US3573530A

US3573530A - Electroluminescent panel display device

Info

Publication number: US3573530A
Application number: US728546A
Authority: US
Inventors: Tadao Kohashi
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1967-05-19
Filing date: 1968-05-13
Publication date: 1971-04-06
Anticipated expiration: 1988-04-06
Also published as: DE1764330C3; NL139630B; DE1764330B2; FR1570089A; DE1764330A1; NL6807007A; GB1161977A

Abstract

A luminescent memory and display device which receives visible light or X-rays as an input signal, converts said signal into a variation in DC voltage with an amplifying effect, and displays the corresponding signal in an AC excited luminescent output or stores the signal if required; said device comprising an electroluminescent element, an energy-responsive element such as a photoconductive element, a resistive element, a capacitive element, an AC voltage source and a DC voltage source.

Description

United States Patent Inventor Appl. No.

Filed Patented Assignee Priority ELECTROLUMINESCENT PANEL DISPLAY [56] Reierences Cited UNITED STATES PATENTS 2,931,915 4/1960 Jay,.lr. 313/108AX 2,975,290 3/1961 Spitzer 313/108AX 3,300,645 1/1967 Winslow 3 l 3/108AX Primary ExaminerRobert Segal Att0rneyStevens, Davis, Miller & Mosher ABSTRACT: A luminescent memory and display device 3 D which receives visible light or X-rays as an input signal, conalms rawmg verts said signal intoavariation in DC voltage withanamplify- 11.8. C1 313/108, ing effect, and displays the corresponding signal in an AC 315/169 excited luminescent output or stores the signal if required; 1nt.Cl H0lj 1/66, said device comprising an electroluminescent element, an

H01j 1/70,l-l05j 33/10 energy-responsive element such as a photoconductive ele- Fieldl of Search 313/108 ment, a resistive element, a capacitive element, an AC voltage (A); 250/213; 315/169, 169 (TV) source and a DC voltage source.

1 LI 1 l 5 l 3 1\ 1\ 1\ 11 l\ l 4 l8 /6 /4 \6 g A 6 \n/ ,,,q,,.vj N 31/ r./-/'/ /2 x" x J x x /0 ,1 I i i l Ptented April 1971 MENTOR TED 9p KOHRJW ELECTlltDL UTt/MNESCENT PANEL DllSllLAlt DEVIICE This invention relates to an improvement in the energyresponsive luminescent display device used for conversion and amplification as well as memory and display of an incident energy signal, comprising an energy'responsive element such as a photoconductive element, a magnetoresistive element or a piezoresistive element which varies at least its electric resistance in response to incident energy such as light, radioactive rays, a magnetic force or elastic waves respectively, combined with an electroluminescent element (hereafter, referred to as an AC-DC EL element) which luminesces by excitation with an AC electric field and of which the waveform of luminescent output is controlled by a unidirectional (DC) electric field applied thereto.

There are several types of composition of the above-mentioned AC-DC EL element. The first type comprises an electroluminescent (hereafter, referred to as EL) material dispersed in a substantially resistive (for example, having a specific resistivity of to 100 ohms-cm.) dielectric substrate.

The second type of the AC-DC EL element comprises an EL material contained in a dielectric material which supports the internal electric field when an external polarizing unidirectional voltage is applied thereto, and which maintains the residual component of said electric field when said voltage has been removed.

The dielectric material for the latter type of element may be made of, for example, tricresyl phosphate or glycerine.

Or, the AC-DC EL element of the second type may be produced from a mixture of powder of a glass enamel containing at least lithium oxide and further Ti if desired, powder of a semiconductive metal oxide such as SnO and powder of BL fluorescent material said mixture of powder being heated and fused.

The EL material may comprise powder of fluorescent material such as ZnS.

