Field emission cathode device and formation method of the field emission cathode device

Abstract

To require reduction of a negative electrode deterioration that may be caused by an ion impact while avoiding a potential gate electrode damage caused by a negative electrode hot spot.SOLUTION: A field emission cathode device 100 and a formation method of the same, contains: a magnetic field discharge negative electrode 200 that is a rotational magnetic field discharge negative electrode 200 containing a magnetic field discharge material to be accumulated to a front surface, is rotated as a center of a shaft, and is electrically grounded; and a flat surface gate electrode 300 that is extended in parallel to the front surface of the rotational magnetic field discharge negative electrode 200, and defines a gap 350 thereto. A gate voltage source 400 is electrically connected to the gate electrode 300, and is arranged so as to generate a magnetic field by being alternately acted with the gate electrode 300. The magnetic field introduces one part of the front surface of the magnetic field discharge negative electrode 200 that is adjacent to the gate electrode 300, and makes an electron 500 to be discharged via the gate electrode 300 toward the gate electrode 300 from the magnetic field discharge material.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present application relates to a field emission cathode device, and more particularly, to a field emission cathode device and a method of forming the field emission cathode device.

Background Art

[0002] A typical field emission cathode assembly includes a field emission cathode and an extraction gate structure, having a specific gap distance therebetween, and an example of the field emission cathode assembly is shown in FIG. 1. The cathode is generally a conductive substrate having a deposited layer of a field emission material on a cathode surface adjacent to the extraction gate structure. In such an example of the prior art, in order to extract field emission electrons (e.g., field emission current) from the cathode surface, an external voltage (V G ) is applied to the gate electrode, and the cathode is electrically grounded.

[0003] The emission area of the cathode is defined by the total area of the deposited layer of the field emission material. In order to generate a stable field emission current, the field emission cathode can operate continuously only below a specific threshold of the maximum current density, as shown in FIG. 2. In many cases, in high-power / high-current situations, the cathode can operate stably only in a pulse mode having a particularly short pulse width or duration (e.g., generating current intermittently at a specific duty cycle over a selected time to achieve stable operation). As shown in FIG. 3A, it is possible to achieve a higher peak current while operating in a pulse mode as compared to the DC (continuous) mode of FIG. 2. The pulse width (duration) is even shorter than that shown in FIG. 3A, and as shown in FIG. 3B, the peak current can be further increased without causing cathode degradation.

[0004] However, operating the cathode in this way can result in, for example, damage to the gate electrode due to cathode hot spots (e.g., non-uniformities in the field emission layer on the cathode surface can cause higher peak currents in some regions of the cathode than in others) and / or damage to the cathode due to electron bombardment (e.g., reflection of electrons returning from the gate electrode to the cathode). Higher peak currents can also apply stress to the cathode and, in some cases, reduce its service life. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] Therefore, there is a need for a field emission cathode and a method of forming a field emission cathode that increase the maximum current output (electron emission) of a field emission cathode with improved uniformity and minimize cathode stress to extend the service life of the cathode. Such a cathode and method of forming it should desirably avoid potential gate electrode damage caused by cathode hot spots and reduce possible cathode degradation due to ion bombardment. MEANS FOR SOLVING THE PROBLEMS

[0006] The above and other needs are met by aspects of the present disclosure including, but not limited to, the following exemplary embodiments. One particular aspect provides a field emission cathode device, such a device comprising a rotating field emission cathode including a field emission material deposited on the surface of the device, the field emission cathode rotating about an axis and being electrically grounded. A planar gate electrode extends parallel to the surface of the rotating field emission cathode, defining a gap therebetween. A gate voltage source is electrically connected to the gate electrode and arranged to interact with the gate electrode to generate an electric field. The electric field induces a portion of the surface of the rotating field emission cathode adjacent to the gate electrode to emit electrons from the field emission material toward and through the gate electrode.

[0007] Another exemplary aspect provides a method of forming a field emission cathode device including the step of disposing a planar gate electrode adjacent to and parallel to the surface of a rotating field emission cathode to define a gap therebetween, the rotating field emission cathode including a field emission material deposited on its surface, being electrically grounded, and rotating about an axis extending therethrough. A gate voltage source interacts with a gate electrode electrically connected to the gate voltage source to generate an electric field, the electric field being arranged to induce a portion of the surface of the rotating field emission cathode adjacent to the gate electrode to emit electrons from the field emission material toward and through the gate electrode.

