US3579015A

US3579015A - Electron beam addressed plasma display panel

Info

Publication number: US3579015A
Application number: US808195A
Authority: US
Inventors: Robert O Gregory
Original assignee: Monsanto Co
Current assignee: Monsanto Co
Priority date: 1969-03-18
Filing date: 1969-03-18
Publication date: 1971-05-18
Anticipated expiration: 1988-05-18
Also published as: FR2035038A1; GB1309591A; DE2012664A1; NL7003749A; CA934030A

Abstract

A combination display and storage tube of the type having gasfilled cells sandwiched between flat insulating sheets. One of the two electrodes for applying the sustaining voltage to the gas-filled cells is provided with apertures so that an electron beam may be used to initiate or extinguish the discharge of selected cells.

Description

United; States Patent.

Robert 0. Gregory St. Louis, Mo. 808,1 95

Mar. 18, 1969 May 18, 1971 Monsanto Company St. Louis, Mo.

Inventor Appl. No. Filed Patented Assignee ELECTRON BEAM ADDRESSED PLASMA DISPLAY PANEL 8 Claims, 7 Drawing Figs.

11.5. C1 313/89, l78/7.5D, 313/108B, 313/329, 315/169TV Int. Cl H01 j 29/10, H05b 33/02 Field of Search 313/108,

[56] References Cited UNITED STATES PATENTS 2,500,929 3/1950 Chilowsky 313/109X 2,972,707 2/1961 Wood 315/362 3,262,010 7/1966 Kazan 315/63 3,334,269 8/1967 LHeureux 313/89X 3,499,167 3/1970 Baker et a1 315/169 3,509,421 4/1970 Holz 3 l 5/169X Primary ExaminerRoy Lake Assistant Examiner-E. R. La Roche Attorneys-John D. Upham, Herman O. Bauermeister and Harold R. Patton ABSTRACT: A combination display and storage tube of the type having gas-tilled cells sandwiched between flat insulating sheets. One of the two electrodes for applying the sustaining voltage to the gas-filled cells is provided with apertures so that an electron beam may be used to initiate or extinguish the discharge of selected cells.

Patented May 18, 1971 3,579,015

Cvons) FIG.6

| CvoLTs) l I l INVENTOR C ROBERT GREGORY ATTORNEY ELECTRON BEAM ADDRESSED PLASMA DISPLAY PANEL FIELD OF THE INVENTION The present invention relates generally to an information storage and/or display tube of the plasma or gas discharge type, and more particularly, to a storage tube having lightemitting elements which may be turned on and off by means of an electron beam.

BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART In the field dealing with the storage and display of information, it has been suggested that plasma display panels be employed to take advantage of their inherent memory; i.e. bistable mode of operation, long life and high brightness. See for example, proceedings, Fall Joint Computer Conference The Plasma Display-A Digitally Addressable Display With Inherent memory, by D. L. Bitzer and H. G. Slottow, Nov. i966, p. 541, Such plasma display panels generally comprise three laminated sheets of flat glass plates. The center glass laminate being provided with an array of small gas-filled apertures, referred to as bistable plasma display cells. A visual gas discharge may be achieved by proper selection of the gas mixture and the application of a voltage signal of an appropriate value to selected cells.

The discharge of each cell can be made independent of all other cells and is bistable in nature. That is, a sustaining AC voltage having a value less than the critical firing voltage may be applied across all cells, and although it is sufficient to sustain half-cycle discharges once initiated, it effects no discharge until it is combined with an actuation voltage to render the total cell voltage greater than the critical firing voltage. Once the half-cycle discharge is initiated, the information signal may be removed, yet the cell will continue to emit light under the influence of the sustaining field. Thus, bistable operation is achieved.

I-leretofore, the outer laminates of plasma display panels of the type just described have been provided with a crossed-grid arrangement of electrical conductive strips for the purpose of applying the "sustaining and actuation voltages to the cells selected for discharge operation. Application of an actuation voltage pulse to two crossed-grid conductors results in the energization or discharge of the gas-filled cell provided at the intersection of the two conductive strips,

The crossed-grid conductor arrangement for addressing the light-emitting cells of plasma display panels has been employed satisfactorily in certain applications. However, the deposition of conductive strips is a time-consuming and an expensive step in the manufacture of panel displays embodying a large number of cells for high resolution. Furthermore, elaborate switching circuitry capable of handling voltages of several hundred volts, is required to properly select the proper conductive strips required to store or display the information.

