Cathode Ray Storage Tube Having a Target Dielectric Provided With Collector Electrode Segments Extending Therethrough

The present invention relates to cathode ray tubes and more particularly to cathode ray tubes providing improved storage operation, improved storage target thereof and method of making such storage targets.

U.S. Pat. No. 3,531,675 discloses a cathode ray storage tube in which the storage target is provided with protrusions that have been etched from the insulating substrate and they and the surface from which they protrude are coated with a thin layer of transparent conductive metal oxide thereby defining a collector electrode. A dielectric layer is disposed onto this collector electrode and the other portions of the protrusions extend outwardly beyond the dielectric layer. This storage target is expensive to manufacture due to the etching of the substrate to form the protrusions and the subsequent formation of the dielectric layer can vary in thickness at various locations over the target due to variance in the etching that takes place. The area of the protrusions also vary due to non-uniformities of the substrate and the fabrication thereof. The etched configuration of the substrate makes it difficult to discern non-uniformities and defects of the protrusions and dielectric layer. The operating areas of the protrusions can be impaired due to phosphor adhering too far up the protrusions thereby reducing the collection efficiency.

This patent also discloses the use of frit projections adhered onto a flat surface of the insulating substrate, a thin layer of conductive material is coated onto the flat surface and frit projections whereafter disposed onto the conductive layer. It has been found in this type of target that the frit does not provide high enough projections due to frit spreading out onto the flat surface when it is melted.

U.S. Pat. application Ser. No. 356,029, filed Apr. 30, 1973, now U.S. Pat. No. 3,956,662 describes an invention which is directed to a conductive coating applied onto a smooth surface of an insulating support plate, dots or protrusions of metallic particles are provided on the conductive coating and storage dielectric is disposed on the conductive coating with the outer ends of the protrusions extending beyond the top surface of the dielectric. This target has proven satisfactory; however, it has been found that the metallic protrusions do not adhere to the conductive coating as desired and the cobalt metal particles that form the protrusions are becoming too expensive to use.

The present invention is directed to a cathode ray tube in which a storage target is provided. The storage target includes a dielectric support member on which an array of glass beads is disposed thereby providing dots or protrusions of glass beads or particles of substantially conical or continuous configuration that have their bases connected to the support member and their apices extending thereabove. A conductive layer covers the array of glass beads and support member and a storage dielectric layer is applied onto the conductive layer and the conductively-coated apices of the glass beads extend outwardly from the top surface of the storage dielectric layer thereby defining collector areas for collecting secondary emitted electrons from the dielectric.

Such a storage target provides better collection efficiency because the phosphor area surrounding or adjacent the collector dots or protrusions is controlled so that the collector dots or protrusions provide more collector area. This enables the storage target to write information thereon via the electron beam at a faster rate and luminance is greater. The life of this storage target is longer as a result of being able to operate at a lower potential since target degradation is slower at lower operating potentials. The storage target of the present invention is easier to fabricate, therefore it is more economical; it is reclaimable, because the collector dots or protrusions with the conductive layer thereon can be reusable to fabricate a new target. The fabrication of the present storage target can more effectively be controlled which provides better yields.

In accordance with the method aspects of the present invention, a storage target is advantageously fabricated by applying a layer of photopolymerizable material containing a dispersion of glass beads and vitreous frit particles therein onto a surface of a support member. The layer of photopolymerizable material is exposed to light through a mask having the desired pattern for the collector members causing the photopolymerizable material to polymerize in the areas activated by the light. The photopolymerizable material is washed leaving behind the collective members of glass beads and vitreous frit particles having a distinct pattern. The support member with the pattern of glass beads and vitreous frit particles is baked; the frit passing through a liquid state and resolidifying thereby cementing the glass beads in place on the support member. A conductive coating is applied onto the pattern of glass beads and support member to provide a conductive layer and collector pattern. A layer of photopolymerizable material containing phosphor particles is applied onto the conductive layer and collector pattern whereafter light is applied through the collector pattern causing the photopolymerizable material to polymerize in the areas activated by the light. This layer of photopolymerizable material is washed removing the nonactivated photopolymerizable material around the collector members and leaving behind the phosphor particles defining the storage dielectric layer with the apices of the collector members extending above the outer surface of the storage dielectric.

An object of the present invention is to provide a cathode ray tube having a storage target provided with a faceplate having an array of glass beads secured thereon defining a pattern of protrusions connected thereto with a conductive layer thereover and a dielectric storage layer disposed on the conductive layer with the outer portions of the conductive protrusions defining collector members extending above the outer surface of the dielectric storage layer.

Another object of this invention is the provision of a storage target for a cathode ray tube with improved means for collecting secondary electrons due to larger surface area of the collecting means thereby increasing collection efficiency.

