US2969481A

US2969481A - Display device

Info

Publication number: US2969481A
Application number: US765083A
Authority: US
Inventors: Jr Edgar A Sack
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1958-10-03
Filing date: 1958-10-03
Publication date: 1961-01-24
Anticipated expiration: 1978-01-24

Description

Jan. 24, 1961 Filed Oct. 3, 1958 NONLINEAR DIELECTRIC Fig.2.

NON LINEAR DIELECTRIC E. A. SACK, JR

DISPLAY DEVICE 2 Sheets- Sheet 1 Video Source Fig.3.

NONLINEAR DIELECTRIC Fig.4.

lNV ENTOR Edgar A. Sock, Jr.

ATTORNEY Jan. 24, 1961 E. A. SACK, JR 81 DISPLAY DEVICE Filed Oct. 3, 1958 2 Sheets-Sheet '2 89 (91 93 85 95 87 93 a5 87 9| 2E E 93 85 95 97 I 93 F|g.5. Fig.7.

United States Patent-C DISPLAY DEVICE Edgar A. Sack, Jr., Penn Hills, Pa., assiguor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 3, 1958, Ser. No. 765,083

7 Claims. (Cl. 315-169) This invention relates to display devices and, more particularly, to a storage-type display device of the solid state type.

The most common display tube known in the art is the conventional cathode ray tube. In the cathode ray tube it is necessary for the electron beam to supply the energy to produce the light output from a phosphor screen as well as distribute the video information over the entire display area. In order to produce an image, it is required that the electron beam excite a particular point on the phosphor screen once every scan period and the decay time of the phosphor and the persistance of the eye must combine to produce the impression of a continuous light output from the screen. If a high average brightness is desired from the display, it is found that the design requirements for a cathode ray tube to provide sutlicient electron beam power become prohibitive. lacksin adequate brightness, but also exhibits a certain amount of flicker and objectionable line structurein the image'as far as the viewer is concerned. The present type'cathode ray tube is also the primary limitation in reduction of depth of television receivers.

Some attention has been given to building solid state display screens utilizing electroluminescent light producing display areas. The electroluminescent display areas are excited by means of a separate power source normally, of a time varying voltage. The amount of voltage applied to the electroluminescent cell and the corresponding light output is controlled by the use of one or more nonlinear capacitors which are associated with the electroluminescent cell. The nonlinear dielectric capacitors respond to a direct current control bias to modify the capacitance and thereby modify the amount of voltage applied to the electroluminescent :cell. These display screens have advantages over conventional display devices in that they give high brightness and adequate storage of display information.

In US. Patent 2,875,380, entitled Display Systems, by P. M. G. Toulon, issued February 24, 1959, and assigned to the same assignee as the present invention, there is described a particular circuit configuration including nonlinear dielectric capacitors and voltage sources for exciting and controlling the light output from an eleetro-luminescent cell. This circuit configuration has been referred to as a bridge and has been found to be highly desirable in controlling light output from an electroluminescent cell. This invention is directed to an improvement over the above mentioned patent in order to provide an improved display device. It is, accordingly, an object of this invention to. pro.- vide. an improved solid state display device.

It is another object to provide an improved solid state display device in which a bridge-type circuit configuration is utilized to control the light output from an electroluminescent cell.

It is another object to provide an improved solid state display device which substantially reduces the The present cathode ray tube not only;

amount of excitation necessary to provide the desired amount of light output.

It is another object to provide an improved solid state display device which substantially reduces the danger of breakdown of the electroluminescent cell during normal operation.

It is another object to provide an improved solid state display device which adapts itself to ease in fabrication.

It is another object to provide an improved bridgetype circuit configuration which is more sensitive to control signals.

