Note: Descriptions are shown in the official language in which they were submitted.
1~5~7q
BACKGROUND OF THE INVENTION
Field of the Invention
The pre~ent invention relates to a resistor and
electrodes formed on a substrate and which is coated with a
glass layer and particular wherein said resistor and electrode
is useable in an electron gun of a television set.
Description of the Prior Art
In a conventional color television picture tube, a
high voltage such as 25r~30 KV is applied to the last
accelerating electrode of an electron gun unit and a picture
screen through an anode button mounted at the funnel portion of
a picture tube. At the same ti~e, a voltage of 0 ~ 5 KV is
applied to a focusing electrode forming a focusing electron lens
positioned near the last accelerating electrode, through a
terminal pin provided at the end of a neck portion of the picture
tube.
In order to make a small beam spot on the picture
screen which results in a more precise and clear picture, it is
desirable to reduce the aberration of the focuing lens as much as
possible. To reduce the aberration of the focusing lens, it is
necessary to relax the voltage gradient between the elec~rodes.
To achieve this, there are such methods as widening the
distance between the electrodes, applying close voltage to the
electrodes, and a combination of the above.
In the case of applying a similar voltage to the
electrodes, it is necessary to apply a high voltage of more than
10 KV to the focusing electrode next to the last accelerating
--3-- ~
- ~54877
electrode. Such high voltage cannot be applied through a
terminal pin provided at the end of the neck portion of the
picture tube, because there occurs an electric discharge (spark)
between the terminal pin and the ot~her terminal pins which supply
voltage to other electrodes of the electron gun unit, for
example, heaters. Then, it can be supplied through another
button provided at the funnel portion, however, it causes
complicated assembly and a substantial cost-up.
In the case of a picture tube widely known as a
"Trinitron" (regjistered Trademark of Sony Corporation, the
assignee of the present invention), three electron beams are
focused by a single electron.lens, in which each beam passes
through the center of a single electron lens of large diameter.
The focused three electron beams are deflected to hit the same
position of an apertured grille provided in front of the picture
screen by four convergence electrodes provided at the top end o~
the electron gun unit which makes three passages therebetween
for each of the electron beams. Two inner electrodes of the
convergence electrode are applied by the same potential as the
anode potential. Two outer electrodes of the convergence
electrodes are applied by a lower voltage than the anode potential
by 0.4 ~ 1~5 KV, so that the electron beams which pass through
the convergence electrodes are deflected to the side of the
center beam.
~ t one time, the voltages were applied through another
button provided at the funnel portion and an electrically
shielded cable connected to the button and the outer electrodes.
Now, a co-axial anode button, which has two cylindrical
electrodes electrically insulated from ~ach other, is used to
provide an anode voltage through an outer electrode of the anode
button, and conve~gence voltage through an inner electrode of
-4- ,~
- ~15~17''~
the anode button and an electrically shielded cable connecting
the in~er electrode and the convergence electrodes. By the
above co-axial anode button, it is not necessary to provide two
buttDns at the funnel porti~n of the picture tube, however, still
it is troublesome to connect the inner electrode of the anode
button and outer convergence electrodes by the electrically
shielded cable.
Other specific disclosures of possible int;erest are
Japanese Publication 40987/72 and U.S. Patent 3,514,663, both assigned
to the same assi~nee as the present invention and U.S. Patent
3,932,786.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an
improved electron gun unit for use in a cathode ray tube.
It is another object of the present invPntion to provide
an electron gun unit in which desired potential to the
electrode is applied by a simple construction.
According to an aspect of the present invention, there
is provided an improved electron gun which comDrises a plurality
of electrodes for focusing and accelerating an electron beam
arranged along an axis of a neck portion of the cathode ray tube.
There is also provided a resistor formed in a zig-zag pattern
and electrodes on both ends and intermediate points of the resistor
on a ceramic base, which is overcoated with a layer of glass,
located within the neck of the picture tube.
One end of the resistor is applied with high voltage
whic~ i~ the same as the anode voltage. Desirable voltages for
focusing and/or convergence are obtained from intermediate taps
of the resistor, while another end of the resistor is connected
to the substantially low voltage.
The resistor is coated with a glass mixture layer to
_ 1
`: ~1S~8~
reduce voltage breakdown and the coefficient of thermal
expansion of the substrate and glass mixture are chosen
to be similar.
More particularly, there is provided:
An eIectron gun which is used for television picture
tube having an evacuated bulb including a funnel portion, a
neck portion and screen portion including a plurality of
electrodes for focusing and accelerating an electron beam
generated by a cathode, aligned along the axis of said neck
portion, comprising a resistor formed of an insulating substrate
on which a resistive path is formed, said substrate being
mounted along said plurality of electrodes and sealed in said
neck portion, said resistive path having one end tap, another
end tap and at least one intermediate tap between said end taps,
said one end tap being supplied with the same voltage as the
voltage supplied to said screen portion, said another end tap
being connected to a terminal pin provided at one end tap of
said neck portion for connection to a voltage low enough to
avoid an electric discharge between electrodes and said terminal
pin, an operating voltage for the electrodes being obtained
from said intermediate tap by dividing the voltage between
both of said end taps, said resistive path comprising a mixture
of ruthenium oxide and glass, and said substrate and said
resistive path being overcoated with at least one layer of
glass, said layer of glass containing alumina powder~ -~
There is also provided:
A resistor for a cathode ray tube which is subjected
to high voltages comprising a substrate of insulating material,
a resistive path formed on said substrate and comprising a
mixture of borosilicate glass and ruthenium oxide, and
electrodes formed on said substrate to engage said resistive
path and comprising a mixture of glass and ruthenium oxide.
,~ -6-
S9L~
Other objects, features and advantages of the
invention will be readily apparent from the following
description of certain preferred embodiments thereof taken
in conjunction with the accompanying drawings although
variations and modifications may be effected without departing
from the spirit and scope of the novel concepts of the
disclosure and in which:
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view of an electron gun
unit of the present invention;
Fig. 2 is a schematic drawing to show the connection
between electrodes and the resistor;
Fig. 3 is a schematic side elevational sectional
view to show the electron gun unit of the present invention ~`
sealed in a neck portion of the cathode ray tube;
Fig. 4 graphically illustrates the characteristic
relation between gas evaporation and temperature of the
resistor according to the present invention and the prior
art, respectively;
Figs. 5A, B are plane and side elevational views to
show the first embodiment of the resistor of the present
invention;
Fig. 6 is a side elevational view to show a second
embodiment of the resistor of the present invention;
Figs. 7A and B are plane and side elevational views
to show the third embodiment of the resistor of the present
invention, respectively;
Fig. 8 graphically illustrates the characteristic
relation between the thickness of overcoating glass layer and
-fia-
D~
`~ 115~8
the resistivity variation, and;
Fig. 9 graphically illustrates the characteristic
relation between gas evaporation and temperature of the
electrode according to the pEesent invention and the prior art,
respectively.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
_
The first embodiment of the invention will be
explained with reference to the drawings, in which an electron
gun unit with a uni-potential electron lens is applied to a
'Trinitron" picture tube.
As seen in Figures l, 2, an electron gun 1 (s~e
Figure 1) is mounted in the neck of the tube. The gun l
includes three cathodes KR, KG and KB aligned in a horizontal
plane. The three cathodes are positioned behind a control grid
Gl which in turn are followed by prefocusing grids G2 and G3.
Next in line is the main focusing lens which is formed by grid
G4. Grids G3, G4 and G5 are accelerating grids. Thereafter,
there is formed the convergence electrodes 8 and 9 and ll and 12.
In passing to screen the electron beam from cathode KR passes
through its associated openlng in grid Gl and Grid G2,
respectively, then through G3, G4 and G5 and finally between
plate electrodes 9 and 12. The electron beam from cathode KG
passes straight through the electron gun l and out between
convergence plates 8 and 9 before reaching the apertured grille
AG. The electron beam from cathode XB passes through its
associated apertures in grid Gl and grid G2, ~hen through G3, G4
and G5, and finally between convergence electrodes 8 and ll
before reaching the apertured grille AG.
A conductive carbon coating is formed over the inner
surface of the funnel of the picture tube, and this coating also
extends over the inner surface of ~he nec~. of the tube back to
-7
- 1154~
the area of the convergence electrodes 8, 9, 11 and 12.
Terminal pins 4 are formed at the end of the stem 2.
Figure 1 shows an electron gùn unit of the pxesent
invention which ~s sealed in.the ne~ck portion of the picture
tube, and Figure 2 shows a connection diagram between the
electrodes of the electron gun unit and a resistor 15. In
Figures l and 2, a reference number l designates an electron gun
unit generally. There are provided a stem 2 made of glass, and
an evacuation pipe 3 integrally formed with the stem 2 an~
terminal pins 4 are mounted on the stem 2. The terminal pins
are connected to various electrodes, for example, heaters of the
cathodesin the picture tube.,There are also provided electrodes
(grids) Gl, G2, G3, G4, G5, arranged coaxially, each having a
cylindrical shape and supported integrally by a pair of supporters
5, 6 made of bead glass. Convergence electrodes 8, 9 are
attached to a flange portion lO of the fith grid G5, and
convergence electrodes ll, 12 are supported by the bead glass
supporter 5, 6 through a supporting piece 13. A connecting piece
14 is also integrally provided with the flange portion lO. As
will be explained, the connecting pieces 14 contact the carbon
layer on the inner wall of a funnel portion of the picture
tube, through which a desired high voltage Eb which is the same
voltage as applied to the picture screen (i.e., the anode
voltage ), is supplied to the fifth grid G5. There is provided
a resistor 15 along the grids Gl G5 supported at one end by
a metal supporting piece 16, and at another end by a lead 22~
The resistor 15 is formed with a printed resistive path 17 on
one sur~ace of a substrate made o~ an insulating material, for
example, a ceramic substrate. The printed resistive path is
covered with a glass layer. The size of the resistor is, for
example, lO mm wid~h, 50 mm length, 1.5 mm thickness. An
-8- ,\
8~
edge of the resistive path 17 and the fifth grid G5 are
electrically connected by the supporting piece 16, and the fifth
grid G5 and the third grid G3 are electrically connected by a
lead l9. A predetermined position ~ which is spaced a
predetermined length from one end of the resistive path 17 and
the fourth grid G4 are electrically connected by a lead 20,
and another position a which is spaced a predetermined length from
one end o~ the resistive path 17 is electrically connected to
the convergence electrodes ll and 12 by a lead 21. ~lother end
of the resistive,path l?.is electrically connected to a terminal .
pin ~a by a lead 22. The convergence electrodes ll and 12 are
electrically connected with each other.
The above constructed electron gun unit is sealed in
a neck portion 23 of the picture tube, as shown in Figure 3.
There is provided a carbon coating layer 24 on the inner wall
of the neck portion 23 and on the funnel portion (which is
not shown in the drawings) of the picture tube, which the
connecting pieces 14 engage. The carbon coating layer ~4 is
electrically connected to a button provided on a funnel portion
of the picture tube, through which a high voltage of, for
example, 30 KV is applied from the outside of the picture tube.
With the above construction, the high voltage applied to the
carbon coating layer 24 is applied to the convergence electrodes
8, 9 and the fifth grid G5 through the connecting piece 14,
and the same voltage is applied to the third grid G3 through
the connecting lead 19 and one end of the resistive path 17
through the supporting piece 16. Thus, the convergence electrodes
8, 9 and the grids G3, G5 are applied with the sa~e potential.
The high voltage supplied from the anode button i.s also applied
to the picture screen.
The high voltage applied to the end of the resistive
-9- ,!
llS487~
path 17 is divided at the intermediate tap a by the voltage
drop caused by the resistive path between the high voltage end
and the intermediate tap a, and the derived voltage is applied
to the convergence electrodes 11, 12 through the lead 21. It
is also divided at the tap b to derive a lower voltage than the
anode voltage by the voltage drop between the high voltage end
and the tap b, and the derived voltage is applied to the fourth
grid G4 through the lead 20. There are provided claws on the
leads 21 and 20 which can be attached to the intermediate taps.
