Patent Grant
10720297
The present disclosure relates to vacuum electronics devices.
Vacuum electronics devices include devices such as field emitter arrays, vacuum tubes, electric thrusters, gyrotrons, klystrons, travelling wave tubes, thermionic converters, and the like. In vacuum electronics devices, it may be beneficial to place a conductive grid (for example, a control grid, suppressor grid, screen grid, accelerator grid, focus grid, or the like) closely adjacent to an electrode (for example, a cathode or an anode). Such a grid may use a bias voltage to control and/or modulate the flow of charged particles in the vacuum electronics device.
Suspended grids separate the grids and electrodes by a vacuum gap. Unlike charge conduction in a solid, the electrons and ions travelling between the electrodes can travel ballistically through the emptiness of even an imperfect vacuum. The charges are accelerated by the suspended grids and can reach very high velocities with infrequent collisions. Furthermore, vacuum is the best medium to prevent electrical breakdown and can help to mitigate dielectric material failure when a large voltage bias is applied between the grid and the electrodes. Conventionally, a suspended grid is fabricated separately from the electrode. An example of a suspended grid is a triode vacuum tube. See U.S. Pat. No. 1,630,443.
Disclosed embodiments include vacuum electronics devices and methods of fabricating a vacuum electronics device.
In a non-limiting embodiment, a vacuum electronics device includes: an electrode; a first film layer disposed on the electrode about a periphery of the electrode; and a second film layer disposed on the first film layer, the second film layer including a plurality of electrically conductive grid lines patterned therein that are supported only at the periphery of the electrode by the first film layer.
In another non-limiting embodiment, a method of fabricating a vacuum electronics device includes: providing an electrically conductive substrate; depositing a first film layer on the substrate; depositing a second film layer on the first film layer; defining a plurality of grid lines in the second layer; and selectively removing a portion of the first film layer such that the first film layer supports the plurality of grid lines only at a periphery of the substrate.
In another non-limiting embodiment, a method of fabricating a vacuum electronics device includes: coating a stack of an electrode and a first film layer disposed on the electrode with resist; exposing the resist; developing the resist; etching the first film layer; removing the resist; and depositing the second film layer.
The foregoing is a summary and thus may contain simplifications, generalizations, inclusions, and/or omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is NOT intended to be in any way limiting. Other aspects, features, and advantages of the devices and/or processes and/or other subject matter described herein will become apparent in the text (e.g., claims and/or detailed description) and/or drawings of the present disclosure.
Illustrative embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.
In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, the use of the same symbols in different drawings typically indicates similar or identical items unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here.
Given by way of overview, various disclosed embodiments provide a suspended grid that is fabricated along with the electrode. Still by way of overview, various embodiments pattern a multilayer film (such as a top film of a multilayer film stack) and selectively etch away or undercut the film and, in some embodiments, the substrate underneath (such as the bottom film of a multilayer film stack or the substrate underneath the film stack). In these embodiments, material in the film layer underneath under the film layer that forms the grid lines may be etched away completely (except for supporting material at the ends of the grid lines), thereby creating suspended grid lines.
Such suspended structures may help to improve the voltage breakdown strength of vacuum electronics by separating the grid lines and the electrodes with a vacuum gap. During operation, because of the vacuum gap the suspended grid may be able to sustain a higher voltage bias (compared to conventional grids that are supported by a layer of dielectric material) without catastrophic material failure when a voltage bias is applied between the suspended grid and the electrode. This is because some embodiments of devices disclosed herein include suspended grid lines that are supported only by material (deposited on the electrode) at ends of the grid lines. Such embodiments can help improve electrical breakdown strength of the grid structure, thereby helping reduce likelihood of a typical grid failure mechanism of dielectric material breakdown under high voltage bias.
Such suspended structures may also help to allow the grid/electrodes gap in some embodiments to be extremely small yet tunable (such as by electrostatic force applied between the grid and electrodes to fine tune the vacuum gap), thereby helping to permit increasing the electric field strength by decreasing the gap distance between the suspended grid and the electrode instead of the conventional method of simply increasing grid voltage. It will be appreciated that a tunable vacuum gap between the grid and the electrodes may be desirable in certain applications of vacuum electronics, for example without limitation in field emission- or electric field induced-tunneling, where increasing the electric field at low grid voltages can help increase device efficiency and reliability.
It will be appreciated that nano-scale devices and their fabrication processes may have an inherent nexus. For example, the choice of materials and fabrication steps for a device may take part in helping to define the device—just as the reverse may occur. It will also be appreciated that some of these choices may be brought about by issues regarding fabrication compatibility (for example and without limitation, using a doped semiconductor versus using a metal for a certain film).
It will be appreciated that disclosed embodiments are applicable to use of a grid that is closely separated from an electrode and supported only at the periphery of the electrode on any of the dielectric support structures disclosed herein or made by fabrication processes disclosed herein for vacuum electronics applications, including without limitation: thermionic devices, amplifiers, travelling wave tubes, klystrons, triodes, diodes, tetrodes, pentodes, mass spectrometers, residual gas analyzers, ion pumps, electron or ion or charged particle beam systems (such as electron microscopes, ion beams for milling, and the like), electrostatic or electromagnetic lenses, and other vacuum devices. It will also be appreciated that dielectric geometry may help to minimize surface and bulk dielectric leakage current and maximize dielectric breakdown strength between the grid and the electrode, so that different potentials may be applied to each.