These and other objects are effected by my invention, as will be apparent from the following description, taken in accordance with the accompanying drawings throughout'which like reference characters indicate like parts, and in which:

Fig. l is a perspective view of a portion of a display screen structure embodying the principles of my invention;

Fig. 2 illustrates a cross sectional view taken along line (II-11) of Fig. 1;

Fig. 3 is a cross sectional view of a modified structure similar to that shown in Figs. 1 and 2;

Fig. 4 illustrates a circuit equivalent of the screen structures illustrated in Figs. l, 2 and 3;

Fig. 5 is a cross sectional view of a modified screen structure in accordance with the teachings of my invention;

Fig. 6 is a perspective view of the screen structure illustrated in Fig. 5; and

Fig. 7 illustrates a'modified structure similar to that shown in Figs. 5 and 6.,

Referring in detail to Figs. 1 and 2, there'is .shown an embodiment of a device constructed in accordance with my invention. The structure shown in Fig. 1 illustrates two complete light producing elements with associated control elements. The number of light elements and associated control elements utilized in a display screen will depend on the conditions to be met. It should be appreciated that hundreds of light elements could be assembled into one screen to meet certain display problems that may be presented.

In the specific embodiment shown in Figs. 1 and 2, the portionof the display screen is comprised of a light transmissive support layer 12 of a suitable material such as glass. On one surface of the glass support layer 12 opposite with respect to the viewer is deposited a thin electrically conductive coating 14 of light transmissive material for providing one electrode hereinafter referred to as the front electrode of the light producing element. Any suitable electrically conductive material that is light transmissive may be utilized such as stannic oxide.

A layer 16 of suitable phosphor material which exhibits the property of electroluminescence is deposited on the front electrode 14. In the specific embodiment shown the front electrode 14 and the phosphor layer 16 are in the form of continuous layers extending across the entire screen and are common to all of the light producing cells. It is obvious that if so desired, each of the cells in the screen could be provided with sesparate and distinct layers. Examples of suitable phosphors which exhibit the property of electroluminescence are zinc sulfide copper and manganese activated or zinc sulfide copper activated to mention a few of these well known phosphors. The phosphor material may be dispersed within a suitable plastic dielectric material or an inor I ganic material such as glass.

on the phosphor layer 16 by evaporating a suitable material such as aluminum through a suitable mesh structure as is well known in the art. The size and the shape of the electrodes 18 and the number will depend on the type of display device desired. In the embodiment shown, the electrodes 18 are small in area and spaced from each other a sutficient distance so that applied current to one of the electrodes 18 will excite only that elemental area of the display screen. The light producing structure just described which consists of -a phosphor layer 16 with two electrically

conductive electrode contacts

14 and 18 provides a light producing element which will emit light in response to field excitation applied by voltage to the electrodes 14 and 13. This type of light producing device is discussed more fully in an article entitled Electroluminescence and Related Topics, by G. Destriau and Ivey, in the December 1955 issue of the Proceedings of the I.R.E.

By way of explanation, electroluminescence was first completely disclosed by G. Destriau in the London, Edinburgh and Dublin, Philosophical Magazine, series 7.. volume 38, No. 285, pages 700-737, October 1947, in an article entitled The New Phenomena of Elcctroluminescence. In the phenomena of electroluminescence selected phosphor materials are placed within the influence of an electric field such as by sandwiching the phosphor materials between two spaced electrodes and applying I an alternating or time varying potential between these llrodes The resulting electric field which is created across the electrodes excites the phosphor material to luminescence, and the phosphor materials which display this electroluminescence are thus termed field responsive. Such phosphor materials are normally admixed with a dielectric material or a separate layer of dielectric inaterial which is included between the electrodes in order i pre ent any r ing. t r aerqs which m shtl t out the electroluminescent cell. Normally the spaced electrodes are parallel but they need not be as where graded field intensities are desired.

The phosphor material layer 16 may be deposited on the front electrodev 14 by any suitable method. For example, a finely divided phosphor material such as zinc d acti a d by copper m y b xe h a vent such as butyl acetate and with a polyvinyl chloride lacquer. The proportions of the constituents are not critica and may var th n wide l m s, but as a p ifi e amp e r e par s by ei ph sph m y b i d with 5Qparts by weightofthinner and 35, parts by weight oi polyvinyl chloride lacquer. The foregoing admixture may be sprayed in a plurality of coatings, for example four, according to the desired thickness, drying between each oi the coatings. Other dielectrics and solvents may be substituted for the foregoing specific examples as is well known. It is also possible to utilize a sintercd type phosphor layer.

