US3398317A

US3398317A - Information storage tube

Info

Publication number: US3398317A
Application number: US424956A
Authority: US
Inventors: Kenneth R Shoulders
Original assignee: Stanford Research Institute
Current assignee: SRI International Inc
Priority date: 1965-01-12
Filing date: 1965-01-12
Publication date: 1968-08-20
Anticipated expiration: 1985-08-20

Description

8- 1968 K. R. SHOULDERS 3,398,317

INFORMATION STORAGE TUBE Filed Jan. 12, 1965 2 Sheets-Sheet 1 POTE N'HAL SOURCE //v VEA/TOI? KENNETH 1Q SHouL DERS A FOAM/Er 0, 1968 K. R. SHOULDERS 3,398,317

INFORMATION STORAGE TUBE Filed Jan. 12, 1965 2 Sheets-Sheet 2 VELOCH'Y ELECTRON 5o SELECTOR GUN 56 /-ELECTRON MULT\PL\ER I STORAGE 50v \ov SOURCEOF E- TARGET 17- 4 ADDRESS 50 saeNALs $6 59 42 52 5 I I 4 i 4 SOURCE OF DETECTOR PoTENnAL Soumca T 34-56 OF BEAM CONTROL 24 u 5 GNA SOuRQEOF TARGET POTEN'HAL lzy. 5

KE/VIVE'TH 2 Slim/06785 United States Patent 3,398,317 INFORMATION STORAGE TUBE Kenneth R. Shoulders, Woodside, Calif., assignor to Stanford Research Institute, Menlo Park, Calif., a corporation of California Filed Jan. 12, 1965, Ser. No. 424,956 7 Claims. (Cl. 315-12) ABSTRACT OF THE DISCLOSURE A data storage target is provided for use in an information storage tube wherein, an electron gun is at one end of the tube and a storage mosaic at the other end. The storage mosaic comprises a Substrate which supports a metal layer on which a dielectric layer is placed. The second metal layer is placed on the dielectric layer. A plurality of spaced holes are provided each of which extends through the second metal layer, the dielectric layer and partially into the first metal layer. Within each hole there is provided a microcapacitor which comprises dielectric material on the exposed first metal layer on top of which a metal deposit is placed.

This invention relates to information storage tubes, and more particularly to improvements therein.

An object of this invention is the provision of a storage tube having high density information storage capabilities.

Another object of this invention is the provision of a novel and useful high density information storage device.

Still another object of the present invention is the provision of a high density information storage tube which is substantially smaller than other information storage tubes.

These and other objects of the present invention are achieved by providing an information storage tube wherein within the tube envelope there is an electron gun at one end and a storage mosaic at the other end. This storage mosaic comprises a substrate supported metaldielectric-metal film sandwich, containing a rectangular array of holes. By way of illustration, but not to be construed as a limitation, these holes may be on the order of one-half micron in diameter and are spaced on one micron centers. Each hole passes through the surface metal film and the dielectric, but only partially extends into the underlying metal film which is relatively thick. Within each hole, there is a microcapacitor, having an exposed electrode which is electrically isolated from the remainder of the structure.

Binary and analog data is stored in each of the microcapacitors by controlling the energy in an electron beam which is directed to that microcapacitor. With the energy of the electron beam set high enough, it can penetrate through the dielectric layer of the microcapacitor thereby discharging it by bombardment-induced conductivity. At electron beam voltages which are insufiicient for complete penetration of the dielectric layer of the microcapacitor, but still between the unitary secondary emission ratio cross over values, the electron beam can be used to charge the microcapacitor to the surface potential of the sandwich.

Readout is performed with a nonpenetrating secondary emission producing beam from the same electron gun as is used for information storage. With a microcapacitor that has been set to its lowest potential, i.e., completely discharged, any secondary electrons which are produced by the reading beam experience the full acceleration voltage of the metal-dielectric-metal sandwich and a large fraction of them can emerge from the hole. The electron optics of a hole are such that the paths of true secondary electrons are bent away from the symmetry axis of the hole. Thus, an electron multiplier located outside of the primary beam area can be used to detect and amplify the secondary emission current. Where a microcapacitor has been set to the full metal-dielectric-metal sandwich potential, the region within the hole is essentially field free, so that very few of the secondaries produced by the read beam can emerge. Thus, the output of a detecting electron multiplier will be substantially zero. Analog storage can be provided by charging the microcapacitors to intermediate potentials, whereby the detected secondary electron current of the electron multiplier is proportional to the difference between the surface and microcapacitor potential.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

FIGURE 1 is a perspective view illustrating the appearance of a section of the storage mosaic made in accordance with this invention;

FIGURE 2 is a cross-sectional view along the lines 2-2 of the storage mosaic shown in FIGURE 1;

FIGURE 3 is a schematic diagram shown to assist in an understanding of the operation of the invention;

FIGURE 4 is an illustration of the appearance of a storage tube in accordance with this invention; and

FIGURE 5 is a diagram illustrating the appearance of the target during a step of the manufacture thereof.

