Patent Publication Number: US-2013235976-A1

Title: X-ray source device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Korean Patent Application No. 10-2012-0022888, filed on Mar. 6, 2012, and all the benefits accruing therefrom under 35 U.S.C. §119, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field 
     Provided is an X-ray source device capable of stably emitting electrons by amplifying them. 
     2. Description of the Related Art 
     With the constant increase in consumer health awareness, many studies have been performed on various pieces of medical equipment. An X-ray source device is an example of such medical equipment. Carbon nanotube is generally used for an emitter in an X-ray source device since an electron beam can be focused via a high emission current and a relatively simple structure. Also, since an on/off switching speed of an emitter using the carbon nanotube is fast, an X-ray source device including an emitter using the carbon nanotube has been actively researched. 
     The X-ray source device requires a high current, and a high electric field is needed to emit the high current. However, a high electric field may affect the stability of the electron emission of the carbon nanotube, and a structural stability between an electrode such as a cathode including the carbon nanotube and an electrode such as a gate, inducing a voltage. Since current flows beyond a current density limit in a portion of the carbon nanotube where the electric field is concentrated, the carbon nanotube may be undesirably destructed or detached from a substrate due to the high electric field. Also, as a gate may be detached, the gate may be undesirably attached to the cathode due to the high electric field between the gate and the cathode. 
     SUMMARY 
     Provided is one or more embodiment of an X-ray source device capable of stably emitting electrons by amplifying the electrons. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments. 
     Provided is an X-ray source device including a substrate, a cathode electrode on the substrate, an emitter on the cathode electrode, an insulation body provided around the cathode electrode, a gate electrode provided on the insulation body, a first secondary electron emission layer provided at a side wall of the gate electrode and emitting secondary electrons upon collision with an electron beam emitted by the emitter, and an anode electrode arranged to be separated from the gate electrode. 
     The gate electrode may have a mesh structure. 
     A second secondary electrons emission layer may be further provided between the gate electrode and the insulation body. 
     The first secondary electron emission layer may include a metal oxide, an inorganic material or a combination thereof. 
     The first secondary electron emission layer may include SiO 2 , MgO, Al 2 O 3  or a combination thereof. 
     An adhesion layer may be further provided between the insulation body and the gate electrode. 
     The adhesion layer may include a glass material. 
     The adhesion layer may include glass frit. 
     The emitter may include a carbon nanotube. 
     The emitter may be formed by a printing method using paste, a chemical vapor deposition method, an electrophoresis method, a transfer method or a combination thereof. 
     The gate electrode may include a hole separated from an outer edge of the gate electrode. 
     A width of a lower surface of the gate electrode may be greater than a width of an upper surface of the insulation body. 
     A width of the insulation body may decrease from a lower surface of the insulating body to the upper surface of the insulation body. 
     The insulation body may include a groove, the cathode electrode may be provided in the groove, and the groove may have a reversed trapezoidal cross-sectional shape. 
     The first secondary electron emission layer may be formed by a chemical vapor deposition method, a sputtering method, a thermal oxidation method, a liquid coating method or a combination thereof. 
     The first secondary electron emission layer and the second secondary electron emission layer may be integral. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a cross-sectional view schematically illustrating an X-ray source device, according to an embodiment of the present invention; 
         FIG. 2  is a plan view illustrating the X-ray source device of  FIG. 1  without an anode electrode, according to an embodiment of the present invention; 
         FIG. 3  is a graph showing a change in a secondary electron emission coefficient according to incident energy in units of electron volts (eV) in an X-ray source device, according to an embodiment of the present invention; 
         FIG. 4  is a graph showing a change in anode current in units of amperes (A) according to a gate voltage in units of volts (V) with respect to the existence and absence of a secondary electron emission layer in an X-ray source device, according to an embodiment of the present invention; and 
         FIG. 5  is a graph of load in units of newtons (N) according to time in units of seconds for showing an adhesion force between a gate electrode and an insulation layer with respect to the existence of absence of a secondary electron emission layer in an X-ray source device, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. 
