US2905849A

US2905849A - Storage tube

Info

Publication number: US2905849A
Application number: US551705A
Authority: US
Inventors: Kazan Benjamin
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1955-12-07
Filing date: 1955-12-07
Publication date: 1959-09-22
Anticipated expiration: 1976-09-22

Description

Sept. 22, 1959 B. KAZAN sToRAGEmUBE Filed Dec. 7, ,1955

NNN SSS IN VEN TOR. BE Nimm KAZ AN TORNEY Ainem! Patented Sept. 22, 1959 hice STORAGE TUBE Benjamin Kazan, Princeton, NJ., assignor to Radio Corporation of America, a corporation of Delaware Application December 7, 1955, Serial No. 551,705

8 Claims. (Cl. 313-92) This invention relates to storage devices and particularly to storage devices having improved sensitivity. Also, this .invention relates to storage devices that store images in half tone quantities.

This invention contemplates the provision of devices for use in promoting the production and -storage of light by a luminescent phosphor under the controlling influence of a variable reactance device, with the reactance being varied by input signals. It is known in the electronics att that a luminescent phosphor can be made to produce light by the application of an electric eld across the phosphor. This phenomenon is known as electroluminescence. The theory of electroluminescence is `not well understood. However, it seems to be agreed that electroluminescence results from a redistribution of electrons in the crystal structure of the electroluminescent phosphor material and the con-sequent emission of radiation from such material.

There lare devices presently known which may be used to produce light images in response to an energizing Aforce of yone kind or another. Storage devices are also well known in the However, the known devices are complicated; some of them have a relatively low sensitivity; others have la comparatively low response speed; While others have a relatively low light output or picture resolution. Some of the storage devices that are known `are not capable of `halt tone quanti-ty storage, i.e. the storage of intermediate shades between black and white.

Accordingly, an object of this invention is to provide an :improved storage device.

'It is anotherobject of this invention to provide a novel storage device having increased sensitivity, or light output.

AIt lis fa further object of this invention to provide an improved picture storage device that is capable `of reproducing lhalf tone scenes.

In general, the purposes and objects of this invention are accomplished by the provision of a new storage tube including a novel electroluminescent target formed of new and improved elemental units. Each of the novel elemental units of the target comprises a ferro-electric element and a-n electroluminescent element. A eld is applied across the .electroluminescent element. The magnitude of the field is controlled by varying the `impedance `of the ferro-electric element in response to an `electron beam. The current or energy of the electron beam .is varied in response to input signals.

This invention will be more clearly understood by reference to the following specification when read in conjunction With the accompanying single sheet of drawings wherein:

Figure l is a schematic representation of an elemental unit of a targetof a storage device in accordance with this invention;

Figure 2 `is a sectional view, of a storage tube .in accordance with this invention; and

Figure 3 is -an enlarged fragmentary sectional view `of 'the target shown in Figure 2.

Referring new to Figure l there is shown a schematic representation of an elemental unit of an electroluminescent target for a storage device in accordance with this invention. The elemental unit includes a pair of ferroelectric elements 10 and 12 that are connected electrically in series with a pair of electroluminescent elements 14 and 16. Ferro-electric elements are dielectric elements that change their reactance in response to the voltage across the elements. Ferro-electric elements frequently exhibit hysteresis elects. 'The electroluminescent elements are elements that produce light in response to the voltage applied across the electroluminescent element. The series circuit of the ferro-electric elements 10 and 12 and the electroluminescent elements 14 and 16 is connected across the secondary 18 of a transformer 20. The primary 22 of the transformer 20 is connected to a source of alternating current potential. The secondary coil 18 of transformer 20 has a grounded center tap 24. Between the ferro-electric elements 10 and 12 is a junction '26. The potential of the Ajunction 26 as will hereinafter be explained, is controlled by an electron beam.

With zero potential applied to connection 26, the circuit vof an elemental unit, as shown in Figure l, operates as follows: The alternating current source applied to the primary of `transformer 22 establishes a varying electric field across each ferro-electric element 10 and 12 and its associated electroluminescent elements 14 and 16 respectively. The magnitude of the `alternating current source is selected so that the ferroelectric elements operate in their low impedance range. The electroluminescent elements are selected to have a high impedance, as compared to Vthe ferro-'electric elements at this potential, so that most of the alternating current voltage is thus applied across the electroluminescent elements. Since most of the alternating current voltage is across the electroluminescent elements 14 and 16, these elements luminesce. With zero direct current potential applied to connection 26 the direct current potential at point `42 is zero.

