US2979633A - Storage electrode - Google Patents

Description

April 11, 1961 F. H. HARRls 2,979,633

STORAGE ELECTRODE Original Filed May l, 1957 FRANKLIN H. HARRIS INVENTOR ATTORNEY United* States. Patent ammessi STORAGE ELECTRODE;

Franklin H. fHarris, Accokeek, Md., assigner toE the United States of Americaas` represented. bythe. Seci retary'of theNavyy f Original applicat'on May 26 1958,. Sel'.l No. 737,986

now' Patent No. 2,926,419; dated Mar. 1, 1960. Divided and-application'May'119575501?. No: 656,471, now- Patent No. 2,957,1f'40, datedct18g`v1v960t Again 3"Claims. (Cl..313-8`9),` (Grantedf under Title 35,1. U.S. Code: (11952),.se'c'. 266) The invention described herein may be` manufactured and used` by or forA the 'Government of: the. United States of America for governmental purposes without the`V pay.- ment of any royalties thereon or therefor.

This application is a division'of'application Serial No. 737,986 filed May 26, 195'8, now Patent No. 2,926,419,

which inv turn is a division of application Serial No..

656,471-, led May 1, 1957, now Patent Number 2,957,- 140 issued on Oct. 1.8, 1960, and relates. toa. cathode ray signal storageelement or electrode.

lCathoderay tubes are well knownt in;r the prior art which will .perform Vthe sequential functions of.` anVV information dex/ice,- namely recording, storage, reproduction andV erasure of an-'information signal. Theseelectron dischargetubes operate uponthe principle ottranslating received information into, charges-,and coincident poten-- tials upon the surfaceof an insulating material and sub,-

sequently recovering this informationby exploring the.

surface; with a vfocused electron. beam,. As a'. result of the; extremely high impedance ofered by an insulator to the ow of current to and from a charged area, in thef element. f Y v Inl accordance tothe present invention a cathode rayf absence of a reproduction operationv thejchargesY and coincidentV potentials 'initiallytimpressedV uponV the die electric. will persist without substantial deterioration vover'- f a period of time during which the informationwhh they represent may be made available. When elicitation ofy the information stored is!` accomplished, however, by

scansion of the insulating surface withan electron reajd- 2,979,633 Patented Apr. 1l, 1961Y ICC 2' surfacefonl` whichy they information is; written on one. sideV ofthe screenandthe informationis-i read' from the op.- posite side.` This'requires, a1 rearrangement.' of the. electron guns such'that the read and write` guns are directly opposite each other and on oppositezsides of the storage surface. The present invention ismore specifically ref :lated to the storage surface.l

The `present inventionV also provides .ani improvement over the prior art tubes rwhich have read. and write` guns oni-opposite lsides of the: storage: screen.` In the prior artfdevioes` aff collector.v is: associated with the screen in thel form off' a coatinglon the'tube` surface. or. a charged screen` adjacent toVv they storage screen? surface; The; new mosaic tuben off thef presentv invention#A does: away with.: thei usualv collector through. the-"usen of an. improved storage screen which: serves: to; carrylout: proper" storage andi' also: acts'as thecollectorf- -Y It is. therefore; an object; of4 theapresent invention to provide; an improved: signal-storage4 device capable of' halftonerstorage.'andreproduction;

Yet; another.` object is to provide an vimproved two-sided Y mosaic'. which` is: simply-'and' cheaply manufacturedandl yet provides. good' control without. any.. deteriorationiofY the originalzstore'd pattern. i

A stillV further-object is to provide a; new and ineXpen-' sive two-sided mosaic.

Other and 'more specific objectsv of this inventiony will become apparent upon a more; careful consid-eratiomof' thefollowingf detailed. description when, taken; together` with the accompanying'drawingsin which:

Fig. 1 illustrates a cathoderay storageptubeincluding` y the mosaic made according to, the methodofj thefpresent invention"v and\ including aI writef'gun on one end and. ai* gun-r on the, oppositeend for'both holding-and reading;`

f FigVi 2 is algreatly enlargedcross` s ectionzofthe storag'e surface which illustrates the. relationshiprgbetweensithcf metal screenj andA the dielectric;n

isl anA enlarged view. Kof

i' storage tube yprovidedWithfa:mosaicmadein accordance to the structure of this invention is` capable o-f capturing-r ing beam, the information being recovered either as a] secondary emission-current `from tiret-dielectric or as` capacitively induced current dueto ajshiftinpotential of.-y Y

the initially impressed potentials,in-"thepriorl artzthe;

information: bearing charges -and'rpotentials are.A progres sivel'y destroyedwithsuccessive repetitionswofthe reading operation; yThusfinmost of the'priorgart vdevices information reproductioncan only beeffected by-destructive.

