US2877376A - Phosphor screen device - Google Patents

Description

March 10, 1959 R. K. ORTHUBER 2,877,376 PHOSPHOR SCREEN DEVICE Filed Sept. 6, 1955 2 SheetsSheet 1 I SIGNAL SOURCE F E RRO-E LE CTRIC WINDOW CONDUCTIVE STRIP 2 I INVENTOR.

F, 4 BY RlCIj/ARD ORTHUBER J2 fizwf A T TORNE Y March 1959 R. K. ORTHU BER PHOSPHOR SCREEN DEVICE 2 Sheets-Sheet 2 Filed Sept. 6, 1955 .0 VIDEO AND SCANNING CIRCUITS F ERRO-ELE CTR/C LAYER PHOSPHOR IN V EN TOR RICHA RD K. 0R THUBER 3 KM ATTORNEY United States Patent PHOSPHOR SCREEN DEVICE Richard K. Orthuber, Fort Wayne, Ind., assignor to International Telephone and Telegraph Corporation Application September 6, 1955, Serial No. 532,399

4 Claims. (Cl. 315-12) The present invention relates to a phosphor screen device, and more particularly to an electroluminescent screen which is excited by means of a crossed grid conductor system.

In Orthuber et al. application Ser. No. 528,765 filed August 16, 1955, and entitled Information Display Device a crossed grid electroluminescent display device was disclosed and claimed. This device consisted essentially of a layer of electroluminescent phosphor material sandwiched between two different sets of conductors, the conductors of each set extending substantially at right angles to each other. By sequentially applying signal voltages to the individual conductors of each set, it was possible to excite the phosphor material into producing a pattern or image.

The device of this earlier application utilized mechanical switching means for applying the signal voltages sequentially to the individual conductors. While such mechanical means is efiiciently operable for slow scanning or switching rates, it is not entirely satisfactory when operated at conventional television scanning frequencies.

In view of the foregoing, it is an obect of this in vention to provide a phosphor screen device which is capable of operating at the usual television scanning frequencies.

It is another object of this invention to provide an electroluminescent phosphor screen device for reproducing television images.

It is still another object of this invention to provide an essentially flat television picture-reproducing device which does not require the utilization of a conventional cathode ray projection tube for exciting an electroluminescent phosphor screen.

In the accomplishment of this invention there is provided a layer of electroluminescent phosphor material,

a first grid of spaced parallel conductors on one side of said layer, a second grid of spaced parallel conductors on the other side of said layer, the conductors of the respective grids extending transversely of each other, a first layer of dielectric material on said first grid, a second layer of dielectric material on the second grid, a first electron beam scanning the first layer for producing electrostatic charges thereon which are to be capacitively coupled to the first grid conductors, a second electron beam scanning the second layer for producing electrostatic charges thereon which are thereby capacitively coupled to the second grid conductors, and means for. modulating both of said electron beams.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken'in conjunction with the accompanying drawings, wherein:

Fig. 1 is a front elevation of one phosphor display screen which utilizes mechanical means for applying a signal voltage to the crossed grids;

Fig. 2 is a front view of one embodiment of this invention;

Fig. 3 is a sectional view taken substantiallyalong the section line 3-3 of Fig. 2; and

Fig. 4 is a fragmentary cross-section of a slightly different embodiment of this invention.

Referring to the drawings, and more particularly to Fig. 1, a layer 1 of electroluminescent phosphor material is sandwiched between first and second grids indicated generally by the reference numerals 2 and 3, respectively. The grid 2 is composed of a plurality of conductive spaced parallel strips 4, and the grid 3 is composed of similar strips 5 which extend in a direction perpendicular to that of the conductors 4. Rotary switch means composed of two mechanical switches 6 and 7 are conductively connected, respectively, to the individual grid conductors 4 and 5, and a source 8 of signal voltage is coupled to the switch rotors 9 and 10, respectively. As the rotors 9 and 10 revolve, the respective conductors 4 and 5 are individually and sequentially connected to the signal source 8. With the amplitude of the signal voltage derived from the source 8 properly adjusted, the phosphor layer 1 may be made to luminesce at the intersections or points of the conductors 4 and 5 which are connected into the source circuit. For further information regarding the construction and operation of this device of Fig. 1, reference is made to the aforementioned Orthuber et al. application and also to the description of a similar device found in Piper Patent No. 2,698,915. Suitable electroluminescent phosphor materials are described in Mager Patent No. 2,566,349 and Piper Patent No. 2,698,915.