A further object of this invention is to provide a storage target for a cathode ray tube that will write at a faster rate and has increased luminance.

An additional object of the present invention is the provision of a storage target for a cathode ray tube that will have longer life as a result of being able to operate at a lower potential because target degradation is slower at lower operating potentials.

A still further object of this invention is to provide a storage target for a cathode ray tube that is easier and more economical to make due to better control over its fabrication which provides increased yield, and the support plate with conductive layer thereon is reclaimable because the storage dielect ic layer can be readily removed and a new layer applied thereover.

Still an additional object of the present invention is the method for making the storage target for a cathode ray tube.

Still another object of this invention is the provision of using the conductively-coated collector pattern fabricated on a support member as an integral photomask when fabricating the dielectric storage target.

Other objects and advantages of the present invention will be apparent from the following detailed description of preferred embodiments thereof and from the attached drawings of which:

FIG. 1 is a schematic representation of a cathode ray storage tube according to the present invention;

FIG. 2 is a cross-sectional view illustrating the fabrication of a glass bead and vitreous frit dot pattern on the surface of a support member;

FIG. 3 is a cross-sectional view of the glass bead and vitreous frit dots on the surface of the support member;

FIG. 4 is a cross-sectional view of the conductive coating on the surface of the support member and the glass bead dots secured on such surface;

FIG. 5 is a cross-sectional view of the fabrication of the dielectric storage target;

FIG. 6 is a perspective view, partly broken away and partly in cross section, of the completed storage target structure;

FIG. 7 is an enlarged cross section of a part of the storage target of FIG. 6;

FIGS. 8a and 8b are broken perspective views of alternative embodiments of the storage target; and

FIG. 9 is a perspective view of a corner of a front panel of a curved faceplate for a large-viewing cathode ray tube using the glass bead dot pattern of collector members of the present invention.

Referring to FIG. 1, a cathode ray storage tube 10 includes an envelope 12 formed of insulating material which houses an electron gun including a filament 14, a cathode 16 for connection to a high negative voltage source, a control grid 18 and a focusing and accelerating structure 20. Electron beam 22 of high velocity electrons produced by the electron gun is deflected horizontally via horizontal deflection plates 24 and vertically by vertical deflection plates 26 in accordance with an input signal applied to input terminal 28 which operates conventional deflection circuits 30 connected to the horizontal and vertical deflection plates so that the electron beam is selectively positioned along storage target 32 at the end of envelope 12 opposite the electron gun in correspondence with the input signal.

One or more flood electron guns 34 is provided in the storage, tube, each flood gun including a cathode 36, a control grid 38 and an anode 40. Flood guns 34 are supported inside envelope 12 adjacent output ends of vertical deflection plates 26. Cathodes 36 are conventionally operated at a low voltage level which is typically ground level, whereas grids 38 are connected to a low negative voltage. Low velocity electrons emitted from flood guns 34 diverge into a conically-shaped beam and they are uniformly distributed over target 32.

A plurality of electrodes are disposed on the inner surface of envelope 12 between flood guns 34 and target 32. These electrodes are preferably provided as spaced coatings of conductive material and the first coating 42 functions primarily as a focusing electrode for the flood electrons emitted from the flood guns; it is connected to a suitable source of positive electrical potential. A second electrode coating 44 is spaced from coating 42; it is also electrically connected to a positive potential and functions as a focusing and collimating electrode. A third coating electrode 46 is spaced from coating 44, is connected to a positive potential and functions too as a focusing and collimating electrode. As a result of the collimating action of the electrode coatings, the electrons from the flood guns 34 are uniformly distributed over the inner surface of target 32.

A fourth electrode coating 48 is disposed between and spaced from wall coating 46 and storage target 32 and it is connected to positive voltage. Coating 48 also functions as a focusing and collimating electrode for the flood electrons as well as an auxiliary collector electrode to collect the secondary electrons emitted from storage target 32 adjacent coating 48 and those secondary electrons that are not collected by the collector electrodes.

Electrodes 42, 44, 46 and 48 are connected to descending positive potentials with the highest positive potential being connected to electrode 42 for optimum operation.

Storage target 32 comprises insulative end plate 50 having a smooth and nonanomalous surface on which a series of dots 54 in the form of micro glass beads are secured to plate 50 defining a dot pattern, a coating 52 of transparent conductive material defining a target electrode, and a dielectric layer 56. The insulative end plate 50 defines a support member and is made of transparent material, e.g. glass. Target electrode 52 is a thin transparent coating of preferably tin oxide which is suitably connected to the midpoint of a voltage divider which includes resistors 58 and 60 connected between a positive potential and ground. Resistor 58 is variable and is adjusted so that a proper operating voltage is applied to target electrode 52. Alternatively, target electrode 52 may be connected to amplifying means for providing an electrical readout of information stored on the storage target.

Dots 54 are particles, preferably of conventional glass beads of about 10-20 microns in diameter secured together and onto the glass plate 50 via vitreous frit, and have a preferably substantially conical configuration which have their bases connected to glass plate 50 and apices extending outwardly from the outer surface of dielectric layer 56. The surface of glass plate 50 containing dots 54 and the dots themselves are coated with conductive coating 52 and the conductively-coated glass beads define collector electrodes which will be more fully described hereinafter and the dots can be configurations other than conical, e.g. pyramidal, triangular, etc. Dielectric layer 56 is phosphor and preferably P-1 type phosphor.

Information is written on storage target 32 via electron beam 22, and it may be in the form of a waveform applied to vertical deflection plates 26 while the beam is scanned horizontally via horizontal deflection plates 24. In addition to electrical readout, the information written on the storage target is visibly displayed through transparent support member 50. During operation, the tube potentials are adjusted such that beam 22 has a relatively high velocity for writing and is capable of producing secondary electrons when it strikes storage dielectric 56. The area engaged by beam 22 is raised to the potential of collector electrodes 54 and target electrode 52 from ground level thus causing the dielectric target to phosphoresce thereat. These secondary electrons are then collected by collector electrodes 54, and the areas of storage dielectric engaged by beam 22 are positively charged so that flood electrons from flood guns 34 are attracted to these positively-charged areas; they emit secondary electrons at a ratio of one therefrom, the secondary electrons being collected via collector electrodes 54 adjacent the positively charged (written) areas of storage dielectric 56 thereby causing the information to be visually observed and to remain indefinitely for purposes of study or being photographed. The target can be erased in a conventional manner by pulsing the target electrode to raise the storage dielectric to the potential of the collector electrodes and then lowering it to ground level so that the flood electrons maintain it thereat until beam 22 writes information thereon again. Reference is made to the heretofore identified U.S. Pat. No. 3,531,675 for further information concerning the operation of bistable storage targets of this type.

Attention is directed to FIGS. 2-7 for a description of the fabrication of the storage target 32. As shown in FIG. 2, a transparent member 62 has a photomask 64 which has a hole pattern disposed thereon. Transparent support member 50 is positioned on photomask 64. A frame 66 is disposed around the periphery of support member 50 and a photopolymerizable slurry 68 of polyvinyl alcohol, water, ammonium dichromate, 50--50 mixture of No. 89 frit manufactured by Corning Glass Company and micro glass beads (10-20 microns in diameter) and isopropyl alcohol is poured onto conductive layer 52.

While the mixture of glass frit and glass beads is preferably 50--50, the ratio of glass frit to glass beads should be such that sufficient frit is present to assure adhesion of the glass beads together and in position on the support member. The vitreous frit has substantially the same coefficient of expansion as the glass faceplate. Materials other than glass beads can be used so long as they can be fused into position.

Collimated light source 70 is utilized to transmit light rays 72 through transparent member 62, the holes in photomask 64, support member 50 and into slurry 68 so that light activates slurry 68 thereby polymerizing the polyvinyl alcohol in these areas and fixing a mixture of glass beads and vitreous frit thereat.

The frame 66 is removed and the target structure is washed with water which removes the non-activated slurry and leaves behind a dot pattern of a mixture of glass beads and vitreous frit.

A shrinking agent is applied to the target structure such as acetone, aqueous ammonium sulfate, alcohols or other hydrophyllic agents and this shrinking agent shrinks the glass beads and vitreous frit particles into a denser mass by rapid extraction of H.sub.2 O thereby providing dots 54 defining a distinct dot pattern. The target structure is then placed upside down in a baking oven and it is baked in a conventional frit cycle. During the bake cycle, of about 400.degree.-500.degree. C., the frit passes through a liquid state and resolidifies thereby cementing the glass beads together and to the support member 50.

The reason the target structure with the dot pattern of the glass beads and vitreous frit mixture is baked upside down is to provide the dots with proper height and a somewhat conical configuration as shown in FIG. 3.

The dot pattern target structure after the baking cycle then undergoes a spraying operation wherein tin oxide is sprayed onto the surface containing the dots 54 thereby resulting in a conductive coating of transparent conductive material 52 as shown in FIG. 4.

A photopolymerizable slurry 74 of polyvinyl alcohol, water, dimethyl sulfoxide, ammonium dichromate and phosphor is introduced onto conductive layer 52 and conductively-coated dots 54 as shown in FIG. 5, whereafter collimated light source 70 transmits light rays 72 through support member 50, conductive layer 52 and into slurry 74 and the light rays activate slurry 74 in the areas where no dots are located thereby polymerizing the polyvinyl alcohol in these areas.

