US2872612A - Non-volatile barium titanate storage tube - Google Patents

Description

Feb 3 i959 R. B. DE LANo, JR., ETAL 72,612

NoN-voLATILE BARIUM TITANATE STORAGE TUBE Filed March 2s, 1955 G(2e WRITE "1" 44 ADDRESS O BEAM oN ,5N

JNVENToRs L A Z/s DONALD R.YouNG fw RALPH a. DE LANo JR.

,mig Patented Feb. 3, 1959 NoN-voLA'rnn Bamm/i rrrANArn sronaor roar Ralph B. De Lario, Jr., and Donald R. Young, Perugia-1 keepsie, N. Y., assigner-sto `internatiunal Business Machines Corporation, New York, N. Y., a corporation of New York Application March 28, 1955, Serial No. 497,164

8 Claims. (Cl. 315-12) This invention relates to electron discharge devices and more particularly to that type of electron discharge device employed for storage of intelligence signals.

Cathode ray electrostatic memory tubes heretofore known and used in computers, target indicating radar systems and the like, store information in the form of charges established on an insulated target electrode upon which the beam impinges. VSubsequent bombardment of elemental regions of the target by the beam develops distinctive output signals corresponding with the stored information through the phenomenon of secondary electron emission. In previously devised tubes, however, the charges established tend to dissipate themselves over a relatively short time interval and must be systematically regenerated.

In accordance with the present invention a conducting target cathode ray storage tube is provided which does not require regeneration over periods of normal usage and may be termed a permanent storage device. The conducting target comprises a ferroel'ectric material covered with a resistive lm upon which the beam is directed in developing a surface charge at the elemental spot bombarded and whichcharge approaches an equilibrium potential with respect to a collector electrode. This charge establishes an electrostatic field across the elemental region of ferroelectric material beneath the bombarded spot of the resistive film and switches that region from one to the. other stable direction of polarization. By pulsing a metallic coating provided on the side of the ferroelectric target away from the beam and simultaneously bombarding the resistive iilm spot, the eld is reversed to reestablish the initial polarization state.

An object of the present invention is to provide a storage tube wherein binary intelligence signals are stored and distinguished by relative directions or by different degrees of polarization of elemental regions of a ferroelectric target.

Another object of the invention is to provide'an improved memory system wherein information is stored and retained without requiring regeneration at periodic intervals.

A more general object of the invention is to provide a nonfvolatile electrostatic storage tube of the type described.

Other objects/of the invention will be pointed out in the following description and claims and illustrated in theaccompanying.drawings, which disclose, by way of example, the principle of the invention and the best mode which has been contemplated of applying that principle.

in the drawings:

Y Figure 1 is a diagram off the hysteresis characteristic exhibited by ferroelectric materials such as that employed in the storage device.

Figure 2 is a schematic representation of a cathode ray tube constructed in accordance with the present invention and shown with the necessary circuit connections.

Ferroelectric materials comprise a class of dielectrics which depend upon vinternal polarization rather than surface charge for the storage of information and a ferroelectric crystal, such as barium titanate, exhibits a substantially rectangular hysteresis characteristic as illustrated in Figure l. In thisgure the vertical axis represents the degree of polarization P and the horizontal axis the applied electric iield E. In representing information the residual polarization states designated a and b, are arbitrarily selected to indicate a stored. binary one and binary zero, respectively. A discussion of ferroelectric materials as employed for representing binary information may be found, for example, in Patent No. 2,717,373 issued September 6, 1955 to l.v R. Anderson.

With an elemental body of ferroelectric material initially polarized in a binary zero state or at point b, a binary one may be stored by application of a positive potential, greater than the coercive force between the faces of the material which causes the hysteresis loop to be transversed from residual point b to saturation point c and, on termination of this positive electric eld, to return to point a.

To determine if a binary oneV or binary zero has been stored at some subsequent time, a negative iield is applied which drives the ferroelectric from point a to point d if a binary one is stored or from pointb to point d if a binary zero is stored. The slope of the hysteresis curve is proportional to the capacitance presented be tween the faces to the applied field, and, in going from point a to point d a large capacitance is presented while in going from point b to point d a low capacitance is presented, so that the two charge states may be distinguished by current flow in a circuit coupling electrodes provided on the crystal faces.

