JP2003332266A - Wiring method for nanotube and control circuit for nanotube wiring - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for easily and surely wiring nanotubes in an objective position. <P>SOLUTION: Ethanol 16 where the nanotubes 17 are dispersed is dropped between an electrode 13 and an electrode 14. A high frequency voltage is applied between the electrode 13 and the electrode 14 by using AC power 18. The nanotubes 17 in ethanol 16 electrically and freely move. When one of the tubes comes to a position connecting the electrodes, it is bonded to both electrodes by van der Waals force. When the tube is once bonded, the nanotube is prevented from easily being removed from the electrode by van der Walls force. A circuit for detecting that the nanotube 17 is bonded to a part between the electrodes and for automatically stopping application of the high frequency voltage by monitoring an electric resistance value between the electrode 13 and the electrode 14 can be used. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to the field of manufacturing semiconductors and electronic devices using nanotubes, and research and development related to nanotubes.

[0002]

2. Description of the Related Art In order to improve the performance of semiconductor integrated circuits, it is essential to improve the degree of integration. For that purpose, miniaturization of the circuit is effective. In the current circuits using silicon, the size of the constituent elements is a minimum of about 100 nm on each side. This value has been decreasing year by year due to improvements in microfabrication technology, but in order to meet the demand for further miniaturization in the future, fundamental review of the material is being considered. The nanotubes typified by carbon nanotubes are attracting the most attention as the material.

Nanotubes have a one-dimensional structure, and their width is in nanometer units. There are both those showing metallic electrical conductivity and those having semiconductor-like electrical conductivity due to the difference in structure. By using these as elements such as capacitors and transistors and wiring materials, it is expected that the circuit will be miniaturized and an integrated circuit having a degree of integration higher than that of the conventional one by about two orders of magnitude will be obtained. Further, since nanotubes exhibiting metallic electrical conductivity have high electrical conductivity close to ballistic conduction, it is expected that the operation speed of the device will be further increased.

In order to put an integrated circuit using nanotubes into practical use, it is necessary to be able to process wiring and the like.
In the case of wiring nanotubes to electrodes, until now, the nanotubes were dispersed on a substrate and then the electrodes were deposited using a lithographic method, or the nanotubes were moved one by one using a scanning probe microscope technique. Techniques such as forming circuits have been used.

[0005]

The former method using lithography is a method that is an extension of the conventional semiconductor device manufacturing technology. However, the means for surely arranging the nanotube at the target position has not been established, and since the nanotube that happens to come to the target position is used, the reliability is low and the efficiency is low. Also, when the latter scanning probe microscope is used, the nanotube can be placed at the target position, but it is difficult to automate and it takes time even if it depends on human hands, so it is practical in terms of mass production. Not a traditional method.

Also, in the field of research and development of nanotubes, since the above two methods are used for wiring for measuring the physical properties, labor is spent. For example, even if a new type of nanotube is discovered, the problem is that it takes time to measure the physical properties of the nanotube and obtain the results of the research.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a method for easily and surely wiring a nanotube at a desired position. Also provided is a control circuit used to implement the method.

[0008]

In order to solve the above-mentioned problems, a method of wiring nanotubes according to the present invention is designed so that a solvent in which nanotubes are dispersed is dropped between electrodes and an AC voltage is applied between the electrodes. This is characterized in that the nanotubes are wired between the electrodes.

In the nanotube wiring method, a change in electric resistance between electrodes is monitored, and when it is detected that the nanotubes are wired between the electrodes, an AC voltage is applied between the electrodes. It is desirable to stop.

The nanotube wiring control circuit according to the present invention, which realizes such a method, comprises: a) an AC power supply for applying an AC voltage between electrodes for wiring nanotubes; and b) an electric resistance value between the electrodes. It is characterized by including an electric resistance value detection circuit for detecting, and c) a disconnection circuit for stopping application of an AC voltage between the electrodes when the electric resistance value becomes equal to or lower than a predetermined value.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The method of wiring a nanotube according to the present invention is as follows.

First, the nanotubes are dispersed in a solvent. Here, “dispersion” means that individual nanotubes exist in the solvent in a scattered manner. As the solvent, for example, methanol or ethanol can be used,
Other solvents may be used.

