Patent Publication Number: US-11387069-B2

Title: Electron-emitting electrode including multiple diamond members and magnetron including same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2020-201039, filed on Dec. 3, 2020; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an electron-emitting electrode and a magnetron. 
     BACKGROUND 
     For example, an electron-emitting electrode such as a thermionic element or the like is provided in a magnetron. It is desirable to increase the efficiency of the electron-emitting electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A to 1D  are schematic views illustrating an electron-emitting electrode according to a first embodiment; 
         FIGS. 2A and 2B  are schematic cross-sectional views illustrating the electron-emitting electrode according to the first embodiment; 
         FIGS. 3A to 3C  are schematic perspective views illustrating a portion of the electron-emitting electrode according to the first embodiment; 
         FIGS. 4A to 4D  are schematic views illustrating an electron-emitting electrode according to a second embodiment; 
         FIGS. 5A and 5B  are schematic cross-sectional views illustrating the electron-emitting electrode according to the second embodiment; 
         FIGS. 6A and 6B  are schematic views illustrating a magnetron according to a third embodiment; and 
         FIG. 7  is a schematic cross-sectional view illustrating the magnetron according to the third embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     According to one embodiment, an electron-emitting electrode includes a first member, a first diamond member, and a second diamond member. A surface of the first member includes a first region and a second region. The first diamond member is provided at the first region. The first diamond member includes a first element. The first element includes at least one selected from the group consisting of nitrogen, phosphorus, arsenic, antimony, and bismuth. The second diamond member is provided at the second region. The second diamond member includes a second element. The second element including at least one selected from the group consisting of boron, aluminum, gallium, and indium. 
     According to one embodiment, a magnetron includes the electron-emitting electrode described above, and an opposite electrode facing the electron-emitting electrode. A gap is provided between the electron-emitting electrode and the opposite electrode. 
     Various embodiments are described below with reference to the accompanying drawings. 
     The drawings are schematic and conceptual; and the relationships between the thickness and width of portions, the proportions of sizes among portions, etc., are not necessarily the same as the actual values. The dimensions and proportions may be illustrated differently among drawings, even for identical portions. 
     In the specification and drawings, components similar to those described previously or illustrated in an antecedent drawing are marked with like reference numerals, and a detailed description is omitted as appropriate. 
     First Embodiment 
       FIGS. 1A to 1D  are schematic views illustrating an electron-emitting electrode according to a first embodiment. 
       FIG. 1A  is a side view.  FIG. 1B  is a perspective view in which a portion  10 A of  FIG. 1A  is extracted.  FIG. 1C  is a cross-sectional view of one example of the electron-emitting electrode.  FIG. 1D  is a cross-sectional view of another example of the electron-emitting electrode. 
     As shown in  FIGS. 1A and 1B , the electron-emitting electrode  110  according to the embodiment includes a first member  10 , a first diamond member  21 , and a second diamond member  22 . 
     In the example as shown in  FIG. 1A , the first member  10  is spiral-shaped. The first member  10  is, for example, a filament. The first member  10  includes, for example, tungsten. The first member  10  may include, for example, tungsten and at least one selected from the group consisting of thorium oxide and cerium oxide. The tungsten concentration in the first member  10  is, for example, not less than 90%. The melting points of these materials are high. For example, any material that has a melting point that is not less than 1200° C. may be used as the first member  10 . The first member  10  is, for example, conductive. 
     As shown in  FIGS. 1B to 1D , a surface  10 F of the first member  10  includes a first region  11  and a second region  12 . In the example as shown in  FIG. 1B , the first region  11  and the second region  12  are along a direction Dx 1  in which the first member  10  extends. 
     The first diamond member  21  is located at the first region  11 . The first diamond member  21  includes diamond and a first element. The first element includes at least one selected from the group consisting of nitrogen, phosphorus, arsenic, antimony, and bismuth. For example, the first diamond member  21  is of an n-type. 
     The second diamond member  22  is located at the second region  12 . The second diamond member  22  includes diamond and a second element. The second element includes at least one selected from the group consisting of boron, aluminum, gallium, and indium. For example, the second diamond member  22  is of a p-type. 
