EP0401068A1 - Impregnated thermionic cathode for electron tube - Google Patents

Impregnated thermionic cathode for electron tube Download PDF

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Publication number
EP0401068A1
EP0401068A1 EP90401216A EP90401216A EP0401068A1 EP 0401068 A1 EP0401068 A1 EP 0401068A1 EP 90401216 A EP90401216 A EP 90401216A EP 90401216 A EP90401216 A EP 90401216A EP 0401068 A1 EP0401068 A1 EP 0401068A1
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Prior art keywords
layer
cathode
micrometers
thermoelectronic
emissive
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German (de)
French (fr)
Inventor
Arvind Shroff
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Thales Electron Devices SA
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Thomson Tubes Electroniques
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/13—Solid thermionic cathodes
    • H01J1/20—Cathodes heated indirectly by an electric current; Cathodes heated by electron or ion bombardment
    • H01J1/28—Dispenser-type cathodes, e.g. L-cathode

Definitions

  • thermo-electronic cathode impregnated for electronic tube such as a tube with localized interaction (triode or tube with more than 3 electrodes) or with distributed interaction (klystron, traveling wave tube, magnetron, gyrotron, etc. ).
  • thermoelectronic cathodes which can emit, under certain conditions of manufacture and operating temperature, current densities of up to 10 to 12 A / cm2.
  • cathodes are made from a porous Tungsten matrix whose porosity, which is low and of the order of 18% to fix ideas, is completely random. This porous body is impregnated with Barium aluminates and Calcium. A mixture is then obtained which, melting at high temperature, has the advantage of remaining solid at the operating temperature of these cathodes which is generally between 980 and 1100 degrees centigrade.
  • the diameter of the pore tends, up to a certain depth which can go up to 200 micrometers, to decrease due to the chemical reactions between Tungsten and Aluminates of Barium and Calcium, which decreases the conductance correspondingly and leads to the need for a higher pressure of Barium so that the latter can migrate towards the surface of the cathode.
  • the channel which constitutes the pore has thus narrowed to a height greater than 200 micrometers, the Barium can no longer rise, despite the use of a higher pressure, so that the cathode can no longer function.
  • thermoelectronic cathode comprising inside a cylindrical envelope, made of molybdenum for example, a heating filament located in the lower part of this envelope and, in the upper part of the latter, a chamber filled with a certain amount of a porous material which comprises two separate superimposed parts, namely a first part made of porous material impregnated with emissive material covered with a second part made of porous material not impregnated.
  • cathodes have the disadvantage of being difficult to produce technologically.
  • the presence at the front of the emissive matrix of a thick porous element can be a source of restarting problems for these cathodes due to the gases which are likely to be absorbed in this porous element.
  • the invention relates to an impregnated thermoelectronic cathode which does not have the aforementioned drawbacks of impregnated cathodes known hitherto and which moreover allows better migration of the emissive material on its surface.
  • This cathode is of the type comprising, inside a generally cylindrical envelope made of molybdenum for example, a heating filament located in the lower part of this envelope and, in the upper part of this same envelope, a chamber filled with a porous material impregnated with emissive material.
  • This porous material is covered, to form the emissive surface of the cathode, with a layer of a non-porous refractory metal and artificially pierced with a set of fine slits which are distributed in an orderly manner and so as to obtain, for this cathode, a determined surface porosity, for example a low porosity of the order of 16 to 21%, capable of allowing the migration of the emissive product (in this case Barium) over the entire emissive surface of this cathode.
  • a determined surface porosity for example a low porosity of the order of 16 to 21%
  • the minimum distance which separates two neighboring slits must be sufficient (preferably just sufficient) to allow this migration, and typically has a value of the order of one to two tens of micrometers.
  • this impregnated cathode is constituted by a tube 1 made of molybdenum, divided into two cavities by a transverse disc 2, also made of molybdenum: . a lower cavity which contains the heating filament 3; . an upper cavity which contains a body 4 of porous Tungsten impregnated with Barium aluminates and Calcium.
  • the porous body 4 is covered, to form the emissive surface of the cathode, with a layer 5 of non-porous Tungsten and pierced, by etching, of a set of fine slots 6 which, as seen more precisely in FIG. 2, are regularly distributed over the surface of this metal layer 5.
  • Layer 5 is relatively thick, its thickness being for example between 100 and 250 micrometers.
  • the slits 6, which each typically have a length of the order of 20 micrometers and a width of the order of 5 micrometers, are distributed in an orderly fashion over the surface of the layer 5, so that the distance d which separates two neighboring slits (see FIG. 3 which is an enlarged view of detail A in FIG. 2) is advantageously calculated to be substantially equal to twice the minimum migration distance of the Barium on the surface of the cathode (emissive surface), when the 'This cathode is heated by carrying the filament 3 to incandescent. This distance d is of the order of one to two tens of micrometers.
  • the porous body 4 is on the contrary chosen to be of high porosity, its porosity being for example greater than 30%.
  • this layer 5 is deposited by the conventional process of chemical decomposition in the gas phase, or CVD ("Chemical Vapor Deposition "), more precisely by reduction of Sulfur Hexafluoride by Hydrogen, at low pressure and temperature.
  • the slots 6 are obtained by reactive ion machining, or "reactive ion etching under plasma", using either an Argon-Chlorine mixture, or a mixture of Sulfur Hexafluoride, Argon, and Oxygen, or a mixture of Sulfur Hexafluoride and Oxygen, by conventional photogravure or chemical etching techniques.
  • FIGS. 4 to 9 illustrate a practical example of the thermoelectronic cathode of FIG. 1.
  • This body 4 is then covered, by chemical decomposition in the gas phase, with a layer 5 of non-porous tungsten, with a thickness of the order of 100 to 200 micrometers.
  • a thin film of aluminum is then deposited with a thickness of a few micrometers (typically of the order of 2 to 5 micrometers).
  • FIG. 7 After elimination of the photosensitive resin 8, there remains (FIG. 7) on the layer of Tungsten 5, a mask 7 of Aluminum, of shape identical to that of the filter 5 (FIG. 2) to be obtained.
  • the production of the mask 7 made of aluminum (or other metal, such as chromium, able to resist sulfur hexafluoride) is required by the fact that the known photosensitive resins do not resist not to reactive ion etching operations under plasma.
  • the machining (FIG. 8) of the layer of Tungsten 5 is then carried out by reactive ion etching under plasma, under reduced pressure of a mixture of the three gases: Argon, Oxygen and Sulfur Hexafluoride.
  • the attack speed depending on the partial pressure in the enclosure used and the applied voltage, is of the order of 1 to 10 micrometers per minute.
  • the body 4 After a chemical cleaning carried out to remove the excess of Barium aluminate over the thickness of the etched layer 5, the body 4 is placed in the molybdenum tube 1, and the heating filament 3 is also put in place.
  • the layer, non-porous and with a thickness at least equal to 100 micrometers, 5 can be made of another refractory metal than Tungsten, for example Rhenium, Iridium, and Osmium, which are all metals well suited to the thermoelectronic emission phenomenon of cathodes.
  • This same upper layer 5 with ordered porosity can also be made of an alloy refractory, for example a Tungsten-Osmium, Tungsten-Iridium, or Tungsten-Rhenium alloy.
  • layer 5 can of course also consist of an added layer and therefore ultimately independent of the porous body.

