US3218496A

US3218496A - Storage tube and target element therefor having an irregular surface

Info

Publication number: US3218496A
Application number: US136330A
Authority: US
Inventors: Arthur S Jensen; Walter G Reininger
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1961-09-06
Filing date: 1961-09-06
Publication date: 1965-11-16
Anticipated expiration: 1982-11-16
Also published as: DE1439933A1; GB999640A; NL282811A

Description

Nbv. 16, 1965 A. S. JENSE STORAGE TUBE AND TARGET ETAL EMENT THEREFO AVING AN IRREGULAR SURFACE Filed Sept. 6. 1961 Fig.6.

ATToNEY United States Patent 3,218,496 STORAGE TUBE AND TARGET ELEI'VHENT THERE- FOR HAVING AN IRREGULAR SURFACE Arthur S. Jensen, Baltimore, and Walter G. Reininger, Catonsville, Md, assignors to Westinghouse Electric Corporation, East Pittsburgh, Pin, a corporation of Pennsylvania Filed Sept. 6, 1961, Ser. No. 136,330 12 Claims. (Cl. 313--67) This invention relates generally to electron discharge devices and more particularly to improved storage targets for use in cathode ray type memory tubes.

In the conventional electrostatic storage tube, information is written onto the surface of a dielectric target by means of an electron beam (writing beam) and is stored in the form of charges established on the surface of that target. The establishment of these charges may be accomplished either by secondary emission effect or by inducing a current within the dielectric by electron bombardment. Both these methods of establishing the charge are well known in the art.

A reading beam is then utilized to scan the target and derive an output in accordance with the charge information. In one form of storage tube the entire surface of the storage target upon which the reading beam is incident is a dielectric. Upon its impingement, the reading beam removes the stored charge, returning the surface close to a common reference potential, as in a vidicon the differential charge removed is coupled capacitively to an output signal amplifier, or as in an image orthicon the return beam, deficient by the differential charge deposited, is collected and amplified. The preferred method of reading utilizes a storage target surface which is approximately 50% dielectric and 50% interconnected conductor. The reading beam electrons approach the storage target slowly, having only about one or two electron-volts energy when they impinge upon the conductor areas. The dielectric areas are just sufficiently negative that the reading beam electrons cannot land on them. The stored signal charges are such that they make the areas where they are located still more negative. These negative areas act as a coplanar grid to modulate the amount of the reading beam which impinges upon the conductor areas. Either this differential current which impinges upon the conductor areas can be amplified or the reflected return beam deficient by this differential current can be collected and amplified. This preferred reading operation is that utilized by Louis Pensak in US. Patent 2,728,020 and The Metrechon-A Halftone-Picture Storage Tube, RCA Review, vol. XV, No.2, pp. 145-162, June 1954.

In order that information stored on the target be faithfully retained, it is necessary that no extraneous charging or discharging be allowed to affect the dielectric target surface. In the case of a storage target of the tape variety, which is designed to be wound upon itself to permit a multiplicity of storage areas to be sequentially utilized, the problem becomes particularly acute. Frictional or triboelectric effects resulting from the reeling and unreeling of the tape itself and from the tape running over such elements as idler pulleys may produce sufficient triboelectric charge to impair seriously the quality of the information stored on the dielectric target. In addition, contact of the storage surface with the back of the successive "layer of tape may permit the charged area to discharge to the back of that layer, thus affecting the stored information.

It has been suggested in the prior art, see for example RCA Technical Note No. 45, Tape Storage Tube, by Arthus S. Jensen, that a tape be constructed of a flexible dielectric storage strip or tape, one side of which is coated with a thin conducting layer. A fine metallic mesh or grid Patented Nov. 16, 1965 is then applied to the other side which, inter alia, serves to prevent the back of subsequent layers of tape from coming into contact with the dielectric storage surface when the tape is being reeled or unreeled. Tapes of this nature have proven to be generally unsatisfactory. As the metallic grid or mesh positioned on the dielectric surface is generally in the order of 1 micron thick, dust particles or slight irregularities in the conducting layer on the back of the subsequent layer of tape will bring this layer into contact with the dielectric storage surface. This contact is detrimental from two aspects. First of all, this contact permits the discharging of the stored information from the dielectric surface to the conducting layer of the subsequent layer of tape. Secondly, this contact may produce frictional or triboelectric charges during the reeling and unreeling of the tape. The accumulative effect of the discharging to the metallic layer and that of the triboelectric charges may be sufficient to destroy the resolution of the information stored upon the dielectric target surface.