SUMMARY OF THE INVENTION The general purpose of this invention is to provide a storage tube of the plasma display type, which embraces all of the ad vantages of similar plasma display panels yet does not possess the aforedescribed disadvantages. To attain this, the present invention utilizes an electron beam addressing arrangement for energizing and deenergizing selected plasma display cells.

An object of the present invention is the provision of a plasma-display-type direct view storage tube, the manufacture of which is susceptible to relatively simple production techniques.

Another object of the present invention is the provision of a direct view storage tube, wherein information can be selec tively stored or erased at electron beam scanning speeds.

In the present invention these purposes (as well as others apparent herein) are achieved generally by a storage tube having substantially flat insulating members separated by a plurality of plasma discharge cells. The cells are filled with an ionizable gas or gas mixture and electrodes are secured to the outer surfaces of the insulating members. One of the electrodes is continuous and transparent, while the other is a thin conductive metal layer having apertures arranged over gasfilled cells. An AC power supply is connected between the two electrodes to provide a sustaining potential. An electron beam addressing system is employed to direct an electron beam through the apertures of the metal electrode to energize and deenergize selected cells.

BRIEF DESCRIPTION OF THE DRAWINGS Utilization of the present invention will become apparent to those skilled in the art from the disclosures made in the following description, as illustrated in the accompanying drawings; in which FIG. 1 is a perspective view of a storage tube constructed in accordance with the present invention;

FIG. 2 is an enlarged broken-away, cross-sectional view of a display panel portion of the storage tube of FIG. 1;

FIG. 3 is an enlarged, detailed view revealing a portion of one of the electrodes deposited on the display panel portion of FIG. 2;

FIG. 4 is a schematic view of the electron beam addressing system and circuit connections of the storage tube of FIG. 1;

FIG. 5 is a schematic representation of wall charge accumulation during a portion of the operation of the storage tube of FIG. l;'and

FIG. 6 is a graphical representation of waveforms corresponding to the wall charges and applied voltages when the cell in in the on state, employed to store and display information by means of the storage tube of FIG. 1.

THE INVENTION Referring now to the drawing, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIG. 1 a storage tube, designated 10. The storage tube 10 consists generally of a gas discharge or plasma display panel 12 having a viewing surface 14, an evacuated glass envelope 16 sealed to and extending from the panel 12, and an electron beam addressing system 18. The evacuated glass envelope 16 is sealed to the plasma display panel 12 and encloses the electron panel addressing system 18. It may be constructed in accordance with wellknown cathode ray tube fabrication techniques.

Referring to FIG. 2, it may be seen that the plasma display panel of the present invention consists of three fiat sheets of insulating material, such as glass. A center sheet 20 is sandwiched between two

outer laminates

22 and 24, and has a plurality of apertures or cells 26 formed through it, by drilling, etching or other means. The density of the cells 26 determines, in part, the resolution of the panel 12. In my experiments, I have used glass sheets 0.006 inch in thickness with a distance between adjacent cells of 0.025 inch, thereby providing a cell density of approximately 1,600 cells per square inch.

The cells 26 are charged with a suitable gas or gas mixture; for example, a mixture of percent neon and 5 percent nitrogen at a pressure of 300 Torr has been found to provide an extremely fast, bright discharge.

The outer surface of the glass sheet 22 is covered by a continuous, transparent electrode 28 such as stannous oxide, SnO while the outer surface of the outer laminant 24 is provided with a conductive-metal electrode 30, such as an aluminum film layer. The electrode 30 is provided with apertures or openings 32 arranged in registration with the gas-filled cells 26, as may best be seen in FIG. 3.

Referring now to FIG. 4, the electron beam addressing system 18 of the present invention is shown in schematic form, the evacuated envelope, mounting elements, and external terminals being omitted for purposes of clarity. The electron gun structure 34 consists of a suitably grounded cathode electrode 36, heated by a filament 38. An accelerating potential represented by a battery 40 is connected between the cathode 36 of the electron gun and the electrode 30 of the gas discharge panel 12. Alternatively, the apertured electrode, 30, may be operated at ground potential with the cathode at a high negative potential. By way of example, the electron gun structure 34 may be an electron gun commercially available from Superior Electronics Company and referred to as a SAQP electron gun, and the accelerating potential may be 6.5 kv.

