EP0324676B1 - Method to manufacture a photocathode for an image intensifier tube - Google Patents

Method to manufacture a photocathode for an image intensifier tube Download PDF

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Publication number
EP0324676B1
EP0324676B1 EP89400065A EP89400065A EP0324676B1 EP 0324676 B1 EP0324676 B1 EP 0324676B1 EP 89400065 A EP89400065 A EP 89400065A EP 89400065 A EP89400065 A EP 89400065A EP 0324676 B1 EP0324676 B1 EP 0324676B1
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EP
European Patent Office
Prior art keywords
photocathode
tube
light source
enclosure
manufacturing
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EP89400065A
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German (de)
French (fr)
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EP0324676A1 (en
Inventor
Gérard Vieux
Daniel Boisson
Paul De Groot
Gilbert-René Colomb
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Thales SA
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Thomson CSF SA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
    • H01J9/02—Manufacture of electrodes or electrode systems
    • H01J9/12—Manufacture of electrodes or electrode systems of photo-emissive cathodes; of secondary-emission electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2201/00—Electrodes common to discharge tubes
    • H01J2201/34—Photoemissive electrodes
    • H01J2201/342—Cathodes
    • H01J2201/3421—Composition of the emitting surface
    • H01J2201/3426—Alkaline metal compounds, e.g. Na-K-Sb

