GB1584163A - Bistable storage cathode ray tube storage target therefor and method of making same - Google Patents

Description

(54) BISTABLE STORAGE CATHODE RAY TUBE, STORAGE TARGET THEREFOR AND METHOD OF MAKING SAME (71) We, TEKTRONIX, INC., of 14150 Southwest Karl Braun Drive, Tektronix Industrial Park, Beaverton, Oregon 97077, United States of America; a corporation organized and existing under the laws of the State of Oregon, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to cathode ray tubes and more particularly to bistable storage targets therefor and the method of making same.

In U.S. Patents Nos. 3,531,675 and 3,956,662, bistable storage targets of storage cathode ray tubes are disclosed wherein the storage target has a multiplicity of collector electrode members extending through a layer of storage dielectric material which is in intimate engagement with the collector electrode members and collector or target electrode thereunder.Since the dielectric storage layer in these storage targets is in direct contact with the collector electrode members, background luminance during operation of the cathode ray tube takes place around the collector electrode members because collection efficiency of primary flood electrons from the flood gun means and secondary electrons emitted from written areas of the storage dielectric at the interface of the storage dielectric and the exposed collector electrode members is high due to the large area of the collector electrode members being exposed which increases the current density thereat.

This background luminance is undesirable since it results in impaired performance as it decreases contrast and presentation of the information is not precise which hinders viewability of the displayed information as well as reading out the displayed information therefrom.

The collector electrode members of U.S.

Patent No.3,531,675 can be insulated from the dielectric storage layer, but the etching of the faceplate that forms the projections which provide the basis for the collector electrode members is expensive to fabricate, and it is difficult to hold the configuration of the projection constant.

In the case of the target structure in British Patent No. 1,502,737 the formation of the collector electrode members by means of glass beads frit secured to the glass faceplate which are covered with a conductive layer provides an economical target structure to fabricate which is rugged; however, the configuration of the collector electrode members is not uniform which makes it difficult to apply an insulating layer therearound.

The collector electrode members of the target structure of U.S. Patent No. 3,956,662 is formed from metal particles which are not rugged, have nonuniform configuration and are difficult to apply insulating material therearound.

An object of the present invention is to provide a storage target for a cathode ray tube that has collector electrode members extending through a storage dielectric layer with the outer ends of the collector electrode members being exposed to collect secondary electrons from written areas of the storage dielectric layer.

According to the present invention there is provided a storage target for a cathode ray tube comprising: an insulative support member having a conductive layer provided on an inside surface thereof; a pattern of collector electrode members provided on said conductive layer for collecting secondary electrons emitted from written areas of said target, each collector electrode member including an inner and an outer metallic layer, each said metallic layer being of a different material to the other of said metallic layers and of a different material from said conductive layer, said inner metallic layer electrically connecting said outer metallic layer to said conductive layer; insulating material provided at least around each of said collector electrode members except for an outer exposed area of each collector electrode member; and a dielectric storage layer extending along and contiguous with said conductive layer, or along and contiguous with said insulating material when said insulating material extends along and covers the conductive layer, said dielectric storage layer engaging said insulating material around said collector electrode members so that said collector electrode members are isolated from said dielectric storage layer whilst leaving said outer exposed areas of said collector electrode members exposed.

The present invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic representation of a cathode ray storage tube including a storage target according to the present invention; Figure 2 is a cross section of part of an insulating support member having metallic layers on one surface thereof; Figure 3 is similar to Figure 2 showing another metal layer on the existing metallic layers; Figure 4 is similar to Figure 3 showing a photoresist on the outer metal layer and a photomask thereon; Figure 5 is similar to Figure 4 showing the photomask removed and nonpolymerized areas of the photoresist removed thereby forming openings therein; Figure 6 is similar to Figure 5 showing metal deposited within the openings of the photoresist;; Figure 7 is similar to Figure 6 showing metal caps deposited onto the metal in the openings of the photoresist; Figure 8 is similar to Figure 7 showing the polymerized photoresist removed; Figure 9 is similar to Figure 8 showing the outer metal layer removed except under the collector electrode members; Figure 10 is similar to Figure 9 showing the next metal layer removed except under the collector electrode members; Figure 11 is similar to Figure 10 showing a layer of insulating material covering the inner conductive layer, the collector electrode members and the metal cap thereon; Figure 12 is similar to Figure 11 showing a layer of dielectric storage material formed on the insulating layer; Figure 13 is similar to Figure 12 showing the insulated metal caps removed; Figure 14 is a cross-sectional view of an alternative embodiment of the bistable storage target; and Figure 15 is a part cross-sectional view of a further embodiment of the bistable storage target.