Thus, the po~en,tial applied to the convergence electrodes 11
and 12 is a little lower than the potential applied to the
convergence electrodes 8 and 9, for example, 29 KV and the
potential of the fourth grid G4 is still lower than that or
about 12 KV. The other end of the resistive path 17 is
electrically connected to the terminal pin 4a mounted in the
stem 2 through the lead 22. The terminal pin 4a is connected
to ~round potential through a variable resistor 25. The
variable resistor 25 is provided to provide fine control o~ the
potential applied to the convergence electrodes 11 and 12 and
the fourth grid G4. The first grid Gl and the second grid G2
are supplied with a predetermined voltage through terminal pins
4 from outside of the picture tube. A current for a heater
of the cathode is also supplied through predetermined terminal pins.
Thus, each of the electrodes are applied with a desired
voltage which is derived from an intermediate tap of the resistor
based on the anode voltage obtained by the connecting piece 14
In the above example, both the convergence voltage
and the focusing voltage are obtained by dividing the anode
voltage using the resistor. Of course, it is possible to obtain
only the convergence voltage or the ~ocusin~ voltage. In the case
when only the convergence voltage is obtained by dividing the
-lo- ,!
5~7
anode voltage, low convergence voltage of 0 ~ 5 KV can be
supplied through the terminal pin 4.
In the conventional pictu~e tube other than the
"Trinitron" ~TM) picture tube, only.the focusing voltage is
obtained by dividing the anode voltage. According to the
above-mentioned structure, it is sufficient to provide only one
anode button without any special structure, such as a coaxial
button. ~urther, the cable which connects the anode button and
the convergence electrodes is not necessary so the assembly is
simplified.
As shown in Fig. 1 and Fig. 2, the resis~or with a
thick layer of resistive material thereon is constructed of an
insulating substrate 15; a resistive layer 17 and electrodes
30a to 30d formed on the substrate.
There are some conditions required for the resistive
material so it can be used in resistor 17 assembled into a
cathode ray tube. First, the temperature characteristic must
not change at high temperatures. Second, it should not vaporize.
Third, it should resist a sputtering reation. Fourth, there ;
should be only small resistance variations.
Especially in the manufacturing process for making a
cathode ray tube there is used, for example, a knocking process
and it is very undesirable for the resistive material to have
a tendency to vaporize at the temperatures of the knocking process.
Generally, decrease in vacuum is one of the factors which
determines the lifetime of vacuum apparatus such as cathode
ray tubes.
Thus, since the vaporizing of material used within a
vacuum apparatus is very~harmful to such apparatus, the selection
of materials and previous treatments must be carefully considered
After assembly of the electron ~un, during the
-11~ 1'
~5~87~
knocking process, high voltage of two times the rated voltage,
for example, 50 to 60 KV, is applied between the convergence
electrode and terminal pin to cause discharge among the grid
electrodes such as Gl to G5,.which causes fine scraps of
material which occur at the rough cut edges of the cylindrical
grid electrodes to be removed. Since the high voltage is also
applied to the resistor 17, heat will be produced in the
resistor 17 based on I2R, as the product of resistivity R and
current I passing therethrough. Accordingly, it is necessary to
prevent the resistivity R of the resistor 17 from changing
and the resistive material from vaporizing due to the heat
produced by Jule's Law.
The resistivity R is selected to be between 300 to 1000
Meg ohm, but the resistance variation should be as small as
possible. As shown in Fig. 2, the resistance of the resistive path
17 is Rl between the electrode 30a and the point a and is R2
between the point a and the electrode 3Od. The value of
Rl must stay within ~0.3 per cent of the predetermined
Rl + R~
value to stabilize the resistivity.
Another serious problem is the surface discharge
produced by the high voltage electrlc field during the knocking
process, which causes a sputtering reaction along the pattern of
resistor 17. The resistivity R changes and the sputtered material
is harmfull to the electron gun due to the sputtering. Therefore,
a sputtering reaction should be prevented.
