US3678325A - High-field emission cathodes and methods for preparing the cathodes - Google Patents

High-field emission cathodes and methods for preparing the cathodes Download PDF

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Publication number
US3678325A
US3678325A US18176A US3678325DA US3678325A US 3678325 A US3678325 A US 3678325A US 18176 A US18176 A US 18176A US 3678325D A US3678325D A US 3678325DA US 3678325 A US3678325 A US 3678325A
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Prior art keywords
metal
field emission
substrate
cathode
cathodes
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US18176A
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English (en)
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Jun Nishida
Takahumi Ohhara
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Panasonic Holdings Corp
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Matsushita Electric Industrial Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
    • H01J9/02—Manufacture of electrodes or electrode systems
    • H01J9/022—Manufacture of electrodes or electrode systems of cold cathodes
    • H01J9/025—Manufacture of electrodes or electrode systems of cold cathodes of field emission cathodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/30—Cold cathodes, e.g. field-emissive cathode
    • H01J1/304—Field-emissive cathodes

Definitions

  • This invention relates to cathodes as applicable to electron tubes and particularly to high-field emission cathodes used as a point source of an electron beam.
  • the surface potential barrier is closely dependent upon the surface conditions. For example, the cleanliness of the surface, and whether the surface is coated with another metal or with adsorbed gas atoms are two of the important factors dictating the height of the surface potential barrier. Therefore, a low work function and stability at a high temperature are desirable features for the high-field emission cathodes. The low work function is required for these ertness to gases including oxygen and stability at a high temperature.
  • a low work function material such as barium is evaporated in a vacuum and coated on a fine tungsten wire having an etched tip.
  • the binding force between the tungsten and barium is deficient except in there several-atom layer.
  • the tungsten tip coated with barium is then taken out from the vacuum and ex posed to the surrounding air before it is accommodated as a cathode in an electron tube. While being exposed to the air, however, the coated barium is subject to oxygen gases existing in the air, resulting in the formation of an oxide layer on the tip surface.
  • the coated metal material together with the tungsten wire is subjected to a heat treatment at an elevated temperature.
  • the wire cathode be accommodated in the tube and subjected to a subsequent heat treatment to degas the tube itself. In this manner, a high-field emission cathode usable at a low operating voltage is obtained by such prior art method.
  • the coated metal material is located as a barium layer directly on the surface of the substrate of the cathode so that it is easily affected by the surrounding gas molecules when exposed thereto. On top of this, the metal material tends to evaporate into the surrounding vacuum during the heat treatments. Even though the material is partially penetrated into the cathode, say, into the severalatom layer of the coated metal material, the penetration depth is not great enough. This is reflected by the likelihood of diffusion and surface migration of the metal atoms when the metal material is heated for activation, thus leading to a shortened operating life of the existing cathodes.
  • FIG. 1 is a schematic view illustrating the operating concept of a high-field emission cathode of the invention
  • FIG. 2(a) shows, in an explanatory manner, the energy level of tungsten placed in a vacuum
  • FIG. 2(b) is similar to FIG. 2(a) but shows the energy level with a high electric field built up;
  • FIG. 3(a) shows, also in an explanatory manner, the energy level of tungsten coated thereon with barium and placed in a vacuum;
  • FIG. 3(b) is similar to FIG. 3(a) but shows the energy level with a high electric field built up
  • FIG. 4 is a graphical representation of the distribution of the low work function metal atoms implanted in the fonn of ions into the substrate of the cathode. 1
  • a typical high-field emission cathode as designated by 10 is provided with a pointed tip which is produced, for example, by electro-chemically etching or by arcing in disruptive breakdown discharge.
  • metal ions of low work function by establishing an accelerating electric field.
  • the initial cathode 10 and the metal ions may be made of tungsten and barium, respectively, by way of example.
  • An electrode 11 acting as an anode is located opposite to the cathode 10.
  • An appropriate voltage is applied from a power source 12 between the two electrodes 10 and 11. In operation, when a high electric field is established between the electrodes 10 and II with the applied voltage, this field serves to lower the surface potential barrier and draws electrons through the surface.
  • the electric field required to overcome the surface barrier is so high that the electrons hardly escape from the surface, provided the cathode 10 has thereon no metal of low work function:
  • the work function of the cathode as a whole is lowered.
  • the electric field now makes the electrons escape through the potential barrier at the surface, thus constituting a flow of electrons, as designated by letter e, from the surface under the influence of the field.
