US3701918A

US3701918A - Gaseous-flow, discharge display device with an array of hollow cathodes

Info

Publication number: US3701918A
Application number: US108965A
Authority: US
Inventors: David Henry Odhams Allen; Raymond Frederick Hall; George Frederick Weston
Original assignee: US Philips Corp
Current assignee: US Philips Corp
Priority date: 1968-08-29
Filing date: 1971-01-22
Publication date: 1972-10-31
Anticipated expiration: 1989-10-31

Abstract

An electrical display device employing an array of electrically conductive dot cathodes and an anode or anodes for cooperating therewith to define an array of glow discharge paths, the dimensions and relative locations of the cathodes and anodes and pressure and composition of the atmosphere being such that only a negative flow discharge is produced and the positive column is suppressed.

Description

United States Patent Allen et a1.

GASEOUS-FLOW, DISCHARGE DISPLAY DEVICE WITH AN ARRAY OF HOLLOW CATHODES lnventors: David Henry Odhams Allen, East Grinstead, Sussex; Raymond Frederick Hall, Crawley, Sussex; George Frederick Weston, Merstham, Surray, all of England Assignee: U.S. Philips Corporation, New

York,N.Y.

Filed: Jan. 22, 1971 Appl. No.: 108,965

Related U.S. Application Data Continuation of Ser. No. 766,525, Oct. 10, 1968, abandoned.

Foreign Application Priority Data Aug. 29, 1968 Great Britain ..46,406/68 U.S. Cl. ..313/209, 313/210, 313/217,

313/220, 315/169 TV Int. Cl. ..H0lj 61/06, H01 j 61/64 Field of Search.....315/l69 R, 169 TV; 313/210, 313/220, 109.5, 217, 209

[15] [451 Oct. 31, 1972 [56] References Cited UNITED STATES PATENTS 2,848,638 8/1958 Smith ..3l3/2l7 X 3,042,823 7/ 1962 Willard ..315/169 TV 3,206,638 9/ 1965 Moore ..315/169 TV 3,260,880 7/1966 Kupsky ..313/210 X 3,334,269 8/1967 Ll-levreux ..315/169 TV 3,346,759 10/1967 l-lardwick ..313/l09.5 3,042,823 7/1962 Willard ..315/169 X 3,206,638 9/1965 Moore ..315/161 3,334,269 8/1967 LHevreux ..315/58 Primary ExaminerPalmer C. Demeo Attorney-Frank R. Trifari [5 7] ABSTRACT An electrical display device employing an array of electrically conductive dot cathodes and an anode or anodes for cooperating therewith to define an array of glow discharge paths, the dimensions and relative locations of the cathodes and anodes and pressure and composition of the atmosphere being such that only a negative flow discharge is produced and the positive column is suppressed.

2 Claims, 7 Drawing Figures minno s] m2 SHEET 1 BF 2 FIGI.

m m E V W.

F E D F HA DAVIDH.O. ALL

GEORGE w s'row BY RAYMON H7 AGENT I P'A'TE'N'TEDum 31 I972 SHEET 2 OF 2 INVENTOR.

A VID H. O. A LLt N $5 BYD GASEOUS-FLOW, DISCHARGE DISPLAY DEVICE WITH AN ARRAY F HOLLOW CATI-IODES This application is a streamline continuation of Ser. No. 766,525, filed Oct. 10, 1968, and now abandoned.

This invention relates to electrical display devices. Such devices may be used for displaying simple patterns such as diagrams, numerals, words or the like which do not require half-tone capabilities.

During the past few years an increasing amount of effort has been devoted to flat display systems of one kind or another. Some such systems use electroluminescence as the light-emitting phenomenon. In these systems the present state of the art does not permit a brightness in excess of a few tens of ft. L. This is not sufficient for daylight viewing purposes as required in the majority of the possible applications.

For this reason it has been proposed to employ a twodimensional array of cold-cathode glow-discharge cells as the light sources for the individual elements for the display. An early example of such an arrangement is described in US. Pat. Nos. 2,991,394 and 2,965,801

and illustrated in FIGS. and 11 thereof.

