U.S. patent number RE38,223 [Application Number 09/504,635] was granted by the patent office on 2003-08-19 for field emission cathode having an electrically conducting material shaped of a narrow rod or knife edge.
This patent grant is currently assigned to Till Keesmann. Invention is credited to Hubert Grosse-Wilde, Till Keesmann.
United States Patent |
RE38,223 |
Keesmann , et al. |
August 19, 2003 |
Field emission cathode having an electrically conducting material
shaped of a narrow rod or knife edge
Abstract
A field emission cathode device consisting of an electrically
conducting material and with a narrow, rod-shaped geometry or a
knife edge, to achieve a high amplification of the electric field
strength is characterized in that the electron-emitting part of the
field emission cathode at least partly has preferred cylindrical
host molecules and/or compounds with host compounds and/or
cylindrical atomic networks, possibly with end caps with diameters
measuring in the nanometer range.
Inventors: |
Keesmann; Till (69115
Heidelberg, DE), Grosse-Wilde; Hubert (Neunkirchen,
DE) |
Assignee: |
Keesmann; Till
(DE)
|
Family
ID: |
6510961 |
Appl.
No.: |
09/504,635 |
Filed: |
February 15, 2000 |
PCT
Filed: |
February 22, 1995 |
PCT No.: |
PCT/DE95/00221 |
PCT
Pub. No.: |
WO95/23424 |
PCT
Pub. Date: |
August 31, 1995 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
702684 |
Aug 23, 1996 |
05773921 |
Jun 30, 1998 |
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Foreign Application Priority Data
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Feb 23, 1994 [DE] |
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44 05 768 |
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Current U.S.
Class: |
313/309; 313/336;
313/351; 977/750; 977/752; 977/788; 977/939 |
Current CPC
Class: |
H01J
1/3042 (20130101); B82Y 10/00 (20130101); H01J
2201/30423 (20130101); H01J 2201/30469 (20130101); Y10S
977/939 (20130101); Y10S 977/876 (20130101) |
Current International
Class: |
H01J
1/304 (20060101); H01J 1/30 (20060101); H01J
001/05 (); H01J 001/304 (); H01J 019/24 () |
Field of
Search: |
;313/309,336,351,495,496,497 ;445/50,51 |
References Cited
[Referenced By]
U.S. Patent Documents
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5089742 |
February 1992 |
Kirkpatrick et al. |
5138220 |
August 1992 |
Kirkpatrick |
5449970 |
September 1995 |
Kumar et al. |
5495143 |
February 1996 |
Lengyel et al. |
|
Other References
Ajayan et al., Nature, 361:333-334, Jan. 1993.* .
Kirkpatrick et al., Applied Physics Latters, 60:1556-1558, Mar.
1992.* .
Lin et al., Physics Review, 47:7546-7553, Mar. 1993.* .
Saito et al., Materials Science and Engineering, B19:185-191, 1993.
(no month).* .
IBM Technical Disclosure Bulletin, 35:410-411, Dec. 1992.* .
Iijima, Helical Microtubules of Graphite Carbon, Nature, 354 (Nov.
7, 1991), pp 56-58.* .
Iijima et al., Single-Shell Carbon Nanotubes of 1-nm diameter,
Nature, 363 (Jun. 17, 1993), pp 603-605.* .
Iijima, Growth of Carbon Nanotubes, Materials Science and
Engineering, (1993), pp. 172-180.* .
Jose-Yacaman et al., Catalytic Growtth of Carbon Microtubules with
Fullerene Structure, Applied Physics Letters, 62, No. 6 (Feb. 8,
1993) pp 657-659.* .
Ge et al., Vapor-Condensation Generation and STM Analysis of
Fullerence Tubes, Science 260 (Apr. 23, 1993), pp 515-518.* .
Kosakovskaya et al., Nanofilament Carbon Structure, JETP Letters,
56 (Jul.-Dec. 1992), pp 26-30.* .
