US3825791A

US3825791A - Field-effect storage tube

Info

Publication number: US3825791A
Application number: US00267878A
Authority: US
Inventors: B Kazan
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1972-06-30
Filing date: 1972-06-30
Publication date: 1974-07-23
Anticipated expiration: 1991-07-23

Abstract

A field-effect storage cathode ray tube with layer of electroluminescent phosphor external to the tube to allow removal and replacement thereof. The inner surface of the tube faceplace is contacted with a conductive mesh. A layer of semicondutor then contacts the exposed inner surface of the faceplate in the mesh openings and a layer of insulator contacts the layer of semiconductor. An array of conductive pins extends through the faceplate from the layer of phosphor in contact with its outer surface to the semiconductor within the respective mesh openings. A charge pattern written on the layer of insulator acts to vary local conductivity in the semiconductor and thus vary alternating current flow through local pins to cause a pattern of light emission from the phosphor corresponding to the charge pattern.

Description

11 ited Etates Kazan atet [191 FIELD-EFFECT STORAGE TUBE [75] Inventor: Benjamin Kazan, Bedford Hills,

22 Filed: June 30,1972 21 Appl. No.: 267,878

[52] US. Cl......313/398, 313/329} 315/12, 313/400 [51] int. Cl H01j 31/08, HOlj 29/08 [58] Field of Search 313/68 D [56] References Cited UNITED STATES PATENTS 3/1950 Chilowsky ..313/169'TV 11/1957 Kalfaian ,Euly 23, 1974 3,644,741 2/1972 Ovshinsky 250/213 R Primary ExaminerRobert Sega] Attorney, Agent, or Firm-John A. Jordan [57] ABSTRACT A field-effect storage cathode ray tube with layer of electroluminescent phosphor external to the tube to allow removal and replacement thereof. The inner surface of the tube faceplace is contacted with a conductive mesh. A layer of semicondutor then contacts the exposed inner surface of the faceplate in the mesh openings and a layer of insulator contacts the layer of semiconductor. An array of conductive pins extends through the faceplate from the layer of phosphor in contact with its outer surface to the semiconductor within the respective mesh openings. A charge pattern written on the layer of insulator acts to vary local conductivity in the semiconductor and thus vary alternating current flow through local pinsto cause a pattern of light emission from the phosphor corresponding to the charge pattern.

6 Claims, 2 Drawing Figures 1 FIELD-EFFECT STORAGE TUBE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to electronic storage and display devices, and more particularly, to cathode ray electronic storage and display tubes using fieldeffect conductivity control and a replaceable electroluminescent phosphor output medium.

2. Description of the Prior Art Field-effect cathode ray storage tubes are known, in general, in the prior art. Representative of the prior art teachings, in this area of storage technology, are those of Kazan and Winslow, in their article entitled Viewing Storage Tubes Based Upon Field-effect Conductivity Control, appearing in the 1968' Proceeding of IEEE, Vol. 56, pp. 1716-1717 Typically, storage and I display tubes based upon field-effect conductivity control utilize a charge storage layer in contact with a semiconductor layer for controlling, at discrete points, the illumination of electroluminescent phosphor. However, one of the major difficulties encountered in such arrangements, resides in the fact that the effective phosphor lifetime is short. Thus, as the phosphor ages, its brightness diminishes, and the point is eventually reached whereby the complete tube must be discarded and replaced by a new tube.

Various schemes have been proposed, in general, in the prior art technology of cathode ray display tubes to overcome the problem of phosphor deterioration and resultant need for complete tube replacement. In the main, these efforts have been directed. toward replacing the phosphor with a material which exhibits a longer lifetime. For example, efforts have been made to employ glow-discharge gas arrangements whereby the relatively long-lifetime gas is housed in an array of separate chambers, external to the cathode ray tube (CRT). In accordance with such an arrangement, an electron beam is employed to scan the inner surface of the CRT 1 to ignite, via conductors, the gas at the discrete points,

in the separate chambers. Exemplary of such arrangements, is that described by D.M. l-Iart in an article entitled, Gas-Discharge Display Device, appearing in the IBM Technical Disclosure Bulletin, Vol. 12, No. 12, May 1970.

Likewise, viewing storage tubes based upon fieldeffect conductivity control, in combination with a relatively long-lifetime glow-discharge gas, are known. Such an arrangement has been described in applicants co-pending application Ser. No. 265018, filed June 21,

1972, and assigned to the assignee of the present inventron.

One of the difficulties with viewing storage tubes employing glow-discharge gas,-resides in their costliness. In addition, although the glow-discharge process in a gas fundamentally allows obtaining a long lifetime display medium, in practice, due to sputtering and other effects, the effective lifetime and usefulness may be limited. Accordingly, as with the case where electroluminescent phosphor is employed with viewing storage tubes, at the expiration of the effective life of the display medium, the complete tube must be replaced. However, it is clear that in such instances, the major portion of the viewing storage tube is still useful. Thus, it is evident that it is quite'advantageous and desirable to be able to provide an arrangement whereby the display medium is replaceable. Since an electroluminescent phosphor layer is simple in form and low in cost, it provides a particularly desirable replaceable display medium.

' .Although electroluminescent display devices exist in the prior art in a variety of types and forms, electroliuminescent viewing storage tubes based upon fieldeffect conductivity control, with replaceable electroluminescent phosphor, have not heretofor been achieved. Exemplary of the variety and types of electroluminescent display devices, in general, existing in the prior art are those described by Frank] in U.S. Pat. No. 3,235,736; Logan in U.S. Pat. No. 3,290,537; Chaberski in U.S. Pat. No. 3,385,992; and Dixon, Jr., et al, in U.S. Pat. No. 3,517,245.

SUMMARY OF THE INVENTION- In accordance with the principles of the present invention, an improved viewing storage CRT is obtained by providing an arrangement whereby the display medium may be. made to operate external to the tube, so that the medium may readily by replaced by a new medium, upon the expiration of the life thereof. More particularly, in accordance with the principles of the present invention, an improved viewing storage CRT is provided, whereby field-effect conductivity controlis utilized within the tube and made to selectively control electroluminescence external to the tube. In accordance with such. an arrangement, the electroluminescent phosphor display medium, which is external to the CRT, is readily replaceable at low cost,'and yet provides effective viewing with a simple design.

To achieve this end, a CRT is arranged so that its face plate has, deposited upon the inner surface thereof, a conductive grid or. mesh pattern. Deposited upon the conductive grid or mesh pattern, and upon the inner surface of the faceplate within the grid or mesh openings, is a'layer of semiconductor material. The layer of semiconductor material has deposited thereupon, a layer of insulating material. An array of conductive pinsgxtend from the outer surface of the faceplate to the semiconductor material within the respe ctive grid or. mesh openings, on the inner surface thereof. Each pin of the array terminates at the outer surface, with a conductive cap. An electroluminescent phosphor display medium is contacted to the conductive caps with an adhesive which permits subsequent removal and replacement of the medium. A charge storage pattern, written upon the layer of insulating material, acts to control local conductivity in the layer of semiconductor material, which in turn acts to control the voltage locally applied across the external electroluminescent layer, to thereby provide a visible pattern, in accordance with the written charge pattern.

It is, therefore, an object of the present invention to provide an improved storage and display tube.

It is further-object of the present invention to provide an improved viewing storage tube based upon fieldeffect conductivity control.

It is yet a further object of the present invention to provide a field-effect viewing storage tube, with a replaceable viewing medium.

It is yet still a further object of the present invention to provide a' viewing storage tube based upon fieldeffect conductivity control and electroluminescence, whereby the electroluminescent material thereof is readily replaceable.

' It is yet still a further object of the present invention to provide an improved field-effect storage and display tube which is effective in performance, and low in cost.

It is another object of the present invention to provide a viewing storage tube which employs field-effect conductivity control internal to the tube, and controlled electroluminescence external to the tube.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiment of the invention as illustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a cross-sectional view of the field-effect type storage tube, with replaceable electroluminescent phosphor output, in accordance with the principles of the present invention.

FIG. 1A shows an enlarged cross-sectional portion of the layers of materials employed at the face plate, as shown in the cross-sectional view of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 there is shown an embodied arrangement of the field-effect viewing storage tube with replaceable electroluminescent layer, in accordance with the principles of the present invention. The overall configuration of the storage tube,-it can be seen is,in general, analagous to any of the variety of conventional CRT- type storage and display devices heretofor employed in the prior art. Typically, the faceplate 1 and envelope 3 of the tube may be made of glass or ceramic. The high energy electron writing gun, shown at 5, comprises a conventional configuration whereby a charge pattern may be selectively written upon an appropriate surface. In particular, it can be seen in the arrangement shown that electron source 7 acts to emit electrons through focusing element 9, and the field created by the vertical deflection plates 11 and 13. As is well known to those skilled in the art, deflection plates 11 and 13 act to control the vertical position of the electron beam. For the sake of simplicity, horizontal deflection plates have not been shown. However, as is understood by those skilled in the art, the omitted pair of horizontal deflection plates acts to control the horizontal position of the electron beam. v

The inner surface of faceplate 1 has in contact therewith a grid or mesh pattern of narrow conductive lines 15. It is clear, that this grid or mesh pattern may first be fabricated and then affixed to the inner surface of plate 1. Alternatively, the lines 15 of the grid or mesh pattern maybe fabricated by depositing a layer of con 27 of the array of conductive pins to be described here- 7 inafter. With such an arrangement, the conductive lines would form a grid pattern which is positioned upon the inner surface of glass plate 1 so that the respeeti-vegrid lines are between respective rowsof conduqtivepins.

However, in the preferred mode, lines 15 would be arranged both horizontally and vertically, so as to form a conductive mesh pattern. Such a mesh pattern may be positioned so that the respective pins 27 are positioned at the approximate geometric center of the respective mesh openings. The mesh is maintained at ground potential, as shown, by ground connection wire 19. In this regard, it should be noted that wire 19 has been shown as extending up through the cross-section to commonly connect each conductive line. However, it should be understood that this wire is shown merely to schematically represent the fact that all conductive lines are electrically connected to ground. In actual fact, such wire would not exist as shown. For example, if a conductive mesh were employed, it is clear that the wire would only run to some point on the periphery thereof.

After the mesh pattern of narrow conductive lines 15 has been formed upon the inner surface of faceplate 1, a layer of semiconductor material 17 is deposited upon the narrowconductive lines of the mesh pattern, and

upon the exposed inner surface of faceplate 1, in the openings of the mesh pattern. This is more clearly shown in FIG. 1A. In this regard, it can be seen that FIG. 1A provides a blown-up view of the materials employed in contact with the faceplate, taken, for example, at 1A, in FIG. 1. After layer of semiconductor 17 has been formed, a thin layer 21 of insulating material is deposited thereon. It is clear that the insulating material of layer 21 may comprise any of the variety of conventional insulators. Likewise, it is clear that layer 17 of semiconductor material and layer 21 of insulating material may be deposited by any of a variety of conventional deposition techniques. Typically, layer of semiconductor material 17 may be fabricated, for example, from any one of CdO, ZnO, CdS or CdSe, and layer 21 of insulating material may be fabricated, for example, from any one of SiO, SiO or MgF Finally, collector grid 23 is positioned adjacent the thininsulator layer 21. As shown, the cross-section of the collector grid is depicted as a series of circles. It is to be understood, however, that these circles represent the main conductive members or elements (e.g., wires) of the collector grid, all of which members are conductively coupled together in a grid pattern. As can be seen, collector grid 23 is connected to input signal source 25. As is evident to those skilled in the art, signal source 25 acts to control or modulate the potential of surface elements of the insulator, creating a stored charge pattern in accordance with the time-varying input signal. I

As shown, the array of conductive pins 27 is arranged -to extend from the outer surface of faceplate 1 to the layer of semiconductor material 17, in the vicinity of the central portion of the respective mesh openings of the mesh pattern of conducting lines 15. In this regard, it can be seen that the array of pins respectively match, on a one-to-one basis, the array of mesh openings in the mesh pattern, whereby each conductive pin meets the semiconductor material at the approximate geometric center of a corresponding mesh opening. It is clear, however, that more than one pin may be associated with each mesh'opening. However, in the preferred embodiment, a one-to-one correspondence between conductive pin and mesh opening exists. As can be seen, the outer end-of each conductive pin'te-rminates on the outer surface of faceplate 1 with a conductive cap 29.

