U.S. patent number 3,701,919 [Application Number 04/864,031] was granted by the patent office on 1972-10-31 for integrated vacuum circuits.
This patent grant is currently assigned to Electron Emission Systems. Invention is credited to Donovan V. Geppert.
United States Patent |
3,701,919 |
|
October 31, 1972 |
INTEGRATED VACUUM CIRCUITS
Abstract
An integrated circuit operative in vacuum and having all circuit
elements formed in coplanar fashion on a single surface of a
substrate to provide superior performance even in the presence of
adverse environmental conditions. The circuit is especially adapted
to microminiaturization and includes a unique electron discharge
device having coplanar electrodes easily formed on a substrate
surface by relatively simple film deposition techniques.
Inventors: |
Donovan V. Geppert (Sunnyvale,
CA) |
Assignee: |
Electron Emission Systems
(Inc., Tucson)
|
Family
ID: |
25342360 |
Appl.
No.: |
04/864,031 |
Filed: |
October 6, 1969 |
Current U.S.
Class: |
313/250; 313/289;
313/268; 313/308 |
Current CPC
Class: |
H01J
19/78 (20130101) |
Current International
Class: |
H01J
19/00 (20060101); H01J 19/78 (20060101); H01j
001/88 (); H01j 019/42 () |
Field of
Search: |
;313/250,256,259,262,268,289 ;117/212 |
Foreign Patent Documents
Primary Examiner: David Schonberg
Assistant Examiner: Paul A. Sacher
Attorney, Agent or Firm: William Breunig Hyman Hurvitz
Claims
1. An electron discharge device comprising: a substrate of
electrically insulative material; a plurality of electrodes formed
in coplanar manner on a surface of said substrate, said plurality
including: an anode electrode formed as a conductive film on said
substrate surface; a cathode electrode formed as a conductive film
on said substrate surface and having an electron emissive coating
thereon, said cathode electrode being in arcuate spaced
relationship with and at least partially surrounding said anode
electrode; a gate electrode formed as a conductive film on said
substrate surface between said cathode and anode electrodes and in
arcuate spaced relationship therewith and at least partially
surrounding said cathode electrode; said cathode and gate
electrodes each having an effective length to provide predetermined
device current and impedance characteristics while also providing
electron focussing action and minimization of spurious flux
leakage; means for heating said substrate to an operating
temperature such that thermionic emission occurs essentially from
only said cathode electrode; and
2. A device according to claim 1 wherein said heater means includes
a heater element formed as a film on a surface of said substrate
opposite to
3. A device according to claim 1 wherein said heater means includes
a foil-like heater element and means for supporting said heater
element in intimate thermal contact with a surface of said
substrate opposite to the
4. A device according to claim 2 wherein said heater element is a
sinuous path formed on the substrate surface and having terminals
for electrical
5. A device according to claim 1 wherein said gate electrode
extends beyond the effective extremities of said cathode and anode
electrodes to provide
6. A device according to claim 1 wherein said plurality of
electrodes includes a second gate electrode formed as a conductive
film on said substrate surface between said anode and gate
electrodes and in spaced
7. A device according to claim 1 wherein said cathode and gate
electrodes are arranged on said substrate in parallel spaced
relationship and each include a curved central portion and
extending linear portions, the linear portions being of a length to
provide said predetermined current and
8. A device according to claim 1 further including: an evacuated
enclosure; means for supporting said substrate within said
enclosure; a first conductive member supported within said
enclosure in spaced relationship with and confronting the surface
of said substrate containing said electrodes and the edge of said
substrate; a second conductive member supported within said
enclosure in spaced relationship with an opposite surface of said
substrate; said first and second members providing a shielding
structure for said
9. A device according to claim 2 including: an evacuated enclosure
having a plurality of electrical terminals therethrough; means for
supporting said substrate within said enclosure, said means also
serving as electrical connections to said heater element; and means
for providing electrical connections between respective ones of
said
10. An integrated vacuum circuit comprising: a substrate of
electrically insulative material and having a surface supporting a
film circuit pattern thereon; a film circuit pattern formed on said
substrate surface, said circuit pattern including: at least one
electron discharge device each having all electrodes formed in
coplanar manner as conductive films on selected areas of said
substrate surface; at least one passive element formed in film form
on selected other areas of said substrate surface; conductive film
paths formed on said substrate surface in a configuration
selectively interconnecting each of said at least one electron
discharge device and passive element to provide an intended
circuit; means for heating said substrate to a predetermined
operating temperature to permit thermionic emission from selected
areas of said circuit pattern; and
11. A circuit according to claim 10 wherein said heater means
includes a heater element formed as a film on a surface of said
substrate opposite to
12. A circuit according to claim 10 wherein said at least one
passive element is an electron discharge device having the
electrodes thereof formed as conductive films on said selected
other areas of said substrate
13. A circuit according to claim 10 wherein said at least one
electron discharge device includes: an anode electrode formed as a
conductive film on said substrate surface; a cathode electrode
formed as a conductive film on said substrate surface and having an
electron emissive coating thereon; and a gate electrode formed as a
conductive film on said substrate surface
