US2926419A

US2926419A - Method of forming a storage electrode

Info

Publication number: US2926419A
Application number: US737986A
Authority: US
Inventors: Franklin H Harris
Original assignee: Individual
Current assignee: Individual
Priority date: 1957-05-01
Filing date: 1958-05-26
Publication date: 1960-03-01
Anticipated expiration: 1977-03-01

Description

March 1', 1960 F. H. HARRIS METHOD OF FORMING A STORAGE ELECTRODE OriginalFiled llay 1, 1957 3 Sheets-Sheet 1 j a m w. .v m s m E l O v. n+ MM w A .A 5 mm H 5 09 mm m L F. mm o ov K 8 Wm M 6 09 F I we C Y 35+ omm+ v m B NN O March I 1 960 js 2,926,419

METHOD OF FORMING A STORAGE ELECTRODE Original Filed llay 1, 1957 3 Sheets-Sheet 2 &. am mm w: a ssmm 1 w msxwmsamsss INVENTOR FRANKLIN H. HARRIS i ATTORNEY) shown by illustration inv Fig. 1 comprises an evacuated 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 respec tively in opposite ends of the tube on opposite sides of the storage electrode and are magnetically focused and deflected in the conventional manner as used in television picture tubes.

Conductive coatings

15 and 16 of silver paint are respectively provided on the inside and the outside of each end of the 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 coatings 15 merge with transparent 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. A cylinder 18 positioned within the envelope on the readbeam 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 t'abs or lugs 22 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 tube is provided with a getter 27 to keep the residual gas pressure low during operation.

Fig. 2 illustrates the relationship of the collimating cylinder and the mosaic surface. The mosaic surface is formed between two hoops or

rings

23 and 24, one fitted into the other to hold the mosaic surface therebetween and then assembled between a metal disc 25 through which electrical connections are made to the metal screen of the storage surface and mica disc 26 made of several layers of mica by three bolts 28 and nuts 29. Any suitable insulators 31 such as glass, are provided to insulate the metal disc from the bolts and also to provide space between the metal disc 25 and mica disc 26 in which space the mosaic is positioned. Mica disc 26 has a metal disc 32 secured thereto by tabs 33 which are bent over along the surfaces of the metal disc 32 and connected to a few of the mica layers of the'mica disc 26. Metal disc 32 is cut away in the vicinity of the bolts 28 and therefore does not have to be insulated therefrom. The ends of bolts 28 are insertedthrough lugs 22 and connected thereto by nuts 34 and the mica disc and the metal disc 25 is connected to thebolts by nuts 29 screwed on the ends of the bolt, the collimating cylinder and mosaic surface is now ready for assembly in the envelope and connected to the proper lead lines from suitable pins in the connector 30. I

The mosaic is made of a very thin metal screen 35 having a thickness from about 0.00005 to 0.0006 inch and with from about 300 to 1000 mesh per inch. The thin metal screen is covered with bentonite clay by a method to be described later to form a very, very thin dielectric surface 36 which fills the openings or interstices of the screens and also covers the screen surfaces,

however, that portion of the dielectric which covers the screen surface is much thinner than that which fills the openings and the dielectric effect of that covering the screen is negligible since it is so thin; therefore, in effect, the dielectric film in each of the interstices form individual isolated cells separated by the conducting portions of the screen. The mosaic is secured to the collimating cylinder and preferably positioned to receive the write beam on the dielectric side of the wire screen.

