In solid-state physics, the work function defines the minimum energy required to remove an electron from a solid to a point immediately outside the surface of the solid. In other words, the work function is the amount of energy needed to move the electron from the highest filled Fermi level into the vacuum immediately outside the solid surface. This amount of energy is typically measured in electron volts, and as opposed to being a property of a bulk material itself, the work function is a characteristic property for a surface of the material.
One embodiment relates to a horizontal multilayer junction-edge field emitter (HMJFE). The HMJFE includes a plurality of vertically-stacked multilayer structures, separated by isolation layers, each structure being configured to produce a 2-dimensional electron gas (2DEG) at a junction between two layers within the structure. The HMJFE includes an exposed surface intersecting the 2DEG of each of the plurality of vertically-stacked multilayer structures to form a plurality of effectively one-dimensional horizontal line sources of electron emission.
Another embodiment relates to a HMJFE. The HMJFE includes a first substrate including a first surface. The HMJFE includes a first plurality of vertically-stacked multilayer structures. The first plurality of vertically-stacked multilayer structures are separated by isolation layers, configured to produce a first 2DEG at a junction between two layers within the structure, and attached to the first surface. The HMJFE includes a second plurality of vertically-stacked multilayer structures. The second plurality of vertically-stacked multilayer structures are separated by isolation layers, configured to produce a second 2DEG at a junction between two layers within the structure, and attached to the first surface. The HMJFE includes a first anode attached to the first surface of the first substrate and configured to collect electrons emitted by the first 2DEG.
Another embodiment relates to a method of fabricating a HMJFE. The method includes disposing a first multilayer structure on a first substrate including a first surface, the first multilayer structure being configured to produce a first 2DEG at a junction between two layers within the first multilayer structure. The method includes disposing a first isolation layer on the first multilayer structure. The method includes disposing a second multilayer structure on the first isolation layer, the second multilayer structure configured to produce a second 2DEG at a junction between two layers within the second multilayer structure. The method includes disposing a first anode on the first surface of the first substrate, the first anode configured to collect electrons emitted by the first 2DEG.
Another embodiment relates to a vertical-emitting junction-edge field emitter structure (VEJFE). The VEJFE includes a plurality of vertical structures formed on a substrate, each vertical structure including at least two vertically oriented layers. Each vertical structure is configured to produce a 2DEG at a junction between two vertically-oriented layers of the vertical structure. Each vertical structure is truncated to expose an edge of the 2DEG.
Another embodiment relates to a method of fabricating a VEFJE structure. The method includes forming a plurality of vertical structures on a substrate, wherein forming each vertical structure includes positioning at least two vertically oriented layers adjacent to one another to create a junction between the two vertically oriented layers. The method includes truncating the plurality of vertical structures on an opposite side of the plurality of vertical structures from the substrate to expose an edge of the junction, the junction configured to produce a 2DEG.
The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, 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 scope of the subject matter presented here.
Referring generally to the figures, various embodiments for microstructured surfaces having low work functions are shown and described. As discussed by Srisonphan, Jung, and Kim in their article, Metal-oxide-semiconductor field-effect transistor with a vacuum channel, Nature Nanotechnology, vol. 7, 504-508 (2012), electrons can be emitted from the 1-dimensional edge of a 2-dimensional electron gas with a low work function. For example, electrons may be emitted from an edge formed by the interfacial layer of an oxide or metal on a semiconductor. According to the disclosure herein, such emission may be achieved over a wide area by microstructuring the interfacial layer so that there are many edges in order to provide multiple emissions. As an example, lithographic masking techniques may be used when forming such an interface to create interfacial dots, holes, or lines at the surface to provide multiple electron emissions with low work functions.
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In some embodiments, at least two of the non-insulating layers may be biased relative to each other by an external voltage source 120, forming either a biased junction or a field effect device. In some embodiments, one or more layers may be atomically thin, e.g., a layer of graphene or molybdenum disulfide. In some embodiments, the 2DEG is confined to such an atomically thin layer. In other embodiments, a 2DEG may be formed between two layers comprising different insulators (e.g., ZnO/ZnMgO); in such embodiments, an electrical contact or tunnel junction may be provided to introduce electrons into, or remove electrons from, the 2DEG. Other configurations, without limitation, may be used to create a 2DEG.
