US3539862A

US3539862A - Dual conductor storage panel

Info

Publication number: US3539862A
Application number: US722285A
Authority: US
Inventors: Benjamin Kazan
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1968-04-18
Filing date: 1968-04-18
Publication date: 1970-11-10
Anticipated expiration: 1987-11-10
Also published as: BR6905983D0; DE1808238B2; GB1235310A; FR1591040A; DE1808238C3; BE723721A; JPS494999B1; CH493930A; NL150616B; SE345341B; DE1808238A1; NL6816080A; ES360366A1

Description

United States Patent O 3,539,862 DUAL CONDUCTOR STORAGE PANEL Benjamin Kazan, Pasadena, Calif., assignor to Xerox Corporation, Rochester, NX., a corporation of New York Filed Apr. i8, 1968, Ser. No. 722,285 int. Cl. Htlb `7/00; Hlj 1/62 US. Cl. 315-169 35 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to electroluminescent devices and, in particular, to electroluminescent devices of the type adapted to store electrical signals. More particularly, this invention relates to an electroluminescent device of the storage type wherein an optical input image causes the formation of an electrostatic charge pattern on the surface of a field effect semiconductor material, said field effect semiconductor material operating to regulate the flow of current through the storage device and thereby regulate the output image.

At present, a variety of solid state imaging devices are known but have not received significant utilization because of the practical problems encountered in their production and operation. The storage action of these devices depends on one of several different phenomena including the slow decay of conductivity after excitation of a photoconductive material, the hysteresis effect in photoconductors, and optical feedback. Some of the factors operating against the practical use of such solid state imaging devices include low sensitivity to input radiation, low light output, poor or no half-tones, difculty in providing image erasure, and a relatively low ratio of output light to background light.

For example, one type of solid state imaging device involves a display panel consisting of a layer of variable impedance material in series with a layer of electroluminescent material as described in the patents to Benjamin Kazan U.S. No. 2,768,310 issued Oct. 23, 1956 and U.S. No. 2,949,527 issued Aug. 16, 1960. As described therein, the image is produced by the increase in conductivity of the portions of the variable impedance material, in this instance, a photoconductive material, upon which incident radiation impinges. Such conductivity increase produces a corresponding luminescence in the adjoining portion of the electroluminescent material.

In copending application Serial No. 582,856 filed Sept. 29, 1966, a continuation-in-part application of Serial No. 514,860 filed Dec. 20, 1965, and now abandoned, there is disclosed a new and improved electroluminescent storage device which is not subject to defects which plague the operation of prior known storage panels. The storage device involves a display panel comprising a plurality of spaced electrodes on one surface of a supporting substrate, a layer of electroluminescent material overlying the plurality of electrodes and forming a part of the electrical connection between the electrodes, and a layer of a field effect semiconductor material overlying the layer of electroluminescent material and forming a succeeding part of the electrical connection between the electrodes, the panel having a charge-retaining surice face adapted to store an electrostatic charge pattern thereon. Such a panel is used in combination with means for forming and/or depositing a charge pattern on the chargeretaining surface. In operation, an alternating current voltage is applied between the spaced electrodes which is sufcient to induce electroluminescence when the field effect semiconductor is at its low impedance state. It was found that the deposition of an electrostatic charge on the charge-retaining surface of the display panel could be used to control the flow of current from electrode to electrode. Deposition of electrostatic charge increases the impedance of the field effect semiconductor thereby reducing or interrupting the flow of current in adjacent areas. Reduction of current iiow causes a corresponding reduction in light output from the electroluminescent layer resulting in a half-toned response. If the current is lowered below that which is sufcient to induce electroluminescence, luminescence will not occur and that particular portion of the storage device will appear dark. Conversely, the impedance is lowered and current flow increased as the charges are neutralized or removed from the surface thereby resulting in the restoration of light output in adjacent areas. By selectively placing or modifying a charge pattern on the surface of the display panel an image can Ibe produced and stored for long periods of time.

Additionally, the impedance of the field effect semiconductor layer can be lowered and current flow increased if charges of a proper polarity are placed on the charge retaining surface. Thus, if current iiow is initially insuflicient to cause luminescence, current flow can be increased by depositing such charges of proper polarity whereby light output can be obtained from adjacent portions of the storage device. Current flow between electrodes can be decreased by neutralizing or eliminating the surface charge and, as with the above, if olw is decreased below a certain threshold value, light output will be terminated. By operating in this manner, images can be produced and stored for long periods of time.