     As shown in  FIG. 1A , the electron-emitting electrode  110  may include a first electrode terminal T 1  and a second electrode terminal T 2 . The first electrode terminal T 1  is electrically connected with a first end portion  10   e  of the first member  10 . The second electrode terminal T 2  is electrically connected with a first other-end portion  10   f  of the first member  10 . The temperature of the first member  10  is increased by supplying a current to these terminals. Electrons are emitted from the first and second diamond members  21  and  22  as the temperature of the first member  10  increases. 
     For example, thermions are emitted from the first diamond member  21 . For example, primary electrons are emitted from the first diamond member  21 . For example, secondary electrons are emitted from the second diamond member  22 . For example, the electron-emitting electrode  110  is applicable as the cathode of a magnetron, etc. In such a case, for example, the electrons that are emitted from the first diamond member  21  are incident on the second diamond member  22 . Thereby, secondary electrons are emitted from the second diamond member  22 . 
     For example, conductive diamond has negative electron affinity. The conduction band level of such a material is higher than the vacuum level. Electrons are easily emitted from such a material. Electrons are easily emitted by the cathode that includes conductive diamond even when the temperature of the first member  10  is low. For example, n-type diamond is used as the conductive diamond that emits the primary electrons. 
     For example, when the electron-emitting electrode  110  is used as the cathode of a magnetron, etc., a portion of the thermions that are emitted has cyclotron motion and strikes the cathode due to a reverse impact phenomenon. The cathode can efficiently emit secondary electrons by including a material that has a high emission efficiency of secondary electrons. Conductive diamond can be used as the material that emits secondary electrons. For example, p-type diamond is used as the material that emits secondary electrons. 
     According to the embodiment, the electron emission of the second diamond member  22  can be utilized in addition to the emission of the electrons from the first diamond member  21 . A highly efficient electron emission is obtained thereby. According to the embodiment, an electron-emitting electrode is provided in which the efficiency can be increased. 
     For example, a reference example may be considered in which a metal oxide or the like is provided instead of p-type diamond. The emission efficiency of secondary electrons of the reference example is low. According to the embodiment, secondary electrons can be emitted with high efficiency by providing the p-type second diamond member  22 . 
     As shown in  FIGS. 1C and 1D , the first diamond member  21  and the second diamond member  22  are separated from each other. 
     The surface of one of the first diamond member  21  or the second diamond member  22  may include a surface asperity. For example, the surface asperity of these members may be caused by the diamond crystal grains. 
     For example, the second diamond member  22  may include an uneven configuration (including a protruding shape) having a depth that is not more than 50 μm. Secondary electrons are easily emitted by the uneven configuration. 
     As shown in  FIGS. 1C and 1D , the height of the first diamond member  21  referenced to the first region  11  (the surface  10 F of the first member  10 ) is taken as a first height H 1 . For example, the first height H 1  corresponds to the thickness of the first diamond member  21 . The height of the second diamond member  22  referenced to the second region  12  (the surface  10 F of the first member  10 ) is taken as a second height H 2 . For example, the second height H 2  corresponds to the thickness of the second diamond member  22 . According to the embodiment, it is favorable for the second height H 2  to be greater than the first height H 1 . The surface area of the surface of the second diamond member  22  is substantially increased thereby. Thereby, for example, the incidence of the electrons on the second diamond member  22  and the emission of the electrons from the second diamond member  22  are more efficient. A higher efficiency is obtained. 
     According to the embodiment, the second height H 2  is not less than 1.5 times and not more than 10 times the first height H 1 . For example, the second height H 2  is not more than 5 μm. Thereby, the emission of the electrons from the second diamond member  22  is easier. 
     As shown in  FIG. 1C , the top of the second diamond member  22  may be conic. The top of the second diamond member  22  may be planar. 
     According to the embodiment, it is favorable for the ratio of the surface area of the second region  12  to the surface area of the first region  11  to be not more than 0.1. For example, the surface area of the first region  11  is not less than 10 times the surface area of the second region  12 . For example, the surface area of the first diamond member  21  is not less than 10 times the surface area of the second diamond member  22 . Thereby, a high amount of primary electrons is emitted from the first diamond member  21 . A high amount of primary electrons increases the amount of the electrons incident on the second diamond member  22 . As a result, a high amount of secondary electrons is emitted from the second diamond member  22 . 