[0008] Accordingly, the present disclosure includes, but is not limited to, the following exemplary embodiments.

[0009] Exemplary Embodiment 1: A field emission cathode device comprising a rotating field emission cathode including a field emission material deposited on its surface, rotating about an axis, and being electrically grounded; a planar gate electrode extending parallel to the surface of the rotating field emission cathode and defining a gap therebetween; and a gate voltage source electrically connected to the gate electrode and arranged to interact with the gate electrode to generate an electric field, the electric field being arranged to induce a portion of the surface of the rotating field emission cathode adjacent to the gate electrode to emit electrons from the field emission material toward and through the gate electrode.

[0010] Exemplary Embodiment 2: The surface of the field emission cathode is the cylindrical surface of a cylindrical substrate, and the axis is the longitudinal axis extending along the cylindrical substrate, for any of the devices of the foregoing exemplary embodiments or combinations thereof.

[0011] Exemplary Embodiment 3: The gate electrode extends parallel to the cylindrical surface of the cylindrical substrate, for any of the devices of the foregoing exemplary embodiments or combinations thereof.

[0012] Exemplary Embodiment 4: The electric field generated by the gate voltage source induces a portion that extends angularly along the cylindrical surface of the rotating cylindrical substrate adjacent to the gate electrode, and is arranged to cause electrons to be emitted from the field emission material toward and through the gate electrode, for any device of the foregoing exemplary embodiments or a combination thereof.

[0013] Exemplary Embodiment 5: The size of the portion that extends angularly along the cylindrical surface is proportional to the dimension of the gap between the gate electrode and the cylindrical surface, for any device of the foregoing exemplary embodiments or a combination thereof.

[0014] Exemplary Embodiment 6: The gate voltage source is arranged to apply a constant (DC) voltage or a pulsed voltage to the gate electrode, for any device of the foregoing exemplary embodiments or a combination thereof.

[0015] Exemplary Embodiment 7: The gate voltage source is configured to apply a pulsed voltage to the gate electrode, and the magnitude of the pulsed voltage is inversely proportional to the pulse duration of the pulsed voltage, for any device of the foregoing exemplary embodiments or a combination thereof.

[0016] Exemplary Embodiment 8: The surface of the field emission cathode is a circular surface that extends laterally from the disk-shaped substrate, and the axis extends perpendicularly through the disk-shaped substrate to the circular surface, for any device of the foregoing exemplary embodiments or a combination thereof.

[0017] Exemplary Embodiment 9: The gate electrode extends parallel to and adjacent to a part of the circular surface of the disk-shaped substrate at least between the axis and the outer periphery of the circular surface, for any device of the foregoing exemplary embodiments or a combination thereof.

[0018] Exemplary Embodiment 10: The electric field generated by the gate voltage source induces a portion adjacent to the gate electrode on the circular surface of the rotating disk-shaped substrate, and is arranged to cause electrons to be emitted from the field emission material toward and through the gate electrode, for any device of the foregoing exemplary embodiments or a combination thereof.

[0019] Exemplary Embodiment 11: The size of that portion of the circular surface is proportional to the angular dimension of the gate electrode, an apparatus of any of the foregoing exemplary embodiments or a combination thereof.

[0020] Exemplary Embodiment 12: A method of forming a field emission cathode device, comprising the steps of disposing a planar gate electrode adjacent to and parallel to the surface of a rotating field emission cathode, defining a gap therebetween, wherein the rotating field emission cathode includes a field emission material deposited on the surface, is electrically grounded, and rotates about an axis extending through the rotating field emission cathode, and interacting a gate voltage source with the gate electrode electrically connected to the gate voltage source to generate an electric field, the electric field being arranged to induce a portion of the surface of the rotating field emission cathode adjacent to the gate electrode to emit electrons from the field emission material toward and through the gate electrode.

[0021] Exemplary Embodiment 13: The step of disposing the planar gate electrode includes the step of disposing the planar gate electrode adjacent to and parallel to the cylindrical surface of a cylindrical substrate of the rotating field emission cathode, the axis being a longitudinal axis extending along the cylindrical substrate, any method of any of the foregoing exemplary embodiments or a combination thereof.

