Electron source

Abstract

To provide an electron source in which a plurality of field emission elements are arranged in an array, capable of suppressing deterioration of an electron discharged from each field emission elements arranged at an outer peripheral end.SOLUTION: An electron source 100 of the present invention includes: a field emission element 102 that emits electrons to an external space on one surface 101a side of a substrate 101; and a dummy element 103 that surrounds the periphery of the field emission element 102. The field emission element 102 and the dummy element 103 each include: an emitter 104 whose one end 104a side is pointed; a gate electrode 105 that surrounds the periphery of the one end 104a side of the emitter; and a focusing electrode 106 that surrounds the periphery of the gate electrode 105. The one end 104a of the emitter included in the dummy element 103 is electrically insulated from an external space.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a field emission electron source, and more particularly to a structure of an electron source in which an extraction gate electrode for extracting electrons and a focusing electrode for focusing an electron beam are integrated. [Background technology]

[0002] Field emission devices are used in flat panel displays, electron sources for X-ray sources, traveling wave tubes (TWTs) that amplify high-frequency and high-output signals on the order of GHz, and other devices. A field emission device is primarily composed of an emitter with a sharp tip and an extraction gate electrode surrounding the emitter. The extraction gate electrode is an electrode that applies an extraction voltage to cause electrons to be emitted from the emitter. In a field emission device, when a voltage of about 10 V to 60 V is applied to the gate electrode, a very high electric field is generated at the tip of the emitter, from which electrons are emitted. The emitted electrons can be captured or accelerated using an anode (also called a collector or anode).

[0003] The electrons that can be emitted from one field emission device are equivalent to a current of only a few μA at most, but by arranging a large number of field emission devices in an array along a plane, it is possible to obtain a large current exceeding mA. For example, Non-Patent Document 1 discloses that by integrating 16,000 field emission devices, it is possible to emit electrons equivalent to a current of 10 mA.

[0004] On the other hand, in order to use field emission devices in various applications, a technology for focusing the electron beam emitted from the tip of the emitter is important. The present inventors have disclosed a structure in which a focusing electrode is integrated into a field emission device in order to focus the emitted electron beam. For example, Patent Document 1 discloses that electron beam focusing can be achieved by structuring the extraction gate electrode like a volcanic crater and integrating the focusing electrodes in multiple stages. Furthermore, Non-Patent Document 2 discloses a simpler structure in which the opening of the extraction gate electrode is arranged to protrude outward from the focusing electrode. This structure makes it possible to significantly suppress the current reduction during focusing. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5062761 [Non-patent literature]

[0006] [Non-Patent Document 1] T. Sato, S. Yamamoto, M. Nagao, T. Matsukawa, S. Kanemaru, J. Itoh, Journal of Vacuum Science & Technology B21(4), p.1589, (2003). [Non-patent document 2] Y. Neo, T. Soda, M. Takeda, M. Nagao, T. Yoshida, C. Yasumuro,S. Kanemaru, T. Sakai, K. Hagiwara, N. Saito, T. Aoki, H. Mimura: Applied Physics Ex press, 1 (2008) 053001. [Non-patent document 3] Masaaki Nagao, J. Vac. Soc. Jpn, Vol. 59, No. 4 (2016) pp.36-39. Summary of the Invention [Problem to be solved by the invention]

[0007] When multiple field emission element emitters 304 are arranged in an array, the emitter 304A (304) arranged near the center and the emitter 304B (304) arranged at the outer periphery generate different potential distributions near them. Figure 15 shows a cross-sectional view of the emitter array constituting the electron source 300 near the outer periphery. In the central portion of the electron source 300, the emitters 304 are periodically arranged together with the electron-emitting elements 302. A focusing electrode 306 extends beyond the outer periphery 302E of the emitter array (to the right in the figure). Inside the outer periphery 302E, a potential distribution is formed in which a high potential H generated by the gate electrode 305 and a low potential L generated by the focusing electrode 306A (306) alternate. However, outside the outer periphery 302E, only the low potential L generated by the focusing electrode 306B (306) is present.