After the solvent is dropped between the electrodes, an AC voltage is applied between the electrodes. The dropped nanotubes in the solvent are electrophoresed by the electric field between the electrodes. here,
When a DC voltage is applied instead of an AC voltage, the nanotubes are rapidly attracted to the electrodes, making it difficult to pass the nanotubes between the electrodes. By applying an alternating voltage, the nanotubes will be correctly positioned between the electrodes by electrophoresis. The frequency of the alternating voltage is preferably 10 MHz or less in order to cause such electrophoretic movement of the nanotubes in the solvent. Also,
The magnitude of the applied voltage is determined in consideration of the electrophoretic driving force and the discharge.
It should be appropriately adjusted according to the distance between the electrodes and the type of solvent, but it is generally desirable to set it to 0.1V to 10V.

One of many nanotubes passes between the electrodes, that is, one end of one nanotube comes to the position of one electrode, and the other end comes to the position of the other electrode. Then both ends of the nanotube are attached to their respective electrodes by Van der Waals forces, and
The central portion also adheres to the substrate between the electrodes, and the entire nanotube is fixed between the electrodes. Since the nanotubes have a small diameter, they have a strong fixing force due to Van der Waals forces, and once attached to the electrodes, they cannot be easily detached.

The operation described above completes the work of wiring the nanotubes between the electrodes. By collecting the remaining solvent, it is possible to remove the extra unwired nanotubes remaining in the solvent.

By providing a location where the electric field is concentrated at the opposing portions of both electrodes, the wiring position of the nanotube can be controlled. For example, by forming at least one of the facing portions of both electrodes into a pointed shape (it may be an obtuse angle), electric lines of force connecting both electrodes are concentrated in the pointed portion. As a result, the nanotubes are oriented so that their longitudinal directions are along the lines of electric force, and adhere to the sharp parts of the electrodes.

In addition to the most commonly used carbon nanotubes at the present time, the method according to the present invention is a boron carbon in which some or all of the carbon atoms are replaced with boron (B) or nitrogen (N). It is believed that the properties related to electrophoresis are similar for nitrogen nanotubes (BCN nanotubes), boron nitrogen nanotubes (BN nanotubes), and other nanotubes that have been chemically modified for the purpose of high functionality. Therefore, it can be applied.

At the moment when the nanotubes are wired, the electric resistance value between both electrodes changes from infinity to finite value. If a circuit that detects this change and a disconnection circuit that stops the application of AC voltage between the electrodes when the change is detected are provided, the wiring work will be performed automatically without wiring a predetermined number of nanotubes or more. Can be finished.

By properly setting the parameters of this circuit, the application of the AC voltage can be stopped when only one nanotube is attached, and only one nanotube can be wired between the electrodes. .

[0020]

According to the present invention, it becomes possible to wire nanotubes between electrodes more easily and reliably than in the conventional method. Therefore, the field effect transistor (F
It becomes easy to use nanotubes as a material for electronic circuits or electronic element devices such as ET), and mass production becomes possible. Also, in the research and development of nanotubes, the labor can be reduced by using this method, and the speed of research and development can be increased.

[0021]

EXAMPLES (1) One Example of Method for Wiring Nanotubes As an example of the present invention, a method for wiring a carbon nanotube of a semiconductor as a channel between a source electrode and a drain electrode of a FET will be described. FIG. 1 shows a cross-sectional view (completed view) of an FET using carbon nanotubes. The insulating layer 12 is provided on the gate electrode 11, and the source electrode 13 and the drain electrode 14 are arranged thereon. In this example, silicon (Si) was used for the gate electrode 11, and gold (Au) was used for the source electrode 13 and the drain electrode 14. The insulating layer 12 is
The surface of the gate electrode 11 was an oxidized SiO ₂ film.

In this embodiment, the source electrode 13 and the drain electrode 14 are comb-shaped electrodes as shown in FIG. A wide channel width can be obtained by using a comb-shaped electrode. In the comb-shaped electrode of the present embodiment, the width w of the arms forming the comb is 2
μm, and the gap d between the arms was 2 μm.

Ethanol 16 is dropped between the source electrode 13 and the drain electrode 14 and on both electrodes as shown in FIG. The carbon nanotubes 17 dispersed in the ethanol 16 at a concentration of about 10 ⁻⁵ g / L are included. If this concentration is too high, a large number of carbon nanotubes will be passed between the electrodes in a short time, and it will be difficult to control by a circuit described later. Therefore, it is necessary to select this concentration appropriately. The carbon nanotubes used have a length of 10 μm or less. Further, in this embodiment, since the carbon nanotube is used as the channel between the source and the drain of the FET, the single wall carbon nanotube which is a semiconductor is used. AC power supply 18 is applied to the source electrode 13 and the drain electrode 14.
Was connected and a high frequency voltage of 5 V and 5 MHz was applied.