Referring now to-Figure 2, a ferroelectric crystal 10 of the type described is shown enclosed in an envelope 12 whichY may be in the form of a cathode ray tube. This envelope also contains the usual electrodes of a 'cathode ray tube including an electron gun having a cathode 13, control electrode 14, focussing electrodes 15 and beam deflection means such as the electrostatic deflection plates 16. The ferroelectric t beam from charging undesired regions of the Crystalsurface. A further grid electrodeV 20, termed a collector, is spaced a short distance from the storage 'surface with the geometry of the grid arrangement such thatxthe collector determines the potential of the resistive ilm area under bombardment.'

As shown in Figure 2 the backplate .17 and gridjw are interconnected by a circuit which includes a resistor 21 with a back plate lead 22 connected to the plateof a tube 23. The cathode of the tube 23 is biased negative by a source 24 and its grid` is connected to a source 25 through a resistor 26 so as to normally bias the tube 23 to non-conduction. lInput .wire'pulses are of positive polarity and are applied'via a lead 28 to the tube grid. The resistive film 18 and grid 19 of the storage tube 12 are biased positively bya source 3l) to which connection is made through resistors 32 and 33, with the source 3l? and resistor 33 shunted by a diode 35. 'The junction of the resistor 32 and diode 35 is connected to 3 type may be employed. The collector grid is biased positively by a source andthe cathode 13, accelerating anode and focussing electrodes 15 biased by a source 42, as shown. A lead 43 is coupled'toj the beam control'14 and leads 44 are coupled to the deflection plates 16. c

The circuitry shown and described in connection with the storage tube is similar to that'employed in the copending U. S; patent application No. 357,608 entitled Electrostatic Memory System, filed May 2,6, 1953, on behalf of R. B. De Lano andD. R. Young, and assigned to the same assignee. It is to be understood, however, that this environment is not essential for the use of the tube and other systems may be employed as will be explained further.

The principle of electrostatic storage broadly involves the establishment of distinctive chargeV states at discrete target regions which states are assigned f to represent one or the other binary digit. During bombardment,

a silver or platinum deposit aixed in any well known manner with a resistance such that only with a beam current of sufcient intensity will the potential of a bombarded area be made to approximate that of the collector. Stray current densities are not sufficiently high to develop a voltage to overcome the coercive force of the f erroelectric material in other regions. The fact that the lm is somewhaty conductive does not destroy a primary beam of electrons is developed by the gun and is directed to a particular target region in accorddance with the address selecting potential applied to the deection plates 16 via the leads 44 and secondary electrons are emitted from the target surfaceand are attracted toward the collector electrode 20. The number of secondary electrons leaving the region and the number of primary electrons arriving at the region determine its charge. This broad principle of operation is common to all electrostatic storage systems with the manner of controlling the electron ow generally being the feature of deviation. One method for controlling electron ilow comprises varying the collector electrode potential between two values and therefore controlling the potential of the bombarded elemental target region which tends to equalize its potential with that of the collector. Another method comprises maintaining the collector potential stable while varying the beam intensity or velocity.

A further method, and the one employed for illustra-V tion in the present instance, comprises modulation of the potential of the target electrode during bombardment.

In the illustrated system, the'beam is turned on under control of signals'applied to the lead 43 and the grid 14, and is directed to a particular elemental area of the target 10 by the potentials applied to the leads 44. The dellection plates 16 are physically arranged at right angles to one another and may receive random addressing potentials or varying voltages producing a systematic scanning of the entire target raster as in conventional practice. Each elemental target region comprises an individual capacitor with the backplate 17 providing one common terminal. As the beam impinges the resistive lilm 18 or other terminal of an elemental condenser selected as described, secondary electrons are emitted and collector potential an electric field of one polarity is developed across the capacitor and with the backplate held below the collector potential an electric iield of opposite polarity is developed. Therefore, in vstoring binary representations, the bias potential of the backplate may be made lower or higher than collector potential with the write pulse raising or lowering this potential either above or below collector potential.

