US3777209A - Non-thermionic electron emissive tube comprising a ceramic heater substrate - Google Patents

Non-thermionic electron emissive tube comprising a ceramic heater substrate Download PDF

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Publication number
US3777209A
US3777209A US00254259A US3777209DA US3777209A US 3777209 A US3777209 A US 3777209A US 00254259 A US00254259 A US 00254259A US 3777209D A US3777209D A US 3777209DA US 3777209 A US3777209 A US 3777209A
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United States
Prior art keywords
cathode
tube
layer
electron emissive
substrate
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Expired - Lifetime
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US00254259A
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English (en)
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A Mcdonie
R Faulkner
J Rhoads
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RCA Corp
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RCA Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J40/00—Photoelectric discharge tubes not involving the ionisation of a gas
    • H01J40/02—Details
    • H01J40/04—Electrodes
    • H01J40/06—Photo-emissive cathodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J43/00—Secondary-emission tubes; Electron-multiplier tubes
    • H01J43/04—Electron multipliers
    • H01J43/06—Electrode arrangements
    • H01J43/08—Cathode arrangements

Definitions

  • ABSTRACT A non-thermionic electron emissive tube of the type comprising an evacuated envelope, an electron emis sive cathode assembly in the envelope, and a collector anode for electrons emitted from the emissive layer.
  • the cathode assembly comprises a thin ceramic substrate. On one face of the substrate is a nonthermionic cathode. On the opposite surface is a heater pattern of resistive metallizing.
  • the invention relates to non-thermionic electron emissive tubes.
  • Non-thermionic electron emissive tubes generally contain an electron emitting surface, or cathode which need not be heated for operation.
  • the cathode commonly is a layer of semiconductor material, the surface of which is cesiated by application thereon of a workfunction-reducing layer of cesium or cesium and oxygen.
  • the process for applying the work-function-reducing layer includes heating the cathode layer to a relatively high temperature, on the order of 400C to 600C, after the cathode layer has been mounted in the tube, but before the work function reducing layer is applied thereon.
  • One present means for providingthe'heating is by a resistance heated filament wire situated in closeproximity to the back side of a metal substrate on which the semiconductor layer is disposed.
  • a resistance heated filament wire situated in closeproximity to the back side of a metal substrate on which the semiconductor layer is disposed.
  • the filament is heated,'radient energy therefrom heats the metal substrate and the cathode layer.
  • Another present means for the heating is the use of a focussed external intense light source, such as a high intensity quartz lamp in conjunction with a parabolic mirror. The light is focussed through the transparent tube envelope directly onto the cathode material. Both of these approaches utilize transfer of heat by radiant energy, and result in substantial losses of heat to other structures of the tube.
  • some radiant energy given off by the filament can pass by the cathode substrate as stray radiation and heat nearby dynodes so that they are damaged. Also, some of the radiant energy is reflected from the metal substrate of the cathode to other components. Similarly, the focussed light from the external light source is reflected on passing through the tube envelope, and further reflected from the cathode layer itself to other internal tube components.
  • the dynodes having an antimony layer for later cesiation to cesium antimonide, are heated during the heating of the cathode, the antimony evaporates from the surface onto other portions of the tube envelope, thus degrading the quality of the tube.
  • Another difficulty with present heating means is that the heating is often nonuniform. This results in nonuniformities in the characteristics of the activated cathode.
  • a cathode assembly comprising a thin ceramic substrate on which a cathode 2 is disposed.
  • a heater pattern of metallizing is provided on the substrate in direct thermally conducting contact with the cathode.
  • the cathode is heated by thermal conduction rather than by radiation.
  • the direct thermal contact provides much more efficient heat transfer between the heater and the cathode. Therefore, the heater need not be heated to temperatures so high as to result in damaging stray radiation to other tube components. Also, the heating of the cathode layer is uniform. After activation of the cathode, the heater pattern becomes a passive structure, since the non-thermionic cathode need not be heated for operation.
  • FIG. 1 is a side view of a photomultiplier tube in accordance with the preferred embodiment of the invention.
  • FIG. 3 is a plan view of one face of the cathode substrate of the tube of FIGS. 1 and 2.
  • FIG. 4 is a plan view of the opposite face of the substrate of FIG. 3.
  • a photomultiplier tube 10 shown in FIGS. 1 and 2 includes a photocathode assembly 12 in accordance with the invention.
