Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS3497929 A
Publication typeGrant
Publication dateMar 3, 1970
Filing dateNov 22, 1968
Priority dateMay 31, 1966
Publication numberUS 3497929 A, US 3497929A, US-A-3497929, US3497929 A, US3497929A
InventorsHeynick Louis N, Shoulders Kenneth R
Original AssigneeStanford Research Inst
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method of making a needle-type electron source
US 3497929 A
Images(1)
Previous page
Next page
Description  (OCR text may contain errors)

March 3, 1970' K. R. SHQL LDERS EI'AL 3,497,929

9 METHOD OF MAKING A NEEDLE TYPE ELECTRON SOURCE v Original Filed May 31. 1966 VAR\ABLE POTENTAL SOU RCE INVENTORS kswsm sh'ouwms Lou/5 N. HEYN/CK United States Patent 3,497,929 METHOD OF MAKING A NEEDLE-TYPE ELECTRON SOURCE Kenneth R. Shoulders, Woodside, and Louis N. Heynick,

Palo Alto, Calif., assignors to Stanford Research Institute, Menlo Park, Calif., a corporation of California Original application May 31, 1966, Ser. No. 553,832, now Patent No. 3,453,478, dated July 1, 1969. Divided and this application Nov. 22, 1968, Ser. No. 778,278

Int. Cl. P01j 17/00; H011 7/00 US. Cl. 2925.17 3 Claims ABSTRACT THE DISCLOSURE A multiple needle electron emitting source is provided comprising a conductive layer having spaced thereover a plurality of sharp raised points, and successively placed thereover, with holes therethrough to permit exposure of these needle points, an insulating surface and a conductive surface on top thereof, said conductive surface comprising an accelerator electrode.

This application is a division of application Ser. No. 553,832, filed May 31, 1966, now US. Patent 3,453,478, issued July 1, 1969, for Needle-Type Electron Source, by these inventors.

This invention relates to cold electron emitting structures and more particularly to improvements therein.

It is well known that electric fields on the order of several megavolts per centimeter can be used to produce electron emission from metals. In order to reduce the voltage required for producing such electron emission to a level more reasonable, such as on the order of kilovolts, sharp needles or points are used as emitters, a positive electrode is spaced from the emitter and a voltage is applied therebetween. Despite the high emission currentdensity capability of such field emission (on the order of a million amperes per centimeter squared), the total emission current from a needle emitter is low, because of the smallness of its emitting area. Furthermore, the electrons are emitted over a large solid angle, and they obtain almost the total energy of the applied voltage within a short distance from the emitter surface. Therefore, the formation of narrow electron beams that are suitable, for example, for use in high power beam type of electron tubes, requires elaborate and expensive focusing apparatus.

The operation of many needle emitters in parallel to increase the total current is feasible, but the problem of forming narrow beams of electrons from a plurality of needle emitters is extremely diflicult. Also, each needle, of a multiple needle cathode experiences partial electrostatic shielding by its neighbors, from the common, relatively distant positive electrode producing the field, to an extent dependent on the separation between the needles. Therefore, the field required to produce a given emission current from each needle is higher than that needed for an isolated needle of the same sharpness. Conversely, for a given applied voltage, this effect limits the possible packing density of multiple needle cathodes.

An object of this invention is the provision of a multiple needle cathode which permits the forming of narrow electron beams.

Another object of the present invention is the provision of a high packing density multiple needle cathode.

Still another object of the present invention is the provision of a novel, useful, multiple needle cathode assembly operable at relatively low voltages.

Yet another object of the present invention is the provision of a field emission cathode structure in which the ICC positive electrode can be used to control the emission, in the manner of a grid.

These and other objects of the invention are achieved by providing a construction for a multiple needle cathode which effectively comprises two closely spaced surfaces. On the first or emitter surface, a large number of sharp field emitting sites are distributed with a packing density limited only by the fabrication technology used. This surface can be planar or curved and of a size to suit the intended application. The second surface, also called the accelerator surface, is the electrode used to produce the field. It consists of a very thin foil or film of metal of the same contour as the surface with the emitter site, and is suitably supported and electrically insulated therefrom at spacings ranging from a fraction of a micron to several microns. The accelerator has holes therethrough the number and distribution of which correspond substantially to the number and distribution of the emitting sites. Because of the minimal separation range between the emitter surface and the accelerator surface, the voltage needed to produce field emission ranges from only a few volts to about one hundred volts, and the emitted electrons emerge from the holes in the accelerator with correspondingly low energies.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

FIGURE 1 is an enlarged isometric view of a portion of an electron emitter in accordance with this invention; and

FIGURE 2 is a cross-sectional view taken along the lines 22 of FIGURE 1 showing the structure of a field emitting site, in accordance with this invention.

Referring now to FIGURE 1, the structure of a cathode in accordance with this invention comprises an insulating substrate 10 which may be made of a ceramic material, upon which a metal film 12 is deposited. The film 12 is made of a material which has desired characteristics for emitting electrons in response to a voltage. A film made of a refractory metal such as molybdenum or tungsten is suitable. A support structure for the accelerator can be a dielectric film 14, such as aluminum oxide, which is deposited over the emitter surface 12 in the form of a cellular grid having a desired mesh size. This mesh is produced by the use of a suitable mask over the film 12 at the time of the insulating film in accordance with well known techniques. Alternatively, the dielectric can be deposited as a continuous film and subsequently micromachined to yield the desired mesh structure. Techniques for doing this are also quite well known.

The needles 16, at the emission sites, are then formed on the exposed areas of the emitter surface by promoting metal migration under proper surface tension whereby small sharp surfaced protuberances 16 are formed.

The accelerator film 18 can then be formed by depositing a metal layer onto the dielectric film, at almost grazing incidence while rotating the substrate around an axis normal to its surface. For producing the desired field emission, a potential source 20 has its positive terminal connected to the accelerator 18 and its negative terminal connected to the emitter film 12. The potential source may be made variable for the purpose of controlling the electron emission current.

FIGURE 2 is a cross-sectional view of an emitter site along the lines 22. They illustrate a plurality of protuberances or needles on the field emitting site. Electrons are emitted therefrom under the influence of the field es- '3 tablished by the potential applied between the accelerator film and the emitter film.

The substrate can be given any desired shape such as a parabola, or a curve whereby the electrons which are emitted from the field sites will be converged at the focus of the curve. By way of illustration, but not to be considered as a limitation on the invention, a typical method of manufacturing a cathode in accordance with this invention would comprise the step of depositing on a ceramic substrate a refractory or emitting metal film of molybdenum or tungsten. Thereafter, a dielectric film is deposited over the emitting film. The dielectric film has a thickness on the order of a few microns and may be made of a material such as aluminum oxide.

If desired, at this point electron beam technology may be employed to micromachine holes through the dielectric film at a plurality of desired locations to uncover the emitter film surface. Alternatively, the accelerator film, which may also be made of molybdenum or tungsten, may be deposited over the dielectric film and then electron beam techniques may be employed to micromachine holes therethrough until the emitting surface film is reached.

At this point, a film of a relatively low melting point material, such as aluminum, is deposited over the entire surface of the cathode, namely, over the accelerator surface as well as over those portions of the emitting surface as are exposed through the holes. Then, under vacuum conditions, the entire substrate is heated to about 1150 C. This temperature is above the vaporization temperature of the aluminum but not of the molybdenum or tungsten, whichever metal is used for the emitter surface and accelerator surface. Neither is this temperature above the melting point temperature of the substrate or insulating layer materials. The phenomenon which occurs at this temperature, and precisely why is not really understood, is that either some kind of surface migration or surface tension forces cause protuberances of the metal of the emitter surface to be formed at the location of the holes, which protuberances resemble the protuberance 16 represented by the drawing. In order to give some indication of the sizes or dimensions of the various films and holes, the initial emitter film of molybdenum or tungsten may be deposited to a thickness of from one-quarter to one micron on a substrate which may be a ceramic material or may be sapphire. The insulating film of aluminum oxide may also be any where from one-quarter to one micron. The accelerating film may be on the order of 30 to 500 angstroms. The aluminum film may be on the order of 30 to 300 angstroms. The holes exposing the emit- .ter sites may been the order of one-tenth to several microns.

