Device comprising nanostructures and method of manufacturing thereof

Abstract

A method for manufacturing of a device (300, 410-412) comprising a substrate (201) comprising a plurality of sets of nanostructures (207) arranged on the substrate, wherein each of the sets of nanostructures is individually electrically addressable, the method comprising the steps of: providing (101) the substrate (200) having a first (202) face, the substrate having an insulating layer (210) comprising an insulating material arranged on the first face (202) of the substrate forming an interface (203) between the insulating layer and the substrate; providing (102) a plurality of stacks (204) on the substrate, the stacks being spaced apart from each other, wherein each stack comprises a first conductive layer (205) comprising a first conductive material and a second conductive layer (206) comprising a second conductive material different from the first material, the second conductive layer being arranged on the first conductive layer for catalyzing nanostructure growth; heating (103) the substrate having the plurality of stacks arranged thereon in a reducing atmosphere to enable formation of nanostructures on the second conductive material; heating (103) the substrate having the plurality of stacks (204) arranged thereon in an atmosphere such that nanostructures (207) are formed on the second layer (206); wherein the insulating material and the first conductive material are selected such that during the heating steps, the first conductive material interacts with the insulating material to form an electrically conductive portion (208) within the insulating layer (201) below each of the stacks (204), wherein the electrically conductive por tion comprises a mixture of the first conductive material and the insulating material and/or reaction adducts thereof.

Claims

1. A method for manufacturing of a device comprising a first substrate comprising a plurality of sets of nanostructures arranged on said first substrate, wherein each of said sets of nanostructures is individually electrically addressable, said method comprising the steps of: providing a substrate having a first face, said substrate having an insulating layer comprising an insulating material arranged on said first face of said substrate forming an interface between said insulating layer and said substrate; providing a plurality of stacks on said first substrate, said stacks being spaced apart from each other, wherein each stack comprises a first conductive layer comprising a first conductive material and a second conductive layer comprising a second conductive material different from said first material, said second conductive layer being arranged on said first conductive layer for catalyzing nanostructure growth; heating said first substrate having said plurality of stacks arranged thereon in a reducing atmosphere to enable formation of nanostructures on said second conductive material; heating said first substrate having said plurality of stacks arranged thereon in an atmosphere such that nanostructures are formed on said second layer; wherein said insulating material and said first conductive material are selected such that during said heating steps, said first conductive material interacts with said insulating material to form an electrically conductive portion within said insulating layer below each of said stacks, wherein said electrically conductive portion comprises a mixture of said first conductive material and said insulating material and/or reaction adducts thereof.

2. The method according to claim 1, wherein said first material and/or said insulating material are chosen such that a diffusion of said first material into said first substrate and/or a chemical reaction between said first material and said insulating material is achievable by heating said first substrate having said stacks arranged thereon to within a temperature interval of from 100 C. to 1000 C.

3. The method according to claim 2, wherein said temperature interval is preferably between 500 C. and 1000 C.

4. The method according to claim 1, wherein said electrically conductive portion is a path formed through said insulating layer such that each of said set of nanostructures is electrically connectable via each of said electrical connection junctions.

5. The method according to claim 1, wherein said method further comprises the step of providing a connecting structure configured to provide a first electrical connection to each of said sets of nanostructures via a respective one of said electrically conductive portions.

6. The method according to claim 1, wherein said stacks comprises an intermediate layer arranged in between said second and said first layer, wherein said intermediate layer comprises an electrically conductive and/or semi-conductive material, and wherein each of said intermediate layer is electrically connectable to a power source or a sensing device, thereby providing a second individually addressable electrical connection to each set of nanostructures.

7. The method according to claim 1, wherein said first conductive material comprises a metal.

8. The method according to claim 1, wherein said first conductive material comprises Al or Au.

9. The method according to claim 1, wherein said insulating material comprises at least one of SiO.sub.2 and Si.sub.3N.sub.4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing exemplary embodiment(s) of the invention, wherein:

(2) FIG. 1 is a flow-chart schematically illustrating a method for manufacturing a device comprising set of nanostructures according to an embodiment of the present invention;

(3) FIGS. 2a-d are enlarged cross-sectional views of the device, where each view corresponds to a stage of the manufacturing process according to the method of FIG. 1;

(4) FIG. 3 shows a perspective view of an embodiment of the device according to the invention; and

(5) FIGS. 4a-c show a cross-sectional side view of exemplary embodiments of the device according to the present invention.

DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE PRESENT INVENTION

(6) In the following description, the present invention is described with reference to a method for manufacturing of a device comprising a first substrate comprising a plurality of sets of nanostructures arranged on the first substrate, wherein each of the sets of nanostructures is individually electrically controllable.

