US2434931A - Method and apparatus for ionic discharge coating - Google Patents

Description

Jan. 27, 194s. J, E', JOHNSON 2,434,931

METHOD AND APPARATUS FOR IONIC DISCHARGE COATING /N VEA/ro@ J B. JOHNSON BV w@ ATTORNEY Jan. 27, 1948. I J, B, JQHNSON 2,434,931

METHOD AND APPARATUS FOR IONIC DISCHARGE COATING Filed Deo. 1, 1944 2 sheets-sheet 2 y 4o 62 6/ /2 l43 42 4/ f4 s i l I I 6/ /NVENTOR J B. JOHNS ON ATTORNEY Patented Jan. 27, 1948 "METHOD AND APPARATUS FOR IONIC DISCH'ARGE COATING John B. .iohnso'mMaplewooi N. J., assignorlto .Bell Telephone Laboratories, Incorporated, ,New ,York,.N.azcorporatoniof New York Application jDecember 1, 1944, Serial' No. 566,063

.fg-Claims. f1

Thi'sinvention Vrelates to method-'and apparatus for ionic `discharge coating and `more specifically to .methods of andr means for A'generating 'positive ionbeams Vand lfor utilizing said 'ideama-for example, iin the `formation` of 'targets for lectron `beams in electron cameratubes.

.'One well-known type of `electronfcamera tube is 'called'.th'e iconoscopei vIn the'usualiorm of J this tube, there 'is provided 'a mosaic target com- 'prising a metal .backing or signalplateyaninsulating layer onithe signal plate 'and ra discontinuous layer vof photosensitized metallic -globules y or Vparticles-on1the insulating layer. Radiations from fan object are applied to ythis `target .and it is scanned with a beamo'f electrons to pro- 'ducefazsignalrcurrent'inea resistor which is foon- `nected to the l'signal plate. IIn A-a welliknown -ymethod offmaki-ng mosaic targetsfthe insulating layer which fusually is 'of lmicafor glass is coated with a metallic Alayer-of A'silver -andfby a heating 'process vthe'silver is'broken up into discontinuous particles which vare oxidized 'andsensitized 'with v'caesium to form caesiumeoxidesilver globules. In screens made by this process,theparticle`s 'are fof irregular shape anddistribut-ion, f thus leading Ato non-uniformity -of photos'ensit'ivity over the *surface ofthe mosaic. "This inventioniihone yof l"its primary aspects `relates -to 'mosaic targets VAin which this non-uniformity is avoided 'or greatly reduced.

It is'ian object of'thisinventionito provide novel rrietl'iodsy offandlmean's for making mosaicltargets for'electrons,the-particles of the mosaic being of 4substantially "uniform shape, `size =and `ldistribution.

In fa I`oop'en'ding application 'of the same `linventor, .Serial No,'lf84966, 'Tfiled eAprl 29, 194B, thereis :described various methods "and means "of 'utili'zingib'eans of positive'ion's o'i metallic "ma- 'terial .in '..the formation off mosaic "tar-gets. The rions may @be :of faim-etal which is lphotosensiti-ve, fsuchias Ianfaikali or :alkaline earth metal,`orthey :may .be of metal .wlfiich .is fnotfappreciably pho- .tosensitive .In i latter instance, the 'rnetailic .spotsformedibyith'efmethod described'in thecopending. application are'photosensitize'd as inthe usual ".iconoscope *target technique. In fa #sec- -fond fscopending application 'of the Esame inventor, SerialfNo. .55iigillledliec'emberi, 31914442'. beam foi fp'ositively :charged fhydrogen 'I ions is produced byion-optical means andutilized to k'scan-'lia' 'metallic oxideior other suitable none-conducting.reduciblejayer'to vproduce ionsfotmetalfin a".seavoi iinsulation. :Oxides of aluminum 'or :one :of the solidimetalsfrom fgroup IIA in :the `.periodic vtable Yaio are suitable'for `this'purposel y"The ions of v'metal vare then photosensitized asinithe .usual iconofscope technique.

