This description relates to the fabrication of high aspect ratio tall free standing posts using carbon-nanotube (CNT) templated microfabrication with subsequent plasma etching.
In a general aspect, an apparatus can include a substrate and a post disposed on the substrate. The post can include a plurality of nanotubes and extend substantially vertically from the substrate. The post can have an aspect ratio of a height of the post to a diameter of the post of greater than or equal to 25:1.
Implementations can include one more of the following features. For example, the diameter of the post can be in a range of 5 micrometers (μm) to 100 μm. The post can be substantially cylindrical. The height of the post can be greater than or equal to 1 millimeter (mm).
The plurality of nanotubes can include a plurality of carbon nanotubes (CNTs). At least a portion of the plurality of nanotubes of the post can be infiltrated with carbon (C). At least a portion of the plurality of nanotubes of the post can be infiltrated with at least one of silicon (Si) and silicon nitride (SiN). At least a portion of the plurality of nanotubes of the post can be plated with a metal.
The post can be a first post and the apparatus can include a second post disposed on the substrate and laterally spaced from the first post, the second post including a plurality of nanotubes and extending substantially vertically from the substrate, the second post having an aspect ratio of a height of the second post to a diameter of the second post of greater than or equal to 25:1.
The substrate can include a silicon (Si) wafer having an aluminum oxide (Al2O3) layer disposed thereon. The substrate can include a glass substrate or a metal substrate.
In another general aspect, a method can include providing a substrate and forming a patterned catalyst layer on the substrate. The patterned catalyst layer can define a template for carbon nanotube growth. The template can define a pattern for formation of a first carbon nanotube post, a second carbon nanotube post and a supporting structure disposed between the first carbon nanotube post and the second carbon nanotube post. The method can further include growing carbon nanotubes on the patterned catalyst layer to form the first carbon nanotube post, the second carbon nanotube post and the supporting structure. The first carbon nanotube post and the second carbon nanotube post can each have an aspect ratio of a height to a diameter of greater than or equal to 25:1. The supporting structure can have an aspect ratio of a height to a width of greater than or equal to 200:1. The method can further include removing the supporting structure, such that each of the first carbon nanotube post and the second carbon nanotube post are freestanding and extend substantially vertically from the substrate.
Implementations can include one more of the following features. For example, prior to removal of the supporting structure, a height of the first carbon nanotube post, a height of the second carbon nanotube post and a height of the supporting structure can be substantially a same height. The same height can be greater than or equal to 1 millimeter (mm).
The method can include infiltrating the first carbon nanotube post and the second carbon nanotube post with carbon (C). The method can include infiltrating the first carbon nanotube post and the second carbon nanotube post with at least one of silicon (Si) and silicon nitride (SiN). The method can include plating the first carbon nanotube post and the second carbon nanotube post with a metal.
Removing the supporting structure can include performing a non-directional plasma etch to remove an upper portion of the supporting structure, such that a lower portion of the supporting structure remains, the lower portion of the supporting structure being disposed on the substrate; infiltrating the first carbon nanotube post, the second carbon nanotube post and the lower portion of the supporting structure with carbon (C); and performing a directional plasma etch to remove the lower portion of the supporting structure.
The substrate can include a Si wafer having an Al2O3 layer disposed thereon. The patterned catalyst layer can be formed on the Al2O3 layer. Forming the patterned catalyst layer can include forming, using photolithography, a patterned iron (Fe) layer, the Al2O3 layer preventing diffusion of the patterned Fe layer into the Si wafer. The substrate can include a metal substrate or a glass substrate.
In another general aspect, an apparatus can include a substrate and an array of carbon nanotube posts disposed on the substrate. Each carbon nanotube post of the array of carbon nanotube posts can include a plurality of nanotubes and can extend substantially vertically from the substrate. Each carbon nanotube post of the array of carbon nanotube posts can have an aspect ratio of a height of the post to a diameter of the post of greater than or equal to 25:1.
Like reference symbols in the various drawings may indicate like and/or similar elements.
