TECHNICAL FIELD
The present disclosure relates to vacuum electronic devices.
BACKGROUND
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.
SUMMARY
Disclosed embodiments include vacuum electronics devices and methods of fabricating a vacuum electronics device.
In a non-limiting embodiment, a vacuum electronic device includes an electrode that defines discrete support structures therein. A first film layer is disposed on the electrode about a periphery of the electrode and on the support structures. A second film layer is disposed on the first film layer. The second film layer includes electrically conductive grid lines patterned therein that are supported by and suspended between the support structures.
In another non-limiting embodiment, a vacuum electronic device includes an electrode that defines discrete support structures therein. A film layer is disposed on the electrode about a periphery of the electrode and on the support structures. The film layer includes electrically conductive grid lines patterned therein that are supported by and suspended between the support structures.
In another non-limiting embodiment, a method of fabricating a vacuum electronic device includes: providing an electrically conductive substrate; forming a plurality of discrete support structures in the substrate; depositing a first film layer on the substrate and the plurality of support structures; depositing a second film layer on the first film layer; defining a plurality of grid lines in the second film layer; and selectively removing a portion of the first film layer such that the first film layer supports the plurality of grid lines at a periphery of the substrate and on the support structures.
In another non-limiting embodiment, a method of fabricating a vacuum electronic device includes: providing an electrically conductive substrate; forming a plurality of discrete support structures in the substrate; depositing a film layer on the substrate and the plurality of support structures; defining a plurality of grid lines in the film layer such that the plurality of grid lines are supported at a periphery of the substrate and on the support structures.
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.
BRIEF DESCRIPTION OF THE FIGURES
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.
FIG. 1A is a cross-sectional end plan view in partial schematic form of an illustrative tunable suspended grid structure.
FIG. 1B is a top plan view of the tunable suspended grid structure of FIG. 1A.
FIG. 1C is a cross-sectional end plan view in partial schematic form of another illustrative tunable suspended grid structure.
FIG. 1D is a top plan view of the tunable suspended grid structure of FIG. 1C.
FIG. 1E is a cross-sectional end plan view in partial schematic form of another illustrative tunable suspended grid structure.
FIG. 2A is a cross-sectional end plan view in partial schematic form of another illustrative tunable suspended grid structure.
FIG. 2B is a top plan view of the tunable suspended grid structure of FIG. 2A.
FIG. 3A is a cross-sectional end plan view in partial schematic form of another illustrative tunable suspended grid structure.
FIG. 3B is a top plan view of the tunable suspended grid structure of FIG. 3A.
FIGS. 4A-4C are cross-sectional side plan views in partial schematic form of other illustrative tunable suspended grid structures.
FIG. 4D is a top plan view of the tunable suspended grid structures of FIGS. 4A-4C.
FIG. 5A is a cross-sectional end plan view in partial schematic form of another illustrative tunable suspended grid structure.
FIG. 5B is a top plan view of the tunable suspended grid structure of FIG. 5A.
FIGS. 6A-6F illustrate steps in a method of fabricating the device of FIG. 1A.
FIGS. 7A-7F illustrate steps in a method of fabricating the device of FIG. 3A.
FIGS. 8A-8F illustrate steps in a method of fabricating the device of FIGS. 4A-4C.
FIGS. 9A-9N illustrate steps in a method of fabricating the device of FIGS. 1C-1D.
FIGS. 10A-10M illustrate steps in a method of fabricating the device of FIG. 1E.
DETAILED DESCRIPTION
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 FIGS. 1A and 1B, in various embodiments an illustrative vacuum electronics device 10 includes an electrode 12. A first film layer 14 is disposed on the electrode 12 about a periphery of the electrode 12. A second film layer 16 is disposed on the first film layer 14. The second film layer 16 includes electrically conductive grid lines 18 patterned therein that are supported only at the periphery of the electrode 12 by the first film layer 14. As such, it will be appreciated that in various embodiments the suspended grid lines 18 are fabricated along with—not separately from—the electrode 12.
It will be appreciated that, as shown in FIGS. 1A and 1B, in some embodiments, if desired, optional grid lines 20 may be patterned in the second film layer 16 and supported on supports 22 defined in the first film layer 14 as desired for a particular application. It is emphasized that such grid lines 20 and supports 22 are not required and are optional. It is also emphasized 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.
