US 3602756 A
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United States Patent Robert E. Bonnet Murray Hill, NJ.
Dec. 22, 1969 Aug. 31, 1971 Engelhard Minerals 8: Chemicals Company Inventor App]. No. Filed Patented Assignee GAS IONIZATION DISPLAY DEVICE 6 Claims, 2 Drawing Figs.
US. 313/ 109.5, 313/203, 313/217, 313/268 Int. Cl H0lj 61/64 Field ofSearch 313/109.5, 210, 203, 268, 217, 108; 315/169 TV, 167, 337
References Cited UNITED STATES PATENTS 7/1937 Brion et a1. 315/337 X 2,925,525 2/1960 Davis 313/108 X 3,013,182 12/1961 Russell 313/108 X 3,043,988 7/1962 Hurvitzm. 313/108 X 3,278,784 10/1966 Masaharu.... 313/108 3,497,751 2/1970 Cullis,.1r 313/109.5
Primary Examiner-Roy Lake Assistant Examiner-Palmer C. Demeo Attorneys-Miriam W. Leff and Samuel Kahn ABSTRACT: A gas ionization display device is provided which comprises a woven wire mesh having noncontacting intersecting wires in hermetically sealed dielectric panels. An
inert ionizable gas is encapsulated between the hermetically sealed panels. The device is made by sandwiching the woven wire mesh between two glass panels, with the wires extending beyond the edges of the panels, and sealing the panels, in an atmosphere of an ionizing gas, e.g. neon or argon.
PATENTED M1631 l9?! 3.602756 INVENTOR.
ROBERT E. BONNET GAS IONIZATION DISPLAY DEVICE BACKGROUND OF THE INVENTION This invention relates to a gas ionization display device for providing illuminated patterns on a transparent panel and to a method of fabricating, such device.
Readout devices which provide a visual presentation of stored information are required in many forms of modern electronic equipment. The stored data is displayed on a panel in illuminated form in ways well known in the art.
Recently illuminated readout panels have been developed which utilize illumination derived from gas ionization as a means of displaying the desired information on a flat glass surface. These devices, which are referred to as plasma display panels, use glass panels separated by a gas-filled narrow gap, e.g. about mils wide. The inner opposite faces of two glass panels are fitted with a series of parallel conduits, e.g. wires or thin metal strips, and these panels are positioned so that the series of electrical conductors of the two faces are normal to each other. Contacts lead out from every conductor and the glass panels are sealed around the edges of the glass. By applying a proper voltage to a set of coordinate conductors, that is strips or wires which have a common intersection, a glow will appear at the intersection. These glows or dots form the display pattern, and by proper selection of the conductors in both plates the patterns may appear in the fonn of numbers, letters, words, graphs, or figures, as desired. In operation the devices are maintained at a sustaining voltage and to turn on an individual spot only a surge in the voltage of the magnitude to initiate an ionization discharge is necessary. Thereafter the glow is maintained at the sustaining voltage until the voltage is lowered to an erase level. The voltages required are a function of the gas, the gas pressure, and the gap between the electrical conductors, and the metallic nature of the surface of the electrical conductors, as is well known in the art. If the electrical impulses are computer controlled switching of a whole display can be achieved in milliseconds.
Many problems have been encountered in the fabrication of these devices. They are difficult to assemble, and it is hard to maintain the gap between the closely spaced electrical conductors. Moreover it has been difficult to provide suitable conductors and/or contacts extending from the conductors in the sealed assemblies. l-leretofore some of the devices have been provided with thin metal films, e.g. by vapor deposition, as the conductors. The problems in forming on the dielectric materials thin metal films of sufficient thickness for good electrical capacity and also good adherence are well known. If the film is too thick it tends to peel and if it is too thin the current carrying capability is limited. Another method of providing the conducting strips has been to position wires by potting in the dielectric panels. This technique has not been satisfactory since it has been difiicult to position and maintain the wires accurately, especially when the wires are closely spaced. Not only are the labor costs high for this highly exacting work, but the resulting devices are limited in both size and the number of wires per inch that can be made by this method. It will be appreciated that the clarity of the pattern is directly related to the spacing of the wire. By increasing the number of wires per inch, a better resolution of the illuminated pattern can be achieved.
In the present invention a plasma display device is provided which is easy to assemble and which permits the use of larger panels and a greater number of wires per inch than previously known devices in this field.