In the aforementioned Orthuber et al. application there is disclosed and claimed a particular screen construction which utilizes a nonlinear impedance material in layer form in cooperative relationship with the phosphor layer. This nonlinear impedance layer was disclosed as being composed of either polaristor or ferroelectric material, and since either of these materials may be utilized in this invention, and in the same manner as disclosed in the prior Orthuber et al. application, so much of this prior application as is necessary to a full understanding of this invention is included herein by reference.

Having now explained the rudiments involved in exciting the phosphor layer 1 of Fig. 1, reference is I now made to Figs. 2 and 3 which illustrate the first embodiment of this invention. A phosphor layer 1 and a contiguous ferroelectric layer 11 are sandwiched between the crossed grids 2 and 3, respectively. The individual conductors composing these grids project a suitable distance beyond the layers 1 and 11 as indicated by the numerals 12 and 13, respectively. Bus bars or biasing electrodes 14 and 15 are coupled respectively to the individual grid conductors 5 and 4 by means of suitable isolating resistors 16 and 17. The purpose of these resistors is to prevent shorting of the respective grid conductors. A battery 18 supplies a suitable biasing potential to the two bus bars 14 and 15 for driving the ferroelectric layer 11 into the range of near-saturation, this particular feature being fully disclosed in the aforementioned Orthuber et al. application.

By applying a suitable exciting voltage to any two of the selected grid conductors, such as conductors 19 and 20, the phosphor material is caused to luminesce at a spot 21 corresponding to the intersection thereof. Thus by sequentially and rapidly applying an exciting voltage to the respective conductors of the grids 2 and 3, it is seen that a visible contrasting pattern may be produced.

Two cathode ray devices 22 and 23 are mounted on the projecting conductor ends 12 and 13 as shown. Since these two devices or tubes 22 and 23 may be'identical only one such device need be described in detail. The tube comprises an evacuated envelope 24 of glass or the like which is elongated and essentially round in crosssection except for the flat side 25 which contiguously lies on the conductor extensions 12. A suitable conductive coating 26 is applied to the inner wall of thetube except for the flattened side 25 for a purpose which will become apparent hereafter. An electron gun 27 of conventional design is mounted in one end of the envelope 24 to produce a beam of electrons which normally follows a path parallel to the plane of the grid conductor extensions 12 and transversely of the extensions. Suitable beam deflecting means such as electrostatic deflecting plates 28 are positioned adjacent the gun 27 for defleeting the electron beam in one plane only, that plane being normal to the plane of the conductor extensions 12. Thus, by applying suitable deflecting voltages to the plates 28, the beam may be scanned sequentially and transversely across all of the conductor extensions 12.

Now considering both of the tubes 22 and 23, it is seen that the electron beams thereof may be scanned over the respective wall sections 25 opposite conductor extensions 12 and 13 at either the same or different rates. For producing a conventional television picture, the scanning rate of the tube 22 would correspond to the frame or field scanning frequency while the scanning of the tube 23 will correspond to the horizontal or line scanning frequency.

At this point it is well to discuss briefly a preferred construction for the electron guns 27. In operation, it is desired that the current of the electron beams be high, and such currents are conventionally produced by means of the so-called Pierce guns or by means of conventional triode guns which produce ribbon-type beams of rectangular cross-section. Such a ribbon beam is indicated by the dashed line beams 29 and 30 emanating from the guns of the two tubes 22 and 23. The importance of the high current beam will become apparent from the following.

In operation, a video signal is applied to the control grids, or other suitable electrodes, of the guns of the two tubes 22 and 23 for intensity modulating the respective beams. By application of the deflecting signals to the two tubes, the impact point with wall 25 travels along in a straight-line path and releases secondary electrons from the wall 25 at a ratio greater than unit, which electrons are collected by the conductive wall coating 26. As a consequence, the electron beam produces positive charges on the flattened wall section 25 of values corresponding to the instantaneous video signal amplitude. During the build-up period of this charge opposite a particular conductor extension 12 or 13, a pulse of voltage will be produced on this extension by capacitive coupling through the interposed Wall element. While one tube is producing such a charge or pulse of energy for one of the respective grid conductors, the other tube is producing corresponding pulses onthe conductors of the other grid. Thus,

assuming the instantaneous condition at which the beam .29 is producing a charge over the conductor 20 and the beam 30 is producing a charge over the conductor 19, a

spot of light will be produced at the intersection 21. By scanning the beam 29 over the respective conductors at a television field or frame frequency and the beam 30 over its conductors at the horizontal line frequency, a

conventional raster pattern will be produced on the phosphor screen 1.

In order to produce pulses of suflicient intensity on the grid conductors, it is important that (1) the coupling capacity between the inner surface of the tube and the conductors be high, and (2) the beam intensity be high. High coupling capacity may be achieved by observing the following conditions: (a) The flat wall section 25 should be as thin as conditions will permit; and (b) Airinterspaces between the outside of the flat wall section 25 and the conductor extensions should be avoided by application of a plastic material having a high dielectric conmosphere.

stant, this plastic material serving as a coupling film between the tube wall 25 and the conductor extensions.