Knife-Edge Thin Film Field Emission Cathodes on (110) Silicon
Wafers, PP 644-647, by Elliott et al., Jul. 1993.* .
Heinrich, et al., Energy Distribution of Post-Accelerated Electrons
Field-Emitted from Carbon Fibres, Applied Physics 12, pp 197-202
(1977, no month)..
|
Primary Examiner: Day; Michael H.
Attorney, Agent or Firm: Winstead Sechrest & Minick
P.C.
Claims
What is claimed is:
1. A field emission cathode which consists of an electrically
conducting material having the shape of a narrow rod or a knife
edge to achieve high magnification of the electric field strength,
such that the electron-emitting part of the field emission cathode
has cylindrical molecules formed at least in part as single-shell
or multiple-shell carbon nano-cylinders.
2. The device of claim 1, wherein the carbon nano-cylinders have
end caps.
3. The device of claim 1, wherein the single- or multiple-shell
carbon nano-cylinders are collected into bundles.
4. The device of claim 1, wherein the carbon nano-cylinders are
filled with metal.
5. The device of claim 1, wherein the carbon nano-cylinders at
least partly have endohedral or exohedral compounds with other
atoms or molecules.
6. The device of claim 1, wherein the field emission cathode forms
the tip of a field electron microscope, a field ion microscope, a
scanning tunnel microscope, or a scanning power microscope.
7. The device of claim 1, wherein a plurality of similar field
emission cathodes is disposed in a line or a plane, and thereby
forms a linear or planar electron source.
8. The device of claim 1, wherein a plurality of similar field
emission cathodes is disposed in a plane in the form of a matrix,
and the field emission cathodes can be driven individually, and the
field emission cathodes represent the electron sources for the
image points of a visual display system.
9. The device of claim 8, wherein the plurality of similar field
emission cathodes is in the range of 10,000 to 100,000
molecules..Iadd.
10. A field emission cathode comprising an electron-emitting part
which is formed at least in part as a carbon nano-cylinder, wherein
the carbon nano-cylinder serves as a coating over a cathode tip
structure..Iaddend..Iadd.
11. A field emission cathode comprising: a substrate; a conducting
material deposited over the substrate; and a carbon nano-cylinder
deposited over the conducting material..Iaddend..Iadd.
12. The field emission cathode of claim 11, wherein the carbon
nano-cylinder comprises a single-walled carbon
nano-cylinder..Iaddend..Iadd.
13. The field emission cathode of claim 11, wherein the carbon
nano-cylinder comprises a multi-walled carbon
nano-cylinder..Iaddend..Iadd.
14. The field emission cathode of claim 11, wherein the carbon
nano-cylinder at its end cap is open..Iaddend..Iadd.
15. The field emission cathode of claim 11, wherein the conducting
material is in a form of a cone..Iaddend..Iadd.
16. The field emission cathode of claim 11, further comprising: a
catalyst material deposited on the conducting material..Iaddend.
Description
The invention relates to a field emission cathode device of an
electrically conducting material and with a narrow, rod-shaped
geometry or a knife edge to achieve high amplification of the
electric field strength, such that the electron-emitting part of
the field emission cathode has cylindrical molecules. The invention
also relates to a method for producing such a field emission
cathode device.
Field emission means the emission of electrons from the surface of
an electric conductor under the action of an electric field
exceeding 10.sub.9 V/m. In practice, such field strengths are
realized at sharp edges or tips, where the field strength is
amplified. High vacuum is necessary to avoid gas discharges.
DESCRIPTION OF THE PRIOR ART
Field emission cathodes are used, for example, in field electron
microscopes, in electron accelerators, in high-power switches (OS
DE 39 24 745 A1) and in field emission diodes and field emitter
arrays for vacuum microelectronics (thus for example Busta, Vacuum
microelectronics--1992, Journal of Micromechanics and
Microengineering, 2 (1992), pp. 53-60, and Iannazzo, A survey of
the present status of vacuum microelectronics, Solid State
Electronics, 36 (1993), pp. 301 to 320). A tungsten wire can be
used as the field emission cathode, whose tip becomes so fine by
etching that it can no longer be seen in an optical microscope.
