US3284654A - Cathode ray storage tube for displaying stored and non-stored displays in different colors - Google Patents

Description

Nov. 8, i966 .L BRAMLEY ETAL 3,284,554

CATHODE RAY STORAGE TUBE FOR DISPLAYING STORED AND NON-STORED DISPLAYS IN DIFFERENT COLORS Filed Jan. z, 1963 AND EFLECTION CURRENT GENERATOR l I NVE NTORS.

1 O Norman H. Lehrer, l

Z55 Jenny Bromley, N- B United States Patent Ofice 3,284,654 Patented Nov. 8, 1966 3,284,654 CATHODE RAY STORAGE TUBE FOR DISPLAY- ING STORED AND NON-STORE!) DISPLAYS IN DIFFERENT COLORS Jenny Bramley, Falls Church, Va., and Norman H. Lehrer, Pacific Palisades, Calif., assignors to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware l Filed Jan. 2, 1963, Ser. No. 249,018 1 Claim. (Cl. 313-92) This invention relates to visual display storage tubes. More particularly, the invention relates to color display storage tubes whereby stored displays or any portion thereof may be selectively erased and both stored and non-stored displays may be simultaneously presented in different colors.

Heretofore, the most practical and useful visual display storage tubes have utilized storage targets which have operated primarily, if not entirely, on the phenomenon of secondary electron emission from the storage surface. However, in the co-pending application of Norman H. Lehrer, Serial No. 59,590 filed September 30, 1960, now U.S. Patent No. 3,086,139 issued April 16, 1963, a novel cathode ray storage tube utilizing the phenomenon -of bombardment induced conductivity is described. As explained therein such a storage tube permits selective erasure of stored displays or any portion thereof as well as the simultaneous display of both stored and non-stored information.

In general, this tube employes a target comprising a conductive support member having a thin film thereon of cubic zinc sulde. The cubic zinc sulfide surface is responsive to the energy level of an electron beam impinging thereon whereby at one beam energy level the principal effect is secondary electron emission greater than unity while at a different beam energy level the principal effect is bombardment induced conductivity. Thus, while at the first beam energy level some bombardment induced conductivity may occur, it is completely dominated or overridden by the secondary electron emission phenomenon. Such a storage target is capable of being charged in opposite electrical senses. by selectively utilizing these two phenomena. It is thus possible, by switching the electron beam energy level, to write or store information on the lstorage surface by one phenomenon and to erase by selective scanning any portion of the stored information by the second phenomenon. Thus, for example, a normally negatively charged storage target may be driven selectively positive by secondary electron emission in accordance with information to be stored by scanning the target with an electron beam of 2.5 kv. This permits relatively low energy flood electrons to penetrate the storl l age target and excite the phosphor screen into luminescence in accordance with the charge pattern thereon. Bombardment of these positively charged portions with an electron beam of 7.0 kv., for example, induces those portions to become conductive so that they return to or assume the normally negative potential of the sto-rage target. It is also possible by utilizing an electron beam having an intermediate energy level (i.e., 4.5 kv.) to cause the beam to pass through the storage target without altering the stored pattern or other potential conditions of the target. Thus stored information may be displayed simultaneously with non-stored or live information. The present invention is directed toward providing means for readily distinguishing stored information from non-stored information.

One object of the present invention is to provide an improved cathode ray storage tube.

Another object of the invention is to provide an improved cathode ray color storage tube utilizing the phenomenon of bombardment induced conductivity and being capable of providing stored and non-stored displays in different colors.

These and other objects and advantages of the invention are realized by providing a multi-layer phosphor viewing screen in a bombardment induced conductivity storage tube and controlling the excitation of particular phosphor layer in accordance with electron velocity. Thus, in the type of tube described in the aforementioned co-pending application, one phosphor layer would be excited to produce green light, for example, by the action of relatively low velocity flood electrons for stored displays, and a second phosphor layer would be excited to produce red light, for example, by the action of the higher velocity electrons of the non-storage electron beam of 4.5 kv.

The invention will be described in greater detail by reference to the following drawings in which:

FIGURE l is a partially cross-sectional and partially schematic view of a cathode ray storage tube employing a multi-layer phosphor viewing screen according to the present invention; and

FIGURE 2 is a cross-sectional elevational view of an arrangement of a multi-layer phosphor viewing screen according to the present invention.

