Electron source

Abstract

An electron source (100) according to the present invention in which one surface (101a) side of a substrate (101) thereof is provided with a field emission element (102) that emits electrons to an external space, and a dummy element (103) that surrounds the field emission element (102), wherein: the field emission element (102) and the dummy element (103) each comprise an emitter (104), one end (104a) side of which is pointed, a gate electrode (105) surrounding the one end (104a) side of the emitter, and a focusing electrode (106) surrounding the gate electrode (105); and the one end (104a) side of the emitter of the dummy element (103) is electrically insulated from the external space.

Description

electron source

[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. This application claims priority to Japanese Patent Application No. 2024-073041, filed on April 26, 2024, the contents of which are incorporated herein by reference.

[0002] Field emission devices are used in devices such as flat panel displays, electron sources for X-ray sources, and traveling wave tubes (TWTs) that amplify high-frequency, high-output signals in the GHz range. Field emission devices are 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 approximately 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, as a simpler structure, Non-Patent Document 2 discloses a 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.

[0005] Patent No. 5062761

[0006] T. Sato, S. Yamamoto, M. Nagao, T. Matsukawa, S. Kanemaru, J. Itoh, Journal of Vacuum Science & Technology B21(4), p.1589, (2003).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.Masayoshi Nagao, J. Vac. Soc. Jpn, Vol. 59, No. 4 (2016) pp.36-39.

[0007] When multiple field emission element emitters 304 are arranged in an array, the potential distribution generated near the emitter 304A (304) arranged near the center differs from that generated near the emitter 304B (304) arranged at the outer periphery. Figure 15 is a cross-sectional view of the vicinity of the outer periphery of the emitter array constituting the electron source 300. 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 a distribution of the low potential L generated by the focusing electrode 306B (306) exists.

[0008] In this potential distribution, electrons emitted from the emitter 304B located at the outer periphery are affected by the low potential L created by the focusing electrode 306B outside the outer periphery and follow a different trajectory from the electrons emitted from the emitter 304A near the center. Such electrons may follow an abnormal trajectory that does not reach the anode and may be incident on the gate electrode 305. Under normal operation, almost no electrons are incident on the gate electrode 305. However, if an increasing number of electrons follow such abnormal trajectories and enter the gate electrode 305, gas is emitted from the gate electrode 305. The emitted gas collides with electrons emitted from the emitter 304A and is ionized. These ions bombard the emitter 304, shortening the life of the 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.

[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 according to (1), the emitter of the dummy element may be made of a conductive material, and one end of the emitter may be covered with a first insulating film.

[0013] (3) In the electron source according to (2), it is preferable that the first insulating film is made of a material having a relative dielectric constant of 1.0 or more and 10.0 or less. It is more preferable that the relative dielectric constant is 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 according to (1), 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 1 / 5 or more of the width of the second region in which the field emission elements are arranged.

[0018] (8) In the electron source described in any one of (1) to (7), a third region is provided 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, and it is preferable that the width of the third region is 300% or less of the width of one of the field emission elements.

[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.

[0020] 1 is a perspective view of an electron source according to a first embodiment of the present invention; FIG. 2 is a cross-sectional view of a portion of the electron source according to the embodiment; FIG. 3 is a cross-sectional view of a field emission device constituting the electron source according to the embodiment; FIG. 4 is a cross-sectional view of a dummy element constituting the electron source according to the embodiment; FIG. 5 is a view illustrating a potential distribution obtained when the electron source according to the embodiment is operated; FIG. 6 is a view illustrating an example of an arrangement of field emission devices and dummy elements constituting the electron source according to the embodiment; FIG. 7 is a view illustrating step A of the manufacturing method of the electron source according to the embodiment; FIG. 8 is a view illustrating step B of the manufacturing method of the electron source according to the embodiment; FIG. 9 is a view illustrating step C of the manufacturing method of the electron source according to the embodiment; FIG. 10 is a view illustrating step D of the manufacturing method of the electron source according to the embodiment; FIG. 11 is a view illustrating step E of the manufacturing method of the electron source according to the embodiment; FIG. 12 is a view illustrating step F of the manufacturing method of the electron source according to the embodiment; FIG. 13 is a view illustrating step G of the manufacturing method of the electron source according to the embodiment; FIG. 14 is a view illustrating step H of the manufacturing method of the electron source according to the embodiment; FIG. 15 is a view illustrating step A' of a modified example of the manufacturing method of the electron source according to the embodiment; FIG. 16 is a view illustrating step B' of a modified example of the manufacturing method of the electron source according to the embodiment; FIG. 17 is a view illustrating step C' of a modified example of the manufacturing method of the electron source according to the embodiment; FIG. 18 is a view illustrating step I' of a modified example of the manufacturing method of the electron source according to the embodiment; FIG. 1 is a diagram illustrating a step J' of a modified example of the manufacturing method of the electron source according to the embodiment. FIG. 2 is a perspective view of an electron source according to a second embodiment of the present invention. FIG. 3 is a cross-sectional view of a part of the electron source according to the embodiment. FIG. 4 is a diagram illustrating a potential distribution obtained when the electron source of the embodiment is operated. FIG. 5 is a graph showing electrical characteristics obtained by Example 1 and Comparative Example 1 of the present invention. FIG. 6 is a diagram illustrating a potential distribution obtained when an electron source of the prior art is operated.

