US 3630590 A
Description (OCR text may contain errors)
United States Patent  Inventors Heinrich Strublg Darmstadt; Werner Tretner, Weiterstadt; Gunter Flasche, Dannstndt, all of Germany  Appl. No. 19,421
 Filed Mar. 13, 1970  Patented Dec. 28, 1971  Assignee Fernaeh Gmbll Darmstadt, Germany  Priority Mar. 27, 1969  Germany  METHOD FOR TRANSFERRING LAYERS PRODUCED IN A VACUUM 10 Claims, 2 Drawing Figs.
[52} U.S.Cl 316/4, 316/1, 316/10, 316/12, 316/19  1nt.Cl 1110139/18, l-lOlj 9/38  Fleld 01 Search 316/17, 18, 19, 20,1, 3,4,l0,12;53/7,9
 References Cited UNITED STATES PATENTS 2,984,759 5/1961 Vine 316/17 X 3,353,889 11/1967 Legoux Primary Examiner-John F. Campbell Assistant Examiner-Richard Bernard Lazarus Attorney-Littlepage, Quaintance, Wray and Aisenberg ABSTRACT: Method for constructing operational layers, such as photosensitive layers, outside the operational containers, such as camera tubes, in which they are to be used ultimately, testing the layers, then transferring them to the operational containers.
mama) 052281571 316130.590
In ven tor Dr Heinrich Sfrdbig Dr Werner Tretn er A ttornevs METHOD FOR TRANSFERRING LAYERS PRODUCED IN A VACUUM BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a method for transferring operational layers of various types, which have been produced in a vacuum and which are very sensitive to other gases, from a first vacuum container into an operational vacuum container, in which the layer is to be used. The invention relates particularly to the transfer of layers for forming photocathodes with photoelectric emission for these layers are extremely sensitive to other gases and a very high quality and homogeneity is desired. However, the invention is not restricted to this application.
2. Description of the Prior Art In television camera tubes with photocathodes, a layer is required which is very uniform over the entire surface on which the image for transmitting is projected, and which is extremely sensitive and nearly completely free of spots, defects, etc. The known method for producing the photocathode directly in the camera tube result in a great amount of waste, since defects of the photocathode can not be determined completely before the final manufacturing step. In this known method if the photocathode includes defects or has too low a sensitivity and homogeneity, the whole camera tube must be scrapped.
SUMMARY OF THE INVENTION Therefore, it is highly desirable to have a method for producing a layer, such as a photocathode layer, in a separate area under optimum conditions; for example, in a separate bulb which includes all devices for producing the photocathode, but includes no other electrodes, so that this layer can be tested to determine the quality of the photocathode and to eliminate faulty units at this stage of the manufacturing process. During the further steps of this desired method the tested photocathode must be removed from the bulb and transferred to the tube, in which it will ultimately operate. This tube may be a television camera tube or the like. However, the transfer of such a layer from one unit to another is a step which is difficult to carry out, since during the transfer the layer comes into contact with surrounding environments which are different from the surroundings in which the photocathode has been produced and which have ensured its stability. Moreover, it was discovered that the surroundings of the photocathode in the new tube should conform to the surroundings in the original chamber. If these conditions are not provided, the sensitivity of the photocathode after sealing in the new tube does not correspond to the sensitivity in the original chamber where the photocathode was produced, and the sensitivity will decrease during storage.
Because of the above-mentioned difficulties, a corresponding method has not been discovered, or used, for conventional tubes which have sufficient room for one to place the devices for producing the photosensitive layers in the tubes. In other devices not having sufficient room for the device for producing the layer, as for instance in a so-called sandwich-imageconverter tubes" where the photocathode and the screen are at a small distance from each other, attempts have been made to achieve the transfer by means of a vacuum bell jar surrounding both the open image-converter tube without photocathode and the device for producing photocathodes. First the photocathode was produced in the bell jar and it was then transferred into the opening of the tube. However, this method does not permit testing of the photocathode before transferring it and does not permit elimination of faulty photocathodes before being transferred to the converter tube.
The method for producing a photosensitive (light-reactive) layer in an image-converter tube according to this invention avoids these and other disadvantages by producing the photosensitive layer in a closed container which is not the ultimate container of the image-converter tube, testing the quality of the layer, e.g. by flying-spot scanning, preparing the image-converter tube and its electrodes, except the photosensitive layer and the faceplate for supporting the layer, and installing these elements in a dismountable vacuum container, in which the container of the photocathode is also installed, evacuating the vacuum container, baking out the image-converter tube if necessary and treating its inside wall to produce favorable surroundings into which the photosensitive layer may be inserted, separating the carrier of the photosensitive layer from said container and bringing it quickly in front of the opening of the image-converter tube, connecting the carrier of the photocathode and the image-converter tube in a vacuum tight manner, and finally ventilating the vacuum container and removing the finished tube.
