JP7012347B2 - Laminate of two-dimensional layered material - Google Patents

Description

The present invention relates to a laminate of two-dimensional layered materials useful as electronic components.

Layered materials in which two-dimensional materials such as graphene are laminated on a flat surface or a curved surface have attracted a great deal of attention in recent years as next-generation flexible functional materials. The layers of the laminated body of this layered material are bonded by a weak van der Waals force. Therefore, in this laminated body, the transmission of physical quantities such as electricity and heat in the stacking direction is much weaker than the transmission in the plane direction. For example, graphite, which is a laminate of graphene, has an in-plane electrical conductivity of 25,000 S / cm, whereas the graphite has an electrical conductivity of 5 S / cm.

In a material in which a physical quantity is uniformly diffused, a pair of electrodes are provided at both ends of the upper surface of the material, and when a voltage is applied between these electrodes, a current flows through the entire material. That is, if the contact between the electrode and the material is appropriate, the performance of the material is appropriately exhibited. On the other hand, in a laminated body in which physical quantities are easily transmitted in the plane direction and difficult to be transmitted in the stacking direction, a pair of electrodes are provided at both ends of the upper surface, and even if a voltage is applied between these electrodes, a current is transmitted in the plane direction in the uppermost layer. Although it flows, not much current flows in the second and lower layers from the top. Therefore, the performance of the material cannot be exhibited in most parts of this laminate.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a laminated body of layered materials capable of appropriately exhibiting internal performance.

In the laminated body of the present invention, layered materials containing a conductive layer having electrical conductivity in the plane direction are laminated so as to have a step, and at least a part of the upper surface and the side surface of the conductive layer of each layered material by the step. Is exposed. The electronic component of the present invention has a laminate of the present invention having steps at both ends in the plane direction, and a conductor provided at the steps at both ends. The method for producing a laminated body of the present invention includes a step of inducing plasma in a direction away from the surface while bringing plasma of a processing gas into contact with the surface of the laminated layered material to form a step in the layered material.

The laminate of the present invention has a step in which at least one of the upper surface and the side surface of the conductive layer of the layered material is exposed. For this reason, for example, if conductors are provided on the stages formed at both ends of the laminate and a voltage is applied between these conductors, a voltage is applied to the conductive layer of each layered material of the laminate, and the entire laminate Current can flow in the plane direction.

FIG. 6 is a schematic cross-sectional view showing a laminated structure in which a layered material containing a conductive layer having electrical conductivity in the plane direction is laminated. Schematic diagram of a cross section for explaining the anisotropy of current in a laminated structure. The sectional drawing of the laminated body of an embodiment. The cross-sectional schematic diagram of the electronic component which provided the conductor in the laminated body of an embodiment. The cross-sectional schematic diagram of the electronic component which provided the conductor in the laminated body of another embodiment. Schematic diagram of a cross section of a plasma etching apparatus for manufacturing a laminate. The scanning tunneling microscope image of the laminated body obtained in Example 1 and the graph which shows the thickness of a laminated body. The scanning tunneling microscope image of the laminated body obtained in Example 2 and the graph which shows the thickness of a laminated body. The scanning tunneling microscope image of the laminated body obtained in Example 3 and the graph which shows the thickness of a laminated body. The scanning tunneling microscope image of the laminated body obtained in Example 4 and the graph which shows the thickness of a laminated body. Scanning tunneling microscope image of the laminate obtained in Example 5. The graph which shows the current-voltage characteristic of the laminated body obtained in Example 6.

Hereinafter, the laminate, the electronic component, and the method for manufacturing the laminate of the present invention will be described with reference to the drawings, based on the embodiments and examples. The drawings schematically show the laminated body, the constituent members of the laminated body, the peripheral members of the laminated body, the manufacturing apparatus of the laminated body, and the like. The dimensions and dimensional ratios on the drawings do not always match the actual products such as laminated bodies. In addition, duplicate explanations will be omitted as appropriate.