14. An electron discharge device comprising a substrate of
electrically insulative material: first and second like electron
discharge devices formed in coplanar manner on a surface of said
substrate each of said devices including: an anode electrode formed
as a conductive film on said substrate surface; a cathode electrode
formed as a conductive film on said substrate surface and having an
electron emissive coating thereon, said cathode electrode being in
arcuate spaced relationship with and at least partially surrounding
said anode electrode; a gate electrode formed as a conductive film
on said substrate surface between said cathode and anode electrodes
and in arcuate spaced relationship therewith and at least partially
surrounding said cathode electrode; said cathode and gate
electrodes each having an effective length to provide predetermined
device current and impedance characteristics while also providing
electron focusing action and minimization of spurious flux leakage;
a conductive film path formed on said substrate surface between
said first and second devices and including first and second
arcuate first portions each confronting and in spaced relationship
with a respective cathode electrode and joined with a second
portion separating said first and second devices, said conductive
film path being operative to electrically isolate each device from
the other; means for maintaining said device in a vacuum; and means
for heating said substrate to an operating temperature such that
thermionic emission occurs essentially from only said cathode
electrodes.
15. A device according to claim 14 wherein said electrodes and said
conductive film path each terminate in a conductive terminal area
on said substrate surface.
Description
FIELD OF THE INVENTION
This invention relates in general to integrated electronic circuits
and more particularly to circuits employing electron discharge
devices especially adapted for microminiaturization, and capable of
effective performance under widely varying operating
conditions.
Semiconductor devices are widely employed and for many purposes
have replaced vacuum tubes by reason of extremely small size, low
power consumption, excellent dependability and relatively low
manufacturing cost in volume production. Semiconductor integrated
circuits similarly are now replacing circuits fabricated of
discrete components, since such integrated circuits also offer the
advantages of small size, excellent reliability, low power
consumption and relatively low manufacturing cost. Semiconductor
integrated circuits are however, generally limited to low power
applications and to operation within specific, relatively narrow
environmental ranges. For example, semiconductor devices and
integrated circuits suffer serious performance degradation at
elevated temperature which can be present in many practical systems
and often catastrophic performance degradation also occurs in the
presence of nuclear radiation, which limits the utility of such
semiconductor devices and integrated circuits in many aerospace
systems. The performance of semiconductor integrated circuits is
dependent upon a highly sophisticated and carefully controlled
manufacturing process in which selected regions of different
conductivities are formed within a bulk of semiconductor material.
Control of the working materials and of the process variables to
provide a particular circuit is extremely critical, and becomes
increasingly more critical with the complexity of a particular
circuit. Imperfections within the semiconductor material itself can
also result in a defective device and contribute to the low yields
experienced in the fabrication of semiconductor integrated
circuits, especially in the fabrication of complex circuits. From a
physical point of view the most advantageous medium in which to
control the flow of electrons is still in a high vacuum, and in
this light, it is an object of the present invention to provide
integrated circuits in which electron flow in a vacuum is employed
in structures commensurate in size and packing density with
semiconductor devices and circuits.
In accordance with the present invention, integrated circuits are
formed by configurations of coplanar elements on a single surface
of an insulative substrate. The circuits can be formed in
microminiature size and are operative in vacuum to provide superior
performance even under deleterious operating conditions. The
invention includes a unique electron discharge device having
coplanar electrodes formed on a common substrate surface and
especially adapted to achieve effective thermionic operation at a
uniform relatively low temperature. These unique electron discharge
devices can be embodied in a circuit array which can include
passive circuits elements to provide a vacuum integrated circuit
according to the invention or the discharge devices can be employed
individually or in groups as active elements. The electron
discharge devices and associated passive elements and
interconnecting paths are formed on a common surface of a substrate
by well-known film deposition techniques such as by masking and
photoetching techniques. The size of particular devices and
circuits depends upon the intended operating power levels and upon
the intended operating frequencies. Means are provided for heating
the integrated vacuum circuit to an operating temperature in order
to provide predetermined electron emission to enable circuit
operation. Such heater means, typically includes a heater element
of planar configuration formed on the opposite surface of the
circuit substrate and operative to raise the temperature of the
substrate and associated circuit to the requisite operating
temperature. The substrate, including the circuit and associated
heater element, is packaged within a suitable vacuous enclosure
which includes electrical leads for supplying power to the heater
element and for providing interconnection to the circuit. Means may
be provided for electrically and thermally shielding the substrate
to minimize radiation heat loss and to isolate the circuit from
spurious electrical fields.
