EP1543536B1 - Plasma display panel having coplanar electrodes with constant width - Google Patents

Abstract

The invention concerns a panel comprising a network of barriers (15) having each a base resting on a faceplate (12) and a top in contact with another faceplate (11) including at least two coplanar electrode arrays (Y, Y') having each preferably a constant width. The invention is characterized in that said barriers (15) have, at their top, a low permittivity zone (15b) of thickness (Db) more than 3 νm and not less than one-fifth of their total height which has an average dielectric permittivity (Eb) at least three times lower than the dielectric permittivity (Ea) of said barriers evaluated at their base. The invention enables the plasma discharge confinement to be enhanced well away from the barriers (15).

Description

Referring to Figures 1A, 1B, the invention relates to a plasma display panel comprising a first slab 11 and a second slab 12 between them a space filled with compartmentalized discharge gas in a set of discharge cells 18 disposed in lines and in columns, also comprising a network of insulating barriers comprising barriers 15 separating, each, two adjacent columns of cells, the first slab comprising at least two networks of electrodes Y, Y 'coplanar said maintenance, oriented in directions general parallel to each other and perpendicular to said barriers, having a constant width perpendicular to these general directions, arranged so that each discharge cell is traversed by an electrode of each network.

Since the barriers 15 each separate two adjacent columns of cells, these barriers are called column barriers, as opposed to the line barriers described hereinafter.

Each discharge cell is therefore traversed by a pair of maintenance electrodes and each pair of maintenance electrodes thus serves a line of discharge cells; all the adjacent cells of the same line are separated by a column barrier made of insulating material; in this way, in the general direction of the coplanar electrodes, the widths of the different cells of the same line are limited by these column barriers; these barriers generally serve as spacers between the slabs of the panel.

Coplanar electrodes are covered with a dielectric layer 13 itself coated with a protective layer and secondary electron emission 14, generally based on magnesia.

The second slab comprises a third array of so-called addressing electrodes X arranged each between two column barriers; thus, each addressing electrode thus serves a column of discharge cells; these addressing electrodes may also be covered with a dielectric layer 17.

The network of barriers of some panels of the prior art also comprises barriers 16 called line barriers each separating two adjacent rows of cells, so that each cell of the panel is then delimited on all of its periphery by barriers as shown in Figures 1A, 1B.

The control of the plasma panels conventionally comprises addressing periods for activating the cells to be lit, followed by maintenance periods during which a series of maintenance voltage pulses are applied between the maintenance electrodes Y , Y 'serving a line of cells, in the gap or gap G between these electrodes; the height of these maintenance pulses must be sufficient to cause discharges in the previously activated cells of the line, but insufficient to cause discharges in the cells of this line not previously activated.

The addressing of the discharge cells generally takes place between a column electrode and one of the line electrodes which is also used for maintenance.

The discharge cells and the space between the slabs are filled with a gas under low pressure suitable for obtaining discharges emitting ultraviolet radiation.

The walls of each cell are generally provided with a layer of phosphor capable of emitting visible radiation, in particular red, green or blue, when it is excited by the ultraviolet radiation of the discharges; these layers are usually deposited on the second slab and on the slopes of the barriers.

In the case of panels emitting three primary colors, red, green and blue, the adjacent discharge cells comprise phosphors of different colors so that we obtain discharges emitting indirectly in red, green and blue.

It is usually the first slab, the one carrying the coplanar electrodes, which serves as a front slab oriented towards the observer of the images that the panel is likely to display; to prevent slab electrodes before absorbing too much of the visible radiation from cells, the coplanar electrodes are preferably made of a material that is both conductive and transparent, such as tin oxide or mixed tin-indium oxide ("ITO"), for Indium-Tin Oxide in the tongue English) since these transparent electrodes are generally not sufficiently conductive, the transparent electrode arrays of opaque metallic conductors, which are called "bus conductors", are generally "doubled" because they distribute the discharge electric current to the transparent electrodes ; conventionally, the linear electrical conductivity of the bus is greater than that of the priming conductor; the bus is made of highly conductive metallic material, such as silver; it is therefore opaque to light.

