US2434930A - Method and apparatus for ionic discharge coating - Google Patents

Description

' Jan. 27, 1948. J. B. JOHNSON 2,434,930-

vMETHOD AND APPARATUS FOR IONIC DISHARGE COATING Filed Dec. l, 19421 2 Sheets-Sheet 2 SLOW FAST

/NVENTOR l J. B. Jo/-l//vso/v BV ATTORNEY Patented Jan. 27, 1,948

METHOD AND APPARATUS FoR IoNic .DISCHARGE coA'rING- John B. Johnson, Maplewood, N. J., assgnor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 1, 1944, Serial No. 566,062

This invention relates to method and apparatus for ionic discharge coating and more specically to methods of and means Lfor generating positive ion beams and for `utilizing said beams, for example, inthe formation` of targets for electron beamsin electron camera tubes.

Onewell-known type of electron camera tube is called -the iconoscopa In the usual form` of this tube there is provided a mosaic target comprising-a metal backing vor signal plate, an insulating layer on the signal plate, and a discontinuous layer of -photosensitized `metallic globules or particles on the insulating layer. Radiations from an object are applied to this target and it is scanned with a beam of electrons to produce a signal current in -a resistor which is connected to the 'signal plate. vIn a Well-known method ofrmaking mosaic targets, the insulating layer, which usually is of mica or glass, is coated kwith-a metallic layer Aof silver 'and by a heating process the silver is broken .up into discontinuous particles which are oxidized and sensitized with caesium to form caesium-oxlde-silver globules. In screens made by this process, the particles are of irregular shape and distribution, thus leading to non-uniformity of photosensitivity over the surface of the mosaic. This invention in one of itsprimary aspects relates tomosaic targets in which this non-uniformity is avoided or greatly reduced. y,

It is an object ofthis invention to provide novel methods of and means for making mosaic targets forelectrons, the particles of the mosaic being of substantially uniform shape, size and distribution.

` Ina copendlng application of the same inventor, Serial No. 484,966, filed April 29, 1943, there aredescribed various methods and means of utilizing beams of positiveions of metallic material in the formation of mosaic targets. The ions may be of'a meta1 which is photosensitive, such as anv alkali or alkaline earth metal, or they may be of a metal which is not appreciably photosensitive. In this latter instance, the metallic spots formed bythemethod described in this copending application are photosensitized as in the usual iconoscope target technique.

In accordance with the present' invention, a reducing positive ion beamas, for example, a beam of positively charged hydrogen ions, is produced by ion-optical means and utilized to scan a metallic oxide or other suitable non-conducting layer tol produce islands of metal in a "sea of insulation. Oxides of aluminum or beryllium, for example, are suitable for this purpose. In general, any of the oxides of the solid metals of group II of thev periodic table according to Mendeleeff can be used. The islands of metal are then photosensitized as in the usual-iconoscope technique.-

12 Claims. (Cl. 117-332) More specifically, in accordance with an exemplary form of the invention, a hydrogen positive ion beam is generated in a side tube connected to the camera tube. This side tube comprises an evacuated container enclosing a rst electrode member and one or more additional electrode members. Hydrogen is introduced into the side tube and a positive ion discharge is set up within the container which discharge is formed into a beam of ions by placing the additional electrode members at appropriate negative potentials with respect to the rst electrode member to focus the positive ions into a beam. This beam of hydrogen positive ions is directed into the tube con taining the target to be formed and there utilized as described above.

The target can have as a backing an insulating plate such as mica, backed by a metallic electrode. The aluminum or other oxide coating can be formed by rst plating a coat of aluminum on the mica and then oxidizing this coating by f of a lesser depth than the oxide so that the oxide layer insulates under the islands as Well as around them,

In the presence of normal hydrogen, the metal oxides are reduced extremely slowly, but under the implngement of ionized hydrogen the reduction is accelerated if at the same time the water vapor which is the decomposition product isV pumped away thoroughly. The processtherefore contemplates the circulation of very dry hydrogen at low pressure through the tube during the reduction operation.