According to this invention, Ruthenium oxide-glass
is used for the material of resistor 17. Such a material is
made from a mixture of a binder, for example, borosilicate glass,
ruthenium oxide powder with additions such as Ti or A1203, an
organic binder such as ethylcellulose and solvent such as
butyl carbitol acetate to obtain the desired characteristics.
-12 ,l
1~5~8~
A paste for making the resistor is obtained by ;
stirring up the above materials then the paste is printed in
zi~-zag pattern, as shown in Fig. l and 2, on a ceramic
substrate 15 having a composition, for example, of 90 to 97%
alumina.
The printed substrate is then baked at the temperature
range of 750C to 850C for 40 to 60 minutes, and the coatiny
glass is applied over the resistive path and electrodes. In
the paste of ruthenium oxide and glass, as the ratio of
. ~
RuO2 (weight), is in~reased the surface resistivity decreases.
glass
As the grain size of ruthenium oxide increases the surface
resistivity increases. '
Ru02
According to this invention, the ratio of glass
is selected to be about 80.
After baking, the thickness of resistor 17 is 10 to
15 ~ m. Even though the resistor produced is treated under high
termperture and high pressure in the knocking process, the
variation of resistivity will be less than 10% and almost no
vaporization occurs. Moreover, since ruthenium oxide has a
small sputtering coefficient, damage to electron gun by
sputtering material can be reduced relative to prior art systems.
The electrodes 30a to 30d can be constructed in the
following manner.
Generally, Ag or Ag-Pd is usually used for the
electrode material of resistor elements of this type and is formed
of a thic~er layer. When the resistor element is installed
within a vacuum apparatus such as a cathode ray tube, the
aforementioned condition l to 4 are applicable to the electrodes
as well as to resistor 17~
The most serious problem is vaporization from the
electrode material and a sputtering reaction to the electrode
~13 ,!
11'5~
material under the high temperature and high electric field
applied during the knocking process. Experiments during
knocking on the resistor element comprising electrodes of Ag or
Ag-Pd and with the resistor 17~therebetween and formed with Ruo2-
glass formed on the alumina substrate, xespectively, as shown
in Fig. 4, results in more vaporizing from the electrodes than
in the case of electrodes of RuO2 glass and the arc
discharge is apt to concentrate on the ;urface of the electrodes
during the knocking process.
According to~this invention, the electrodes are formed
from the same material as the resistor :L7, for example, of
uO2-glass. Also, material with a high ratio of RU2 and a
glass
lower sheet resistivity than that used for resistor 17 is
suitable for use as the electrodes.
The first embodiment of the resistor according to the
present invention is shown in ~igs. 5A, B. The method of
manufacturing of the resistor is as follows.
The electrodes 30a, 30b, 30c and 30d ana resistor
are formed on the substrate 15 in the pattern shown. After
baking, the thickness of electrodes 30a to 30d is about lO~m.
The experimental analysis of the resistor element,
shown in Fig. 4, shows that the vaporization from the RuO2
electrode was less than that from electrodes of Ag or Ag~Pd. ~he
composition of the gas vaporized ~rom Ag or Ag-Pd electrodes
is mostly oxygen. When Ag paste is baked at high temperature r
it is subject to be oxidized to produce the mixture of a stable
oxide, for example, Ag2O.
First, the electrodes 30a to 30d are formed in
predetermined shapes on the surface of the alumina substrate
15 by coating, as for example, by screen printing. The glass
paste with a ratio of RU2 greater than 35 is used for the
-14- ,l
~5
electrodes.
The resistive path 17 is formed in a zi~-zag pattern
between the electrodes by coating RuO2-glass paste having high
sheet resistivity as shown^in F~ig. 5A. In this case, the guard
patterns 31a through 31f are formed to cover the opposite
edges of the electrodes. The resistor element as shown i~ Figs.
5A, B is manufactured by baking the alumina substrate with an
unstable oxide, for example, AgO or Ag2O2 and the unstable oxide
will be decomposed into Ag2O and 2 to form a stable oxide. In the
resistor element,accord~ng to the presen~ invention, the guard
pattern 31a through 31f have high resistivity and cover the
opposite edges of the electrodes which have low resistivity.