It should be apparent that electrons emitted from the cathode 36 of the electron gun structure 34 are caused to be accelerated by the accelerating potential 40 along a path toward the apertured electrode 30 of the panel display 12. Between the panel display 12 and the electron gun assembly 34, there are provided horizontal and

vertical deflection plates

42 and 44, between which the electron beam passes and to which appropriate deflection circuitry (not shown) may be externally connected for the purpose of directing the electron beam to selected apertures 32. A beam-gating grid 46 is disposed between the horizontal deflection plates 42 and the electron gun assembly 34 and is connected to beam-gating input terminal, as indicated at 48. The beam-gating input terminals 48 may be connected to an appropriate input signal source synchronized with the external deflection circuitry in accordance with well-known techniques. Thus, it is possible to modulate the intensity of the electron beam emanating from the electron gun assembly 34 during the scanning or sweeping of the beam across the display panel 12.

As may be seen in FIG. 4, an AC voltage source 50 is connected between the

electrodes

28 and 30 of the gas discharge panel 12. The AC signal source 50 may be chosen to provide to the electrodes 28 and 30 a 500 volt peak sustaining voltage at a frequency of 300 kHz.

In operation, the AC voltage source 50 is applied to the

electrodes

28 and 30 of the plasma display panel 12 to provide the necessary sustaining potential. In the absence of any additional potential across the cells, the sustaining voltage is insufficient to develop the critical firing voltage V, required to initiate plasma discharge of the gas within the cells 26.

Information can be written" on or stored within the storage tube 10 by applying an input signal to the beam-gating input terminal 48 so that the beam-gating grid 46 allows electrons to be accelerated from the electron gun cathode 36. These electrons are then deflected by the horizontal and

vertical deflection plates

42 and 44; the amount of horizontal and vertical deflection corresponding to deflection potentials applied thereto. The deflection signals may be synchronized with the application of the input signal in any well-known fashion so that selected cells are properly energized.

The deflection plates direct the accelerated electrons to the selected aperture of the aluminum electrode 30, where they accumulate on the surface of the glass sheet laminate 24. This electron accumulation results in an electrical charge, and therefore electrical field, across the gas-filled cells arranged in registration with the aperture to which the electrons have been directed. The electrical field so established will aid the field resulting from the sustaining voltage during one-half cycle. Although the initial potential across the gas-filled cells is insufficient to produce plasma discharge, the additional potential provided by the accumulation of electrons at the aperture surface of glass sheet 24 will trigger the selected cell to its on state. Subsequently, the electron beam may be turned off by the beam-gating grid 46 of the electron beam structure 34, yet the energized cell will remain in its on state. For the cell to be later extinguished, on command, requires that the charge deposited on the dielectric surface by the electron beam be dissipated after having triggered the cell into the "on" state. I have observed that in the range of vacuum normally used for high-vacuum tubes (l torr) that the charge dissipates in approximately IO seconds. This is due to positive ion bombardment from the residual gas in the vacuum and surface leakage. By proper surface treatment, such as application of a thin, high resistivity, layer of stannous oxide to the surface; the decay of electron beam deposited charge can be made as rapid as desired.

The electron beam can then be repositioned by means of the horizontal and

vertical deflection plates

42 and 44 to energize another gas-filled cell in a like manner. The sustaining voltage provided by the AC voltage source 50 serves to maintain the plasma discharge of those cells which are triggered on by means of the electron beam, even after the electron beam has been turned off or removed.

Thus, it may be seen that information, such as alphanumeric characters, may be written on the plasma display panel 12, where it may be stored indefinitely. The plasma discharge provides a bright visual display of the information, When it becomes desirable to erase an entire character or all of the information displayed by the storage tube 10, the AC voltage source 50 may be turned off, thereby reducing the potential across the actuated cells to a level insufficient to maintain the plasma discharge.