The AC-DC EL material is interposed between a pair of electrodes of which at least one may be light transmitting.

in the AC-DC EL element of said first type, the amplitude of the AC excited luminescent output can be controlled by a DC electric field applied to it, said control being reversible with the illumination decreasing in relation to an increase in intensity of the DC electric field.

in the AC-DC EL element, said amplitude of the luminescent output can be reversibly and decreasingly controlled by imposing a DC electric field on the element in such a manner that the intended luminescent output side of the AC-DC EL element becomes negative in polarity.

The above-mentioned controllability is utilized for conversion and amplification of the incident (input) energy signal or image.

Further, in the AC-DC EL element of the second type, the amplitude of the AC excited luminescent output can be controlled also by imposing a DC electric field on the element in such a manner that the intended output side of the element is positive in polarity. Even after the DC electric field is removed, a residual DC electric field remains in the AC-DC EL element. This control can be either increasing or decreasing in relation to an increase in intensity of the applied DC field depending on the polarity of said electric field. This controllability is utilized for memory and luminescent display of the incident energy signal or image.

In the iUlOWll devices, the DC control of the AC-DC EL element is achieved with the energy-responsive element connected in series with the EL element. Accordingly, the matching of the electric resistances of the AC-DC EL element and the energy-responsive element must be attained by adjustment of the resistivity of these elements.

However, it is very difficult to attain the matching of said resistances by the above-mentioned method. This is because the change in resistivity of the AC-DC EL element will affect the controllability of the device which is closely related to the resisn'vity of the element.

Control of the resistivity of the energy-responsive element is possible to some extent if the element is a photoconductive element of the visible light range. However, a slight deviation from the required value of the resistance might cause serious degeneration of the operating characteristics, as the device is highly sensitive.

Further, the control of the resistivity by choice of material is generally very difficult to accomplish. Therefore, substantially perfect matching of the resistances will be practically impossible to achieve.

If the energy-responsive element is one having a low specific resistivity such as a photoconductive element of the infrared range, matching is impossible in principle.

Moreover, with the above-described constitution of the device, the DC electric field across the ACDC EL element will increase in response to a decrease in the resistance of the energy-responsive element. Accordingly, in the previously described controlling operation, the amplitude of the AC luminescent output decreases when the intensity of the incident energy is increased, thereby producing a signal or image of negative polarity in response to a normal incident energy signal or image. This is another difficulty involved in such a known device. The above-mentioned dimculties have been eliminated by this invention, in which the energy-responsive element is coupled, in a DC circuit, with a resistor or resistive component so that the unidirectional electric field across the AC-DC EL element is controlled in relation to the variation in the resistance of the energy-responsive element, and the AC-DC EL element is associated, in an AC circuit, with a capacitor or capacitive component other than the energyresponsive element so that the AC-DC EL element is excited to luminescence by the AC electric field.

ll-lereunder, this invention will be described in connection with embodiments thereof, referring to the attached drawings, in which:

FIGS. 11 and 2 show electrical wiring diagrams of two types of embodiments of the energy-responsive luminescent display device according to this invention; and

FIG. 3 is a sectional view of another embodiment of this invention shown with the related wiring diagram.

Now, referring to lFlG. l which relates to an embodiment of this invention, the parallel connected circuit consisting of the resistor R, and the capacitor C,,, and another parallel connected circuit consisting of the EL element l which luminesces with excitation by an AC electric field and the waveform of the luminescent output is controlled by a DC electric field applied to it and the energy-responsive element 2 which varies at least the electric resistance V, thereof in response to the incident energy L,, are connected in series to the

voltage source

5 and 6. AC voltage V,, is imposed on said EL element ii to excite it with the AC electric field. The device is arranged so that the unidirectional DC voltage V, imposed on the EL element ll decreases in response to the decrease in the electric resistance R, of said energy-responsive element 2.

The capacitor C, and the resistor l t, may be separate elements, or they may be included in a single resistive capacitor element.

The AC-DC EL element 1 is composed as described previously. The energy-responsive element 2 is infrared photoconductive element such as CdSe or CdTe-l-lg'le provided with the electrodes 2' and 2", one of which pervious to infrared raysL that is, the incident energy.

