US2540635A

US2540635A - Cesiated monoscope

Info

Publication number: US2540635A
Application number: US29578A
Authority: US
Inventors: Henry P Steier
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1948-05-27
Filing date: 1948-05-27
Publication date: 1951-02-06
Anticipated expiration: 1968-02-06

Description

Feb.,6, 1951 H. P. S TElER CESIATED- MONOSCOPE Filed May 27,' 1948 I A I Bnventor HENRY F. STEIEB Gttorneg Patented Feb. 6, 1951 7 2,540,635 f CESIATED MONOSCOPE Henry P. Steier, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application May 27, 1948, Serial No. 29,578

11 Claims. (01. 250-164) My invention relates to improvements in cathode ray signal generator. tubes and particularly to an improved target electrode for 7 use in such tubes.

In the usual form of cathode ray signal generator tube such as is used for developing signals representative of a single picture it is customary to scan with an electron beam a target having on its scanned surface a pattern or picture outline composed of a material having secondary electron emission characteristics different from those of the rest of the target. Thus, it has been customary to print or otherwise apply a pattern or picture upon a metal foundation using material such as a carbon ink having different secondary electron emitting properties than the metal.

Printing a target electrode with carbon ink has many objections and limitations. Difficulties have arisen in the non-uniformity of theprinting due to such causes as uneven spreading of the ink, the varying of pressure in the printing process, the non-uniformity in size of the carbon particles used, etc., all which result in non-uniform target surfaces. Also, printing targets with ink depends upon humidity and temperatur conditions. These difiiculties result in target designs which vary from target to target making it difiicult to standardize the generator tube.

It is an object of my invention to provide a cathode ray tube of the signal generating type wherein the pattern carried by the target and scanned by the electron beam has the desired uniform properties. It is a further object of my invention to provide such a tube wherein the signal response is uniform and the variation between the cperation of various tubes in electrical properties is negligible. It is a still, further object of m invention to provide a tube and electrode structure therefor, which may be easily manufactured and in which the processing steps may bevaried over wide limits without undulyv tion itself will be best understood by reference to the following description ,1 taken in connection with the accompanying drawing, in which:

Figure 1 is a cross-sectional view of a signal generating tube embodyingmy invention.

"Figures 2 through 5 inclusive are sectional views of the target electrode of the tube of Figure lshowing the target at various stages of its manufacture.

:t. In- Flgurerl,..the; signal generator w l 'Qema 2 prises an envelope of glass or vitreous material having a cylindrical neck portion enclosing a conventional electron'gun structure and a com-- cal section enclosing a target electrode I21 Envelope I0 is highly evacuated.

. The electron gun, mounted in the neck section of envelope [0, comprises a thermionic cathode electrode 14 having activated oxides of barium and strontium fixed to a plate closing one end of the cylinder M. Th oxides, well-known in the art, provide a source of electrons when heated to appropriate temperatures. Mounted close to the endplate of cylinder I4 is a control grid [5 comprising an apertured plate closing the end of a supporting cylinder Hi. In a successfully operated tube of this type, grid I5 is normall maintained at close to anegative 50 volts relative to the cathode potential during tube operation. A tubular accelerating electrode [8 is mounted coaxial with the cathode l4 and is maintained at close to 1,000 volts positive relative to cathode potential. A second tubular electrode 20 maintained at close to 300 volts positive relative to cathode potential provideselectrostatic focusing of the electron beam on the target electrode l2. An anode electrode 22 comprises a wall coating of conductivematerial, such as colloidal graphite, extending from a point adjacent focusing electrode 20 onto the conical portion of the envelope in to a point closely adjacent to the target electrode l2. Anode 22 is maintained at close to 1,050 volts positive relative to cathode potential and provides with electrode 20 further focusing fields for the electron beam. Th electron beam generated and focused by the electrode gun struc- ,ture, just described, is caused to sweep over the target I 2 by any appropriate means such as, for example; perpendicular magnetic fields provided by two ,pairs of conventional deflection c0ils'24 -and 26 respectively. Coils 24 and 26 are connected to appropriate circuits (not, shown) for providing the required deflecting fields, as is well known inthe art. In this manner the electron beam iscaused to scan the target electrode l2 in] any desired manner;