Definitions

  • the present invention relates to a method for manufacturing a photocathode for a light image intensifier tube (IIL tube) or radiological images (IIR tube).
  • IIL tube light image intensifier tube
  • IIR tube radiological images
  • These tubes are used for the study of light phenomena or for radiology. In the case of radiology, these tubes are associated with scintillators which convert the incident X photons into light photons.
  • these tubes include, in a vacuum enclosure generally made of glass, an input screen, an output screen, a photocathode close to the input screen, an anode close to the output screen and an optical system.
  • electronics comprising electrodes for accelerating and focusing the electrons emitted by the photocathode, these electrodes being located between the photocathode and the anode.
  • the input screen includes a scintillator which converts the incident X photons into visible photons.
  • the input screen directly receives the incident photons.
  • the visible photons strike the photocathode, generally constituted by a conductive substrate covered with a photoelectric deposit; this photocathode then generates a stream of electrons which are transmitted, thanks to the intermediate electrodes, to an anode where they are focused.
  • the electrons thus focused are directed towards the observation screen made up of a luminophore which then emits visible light. This light can then be transmitted to a camera or camera, to be processed and analyzed.
  • the photocathodes most used consist of a deposit of an alkaline antimonide which can have one of the following chemical compositions: SbCs3, SbK3, SbK2Cs, SbKNaCs, SbKRbCs, ...
  • This composition contains antimony and a or several alkali metals.
  • photocathodes can be obtained by alternately depositing on a substrate, layers of antimony and layers of alkali metals, until the desired sensitivity is obtained. It is thus possible, for example, to produce the following stack: Sb, K, Sb, K, Sb, ... etc.
  • the manufacture of photocathodes consists in placing in the vacuum enclosure of an IIR or IIL tube, an antimony generator and a certain number of alkaline generators, equal to the number of alkali metals which enter into the composition of the photocathode.
  • the photocathode is manufactured in the vacuum chamber of the tube because the alkali metals are very reactive and must be created under vacuum to be stable.
  • the antimony generator comprises a crucible containing antimony, which is caused to evaporate by heating the crucible, by Joule effect for example.
  • Each alkaline generator includes a crucible containing a chromate of an alkali metal and aluminum, or silicon.
  • the heating of the generator generally by Joule effect, produces the aluminothermy or the silicothermic of the compound and releases the alkali metal in question as well as reaction products.
  • FIG. 1 schematically represents an IIR tube and makes it possible to better understand the fabrication of the photocathode, according to a method known in the state of the art from document US-A-4 407 857, for example.
  • This tube comprises a vacuum enclosure 1, a scintillator 2 which forms part of the input screen.
  • the photocathode is generally not deposited directly on the scintillator but on an electrically conductive sub-layer 3 which makes it possible to reconstitute the charges of the material of the photocathode.
  • This sublayer may consist for example of alumina, indium oxide or a mixture of these two bodies.
  • the electronic optics system of the IIR comprises electrodes G1, G2, G3 and an anode A.
  • the reference screen for the IIR tube is designated by the reference 4.
  • the antimony generator 5 and the alkaline generator 6 are used in the vacuum enclosure 1.
  • the alkaline generator 6 is carried by the grid G3.
  • the antimony generator 5 is placed on the path of the electrons, which explains why it is removed from the enclosure, once the photocathode is finished.
  • This generator can be carried by removable means comprising for example a rail 9 sliding on a guide 10 situated in a lateral appendage 11 of the enclosure 1.
  • the rail 9 and the antimony generator 5 are brought into appendix 11 which is then separated from the enclosure by fusion of its junction with the enclosure.
  • the antimony generator 5 consists of a crucible containing antimony, which is caused to evaporate by heating the crucible, by Joule effect for example.
  • the alkaline generator consists of a crucible, the contents of which are evaporated by heating, for example by the Joule effect.
  • photocathode In order to manufacture a photocathode, it must be permanently lit during its manufacture. Indeed, the photoelectricity of the photocathode, that is to say the photoelectric current which it produces when it is illuminated, evolves during manufacturing. This development is linked to the amount of antimony and alkali gradually deposited on the substrate. The measurement of the photoelectric current therefore serves to control the transparency of the photocathode and therefore the dosage of the various components of the deposit constituting this photocathode.
  • the current measurement is carried out by an intensity measurement device 13, connected for example to the conductive sublayer 3 and to the anode A. This current measurement makes it possible to determine the transparency of the deposit during manufacture. Insulating and waterproof bushings 14, 15 are of course provided to ensure the passage of the connection wires of the measuring device 13, in the walls of the enclosure 1.
  • a second layer of antimony is then deposited, and the value of the photoelectric current decreases.
  • a limit value is reached, one stops depositing antimony.
  • layers of alkali metals and antimony are deposited alternately.
  • the value of the photoelectric current increases and decreases as indicated above, during these successive deposits.
  • the manufacturing is finished.
  • FIG. 2 is a diagram which represents the variations of the intensity I of the photoelectric current during the time E of development of the photocathode.
  • the distribution between the different layers of alkali metals can be controlled by photoelectric current threshold values. All these current measurements in fact give the transparency of the photocathode.
  • the lamp 12 which is located outside the enclosure 1 of the tube as taught in document US-A-4 407 857, for example, towards the foot thereof, does not give satisfactory illumination of the photocathode, even if the enclosure is made of glass, as in the case of IIR tubes. Even more significant lighting problems arise if the enclosure is metallic, since in this case a transparent window must be provided in the enclosure to be able to light the photocathode. If a window is impossible to make, any lighting is then prohibited and the fabrication of the photocathode is then very random. The measurement of the photoelectric current as it is carried out directly from the substrate is not very precise.
  • the object of the invention is to remedy these drawbacks and in particular to produce a photocathode by measuring the values of the photoelectric currents produced during manufacture, by illuminating the photocathode by a light source situated inside the enclosure, so as to avoid any attenuation of light for the walls of the enclosure, or even any impossibility of lighting the photocathode when the enclosure is completely opaque.
  • the method also makes it possible to carry out a much more precise measurement of the photoelectric current, during manufacture.
  • the invention therefore relates to a method of manufacturing a photocathode for an image intensifier tube, this tube comprising a vacuum enclosure containing the photocathode, an anode and one or more electrodes situated between the anode and the photocathode, the method consisting depositing a photoelectric material on a conductive substrate, by evaporation under vacuum of said material, to be determined during evaporation, the optical transparency of the deposit, by illuminating this deposit by a light source, characterized in that it consists in illuminate the photoelectric deposit with a light source located inside the tube, this source being protected from the vapors of said material.
  • the optical transparency of the deposit is determined by a device for measuring the photoelectric conduction of the deposit connected to the substrate and located outside the tube.
  • the optical transparency of the deposit is determined by a measuring device connected to photoelectric means internal to the tube and sensitive to the thickness of said deposit.
  • the sensitive photoelectric means consist of a photodiode located near said substrate outside the path of the electrons and covered by said deposit at the same time as the substrate during the evaporation of said material.
  • the light source is protected by one of the electrodes.
  • the light source is supported by one of the electrodes, outside the path of the electrons emitted by the photocathode.
  • the light source is connected to an electrical source external to the tube, by connection wires crossing the tube by insulating bushings.
  • the light source is activated by a high frequency generator external to the tube.
  • the light source is removed from the vacuum enclosure at the end of the manufacturing.
  • said photoelectric material is an alkaline antimonide.
  • the alkaline antimonide is obtained by evaporation of antimony and of alkali metals contained in crucibles heated inside the enclosure.
  • the light source is mounted on a removable system to be removed from the enclosure at the end of manufacturing.
  • At least one of the crucibles is mounted on a removable system to be removed from the enclosure at the end of manufacture.
  • the method according to the invention makes it possible, as illustrated diagrammatically in FIG. 3, to manufacture a photocathode 7 for an image intensifier tube IIL or IIR whose vacuum enclosure is represented in 1.
  • the tube is of type IIR and that it comprises, in addition to the photocathode formed on the conductive substrate 3, a scintillator 2.
  • This tube also comprises an anode A, and between photocathode 7 and anode A, a electronic optics comprising the electrodes G1, G2, G3.
  • An output screen 4 is also shown in this figure, behind the anode A.
  • the method consists, in a known manner, of depositing a photoelectric material such as an alkaline antimonide, on the conductive substrate 3, by evaporation under vacuum.
  • a photoelectric material such as an alkaline antimonide
  • the antimony generator 5 is a crucible heated by the Joule effect
  • the alkali metal generator is a crucible 6 also heated by the Joule effect.
  • the antimony generator 5, can be fixed to a rail 9, sliding on a rod 10 located in appendix 11, to allow the removal of this generator at the end of manufacture.
  • this light source 12 is located inside the enclosure 1 of the tube to produce direct illumination 8 of the deposit, without attenuation of the light.
  • the light source 12 is protected from the vapors of photoelectric material by being placed near one of the electrodes (G3 for example), on the side of one of the faces of this electrode, while the generator 6 is located on the side on the other side of this electrode.
  • the generator 5 is located near the electrode G1.
  • the light source 12, such as an electric lamp for example is "in the shade" of the electrode G3, sheltered from the vapors coming from the generators.
  • the optical deposit transparency is obtained by measuring the photoelectric conduction of the deposit 7, subjected to the illumination of the source 12, using a current measurement device 13 outside the enclosure 1 connected to the substrate 3 and at the anode A.
  • photoelectric means internal to the tube such as a photodiode 16.
  • photoelectric means internal to the tube such as a photodiode 16.
  • the measurement of the transparency of the photodiode is then equivalent to the measurement of the transparency of the deposit made on the substrate, this measurement is however much more precise.
  • the photodiode 16 is located near the substrate 3, preferably in the vicinity of the around it, outside the path of the electrons which will be emitted by the photocathode, when the tube will be used in normal operation after its manufacture. It can indeed be envisaged to leave the photodiode inside the tube, so as not to complicate the manufacturing process.
  • the light source 12 which is protected from projections of photoelectric material by the electrode G3, can also be supported by this electrode. In this case, this source can be located outside the path of the electrons emitted by the photocathode and arriving at the anode, and can remain in the tube at the end of manufacturing.
  • This light source can be a lamp powered by an electrical power source 18 to which it is connected by conductive wires which enter the tube by insulating bushings 19.
  • the light source 12 can be a filament activated by a high frequency generator 20, outside the tube.
  • This solution has the advantage of avoiding any connection by wire with an external electrical supply.
  • the light source 12 while being located near the electrode G3, but without being fixed to it, is placed at the end of a removable system such that rails 21 can slide on a guide rod 22 located in a lateral appendage 23 of the enclosure 1.
  • the light source can be a lamp powered by the electrical source 18, or a filament activated by the high generator frequency 20.
  • the light source 12 can be removed from the tube by sliding the rail 21 inside the appendix 23, which is then separated from the enclosure 1 by fusion of the junction of this appendix with the enclosure.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Image-Pickup Tubes, Image-Amplification Tubes, And Storage Tubes (AREA)
  • Formation Of Various Coating Films On Cathode Ray Tubes And Lamps (AREA)
  • Manufacture Of Electron Tubes, Discharge Lamp Vessels, Lead-In Wires, And The Like (AREA)

