US2856553A - Electroluminescent display device - Google Patents

Description

Oct. 14, 1958 H. K. HENIS\CH 2,856,553

ELECTROLUMINESCENT DISPLAY DEVICE Filed April 24, 1956 CONDUCTIVE FILM l2 v ELECTROLUMINESCENT LAYER l4 CONDUCTIVE FILM l6 INSULATING LAYER l8 POWER 28 SUPPLY 'POI Tco TAc 2 j 30) N N T 2 unlconoua-roiz Lm/zz 20 --o usuuA-ruua LAYER l8 -24 23222334122323 FF-flr$a$va F'n. l7.

(ii-A ss lo 22mm 22 c:i- 1'Ac-;- 30 F/6f4 POWER SUPPLY J'LHJ'L 4 INCOMING SIGNAL mco l STEPPING SWITCH ]1 H2 PULSE TRAINl I MECHANISM 204 POWER I INCOMING I 2I4 I i I G NAL 222 .J'U'LIL I STEPPING SWITCH STEPPING SWITCH INCOMING 2 MECHANISM MECHANISM l; l UL E TRAIN T INVENTOR.

' HEM/Z A. HEN/86H 226 PULSE GENERATOR BY FIG 3 KZI ATTORNEY= United States Patent 2,856,553 ELECTROLUMINESCENT DISPLAY DEVICE Heinz Henisch, Flushing, N. Y., assignor to Sylvania Electric Products Inc., a corporation of Massachusetts Application April 24, 1956, Serial No. 580,382 9 Claims. (Cl. 313-108) My invention is directed toward electroluminescent display devices.

Certain types of phosphors luminesce when under the influences of an externally applied electric field, the intensity of the emitted light being some function of the strength of this applied field. Consequently, films or layers formed from such phosphors can be used as transducers for transforming electrical energy to light energy. Phosphors of this type are said to be electroluminescent.

It is known that first and second mutually orthogonal, for example, horizontal and vertical arrays of parallel, separated electrical conductors can be positioned on each side of such a film or layer to form a crossed-grid structure wherein a portion of the film (defined as a cell) is connected between a horizontal conductor and one vertical conductor. When a suitable electric potential ditference is applied between any one horizontal-vertical conductor pair, the cell connected between this pair will luminesce.

Further it has been proposed to switch or commutate these applied potentials in such manner as to successively energize each cell in turn, thus producing an effect analogous to the cathode ray tube scanning operation as developed in a conventional television receiver. In this manner, it is possible to produce a flat electroluminescent panel which may be adapted for use as a replacement for a cathode ray tube in a television receiver.

It will be apparent that these known devices display an electroluminescent image against an unlit or dark background.

In contradistinction, I have invented a new type of electroluminescent image display device in which the image to be displayed forms a dark or unlit pattern displayed against an electroluminescent background. To distinguish the new device from the types described above, the term electro-tenebrescent will be applied thereto.

Accordingly, it is an object of the present invention to provide a new and improved device of the character indicated.

Another object is to improve electroluminescent image display devices in such manner that the image to be displayed forms a dark or unlit trace displayed against an electroluminescent background.

.Still another object is to improve electroluminescent image display devices through the use of infra-red quench- 1ng.

Yet another object is to provide a new and improved electroluminescent image display device in which a dark image is produced by selectively quenching electroluminescent radiation at selected areas on an energized electroluminescent panel.

Still a further object is to provide a new electrotenebrescent image display device.

These and other objects of my invention will either be explained or will become apparent hereinafter.

It is known that electroluminescence can be quenched 0r extinguished by infra-red radiation of an appropriate plication.

wave length. It is also known that certain semiconductor materials, such as germanium, silicon and certain intermetallic compounds, can be used as a source of such radiation. For; example, when minority carriers are injected by a p-n juction or a metallic pont contact into such a semiconductor, some radiative recombination will ensue, and infra-red radiation will be emitted as a result of this recombination. (The technique of injecting carriers by a p-n junction or by a point contact is known to the art and will not be described in detail in this ap- Further information on carrier injection can be found for example in the textbook Transistors, Theory and Application written by Coblenz and Owens and published in 1955 by the McGraw-Hill Book Company.

In my invention there is provided an energized electroluminescent panel which emits uniform electroluminescent radiation. Adjacent one surface of this panel is placed a semiconductor layer which contains one or more p-n junctions or alternatively contains one or more metallic point contacts. The layer is insulated from the panel. When minority carriers are injected into the semiconductor layer by at least one of the junctions or point contacts, radiative recombination occurs and localized infra-red radiation is produced in the region of the said junction or point contact.

I further provide means to inject said carriers by a selected one of said junctions or a selected point contact, the radiation produced in the region of said junction or contact penetrating into said panel and quenching the electroluminescent radiation of a corresponding small region in the electroluminescent panel.