The target. electrode 12 consists of a metal plate 36 arranged transversel to the path of the y electron beam. Thesurface of the metal late 38 facingQthe electron gun is coated on successive portions thereof with a film of chromium oxide 40 and a. film of aluminum oxide 38. As will be described below, the chromium oxide layer 40 may begput down" on the surface of plate 36 in any plate 36 lying between the chromium oxide portions 40. The aluminum plate 36 is connected by a lead 31 passing through the envelope wall Ill to a high resistance 43, which is grounded as is shown. The variou electrodes of the signal generator tube are provided with appropriate potentials by being connected, as shown in Figure 1, to a D. C. voltage supply tnrough a voltage divider 28 connected across the terminals 30 and 32 of the supply. Terminal 32 is grounded as is shown and a battery 23 is connected between terminal 32 and anode coating 22. This arrangement maintains the anode electrode 22 at approximately 50 volts positive relative to the grounded target electrode I2. The voltages described as being applied to th various electrodes of tube I B, are for illustration only, and are those which have been used on a successfull operated.

sample of the tube. However, these voltages are in no way limiting. The invention is not con- The operation of the tube of Figure 1 is such that an electron beam is developed and focused by the gun structure upon the target electrode 12. Upon being scanned across the target surface by the deflecting fields of coils 24 and 25, 1 the electron beam will strike the surface of the chromium oxide and the aluminum oxide films, f *40 and 38 respectively, at an energy of around i 1,000 volts. the surface of target I2, a secondary electron emission is initiated from both the aluminum oxide and the chromium oxide surface and changes the potential of these areas relative to that of the signal plate 35. However, the second-- ary emission from the aluminum oxide surfaces 33 is much greater than that from the chromium f oxide surfaces 40. 1 the secondary emission from the aluminum oxide surface produces, by capacity coupling, a much fstronger signal in the circuit of signal plate 33 than is produced by secondary emission from the chromium oxide surfaces.

The anode electrode 22 operated at a voltage positive with respect to the target electrode I2 Y acts as a collector for practically all of the secondary electrons emitted from the target surfaces 38 and 4G. Collector electrode 22 and target electrode I2 are connected in a common circuit with battery 23 and load resistor 43. rent flow through the load resistor has two com- 1 ponen-ts: one, the flow of beam electrons to the target electrode I2 and, two, the fiow of secondary electrons from the target electrode I2 to the. conductor electrode 22. The current in the load resistor-43 is equal to the difference between these two components.

As the electron beam scans across Thus, during tube operation,

The cur- Since the secondary electron emission current varies as the beam moves over 'The voltage drop across the The areas of the target surface covered by chromium oxide portion 40 and aluminum oxideportion 38, having a relatively different secondary .electron emission, may be formed into any desired pattern or design. -r-the pattern electrode I2 is somewhat involved "and is 'describedin detailas follows:

The formation of The metal plate 36 (Figure 2) comprises a thin aluminum foil upon which is deposited a layer 48 of sensitized albumen, made from albumen mixed with potassium dichromate or ammonium dichromate as a sensitizer. This material is well known to the photo-engraving art. Over the albumen layer 48 is placed a transparency or negative 45. This negative or transparency may be made by photographing a large black and white drawing of the pattern which it is desired to reproduce on the target electrode. The transparency or negative formed consists of opaque areas 46 and transparent areas 4! and is placed in close contact with the emulsion layer 48. Upon the exposure of the target I2, of Figure 2, to a blue light from carbon arc lamps, the portions of the albumen emulsion exposed through the transparency are rendered insoluble, due to a photo-chemical action of the dichromate and albumen. 'The negative or transparency 45 is removed and the target electrode I2 is washed in water to remove the soluble or unexposed portions of the albumen. 'What is left 0 43 created by light leaking around the edges of the masked areas 48.

