US2197753A - Multiple grid structure and method of producing the same - Google Patents

Description

April 23, 1940.

e. LIEBMANN 2,197,753 MULTIPLE GRID STRUCTURE AND METHOD OF PRODUCING THE Filed June a, 1957 SAME //7 vent-0P.

Patented Apr. 23, 1940 UNITED STATES MULTIPLE GRID STRUCTURE AND METHOD OF PRODUCING THE SAME Gerhard Liebmann, Berlin, Germany Application June 8, 1937, Serial No. 147,157 In Germany June 16, 1936 1 Claim.

In the patent application Ser. No. 120,774 filed January 15, 1937 image-reproducing tubes for television receivers have been described inwhich a very bright and non-flickering image is pro duced by causing the cathode ray which moves over the screen area and is controlled in its intensity to create a persistent charge image on a two-dimensional structure, termed a multiple grid, which controls in corresponding fashion the electron emission from a two-dimensional cathode.

A multiple grid useful for the purpose in question must comply with a number of conditions which are diflicult to fulfil. In the first place it is necessary for the same to consist of a very large number of conductive elements which are well insulated one against the other. These elements should be at least equal in number to the number of image elements to be transmitted, or should preferably be even a multiple thereof. Further, the grid must be so dense that it entirely prevents the passage of electrons from the oathode ray into the image-producing space, as otherwise the image made visible would be interfered with. In addition it of course must be perfectly satisfactory from the point of view of vacuum technic.

Although it has been found that a mosaic electrode which is deposited on an insulator, such as employed, for example, in television transmission tubes operating according to the ikonoscope principle, is in certain circumstances capable of being employed for brief periods as a multiple grid when the insulating surface is made to face the two-dimensional cathode, interferences of such extent occur owing to the inavoidable charging of the insulating front surface that it is necessary to employ multiple grids, in which there is no insulator between the points charged by the cathode ray and the cathode of the image-generating system.

The object of the present invention is to provide a suitable construction of a multiple grid and a method of producing the same. In the drawing Fig. 1 is a side view,

Figs. 2 and 3 are top views showing different stages of manufacture, whilst Fig. 4 shows a structure having a conductive coating applied to the insulator surfaces.

For this purpose there are cut a sufficiently large number of comparatively long aluminium wires, which are coated with a layer of aluminium. oxide. It is naturally also possible to employ any other metal wire furnished with a vacuum-resisting and heat-resisting insulating layer. Owing to their length these wires may be very conveniently combined into bundles. Over a bundle 1 of wire of this nature there are now passed seamless rings 8 consisting of a sufficiently formed i material, such as steel. These rings have the form of a tube of short cut off sections, and are so narrow that they can just be fitted comfortably over the bundle of wires. A ring of this nature having a circular cross-section, is now clamped, together with the bundle of wires located therein in a four-jaw vice and pressed together to get asquare cross-section. In this manner there results a reduction in cross-section in the ratio of 4hr. Even if it is considered that previously the wires did not completelyfill'out the original cross-section, the reduction in crosssection caused by the variation in the form of the holding ring is in any case sufficient to press the wires together very firmly. The plates which are produced by cutting the wires along the edges of the now square frame now possess a sufficient strength. In addition all gaps between the wires have been completely closed, so that the possibility is removed of electrons passing through from the cathode ray space into an image-gen.- erating space. It is also possible to fit a large number of rings over a comparatively long bundle of wire, to press at a time one ring, out off the latter, etc.

Multiple grid plates which are produced by embedding wires in a ceramic substance possess of necessity the characteristic that the thickness of the insulating material is of the same order as I This property may be the thickness of the wire. utilised for the assembly with the thermal cathode itself, the emission of which is to be controlled by means of the multiple grids, by grinding a plate of this nature to be well flat on one surface, providing, by etching or similar methods, for the end surface of the wires to be situated somewhat below the surface of the plate, and furnishing the resulting perforated insulating surface with a conductive coating which acts as equipotential cathode and at the same time serves as a support for a material emitting thermal or photo electric electrons.

