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Патент USA US3067360

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Dec. 4, 1962
S. A. ocHs
3,067,348
PICKUP TUBE TARGET STRUCTURE
Filed Dec. 21, 1959
in?\ T1, 1
Airmail-7’
3,957,348
".
Patented Dec. 4, 1962
1
2
In still further types of targets that are known in the
prior art a sufficiently large number of conductors per
unit area have been provided. However, these structures
have been used with the conventional mesh collector
electrode screens and the problem of microphonics has
remained.
It is therefore an object of this invention to provide an
improved target electrode assembly for use in an image
3,067,348
PICKUP TUBE TARGET STRUC
Stefan Albert Ochs, Princeton, N.J., assignor to Radio
Corporation of America, a corporation of Delaware
Filed Dec. 21, 1959, Ser. No. 860,988
7 Claims. (Cl. 313-67)
This invention relates to target structures for use in
pickup or camera tubes. In particular, this invention re
orthicon type pickup tube.
lates to two-sided target structures for use in photoemis 10
It is a further object of this invention to provide an
m1
sive type pickup tubes.
During operation of a conventional image orthicon
type camera tube, photoemission, in proportion to the
light from a scene to be reproduced, is directed onto one
side of a semi-conducting type glass target. Just prior to reaching the target, the photoelectrons pass through
an apertured mesh screen or collector electrode.
improved pickup tube characterized in its substantial free
dom from microphonics and its high picture de?nition.
These and other objects are accomplished in accord
ance with this invention by providing a novel pickup
15 tube including a sub-assembly sheet comprising a semi
When
the photoelectrons land on the target, these photoelec
trons produce a potential variation or stored image on
conducting oxidized metal, having a large number of
conducting plugs extending partway therethrough, and
with a mesh collector electrode attached to the oxidized
metal in such a manner as to be spaced from the conduct
the opposite side of the target corresponding to the photo
ing plugs. The integral target and mesh electrodes are
arranged so that, although the mesh electrode is elec
trically insulated from the conducting plugs by means of
produces an output signal in proportion to the original
the oxidized metal, only electrode surfaces are exposed
photoelectron image.
to the photoelectron beam.
The targets used for image orthicon type camera tubes 25
The invention will be more clearly understood by ref
prior to this invention have been made of a thin mem
erence to the accompanying single sheet of drawings
brane of lime glass. It has been found that, when using
wherein:
'
targets of this type, the resistivity of the target increases
FIG. 1 is a transverse sectional view of an improved
electron image. An electron beam is then used to scan
the stored image, which removes the stored image, and
somewhat as the tube is operated. The cause of this in
image orthicon tube utilizing this invention;
'
crease in resistivity is not known completely but may, in 80
FIG. 2 is an enlarged fragmentary plan view of the
part, be due to a depletion of the positive ions on the
target shown in FIG. 1; and
image side of the target. As the resistivity increase oc
FIG. 3 is a sectional view of the target shown in
curs, excessive “sticking” or picture retention occurs
FIG. 2.
which limits the useful life of the tube.
Referring now to the ?gures in detail, and speci?cally
In the prior art tubes of this type, it has been found 35 FIG. 1, an image orthicon tube 10 is shown. The image
that the tube is highly sensitive to mechanical movement
orthicon tube 10 comprises an evacuated envelope 12
such as shock or vibration. One of the reasons for this
sensitivity is that the target and the mesh screen are two’
stretched membranes that are mounted very close to
gether and parallel to each other. Vibration of the tube 40
having an electron gun 14 in one end thereof. Sur
rounding the electrode gun 14 is an electron multiplier
structure 16. The electron gun 14 is designed to pro
may therefore cause variations in the spacing between the
two membranes, thus causing variations in the electri
cal capacitance between the two membranes. The capaci
side of a novel target electrode 20.
~ On the opposite side of the target electrode 20, and
within an enlarged end of the envelope 12, there is an
duce an electron beam 18 which is scanned over one
tance variations cause ?uctuations or “microphonics” in
image section 22.
the output electrical signal.
photoemissive cathode 24 and its associated electrodes.
_
It has been suggested that a target structure ‘be con
structed using a conducting plate having a plurality of
The image section 22 comprises a
During operation of the tube 10, the photocathode 24
produces an electron image corresponding to the light
apertures therethrough, with insulating material posi
from a scene to be reproduced. The photoelectron image
tioned in each aperture. One of the di?iculties of this
is directed onto the target assembly 20.
type of target structure is that the number of insulators, 50
The particular elements that have been described, other.
or conductors surrounded by insulators, that can be
than the novel target assembly 20, may be conventional
provided in a given area is low as compared to the num
and form no part of this invention except for their co
ber that are desired for high picture de?nition. A still
operation with the novel target 20. If desired, a more
further di?iculty is that both conducting surfaces and in
detailed description of an image orthicon pickup tube
sulating surfaces are exposed to the photoelectron image. 55 may be obtained by referring to one or more of many
Because of this exposure, the insulating surfaces tend
issued patents, such as Weimer Patent No. 2,537,250,
to build up a potential difference between the two sur
Law Patent No. 2,460,093, or Weimer Patent No. 2,433,
941.