Referring to Figure 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 focusirig and accelerating structure 20. Electron beam 22 of high velocity electrons produce 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 wall 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 wall coatings, the electrons from the flood guns 34 are uniformly distributed over the surface target 32.

A fourth electrode wall coating 48 is disposed between and spaced from wall coating 46 and storage target 32 and it is connected as a focusing and collimating electrode for the flood electrons.

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 as best illustrated in Figure 13 comprises insulative end plate 50 having a transparent target or collector electrode 52 over which is disposed a series of conductive collector electrode members 54 in the form of a dot pattern and an insulating layer 56 that covers collector electrode 52 and surrounds collector electrode members 54 except for the outer exposed ends thereof. A layer of dielectric storage material 58 covers insulating layer 56 except for the locations where the insulated collector electrode members 54 extend therethrough and beyond the outer surface of layer 58.

The insulative end plate defines a support member and is made of transparent material, e.g. glass. Target or collector 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 60 and 62 connected between a positive potential and ground. Resistor 62 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 which can then be dis played in raster fashion as disclosed in U:S.

Patent No. 3,214,516 or hard copies of the information can be made as disclosed in U.S.

Patent No. 3,811,007.

Collector electrode members 54 have outer portions preferably made of nickel and laminated inner metal layers 64 and 66, and a preferably frustrum of a cone configuration connected to collector electrode 52. Layer 64 is preferably chromium and layer 66 is preferably copper. Collector electrode members 54 can have a configuration other than frustrum of a cone, frustrum of a cone reverse to those illustrated or, part spherical.

Insulating layer 56 is preferably aluminum oxide or thorium oxide or any suitable oxide that can be electrophoretically deposited so as to extend over and be contiguous with electrode 52 and surround said collector electrode members 54 except for the outer ends thereof, or so as to only surround the collector electrode members 54 except for the outer ends thereof. Dielectric layer 58 is phosphor material and preferably P-l type phosphor or it can be an admixture of P-l phosphor and yttrium oxide or yttrium oxysulfide or yttrium oxide or yttrium oxysulfide activated by a rare earth element as disclosed in U.K. Patent Application No. 54016/76. (Serial No.

1568561) 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 58. The area engaged by beam 22 is raised to the potential of collector electrode members 54 and target electrode 52 from ground level thus causing the dielectric target to phosphoresce thereat.

These secondary electrons are then collected by the exposed areas of collector electrode members 54, and the areas of storage dielectric 58 engaged by beam 22 are positively charged so that flood electrons from flood guns 34 are attracted to these positively-charged areas; they then emit secondary electrons at a ratio of one therefrom, the secondary electrons being collected via collector electrode member 54 adjacent the positively charged (written) areas of storage dielectric 58 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 electrode members 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 U.S. Patent Nos.

3,293,473 and 3,531,675 for further information concerning the operation of bistable storage targets of this type.

Attention is now directed to Figures 2-13 for a description of the fabrication of storage target 32. As shown by Figure 4, transparent support member 50 has a conductive layer 52 of tin oxide covering the clean inside surface thereof which has been deposited thereon by vacuum deposition to a thickness of 5000 angstroms. The conductive tin oxide layer 52 has vacuum deposited thereover a thin conductive coating 64 of chromium having a thickness of 100-200 angstroms. The chromium coating is included for adhesion purposes. A layer 66 of copper of about 1 micron thickness, as shown in Figure 3, is vacuum deposited onto chromium coating 64. The copper layer provides uniform current density over the target surface.

A layer 68 of photoresist, such as that manufactured by E.I. Dupont de Nemours, Inc. under the trademark RISTON, is applied onto copper layer 66 to a suitable thickness.

A photomask 70 is placed onto photoresist 68 and light rays from collimated light source 72 pass through the transparent areas in photomask 70 into the photoresist thereby polymerizing the photoresist in these areas, and the areas of the photomask which do not permit light rays to activate the photoresist, the photoresist is nonpolymerized and is removed by a conventional solvent, such as butyl cellosolve, leaving openings 74, exposing areas of the copper layer 66 in photoresist 68 which conform to the configuration of the areas in photomask 70 that do not permit light to pass therethrough. Thus, openings 74 can have a configuration of a frustrum of a cone with the smallest diameter section at the outer end, a frustrum of a cone with the smallest diameter section at the inner end, part of a sphere, etc.

