US3619714A

US3619714A - Panel display device

Info

Publication number: US3619714A
Application number: US815570A
Authority: US
Inventors: Paul F Evans; Harold D Lees; Martin S Maltz
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1969-04-14
Filing date: 1969-04-14
Publication date: 1971-11-09
Anticipated expiration: 1988-11-09

Abstract

An electroluminescent display panel having solid state storage layers, an excitation source and an ion-generating source. The application of excitation current causes luminescence of the panel. Ions carried through a dielectric layer are injected into a semiconductor control layer to alter the impedance state thereof. The change in the impedance state of the control layer alters the current flow within the panel resulting in a corresponding change in the level of luminescence. By selectively addressing the conductors either sequentially or simultaneously a pattern or image is formed on the panel face. The panel may be erased by the addressing voltage or by a separate erasing voltage source.

Description

United States Patent [72] Inventors Paul F. Evans Pittsford; Harold D. Lees, Rochester; Martin S. Maltz, Fairport, all of N.Y. [21] AppL No. 815,570 [22] Filed Apr. 14, 1969 [45] Patented Nov. 9, 1971 [73] Assignee Xerox Corporation Rochester, N.Y.

[54] PANEL DISPLAY DEVICE 9 Claims, 4 Drawing Figs.

[52] U.S.Cl 315/169, 313/108 [51] Int. Cl 1105b 37/00, I-I01j 1/62 [50] FieldofSearch 313/108.1; 315/109,169 TV [56] References Cited UNITED STATES PATENTS 2,928,993 3/1960 Liebson 315/169 2,932,770 4/1960 Livingston 315/169 TV 3,136,912 6/1964 Evans etal 313/108 3,264,479 8/1966 Peek 315/169 TV Primary Examiner Roy Lake Assistant ExaminerLawrence .l. Dahl Attorneys-James J. Ralabate, John E. Beck and Laurence A.

Wright ABSTRACT: An electroluminescent display panel having solid state storage layers, an excitation source and an iongenerating source. The application of excitation current causes luminescence of the panel. Ions carried through a dielectric layer are injected into a semiconductor control layer to alter the impedance state thereof. The change in the impedance state of the control layer alters the current flow within the panel resulting in a corresponding change in the level of luminescence. By selectively addressing the conductors either sequentially or simultaneously a pattern or image is formed on the panel face. The panel may be erased by the addressing voltage or by a separate erasing voltage source.

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Y SELECTOR X SELECTOR Y3 FIG. 4

PANEL DISPLAY DEVICE This invention relates to display panel devices. More particularly, this invention relates to electroluminescence panel display devices wherein a panel segment of the display device may be addressed when a pair of coincident voltages are applied to a pair of angularly displaced conductors.

BACKGROUND OF THE INVENTION The panel display is a flat device in that its depth is usually a much smaller dimension than its square area dimension. The display device may be considered a transducer which converts electrical input into an optical output for human observation. In the conventional electroluminescent display panel device a layer of luminescent material is sandwiched between a pair of conductors. See, for example, US. Pat. No. 2,932,770 to Livingston. This combination then is deposited on a substrate such as glass. Altemately, the device may comprise a plurality of layers beginning with a glass substrate, a conductive layer, an electroluminescent layer, and an optional photoconductive layer. The exact arrangement and materials will of course depend upon the desired use and function of the display. Generally, the electroluminescent materials which are employed are made up of phosphors. These phosphors exhibit the characteristic of giving off light or luminescing when a changing electric field is applied to the electrodes on either side of the phosphor material. Electroluminescent panels of the type described have many applications notably in the display of radar data and reproductions of pictures. Other uses may be as an indicating device of a system to be measured, as a wall television receiver screen or as a means for computer X-Y readout.

In the past, where an electroluminescent display panel was to be employed in a matrix address system several problems became apparent. Among these was the problem of providing a panel which had the desired storage capability. Another problem was insuring that when a chosen X-Y coordinate was selected no other coordinate would actuate because of spurious events. A third problem was to build electroluminescent display panels of large size. Where the same source is sought to be used for both the excitation of the phosphor and for addressing the panel, storage capability may be sacrificed in order to achieve rapid addressing. A further problem encountered in prior art devices was in controlling luminescent intensity or brightness. Brightness of the excited phosphor depends among other factors on the level and the frequency of the applied voltage. It is evident that where the addressing voltage and the excitation voltage emanate from the same source, control of the brightness of the phosphor is limited and inflexible.