It is a particular feature of the invention that the entire circuit
can be heated to a uniform temperature while providing efficient
thermionic emission only from selected circuit areas. For example,
the electrodes of electron discharge devices formed according to
the invention can all be at the same temperature; however, the
electrodes other than the cathode are substantially non-emitting
while the cathode, which is at the same temperature as the
associated electrodes, provides efficient thermionic emission. As a
result, the novel thermionic devices provide superior operation
without the necessity of selective heating of a cathode. The
present invention thus permits the provision of large numbers of
active devices and complete integrated circuits on a single
substrate surface which can be heated to a predetermined
temperature at which thermionic operation is achieved only where
desired.
The active devices of the integrated vacuum circuit are fabricated
by forming on a substrate surface the electrodes of the device in a
predetermined configuration to yield the intended device
characteristics. For example, to form a triode, a conductive
pattern is formed on the substrate surface to delineate the
cathode, gate and anode electrodes and an electron emissive
material is formed over the cathode area to provide a
thermionically emissive structure. When heated to an operating
temperature, the coated cathode area will emit an electron stream
to permit triode operation when the device is suitably biased in
vacuum. By reason of contact potential differences between the gate
and cathode electrodes, a triode implemented according to the
invention, will exhibit an inherent negative bias, of for example,
about 2.0 - 4.0 volts. For anode voltages which are not excessive,
the triode remains cut-off with zero external gate bias, and a
positive gate bias must be applied to drive the triode to a
conducting state. As a result, direct coupling can be employed
between stages of a circuit and in addition, no cathode resistors
or by-pass capacitors need be employed. Consequently, circuits
constructed utilizing such novel electron discharge devices are
relatively simple and require a minimum of components.
Integrated vacuum circuits according to the invention are
particularly suitable to operation at high ambient temperatures and
in the presence of nuclear radiation. Moreover, these circuits are
relatively immune to catastrophic failure from exposure to
electromagnetic environments and transient overloads. The
performance of such circuits, especially under adverse conditions
thus offers a marked improvement over semiconductor devices and
integrated circuits which are extremely sensitive to such adverse
conditions.
DESCRIPTION OF THE DRAWINGS
The invention will be more fully understood from the following
detailed description, taken in conjunction with the accompanying
drawings in which:
FIG. 1 is an enlarged pictorial view, partly cut away, of an
embodiment of the invention;
FIG. 2 is an enlarged elevation view, partly cut away, of the
embodiment of FIG. 1;
FIG. 3A is an enlarged pictorial view of the integrated vacuum
circuit of FIG. 1;
FIG. 3B is an enlarged pictorial view, partly cut away, of a
variation of the embodiment of FIG. 3A;
FIG. 4 is an enlarged pictorial view of the heater element of FIG.
1;
FIG. 5 depicts the anode current versus anode voltage
characteristic curves of a dual triode according to the
invention;
FIG. 6 is an enlarged pictorial view of an alternative embodiment
of the invention;
FIG. 7A is a schematic diagram of a triode circuit, and FIG. 7B is
an enlarged broken away pictorial view of this circuit constructed
according to the invention;
FIG. 8 is an enlarged elevation view of an alternative embodiment
of the invention;
FIG. 9 is an enlarged broken away pictorial view of a further
embodiment of the invention;
FIG. 10 is an enlarged elevation view of a variation of the
embodiment of FIG. 8;
FIG. 11 is an enlarged pictorial view of the heater element of FIG.
10;
FIG. 12 is an enlarged pictorial view of still another embodiment
of the invention;
FIG. 13 is an enlarged pictorial view of a further embodiment of
the invention; and
FIG. 14 is an enlarged plan view of a still further embodiment of
the invention.
