US2901662A - Electronic storage device - Google Patents

Description

s. NozlcK ELECTRONIC STORAGE DEVICE v Filed March 15, 1955 E. Y n M .JA w a swf Aug. 25, 1959 United States Patent O ELECTRONIC STORAGE DEVICE Seymour Nozick, New York, N.Y.

Application March 15, 1955, Serial No. 494,591

12 Claims. (Cl. 315-12) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes Without the payment of any royalties thereon or therefor.

This invention relates to electronic storage devices, and more particularly, to improved electronic storage devices which store information vastly longer than the type of electronic storage devices whose operation is based upon principles of storage of electrostatic charge on the surface of dielectrics.

Broadly, electronic storage devices have been known and used for some time. Some background information on conventional electronic storage devices may be found in Storage Tubes by Max Knoll and Benjamin Kazan, published by Wiley. All of these` electronic storage devices operate on a principle of electrostatic charge deposited and stored on the surface of a dielectric. These storage devices generally include a conductor and a dielectric disposed in the path of and transverse to an electron beam. The beam current is either intensity modulated or deflection modulated and surface charge is deposited and stored by the beam on the surface of the dielectric by the action of modulated beam current. A constant current scanning beam is used for reading out the stored information. The readout information is obtained either by taking advantage of the variation in secondary emission from the surface of a dielectric when scanned by a constant current beam which variation is a function of the density of stored charge at each point in its surface or by taking advantage of the variation in percentage of `beam current that passes through a grid like storage element which variation is also a function of the stored charge at each point in its surface. The readout information is developed across a load resistor which is connected in series with the storage device element through which the resultant varying current flows.

A11 electronic storage devices which operate on the basis of deposited surface charge suffer from the disad vantage that surface charge spreads and decays rapidly, e.g. from a few seconds to a few hours depending upon several variables. The spreading is a function of the resistivity of the dielectric. The decay is due to presence of positive ions within the envelope.

To date, no method has been developed for evacuating the envelope of an electronic discharge device so that it is completely devoid of all gases. Even after resort to the most thorough evacuation processes known, some gas remains in the envelope. As a consequence, positive ions are present in the envelope partly by the action of the electron beam in colliding with gas molecules. The gas ions operate to neutralize negative charges in the cnvelope and thus operate to neutralize surface charge on any element in the envelope.

Most of the prior art electronic storage devices can store information for only a few minutes at the most. The number of tones discernible at the instant of storage begins to decrease instantaneously. Long before the sur-- face charge which bore the information deposited, com- ICC 2 pletely decayed, the number of discernible tones decreased considerably. Where the information is deposited by virtue of deflection modulation of an electron beam, tones are not important; but if information is deposited by virtue of an intensitymodulated beam, the information is available for eifective utilization for only 'a fraction of the time it takes forthe surface charge to decay to zero. For example, if the tonal range decreases to a certain level, the information is effectively gone, especially so, if that information was to be used in an integration process.

The results obtained by resort to the above referred to electrostatic storage process is comparable to the results obtainable in printing a half-tone on very porous paper with slow-drying, very thin ink which fades rapidly in sunlight, and then holding the printed sheet in sunlight. Two things happen. The ink spreads because it is very thin and the paper is very porous continuously reducing the tonal range and resolution of the half-tone. In addition, the ink fades continuously until every vestige of the ink which manifested the information, itself disappears. As opposed to the action in storage processes of the prior art, in the process of this invention the ink neither spreads nor fades for all practical purposes.

This invention is comparable to a dark trace tube for most of its structural features. For some background information on dark trace tubes, reference is made to chapter 18 in volume 22 of the Radiation Laboratories Series of the Massachusetts Institute of Technology, published by McGraw-Hill. The dark trace tube stores information by the medium of electrons captured in crystal matrices of a target screen. The target screen includes signal storage material of ionic crystals which are described on page l of U. S. Patent 2,330,171. In the past the storage screen generally was vformed from potassium chloride. The stored information is read in light reflected back from the screen when 4the screen is illuminated. The information is visible in the light reflected back from the screen. This information is in the character of tones of purple on a white field. This invention is based in part upon the principles governing the operation of dark tracetubes.

