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

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.

BACKGROUND

Field of the Disclosure

The present application relates to field emission cathode devices and, more particularly, to a field emission cathode device and method for forming a field emission cathode device.

Description of Related Art

A field emission cathode device/assembly generally includes a field emission cathode disposed in relation to an extraction gate structure (e.g., a gate electrode) so as to define a gap therebetween (see, e.g., the prior art shown inFIG.1). An external gate voltage (Vg) is applied to the gate electrode, with the cathode being connected to ground, such that the generated electric field extracts field emission electrons from the cathode surface. Once the electrons are emitted from the cathode surface, some of the electrons will pass through the opening(s) of the gate electrode, while other electrons are absorbed by the gate electrode (e.g., some emitted electrons will bombard the gate electrode).

The gate electrode in the prior art can have different forms. In some instances, the gate electrode is configured to include multiple linear bars in a grill-like structure (see, e.g.,FIG.2A). In other instances, the gate electrode is configured as a mesh-like structure (see, e.g.,FIG.2B). Moreover, the gate electrode is generally comprised of a conductive material with a high melting temperature, such as, for example, tungsten, molybdenum, stainless steel, or doped silicon. The gate electrode, whether the grill structure or the mesh structure, generally defines a physical opening portion that ranges from about 50% to over 80% open area (e.g., the area portion of the gate electrode that is open space). The physical opening portion of the gate electrode is required in order to allow the emitted electrons from the cathode surface to pass through the gate electrode so as to form an electron beam. The percentage of electrons emitted from the cathode surface and passing through the gate electrode is called the electron transmission rate, wherein the higher the transmission rate, the higher usage efficiency of the generated and emitted electrons.

If the physical opening portion of the gate electrode is relatively low (see, e.g.,FIG.4—a dense mesh with less open area), more of the emitted electrons will be absorbed by the gate electrode, and the electron transmission rate decreases (sometimes significantly). However, 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.

Thus, there exists a need for a field emission cathode device, and a method of forming such a field emission cathode device, wherein the field emission cathode device is arranged to generate and exhibit a substantially uniform electric field at the cathode surface and within the gap between the gate electrode and the cathode. Such a substantially uniform electric field at the cathode surface of the field mission cathode device should also desirably increase the efficiency of field emission electron generation. The gate element should also desirably be structured to increase the gate transmission rate, and also reduce ion bombardment of the cathode surface.

SUMMARY OF THE DISCLOSURE

The above and other needs are met by aspects of the present disclosure which includes, without limitation, the following example embodiments and, in one particular aspect, provides a field emission cathode device, wherein such a device comprises 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.

Another example aspect provides a method of forming a field emission cathode device, wherein such a method comprises 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, with the gate electrode element having a plurality of parallel grill members or a mesh structure laterally-extending between opposing anchored ends; and engaging a film element with the gate electrode element, the film element laterally co-extending with the gate electrode element and 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.

The present disclosure thus includes, without limitation, the following example embodiments:

Example Embodiment 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; and a film element laterally co-extending and engaged with the gate electrode element, 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.

Example Embodiment 2: The device of any preceding example embodiment, or combinations thereof, 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.

Example Embodiment 3: The device of any preceding example embodiment, or combinations thereof, wherein the plurality of parallel grill members or the mesh structure of the gate electrode element has an open area of at least about 75%.

Example Embodiment 4: The device of any preceding example embodiment, or combinations thereof, wherein the film element is comprised of a metal, conductive silicon nitride, or carbon.

Example Embodiment 5: The device of any preceding example embodiment, or combinations thereof, wherein the metal comprises beryllium, aluminum, gold, or combinations thereof.

Example Embodiment 6: The device of any preceding example embodiment, or combinations thereof, wherein the film element is a thin film having a thickness of less than about 50 nm.

Example Embodiment 7: The device of any preceding example embodiment, or combinations thereof, wherein the gate electrode element is comprised of a conductive material having a high melting temperature.

Example Embodiment 8: The device of any preceding example embodiment, or combinations thereof, wherein the gate electrode element is comprised of tungsten, molybdenum, stainless steel, doped silicon, or combinations thereof.