Illustrations of my invention will be described with reference to the accompanying drawings, wherein Figs. 1, 2 and 3 illustrate different embodiments of my invention, and Fig. 4 is a cross sectional view of the embodiment of Fig. 1.

Referring now to Figs. 1 and 4, there is provided a multi-layer structure including in the order named, a glass layer It), a first conductive film 12, and electroluminescent layer 14, a second conductive film 16, an electrically insulating layer 18 (which is transparent to the infra-red radiation) and a semiconductor (11 type) layer 20. Secured to a surface of layer 20 remote from the glass layer 10, is a metallic point contact 22 and a base contact 30. Base contact 36 and point contact 22 are electrically interconnected through a series network including, in the order named, a battery 24 and a switch 26. (As indicated previously, the point contact can be replaced by a p-n junction, if desired.) The conductive films 12 and 16 are connected to a power supply 28. This arrangement operates in the following manner.

The electroluminescent layer is energized (by virtue of the connection between the conductive films and the power supply 28) and exhibits uniform electroluminescent radiation which can be visibly observed on the exposed surface of the glass layer 10.

The small portion of the semiconductor 20 in juxtaposition with point contact 22 constitutes (together with point contact 22) a p-n or rectifying junction. When switch 26 is closed, layer 20 is coupled through the p-n junction and switch 26 to the positive terminal of battery 24. In addition, layer 20 is coupled through the base or ohmic contact 30 to the negative terminal of battery 24. Consequently, the junction is biased in the forward current or low resistant direction; majority charged carriers (electrons) flow out of the layer and through the point contact, while the minority charged carriers (holes) flow through the contact into the semiconductor layer. This action of the minority charged carriers is termed injection. When the minority charged carriers are so injected, some of these minority charged carriers recombine radiatively with the majority charged carriers present in the semi-conductor layer; this action produces infra-red radiation. The radiation penetrates through the various intermediate layers into the electroluminescent layer 14 and extinguishes the electroluminescent radiation therein in a region which corresponds approximately to the area of the point contact 22. In this manner, a selected area of the electroluminescent layer 14 is quenched when switch 26 is closed.

Referring now to Fig. 2, there is shown a structure similar to Fig. 1. However, in Fig. 2 the single point contact 22 of Fig 1 is replaced by a plurality of point contacts, in this example point contacts 100, 102, 104. Each of these point contacts is connected to a corresponding fixed contact of stepping switch 106. The position of the stepping switch arm 108 is controlled by a conventional stepping switch mechanism 110. Incoming pulses carried in a pulse train are supplied to the stepping switch. Each time a pulse is supplied the mechanism, the stepping switch arm is advanced one step.

The semiconductor layer 20 is grounded. An incoming signal is supplied through terminals 112 and thereafter supplied through stepping switch arm 108 and the semi-conductor layer. Dependent upon the position of the stepping switch, a selected one of the three different electroluminescent radiation areas of the electroluminescent layer 14 is extinguished in accordance with the incoming signal. As the amplitude of the incoming signal increases, the number of injected carriers increases, the amount of radiation produced increases, and the degree or intensity of quenching increases accordingly.

It will be obvious that by increasing the number of point contacts and correspondingly increasing the number of fixed contacts of the stepping switch, the entire surface of the semiconductor can be divided into radiation areas which can be selectively quenched in the manner indicated.

In Fig. 3, the device shown in Fig. 2 is modified in such manner that the electroluminescent layer can be scanned to produce a dark trace in a manner analogous to known cathode ray tubes of the dark trace type.

In Fig. 3, there is provided a plurality of coplanar semiconductor layers, in this example three layers 200, 202, 204. These layers are separated from each other by insulating layers 206. Secured to a selected surface of each of these semiconductor layers is a second plurality, in this example a like plurality of thin point contact layers 208, 210, 212.

Each of the semiconductor layers is provided with corresponding base contacts 230, 232, 234. Each base contact is connected to a corresponding fixed contact of a stepping switch 214. Each of the point contact layers is connected to a corresponding fixed contact of a second stepping switch 216. An incoming video type signal is applied between terminals 112. One of these terminals is grounded, the other is connected to the arm 218 of stepping switch 216. The arm of stepping switch 214 is grounded. Incoming pulses, which can be line synchronization pulses which are carried along with the incoming video type signal and subsequently separated therefrom in a conventional manner (not shown), are supplied to the stepping switch mechanism 220 which controls the position of the switch arm 222 of stepping switch 214.