Another principle of physics upon which this invention is based is that of secondary emission ratios. The secondary emission ratio from any point in the surface of a material from the alkali-halide group, when the material.

is scanned by a constant current electron beam, is a function of the density of electrons captured in crystal matrices of the material under that point. ground information on the afore-mentioned variation in secondary emission is found in the German periodical publication Zeitschrift fr Physik, volume 122, 1944, pages 137-162, entitled Zum Mechanismus der Sekundarmitton by M. Knoll, O. Hachenberg and l. Radliner.l

Another principle upon which this invention is basedtion for electronic readout for a long time after the information was deposited.

A further object is to provide an improved electronic discharge storage device that permits stored information to be read out many times with substantially no sacrice in tonal range of the information stored.

Some backv A further object is to provide an improved electronic discharge storage device that is adapted to store superposed pieces of informations deposited at considerably spaced time intervals and to provide an integrated readout of the stored information.

A further object is to provide an improved electronic discharge storage device that is adapted to store some information, to permit a readout of the stored information; to permit additional information to be superposed at a later time on the previously deposited information; and to permit readout of the integrated resultant of the separately deposited pieces of information.

A further object is to provide an electronic discharge storage device that is adapted to store pulse information along one long time base for use by other electronic equipment, or to store pictorial information for subsequent use, or to store graphic information for subsequent use, or to store mathematical information for use in an electronic computation process, or to store separately deposited pieces of superposed mathematical information for providing an integrated result.

A further object is to provide an improved electronic discharge storage device that is adapted to store information for a long period of time with negligible sacrifice in tonal range during that time.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. 1 is an illustration of an embodiment of this invention including some elements illustrated structurally and some elements illustrated schematically with a broken line block enclosing that which is conventional;

Fig. 2 is enlarged fragmentary View illustrating an embodiment of this invention;

Fig. 3 is a sketch illustrating a small modification of the modification of Fig. 2; and

Fig. 4 is a sectional elevation of another modification of the invention.

This invention includes elements for generating electron discharge; these elements are conventional and are shown inside the broken line block 10. The elements shown include the envelope 12 of a conventional cathode ray tube. There is no critical limitation on the type or shape of envelope 12 used in this invention. It may be of glass or metal or other materials used for this purpose and known in the art. At one end of the envelope 12 there is mounted a conventional electron emitting cathode 14. Conventional electron gun structure is mounted in the envelope 12 and includes a first anode 16 adjacent cathode 14. A second anode 18 e.g. aquadag, is supported by envelope 12. A high voltage direct current adjustable power supply 22 is connected to the anodes 16 and 18. A beam current adjusting resistor 23 is connected between power supply 22 and cathode 14. A control grid 24 is supported in the envelope adjacent the cathode 14. A direct current grid bias supply 26 is connected in series with the cathode 14. An intensity modulating signal source 28 is connected between the bias supply 26 and the control grid 24. Under deflection modulation operation, the signal source 28 is omitted. Conventional electrostatic or electromagnetic deflection means 29 and the necessary circuitry therefor, commonly known and used in the art, is part of the basic structure.

Conventional cathode ray tubes include a target. In tubes used for direct viewing the target is generally a layer of phosphor. In tubes used for storing information that can be viewed directly, e.g. dark trace tubes, the target is generally a layer of potassium chloride. In tubes used for storing information electrostatically, the target is a combination of metal and dielectric layers.

A novel target 32 is supported by the inside surface of the face of the envelope 12. The target 32 includes a layer of conductor 36 overlaid with a thin film of alkalihalide 38. The thickness of the layer of conductor 36 is not at all critical. For best results the material preferably is one of the better conductors such as silver. However, the conductivity of the layer 36 is not too critical. Aluminum and other metals are satisfactory for most purposes for which the storage device may be used. For some very accurate mathematical processes the layer 36 should be of higher conductivity. A uniform film of alkali-halide 38, several microns thick, is overlaid over the layer of conductor 36. Conventional processes such as evaporation, settling out, and others equally well known, may be resorted to for forming the target 32.