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 FIG. 1B) through the first film layer 14 may be provided, if desired, as an optional feature for electrically accessing the electrode 12 from the top.
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 FIGS. 1A and 1B, in various embodiments the second film layer 16 is partially supported by the first film layer 14 at the periphery of the electrode 12 and the grid lines 18 patterned in the second film layer 16 are suspended over the electrode 12. For purposes of clarity, only two grid lines 18 are shown in FIGS. 1A and 1B. In this non-limiting embodiment, a film stack is initially deposited on top of the electrode 12. The stack is patterned and can be etched. One or more grids sits atop the stack, and could be suspended over the electrode 12. In the non-limiting example shown in FIG. 1A, the first film layer 14 helps support part of the second film layer 16 (specifically, the ends of the grid lines 18), such that a majority of the grid lines 18 can be suspended over the electrode 12.
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 FIGS. 1A and 1B can support an electric field without causing electrical breakdown. As such, it will be appreciated that the non-limiting embodiment of FIGS. 1A and 1B may entail a gap between the grid lines 18 (and, when optionally provided as desired, the optional grid lines 20) and the electrode 12 on the order of around a few hundred nanometers to a few micrometers or so. In some embodiments, if desired, gap distance between the electrode 12 and portions of the grid lines 18 that are not supported by the first film layer 14 are variable responsive to application of an electrostatic force between the electrode 12 and the grid lines 18. The electrostatic force may be applied to the grid electrodes (that is, the grid lines 18) as part of the normal biasing of the grid electrodes with DC voltages or by modulating the normal electrode DC bias with an additional driving voltage to cause movement in the suspended grid lines 18. By way of example only, amplitude modulation can be used to adjust electrostatic forces to control fine motion.
Referring additionally to FIGS. 1C-1E, in various other embodiments the grid lines 18 also may be suspended between laterally spaced-apart support structures 23. Given by way of non-limiting example, an illustrative vacuum electronics device 10 includes the electrode 12. The electrode 12 defines support structures 23 therein. The first film layer 14 is disposed on the electrode 12 about a periphery of the electrode 12 and on the support structures 23. The second film layer 16 is disposed on the first film layer 14. The second film layer 16 includes the electrically conductive grid lines 18 patterned therein that are also supported by and suspended between the support structures 23. The support structures 23 are shown as pillars in FIGS. 1C-1E, but other shapes may be used. The support structures 23 are shown as a set of equally-spaced columns, but other spacing is possible. It will be appreciated that the support structures 23 are discrete and, as such, are not continuous. In some embodiments, the first film layer 14 electrically isolates the electrode 12 from the grid lines 18. In some other embodiments and as shown in FIG. 1E, the grid lines 18 need not be electrically isolated from the electrode 12 and the first film layer 14 need not be provided.
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 some embodiments the electrode 12 may be highly doped silicon, highly doped silicon coated with metal, or undoped silicon coated with a metal. Metal coating may include aluminum, chromium, platinum, nickel, tungsten, molybdenum, niobium, tantalum, or other appropriate metals. In various embodiments the electrode 12 may be an anode in a vacuum electronic device, as desired for a particular application. It will be appreciated that a larger opening (shown to the right in FIGS. 1C-1E) through the first film layer 14 may be provided, if desired, as an optional feature for electrically accessing the electrode 12 from the top.
In various embodiments the first film layer 14 may include a dielectric, an electrical insulator, a ceramic, silicon oxide, silicon nitride, and/or aluminum oxide. In various embodiments, the second film layer 16 may include an electrical conductor, such as without limitation, aluminum, chromium, platinum, nickel, tungsten, molybdenum, niobium, tantalum, or other appropriate metals. In some such embodiments, the electrical conductor may be electrically insulated from the electrode 12.
As shown in FIGS. 1C and 1D, in various embodiments the second film layer 16 is fully supported by the first film layer 14 at the periphery of the electrode 12 and on the support structures 23. In such embodiments, the grid lines 18 are suspended over the electrode 12 between the support structures 23. As shown in FIG. 1E, in various embodiments the second film layer 16 is fully supported by the electrode 12 at the periphery of the electrode 12 and on the support structures 23. In such embodiments, the grid lines 18 are suspended over the electrode 12 between the support structures 23. For purposes of clarity, only three grid lines 18 are shown in FIGS. 1C-1E. In such non-limiting embodiments, a film stack is initially deposited on top of the electrode 12. The stack is patterned and can be etched. One or more grids sits atop the stack, and could be suspended over the electrode 12.
