Emitter

Abstract

To provide an emitter which can effectively suppress generation of excess electrons and can improve structural stability, while suppressing variation in electron emission characteristics.SOLUTION: An emitter comprises: an electron source 2; and a heater 3 for heating the electron source 2. The electron source 2 has: an electron emission member 10 which is made of a first material; and a surrounding member 20 which is made of a second material having a work function greater than that of the first material. The electron emission member 10 has: a first portion 11; and a second portion 12 which is made integral with the first portion 11. The surrounding member 20 is fixed to the electron emission member 10, and it surrounds the first portion 11 when viewed from a direction A. The minimum thickness of the surrounding member 20 is 20 μm or more. The heater 3 is in contact with the second portion 12.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an emitter.

Background Art

[0002] For example, Patent Document 1 describes an emitter including an electron source and a heater. In this emitter, the electron source includes a columnar portion having electron emission characteristics and an electron emission limiting member disposed so as to surround the columnar portion. The heater is in contact with the electron emission limiting member and heats the columnar portion via the electron emission limiting member. The heated columnar portion emits electrons.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the emitter as described above, it is preferable that the variation in electron emission characteristics is small. Further, it is preferable that the generation of surplus electrons can be effectively suppressed, and it is preferable that the structure is stable.

[0005] Therefore, an object of the present invention is to provide an emitter capable of suppressing the variation in electron emission characteristics, effectively suppressing the generation of surplus electrons, and improving the structural stability.

Means for Solving the Problems

[0006] The emitter of the present invention is "[1] an emitter comprising an electron source and a heater for heating the electron source, wherein the electron source has an electron-emitting member formed of a first material and an enclosing member formed of a second material having a work function larger than that of the first material, the electron-emitting member has a first portion and a second portion integrally formed with the first portion, the enclosing member is fixed to the electron-emitting member and encloses the first portion when viewed from a predetermined direction, the minimum thickness of the enclosing member is 20 μm or more, and the heater is in contact with the second portion."

[0007] In this emitter, the first portion of the electron-emitting member is enclosed by an enclosing member formed of a second material having a work function larger than that of the first material constituting the electron-emitting member. Thereby, generation of surplus electrons from other than the tip of the first portion can be suppressed, and electrons can be suitably emitted. Further, in this emitter, the heater is in contact with the second portion of the electron-emitting member. Thereby, the electron-emitting member can be directly heated by the heater. Therefore, for example, compared with the case where the heater contacts the enclosing member and heats the electron-emitting member through the enclosing member, the electron-emitting member can be stably heated by the heater. As a result, for example, even when used for a long period of time, fluctuations in electron emission characteristics can be suppressed. Furthermore, in this emitter, the minimum thickness of the enclosing member is 20 μm or more. Thereby, the effect of suppressing the generation of surplus electrons by the enclosing member is effectively exhibited. Also, since the enclosing member is thick, the strength of the enclosing member can be ensured and the structural stability can be improved. Therefore, according to this emitter, fluctuations in electron emission characteristics can be suppressed, and effective suppression of the generation of surplus electrons and improvement of structural stability can be achieved.

[0008] The emitter of the present invention may be "[2] the emitter according to [1], wherein the end portion of the first portion on the side opposite to the second portion is formed in a tapered shape so as to become thinner toward the tip." In this case, electrons can be suitably emitted from the first portion.

[0009] The emitter of the present invention may be the emitter described in [3] "The surrounding member is joined to the electron-emitting member by a joining material, and the joining material is formed of the same material as the second material, as described in [1] or [2]". In this case, the joining strength between the surrounding member and the electron-emitting member can be increased.

[0010] The emitter of the present invention may be the emitter described in [4] "The boundary between the second portion and the first portion in the first portion is not surrounded by the surrounding member and is covered by the joining material, as described in [3]". In this case, the generation of surplus electrons from other than the tip of the first portion can be effectively suppressed.

[0011] The emitter of the present invention may be the emitter described in [5] "In the width direction perpendicular to the predetermined direction, the width of the second portion is wider than the width of the first portion, and the electron source is fixed to the heater by the second portion being sandwiched by the heater along the width direction, as described in any one of [1] to [4]". In this case, it is possible to suppress the occurrence of damage or the like at the fixing portion by the heater in the electron source, and the structural stability can be further improved.