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Abstract

Cathode comprising a matrix (4) made of a porous material impregnated with an emissive product (aluminates of barium and of calcium). The porous body (4) is covered with a layer (5) of a non-porous refractory material and has prescribed porosity thanks to a set of narrow slots (6) obtained by etching. This layer is advantageously obtained by chemical vapour-phase deposition (C.V.D.) and has a thickness of the order of one to several hundred micrometres. <IMAGE>

Description

La présente invention se rapporte à une cathode thermo-électronique imprègnée pour tube électronique tel qu'un tube à interaction localisée (triode ou tube à plus de 3 électrodes) ou à interaction répartie (klystron, tube à ondes progressives, magnetron, gyrotron, etc...).The present invention relates to a thermo-electronic cathode impregnated for electronic tube such as a tube with localized interaction (triode or tube with more than 3 electrodes) or with distributed interaction (klystron, traveling wave tube, magnetron, gyrotron, etc. ...).

La majorité des tubes électroniques réalisés à l'heure actuelle utilisent des cathodes thermo-­électroniques imprègnées qui peuvent émettre, sous certaines conditions de fabrication et de température de fonctionnement, des densités de courant pouvant aller jusqu'à 10 à 12 A/cm².The majority of electronic tubes produced today use impregnated thermoelectronic cathodes which can emit, under certain conditions of manufacture and operating temperature, current densities of up to 10 to 12 A / cm².

Ces cathodes sont fabriquées à partir d'une matrice en Tungstène poreux dont la porosité, qui est faible et de l'ordre de 18% pour fixer les idées, est totalement aléatoire. Ce corps poreux est imprègné à l'aide d'Aluminates de Barium et de Calcium. On obtient alors un mélange qui, fondant à haute température, a l'avantage de rester solide à la température de fonctionnement de ces cathodes qui est généralement comprise entre 980 et 1100 degrés centigrade.These cathodes are made from a porous Tungsten matrix whose porosity, which is low and of the order of 18% to fix ideas, is completely random. This porous body is impregnated with Barium aluminates and Calcium. A mixture is then obtained which, melting at high temperature, has the advantage of remaining solid at the operating temperature of these cathodes which is generally between 980 and 1100 degrees centigrade.