Description

La présente invention concerne un procédé de fabrication d'une photocathode pour tube intensificateur d'images lumineuses (tube IIL) ou d'images radiologiques (tube IIR).The present invention relates to a method for manufacturing a photocathode for a light image intensifier tube (IIL tube) or radiological images (IIR tube).

Ces tubes sont utilisés pour l'étude de phénomènes lumineux ou pour la radiologie. Dans le cas de la radiologie, ces tubes sont associés à des scintillateurs qui convertissent les photons X incidents, en photons lumineux.These tubes are used for the study of light phenomena or for radiology. In the case of radiology, these tubes are associated with scintillators which convert the incident X photons into light photons.

On sait que ces tubes comprennent, dans une enceinte à vide généralement en verre, un écran d'entrée, un écran de sortie, une photocathode proche de l'écran d'entrée, une anode proche de l'écran de sortie et une optique électronique comportant des électrodes d'accélération et de focalisation des électrons émis par la photocathode, ces électrodes étant situées entre la photocathode et l'anode. Dans les tubes de type IIR, l'écran d'entrée comporte un scintillateur qui convertit les photons X incidents en photons visibles. Dans les tubes de type IIL, l'écran d'entrée reçoit directement les photons incidents.We know that these tubes include, in a vacuum enclosure generally made of glass, an input screen, an output screen, a photocathode close to the input screen, an anode close to the output screen and an optical system. electronics comprising electrodes for accelerating and focusing the electrons emitted by the photocathode, these electrodes being located between the photocathode and the anode. In type IIR tubes, the input screen includes a scintillator which converts the incident X photons into visible photons. In IIL type tubes, the input screen directly receives the incident photons.

Les photons visibles viennent frapper la photocathode, généralement constituée par un substrat conducteur recouvert d'un dépôt photoélectrique ; cette photocathode génère alors un flux d'électrons qui sont transmis, grâce aux électrodes intermédiaires, vers une anode où ils sont focalisés. Les électrons ainsi focalisés sont dirigés vers l'écran d'observation constitué d'une luminophore qui émet alors une lumière visible. Cette lumière peut ensuite être transmise vers une caméra ou un appareil de photographie, pour être traitée et analysée.The visible photons strike the photocathode, generally constituted by a conductive substrate covered with a photoelectric deposit; this photocathode then generates a stream of electrons which are transmitted, thanks to the intermediate electrodes, to an anode where they are focused. The electrons thus focused are directed towards the observation screen made up of a luminophore which then emits visible light. This light can then be transmitted to a camera or camera, to be processed and analyzed.

Les photocathodes les plus utilisées, sont constituées d'un dépôt d'un antimoniure alcalin qui peut avoir l'une des compositions chimiques suivantes : SbCs₃, SbK₃, SbK₂Cs, SbKNaCs, SbKRbCs, ... Cette composition contient de l'antimoine et un ou plusieurs métaux alcalins.The photocathodes most used, consist of a deposit of an alkaline antimonide which can have one of the following chemical compositions: SbCs₃, SbK₃, SbK₂Cs, SbKNaCs, SbKRbCs, ... This composition contains antimony and a or several alkali metals.

Ces photocathodes peuvent être obtenues en déposant alternativement sur un substrat, des couches d'antimoine et des couches de métaux alcalins, jusqu'à l'obtention de la sensibilité recherchée. On peut ainsi réaliser par exemple, l'empilement suivant : Sb, K, Sb, K, Sb, ... etc.These photocathodes can be obtained by alternately depositing on a substrate, layers of antimony and layers of alkali metals, until the desired sensitivity is obtained. It is thus possible, for example, to produce the following stack: Sb, K, Sb, K, Sb, ... etc.

Il est également possible d'obtenir ces photocathodes en déposant en même temps sur le substrat, l'antimoine et les métaux alcalins.It is also possible to obtain these photocathodes by depositing antimony and alkali metals on the substrate at the same time.

De façon connue, la fabrication de photocathodes consiste à placer dans l'enceinte à vide d'un tube IIR ou IIL, un générateur d'antimoine et un certain nombre de générateurs alcalins, égal au nombre de métaux alcalins qui entrent dans la composition de la photocathode. La fabrication de la photocathode se fait dans l'enceinte à vide du tube car les métaux alcalins sont très réactifs et doivent être créés sous vide pour être stables.In known manner, the manufacture of photocathodes consists in placing in the vacuum enclosure of an IIR or IIL tube, an antimony generator and a certain number of alkaline generators, equal to the number of alkali metals which enter into the composition of the photocathode. The photocathode is manufactured in the vacuum chamber of the tube because the alkali metals are very reactive and must be created under vacuum to be stable.

Le générateur d'antimoine comprend un creuset contenant de l'antimoine, dont on provoque l'évaporation en chauffant le creuset, par effet Joule par exemple.The antimony generator comprises a crucible containing antimony, which is caused to evaporate by heating the crucible, by Joule effect for example.

Chaque générateur alcalin comprend un creuset contenant un chromate d'un métal alcalin et de l'aluminium, ou du silicium. Le chauffage du générateur, généralement par effet Joule, produit l'aluminothermie ou la silicothermie du composé et libère le métal alcalin en question ainsi que des produits de réaction.Each alkaline generator includes a crucible containing a chromate of an alkali metal and aluminum, or silicon. The heating of the generator, generally by Joule effect, produces the aluminothermy or the silicothermic of the compound and releases the alkali metal in question as well as reaction products.