[0022] Exemplary Embodiment 14: The step of disposing the planar gate electrode includes the step of disposing the planar gate electrode adjacent to and parallel to the cylindrical surface of a cylindrical substrate, any method of any of the foregoing exemplary embodiments or a combination thereof.

[0023] Exemplary Embodiment 15: The step of interacting the gate voltage source with the gate electrode includes the step of interacting the gate voltage source with the gate electrode such that the electric field generated by the gate voltage source induces a radially extending portion of the cylindrical surface of a rotating cylindrical substrate adjacent to the gate electrode to emit electrons from the field emission material, any method of any of the foregoing exemplary embodiments or a combination thereof.

[0024] Exemplary Embodiment 16: The step of arranging the planar gate electrode includes arranging the planar gate electrode adjacent to and parallel to the surface of the rotational field emission cathode such that the size of the angularly extending portion of the cylindrical surface is proportional to the dimension of the gap between the gate electrode and the cylindrical surface, any method of the foregoing exemplary embodiments or a combination thereof.

[0025] Exemplary Embodiment 17: The step of causing the gate voltage source to interact with the gate electrode includes causing the gate voltage source to interact with the gate electrode to apply a constant (DC) voltage or a pulsed voltage to the gate electrode, any method of the foregoing exemplary embodiments or a combination thereof.

[0026] Exemplary Embodiment 18: The step of causing the gate voltage source to interact with the gate electrode includes causing the gate voltage source to interact with the gate electrode to apply a pulsed voltage to the gate electrode, and the magnitude of the pulsed voltage is inversely proportional to the pulse duration of the pulsed voltage, any method of the foregoing exemplary embodiments or a combination thereof.

[0027] Exemplary Embodiment 19: The step of arranging the planar gate electrode includes arranging the planar gate electrode adjacent to and parallel to a circular surface extending laterally of a disc-shaped substrate, with the axis extending perpendicularly through the disc-shaped substrate to the circular surface, any method of the foregoing exemplary embodiments or a combination thereof.

[0028] Exemplary Embodiment 20: The step of arranging the planar gate electrode includes arranging the planar gate electrode parallel to and adjacent to a part of the circular surface of the disc-shaped substrate, at least between the axis and the outer periphery of the circular surface, any method of the foregoing exemplary embodiments or a combination thereof.

[0029] Exemplary Embodiment 21: The step of interacting the gate voltage source with the gate electrode includes arranging the gate voltage source to interact with the gate electrode such that the electric field generated by the gate voltage source induces a portion adjacent to the gate electrode on the circular surface of the rotating disk-shaped substrate to emit electrons from the field emission material, according to any method or combination thereof of the foregoing exemplary embodiments.

[0030] Exemplary Embodiment 22: The step of arranging the planar gate electrode includes arranging the planar gate electrode adjacent to and parallel to the surface of the rotating field emission cathode such that the size of that portion of the circular surface is proportional to the angular dimension of the gate electrode, according to any method or combination thereof of the foregoing exemplary embodiments.

[0031] These and other features, aspects, and advantages of the present disclosure will become apparent from the following detailed description when read in conjunction with the accompanying drawings, which are briefly described below. The present disclosure includes any combination of such features or elements, regardless of whether two, three, four, or more such features or elements are explicitly combined or otherwise recited in the description of specific embodiments herein. The present disclosure is intended to be construed comprehensively, and any separable feature or element of the present disclosure should be regarded as intended, i.e., combinable, in any of its aspects and embodiments, unless the context of the present disclosure clearly indicates otherwise.

[0032] It should be understood that the summary in this specification is provided only for the purpose of summarizing some exemplary aspects to provide a basic understanding of the present disclosure. Therefore, it should be understood that the exemplary aspects described above are merely examples and should in no way be construed as narrowing the scope or spirit of the present disclosure. The scope of the present disclosure is understood to encompass many potential aspects. Some of them will be further described in detail below in addition to the aspects summarized herein. Furthermore, other aspects and advantages of such aspects disclosed herein will become apparent from the following detailed description considered in conjunction with the accompanying drawings that illustrate the principles of the described aspects by way of example.

