US2380505A - Method of manufacturing mosaic electrodes - Google Patents

Description

July 31, 1945. H. B. DE V ORE METHOD MANUFACTURING MOSAIC ELECTRODES Filed June 26, 1941 INVENTORY HENRY 3. DE VORE BY W ATTORNEY +|F Q \G 2 Q Q m |l| mos QR m m Q n Emma m NJ 5535 6 WWzwNmQQm W 5R3: W lm 3 f I F E lll N w I W .m. v W l ii a u m m:

0 o o o owowon 0 Patented July3l, 1945 METHOD OF MANUFACTURING MOSAIC ILEUI'IODIS llenryi. De v65; Newari, N. 3., asslgnor aa--- 1110 Corporation of America. a

- Delaware corporation of strut-um}... 2t, 1941, smalsasoassr I n scam (cues-1:)

My invention relates to television transmitting tubes and more particularly toelectrode structure of the so-called mosaic type foruse in such tubes.

. It is known that a sensitive television transmitting or pickup tube of the type in which the picture is transmitted by scanning a mosaic-like target with an electron beamcan be made. by employing a two-sided mosaic target. In this E type of tube an optical image is formed-on a photocathode to liberate electrons as an electron image which is focused on one'side or face of the target, forming an equivalent electrostatic'charge image thereon. Alternatively the charge image may be formed by focusing the optical image on the mosaic directly, provided the side of the mosaic receiving the light image is photo-emissive. This charge image is transmitted c0nductively structure. em

- 7 tofore. It is a further object to'provide new and novel mosaic electrode structure for; use in such tubes as well as a method of manufacturing such In accordance with my tube having a 'mosaic-typeelectrode wherein the electrode comprises a sheet of porous insulating material impregnated with metallic particles and wherein the electrical resistance through the sheet normal to its surface is relativelylow in "comparison with the electrical resistance measured laterally o1 theporous insulatingsheet. In-

- 'asmuch as the sheet does-not include an electrically conducting foundation, I provide an electron permeable electrode closely adjacent and uniformly spaced from the porousinsulating sheet I containing the metal particles impregnated therethrough the targetto the opposite surface which is scanned by an electron beam. The discharge of elemental areas of the target by thescanning process generates a television signal on a' signal electrode which is in capacitive relationship with in. Further in accordance with my invention I provide a method of manufacturing a mosaictype electrode wherein a thin porous sheet of insulating material is coated over various'areas thereof or impregnated with a metal salt which is then fused and'reduced or converted into the the elements of the mosaic target.

The conductivity through the permit the rapid transfer of the charge from the picture side to the scanned side of the target. The conductivity along the target from one elemental area to another must be very low in order to have good resolution in the transmitted pic- -ture. In additiomthe capacity between each elementand the signal plate or electrode should be high in order that a large charge may be stored for the production of a large picture signal. Fur-- thermore, the side of the target on which the electron image is focused should have a high secondary electron emission ratio'in order that the intensity of the electrostatic charge image may be increased by secondary electron emission from the target. It has been customary to provide such targets by electrically insulating a wire mesh target over each elemental picture area must be relatively high to screen and filling the interstices of the insulated screen with metal plugs. form such a structure having over 100,000 elec-, tricallydisc'rete highly insulated metal plugs. and in addition. even though such electrodes-are prepared with exceptional care it has iieen'i'ound that in o eration a spurious signal not representative of the electron or optical image is produced which is probably due to electrical and mechanical ncnuniformities over the target surface.

It is an object of my invention to provide a television transmitting tifbe having higher sensitivity with lower distortion than tubes constructed here- It is very dimclllt to type of tube referred to ab'ove. I provide a time metal which is one of the components of the salt. Alternately my method of manufacture may include a reduction or conversion of :the metallic salt without the fusing step. These and other obiects. features and advantages of my invention will become apparent when in connection with the following description and the accomdrawing in which:

Figure 1 isia longitudinal cross-sectional view of atelevision transmitting tube incorporating my invention;

Figure 2 is a view of a portion ofthe electrode structure shown in Figure 1. and

Figure 3 is a greatly enlarged sectional view of a portion of the electrode target structure shovm in Figur l and 2.

Whil I I will particularly describe a type of transmitting tube incorporating means to form an electrostatic image on a mosaic electrode by directing electrons thereon and intensifying the electrostatic image by secondary electron emission, it will be appreciated that my invention is not'limited to the use of my new and improved electrode structure in such a time, but that it may be used to equal advantase in arrang ments 7 wherein the electrostatic image is formed on the mosaic electrode directly by the emission of photoelectrons under the influence of the optical image of which an image replica is to be transmitted.