In some embodiments, the grid lines 18 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 may have the same shape or geometry. However, the grid lines 18 need not have the same shape or geometry. To that end, in some other embodiments the grid lines have different shapes or geometries.
Regardless of geometry, it will be appreciated that the non-limiting embodiments of FIGS. 1C-1E can help support an electric field without causing electrical breakdown. As such, it will be appreciated that the non-limiting embodiments of FIGS. 1C-1E may entail a gap between the grid lines 18 and the electrode 12 on the order of around a few hundred nanometers to 150 micrometers or so. In some embodiments, if desired, gap distance between the electrode 12 and portions of the grid lines 18 that are not supported by the first film layer 14 are variable responsive to application of an electrostatic force between the electrode 12 and the grid lines 18. The electrostatic force may be applied to the grid electrodes (that is, the grid lines 18) as part of the normal biasing of the grid electrodes with DC voltages or by modulating the normal electrode DC bias with an additional driving voltage to cause movement in the suspended grid lines 18. By way of example only, amplitude modulation can be used to adjust electrostatic forces to control fine motion.
As mentioned above, as shown in FIG. 1E, in some applications the grid lines 18 need not be electrically isolated from the electrode 12 and the first film layer 14 need not be provided. In such embodiments, the grid lines 18 are shorted to the electrode 12. In such embodiments, it will be appreciated that the combination of the grid lines 18 and the electrode 12 can form a structured electrode for purposes of steering electron trajectories or as a mechanism for creating a micro-structured collector surface for enhanced electron absorption.
Referring additionally to FIGS. 2A, 2B, 3A, 3B, 4A-4D, 5A, and 5B, it will be appreciated that various embodiments may entail various configurations as desired for various applications.
While FIGS. 1A, 1B, 2A, 2B, 3A, 3B, 4D, 5A, and 5B show only two suspended grid lines 18 for purposes of clarity, it will be appreciated that any number of grid lines 18 may be provided as desired for a particular application.
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 FIGS. 2A and 2B, in various embodiments a vacuum electronics device 200 includes the electrode 12. The first film layer 14 is disposed on the electrode 12 about a periphery of the electrode 12. The second film layer 16 is disposed on the first film layer 14. The second film layer 16 includes electrically conductive grid lines 18 patterned therein that are supported only at the periphery of the electrode 12 by the first film layer 14. A layer of electrically conductive material 24 is disposed on the grid lines 18. In some such embodiments, a layer of the electrically conductive material 24 may be disposed on the electrode 12. In some embodiments, a layer of the electrically conductive material 24 may be disposed on the optional grid lines 20 (when optionally provided as desired).
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 FIGS. 3A and 3B, various embodiments a vacuum electronics device 300 may have a grid structure that is further separated from the electrode 12 than are typical grid structures. In such embodiments, the vacuum electronics device 300 includes the electrode 12. The first film layer 14 is disposed on the electrode 12 about a periphery of the electrode 12. The second film layer 16 is disposed on the first film layer 14. The second film layer 16 includes electrically conductive grid lines 18 patterned therein that are supported only at the periphery of the electrode 12 by the first film layer 14. In such embodiments, the substrate material underneath the first film layer 14 (that is, the electrode 12) can also be etched during the fabrication process. For instance, following the patterning of the first film layer 14 and the second film layer 16, the substrate underneath (that is, the electrode 12) can be further etched by wet or dry etching methods. As such, it will be appreciated that the vacuum electronics device 300 may have a grid structure that is separated further from the electrode 12 than are typical suspended grid structures. To that end, in various embodiments of the vacuum electronics device 300, the gap between the suspended grid lines 18 and the electrode 12 may be on the order of a few microns or tens of microns.
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 I×V 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 FIGS. 4A-4D, 5A, and 5B, in some embodiments a vacuum electronics device 400 may include a varied vacuum gap distance between the suspended grid lines 18 and the electrode 12. In some embodiments, the vacuum electronics device 400 includes the electrode 12. The first film layer 14 is disposed on the electrode 12 about a periphery of the electrode 12. The second film layer 16 is disposed on the first film layer 14. The second film layer 16 includes the electrically conductive grid lines 18 patterned therein that are supported only at the periphery of the electrode 12 by the first film layer 14, wherein a gap distance between the electrode 12 and the suspended grid lines 18 is varied.