In bombarding an elemental target region Vthere is a 'tendency for some of the emitted secondary electrons to spill back on neighboring charged -regions along with kfringe electrons in the primary beam. The resistive coating-18 and conductive grid 19y are provided Vto limit the storage area and prevent spill from charging other surface regions. The coating 1,8. may take the form of the stored information in any region since there is no` net ield in the condenser or external to it and the polarization charge is equal and opposite to the surface charge. Y

The resistive coating 18 is preferably applied by evaporation of a platinum wire wound about a tungsten lilament and throughY which current is passed. The barium source 30 inV the absence of other circuit operation,V

which bias is more positive than that of the collector as provided by the source 40. In storing a binary zero, the beam is turned on and the bombarded spot'on the lm 18 to which the beam is Vdirected attains a potential approaching that of the collector. An electric lield of a first sense is now established across theY selected elemental ferroelectric condenser and it is caused to assumeor example, state d, and then state b (Fig.' 1) when the beam is blanked or deected to another target region. To store a binary one as the opposite polarization state, assuming all of the elemental condensers are in state b initially, a positive pulse is applied to the lead 28, overcoming the bias from battery 25, causing the tube 23Yto conduct and lead 22 to assume a-potential approximately that of the negative bias source 24, the combined resistance of resistors 21 and 32 being of high ohmic value. This change in potential of the backing plateis applied to Veach element of the target but is suiciently less than the coercive force of the ferroelectric lso that no change instate occurs since the resistor 21 is of low ohmic value. Bombardrnent of an elemental region, however, subsequently raises the potential of the resistivelm of the elemental bombarded surface area and afiield of reverse V*sense is developed across the selected ferroelectric capacitor, with the hysteresis loop traversed from b to crandrthence` to a v/hen'the beam is blanked.

so far asto develop a useful output signal on interrogation. Further, since available ferroelectric materials do not exhibit a precise coercive field below which no permanent change in polarization takes place it is not contemplated that storage may be termed permanent, however, with present materials the required select to nonselect eld ratio may be' made suicient to allow the storage to remain recognizably for periods Vot" twentyfour hours Vor better withoutV requiring regeneration. Selection ratios of the order of 25 havebeen obtained with information'V bits or adjacent Velemental regions employed for storage Yspaced two bearnV diameters apart.

in Vreading out a storage position to determine the polarization state attained as a result lof a previous writing operation, thebeam is turned ,on yas in writing a zero and if theI elemental Ycondenser addressed 1s 1n a state representing la binary zero or state b, a short duration c signal pulse is developed while if it is in a state representing a binary one or state a, a pulse of considerable duration is obtained. In the illustrated system, current ow in both instances is in a path including the resistor 33 and diode 35 and a negative voltage pulse is applied to the input of amplifier 38 to be time sampled with respect to the beam-on pulse in conventional manner. In the zero representing polarization state, current flow results from the fact that the region beneath the bombarded resistive film spot again is lowered in potential to approach equilibrium potential with respect to the collector 20 and the number of secondary electrons departing from the surface is greater than the number of primary electrons delivered by the beam for a time period suicient only to reestablish this negative charge. On the other hand, in the one representing polarization state the surface charge is established while the ferroelectric material switches states from point a to point b with a greater number of secondary electrons owing to the collector and the current ow consequently of greater duration. At this point it may be noted that these output signals may be detected in an alternative manner through the use of a resistor connected in series with the collector electrode with the voltage drop thereacross applied to the amplifier input.

As mentioned earlier in the description, the function of the resistive iilm 18 resides in preventing stray current densities building up and developing charges sufhcient to overcome the coercive force of the ferroelectric material at regions not under bombardment. The ferroelectric nature of the storage media permits the use of this resistive film in that its conductance does not destroy the stored information. However, it is contemplated that the barium titanate material itself may be rendered somewhat conductive and the conducting film eliminated. Barium titanate crystals have been made conductive by reduction in a hydrogen furnace, however, due to the fact that variations in conductivity are experienced. The use of a resistive film surface coating is considered preferable.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the in- 'tention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

l. In combination, a cathode ray tube having electron emitting and focusing electrodes, a pair of beam deecting electrodes, a ferroelectric crystal target having one face presented to the electron beam, a resistive coating electrode on said one face, a backplate electrode on the opposite target face, a collector electrode positioned intermediate said electron emitting electrodes and said target, and circuit means for applying potentials to said electrodes in selectively causing elemental regions of said ferroelectric target to assume one or the other stable state of residual polarization.