The metallic layers 52, 64, 66 are connected to a negative electrode as shown in Figure 6 and the target assembly as formed is placed in an electrolyte of metal ions such as nickel, but any other metal that is capable of being deposited from an aqueous electrolyte onto the metallic areas of copper layer 66 delimited by holes 74 from which the nonpolymerized photoresist has been removed can be utilized thereby forming the outer metallic layer of the collector electrode members 54. If desired, the desired metal ions can be deposited onto the areas of copper layer 66 delimited by holes 74 in accordance with conventional electroless deposition techniques and no deposition of metal ions takes place where polymerized photoresis is present.

After the collector electrode members 54 have been formed, the target assembly is then, if desired, placed in another electrolyte containing metal ions of a dissimilar metal which is preferably tin and caps 76 are formed onto the tops of collector electrode members 54 in a mushroom configuration as shown in Figure 7. The same metal as that of collector electrode members 54 can be used.

The polymerized photoresist material 68 is then removed by use of a conventional solvent such as methylene chloride as shown in Figure 8 leaving the mushroomshaped collector electrode members standing free.

A solution of chromic and sulfuric acids is placed on the target assembly to remove the copper layer 66 except under the collector electrode members as shown in Figure 9 and thereafter the chromium coating 64 is also partially removed as shown in Figure 10 by the use of a solution of hydrochloric acid and glycerol.

The target electrode 52, and collector electrode members 54 including laminated layers of chromium 64 and copper 66 are completely covered with an insulating coating 56 of aluminum oxide or thorium oxide having a thickness of about 2-5 microns as shown in Figure 11. This is accomplished in accordance with the teaching of U.K. Patent Application No. 25210/77, (Serial No.

1584164) wherein the target electrode 52 is connected to a negative terminal of a constant voltage DC source of supply of 240v. and the target assembly is placed in a collodial suspension of insulating material opposite a counterpoise electrode that is connected to the positive terminal of the 240v DC supply. The collodial suspension of aluminum oxide or thorium oxide is in isopropyl alcohol, water and electrolyte of aluminum nitrate in the case of aluminum oxide or thorium nitrate when using thorium oxide. The oxide is electrophoretically deposited onto target electrode 52 and collector electrode members 54 including chromium layer 64 and copper layer 66 when DC voltage is applied to the target electrode and counterpoise electrode whereby a continuous insulating layer or coating 56 is formed thereover.Use of aluminum oxide as the insulating material is preferred because it provides increased secondary electron emission characteristics which results in increased writing speed of the storage target.

Other oxides that are capable of being deposited by electrophoresis can of course be used.

The target assembly of Figure 11 then has a frame placed around its periphery, a photopolymerizable slurry of polyvinyl alcohol, water dimethyl sulfoxide, ammonium dichromate and phosphor composition as disclosed in U.K. application No. 54016/76, (Serial No.

1568561) aspreviously mentioned introduced onto insulating layer 56 to a depth of at least half the height of collector electrode members 54, and a collimated source of light, such as that of light source 72 of Figure 4, is shown through transparent support member 50, transparent conductive layer 52 and insulating layer 56 into the slurry whereby the light rays activate the slurry in the areas where no collector electrode members 54 are located thereby polymerizing the polyvinyl alcohol in these areas. No photomask is needed for this operation because collector electrode members 54 provide an in situ photomask so that in the area of each collector electrode member, no polymerization of the polyvinyl alcohol will take place. This operation is also completely disclosed in U.S. Patent No. 3,956,662.

The target assembly of Figure 12 is next immersed in an aqueous solution such as sodium hydroxide and sodium thiosulfate which enters the insulated caps 76 at the juncture of collector electrode members 54 and caps 76 because of small openings in the insulating layer 56 at such juncture. The solution dissolves the tin caps 76 thereby causing the insulating layer 56 thereover to collapse and separate from the target structure which exposes the top surfaces of collector electrode members 54.

An alternative approach would be to remove caps 76 as described above, then storage dielectric layer 58 is formed onto the insulating layer 56 as described hereinabove.