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 FIGS. 4A-4C are given by way of illustration only and not of limitation. To that end, it will be appreciated that the suspended grid lines 18 may have any shape as desired for a particular application. Moreover, it will be appreciated that, as shown in FIG. 5A, different ones of the suspended grid lines 18 may have different vacuum gap distances as desired for a particular application.
Illustrative fabrication techniques for fabrication various embodiments of vacuum electronics devices are discussed below by way of non-limiting examples.
Referring additionally to FIGS. 6A-6F, an illustrative 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 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 FIG. 6A, the substrate 12 is spin coated with an image resist 26.
As shown in FIG. 6B, a sacrificial pattern is disposed on top of the second film layer 16 through standard lithography or exposure methods (for example, electron beam lithography, optical lithography, or imprinting lithography, block copolymer lithography, or the like).
As shown in FIG. 6C, the resist 26 is used as a masking layer.
As shown in FIG. 6D, a selective etch into the second film layer 16 is performed to transfer the sacrificial pattern, and etching in the first film layer 14 is stopped at a predetermined point. As discussed above, the process may over-etch into the electrode 12 as desired for a particular application (See FIG. 3A).
As shown in FIG. 6E, the resist is removed.
As shown in FIG. 6F, the first film layer 14 is selectively (that is, completely) undercut to suspend the pattern in the second film layer 16 (that is, the suspended grid lines 18). In some other embodiments, the first film layer 14 may be selectively (in this case, less-than-completely) undercut to pattern or define the supports 22 in the second film layer 16 for the optional grid lines 20, if desired. In some embodiments, a metal film (or a multi-layer metal film stack) 24 may be deposited on the already-suspended grid structure (not shown in FIGS. 6A-6F). See FIGS. 2A and 2B.
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 (FIGS. 2A and 2B) was deposited on top of the suspended low-stressed dielectric grid to make the grid lines 18 and, when optionally provided, the optional grid lines 20 conductive.
Referring additionally to FIGS. 7A-7F, a method may be used to fabricate the vacuum electronics device 300 with a grid structure that is further separated from the electrode 12 than are typical grid structures. Such an illustrative method includes: providing an electrically conductive substrate 12; depositing a first film layer 14 on the substrate; depositing a second film layer 16 on the first film layer 14; defining a plurality of grid lines 18 in the second film layer 16; selectively removing a portion of the first film layer 14 such that the first film layer 16 supports the plurality of grid lines 18 only at a periphery of the substrate 12; and selectively removing a portion of the substrate 12.
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 FIGS. 7A-7F) may be deposited on the grid lines 18 and, when optionally provided, the optional grid lines 20.
Referring additionally to FIGS. 8A-8F, a method may be used to fabricate the vacuum electronics device 400 with a varied vacuum gap distance between the suspended grid lines 18 and the electrode 12. It will be appreciated that an illustrative fabrication process of suspended patterns with varied gap distance involves patterning of the second film layer 16 to a specific shape (that is, before suspending the grid structure 18 from the electrode 12). To that end, a non-limiting process given by way illustration only includes: coating a stack of the electrode 12 and the first film layer 14 stack with resist 26 (FIG. 8A); exposing the resist 26 (FIG. 8B); developing the resist 26 (FIG. 8C); etching the first film layer 14 (FIG. 8D); removing the resist 26 (FIG. 8E); and depositing the second film layer 16 (FIG. 8F).
Referring now to FIGS. 9A-9N, an illustrative method is provided for fabricating a vacuum electronics device, such as the device 10 shown in FIGS. 1C and 1D. By way of overview, in various embodiments the method includes: providing an electrically conductive substrate; forming a plurality of discrete support structures in the substrate; depositing a first film layer on the substrate and the plurality of support structures; depositing a second film layer on the first film layer; defining a plurality of grid lines in the second film layer; and selectively removing a portion of the first film layer such that the first film layer supports the plurality of grid lines at a periphery of the substrate and on the support structures.
Details are provided below by way of non-limiting examples.
As shown in FIG. 9A, an electrically-conductive substrate 12 is provided. In some embodiments, the substrate 12 may include a highly-doped silicon substrate.
As shown in FIGS. 9B-9E, discrete support structures 23 are formed in the substrate 12. As shown in FIG. 9B, the substrate 12 is spin coated with an image resist 26. As shown in FIG. 9C, a sacrificial pattern is formed in the resist 26 through standard lithography or exposure methods (for example, electron beam lithography, optical lithography, imprinting lithography, block copolymer lithography, or the like). As shown in FIG. 9D, exposed areas of resist 26 are removed to create masking areas for forming the support structures in the bulk doped silicon substrate 12. As shown in FIG. 9E, the support structures 23 are formed in the doped silicon substrate 12 through an etching process such as Deep Reactive Ion Etching (“DRIE”). The mask 26 formed over the substrate 12 does not allow etching of the silicon over these areas, thereby forming the silicon support structures 23 that will support the grid lines. It will be appreciated that, in some embodiments, if desired the substrate 12 may be metallized after the silicon support structures 23 have been formed to increase electrical conductivity and/or alter surface chemistry.
As shown in FIG. 9F, spaces where silicon was removed with DRIE are filled with silicon oxide or other suitable material 28 that can be selectively etched as a sacrificial material that will later be etched away. This sacrificial material may be deposited through one or more deposition processes such as chemical vapor deposition (“CVD”) or sputtering. As shown in FIG. 9G, the uneven surface formed by filling voids (that is, regions where doped silicon has been removed by DRIE to form the support structures 23) in the doped silicon are removed by planarizing the surface using chemical assisted polishing (“CAP”) or other suitable methods. This provides a sacrificial surface for temporarily supporting the first film layer and the second film layer from which the grid lines will be formed.
As shown in FIG. 9H, a first film layer 14 is deposited on the substrate 12 and the support structures 23. It will be appreciated that the first film layer 14 is an electrically insulating film layer used in embodiments in which it is desired to keep the metal grid lines electrically insulated from the electrode 12. The first film layer 14 may include another oxide that is etch resistant to the isotropic oxide etch used to remove the sacrificial silicon oxide material. This insulating first film layer 14 may include other insulating materials, such as by way of example only, silicon nitride, alumina, or other suitable insulator that is not removed by the silicon oxide etch. In various embodiments, depositing the first film layer 14 on the substrate 12 and the support structures 23 may be performed via a process such as chemical vapor deposition, physical vapor deposition, evaporation, sputtering, electroplating, atomic layer deposition, or the like.
As also shown in FIG. 9H, a second film layer 16 is deposited on the first film layer 14. For example, the second film layer 16 is a metal film that is deposited over the first film layer 14. In various embodiments, depositing the second film layer 16 on the first film layer 14 may be performed via a process such as chemical vapor deposition, physical vapor deposition, evaporation, sputtering, electroplating, atomic layer deposition, or the like.
As shown in FIGS. 9I-9L, a plurality of grid lines are defined in the second film layer 16. As shown in FIG. 9I, a resist film 26 is deposited over the metal film 16. As shown in FIG. 9J, the resist 26 is patterned by use of a mask and then exposing the resist 26 (as is done in standard lithography processes). In some such embodiments, patterning the second film layer 16 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. As shown in FIG. 9K, the remaining resist 26 forms a protective pattern used in forming the grid lines in the metal film 16. As shown in FIG. 9L, the exposed metal in the second film layer 16 and the underlying portions of the first film layer 14 is etched away, thereby forming the grid lines 18. In some such embodiments, etching the second film layer 16 and the first film layer 14 may be performed via a process such as wet etching, dry etching, plasma etching, ion bombardment, reactive-ion etching, isotropic etching, or anisotropic etching.
As shown in FIG. 9M, the sacrificial material 28 is removed by isotropic etching using well known methods in the art, thereby leaving behind the suspended grid lines 18 that are supported by and suspended between the support structures 23.
As shown in FIG. 9N, a portion of the first film layer 14 is selectively removed such that the first film layer 14 supports the plurality of grid lines 18 at a periphery of the substrate 12 and on the support structures 23. For example, in some embodiments it may be desirable to undercut the insulating first film layer 14 by etching it with appropriate etching material after the grid lines 18 are etched or before the grid lines 18 are fully etched, such that the grid lines 18 extend past edges of the insulating first film layer 14. This undercutting can be done without destroying the grid lines 18 because etching for various oxides and insulating materials can be material specific. In cases where the undercut is done before the grid lines 18 are fully etched, a second metal etch can be done to finish and clean up the grid lines 18 after the undercut of the insulating first film layer 14 is complete.