This instant method provides many technological and economical advantages. In the above-mentioned prior art method the transition between the point of time, at which the photocathode is finished and the point of time at which it is installed in the other container is undetermined, since each photocathode acts differently during its forming. On the other hand, the novel method hereof permits a short, exactly determinable time interval during which the photocathode is kept in the vacuum container which depends only on the mechanical conditions of transfer. For instance, it is possible to separate the photocathode from the container and transfer it on to the other tube within 1 second. This very short period of time causes no damages to the photocathode in the very high vacuum since the tube which will ultimately contain the photocathode has been treated before to create conditions which ensure the stability of the cathode. The previous testing to determine defects and sensitivity of the photocathode guarantees an extremely low scrap rate, which is particularly economical for the production of tubes having a very complex electrode arrangement. Finally, a tube is removed from the vacuum container which includes a high-quality photocathode. The method of this invention importantly permits production of tubes having a compact arrangements, which prevent installation of evaporation devices for producing the photocathode. The produced tubes have a higher sensitivity and a higher quality than the tubes produced according to the known methods.
It has been discovered that in the production of photocathodes of type S 20, it is advantageous to treat the faces of the inner parts of the tube ultimately containing the cathode with the vapor of one or more alkali metals preferably potassium, sodium or cesium. For that purpose it is suitable to close the interior of the tube by a removable cover, bake out the tube, evaporate potassium and sodium and/or cesium with an evaporator for the metal, cool down the tube and evaporate again an amount of alkali metal vapor, which condenses on the wall of the tube thereby forming metallic droplets which act as a reserve of alkali metal. The source of alkali metal vapor may be located somewhere in the container at a place where it does not affect the electrooptical function, e.g. close to the beam system. Then the photocathode is separated from the first container and the photosensitive layer is transferred to the electron tube, simultaneously removing the cover from the tube, and the tube is closed by means of a suitable sealing method.
The separating of the photocathode carrier from the first container (auxiliary container) and the sealing of the photocathode carrier and the electron tube may be facilitated by providing defined faces for the sealing of the container, for instance by grinding a wedge-shaped groove into the separating area with the wedge surface perpendicular to the cathode carrier and optically polished. The depth of the wedge-shaped groove may be chosen so that the remaining wall-thickness is less than a millimeter, e.g. half a millimeter. Then a heated filament is inserted into the wedge-shaped groove and heated, whereby the photocathode carrier is separated (blown off) and a well-defined surface for the connection of the photocathode carrier and the electron tube is produced.
To connect the photocathode carrier and the electron tube, the so-called "cold-seal method" has been used with very satisfactory results. In this known method, a ring of indium, which has been freed of any residual oxide by burning off or by chemical treatment, is provided at the bond of both parts. Then the photocathode carrier is placed onto the container carrying the ring of indium and pressed on, so that the indium flows into the split between the two parts and is partially squeezed out, whereby the smooth edges of the photocathode carrier and the electron tube are connected strongly, so that a good vacuumtight seal is achieved.
The vacuum in the finished electron tube is, of course, dependent on the vacuum in the surroundings, ie in the vacuum container, which encloses the electron tube as well as the first or auxiliary container. Using modern vacuum pumps, a vacuum of 10* can easily be achieved in a dismountable vacuum chamber, which vacuum is sufficient for the stability of a photocathode within the transfer period. An elastically or plastically deformable metal body for transferring compressive forces onto the tube from the outside may be used to accomplish the necessary mechanical pressure, thereby guaranteeing a vacuumtight connection of the electron tube and the photocathode carrier.
BRIEF DESCRIPTION OF THE DRAWINGS The method according to the invention will be described with the aid of the accompanying drawings and in which:
FIG. I is a schematic diagram of an apparatus to carry out the method.