[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, etc. The distance between adjacent field emission elements 102 is determined by manufacturing conditions. The number of dummy elements 103 is not particularly limited, but it is preferable that it is as large as possible within the range allowed by the device design. For example, on one surface 101a of the substrate, a first region R where the dummy elements 103 are arranged is １ Width W １ is preferably equal to or greater than one field emission element 102, and more preferably equal to or greater than five field emission elements. １ Width W １ is a second region R in which the field emission elements 102 are arranged. ２ Width W ２ It is preferable that the value is 1 / 5 or more of the above.

[0024] 3 is an enlarged view of a cross section of the field emission element 102. The field emission element is a field emitter integrated with a 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 periphery (wall) of the one end 104a of the emitter, 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 electrode 105 of the field emission element 102 at the outer periphery extends 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 conductive materials such as silicon, niobium, and 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 insulating materials such as silicon nitride, silicon oxide, and aluminum oxide. There is no problem if the insulating film 107A and the insulating film 107B are 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 104 a 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 cross-sectional view of the dummy element 103. Like the field emission element 102, the dummy element 103 includes an emitter 104, a gate electrode 105, and a focusing electrode 106. There is no difference between the field emission element 102 and the dummy element 103 in the configuration (shape, size, etc.) of the electrode structure including the emitter 104, the gate electrode 105, and the focusing electrode 106. However, since one end 104a of the emitter included in the dummy element 103 is electrically insulated from the external space, the dummy element 103 does not have the function of emitting electrons into the 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. When the emitter 104 of the dummy element 103 is made of an insulating material, the insulating film 108 is unnecessary.

[0034] From the viewpoint of minimizing the influence on the potential distribution created by the gate electrode 105 and the focusing electrode 106, the insulating film 108 is preferably made of a material having a relative dielectric constant of 1.0 or more and 10.0 or less. A relative dielectric constant of 1.0 or more and 5.0 or less is even more preferable. From the same viewpoint, the thickness 108a of the insulating film 108 is preferably 5 nm or more and less than the sum of the thicknesses of the insulating films 107A and 107B. A thickness 108a of 5 nm or less is undesirable because it may emit electrons when a strong electric field is applied. By setting the relative dielectric constant and thickness 108a of the insulating film 108 within these ranges, the potential distribution created by the dummy elements 103 covered with the insulating film 108 can be made closer to the potential distribution created by the 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 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 of 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, and therefore electrons E are not emitted from emitter 104.

[0039] By disposing the dummy elements 103 around the field emission elements 102, a potential distribution in which high potentials and low potentials alternate is formed in the second region R where the field emission elements 102 are disposed. ２ The dummy elements 103 are also formed on the outer side. The dummy elements 103 are arranged side by side at the same pitch as the field emission elements 102. Therefore, the second region R ２ The potential distribution due to the field emission elements 102 arranged at the outer periphery of the second region R ２ The potential distribution is almost the same as that of the field emission element 102 disposed at the center of the array.

[0040] If the dummy elements 103 were not provided, the influence 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 devices 102 and the dummy devices 103 are arranged in a square lattice pattern, but the field emission devices 102 and the dummy devices 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 devices 102 and the dummy devices 103. In Fig. 6, the field emission devices 102 and the dummy devices 103 are arranged in a hexagonal close-packed pattern. The hexagonal close-packed arrangement is an effective arrangement when the number of field emission devices 102 and dummy devices 103 arranged is large.

[0042] 7A to 7G, 8A and 8B 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] 7A, 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 are 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 are 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 formed wider than the micropores in the photoresist 110, thereby forming an overhang structure as shown in FIG.