Capacitive coupling through the tube wall to the conductors may be achieved by a slightly different embodiment of this invention as is illustrated in Fig. 4. Like reference numerals will indicate like parts. Instead of flattening one side of the tube to achieve the flattened wall section 25 of Fig. 3, a fiat piece or Window 31 of ferroelectric material is used. This material may be the same as that used in layer 11 of the display screen itself. Suitable brackets or junctions 32 are used to seal the window 31 to the tube envelope proper and this window 31 is superposed on the conductor extensions 12 in the same manner as the flattened section 25.

Since the ferroelectric window possesses high dielectric permitivity, it is seen that high coupling capacity to the strip extensions 12 is possible.

Since the electron beam of the tube rapidly scans the flattened wall section, it may develop in some instances that the electrostatic charges produced by one scanning action will not disappear rapidly enough, in which case it is desirable to use a semi-conductive coating on the inner wall of the flattened wall section to erase or remove the charge soon after it is produced. A suitable semiconductive material is found in titanium-oxide-dioxide which is evaporated onto the tube wall in an oxygen at- The evaporated film may be baked in either vacuum or oxygen in order to obtain the desired resistance characteristic. Another possible way to erase the charges produced by one beam-scanning action prior to the next is to reduce the velocity of the beam electrons during the retrace period to a value below that required to produce secondary emission. Thus on the active scanning cycle beam electron velocity is made high to produce the necessary secondary emission, but on retrace or beam return, the electron velocity is reduced so that the secondary emission ratio drops below 1. Other methods of erasing charges between active scanning periods will occur as obvious to a person skilled in the art.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by Way of example and not as a limitation to the scope of my invention.

What is claimed is:

l. A high speed switching system comprising: a cathode ray tube having an elongated envelope formed of dielectric material with an electron gun disposed at one end thereof and arranged to direct an electron beam along the longitudinal axis of said envelope, electron beam deflecting means operatively associated with said electron gun and arranged to scan said electron beam in a straight line path longitudinally along the side wall of said envelope in one plane only whereby said electron beam impinges on said side wall; and a plurality of spaced parallel conductors abutting the outer surface of said envelope side wall along the path of said electron beam scanning and disposed transversely thereto whereby said scanning of said electron beam along said side wall produces incremental charges thereon thereby sequentially producing voltage pulses in said conductors by capacitive coupling through said envelope side wall.

2. A high speed switching system comprising: a cathode ray tube having an elongated envelope with an electron gun disposed in a first portion at one end thereof and arranged to direct an electron beam along the longitudinal axis of said envelope, said envelope including another portion adjacent said first portion and having a generally semi-circular cross-section with at least its flat wall section being formed of thin dielectric material, electron beam deflecting means operatively associated with said electron gun and arranged to scan said electron beam in a straight line path along the longitudinal axis of said fiat wall in one plane only normal to said flat wall whereby said electron beam impinges thereon; and a plurality of spaced parallel conductors respectively having flat sides abutting the outer side of said flat wall and disposed transversely of the longitudinal axis thereof whereby scanning of said electron beam along said longitudinal axis of said fiat wall produces incremental charges thereon thereby sequentially producing voltage pulses in said conductors by capacitive coupling through said envelope side wall.

3. The system of claim 2 in which said fiat wall section of said envelope is formed of thin ferroelectric material.

4. A high speed switching system comprising: a cathode ray tube having an elongated envelope with an electron gun disposed in a first portion at one end thereof and arranged to direct a high current ribbon type electron beam of rectangular cross-section along the longitudinal axis of said envelope, said envelope including another portion adjacent said first portion and having a generally semi-circular cross-section with at least its flat wall section being formed of thin dielectric material, electron beam deflecting means operatively associated with said electron gun and arranged to scan said electron beam in a straight line path along the longitudinal axis of said fiat wall in one plane only normal to said flat wall whereby said electron beam impinges thereon, said envelope having a conductive coating on the curved portion of the inner wall of said other envelope portion facing said flat wall for collecting secondary electrons emitted by impingement of said electron beam on said fiat wall; and a plurality of spaced parallel flat conductors abutting the outer side of said flat wall and disposed transversely of the longitudinal axis thereof whereby scanning of said electron beam along said longitudinal axis of said fiat wall produces incremental positive charges thereon due to secondary emission thereby sequentially producing voltage pulses in said conductors by capacitive coupling through said flat wall.

References Cited in the file of this patent UNITED STATES PATENTS

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