FIG. 2 is a partial view of the first or auxiliary container 12 shown in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a dismantleable vacuum system comprising a baseplate l, a cylindrical glass body 2, a cover plate 3, and a pump 4. The cover plate 3 can be removed after ventilation of the vacuum system. The following elements are installed in the vacuum apparatus: a swiveling device 5 having two arms 50 and 5b, a baking-out oven 6 for reception of the electron tube to be produced, a supporting device 7 for supporting the electron tube to be produced, a pressing device 8, 9 and 10 comprising a plunger 8 mounted on a flexible metallic bellows 9 and adjustable in the vertical direction by means of a threaded spindle and a handwheel 10. In the process of producing the electron tube 11 the auxiliary container 12 is inserted into this apparatus. The container 12 comprises a highly sensitive and pretested photocathode on the photocathode carrier 13, which is mounted on the arm 5a by means of a gripping device. Thus, the carrier can be separated from the auxiliary container and put down at another place by the swiveling device 5 after the groove 12a is cracked. The electron tube 11 is held in the supporting device 7, located in the vacuum container opposite the position of the photocathode. The supporting device 7 permits adjustment and support of the electron tube 11. The tube is closed by a cover 14 mounted on the arm 5b of the swiveling device 5. A ring of indium located on the upper edge of the open tube 11 (later used for melting or sealing) is shielded against radiant heat from the oven 6 which encloses the tube and the supporting device. The oven 6 serves to bake out the tube whereby the rest of the water on the glass wall is eliminated. The electron tube 11 might be, for example, an image orthicon including electrodes in an arrangement conventional for those tubes. However, such a tube does not include evaporating devices for producing the photocathode. In order to give the clear illustration of the invention, the figure does not show the electrical devices and their wiring and the auxiliary mechanical devices, e.g. for stripping the photocathode carrier 13 off the gripping clip. Moreover, the electrical equipment for producing alkali metal vapor within the tube 11 is not shown. Alkali metal evaporators are known in the art and need not be described.
EXECUTION OF THE METHOD A finished electron tube is produced by means of the abovedescribed apparatus as follows. First the auxiliary container 12 and the tube 11 are inserted, when the cover plate 3 is opened and the arms 5a, 5b are set perpendicular to the plane of the drawing. The auxiliary container and the tube are adjusted so that the plane of the groove 12a of the auxiliary container 12 nearly coincides with the plane of the upper edge of the tube 11. Then the arms 5a and 5b are brought in the position shown in FIG. I, and the upper portion of the auxiliary container 12 comprising he photocathode carrier 13 is held by a gripping device. The auxiliary container 12 is selected to have certain quality characteristics and to include a highly sensitive photocathode, free of defects. Now the opening of the glass cylinder 2 is closed by the cover plate 3, and the pump 4 starts generating a high vacuum in the vacuum container and in the interior of the tube 11. It may be advantageous to place the cover 14 only loosely on the tube 11 or to provide openings in the cover to avoid substantial pressure differences between the interior of the tube 11 and the interior of the vacuum container. Then the over 6 is turned on and the interior of the tube is heated to the range from about 200 C. to 300 C. After that, alkali metal vapor is produced within the tube 11 by means of an evaporator (not illustrated), which may be fed with electric current through supply leads at the socket or base of the tube. This working condition may be maintained for about 1 to 1% hours, after which the tube is cooled down, and after cooling down to the range from about C. to C., alkali metal vapor is produced again. Then electric current is fed through leads (not illustrated) to the heated filament located at 12a in the wedge-shaped groove in the tube 12, whereby the photocathode carrier is separated (blown off). The swiveling device 5 is then actuated as fast as possible to bring the photocathode carrier 13 in front of the opening of the electron tube 11 by I80 rotation. The photocathode carrier is put down by a releasing mechanism, the arms of the swiveling device 5 is set in the position perpendicular to the plane of the drawing, and then the pressing device 8, 9 and I0 is actuated, which permits the exertion of pressure on the photocathode carrier by means of the hand wheel 10. This pressure causes deforming of the indium ring located in plane 15. The indium fills the space between the edges of the photocathode carrier and the electron tube II so that vacuumtight sealing is achieved. Now the vacuum system is ventilated, the cover plate 3 removed and the finished tube taken out. To achieve a good baking out of the upper part of the electron test, it may be desirable not to place the ring ofindium on the upper edge of the open tube, but to fasten it on the photocathode carrier in an intermediate position of the swiveling device, since the indium melts at 160C.
