EP0802559A1 - Flat panel display with hydrogen source - Google Patents

Flat panel display with hydrogen source Download PDF

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Publication number
EP0802559A1
EP0802559A1 EP97410044A EP97410044A EP0802559A1 EP 0802559 A1 EP0802559 A1 EP 0802559A1 EP 97410044 A EP97410044 A EP 97410044A EP 97410044 A EP97410044 A EP 97410044A EP 0802559 A1 EP0802559 A1 EP 0802559A1
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Prior art keywords
hydrogen
source
screen
cathode
anode
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German (de)
French (fr)
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EP0802559B1 (en
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Stéphane Mougin
Philippe Catania
Olivier Hamon
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Pixtech SA
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Pixtech SA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/86—Vessels; Containers; Vacuum locks
    • H01J29/88—Vessels; Containers; Vacuum locks provided with coatings on the walls thereof; Selection of materials for the coatings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/94—Selection of substances for gas fillings; Means for obtaining or maintaining the desired pressure within the tube, e.g. by gettering
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2201/00—Electrodes common to discharge tubes
    • H01J2201/30—Cold cathodes
    • H01J2201/304—Field emission cathodes
    • H01J2201/30403—Field emission cathodes characterised by the emitter shape
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2329/00—Electron emission display panels, e.g. field emission display panels