La figure 1 représente schématiquement un tube IIR et permet de mieux comprendre la fabrication de la photocathode, selon un procédé connu dans l'état de la technique par le document US-A-4 407 857, par exemple. Ce tube comprend une enceinte à vide 1, un scintillateur 2 qui fait partie de l'écran d'entrée. La photocathode n'est généralement pas déposée directement sur le scintillateur mais sur une sous-couche conductrice de l'électricité 3 qui permet de reconstituer les charges du matériau de la photocathode. Cette sous-couche peut être constituée par exemple d'alumine, d'oxyde d'indium ou d'un mélange de ces deux corps. Le système d'optique électronique de L'IIR comporte des électrodes G₁, G₂, G₃ et une anode A. On désigne par la référence 4 l'écran d'observation du tube IIR.FIG. 1 schematically represents an IIR tube and makes it possible to better understand the fabrication of the photocathode, according to a method known in the state of the art from document US-A-4 407 857, for example. This tube comprises a vacuum enclosure 1, a scintillator 2 which forms part of the input screen. The photocathode is generally not deposited directly on the scintillator but on an electrically conductive sub-layer 3 which makes it possible to reconstitute the charges of the material of the photocathode. This sublayer may consist for example of alumina, indium oxide or a mixture of these two bodies. The electronic optics system of the IIR comprises electrodes G₁, G₂, G₃ and an anode A. The reference screen for the IIR tube is designated by the reference 4.

On a represénté dans l'enceinte à vide 1 le générateur d'antimoine 5 et le générateur alcalin 6 qui sont utilisés. Dans le mode de réalisation représenté sur la figure, le générateur alcalin 6 est porté par la grille G₃. Le générateur d'antimoine 5 est placé sur le trajet des électrons, ce qui explique qu'on l'enlève de l'enceinte, une fois la photocathode terminée. Ce générateur peut être porté par des moyens amovibles comprenant par exemple un rail 9 coulissant sur un guide 10 situé dans un appendice 11 latéral de l'enceinte 1. A la fin de la fabrication de la photocathode le rail 9 et le générateur d'antimoine 5, sont amenés dans l'appendice 11 qui est alors séparé de l'enceinte par fusion de sa jonction avec l'enceinte.The antimony generator 5 and the alkaline generator 6 are used in the vacuum enclosure 1. In the embodiment shown in the figure, the alkaline generator 6 is carried by the grid G₃. The antimony generator 5 is placed on the path of the electrons, which explains why it is removed from the enclosure, once the photocathode is finished. This generator can be carried by removable means comprising for example a rail 9 sliding on a guide 10 situated in a lateral appendage 11 of the enclosure 1. At the end of the manufacture of the photocathode, the rail 9 and the antimony generator 5, are brought into appendix 11 which is then separated from the enclosure by fusion of its junction with the enclosure.

Le générateur d'antimoine 5 est constitué par un creuset contenant de l'antimoine, dont on provoque l'évaporation en chauffant le creuset, par effet Joule par exemple.The antimony generator 5 consists of a crucible containing antimony, which is caused to evaporate by heating the crucible, by Joule effect for example.

Le générateur alcalin est constitué par un creuset dont le contenu est évaporé par chauffage, par effet Joule par exemple.The alkaline generator consists of a crucible, the contents of which are evaporated by heating, for example by the Joule effect.

Il est nécessaire, pour fabriquer une photocathode, de l'éclairer en permanence au cours de sa fabrication. En effet, la photoélectricité de la photocathode, c'est-à-dire le courant photoélectrique qu'elle produit lorsqu'elle est éclairée, évolue au cours de la fabrication. Cette évolution est liée à la quantité d'antimoine et d'alcalin déposée progressivement sur le substrat. La mesure du courant photoélectrique sert donc à contrôler la transparence de la photocathode et donc le dosage des différents composants du dépôt constituant cette photocathode.In order to manufacture a photocathode, it must be permanently lit during its manufacture. Indeed, the photoelectricity of the photocathode, that is to say the photoelectric current which it produces when it is illuminated, evolves during manufacturing. This development is linked to the amount of antimony and alkali gradually deposited on the substrate. The measurement of the photoelectric current therefore serves to control the transparency of the photocathode and therefore the dosage of the various components of the deposit constituting this photocathode.

En se référant à la figure 1 et de façon connue un procédé de fabrication d'une photocathode 7, se déroule donc de la manière suivante.Referring to Figure 1 and in known manner a method of manufacturing a photocathode 7, therefore takes place in the following manner.

Au cours du dépôt d'une première couche d'un métal alcalin, par exemple du Césium ou du Potassium, on mesure le courant photoélectrique produit par l'éclairement 8 de cette couche par une lampe 12 située à l'extérieur de l'enceinte 1, en regard de la couche en cours d'élaboration, tel que nous enseigne le document US-A-4 407 857, par exemple. La mesure du courant est effectuée par un appareil de mesure d'intensité 13, relié par exemple à la sous-couche conductrice 3 et à l'anode A. Cette mesure de courant permet de déterminer la transparence du dépôt au cours de la fabrication. Des traversées isolantes et étanches 14, 15 sont bien entendu prévues pour assurer le passage des fils de connexion de l'appareil de mesure 13, dans les parois de l'enceinte 1. Lorsque le courant photoélectrique produit par l'éclairement de la première couche atteint une valeur prédéterminée, on arrête alors le dépôt de cette première couche.During the deposition of a first layer of an alkali metal, for example Cesium or Potassium, the photoelectric current produced by the illumination 8 of this layer by a lamp 12 located outside the enclosure 1, facing the layer being developed, as taught in document US-A-4 407 857 , for example. The current measurement is carried out by an intensity measurement device 13, connected for example to the conductive sublayer 3 and to the anode A. This current measurement makes it possible to determine the transparency of the deposit during manufacture. Insulating and waterproof bushings 14, 15 are of course provided to ensure the passage of the connection wires of the measuring device 13, in the walls of the enclosure 1. When the photoelectric current produced by the illumination of the first layer reaches a predetermined value, the deposition of this first layer is then stopped.