The fabrication of high aspect ratio tall free standing posts (e.g., post arrays) can be produced using Carbon Nanotube (CNT) templated microfabrication with a sacrificial supporting structure. Carbon-nanotube-templated microfabrication (CNT-M) can be used to form precise high aspect ratio features in, for example, interconnected geometries. The feature of fabrication of isolated posts can be challenging, however. In some implementations, a CNT shape, when grown in, for example, forests (e.g., a dense collection of CNT structures), can be used to produce, for example, three dimensional (3D) complex structures. In some implementations, if those structures are relatively tall and relatively thin (have a high aspect ratio), the structures can lose at least some aspects of the important vertical nature of the growth (e.g., bend, break, tip, etc.). The implementations described herein can enable the retention of the vertical structure for very tall features. In some implementations, CNT members (e.g., needles) of, for example, ˜10-40 micrometers (μm) in diameter can be grown to, for example, millimeter heights. In implementations, such CNT members can have a range of spacing between them (e.g., lateral spacing on the substrate), such as 100-400 μm center-to-center spacing. Depending on the implementation (and the particular CNT structures being produced) the spacing could be less than 100 μm center-to-center or greater than 400 μm center-to-center.
A process is described herein that includes fabrication of CNT posts connected by supporting structures using, for example, CNT-M techniques followed by plasma etching (e.g., oxygen plasma etching) to remove the sacrificial supporting structures. The fabrication of posts can be achieved with diameters from, for example, 10-40 um and heights up to, for example, 1.3 mm using sacrificial supporting structures of, for example, 1-5 um in width, with spacing such as those discussed above. With the CNT template, isolated free standing posts from a variety of materials can be made. For example, silicon or silicon nitride posts can be fabricated by infiltration with silicon or silicon nitride. In some implementations, the creation of hybrid carbon/metal (copper, nickel) posts can also be realized through pulse electroplating.
Low aspect ratio carbon nanotube (CNT) posts (also can be referred to as members) can be produced using direct growth techniques. However, as noted above, direct growth of high aspect ratio CNT posts can be challenging, or impossible to achieve. High aspect ratio CNT posts formed using direct growth techniques can bend in random directions (break, tip, etc.) as they grow tall depending on the aspect ratio. Examples of such occurrences are shown in
In some implementations, straight (substantially straight, vertical, substantially vertical, and so forth) millimeter-tall CNT posts (e.g., CNT posts 110) with diameters of, for example, 10-40 μm or 5-100 μm can be grown using supporting CNT structures (e.g. supporting structures 120). For instance, CNT posts can be grown where a vertical line through a center of a cross-section of one end of the CNT post would intersect a cross-section take at an opposite end of the CNT post. While the CNT posts 110 are illustrated as being cylindrical in cross-section, in other implementations CNT posts (or other tall, vertical CNT structures) having other cross-sectional geometries (e.g., square, triangle, hexagon, or other shape) can be produced using the approaches described herein. Further, the final geometries of a given CNT structure can affected by the removal (e.g., etching) of associated supporting structures.
In some implementations, such free standing mm-tall CNT posts can be produced by removing the sacrificial supporting CNT structures by, for example, a combination of non-directional plasma etching, carbon infiltration, and followed directional plasma etching, such as illustrated by and described with respect to
In some implementations, a sacrificial structure or connector, such as the supporting structures 120, can be used to link pattern features (CNT posts) together during growth of a CNT pattern. In some implementations, the linked features can, during growth, be constrained by their connection to remain in a vertical (substantially vertical) orientation. In some implementations, this sacrificial feature can then be removed, leaving the desired feature(s), such as CNT posts, behind.
In some implementations, the supporting structure features can be sufficiently robust to constrain the growth (supporting structure features with widths as small as 1 um can be sufficient) and can be removed without damaging the final intended structure.