The structure is washed with water which removes the nonactivated slurry and leaves behind a layer of light activated slurry defining a dielectric storage layer. While the photopolymerizable material for formulating the pattern of conductive collector electrode members 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 Figures 12 and 13, the area of the storage dielectric layer 58 surrounding each of electrode members 54 engages insulating layer 56 thereby insulating the storage dielectric layer 58 therefrom in order to minimize luminance around the collector electrode members by decreasing the flood gun primary electron collection efficiency at the interface of the edge of the storage dielectric layer and the insulating layer 56.The exposed outer areas of collector electrode members 54 extend above the outer surface of dielectric storage layer 58.

After the storage target structure has been fabricated, it is baked in an oven at a suitable temperature to remove organic binders and leave the dielectric storage layer comprising essentially phosphor material as disclosed in the target of U.K. application No. 54016/76 (Serial No. 1568561). 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.

An alternative embodiment of the target structure is shown in Figure 14 wherein insulating collars 56a surround each of collector electrode members 54a, with the laminated metal layers of chromium 64a and copper 66a, and dielectric storage layer 58a is applied onto conductive layer 52a and engages insulating collars 56a thereby isolating collector electrode members 54a from dielectric storage layer 58a.

The bistable storage target of Figure 14 is fabricated by taking the target structure of Figure 10, introducing a slurry of insulating material in polyvinyl alcohol onto conductive layer 52 to the level or about the level of caps 76. The insulating material can preferably be deactivated yttrium oxide or deactivated yttrium oxysulfide. A photomask is positioned onto the outside surface of the support member with holes at the location of each collector electrode member slightly larger in diameter than caps 76. Collimated light is shown through the holes in the photomask, the support member, the conductive layer and into the slurry thereby polymerizing the slurry at the hole locations around each of the collector electrode members. The nonpolymerized slurry is washed away by water and each collector electrode member is surrounded by an insulating collar 56a of insulating material.

Caps 76 are removed and dielectric storage layer 58a is applied onto conductive layer 52a and is in engagement with insulating collars 56a as hereinbefore described. If desired, caps 76 can remain in position until after the dielectric storage layer 58a is affixed onto conductive layer 52a whereafter caps 76 are removed.

The pattern of collector electrode members 54 representing the collector electrode structure is preferably such that the center-to-center distance between adjacent collector electrode members 54 is less than the diameter of electron beam 22 and this provides improved collector means for collecting secondary electrons, optimum resolution of the information that is displayed on the target, elimination of trace shadowing, improved visible display, minimized luminance around the collector electrode members and readout accuracy of the stored information on the bistable storage target. The collection efficiency of secondary electrons by the collector electrode members is increased due to the substantially uniform potential provided by the pattern of collector electrode members.

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.

The embodiments hereinbefore described are directed to a planar support member having the thin layer of conductive coating thereon and on which the metallic layers defining the collector electrode members are connected to a conductive layer. An insulating layer either covers the conductive coating and the collector electrode members except for the outer exposed sections, merely covers the collector electrode members except for the outer exposed sections. Then, a layer of dielectric storage material respectively either covers the insulating layer and is isolated from the collector electrode members by the insulating layer, or covers the conductive layer and is isolated from the collector electrode members by insulating collars around the collector electrode members.The apices of the exposed collector electrode members extend above the top or outer surface of the dielectric layer thereby defining a storage target of planar construction. The support member can be planar or curved depending on the size of the target to be fabricated.

Figure 15 illustrates a target structure whereit support member 50b is dish-shaped and has a curved or radiused section over which conductive layer 52b, collector electrode members 54b including laminated layers of chromium 64b and copper 66b, insulated layer 56b and dielectric storage layer 58b is disposed. As can be discerned collimating electrode 48b is located on the inside surface of the wall of support member 50b and is spaced from conductive layer 52b. Insulating layer 56b and storage layer 58b cover the space between conductive layer 52b and engage the inner end of collimating electrode 48b in order to eliminate the halo effect at the periphery of the target display area. This target is of course fabricated as hereinabove disclosed.

The storage target of the present invention is easier to fabricate and therefore is economical.

The support member with collector electrode members thereon is reclaimable, because the dielectric storage layer can be removed if it has faulty areas therein and a new layer of dielectric storage material fixed in place.

Better control can be exercised over the fabrication of the present storage targets thereby resulting in better production yields.

The targets are more rugged due to preferably plated in place collector electrode members, provide better conductor material for the collector electrode members, are easier to build to form higher collector electrode members of given or selected configuration, provide better readout capability because of better signal to noise ratio for readout purposes, provide faster erasure of the stored information on the target because shorter time interval of positive portion of erase pulse is used which results in substantially flashless erasure, and the collector electrode members are easy to insulate due to their simple and permanent construction.

