially increased so that the discharges between these two electrodes are only possible via a low intensity tripping discharge. As illustrated on the Figure 2A such a triggering discharge D _M is obtained as a result of a trigger signal, automatically induced or voluntarily applied, between a Y 'of the maintenance electrodes serving as a cathode and the addressing electrode X serving as anode intermediate. As illustrated on the Figure 2B the electrons moving faster than the ions, these follow the lines of increasing potential to the second maintenance electrode Y serving as anode, and, as illustrated in FIG. Figure 2C , establish a current between the two maintenance electrodes, creating a long positive pseudo-column DE in which the excitation of the gas is very efficient in generally UV light emission. This significantly improves the luminous efficiency of the plasma panels.

• le rendement des décharges de déclenchement dans les zones de déclenchement ou de décharge matricielle,
• le rendement des pseudo-colonnes positives dans les zones d'expansion, entre les électrodes d'entretien.

It can be seen that the performance of maintenance discharges is conditioned by:

• the performance of tripping discharges in the tripping or discharging areas,
• the efficiency of the positive pseudo-columns in the expansion zones, between the maintenance electrodes.

Due to the small distance between the maintenance electrode and the addressing electrode within each matrix discharge zone or trigger zone, the matrix discharge may be inefficient if the current density is too high. because, then, the electric field is important. To limit the matrix discharge current density and thus limit the development of a strong cathodic sheath within these discharges, it is therefore preferable to work with a low capacitance between the electrodes crossing in the tripping zone, so as to that the anodic spreading is very fast and that the increase of the current density occurs only when the discharge is transformed into coplanar discharge and is completely extended in the coplanar discharge expansion zone between the electrodes 'interview ( Figure 2C ), and not when the discharge is still in the matrix state ( Figure 2A ) and that the pseudo-positive column is not yet formed (which would cause the equivalent of a short circuit). But if we decrease the capacity between the electrodes at the trigger zones, we increase the operating voltages of the panel, which is annoying. To reduce these voltages, it is necessary to increase the avalanche gain: this is achieved, according to a first essential characteristic of the invention, by moving the barriers away from the triggering zones, so as to widen these zones or to increase the surface of their section.

• en rapprochant les barrières au niveau de la zone d'expansion entre les zones de déclenchement,
• en subdivisant la zone située entre les zones de déclenchement en au moins deux zones d'expansion plus étroites en parallèle, à l'aide d'éléments de séparation intra-cellule.

The luminous efficiency of the positive pseudo-column of the coplanar discharge is directly related to the density of the current flowing through it. If the current density decreases, the efficiency increases. In order to reduce the current density, it is proposed, according to a second essential characteristic of the invention, to reduce the available section for the positive pseudo-column of the coplanar discharge at the level of the expansion zone by means of appropriate constriction. , for example :

• by bringing the barriers at the expansion zone closer together between the tripping zones,
• subdividing the area between the triggering zones into at least two narrower expansion zones in parallel using intra-cell separation elements.

This increases the diffusion of the electrons and decreases the current density during the coplanar expansion phase of the discharges.

A further improvement in the luminous efficiency of the plasma panels is thus obtained, by enlarging the cells at the point of ignition of the discharges, that is to say in the trigger zones, and in narrowing the cells or subdividing them at the expansion zones. Thus, according to the invention, for each cell, the section of one or the other of the triggering zones has a surface greater than the sections of each expansion zone. The invention thus proposes an optimization of the profile of the barriers of the panel so as to favor an ignition with low anodic capacity with a large cathode surface, while maintaining a high efficiency of pseudo-positive column.

In summary, the plasma panel according to the invention as defined in claim 1 comprises two slabs separated by a gaseous space partitioned by separation elements forming a network of barriers, and networks of coplanar electrodes maintenance and d addressing; each cell being subdivided into a trip zone at each of the crossings of an addressing electrode with a maintenance electrode, and at least one coplanar discharge expansion zone extending between the trip zones, the A barrier network is adapted so that, at each cell, each coplanar expansion zone has a width that is smaller, preferably at least 15%, than the width of all the trigger zones.

According to a first embodiment, each cell comprises only one expansion zone between two adjacent tripping zones.

In this case, the separation elements that delimit trigger zones or expansion zones also delimit the cells: they are inter-cell separation elements, which are part of the barrier network and which separate, each , two adjacent columns of cells. According to the invention, each cell then has a narrowing only at its expansion zone and an enlargement at each trigger zone. These narrowing and widening can be obtained in particular by an adaptation of the network of barriers: the separation elements between the columns are widened at the location of the narrowing and narrowed at the location of the enlargements.