Referring now to FIGURES 1 and 2, FIGURE 1 illustrates the appearance of a section of the target of a storage tube in accordance with this invention. FIGURE 2 represents a cross-sectional view along the lines 22 of FIGURE 1. The storage mosaic comprises a substrate 10 which may be sapphire, for example, on which there is deposited a metal layer 12. By way of example, this metal may be molybdenum. A dielectric layer 14, which may be of aluminum oxide, by way of example, is deposited on the metal layer. Another metal layer 16 which is thinner than the metal layer 12 is deposited over the dielectric layer 14. This metal layer may also be molybdenum, by way of example.

A rectangular array of holes 18A through 18F are formed in the sandwich comprised of a metal layer 12, dielectric layer 14 and metal layer 16. Each hole extends through the surface metal film and the dielectric but only partially extends into the underlying metal layer 12 which is relatively thick compared to the metal layer 16. Each h-ole contains a dielectric film 20 which is resting on the metal film 12 and on which there is a metal film 22. As may be seen in FIGURE 2, the metal film 22 is supported on the dielectric 20 so that it is below metal film 16 and is not in contact with the metal film 12. As previously stated, by way of illustration and not to be considered as a limitation herein, the size of the holes may be on the order of one-half micron in diameter which are spaced on one micron centers. The mosaic target can be made [to occupy a total area of about 4 millimeters by 4 millimeters within which it can contain an array of about 10' elements. The area of the mosaic is determined to accommodate the deflection limit of an electron gun which in turn is determined by the required spot size. A potential source 24 which may be on the order of 50 volts, by way of example, is connected to the two

metal film layers

12, 16. The metal film layer 12 is made negative with respect to the metal film layer 16.

FIGURE 3 is a schematic diagram illustrating a single storage element and associated structures which is shown in order to afford an understanding of the operation of this invention. Basically, the structure shown comprises an electron gun 30, a mosaic element 32, a velocity selector 34, and an electron multiplier 36. The velocity selector comprises two parallel spaced-apart plates. A biasing potential on the order of 12 volts is applied to the upper velocity selector plate and volts to the lower velocity selector plate. A potential on the order of volts is applied to the entrance dynodes of the electron multiplier. As previously stated, a fixed DC potential of approximately volts may be maintained across the film sandwich of the mosaic 32 with the polarity shown. The electron gun 30 may then be used to perform the binary storage function, or, as will be shown, an analog storage function, by determining the energy with which the electron beam bombards a capacity which is in a hole. These capacitors may be addressed, as desired, on a random basis or in sequence, using well-known addressing techniques.

In order to store information in each one of the microcapacitors which are within the holes, the electron beam energy may be set high enough to penetrate completely through the dielectric layer of the microcapacitor whereby the capacitor is discharged so that the top film 22 is substantially at the potential of the base film 12. Alternatively, a beam may be generated from the electron gun 30 which has insufficient energy for the complete penetration of the dielectric layer of a microcapacitor, but is high enough to yield a secondary emission ratio greater than unity. At this potential, the electron beam causes the metal film 22 to lose electrons whereby the microcapacitor charges up to the surface potential of the layer 16. The foregoing operations constitute binary information storage. Intermediate potential states representing analog storage can be set by controlling the total charge delivered by the electron beam.

Readout is performed with a nonpenetrating secondary emission producing beam from the same gun used for information storage. For any microcapacitor that has been set to its lowest potential, i.e., completely discharged, the secondary electrons produced by the reading beam experience the full acceleration voltage of the target sandwich and therefore a large fraction of the secondary electrons will emerge from the hole. The electron optics of a hole are such that the paths of true secondary electrons are bent away from the symmetry axis of the hole. Thus, an electron multiplier 36 which is located outside of the primary beam area can be used to detect and amplify the secondary emission current. For any microcapacitor that has been charged to the full sandwich potential, the region within the hole is essentially field free, so that very few of the secondary electrons produced by the reading beam can emerge. This will be appreciated by the fact that the potential of the top film 22 of the dielectric and that the top film 16 of the sandwich are substantially the same. For microcapacitors set to intermediate potentials, the detected secondary electron current is proportional to the difference between the surface and microcapacitor potentials.

When the readout beam is swept in raster fashion, and therefore impinges on the surface of the target sandwich, as well as on the surface of the microcapacitors, if the resulting secondary and reflected primary electrons from the surface are not suppressed, they will tend to degrade the contrast in signals detected between the surface and the holes. Suppression of surface secondary electrons may" be easily accomplished by biasing the electron multiplier 36 relative to the mosaic surface to an appropriate negative voltage value smaller than the sandwich potential.

