Patent Application
20070122313
N/A
1. Technical Field
The invention relates to nanotechnology. In particular, the invention relates to an apparatus having embedded nanochannels with open distal ends, a nanofluidic system including the apparatus, and the fabrication of the apparatus using nanowires as templates.
2. Description of Related Art
Nanotechnology is concerned with the fabrication and application of nano-scale structures, structures having at least one linear dimension between about 1 nm and about 200 nm. These nano-scale structures are often 50 to 100 times smaller than conventional semiconductor structures. Nanowires, nanopores and nanochannels are some examples of nano-structures useful in devices, such as sensors and lasers. There are many techniques known in the art for growing or synthesizing nanowires. However, there are fewer techniques for forming a nanochannel or a nanopore. Natural materials, such as the toxin protein alpha-hemolysin, form a microscopic pathway or tunnel through a cellular membrane having a pore size in the angstrom range. However, a natural pore material has an intrinsic short life time such that their use in device manufacture is limited. A nanofluidic device having a synthetic nanochannel or nanopore capable of mimicking the pathway provided by a natural protein like alpha-hemolysin would be useful in genome sequencing, chemical sensing, biological sensing, or both, and molecule separation, for example.
Synthetic inorganic nanopores and nanochannels have been made from silicon dioxide or silicon nitride, for example, which have greater stability over time than their natural organic counterparts. One or more of ion-sculpting, TEM drilling, and nanoimprinting have been used to form the synthetic nanopores and nanochannels. Such methods of fabrication require expensive instrumentation that lack precise control of one or both of the number and the dimensions of the nanochannels and the nanopores fabricated. This lack of precise control limits the applications for which these synthetic nanostructures are useful.
Moreover, nanotubes have been used as nanochannels in nanofluidic devices. The nanotube is fabricated using a nanowire as a sacrificial core on which a nanotube sheath is formed or grown. Two techniques of forming the nanotubes have been reported that include an epitaxial casting technique and an oxidation and etching technique. The fabricated nanotubes are subsequently harvested from the fabrication substrate for later installation or deposition in or on a device, which is a tedious serial process that may be impractical for some applications.
Accordingly, it would be desirable to have a fabrication technique for nanochannels or nanopores that is conducive to a manufacturing environment of a variety of nano-scale devices that utilize such nanochannels or nanopores. Moreover, it would be desirable if such a fabrication technique was also cost-efficient. Such a technique would solve a long-standing need in the developing area of a “bottom-up” fabrication approach in nanotechnology.
In some embodiments of the present invention, a nanochannel apparatus is provided. The nanochannel apparatus comprises a permanent support, and an array of nanochannels embedded in the permanent support. The array of nanochannels extends through a dimension of the support, such that distal ends of the nanochannels are exposed.
In some embodiments of the present invention, a nanofluidic system is provided. The nanofluidic system comprises a nanochannel apparatus that comprises an array of nanochannels embedded in a permanent support. The nanochannel array extends through a dimension of the permanent support, such that distal ends of the nanochannel apparatus are exposed. The nanofluidic system further comprises a fluidic interface adjacent to at least one of the distal ends of the nanochannel apparatus. The nanofluidic system further comprises a component interfaced to the nanochannel apparatus that facilitates one or more of analysis, detection and control of a fluid.
In some embodiments of the present invention, a method of fabricating a nanochannel apparatus is provided. The method of fabricating comprises encasing an array of nanowires in a support. The method of fabricating further comprises forming an array of nanochannels in situ through the support in locations of the nanowires, such. that distal ends of the nanochannels are exposed. The support is a permanent support for the nanochannels of the apparatus.
Certain embodiments of the present invention have other features that are one or more of in addition to and in lieu of the features described hereinabove. These and other features of some embodiments of the invention are detailed below with reference to the following drawings.
The various features of embodiments of the present invention may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, where like reference numerals designate like structural elements, and in which:
Some embodiments of the present invention are directed to a nanochannel formed from a nanowire grown to bridge between horizontally spaced apart vertical surfaces, wherein the nanowire is embedded in a support material and subsequently removed from the material. The vertical surface from which the horizontal nanowire grows is a (111) surface of a [110] oriented semiconductor crystal lattice. Other embodiments of the present invention are directed to a nanochannel formed from a nanowire grown vertically from a horizontal surface, wherein the nanowire is embedded in a support material and subsequently removed from the material. The horizontal surface from which the nanowire grows is a (111) surface of a [110] oriented semiconductor crystal lattice.
