WO2009066968A2

WO2009066968A2 - Method for arranging nanostructures and manufacturing nano devices using the same

Info

Publication number: WO2009066968A2
Application number: PCT/KR2008/006927
Authority: WO
Inventors: Seung-Hun Hong; Byung-Yang Lee
Original assignee: Seoul National University Industry Foundation
Priority date: 2007-11-23
Filing date: 2008-11-24
Publication date: 2009-05-28
Also published as: WO2009066968A3

Abstract

Disclosed is a method for arranging nanostructures and a method for fabricating a nano device. The method for arranging nanostructures in a certain direction includes: forming a sacrificial structure having a face in the certain direction on a substrate; forming the nanostructures at least on the face of the certain direction of the sacrificial structure; and removing the sacrificial structure.

Description

DESCRIPTION

METHOD FOR ARRANGING NANOSTRUCTURES AND MANUFACTURING NANO

DEVICES USING THE SAME

TECHNICAL FIELD

The present invention relates to nano technology; and, more particularly, to a method for arranging nanostructures , such as nanotube and nanowire, and a method for fabricating a nano device employing the nanostructures.

BACKGROUND ART

A new sector of technology called nano technology is quickened as recent researches report new physical phenomena and improved material characteristics in a nanometer-size ultrafine area. The so-called nano technology is an advanced scientific technology to lead the 21^st century and it is spotlighted as future technology in a wide variety of areas, such as electronic information communication, medicines and pharmaceutics, materials, manufacturing process, environment, energy and the like.

As nano technology advances, diverse materials such as nanowire, e.g., Si, Ge, SiO_x, GeO_x, a nanotube formed of a single element or multiple elements, e.g., C, B_xNy, C_xB_yN_z, MoS₂, and WS₂, are under development. These materials are all called ^λnanostructures . '

One of the common features of nanostructures is a basic constituent block. A piece of nanowire or nanotube has a length of less than tens to hundreds of nanometers (nm) at least in one direction. These materials are known to have specific characteristics in common that draw the interests from diverse areas and processes. Particularly, nanostructures, such as nanotube and nanowire, have wide surface area and high electrical sensitivity to an external environment in common. These characteristics make them applicable to the field of sensors .

Among the nanostructures , carbon nanotube (CNT) and semiconductor nanowire have recognition as representative materials for the next-generation nano devices .

The nanostructures are required to be arranged at a specific location in a specific direction to form specific devices, e.g., a memory device or a sensor.

One of the methods for arranging nanostructures at a specific location on a substrate is a technology for assembling nanostructures by themselves based on the adsorption property between a molecular layer and the nanostructures. Examples of the nanostructure self- assembling technology include a linker molecular patterning technology (disclosed in Nature 425, 36, 2003) which arranges carbon nanotube or nanoparticles on a solid surface by using a linker molecular layer, and an anti-adsorption molecular layer patterning technology (disclosed in Korean Patent Publication No. 10-2007- 0112733) which arranges nanowire on a solid surface by using an anti-adsorption molecular layer pattern. Both of the two technologies arrange nanostructures by taking advantage of the adsorption property between a molecular layer and the nanostructures and, particularly, they arrange nanostructures horizontally to the surface of a substrate .

Meanwhile, other than horizontal arrangement of nanostructures on a substrate, there is an increasing number of cases requiring vertical arrangement of nanostructures from the perspective of increasing integrity of a memory device or improving susceptibility of a sensor. Many researchers are studying for the vertical arrangement of nanostructures. To take an example, researchers are studying a technology for performing Vapor-Liquid-Solid (VLS) growth process onto carbon nanotube or Si nanowire by using a catalytic metal (disclosed in Nature 399, 48, 1999), or a technology for vertically growing carbon nanotube through a Chemical Vapor Deposition (CVD) method.

However, most technologies developed up until now for the vertical growth of nanostructures , including the aforementioned technologies, not only require high- temperature process but also have a shortcoming that it is difficult to substantially control the growth angle of the nanostructures. In other words, it is substantially difficult to fabricate a device where nanostructures, such as nanotube or nanowire, are arranged vertically. Therefore, it is required to develop a technology that can relieve the difficulty in vertically arranging nanostructures .

DISCLOSURE TECHNICAL PROBLEM

An embodiment of the present invention, which is devised to overcome the problem(s) of conventional technology, is directed to providing a nanostructure arrangement method that can ease the difficulty of a fabrication process, compared to conventional technology, and a method for fabricating a nano device based on the nanostructure arrangement method.

TECHNICAL SOLUTION In accordance with an aspect of the present invention, there is provided a method for arranging nanostructures in a certain direction, the method including: forming a sacrificial structure having a face in the certain direction on a substrate; forming the nanostructures at least on the face of the certain direction of the sacrificial structure; and removing the sacrificial structure.

In accordance with another aspect of the present invention, there is provided a method for fabricating a nano device including a first electrode and a second electrode spaced apart from each other in a vertical direction, and nanostructures arranged to connect the first and second electrodes, the method including: forming a sacrificial structure connected to a vertical face and a horizontal face on the substrate and having the horizontal face in parallel to a substrate; forming the nanostructures at least on the vertical face of the sacrificial structure; forming the first and second electrodes on the horizontal face and the substrate at both ends of the nanostructures; and removing the sacrificial structure.

ADVANTAGEOUS EFFECTS

The nanostructure arrangement method of the present invention described above and the nano device fabrication method employing the same make processes easier than conventional technology by using a sacrificial structure to arrange nanostructures in a desired direction.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a flowchart describing a method for arranging nanostructures in accordance with an embodiment of the present invention. Fig. 2 is a perspective view illustrating a method for fabricating a nano device in accordance with an embodiment of the present invention.

Fig. 3 is a photograph showing an exemplary nano device fabricated according to the method of Fig. 2. * Description of primary constituent elements shown in the drawings 20: substrate 21: sacrificial structure 22: nanostructure

23a, 23b: first electrode, second electrode

BEST MODE FOR THE INVENTION

The advantages, features and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter.

Fig. 1 is a flowchart describing a method for arranging nanostructures in accordance with an embodiment of the present invention.

In step SlO, a predetermined substrate is provided. There is no specific limitation in the kind of substrate, and examples of the substrate include a Si substrate, an SiC>₂ substrate, a glass substrate, a metal substrate and so forth.

In step SIl, a sacrificial structure is formed on the substrate. The sacrificial structure supports nanostructures, which will be formed later, to be formed in a desired direction. To serve as a supporter, the sacrificial structure should have at least one face in a direction that the nanostructures are to be formed. For instance, when the nanostructures are supposed to be formed perpendicularly to the substrate, the sacrificial structure should have a face perpendicular to the substrate. There is not much limitation for the material used as the sacrificial structure, and any material is available as long as the material can be patterned easily and readily removed during a subsequent process. A metal or semiconductor material can be used for forming the sacrificial structure as well. Subsequently, in step S12, nanostructures are formed on the sacrificial structure, particularly, at least on the face of a direction that the nanostructures are to be formed. For example, if the nanostructures are formed on a face perpendicular to the substrate of the sacrificial structure, the nanostructures can be arranged vertically. As described earlier, it is possible to use nanotube (e.g., carbon nanotube), nanowire (e.g., semiconductor nanowire) as nanostructures. The nanostructures may be arranged on the substrate by using the well-known linker molecular layer patterning method or the anti-adsorption molecular layer patterning method. This will be described in detail hereafter with reference to Fig. 2. In step S13, the sacrificial structure is removed. The sacrificial structure can be removed by selecting a sacrificial structure removing method in consideration of the material used to form the sacrificial structure. The sacrificial structure removing method may be a wet etching method where the resultant substrate is immersed in a solution capable of melting the sacrificial structure .

With this process, it is possible to easily arrange the nanostructures in a desired direction on the substrate. According to conventional technology, when the nanostructures should be arranged vertically, it is quite difficult to vertically grow nanostructures because the process is performed at high temperature, and to control the growth angle. However, if we use the sacrificial structure as suggested in the present invention, it does not have to go through the high- temperature process just as the nanostructures are arranged on a plane and it is possible to control the angle of the nanostructures by adjusting the angle of the sacrificial structure. Therefore, it is easy to perform the process.