In a specific method of operation, the hydrogen ion beam is caused to scan (by electromagf netic or electrostatic means) every elemental area of the desired portionof the non-conducting reducible material on which the discontinuous photosensitive elements are to be formed. The beam is varied in intensity during scanning so as to produce a regular pattern. One Way of doing this is to cut oli the beam in alternate spot scanning periods and also to cut ofi the beam during alternate line scanning periods so that a regular pattern of dots or squares interspersed with insulating areas is produced. The size of each dot or square is preferably made smaller than a picture element as determined by the size of the electron beam in the electron camera tube a1- though it can be as large as the picture element or even larger. It will take manyv seconds or even minutes to scan the complete target in order arid 43"connected as shown in Fig. 1 of the drawing, the element 42 is at a negative potential with respect to the electrode member 4I inasmuch as the top half (as shown in Fig. 1) of each 'of .the contact members 45 and 46 is oi conducting. material, while the bottom half of each is of nonconducting material. A stream of hydrogen positive ions is thus formed between the members 4I and 42. This stream is focussed into a beam by means of the electrostatic iields between members 42 and 43 which are at appropriate negative potentials with respect to the member 4| and thus .accelerate the positive ions to produce a focussing action thereon in a manner similar to that produced on electrons by cylinders connected at positive potentials with respect to a cathode. This beam is focussed to a small cross-section at the surface of the target i4, the beam being bent by the constant current applied to the magnetic coil represented schematically by the circle 50. Source 48 can be omitted but in many cases it may be desirable to have an additional accelerating eld between the electrode element 43 and the target I4. If saw-tooth current waves which are of uniform slope are applied to the coils I6, I8 and I1, Il, the frequency 'of these waves canbe of the order, respectively, of the line scanning and frame scanning frequencies used in the usual television system. The members 45 and 45 are rotated at such speeds respectively that the member 45 makes contact for a period of time necessary to form an elemental particle 52 (see Fig. 2) and breaks contact (cutting oil the beam) for a period of time corresponding to the distance between adjacent elemental particles 52. The member 45 is rotated at a somewhat slower speed and it acts to cut off the ion beam during alternate line scanning intervals so as to leave a space between lines as shown in Fig. 2. The frequency of rotation of the member i5 is equal to one-half the line scanning frequency of the wave applied to one of the coils I6, I6 or Il, Il, while the frequency of operation of the member 46 is equal to that of the member 45 divided by the number of elemental particles 52 it is desired to make ina line. If desired, the member 45 can be omitted and every line scanned, the-beam being a little narrower than the line. Alternatively, the member 45 can be replaced by a corresponding member having a, very narrow insulating segment t0 cut o the beam on the return trace between lines. Each particle 52 may be much less than an elemental area as determined by the size of the electron beam from the gun I5, or it may be subs tantially equal to the size of an elemental area, and an adjacent insulating area or substantially as wide as an elemental area if the path of the electron beam is carefully controlled so that it goes over lines of sensitized metal islands and skips, by one means or another, the lines of insulation only. Each particle 52 is formed by re.. duction of the non-conducting metallic oxide by means of the hydrogen ions to produce a conducting metallic particle 52. In the presence of gen can enter through tube 49 and leave through tube 1li, these two tubes being later sealed oil. By means of the scanning method described above, each particle 52 is built up by successive scannings of the ion beam over a surface of the insulating layers 3I containing the non-conducting oxide coating 32. At present it is believed that each particle 52 should be of the order of several hundred molecules thick and may take many seconds or even several minutes before such a thickness is reached. If desired, the insulating spaces between particles 52 can be made less than or greater than the width of one of these particles. Preferably the insulating portions should be as small as possible in order to provide as large an active area as possible.