The panel display has certain distinct advantages over the conventional cathode-ray tube. The panel display has a shallow depth, it obviates the need for deflection coils and associated circuitry and it is capable of being constructed in large sizes such as 3X4 feet, 4X5 feet and up to 20x40 feet. The panel display may be made to give high light outputs with good contrast and resolution. In addition, the panel is relatively insensitive to vibration and shock.

BRIEF DESCRIPTION OF THE INVENTION The disadvantages of the aforementioned devices have been overcome by the present invention to be described more fully hereinafter. The electroluminescent display device of the present invention provides a flat panel having a depth of approximately one-half inch which has high storage capability, isolation between selected X-Y coordinates, isolation between the excitation source and the addressing source and the capability of being made into large sizes. More particularly, the present invention provides an electroluminescent panel in which a first plurality of parallel conductive lines are deposited upon a substrate. The conductive lines are insulated from each other by a nonconductive material. Overlying the conductive lines there is a layer of luminescent material.

Above the luminescent material there are a control layer, a dielectric layer and a plurality of transparent conductors positioned orthogonally in relation to the first plurality of conductors. A time-varying excitation current applied to alternate conductive lines excites the electroluminescent material when current flows through it by way of adjacent conductive lines. When the panel is addressed by injecting negative or positive ions into the control layer at the selected X-Y coordinate, the selected area of the panel darkens or lightens because of the increased or decreased impedance of the control layer.

Accordingly, it is an object of this invention to provide an electroluminescent panel which has high storage capability.

Another object of this invention is to provide a means of addressing the electroluminescent panel which eliminates crosstalk or actuation of unselected array elements.

Another object of this invention is to provide a separate source for exciting the electroluminescent material and a separate source for addressing the panel.

Yet another object of this invention is to provide a electroluminescent display which is not limited as to size.

These and further objects of the present invention will be more fully understood by reference to the descriptions which follows and the accompanying drawings wherein:

FIG. 1 illustrates a section of the X-Y addressable panel showing the components thereof,

FIG. 2 is a view similar to FIG. 1 showing the excitation voltage source,

FIG. 3 illustrates a panel which uses a solid or gaseous dielectric, and

FIG. 4 illustrates the electrical switching arrangement which may be employed with the panel display device.

Turning now to FIG. 1, there is shown greatly enlarged for the sake of clarity a section of the display panel of the invention. Reference numeral 11 is a substrate or support means which may be glass, Mylar or any suitable nonconductor. Overlying substrate 11 are a plurality of parallel electrically conductive wire elements I4 and IS. The wire elements are insulated from each other and bound to substrate 11 by an adhesive 12. Each wire element 14 or 15 is coated with an insulat ing layer 13 and has been abraded to expose the conductive material. A portion of the conductive material has been etched away so that each wire element is contained in a trough made up of the insulating varnish 13. The area above the conductive material in the trough is filled with electroluminescent material 16. Each conductive element has its exposed electroluminescent surface in a coplanar relation to its adjacent conductive element. As a result, the control layer of semiconductor material 17 is evenly placed over the electroluminescent phosphor. Dielectric layer 18 is placed over control layer 17 and transparent conductors 19 are placed over dielectric layer 18. Transparent conductors 19 are spaced from each other and mounted perpendicularly to conductive elements 14. The panel is viewed facing the transparent conductors 19. In FIG. 1 every fifth conductive element is omitted so that one spaced transparent conductor coacts with a group of four conductive elements.

The conductive material of conductive element 14 or 15 may be made of any good electrically conductive material such as copper, silver, platinum, brass or steel alloys. Insulating material 13 is selected to withstand the etching agents used to form the trough for electroluminescent phosphor l6 and conductive elements 14 and 15. Although zinc sulfides may be used as a suitable electroluminescent material, a mixture of copper chloride and magnesium-activated zinc sulfide in a binder will yield similar results. Moreover, any of the wellknown electroluminescent phosphors may be utilized and tailored to furnish the desired response and spectral output.

For the control layer zinc oxide, cadmium sulfide, cadmium oxide, cadmium selenide, germanium, zinc sulfide, activated zinc sulfide, lead oxide and the like may be employed. The control layer 17 should have the properties of a field-effect semiconductor. A field-effect semiconductor in the context of this invention refers to a material capable of conducting current through the body thereof. However, the conduction of current through the material is modified by applying an electric field perpendicular to the current flow creating a region that effectively changes the cross-sectional conducting area of the semiconductor material or the conductivity of the material itself.

The dielectric material may be cellophane, glass, a transparent plastic, such as polystyrene, polyvinyl chloride or shellac. The light from the phosphor should pass through the control and dielectric layers thus, the dielectric layer must be transparent. The dielectric material employed should be able to furnish ions to the control layer.

The transparent conductors 19 may be NESA glass or may comprise thin layers of copper oxide, copper iodide, tin oxide, or gold either alone or on a transparent substrate.

At least one portion of the electroluminescent material forms part of the electrical circuit between the electrodes with the successive part of the electrical circuit being formed by a storing portion of the semiconductor material. The semiconductor material is capable of conducting current therethrough without substantially altering the electrostatic charge pattern on the charge retaining surface. When an alternating current beyond a threshold level is applied to the spaced electrodes, electroluminescence will be induced, assuming that the semiconductor is in a low impedance state. It can be demonstrated that the deposition and retention of an electrostatic charge on the control layer of the electroluminescent panel can be used to control the flow of current through the panel. When a negative electrostatic charge is deposited upon a given area of the panel the impedance of the semiconductor in that area is increased with a concomitant reduction or interruption of current flow in that area. The diminution of current flow will result in a corresponding diminution in light output from the electroluminescent layer resulting in contrasting areas of light and dark on the panel or half-toned response. Further reduction in current flow below a threshold value will cause that portion of the panel to cease luminescence altogether and that portion of the panel will appear dark. Conversely, the impedance of the semiconductor material is lowered and current flow increased as the charges are neutralized or removed from the surface as by injection of positive ions. Accordingly, by selectively depositing and maintaining a charge pattern on the surface of the electroluminescent panel an image or pattern can be produced and stored by the device.

Turning now to FIG. 2 there is shown a section of the electroluminescent panel with an alternating excitation current source 9 supplying a voltage between 300 volts and 800 volts and connected to conductive elements 14 and 15. A lead from the excitation current source is connected to the first and third conductive elements starting from the left. The other lead from the excitation voltage source is connected to the second and fourth conducting elements. Current flow through the panel will follow a path from lead 7 of the excitation voltage source 9 to first and third conductive elements, through the phosphor layer 16 of these elements, through the control layer 17, through the second and fourth conductive elements, through lead 8 and the other side of the excitation source. The conduction of alternating current through the phosphor 16 will cause it to luminesce or give off light. The brightness of the light given off will depend among other factors on the level and frequency of the applied excitation voltage and the impedance of semiconductor control layer I7. Thus, where control laycr I7 is in a low impedance state the excited segment of the panel will furnish a bright light. Control layer 17 will also determine the storage capability of the panel by regulating the current flow through the device.

The impedance of the control layer can be affected by the injection of positive or negative ions therein. The injection of negative ions into the control layer will create a depletion layer and the control layer will exhibit a high impedance state causing the electroluminescentmaterial beneath the high impedance portion of the control layer to cease glowing. Conversely, upon injection of positive ions, or by irradiating the panel with ultraviolet light, the control layer will exhibit a low impedance causing the electroluminescent material under the low impedance portion of the control layer to glow brightly. Although the optical sensitivity (e.g. to ultraviolet radiation) may be desirable in some applications, in matrix addressing usages it is contemplated to avoid this sensitivity by employing filters or by properly treating the control layer. Howeventhe sensitivity to ion injection is retained, since the light output from a given array element is controlled by injecting either positive or negative ions into the control layer of the element. Moreover, the panel may be erased point by point or overall by the addressing voltage power supply or from a separate erase voltage source.

In FIG. 3 there is shown another embodiment of the invention. Reference numeral 37 is a substrate or support which may comprise materials similar to that described above. A plurality of etched conductive lines 33 are supported upon substrate and are contained in a trough 39. The conductive lines are insulated from each other by adhesive material 38. Overlying conductive lines 33 is the control layer 36. There is airgap 31 separating conductive lines 33 from control layer 36. Airgap 31 serves as a dielectric. However, other solid or gaseous dielectric materials may be interposed in lieu of the airgap. Overlying control layer 36 is electroluminescent layer 32. Above and overlying the electroluminescent layer 32 and positioned perpendicular to control lines 33, there are a plurality of spaced parallel transparent conductors 34. Finally. a layer of transparent glass 30 from which the panel is viewed overlies transparent conductor 34.

