KR100988322B1 - Carbon ananotube Schottky diode and a method for fabricating the same - Google Patents

Abstract

The present invention is an insulating layer formed on a substrate;

Two electrodes spaced apart from each other on the insulating layer; And

It includes; a channel consisting of carbon nanotubes connecting the two electrodes,

The two electrodes are the same metal,

Disclosed is a carbon nanotube Schottky diode in which a metal having a lower work function or an oxide thereof is present at a contact point between any one of the two electrodes and the channel.

Carbon ananotube, Schottky diode

Description

Carbon ananotube Schottky diode and a method for fabricating the same

The present invention relates to a carbon nanotube schottky diode and a method of manufacturing the same, and more particularly, to a carbon nanotube schottky diode having a metal having a lower work function than the electrode at a contact point between an electrode and a carbon nanotube and a manufacturing method thereof. It is about a method.

Among the one-dimensional nanostructures, carbon nanotubes are suitable for use as one component of high-performance nanoelectronic devices because of their excellent electrical characteristics. For example, single-wall carbon nanotube field effect transistors (SWNT-FETs) can be used to understand the intrinsic electrical properties and implementation of sensitive chemical and biological sensors.

Compared to field effect transistor devices, carbon nanobutte diode devices are of relatively low interest due to complex manufacturing processes.

In order to manufacture p-n junction carbon nanotube diodes, a complicated process of preparing p-type and n-type semiconducting carbon nanotubes by chemical doping is essential.

Carbon nanotube Schottky diodes, due to asymmetric work function energy levels, can be obtained by contacting metallic electrodes that are energy asymmetric. Schottky diodes have advantages such as low forward resistance and low levels of noise over p-n junction diodes. However, there is still a need for a complex lithography process in which two different kinds of metal electrodes must be arranged sequentially.

Carbon nanotube Schottky diodes are described in Appl. Phs. Lett. 2002, 87 , 253116; J. Appl . Phys . Lett . 2006, 88 , 133501, and the like.

Therefore, there is still a need for a method of manufacturing a simpler carbon nanotube Schottky diode.

An insulating layer formed on the substrate;

Two electrodes spaced apart from each other on the insulating layer; And

It includes; a channel consisting of carbon nanotubes connecting the two electrodes,

The two electrodes are the same metal,

A carbon nanotube Schottky diode in which a metal having a lower work function or an oxide thereof is present at a contact point of one of the two electrodes and the channel.

Preparing a substrate having an insulating layer formed on one surface thereof;

Forming a channel made of carbon nanotubes on the surface of the insulating layer;

Forming two electrodes spaced apart from each other to be connected to the channel on a surface of the insulating layer;

Attaching a compound including an aromatic hydrocarbon ring fused to a surface of the carbon nanotubes;

Injecting metal ions between the carbon nanotubes and the compound including an aromatic hydrocarbon ring fused to the carbon nanotubes; And

Provided is a method of manufacturing a carbon nanotube Schottky diode comprising a; applying a bias voltage between the two electrodes.

Hereinafter, a carbon nanobute Schottky diode and a method of manufacturing the same according to a preferred embodiment of the present invention will be described in more detail.

According to an embodiment of the present invention, the carbon nanotube Schottky DIO, with reference to FIG. 1, may include an insulating layer 12 formed on the substrate 11; Two electrodes 13a and 13b spaced apart from each other at predetermined intervals on the insulating layer 12; And a channel 14 made of carbon nanotubes connecting the two electrodes, wherein the two electrodes are the same metal, and one of the two electrodes 13a and the channel 14 is formed. At the contact point, there is a metal 15 or an oxide thereof having a lower work function compared to the metal constituting the electrode.

The carbon nanobute Schottky diode differs in the work function of the two electrodes due to the presence of metal having a lower work function than the metal forming the electrode at the contact point of one of the same two electrodes and the carbon nanobube. As a result, a carbon nanotube Schottky diode can be realized.

For convenience of description, the electrode 13a in which the metal having a low work function is present at the contact point is called a drain electrode and the other electrode 13b is called a source electrode.