'
faces of the target and, after a change in the con?gura
tion of the charge image, this potential difference re
' As was previously pointed out, the image orthicon type
quires an appreciable length of time before it has de 60 pickup tubes using'the prior art targets, such as lime
glass, have a tendency to retain a picture after a certain
cayed. This effect tends to result in objectionable vari
period of tube operation. Thus, the life of these tubes
tions in the output signal or stored image.
.
.
is limited by picture “sticking.” Two of the factors which
Other mosaic type targets suggested in the prior art
are believed to be signi?cant in the appearance of ex
include the use of highly insulating members, such as
mica, through which a plurality of holes have been drilled 65 cessive sticking are the operating temperature and the
and which have been ?lled with conducting plugs. These
targets have also suffered from lack of picture de?nition
due to the small number of plugs per unit of area that
can be drilled. Furthermore, in the known structures of
ionic conduction of the glass target.
In accordance with this invention, the target 20 com
prises a mosaic-like plug type structure. The target 20,
which is shown more clearly in FIGS. 2 and 3, includes a
thin metal member 30 which has been oxidized, pref
this general type, the insulating material is exposed to 70 erably by anodizing, so that the metal member 30 is an
beam bombardment resulting in spurious charges.
electrical insulator or a highly resistive type semiconduc
3,067,348
3
tor. The oxidized metal member 30 should have a re
sistivity of at least 1011 ohm-centimeter, in order that the
charge deposited on any one conducting plug, to be de
scribed, will not leak onto any neighboring plugs in such
a way‘ as to impair the resolution of the charge image
stored on the target.
The member 30 may be made en
tirely of a material such as aluminum oxide, magnesium
oxide or other metal oxide which is strong enough to be
4
positioned toward the photocathode 24. The aluminum
evaporation forms the collector grid 34 and also places
another layer of conductor 38 (FIGS. 2 and 3) onto the
conducting plugs 32. Thus the conductor 34 is a continu
ous mesh and, during tube operation, functions as a
collector grid. It should be noted that the collector grid
34 is insulatingly spaced from the conducting plugs 32
by means of the oxidized metal member 30.
One advantage of the conducting layer 38 is that the
self-supporting while resistive enough to prevent spread~
ing of the electrical charges.
10 evaporated aluminum 38 increases the secondary elec
tron emission ratio of the conducting plugs 32, thereby
In the metal oxide member 30 there is provided a rela
improving the overall sensitivity of the tube. Other
tively large plurality of extremely ?ne metal plugs 32.
The metallic plugs, or buttons, 32 comprise an electrically
conductive material, such as copper or nickel, which may
metals can be used for collector grids 34 such as gold or
copper. Electrical connection is made to the collector
be plated into the apertures in the insulating oxidized 15 grid 34 by means of a target ring 40 (FIG. 1) to which
electrical potentials can be applied.
metal 30. The metal plugs 32 form the only electrical
During operation of the device 10 shown in FIG. l,
conductive paths from one side to another of the target
photoelectrons from the photocathode 24 are directed
20. For proper picture de?nition, a relatively large num
onto one side of the plug type target 20 by conventional
ber of plugs per inch, each electrically insulated from
the other, is required. Targets having as many as 1,500 20 focusing and accelerating means such as those shown in
FIG. 1. The photoelectron image lands on the coating
plugs per'linear inch have been made by the subsequently
38 on the individual plugs 32 and, ‘by means. of sec
described process. Targets having approximately 750
ondary electron emission, produces a charge pattern on
plugs per linear inch or greater have been found to operate
the coated plugs 32. Due to the large number of plugs
satisfactorily.
Spaced in a plane slightly removed from the plane of 25 per unit of area, a high de?nition charge image is formed.
When the electron beam scans the opposite side of the
the plugs 32 is a collector grid 34. The collector 'grid 34?
charged plugs 32, electrons are deposited to neutralize
comprises an evaporated layer of aluminum, or other
the charge image. Once the charge has been neutralized,
conducting metal, which has been deposited on the elec
no further electrons land on the target and the beam
trically insulating metallic member. 30 that surrounds the
returns toward the electron gun to be multiplied and thus
plugs 32. It should be noted that the collector grid 34
produce an output, signal.