When a direct current Apotential is applied to point 42, i.e. between the :ferro-electric elements 10 and I2, a direct current field is established across both of the ferroelectric `elements 10 and 12.. Substantially no direct cur rent lfield is built up across the electroluminescent elements 14 Yand :16 because of the

leakage resistors

38 and 40 respectively. This direct current voltage, superimposed upon the alternating current voltage, in the series circuit connected across the secondary 18, increases the reactance of the ferro-electric elements 10 and 12 to a higher value. Due to the increased reactance of the ferro-electric elements there is an increase in potential drop across the ferro-electric elements 10 and 12 and a corresponding decrease in the Vpotential drop across the electroluminescent elements 14 and 16. Thus, the electroluminescent elements 14 and 16 produces less light. When the potential of terminal 26 is raised until the po tential drop across the ferro-electric elements 10 and 12 is sufficiently high, the luminescence from the electro` luminescent elements is cut ol completely.

Referring now to Figure 2 there is shown a longitudinal sectional view of an electroluminescent storage tube 30 having a target 54 including a plurality of the elemental units ofthe type shown in Figure l. The storage tube 30 comprises an evacuated .envelope 32 having an electron gun 34 in one end thereof. The gun 34 may be yof any known type and may comprise the usual cathode 36 control `electrode 43, and one or more accelerating

electrodes

45 and 46. A nal accelerating electrode 48 takes the form of a wall coating on the inner surface of the envelope 32. During operation the gun 34 produces an electron beam '53 which is directed toward and focused onto target 34. Also within the envelope 32 there is provided a means for sdeecting the electron 'beam 53, such as pairs of vertical and horizontal deflection plates S0 and 52 respectively (of which only one plate 52 is shown). It should be understood that other well known decction means may also be used and electrostatic deection is shown merely as yan example of operation.

Within the other end of envelope 32 there is provided a target electrode 54. The target 54 comprises a plurality of elemental units of the type -described in connection with Figure l. Supported adjacent to the target electrode 54 is a mesh screen 56 which is preferably a relatively ne mesh, e.g. 500 wires per inch. The mesh screen 56 is supported across a ring 55 that is supported by rods 57 extending through the envelope. The mesh screen S6 may be made of any conducting material, e.g. nickel. Extending from the target through the envelope 32 is a plurality of lead-in wires 58 to energize portions of the target 54. It should be understood that the lead-in wires 5S are shown as extending through the face plate of envelope 32 merely for simplicity of illustration. Also, only a few elemental units are shown in the target 54. In actual practice a large number of units would be used to provide high definition in the picture. y 'Y The target 54 comprises a transparent support plate 60, that is supported by support rods59, sealed through the wall of envelope 32. 4On one surface of plate 60 are a plurality of spaced apart transparent conductive strips 62 running substantially parallel. Covering the transparent conductive strips 62 in a layer of electroluminescent material 64 which in turn is covered by a layer of ferro-electric material 66. Spaced apart on the layer of ferro-electric material 66 is a plurality of conducting elements 68. The conducting elements 68 are shown in the form of conducting squares positioned adjacent to the space between conducting strips 62. The alternate conductive strips 62 are connected to one side of the secondary of a transformer 20' while the intermediate of the conductive strips 62 are connected to theother side of the secondary of transformer 20.

The target 54, which is sho-wn more clearly in -Figure 3, may be constructed of the following materials and processes. It should be understood' that the thicknesses of the layers'in target 54 are shown greatly exaggerated for simplicity of illustration while in actual practice the layer-s are relatively thin. The transparent support member 60 may be of `a. material such as Pyrex glass` or mica and may be approximately one quarter of an inch in thickness.

