Field Emission Device

Abstract

To provide a field emission device which can obtain prescribed voltage resistance even when a drawing amount of an emitter is small.SOLUTION: A field emission device comprises: a vacuum container which includes a vacuum chamber; an emitter which has an electron generation part that is located on one side in the axial direction of the vacuum chamber and is opposed to the other side in the axial direction of the vacuum chamber; a target which is located on the other side of the vacuum chamber and is provided so as to be opposed to the emitter; a guard electrode which is a cylindrical body that is provided on the outer peripheral side of the emitter, and in which the one side thereof is fixed to the vacuum container and the other side has an opening; a support which makes the emitter movable in the axial direction on the inner side of the guard electrode; and a field shielding body which is made of a conductor that is connected to the guard electrode and is arranged on one side of a guard electrode edge part. The field shielding body is arranged so as to partially overlap the opening on a projection surface in the axis direction and is formed into the shape that partitions the opening into a plurality of regions.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a field emission device that can be applied to various devices such as X-ray devices, electron tubes, and lighting devices. [Background technology]

[0002] Conventional field emission devices are applied to various devices such as X-ray devices, electron tubes, and lighting devices. A field emission device has an emitter (an electron source such as carbon) and a target that are arranged facing each other at a predetermined distance in a vacuum chamber of a vacuum vessel. In a field emission device, an electron beam is emitted from the emitter by applying a voltage between the emitter and the target (field emission). When this electron beam collides with the target, it exhibits a desired function, such as radioscopic resolution, by externally emitting X-rays.

[0003] The emitter in the field emission device disclosed in Patent Document 1 is configured such that a voltage is applied to the guard electrode while the electron generating section of the emitter and the guard electrode are spaced apart by manipulating the support section. This allows Patent Document 1 to modify at least the guard electrode in the vacuum chamber, making it possible to obtain a desired withstand voltage in the field emission device. Furthermore, the field emission device disclosed in Patent Document 1 allows the electron generating section and the guard electrode to be spaced apart by manipulating the support section, as described above, thereby making it possible to reduce the size of the field emission device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6135827 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the longitudinal dimension of the field emission device is shortened to downsize the device, the bellows and support (emitter support part) are shortened, resulting in an insufficient amount of emitter retraction. As a result, even if the emitter is retracted to the maximum extent, if a sufficient voltage is applied during the modification process of the field emission device, excessive electrons will be emitted from the emitter, damaging the emitter. If the voltage is set low to prevent emitter damage, the field emission device may not be modified sufficiently to obtain the desired withstand voltage.

[0006] The present invention has been made in view of the above circumstances, and has as its object to provide a field emission device that can obtain a predetermined withstand voltage even when the amount of pull-in of the emitter is small. [Means for solving the problem]

[0007] One aspect of the present invention is a field emission device comprising: a vacuum vessel having a vacuum chamber; an emitter located on one axial side of the vacuum chamber and having an electron generating unit facing the other axial side of the vacuum chamber; a target located on the other axial side of the vacuum chamber and disposed opposite the emitter; a guard electrode that is a cylindrical body disposed on the outer periphery of the emitter, the one side of which is fixed relative to the vacuum vessel and has an opening on an inner edge of the other side; a support that moves the emitter in the axial direction inside the guard electrode; and an electric field shield that is composed of a conductor connected to the guard electrode and is disposed on one side of the opening on the edge of the guard electrode, the electric field shield being disposed so as to partially overlap the opening on a projection plane in the axial direction, and that when the emitter is pushed out to the other axial side by the support, crushes the electron generating unit to divide the opening into a plurality of regions. To the electron generating unit An edge portion is formed.

[0008] In the above field emission device, the electric field shield may be composed of one or more linear members fixed to the edge of the opening. In the above field emission device, the electric field shield may be formed of linear members arranged in a lattice pattern. In the above field emission device, the electric field shield may be formed in the shape of a plate having a plurality of through holes.

[0009] the above In the field emission device, at least one surface of the emitter or the support may be electrically insulating at the contact portion between the emitter and the support.