While the storage panel described in the aforementioned copending applications is not subject to the disadvanta-ges of prior storage devices, it is subject to a major drawback which limits the practical application thereof. When employing electrode strips of transparent conductive tin oxide (commercially available from Pittsburgh Plate Glass Company of Pittsburgh, Pa. under the trademark NESA glass) so that the output of the panel can be viewed from the side opposite the input side, only relatively small panels, for example l to 2 feet square, can be produced because of the electrical resistance of the conductive electrode strips. That is, since the NESA strips have a limited surface conductivity, there is a practical limit to the length of the conducting lines of a given width deposited on the supporting substrate through which current will flow at desirable operable current levels. The use of more conductive electrodes is not feasible since any substantial reduction of the resistance causes a serious drop in light transmission of the NESA electrode material. Similar problems arise if evaporated metal lms are used for the electrode strips. In addition to this, the fabrication of large area panels places severe requirements on the perfection of the electrode strips. Any surface scratches or other defects, such as broken lines, render adjacent portions of the panel inoperative. To fabricate a. panel several feet or more in size without such defects would require impractical degrees of perfection in both materials and fabrication techniques and would result in a panel having a prohibitively high production cost.

OBJECTS OF THE INVENTION It is, therefore, an object of this invention to provide a novel electroluminescent storage device.

It is an object of this invention to provide an improved electroluminescent storage device not subject to the aforementioned deficiency in that relatively large panels can be easily fabricated.

A further object of this invention is to provide a relatively large storage device having good output brightness, long storage, and good halfatone response along with simplicity of image production and rapid erasure.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed disclosure of specific exemplary embodiments.

SUMMARY OF' THE INVENTION In its broadest aspects, the above and still further objects may be accomplished in accordance with the present invention by providing a solid state storage panel comprising a plurality of narrow opaque conductors disposed on the surface of a supporting substrate, a conductive strip overlying each opaque conductor, a segment of electroluminescent material overlying the plurality of conductive strips, a segment of insulating material positioned between adjacent conductive strips and segments of electroluminescent material, and a layer of a field effect semiconductor material overlying the segments of electroluminescent material and insulating material, said storage panel having a surface capable of retaining an electrostatic charge pattern thereon, said charge-retaining surface not being a portion of said supporting substrate.

In an alternative embodiment, the solid state storage panel comprises a plurality of narow opaque conductors disposed on one surface of a supporting substrate, a conductive strip overlying each opaque conductor, a segment of insulating material positioned between adjacent conductive strips, a layer of electroluminescent material overlying the plurality of conductive strips and segments of insulating material, and a layer of a field effect semiconductor material overlying the layer of electroluminescent material, said storage panel having a surface capable of retaining an electrostatic charge pattern thereon, said charge-retaining surface not being a portion of said supporting substrate. This alternative embodiment differs from the preceding embodiment in that it has a continuous layer of electroluminescent material whereas the preceding embodiment has segments of electroluminescent material separated from each other by segments of insulating material. In this, as well as the preceding embodiment, it is presently preferred to have each conductive strip contacting that portion of each opaque conductor not in contact With the supporting substrate.

At present, the embodiment disclosed in the second preceding paragraph is preferred because imaging current must, during image output, flow through the field effect semiconductor layer. This affords maximum current control through charge deposition and/or neutralization. This is not necessarily true with the embodiment of the preceding paragraph wherein, as shown in FIG. 2, there is substantial current flow through the electroluminescent layer. Such current flow is not as subject to external control, through charge deposition and/or neutralization, as that which takes place through the field effect semiconductor layer. Current ow through the electroluminescent layer increases background light and, therefore, reduces contrast between image and background. As this is undesirable, it is corrected by utilizing the structure of FIG. 1 wherein maximum control of current flow can be achieved.