On réalise ensuite un dépôt d'une deuxième couche d'antimoine, et la valeur du courant photoélectrique décroît. Quand une valeur limite est atteinte, on cesse de déposer de l'antimoine. On réalise ensuite alternativement des dépôts de couches de métaux alcalins et d'antimoine. La valeur du courant photoélectrique augmente et diminue comme indiqué plus haut, au cours de ces dépôts successifs. Quand la valeur du courant photoélectrique atteint une valeur maximum prédéterminée, la fabrication est terminée.A second layer of antimony is then deposited, and the value of the photoelectric current decreases. When a limit value is reached, one stops depositing antimony. Then, layers of alkali metals and antimony are deposited alternately. The value of the photoelectric current increases and decreases as indicated above, during these successive deposits. When the value of the photoelectric current reaches a predetermined maximum value, the manufacturing is finished.

La figure 2 est un diagramme qui représente les variations de l'intensité I du courant photoélectrique au cours du temps E d'élaboration de la photocathode.FIG. 2 is a diagram which represents the variations of the intensity I of the photoelectric current during the time E of development of the photocathode.

Si l'on choisit de déposer toute l'antimoine au début, la répartition entre les différentes couches de métaux alcalins peut être contrôlée par des valeurs de seuil de courant photoélectrique. Toutes ces mesures de courants donnent en fait la transparence de la photocathode.If one chooses to deposit all the antimony at the start, the distribution between the different layers of alkali metals can be controlled by photoelectric current threshold values. All these current measurements in fact give the transparency of the photocathode.

La lampe 12 qui est située à l'extérieur de l'enceinte 1 du tube tel que nous enseigne le document US-A-4 407 857, par exemple, vers le pied de celui-ci, ne donne pas un éclairement satisfaisant de la photocathode, même si l'enceinte est en verre, comme dans le cas de tubes IIR. Des problèmes d'éclairement encore plus importants apparaissent si l'enceinte est métallique, car on doit dans ce cas ménager une fenêtre transparente dans l'enceinte pour pouvoir éclairer la photocathode. Si une fenêtre est impossible à réaliser, tout éclairement est alors interdit et la fabrication de la photocathode est alors très aléatoire. La mesure du courant photoélectrique tel qu'il est effectué directement à partir du substrat, n'est pas très précise.The lamp 12 which is located outside the enclosure 1 of the tube as taught in document US-A-4 407 857, for example, towards the foot thereof, does not give satisfactory illumination of the photocathode, even if the enclosure is made of glass, as in the case of IIR tubes. Even more significant lighting problems arise if the enclosure is metallic, since in this case a transparent window must be provided in the enclosure to be able to light the photocathode. If a window is impossible to make, any lighting is then prohibited and the fabrication of the photocathode is then very random. The measurement of the photoelectric current as it is carried out directly from the substrate is not very precise.

L'invention a pour but de remédier à ces inconvénients et notamment de réaliser une photocathode en mesurant les valeurs des courants photoélectriques produits au cours de la fabrication, en éclairant la photocathode par une source de lumière située à l'intérieur de l'enceinte, de manière à éviter toute atténuation de lumière pour les parois de l'enceinte, ou même toute impossibilité d'éclairement de la photocathode lorsque l'enceinte est complètement opaque. Le procédé permet de plus d'effectuer une mesure bien plus précise du courant photoélectrique, au cours de la fabrication.The object of the invention is to remedy these drawbacks and in particular to produce a photocathode by measuring the values of the photoelectric currents produced during manufacture, by illuminating the photocathode by a light source situated inside the enclosure, so as to avoid any attenuation of light for the walls of the enclosure, or even any impossibility of lighting the photocathode when the enclosure is completely opaque. The method also makes it possible to carry out a much more precise measurement of the photoelectric current, during manufacture.

L'invention concerne donc un procédé de fabrication d'une photocathode pour tube intensificateur d'images, ce tube comprenant une enceinte à vide contenant la photocathode, une anode et une ou plusieurs électrodes situées entre l'anode et la photocathode, le procédé consistant à déposer un matériau photoélectrique sur un substrat conducteur, par évaporation sous vide dudit matériau, à déterminer au cours de l'évaporation, la transparence optique du dépôt, en éclairant ce dépôt par une source de lumière, caractérisé en ce qu'il consiste à éclairer le dépôt photoélectrique par une source de lumière située à l'intérieur du tube, cette source étant protégée des vapeurs dudit matériau.The invention therefore relates to a method of manufacturing a photocathode for an image intensifier tube, this tube comprising a vacuum enclosure containing the photocathode, an anode and one or more electrodes situated between the anode and the photocathode, the method consisting depositing a photoelectric material on a conductive substrate, by evaporation under vacuum of said material, to be determined during evaporation, the optical transparency of the deposit, by illuminating this deposit by a light source, characterized in that it consists in illuminate the photoelectric deposit with a light source located inside the tube, this source being protected from the vapors of said material.

Selon un mode de mise en oeuvre du procédé de l'invention, la transparence optique du dépôt est déterminée par un appareil de mesure de la conduction photoélectrique du dépôt relié au substrat et situé à l'extérieur du tube.According to an embodiment of the method of the invention, the optical transparency of the deposit is determined by a device for measuring the photoelectric conduction of the deposit connected to the substrate and located outside the tube.

Selon un autre mode de mise en oeuvre du procédé, la transparence optique du dépôt est déterminée par un appareil de mesure relié à des moyens photoélectriques internes au tube et sensibles à l'épaisseur dudit dépôt.According to another embodiment of the method, the optical transparency of the deposit is determined by a measuring device connected to photoelectric means internal to the tube and sensitive to the thickness of said deposit.