As can be discerned, no photomask is needed for this operation because the conductively-coated dots provide an integral photomask so that in the area of each conductively-coated dot, no polymerization of the polyvinyl alcohol will take place.

The structure is washed with water which removes the nonactivated slurry and leaves behind a layer of light activated slurry defining a dielectric layer. This target structure is then soaked by the shrinking agent used to shrink the conductive particles of the dots, and this shrinking operation shrinks the dielectric layer into a more dense configuration so that the dielectric surrounding each conductively-coated dot is shrunk back away therefrom exposing a large area of each conductively-coated dot. While the photopolymerizable material for formulating the pattern of glass beads and dielectric layer is in the form of a slurry, it can be in the form of a photopolymerizable dry film. As can be discerned from FIGS. 6 and 7, the area of the storage dielectric layer 56 surrounding each of conductively-coated dots 54 slopes upwardly and away from the dots defining an annular surface 76 therearound and best defined as being in the form of a beveled hole hence the increased collector area provided by each collector dot 54 for more effectively collecting the secondary electrons emitted from dielectric layer 56. The conductively-coated dots 54 also extend above the outer surface of dielectric storage layer 56 about one-half the height of the dots.

After the storage target structure has been shrunk, it is baked in an oven at a suitable temperature to remove organic binders and leave the dielectric storage layer comprising essentially phosphor material. The storage target is now completed and is assembled in position on envelope 12 in accordance with conventional frit-sealing techniques with the support member defining the faceplate.

The dot pattern of conductively-coated dots 54 representing the collector electrode structure is preferably such that the center-to-center distance between adjacent dots is less than the diameter of electron beam 22 and this provides improved collector means for collecting secondary electrons, optimum resolution of the target, elimination of trace shadowing and improved visible display and readout accuracy of the stored information on the bistable storage target. The collection efficiency of secondary electrons by collector dots 54 is increased due to larger surface area and the control of phosphor area surrounding the dots. This provides faster writing rate and improved luminance of the target. The life of the storage target is increased because the target operates at a lower operating potential since target degradation is slower at lower operating potentials.

FIG. 9a illustrates an embodiment of the storage target wherein the conductively-coated collector segments 54a of frit-secured glass beads are continuous and generally wedge-shaped protrusions that have their bases connected to glass plate 50a and their apices extending above the outer surface of dielectric layer 56a. Thus, alternate rows of the dielectric layer and conductive collector segments define the target structure of FIG. 9a. Conductively-coated collector segments 54b can also be discontinuous as illustrated in FIG. 9b, and the dielectric layer 56b is continuous in the areas where the collector segments are not continuous.

The areas of the dielectric layer 56a and 56b adjacent the collector segments 54a and 54b are beveled to provide greater collector area in the same manner as the collector dot pattern of FIGS. 2-7.

The target structures of FIGS. 7a and 7b are fabricated in the same manner as that of FIGS. 2-6 and the collector segments of conductive particles can take any configuration as desired to achieve the intended result.

The embodiments hereinbefore described are directed to a planar support member having the thin layer of conductive coating covering the frit secured glass bead particles defining the conductively-coated collector dots or collector segments, a layer of dielectric storage material covers the conductive layer with the dielectric layer adjacent the conductively-coated dots or segments being provided with beveled surface means, and the apices of the dots or segments extending above the top or outer surface of the dielectric layer thereby defining a storage target of planar construction.

In the embodiment of FIG. 8, a storage target comprises a glass front panel 78 which has curved inner and outer surfaces with the inner surface having frit-secured glass beads defining collector dots 54c thereon which are covered by conductive coating 52c and dielectric layer 56c, which is fabricated in the same manner as hereinbefore described. Front panel 78 includes an integral wall 80 for securing onto the tube envelope of a larger cathode ray tube. Thus, the embodiment of FIG. 8 is directed to a curved storage target for use in conjunction with storage cathode ray tubes having a large viewing area.

The storage target of the present invention is easier to fabricate and therefore is more economical. The support member with frit-secured glass beads and with a conductive layer thereon is reclaimable, because the dielectric layer can be removed so that the support member with conductive layer thereon is reusable to fabricate a new storage target. Better control can be exercised over the fabrication of the present storage targets therefore resulting in better production yields.

While preferred embodiments of the present invention have been illustrated and described, it will be apparent that changes and modifications may be made to this invention without departing therefrom in its broad aspects. The appended claims therefore cover all such changes and modifications as fall therewithin.