The panel of FIG. 3 operates in essentially the same way as the panel of FIG. I. There will be a current flow from one side of the transformer to the transparent conductor 34 through the electroluminescent phosphor layer 32, through the control layer 36, through the adjacent transparent conductor 34 back to the other side of transformer T1. Assuming that control layer 36 is in its low-impedance state, the current flow will cause the electroluminescent phosphor to glow along the excited transparent conductors. The luminance of the area under a selected conductive line 33 may be changed by driving the line to a large negative or positive potential thereby generating negative or positive ions which will migrate across the dielectric to control layer 36. When the ions reach control layer 36 the impedance state thereof will increase or decrease thereby causing the current flow through it to change resulting in darkening or lightning of the panel under the selected line. The embodiment of FIG. 3 is intended to comprise materials similar to that disclosed with regard to FIG. 1. It is further intended that similar address circuitry as shown in FIG. 4 may be connected to the panel of FIG. 3 or FIG. 1.

Referring now to FIG. 4, there is shown an electrical switching circuit for actuating portions of the device. It is understood that although manual or mechanical switching is shown it will occur to those skilled in the art that electronic switching could be substituted in lieu thereof. It is therefore within the scope of the invention to employ electronic switching where it is desired. In FIG. 4, an alternating current source 9 furnishes excitation voltage to the electroluminescent phosphor via leads 7 and 8 and the contacts of ganged switch S4 to interdigitated

panel wires

24 and 23. As described above, interdigitated panel wires are connected to alternate conductive elements such that a given cell comprising four conductive elements has its first and third elements connected to one side of source 9 and its second and fourth elements connected to the other side of source 9. During the time that S4 is closed an excitation current passes through the panel causing the panel to glow brightly. When the excitation current is removed by opening S4 the panel will continue in its low impedance state but will cease to glow. The X selector switch S3 is then closed and grounds X, The Y selector switch S2 is connected to the desired transparent electrode Y, and when the write switch S1 is closed, the selected electrode is driven sufficiently negative (approximately 3KV) to inject negative ions by way of the dielectric layer into the control layer of the selected element. This will cause the electroluminescent phosphor in the selected element to fail to glow, darkening the selected panel segment as shown when the AC voltage is reapplied by closing switch S4.

The DC power supply 22 has its negative terminal connected to the junction of one plate of capacitor C1 and ground. The positive terminal of the power supply is connected to resistor R1. The write switch 81 when closed connects the negative voltage appearing at the junction of R1 and C1 to the Y selector switch S2. Altemately, power supply 22 could furnish a source of positive ions to the display by interchanging ten-ninal connections, in which case the selected panel element would lighten.

When write switch S1, Y Selector switch S2 and X selector switch S3 are closed smaller voltages would tend to appear across the unselected elements of the array as well as the desired element. In order to keep these unselected elements from being affected, it is necessary that the system provide a sharp threshold voltage for negative ion injection. The dielectric layer 18 of FIG. 1, or the gaseous or solid dielectric layer 31 of FIG. 3 affords this protection thereby restricting ion injection to the selected elements of the array. Moreover, the fact that every fifth conductive element has been removed dividing the panel into a series of electrically isolated strips further insures isolation of the selected elements from the unselected elements.

It is understood that FIGS. 14 represent only a portion of an actual panel display device. In an actual display panel having a dimension, for example, of 5X5 feet or larger the conductive lines and the transparent conductors would be far more numerous giving access to more panel segments. In the contemplated layer panel display device numerous segments of the panel would be addressed or scanned sequentially or simultaneously so as to build up visual information on the panel. The individual address conductors may also be modulated to control the brightness of the panel and to furnish degrees of contrast where images are to be displayed.

From the foregoing disclosure it has been demonstrated that the invention provides a matrix address electroluminescent panel device which is capable of isolating the selected panel areas from the unselected areas. Moreover, it has been shown that electroluminescent panels of large size and high storage capability can be made.

What is claimed is:

1. An electroluminescent display panel comprising:

a plurality of parallel first conductors,

a first layer of electroluminescent material overlying each of said first conductors,

a second layer of semiconductor material overlying said first layer and adapted to change its conductivity upon the injection of ions therein,

a plurality of parallel second conductors overlying said semiconductor layer and positioned angularly in relation to said first conductors, and

means for applying a pair of coincident voltages to a group of conductors of said first conductors and a single conductor of said second conductors to inject ions into said second layer changing its conductivity whereby the luminescence of the selected area of said display device is changed.

2. The apparatus of claim 1 comprising a support connected to said panel.

3. The apparatus of claim 2 comprising a separate source of excitation current for the electroluminescent layer of said panel.