[0033] Having thus generally described the present disclosure, the accompanying drawings will now be described. The drawings are not necessarily drawn to an exact scale.

Brief Description of the Drawings

[0034]

Figure 1A

Figure 1B

Figure 2

Figure 3A

Figure 3B

Figure 4

Figure 5A

Figure 5B

Figure 6

Figure 7

[0035] The present disclosure will be described in more detail below with reference to the accompanying drawings. The drawings show some aspects, but not all, of the present disclosure. In fact, the present disclosure may be embodied in many different forms and should not be construed as limited to the aspects described herein. Rather, these aspects are provided so that the present disclosure meets applicable legal requirements. Throughout, like numbers refer to like elements.

[0036] As described herein, a field emission cathode device that shows an increase in the maximum current output (electron emission) of a field emission cathode with improved electron emission uniformity while minimizing cathode stress is desirable. However, operating a prior art field emission cathode device in this way can result in damage to the gate electrode due to, for example, cathode hot spots (e.g., non-uniformities in the field emission layer on the cathode surface can cause higher peak currents in some regions of the cathode than in others), and / or damage to the cathode due to electron bombardment (e.g., reflection of electrons returning from the gate electrode to the cathode). Higher peak currents can also stress the cathode and, in some cases, shorten its service life.

[0037] Figures 4, 6, and 7 illustrate various aspects of the field emission cathode device 100 according to the present disclosure. In some aspects, the field emission cathode device 100 includes a rotating field emission cathode 200 (see, e.g., FIG. 4), and the cathode 200 has a field emission material 225 deposited on its surface 250 (see, e.g., FIG. 1A). The field emission cathode 200 is further arranged to rotate about an axis and is electrically grounded. The planar gate electrode 300 extends parallel to the surface 250 of the rotating field emission cathode 200, with a gap 350 defined therebetween. The gate voltage source 400 is electrically connected to the gate electrode 300 and is arranged to interact with the gate electrode 300 to generate an electric field between the gate electrode 300 and the cathode 200. The generated electric field interacts with the surface 250 of the cathode 200 to induce a portion of the surface 250 of the rotating field emission cathode 200 adjacent to the gate electrode 300 (which has the field emission material 225 deposited thereon) to emit electrons 500 from the field emission material 225 toward and through the gate electrode 300.

[0038] Therefore, the portion of the cathode surface 250 that is adjacent to and faces the gate electrode 300 and is exposed to the electric field is the only portion of the cathode 200 that emits electrons 500 at any point during the rotation of the cathode 200. Thus, detrimental factors such as hot spots and local non-uniformities of the field emission material 225 and surface roughness are minimized or eliminated in consideration of the rotation of the cathode 200 during operation of the field emission cathode device 100. Further, the possibility of cathode degradation due to ion bombardment is also minimized or eliminated. Thus, the improvement in uniformity and the elimination / minimization of detrimental factors improve the maximum current output (electron emission) of the field emission cathode while minimizing the cathode stress (e.g., only a portion of the cathode is energized for a given time and that portion is not energized again until the cathode has completed a full rotation). Therefore, it is expected that the service life of the cathode will be extended.

[0039] In certain embodiments, the substrate 210 (see, e.g., FIG. 1A) that defines the cathode 200 is made of a metal or other conductive material such as stainless steel, tungsten, molybdenum, doped silicon, or the like. In such embodiments, the field emission material 225 deposited on the surface of the substrate 210 includes a layer of nanotubes, nanowires, graphene, amorphous carbon, or combinations thereof. The gate electrode 300 generally consists of a conductive material having a high melting temperature such as, for example, tungsten, molybdenum, stainless steel, or doped silicon. Further, in some embodiments, the gap 350 defined between the gate electrode 300 and the surface 250 of the substrate 200 (the gap 350 is actually defined between the surface of the field emission material 225 deposited on the surface 250 of the substrate 210 / cathode 200 and the gate electrode 300, and references herein to the surface 250 of the substrate 210 or cathode 200 are expressly intended to mean the surface of the field emission material 225 where appropriate) is, for example, from about 100 μm to about 1 mm.