The adaptation of the network of barriers then leads overall to an increase in the overall surface of the tops of the barriers, which advantageously increases the surface of the black contrast network that is generally applies to the top of the barriers, and thus increase the contrast of viewing images in ambient light.

According to a variant of this embodiment, the cells of the same column of the panel are shifted in the general direction of the columns relative to the cells of an adjacent column, so as to obtain better nesting of the cells, which allows to advantageously increase the density or the surface of the cells of the panel.

According to a second embodiment, each cell comprises a plurality of expansion zones between two adjacent tripping zones.

These different expansion zones of the same cell are therefore arranged in parallel between two same triggering zones; this subdivision of the cells in the direction of the width, only between the triggering zones and not at the level of the triggering areas themselves, is another advantageous means of constricting the expansion zones. The reduction of the expansion zones provides a significant improvement in the luminous efficiency of the panel.

Preferably, according to this second embodiment of the invention, each cell is subdivided by at least one intra-cell separation element which extends in the direction of the columns in said interval situated between the triggering zones and which delimits two adjacent expansion areas of this cell.

These intra-cell separation elements are also part of the barrier network. Their dimensions are adapted to obtain the plurality of expansion zones operating in parallel. These intra-cell separation elements are generally not carrying, that is to say that their height is generally less than that of inter-cell separation elements, also less than the distance between the slabs.

Thanks to this subdivision of the cells provided by intra-cell separation elements which do not extend over the entire length of the cells but only over an interval comprised between the coplanar electrodes, according to the invention, zones of narrower expansion without changing the width of the trigger zones.

Unlike the intra-cell separation elements described in the document US6376995 , in particular in FIG. 21 of this document, the intra-cell barrier elements according to the invention are interrupted at the level of the triggering matrix discharge zones, that is to say generally at the crossings of the addressing electrodes and the maintenance electrodes, so as to provide a larger space for trigger matrix discharges.

Each cell is preferably crossed only by a single addressing electrode; preferably, the intra-cell separation element is then positioned with respect to this addressing electrode, unlike the panel shown in FIG. US6376995 .

Preferably, the coplanar electrodes are coated with a dielectric layer and a protective layer and secondary electron emission. The dielectric layer thus provides the memory effect which makes it possible to control the panel by a succession of addressing and maintenance operations; the protective layer and secondary electron emission allows in particular to lower the operating voltages of the panel.

Preferably, at each cell, the distance separating the electrodes of the different coplanar networks is greater than the distance separating the slabs. Such a panel structure is particularly advantageous in the case of the use of control means and electrode supply adapted so that each coplanar discharge is triggered by a matrix discharge.

The distance separating two maintenance electrodes corresponds to the coplanar gap; the distance between the slabs corresponds to the thickness of the gaseous space between the slabs; the invention therefore preferably applies to so-called "large gap" panels which are particularly suitable for control by matrix triggering; in practice, a "gap" of the order of 500 μm is commonly used.

The invention as defined in claim 1 also relates to an image display device comprising a plasma panel according to the invention characterized in that it comprises means for controlling and supplying the electrodes of this panel able to apply to these electrodes signals adapted to generate, at the level of each cell, coplanar discharges between the different coplanar electrodes passing through it and for these discharges to be triggered each by a matrix discharge between the addressing electrode passing through it and one of said coplanar electrodes.

In a manner known per se, for controlling the panel, the frames of the images to be displayed are generally subdivided into subframes capable of generating, by their succession, the gray levels necessary for viewing.

In a manner known per se, for controlling the panel, the visualization of a sub-frame generally comprises an addressing step and a maintenance step; the addressing step, which generally comprises a single voltage pulse, is intended to generate the surface charges necessary to trigger the first coplanar maintenance discharge of the next step, only and selectively in the cells of the panel which must be activated during the subframe considered; the following maintenance step comprises as many voltage pulses as coplanar discharges to generate in the subframe; during this step and unlike the previous one, the same voltage pulses are applied between the coplanar electrodes of a set of cells, whether previously activated or not; during this step, the coplanar discharges will take place only in the previously activated cells; according to the invention, each of the coplanar discharges of this maintenance step is triggered by a matrix discharge between an addressing electrode carried by a slab and a coplanar electrode carried by the other slab.

