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Патент USA US3027228

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March 27, 1962
P. SCHAGEN ETAL
3,027,218
MANUFACTURE OF ELECTRON DISCHARGE TUBES
HAVING A PHOTO-CONDUCTIVE TARGET
Filed Feb. 18, 1959
2 Sheets-Sheet 2
7
RED ANTIMONY TRISULPHIDE\§
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RED ANTIMONY TRISULPHIDE
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FIG. 5
PIE TER SCHAGEN
ANDREW A. TURNBULL.
BY
952M K
AGE
Unite
States Patent 0 '
,
3,627,218
Patented Mar. 27, 1962
1
2
3,027,218
withdrawn into the side arm which is then sealed off
close to the main envelope.
MANUFACTURE OF ELECTRON DISCHARGE
TUBES HAVING A PHQTO-CONDUCTIVE
TARGET
in the manufacture of electron discharge tubes having
photo-conductive targets it is very important to use for
Pieter Schagen, Redhill, and Andrew Alfred Turnhull,
Merton Park, London, England, assignors to North
American Philips Company, Inc., New York, N.Y., a
the target a material which is very pure and furthermore
to maintain this purity while carrying out the manufac
turing steps subsequent to the deposition of the target.
Even the gases which are evolved in sealing glass parts
corporation of Delaware
Filed Feb. 18, 1959, Ser. No. 794,041
Claims priority, application Great Britain Nov. 7, 1958 10 of the envelope of a tube can contaminate a target and
this is one reason why in the second method above
7 Claims. (Cl. 316-9)
described the electrode structure is ?tted in position and
This invention relates to the manufacture of electron
the foot or base of the tube sealed to the main envelope
discharge tubes having a target constituted by a layer of
before the target layer is formed. However, even in this
photo-conductive material evaporated onto a supporting
method apart from being relatively complex due to the
base. An example of such a tube is the television camera 15 use of the side arm, a sealing operation is carried out
tube known as the “Vidicon.”
close to the target after its formation and this may give
For a target material such as, for example, red antimony
rise to contamination of the target.
trisulphide, although a satisfactory target layer can be
An object of the invention is to provide a simpler
produced by evaporation of the material in a high vacuum
method of forming such target layers by evaporation of
from a crucible or like container spaced from the sup
photo-conductive material either in a vacuum or a gas
porting base, a layer having a porous texture and having
a much higher resistivity in the dark is produced when
the evaporation is carried out in an atmosphere (prefer
atmosphere which method does not necessitate the use of
a side-arm but which still eliminates contact between the
target layer and air.
ably of an inert gas such as argon) at a pressure of from
According to one aspect of the present invention there
a tenth of a millimetre to a few millimetres of mercury. 25 is provided a method of depositing a target layer of a
However, the presence of the gas atmosphere consider
photo~conductive material on a supporting base within
ably reduces the mean free path length of the molecules
of the vapourised photo-conductive material as the latter
is carried from the crucible to the supporting base by
the convection currents that are set up in the gas atmos
phere during the evaporation.
It has previously been proposed in Patent No.
2,745,032, issued to S. V. Forgue et al. on May 8, 1956
and entitled “Photo-Conductive Targets For Cathode Ray
an electron discharge tube envelope by evaporation of a
supply of the material, which method comprises the steps
30
of forming the supply on part of the internal structure
for the tube, positioning within the tube envelope the
said structure, sealing a foot or base to the envelope,
evacuating the envelope through an exhaust tube, evapo
rating the supply of the photo-conductive material to
form the target layer on the supporting base, and sealing
otf the exhaust tube, which sealing-off operation may be
Devices,” to carry out the deposition in vacuum or in 35
such a gas atmosphere and after the evaporation to return
effected either before or after the evaporation of the
the envelope of the electron discharge tube to atmos
supply of photo-conductive material. The sealing-off
pheric pressure and then introduce the electron gun
operation is preferably carried out after the evaporation
assembly. Thereafter, the evacuating and sealing proc
of the photo-conductive material since any gases liber
esses are carried out. However, this method has the dis
ated from the electrode structure of the tube during the
advantage that the deposited target layer is liable to
evaporation step can be withdrawn through the exhaust
tube prior to its sealing.
the discharge tube envelope is returned to atmospheric
By “internal structure” is meant any structure within
pressure.