To remove the partially hardened portions 49 at the edges of the hard albumen portions 48, the tar'g t plate i2 is further washed in a saturated solution of sodium chloride in water with about 30 cc. of concentrated acetic acid per 300 cc. of the sodium chloride solution. Afterward the plate is further washed with distilled water. The treatment leaves the hardened albumen areas 48 with cleanly defined edges.

At this point the image or pattern formed on the target plate I2 by the hardened albumen areas 48 may be made more apparent for inspection by dipping the plate in an aniline dye, usually purple. The target I2 .is then mounted in the envelope of the tube IS] in a position shown in Figure 1. The mounting structure may be of any desired design, which is not shown in the figure. The bulb and neck of envelope ID are sealed together while carbon dioxide or forming gas is passed into the tube at about four to five cubic feet a minute. This expediency prevents undue burning of the image material 48 on" the target plate I2. The anode coating 22 is applied to the inner surface of the envelope I3 and the bulb is baked out in air. After the seal has been made, the electron gun structure is mounted within the tube and the tube exhausted, degassed, and the cathode activated in a conventional manner, well known in the art. During this processing of the tube, the organic albumen 48 is burned off and there is left behind a layer to' of chromium oxide 4%]- (Fig. 4) formed from the dichr'omate sensitier used. Oxygen is introduced into the tube It at a pressure of approximately 2 atmospheres and the aluminum plate I2 is heated "for example, by high frequency induction, to a visible red temperature for a period of three minutes. This results in forming a heavy layer of f aluminum oxide 38 (Fig. 5) on the surface of the aluminum plate 36 between the portions of the target surface coated by the'chromium oxide pattern 43. The oxygen is removed from the bum envelope IE! and the tube is exhausted and sealed off in the normal manner.

A thin film or layer 44 of caesium material is then'put down over the surface of the target I2. This -may be iormcdbyivaporizins a pellet of "caesium within the envelope. The vaporized metal will condense upon the target surface. For example, a milligram pellet of caesium is attached to a refractory filament or placed on a capsule approximately two and one-half inches from the target surface. Upon heating the filament by a passage of current therethrough or the capsule by a high frequencyfield, the caesium material is vaporized and condenses upon the target surface. The thickness of the caesium film '44 is rather critical, as it must remain permeable to the primary electrons of the scanning beam and to the secondary electrons emitted from the chromium oxide and aluminum oxide portions 'of the target surface. However, the caesium film should be sufficiently thick to provide a semiconducting layer over the target surface exposed to the scanning electron beam. A caesium layer of approximately 1000 A. has been found to possess the desired properties.

When the electron beam scans the target surface, the potential of the aluminum oxide areas '38 are driven more positively than are the chromium oxide areas with reference to the potential of the signal plate 36, as described above. To produce a clear and distinct signal from all portions of the target surface, each elemental area should be discharged to the reference potential of the signal plate 30, between successive scansions of the electron beam. Since chromium oxide is an excellent insulator, there is an insuilicient leakage of current between the charged surface of the chromium oxide areas 49 and the signal lplate 36'to return the chromium oxide areas 40 to signal plate potential between scans. Consequently, during tube operation, these chromium oxide portions of the target become more and more charged until the secondary emission signal from these areas is radically changed and the picture signal will reverse polarity. The caesium film 44 eliminates these diificulties by providing a semi-conducting path between the chromium oxide portions of the target surface and the signal plate 36, and its supporting structure. Thus, between successive scansions of the electron beam, any particular portion of the target surface which has been charged by the beam, will tendto be discharged to the potential of plate 36 through the semi-conducting film 44.