Referring now to FIGURE 1 a half-tone visual display cathode ray tube 12 is shown according to the present invention. The tube 12 comprises an evacuated envelope formed by a comparatively large cylindrical section 14 and a narrower neck portion 16 communicating therewith at one side thereof (hereinafter referred to the neck or gun side). The neck section 16 may be disposed, as shown, at an angle with respect to the main longitudinal axis of the larger cylindrical section 14. The side of the large cylindrical section 14 opposite the neck side comprises a face-plate 18 over the inner surface of which is a multi-layer phosphor target which will be described in greater detail hereinafter. Adjacent and coextensive with the face-plate 18 is a storage target 2 as described in the vaforementioned co-pending application. The `storage target 2 may comprise a nickel mesh, which may be electroformed, having disposed on one side thereof a thin layer or film of cubic zinc sulfide which has both secondary electron emission and bombardment induced conductivity properties. The mesh may have from to 400 meshes per inch, preferably 250 meshes per inch, and a thickness of about 1 to 2 mils. Such a mesh with a pitch of 250 meshes per inch will have an overall transparency'of about 60%. The cubic zinc sulfide layer is disposed coextensive with the meshes of the screen and may be about one to two microns thick, for example.

It may also be desirable and preferred to provide a supplementary layer of secondary electron emissive material over the cubic zinc sulfide lm in order to enhance the secondary electron emission characteristics of the storage target. Thus, for example, a thin film of magnesium fluoride may be evaporated onto and over the layer of cubic zinc sulfide. The film of magnesium fluoride may be about 500 Angstroms thick, for example. This supplemental secondary electron emissive layer should be thin enough to allow a high energy level (i.e., 7 kv.) electron beam to penetrate therethrough to the cubic zinc sulfide layer so as to raise electrons therein to the conductive energy level and thick enough to provide high secondary electron emission when bombarded by a relatively low energy level (i.e., 2.5 kv.) electron beam.

Continuing to proceed from the viewing screen end of the tube toward the gun section, a collector grid 24 is disposed adjacent and -coextensive with the storage target 2. The collector grid 24 comprises a conductive screen supported about its periphery by an annular ring 26. The transparency of this screen is preferably of the order ofY 80%; the function of the grid 24` is to collect secondary electrons emitted from the storage target 2. Adjacent -the collector grid 24 is a collimating electrode 28 in the form of .a cylindrical can, the purpose of which is to collimate ood or viewing electrons from the flood gun 30 which is disposed at the gun side of the tube section 14.

The ood gun 30, which may be on the longitudinal axis of the larger cylindrical portion 14 of the tube 12, comprises a cathode 32 and an intensity electrode 34 which encloses the cathode 32 except for a small aperture 36 disposed over the central portion of the cathode 32. An annular electrode 33 is disposed adjacent the intensity electrode 34 and coaxially with respect to the longitudinal axis of the tube 12 which also passes through the center of the aperture 36 in the intensity electrode 38.

The neck portion 16 of the tube 12 houses an electron gun 40 which may be of conventional construction. The gun 40 comprises a cathode 42, an intensity electrode grid 44, and a cylindrical beam-forming section 46.

An equipotential region is maintained throughout the neck portion 16 of the larger cylindrical section 14 of the tube 12 by means of a conductive layer 48 which A may be coated over the interior surfaces of the tube as shown. During operation, a potential of about 5 volts positive may be maintained on this conductive layer.