The opaque conductors provide the necessary conductivity along the electrode lines or strips. The conductivity of the conductive strips need only be sufficient to carry current from the central opaque conductor to the edge of the conductive strip. Therefore, a conductive strip whose conductivity is many orders of magnitude less than the electrode strips as shown in the aforementioned pending application can be used. Conuductive materials for these electrode strips having surface resistivities less than about 4 105 ohms/ square centimeter have been found suitable for use in the fabrication of the herein disclosed panel. Such panels are no longer subject to the previously mentioned deficiencies since the opaque conductors can be easily made with sufficient mechanical strength and are not easily scratched or damaged during production. Further, their high conductivity permits production of panels of arbitrarily large size since adequate current flow can be maintained at large distances from the potential source.

Suitable opaque conductors include thin copper wires, silver paint in a plastic binder, etc. When using a conductive paint, the thin conductive lines can be put down in the pattern desired or the entire substrate surface can be covered and then intermediate portions of the conductive paint removed.

If it is deisred to view the storage device from the side opposite the field effect semiconductor side, then the supporting substrate and the conductive strips should be lighttransmitting. Optionally, the segments of insulating material may be lightetransmitting also. A suitable substrateelectrode combination is optically transparent glass having thin opaque wires or silver paint strips disposed thereon with overlying optically transparent conductive strips of tin oxide or evaporated gold. For example, the transparent conductive strips may be produced by applying tin oXide produced by the vaporous reaction of stannic acid, water and methanal through a suitable mask.

The structure herein disclosed is particularly useful for the fabrication of storage panels on plastic substrates, such as Mylan which are of arbitrarily large size and can be fiexible if desired. Since suitable techniques for producing NESA (tin oxide) coatings on plastic are not available, transparent conducting strips such as powderplastic mixtures of zinc oxide or indium oxide (In2O3) in a transparent, electrically insulating resinous binder, such as an epoxy resin are suitable for deposition on the plastic substrate. Such a mixture may include about 60% to about 95% conductive powder. Depending upon the materials utilized, an optimum preferred range is about to about conductive powder. These mixtures need not be vacuum deposited on the supporting substrate Wherefore the entire plastic-supported panel can be fabricated without the need for vacuum deposition techniques and equipment.

If desired, the storage panel can be viewed from the field effect semiconductor side of the unit. In such a situation, the panel can be fabricated on an opaque insulating base using opaque conductive strips. The field effect semiconductor layer, however, should be transparent to the light emitted from the electroluminescent layer.

The storage panel is used in combination with means for depositing a charge pattern on the charge-retaining surface. At least one portion of the electroluminescent material forms part of the electrical connection between adjacent electrodes (an electrode being defined as thin opaque conductor having an overlyingr conductive strip) with the successive part of the electrical connection being formed by a portion of the field effect semiconductor material. That is, current flows from one electrode through a portion of the electroluminescent material, a portion of the eld effect semiconductor material and then through a different portion of the electroluminescent material to an adjacent electrode. By formation and/or modification of an electrostatic charge pattern on the charge-retaining surface, a corresponding output image can be produced and stored on the electroluminescent device.

As used in this application, the term field effect semiconductor refers to a material capable of conducting current through the body thereof but which has the conductance thereof modified by applying an electric field perpendicular to the current flow thereby creating a region which effectively changes the conducting cross-section of the semiconducting material or changes the conductivity of the material itself. In the preferred embodiment, the field effect semiconductor material should be capable of retaining for substantial periods of time an electrostatic charge pattern on its surface and conducting current through the body thereof without substantially altering the surface charge pattern. When a single material has both of these physical properties it will be referred to as a storing field effect semiconductor. That is, the storing field effect semiconductor is capable of retaining an electrostatic charge pattern on its surface which then produces the perpendicular electric field for modifying the conductance of the semiconductor material. Suitable materials exhibiting this combination of characteristics include zinc oxide, lead oxide, and cadmium oxide.

Where the field effect semconductor material is a storing field effect semiconductor as herein defined, the charge-retaining surface of the storage panel is the exposed surface of the field effect semi-conductor. However, where the field effect semiconductor material is incapable of retaining an electrostatic charge pattern on its exposed surface for the desired period of time, a thin electrically insulating layer is disposed thereover and the exposed surface thereof functions as the charge-retaining surface. Thus, many semiconductors which exhibit the field eect phenomena can be adapted to the practice of this invention even though they are, initially, incapable of retaining an electrostatic charge pattern on their surface for the desired period of time. Typical semiconductors exhibiting the field effect phenomena which can be so modified include cadmium sulfide, zinc sulfide, cadmium selenide, etc. Additionally, zinc oxide and the other storing field effect semiconductors can have an insulating layer deposited thereon if desired. Alternatively, a barrier layer can be produced along the outer surface of the semiconductor material by suitably doping the semiconductor to provide a p-n junction. The junction will act as a blocking layer preventing the passage of surface charge into the underlying material.