THE INVENTION In accordance with this invention a gas ionization device having a confined inert ionization gas to display information and having a first and second set of electrical conductors substantially at right angles to each other, each set consisting of a plurality of substantially parallel wires, is provided, which comprises: two dielectric panels, at least one of which permits transmission of visible radiation of gaseous discharge, said panels being hermetically sealed to each other and having a pocket therebetween; a woven wire mesh having noncontacting intersecting wires which form the first and second set of conductors, said woven wire mesh being sandwiched between the dielectric panels and having the wires thereof extending beyond the panels and thereby available as electrical contacts;
and an inert ionizable gas encapsulated in said pocket between I the panels, said encapsulated gas and said noncontacting wires at the intersection sites forming a plurality of closely spaced discrete gas ionization points in the device.
The woven wire mesh is made of a fine gauze metal, e.g. about 0.001 to 0.050 inch diameter, which is a good electrical conductor. Suitable conducting metals are well known in the art and they include such metals as copper, silver, Nichrome, and various alloys such as Kovar which have been specially developed for making good glass-to-metal seals. It will be noted that the wire mesh must be sealed in the panels with wires extending beyond the edges of the sealed panels, and the seal must be leaktight. One method of insuring that there is no leakage at the wires is to use a metal of the type that is wet by the material of which the panel is made and has a coefi'lcient of expansion which matches that of the panel. However, alternative techniques for forming leaktight seals are well known in the art.
As indicated previously the wires of the wire mesh do not contact each other at the cross over points, i.e. the intersections. In a preferred embodiment either the woof or the warp wires are coated with a thin electrical insulation coating which maintains a uniform gap or separation between the intersecting wires. The coating is of suitable penneability for the gaseous environment within the panels. Although it is possible to have both the woof and warp wires coated with an electrical insulation material, it is not preferred to do so since this is unnecessary to maintain the gap The electrical insulation coating is preferably a fibrous or porous material, e.g. fiberglass or asbestos, for the reason that it provides the nonconducting separation between the wires without substantially changing the discharge voltage requirements required for a gap of similar size without the insulation. Organic insulation material, generally, should be avoided since it tends to carbonize if heated and this may short the wires. Alternatively, the gap may be provided by crimping the wires so that they do not contact each other at the intersections. This crimping is not preferred since it is more difiicult to maintain the uniformity in the gap throughout the mesh.
The inert ionizable gas in the pocket between the panels may be, for example, neon, argon, xenon, krypton, and mixtures thereof. Such gas is contained between the panels at a pressure capable of sustaining a glowdischarge.
The encapsulating hermetically sealed panels are made of a dielectric material, at least one of the panels permitting transmission of a visible radiation of the gaseous discharge. Preferably, one of the panels is transparent. Glass is a preferred material, but other materials such as quartz, ceramics, and certain plastics may be used.
It will be appreciated that the operation of the device and the materials of construction, including the ionizing gas are themselves well known in the field of gas ionization or neon" lighting as well as in the field of display devices, and the materials and operation of the device can be chosen accordingly.
In accordance with another aspect of this invention, the above'described display device is fabricated by a method comprising, sandwiching the woven wire mesh between two dielectric panels with the wires of the mesh extending beyond the panels, and sealing the panels in an atmosphere of an inert ionizing gas.
Sealing can be achieved with some materials such as glass by heating to the softening point in the ionizing gas atmosphere to form a hermetic, or gastight seal around the edges of the panels with an inert ionizing gas entrapped therein. The extending wires are used as electrical contacts.
Alternative methods of sealing may be used. For example, if the dielectric panels are made of high temperature ceramics, quartz, or unlike materials which cannot be sealed practically by just heating, suitable sealants may be used to obtain a leaktight envelope for the mesh. For example, glass frit or thermosetting resins may be used, in accordance with well-known procedures.
In operation a sustaining voltage is continuously applied in the mesh. When a higher discharge voltage is applied to two wires normal to each other, a glow point will occur at the intersection thereof. A combination of applied voltages produces an array of lights which form the desired pattern. A dropped voltage erases a light. The operation of the devices can be computer controlled. As indicated above, such operation is well known in the art.
The present device is an improvement over the art in that the devices are relatively simple to assemble and known techniques such as those used to make safety glass can be applied. Moreover, there is no size limitation on the woven wire mesh, other than what is required for mechanical handling and bonding. In addition, the number of points of intersection in a given area is only limited by the diameter of the wires. This allows a greater number of points per square inch than has been possible hitherto with the methods of the prior art.
The accompanying figures are provided to aid in the understanding of this invention:
FIG. 1 is a schematic plan view of a plasma display device in accordance with this invention; and
FIG. 2 is a cross-sectional view taken along lines 2-2 FIG. 1.