A more recent example is reported in Electronics News of July 26th 1965. In this proposal the individual cells consist of short gas discharge-spaces arranged in the form of a two-dimensional matrix of small apertures in a sheet of insulating material placed between two electrode systems of parallel wires or semi-transparent conductive strips in a cross-bar arrangement. Light emission can be caused to arise from any element by passing a gas discharge through a hole in the insulating matrix at the cross-over point of the two corresponding electrode strips.

A difficulty with gas discharges of this type is the sputtering which takes place at the cathode, due to bombardment with positive ions. This can severely limit the life of the device, and especially semi-transparent electrodes are very vulnerable in this respect.

Recent work has indicated that this problem can be successfully overcome by the use of an array of hollow cathode discharge elements where each cathode is recessed in a slab of insulating material. Arrangements of this character are described in US. Pat. No. 3,465,194.

According to the present invention an electrical display device comprises an envelope containing an array of separate cathode assemblies each of which comprises an electrically conductive cathode situated within a cavity which is open at one end and whose wall is electrically insulating, the envelope also containing at least one anode facing said ends for co-operating with said cathodes to define an array of glow-discharge paths which extend through a gas atmosphere, a gap containing said atmosphere being present between said ends and the anode, the dimensions and relative locations of said cathodes and said anode and the pressure and composition of said atmosphere being such that with the application of an operating potential across each path negative-glow optical radiation in the resultant glow-discharge is generated and the positive column part of the discharge is substantially sup pressed.

Embodiments of the invention will now be described, by way of example, with reference to FIGS. 1 and 2 of the accompanying drawings in which FIG. 1 shows an embodiment of an alpha-numeric indicator tube and FIG. 2 shows a modification to the embodiment of FIG. 1.

In the drawings FIG. 1 shows an exploded view of an alpha-numeric indicator tube. The parts denoted by reference letters a to f are:

FIG. 1a viewing window.

FIG. 1b side wall of envelope.

FIG. 10 anode.

- FIG. 1d matrix of holes in an electrically insulating plate.

FIG. 1e spacer for anode.

FIG. 1f cathode matrix.

The cathode matrix of FIG. 1f comprises an array of separate cathodes 1 provided on an electrically insulating substrate 2. These cathodes are brought out to terminals 3 for connection to an external source (not shown) of operating potential. The substrate 2 may be made of glass or ceramic material and the array of cathodes 1 together with the connections therefrom to the terminals 3 may be vacuum-deposited thereon. Preferably, however, the array of cathodes 1 together with the terminals 3 and the connections from the cathodes to these terminals may be obtained by etching a sheet of metal, for example nickel-iron or chromeiron, so that the desired configuration is formed.

The resulting configuration may then be moulded into the surface of the substrate 2 by holding it in contact therewith and forming at a high temperature, the connectors from the cathodes to the terminals 3 being subsequently bent round the edges of the substrate. In the same operation the spacer of FIG. 1e may be moulded onto. the top surface of the substrate and the cathode array.

The insulating plate of FIG. 1e may be made, for ex-v ample, of glass or ceramic material. It is provided with a matrix of holes extending from one major face thereof to the other and in positions such that they coincide with the array of cathodes 1 when the insulating plate is placed in contact with the substrate assembly l, 2, 3. The insulating plate is of such size that it fits snuglyin the aperture provided in the spacer of FIG. 1e and rests in contact with the top surface of the substrate 2 provided with the cathodes.

The spacer of FIG. la is of a greater depth than the thickness of the insulating plate 5 and thus provides a ridge around the edge of the insulating plate 5 when assembled. On this ridge rests an optically transmissive electrically conductive anode plate 6 shown in FIG. 1e so that the plate 6 is spaced from the plate 5. The anode 6 may be in the form of a perforated metal plate, the perforations coinciding with the apertures 4 when assembled to enable it to be optically transmissive and hence to enable optical radiation generated in the apertures 4 to be observed through the top face of the anode. As an alternative the anode 6 may comprise a fine wire mesh or, as a further alternative, it may comprise a layer of optically transparent tin oxide deposited on the underside of an optically transparent substrate (not shown).

