US3887835A - Field emission electron gun - Google Patents

Field emission electron gun Download PDF

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Publication number
US3887835A
US3887835A US368520A US36852073A US3887835A US 3887835 A US3887835 A US 3887835A US 368520 A US368520 A US 368520A US 36852073 A US36852073 A US 36852073A US 3887835 A US3887835 A US 3887835A
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Prior art keywords
cathode
anode
electron gun
field
emission electron
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Expired - Lifetime
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US368520A
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English (en)
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Setsuo Nomura
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Hitachi Ltd
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Hitachi Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J3/00—Details of electron-optical or ion-optical arrangements or of ion traps common to two or more basic types of discharge tubes or lamps
    • H01J3/02—Electron guns
    • H01J3/021—Electron guns using a field emission, photo emission, or secondary emission electron source

Definitions

  • FIG 6 relates to a field-emission electron gun. More particularly, it relates to a fieldemission electron gun in which a cathode is steadily heated to a fixed temperature, whereby the electron current to be emitted from the cathode is stabilized.
  • the field-emission electron gun is so constructed that a great field for drawing out electrons is applied to the surface of a cathode which is placed in a vacuum, to thus cause electrons to emit from the cathode surface.
  • the electron current density of the electron gun of this type is much higher when compared with that of a prior art electron gun of the thermionic emission type.
  • the energy width possessed by the emitted electrons is smaller than in the thermionic-emission electron gun.
  • the field-emission electron gun is recently regarded as very important as an electron gun for electro-optic devices. It has, however, the disadvantage that since the emission electron current density is sensitively affected by surface conditions of the cathode, the period of time during which a stable electron current is acquired is extremely short.
  • FIG. 1 illustrates the changes-versus-time of an emitted electron current i during the state under which a cathode is held at room temperature without being heated in a prior art field-emission electron gun.
  • the electron current Upon completion of the stable state, the electron current becomes unstable, and its magnitude increases gradually. These phenomena are caused by the adsorption of excessive gas and the generation of microscopic disorders on the cathode surface as results from ion bombardment. It is thought that the electron current fluctuates due to the adsorption of an excessive amount of gas, and that the electron current density increases because high electric field strengths act locally on protrusion-shaped parts having arisen as the result of the bombardment on the cathode surface by positive ions created by the emitted electron current. If allowed to stand, the increase in the electron current density gradually becomes larger and more erratic with time, finally leading to destruction of the cathode due to the Joule heat and the strong electric field.
  • the electric field for effecting the electron emission is cut off to stop the operation of the electron gun, and that the cathode is heated to a high temperature to perform restoration or flashing (cleaning and smoothing) of the surface thereof.
  • the stable characteristic is attained only for the period T as stated above. How the stable state may be maintained for a long period is accordingly a very important subject. It has therefore been hitherto endeavored to enhance the degree of vacuum of the device as far as possible, so as to maintain the conditions of the cathode surface as uniform as possible. Besides, in order to avoid contamination due to the adsorbed gas, there has been proposed a method by which the cathode is heated above 1,000C. during the operation of the electron gun. According to the method, the cathode surface is kept clean, and the minute disorders in the surface do not appear. The method, however, had disadvantages, as mentioned below.
  • Atoms are continually moving on the cathode surface, so that the emission electron current flickers.
  • the energy width of emitted electrons spreads, which deprives the field-emission electron gun of the characterizing feature that the energy width is narrow.
  • the proposed method is not readily adopted in practice.
  • the conventional field-emission electron gun is used with the cathode left at room temperature on the condition that the degree of vacuum of the device is brought to the best possible value.
  • the stability of the electron current is not satisfactory. Since, in addition, a high-temperature heating operation for cleaning the cathode is frequently required, the tip end of the cathode becomes blunt early in the operation, and the life of the electron gun is therefore quite short.
  • a further object of the present invention is to provide a field-emission electron gun which has a long life without the necessity for effecting a cleaning operation for the cathode.
  • the fieldemission electron gun of the present invention is characterized in that the cathode is continually heated to a low temperature of C.- 500C.