A load resistor 42 is connected in circuit between the layer of conductor 36 and the cathode 14. During readout, stored information is developed as a varying voltage across the resistor 42.

In operation for storing information by intensity modulation, the modification of the invention illustrated in Fig. l is connected in circuit with a signal input source 28. An electron beam is formed by the operation of the conventional cathode ray tube structure shown in the broken line block 10 and is caused to scan the target 32 under the influence of the deflection means 29. The electron beam is intensity modulated i.e. the beam current varies in accordance with the signal voltage from source 28. The anode voltage of the power supply 22 is on the order of five kilovolts when the film of alkali-halide is potassium chloride, about five microns thick. The magnitude of the anode voltage is related to the particular alkalihalide material used for the film 38, and to the thickness of the film 38.

To store information in the alkali-halide film 38, electrons in the electron beam are afforded sufficient power by the power supply 22 to penetrate into crystal matrices of the film of alkali-halide 38. The electrons are deposited and imprisoned or captured in crystal matrices which are discontinuities in the pattern of the crystalline structure of the alkali-halide; the discontinuities result from the presence of the small percentage of impurities dispersed throughout the alkali-halide. This portion of the operation corresponds to that of a' dark trace tube. If the anode voltage is too small, the electrons will not be afforded sufficient power to penetrate and will at best have only sufiicient power to be deposited as electrostatic surface charges on the film of alkali-halide 38 in the manner corresponding to that in electrostatic storage tubes. If the anode voltage is too high, the electrons in the electron beam will be provided with sufhcient power not only to penetrate the film of alkali-halide 38 but to actually pass clear through the film. The density of electrons captured in the crystal matrices of the film 38 under every point of imagined coordinates on the surface of target 32, is a function of the beam current at the instant the electron beam scans over that point. To store information in the target 32, the electron beam may scan the target once or a considerable number of times. In the case of the latter, the scans may be successive or spaced lengthy time intervals apart. One purpose of a series of scans is to perform an integration. Another is for decoding.

The film 38 is saturable; it can capture and store up to a particular maximum density of electrons in its crystal matrices. Saturation is a function of the particular material. The beam current must be limited in accordance with the saturation level. If only one frame of information is to be written on the film 38 by intensity modulation or if graphic information is to be Written by deflection modulation, and if only one readout is required in each instance, the beam current level may be anywhere between the minimum which provides a satisfactory signal-to-noise ratio and the maximum which is the saturation level for the screen. If a plurality of superposed frame are written on the target 32, the mean Value of the beam current and the maximum amplitude of current variation must be adjusted so that the information written by the total number frames do not cause the target 32 to become saturated. Saturation of a film 38 of potassium chloride corresponds to that condition where the screen just barely affords a visible output when illuminated. In other words, the current level of the electron beam used in conventional dark trace tubes saturates portions of the film 38. The level of the beam current used in this invention preferably is less than one one-hundreth of that normally used for writing in a dark trace tube. This permits several frames to be superposed; it permits more readouts for reasons pointed out below.

The writing electron beam is provided with sufficient power by power supply 22 to permit the capture of electrons in crystal matrices of the film 38. The electron beam not only deposits electrons as indicated above but also collides with and knocks electrons from the surface of the film 38, i.e. secondary emission. The electrons released by secondary emission from the surface of the film 38 are attracted by the anode 18 and returned to cathode 14. The surface pattern which results is analogous to that created in a conventional electrostatic storage tube; it is dissipated in a relatively short time and thus has substantially no effect on subsequent frames of writing. Even if a series of frames are written in succession, local potential buildups on the surface of film 38 due to surface charge would not exceed the level of about 50 volts. Even such local peaks in potential are virtually negligible in comparison to an anode voltage of 5000 volts. Therefore for most purposes the electrostatic surface charge produced in the process of writing has negligible adverse effect. Though the foregoing explanation has been concerned generally with intensity modulated electron beams, this invention performs equally well with defiection modulated beams.

