Gas discharge device having wide electrode in border pilot cell
United States Patent Fein et al.  
 1 Apr. 15, 1975 GAS DISCHARGE DEVICE HAVING WIDE ELECTRODE IN BORDER PILOT CELL Inventors: Michael E. Fein; H. Joseph I-Ioehn,  
 both of Toledo. Ohio Assignee: Owens-Illinois, Inc., Toledo, &#39;Ohio Filed: Sept. 7, 1972 Appl. No.: 286,868  
 US. Cl. 313/217; 313/188; 313/201; 315/169 TV Int. Cl. HOlj 17/04 Field of Search 313/1095, 188, 201, 217; 315/169 TV, 169 R References Cited UNITED STATES PATENTS 2/1972 Kupsky 315/169 TV X Primary ExaminerRud0lph V. Rolinec Assistant Examiner-Lawrence .l. Dahl Attorney, Agent, or Firm-Donald Keith Wedding [57] ABSTRACT 9 Claims, 5 Drawing Figures PATENTEDAPR 1 5191s 3.878 ,420 sum a 95 3 GAS DISCHARGE DEVICE HAVING WIDE ELECTRODE IN BORDER PILOT CELL BACKGROUND OF THE INVENTION This invention relates to the simultaneous conditioning and addressing of multiple gas discharge devices within the same sustaining voltage cycle, especially where the multiple gas discharge devices are display/- memory panels or units which have an electrical memory and which are capable of producing a visual display or representation of data such as numerals, letters, radar displays, aircraft displays, binary words, educational displays. etc.  
  Multiple gas discharge display and/or memory panels of one particular type with which the present invention is concerned are characterized by an ionizable gaseous medium, usually a mixture of at least two gases at an appropriate gas pressure, in a thin gas chamber or space between a pair of opposed dielectric charge storage members which are backed by conductor (electrode) members, the conductor members backing each dielectric member typically being appropriately oriented so as to define a plurality of discrete gas discharge units or cells.  
  In some prior art panels the discharge cells are additionally defined by surrounding or confining physical structure such as apertures in perforated glass plates and the like so as to be physically isolated relative to other cells. In either case, with or without the confining physical structure, charges (electrons, ions) produced upon ionization of the elemental gas volume of a selected discharge cell, when proper alternating operating potentials are applied to selected conductors thereof, are collected upon the surfaces of the dielectric at specifically defined locations and constitute an electrical field opposing the electrical field which created them so as to terminate the discharge for the remainder of the half cycle and aid in the initiation of a discharge on a succeeding opposite half cycle of applied voltage, such charges as are stored constituting an electrical memory.  
  Thus, the dielectric layers prevent the passage of substantial conductive current from the conductor members to the gaseous medium and also serve as collecting surfaces for ionized gaseous medium charges (electrons, ions) during the alternate half cycles of the A.C. operating potentials, such charges collecting first on one elemental or discrete dielectric surface area and then on an opposing elemental or discrete dielectric surface area on alternate half cycles to constitute an electrical memory.  
  An example of a panel structure containing non-physically-isolated or open discharge cells is disclosed in U.S. Pat. No. 3,499,167 issued to Theodore C. Baker, et al.  
  An example of a panel containing physically isolated cells is disclosed in the article by D. L. Bitzer and H. G. Slottow entitled The Plasma Display Panel A Digitally Addressable Display With Inherent Memory&#34;, Proceeding of the Fall Joint Computer Conference, IEEE, San Francisco, Calif, Nov. 1966, pp. 541-547. Also reference is made to U.S. Pat. No. 3,559,190.  
  In the construction of the panel, a continuous volume of ionizable gas is confined between a pair of dielectric surfaces backed by conductor arrays typically forming matrix elements. The cross conductor arrays may be orthogonally related (but any other configuration of conductor arrays may be used) to define a plurality of opposed pairs of charge storage areas on the surfaces of the dielectric bounding or confining the gas. Thus, for a conductor matrix having H rows and C columns the number of elemental discharge cells will be the product H X C and the number of elemental or discrete areas will be twice the number of such elemental discharge cells.  