FIG. 1 shows a laminated structure 14 in which a layered material 12 containing a conductive layer 10 having electrical conductivity in the plane direction is laminated. In the laminated structure 14, electricity easily flows in the surface direction of the layered substance 12, and almost no current flows in the laminated direction. Examples of the laminated structure 14 include transition metal chalcogenides such as graphite and MoS ₂ . For example, when the laminated structure 14 is MoS ₂ , the conductive layer 10 is Mo, and the insulating layer 16 sandwiching the conductive layer 10 is the space between S and the layers. When the laminated structure 14 is graphite, the conductive layer 10 is graphene, and the space between the layers of graphene corresponds to the insulating layer 16. In the present embodiment, the layered material 12 in which the laminated body structure 14 contains the conductive layer 10 having electrical conductivity in the surface direction is laminated, but the laminated body has heat, magnetism, light, and electromagnetic waves in the surface direction. A layered material containing a layer that transmits energy such as vibration and sound may be laminated.

The laminated structure 14 includes graphite, multi-walled carbon nanotubes (MW-CNT), multi-walled carbon nanohorns, carbon fibers, amorphous carbon materials, carbon black, activated carbon, etc., in addition to transition metal chalcogenides such as graphite and MoS ₂ . Carbon-based materials, boron nitride, inorganic nanosheets, organic nanosheets, low-dimensional electride materials, low-dimensional heat-diffusing materials, low-dimensional magnetic-diffusing materials, and low-dimensional light-diffusing materials. The laminated structure 14 may have a planar shape or a curved surface shape. When a pair of electrodes 18 are provided on the conductive layer 10 portion of the uppermost layered material 12 of the laminated structure 14 and a voltage is applied between the electrodes 18, as shown in FIG. 2, in the plane direction of the uppermost layered material 12. Current flows. However, almost no current flows in the stacking direction and the surface direction of the layered substance 12 which is the second layer or less from the top.

FIG. 3 shows a cross section of the laminated body 20 according to the embodiment of the present invention. In the laminated body 20, the layered material 12 containing the conductive layer 10 having electrical conductivity in the plane direction is laminated so as to have the step 22, and the upper surface 10a of the conductive layer 10 of each layered material 12 and the laminated body 20 are laminated by the step 22. At least a part of the side surface 10b is exposed. Although the upper surface 10a and the side surface 10b of the conductive layer 10 are flat on the drawing, the upper surface 10a and the side surface 10b may be exposed so as to be a slope, a curved surface, or an uneven surface, and may be partially insulated from the upper surface 10a. The layer 16 may remain. Further, the boundary between the upper surface 10a and the side surface 10b does not necessarily have to be clear.

When the laminated body 20 has steps 22 at both ends in the plane direction and the conductors 24 and 26 are provided at both ends of the steps 22, as shown in FIG. 4, the conductive layer of each layered material 12 of the laminated body 20 is provided. The upper surface 10a and the side surface 10b of 10 are conducted via the conductor 24 or the conductor 26. Therefore, a current flows in the surface direction of the conductive layer 10 of each layered material 12. That is, a current can flow in the plane direction of the entire laminated body 20. Therefore, if the conductors 24 and 26 are provided on the laminated body 20, they can be used as electronic components. In order to ensure the conduction between the conductive layers 10 of each layered material 12, it is preferable that a part of the upper surface 10a and the side surface 10b of the conductive layer 10 are exposed by the step 22. Further, the structure having the stage 22 of the present embodiment is effective for the laminated body 20 in which the electric conductivity in the stacking direction is smaller than the electric conductivity in the surface direction of the layered material 12.