[0012] The emitter of the present invention may be the emitter described in [6] "The surrounding member is composed of a sintered body, as described in any one of [1] to [5]". In this case, the generation of surplus electrons can be effectively suppressed, and the structural stability can be effectively improved.

Effects of the Invention

[0013] According to the present invention, it is possible to provide an emitter that can suppress fluctuations in electron emission characteristics, effectively suppress the generation of surplus electrons, and improve structural stability.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

[0015] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same or corresponding elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0016] As shown in FIG. 1, the emitter 1 includes an electron source 2, a heater 3, an insulator 4, a pair of electrode pins 5, and a suppressor electrode 6. The electron source 2 emits electrons. Details of the electron source 2 will be described later. The electron source 2 is fixed to the heater 3 and heated by the heater 3. The heater 3 is formed in a block shape, for example, of pyrolytic carbon, and is energized through a pair of electrode pins 5 to generate heat. The electrode pins 5 are provided so as to penetrate the insulator 4 and are connected to the heater 3. The suppressor electrode 6 is disposed around the electron source 2. The suppressor electrode 6 suppresses lateral electron emission from the electron source 2. In the emitter 1, when the electron source 2 is heated by energizing the heater 3 and a voltage is applied between the electron source 2 and a draw-out electrode (not shown), electrons are output from the tip of the electron source 2.

[0017] As shown in FIGS. 2 and 3, the electron source 2 has an electron emission member 10 and a surrounding member 20. The electron emission member 10 is formed of a first material (electron emission material) having electron emission characteristics. The surrounding member 20 is formed of a second material (electron emission limiting material) having a work function larger than that of the first material.

[0018] The first material is a material that can be heated to emit electrons. The first material has a smaller work function than the second material. Examples of the first material include rare earth borides such as lanthanum boride (LaB6) and cerium boride (CeB6); high melting point metals such as tungsten, tantalum, and hafnium, as well as their oxides, carbides, and nitrides; and noble metal-rare earth alloys such as iridium cerium. The work functions of these materials are as follows. · Lanthanum boride (LaB6): 2.8 eV · Cerium boride (CeB6): 2.8 eV · Tantalum carbide: 3.2 eV · Hafnium carbide: 3.3 eV

[0019] The second material has a larger work function than the first material. By surrounding the electron-emitting member 10 made of the first material with the surrounding member 20 made of the second material, the emission of electrons from the side surface of the electron-emitting member 10 is suppressed. The difference between the work function of the second material and the work function of the first material is preferably 0.5 eV or more, more preferably 1.0 eV or more, and still more preferably 1.6 eV or more.

[0020] The second material preferably contains a high melting point metal or its carbide, and preferably contains at least one of metal tantalum, metal titanium, metal zirconium, metal tungsten, metal molybdenum, metal rhenium, tantalum carbide, titanium carbide, and zirconium carbide. The second material may contain at least one of boron carbide and graphite (carbon material). The second material may contain at least one of niobium, hafnium, and vanadium. As the second material, glassy carbon (for example, glassy carbon (trade name, manufactured by Rayho Manufacturing Co., Ltd.)) may be used. The work functions of these materials are as follows. · Metal rhenium: 4.9 eV · Boron carbide: 5.2 eV · Graphite: 5.0 eV

[0021] The first material and the second material may be appropriately selected and used in combination based on, for example, their work functions and strengths. Preferred examples of the first material include lanthanum boride (LaB6), cerium boride (CeB6), hafnium carbide, and iridium cerium. Preferred examples of the second material include metallic rhenium, boron carbide, and graphite (including glassy carbon). Note that some of the materials that can be used as the first material can also be used as the second material. For example, materials with a work function of about 3.2 to 4.5 eV can be used as both the first material and the second material. Such materials include metallic tungsten (work function: 4.5 eV), metallic tantalum (work function: 3.2 eV), and hafnium carbide (work function: 3.3 eV).

