US3712700A - Method of making an electron emitter device - Google Patents

Method of making an electron emitter device Download PDF

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Publication number
US3712700A
US3712700A US00107372A US3712700DA US3712700A US 3712700 A US3712700 A US 3712700A US 00107372 A US00107372 A US 00107372A US 3712700D A US3712700D A US 3712700DA US 3712700 A US3712700 A US 3712700A
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Prior art keywords
emitter
temperature
envelope
protective layer
electron
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US00107372A
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English (en)
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A Sommer
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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
    • 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
    • H01J9/12—Manufacture of electrodes or electrode systems of photo-emissive cathodes; of secondary-emission electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2201/00—Electrodes common to discharge tubes
    • H01J2201/32—Secondary emission electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2201/00—Electrodes common to discharge tubes
    • H01J2201/34—Photoemissive electrodes

Definitions

  • ABSTRACT A method comprising coating an uncontaminated emitter surface of an emitter body with a non-contaminating protective layer and then mounting the body so that the coated surface is in the interior of an envelope. The envelope and body are then heated to a first temperature to drive contaminant gases from surfaces of the envelope interior while these gases are simultaneously pumped out. The first temperature is low enough that the protective layer remains.
  • the body is heated to a second temperature, higher than the first, and the protective layer evaporated off the surface while the envelope is maintained at a temperature below the first temperature. Thereafter the emitter surface is activated by the application thereto of a material which lowers the work function.
  • Electron emitters are used, for example, as photocathodes and as secondary emitting dynodes in electron tubes such as image tubes and photomultipliers.
  • an electron emitter consists of an emitter body having a surface which has been activated to increase its electron emission. Activation is achieved by the application of an electropositive substance such as cesium, either alone or with an electronegative substance such as oxygen, to lower the work function.
  • an electropositive substance such as cesium
  • an electronegative substance such as oxygen
  • the emitter surface be free of contaminants at the time of activation.
  • the emitter bulk of some emitters, such as antimony, may be evaporated from a bead in an electron tube envelope after contaminants have been removed from the interior of the envelope by a bakeout, a heating of the envelope and simultaneously evacuation of contaminant gases evolved from the envelope walls and from internal elements.
  • Other emitters, however, which cannot readily be evaporated from a bead are considerably more difficult to incorporate into an electron tube.
  • binary and ternary semiconductor compounds such as GaAs, Cal, and InGa, ,As,, as well as the elementary semiconductor silicon, are highly suitable materials for electron emitters but cannot be readily evaporated from a bead.
  • silicon evaporation is difficult because of the high evaporation temperature of silicon.
  • evaporation is difficult because the unequal rates of evaporation of the elements of the compounds at a given temperature result in decomposition of the compound.
  • evaporation emitter bodies having the characteristics needed for a sufficiently effective emitter surface.
  • These other emitters are generally incorporated in an electron tube envelope by mounting the already-formed emitter body in the envelope prior to the envelope bakeout.
  • the bakeout should be at a temperature of at least about 350C, preferably 400C.
  • the higher the bakeout temperature the more rapid and complete is the removal of contaminants. It is found, however, that heating the tube to about 350C even for a short time, on the order of several minutes or less, results in contamination of the emitter surface by chemical reaction of the released gases with the emitter body material. The emitter surface may then be permanently contaminated or must be recleaned inside the envelope by separate heating or sputtering prior to activation. Such recleaning is difficult to perform in the complex geometry of photomultiplier or image tubes. While some IIIV semiconductor compounds can be cleaned by heating for about 1 minute to about 25C below their decomposition temperature, some other semiconductors require more intense cleaning processes.
  • Silicon for example, is generally cleaned by bombardment with high energy electrons with subsequent annealing at about 1,000C for about 1 hour or more. Since in practice it is extremely difficult to perform such a cleaning process on a silicon emitter after it has been assembled inside an envelope, the use of silicon as an electron emissive surface in electron tubes has been severely restricted, despite the fact that silicon is otherwise highly desirable for such an application.
  • the novel method for making an electron emitter device comprises coating an uncontaminated electron emitter surface of an emitter body with a non-contaminating protective layer to protect it from contamination during further device fabrication. At a later stage of device fabrication, when ambient contaminants have been substantially removed, the layer is removed by evaporation from the emitter surface. Thereafter, the emitter surface is activated by the application thereto of a material which lowers the work function.
  • the emitter body When the uncontaminated emitter surface is covered with a protective layer until just priorto activation, the emitter body may be exposed to contaminants during bakeout of a tube envelope in which it is mounted without degradation. After removal of the protective layer, the emitter surface need not be recleaned prior to activation. Furthermore, semiconductors such as silicon which require cleaning processes which previously restricted them from commercial applications as electron emitters in electron tubes may now be so utilized with the novel method.
  • FIG. 1 is a flow chart outlining the steps of a preferred embodiment of the novel method.
  • FIG. 2 is a sectional view of a photomultiplier tube provided with a photocathode by the method of FIG. 1 and shown at a stage of processing between the third and the fourth steps of FIG. 1.
  • a circular cage photomultiplier tube shown in FIG. 2 is provided with an opaque semiconductor compound photoeathode l2 emitter body.
  • the tube 10 is shown in FIG. 2 during a stage of processing prior to the activation of the photocathode 12.
  • the tube 10 includes a glass envelope 14, a number of electron multiplying dynodes l6, 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.
  • Behind the photocathode 12 is a heating filament 24.
  • sources of cesium and oxygen for activating the photocathode 12.
  • the envelope 14 is connected by a short length of exhaust tubulation to a high-speed vacuum pump, also not shown.
  • the photocathode 12 comprises a y-inch square gallium arsenide substrate 26 about 50 microns thick having on one face an epitaxial layer 28 of gallium arsenide emitter bulk about 10 microns thick with an emitter surface 30.
  • the emitter surface 30 is coated with a protective layer 32 of potassium chloride (KCI) about 0.05 microns thick.
  • KCI potassium chloride
  • the protective layer 32 is evaporated on the emitter surface 30 as follows: First the emitter surface 30 is cleaned of contaminants in a continuously evacuated chamber, in which it is baked for at least 1 hour at a pressure of about 10' torr or lower and a temperature of about 200C and cooled back to room temperature. Then, the substrate 26 and emitter bulk 28 are heated for about 1 minute to about 650C, a temperature which is near but somewhat below the decomposition temperature of gallium arsenide, by heat radiated from a nearby resistance heated filament and again cooled to room temperature. Now the protective layer 32 is applied to the emitter surface 30 by evaporation from a potassium chloride bead on a second resistance heated wire.
  • the coated photocathode 12 is mounted in the interior of the envelope 14.
  • the envelope 14 is continuously evacuated by the vacuum pump through the exhaust tubulation to a pressure of about 10' torr or less while the envelope 14 is baked out at about 350C for at least 1 hour before being cooled back to room temperature.
  • the interior of the envelope 14 is thus cleaned of contaminating gases while the emitter surface 30 is shielded from these contaminating gases by the protective layer 32.
  • the photocathode 12 is heated from the side opposite the protective layer 32 by radiation from the filament 24 to about 500C with the remainder of the tube 10 at room temperature until the potassium chloride is evaporated off the emitter surface 30, from where it is either deposited elsewhere in the interior of the tube 10 or is pumped away by the vacuum pump. Finally, the emitter surface 30 is activated with cesium and oxygen and the exhaust tubulation sealed off under vacuum between the tube 10 and the pump.
  • EXAMPLE II v
  • a photomultiplier tube is provided with an opaque photocathode as in EXAMPLE I, but by use of a protective layer 32 of cesium iodide (Csl) instead of potassium chloride. Processing is generally the same as described for EXAMPLE I, except that since cesium iodide evaporates at a lower temperature than potassium chloride, the bakeout temperature is about 300C and the temperature to which the photocathode 12 is heated for removal of the protective layer is about 400C.
  • cesium iodide evaporates at a lower temperature than potassium chloride
  • cesium iodide is useful primarily for emitter bodies which themselves have relatively low evaporation (or decomposition) temperatures such as, for example, indium antimonide semiconductor alloy, some compositions of which decompose at about 450C.
  • the novel method may be used for protecting different emitter materials, whether metal, semiconductor or insulator, provided that the evaporation temperature (or decomposition temperature in the case of an alloy or compound) of the emitter bulk is higher than that of the protective layer, so that the protective layer may be removed therefrom without injury to the emitter surface.
  • a potassium chloride layer may be applied to an uncontaminated silicon emitter surface and then evaporated off without significant degrada tion of the surface, even through silicon is a relatively reactive material as compared to, for instance, III-V semiconductor compounds.
  • the emitter bulk is a vapor phase grown semiconductor
  • the protective layer before the emitter is ever exposed to the atmosphere.
  • potassium chloride may be evaporated on the emitter surface of vapor phase grown gallium arsenide or silicon while the emitter surface is yet in its growth chamber and in a rarified inert atmosphere such as helium. In this way the step of cleaning the emitter surface of contaminants prior to the application of the protective layer is eliminated.
  • the critical requirements for the protective layer material are that, (1) it does not itself contaminate the emitter surface, (2) it may be removed by evaporation without degrading the tube when it condenses on the inside envelope walls and on internal components (thus for photomultiplier tubes it should be transparent and electrically insulating); (3) it be a chemically stable layer to at least the bakeout temperature required for the tube; (4) as a layer, it be substantially impervious to contaminants in the tube and substantially unaffected by water vapor.
  • the emitter surface was activated with cesium and oxygen
  • the activation may be achieved with any of a number of techniques for lowering the work function.
  • Such techniques generally include the application to the surface of one or more electropositive materials such-as potassium, cesium or sodium either alone or together with one or more electronegative materials such as oxygen or fluorine.
  • the evaporation temperatures for protective layer materials herein are temperatures at which that material will vaporize at a sufficiently rapid rate to remove the layer from the emitter surface within a reasonably short time span, e.g., on the order of minutes.
  • This evaporation temperature is relatively non-critical and is generally a temperature at which the material has a vapor pressure of about torr to about 10- torr. Substantially lower temperatures require a much longer time to evaporate such a layer.
  • the decomposition temperature is referred to instead of an evaporation temperature.
  • the evaporation temperature for potassium chloride may be taken to be about 450C or higher but for practical purposes is between 450C and 500C.
  • the evaporation temperature for cesium iodide is between about 350C and 400C.
  • the decomposition temperature for gallium arsenide is between about 625C and about 675C, whereas the evaporation temperature for silicon is upwards of l,000C.
  • the novel method is not limited to a particular type of emitter body.
  • Semitransparent photocathodes or electron-multiplying dynodes may also be made by the novel method.
  • a Semitransparent emitter body may itself be a faceplate and thus act as a portion of the envelope, with the emitting surface being inside the envelope. Such an arrangement may require a different means of separately heating the emitter body to remove the protective layer.
  • the novel method is particularly advantageous for semiconductor emitter bodies because of the sensitivity of semiconductor surfaces to contamination and the difficulties in evaporating semiconductor layers inside a tube envelope, the novel method is also applicable to where the emitter body is a metal, such as for example tungsten, or an insulator, such as for example magnesium oxide.
  • a method of making an electron emitter device comprising:

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Cold Cathode And The Manufacture (AREA)
  • Formation Of Various Coating Films On Cathode Ray Tubes And Lamps (AREA)
  • Common Detailed Techniques For Electron Tubes Or Discharge Tubes (AREA)
  • Electron Sources, Ion Sources (AREA)
US00107372A 1971-01-18 1971-01-18 Method of making an electron emitter device Expired - Lifetime US3712700A (en)

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US10737271A 1971-01-18 1971-01-18

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US (1) US3712700A (OSRAM)
AU (1) AU476019B2 (OSRAM)
CA (1) CA950964A (OSRAM)
DE (1) DE2202217C3 (OSRAM)
FR (1) FR2122455B1 (OSRAM)
GB (1) GB1357693A (OSRAM)
NL (1) NL7200649A (OSRAM)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3858955A (en) * 1973-01-15 1975-01-07 Rca Corp Method of making a iii-v compound electron-emissive cathode
US4058875A (en) * 1976-08-18 1977-11-22 Rca Corporation Method of assembling a mask-panel assembly of a shadow-mask cathode-ray tube
US4073558A (en) * 1977-04-25 1978-02-14 Gte Sylvania Incorporated Cathode ray tube fabricating process
US5552595A (en) * 1994-03-24 1996-09-03 Hiroshima University Narrow band high sensitivity photodetector for inverse photoemission spectroscopy
US5554844A (en) * 1994-03-24 1996-09-10 Hiroshima University Passband-adjustable photo-detector for inverse photoemission spectroscopy
WO1998050934A1 (en) * 1997-05-04 1998-11-12 Yeda Research And Development Co. Ltd. Protection of photocathodes with thin films

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1555762A (en) * 1975-08-14 1979-11-14 Mullard Ltd Method of cleaning surfaces
DE102009054322A1 (de) 2009-11-24 2011-05-26 Huhtamaki Forchheim Zweigniederlassung Der Huhtamaki Deutschland Gmbh & Co. Kg Trennfolie mit Schaumstruktur

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2184323A (en) * 1933-06-23 1939-12-26 Hans J Spanner Cathode activation and degassing
US2441810A (en) * 1943-01-01 1948-05-18 Rca Corp Phototube and method of manufacture
US2505909A (en) * 1948-02-26 1950-05-02 Bishop H Russell Cathode-ray tube with oxide coated cathode
US3353890A (en) * 1965-02-23 1967-11-21 Philips Corp Methods of manufacturing electron tubes having a photo-sensitive layer in a vacuum space tubes manufactured by said methods and devices for carrying out said methods
US3390012A (en) * 1964-05-14 1968-06-25 Texas Instruments Inc Method of making dielectric bodies having conducting portions

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1298362A (en) * 1969-03-31 1972-11-29 Mullard Ltd Improvements relating to electric discharge tubes comprising photo-cathodes

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2184323A (en) * 1933-06-23 1939-12-26 Hans J Spanner Cathode activation and degassing
US2441810A (en) * 1943-01-01 1948-05-18 Rca Corp Phototube and method of manufacture
US2505909A (en) * 1948-02-26 1950-05-02 Bishop H Russell Cathode-ray tube with oxide coated cathode
US3390012A (en) * 1964-05-14 1968-06-25 Texas Instruments Inc Method of making dielectric bodies having conducting portions
US3353890A (en) * 1965-02-23 1967-11-21 Philips Corp Methods of manufacturing electron tubes having a photo-sensitive layer in a vacuum space tubes manufactured by said methods and devices for carrying out said methods

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3858955A (en) * 1973-01-15 1975-01-07 Rca Corp Method of making a iii-v compound electron-emissive cathode
US4058875A (en) * 1976-08-18 1977-11-22 Rca Corporation Method of assembling a mask-panel assembly of a shadow-mask cathode-ray tube
US4073558A (en) * 1977-04-25 1978-02-14 Gte Sylvania Incorporated Cathode ray tube fabricating process
US5552595A (en) * 1994-03-24 1996-09-03 Hiroshima University Narrow band high sensitivity photodetector for inverse photoemission spectroscopy
US5554844A (en) * 1994-03-24 1996-09-10 Hiroshima University Passband-adjustable photo-detector for inverse photoemission spectroscopy
WO1998050934A1 (en) * 1997-05-04 1998-11-12 Yeda Research And Development Co. Ltd. Protection of photocathodes with thin films
US6531816B1 (en) 1997-05-04 2003-03-11 Yeda Research & Development Co. Ltd. Protection of photocathodes with thin film of cesium bromide

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Publication number Publication date
GB1357693A (en) 1974-06-26
FR2122455B1 (OSRAM) 1975-10-03
FR2122455A1 (OSRAM) 1972-09-01
DE2202217C3 (de) 1975-12-18
AU3793472A (en) 1973-07-19
CA950964A (en) 1974-07-09
AU476019B2 (en) 1976-09-09
NL7200649A (OSRAM) 1972-07-20
DE2202217A1 (de) 1972-08-03
DE2202217B2 (de) 1975-05-15

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