A protective portion is provided on the exposed surfaces of the contacts 18 and consists of a continuous layer 15 of a nonlinear dielectric material. The thickness of the layer 15 may be about 8 mils. The thickness is dependent on voltages to be used with the device.

A plurality of electrically conductive contacts 17 are provided on the opposite surface of the nonlinear dielectric layer 15 of similar number, pattern, and material as the QDifiCts 18. The contacts 17 arev in alignment with the contacts 18, The resulting structure comprised of the dielectric layer 15 and the

contacts

17 and 18 provides a plurality of substantially insulated nonlinear capacitors, a

The control portion of the display screen: comprises a separate controlstructure for each of the back electrode members 18 provided on the phosphor layer 16 to control the. light output from each light element. The control portion is electrically connected to the back electrodes 18 of the light portion by way of the dielectric layer 15 and the electrodes 17. In the specific embodiment shown, the control element structure is comprised of a U-shaped member 20 of electrically conductive material having its central portion 22 in electrical contact with the electrode member 17 and with the

leg portions

23 and 25 projecting outwardly from the electrode member 17. A layer 24 of a nonlinear dielectric material is provided on the end of one of theleg members 23 and a layer 26 of similar material is provided on the other leg 25. An electrically conductive bus bar 28 is provided for each row of the leg portions 25 and is in physical contact with the opposite surface of the layer 26 to form a capacitor with each leg portion 25. The capacitor consists of the conductive bus bar 28 and the leg member 25, which form the electrodes, with the nonlinear dielectric material layer 26 sandwiched between the

members

25 and 28. An electrically conductive bus bar 30 is provided for each row of the leg portions 23 and is in physical contact with the opposite surface of the layer 24 to form a capacitor with each leg portion 23. The capacitor consists of the conductive bus bar 30 and the leg member 23, which form the electrodes, with nonlinear dielectric material layer 24 sandwiched between the

members

23 and 30. The bus bars 28 and 39 are normally parallel and extend across the screen structure contacting each control element in the row in a similar manner. The design of the control structure is primarily for mechanical reasons and the electrical equivalent of a single screen element is two separate nonlinear capacitor's having a common connection to a light producing element provided by the U-shaped conducting member 20 in contact with electrode member 17 and having their remaining terminals connected to two bus bars.

The nonlinear dielectric material in

layers

15, 24 and 26 may be of any suitable material such as ferroelec'tric dielectric material selected from the group which' ineludes, for example, barium titanate, barium-strontium titanat, barium stannate, sodium columbate, sodium tahtalate, potassium columbate and potassium tantalate. An ideal or lossless nonlinear dielectric material may-be defined as a material in which the functional relation ship between the electric displacement in a given principal direction and the electric field in the same direction while single valued is not that of a straight line in Cartesian coordinates. One particular class of materials that has been found satisfactory in this application are ferroelectric dielectric materials. The preparation of titanate ceramics is fully disclosed in an article-entitled Preparation of Reproducible. Barium Titanate, by R. M. Callahan and J. F. Murray, page 131 of the May 1954 issue of the Bulletin of The American Ceramic Society. I

One method of preparing the control structure for the entire screen is to provide a thin. fiat dielectric sheet approximately 10 mils in thickness. The sheet is coated on both sides with a suitable paint such as one which contains finely divided silver, frit and possibly a flux. After the paint has air-dried, the coated dielectric member may be baked in an oven for 15 to 30 minutes at a temperature of about 700 C. Both sides of the ceramic sheet are, then, tinned with a suitable solder, such as one containing 36% lead, 62% tin and 2% silver. Two sheets of electrically conductive material such as brass are also tinned on one side with a solder similar to that used on the dielectric sheet. The ceramic sheet is, then, positioned between the two brass sheets with the tinned side of the brass sheets adjacent the dielectric sheet. The sandwich of the two brass sheets with the ceramic sheet is, heated to a temperature of about 230 and, then, cooled. The resulting lamination may, then, be machined to form the control structure illustrated in Figs. 1 and 2. I

The resulting control structure may be attached to the electrodes, 17 ofithe light producing structure of the screen' by an electrically conductive varnish or cement applied between the U-shaped portions 20 of the control structure and the electrodes 17. The entire screen structure may be imbedded in a suitable light transmissive plastic material.