Fig. 3 is a schematic of the tube illustrating the operating voltages for the various elements and in operation of an assembled tube, magnetic focusing and electron acceleration is carried out by conventional television type scan circuits 37 illustrated in block form by Fig. 4 in which the accelerating and focusing assemblies are maintained at a positive potential with respect to ground. The write cathode 41 is maintained at an operating negative voltage of about 1000 volts by any suitable grounded voltage source not shown and has connected thereto a variable write beam current control 42 of volts for controlling the period during which writing proceeds. Electrons emitted by the cathode are resolved in the usual mannerv by the accelerating and focusing mechanism into a-writing beam of small cross sectional diameter and high intensity, the intensity of which may be modulated by information signals originating with an information signal source 43 and impressed upon the write control grid 44 in the form of v,varying voltages. The bias of the control grid relative to thecathode may be adjusted as desired by a variable tap 45 on the current control 42and has a decoupling resistor 46 connected between the grid and the tap. The first anode 47 is placed at a relatively high potential such as positive 1.5 kvcwith respect to the cathode and a second anode 48 is placed at a potential still higher than the first anode such as a positive 3 kv. with respect to the cathode. The second anode is the same as the inner coating 17 and has an additional purposeof collecting secondary electrons which escape from the mosaic. Between the first anode and the write grid a second grid 49 with a negative voltage of about 500 volts is placed. The electrons from the write gun strike the insulation with sufficient energy to generate secondary electrons in excess of the primary electrons on the insulator. The mosaic is maintained at zero potential and is brought out through an external load resistor 51 to ground. The video output from the mosaic is taken off by a terminal between the resistor and the mosaic and connected to the input circuit of a video amplifier 52 which is then connected to the control grid of a monitoring cathode-ray picture tube 53. 1

The read beam and holding electron gun assembly 13 islocated on the opposite side of the mosaic from thewrite gun 14 and focuses the read beam current onto the metallic screen and insulator cells of the storage mesh with a constant beam current. The read cathode 54 has a negative potential of about 40 volts for holding without any decay. The cathode has connected thereto a read beam current control 55 which is connected to a control grid 56 by a variable tap 57. A second control grid 58 having a positive potential of 400 volts relative to the cathode is positioned about the cathode between control grid 56 and a first anode 61 which has a positive potential of 1.5 kv. with respect to the cathode. Asecond anode connection 62 connects with the inner coating 15 and the transparent coating which forms the second and has an additional purpose of collecting stray electrons and to help protect the mosaic from electrostatic forces. Collimating cylinder 18 having a positive potential of 350 v. is positioned on the read beam side of the tube adjacent to mosaic 12 and serves to collimate at right angles the read beam electrons with respect to the mosaic surface. Metal disc 32 connected to the mica plate 27 is electrically connected to an outside terminal and adapted to be provided with a positive potential, if additional electron correcting features are required for collimation. I

In the preferred operation of the device, the insulatorcells of the mosaic are erased and prepared for writing by priming to the black" by means of a priming cycle. This is done by scanning the insulator-cells with a read beam whose cathode voltage is nearly at zero, then in a short time about second, the cathode voltage is re I tra nee-n You the surface of the envelope.- i g v V I In reading the stored signal, the electronsfrom the insnlator -ce s.

fead eathode voltage, and th-us iriainta I u trons, ebnsequently, very few secondary electrons are released-by the surface. The efiectof primingthe mosaic is' to cause negative charges to appear on the write side a w velocity of arriving read else-- [write electrons with 1000 volt's energy strikes the in= of the-insulator wherein during the Writing period, electrons with; about 1000 volts} energy strike the insulator Wit ample velocity to" genefate'secondary electron'sin exces of; the primary-electrons from the ;Write-:cathode.

The escaping secondary electrbns in excess of the numberet beam electrons striking-the insulator results in a net;positive charging of the insulator and results in writing on the mosaic. The escapin secondary electrons are collected by. the positive co-ating'of the secendanode readelectron gun 13 providing 'the read beam are fo 'rentfrom thei'conductive metallic mesh, owing to charges in the insulatorlcells; register as" variations in the current 'throughtheload resistor 51-;corinected externally to. the eionduc't' emesh and constitute the output-reading current. The load resistor "51 has negligible D.C.