[0008] In this potential distribution, electrons emitted from emitter 304B located at the outer edge are influenced by the low potential L created by focusing electrode 306B outside the outer edge and follow a different trajectory from electrons emitted from emitter 304A near the center. Such electrons may follow an abnormal trajectory that does not reach the anode and may enter gate electrode 305. Under normal operation, almost no electrons enter gate electrode 305. However, if an increasing number of electrons follow such abnormal trajectories and enter gate electrode 305, gas emission from gate electrode 305 occurs. The emitted gas collides with electrons emitted from emitter 304A and is ionized. The ions then bombard emitter 304, shortening the life of emitter 304. Furthermore, excessive gas emission can cause arc discharge, often destroying the electron source.

[0009] The present invention has been made in view of the above circumstances, and aims to provide an electron source in which a plurality of field emission elements are arranged in an array, and which is capable of suppressing a decrease in the focusing ability of electrons emitted from the field emission elements arranged at the outer peripheral end. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention employs the following means.

[0011] (1) An electron source according to one aspect of the present invention comprises, on one side of a substrate, a field emission element that emits electrons into an external space, and a dummy element that surrounds the field emission element, wherein the field emission element and the dummy element each comprise an emitter having a pointed end, a gate electrode that surrounds the one end of the emitter, and a focusing electrode that surrounds the gate electrode, and the one end of the emitter of the dummy element is electrically insulated from the external space.

[0012] (2) In the electron source described in (1) above, the emitter of the dummy element may be made of a conductive material, and one end side of the emitter may be covered with a first insulating film.

[0013] (3) In the electron source described in (2), the first insulating film is preferably made of a material having a relative dielectric constant of 1.0 or more and 10.0 or less, more preferably 1.0 or more and 5.0 or less.

[0014] (4) In the electron source described in either (2) or (3), it is preferable that the thickness of the first insulating film is 5 nm or more and is equal to or less than the sum of the thicknesses of the second insulating film and the third insulating film, the second insulating film is an insulating film formed between the emitter and the gate electrode, and the third insulating film is an insulating film formed between the gate electrode and the focusing electrode.

[0015] (5) In the electron source according to either (2) or (3) above, it is preferable that the gate electrode of the dummy element is covered with the first insulating film.

[0016] (6) In the electron source described in (1) above, the emitter of the dummy element may be made of an insulating material.

[0017] (7) In the electron source described in any one of (1) to (6), it is preferable that the width of the first region on the one surface in which the dummy elements are arranged is at least 1 / 5 of the width of the second region in which the field emission elements are arranged.

[0018] (8) The electron source according to any one of (1) to (7) above, further comprising a third region along the one surface between the first region in which the dummy elements are arranged and the second region in which the field emission elements are arranged, in which neither the field emission elements nor the dummy elements are arranged, It is preferable that the width of the third region is 300% or less of the width of one of the field emission elements. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide an electron source in which a plurality of field emission elements are arranged in an array, and which is capable of suppressing a decrease in the focusing ability of electrons emitted from the field emission elements arranged at the outer peripheral end. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a perspective view of an electron source according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of a part of the electron source according to the embodiment. [Figure 3] FIG. 2 is a cross-sectional view of a field emission element constituting the electron source of the embodiment. [Figure 4] FIG. 2 is a cross-sectional view of a dummy element constituting the electron source of the embodiment. [Figure 5]3A to 3C are diagrams illustrating a potential distribution obtained when the electron source of the embodiment is operated. [Figure 6] FIG. 2 is a diagram showing an example of the arrangement of field emission devices and dummy devices that constitute the electron source of the embodiment. [Figure 7] 5(a) to 5(g) are diagrams illustrating a method for manufacturing an electron source according to the embodiment. [Figure 8] 5A and 5B are diagrams illustrating a method for manufacturing an electron source according to the embodiment. [Figure 9] 10(a) to 10(d) are diagrams illustrating a modified example of the method for manufacturing the electron source according to the embodiment. [Figure 10] 10(a) and 10(b) are diagrams illustrating a modified example of the method for manufacturing the electron source according to the embodiment. [Figure 11] FIG. 10 is a perspective view of an electron source according to a second embodiment of the present invention. [Figure 12] FIG. 2 is a cross-sectional view of a part of the electron source according to the embodiment. [Figure 13] 3A to 3C are diagrams illustrating a potential distribution obtained when the electron source of the embodiment is operated. [Figure 14] 1 is a graph showing electrical properties obtained in Example 1 of the present invention and Comparative Example 1. [Figure 15] 1A and 1B are diagrams illustrating a potential distribution obtained when an electron source according to a conventional technique is operated. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, electron sources according to embodiments of the present invention will be described in detail with reference to the drawings. Note that the drawings used in the following description may show characteristic portions enlarged for the sake of convenience in order to make the characteristics easier to understand, and the dimensional ratios of the components may not necessarily be the same as those in reality. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto, and can be appropriately modified and implemented within the scope of the present invention.