FIG. 5 shows a cross section of an electronic component in which a conductor 24 is provided on a laminated body 30 according to another embodiment of the present invention. The laminate 30 is provided with a hole 32, and the side surface of the hole 32 is provided with a step 34. The conductor 24 is filled in the hole 32. Therefore, the conductive layer 10 of each layered material 12 of the laminated body 30 is conducted through the conductor 24. The structures of the laminated body 20 and the laminated body 30 may be combined, and a conductor may be provided in the step 22 and the hole 32 at the end to form an electronic component.

In the method for manufacturing the laminated bodies 20 and 30, the plasma of the processing gas is brought into contact with the surface of the laminated layered material 12 and the plasma is guided in a direction away from the surface to form the stages 22 and 34 on the layered material 12. It has a process. By this step, the insulating layer 16 of each layered material 12 is removed. Then, the insulating layer 16 and the conductive layer 10 are further removed so that the upper surface 10a or the side surface 10b of the conductive layer 10 of each layered material 12 is exposed, and a step structure is formed.

The laminate of the present invention was manufactured using a plasma etching apparatus (Sanyu Seisakusho, suction type plasma apparatus) as shown in FIG. First, a sample as a laminated structure was placed on a sample table, and an etching gas whose flow rate was adjusted to 7 to 16 sccm through a mass flow controller (MFC) was introduced into the etching chamber. As the etching gas, CF ₄ alone or a mixed gas of CF ₄ and Ar was used. The introduced etching gas is exhausted through an alumina suction tube (capillary tube having an inner diameter of 4 mm) whose tip is narrowed to an inner diameter of 1 mm.

Next, high-frequency energy having a power of 30 to 40 W and a frequency of 13.56 MHz was applied to the cylindrical electrodes arranged around the suction tube to turn the etching gas into plasma in the suction tube. A part of the plasma seeps out from the tip of the suction tube against the gas flow. By placing the sample at a distance of about 0.1 mm from the tip of the suction tube, plasma is localized between the tip of the suction tube and the sample within a diameter range similar to the inner diameter of 1 mm at the tip of the suction tube. Local etching of the sample is possible.

(Example 1)
The laminated structure MoS ₂ which is a sample is installed on the sample table, 10 SCCM of CF ₄ gas is introduced into the vacuum chamber, power is supplied from the RF power supply at an output of 30 W to plasma the CF ₄ gas, and the pressure is 932 Pa for 30 seconds. A laminate was obtained by plasma etching. FIG. 7 shows a scanning tunneling microscope image of this laminate and the thickness of the laminate in the white line portion of this image. The thickness of the laminate was measured by directly analyzing the cross-sectional height with a probe of a scanning tunneling microscope (the same applies hereinafter). The observation position of the scanning tunneling microscope is a position several mm outside the etching center. As shown in FIG. 7, a laminate having a shallow hole and having a step on the side surface of the hole was obtained.

(Example 2)
The laminated structure MoS ₂ which is a sample is installed on the sample table, 10 SCCM of CF ₄ gas is introduced into the vacuum chamber, power is supplied from the RF power supply at an output of 30 W to plasma the CF ₄ gas, and the pressure is 932 Pa for 30 seconds. A laminate was obtained by plasma etching. FIG. 8 shows a scanning tunneling microscope image of this laminate and the thickness of the laminate in the white line portion of this image. The observation position of the scanning tunneling microscope is near the etching center. As shown in FIG. 8, a laminate having a deep hole and having a step on the side surface of the hole was obtained.

(Example 3)
The laminated structure WSe ₂ which is a sample is installed on the sample table, 10SCCM of CF ₄ gas is introduced into the vacuum chamber, power is supplied from the RF power supply at an output of 30 W to plasma the CF ₄ gas, and the pressure is 1300 Pa for 30 seconds. A laminate was obtained by plasma etching. FIG. 9 shows a scanning tunneling microscope image of this laminate and the thickness of the laminate in the white line portion of this image. The observation position of the scanning tunneling microscope is near the etching center. As shown in FIG. 9, a laminated body having steps was obtained.