  • the tube 10 includes a glass envelope 14, a number of cesium-antimonide-coated electron multiplying dynodes 16, a number of field electrodes 18, and an anode 20 for collecting multiplied electrons which travel from one dynode 16 to another generally along the path indicated by the dashed lines 22.
  • the photocathode assembly 12 is shown in more detail in FIGS. 3 and 4.
  • the assembly 12 comprises a thin rectangular wafer 24 ofaluminum oxide (A1 0 about 1 cm (centimeter) wide, 3.5 cm long, and 0.5 mm thick.
  • A1 0 about 1 cm (centimeter) wide, 3.5 cm long, and 0.5 mm thick.
  • One surface of the wafer is provided with a rectangular pad 26 of molybdenum metallizing about 25 pm thick, which is applied by screen printing and firing a molybdenum-steatite metallizing ink commonly used for metallizing ceramics.
  • a lead portion 28 of the pad 26 extends to a contact-fastening hole 30 at the base end of the wafer 24.
  • a thin photocathodelayer 31 of vapor-phase-grown polycrystalline gallium arsenide phosphide between about 5pm and 30 um thick containing about percent gallium arsenide. Details of vaporphase-growth are described, for instance, in U.S. Pat. No. 3,218,205 issued 16 Nov. 1965 to Ruehrwein.
  • the opposite face of the wafer 24 is provided with a zig-zag pattern of molybdenum about 25 pm thick to form a resistance heater strip 32 in contact with the wafer 24.
  • a resistance heater strip 32 in contact with the wafer 24.
  • These apertures 36, 38 provide heat dams to improve the uniformity of heating by minimizing end heat losses.
  • the heater strip 32 is narrowed somewhat at portions 40, 42 near the heat dams 36, 38. The purpose of this is to increase the heat output from the heater in these regions to compensate for heat losses which occur at the top and bottom ends despite the heat dams.
  • heating of the photocathode layer 26 is by direct thermal conduction. Since there is relatively little heat loss to other tube components such as the dynodes 16, undesirable evaporation of antimony from the dynodes 16 is avoided.
  • Electrical leads 44 of high temperature spring metal are connected to the wafer 24 through the holes 30, 34 in the base of the wafer 24 after it is mounted in the tube, as shown in FIG. 1.
  • the invention has utility in various types of electron emissive tubes utilizing non-thermionic cathodes, and in which it is desirable to avoid unnecessary heating of other internal components of the tube when activating the cathode.
  • non-thermionic cathodes are generally cesiated.
  • the cathode can be a forward-biasedjunction emitter cathode, photocathode, or secondary emitter.
  • the semiconductor can be any semiconductor suitable for a cathode layer. It may be, for instance, silicon or a compound or alloy from Groups lIlA and VA or IIB and VIA of the Periodic Chart of the Elements.
  • the thickness of the ceramic wafer material is preferably great enough to result in a relatively uniform temperature on the cathode side. If the substrate wafer is too thick, however, there may be spalling of the ceramic due to thermal stress.
  • the pattern of the heater element can be any of various patterns which result in a relatively uniform heat output over the surface. It is desirable, however, where the substrate wafer iselongated, as in the preferred embodiment, to provide for additional heat input to the substrate wafer near the ends of the substrate.
  • Various metals can be used for the heater pattern and for the metallizing on the emitter cathode face.
  • Refractory metals such as molybdenum and tungsten are preferably used where the cathode layer must be grown on the substrate wafer directly by vapor deposition. This is due to the severe conditions in the growth furnace for Ill-V compound vapor phase deposition.
  • the substrate wafer is exposed to highly reactive gases at temperatures on the order of 600C to 1,000C.
  • Molybdenum and tungsten are the only metals in general use which can withstand such conditions and which are compatible with Ill-V compounds to the extent needed for growing a layer of sufficiently regular crystallinity for efficient performance of the cathode layer.
  • the cathode layer is itself sufficiently conductive to operate without a metallizing pad under it, the cathode layer may be deposited directly on the ceramic.
  • the heater pattern may be on the same side of the ceramic substrate wafer as the cathode, and may be separated from the cathode layer by an interposed electrically insulating layer such as silicon dioxide or be in direct physical contact with the cathode layer.
  • the heater pattern is in direct thermally conductive contact with the cathode layer.
  • Direct thermally conductive contact means that the heat transfer from the heater to the cathode layer is primarily by thermal conduction, either by direct physical contact, or through intermediate thermally conducting material.
  • An electron emissive tube of the type comprising:
  • a non-thermionic, electron emissive cathode having a photocathode layer and a work function reducing material on said photocathode layer, in the envelope, and
  • a ceramic substrate on one surface of which the cathode is disposed, and a heater pattern of metallizing on the substrate in direct thermally conducting contact with the cathode.
  • the semiconductor comprises at least one element from Groups lIIA, VA, 11B, and VIA of the Periodic Chart of the Elements.
  • An electron emissive tube in accordance with claim 1 characterized in that the ceramic substrate has a pair of spaced apertures therethrough and said heater pattern of metallizing extends over the ceramic substrate between-the apertures.

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  • Electrodes For Cathode-Ray Tubes (AREA)
  • Common Detailed Techniques For Electron Tubes Or Discharge Tubes (AREA)
  • Cold Cathode And The Manufacture (AREA)
  • Electron Beam Exposure (AREA)
US00254259A 1972-05-17 1972-05-17 Non-thermionic electron emissive tube comprising a ceramic heater substrate Expired - Lifetime US3777209A (en)

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US25425972A 1972-05-17 1972-05-17

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US3777209A true US3777209A (en) 1973-12-04

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Country Status (7)

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US (1) US3777209A (enrdf_load_stackoverflow)
JP (1) JPS4950863A (enrdf_load_stackoverflow)
CA (1) CA998732A (enrdf_load_stackoverflow)
DE (1) DE2325136B2 (enrdf_load_stackoverflow)
FR (1) FR2184980B1 (enrdf_load_stackoverflow)
GB (1) GB1425194A (enrdf_load_stackoverflow)
NL (1) NL7306812A (enrdf_load_stackoverflow)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3930139A (en) * 1974-05-28 1975-12-30 David Grigorievich Bykhovsky Nonconsumable electrode for oxygen arc working
US6259193B1 (en) * 1998-06-08 2001-07-10 General Electric Company Emissive filament and support structure

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3066236A (en) * 1958-05-14 1962-11-27 Int Standard Electric Corp Electron discharge devices
AU281761A (en) * 1960-03-30 1963-03-28 Westinghouse Brake (australasia ) Proprietary Limited Improvements relating to fluid pressure engines
FR1432317A (fr) * 1964-05-05 1966-03-18 Philips Nv Procédé de fabrication d'une cathode à chauffage indirect et cathode obtenue par ce procédé
US3307974A (en) * 1962-03-19 1967-03-07 Rank Radio And Television Ltd Method of forming thermionic cathodes
US3330991A (en) * 1963-07-12 1967-07-11 Raytheon Co Non-thermionic electron emission devices
US3408521A (en) * 1965-11-22 1968-10-29 Stanford Research Inst Semiconductor-type photocathode for an infrared device

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3066236A (en) * 1958-05-14 1962-11-27 Int Standard Electric Corp Electron discharge devices
AU281761A (en) * 1960-03-30 1963-03-28 Westinghouse Brake (australasia ) Proprietary Limited Improvements relating to fluid pressure engines
US3307974A (en) * 1962-03-19 1967-03-07 Rank Radio And Television Ltd Method of forming thermionic cathodes
US3330991A (en) * 1963-07-12 1967-07-11 Raytheon Co Non-thermionic electron emission devices
FR1432317A (fr) * 1964-05-05 1966-03-18 Philips Nv Procédé de fabrication d'une cathode à chauffage indirect et cathode obtenue par ce procédé
US3408521A (en) * 1965-11-22 1968-10-29 Stanford Research Inst Semiconductor-type photocathode for an infrared device

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3930139A (en) * 1974-05-28 1975-12-30 David Grigorievich Bykhovsky Nonconsumable electrode for oxygen arc working
US6259193B1 (en) * 1998-06-08 2001-07-10 General Electric Company Emissive filament and support structure
US6464551B1 (en) * 1998-06-08 2002-10-15 General Electric Company Filament design, method, and support structure

Also Published As

Publication number Publication date
FR2184980A1 (enrdf_load_stackoverflow) 1973-12-28
FR2184980B1 (enrdf_load_stackoverflow) 1977-12-30
DE2325136B2 (de) 1977-09-01
CA998732A (en) 1976-10-19
NL7306812A (enrdf_load_stackoverflow) 1973-11-20
DE2325136A1 (de) 1973-11-29
DE2325136C3 (enrdf_load_stackoverflow) 1978-05-11
GB1425194A (en) 1976-02-18
JPS4950863A (enrdf_load_stackoverflow) 1974-05-17

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