Thus, for example, with the surface of the sandwich at zero potential and the other sandwich electrode at 50 volts, the electron multiplier potential is made l0 volts. In this manner, secondaries originating at the surface are repelled by the multiplier, whereas those originating in the holes experience a net positive voltage and can reach the multiplier. However, the reflected primary electrons (or those in the high energy tail of the secondary elec' tron velocity distribution) will not be repelled in this manner, and can enter the multiplier.

Although it is believed that the latter effect is small, it may be desirable to reduce it further by using a pair of deflection plates, designated as velocity selector 34, which are positioned at the entrance to the multiplier. The upper of these plates is biased to l2 volts and the lower to -10 volts. Both values are SllifiClCl'lt to suppress secondary electrons originating at the mosaic surface. Also, the two-volt difference provides for the collection by the lower plate, of the sec-ondary electrons produced at the upper plate by reflected primary electrons, from the mosaic. Nevertheless, electrons originating in mosaic holes can pass through the velocity selector to the electron multiplier, which is biased to a somewhat higher negative value, say 20 volts.

It should be evident that the secondary emission readout process at any element increases its voltage, by an amount proportional to the charge alteration produced by the beam. The degree of significance of this eflect is determined in part by the intended application. At one extreme, the informational loss can be minimized by using low-current reading beams and/or rapid scanning speeds consistent with the number of levels to be distinguished and the available detection sensitivity. These factors in turn will determine the number of useful readout cycles for various information processing functions, including the possibility of information regeneration, if desired. At the other extreme, for applications not requiring more than one readout cycle, a reading beam sufficient to fully erase all elements can be used, with a corresponding reduction in detection sensitivity requirements. In this case, the output current pulse is proportional to the difference between the sandwich pot ntial and the initial state of an element.

The maximum storage time between write and readout cycles depends primarily on the leakage characteristics of the dielectric material used. Reasonably good dielectrics, such as properly prepared aluminum oxide, have time constants on the order of one day, which is quite adequate for applications requiring only temporary storage. Binary information can be easily retained for as long as desired by the use of a continuous, low-current, flood beam from an auxiliary gun operated at a potential such that the secondary emission ratio is greater than unity for fully charged elements, and less than unity for discharged elements. Thus, each microcapacitor element will be clamped to its previously set potential by the flood beam.

The flood beam may also prove useful in making the readout of binary information nondestructive, by regenerating the information during each sequential readout cycle. By way of example, the flood beam current may be set to about 1 thousandth of the read beam current, so that the flood beam can illuminate all elements continuously without significantly effecting the readout contrast. Then the charge change produced by the flood beam at each element during a full readout cycle can more than offset the effect of the readout beam during its dwell time on the element.

FIGURE 4 represents the appearance of the embodiment of the invention when the target is mounted in a tube envelope 40. The structure shown in the tube envelope, which functions similarly to those structures previously described, will bear the same reference numerals. Thus, the electron gun 30 is controlled from a source of beam control signals 41. These are the signals which determine the energy with which the beam will impinge on the target both for reading and writing. Deflecting electrodes respectively 42, 44 have potentials applied thereto from a source of target address signals 46. These determine the address or location at which the beam which is emitted from the electron gun 30 will fall on the mosaic target 32. Two detectors, which are designated by

reference numerals

34, 36, are shown which comprise the velocity selector 34 and the electron multiplier 36. These are positioned adjacent the storage mosaic 32 for the purpose of capturing secondary electrons which are emitted from the holes. They are connected in parallel to a source of detector potential 48 through a load resistor 50. Output is taken from across the load resistor 50. The source of target potential 24 is connected across the mosaic sandwich 32. It is believed that the operation of the embodiment of the invention which is shown in FIGURE 4 has been made apparent from the foregoing description and therefore will not be repeated here.

By way of illustration, but not to serve as a limitation upon the invention, a method of manufacturing the storage mosaic target will be described. First, by vacuum evaporation, a molybdenum film on the order of onehalf micron thick may be deposited on a clean sapphire substrate. Thereafter, on the molybdenum film there is deposited a thin film (on the order of 30 to 100 angstroms) of a silicon bearing polymerizable material, such as triphenylsilanol, and then a comparably thin aluminum film is used to cover the polymerizable material to prevent its charging during the next step of the manufacture.

An electron beam having a spot size on the order of one-half micron is then programmed to polymerize and convert the film into silica, first along a raster of parallel liner spaced one micron apart (center-to-center), then over the same area along an identical raster at right angles to the first.