Alternatively the glass face plate of envelope 32 may be used as the target support plate. The transparent conductive strips 62, which may be about l mils wide and spaced 5 mils apart, may be of a material such as tin oxide or tin chloride and may be deposited by any well known technique through a suitable mask to provide the separate strips. The electroluminescent layer 64, which may be approximately l mil in thickness, may be any of the well known electroluminescent phosphors such as copper activated zinc sulphide phosphor and may be deposited by any of the known techniques such as settling or silk screening. The ferro-electric layer 66, which may be within the approximate range of 5 to l0 mils in thickness, may be ofra material such as Rochelle salt, barium titanate, barium strontium titanate or the like and may comprise a sintered layer, an array of small crystals, or a single at crystal. The conducting squares 68, which maybe about mils square and spaced apart'about 5 mils, may be of any material such as gold, or silver. The conducting squares 68 may be deposited by evaporating materials through a suitable mask. No specic provision is made in target 54 for leakage resistance, similar to

resistors

38 and 40 shownin Figure l, around the electroluminescent layer 64. The reason for this is that the electroluminescent layer 64 will have a certain amount of leakage resistance. If this resistance is too high, the electroluminescent phosphor may be mixed with a conducting powder such as line carbon particles or the like.

The operation of the target 54 is substantially the same as that of a plurality of the elemental units shown in Figure l. As was described in connection with Figure l the transformer 20' appliesan alternating voltage in a circuit extending from a conducting strip 62 through the electroluminescent layer 64, through the ferro-electric layer 66 to a conducting square 68, back through the ferro-electric layer 66 and the electroluminescent layer 64 to an adjacent conducting stripl 62. This alternating voltage produces an alternating current from a strip 62 through the layers to a conducting square 68 back through the layers to the adjacent transparent conductive strip 62. Thus, current is conducted transversely, i.e. in the direction kindicated by dotted lines 69, through the target 54. It should be understood that the various layers of material in target 54 are shown as being greatly enlarged for purposes of illustration and in actual fact these layers are relatively thin. Due to this thinness, there is substantially no charge conducted between adjacent transparent conductive strips laterally through they insulating electroluminescent layer 64. Ifthere should be a noticeable amount of charge conducted laterally between adjacent strips 62, the area between the strips 62 may be filled with a non-luminescent insulating material (not shown) such as glass.

By means of the electron beam 53 the potential of the conductingV squares, i.e. corresponding to point 42 in Figure l, can be controlled or varied. Thus, the reactance of the ferro-electric layer 66 is varied by the electron beam 53. Dueto the change in the impedance across the ferroelectric layer 66 the light emitted by the electroluminescent layer 64 in the areas struck by the beam 53 is correspondingly changed in the manner described above for the device of Figure 1.

During tube operation, with potentials such as those shown in Figure 2 are applied tothe tube,vthe electron beam 53 is scanned over the target 54. The scanning of beam 53 will drive the scanned surface of target 54 substantially to the potential of the collector screen 56 by secondary emission. With the collector screen S6 at zero or ground potential, i.e. no signal applied, the beam 53 drives the exposed surface of target 54 to an equilibrium potential of approximately zero or ground. With this zero potential applied to all of the elemental units;across the target 54, i.e.'to all of the points 42, the potential drop of the alternating current source is 'substantially across the electroluminescent layer 64 only, because the impedance of the vferro-electric layer 66 is low and light is produced in all areas of the target.V When input signals are applied through capacitor 71 to the collector screen 56, a charge is established by secondary emission on the areas of the target S4 that are struck by the beam 53. The amount of charge established depends upon the mag'- nitude of the input signal applied to the collector screen 56 because the amount of secondary emission depends upon the signal applied to the screen 56. The polarity of the signal may be either positive or negative with respect to ground. .When a charge pattern is developed on the elemental areas of target 54, the ferro-electric layer 66 is biased with a corresponding variation in reactance, in these elemental areas. Due to the change in impedance of the ferro-electric layer, more of the voltage from the alternating current source is applied across -thc ferroelectric layer 66 in the excited areas, and the light from the electroluminescent layer is decreased in these areas of the target S4. As the potential applied to points 42 by the beam 53 is increased, the impedance of the ferro-electric layer is increased, and the light from the electro'- luminescent layer is decreased. This type of charging is the writing of a black picture, with intermediate shades, on a white background. A separate erasing process is not necessary in this method of operation because the writing of a subsequent picture erases a previous picture.

When it is desired to write a white picture on a black background the collector screen 56 is biased with no input signal applied, either positively or negatively `with respect to ground. The biasing potential is such that, r i711 the absence of input signals, the electroluminescent layer does not produce light. When signals are applied, the scanned surface of target 54 is driven toward ground potential and the impedance of ferroelectric layer is decreased to the point where the electroluminescent layer 64 produces light. This method of operation also produces intermediate shades and is a writing of white information on a black background.