Each coplanar discharge, ie a discharge between two electrodes carried by the same slab, is triggered by a matrix discharge, ie a discharge between two electrodes carried by two different slabs; this trip discharge is different from an addressing discharge, which also takes place between two electrodes carried by two different slabs but only in preparation for a maintenance phase.

It will be noted that the display device described in the document US2003 / 0080683 , describes a plasma panel with an array of electrodes addressing and four coplanar electrode arrays; as indicated in §30 of this document, the electrodes X ', Y' of the first two networks of coplanar electrodes are close (low "gap") so as to facilitate the creation of coplanar discharges; these low-gap coplanar discharges are used to trigger high-gap "main" coplanar discharges between X, Y electrodes of the other two coplanar networks that are much more distant.

Thus, contrary to the invention, in the document US2003 / 0080683 it is not a matrix discharge between an addressing electrode and a coplanar electrode that triggers each main coplanar discharge, but a coplanar discharge with a small "gap" between two coplanar electrodes with a small "gap". Thus, contrary to the invention, in the document US2003 / 0080683 , the trip electrode, X 'or Y', does not cross an electrode of each maintenance network at each cell.

• les figures 1A et 1B, déjà décrites, représentent respectivement une vue de dessus et une coupe d'une cellule d'un panneau à plasma selon l'art antérieur ;
• les figures 2A, 2B, et 2C déjà décrites, représentent les différentes étapes de développement d'une décharge d'entretien déclenchées par une décharge matricielle dans la cellule de la figure 1, représentée schématiquement en coupe avec, seulement, les électrodes et les couches diélectriques les recouvrant ;
• les figures 3 et 4 illustrent une première famille de modes de réalisation de l'invention où chaque cellule ne comprend qu'une zone d'expansion, et représentent, en vue de dessus, un ensemble de trois cellules d'un panneau selon l'invention où les cellules adjacentes d'une même ligne sont décalées les unes par rapport aux autres, et où, pour chaque cellule, la largeur des zones de déclenchement est supérieure à la largeur de l'unique zone d'expansion :
  • o figure 3 : les électrodes d'entretien ne sont pas rectilignes, desservent directement les cellules, et ne sont pas dotées de dérivations ;
  • o figure 4 : les électrodes d'entretien sont rectilignes, et sont dotées de dérivations pour desservir les cellules ;
• les figures 5 et 6 illustrent une deuxième famille de modes de réalisation de l'invention où chaque cellule comprend deux zones d'expansion en parallèle, et représentent, en vue de dessus, un ensemble de trois cellules d'un panneau selon l'invention où chaque cellule est divisée par un élément de séparation intra-cellule s'étendant uniquement entre les électrodes d'entretien :
  • o figure 5 : chaque électrode coplanaire ne dessert qu'une seule ligne de cellules ;
  • o figure 6 : chaque électrode coplanaire dessert deux lignes adjacentes de cellules ;

The invention will be better understood on reading the description which follows, given by way of nonlimiting example, and with reference to the appended figures in which:

• the Figures 1A and 1B , already described, represent respectively a top view and a section of a cell of a plasma panel according to the prior art;
• the FIGS. 2A, 2B, and 2C already described, represent the different stages of development of a maintenance discharge triggered by a matrix discharge in the cell of the figure 1 , schematically shown in section with only the electrodes and the dielectric layers covering them;
• the Figures 3 and 4 illustrate a first family of embodiments of the invention where each cell comprises only one expansion zone, and represent, in top view, a set of three cells of a panel according to the invention where the adjacent cells of the same line are shifted relative to each other, and where, for each cell, the width of the triggering areas is greater than the width of the single expansion zone:
  • o figure 3 : the maintenance electrodes are not straight, directly serve the cells, and are not equipped with taps;
  • o figure 4 the maintenance electrodes are rectilinear and are provided with branches to serve the cells;
• the Figures 5 and 6 illustrate a second family of embodiments of the invention wherein each cell comprises two expansion zones in parallel, and represent, in top view, a set of three cells of a panel according to the invention where each cell is divided by an intra-cell separating element extending only between the maintenance electrodes:
  • o figure 5 : each coplanar electrode serves only one line of cells;
  • o figure 6 each coplanar electrode serves two adjacent lines of cells;

In order to simplify the description and to show the differences and advantages that the invention presents with respect to the prior art, identical references are used for the elements that provide the same functions.