In FIG. 1 the woven wire mesh in the schematic view shows the warp wires 11 and woof wires 12 which are normal to each other, spaced-apart in an exaggerated fashion for better understanding of the configuration. In this embodiment of the invention the wires 11 are bare and each of the wires 12 are coated with a porous electrical insulation material 13. The wires 1 1, and 12 are 2.0 mil dia., and the insulation material is fiberglass and of a thickness of about 1.0 mils. The total diameter of the wire 12 and the insulation 13 is 4.0 mils. The wire mesh 10 may be for example 100 mesh.
The pocket 14 formed between the two panels 15 and 16 is filled with an inert gas (not shown), e.g. neon, at a pressure of, for example, 0.33 atm.
As shown in the view of FIG. 2, the wire mesh 10 and pocket 14 are encased in transparent panels 15 and 16, e.g. of Pyrex 7740 glass. The wires 11 and 12 extend freely beyond the panels and are available as electrical contacts for connection to an outside source of electricity (not shown).
The transparent dielectric panels 15 and 16 are hermetically sealed to each other around their peripheral edges so that the inert gas is encapsulated in the free space, i.e. pocket 14 therebetween.
EXAMPLE A 100 mesh screen is woven using a standard procedure. The screen consists of 0.002 inches diameter bare Kovar wire in the x plane and 0.004 inches diameter porous fiber glasscovered Kovar wire in the y" plane. The fiberglass cover of the wire in the y" plane is0.001 inches thick, the Kovar wire diameter is 0.002 inches.
To construct a 6 inch X 6 inch display matrix, a screen is cut to a size 9 inches X 9 inches. For a distance of 1% inches on the right and left side of the screen, all of the y" wires are removed leaving only the .r" wires. A similar procedure is followed for the top and bottom of the screen, only this time removing 1% inches of the x" wires and leaving the y wires. The fiberglass is stripped from the ends of the y wires for a length of 1% inches, within )6 inches of where the last "x" wire was removed. Remaining is the 6 inches M6 inches original mesh bordered by 1% inches of bare Kovar wires on two opposing sides and 1% inches bare Kovar wires on the top and bottom.
Two pieces of /4 inches thick Pyrex glass are cut to a 7% inches X 7% inches dimension. The prepared screen is then centered on one of the glass plates and the other glass plate is placed over it. This sandwich-type assembly is than placed in an oven with a weight resting on the top plate. The oven is evacuated, repressurized with pure neon gas to about 0.5 atmospheres and the assembly is heated to the softening point of the Pyrex glass, approximately 830 C.
When the glass softens, the neon gas is trapped in the area of the screen. The sofiened edges of the glass plates bond together forming a seal of approximately A inches in width over the bare Kovar wires on all four sides, thereby creating a leakproof envelope around the prepared screen, with the wire ends protruding 5'4 inches beyond the glass surface. The oven is cooled, completing the formation of the display matrix.
Operation of the display matrix requires resistors of 27,000 ohms to be attached to each of the x wires to limit the current to about 12 milliamps. A voltage of approximately 270 volts AC is applied to all of the x and y" wires. This voltage is not enough to cause ionization. When the voltage is pulsed to 300 volts AC in one of the x" wires and a corresponding y wire, the neon gas at the intersection becomes ionized and a glow appears. This occurs at the cross outer point of any x and y wire so pulsed. Ionization is maintained by the 270 volts AC. Removing this holding voltage from the x, y" connections, extinguishes the glow at the ionized intersections.
1. A display device having a confined inert'ionizable gas to display information and having a first and second set of electrical conductors substantially at right angles to each other, each set consisting of a plurality of substantially parallel wires which comprises:
a. two dielectric panels, at least one of which permits transmission of visible radiation of gaseous discharge, said panels being hermetically sealed to each other and having a pocket therebetween;
b. a woven wire mesh having noncontacting intersecting wires which form the first and second set of conductors, said woven wire mesh being sandwiched between the dielectric panels and having the wires thereof extending beyond the panels and thereby available as electrical contacts;
c. a coating of thin electrical insulation material on at least one set of electrical conductors in the woven wire mesh sandwiched between the panels; and
d. an inert ionizable gas encapsulated in said pocket between the panels, said encapsulated gas and said noncontacting wires at the intersection sites forming a plurality of closely spaced discrete gas ionization points in the device.
2. A device in accordance with claim 1 wherein at least one of the panels is transparent.
3. A device in accordance with claim 2 wherein the transparent panel is glass.
4. A device in accordance with claim 1 wherein the thin electrical insulation coating is gas permeable.
5. A device in accordance with claim 4 wherein the gas permeable insulation is fiberglass or asbestos.
6. A device in accordance with claim 5 wherein the woven wire mesh is made of a metal wire which is wet by the panels and has substantially the same coefficient of expansion as the panels.