  • vacuum energy level of tungsten is on the flat and the potential barrier is, as a whole, in a stepped form.
  • the work function the value of which is exemplified as 4.5eV in this instance, is defined as a difference between the vacuum level V.L. and so-called Fermi level as abbreviated to FL.
  • the work function is an energy required to have an electron at the Fermi level F.L. freed out of the surface of the tungsten.
  • the vacuum level V.L. drops with a certain slope and the potential barrier appears as a triangular hump, as shown in FIG. 2(b).
  • the vacuum level V.L. is lowered so that the value of the work function shifts from 4.5eV to l.5eV, as shown in FIG. 3(a). It follows that the electrons inside the tungsten bulk are pulled out or pass over the barrier easily from the surface if the attractive electric field is relatively intense. Referring further to FIG. 3(b), the potential barrier assumes in turn a sharp triangular hump lowered with respect to the Fermi level F.L. when a high-field develops. The vacuum level V.L. has also a negative slope, which grows steeper as electric field is increased. In this instance, even the electrons having energies below the Fermi level can tunnel through the narrow portion of the potential barrier. This phenomenon is well known as the tunnel Effect and is used in the high-field emission cathode of this invention.
  • metal of low work function is accelerated in the form of ions by an intense electric field and thereafter implanted deep into the inside of a substrate made of a usual cathode material.
  • the cathode obtained is taken out into the open air.
  • the cathode may be subjected to a heat treatment in a vacuum, preferably in an electron tube, to remove a oxidized part of a resulting oxide layer and adsorbed gases in the surface layer, if any.
  • the tube is degassed and the surface of the cathode activated by diffusing the metal ions from the substrate bulk to the surface.
  • the ion-implantation is, in this instance, accomplished in a manner as follows:
  • the barium ions are obtained from a plasma, where the barium is at least partially ionized at an elevated temperature. Practically, with an intense accelerating voltage of, for instance, about 40kV established, the barium ions are oriented in a uniform direction thereby to form a beam. This barium-ion beam is implanted deep into the inside of the cathode substrate of tungsten.
  • the distribution of the implanted barium ion content is illustrated in FIG. 4 in terms of the penetration depth from the substrate surface. It will be appreciated from FIG. 4 that the summit of the distribution is located at a distance inboard from the surface, namely, not at the very surface and that the barium ions penetrate as deep as l,000 to 3,000 angstroms into the substrate bulk. This deep penetration is conducive to maintaining the surface of the ion-implanted tungsten unaffected by the surrounding gas molecules. Therefore, the surface of the tungsten fabricated by the method ofthe invention behaves as a simple substance.
  • a high-field emission cathode offers advantages that the cathode stays so stable as to be free from evaporation at an elevated temperature and chemically inert to gas molecules and that the cathode can operate stably with reduced operating voltage for a prolonged period of time.
  • metals as usable in the invention to be implanted into the substrate are alkali metals such as lithium (Li), sodium (Na), potassium (K) and cesium (Cs); alkaline earth metals such as barium (Ba strontium(Sr) and calcium(Ca) and other metals-such ast orium (Th) and zirconium (Zr). As has been described in detail, these metals have low work functions and easily ionize at a high temperature.
  • the usual simple substance cathode is once coated with a material to improve the implantation of the low work function metals, namely, to permit more amount of metals to penetrate deeper into the substrate material.
  • the ion-implantation is accomplished to the once coated substrate.
  • the coating material may preferably by oxides or carbides of the substrate material such as tungsten (W), molybdenum (Mo), tantalum (Ta) or rhenium(Re) and should also be stable at an elevated temperature, chemically inert to gases including oxygen and adapted to be coated on the substrate surface.
  • the high-field emission cathodes of the invention can be used, in general, as a point source of an electron beam with less operating voltages. Furthermore, the cathodes will find a wide variety of applications for an emitter of an electron tube, especially, for a cathode of an electron gun.
  • a high-field emission cathode composed of a substrate having a pointed tip portion and a low work function metal, said metal being implanted deep into said pointed tip portion of said substrate, which cathode is produced by a process comprising, obtaining ions of said metal from a plasma having ions of said metal accelerating said ions of said metal by applying high voltage of about 40 kV thereto for forming a high speed ion beam, and implanting said ion beam into said substrate.
  • a high-field emission cathode according to claim 1 wherein said metal is selected from the group consisting of lithium, sodium, potassium, cesium, barium strontium, calcium, thorium and zirconium.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Cold Cathode And The Manufacture (AREA)
US18176A 1969-03-14 1970-03-10 High-field emission cathodes and methods for preparing the cathodes Expired - Lifetime US3678325A (en)