FIG. 4 shows a scanning electron microscope (SEM) photograph of the FET manufactured by the above method. In the arms of the four Au electrodes extending in the left-right direction shown in this figure, the first and third from the top are for one electrode, and the second and fourth from the top are for the other electrode. FIG. 5 is a clear redraw of the lower half of FIG. The two arms extending in the left-right direction in FIG.
Lower two arms, ie each arm of two Au electrodes
It corresponds to each book. The carbon nanotubes are shown by white lines extending between the electrodes in FIG. 4 and by black lines between the electrodes in FIG. It can be confirmed that the carbon nanotubes are wired between the electrodes.

The characteristics of the FET manufactured in this example were evaluated. FIG. 6 shows current-voltage characteristics at various gate voltages Vg. The horizontal axis represents the voltage Vsd between the source electrode 13 and the drain electrode 14, and the vertical axis represents the current Id flowing out from the drain electrode 14. The current Id is larger when the negative gate voltage Vg is applied than when the positive gate voltage Vg is applied. This indicates that the FET manufactured in this example is an n-channel type. The carbon nanotube used
This is because it has properties as an n-type semiconductor. Since some carbon nanotubes have a property as a p-type semiconductor, a p-channel FET can be manufactured by the method of this embodiment.

FIG. 7 shows the relationship between the gate voltage Vg and the current Id when the source-drain voltage Vsd is 0.5V. When the gate voltage Vg is positive, the current Id becomes several orders of magnitude smaller than when the gate voltage Vg is negative. For example, the gate voltage Vg is + 0.5V
The current Id at is the current Id when the gate voltage Vg is -0.5V.
Of 1 / 100,000. In the FET manufactured in this example, the switch is ON when the gate voltage Vg is -0.5 V, and the gate voltage Vg is +0.
It can be used as a switching element that is switched off at 5V. The ON / OFF ratio, which represents the performance as a switching element, is approximately 10 ^5, which is sufficiently high for practical use.

By extrapolating the curve when the gate voltage Vg is negative in FIG. 7 as shown by the broken line in the figure, the rising voltage which is the gate voltage when the current Id is 0 becomes 0.

The mobility of electrons can be obtained from the slope of the broken line in FIG. Assuming that the channel width represented by the width of the charge passage between the source electrode and the drain electrode is 25 μm, which is the entire width where the source electrode and the drain electrode face each other, the mobility is 1.53 cm ² / Vsec. . However, in reality, the channel width is the width of the carbon nanotube that crosses between the electrodes, and its size is at most several hundreds nm, so the actual mobility is 0.1 to ¹ cm ² / Vsec which is practically necessary. It is considered to be about 100 cm ² / Vsec, which is sufficiently larger than the above.

As shown in FIG. 8, by making the facing portions of both electrodes sharp, the lines of electric force connecting both electrodes are concentrated at the sharp portions. As a result, the nanotubes are oriented so that their longitudinal directions are along the lines of electric force, and are selectively attached to the sharp portions of the electrodes. Note that only one of the electrodes may be sharpened.

(2) One Embodiment of Nanotube Wiring Control Circuit Next, FIG. 9 shows one embodiment of the nanotube wiring control circuit according to the present invention. An AC power supply 18 is connected between the source electrode 13 and the drain electrode 14 of the FET,
The switching transistor 3 between the drain electrode 14 and the drain electrode 14.
5 is provided. The voltage applied to the source electrode 13 is applied to the amplifier 31.
Amplify with and convert to DC with the DC converter 32, and then the comparator 3
Input to one terminal of 4. The output terminal of the reference voltage generation circuit 33 is connected to the other terminal of the comparator 34.
The output terminal of the comparator 34 is connected to the gate of the switching transistor 35. 1 carbon nanotube
The variable resistance 37 in the reference voltage generation circuit 33 is set so that the output voltage Vsc of the DC converter 32 when only the number of wires is wired becomes a value slightly smaller than the reference voltage Vr output by the reference voltage generation circuit 33. Is set.

When the switch 36 is turned on, the reference voltage Vr is generated and the signal is sent to the comparator 34. When the AC power supply 18 is turned ON in that state, the output voltage Vs output from the DC converter 32 is compared with the reference voltage Vr. If Vs> Vr, the comparator 34 has almost zero potential, V
If s <Vr, a positive potential signal is sent to the switching transistor 35. As a result, if Vs> Vr, the AC power supply 18 is continuously applied, and if Vs <Vr, the application is stopped.