Readout of the information stored in the film 38 is accomplished by taking advantage of either of two principles known to those skilled in the art and presented earlier in this description. One principle is that secondary emission from the surface of film 38, as a result of being scanned by a constant current beam, varies as a function of the density of captured electrons under every point. The second principle is that the resistance between the opposite surfaces of the film 38 at every point is a function of the density of captured electrons under that point. To readout by taking advantage of the secondary emission principle, the target 32 is scanned by a constant current beam substantially equal to the mean current of the writing beam and with substantially the same anode voltage as was used for writing. A uniform density of electrons is deposited in the film 38 by the readout beam but is not of interest in itself except that it causes the number of possible readouts to be limited since each readout scan brings the film 38 closer to saturation. The instantaneous surface charge at each point resulting from the4 secondary emission current at that point as the film is scanned causes a corresponding charge to be induced at the point in the surface of conductor 36 aligned therewith and as a result causes an instantaneously corresponding current to flow through4 load resistor 42. The voltage developed across resistor 42 contains the readout information. To readout by taking advantage of the variation in resistance principle, the target 32 is scanned by an electron beam whose mean level is substantially equal to the mean current of the writing beam but at an anode voltage about two kilovolts higher than used for Writing. As above, a substantially uniform density of electrons is deposited in the film 38 by the readout beam but is not of interest in itself except that it causes the number of possible readouts to be limited since each readout scan brings the film 38 closer to saturation. As above, the instantaneous surface charge at each point resulting from the secondary emission at that point, as the film 38 is scanned, causes a corresponding charge to be induced at the point the surface of conductor 36 aligned therewith and as a result causes a corresponding coincident current to flow through the load resistor 42. So far this is the same situation as was described for the secondary emission principle. However, an additional effect is realized. Most of the beam current penetrates through the lm 38 to the conductor 36. The resistance of the beam current circuit varies because the resistance of the film 38 at each point under the beam is a function of the electrons captured there. Consequently, the beam current and the penetration current varies thus producing a variable voltage across the load resistor 42. The resultant voltage at each instant is a function of the density of captured electrons in the film 38 under the scanning beam at that instant. The readout voltage developed across the output resistor 42 is adapted to be amplified through resort to conventional amplifier circuit techniques. The amplifier circuitry is adapted to include conventional means for linearizing the output corresponding to the means resorted to for gamma correction in ordinary cathode ray tube circuits. The readout output voltage may be applied to the control grid of a cathode ray tube or to a computer or to other electronic apparatus.

Fig. 2 shows a modification of the target 32 that is adapted for eliminating local potential peaks due to surface charges on the film 38 and for eliminating adverse effects resulting therefrom. A conducting film 36a, on the order of one micron thin, is deposited on the film 38. Little additional penetration power need be provided to the electron beam by power supply 22 when film 36a is very thin. The function of fihn 36a is to uniformly distribute all surface charge, whether deposited or resulting from secondary emission. A suitable resistor 36b may be used for connecting film 36a to the cathode 14 through conductor 36e to allow the charge to leak off quickly. The proper solid state operation, as stated on the drawing, Fig. 2, means that different material may be used and the voltages necessary for this type of operation will vary with the crystal material used and the impurities in such crystal material. A slight modification of this arrangement is to eliminate conductor 36 and to connect the output or load resistor in circuit with the film 36a as shown in Fig. 3. The read out current would be the secondary emission current.

Another modification for achieving somewhat the same effect achieved by the film 36a is to mix the alkali-halide of film 38 with a controlled percentage of conductor.

Where the face of the envelope 12 is metallic, another modification is to make the structure shown on the drawing minus the conductor 36. Though the metal for the face of the envelope may be of lower conductivity than that contemplated for conductor 36, it would be suitable for purposes where high fidelity readout is not essential. The resultant structural combination would be less expensive. The disadvantages to the storage device stemming from the use of a lower conductivity metal behind the film 38 is that it introduces reactance lwhich is particularly objectional at the higher frequencies and introduces a lag in the induced current flowing through the output resistor 42 during readout because with the film 38 it forms an RC combination of measurable time constant.

Those Who are skilled in the art of storage tubes know' ing known effects and performance characteristics by resort to the respective expedients well known by those skilled in the art.

One modification concerns the addition of a mesh parallel to the target 32 for modifying the electric field at the target to achieve greater efiiciency and specific' 7 effects. The potential of the mesh would be raised to that necessary as is conventional.