The aluminum plate 36 is obtained from aluminum foil developed for advertising and packing purposes. It is approximately 4 mils thick although this thickness is not critical. However, the surface of thefoil should have a bright finish,

as imparted to it by the method of rolling the metal, which is done commercially for labels, wrapping, etc. scratches which can be seen in reflected light. The target plate 36 is not necessarily limited to aluminum. Othermetals may be used which are .easily oxidized and whose oxides will provide secondary emission characteristics of the desired yp The particular method of forming the target electrode I: as described above need not be entirely limited to the materials used. The transparency or negative 45 may be of any desired form such as an opaque metallic screen or stencil.- Also, the transparency 45 is not necessarily limitedto a black and white pattern but may be formed from any photograph and the pattern design printed upon plate 36 through a halftone screen.

The surface should have no The semi-conductingfilm 44 need not be limitf t a itispossible. also to use a mm at 8 aluminum or beryllium film or any metallic layer which would not reduce the secondary emission from the aluminum oxide and yet would provide the desired degree of conductivity.

A target having a signal generating tube constructed according to my invention eliminates the difficulties inherent in a signal electrode formed from carbon lprinting. The signal electrode according to this invention, is not limited in picture resolution to the extent that carbon printing is. With this new process it is possible to form on the target surface up to 2000 elements per inch, which is better resolution than needed at the present time for television purposes. The television picture resulting from the use of the signal target of this invention shows greatly improved contrast and freedom from blemishes. The resulting increased contrast makes possible the use of less amplification and the production of an image signal freer of noise. The process of target formation, according to this invention, makes possible an accurate half-tone gray scale reproduction. The target formation also results in the possibility of increased definition, as for example, an increased number of lines or elements in a given pattern height.

WhileI have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but

that many modifications may be made without having a secondary electron emission greaterv than unity when struck by said electron beam and a second portion having a secondary electron emission ratio difierent from that of said first portion when struck by said electron beam, and a thin conductive coating connecting said target surface portions.

2. A signal generating tube comprising an envelope, an electron gun within said envelope for developing a beam of electrons of predetermined energy along a normal path, a target electrode within said envelope 'having a surface thereof transverse to the normal path of said electron beam to be scanned thereby, a portion of said target surface having a secondary electron emission greater than unitywhen struck by said electron beam, the remainder of said target surface having a secondary emission ratio different from that of said first portion when struck by said electron beam, and a conductive coating over-said target surface. s

3. A signal generating tube comprising an envelope, an electron gun within said envelope for developing a beam of electrons of predetermined energy along a norma'l'path, a target electrode within said envelope' having a surface thereof transverse to the normal path of said electron beam to be scanned thereby, an insulating 'material deposited over spaced portions of said target surface, said material having a secondary emission when struck: by said electron beam, said target surface between said spaced portions hav-'- ing a secondary emission; greater'than that of said insulating material struck. bysaid electron beam; and a'conductive coating over said target surface connecting said insulating material to the target surface between said spaced portions.

4. A signal generating tube comprising an envelope, an electron gun within said envelope for developing a beam of electrons of predetermined energy along a normal path, a target electrode having ametal sheet transverse to the normal path of said electron beam to be scanned thereby, an insulating material deposited over spaced portions of said metal sheet, said material having a secondary emission when struck bysaid electron beam, the surface of said metal sheet between said spaced portions having an oxide coating with a secondary emission greater than that of said insulating material when struck by said electron beam, and a thin metal film coating said insulating material and said oxide coating.

9 5. A' signal generating tube comprising an envelope, an electron gun within said envelope for developing a beam of electrons of predetermined energ along a normal path, a target electrode having a metal sheet transverse to the-normal path of said electron beam to be scanned thereby, ametal oxide material deposited over spaced portions of said metal sheet, said material havinga secondary emission when struck by said electron beam, the surface of said metal plate between said spaced portions having an oxide coating with a secondary emission greater than that of said metal oxide material when struck by said electron beam, and a conductive film over said target connecting said metal oxide material to said oxide coating between said spaced portions.