Definitions

  • the present invention relates to flat display screens, and more particularly to cathodoluminescence screens, the anode of which carries luminescent elements, separated from each other by insulating zones, and liable to be excited by electronic bombardment from microtips.
  • the appended figure represents an example of a color microtip flat screen of the type to which the present invention relates.
  • Such a microtip screen essentially consists of a cathode 1 with microtips 2 and a grid 3 provided with holes 4 corresponding to the locations of the microtips 2.
  • the cathode 1 is placed opposite a cathodoluminescent anode 5 including a substrate of glass 6 constitutes the screen surface.
  • microtip screen The operating principle and a particular embodiment of a microtip screen are described, in particular, in American patent n ° 4,940,916 of the French Atomic Energy Commission.
  • the cathode 1 is organized in columns and consists, on a glass substrate 10, of cathode conductors organized in meshes from a conductive layer.
  • the microtips 2 are produced on a resistive layer 11 deposited on the cathode conductors and are arranged inside the meshes defined by the cathode conductors.
  • the figure partially represents the interior of a mesh and the cathode conductors do not appear in this figure.
  • the cathode 1 is associated with the grid 3 organized in lines. The intersection of a line of the grid 3 and a column of the cathode 1 defines a pixel.
  • This device uses the electric field which is created between the cathode 1 and the grid 3 so that electrons are extracted from the microtips 2. These electrons are then attracted by phosphor elements 7 from the anode 5 if these are suitably polarized.
  • the anode 5 is provided with alternating bands of phosphor elements 7r, 7g, 7b each corresponding to a color (Red, Green, Blue). The strips are parallel to the columns of the cathode and are separated from each other by an insulator 8, generally silicon oxide (SiO 2 ).
  • the phosphors 7 are deposited on electrodes 9, made up of corresponding strips of a transparent conductive layer such as indium tin oxide (ITO).
  • ITO indium tin oxide
  • the sets of red, green and blue bands are alternately polarized with respect to the cathode 1, so that electrons extracted from the microtips 2 of a pixel of the cathode / grid are alternately directed towards the phosphors 7 opposite each of the colors.
  • the command to select the phosphor 7 (the phosphor 7g in the figure) which must be bombarded by the electrons coming from the microdots of the cathode 1 requires to selectively control the polarization of the phosphor elements 7 of the anode 5, color by color .
  • the rows of the grid 3 are sequentially polarized at a potential of the order of 80 volts, while the strips of phosphor elements (for example 7g) to be excited are polarized under a voltage of the order of 400 volts via the ITO strip on which these phosphor elements are deposited.
  • ITO bands, carrying the other bands of phosphor elements (for example 7r and 7b) are at low or zero potential.
  • the columns of cathode 1 are brought to respective potentials between a maximum emission potential and a non-emission potential (for example, 0 and 30 volts respectively). The brightness of a color component of each of the pixels of a line is thus fixed.
  • the choice of the values of the polarization potentials is linked to the characteristics of the phosphors 7 and of the microtips 2. Conventionally, below a potential difference of 50 volts between the cathode and the grid, there is no electronic emission. , and the maximum emission used corresponds to a potential difference of 80 volts.
  • a disadvantage of conventional screens is that the microtips gradually lose their emissivity. This phenomenon can be seen by measuring the current in the cathode conductors. This results in a gradual decrease in the brightness of the screen, which adversely affects the life of conventional screens.
  • the present invention aims to overcome this drawback by making the emissive power of the microtips substantially constant.
  • the present invention also aims to propose a screen with automatic regulation of the emitting power of the microtips.
  • the present invention further aims to propose a method for producing a screen, the microtips of which have a substantially constant emissive power without modifying either the structure of the screen or the means of controlling the screen.
  • the present invention provides a flat display screen comprising a microtip cathode of electron bombardment of an anode provided with phosphor elements, the anode and the cathode being separated by a vacuum space, containing a source to gradual release of hydrogen.
  • the source of hydrogen consists of a thin layer deposit of a hydrogenated material.
  • the source of hydrogen consists of a resistive layer of the cathode on which the microtips are arranged.
  • the source of hydrogen consists of isolation bands separating bands of phosphor elements from the anode.
  • the source of hydrogen is produced on the periphery of the active area of the anode carrying the phosphors, a source of excitation of said source of hydrogen being produced, cathode side, opposite of said hydrogen source.
  • the present invention also provides a method of manufacturing a flat display screen, comprising the step of hydrogenating at least one of the constituent layers formed inside this screen.
  • the hydrogenated layer is obtained by chemical vapor deposition assisted by plasma from at least one precursor enriched in hydrogen.
  • the present invention originates from an interpretation of the phenomena which give rise to the abovementioned problems in conventional screens.
  • the inventors consider that these problems are due, in particular to an oxidation of the microdots of the cathode.
  • the surface layers of the anode are, from a chemical point of view, oxides, whether they are the phosphors 7 or the insulator 8.
  • the microtips are generally metallic , for example molybdenum (Mo).
  • the oxide layers tend to shrink under the effect of electron bombardment, i.e. to release oxygen which oxidizes the surface of the microtips which then lose their emissive power.
  • the present invention proposes to control this oxidation phenomenon of the cathode microtips by introducing into the inter-electrode space of the screen, a partial pressure of hydrogen.
  • the most negative potential consists of the metallic cathode material and the H + or H 2 + ions are therefore attracted by the microtips to reduce them if they are oxidized.
  • these H + or H 2 + ions are repelled by the anode and do not risk damaging the phosphor elements.
  • the water vapor (H 2 O) formed by the recombination of the H + or H 2 + ions is then trapped by an element for trapping impurities, generally called a "getter", communicating with the inter-electrode space.
  • a microtip screen is generally provided with an element for trapping impurities whose role is to absorb various pollutions resulting from the degassing of the layers of the screen in contact with the vacuum.
  • this getter does not succeed in effectively trapping the oxygen degassed by the phosphors 7 and the insulating layers 8 insofar as these degassings are carried out essentially in a positive ionic form (O 2 + ) which then finds itself attracted to the microtips before it can be trapped by the getter.
  • the water vapor obtained by the reduction of oxygen by hydrogen ions constitutes a neutral molecule which is then no longer attracted by the microtips and can be trapped by the getter.
  • the partial pressure of hydrogen should not, however, be too high so as not to affect the operation of the screen.
  • the presence of hydrogen in the vicinity of the microtips generates the formation of a microplasma of hydrogen in the vicinity of the microtips.
  • This plasma must remain at a sufficiently low pressure and be located around the tips to do not disturb the operation of the screen. In particular, if this plasma develops, there is a risk of an arc appearing between the anode and the cathode of the screen.
  • the partial pressure of hydrogen is according to the invention chosen as a function of the inter-electrode distance and the quality of the vacuum in the screen, in particular, of the partial pressure of the oxidizing species all combined.
  • a partial hydrogen pressure of 5.10 -4 millibars (5 10 -2 Pa) constitutes a limit pressure for an inter-electrode distance of approximately 0.2 min.
  • the partial pressure of hydrogen must be maintained at the chosen level even when the hydrogen is consumed and trapped by the getter.
  • a characteristic of the present invention is to provide, inside the inter-electrode space, a source of hydrogen which gradually releases H + ions as the screen operates, ie progressively degassing of oxidizing species from the anode.
  • this source is arranged near the tips, so that the released hydrogen is not trapped by the getter before reaching the microtips.
  • the source material must be able to release hydrogen only under excitation.
  • This excitation can be thermal. In this case, the temperature rise inside the screen during its operation causes a release of hydrogen. This excitation can also result from an electronic or ionic bombardment.
  • the hydrogen source is integrated in the insulating strips 8 which separate the strips of phosphor elements from the anode.
  • the activation of the hydrogen source takes place essentially by electron bombardment.
  • some electrons emitted by the microtips touch the edges of the insulating tracks.
  • the hydrogen source is produced on the cathode side and is for example integrated into the resistive layer which supports the microtips. The activation of the source is then thermal, the cathode not being bombarded.
  • a common advantage of the two embodiments described above is that they distribute the source of hydrogen over the entire surface of the screen and thus guarantee a homogeneous antioxidant effect in the screen.
  • Another advantage is that they allow automatic regulation of the partial pressure of hydrogen in the inter-electrode space, therefore of the antioxidant means of the microtips of the cathode. Indeed, the activation (thermal or by electron bombardment) of the hydrogen source is localized in the region of the microtips which emit and which are therefore liable to be oxidized.
  • Another advantage is that they do not require any modification of the structure of the screen, but only of the conditions of deposition of the insulating tracks 8 or of the resistive layer 11, as will be seen below.
  • the deposition parameters of at least one layer chosen are adjusted to cause the incorporation of hydrogen into the material of this layer.
  • the hydrogen diffusion incorporation is adjusted as a function of the quantity of hydrogen which it is desired to see released by the material during the operation of the screen, that is to say as a function of the quality of the vacuum in the inter-electrode space, in particular the partial pressure of the oxidizing species, and the excitation means chosen for the hydrogen source.
  • the hydrogen source consists of dedicated zones, arranged outside the active zone of the screen, for example, at the periphery of the anode. An excitation source is then produced on the cathode side opposite of these dedicated areas.
  • the excitation source may consist of a microtip zone opposite the hydrogen source outside the active zone of the screen.
  • the dedicated excitation source can be controlled at regular intervals to cause regeneration of the microtips. It can also be provided that this dedicated source is controlled from a measurement of the current flowing in the cathode conductors to cause a phase of regeneration of the microtips as a function of a current threshold from which it is considered desirable. to regenerate the microtips.
  • the various layers used in the manufacture of a screen are generally deposited by a plasma assisted chemical vapor deposition (PECVD).
  • PECVD plasma assisted chemical vapor deposition
  • Such a deposition method uses mixtures of precursor compounds of the material to be deposited. It is easy to control the content of hydrogen added to the precursors. This technique makes it possible to obtain highly hydrogenated deposits and to easily control the quantity of hydrogen by varying the deposition parameters (deposition temperature, self-biasing voltage, deposition pressure, annealing temperature, etc.).
  • the choice of material used depends, in particular, on the location of the hydrogen source.
  • the hydrogen source is produced on the cathode side, it will be possible to hydrogenate the silicon usually constituting the resistive layer 11 which dispenses hydrogen.
  • the hydrogen source consists of the insulating strips 8 between the strips of phosphor elements of the anode
  • a material will be chosen which is both dielectric and easily hydrogenable, for example, silicon carbide or silicon oxide.
  • silicon nitride which also has the advantage of minimizing the oxygen contained in the insulating strips so that the hydrogen released has the task of reducing the oxidizing species degassed essentially by the phosphor elements.
  • an amorphous compound When this is compatible with the role of the layer chosen to also constitute the source of hydrogen, an amorphous compound will preferably be chosen insofar as it can generate a large quantity of hydrogen since its concentration is not limited by a crystal structure.
  • the invention has been described above in relation to a color microtip screen, it also applies to a monochrome screen. If the anode of such a monochrome screen consists of two sets of alternating bands of phosphor elements, all the embodiments described above can be implemented. On the other hand, if the anode of the monochrome screen consists of a phosphor plane, the hydrogen source will be constituted either by a dedicated source external to the active area of the screen, or by the resistive layer on the cathode side. .

