CA1081760A - Indicator display tube - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An indicator display tube in which indicator electrode units, each consisting of anode and cathode segments, lie in the same plane and in which all of the cathode segments are simul-taneously energized and the anode electrodes are energized on a time sequential basis in such a manner that only the indicator electrode unit having its anode electrodes energized will glow at a particular time. The cathode segments of each indicator unit are connected in parallel which substantially reduces the number of leads to the display tube over conventional indicators which require a separate lead for energizing each of the cathode segments. The indicator display tube has a barrier electrode formed so as to lie between adjacent indicator units for prevent-ing accidental discharge of adjacent indicator units which would produce erroneous message displays.

Description

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BACKGROUND OF THE INVENTION
Field of the Invention:
This invention relates in general to an indicator display tube and, in particular, to a novel indicator display tube and to a method for making it.
Description of the Prior Art:
Generally, indicator display tubes, which are of the type including a plurality of indicator units mounted inside a transparent envelope for displaying numerals, symbols, let-ters, or the like, have been used with electronic counters and other various indicating devices. One example of such indicator display tubes is the so-called "Nixie" tube in which an anode and a plurality of cathodes are aligned in a stack one above another and the cathods are selectively energized to provide a display of a desired numeral or letter. Another type of indicator display tube utilizes cathode segments mounted in a common plane and an anode in the form of a wire screen or mesh mounted in a second plane.
For displaying a number containing a plurality of figures with the *Nixie tube, it is necessary to employ the same number of Nixie tubes as that of the figures, which nevitably leads to bulkiness of an indicator display device.
Accordingly, the *Nixie tube is not suitable for such number display. The indicator display tube with cathodes in a com-mon plane is small and thin but requires the same number of leads as used in Nixie tubes. The large number of leads are ` difficult to form and to lead out of the envelope and results , in complexity in the external wiring.
-i United States Patent No. 3,588,571 discloses an in-i 30 dicator display tube of the type in which many indicator 1, .
electrode units, each consisting of an anode and a plurality * Trademark - 1 - *~ ,~

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of cathode segments are formed on an insulating plate with the cathode segments in each unit connec-ted in common to those in the other units and connected to common energizing leads but in which the anodes are connected to separate en-ergizing leads which are led out of the envelope. This in-dicator display tube had advantages in that the number of the leads required is smaller than that of the prior art tubes. However, such tube is likely to provide an incorrect message display because the indicator units are driven on a time sequential basis and the repeating glow discharge causes the ionizable gas, for example argon or neon which is sealed in the envelope, to produce ions which diffuse toward - electrodes of adjacent units which lowers the discharge initiating voltage between anode and cathode segments of the adjaeent eleetrode units and eauses them to glow.
SUMMARY OF THE INVENTION
The present invention relates to an indieator dis-~ play tube which has a number o-f indicator electrode units - with their anode and cathode segments formed in a common plane and includes means provided between adjacent indieator elee-trode units to prevent aecidental discharges. The eathode segments of eaeh electrode unit are eleetrieally intereon-nected to eorresponding ones of the other units and are simultaneously energized. The anodes of each unit are ener-gized on a time-sequential basis in sueh a manner that a partieular eleetrode unit whieh has its anode energized pro-vides a display.
Aecordingly, one objeet of this invention is to pro-vide an improved indieator display tube which is provided with many indieator electrode units.
Another object of this invention is to provide an ., :

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indicator display tube which is adapted to prevent an incor-rect message display and which is simple in eonstruction.
A further object of this invention is to provide an indicator display tube which is compact, eonvenient and has long life.
Still a further object of this invention is to pro-vide an indicator display tube which is easy to manufacture.
Other objects, features and advantages of this invention will beeome apparent from the following description taken in conjunction with the aceompany drawings.
BRIEF DESCRIPTION OF THE DRAWINGS -FIGURE 1 is a plan view schematically illustrating one example of an indicator display tube of this invention;
FIGURE 2 is a plan view of a cover plate of the indicator display tube of this invention;
FIGURE 3 is a plan view of the glass backing plate of the invention;
FIGURE 4 is a sectional view taken on line IV-IV of FIGURE 2;
FIGURE 5 is a seetional view taken on line V-V of FIGURE 3;
FIGURE 6 is a plan view of the baeking plate il-lustrated in E'IGURE 3 wi-th a plurality of intereonneeting leads formed thereon; ,-FIGURE 7 is a plan view of the baeking plate of FIGURE 6 with an insulating layer formed over the intereon-neeting leads;
FIGURE 8 is a plan view of the baeking plate of FIGURE 7 with a plurality of indieating units and seleeting leads formed over the insulating layer;
FIGURE 9 is a plan view of the baeking plate of FIGURE 8 with an insulating layer formed thereon;