During a maintenance period, when a voltage pulse of sufficient amplitude is applied between two coplanar electrodes Y, Y 'of the same pair, in a cell powered by these electrodes and previously activated during a period of addressing, initiates a discharge in the gap G at the priming edge 191 of one of these electrodes, on a front which extends between the column barriers 15 which delimit this cell width to this in law ; with reference to FIG. 1A, the initiation of the discharge in this cell takes place in a priming zone Z _a of the portion of this electrode corresponding to this cell; it is preferable that the surface potential properties of the dielectric layer 13 coating this electrode are sufficiently uniform to allow low voltage firing of the discharge; after initiation, the discharge extends perpendicularly to the general direction of the coplanar electrodes to the discharge end edge 192 of the electrode, opposite the priming edge; the phase of spreading of the discharge, called expansion phase, allows the formation of a discharge zone with a very low electric field that is very efficient for the excitation of the gas and the production of ultraviolet photons; the expansion phase thus makes it possible to improve the light output of the discharges. During the expansion phase of the discharge to the discharge end edge of the electrode, the discharge occupies almost all of the gas space delimited by the two column barriers 15 bounding the cell width.

During a maintenance period, immediately before the application of an electrical voltage pulse between two coplanar electrodes Y, Y 'of the same pair passing through a cell, the dielectric layer area which covers these electrodes is generally covered residual charges called "memory charges", especially from the previous discharge in this cell. Immediately at the beginning of the application of an electric voltage pulse and before any new discharge, the zone of discharge gas between these two electrodes is then subjected to the sum of the voltage applied between these electrodes and the voltage resulting from memory charges from the previous maintenance pulse.

FIG. 3 represents, at the beginning of a maintenance voltage pulse of a value of 100 V applied to the electrodes, which follows other identical alternating pulses having left memory charges, the distribution of the equipotential voltage lines according to a A1-A1 'section of the discharge expansion zone, between the middle of a column barrier 15 and the middle of the cell, this interval corresponding to the half distance between the media of two adjacent columns barriers, is at say to the half width of a discharge cell; the equipotential lines in solid lines correspond to positive values of the potential; the equipotential lines in broken lines correspond to negative values of the potential; the potential difference between two adjacent equipotential curves is constant and adapted to obtain twenty "positive" equipotential curves in continuous lines; during the 100 V voltage pulse that starts, it is assumed here that the electrode Y considered plays the role of cathode, and that the negative memory charges stored in this cell on the surface of the dielectric layer 13 come from the discharge generated by the previous maintenance voltage pulse of the same series, of opposite sign. In this figure, the equipotential curve V corresponds to the first negative equipotential (discontinuous lines, as opposed to the continuous lines of positive equipotentials), and testifies to the presence of a negative charge deposited at this level on the surface of the column barrier 15 The distribution of this equipotential depth in the column barrier indicates that, after initiation caused by the pulse in progress, the discharge will spread on the slopes of the barriers, therefore, beyond the surface of the dielectric layer 13 and the protective layer 14 covering the electrode Y. During maintenance periods when the panel emits light, the barriers will therefore be in significant contact with the discharges. This phenomenon leads to an increase in the losses of charged species on the barriers and to an accelerated deterioration of the phosphor material covering these barriers, with a consequent decrease in light output and a reduction in the service life of the panel.

The prior art, illustrated for example by the document EP0782167-PIONEER, proposes a solution to this problem which is shown in FIG. 2. FIG. 2 shows a schematic top view of the structure of a cell of a panel of a coplanar plasma display which differs from the structure presented previously in FIGS. 1A and 1B in that the coplanar electrodes no longer extend over the entire width of the cells: each electrode Y comprises a conductive bus Y _b continuous at the edge of the end of discharge 192 which passes through all the cells of a same line and, at each cell, a tongue-shaped electrode element Y _p , centered on this cell, having a width less than this cell, and extending from the bus to the level of the priming edge 191. The electrode elements Y _p of each cell are dimensioned so that their lateral edges are positioned at a non-zero distance D the surface of the nearest column barriers 15 which delimit this cell.