I The removable electroluminescent phosphor output display medium 31 comprises an outer layer 33 of transparent insulator such as MYLAR, coated with a in a binder, for example, to form a layer 37 about 2 mils thick. In this regard, any of the variety of well known electroluminescent phosphorpowders' and binders may be employed. As is evident, the MYLARsheet is employed for support and insulating protection. Accordingly, other transparent insulating materials may readily be employed for this purpose. As depicted in FIG. 1, electroluminescent phosphor display medium 31 is intended to be readily removable Thus, the medium may be adheredto the outer surface of the tube faceplate and conductive caps thereon by any suitable insupattern of narrow conductive lines 15 connected to ground via conductor 19 as shown, and withv an AC voltage maintained on the inner surface of transparent MYLAR 33 via the outer transparent conductive layer 35 and AC source 39, then, an AC voltage is developed between these inner conductive lines 15 and the outer transparent conductive layer 35. It is clear that the amount of current drawn between a particular one of the conductive lines 15, and conductive layer 35 will depend upon the local conductivity in semiconductor layer 17, the localconductivity of the latter varying in accordance with the polarity and density of the local charge stored on insulator layer 21. 7

Thus, where a high density of negative charge exists locally in the neighborhood of a given mesh opening, the conductivity of the corresponding area ofsemicon- 21. After a charge pattern has been written upon insulator layer 21, it will be retained thereat for a considerable time, depending on the resistivity of the insulator. Where it is desired to maintain the image for an even longer time, electron gun 5 may be caused to intermittently refresh the charge pattern on the insulator layer. Typically, AC source 39 may comprise a 300 volt source, at lkHz. However, it is clear that these values are not critical.

As will be recognized by those skilled in the art, with continued operation of the electroluminescent display medium, the phosphor brightnessdrops. In accordance with the principles of the present invention, when the phosphor brightness is no longer adequate, the used electroluminescent phosphor display medium 31 may be removed from the tube face, and a fresh layer placed in contact with the faceplate. Thus, the operation of the display tube can readily be restored to its original effectiveness.

'It can 'be seen that replaceable electroluminescent display medium 31 basically comprises a phosphorcoated MYLAR sheet, with 'interposing transparent conductor. In this regard, any of a variety of transparent conductors may be employed for this purpose. Electroluminescent phosphor layer 37 may comprise an electroluminescent phosphor, in powder form, imbedded in an organic dielectric binder. For example,

' layer 37 may comprise Cu doped ZnS uniformly mixed ductor (assumed, for this example, to be p-type) within this mesh opening is increased, and the current flow between the mesh (which is grounded) and transparent conductor 35 increases through the local pin. This increasein current flow causes an increase in the local alternating field across electroluminescent layer 37, thereby causing increasing local luminescence thereat.

layer 21 via electron gun 5, and a corresponding pattern of luminescence is created in electroluminescent layer 37, of the removable electroluminescent output display medium 31. It is clear that conventionalgray scale operation is thereby achieved, since the magnitude of the current conducted locally through the pins and electroluminescent layer 37 varies as a function of the local charge density written upon insulator layer made of DC phosphor material, whereby electroluminescence occurs as a result of the application of a DC potential across the phosphor. In such an arrangement it is clear that AC source '39 would be replacedby an appropriate DCsource. Thus, in accordance with the principles of the present invention, any of a'variety of electroluminescent phosphors may be employed.