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US (1) US3678325A (enExample)
DE (1) DE2012101B2 (enExample)
FR (1) FR2034947B1 (enExample)
GB (1) GB1309423A (enExample)
NL (1) NL149947B (enExample)

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3814975A (en) * 1969-08-06 1974-06-04 Gen Electric Electron emission system
US4325000A (en) * 1980-04-20 1982-04-13 Burroughs Corporation Low work function cathode
US4827177A (en) * 1986-09-08 1989-05-02 The General Electric Company, P.L.C. Field emission vacuum devices
US5089292A (en) * 1990-07-20 1992-02-18 Coloray Display Corporation Field emission cathode array coated with electron work function reducing material, and method
EP0736891A1 (en) * 1995-04-03 1996-10-09 SHARP Corporation Process of fabricating field-emission type electron source, electron source fabricated thereby and element structure of electron source
WO1997036693A1 (en) * 1996-04-01 1997-10-09 The Regents Of The University Of California Process to modify work functions using ion implantation
WO1998021737A1 (en) * 1996-11-13 1998-05-22 Board Of Trustees Of The Leland Stanford Junior University Carbon-containing cathodes for enhanced electron emission
WO1998051417A1 (en) * 1997-05-16 1998-11-19 The Board Of Trustees Of The Leland Stanford Junior University Method and apparatus for making thermionic oxide cathodes
WO1999044218A1 (en) * 1998-02-27 1999-09-02 Micron Technology, Inc. Large-area fed apparatus and method for making same
US5990604A (en) * 1995-05-02 1999-11-23 Massacusetts Institute Of Technology Field emmitters of wide-bandgap materials
WO1999060598A1 (en) * 1998-05-18 1999-11-25 The Regents Of The University Of California Low work function, stable compound clusters and generation process
WO2001052296A1 (fr) * 2000-01-14 2001-07-19 Thomson Tubes Electroniques Cathode generatrice d"electrons et son procede de fabrication
US20060251145A1 (en) * 2005-05-05 2006-11-09 Brushwyler Kevin R Automated calorimeter

Families Citing this family (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2177497B1 (enExample) * 1972-03-27 1978-09-29 Labo Electronique Physique
USRE40062E1 (en) * 1987-07-15 2008-02-12 Canon Kabushiki Kaisha Display device with electron-emitting device with electron-emitting region insulated from electrodes
USRE39633E1 (en) * 1987-07-15 2007-05-15 Canon Kabushiki Kaisha Display device with electron-emitting device with electron-emitting region insulated from electrodes
EP0299461B1 (en) * 1987-07-15 1995-05-10 Canon Kabushiki Kaisha Electron-emitting device
USRE40566E1 (en) * 1987-07-15 2008-11-11 Canon Kabushiki Kaisha Flat panel display including electron emitting device
US5749763A (en) * 1987-07-15 1998-05-12 Canon Kabushiki Kaisha Display device with electron-emitting device with electron-emitting region insulted from electrodes
SE504603C2 (sv) * 1995-02-15 1997-03-17 Lightlab Ab Metod vid tillverkning av en fältemissionskatod samt fältemissionskatod
CA2227322A1 (en) * 1995-08-04 1997-02-20 Printable Field Emitters Limited Field electron emission materials and devices
US8058159B2 (en) 2008-08-27 2011-11-15 General Electric Company Method of making low work function component