In some implementations, straight millimeter-tall CNT post arrays, such as shown in
In some implementations, such nanotube posts can be nanotube posts that include nanotubes including materials other than carbon. For instance, a layer of silicon could be deposited on a CNT post (or array of CNT posts). After depositing the silicon layer, the CNT post(s) could be oxidized to convert the deposited silicon to silicon dioxide (SiO2 or silica) and also convert the carbon of the CNTs to carbon dioxide (which can be vent out of an oxidation furnace), resulting in a nanotube post (or posts) that include silica nanotubes.
As shown in
As shown in
After CNT growth to form the CNT posts 110 and the interconnecting supporting structures 120, the supporting structures 120 can be removed, as shown in
In some implementations, removal of the sacrificial structure can be performed by plasma etching or some other form of removal. For example,
In
As shown in
In the method 700, after the etch 710, carbon infiltration 720 can be performed, which can link the CNTs together with carbon 724 to strengthen the final structures against tipping, breaking, etc. During carbon infiltration 720, the CNT structures 712 can be heated 722 to various temperatures (e.g., in a range 850-900 C). Further, carbon infiltration 720 can be performed using different reaction gas flow rates (e.g., with a gas flow of C2H2 and H2) and different infiltration times. In some implementations, an amount carbon 724 that is infiltrated in the CNT structures can affect the amount of time needed to remove the carbon infiltrated supporting structures 120. In an example implementation, carbon infiltration 720 can be performed for 1.5 minutes at 900° C. or lower.
As shown in
In some implementations, the combination of a non-directional etch targeting the top down of supporting structures and a directional etch targeting the bottom up of supporting structure can be used on a wide variety of feature geometries.
In some implementations, a structure (e.g., a final structure) can be etched by the processes of the method 700, which can cause a reduction in dimensions of the final structure. Such reductions in dimension can be accounted for in an initial design of a desired (final) CNT structure (e.g., CNT post).
In an implementation, a CNT post array (such as those illustrated herein) can be used as a neural probe, for example, to detect dopamine. Such an implementation can aid in the production of medical implants used to improve the quality of life for people suffering from health conditions such as heart disease and neurological disorders. Such approaches could also be implemented using a single CNT post.
As noted above, the results shown in
Further implementations are summarized in the following examples:
An apparatus comprising: a substrate; and a post disposed on the substrate, the post including a plurality of nanotubes and extending substantially vertically from the substrate, the post having an aspect ratio of a height of the post to a diameter of the post of greater than or equal to 25:1.
The apparatus of example 1, wherein the diameter of the post is in a range of 5 micrometers (μm) to 100 μm.
The apparatus of example 1 or 2, wherein the post is substantially cylindrical.
The apparatus of one of examples 1 to 3, wherein the height of the post is greater than or equal to 1 millimeter (mm).
The apparatus of one of examples 1 to 4, wherein the plurality of nanotubes includes a plurality of carbon nanotubes (CNTs).
The apparatus of one of examples 1 to 5, wherein at least a portion of the plurality of nanotubes of the post are infiltrated with carbon (C).
The apparatus of one of examples 1 to 6, wherein at least a portion of the plurality of nanotubes of the post are infiltrated with at least one of silicon (Si) and silicon nitride (SiN).
The apparatus of one of examples 1 to 7, wherein at least a portion of the plurality of nanotubes of the post are plated with a metal.
The apparatus of one of examples 1 to 8, wherein the post is a first post, the apparatus further comprising a second post disposed on the substrate and laterally spaced from the first post, the second post including a plurality of nanotubes and extending substantially vertically from the substrate, the second post having an aspect ratio of a height of the second post to a diameter of the second post of greater than or equal to 25:1.
The apparatus of one of examples 1 to 9, wherein the substrate includes a silicon (Si) wafer having an aluminum oxide (Al2O3) layer disposed thereon.