In any event, it should .be understood that regardless of the specific materials employed, the arrangement basically comprises a phosphor-coated transparent sheet of insulating material, and accordingly, in general, can be produced at relatively low cost. Thus, the cost of the storage-display device in accordance with the principles of the present invention, is'determined mainly by the cost of the remaining tube structure.

In a typical design configuration, the tube structure may comprise an arrangement having a 10 inch diameter faceplate A tube with a 10 inch diameter faceplate, having an array of conducting pins or wires extending therethrough on 10 mil centers, would provide a resolution of about 1,000 lines, adequate for most display purposes.

While the invention has been particularly shown and described with reference to' a preferred embodiment and variations thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

We claim:

1. In a viewing storage tube using field-effect conductivity control to ,locally control the conductivity of semiconductor material therein in response to selected charge patterns created by the electron beam of an electron write gun, the improvement comprising:

an array of conductive pins extending through said W tube faceplate means with each pin of said array of conductive pins terminating at the outer surface of said faceplate means with a conductive cap, each of the said conductive pins of said array of conductive pins extending from points contacting said layer of semiconductor material between respective ones of said grid lines to its associated conductive cap on the said outer surface of said faceplate means;

display means including a layer of transparent conductor means and a layer including electroluminescent phosphor material with said layer including electroluminescent phosphor material having one side thereof in contact with said layer of transparent conductor means and the other side thereof adhered by an insulating adhesive to said conductive caps such that local electroluminescence may be effected in said electroluminescent phosphor material in accordance with the pattern of local conduc tivity in said layer of semiconductor material; and

means for making electrical contact to said array of conducting lines and said layer of transparent conducor means.

2. The viewing storage tube as set forth in claim 1 wherein said charge storage means includes means to selectively modulate the density of said selected charge patterns so that the said local conductivity of said layer of semiconductor material varies as a function of said density to thereby provide output illumination with gray scale characteristics.

3, The viewing storage tube as set forth in claim 2 wherein the said local conductivity of said layer of semiconductor material increases with charge density.

4. The viewing storage tube as set forth in claim 2 wherein the said local conductivity of said layer of semiconductor material decreases with charge density.

spective openings of said conductive mesh pattern.

Claims

1. In a viewing storage tube using field-effect conductivity control to locally control the conductivity of semiconductor material therein in response to selected charge patterns created by the electron beam of an electron write gun, the improvement comprising: tube faceplate means having an outer surface and an inner surface with said inner surface having an array of conducting lines in contact therewith and arranged to form a grid pattern of conducting lines on said inner surface; a layer of semiconductor material of a single conductivity type in contact with both the lines of said array of conducting lines and the said inner surface of said faceplate means between the lines of said array of conducting lines; a charge storage means disposed adjacent to said layer of semiconductor material for producing in response to said electron beam selected charge patterns which vary the local conductivity of the adjacent layer of semiconductor material in accordance with said charge pattern; an array of conductive pins extending through said tube faceplate means with each pin of said array of conductive pins terminating at the outer surface of said faceplate means with a conductive cap, each of the said conductive pins of said array of conductive pins extending from points contacting said layer of semiconductor material between respective ones of said grid lines to its associated conductive cap on the said outer surface of said faceplate means; display means including a layer of transparent conductor means and a layer including electroluminescent phosphor material with said layer including electroluminescent phosphor material having one side thereof in contact with said layer of transparent conductor means and the other side thereof adhered by an insulating adhesive to said conductive caps such that local electroluminescence may be effected in said electroluminescent phosphor material in accordance with the pattern of local conductivity in said layer of semiconductor material; and means for making electrical contact to said array of conducting lines and said layer of transparent conducor means.

3. The viewing storage tube as set forth in claim 2 wherein the said local conductivity of said layer of semiconductor material increases with charge density.

5. The viewing storage tube as set forth in claim 2 wherein the said array of conducting lines comprises an array of horizontal and vertical conducting lines which conductively cross one another so as to form a conductive mesh pattern.

6. The viewing storage tube as set forth in claim 5 wherein single ones of the respective pins of said array of conductive pins contact said layer of semiconductor material within different ones of the openings of the respective openings of said conductive mesh pattern.