U.S. patent number [Application Number ] was granted by the patent office on 1971-10-05 for thin film room-temperature electron emitter.
United States Patent |
3,611,077 |
Smith |
October 5, 1971 |
THIN FILM ROOM-TEMPERATURE ELECTRON EMITTER
Abstract
A vacuum enclosure containing an anode and a cathode, wherein a
first embment of the cathode comprises a continuous thin film of
semiconductive material deposited on an electrically insulating
substrate and adapted to have a potential difference placed
thereacross. A break in the film exists so as to produce a high
impedance to the flow of current. A second embodiment of the
cathode comprises a noncontiguous thin film of semiconductive and
metallic material deposited at random in small droplets on a
substrate and adapted to have a potential difference placed
thereacross.
Inventors: |
Smith; Sidney T. (Alexandria,
VA) |
Assignee: |
The United States of America as
represented by the Secretary of the Navy (N/A)
|
Family
ID: |
25183940 |
Appl.
No.: |
04/802,527 |
Filed: |
February 26, 1969 |
Current U.S.
Class: |
315/94; 257/10;
313/310; 313/311; 313/326; 313/346R |
Current CPC
Class: |
H01J
1/316 (20130101) |
Current International
Class: |
H01J
1/316 (20060101); H01J 1/30 (20060101); H01j
001/14 (); H01j 019/06 () |
Field of
Search: |
;307/293,308 ;315/169,94
;317/234 (8)/ ;317/234 (8.1)/
;313/311,336,346,355,235,310,326,329,341,342 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
782,063 |
|
Apr 1968 |
|
CA |
|
1,004,396 |
|
Sep 1965 |
|
GB |
|
Primary Examiner: Lake; Roy
Assistant Examiner: La Roche; E. R.
Claims
What is claimed and desired to be secured by Letters patent of the
United States is:
1. A cold-cathode vacuum tube, comprising:
an enclosure defining a space containing a vacuum;
means mounted within said space for providing emission of free
electrons at room temperatures, said means including:
an electrically insulation substrate,
a thin film of semiconductive material deposited onto said
substrate, said film having a uniform break entirely across and
substantially parallel to one side thereof, and
means electrically coupled to said thin film for establishing a
longitudinal electric field therein in a direction normal to said
break; and
means mounted within said space for generating an electric field
having a direction normal to the direction of said longitudinal
electric field and said break to thereby attract said free
electrons.
2. The device of claim 1, wherein said thin film has a thickness of
approximately 1 micron.
3. The device of claim 2, wherein said means for generating an
electric field having a direction normal to the direction of said
longitudinal field and said break, comprises:
a source of high positive electric potential, and
an anode coupled to said source.
4. The device of claim 3, wherein said means for establishing a
longitudinal electric field is variable to thereby control the
emission of said free electrons.
5. In a vacuum tube, a room temperature electron emitter,
comprising:
an electrically insulating substrate;
a thin film of semiconductive material deposited onto said
substrate, said thin film having a uniform break entirely across
and substantially parallel to one side thereof; and
means electrically coupled to said thin film for establishing a
longitudinal electric field therein in a direction normal to said
break.
6. The device of claim 5, wherein said thin film has a thickness of
approximately 1 micron.
7. The device of claim 6, wherein said means for establishing a
longitudinal electric field is variable to thereby control the
emission of said free electrons.
8. A cold-cathode vacuum tube, comprising:
an enclosure defining a space containing a vacuum;
means mounted within said space for providing emission of free
electrons at room temperatures, said means including:
an electrically insulating substrate,
a plurality of noncontiguous droplets of semiconductive material
deposited onto said substrate at random,
a plurality of noncontiguous droplets of metal deposited onto said
substrate at random and in contact with said semiconductive
material;
means electrically coupled to said substrate for establishing a
longitudinal electric field thereacross; and
means mounted within said space for generating an electric field
having a direction normal to the direction of said longitudinal
electric field to thereby attract said free electrons away from
said electron emission providing means.
9. The device of claim 8, wherein said means for generating an
electric field having a direction normal to the direction of said
longitudinal field, comprises:
a source of high positive electrical potential, and
superconducting
anode coupled to said source.
10. The device of claim 9, wherein said means for establishing a
longitudinal electric field is variable to thereby control the
emission of said free electrons.