     In the example as shown in  FIG. 1B , the second diamond member  22  extends along the direction Dx 1  in which the first member  10  extends. In the example, the first region  11  is located along a portion of the circumference having the direction Dx 1  in which the first member  10  extends as the center; and the second region  12  is located at the other portion of the circumference. 
     According to the embodiment, the surface  10 F of the first member  10  may include multiple first regions  11 . For example, multiple first diamond members  21  may be provided. The second region  12  may be located between one of the multiple first regions  11  and another one of the multiple first regions  11 . For example, one of the multiple first diamond members  21  is located at the one of the multiple first regions  11 . Another one of the multiple first diamond members  21  is located at the other one of the multiple first regions  11 . For example, the ratio of the surface area of the second region  12  to the sum of the surface areas of the multiple first regions  11  is not more than 0.1. For example, the ratio of the surface area of the second diamond member  22  to the sum of the surface areas of the multiple first diamond members  21  is not more than 0.1. 
     According to the embodiment, the surface  10 F of the first member  10  may include multiple second regions  12 . For example, multiple second diamond members  22  may be provided. For example, the one of the multiple first regions  11  may be between one of the multiple second regions  12  and another one of the multiple second regions  12 . One of the multiple second diamond members  22  is located at the one of the multiple second regions  12 . Another one of the multiple second diamond members  22  is located at the other one of the multiple second regions  12 . For example, the ratio of the sum of the surface areas of the multiple second regions  12  to the sum of the surface areas of the multiple first regions  11  is not more than 0.1. For example, the ratio of the sum of the surface areas of the multiple second diamond members  22  to the sum of the surface areas of the multiple first diamond members  21  is not more than 0.1. 
       FIGS. 2A and 2B  are schematic cross-sectional views illustrating the electron-emitting electrode according to the first embodiment. 
     As shown in  FIGS. 2A and 2B , the first diamond member  21  includes a first polycrystal  21   c . The first diamond member  21  may include a first hydrogen region  21   f . The first hydrogen region  21   f  is located at the surface of the first polycrystal  21   c . The first hydrogen region  21   f  includes hydrogen. The first hydrogen region  21   f  is, for example, a hydrogen termination region. 
     As shown in  FIGS. 2A and 2B , the second diamond member  22  includes a second polycrystal  22   c . The second diamond member  22  may include a second hydrogen region  22   f . The second hydrogen region  22   f  is located at the surface of the second polycrystal  22   c . The second hydrogen region  22   f  includes hydrogen. The second hydrogen region  22   f  is, for example, a hydrogen termination region. 
     For example, a homogeneous diamond member is easily obtained by the diamond member including a polycrystal. For example, an efficient electron emission is stably and easily obtained by the diamond member including a hydrogen region. 
       FIGS. 3A to 3C  are schematic perspective views illustrating a portion of the electron-emitting electrode according to the first embodiment. 
     These drawings illustrate the first polycrystal  21   c  or the second polycrystal  22   c.    
     In the example of  FIG. 3A , at least one of the first polycrystal  21   c  or the second polycrystal  22   c  includes a (100) plane and a (111) plane. The proportion of the (111) plane is greater than the proportion of the (100) plane. 
     In the example of  FIG. 3B  as well, at least one of the first polycrystal  21   c  or the second polycrystal  22   c  includes the (100) plane and the (111) plane. In the example of  FIG. 3B , the proportion of the (111) plane is even greater than the proportion of the (100) plane. 
     In the example of  FIG. 3C  as well, at least one of the first polycrystal  21   c  or the second polycrystal  22   c  includes the (111) plane. The (100) plane is substantially not provided. 
     For example, the emission of the secondary electrons from the second diamond member  22  is more efficiently performed by increasing the proportion of the (111) plane. 
     For example, the second polycrystal  22   c  includes the (111) plane. The second polycrystal  22   c  does not include the (100) plane. Or, the proportion of the (100) plane in the second polycrystal  22   c  is less than the proportion of the (111) plane in the second polycrystal  22   c . A highly efficient electron emission is easily obtained thereby. 
     Second Embodiment 
       FIGS. 4A to 4D  are schematic views illustrating an electron-emitting electrode according to a second embodiment. 