(7) The present inventor has found a method for growing sets of nanostructures on top of an insulating layer comprising an insulating material and during the same heating cycle forming individually addressable electrical connections to each set of nanostructures within the insulating layer.

(8) An embodiment according to the method of to the invention will now be described in detail with reference to FIG. 1 which schematically illustrates the steps 101-104 according to one embodiment of the inventive method, and FIGS. 2a-d which show the resulting device after each of these steps.

(9) The first step 101 involves providing a first substrate 200 having an insulating layer comprising an insulating material. The insulating material may, for example, be one of SiO.sub.2 or Si.sub.3N.sub.4. The substrate may be any type of insulating or semiconducting substrate commonly used in semiconductor processing such as Si, SiO2, quartz or the like.

(10) The second step 102 involves providing a plurality of stacks 204 on a first face 202 of the insulating layer. As shown in FIG. 2b the stacks are arranged on the first face 202 such that they are separated from each other. The stacks 204 may typically have a length and/or a width (or diameter) in the range of nanometer to micrometer. Moreover, each stack comprises a first layer 205 comprising a first conductive material arranged in direct contact with the insulating layer 201, and a second layer 206 comprising a second material arranged on the first layer. The first material is typically different from the second material, wherein the second material catalyses the formation of nanostructures.

(11) Examples of second materials having nanostructure catalytic activity include, but are not limited to, Fe, Ni and Co.

(12) In one embodiment of the invention each stack 204 is provided on the first face 202 of the first substrate by first depositing the first layer 205 on the first substrate and subsequently depositing the second layer 206 thereon. Alternatively, in another embodiment of the invention, the second layer 206 is first deposited onto the first layer 205, and subsequently, the resulting stack 204 comprising the first 205 and the second 206 layer is deposited onto the first substrate 201. The pattern of the stacks may for example be defined through photolithography and subsequent etching. Alternatively, a shadow mask may be used while depositing the first and second layer.

(13) The third step 103, involves heating the substrate 200 having the plurality of stacks arranged thereon in an atmosphere such that sets of nanostructures 207, as shown in FIG. 2c, are formed on the second layer 206 and such that the first material of the first conductive layer 205 diffuses into the insulating layer 201 and/or reacts with the insulating material of the insulating layer 201 to form an electrically conductive portion 208 within the insulating layer 201 below each of the sets of nanostructures 207, wherein the electrically conductive portions are electrically conductive and/or semi-conductive and comprise a mixture of the first material and the insulating material and/or reaction adducts thereof, thereby each of the electrically conductive portions 208 allows for individual electrical control of a respective one of the set of nanostructures 207.

(14) By separating the stacks 204 from each other on the insulating layer, sets of nanostructures may be achieved thereon, wherein each of the set of nanostructures 207 corresponds to the nanostructures grown on each stack 204.

(15) The electrically conductive portions 208 may thus be electrically conductive and/or semi-conductive due to the presence of a conductive and/or semi-conductive first material which has diffused into the underlying insulating material. In addition, or alternatively, the first material may react with the insulating material to give reaction product(s) which may be electrically conductive and/or semi-conductive, in which case the first material does not need to be electrically conductive and/or semi-conductive in itself in order to achieve the electrically conductive and/or semi-conductive electrically conductive portions.

(16) In an exemplary embodiment, the first material is Al and the insulating material is SiO.sub.2, in which case a thermal reaction therebetween typically produces Al.sub.2O.sub.3 having insulating properties and Si having semi-conductive properties. Thus, in such case the electrically conductive portions may comprise a mixture of Al, Si, SiO.sub.2, Al.sub.x(SiO.sub.2).sub.y and Al.sub.2O.sub.3.

(17) It should, however, be emphasized that it is expected that many other material combinations of a conductive material and an insulating material can provide the desired conductive portions. One of ordinary skill in the art will be able to determine, without undue burden, if such conductive portions have been formed by a process similar to that described under the heading Example fabrication process.

(18) The electrical properties of the electrically conductive portions can thus easily be configured, for example to fit with a desired application, through the selection of the first conductive material and the insulating material, the thickness of the insulating layer and the thickness of the first layer, diffusion/reaction temperature, and time of heating.

(19) Similarly, the shape of the electrically conductive portions may also be controlled by, for example, adapting the thickness of the first layer 205 and insulating layer 201, and/or diffusion/reaction temperature and time of heating, thus configuring the shape to fit with a given application. For example, according to one embodiment of the invention, as embodied in FIG. 2c, the electrically conductive portions 208 are paths extending from through the insulating layer. Thereby, each electrically conductive portion is directly electrically addressable at the interface 203 between the insulating layer and the substrate. Alternatively, in another embodiment of the invention (not shown in FIG. 2c), the electrically conductive portions may be configured to not extend through the insulating layer such that each electrically conductive portion is electrically isolated from the substrate and thereby enabling a capacitive and/or inductive electrical connection at the interface between the insulating layer and the substrate to the electrically conductive portions.

(20) The invention is not limited to any specific method of growing nanostructures so the composition of the atmosphere in the growth step may therefore depend on the type of nanostructures grown (e.g. carbon nanotube, single or multi-walled, carbon nanofibers, ZnO nano wires, etc). Methods such as chemical vapor deposition, plasma enhanced chemical vapor deposition, arc discharge, laser ablation, or any other suitable methods known to the skilled person, may typically be used. Thus, the atmosphere may typically comprise at least one of ethylene, argon, plasma, hydrogen, nitrogen and ammonia (for carbon nanotube growth).

(21) The nanostructures may advantageously be carbon nanotubes, particularly multi-walled carbon nanotubes arranged in bundles having a length in the nanometer to micrometer range, depending on the desired application.

(22) Advantageously, the first material and/or the insulating material may be chosen such that a diffusion of the first material into the first substrate and/or a reaction between the first material and the insulating material is achievable by heating said first substrate having the stack arranged thereon to within a preferred temperature interval of from 100 C. to 1000 C., preferably between 500 C. and 1000 C., more preferably between 700 C. and 900 C., and most preferably between 750 C. and 800 C. The chosen temperature depends on the growth requirement parameters of the particular nanostructure desired and on the temperature required for achieving the conductive portions for a given material combination.

(23) According to one embodiment of the invention the method further comprises a fourth step 104, which involves providing a second substrate 209 underlying the insulating layer 201, as shown in FIG. 2d, wherein the second substrate 209 comprises a connecting structure 210 configured to provide a first electrical connection to each of the sets of nanostructures 207 via a respective one of the electrically conductive portions 208.

(24) For example, as illustrated in FIG. 2d, the connecting structure may be embodied as a plurality of wells 210 comprising an electrically conductive or semi-conductive material, wherein each well 210 is electrically connectable to a power source or sensing device and thus individually addressable.

(25) Alternatively, in another embodiment of the method according to the invention, the second substrate 209 may be provided at any step prior to the heating step 103, for example in the first step, and thereby the first electrical connection through the connecting structure 210 is achieved immediately upon heating. Moreover, a similar connecting structure may be incorporated in the first substrate.

(26) It should be noted, that in embodiments of the method according to the invention, a second individually addressable electrical connection to each set of nanostructure may be by providing an intermediate layer (not shown in FIGS. 2a-d) comprising an electrically conductive and/or semi-conductive material in between the first and second layer of each stack, which intermediate layer is electrically connectable to a power source, through for example a connecting structure on top of the insulating layer.

(27) FIG. 3 shows a perspective view of an embodiment of the device 300 according to the invention, comprising an insulating layer 201 having a first face 202 and a second face 203, the insulating layer 201 comprising an insulating material. A plurality of sets of nanostructures 207 are comprised on the first face 202 of the substrate, and as shown in FIG. 3 the sets of nanostructures 207 are spaced apart from each other. Further, the insulating layer 201 comprises a plurality of electrically conductive portions 208, each electrically conductive portion 208 underlying a respective one of the sets of nanostructures 207 such that each electrically conductive portion 208 is in electrical connection with a respective one of the sets of nanostructures 207. The electrically conductive portions 208 are electrically conductive and/or semi-conductive.

(28) In embodiments of the device according to the invention, as shown in FIG. 3, the device further comprises a substrate 209 underlying the insulating layer 201, wherein the substrate 209 comprises a connecting structure connectable to a power source or sensing device and configured to provide a first electrical connection to each of the electrically conductive portions 208, and thereby enabling individually addressing of each set of nanostructures 207. The power source include, for example, be a conventional AC or DC power source, a battery, a capacitor system, and the sensing device may, for example, be a multimeter or equivalents (e.g. volt meter or ampere meter), depending on the desired application of the device.

(29) In embodiments of the device, the sets of nanostructures may advantageously be substantially vertically aligned to the substrate.

(30) Typically, the set of nanostructures correspond to a length and/or a width (or diameter) in the range of nanometers to micrometers.

(31) In embodiments of the device the sets of nanostructures may comprise multiwall carbon nanotubes arranged in bundles.

(32) FIGS. 4a-c show a cross-sectional side view of embodiments of the device according to the invention. As is illustrated in FIGS. 4a-c, the connecting structure 210 comprises a plurality of wells 210 comprising an electrically conductive and/or semi-conductive material and which wells are electrically connectable to a power source. Thereby, each well provides a first electrical connection to each of the electrically conductive portions 208.

(33) In embodiments of the device 410 according to the invention, as shown in FIG. 4a, the electrically conductive portions may be embodied as paths extending from the first face 202 of the insulating layer to the interface 203 between the insulating layer and the substrate, thereby the first electrical connection is a direct electrical connection between the electrically conductive portions 208 and the connecting structure 210.

(34) In embodiments of the device 411 according to the invention, as shown in FIG. 4b, the electrically conductive portions extend into the insulating layer 201 from the first face 202 thereof to a desirable depth such that the electrically conductive portions are separated from the interface 203 between the insulating layer and the substrate, thereby the first electrical connection to each of the electrically conductive portions 208 corresponds to a capacitive electrical connection.

(35) As is illustrated in FIG. 4c, the device 412 according to the invention may comprise an electrically conductive and/or semi-conductive intermediate layer 402 arranged on the first face 202 of the insulating layer in between each set of nanostructures 207 and the underlying electrically conductive portions 208, and each intermediate layer may be electrically connectable through a connecting structure 403 on the first face 202 of the insulating layer 201, thus providing a second individually addressable electrical connection to each set of nanostructures 207.

(36) In various embodiments of the invention, the conducting path may comprises at least one rectifying junction which may be tailored to exhibit desired characteristics based on the selected materials, thereby enabling fabrication of devices such as solar cells and transistors and super capacitors. For example additional conductive layers may be arranged between the first conductive layer and the insulating layer as long as the material of the first conductive layer may reach the insulating layer to form the electrically conductive portion. The first conductive layer may interact with such an intermediate conductive layer for example by diffusion or through a chemical reaction. Thus, rectifying junctions may be formed in the electrically conductive portion as different materials have different diffusion/reaction properties within the insulating layer. Furthermore, the position of such rectifying junctions may be controlled by selecting the thickness of the layers. By controlling the positions and properties of rectifying junctions in the electrically conductive portions, various devices such as transistors and photovoltaic devices may be formed.

(37) Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. For example, a surface of the insulating layer may be etched and the stacks may be arranged on the etched surface, thus the produced nanostructures may be substantially aligned to the etched surface. Furthermore, the second layer of the stacks which is arranged on the first layer of the stacks may only cover a portion of the first layer.

(38) In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.

(39) Example Fabrication Process:

(40) Growth of Conductive Carbon Nanotube Forests:

(41) The device was fabricated using a silicon wafer with 0.5 m of oxide layer on it. Metal and catalyst (300 nm of aluminum and 1 nm of iron) was patterned using photolithography, metal evaporation, and lift off. The catalyst was annealed at 775 C. for 20 minutes under a flow of 100 sccm of hydrogen and 400 sccm of helium to activate the catalyst material. Immediately after the annealing, while maintaining the same temperature, growth of carbon nanotubes was performed by introducing 100 sccm of ethylene into the quartz tube for 30 minutes, before cooling the sample.
The recipe used to grow nanostructures is summarized in Table 1:

(42) TABLE-US-00001 TABLE 1 Time Hydrogen Ethylene Helium Temp Step (min) (sccm) (sccm) (sccm) ( C.) 1 5 0 0 1000 25 2 5 100 0 400 25 3 10 100 0 400 775 4 30 100 100 400 775 5 1 100 100 400 25 6 15 100 100 400 25 7 5 0 0 1000 25
where time is in minutes, gases are in sccm, temperature is in degrees Celsius. When the step temperature is different from the previous step temperature it means the temperature is changed by ramping. For instance, step 3 involves ramping of the temperature from 25 C. to 775 C. over 10 minutes. Furthermore, step 5 is the step where nanostructures are grown. Thus, the growth time is 30 minutes. It has been shown that Al may reduce SiO2 to form an electrically conductive material, see Dadabhai et al., Journal of Applied Physics 80 (11) pp. 6505-6509 (1996), hereby incorporated by reference. As readily understood by the person skilled in the art, the above referenced parameter values may be varied while still being within the scope of the invention. For example, Helium may be replaced by another inert gas such as Ar or N, the temperature ramps may vary, growth temperatures may be varied and so on. In particular, the step where nanostructures are grown, i.e. step 4 in Table 1, may for example comprise:

(43) 200 sccm Ethylene, 80 sccm Hydrogen, 150 sccm Argon at 750 C. for 30 min.

(44) 150 sccm Ethylene, 400 sccm Hydrogen, 200 sccm Argon at 700 C. for 30 min.

(45) 200 sccm Acetylene, 200 sccm Hydrogen, 700 C. for 30 min.

(46) Furthermore, the temperature of steps 3 and four may vary depending on the selected material combinations.