It is, therefore, an object of this invention to provide a cathode ray type memory tube having an improved storage target.

A further object of this invention is to provide an improved tape type storage target adapted to be wound upon itself.

A still further object of this invention is to provide a tape storage target in which the contact of the storage surface with subsequent layers of storage tape is reduced to a minimum.

Another object of this invention is to provide an improved storage surface for a dielectric target.

Still another object of this invention is to provide an improved electrostatic storage target which is easy and economicai to manufacture and which possesses a high degree of resolution.

Stated briefly, the tape storage target in accordance with the present invention comprises a supporting structure having a roughened surface with a dielectric storage material disposed upon a portion of the roughened surface. The dielectric material is positioned so that it lies in planes or on surfaces which are transverse to the plane of the tape. This positioning of the dielectric material reduces the possible area of contact with subsequent layers of tape and serves to prevent spurious charging and discharging of the storage elements.

Further objects and advantages of the invention will be come apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to the accompanying drawings, in which:

FIGURE 1 is a schematic view of a cathode ray tube utilizing the present invention;

FIG. 2 is a side elevational view, in section, showing an enlarged portion of the storage target embodied in FIG' 1;

FIG. 3 is a top plan view of a target shown in FIG. 2;

FIG. 4 is a top plan view showing a first embodiment of the storage target embodied in FIG. 1;

FIG. 5 is a cross sectional view of an embodiment of FIG. 4 taken along the line VV of FIG. 4;

FIG. 6 is a side elevational view, in section, showing another embodiment of the present invention;

FIG. 7 is an end view, in section showing a further modification of the present invention; and

FIG. 8 is a side elevational view, in section, of a further embodiment of the present invention, in which the dielectric storage elements are randomly spaced.

Referring to FIG. 1, the memory tube comprises an envelope 11 of glass or other suitable material within which is positioned an electron gun, indicated generally at 2, for forming and focusing an electron beam upon a storage target 31. The beam electrons are produced by a thermionic cathode 13 and are controlled by an apertured control grid 15. An accelerating electrode 17 is positioned in alignment with the beam and accelerates the electrons emitted from the cathode 13.

Elements

19, 21 and 23 are electrodes which serve to focus the accelerated electrons into a defined beam. Pairs of vertical and horizontal deflection plates, 25 and 27 respectively, direct the beam to particular elemental regions on the surface of the target 31.

Cylindrical electrodes

55, 57 and 59 form a collimating lens which insures that the electron beam impinges perpendicularly upon a decelerator grid 29 and the storage target 31. The decelerator grid 29, located in close proximity to the target, is biased several volts positive with respect to the potential of the target 31 and serves to collect secondarily emitted electrons during the erasing, priming and writing operations. The decelerator grid 29 also serves in the establishment of a uniform electric field in the target area which decelerates the incident reading beam electrons from a high energy level at the grid 29 to a lower level of from zero to approximately two volts in close proximity to the storage target 31. The above elements are supported within the tube and are connected to suitable sources of voltage, which have not been shown, by suitable leads (also not shown) extending and sealed through the envelope 11.

Although the target may be fixed and rigid if the device is to be operated as a conventional storage tube, e.g. for scan conversion, the specific embodiment of FIG. 1 shows the target 31 to be of the flexible tape variety which is disposed within the envelope 11 at the opposite end from the electron gun assembly 2 and positioned so as to be acted upon by the electron beam. The tape 31 is preferably wound upon reels which are driven by means, which have not been shown, external to the envelope.

With reference to FIG. 2, there is shown a storage target 31 which may be of the tape variety, such as is utilized in the structure of FIG. 1 and which embodies the present invention. A base layer 33, which may be a polyester resin such as that sold by E. I. du Pont de Nemours and Company under the trade name Mylar, is debossed on one surface. This debossing may be achieved by bringing the base 33 into pressure contact with a steel roller having a series of grooves or lenticulations in the form of substantially straight line debossments formed into its surface parallel to its axis. The base 33 then receives uniformly

thick conducting coatings

35 and 37. on both sides, which may be metal which has been deposited by vacuum evaporation. The debossed side is then uniformly coated with a dielectric material such as magnesium fluoride to form another layer 39 which is approximately one micron thick and lies in planes which are transverse to the plane of the tape. By virtue of the uniform thickness of the

layers

37 and 39, the debossed grooves of the base 33 are carried through to the surface of the dielectric layer 39. By suitable means, such as shadow evaporation, one side of the grooves in the layer 39 receives a coating 41 of conductive material to form bars which are a part of a grid network as is shown in FIG. 3. A further evaporation deposits two Conducting strips 43 lengthwise near the edges of the tape which serve to connect electrically the grid bars 41.