     It will also be understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. Like reference numerals in the drawings denote like elements, and thus their description will be omitted. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
     It will be understood that, although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the invention. 
     Spatially relative terms, such as “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe the relationship of one element or feature to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation, in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “lower” relative to other elements or features would then be oriented “above” relative to the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Embodiments of the invention are described herein with reference to cross-section illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of the invention. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the invention should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Hereinafter, the invention will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a cross-sectional view schematically illustrating an X-ray source device  1 , according to an embodiment of the present invention. Referring to  FIG. 1 , the X-ray source device  1  includes a substrate  10 , a cathode electrode  15  provided on the substrate  10 , and an emitter  17  provided on the cathode electrode  15  and emitting an electron beam. The substrate  10  may include, for example, invar, stainless steel, glass, etc., but is not limited thereto or thereby. An insulation body  20  may be provided around the cathode electrode  15  to expose the emitter  17  and the cathode electrode  15 . A gate electrode  35  may be provided above the insulation body  20  and may expose the emitter  17  and the cathode electrode  15 . The insulation body  20  may surround the cathode electrode  15  and have a thickness greater than that of the cathode electrode  35  in a direction perpendicular to the substrate  10 . An anode electrode  50  may be provided at a predetermined distance above the gate electrode  35 . 
     As such, the X-ray source device  1  according to the present embodiment may have a triode structure including the cathode electrode  15 , the gate electrode  35  and the anode electrode  50 . The emitter  17  emits electrons and may have a slender, fine-pointed rod-like shape to facilitate the emission of the electrons. When a voltage is applied to the emitter  17 , the electrons may be instantly emitted from the fine-pointed tip of the emitter  17 . 
     The emitter  17  may include, for example, a dispenser cathode material for emitting thermions, a molybdenum (Mo) or carbon (C) based material, such as a compound having at least one Mo or C atom, or zinc oxide (ZnO). The dispenser cathode material may include, for example, porous tungsten (W), barium oxide (BaO), barium strontium oxide (BaSrO), calcium oxide (CaO), aluminum oxide (Al 2 O 3 ), or lanthanum hexaboride (LaB 6 ). The carbon based material may include, for example, carbon nanotube or diamond-like carbon (“DLC”). In one embodiment, for example, when the emitter  17  includes carbon nanotube, the emitter  17  may be formed by a printing method using paste, a chemical vapor deposition (“CVD”) method, an electrophoresis method, a transfer method or a combination thereof, but is not limited thereto or thereby. Such forming methods may dispose the emitter  17  on the cathode electrode  15 . When a voltage is applied to the gate electrode  35 , the emitter  17  emits an electron beam. Otherwise, no electron beam is emitted. Accordingly, the gate electrode  35  may function as a switch of an electron beam. 
       FIG. 2  is a plan view illustrating the X-ray source device  1  without an anode electrode, according to an embodiment of the present invention. Referring to  FIG. 2 , the X-ray source device  1  may include a plurality of cells  5  that may be arranged in a matrix form.  FIG. 1  illustrates one cell outlined by a dotted line. 
     The gate electrode  35  may be a single, unitary, indivisible member, but is not limited thereto or thereby. The gate electrode  35  may include a hole  36  extended through a thickness thereof, such that the hole  36  may be defined solely by the gate electrode  35 , but is not limited thereto or thereby. The hole  36  is separated from an outer edge of the gate electrode  35 , and may be in a center of of the gate electrode  35  and/or a center of a cell  5 , but is not limited thereto or thereby. The gate electrode  35  may include a plurality of holes  36  arranged in a matrix form, defining a mesh-shaped structure of the gate electrode  35 . Although the holes  36  are illustrated to have a rectangular planar shape, the present invention is not limited thereto and the holes  36  may have a variety of shapes such as a circular shape or a polygonal shape in the plan view. 