voltagefdroplas a consequence of the read or wr'ite'b'eam curr" ts.' Simultaneous with reading, the read beam re% The variations in secondary escape curreturn to their normal temperatures whereby the screen generates original Written charges within-Z each insulator" c'ell by' its holding "action. {The bombarding velocity has the same value of all parts of the mosaic because the =deflection'angles" are cancelled out by the lens produced by the col-liniating cylinder. At read-beamf bombarding energies less than thecritical potential; V (the p'otentialofthe bombardeddielectric portionwith respect to V the electron source, where the total number of'secondary "electrons es'caping from the surface of the dielectric equals the totalfnurnber of primary electrons absorbed by it) the insulator-"cells accumulate electronsand charge negatively to a potential Y At'read-beam bombarding energies higher than V the insulator cells lose electrons and charge positively to an equilibrium potential V where the potential of the insulator cells equals the po tential of'the conducting member. The holding action ofthefread-beam overcomes electrical leakage and other deleterious effects, and thus the charge pattern established by the ,writebeam is maintained withirfeach storage cell v at either the positive equilibrium potential V (white) or the negative equilibrium potential V tblack),

Airnore complete and detailed discussion of the elec- 'tri'cal-;-operation of tlie r'nosaic due to the incident beam from the Writing and reading guns is set .forth in my copending application Serial No. 288,365, filed May 16,

It is to be understood that the new mosaic of the present invention can" be used with a three gun tubewherein fthe read and write guns are onv oppositetsides of the :mosaic and the holding gun isset oii to one side on-the read side of the mosaic. The operation of the holding gun is substantially the sameas described in my re ferred to copending application andthe holding beam is properly focused onto the mosaic by, the .collirnating cylinder.

"In operation of the two gun s'torage 'tube for'long time storage the mosaic isrprimed to charge the insulator cells ne'ga'tivelyiin order to maintain low velocity of arriving flp'laced with the 2.8Xl0- parts solidf -'bentonite ela y read electrons, during priming negative charges are caused to appear" on the {write side-sot the insulator;

sulator with "am le velocity to generate s'econdaryelec trons in excess of the primary electrons. The excessj I secondary electrons escape to'result in"- a net positive charge on the insulator which corresponds to writing white. The net positive charge remains on the" insulator .s'urface, then the read beam of a negative 40' volts is focused on-the read side of the screen. The read beam scans'the metallic screen and insulator cells of the storage surface to provide'secondary electrons. Due to: the charge of the. screen and, insulator; the secondaries are emitted with very low velocities and are easily controlled by the nearby electric fields of the insulator cellstThe, variationin secondary escape current, from the metallic screen mesh due to the charges in'the insulator cells, register as variations in the current through the load re: sistor connected to the screen mesh and constitute the output signal (reading current) to'the cathode ray tube circuitry where the signal is reproduced on the screen of the'cathode raytube. i

The mosaic comprisesathin dielectric film h ving a thickness of from about 102 micron to about 1.3 mi;

crons' which bridge the openings of a fine mesh nickel screen having a thickness of about 0.00005 to about 0.0005 inch and fro-m 300 to 1000 meshfper inch-and formed according to' the following method; The -screen is -placed over a nickel-plated steel ring OIfhOOp 23,

stretchedtaut and then held in position by placing ring 23 into a second like ring 24 of larger diameterr ln orderto positionring 23 with the'fine mesh over it. into ring 24, ring 23 is cooled to shrink the ring and ring 24 is heated to expand it. The screen covered .r'-in'g is illeli slidQiZlitQ 'ring24 and thering's are allowed to and ring is held tightly in ring 24. The assembly is then cleaned by Washing it in water with a detergent and then'in acetonejto remove any foreign solids, salts or oils. LThen the assembly is placed on a level surface and water is applied to the screen surface for wetting purposes.

The dielectric film is formed from a preparatio-n of vbentonite clay hydrosol made from bentonite clay (montmorillonite) which is a natural mineral classed as an 'alurninosilicate Al (Si O ).xH O. A refined form of bentonite clay hydrosol containing 2.3% solids by weight is diluted with distilled Water to form a'fluid which contains a much lower concentration of solids about 2r8 l0f parts by weight In percentage concentrations of 1% or more, the hydrosol has the property of being a thixotropic gel (the property of becomingfliiid when agitated and returning to a gel when left undisturbed). '1l1e"dilute'2.8 10-' parts solid hydrosol appears to have the properties of viscosity and surface ten sion identical to those of distilled water and can be applied to the screen in liquid form. I s s The screen is prepared for coating as described above and the surface thereof wet: with a pool of distilled water one to two millimeters deep for approximately twenty minutes. The'small meshof the screen and the-surface tension of the water serves-to prevent the water from going through the screen; howevenif the screen'is extremely clean the Water will run through. In. order to obviate this, the screen is purposelycontaminated with any suitable solution, for example by immersing the screenmomentarily in a solution of amyl acetate and 10* parts by volume of co'llodion. Thisis allowed '0 dry and then the distiiled'water is placed onthe surfaee as described above. c