Such a structure applied to the coplanar electrodes Y, Y 'makes it possible to reduce the potential on the slopes of the column barriers and on the surface portions of the protective layer that are close to these barriers along the lateral edges of the electrode elements Y _p , as illustrated in FIG. 4 representing the distribution of the electrical equipotential curves in the cell represented in FIG. 2, in a section A2-A2 'in the half-cell width, according to the same assumptions and conventions as for FIG. 3 previously described; in this FIG. 4, it can be seen that the first negative equipotential curve in broken lines meets the V-shaped column barrier at the top of this barrier, at the interface with the protective layer and the dielectric layer 13; of these dielectric properties illustrated by the equipotential curves, it results a better confinement of the maintenance discharges at a distance from the column barriers at the beginning of expansion in the panels described in document EP0782167 or with reference to FIG. 2 with respect to the panels previously described with reference to FIGS. Figures 1A and 1B; this improves the light output and the service life.

On the other hand, at the end of the expansion of the discharges, ie at the level of the buses Y _b of the coplanar electrodes, one encounters the same problem as before since the electrodes extend at this level over the entire width of the cells: the potential along the barrier surface and at the surface of the protective layer remains high in the vicinity of the electrode portions Y _b corresponding to the buses; the improvement of the light output and the lifetime therefore remains limited.

In addition, such an electrode element structure is more difficult to produce than that of FIGS. 1A and 1B and requires an expensive operation of horizontal alignment of the slabs 11 and 12 so that the electrode elements specific to each cell are perfectly centered on each cell, equidistant from two adjacent columns barriers.

The object of the invention is to increase the luminous efficiency of plasma panels and their service life while avoiding these limitations and disadvantages.

For this purpose the invention relates to a plasma display panel comprising a first slab and a second slab between them a space filled with partitioned waste gas in a set of discharge cells disposed in rows and columns, also comprising a network of insulating barriers comprising barriers separating, each, two adjacent columns of cells and each having a base resting on said second slab and a top in contact with said first slab, this first slab comprising at least two arrays of electrodes Y, Y 'coplanar maintenance said, which are oriented in general directions parallel to each other and to said lines, which are arranged so that each discharge cell is traversed by an electrode of each network then forming a pair, and which have so-called edges primers which face each other on either side of the gap separating the electrodes of each pair, characterized in that each column separation barrier comprises, at its vertex and over its entire width, a succession of zones of low permittivity which extend on either side of the gap separating the electrodes of each pair at least from a line 80 μm behind the initiation edges of the electrodes of this pair, and which have a greater thickness at 3 μm and less than or equal to one fifth of the total height of said barriers, and a mean dielectric permittivity at least three times less than the dielectric permittivity of said barriers evaluated at their base.

The zones of low permittivity thus extend at least on each side of the gap of each cell.

The thickness of a zone of low permittivity on a barrier is measured from the top of this barrier in contact with the first slab; each of these zones extends approximately over the entire width of the barrier, to the thickness of a possible phosphor layer near.

If the coplanar electrodes do not have a constant width, for example as in the structure of the prior art described with reference to FIG. 2, the invention makes it possible to combine the performance advantages already described of this structure and those specific to the invention described hereinafter.

The invention applies in particular to cases where the coplanar electrodes each have a constant width over their entire effective length; useful length of an electrode means the length corresponding to all the cells served by this electrode; the width of this electrode is understood as the width measured perpendicular to its general direction; as the width of the coplanar electrodes is constant as in the structure of the prior art described with reference to FIGS. 1A and 1B, the electrode arrays are more economical to produce and the assembly of the slabs is not penalized by constraints alignment: thus avoids the disadvantages of the structure of the prior art described with reference to Figure 2, while obtaining advantages at least identical if not higher in terms of light output and life, as explained below.

The invention proposes in fact to modify the distribution of the equipotential curves not by modifying the shape and position of the electrodes at the level of each cell as previously described with reference to FIGS. 2 and 3, but by varying the dielectric permittivity within the barriers. in a manner adapted to tighten and bring closer, at the level of each cell, the equipotential curves in the vicinity of the dielectric layer and the protective layer, so as to reduce the electric potential on the slope of these barriers, particularly in the vicinity of these layers.

Thanks to the thickness specific to the invention of the zones of low permittivity and thanks to the average dielectric permittivity specific to the invention of these zones, one then obtains a better confinement of the maintenance discharges on the surface of the dielectric layer and of the protective layer, away from the barriers, which reduces the loss of plasma charged species and the degradation of the phosphors on these barriers by the plasma in the expansion zone of the discharges.