  In addition, the panel may comprise a so-called monolithic structure in which the conductor arrays are created on a single substrate and wherein two or more arrays are separated from each other and from the gaseous medium by at least one insulating member. In such a device the gas discharge takes place not between two opposing electrodes, but between two contiguous or adjacent electrodes on the same substrate; the gas being confined between the substrate and an outer retaining wall.  
  It is also feasible to have a gas discharge device wherein some of the conductive or electrodes members are in direct contact with the gaseous medium and the remaining electrode members are appropriately insulated from such gas, i.e., at least one insulated electrode.  
  In addition to the matrix configuration, the conductor arrays may be shaped otherwise. Accordingly, while the preferred conductor arrangement is of the crossed grid type as discussed herein, it is likewise apparent that where a maximal variety of two dimensional display patterns is not necessary, as where specific standardized visual shapes (e.g., numerals, letters, words, etc.) are to be formed and image resolution is not critical, the conductors may be shaped accordingly, i.e., a segmented display.  
  The gas is one which produces visible light or invisible radiation which stimulates a phosphor (if visual display is an objective) and a copious supply of charges (ions and electrons) during discharge.  
  In prior art, a wide variety of gases and gas mixtures have been utilized as the gaseous medium in a gas discharge device. Typical of such gases include C0; C0 halogens; nitrogen; NH oxygen; water vapor; hydrogen; hydrocarbons; P 0 boron fluoride, acid fumes; TiCl,,; Group VIII gases; air; H 0 vapors of sodium, mercury, thallium, cadmium, rubidium, and cesium; carbon disulfide, laughing gas; H 5; deoxygenated air; phosphorus vapors; C H CH naphthalene vapor; anthracene; freon; ethyl alcohol; methylene bromide; heavy hydrogen; electron attaching gases; sulfur hexafluoride, tritium; radioactive gases; and the rare or inert gases.  
  In one preferred embodiment hereof the medium comprises at least one rare gas, more preferably at least two, selected from helium, neon, argon, krypton, or xenon.  
  In an open cell Baker, et al. type panel, the gas pressure and the electrical field are sufficient to laterally confine charges generated on discharge within elemental or discrete dielectric areas within the perimeter of such areas, especially in a panel containing nonisolated discharge cells. As described in the Baker, et al. patent, the space between the dielectric surfaces occupied by the gas is such as to permit photons gener ated on discharge in a selected discrete or elemental volume of gas to pass freely through the gas space and strike surface areas of dielectric remote from the selected discrete volumes, such remote, photon struck dielectric surface areas thereby emitting electrons so as to condition at least one elemental volume other than the elemental volume in which the photons originated.  
  With respect to the memory function of a given discharge panel, the allowable distance or spacing between the dielectric surfaces depends, inter alia, on the frequency of the alternating current supply, the distance typically being greater for lower frequencies.  
  While the prior art does disclose gaseous discharge devices having externally positioned electrodes for initiating a gaseous discharge, sometimes called electrodeless discharge&#34;, such prior art devices utilized frequencies and spacing or discharge volumes and operating pressures such that although discharges are initiated in the gaseous medium, such discharges are ineffective or not utilized for charge generation and storage at high frequencies; although charge storage may be realized at lower frequencies, such charge storage has not been utilized in a display/memory device in the manner of the Bitzer-Slottow or Baker, et al. invention.  
 The term memory margin&#34; is defined herein as Where V, is the half amplitude of the smallest sustaining voltage signal which results in a discharge every half cycle, but at which the cell is not bi-stable and V is the half amplitude of the minimum applied voltage sufficient to sustain discharges once initiated.  
  It will be understood that the basic electrical phenomenon utilized in this invention is the generation of charges (ions and electrons) alternately storable at pairs of opposed or facing discrete points or areas on a pair of dielectric surfaces backed by conductors connected to a source of operating potential. Such stored charges result in an electrical field opposing the field produced by the applied potential that created them and hence operate to terminate ionization in the elemental gas volume between opposed or facing discrete points or areas of dielectric surface. The term sustain a discharge means producing a sequence of momentary discharges, at least one discharge foreach half cycle of applied alternating sustaining voltage, once the elemental gas volume has been fired, to maintain alternate storing of charges at pairs of opposed discrete areas on the dielectric surfaces.  
  As used herein, a cell is in the on state&#34; when a quantity of charge is stored in the cell such that on each half cycle of the sustaining voltage, a gaseous discharge is produced.  
  In addition to the sustaining voltage, other voltages may be utilized to operate the panel, such as firing, addressing, and writing voltages.  
  A firing voltage is any voltage, regardless of source, required to discharge a cell. Such voltages may be completely external in origin or may be comprised of internal cell wall voltage in combination with externally originated voltages.  
  An addressing voltage&#34; is a voltage produced on the panel X a Y electrode coordinates such that at the selected cell or cells, the total voltage applied across the cell is equal to or greater than the firing voltage whereby the cell is discharged.  
  A writing voltage is an addressing voltage of sufficient magnitude to ensure that on subsequent sustaining voltage half cycles, the cell will be in the on state.  
  In the operation of a multiple gaseous discharge device, of the type described hereinbefore, it is necessary to condition the discrete elemental gas volume of each discharge cell by supplying at least one free electron thereto such that a gaseous discharge can be initiated when the cell is addressed with an appropriate voltage signal.  
  The prior art has disclosed and practiced various means for conditioning gaseous discharge cells.  
  One such means of panel conditioning comprises a socalled electronic process whereby an electronic conditioning signal or pulse is periodically applied to all of the panel discharge cells, as disclosed for example in British patent specification 1,161,832, page 8, lines 56 to 76. Reference is also made to U.S. Pat. No. 3,559,190 and The Device Characteristics of the Plasma Display Element by Johnson, et al., IEEE Transactions On Electron Device, September, 1971. However, electronic conditioning is self-conditioning and is only effective after a discharge cell has been previously conditioned; that is, electronic conditioning involves periodically discharging a cell and is therefore a way of maintaining the presence of free electrons. Accordingly, one cannot wait too long between the periodically applied conditioning pulses since there must be at least one free electron present in order to discharge and condition a cell.  
  Another conditioning method comprises the use of external radiation, such as flooding part or all of the gaseous medium of the panel with ultraviolet radiation. This external conditioning method has the obvious disadvantage that it is not always convenient or possible to provide external radiation to a panel, especially if the panel is in a remote position. Likewise, an external UV source requires auxiliary equipment. Accordingly, the use of internal conditioning is generally preferred.  
  One internal conditioning means comprises using internal radiation, such as by the inclusion of a radioactive material.  
 Another means of internal conditioning, which we call internal photon conditioning, comprises using one or more socalled pilot discharge cells in the on state for the generation of photons. This is particularly effective in a so-called open cell construction (as described in the Baker, et al. patent) wherein the space between the dielectric surfaces occupied by the gas is such as to permit photons generated on discharge in a selected discrete or elemental volume of gas (discharge cell) to pass freely through the panel gas space so as to plurality of such pilot cells.  
  More particularly, there is provided a multiple gas discharge display panel comprising a matrix of display cells formed by intersecting electrodes and having one or more pilot cells in the on state for the conditioning of the display cells, the pilot cells being located in the border of the panel matrix and each pilot cell being defined by the intersection of one electrode common to at least one display cell and another electrode not common to any display cell. the geometric width of the common electrode being greater for each pilot cell than for any display cell.  
  In one specific embodiment of this invention. the geometric width of the not common electrode is greater than the geometric width of the common electrode in any display cell such that each pilot cell is formed by two wide electrodes. In this embodiment, the wide electrodes may be of equal or unequal width.  
  In another specific embodiment of this invention, the separation or spacing between the border electrode(s) not common to any display cells and the closest parallel electrode common to a display cell is greater than the maximum spacing between any two adjacent display cell common electrodes.  