Example Embodiment 9: The device of any preceding example embodiment, or combinations thereof, wherein the film element defines one or more openings in the open area of the plurality of parallel grill members or the mesh structure of the gate electrode element.

Example Embodiment 10: The device of any preceding example embodiment, or combinations thereof, wherein the film element is comprised of a conductive material having a high melting temperature, and wherein the film element is arranged to directly engage the gate electrode element.

Example Embodiment 11: The device of any preceding example embodiment, or combinations thereof, wherein the film element is comprised of a conductive material having 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.

Example Embodiment 12: The device of any preceding example embodiment, or combinations thereof, wherein the insulator element is arranged to electrically insulate the film element from the gate electrode element.

Example Embodiment 13: The device of any preceding example embodiment, or combinations thereof, 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.

Example Embodiment 14: 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; and engaging a film element with the gate electrode element, the film element laterally co-extending with the gate electrode element and 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.

Example Embodiment 15: The method of any preceding example embodiment, or combinations thereof, 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.

Example Embodiment 16: The method of any preceding example embodiment, or combinations thereof, 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 plurality of parallel grill members or the mesh structure of the gate electrode element has an open area of at least about 75%, in spaced-apart relation to the field emission surface.

Example Embodiment 17: The method of any preceding example embodiment, or combinations thereof, 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.

Example Embodiment 18: The method of any preceding example embodiment, or combinations thereof, 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.

Example Embodiment 19: The method of any preceding example embodiment, or combinations thereof, 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.

Example Embodiment 20: The method of any preceding example embodiment, or combinations thereof, 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.

Example Embodiment 21: The method of any preceding example embodiment, or combinations thereof, 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.

Example Embodiment 22: The method of any preceding example embodiment, or combinations thereof, wherein engaging the film element with the gate electrode element comprises engaging the film element, defining one or more openings in the open area of the plurality of parallel grill members or the mesh structure of the gate electrode element, with the gate electrode element.

Example Embodiment 23: The method of any preceding example embodiment, or combinations thereof, wherein engaging the film element with the gate electrode element comprises directly engaging the film element, comprised of a conductive material having a high melting temperature, with the gate electrode element.

Example Embodiment 24: The method of any preceding example embodiment, or combinations thereof, wherein engaging the film element with the gate electrode element comprises engaging the film element, comprised of a conductive material having a low melting temperature, with the gate electrode element.

Example Embodiment 25: The method of any preceding example embodiment, or combinations thereof, 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.

Example Embodiment 26: The method of any preceding example embodiment, or combinations thereof, 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.

Example Embodiment 27: The method of any preceding example embodiment, or combinations thereof, 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.

It will be appreciated that the summary herein is provided merely for purposes of summarizing some example aspects so as to provide a basic understanding of the disclosure. As such, it will be appreciated that the above described example aspects are merely examples and should not be construed to narrow the scope or spirit of the disclosure in any way. It will be appreciated that the scope of the disclosure encompasses many potential aspects, some of which will be further described below, in addition to those herein summarized. Further, other aspects and advantages of such aspects disclosed herein will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described aspects.

DETAILED DESCRIPTION OF THE DISCLOSURE

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.

FIGS.5A,5B,6A,6B, and7illustrate various aspects of a gate electrode200for a field emission cathode device100(see, e.g.,FIG.1). Such a field emission cathode device100generally includes a cathode300comprising a substrate325(usually comprised of a metal or other conducting material such as stainless steel, tungsten, molybdenum, doped silicon), a layer of a field emission material350(e.g., a mixture of nanomaterials such as nanotubes, graphene, nanowires, etc.) disposed on the substrate325, and, if necessary, an additional layer of an adhesion material (not shown) disposed between the substrate325and the field emission material350.

A field emission cathode device/assembly100generally includes a field emission cathode300disposed in a spaced-apart relation to such a gate electrode200so as to define a gap250therebetween. An external gate voltage (Vgor +V) is applied to the gate electrode200, with the cathode300being connected to ground, such that the generated electric field extracts field emission electrons400from the field emission material350on the substrate325surface. Once the electrons400are emitted from the field emission material350on the substrate325surface, some of the electrons400will pass through the opening(s) or open area of the gate electrode200, while other electrons400are absorbed by the gate electrode200(e.g., some emitted electrons will bombard the gate electrode).