11. In a vacuum tube, a room temperature electron emitter,
comprising:
an electrically insulating substrate;
a plurality of noncontiguous droplets of semiconductive material
deposited onto said substrate at random,
a plurality of noncontiguous droplets of metal deposited onto said
substrate at random, said metal droplets in contact with said
semiconductive material; and
means electrically coupled to said substrate for establishing a
longitudinal electric field thereacross.
12. The device of claim 11, wherein said means for establishing a
longitudinal electric field is variable to thereby control the
emission of said free electrons.
Description
STATEMENT OF GOVERNMENT INTEREST
The invention described herein may be manufactured and used by or
for the Government of the United States of America for governmental
purposes without the payment of an royalties thereon or
therefor.
BACKGROUND OF THE INVENTION
The present invention relates generally to vacuum tube devices and
more particularly to room temperature electron emission vacuum
tubes which require no filament and no filament power.
Those concerned with the development of effective room temperature
electron devices have long recognized the need for a practical
vacuum device which produces controllable electron emission Such a
device eliminates the necessity for filament heat and simplifies
the circuitry of any system by obviating the need for a filament
power supply.
Technology has heretofore provided numerous devices for the
generation of room temperature emission, but they all have serious
limitations in either their construction or operation which renders
them highly unsatisfactory for use as practical design tools. For
example, an ultra-light vacuum is necessary for many known devices,
while other tubes require elaborate schemes to effectuate normal
grid control.
SUMMARY OF THE INVENTION
The general purpose of this invention is to provide a room
temperature electron emission vacuum tube which embraces all the
advantages of similarly employed prior art devices and possesses
none of the aforedescribed disadvantages.
It is accordingly one object of the present invention to provide
practical room temperature electron emission vacuum tube
devices.
One further object is the provision of a vacuum tube device having
general utility and requiring no filament power supply.
A still further object is the provision of a vacuum tube having no
filament and being easy to construct.
The invention can be summarized as an electrical device comprising
a vacuum enclosure containing an anode having a high voltage
potential with respect to ground mounted within the enclosure and a
cathode mounted within the enclosure in proximity with the anode.
The cathode comprises an electrically insulating substrate material
upon which is affixed at least two terminals. In one embodiment, a
noncontiguous thin film of semiconductive and metallic material is
deposited at random in small droplets onto the substrate between
the terminals to provide electron emission when a potential
difference is applied thereacross. A second embodiment includes a
thin film of semiconductive material deposited onto a substrate and
having a break therein to thereby produce electron emission.
One advantage of the invention is its ease of construction. In
addition, the present device provides effective electron emission
and, accordingly, improves the operation of electronic display
devices, photocathode night-vision tubes, and the like.
Other objects, advantages, and novel features of the invention will
become more fully apparent from the following detailed description
of the invention when considered in conjunction with the
accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 illustrates a sectional view of the invention;
FIG. 2A shows a plan view of one embodiment of the electron emitter
used in the device of FIG. 1;
FIG. 2B shows a cross-sectional view of the electron emitter taken
along line 2B--2B of FIG. 2A looking in the direction of the
arrows;
FIG. 3A shows a plan view of a second embodiment of the electron
emitter used in the device if FIG. 1; and
FIG. 3B shows a cross-sectional view of the electron emitter taken
on line 3B--3B of FIG. 3A looking in the direction of the
arrows;
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, there is illustrated in FIG. 1 a
vacuum enclosure 10 which can be constructed from any suitable
material, such as glass. The interior of enclosure 10 is maintained
at a low vacuum and contains an anode element 12 and a cathode
element 14, to be described more fully below. The anode is coupled
via lead 16 to a source of high positive electric potential 18. The
other end of source 18 is coupled to a common reference point 20
which is further coupled to one electrode 22 of cathode 14 via lead
24. The other electrode 26 of cathode 14 is coupled via lead 28 to
variable source 30 to complete the circuit.