The tape as is shown in FIG. 2 may be utilized for electron bombardment induced conductivity (EBIC) writing. The conducting layer 37 serves to take up the electrons of the primary beam and the electrons from the discharge of the dielectric surface during writing as well as providing for biasing during the priming period of the target. The grid assembly comprising the conducting bars 41 and strips 43 prevents redistribution of charges by secondary emission effect during the writing period. Information is stored on surface elements 47 of the dielectric material 39. As may be readily seen, if the tape shown in FIG. 2 is wound upon itself, the conducting layer 35 contacts only the

grid structure

41, 43. Any triboelectric charges generated during the reeling or unreeling, or by movement of the tape over pulleys, etc. within the system, are effectively removed by the conducting layer 35 and

grid assembly

41, 43. Also, by disposing the storage elements 47 within the recesses formed by the grooved structure, there is little opportunity for the contact of these elements with subsequent layers of tape and hence little change for the drainage of stored information from the storage elements to subsequent'layers of tape.

While the above structure was described with respect to electron bombardment induced condutivity (EBIC) writing, it is readily apparent that the target structure would be equally effective for secondary emission writing. if secondary emission writing were used, however, the conducting layer 37 would not be necessary.

A simplified embodiment of this invention is shown in FIGS. 4 and 5. The tape 31 of this embodiment comprises a conducting strip 49, such as stainless steel or copper, which is debossed by a series of grooves parallel to the length of the tape. The debossing may be accomplished either by pressure contact or electro-forming with a roller having grooves formed circumferentially in its surface. After the debossing of the steel tape has been accomplished, a suitable dielectric storage material 51, such as manganese fluoride, is shadow evaporated onto one face of the groove so that, as previously stated, the dielectric lies in planes or on surfaces which are transverse to that of the tape. This dielectric material forms elemental areas for the storage of information either by EBIC or secondary emission writing. While it is evident that in this embodiment the dielectric material will come into contact with the bottom of subsequent layers of the stainless steel or copper tape when the tape is wound upon itself, it is not that the area of contact is very small. Because of this small contact area, the amount of information discharged from the storage areas 51 to the subsequent base layer 49 is insignificant. Also, because of the small area of contact, no significant triboelectric effects will be generated.

The embodiment shown in FIG. 6 differs only from that of FIGS. 4 and 5 insofar as the grooves are formed perpendicular to the length of the tape. From this, it is evident that the direction of the grooves is unimportant and that they may be formed at any angle to the length of the tape.

A further modification of the present invention which incorporates features of the preceding embodiments is illustrated in FIG. 7. Here, the grooved base layer 33 is again made of a plastic such as Mylar, and, as has been previously stated, the grooves may be positioned at any angle with respect to the length of the tape. A uniformly thick conducting layer 35 is then applied to the underneath side of the layer 33 and incremental storage element 51 of dielectric storage material are deposited, preferably by means of shadow evaporation to a portion of the groove faces. The operation of the target of this modification is the same as that described with respect to the previous embodiments.

The embodiment shown in FIG. 8 differs from that shown in FIGS. 4 through 6, in that, the regular groove structure of the earlier figures is replaced by randomly spaced depressions 53, of irregular size, within the surface of the steel tape 49. These randomly spaced depressions may be formed by sandblasting, abrading or by any other suitable method. The dielectric material 51, however, is again shadow evaporated onto only a portion of the exposed roughened surface which is transverse to the plane of the tape. While the structure of this embodiment possesses a lower resolution than those of the preceding embodiments, in which the storage elements were disposed in the regular pattern, the structure is more economical to manufacture and has a resolution which is sufiicient for many applications.

While there have been shown and described what are presently considered to be the preferred embodiments of the invention, modifications thereto will readily occur to those skilled in the art. Although the type of structure has been described mainly with reference to an elongated tape, it is apparent that a section of the tape will serve equally well as a stationary target. It is not desired, therefore, that the invention be limited to the specific arrangement shown and described and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

We claim as our invention:

1. A storage target comprising a base member having a roughened surface and a coating of dielectric storage material in contact with said roughened surface, said dielectric material being disposed in portions of the roughened surface which are transverse to the plane of said base member and so that the exposed surface of said dielectric material substantially follows the contour of said roughened surface.

2. A storage target comprising a base member having a plurality of irregularities disposed within one face of said base member, a coating of dielectric storage material disposed upon portions of said irregularities, a substantial portion of the exposed surface of said dielectric storage material being disposed beneath a plane defined by the points of maximum height of said irregularities.