When this circuit is used in the FET manufacturing process, it is as follows. Source electrode 13 and drain electrode 1
The output voltage Vs (= Vsc) becomes smaller than the reference voltage Vr at the moment when one carbon nanotube is wired between 4 and
The comparator 34 outputs a positive voltage. As a result, the switching transistor 35 is turned off, the application of the AC voltage between the source electrode 13 and the drain electrode 14 is stopped,
The wiring work of carbon nanotubes is automatically completed.

In the above, the carbon nanotube is 1
The application of the AC voltage is stopped when only the wires are wired. However, by appropriately setting the value of the variable resistor 37, it is possible to stop the application of the AC voltage when a plurality of carbon nanotubes are arranged. You can also

The nanotube wiring method itself according to the present invention can be carried out without using the nanotube wiring control circuit. For example, when it is not necessary to strictly determine the number of nanotubes to be wired, or when the number of nanotubes to be wired is expected to some extent depending on the application time of the AC voltage, without using the above circuit,
For example, a timer may be used to control the time.
However, when precise control is required such as when only one carbon nanotube is wired, it is effective to use the above circuit.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an FET using carbon nanotubes manufactured according to an embodiment of the present invention.

FIG. 2 is a plan view showing a comb-shaped electrode of a FET using carbon nanotubes, which is manufactured according to an embodiment of the present invention.

FIG. 3 is a view showing a state where ethanol containing carbon nanotubes is dropped on a comb-shaped electrode.

FIG. 4 is a scanning electron micrograph of an electrode and a carbon nanotube produced in one example of the present invention.

FIG. 5 is a diagram in which a part of the micrograph of FIG. 4 is clearly redrawn.

[Figure 6] Source-drain voltage Vsd and drain current Id
The graph which showed the relationship of about various gate voltage Vg.

FIG. 7 is a graph showing an example of the relationship between the gate voltage Vg and the drain current Id.

FIG. 8 is a plan view showing an example in which electric field concentration portions are provided on both electrodes facing each other.

FIG. 9 is a circuit diagram showing a configuration example of a nanotube wiring control circuit.

[Explanation of symbols]

11 ... Gate electrode 12, 22 ... Insulating layer 13, 23 ... Source electrode 14, 24 ... Drain electrodes 15, 17, 25 ... Carbon nanotube 16 ... ethanol 18 ... AC power supply 31 ... Amplifier 32 ... DC converter 33 ... Reference voltage generation circuit 34 ... Comparator 35 ... Switching transistor

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01L 21/28 301 H01L 21/28 301Z 21/3205 29/78 618B 29/786 21/88 M (72) Inventor Kazumi Matsushige Yoshida Honcho, Sakyo-ku, Kyoto City F-term in Venture Business Laboratory (reference) 4G146 AA11 AB06 AD28 AD30 BA04 CB05 CB07 4M104 BB01 BB09 BB36 CC01 CC05 DD51 EE03 EE16 GG09 5F033 HH32 H0836A05A26A25 FF02 GG01 GG41 HK02

Claims (8)

[Claims] 1. A method of wiring nanotubes, characterized in that a solvent in which nanotubes are dispersed is dropped between two electrodes and an alternating voltage is applied between the electrodes to wire the nanotubes between the electrodes. 2. The nanotube wiring method according to claim 1, wherein an electric field concentration portion is provided on at least one of the facing portions of the both electrodes. 3. The application of an AC voltage between the electrodes is stopped when it is detected that the nanotubes are wired between the electrodes by monitoring a change in electric resistance between the electrodes. The method of wiring a nanotube according to claim 1 or 2. 4. The nanotube wiring method according to claim 1, wherein the nanotubes are carbon nanotubes. 5. The nanotube wiring method according to claim 1, wherein the nanotube is a boron carbon nitrogen nanotube or a boron nitrogen nanotube. 6. The nanotube wiring method according to claim 1, wherein the nanotubes are chemically modified nanotubes. 7. A method of manufacturing an electronic circuit or electronic element using nanotubes, characterized in that the wiring method according to any one of claims 1 to 6 is used. 8. An a) AC power supply for applying an AC voltage between electrodes for wiring nanotubes; b) an electric resistance value detection circuit for detecting an electric resistance value between the electrodes; and c) a predetermined electric resistance value. And a disconnection circuit that stops application of an AC voltage between the electrodes when the value becomes equal to or less than the value of.