Now that a non-limiting overview has been provided, illustrative details will be set forth below by way of non-limiting examples and not of limitation.
Referring to
It will be appreciated that, as shown in
In various embodiments, the electrode 12 may be provided as an electrically conductive substrate which may include, by way of non-limiting examples, chromium, platinum, nickel, tungsten, molybdenum, niobium, tantalum, or other appropriate metals. In various embodiments the electrode 12 may be an anode in a vacuum electronics device, as desired for a particular application. It will be appreciated that a larger opening (shown to the right in
In various embodiments the first film layer 14 may include a dielectric, an electrical insulator, a ceramic, silicon oxide, silicon nitride, and and/or aluminum oxide. In various embodiments, the second film layer 16 may include an electrical conductor, such as without limitation, chromium, platinum, nickel, tungsten, molybdenum, niobium, tantalum, or other appropriate metals. In some such embodiments, the electrical conductor may be disposed within an electrical insulator.
Still referring to
In some embodiments, the grid lines 18 (and, when optionally provided as desired, the optional grid lines 20) may include a geometry such as, without limitation, a substantially straight line, a curved line, a circle array, a triangle array, and/or a hexagon array. In some of these embodiments, the grid lines 18 and, when optionally provided as desired, the optional grid lines 20 may have the same shape or geometry. However, the grid lines 18 (and, when optionally provided as desired, the optional grid lines 20) need not have the same shape or geometry. To that end, in some other embodiments the grid lines 18 (and, when optionally provided as desired, the optional grid lines 20) have different shapes or geometries.
Regardless of geometry, it will be appreciated that the non-limiting embodiment of
Referring additionally to
While
It will also be appreciated that, as shown in 2A, 2B, 3A, 3B, 4A-4D, 5A, and 5B, in some embodiments, if desired, the optional grid lines 20 may be patterned in the second film layer 16 and supported on the supports 22 defined in the first film layer 14 as desired for a particular application. It is emphasized again that such grid lines 20 and supports 22 are not required and are optional. It is also emphasized again that required inclusion of the grid lines 20 and the supports 22 is not intended and is not to be inferred. To that end, various embodiments do not include the grid lines 20 and the supports 22.
Given by way of non-limiting example and as shown in
In various embodiments, the conductive material 24 may include chromium, platinum, and/or the like, and the first film layer 14 may include silicon dioxide. In various embodiments, the second film layer 16 may include low-stressed material, such as without limitation silicon nitride, thereby helping to reduce associated stresses such that probability of cracking may be reduced when materials may be suspended from the second film layer 16. In some such embodiments, the conductive material 24 may serve as the conductive grid.
It will be appreciated that in some embodiments the electrically conductive material 24 disposed on the electrode 12 may be considered an artifact of deposition of the electrically conductive material 24 on the grid lines 18 (and, when optionally provided as desired, the optional grid lines 20). However, the electrically conductive material 24 disposed on the electrode 12 may help prevent particle bombardment. Also, the electrically conductive material 24 disposed on the electrode 12 may help reduce the gap between the grid and the electrode 12, thereby helping to increase the electric field and, accordingly, helping to enable quantum tunneling and helping to increase efficiency. It will be further appreciated that the conductive material 24 may be evaporated on top after the grid lines 18 have been suspended. It will be appreciated that the vacuum electronics device 200 may be suited for use in a field emission heat engine (which entails quantum tunneling).
Given by way of non-limiting example and as shown in
Various embodiments of the vacuum electronics device 300 may have a low fill factor (that is the ratio of area of the grid lines to the total area of the device) such as on the order of less than 2% or so. It will be appreciated that such a low fill factor can help to reduce grid loss (that is, electrons getting collected by the grid, thereby resulting in an IxV power loss) during operation. Moreover, because the grid lines 18 are moved further away from the electrode 12 than in a typical suspended grid structure, the grid lines 18 may be suspended across a longer distance than in a typical suspended grid structure. As a result, the suspended grid lines 18 may be stretched more than typical suspended grid lines without significantly increasing risk of shorting the suspended grid lines 18 to the electrode 12.
It will be appreciated that the vacuum electronics device 300 may be used in thermionic heat engines which do not entail quantum tunneling. Given by way of non-limiting example, the vacuum electronics device 300 may include a vacuum gap between the suspended grid lines 18 and the electrode 12 and may have an applied voltage bias. In such a case, it will be appreciated that the resulting electric field may be on the order of between 0.5 mV/nm-1 mV/nm.
Referring additionally to
It will be appreciated that varying the distance of the vacuum gap between the suspended grid lines 18 and the electrode 12 can vary and, in some cases to help optimize, the electric field between the grid and the electrode 12. It will also be appreciated that the shapes of the suspended grid lines 18 shown in
Illustrative fabrication techniques for fabrication various embodiments of vacuum electronics devices are discussed below by way of non-limiting examples.