A method comprising: providing a substrate; forming a patterned catalyst layer on the substrate, the patterned catalyst layer defining a template for carbon nanotube growth, the template defining a pattern for formation of: a first carbon nanotube post; a second carbon nanotube post; and a supporting structure disposed between the first carbon nanotube post and the second carbon nanotube post. The method further comprising growing carbon nanotubes on the patterned catalyst layer to form the first carbon nanotube post, the second carbon nanotube post and the supporting structure, the first carbon nanotube post and the second carbon nanotube post each having an aspect ratio of a height to a diameter of greater than or equal to 25:1, the supporting structure having an aspect ratio of a height to a width of greater than or equal to 200:1; and removing the supporting structure, such that each of the first carbon nanotube post and the second carbon nanotube post are freestanding and extend substantially vertically from the substrate.
The method of example 11, wherein, prior to removal of the supporting structure, a height of the first carbon nanotube post, a height of the second carbon nanotube post and a height of the supporting structure are substantially a same height.
The method of example 12, wherein the same height is greater than or equal to 1 millimeter (mm).
The method of one of examples 11 to 13, further comprising infiltrating the first carbon nanotube post and the second carbon nanotube post with carbon (C).
The method of one of examples 11 to 14, further comprising infiltrating the first carbon nanotube post and the second carbon nanotube post with at least one of silicon (Si) and silicon nitride (SiN).
The method of one of examples 11 to 15, further comprising plating the first carbon nanotube post and the second carbon nanotube post with a metal.
The method of one of examples 11 to 16, wherein removing the supporting structure includes: performing a non-directional plasma etch to remove an upper portion of the support structure, such that a lower portion of the support structure remains, the lower portion of the support structure being disposed on the substrate; infiltrating the first carbon nanotube post, the second carbon nanotube post and the lower portion of the support structure with carbon (C); and performing a directional plasma etch to remove the lower portion of the support structure.
The method of one of examples 11 to 18, wherein the substrate includes a silicon (Si) wafer having an aluminum oxide (Al2O3) layer disposed thereon, the patterned catalyst layer being formed on the Al2O3 layer.
The method of example 18, wherein forming the patterned catalyst layer includes forming, using photolithography, a patterned iron (Fe) layer, the Al2O3 layer preventing diffusion of the patterned Fe layer into the Si wafer.
An apparatus comprising: a substrate; and an array of carbon nanotube posts disposed on the substrate, each carbon nanotube post of the array of carbon nanotube posts including a plurality of nanotubes and extending substantially vertically from the substrate, each carbon nanotube post of the array of carbon nanotube posts having an aspect ratio of a height of the post to a diameter of the post of greater than or equal to 25:1.
It will also be understood that when an element, such as a layer, a region, or a substrate, is referred to as being on, connected to, electrically connected to, coupled to, or electrically coupled to another element, it may be directly on, connected or coupled to the other element, or one or more intervening elements may be present. In contrast, when an element is referred to as being directly on, directly connected to or directly coupled to another element or layer, there are no intervening elements or layers present. Although the terms directly on, directly connected to, or directly coupled to may not be used throughout the detailed description, elements that are shown as being directly on, directly connected or directly coupled can be referred to as such. The claims of the application may be amended to recite exemplary relationships described in the specification or shown in the figures.
As used in this specification, a singular form may, unless definitely indicating a particular case in terms of the context, include a plural form. Spatially relative terms (e.g., over, above, upper, under, beneath, below, lower, and so forth) are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. In some implementations, the relative terms above and below can, respectively, include vertically above and vertically below. In some implementations, the term adjacent can include laterally adjacent to or horizontally adjacent to.
While certain features of the described implementations have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the scope of the implementations. It should be understood that they have been presented by way of example only, not limitation, and various changes in form and details may be made. Any portion of the apparatus and/or methods described herein may be combined in any combination, except mutually exclusive combinations. The implementations described herein can include various combinations and/or sub-combinations of the functions, components and/or features of the different implementations described.
This application is a Non-provisional of, and claims priority to, U.S. Provisional Patent Application No. 62/244,145, filed on Oct. 20, 2015, entitled “Fabrication of High Aspect Ratio Tall Free Standing Posts Using Carbon-Nanotube (CNT) Templated Microfabrication”, which is incorporated by reference herein in its entirety.
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