A ces températures, il se produit, entre les Aluminates et le Tungstène poreux, une réaction chimique dont le résultat est de libérer du Barium, ce dernier venant migrer sur la surface émissive de la cathode pour finalement la recouvrir totalement en créant, avec de l'Oxygène qui est généré dans le corps poreux, des dipoles Barium-Oxygène. Cela a pour résultat de diminuer le travail de sortie des électrons, et par suite de leur permettre de franchir la barrière de potentiel, et par conséquent de partir du solide vers le vide.At these temperatures, a chemical reaction takes place between the aluminates and the porous tungsten, the result of which is to release the Barium, the latter migrating onto the emissive surface of the cathode and finally covering it completely, creating with l 'Oxygen that is generated in the porous body, Barium-Oxygen dipoles. This has the result of reducing the work of output of the electrons, and consequently of allowing them to cross the barrier of potential, and consequently to leave from the solid towards the vacuum.

La durée de vie de ces cathodes imprègnées est cependant limitée par le fait qu'on est amené à les chauffer à des températures de plus en plus élevées, ce qui favorise l'évaporation de la matière émissive et la modification métallurgique du corps poreux.En début de vie, les pores ont, en surface, une forme généralement lenticulaire, plutôt allongée, ce qui permet au Barium de migrer sur une assez grande surface. Au cours de la durée, et en particulier si l'on chauffe trop la cathode, ces pores allongés tendent à se fragmenter pour finalement se transformer en des pores circulaires plus petits et plus éloignés les uns des autres : la porosité en surface diminue, de sorte que la migration du Barium y devient plus difficile.The lifetime of these impregnated cathodes is however limited by the fact that they are brought to heat them at increasingly higher temperatures, which which promotes the evaporation of the emissive material and the metallurgical modification of the porous body. At the beginning of life, the pores have, on the surface, a generally lenticular shape, rather elongated, which allows the Barium to migrate over a fairly large area. Over time, and in particular if the cathode is heated too much, these elongated pores tend to fragment and ultimately transform into smaller circular pores which are more distant from each other: the surface porosity decreases, by so that the migration of the Barium becomes more difficult there.

Simultanément, une évolution importante s'effectue dans le volume de ce corps poreux : le diamètre du pore tend, jusqu'à une certaine profondeur pouvant aller jusqu'à 200 micromètres, à diminuer du fait des réactions chimiques entre le Tungstène et les Aluminates de Barium et de Calcium, ce qui diminue d'autant la conductance et entraîne la nécessité d'une pression plus élevée de Barium pour que ce dernier puisse migrer vers la surface de la cathode. Lorsque le canal qui constitue le pore s'est ainsi rétréci sur une hauteur supérieure à 200 micromètres, le Barium n'arrive plus à monter, malgré l'utilisation d'une pression plus élevée, de sorte que la cathode ne peut plus fonctionner.
Pour combattre ce phénomène, un moyen connu consiste à séparer la région où s'effectue la réaction chimique et la région qui sert effectivement à l'émission thermo-­électronique. Comme illustration de ce genre de solution peut être cité le document EP-A-52047, qui concerne spécifiquement une cathode thermo-électronique comprenant à l'intérieur d'une enveloppe cylindrique, en molybdène par exemple, un filament chauffant situé dans la partie inférieure de cette enveloppe et, dans la partie supérieure de cette dernière, une chambre remplie d'une certaine quantité d'un matériau poreux qui comprend deux parties distinctes superposées, à savoir une première partie en un matériau poreux imprègné de matière émissive recouverte d'une seconde partie en matériau poreux non imprègné.Simultaneously, an important evolution takes place in the volume of this porous body: the diameter of the pore tends, up to a certain depth which can go up to 200 micrometers, to decrease due to the chemical reactions between Tungsten and Aluminates of Barium and Calcium, which decreases the conductance correspondingly and leads to the need for a higher pressure of Barium so that the latter can migrate towards the surface of the cathode. When the channel which constitutes the pore has thus narrowed to a height greater than 200 micrometers, the Barium can no longer rise, despite the use of a higher pressure, so that the cathode can no longer function.
To combat this phenomenon, a known means consists in separating the region where the chemical reaction takes place and the region which is actually used for thermoelectronic emission. As an illustration of this kind of solution can be cited the document EP-A-52047, which specifically relates to a thermoelectronic cathode comprising inside a cylindrical envelope, made of molybdenum for example, a heating filament located in the lower part of this envelope and, in the upper part of the latter, a chamber filled with a certain amount of a porous material which comprises two separate superimposed parts, namely a first part made of porous material impregnated with emissive material covered with a second part made of porous material not impregnated.