Side-walls 7 and an optically transparent viewing window 8 complete the assembly, these being sealed together and to the top surface of spacer 1e in a vacuum-tight manner so that the electrode assembly is enclosed within an envelope. After assembly the envelope may be evacuated through a pump stem 9 which may be subsequently sealed close to where it joins the side walls 7 and removed. r

In a practical embodiment the holes 4 were 1 mm. in

diameter spaced 2 mm. between their centers The spacing between the top surface of the plate 5 and the bottom surface of the anode 6 were approximately 0.1 mm. The cathodes 1 and apertures in the anode 6 were 1 mm. in diameter and again spaced 2 nun. between their centers so as to line up with the apertures in the plate 5. The envelope was evacuated and then filled with pure neon or neon containing 2 percent argon to a pressure of 150 Torr. These dimensions and pressure were such that the application of an operating potential difference of at least 280V for Neon and 160V for Ne- Ar between the anode and a given cathode or cathodes resulted in a glow-discharge in the discharge path or paths defined by the anode and this cathode or cathodes, which discharge gave rise to optical radiation from only the negative-glow portion of the discharge, the positive column portion thereof being completely suppressed. This radiation could be observed through the corresponding hole or holes in the anode 6, and the application of the operating potential to selected cathodes resulted in the production of a pattern determined by this selection, which pattern was observable through the window 8. By suitable selection of the cathodes energized it was found possible to display successively a pattern making up each of the digits of the decimal system, the cathodes being located in a 7 X 5 arrayj lt was also found to be possible to display letters and other symbols.

FIG. 2 shows a possible alternative construction for the substrate/cathode/terminal assembly of FIG. 1f. In the substrate assembly the substrate 2 is pierced by metal wires 10 which are sealed into the substrate 2. These wires may be again made of nickel-iron or chrome-iron and they terminate flush with the top surface of the substrate 2 to form the cathode 1. Their other ends may be used as terminals for connection to external circuitry. In both embodiments nickel-iron or chrome-iron is preferred for the cathode material because this material may be easily sealed to a soft glass.

In a further embodiment a substrate assembly similar to that shown in FIG. 2 may be used but the tops of the wires 10 may be etched so that the wires 10 terminate some distance below the top surface of the substrate 2. In this way the matrix of FIG. 1d may be effectively formed integrally with the substrate 2, this rendering the provision of a separate matrix plate 5 unnecessary. In this particular embodiment an array of cathodes will be formed similar to those described in the aforesaid co-pending British Pat. Application No. 44937/66.

The constructions described above with reference to FIGS. 1 and 2 have been found to be prone to electrical leakage across the interface between the plate 5 and the

substrate assembly

1, 2, 3, and hence to activation of discharge from cathodes which are not directly energized.

This disadvantage can be overcome by moulding the plate 5 (FIG. 1d), the spacer of FIG. 1e and the substrate 2 (FIG. 1 in one piece around the cathodes 1 and the connections to the terminals 3 (FIG. 1]). Assembly may also be facilitated by providing the window 8 and the side wall F of the envelope in one piece. A construction made in this way was manufactured as follows:

The array of cathodes 1 of FIG. 1, together with the terminals 3 and the connection from the cathodes to these terminals was initially etched from a flat sheet of metal available under the Registered Trade Mark Kovar, portions of the sheet mechanically interconnecting the ends of the terminals 3 being left in situ for the moment in order to hold the cathodes l in their correct spaced relationship.

The resulting array was then placed in a mould with the terminals 3 protruding from the side thereof. The interior of the mould had a flat bottom surrounded by a circumferential groove about 0.25 mm. deep. An array of vertical posts extended from the flat bottom. These posts had cross-sections and relative positions identical with those of the array of cavities (similar to 4; FIG. 1d) which it was desired to form in the electrical insulator. The tops of these posts terminated at individual cathodes 1. The interior of the other half of the mould had the shape of the substrate 2 (FIG. 1]). After the mould was closed it was filled with glass material available under the Registered Trade Mark F usite K and held at 1,000 C in an inert gas atmosphere for 1 hour. This particular glass was found not to wet the cathode material when molten. On cooling a construction similar to a combination of the components shown in FIG. 1d, 10 and 1 f was obtained after the leads 3 had been separated by removing the portions of the sheet of cathode material which had previously connected them.

