CA1114000A - Gas panel spacer - Google Patents

Abstract

IMPROVED GAS PANEL SPACER
ABSTRACT OF THE DISCLOSURE
Gaseous discharge display systems represent a sophisticated technology which requires that the physical parameters of the de-vice such as the discharge gap be maintained within close tolerances.
To provide a uniform discharge gap over the entire surface of the display panel, particularly in large size displays, metallic spacers are bonded to the dielectric of one of the plates at predetermined intervals, and the metallic spacers are protected from interaction with the gas particles by a layer of refractory material applied thereover. Also disclosed are means for modifying the physical characteristics of the spacers to eliminate reflected light and render the spacers substantially invisible.

Description

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- BACKGROUND OF THE INVENTION
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This inventio~ relates to gaseous discharge display and/or memory devices and more particularly to large size high resolution 1 ;
devices of this type embodying a method of spacing the plates with spacer ele~ents that do not inhibit the flow of gas particles within the panel, which are substantially invisible and which are inter- :
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.: ' ., , ' '' ~' 1 the display surface at predetermined intervals to maintain a uniform discharge gap between opposing cell electrodes across the entire display surface. Various methods have been employed in the prior art for pro-viding and maintaining a uniform discharge gap between opposing walls of a gas discharge device, primarily involving the use of glass space}s in rod form, and various methods of gas panel assembly using such spacers have been proposed. Other arrangements modify the gas panel structure by cutting grooves in one or both of the glass plates and forming con-ductor arrays within the grooves whereby the plates themseives consti-tute the spacer elements. However, such devices are difficult to fab-ricate, particularly in high resolution panels which may contain about 5,000 cells per square inch. A further method disclosed in the U.S.
Patent No. 4,091,305, issued May 23, 1978, utilizes metallic spacers which are formed under the dielectric coating and positioned at pre-determined or random intervals on the gas panel surface, and then, together with the conductors, overcoated with a dielectric layer. Such apparatus, however, makes it extremely difficult or impossible to provide a uniform dielectric layer over the entire surface of the panel such that the dielectric surfaces in the spacer areas are not perfectly flat and mechanically weak, unstable point contacts result. Addition-ally difference in dielectric thickness of individual cells resulting from such arrange~ents produce or require variation in the electrical -parameters of control signals utilized to control the device and elimin-ate or severely restrict the panel margin. The operation of cells which ~; are KIg-77-003 - 2 -':

1 located adjacent to the spacer elements in prior art spacer systems is adversely affected due to the meniscus effect of the dielectric reflow, since perturbations of the glass dielectric surface alters the dielectric thickness over lines adjacent to the spacer elements, thereby preventing reliable operation of such cells or sites. Final-ly, the reflective properties of metallic spacers formed as a`bove described renders them substantially invisible to all viewers except those directly ahead of the display, and the resulting distraction is undesirable from an aesthetic and human factors standpoint. Thus there exists a need for a spacer technology in a gaseous discharge displa~v device which will provide uniform spacing between glass plates, and particularly in gaseous discharging devices having large display areas of high resolution, which will minimize the size and number of the spacer elements and minimize the visibility of such spacer elements.
SUMMARY OF THE INVENTION

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Toward this end and according to the present invention, it has been found that these ob~ectives can be achieved by an improved gaseous discharge display and/or memory device and method. Gaseous discharge display devices are characterised by a gaseous medium enclosed under appropriate pressure in a gas chamber, the walls of said chamber com-prising arrays of parallel conductors formed on glass plates and over-coated with a dielectric layer, the conductor arrays being oriented in a substantially orthogonal relationship whereby the intersection,s of said conductors define discrete gaseous discharge sites or cells. In accordance with the present invention, the glass DLN/~47 :: :

l plate~ of the display devic~ are held preci~ely spaced at

2 preselected uniform ~i~tances hy metallic spacer elements

3 which are attached directly to the dielectric surface and

4 positioned in the area between adjacent conductor~ in either

5 one or both axial directions. The positioning of the

6 me~allic spacer elements is determined for load bearing

7 requirements or a specific size panel and, in accordance

8 with a pre~exred embodiment of the invention having a

9 lO x 12 display surface, the spacer element~ are positioned lO two inche~ apart center to center in each axial direction. s ll For a panel having a 12" x 10" display surface with a 70 12 line/inch~ thirty-five spacers would be employed. The 13 spacer elements comprise a nickel-iron alloy havin~ a S0%
14 composition by weight of the nickel and iron elements. ~he 15 spacers are oxidized on their outer surface to provide ~6 improved adhesion between the glass surface to which they 17 are bonded and to reduce light reflection and ensuing ., ,r:~
l~ visibility of the spacer elements. ~he spacers are attached ~ ;
l9 to the dielectric sur~ace by ultrasonic compression or ;
thermal bonding or a combination thereof~
21 A further characteristic o the invention relates to 2~ t~e inverted trapezoidal shape of the spacer element~ to 23 direct r¢flection originating from plasma display elements 24 in the plane o the panel bacX into the di~play device rather than forwaxd to the viewer t~ further reduce~~iai~b~
26 lity of the spacers. The si~e of the spacer elements is 27 determined by the a~ailable space between the conductors 28 for the particular display and ~le load bearing require-29 ments are such that the spacers are provided in rectangular or trapezoidal rod form. ~ny potential interaction XI9-77-~03 -4-.:

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1 between the metallic sp~cer elements and the ga~ particle~
2 durin~ ionization iB prevented by providing a dielectric overcoat of a secondary emi3~ive material such a~ ma~nesium oxide which is normally employed to eliminate sputtering of S the dielectric ~urface durin~ ionization. In the preferred 6 embodiment, the spacer is attached to the front plate with 7 the wide side down, as shown in Figure 2 to permit coverage 8 of the entire ~pacer element with the Mg~ iayer. For 9 automated gas panel production, automatic bonding apparatu~
would be programmed to move to the designated areas of the 11 glass plate for bonding of the spacer elements to the 12 dielectric glass. By operating in this manner, the uniform 13 deposition of the dielectric i9 not adversely affected a~
when the spacer is beneath the dielectric, and when appro-priately positioned as hereinafter described, electrical interference b~tween the spacer and adjacent cells is 17 minimized .~,~,s~
18 Accordingly, a primary object o~ the present inventi~n ~-19 is to provide an improved means and method for maintai~ing ~0 a-predetermined uniform distance between the plates of the ~1 ga3eous discharge device.
2~ ~nother object of the present invention i~ to provide 23 an improved spacer technology for a gaseou~ discharge 24 display and~or memory device utilizing metallic s-p~acer~
Another object of the present invention i9 to pxovide 2G an improved spacer technology u~n~ metallic spacers which 27 are bonded to the dielectric surface of the plate at prese-a lected locations between or adjacent to conductors.
29 Another object of the present invention i3 to provide an improved spacer technology whereln metallic spacers are .

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attached to the dielectric formed over the conductor arrays, and are separated from gas particles during ionization by a coating of a refractory secondary emissive material applied over the dielectric surface and associated spacers.
The foregoing and other objects, features and advantages of the present invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an enlarged view of a portion of a gaseous display device illustrating one embodiment of the present invention.
Fig. 2 illustrates a sectional view of the device shown in Fig. 1 taken along the lines 2-2 of Fig. 1.
Fig. 3 is a diagrammatic view of light reflection by a trapezoidal spacer.
DESCRIPTION OF A PREFFERRED EMBODIMENT
Referring now to the drawings and more particularly to Fig. 1 thereof, there is illustrated a schematic plan view of a portion of a gaseous discharge display device. The gas panel display device of the instant invention corresponds to that shown and described in U.S. Patent 3,837,724 to Haberland et al, and the general fabrication steps are similar except as they relate to details of the instant invention pointed out below. It should be again pointed out that the drawings in Fig. 1 and Fig. 2 are not drawn to scale, but are intended to illustrate and clarify the novel aspects of the instant i~vention. However, the : . . : , ' ' ' 1 working parameters including line dimensions, size, dimension and placement of spacer units will be identified hereinafter as represen- ~
tative of the specific parameters of the instant invention. In the diagrammatic view shown in Fig. 1, a matrix of vertical lines includes a group of vertical lines designated as V3, and two groups of horizontal lines designated H5 and H7. The horizontal lines will be formed on the front plate of the device, while the vertical lines V3 will be formed on the back plate of the panel. As representative of a line matrix which could be used to generate an alpha-numeric character, a 7 x 9 dot matrix, each of the character matrices comprises eight vertical lines and nine horizontal lines could be utilized to generate 7 x 9 dot characters with a space between characters.
The embodiment shown in Fig.-l portrays an idealized situation, since the spacing members 9 are interspaced between rows of characters which, in a pract;cal application, would be difficult or impossible to achieve. Rather, the spacing members are designed for and are normally positioned bétween drive lines, in the preferred embodiment between horizontal drive lines, and permits a uniform placement of spacers over the display surface to provide optimum load bearing characteristics.
As further described in the referenced Haberland et al patent, the horizontal and vertical conductors comprise chrome-copper chrome conductors which in the preferred embodiment have a resolution of 70 lines per inch in each direction and in which 3 mil. conductors are spaced on 14 mil. centers, or 11 mils. between adjacent conductors.
The spacer elements of this preferred embodiment may be 5 mils. wide, 4 mils.

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thic~ and 2s0 mils. long an~ are positioned cent~r to center 2 in both directions ~ h respect to adjacent ~pacers 2,000 3 mils. or 2 inches. It has been deter~ined that the spacer 4 elements must be se~arated ~rom the adjacent conductors by 2 mils. to avoid the adverse effect on the electrical 6 characteristics on adjacent conductors, particularly the panel margin or the difference between Vs maY~ and V~ min 8 wh~re Vs represents the sustain signal. Thus the spacers 9 g must be positioned within ~ 1 mil. of the center to avoid

10 ,such pro~lems.

11 Conventional rectangular g~ass rods or other brittle

12 spacers tend to ~rack the dielectric in large panels, while

13 round rods cause fracture of the ~ielectric coating. Any

14 such injury to the dielectric surface modifies the elec-trical characteristics of the affec~ed area to the point 16 where the panel does not meet specification~. One of the 17 problems associated with conven~ional spacers relates to 18 visibility, which is caused primarily by reflectivity o~,the ~ '' 19 round or rectangular surface of the spacing members such~
that the spacers are readily visible to viewers positioned 21 at even a slight anyle from the display surface. One of the 22 ways of reducing reflection of metal spacers is to oxidize 23 the surface of tlle spacers to reduce the reflectivity. The 24 spacers 9 are composed of a nickel iron alloy having appxoximately equal percentage by wei~ht of the two,~om~
26 ponent elements. ~ne adclitio~al advantage of the oxide 27 coatina is that the spacer elements 9 are further protected 28 from the plasma during operation. The spacers axe secured 29 to the dielectric ~y conventional thermal compression or ultrasonic boncling techniques depending on the ~onding . .

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medium. In one form of bonding, a drop of solder glassapproximately 5 mils. in diameter and 1 mil. thick i~
3 applied to the surface of the spacer to be bonded to the 4 dielectric. The ~pacer is then positioned on the dielectric surface under appropriate loading ~uch as 15 6 grams and sufficient heat is applied to effect a glass 7 solder bond. Load and heat are chosen to optimize the 8 strength of the bond and the reliability of the sverall 9 process.
With respect to po~itioning the ~pacers on the glas-~
11 plates, techniques for automated placement as well a~ ~ ~
12 bonding to glass are well known in the art, and positioning ~ ;
13 of the spacers as hexetofore described could ~e controlled 14 by a modified X-Y table which could operate under digital programming control to position the spacers at any sel~cted 16 location utilizing digital controlled servo devices to 17 move in a horizontal, vertical or both directions as ,~.~,~, 18 ~pecifled. The positioning, a~ previously described, ha~
19 been designed to represent ~he best configuration for maximum load bearin~, since loads of up to 50,000 PSI, 21 neas the breaklng poin~ of the dielectric glass, may be 22 encountered during the backfill operation or under maximum 23 vacuum conditions. In addition to reducing spacer 24 visibility, the oxidized surface of the spacer improves the adhesion between the solder glass and the ~pacer! and 26 al~o improves the adhesion of the MgO layer which 1s 27 applied over the dielectric and the spacers to provid* a 28 refractory surface which protects the device from 29 sputtering of the dielectric or the spacer~ and simul-taneou ly by virtue of lts secondary emission charac-' 1 teristics permits lower operating voltage~. The use 2 f magnesium oxide for both purpo~es iq consldered well 3 ~nown in the art. The nickel-iron alloy was alRo 4 developed so that it~ coefficient of thermal expan~ion would match that of the plate glass on which it is 6 mounted. The final feature of the spacer element~ of 7 the instant invention relates to the spacer configuration 8 while the metallic ~pacers 9 are essentially in rod form g which may take various cross-sectional configura~ion~, the preferred cross-sectional configuration for visibility 11 purposes, correspond~ to an inverted trapezoid as shown 12 in Fig. 2. Referring briefly to ~ig. 3, it will be seen .
13 that if incident light is applied to any portion of the 14 slope surface or edge of the trapezoid, as shown by lS horizontal light sources 15 and 13 eminating from opposite 16 Qides of the spacer, the light will be reflected down-17 wardly into the panel, as shown by the associated 18 reflective light paths 17 and 19, such that the reflective 19 Iight is applied into the display rather than outwardiy from the display, thus eliminating the reflective light 21 which xepresents the primary source of visibility -of the 2~ spacers, This combined with the oxidation of the surface 23 of the spacers renders them substantially invisible durlng normal panel operation, a highly desirable result.