Abstract

The screen has a cathode composed of microdots (2) for electron bombardment of an anode (5) provided with luminophores (7) of the primary colours. The source of progressive emission is a resistive coating (11) of hydrogenated silicon or its carbide, nitride or oxide, or hydrogenated carbon or germanium. An alternative source comprises a number of insulating strips or tracks (8) which separate the luminophores on the anode side of the evacuated space (12). Either source may be formed by plasma-enhanced chemical vapour deposition with controlled temperature, pressure or self-bias voltage.

Description

La présente invention concerne les écrans plats de visualisation, et plus particulièrement des écrans dit à cathodoluminescence, dont l'anode porte des éléments luminescents, séparés les uns des autres par des zones isolantes, et susceptibles d'être excités par un bombardement électronique provenant de micropointes.The present invention relates to flat display screens, and more particularly to cathodoluminescence screens, the anode of which carries luminescent elements, separated from each other by insulating zones, and liable to be excited by electronic bombardment from microtips.

La figure annexée représente un exemple d'écran plat couleur à micropointes du type auquel se rapporte la présente invention.The appended figure represents an example of a color microtip flat screen of the type to which the present invention relates.

Un tel écran à micropointes est essentiellement constitué d'une cathode 1 à micropointes 2 et d'une grille 3 pourvue de trous 4 correspondant aux emplacements des micropointes 2. La cathode 1 est placée en regard d'une anode cathodoluminescente 5 dont un substrat de verre 6 constitue la surface d'écran.Such a microtip screen essentially consists of a cathode 1 with microtips 2 and a grid 3 provided with holes 4 corresponding to the locations of the microtips 2. The cathode 1 is placed opposite a cathodoluminescent anode 5 including a substrate of glass 6 constitutes the screen surface.

Le principe de fonctionnement et un mode de réalisation particulier d'un écran à micropointes sont décrits, en particulier, dans le brevet américain n° 4 940 916 du Commissariat à l'Énergie Atomique.The operating principle and a particular embodiment of a microtip screen are described, in particular, in American patent n ° 4,940,916 of the French Atomic Energy Commission.

La cathode 1 est organisée en colonnes et est constituée, sur un substrat de verre 10, de conducteurs de cathode organisés en mailles à partir d'une couche conductrice. Les micropointes 2 sont réalisées sur une couche résistive 11 déposée sur les conducteurs de cathode et sont disposées à l'intérieur des mailles définies par les conducteurs de cathode. La figure représente partiellement l'intérieur d'une maille et les conducteurs de cathode n'apparaissent pas sur cette figure. La cathode 1 est associée à la grille 3 organisée en lignes. L'intersection d'une ligne de la grille 3 et d'une colonne de la cathode 1 définit un pixel.The cathode 1 is organized in columns and consists, on a glass substrate 10, of cathode conductors organized in meshes from a conductive layer. The microtips 2 are produced on a resistive layer 11 deposited on the cathode conductors and are arranged inside the meshes defined by the cathode conductors. The figure partially represents the interior of a mesh and the cathode conductors do not appear in this figure. The cathode 1 is associated with the grid 3 organized in lines. The intersection of a line of the grid 3 and a column of the cathode 1 defines a pixel.

Ce dispositif utilise le champ électrique qui est créé entre la cathode 1 et la grille 3 pour que des électrons soient extraits des micropointes 2. Ces électrons sont ensuite attirés par des éléments luminophores 7 de l'anode 5 si ceux-ci sont convenablement polarisés. Dans le cas d'un écran couleur, l'anode 5 est pourvue de bandes alternées d'éléments luminophores 7r, 7g, 7b correspondant chacune à une couleur (Rouge, Vert, Bleu). Les bandes sont parallèles aux colonnes de la cathode et sont séparées les unes des autres par un isolant 8, généralement de l'oxyde de silicium (SiO2). Les luminophores 7 sont déposés sur des électrodes 9, constituées de bandes correspondantes d'une couche conductrice transparente telle que de l'oxyde d'indium et d'étain (ITO). Les ensembles de bandes rouges, vertes, bleues sont alternativement polarisés par rapport à la cathode 1, pour que des électrons extraits des micropointes 2 d'un pixel de la cathode/grille soient alternativement dirigés vers les luminophores 7 en vis-à-vis de chacune des couleurs.This device uses the electric field which is created between the cathode 1 and the grid 3 so that electrons are extracted from the microtips 2. These electrons are then attracted by phosphor elements 7 from the anode 5 if these are suitably polarized. In the case of a color screen, the anode 5 is provided with alternating bands of phosphor elements 7r, 7g, 7b each corresponding to a color (Red, Green, Blue). The strips are parallel to the columns of the cathode and are separated from each other by an insulator 8, generally silicon oxide (SiO 2 ). The phosphors 7 are deposited on electrodes 9, made up of corresponding strips of a transparent conductive layer such as indium tin oxide (ITO). The sets of red, green and blue bands are alternately polarized with respect to the cathode 1, so that electrons extracted from the microtips 2 of a pixel of the cathode / grid are alternately directed towards the phosphors 7 opposite each of the colors.