[0022] The electron-emitting member 10 has a first portion 11 and a second portion 12 formed integrally with the first portion 11. In this example, the first portion 11 has an octagonal columnar pillar portion 13 and a tapered portion 14 formed in a tapered shape. The pillar portion 13 extends along the direction A (predetermined direction) from the second portion 12. The tapered portion 14 is provided on the side opposite to the second portion 12 with respect to the pillar portion 13 (the upper side in FIG. 2), and constitutes an end portion 11a on the side opposite to the second portion 12 in the first portion 11. The tapered portion 14 is formed in a tapered shape so as to become thinner toward the tip. The end face 10a of the electron-emitting member 10 (tapered portion 14) is an electron-emitting surface. The end face 10a is, for example, a flat surface perpendicular to the direction A, and electrons are emitted along the direction A from the end face 10a.

[0023] The second portion 12 is formed in a shape wider than the pillar portion 13. That is, in the direction B (width direction) perpendicular to the direction A, the width W12 of the second portion 12 is wider than the width W11 of the first portion 11. In this example, the electron source 2 is fixed to the heater 3 by sandwiching the second portion 12 with the heater 3 along the direction B. The heater 3 is in contact with the second portion 12. In this example, the heater 3 is in contact with the entire second portion 12 in the direction A. The second portion 12 is formed, for example, in a rectangular shape in a cross section perpendicular to the direction A.

[0024] The surrounding member 20 is formed in a substantially cylindrical shape and surrounds the first portion 11 of the electron-emitting member 10 when viewed from direction A. More specifically, the surrounding member 20 does not cover the end portion 11b (the boundary portion between the first portion 11 and the second portion 12) on the second portion 12 side of the first portion 11, and surrounds the entire portion other than the end portion 11b. That is, in direction A, there is a gap between the surrounding member 20 and the second portion 12 of the electron-emitting member 10. The end portion 11b is covered by a bonding material 30 described later.

[0025] The surrounding member 20 has a first surrounding portion 21 that surrounds the column portion 13 of the first portion 11 and a second surrounding portion 22 that surrounds the tapered portion 14 of the first portion 11. In this example, the second surrounding portion 22 also surrounds the end portion of the column portion 13 on the tapered portion 14 side. The first surrounding portion 21 is formed in a cylindrical shape having, for example, a rectangular outer shape. The second surrounding portion 22 is formed in a tapered shape so as to become thinner toward the tip. The taper angle of the outer surface of the second surrounding portion 22 is larger than the taper angle of the outer surface of the tapered portion 14. As a result, the thickness of the second surrounding portion 22 becomes thinner toward the tip side (the side opposite to the second portion 12).

[0026] The surrounding member 20 is formed of glassy carbon in this example. More specifically, the surrounding member 20 is constituted by a sintered body of glassy carbon formed by vacuum sintering a phenolic resin. The minimum thickness of the surrounding member 20 is 20 μm or more. In this example, the surrounding member 20 is thinnest at the tip portion of the second surrounding portion 22, and its thickness is, for example, 40 μm. The thickness of the first surrounding portion 21 is, for example, about 150 μm. The minimum thickness of the surrounding member 20 is preferably 25 μm or more, and more preferably 30 μm or more.

[0027] The surrounding member 20 is joined to the electron-emitting member 10 by the joining material 30. The joining material 30 is disposed between the first surrounding portion 21 of the surrounding member 20 and the column portion 13 of the first portion 11 of the electron-emitting member 10. The joining material 30 is also disposed between the first surrounding portion 21 and the second portion 12 of the electron-emitting member 10. Thus, as described above, the joining material 30 covers the end portion 11b (the portion of the first portion 11 exposed from the surrounding member 20) on the second portion 12 side in the first portion 11. In this example, the joining material 30 is formed of the same material (for example, glassy carbon) as the second material constituting the surrounding member 20. More specifically, the joining material 30 is constituted by a sintered body of glassy carbon formed by disposing a phenolic resin at predetermined locations and then performing vacuum sintering.