For brevity, all forms of the field effect semiconducting material will be referred to herein as the semiconducting material or the field effect semiconducting material, it being understood that the storage panel has an exterior nonsupporting substrate surface which is capable of retaining an electrostatic charge pattern thereon for substantial periods of time.

It is thus apparent that the term field semiconductor has been defined to include single layer materials as well as a two-layered structure wherein the semiconductor material is modified as stated above. While these materials have been drawn together for purposes of definition, they are not true equivalents for, in many circumstances as will hereinafter be described, they have different modes of operation. More importantly, though the results attained with these different structures may be equivalent from an operational point of view, it should be appreciated that the capability of achieving a desired result with a single material renders that material superior to a second material which must be modified, in a stated manner, to achieve the same result.

In the preferred technique of operation, an alternating current voltage is applied between the spaced electrodes which is sufhcient to induce electroluminescene 'when the semiconductor material is in low impedance state. It has been found that the deposition and retention of an electrostatic charge on the charge-retaining surface of the electroluminescent panel can be used to control the flow of current from electrode to electrode. Deposition of the electrostatic charge increases the impedance of the semiconductor thereby reducing or interrupting the flow of current in adjacent areas. Reduction of current liow will cause a corresponding reduction in light output from the electroluminescent layer resulting in a halftoned response. If the current is lowered below that which is sufficient to induce electroluminescene, luminescence will not occur and that particular portion of the storage device will appear dark. Conversely, the impedance is lowered and current flow increased as the charges are neutralized or removed from the surface. Accordingly, by selectively placing and maintaining a charge pattern on the surface of the electroluminescent panel an image can be porduced and stored upon the device.

In an alternate technique of operation, an alternating current voltage is applied between the spaced electrodes which is slightly insufficient to induce electroluminescence when the semiconductor material is in its normal impedance state. By forming an electrostaic charge of proper polarity on the charge-retaining surface of the electroluminescent panel the impedance of the semiconductor material can be lowered so that current will ow between spaced electrodes through the electroluminescent layer thereby resulting in light output. Conversely, the impedance is increased and current ow decreased as these charges of proper polarity are neutralized or removed from the charge-retaining surface. Once the impedance increases to a point where the current is lowered below that which is sufficient to induce electroluminescence, luminescence will not occur and that particular portion of the storage -device will appear dark. Thus, images can be produced and stored upon this device by selectively placing and maintaining a charge pattern on the chargeretaining surface.

The polarity of surface charge which will reduce conductivity through the field effect semiconductor layer is the same as the polarity of charges which are preferentially conducted through that layer. That is, an n-type semiconductor will have the conductivity therethrough diminished by the deposition of negative charges ou the chargeretaining surface. Conversely, a p-type semiconductor will have the conductivity therethrough diminished vby the deposition of positive charges on the charge-retaining surface. On the other hand, conductivity may be increased by depositing charges of opposite polarity to the polarity of charges which are preferentially conducted through the semiconductor layer. By manipulating the operating conditions properly, and by depositing charge of opposite polarity to that preferentially carried by the semiconductor layer, the storage panel in adjacent areas can be made to either glow more brightly or to emit light from previously darkened portions.

When it is desired to produce a White picture on a black background, an electorstatic charge is uniformly deposited over the entire charge retention surface. Neutralizing or removing a portion of the charge will cause current flow in adjacent areas thereby resulting in luminescence of the phosphor layer beneath the areas Where charge has been neutralized or removed. A white picture on a black background can also be obtained by depositing a selected electrostatic charge pattern wherein dark background areas correspond to areas of charge deposition. Luminescence of the phosphor layer beneath those areas of the semiconductor layer where no charge resides will produce a white picture on a black background.

When it is desired to have a black picture on a white background, a selected electrostatic charge pattern is placed on the charge retention surface. This results is an increase in the impedance of the semiconductor thereby interrupting the fiow of current in adjacent areas. When current flo'w falls below the level which is sufiicient to induce electroluminescence, that portion of the storage device where the charge resides will appear dark, and a black on white picture will be obtained. Alternatively, a uniform electrostatic charge can be applied to the charge retaining surface and then a portion of the charge corresponding to the white background areas can be removed or neutralized to produce the desired result of a black picture on a white background.