45 the tube envelope which is not removed from the tube
In a second method of producing a porous target layer
and remains in the tube after ?nal sealing.
in the manufacture of a Vidicon camera tube, in which
According to a second aspect of the invention therev
method contact between the target layer and air is avoided,
is provided a method of depositing a target layer of a
the tube is provided initially with a tubular side arm
photo-conductive material onto a supporting base within
extending from the main envelope at right angles thereto 50 an electron discharge tube envelope by evaporation of a
near the end face or Window of the tube constituting the
supply of the material, which method comprises the steps
supporting base onto which the target material is to be
of forming the supply on part of the internal structure for
deposited. At a stage when the electrode structure has
the tube, positioning within the tube envelope the said.
structure, sealing a foot or base to the envelope, with
been assembled, a glass foot or base sealed to the main
envelope, the air removed and argon or other inert gas 55 drawing air from the envelope through an exhaust tube,
introducing into the envelope gas at a low pressure,
at a low pressure introduced, and with the tube arranged
evaporating the supply of the photo-conductive material
With its end face uppermost and the side arm horizontal,
to form the target layer on the supporting base, evacuat—
a crucible containing the photo-conductive material
ing the envelope and sealing-off the exhaust tube. The
located in the side arm is moved into the main envelope
to a central position some distance below the collector 60 gas introduced into the envelope is preferably an inert
gas such as argon.
electrode grid mesh of the tube, which mesh is arranged
The photo-conductive material may be evaporated from
close to the end face of the tube. The crucible, collector
part of the internal electrode structure of the tube.
mesh and collector anode in the region of the crucible are
In a preferred method in accordance with the invention
then heated and the photo-conductive material, which may
in which the electrode structure for the tube includes a
suffer deleterious effects due to contact with air when
be antimony trisulphide, is evaporated from the crucible
and passes through the hot mesh to deposit on the end
face of the tube. Any photo-conductive material which
collector electrode grid mesh which, when in position
in the tube envelope, is close to the supporting base on
which the target layer is formed, the supply of photo
has deposited on the collector anode or mesh is then
conductive material is formed as a layer on the side of
re-evaporated or converted into a conductive form by a 70 the collector mesh that is to be adjacent the supporting
separate heating operation. The inert gas is then pumped
out and the exhaust tube sealed and ?nally the crucible is
base.
The supply of material may be formed by evapo~
ration in a vacuum.
3,027,218
As has been remarked previously, when evaporating
photo-conductive material in a gas atmosphere, the mate
rial is carried to the supporting base on which the target
4
FIGURE 1 shows a view of a collector electrode grid
mesh assembly of a Vidicon camera tube with the parts
layer is formed by the convection currents set up in the
gas. It is generally difficult, however, to control the
heating conditions in such manner that the convection
of the assembly slightly separated in the interests of
clarity and comprising a very ?ne metal grid mesh 1
located between a ?at ring 2 and a cylindrical ring 3
having an inward ?ange 4. The ring 2 and ?ange'4
currents set up give rise to a target layer of uniform
are spot welded at a number of points around the ring
thus ?rmly securing the mesh 1. The mesh 1 is made
of copper which is ?rst nickel plated and then rhodium
material is evaporated from a crucible or boat beneath
the collector grid mesh and has to pass through the mesh 10 plated. The ring 2 and cylinder 3 are made of copper
nickel alloy which is ?rst nickel plated and then rhodium
as in the above-described second method. However, by
plated. Typical dimensions for the assembly are:
forming the supply of photo-conductive material as a
Mm.