DETAILED DESCRIPTION OF THE INVENTION
An integrated vacuum circuit according to the invention is
illustrated in exaggerated form in FIGS. 1 and 2 and is disposed
within an evacuated enclosure having terminal pins depending
therefrom to provide means for interconnection thereto. An
electrically insulative substrate 10 of circular disc-like
configuration has formed on the upper surface thereof a circuit
configuration 12 which, in the illustrated embodiment is a dual
triode. A heater 13 is formed on the opposite surface of substrate
10 for raising the circuit temperature to a level for proper device
operation, as will be explained. Substrate 10 with associated
circuit 12 and heater 13 is disposed within an evacuated enclosure
14 and is supported therein by means of a plurality of conductive
pins 16a spaced symmetrically about the periphery of the substrate,
these pins also providing electrical connection to the heater 13 to
permit application of heater current thereto. Electrical connection
to circuit 12 is accomplished by means of the other ones of the
conductive pins 16, also spaced about the periphery of substrate 10
and connected to respective circuit elements by means of respective
lead wires 18. The vacuous enclosure 14, includes a circular base
member 20 to enable evacuation of the enclosure 14 and for
introduction of an inert gas which may be desirable in particular
instances.
In order to minimize the effects of spurious electrical fields on
the vacuum integrated circuit, and also to minimize spurious
radiation from the circuit to the operating environment which may
occur especially at high frequencies of operation, it is often
desirable to provide shielding means within enclosure 14. Such
shielding means as illustrated in FIGS. 1 and 2 includes a
cup-shaped conductive member 26 and a disc-shaped conductive member
28 which cooperate to substantially surround substrate 10 and
circuit 12 formed thereon. Disc 28 is attached to rim of member 26
by radial arms 30 and the shield is supported in spaced disposition
around substrate 10 by a plurality of posts 32 extending between
enclosure base member 20 and disc 28. The shielding structure in
addition to proving electrical isolation also minimizes thermal
radiation losses from heater 13 and therefore improves the thermal
efficiency of the device. As an alternative to employing a separate
shielding structure within enclosure 14, the enclosure cover itself
can be formed of an electrically conductive material to serve as a
shield. In certain applications, shielding may not be necessary at
all and the shielding structure need not therefore be employed.
The dual triode circuit 12 is illustrated more clearly in FIG. 3A
and includes first and second identical circuits separated by an
isolation or guard electrode which substantially prevents
electrical interaction therebetween. Each triode includes an
arcuate cathode electrode 40, an arcuate gate electrode 42 disposed
in parallel relationship therewith, and an anode electrode 44
disposed within the opening defined by gate electrode 42. Each
electrode is connected to a respective conductive terminal pad 46
via a conductive path 48. An isolation electrode 50 is provided
between the adjacent triode structures and includes first and
second arcuate arms 52a and 52b each in parallel disposition with
respective cathode electrodes 40, which join to form an elongated
conductive arm 54 disposed between the triodes and which terminates
in a terminal pad 56. The illustrated arcuate electrode
configuration is effective to focus or concentrate electrons
emitted from the cathode onto the anode electrode and substantially
eliminates the possibility of electron overshooting of the anode.
Isolation electrode 50 is also operative to assist in electron
focusing and acts to minimize spurious fields which may tend to
develop in the region of the electrodes. The circuit configuration
can be formed in a variety of sizes depending on the power
capability desired and the intended frequency of operation. In
general, the smaller the electrode dimensions and spacings, the
higher the cutoff frequency of the device.
The effective length of the electrodes can be increased to provide
higher currents and lower impedance. As shown in FIG. 3B, cathode
40a and gate 42a are generally of the arcuate configuration
illustrated in FIG. 3A but with the effective length thereof being
greater by virtue of the linear extension of these electrodes. The
effective length of anode 44a is correspondingly increased. The
active length of the electrodes is most easily varied by increasing
or decreasing the linear portions of the electrodes, such as the
linear portions 41 of the cathode and linear portions 43 of the
gate. Thus, according to this embodiment of the invention,
particular currents and device impedance can be easily provided
while also maintaining electron focusing action as in the
embodiment of FIG. 3A. Of course, it will be appreciated that the
circuit of FIG. 3B can be employed as a single triode, or, as in
FIG. 3A, can be employed together with an isolation electrode in a
dual triode configuration.
The substrate on which the integrated vacuum circuit is formed is
fabricated of an electrically insulative material capable of
operation at the elevated operating temperatures of the circuit.
More particularly, the substrate should have a volume resistivity
at operating temperature such that leakage currents are within
tolerable levels. In addition the substrate should have a surface
finish, on the surface on which the vacuum circuit is formed, of a
degree commensurate with the size of the circuit elements formed
thereon, since the line width and line spacing of circuit elements
which can be achieved on a given substrate surface is a function of
the degree of surface finish. The substrate should also have
desirable vacuum properties at operating temperature and chemical
resistance to the selective eches employed in the fabrication of
the circuitry. In general, ceramic materials provide the intended
substrate characteristics. Typically, alumina can be employed
having a surface polished to a desired degree of finish according
to the intended degree of miniaturization of the circuit formed
thereon. An 8 microinch surface finish has been found suitable to
support integrated vacuum circuitry in which the patterns have line
widths and spacings of 1 mil or more. For line widths and spacings
less than one mil, the surface finish of the substrate becomes
somewhat more critical in that any surface imperfections can result
in portions of the circuit pattern being inoperative or imperfectly
formed. With careful polishing however highly finished surfaces can
be provided on alumina or other substrates to achieve the intended
degree of circuit miniaturization. A single crystal material, such
as sapphire, can be employed in the present invention and although
sapphire is relatively more expensive than polycrystalline alumina,
the costs tend to balance since highly finished sapphire substrate
surfaces can be more easily attained.
As stated above, the volume resistivity of the substrate should be
maintained above minimum predetermined levels at operating
temperature in order to correspondingly maintain electrical leakage
at acceptable levels. The allowable degree of substrate leakage is
affected by the electrode voltages employed and the cathode current
density. The circuits of the invention are operative at relatively
low voltages, with the result that substrate volume resistivity
becomes a less critical parameter. Moreover, high cathode current
densities can be provided in circuits according to the invention at
lower temperatures than usually required thereby further enlarging
the choice of acceptable volume resistivities.
The circuit patterns of FIGS. 3A and 3B are formed by well known
film deposition technique, such as by photolithography or
photoetching. In general, a surface of a substrate having the
desired degree of surface finish is coated, as for example by
evaporation in a vacuum, with a metal, such as titanium, which will
not emit electrons when coated with an electron-emissive material.
A photoresist pattern then is employed as a mask to delineate, as
for example by sputter etching, all electrodes (except cathodes)
and associated conductive paths. The photoresist is removed, and a
second metal, such as tungsten, which will emit electrons when
coated with an emissive material, is deposited, for example by RF
sputtering, over the substrate. Another photoresist pattern is then
used as a mask for delineating, as for example by sputter etching,
the cathode areas. Then a cathode-emissive material, typically
triple carbonate, is applied to the tungsten cathode areas. Of
course, a variety of deposition techniques well known in the art
can be employed to form the metal patterns and emissive coatings of
the novel vacuum circuitry, and such techniques need not be
described in detail herein. By such relatively simple film
disposition techniques, a reliable and highly effective circuit can
be provided of sizes comparable to semiconductor devices and
circuits but without the limitations associated therewith.
In the circuits illustrated in FIGS. 3A and 3B, no conductive path
crosses any other conductive path. In some instances, however, as
in relatively more complex circuitry in which a plurality of
integrated vacuum circuits are interconnected to form a circuit
array, it may be desirable to provide conductive paths which cross
over each other. Such cross-overs can be fabricated by well known
photoetching or photolithographic techniques. For example, a
photoresist can be deposited and developed to provide a metal pad
area on each side of a conductive path to be traversed, with the
undeveloped photoresist extending across the underlying conductive
path between the metal pad areas. A metal layer can then be formed
over the photoresist and this layer plated to a desired thickness
which, after removal of the underlying photoresist, provides a self
supporting conductive bridge over the underlying conductive
path.
The heater element 13 is formed on the opposite surface of
substrate 10 than circuit 12 and is illustrated more clearly in
FIG. 4. In the illustrated embodiment, the heater is a sinuous path
58 having terminals 62a, 62c provided respectively at the ends
thereof and a terminal 62b provided centrally of path 58 as a
center-tap connection. Typically, sinuous path 58 is formed by
coating the substrate surface with a resistive material such as
tungsten or molybdenum and selectively removing portions of the
material to provide the intended heater path. As evident from FIG.
4, first and second interdigitated parallel arrays of grooves 60
are formed to selectively remove the resistive material to provide
heater path 58. The conductive terminals 62a, 62b and 62c are
connected to respective mounting pins 16a to provide electrical
connection to the heater as well as providing mechanical support
for substrate 10, as described hereinabove. In operation, a
suitable electrical current is applied to heater element 13 to
raise the temperature of substrate 10 and the associated cathode
electrodes such that the thermionic emission occurs and, with
suitable potentials on the gate and anode electrodes triode
operation achieved.
The characteristic curves of a dual triode of the type illustrated
in FIG. 3A are depicted in FIG. 5. The dual triode was formed on a
sapphire substrate 1/2 inch in diameter. The deposited line widths
were approximately 5 mils and the spacings between lines was
approximately 5 mils. An amplification factor of about 10 is
maintained over the operating range, and no significant interaction
occurs between adjacent triodes.
As alternative triode electrode configuration is illustrated in
FIG. 6 and includes in parallel disposition a linear cathode
electrode 64, a gate electrode 66, and an anode electrode 68.
Cathode electrode 64 is connected via an orthogonally disposed
conductive path 70 to a conductive terminal pad 72. Similarly anode
electrode 68 is coupled to a terminal pad 74 via a conductive path
76, while gate electrode 66 extends outwardly from the electrode to
terminate in a terminal pad 78. The electrode pattern is, except
for the cathodes, formed of a suitable non-emissive metal, such as
for example titanium, while the cathode 64 formed of another metal
such as tungsten or nickel is coated with an electron emissive
material. The electrodes can be fabricated by photoetching or
photolithographic techniques such as described hereinabove.
The triode configuration illustrated thus far can be employed
singly or in multiple arrays and can also be formed together with
interconnecting passive elements and conductive paths to provide
complete circuit networks. As an example, the schematic diagram of
FIG. 7A depicts a circuit, which includes a triode 80 and
associated gate resistor 84 and anode resistor 82, and which can be
implemented according to the invention in the manner illustrated in
FIG. 7B. The triode electrodes are formed similarly to that
depicted in FIG. 6 by forming a gate electrode 88, an anode
electrode 90 and an emissive cathode electrode 86 on a surface of
substrate 108. The resistors 82 and 84 are formed according to the
invention as thermionic bi-directional diodes. Resistor 82 is
formed by depositing an electron emissive electrode pair 92 and 94
in parallel spaced apart relationship on substrate 108, with
electrode 94 connected to anode 90 by means of a conductive path
96. Similarly, resistor 84 is provided by a pair of deposited
electron emissive parallel electrodes 98 and 100, with electrode 98
being coupled via a conductive path 102 to gate electrode 88.
Connection is made to the circuit via conductive pads 104 and
associated conductive paths 106 formed in desired locations on the
substrate 108.
Resistors can be formed either as bi-directional (non-rectifying)
or uni-directional (rectifying) thermionic diodes as may be
required in particular operating circuits. A unidirectional device
need only have one emissive electrode, while in a bi-directional
device, both electrodes are emissive, as illustrated in FIG. 7B.
The effective resistance of the thermionic diode is determined by
the electrode spacing and electrode areas of the device. For
example, a diode having interelectrode spacing of about five to ten
times that of a triode has been found suitable.
An alternative embodiment of the invention is illustrated in FIG. 8
wherein a heater is formed on the surface of a separate substrate
which is supported in intimate contact with a substrate containing
the novel circuitry. A heater element 110 which may be for example
the sinuous path illustrated in FIG. 4, is formed on a surface of
an insulative substrate 112, while the integrated vacuum circuit
114 is formed on a surface of insulative substrate 116. The
substrates 112 and 116 are supported with heater 110 in intimate
thermal contact with the surface of substrate 116 opposite to the
surface having circuit 114 formed thereon. The heater is maintained
in intimate contact with substrate 116 by means of a plurality of
clamps 118 spaced about the periphery of the substrates, each clamp
being connected to a respective mounting pin 120. Mounting pins 120
are supported by and are in hermetic sealing relationship with an
insulative base member 122 which can serve as the base for a
vacuous enclosure, as described hereinabove. Clamps 118 are formed
of a resilient conductive material and electrical connection is
made to heater 110 by means of lead wires 124 connected between
respective clamps and respective terminals of heater 110. A
suitable electrical current can thus be applied to heater 110 by
means of the associated conductive pins and clamps in order to
uniformly heat substrate 116 and the associated circuit 114 to
cause selected thermionic emission of the electron discharge
devices which are part of circuit 114 and thereby enable circuit
operation as described hereinabove. It will be recalled that the
invention offers unique advantages in that thermionic emission
occurs essentially from only the cathode areas of the circuit
although the entire circuit is uniformly heated to a relatively low
temperature. Thus, although other electrodes of the thermionic
devices are at the same temperature as the cathode electrode, these
other heated electrodes are substantially non-emitting while the
efficient cathode structure provided herein provides the intended
thermionic emission to achieve effective circuit operation.
The present invention can be employed in the implementation of a
variety of thermionic devices and circuits. For example, individual
thermionic devices such as the diodes and triodes illustrated
hereinabove can be provided according to the invention and
pluralities of such devices can be formed on a single substrate for
use in those instances where an array of active elements is
desirable. Additionally, one or more active thermionic devices can
be provided along with associated conductive paths and/or passive
circuit elements to provide complete integrated circuitry formed in
a coplanar manner on a single substrate surface. Such integrated
circuitry can be for digital or analog purposes. For digital
purposes, circuitry according to the invention can be provided of a
size comparable with semiconductor integrated circuits and which
offer substantial immunity to adverse operating conditions.
Employment of the invention to provide analog integrated circuits
offers the advantage of relatively high power for extremely small
size, which small size also permits circuit operation at extremely
high frequencies such as in the microwave spectrum.
As an example of a typical digital circuit which can be formed
according to the invention, there is shown in FIG. 9 a portion of a
flip-flop in which all circuit elements are formed in a coplanar
manner on a single substrate surface. A pair of triodes 126 and 128
are formed on a surface of a substrate 130 by providing conductive
films in selective configurations to define the electrodes of the
thermionic devices, as described. Cathode electrodes 132 and 134
are formed in adjacent relationship on the substrate surface and
are connected to a common conductive path 136 also formed on the
substrate surface. A gate electrode 138 is formed in spaced
relation to cathode 132 and extends outwardly toward the periphery
of substrate 130 terminating in a conductive terminal 140. A gate
electrode 142 is formed in spaced relation to cathode 134 and
continues as a conductive path on the substrate surface for
interconnection to portions of the circuitry not shown. A
conductive film path 144 provided in spaced relation to gate
electrodes 138 and 142 serves as the anode electrode for both
thermionic devices.
The anode electrodes formed of film 144 are connected via
conductive paths formed on the substrate surface to terminal
portion 146 and via conductive path 148 to other portions of the
circuit, not shown. The anode electrodes are also coupled to a
suitable source (not shown) of anode voltage via a thermionic
bi-directional diode formed of parallel electron emissive
electrodes 150 and 152 which is operative as an anode resistor.
Similar circuitry is provided on the broken away portion of
substrate 130 with conductive path 148 being connected to one gate
electrode of a triode of the other triode pair and with gate
electrode 142 being connected to the anode electrodes of the other
triode pair. Suitable control terminals are also provided on the
remaining portion of the circuit as are suitable power terminals.
It should be evident that terminals 140 and 146 provide respective
set and reset terminals, like terminals being provided on remaining
portions of the circuit to accomplish bistable digital
operation.
It is evident that, in the embodiment of FIG. 9, a single
conductive path 144 serves as a common anode for a pair of gates
140 and 142, and a pair of cathodes 128 and 134. In a similar
manner, the invention can provide of other vacuum devices and
circuits in which a common electrode is employed in conjunction
with a plurality of individual electrodes, and such configurations
are efficiently achieved by virtue of the novel planar geometry of
the invention.
A further embodiment of the invention is illustrated in FIG. 10
wherein a separate heater element is disposed between first and
second substrates, each substrate containing novel circuitry as
described hereinabove. Referring to FIG. 10, it will be appreciated
that the circuit and heater structures are mounted in a similar
manner to the embodiment in FIG. 8 previously described, and like
components of this embodiment are designated by the same reference
numerals as in FIG. 8. A heater element 160, to be described in
detail hereinbelow is disposed between a first substrate 162 and a
second substrate 164 and in intimate contact with the confronting
surfaces thereof. An integrated vacuum circuit 166 is formed on the
exposed surface of substrate 162, while an integrated vacuum
circuit 168 is formed on the exposed surface of substrate 164. The
substrates 162 and 164 are supported with heater element 160
therebetween in intimate thermal contact by means of a plurality of
clamps 118 spaced about the periphery of the substrate, each clamp
being connected to a respective mounting pin 120. Mounting pins 120
are supported by and are in hermetic sealing relationship with an
insulative base member 122 which, as described above, can serve as
the base for a vacuous enclosure. As described in connection with
FIG. 8, clamps 118 are formed of a resilient conductive material,
with electrical connection being made to heater element 160 by
means of lead wire 124 connected between respective clamps and
respective terminals of heater 160. In order to uniformly heat
substrates 162 and 164 and the associated circuitry 166 and 168 to
cause selected thermionic emission of the electron discharge
devices which are part of the novel circuitry, a suitable
electrical current can be applied to heater element 160 by means of
the associated pins and clamps. Circuit operation as previously
described is thus achieved.