[0040] Accordingly, aspects of the present disclosure improve the uniformity of electron field emission from the rotating cathode 200 even when the rotating field emission cathode 200 may have a relatively rough surface morphology and non-uniform emitter deposition (see, e.g., FIG. 6). For example, detrimental factors that cause non-uniform field emission current, including potential hot spots (which cause damage to the gate electrode), are minimized or eliminated while the cathode 200 is rotating during operation, resulting in improved overall field emission uniformity. Thus, aspects of the present disclosure reduce, minimize, or eliminate potential hot spots that concentrate or emit an excessive amount of (electron) current from small local regions of the cathode 200 that can potentially cause damage to the gate electrode due to ion bombardment. Rotation of the cathode 200 disperses or otherwise minimizes the hot spot current over a larger area (due to rotation of the cathode) to reduce the risk of gate electrode damage, but also reduces cathode degradation due to ion bombardment. That is, while the cathode 200 is rotating, only a small / local portion of the cathode is exposed to the openings of the gate mesh (and thus ion bombardment due to reflection of electrons from the gate electrode), which extends the cathode's service life by minimizing the cathode's exposure to ion bombardment.

[0041] In one particular aspect, as shown in FIGS. 4 and 6, the surface 250 of the field emission cathode 200 is the cylindrical surface of a cylindrical substrate. In such an aspect, the axis is the longitudinal axis extending along and through the cylindrical substrate (e.g., the cylindrical cathode 200 rotates about the longitudinal axis of the cylinder). Accordingly, the field emission material 225 is deposited on the outer cylindrical surface of the cylinder (see, e.g., FIG. 6). In such an aspect, the planar gate electrode 300 extends parallel to the cylindrical surface of the cylindrical substrate. The gate electrode is disclosed as being flat in this aspect, but those skilled in the art will understand that other configurations of the gate electrode are also contemplated. For example, the cross-section of the gate electrode can be arcuate, within the scope of the present disclosure, whether concave or convex with respect to the cylindrical substrate.

[0042] In an embodiment including the rotating cylindrical cathode 200, the electric field generated by the gate voltage source 400 and the gate electrode 300 induces a portion of the cylindrical surface of the rotating cylindrical substrate adjacent to the gate electrode 300 that extends angularly (e.g., a sector or angular portion of the cylinder that extends along the length of the cylinder as viewed in cross-section), and is arranged to emit electrons 500 from the field emission material 225 toward and through the gate electrode 300. In a particular example, the size of the angularly extending portion of the cylindrical surface induced by the electric field is proportional to the dimension of the gap 350 between the gate electrode 300 and the cylindrical surface, or the dimension (length and / or width) of the gate electrode 300. In such a configuration, any given region of the cylindrical surface is induced to emit electrons in a shorter time, for example, compared to a prior art field emission cathode device as shown in FIGS. 1A and 1B.

[0043] In some embodiments, the gate voltage source 400 is configured to apply a constant (DC) voltage (e.g., see FIG. 5A) or a pulsed voltage (e.g., see FIG. 5B) to the gate electrode 300. When the gate voltage source 400 is configured to apply a pulsed voltage to the gate electrode 300, the magnitude of the pulsed voltage is inversely proportional to the pulse duration of the pulsed voltage. That is, a sufficiently large field emission current can be obtained by applying a relatively low gate voltage to the gate electrode 300 for a relatively long time without causing breakdown of the cathode 200 (or the gate electrode 300) or shortening the service life, for example, due to cathode hot spots, non-uniform emission current, electron bombardment, etc. (e.g., see FIG. 5B). Further, as the cathode 200 rotates continuously while emitting electrons 500, any given emission region on the rotating surface emits electrons for a much shorter time compared to a prior art field emission cathode device (e.g., the cathode device shown in FIGS. 1A and 1B, etc.). Thus, a higher emission current can be generated for a long time in either the DC mode (FIG. 5A) or a longer pulse mode (FIG. 5B) compared to such a prior art field emission cathode device.