[0010] In the above field emission device, the electric field shield may be formed so that its axial height is smaller than that of the electron generating section. In the above field emission device, the electric field shield may be formed integrally with the guard electrode. [Effects of the Invention]

[0011] According to the present invention, a predetermined withstand voltage can be obtained even when the amount of pull-in of the emitter is small. [Brief explanation of the drawings]

[0012] [Figure 1] 2 is an enlarged cross-sectional view of the electric field shielding structure of the field emission device according to the first embodiment. FIG. [Figure 2] FIG. 2 is a schematic plan view of the electric field shielding structure of FIG. [Figure 3] 1 is a schematic cross-sectional view of the electric field shielding structure of the first embodiment when the emitter is retracted. FIG. [Figure 4] 3 is a schematic cross-sectional view of the electric field shielding structure of the first embodiment when the emitter is pushed out. FIG. [Figure 5] 1 is a schematic cross-sectional view showing an example of a field emission device according to a first embodiment. [Figure 6] 1 is a diagram showing a test specimen assuming the absence of the electric field shielding structure of the first embodiment. [Figure 7] 1 is a diagram showing a test specimen assuming the presence of the electric field shielding structure of the first embodiment. [Figure 8]FIG. 8 is a diagram showing the results of electronic analysis using the test specimens of FIGS. 6 and 7. [Figure 9] FIG. 10 is a schematic plan view of an electric field shielding structure of a field emission device according to a second embodiment. [Figure 10] FIG. 10 is a schematic plan view of an electric field shielding structure of a field emission device according to a third embodiment. [Figure 11] FIG. 1 is a schematic cross-sectional view of a conventional emitter unit. [Figure 12] FIG. 12 is a schematic plan view of the emitter unit of FIG. 11. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In each drawing, the same members or elements are designated by the same reference numerals, and duplicated descriptions will be omitted or simplified.

[0014] [Embodiment 1] Fig. 1 is an enlarged cross-sectional view of the electric field shielding structure of a field emission device 10 according to embodiment 1. Fig. 2 is a schematic plan view of the electric field shielding structure of embodiment 1 shown in Fig. 1. Fig. 5 is a schematic cross-sectional view showing an example of the field emission device 10 of embodiment 1. The electric field shielding structure according to one aspect of the present invention shown in Figs. 1 and 2 is applied to field emission devices 10 including, for example, X-ray devices, electron tubes, lighting devices, etc.

[0015] The field emission device 10 of the first embodiment will be described below with reference to the field emission device 10 shown in Fig. 5. The field emission device 10 of the first embodiment includes a vacuum vessel 2, an emitter unit 3, and a target unit 4. The emitter unit 3 side shown in Fig. 5 is referred to as one side, and the target unit 4 side as the other side. The direction from the one side to the other side is referred to as the axial direction. The direction perpendicular to (intersecting with) the axial direction is referred to as the radial direction (transverse direction).

[0016] (vacuum container 2) The vacuum vessel 2 has a cylindrical insulator 21 extending in the axial direction. The insulator 21 insulates the emitter unit 3 and the target unit 4 from each other and forms a vacuum chamber 20 inside (on the inner wall side of) the vacuum vessel 2. The insulator 21 may be made of an insulating material such as ceramic, as long as it can insulate the emitter unit 3 and the target unit 4 from each other and form the vacuum chamber 20 inside as described above. The vacuum vessel 2 includes cylindrical insulating members 21a and 21b arranged in series. The vacuum vessel 2 may further be configured by assembling the insulating members 21a and 21b to each other by brazing or the like, with a grid electrode 22 interposed between them.

[0017] A grid electrode 22 extending in the radial direction of the vacuum chamber 20 is provided between the emitter unit 3 and the target unit 4. The grid electrode 22 can be of various configurations as long as it is interposed between the emitter unit 3 and the target unit 4 and is capable of appropriately controlling the electron beam L1 passing through the grid electrode 22. The grid electrode 22 includes, for example, an electrode portion 24 and an extraction terminal 25. The electrode portion 24 is, for example, a mesh-shaped electrode and extends in the radial direction of the vacuum chamber 20. The electrode portion 24 has a passage hole 23 formed therein through which the electron beam L1 passes. The extraction terminal 25 penetrates the insulator 21 in the radial direction and is connected to the electrode portion 24.

[0018] (Emitter Unit 3) The emitter unit 3 includes an emitter 30 , an emitter support (support) 31 , and a guard electrode 32 .