An anode similar to that described with reference to FIG. 10 was then placed opposite the open ends of the cavities, resting on the circumferential ridge formed by the mould groove on that surface of the now solidified glass into which the cavities opened. Over this was then placed an envelope portion similar to a combination of parts 7 and 8 in FIG. 1. This portion was made up of material available under the Registered Trade Mark Kodial and was sealed to the substrate 2 by means of a solder glass. The envelope thus formed was filled with neon containing 2 percent argon at a total pressure of Torr.

The resulting display device was then aged by applying an operating potential of Volts or greater between each cathode and the anode and continuing this application until sputtering from the cathodes due to the resulting electric discharge caused an appreciable amount of cathode material to be deposited on the cavity walls, the cathodes being of sufiicient size so that this cathode material contacted the cathode proper. Such sputtering inevitably occurs during operation and the aging was carried out in order that the completed device should have predictable characteristics which would not then change appreciably with aging. It should be noted that the anode is spaced from the open ends of the cavities so that this sputtered material cannot form a short circuit between cathode and anode. The display device was then ready for use and had the following dimensions and characteristics.

Cavity cross-section: square of 1 mm side Cavity depth: 1 mm Cavity spacing: 2 mm between centers in a 7 X 5 array It may be advantageous to form a pattern of grooves between the open ends of each cavity in order to increase the electrical leakage path length between the open end of each cavity and the next to provide additional protection against leakage across this path.

A similar device to this and having substantially equivalent properties was also obtained by replacing the anode 6 of FIG. 1 by a mesh-like anode formed by mechanically expanding a plate of the material available under the Registered Trade Mark Kovar.to such an extent that it had a satisfactory overall optical transmission.

What we claiin is:

1. An electrical display device comprising an envelope, an insulating body having a plurality of cavities therein disposed within the envelope, an electrically conductive cathode at one end of each cavity, the walls of said cavities having a layer of cathode material thereon in contact with said cathodes, electrical supply conductors for each cathode, said cathodes and the end portions of said conductors which adjoin said cathode lying substantially in one plane, at least one anode within said envelope facing said cathodes and spaced from the edges of said cavities, an ionizable gas filling in said envelope, said anode and said cathodes defining an array of glow discharge paths which extend through the gas, the dimensions and relative locations of said cathodes and said anode and the pressure and composition of said atmosphere being such that with the application of an operating potential across each path nega tive-glow optical radiation in the resultant glow discharge is generated and is retained within said cavities and the positive column part of the discharge is suppressed.

- 2. A device as claimed in claim 1 wherein said body is substantially plate-shaped and the anode comprises an optically transmissive electrically conductive plate situated adjacent to major face of said body'and spaced therefrom.

Claims

1. An electrical display device comprising an envelope, an insulating body having a plurality of cavities therein disposed within the envelope, an electrically conductive cathode at one end of each cavity, the walls of said cavities having a layer of cathode material thereon in contact with said cathodes, electrical supply Conductors for each cathode, said cathodes and the end portions of said conductors which adjoin said cathode lying substantially in one plane, at least one anode within said envelope facing said cathodes and spaced from the edges of said cavities, an ionizable gas filling in said envelope, said anode and said cathodes defining an array of glow discharge paths which extend through the gas, the dimensions and relative locations of said cathodes and said anode and the pressure and composition of said atmosphere being such that with the application of an operating potential across each path negative-glow optical radiation in the resultant glow discharge is generated and is retained within said cavities and the positive column part of the discharge is suppressed.

2. A device as claimed in claim 1 wherein said body is substantially plate-shaped and the anode comprises an optically transmissive electrically conductive plate situated adjacent a major face of said body and spaced therefrom.