According to a first family of embodiments, the plasma panel according to the invention differs mainly from the panel previously described with reference to the Figures 1A and 1B in that the column separating elements 15 have a variable width, as illustrated in FIG. figure 3 : thus, the cell width L _M measured in the zones Z _M , Z ' _M triggering matrix discharge, that is to say at the crossroads between the addressing electrode and one of the maintenance electrodes Y, Y 'is greater than or equal to the distribution pitch p of the electrodes X of the addressing network, whereas the cell width LE measured in the expansion zone Z _E , ie between the electrodes of Y, Y 'maintenance is less than the same step p.

Thus, in pilot coplanar discharges by matrix triggering, the avalanche gain is increased in the tripping matrix discharge zone, and the diffusion and the discharge efficiency are increased in the expansion zone of the positive pseudo-column. .

The cells of the panel are arranged in staggered relation to each other, so as to best distribute the parts of cells which are the widest, that is to say the areas of matrix discharge; as shown in figure 3 , each matrix discharge zone of a cell belonging to a column (not bordering) of the panel is located, either between the expansion zones of adjacent column cells (Z " _{M case} in the figure), or between the zones separating two cells of different lines in these adjacent columns (in the case of Z _M , Z ' _M ), thus the cells of any one column of the panel are shifted in the general direction of the columns relative to the cells of an adjacent column .

This family of embodiments makes it possible, in addition, to increase the possible surface of black grating arranged for example at the top of the barriers and intended to improve the display contrast of the images, which makes it possible to limit the use of a neutral filter of low transmission, and further improves the final light output of the plasma panel.

The staggered arrangement of the cells leads, as shown in FIG. figure 3 , to maintenance electrodes which have a non-rectilinear sinuous profile.

The figure 4 illustrates a variant of the panel shown in figure 3 , where the cells are also arranged in staggered rows but where the maintenance electrodes nevertheless have a rectilinear path: the maintenance electrodes Y, Y 'are here provided with bypass 18 which extend towards the center of the zones of Z matrix discharges _M , Z ' _M. These branches may be made of transparent conductive material such as ITO.

According to a second family of embodiments of the invention, the plasma panel according to the invention differs mainly from the panel previously described with reference to the Figures 1A and 1B in that, as shown in figure 5 each cell is provided with an intra-cell separation element 19 which extends only between the maintenance electrodes Y, Y ', so as to obtain two expansion zones Z _E1 , Z _E2 in parallel. This further improves the luminous efficiency of the panel. The dimensions and the material of this separating element are adapted in a known manner in itself to obtain this separation in two of the positive pseudo-column, in order to strongly bring the plasma of wall elements of the cell, namely the separation elements 15, 19. In practice, the internal separation elements -cellule 19 are integrated in the network of barriers and made at the same time and in the same material as the inter-cell separation elements 15. In practice, the width of the intra-cell separation elements 19 is greater than or equal to 40 microns.

Thanks to these intra-cell separation elements arranged only between the maintenance electrodes outside the matrix discharging zones, we obtain, even though the distance between the inter-cell separation elements 15 is constant over almost the entire length of the cells. cells, a decrease or a constriction of the section of the cells at the level of the expansion zones: thus the width L _M of the cells at the zones Z _M , Z ' _M of the matrix discharge is greater than the width L _E1 , L _E2 each expansion zone Z _E1 , Z _E2 .

This second family of embodiments of the invention is also advantageous with respect to the first family because it makes it possible to increase the surface area available for the phosphors in each cell, in particular on the slope of the inter and intra separation elements. -cellules. Note that the phosphor layer is not shown in the figures. This increase in the surface area available for the luminophore contributes to the improvement of the luminous efficiency.

Due to the manufacturing constraints, the pitch p between cell columns may interfere with the phosphor deposition in the two expansion zones Z _E1 , Z _E2 ; it is then preferable to use a so-called staggered cell arrangement as shown in FIG. figure 6 . In this variant of the panel of the figure 5 each maintenance electrode simultaneously serves two consecutive rows of cells.

In the case where there is only one X addressing electrode per cell, it is advantageous to arrange this electrode under the intra-cell separation elements 19 as shown in FIGS. Figures 5 and 6 , so as to increase the dielectric thickness on these electrodes and thus greatly reduce the anodic capacity, which makes it possible to increase the speed of electron spreading and the formation of the positive column.