The emitting structure 101 is truncated at surface 116, exposing an effectively one-dimensional edge 110 of the generally planar 2DEG 108. Such an exposed edge 110 of a 2DEG can emit electrons with a low work function compared to emission of electrons from a conventional material surface.
In some embodiments, structure 100 further includes an anode 112 spaced from the surface 116 and configured to capture electrons emitted from one-dimensional edge 110. The anode 112 may be configured to be a constant distance from at least a portion of edge 110, such that the electric field near edge 110 is uniform along edge 110. The anode 112 may be biased relative to the 2DEG to increase or decrease field emission of electrons from the one-dimensional edge 110.
In some embodiments, structure 100 may further include one or more grids located between the edge 110 and the anode 112. These grids may be biased to alter the electric field distribution between edge 110 and anode 112, and thereby control the rate and trajectory of electrons emitted from edge 110.
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In some embodiments, the surface 116 may be formed by depositing materials forming multilevel emitter structure 131 over a limited area of substrate 122, e.g., by deposition through a mask. In other embodiments, the surface 116 may be formed by depositing the materials forming emitter structure 131 over a larger area of substrate 122, and then removing material, e.g. by an etching or milling process, to expose surface 116. For example, a vertically-sided trench in a multilayer-coated area may be formed via focused ion beam milling (e.g., a trench or channel having a cross-section of 0.25×0.25 μm2, 0.5×0.5 μm2, 1×1 μm2, etc.).
The surface 116 may be straight or curved as viewed perpendicular to the substrate, and in some embodiments may form one or both walls of one or more channels or trenches through the deposited layers 102-106. In other embodiments the surface 116 may form the inner wall of cylindrical or conical holes in layers 102-106, or the outer wall of cylindrical or conical posts, or other geometric configurations.
A common anode 112 may be used to collect electrons emitted from edges 110A and 110B. In some embodiments a common voltage may be present between the anode 112 and all emitting structures 101A, 101B, etc.; in other embodiments the voltages between the anode 112 and each emitting structure may be separately regulated. In such embodiments, the separate voltage regulation may be used to maintain a desired current or current density from each emitting structure despite variation in separation between the emitting structures and the anode 112; e.g., due to tilting of or irregularities in surface 116 or the surface of anode 112.
In some embodiments, one or more grids may be located between the emitting structure 131 and anode 112.
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Structure 200 includes anode 216 provided on substrate 212. In some embodiments, anode 216 is provided on substrate 212. For example, anode 216 may be provided on substrate 212, after which multilayer emitters 204, 208 are deposited on substrate 212 (e.g., by deposition through a mask); anode 216 may also be deposited on substrate 212 after material has been removed to form multilayer emitters 204, 208 and expose surfaces 206, 210.
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If additional multilayer structures are not required, then at 312, edges of 2DEGs of the HMJFE structure are exposed. In some embodiments, material is removed from the HMJFE, such as by an etching or milling process, to expose the edges. In some embodiments, the multi-layer structures were deposited through a mask over a limited area of the substrate. In various embodiments, the order of providing multilayer structures or layers thereof, along with exposing edges of 2DEGs of the HMJFE structure, may be modified as desired.
Vertical-emitting structures (e.g., structures emitting electrons in a direction perpendicular to a substrate) having a low work function may also be formed. Referring to
Structures 400a, 400b, and 400c may be deposited on a substrate 408. The substrate 408 may be similar to the substrates 122, 212, 252, 282, or 284 discussed above with respect to
In some embodiments, the anode or grid is provided as a conducting layer which is exposed near the exposed emitting edges of the structures 400a, 400b, 400c. For example, a grid may extend to the truncated end of the vertical structure and be exposed by truncation in the same plane as the exposed emitted edge. Differential etching may also be used to expose the grid at a greater distance from the substrate 408 (e.g., further “above” the substrate 408) than the exposed emitting edge. The grid may be provided on the outside of one or more of the structures 400a, 400b, and 400c, and may act as a gate for electron emission. In some embodiments, the anode or grid is connected through a biasing layer in the substrate 408 that allows for biasing the anode or grid.