'-In accordance with vthe present invention, :an

unmodulated oxygen 'positive ion `beam rproduced sensitivity increased by rsensitizing it after the -oxygenion treatment With a suitable alkali 'metal A'such as caesium. A very uniform pattern is produced by this method.

More 'specically, in accordance with an exemplary form of the invention, an oxygen positive ion beam is generated in aside tube connected to the camera tube. This side tube comprises an evacuated container venclosing `a rst electrode member and one or more additional `electrode members. Oxygen is introduced into the side tube and a'posit'i've ion discharge is set upwithin the container which discharge is formed into a beam of'ions 'by placing the additional electrode members kat appropriate negative potentials with respect to the rst electrode member. This beam of oxygen positiveions is directedinto `the tube containing the target'to be 'formed'and .there uti-` lized as described above.

Oxygen `gas is present in the space adjacent the target, Vand tends to slowly oxidize the whole target surface. A metal is chosen which has a normally low rat-e of oxidation. Such a metal'is aluminum or vone yof 'the solid metals of group "II in the periodic table. Th'eionic oxygen of the scanning beam, however, has a much greater abilityfto combine with the metal, and oxidation Awillbe-'greatly accelerated at the contact of the `'beam with "the surface.

The 'density of normal oxygen near the target is'kept low by means of a pump applied to tubulation 10 vso as to inhibit'the general oxidation iover'the surface.

AIna specific method of operation, the oxygen 'positive ion beam is caused 'to scan 'the `target (by electromagnetic or Aelectrostatic means) vin'parallel lines, the vbeam being cut off in alternate iinescanning periods so that oxide strips sepa- :rated by metallic strips are produced. Many seconds or even `minutes maybe necessary torscan the complete .target in orderto oxidize lalternate 'strips of'the'target to therequired thickness. The

beam is 'then caused to "scan alternate .strips gin fia :directioneo .degreesff from ythe former direction so as to produce spaced oxidized lines perpendicular to those produced during the first scanning. After this scanning, conducting islands are left between oxide lines. A very uniform pattern of square metal islands is produced. In an alternative method, the target is formed by repeated scanning, that is, the spaced oxide strips are lbuilt up or increased in density on successive scannings until the complete oxide lines are built up. The direction of scanning is then changed as before and the oxide lines at 90 degrees with respect to the first series of lines are built up by successive scannings.

As the photosensitized target loses its sensitivity when exposed to air, the gun system for the electron beam is preferably mounted in the tube before the ionizing process. The gun system for the positive ion beam is mounted in a side tube which is joined to the main tube. Oxygen is admitted into the side tube and the positive ion beam is formed by the electi'odes therein and the ion beam is caused to scan the target in the main tube. After the target is oxidized by the ion beam, the connection between the main tube and the side tube is broken, the main tube is sealed off and pumped and the target is subjected to any heat treatments which are necessary.

The invention will be more readily understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof in which:

Fig. 1 is a schematic diagram to illustrate a process, in accordance with this invention, of making a target for an electron camera tube by means of an oxidizing ion beam;

Fig. 2 is an enlarged view of a portion of the target for the ion beam; and

Fig. 3 is a modification of the arrangement shown in Fig. l.

Referring more specifically to the drawings, Fig. 1 shows an arrangement for forming an oxygen positive ion beam and for utilizing this beam to form a mosaic target for electrons, the target being contained in an electron camera tube attached during the process to the tube wherein the ion beam is generated. The main tube I containing the target I4 is shown connected to the auxiliary tube II by means of a narrow neck I2 which is adapted to be cut and the ends sealed after the mosaic target in the main tube has been formed. The main tube IU comprises an evacuated container I3 enclosing the target I4 which is to have a mosaic surface formed thereon, an electron gun I5 suitable for generating and focussing a beam of electrons upon the target, and two sets of deiiecting elements comprising the magnetic coils I5, I6 and I1, I1. The electron gun comprises, for example, a cathode 20, a cathode heater 2I, a control electrode 22, a rst anode 23, a second anode 24, and a conducting coating 25 which is preferably placed at the sam potential as the second anode 24.