An electrical conductive lead is provided from each of the elements 20 of the control structure illustrated as leads 32 and 34 in Fig. 1 and are connected to fixed contacts of a suitable switching means 40 illustrated as a mechanical switch. An electronic switch may be used. Other control elements of screen could be connected to the other fixed contacts. The movable contact of the switch 40 is connected through a bias source 42 to a source 45 of video signals. An'electrically conductive lead 44 is brought out from the front electrode 14 and connected to ground. The conductive bus bars 28 and 30 are also brought out of the screen structure and connected to suitable voltage supplies. The conductive bus bar 28 is connected to a suitable light power source 48 'for providing a time-varying voltage. The opposite terminal of the light power source 48 is connected to the positive terminal of a bias source 50 illustrated as a battery. The negative terminal of the bias battery 50 is connected to ground. The other conductive bus bar 30 is connected to one terminal of a light power source 46 which also provides a time varying voltage and the other terminal of the light power source 46 is connected to ground.

The operation of the device can be best described by reference to Fig. 4. The equivalent circuit of each light producing element and its associated control element is illustrated in Fig. 4. That portion of the circuit which 18 contained within the dotted lines represents one element of a multielementary screen. The remainder of the circuit maybe and is usually common to all the elements of the screen with, of course, the control voltage being selectively impressed by means of the switch means 40. The circuit shown may be considered to be comprised of an upper branch, at lower branch and a center branch. The upper branch of the circuit includes, beginning at the junction 60 which is connected to ground, the light power source 48, the bias source 50, the nonlinear dielectric capacitor 62 (formed by the

members

28, 26 and 25 in Fig. l) and ends at junction 64. These circuit elements are connected in series arrangement by suitable conducting members of which conductor 28 corresponds to the bus 28 of Fig. l. The junction 64 is the member 22 of the control element of the screen in Fig. 1.

In a like manner, the lower branch of the circuit compnses'in series arrangement beginning at junction 60, the

.light power source 46, a nonlinear dielectric capacitor 66 (formed by the

members

30, 24 and 23 in Fig. 1) and ends at junction 64.

Extending from the junction 69 to the junction 64 between the two nonlinear dielectric capacitors 62 and 66 is the center branch of the circuit containing an electroluminescent element or cell 68 (formed by

members

14, 16 and 18 in Fig. l) and a nonlinear dielectric capacitor 69 (formed by

members

15, 17 and 18 in Fig. 1).

The complete circuit has the nature of a bridge circuit in which the upper and lower branches determine what current, if any, passes through the center arm which contains the electroluminescent light producing element 68. At the ungrounded junction 64 of the upper and lower branches and the center branch is the connection to the control voltage which is here represented by a battery 76 having its negative terminal connected to ground. An isolation resistor 31 may be used to prevent shorting the alternating current voltage in the bridge.

This circuit is in efiect a conventional type bridge circuit with the exception of the ferroelectric breakdown protective capacitor 69 inserted in series with the electroluminescent cell. There are many modes of operation possible for the bridge type circuit illustrated in the drawing. In order to explain the operation of the circuit it will be first assumed that the control voltage from the source 70 is at zero potential. Then, in view of the design or the adjustment of the members of the circuit system the periodic voltage applied at the junction 64 will be substantially different than that applied at junction 60, and light power potential will be applied across the electroluminescent cell 68. The circuit in this condition is unbalanced. This initial unbalance within the circuit may be accomplished in several ways; for example, the