Therefore, during the knocking process, it is difficult
for arc discharge to concentrate on the electrodes and
sputtering reaction is effectively prohibited.
In the second embodiment shown as Fig. 6, each electrode
30a to 30d can be completely covered with the resistor 17. In
this case, though the contact resistivity increases a small amount,
no problem is caused because of the thin layer of the resistor
coated over the electrodes.
In the third embodiment sho~n in Figs. 7A and B, there
is provided a rèsistor 17 and electrodes 30a through 30d formed on
a substrate 15 with a layer of glass 32 overcoating the whole
surface thereof. Such a overcoating layer of glass prevents the
electrodes and the resistor from vaporizing at the high temperatures
and the resistivity from changing due to sputtering reaction.
A paste containing borosilicate lead glass and 10 to
40 weight % A12O3 grained powder is used for a layer of glass 32.
The ratio of borosilicate lead glass to alumina (glaos) is
selected in ratios, for example, of T~ 80 and 275 and all ratios
between these examples.
-15-
77
~ The mixture of borosilicate lead glas~, and alumina
of the predetermined mixing ratio and 10 to 20 percent organic
binder and solvent is coated on the resistor element by screen
printing. In this case, in order to make the layer thick,
double or triple layers are formed by printing using 50 to 100-
mesh screen (200 to 300~ m thickness). A layer of glass 32
having 200 to 400~ m thickness is obtained by baking in the
temperature range of 550 to 650~C for 20 to 30 minutes.
The purpose of mixing A1203 powder into the glass
material is to improve~the mechanical strength of the glass layer
32. Generally, when the glass layer 32 becomes thick, it is
subject to cracks due to incidental forces. However, t~e
mixtur~ of A12O3 into the glass material prevents the glass layer
from cracking. Moreover, it is possible for the expansion
coefficient of the glass layer 32 to match that of the alumina
substrate 15. The variation of resistivity of the resistor
overcoated by glass containing A1203 after the process of knocking
is shown in Fig. 8. The glass paste containing A1203 is used
and the mixing ratio of A1203 to glass is varied as shown by the
upper curve with 0~ A1203, 20% A12O3 by the middle curve and
10% A1203 in the lower curve.
The resistor is overcoated by the glass layers and the
thickness of the layer is varied as shown.
The electron gun according to the invention is processed
by knocking. The variation of resist,ivity after the knocking
process is adjusted with a variable resistor ~5 shown in
Fig. 2, and the adjusted resistivity of the variable resistor 25 is
shown on the ordinate axis of Fig. 8. According to Fig. 8, when
the thickness of the glass layer 32 containing 10 to 20 weight %
A1203 is selected to be in the range of 200 to 400~m, the
variation of resistivity is very small because the curve is
-16~- "
.,
1~5~ t~
almost flat and is less than the other illustrated exam~les.
On the other hand, if the glass layer doesnlt contain any
Al2O3, the thickness of the glass layer cannot be over 80 to
100 ~ m in thickness because of the~ mechanical strength and
the stability of resistivitv. In the case o~ thicknesses of the
glass layer without any Al2O3 under 80 to 100~ m, the variation
of resistivity is so large due to the sputtering process and the
high temperature treatment that a glass of that composition
cannot be practically used.
Moreover, if the glass layer contains Al2O3 over 40
weight %, it becomes porous, and therefore .it cannot protect
the resistor 17 and the electrodes 30a through 30d from the
influence of the sputtering reaction and arc discharge
concentration. Although the electrodes 30a through 30d are
not covered with the guard pattern in the embodiment of Fig. 7,
they are effectively 2rotected from the sputtering reaction as well
as in the case where the glass layer 32 overcoats the resistor
shown in Fig. 5 or Fig. 6, and even if the u~permost layer
portion of the glass layers 32 is constructed of a glass layex
without Al2O3 with thickness in the range of 50 to 100~ m it
can be practically used. Generally, when the glass layer contains
A1~03 in the mixture, the threshold voltage is slightly decreased.
But according to the above-mentioned structure, the variations
of resistivity can be reduced and the threshold voltage will be
high.
