US2403224A - Electrode structure and method of manufacture - Google Patents

Description

y 1946- H. B. LAW

ELECTRODE STRUCTURE AND METHOD OF MANUFACTURE Filed Oct. 25, 1942 INVENTOR 5 l RNEY Patented July 2,' l946 ELECTRODE STRUCTURE AND METHOD OE MANUFACTURE Harold B. Law, Princeton, N. J assignor to Radio Corporation of America, a corporation of Delaware Application October 23, 1942, Serial No. 463,065

7 Claims.- (Cl. 49-79) My invention relates to television transmittin tubes and electrode structures and more particularly to methods of manufacturing target structures suitable for use n tubes of the low velocity electron beam scanning and electron image types.

-In television transmitting tubes utilizing electron beam scanning with optical or electrical imageproiection on a surface other than the surface scanned by the electron beam, it has been proposed to utilize an image grid mosaic-type target, such as disclosed by Iams in his U. S. Patent No. 2,213,179. Such target electrode usually have a wire mesh foundation and are exceedingly difficult toconstruct, the task of forming a struc ture having over 100,000 electrically discrete highly insulated metal plugs extending through the target and insulated from the signal screen embedded in the target being a tedious and difficult manufacturing problem. In addition, such electrodes, even though prepared with exceptional care, produce a spurious signal not representative of the electron or of the optical image due to electrical or mechanical non-uniformities over the target surface. Such u'niformities are accentuated when the electrode is used in electron beam seaming tubes utilizing low velocity electron beams.

It is an object of my invention to provide tarprovide apertures through theiorindation opposite the depressions or bubble sections about or in which I provide a mosaic which may b photosensitive or'secondary electron emissive.

These and other objects, features, and advantages of my invention will be apparentfrom the followin description and with reference to the.

accompanying drawing wherein:

9 Figures 1 through 6 are sectioned views of a target structure following'six successive steps of manufacture.

It will be appreciated that the target structure made in accordance with my invention i useful in many types of television transmitting tubes, and consequently, I have not shown in the drawing any particular type of tube to which it i ap-.

plicable. For example, the target structure may be utilized in image tubes scanned by alow velocity electron beam such as described by Iams in his U. S. Patent 2,213,179, although one modiflcation thereof may be utilized as a double-sided et structures for electron beam tubes such as of the television transmitting type producing higher sensitivity and lower distortion than structures constructed heretofore, as well as a method whereby such structures may be manufactured with ease and at low cost. It is another object to provide a target without an electrically conductive foundation to which leakage may occur. It is a further object of my invention to provide methods of manufacturing television transmitting tube targets suitable for use for low velocity.electron beam scanning which are capable of exceptionally high sensitivity with substantial elimination of all spurious signals. It i a still further object to provide a tube having a target structure which may be manufactured with-high uniformity and with ease and at low cost.

In accordance with my invention! rovide a thin sheet of insulating material preferably of vitreous construction and I develop a great multiplicity of very small depressions or bubbles in the foundation by coating the foundation with a tacky or adhesive preferably volatile material. dismosaic electrode such as in a tube described by Iams in his U. S. Patent 2,213,178. While the target electrodes of these tubes are somewhat different, my method of manufacture provides electrodes suitable for such use.

Referring to Figure 1, the target foundation comprises a very thin initially imperforate foundation sheet I of electrically insulating or semiinsulating material such a glass havinga resistance greater than 10 ohm-centimeters. Preferably, an exceptionally thin homogeneous sheet of vitreous material such as glass having the desired specific resistance depending upon its specific use as referred to'hereinafter and being smooth and of uniform thickness may be used. I have used glass known in the trade as Corning705 glass with satisfactory results. Preferably, the target foundation'sheet i has an initial thickness of from 0.001" to 0.005". Such a thin sheet of vitreous material may be made by the cylinder proc- 1 cylinder longitudinally, and then opening out and tributing small particles or crystals of refractory 1 material over the adhesive and baking to provide asreat multiplicity of bubbles in the foundation. Further in accordance with my invention I may flattening the split cylinder on a flattening stone in a flattening oven. Following preparation of the thin foundation sheet I and in accordance I with my invention, I coat one surface of the sheet with a thin coating 3 comprising a tackly, adhesive, and preferably volatile material which durdissolved in a solvent. ment known as Best-Test'as supplied by thev 3 1 small refractory particles as shown in Figure 2, the average size of the particles preferably being less than the thickness of the sheet I. These pardiflerent siz so that the results obtained with such variation in particle sizemay be differentiated. Following the application of the coating 3 and the distribution of the particles 5 over its exposed surface, I place the sheet I in aif'urnace.

or oven and heat the sheet to a temperature slightly exceeding its softening point. During the initial-stages of this hakingthe coating 3 vaticles are preferably of uniform size and shape. 6 although I have shown the particles 5 as being of be opened by this treatment as shown at the right in Figure 4. However, as is usually the case, if diflerent sized bubbles are formed as shown at the left of Figure 3, some bubbles mayinot be opened on the opposite side of the-sheet as shown at "the ,left of Figure 4. .For, thedouble-sided mosaic structure, it is desirable that as many as possible of the bubbles extend completely through the foundation sheet and I-then fill the apertures thus formed-with metal plugs 9 as shown in Fi ure 5. A suitable method of filling the apertures and forming the metal plugs is described by Rose in his U. S. Patent 2,175,701.,

porizes and as the'temperature isfurther raised i small bubbles or depressions I-are formed-in thevitreous foundation sheet I as shown in Figure 3. I. have not been able to explain the-action upon heating the sheet bearingthe particles, but the 7 average size of thebubbles depends upon the time of heating to a great extent.