value of the capacitance of the nonlinear dielectric capacitors 62 and 66 may be selected to be of the same value. The voltage supplies 46 and 48 may also be selected to be identical in value and identical in phase. The direct current bias supplied by the battery 50 is such that the nonlinear capacitor 62 in the upper branch of the circuit is under a bias stress so that the value of the capacitance of the nonlinear capacitor 62 is less than that of the capacitor 66. It can therefore be seen that the bias battery 50 places a bias stress on the capacitor 62 resulting in the upper and lower branches being unbalanced. By varying the control voltage or signal supplied from the source 70, which may be a video source, the luminosity of the electroluminescent cell 68 may be varied as desired. As the control signal from source 70 increases from zero, the bias on the capacitor 62 in the upper branch will decrease due to the opposition of the bias battery and the control signal. The effect on the capacitor 66 in the lower branch is such as to increase the bias so as to decrease the capacitance of the capacitor 66. Thus, while the bridge circuit was initially unbalanced, the control signal caused the circuit to become more balanced with the application of increased control poten tial. The result is that the voltage across the electroluminescent cell 68 will decrease, and the element will cease to give off light when the circuit is in balanced condition. In the above explanation the effect of the nonlinear capacitor 69 in the central branch was not considered. As previously stated, the capacitor 69 provides protection against breakdown of the cell due to the DC. control bias applied by the source 70. The capacitor 69 also provides additional control and thereby improves the sensitivity of the circuit. As a control bias is applied to the terminal 64, the capacitor 69 will also be under stress so that the capacitance will decrease. This results in less of the light power potential being applied to the series arrangement appearing across the electroluminescent cell 68. The net result of'the cooperating action between the nonlinear capacitors 62 and 66 in the upper and lower branch and the capacitor 69 in the center branch results in the bridge becoming more balanced, thus providing lower and lower power excitation to the center branch, and the ferroelectric protective capacitor 69 saturates applying still less excitation .to the electroluminescent cell 68. This results in a highly sensitive circuit configuration for control of an electroluminescent light cell.

Therefore, when a plurality of light producing elements are provided and controlled in accordance with predetermined signals, any predetermined image may be presented on the display screen. As the control signal contact is removed from one of the elements, the electroluminescent cell will emit light until the control charge gradually leaks I off or the charge is modified by the next signal contact to the individual element. The utilization of the capacitor 69 in the center branch of the circuit also provides a system of additional storage time in that most electroluminescent cells are relatively leaky, and therefore, the charge may leak off in a very short time.

Under some circumstances it may be desirable to have the system set such that the circuit is in balance without application of control potential. This may be readily efiected by proper selection of the circuit elements. The application of control signals in this case will tend to drive the circuit toward an unbalanced state and thereby increase the light output from the cell.

It should be also noted that the capacitor 69 illustrated in Figs. 1 and 2. is mounted within the screen structure 2' such that conductive electrodes 18 are provided between the electroluminescent layer 16 and'the dielectric layer 15. In Fig. 3, the dielectric layer 15 is placed in intimate contact with the electroluminescent layer 16, and the electrode layer between the two layers is not required. The operation of this structure in Fig. 3 is similar to that of Figs. 1 and 2.

As illustrated in Fig. 1, it may be suitable to use in addition to the signal, a constant voltage or bias source 42 which is continuously on only during the time that the signal pulse is being applied to the individual element. The purpose of this bias is to assure that the control element operates over the optimum portion of its characteristic.

As a representative example, an electroluminescent cell 68 may have an electrode contact of an area of A square inch and a capacitance of about 80 micromicrofarads. The dielectric capacitors 62 and 66 would have an apparent capacity of about 400 micromicrofarads with no direct current voltage and 100 volts r.m.s. at a frequency of 6000 cycles. The area of the dielectric layer in the capacitors 62 and 66 would be about 320 square mils and the layer 12 mils in thickness. The

sources

46 and 48 would be in phase with the source 46 of about 200 volts r.rn.s. at a frequency of 6000 cycles. The source 43 would be of a voltage of 200 volts r.m.s. at a frequency of 6000 cycles. The direct current bias source 50 would be of about 300 volts. The direct current control bias range could be from zero volt to about 150 volts.

In Figs. 5, 6 and 7, a laminated-type screen structure is illustrated. This general type of construction is described in U.S. Patent 2,922,076, issued January 19, 1960, entitled Display Device, by E. A. Sack, Jr., and J.