[0022] First Embodiment Fig. 1 is a perspective view of an electron source 100 according to a first embodiment of the present invention. Fig. 2 is a partial cross-sectional view of the electron source 100 taken along the α-α line in Fig. 1. The electron source 100 includes one or more field emission elements 102 and dummy elements 103 arranged in an array on one surface 101a of a substrate 101.

[0023] The number of field emission elements 102 is determined by the amount of current required for the electron source 100, the diameter of the focused beam, and other factors. The distance between adjacent field emission elements 102 is determined by manufacturing conditions. The number of dummy elements 103 is not particularly limited, but the greater the number within the range permitted by device design, the better. For example, on one surface 101a of the substrate, the width W1 of the first region R1 where the dummy elements 103 are arranged is preferably at least one field emission element 102, and more preferably at least five field emission elements. Furthermore, the width W1 of the first region R1 is preferably at least 1 / 5 of the width W2 of the second region R2 where the field emission elements 102 are arranged.

[0024] 3 is an enlarged cross-sectional view of a field emission element 102. The field emission element is a field emitter with an integrated focusing electrode, and has the function of emitting electrons (electron beam) into external space (vacuum), and mainly comprises an emitter 104, a gate electrode 105, and a focusing electrode 106.

[0025] The emitter 104 has a conical shape at one end (tip) 104a, and is tapered toward the end 104a. The surface of the emitter 104 may be coated with another material having electron emission properties. Examples of the coating material include materials with a low work function and a high melting point, such as nitrides and carbides of transition metals.

[0026] The gate electrode 105 has an opening 105a exposing one end 104a of the emitter 104, surrounds the one end 104a side of the emitter (wall surface), and has a portion shaped like the periphery of the crater of a volcano. From the viewpoint of improving the focusing of electrons emitted from the emitter 104, it is preferable that the position of the opening 105a of the gate electrode is higher than the one end 104a of the emitter with respect to the one surface 101a of the substrate. The gate electrodes 105 of adjacent field emission elements 102 are connected to each other on the opposite side of the opening. The gate electrodes 105 of the field emission elements 102 at the outer periphery extend along the one surface 101a of the substrate on the side opposite to the opening.

[0027] The focusing electrode 106 has an opening 106a similar to that of the gate electrode 105, and surrounds the gate electrode 105. From the viewpoint of improving the focusing of electrons emitted from the emitter 104, it is preferable that the position of the opening 106a of the focusing electrode is lower than one end 104a of the emitter with respect to one surface 101a of the substrate. The focusing electrodes 106 of adjacent field emission elements 102 are connected to each other on the side opposite the opening. The focusing electrodes 106 of the field emission elements 102 at the outer periphery each extend along one surface 101a of the substrate on the side opposite the opening. Although the present embodiment illustrates a case where only one stage of the focusing electrode 106 is provided, multiple stages may be provided.

[0028] The emitter 104, gate electrode 105, and focusing electrode 106 are made of a conductive material such as silicon, niobium, or molybdenum. In a direction parallel to one surface 101a of the substrate, an insulating film (second insulating film) 107A is formed between the emitter 104 and gate electrode 105, and an insulating film (third insulating film) 107B is formed between the gate electrode 105 and focusing electrode 106. The insulating films 107A and 107B are made of an insulating material such as silicon nitride, silicon oxide, or aluminum oxide. The insulating film 107A and the insulating film 107B may be made of different materials.

[0029] When electrons are to be emitted from the field emission element 102, the potential of the gate electrode 105 is made higher than the potential of the emitter 104. For example, the emitter 104 is fixed at ground potential, and a voltage is applied between the emitter 104 and the gate electrode 105 so that the gate electrode 105 becomes positive. The applied voltage may be, for example, about 20 V to 100 V. This voltage draws electrons from one end 104a of the emitter and releases them into external space.