An additional advantage of the panel structure according to the invention results from the fact that the desired confinement of the discharges is obtained even at the end of expansion: unlike the structure described with reference to FIG. 2, the potential on the slope of the barriers and at the surface of the protective layer and the dielectric layer is also lowered in the vicinity of the electrode portions corresponding to the end of discharge, which allows a greater improvement of the light output and the service life.

If the first slab comprises three electrode arrays, each cell is then traversed by three electrodes, one of each network, which then form a triad.

The term "gap" means the zone separating the electrodes of each pair, or, where appropriate, the zones separating the electrodes of each triad; when the width of the coplanar electrodes is constant, the width of the zones separating the electrodes is also constant.

The zone of low permittivity located at the top of the barriers can therefore be discontinuous, that is to say that it can be interrupted at the gap separating the coplanar electrodes of each pair up to a maximum of 80 μm on either side. electrode edges, beyond this gap; the areas of low permittivity then extend on each side of the gap, especially at the expansion zones of the discharges, that is to say with respect to the surface of the electrodes. The zone of low permittivity can extend further, for example when it is interrupted exactly at the gaps separating the coplanar electrodes.

According to a simpler and more economical variant to manufacture, the succession of zones of low permittivity at the top of each barrier forms a continuous zone of low permittivity, without interruption in the gaps.

According to another variant allowing a better control of the confinement of the discharges and a greater improvement of the luminous efficiency and the lifetime, at the top of each barrier separating two columns, the zones of low permittivity are discontinuous and interrupted at the gap separating the electrodes of each pair.

In summary, the subject of the invention is a plasma display panel comprising a network of barriers each having a base resting on a slab and a peak in contact with another slab comprising at least two coplanar electrode arrays, characterized in that these barriers have, at their apex, a zone of low permittivity with a thickness greater than 3 μm and less than or equal to one-fifth of their total height, which has a mean dielectric permittivity at least three times lower than the dielectric permittivity of these barriers evaluated at their base.

• l'épaisseur des zones de faible permittivité est au moins égale à 5 µm.
• les barrières de séparation de colonne présentent en outre des zones intercalaires de forte permittivité, qui sont intercalées entre la base des barrières et les zones de faible permittivité, qui présentent une épaisseur supérieure à l'épaisseur des zones de faible permittivité, et qui présentent une permittivité diélectrique moyenne supérieure à la permittivité diélectrique de ces barrières évaluée au niveau de leur base ; de préférence, la permittivité diélectrique moyenne de ces zones intercalaires de forte permittivité est supérieure ou égale à cinq fois la permittivité diélectrique des barrières évaluée au niveau de leur base ; la succession de zones intercalaires de forte permittivité peut former une zone intercalaire continue de forte permittivité ; à l'inverse, au sommet de chaque barrière, les zones de forte permittivité peuvent être discontinues et interrompues au niveau du gap séparant les électrodes de chaque paire.

In order to further improve the confinement of maintenance discharges away from the slopes of the barriers, the invention may also have one or more of the following characteristics:

• the thickness of the zones of low permittivity is at least equal to 5 μm.
• the column separation barriers also have high permittivity interspaces, which are interposed between the base of the barriers and the zones of low permittivity, which have a thickness greater than the thickness of the zones of low permittivity, and which have a high average dielectric permittivity greater than the dielectric permittivity of these barriers evaluated at their base; preferably, the average dielectric permittivity of these zones interleaves of high permittivity is greater than or equal to five times the dielectric permittivity of the barriers evaluated at their base; the succession of intermediate zones of high permittivity can form a continuous intermediate zone of high permittivity; conversely, at the top of each barrier, the areas of high permittivity may be discontinuous and interrupted at the gap separating the electrodes of each pair.

• les directions générales des électrodes coplanaires sont perpendiculaires aux barrières de séparation de colonnes.
• les électrodes coplanaires Y, Y' sont revêtues d'une couche diélectrique et d'une couche de protection et d'émission d'électrons secondaires, généralement à base de magnésie.
• la deuxième dalle comprend un troisième réseau d'électrodes X dites d'adressage disposées, chacune, au niveau d'une colonne de cellules.
• le réseau de barrières comprend également des barrières séparant, chacune, deux lignes adjacentes de cellules.
• les barrières présentent une hauteur d'au moins 100 µm.

The invention may further have one or more of the following features:

• the general directions of the coplanar electrodes are perpendicular to the column separation barriers.
• the coplanar electrodes Y, Y 'are coated with a dielectric layer and a protective and secondary electron emission layer, generally based on magnesia.
• the second slab comprises a third array of so-called addressing electrodes X, each arranged at a column of cells.
• the barrier network also includes barriers separating, each, two adjacent rows of cells.
• the barriers have a height of at least 100 μm.

Documents JP2000-306517 and JP07-262930 (see ^2nd embodiment associated with Figure 3 of this document) describe plasma panels where it is the dielectric layer positioned on the first slab which has low permittivity zones; in JP07-262930, these areas are located between the cell lines and not between the columns as in the invention; such zones make it possible to limit the expansion of the discharges in the vertical direction of the columns whereas the invention also makes it possible to limit the expansion of the discharges in the horizontal direction of the lines; in these two documents, these zones extend continuously over the entire width or the useful height of the panel and may be in contact with the top of the barriers separating the columns (Figure 1 of JP2000-306517); note that such areas of low permittivity are particularly difficult to achieve in the thickness of the dielectric layer while the Low permittivity zones according to the invention are much easier to achieve at the top of the barriers.

• les figures 1A et 1B, déjà décrites, représentent respectivement une vue de dessus et une coupe longitudinale d'une cellule à électrodes coplanaires de largeur constante d'un panneau à plasma selon l'art antérieur ;
• la figure 2, déjà décrite, représente une vue de dessus d'une cellule à électrodes coplanaires de largeur variable d'un panneau à plasma selon l'art antérieur ;
• les figures 3 et 4, déjà décrites, représentent la distribution du potentiel respectivement selon une coupe A1-A'1 de la moitié d'une cellule de la figure 1A et selon une coupe A2-A'2 de la moitié d'une cellule de la figure 2, au début de l'application d'une impulsion de tension de 100 V à l'électrode coplanaire de cette moitié de cellule ;
• la figure 5 représente une coupe transversale d'une cellule d'un panneau à plasma selon un premier mode de réalisation de l'invention ;
• les figures 6 et 7 représentent deux exemples de la distribution du potentiel qu'on obtient selon une coupe A1-A'1 dans la moitié d'une cellule représentée à la figure 5, selon les mêmes conventions que pour les figures 3 et 4 ;
• la figure 8 représente une coupe transversale d'une cellule d'un panneau à plasma selon un deuxième mode de réalisation de l'invention;
• les figures 9 et 10 représentent la distribution du potentiel qu'on obtient respectivement selon une coupe A1-A'1 dans la moitié d'une cellule représentée à la figure 8 et selon une coupe A1-A'1 dans la moitié d'une cellule représentée à la figure 11, toujours selon les mêmes conventions que pour les figures 3 et 4 ;
• la figure 11 représente une coupe transversale d'une cellule d'un panneau à plasma selon un troisième mode de réalisation de l'invention ;
• la figure 12 représente une variante du premier mode de réalisation de l'invention de la figure 5, où le sommet des barrières ne comporte une zone de faible permittivité qu'au niveau des zones d'expansion des décharges.

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:

• FIGS. 1A and 1B, already described, respectively represent a top view and a longitudinal section of a cell with coplanar electrodes of constant width of a plasma panel according to the prior art;
• FIG. 2, already described, represents a view from above of a variable-width coplanar electrode cell of a plasma panel according to the prior art;
• FIGS. 3 and 4, already described, represent the potential distribution respectively according to a section A1-A'1 of the half of a cell of FIG. 1A and in a section A2-A'2 of the half of a cell of FIG. 2, at the beginning of the application of a voltage pulse of 100 V to the coplanar electrode of this half-cell;
• Figure 5 shows a cross section of a cell of a plasma panel according to a first embodiment of the invention;
• FIGS. 6 and 7 show two examples of the potential distribution obtained according to a section A1-A1 in half of a cell shown in FIG. 5, according to the same conventions as for FIGS. 3 and 4;
• Figure 8 shows a cross section of a cell of a plasma panel according to a second embodiment of the invention;
• FIGS. 9 and 10 represent the distribution of the potential obtained respectively according to a section A1-A'1 in the half of a cell represented in FIG. 8 and in a section A1-A'1 in the half of a cell shown in Figure 11, still according to the same conventions as for Figures 3 and 4;
• Figure 11 shows a cross section of a cell of a plasma panel according to a third embodiment of the invention;
• Figure 12 shows a variant of the first embodiment of the invention of Figure 5, where the top of the barriers has a zone of low permittivity at the expansion areas of landfills.