The storage characteristic of a plasma display panel arises from the wall charge generated in each cell 26 as free charges during the gas discharge. These wall charges tend to migrate to the cell walls under the influence of the sustaining AC potential, and therefore arrange themselves so as to aid or add to the applied AC field at the beginning of each half-cycle of the applied AC sustaining voltage. These wall charges are represented in FIG. 5 for a single gas-filled, energized cell. Waveform representation of the applied AC sustaining voltage is shown in FIG. 6a, while a similar representation of the wall charge potential is shown in FIG. 6b.

Referring specifically to the time interval indicated between the time 1,, and time t, in FIG. 6, it may be seen at time I, the combined electrical field resulting from the wall charge and that of the AC sustaining voltage signal is sufficient to fire or discharge the cell. As may be seen, the discharge of the cell reverses its wall charge polarity very rapidly so that the next half-cycle of operation repeats the discharge'phenomenon.

However, I have found that during the time interval between time t and t the electron beam may be pulsed to erase or deenergize a cell which is in its on state. The pulsed electron beam deposits a charge on the dielectric surface upon which it impinges after passing through a selected aperture of the aluminum electrode 30. The deposited charge opposes the electric field of the wall charge during the time period between time t and time t,. Therefore, if the deposited charge is sufficiently large and if it is applied between time t and 1,, the total electrical field across the cell will be insufficient to sustain the discharge which would otherwise occur at time 1,, resulting in the cell reverting to its off condition during the next half-cycle of the AC sustaining voltage signal. If the decay of the charge deposited by the electron beam is not too 7 fast relative to the decay of the wall charge, the cell will remain off for all subsequent half-cycles of operation, or until again energized by the electron beam. Hence, an energized cell may be efficiently extinguished in accordance with my invention.

In summary, the storage tube of the present invention employs a unique electron beam addressing system directly applied to the dielectric surface material of a plasma-displaytype panel in registration with cells to be triggered on or off. Such a storage tube may be advantageously used as a storage oscilloscope where it is important that there by no loss of resolution of a displayed signal trace with the passage of time. Another application of my storage tube would be that of a data display or storage memory; for example, in computer time-sharing scientific and educational applications. In these latter applications the resolution, indefinite storage time and selective erasure, present advantages not available with other types of data display system.

Many modifications and variations of the present invention are possible in view of the above teachings. Therefore, it is to be understood that the invention may be practiced otherwise than as specifically described.

I claim:

l. A storage tube Comprising a plurality of substantially flat insulating members defining storage cells therebetween,

an ioniz'able gas within and filling said storage cells,

a pair of electrodes external to and separated from said cells by said insulating members, one of said electrodes defining apertures registered with said gas-filled cells,

power supply means connected to said electrodes for providing a sustaining potential less than that required to initiate a plasma discharge of said gas-filled cells but sufficient to sustain such discharge once initiated,

electron beam addressing means positioned to direct an electron beam through selective apertures of said one electrode and onto the surface of one of said insulating 'members,

whereby electrical charges may be applied to said gas-filled cells to selectively initiate discharge or terminate discharge of the gas provided therein.

2. The storage tube, as defined in claim I, wherein said power'supply means is an AC voltage source.

3. A storage tube, as defined in claim 1, wherein the other of said electrodes is a continuous transparent material.

4. The storage tube, as defined in claim 1, wherein said one electrode having apertures therein is a substantially continuous thin-film conducting layer.

5. The storage tube, as defined in claim 1, wherein said electron beam addressing means, comprises an electron gun,

a DC potential source connected between said gun and said one electrode to accelerate electrons emitted by said gun,

deflection plates positioned between said electron gun and said one electrode for directing electrons emitted by said gun to selected apertures provided in said one electrode, and

an electron beam-gating grid positioned between said deflection means and said electron gun for gating the emission of electrons from said gun in response to electrical signals applied to said grid.

6. A combination display and storage tube, comprising an evacuated envelope housing an electron gun, deflection plates, and an electron beam-gating grid,

a face plate including a panellikestructure of an insulating material and having a plurality of gas-filled cavities formed therein, the gas-filled cavities being charged with an ionizable gas,

a pair of electrodes external to and separated from said gas filled cells by said insulating material, one of said electrodes defining apertures registered with said gas-filled cells, the other electrode being a continuous transparent electrode,

an AC power supply means connected between said electrodes for providing a sustaining potential less than that required to initiate discharge of said gas-filled cells, but sufficient to sustain such discharge once initiated,

means for controlling an electron beam emitted by said electron gun, whereby said electron beam may be selectively applied to said gas-filled cells through said apertures of said one electrode to initiate and extinguish the plasma discharge of gas provided therein.