In one embodiment, structure 400a is a cylindrical structure including doped semiconductor 402a. In another embodiment, structure 400b is a pyramid-shaped structure including doped semiconductor 402b. In another embodiment, structure 400c is a conical structure including doped semiconductor 402c. An insulating layer can be deposited over the doped semiconductor layer. For example, insulators 404a, 404b, and 404c, may each be formed over doped semiconductors 402a, 402b, and 402c, respectively. A conducting layer may then be deposited over at least part of the insulating layer. For example, conductors 406a, 406b, and 406c, may each be formed at least partially over insulators 404a, 404b, and 404c, respectively. In various embodiments, the selection of doped semiconductor layers, conducting layers, and/or insulator layers may be interchanged for each of the structures 400a, 400b, 400c. In some embodiments, one or more of the vertical structures are provided in a ridge shape (e.g., having a cross-section similar to structure 400b but extending in a direction normal to the plane of
In order to form effectively 1-dimensional electron emitters, the tops of the vertical structures (e.g., 400a, 400b, and 400c) may be exposed. For example, the tops of structures 400a, 400b, and 400c may be polished, ground, or otherwise machined to expose the edges of the doped semiconductor/insulator junctions within the structures. As a result, and depending on the shape of base structure (e.g., cylinder, pyramid, cone, etc.), a circular, linear, oval, etc., shaped emitting area with a low work function can be formed on the top of the vertical structure. A plurality of vertical structures (e.g., structures 400a-c) may then be arranged in an array. In some embodiments, an anode or electrode grid is arranged over the tops of the vertical structures. The grid can control the emission of electrons from the exposed edges of the doped semiconductor/insulator junctions of the structures. The anodes can capture and, in some embodiments, control the emission of electrons from the exposed edges of the doped semiconductor/insulator junctions of the structures.
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At 506, a junction is created between two vertically oriented layers. A 2DEG is produced at the junction. At 508, a determination is made as to whether additional vertical structures are required. If additional vertical structures are required, then the steps 504-506 may be repeated as necessary. If additional vertical structures are not required, then at 510, the vertical structures are truncated on an opposite side of the vertical structures to expose an edge of the junction of each vertical structure. In some embodiments, vertical structures are individually truncated before additional vertical structures are provided. As such, the tops of one or more vertical structures are removed to expose each edge of each junction of each vertical structure. For example, the tops of the vertical structures may be polished, ground, or otherwise machined to expose the edges. In some embodiments, an electrode structure is provided as an anode or electrode grid and arranged over the tops of the vertical structures, and the anode or electrode grid is configured to control the emission of electrons from the exposed edges of the structures. In some embodiments, an electrode structure is formed as part of one or more individual vertical structures.
The construction and arrangement of the systems and methods as shown in the various embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.). For example, the position of elements may be reversed or otherwise varied and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present disclosure. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions and arrangement of the embodiments without departing from the scope of the present disclosure.
The present disclosure contemplates methods, systems and program products on any machine-readable media for accomplishing various operations. The embodiments of the present disclosure may be implemented or modeled using existing computer processors, or by a special purpose computer processor for an appropriate system, incorporated for this or another purpose, or by a hardwired system. Embodiments within the scope of the present disclosure include program products comprising machine-readable media for carrying or having machine-executable instructions or data structures stored thereon. Such machine-readable media can be any available media that can be accessed by a general purpose or special purpose computer or other machine with a processor. By way of example, such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer or other machine with a processor. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a machine, the machine properly views the connection as a machine-readable medium. Thus, any such connection is properly termed a machine-readable medium. Combinations of the above are also included within the scope of machine-readable media. Machine-executable instructions include, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing machines to perform a certain function or group of functions.
Although the figures may show a specific order of method steps, the order of the steps may differ from what is depicted. Also two or more steps may be performed concurrently or with partial concurrence. All such variations are within the scope of the disclosure. Likewise, software implementations could be accomplished with standard programming techniques with rule-based logic and other logic to accomplish the various connection steps, processing steps, comparison steps and decision steps.
While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope being indicated by the following claims.
The present application is a continuation of application Ser. No. 15/396,701, filed Jan. 2, 2017, which is a continuation of application Ser. No. 15/013,699, filed Feb. 2, 2016, both of which are incorporated herein by reference in their entireties.
Number | Date | Country | |
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Parent | 15396701 | Jan 2017 | US |
Child | 15783394 | US | |
Parent | 15013699 | Feb 2016 | US |
Child | 15396701 | US |