CA1053310A - Segmented gas discharge display panel device and method of manufacturing same - Google Patents

Abstract

SEGMENTED GAS DISCHARGE DISPLAY PANEL DEVICE
AND METHOD OF MANUFACTURING SAME

ABSTRACT OF THE DISCLOSURE

A gaseous breakdown display device is disclosed which comprises a dielectric substrate, information display cathode electrodes on the dielectric substrate and conductors connecting the cathode elements to edge terminals on one side of the dielectric substrate. The cathode electrodes and conductors are printed with a conductive ink on the dielectric substrate and at least the conductive ink of the cathode electrodes have incorporated therein a sputter-resistant material in powder form selected from the group consisting of silicon carbide, tungsten boride, nickel boride, molybdenum disilicide, chromium boride and molybdenum boride. A viewing plate is provided which has at least one transparent anode electrode on the viewing plate and over the cathode electrode with a spacer sealant means joining the viewing plate to the dielectric substrate in sealing engagement therewith and a gaseous display medium is provided between the anode and cathode electrodes.

Description

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: BACKGRO~ND OF THE IN~ENTION :
Fabrication of gas discharge display devices generally ~- of the character disclosed herein have been accomplished in the . ~. ,. :
past. That is, individual gl~ss substrates and/or ceramic substrates are provided upon which the conductor runs are printed and then the dielectric masks are printed over the conductor runs and in the openings in the conductor runs fox : .
the cathode electrodes, the cathode materials which interface ~ :
with the gas discharge medium are printed thereon and all of these being subsequently fired and cured. Such devices are .:
subsequently assembled usually by the use of a gas illing tubulation but in some cases tubulationless devices have .
been fabricated in which final hermetic seal of two spaced `''~
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apart substrate~ i9 accompli3hed by utill~ation o~ an ~n-~used seallng ~rame, ~vacuating the entlre uni~ and back ~lllin~ with an-elevated temperature and th~n heating the a~sembled p~rts spaced b~tween the eiectrode elements whlle ~ :
retaining the gas in the assembl~ until thç glass parts have .
been so~tened to a sealing temperature to result in a rusion ~:
sealing o~ the ~rame element and thereby ~lnal assem~ly o~
the device. This process is dlf~lcult and cumbersome and does not lend itsel~ well to batch processing of lndividual dlsplay element~. .
. In Boswau U.S. patent 2,142,106 issued January 3, i 1939 to Boswau, a gaseous discharge display device having small ~
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glass discs car~rying shaped cathode elements and individual anode elements are stacked in a disc with the interstices between the discs sealed in a manner around the periphery to :

prevent electrode interference between each other, a small aperture being left at one point in the periphery by leaving out the sealing oparation at this point to provlde communLcation wi~h the main gas chamber formed by an overall glass envelope or bulb~ In the Boswau patent, the bulb is subsequently . .

exhausted and filled with the gas at a proper pressure, the ;.
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exhausting and back filling processes extending through and communicating through the aperture to the individual gas chambers formed in the spaced disc and the aperture then is f.illed with a suitable sealing material which permits the gas to permeate during the exhausting and filling operation thereafter this individual seal element or plug is sealed by heating means of electronic bombardment ~

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.,, I . ' . :-.,. . . ,. , . ,, '; ~. -, ' ' '. . ' . . ' ' . ' . ' , 5~3~9 or other sealing means. The present invention is a direct and distinct improvement over the sealing techniques disclosed in the Boswau patent in that the present invention adapts a portion of that technique of the Boswau patent to incorporate spacer elements in the sealant and extends same to batch pro-cessing of thousands of individual discrete gaseous discharge panel elements in a manner and fashion not heretofore avail-able, with yield factors significa~tly greater than those of the prior art. A small opening or space between the ends ~-; 10 of the rod is provided. Large numbers of the device may be ,~ stacked in trays and back filling with any desired gas composi-t~on of large numbers of individual devices in a ~ingle opera- i tion.

, In accordance with this invention, instead of using a ., .
ceramic substrate, simple, inexpensive glass substrates are ~, used. The conductor elements forming the cathode electrodes `
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; which interface with the gas medium are printed first and r cured. At this time, the portions of the conductive printing ~`, which are actual anode elements, may be nickel plated with electrodeless nickel to reduce sputtering. During the nickel ~;~ plating, the conductor portion to the exterior of the device are shi~lded. The reason for shielding is that the seal area must be sintered and not porous.
In the sealing operation described earlier herein, ~; 25 it has also been found that the use of screened on sealing -i materials in an unfused state permits the incorporation of the spacer therein and the forming of the seal under non-vacuum conditions permits such seals to be made, particularly when the glass gob sealing technique is utilized.
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Then, after the gas filling has been introduced to the devices, the devices are heated by Calarod heaters inside the chamber so as to effect a melting of small glass sealing gobs in the fill ports or openings described earlier herein.
Thus, in accordance with the present teachings, there is provided a gaseous breakdown display device which comprises .'.3 a dielectric substrate, information display cathode electrodes on the dielectric substrat~ and conductors connecting the cathode `~
electrode to edge terminals at one edge of the dielectric ... ~ ..
~ 10 substrate. The cathode electrodes and ~he conductors are printed .-,, ~- with a conductive ink on the dielectric substrate with at least .~, the conductive ink of the cathode electrodes having incorporated.,~ , .
therein a sputter-resistant material in powder form selected from the group consisting of silicon carbide, tungsten boride, nickel - boride, molybdenum disilicide, chromium boride and molybdenum boride. A viewing plate is provided which has at least one transparent electrode on the viewing plate and over the cathode ~1 electrode with a spacer sealant means joining the viewing plate ;: to the dielectric substxate in sealing engagement and a gaseous .
display med~um provided between the anode and cathode electrodes.

~ DESCRIPTION OF THE DRAWINGS
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The above and other objects, advantages and features of the invention will become apparent from the following description taken in conjunction with the accompanying drawings ,, ,: .
wherein: ;
Figure 1 illustrates a glass substrate upon which a first conductive pattern has been printed, one such pattern being shown in the top left hand corner thereof with the dash lines indicating the positions of a large number of other -such patterns not shown in this drawing for purposes of clarity '~ of explanation.
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Figure 2 illustrates the glass plate of Figure 1 upon which has been printed the first dielectric mask (a black ~
colored dielectric but shown white in Figure 2), . :
Figure 3 is :the plate shown in Figure 2 having the ~.
crossover conductors printed on the mask of Figure 2 inter- :~
connecting the different elements shown, it being und~rstood that a simi1ar printing has occurred with respect to the other 1. substrate elements shown in Figure 3, ;s In Figure 4, a further dielectric printing has bean ;., , A 10 accomplished over the crossover elements shown in Figure 3, - .`,'~, ',`

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` Figure 5 is an exploded view showing the sequance -~ of assembly of the different components into a device ready for gas fill and seal operations, Figure 6 is a top plan view of a completely assem-bled device, ; Figure 7 is an enlarged sectional view showing the placement of the gob of sealing glass bridging the gap on the . fused seal frame, ~1 ..
Figure 8 shows the mercury capsule in position with a laser beam directed thereto for fracturing same, Figure 9 is a process flow chart showing the indi-.. , - . .. :
vidual printing and curing operations utilized in the manu- -facture of the devices.
DETAILED DESCRIPT~QN
Referring now to Figures 1-8 in conjunction with ~ Figure 9, Figure 1 shows a glass plate 10 which, in a specific ¦ example, may be ten inches by twelve inches sinyle strength glass, h~s printed thereon individual cathode electrode ' patterns ll~l~ 2, ll-N and cathode period elements 12 12-N. Each cathode pattern constitutes a digit position, , ~ .
the illustrated embodiment being for a nine digit numbri~
display (n-9). It will be appreciated that the invention is equally applicable to alphanumeric segmentation as well as ;`
; crosspoint matrix display. These elements have cathode electrode segments 13A, 13B etc., which, in the embodiment . 1 . . ~. , .
of this invention, constitute the cathode electrode elements defining the glow discharge portions of the display. It will be noted that certain ones of these cathode segments 13A, for example, has a further direct conductive portion 14-A leading to a conductor pad 15-A. In the embodiment of this invention .~ - - -''" ".' ' :, :
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to be described herein, each of the corresponding segments 13-A in all of the digit positions 11-1, 11-2... ll-N, are interconnected electrically, some of which are directly inter-connected in the initial electrode printing shown in Fig. 1.
For example, the center bar segment 13-C is shown as being an interconnected horizontal segment electrode and by conductor portion 14-C to a pad 15~C. Alternate pads are also printed ~ at this time for subsequent connection to the anode elements ; to be described later herein. In like manner, the cathode electrode 13-B in digit position 11-1 is interconnected to `~ every cathode segment designat~d with the numeral B by a `;s conductor portion 14-B and thereby to a pad 15-B.
However, in accordance with the present embodiment, some of the cathode segments are not directly connected to conduc-. I .
~ 15 tors extending to the individual pad elements 15. In the il-.,, lustrated embodiment, a first dielectric mask element 16 shown in Figure 2 is printed over the conductor segments leaving openings or vias 18-1, 18-2, 18-N and 19-1, 19-2, ~( l9-N and 20-1, 20-Nj 21~1, 2~-N;and 22~ throu~h 22-N, all of which~are in r~g~stryi~ith an underlylng-conductor~portions or areas. These vias are simply opening or spaces left vacant in the dielectric mask or layer 16. In addition to the vias or openings le~t for crossover connections, to be described later in connection with Figure 3, it will be noted that the individual cathode segments 13-A, 13-B, etc. and the periods therefor 12-1....12-N, are left open. As has been described : .
earlier, no ~urther conductive material is applied to these cathode elements because they have been cured at a higher .. . . .
temperature to thereby anneal and/or provide smooth surfaces for the discharge per se. However, theRe cathode eegme~ta ~, .

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may preferably be plated with electrodeless nickel in a conventional plating batch or process, be~ore or after the dielectric mask has been applied, care being taken to assure that at least the~conductors in the seal area are shielded from the plating operation which assures a good seal being made. In reference to Fig. 9, this plating operation may -be done in place of steps 6-8 in which case the mask print~
dry and cure steps are performed as steps 9-11. Alternatively, the plating of the cathode segments (the conductor portions in contact with the gas) may be done through the cathode openings in the mask. The crossover vias, 18-1~..18-N, 19-1, ...lg-N, 20-1...20-N and 22-1...22-N are left open for the purpose of permitting the conductor material which is printed .. ~ .
in a manner shown in Figure 3 to make electrical contact with lB the conductor elements exposed by the vias. These form the electrical crossover connections shown in the pattern of Figure 3. It will be appreciated that conductor patterns may be devised so that the prin~m~ of such crossovers is eliminated or minimi~ed. It should be understood that while the dielectric mask is shown as white, it is a black mask for highlighting the glow discharges at the cathode segments, and that the cathode materaal is white or silver colored in ;
appearance and, in fact, is basically a silver in a suitable vehicle. Furthermore, clear or transparent areas of glass ;~
have been stippled. Of course the anode glass subst~ate `
could be translucent.
In addition to the openings or vias to make the cross-over connections and in addition to the opening for permit-ting the cathQde seg~ents to ke viewed in direct conductive contact with the gas~ a pair of windows 25A and 25B are pro-,.

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vided so that the glass substrate 10 is direc~ly viewable through these openings 24 and 25. ~hese openings are for the purpose to be described more fully hereinafter.
Not shown in Figures 1 or 2 are conventional registra-tion marks, the registration marks simply being marks which ; are printed in dielectric material upon the substrate 10 and in any subsequent printing upon the substrate 10 when the dielectric material is printed so as to assure registra-tion thereof. In like manner, in the following pace which . ., also follows, Eurther printings of the registration marks are made to assure the proper registrations are achieved.
The term printing is used principally to encompass stencil ;
screen printing etc., but other forms of printing may be used.
As shown in Figure 3 the crossover interconnecting via 19-1~ through via l9-N is designated with the numeral 30 and the crossovers connecting the vias 18 1...18-N are desig-:`
nated 31. In like manner, crossover conductor means 32, 33 and 34 are conductor printings upon the dielectric. The -~ printing operations are simply screening or otherwise applying the conductive material directly upon the dielectric sur-faces of the substrate with thè co`nductive material entering the vias and making the electrical contacts with the conductor previously pxinted. It will also be noted that a pair of crossovers 36 and 37 have also been printed upon the conductor solely for the purpose of making the crossover connections between the conductor elements as shown.
It will be noted that the conductive cathode segments for each of the digit positions remains exposed and these elements are, in`effect, continuing to receive the temperature treatments (albeib at lower temperatures) for the curing of , . ~ .
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the dielectric layer 16 and the individual crossover layers as shown.
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In a final printing operation, the final dielectric layer is applied over the crossover, the windows 25A and 25B
- 5 being maintained. The purpose of this final printing is, as is well known, to avoid any glowing of conductor areas or portions which it i~ m~t-desired to glow.
Referring now to Figure 9, it should be noted that àn important step in the process just described in the fabrica-tion of the back substrate is that the electrodes which form the cathode segments for the display have been printed in an initial printing operation and that the cathode portions have -c` been plated with electrodeless nickel without adversely affecting the conducting properties of the different conductor elements used in providing exterior connections for the device.
As shown in Figure 9, the initial mask is printed in a two .,. I . .
step operation of, first, printing the mask a first time, drying the mask and then curing the mask. A second mask printing, drying and curing operation is effected but it will : ., .
20 be appreaiated that these may be done in a single step. In ~'-' some cases, the mask may be fabricat~d as a film and trans-!~ ferred to the substrate. However, it is important to asaure ; that the mask is of a sufficient thickness that the gap ad-jacent cathode segments is separated by a physical barrier 25 of dielectric material. Thus, this second step is an impor-tant assurance that the dielectric hetween the ends of in-.. ..
dividual cathode segments is hiyh enough to provide a barrier `
, which avoids or mi.nimizes shorting between nearby cathode segments.
The crossover printing is done with the same conductive ~', ' .
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material as is used in the first printing operation of con-ductive material and it will be noted that in each case, the conductive material is dryed and then cured at higher tempera-ture This material is a frit based thick film paste primar-ily of silver. The third mask printing operation, while it could have been limited to printing simply over the cross-overs, was, in effect, a full printing since this further assured a sufficient barrier between the individual cathode segments on the substr~te. Thus, in addition to being able to print, dry and cure the cathode electrodes at a high enough temperature (a typical conveyor oven being about 50 ft.
long, one foot per minute, there being about 15 heat zones ;' with a maximum temperature of 1100C.) as to assure a good, clean, smooth silver surface for the cathode electrode, printing the cathode electrodes in a first printing step permits a good plating operation to be performed and to mask areas of sufficient barriers between the individual cathode segments as to reduce the possibillty of conductive connec~ -tions between the lndividual cathode elements due to the sputtering, etc. and thereby enhance the active life of the device.
As illustrated at box 18 of Figure 9, the device is scribed along the dash-dot lines and separated to provide ;~
individual back substrates illustrated in Figure 5 as element 50. Element 50 is identical to the different element 50 shown in ~igure 4.
Referring now to Figure 5, the back substrate now de-signated as element 50, is identical to the back substrate component shown in Figure 4. A1SQ shown in Figure 5 is an i`
anode su~strate 51 having printed thereon individual anode ~
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elements 52-1, 52-2, 52-N, there being one such anode elec-trode element for each digit position and adapted to overlie the individual cathode segments and the cathode period element 12-1 at a given digit position. The anode conductors are transparent tin oxide which are printed and fired on a single strength glass~substrate~S3. It will be appreciated that the printing and firing of these conductors may be done in a batch process, very much like the printing of the back sub-strate with cathode elements. The use of tin oxide as a trans-parent anode element is conventional in the art and is notdescribed in detail herein except to say that the process of ; printing same with large numbers of devices on a thin glass ; .
substrate is useful for the purpose of batch producing de-` vices.
The top substrate or anode plate 51 is joined to the bottom substrate by means of a screen printed sealing ele-ment or member 55 which, in a preferred embodiment, has been shaped so as to have the ends thereof 56 and 57 spaced by about a 1/4 inch-~to about 1~16 inch. -~he~sealing element 55 is screened upon the black dielectric masked element and at the same time small glass spacer beads 58 are likewise tempo-rarily held in position by tacking as by the use of unfused dielectric. Spacer beads 58 and S9 consist of a hard glass composition having a higher softening temperature than the sealing element 55. The seal eIement 55 is conventional solder glass sealant which has a fusing or seal temperature ,1 , below the melting point of the glass substrate 10 and spacer beads 58. Beads 58 provide accurate spacing for the discharge gaps. `
; 30 In addition, a small mercury capsule 60 is held in ;'.

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; place in positorl over window 25A~by a white unfused dielec-tric which is of essentially the same composition as the di-electric forming the mask but which does no-t have any pig- i~
mentation in it. The purpose of using a white unfused di-electric is so that a laserx~energy which is used to rupture the capsule 60 is not absorbed by the black dielectric to ;' create heat in the black dielectric and thereby destroy the device. It is also for -this reason that a pair of windows 25A and 2SB is provided.
After the sealin~ member 55 and spacer beads 58 and , mercury capsule 60 have been positioned in the device, the anode plate 51 is positioned over these elements and a weight is applied thereto. The entire assembly is passed through a heating oven to fuse or join the se~ling member 55 to anode plate 51 and back substrate pla~e 5Q. A glass sealing gob 66 is simply laid in the g~p or crlvice between back sub~
strate plate 50 and anode plate 51 and constitutes the glass ~;
' plug illustrated in block 23 of Figure 9. The resulting ~-'l, device is illustrated in Figure 6.
The only size criteria of the spacer is that it defines the discharge gap and be a high melting temperature glass `, and have a fiber softening point below that of seal member 55.
As shown in Figure 6 alternate ones of contact pads 15 ; are connected to the cathode electrode on cathode plate 50 and the intervening ones are connected by means of an ex-truded conductive silver epo~y connectors 70-1, 70-2 as an improvement over prior art metal insert connectors previously ." . . .
,l used for this purpose. It is ~mportant to cure the epoxy at ~-:j :
; a temperature such that bubbles are not formed. Bubbles r~' 30 tend to cause concentrations of current flow in the tin oxized .J . .
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coatings and thereby lmpair or dest~oy the connection theret~.
As shown in Figure d, the mercury giver 60 is a flla-mentary glass tube (18 mils in outside diameter) which is laser energy transparent. It ls positioned between a wlndow 25A an~ the cathode plate 50 and a transparent portion of the anode plate 51 (which may also be designated as a "window~
and held in place for assembly purposes by a white dielectrlc.
The aluminum or copper block serves as a heat sink and should , i not be highly re1ective for safety reasons. Instead of a i 10glass capsule ~he giver may be any other radiant energy ac- 1 .
tuable device, such as S~ES type 150 giver from the SAES
company of Italy. It will be understood that by nickel , plating the cathode segments; sputtering of the cathode seg-ments is minimized.
the cathode segments; sputtering of the cathode segments is minimized.
The gas filling may be a mixture of neon and argon, i~ such as 99.5~ neon and 0.5'~ argon. As is conventional, radio- ~