Selon une autre caractéristique, les moyens photoélectriques sensibles sont constitués par une photodiode située à proximité dudit substrat en dehors du parcours des électrons et recouverte par ledit dépôt en même temps que le substrat au cours de l'évaporation dudit matériau. Dans ce cas, on s'intéresse à l'affaiblissement du signal émis par la photodiode sous éclairement, dû à son opacification par le dépôt photocathodique. On a alors accès à la transparence optique de la photocathode.According to another characteristic, the sensitive photoelectric means consist of a photodiode located near said substrate outside the path of the electrons and covered by said deposit at the same time as the substrate during the evaporation of said material. In this case, we are interested in the weakening of the signal emitted by the photodiode under illumination, due to its opacification by the photocathode deposition. We then have access to the optical transparency of the photocathode.

Selon un autre mode de mise en oeuvre du procédé, la source de lumière est protégée par l'une des électrodes.According to another embodiment of the method, the light source is protected by one of the electrodes.

Selon une autre caractéristique, la source de lumière est supportée par l'une des électrodes, en dehors du parcours des électrons émis par la photocathode.According to another characteristic, the light source is supported by one of the electrodes, outside the path of the electrons emitted by the photocathode.

Selon un autre mode de mise en oeuvre du procédé, la source de lumière est reliée à une source électrique extérieure au tube, par des fils de connexion tranversant le tube par des traversées isolantes.According to another embodiment of the method, the light source is connected to an electrical source external to the tube, by connection wires crossing the tube by insulating bushings.

Selon une autre caractéristique, la source de lumière est activée par un générateur haute fréquence extérieur au tube.According to another characteristic, the light source is activated by a high frequency generator external to the tube.

Selon une autre caractéristique, la source de lumière est retirée de l'enceinte à vide à la fin de la fabrication.According to another characteristic, the light source is removed from the vacuum enclosure at the end of the manufacturing.

Selon une autre caractéristique, ledit matériau photoélectrique est un antimoniure alcalin.According to another characteristic, said photoelectric material is an alkaline antimonide.

Selon une caractéristique particulière, l'antimoniure alcalin est obtenu par évaporation d'antimoine et de métaux alcalins contenus dans des creusets chauffés à l'intérieur de l'enceinte.According to a particular characteristic, the alkaline antimonide is obtained by evaporation of antimony and of alkali metals contained in crucibles heated inside the enclosure.

Selon une caractéristique particulière, la source de lumière est montée sur un système amovible pour être retirée de l'enceinte à la fin de la fabrication.According to a particular characteristic, the light source is mounted on a removable system to be removed from the enclosure at the end of manufacturing.

Selon une autre caractéristique, au moins l'un des creusets est monté sur un système amovible pour être retiré de l'enceinte à la fin de la fabrication.According to another characteristic, at least one of the crucibles is mounted on a removable system to be removed from the enclosure at the end of manufacture.

Les caractéristiques et avantages de l'invention ressortiront mieux de la description qui va suivre, donnée en référence aux dessins annexés dans lesquels :

  • - la figure 1 a déjà été décrite et représente schématiquement un tube connu de type IIR, au cours de sa fabrication selon un procédé connu dans l'art antérieur,
  • - la figure 2 a déjà été décrite et représente un diagramme de l'évolution de la valeur de l'intensité du courant photoélectrique produit par une photocathode éclairée, au cours de sa fabrication,
  • - la figure 3 représente schématiquement un tube de type IIR, au cours de sa fabrication selon le procédé de l'invention.
The characteristics and advantages of the invention will emerge more clearly from the description which follows, given with reference to the appended drawings in which:
  • FIG. 1 has already been described and schematically represents a known tube of type IIR, during its manufacture according to a method known in the prior art,
  • FIG. 2 has already been described and represents a diagram of the evolution of the value of the intensity of the photoelectric current produced by an illuminated photocathode, during its manufacture,
  • - Figure 3 schematically shows a type IIR tube, during its manufacture according to the method of the invention.

Les mêmes éléments portent les mêmes références sur la figure 3 et sur la figure 1.The same elements have the same references in FIG. 3 and in FIG. 1.

Le procédé selon l'invention permet, comme illustré schématiquement sur la figure 3, de fabriquer une photocathode 7 pour un tube intensificateur d'images IIL ou IIR dont l'enceinte à vide est représentée en 1. Dans l'exemple représenté sur cette figure, on suppose que le tube est de type IIR et qu'il comporte, outre la photocathode formée sur le substrat conducteur 3, un scintillateur 2. Ce tube comprend aussi une anode A, et entre la photocathode 7 et l'anode A, une optique électronique comportant les électrodes G1, G2, G3. Un écran de sortie 4 est aussi représenté sur cette figure, derrière l'anode A. Le procédé consiste de façon connue, à déposer un matériau photoélectrique tel qu'un antimoniure alcalin, sur le substrat conducteur 3, par évaporation sous vide. Comme dans l'état de la technique, le générateur 5 d'antimoine est un creuset chauffé par effet Joule, tandis que le générateur de métaux alcalins est un creuset 6 chauffé lui aussi par effet Joule. Le générateur d'antimoine 5, peut être fixé à un rail 9, coulissant sur une tige 10 située dans l'appendice 11, pour permettre l'enlèvement de ce générateur à la fin de la fabrication. On mesure aussi, comme dans l'état de la technique, la conduction photoélectrique du dépôt photoémissif, en l'éclairant par une source de lumière.The method according to the invention makes it possible, as illustrated diagrammatically in FIG. 3, to manufacture a photocathode 7 for an image intensifier tube IIL or IIR whose vacuum enclosure is represented in 1. In the example represented in this figure , it is assumed that the tube is of type IIR and that it comprises, in addition to the photocathode formed on the conductive substrate 3, a scintillator 2. This tube also comprises an anode A, and between photocathode 7 and anode A, a electronic optics comprising the electrodes G1, G2, G3. An output screen 4 is also shown in this figure, behind the anode A. The method consists, in a known manner, of depositing a photoelectric material such as an alkaline antimonide, on the conductive substrate 3, by evaporation under vacuum. As in the prior art, the antimony generator 5 is a crucible heated by the Joule effect, while the alkali metal generator is a crucible 6 also heated by the Joule effect. The antimony generator 5, can be fixed to a rail 9, sliding on a rod 10 located in appendix 11, to allow the removal of this generator at the end of manufacture. We also measure, as in the prior art, the photoelectric conduction of the photoemissive deposit, by illuminating it with a light source.