The above optical output can also be achieved by applying an alternating current voltage between the spaced electrodes which is insufficient to induce electroluminescence when the semiconductor material is in its normal impedance state. Deposition of charge of proper polarity will cause a decease in impedance with a corresponding light output in adjacent areas. Whether a black picture on a white background or vice versa results will depend upon the charge deposition and/or removal steps in a manner analogous to that described in the preceding two paragraphs.

BRIEF DESCRIPTION OF THE DRAWINGS The nature of the invention will more easily be understood when it is considered in conjunction with the accompanying drawings of exemplary preferred embodiments of the invention wherein:

FIG. 1 is a cross-sectional schematic illustration of the presently preferred solid state storage panel of the present invention; and

FIG. 2 is a cross-section schematic illustration of an alternate embodiment of the solid state storage panel.

Referring to FIG. 1, there is shown a storage panel having a plurality of thin, opaque, parallel spaced conductors 11 mounted on supporting substrate 12. Overlying each opaque conductor 11 is a strip 13 of conductive material. As shown, these conductive strips 13v are in contact with the entire surface area of opaque conductors 11 not in contact with the supporting substrate 12. Overlying each conductive strip 13 is a segment of eletroluminescent material 14. Electrically isolating each vertical stacking of opaque conductor 11, conductive strip 13 and electroluminescent material segment 14 is an electrically insulating segment 15. The upper surfaces of

segments

14 and 15 are substantially coplanar whereby a field effect semiconductor material layer 16 can be uniformly disposed thereover. Electrical connections 17 are made to electrodes 11 to enable the application of a voltage therebetween. Alternating electrodes are connected to one side of an alternating current potential source 1S with the intermediate electrodes being connected to the other side of the potential source. When the output from the panel is to be viewed on the side opposite the field effect semiconductor side, the supporting substrate 12 and the conductive strips 13 should transmit radiation emitted from the electroluminescent material.

Referring to FIG. 2, there is shown an alternative embodiment of the storage panel of the present invention wherein like numerals are utilized to represent like elements as shown in FIG. 1. The storage panel comprises a plurality of thin, opaque, parallel spaced conductors 11 mounted on a supporting substrate 12. Overlying and partially surrounding each conductor 11 is a strip 13 of conductive material. Each strip 13 is electrically isolated from adjacent strips by segments of electrically insulating material. The upper surfaces of strips 13 and segments 15 are substantially coplanar so that a layer 14 of electroluminescent material can be disposed thereon. A layer of field effect semiconductor material 16 is disposed over the layer 14 of electroluminescent material. The same electrical connections are made as in FIG. 1 and, if the output is to be viewed from the side opposite the field effect semiconductor side, the materials noted in the preceding paragraph should be transparent to the emitted radiation.

In operation, alternating current voltage is maintained between adjacent electrodes. Depending upon the local conductivity of the field effect semiconductor layer, more or less alternating current will follow the path indicated by the dashed lines in FIGS. l and 2 from one electrode to the next. Referring to FIG. l, it can be seen that current fiows from one electrode through the electroluminescent layer, the field effect semiconductor layer and then back through the electroluminescent layer to an adjacent electrode to complete the circuit. When sufficient current fiows through the electroluminescent layer, it emits light in areas adjacent the electrodes between which current fiows.

The operational technique involved includes providing a device such as set forth in the gures having a chargeretaining surface, such as surface 19. As previously indicated, the charge-retaining surface will be (1) the exposed surface of the field effect semiconductor material if it is a storing field effect semiconductor or (2) the exposed surface of a thin electrically insulating layer disposed over the semiconductor material if it is not a storing field effect semiconductor. The electrostatic charge pattern 20 controls the fiow of current between adjacent electrodes. In one mode of operation, the electrostatic charge pattern reduces the conductivity of the field effect semiconductor layer and, if proper operating conditions are established, current fiow between adjacent electrodes is either diminished or entirely prevented. Adjacent portions of the storage device appear dark. Where no charge is deposited, however, current flows without interruption from one electrode to another with resultant light output from adjacent portions of the electroluminescent material.