[0030] The emitted electrons can be captured or accelerated by, for example, an anode electrode (not shown). The anode electrode is disposed opposite one end 104a of the emitter. A voltage higher than that applied to the gate electrode 105 is applied to the anode electrode. The voltage value is determined depending on the application and may be, for example, 1 kV.

[0031] A member made of a predetermined material can be used as an X-ray source by replacing the anode electrode or by arranging this member in front of the anode electrode.

[0032] 4 is an enlarged view of a cross section of dummy element 103. Like field emission element 102, dummy element 103 includes emitter 104, gate electrode 105, and focusing electrode 106. There is no difference between field emission element 102 and dummy element 103 in the configuration (shape, size, etc.) of the electrode structure including emitter 104, gate electrode 105, and focusing electrode 106. However, one end 104a of the emitter included in dummy element 103 is electrically insulated from external space, and therefore dummy element 103 does not have the function of emitting electrons into external space.

[0033] The configuration for electrically insulating the emitter 104 from the external space is not particularly limited. Fig. 4 illustrates a configuration in which, when the emitter 104 of the dummy element 103 is made of a conductive material, one end 104a of the emitter is covered with an insulating film (first insulating film) 108, thereby isolating the emitter from the external space. As illustrated here, the gate electrode 105 of the dummy element 103 may be covered with the insulating film 108. If the emitter 104 of the dummy element 103 is made of an insulating material, the insulating film 108 becomes unnecessary.

[0034] To minimize the effect on the potential distribution created by gate electrode 105 and focusing electrode 106, insulating film 108 is preferably made of a material with a dielectric constant of 1.0 or more and 10.0 or less. A dielectric constant of 1.0 or more and 5.0 or less is even more preferable. From the same perspective, thickness 108a of insulating film 108 is preferably 5 nm or more and less than the sum of the thicknesses of insulating films 107A and 107B. Setting thickness 108a to 5 nm or less is undesirable because it may cause electron emission when a strong electric field is applied. By setting the dielectric constant and thickness 108a of insulating film 108 within these ranges, the potential distribution created by dummy elements 103 covered with insulating film 108 can be made closer to the potential distribution created by field emission elements 102 exposed to vacuum.

[0035] 5 is a diagram illustrating the potential distribution around the field emission elements 102 and the dummy elements 103 obtained when the electron source 100 is operated. The electron source 100 is operated by applying predetermined voltages to the emitters 104, gate electrodes 105, and focusing electrodes 106 of the field emission elements 102 and the dummy elements 103, respectively.

[0036] In the field emission element 102, the region near one end 104a of the emitter is set to a high potential H by the high voltage applied to the gate electrode 105, and the peripheral region away from one end 104a of the emitter is set to a low potential L by the low voltage applied to the focusing electrode 106. As a result, a potential distribution is formed above the field emission element 102, in which regions of high potential H and regions of low potential L are alternately arranged.

[0037] A high voltage applied between the emitter 104 and the gate electrode 105 generates a high electric field at one end 104a of the emitter, from which electrons E are emitted. The emitted electrons E are drawn toward the high-potential gate electrode 105. Because the focusing electrode 106 keeps the area around the gate electrode 105 at a low potential, the electrons E are prevented from diffusing in a direction parallel to the surface 101a of the substrate, and are instead emitted in a focused state in a direction perpendicular to the surface 101a.

[0038] Dummy element 103 has emitter 104, gate electrode 105, and focusing electrode 106, which have the same configuration as field emission element 102, and therefore a potential distribution substantially similar to the potential distribution formed above field emission element 102 is also formed above dummy element 103. However, in dummy element 103, one end 104a of the emitter is electrically insulated from the external space, so electrons E are not emitted from emitter 104.

[0039] By arranging the dummy elements 103 around the field emission elements 102, a potential distribution in which high potential and low potential alternate is also formed outside the second region R2 in which the field emission elements 102 are arranged. The dummy elements 103 are arranged side by side at the same pitch as the field emission elements 102. Therefore, the potential distribution caused by the field emission elements 102 arranged at the outer periphery of the second region R2 is substantially the same as the potential distribution caused by the field emission elements 102 arranged in the center of the second region R2.