Also by etching, the ends of carbon fibers can be made sufficiently
fine (Heinrich, Essig, Geiger, Appl. Phys. (1977) 12, pp. 197-202)
to serve as a field emission cathode.
In vacuum microelectronics, field emission cathodes generally are
produced by the methods of microprocess technology, by etching and
sputtering, using lithographically produced masks (see Busta,
Vacuum microelectronics--1992, Journal of Micromechanics and
Microengineering, 2 (1992), pp. 53-60). By this method, one can
produce conical tips with a radius of curvature of a few nm or
wedge-shaped cutting edges with comparable radii of curvature. As
materials for the cathode, one can use, for example, molybdenum,
lanthanum hexaboride, hafnium, diamond-like carbon (B. C. Djubua,
N. N. Chubun, Emission properties of Spindt-type cold cathodes with
different emission cone material, IEEE Transactions on Electron
Devices, 38 (1991) No. 10, pp. 2314-2316).
A disadvantage in the use of tips and edges, which have been
produced by the known methods, is that the electron stream declines
with operating time, since the tips or edges are destroyed by the
positive ions of the unavoidable residual gas in the system. The
like applies to field emission cathodes which are produced by
sputtering techniques. The reason for this primarily is that the
material structure of the emission tips is not uniquely defined.
Thus, the geometry and microstructure of the tip and thus the work
function of the electrons can vary within such wide limits that the
electron streams from several tips, which were produced in one
process, can differ by orders of magnitude, and furthermore change
with operating time.
Furthermore, field emission cathodes for vacuum microelectronics
cannot be produced in their optimal geometry by the prior art.
Field strength calculations for various geometries of the tips show
that the best shape of a field emission cathode is a narrow rod
(Utsumi, Vacuum microelectronics: What's new and exciting, IEEE
Transactions on Electron Devices 38 (1991), pp. 2276-2283). The
present methods of microstructure technology can produce at most
wedge-shaped tips in a defined manner.
Carbon nano-cylinders were observed for the first time in an
electron microscope by Iijima (Nature, 354 (1991), p. 56). They can
now be produced in large quantities, for example at the cathode of
a visible arc (Iijima, Materials Science and Engineering, B19
(1993), pp. 172-180). In the presence of iron or cobalt, one can
produce single-shell carbon nano-cylinders. Theoretical
calculations show that, depending on the helicity of the hexagonal
ring structure, the walls of the carbon nano-cylinders are
electrically conducting or semiconducting (Saito, Fujita,
Dresselhaus, Dresselhaus, Materials Science and Engineering, B19
(1993), pp. 185-191). The carbon nano-cylinders can also be filled
with metals, for example with lead. Other methods for producing
carbon nano-cylinders are described in the literature:
Carbon nano-cylinders can be produced by the catalytic
decomposition of acetylene through iron particles at about
700.degree. C. (Jose-Yacaman, Miki-Yoshida, Rendon, Applied Physics
Letters 62 (6) 1993, pp. 657-659).
In the presence of methane, argon, and iron vapor, single-shell
carbon nano-cylinders can be found in the carbon deposit on the
chamber walls of a visible arc apparatus (Iijima, Nature 363
(1993), pp. 603-605).
By sputtering a carbon film in high vacuum, multiple-shell carbon
nano-cylinders can be deposited on a graphite surface (Ge, Sattler,
Science 260 (1993), pp. 515-518).
By sputtering ultra-pure graphite with electron beams in vacuum,
carbon nano-cylinders can be produced on substrates consisting of
various materials, such that the carbon nano-cylinders are aligned
in the direction of the vapor jet (Kosakovskaya et al., JETP Lett.,
56 (1992), p. 26).