In the two families of embodiments which have just been described, at the level of the zones separating two cells of different lines, the distance between the inter-cell separation elements delimiting these cells is reduced but not zero; this distance is less than the width of the expansion zones L _E , L _E1 , L _E2 ; this distance is not zero to advantageously provide a recess which facilitates the deposition of phosphors in the columns, which limits the risk of phosphor deposition on the tops of the barriers.

The plasma panels that have just been described can be made by methods known in themselves which will not be described here.

The present invention can be applied to other types of plasma panels without departing from the scope of the claims below.

These plasma panels are advantageously integrated into display devices which comprise supply and control means which make it possible in particular to generate maintenance operations where each maintenance discharge is triggered by a matrix discharge; such supply and control means are known to those skilled in the art, have been briefly described above, are described in more detail for example in the document US6184848 already cited.

Claims (9)

1. Image-display device comprising a plasma panel comprising itself a first tile (11) and a second tile (12) creating between them a space that is filled with discharge gas and partitioned, notably by means of a network of barrier ribs, into a plurality of discharge cells (17) disposed in rows and columns,

   - the said first tile (11) comprising at least two arrays of coplanar electrodes called sustain electrodes (Y, Y') which are aligned in general directions that are parallel to one another and to the said rows,

   - the said second tile (12) comprising at least one array of electrodes called address electrodes (X) which are aligned in general directions that are parallel to one another and to the said columns,

   - the said electrodes being disposed such that, within each cell (17), one address electrode crosses one electrode from each sustain array,

   - each cell (17) being subdivided into at least two trigger regions (Z_M, Z_M') each situated at a point where the address electrode crosses a sustain electrode, and into at least one coplanar discharge expansion region (Z_E; Z_E1, Z_E2) running between the trigger regions (Z_M, Z_M'),

   - the said network of barrier ribs comprising inter-column separation elements (15) each separating two adjacent columns of cells, and being designed such that, within each cell, each coplanar expansion region (Z_E; Z_E1, Z_E2) has, in an interval situated between the trigger regions (Z_M, Z_M) that define its limits in the column direction, a width that, when it is measured between two adjacent separation elements (15; 15, 19) that define its limits in the row direction, is less than the width of all the trigger regions (Z_M, Z_M') measured between two adjacent separation elements (15) defining the limits of these regions also in the row direction,

   - the said image-display device comprising means for driving and powering the electrodes of this display which are capable of applying signals to these electrodes, which signals are designed :

   - to generate, within each cell, coplanar discharges between the different coplanar electrodes traversing the cell,

   - and such that these discharges are each triggered by a matrix discharge between the address electrode traversing the cell and one of the said coplanar electrodes.
2. Image-display device according to Claim 1 characterized in that, for the said plasma panel, the first tile comprises only two coplanar sustain electrode arrays.
3. Image-display device according to either one of the preceding claims characterized in that, for the said plasma panel, the said inter-column separation elements extend continuously over approximately the whole height of the said space between the tiles.
4. Image-display device according to any one of the preceding claims characterized in that, within each cell (17) of said plasma panel, the distance separating the electrodes (Y, Y') of the different coplanar arrays is greater than the distance separating the tiles (11, 12).
5. Image-display device according to any one of the preceding claims characterized in that the said network of barrier ribs of said plasma panel is designed such that, within each cell (17), the width of each coplanar expansion region, measured in the row direction between two adjacent separation elements defining its limits, is at least 15% less than the width of all the trigger regions, measured in the row direction between two adjacent separation elements defining their limits.
6. Image-display device according to any one of Claims 1 to 5, characterized in that each cell (17) of said plasma panel only comprises a single expansion region (Z_E) between two adjacent trigger regions (Z_M, Z_M').
7. Image-display device according to any one of Claims 1 to 5, characterized in that each cell of said plasma panel comprises a plurality of expansion regions (Z_E1, Z_E2) between two adjacent trigger regions (Z_M, Z_M').
8. Image-display device according to Claim 7, characterized in that each cell of said plasma panel is subdivided by at least one intra-cell separation element (19) which runs in the column direction within the said interval situated between the trigger regions and which defines the limits of two adjacent expansion regions (Z_E1, Z_E2) of this cell.
9. Image-display device according to any one of the preceding claims characterized in that the said coplanar electrodes of said plasma panel are coated with a dielectric layer (13) and with a secondary-electron emission and protection layer (14).

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