Hereinafter, the operating principle of the carbon nanotube Schottky diode will be described in more detail with reference to FIGS. 1 and 2. The following description is to aid the understanding of the present invention and is not intended to limit the scope of the present invention to the following description.

The metal 15 or oxide thereof having a lower work function than the metal forming the drain electrode 13a, which is present at the contact point of the drain electrode 13a and the carbon nanotube channel 14, is formed of the drain electrode 13a. Reduce work function (Δμ _f ). As a result, a Schottky barrier (SB) is increased at the contact point of the drain electrode 13a and the carbon nanotube 14. In contrast, the energy level of the contact point of the source electrode 13b and the carbon nanotube 14 is kept constant without change. As a result, when a negative bias voltage is applied to the diode, the transfer of holes from the drain electrode 13a to the carbon nanotubes 14 is prevented, so that no current flows, and conversely, a positive bias When a voltage is applied, holes are easily transferred from the source electrode 13b to the carbon nanobuttes 14, so that a current flows in proportion to the magnitude of the bias voltage. As a result, the characteristics of the Schottky diode are realized.

According to another embodiment of the present invention, it is preferable that a compound including an aromatic hydrocarbon ring fused to the surface of the carbon nanotubes is present. The fused aromatic hydrocarbon ring included in the compound has a structure similar to graphene (graphene) can be physically adsorbed on the surface of the carbon nanotubes through Van der Waals force. The number of carbon atoms contained in the fused aromatic hydrocarbon ring is preferably 10 to 50. The compound containing the fused aromatic hydrocarbon ring is preferably 1-pyrenemethylamine, anthracene, pentacene, coronine, or a mixture thereof.

According to another embodiment of the present invention, metal ions are preferably inserted between the carbon nanotube and the compound including the fused aromatic hydrocarbon ring. Since the compound including the fused aromatic hydrocarbon ring and the carbon nanotubes each have a structure similar to graphene, the graphene is similar to graphite, in which the graphene is sequentially stacked. Lithium ions are intercalated between the graphenes of graphite used as a negative electrode during charge and discharge in lithium batteries. Thus, metal ions can be inserted between the carbon nanotubes and the compound containing the fused aromatic hydrocarbon ring in a similar manner as in the lithium battery. The metal ions are preferably lithium ions, sodium ions, potassium ions, cesium ions or a mixture thereof.

According to another embodiment of the present invention, in the carbon nanotube Schottky diode, the metal having a lower work function than the metal constituting the electrode is preferably lithium, sodium, potassium, or an alloy thereof, and has a low work function. The metal oxide is preferably lithium oxide, sodium oxide or the like. The metal constituting the electrode is not particularly limited as long as it is a metal used in the manufacture of electrodes such as diodes and transistors in the art, for example, gold (Au), silver (Ag), aluminum (Al) and the like.

According to another embodiment of the present invention, the carbon nanotubes constituting the carbon nanotube channel in the carbon nanotube Schottky diode are particularly preferably single-walled carbon nanotubes (SWNT) having semiconductor properties.

According to another embodiment of the present invention, a method of manufacturing a carbon nanotube Schottky diode may include preparing a substrate 11 having an insulating layer 12 formed on one surface thereof; Forming a channel 14 made of carbon nanotubes on a surface of the insulating layer to a predetermined length; Forming two electrodes 13a and 13b spaced apart from each other at predetermined intervals so as to be connected to the channel made of carbon nanobutres on the surface of the insulating layer; Attaching a compound including an aromatic hydrocarbon ring fused to a surface of the carbon nanotubes; Injecting metal ions between the carbon nanotubes and the compound including an aromatic hydrocarbon ring fused to the carbon nanotubes; And applying a predetermined bias voltage between the two electrodes.

In the manufacturing method, metal ions implanted between the carbon nanotubes and the compound including the aromatic hydrocarbon ring fused by the bias voltage are moved to one of the two electrodes, and thus the carbon nanotubes. Reduced at the junction of, the work function of the metal ions is lower than the work function of the metal forming the electrode, resulting in a lower work function of the electrode.

