Back-gated field emission electron source

Abstract

A field emitter device consistent with certain embodiments has a substantially planar conductor forming a gate electrode. A conductive stripe forms a cathode on the insulating layer. An insulating layer covers at least a portion of the surface between the cathode and the gate. An anode is positioned above the cathode. An emitter structure, for example of carbon nanotubes is disposed on a surface of the cathodes closest to the anode. When an electric field is generated across the insulating layer, the cathode/emitter structure has a combination of work function and aspect ratio that causes electron emission from the emitter structure toward the anode at a field strength that is lower than that which causes emissions from other regions of the cathode. This abstract is not to be considered limiting, since other embodiments may deviate from the features described in this abstract.

1 . A field emitter device comprising: 
 a substantially planar conducting material forming a gate electrode;    an electric insulating layer juxtaposed to said gate electrode;    a plurality of parallel conductive stripes having length and forming cathodes, wherein the insulating layer is between said gate and said cathode;    wherein said cathodes are positioned in a substantially parallel relation with said gate electrode, the cathodes each having a cross-section taken normal to said length;    wherein a cross-sectional width, divided by a cross-sectional height of said cathodes is less than approximately 10, said cross-section being substantially uniform along the length of the cathode stripes;    at least one conductive anode, positioned above and in a parallel relation to the cathode stripes, where the electrons are collected, said anode having its width approximately the same or larger than the width of the cathode stripes; and    a strip of low effective work-function material disposed along a crest of the cathodes facing said anode.    
     
     
         2 . A field emitter device as claimed in  claim 1 , wherein the substantially planar conducting material forming the gate comprises a conductor or doped semiconductor material which has a stable oxide.  
     
     
         3 . A field emitter device as claimed in  claim 2 , wherein the electric insulating layer comprises an oxide of said gate material.  
     
     
         4 . A field emitter device as claimed in  claim 3 , wherein the substantially planar conducting material forming the gate comprises one of doped Silicon and Aluminum, and wherein the electric insulating layer correspondingly comprises one of thermally grown Silicon Oxide and anodized Aluminum oxide.  
     
     
         5 . A field emitter device as claimed in  claim 1 , wherein said cathode stripes are substantially prismatic with any number of longitudinal faces joined at edges, with a cross-section aspect ratio that is less than approximately 2, said prismatic cathode stripes presenting all longitudinal faces substantially flat.  
     
     
         6 . A field emitter device as claimed in  claim 5 , wherein at least a portion of the edges of said prismatic cathode stripes are rounded.  
     
     
         7 . A field emitter device as claimed in  claim 5 , wherein at least one of the faces of said prismatic cathode is rounded.  
     
     
         8 . A field emitter device as claimed in  claim 1 , wherein said low effective-work-function material comprises carbon nanotubes placed along a strip on regions around said crest of the conductive cathodes.  
     
     
         9 . A field emitter device as claimed in  claim 1 , wherein said strip of low effective-work-function material is not continuous.  
     
     
         10 . A field emitter device as claimed in  claim 1 , wherein said substantially planar conducting material that forms the gate electrode overlays an insulating substrate.  
     
     
         11 . A field emitter device as claimed in  claim 10 , wherein the substantially planar conducting material that forms the gate comprises a thin metallic film coating a flat glass.  
     
     
         12 . A field emitter device as claimed in  claim 1 , wherein the electric insulating layer juxtaposed to the gate contains trenches at a surface on the cathode side of the insulating layer.  
     
     
         13 . A field emitter device as claimed in  claim 12 , wherein said cathode stripes are at least partially formed within said trenches.  
     