The foundation as shown in the drawing may ;be etched to a greater extentthan shown in Figure" 5 to assure the formation of the maximum I number of apertures. especially if the size of the I have obtained the best results in practicing my invention by utilizing silicon carbide particles,

Unio'n Rubber and Asbestos Company, of Trenton, N. J., is suitable for this purpose. The rubber cement is applied and allowed to dry for a few minutes and then the Carborundum particles grade. 600 are brushed over the rubber coating.

particles 5 'is'non-unifo'rmas shown in Figure 3.. I have shown in Fi re 6 a target foundation made in accordance with my invention particularly adapted to tubes of the type described in the first-mentioned Iams patent wherein the apertures I I of the sheet I are allowed to remain open but are surrounded with small mosaic globules I3. The globules I3 may be of silver and may be photosensitized as described by Iams to limit the flow of electrons through the apertures II in accordance with charges developedby an optical image formed on the globules It. Obviously, the globules I3 may be made photosensitive or secondary electron emissive by superficial- The rubber film being tacky does not materially I wet the Carborundum particles so that only a single layer of the particles sticks to the film.

The firing or baking operation is somewhat critical as to temperature and time, although the bubbles begin to form around 775 C. for the 705 glass. However, I prefer to place the prepared foundation in an oven which has been heated previously to approximately 800 0., allowing the foundation to remain in the oven for 5 minutes.

following which it is removed from the oven and cooled. Alternatively the prepared foundation may be placed in a cold oven and the temperature raised to 800 C., the foundation being allowed to remain for 2 to 5 minutes after reaching this terns perature. The small Carborundum particles are actually fused to the glass at this temperature.

Following the firing operation, I immerse the sheet in a hydrofluoric acid solution which dissolves the Carborundum particles as well as a portion of the glass foundation. Consequently, the

thickness of the original glass sheet is chosen to allow for this step. An aqueous solution of 10 parts water to 1 part concentrated hydrofiunric acid is preferred. The foundation then may be processed further depending upon the partionlar type: of tube for which the target is designed, that is, whether of the double-sided mosaic type or of the perforated image type.

For providing a target of the double-sided type shown in Figure 5, I prefer to provide perforations in the foundation sheet by opening .the

' bubbles to the opposite side of the sheet from that originally bearing the particles 5. For example, the sheet may be immersed in the hydrofluoric acid to further reduce the thickness of the sheet, thereby opening the bubbles to form apertures 8 extending completely through the sheet. Pro- ,vide'd the bubbles were originally of substantially the same size, substantially all of the bubbles will ly oxidizing the globules and subjecting them to caesium or other alkali metal vapor.

Instead of distributing the refractory particles 5 over the entire surface of the adhesive coated foundation they may be deposited as a regular array such as by settling the particles through, the interstices of a wire mesh or otherwise apertured screen. This procedure allows spaces between groups of bubbles which may be of advantage in certain applications. Furthermore, substantially spherical bubbles may be formed by r moving the Carborundum particles following firingwithout the use of'acid. Thus the'partlcles may be removed by an abrasive action such as by rubbing the top surface of the foundation with fine emery paper. If this method is followed, there will be substantially no rounding of the bubble openings and the bubbles will be substantially spherical. I

I claim:

1. The method of manufacturing a foundation for an electrode structure comprising heating a vitreous insulating sheet bearing fine particles of a refractory material at a temperature suficient to form bubbles in said sheet underlying the said particles of refractory material and removing said particles from said sheet.-

v2. The method of manufacturing a foundation for an electrode structure comprising coating a tsheet of glass with an adhesive, distributing over said adhesive small particles of a refractory material, heating said sheet bearingsaid particles to a temperature sufiicient to cause the formation of bubbles in said sheet underlying said particles and removing said particles to expose said bubbles.'

3. The method of manufacturing a foundation for an electrode structure comprising the steps of coating a thin sheet of glass with small parti- 4 acoaaaa said particles to expose said bubbles to the atmosphere.

4. The method of manufacturing a foundation A structure for a mosaic electrode comprising forming a thin sheet of vitreous material, forming a tacky adhesive coating on one side of said sheet, affixing small silicon carbide particles to said coating, the size of said particles being less than the thickness of said thin sheet, heating said coated sheet and particles for a period of time suflicient to form bubbles on saidsheet under said particles and removing said particles from said sheet.

5. The method of manufacturing a mosaic electrode foundation comprising the steps of forming a thin sheet of glass between one thousandth and five thousandths inches in thickness, coating said sheet of glass with a volatile rubber base adhesive, distributing particles of silicon carbide over the surface of said adhesive, heating said glass bearing said particles to a temperature at which said glass softens and develops bubbles underly- 6 6. The method of manufacturing a mosaic electrode foundation comprising forming a thin sheet of glass having a softening point below 800 C.,

, electrode foundation comprising forming a thin ing said particles, cooling said sheet and immersing said sheet in an acid which is capable of dissolving said particles to remove said particles from said sheet leaving said bubbles exposed on one surface thereof.

sheet of glass of from one thousandth to five thousandths inch in thickness, coating one surface of said glass sheet with a rubber containing adhesive, forming a layer of silicon carbide particles having an average size less than the thickness of said sheet on said adhesive, heating said sheet of glass to a temperature above 775 C. for a time suflicient to form bubbles under the said particles, cooling said sheet and removing said particles to expose said bubbles.

HAROLD B. LAW.

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