     A first secondary electron emission layer  40  may be provided at a side wall of the gate electrode  35 . The secondary electron emission layer  40  may induce emission of one or more secondary electrons from the electrons emitted by the emitter  17 . The first secondary electron emission layer  40  may include a metal oxide or an inorganic material. In one embodiment, for example, the first secondary electron emission layer  40  may include SiO 2 , MgO, Al 2 O 3 , a combination thereof, etc., but is not limited thereto or thereby. The first secondary electron emission layer  40  may be formed by a CVD method, a sputtering method, a thermal oxidation method or a liquid coating method, but is not limited thereto or thereby. 
     Primary electrons emitted by the emitter  17  and the secondary electrons emitted by the first secondary electron emission layer  40  are accelerated to collide against the anode electrode  50 . Accordingly, an X-ray may be induced and emitted by the anode electrode  50 . 
     The insulation body  20  includes portions around the cathode electrode  15  and grooves  21  aligned with or corresponding to the holes  36  of the gate electrode  35 . The insulation body  20  may have, for example, a mesh structure defined by the portions around the cathode electrode  15  and the grooves  21 . The cathode electrode  15  may be in the groove  21  of the insulation body  20 . When a voltage is applied to the cathode electrode  15  and the gate electrode  35 , the insulation body  20  may reduce or effectively prevent an electrical short-circuit between the cathode electrode  15  and the gate electrode  35 . 
     The insulation body  20  may have a cross-sectional shape such that a width of the portions around the cathode electrode  35  gradually decreases in a direction from a lower portion toward an upper portion thereof. In one embodiment, for example, the portions of the insulation body  20  around the cathode electrode  15  may have a trapezoidal cross-sectional shape, and the groove  21  of the insulation body  20  may have a reversed trapezoidal cross-sectional shape. An efficiency of reflecting the electrons emitted by the emitter  17  may be increased according to the shape of the groove  21 . An adhesion layer  30  may be provided between the gate electrode  35  and the insulation body  20  to bond the gate electrode  35  and the insulation body  20  to each other. 
     As described above, the first secondary electron emission layer  40  may be provided at the side wall of the gate electrode  35 . The primary electrons emitted by the emitter  17  may be incident on the first secondary electron emission layer  40  to induce emission of one or more secondary electrons. A second secondary electron emission layer  41  may be further provided on a lower surface of the gate electrode  35 . 
     A width of the lower surface of the gate electrode  35  may be larger than that of an upper surface of the insulation body  20 . When the second secondary electron emission layer  41  is arranged on the lower surface of the gate electrode  35 , a surface of the second secondary electron emission layer  41  may be exposed to the outside or to the emitter  17 . Thus, when the second secondary electron emission layer  41  is further arranged on the lower surface of the gate electrode  35 , an electron emission efficiency of secondarily amplifying the primary electrons emitted by the emitter  17  in the secondary electrons emission layer  41  may be further improved. The first secondary electron emission layer  40  and the second secondary electron emission layer  41  may be integral to define a single, unitary, indivisible member, but is not limited thereto or thereby. 
     The adhesion layer  30  may include a glass material, for example, glass frit. When the adhesion layer  30  includes a glass material, an adhesion force between the gate electrode  35  and the insulation body  20  may be small. When the second secondary electron emission layer  41  is further provided between the gate electrode  35  and the insulation body  20 , the adhesion force between the gate electrode  35  and the insulation body  20  may be increased. Since the second secondary electron emission layer  41  exhibits a superior adhesion force to glass, the adhesion force between the gate electrode  35  and the insulation body  20  may be increased. 
     In one embodiment, the gate electrode  35  and the insulation body  20  are combined by using glass frit and then sintered so that the gate electrode  35  and the insulation body  20  may be bonded to each other. The adhesion force may be improved by the second secondary electron emission layer  41 . Thus, a high electric field between the gate electrode  35  and the insulation body  20  may reduce or effectively prevent detachment of the gate electrode  35  from the insulation body  20 . As such, the second secondary electron emission layer  41  may amplify the secondary electrons and simultaneously improve the adhesion force between the gate electrode  35  and the insulation body  20 . 