La commande de sélection du luminophore 7 (le luminophore 7g à la figure) qui doit être bombardé par les électrons issus des micropointes de la cathode 1 impose de commander, sélectivement, la polarisation des éléments luminophores 7 de l'anode 5, couleur par couleur.The command to select the phosphor 7 (the phosphor 7g in the figure) which must be bombarded by the electrons coming from the microdots of the cathode 1 requires to selectively control the polarization of the phosphor elements 7 of the anode 5, color by color .

Généralement, les rangées de la grille 3 sont séquentiellement polarisées à un potentiel de l'ordre de 80 volts, tandis que les bandes d'éléments luminophores (par exemple 7g) devant être excités sont polarisées sous une tension de l'ordre de 400 volts par l'intermédiaire de la bande d'ITO sur laquelle ces éléments luminophores sont déposés. Les bandes d'ITO, portant les autres bandes d'éléments luminophores (par exemple 7r et 7b), sont à un potentiel faible ou nul. Les colonnes de la cathode 1 sont portées à des potentiels respectifs compris entre un potentiel d'émission maximale et un potentiel d'absence d'émission (par exemple, respectivement 0 et 30 volts). On fixe ainsi la brillance d'une composante couleur de chacun des pixels d'une ligne.Generally, the rows of the grid 3 are sequentially polarized at a potential of the order of 80 volts, while the strips of phosphor elements (for example 7g) to be excited are polarized under a voltage of the order of 400 volts via the ITO strip on which these phosphor elements are deposited. ITO bands, carrying the other bands of phosphor elements (for example 7r and 7b) are at low or zero potential. The columns of cathode 1 are brought to respective potentials between a maximum emission potential and a non-emission potential (for example, 0 and 30 volts respectively). The brightness of a color component of each of the pixels of a line is thus fixed.

Le choix des valeurs des potentiels de polarisation est lié aux caractéristiques des luminophores 7 et des micropointes 2. Classiquement, en dessous d'une différence de potentiel de 50 volts entre la cathode et la grille, il n'y a pas d'émission électronique, et l'émission maximale utilisée correspond à une différence de potentiel de 80 volts.The choice of the values of the polarization potentials is linked to the characteristics of the phosphors 7 and of the microtips 2. Conventionally, below a potential difference of 50 volts between the cathode and the grid, there is no electronic emission. , and the maximum emission used corresponds to a potential difference of 80 volts.

Un inconvénient des écrans classiques est que les micropointes perdent progressivement leur pouvoir émissif. On peut constater ce phénomène en mesurant le courant dans les conducteurs de cathode. Il en résulte une diminution progressive de la brillance de l'écran, ce qui nuit à la durée de vie des écrans classiques.A disadvantage of conventional screens is that the microtips gradually lose their emissivity. This phenomenon can be seen by measuring the current in the cathode conductors. This results in a gradual decrease in the brightness of the screen, which adversely affects the life of conventional screens.

La présente invention vise à pallier cet inconvénient en rendant sensiblement constant le pouvoir émissif des micropointes.The present invention aims to overcome this drawback by making the emissive power of the microtips substantially constant.

La présente invention vise également à proposer un écran à régulation automatique du pouvoir émissif des micropointes.The present invention also aims to propose a screen with automatic regulation of the emitting power of the microtips.

La présente invention vise en outre à proposer un procédé de réalisation d'un écran dont les micropointes ont un pouvoir émissif sensiblement constant sans modifier, ni la structure de l'écran, ni les moyens de commande de l'écran.The present invention further aims to propose a method for producing a screen, the microtips of which have a substantially constant emissive power without modifying either the structure of the screen or the means of controlling the screen.

Pour atteindre ces objets, la présente invention prévoit un écran plat de visualisation comportant une cathode à micropointes de bombardement électronique d'une anode pourvue d'éléments luminophores, l'anode et la cathode étant séparées par un espace sous vide, contenant une source à libération progressive d'hydrogène.To achieve these objects, the present invention provides a flat display screen comprising a microtip cathode of electron bombardment of an anode provided with phosphor elements, the anode and the cathode being separated by a vacuum space, containing a source to gradual release of hydrogen.

Selon un mode de réalisation de la présente invention, la source d'hydrogène est constituée d'un dépôt en couche mince d'un matériau hydrogéné.According to an embodiment of the present invention, the source of hydrogen consists of a thin layer deposit of a hydrogenated material.

Selon un mode de réalisation de la présente invention, la source d'hydrogène est constituée par une couche résistive de la cathode sur laquelle sont disposées les micropointes.According to an embodiment of the present invention, the source of hydrogen consists of a resistive layer of the cathode on which the microtips are arranged.