The synchronization pulses are also supplied to the conditioning electrode of gate 224. A pulse generator 226 supplies pulses to the input of gate 224 and the output of gate 224 is connected to the input of the stepping switch mechanism 226 which controls the position of the switch arm 218 of the stepping switch 216. The pulse generator generates pulses at a recurrence frequency three times as high as the recurrence frequency of the synchronization pulse.

Gate 224 is normally closed and is opened only upon arrival of each synchronization pulse. The time delay of gate 224 is so adjusted that upon the arrival of this synchronization pulse, gate 224 remains open for sufficient time to permit three separate sequential pulses generated by the pulse generator 226 to pass through the gate and control the operation of stepping switch mechanism 226. At this point, gate 224 is closed and opened again only upon the arrival of the next synchronization pulse. In this manner, each point contact of semiconductor layer 200 is selectively energized in turn. Then the contacts of semiconductor 202 and 204 are selectively energized sequentially in the same manner. In other words, the operation produced is analogous to the scanning operation of a dark trace cathode ray tube.

Certain known electroluminescent layers are formed from electroluminescent powders which are in contact with each other. When such layers are used, power supply 28 can be either of the direct current or alternating current types. Other known electroluminescent layers are formed from electroluminescent powders which are separated from each other by some dielectric material. In this situation an alternating current power supply must be used.

While I have shown and pointed out my invention as applied above, it will be apparent to those skilled in the art that many modifications can be made within the scope and sphere of my invention as defined in the claims which follow.

What is claimed is:

1. In combination, an electroluminescent layer; first and second electrically conductive films coating opposite surfaces of said electroluminescent layer; and a semiconductor layer positioned adjacent the second film and insulated therefrom.

2. The combination as set forth in claim 1, wherein said semiconductor layer is characterized by radiative recombination of oppositely charged carriers.

3. In combination, an electroluminescent layer; first and second electrically conductive films coating opposite surfaces of said electroluminescent layer, said first coating being optically transparent, said second coating being transparent to infra-red radiation; and a semiconductor layer positioned adjacent said second film and insulated therefrom in a manner at which infra-red radiation produced in said semiconductor layer travels through said second film into said electroluminescent layer, said semiconductor layer being formed from a semiconductor material in which infra-red radiation is produced when oppositely charged carriers recombine therein.

4. In combination with an electroluminescent panel, a semiconductor layer positioned adjacent said panel and insulated therefrom; and means coupled to said layer to generate infra-red radiation in a selected region of said layer, said radiation passing out of said layer into a corresponding region of said panel.

5. In combination, an energized electroluminescent panel emitting uniform electroluminescent radiation, said panel containing a large plurality of radiating point elements; a semiconductor layer containing a like plurality of p-n junctions, said layer being insulated from said panel and being positioned adjacent said panel in a manner at which each junction is aligned with the corresponding point element, said layer, when minority carriers are injected thereinto by at least one of said junctions producing localized infra-red radiation in the region of said one junction, said radiation resulting from radiative recombination of said injected carriers; and means to cause carriers to be injected into said layer by a selected one of said junctions, the radiation produced in the region of said selected junction penetrating into said panel and quenching the electroluminescent radiation of the corresponding point element.

6. An electroluminescent display device responsive to an incoming video signal and comprising an energized electroluminescent panel emitting uniform electroluminescent radiation, said panel containing a large plurality of radiating point elements; a like plurality of radiation generators, each generator, when energized by said signal, emitting infra-red radiation which thereafter impinges on the corresponding point element and quenches the electroluminescent radiation emitted by said corresponding element, the degree of quenching increasing as the amplitude of the video signal increases; and means to supply said signal successively to each of a selected number of said generators in turn, whereby the resulting quenching action produces a dark visual image defined against an electroluminescent background.

7. In combination, an electroluminescent panel, a layer of semiconductor material positioned adajcent one surface of said panel and insulated therefrom; and at least one point contact secured to the surface of said layer remote from said panel.

8. A device for extinguishing electroluminescent radiation emitted from a selected point element in an energized electroluminescent panel, said device comprising a generating element which when energized produces infra-red radiation, said element being mounted adjacent said panel in a position at which said infra-red radiation passes into said panel and extinguishes the electro luminescent radiation emitted from said point element, said generating element being insulated from said panel; and means to selectively energize and deenergize said generating element.

9. A device for extinguishing electroluminescent radiation emitted from a plurality of point elements in an energized electroluminescent panel, said device comprising a like plurality of generating elements, each of which when energized produces infra-red radiation, each of said elements being mounted adjacent said panel in positions at which the infra-red radiation produced by any one element passes into said panel and extinguishes the electroluminescent radiation emitted from the corresponding point element, each generating element being insulated from said panel; and means to selectively energize and deenergize selected ones of said generating elements in a predetermined pattern and sequence.

References Cited in the file of this patent UNITED STATES PATENTS

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