Note: Descriptions are shown in the official language in which they were submitted.
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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
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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
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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
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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
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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
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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
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-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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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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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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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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