De telles cathodes ont cependant pour inconvénient d'être de réalisation technologique difficile. En outre, la présence à l'avant de la matrice émissive d'un élément poreux épais peut être source de problèmes de redémarrage de ces cathodes en raison des gaz qui risquent d'être absorbés dans cet élément poreux.However, such cathodes have the disadvantage of being difficult to produce technologically. In addition, the presence at the front of the emissive matrix of a thick porous element can be a source of restarting problems for these cathodes due to the gases which are likely to be absorbed in this porous element.

L'invention se rapporte à une cathode thermo-­électronique imprègnée qui ne présente pas les inconvénients précités des cathodes imprègnées connues jusqu'alors et qui permet de surcroît une meilleure migration de la matière émissive sur sa surface. Cette cathode est du type comprenant, à l'intérieur d'une enveloppe généralement cylindrique constituée en molybdène par exemple, un filament chauffant situé dans la partie inférieure de cette enveloppe et, dans la partie supérieure de cette même enveloppe, une chambre remplie d'un matériau poreux imprègné de matière émissive. Ce matériau poreux est recouvert, pour former la surface émissive de la cathode, d'une couche d'un métal réfractaire non poreux et percé artificiellement d'un ensemble de fines fentes qui sont réparties de manière ordonnée et de façon à obtenir, pour cette cathode, une porosité de surface déterminée, par exemple une porosité faible de l'ordre de 16 à 21%, apte à permettre la migration du produit émissif (en l'occurrence le Barium) sur toute la surface émissive de cette cathode.
Il s'agit typiquement d'une couche d'une épaisseur de l'ordre d'une centaine à quelques centaines de micromètres, qui est de préférence déposée par décomposition chimique en phase gazeuse, ou C.V.D. ("Chemical Vapour Deposition"), de manière à réaliser un continuum entre la matrice poreuse imprègnée de matière émissive et ce filtre supérieur à porosité ordonnée.
Les fines fentes dont il s'agit sont typiquement obtenues par photogravure. Elles ont par exemple chacune une dimension de l'ordre de 5 x 20 micromètres, et elles sont régulièrement réparties de façon à permettre la migration du Barium sur l'intégralité de la surface de la cathode : de ce fait, la distance minimale qui sépare deux fentes voisines doit être suffisante (préférentiellement juste suffisante) pour permettre cette migration, et a typiquement une valeur de l'ordre de une à deux dizaines de micromètres.The invention relates to an impregnated thermoelectronic cathode which does not have the aforementioned drawbacks of impregnated cathodes known hitherto and which moreover allows better migration of the emissive material on its surface. This cathode is of the type comprising, inside a generally cylindrical envelope made of molybdenum for example, a heating filament located in the lower part of this envelope and, in the upper part of this same envelope, a chamber filled with a porous material impregnated with emissive material. This porous material is covered, to form the emissive surface of the cathode, with a layer of a non-porous refractory metal and artificially pierced with a set of fine slits which are distributed in an orderly manner and so as to obtain, for this cathode, a determined surface porosity, for example a low porosity of the order of 16 to 21%, capable of allowing the migration of the emissive product (in this case Barium) over the entire emissive surface of this cathode.
It is typically a layer with a thickness of the order of a hundred to a few hundred micrometers, which is preferably deposited by chemical decomposition in the gas phase, or CVD ("Chemical Vapor Deposition"), so as to create a continuum between the porous matrix impregnated with emissive material and this superior filter with ordered porosity.
The fine slits in question are typically obtained by photoengraving. They each have, for example, a dimension of the order of 5 × 20 micrometers, and they are regularly distributed so as to allow the migration of the Barium over the entire surface of the cathode: therefore, the minimum distance which separates two neighboring slits must be sufficient (preferably just sufficient) to allow this migration, and typically has a value of the order of one to two tens of micrometers.

De toute façon, l'invention sera bien comprise, et ses avantages et autres caractéristiques ressortiront, lors de la description suivante d'un exemple non limitatif de réalisation d'une telle cathode imprègnée à surface émissive de porosité ordonnée, en référence au dessin schématique annexé dans lequel :

  • - Figure 1 est une vue en coupe longitudinale de cette cathode ;
  • - Figure 2 est une vue de dessus de la cathode selon cette figure 1 ;
  • - Figure 3 est une vue de détail agrandie de la face supérieure de cette cathode ; et
  • - Figures 4 à 9 montrent les étapes essentielles de sa fabrication, utilisant une technique de photogravure.
In any case, the invention will be well understood, and its advantages and other characteristics will emerge during the following description of a nonlimiting example of embodiment of such an impregnated cathode with an emissive surface of ordered porosity, with reference to the schematic drawing. annexed in which:
  • - Figure 1 is a longitudinal sectional view of this cathode;
  • - Figure 2 is a top view of the cathode according to this Figure 1;
  • - Figure 3 is an enlarged detail view of the upper face of this cathode; and
  • - Figures 4 to 9 show the essential stages of its manufacture, using a photoengraving technique.