Fig. 2 is a perspective view illustrating a method for fabricating a nano device in accordance with an embodiment of the present invention. In particular, the present specification describes fabrication of a nano device including a first electrode and a second electrode spaced apart from each other in a vertical direction, and nanostructures connecting the first electrode with the second electrode. The nano device may be used as a sensor.

As shown in (a) of Fig. 2, a substrate 20 is provided. The substrate 20 may be a Si substrate, a SiO₂ substrate, a glass substrate, a metal substrate and so forth. In an embodiment of the present invention, it is assumed that the substrate is a SiO₂ substrate.

Subsequently, a sacrificial structure 21 is formed on the substrate 20. The sacrificial structure 21 includes a vertical face, which is perpendicular to the substrate 20, and a horizontal face, which is disposed in parallel to the substrate 20 on top of the substrate 20 while connected to the vertical face. In an embodiment of the present invention, the sacrificial structure has a shape of a rectangular hexahedron. The vertical face of the sacrificial structure 21 is for subsequent formation of nanostructures, and the horizontal face is for subsequent fabrication of a second electrode.

The sacrificial structure 21 may be formed of a metal or semiconductor material. In the embodiment of the present invention, the sacrificial structure 21 is formed of Al.

Referring to (b) of Fig. 2, nanostructures 22 are formed in a certain region (see ^ΛB' ) on the substrate 20 including the sacrificial structure 21. The nanostructures 22 may be nanotube or nanowire. In the embodiment of the present invention, the nanostructures 22 are formed using the well-known linker molecular layer patterning method or anti-adsorption molecular layer patterning method. The process of forming the nanostructures 22 will be described in detail hereafter. First of all, a molecular layer for discriminating a region B where the nanostructures are to be arranged among the regions on the substrate 20 with the sacrificial structure 21 from the other regions (see ^λA' ) are formed. When the degree of adsorption between the molecular layer and the nanostructures is low, the molecular layer is patterned to exist in the A region. For instance, if the nanostructures 22 are nanowire with an oxide in the surface, a hydrophobic molecular layer, e.g., octadecytrichlorosilane (OTS), is patterned to exist in the A region. On the other hand, when the degree of adsorption between the molecular layer and the nanostructures is high, the molecular layer is patterned to exist in the B region. For instance, if the nanostructures 22 are nanowire with an oxide in the surface, a hydrophilic molecular layer is patterned to exist in the B region.

Subsequently, when the resultant substrate with the molecular layer formed therein is immersed in a solution including the nanostructures 22, the nanostructures 22 are self-assembled on the surface of the resultant substrate according to the degree of adsorption between the molecular layer and the nanostructures 22. To be specific, the nanostructures 22 are arranged in the B region of the substrate 20 including the sacrificial structure 21, as the nanostructures 22 are adsorbed to the surface of the B region of the substrate 20 (which is a case that a molecular layer with a low adsorption degree to the nanostructures 22 is patterned to exist in the A region), or as the nanostructures 22 are adsorbed to the molecular layer of the B region (which is a case that a molecular layer with a high adsorption degree to the nanostructures 22 is patterned to exist in the B region).

Consequently, the nanostructures 22 are formed in a certain region (where the nanostructures 22 are to be arranged) on the resultant substrate with a sacrificial structure. However, since the nanostructures 22 are formed along the surface of the sacrificial structure 21 in the lower part, the nanostructures 22 are perpendicularly arranged relying on the vertical face of the sacrificial structure 21.

Referring to (c) of Fig. 2, a first electrode 23a and a second electrode 23b are formed to expose nanostructures 22 on one side (see ^ΛC ) among the nanostructures 22 vertically arranged on a pair of vertical faces of the sacrificial structure 21 and to cover the other nanostructures 22.

Consequently, the first electrode 23a and the second electrode 23b are formed apart from each other in a vertical direction to both ends of the nanostructures 22. The method of forming the first electrode 23a and the second electrode 23b will be described in detail hereafter .