Another modification is to add a conventional filament for heating the film 38 for erasing the stored information.

Another modification is to form the target 32 on a support separate from the face of the envelope 12. For example a thin sheet of mica is suitable. In this aI- rangement, the target 32 and its mica support has a 10W heat capacity because `it is so thin. Erasure, through the use of an erase filament, can be accomplished in a fraction of a second.

Another modification is shown in Fig. 4 in which the target 32 is formed on a supporting mesh. The target and its supporting mesh are mounted in envelope 12 contiguous with or spaced about one-thousandths of an inch away from the transparent face of envelope 12. The envelope face is coated with a phosphor, so that a visible readout may be obtained by setting the anode voltage so that the electron beam current used for scanning penetrates through to the phosphor.

Correspondingly, other modifications of the forms shown on the drawing may be made in accordance with the teachings of the prior art.

The stored information may be erased -as suggested above through the use of an erase filament. Forms of energy other than heat may be applied to the storage film 38 to erase the stored information. A source of bright light, a source of ultrasonic vibration, or a high intensity electron beam can be used for erasure. An erase filament has proven to be the most desirable to date.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. An electronic storage device comprising; a support; a target mounted on said support and including a conductor, one side of said conductor being formed with a continuous, substantially at surface, a film of signal storage material of ionic crystals covering the one side of said conductor and of uniform thickness and surface continuity over its entire face area, the thickness of said film of signal storage material being on the order of several microns, and a uniform film of conductor covering said film of signal storage material; said film of conductor having a thickness on the order of one micron; first means adapted to emit electrons mounted on said support on the film of conductor side of said target; second means mounted on said support between said first means and said target and adapted for forming into a beam the electrons emitted from said iirst means and for directing the beam toward said target to reach said crystals before said conductor; third means mounted on said support between said first means and said target and adapted for modulating the electron beam, a high voltage power supply connected between said first means and said second means; means for connecting said film of conductor directly to said first means whereby they are at substantially the same potential; an output load resistor connected at one end to said first-mentioned conductor; and a second high voltage power supply connected between the other end of said output load resistor and said first means.

2. The method of reading out information written in and stored in a signal storage screen employing a layer of uniform thickness and surface continuity over its entire face area of opacity controllable ionic crystals confined on the face of an imperforate metal plate comprising the steps of directing a readout electron beam against the storage screen at a voltage that is higher than used for writing, passing through a circuit including said plate and a resistance the readout electron beam current that penetrates through the layer of crystals of the storage screen to said metal plate, whereby the voltage variations across the resistance indicate the information stored on the storage screen.

3. An electronic storage device comprising a cathode ray tube having a cathode for sending an electron beam, means for modulating said beam, a target in the path of said beam in a plane crosswise of the beam and spaced from said cathode, said target being formed of three layers disposed in face to face alignment and contact, sandwich-like, the outer layers being of conducting material, with the layer nearest the cathode of film like thickness, and the intermediate layer being of ionic crystals of signal storage material, means electrically connecting said outer layer nearer the cathode directly to said cathode, means connecting the other outer layer also to said cathode but having in series therein a D.C. power supply and a load resistor, and output terminals connected to the ends of said load resistor whereby voltage variations across said load resistor caused by a readout scanning movement of the beam will correspond to the information stored by said crystals along the path of the readout beam.

4. An electronic device for storing information comprising a cathode ray tube having near one end thereof an electron creating cathode and means forming said electrons into a beam, and near the other end thereof a planar target disposed crosswise of said electron beam, and means for selectively modulating said beam, said target being formed of three layers that are uniformly continuous over their face areas in face to face alignment and contact, the outer layer furthest from said cathode being a sheet of metal, the intermediate layer being ionic crystals of signal storage material, and the other outer layer being a thin lm of metal, conducting means connecting said iilm directly to said cathode, other conducting means connecting said outer layer that is furthest from said cathode to said cathode and having in series therein a load resistor and a D.C. power supply, whereby the voltage variations across said load resistor that are caused by a readout scanning movement of the beam will correspond to the information stored in said crystals along the path of the readout beam.