[0028] The end face 20a of the surrounding member 20 (the second surrounding portion 22) is flush with the end face 10a (electron-emitting face) of the electron-emitting member 10. Also, the side face of the first portion 11 of the electron-emitting member 10 is covered by the surrounding member 20 and the joining material 30. By not exposing the side face of the first portion 11 in this way, it is possible to effectively suppress the emission of unnecessary electrons, that is, the emission of electrons to the side. For example, in order to obtain electrons of a larger current, the electron source 2 is heated to a high temperature of about 1550 °C and a high electric field of several kV is applied to the electron source 2. When such a high electric field is applied, surplus electrons may be generated from other than the tip of the electron source 2. These surplus electrons may, due to the space charge effect, reduce the brightness of the electron beam from the tip or cause unnecessary heating of the surrounding electrode components. To prevent this, only the electron-emitting portion (the end face 10a of the electron-emitting member 10) of the electron source 2 is exposed, and the other faces are covered by the surrounding member 20 and the joining material 30, so that only a high-brightness electron beam from the tip can be obtained.

[0029] By covering the side surface of the first portion 11 of the electron-emitting member 10 with the surrounding member 20 and the bonding material 30, an effect of suppressing the occurrence of a phenomenon called microdischarge can also be achieved. That is, in thermionic emission, electrons are emitted by heating the electron source to a high temperature. Along with this, when the electron-emitting material evaporates, it adheres to the surrounding electrode components and becomes fibrous crystals called whiskers. When charges accumulate on these whiskers, microdischarge is caused. Microdischarge can destabilize the electron beam and be a factor in degrading the device performance. By covering the side surface of the first portion 11 with the surrounding member 20 and the bonding material 30, the sublimated electron-emitting material is trapped by the surrounding member 20 and the bonding material 30, reducing the amount of adhesion to the surrounding electrode components and making it difficult to cause microdischarge. Note that the surrounding member 20 and the bonding material 30 do not have a cut in a part of the circumferential direction and cover the first portion 11 over the entire circumference. Thereby, the emission of electrons to the side can be effectively suppressed. [Function and Effect]

[0030] In the emitter 1, a first portion 11 of the electron emission member 10 is surrounded by a surrounding member 20 formed of a second material having a work function greater than that of the first material constituting the electron emission member 10. Thereby, generation of surplus electrons from other than the tip of the first portion 11 can be suppressed, and electrons can be preferably emitted. Further, in the emitter 1, the heater 3 is in contact with a second portion 12 of the electron emission member 10. Thereby, the electron emission member 10 can be directly heated by the heater 3. Therefore, for example, compared with the case where the heater contacts the surrounding member and heats the electron emission member through the surrounding member, the electron emission member 10 can be stably heated by the heater 3. As a result, for example, even when used for a long period of time, it is possible to suppress fluctuations in electron emission characteristics. That is, for example, when a configuration is adopted in which the heater contacts the surrounding member and heats the electron emission member through the surrounding member, if the emitter is continuously used for a long period of time (for example, two months), for example, the surrounding member is consumed by heating, and the contact state between the surrounding member and the electron emission member changes, and the output may fluctuate sporadically. This is considered to be because fluctuations occur in the heat conduction from the heater to the electron emission member due to a change in the contact state between the surrounding member and the electron emission member. In this regard, in the emitter 1 of the embodiment, since the electron emission member 10 is directly heated by the heater 3, it is possible to suppress the occurrence of such fluctuations in heat conduction and suppress fluctuations in electron emission characteristics. Further, in the emitter 1, the minimum thickness of the surrounding member 20 is 20 μm or more. Thereby, the effect of suppressing the generation of surplus electrons by the surrounding member 20 is effectively exhibited. Further, since the surrounding member 20 is thick, the strength of the surrounding member 20 can be ensured, and the structural stability can be improved. Therefore, according to the emitter 1, it is possible to suppress fluctuations in electron emission characteristics, and to effectively suppress the generation of surplus electrons and improve the structural stability.