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FIGURE 10 is a sectio:nal view taken on line X-X of FIGURE l;

FIGURE 11 is a eircuit diagram showing the indica-tor assembly of FIGURE 1 together with a drive circuit there-for;
FIGURE 12 is a fragmentary sectional view schemati-eally illustrating a modified form of the indicator display tube of this invention;
FIGURES 13 and 14 are sectional views showing the steps involved in~the making of a cover of the tube depicted in FIGURE 12;

FIGURE 15 is a sectional view schematieally show- .
ing another modification of the indicator display tube of this invention;
FIGURE 16 is a plan view schematieally illustrating another modifieation of the indicator display tube of this invention;
FIGURE 17 is a sectional view taken on the line .
XVII-XVII in FIGURE 16; -FIGURES 18 and 19 are a plan view and a sectional .
view schematieally illustrating other modifieations of this invention;
FIGURE 20 is an enlarged fragmentary sectional view of the baeking plate of FIGURE 9; and FIG~RES 21 to 23 are seetional views~ similar to FIGURE 20, showing other modified forms of this invention. ;
DESCRIPTION OF THE PREFERRED EMBODIMENT

In Figure 1 there is illustrated generally one ex-ample of a gaseous glow type indicator display tube 1 pro- :
. 30 dueed aeeording to this invention. The indieator display . tube 1 is made up of a base plate 2 of an insulating ma-terial.

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as, for example, glass. A plurality of indicator units 40, 41, 42, 43, 44, and 45, of the same pattern are formed by printing techniques on the base plate 2 in alignment with one another and a transparent cover plate 3, as of glass, is attached at its periphery in an air-tight manner to the base plate 2 and its center is spaced a predetermined distance from the indicator units.
The indicator display tube 1 of the present inven-tion is constructed in the following manner: The insulating base plate 2 such as illustrated in Figure 3 has the indica-tor units and the interconnecting leads formed thereon. The transparent cover plate 3 is attached to the base plate 2 after the indicator units are formed. The cover plate 3 is formed with a depression or hollow portion 4 in which the indicator units are received as shown in Figure 4.
Both of the plates 2 and 3 may be made of glass and ~;
generally the base plate 2 is larger in area than the cover plate 3 as may be observed by comparing Figures 2 and 3.
Figure 4 is a sectional view taken on line IV-IV
of Figure 2 and illustrates the depression 4 in the cover plate 3.
Figure 5 is a sectional view taken on line V-V of Figure 3.
Figure 6 is an enlarged plan view of the base plate 2 and illustrates a plurali~y of interconnecting leads 10 to 18 which are formed on the insulating base plate 2 by suitable thin film techniques such as, for example, by print-ing. It is to be particularly noted that the interconnecting leads 10 to 18 are grouped 50 that they will align with in-dicator units to be formed above a particular group. Thus, the interconnecting leads for the first indicator unit are , _ 5 _ l7~;~
,, designated by numerals 10 to 18 and the interconnected leads for the second unlt are designated by numerals 10' to 18'.
The interconnecting leads are formed of silver paste which adheres well to the glass base plate 2.
After the interconnec:ting leads are formed by print-ed circuit techniques on the base plate 2, the plate and leads are baked to provide suitable bonding.
I-t is to be realized that the lengths of the inter-connecting leads 10 to 18 are such that they will be capable of interconnecting the cathode and anode elements of the indi-cator units to suitable selecting leads as will become more apparent in the description.
Figure 7 is a plan view of the base plate 2 in which a glass insulating layer 20 has been deposited on the base pla-te 2 so as to cover a substantial portion of the ~ . .... .
interconnecting leads 10 to 18. The insulating layer 20 may be formed by a glass coating method by applying glass coating by spraying two or three times and then by drying it to provide it with a suitable insulation coating 20 over the interconnecting leads.
Windows are formed in ~he insulating layer 20 at opposite ends at each of the interconnecting leads 10 to 18 so as to allow electrical conducting paths to be formed through the insulating layer 20 to the interconnecting leads 10 to 18. For example, windows 30a and 30b are formed through the insulating layer 20 at opposite ends of the interconnecting lead 10. Windows 31a and 31b are formed at opposite ends of the interconnecting lead 11 and additional windows 32a and 32b through 38a and 38b are respectively formed at opposite ends of leads 12 to 18. Additional windows intermediate the ends of lead 14 are formed and are designated 3~c and 34d. ~

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It is to be realized, of course, that the windows formed through the layer 20 are formed for each of the in-dicator units although they are only particularly numbered in Figure 7 for the first indicator unit.
Figure 8 illustrates the next step of the method of making the indicator unit and illustrates a plurality of indicating units 40 to 45 which are formed on the top of the insulating layer 20.
In the next step the plurality of indicator units 40 to 45 (the number depending upon the desired number) are formed on the insulating layer 20 and aligned with the win-dows through the layer 20 so that electrical contact will be made with the interconnecting leads. Each of the indicator units comprises electrically conducting anode segments 51, 52 and 53 as well as an associated plurality of cathode ele-ments 61 to 68. At the same time, a plurality of selecting leads 71 to 78 are formed on the insulating layer 20 with the leads 71 to 74 extending along the top of the indictor units 40 to 45 as shown in Figure 8 and selecting leads 75 to 78 extending along the bottom of the indicator units 40 to 45 as shown in Figure B. The anode and cathode segments and selecting leads are formed by suitable thin film techniques and are formed so as to align with the windows 30a to 38a and 30b to 38b so that electrical connections will be made between the selecting leads 71 to 78 and the anode and cathode seg-ments.
A plurality of external leads 81 to 84 are formed ; on the insulating plate 2 adjacent the lower edge relative to Figure 8 and are respectively connected to the selecting leads 71 and 74. A plurality of external leads 91 to 94 are respectively connected to the selecting leads 75 to 78 _ 7 _ L'76~

and are formed on the insulating plate 2 along the bottom edge as shown in Figure 8.
It is to be realized -that the indicator units 40 to 45, the selecting leads 71 to 78 and the external leads 81 to 84 and 91 to 94 are formed at the same time by a silk screen process and when the indicator units 40 to 45 and selecting leads 71 to 78 are prin-ted on the insulating layer 20, each of the elements 61 to 68 and 51 to 53 are respec-tively connected to the associated selecting leads through the windows 30a to 38d formed in the insulating layer 20.
For example, the cathode element 62 is formed so tha-t it aligns with window 31b which connects it to one end of the interconnecting lead 11 and the selecting lead 74 is formed over the window 31a so that the selecting lead 7~ is connect-ed to the cathode segment 62 through the interconnecting lead 11. Simultaneously, all of the corresponding cathode seg-ments 62 of all of the indicator units 40 -to 45 are connect-ed to lead 74 through associated windows and thus all of the segments 62 of all of the indicator units are electrically connected together and to the external lead 84. Similarly, all of the cathode segments 61 are connected by lnterconnect-ing lead 10 to selecting lead 72 and to external lead 82.
All of the cathode segments 63 are connected by interconnect-ing leads 13 to selecting lead 73 which is connected to ex-; ternal lead 83. Each of the cathode segments 64 is connected by interconnecting lead 12 to selecting lead 71 which is con-nected to external lead 810 Each of the cathode segments 65 is connected by interconnecting lead 15 to selecting lead 75 and to external lead 91. Each of the cathode segments 66 is connected by interconnecting lead 16 to selecting lead 76 which is connected to external lead 92. Each of the cathode ~.