7. A method of addressing a storage tube of the type having a plasma display panel comprising a plurality of gas-filled, light-emitting cells formed within an insulating material, comprising the steps of I applying to said gas-filled cells by means of electrodes external thereto an AC voltage signal having a magnitude insufficient to initiate discharge of the gas therein, but sufficient to sustain the light-emitting discharge once initiated, and

directing an electron beam onto the surface of said insulating material in registration with selected gas-filled cells, said electron beam having an intensity sufficient in combination with said AC voltage signal to trigger the individual disglae cells to theirplasma dischar e state. 8. The metho o returning individual gas-fille cells formed within insulating material of a plasma display storage panel to their initial nonlight-emitting states, comprising the steps of directing an electron beam to the surface of said insulating material in registration with cells to be returned to their off state, and pulsing an electron beam during an appropriate half-cycle time interval to deposit a charge on said surface in op- 7 position to wall charges developed within said cells.

Claims

1. A storage tube comprising a plurality of substantially flat insulating members defining storage cells therebetween, an ionizable gas within and filling said storage cells, a pair of electrodes external to and separated from said cells by said insulating members, one of said electrodes defining apertures registered with said gas-filled cells, power supply means connected to said electrodes for providing a sustaining potential less than that required to initiate a plasma discharge of said gas-filled cells but sufficient to sustain such discharge once initiated, electron beam addressing means positioned to direct an electron beam through selective apertures of said one electrode and onto the surface of one of said insulating members, whereby electrical charges may be applied to said gas-filled cells to selectively initiate discharge or terminate discharge of the gas provided therein.

2. The storage tube, as defined in claim 1, wherein said power supply means is an AC voltage source.

5. The storage tube, as defined in claim 1, wherein said electron beam addressing means, comprises an electron gun, a DC potential source connected between said gun and said one electrode to accelerate electrons emitted by said gun, deflection plates positioned between said electron gun and said one electrode for directing electrons emitted by said gun to selected apertures provided in said one electrode, and an electron beam-gating grid positioned between said deflection means and said electron gun for gating the emission of electrons from said gun in response to electrical signals applied to said grid.

6. A combination display and storage tube, comprising an evacuated envelope housing an electron gun, deflection plates, and an electron beam-gating grid, a face plate including a panellike structure of an insulating material and having a plurality of gas-filled cavities formed therein, the gas-Filled cavities being charged with an ionizable gas, a pair of electrodes external to and separated from said gas-filled cells by said insulating material, one of said electrodes defining apertures registered with said gas-filled cells, the other electrode being a continuous transparent electrode, an AC power supply means connected between said electrodes for providing a sustaining potential less than that required to initiate discharge of said gas-filled cells, but sufficient to sustain such discharge once initiated, means for controlling an electron beam emitted by said electron gun, whereby said electron beam may be selectively applied to said gas-filled cells through said apertures of said one electrode to initiate and extinguish the plasma discharge of gas provided therein.

7. A method of addressing a storage tube of the type having a plasma display panel comprising a plurality of gas-filled, light-emitting cells formed within an insulating material, comprising the steps of applying to said gas-filled cells by means of electrodes external thereto an AC voltage signal having a magnitude insufficient to initiate discharge of the gas therein, but sufficient to sustain the light-emitting discharge once initiated, and directing an electron beam onto the surface of said insulating material in registration with selected gas-filled cells, said electron beam having an intensity sufficient in combination with said AC voltage signal to trigger the individual display cells to their plasma discharge state.

8. The method of returning individual gas-filled cells formed within insulating material of a plasma display storage panel to their initial nonlight-emitting states, comprising the steps of directing an electron beam to the surface of said insulating material in registration with cells to be returned to their ''''off'''' state, and pulsing an electron beam during an appropriate half-cycle time interval to deposit a charge on said surface in opposition to wall charges developed within said cells.