Selon un mode de réalisation de la présente invention, la source d'hydrogène est constituée par des bandes d'isolement séparant des bandes d'éléments luminophores de l'anode.According to an embodiment of the present invention, the source of hydrogen consists of isolation bands separating bands of phosphor elements from the anode.

Selon un mode de réalisation de la présente invention, la source d'hydrogène est réalisée en périphérie de la zone active de l'anode portant les luminophores, une source d'excitation de ladite source d'hydrogène étant réalisée, côté cathode, en regard de ladite source d'hydrogène.According to one embodiment of the present invention, the source of hydrogen is produced on the periphery of the active area of the anode carrying the phosphors, a source of excitation of said source of hydrogen being produced, cathode side, opposite of said hydrogen source.

La présente invention prévoit aussi un procédé de fabrication d'un écran plat de visualisation, comprenant l'étape consistant à hydrogéner l'une au moins des couches constitutives formées à l'intérieur de cet écran.The present invention also provides a method of manufacturing a flat display screen, comprising the step of hydrogenating at least one of the constituent layers formed inside this screen.

Selon un mode de réalisation de la présente invention, la couche hydrogénée est obtenue par un dépôt chimique en phase vapeur assisté par plasma à partir d'au moins un précurseur enrichi en hydrogène.According to an embodiment of the present invention, the hydrogenated layer is obtained by chemical vapor deposition assisted by plasma from at least one precursor enriched in hydrogen.

La présente invention a pour origine une interprétation des phénomènes qui engendrent les problèmes susmentionnés dans les écrans classiques.The present invention originates from an interpretation of the phenomena which give rise to the abovementioned problems in conventional screens.

Les inventeurs considèrent que ces problèmes sont dus, en particulier à une oxydation des micropointes de la cathode.The inventors consider that these problems are due, in particular to an oxidation of the microdots of the cathode.

Dans un écran à micropointes, les couches de surface de l'anode sont, d'un point de vue chimique, des oxydes, que ce soient les luminophores 7 ou l'isolant 8. Par contre, côté cathode, les micropointes sont généralement métalliques, par exemple en molybdène (Mo).In a microtip screen, the surface layers of the anode are, from a chemical point of view, oxides, whether they are the phosphors 7 or the insulator 8. On the other hand, on the cathode side, the microtips are generally metallic , for example molybdenum (Mo).

Les couches d'oxyde tendent à se réduire sous l'effet du bombardement électronique, c'est-à-dire à libérer de l'oxygène qui vient oxyder la surface des micropointes qui perdent alors leur pouvoir émissif.The oxide layers tend to shrink under the effect of electron bombardment, i.e. to release oxygen which oxidizes the surface of the microtips which then lose their emissive power.

A partir de cette analyse, la présente invention propose de contrôler ce phénomène d'oxydation des micropointes de la cathode en introduisant dans l'espace inter-électrodes de l'écran, une pression partielle d'hydrogène.From this analysis, the present invention proposes to control this oxidation phenomenon of the cathode microtips by introducing into the inter-electrode space of the screen, a partial pressure of hydrogen.

Dans un écran à micropointes, en fonctionnement, le potentiel le plus négatif est constitué par le matériau métallique de cathode et les ions H+ ou H2 + sont donc attirés par les micropointes pour venir les réduire si elles sont oxydées. Par contre, ces ions H+ ou H2 + sont repoussés par l'anode et ne risquent pas d'endommager les éléments luminophores.In a microtip screen, in operation, the most negative potential consists of the metallic cathode material and the H + or H 2 + ions are therefore attracted by the microtips to reduce them if they are oxidized. On the other hand, these H + or H 2 + ions are repelled by the anode and do not risk damaging the phosphor elements.

La vapeur d'eau (H2O) formée par la recombinaison des ions H+ ou H2 + est alors piégée par un élément de piégeage d'impuretés, généralement appelé "getter", communiquant avec l'espace inter-électrodes.The water vapor (H 2 O) formed by the recombination of the H + or H 2 + ions is then trapped by an element for trapping impurities, generally called a "getter", communicating with the inter-electrode space.

En effet, un écran à micropointes est généralement pourvu d'un élément de piégeage d'impuretés dont le rôle est d'absorber les pollutions diverses issues du dégazage des couches de l'écran en contact avec le vide. Cependant, dans les écrans classiques, ce getter ne parvient pas à piéger efficacement l'oxygène dégazé par les luminophores 7 et les couches isolantes 8 dans la mesure où ces dégazages s'effectuent essentiellement sous une forme ionique positive (O2 +) qui se trouve alors attirée par les micropointes avant d'avoir pu être piégée par le getter.Indeed, a microtip screen is generally provided with an element for trapping impurities whose role is to absorb various pollutions resulting from the degassing of the layers of the screen in contact with the vacuum. However, in conventional screens, this getter does not succeed in effectively trapping the oxygen degassed by the phosphors 7 and the insulating layers 8 insofar as these degassings are carried out essentially in a positive ionic form (O 2 + ) which then finds itself attracted to the microtips before it can be trapped by the getter.

A l'inverse, la vapeur d'eau obtenue par la réduction de l'oxygène par les ions d'hydrogène constitue une molécule neutre qui n'est alors plus attirée par les micropointes et peut être piégée par le getter.Conversely, the water vapor obtained by the reduction of oxygen by hydrogen ions constitutes a neutral molecule which is then no longer attracted by the microtips and can be trapped by the getter.