Asars, and assigned to the same assignee as the present invention. This structure may be broken down into four components: the electroluminescent cell 80, the protective layer 82, a connective layer 84, and a control structure 86. The electroluminescent cell 80 and the protective layer 82 are similar to those described with respect to Figs. 1 and 2. The connective layer 84 consists of a layer 83 of insulating material having a plurality of conductive pillars or plugs 85 therein and in alignment with the contact electrodes 17 on the protective layer 82. The number of conductive pillars is of similar number as the conductive contacts 17 and of similar configuration and alignment; The connective layer 84 may consist of a photoform mesh having a plurality of conductive plugs therein of a conductive material such as conductive rubber. The control layer 86 has on its surface adjacent the connective layer 84 a pattern or configuration of conductive contacts 87 in parallel rows and in alignment with the conductive plugs 85 in the connective layer 84. The contacts 87 make electrical contact with a nonlinear dielectric layer 89. Positioned on the same surface as the conductive contacts are a plurality of parallel electrically conductive strips 9 1. These strips are positioned such as to provide a conductive strip between each row of conductive contacts 87. A printed diode 93 is also provided for each contact 87 and extends to one of the adjoining conductive strips 91. An insulating layer may be provided between diodes 93, strips 91 and layer 89 to avoid parasitic capacitance. This provides a distribution matrix such that input control signals are sequentially supplied to the elements of the screen. On the opposite surface of the dielectric layer 89 with respect to, the conductive contacts 87 are a plurality of conductive strips. These strips are arranged such that a strip 95 and a strip 97 are positioned parallel and opposite to each row of conductive contacts 87. All or the conductive strips 95. are connected together and tied to one terminal of the voltage source while the other conductive strips 97 are connected together and tied to the terminal of the other voltage source. The potential sources and connections thereto for the devices shown in Figs. 5, 6 and 7 may be substantially as shown in Fig. 1 with the strip electrodes and 96 connected to the potential sources in the manner shown for the bus bars 28 and 30. It can, therefore, be seen that the conductive contacts 87 form a common plate of two capacitors with the other plates formed by the opposite

conductive strips

95 and 97. The operation of this structure is similar to that described with respect to Figs. 1, 2, 3 and 4.

While I have shown my invention in several forms, it will be obvious to those skilled in the art that it is not so limited but is susceptible of various other changes and modifications without departing from the spirit and scope thereof.

I claim as my invention:

1. In a solid state display element in combination, a plurality of circuit systems connected in cooperative relationship with a common circuit portion between them, one circuit system comprising a nonlinear dielectric capacitor and a time varying potential source connected in series circuit relationship, the other circuit system comprising a nonlinear dielectric capacitor and a time varying potental source connected in series circuit relationship, an electroluminescent cell and a nonlinear dielectric capacitor connected in the common circuit portion.

2. In a display device in combination, a first and a second nonlinear dielectric material member, a first time varying potential source and a second time varying potential source all connected in series circuit relationship providing a first loop circuit, a center circuit branch comprising an electroluminescent material member and a third nonlinear dielectric material member connected across the first loop circuit from a point between said first and second nonlinear dielectric material members to a point between said first and second time varying potential sources providing second and third loop circuits having said center circuit branch in common, the second and third loop circuits being in substantial balance whereby substantially no time varying potential is impressed across the electroluminescent material member, and means for impressing a signal on said second and third loop circuits to eflect an unbalance and the impressing of a time varying potential across the electroluminescent material member, the time varying potential impressed on the electroluminescent material member having a predetermined relationship to said signal whereby the luminosity of the electroluminescent material member varies with the signal.

3. [In a solid state display element in combination, a plurality of circuit systems connected in cooperative relationship with'a common circuit portion between them, one circuit system comprising a first nonlinear dielectric capacitor and a time varying potential source connected in series circuit relationship, the other circuit system comprising a second nonlinear dielectric capacitor and a time varying potential source connected in series circuit relationship, an electroluminescent cell connected in the common circuit portion, said cell including a layer of nonlinear dielectric material of high permittivity separate from the nonlinear dielectric material in said first and second nonlinear dielectric capacitors, the members of said plurality of circuit systems being so proportioned that they are in substantial balance with substantially no time varying potential applied to the electroluminescent cell, and means for delivering signals to said plurality of circuit systems to effect an unbalance and impress a time varying potential across said electroluminescent cell to render it luminous.