A semiconductor nanowire will grow preferentially nearly normal to the (111) surface. On a vertically oriented (111) surface, the nanowire will grow horizontally from, or essentially perpendicular to, the vertical (111) surface. On a horizontally oriented (111) surface, the nanowire will grow vertically from, or essentially perpendicular to, the horizontal (111) surface. The nanowire will grow substantially perpendicular to the (111) surface until the growth is intentionally stopped or until the nanowire contacts a facing surface that is respectively vertical or horizontal. By ‘essentially perpendicular’, ‘substantially perpendicular’ and ‘nearly normal’ it is meant that the nanowire will grow from the (111) surface predominantly in a direction to contact the respective facing surface. Once contacted, the nanowire will attach or connect to the respective facing surface.
The use of brackets ‘[ ]’ herein in conjunction with such numbers as ‘111’ and ‘110’ pertains to a direction or orientation of a crystal lattice and is intended to include directions ‘< >’ within its scope, for simplicity herein. The use of parenthesis ‘( )’ herein with respect to such numbers ‘111’ and ‘110’ pertains to a plane or a planar surface of a crystal lattice and is intended to include planes ‘{ }’ within its scope for simplicity herein. Such use is intended to follow common crystallographic nomenclature known in the art.
The materials useful for the various embodiments of the present invention include, but are not limited to, group IV, group IV-IV, group III-V and group II-VI materials, including compound semiconductor materials, from the Periodic Table of the Elements. For example and not by way of limitation, the nanowire may be made from a semiconductor including, but not limited to, any of silicon (Si), germanium (Ge), silicon carbide (SiC), gallium arsenide (GaAs), gallium nitride (GaN), gallium phosphide (GaP), indium phosphide (InP), indium arsenide (InAs), aluminum nitride (AlN), zinc oxide (ZnO), indium oxide (InO), indium tin oxide (ITO) and cadmium sulfide (CdS), for example, or a metal-semiconductor alloy. Numerous nanowire materials are known in the art. The scope of the various embodiments of the present invention is intended to include all such materials. In some embodiments, the nanowire is a single crystal structure, while in other embodiments, the nanowire may be an amorphous or multi-crystalline structure. A semiconductor nanowire can be grown such that one or more of length, diameter, shape, direction of growth, and position of the semiconductor nanowire are controlled in accordance with some embodiments of the present invention. Moreover, the nanowires may be grown from a substrate used for semiconductor device fabrication.
The substrate material comprises one or more of the semiconductor materials listed above, and may include, but is not limited to, the list of nanowire materials from above. For example, a silicon nanowire will grow in a direction that is nearly normal to a (111) plane of a crystal lattice of, for example, a semiconductor substrate or wafer made of Si or GaAs. Moreover, the support material described below comprises one or more of the semiconductor materials listed above, an insulator material and a metal. For example, the support material may be an oxide or a nitride of the above materials including, but not limited to, silicon dioxide, silicon nitride and aluminum oxide. For the purposes of the embodiments herein, the support material is intended to be a permanent support for the nanochannel, while the substrate may provide either temporary or permanent support to the apparatus.
In some embodiments of the present invention, a nanochannel apparatus 10 is provided.
According to another embodiment of the present invention, a method of fabricating a nanochannel apparatus is provided. The method of fabricating comprises encasing a plurality of nanowires in a support on a substrate; and forming an array of nanochannels in the support in the locations of the nanowires, such that the nanochannels of the array have distal open ends. The support is a permanent support for the nanochannels of the apparatus, while the substrate is either temporary or permanent, depending on the embodiment. Moreover, the nanowires are grown in situ on the substrate before being encased, and the nanochannels are formed in situ in the support. The nanochannels correspond in size to that of the encased nanowires. The resultant nanochannel apparatus is an in situ nanochannel apparatus.
In some embodiments, a method 200 of fabricating a nanochannel apparatus having an array of horizontal-oriented nanochannels is provided.
As illustrated in
The method 200 of fabricating further comprises growing 220 nanowires from the vertical (111) surface of a first island of the created islands 201 to a second island of the created islands 201. Since a nanowire preferentially grows nearly normal to a (111) surface, the nanowire will grow preferentially horizontal to the vertical (111) surface.