That is, by injecting and reducing metal ions having a lower work function than the metal forming the electrode, the result is substantially the same as that of a carbon nanotube Schottky diode in which electrodes are formed of two metals having different work functions. to provide. Therefore, a carbon nanotube Schottky diode having an asymmetric work function energy level can be manufactured by a simpler method than in the related art.

A method of manufacturing the carbon nanotube Schottky diode will be described in more detail below.

A substrate having an insulating layer formed on one surface is prepared. The substrate is preferably a semiconductor substrate, for example a p-type silicon substrate. The insulating layer may be formed by oxidizing the substrate. Subsequently, a channel made of carbon nanotubes is formed on the surface of the insulating layer to have a predetermined length. The carbon nanobubble channel may be formed by directly synthesizing carbon nanotubes on the surface of the insulating layer. The method for forming a channel made of carbon nanotubes is a method for synthesizing carbon nanotubes, and any method used in the art may be used without particular limitation. The channel is not particularly limited in length if the carbon nanotubes are electrically connected. Subsequently, two electrodes spaced at predetermined intervals are formed on the surface of the insulating layer so as to be connected to the channels made of the carbon nanobutres. The formation of the electrode can be carried out in a conventional lithographic manner. For example, a metal thin film layer may be formed on the insulating layer on which the carbon nanotube channel is formed, and the thin film layer may be patterned in an electrode form by lithography. Subsequently, the substrate is immersed in a solution in which the compound including the fused aromatic hydrocarbon ring is dissolved for a predetermined time to attach the compound including the fused aromatic hydrocarbon ring to the surface of the carbon nanotube. Subsequently, the substrate to which the compound containing the fused aromatic hydrocarbon ring is attached is immersed in a solution containing lithium salt, and thus, between the carbon nanotube and the graphene plane of the compound containing the fused aromatic hydrocarbon ring. Inject metal ions. Finally, a predetermined bias voltage is applied between the two electrodes to reduce the metal ions at the contact between one of the electrodes and the carbon nanotube, thereby lowering the work function, thereby making the work function of the two metals asymmetric. It will have one value.

The present invention is described in more detail through the following examples and comparative examples. However, the examples are provided to illustrate the present invention, and the scope of the present invention is not limited only to these examples.

(Manufacture of Carbon Nanobutte Field Effect Transistor)

Production Example  One

Channels made of single-walled carbon nanotubes were directly synthesized on SiO ₂ / Si substrates to form channels of constant length. Carbon nanotubes were synthesized by chemical vapor deposition on the SiO ₂ / Si substrate (doped p-type silicon (111) substrate having a 300 nm thick SiO ₂ layer formed thereon). . Subsequently, two Cr (5 nm) / Au (20 nm) electrodes were formed to be spaced apart when connected to the channel by a conventional lithography method. The substrate was immersed for 30 minutes in a dimethylformamide (DMF) solution of 6 mM 1-pyrenemethylamine at room temperature. The substrate was then washed thoroughly with dimethylformamide and isopropyl alcohol. Subsequently, the substrate was immersed in 0.1 M LiPF ₆ solution using a mixed solvent of propylene carbonate (PC) and dimethoxyethane (DME) (mixing ratio of 1: 1 by volume) for 3 hours. Subsequently, the substrate was washed sequentially with a mixed solvent of propylene carbonate (PC) and dimethoxyethane (DME) and isopropyl alcohol, and then dried in a nitrogen atmosphere. The two electrodes are a drain electrode and a source electrode, respectively. The substrate may be used as a bottom gate to have a transistor structure.

Production Example 2

A transistor was manufactured in the same manner as in Preparation Example 1, except that dozens of channels including the single-walled carbon nanotubes were formed at regular intervals.

(Manufacture of Carbon Nano Butte Schottky Diode)

Example 1

Applying a bias voltage between the electrodes such that the drain electrode of the transistor prepared in Preparation Example 1 becomes (-) and the source electrode is (+), the lithium ions are reduced on the surface of the drain electrode to form a carbon nanotube Schottky diode Was produced.