Referring additionally to FIGS. 10A-10M, an illustrative method is provided for fabricating a vacuum electronics device, such as the device 10 shown in FIG. 1E. By way of overview, in various embodiments the method includes: providing an electrically conductive substrate; forming a plurality of discrete support structures in the substrate; depositing a film layer on the substrate and the plurality of support structures; defining a plurality of grid lines in the film layer such that the plurality of grid lines are supported at a periphery of the substrate and on the support structures.
It will be appreciated that processes shown in FIG. 10A-10M are the same as those shown in FIGS. 9A-9M except that the film layer 14 is not deposited and defined in the process shown in FIGS. 10-10M. The processes for FIGS. 10A-10G are identical to those for FIGS. 9A-9G and their details need not be repeated for an understanding.
As shown in FIG. 10H, the film layer 16 is deposited on the substrate 12 and the support structures 23. All remaining processes shown in FIGS. 10H-10M are the same as discussed above for FIGS. 9H-9M with the exception that no insulating film layer 14 is present. As such, their details need not be repeated for an understanding.
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:
- 1. A vacuum electronic device comprising:
- an electrode that defines a plurality of discrete support structures therein;
- a first film layer disposed on the electrode about a periphery of the electrode and on the plurality of support structures; and
- a second film layer disposed on the first film layer, the second film layer including electrically conductive grid lines patterned therein that are supported by and suspended between the plurality of support structures.
- 2. The device of Clause 1, wherein the electrode includes an electrically conductive substrate.
- 3. The device of Clause 2, wherein the electrically conductive substrate includes at least one material chosen from chromium, platinum, nickel, tungsten, molybdenum, niobium, and tantalum.
- 4. The device of Clause 2, wherein the electrically conductive substrate includes one of doped silicon, doped silicon coated with metal, and undoped silicon coated with a metal.
- 5. The device of Clause 4, wherein the metal includes a metal chosen from aluminum, chromium, platinum, nickel, tungsten, molybdenum, niobium, and tantalum.
- 6. The device of Clause 1, wherein the plurality of support structures include pillars.
- 7. The device of Clause 1, wherein the plurality of support structures are spaced apart from each other in a spacing manner chosen from equally-spaced and not-equally-spaced.
- 8. The device of Clause 1, wherein the first film layer includes at least one material chosen from a dielectric, an electrical insulator, a ceramic, silicon oxide, silicon nitride, and aluminum oxide
- 9. The device of Clause 1, wherein the second film layer includes an electrical conductor.
- 10. The device of Clause 9, wherein the electrical conductor includes a material chosen from aluminum, chromium, platinum, nickel, tungsten, molybdenum, niobium, and tantalum.
- 11. The device of Clause 1, wherein the plurality of grid lines include at least one geometry chosen from a substantially straight line, a curved line, a circle array, a triangle array, and a hexagon array.
- 12. The device of Clause 1, wherein gap distance between the electrode and portions of the plurality of grid lines that are not supported by the first film layer are variable responsive to application of an electrostatic force between the electrode and the plurality of grid lines.
- 13. A vacuum electronic device comprising:
- an electrode that defines a plurality of discrete support structures therein; and
- a film layer disposed on the electrode about a periphery of the electrode and on the plurality of support structures, the film layer including electrically conductive grid lines patterned therein that are supported by and suspended between the plurality of support structures.
- 14. The device of Clause 13, wherein the electrode includes an electrically conductive substrate.
- 15. The device of Clause 14, wherein the electrically conductive substrate includes at least one material chosen from chromium, platinum, nickel, tungsten, molybdenum, niobium, and tantalum.
- 16. The device of Clause 14, wherein the electrically conductive substrate includes one of doped silicon, doped silicon coated with metal, and undoped silicon coated with a metal.
- 17. The device of Clause 16, wherein the metal includes a metal chosen from aluminum, chromium, platinum, nickel, tungsten, molybdenum, niobium, and tantalum.
- 18. The device of Clause 13, wherein the plurality of support structures include pillars.