[0040] If the dummy elements 103 were not provided, the effect of the low potential due to the focusing electrode 106 would be increased, the trajectory of the electrons emitted from the field emission elements 102 at the outer periphery would be significantly bent, and the focusing of the electrons would be reduced, as shown in Fig. 15. In this embodiment, in which the dummy elements 103 are provided, such a problem can be avoided.

[0041] 1 illustrates an example in which the field emission elements 102 and the dummy elements 103 are arranged in a square lattice pattern, but the field emission elements 102 and the dummy elements 103 may be arranged in any manner as long as a potential distribution in which high potentials and low potentials alternate is formed. FIG. 6 is a diagram showing an example of the arrangement of the field emission elements 102 and the dummy elements 103. In FIG. 6, the field emission elements 102 and the dummy elements 103 are arranged in a hexagonal close-packed pattern. The hexagonal close-packed arrangement is effective when the number of field emission elements 102 and dummy elements 103 arranged is large.

[0042] 7(a) to 7(g) and 8(a) and 8(b) are diagrams illustrating a method for manufacturing the electron source 100 of this embodiment. The electron source 100 can be manufactured mainly through the following steps A to I.

[0043] (Process A) As shown in Figure 7(a), lift-off resist (LOR: LOR-7A manufactured by MicroChem, etc.) 109 and normal photoresist 110 are applied in this order to one surface 101a of the substrate. Portions 110A of the photoresist 110 that will become the micropores (spaces) in which the emitters 104 will be formed are exposed to light and developed (removed). Subsequently, portions 109A of the lift-off resist 109 that will become the micropores in which the emitters 104 will be formed are also exposed to light and developed (removed).

[0044] The lift-off resist 109 has the property of being isotropically etched by development, and etching also progresses in a direction parallel to the surface 101a of the substrate (here, the lateral direction) H. Therefore, the micropores in the lift-off resist 109 can be made wider than the micropores in the photoresist 110, resulting in an overhang structure as shown in FIG.

[0045] (Process B) Using electron beam evaporation or the like, emitter material 104A is supplied from a direction V perpendicular to one surface 101a of the substrate, as shown in FIG. 7(b), and a film is formed on the one surface 101a of the substrate. In this film formation, the film deposited on the photoresist 110 grows so as to gradually block the top of the microhole 110A. Therefore, the film deposited in the microhole 109A of the lift-off resist 109 grows in a tapered shape as the supply of material gradually decreases. As a result, a conical emitter 104 is formed inside the microhole 109A, as shown in FIG. 7(b).

[0046] (Process C) The lift-off resist 109 and the photoresist 110 are dissolved using a predetermined organic solvent, and as shown in FIG. 7(c), the portions other than the cone-shaped emitter 104 are removed from the surface 101a of the substrate.

[0047] (Process D) 7(d), an insulating film 107A is formed on the emitter 104 and one surface 101a of the substrate, and a metal film 105A that will become the gate electrode is formed on the insulating film 107A. The insulating film 107A can be formed by, for example, chemical vapor deposition (CVD). The metal film 105A can be formed by, for example, sputtering.

[0048] (Process E) Photoresist 111 is applied to the entire metal film 105A. Next, to open the metal film 105A (gate electrode 105) above one end 104a of the emitter, the photoresist 111 and a portion of the metal film 105A are etched as shown in FIG. 7(e). Thereafter, the photoresist 111 is removed using a predetermined chemical solution.

[0049] (Process F) As in step D, an insulating film 107B and a metal film 106A that will become a focusing electrode are formed in this order on the exposed metal film 105A and insulating film 107A, as shown in FIG. 7(f).

[0050] (Process G) Photoresist 112 is applied to the entire metal film 106A. Then, to open the metal film 106A (focusing electrode 106) above one end 104a of the emitter, the photoresist 112 and a portion of the metal film 106A are etched as shown in Fig. 7(g). It is preferable to open the metal film 106A on the side closer to the substrate 101 than the metal film 105A (here, the lower side).

[0051] (Process H) As shown in Figure 8(a), the photoresist 112 is removed using a predetermined chemical solution. Figure 8(a) depicts multiple elements. Also, the boundary between the insulating film 107A and the insulating film 107B depicted near the emitter 104 in Figures 7(f) and 7(g) is omitted.