In the other mode of operation previously discussed, the electrostatic charge pattern increases the conductivity of the field effect semiconductor layer and, once again, if proper operating conditions are established, current fiow between adjacent electrodes is increased under areas of charge deposition. Adjacent portions of the storage panel glow more brightly and/ or begin to emit radiation. Where no charge is deposited, however, current does not fiow from one electrode to the next and adjacent portions of the storage panel remain dark.

The electrostatic charge pattern can be produced on the surface of the electroluminescent device by any suitable means. For example, it is contemplated that optical or electrical means can be utilized to deposit the desired charge pattern.

One manner of producing a charge pattern is by uniformly depositing charge ions on the charge-retaining surface and then dissipating a portion of said ions to form either a positive or a negative of the image to be reproduced. For example, if the field effect semiconductor also has photo-conductive insulating properties, such as is the case with zinc oxide, the uniform electrostatic charge can be deposited by any well known means, including corona discharge. Selective dissipation of a portion of a surface charge can be achieved by exposing only selected portions of the field effect semiconductor material to actinic radiation. The latent electrostatic image which results acts to control current flow between adjacent electrodes.

In contrast to where the storage panel is exposed to a full frame light image, one or more point sources of light can be made to scan the charge-retaining surface. Modulation of the intensity of the input light will result in a corresponding half-tone output image.

Alternatively, means can be provided for initially depositing charge ions in the desired charge pattern. For example, electrostatic charges can be deposited by using the apparatus disclosed by Schwertz in U.S. Pat. No. 3,023,731. Specifically, the recording heads of FIGS. 5 and 7, or the character drum of FIG. 3 of that reference, can be used in the manner as disclosed therein to deposit a selective ionic charge pattern upon the charge-retaining surface of the present storage device. A charge pattern can also be deposited on the charge-retaining surface, for example, by corona charging through a pattern-defining mask. Or, as shown in the aforementioned copending application, the corona charging device of FIG. 8 can be sequentially scanned along vertical and horizontal conductors to cause corona emission at selected junctions and thereby selectively charge portions of an underlying storage panel. A further device for depositing the electrostatic charge pattern comprises one or more corona point sources which can be caused to scan the charge-retaining surface. The simultaneous application of electrical input signals to the corona points with the resultant deposition of electrostatic charge will either produce or modify an image on the electroluminescent storage device. In this embodiment, either the corona point system can be caused to scan back and forth or, in the alternative, the storage device itself can be made to oscillate under one or more corona point sources.

As is apparent, the output from the storage device can be modified by modifying the existing charge pattern stored on the charge-retaining surface. Such modifications include complete neutralization, partial neutralization or addition of new surface charge to the existing charge pattern.

The particular physical characteristics of zinc oxide, lead oxide, and cadmium oxide enable one to store a negative ionic charge pattern on its surface and control current flow through the body thereof by means of said charge pattern without substantially altering the charge pattern. Negative oxygen atoms, such as obtained by corona discharge or the electrostatic discharge disclosed by Schwertz in the aforementioned patent, are particularly suitable for controlling current flow. It has been found, however, that deposition of electron of positive ionic charge patterns may not have controlling effect because the field effect semiconductor will not retain such a charge on its surface. Accordingly, it may be necessary to provide an insulating layer ovei the field effect semiconductor material when one wishes to control current fiow by means of electron of positive ionic charge patterns.

DESCRIPTION OF SPECIFIC EMBODIMENT The following example is given to enable those skilled in the art to more clearly understand and practice the invention. It should not be considered as a limitation upon the scope of the invention but merely as being illustrative thereof.

A Plexiglas (poly methyl methacrylate type polymer) substrate, about six inches square, is first coated with a conductive layer of 90% by weight silver fiake in an epoxy resinous binder. After curing, a portion of the silver coating is removed leaving silver lines mils wide on 50 mil centers ovei the entire surface. A layer of 80% by weight indium oxide (In2O3) in an epoxy binder is then sprayed over the surface to produce a layer about 3 mils thick. After curing, the surface is coated with an electroluminescent Phosphor powder layer having 75% by weight zinc sulfide in an epoxy binder to form another layer about 3 mils thick. After curing, a portion of the indium oxide and the zinc sulfide phosphor layers are removed leaving strips of indium oxide overcoated with zinc sulfide phosphor mils wide on 50-mil centers and centered over the 5-mil silver lines. The spaces left by removing the portions of the indium oxide and zinc sulfide phosphor layers are filled with a clear epoxy resin to produce a substantially flat surface. The surface is then coated with a field effect semiconductor layer having 90% zinc oxide powder in a styrene-butadiene copolymer resin. Finally, the silver lines at the edges of the panel are interdigitally connected into two groups across which the AC supply voltage is connected. In operation, with 600 volts AC applied to the silver-indium oxide electrodes, stored images are obtained with a highlight brightness of about 13 foot-lamberts from the zinc oxide field effect semiconductor side of the panel and a brightness of about ten foot-lamberts from the plastic substrate side of the panel.