The target I4 is placed in position within the camera tube so that it can be struck by the electron beam generated and focussed by the gun I5 and also opposite an opening 26 in the conducting coating 25 through -which radiations from an object are adapted to be applied to the target when the tube is finally completed and operating. During the formation of the mosaic surface on the target I4, however, the electron gun I5 is not operative nor are radiations applied to the target. The target I4 preferably comprises a metallic backing plate 3U and a thin layer of mica 4 or glass 3| thereon held to the metal backing plate 30 by any suitable means such as by screws or clamps (not shown). The insulating coating 3| has applied thereto a thin layer of a readily oxidizable (by ionic oxygen) metal, such as, for example, aluminum. Other suitable metals are those in group II of the periodic table. The layer 32 is then treated by means of the ion beam generated in the side tube I I in a manner which will be described more fully below.

The tube II which is connected to the tube I3 f by means of the neck I2 at a point thereof somewhere between the region of the gun I5 and the deilecting coils I6, I6 and I1, I1 comprises an evacuated container 40 enclosing therein a first electrode 4I, a second electrode 42 and a third electrode 43. The electrode 4I is shown as a fiat plate while the electrodes 42 and 43 are shown as cylinders, the cylinder 43 being of larger diameter than the cylinder 42. Electrode member 4I is connected to the electrode 42 through a source 44 and a make-and-break contact member 45, the purpose of which will be described below. The positive pole of the source 44 is connected to the electrode member 4I and the negative pole thereof is connected through the member 45 to the electrode member 42. The electrode 43 is placed at a negative potential with respect to the member 42 by means of a source 41 while the backing plate 3i) of the target I4 in the tube I3 is placed at a negative potential with respect to the electrode member 43 by means of the source 48. Within a side tube 49, oxygen is produced and applied to the evacuated container 40.

The manner in which the apparatus shown in Fig. 1 operates to produce metallic particles 52 (see Fig. 2) surrounded on all sides by oxide strips 53 and 54 is as follows: The tube II is connected to the tube I0 by means of the glass neck I2. If it is desired to photosensitize the target while it is in the camera tube, the target cannot be exposed to the air without losing its photosensitivity. For this reason the electron gun I5 is mounted in the tube I D and a conducting coating 25 is applied t0 the portion of the walls in the enclosure by well-known means before the tube I I is joined to the tube I0. Moreover the target structure comprising the signal plate 3l) and the insulating layer 3I and the coating of suitable metal such as aluminum is placed in position before these two tubes are joined together. A yoke holding the magnetic coils I6, I5 and I1, I1 is placed around the tube I0 (in some cases it may be desirable to also perform this step before the tube is connected to the tube II) and magnetic deflecting current is applied to these coils, which current is preferably of saw-toothed wave form. No potentials are applied to the members of the electron gun I5 as the electron beam does not enter into the process of making the mosaic target coating. A magnetic coil schematically represented bythe circle 50 is placed in posit-ion so that the beam of oxygen positive ions when formed in the side tube I I is directed toward the target I4. Before admitting oxygen into the tube II all gases are removed from this tube by means of side tube 5I, heat being applied during this step if desired. The side tube is sealed off after all occluded gases are removed from both the tube II and the tube I0. With the electrode elements 4I, 42 and 43 connected as shown in Fig. l 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. l) of the contact member arrancar l-isiofc'onductingv material while the' bottom half inA ofi` noni-conducting material; Arv streamv of positive' ions is thus formed" between membersi 4! `and 42'. This stream. is focussed into abeam by means' of the electrostatic field between` these' members and between the members 42 andi 43, which are at. appropriate negative potentials. with respect'A to the member' 41| and thus. accelerate the positive ions and produce a: focussing. action on the' positive ions in a mannerv similar" to that produced on electrons by cylinders'vr connected at positive potentials with respect to a cathode. This positive ion beam is focussed' to' a small' cross-section at the surface off. the. target' I4, the' be'am being bent' by th'e constant currenty applied to the magnetic coil 5U.. The' source. 48 can be omitted but in many cases' it? may be desirable to` have an additional accelerating eld between the' electrode ele:- ments 43r and" thetarget' lll. Saw-toothed current waves of linearV slope are applied to the' coils t6, t5: and Il, |11. The frequency of these waves can: of; the; order, respectively, of the line scanning; and. frame' scanning frequencies 1 used in the.' usual television system; The member l5` is rotated. at.' such. a speed' that it.' cuts: off the: ion beam'. during' alternate line scanning intervals sof asi to leave' a space between horizontal lines 53 as. shown in. Fig. 2. The: frequency of rotations of the member 45' is, for example, equal to one-half the line scanningy frequency of the wave appliedtoloneofv the coils I6, I6 or l1, il. Each line 5:3r may b'e of a width whichis much less than thewidth' of an elemental area as determined by'v the sizeof electron beam in the gun I5 or may be substantially equal in widthv to that of elemental areav and an adjacent insulating area. or.' substantiallyr as` wide as an elemental area. if' the. pathof the electron beam is carefully controlled so'that it goes'over lines of sensitiz'ed" metal islands and skips, by one means' or anothen the; lines of insulation only. By means of. this. method,4 eaclr horizontal line 53 is formed by cumulative oxidation ofV the aluminum inthe layer.Y 3.2. Itmay' take many seconds or even several minutesv before a satisfactory thickness of. insulation. producedl by the oxidation of aluminum of the member 32 by the oxygen positive ionibe am isn reached.

In al1-alternative way of operating the arrangementfshown inFig. 1-, stepped saw-toothed waves of frame scanning frequency are appliedv to one o! the.: sets ofy coils I 6 le and l1, H, while a saw-toothed wave form of line scanning frequency'isapplied to' theY other sety of coils. These waves.` are preferably of such low frequency' that one complete scanning of the target is sufficient to build'. up` ea'ch oxide line' 53 to the` desired thickness. Because of the waves beingv stepped, the ion'. beam. remains. onV oner line until the end thereof is' thenalmost instantaneously jimped. tot the next. element. line' 53,. leaving, a. blank' .spacci between these two lines; as shown in: Fig..21 Such a stepped wave canv be; pro.- duced by a potentiometer having' a number of' taps. witharotating member connecting. each of these taps in` turn to' the` magneticy coils. An:- other' potentiometerl comprising a slidingY contact on afcoil can bie'-v used to produce the? saw-toothed wave- (the upper wave shown atv the right. of Fig. 1);. The two potentiometers can be geared together tol maintain the two waves in. propertime relation: with. e'a'ch other but thisy may be' done electrically' as` in. ordinary' television scanning'. Ituwill be clear thats the frequency of the. saw'- toothed. wave. applied to: one: sety of coils the frequency'ofthestepped wave applied to: thefother setoff coilshave thesameratio asthe frequencies of 'the two saw-toothed waves. described above. When such current' waves are used' in the; coil, the' member 45 can be. removed` and` replaced by a directconneiction betweenv the` negative pole of the source. 44 and the. positive pole. ofA the source 4.1. or' allowed to remain stationary in the conducting position..

After' the'. horizontal oxide lines 53 are formed on'. the metallic layer: 312, the direction of scanning. is shifted. by 9,0 degrees by any suitable means such' as, for example, by applying the line scanning frequency' current to the. coil formerly producing the frame scanning and the frame scanning frequency current to the coil formerly producing theline frequency scanning. The vertical lines 54. (shown in Fig. 2) arevthus produced in the manner corresponding to the-horizontal line 53. This leaves metal islands 52 ,having their surfaces slightly oxidized by the generali pressure of oxygen and completely surrounded. by oxide lines. These. metal islands. 52 are thus of rectangular shape and the pattern is.veryuniform'.y

After the oxide lines 53 and 5t` are formed, leaving the metal islands 52, the neck. I2 is sealed off and'- the tube Hll baked out and evacuated so that' all of the elements-off the tube are thoroughly degassed. The tube is then allowed to cool to room temperature. A known amount of caesiurn is then admitted into the bulb by flashing a caesium pill. The pill is flashed in a side tube or in the tube il. so that caesium vapor passes into or is present in the tube to photosensitizey the surfacel oxidized metallic particles 52. A description of a suitable process of photosensitizing with a caesium pill and the composition of such a pill may be found in British Patent 381,606, to George. R. Stilwell and Charles H.