Thereafter, the substrate is heated to about 400 C. in a vacuum, thereby driving off the unconverted material. The resulting surface should appear as shown in FIGURE 5. The squares 52 represent exposed molybdenum and the region between them 54 comprises the silica mesh.

Next, a low-pressure molecular beam of a molybdenum etchant, such as chlorine gas, is used to etch the exposed molybdenum areas down through the substrate; alternatively, aqueous etching may prove satisfactory.

A molybdenum film about 100 angstroms thick is then deposited over the entire surface, using a source having a relatively large subtended angle. This step serves to provide a metal layer at the bottom of each hole and, incidentally to encapsulate the silica resist layer in metal. Alternatively, the silica may be removed with an appropriate molecular beam etchant prior to this step.

Next, vacuum evaporate, aluminum oxide, or silicon monoxide, to a thickness on the order of 2,000 angstroms, using a source having a relatively large subtended angle. As the deposition proceeds overhanging lips will be formed which in turn will shape the rn'esas within the holes as may be seen by the structure in FIGURE 2.

Now, using a molecular beam normal to the surface, an overlying 100 angstrom film of molybdenum is deposited which completes the mosaic structure.

There has accordingly been described and shown herein a novel, useful structure for a high density information storage tube.

What is claimed is:

1. A storage target for an information storage tube comprising a first metal layer, a first dielectric layer deposited over a surface of said metal layer, a second metal layer deposited on the surface of said dielectric layer, an array of spaced holes extending through said second metal layer and dielectric layer and part way through said first metal layer, and a microcapacitor means deposited within each of said holes.

2. A target as recited in claim 1 wherein each of said microcapacitor means within each of said holes comprises a dielectric material in each of said holes deposited on said first metal layer in the base of each of said holes which dielectric material extends toward the opening of each said hole and does not contact the walls forming said holes, and a metal film deposited on the upper surface of each one of said dielectric material deposits in each of said holes, said metal film being deposited to be out of contact with the walls in each of said holes.

3. An improved storage target for data storage tubes comprising a substrate, a first metal film deposited over said substrate, a dielectric film deposited over the exposed surface of said first metal film, a second metal film deposited over the exposed surface of said dielectric film, said second metal film being thinner than said first metal film, a plurality of spaced holes in said storage target, each of which extends through said second metal film, through said dielectric film, and part way through said first metal film, each of said holes containing a deposit of a dielectric material in the bottom thereof, and a metal film deposited on the upper surface of said dielectric material to be supported thereby out of contact with said first metal layer, said deposited dielectric material and metal film forming with said first metal layer a plurality of microcapacitors which are completely contained within said plurality of holes.

4. A data storage tube having a storage target comprising a first metal layer, a dielectric layer deposited on one surface of said metal layer, a second metal layer deposited on the exposed surface of said dielectric layer, a plurality of holes in said storage target each of which extends through said second metal layer through said dielectric layer and part way through said first metal layer, microcapacitor means deposited within each of said holes, means for respectively applying a different potential to said first and second metal layers, and means for establishing a potential across each of said microcapacitor means between the potentials applied to said first and second metal layers to thereby store data in said storage target.

5. A data storage tube having a storage target comprising a first metal layer, a dielectric layer deposited on one surface of said metal layer, a second metal layer deposited on the exposed surface of said dielectric layer, a plurality of holes in said storage target each of which extends through said second metal layer through said dielectric layer and part Way through said first metal layer, microcapacitor means deposited within each of said holes, means for respectively applying a different potential to said first and second metal layers, means for generating an electron beam in said tube, means for selectively directing said electron beam at predetermined ones of said microcapacitor means, and means for controlling the energy of said electron beam means for storing data in said microcapacitor means and for reading out the data stored therein.

6. A storage target as recited in claim 5 wherein each of said microcapacitor means within each of said holes comprises a dielectric material in each of said holes deposited on said first metal layer in the base of each of said holes which dielectric material extends toward the opening of each said hole and does not contact the walls forming said holes, and a metal film deposited on the upper surface of each one of said dielectric material deposits in each of said holes, said metal film being deposited to be out of contact with the walls in each of said holes.

7. A data storage tube comprising a source of electrons, a storage target spaced from said source of electrons, means for selectively deflecting electrons from said source to predetermined regions of said storage target including a first metal layer, a dielectric layer deposited on one surface of said metal layer, a second metal layer deposited on the exposed surface of said dielectric layer, a plurality of openings within said storage for detecting the storage state of each of the micro- 1o capacitors within each of said openings.

ROBERT L.

References Cited UNITED STATES PATENTS 10/1939 Iams 250164 6/1946 Law 1787.2 5/1950 Cassman 250164 8/1965 Orthuber et al. 313-95 8/1965 Davis 3l389 GRIFFIN, Primary Examiner.

R. BLUM, Assistant Examiner.