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segments 67 is connected by interconnecting lead 17 to selecting lead 77 which is connected to external lead 93.
Each of the cathode segmen-ts 68 is connected by intercon-necting lead 18 to selecting lead 78 which is connected to the external lead 94.
Thus, in the structure defined thus far, the asso-ciated cathode segments of all of the indicator units 40-to 45 are electrically connected together and thus can be elec-trically energized by the eight cathode selecting leads 81 to 84 and 91 to 94. The three anode segments 51, 52 and 53 of each of the indicator units 40 to 45 are interconnected together by the interconnecting lead 14 and a separate external lead is formed along the lower edge of the insulating plate 2 so that the anode segments of each of the indicator units can be individually energized. For example, an external lead 110 is connected to interconnecting lead 14 of the in-dicator unit 40 which is connected to the anode segments 51, 52 and 53 of the indicator unit 40 and the indicator unit 40 will be energized when the external lead 110 is energized : 20 with a selective pattern of the cathode segments.
Likewise, the anode segments of the indicator unit 41 are connected through an interconnecting lead to the ex- -ternal anode lead 111 for the indicator unit 41. An external lead 112 is connected to the associated anode se~ments of the indicator unit 42 in a similar manner. An external lead .
113 is connected to the anode segments of the indicator unit 43 and an external lead 114 is connected to the anode segments of the indicator unit 44. An external lead 115 is connected to the anode segments of the indicator unit 45.
The indicator display tube of the present invention is adapted to prevent an incorrect message display which is _ g --- , . . . . . .
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7~3 caused by accidental discharge of the indicator units. For this purpose in the illustrated example an auxiliary electrode or barrier electrode designated at 100 is utilized. The barrier electrode 100 may be formed around the indicator units 40 to 45 on the insulating layer 20 at the same time as the indicator units and leads and has suitable windows for the indicator units as shown. A lead 101 is also formed on the insulating layer 20 and extends from the barrier electrode 100 to an external lead 102 so that a suitable voltage may be applied. The leads 101 and 102 are formed at the same time that the barrier electrode 100 is formed. The leads, cathode and anode segments and barrier electrode are all formed of silver paste which adheres well to the glass insulating layer 20.
In the next step, as shown in Figure 9, a second insulating layer 120 of glass is deposited over the selecting -.
leads 71 to 78 and 101 but the indicator units are left un-covered by this second insulating layer 120. In other words, the cathode segments 61 to 68 and the anode segments 51 to ~ -53 of each of the indicator units are left uncovered by the second insulating layer 120. The external leads are also left uncovered by the second insulating layer 120.
Since the cathode segments of each indicator unit are bombarded by ioni2ed ions emitted from the space dis-charge layer which can cause them to sputter, it is necessary to form the catho~e segments of a metal which resists sput-tering and which has a low work function.
For accomplishing this, a thin nickel layer is formed on the plurality of indicator units 40 to 45 and over the barrier electrode 100 by electroplating in a plating bath as described below.
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For nickel plating, a neutral plating bath is em-ployed and the thickness of a plated layer is selected so that deposition of the nickel layer on the silver paste is en-hanced. The preferred composition of the plating bath and the plating conditions are as follows:
Composition of Plating Bath Nickel sulfate240g/1 Nickel chloride45g/1 Boric acid 25g/1 Nickel carbonate 5g/1 Nickel hydroxide 5g/1 Plating Conditions PH = 5 Bath temperature 40 to 50C
Plating time 1 to 1.5 minutes Current density 30 to 40 mA/cm These conditions cause the nickel layer to be de-posited 5 to 10 microns thick on the silver paste layer.
After the indicator units are formed on the base plate 2, the cover plate 3 is attached to the base plate 2 as shown in Figure 10 by suitable cement or other means so as to form a sealed chamber between the base plate 2 and cover plate 3 which encloses the indicator units. The external leads have portions which extend beyond the cover plate 3 on the base plate 2 so that electrical connection can be made.
The base plate 2 is formed with an opening to which an exhaust tube (not shown) may be connected so as to evacuate the space between the cover plate 3 and the base plate 2 and a suitable ionizing gas may be inserted into the space between the cover plate 3 and the base plate 2 and the opening sealed by a suitable seal in a conventional manner.

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Figure 11 schematically shows the indicator tube assembly of Figure 10 with a driving circuit. The indicator display tube of this invention operates as follows:
Assume that the number "1.8" is to be displayed.
Switches Sl, S2 and S3 are closed to ground the cathode seg-ments 63, 67, and 68 and an anode voltage supply switch Kl is closed to supply an anode voltage to the anode segments 51, 52, and 53 of the indicator unit 40 causing the cathode segments 63, 67 and 68 to glow to display "1.".
Then, the switches Sl, S2, S3 and Kl are opened and a switch K2 to the anodes of indicator 41 is closed together with switches Sl, S2 and S4 to S8 to cause the cathode seg-ments 61 to 67 of the indicator unit 41 to glow so that in~ ~-dicator 41 displays "8". Thereafter, "1." and "8" are alter-nately displayed by the indicator units 40 and 41. The switch-ing speeds can be increased until the "1." and "8" appear to an observer to be simultaneously displayed. Electronic ;
matrix switching means for sequentially closing switches as above are well-known and will not be described.
Conventional indicator tubes which do not have a barrier electrode as employed in the present invention can give an incorrect message display because as the glow dis-charge is repeated for predetermined periods o~ time the in-ert gas, such as for example, neon or argon which is sealed ; in the envelope, will be ionized and the ions will diffuse through the envelope and lower the discharge initiating voltage between and cathodesegments of indicator units which should not glow. Thus when the indicator unit 40 displays "1." the cathode segments 63, 67 and 68 of the remaining indicator units 41 to 46 are all grounded together as well as those of unit 40 and even if no anode voltage is supplied to , , ~ , ~ , -the anode segments of the units 41 to ~5, glow discharge will be produced between the anode segments 51 to 53 of unit 40 and the cathode segments 63, 67 and 68 of the other units and produce an erroneous display such as "1.1.1.".
In the present inventicn, the barrier electrode 100 is formed so that it surrounds the indicator uni-ts 40 to 45 and is supplied, through a switch KO, with a positive voltage which is lower than a voltage supporting discharge between the anode and cathode segments and which does not exceed the discharge initiating voltage between the electrode 100 and the anode and cathode segments. For example, when a positive voltage of 175V is impressed on the anode segments 51 to 53 of the indicator unit 40, the barrier electrode 100 is supplied with a positive voltage of about lOOV. Thus, positive ions produced in the vicinity of the indicator unit 40 are repelled by the positive voltage fed to the barrier electrode 100 toward the inner wall of the cover plate 3 and electrons are attracted by the barrier electrode 100 and the anode segments 51 to 53 which are being energized. Thus, ions are prevented from-di~fusing or spreading in the envelope and hence do not cause neighboring indicator units to glow~ That is, the provision of -the barrier electrode effectively avoids the possibility of an incorrect display from resulting because of the diffusion of ionized ions.
In the foregoing example, the barrier electrode 100 is formed integrally over the entire area of the base plate

2 but the same effect can be obtained by forming separate barrier electrodes between adjacent indicator units.
Figure 12 shows in cross section a modified form of the indicator display tube of this invention. In this ex-ample, the error preventing means comprise a cover plate 121 ~
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rather than the barrier electrode 100 mentioned above. The cover plate 121 is formed with projections 150 to 154 as shown and is mounted on base plate 131 in such a manner that each of the projections 150-154 lie between adjacent indicator units 140 to 145 formed on the base plate 131, as clearly shown in Figure 12. With such an arrangement, when the indica-tor unit, for example, 140 is energized and glows, ions pro-duced by glow discharge will tend to move towards the neigh-boring indicator unit 141 but are stopped by the projection 150 formed in the cover plate 121, thus preventing an erron-eous message display as a result of accidental discharge be-tween neighboring indicator units.
Figures 13 and 14 illustrate the manner in which the projections 150-154 of the cover plate 121 are formed. As shown in Figure 13, a thin sheet of glass 121 is placed on a support 160 which is formed of a heat-resisting material, for example, carbon, and has a depression 161 and stepped portions 162 and 163 at both ends. In the depression 161 of the support 160 a plurality of support pieces 164 are mounted at regular intervals which correspond to the spacings of the indicator units 140 to 145. The support pieces 164 may be formed integrally with the support 160 or may be formed by embedding in the support 161 inverted U-shaped metal wires (which preferably is wire made of an Ni-Co-Fe alloy which has the same temperature coefficient of expansion as glassj. The support pieces 164 are sprayed with carbon which serves as a mold releasing agent.
The cover plate 121 is placed on the support 160 with its edges resting on the stepped portions 162 and 163 which extend around its periphery. It is then heated to the range of 630C. to 700C. in an atmosphere of nitrogen gas - .

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o in a furnace for about twenty minutes. The cover plate 121 softens and sags down into the depression 161. The cover plate 121 is prevented by the upwardly projecting support pieces 163 from sagging down where the pieces are located.
The cover plate 121 conforms to the depression 161 but the projections 150 154 are formed over the support pieces 164 as shown in Figure 14.
Then, the cover plate 121 in which the projections 150 to 154 have been formed is removed from the support 160 and is mounted on the base plate 131 to cover the indicator units formed thereon to obtain the structure shown in Figure 12. The cover plate 121 is mounted on the base plate 131 so that each of the depressions formed in the cover plate 121 enclose corresponding indicator units. Then, the cover plate 121 and the base plate 131 are sealed by frit glass at their marginal portions to provide an indicator display tube 170 such as depicted in Figure 12.
Further, an ionizing gas, for example~ argon, neon or the like, is sealed in the tube 170 and, if necessary, a getter is activated in the tube to provide a finished tube.
This embodiment prevents undesired accidental discharges by using a cover plate of a particular shape which is easy to produce. Further, the tube is formed with only two glass plates, and hence can be simply produced.
Also by the use of this method, the envelope can ~ ~
be formed extremely thin as in the example of Figure 1. ~ ;
Further, since the front portion of the indicator display tube is cylindrical at those areas covering the indicator units, a lens ef~ect is obtained which facilitates inter~
pretation of the messages being displayed. ~ ~
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Figure 15 schematically shows in cross section an-other modified form of this invention. In this example in-dicator units 180 to 185 are formed on a glass base plate 175 and a cover plate 192 is corrugated as shown in Figures - 13 and 14 to form projections 186 to 190 which lie between adjacent ones of the indicator units in the finished tube.
Also, additional or barrier electrodes 195-199 to which are supplied a predetermined potential, are formed on base plate 175 between a~jacent indicator units. Thus, it is seen that in this example undesired accidental discharge of the indicator units can be more effectively prevented by both the barrier elec-trodes 195 to 199 and the projections 186 to 190.
In Figures 16 and 17 there is illustrated another modification of this invention, in which indicator units 220 to 224 each consisting of a plurality of cathode segments 230 and anode segments 231 are formed on a glass base plate 210 in the same manner as in the foregoing e~amples. A trans-parent insulating cover plate 240 is mounted on the base plate 210 in a predetermined spaced relation to the indicator units 220 to 224 and the cover plate 240 and the base plate 210 are sealed at their opposing peripheral portions with a frit -~ glass seal. The envelope designated generally as 241 is con-structed such that the distance t between the flat base plate 210 and the cover plate 240 is uniform at any place in the envelope.
~ Also, the inner surface 240a of the cover plate 240 ; is roughened to provide an area on which the recombination of ionized ions occurs. The entire area of the inner surface of the cover plate 240 may be roughened as shown in Figure 16 and the indicator units show through. In E'igure 18 the inner surface of the cover plate 240 is roughened until it is opaque except at those areas covering indicator units 220 to 240.

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The inner surface of -the cover plate 240 can be easily roughened by means of sandblasting or by rinsing the cover plate with fluoric acid, such as by soaking the cover plate in a 5% dilute solution of fluoric acid for about 5 to 20 seconds.
The roughened inner surface of the cover plate 240 substantially increases the recombination area of the ionized ions so that the ionized ions produced by glow discharge of a selected one of the indicator units nearly all recombine and are thus prevented from moving toward neighboring in~
dicator units, thus ensuring avoidance of an incorrect message display.
In the above example the inner surface of the cover plate 240 is roughened to prevent undesired discharge between the indicator units. It is àlso possible as shown in Figure 19 to deposit over the roughened inner surface 240 a of the cover plate 240 a transparent conductive layer (a *Nesa electrode) 250 and apply a suitable potential such as ground to layer 250. In this case, the transparent conductive layer may also be deposited by evaporation on those areas of the roughened surface corresponding to the spaces between adja-cent indicator units.
Thus, charge stored on the inside of the envelope ; will be grounded through the transparent conductive layer 250 to further ensure the elimination of erroneous message dis-plays. ~i-In addition, erroneous message displays due to neighboring indicator units can be prevented more effectively ;~
by providing a barrier electrode 265 between adjacent indica-tor units as depicted in ~igures 16 and 19.
The anode and cathode segments of the indicator .:.

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display tube of this invention are formed by plating nickel on silver paste coated on the glass base plate because silver paste has a low firing temperature and adhere well to the glass base plate. In general~ however, silver sputters easily in an atmosphere of a neonr argon or like gas within a dis-charge tube and for this reason nickel which does not sputter easily is plated on the silver paste to prevent sputtering.
Figure 20 is an enlarged fragmentary cross-sectional view of the indicator unit shown in Figure 9. It can be noted in this figure that nickel has not been deposited in sufficient thickness on the edges 260 of the silver paste layer 61 and there is the possibility that the silver will sputter and cause an incorrect message display or shorten the service life of the indicator display tube.
Figure 21 schematically illustrates in section one portion of an improved indicator unit which avoids the defect caused by the edges of the silver paste not being covered.
In the illustrated example an interconnecting lead 300 con-nected to a selecting lead is formed of silver paste on the glass base plate 2 and an insulating glass layer 20 of a low melting point is formed on the base plate 2 over the inter-connecting lead 300. A window 30a is formed in the glass layer 20 at a location corresponding to one portion of the interconnecting lead 300.
Then, nickel is electro-plated in the window 30a of ;~ the glass layer 20 to form a nickel plated layer 301 therein.
Then a nickel layer 302 about one micron thick is formed by non-electrolytic plating over the entire area of . . .
the insulating glass layer 20 including the nickel plated layer 301 and then a nickel layer 303 about 5 to 10 microns in thickness is formed by electroplating over the nickel lay-er 302.
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7~a9 Then an etching mask layer (not shown) of the same pattern as that of the electrocles to be ultimately formed is deposited on the upper-most nickel layer 303 and the nickel layers 302 and 303 are selectively etched away through the etching mask layer. Thereafter, the etching mask layer is removed. In this manner, electrode segments of a desired pattern are formed on nickel on the glass layer 20 to provide a desired indicator unit.
Thus, the cathode and anode segments are all formed of nickel, and hence will resist sputtering and will with-stand long usage. Also, the lead 300 connected to the elec-trode segment is formed of silver paste which adheres well to the glass base plate 2 and the mechanical bonding of the electrodes is excellent.
Figure 22 illustrates another modification of this invention in which an interconnecting lead 310 is formed of ---silver paste on the glass base plate 2 and an insulating glass layer 20 is formed on the interconnecting lead 310 with one portion of the latter left uncovered to form a window 30a. Then, silver paste of the same pattern as an electrode ~ ;to be ultimately formed is printed by printing techniques on the glass layer 20 including the window 30a and is baked to form a sub-structure layer 311 constituting one portion oE
the electrode segment. The layer 311 and the interconnecting lead 310 are both formed of the same silver paste and they will be firmly joined together mechanically through the win dow 30a in the glass layer 20.
Thereafter, the layer 311 is plated with a copper layer 312, which is then plated with a nickel layer 313. The entire structure is heated to a range of about 350 to 430C.
in an oxidizing atmosphere to oxidize the edge portion 260 ~' .. ...