After the distilled water has been on the screen surface approximately 20 rninutes,.most of the water is drained ofi'with the aid of an aspirator or any other convenient means. The removed .distilled water immediately rehydrosol which has been vigorously stirred to-insnrea thorough dispersal of the solids. Approximatelytfour evaporates from the solution and the surface of the screen, to leave a uniform film of bentonite clay which weighs approximately 1.1 milligrams and having a thickness of 0.1 micron (4X inches). The average thickness of the film is determined by the formula where d is the thickness in microns, w is the weight in grams of the formed film, S.G. the specific gravity, and A is the area- (cm?) of the covered screen. The above values for forming the dielectric film are typical values for a preferred dielectric film and other concentration of solids may be used to form films having different thickness. Hydrosols containing 8.25 1O' to 2.0 1O- solids by-weight will form suitable dielectric films having a thickness of from about 0.02 micron to about 1.3 microns, the thickness of the dielectric film is limited by the thickness and strength of the screen surface. If the hydrosol placed on the screen is too heavythe screen will tear away and films cannot be formed; therefore, the thickness of the film is limited to the strength of the screen. 4 7

It is highly important that dust particles do not settle on the screen during forming and that the film have uniform thickness. For this purpose the screen is placed on a stationary level stand or fiat surface and a glass cover is placed over the screen as soon as the hydrosol has been placed on it. Since the screen is covered, drying proceeds slowly wherein the water is forced to evaporate primarily from the underside through the openings in the screenf Since the hydrosol has approximately the properties of viscosity and surface tension of distilled water, the fluid is pulled by gravity into the interstices of the screen wherein the fluid clings to the screen surface due to surface tension, this forms a uniform film within the interstices which is thicker than the film over the screen surface. When the water has evaporated and the film formed onto the screen, the screen is removed from the. glass cover. The screen in this state can be used as a storage surface; however, the film does not demonstrate as low an electrical conductivity as mica and has slight electrical leakage, therefore it is necessary to further treat the film to obtain the desired dielectric qualities.

The bentonite clay film can-be converted to a lowconductivity material similar. to mica by either of the following two methods. In one method, the storage screen is removed from under the glass cover and placed in a container such as a stainless steel vented container and heated at approximately 1000 degrees for minutes in hydrogen. The stainless steel vented container serves to shield the screen from the heating flame of the hydrogen furnace and'also provides thermal lag which prevents rupture of the storage surface when the container is removed from the furnace. The screen being thin would 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 significantly harmful for operation in the tube of the present invention.

1 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 sereenis sodium bentonite clay. The assembly of the 8 screen with the dried film thereon isimrnersed in a concentrated lead-nitrate solution. A base exchange reaction occurs inwhich 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 films is comparable to that of mica, and this, combined with their thinness results in negligible conductance along their plane. Even though the films are verythin, they can withstand the high bake temperature (400 C.) required to outgas the tube. In addition sodium-bentonite films 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 film cover.- ing 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 bombards 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 ofi.

In some other type cathode ray tubes it may be desirable to make a conductivescreen with a thicker insulator surface in which it is essential that one face surface of the screen be in contact with the insulator material. For such tubes, the storage electrode made 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 added thereto by any 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 fiow into the interstices fill the interstices and then provide a smooth outer surface. In the evaporation method the insulation would buildup over the screen surface as well as in the interstices. The method used depends on the outer surface desired.