     
         14 . A field emitter device comprising: 
 a substantially planar conducting plate forming a gate electrode;    an electric insulating layer juxtaposed to one side of said conducting plate; and    a plurality of parallel conductive stripes forming cathodes placed over said insulating layer in a way that this insulating layer avoids the flow of electrical current between the gate and the cathodes;    at least one conductive anode positioned in a parallel relation to the gate plate, said anode for collecting electrons and having its width approximately the same or larger than the width of the cathode stripes;    wherein one side of the substantially planar conducting plate forming the gate contains trenches, said trenches having a mirror type longitudinal symmetry plane which is perpendicular to the plane defined by the gate plate;    the electric insulating layer being juxtaposed to the side of the gate plate where the trenches are present, such that the insulating layer presents trenches which are substantially conformal with the trenches present in the gate surface; and    wherein the conductive cathode stripes are formed within the trenches formed in the insulating layer, said cathode stripes presenting an exposed side that faces away from the conductive gate, and    said exposed sides of the cathode stripes being at least partially covered with a low-effective-work-function layer.    
     
     
         15 . A field emitter device as in  claim 14 , wherein electrical potentials can be applied to gate, cathode and anode independently by lateral contacts.  
     
     
         16 . A field emitter device as claimed in  claim 14 , wherein the exposed sides of the conductive cathode stripes are at approximately a level of a top opening of the trench present on the gate material.  
     
     
         17 . A field emitter device as claimed in  claim 14 , wherein the exposed sides of the conductive cathode stripes are above the level of a top opening of the trench present on the gate conductive material.  
     
     
         18 . A field emitter device as claimed in  claim 14 , wherein the exposed sides of the conductive cathode stripes are below the level of a top opening of the trench present on the gate conductive material.  
     
     
         19 . A field emitter device as claimed in  claim 14 , wherein the trenches formed on the gate plate present a width that is smaller than a depth.  
     
     
         20 . A field emitter device as claimed in  claim 14 , wherein the gate comprises a metal and the insulating layer juxtaposed to the trenches comprises a dielectric material.  
     
     
         21 . A field emitter device as claimed in  claim 14 , wherein the substantially planar conducting material forming the gate with trenches comprises a conductor or a doped semiconductor material which has a stable oxide.  
     
     
         22 . A field emitter device as claimed in  claim 21 , wherein the insulating layer juxtaposed to said conducting material is formed by the oxidation of the gate conducting material, in order to form a conformal insulating and stable oxide layer.  
     
     
         23 . A field emitter device as claimed in  claim 21 , wherein the substantially planar conducting material forming the gate with trenches comprises one of Aluminum and doped Silicon, and wherein said dielectric layer correspondingly comprises one of Aluminum Oxide and Silicon Oxide.  
     
     
         24 . A field emitter device comprising: 
 a substantially planar insulating plate, constituting a self-standing substrate;    a plurality of trenches on a surface of said insulating plate, said trenches presenting a mirror type longitudinal symmetry along a plane that is perpendicular to the insulating plate;    a first conducting layer that overlays a surface of said insulating plate that contains the trenches and conforms with the surface, forming at least one gate electrode;    a dielectric layer juxtaposed to said first conducting layer and in conformation with said conducting layer, forming trenches that present mirror type longitudinal symmetry along a plane that coincides to the symmetry plane of the trenches present in the insulating plate;    a plurality of cathode stripes formed within the trenches formed on said dielectric layer, a width and a height of a cross-section of said cathodes having an aspect ratio that is less that approximately 10; and    a crest portion of said cathodes facing away from the gate electrode being at least partially overlaid with a strip of low effective-work-function material; and    at least one conductive anode positioned in a parallel relation to the insulating plate, where the electrons are collected, said anode having its width approximately equal to or larger than the width of the cathode stripes.    
     
     
         25 . A field emitter device as claimed in  claim 24 , wherein potentials can be applied to the gate, cathode and anode and can be set independently using lateral contacts.  
     
     
         26 . A field emitter device as claimed in  claim 24 , wherein said trenches in the insulating plate present its width smaller than its depth.  
     
     
         27 . A field emitter device as claimed in  claim 24 , wherein inner walls of the trenches are free of said first conducting layer.  
     
     
         28 . A field emitter device as claimed in  claim 24 , wherein said first conducting layer is fashioned as a plurality of parallel strips arranged at an angle in relation to the trenches engraved on the surface of said substrate, such that said dielectric layer is in direct contact with the substantially planar insulating substrate in places where the conducting parallel strips are not present.  
     
     
         29 . A field emitter device as claimed in  claim 24 , wherein said first conducting layer comprises a metal.  
     
     
         30 . A field emitter device as claimed in  claim 24 , wherein said insulating layer comprises a dielectric material.  
     
     
         31 . A field emitter device fabrication process, comprising: 
 providing a conducting material plate gate electrode;    providing a dielectric layer over the surface of said gate electrode;    coating said dielectric layer with photo-resist;    patterning said resist with a plurality of channels, the bottom of said channels exposing the surface of said dielectric layer;    depositing a conducting layer covering the patterned resist surface as well as the exposed surface of the dielectric layer at the bottom of said channels;    lifting-off the resist leaving the conductive stripes deposited on the dielectric layer surface forming the cathodes; and    overlaying the crest of said cathodes with a low effective-work-function material.    
     
     
         32 . A field emitter device fabrication process according to  claim 31 , wherein said conducting material comprises a material that can form a stable oxide.  
     
     
         33 . A field emitter device fabrication process according to  claim 32 , wherein the dielectric layer is provided by oxidizing a surface of said conducting material that can form a stable oxide.  
     
     
         34 . A field emitter device fabrication process according to  claim 33 , wherein said conducting material comprises a doped silicon wafer and said dielectric layer is provided by thermally oxidizing the surface of said wafer.  
     
     
         35 . A field emitter device fabrication process according to  claim 33 , wherein said conducting material comprises an Aluminum plate and said dielectric layer is provided by growing a layer of Aluminum oxide by anodizing.  
     
     
         36 . A field emitter device fabrication process according to  claim 31 , wherein said dielectric layer is provided by depositing a stable oxide.  
     
     
         37 . A field emitter device fabrication process according to  claim 31 , further comprising: 
 depositing a catalyst layer over the conducting layer prior to lift-off of the resist; and    growing a layer of carbon nanotubes in-situ over said catalyst layer using chemical vapor deposition.    
     
     
         38 . A field emitter device fabrication process according to  claim 37 , further comprising forming a conductive diffusion barrier between the catalyst and the cathode surface.  
     
     
         39 . A field emitter device fabrication process comprising: 
 providing a conducting material plate gate electrode;    producing a plurality of trenches in a surface of said plate with a plurality of trenches;    providing a dielectric layer over the surface of said plate;    providing conducting cathodes at least partly inlaid within said trenches; and    overlaying a crest of said cathodes with a low effective-work-function material.    
     
     
         40 . A field emitter device fabrication process according to  claim 39 , wherein the low effective-work-function material comprises at least one of, MoC, WC, TiC, LaB 6 , ZrC, NbC, HfC carbon nanotubes coated with dielectrics (MgO), carbon nanotubes, coated carbon nanotubes, boron nitride nanotubes, silicon nanotubes, silicon carbide nanorods, diamond nanorods, carbon nanoflakes, carbon nanosheets, porous interconnected grapheene morphologies, porous conducting nanostructures, nanostructured diamond-like carbon; carbon, metal, Au, Ag or Ni nanowires, composites having a polymer matrix with incorporated nanostructures, hybrid structures of carbon nanotubes and nanodiamond or metal particles, doped nanostructures, a coating formed by electrophoretic deposition of nanodiamond particles or a nanodiamond thin film grown by CVD over the cathode crest area, and, thin films of wide band-gap dielectrics.  
     
     
         41 . A field emitter device fabrication process according to  claim 39 , wherein said conducting material comprises a doped silicon wafer and said dielectric layer is provided by thermally oxidizing the surface of said wafer.  
     
     
         42 . A field emitter device fabrication process according to  claim 39 , wherein said conducting material comprises an Aluminum plate and said dielectric layer is provided by growing a layer of Aluminum oxide by anodizing.  
     
     
         43 . A field emitter device fabrication process, comprising: 
 providing an insulating substrate;    producing a plurality of trenches in a surface of said insulating substrate;    providing a first conducting layer overlaying said substrate and conforming with its surface, forming at least one gate electrode;    providing a dielectric layer overlaying said first conducting layer and conforming with said conducting layer forming trenches substantially concentric with the trenches engraved on the surface of said substrate;    providing a plurality of cathode stripes cathode stripes formed at least partly within said trenches, the width and height of the cross-section of said cathodes being comparable; and    overlaying the portion of said cathodes facing away from the gate electrode (crest of the cathode) with a strip of low effective-work-function material.    
     
     
         44 . A field emitter device fabrication process according to  claim 43 , wherein the low effective-work-function material comprises at least one of, MoC, WC, TiC, LaB 6 , ZrC, NbC, HfC carbon nanotubes coated with dielectrics (MgO), carbon nanotubes, coated carbon nanotubes, boron nitride nanotubes, silicon nanotubes, silicon carbide nanorods, diamond nanorods, carbon nanoflakes, carbon nanosheets, porous interconnected grapheene morphologies, porous conducting nanostructures, nanostructured diamond-like carbon; carbon, metal, Au, Ag or Ni nanowires, composites having a polymer matrix with incorporated nanostructures, hybrid structures of carbon nanotubes and nanodiamond or metal particles, doped nanostructures, a coating formed by electrophoretic deposition of nanodiamond particles or a nanodiamond thin film grown by CVD over the cathode crest area, and, thin films of wide band-gap dielectrics.  
     
     
         45 . A field emitter device fabricated according to  claim 43 , wherein said cathodes are fed from a larger conductor forming a fish-bone arrangement.  
     
     
         46 . A field emitter device, comprising: 
 a substantially planar conducting material forming a gate electrode layer having a first surface;    an electric insulating layer covering at least a portion of said first surface of said gate electrode;    a conductive stripe forming a cathode on said insulating layer, said conductive stripe having a cross-sectional maximum width W parallel with said gate and a cross-sectional maximum height H, with an aspect ratio defined by W/H;    at least one conductive anode, positioned above said cathode, which collects electrons;    an emitter structure disposed on a surface of said cathodes closest to said anode to form a cathode/emitter structure;    wherein when an electric field is generated across the insulating layer, said cathode/emitter structure has a combination of work function and aspect ratio that causes electron emission from the emitter structure toward the anode at a field strength that is lower than that which causes emissions from other regions of the cathode; and    wherein substantially all electron emissions occur between said emitter structure and said anode, and substantially no electron emissions occur from the cathode toward the gate.    
     
     
         47 . The field emitter device according to  claim 46 , wherein the aspect ratio is less than approximately 10.  
     
     
         48 . The field emitter device according to  claim 46 , wherein the aspect ratio is less than approximately 2.  
     
     
         49 . The field emitter device according to  claim 46 , wherein the cathode/emitter structure has an effective work function of less than approximately 3 eV.  
     
     
         50 . The field emitter device according to  claim 46 , wherein emitter comprises a low effective work function material.  
     
     
         51 . A field emitter device fabrication process according to  claim 46 , wherein the low effective-work-function material comprises at least one of, MoC, WC, TiC, LaB 6 , ZrC, NbC, HfC carbon nanotubes coated with dielectrics (MgO), carbon nanotubes, coated carbon nanotubes, boron nitride nanotubes, silicon nanotubes, silicon carbide nanorods, diamond nanorods, carbon nanoflakes, carbon nanosheets, porous interconnected grapheene morphologies, porous conducting nanostructures, nanostructured diamond-like carbon; carbon, metal, Au, Ag or Ni nanowires, composites having a polymer matrix with incorporated nanostructures, hybrid structures of carbon nanotubes and nanodiamond or metal particles, doped nanostructures, a coating formed by electrophoretic deposition of nanodiamond particles or a nanodiamond thin film grown by CVD over the cathode crest area, and, thin films of wide band-gap dielectrics.