Prescott, Jr., complete accepted October 10, 1932'. The tube is then sealed off.` I

The operation of the mosaic screen in the cathode ray tube Ii! is similar to that of the well'- known iconoscope tube described in an article entitled The iconoscope, by V. K. Zworykin in the January 1934 Proceedings of the Institute of Radio Engineers, pages 16 to 32, inclusive, and an article by the same author in the July 1936v RCA Review, page 60, entitled Iconoscope and kinescopes in television.

The tube Il, as mentioned above, can be used over and over again for. the preparation of targets n storagetype. tubes, it being merely necessary to connect it to each tube in turn,r go through the process described above, and then break theconnection between the two.

Fig. 3 shows. apparatus. ofY somewhat different form fromy that shown. in Fig. 1 for utilizing, an oxygen positive ion beam to form a mosaic target for electrons.` In. the arrangement shownin Fig, 3,'.def1ectng plates Eil and. El., lil. are used to replacethe magnetic. coils l5, le and. Il. l1 of Fig.. 1 which are used to cause. the oxygen positive ion, beam tor scan the mosaic target I4.. The magnetic bending field 5t is not required in the arrangement of Fig. 3 due to the. factr that the tube H' is joined tothe tube i0 at such an angle thatthe axis of the ion beam in its undeected position'. strikes the center. of the target 1.4.. Each of. the elements of the apparatus which. is com mon to. the. structures shown in Figs. 1 and. 3 has been given the same reference character in both figures. The oxygen positive'.v ion beam is; formed in the tube Il in the manner described above in connection with Fig. 1 and the photosensitlve mosaic is formed on the target I4 as described .above with the exception that the scanning is caused by means of voltage waves applied to the deecting plates E0, 6e and 6|, 6l instead of current waves passed through the magnetic coils iB, I6 and l1, l?. After the formation of the oxide surfaces 53 and 54, thus leaving metallic particles 52 as metal islands, the neck l2 is sealed ofi' and tube le evacuated and allowed to cool. The metal particles 52 are then photosensitized as in the process described above. The deflecting plates GS, 60 and 6i, 6l are left within the tube l0. The process performed by the apparatus of Fig. 3 in some respects is preferable to that of Fig. 1 inasmuch as it is somewhat difiicult to bend an ion beam by electromagnetic means due to the large mass of the ion as compared with that of the electron whereas electrostatic deiiection may be obtained with neld strengths of the order of those commonly used to deect an elec tron beam. Another advantage is simplification` the magnetic bending eld or an electrostatic equivalent thereof not being required.

As the metal used as the material of the layer 32 has to be subsequently photosensitized, the mosaic pattern can be applied in a separate tube or receptacle and then exposed to the air before being inserted in the cathode ray transmitter tube. The transmitter tube in this modied arrange ment has means for admitting the sensitizing metallic vapor but has no positive ion gun associated with it in any stage of the process. 1n this arrangement, the target is preferably placed at right angles to the beam.

Alternatively, a tube such as tube H of Fig. 3 can be connected to the tube l0 by means of a rubber hose or similar connection 62. After the target has been formed with its pattern of crossed-lines 53 and 5G, leaving many metallic islands 52, air can be admitted, the connection 62 broken and the opening sealed up. In this alternative arrangement, handling of the target after the formation of the pattern thereon is reduced. The tube ii) is then degassed and sensitized in any known manner.