4. The apparatus of claim 3 wherein periodic conductors in said first plurality of conductors are omitted.

5. The apparatus of claim 4 comprising transparent conductors for said plurality of second conductors.

6. The apparatus of claim 5 comprising a dielectric layer adapted to inject ions into said second layer said dielectric layer being interposed between said electroluminescent material and said second plurality of conductors.

7. The apparatus of claim 6 wherein said means for applying coincident voltages to said plurality of first and second con-' ductors comprises a first array of switches connected to a voltage source for said first conductors and a second array of switches connected to a voltage source for said second conductors, whereby any segment of said panel may be addressed.

8. An electroluminescent display panel comprising:

a substrate,

a first plurality of parallel conductors etched in an insulating binder and connected to said substrate,

a layer of electroluminescent material overlying each of said first conductors,

a layer of semiconductor material adapted to change its conductivity upon the injection of ions therein overlying said electroluminescent material,

a second plurality of parallel conductors overlying said semiconductor layer and positioned angularly in relation to said first conductors,

means for applying an excitation current to said electroluminescent and semiconductor layers through alternate ones of said first conductors to cause said electrolu minescent material to glow, and

means for applying pair of coincident voltages to a group of conductors of said first plurality of conductors and to a single conductor of said second plurality of conductors to inject ions into said second layer from said second conductor whereby the luminance of a predetermined segment of said display panel is controlled.

9. An electroluminescent display panel comprising:

a substrate,

a plurality of parallel first conductors etched in an insulating binder and connected to said substrate,

a layer of semiconductor material adapted to change its conductivity upon the injection of ions therein overlying said first conductors,

a layer of electroluminescent material overlying said semiconductor layer,

a plurality of parallel transparent second conductors overlying said electroluminescent material,

means for applying an excitation current to said electroluminescent and semiconductor layers through alternate lines of said second conductors to cause said electroluminescent material to glow, and

means for applying a pair of coincident voltages to a group of conductors of said first conductors and to a group of conductors of said second conductors to inject ions into I said semiconductor layer from said first conductors whereby the luminance of a predetermined segment of said display panel is controlled.

Claims

1. An electroluminescent display panel comprising: a plurality of parallel first conductors, a first layer of electroluminescent material overlying each of said first conductors, a second layer of semiconductor material overlying said first layer and adapted to change its conductivity upon the injection of ions therein, a plurality of parallel second conductors overlying said semiconductor layer and positioned angularly in relation to said first conductors, and means for applying a pair of coincident voltages to a group of conductors of said first conductors and a single conductor of said second conductors to inject ions into said second layer changing its conductivity whereby the luminescence of the selected area of said display device is changed.

2. The apparatus of claim 1 comprising a support connected to said panel.

7. The apparatus of claim 6 wherein said means for applying coincident voltages to said plurality of first and second conductors comprises a first array of switches connected to a voltage source for said first conductors and a second array of switches connected to a voltage source for said second conductors, whereby any segment of said panel may be addressed.

8. An electroluminescent display panel comprising: a substrate, a first plurality of parallel conductors etched in an insulating binder and connected to said substrate, a layer of electroluminescent material overlying each of said first conductors, a layer of semiconductor material adapted to change its conductivity upon the injection of ions therein overlying said electroluminescent material, a second plurality of parallel conductors overlying said semiconductor layer and positioned angularly in relation to said first conductors, means for applying an excitation current to said electroluminescent and semiconductor layers through alternate ones of said first conductors to cause said electroluminescent material to glow, and means for applying pair of coincident voltages to a group of conductors of said first plurality of conductors and to a single conductor of said second plurality of conductors to inject ions into said second layer from said second conductor whereby the luminance of a predetermined segment of said display panel is controlled.

9. An electroluminescent display panel comprising: a substrate, a plurality of parallel first conductors etched in an insulAting binder and connected to said substrate, a layer of semiconductor material adapted to change its conductivity upon the injection of ions therein overlying said first conductors, a layer of electroluminescent material overlying said semiconductor layer, a plurality of parallel transparent second conductors overlying said electroluminescent material, means for applying an excitation current to said electroluminescent and semiconductor layers through alternate lines of said second conductors to cause said electroluminescent material to glow, and means for applying a pair of coincident voltages to a group of conductors of said first conductors and to a group of conductors of said second conductors to inject ions into said semiconductor layer from said first conductors whereby the luminance of a predetermined segment of said display panel is controlled.