The AC voltage source 5 and the DC voltage source t5 may be included in a single composite voltage source, if desired. The DC voltage source a can be connected between the terminals c and d, or between the terminals 0 and b it the capaci tor C, and the resistor R, are separate elements provided with electrodes.

AC excitation of the AC-DC EL clement ll is carried out by supplying AC current from the voltage source d mainly through the capacitor C,,. Therefore, the element ll can be excited effectively by the AC voltage V with very small voltage loss if the AC impedance of the capacitive element C, is

selected to be appropriately lower than that of the of the parallel connected circuit of the

elements

1 and 2.

Further, the voltage V, can be maintained substantially at a constant level, regardless of the variation in the resistance R, of the energy-responsive element due to the incident energy On the other hand, the DC voltage V, imposed on the EL element 1 is controlled by the variation of the resistance R, due to the incident energy L,, the ratio of the DC voltage V, to the DC source voltage being determined by the relation of the resistance R, to the value of the resistor R,.

Generally, the effective range of the resistivity of the EL element 1 in which the waveform of the luminescent output can be etTectively controlled, is in the order of to 10 ohms-cm, being a much higher value as compared with the dark resistance of an infrared photoconductive element or the like. Accordingly, is very difficult to match the resistances of the elements I and 2.

According to the arrangement of this embodiment, however, an optimum matching of the resistances is obtained without any limitation by the resistance of the ACDC EL element, by selecting the value of the resistor R, so as to be of the same order as the dark resistance of the element 2 or higher than that.

Therefore, the DC voltage V, imposed on the EL element I can be decreasingly controlled with high sensitivity in response to the increase of the infrared ray input L,. Accordingly, the AC luminescent output L, from the EL element 1 remarkably increases in response to an increase of incident energy L,. Thus, a visible luminescent output signal L is ob tained in a positive image from an infrared input signal L,

The AC luminescent output L from the ACDC EL element 1 comprises two luminescent pulses for each cycle of the exciting AC field. However, it should be noted that the control effect of the DC electric field upon the AC excited luminescence is different for each half of one cycle, that is, the two luminescent pulses are controlled at a different rate by the DC electric field. One of the luminescent pulses which is controlled at a higher rate can be extracted if a mechanical light dropper 7 is provided as shown in FIG. I. The chopper 7 is operated by synchronizing the frequency as well as the phase with the AC voltage from the voltage source 5. The light chopper 7 may comprise, for example, a synchronous motor 7' and a disc-type chopper 7" driven by said motor 7 It will be understood that the above-described selection and separation of the luminescent pulses are applicable to any embodiment of this invention.

The memory and display operation is achieved by controlling the residual field of the element 1 with the DC voltage from the voltage source 6 of which the polarity is selected in accordance with the above-described operating principle of the ACDC EL element.

If a DC field is applied to the EL element I of such polarity that the luminescent output side of the element is positive, a polarized electric field is maintained within the element 1 even after the applied DC field has been removed, and the luminescent output is not the same as obtained before the DC electric field is applied. Under this condition, when the AC electric field is applied across the EL element, a storage effect is presented. In this state, if a DC voltage of opposite polarity is applied to the element, the polarized field within the element will be extinguished.

In FIG. 2 which shows another embodiment of this invention, the resistor R, and the energy-responsive element 2 are seen in exchanged positions compared with FIG. I.

In this embodiment of this invention, the resistor the DC voltage V, imposed on the EL element 1 increases in response to a decrease of the resistance R, due to the incident energy, that is, the infrared rays L,. Thus the luminescent output from the EL element 1 decreases. Therefore, an image of negative polarity is obtained when the normal incident energy L, is applied.

As shown in FIG. 2, the capacitance C, and the resistance R, are given by separate elements of the capacitor 8 and the resistor 9 respectively.

An optimum matching of the resistances is attained to make possible an operation with high sensitivity, by selecting the resistance R, to be of the same order as the dark resistance of the energy-responsive element 2 or lower than that regardless of the resistance of the ACDC EL element 1.