[0019] The emitter 30 includes an electron generating section 33 at a position (site) axially facing the target 41 of the target unit 4. The electron generating section 33 generates electrons when a voltage is applied, and emits an electron beam L1. The electron generating section 33 can be configured in various forms as long as it is capable of emitting the electron beam L1 (radiator) as shown in FIG. 5 . For example, the electron generating section 33 can be made of a material such as carbon nanotubes or carbon fibers. Alternatively, the electron generating section 33 may be configured as an emitter 30 formed by molding a material such as carbon into a block or vapor-depositing it into a thin film. Furthermore, it is preferable that the surface of the electron generating section 33 facing the target 41 of the target unit 4 be concave or curved to facilitate focusing of the electron beam L1.

[0020] The emitter support part 31 is movable (movable) in the axial direction inside the guard electrode 32, and supports the emitter 30 with the electron generating part 33 facing the target 41. The base end side of the emitter 30 (the side opposite the electron generating part 33) is joined to the emitter support part 31 by brazing or the like, for example.

[0021] An operating unit 35 for operating the emitter support 31 is connected (attached) to the emitter support 31 via a bellows 34 that is expandable and contractible in the axial direction. Operating the operating unit 35 expands and contracts the bellows 34, causing the emitter support 31 to move axially, and the emitter 30 also moves in the same direction as the emitter support 31. In the first embodiment, the operating unit 35 extends partially from the opposite side of the emitter 30 and is configured integrally with the emitter support 31. However, this is not limiting, and the operating unit 35 may be configured as separate, detachable components. At least one surface of the emitter 30 or the emitter support 31 at the contact point between the emitter support 31 and the emitter 30 may be electrically insulating. For example, when the electron generating unit 33 is formed of carbon nanotubes, forming the base end of the emitter 30 from an insulator allows efficient growth of carbon nanotubes using the insulator as a base.

[0022] By appropriately manipulating the emitter support 31, the distance between the electron generating unit 33 of the emitter 30 and the target 41 can be changed. For example, when the electron generating unit 33 is in a non-discharge position spaced apart from the guard electrode 32 as shown in FIG. 1 and field emission is suppressed, desired modification processes can be performed on the guard electrode 32, the target 41, the grid electrode 22, and the like. Examples of such modification processes include melting and smoothing the surface of the guard electrode 32. Furthermore, the field emission device 10 equipped with the operation unit 35 can be easily miniaturized compared to conventional field emission devices equipped with large-diameter exhaust pipes, which can also reduce manufacturing steps and production costs.

[0023] The modification process of the guard electrode 32 of the field emission device 10 will now be described. First, the operation part 35 of the emitter support part 31 is operated to move the emitter 30 toward one axial side (toward the emitter unit 3, or the right side in FIG. 5 ). This moves the emitter 30 to a non-discharge position away from the guard electrode 32, thereby suppressing field emission from the electron generating part 33. At this time, the electron generating part 33 of the emitter 30 and the edge part 36 of the guard electrode 32 are not in contact with each other. In this state, for example, by appropriately applying a desired voltage between the guard electrode 32 and the grid electrode 22, discharge is repeated in the guard electrode 32, and the guard electrode 32 is modified.

[0024] After the above-described modification process, the operating part 35 of the emitter support part 31 is again operated to move the emitter 30 from the non-discharge position toward the other axial side (toward the target unit 4, left side in FIG. 5 ) and contact the guard electrode 32 to the discharge position, where the electron generating part 33 can emit a field. At the discharge position, the electron generating part 33 of the emitter 30 and the edge part 36 of the guard electrode 32 are in contact with each other (e.g., due to the vacuum pressure of the vacuum chamber 2), as shown in FIGS. 4 and 5 . At the discharge position, the electron generating part 33 of the emitter 30 and the guard electrode 32 are at the same potential. At the discharge position, for example, when a desired voltage is applied between the emitter 30 and the target 41, electrons are generated from the electron generating part 33 of the emitter 30, and an electron beam L1 is emitted. The electron beam L1 is emitted from the protrusions on the surface of the guard electrode 32, which heat, melt, and smooth the protrusions, thereby modifying the surface of the guard electrode 32.

[0025] The modification process described above can suppress phenomena such as flashover (electron generation) from the guard electrode 32 in the field emission device 10, stabilizing the amount of electrons generated by the field emission device 10. In addition, the electron beam L1 can be made into a focused electron beam, which makes it easier to converge the focus of the X-rays L2, thereby enabling high fluoroscopic resolution to be obtained.