[0044] Those skilled in the art will understand that different variants of the field emission cathode device 100 implementing the rotating cathode 200 are also contemplated in the present disclosure. For example, as shown in FIG. 7, some alternative embodiments of the present disclosure have a field emission material 225 deposited on a circular surface extending laterally from the side of the rotating disk, and the field emission cathode 200 is arranged as a rotating disk that rotates about an axis perpendicular to the laterally extending circular surface. In such an embodiment, the gate electrode 300 is arranged adjacent to and parallel to the circular surface extending laterally from the disk so as to define a specific gap therebetween. Thus, while the disk is rotating about the axis, only the region of the cathode directly adjacent to the gate structure emits electrons in response to the electric field.

[0045] That is, in the alternative embodiment, the surface of the field emission cathode 200 is a circular surface extending laterally from the side of the disk-shaped substrate, and the rotation axis extends through the disk-shaped substrate perpendicular to the circular surface. By rotating the disk-shaped substrate about the rotation axis, the gate electrode 300 extends parallel to and adjacent to a part of the circular surface of the disk-shaped substrate at least between the axis and the outer periphery of the circular surface. Thus, the electric field generated by the gate voltage source 400 induces the portion adjacent to the gate electrode 300 on the circular surface of the rotating disk-shaped substrate to emit electrons from the field emission material toward and through the gate electrode 300 at any point during the rotation of the disk-shaped cathode. In a particular embodiment, the size of that portion of the circular surface is proportional to the angular dimension or area of the gate electrode 300 adjacent to the disk-shaped cathode.

[0046] Many modifications and other embodiments of the invention described will come to the mind of those skilled in the art related to embodiments of the present disclosure who benefit from the teachings presented in the above description and the related drawings. Accordingly, it is to be understood that embodiments of the invention are not limited to the specific embodiments disclosed, and that modifications and other embodiments are intended to be included within the scope of the invention. Further, the above description and the related drawings illustrate exemplary embodiments in a specific exemplary combination of elements and / or functions, but it is to be understood that alternative embodiments may provide different combinations of elements and / or functions without departing from the scope of the present disclosure. In this regard, for example, within the scope of the present disclosure, combinations of elements and / or functions different from those explicitly described above are also contemplated. Although specific terms are used herein, these terms are used in a general and descriptive sense and are not intended to be limiting.

[0047] Terms such as "first" and "second" may be used herein to describe various steps or predictions, and it is to be understood that these steps or predictions should not be limited by these terms. These terms are only used to distinguish one operation or prediction from another. For example, without departing from the scope of the present disclosure, a first prediction may sometimes be referred to as a second prediction, and similarly, a second step may sometimes be referred to as a first step. As used herein, the term "and / or" and the symbol " / " include any and all combinations of one or more of the associated listed items.

[0048] As used herein, unless the context clearly dictates otherwise, the singular forms “a,” “an,” and “the” include plural referents. The terms “comprises,” “comprising,” “includes,” and / or “including,” as 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. Accordingly, the terms used herein are for the purpose of describing particular embodiments only and are not limiting.

Claims

1. a rotating field emission cathode including a field emission material deposited on a surface thereof, the rotating field emission cathode rotating about an axis and electrically grounded; a planar gate electrode extending parallel to the surface of the rotating field emission cathode and defining a gap therebetween; a gate voltage source electrically connected to the gate electrode and positioned to interact with the gate electrode to generate an electric field that induces a portion of the surface of the rotating field emission cathode adjacent the gate electrode to emit electrons from the field emission material toward and through the gate electrode; A field emission cathode device comprising:

2. 2. The apparatus of claim 1, wherein the surface of the field emission cathode is a cylindrical surface of a cylindrical substrate and the axis is a longitudinal axis extending along the cylindrical substrate.

3. The device of claim 2 , wherein the gate electrode extends parallel to the cylindrical surface of the cylindrical substrate.

4. 4. The apparatus of claim 3, wherein the electric field generated by the gate voltage source is arranged to induce an angular extension of the cylindrical surface of the rotating cylindrical substrate adjacent the gate electrode to emit electrons from the field emission material towards and through the gate electrode.

5. The device of claim 4 , wherein a size of the angular extension of the cylindrical surface is proportional to a dimension of the gap between the gate electrode and the cylindrical surface.

6. The apparatus of claim 1 , wherein the gate voltage source is arranged to apply a constant (DC) or pulsed voltage to the gate electrode.