- 19. The device of Clause 13, wherein the plurality of support structures are spaced apart from each other in a spacing manner chosen from equally-spaced and not-equally-spaced.
- 20. The device of Clause 13, wherein the film layer includes an electrical conductor.
- 21. The device of Clause 20, wherein the electrical conductor includes a material chosen from aluminum, chromium, platinum, nickel, tungsten, molybdenum, niobium, and tantalum.
- 22. The device of Clause 13, wherein the plurality of grid lines include at least one geometry chosen from a substantially straight line, a curved line, a circle array, a triangle array, and a hexagon array.
- 23. The device of Clause 13, wherein gap distance between the electrode and portions of the plurality of grid lines that are not supported by the plurality of support structures are variable responsive to application of an electrostatic force between the electrode and the plurality of grid lines.
- 24. A method of fabricating a vacuum electronic device, the method comprising:
- providing an electrically conductive substrate;
- forming a plurality of discrete support structures in the substrate;
- depositing a first film layer on the substrate and the plurality of support structures;
- depositing a second film layer on the first film layer;
- defining a plurality of grid lines in the second film layer; and
- selectively removing a portion of the first film layer such that the first film layer supports the plurality of grid lines at a periphery of the substrate and on the support structures.
- 25. The method of Clause 24, further comprising metallizing the substrate after the support structures have been formed.
- 26. The method of Clause 24, further comprising providing a sacrificial surface for temporarily supporting the first film layer and the second film layer.
- 27. The method of Clause 24, wherein at least one of depositing the first film layer on the substrate and the plurality of support structures and depositing the second film layer on the first film layer is performed via a process including at least one of chemical vapor deposition, physical vapor deposition, evaporation, sputtering, electroplating, and atomic layer deposition.
- 28. The method of Clause 24, wherein defining a plurality of grid lines in the second film layer includes:
- patterning the second film layer; and
- etching the second film layer and the first film layer.
- 29. The method of Clause 28, wherein patterning the second film layer is performed via a process chosen from lithography, photolithography, electron-beam lithography, block co-polymer lithography, nanosphere lithography, nanoimprint lithography, self-aligned double patterning, and double patterning.
- 30. The method of Clause 28, wherein etching the second film layer and the first film layer is performed via a process chosen from wet etching, dry etching, plasma etching, ion bombardment, reactive-ion etching, isotropic etching, and anisotropic etching.
- 31. The method of Clause 26, further comprising removing the sacrificial material.
- 32. The method of Clause 26, wherein selectively removing a portion of the first film layer such that the first film layer supports the plurality of grid lines at a periphery of the substrate and on the support structures includes selectively removing a portion of the first film layer such that the first film layer supports the plurality of grid lines at a periphery of the substrate and on the support structures and such that the plurality of grid lines extend past edges of the first film layer.
- 33. A method of fabricating a vacuum electronic device, the method comprising:
- providing an electrically conductive substrate;
- forming a plurality of discrete support structures in the substrate;
- depositing a film layer on the substrate and the plurality of support structures; and
- defining a plurality of grid lines in the film layer such that the plurality of grid lines are supported at a periphery of the substrate and on the support structures.
- 34. The method of Clause 33, further comprising metallizing the substrate after the support structures have been formed.
- 35. The method of Clause 33, further comprising providing a sacrificial surface for temporarily supporting the film layer.
- 36. The method of Clause 33, wherein depositing the film layer on the substrate and the plurality of support structures is performed via a process including at least one of chemical vapor deposition, physical vapor deposition, evaporation, sputtering, electroplating, and atomic layer deposition.
- 37. The method of Clause 33, wherein defining a plurality of grid lines in the film layer includes:
- patterning the film layer; and
- etching the film layer.
- 38. The method of Clause 37, wherein patterning the film layer is performed via a process chosen from lithography, photolithography, electron-beam lithography, block co-polymer lithography, nanosphere lithography, nanoimprint lithography, self-aligned double patterning, and double patterning.
- 39. The method of Clause 37, wherein etching the film layer is performed via a process chosen from wet etching, dry etching, plasma etching, ion bombardment, reactive-ion etching, isotropic etching, and anisotropic etching.
- 40. The method of Clause 33, further comprising removing the sacrificial material.
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.
Patent Application
20200075286