FIG. 3 shows the structure of the energy-responsive luminescent display device in another embodiment of this invention and the voltage supply system thereof.

In this embodiment, the incident energy L, is given in the form of light, X-rays or the like and is converted and amplified or stored and displayed in the form of an image of visible light.

In FIG. 3, the reference numeral 10 indicates a light-pervious support plate made of glass or the like, and 11 shows a light-pervious electrode of, for example, tin oxide deposited on the surface of the support plate 10. The ACDC EL element 1 is formed in a layer of 50 to I00 microns in thickness with the composition as described previously, Numeral 12 indicates an electroresistive light shielding layer of about 10 microns in thickness. Numeral 13 indicates the energy-responsive element of layer-fon'n, that is a photoconductive layer made of Cds, CdSe, CdTe-HgTe or the like, in this embodiment formed by vapor deposition, sintering or binding. The thickness of this layer is selected, according to the composition of the layer, so that the photoconductivity in the lateral direction of the layer, that is, in the direction perpendicular to the thickness direction thereof, is sufficiently high. In this embodiment, the layer is formed in a thickness of 30 to microns by sintering or binding. In this layer 13 is disposed a grid-shaped electrode 14 which consists of tungsten wires or the like of about l0 microns in diameter and juxtaposed in parallel with a pitch of about 500 microns.

The strip-shaped capacitive layers 15 of polyester film or glass enamel layer, for example, of about 10 to 20 microns in thickness are juxtaposed in parallel on the layer 13.

The narrow strip-shaped resistive layers 16 are disposed at approximately midpoints between two adjacent gn'd members of the electrode 14, also forming a parallel grid. These resistive layers 16 are formed approximately in the same thickness as the capacitive layer 15, for example, with electroresistive metal oxide mixed with plastics binder or electroresistive glass enamel.

The juxtaposed strip-shaped

electrodes

17 and 18 respectively disposed on the capacitive layer 15 and the resistive layer 16 are made of electroconductive film such as vapordeposited metal film or tin oxide film, or electroconductive paint including, for example, silver.

Among the layers and electrodes, at least the capacitive layer 15 and the electrode 17 must be pervious to incident energy, that is, to the light or X-ray image L,. The

electrodes

14, 17 and 18 which are respectively grouped together, as well as the electrode 11, are connected, through the switch S, to the AC voltage source 5 and the DC voltage source 6 which are connected in series.

The incident energy L, excites the photoconductive layer 13 through the

electrodes

17 and 18 and the capacitive layers 15 and resistive layers 16. The resistance R, shown in FIGS. 1 and 2 corresponds tothe resistance of the energy-responsive layer 13 in the lateral direction thereof between the resistive layer 16 and the adjacent electrodes 14, the capacitance C, to the capacitance of the capacitive layer 15 between the electrode I7 and the layer 13, and the resistance R, to the resistance of the resistive layer 16 between the electrode 18 and the layer 13.

The construction in which the capacitance C, and the resistance R, in FIG. 1 are included in a single resistive capacitance element, corresponds to a formation in which the

layers

15 and 16 are replaced by a single uniform layer of resistive glass enamel provided thereon with an incident energy L, pervious electrode.

ln FlG. 3, the equivalent circuit corresponds to the circuit shown in FIG. 1 when the DPDT S is turned to the side A, while it corresponds to the circuit of FIG. 2 when the switch S is turned to the side B, thus making possible both types of operations. In this arrangement, it is preferable for the resistances R, of the resistive layer 16 and the dark value of resistance R, of the energy-responsive layer 13 in the lateral direction thereof to be selected so as to be roughly the same in both types of operation.

In this manner, the incident energy image such as the light image or X-ray image can be converted and amplified as well as stored and displayed either in a positive or negative visible image.

It will be understood that the energy-responsive element can be constituted withother materials according to particular requirements, as previously mentioned.