The gate electrode200, in some instances, is configured to include multiple linear bars in a grill-like structure (see, e.g., the plan view inFIG.2A). In other instances, the gate electrode is configured as a mesh-like structure (see, e.g., the plan view inFIG.2B). Moreover, the gate electrode200is generally comprised of a conductive material with a high melting temperature, such as, for example, tungsten, molybdenum, stainless steel, or doped silicon.

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.4—a 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.

Aspects of the present disclosure thus provide a field emission cathode device100(see, e.g.,FIGS.5A and5B), wherein the device100includes a cathode element300having a field emission material350on a surface of the substrate325, and a gate electrode element200disposed in spaced-apart relation to the field emission material350of the cathode element300so as to define a gap250therebetween. The gate electrode element200includes a plurality of parallel grill members or a mesh structure laterally-extending between opposing anchored ends (see, e.g.,FIGS.2A and2B). A film element500laterally co-extends and is engaged with the gate electrode element200. In particular aspects, the film element500is arranged to allowed electrons400emitted from the field emission material350of the cathode element300to pass therethrough (“gate transmission”). In addition, the film element500is also arranged to cooperate with the gate electrode element200and the cathode element300to form a substantially uniform electric field within the gap250and about the field emission material350of the cathode element300. In particular aspects, a gate voltage source600is electrically connected to the gate electrode element200, with the cathode element300electrically connected to ground. In such instances, the gate voltage source600is arranged to interact between the gate electrode element200and the cathode element300to generate the electric field within the gap250for inducing the field emission material350to emit the electrons400therefrom toward the gate electrode element200.

In some aspects, the gate electrode element200, 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 element200, 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 element200(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%.

In some aspects, the film element500is comprised of a metal, conductive silicon nitride, or carbon. In instances where the film element500is comprised of a metal, the metal comprises beryllium, aluminum, gold, or combinations thereof. The film element500is a thin film having a thickness on the order of nanometers (e.g., less than about 50 nm). The material of the film element500, as well as the thickness of that material500, 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 element500contributes to the formation of a substantially or relatively more uniform electric field generated in the gap250and 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 material350) that increases the efficiency of field emission electron generation, while the implementation of the film element500potentially reduces ion bombardment of the cathode surface.

In some aspects, the conductive film element500can be, but is not required to be, a continuous sheet member (e.g., a continuous nonporous planar element). For example, as shown inFIGS.6A and6B, the film element500engaged with the gate electrode200structure includes and defines some openings550, particularly associated with the open areas of the gate electrode element200, in order to facilitate maintenance of a sufficient vacuum between the gate electrode element200and the cathode element300. That is, as particularly shown in the example ofFIG.6A, the openings550are defined and disposed in the film element500so 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 member500defining one or more openings550corresponding to the open areas of the gate electrode element200still facilitates the formation of a substantially uniform electric field in the gap250about the cathode surface, for example, as long as each of the one or more openings550is relatively small (e.g., <30%) of the corresponding open area of the gate electrode200.

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 element500is comprised of a conductive material having a high melting temperature (e.g., silicon nitride), the film element500is arranged to directly engage (e.g., be in direct thermal/electrical contact with) the gate electrode element200(see, e.g.,FIGS.5A,5B,6A,6B). In another example, in instances where the film element500is comprised of a conductive material having a low melting temperature (e.g., beryllium), the film element500and the gate electrode element200are arranged to include an insulator element575disposed therebetween to thermally insulate the film element500from the gate electrode element200(see, e.g.,FIG.7—to protect the film element from high temperatures in operation due to electron bombardment of the structure of the gate electrode element).

In some aspects, the insulator element575is also arranged to electrically insulate the film element500from the gate electrode element200. In such instances, a film voltage source700(Vf) is optionally electrically connected to the film element500, with the cathode element300electrically connected to ground (see, e.g.,FIG.7). The film voltage source700(Vf) is thus arranged to interact with the gate electrode element200(electrically connected to the gate voltage source600(Vg)) and the cathode element300(electrically connected to ground) to generate the electric field within the gap250with the desirable characteristics (e.g., substantially uniform electric field providing a substantially uniform electron emission from the cathode surface), as disclosed herein.

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.