7. 2. The apparatus of claim 1, wherein the gate voltage source is configured to apply a pulsed voltage to the gate electrode, the magnitude of the pulsed voltage being inversely proportional to a pulse duration of the pulsed voltage.

8. 2. The apparatus of claim 1, wherein said surface of said field emission cathode is a circular surface extending laterally of a disk-shaped substrate, and said axis extends through said disk-shaped substrate perpendicular to said circular surface.

9. The apparatus of claim 8 , wherein the gate electrode extends parallel to and adjacent to a portion of the circular surface of the disk-shaped substrate, at least between the axis and an outer periphery of the circular surface.

10. 10. The apparatus of claim 9, wherein the electric field generated by the gate voltage source is arranged to induce a portion of the circular surface of the rotating disk-shaped substrate adjacent to the gate electrode to emit electrons from the field emission material toward and through the gate electrode.

11. The device of claim 10 , wherein a size of the portion of the circular surface is proportional to an angular dimension of the gate electrode.

12. 1. A method of forming a field emission cathode device, comprising the steps of: disposing a planar gate electrode adjacent to and parallel to a surface of a rotating field emission cathode to define a gap between the surface of the planar gate electrode and the rotating field emission cathode, the rotating field emission cathode including a field emission material deposited on its surface, electrically grounded, and rotating about an axis extending through the rotating field emission cathode; interacting a gate voltage source with the gate electrode electrically connected to the gate voltage source to generate an electric field, the electric field being arranged to induce a portion of the surface of the rotating field emission cathode adjacent the gate electrode to emit electrons from the field emission material towards and through the gate electrode; A method comprising:

13. 13. The method of claim 12, wherein the step of disposing the planar gate electrode comprises disposing the planar gate electrode adjacent to and parallel to a cylindrical surface of a cylindrical substrate of the rotating field emission cathode, the axis being a longitudinal axis extending along the cylindrical substrate.

14. 14. The method of claim 13, wherein disposing the planar gate electrode comprises disposing the planar gate electrode adjacent to and parallel to the cylindrical surface of the cylindrical substrate.

15. 15. The method of claim 14, wherein interacting the gate voltage source with the gate electrode comprises interacting the gate voltage source with the gate electrode such that the electric field generated by the gate voltage source is positioned to induce an angular extension of the cylindrical surface of the rotating cylindrical substrate adjacent the gate electrode to emit electrons from the field emission material.

16. 16. The method of claim 15, wherein the step of positioning the planar gate electrode comprises positioning the planar gate electrode adjacent to and parallel to the surface of the rotating field emission cathode such that a size of the angular extension of the cylindrical surface is proportional to a dimension of a gap between the gate electrode and the cylindrical surface.

17. 13. The method of claim 12, wherein interacting the gate voltage source with the gate electrode comprises interacting the gate voltage source with the gate electrode to apply a constant (DC) voltage or a pulsed voltage to the gate electrode.

18. 13. The method of claim 12, wherein interacting the gate voltage source with the gate electrode comprises interacting the gate voltage source with the gate electrode to apply a pulse voltage to the gate electrode, the magnitude of the pulse voltage being inversely proportional to a pulse duration of the pulse voltage.

19. 13. The method of claim 12, wherein disposing the planar gate electrode comprises disposing the planar gate electrode adjacent to and parallel to a laterally extending circular surface of a disc-shaped substrate, the axis extending through the disc-shaped substrate perpendicular to the circular surface.

20. 20. The method of claim 19, wherein disposing the planar gate electrode comprises disposing the planar gate electrode parallel to and adjacent to a portion of the circular surface of the disk-shaped substrate, at least between the axis and an outer periphery of the circular surface.

21. 21. The method of claim 20, wherein interacting the gate voltage source with the gate electrode includes interacting the gate voltage source with the gate electrode such that an electric field generated by the gate voltage source is arranged to induce a portion of the circular surface of the rotating disk-shaped substrate adjacent the gate electrode to emit electrons from the field emission material.

22. 22. The method of claim 21 , wherein the step of positioning the planar gate electrode comprises positioning the planar gate electrode adjacent to and parallel to the surface of the rotating field emission cathode such that a size of the portion of the circular surface is proportional to an angular dimension of the gate electrode.

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