In an alternative Way of operating the arrange ment shown in Fig. l, stepped saw-toothed waves of line and frame scanning frequencies are ap# plied to the coils I6, I6 and I1, I1. These waves are preferably of such low frequencies that one complete scanning of the target is suicient to form by reduction each particle 52 of the desired density. By means of the stepped wave, the hydrogen ion beam is held stationary over an elemental area and remains on that elemental area until a suicient amount of oxide is reduced to a conducting metal of the desired thickness on .the target. Then the beam is almost instantaneously jumped to the next elemental area leaving a. space between the elemental areas blank as shownin Fig. 2. Such a stepped Wave can be produced by a potentiometer having a number of taps with a rotating member connecting each of these taps in turn to the magnetic coils. The potentiometers (one for the line and one for the frame scanning.) can Abe geared together to maintain the two Waves in proper time relation with each other or this may be done electrically as in ordinary television scanning. It will be clear that the frequency of the wave applied to one set of coils I6, I6 and of that applied to the other set of coils I'I, I1 have the same ratio as the two sawtoothed waves described above. When such current waves are used in the coils I6, I6 and Il, I1. the members -45 and 46 can be removed and replaced by a direct connection between the neganormal hydrogen the metal oxides are reduced extremely slowly, but under the impingement of combining' with the reduced metal. The hydro-A tive pole of the source 44 and the positive pole of the source 41.

After the metal particles 52 are formed on the insulating layer 3l by reducing portions of the oxide layer 32, the neck I2 is sealed off and the tube IIl evacuated and baked out so that all of the elements in the tube are thoroughly degassed.

The tube is allowed to cool to room temperature and oxygen is then admitted so as to oxidize a very thin layer of metallic particles. At the conclusion of the oxidation process, excess gas is removed by evacuation and a known amount of caesium is admitted into the bulb by flashing a caesium pill. The pill is flashed in a side tube or in the tube I0 so that caesium vapor passes into the latter to photosensitize the metallic particles 52. photosensitizing with a "caesium pill and the composition of such a pill may be found in British Patent 381,606 to George R. Stillwell and Charles H. Prescott, Jr., complete accepted October 10, 1932. -The tube. II) is then baked at a temperature of about 200 to 225 C. for varying periods of time to remove all gases. The operation of the mosaic screen inthe cathode ray tube III is similar to that of the ,well-known iconoscope tube described in an article entitled The iconoscope. by Zworykin in the January 1934i- A description of a suitable process of Eroceed-ings of the Institute ,oi 'RadimEngineera pages 1 6 to 32; inclusive, and. an article-bythe Same. author inthe duly 1936 RCA Review-3f page 6 0-, entitled Iconoscopes. and Kinescopes in Tele.- visioni- L.alternate way of forming .the target v:is to use .fa-plate of aluminum or a pla-teef other metal on which aluminum is Plated. oxidize ,the` alu-minum to a predetermined depth, andthenproduce bythe reduction process. outlined .above metal islands of a lesser depth tl'ian` the. oxide soithat thepxide layer nsulagtesfunder the-islands aswell asamimdthem.

The tube il, as mentionedabove .can be usedover andY over again for the,preparation-oiftarrgets in storage type tubesitbeing merely necessary to connect it to each tube in. -turnpeo through .the process described. above and. then. breaktheconnection between the-tubes.

Fis. 3 shows apparatus .of somewhat.. different form from that shown fiiig. il; for utilizing a. hydrogen positive ion bearnto .form aA mosaic target for electrons. In the .-arrangementpfylig. S,.deetins plates ,60, -i and;;.6.l., 6il are used :to replace the magnetic coiled-,6, 116 and. Il, l-'l o fFig. 1 which are usedto cause -thelivdrogen` iorrbeam to scan .the mosaic target 1 ;4.. The magnetic bending eld is not required in the.finalisement Qf-Flg. 3 due tothe fact-.that the tube n .is ioined to the tube I Qat such. an .angle that the axis of the :hydrogen positive` ion-beam in its un, dedected-position strikesithe centeror the target I4. YEach of theelementsot theapparatuswhich isVv .common to the structures-.showninFigs.. Land 3 has `been given mesme-.reference character inboth figures. The hydrogenipostveion beamformed in the tube Il' inf-tbe manner describedabove in connection with .-Eig. 1 fandthephotoe. sensitive mosaic is formed,l on the target litas described above-.With the exceptonfthat-.the,scanfning is caused by-means of voltage Wavesappled to the deecting plates =60,;,6.0;andr6.l-, 6l instead of current Waves passed, thro ughthe magnetic` coils I6, i6 and ll, 1:1,