The information that is written by any of the methods described above is stored for a period of time determined primarily by the leakage of the ferro-electric layer. This may be several seconds or more. When it is desired to replace the stored information with subsequent new information, the writing process is repeated since the writing of new information erases the old information. Thus, the amount of variation of charge on an elemental unit is the difference between the input'signal and the charge on the target 54.

The writing of information may also be done by a nonequilibrium process with input signals applied to the grid of the electron gun. Using this method, and assuming that the collector screen 56 is grounded, an unmodulated beam is scanned over the surface of target 54 to erase any previously stored information. When information is to be stored, the collector screen is biased, e.g. 200 volts positive, and the video signal current-modulated beam is scanned over the target. The scanning of a modulated beam drives the target toward collector potential by an amount corresponding to the signals applied to the beam. When it is desired to erase the stored information, the collector screen 56 is connected to ground and the unmodulated beam is scanned over the target to drive all areas of the target to collector potential, i.e. substantially zero. The method of operation described above is a writing of black information on a white background as was explained.

When it is desired to use a non-equilibrium, white on black method of operation, the collector screen 56 is biased for the erasing process and grounded for the writing process.

Storage tubes in accordance with this invention have a high sensitivity in that a relatively small signal voltage is capable of producing a bright signal. Also, the storage tubes in accordance with this invention are capable of reproducing intermediate shades of black and white.

What is claimed is:

1. An evacuated storage tube having a target, said target comprising an electroluminescent phosphor and a ferro-electric element.

2. A storage tube comprising an evacuated envelope, an electron gun in one end of said envelope for producing an electron beam, a target electrode in the path of said beam, said target including an electroluminescent phosphor and a ferro-electric element.

3. An evacuated storage tube having a target, said target comprising a support plate, a plurality of strips of conductive material on said support plate, a layer of electroluminescent phosphor on said strips of conductive material, and a layer of ferro-electric material on said first-named layer.

4. An evacuated storage tube having a target, said target comprising a support member, a plurality of transparent conductive strips on said member, a layer of electroluminescent phosphor on said strips, a layer of ferroelectric material on said phosphor, and a plurality of conducting elements on said material.

5. A storage tube comprising an evacuated envelope, an electron gun for producing an electron beam within. said envelope, a target electrode in the path of said beam, said trget electrode comprising a plurality of spaced apart transparent conductive strips, a layer of electroluminescent phosphor on said strips, a layer of ferro-electric material on said phosphor, and a plurality of conducting elements on said material and on the gun side of said target.

6. A storage tube as in claim 5, further comprising a ne mesh screen electrode adjacent to said target electrode Vand between said electron gunrand'saidrtarget elec-n trode.

7. A cathode ray tube comprising an evacuated envelope, means to produce an electron beam in one end of said envelope, a target in the path of said beam and comprising a plurality of conductive strips, the alternate ones of said conductive strips being electrically connected together, the intermediate ones of said conductive strips being electrically connected together, a layer of electroluminescent phosphor on said conductive strips, a layer of ferro-electric material on said phosphor.

8. A storage tube comprising an evacuated envelope, an electron gun for producing an electron beam in one end of said envelope, a target electrode in the path of said beam and in the other end of said envelope, said target electrode comprising a transparent support plate, a plurality of transparent conductive strips spaced apart on the surface of said support plate toward said electron gun, the alternate ones of said conductive strips being electrically connected together and being adapted to be connected to one terminal of a source of alternating current, the intermediate ones of said conductive strips being electrically connected together and being adapted to be connected to another terminal of said source of alternating current, a layer of electroluminescent phosphor on said conductive strips, a layer of ferro-electric material on said phosphor, a plurality of conductive squares on said material, said conductive squares being positioned substantially over the space between said conductive strips, and a line mesh screen electrode between said target electrode and said electron gun and within said envelope.

References Cited in the file of this patent UNITED STATES PATENTS 2,728,815 Kalfaian Dec. 27, 1955 2,768,310 Kazan et al. Oct. 23, 1956 2,793,288 Pulvari May 21, 1957 FOREIGN PATENTS 157,101 Australia June 16, 1954 OTHER REFERENCES Eckert: A Survey of Digital Computer Memory Systems, I.R.E. Proc., October 1953, page 1403.