JP2008071898A - Carbon nanotube field-effect transistor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon nanotube field-effect transistor enabled in rapid switching by suppressing hysteresis in a current flowing between a source electrode and a drain electrode which depends on a gate voltage. <P>SOLUTION: The carbon nanotube field-effect transistor comprises a channel 4 electrically connecting the source electrode 2 and the drain electrode 3 structure by a carbon nanotube and arranged on the surface of a gate insulating film 5 formed on the gate electrode 1, and uses a dielectric material having relative permittivity higher than that of an SiO<SB>2</SB>as a material of the gate insulating film 5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a carbon nanotube field effect transistor in which a channel portion that electrically connects a source electrode and a drain electrode is formed of carbon nanotubes, and a manufacturing method thereof.

In a conventional carbon nanotube field effect transistor, a SiO ₂ film as a gate insulating film is formed on the surface of a silicon substrate constituting a gate electrode, and a source electrode, a drain electrode, and a source electrode and a drain are formed on the surface of the gate insulating film. A channel portion that electrically connects the electrodes is disposed, and the channel portion is formed of carbon nanotubes.
When driving such a carbon nanotube field effect transistor, a gate voltage is applied to the gate electrode, and the magnitude of the current flowing through the channel portion between the source electrode and the drain electrode changes due to the change in the gate voltage (for example, non- Patent Document 1).
Woong Kim et al., Nano Lett., Vol.3, No.2 (2003) p.193-p.198

However, in the conventional carbon nanotube field effect transistor, the state of the current flowing between the source electrode and the drain electrode is changed when the gate voltage is changed from the minus side to the plus side and when the gate voltage is changed from the plus side to the minus side. It is very different from the case of changing. That is, a large hysteresis appears in the gate voltage dependency of the current flowing between the source electrode and the drain electrode. Such hysteresis prevents fast switching of the field effect transistor.
Accordingly, an object of the present invention is to provide a carbon nanotube field effect transistor that can be switched at high speed by suppressing hysteresis that appears in the gate voltage dependency of the current flowing between the source electrode and the drain electrode.

In the carbon nanotube field effect transistor of the present invention, the channel portion (4) for electrically connecting the source electrode (2) and the drain electrode (3) is formed of carbon nanotubes and formed on the gate electrode (1). A dielectric material having a relative dielectric constant higher than that of SiO ₂ was used as a material for the gate insulating film (5).

In the carbon nanotube field effect transistor of the present invention, a constant voltage is applied between the source electrode (2) and the drain electrode (3), and the source electrode is changed by changing the gate voltage applied to the gate electrode (1). The current flowing between (2) and the drain electrode (3) changes.
This is because effective Schottky barriers are formed at the interface between the channel portion (4) and the drain electrode (3) and at the interface between the channel portion (4) and the source electrode (2), and the gate voltage. The band bending of the channel part (4) changes due to the change of the channel part, and the interface between the channel part (4) and the drain electrode (3) and the channel part (by the change of the band bending of the channel part (4)) This is because the effective Schottky barrier thickness at the interface between 4) and the source electrode (2) changes.

By the way, in the conventional carbon nanotube field effect transistor, many adsorbing components such as water molecules exist on the surface of the gate insulating film using SiO ₂ as a material. Since a leakage electric field is generated from the channel portion by application of the gate voltage, ionized adsorption components are attracted to the channel portion. The adsorbed component that has reached the channel portion acts as a charge trap for the channel portion. The existence of such a charge trap affects the current flowing between the source electrode and the drain electrode, which is considered to be a factor of hysteresis.

On the other hand, according to the above-described carbon nanotube field effect transistor of the present invention, the adsorption component is less likely to be generated on the surface of the gate insulating film (5) than the gate insulating film using SiO ₂ as a material, and the adsorbing component is removed. It is clear from the capacitance measurement (CV measurement) of the gate insulating film that it is easily performed.
Therefore, generation of charge traps due to adsorbed components in the channel portion (4) is suppressed, and the current flowing between the source electrode (2) and the drain electrode (3) is not greatly affected by the presence of charge traps. Hysteresis is suppressed and high-speed switching of the carbon nanotube field effect transistor becomes possible.

