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.
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0. 10. A field emission cathode comprising an electron-emitting part of the cathode formed at least in part as a carbon nano-cylinder.
0. 15. A field emission apparatus comprising:
a substrate; a carbon nanotube deposited over the substrate; and an electrode operable for creating an electric field in order to promote an emission of electrons from the carbon nanotube.
0. 23. A field emission apparatus, comprising:
a substrate; and one or more electron emitter structures comprising a carbon nano-cylinder deposited on a growth surface over the substrate, wherein the carbon nano-cylinder is grown catalytically in situ on the growth surface from a carbon-containing precursor material.
0. 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.
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0. 11. The field emission cathode of
0. 12. The field emission cathode of
0. 13. The field emission cathode of
0. 14. The field emission cathode of
0. 16. The field emission apparatus of
0. 17. The field emission apparatus of
0. 18. The field emission apparatus of
0. 19. The field emission cathode of
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0. 21. The field emission apparatus of
0. 22. The field emission cathode of
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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.
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.
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.).
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.
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 UG 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 μm-108 V/m; because the field strength is amplified at the tip, it there rises to over about 109 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).
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 μm. It is here advantageous to modulate the gate voltage UG slightly. The quotient dIc/dUG 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
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°C to 700°C C. (degrees Celsius), preferably 300-400°C 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 M3C60 or M3C70, 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 C60 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.
Keesmann, Till, Grosse-Wilde, Hubert
| Patent | Priority | Assignee | Title |
| 10835199, | Feb 01 2016 | The University of North Carolina at Chapel Hill | Optical geometry calibration devices, systems, and related methods for three dimensional x-ray imaging |
| 10980494, | Oct 20 2014 | The University of North Carolina at Chapel Hill | Systems and related methods for stationary digital chest tomosynthesis (s-DCT) imaging |
| 11778717, | Jun 30 2020 | VEC Imaging GmbH & Co. KG; VAREX IMAGING CORPORATION; VEC IMAGING GMBH & CO KG | X-ray source with multiple grids |
| 6980627, | Oct 06 2000 | NURAY TECHNOLOGY CO , LTD | Devices and methods for producing multiple x-ray beams from multiple locations |
| 7082182, | Oct 06 2000 | UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL, THE | Computed tomography system for imaging of human and small animal |
| 7245692, | Apr 25 2005 | The University of North Carolina at Chapel Hill | X-ray imaging systems and methods using temporal digital signal processing for reducing noise and for obtaining multiple images simultaneously |
| 7359484, | Oct 06 2000 | NURAY TECHNOLOGY CO , LTD | Devices and methods for producing multiple x-ray beams from multiple locations |
| 7751528, | Jul 19 2007 | UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL, THE | Stationary x-ray digital breast tomosynthesis systems and related methods |
| 7839067, | Aug 10 2005 | PURERON JAPAN CO , LTD | Carbon film having shape suitable for field emission |
| 8155262, | Apr 25 2005 | The University of North Carolina at Chapel Hill; Xintek, Inc. | Methods, systems, and computer program products for multiplexing computed tomography |
| 8189893, | May 19 2006 | North Carolina State University | Methods, systems, and computer program products for binary multiplexing x-ray radiography |
| 8358739, | Sep 03 2010 | UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL, THE | Systems and methods for temporal multiplexing X-ray imaging |
| 8421330, | Aug 10 2005 | Pureron Japan Co., Ltd | Carbon film having shape suitable for field emission |
| 8600003, | Jan 16 2009 | UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL, THE | Compact microbeam radiation therapy systems and methods for cancer treatment and research |
| 8729787, | Dec 18 2006 | U S BANK NATIONAL ASSOCIATION, AS COLLATERAL AGENT | Field emission devices and methods for making the same |
| 8866068, | Dec 27 2012 | Schlumberger Technology Corporation | Ion source with cathode having an array of nano-sized projections |
| 8995608, | Jan 15 2010 | The University of North Carolina at Chapel Hill | Compact microbeam radiation therapy systems and methods for cancer treatment and research |
| 9099272, | Dec 18 2006 | U S BANK NATIONAL ASSOCIATION, AS COLLATERAL AGENT | Field emission devices and methods for making the same |
| 9782136, | Jun 17 2014 | XINVIVO, INC | Intraoral tomosynthesis systems, methods, and computer readable media for dental imaging |
| 9907520, | Jun 17 2014 | XINVIVO, INC | Digital tomosynthesis systems, methods, and computer readable media for intraoral dental tomosynthesis imaging |
| 9916960, | Dec 22 2014 | SIEMENS HEALTHINEERS AG | Device for producing an electron beam |
| Patent | Priority | Assignee | Title |
| 5089742, | Sep 28 1990 | UNITED STATES OF AMERICA, THE, AS REPRESENTED BY THE SECRETARY OF THE NAVY | Electron beam source formed with biologically derived tubule materials |
| 5138220, | Dec 05 1990 | Science Applications International Corporation | Field emission cathode of bio-molecular or semiconductor-metal eutectic composite microstructures |
| 5449970, | Mar 16 1992 | APPLIED NANOTECH HOLDINGS, INC | Diode structure flat panel display |
| 5495143, | Aug 12 1993 | Leidos, Inc | Gas discharge device having a field emitter array with microscopic emitter elements |
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