After the stated strong etching a multiple grid plate of this kind possesses the structure of a honeycomb. The advantage of a multiple grid plate produced according to the method as last described resides not only in the density and strength already referred to, but also in an easy manufacture and in the possibility of obtaining a very large number of image points, as very thin' wires can be employed. Thus, for example, it is possible to use Eloxal aluminium wires of 0.1 mm. in diameter, although thin wire of this nature can be coated with aluminium oxide according to the Eloxal process only in such short lengths that a winding of coils or a similar method is quite out of the question. For the method as last de-- scribed the length of the single wires employed is of no importance in practice.

Multiple grids of the character described may naturally also be furnished with coatings of any desired kind. It is possible, for example, to activate the individual points photo-electrically or for the emission of secondary electronsor the emission of thermal electrons. For this purpose the known methods may be employed, particularly in the case of the honeycomb construction as last described. For example, a photo-electric layer can be produced by coating the multiple grid plate by vacuum atomization with a layer of silver interrupted by the insulating edges, oX-

idizing it and sensitizing it by means of caesium. It is also possible to make it suitable by means of a barium coating for the emission of thermal electrons, or to coat it with any other desired layers.

The projecting edge of the insulating material resulting from the etching operation may at the same time serve to ensure the requisite spacing between the metallic wires of the multiple grid and the cathode net which may then be placed immediately on to the grid, without danger of short-circuiting. It is only in this way that it is possible to maintain extremely small spacings. In Fig. 4 there is shown the manner in which by the etching away of the metal I intermediate structures 6 are formed, which maybe furnished with a coating 9 of silver or similar metal.

A multiple grid plate of this nature may be employed not only in the image receiving tubes with persistent image referred to at the commencement, but other possibilities of use are also conceivable both in the normal amplifying tube art as well as above all in the television image transmission art. For example, a plate of this kind may be suitable to replace the mosaic plate of a transmission tube which operates for example in a manner similar to the principle of the ikonoscope. In this case it is possible by applying'the grid to a sheet of mica, the rear of which is furnished with a metallic coating, to obtain a capacitative picking-up, it being as well possible to employ the conductive connection of each grid element of the one side with one grid element of the other side for any other singlesided or double-sided scanning by means of cathode rays or rays of light.

It has been found desirable to furnish the single wires insulated one against the other and constituting the multiple grid with a common screening means, so that the wires of the multiple grid are, as it were, embedded in insulated fashion in a conductive net. This screening means may be connected with a desired fixed potential, for example with earth. According to a further feature of the invention, this conductive net is produced by its coating prior to the assembly,-

each of the insulated wires which form the multiple grid with a conductive outer layer. In the event of Eloxal aluminium Wire being employed the production of a conductive layer is not readily possible without reducing the insulation to an inadmissibly low value owing to the porous nature of the insulating jacket. The pores can be filled however by preliminary treatment of the Eloxal wires with aluminium nitrate or another inorganic insulating material, whereupon a metal deposit is formed by chemical decomposition in a'manner known per se. This filling of the pores is not required if metal or graphite in solid and very finely distributed form is. taken as a basis. In this case it is sufficient to dip the Eloxal aluminium wire into the conductive powder. Owing to the fine granular structure of this powder so much of the latter remains adhering to the wire, even after shaking, that the conductivity is adequate. This dusting on of the metallic powder is performed after the bundling but prior to the compression of the wires. Owing to thesubsequent compression the conductive particles are also prevented from falling out, so that the desired object is obtained in full extent, as the metal skins surrounding the individual grid wires touch each other and accordingly establish contact.

It will be understood that in the case that multiple grid plates are produced from insulated wires, in which each layer has a smooth surface, for example from enamelled wires, the known methods of producing a conductive de-- posit, for example application by vaporization, separation from a solution, spraying on or electrolytic application may be employed without difiiculty.

A method of producing a photo-electric grid structure consisting of an insulating plate penetrated by a large number of thin wires insulated from each other, said method consisting in the steps of forming a round bundle of insulated wires, putting metallic rings upon said bundle, compressing the whole to a smaller cross-section, cutting a plate of said framed bundle, removing the burr from the surface of said plate by etching, and continuing the etching until the end of each wire is substantially below the surface of the insulating plate.

GERHARD LIEBMANN'.

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