The figures do not take into account a scale of values to better reveal certain details that would not be clear if the proportions had been respected.

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 the first embodiment of the invention shown in FIG. 5, the plasma panel comprises the same elements arranged according to the same structure as the panel of the prior art previously described with reference to FIGS. 1A and 1B, unlike FIG. in that the column barriers 15 comprise a base layer 15a in contact with the dielectric layer 17 covering the electrode array X of the second slab 12, and a continuous top layer 15b, which is applied to the base layer 15a and which extends to the dielectric layer 13 and the protective layer 14 covering the coplanar electrode arrays Y, Y 'of the first slab 11. Here, the coplanar electrodes each have a constant width over their entire useful length, and the electrode arrays are more economical to perform and the assembly of the slabs is not penalized by alignment constraints.

According to this embodiment, the thickness or height D _a of the base layer and the average dielectric permittivity E _a of the material which constitutes it on the one hand, the thickness or height D _b of the top layer and the permittivity dielectric average E _b of the material which constitutes the other hand, are adapted so that _E is greater than E _b and that _D is greater than D _b, of preference for _E ≥ E _b and 3 for _D 4 D ≥ _b; the top layer therefore corresponds to a continuous zone of low permittivity of the barriers; the thickness of the crown layer thus represents at most one fifth of the total height of the barriers; to obtain a significant confinement effect, the thickness of this layer should be greater than 3 μm.

As this first embodiment of the invention illustrates, the principle of the invention therefore consists in substantially lowering the capacity of the column barriers at their top, here on a small part D _b of the height of these barriers, that is to say in the vicinity of the protective layer 14 and the dielectric layer 13 on which the maintenance discharges are spread out, so that the electrical capacitance is very low in the upper part of these barriers in contact with the coplanar slab 11, and that it is higher in the other part of these barriers. This heterogeneity of electric capacitance of the barriers specific to the invention makes it possible to tighten the equipotential lines in the zone of low capacitance situated on the surface of the dielectric layer and the protective layer covering the coplanar electrodes of the slab 11, and therefore better confining the spread of maintenance discharges to the dielectric surface without "overflow" on the sides of the barriers. The higher the height D _b of the crown layer is smaller than the height of the base layer D _a and the lower the dielectric permittivity E _b of the crown layer is in front of the average dielectric permittivity E _a of the base layer, more the electric potential is low on the spreading surface of the discharges near these barriers, by capacitive divider effect resulting from the two-layer structure previously described barriers.

FIG. 6 represents the distribution of the equipotential lines obtained on this spreading surface by using a discharge cell structure according to the first embodiment just described, with E _a = 3 E _b and D _a = 4 D _b , when a voltage pulse of 100 V is applied to the Y electrode and this electrode acts as a cathode for this pulse; this distribution corresponds to the distribution of the potential at the beginning of the application of the pulse, before the priming of the discharge, according to the same assumptions and conventions as for Figures 3 and 4 previously described, the corresponding equipotential curves in solid lines to potentials positive and equipotential curves in broken lines corresponding to negative potentials; in this FIG. 4, it can be seen that the rate of confinement of the discharges illustrated by the position V of the first negative equipotential in dashed lines is close to the case of the prior art previously described with reference to FIGS. 2 and 4, where the coplanar electrodes present elements specific to each cell that are difficult and expensive to produce; thanks to this confinement, we thus obtain at a lower price an improvement at least comparable in light output and the life of the panel.

FIG. 7 represents, according to the same conventions as FIG. 6, the distribution of the equipotential lines obtained for a panel according to the first embodiment where, this time, E _a = 5 E _b and D _a = 10 D _b . The position V of the first negative equipotential is here merged with the surface of the dielectric layer and the protective layer covering the electrode Y. During maintenance periods, the discharges will therefore no longer spread over the barriers, which corresponds to the general objective pursued by the invention.

According to a variant of the first embodiment of the invention shown in Figure 12, 15b the layer of low permittivity E _b is formed atop the barrier at the level of barrier portions that correspond to the expansion zone of the discharge, so that at the barrier portions which correspond to the inter-electrode gap G and to the initiation zone, the top of the barriers has a permittivity E _a identical to that of the base layer.

According to this variant, each column separation barrier comprises, at its vertex and over its entire width, a succession of zones of low permittivity 15b 'which extend on either side of the gap separating the electrodes of each pair from a line at the boundary between the priming zone Z _a and the expansion zone Z _b , behind the priming edges 191 of the electrodes of this pair; conventionally, this boundary line is separated from the initiation edge of at most 80 microns; in other words, the width of the initiation zone Z _a is at most 80 μm; these areas of low permittivity the same thickness and the same dielectric permittivity as the zone of low permittivity previously described.

As the zone of initiation of low permittivity barrier zone discharges, it is then advantageously obtained a more uniform electric field over the entire length of the priming edges 191 of the electrodes, which advantageously allows to obtain the same properties of ignition only in the panels of the prior art previously described. In areas of landfill expansion in which the slopes of the barriers may be subject to the particles charged landfills, areas of low permittivity 15b 'according to the invention can confine landfills as described above, depending on the objective of the invention.

FIG. 8 illustrates, compared with FIG. 5, a second embodiment of the invention in which the barriers comprise a continuous top layer 15c comparable to the above-described top layer 15b; this upper layer 15c also has a small thickness D _c and a low permittivity E _c ; this upper layer 15c not only covers, as above, the top of the barriers, but here extends continuously over the entire active surface of the second slab 12; such a configuration is advantageously easier to achieve than that previously described, for example by using a screen printing method for depositing said upper layer; holding E _a = 5 E _c and D _a = 5 D _c and under the same conditions as above, a distribution of the surface potentials shown in FIG. 9 is obtained; this figure shows that the effect of confinement discharges obtained is quite comparable with that obtained with the embodiment described with reference to Figure 7. Comparing Figures 7 and 9, we see that the replacement of a top layer of the barriers by a continuous upper layer of coating of the whole of the second slab does not substantially alter the distribution of the equipotential lines, so that one always gets the benefits of the invention.

According to this embodiment, the thickness or height D _a of the base layer and the average dielectric permittivity E _a of the material constituting it. on the one hand, the thickness or height D _c of the upper layer and the mean dielectric permittivity E _c of the material which constitutes the other hand, are designed such that _E is greater than E _c and that _D is greater than D _c, preferably for _E ≥ E _c and 3 so that _D ≥ 4 D _c; the upper layer corresponds to a zone of low permittivity of the barriers; the thickness of the upper layer thus represents at most one fifth of the total height of the barriers; to obtain a significant confinement effect, the thickness of this layer should be greater than 3 μm.

For the first and second embodiments, the zone 15b or 15c of low permittivity may for example be formed by a porous layer of aluminum oxide, the remainder of the barriers namely here the base layer 15a of higher permittivity for example being formed of a vitreous layer of lead oxide.

FIG. 11 represents a third embodiment of the invention that combines the first and the second embodiments described above; the barriers thus comprise three superposed layers: a first base layer 15a of thickness D _a and of relative permittivity E _a resting on the dielectric layer 17 covering the electrode array X of the second slab 12, a second layer 15c 'of thickness D _'c and relative permittivity E' _c covering the whole of the second plate 12 as in the second embodiment, and a third layer 15b thickness D _b and E _b relative permittivity covering only the top barriers as in the first embodiment.

In addition, according to this third embodiment, E ' _c > E _a > E _b and D _a >D' _c ≥ D _b ; preferably, E ' _c ≥ 5 E _a and E _a ≥ 3 E _b , with D _a ≥ 4 D' _c and D ' _c ≥ D _b .