  The use of at least one wide border electrode in accordance with this invention decreases the required firing voltage of the pilot cell. Likewise, improved photon conditioning is achieved, because of the increased conditioning radiation emitted by the enlarged pilot cell.  
  Pilot cells containing wide electrodes have been disclosed in U.S. Pat. No. 3,609,658 issued to Soltan of IBM. However, Soltan utilizes electrodes which are completely independent; i.e., his pilot cells have no electrodes in common with any display cells.  
  The use of electrodes common to border cells and display cells has the advantage that pilot cells may be conveniently provided all along the borders of a panel, with no additional processing steps being required in manufacture beyond those steps already needed to provide the display cells. It will be noted in Soltans example that he provides pilot cells only at the corners of panels and not all along the perimeter. Otherwise, he would be unable to maintain his desired condition of having no pilot cells sharing an electrode with a display cell, unless he were to add processing steps whereby pilot cell electrodes would be insulated from display cell electrodes.  
  The above, as well as other objects, features and advantages of the invention will become apparent and better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
  FIG. 1 is a partially cut-away plan view of a gaseous discharge display/memory panel as connected to a diagrammatically illustrated source of operating potentials,  
  FIG. 2 is a cross-sectional view (enlarged, but not to proportional scale since-the thickness of the gas volume, dielectric members and conductor arrays have been enlarged for purposes of illustration) taken on lines 2 2 of FIG. 1,  
  FIG. 3 is an explanatory partial cross-sectional view similar to FIG. 2 (enlarged, but not to proportional scale),  
  FIG. 4 is an isometric view of a gaseous discharge display/memory panel, I  
  FIG. 5 is a plan view of a portion of a panel matrix utilizing wide border electrodes in accordance with this invention.  
  The invention utilizes a pair of dielectric films 10 and 11 separated by a thin layer or volume ofa gaseous discharge medium 12, the medium 12 producing a copious supply of charges (ions and electrons) which are alternately collectable on the surfaces of the dielectric members at opposed or facing elemental or discrete areas X and Y defined by the conductor matrix on nongas-contacting sides of the dielectric members, each dielectric member presenting large open surface areas and a plurality of pairs of elemental X and Y areas. While the electrically operative structural members such as the dielectric members 10 and 11 and conductor matrixes l3 and 14 are all relatively thin (being exaggerated in thickness in the drawings) they are formed on and supported by rigid nonconductive support members 16 and 17 respectively.  
  Preferably, one or both of nonconductive support members 16 and 17 pass light produced by discharge in the elemental gas volumes. Preferably, they are transparent glass members and these members essentially define the overall thickness and strength of the panel. For example, the thickness of gas layer 12 as determined by spacer 15 is usually under 10 mils and preferably about 4 to 6 mils, dielectric layers 10 and 11 (over the conductors at the elemental or discrete X and Y areas) are usually between 1 and 2 mils thick, and conductors l3 and 14 about 8,000 angstroms thick. However, support members 16 and 17 are much thicker (particularly in larger panels) so as to provide as much ruggedness as may be desired to compensate for stresses in the panel. Support members 16 and 17 also serve as heat sinks for heat generated by discharges and thus minimize the effect of temperature on operation of the device. If it is desired that only the memory function be utilized, then none of the members need be transparent to light.  
  Except for being nonconductive or good insulators the electrical properties of support members 16 and 17 are not critical. The main function of support members 16 and 17 is to provide mechanical support and strength for the entire panel, particularly with respect to pressure differential acting on the panel and thermal shock. As noted earlier, they should have thermal expansion characteristics substantially matching the thermal expansion characteristics of dielectric layers 10 and 11. Ordinary one-fourth inch commercial grade soda lime plate glasses have been used for this purpose. Other glasses such as low expansion glasses or transparent devitrified glasses can be used provided they can withstand processing and have expansion characteristics substantially matching expansion characteristics of the dielectric coatings l0 and 11. For given pressure differentials and thickness of plates, the stress and deflection of plates may be determined by following standard stress and strain formulas (see R. J. Roark, Formulas for Stress and Strain, McGraw-Hill, 1954).  
  Spacer 15 may be made of the same glass material as dielectric films 10 and 11 and may be an integral rib formed on one of the dielectric members and fused to the other members to form a bakeable hermetic seal enclosing and confining the ionizable gas volume 12. However, a separate final hermetic seal may be effected by a high strength devitrified glass sealant 15S. Tubulation 18 is provided for exhausting the space between dielectric members 10 and 11 and filling that space with the volume of ionizable gas. For large panels small beadlike solder glass spacers such as shown at 158 may be located between conductor intersections and fused to dielectric member 10 and 11 to aid in withstanding stress on the panel and maintain uniformity of thickness of gas volume 12.  
 Conductor arrays 13 and 14 may be formed on support members 16 and 17 by a number of well-known processes, such as photoetching, vacuum deposition, stencil screening. etc. In the panel shown in FIG. 4, the center-to-center spacing of conductors in the respective arrays is about 17 mils. Transparent or semitransparent conductive material such as tin oxide, gold or aluminum can be used to form the conductor arrays and should have a resistance less than 3000 ohms per line. Narrow opaque electrodes may alternately be used so that discharge light passes around the edges of the electrodes to the viewer. It is important to select a conductor material that is not attacked during processing by the dielectric material.  
  It will be appreciated that conductor arrays 13 and 14 may be wires or filaments of copper, gold, silver or aluminum or any other conductive metal or material. For example 1 mil wire filaments are commercially available and may be used in the invention. However, formed in situ conductor arrays are preferred since they may be more easily and uniformly placed on and adhered to the support plates 16 and 17.  
  Dielectric layer members 10 and 11 are formed of an inorganic material and are preferably formed in situ as an adherent film or coating which is not chemically or physically effected during bake-out of the panel. One such material is a solder glass such as Kimble SG-68 manufactured by and commercially available from the assignee of the present invention.  
  This glass has thermal expansion characteristics substantially matching the thermal expansion characteristics of certain soda-lime glasses, and can be used as the dielectric layer when the support members 16 and 17 are soda-lime glass plates. Dielectric layers 10 and 11 must be smooth and have a dielectric strength of about 1000 v. and be electrically homogeneous on a microscopic scale (e.g., no cracks, bubbles, crystals, dirt, surface films. etc.). In addition, the surfaces of dielectric layers 10 and 11 should be good photoemitters of electrons in a baked out condition. Alternatively, dielectric layers 10 and 11 may be overcoated with materials designed to produce good electron emission, as in US. Pat. No. 3,634,719, issued to Roger E. Ernsthausen. Of course, for an optical display at least one of dielectric layers 10 and 11 should pass light generated on discharge and be transparent or translucent and, preferably, both layers are optically transparent.  
  The preferred spacing between surfaces of the dielectric films is about 4 to 6 mils with conductor arrays 13 and 14 having centento-center spacing of about 17 mils.  
  The ends of conductors 14-1 14-4 and support member 17 extend beyond the enclosed gas volume 12 and are exposed for the purpose of making electrical connection to interface and addressing circuitry 19. Likewise, the ends of conductors 13-1 13-4 on support member 16 extend beyond the enclosed gas volume l2 and are exposed for the purpose of making electrical connection to interface and addressing circuitry l9.  
  As in known display systems, the interface and addressing circuitry or system 19 may be relatively inexpensive line scan systems or the somewhat more expensive high speed random access systems. In either case, it is to be noted that a lower amplitude of operating potentials helps to reduce problems associated with the interface circuitry between the addressing system and the display/memory panel, per se. Thus, by providing a panel having greater uniformity in the discharge characteristics throughout the panel, tolerances and operating characteristics of the panel with which the interfacing circuitry cooperate, are made less rigid.  
  In FIG. 5 there is shown a plan view of a portion of a panel matrix comprised of intersecting row electrodes R and column electrodes C forming a plurality of display cells D... The perimeter or border of the matrix is comprised of pilot cells P,- formed by intersecting border row electrode R and border column electrodes C the latter being widened extensions of the column electrodes forming the display cells. Although not illustrated in FIG. 5, it is also feasible to utilize one or more widened border row electrodes R,,, each of which is equal or unequal in width to C In such embodiment, R,, is wider than either electrodes R or C. Also in another embodiment not illustrated in FIG. 5, the distance between R and the closest electrode R is greater than the distance between any two adjacent electrodes R or adjacent electrodes C.  
 I claim:  
  1. In a multiple gas discharge display/memory panel comprising a matrix of display cells formed by intersecting electrodes, each cell having opposed dielectric members for the storage of charges, at least one cell in the border of the panel matrix being in the ON state for the conditioning of the matrix display cells,  
 the improvement wherein each pilot cell is defined by the intersection of one electrode common to at least one matrix display cell and another electrode not common to any matrix display cell, the geometric width of the common electrode being greater in its pilot cell than in its display cells.  
  2. The invention of claim 1 wherein the spacing distance between each border electrode not common to any matrix display cell and the closest parallel display cell electrode is greater-than the spacing between any two parallel display cell electrodes.  
  3. The invention of claim 1 wherein the not common pilot cell electrode is wider than any electrode forming a display cell.  
  4. In a gaseous discharge display/memory panel characterized by an ionizable gaseous medium in a gas chamber formed by a pair of opposed dielectric charge storage members which are respectively backed by an array of electrode members, the electrode members behind each dielectric member being transversely oriented relative to the electrode members behind the opposing dielectric member so as to define a plurality of discrete discharge volumes in open photonic communication at the intersections of pairs of electrode members, one from each array, each of said discrete discharge volumes constituting a discharge unit, at least one discharge unit in the border of the panel being in the ON state so as to serve as a pilot cell for the gaseous medium conditioning of the other discharge units to be addressed, the improvement wherein each pilot cell is defined by the intersection of one electrode member common to at least one other discharge unit and another electrode member not common to any other discharge unit. the geometric width of the common electrode member being greater in its pilot cell than in its other discharge units. wherein the required firing voltage of each pilot cell is decreased and photon conditioning of the other discharge units is improved.  
 &#39; 5. The invention of claim 4 wherein the spacing between each electrode at a pilot cell not common to any other discharge unit and the closest parallel electrode is greater than the spacing between any two parallel electrodes at said other discharge units.  
  6. The invention of claim 5 wherein the electrode at a pilot cell not common to any other discharge unit is wider than any electrode at any of said other discharge units.  
  7. In the operation of a gaseous discharge display/- memory panel comprising an ionizable gaseous medium between a pair of opposed dielectric charge storage members which are respectively backed by a plurality of electrode members. the electrode members behind each dielectric member being transversely oriented relative to the electrode members behind the opposing dielectric member so as to define a plurality of discrete discharge volumes in open photonic communication, each of which constitutes a discharge unit, at least one discharge unit in the border of the panel being in the ON state so as to serve as a pilot cell for the gaseous medium conditioning of the other discharge units to be addressed and wherein the gaseous medium is selectively ionized within each of said discharge units by a firing alternating current voltage applied to the trans-.  
 versely oriented electrode members and charges are stored on said charge storage surfaces during each halfcycle of operation, the improvement which comprises decreasing the required firing voltage of each pilot cell and improving the photon conditioning of the panel by the utilization of a wide electrode in each pilot cell, each pilot cell being defined by the intersection of one electrode common to at least one of said other discharge units and another electrode not common to any of said other discharge units, the geometric width of the common electrode being greater in the pilot cell than the geometric width of the common electrode in any of said other discharge units.  
  8. The invention of claim 7 wherein the spacing between each electrode at a pilot cell not common to any other discharge unit and the closest parallel electrode is greater than the spacing between any two parallel electrodes at said other discharge units.  
  9. The invention of claim 7 wherein the electrode at a pilot cell not common to any other discharge unit is wider than any electrode at any of said other discharge