l.2is broken and tube l0 is sealed up; ,evacuated andallovvedfto cool. Thegmetallcfpartic-.es 5 2 are. then wholly-Kor partially. oxidized by any-.suitable method and photosensitized as in theprocessdescribed above. The de fiecting plates 6l). 6 0. and 6 4, .6l are. left within the tuba-,HL The process performed by the apparatus ofnfig. 3;- in some respects is preferable. to gthatof .Fig. .linasmuch as it is somewhatdieultrto bend-anfion-beam. br` electromagnetic mea-ns due--tQthe-largemass of theion as compared withv that-onlibe ,electron target is preferably. placed: at right;.anglesitotheL beam.

Alternatively,y atube such as tube fly-lofriFlg. f3. can be connected to .-the.-tube f. l 0.. by-means..o1 -.a

After the tiny particles 52 are formed on the-insulatinglayer :3i-thermischrubber hose-.or similar connection 2-, Aitor .the target-naspelen provided with a metailicpattern. by the. reducing process described above, air can be admitted, the connection 62 broken and the opening sealed up. This alternative arrangementreducesv the.` handling of the .targetafter the formation of the patternthereon'. The tube .-I0 is then degassed, oxidized and ysensitized in any known manner.

While .the invention .in its 4primary aspectsref.l lates to processes of .or-- means for .forming a mosaic target for use with .anfelectron beam', Ai1;- willz -be appreciated that the invention. in .its broader Aaspectsis not limited to producingatariget asthecoating may be. provided for some .other purposes for which coatings .arelused vIt will be' understood .also thatvarious modcations can be made the' specic embodiments described abovev without departingV from the. principles upon which the invention isbased.

What-isclaimed is:

-.1. The combination with avessel, of means/.for producing a hydrogen atmospheretherein;spaced` electrodeswithin said container between which said hydrogen is present, a source of potential electrodeswithin said container-between vvhich` said hydrogen is present, a source of potential having its .terminals connected to said electrodesrespectively. whereby hydrogenpositive lions move to one. of said electrodes and electrons move to the vother of said electrodes, an aperture in- 'sa-idv electrode. towardwhich said positive ions moveand-throughwhich some oflthempass, and a target -forireceiving said positive-hydrogen ions'i saidtarget comprising lportions of a material which canibereduced by hydrogen.

3. The combination Vwith a vessel, of meansfor .producing a hydrogen atmosphere therei'ri, spaced lelectrodes withinsaid container betweenwhich said-hydrogen ispresent, a source of potential vhaving its terminalsconnected'to sai'd electrodes .respectively whereby hydrogen positive ionsimove-to-one of said electrodes and' electrons move-tothe .other of said electrodes, an apr-` turein said electrode toward which said positiveions move and. through which some of1ther`n'pass,v a-targetfor receiving said hydrogen positive ions, said target-comprising an element of-iinsulating: material containinga coating of i non-conducting metallic oxide and Yaiconducting backing-for-.saidinsulatingrmaterial which backing-is electricallyconnected; to said-apertured .electrodes and means'- for causing said positiveA ion beamto scan'said target,. whereby saidcoating is producedfji'n apro-y gressive manner.

1,4. 'Il'ie-..cmbination.with .a vessel, of means` for" producing. al hydrogen atmosphere thereimspacedf electrodes .within said container between jwhichv said hydrogen-is present, a source of potential; havingits terminals connectedy to said electrodes` respectivelylwherein hydrogen positive ions-Inove-l to one of said electrodes and electrons move to the other of said electrodes, an aperture in said electrode toward which said positive ions move and through which some of them pass, a target for receiving said positive hydrogen ions, said target comprising an element of insulating material containing a coating of non-conducting metallic oxide and a conducting backing for said insulating material which backing is electrically connected to said apertured electrode, and means including apparatus for causing said positive ion beam to impinge on discrete elemental areas of said target in succession to cause said coating to be produced by reduction in the form of discrete portions forming a regular pattern.