The viewing screen according to the present invention comprises a first phosphor layer 22 disposed on the internal surface of the tube face-plate 18, for example, a second phosphor layer 22 disposed over the first phosphor layer, and an electrically conductive, electron transparent, optically .reflecting coating 23 disposed over the second phosphor layer. The reflective coating 23 may comprise a thin film of aluminum, for example, the application and use of which are well known in the cathode ray tube art. These phosphor layers may be either of the settled type with a microcrystalline structure or ofthe evaporated type, which are transparent. The latter embodiment may be preferable from the point of view of improved resolution. The first phosphor layer 22 should be of a phosphor material which is excitable by relatively high velocity electrons, as for exam-ple the electrons in the nonstorage electron beam. A suitable phosphor for this purpose is magnesium fiuoride, for example.` This phosphor emits red light upon excitation. The second phosphor layer 22 should be of a phosphor material which is excitable principally by only relatively low velocity electrons, as for example the flood or viewing electrons. This second phosphor layer should also be capable of emitting a different color light in comparison with the light emitted by the first phosphor layer. A suitable phosphor for the second phosphor layer is zinc orthosilicate which emits green light upon excitation. The principle of color selection by the use of such a multi-layer viewing screen is based on the fact that for a given phosphor layer thickness the light emitted does not continuously increase with beam energy but reaches a maximum and then declines. In addition, the velocity of the impinging electrons will determine which layer the electrons lose most of their velocity in and produce light most efiiciently. For the electron velocities involved in a tube as described herein the thickness of the phosphor layers may be about one micron each.

In FIGURE 2 an alternate phosphor layer arrangement is shown, the principal difference being the incorporation of an additional layer 23 between the phosphor layers 22, 22. This layer 23 may be of zirconium silicate and its purpose is to prevent impurity in the colors presented by the various electron-beam energy levels. For example, in the case of the electrons from the flood gun which strike the viewing screen with 6 kv. energy, if some of these electrons completely penetrate the irst phosphor layer, then they could cause the second phosphor layer to luminesce resulting in color impurity. By the addition of the non-luminescing layer (zirconium silicate) between the two phosphor layers, these electrons are absorbed and such color contamination is prevented.

The storage target characteristic is such that with a beam energy of about l kv., charging (which means charging the potential of the storage surface) is at a maximum and is almost entirely due to -the secondary electron emission phenomenon, any charging due to bombardment induced conductivity being negligible and rather completely overridden by the secondary emission eiiect. Thus with a primary beam energy of from 1 to 4.5 kv. the storage target is charged positively by the secondary emission phenomenon.

At about 4.5 kv. secondary emission still occurs but bombardment induced conductivity effects will have increased to the point where both phenomena charge the storage surface in equal but opposite electrical senses, hence the storage surface potential will be undisturbed when the storage target is bombarded by a beam of about 4.5 kv. With beam energies greater than about 4.5 kv. the bombardment induced conductivity effect increases further and rather completely overrides the secondary emission effect which continues to diminish. The net charging effect on the storage surface hence is to -drive it negatively to an equilibrium potential by the bombardment induced conductivity effect.

It will thus be appreciated that the storage target of the present invention utilizes two Aphenomena to produce charging effects in opposite electrical senses which effects may be balanced so as to result in no net charging effect in either electrical sense. This is possible because there is a continuous range of electron beam energy levels where both secondary electron emission and bombardment induced conductivity occur and because at different portions of this range either of these phenomena can be made dominant or the two phenomena can be balanced. The capability of balancing these two phenomena is of utmost significance where it is desired to provide a storage target which can be written through to present direct or live information without altering the potentials on the storage target. Thus if these two phenomena did not overlap over a continuous range of electron -beam energy levels, one could still store by one phenomenon (i.e., secondary emission) and erase by the other (i.e., bombardment induced conductivity) simply by switching the 'beam energy levels but there would be no energy level where one could write through since changing the beam energy level only would result in establishing one of the two phenomena as the dominant one. The charging speed of the target is at a maximum for beam energies of less than about 2 kv. and more than about 7 kv. It is at a mlnimum for a beam energy of about 4.5 kv. Because greater display resolution can be obtained with a pnimary beam energy of 2 to 3 kilovolts, charging by secondary emission is preferably accomplished by utilizing a beam of about 2.5 kv. rather than 1 kv. or less at a slight sacmfice in charging speed. Charging by bomba-rdment induced conductivity is preferably accomplished by utilizlng a beam of about 7 kv. in order to achieve a charging speed comparable to that of secondary emission charging which is about 50,000 to 100,000 inch-volts per second. Beam energies of greater than 7 kv. begin to introduce serious problems of electrical insulation.

Operation of a selective erasure storage tube may be accomplished as follows. A potential of about 9 volts negative relative to ground is applied to the nickel mesh support of the storage target. The flood or viewing gun cathode 32 may be maintained at ground potential while the intensity electrode 34 and the annular electrode 38 may be maintained, respectively, at potentials of about 20 volts negative and 100 volts positive with respect to ground. Under these cirmustances ood electrons from the gun 30 will be prevented from penetrating the storage target 2 (because of the 9-volt negative potential thereon).

