Low voltage electron source with self aligned gate apertures, fabrication method thereof, and x-ray generator using the electron source

Abstract

An x-ray generating device includes at least a nano-structure based field emission electron source having a self-aligned gate aperture incorporated on a substrate. The device further includes at least an anode target. Associated fabrication method is also described.

1 . An x-ray generating device comprising:
 an electron source that includes:
 a cathode electrode disposed on a substrate, the cathode electrode for providing a source of electrons; 
 an emitter layer being deposited over the cathode electrode and formed from a composition of a embedding material and one or a plurality of single or small cluster of nano-structures embedded therein, the emitter layer having a surface above which portion of the nano-structures protrude to emit electrons; 
 an insulator disposed over the emitter layer, the insulator having one or a plurality of apertures, each exposing at least the ends of the single or small cluster of nano-structures in the emitter layer; and 
 a gate electrode disposed over the insulator and having one or a plurality of apertures, wherein each aperture exposes a single or small cluster of nano-structures and is concentrically aligned with the single or small cluster of nano-structures, the gate electrode being operative to control the emission of electrons through the apertures from the exposed nano-structures; and 
   an anode target positioned opposite to said electron source with a vacuum gap disposed therebetween;   whereby electrons are emitted from said nano-structures by applying a voltage between said cathode and gate electrodes, and are made incident on the target by applying a high voltage between said cathode and the target to generate x-rays characteristic of the material upon which the electrons intersect with the target.   
     
     
         2 . An x-ray generating device as recited in  claim 1 , wherein one or a plurality of electron optical or magnetic lenses are inserted between said electron source and the target for conditioning the electron beam, wherein said conditioning includes focusing, deflecting and splitting the election beam. 
     
     
         3 . An x-ray generating device as recited in  claim 1 ,
 wherein said electron source and target are enclosed in a vacuum envelope, wherein said vacuum envelope includes a x-ray transparent window, whereby generated x-rays exit.   
     
     
         4 . An x-ray generating device as recited in  claim 1 ,
 wherein the cathode electrode is configured as a plurality of electrically isolated cathode electrodes, each for supplying an independent source of electrons;   whereby activation of a selected cathode electrode determines an area along said cathode electrode where the nano-structures emit electrons through gate apertures and is made incident on a corresponding area on the target.   
     
     
         5 . An x-ray generating device as recited in  claim 1 ,
 wherein the gate electrode is configured as a plurality of electrically isolated electrodes, each gate electrode being operative to control the emission of electrons through the apertures along the gate electrode;   whereby activation of a selected gate electrode determines an area along the gate electrode where the nano-structures emit electrons and is made incident on a corresponding area on the target.   
     
     
         6 . An x-ray generating device as recited in  claim 1 ,
 wherein the cathode electrode is configured as a plurality of electrically isolated cathode electrodes, each for supplying an independent source of electrons;   wherein the gate electrode is configured as a plurality of electrically isolated electrodes, each intersecting with said plurality of cathode electrodes and having one or a plurality of apertures at each intersection, each gate electrode being operative to control the emission of electrons through the apertures along the gate electrode;   whereby activation of a selected cathode and a selected gate electrode determines an intersection where the nano-structures emit electrons and is made incident on a corresponding area on the target.   
     
     
         7 . An x-ray generating device as recited in  claim 6 ,
 wherein the cathode electrode is configured as a plurality of strip-like cathode electrodes extending substantially in the same direction in such a manner as to be spaced from each other at intervals in the transverse direction;   wherein the gate electrode is configured as a plurality of strip-like gate electrodes extending in such a manner as to intersect said plurality of cathode electrodes and to be spaced from each other at intervals in the direction transverse to the gate strip;   wherein the target is positioned opposite to said electron source.   
     
     
         8 . An x-ray generating device as recited in  claim 1 , wherein the target comprises a plurality of spaced regions of different metal materials, each for generating x-rays characteristic of the material. 
     
     
         9 . An x-ray generating device as recited in  claim 9 , wherein said spaced regions of different metal materials are formed by depositing a layer of each metal on the different and spaced region of a single target block. 
     
     
         10 . An x-ray generating device as recited in  claim 1 , wherein the substrate surface of said electron source is in a predetermined shape for controlling distribution of emitted electrons. 
     
     
         11 . An x-ray generating device as recited in  claim 11 , wherein the said substrate surface is in a concaved shape. 
     
     
         12 . An x-ray generating device as recited in  claim 1 , wherein the shape of said gate aperture is substantially same as the cross contour of the exposed single or cluster of nano-structures at the gate electrode and the size of said gate aperture varies in accordance with the size of the exposed single or cluster nano-structures, such that each exposed end of the nano-structures on the perimeter of the cluster has substantially same distance from the gate electrode. 
     
     
         13 . An x-ray generating device as recited in  claim 1 ,
 wherein the surface of the emitter layer is substantially parallel to the substrate surface and said nano-structures protrude above the embedding material at substantially same length.   
     
     
         14 . An x-ray generating device as recited in  claim 1 , wherein said single or small cluster of nano-structures is randomly located. 
     
     
         15 . An x-ray generating device as recited in  claim 1 , wherein said insulator functions also as the embedding material. 
     
     
         16 . An x-ray generating device as recited in  claim 1 , wherein said plurality of single or cluster of nano-structures is a random mix of singles and various clusters of nano-structures. 
     
     
         17 . An x-ray generating device as recited in  claim 1 , wherein the nano-structure comprises a core and a shell, wherein said core-and-shell nano-structure includes nano-structures with a nonconductive core and a conductive shell, nano-structures with a conductive core and a nonconductive shell, and nano-structures with a plurality of alternating conductive and non-conductive layers. 
     
     
         18 . An x-ray generating device comprising:
 an electron source that includes:
 a cathode electrode disposed on a substrate, the cathode electrode for providing a source of electrons; 
 one or a plurality of single or small cluster of nano-structures disposed over the cathode electrode to emit electrons; 
 an insulator disposed over the cathode electrode and having one or a plurality of apertures, wherein each aperture exposes said single or small cluster of nano-structures; and 
 a gate electrode disposed over the insulator and having one or a plurality of apertures, wherein each aperture exposes and is concentrically aligned the single or small cluster of nano-structures, wherein the shape of the aperture is substantially the same as the shape of the cross contour of the exposed single or cluster of nano-structures at the gate electrode, the gate electrode being operative to control the emission of electrons through the apertures from the exposed nano-structures; and 
   an anode target positioned opposite to said electron source with a vacuum gap disposed therebetween;   whereby electrons are emitted from said nano-structures by applying a voltage between said cathode and gate electrodes, and are made incident on the target by applying a high voltage between said cathode and the target to generate x-rays characteristic of the material upon which the electrons intersect with the target.   
     
     
         19 . An x-ray generating device as recited in  claim 18 , wherein said plurality of single or cluster of nano-structures is a random mix of singles and various clusters of nano-structures. 
     
     
         20 . An x-ray generating device as recited in  claim 18 , wherein said single or small cluster of nano-structures is randomly located.