Selon l'invention, cette source de lumière 12, est située à l'intérieur de l'enceinte 1 du tube pour produire un éclairement direct 8 du dépôt, sans atténuation de la lumière. La source de lumière 12 est protégée des vapeurs de matériau photoélectrique en étant placée à proximité de l'une des électrodes (G3 par exemple), du côté de l'une des faces de cette électrode, tandis que le générateur 6 est situé du côté de l'autre face de cette électrode. Le générateur 5 se trouve à proximité de l'électrode G1. Il en résulte que la source de lumière 12, telle qu'une lampe électrique par exemple se trouve "dans l'ombre" de l'électrode G3, à l'abri des vapeurs provenant des générateurs.According to the invention, this light source 12 is located inside the enclosure 1 of the tube to produce direct illumination 8 of the deposit, without attenuation of the light. The light source 12 is protected from the vapors of photoelectric material by being placed near one of the electrodes (G3 for example), on the side of one of the faces of this electrode, while the generator 6 is located on the side on the other side of this electrode. The generator 5 is located near the electrode G1. As a result, the light source 12, such as an electric lamp for example, is "in the shade" of the electrode G3, sheltered from the vapors coming from the generators.

La transparence optique de dépôt est obtenue en mesurant la conduction photoélectrique du dépôt 7, soumis à l'éclairement de la source 12, à l'aide d'un appareil de mesure de courant 13 extérieur à l'enceinte 1 reliée au substrat 3 et à l'anode A. On peut également avoir accès à la transparence du dépôt, par mesure par l'appareil 13, en reliant celui-ci à des moyens photoélectriques internes au tube, tels qu'une photodiode 16. Au cours du dépôt de matériau photoélectrique sur le substrat, celui-ci se dépose aussi sur la photodiode, avec la même épaisseur. La mesure de la transparence de la photodiode est alors équivalente à la mesure de la transparence du dépôt effectué sur le substrat, cette mesure est toutefois bien plus précise. Les fils conducteurs de liaison de l'appareil de mesure 13 avec le substrat 3 ou avec la photodiode 16, pénètrent dans le tube par des traversées isolantes 14, 17. La photodiode 16 est située à proximité du substrat 3, de préférence au voisinage du pourtour de celui-ci, en dehors du parcours des électrons qui seront émis par la photocathode, lorsque le tube sera utilisé en fonctionnement normal après sa fabrication. Il peut en effet être envisagé de laisser la photodiode à l'intérieur du tube, pour ne pas compliquer le procédé de fabrication.The optical deposit transparency is obtained by measuring the photoelectric conduction of the deposit 7, subjected to the illumination of the source 12, using a current measurement device 13 outside the enclosure 1 connected to the substrate 3 and at the anode A. One can also have access to the transparency of the deposit, by measurement by the device 13, by connecting the latter to photoelectric means internal to the tube, such as a photodiode 16. During the deposition of photoelectric material on the substrate, it also deposits on the photodiode, with the same thickness. The measurement of the transparency of the photodiode is then equivalent to the measurement of the transparency of the deposit made on the substrate, this measurement is however much more precise. The conductive wires connecting the measuring device 13 with the substrate 3 or with the photodiode 16, penetrate the tube by insulating bushings 14, 17. The photodiode 16 is located near the substrate 3, preferably in the vicinity of the around it, outside the path of the electrons which will be emitted by the photocathode, when the tube will be used in normal operation after its manufacture. It can indeed be envisaged to leave the photodiode inside the tube, so as not to complicate the manufacturing process.

La source 12 de lumière, qui est protégée des projections de matériau photoélectrique par l'électrode G3, peut aussi être supportée par cette électrode. Dans ce cas, cette source peut être située en dehors du parcours des électrons émis par la photocathode et parvenant à l'anode, et peut demeurer dans le tube à la fin de la fabrication. Cette source de lumière peut être une lampe alimentée par une source électrique d'alimentation 18 à laquelle elle est reliée par des fils conducteurs qui pénètrent dans le tube par des traversées isolantes 19.The light source 12, which is protected from projections of photoelectric material by the electrode G3, can also be supported by this electrode. In this case, this source can be located outside the path of the electrons emitted by the photocathode and arriving at the anode, and can remain in the tube at the end of manufacturing. This light source can be a lamp powered by an electrical power source 18 to which it is connected by conductive wires which enter the tube by insulating bushings 19.

Selon un autre mode de mise en oeuvre du procédé, la source de lumière 12 peut être un filament activé par un générateur haute fréquence 20, extérieur au tube. Cette solution a pour avantage d'éviter toute liaison par fil avec une alimentation électrique extérieure. Dans un autre mode de mise en oeuvre du procédé, la source de lumière 12, tout en étant située à proximité de l'électrode G3, mais sans être fixée à celle-ci, est placée à l'extrémité d'un système amovible tel que des rails 21 pouvant coulisser sur une tige de guidage 22 située dans un appendice latéral 23 de l'enceinte 1. Comme précédemment, la source de lumière peut être une lampe alimentée par la source électrique 18, ou un filament activé par le générateur haute fréquence 20. A la fin de la fabrication, la source de lumière 12 peut être retirée du tube en faisant coulisser le rail 21 à l'intérieur de l'appendice 23, qui est alors séparé de l'enceinte 1 par fusion de la jonction de cet appendice avec l'enceinte.According to another embodiment of the method, the light source 12 can be a filament activated by a high frequency generator 20, outside the tube. This solution has the advantage of avoiding any connection by wire with an external electrical supply. In another embodiment of the method, the light source 12, while being located near the electrode G3, but without being fixed to it, is placed at the end of a removable system such that rails 21 can slide on a guide rod 22 located in a lateral appendage 23 of the enclosure 1. As before, the light source can be a lamp powered by the electrical source 18, or a filament activated by the high generator frequency 20. At the end of manufacturing, the light source 12 can be removed from the tube by sliding the rail 21 inside the appendix 23, which is then separated from the enclosure 1 by fusion of the junction of this appendix with the enclosure.