Example 2

A diode was manufactured in the same manner except for using the transistor prepared in Preparation Example 2 instead of the transistor prepared in Preparation Example 1.

Evaluation Example 1 Evaluation of Electrical Characteristics of Diodes

The results of evaluating the electrical characteristics of the carbon nanobute Schottky diode manufactured in Example 1 are shown in FIG. 3. In FIG. 3, the gate voltage is 0V.

As shown in blue in FIG. 3, when the voltage V _ds between the drain electrode and the source electrode is in the forward direction, the current value is proportional to the magnitude of the voltage, but when the reverse direction is not, the current does not flow. Thus, the electrical properties of a typical Schottky diode are shown.

The graphs shown in black and red in FIG. 3 are the results of evaluating the electrical characteristics of the device before 1-pyrenemethylamine is attached and the device before lithium ion is injected. The results show that the electrical properties of the field effect transistor (FET) are simply shown before the lithium ions are reduced at the junction of the drain electrode and the carbon nanotube.

Evaluation Example 2; Measurement of the distribution of lithium

The distribution of lithium ions injected into the carbon nanobute channel of the diode prepared in Example 2 was measured and shown in FIGS. 4A to 4D.

As shown in (d) of FIG. 4, the closer the drain electrode is, the higher the concentration of lithium is. Accordingly, it can be seen that lithium ions move toward the drain electrode due to the bias voltage, and thus reduction occurs at the contact point between the drain electrode and the carbon nanotube.

Evaluation Example 3: AFM Measurement

In Example 1, the single-wall carbon nanotube channel before immersion in 1-pyrenemethylamine solution, the carbon nanotube channel after 1-pyrenemethylamine was attached, and the carbon nanotube channel after lithium ion was injected, respectively. The atomic force microscope (AFM) was measured at the same position, and the appearance and height thereof were compared, and are represented by (c) to (e) in FIG. 5.

As shown in (c) to (e) of FIG. 5, the topology of the carbon nanotube channel was almost unchanged even after immersion in 1-pyrenemethylamine solution and after immersion in lithium ion solution. . However, the height of the carbon nanotube channel increased from 1.71nm to 2.52nm and 2.62nm, respectively. These results show that 1-pyrenemethylamine is attached to the carbon nanotubes and lithium ions are injected between the 1-pyrenemethylamine and the carbon nanotubes.

If the lithium ions are not implanted between 1-pyrenemethylamine and carbon nanotubes, they will form clusters by electrostatic attraction on the surface of the carbon nanotubes. The formation of such clusters is found a lot from common metal ions. Carbon nano with 1-pyrenemethamine attached to 100 mM CuCl ₂ (ethanol) solution (a), RuCl ₂ (ethanol) solution (b), SnCl ₄ (methanol) solution and ZnCl ₂ (acetone) solution (d) The clusters can be confirmed from FIGS. 6A to 6D, which are AFM results measured after immersing the substrate on which the tube channel is formed. In the figure, indicated by a red dot is a cluster.

Evaluation Example 4: UV-Vis Spectrum Measurement

Carbon nanotubes (a) before being immersed in 1-pyrenemethylamine solution, 60mM 1-pyrenemethylamine (b) dissolved in DMF solvent, and carbon nanotubes after immersing in 1-pyrenemethylamine solution (c ) And UV-Vis spectra for each of the carbon nanotubes (d) immersed in a lithium ion solution are shown in FIG. 7.

After immersion, not 1-pyrenemethyl, in the UV-vis spectrum, peaks due to pyrenemethylamine are identified, unlike the spectrum of carbon nanotubes before immersion. From the results of FIG. 7, it can be seen that 1-pyrenemethylamine was successfully attached to the surface of the carbon nanotubes.

1 is a schematic view showing the structure of a carbon nanotube Schottky diode according to an embodiment of the present invention.

Figure 2 is a battery level diagram illustrating the operating principle of the carbon nanotube Schottky diode according to an embodiment of the present invention.

3 is a graph showing the electrical characteristics of the carbon nanotube Schottky diode according to an embodiment of the present invention.