,
is bonded to the electrically insulating metal oxide mem
Due to the close spacing between- the collector grid 34
ber 30 as are the conducting plugs‘ 32. Because of this
and the metal plugs 32 the target capacitance for a target
con?guration, relative movement of the collector grid
diameter of about one to two inches is approximately
34 and the conducting plugs 32 is eliminated and micro
phonics are susbtantially avoided.
35 100 micromicrofarads. Due to the fact that the grid 34
is ?xed to, or integral with, the insulating member 30, as
It should further be noted that no areas of the electri
are the metal plugs; 32, microphonics, due to the physical
cally insulating metal oxide member 30: are exposed di
rectly to the photoelectron image. In other Words, the
vibration of the device 10 are substantially completely
eliminated.
,
photoelectrons “see” either the collector grid 34 or the
What isclaimed is: conducting plugs 32 and not the insulating oxidized metal; 40
1. 'A pickup tube comprising an evacuated envelope
Thus, charges will not be developed on the electrical
having a photocathode in one end thereof, an electron
insulator 30.
gun in the other end thereof, a target electrode within
The target 20 may be manufactured by anodizing, or
said envelope and between said photocathode and said
otherwise oxidizing, a portion of aluminum sheet to pro
electron gun, said target electrode comprising an oxidized
vide a metal oxide to a depth of approximately ?fteen
metal member, said member having a plurality of aper
microns. Then, using a photoresist material on the sheet
tures extending therethrough, a plurality of electrically
and a negative of a shadow mesh (not shown), a pattern
conducting plugs each in a different one of said apertures,
of holes is exposed on the resist through the mesh and
the length of said plugs being substantially less than the
then the oxide is etched completely through the anodized
‘portion of the aluminum sheet. vThe resultant holes are 50 thickness of said member, one end of said plugs being
substantially coplanar‘ with one side of said member, and
then partially ?lled with metal, such as nickel, by any
an electrically conductive grid ?xed to'the other side of
known means, such as plating, to form the metal plugs
said member, and said grid having a plurality of apertures
32. The base portion, or un-anodized part, of the alt!’
therethrough each being in registry with a different one
minum plate is then removed from the aluminum oxide
plug structure. This may be done by dissolving the al-u 55 of said conducting plugs.
2. A pickup tube comprising an elongated envelope,’v
minum sheet in a dilute hydrochloric acid bath. This dis
solving process is continued until only the aluminum
an electron gun in one end of said envelope, a photo
cathode iu the other end of said enevlope, a target elec
oxide portion 30 remains which includes the conducting
trode between said electron gun and said photocathode,
metal plugs 32. The aluminum oxide sheet 30 is trans~
lucent due to its thinness. Thus, when the sheet 30‘ be 60 said target electrode comprising a membrane of oxidized
metal having a plurality of apertures extending there
comes, translucent during the etching process, the alu- ,
through, a plurality of conductors each in a different one;
minum has been completely dissolved away and the
of said apertures, and a conducting mesh screen on said
process is stopped. One method of manufacturing the
oxidized metal and insulated from said conductors, said
aluminum oxide-plug structure may be that described in
the copending application Serial Number 721,904, ?led 65 conducting mesh screen having apertures in registration
with said conductors.
March 17, 1958, by C. H. F. Morris, and assigned to the
3.v A pickup tube as in claim 2 wherein said membrane
same‘ assignee as the assignee of this application.
After the aluminum oxide-plug structure has been
is made of aluminum oxide.
.
4. A pickup tube as in claim 2 wherein the number of
manufactured, it is mounted onto'a glass ring 36 (FIG.
1) with a suitable glass‘ frit, e.g. lead borosilicateglass. 70 said apertures per linear inch is at least 750.
At this stage in the manufacturing process, the target 20
5. A pickup tube as in claim 2 wherein the resistivity
and the ring 36 are baked in air at approximately 450° C.
vofsaid oxidized metal is atv least 1011 ohm-centimeters.
6. A pickup tube as in claim 2 wherein the thickness
for approximately one hour in order to completely re
of said target is less than 100 microns.
move the photoresist material. After the bake, aluminum
is. evaporated onto the side of the target 20‘ that will be 75
7. A pickup tube as in claim 2 wherein said mesh‘
5
8,067,348
screen substantially covers said oxidized metal whereby
only electrode surfaces are exposed to said photocathode.
References Cited in the ?le of this patent
UNITED STATES PATENTS
2,157,048
Zworykin _____________ __ May 2, 1939
6
2,369,569‘
2,416,720
2,507,958
Hulbert _____________ __ Feb. 13, 1945
Teal ________________ __ Mar. 4, 1947
Cassman ____________ __ May 16, 1950
2,617,058
2,777,040
2,793,178
Kazan _______________ __ Jan. 8, 1957
De Boer _____________ __ Nov. 4, 1952
Morris ______________ _.. May 21, 1957
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