,l active Krypton (Rrypton 85~ may be added to the fill mixture ~-:~1 20 to lower the operating voltage. However, it will be noted that there are two unused contact pads 15 which could be used 1 . , .. ~
to operate a keep alive discharge as is also conventional in ;i the art. If desired the top horizontal run of seal member 55 may be located closer to the edge so that upon ~usion the ~¦ 25 seal material of elemcnt 55 will be pressed flat as shown in ..
Figure 8 and the seal plug 66 held inposition. The panel ;~ . . ..
assemblies, with glass seal gob 66 in the notch or space and bridging the ends of the seal element 55, the panels are stac]ced, in stainl,~ss trays with the port or space 65 up and ` 30 the glass gob 66 in place. A high temperature glass shim, ! :
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' n(-t shown, is located ~etween the lower edge of anode plate 51 to maintain the proper relationship between the anode and cathode plates while the heating of seal rod 66 is performed.
Seal element 55 is a bubble-free glass to avoid "worm" ;:
holes therein. The glass plugging element or gob 66, placed .... .
across the opening or port 65 as shown, has softening point below that of the sealing member 55; a ~imilar glass with a ~ softening point 20 to 30 degrees lower is satisfactory.
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~he gas process proccdure is the evacu~tion o~ the system, the introduction of the proper gas at ambient room _ temperature to the proper pressure, about 120 torr, and the heating of the seal rod 50 it closes the envelope with the S desired gas condition. In the system described above~ the ¦;
cycle is 6 hours with 2000 devices per cycle~ Each chamber can be large enough to handle as many as 5000 devices. The `
~, cycle may be reduced to`l-1/2 hours. After the sealed devices are removed from the gas process system, each one is placed ,.,., ; 1'' ~lO under a laser which is projected through window 25A in the device to crack the capsule and rele~se mercury into the envelope. As ls conventional~in the art some panel aging time may be performed be~ore releasing the mércury.
One method of eli~inating mercury is the use of `L5 cathode materials ot~er than the silver o~ other precious ~ metals previously used in these devices. The materials to be ,J used according to this invention are silicon carbide3 nickel ~'!

boride, molybdenum disilicide, tungsten boride, chromium boride, molybdenum boride, and a number of other elements 2~ of this nature. Althbugh these materials are known to be sputter resistant they could not be used prior to the present I invention because they are extremely hard and brittle and could not be rolled into strip form to be used as cathode elements. However, these materials can be obtained in powder form and incorporated into the conductive inks of this invention and printed in accordance with the above-mentioned process~ ¦
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Also thls invention encompasses pl~ting or covering cathode elements with various nickel plating solutions which are extremely resistant to sputtering. One such coating is nickel boride. Nickel itself if printed in a glass frit and fired in air will be oxidized rapidly to a nonconductive and use less nickel oxide. By contrast the nickel boride coating on a standard precious metal or other type cathode ~
substantially eliminates all sputtering and provides a long S
lasting display device. The embodiments of this invention eliminating use of mercury vapor substantially reduce the cost of producing a display device as well as .insure freedom from the well-known health hazards of mercury and mercury vapor.
, ~ However, other aspects of thls invention may be used in con-,` junction with mercury capsule 66.
It will be appreciated that while a number of modifi-cations have been referred to, others will become apparent to those skilled in the art and it is to be understood that such obvious modifications may be made without departing ,~, from the true spirit and scope of the claims appended hereto.
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Claims

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

1. A gaseous breakdown display device comprising a dielectric substrate, information display cathode electrodes on said dielectric substrate and conductors connecting said cathode electrodes to edge terminals at one edge of said dielectric substrate, said cathode electrodes and said conductors being printed with a conductive ink on said dielectric substrate and at least the conductive ink of said cathode electrodes having incorporated therein a sputter-resistant material in powder form selected from the group consisting of silicon carbide, tungsten boride, nickel boride, molybdenum disilicide, chromium boride and molybdenum boride, a viewing plate, at least one transparent anode electrode on said viewing plate and over said cathode electrode, a spacer sealant means joining said viewing plate to said dielectric substrate in sealing engagement therewith and a gaseous display medium between said anode and cathode electrodes.