US3136916A

US3136916A - Image orthicon tube having specially coated decelerating field electrode

Info

Publication number: US3136916A
Application number: US110817A
Authority: US
Inventors: Donald L Schaefer
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1961-05-17
Filing date: 1961-05-17
Publication date: 1964-06-09
Anticipated expiration: 1981-06-09
Also published as: GB946173A

Description

' June 9 1964 D. L. SCHAEFER 3 l IMAGE ORTHICON TUBEYHAVING SPECIALLY COATED 36916 DECELERATING FIELD ELECTRODE Filed May 17, 1961 FIG.3. 20 f 2 El INVENTOR:

%LD L. SCHAEFER, BY M HIS TORNEY.

United States Patent 7 3,136,916 IMAGE ORTHICON TUBE HAVING SPECIALLY COATED DECELERATING FIELD ELECTRODE Donald L. Schaeter, Scotia, N.Y., assignor to General Electric Company, a corporation of New York Filed May 17, 1961, Ser. No. 110,817 4 Claims. .(Cl. 315-) This invention relates to cathode ray tubes and more specifically to picture signal generating tubes of the kind in which video signals are obtained by scanning with an electron beam a planar electric charge-storing target. More particularly the invention relates to improvements in camera tubes of the image orthicon type wherein the charge storing target is mounted in confronting adjacent relationship with a decelerating field forming foraminate electrode disposed in the path of the target-scanning electron beam.

As is known to those skilled in the art, the stored charge pattern on the target of a tube of the image orthicon type is read by the charge neutralizing etiect of deposition on the target of some of the electrons of the scanning electron beam, and the resulting modulation of beam current is amplified in the electron multiplier portion of the tube to which the scanning beam is returned.

It has also been recognized that, in image orthicon type tubes having a decelerating field-forming forarninate or mesh electrode disposed opposite the target in the path of the scanning electron beam, secondary electrons are emitted from such decelerating field forming mesh elect'rode by impingement oh the mesh of primary electrons of the target-scanning electron beam. Some of such secondary electrons are drawn or accelerated to the electron multiplier portion of the tube and thereby result in the generation of spurious signals which deleteriously efiect the overall signal to noiseratio of the tube.

Accordingly, a principal object of the present invention is to provide an image orthicon tube including a decelerating field forming mesh, hereinafter called field mesh, having improved output signal to noise ratio.

Another object is to provide a field mesh image orthicon having reduced emission of secondary electrons from the field mesh electrode.

Another object is to provide an improved field mesh electrode for an image orthicon of the field mesh type, having minimized secondary electron emission capability.

These and other objects of the invention will be apparent from the following description and the accompanying drawing wherein:

FIGURE 1 is a fragmentary View, partially broken away in transverse section, of a portion of an image orthicon type camera tube constructed in accordance with the present invention;

FIGURE 2 is an exploded perspective view of a portion of the structure shown in FIGURE 1;

FIGURE 3 is an enlarged fragmentary sectional view of a portion of the structure shown in FIGURE 1.

Briefly, according to the present invention I have discovered that substantial reduction of spurious signals resulting from the field mesh electrode of a field mesh type image orthicon can be obtained by making at least the surface portions of said field mesh electrode facing normal to the scanning electron beam of a material which has a secondary electron emission characteristic of less than 1.0. Preferably I secure this low secondary emission characteristic by coating such surfaces of the field mesh electrode with chromium.

Alternative to chromium, other low secondary emission characteristic materials compatible with the environment may also be employed for such surfaces, such as a material from the group consisting of manganese, ti-

tanium, vanadium, and alloys and intermetallic compounds thereof.

Turning to FIGURE 1 of the drawing, the target end portion of the camera tube there shown includes an envelope 2 having a window 4 on the inside surface of which is a photo-cathode 6. Arranged opposite the photo-cathode is an accelerating electrode 8 and a target support electrode 10 on which is mounted a suitable planar chargestoring target 12 and an associated mesh collector electrode 14. As is well known in the art the face of the target 12 remote from the photo-cathode 6 is arranged to be scanned by an electron beam 16 generated in the electron gun portion of the. tube (not shown).

Disposed in spaced-confronting relation with target 12 and a plane parallel to the target in the path of the scanning electron beam is a foraminate decelerating fieldforming, or field mesh, electrode 20 carried by an annular support 22. The field mesh 20 may have a suitable potential of, for example, approximately +200 volts positive with respect to the cathode of the electron gun, which potential may be applied through a conductive finger 24 engageable with the cylindrical conductive coating 26 which forms a focus electrode ,for electron beam 16. After passing through the field mesh electrode 20 the electrons of the electron beam are decelerated by the electrostatic field between the field mesh 20 and the target 12, which may have a potential of, for example, +2 volts relative to the electron gun cathode, and hence the electrons of the beam 16 arrive at the surface of the target with a very low velocity of the order of a few volts. An additional annular electrode 28', which may have a variable potential, facilitates adjustment of the peripheral portion of the decelerating field.

After the scanning beam has performed the desired charge neutralization at the target surface, the remaining electrons of the beam are reaccelerated in the reverse direction, i.e., to the right as shown at 32 in FIGURE 1, and returned through the field mesh electrode 20 to the electron multiplier portion of the tube (not shown). Some of the secondary electrons emitted from the field mesh electrode 20 as a result of impingement of the scanning electron beam thereon are likewise accelerated toward the electron multiplier portion of the tube and therein serve as a source of spurious signals.