Fig. 9 shows a dashed curve plotted from one resistor
with electrodes consisting of ~g and without a glass layer
overcoating and the solid line curve is plotted for a resistor
with electrodes consisting of RuO2. The graph illustrates the
quantity of vaporizing 2 gas from the electrodes material at
various temperatures is shown in Fig. 9. The quantity of
-17- ,!
11~48~
vaporizing 2 ~as is indicated by the ionized current is
converted by mass spectrometer analysis of 2 gas vaporizing
veIocity as shown in the ordinate axis of Fig. 9. According to
this invention, the resistor having a thick layer with highly
accurate resistivity can be obtained that is stable in electric
characteristics under high temperatures and high pressures
required in the manufacturing process o cathode ray tubes.
Thus, in the present invention, a glass insulating
layer is coated over the entire surface of the resistor which
keeps it from sputtering when the electron gun is subjected
to the knocking process which utilizes a double voltage that
is applied to the high voltage terminal. The knocking process
removes burrs due to the discharges.
If a glass insulating overcoating layer was not used,
the resistor is likely to be damaged due to arcing between
portions of the resistor during the knocking process and the
present invention provides protection of the resistor~ Also,
if resistors are constructed of the conventional material such
as silver or silver compounds the resistivity variation will
be large after the knocking process. Also, when silver material
is used, oxygen gas will be released during the knocking process
and when the temperature of the resistive material increases ;
some of the oxygen gas will be evporated which is injurious
to the evacuated apparatus.
In the present invention, the use of ruthenium oxide
does not result in a resistor which evaporates oxygen during
the knocking process and the addition of a glass layer over the
resistive layer protects the resistor. Such structure is
illustrated in Figs. 7A and 7B, for example. By coating the
resistive paths with glass of predetermined thicknesses the
~ -18-
~54~
resistor is completely protected from damage. Usually, when
thick layers of glass are coated, they are ~pt to be porous and a
porous layer is not effective for arc discharge. Also, it is
dif~icult to coat glass thicker tha`n 100~ m. In the present
invention, however, the overcoating glass layer is mixed with
aluminum powder A12O3 so that the mixture makes a coating glass
layer which is very strong and which has a substantially
increased voltage breakdown characteristic and also the glass
is not porous.
The resistor -is formed of ruthenium oxide and glass
and the terminal at the top has a lower resistivity than the
main part of the resistor.
In the present invention, the temperature thermal
expansion coefficient of the glass layer is about the same as
~hat of the substrate. The substrate is made of a ceramic such
as A12O3 and the glass layer contains A12O3 powder, hinder,
solvent and glass so that the ratio of the A12O3 to glass is
selected so that the temperature coefficient of thermal expansion
of the coating in the ceramic substrate will be very similar.
As shown in Figure 8, if the glass layer contains
no A12O3 the ~esistance characteristic change is very high as
shown by the top curve. Also, if 100% glass layer with no
A12O3 is used, it can be easily cracked by being hit accidentally.
By adding A12O3 as shown by the curves labeled 10% and
20%, respectively, the resistance to cracking will be improved.
The glass should not contain more than 40% of A12O3
because the glass layer will become porous.
When the A12O3 is mixed with glass with the A12O3,
being in the range of 10 to 40% by weight, the mechanical strength
and the sputtering characteristics will be good and the thickness
--1 9-- '
~ 8~'~
of the layer can be in the range of 100 to 400~ m which gives
very good characteristics.
Thus, as shown in Figure 8 in the thickness xange
bet~een 200-400~ m, ~he change in resistance is very low afte~
knoc~ng and is less than 10M~. The resist.ivity can be
adjus'ted with,the resistor 25, but if the re,sistivity variation
is high it cannot be effectively adjustedO
'In ~igure 5, the terminal top is covered with
resistive pattern and the top is protected from arc discharge
by the resistive, pattern,. One portion must ;remain uncoated
to allow electrical contact to be made to the electrode.
It is seen that this invention provides a new and
novel resistor for an electron gun and although it has been
described with respect to preferred embodiments, it is not to
be so limited as changes and modifications may be made therein
which are within the full intended scope as defined by the
appended claims.
~ ~ .
.. ~.~.;,, , ~
-20-