Referring tongue 1 which shows the former comprising an evacuated envelope lat invention! provide a one endanelecirongunorbcam forming structure 2 and at the opposite end a semitransparent photocathode 8 of the conventional type with a target or mosaic electrode 4 intermediate the structure I and photocathode positioned to be scanned on one side by an electron beam, and to have an electrostatic image formed on the 01 9 on the rear surface of the target dby projecting light, such as represented by .the object arrow B, through the lens t upon the photocathode 3 to liberate electrons therefrom, and focusing the electrons to form an electron image on the target structureeapableorresolvinganelectronbeam "site side. This electrostatic image may be formed 7 coextensivewithandverycloselyspacedwith' by well-known electron lens structures, or the light may be projected directly upon the rear surface of the target in accordance with the latter which electrons may be directed toward the target 0, the anode I being maintained at a positive;

potential withrrespect to the cathode by a battery or potential source ll.-

Intermediate the electron gun I and the target I I provide apair of deflection plates i i which are curved to produce a uniformly increasing and decreasing electrostatic deflection fleld, a pair of shield plates iI-ll, one on either side of the deflection plates Ii having slots for the passage of the electron beam. and a conductive wall coating ll. The plates II are connected to a source of deflection potential and to the shield plates ll-il and coating ll, through a'center-tapped resistance of 1 to 10 megohms. To produce the desired deflection and focus of the electron beam I provide means to wholly immerse the deflection plates in a uniform magneticfleld which is preferably generated by a magnetic coil I! of larger diameter than the envelope I extending over and beyond the space between the electron gun I and target 4. In the modification of my invention shown in Figure 1 the coil ll preferably extends beyond the photocathode 3 to focus the electron beam from the photocathode upon the rear surface oi .the target 4, although an auxiliary short coll may be used between the photocathode 3 and target I, or a known electrostatic electron image forming structure may be used. The electrons from the photocathode 3 are accelerated over a portion of their path by an electrostatic fleld such as generated by the walicoating It operated' ata' positive potential with' respect to j the cathode I by a battery or other potential of the electron beam in a direction some produced by the plates ii is aca pair of deflection polls it. This ispreferably the frame or vertical deflsctlcn, since'in standard television systems the frame is'of lower frequency than the horizontal line deflection. the coils is therefore being operated atthe' lower of the two treouem clss. The deflection coi It may. of course. be replaced hy'a second pair of deflection plates or 40 the electrolytic current density is maintained substantially constant. As I have pointed out in maybeusedintheplaceofthossdescribsd.

Inaccordancewithmyinventionthetaract comprises a verythin imperiorate target sheet I. of homogeneous electrically nonconduoting material supported as shown in l 'igure i-in a plane normal tothe longitudinal axis of themvelope l and consequently normal'to the pro- .iectedelectron beam. Closely associated with the target sheet I! of electrically nonconducting materiaiand preferably adjacent the rear surface of the sheet I provide a signal electrode ll respecttotherearsurfaceoftheshect It. The signal electrode II is election permeable such as awiremeshscreenandisconnectedtotheinput eircuitofatranslating device I! andthrough an output impedance I! to the cathode I either directlyorthroughaportionof-the potential source it. Further in accordance with my invention,andasbestshowninFigurcs2and3,I provide the target sheet ll of porous material capable of absorbing the metal or metal salt with which I impregnate the sheet during the manufacturing process to form individual mutually separated particles 28 which are preferably "highly insulated one from another. For the sheet I. of porous nonconducting material I prefer to utilise a sheet of aluminum oxide which is formed by oxidation 0! a thin sheet of aluminum by an electrolytic method such as disclosed in my -copending application, Serial No. 888,237, flied April 12, 1941. The method therein disclosed comprises the complete oxidation of a metal sheetbygradualimmersion'oithesheetinan' electrolytic bath of such nature that the bath has the property of dissolving a portion of the formed oxide and wherein the level of the bath is varied during the immersion of the sheet, and

the said application,- the electrolytic bath may be a solution including sulphuric or oxalic acids and the thickness or the formedoxide'may be increased indefinitely if proper precautions are taken with respect to cooling the metal sheet and the formed oxide-although I prefer to use for the present application an oxidesheet havcordance with myprior manufacturing method are sufliciently thin, havehigh electrical resistance and are sufiicientlyfporous. The pores of an oxide sheet made as described above extend normal to the surface of the sheet and it is for this reason that such an oxide sheet is ideally suited foriorming'amosaic electrode in accordance with myteaching. As aresultof this'preferential alignment of the pores, the conductivity of my completed electrode is low laterally oi the sheet but sufliciently high normal to the surface for satisfactory use as a mosaic.