[0052] (Process I) 8(b), only the first region R1 where the dummy elements 103 are to be disposed is covered with photoresist 113. Then, in the second region R2 where the field emission elements 102 are to be disposed, the insulating films 107A and 107B are removed using hydrofluoric acid or the like to expose one end 104a of the emitter and the opening ends 105a and 106a of the metal films 105A and 106A. Thereafter, in the region where the dummy elements 103 are to be disposed, only the photoresist 113 is removed, leaving one end 104a of the emitter and the opening ends 105a of the metal films 105a and 105B covered with the insulating films 107A and 107B.

[0053] 9(a) to 9(d) are diagrams illustrating a modified example of the method for forming an emitter by the above steps A to C. In steps A to C, an emitter is formed by evaporating a conductive material onto the substrate 101, but the emitter may also be formed in the following steps A' to D'.

[0054] (Process A') 9(a), a mask layer 114 made of an oxide such as SiO2 is formed on one surface 101b of a silicon substrate 101 by using a thermal oxidation method, a plasma CVD method, or the like. Next, the mask layer 114 is removed using photolithography and etching methods except for a portion 114A located directly above the emitter.

[0055] (Process B') The silicon is isotropically etched from the side of the first surface 101b of the substrate using a predetermined chemical solution. The etching proceeds in the depth direction around the mask layer 114A and also in a direction perpendicular to the depth direction, so that the outermost portion of the silicon directly below the mask layer 114A is removed, as shown in FIG. 9(b). The closer to the mask layer 114A, the more etching proceeds, and the more silicon is removed.

[0056] (Process C') As shown in FIG. 9(c), the surface (exposed surface) 101c after etching is subjected to thermal oxidation to form an oxide film 115.

[0057] (Process D') By removing the oxide film 115 and the mask layer 114A using hydrofluoric acid or the like, only the emitter 104 with a pointed end 104a remains on one surface 101a of the newly formed substrate, as shown in FIG. 9(d).

[0058] 10(a) and 10(b) are diagrams illustrating a modified example of the method for forming the insulating film in the above-mentioned step I. In step I, only the insulating films 107A and 107B on the field emission elements 102 are removed, but after removing the insulating films 107A and 107B on the field emission elements 102 and the dummy elements 103, an insulating film may be formed only in the region where the dummy elements 103 are to be disposed in the next steps I' and J'.

[0059] (Process I') 10(a), only the area where the field emission elements 102 are to be disposed is covered with photoresist 116. Then, an insulating film 107D is formed by vacuum deposition, sputtering, or the like so as to cover one end 104a of the emitter of the dummy element 103, the opening ends 105a and 106a of the metal films 105A and 106A, and other exposed portions.

[0060] (Process J') As shown in FIG. 10(b), the photoresist 116 and the insulating film 107D formed thereon are removed.

[0061] As described above, in the electron source 100 of this embodiment, dummy elements 103 having the same electrode structure as the field emitter elements 102 are arranged around the field emitter elements 102 arranged in an array. Therefore, when the electron source 100 is operated, the distribution of high and low potentials formed on the field emitter elements 102 can also be formed on the dummy elements 103. The potential distribution around the field emitter elements 102 arranged at the outer periphery of the array is substantially the same as the potential distribution around the field emitter element 102 arranged at the center of the array. Therefore, the electrons E emitted from the field emitter elements 102 at the outer periphery are not strongly affected by the low potential from the surrounding focusing electrode 106. Therefore, the electrons E emitted from the field emitter elements 102 at the outer periphery can be focused, similar to the electrons E emitted from the central field emitter elements 102. This makes it possible to suppress a decrease in focusing ability due to a strong influence of the surrounding low potential. As a result, electrons emitted along abnormal trajectories can be prevented from being incident on the gate electrode, and the risk of discharge breakdown due to an increase in gate current can be reduced.

[0062] Second Embodiment FIG. 11 is a perspective view of an electron source 200 according to a second embodiment of the present invention. FIG. 12 is a partial cross-sectional view of the electron source 200 taken along the β-β line in FIG. 11. The electron source 200 differs from the electron source 100 of the first embodiment in that it includes a third region R3 (gap) between the first region R1 and the second region R2 along one surface 101a of the substrate, in which neither the field emission elements 102 nor the dummy elements 103 are arranged. The configuration other than the third region R3 is the same as that of the first embodiment, and the same reference numerals are used to denote corresponding components. The electron source 200 can achieve at least the effects obtained by the electron source 100 of the first embodiment.