[0026] As described above, various configurations can be applied to the emitter support portion 31 as long as it can support the emitter 30 movably in the axial direction. The emitter support portion 31 can be made of various materials, and is not particularly limited, but conductive metal materials such as stainless steel (SUS material, etc.), copper, silver, etc. can be used.

[0027] As long as the bellows 34 is expandable and contractible in the axial direction as described above, various configurations can be used, for example, a molded product obtained by appropriately processing a thin metal plate material, etc. Furthermore, the bellows 34 may be configured in a bellows shape that extends in the axial direction so as to surround the outer periphery of the emitter support part 31 or the operation part 35, for example.

[0028] The guard electrode 32 is disposed on one side of the vacuum chamber 20 in a position facing the target 41. The guard electrode 32 is a cylindrical electrode (cylinder) made of a metal material such as stainless steel (SUS material) and is disposed on the outer periphery of the electron generating portion 33 of the emitter 30. The guard electrode 32 has a flange-shaped edge 36 that protrudes toward the inner periphery. The guard electrode 32 has an opening 310 inside the flange-shaped edge 36. The guard electrode 32 also has a first housing portion 37 and a second housing portion 38 that communicates with the first housing portion 37. The first housing portion 37 houses the emitter 30 and the emitter support portion 31. The second housing portion 38 is located on one side of the first housing portion 37 and houses the bellows 34 and the operation portion 35. The second housing portion 38 is fixed to the edge of the insulating member 21b of the vacuum vessel 2 via a flange portion 39.

[0029] Furthermore, the guard electrode 32 includes an electric field shield 1 disposed in the opening 310 of the edge 36. The electric field shield 1 in the first embodiment is formed of a conductor, and serves to suppress electron emission from the emitter 30 by weakening the electric field applied to the emitter 30 when a high voltage is applied between the guard electrode 32 and the target 41 for the modification process.

[0030] Electric field shield 1 is connected to guard electrode 32 and has the same potential as guard electrode 32. As shown in Fig. 2, electric field shield 1 is arranged so as to partially overlap opening 310 of guard electrode 32 on a projection plane in the axial direction, and is made of a linear member such as a strand or wire. Electric field shield 1 is formed in a shape that radially partitions (divides) opening 310 of guard electrode 32.

[0031] By dividing the opening 310 in the radial direction, the opening 310 can be divided into a plurality of regions. The electric field shield 1 may be made of any conductive metal material, such as iron, stainless steel (e.g., SUS material), copper, or silver, but is not limited to these. Various other materials may be used. The guard electrode 32 and the electric field shield 1 are preferably made of the same material, but different conductive metal materials may be used. In the first embodiment, a single electric field shield 1 is used to divide the opening 310 of the guard electrode 32 into two regions. However, the present invention is not limited to this, and one or more electric field shields 1 may be fixed to the opening 310 of the guard electrode 32 to divide the opening 310 into two or more regions.

[0032] Furthermore, the electric field shield 1 is not limited to existing members such as strands or wires, and a conductive metal material processed to have a cross section in a cylindrical, elliptical, flat, or substantially rectangular shape may be used as the electric field shield 1. In this case, the electric field shield 1 is formed from a conductive metal material similar to strands or wires.

[0033] The electric field shield 1 is fixed (connected) to the edge (opening edge) of the opening 310 of the guard electrode 32. As shown in FIGS. 1 and 3, the electric field shield 1 is disposed on one side (the emitter 30 side, the lower side in FIGS. 1 and 3) of the edge 36 of the guard electrode 32. In the first embodiment, as shown in FIG. 2, the electric field shield 1 is fixed with one end of the electric field shield 1 abutting against the opening edge, and the other end of the electric field shield 1 abutting against the opening edge located opposite the one end of the electric field shield 1. As a result, the opening 310 of the guard electrode 32 is partitioned in the radial direction by the electric field shield 1, dividing the area of ​​the opening 310 into two. The electric field shield 1 can be fixed to the opening edge of the guard electrode 32 by any method that does not cause the electric field shield 1 to come off. For example, the electric field shield 1 and the guard electrode 32 may be mechanically connected or joined, or may be fixed by caulking or welding, or may be fixed by welding or the like.