5. The method of metallic coating which comprises ionizing hydrogen in an electric eld formed between two electrodes in an evacuated container, focussing the positive ions formed by said ionization into a beam which is highly concentrated and of relatively small cross-sectional area, and causing said beam to scan a two-dimensional portion of a target surface comprising an electrically non-conducting compound of one of the metals from the group consisting of the solid metals in group II in the periodic table and aluminum.

6. The method of making a mosaic target for an electron beam which comprises ionizing hydrogen in an electric iield formed between two electrodes in an evacuated container, focussing the positive ions formed by said ionization into a beam which is highly concentrated and of relatively small cross-sectional area, and causing said beam to scan a two-dimensional pattern on a target surface comprising an electrically nonconducting compound of one of the metals from the group consisting of the solid metals of group II in the periodic table and aluminum to produce by reduction a uniform pattern of metallic and non-conducting portions, and photosensitizing the metallic portions of said pattern.

7. The method of making a mosaic target for an electron beam which comprises ionizing hydrogen in an electric field formed between two electrodes in an evacuated container, focussing the positive ions formed by said ionization into a beam which is highly concentrated and of relatively small cross-se-ctional area, and causing said beam to scan a two-dimensional pattern on a target surface comprising an electrically nonconducting oxide of one of the metals from the group consisting of the solid metals of group II in the periodic table and aluminum to produce by reduction a uniform pattern of metallic and non-conducting portions, and photosensitizing the metallic portions of said pattern.

8. The method of making a mosaic target for an electron beam which comprises ionizing hydrogen in an electric field formed between two electrodes in an evacuated container, focussing the positive ions formed by said ionization into a beam which is highly concentrated and of relatively small cross-section-al area, causing said beam to scan a two-dimensional pattern on a target surface comprising an electrically nonconducting oxide of one of the metals of the group consisting of the solid metals of group II in the periodic table and aluminum to produce by reduction a uniform metallic pattern, rapidly removing during the reduction the Water vapor produced thereby, and after the pattern is produced photosensitizing the metallic portions of said pattern.

9. The method of metallic coating which comprises ionizing hydrogen in an electric eld formed between two electrodes in an evacuated container, focussing the positive ions formed by said ionization into a beam which is highly concentrated and of relatively small cross-sectional area, causing said beam to scan a two-dimensional portion of a target surface comprising an electrically non-conducting oxide of one of the metals from the group consisting of the solid metals of group II in the periodic table and aluminum to produce by reduction a uniform pattern of metallic particles separated by nonconducting oxide particles, and circulating dry hydrogen during the reduction process to rapidly remove the Water vapor produced during said process.

10. The method of metallic coating which comprises ionizing hydrogen in an electric field formed between two electrodes in an evacuated container, focussing the positive ions formed by said ionization into a beam which is highly concentrated and of relatively small cross-sectional area, and causing said beam to scan a two-dimensional portion of a target surface comprising an electrically non-conducting compound of one of the metals in the group consisting of the solid metals of group II in the periodic table and aluminum in a manner to produce a multiplicity of metallic islands, said islands being of less depth than the non-conducting compound whereby each island has some of the non-conducting compound under it as Well as around it.

11. In the method of making a mosaic target for an electron beam, the combination of the steps of ionizing hydrogen in an electric neld formed between two electrodes in an evacuated container, focussing the positive ions formed by said ionization into a beam which is highly concentrated and of relatively small cross-sectional area, and causing said beam to scan a two-dimensional portion of a target surface comprising an electrically non-conducting oxide of one of the metals from the group consisting of the solid metals of group II of the periodic table and aluminum in a manner to produce a multiplicity of metal islands.

12. In the method of making a mosaic target for an electron beam, the combination of the steps of plating a metal from the group consisting of the solid metals of group II of the periodic table and aluminum on another metal, oxidizing the metal plating to a predetermined depth, reducing selected portions of the oxide layer to s uch an extent that metal islands of less depth than the oxide layer are produced, whereby each island has oxide under it as Well as around it, and photosensitizing the metal islands.

JOHN B. JOHNSON.

REFERENCES CITED I The following references are of record in the le of this patent:

UNITED STATES PATENTS Number

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