[0063] The width W3 of the third region R3 is adjusted to such an extent that the trajectory of the electrons E emitted from the field emission elements 102 at the outer periphery of the second region R2 is not bent, and is preferably 200% or less, and more preferably 100% or less, of the width of one field emission element 102. By providing the third region R3, the electron source 200 can avoid the following problems related to photolithography.

[0064] When the first region R1 and the second region R2 are adjacent to each other, the process of selectively forming the insulating film 108 only in the first region R1 where the dummy elements 103 are arranged is performed using a photolithography method. Specifically, as shown in Figures 8(a) and 8(b), of the insulating film 108 once formed over the entire surface, only the first region R1 is covered with a resist, and only the insulating film 108 in the second region R2 that is not covered with the resist is removed. Alternatively, as shown in Figures 10(a) and 10(b), only the second region R2 is covered with a resist, and the insulating film 108 is formed only in the first region R1 that is not covered with the resist.

[0065] However, coating the resist so that it precisely matches the boundary between the first region R1 and the second region R2 requires an expensive lithography system with high alignment accuracy. If the lithography accuracy is low and alignment is off, for example, even if you try to coat only the first region R1 with resist, a portion of the first region R1 may not be coated, or a portion of the second region R2 may be overcoated. Conversely, even if you try to coat only the second region R2 with resist, a portion of the second region R2 may be exposed near the boundary with the first region R1, or a portion of the first region R1 may be overcoated.

[0066] If there is a defect in the coverage due to such misalignment, a part of the field emission element 102 may be partially covered with the insulating film 108, resulting in a defect that the electrons E cannot be sufficiently emitted or the trajectory of the emitted electrons E may be bent. Also, there may be a defect that the insulating film 108 of the dummy element 103 is partially opened, resulting in a defect that excess electrons E are emitted from there. Such a defect may cause the electron source 200 to be destroyed.

[0067] The electron source 200 of this embodiment includes a third region R3 between the first region R1 and the second region R2, in which neither the electron emitters 102 nor the dummy elements 103 are arranged. This allows the third region R3 to absorb the excess (margin) when the resist applied only to the first region R1 overflows from the first region R1, or when the resist applied only to the second region R2 overflows from the second region R2. Because neither the field emitters 102 nor the dummy elements 103 are arranged in the third region R3, even if there is misalignment within the width W3 of the third region R3, no problems with potential distribution will occur, as will be described below.

[0068] 13 is a diagram illustrating the potential distribution around the field emission elements 102 and the dummy elements 103 obtained when the electron source 200 is operated. In the third region R3, only a low potential distribution created by the focusing electrode 106 exists. In the first region R1 and the second region R2, as in the first embodiment, a distribution in which a high potential created by the gate electrode 105 and a low potential created by the focusing electrode 106 alternate exists. Therefore, the potential distribution is such that high potentials and low potentials alternate throughout the entire electron source 200. This makes it possible to avoid the problem that the influence of the low potential created by the focusing electrode 106 is locally increased, significantly bending the trajectory of electrons E emitted from the field emission elements 102 in the vicinity, and reducing the focusing ability of the electrons E. [Example]

[0069] The effects of the present invention will be made clearer by the following examples. Note that the present invention is not limited to the following examples and can be practiced with appropriate modifications within the scope of the present invention.

[0070] Example 1 The electron source of the second embodiment was fabricated. 2 In the second area (45 μm × 45 μm), pieces The width of the third region around the second region was set to 3 μm. The width of the first region around the third region was set to 30 μm, and 10 rows of dummy elements were fabricated in the first region. The following materials were used for the components of the electron source. Substrate: Si Emitter: Si Gate electrode: Nb Focusing electrode: Nb Insulating film: SiO2

[0071] (Comparative Example 1) Except for not forming a dummy element in the first region, an electron source was fabricated in the same manner as in Example 1. The third region was configured to extend around the second region.

[0072] A predetermined voltage was applied to each electrode, and the gate current generated when the electron sources of Example 1 and Comparative Example 1 were operated was measured. Figure 14 is a graph showing the measurement results. The horizontal axis of the graph represents the focusing voltage (V), and the vertical axis of the graph represents the anode current I a Gate current I g The ratio (I g / I a ) (%).