Le procédé qui vient d'être décrit permet bien d'atteindre les buts mentionnés plus haut : grâce aux moyens d'éclairement internes, le contrôle de la fabrication de la photocathode est beaucoup plus efficace. La photodiode qui permet la mesure de la transparence du dépôt permet elle aussi un contrôle plus précis de la fabrication.The process which has just been described makes it possible to achieve the goals mentioned above: thanks to the internal lighting means, the control of the fabrication of the photocathode is much more effective. The photodiode which allows the measurement of the transparency of the deposit also allows a more precise control of the manufacturing.

Claims (13)

1. A method of manufacturing a photocathode for an image intensifier tube, this photocathode being an integrating part of the tube during its manufacturing, the photocatode being further constituted by a photoelectric material (7) deposited on an electrically conducting substrate (3), said tube comprising a vacuum enclosure (1) containing the photocathode, an anode (A) and one or more electrodes (G1, G2, G3) situated between the anode and the photocathode, the method consisting in depositing a photoelectric material (7) on the electrically conducting substrate (3) by evaporating said material under vacuum, and in determining during the evaporation the optical transparency of the layer (7) by illuminating said layer from a light source (12), characterized in that said light source is situated inside the vacuum enclosure during the evaporation and it is protected against the vapours of said material during the evaporation.
2. A manufacturing method according to claim 1, characterized in that the optical transparency of the layer (7) is measured by a device which measures the photoelectric conduction of the layer (13) and which is connected to the substrate (3) and situated outside the tube.
3. A manufacturing method according to claim 1, characterized in that the optical transparency of the layer (7) is measured by a measuring device (13) connected to photoelectric means (16) which are located inside the tube and are sensitive to the thickness of said layer.
4. A manufacturing method according to claim 3, characterized in that the sensitive photoelectric means (16) are constituted by a photodiode situated close to the substrate and outside of the path of the electrons, said photodiode being coated by said layer simultaneously with the substrate (3) during the evaporation of said material.
5. A method according to any one of claims 1 to 4, characterized in that said light source (12) is protected by one of the electrodes (G3).
6. A method according to claim 5, characterized in that the light source (12) is supported by one of the electrodes (G3) out of the way of the electrons emitted by the photocathode (7).
7. A method according to claim 5, characterized in that the light source (12) is connected to an electric supply (18) outside of the tube via connecting wires which pass through the tube wall via insulating passages (19).
8. A method according to claim 5, characterized in that the light source (12) is activated by a high frequency generator (20) located outside the tube.
9. A method according to claim 5, characterized in that the light source (12) is withdrawn from the vacuum enclosure at the end of the manufacturing phase.
10. A method according to claim 5, characterized in that said photoelectric material (7) is an alkali antimonide.
11. A method according to claim 10, characterized in that the alkali antimonide is obtained by evaporating antimon and alkali metals contained in heated crucibles (5, 6) located in the enclosure.
12. A method according to claim 11, characterized in that the light source (12) is mounted on a removable system (21, 22) in order to be withdrawn from the enclosure at the end of the manufacturing phase.
13. A method according to claim 12, characterized in that at least one of the crucibles (5) is mounted on a removable system (9, 16) in order to be withdrawn from the enclosure at the end of the manufacturing phase.
EP89400065A 1988-01-15 1989-01-10 Method to manufacture a photocathode for an image intensifier tube Expired - Lifetime EP0324676B1 (en)

Applications Claiming Priority (2)

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FR8800411 1988-01-15
FR8800411A FR2626106B1 (en) 1988-01-15 1988-01-15 METHOD FOR MANUFACTURING A PHOTOCATHODE FOR IMAGE ENHANCER TUBE

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EP0324676B1 true EP0324676B1 (en) 1992-04-08

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FR2688343A1 (en) * 1992-03-06 1993-09-10 Thomson Tubes Electroniques INTENSIFYING IMAGE TUBE, IN PARTICULAR RADIOLOGICAL, OF THE TYPE A GALETTE OF MICROCHANNELS.
FR2698482B1 (en) * 1992-11-20 1994-12-23 Thomson Tubes Electroniques Device for generating images by luminescence effect.
FR2777112B1 (en) 1998-04-07 2000-06-16 Thomson Tubes Electroniques IMAGE CONVERSION DEVICE
FR2782388B1 (en) 1998-08-11 2000-11-03 Trixell Sas SOLID STATE RADIATION DETECTOR WITH INCREASED LIFE
US7114851B2 (en) * 2004-03-19 2006-10-03 General Electric Company Methods and systems for calibrating medical imaging devices
JP5889591B2 (en) * 2011-10-06 2016-03-22 株式会社東芝 X-ray image tube manufacturing method

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US2676282A (en) * 1951-04-09 1954-04-20 Rca Corp Photocathode for multiplier tubes
US4305972A (en) * 1980-06-30 1981-12-15 Rca Corporation Method for expeditiously processing a sodium-potassium-cesium-antimony photocathode
US4407857A (en) * 1981-06-30 1983-10-04 Rca Corporation Method for processing a lithium-sodium-antimony photocathode
US4525376A (en) * 1982-03-16 1985-06-25 Energy Conversion Devices, Inc. Optical methods for controlling layer thickness
JPS6251132A (en) * 1985-08-30 1987-03-05 Toshiba Corp Manufacture of electron tube having photoelectric surface
FR2594258B1 (en) * 1986-02-11 1988-10-14 Thomson Csf PROCESS FOR MANUFACTURING AN ALKALI ANTIMONIURE PHOTOCATHODE AND IMAGE ENHANCER TUBE INCLUDING SUCH A PHOTOCATHODE.

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DE68901139D1 (en) 1992-05-14
FR2626106A1 (en) 1989-07-21
FR2626106B1 (en) 1990-05-04

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