[0045] (Step 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. 7B, and a film is formed on one surface 101a of the substrate. In this film formation, the film evaporated on the photoresist 110 grows so as to gradually block the top of the microhole 110A. Therefore, the film evaporated 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. 7B.

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

[0047] 7D, an insulating film 107A is formed on the emitter 104 and the first surface 101a of the substrate, and a metal film 105A, which will serve as a 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] (Step 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. 7E. Thereafter, the photoresist 111 is removed using a predetermined chemical solution.

[0049] (Step 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. 7F.

[0050] (Step G) Photoresist 112 is applied to the entire metal film 106A. Next, 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. 7G. 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] (Step H) As shown in Fig. 8A, the photoresist 112 is removed using a predetermined chemical solution. Fig. 8A depicts multiple elements. The boundary between the insulating film 107A and the insulating film 107B depicted near the emitter 104 in Figs. 7F and 7G is omitted.

[0052] (Step I) As shown in FIG. 8B, a first region R in which the dummy elements 103 are arranged is formed. １ Only the second region R where the field emission element 102 is to be disposed is covered with a photoresist 113. ２ Then, insulating films 107A and 107B are removed using hydrofluoric acid or the like to expose one end 104a of the emitter and opening ends 105a and 106a of metal films 105A and 106A. Thereafter, in the region where dummy element 103 is to be disposed, only photoresist 113 is removed, leaving one end 104a of the emitter and opening ends 105a of metal films 105a and 105B covered with insulating films 107A and 107B.

[0053] 9A to 9D are diagrams illustrating a modified example of the emitter formation method according to the above-described steps A to C. In steps A to C, the 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] (Step A') As shown in FIG. 9A, a SiO 2 film is formed on one surface 101b of a silicon substrate 101 by using a thermal oxidation method, a plasma CVD method, or the like. ２ A mask layer 114 made of an oxide such as silicon dioxide is formed on the mask layer 114. Subsequently, the mask layer 114 is removed using photolithography and etching except for a portion 114A located directly above the emitter.

[0055] (Step B') Isotropic etching of silicon is performed from the side of one surface 101b of the substrate using a predetermined chemical solution. The etching proceeds in the depth direction around the periphery of 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 Figure 9B. The closer to the mask layer 114A, the more etching progresses, and the more silicon is removed.

[0056] (Step C') As shown in FIG. 9C, the etched surface (exposed surface) 101c is thermally oxidized to form an oxide film 115.

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

[0058] 10A and 10B are diagrams illustrating a modified example of the method for forming the insulating film by 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] 10A, only the region where the field emission elements 102 are to be disposed is covered with photoresist 116. Then, by vacuum deposition, sputtering, or the like, an insulating film 107D is formed 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] (Step J') As shown in FIG. 10B, 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 emission elements 102 are arranged around the plurality of field emission 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 emission elements 102 can also be formed on the dummy elements 103. The potential distribution around the field emission elements 102 arranged at the outer periphery of the array is substantially the same as the potential distribution around the field emission elements 102 arranged in the center of the array. Therefore, the electrons E emitted from the field emission elements 102 at the outer periphery are not strongly influenced by the low potential from the surrounding focusing electrode 106. Therefore, the electrons E emitted from the field emission elements 102 at the outer periphery can be focused, similar to the electrons E emitted from the central field emission elements 102, and a decrease in focusing ability due to a strong influence of the surrounding low potential can be suppressed. 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 has a first region R １ and the second region R ２ and a third region R in which neither the field emission elements 102 nor the dummy elements 103 are arranged. ３ The electron source 100 of the first embodiment differs from the electron source 100 of the first embodiment in that it includes a third region R ３ The other configurations are the same as those of the first embodiment, and the corresponding configurations are denoted by the same reference numerals. The electron source 200 can achieve at least the same effects as those of the electron source 100 of the first embodiment.

[0063] Third area R ３ Width W ３ is the second region R ２The width of the electron source 200 is adjusted to such an extent that the trajectory of the electrons E emitted from the field emission elements 102 at the outer peripheral edge of the third region R is not bent, and is preferably 200% or less of the width of one field emission element 102, and more preferably 100% or less. ３ By providing the above, the following problems with photolithography can be avoided.