In a specific configuration, the dielectric material has a relative dielectric constant of 50 or more, and in a more specific configuration, as a material of the gate insulating film (5), Ba _0.4 Sr _0.6 Ti _0.96 O ₃ is used.
According to the specific configuration, the effect of suppressing hysteresis is further enhanced.

  In a more specific configuration, the channel portion (4) is composed of one or a plurality of single-walled carbon nanotubes.

The mobility of the channel part (4) constituted by one carbon nanotube is larger than the mobility of the channel part (4) constituted by a plurality of carbon nanotubes.
On the other hand, the channel part (4) constituted by a plurality of carbon nanotubes can be generally produced by a process at a lower temperature than the channel part (4) constituted by one carbon nanotube.

  In a specific configuration, a silicon substrate constituting the gate electrode (1) is provided, and a gate insulating film (5) is formed on the surface of the silicon substrate.

  In another specific configuration, the gate electrode (1) is formed on a flexible substrate. More specifically, the flexible substrate is transparent and formed from polyethylene terephthalate.

The carbon nanotube field effect transistor manufacturing method includes a first step of forming a gate insulating film (5) on a gate electrode (1) using a dielectric material having a relative dielectric constant higher than that of SiO ₂ , A second step of forming a source electrode (2) and a drain electrode (3) on the surface of the gate insulating film (5); and a third step of forming a channel portion (4) on the surface of the gate insulating film (5). .

In a specific configuration, Ba _0.4 Sr _0.6 Ti _0.96 O ₃ is used as a material of the gate insulating film (5), and the gate insulating film (5) is formed by a sol-gel method.

  In a specific configuration, a solution in which a plurality of carbon nanotubes are dispersed in an organic solvent is dropped between the source electrode (2) and the drain electrode (3) on the surface of the gate insulating film (5). In a more specific configuration, the organic solvent is ethanol, dimethylformamide, sodium lauryl sulfate, or sodium deoxycholate.

  According to this specific configuration, the channel portion (4) composed of a plurality of carbon nanotubes can be formed by a low temperature process.

  In another specific configuration, carbon nanotubes are grown on the surface of the gate insulating film (5) by chemical vapor deposition.

  According to the specific configuration, the channel portion (4) configured by one carbon nanotube can be formed.

  According to the carbon nanotube field effect transistor of the present invention, the gate voltage-dependent hysteresis of the current flowing between the source electrode and the drain electrode is suppressed, and high-speed switching is possible.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. In the carbon nanotube field effect transistor of the present invention, as shown in FIG. 1, the upper surface of the gate electrode (1) is covered with the gate insulating film (5), and the source electrode is formed on the surface of the gate insulating film (5). (2) A drain electrode (3) and a channel portion (4) for electrically connecting the source electrode (2) and the drain electrode (3) are formed. The channel portion (4) is composed of a plurality of carbon nanotube bundles (40).

The gate electrode (1) is composed of a p-type silicon substrate, and the silicon substrate has a metallic property due to a very high hole doping concentration. The polarity of the silicon substrate may be n-type, and it is important that the gate electrode (1) has metallic properties.
Further, as shown in FIG. 2, a metal electrode portion (11) made of silver paste is formed on the back surface of the gate electrode (1). In FIG. 2, for simplification, the channel portion (4) is schematically shown as one carbon nanotube.

As a material of the gate insulating film (5), Ba _0.4 Sr _0.6 Ti _0.96 O ₃ (BST) having a high relative dielectric constant of about 100 is used. On the other hand, the relative dielectric constant of SiO ₂ conventionally used as a material for the gate insulating film is about 4. The thickness of the gate insulating film (5) is 270 nm.

As shown in FIG. 3, the source electrode (2) and the drain electrode (3) are formed in the same rectangular pattern. The distance between the source electrode (2) and the drain electrode (3), that is, the gate length (L _SD ) is 5 μm, and the source electrode (2) and the drain electrode (3) in the direction orthogonal to the gate length direction. The dimension, that is, the gate width (W) is 50 μm.
Both the source electrode (2) and the drain electrode (3) are a laminate comprising a gold thin film formed on the surface of the gate insulating film (5) and a chromium thin film formed on the surface of the gold thin film. The thin film and chromium thin film thicknesses are 50 nm and 10 nm, respectively. In FIG. 3, for simplification, the channel portion (4) is schematically shown as one carbon nanotube.

  As shown in FIG. 1, the channel portion (4) is composed of a plurality of carbon nanotube bundles (40), and each of these carbon nanotube bundles (40) is composed of a plurality of carbon nanotubes. These carbon nanotubes are single-walled carbon nanotubes having a diameter of about 1.4 nm.

  These carbon nanotube bundles (40) are randomly arranged between the source electrode (2) and the drain electrode (3). A part of the carbon nanotube bundle (40) in contact with the source electrode (2), a part of the carbon nanotube bundle (40) in contact with the drain electrode (3), and the source electrode (2) and the drain The source electrode (2) and the drain electrode (3) are connected by a plurality of carbon nanotube bundles (40) in contact with each other between the electrodes (3).

Next, a method for manufacturing the carbon nanotube field effect transistor according to the present invention shown in FIG. 1 will be described. First, a silicon substrate used as the gate electrode (1) is prepared. Since the surface of the silicon substrate is covered with the SiO ₂ film oxidized by oxygen in the air, the silicon substrate is subjected to hydrofluoric acid treatment to remove the SiO ₂ film. The silicon substrate from which the SiO ₂ film has been removed is washed and subjected to a heat treatment heated to 350 ° C., and then a gate insulating film (5) is formed on the exposed surface of the silicon substrate.

  In the step of forming the gate insulating film (5), a BST film serving as the gate insulating film (5) is formed by a sol-gel method. First, a sol-gel solution for preparing a BST film is prepared, and this sol-gel solution is applied to the surface of a silicon substrate by spin coating. Next, the applied sol-gel solution film is heat-treated at 350 ° C., and then the heat-treated film is annealed. The annealing process is performed in an oxygen gas flow of 100 ml / min, and the processing temperature is 700 ° C.

  Subsequently, a sol-gel solution is further applied on the annealed film, and the applied film is also subjected to heat treatment and annealing under the same conditions as described above. In this manner, the step of further applying the sol-gel solution on the annealed film is repeated to form the gate insulating film (5) having a desired film thickness (270 nm). For example, if the thickness of the film formed at one time is 90 nm, the application of the sol-gel solution is repeated three times.

  After forming the gate insulating film (5), a source electrode (2) and a drain electrode (3) are formed on the surface of the gate insulating film (5). In the step of forming the source electrode (2) and the drain electrode (3), a gold thin film is formed on the surface of the gate insulating film (5) by vapor deposition, and then a chromium thin film is formed on the surface of the gold thin film by vapor deposition. Form. Then, the gold thin film and the chromium thin film formed on the surface of the gold thin film are processed into the shape of the source electrode (2) and the drain electrode (3) by photolithography.

After forming the source electrode (2) and the drain electrode (3) on the surface of the gate insulating film (5), the channel part (4) is formed on the surface of the gate insulating film (5). In the step of forming the channel portion (4), first, a carbon nanotube sheet is prepared by forming a plurality of carbon nanotube bundles (40) into a sheet shape. The plurality of carbon nanotube bundles (40) constituting the carbon nanotube sheet are each composed of a plurality of single-walled carbon nanotubes, which are synthesized by laser evaporation using nickel and cobalt as catalyst metals and then purified. is there.
By the way, 2/3 of the single-walled carbon nanotubes show semiconducting properties, and the remaining 1/3 of the single-walled carbon nanotubes show metallic properties. The single-walled carbon tube shown is removed, and only single-walled carbon nanotubes showing semiconducting properties are used. The size of the carbon nanotube sheet is 5 mm × 5 mm.