  • FIG. 1 is a diagram of a curve showing the changeswith-time of an emission electron current from a cathode held at room temperature;
  • FIG. 2 is a schematic longitudinal sectional view showing an example of the construction of a fieldemission electron gun according to the present invention
  • FIG. 3 is a diagram of a curve showing the changeswith-time of the emission current in the case where, after having the cathode surface cleaned, the electron gun is operated with the cathode held at 250C;
  • FIG. 4 is a diagram of a curve showing the changeswith-time of the emission current in the case where the cathode is allowed to stand at room temperature after the operation, and then the electron gun is operated without cleaning the cathode surface;
  • FIG. is a diagram of a curve showing the changeswith-time of the emission current in the case where the cathode is kept at 250C. even after cessation of the operation, and thereafter the operation is restarted;
  • FIG. 6 is a diagram of a curve showing the rate A of gradual increase in the electron current per unit time as taken versus the cathode temperature.
  • FIG. 7 is a diagram of a curve showing the rate B of high-frequency noises as taken versus the cathode temperature.
  • reference numeral 1 designates a cathode, which is steadily heated by supplying a heating current i to a filament 2 from a power source 3.
  • a high-voltage power source 6 is connected between the cathode 1 and the first anode 4, to form an electric field for drawing out electrons from the cathode 1.
  • an accelerating power source 7 is connected between the first anode 4 and the second anode 5 .
  • the electron beam current i which is field-emitted from the cathode 1, passes through an opening portion 4a of the first anode 4. Further, it is accelerated by an electric field formed between the first anode 4 and the second anode 5. Thereafter, it is ejected from an opening portion 5a of the second anode 5.
  • character A denotes the rate of the increase of the electron current per unit time as taken versus the cathode temperature, the increase occurring after the time when the cathode surface has been saturated with the appropriate amount of adsorbed gas. It is understood from the graph that the cathode need be heated to at least 100C. in order that the emission electron current may not increase by 30% or more even with a lapse of time of 1 hour.
  • the cathode temperature of or above C. is required in order to make the gradual increase of the electron current 30% or less per hour, while the cathode must not be heated above 500C. in order to restrain the rate of the highfrequency noises of the electron current to or below
  • the allowable varying range for stably maintaining the emission electron current as actually required in a device employing a field-emission electron gun, such as a scanning type electron microscope, is at most 30% per hour as to the gradual increase of the electron current and is at most 5% as to the rate of the highfrequency noises at the electron current.
  • FIG. 3 illustrates the change-versus-time of the emission electron current in the case where the field emission is carried out with the cathode temperature held at 250C.
  • the cathode of the prior art field-emission electron gun Since the cathode of the prior art field-emission electron gun is kept at room temperature, large quantities of gas are adsorbed. When the operation is started without conducting the cleaning of the cathode surface, the excessive gas moves about on the cathode surface, with the result that the emission electron current is very unstable, as illustrated in FIG. 4. It is therefore necessary that, at the beginning of the operation, the cathode is first heated to a high temperature to thereby clean its surface. It is true, as previously stated, that this procedure renders the cathode blunt, to shorten the life of the electron gun.
  • the cathode 1 can be held at the same temperature as that during the operation. Therefore, the adsorption of the excessive gas is avoided for the period, and the cathode surface is retained in the stable state.
  • the cathode 1 is kept heated to 250C. during the cessation of the operation and where the operation is started again at the cathode temperature, the subsequent changes-versus-time of the emission electron current become as shown in FIG. 5. In this case, a stable emission current is produced under quite the same conditions as in the preceding operation.
  • a field-emission electron gun comprising a cathode, a first anode, a second anode, a source of a first electric potential connected between said cathode and said first anode to form an electric field for drawing out electrons from said cathode, a source of a second electric potential connected between said first anode and said second anode to form an accelerating electric field for accelerating the electrons drawn out from said cathode, and power supply means for continuously heating said cathode to a fixed temperature within a range of from 100C. to 500C. during a state under which said electrons are being emitted from said cathode.
  • a method of stabilizing an emission electron current in a field-emission electron gun during a state under which electrons are being emitted by an electric field formed between a cathode and a first anode, the improvement comprising the step of supplying a heating current continuously to a filament attached to said cathode to steadily heat said cathode so as to hold it at a fixed temperature within a range of from C. to 500C.

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  • Cold Cathode And The Manufacture (AREA)
  • Electron Sources, Ion Sources (AREA)
  • Particle Accelerators (AREA)
  • Solid Thermionic Cathode (AREA)
US368520A 1972-06-09 1973-06-11 Field emission electron gun Expired - Lifetime US3887835A (en)

Applications Claiming Priority (1)

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JP5691072A JPS5420828B2 (enrdf_load_stackoverflow) 1972-06-09 1972-06-09

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JP (1) JPS5420828B2 (enrdf_load_stackoverflow)
GB (1) GB1426509A (enrdf_load_stackoverflow)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4059783A (en) * 1976-01-21 1977-11-22 Hitachi, Ltd. Field emission apparatus
US5118991A (en) * 1989-09-09 1992-06-02 Ptr Prazisionstechnik Gmbh Electron beam generator for an electron gun
US5373158A (en) * 1992-06-05 1994-12-13 Hitachi, Ltd. Field-emission transmission electron microscope and operation method thereof
FR2714208A1 (fr) * 1993-12-22 1995-06-23 Mitsubishi Electric Corp Cathode, canon à électrons comportant une telle cathode et tube à rayons cathodiques comportant un tel canon.
FR2792770A1 (fr) * 1999-04-22 2000-10-27 Cit Alcatel Fonctionnement a haute pression d'une cathode froide a emission de champ
US20110221360A1 (en) * 2010-03-10 2011-09-15 ICT Integrated Circuit Testing Gesellschaft für Halbleiterprüftechnik mbH Feedback loop for emitter flashing
US20230154720A1 (en) * 2021-11-16 2023-05-18 Nuflare Technology, Inc. Method for estimating cathode lifetime of electron gun, and electron beam writing apparatus

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4714600A (en) * 1984-12-24 1987-12-22 Mobil Oil Corporation Process for production of phosphoric acid from dry matrix by SO3 treatment and extraction

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3678333A (en) * 1970-06-15 1972-07-18 American Optical Corp Field emission electron gun utilizing means for protecting the field emission tip from high voltage discharges
US3786268A (en) * 1971-04-12 1974-01-15 Hitachi Ltd Electron gun device of field emission type

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2637107C2 (de) * 1976-08-18 1978-09-14 Danfoss A/S, Nordborg (Daenemark) Schaltungsanordnung zum Ermitteln physikalischer Größen strömender Medien nach der Ultraschallmethode

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3678333A (en) * 1970-06-15 1972-07-18 American Optical Corp Field emission electron gun utilizing means for protecting the field emission tip from high voltage discharges
US3784815A (en) * 1970-06-15 1974-01-08 American Optical Corp Low voltage field emission scanning electron microscope
US3786268A (en) * 1971-04-12 1974-01-15 Hitachi Ltd Electron gun device of field emission type

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4059783A (en) * 1976-01-21 1977-11-22 Hitachi, Ltd. Field emission apparatus
US5118991A (en) * 1989-09-09 1992-06-02 Ptr Prazisionstechnik Gmbh Electron beam generator for an electron gun
US5373158A (en) * 1992-06-05 1994-12-13 Hitachi, Ltd. Field-emission transmission electron microscope and operation method thereof
FR2714208A1 (fr) * 1993-12-22 1995-06-23 Mitsubishi Electric Corp Cathode, canon à électrons comportant une telle cathode et tube à rayons cathodiques comportant un tel canon.
FR2792770A1 (fr) * 1999-04-22 2000-10-27 Cit Alcatel Fonctionnement a haute pression d'une cathode froide a emission de champ
EP1052668A1 (fr) * 1999-04-22 2000-11-15 Alcatel Fonctionnement à haute pression d'une cathode froide à émission de champ
US6559442B1 (en) 1999-04-22 2003-05-06 Alcatel High-pressure operation of a field-emission cold cathode
US20110221360A1 (en) * 2010-03-10 2011-09-15 ICT Integrated Circuit Testing Gesellschaft für Halbleiterprüftechnik mbH Feedback loop for emitter flashing
US8674300B2 (en) * 2010-03-10 2014-03-18 ICT Integrated Circuit Testing Gesellschaft fur Halbleiterprüftechnik mbH Feedback loop for emitter flashing
US20230154720A1 (en) * 2021-11-16 2023-05-18 Nuflare Technology, Inc. Method for estimating cathode lifetime of electron gun, and electron beam writing apparatus

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GB1426509A (en) 1976-03-03
JPS4918258A (enrdf_load_stackoverflow) 1974-02-18
JPS5420828B2 (enrdf_load_stackoverflow) 1979-07-25

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