En se reportant à la figure 1, cette cathode imprègnée est constituée par un tube 1 en molybdène, divisé en deux cavités par un disque transversal 2, en molybdène lui-aussi :
. une cavité inférieure qui contient le filament chauffant 3 ;
. une cavité supérieure qui contient un corps 4 en Tungstène poreux imprègné d'Aluminates de Barium et de Calcium.Referring to FIG. 1, this impregnated cathode is constituted by a tube 1 made of molybdenum, divided into two cavities by a transverse disc 2, also made of molybdenum:
. a lower cavity which contains the heating filament 3;
. an upper cavity which contains a body 4 of porous Tungsten impregnated with Barium aluminates and Calcium.

Conformément à l'invention, le corps poreux 4 est recouvert, pour former la surface émissive de la cathode, d'une couche 5 de Tungstène non poreux et percée, par gravure, d'un ensemble de fines fentes 6 qui, comme on le voit plus précisément sur la figure 2, sont régulièrement réparties sur la surface de cette couche métallique 5.According to the invention, the porous body 4 is covered, to form the emissive surface of the cathode, with a layer 5 of non-porous Tungsten and pierced, by etching, of a set of fine slots 6 which, as seen more precisely in FIG. 2, are regularly distributed over the surface of this metal layer 5.

La couche 5 est relativement épaisse, son épaisseur étant par exemple comprise entre 100 et 250 micromètres. Les fentes 6, qui ont typiquement chacune une longueur de l'ordre de 20 micromètres et une largeur de l'ordre de 5 micromètres, sont réparties de manière ordonnée sur la surface de la couche 5, de façon que la distance d qui sépare deux fentes voisines (voir la figure 3 qui est une vue agrandie du détail A de la figure 2) soit avantageusement calculée pour être sensiblement égale au double de la distance minimale de migration du Barium sur la surface de la cathode (surface émissive), lorsque l'on chauffe cette cathode en portant le filament 3 à incandescence. Cette distance d est de la sorte de l'ordre de une à deux dizaines de micromètres.Layer 5 is relatively thick, its thickness being for example between 100 and 250 micrometers. The slits 6, which each typically have a length of the order of 20 micrometers and a width of the order of 5 micrometers, are distributed in an orderly fashion over the surface of the layer 5, so that the distance d which separates two neighboring slits (see FIG. 3 which is an enlarged view of detail A in FIG. 2) is advantageously calculated to be substantially equal to twice the minimum migration distance of the Barium on the surface of the cathode (emissive surface), when the 'This cathode is heated by carrying the filament 3 to incandescent. This distance d is of the order of one to two tens of micrometers.

Il en résulte pour cette surface émissive, une porosité ordonnée de l'ordre de 18 à 20%, donc plutôt faible, ce qui correspond à environ 800.000 fentes par centimètre carré.The result for this emissive surface, an ordered porosity of the order of 18 to 20%, therefore rather low, which corresponds to about 800,000 slots per square centimeter.

De façon à lui permettre de contenir un maximum de matière émissive, le corps poreux 4 est à contrario choisi de forte porosité, sa porosité étant par exemple supérieure à 30%.In order to allow it to contain a maximum of emissive material, the porous body 4 is on the contrary chosen to be of high porosity, its porosity being for example greater than 30%.

Avantageusement, de façon à réaliser un continuum entre le corps poreux 4 et la couche 5, non poreuse mais percée de fentes artificielles 6, cette couche 5 est déposée par le procédé classique de décomposition chimique en phase gazeuse, ou C.V.D. ("Chemical Vapor Deposition"),plus précisément par réduction d'Hexafluorure de Soufre par de l'Hydrogène, à basses pression et température. Les fentes 6 sont obtenues par usinage ionique réactif, ou "gravure ionique réactive sous plasma", en utilisant soit un mélange Argon-Chlore, soit un mélange d'Hexafluorure de Soufre,d'Argon, et d'Oxygène, soit un mélange d'Hexafluorure de Soufre et d'Oxygène, par des techniques de photogravure ou de gravure chimique classiques.Advantageously, so as to produce a continuum between the porous body 4 and the layer 5, non-porous but pierced with artificial slits 6, this layer 5 is deposited by the conventional process of chemical decomposition in the gas phase, or CVD ("Chemical Vapor Deposition "), more precisely by reduction of Sulfur Hexafluoride by Hydrogen, at low pressure and temperature. The slots 6 are obtained by reactive ion machining, or "reactive ion etching under plasma", using either an Argon-Chlorine mixture, or a mixture of Sulfur Hexafluoride, Argon, and Oxygen, or a mixture of Sulfur Hexafluoride and Oxygen, by conventional photogravure or chemical etching techniques.