In addition to the carbon nano-cylinders, disordered carbon
particles generally are also deposited on the substrate. These can
be removed, for example, by treatment in an oxidizing atmosphere at
an elevated temperature up to 500.degree. C., preferably
400.degree. C. The carbon nano-cylinders at the end caps can be
opened in a similar manner in an oxidizing atmosphere (air,
CO.sub.2, or pure oxygen). This offers the possibility of filling
the carbon nano-cylinders with metals, as described for a filling
with lead by Ajayan and Iijima in Nature 361, p. 333.
In principle, it is possible to fasten these carbon nano-cylinders,
produced by one of the above methods, on a suitable substrate, by
means of micro-manipulators, and thus to produce a field emission
cathode. However, this method is impractical, and in particular is
not suited for field electron arrays with many cathode tips, as is
desired in vacuum microelectronics.
Field emission cathodes with emission tips of biomolecular
microstructures or a metal-semiconductor-eutectic are known from
the U.S. Pat. No. 5,138,220. The diameter of these structures
measures in the micrometer range, and subsequent metallization is
necessary to achieve adequate emission.
The publication IBM Technical Disclosure Bulletin, Vol. 35, No. 7,
December 1992, pp. 410-411 describes the use of Buckminster
fullerene molecules as the tip of scanning-probe microscopes.
Besides spherical C.sub.60 molecules, derivatives of C.sub.60 - and
hetero-fullerenes are mentioned, that is host molecules in which
individual C-atoms have been substituted by boron or nitrogen.
BRIEF SUMMARY OF THE INVENTION
The present invention is based on the object or on the technical
problem of specifying a field emission cathode which avoids the
disadvantages of the prior art, assures high emission quality,
makes possible a longer lifetime, and in particular resists
bombardment with residual gas ions. Furthermore, the present
invention is based on the object or on the technical problem of
specifying a method for producing a field emission cathode of the
type mentioned in the introduction, so as to assure technically
optimal manufacture together with economy.
The inventive field emission cathode device consists of an
electrically conducting material and having the shape of a narrow
rod or a knife edge to achieve high magnification of the electric
field strength, such that the electron emitting part of the field
emission cathode has cylindrical molecules, wherein the cylindrical
molecules are formed at least in part as single-shell or
multiple-shell carbon nano-cylinders. The inventive method for
producing the field emission cathode device with carbon
non-cylinders which have been expanded during the gas phase.
Advantageous modifications and developments are the subject of the
subclaims.
An especially preferred design of the inventive field emission
cathode is characterized in that carbon nano-cylinders are used as
field emission cathodes. Single-shell carbon nano-cylinders with a
diameter of about 1 nanometer and a length greater than 1
micrometer, or also multiple-shell ones with a diameter up to
several nanometers can be produced. Bundles of single-shell carbon
nano-cylinders with diameters of about 5 nanometers can also be
produced. The walls of the carbon nano-cylinders consist of carbon
atoms in a hexagonal pattern, while the end caps additionally
contain 5-ring structures. The individual carbon atoms of the
carbon nano-cylinders are strongly bound chemically, as a result of
which the carbon nano-cylinders have extremely great mechanical
strength. This also results in their high sputtering strength in
comparison to randomly grown tips, which are sputtered according to
the prior art.
Using well-known carbon nano-cylinders as a field emission cathode
thus combines the advantage of optimal geometry with high strength,
thus assuring that the emission properties of such field emission
cathodes will not change during their operation, in contrast to
previously used cathode tips.
So that the above advantages of the carbon nano-cylinders can also
be used for making the field emission cathode arrays of vacuum
microelectronics, the known methods for producing such arrays must
be modified according to the invention, in such a way that the
carbon nano-cylinders grow on appropriately prepared locations of a
substrate.
The production method can be used to produce either individual
field emission cathodes or also field emission cathode arrays.
Further embodiments and advantages of the invention derive from the
other characteristics cited in the claims, and from the embodiments
given below. The characteristics of the inventions can be combined
with one another in arbitrary fashion, unless they obviously
exclude one another.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention as well as advantageous embodiments and developments
thereof are described and elucidated in more detail below in terms
of the examples shown in the drawings. The features contained in
the description and in the drawings can be used inventively
individually by themselves or in various combinations.
FIG. 1 shows an individual field emission element of a field
emitter array, such as can be produced by the prior art.
FIG. 2 shows the same element in accordance with the first
inventive process step, so as to provide the emission tip with
carbon nano-cylinders.
FIG. 3 shows the same element after carbon has been sputtered.
FIG. 4 shows the same element after the last process step, in its
final state.
FIG. 5 shows a section of a field emitter array with individually
actuatable emission tips.
FIG. 6 shows the cross section of a graphite wafer with a knife
edge.
FIG. 7 shows in cross section a prepared block of ten graphite
wafers with a clamping fixture for sputtering carbon
nano-cylinders.
FIG. 8 shows a diode for the power pulse technique with an
inventively prepared field emission cathode.
DETAILED DESCRIPTION OF THE INVENTION
Below it will be explained, by way of an example, how field
emission cathodes of carbon nano-cylinders can be produced, such as
can be used, for example, as cathodes for diodes or switches. By
way of a second example, it will be explained how field emission
cathodes for a field emitter array can be produced by the methods
of microstructure technology.
Example: Production of individual cathodes on a knife edge
Square graphite wafers about 1 cm (centimeter) on a side, and 1 mm
(millimeter) thick are ground or etched to a knife edge on one
side. FIG. 6 shows such a graphite wafer 100 with a knife edge 101,
beveled on one side. FIG. 7 shows how ten of these graphite wafers
100a to 100j are collected together into a block in a clamping
fixture 103, in such a way that the knife edges 101a to 101j on one
side of the block lie in one plane and an aluminum foil or Teflon
foil is situated between each of the graphite wafers as a spacer
102a to 102j. The clamping fixture consists of two brass blocks,
into which recesses have been milled to receive the ten graphite
wafers with their spacer foils. These blocks are screwed together
by two screws 104.
The prepared block is installed in a vacuum apparatus, in which a
target of ultra-pure graphite is sputtered with an electron beam.
The graphite target and the block are arranged here in such a way
that the carbon vapor strikes the plane of the graphite knife edges
perpendicularly. Under these conditions, carbon nano-cylinders grow
on the knife edges individually and in bundles of several
cylinders, in the direction of the carbon vapor beam. When a layer
several tenths of a micrometer thick has been reached, the
sputtering process is terminated.
The knife edges and the beveled surfaces of the graphite wafers are
now coated with carbon nano-cylinders, which have extremely high
mechanical strength. The microstructure of the surface is
characterized by cylindrical elevations with sharp tips which have
a radius of curvature of a few nanometers.
FIG. 8 shows how a graphite wafer prepared in this manner can be
used in a diode that operates as a switching element. An anode 112
with a large surface and a cathode pin 111 are fused in an
evacuated glass flask 110. The graphite wafer 100 with its knife
edge 101 is fastened on the cathode pin in such a way that it is
situated opposite the anode at a distance of about 1 mm. If a
sufficiently high negative voltage is applied to the cathode, an
electrical current can flow through the diode.
In the same manner, several knife edges instead of a single knife
edge can be used as a cathode.
These knife edges are characterized in that, in contrast to knife
edges without carbon nano-cylinders, they amplify the electric
field much more. A consequence of this is that, given the same
voltage, the field emission current is much greater. Furthermore,
the emission tips are not already destroyed after a brief operating
time by the ions of the residual gas.
The production method described above can easily be transferred to
a rather large number of graphite wafers with longer knife edges.
Also, the edge angle and the spacing between the knife edges can be
varied within broad limits. This therefore represents a field
emission cathode whose electron-emitting surface and current
density can be adapted to many applications, for example in power
pulse technology.
Example: Production of field emission cathodes as an array
First, an array of field emitter cathodes and gate electrodes of
molybdenum will be produced on a doped silicon substrate, in
accordance with a previously known method, and specifically by the
methods of silicon processing technology, as is described, for
example, in the article, Spindt et al., J. Appl. Physics 47 (1976),
p. 5248ff (see also Busta loc. cit. and Iannazzo loc. cit.). FIG. 1
shows a field emitter cathode with a gate electrode. Reference No.
10 designates the electrically conducting, n-doped silicon
substrate, 11 designates a sputtered insulating layer about 2 .mu.m
thick and consisting of SiO.sub.2. Reference No. 12 designates the
sputtered molybdenum gate electrode, about 0.5 .mu.m thick.
Reference No. 13 designates the tip-shaped field emission cathode
of molybdenum. The gate openings 14 of the molybdenum layer are
preferably chosen to lie between 0.4 and 0.8 .mu.m. By means of the
above-cited production method, one thus achieves the result that
the cathode cone tips lie about 0.5 .mu.m below the gate
electrodes.
In a following process step, a sacrificial layer of aluminum is
applied to the field emitter array which, in this form, already
corresponds to the prior art. This is done by rotating the
substrate perpendicular to the surface and sputtering it with
aluminum at slant incidence. This type of sputtering prevents the
aluminum from depositing in the cathode openings. FIG. 2 shows a
field emitter element produced in accordance with this process
step; the aluminum sacrificial layer is designated by 20.
In a subsequent process step, the graphite target disposed above
the field emitter array is sputtered by an electron beam, and the
carbon is deposited on the field emitter array. A portion of the
carbon atomic beam penetrates through the gate opening and deposits
on the cathode tips. As is known from a publication by Kosakovskaya
et al., JETP Lett., 56 (1992) 26, cylindrical, parallel graphite
fibers thus form in the direction of the incident atomic beam. The
growth process is improved if, during this process step, a voltage
U.sub.G of the order of 50 V is applied between the cathode and
gate layer. The average field strength is then of the order of 50
V/0.5 .mu.m=10.sup.8 V/m; because the field strength is amplified
at the tip, it there rises to over about 10.sup.9 V/m. The high
field strength at the fiber tip evidently causes the fiber ends to
remain open and improves the growth of the fibers (Smalley, loc.
cit. p. 4). FIG. 3 shows a field emitter element made in accordance
with this process step. Here, 30 designates the deposited carbon
layer on the gate electrode, and 31 designates one or more carbon
nano-cylinders on the molybdenum tip. The voltage source to create
the field strength at the cathode tip is also shown
schematically.
The growth of the carbon nano-cylinders can be controlled through
the emission current Ic. The longer the grown carbon
nano-cylinders, the stronger becomes the emission current. The
process must be terminated at the proper time, when the carbon
nano-cylinders have reached a length of several tenths of a .mu.m.
It is here advantageous to modulate the gate voltage V.sub.G
slightly. The quotient dIc/dU.sub.G is designated as the
differential slope and can be used as a measure of the quality of
the field emitter array.
In a last step, the carbon layer with the aluminum sacrificial
layer is etched off, so that, after this step, the field emitter
element looks as shown in FIG. 4.
In a modification of the production process described above,
instead of producing the cathodes so as to be electrically
connected in their totality and lying at the same potential, they
can also be produced in such a way that only one row of them is
electrically coupled together. In the same manner, the gate
electrodes can be produced in such a way that only one row of them
is electrically coupled together, although perpendicular to the
direction of the row of cathodes that are connected together. This
then offers the possibility of driving each cathode individually.