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of the copper layer 312 to which the nickel plated 313 has difficulty in adhering and a copper oxide layer 315 such as Cu2O, CuO will be formed to form the desired electrode.
With such an arrangement, the upper surfaces of the silver paste layer constituting the cathode or anode segment are covered by the nickel layer 313 over the copper layer 312 and the peripheral edge portion 260 is covered by the copper oxide layer 315, so that sputtering of the silver paste will be completely prevented.
Figure 23 shows a further modification of the inven-tion in which an interconnecting lead 320 is formed of silver paste on the glass base plate 2 and an insulating glass layer 20 is formed over the base 2 and has a window 30a to expose one portion of the interconnecting lead 320. Then, a platinum paste layer 321 of a predetermined pattern is printed by print-ing techniques on the insulating glass layer 20 and over the window 30a and the entire structure is baked. A nickel layer 322 is then plated onto the platinum paste layer 321 to pro-vide desired cathode and anode segments.
` 20 The platinum paste has a baking temperature of about 560C. and adheres well to glass.
- With the above arrangement, the sub-structures of the cathode and anode segments are formed of platinum which does not sputter and the electrode segments will have long life.
~; Furthermore, in order to prevent oxidation of the surface of anode segments, a precious metal, for example platlnum or goldj may be used for anode segments. For this purpose the cathode segments may be formed by plating nickel on siIver paste as described above.

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; - 20 -.7~0 As described above, the provision of a barrier means prevents incorrect message displays and a suitable selection of the material of the electrode segments provides an indicator display tube which has long service life.
The indicator tube of this invention provides an improved method of producing an indicator tube wherein a plurality of indicating leads are initially formed on the insulating plate 2 and each of the elements of the indicator unit is formed 90 as to connect through an insulating layer to the interconnecting leads. For example, the cathode ele-ment 62 is directly connected to the interconnecting lead ll through the hole 31b in the insulating layer 20 and it is therefore free from undesired discharges wh~ich would result in incorrect indications on the indicator tube.
In prior art devices mis-discharges and incorrect indications occur because the elements of the cathode have an external lead which is connected to a selecting lead which is not covered by an insulating layer as in the present invention.
Thus, when a voltage is applied to the desired cathode seg-ment an electrical discharge will occur not only between the desired cathode segment and its associated anode but it may also occur between the anode and a lead wh~ich passes to one of the other cathode segments. Such discharge is undesir-able and causes a mis-discharge or inaccurate indication to the operator. The insulating layers 20 and 110 prevent this in that the interconnecting leads in the present indicator tube are covered by an insulating layer which eliminates such undesired discharges.
It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of this invention.

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Claims (7)

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

1. An indicator display tube comprising:
a plurality of indicator units formed on an insulating layer, each of said plurality of indicator units consisting of a plurality of first electrode segments and at least one second electrode corresponding to said first electrode segments;
a barrier electrode formed adjacent said indicator units for preventing erroneous displays by said indicator units;
a transparent cover to form an envelope with said indicator units enclosed therein; and an ionizable gas sealed in said envelope.

2. An indicator display tube according to Claim 1 wherein said barrier electrode is supplied with a voltage which is lower than a voltage necessary to support discharge between said second electrode and said first electrode segments and lower than a voltage necessary to initiate discharge between said barrier electrode and said second electrode.

3. An indicator display tube according to Claim 1, wherein said barrier electrode is formed on said insulating layer so as to lie between adjacent indicator units and wherein said cover has formed therein projections which extend toward said insulating layer between adjacent indicator units.

4. An indicator display tube according to Claim 3 wherein said barrier electrode is formed around said indicator units.

5. An indicator display tube according to Claim 3 wherein said barrier electrode is supplied with a voltage which is lower than that necessary to support discharge between said second electrode and said first electrode segments and lower than that necessary to initiate discharge between said barrier electrode and said second electrode.

6. A method of making an indicator display tube com-prising the steps of:
forming a plurality of indicating units each having a number of strip conductive elements and a plurality of selecting leads on a first insulating layer, said number of strip con-ductive elements consisting of a plurality of cathode conductive elements and at least one anode conductive element, and said selecting leads and said cathode and anode conductive elements being coplanar;
forming a layer of a conductive material on said in-sulating layer with windows surrounding said indicator units at the same time that said indicator units are formed;
depositing a second insulating layer on said selecting leads; and coating said cathode and anode elements and said layer of conductive material with nickel.

7. The method of Claim 6 wherein said first insulating layer is formed of glass and said indicator units is of silver.