The 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 skilled in the art to use thin dielectric films for other uses; therefore, it is to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. 1

What is claimed is:

l. The method of making a storage electrode for a signal device comprising a grid-like structure having a plurality of interstices therein mounting said grid-like structure under slight tension between the outer and inner surfaces of two loops, cleansing said structure to remove foreign solids, salts and oils, placing said structure on a level surface, wetting said grid-like structure with a deepness of from about one to two millimeters of distilled water, draining the major portion of said distilled water from said surface, replacing said water with sufficient fluid bentonite clay hydrosol to cover said grid-like structure and allowing said liquid to dry slowly to form a film of bentonite clay over the surface of said grid-like structure and across and into said plurality of interstices in a 9 plane midway between the outer surfaces of said grid like structure.

2. The method of making a 'storage electrode for a signal storage device comprising a grid-like structure having a plurality of interstices therein, mounting said gridlike structure under slight tension between the outer surface of one hoop and the inner surface of a second loop,

cleansing said structure to remove foreign solids, salts and oils, placing said structure on a level surface, wetting said grid like structure with a'deepness of from about one to twomillimeters of distilled water for about 20 minutes, draining the major portion of said distilledwater from said surface, replacing said water with sufficient fluid bentonite clay hydrosol to cover said grid-like structure with a pool one millimeter deep, allowing said liquid'to dryslowly to form a film of bentoniteclay over thefsurplurality of interstices in a plane: midway between the outer surfaces of said grid-like structure. 7

3. The me'thodas claimed in claim 2 wherein a cover is placed over the grid-like structure. during drying to prevent dust particles from falling thereon. q

4. The method of making a storage electrode for a signal storage device comprising a nickel grid like struc ture having a plurality of interstices therein, mounting saidgrid-like'structureunder slight tension between the outer surface of one nickel-plated steel hoop and the inner surface of a second nickel-plated steel hoop, cleansing said structure by washing .first in water with a detergent, then in acetone, to remove any foreign'so lids, salts and oils, contaminating said grid-like structure by immersing it momentarily in a suitablesolution, placing said struc- 'ture on a level surface, wetting said grid-like structure by covering the surface rwith' a pool of distilled water one to two millimetersdee'p for about '20 minutes; draining said distilled water fromfthe surface of said structure, replacing said distilled water with a one millimeter deep pool of liquid bentonite clay hydr osol over theentire surface, covering the structure and allowing the liquid to evaporate to form a film of bentonite clay on one surface of said gridlike structure and into and across said interstices in ,a

' plane midway between the outer surfaces of said grid-like" structure.

5. The method of making a storage electrode for a signal storage device comprising-a nickel grid' 'like structure having a plurality of interstices therein, mounting 'face" of said grid-like structure and across and into said nitrate solution for approximately five minutes, removing said grid-like structure under slight'tension between the outer surface of one nickel-plated steel hoop end the, in-

ner surface of a second nickel-plated steel hoop, cleansing said structure by Washing first in water with a detergent,

then in acetone, to remove any foreign solids, salts and oils, contaminating said grid-like structure by immersing it momentarily in a suitable solution of amyl acetate and about 10 parts by volume of collodion, allowing said contaminated structure to dry, placing said structure on .a level surface, wetting said grid-like structure by covering the surface with a pool of distilled water one'to two millimeters deep for about 20 minutes, draining said distilled water from the surface of said structure, replacing said distilled water with aone millimeter deep pool'of liquid bentonitefclay'hydrosol over the entire surface, covering the structure and allowing the liquid torevapo- 7 rate to form a film of bentonite clay on one surface of said grid-likestructure and into andracross saidtinterstices in a plane midway between the outer surfaces of I said grid-like structure. I V t V 6. The method as claimed in claim 4 wherein the formed film is further treated to form a low-conductivity insulator material. v

7. The method as claimed in claim 4 wherein the formed film is treated to form a low-conductivity insu- -lator material by placing said structure in a container and firing the storage structure at about 1000 C. for about 20rninutes in hydrogen, allowing the surface to cool down to approximately 400 C., removing the container from the hydrogen atmosphere and allowing said structure to cool within said container in air.

8. The method as claimed in claim 4 wherein the film is treated to form a low-conductivity insulator material by immersing the'storage structure in a concentrated leadthe structure from said lead-nitrate solution, rinsing in distilled waterand allowing the storage, structure to dry.

T References Cited in the file of this patent UNITED STATES PATENTS