layer on the side of the collector mesh adjacent the sup
Outer diameter of ring 2 _____________________ __ 22
porting base the control of the evaporation conditions
are very much less critical because the photo-conductive 15 Inner diameter of ring 2 _____________________ __ 19
Height of ring 3 ____________________________ __
3
material does not have to pass through the mesh and,
furthermore, by reason of the fact that the mesh is close
Referring now to FIGURE 2, this ?gure shows a
to the supporting base on which the target layer is
bell-jar 5 resting on a ?at base 6,, a sealing gasket being
formed, the production of a target layer of uniform
thickness is less dependent on a symmetrical distribution 20 designated 7. The space within the jar 5 is connected
by a pipe 8 to an exhaust pump 9 ‘for evacuating the
of convection currents. Evaporation of photo-conductive
said space. Resting on the base 6 within the bell-jar 5
material from the collector mesh also results in a simpli
is a platinum crucible 16 containing a supply 25" of
?cation of the evaporation stage compared with the side
pure red antimony trisulphide. The crucible 10 is elec
arm technique in that in the latter the sequence in which
the various parts must be heated is critical whereas in 25 trically connected to terminals 11 and 12 which pass
through the base 6 and are connected by conductors 13
the former method the evaporation is carried out in a
thickness. This is particularly so when photo-conductive
single stage by heating the mesh.
and 14 to a current supply source 15.
Extending from
the base 6 and within the bell-jar 5 is a support 16 having
an arm 17 for holding (by means not shown) the mesh
also facilitated in that the supply of photo-conductive 30 assembly 1-4 symmetrically above the crucible 10 and
spaced therefrom at a distance of, for example, about
material can be readily formed on the collector mesh in
4.5 inches. To evaporate the antimony trisulphide, the
a uniform layer by evaporation in a vacuum.
bell-jar 5 is ?rst exhausted to 10-4 mm. of Hg by pump 9
The methods in accordance with the invention permits
and the crucible 10 and then heated by current from
a sealing operation to be carried out after the formation
of the target, because the exhaust tube, which in prac 35 source 15. By carrying out the evaporation in the high
The production of a very uniform target layer by the
preferred method in accordance with the invention is
tice is remote from the target layer, is integral with the
foot or base of the tube. It will be appreciated, there
fore, that negligible contamination (if any) of the target
layer takes place after its formation due to gases released
from glass parts during sealing.
The target layer may be formed, if desired, after
degassing the electrode structure of the tube and activat
ing the cathode. In general, the electrode structure will
be partially degassed before being positioned within the
tube envelope. During degassing operations carried out
with the electrode structure within the envelope, either
before or after the formation of the target, it will be
necessary to ensure that the temperature at which the
tube is baked for degassing is less than the vaporisation
vacuum a very uniform layer can be produced on the
mesh 1 and ring 2.
The vacuum is then released and
the coated ring-mesh assembly ?tted into position into
the Vidicon camera tube envelope together with the
40 other electrode parts of the tube as shown in FIGURE 3.
In FIGURE 3, reference numeral 18 designates the
cylindrical glass envelope of the Vidicon, to which
envelope a ?at circular glass window 18' is sealed via
a ?at metal ring 19 of fernico alloy. Within the envelope
45 18 is located the cylindrical anode 20 of the tube which
extends from the region of the electron gun structure
comprising cathode 21, control grid 22 and ?rst anode
23, to near the window 18'.
As illustrated in FIG
URE 6A, window 18' comprises a layer of glass 40, the
or sublimation temperature of the photo-conductive mate 50 inner surface of which is coated with a transparent con
rial. If degassing is completed after the target layer has
been produced, the possibility of vaporisation or sublima
ducting ?lm 41 of tin oxide and provides the supporting
base for the photo-conductive target to be deposited.
The anode 20 is maintained central within the envelope 18
tion of the target material can also be reduced by cool
by springs 24 which are welded to the anode 20 and
ing the supporting base by, for example, a jet of cold air.
Embodiments of the invention will now be described 55 are urged against the inner wall of the envelope 13. Sup
ported by the collector anode 20 is the ring- esh assem
with reference to the diagrammatic drawings in which
bly 1—4, the cylindrical ring 3 of which is slid over the
FIGURE 1 shows a cross-sectional view of a collector
end of the anode 20. Layer 25 of antimony trisulphidc
ring and grid mesh assembly of a Vidicon camera tube
produced as has been described with reference to FIG
with the parts of the assembly slightly separated for
URE-2 is thus adjacent and close to the window 18’.
reasons of clarity,
After the collector anode 20 carrying the ring-mesh
FIGURE 2 shows a bell-jar in which photo-conductive
assembly 1 to 4, and the electron gun structure have
target material is evaporated onto the collector mesh,
been introduced into the envelope 18, a glass foot or
FIGURE 3 shows a diagrammatic cross-sectional view
base 26 is sealed to the envelope 18. The envelope is
of the tube with the collector mesh and other electrode
parts in position,
FIGURE 4 illustrates the manner in which the mesh is
65 then exhausted via tube 27 and argon at a pressure of a
few millimetres of mercury is introduced.
Reference
numerals 28 designate electrode pins.
FIGURE 4 represents diagrammatically apparatus for
FIGURE 5 shows an alternative embodiment of the
evaporating the layer 25 (of FIGURE 3) onto window
invention in which photo-conductive target material is
evaporated from an annular cup or boat forming part 70 18' to form the target layer 25’. This ?gure shows the
upper part of the Vidicon envelope 18 surrounded by a
of the collector anode of the tube, and
cooling jacket 29 containing water 30. The heat neces
FIGURES 6A-6B show diagrammatic cross-sectional
sary for evaporating the layer 25 is provided by an eddy
views of the window of the tube before and after, respec
heated to evaporate off the photo-conductive material,
tively, the deposition of the photo-conductive target
material thereon.
current heating coil 31 connected to a source 32 of high
75 frequency current. Closely surrounding the fernico ring
3,027,218
v19 is a metal cylinder 33. To evaporate the photo-con
ductive layer from the mesh 1 to form the target 25’ as
indicated in FIGURE 6B, current from the source 32
is passed through the coil 31. The cylinder 33 prevents
undue heating of the ring 19 by absorbing radiation
from the coil 31. Undue heating of the ring 19 is very
undesirable since this may damage the seal between the
6
2. A method of making an electron device comprising
a sealed envelope and within the envelope an electrode
structure including a layer of a contaminant-sensitive
photo-conductive material on a support, comprising the
steps of ?rst providing an element of the electrode struc
ture outside of the envelope and forming by vaporization
and condensation on said element outside of the envelope
window 18’ and envelope 18. The water jacket 30, 31
a layer of said photo-conductive material, thereafter
serves to maintain the window 18' cool during the
locating Within the envelope in its proper position the
evaporation process. The coil 31 is positioned so that 10 electrode structure including the element containing the
a region of the anode 20 some distance from the mesh
1 and indicated generally by arrows 34 is heated to bright
red heat, parts of the anode on either side of this region
being heated to dull red heat. The mesh 1 and ring 2
are heated by the heat radiated from the anode region 34
and also by heat conduction through the anode 20. By
reason inter alia of the close proximity of the mesh 1
and window 18', which are usually about 2.5 mm. apart,
a very even target layer 25' as indicated in FIGURE 6B
can be produced on the window.
layer of the photo-conductive material, thereafter closing
oif permanently the envelope from the outside atmos
phere, thereafter evacuating the envelope and introduc
ing therein a low pressure gas, thereafter heating the said
element to vaporize the photo-conductive material there
on and deposit same on the said support, and thereafter
reevacuating the envelope and sealing it off.
3. A method of making a television pick-up device
comprising a sealed envelope and within the envelope on
its end wall a layer of a contaminant-sensitive photo-con
ductive material and an electrode structure including a
After the target 25’ has thus been formed the argon
is pumped out via exhaust tube 27 which is then ?nally
grid mesh adjacent the end wall, comprising the steps
sealed off close to the foot 26.
of ?rst providing said grid mesh outside of the envelope
Another embodiment of the invention is illustrated in
and forming on said mesh outside of the tube envelope
FIGURE 5. In this embodiment the antimony trisul 25 by evaporation and condensation a layer of said photo
phide is evaporated from an annular cup or boat 35
conductive material, thereafter mounting the grid mesh
forming part of the collector anode structure. The
on the electrode structure and mounting the latter Within
antimony trisulphide is evaporated through the collec
the envelope, thereafter closing-01f permanently the en
tor mesh 1 and onto the window 18' to form the target
velope to the outside atmosphere, thereafter heating the
25'.