[0073] In the electron source of Comparative Example 1, which does not have a dummy element, the gate current begins to increase when the focusing voltage is lowered to around 20 V. When the focusing voltage is set to 0 V, the ratio of the gate current (I g / I a ) reaches 4%, which means that 4% of the electrons emitted toward the anode electrode return to the gate electrode. This is thought to be because, when the focusing voltage of the electron source in Comparative Example 1 is lowered, the electrons emitted from the emitter located at the outer edge of the second region follow an abnormal trajectory due to the influence of the low potential created by the focusing electrode outside the outer edge, and are incident on the gate electrode.

[0074] On the other hand, in the electron source of Example 1 having the dummy element, even if the focusing voltage is lowered to around 0 V, the gate current hardly increases. Even if the focusing voltage is lowered to around -20 V, the ratio of the gate current (I g / I a ) is about 3%, which shows that the ratio of electrons returning to the gate electrode among the electrons emitted toward the anode electrode is suppressed to about 3%. This is thought to be because, in the electron source of Example 1, the dummy elements form a potential distribution almost similar to that of the field emission elements, and even if the focusing voltage is lowered, the electrons emitted from the emitters arranged at the outer edge of the second region are hardly affected by the potential outside the outer edge. It is thought that the electron source of Example 1 has improved focusing of the emitted electrons compared to the electron source of Comparative Example 1.

[0075] As the gate current increases, the probability of discharge breakdown increases. g / I a) exceeds 10%, the probability of discharge breakdown increases sharply. From the graph of FIG. 14, it can be seen that in the electron source of Example 1, the gate current ratio (I g / I a ) is kept to within 10%, which means that the risk of discharge breakdown is low.

[0076] In addition, when the electron source of the first embodiment is used as the electron source of Example 1, the regularity of the potential distribution is increased by the absence of the third region, and the number of electrons whose trajectories are bent is reduced, so that it is considered that the gate current is reduced and the electron focusing can be further improved. [Explanation of symbols]

[0077] 100, 200, 300...electron source 101... board 101a: One side of the board 102 Field emission device 103 Dummy element 104, 304... emitter 104a...One end of emitter 105, 305 Gate electrode 105a: Gate electrode opening 106, 306...Focusing electrode 106a...Aperture of focusing electrode 107, 107A, 107B, 108....insulating film 109 Lift-off resist 110, 111, 112, 113, 115, 116... Photoresist 114 Mask layer E...electronic R1...first area R2...Second area R3...Third area

Claims

1. a field emission element that emits electrons into an external space and a dummy element that surrounds the field emission element, on one side of the substrate; The field emission elements and the dummy elements are each An emitter having a pointed end; a gate electrode surrounding one end of the emitter; a focusing electrode surrounding the gate electrode; The electron source according to claim 1, wherein the one end side of the emitter included in the dummy element is electrically insulated from the external space.

2. 2. The electron source according to claim 1, wherein the emitter of the dummy element is made of a conductive material, and one end side of the emitter is covered with a first insulating film.

3. 3. The electron source according to claim 2, wherein the first insulating film is made of a material having a relative dielectric constant of 1.0 or more and 10.0 or less.

4. the thickness of the first insulating film is 5 nm or more and is equal to or less than the sum of the thicknesses of the second insulating film and the third insulating film; the second insulating film is an insulating film formed between the emitter and the gate electrode, 4. The electron source according to claim 2, wherein the third insulating film is an insulating film formed between the gate electrode and the focusing electrode.

5. 4. The electron source according to claim 2, wherein the gate electrode of the dummy element is covered with the first insulating film.

6. 2. The electron source according to claim 1, wherein the emitter of the dummy element is made of an insulating material.

7. 3. The electron source according to claim 1, wherein, on said one surface, a width of a first region in which said dummy elements are arranged is equal to or greater than 1 / 5 of a width of a second region in which said field emission elements are arranged.

8. a third region, along the one surface, between a first region in which the dummy elements are arranged and a second region in which the field emission elements are arranged, in which neither the field emission elements nor the dummy elements are arranged; 3. The electron source according to claim 1, wherein the width of said third region is 300% or less of the width of one of said field emission elements.

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