La pression partielle d'hydrogène ne doit cependant pas être trop élevée pour ne pas nuire au fonctionnement de l'écran. En effet, la présence d'hydrogène au voisinage des micropointes engendre la formation d'un microplasma d'hydrogène au voisinage des micropointes. Ce plasma doit rester à une pression suffisamment faible et être localisé autour des pointes pour ne pas perturber le fonctionnement de l'écran. En particulier, si ce plasma se développe, on risque de voir apparaître un arc entre l'anode et la cathode de l'écran.The partial pressure of hydrogen should not, however, be too high so as not to affect the operation of the screen. In fact, the presence of hydrogen in the vicinity of the microtips generates the formation of a microplasma of hydrogen in the vicinity of the microtips. This plasma must remain at a sufficiently low pressure and be located around the tips to do not disturb the operation of the screen. In particular, if this plasma develops, there is a risk of an arc appearing between the anode and the cathode of the screen.

La pression partielle d'hydrogène est selon l'invention choisie en fonction de la distance inter-électrodes et de la qualité du vide dans l'écran, en particulier, de la pression partielle des espèces oxydantes toutes confondues.The partial pressure of hydrogen is according to the invention chosen as a function of the inter-electrode distance and the quality of the vacuum in the screen, in particular, of the partial pressure of the oxidizing species all combined.

A titre d'exemple particulier, une pression partielle d'hydrogène de 5.10-4 millibars (5 10-2 Pa) constitue une pression limite pour une distance inter-électrodes d'environ 0,2 mn.As a particular example, a partial hydrogen pressure of 5.10 -4 millibars (5 10 -2 Pa) constitutes a limit pressure for an inter-electrode distance of approximately 0.2 min.

Cependant, la pression partielle d'hydrogène doit être maintenue au niveau choisi alors même que l'hydrogène est consommé et piégé par le getter.However, the partial pressure of hydrogen must be maintained at the chosen level even when the hydrogen is consumed and trapped by the getter.

Une caractéristique de la présente invention est de prévoir, à l'intérieur de l'espace inter-électrodes, une source d'hydrogène qui libère progressivement des ions H+ au fur et à mesure du fonctionnement de l'écran, c'est-à-dire au fur et à mesure des dégazages d'espèces oxydantes depuis l'anode.A characteristic of the present invention is to provide, inside the inter-electrode space, a source of hydrogen which gradually releases H + ions as the screen operates, ie progressively degassing of oxidizing species from the anode.

De préférence, cette source est disposée à proximité des pointes, de manière que l'hydrogène libéré ne soit pas piégé par le getter avant d'atteindre les micropointes.Preferably, this source is arranged near the tips, so that the released hydrogen is not trapped by the getter before reaching the microtips.

Pour permettre une libération progressive de l'hydrogène, le matériau de la source doit être capable de dégager de l'hydrogène uniquement sous excitation.To allow a gradual release of hydrogen, the source material must be able to release hydrogen only under excitation.

Cette excitation peut être thermique. Dans ce cas, l'élévation de température à l'intérieur de l'écran lors de son fonctionnement provoque un dégagement d'hydrogène. Cette excitation peut aussi résulter d'un bombardement électronique ou ionique.This excitation can be thermal. In this case, the temperature rise inside the screen during its operation causes a release of hydrogen. This excitation can also result from an electronic or ionic bombardment.

Selon un premier mode de réalisation de la présente invention, la source d'hydrogène est intégrée dans les bandes isolantes 8 qui séparent les bandes d'éléments luminophores de l'anode. Dans ce cas, l'activation de la source d'hydrogène s'effectue essentiellement par bombardement électronique. En effet, certains électrons émis par les micropointes touchent les bords des pistes isolantes.According to a first embodiment of the present invention, the hydrogen source is integrated in the insulating strips 8 which separate the strips of phosphor elements from the anode. In this case, the activation of the hydrogen source takes place essentially by electron bombardment. In Indeed, some electrons emitted by the microtips touch the edges of the insulating tracks.

Selon un deuxième mode de réalisation, la source d'hydrogène est réalisée côté cathode et est par exemple intégrée à la couche résistive qui supporte les micropointes. L'activation de la source est alors thermique, la cathode n'étant pas bombardée.According to a second embodiment, the hydrogen source is produced on the cathode side and is for example integrated into the resistive layer which supports the microtips. The activation of the source is then thermal, the cathode not being bombarded.

Un avantage commun aux deux modes de réalisation décrits ci-dessus est qu'ils répartissent la source d'hydrogène sur toute la surface de l'écran et garantissent ainsi un effet antioxydant homogène dans l'écran.A common advantage of the two embodiments described above is that they distribute the source of hydrogen over the entire surface of the screen and thus guarantee a homogeneous antioxidant effect in the screen.

Un autre avantage est qu'ils permettent une régulation automatique de la pression partielle d'hydrogène dans l'espace inter-électrodes, donc du moyen antioxydant des micropointes de la cathode. En effet, l'activation (thermique ou par bombardement électronique) de la source d'hydrogène est localisée dans la région des micropointes qui émettent et qui sont donc susceptibles d'être oxydées.Another advantage is that they allow automatic regulation of the partial pressure of hydrogen in the inter-electrode space, therefore of the antioxidant means of the microtips of the cathode. Indeed, the activation (thermal or by electron bombardment) of the hydrogen source is localized in the region of the microtips which emit and which are therefore liable to be oxidized.

Un autre avantage est qu'ils ne nécessitent aucune modification de la structure de l'écran, mais uniquement des conditions de dépôts des pistes isolantes 8 ou de la couche résistive 11, comme on le verra ci-après.Another advantage is that they do not require any modification of the structure of the screen, but only of the conditions of deposition of the insulating tracks 8 or of the resistive layer 11, as will be seen below.

Selon l'invention, on ajuste les paramètres de dépôt d'au moins une couche choisie pour provoquer l'incorporation d'hydrogène dans le matériau de cette couche. L'incorporation diffusion d'hydrogène est ajustée en fonction de la quantité d'hydrogène que l'on souhaite voir libérer par le matériau lors du fonctionnement de l'écran, c'est-à-dire en fonction de la qualité du vide dans l'espace inter-électrodes, en particulier de la pression partielle des espèces oxydantes, et du moyen d'excitation choisi pour la source d'hydrogène.According to the invention, the deposition parameters of at least one layer chosen are adjusted to cause the incorporation of hydrogen into the material of this layer. The hydrogen diffusion incorporation is adjusted as a function of the quantity of hydrogen which it is desired to see released by the material during the operation of the screen, that is to say as a function of the quality of the vacuum in the inter-electrode space, in particular the partial pressure of the oxidizing species, and the excitation means chosen for the hydrogen source.

Selon un troisième mode de réalisation, la source d'hydrogène est constituée de zones dédiées, disposées hors de la zone active de l'écran, par exemple, en périphérie de l'anode. Une source d'excitation est alors réalisée côté cathode en regard de ces zones dédiées. La source d'excitation peut être constituée d'une zone de micropointes en regard de la source d'hydrogène hors de la zone active de l'écran.According to a third embodiment, the hydrogen source consists of dedicated zones, arranged outside the active zone of the screen, for example, at the periphery of the anode. An excitation source is then produced on the cathode side opposite of these dedicated areas. The excitation source may consist of a microtip zone opposite the hydrogen source outside the active zone of the screen.

Si un tel mode de réalisation requiert de modifier la structure de l'écran, il présente l'avantage de fournir un moyen antioxydant commandable indépendamment du fonctionnement de l'écran. Ainsi, on peut prévoir que la source d'excitation dédiée soit commandée à intervalles réguliers pour provoquer une régénération des micropointes. On peut également prévoir que cette source dédiée soit commandée à partir d'une mesure du courant circulant dans les conducteurs de cathode pour provoquer une phase de régénération des micropointes en fonction d'un seuil de courant à partir duquel on considère qu'il est souhaitable de régénérer les micropointes.If such an embodiment requires modifying the structure of the screen, it has the advantage of providing an antioxidant means which can be controlled independently of the functioning of the screen. Thus, provision can be made for the dedicated excitation source to be controlled at regular intervals to cause regeneration of the microtips. It can also be provided that this dedicated source is controlled from a measurement of the current flowing in the cathode conductors to cause a phase of regeneration of the microtips as a function of a current threshold from which it is considered desirable. to regenerate the microtips.

On indiquera par la suite plusieurs exemples de matériaux qui peuvent être choisis pour constituer la source d'hydrogène.Several examples of materials which can be chosen to constitute the source of hydrogen will be indicated below.

Le dépôt des diverses couches utilisées dans la fabrication d'un écran s'effectue généralement par un dépôt chimique en phase vapeur assisté par plasma (PECVD). Un tel mode de dépôt utilise des mélanges de composés précurseurs du matériau à déposer. Il est aisé de contrôler la teneur en hydrogène ajouté aux précurseurs. Cette technique permet l'obtention de dépôts fortement hydrogénés et de contrôler aisément la quantité d'hydrogène en jouant sur les paramètres de dépôt (température de dépôt, tension d'auto-polarisation, pression de dépôt, température de recuit, etc.).The various layers used in the manufacture of a screen are generally deposited by a plasma assisted chemical vapor deposition (PECVD). Such a deposition method uses mixtures of precursor compounds of the material to be deposited. It is easy to control the content of hydrogen added to the precursors. This technique makes it possible to obtain highly hydrogenated deposits and to easily control the quantity of hydrogen by varying the deposition parameters (deposition temperature, self-biasing voltage, deposition pressure, annealing temperature, etc.).

Parmi les matériaux qui sont susceptibles d'être déposés avec un fort pourcentage d'hydrogène et de perdre cet hydrogène sous une activation thermique, ionique ou électronique, on trouve en particulier les matériaux à base de silicium hydrogéné, de carbure de silicium hydrogéné, de nitrure de silicium hydrogéné, d'oxyde de silicium hydrogéné, de carbone hydrogéné, de germanium hydrogéné et d'oxynitrure hydrogéné.Among the materials which are liable to be deposited with a high percentage of hydrogen and to lose this hydrogen under thermal, ionic or electronic activation, there are in particular materials based on hydrogenated silicon, hydrogenated silicon carbide, hydrogenated silicon nitride, hydrogenated silicon oxide, hydrogenated carbon, hydrogenated germanium and hydrogenated oxynitride.

Le choix du matériau utilisé dépend, en particulier, du lieu de la source d'hydrogène.The choice of material used depends, in particular, on the location of the hydrogen source.

Si la source d'hydrogène est réalisée côté cathode, on pourra hydrogéner le silicium constituant habituellement la couche résistive 11 qui dispense de l'hydrogène.If the hydrogen source is produced on the cathode side, it will be possible to hydrogenate the silicon usually constituting the resistive layer 11 which dispenses hydrogen.

Si la source d'hydrogène est constituée par les bandes isolantes 8 entre les bandes d'éléments luminophores de l'anode, on choisira un matériau qui soit à la fois diélectrique et facilement hydrogénable, par exemple, du carbure de silicium ou de l'oxyde de silicium. On pourra également choisir du nitrure de silicium qui présente en outre l'avantage de minimiser l'oxygène contenu dans les bandes isolantes de sorte que l'hydrogène libéré a pour tâche de réduire les espèces oxydantes dégazées essentiellement par les éléments luminophores.If the hydrogen source consists of the insulating strips 8 between the strips of phosphor elements of the anode, a material will be chosen which is both dielectric and easily hydrogenable, for example, silicon carbide or silicon oxide. We can also choose silicon nitride which also has the advantage of minimizing the oxygen contained in the insulating strips so that the hydrogen released has the task of reducing the oxidizing species degassed essentially by the phosphor elements.