Figure 4 (a) is an optical microscope image of a carbon nanotube Schottky diode according to an embodiment of the present invention, (b) is a scanning photomicroscope Au 4f intensity distribution image for the diode, (c) is The space-resolved XPS Li1s spectrum obtained between the electrodes after lithium movement to the A, B, C, and D positions indicated in (b), and (d) is the Li 1s peak with distance from the source electrode. A graph showing the area strength of

Figure 5 (c) is a single-wall carbon nanotubes before immersion in 1-pyrenemethylamine solution, (d) is a single-wall carbon nanotubes after immersion in 1-pyrenemethylamine solution, (e) is lithium An atomic force microscope (AFM) image of a single-walled carbon nanotube after immersion in a salt solution.

(A) after immersing in 100 mM CuCl ₂ ethanol solution, (b) after immersing in 100 mM RuCl ₂ ethanol solution, (c) after immersing in 100 mM SnCl ₄ methanol solution and (d ) Atomic force microscope images of single-walled carbon or notubes with 1-pyrenemethamine after immersion in 100 mM ZnCl ₂ acetone solution.

Figure 7 (a) is a single-walled carbon nanobute before immersion in 1-pyrene methyl solution, (b) 60-mM 1-pyrenemethylamine dimethylformamide solution, (c) 1-pyrenemethylamine attached UV-Vis spectra for single-walled carbon nanotubes, and single-walled carbon nanotubes after lithium injection.

Claims (12)

An insulating layer formed on the substrate; Two electrodes spaced apart from each other on the insulating layer; It includes; a channel consisting of carbon nanotubes connecting the two electrodes, The two electrodes are the same metal, A carbon nanotube Schottky diode having a metal having a lower work function or an oxide thereof at a contact point of one of the two electrodes and the channel, compared to a metal constituting the electrode. The carbon nanotube Schottky diode according to claim 1, wherein a compound including an aromatic hydrocarbon ring fused to the surface of the carbon nanotube is present. 3. The carbon nanotube Schottky diode according to claim 2, wherein the compound containing the fused aromatic hydrocarbon ring is at least one selected from the group consisting of 1-pyrenemethylamine, anthracene, pentacene and coronine. 3. The carbon nanotube schottky diode according to claim 2, wherein a metal ion is inserted between the carbon nanotube and the compound containing the fused aromatic hydrocarbon ring. 5. The carbon nanotube schottky diode according to claim 4, wherein the metal ion is at least one metal ion selected from the group consisting of lithium ions, sodium ions, potassium ions and cesium ions. The carbon nanotube Schottky diode according to claim 1, wherein the metal having a lower work function than the metal constituting the electrode is at least one metal selected from the group consisting of lithium, sodium, potassium, and cesium. The carbon nanotube schottky diode of claim 1, wherein the oxide having a lower work function than the metal constituting the electrode is at least one metal oxide selected from the group consisting of lithium oxide and sodium oxide. 2. The Schottky diode of claim 1, wherein the carbon nanotubes are made of single-walled carbon nanotubes having semiconductor properties. Preparing a substrate having an insulating layer formed on one surface thereof; Forming a channel made of carbon nanotubes on the surface of the insulating layer; Forming two electrodes spaced apart from each other on the surface of the insulating layer so as to be connected to the channel; Attaching a compound including an aromatic hydrocarbon ring fused to a surface of the carbon nanotubes; Injecting metal ions between the carbon nanotubes and the compound including an aromatic hydrocarbon ring fused to the carbon nanotubes; And Applying a bias voltage between the two electrodes; and manufacturing a carbon nanotube Schottky diode. 10. The method of claim 9, wherein the compound comprising the fused aromatic hydrocarbon ring is at least one selected from the group consisting of 1-pyrenemethylamine, anthracene, pentacene and coronine. Way. 10. The method of claim 9, wherein the metal ion has a lower work function than the metal forming the electrode. 10. The method of claim 9, wherein the metal ion is at least one metal ion selected from the group consisting of lithium ions, sodium ions, potassium ions, and cesium ions.

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