Les figures 4 à 9 illustrent un exemple de réalisation pratique de la cathode thermo-électronique de la figure 1.
On part d'un corps 4 en Tungstène poreux, à plus de 30% de porosité, que l'on commence par infiltrer de Cuivre, ce métal étant destiné à jouer le rôle de lubrifiant à l'usinage et à permettre d'effectuer le dépôt de la couche 5 par décomposition chimique en phase gazeuse sans que cette opération ne puisse entraîner le bouchage malencontreux des pores du corps 4.FIGS. 4 to 9 illustrate a practical example of the thermoelectronic cathode of FIG. 1.
We start from a body 4 made of porous Tungsten, with a porosity of more than 30%, which we begin by infiltrating with Copper, this metal being intended to play the role of lubricant during machining and to enable the deposition of layer 5 by chemical decomposition in the gaseous phase without this operation being able to cause the clogging of the pores of the body 4.

Ce corps 4 est ensuite recouvert, par décomposition chimique en phase gazeuse, d'une couche 5 de Tungstène non-poreux, d'une épaisseur de l'ordre de 100 à 200 micromètres.This body 4 is then covered, by chemical decomposition in the gas phase, with a layer 5 of non-porous tungsten, with a thickness of the order of 100 to 200 micrometers.

On dépose ensuite un mince film d'Aluminium d'une épaisseur de quelques micromètres (typiquement de l'ordre de 2 à 5 micromètres).A thin film of aluminum is then deposited with a thickness of a few micrometers (typically of the order of 2 to 5 micrometers).

On dépose ensuite, sur le film d'Aluminium 7, une couche 8 de résine photosensible que l'on isole (figure 4) à travers un masque 9 de forme complémentaire de celle du filtre 5 à obtenir (cf. figure 2).Then deposited on the aluminum film 7, a layer 8 of photosensitive resin which is isolated (Figure 4) through a mask 9 of shape complementary to that of the filter 5 to be obtained (see Figure 2).

Après élimination des parties non isolées 10 de la couche de résine 8 (figure 5), les parties alors visibles de la couche d'Aluminium 7 sont éliminées à l'acide Chlorhydrique (figure 6).After elimination of the non-isolated parts 10 of the resin layer 8 (FIG. 5), the then visible parts of the aluminum layer 7 are eliminated with hydrochloric acid (FIG. 6).

Après élimination de la résine photosensible 8, il reste (figure 7) sur la couche de Tungstène 5, un masque 7 d'Aluminium, de forme identique à celle du filtre 5 (figure 2) à obtenir. la réalisation du masque 7 en Aluminium (ou autre métal, tel que le Chrome, apte à résister à l'Hexafluorure de Soufre) est nécessitée par le fait que les résines photosensibles connues ne résistent pas aux opérations de gravure ionique réactive sous plasma.After elimination of the photosensitive resin 8, there remains (FIG. 7) on the layer of Tungsten 5, a mask 7 of Aluminum, of shape identical to that of the filter 5 (FIG. 2) to be obtained. the production of the mask 7 made of aluminum (or other metal, such as chromium, able to resist sulfur hexafluoride) is required by the fact that the known photosensitive resins do not resist not to reactive ion etching operations under plasma.

L'usinage (figure 8) de la couche de Tungstène 5 s'effectue ensuite par gravure ionique réactive sous plasma, sous pression réduite d'un mélange des trois gaz : Argon, Oxygène et Hexafluorure de Soufre. A titre d'exemple, la vitesse d'attaque, suivant la pression partielle dans l'enceinte utilisée et la tension appliquée, est de l'ordre de 1 à 10 micromètres par minute.The machining (FIG. 8) of the layer of Tungsten 5 is then carried out by reactive ion etching under plasma, under reduced pressure of a mixture of the three gases: Argon, Oxygen and Sulfur Hexafluoride. For example, the attack speed, depending on the partial pressure in the enclosure used and the applied voltage, is of the order of 1 to 10 micrometers per minute.