First, a photoresist pattern (not shown) exposing a region where the first electrode 23a and the second electrode 23b are to be formed is formed over the profile of the resultant structure. Subsequently, a conductive material, e.g., metal, for forming electrodes is deposited on the resultant structure including the photoresist pattern. Herein, metal is deposited in a diagonal direction (see arrow mark) from a direction of a first side which is a vertical face confronting a vertical face of the sacrificial structure 21 with the nanostructures 22 (C) to be exposed by the formation of the first and second electrodes 23a and 23b between a pair of vertical phases of the sacrificial structure 21. As a result, although metal is disposed in a region where the first and second electrodes 23a and 23b are to be formed, it exposes the part (C) of the nanostructures 22 vertically arranged in a second side of the sacrificial structure 21. Lastly, the photoresist pattern is removed to thereby complete the formation of the first and second electrodes 23a and 23b.

Referring to (d) of Fig. 2, the sacrificial structure 21 is removed. The sacrificial structure 21 is removed by immersing the resultant structure in a solution capable of dissolving the sacrificial structure

21 away, which is called a wet etching method. When the sacrificial structure 21 is formed of Al as depicted in the embodiment of the present invention, the sacrificial structure 21 can be dissolved by using an acid solution.

The resultant structure without the sacrificial structure 21 is dried. Herein, it is advantageous to dry the resultant structure by using a Critical Point Dryer (CPD) from the perspective of throughput.

As a result of the process shown in the drawing, a nano device with the entire surface of the part (C) of the vertically arranged nanostructures 22 exposed and the first and second electrodes 23a and 23b disposed at both ends is fabricated.

The method of the present invention can easily fabricate a nano device with vertically arranged nanostructures at relatively low temperature.

Furthermore, when the nano device is used as a sensor, it is possible to improve the susceptibility of the sensor because the nanostructures, which is a sensing unit, is exposed in all directions of 360°.

Also, since the electrodes disposed at both ends of the nanostructures stretch out the nanostructures in the upper and lower parts, the sensor becomes insensitive to minor external mechanical noises, which is advantageous .

Fig. 3 is a photograph showing an exemplary nano device fabricated according to the method of Fig. 2. While the present invention has been described with respect to the specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.

Claims

WHAT IS CLAIMED IS

1. A method for arranging nanostructures in a certain direction, comprising: forming a sacrificial structure having a face in the certain direction on a substrate; forming the nanostructures at least on the face of the certain direction of the sacrificial structure; and removing the sacrificial structure.

2. The method of claim 1, wherein said forming the nanostructures at least on the face of the certain direction of the sacrificial structure includes: forming a molecular layer for discriminating a region where the nanostructures are to be formed on a resultant structure including the sacrificial structure from other regions; and self-assembling the nanostructures in the region where the nanostructures are to be formed based on a degree of adsorption between the molecular layer and the nanostructures .

3. The method of claim 1, wherein the nanostructures are nanowire or nanotube.

4. The method of claim 1, wherein the sacrificial structure is removed through a wet etching method.

5. A method for fabricating a nano device including a first electrode and a second electrode spaced apart from each other in a vertical direction, and nanostructures arranged to connect the first and second electrodes, comprising: forming a sacrificial structure connected to a vertical face and a horizontal face on the substrate and having the horizontal face in parallel to a substrate; forming the nanostructures at least on the vertical face of the sacrificial structure; forming the first and second electrodes on the horizontal face and the substrate at both ends of the nanostructures; and removing the sacrificial structure.

6. The method of claim 5, wherein said forming the nanostructures at least on the vertical face of the sacrificial structure includes: forming a molecular layer for discriminating a region where the nanostructures are to be formed on a resultant structure including the sacrificial structure from other regions; and self-assembling the nanostructures in the region where the nanostructures are to be formed based on a degree of adsorption between the molecular layer and the nanostructures .

7. The method of claim 5, wherein the nanostructures are arranged in the region where the first and second electrodes are to be formed.

8. The method of claim 5, wherein the nanostructures are nanowire or nanotube .

9. The method of claim 5, wherein the sacrificial structure is removed through a wet etching method.

10. The method of claim 5, further comprising: drying the resultant structure after removing the sacrificial structure.

11. The method of claim 9, further comprising: drying the resultant structure after removing the sacrificial structure.

12. The method of claim 5, wherein the nano device is a sensor.