FIG. 2 shows a part of the auxiliary container 12 with the wedge-shaped groove. In this figure, numeral 16 indicates a part of the container 12 with the photocathode carrier I3 comprising the formed photocathode layer 13a. A groove I7 is ground into the container wall by a diamond grinding-wheel, which is shaped wedgelike. A wedge surface is arranged exactly parallel to the photocathode carrier 13a. This surface will be provided with an optical polish. To separate the photocathode carrier 13, a thin tungsten filament is inserted into the wedge-shaped groove and heated by a current pulse at the suitable time. Then the cathode carrier 13 cracks off in an exactly defined plane, whereby the groove ensures that the force of separation coincides with the ground wedge surface. Small variations are possible, but do not affect the tightness of the sealing with the tube II, because of the resilience of the ring of indium. For exact adjustment of the photocathode carrier on electron tube 11 in relation to its axis, a gauge stop 18 may be provided against which the hand wheel 10 abuts after a certain lifting of the pressing device 8, 9 and 10. The precision of this adjustment is at least equal to those of the conventional methods of melting the photocathode carrier an the container as used in the glass technology.
The invention includes some modifications not yet described. For example, the shape of the groove in the auxiliary container may be semicircular or rectangular, since the scaling is mainly accomplished in the separation surface. Moreover, additional alkali metal vapor may be produced in the already closed tube, for instance to correct the photocathode.
According to another modification of the invention, the electron tube may be produced without the transferred photocathode at first and be provided with an auxiliary photocathode instead of the final photocathode. This auxiliary photocathode need not have high quality; it is only used to test the function of the remaining parts of the tube.
Therefore, the vacuum container comprises the camera tube having an auxiliary photocathode with a tested system and a container with a tested photocathode of high quality.
To finish the camera tube both photocathodes are separated from their containers in the high vacuum of the vacuum container according to the described method. Then the tested cathode is transferred to the tested electron tube and placed into the opening produced by the separation of the auxiliary photocathode. The connection of the photocathode and the electron tube corresponds to the above-described method, and the cold-seal method may be used.
1. A method for producing an operational layer contained within an operational container comprising the steps of A. producing the operational layer on a carrier (13) in a closed container (12) outside the operational container,
B. testing the quality of the layer within the closed container,
C. providing the operational container l l including internal elements other than the operational layer and support means for said layer, and enclosing the operational container and the closed container in a dismantleable vacuum container (1,2,3).
D. evacuating the dismantleable vacuum container, heating the operational container (11) and treating he inner surface of the operational container to create favorable conditions in the operational container into which the operational layer may be inserted,
E. separating said carrier (13) from said closed container F. placing said carrier quickly into said operational container,
G. sealing the carrier and the operational container,
6. sealing the carrier and the operational container in a vacuum tight manner, and
H. finally ventilating the dismantleable container and removing the operational container.
2. A method according to claim 1 in which said operational layer is a photosensitive layer and said operational container is a television camera tube.
3. A method according to claim I wherein the step of treating the inner surface comprises producing metallic vapors within the operational container to treat said inner surface.
4. A method according to claim 3 wherein said metallic vapors are alkali metal vapors.
5. A method according to claim 4 wherein the operational container is cooled down in the presence of said alkali metal vapors and is then again treated with alkali metal vapors.
6. A method according to claim 5 wherein the separation of said carrier from said closed container is enhanced by providing said closed container with a wedge-shaped groove produced by grinding, whereby a wedge surface is arranged perpendicular to said carrier and is optically polished.
7. A method according to claim 6 wherein a heated filament is inserted into said groove and is momentarily heated so that said carrier is cracked off from the closed container.
8. A method according to claim 6 wherein a cover (14) is removed from an opening of the closed container during the quick transfer of said carrier (13) to an opening in the front of said operationalcontainer(ll).
9. method according to claim 1 wherein said sealing between the carrier and the operational container is achieved by inserting a ring of indium in the connection region and by pressing the carrier onto the ring of indium by mechanical force, whereby the space between the operational container (11) and the carrier (13) becomes sealed in a vacuumtight manner.
10. A method according to claim 9, wherein a gauge is provided for limiting the lift of a plunger which presses the carrier (13) onto the operational container (11) whereby the exact position of the carrier in relation to the axis of the operational carrier is determined when the gauge is touched.
UNlTED STATES PATENT OFFICE CEER'HFICATE 0F CORRECTION Patent No. 3 630 590 Dated 2' 1 Q I fl Heinrich Strubig, Wernet Tretner, Gunter Flasche It is certified that error appears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:
IN THE CLAIMS:
Claim 1, D., line 2, change "he" to -the-.
Claim 1, column 6, delete line 3 Signed and sealed this 27th day of June 1 972.
EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents