Patent Publication Number: US-9837241-B2

Title: Tera Hertz reflex klystron

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims all benefits accruing under 35 U.S.C. §119 from China Patent Application No. 201510525276.6, filed on Jun. 25, 2015 in the China Intellectual Property Office, disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a Tera Hertz reflex klystron and a micro Tera Hertz reflex klystron array. 
     2. Description of Related Art 
     In general, the Tera Hertz (THz) wave refers to an electromagnetic wave whose frequency ranging from 0.3 THz to 3 THz or 0.1 THz to 10 THz. The band of THz wave lies between the infrared wave and the millimeter wave. The THz wave has excellent properties. For example, THz wave has certain ability to penetrate objects, and the photon energy is small, thus the THz will not cause damage to the objects. At the same time, a lot of material can absorb the THz wave. 
     A reflex klystron is used to emit electromagnetic waves. In order to emit THz waves, the feature size of the reflex klystron should be small and the current density of the electron rejection should be high. A traditional Tera Hertz reflex klystron includes a resonant cavity. The resonant cavity includes two coupling outputting holes located on two opposite side walls. The resonant cavity should have a large width, and the size of the Tera Hertz reflex klystron should be large enough. It is hard to decrease the size of the Tera Hertz reflex klystron, and a micro Tera Hertz reflex klystron array cannot be obtained. 
     What is needed, therefore, is a Tera Hertz reflex klystron that overcomes the problems as discussed above. 
     A Tera Hertz reflex klystron is provided, which includes: an electron emission unit being configured to emit a plurality of electrons, the electron emission unit defines a first opening; a resonant unit comprising a resonant cavity frame, the resonant cavity frame comprises a top wall and a bottom wall and defining a resonant cavity; the top wall and the bottom wall facing each other; and the bottom wall comprising a bottom opening, the top wall comprising a top opening and at least one outputting hole, and the bottom opening and the first opening are merged with each other; an output unit being configured to output Tera Hertz waves, and the plurality of electrons are transferred to the output unit from the at least one outputting hole. 
     Compared with the conventional Tera Hertz reflex klystron, the Tera Hertz reflex klystron includes at least one outputting hole. The at least one outputting hole is located on the top wall of the resonant cavity frame, a width of the resonant cavity frame can be small, and as such, the Tera Hertz reflex klystron can have a small size. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a schematic section view of one embodiment of a Tera Hertz reflex klystron. 
         FIG. 2  is a schematic view of an electron emission unit used in the Tera Hertz reflex klystron of  FIG. 1 . 
         FIG. 3  is an scanning electron microscope (SEM) image of a carbon nanotube wire used in the electron emission unit of  FIG. 2 . 
         FIG. 4  shows a vertical view of a first grid according to one embodiment. 
         FIG. 5  shows a vertical schematic view of one embodiment of a micro Tera Hertz reflex klystron array. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
     References will now be made to the drawings to describe, in detail, various embodiments of the present ionization electron emission unit. 
     Referring to  FIG. 1 , a Tera Hertz reflex klystron  10 , according to one embodiment, is provided. The Tera Hertz reflex klystron  10  includes an electron emission unit  11 , a resonant unit (not labeled) and an output unit  14 . The electron emission unit  11 , the resonant unit and the output unit  14  connect with each other. The resonant unit is located between the electron emission unit  11  and the output unit  14 . The electron emission unit  11  is used to emit electrons. The resonant unit includes a resonant cavity  121  which is connected with the electron emission unit  11 . The electrons are emitted from the electron emission unit  11  and get into the resonant cavity  121 . The resonant cavity  121  includes at least one outputting holes  123 . The output unit  14  and the resonant unit  12  face each other. The output unit  14  and the resonant unit  12  are communicant with each other through the outputting holes  123 . The resonant unit emits Tera Hertz (THz) waves which are transmitted to the output unit  14 . 
     The electron emission unit  11  includes an insulating substrate  110 , a cathode  111 , an electron emitter unit  114 , an electron injection layer  113 , an insulating layer  116 , and an electron extraction grid  115 . The cathode  111  is located on the insulating substrate  110 . The electron emitter unit  114  is electrically connected to the cathode  111 . The electron injection layer  113  is located above and insulated from the cathode  111  via the insulating layer  116 . The electron injection layer  113  defines a hollow space  1130 , and the electron emitter unit  114  is located in the hollow space  1130 . The hollow space  1130  defines a first opening, the electron extraction grid  115  covers the first opening. 
     A material of the insulating substrate  110  can be silicon, glass, ceramics, plastics, or polymers. A shape and a thickness of insulating base can be selected according to actual needs. The shape of the insulating substrate  110  can be circular, square, or rectangular. In one embodiment, the insulating substrate  110  is square, the length is about 10 mm, and the thickness is about 1 mm. 
     The cathode  111  is located on a surface of the insulating substrate  110 . The insulating layer  116  covers the cathode  111 . A first portion of the cathode  111  is exposed to and faces the electron extraction grid  115 , and a second portion of the cathode  111  is covered by the electron injection layer  113 . The electron emitter unit  114  is located on the first portion of the cathode  111  and electrically connected to the cathode  111 . The electron emitter unit  114  faces the electron extraction grid  115 . The first portion of the cathode  111  is exposed out through the hollow space  1130 . 
     The cathode  111  is a conductive layer. A material of the cathode  111  can be pure metal, alloy, semiconductor, indium tin oxide, or conductive paste. In one embodiment, the material of the insulating substrate  110  is silicon, and the cathode  111  can be doped silicon. In one embodiment, the material of the cathode  111  is an aluminum film with 20 micrometers. The aluminum film can be deposited on the insulating substrate  110  via magnetron sputtering method. 
     A material of the electron injection layer  113  can be silicon, chromium. A thickness of the electron injection layer  113  can be greater than 10 micrometers. In one embodiment, the thickness of the electron injection layer  113  ranges from about 30 micrometers to about 60 micrometers. 
     The electron injection layer  113  can have an oblique sidewall around the hollow space  1130 . The hollow space  1130  can be in a shape of inversed funnel, and the size of hollow space  1130  is gradually narrowed along a direction away from the cathode  111 . The electron emitter unit  114  can be received in hollow space  1130 . 
     The insulating layer  116  located on a surface of the electron injection layer  113 . The insulating layer  116  has two potions, a first portion of the insulating layer  116  is located between the electron injection layer  113  and the cathode  111 , a second portion of the insulating layer  116  is located in the hollow space  1130  and on an inside surface of the electron injection layer  113 . The insulating layer  116  can be resin, plastic, glass, ceramic, oxide, or their mixture. The oxide can be silica, aluminum oxide, or bismuth oxide. In one embodiment, the thickness of insulating layer  116  is about 100 micrometers. The material of the insulating layer  116  is a circular photoresist. In one embodiment, a secondary electron multiply material can be coated on a surface of the second portion of the insulating layer  116 . The secondary electron multiply material can be magnesium oxide, beryllium oxide or diamond. The secondary electron multiply material can improve number of the electrons when the electrons emitted from the electron emitters  1140  hit the side wall of the hollow space  1130 . 
     Referring to  FIG. 2 , the electron emitter unit  114  has a tapered shape defining a peak. A height of the electron emitter unit  114  at the central portion is the highest, and the height is gradually decreased along a direction away from the center. Furthermore, the central portion of the electron emitter unit  114  and the center of hollow space  1130  are in a same location. The electron emitter unit  114  includes a plurality of electron emitters  1140 . The plurality of electron emitters  1140  are parallel with each other. The electron emitter  1140  at the center of the electron emitter unit  114  is the highest. The height of the electron emitter unit  114  are gradually decreased along the direction away from the center of the electron emitter unit  114 . 
     The material of the electron emitters  1140  can be carbon nanotube, carbon fiber, or silicon nanofiber. Each of the plurality of electron emitters  1140  includes a first end and a second end, opposite to the first end. The second end is adjacent and electrically connected to the cathode  111 , and the first end extends toward the anode  112 . The first end is configured to emit electrons as an electron emission terminal. The height of the plurality of electron emitter unit  114  is greater than the thickness of the insulating layer  116 . 
     The electron emitter unit  114  is spaced from the sidewall of hollow space  1130 . The electron emitter unit  114  defines an emitting surface that is away from the insulating substrate  110 . The emitting surface of the electron emitter unit  114  can be parallel with the sidewall. In detail, a distance between each first end of the electron emitters  1140  and the sidewall of hollow space  1130  is substantially the same. Thus the plurality of first ends and the sidewall have substantially the same distances. The electron emitters  1140  can be carbon nanotubes, carbon fibers, silicon nanowires or silicon tips. Referring to  FIG. 3 , in one embodiment, the electron emitter unit  114  can be a carbon nanotube wire. The carbon nanotube wire includes a plurality of carbon nanotubes parallel with each other or twisted with other. 
     Furthermore, an ion bombardment resistance material can be deposited on each of the plurality of electron emitters  1140 . The ion bombardment resistance material can be zirconium carbide, hafnium carbide, or lanthanum hexaboride. The ion bombardment resistance material can protect the plurality of electron emitters  1140  from damage. Thus the lifespan of the electron emitters  1140  can be prolonged. 
     The electron emission unit  11  can further include a resistor layer (not shown). The resistor layer is sandwiched between the electron emitter unit  114  and the cathode  111 . The electron emitter unit  114  is electrically connected to the cathode  111 . The resistance of the resistor layer is greater than 10GΩ to ensure that the cathode  111  can uniformly apply current to the electron emitter unit  114 . The material of the resistor layer can be metallic alloy of nickel, copper, cobalt; the material of the resistor layer can also be metallic alloy, metallic oxide, inorganic composition doped with phosphorus. 
     The electron extraction grid  115  is used to leading the electrons emitter from the electron emitter unit  114 . The electron extraction grid  115  is spaced from the electron injection layer  113  and cover the first opening of the hollow space  1130 . While a voltage is applied on the electron extraction grid  115 , the electrons can be extracted from the electron emitter unit  114 . 
     The electron extraction grid  115  can be a carbon nanotube composite layer, a carbon nanotube layer, or a graphene layer. An electron transmittance rate of the graphene layer can reach to 98%. Referring to  FIG. 4 , in one embodiment, the electron extraction grid  115  is a carbon nanotube composite layer. The carbon nanotube composite layer has a net structure comprising a carbon nanotube layer  24  and coating layer  23 . 
     The carbon nanotube composite structure defines a plurality of apertures  28  to let the electrons pass through. A size of the aperture  28  can range from about 1 nanometer to about 200 micrometers, particularly, it is ranged from 10 nanometers to 10 millimeters. 
     The carbon nanotube layer forms a pattern. The patterned carbon nanotube layer defines the plurality of holes  25 . The holes  25  can be dispersed uniformly. The holes  25  extend throughout the carbon nanotube layer along the thickness direction thereof. The holes  25  can be defined by several adjacent carbon nanotubes, or a gap defined by two substantially parallel carbon nanotubes and extending along axial direction of the carbon nanotubes. The coating layer  23  is coated on the plurality of carbon nanotubes in the carbon nanotube layer. After the coating layer formed, the size of the holes  25  decreases to form the apertures  28 . The coating layer  23  is used to protect the carbon nanotube layer  24 . A material of the coating layer  23  can be silicon, silicon dioxide, silicon oxide, or aluminum oxide. A thickness of the coating layer  23  ranges from 1 nanometer to 100 micrometers, particularly, it ranges from 5 nanometers to 100 nanometers. 
     The resonant unit  12  includes a resonant cavity frame  128 , an insulating support  126 , a first grid electrode  124 , a second grid electrode  125 , at least one outputting hole  123 , a reflective room  122  and a reflective electrode  127 . The resonant cavity frame  128  defines a resonant cavity  121 . The resonant cavity frame  128  is located on and above the electron injection layer  113 . The resonant cavity frame  128  defines a bottom opening (not labeled) and a top opening (not labeled). The first opening, the bottom opening and the top opening are running through with each other. The bottom opening is located above the first opening. The bottom opening and the first opening are merged with each other. The insulating support  126  is located around the bottom opening. The first grid electrode  124  is located above and parallel with the electron extraction grid  115 . The first grid electrode  124  is supported by the insulating support  126  separated from the electron extraction grid  115 . 
     A material of the resonant cavity frame  128  can be silicon or chromium. A width of the resonant cavity  121  can be in a range of 70 micrometers to 300 micrometers. A inside wall of the resonant cavity frame  128  is coated by metal, such as copper, aluminum and other conductive material. In one embodiment, the resonant cavity frame  128  has a tube structure defines the resonant cavity  121 . A diameter of the resonant cavity  121  is 300 micrometers, the output frequency. 
     The resonant cavity frame  128  includes a bottom wall and a top wall. The bottom wall is located on the electron extraction grid  115 . The top wall is located above the bottom wall. The bottom opening is defined by the bottom wall. The top opening is defined by the top wall. The at least one outputting hole  123  is located in the top wall. The second grid electrode  125  covers the top opening. The electron extraction grid  115 , the first grid electrode  124  and the second grid electrode  125  are arranged in that order and overlapped with each other. 