Lorsque cela est compatible avec le rôle de la couche choisie pour constituer également la source d'hydrogène, on choisira, de préférence, un composé amorphe dans la mesure où il peut engendrer une quantité d'hydrogène importante car sa concentration n'est pas limitée par une structure cristalline.When this is compatible with the role of the layer chosen to also constitute the source of hydrogen, an amorphous compound will preferably be chosen insofar as it can generate a large quantity of hydrogen since its concentration is not limited by a crystal structure.

On peut également combiner l'effet antioxydant avec un effet de matriçage de l'anode qui améliore le contraste de l'écran. Un tel matriçage est généralement désigné par son appellation anglo-saxonne "black matrix" et crée des zones noires entre les bandes d'éléments luminophores de l'anode. Pour ce faire, on utilisera, par exemple, un composé à base de carbone hydrogéné pour réaliser les bandes 8.We can also combine the antioxidant effect with an anode matrixing effect which improves the contrast of the screen. Such matrixing is generally designated by its Anglo-Saxon designation "black matrix" and creates black zones between the bands of phosphor elements of the anode. To do this, use will be made, for example, of a compound based on hydrogenated carbon to produce the strips 8.

Bien entendu, la présente invention est susceptible de diverses variantes et modifications qui apparaîtront à l'homme de l'art. En particulier, l'adaptation du procédé de fabrication d'un écran plat pour mettre en oeuvre la présente invention est à la portée de l'homme de l'art en fonction des indications fonctionnelles données ci-dessus.Of course, the present invention is susceptible of various variants and modifications which will appear to those skilled in the art. In particular, the adaptation of the method of manufacturing a flat screen to implement the present invention is within the reach of those skilled in the art according to the functional indications given above.

De plus, bien que l'invention ait été décrite ci-dessus en relation avec un écran couleur à micropointes, elle s'applique également à un écran monochrome. Si l'anode d'un tel écran monochrome est constituée de deux ensembles de bandes alternées d'éléments luminophores, tous les modes de réalisation décrits ci-dessus peuvent être mis en oeuvre. Par contre, si l'anode de l'écran monochrome est constituée d'un plan de luminophores, la source d'hydrogène sera constituée soit par une source dédiée externe à la zone active de l'écran, soit par la couche résistive côté cathode.In addition, although the invention has been described above in relation to a color microtip screen, it also applies to a monochrome screen. If the anode of such a monochrome screen consists of two sets of alternating bands of phosphor elements, all the embodiments described above can be implemented. On the other hand, if the anode of the monochrome screen consists of a phosphor plane, the hydrogen source will be constituted either by a dedicated source external to the active area of the screen, or by the resistive layer on the cathode side. .

Claims (6)

Écran plat de visualisation comportant une cathode à micropointes de bombardement électronique d'une anode (5) pourvue d'éléments luminophores (7), l'anode (5) et la cathode (1) étant séparées par un espace sous vide (12), caractérisé en ce qu'il contient une source à libération progressive d'hydrogène, constituée d'un dépôt en couche mince d'un matériau hydrogéné.Flat display screen comprising a microtip cathode for electron bombardment of an anode (5) provided with phosphor elements (7), the anode (5) and the cathode (1) being separated by a vacuum space (12) , characterized in that it contains a progressive release source of hydrogen, consisting of a thin layer deposit of a hydrogenated material. Écran selon la revendication 1, caractérisé en ce que ladite source d'hydrogène est constituée par une couche résistive (11) de la cathode (1) sur laquelle sont disposées les micropointes (2).Screen according to claim 1, characterized in that said source of hydrogen consists of a resistive layer (11) of the cathode (1) on which the microtips (2) are arranged. Écran selon la revendication 1, caractérisé en ce que ladite source d'hydrogène est constituée par des bandes d'isolement (8) séparant des bandes d'éléments luminophores (7) de l'anode (5).Screen according to claim 1, characterized in that said hydrogen source is constituted by isolation strips (8) separating strips of phosphor elements (7) from the anode (5). Écran selon la revendication 1, caractérisé en ce que ladite source d'hydrogène est réalisée en périphérie de la zone active de l'anode (5) portant les luminophores (7), une source d'excitation de ladite source d'hydrogène étant réalisée, côté cathode (11), en regard de ladite source d'hydrogène.Screen according to claim 1, characterized in that said source of hydrogen is produced on the periphery of the active area of the anode (5) carrying the phosphors (7), a source of excitation of said source of hydrogen being produced , cathode side (11), facing said source of hydrogen. Procédé de fabrication d'un écran plat de visualisation, caractérisé en ce qu'il comprend l'étape consistant à hydrogéner l'une au moins des couches constitutives formées à l'intérieur de cet écran.A method of manufacturing a flat display screen, characterized in that it comprises the step consisting in hydrogenating at least one of the constituent layers formed inside this screen. Procédé selon la revendication 5, caractérisé en ce que ladite couche est obtenue par un dépôt chimique en phase vapeur assisté par plasma à partir d'au moins un précurseur enrichi en hydrogène.A method according to claim 5, characterized in that said layer is obtained by a chemical vapor deposition assisted by plasma from at least one precursor enriched in hydrogen.
EP97410044A 1996-04-18 1997-04-15 Flat panel display with hydrogen source Revoked EP0802559B1 (en)

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