There has accordingly been described and shown herein a novel, useful and improved source of electrons.

Although particular embodiments of the invention have been described and illusrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art and consequently it is intended that the claims be interpreted to cover such modifications and equivalents.

What is claimed is:

1. The method of manufacturing a field emitting cathode comprising depositing a first refractory metal film on an insulating substrate, depositing a dielectric film of refractory material over said first metal film, depositing a second metal film of a refractory metal over said dielectric film, micromachining a plurality of holes through said second metal film and said dielectric film to expose said first metal film through said holes, depositing a third metal film over the exposed first metal film through said holes, the melting point of said third metal film being low relative to the melting point of said first and second metal films, and heating said substrate in a vacuum to a predetermined temperature above the vaporization temperature of said third metal film but below the melting temperature of said first metal film until a plurality of protuberances form in said first metal film as may be seen through the holes in said dielectric film.

2. The method of manufacturing a field emitting cathode as recited in claim 1 wherein said third metal film is made of aluminum and said first and second metal films are one of the group consisting of tungsten and molybdenum.

3. The method of manufacturing a field emitting cath ode as recited in claim 1 wherein said dielectric film is made of aluminum oxide.

References Cited UNITED STATES PATENTS PAUL M. COHEN, Primary Examiner US. Cl. X.R. 29576, 578