In accordance with my invention 1 flli the pores of theformed metal oxide sheet with-electrically the deflection plates may be replaced by a secand pair of deflection coils. and in fact. an other *Ul eolabctrmgnnandassociateddeilecflcn conductive material so that the resistance from one surface of the sheet to the other is relatively lowintheregionoithefllledpol'cs. Priortofllling the pores with conductive material I thoroughly dry the formed oxide sheet following the electrolytic formation process. I then deposit on one surface of the sheet a metal compound such as a metal salt which may be easily reduced to the metal. For example, particles of silver nitrate may be applied at random to one surface of the sheet by a dusting or spraying operation. The silver nitrate is preferably-in solid form rather than in solution, although for certain purposes a solution may be used. If, however, the solid silver nitrate is applied to the sheet reduce the silver nitrate to metallic silver. This baking step and resultant reduction of the metal salt to the metal requires only a shorttime, such as from to seconds. In the event that a solution of ametal compound or salt is used, the

, electron emissive under intermediate step of fusing the material and allowing the fused salt to soak into the porous sheet vmay be unnecessary, in which case the sheet maybe placed directly in the oven for the purpose of reducing the metal salt to the desired metal. I have disclosed the use of'silver nitrate as an example of reducible metal salt because silver is one of, the most suitable metals for use in combination with a mosaic electrode of the photosensitive type. Thus I do not wish to limit myself in practicing my invention to theuse of a salt reducible to silver inasmuch as other metal salts such as gold chloride or platinum chloride i or other compounds can conveniently be reduced to the free metaL- These compounds may be applied by spraying with an oil suspension of the type used to form metal coatings on glass.

Following the preparation and filling of the pores of the insulating sheet with metal, the

same may be sealed within the televisio'ntransmittin device, such as the tube shown in Figure 1, in close proximity to an elect'ron or light permeable electrode such as a wire mesh screen to serve as the signal electrode 20 shown in Figure 1. However, to obtain more uniform spacing between the signal electrode and the thin metal oxide sheet these parts may be assembled prior to introduction within the tube, as shown in Figure 2, by, supporting the metal oxidesheet and the signal electrode in a frame 24 separated'by a border of insulating material such as a cut-out 0 and heating the impregnated oxide sheet until emissive type, the metal particles may be oxidized and treated with an alkali metal as well known in the art. Since a photo-emissive surface is likewise highly secondary electron emissive, a single treatment to render the electrode radiant energy such as electron energy or light may be used. Such processing to render electrodes of the type described highly electron emissive are well known in the art.

While I have described an improved type of mosaic electrode and a method of manufacture, it will be appreciated that I am not limited to the materials herein set forth or the-particular steps or sequence of the method of manufacture but that many variations may be made in both the structure and method whereby the structure is obtained without departing from the scope of the appended claims.

I claim:

1. The method of making a two-sided mosaic electrode for television tubes comprising substantially completely oxidizing a thin sheet of aluminum by electrolytic action in a bath capable of dissolving a portion of the formed oxide and continuing said action until sufllcient oxide is dissolved to form pores extending from one outer surface of the sheet to the other, placing silver nitrate on one surface of the porous sheet of oxide, heating said sheet to the melting point of said nitrate, continuing the heating until said nitrate is drawn away from said outer surface and into said pores, and heating the impregnated oxide sheet until the silver nitrate is reduced and all the silver is held entirely within said pores I and extends from one side of the mosaic to the other with said outer surfaces free thereof.

2. The method ofmaking a two-sided mosaic electrode for television tubes comprising substantially completely oxidizing'a thin sheet of aluminum by'electrolytic action in a bath capable f 'other, placing a metal compound on one surface of the porous sheet of oxide, heating said sheet to the melting point of said compound, continuing the heating until said compound is drawn away from said outer surface. and into said pores,

sheet of mica 2U sp-.-'that the electrode 13 ex-[ posed on one side of the assembly, and the oxide sheet containing the metal particles formed by I l the reduction of the metallic salt is exposed on the opposite side of the assembly.

As indicated above, the .assembly of the oxide 7 sheet and associated signal electrode is assembled in the tube 'with the exposed surface of the oxide sheet facing the electron beam forming structure with the opposite side facing the signal I electrode and the photocathode :3 or the lens, system 0 through which the light forming the optical image is directed. For use in applications where an electron image is directed and focused upon the mosaic electrode it is desirable to treat the surface impinged by the electrons of the imsaid compound is reduced and the metal is'held entirely within mersing a thin sheet of aluminum in an electrolyte capable of slowly dissolving aluminum oxide,

substantially completely transforming said sheet by electrolysis to aluminum oxide, continuing the immersion of said sheet until suiilcient aluminum oxideis dissolved to form .pores extending entirely through said sheet at a multi-. plicity of points, removing the sheet from the" electrolyte, filling the pores thereof with a metal salt reducible at moderate temperature, and

age to renderit highly secondary electron emis- I sive. Such treatment may comprise depositing a metal of low work function such as caesium directly on the exposed surfaces of the metal particles 23. However, if the electrode is to be of the photoheating the impregnated sheet untilthe salt in. said pores is reduced and held entirely within said pores and extends from one side of the mosaic to the other and the outersurfaces are free thereof.

. HENRY 3. DE VORE.

said pores and extends from one side of'the mosaic to the other with said outer

Images