reading.,v

In my-,Patent #2,839,679 there is disclosed-a half-tone'.

memory: tube comprisingthree ele'ct ron:.gun's,y namelya Writing, a reading "and a holding gun positioned inta triangular mount, and a storagev surface-'or target capable I' of storingasignal for long periods of time.` The storage target has a face consisting of an electrically conducting',V member and an indefinitely large;A number ofi separated dielectric m'asses dispersed throughout the surface -of the conducting member in suiiicientconcentration so that A1 ac'onsiderable number of these dielectric masses appear' within :an area approximating `in dimension the, spot. of afi focuseduelectron beam.

The; present .invention is anY improvement over cof..

pending. application andlprovidesa two-sided mosaic i consisting `of a thin film of dielectric formed onan electro,

formed Vnickel screen-. The'rnew' type of mosaic perntitsl'gre'ater writing speeds and'alsoprovidesl afstorage i' "which exists partly ,witbinthe diel within the dielectriqisof no valueand there'fo as thina'spos'sible'. y Y Referring now j tof the vdrawings"wher Ycharactersr represent?` like -f parts thro l a single.. framefof. a televisionspicture which has; good tone'..quality. The storage tube can be ,used forwscamv "conversion, signalintegratiom for capturingsingle .tran-` Y siehts, and fo'r.l-temporary storage ofqdiferent patternsl such as maps forradar display purposes. t

; The storagetube device-is intended for storing electri cal charges and comprises a storage surfacerincluding-a.' conductive tine metal `screen grid-like structure havinga reading:` `In writing, the

chargesojn they write 'sidefo-fvthe dielect c. are 'storedE aspotential energy iniv an;

space between the dielectric'fand the metalscreeh.' Th mechanismsof' holding andrea'diiig' utiliz'ejoirl'y thef trostatic-fieldfin the spacci-near"the screen and the' belminirnized. 'Q For this reason; jdifelect "c 1 s the mosaic screen-struc- The screen 1s glass envelope 11 which encloses a storage electrode or mosaic 12 and two conventional cathode- ray guns 13 and 14. The cathode ray guns are positioned respectively in opposite ends of the tube on opposite sides ofthe storage electrodeand are magnetically focused and deected in the Yconventional manner asY used in television picture tubes. Conductive coatings 1S and 16 of silver paint are respectively provided on the inside and the outside ofv each end of they envelope to shield the storage mosaic from the electrostatic fields of the deflection coil and yet does not interfere with the magnetic fields. The inner as described above.'

coatings 15 merge with transparentV conductive coatings 17, such as a metallic oxide, which serves as the second anodes and are transparent to facilitate inspection of the inside of the tube if desired.k A cylinder 18 positioned within the envelope on the read-beam side of the storage mosaic serves to collimate the read-beam electrons in order to obtain equal values of forward electron velocity over the surface of the mosaic. /The collimating cylinder is provided with a ridge 19 about the outer surface thereof for'the purpose `of securing the cylinder within the envelope; for purpose of illustration, three glass holders 21 are provided for securing the collimating cylinder in position. The inner surface of the collimating cylinder has three equally spaced vtabs or lugs attached thereto along one end about the inner circumference to provide means for securing the mosaic surface in position with respect to the electron guns and the collimating cylinder. The structure for securing the storage element within the storage tube is more fullyr described and shown in the parent Application No. 656,471 filed May l, 1957, now Patent Number 2,957,140 issued on Oct. 18, 1960. The tube is provided with a Vgetter'27 to keep the residual gas pressure low during operation.Y e Y The mosaic comprises a thin dielectric film 36 having a `thickness of' from about .02 micron to about 1.3 microns which bridge the interstices or openings of a fine Vmesh nickel screen 35 having a thickness of about 0.00005 to about 0.0006 inch and from 300 to 1000 mesh per inch and formed according to the following method. The outer edge of the screen is placed over a nickelplated steel ring or hoop 23, stretched taut and then held in position by'placing ring V23 into a second like ring 24 of larger diameter, In order to position ring 23 with the tine mesh over it into ring 24, ring 23Yis cooled to shrink the ring and ring 24 is heated to expand it. The screen covered ring is then slid into ring 24 and the rings are allowed to return to `their normal temperatures whereby the screen and lring is held tightly in ring 24.I

The assembly is then cleaned by washing itin water with a detergent and'then in acetone to remove any foreign solids, salts or oils. Then the assembly is placed on a level surface and water is applied to the screen surface for wetting purposes. i

The dielectric lm is formed from a preparation ofv bentonit'eclay' hydrosol made from bentonite clay (montmorillonite) which is 'a natural mineral classed as an aluminosilicate Al2(Si4O10).XI-I'2O. A refined form ofl bentonite clay hydrosol containing 2.3% solids by weight is diluted with distilled water to form a iiuid which contains a much lower concentrationy of solids about 2.*8X10-4parts by weight. In percentage concentrations of 1% or more, the hydrosol has the property of being a thixotropic gel (the property of becoming uid when agitated and returning to a gel whenleft undisturbed). Ihedilute 2.8 10 4 partsv solid hydrosol appears to have the Yproperties of viscosit-y and surface tension identical Vto those o'f distilled water and can be applied to the screen inlqujd farm-w t l Y, i

I l prepared for coating as described above and the surfacev thereof wet with a pool ofl distilled water one-Vlv to two millimeters deep for approximately twenty minutes. .'ll'he small mesh ofthe screen and the surface nl'of'the water serves topprevent the'water from,

t?, Y going through the screen; however, if the screen is ex- After the distilled water hasbeen on the 'screen'sur-j face approximately minutes, most of thei water; is drained off with the aid of an aspirator or 4any other convenient means. Theremoved distilled water is immediately replaced with the -2;8`X 10'4 parts solid bentonite 1 clay hydrosol which has been vigorously stirred to insurea thorough dispersal of the solids. Approximately four milliliters ofA the hydrosol uid will easily spread over an area of about 40 square centimeters (a 27/a inch diameter screen). to form a pool one millimeter deep. The water evaporatesl from the solution and the surface of the screen, to leave a uniform hlm of bentonite clay which weighs approximately 1.1 milligrams and having a Vthickness of 0.1 micron (4Xl0-5 inches). The averagethicknessof the film is determined by the formula l todos (scum where d isithethickness in microns, w is the weight in grams of the formed lm, S.G. the specific gravity, and

A is the area (cm) of the covered screen. The above values for forming the dielectric film are typicalvalues for a preferred dielectric film and other concentration of solids may be used to form ilms having different thickness. Hydrosols containing 8.25 105 to 2.0 l0-3 solids by weight willv form suitable dielectriciilms having a thickness of from about 0.02 micron to about 1.3 microns, the thickness ofthe dielectric lm is limitedl by the thickness andfstrength of the screen surface. If the hydrosol placed on the screen is too heavy the screen will tear away and' films cannot be formed; therefore,

the thickness of the hlm is' limited to the strength of theV screen.

. It is highlyimportant that dust particles do notV settle on' the screen during V"forming and that the iilm havel uniformY thickness. For 4this purpose the screen is placed on a stationary level stand orf-hat surface and a glassE cover is placed overthe screenras soon as the hydrosol has been placed on it.VA Since the screenis covered, drying proceeds slowly wherein the water is formed to evaporate primarily ,from the underside through the openings in the screne. Since the hydrosol has approximately thepropertiesl of viscosity and surface tension of distilledA water, the 'uid -is pulled by gravity into Vthe-interstices of the screen whereinthe'ffluid clingsgto the screen surface due'to surface tension, this lformsfa uniform film within thev interstices which is thicker than `the hlm over the screen surface. When the water has evaporated and the film formed onto the screen, the screen is removed from the glass cover.'y The screen in this state can be yused as a storage surface; however, the film does' notA l demonstrate as -low an electrical conductivity asN mica and vhas slight electrical leakage, therefore it isy neces` sary to further .treat the hlm to obtain the desired dielec- Vtric qualities. l. r e

Thebentoniterclay;iilmtcan beconverted to aY lowconductivityA material similar to'mica by either of the following two methods. InI one method, the storage screen is removed from under .the glass cover and placed 'in a container such asa stainless steel vented container and heated at approximately 1000 degrees for 20V minutes inf'hydro'gen. The stainless steel"v vented container serves to shield the screen from .theheating llame of the hydrogen furnace and also provides thermal 'lagl which prewould shrink more rapidly than the mounting rings and therefore would rupture if allowed to cool too rapidly. The storage surface is removed from the hydrogen atmosphere while it is hot (approximately 400 degrees centigrade) and cooled within the container'in air. It has been determined that removal from the hydrogen at a temperature below 400 degrees centigrade makes the bentonite film slightly conductive and when removed at temperatures greater than 400 degrees centigrade, a slight oxidation of the nickel screen occurs. Oxidation is not signicantly harmful for operation in the tube of the present invention.

In another method of converting the bentonite clay film to a low-conductivity material, the film is treated with lead. Bentonite clay dispersed in water is necessarily sodium bentonite, therefore the dried film on the screen is sodium bentonite clay. The assembly of the screen with the dried film thereon is immersed in a concentrated lead-nitrate solution. A base exchange reaction occurs in which the sodium of the film is replaced by lead. After about a five-minute immersion in the lead-nitrate solution, the assembly is removed from the solution, rinsed with distilled water and then dried. The

films are nonconductive and have the properties of mica.

Films as thin as 20 millimicrons have been formed by this method, wherein such thin films formed by the first method would disintegrate due to the high heat intensity.

In either method described above, the conductivity of the lms is comparable to that of mica, and this, combined with their thinness, results in negligible conductance along their plane. Even though the films are very thin, they can withstand the high bake temperature (400 C.) required to outgas the tube. In addition sodiumbentonite iilms have excellent mechanical adherence to the nickel screens in order to form the thin films in the interstices of the screen and in which that portion of the lm covering the conducting portions of the screen are thinner than that within the interstices.

A mosaic formed according to the above method combines a metal screen and a very thin insulator in which the insulator is formed in the interstices such that the cells of the insulator are electrically guarded one from the other by the conductor screen. The read beam bombardsV both the conductor and insulator to fulfill read and hold functions, and the write beam can charge the insulator and control the field on the read side. The latter is attained by forming the insulator very thin, so that large voltages cannot exist between the write and read surfaces, and the insulator has high resistivity so that the written charges will not leak off.

In some other typecathode ray tubes it may be desirable to make a conductive screen with a thicker insulator surface in which it is essential that one face surface of'y the screen be in contact with the insulator material. For such tubes, the storage electrode lmade according to the above method can be used wherein the dielectric film side of the storage electrode is used as a substrate and an insulating material 37 added thereto byany Well known method such as the evaporation technique, or the water dispersed colloid suspension method. For example,

. quartz, silicon dioxide or aluminum oxide can be added to the bentonite clay film to increase the thickness of the insulating surface. The application of the additional insulating surface by the colloid suspension method is preferred since the liquid would flow into the interstices,

fill the interstices and then provide a smooth outer surface. In the evaporation method the insulation would build up over the screen surface as well as in the interstices. lThe method used depends on the outer surface desired.

For a more complete and detailed discussion of the electrical operation of the mosaic due to the incident beam from the writing and reading guns and operation of the storage tube is set forth in my Patent No. 2,839,679 and in the parent application Serial No. 656,471, filed May l, A1957, now Patent No. 2,957,140, issued on Y October 18, 1960; vThe present invention is concerned with the use of this dielectric film for the mosaic of a storage tube; however, it would be obvious to anyone skilledin the art to use thindielectric films for other uses. Therefore, it is to be understood that, within the scope ofthe appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:` 1. An electron beam target for a cathode ray device comprising a conductive grid-like structure having a plurality of interstices, a dielectric film distributed on a single surface of said grid-like structure, said film extending into and across said interstices in a plane midwayv between the outer. surfaces of said grid-like structure, said ilmextending into and across said interstices having a ythickness greaterthan the thickness of said film over saidy References Cited in the file of this patent UNITED STATES PATENTS '2,237,681 McGee et a1 Apr. s, 1941 2,905,844 Sternglass --.Sept 22, 1959

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