[0031] The end portion 11a (taper portion 14) on the side opposite to the second portion 12 in the first portion 11 is formed in a tapered shape so as to become thinner toward the tip. Thereby, electrons can be preferably emitted from the first portion 11. On the other hand, when the end portion 11a is formed in a tapered shape, it is difficult to accurately form an electron emission suppressing layer (for example, a layer having a thickness of 10 μm or less) on the end portion 11a by film formation. In this regard, in the emitter 1 of the embodiment, the surrounding member 20 surrounding the first portion 11 is configured as a member (structure) having a thickness of 20 μm or more and is joined to the electron emission member 10 by the joining material 30. Therefore, after the surrounding member 20 is accurately formed, it can be joined to the electron emission member 10.

[0032] The surrounding member 20 is joined to the electron emission member 10 by the joining material 30, and the joining material 30 is formed of the same material as the second material constituting the surrounding member 20. Thereby, the joining strength between the surrounding member 20 and the electron emission member 10 can be increased.

[0033] The end portion 11b (the boundary portion between the first portion 11 and the second portion 12) on the side of the second portion 12 in the first portion 11 is not surrounded by the surrounding member 20 but is covered by the joining material 30. Thereby, generation of surplus electrons from other than the tip portion of the first portion 11 can be effectively suppressed.

[0034] In the direction B (width direction), the width W12 of the second portion 12 is wider than the width W11 of the first portion 11, and the electron source 2 is fixed to the heater 3 by the second portion 12 being sandwiched by the heater 3 along the direction B. Thereby, it is possible to suppress breakage or the like at the fixing portion of the electron source 2 by the heater 3, and the structural stability can be further improved. Further, since the width W12 of the second portion 12 is wider than the width W11 of the first portion 11, it becomes easier to grip the second portion 12, and the handleability can be improved.

[0035] The surrounding member 20 is composed of a sintered body. Thereby, generation of surplus electrons can be effectively suppressed and structural stability can be effectively improved.

[0036] The present invention is not limited to the above-described embodiment. For example, the materials and shapes of the respective components are not limited to the materials and shapes described above, and various materials and shapes can be adopted.

[0037] The first portion 11 of the electron emission member 10 may not have the tapered portion 14, and may have, for example, the same cross-sectional shape over the entire length. The surrounding member 20 may not have a tapered portion (second surrounding portion 22), and may have, for example, the same cross-sectional shape over the entire length. In the above embodiment, the surrounding member 20 did not cover the end portion 11b on the second portion 12 side in the first portion 11, but the surrounding member 20 may cover the entire first portion 11 in the direction A. The bonding material 30 may be formed of a material different from the second material constituting the surrounding member 20. The bonding material 30 may not necessarily be provided, and the surrounding member 20 may be fixed to the electron emission member 10 by another method. In the direction B, the width W12 of the second portion 12 may be the same as the width W11 of the first portion 11, or may be narrower than the width W11.

Explanation of reference numerals

[0038] 1... emitter, 2... electron source, 3... heater, 10... electron emission member, 11... first portion, 11a... end portion, 11b... end portion, 12... second portion, 20... surrounding member, 30... bonding material, A... direction (predetermined direction), B... direction (width direction), W11, W12... width.

Claims

1. An electron source and a heater for heating the electron source, The electron source includes: An electron emission member formed of a first material, A surrounding member formed of a second material having a work function greater than that of the first material, The electron emission member has a first portion and a second portion integrally formed with the first portion, The surrounding member is fixed to the electron emission member and surrounds the first portion when viewed from a predetermined direction, The minimum thickness of the surrounding member is 20 μm or more, The heater is in contact with the second portion, the emitter.

2. The emitter according to claim 1, wherein an end portion of the first portion on the side opposite to the second portion is formed in a tapered shape so as to become thinner toward the tip.

3. The surrounding member is joined to the electron emission member by a joining material, The emitter according to claim 1 or 2, wherein the joining material is formed of the same material as the second material.

4. The emitter according to claim 3, wherein a boundary portion between the first portion and the second portion is not surrounded by the surrounding member and is covered by the joining material.

5. In a width direction perpendicular to the predetermined direction, the width of the second portion is wider than the width of the first portion, The emitter according to claim 1 or 2, wherein the electron source is fixed to the heater by the second portion being sandwiched by the heater along the width direction.

6. The emitter according to claim 1 or 2, wherein the surrounding member is constituted by a sintered body.

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