6. A signal generating tube comprising an envelope, an electron gun within said envelope for developing a beam of electrons along a normal path, a target electrode having an aluminum sheet transverse to the normal path of said electron beam to be scanned thereby, a chromium oxide layer on spaced portions of the surface of the aluminum sheet facing said electron gun, an aluminum oxide coating on said surface of the aluminum sheet between said spaced portions, a

velope, an electron gun within said envelope for developing a beam of electrons along a normal path, a target electrode having an aluminum sheet transverse to the normal path of said electron beam to be scanned thereby, a chromium oxide layer on spaced portions of the surface of the aluminum sheet facing said electron gun, an aluminum oxide coating on said surface of the aluminum sheet between said spaced portions, a thin film of caesium metal on said surface of said aluminum sheet connecting said chromium oxide layer to said aluminum oxide coating.

8. A signal generating tube comprising an envelope, means within said envelope for developing a beam of electrons along a normal path, said means including an electron source and an electrode adapted to be maintained during tube operation at a positive potential relative to said elec tron source, a target electrode having a metal sheet transverse to the normal path of said electron beam to be scanned thereby, means for connecting said target metal sheet to a source of positive potential between that of said electron source and of said electron, an insulating material; deposited over spaced portions of. said metal Sheets.saidamaterial-uhaving' a;- -':'se1m1:irlatryv lem-is.

sion when struck by said electron beam, the sun.- face of said metal sheet between said spaced portions having an oxide coating with a secondary emission greater than that of said insulating ma terial when struck by said electron beam, and a. thin metal film connecting said insulating material and said oxide coating to said metal sheet.

9. A signal generating tube comprising an envelope, means within said envelope for developing a beam of electrons along a normal path, said means including an electron source and an electrode adapted to be maintained during tube operation at a positive potential relative to said electron source, a target electrode having an aluminum sheet transverse to the normal path of said electron beam to be scanned thereby, means for connecting said aluminum target sheet to a source of positive potential between that of said elec tron source and of said electrode, a chromium oxide layer deposited over spaced portions of said aluminum sheet facing said gun, the surface of said aluminum sheet between said spaced portions having an aluminum oxide coating with a secondary emission greater than that of said chromium oxide layer when struck by said electron beam, a thin metal film connecting said chromium oxide layer and said aluminum oxide coating to said aluminum sheet.

10. The method of making a target for a signal generating tube, said method comprising the steps of, coating a surface of a metal plate with albumen sensitized with a metal oxygen salt, exposing said albumen coating to light through a transparency for masking portions thereof from said light, removing the masked portions of said albumen coating from said plate, heating said metal plate to burn off the residual albumen coating and to change the residual metal salt therein to a metal oxide, oxidizing the surface of the plate not covered with the metal oxide coating, and forming a thin metal film on the coated surface of the metal plate.

11. The method of making a target for a signal generating tube, said method comprising the steps of, coating a surface of an aluminum plate with albumen sensitized with a chromium oxygen salt, exposing said albumen coating to light through a transparency for masking portions thereof from said light, removing the masked portions of said albumen coating from said plate, heating said metal plate to burn 01f the residual albumen coating and to change the residual chromium salt therein to chromium oxide, oxidizing the surface of the aluminum plate not covered with the chromium oxide coating, and forming a thin metal film on the coated surface of the aluminum plate.

HENRY P. STEIER..

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

UNITED STATES PATENTS Number Name Date 1,903,778 Conroy Apr. 18, 1983 2,029,639 Schlesinger Feb. 4, 1936 2,069,441 Headrick Feb. 2,193? 2,156,435 Schroter et al. May 2, 1939 2,198,329 Bruining et al. Apr. 23, 1940 2,287,415 Burnett June 23, 1942 2.297,752 Du Mont et a1 Oct. 6, 1942 2,299,471 Du Mont et al. Oct. 20, 1942 2,303,563 Lawn Dec. 1,1942