[0034] When fixing one end of the electric field shield 1 to the opening edge, if wire or the like is used, it is preferable to fix it under a certain tension. If the electric field shield 1 is fixed in a loose state, when it comes into contact with the electron generating section 33 (described later), it will not press the electron generating section 33 evenly, resulting in an insufficient formation of the edge section 33a, and there is a risk that electron emission from the emitter 30 will not be sufficiently improved. Furthermore, although the electric field shield 1 is fixed to the opening edge of the guard electrode 32 as described above, the electric field shield 1 and the guard electrode 32 may be formed integrally.

[0035] (Target Unit 4) 5, the target unit 4 includes a target 41 and a flange portion 42. The target 41 is disposed at a position facing the electron generating portion 33 of the emitter 30 on the other side of the vacuum chamber 20.

[0036] The target 41 has an inclined surface 40 formed at a predetermined angle with respect to the axial direction at a portion facing the electron generating unit 33 of the emitter 30. When the electron beam L1 collides with this inclined surface 40, X-rays L2 are emitted. The X-rays L2 are irradiated in a direction bent from the irradiation direction of the electron beam L1 (for example, the cross-sectional direction of the vacuum chamber 20 shown in FIG. 5). Furthermore, various configurations can be applied to the target 41 as long as the electron beam L1 emitted from the electron generating unit 33 of the emitter 30 collides with the target 41 and X-rays L2 can be emitted. The flange portion 42 is fixed to the edge of the insulating member 21a of the vacuum vessel 2 as shown in FIG. 5.

[0037] (Effects of this embodiment) As described above, in the field emission device 10 of the first embodiment, a voltage is applied to the guard electrode 32 in a state in which the electron generating unit 33 and the guard electrode 32 are spaced apart from each other by operating the emitter support unit 31 with the operation unit 35. This allows at least the guard electrode 32 in the vacuum chamber 20 to be modified, and also allows the field emission device 10 to obtain a desired withstand voltage.

[0038] Here, if the electron generating unit 33 and the guard electrode 32 are configured to be separated from each other by operating the emitter support unit 31 with the operation unit 35 as described above, the field emission device 10 can be made smaller. To achieve this, it is conceivable to shorten the axial (longitudinal) dimension of the field emission device 10 and thereby shorten the bellows 34 and the emitter support unit 31. However, shortening the bellows 34 and the emitter support unit 31 may result in an insufficient amount of attraction of the emitter 30. If the amount of attraction of the emitter 30 is insufficient, even if the emitter 30 is attracted to the maximum extent, applying a sufficient voltage for the modification process of the field emission device 10 may result in excessive electrons being emitted from the emitter 30, damaging the emitter 30. Setting a low voltage to prevent damage to the emitter 30 may result in insufficient modification of the field emission device 10, making it impossible to obtain the desired withstand voltage.

[0039] 1 and 2, an electric field shielding structure in which an electric field shield 1 is disposed in the opening 310 of the guard electrode 32 reduces the electric field on the emitter surface, preventing electron emission from the emitter 30. Therefore, even if the axial dimension of the field emission device 10 is shortened to reduce the size of the field emission device 10, thereby reducing the amount of attraction of the emitter 30, it is possible to shield the electric field on the emitter surface. The electric field shielding structure in embodiment 1 will be described below with reference to FIGS. 3 and 4.

[0040] Fig. 3 is a schematic cross-sectional view of the electric field shielding structure of embodiment 1 when emitter 30 is retracted (non-discharge position), and Fig. 4 is a schematic cross-sectional view of the electric field shielding structure of embodiment 1 when emitter 30 is pushed out (discharge position).

[0041] As shown in FIG. 3, the electric field shield 1 is preferably fixed approximately at the center of the opening 310 of the guard electrode 32 (on a line passing through the radial center point of the opening 310), but the fixing position may be arbitrary. As described above, the electric field shield 1 is disposed on one side of the edge 36 of the guard electrode 32 (the emitter 30 side, the lower side in FIG. 3). Specifically, as shown in FIG. 3, the electric field shield 1 is preferably fixed to the opening edge of the guard electrode 32 so that it is closer to the surface 36b facing one side of the edge 36 than to the surface 36a facing the other side of the edge 36 of the guard electrode 32 (the upper side in FIG. 3). Note that h1 represents the height (length) of the electric field shield 1 in the axial direction, and h2 represents the height of the electron generator 33 in the axial direction. Note that when a strand or wire with a round cross section is used for the electric field shield 1, h1 represents the diameter.

[0042] When the emitter 30 is pushed out, as shown in FIG. 4, a part of the electron generating portion 33 comes into contact with a surface 36b facing one side (the lower side in FIG. 4) of the edge portion 36 of the guard electrode 32, and the contact portion of the electron generating portion 33 is crushed. At this time, the electron generating portion 33 also comes into contact with the electric field shield 1, and the contact portion of the electron generating portion 33 that is in contact with the electric field shield 1 is also crushed. When crushed by the electric field shield 1, a part of the electron generating portion 33 is partitioned, and an edge portion 33a is formed in the electron generating portion 33. The formation of the edge portion 33a in the electron generating portion 33 makes it possible to improve the electron emission efficiency due to the electric field concentration at the edge portion 33a when the electron generating portion 33 generates electrons in response to the application of a voltage and emits the electron beam L1.

[0043] Furthermore, in the first embodiment, it is preferable to set the height h1 of the electric field shield 1 lower (smaller) than the height h2 of the electron generating portion 33. That is, the heights of the electric field shield 1 and the electron generating portion 33 are set so that h2 > h1. Here, it is preferable to set each height so that a portion of the electric field shield 1 does not protrude beyond one end side (edge ​​portion 33a side) of the electron generating portion 33 when the emitter 30 is pushed out (so that the electric field shield 1 is buried in the electron generating portion 33), as shown in FIG. 4 . As described above, in the first embodiment, h2 > h1, and further, the heights h1 and h2 are set so that the electric field shield 1 is hidden (buried) in the electron generating portion 33 when the emitter 30 is pushed in. This makes it possible to avoid the influence of the electric field shielding structure including the electric field shield 1 on the trajectory of the emitted electrons.

[0044] The effect of the electric field shielding structure in embodiment 1 will be described below with reference to Figures 6, 7, 8, 11, and 12. In order to confirm the effect of the electric field shielding structure in embodiment 1, electron analysis was performed on experimental model (test specimen) 5 shown in Figures 6 and 7, assuming that analysis plane X was the electron emission area.

[0045] Fig. 6 is a diagram showing a test model assuming a case where the electric field shielding structure of embodiment 1 is not present. Fig. 7 is a diagram showing a test model assuming a case where the electric field shielding structure of embodiment 1 is present. Fig. 8 is a diagram showing the results of electronic analysis performed using test model 5 shown in Figs. 6 and 7. The vertical axis of Fig. 8 represents electric field strength E (V / m), and the horizontal axis of Fig. 8 represents the horizontal position (mm) of analysis plane X. In Fig. 8, "without shield" represents the analysis results for test model 5 of Fig. 6, and "with shield" represents the analysis results for test model 5 of Fig. 7.

[0046] Fig. 11 is a schematic cross-sectional view of the periphery of the opening in the guard electrode of a conventional emitter unit. Fig. 12 is a schematic plan view of the periphery of the opening in the guard electrode of the emitter unit of Fig. 11. The test model 5 of Fig. 6 imitates the periphery of the opening in the guard electrode of the emitter unit shown in Figs. 11 and 12. The test model 5 of Fig. 7 imitates the periphery of the opening 310 in the guard electrode 32 of the emitter unit 3 of embodiment 1 shown in Figs. 1, 2, etc.

[0047] In the electronic analysis using the test model 5 of FIGS. 6 and 7 described above, the electric field intensity of the analysis surface was analyzed when 5 kV was applied in a vacuum between the anode 51 and cathode 52, which were spaced 2 mm apart by a spacer 53. The opening 54 simulates the opening 310 in the guard electrode 32. The test model 5 in FIG. 7 also has an electric field shield 50 disposed as a conductor simulating the electric field shield 1 similar to that of the first embodiment, providing the same electric field shielding structure as the first embodiment. The analysis surface X was positioned 4 mm recessed from the cathode surface (a position 4 mm lower than the cathode surface) to simulate the retraction of the emitter 30. The results of the electric field intensity analysis performed under the same conditions for each test model 5 described above are described below.

[0048] 7, which has the same electric field shielding structure as in embodiment 1, the electric field strength near the center of the X-plane, where the electric field strength is strongest, is less than one-third of the analysis result when there is no electric field shielding structure. Therefore, the electric field shielding effect of the electric field shielding structure of embodiment 1 can be confirmed.

[0049] As described above, by using the electric field shielding structure of embodiment 1 in the field emission device, the electric field applied to the emitter 30 during the modification process is weakened, and damage to the emitter 30 due to electron emission from the emitter 30 is suppressed. As a result, even if the desired amount of attraction of the emitter 30 is not achieved (the amount of attraction of the emitter 30 becomes small), it is possible to shield the electric field on the emitter surface, and a predetermined withstand voltage can be obtained by applying a sufficiently high voltage between the target 41 and the guard electrode 32 to perform the modification process.

[0050] [Embodiment 2] 9 is a schematic plan view of the electric field shielding structure of the field emission device 10 of embodiment 2. In embodiment 2, the electric field shield 1 is formed of strands or wires arranged in a lattice (mesh) pattern, and other than that, the configuration is the same as that of the field emission device 10 of embodiment 1, and therefore detailed description of the similarities will be omitted as appropriate.

[0051] The electric field shield 1 in the second embodiment is formed by weaving (braiding) conductive linear members such as strands or wires at predetermined intervals to form a grid. Any method for forming the electric field shield 1 is acceptable as long as the electric field shield 1 is woven in a grid pattern. The predetermined intervals may be any interval; for example, the strands or wires may be woven at equal or irregular intervals. When strands and wires are used separately, they may be combined and woven into a grid pattern. By forming the electric field shield 1 in a grid pattern in this way, the strength (physical strength) of the electric field shield 1 constituting the electric field shielding structure can be improved.

[0052] Furthermore, the electric field shield 1 of embodiment 2 can be configured with any diameter, number, and positional intervals of the strands or wires used to form the grid, thereby enabling the electric field shield 1 to be formed in accordance with the required output of the electric field emission device 10.

[0053] Furthermore, the electric field shield 1 of the second embodiment may be configured to be removable when fixed to the opening edge of the guard electrode 32. In this case, a plurality of electric field shields 1 with different diameters, numbers, and positional intervals of the strands or wires used to form a lattice can be prepared, and the electric field shield 1 can be replaced according to the required output of the electric field emission device 10. This also makes it possible to control the output of the electric field emission device 10. Note that the material of the electric field shield 1 and the method of fixing it to the opening edge of the guard electrode 32 in the second embodiment are the same as those in the first embodiment.

[0054] Furthermore, since the electric field shield 1 in the second embodiment has a lattice shape, the electron generating section 33 is crushed by the pull-in of the emitter 30, and the edge sections 33a formed therein are more than those in the first embodiment. Therefore, when the electron generating section 33 generates electrons by applying a voltage and emits the electron beam L1, the electron emission efficiency can be improved compared to the first embodiment due to the electric field concentration at the edge sections 33a.

[0055] As described above, by configuring the electric field shield 1 in a lattice shape, in addition to the effects of embodiment 1, the strength of the electric field shield 1 is increased, and further, the electric field concentration at the multiple edge portions 33a can improve the electron emission efficiency compared to embodiment 1.

[0056] [Embodiment 3] 10 is a schematic plan view of the electric field shielding structure of the field emission device 10 of embodiment 3. In embodiment 3, the electric field shield 1 is formed in a plate shape with a plurality of through holes, and other than that, the configuration is the same as that of the field emission device 10 of embodiment 1, and therefore detailed description of the similar points will be omitted as appropriate.

[0057] The electric field shield 1 in the third embodiment uses a conductive plate formed in a flat plate shape. The conductive plate in the third embodiment has a plurality of through holes formed therein. Furthermore, a conductive foil may be used as the electric field shield 1 in the third embodiment instead of a conductive plate. By using such a flat, plate-shaped electric field shield 1, when the electric field shield 1 crushes the electron generating unit 33 due to the retraction of the emitter 30, the electric field on the emitter surface becomes more uniform than in the first embodiment. The uniformity of the electric field on the emitter surface makes the electron emission generated from the electron generating unit 33 more stable than in the first embodiment. In other words, it is possible to reduce the variation in the output of the electron generating unit 33.

[0058] Furthermore, since the electric field shield 1 in embodiment 3 has a plurality of through holes, the number of edge portions 33a formed is greater than that in embodiment 1. Therefore, when the electron generating unit 33 generates electrons by applying a voltage and emits the electron beam L1, the electron emission efficiency can be improved compared to embodiment 1 due to the electric field concentration at the edge portions 33a.