The panel of the present invention is used in a manner similar to the panels disclosed in copending application Serial No. 582,856 filed Sept. 29, 1966 which is a continuation-in-part application of Serial No. 514,860 filed Dec. 20, 1965. For example, the herein disclosed panel can be utilized as a target for an evacuated storage tube such as shown in FIG. 9 of Serial No. 582,856, using preferably an inert supporting substrate, such as glass and an inorganic material for the binder of the conductive powder material is utilized. Or the panel can be fabricated as shown therein. Accordingly, to complete the disclosure of this aplication, the aforementioned applications are included herein by reference.

While the invention has been described with reference to its preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without deparing from the true spirit and scope of the invention. For example, the opaque conductors may be recessed by providing fine, parallel grooves in the supporting substrate and then filling the grooves with silver paint or appropriately sized wires, etc. In addition, many modifications can be made to adapt a particular situation or material to the spirit of the invention without departing from its essential teachings.

What is claimed is:

1. A solid state storage panel comprising a supporting substrate having a plurality of narrow, opaque conductors disposed on one surface thereof, a conductive strip overlying each opaque conductor, a segment of insulating material positioned between adjacent conductive strips, each conductive strip having in overlying contact therewith a portion of electroluminescent material disposed between said conductive strip and a further overlying layer of field effect semiconductor material.

2. The storage panel of claim 1 wherein said portion of electroluminescent material comprises a layer of electroluminescent material overlying the plurality of conductive strips and segments of insulating material.

3. The storage panel of claim 1 wherein said portion of electroluminescent material comprises a segment of electroluminescent material overlying each conductor strip, said segments of electroluminescent material also being separated from adjacent electroluminescent segments by said segments of insulating material.

4. The storage panel of claim 1 wherein each conductive strip is in contact with that portion of each opaque conductor not in contact with said supporting substrate.

5. The storage panel of claim 1 wherein the conductivity of each conductive strip is at least sufficient to carry current from the opaque conductor in contact therewith to the edge of said conductive strip.

6. The storage panel of claim 1 wherein said supporting substrate and said plurality of conductive strips are light-transmitting.

7. The storage panel of claim 1 wherein said field effect semiconductor layer is light-transmitting.

8. The storage panel of claim 1 further including a thin electrically insulating layer overlying said field effect semiconductor layer.

9. The storage panel of claim Si wherein the insulator layer is a photoconductive insulator layer.

10. The storage panel of claim .l wherein said opaque conductors are thin conductive wires.

11. The storage panel of claim 1 wherein said opaque conductors are narrow lines of silver paint.

12. The storage panel of claim 1 wherein said conductive strips compirse a conductive powder dispersed throughout a resinous binder material.

13. The storage panel of claim 12 wherein said conductive powder is zinc oxide.

14. The storage panel of claim 12 wherein said conductive powder is indium oxide.

15. The storage panel of claim 12 wherein said resinous binder material is an epoxy resin.

16. The storage panel of claim 12 wherein said conductive strips have about 60% to about 95% by weight conductive powder therein.

17. The storage panel of claim 12 wherein said conductive strips have about to about 90% by weight conductive powder therein.

18. The storage panel of claim 1 wherein the field effect semiconductor is a storing field effect semiconductor.

19. The storage panel of claim 18 wherein the storing field effect semiconductor is zinc oxide.

Ztl. The storage panel of claim 18 wherein the storing field effect semiconductor is lead oxide.