[0064] First area R １ and the second region R ２ are adjacent to each other, the first region R in which the dummy element 103 is arranged １ The process of selectively forming the insulating film 108 only in the first region R is performed using a photolithography method. Specifically, as shown in FIGS. 8A and 8B, the insulating film 108 is once formed on the entire surface, and then the insulating film 108 is selectively formed only in the first region R. １ The resist is coated only on the second region R ２ 10A and 10B, only the insulating film 108 in the second region R ２ The resist is coated only on the first region R １ The insulating film 108 is formed only on the insulating film 108 .

[0065] However, the first region R １ and the second region R ２ In order to coat the resist so that it exactly matches the boundary between the first region R and the second region R, an expensive lithography device with high alignment accuracy is required. １ Even if resist is applied only to the first region R １ A part of the second region R is not covered. ２ On the other hand, for example, a part of the second region R ２ Even if we try to coat the resist only on the first region R １ In the vicinity of the boundary with the second region R ２ Part of the first region R １ In some cases, a portion of the coating may be excessively coated.

[0066] If there is a defect in the coating due to such misalignment, a part of the field emission element 102 may be incompletely 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 incompletely 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] In the electron source 200 of this embodiment, the first region R １ and the second region R ２ a third region R in which neither the electron-emitting elements 102 nor the dummy elements 103 are arranged; ３ As a result, the first region R １ The resist applied only to the first region R １ If it protrudes from the second region R ２ The resist applied only to the second region R ２ If it protrudes from the third region R, the protruding portion (margin) is ３ The third region R ３ In the third region R, neither the field emission device 102 nor the dummy device 103 is arranged. ３ Width W ３ Even if there is a misalignment of within 0.5 mm, no problems arise with respect to the potential distribution, 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. ３ In the first region R, only the low potential distribution created by the focusing electrode 106 exists. １ and the second region R ２As in the first embodiment, there is a distribution in which the high potential created by the gate electrode 105 and the low potential created by the focusing electrode 106 are alternately arranged in the electron source 200. Therefore, the potential distribution is such that high potentials and low potentials are alternately arranged over 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, the trajectory of the electrons E emitted from the field emission elements 102 in the vicinity is significantly bent, and the focusing ability of the electrons E is reduced.

[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 An electron source according to the second embodiment was fabricated. ２ 15 x 15 field emission devices were fabricated in a second region (45 μm x 45 μm). 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 devices were fabricated in the first region. The following materials were used for each component of the electron source: Substrate: Si Emitter: Si Gate electrode: Nb Focusing electrode: Nb Insulating film: SiO ２

[0071] Comparative Example 1 An electron source was fabricated in the same manner as in Example 1, except that no dummy elements were fabricated in the first region. 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. Fig. 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 include a dummy element, the gate current begins to increase when the focusing voltage is reduced 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 of Comparative Example 1 is lowered, the electrons emitted from the emitter located at the outer edge of the second region are influenced by the low potential created by the focusing electrode outside the outer edge, draw abnormal trajectories, 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 14, it is known that the probability of discharge breakdown increases sharply when the gate current ratio (I ｇ / I ａ ) is suppressed to within 10%, and it can be seen that the risk of discharge breakdown is reduced.

[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 focusing of electrons can be further improved.

[0077] 100, 200, 300... Electron source 101... Substrate 101a... One surface of substrate 102... Field emission element 103... Dummy element 104, 304... Emitter 104a... One end of emitter 105, 305... Gate electrode 105a... Opening of gate electrode 106, 306... Focusing electrode 106a... Opening of focusing electrode 107, 107A, 107B, 108... Insulating film 109... Lift-off resist 110, 111, 112, 113, 115, 116... Photoresist 114... Mask layer E... Electrons R １ ...First area R ２ ...Second area R ３ ...Third area

Claims

1. An electron source comprising: a field emission element that emits electrons into external space, and a dummy element that surrounds the field emission element, on one side of a substrate; 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 wherein the one end of the emitter included in the dummy element is electrically insulated from the external space.

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

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. An electron source according to either claim 2 or 3, characterized in 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.

5. The electron source according to claim 2 or 3, wherein the gate electrode of the dummy element is covered with the first insulating film.

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

7. An electron source according to claim 1 or 2, characterized in that, on said one surface, the width of a first region in which said dummy elements are arranged is 1 / 5 or more of the width of a second region in which said field emission elements are arranged.

8. An electron source according to claim 1 or 2, characterized in that it comprises a third region along said one surface, between a first region in which said dummy elements are arranged and a second region in which said field emission elements are arranged, in which neither said field emission elements nor said dummy elements are arranged, and the width of said third region is 300% or less of the width of one of said field emission elements.

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