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3259782A (en) * 1961-11-08 1966-07-05 Csf Electron-emissive structure
US3356912A (en) * 1964-10-16 1967-12-05 Gen Electric Porous electrode
US3425111A (en) * 1964-10-08 1969-02-04 Trak Microwave Corp Method of making cathodes by neutron bombardment

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3259782A (en) * 1961-11-08 1966-07-05 Csf Electron-emissive structure
US3425111A (en) * 1964-10-08 1969-02-04 Trak Microwave Corp Method of making cathodes by neutron bombardment
US3356912A (en) * 1964-10-16 1967-12-05 Gen Electric Porous electrode

Cited By (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3814975A (en) * 1969-08-06 1974-06-04 Gen Electric Electron emission system
US4325000A (en) * 1980-04-20 1982-04-13 Burroughs Corporation Low work function cathode
US4827177A (en) * 1986-09-08 1989-05-02 The General Electric Company, P.L.C. Field emission vacuum devices
EP0260075B1 (en) * 1986-09-08 1994-06-08 THE GENERAL ELECTRIC COMPANY, p.l.c. Vacuum devices
US5089292A (en) * 1990-07-20 1992-02-18 Coloray Display Corporation Field emission cathode array coated with electron work function reducing material, and method
EP0736891A1 (en) * 1995-04-03 1996-10-09 SHARP Corporation Process of fabricating field-emission type electron source, electron source fabricated thereby and element structure of electron source
US5800233A (en) * 1995-04-03 1998-09-01 Sharp Kabushiki Kaisha Process of fabricating field-emission type electron source, electron source fabricated thereby and element structure of electron source
US5990604A (en) * 1995-05-02 1999-11-23 Massacusetts Institute Of Technology Field emmitters of wide-bandgap materials
WO1997036693A1 (en) * 1996-04-01 1997-10-09 The Regents Of The University Of California Process to modify work functions using ion implantation
WO1998021737A1 (en) * 1996-11-13 1998-05-22 Board Of Trustees Of The Leland Stanford Junior University Carbon-containing cathodes for enhanced electron emission
WO1998051417A1 (en) * 1997-05-16 1998-11-19 The Board Of Trustees Of The Leland Stanford Junior University Method and apparatus for making thermionic oxide cathodes
WO1999044218A1 (en) * 1998-02-27 1999-09-02 Micron Technology, Inc. Large-area fed apparatus and method for making same
US6255772B1 (en) 1998-02-27 2001-07-03 Micron Technology, Inc. Large-area FED apparatus and method for making same
US6495956B2 (en) 1998-02-27 2002-12-17 Micron Technology, Inc. Large-area FED apparatus and method for making same
US20030038588A1 (en) * 1998-02-27 2003-02-27 Micron Technology, Inc. Large-area FED apparatus and method for making same
US7033238B2 (en) 1998-02-27 2006-04-25 Micron Technology, Inc. Method for making large-area FED apparatus
US20060189244A1 (en) * 1998-02-27 2006-08-24 Cathey David A Method for making large-area FED apparatus
US7462088B2 (en) 1998-02-27 2008-12-09 Micron Technology, Inc. Method for making large-area FED apparatus
WO1999060598A1 (en) * 1998-05-18 1999-11-25 The Regents Of The University Of California Low work function, stable compound clusters and generation process
WO2001052296A1 (fr) * 2000-01-14 2001-07-19 Thomson Tubes Electroniques Cathode generatrice d"electrons et son procede de fabrication
FR2803944A1 (fr) * 2000-01-14 2001-07-20 Thomson Tubes Electroniques Cathode generatrice d'electrons et son procede de fabrication
US20060251145A1 (en) * 2005-05-05 2006-11-09 Brushwyler Kevin R Automated calorimeter

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Publication number Publication date
FR2034947A1 (enExample) 1970-12-18
DE2012101C3 (enExample) 1975-10-09
NL7003616A (enExample) 1970-09-16
DE2012101A1 (de) 1970-09-24
GB1309423A (en) 1973-03-14
FR2034947B1 (enExample) 1974-09-20
NL149947B (nl) 1976-06-15
DE2012101B2 (de) 1975-03-06

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