21. The storage panel of claim 18 wherein the storing field elect semiconductor is cadmium oxide.

22. The storage panel of claim 1 wherein said storage panel has a surface capable of retaining an electrostatic charge pattern thereon, said charge-retaining surface not being a portion of said supporting substrate, and, in combination with said storage panel, means for forming an electrostatic charge patern on said charge-retaining surface.

23. The combination of claim 22 wherein said electrostatic charge pattern forming means comprises means for depositing a uniform electrostatic charge on said charge-retaining surface and means to selectively remove a portion of said charge.

24. The combination of claim 22 wherein said means :for forming an electrostatic charge pattern on said charge-retaining surface comprises means for depositing electrostatic charge in a selected charge patern configuration.

25. The storage combination of claim 22 wherein said means for forming an electrostatic charge pattern on said charge-retaining surface comprises an evacuated storage tube having said storage panel as its target, said storage tube having means for producing an electron -beam and writing means to cause the formation of an electronic charge pattern on the charge-retaining surface of said storage panel.

26. The combination of claim 22 wherein said field effect semiconductor material has photoconductive insulating properties and said electrostatic charge pattern forming means includes means for uniformly charging said charge-retaining surface and optical means for irradiating said charge-retaining surface with electromagnetic radiation actinic to said photoconductive insulating field effect semiconductor material.

27. The solid state storage panel of claim 1 wherein said supporting substrate has a plurality of parallel spaced grooves therein and said opaque conductors are disposed within said parallel grooves.

28. A solid state storage panel comprising a supporting substrate having a plurality of narrow, opaque conductors disposed on one surface thereof, a conductive strip overlying each opaque conductor, a segment of electroluminescent material overlying the plurality of conductive strips, a segment of insulating material positioned between adjacent conductive strips and segments of electroluminescent material, and a layer of yfield effect semiconductor material overlying the segments of electroluminescent material and insulating material.

29. A solid state storage panel comprising a supporting substrate having a plurality of narrow, opaque conductors disposed on one surface thereof, a conductive strip overlying each opaque conductor, a segment of insulating material positioned between adjacent conductive strips, a layer of electroluminescent material overlying the plurality of conductive strips and segments of insulating material, and a layer of field effect semiconductor material overlying the layer of electroluminescent material.

30. A method of creating a viewable image comprising providing the storage panel of claim 1 having a chargeretaining surface, forming an electrostatic charge pattern on at least a portion of said charge-retaining surface, said charge pattern being adapted to regulate the flow of current through said lield effect semiconductor material, and passing current between adjacent electrodes comprising said opaque conductors and said overlying conductive strips through said field eiect semiconductor material and said electroluminescent material.

31. The method of claim 30 wherein said current passed between said electrodes is at least suicient to cause luminescence of those portions of said electroluminescent material beneath those areas of the charge-retaining surface upon which no deposited electrostatic charge resides.

32. The method of claim 30 wherein said current passed between said electrodes is initially insufficient to cause luminescence of said electroluminescent material but, after deposition of an electrostatic charge pattern of a polarity opposite to the polarity of charges preferentially conducted through said field effect semiconductor material, said current ow is sufficient to cause luminescence of those portions of said electroluminescent material beneath those areas of said charge-retaining surface upon which electrostatic charge resides.

33. The method of claim 3|)` wherein said field effect semiconductor material has photoconductive insulating properties and the exposed surface of said field eect semiconductor is the charge-retaining surface of said storage panel, said electrostatic charge pattern being formed by uniformly charging said charge-retaining surface and removing a portion of said electrostatic charge by irradiating said photoconductive insulating field effect semiconductor with sensitizing electromagnetic radiation.

34. The method of claim 30 wherein said electrostatic charge pattern is formed with negatively charged ions.

35. A method of creating a viewable image comprising providing the storage device of claim 25, forming an electronic charge pattern on at least a portion of said charge-retaining surface by the modulated scanning of an electron beam, said electronic charge pattern being adapted to regulate the flow of current through said eld effect semiconductor material, and passing current between said electrodes comprising said opaque conductors and said overlying conductive Strips through said electroluminescent material and said field effect semiconductor material.

References Cited UNITED STATES PATENTS 2,972,692 2/1961 Thornton 313-108 3,440,428 4/ 1969 Kazan 250-213 3,441,736 4/1969 Kazan et al. 250-213 JOHN HUCKERT, Primary Examiner R. F. POLISSACK, Assistant Examiner U.S. Cl. X.R.