[0059] Furthermore, the multiple through holes in the electric field shield 1 of embodiment 3 can be formed at any intervals, and may be, for example, evenly spaced or irregularly spaced. The diameter of the through holes in the electric field shield 1 can also be any size. For example, the diameters of the holes may all be the same, or may be different. Although the shape of the through holes in the electric field shield 1 is circular in embodiment 3, this is not limiting, and the shape of the through holes may be substantially rectangular or polygonal. The number of through holes to be machined is determined depending on the size of the opening 310 in the guard electrode 32 and the diameter of the through holes. That is, the number of through holes in the electric field shield 1 can also be any number.

[0060] In this way, the diameter, spacing, shape, and number of the through holes in the electric field shield 1 can be configured as desired. This allows the electric field shield 1 to be formed according to the required output of the electric field emission device 10. Furthermore, when the electric field shield 1 of embodiment 3 is fixed to the opening edge of the guard electrode 32, it may be configured to be removable. In this case, a plurality of electric field shields 1 each having different diameters, spacing, shapes, and numbers of through holes can be prepared, and the electric field shield 1 can be replaced according to the required output of the electric field emission device 10. This also makes it possible to control the output of the electric field emission device 10.

[0061] The electric field shield 1 of embodiment 3 is formed so that the size of its outer periphery is smaller than the outer periphery (outer diameter) of the opening 310 of the guard electrode 32. This allows it to be inserted into the opening 310 of the guard electrode 32, and it becomes possible to fix the electric field shield 1 to the opening edge of the guard electrode 32 so that it is closer to the surface 36b facing one side of the edge 36 of the guard electrode 32 than to the surface 36a facing the other side. The material of the electric field shield 1 and the method of fixing it to the opening edge of the guard electrode 32 in embodiment 3 are the same as those in embodiment 1.

[0062] As described above, by configuring the electric field shield 1 in a plate shape and forming a plurality of through holes, in addition to the effects of embodiment 1, the strength of the electric field shield 1 is increased, and the electric field on the emitter surface becomes uniform, thereby reducing variations in the output of the electron generating section 33. Furthermore, the electric field concentration at the plurality of edge sections 33a can improve the electron emission efficiency compared to embodiment 1.

[0063] Although the preferred embodiments of the present invention have been described above, various improvements and design changes may be made to the present invention without departing from the spirit of the present invention. [Explanation of symbols]

[0064] 1 Electric field shield 30 Emitters 31 Emitter support 32 Guard electrode 33 Electron Generator 36 Edge 36a The surface facing the other side of the edge 36b The surface facing one side of the edge 310 Opening

Claims

1. a vacuum vessel having a vacuum chamber; an emitter located on one side of the vacuum chamber in the axial direction and having an electron generating portion facing the other side of the vacuum chamber in the axial direction; a target located on the other side of the vacuum chamber and facing the emitter; a guard electrode which is a cylindrical body provided on the outer periphery of the emitter, the one side of which is fixed to the vacuum vessel and the other side of which has an opening on the inside of the edge; a support that moves the emitter in the axial direction inside the guard electrode; an electric field shield formed of a conductor connected to the guard electrode and disposed on one side of the opening in the edge portion of the guard electrode, the electric field shield is disposed so as to partially overlap the opening on a projection plane in the axial direction, and when the emitter is pushed out to the other side in the axial direction by the support, the electric field shield crushes the electron generating portion, thereby dividing the opening into a plurality of regions and forming edge portions in the electron generating portion.

1. A field emission device comprising:

2. 2. The field emission device according to claim 1, wherein the electric field shield is formed of one or more linear members fixed to the edge of the opening.

3. 3. The field emission device according to claim 2, wherein the electric field shield is formed by the linear members arranged in a lattice pattern.

4. 2. The field emission device according to claim 1, wherein the electric field shield is formed in a plate shape having a plurality of through holes.

5. 5. The field emission device according to claim 1, wherein at least one surface of the emitter or the support at the contact portion between the emitter and the support is electrically insulating.

6. 6. The field emission device according to claim 1, wherein the electric field shield has an axial height that is smaller than the axial height of the electron generating portion.

7. 7. The field emission device according to claim 1, wherein the electric field shield is formed integrally with the guard electrode.

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