30 said grid mesh to vaporize the photo-conductive mate
The collector anode structure comprises the main
rial therefrom and condense same on the said end wall,
cylindrical part 20 and a cylindrical part 36 one end of
and thereafter sealing off the envelope.
which is a sliding fit in the cylindrical ring 3 of the mesh
4. A method as set forth in claim 3 wherein the photo
assembly and the other end is inwardly turned up to
conductive material is red antimony trisulphide.
form the cup 35. The anode parts 20 and 36 are joined
5. A method of making a television pick-up device
by metal band 37 to which they are Welded. A coil 38
comprising a sealed envelope and within the envelope on
is shown for heating the annular cup 35, and its high
its end wall a layer of a contaminant-sensitive photo-con
frequency current source is shown at 39. By heat radia
ductive material and an electrode structure including a
tion and conduction from the heated cup 35 the mesh 1
grid mesh adjacent the end wall, comprising the steps of
is heated and condensation thereon of antimony trisul 40 ?rst providing said grid mesh outside of the envelope,
phide thereby prevented. Although in this method the
forming on one side only of said mesh outside of the
supply of antimony trisulphide is spaced some distance
tube envelope by evaporation and condensation a layer
from the window 18' it is found that a satisfactorily
of said photo-conductive material, thereafter mounting
even, i.e., uniform target layer 25' can be formed on
the grid mesh on the electrode structure with the layer
the window 18’. Furthermore, even though this meth 45 facing outward and mounting the electrode structure
od involves evaporating photo-conductive material
Within the envelope so that the grid mesh lies adjacent
through the mesh 1, it has been found by experiment
the said end wall, thereafter closing-off permanently the
envelope to the outside atmosphere and removing the
air therefrom, thereafter heating the said grid mesh to
In the above description the antimony trisulphide is de 50 vaporize the photo-conductive material therefrom and
that the evaporation conditions are less critical than those
of the side-arm technique described above.
scribed and shown deposited on the actual mesh 1 and
ring 2. However, it is not necessary to extend the layer
onto ‘the ring 2.
What is claimed is:
l. A method of making an electron device comprising 55
a sealed envelope and within the envelope an electrode
structure including a layer of a contaminant-sensitive
photo-conductive material on a support, comprising the
steps of ?rst providing an element of the electrode struc
ture outside of the envelope and forming on said element 60
condense same on the said end wall, and thereafter
evacuating the envelope and sealing it off.
6. A method as set forth in claim 5 wherein the va
porization step takes place in the presence of an inert
gas at low pressure within the envelope.
7. A method as set forth in claim 5 wherein the layer
is formed on the grid mesh in avacuum.
References Cited in the ?le of this patent
UNITED STATES PATENTS
outside of the envelope a supply of said photo-conduc
tive material, thereafter locating within the envelope
in its proper position the electrode structure including
the element containing the supply of the photo-conduc
tive material, thereafter closing-01f permanently the en 65
velope from the outside atmosphere, and thereafter heat
ing the said element to vaporize the photo-conductive
material thereon and deposit same on the said support.
2,077,961
2,404,343
2,422,427
2,730,643
2,745,032
2,809,087
Smith _______________ __ Apr. 20,
Henderson et al _______ __ July 16,
Louden ______________ .._ June 17,
Gier et al. ___________ __ Jan. 10,
Forgue et a1. _________ _.. Mar. 8,
Yeith _______________ __ Oct. 8,
1937
1946
1947
1956
1956
1957
UNITED STATES PATENT OFFICE
CERTIFICATE OF CORRECTION
Patent No. 3,027,218
-
-
March 27‘,
1962
Pieter Schagen et a1.
It is hereby certified that error appears in the above numbered pat
ent requiring correction and that the said Letters Patent should read as
corrected below.
Column 1, line 10, for "Nov. 79 1958" read -— Feb. 21,
"'_0
Signed and sealed this 31st day of July 1962.
(SEA L)
I
Attest:
ERNEST W . SWIDER
Attesting Officer
‘
DAVID L. LADD
Commissioner of Patents
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