Fig. 2 illustrates a sectional view of the gas~p~a~nel~
26 fabricated ln accordance with the teachings of the instant a7 invention. The bottom or bac~ glass plate 21 has metallic conductors 23 formed thereon and overcoated with a layer of dlelectric 25. Conductors 23, while shown widely in Figure 2 spaced for reasons of clarity, would ' . . , : , ' , 1 correspond to the vertical drive lines ~uch a~ V3 3hown 2 in Fig. 1. ~ ile not nece~sary to the instant invention, 3 dielectric layer 25 is overcoated with a layer o~ -4 refractory secondary emissive material 27. The upper 5 plate 31 has horizontal conductor~ 3~ formed thereon, `
6 conductors 33 being disposed -~ubstantially orthogonal to 7 conductors 23 which in turn is overcoated with a dielectric a layer 35. Bonded to the dielectric layer 35 are metallic g spacers 9, which in turn are overcoated with ~n a~sociated 10 layer 37 of secondary emis~ive refratory material to 11 protect the dielectric ~urface and facilitate low voltage 12 operationO The spacers 9 of the preferred embodiment would 13 be attached to the fron~ 31 to permit coverage by the MgO
14 which would normally be applied by evaporation, but would

15 be masked on the edges if positioned on the rear plate.

16 Thus, whlle the preferred embodiment i~ illustrated a~
t 17 having the spacer elements disposed on the front plate, the 18 location of spacers having rectangular or other rod form 19 represents a matter of design choice, and the spacers 20 could readily be disposed on the upper plate or dual 21 spacer elements of half the thickness could be formed on 22 each plate of the device. Likewise, where the spacer~ in 23 the illustrated embodiment are shown as disposed in the horizontal plane, this ob~iously repre~ents a ma~ter of 25 design choice, and the spacers could be disposed in a 26 vertical dixection, in which case they would be pos~tioned 27 between ad~acent vertical conductors.
28 It i8 to be understood that the conductor conflguration .
29 and compo~ition, the specific method of fabricating gaseou~
discharge display devices and the appara~us by which the ' ' ' RIg-77-003 -11-1 chamber i~ evacuated and then charged with an illuminable 2 ~as are con~idered ~no~:n in ~he art, and are disclo~ed, for 3 example, in the ~bove-referenced Haberland et al patent 4 3,~37,724. Accordingly certain of such details have been omitted in the in~tant application in the interest of clarity and a~ unneces~ary for an understanding of the 7 present invention.
8 While the invention has been shown and described with g reference to a preferred embodiment thereof, it will be 10 understood that various ~ubstitutions in form and detail 11 may be made by those skilled in the art without departing 12 from the spirit and scope of the invention. Accordingly, 13 the gaseous discharge display and/or memory device herein 14 disclosed and the method of making same are to be con~idered 15 as merely illustrative of the invention, and the ~cope of 1~ the invention i8 to be limited only as speci~ied i~ the

17 claims.

_, r,t~, Docket No. ~I9-77-003 JJC:es .

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Claims (9)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A gaseous discharge display device comprising in combination a pair of glass plates, said glass plates comprising a substrate with an array of parallel conductors formed thereon and overlaid with a dielectric coating, means for sealing said plates in superimposed spaced parallel relationship with said conductor arrays being disposed substantially orthogonal to each other and separated by a discharge gap, and spacer means for maintaining said gap precisely spaced over the entire surface of said display device, said spacer means comprising a plurality of metallic spacer elements attached to the surface of the dielectric of at least one of said plates, said spacer elements being disposed at predetermined positions on said plate and having a geometric configuration adapted to fit between conductors, and said spacer elements and associated dielectric surface being covered with a layer of a refractory material, the composition, location and configuration of said spacer elements interacting to render said spacer elements substantially invisible.

2. A device of the type claimed in Claim 1 wherein said refractory material is also secondary emissive.

3. A device of the type claimed in Claim 1 wherein the composition of said metallic spacer elements comprises an alloy of nickel-iron.

4. A device of the character claimed in Claim 3 wherein the surface of said spacer elements is oxidized to reduce the reflectivity therefrom.

5. A device of the character claimed in Claim 1 wherein said metallic spacer elements are in the shape of rods adapted to fit between adjacent horizontal conductors.

6. A device of the character claimed in Claim 1 wherein said metallic spacer elements are in the shape of rods adapted to fit between adjacent vertical conductors.

7. A device of the type claimed in Claim 1 wherein the cross-section configuration of said spacer elements corresponds to an inverted trapezoid adapted to direct reflected light into the panel.

8. A device of the type claimed in Claim 1 wherein said spacer elements are attached to said dielectric surface by thermal bonding.

9. A device of the type claimed in Claim 5 wherein said spacer rods are 5 mils. wide and 250 mils. long.