Source: https://patents.google.com/patent/US8692226B2/en
Timestamp: 2018-03-19 22:42:44
Document Index: 182143915

Matched Legal Cases: ['Application No. 61', 'Application No. 61', 'Application No. 61', 'Application No. 61', 'Application No. 61', 'Application No. 61', 'Application No. 61', 'Application No. 61', '§119', 'Application No. 61', '§119', 'Application No. 61']

US8692226B2 - Materials and configurations of a field emission device - Google Patents
US8692226B2
US8692226B2 US13587762 US201213587762A US8692226B2 US 8692226 B2 US8692226 B2 US 8692226B2 US 13587762 US13587762 US 13587762 US 201213587762 A US201213587762 A US 201213587762A US 8692226 B2 US8692226 B2 US 8692226B2
US13587762
US20130168635A1 (en )
This application is a continuation of U.S. application Ser. No. 13/374,545, filed Dec. 30, 2011, now U.S. Pat. No. 8,575,842 issued Nov. 5, 2013, and a continuation of U.S. application Ser. No. 13/171,973, filed Jun. 29, 2011, now U.S. Pat. No. 8,384,121 issued Feb. 26, 2013, which claims the benefit of and priority to U.S. Provisional Patent Application No. 61/359,467, filed Jun. 29, 2010, U.S. Provisional Patent Application No. 61/363,179, filled Jul. 9, 2010, U.S. Provisional Patent Application No. 61/376,707, filled Aug. 25, 2010, U.S. Provisional Patent Application No. 61/390,128, filed Oct. 5, 2010, U.S. Provisional Patent Application No. 61/393,027, filed Oct. 14, 2010, U.S. Provisional Patent Application No. 61/433,249, filed Jan. 16, 2011, U.S. Provisional Patent Application No. 61/445,416, filed Feb., 22, 2011, and U.S. Provisional Patent Application No. 61/447,680, filed Feb. 28, 2011. The entire disclosure of each of these applications is hereby incorporated herein by reference.
For purposes of the USPTO extra-statutory requirements, the present application claims priority under 35 USC §119(e) to U.S. Patent Application No. 61/631,270, entitled FIELD EMISSION DEVICE, naming RODERICK A. HYDE, JORDIN T. KARE, NATHAN P. MYHRVOLD, TONY S. PAN, and LOWELL L. WOOD, JR., as inventors, filed 29 Dec. 2011, which is currently co-pending or is an application of which a currently co-pending application is entitled to the benefit of the filing date.
For purposes of the USPTO extra-statutory requirements, the present application constitutes a continuation-in-part of U.S. patent application Ser. No. 13/374,545, entitled FIELD EMISSION DEVICE, naming RODERICK A. HYDE, JORDIN T. KARE, NATHAN P. MYHRVOLD, TONY S. PAN, and LOWELL L. WOOD, JR., as inventors, filed 30 Dec. 2011, which is currently co-pending or is an application of which a currently co-pending application is entitled to the benefit of the filing date.
For purposes of the USPTO extra-statutory requirements, the present application claims priority under 35 USC §119(e) to U.S. Patent Application No. 61/638,986, entitled FIELD EMISSION DEVICE, naming RODERICK A. HYDE, JORDIN T. KARE, NATHAN P. MYHRVOLD, TONY S. PAN, and LOWELL L. WOOD, JR., as inventors, filed 26 Apr. 2012, which is currently co-pending or is an application of which a currently co-pending application is entitled to the benefit of the filing date.
U.S. patent application Ser. No. 13/545,504, entitled PERFORMANCE OPTIMIZATION OF A FIELD EMISSION DEVICE, naming RODERICK A. HYDE, JORDIN T. KARE, NATHAN P. MYHRVOLD, TONY S. PAN, and LOWELL L. WOOD, JR., as inventors, filed 10 Jul. 2012, which is related to the present application.
U.S. patent application Ser. No. 13/666,759, entitled ANODE WITH SUPPRESSOR GRID, naming JESSE R. CHEATHAM, III; PHILIP ANDREW ECKHOFF; WILLIAM GATES; RODERICK A. HYDE; MURIEL Y. ISHIKAWA; JORDIN T. KARE; NATHAN P. MYHRVOLD; TONY S. PAN; ROBERT C. PETROSKI; CLARENCE T. TEGREENE; DAVID B. TUCKERMAN; CHARLES WHITMER; LOWELL L. WOOD, JR.; and VICTORIA Y. H. WOOD as inventors, filed 1 Nov. 2012, which is related to the present application.
U.S. patent application Ser. No. 13/774,893, entitled VARIABLE FIELD EMISSION DEVICE, naming JESSE R. CHEATHAM, III; PHILIP ANDREW ECKHOFF; WILLIAM GATES; RODERICK A. HYDE; MURIEL Y. ISHIKAWA; JORDIN T. KARE; NATHAN P. MYHRVOLD; TONY S. PAN; ROBERT C. PETROSKI; CLARENCE T. TEGREENE; DAVID B. TUCKERMAN; CHARLES WHITMER; LOWELL L. WOOD, JR.; and VICTORIA Y. H. WOOD as inventors, filed 22 Feb. 2013, which is related to the present application.
U.S. patent application Ser. No. 13/790,613, entitled TIME-VARYING FIELD EMISSION DEVICE, naming JESSE R. CHEATHAM, III; PHILIP ANDREW ECKHOFF; WILLIAM GATES; RODERICK A. HYDE; MURIEL Y. ISHIKAWA; JORDIN T. KARE; NATHAN P. MYHRVOLD; TONY S. PAN; ROBERT C. PETROSKI; CLARENCE T. TEGREENE; DAVID B. TUCKERMAN; CHARLES WHITMER; LOWELL L. WOOD, JR.; and VICTORIA Y. H. WOOD as inventors, filed 8 Mar. 2013, which is related to the present application.
In one embodiment, an apparatus comprises: a cathode; an anode, wherein the anode and cathode are receptive to a first power source to produce an anode electric potential higher than a cathode electric potential; a gate positioned between the anode and the cathode, the gate being receptive to a second power source to produce a gate electric potential selected to induce electron emission from the cathode for a first set of electrons having energies above a first threshold energy; and a suppressor positioned between the gate and the anode, the suppressor being receptive to a third power source to produce a suppressor electric potential selected to induce electron emission from the anode.
In another embodiment, an apparatus comprises: a cathode having a spatially-varying slope; an anode having a spatially varying slope that is complementary to the cathode spatially-varying slope, wherein the anode and cathode are receptive to a first power source to produce an anode electric potential higher than a cathode electric potential; a gate positioned between the anode and the cathode, the gate being receptive to a second power source to produce a gate electric potential selected to induce electron emission from the cathode for a first set of electrons; and a suppressor positioned between the gate and the anode, the suppressor being receptive to a third power source to produce a suppressor electric potential selected to induce electron emission from the anode.
In another embodiment, an apparatus comprises: a cathode; an anode, wherein the anode and cathode are receptive to a first power source to produce an anode electric potential higher than a cathode electric potential, and wherein the anode includes a metal layer and a layer including a negative electron affinity material in contact with the metal layer; and a gate positioned between the anode and the cathode, the gate being receptive to a second power source to produce a gate electric potential selected to induce electron emission from the cathode for a first set of electrons having energies above a first threshold energy.
In another embodiment, an apparatus comprises: a cathode; an anode, wherein the anode and cathode are receptive to a first power source to produce an anode electric potential higher than a cathode electric potential, and wherein the anode includes a negative electron affinity material; and a gate positioned between the anode and the cathode, the gate being receptive to a second power source to produce a gate electric potential selected to induce electron emission from the cathode for a first set of electrons having energies above a first threshold energy.
In another embodiment, an apparatus comprises: a substrate; and a pattern on the substrate. The pattern forms: a cathode; an anode, wherein the anode and cathode are receptive to a first power source to produce an anode electric potential higher than a cathode electric potential; a gate receptive to a second power source to produce a gate electric potential selected to induce electron emission from the cathode for a first set of electrons having energies above a first threshold energy; and a suppressor receptive to a third power source to produce a suppressor electric potential selected to induce electron emission from the anode.
In another embodiment, an apparatus comprises: a first substrate having a first pattern; a second substrate having a second pattern. The first and second substrates are arranged such that the first and second patterns form: a cathode; an anode, wherein the anode and cathode are receptive to a first power source to produce an anode electric potential higher than a cathode electric potential; a gate receptive to a second power source to produce a gate electric potential selected to induce electron emission from the cathode for a first set of electrons having energies above a first threshold energy; and a suppressor receptive to a third power source to produce a suppressor electric potential selected to induce electron emission from the anode.
In another embodiment, an apparatus comprises: a cathode; an anode, wherein the anode and cathode are receptive to a first power source to produce an anode electric potential higher than a cathode electric potential; and a suppressor positioned proximate to the anode, the suppressor being receptive to a third power source to produce a suppressor electric potential selected to induce electron emission from the anode and to induce electron emission from the cathode, and configured to produce a net flow of electrons from the cathode to the anode.
In another embodiment, a method comprises: applying a first electric potential to selectively release a first set of electrons from a bound state in a first region; applying a second electric potential to selectively release a second set of electrons from emission from a bound state in a second region different from the first region, the second region having an anode electric potential that is greater than a cathode electric potential of the first region; and passing a portion of the first set of electrons through a gas-filled region and binding the passed portion of the first set of electrons in the second region.
In another embodiment, an apparatus comprises: a cathode; an anode, wherein the anode and cathode are receptive to a first power source to produce an anode electric potential higher than a cathode electric potential; a gate, the gate being receptive to a second power source to produce a gate electric potential selected to induce electron emission from the cathode for a first set of electrons having energies above a first threshold energy; and a suppressor, the suppressor being receptive to a third power source to produce a suppressor electric potential selected to induce electron emission from the anode.
FIG. 9 is a schematic of a portion of a field emission device including a thin film.
FIG. 10 is a schematic of a field emission device having a cathode and anode that form a substantially interlocking structure.
FIG. 11 is a schematic of a field emission device having a substantially tubular cathode and anode.
FIG. 12 is a schematic of a field emission device, wherein the anode includes a thin coating.
FIG. 13 is a schematic of a field emission device having a gate and suppressor that are fabricated on a first substrate, and having a cathode and anode that are fabricated on a second substrate.
FIG. 14 is a schematic of a field emission device having a cathode, anode, and a gate/suppressor.
FIG. 15 is a schematic of the potential corresponding to the schematic of FIG. 14.
FIG. 16 is a schematic of a back-gated field emission device.
FIG. 17 is a schematic of electromagnetic energy incident on a field emission device.
F ⁡ ( E , T ) = 1 1 + ⅇ ( E - μ ) / k ⁢ ⁢ T
In the embodiment of FIG. 1 corresponding to a heat engine, the cathode 102 is hotter than the anode 108 (Ta>Ta) and the anode 108 is biased above the cathode 102 as shown in FIG. 2. In this embodiment, μa=μc+V0, where V0 is the anode electric potential 202. Then the Carnot-efficiency energy is equal to:
D ⁡ ( W ) = ⅇ - ∫ x 1 x 2 ⁢ 8 ⁢ m ℏ 2 ⁢  V ⁡ ( x ) - W  ⁢ ⅆ x
Here, V(x) is the net electric potential (216), x1 and x2 are the roots of V(x)−W=0, m is the mass of an electron, and
is Planck's constant h divided by 2π(
=h/2π).
D SB ⁡ ( W ) = ⅇ - ( b ⁡ ( φ - W ) 3 / 2 F ) ⁢ v ⁡ ( f ) Where ⁢ : b = 4 ⁢ 2 ⁢ m 3 ⁢ ℏ ⁢ ⁢ e ≈ 6.830890 ⁢ ⁢ in ⁢ ⁢ eV - 3 / 2 ⁡ ( V ⁢ ⁢ nm - 1 ) v ⁡ ( f ) ≈ 1 - f + 1 6 ⁢ f ⁢ ⁢ ln ⁢ ⁢ f f = ⅇ 3 4 ⁢ πɛ 0 ⁢ F ( φ - W ) 2 ≈ 1.439964 ⁢ F ( φ - W ) 2 ⁢ ⁢ in ⁢ ⁢ eV 2 ⁡ ( nm ⁢ / ⁢ V )
W > φ - ⅇ 3 ⁢ F 4 ⁢ πɛ 0
N ⁡ ( W ) ⁢ dW = 4 ⁢ π ⁢ ⁢ mkT h 3 ⁢ log ⁡ [ 1 + ⅇ - ( W - μ ) kT ] ⁢ dW
Hence, the summed current depends on the transmission probability D(W), which itself is dependent on WB. Therefore, we can solve for these quantities self-consistently using iterative numerical methods. For example, we can find p by solving for ρ in this equation:
ρ = ∫ V grid + e ⁢ ⁢ ρ 2 ⁢ ɛ 0 ⁢ d 2 4 ∞ ⁢ J sum ⁡ ( W ) ⁢ ⅆ W 2 m ⁢ ( W - V grid - e ⁢ ⁢ ρ 2 ⁢ ɛ 0 ⁢ d 2 4 )
Q . c = ⁢ ∫ 0 ∞ ⁢ [ ( W + kT a - μ c ) ⁢ N a ⁡ ( W ) - ( W + kT c - μ c ) ⁢ N c ⁡ ( W ) ] ⁢ D ⁡ ( W ) ⁢ ⁢ ⅆ W Q . a = ⁢ ∫ 0 ∞ ⁢ [ ( W + kT c - μ a ) ⁢ N c ⁡ ( W ) - ( W + kT a - μ a ) ⁢ N a ⁡ ( W ) ] ⁢ D ⁡ ( W ) ⁢ ⁢ ⅆ W
The thermodynamic efficiency η is the ratio between work gained to heat used, or, equivalently, the ratio of the useful power gained (JnetV0) to the total heat flux density expended (|{dot over (Q)}c+{dot over (Q)}other):
Q . other ≈ W evanescent ≈ 4 × 10 - 12 ⁢ ( 1 d 2 ) ⁢ ⁢ in ⁢ ⁢ Watt ⁢ / ⁢ nm 2 ⁢ / ⁢ K , ⁢ for d < 1000 ⁢ ⁢ nm .
FIG. 8 shows the thermodynamic efficiency plotted versus power for varying gate and suppressor electric potentials 204, 210. FIG. 8 corresponds to a cathode (102) and an anode (108) having no field emission enhancement features (103), such that β=1. For FIG. 8, the cathode temperature Tc=1000 K, the anode temperature Ta=300 K, the work functions of the cathode and anode φ=2.1 eV, the cathode-anode separation (122) is 50 nm, the cathode-gate separation (116) and the suppressor-anode separation 120 are both 2 nm, and the anode electric potential 202 is 4k(Tc−Ta).
In some embodiments, the gate (104) and/or the suppressor (106) may include a thin film (904), as shown in FIG. 9 (FIG. 9 shows an embodiment with a cathode (102), dielectric (902), and thin film (904) that forms the gate (104), however a similar embodiment includes an anode (108), dielectric (902), and thin film (904) that forms the suppressor (106)), where the thin film (904) may be metal and/or graphene, and where graphene may be a single layer or a bilayer film. The graphene may, in some embodiments, include a graphene allotrope, doped graphene, and/or functionalized graphene. The thin film (904) may be fabricated by depositing the dielectric (902) on the cathode (102) and/or anode (108), then depositing the thin film (904) of metal or graphene that forms the gate (104) and/or suppressor (106). In some embodiments, the dielectric (902) can be at least partially etched away, or in other embodiments it may be left in place. Thin film grids as described above that may be used for the gate (104) and/or suppressor (106) have been used for cathodes, such as in metal-insulator-metal tunneling cathodes, and also in metal-oxide-semiconductor cathodes. These emitters include a metal or semiconductor base electrode, an insulator, and a thin top electrode serving as the gate/suppressor. Although FIG. 9 shows a single thin film (904) that forms the gate (104), in some embodiments two or more thin films such as the film (904) may form the gate.
In an embodiment including a dielectric (902) proximate to the cathode (102) and/or anode (108), the gate (104) and/or suppressor (106) may be a thin film as described with respect to FIG. 9, or the gate (104) and/or the suppressor (106) may have a different configuration. The dielectric (902) may be used to support the gate (104) and/or suppressor (106), and/or it may serve to maintain the separation between the cathode (102) and gate (104) and/or the separation between the anode (108) and suppressor (106). In some embodiments, the dielectric (902) may be silicon oxide (SiO2), boron nitride, diamond, and/or a self-healing dielectric, e.g., glassy rather than crystalline materials.
In different embodiments, at least one of the cathode (102) and anode (108) includes at least one of: tungsten, thoriated tungsten, an oxide-coated refractory metal, a boride, lanthanum hexaboride, molybdenum, tantalum, and hafnium.
In particular, in an embodiment where the cathode (102) is heated, the cathode (102) may include thoriated tungsten, which has a work function of approximately 2.5 eV. When heated, the lower-work-function thorium in the material migrates to the surface. In another embodiment of a heated cathode (102), the cathode (102) includes an oxide-coated refractory metal, which has a work function of approximately 2 eV. In yet another embodiment of a heated cathode (102), the cathode (102) includes a boride having a work function of approximately 2.5 eV. In particular, borides such as lanthanum hexaboride are amenable to physical vapor deposition techniques, and the cathode may be relatively easily coated with these materials.
In an embodiment of a heat engine where the cathode (102) is heated, but at a relatively low temperature (e.g., scavenging waste heat), a material with a relatively low work function, such as diamond-like carbon (DLC), may be incorporated as a coating for the cathode (102). In some embodiments the DLC may be doped with nitrogen. DLC is amenable to low temperature deposition techniques, and may be directly coated on Spindt tips, for example.
In some embodiments at least one of the cathode (102) and anode (108) includes diamond, and, in particular, may be coated with diamond. A diamond coating can be deposited from a methane atmosphere. Pure diamond has a relatively high work function, however diamond can be doped (with, for example, hydrogen) to have a low work function, and may be especially useful at relatively low operating temperatures. Hydrogen-terminated diamond surfaces have been found to exhibit negative electron affinity (NEA). To further increase field emission with diamond coatings, the diamond may be selected to have small grain sizes, or nano-crystalline diamond may be used. To take full advantage of the NEA of diamond at relatively low applied fields, the diamond may be n-type doped to place its Fermi level close to the conduction band. Further, since pure diamond can withstand electric field stresses up to about 1-2 V/nm before dielectric breakdown commences, it may be used as the dielectric to support the gate (104) and/or suppressor (106) relative to the anode (102) and/or the cathode (108).
In some embodiments, the cathode (102) and/or the anode (108) may include one or more carbon nanotubes that serve as field emission enhancement feature(s) (103). There may be a single nanotube serving as a single field emission enhancement feature (103) or multiple nanotubes serving as multiple field emission enhancement features (103) depending on the particular embodiment. For embodiments including multiple nanotubes (sometimes called nanotube forests), individual nanotubes may be selectively ablated to control emission. In some embodiments one or more carbon nanobuds may serve as one or more field emission enhancement feature(s) (103).
In some embodiments the cathode (102) and/or the anode may include a semiconductor, which may include silicon. In some embodiments the semiconductor may be doped. Specifically, doping the semiconductor may change its density of states, and so a semiconductor may be doped according to a selected density of states. A semiconductor cathode (102) and/or anode (108) may further be coated in order to vary the electron affinity and/or the work function, and/or to optimize the performance and/or the stability of the heat engine. The semiconductor may further be doped to vary the electron affinity, in some cases producing negative electron affinity (NEA) material.
In some embodiments the cathode (102) and anode (108) may form a substantially interlocking structure (“interlocking combs”), as shown in FIG. 10. In FIG. 10 the gate (104) and the suppressor (106) are shown as being substantially continuous, however in some embodiments they may be discontinuous. Further, the spacings in the gate (104) and suppressor (106) shown in FIG. 10 are largely symbolic, and may be oriented differently according to a particular embodiment. Notably, the comb structure of the cathode (102) and anode (108) are relatively large in comparison with the size of a field emission enhancement structure (103), and an embodiment that employs such a comb structure may also include one or more field emission enhancement structures (103), although these are not shown in FIG. 10. The structure of FIG. 10 shows a cathode (102) having a spatially-varying slope, and an anode (108) also having a spatially varying slope that is complementary to the spatially-varying slope of the cathode (102). The spatially-varying slopes of the cathode (102) and anode (108) shown in FIG. 10 are substantially periodic, however in other embodiments they may be a-periodic and/or quasi-periodic. In some embodiments the slope of the cathode (102) and/or the slope of the anode (108) may be more smoothly varying that what is shown in FIG. 10. As shown in FIG. 10, the cathode-anode separation (122) varies slightly, however this separation is minimized. In some embodiments the cathode-anode separation (122) is substantially constant. In other embodiments, the cathode-anode separation (122) may have greater spatial variations, or in the case where the cathode (102) and anode (108) are substantially sinusoidal, the cathode-anode separation (122) may be configured with very little spatial variation.
In one embodiment, shown in FIG. 11, the cathode (102) and anode (108) are substantially tubular, wherein at least a portion of the anode (108) is substantially circumscribed by at least a portion of the cathode (102). In this embodiment electrons flow radially from the cathode (102) to the anode (108), and vice-versa. Although the cathode (102) and anode (108) are shown as being substantially cylindrical in FIG. 11, in some embodiments there may be deviations from the cylindrical structure (i.e., they may be dented, their cross-sections may be an n-gon such as a hexagon or octagon, or they may form a different type of substantially co-axial structure). In some embodiments, cathode (102) may form the inner structure and the anode (108) may form the outer structure. Further, in some embodiments a coolant or heating structure may be placed inside the inner structure (for example, where the anode (108) forms the inner structure of a heat engine, a coolant may be configured to flow through or proximate to the anode (108), or where the cathode (102) forms the inner structure of a heat engine, a heating mechanism such as a heated fluid may be configured to flow through or proximate the cathode (102)). In some embodiments the gap between the cylinders as shown in FIG. 11 may change as a function of the temperature of the cylinders. Although the gate (104) and suppressor (106) are not shown in FIG. 11 for clarity, in most embodiments of a heat engine at least one grid would be included.
In an embodiment shown in FIG. 12 a thin dielectric coating (1202) is included on the anode (108). The thin dielectric coating may, in some embodiments, include a negative electron affinity (NEA) material such as hydrogen terminated diamond, which may be deposited on a metal that forms the anode (108). Such an embodiment may lower the effective work function of the metal that forms the anode (108). This embodiment may or may not include the suppressor (106).
In one embodiment the NEA material forms the anode (108), and in this embodiment the suppressor (106) may not be included and the device may still function as a heat engine. In this embodiment the NEA material may be chosen or doped such that its electron quasi-Fermi level is close to the conduction band.
In some embodiments, one or more of the gate (104) and suppressor (106) (and/or other grids that may be incorporated in the design) may be at least partially coated with one or more insulating materials.
In one embodiment all or part of the apparatus may be fabricated, e.g. via lithography, on a substrate. For example, in one embodiment the cathode (102), gate (104), suppressor (106), and the anode (108) are formed via lithography on a substrate such that they are all substantially one-dimensional and coplanar.
In another embodiment, a cross-section of which is shown in FIG. 13, the gate (104) and the suppressor (106) are fabricated on a first substrate (1302) and the cathode (102) and anode (108) are fabricated on a second substrate (1304), wherein the first and second substrates (1302, 1304) are then positioned such that together the elements (1302, 1304, 1306, 1308) form the field emission device. In this embodiment the gate (104) and the suppressor (106) are effectively insulated from the cathode (102) and the anode (108) by the second substrate (1304). There are many other embodiments that are similar to this that may be implemented. For example, different elements such as (1302, 1304, 1306, 1308) may each be fabricated on their own substrate. Further, additional layers of insulators or other materials may be incorporated according to the particular embodiment. Further, more or fewer elements such as (1302, 1304, 1306, 1308) may be incorporated in the designs. There are many permutations that may be designed that incorporate the idea of fabricating elements on a substrate and combining the substrates to form a field emission device.
In some embodiments the gate (104) and the suppressor (106) may be created with a single grid, as shown in FIG. 14. The resulting potential (1502) as a function of distance from the cathode in the x-direction 126 is shown in FIG. 15 for the embodiment shown in FIG. 14. This embodiment is similar to that of FIG. 1, but having a single grid (the gate/suppressor 1402) that replaces the gate (104) and the suppressor (106). In this embodiment, the gate/suppressor (1402) is placed close enough to the anode (108) to be able to induce electron emission from the anode (108). Further, it can also be sufficiently close to the cathode (102) to induce electron emission from the cathode (102), and has a gate/suppressor electric potential (1504) that is selected to produce a net flow of electrons from the cathode (102) to the anode (108). There are a number of ways of constructing the apparatus of FIG. 14. In one embodiment, a gated field-emitter array such as a Spindt array is fabricated to produce the cathode (102) and the gate/suppressor (1402), and an anode (108) is arranged proximate to the gate/suppressor (1402). In another embodiment, the gate/suppressor (1402) is supported on and proximate to the anode (108), and there is no additional grid structure supported on the cathode (102), although the cathode (102) may still have field-enhancement structures.
In some embodiments the field emission device is back-gated, as shown in FIG. 16. In FIG. 16, the gate (104) and the suppressor (106) are not positioned between the cathode (102) and anode (108), rather, the cathode (102) and anode (108) are positioned between the gate (104) and suppressor (106). Although the configuration of FIG. 16 is different in this way from the configuration of FIG. 1, they both may be configured as heat engines, such that electrons are emitted from both the cathode (102) and anode (108) and produce a net flow of electrons from the cathode (102) to the anode (108). The embodiment of FIG. 16 may include a dielectric layer between the gate (104) and cathode (102), and or between the anode (108) and suppressor (106). In such an embodiment, the dielectric (an example of a dielectric included between elements is shown in FIG. 9) may be continuous or discontinuous. Further, the apparatus as shown in FIG. 16 may be configured to reduce or remove accumulations of charge that may occur, for example, as a result of a dielectric layer. As described previously with respect to other embodiments described herein, there may be more or fewer elements than shown in FIG. 16. Further, the order of the elements may be different than what is shown in FIG. 16. For example, FIG. 16 shows the order being gate (104), cathode (102), anode (108), suppressor (106). However, in other embodiments the order may be gate (104), cathode (102), suppressor (106), anode (108). Or, the elements may be in a different order.
In some embodiments, emission from the cathode (102) may be enhanced electromagnetically, as shown in FIG. 17. FIG. 17 is shown with the configuration of FIG. 1 as an example, however any of the embodiments described herein may include enhanced cathode emission via electromagnetic energy. FIG. 17 shows electromagnetic energy (1702) incident on the cathode (102). This electromagnetic energy (1702) may be used to increase the number of electrons emitted, the rate of electrons emitted, and/or the energy of the emitted electrons from the cathode (102), which may therefore increase the power density of the device. In some embodiments the properties of the cathode (102) such as the cathode thickness, the cathode materials such as dopants, may be selected such that the photo-excited electrons tend to be emitted from the cathode (102) before they thermalize, or after they thermalize in the conduction band. FIG. 17 shows the electromagnetic energy (1702) hitting the cathode (102) at a single location, however in different embodiments the electromagnetic energy (1702) may impinge on a greater area of the cathode (102). The source of the electromagnetic energy (1702) includes, but is not limited to, solar and/or ambient electromagnetic energy, radiation from a local heat source, one or more lasers, and/or a different source of electromagnetic energy. There are many sources of electromagnetic energy that may be used in an embodiment such as that shown in FIG. 17 and one skilled in the art may select the source according to the particular embodiment. The properties of the electromagnetic energy (1702) such as the frequency, polarization, propagation direction, intensity, and other properties may be selected according to a particular embodiment, and in some embodiments may be selected to enhance the performance of the device. Further, optical elements such as lenses, photonic crystals, mirrors, or other elements may be incorporated in an embodiment such as that shown in FIG. 17, for example, to adjust the properties of the electromagnetic energy. In some embodiments the emission from the cathode (102) may be enhanced sufficiently such that the position and/or electric potentials applied to the gate (104) and/or suppressor (106) may be adjusted according.
an anode, wherein the anode and cathode are receptive to a first power source to produce an anode electric potential higher than a cathode electric potential;
a gate positioned between the anode and the cathode, the gate being receptive to a second power source to produce a gate electric potential selected to induce electron emission from the cathode for a first set of electrons having energies above a first threshold energy; and
a suppressor positioned between the gate and the anode, the suppressor being receptive to a third power source to produce a suppressor electric potential selected to induce electron emission from the anode.
2. The apparatus of claim 1 wherein at least one of the gate and the suppressor includes a thin film, the thin film including at least one of: metal and graphene.
3. The apparatus of claim 1 wherein at least one of the cathode and anode includes at least one of: tungsten, thoriated tungsten, an oxide-coated metal, a boride, molybdenum, tantalum, and hafnium.
4. The apparatus of claim 1 wherein at least one of the cathode and the anode includes diamond-like carbon.
5. The apparatus of claim 4 wherein the diamond-like carbon at least partially forms a coating on at least one of the cathode and the anode.
6. The apparatus of claim 4 wherein the diamond-like carbon includes nitrogen.
7. The apparatus of claim 1 wherein at least one of the cathode and anode includes a field emission enhancement feature, and wherein the field emission enhancement feature includes molybdenum.
8. The apparatus of claim 1 wherein at least one of the cathode and anode includes a field emission enhancement feature, and wherein the field emission enhancement feature is at least partially coated with diamond-like carbon.
9. The apparatus of claim 1 wherein at least one of the cathode and anode includes diamond.
10. The apparatus of claim 9 wherein the diamond is doped with hydrogen.
11. The apparatus of claim 9 wherein the diamond is granular, and wherein a grain of the granular diamond at least partially forms a field emission enhancement structure on at least one of the cathode and anode.
12. The apparatus of claim 9 wherein the diamond includes nanocrystalline diamond.
13. The apparatus of claim 9 wherein the diamond includes n-type doped diamond.
14. The apparatus of claim 1 wherein at least one of the cathode and anode includes an array of carbon nanotubes.
15. The apparatus of claim 1 wherein at least one of the cathode and anode includes a carbon nanobud.
16. The apparatus of claim 1 wherein at least one of the cathode and anode includes a semiconductor.
17. The apparatus of claim 16 wherein the semiconductor includes silicon.
18. The apparatus of claim 16 wherein the semiconductor includes a dopant.
19. The apparatus of claim 18 wherein the dopant is selected to produce a negative electron affinity material.
20. The apparatus of claim 16 wherein the semiconductor is coated.
21. The apparatus of claim 1 wherein the cathode includes a doped semiconductor, and wherein a density of states of the cathode is higher than a density of states of the anode for a selected energy.
22. The apparatus of claim 1 wherein the anode includes a doped semiconductor, and wherein a density of states of the anode is lower than a density of states of the cathode for a selected energy.
23. The apparatus of claim 1 wherein at least one of the cathode and anode includes a field emission enhancement feature, and wherein the field emission enhancement feature includes silicon.
a material positioned between the cathode and gate, the material being at least partially supportive of the gate.
25. The apparatus of claim 24 wherein the material includes at least one of diamond, silicon oxide, silicon nitride, hafnium oxide, titanium oxide, tantalum oxide, zirconium oxide, aluminum oxide, and boron nitride.
26. The apparatus of claim 24 wherein the gate includes at least one thin film deposited on the material.
a material positioned between the anode and suppressor, the material being at least partially supportive of the suppressor.
28. The apparatus of claim 27 wherein the material includes at least one of diamond, silicon oxide, silicon nitride, hafnium oxide, titanium oxide, tantalum oxide, zirconium oxide, aluminum oxide, and boron nitride.
29. The apparatus of claim 27 wherein the suppressor includes at least one thin film deposited on the material.
30. The apparatus of claim 1 wherein the cathode and anode are substantially tubular, and wherein at least a portion of the anode is substantially circumscribed by at least a portion of the cathode.
31. The apparatus of claim 30 further comprising a structure configured to support a flow of a coolant proximate to the anode.
32. The apparatus of claim 31 wherein the structure is at least partially defined by the anode.
33. The apparatus of claim 1 wherein the cathode and anode are substantially tubular, and wherein at least a portion of the cathode is substantially circumscribed by at least a portion of the anode.
34. The apparatus of claim 33 further comprising a structure configured to support a flow of a heated material proximate to the cathode.
35. The apparatus of claim 34 wherein the structure is at least partially defined by the cathode.
36. The apparatus of claim 1 wherein at least one of the gate and suppressor is at least partially coated with an insulator.
37. The apparatus of claim 1 wherein at least two of the cathode, anode, gate, and suppressor are substantially one-dimensional, coplanar, and supported by a substrate.
38. The apparatus of claim 1 wherein the cathode and anode include patterned material on a substrate.
39. The apparatus of claim 38 wherein the material includes metal.
40. The apparatus of claim 38 wherein the substrate is substantially two-dimensional having first and second sides, and wherein the patterned material is on the first side, and wherein at least one of the gate and suppressor is arranged proximate to the second side.
41. The apparatus of claim 1 wherein the cathode has a spatially-varying slope and wherein the anode has a complementary spatially-varying slope.
42. The apparatus of claim 41 wherein the spatially-varying slopes of the cathode and anode form interlocking combs.
43. The apparatus of claim 1 further comprising a source of electromagnetic energy oriented to provide electromagnetic energy to the cathode.
44. The apparatus of claim 43 wherein the source of electromagnetic energy is configured to produce electromagnetic energy having a frequency range that is selected according to a material composition of the cathode.
45. The apparatus of claim 1 wherein the gate is electrically connected to the suppressor.
an anode and a cathode, wherein the anode and cathode are receptive to a first power source to produce an anode electric potential higher than a cathode electric potential, and wherein the anode includes a metal layer and a layer including a negative electron affinity material in contact with the metal layer;
a cathode having a spatially-varying slope;
an anode having a spatially-varying slope that is complementary to the cathode spatially-varying slope, wherein the anode and cathode are receptive to a first power source to produce an anode electric potential higher than a cathode electric potential;
a gate positioned between the anode and the cathode, the gate being receptive to a second power source to produce a gate electric potential selected to induce electron emission from the cathode for a first set of electrons; and
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