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3060013 *Mar 7, 1960Oct 23, 1962Gen Motors CorpMethod of growing copper filaments
US3141051 *Sep 14, 1960Jul 14, 1964Elm Coated Fabrics Company IncMethod and apparatus for preparing special surface finishes
US3178804 *Apr 10, 1962Apr 20, 1965United Aircraft CorpFabrication of encapsuled solid circuits
*DE29854C Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3789471 *Jan 3, 1972Feb 5, 1974Stanford Research InstField emission cathode structures, devices utilizing such structures, and methods of producing such structures
US3812559 *Jan 10, 1972May 28, 1974Stanford Research InstMethods of producing field ionizer and field emission cathode structures
US4874981 *May 10, 1988Oct 17, 1989Sri InternationalAutomatically focusing field emission electrode
US5090932 *Mar 24, 1989Feb 25, 1992Thomson-CsfMethod for the fabrication of field emission type sources, and application thereof to the making of arrays of emitters
US5141459 *Feb 21, 1992Aug 25, 1992International Business Machines CorporationStructures and processes for fabricating field emission cathodes
US5203731 *Mar 5, 1992Apr 20, 1993International Business Machines CorporationProcess and structure of an integrated vacuum microelectronic device
US5334908 *Dec 23, 1992Aug 2, 1994International Business Machines CorporationStructures and processes for fabricating field emission cathode tips using secondary cusp
US5397957 *Nov 10, 1992Mar 14, 1995International Business Machines CorporationProcess and structure of an integrated vacuum microelectronic device
US5462467 *Sep 8, 1993Oct 31, 1995Silicon Video CorporationFabrication of filamentary field-emission device, including self-aligned gate
US5463269 *Mar 6, 1992Oct 31, 1995International Business Machines CorporationProcess and structure of an integrated vacuum microelectronic device
US5559389 *Nov 24, 1993Sep 24, 1996Silicon Video CorporationElectron-emitting devices having variously constituted electron-emissive elements, including cones or pedestals
US5562516 *May 22, 1995Oct 8, 1996Silicon Video CorporationField-emitter fabrication using charged-particle tracks
US5564959 *Jun 29, 1994Oct 15, 1996Silicon Video CorporationUse of charged-particle tracks in fabricating gated electron-emitting devices
US5569973 *Jun 6, 1995Oct 29, 1996International Business Machines CorporationIntegrated microelectronic device
US5578185 *Jan 31, 1995Nov 26, 1996Silicon Video CorporationMethod for creating gated filament structures for field emision displays
US5583393 *Mar 24, 1994Dec 10, 1996Fed CorporationSelectively shaped field emission electron beam source, and phosphor array for use therewith
US5717278 *May 19, 1995Feb 10, 1998International Business Machines CorporationField emission device and method for fabricating it
US5755944 *Jun 7, 1996May 26, 1998Candescent Technologies CorporationFormation of layer having openings produced by utilizing particles deposited under influence of electric field
US5801477 *Jan 31, 1995Sep 1, 1998Candescent Technologies CorporationGated filament structures for a field emission display
US5813892 *Jul 12, 1996Sep 29, 1998Candescent Technologies CorporationUse of charged-particle tracks in fabricating electron-emitting device having resistive layer
US5827099 *Dec 7, 1995Oct 27, 1998Candescent Technologies CorporationUse of early formed lift-off layer in fabricating gated electron-emitting devices
US5851669 *May 22, 1995Dec 22, 1998Candescent Technologies CorporationField-emission device that utilizes filamentary electron-emissive elements and typically has self-aligned gate
US5865657 *Jun 7, 1996Feb 2, 1999Candescent Technologies CorporationFabrication of gated electron-emitting device utilizing distributed particles to form gate openings typically beveled and/or combined with lift-off or electrochemical removal of excess emitter material
US5865659 *Jun 7, 1996Feb 2, 1999Candescent Technologies CorporationFabrication of gated electron-emitting device utilizing distributed particles to define gate openings and utilizing spacer material to control spacing between gate layer and electron-emissive elements
US5913704 *May 12, 1997Jun 22, 1999Candescent Technologies CorporationFabrication of electronic devices by method that involves ion tracking
US6019658 *Sep 11, 1998Feb 1, 2000Candescent Technologies CorporationFabrication of gated electron-emitting device utilizing distributed particles to define gate openings, typically in combination with spacer material to control spacing between gate layer and electron-emissive elements
US6187603Jun 7, 1996Feb 13, 2001Candescent Technologies CorporationFabrication of gated electron-emitting devices utilizing distributed particles to define gate openings, typically in combination with lift-off of excess emitter material
US6204596 *Jun 30, 1998Mar 20, 2001Candescent Technologies CorporationFilamentary electron-emission device having self-aligned gate or/and lower conductive/resistive region
US6515407Aug 28, 1998Feb 4, 2003Candescent Technologies CorporationGated filament structures for a field emission display
US7025892Jan 31, 1995Apr 11, 2006Candescent Technologies CorporationMethod for creating gated filament structures for field emission displays
DE2339949A1 *Aug 7, 1973Feb 28, 1974Prec Thin Film CorpVerfahren und vorrichtung zum auftragen einer duennen schicht auf einer unterlage
DE19534576B4 *Sep 18, 1995Jul 13, 2006Kabushiki Kaisha Toshiba, KawasakiMikrovakuumvorrichtung
DE19800555A1 *Jan 9, 1998Jul 15, 1999IbmField emission component for array of emissive flat display screen
EP0716438A1 *Dec 6, 1994Jun 12, 1996International Business Machines CorporationField emission device and method for fabricating it
EP0945885A1 *Sep 8, 1994Sep 29, 1999Silicon Video CorporationFabrication and structure of electron-emitting devices having high emitter packing density
WO1995007543A1 *Sep 8, 1994Mar 16, 1995Silicon Video CorpFabrication and structure of electron-emitting devices having high emitter packing density
WO1995026037A1 *Mar 24, 1995Sep 28, 1995Fed CorpSelectively shaped field emission electron beam source, and phosphor array for use therewith
Classifications
U.S. Classification445/52, 445/50
International ClassificationH01J9/02, H01J1/304, H01J1/30
Cooperative ClassificationH01J1/3042, H01J9/025
European ClassificationH01J9/02B2, H01J1/304B