While the invention in its primary aspects relates to processes of and means for forming a mosaic target for use with an electron beam, it will be appreciated that the invention in its broader aspects is not limited to producing targets as the coating may be provided for some other purpose for which coatings are used. It

will be understood also that various modifications can be made in the specific embodiments described above without departing from the principles upon which the invention is based. For example, while scanning by the ion beam of every other line of the target has been disclosed it is obvious that the main criterion is that a strip of unscanned target is left between repeated line scannings thereof. Such a strip can be as wide as the ion beam or greater than or less than this width. Preferably the strip should be as small as possible to provide as large an active area as possible.

What is claimed is:

1. The combination with a container, of means 'for introducing oxygen therein, spaced electrodes within said container between which said oxygen is present, a source of potential having its terminals connected to said electrodes respectively whereby oxygen positive ions move 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, and a target for receiving said oxygen positive ions, said target comprising an element of metallic material upon which said positive ions impinge to oxidize the portions of said target struck thereby.

2. The combination with a container, of means for introducing oxygen therein, spaced electrodes Within said container between which said oxygen is present, a source of potential having its terminals connected to said electrodes respectively whereby oxygen positive ions move 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, and a target for receiving said oxygen positive ions, said target comprising elements of insulating material having a coating of an oxidizable metal facing said beam and a backing of a conducting material electrically connected to said apertured electrode.

3. The combination with a container, of means for introducing oxygen therein, spaced electrodes within said container between which said oxygen is present, a source of potential having its terminals connected to said electrodes respectively whereby oxygen positive ions move 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 oxygen positive ions, said target comprising elements of insulating material having a coating of an cxidizable metal facing said beam and a backing of a conducting material electrically connected to'said apertured electrode, and means for causing said beam to scan said target whereby portions of the metallic layer facing said beam are oxidized ina progressive manner.

4. The combination with a container, of means for introducing oxygen therein, spaced electrodes within said container between which said oxygen is present, a source of potential having its terminals connected to said electrodes respectively whereby oxygen positive ions move 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 oxygen positive ions, said target comprising elements of insulating material having a coating of an oxidizable metal facing said beam and a backing of a conducting material electrically connected to said apertured electrode, and means for causing said beam to scan spaced lines of said target and then to scan spaced lines of said target in a direction at degrees with respect to the iirst scanning.

5. The method of metallic coating which comprises ionizing oxygen 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 metallic target surface comprising a metal from the group consisting of the solid metals oi group II in the periodic table and aluminum.

6. The method of metallic coating which comprises ionizing oxygen 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, andcausing said beam to scan in a manner to produce a uniform oxide pattern thereon a two-dimensional portion of a metallic target surface comprising-a metal from the group consisting of the solid mete als of group II in the periodic table and aluminum.

7. The method of metallic coating which comprises ionizing oxygen in an electric eld formed between two electrodes in an evacuated container, focussing the positive ions formed bysaid ioniza: tion into a beam which is highly concentrated and of relatively small cross-sectional area, causing said beam to scan in a manner to produce a uniform oxide pattern thereon a two-dimensional portion of a metallic target surface comprising a metal from the group consisting of the solid metals of group II in the periodic table and aluminum, and photosensitizing the metallic portions of said pattern.

8. The method of metallic coating which comprising ionizing oxygen 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 metallic target surface in spaced crossed lines to produce a pattern of metallic islands between oxide lines, the metal being from the group of the solid metals of group II of the periodic table and aluminum.

9. The method of making a mosaic target for an electron beam which comprises ionizing oxygen 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, causing said beam to scan a two-dimensional portion of a metallic target surface in spaced crossed lines to produce a pattern of metallic islands between oxide lines, the metal being from the group consisting of the solid metals of group II of the periodic table and aluminum, and photosensitizing the metallic islands.

JOHN B. JOHNSON.

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

UNITED STATES PATENTS Number Name Date 2,178,233 Klatzow Oct. 31, 1939 2,239,642 Burkhardt et al. Apr. 22, 1941 2,157,478 Burkhardt et al. May 9, 1939

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