Whilst preferred embodiments of the present invention have been illustrated and described, it will be apparent that changes and modifi cations 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.

In our copending application No. 25210/77 (Serial No. 1584164) there is described and claimed a storage target for a cathode ray tube comprising an insulative support member having a conductive layer provided on an inside surface thereof; a pattern of collector electrode members provided on said conductive layer for collecting secondary electrons emitted from written areas of said target; insulating material provided at least around each of said collector electrode members except for an outer exposed area of each collector electrode member; and a dielectric storage layer extend ing along and contiguous with said conductive layer, or along and contiguous with said insulating material when said insulating material extends along and covers the conductive layer, said dielectric storage layer engaging said insulating material around said collector electrode members so that said collector electrode members are isolated from said dielectric storage layer whilst leaving said outer exposed areas of said collector electrode members exposed.

WHAT WE CLAIM IS: 1. A storage target for a cathode ray tube comprising: an insulative support member having a conductive layer provided on an inside surface thereof; a pattern of collector electrode members provided on said conductive layer for collecting secondary electrons emitted from written areas of said target, each collector electrode member including an inner and an outer metallic layer, each said metallic layer being of a different material to the other of said metallic layers and of a different material from said conductive layer, said inner metallic layer electrically connecting said outer metallic layer to said conductive layer; insulating material provided at least around each of said collector electrode members except for an outer exposed area of each collector electrode member; and a dielectric storage layer extending along and contiguous with said conductive layer, or along and contiguous with said insulating material when said insulating material extends along and covers the conductive layer, said dielectric storage layer engaging said insulating material around said collector electrode members so that said collector electrode members are isolated from said dielectric storage layer whilst leaving said outer exposed areas of said collector electrode members exposed.

2. A storage target according to claim 1 wherein said insulative support member is planar.

3. A storage target according to claim 1 wherein said insulative support member is curved.

4. A storage target according to claim 1 wherein said insulative support member is dishshaped having a wall, collimating electrode means on an inside surface os said wall spaced from said conductive layer, and said insulating material covering the periphery of said conductive layer and an inner end of said collimating electrode means.

5. A storage target according to claim 1 wherein said outer layer of said collector electrode members is of nickel and said inner metallic layer is laminated.

6. A storage target according to claim 5 wherein said laminated metallic layer comprises chromium and copper.

7. A storage target according to claim 1 wherein said support member, said conductive layer and said insulating material are transparent for purposes of viewing information displayed onto said storage target.

8. A storage target according to claim 1 wherein said insulating material is selected from aluminum oxide and thorium oxide.

9. A storage target for cathode ray tubes, substantially as herein described with reference to and as illustrated in the accompanying drawings.

10. A cathode ray tube including a storage target as claimed in any of claims 1 to 9 and having means connected to said conductive layer for providing said conductive layer and said collector electrode members with a predetermined voltage so that the potential over a target surface is substantially uniform; an envelope having said insulative support member sealingly secured thereto and including means for emitting and directing high speed electrons toward and onto said outer exposed ends of said collector electrode members for establishing a charge pattern on said dielectric layer; and means for emitting and directing low velocity electrons toward and onto said outer exposed ends for driving selected areas of said dielectric layer toward one of two stable potentials to retain said charge pattern thereon.

11. A method of making a storage target according to claim 1 for use with a cathode ray tube, comprising the steps of: applying a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (17)

**WARNING** start of CLMS field may overlap end of DESC **. thereby resulting in better production yields. The targets are more rugged due to preferably plated in place collector electrode members, provide better conductor material for the collector electrode members, are easier to build to form higher collector electrode members of given or selected configuration, provide better readout capability because of better signal to noise ratio for readout purposes, provide faster erasure of the stored information on the target because shorter time interval of positive portion of erase pulse is used which results in substantially flashless erasure, and the collector electrode members are easy to insulate due to their simple and permanent construction. Whilst preferred embodiments of the present invention have been illustrated and described, it will be apparent that changes and modifi cations 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. In our copending application No. 25210/77 (Serial No. 1584164) there is described and claimed a storage target for a cathode ray tube comprising an insulative support member having a conductive layer provided on an inside surface thereof; a pattern of collector electrode members provided on said conductive layer for collecting secondary electrons emitted from written areas of said target; insulating material provided at least around each of said collector electrode members except for an outer exposed area of each collector electrode member; and a dielectric storage layer extend ing along and contiguous with said conductive layer, or along and contiguous with said insulating material when said insulating material extends along and covers the conductive layer, said dielectric storage layer engaging said insulating material around said collector electrode members so that said collector electrode members are isolated from said dielectric storage layer whilst leaving said outer exposed areas of said collector electrode members exposed. WHAT WE CLAIM IS:

1. A storage target for a cathode ray tube comprising: an insulative support member having a conductive layer provided on an inside surface thereof; a pattern of collector electrode members provided on said conductive layer for collecting secondary electrons emitted from written areas of said target, each collector electrode member including an inner and an outer metallic layer, each said metallic layer being of a different material to the other of said metallic layers and of a different material from said conductive layer, said inner metallic layer electrically connecting said outer metallic layer to said conductive layer; insulating material provided at least around each of said collector electrode members except for an outer exposed area of each collector electrode member; and a dielectric storage layer extending along and contiguous with said conductive layer, or along and contiguous with said insulating material when said insulating material extends along and covers the conductive layer, said dielectric storage layer engaging said insulating material around said collector electrode members so that said collector electrode members are isolated from said dielectric storage layer whilst leaving said outer exposed areas of said collector electrode members exposed.

2. A storage target according to claim 1 wherein said insulative support member is planar.

3. A storage target according to claim 1 wherein said insulative support member is curved.

4. A storage target according to claim 1 wherein said insulative support member is dishshaped having a wall, collimating electrode means on an inside surface os said wall spaced from said conductive layer, and said insulating material covering the periphery of said conductive layer and an inner end of said collimating electrode means.

5. A storage target according to claim 1 wherein said outer layer of said collector electrode members is of nickel and said inner metallic layer is laminated.

6. A storage target according to claim 5 wherein said laminated metallic layer comprises chromium and copper.

7. A storage target according to claim 1 wherein said support member, said conductive layer and said insulating material are transparent for purposes of viewing information displayed onto said storage target.

8. A storage target according to claim 1 wherein said insulating material is selected from aluminum oxide and thorium oxide.

9. A storage target for cathode ray tubes, substantially as herein described with reference to and as illustrated in the accompanying drawings.

10. A cathode ray tube including a storage target as claimed in any of claims 1 to 9 and having means connected to said conductive layer for providing said conductive layer and said collector electrode members with a predetermined voltage so that the potential over a target surface is substantially uniform; an envelope having said insulative support member sealingly secured thereto and including means for emitting and directing high speed electrons toward and onto said outer exposed ends of said collector electrode members for establishing a charge pattern on said dielectric layer; and means for emitting and directing low velocity electrons toward and onto said outer exposed ends for driving selected areas of said dielectric layer toward one of two stable potentials to retain said charge pattern thereon.

11. A method of making a storage target according to claim 1 for use with a cathode ray tube, comprising the steps of: applying a

conductive layer onto a surface of an insulative support member; covering said conductive layer with one or two metallic layers; introducing a photoresist onto said one or two metallic layers; placing a photomask having a pattern of openings therethrough and a pattern of nonlight transmitting areas onto said photoresist; shining light through said pattern of openings to fix said photoresist in areas thereof corresponding to said pattern of openings, area of the photoresist under said non-light transmitting areas being nonfixed areas; removing the nonfixed areas of said photoresist which provides holes exposing areas of the metallic layer covered by the photoresist; filling said holes with a metal which provides a pattern of metal members; removing the fixed photoresist; removing said one or two metallic layers except under each of said metal members so as to provide collector electrode members; and applying insulating material around each of said collector electrode members except for their exposed outer ends, applying a storage dielectric layer over said conductive layer with said collector electrode members, surrounded by said insulating material, extending through said dielectric storage layer and the outer ends of the collector electrode members being exposed.

12. A method according to claim 11 wherein two metallic layers are provided on said conductive layer, by vapor deposition of a chromium layer onto said conductive layer and vapor deposition of a copper layer onto said chromium layer.

13. A method according to claim 11 wherein the step of filling said holes with a metal comprises electroplating.

14. A method according to claim 11 wherein the step of applying insulating material around each of said collector electrode members comprises electrophoretically deposit ing of said insulating material.

15. A method according to claim 11 wherein said insulating material is also applied as a layer over said conductive layer and said dielectric layer is applied over said insulating layer.

16. A method according to claim 11 wherein prior to the removal of said metallic layers cap members are applied onto said metal members.

17. A method of making a storage target according to claim 11, substantially as herein described.