There are many techniques known in the art for growing nanowires that may be used in this embodiment. In particular, nanowires are grown in the location where they will be used to form a nanochannel in the apparatus (i.e., in situ). Nanowires may be ‘grown’ using methods such as, but not limited to, vapor-liquid-solid (VLS), vapor-solid-solid (VSS), solution-liquid-solid (SLS), which are known in the art, using a catalyst particle. The growth method may be referred to as catalyzed growth or in some embodiments, metal-catalyzed growth. However, any of the in situ growth methods may be substituted for the metal-catalyzed growth and still be within the scope of the embodiments described herein. Metal-catalyzed growth is described in more detail in the co-pending U.S. patent application, Ser. No. 10/738,176, cited and incorporated by reference supra.
For example, in some embodiments, a catalyst material is deposited on the vertical (111) surface of one or both of the parallel islands 201. The catalyst material may be annealed into activated catalyst (i.e., a nanoparticle catalyst) or may be deposited in an activated form. The catalyst material may include, but is not limited to, gold (Au), nickel (Ni), titanium (Ti), iron (Fe), cobalt (Co), and gallium (Ga), and respective alloys thereof. Other catalyst materials may include, but are not limited to, nonmetals, such as SiOx, where x ranges from about 1 to less than 2, for example. The catalyst materials used for growing a Si nanowire, for example, include, but are not limited to, Ti, Au, TiSi2 alloy and Au—Si alloy.
The activated (111) surface is exposed to a controlled temperature, pressure and a gas containing a material of the nanowire to be grown. In some embodiments, the activated vertical (111) surface is exposed to the gas in the reactor chamber of the material deposition system. As such, the temperature and pressure are regulated, and the gas or a gas mixture is introduced and controlled during nanowire growth 220. In some embodiments, the activated (111) surface is exposed to the gas in the reactor chamber under conditions at which the uncatalyzed (i.e., normal) deposition rate is low. The catalyst accelerates the decomposition of the gas, allowing a high ratio of catalyzed-to-normal growth. Material deposition systems including, but not limited to, chemical vapor deposition (CVD) systems, metal organic vapor phase epitaxy (MOVPE) systems, molecular beam epitaxy (MBE) systems, plasma-enhanced CVD (PECVD) systems, resistance-heated-furnace diffusion/annealing systems, and rapid thermal processing (RTP) systems may be employed for the nanowire growth 220, for example. For a Si nanowire, growth 220 using a CVD system and a process that employs a Si-containing gas including, but not limited to, a gas mixture of silane (SiH4) and hydrogen chloride (HCl), a gas of dichlorosilane (SiH2Cl2), or a silicon tetrachloride (SiCl4) vapor in a hydrogen (H2) ambient may be used, for example and not by way of limitation.
The nanowire grows 220 in a columnar shape from the vertical (111) surface adjacent to the activated catalyst particle. A free end of the columnar-shaped growing nanowire contains the activated catalyst particle. The nanowire continues to grow in the environment described above until the free end of the nanowire 203 contacts the vertical surface of the other parallel island 201. In some embodiments, contact of the free end is accompanied by attachment to the vertical surface of the other island 201. The grown nanowires 203 are effectively suspended to bridge across the trench.
The method 200 of fabricating further comprises encasing or enveloping 230 the laterally bridging nanowires 203 in a second layer 204 of material. The second layer 204 may fill the trench formed by the spaced apart islands 201.
Encasing 230 the nanowires 203 comprises depositing the material of the second layer 204 to completely surround the horizontally suspended nanowires 203. The material of the second layer 204 is deposited using any of the deposition or growth techniques known in the art including, but not limited to, one or more of chemical vapor deposition (CVD) and plasma enhanced CVD (PECVD), for example and not by way of limitation, and may depend in part on the material chosen for the second layer 204. Moreover, angled deposition may be used to facilitate the material surrounding the nanowires 203, for example and not by way of limitation.
In some embodiments, encasing 230 the nanowires 203 further comprises removing excess deposited material of the second layer 204 to expose the horizontal (110) planar surface of the islands 201 and form the second layer 204.
The method 200 of fabricating further comprises forming 240 nanochannels in a permanent support of the nanochannel apparatus 20. In some embodiments, forming 240 nanochannels comprises removing 240 the nanowires 203 from the second layer 204 while leaving the second layer 204 or a majority thereof permanently intact. In some embodiments, forming 240 nanochannels further comprises removing 240 the islands 201 either simultaneously or sequentially with the removal of the nanowires. Moreover in some embodiments, forming 240 nanochannels further comprises removing a section of the second layer 204 at an interface immediately adjacent to one or both of the islands 201 to expose a portion of the nanowires 203 from the section.
A section of the second layer 204 may be removed using a variety of techniques known in the art including, but not limited to, one or more of dry etching, for example, reactive ion etching (RIE) or ion milling, wet chemical etching, and lithography, and depends on the material used for the second layer 204. In some embodiments, the technique selectively removes the section of the second layer 204 but not the adjacent islands 201 or the nanowires 203. As such, one or more other techniques that are selective to the removal of the nanowires 203 is used to further remove the nanowires 203, while the islands 201 may be optionally removed also, depending on the embodiment.
In some embodiments, the islands 201 and the nanowires 203 are removed with selective etching, such as using one or more of XeF2 dry chemical etching and a selective wet etching technique, for example and not by way of limitation, and depends on the materials of the islands 201 and of the nanowires 203. The nanowires 203 are removed from the support layer 204 selectively, such that nanochannels 206 in the support layer 204 are created 240 where the horizontally suspended nanowires 203 are removed.
The nanochannel apparatus 20 illustrated in
In another embodiment of the present invention, a nanochannel apparatus 30 is provided.
In another embodiment of the present invention, a method 400 of fabricating a nanochannel apparatus having an array of vertical-oriented nanochannels is provided.
The method 400 of fabricating further comprises growing 420 an array of nanowires from the horizontal (111) surface. Since a nanowire preferentially grows nearly normal to a (111) surface, the nanowires will grow preferentially vertical to the horizontal (111) surface.
A nucleating catalyst material is deposited on the (111) surface in a very thin layer and annealed in a controlled environment (i.e., chamber) to form isolated nanoparticles of the catalyst material. Alternatively, when the nanoparticle catalyst is directly deposited, annealing may be optional. The catalyst material may be lithographically patterned using techniques known in the art to define target locations of the catalyst material on the horizontal (111) surface of the substrate 401 from which nanowires 403 are to be grown 420. As described above for the method 200, a nanowire material-containing gas is introduced into the controlled environment. The nanoparticle catalyst accelerates decomposition of the gas, such that atoms of the nanowire material precipitate between the nanoparticle catalyst and the horizontal (111) surface to initiate nanowire growth 420.
The nanowire 403 will grow 420 from under the nanoparticle on the (111) horizontal surface in columnar form, taking the nanoparticle with it at its tip or free end. The nanowires 403 will continue to grow until growth is terminated, such as by terminating the growth environment in the chamber or removing the substrate 401 from the chamber, for example.
The method 400 of fabricating further comprises encasing or enveloping 430 the grown nanowires 403 in a support layer 404 of material. The support layer 404 may fully encase the nanowires 403 or in some embodiments, may encase a portion of a length of the nanowires 403, such that the free ends of the nanowires 403 are exposed or otherwise not encased 430 in the material of the support layer 404.
In some embodiments, encasing 430 the nanowires 403 further comprises removing excess deposited material of the support layer 404 to expose the free ends of the vertically grown nanowires 403.
The method 400 of fabricating further comprises forming 440 an array of nanochannels in the support layer 404 of the apparatus 40. Forming 440 the nanochannels comprises removing 440 at least a section of the substrate 401 and removing the nanowires 403 from the support layer 404 while leaving the support layer 404 permanently intact.
A section of the substrate 401 may be removed using a variety of techniques known in the art including, but not limited to, one or more of dry etching, for example reactive ion etching (RIE) or ion milling, wet chemical etching, and lithography, and depends on the material used for the substrate. The technique or techniques used will selectively remove the section of the substrate 401, and optionally, will remove the material of the nanowires 403, depending on the embodiment, but will not remove the material of the support layer 404. In some embodiments, the technique(s) used for the removal of the substrate 401 section selectively does not remove the nanowires 403. Where the nanowires 403 are not removed with the section of the substrate 401, another of the above described techniques may be used to selectively remove the nanowires 403. In some embodiments, the entire substrate 401 is removed instead of a section thereof that is coaxial with the nanowires 403. In other embodiments, the section of the substrate 401 is removed, followed by the removal of the nanowires 403, and then the removal of a remainder of the substrate 401.
The nanowires 403 are removed from the support layer 404 selectively, such that an array of nanochannels 406 in a support or block 405 are created 440 where the nanowires 403 are removed.
The nanochannel apparatus 40 illustrated in
According to some embodiments of the present invention, a diameter of the nanochannels 16, 206, 36, 406 may be controlled or adjusted in the respective nanochannel apparatuses 10, 20, 30, 40. For example, in some embodiments of the methods 200, 400 of fabricating a nanochannel apparatus, a thermal oxide may be grown on the nanowires 203, 403, such that a diameter of the nanowires 203, 403 is reduced by the thickness of the thermal oxide layer. During forming 240, 440 nanochannels, the reduced-diameter nanowires 203, 403 (or core nanowire materials) are removed, such that the resultant nanochannels 206, 406 are actually narrower in diameter (by approximately the thickness of the thermal oxide layer) than they would have been without thermal oxidation of the nanowires 203, 403. In an example, silicon nanowires having a diameter of approximately 5 nanometers (nm) may be thermally oxidized prior to forming 240, 440 nanochannels to achieve a resultant nanochannel diameter of approximately 2 nm to approximately 3 nm.
In some embodiments, the nanochannel apparatus 10, 20, 30, 40 may be further processed to include one or more components and structures to provide a variety of nanofluidic devices or systems. For example, one or more of the nanochannels 206, 406 of the apparatus 20, 40 may be interfaced to one or more fluidic components and structures formed on the surface of the substrate 202, 401 for one or more of holding, processing and sensing fluids that travel through the one or more nanochannels 206, 406. A fluid is defined to include one or both of a liquid and a vapor herein. In some embodiments of the present invention, any of the nanochannel apparatuses 10, 20, 30, 40 described above may be used in a variety of miniaturized systems for analysis, detection and control.
In some embodiments of the present invention, a nanofluidic system is provided. The nanofluidic system comprises a nanochannel apparatus 10, 20, 3040; a fluidic interface adjacent to at least one open end of the nanochannel apparatus 10, 20, 3040; and a component interfaced to the nanochannel apparatus 10, 20, 3040. The component is defined herein as a structure or element that facilitates one or more of analysis, detection and control. In some embodiments, the component comprises one or more of an electrode and a sensor. The electrode comprises one or more of a gate electrode, a source electrode and a drain electrode, for example and not by way of limitation. The sensor comprises one or more detectors, nano-detectors and nano- emitters. The sensor includes, but is not limited to, one or more of a nanowire-based sensor, a single electron transistor, an optical detector, and an optoelectronic structure, such as a vertical cavity surface emitting laser (VCSEL), including a nano-VCSEL, for example and not by way of limitation. See, U.S. Pat. No. 6,815,706 B2, issued Nov. 9, 2002; co-pending U.S. patent application Ser. No. 10/982,051, cited supra; and co-pending U.S. patent application Ser. No. 11/084,886, filed Mar. 21, 2005, incorporated herein by reference in their entireties, for some examples of a nano-detector or a nano-device useful in various embodiments of a nanofluidic system according to the present invention. In some embodiments, the nanochannel apparatus 10, 20, 30, 40 may be integrated with a component, as described above, and optionally other devices to form miniaturized systems for fluidic processing of biological materials, such as DNA.
As illustrated in
In another embodiment, the nanofluidic sensor system 500 comprises a sensor 512 interfaced with an open end 51, 53 of the nanochannel apparatus 50, as illustrated in
In some embodiments, the embedded sensor 510 is replaced by an embedded electrode, such as a metal or semiconductor gate of a nanofluidic transistor.
The sensors 510, 512 and the electrodes 604, 606 and 610 may be fabricated using standard semiconductor processing and materials. For example, the sensor 510 or the electrode 610 may be incorporated into the nanochannel apparatus 50, 60 during the fabrication of the nanochannel apparatus. Referring back to the method 200 of fabricating the nanochannel apparatus 20 in
In another example, referring back to the method 400 of fabricating the nanochannel apparatus 40 in
Any of the embodiments of the nanofluidic system 500, 600 illustrated in
Thus, there have been described various embodiments of a nanochannel apparatus, a method of fabricating a nanochannel apparatus and a nanofluidic system. It should be understood that the above-described embodiments are merely illustrative of some of the many specific embodiments that represent the principles of the present invention. Clearly, those skilled in the art can readily devise numerous other arrangements without departing from the scope of the present invention as defined by the following claims.