One embodiment of the cathode 14 used in the device of FIG. 1 is
shown in FIGS. 2A and 2B. In this embodiment, the two electrodes 22
and 26 are affixed to a substrate 32 which may be glass or any
other desired material. The electrodes 22 an 26 may be mechanically
attached to the substrate 32 or may be deposited thereon by vacuum
deposition techniques. Deposited between the electrodes 22 and 26
onto the substrate 32 is a thin continuous film of semiconductive
material 34 having a thickness of approximately one micron. Any of
various well known semiconductive material can be employed such as
silicon, germanium gallium, arsenide, titanium hydride, zirconium
hydride, the oxides of alkaline earth metals, etc. By establishing
a high electric field across the cathode during its fabrication, a
fairly uniform break 35 is produced in the semiconductor film. This
break greatly increases the electrical impedance of the cathode and
produces a number of microplasmas upon the application of a low
potential across the substrate. The potential necessary to maintain
these microplasmas is only a few volts, as compared to the high
potential required by the conventional devices, which obviates the
necessity for complex heat dissipation schemes. The microplasmas
are theorized as being gaseous discharges and produce a large
number of free electrons.
A second embodiment of cathode 14 is shown in FIGS. 3A and 3B. This
cathode is identical to the cathode shown in FIGS. 2A and 2B except
that a metallic material as well as a semiconductive material are
deposited in small droplets 36 onto the surface of the substrate
32. Droplets 36 are deposited in a random fashion such that they
form a noncontiguous thin film, covering the exposed surface of the
substrate between electrodes 22 and 26. By depositing in turn both
semiconductive and metallic droplets in a random fashion onto the
substrate surface, a large number of effective semiconductor to
metal junctions are formed for electron emission. Such junctions
are known to provide barrier layers having correspondingly high
fields; however, they have heretofore been impractical due to the
difficulty experienced in manufacture. It has been found that
effective results can be obtained by the random deposited droplet
embodiment of the present invention at a substantial savings.
The theory behind the operation of the present invention will now
be explained In the semiconductor-metal droplet embodiment, the
primary source of electron emission due to the formation of a large
number of small semiconductor-to-metal junctions. By depositing in
turn both semiconductor and metal droplets in large numbers, many
of the semiconductor droplets will form adjacent to metal droplets
at the precise spacing necessary to establish
semiconductor-to-metal junction emission. It is further theorized
that the junctions formed by the adjacent semiconductor-metal
droplet pairs are more accurately categorized as being transverse
field semiconductor-to-metal junction emitters. This is because the
plane of the droplet junction is believed to exist perpendicular to
the emissive surface. It is noted that in conventional transverse
junction emitters, which have been limited to p-n junction types by
the difficult construction problems involved, the emission is
considered to be inefficient since only the portion of the diode
current flowing very close to the surface is of use. In the present
invention, however, efficient transverse field emission is provided
since the circulating current flow is confined to the surface
region of the emitters, and a large number of emitters are provided
by the random deposition of droplets. The efficiency of the device
is further improved by the fact that those metal and semiconductor
droplets which do not form semiconductor-to-metal junctions provide
tunneling emission as well as hot electron emission, the theory of
which is well known in the art. Thus, the unique and highly
simplified construction of the semiconductor-metal droplet
embodiment of the present invention provides cold electron emission
by a combination of at least three different physical
phenomena.
In the second embodiment, the emission produced by the cathode is
due to a combination of hot electron emission and gaseous discharge
emission. This particular embodiment contains a fairly uniform
break in the semiconductor film across its smaller dimension. When
a small field is set up by source 30, many small discharges or
microplasmas are established to produce electron emission. It is
noted that only a small electric field is necessary to maintain the
plasma discharge; this is substantially reduces many problems
encountered in prior art devices, especially those relating to
substrate temperature and electrical breakdown.
In operation, when variable source 30 in FIG. 1 is applied across
the cathode 14, free electrons are produced on the surface of the
cathode as explained above. These free electrons are attracted to
the anode because of the high positive charge produced thereon by
source 18. This flow of electrons from the cathode to the anode
establishes a current path across the tube as in conventional
filament devices. The current flow produced by the device has many
uses; for example, it can be utilized to provide electrical display
of information by employing an anode which produces light when
struck by electrons. Furthermore, the flow can be effectively
controlled by a grid or by the potential source 30 to thereby
permit efficient use of the invention as the active element in
amplifiers, oscillators, and the like.
Thus, two simple and effective vacuum tube devices are provided
which produce electron emission at room temperatures. The devices
produce controllable electron emission and can be manufactured with
relative ease.
It should be understood, of course, that the foregoing disclosure
relates to only the preferred embodiments of the invention and that
numerous modifications or alterations may be made thereto in light
of the above teachings.
* * * * *