In order to prepare a dispersion solution in which the carbon nanotube bundle (40) is dispersed in an organic solvent, the carbon nanotube sheet is immersed in dimethylformamide as an organic solvent.
Then, the carbon nanotube bundle (40) is dispersed in dimethylformamide by irradiating the dimethylformamide immersed with the carbon nanotube sheet with ultrasonic waves for 5 hours. As an organic solvent, ethanol, sodium lauryl sulfate, or sodium deoxycholate can be used in addition to dimethylformamide.

Further, the dispersion solution is centrifuged, and a supernatant portion where the carbon nanotube bundle (40) is considered to be uniformly dispersed is extracted from the dispersion solution. Then, the extracted dispersion solution is dropped between the source electrode (2) and the drain electrode (3). The extracted dispersion solution is dropped several times by 10 to 20 μl. In the extracted dispersion solution, the weight ratio of carbon nanotubes to dimethylformamide is 5.8 × 10 ⁻⁶ .
After the extracted dispersion solution is dropped between the source electrode (2) and the drain electrode (3), the enemy dispersion solution is heated to 80 ° C. to evaporate dimethylformamide in the dispersion solution. Thus, the channel part (4) is completed by a low temperature process.
The carbon nanotube field effect transistor as shown in FIG. 1 is completed by the above manufacturing method. Further, when the gate electrode (1) of the carbon nanotube field effect transistor is connected to a terminal for applying a gate voltage (not shown), a metal to be connected to the terminal by applying silver paste on the back surface of the gate electrode (1). An electrode part (11) is formed.

  Next, the operation of the carbon nanotube field effect transistor according to the present invention shown in FIG. 1 will be described. In the carbon nanotube field effect transistor, a constant voltage is applied between the source electrode (2) and the drain electrode (3), and a gate voltage is applied to the gate electrode (1) from the metal electrode portion (11). . And the magnitude | size of the electric current which flows between a source electrode (2) and a drain electrode (3) changes with the change of a gate voltage.

Here, the principle that the magnitude of the current flowing between the source electrode (2) and the drain electrode (3) changes due to the change in the gate voltage applied to the gate electrode (1) will be briefly described.
The channel part (4) has a semiconducting property and is effective at the interface between the channel part (4) and the drain electrode (3) and at the interface between the channel part (4) and the source electrode (2). A Schottky barrier is formed. The channel portion (4) faces the gate electrode (1) across the gate insulating film (5), and the band bending of the channel portion (4) is caused by the change of the gate voltage applied to the gate electrode (1). (band bending) changes. Then, due to the change in the band bending of the channel portion (4), the effective Schottky at the interface between the channel portion (4) and the drain electrode (3) and at the interface between the channel portion (4) and the source electrode (2). The thickness of the barrier changes.

For example, when a large gate voltage is applied in the negative direction, the band bending of the channel portion (4) becomes large, and the Schottky barrier at the interface between the channel portion (4) and the drain electrode (3) is effectively thinned. Accordingly, holes are easily injected from the drain electrode (3) into the channel portion (4), and a current due to the holes flows between the source electrode (2) and the drain electrode (3).
When the gate voltage is changed from this state toward the plus side, the band bending of the channel portion (4) disappears in the vicinity of a certain value of the gate voltage, and therefore the interface between the channel portion (4) and the drain electrode (3). The effective Schottky barrier becomes thicker. At this time, since it becomes difficult to inject holes into the channel portion (4), no current flows between the source electrode (2) and the drain electrode (3). This state is an off state.

When the gate voltage is changed further toward the plus side from the off state and a large gate voltage is applied in the plus direction, the band of the channel part (4) is opposite to the case where a large gate voltage is applied in the minus direction. Bend. At this time, the Schottky barrier at the interface between the channel portion (4) and the drain electrode (3) is effectively further thickened, but the Schottky barrier at the interface between the channel portion (4) and the source electrode (2) is effective. Thinner. Therefore, electrons are easily injected from the source electrode (2) into the channel portion (4), and a current due to electrons flows between the source electrode (2) and the drain electrode (3). A state in which a current due to holes or electrons flows between the source electrode (2) and the drain electrode (3) is an ON state.
Here, an example was given in which the gate voltage was changed from the minus side to the plus side. However, even if the gate voltage is changed from the plus side to the minus side, there is a complexity due to the presence of hysteresis, which will be described later, but the basic voltage is changed. The principle of operation is the same.

Next, the dependence of the electrode flowing between the source electrode (2) and the drain electrode (3) on the gate voltage of the embodiment of the carbon nanotube field effect transistor according to the present invention will be described. Here, by connecting the drain electrode (3) to a DC power source and grounding the source electrode (2), a voltage of 0.1 V is applied between the source electrode (2) and the drain electrode (3), and the gate The gate voltage applied to the electrode (1) was changed from -4V to + 4V, or from + 4V to -4V.
Incidentally, the relative dielectric constant of Ba _0.4 Sr _0.6 Ti _0.96 O ₃ used as the material of the gate insulating film (5) of the carbon nanotube field effect transistor according to the example is the gate insulating film (5). Was calculated to be 128 in the atmosphere and 100 in the vacuum from the result of the capacitance measurement of the gate insulating film (5).

  The graph of FIG. 4 shows the gate voltage dependence of the current flowing between the source electrode (2) and the drain electrode (3) when the gate voltage is changed from −4V to + 4V. As can be seen from the graph of FIG. 4, when a gate voltage of −4V to −2.5V is applied, an on state in which a current due to the hole flows appears, and when a gate voltage of −2.5V to −2V is applied. An off-state where almost no current flows appears. And when the gate voltage of -1V to + 4V is applied, the ON state into which the current by an electron flows appears. This shows that the required gate voltage is about 2.5 V or more in driving the carbon nanotube field effect transistor of the example.

  When the gate voltage is constant, the current flowing between the source electrode (2) and the drain electrode (3) depends on the voltage applied between the source electrode (2) and the drain electrode (3). As shown in the graph of FIG. 5, when a gate voltage of -4V or + 4V is applied, the current flowing between the source electrode (2) and the drain electrode (3) is the current flowing between the source electrode (2) and the drain electrode (3). Increases with increasing voltage between. On the other hand, when the gate voltage is set to −2 V corresponding to the off state, the voltage between the source electrode (2) and the drain electrode (3) is increased even if the voltage between the source electrode (2) and the drain electrode (3) is increased. Almost no current flows.

As a comparative example, a carbon nanotube field effect transistor using SiO ₂ as the material of the gate insulating film was produced. The thickness of the gate insulating film of the carbon nanotube field effect transistor as a comparative example is 200 nm. The carbon nanotube field effect transistor of the comparative example is different from the embodiment of the present invention only in the gate insulating film, and other configurations and materials are the same as those of the embodiment of the present invention.

  The graph of FIG. 6 shows the gate voltage dependence of the current flowing between the source electrode and the drain electrode when the gate voltage is changed from −40 V to +40 V for the carbon nanotube field effect transistor of the comparative example. As can be seen from the graph of FIG. 6, when a gate voltage of −30V to −20V is applied, an off state where current hardly flows appears, and when a gate voltage of 0V to + 40V is applied, an on state appears. Yes. From this, it can be seen that in the carbon nanotube field effect transistor of the example, the required gate voltage is about 30 V or more.

  Thus, the carbon nanotube field effect transistor of the example can be driven with a lower gate voltage than the carbon nanotube field effect transistor of the comparative example. Further, in the carbon nanotube field effect transistor of the comparative example, the mutual conductance (change of the current between the source electrode and the drain electrode with respect to the change of the gate voltage) was 0.015 μS, whereas the carbon nanotube field effect transistor of the example was The mutual conductance is 0.18 μS, an increase of more than 10 times.

  Next, in the case where the gate voltage is changed from the minus side to the plus side with respect to the change of the current flowing between the source electrode (2) and the drain electrode (3) of the carbon nanotube field effect transistor according to the embodiment. The difference between the case where the gate voltage is changed from the plus side to the minus side, that is, the hysteresis will be described.

  For the carbon nanotube field effect transistor of the example installed in the atmosphere, when the gate voltage is changed from −4V to + 4V and when the gate voltage is changed from + 4V to −4V, the source electrode The current flowing between (2) and the drain electrode (3) was measured. The result is shown in the graph of FIG. As can be seen from the graph, hysteresis appears in the gate voltage dependency of the current flowing between the source electrode (2) and the drain electrode (3), and when the gate voltage is changed from -4V to + 4V, When a gate voltage of -3V to -2V is applied, an off state appears. When the gate voltage is changed from + 4V to -4V, a gate voltage of + 1V to 0V is applied. An off state appears. The ambient temperature at the time of measurement is room temperature.

  On the other hand, the carbon nanotube field effect transistor of the comparative example was also installed in the same atmosphere as that described above at ambient temperature, and the gate voltage was changed from -40V to + 40V, and the gate voltage was changed from + 40V to -40V. The current flowing between the source electrode and the drain electrode was measured for each case. The result is shown in the graph of FIG. As can be seen from the graph, a large hysteresis appears in the dependence of the current flowing between the source electrode and the drain electrode on the gate voltage. When the gate voltage is changed from −40V to + 40V, the gate near −20V is shown. While the off state appears when a voltage is applied, when the gate voltage is changed from +40 V to −40 V, the off state appears when a gate voltage near +22 V is applied.

  The appearance of such hysteresis is considered to be related to the presence of adsorbed components such as water molecules adsorbed on the surface of the gate insulating film. Here, the relationship between the hysteresis and the adsorption component will be described.

In the driving state of the carbon nanotube field effect transistor, a leakage electric field is generated on the surface of the gate insulating film on both sides of the channel portion by application of the gate voltage. Note that the width dimension with the channel portion in the center of the region where the leakage electric field is generated substantially coincides with the thickness dimension of the gate insulating film.
Due to the generation of such a leakage electric field, ionized adsorption components are attracted to the channel portion. Then, the adsorbed component that has reached the channel portion acts as a charge trap for the channel portion.

  For example, water molecules as adsorbing components act as hole traps. The existence of such charge traps affects the current flowing between the source electrode and the drain electrode, which is considered to be a factor in the appearance of hysteresis.

Therefore, it is considered that hysteresis can be suppressed by removing the adsorbed component on the surface of the gate insulating film. Therefore, when the carbon nanotube field effect transistor of the example is installed in a vacuum and the gate voltage is changed from −4V to + 4V and when the gate voltage is changed from + 4V to −4V, the source electrode The current flowing between (2) and the drain electrode (3) was measured. The result is shown in the graph of FIG. As can be seen from the graph, the change in current flowing between the source electrode (2) and the drain electrode (3) when the gate voltage is changed from -4V to + 4V indicates that the gate voltage is changed from + 4V to -4V. This is almost the same as the change of the current flowing between the source electrode (2) and the drain electrode (3) when changed to, and compared with the measurement result in air shown in the graph of FIG. Has decreased significantly. The degree of vacuum at the time of measurement is about 5 × 10 ⁻⁶ torr, and the ambient temperature at the time of measurement is room temperature.

  From this, it is considered that the adsorbed component on the surface of the gate insulating film (5) was removed in vacuum. Moreover, as a result of calculating the capacity of the gate insulating film (5) in the atmosphere and in vacuum using the semiconductor parameter analyzer, the capacity of the gate insulating film (5) in air was 21 pF, whereas in vacuum The capacity of the gate insulating film (5) was 16 pF. Such a difference in capacitance of the gate insulating film (5) is that the adsorption component on the surface of the gate insulating film (5) behaves as a minute capacitance connected to the capacitance of the gate insulating film (5) in the atmosphere. It is considered that the adsorbed component on the surface of the gate insulating film (5) was removed in vacuum.

  On the other hand, when the carbon nanotube field effect transistor of the comparative example is installed at the ambient temperature in the same vacuum as described above, the gate voltage is changed from -40V to + 40V, and the gate voltage is changed from + 40V to -40V. The gate voltage dependence of the current flowing between the source electrode (2) and the drain electrode (3) when changed was measured. The result is shown in the graph of FIG. As can be seen from the graph of FIG. 10, a large hysteresis appears in the gate voltage dependence of the current flowing between the source electrode and the drain electrode. The magnitude of this hysteresis is shown in the graph of FIG. It is almost the same as the measurement result.

From this, it is considered that the adsorbed component on the surface of the gate insulating film using SiO ₂ is not removed even in vacuum. Compared to such a gate insulating film using SiO ₂ , an adsorption component is hardly generated on the surface of the gate insulating film (5) using BST, or the adsorbing component is removed from the surface of the gate insulating film (5). It is considered easy.

Such surface characteristics of the gate insulating film (5) are considered to have some relationship with the high dielectric constant of BST which is the material of the gate insulating film (5). Therefore, by using a dielectric material having a relative dielectric constant higher than that of SiO ₂ as the material of the gate insulating film (5), hysteresis is suppressed as compared with the case of using SiO ₂ as the material of the gate insulating film. it is conceivable that.

In order to further enhance the effect of suppressing hysteresis, it is considered preferable to use a material having a relative dielectric constant of 50 or more as the material of the gate insulating film. An example of the material having a relative dielectric constant of 50 or more is PbZrTiO ₃ .

  Thus, in the carbon nanotube field effect transistor of the present invention, since the hysteresis that appears in the gate voltage dependency of the current flowing between the source electrode (2) and the drain electrode (3) is suppressed, high-speed switching is achieved. Can be realized.

  In addition, each part structure of this invention is not restricted to the said embodiment, A various deformation | transformation is possible within the technical scope as described in a claim. For example, in the carbon nanotube field effect transistor of the above embodiment, the gate electrode (1) is configured by the silicon substrate, but the gate electrode film is disposed on the flexible film and covers the surface of the gate electrode film. A channel portion (4) may be formed on the surface of the gate insulating film (5). Such a film-type carbon nanotube field effect transistor can be applied as a thin film display such as an organic EL display or a driving transistor for a wireless tag. It is also possible to use a transparent film having flexibility. Examples of the transparent film having flexibility include polyethylene terephthalate.

  The channel portion may be formed from a single carbon nanotube. In order to produce a channel portion composed of one carbon nanotube, the carbon nanotube is directly grown on the surface of the gate insulating film (5) by using a chemical vapor deposition (CVD) method.

1 is a perspective view of a carbon nanotube field effect transistor of the present invention. It is sectional drawing of the carbon nanotube field effect transistor shown in FIG. It is a carbon nanotube field effect transistor top view shown in FIG. It is a graph which shows the gate voltage dependence of the electric current which flows through the carbon nanotube field effect transistor of an Example. It is a graph which shows the change by the voltage applied to the drain electrode of the electric current which flows through the carbon nanotube field effect transistor of an Example in each gate voltage. It is a graph which shows the gate voltage dependence of the electric current which flows through the carbon nanotube field effect transistor made into a comparative example. It is a graph which shows the hysteresis which appears in the gate voltage dependence of the electric current which flows through the carbon nanotube field effect transistor of an Example in air | atmosphere. It is a graph which shows the hysteresis which appears in the gate voltage dependence of the electric current which flows through the carbon nanotube field effect transistor of a comparative example in air | atmosphere. It is a graph which shows the hysteresis which appears in the gate voltage dependence of the electric current which flows through the carbon nanotube field effect transistor of an Example in a vacuum. It is a graph which shows the hysteresis which appears in the gate voltage dependence of the electric current which flows through the carbon nanotube field effect transistor of a comparative example in a vacuum.

Explanation of symbols

(1) Gate electrode
(2) Source electrode
(3) Drain electrode
(4) Channel part
(5) Gate insulation film

Claims (14)

A channel portion (4) for electrically connecting the source electrode (2) and the drain electrode (3) is disposed on the surface of the gate insulating film (5) formed on the gate electrode (1). In the carbon nanotube field effect transistor in which the channel portion (4) is composed of carbon nanotubes,
A carbon nanotube field effect transistor characterized in that a dielectric material having a higher dielectric constant than SiO ₂ is used as a material of the gate insulating film (5).   The carbon nanotube field effect transistor according to claim 1, wherein the dielectric material has a relative dielectric constant of 50 or more. The carbon nanotube field effect transistor according to claim 2, wherein Ba _0.4 Sr _0.6 Ti _0.96 O ₃ is used as a material of the gate insulating film (5).   The carbon channel field effect transistor according to any one of claims 1 to 3, wherein the channel portion (4) is composed of a plurality of single-walled carbon nanotubes.   The carbon channel field effect transistor according to any one of claims 1 to 3, wherein the channel portion (4) is composed of one single-walled carbon nanotube.   The carbon nanotube field effect transistor according to any one of claims 1 to 5, further comprising a silicon substrate constituting the gate electrode (1), wherein a gate insulating film (5) is formed on a surface of the silicon substrate.   The carbon nanotube field effect transistor according to any one of claims 1 to 5, wherein the gate electrode (1) is formed on a flexible substrate.   The carbon nanotube field effect transistor according to claim 7, wherein the flexible substrate is transparent.   The carbon nanotube field effect transistor according to claim 8, wherein polyethylene terephthalate is used as a material of the flexible substrate. A gate insulating film (5) is formed on the gate electrode (1), a source electrode (2) and a drain electrode (3) are formed on the surface of the gate insulating film (5), and the source electrode (2) and A channel part (4) for electrically connecting the drain electrodes (3) is a method of manufacturing a carbon nanotube field effect transistor in which carbon nanotubes are used.
A first step of forming a gate insulating film (5) on the surface of the gate electrode (1) using a dielectric material having a relative dielectric constant higher than that of SiO ₂ ;
A second step of producing a source electrode (2) and a drain electrode (3) on the surface of the gate insulating film (5);
And a third step of forming a channel portion (4) on the surface of the gate insulating film (5). 11. In the first step, Ba _0.4 Sr _0.6 Ti _0.96 O ₃ is used as a material of the gate insulating film (5), and the gate insulating film (5) is produced by a sol-gel method. The manufacturing method of the carbon nanotube field effect transistor as described in any one of.   The solution according to claim 10 or 11, wherein in the third step, a solution in which a plurality of carbon nanotubes are dispersed in an organic solvent is dropped between the source electrode (2) and the drain electrode (3) on the surface of the gate insulating film (5). The manufacturing method of the carbon nanotube field effect transistor of description.   The method of manufacturing a carbon nanotube field effect transistor according to claim 12, wherein the organic solvent is ethanol, dimethylformamide, sodium lauryl sulfate, or sodium deoxycholate.   The method of manufacturing a carbon nanotube field effect transistor according to claim 10 or 11, wherein in the third step, carbon nanotubes are grown on the surface of the gate insulating film (5) by chemical vapor deposition.

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