5. The device as set forth in claim 4, wherein said conducting means connecting said film to said cathode has a resistor in series therein.

6. The device as set forth in claim 4 wherein said outer layers are imperforate across the areas of their faces which may lie in the path of said beam.

7. In an electronic device for storing information, of the type having a cathode ray tube with an electron creating cathode and a beam creating device near one end thereof and a planar target near the opposite end thereof and disposed with its faces crosswise of said electron beam, and means for modulating said beam, that improvement therein which comprises, as said target, a sheet of metal having confined on its face nearest the cathode, a layer of ionic crystals of signal storage material, and means for continuously providing an electron resistance path that begins substantially contiguous with one face of said target and includes said sheet, whereby the electron flow through said resistance path produces voltage variations that correspond to any information stored in said target, said sheet of metal being imperforate across that area of its face corresponding to that upon which said electron beam may fall as it is modulated.

8. The method of electronically storing information in a target and later reading it out, which comprises directing an electron beam, modulated proportionally to the information to be stored, against a screen uniformly continuous over its entire face area and having a layer of ionic crystals of signal storage material of uniform thickness and continuity over its entire face area and confined against a face of a physically imperforate conductor, under a propelling force adequate to cause sub- Sllliial penetration of said layer of crystals and entrapent and storage therein of the penetrating electrons with a beam current level less than that which will cause a visible output to appear on the screen when the screen 1s illuminated, and later reading out the stored information by directing against said layer -a scanning electron beam whose magnitude is on the order of the mean current of said rst mentioned beam and with an anode voltage at least as high as that used with said irst mentioned beam, concurrently and continuously with the latter step providing a resistance path for electrons that begins substantially contiguous with one face of said screen 'whereby electron ilow through said resistance path produces voltage variations across the resistance path that corresponds to the stored information.

9. An electronic device for storing information in a condition to be later read out, which comprises a cathode ray tube having, in one end thereof, a cathode for emitting electrons, in the other end thereof a target formed of a sheet of metal having confined on its face towards said cathode, a layer of ionic crystals of signal storage material of uniform thickness and surface continuity, positioned with its faces crosswise of the length of said tube, means between the target and cathode for directing the electrons emitted by said cathode as a beam towards said target, means for modulating said beam in accordance with information to be stored fin said target, a conductor connecting said cathode to said metal sheet and having a load resistor and a D.C. power supply in series therein and with each other, whereby one may employ the voltage variations across said resistor, while a constant current readout electron beam is scanning said target, to indicate the stored information, and a thin conducting lm covering and in contact with that face of said layer of crystals which is opposite from said metal plate, and conducting means connecting said ilm directly to said cathode to allow any surface charges on the layer of crystals to leak off quickly.

10. An electronic device for storing information in a condition to be later read out, which comprises a cathode ray tube having, in one end thereof, a cathode for emitting electrons, in the other end thereof a target formed of a sheet of metal having confined on its face towards said cathode, a layer of ionic crystals of signal storage material of uniform thickness and surface continuity, positioned with its faces crosswise of the length of said tube, means between the target and cathode for directing the electrons emitted by said cathode as a beam towards said target, means for modulating said beam in accordance with 'information to be stored in said target, a conductor connecting said cathode to said metal sheet and having a load resistor and a D C. power supply in series therein and with each other, whereby one may employ the voltage variations across said resistor, while a constant current read-out electron beam is scanning said target, to indicate the stored information, said layer of crystals being several microns in thickness, and a thin conducting llm of not more than a few microns thickness covering that face of said layer of crystals which is opposite from said metal plate, and conducting means connecting said conducting ilm directly to said cathode to allow any surface charges on the layer of crystals to leak olf quickly.

11. The device as set forth in claim 9, wherein said thin lm is imperforate over substantially the entire face area thereof upon which the electron beam may strike.

12. The device as set forth in claim 9, and a resistor in series in said conducting means.

References Cited in the file of this patent UNITED STATES PATENTS 2,330,171 Rosenthal Sept. 21, 1943 2,533,381 Levy et al. Dec. l2, 1950 2,535,817 Skellett Dec. 26, 1950 2,661,442 Buckbee Dec. 1, 1953

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