Lorsque cet usinage est terminé, le masque d'Aluminium 7 est éliminé à l'acide Chlorhydrique (figure 9), puis le Cuivre contenu dans le corps en Tungstène poreux 4 est éliminé par dissolution dans l'acide Nitrique, ensuite de quoi ce corps 4 est imprègné à l'aide des Aluminates de Barium et de Calcium.When this machining is finished, the Aluminum mask 7 is eliminated with hydrochloric acid (figure 9), then the Copper contained in the body in porous Tungsten 4 is eliminated by dissolution in Nitric acid, then what this body 4 is impregnated using Barium Aluminates and Calcium.

Après un nettoyage chimique effectué pour éliminer l'excédent d'Aluminate de Barium sur l'épaisseur de la couche gravée 5, le corps 4 est mis en place dans le tube en molybdène 1, et le filament chauffant 3 est également mis en place.After a chemical cleaning carried out to remove the excess of Barium aluminate over the thickness of the etched layer 5, the body 4 is placed in the molybdenum tube 1, and the heating filament 3 is also put in place.

Il suffit alors de porter la cathode ainsi obtenue à une température suffisamment élevée pour initier les réactions chimiques entre l'aluminate de Calcium et le Tungstène libérant du Barium dans le corps poreux 4, et migrer celui-ci vers la surface émissive à travers le masque à porosité ordonnée 5.
Comme il va de soi, l'invention n'est pas limitée à l'exemple de réalisation qui vient d'être décrit. C'est ainsi que la couche, non poreuse et d'épaisseur au moins égale à 100 micromètres, 5 peut être constituée en un autre métal réfractaire que le Tungstène, par exemple le Rhénium, l'Iridium, et l'Osmium, qui sont tous des métaux bien adaptés au phénomène d'émission thermo-électronique des cathodes. Cette même couche supérieure 5 à porosité ordonnée peut aussi être constituée en un alliage réfractaire, par exemple un alliage Tungstène-­Osmium,Tungstène-Iridium, ou Tungstène-Rhénium. A lieu d'être déposée par C.V.D. (décomposition chimique en phase gazeuse), la couche 5 peut bien entendu aussi être constituée par une couche rapportée et donc finalement indépendante du corps poreux.It then suffices to bring the cathode thus obtained to a sufficiently high temperature to initiate the chemical reactions between the calcium aluminate and the tungsten releasing from the Barium in the porous body 4, and migrate the latter towards the emissive surface through the mask. with ordered porosity 5.
It goes without saying that the invention is not limited to the embodiment which has just been described. Thus the layer, non-porous and with a thickness at least equal to 100 micrometers, 5 can be made of another refractory metal than Tungsten, for example Rhenium, Iridium, and Osmium, which are all metals well suited to the thermoelectronic emission phenomenon of cathodes. This same upper layer 5 with ordered porosity can also be made of an alloy refractory, for example a Tungsten-Osmium, Tungsten-Iridium, or Tungsten-Rhenium alloy. Instead of being deposited by CVD (chemical decomposition in the gas phase), layer 5 can of course also consist of an added layer and therefore ultimately independent of the porous body.

Claims (10)