     The at least one outputting hole  123  is located around the top opening. In some embodiments, the at least one outputting hole includes a plurality of outputting holes arranged orderly, the plurality of outputting holes are arranged uniformly on a circle, and a center of the circle is a center of the top opening. In the embodiment, a number of the outputting hole  123  is four, and the four outputting holes  123  are arranged in symmetry. 
     The reflective room  122  includes a reflective electrode  127  located therein. The reflective electrode  127  is located above and faces the second grid electrode  125 . The reflective room  122  covers the top opening and open to the top opening. When a voltage is applied on the reflective electrode  127 , the reflective electrode  127  is used to reflect electrons passing through the second grid electrode  125 . A voltage of the reflective electrode  127  is lower than a voltage of the second grid electrode  125 . And, a speed of the electrons getting into the reflective room  122  is decreased by a retarding field between the reflective electrode  127  and the second grid electrode  125 . 
     The output unit  14  includes a wave guide  140 , an absorber  141  and a lens  142 . The wave guide  140  defines a guide room, the absorber  141  is located on a surface of the wave guide  140  and in the guide room. The lens  142  is located at one end of the wave guide and covers an exit of the guide room. 
     In use of the Tera Hertz reflex klystron, the cathode  111 , the electron extraction grid  115 , the first grid electrode  124 , the second grid electrode  125 , the reflective electrode  127  are separately applied voltage. The electrons are emitted by the electron emitter unit  114  and extracted out the first opening by the electron extraction grid  115 , and, pass through the first grid electrode  124 . The electrons can be accelerated by the first grid electrode  124  and the second grid electrode  125  to form an electron beam with enough current density. The electron beam can pass through the first grid electrode  124 , the resonant cavity  121 , and the second grid electrode  125 . Thus the electron beam will be modulated by a microwave field in the resonant cavity  121 . After the electron beam passes through the second grid electrode  125 , the electron beam will be reflected by the reflective electrode  127 . All the electrons will be reflected by the retarding field in the reflective room  122 . Thus the electron beam will be modulated on density in the retarding field and reflected to the resonant cavity  121 . Therefore, the electrons will be oscillated in the resonant cavity  121 . After the electron beam is modulated on density, it will pass through the outputting hole  123  be transferred out into the guide room of the output unit  14 . And, then the Tera Hertz will be formed and output from the lens. 
     The Tera Hertz reflex klystron  10  has following advantages. The at least one outputting hole  123  is located on the top wall of the resonant cavity frame  128 , a width of the resonant cavity frame  128  can be small, and as such, the Tera Hertz reflex klystron  10  can have a small size. Further, because the electron emitter structure has a shape of cone, and the electron emitter in the central portion is highest, thus the shielding effect can be reduced. In addition, the through hole of the electron extraction grid  115  is in the shape of inversed funnel, thus the electrons can be focused by the through hole, and the current emission density can be improved. 
     Referring to  FIG. 5 , a micro Tera Hertz reflex klystron array  20  according to on embodiment is provided. The micro Tera Hertz reflex klystron array includes a substrate  210 , a plurality of first electrodes  220 , a plurality of second electrodes  230 , and a plurality of Tera Hertz reflex klystrons  10 . 
     The plurality of first electrodes  220  are parallel with each other. The plurality of second electrodes  230  are parallel with each other. The plurality of first electrodes  220  and the plurality of second electrodes  230  are perpendicular with each other to from a grid structure. The grid structure includes a plurality of cells. Each cell is defined by adjacent first electrodes  220  and adjacent second electrodes  230 . Each Tera Hertz reflex klystrons  10  is located in the cell and electrically connected with one first electrode  220  and one second electrode  230 . 
     It is to be understood that the above-described embodiments are intended to illustrate rather than limit the disclosure. Any elements described in accordance with any embodiments is understood that they can be used in addition or substituted in other embodiments. Embodiments can also be used together. Variations may be made to the embodiments without departing from the spirit of the disclosure. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure. 
     Depending on the embodiment, certain of the steps of methods described may be removed, others may be added, and the sequence of steps may be altered. It is also to be understood that the description and the claims drawn to a method may include some indication in reference to certain steps. However, the indication used is only to be viewed for identification purposes and not as a suggestion as to an order for the steps.