In addition to a zone of low permittivity at the top of the barriers as in the first and second embodiments, there is therefore here a zone of high permittivity interposed between the base of the barriers and this low permittivity zone.

In comparison with the first and second embodiments of the invention, the insertion, in the barriers, of an intermediate zone of high permittivity, namely the second layer 15c ', makes it possible to loosen and discard the lines equipotentials in the barrier zone corresponding to the first layer 15a and the second layer 15c ', so that the equipotential lines are even narrower than previously at the third layer 15b, which further improves the confinement of landfills; using E _b = E _a / 5, E ' _c = 5 E _a , D _b = D' _c = D _a / 5, we then obtain the distribution of the equipotential lines illustrated in FIG. 10, in the half width d a discharge zone, according to the same conventions as before.

For this third embodiment, the third layer of low permittivity 15b may for example be a porous layer of aluminum oxide, the first layer 15a of higher permittivity may be a vitreous layer of lead oxide and the second layer 15c 'corresponding to the intermediate zone of high permittivity may be for example a layer based on TiO2 or BaTiO3.

To produce a panel according to the invention according to any of the embodiments which have just been described, suitable materials and methods are used that are known in themselves to those skilled in the art of plasma panels.

To control the operation of the plasma panel thus obtained, it proceeds in a conventional manner using a conventional power supply system and control panel plasma.

Claims (10)

1. A plasma display panel comprising a first plate (11) and a second plate (12) leaving between them a space filled with a discharge gas and partitioned into a number of discharge cells (18) that are arranged in rows and columns, which also includes an array of insulating barrier ribs comprising barrier ribs (15) each separating two adjacent columns of cells and each having a base resting on the said second plate and a top in contact with the said first plate, this first plate including at least two arrays of coplanar electrodes (Y, Y') called sustain electrodes, which are oriented along general directions that are parallel to one another and to the said rows, which are placed so that each discharge cell is traversed by an electrode of each array, therefore forming a pair, and which have edges called initiation edges (191) which face one another on either side of the gap separating the electrodes of each pair, each column separation barrier rib comprising, at its top and over its entire width, a succession of low-permittivity regions (15b; 15c) that extend at least on each side of the gap separating the electrodes of each pair,characterized in that said regions extend at least starting from a line located 80 µm to the rear of the initiation edges (191) of the electrodes of this pair, and have a thickness (D_b; D_c) of greater than 3 µm but not exceeding one fifth of the total height of the said barrier ribs, and have a mean dielectric permittivity (E_b, E_c) at least three times smaller than the dielectric permittivity (E_a) of the said barrier ribs measured at their base.
2. The panel as claimed in claim 1, characterized in that said coplanar electrodes (Y, Y') each have a constant width over their entire useful length.
3. The panel as claimed in claim 1 or 2, characterized in that the succession of low-permittivity regions at the top of each barrier rib forms a continuous low-permittivity region.
4. The panel as claimed in claim 1 or 2, characterized in that, at the top of each barrier rib separating two columns, the low-permittivity regions are discontinuous and interrupted at the gap separating the electrodes of each pair.
5. The panel as claimed in any one of the preceding claims, characterized in that the thickness of said low-permittivity regions is at least equal to 5 µm.
6. The panel as claimed in any one of the preceding claims, characterized in that said column separating ribs furthermore have high-permittivity intermediate regions (15_c') that are intermediate between the base of the barrier ribs and said low-permittivity regions and which have a thickness (D'_c) greater than the thickness of said low-permittivity regions and a mean dielectric permittivity (E'_c) greater than the dielectric permittivity (E_a) of said barrier ribs measured at their base.
7. The panel as claimed in any of the preceding claims, characterized in that said coplanar electrodes (Y, Y') are coated with a dielectric layer (13) and which a protective/secondary-electron-emissive layer (14).
8. The panel as claimed in any one of the preceding claims, characterized in that said second plate (12) includes a third array of electrodes (X) called address electrodes, each placed on a column of cells.
9. The panel as claimed in any one of the preceding claims, characterized in that said array of barrier ribs also includes barrier ribs (16) each separating two adjacent rows of cells.
10. The panel as claimed in any one of the preceding claims, characterized in that said barrier ribs have a height of at least 100 µm.

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