3. A storage tape comprising a base member having a surface with a plurality of depressions therein, and a discontinuous coating of dielectric storage material disposed upon portions of said irregularities, the exposed surface of said dielectric material being disposed in planes transverse to the plane of said base member.

4. An elongated, flexible storage tape comprising a base member, a series of parallel grooves disposed within one surface of said base member, said grooves extending substantially parallel to the length of said tape, and a coating of dielectric storage material in contact with a portion of the faces of said grooves, said dielectric material being disposed on said portions which are transverse to the plane of said base member and so that the surface of said dielectric storage material substantially follows the surface of said faces of said grooves.

5. An electrostatic storage target comprising a base member having one surface thereof roughened, said roughened surface comprising a plurality of depressions, said depressions having points of maximum height which define a plane, and dielectric storage material disposed upon portions of said roughened surface, said dielectric material being disposed on portions of the roughened surface which are transverse to said plane and so that a major portion of the exposed surface of said dielectric material lies beneath said plane.

6. A method of constructing a storage target comprising the steps of providing a base member having one side thereof roughened and shadow evaporating a discontinuous coating of dielectric storage material onto said roughened surface, said evaporation being performed from an angle acute to the surface of said base member to provide that only those portions of the roughened surface disposed in planes opposed to the direction of incident vapor are coated, the remaining surfaces remaining exposed.

7. A method of constructing an electrostatic storage target comprising the steps of providing a base member having a plurality of grooves formed in one surface thereof and disposing by shadow evaporation a coating of dielectric storage material on a portion of the surface of said grooves, said shadow evaporation performed from an angle acute to the surface of said base member to provide dielectric material only on those surfaces which lie in a plane opposed to the direction of incident vapor, theremaining surfaces remaining exposed.

8. A cathode ray storage tube comprising an envelope, means within said envelope for forming an electron beam along a path, a storage target within said envelope positioned transverse to said beam, said target comprising a base member having one surface with a plurality of depressions therein, said depressions having points of maximum height which define a plane, and a discontinuous coating of dielectric storage material affixed to said roughened surface so that a major portion of the exposed surface of said dielectric material lies beneath said plane.

9. A cathode ray storage tube comprising an envelope, means within said envelope for forming a beam along a path, a storage target within said envelope positioned transverse to said beam, said storage target comprising an elongated, flexible tape positioned about a dispensing means, said tape having a plurality of depressions, and a layer of dielectric storage material disposed in contact with a portion of the faces of said grooves which lie in a plane transverse to the plane of said base member.

10. An elongated storage tape comprising an electrical- 1y non-conductive strip having first and second major surfaces, a first electrical conductive layer in contact with the first of said major surfaces, at second electrical conductive layer of even thickness in contact with the second of said major surfaces and a layer of dielectric material of even thickness for the storage of electrostatic charges in contact with said second conductive layer, a series of substantially parallel grooves formed in the exposed face of said dielectric material, a series of electrical conductive bars in contact with one corresponding face of each of said grooves and means for electrically connecting said bars.

11. An elongated tape for the storage of electrostatic charges comprising a first non-conductive strip having first and second major surfaces, a first layer of conductive material in contact with the first of said major surfaces, a plurality of substantially parallel grooves formed in said second major surface, a second conductive layer of substantially constant thickness in contact with said second major surface and a layer of dielectric storage material of substantially constant thickness in contact with said second conductive layer to provide a grooved surface in said dielectric layer, a series of conductive strips in contact with a portion of the groove walls and extending upwardly beyond said dielectric and at least one conductive strip extending substantially perpendicular to said series of conducting strips to electrically connect said series of conductive strips.

12. A storage target comprising an electrically nonconductive base, a plurality of grooves formed within one side of said base member, the peaks of said grooves defining a plane, a uniformly thick electrical conductive layer in contact with the opposed side of said base layer, and a discontinuous coating of dielectric storage material disposed upon a portion of the faces of said grooves so that the major portion of the exposed surface of said dielectric storage material lies below said plane.

References Cited by the Examiner UNITED STATES PATENTS 2,538,836 1/1951 Jensen 313-89 2,734,145 2/1956 Reed 313329 X 2,790,228 4/ 1957 Koda et a1 29-25.17 2,859,376 11/1958 Kirkpatrick 313-89 X 2,926,419 3/ 1960 Harris 2925.17 2,979,633 4/1961 Harris 313-89 JOHN W. HUCKERT, Primary Examiner.

RALPH G. NILSON, DAVID J. GALVIN, Examiners.