This type of circuit is already known and is used, for example, for
a screen with digitally actuatable image points, from LETI Company
(described in Busta loc. cit., pp. 69-70). This circuit, for the
case of three rows of cathodes and three rows of gates, is shown
schematically, in a top view, in FIG. 5. Electrically conducting
cathode tracks K1, K2, and K3, for example consisting of n-doped
silicon, are applied on a substrate with an electrically
non-conducting surface 1, along a width of a few micrometers. The
following insulating layer of silicon dioxide (not shown), about 2
micrometers thick, corresponds to the arrangement described by
Spindt. The gate electrodes G1, G2, and G3 are applied in strips
just like the cathodes, but perpendicular to the direction of the
cathode tracks. The further process steps correspond to the steps
used to produce the field emitter cathodes that cannot be
individually actuated.
The center electrode of the last column in FIG. 5 can now be driven
in such a way, for example, that a negative voltage is applied to
the cathode strips K2 and a negative voltage is applied to the gate
strips G3; a field emission current will then flow from this
electrode, which can be measured in the cathode or gate circuit or
which can be detected by a suction anode, which is not shown
here.
In the production method described here, this arrangement of the
cathode strips and gate strips can be used to control specifically
the production process of each individual cathode. It is then
possible to measure the emission current from each field emitter
tip during the production process, and not merely the total amount
from the entire field emitter array. By turning off the voltage at
one field emission cathode, one can favor the formation of an end
cap with 5-ring structures, so that no further growth will
occur.
It is advantageous for the formation of carbon nano-cylinders to
form them at elevated temperatures of 100.degree. to 700.degree. C.
(degrees Celsius), preferably 300.degree.-400.degree. C.
It is also advantageous to apply a layer of iron or cobalt, a few
atomic layers thick, on the molybdenum cathode tips before
sputtering on the carbon. The iron and cobalt evidently have a
positive catalytic effect on the formation of carbon
nano-cylinders.
As a modification of the invention, one can also dispense with the
advantage of the narrow, cylindrical shape of the carbon
nano-cylinders and utilize only the advantage of the high
mechanical stability of host molecules, that is their resistance to
the bombardment of the cathode by positive residual gas ions. In
this case, cathodes produced conventionally--by sputtering in
vacuum by the methods of microstructure technology or by etching,
are coated with electrically conducting host molecules. The host
molecules can be fullerenes, hetero-fullerenes, or their
derivatives, especially also endohedral or exohedral compounds, for
example, of the type M.sub.3 C.sub.60 or M.sub.3 C.sub.70, where M
designates a metal, preferably the alkali metals potassium or
sodium. The host molecules can also be applied to the cathode in
crystalline form, for example C.sub.60 in the form of
fullerite.
The field emission cathodes, whose resistivity and emission
properties have been improved by coating them with carbon
nano-cylinders or also with fullerenes and their derivatives, in
molecular or crystalline form, can be used wherever thermionic
cathodes in vacuum were used previously, and in all applications of
vacuum microelectronics. Typical fields of application will be
listed below, without this listing being exhaustive, and a person
skilled in the art can easily transfer the inventive field emission
cathode to similar applications.
Single emitter tips, emitter edges, or emitter arrays can be used
as electron sources for X-ray tubes, X-ray tubes with planar,
drivable cathodes, for example for computer tomography, electron
beam lithography, miniature electron microscopes, power switching
tubes, diodes or triodes, logic circuit elements, video
screens.
Field emission cathodes can be used in miniaturized electronic
components, such as ultra-high frequency diodes, ultra-high
frequency triodes, diodes and triodes in combination with
semiconductor components, temperature-stable diodes and triodes in
the engines of motor vehicles, temperature-stable logic components,
electronic components with diode and triode functions, which are
particularly resistant to electromagnetic interference and ionizing
radiation, pressure sensors, in which the cathode gate distance is
influenced by the pressure, microwave generators and
amplifiers.
As arrays, field emission cathodes can be used preferably as
electron sources with a large surface, yielding a high current
density, drivable electron sources for planar video screens with a
high light density in monochromatic or color designs.
* * * * *