In accordance with my invention I minimize the generation of secondary electrons at the field mesh electrode by coating the field mesh electrode with a material having minimum secondary electron emission characteristics, particularly in response to impingement of primary electrons having acceleration of about that provided by the potential of electrode 20, e.g., +200 volts. Such a coating is shown at 40 in FIGURE 6, deposited on a mesh-like core or base metal 42, which may be for eX- ample copper or silver having 500-1000 openings per inch. One such coating material is chromium, which may be coated onto the mesh by any suitable method such as evaporation, sputtering, or electrolytic techniques. I have found that with a field mesh having a thickness of the order of 0.2 mil, a coating of chromium on the surfaces of the mesh normal to the scanning electron beam and having a thickness of the order of a few hundred angstroms satisfactorily inhibits emission of secondary electrons.

Other coating materials may be used, such as manganese, titanium, vanadium, or alloys or intermetallic compounds of chromium, manganese, titanium or vanadium. Moreover it is within the contemplation of the present invention that, rather than have such a coating, the field mesh electrode 20 may be made entirely of material such as chromium, manganese, or one of the other members of the group above defined having the desired low secondary emission characteristics. However, as a practhe invention may be' carried out in various ways and.

may take various forms and embodiments other than those illustrative embodiments heretofore described. Accordingly, it is to be understood that the scope of the invention is not limited by the details of the foregoing description, but will be defined in the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A cathode ray tube of the orthicon type comprising in combination a charge imagestoring target, means for forming a charge image on the target, means for scanning an electron beam over said target, and a conductive foraminate electrode disposed in confronting adjacent rela tionship with the target in the path of said electron beam, said foraminate electrode having surfaces exposed to said electron beam which include at least one metal taken from the group consisting of chromium, manganese, titanium, vanadium, and alloys and intermetallic compounds thereof, said surfaces being further characterized by having a secondary electron emission ratio of less than 1.0 upon impingement by primary electrons having energies of approximately 200 volts.

2. A cathode ray tube of the orthicon type comprising in combination a charge image storingtarg'et, means for forming a charge image on the target, means for scanning an electron beam over said target, and a foraminate electrode disposed in confronting adjacent relationship with the target in the path of the electron beam, said foramion the surfaces of said base material exposed to said electron beam including a metal taken from the group consisting of chromium, manganese, titanium, vanadium, and alloys and intermetallic compounds thereof, said coating having a secondary electron emission ratio of less than 1.0 upon impingement by primary'electrons having energies of approximately 200 volts, said foraminate base layer being further characterized by being of a good elec- 1954, p. as,

trically conductive metal having openings in the'rang'e of from about 500 to about 1000 per inch and being about 0.2 mil thickness, said coating being at least about 300 angstroms thickness. f

3. A cathode ray tube :of the orthicon type having a planar charge image storing target, means including a photo-cathode for forming a charge image on one surface of the target, electron beam generating means spaced from the opposite surface of the target, a focusing-electrode surrounding said beam, and means for scanning said electron beam over said opposite surface of said target, a conductive mesh electrode disposed in confronting adjacent relationship with said opposite surface of the target in the path of said electron beam, electrical connector means connecting said mesh to said focusingelectrode, means for applying to said mesh electrode positive voltage relative to said target, to produce an electron decelerating field from said mesh electrode to'said target, an annular control electrode surrounding said decelerating field for peripheral control-thereof, said mesh electrode having surfaces exposed to said electron beam including at least one metal taken from the group consisting of chromium, manganese, titanium, vanadium, and alloys and intermetallic compounds thereof. r 1

4. The invention as recited in claim 3 wherein said conducting mesh electrode includes a base metal mesh having a coating of chromium deposited thereon on the order of about 300 angstroms thickness.

References Cited in the file of this patent 'UNITED STATES PATENTS 1,872,359 Sutherlin Aug. 16, 1932 2,108,132 Loro Feb. 15, 1938 2,846,609 Espersen Aug. 5, 1958 3,086,138 Hendry Apr. 16, 1963 i FOREIGNPATENTS 485,921 Canada -Q. Aug. 19,1952

7 OTHER REFERENCES I Bruining: Physics and Applications of Secondary Electron Emission, McGraw-Hill Book Co., Inc., New York,

Claims

1. A CATHODE RAY TUBE OF THE ORTHICON TYPE COMPRISING IN COMBINATION A CHARGE IMAGE STORING TARGET, MEANS FOR FORMING A CHARGE IMAGE ON THE TARGET, MEANS FOR SCANNING AN ELECTRON BEAM OVER SAID TARGET, AND A CONDUCTIVE FORAMINATE ELECTRODE DISPOSED IN CONFRONTING ADJACENT RELATIONSHIP WITH THE TARGET IN THE PATH OF SAID ELECTRON BEAM, SAID FORAMINATE ELECTRODE HAVING SURFACES EXPOSED TO SAID ELECTRON BEAM WHICH INCLUDE AT LEAST ONE METAL TAKEN FROM THE GROUP CONSISTING OF CHROMIUM, MANGANESE, TITANIUM, VANADIUM, AND ALLOYS AND INTERMETALLIC COMPOUNDS THEREOF, SAID SURFACES BEING FURTHER CHARACTERIZED BY HAVING A SECONDARY ELECTRON EMISSION RATION OF LESS THAN 1.0 UPON IMPINGEMENT BY PRIMARY ELECTRONS HAVING ENERGIES OF APPROXIMATELY 200 VOLTS.