4. In a display device in combination, a first and a second nonlinear dielectric material member, a first time varying potential source, and a second time varying potential source all connected in series circuit relationship providing a first loop circuit, a center circuit branch comprising an electroluminescent material member and a third nonlinear dielectric material member connected across the first loop circuit from a point between said first and second nonlinear dielectric material members to a point between said first and second time varying potential sources providing second and third loop circuits having said center circuit branch in common, the second and third loop circuits being in substantial balance whereby substantially no time varying potential is impressed across the electroluminescent material member, and means for impressing a signal to the common terminal of said nonlinear dielectric members to effect an unbalance of said second and third loop circuits and the impressing of a time varying potential across the electroluminescent material member, the time varying potential impressed on the electroluminescent material member having a predetermined relationship to said signal whereby the luminosity of the electroluminescent material member varies with the signal.

5. In a solid state display element in combination, a plurality of circuit systems connected in cooperative relationship with a center circuit branch between them, one circuit system comprising a nonlinear dielectric capacitor and a time varying potential source connected in series circuit relationship, the other circuit system comprising a nonlinear dielectric capacitor and a source of time varying potential connected in series circuit relationship, an electroluminescent cell and a nonlinear capacitor connected serially in said center circuit branch.

6. A display screen comprising a light producing member comprised of a plurality of separately controllable light producing areas, said light producing member comprising a continuous layer of electroluminescent phosphor sandwiched between a front and a back electrode, said front electrode comprising a continuous layer of electrically conductive material transmissive to radiation emitted by said phosphor layer, a conductive member connected to said front electrode for connection to the common terminal of a first and a second potential source for providing the excitation potential for said phosphor layer, said back electrode comprised of a first group of spaced electrically conductive contacts positioned substantially in parallel rows and equally spaced on the surface of said phosphor layer, a control structure for said light producing member comprising a first continuous sheet of nonlinear dielectric material of similar area as said phosphor layer, a second group of electrically conductive contacts positioned on said first nonlinear dielectric layer remote from said phosphor layer in substantially parallel rows and equally spaced in each roW, said second group of contacts of similar number and aligned with said first group, a second continuous layer of nonlinear dielectric material positioned remote from said phosphor layer relative to said first nonlinear dielectric layer, a third group of electrically conductive contacts positioned on the side of said second nonlinear dielectric layer facing said phosphor layer, a first group of electrically conductive strips provided on the same surface of said second nonlinear dielectric layer as said third group of contacts, said first group of strips being parallel and positioned so as to provide a strip between each row of conductive contacts in said third group and being insulated therefrom, a rectify ing device connected between each contact of said third group of contacts and one of the strips of said first group of strips, means for applying control potentials to said first group of strips to control light emission from said light producing areas, a second group of parallel conduc tive strips positioned on the opposite surface of said second nonlinear dielectric layer with respect to said first group of strips, each of said second group of strips positioned opposite to a row of contacts of said third group to form a first capacitor for each light producing area, a third group of parallel conductive strips parallel to said second group of conductive strips, and positioned on the same surface of said second nonlinear dielectric layer opposite to a row of contacts of said third group of con tacts to form a second capacitor for each light producing area With a contact of said second group of contacts as a common plate, said second group of strips electrically connected together and provided with a conductive member connected to the other terminal of said first potential source and said third group of strips electrically connected together and provided with a conductive member connected to the other terminal of said second potential source.

7. A display screen comprising a light producing member comprised of a plurality of separately controllable light producing areas, said light producing areas each comprising a layer of electroluminescent phosphor sandwiched between a first and a second electrode, said first electrode comprising a continuous layer of electrically conductive material transmissive to radiation emitted by said phosphor layer, a conductive member connected to said first electrode for connection to the common terminal of a first and a second potential source for providing the excitation potential for said phosphor layer, a first layer of nonlinear dielectric material of similar area as said phosphor layer positioned on said second electrode, a third conductive electrode on the exposed surface of said first nonlinear dielectric layer, a second layer of nonlinear dielectric material electrically coupled to said third conductive electrode, a first and a second parallel conductive strip positioned on the exposed surface of said second nonlinear dielectric layer to form two capacitors with said third electrode as a common plate, said first strip electrically connected to a terminal of said first potential source and said second strip electrically connected to a terminal of said second potential source.

No references cited.