1 - Cathode thermo-électronique imprègnée du type comprenant, à l'intérieur d'une enveloppe généralement cylindrique (1), en molybdène par exemple, un filament chauffant (3) situé dans la partie inférieure de cette enveloppe (1) et, dans la partie supérieure de cette même enveloppe, une chambre remplie d'un matériau poreux (4) imprègné de matière émissive, caractérisée en ce que ce matériau poreux (4) est recouvert, pour former la surface émissive de la cathode, d'une couche (5) d'un métal réfractaire non poreux et percé artificiellement, par exemple de gravure, de fines fentes (6) qui sont réparties de manière ordonnée et de façon à obtenir, pour cette cathode, une porosité de surface déterminée et apte à permettre la migration du produit émissif sur toute la surface émissive de cette cathode.1 - Impregnated thermoelectronic cathode of the type comprising, inside a generally cylindrical envelope (1), made of molybdenum for example, a heating filament (3) located in the lower part of this envelope (1) and, in the upper part of this same envelope, a chamber filled with a porous material (4) impregnated with emissive material, characterized in that this porous material (4) is covered, to form the emissive surface of the cathode, with a layer (5) of a non-porous refractory metal artificially pierced, for example by etching, fine slits (6) which are distributed in an orderly manner and so as to obtain, for this cathode, a determined porosity of surface and able to allow the migration of the emissive product over the entire emissive surface of this cathode. 2 - Cathode thermo-électronique selon la revendication 1, caractérisée en ce que cette couche (5) à porosité ordonnée a une épaisseur au moins égale à 100 micromètres.2 - Thermoelectronic cathode according to claim 1, characterized in that this layer (5) with ordered porosity has a thickness at least equal to 100 micrometers. 3 - Cathode thermo-électronique sur la revendication 2, caractérisée en ce que cette couche à porosité ordonnée (5) a une épaisseur de l'ordre d'une centaine à quelques centaines de micromètres.3 - Thermoelectronic cathode according to claim 2, characterized in that this layer with ordered porosity (5) has a thickness of the order of a hundred to a few hundred micrometers. 4 - Cathode thermo-électronique selon la revendication 3, caractérisée en ce que l'épaisseur de cette couche à porosité ordonnée (5) est comprise entre 100 et 200 micromètres.4 - Thermoelectronic cathode according to claim 3, characterized in that the thickness of this layer with ordered porosity (5) is between 100 and 200 micrometers. 5 - Cathode thermo-électronique selon l'une des revendications 1 à 4, caractérisée en ce que le matériau poreux (4) a une porosité supérieure à celle de la couche à porosité ordonnée (5).5 - Thermoelectronic cathode according to one of claims 1 to 4, characterized in that the porous material (4) has a porosity greater than that of the layer with ordered porosity (5). 6 - Cathode thermo-électronique selon l'une des revendications 1 à 5, caractérisée en ce que la distance (d) qui sépare deux fentes voisines (6) pratiquées sur la surface de cette couche (5) à porosités ordonnées est sensiblement égale au double de la distance minimale de migration du matériau émissif sur la surface émissive de cette cathode.6 - Thermoelectronic cathode according to one of claims 1 to 5, characterized in that the distance (d) which separates two neighboring slots (6) formed on the surface of this layer (5) with ordered porosities is substantially equal to double the minimum migration distance of the emissive material on the emissive surface of this cathode. 7 - Cathode thermo-électronique selon la revendication 6, caractérisée en ce que cette distance (d) entre deux fentes voisines (6) est de l'ordre de une à deux dizaines de micromètres.7 - Thermoelectronic cathode according to claim 6, characterized in that this distance (d) between two adjacent slots (6) is of the order of one to two tens of micrometers. 8 - Cathode thermo-électronique selon l'une des revendications 1 à 7, caractérisée en ce que ces fentes (6) ont chacune une longueur de l'ordre de 20 micromètres et une largeur de l'ordre de 5 micromètres.8 - Thermo-electronic cathode according to one of claims 1 to 7, characterized in that these slots (6) each have a length of the order of 20 micrometers and a width of the order of 5 micrometers. 9 - Cathode thermo-électronique selon l'une des revendications 1 à 8, caractérisée en ce que cette couche (5) est déposée par décomposition chimique en phase gazeuse (C.V.D.), de manière à réaliser un continuum avec le corps poreux (4).9 - Thermoelectronic cathode according to one of claims 1 to 8, characterized in that this layer (5) is deposited by chemical decomposition in the gas phase (CVD), so as to produce a continuum with the porous body (4) . 10 - Cathode thermo-électronique selon l'une des revendications 1 à 8, caractérisée en ce que cette couche (5) est rapportée sur le corps poreux (4).10 - Thermoelectronic cathode according to one of claims 1 to 8, characterized in that this layer (5) is attached to the porous body (4).
EP90401216A 1989-05-30 1990-05-07 Impregnated thermionic cathode for electron tube Withdrawn EP0401068A1 (en)

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FR8907084 1989-05-30
FR8907084A FR2647952A1 (en) 1989-05-30 1989-05-30 IMPREGNATED THERMOELECTRONIC CATHODE FOR ELECTRONIC TUBE

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Publication number Priority date Publication date Assignee Title
EP0492763A1 (en) * 1990-12-21 1992-07-01 Hughes Aircraft Company Sputtered scandate coatings for dispenser cathodes and methods for making same
EP0549034A1 (en) * 1991-12-21 1993-06-30 Philips Patentverwaltung GmbH Cathode and method of manufacture
CN103311066A (en) * 2013-06-03 2013-09-18 哈尔滨工业大学 Emitter with inner core for self-held hollow cathode of spacecraft

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US2864028A (en) * 1955-08-15 1958-12-09 Philips Corp Thermionic dispenser cathode
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0492763A1 (en) * 1990-12-21 1992-07-01 Hughes Aircraft Company Sputtered scandate coatings for dispenser cathodes and methods for making same
EP0549034A1 (en) * 1991-12-21 1993-06-30 Philips Patentverwaltung GmbH Cathode and method of manufacture
CN103311066A (en) * 2013-06-03 2013-09-18 哈尔滨工业大学 Emitter with inner core for self-held hollow cathode of spacecraft
CN103311066B (en) * 2013-06-03 2015-08-19 哈尔滨工业大学 There is the emitter of the hollow cathode of controlling oneself for spacecraft of inner core

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FR2647952A1 (en) 1990-12-07

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