Referring additionally to
In some embodiments, the method may also include depositing at least one electrically conductive film layer on the plurality of grid lines. In some such embodiments, depositing at least one electrically conductive film layer on the plurality of grid lines may also include depositing at least one electrically conductive film layer on the substrate.
In various embodiments depositing a first film layer on the substrate and depositing a second film layer on the first film layer may be performed via a process such as chemical vapor deposition, physical vapor deposition, evaporation, sputtering, electroplating, or atomic layer deposition.
In some embodiments, defining a plurality of grid lines in the second layer may include: patterning the second film layer; and etching the second film layer and the first film layer. In some such embodiments, patterning the second film layer may be performed via a process such as lithography, photolithography, electron-beam lithography, block co-polymer lithography, nanosphere lithography, nanoimprint lithography, self-aligned double patterning, or double patterning. In some such embodiments, etching the second film layer and the first film layer may be performed via a process such as wet etching, dry etching, plasma etching, ion bombardment, reactive-ion etching, isotropic etching, and anisotropic etching.
In some embodiments, selectively removing a portion of the first film layer underlying the plurality of third features may include selectively etching the first film layer.
In some embodiments, the method may also include selectively etching at least one of the first film layer and the second film layer to a geometry chosen from a substantially straight line, a curved line, a circle array, a triangle array, and a hexagon array.
In a non-limiting example given by way of illustration only, an illustrative method may be used to fabricate the vacuum electronics device 10. Such an illustrative method includes the following process steps:
As shown in
As shown in
As shown in
As shown in
As shown in
As shown in
In an illustrative, non-limiting implementation of the process described above, a dielectric material such as a wet thermal oxide was used as the first film layer 14, a low-stressed dielectric material such as silicon nitride was used as the second film layer 16, and an i-line resist was used as the image resist 16. Exposure was carried out with an i-line stepper to create the grid pattern. The i-line resist was developed in a Tetramethylammonium Hydroxide (TMAH) developer. Etching of the first film layer 14 and the second film layer 16 was done with an Inductively Coupled Plasma Reactive Ion Etcher (ICP-RIE). Suspending the grid lines 18 was done in a wet chemical etch, which selectively etched the first film layer 14 without compromising the second film layer 16. Finally, in some embodiments a metal film 24 (
Referring additionally to
It will be appreciated that the fabrication process for the vacuum electronics device 300 is similar to the fabrication process for the vacuum electronics device 10, with an additional step to etch/undercut the material of the electrode 12. It will also be appreciated that, after the grid is suspended, a metal film or a multi-layer of metal film stacks 24 (not shown in
Referring additionally to
From the foregoing it will be appreciated that, although specific embodiments have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the disclosure. Furthermore, where an alternative is disclosed for a particular embodiment, this alternative may also apply to other embodiments even if not specifically stated.
One skilled in the art will recognize that the herein described components (e.g., operations), devices, objects, and the discussion accompanying them are used as examples for the sake of conceptual clarity and that various configuration modifications are contemplated. Consequently, as used herein, the specific exemplars set forth and the accompanying discussion are intended to be representative of their more general classes. In general, use of any specific exemplar is intended to be representative of its class, and the non-inclusion of specific components (e.g., operations), devices, and objects should not be taken limiting.
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations are not expressly set forth herein for sake of clarity.
The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely exemplary, and that in fact many other architectures may be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality can be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected”, or “operably coupled,” to each other to achieve the desired functionality, and any two components capable of being so associated can also be viewed as being “operably couplable,” to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components, and/or wirelessly interactable, and/or wirelessly interacting components, and/or logically interacting, and/or logically interactable components.
While particular aspects of the present subject matter described herein have been shown and described, it will be apparent to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from the subject matter described herein and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of the subject matter described herein. It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to claims containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that typically a disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms unless context dictates otherwise. For example, the phrase “A or B” will be typically understood to include the possibilities of “A” or “B” or “A and B.”
With respect to the appended claims, those skilled in the art will appreciate that recited operations therein may generally be performed in any order. Also, although various operational flows are presented in a sequence(s), it should be understood that the various operations may be performed in other orders than those which are illustrated, or may be performed concurrently. Examples of such alternate orderings may include overlapping, interleaved, interrupted, reordered, incremental, preparatory, supplemental, simultaneous, reverse, or other variant orderings, unless context dictates otherwise. Furthermore, terms like “responsive to,” “related to,” or other past-tense adjectives are generally not intended to exclude such variants, unless context dictates otherwise.
Various example embodiments of the disclosed subject matter can be described in view of the following clauses:
While a number of illustrative embodiments and aspects have been illustrated and discussed above, those of skill in the art will recognize certain modifications, permutations, additions, and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions, and sub-combinations as are within their true spirit and scope.
The present application is a continuation of U.S. patent application Ser. No. 16/041,643 filed Jul. 20, 2018, which is related to and claims the benefit of priority of the filing date of U.S. Provisional Patent Application No. 62/535,826 filed Jul. 22, 2017, both of which are herein incorporated by reference in their entirety.
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| Child | 16514361 | US |