     When the X-ray source device  1  according to the present embodiment operates and the primary electrons that are field-emitted by the emitter  17  are incident on the gate electrode  35  coated with the first secondary electron emission layer  40  and the second secondary electron emission layer  41 , one or more secondary electron emissions may be induced. The secondary electrons amplified by the first and second secondary electron emission layers  40  and  41  and the primary electrons emitted without passing through the first and second secondary electron emission layers  40  and  41  are accelerated and collide against the anode  50  so that an X-ray may be induced. 
     As described above, the first and second secondary electron emission layers  40  and  41  may amplify the primary electrons. 
       FIG. 3  is a graph showing a change in a secondary electron emission coefficient δ according to electron energy in units of electron volts (eV) incident on the first and second secondary electron emission layers  40  and  41  when the first and second secondary electron emission layers  40  and  41  include SiO 2 , according to a thickness of each secondary electron emission layer in units of nanometers (nm). The secondary electron emission coefficient δ indicates a ratio of the number of emitted secondary electrons to the number of incident primary electrons. 
     Referring to  FIG. 3 , when the thickness of an SiO 2  secondary electron emission layer is 19 nm, the secondary election emission coefficient at an incident electron energy of 100-500 eV may be 3 or higher. In one embodiment, for example, when one electron emitted by the emitter  17  including carbon nanotube at a gate voltage of 100-500 V is incident on a secondary electron emission layer, three or more secondary electrons may be emitted. According to the graph of  FIG. 3 , the secondary electron emission coefficient may vary with the thickness of a secondary electron emission layer. Referring to  FIG. 3 , when a secondary electron emission layer has a thickness greater than 0 and less than or equal to 80 nm, a secondary electron emission efficiency may be improved. In this case, the secondary electron emission coefficient may be greater than or equal to 2. 
       FIG. 4  is a graph showing a change in a current in units of amperes (A) at an anode according to a drive voltage in units of volts (V), in a comparative example (without SiO 2 ) where an X-ray source device does not include a secondary electron emission layer, and an embodiment of the present invention (with SiO 2 ) where an X-ray source device does include a secondary electron emission layer. The first and second secondary electron emission layers  40  and  41  as a coating including SiO 2  at a thickness of 20 nm are used as the X-ray source device according to the present embodiment (with SiO 2 ). 
     Referring to  FIG. 4 , a drive voltage for the X-ray source with the first and second secondary electron emission layers  40  and  41  (with SiO 2 ) is lower than that for the X-ray source without the first and second secondary electron emission layers  40  and  41 (without SiO 2 ). Since the drive voltage is relatively low, damaging of the emitter  17  during driving of the X-ray source device  1  may be reduced. As such, current may be increased and the drive voltage may be reduced by using the amplification of secondary electrons. Thus, an X-ray source device using field emission of a relatively stable emitter may be manufactured. 
       FIG. 5  is a graph showing results of measuring an adhesion force in units of newtons (N) through a peel test to separate two layers, that is, the gate electrode  35  and the insulation body  20 , when a gate electrode coated with SiO 2  (with SiO 2 ) or a gate electrode not coated with SiO 2  (without SiO 2 ) is attached to a substrate by using glass frit. In view of the maximum load value, an adhesion force of the gate electrode without SiO 2  is lower than that of the gate electrode coated with SiO 2 . As such, when a gate electrode is coated with SiO 2 , structural stability between the gate electrode  35  and the cathode electrode  15  may be improved due to increased adhesion force between the gate electrode  35  and the insulation layer  20 . 
     As described above, an X-ray source device according to one or more embodiment of the present invention includes a secondary electron emission layer on a surface of a gate electrode so that a drive voltage of the gate electrode may be decreased and current flowing through an anode may be increased. Since the drive voltage of the gate electrode is low, damaging of an emitter due to a high drive voltage may be reduced and unstable field emission due to a damaged emitter may be reduced. 
     It should be understood that the exemplary embodiments described therein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments.