Field emission cathode device and method of forming a field emission cathode device

Abstract

A field emission cathode device and method for forming a field emission cathode device involve a cathode element having a field emission surface, and a gate electrode element disposed in spaced-apart relation to the field emission surface of the cathode element so as to define a gap therebetween, with the gate electrode element having a plurality of parallel grill members or a mesh structure laterally-extending between opposing anchored ends. A film element laterally co-extends and is engaged with the gate electrode element, with the film element being arranged to allowed electrons emitted from the field emission surface of the cathode element to pass therethrough, and to cooperate with the gate electrode element and the cathode element to form a substantially uniform electric field within the gap and about the field emission surface.

Claims

1. A field emission cathode device, comprising: a cathode element having a field emission surface; a gate electrode element disposed in spaced-apart relation to the field emission surface of the cathode element so as to define a gap therebetween, the gate electrode element having a plurality of parallel grill members or a mesh structure laterally-extending between opposing anchored ends, the grill members or the mesh structure defining one or more open spaces; and a film element laterally co-extending and engaged with the gate electrode element, the film element defining one or more openings extending therethrough and corresponding to the one or more open spaces of the gate electrode element, the one or more openings in the film element each having an area of less than an area of the corresponding open space defined by the gate electrode element, the film element engaged with the gate electrode element including the film element comprised of a conductive material and the film element being arranged to directly engage the gate electrode element, the film element thereby being arranged to allow electrons emitted from the field emission surface of the cathode element to pass therethrough, and to cooperate with the gate electrode element and the cathode element to form a substantially uniform electric field within the gap and about the field emission surface.

2. The device of claim 1, comprising a gate voltage source electrically connected to the gate electrode element, with the cathode element electrically connected to ground, and arranged to interact therebetween to generate the electric field within the gap for inducing the field emission surface to emit the electrons therefrom toward the gate electrode element.

3. The device of claim 1, wherein the area of the open spaces of the plurality of parallel grill members or the mesh structure of the gate electrode element is at least about 75% of the gate electrode element.

4. The device of claim 1, wherein the film element is comprised of a metal, conductive silicon nitride, or carbon.

5. The device of claim 4, wherein the metal comprises beryllium, aluminum, gold, or combinations thereof.

6. The device of claim 1, wherein the film element is a thin film having a thickness of less than about 50 nm.

7. The device of claim 1, wherein the gate electrode element is comprised of a conductive material having a high melting temperature.

8. The device of claim 1, wherein the gate electrode element is comprised of tungsten, molybdenum, stainless steel, doped silicon, or combinations thereof.

9. The device of claim 1, wherein the conductive material of the film element has a high melting temperature.

10. The device of claim 1, wherein the conductive material of the film element has a low melting temperature, and wherein the film element and the gate electrode element are arranged to include an insulator element disposed therebetween to thermally insulate the film element from the gate electrode element.

11. The device of claim 10, wherein the insulator element is arranged to electrically insulate the film element from the gate electrode element.

12. The device of claim 11, comprising a film voltage source electrically connected to the film element, with the cathode element electrically connected to ground, and arranged to interact with the gate electrode element and the cathode element to generate the electric field within the gap.

13. A method of forming a field emission cathode device, comprising: disposing a gate electrode element in spaced-apart relation to a field emission surface of a cathode element so as to define a gap therebetween, the gate electrode element having a plurality of parallel grill members or a mesh structure laterally-extending between opposing anchored ends, the grill members or the mesh structure defining one or more open spaces; and engaging a film element with the gate electrode element, the film element laterally co-extending with the gate electrode element and defining one or more openings extending therethrough, such that the one or more openings correspond to the one or more open spaces of the gate electrode element, the one or more openings in the film element each having an area of less than an area of the corresponding open space defined by the gate electrode element, the film element engaged with the gate electrode element including the film element comprised of a conductive material and the film element being arranged to directly engage the gate electrode element, the film element thereby being arranged to allow electrons emitted from the field emission surface of the cathode element to pass therethrough, and to cooperate with the gate electrode element and the cathode element to form a substantially uniform electric field within the gap and about the field emission surface.

14. The method of claim 13, comprising electrically connecting a gate voltage source to the gate electrode element, with the cathode element electrically connected to ground, such that the gate voltage source is arranged to interact between the gate electrode element and the cathode element to generate the electric field within the gap for inducing the field emission surface to emit the electrons therefrom toward the gate electrode element.

15. The method of claim 13, wherein disposing the gate electrode element in spaced-apart relation to the field emission surface comprises disposing the gate electrode element, arranged such that the area of the open spaces of the plurality of parallel grill members or the mesh structure of the gate electrode element is at least about 75% of the gate electrode element, in spaced-apart relation to the field emission surface.

16. The method of claim 13, wherein engaging the film element with the gate electrode element comprises engaging the film element, comprised of a metal, conductive silicon nitride, or carbon, with the gate electrode element.

17. The method of claim 16, wherein engaging the film element with the gate electrode element comprises engaging the metal film element, comprised of beryllium, aluminum, gold, or combinations thereof, with the gate electrode element.

18. The method of claim 13, wherein engaging the film element with the gate electrode element comprises engaging the film element, comprising a thin film having a thickness of less than about 50 nm, with the gate electrode element.

19. The method of claim 13, wherein disposing the gate electrode element in spaced-apart relation to the field emission surface comprises disposing the gate electrode element, comprised of a conductive material having a high melting temperature, in spaced-apart relation to the field emission surface.

20. The method of claim 13, wherein disposing the gate electrode element in spaced-apart relation to the field emission surface comprises disposing the gate electrode element, comprised of tungsten, molybdenum, stainless steel, doped silicon, or combinations thereof, in spaced-apart relation to the field emission surface.

21. The method of claim 13, wherein engaging the film element with the gate electrode element comprises engaging the film element, comprised of the conductive material having a high melting temperature, with the gate electrode element.

22. The method of claim 13, wherein engaging the film element with the gate electrode element comprises engaging the film element, comprised of the conductive material having a low melting temperature, with the gate electrode element.

23. The method of claim 22, comprising disposing an insulator element between the film element and the gate electrode element to thermally insulate the film element from the gate electrode element.

24. The method of claim 23, wherein disposing the insulator element between the film element and the gate electrode element comprises disposing the insulator element, arranged to electrically insulate the film element from the gate electrode element, between the film element and the gate electrode element.

25. The method of claim 24, comprising electrically connecting a film voltage source to the film element, with the cathode element electrically connected to ground, such that the film voltage source is arranged to interact with the gate electrode element and the cathode element to generate the electric field within the gap.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

(1) Having thus described the disclosure in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

(2) FIG. 1 schematically illustrates a prior art example of a field emission cathode device;

(3) FIG. 2A schematically illustrates a prior art example of a gate electrode for a field emission cathode device, with the gate electrode having multiple linear bars in a grill-like structure;

(4) FIG. 2B schematically illustrates a prior art example of a gate electrode for a field emission cathode device, with the gate electrode having a mesh-like structure;

(5) FIG. 3 schematically illustrates a prior art example of a field emission cathode device, with a gate electrode having a relatively high open area, resulting in a nonuniform electric field within the gap about the cathode surface;

(6) FIG. 4 schematically illustrates a prior art example of a field emission cathode device, with a gate electrode having a relatively low open area, resulting in a relatively uniform electric field within the gap about the cathode surface, but relatively low electron transmission rate;

(7) FIGS. 5A and 5B schematically illustrates a film element engaged with a gate electrode having a relatively high open area, according to one aspect of a field emission cathode device of the present disclosure, resulting in a relatively uniform electric field within the gap about the cathode surface with a relatively high electron transmission rate;

(8) FIGS. 6A and 6B schematically illustrates a film element engaged with a gate electrode having a relatively high open area, with the film element defining one or more openings in the open areas of the gate electrode, according to another aspect of a field emission cathode device of the present disclosure, resulting in a relatively uniform electric field within the gap about the cathode surface with a relatively high electron transmission rate; and

(9) FIG. 7 schematically illustrates a field emission cathode device according to another aspect of the present disclosure, including an insulator element disposed between the film element and the gate electrode to thermally and/or electrically insulate the film element from the gate electrode.

DETAILED DESCRIPTION OF THE DISCLOSURE

(10) The present disclosure now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all aspects of the disclosure are shown. Indeed, the disclosure may be embodied in many different forms and should not be construed as limited to the aspects set forth herein; rather, these aspects are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

(11) FIGS. 5A, 5B, 6A, 6B, and 7 illustrate various aspects of a gate electrode 200 for a field emission cathode device 100 (see, e.g., FIG. 1). Such a field emission cathode device 100 generally includes a cathode 300 comprising a substrate 325 (usually comprised of a metal or other conducting material such as stainless steel, tungsten, molybdenum, doped silicon), a layer of a field emission material 350 (e.g., a mixture of nanomaterials such as nanotubes, graphene, nanowires, etc.) disposed on the substrate 325, and, if necessary, an additional layer of an adhesion material (not shown) disposed between the substrate 325 and the field emission material 350.

(12) A field emission cathode device/assembly 100 generally includes a field emission cathode 300 disposed in a spaced-apart relation to such a gate electrode 200 so as to define a gap 250 therebetween. An external gate voltage (V.sub.g or +V) is applied to the gate electrode 200, with the cathode 300 being connected to ground, such that the generated electric field extracts field emission electrons 400 from the field emission material 350 on the substrate 325 surface. Once the electrons 400 are emitted from the field emission material 350 on the substrate 325 surface, some of the electrons 400 will pass through the opening(s) or open area of the gate electrode 200, while other electrons 400 are absorbed by the gate electrode 200 (e.g., some emitted electrons will bombard the gate electrode).

(13) The gate electrode 200, in some instances, is configured to include multiple linear bars in a grill-like structure (see, e.g., the plan view in FIG. 2A). In other instances, the gate electrode is configured as a mesh-like structure (see, e.g., the plan view in FIG. 2B). Moreover, the gate electrode 200 is generally comprised of a conductive material with a high melting temperature, such as, for example, tungsten, molybdenum, stainless steel, or doped silicon.

(14) In operation, where a field emission cathode device has a physical opening portion of the gate electrode that is relatively low (see, e.g., FIG. 4a dense mesh with less open area), more of the emitted electrons will be absorbed by the gate electrode, and the electron transmission rate is also relatively low (sometimes significantly). In contrast, if the physical opening portion of the gate electrode is relatively high (see, e.g., FIG. 3), the electric field within the gap and/or about the cathode surface becomes undesirably nonuniform. Since the emission of field emission electrons from the cathode surface is related to the characteristics of the triggering electric field, the nonuniform electric field, in turn, results in a nonuniform electron field emission from the cathode surface, which is not desirable.

(15) Aspects of the present disclosure thus provide a field emission cathode device 100 (see, e.g., FIGS. 5A and 5B), wherein the device 100 includes a cathode element 300 having a field emission material 350 on a surface of the substrate 325, and a gate electrode element 200 disposed in spaced-apart relation to the field emission material 350 of the cathode element 300 so as to define a gap 250 therebetween. The gate electrode element 200 includes a plurality of parallel grill members or a mesh structure laterally-extending between opposing anchored ends (see, e.g., FIGS. 2A and 2B). A film element 500 laterally co-extends and is engaged with the gate electrode element 200. In particular aspects, the film element 500 is arranged to allowed electrons 400 emitted from the field emission material 350 of the cathode element 300 to pass therethrough (gate transmission). In addition, the film element 500 is also arranged to cooperate with the gate electrode element 200 and the cathode element 300 to form a substantially uniform electric field within the gap 250 and about the field emission material 350 of the cathode element 300. In particular aspects, a gate voltage source 600 is electrically connected to the gate electrode element 200, with the cathode element 300 electrically connected to ground. In such instances, the gate voltage source 600 is arranged to interact between the gate electrode element 200 and the cathode element 300 to generate the electric field within the gap 250 for inducing the field emission material 350 to emit the electrons 400 therefrom toward the gate electrode element 200.

(16) In some aspects, the gate electrode element 200, whether having the plurality of parallel grill members or the mesh structure, has an open area of at least about 75%. That is, for a given area of the gate electrode element 200, at least about 75% of that area is open space, with the parallel grill members or the mesh structure occupying the remaining area (e.g., no more than about 25%). The open area of at least about 75% allows for a relatively high gate transmission rate of the gate electrode element 200 (e.g., the relatively high open area provides more opportunity for more of the emitted electrons to pass therethrough instead of bombarding the parallel grill members or the mesh structure). In other aspects, the gate electrode element has an open area of more than 80%.

(17) In some aspects, the film element 500 is comprised of a metal, conductive silicon nitride, or carbon. In instances where the film element 500 is comprised of a metal, the metal comprises beryllium, aluminum, gold, or combinations thereof. The film element 500 is a thin film having a thickness on the order of nanometers (e.g., less than about 50 nm). The material of the film element 500, as well as the thickness of that material 500, contribute to forming a film having a high electron transparency (e.g., an electron transmission rate approaching the electron transmission rate of open area). In addition, the electrically-conductive film element 500 contributes to the formation of a substantially or relatively more uniform electric field generated in the gap 250 and about the cathode surface (see, e.g., FIG. 5B). The combination of the relatively high electron transmission rate coupled with the substantially or relatively more uniform electric field thus addresses the aforementioned need for a field emission cathode device arranged to generate and exhibit a substantially uniform electric field at the cathode surface (e.g., from the field emission material 350) that increases the efficiency of field emission electron generation, while the implementation of the film element 500 potentially reduces ion bombardment of the cathode surface.

(18) In some aspects, the conductive film element 500 can be, but is not required to be, a continuous sheet member (e.g., a continuous nonporous planar element). For example, as shown in FIGS. 6A and 6B, the film element 500 engaged with the gate electrode 200 structure includes and defines some openings 550, particularly associated with the open areas of the gate electrode element 200, in order to facilitate maintenance of a sufficient vacuum between the gate electrode element 200 and the cathode element 300. That is, as particularly shown in the example of FIG. 6A, the openings 550 are defined and disposed in the film element 500 so as to correspond with the open spaces between the parallel grill members or the open spaces within the mesh structure. Such an arrangement of the conductive film member 500 defining one or more openings 550 corresponding to the open areas of the gate electrode element 200 still facilitates the formation of a substantially uniform electric field in the gap 250 about the cathode surface, for example, as long as each of the one or more openings 550 is relatively small (e.g., <30%) of the corresponding open area of the gate electrode 200.

(19) Other arrangements and aspects of a field emission cathode device are within the scope of the present disclosure. For example, in instances where the film element 500 is comprised of a conductive material having a high melting temperature (e.g., silicon nitride), the film element 500 is arranged to directly engage (e.g., be in direct thermal/electrical contact with) the gate electrode element 200 (see, e.g., FIGS. 5A, 5B, 6A, 6B). In another example, in instances where the film element 500 is comprised of a conductive material having a low melting temperature (e.g., beryllium), the film element 500 and the gate electrode element 200 are arranged to include an insulator element 575 disposed therebetween to thermally insulate the film element 500 from the gate electrode element 200 (see, e.g., FIG. 7to protect the film element from high temperatures in operation due to electron bombardment of the structure of the gate electrode element).

(20) In some aspects, the insulator element 575 is also arranged to electrically insulate the film element 500 from the gate electrode element 200. In such instances, a film voltage source 700 (V.sub.f) is optionally electrically connected to the film element 500, with the cathode element 300 electrically connected to ground (see, e.g., FIG. 7). The film voltage source 700 (V.sub.f) is thus arranged to interact with the gate electrode element 200 (electrically connected to the gate voltage source 600 (V.sub.g)) and the cathode element 300 (electrically connected to ground) to generate the electric field within the gap 250 with the desirable characteristics (e.g., substantially uniform electric field providing a substantially uniform electron emission from the cathode surface), as disclosed herein.

(21) Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these disclosed embodiments pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that embodiments of the invention are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the invention. Moreover, although the foregoing descriptions and the associated drawings describe example embodiments in the context of certain example combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative embodiments without departing from the scope of the disclosure. In this regard, for example, different combinations of elements and/or functions than those explicitly described above are also contemplated within the scope of the disclosure. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

(22) It should be understood that although the terms first, second, etc. may be used herein to describe various steps or calculations, these steps or calculations should not be limited by these terms. These terms are only used to distinguish one operation or calculation from another. For example, a first calculation may be termed a second calculation, and, similarly, a second step may be termed a first step, without departing from the scope of this disclosure. As used herein, the term and/or and the / symbol includes any and all combinations of one or more of the associated listed items.

(23) 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 herein, 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. Therefore, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.