As described above, according to this invention, an impedance matching is attached attained in the device having an energy-responsive layer of low impedance and EL element of high impedance, and as a result, an energy-responsive luminescent display device of high sensitivity can be fabricated.

lclaim:

1. An electroluminescent device controlled by an incident energy comprising a first planar electrode of light-pervious material, and electroluminescent layer disposed on said first electrode and which luminesces under the excitation by an AC electric field and of which the waveform of the luminescent output is controlled by a unidirectional electric field applied thereto, a layer of energy-responsive element disposed on said electroluminescent layer and which varies the electric re sistance thereof in response to an incident energy, a second electrode having a grid shape embedded in said layer of energy-responsive element, a layer of dielectric film disposed on said layer of energy-responsive element, said film being divided into sections leaving spaces between sections, resistive elements disposed in said spaces, a plurality of third electrodes each disposed over each section of said dielectric film to constitute a capacitance between it and said energy-responsive layer which varies in response to incident energy, a plurality of fourth electrodes each disposed on each of said resistive elements filling said spaces, means for applying an AC voltage and a DC voltage, in superimposed relationship, between said first electrode and said third electrodes, and switch means for selectively connecting said second electrode and said fourth electrodes in one switch position respectively to said first elec trode and said third electrodes and in another switch position respectively to said third electrodes and said first electrode; the thickness of said layers, the dimensions of each section of said dielectric layer, and the thickness and position of the elemental conductors of said second electrode being selected so that an AC circuit is constituted through said first electrode, said electroluminescent layer, said capacitance formed with said third electrodes and said energy-responsive layer, and through said third electrodes, while a DC circuit is constituted through said fourth electrodes, said filling of resistive elements, lateral resistance of said energy-responsive layer between the end of said resistive element and said second electrode, and through said second electrode, whereby the DC voltage applied to said electroluminescent layer through a virtual conductive plane constituted by said energy-responsive layer is substantially controlled by the variation in the resistance of said energy-responsive layer due to an incident energy.

2. An electroluminescent device according to claim ll, wherein an electrically resistive light shielding layer is provided between said electroluminescent layer and said layer of energy-responsive element.

Claims

1. An electroluminescent device controlled by an incident energy comprising a first planar electrode of light-pervious material, and electroluminescent layer disposed on said first electrode and which luminesces under the excitation by an AC electric field and of which the waveform of the luminescent output is controlled by a unidirectional electric field applied thereto, a layer of energy-responsive element disposed on said electroluminescent layer and which varies the electric resistance thereof in response to an incident energy, a second electrode having a grid shape embedded in said layer of energy-responsive element, a layer of dielectric film disposed on said layer of energyresponsive element, sAid film being divided into sections leaving spaces between sections, resistive elements disposed in said spaces, a plurality of third electrodes each disposed over each section of said dielectric film to constitute a capacitance between it and said energy-responsive layer which varies in response to incident energy, a plurality of fourth electrodes each disposed on each of said resistive elements filling said spaces, means for applying an AC voltage and a DC voltage, in superimposed relationship, between said first electrode and said third electrodes, and switch means for selectively connecting said second electrode and said fourth electrodes in one switch position respectively to said first electrode and said third electrodes and in another switch position respectively to said third electrodes and said first electrode; the thickness of said layers, the dimensions of each section of said dielectric layer, and the thickness and position of the elemental conductors of said second electrode being selected so that an AC circuit is constituted through said first electrode, said electroluminescent layer, said capacitance formed with said third electrodes and said energy-responsive layer, and through said third electrodes, while a DC circuit is constituted through said fourth electrodes, said filling of resistive elements, lateral resistance of said energy-responsive layer between the end of said resistive element and said second electrode, and through said second electrode, whereby the DC voltage applied to said electroluminescent layer through a virtual conductive plane constituted by said energyresponsive layer is substantially controlled by the variation in the resistance of said energy-responsive layer due to an incident energy.

2. An electroluminescent device according to claim 1, wherein an electrically resistive light shielding layer is provided between said electroluminescent layer and said layer of energy-responsive element.