Hence the iiood or viewing electrons cannot reach the viewing screen and excite it into luminescence. This is the initial dark condition of the tube.

To store and display information, the storage target 2 is scanned by an electron beam of elemental cross-sectional area having an energy level of about 2.5 kilovolts. This beam may be generated by means of the electron gun 40 in the neck portion 16 of the tu'be. The cathode 42 of this gun may be maintained at a potential of about 2000 volts negative with respect to ground while the intensity grid 44 may be at a potential of about 75 volts negative with respect to the potential of the cathode 42. The electron beam produced by this gun is modulated and scanned in accordance with information-representative signals derived and applied by conventional techniques. The beam is deflected horizontally and vertically electromagnetically, as shown, by means of the deflection yoke S2 which'is positioned around the neck 16 of the tube.

Areas of the storage target 2 impinged by the 2.5 kv. beam in accordance with the information to be displayed are charged positively due to the emission of electrons therefrom which are collected Iby the collector grid 24 which may be maintained at a potential of 120 volts positive With respect to ground in order to accomplish this function. Viewing or flood electrons from the flood gun 30 may then pass through the storage target 2 at these areas of positive potential and are then accelerated to impinge upon the phosphor layer 22 of the viewing screen `by means of a potential of about 6,000 volts positive with respect to ground which may be maintained on the aluminum lm 20 of the viewing screen. In this manner the information is displayed in green light and the display may be maintained and viewed as long as desired.

Non-stored or live information may also be simultaneously displayed by switching the potential of the cathode 42 of the charging gun 40 to about 4.5 kilovolts. As explained previously a beam of this energy level does not produce any change in the potential of the storage surface. Hence, the -beam passes through the storage target 2 without altering the potential of either positively or negatively charged port-ions, and is accelerated to a velocity of l0 plus kv. to penetrate into the phosphor layer 22 where most of the velocity thereof is dissipated to result in a display of live or non-stored information in red light.

Stored potentials on the storage ta-rget 2 may be selectively erased by switching the potential of the cathode 42 of the charging gun 40 to about 7.0 kilovolts and scanning the storage target with the beam of this energy level in accordance with signals representing the information to be erased. The impingement of a beam of 7.0 kv. on portions of the storage target results in these portions being charged negatively to about the potential of the nickel support mesh 4 (-9 volts) by means of the phenomenon of bombardment induced conductivity, as explained previously.

While the storage tube shown in FIGURE 1 and described so far herein has but one charging electron gun Whose cathode potential is switched to =provide beams of different energy levels (2.5 kv., 4.5 kv., and 7.0 kv.) so as to permit storing, writing-through, and erasing selectively, additional electron guns may be provided to perform these functions independently whereby storing, writing-through, and erasure can be accomplished simultaneously.

There thus has been described a new and improved cathode ray storage tube utilizing the phenomenon of bombardment induced conductivity effectively and in a practical manner which permits selective erasure of stored information as well as the presentation of live information simultaneously with the display of stored information in different or contrasting colors.

What is claimed is:

A half-tone visual display storage tube comprising:

(a) a storage target including a conductive support member having a layer of bombardment induced conductivity material on at least a portion of one side thereof and exhibiting both 'bombardment induced conductivity and secondary electron emission over a continuous range of electron beam energy levels whereby said storage target may be charged in substantially equal and opposite electrical senses at a predetermined portion of said range;

(b) a first electron source for directing flood electrons uniformly over said storage target;

(e) a second electron source for producing a scanning electron beam having an energy level corresponding to said predetermined portion of said range of electron energy levels;

(d) and a viewing target disposed adjacent said storage target on the side thereof opposite the said one side and having phosphor means adapted to produce, respectively, light of different colors in response to impingement thereof by said flood electrons and -by electrons in said scanning beam.

References Cited by the Examiner UNITED STATES PATENTS JAMES W. LAWRENCE, Primary Examiner.

GEORGE N. WESTBY, JAMES W. LAWRENCE,

V. LAFRANCHI, Assistant Examiners.

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