2. In an electrostatic storage tube having beam forming and deflecting means, a target comprising a barium titanate crystal having one surface presented to said beam, a resistive coating on said one surface, a backing plate electrode in intimate contact with the opposite surface of said crystal, secondary electron collecting means within said tube, means for biasing said collecting means, and means for modulating the potential applied to said backing plate during bombardment whereupon predetermined regions of said crystal are selectively caused to attain distinct residual polarization states.

3. In an electrostatic storage tube having beam formmg and deecting means, a target comprising a sheet of ferroelectric material having one surface presented to said beam, a resistive coating on said one surface, a backplate electrode in intimate contact with the opposite surface of said material, a secondary electron collecting electrode within said tube, and means for applying potentials to said electrodes during bombardment of said material in selectively causing predetermined regions of said material to attain distinct states of residual polarization.

4. In combination, a cathode ray tube having beam forming and deilecting means, 'a target comprising a sheet of ferroelectric material having one surface presented to said beam, a resistive coating in intimate contact with said one surface, `a backplate electrode in intimate contact with the opposite surface, a secondary electron collecting electrode within said tube, and means for applying potentials to said electrodes in selectively causing elemental regions of said ferroelectric material to attain distinct states of residual polarization in representing intelligence signals.

5. In 'a cathode ray tube havingr electron emitting and beam deflection means, a ferroelectric target having a resistive coating on one surface and a backplate electrode on the other surface, said target being mounted with the target surface having said resistive coating presented to said beam, a conductive grid in intimate contact with said resistive coating, a secondary electron collector within said tube, means for biasing said collector to a reference potential, and means for selectively varying the potential of said backplate electrode above and below said reference potential in establishing selective fields of opposite sense across said target during bombardment of elemental areas thereof.

6. In combination, a cathode ray tube having beam forming and deflecting means, a target comprising a sheet of ferroelectric material having one surface presented to said beam, a resistive coating in intimate contact with said one surface, a backplate electrode in intimate contact with the opposite surface, a conductive grid in intimate contact with said resistive coating, 'a secondary electron collecting electrode within said tube, and means for applying potentials to said electrodes in selectively causing elemental regions of said ferroelectric material to attain distinct states of polarization in representing intelligence signals.

7. In combination, a cathode ray tube having beam forming and deflecting means, a target comprising a sheet of ferroelectric material having Ione surface presented to said beam, a resistive coating in intimate contact with said one surface, a backplate electrode in intimate contact with the opposite surface, a conductive grid in intimate contact with said resistive coating, a secondary electron collecting electrode within said tube, and means for applying potentials to said electrodes including means for turning said electron beam on and oif in synchronism with the application of varying potentials to said backplate electrode in selectively causing elemental regions of said ferroelectric material to attain distinct states of polarization in representing intelligence signals.

8. A cathode ray discharge tube having electron emitting and focusing electrodes and having a ferroelectric crystal mounted therein, said crystal having a resistive coating on one face, a backplate electrode on the opposite face, a secondary electron collector Within said tube, means for biasing said collector to a reference potential, and means for selectively Varying the potential of said backplate electrode above and below said reference potential in establishing selective electric iiields of opposite sense across said crystal during bombardment of elemental areas thereof.

References Cited in the ile of this patent UNITED STATES PATENTS

Claims (1)

1. IN COMBINATION A CATHODE RAY TUBE HAVING ELECTRON EMITTING AND FORCUSING ELECTRODES, A PAIR OF BEAM DEFLECTING ELECTRODES, A TERROELECTRIC CRYSTAL TARGET HAVING ONE FACE PRESENTED TO THE ELECTRON BEAM, A RESISTIVE COATING ELECTRODE ON SAID ONE FACE, A BACKPLATE ELECTRODE ON THE OPPOSITE TARGET FACE, A COLLECTOR ELECTRODE POSITIONED INTERMEDIATE SAID ELECTRON EMITTING ELECTRODES AND SAID TARGET, AND CIRCUIT MEANS FOR APPLYING POTENTIALS TO SAID ELECTRODES IN SELECTIVE CAUSING ELEMENTAL REGIONS OF SAID FERROELECTRIC TARGET TO ASSUME ONE OR THE OTHER STABLE STATE OF REDIDUAL POLARIZATION.

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