       FIG. 4A  is a cross section and a side view.  FIG. 4B  is a perspective view of a portion of the electron-emitting electrode.  FIG. 4C  is a cross-sectional view of one example of the electron-emitting electrode.  FIG. 4D  is a cross-sectional view of another example of the electron-emitting electrode. 
     As shown in  FIGS. 4A and 4B , the electron-emitting electrode  111  according to the embodiment includes the first member  10 , the first diamond member  21 , the second diamond member  22 , and a second member  15 . 
     The second member  15  is conductive. The second member  15  includes, for example, tungsten. The second member  15  may include, for example, tungsten and at least one selected from the group consisting of thorium oxide and cerium oxide. The tungsten concentration in the second member  15  is, for example, not less than 90%. The melting points of these materials are high. For example, any material that has a melting point that is not less than 1200° C. may be used as the second member  15 . In the example, the second member  15  is spiral-shaped. 
     As shown in  FIG. 4A , the electron-emitting electrode  111  may include the first electrode terminal T 1  and the second electrode terminal T 2 . The first electrode terminal T 1  is electrically connected with a second end portion  15   e  of the second member  15 . The second electrode terminal T 2  is electrically connected with a second other-end portion  15   f  of the second member  15 . 
     In the example as shown in  FIGS. 4A and 4B , the first member  10  that is tubular (including circular tubular) is provided around the second member  15 . As shown in  FIGS. 4C and 4D , for example, the first member  10  is between the second member  15  and the first diamond member  21  and between the second member  15  and the second diamond member  22 . The second member  15  is inside the tubular first member  10 . 
     For example, a current is supplied between the second end portion  15   e  and the second other-end portion  15   f  via the first electrode terminal T 1  and the second electrode terminal T 2 . The second member  15  is heated by the current. The temperature of the first member  10  is increased by the heated second member  15 . Electrons are emitted from the first and second diamond members  21  and  22  as the temperature of the first member  10  increases. For example, primary electrons are emitted from the first diamond member  21 . For example, secondary electrons are emitted from the second diamond member  22 . 
     As shown in  FIGS. 4C and 4D , the height of the first diamond member  21  referenced to the first region  11  (the surface  10 F of the first member  10 ) is taken as the first height H 1 . The height of the second diamond member  22  referenced to the second region  12  (the surface  10 F of the first member  10 ) is taken as the second height H 2 . It is favorable for the second height H 2  to be greater than the first height H 1 . A higher efficiency is obtained. 
     As shown in  FIGS. 4C and 4D , the surface  10 F of the first member  10  may include the multiple first regions  11 . For example, the second region  12  may be located between one of the multiple first regions  11  and another one of the multiple first regions  11 . One of the multiple first diamond members  21  is located at the one of the multiple first regions  11 . Another one of the multiple first diamond members  21  is located at the other one of the multiple first regions  11 . For example, the ratio of the surface area of the second region  12  to the sum of the surface areas of the multiple first regions  11  is not more than 0.1. For example, the ratio of the surface area of the second diamond member  22  to the sum of the surface areas of the multiple first diamond members  21  is not more than 0.1. 
     As shown in  FIGS. 4C and 4D , the surface  10 F of the first member  10  may include the multiple second regions  12 . For example, the one of the multiple first regions  11  may be between one of the multiple second regions  12  and another one of the multiple second regions  12 . One of the multiple second diamond members  22  is located at the one of the multiple second regions  12 . Another one of the multiple second diamond members  22  is located at the other one of the multiple second regions  12 . For example, the ratio of the sum of the surface areas of the multiple second regions  12  to the sum of the surface areas of the multiple first regions  11  is not more than 0.1. For example, the ratio of the sum of the surface areas of the multiple second diamond members  22  to the sum of the surface areas of the multiple first diamond members  21  is not more than 0.1. 
       FIGS. 5A and 5B  are schematic cross-sectional views illustrating the electron-emitting electrode according to the second embodiment. 
     As shown in  FIGS. 5A and 5B , the first diamond member  21  includes the first polycrystal  21   c . The first diamond member  21  may include the first hydrogen region  21   f . The first hydrogen region  21   f  is located at the surface of the first polycrystal  21   c . The first hydrogen region  21   f  includes hydrogen. As shown in  FIGS. 5A and 5B , the second diamond member  22  includes the second polycrystal  22   c . The second diamond member  22  may include the second hydrogen region  22   f . The second hydrogen region  22   f  is located at the surface of the second polycrystal  22   c . The second hydrogen region  22   f  includes hydrogen. Homogeneous diamond members are easily obtained. For example, an efficient electron emission is stably and easily obtained. 
     Third Embodiment 
       FIGS. 6A and 6B  are schematic views illustrating a magnetron according to a third embodiment. 
       FIG. 6A  is a perspective view.  FIG. 6B  is a cross-sectional view. As shown in  FIGS. 6A and 6B , the magnetron  210  according to the embodiment includes an opposite electrode  40  and the electron-emitting electrode according to the first or second embodiment. The electron-emitting electrode  110  is illustrated in the example. The opposite electrode  40  faces the electron-emitting electrode  110 . A gap  40 G is provided between the electron-emitting electrode  110  and the opposite electrode  40 . The air pressure in the gap  40 G is less than 1 atmosphere. The electron-emitting electrode  110  is, for example, a cathode. The opposite electrode  40  is, for example, an anode. 
     A first magnet  51  and a second magnet  52  are provided as shown in  FIG. 6A . The direction from the first magnet  51  toward the second magnet  52  is taken as a Z-axis direction. One direction perpendicular to the Z-axis direction is taken as an X-axis direction. A direction perpendicular to the Z-axis direction and the X-axis direction is taken as a Y-axis direction. The opposite electrode  40  faces the electron-emitting electrode  110  in the X-Y plane. 
     As shown in  FIG. 6B , an electron cloud  45  that is based on the electrons emitted from the electron-emitting electrode  110  is formed by the magnetic field due to these magnets. For example, the electrons of the electron cloud  45  have cyclotron motion. A portion of the electrons that have cyclotron motion are incident on the electron-emitting electrode  110  due to a reverse impact phenomenon. According to the embodiment, the electrons that are included in the electron cloud  45  are incident on the second diamond member  22  of the electron-emitting electrode  110 ; and secondary electrons are emitted from the second diamond member  22 . 
     As shown in  FIG. 6B , a cavity resonator  41  is provided in the opposite electrode  40 . Microwaves are emitted from an output antenna  55 . 
     According to the embodiment, a magnetron can be provided in which the efficiency can be increased. 
       FIG. 7  is a schematic cross-sectional view illustrating the magnetron according to the third embodiment. 
     As shown in  FIG. 7 , a housing  56  is provided in the magnetron  210  according to the embodiment. The electron-emitting electrode  110  and the opposite electrode  40  are located inside the housing  56 . The air pressure inside the housing  56  is less than 1 atmosphere. 
     According to the embodiment, thermions can be obtained at a low temperature. Refractory metal members at the periphery of the hot cathode can be replaced with inexpensive metals. For example, the cooling structures of fins, etc., can be simplified. 
     According to the embodiment, an electron-emitting electrode and a magnetron can be provided in which the efficiency can be increased. 
     In the specification, “a state of electrically connected” includes a state in which multiple conductors physically contact and a current flows between the multiple conductors. “a state of electrically connected” includes a state in which another conductor is inserted between the multiple conductors and a current flows between the multiple conductors. 
     Hereinabove, exemplary embodiments of the invention are described with reference to specific examples. However, the embodiments of the invention are not limited to these specific examples. For example, one skilled in the art may similarly practice the invention by appropriately selecting specific configurations of components included in electron-emitting electrodes such as members, diamond members, terminals, etc., from known art. Such practice is included in the scope of the invention to the extent that similar effects thereto are obtained. 
     Further, any two or more components of the specific examples may be combined within the extent of technical feasibility and are included in the scope of the invention to the extent that the purport of the invention is included. 
     Moreover, all electron-emitting electrodes, and magnetrons practicable by an appropriate design modification by one skilled in the art based on the electron-emitting electrodes, and the magnetrons described above as embodiments of the invention also are within the scope of the invention to the extent that the purport of the invention is included. 
     Various other variations and modifications can be conceived by those skilled in the art within the spirit of the invention, and it is understood that such variations and modifications are also encompassed within the scope of the invention. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.