The heater element 160 in the embodiment illustrated in FIG. 10 can
be formed of a graphite-bearing foil depicted in FIG. 11, sold
commercially under the tradename GRAFOIL. Referring to FIG. 11,
there is shown a heater element 160 formed of an electrically
resistive foil in a sinuous path and having an overall circular
outline to conform to the circular configuration of the substrate
discs. The sinuous path is formed by the interdigitated elements
defined by channels 170 formed in alternate parallel arrays, as
illustrated. Terminals 172a and 172c are provided, respectively, at
the ends of the foil path, with a third terminal 172b provided
centrally of the path as a center-tap connection. The conductive
terminals 172a, 172b and 172c are connected to respective mounting
pins 120 in the embodiment of FIG. 10 by means of respective lead
wires 124 and clips 118. As previously described, a suitable
electrical current applied to heater element 160 will raise the
temperature of the associated substrates 162 and 164 as well as the
associated integrated vacuum circuitry 166 and 168 such that
selective thermionic emission will occur from the cathode
electrodes.
A variation of the arcuate electrode geometry illustrated and
described in connection with FIG. 3 is sown in FIG. 12. A triode
electrode pattern is formed by photolithographic techniques, such
as described hereinabove, on a surface of a substrate 174 with the
cathode electrode being of linear configuration, and the gate and
anode electrodes being of arcuate configuration. Referring to FIG.
12 a cathode electrode 176 is provided on the surface of substrate
174 with a gate electrode 178 disposed in parallel spaced
relationship around the linear cathode 176 and an anode electrode
180 disposed in parallel spaced relationship around gate electrode
178. Each electrode is connected to a respective conductive
terminal pad 182 via a conductive path 184. Cathode 176 includes an
electron emissive material along the active length thereof. It will
be noted that the effective length of gate electrode is greater
than the effective length of anode 180 for reasons to be explained
below. The effect of this arcuate electrode structure is to provide
essentially a double gate, double anode configuration which
minimizes spurious fields which can limit the performance
characteristics of the triode. Extension of the effective ends of
gate electrode 178, such as extremity 186, beyond the effective
extremities of the anode 180 and beyond the active length of
cathode 176 provides efficient end shielding, and efficiently
shields the cathode from the anode along both edges thereof to
substantially eliminate spurious flux leakage from anode 180 to
cathode 176.
It will be appreciated that the invention is not limited to the
illustrated triode structures but may be adapted for use with a
variety of electrode configurations to suit particular
requirements. For example, tetrode structures can be provided in
accordance with the invention, one embodiment being depicted in
FIG. 13. The illustrated tetrode configuration is generally similar
to the triode embodiment of FIG. 12, with the addition of a second
gate electrode 185 formed on a surface of substrate 188 in parallel
spaced relation between the first gate electrode 190 and anode 192.
The second gate electrode 185 functions similarly to the screen
grid of well known electron discharge tubes, and has a larger
effective length than anode 192 and cathode 194 to provide good end
shielding.
A further embodiment of the invention is illustrated in FIG. 14
wherein the gate and anode electrodes completely encircle the
cathode. Cathode electrode 200 is formed of circular configuration,
with the gate electrode 202 formed as an annular ring
concentrically spaced around cathode 200. Anode electrode 204 is
similarly formed as an annular ring concentrically spaced about
gate 202. The electrode portion can be formed by photolithographic
techniques, such as described hereinabove, with an electron
emissive material formed on the cathode 200 to provide a thermionic
emissive structure. In this closed electrode configuration
electrical connection can be made to the electrodes by lead wires
attached to respective electrode regions, or alternatively
connection can be made via plated-through holes in the substrate on
which the electrodes are formed, connecting respective electrodes
on one substrate surface to a lead wire pattern formed on the
opposite surface of the substrate.
Various modifications and alternative implementations will now
occur to those versed in the art and it is not intended to limit
the invention by what has been particularly shown and described.
The substrate on which the novel circuit is formed can also serve
as the base member of a vacuous enclosure rather than mounting the
substrate within a separate enclosure. And, of course, a variety of
mounting and packaging configurations can be employed to provide
device configurations suitable for particular applications and
operating environments. For example, rather than the pin type leads
illustrated, connection to the circuit can be provided by leads
extending in the plane of the circuit substrate and which leads can
themselves be formed on the surface of a mounting substrate.
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