(Example 4)
The laminated structure MoS ₂ which is a sample is installed on the sample table, CF ₄ gas is introduced into the vacuum chamber by 7.5 SCCM, power is supplied from the RF power supply at an output of 30 W, and the CF ₄ gas is turned into plasma at a pressure of 200 Pa. A laminated body was obtained by plasma etching for 0.7 seconds. FIG. 10 shows a scanning tunneling microscope image of this laminate, the thickness of the laminate in the white line portion of this image, and a structural model of the laminate. The observation position of the scanning tunneling microscope is near the etching center. As shown in FIG. 10, a laminate having a step of 0.65 nm corresponding to the thickness of the layered material (one layer of MoS ₂ ) was obtained. It is possible to conduct from the side surface of Mo by this stepped portion. In addition, many S defects were observed in the upper part of this step. It is possible to conduct from the upper surface of Mo by the defective portion of S.

(Example 5)
The sample HOPG (multilayer graphite graphite) is installed on the sample table, CF ₄ gas is introduced into the vacuum chamber by 7.5 SCCM, and power is supplied from the RF power supply at an output of 30 W to plasma the CF ₄ gas and pressurize it. A laminate was obtained by plasma etching at 149.6 Pa for 0.5 seconds. FIG. 11 shows a scanning tunneling microscope image of this laminate. The observation position of the scanning tunneling microscope is near the etching center. A laminated body having a wide step as shown in FIG. 11 (a) and a laminated body having a deep hole as shown in FIG. 11 (b) were obtained. That is, it was found that the required step structure can be obtained by setting the etching conditions.

(Example 6)
WSe ₂ produced by a mechanical peeling method was transferred onto a high-concentration p-type silicon (001) substrate having an oxide film layer having a thickness of 285 nm on the surface. Next, a resist (image reversal AZ5214E type manufactured by Clariant) was spin-coated on WSe ₂ . Then, an exposure / development process was performed using a contact-type exposure machine under the conditions specified by the resist, and the resist was removed only from the electrode-forming portion to obtain an etching sample in which an opening was formed. Next, the etching sample was placed on the sample table, 100 SCCM of O ₂ gas was introduced into the vacuum chamber, power was supplied from the RF power supply at an output of 300 W to plasmaize the O ₂ gas, and plasma etching was performed at a pressure of 140 Pa for 120 seconds. ..

After that, electrode metal nickel (thickness 10 nm) and gold (thickness 50 nm) are vapor-deposited at predetermined positions by an electron beam vapor deposition device, and the electrodes are patterned by a lift-off method to obtain an electrical characteristic evaluation sample that is a backgate type FET. Made. Further, a comparative sample was prepared by the same method as the electrical characteristic evaluation sample except that the etched sample was not plasma-etched. Using a manual prober (LP4D manufactured by Luft Co., Ltd.) and a semiconductor parameter analyzer (4200SCS manufactured by Keithley), the gate voltage was fixed at 0 V in an atmospheric atmosphere, and the drain current and drain voltage were measured.

FIG. 12 shows the measurement results of the drain current and the drain voltage of the comparative sample (without plasma treatment) and the electrical characteristic evaluation sample (with plasma treatment). As shown in FIG. 12, the comparative sample did not carry much current with respect to the change in voltage. On the other hand, in the electrical characteristic evaluation sample, a larger current flowed in response to the change in voltage than in the comparative sample. That is, it was found that by etching the laminated structure, the layer through which the current flows appears not only near the surface but also at a deep position.

The laminate of the present invention is not limited to electronic parts, but also has two-dimensional heat diffusion materials, two-dimensional magnetic materials, two-dimensional optical materials, two-dimensional electromagnetic wave materials, two-dimensional vibration (phonon) materials, two-dimensional acoustic materials, and two-dimensional materials. It may be used as an energy transport material.

10 Conductive layer 10a Top surface 10b Side surface 12 Layered material 14 Laminated structure 16 Insulation layer 18 Electrode 20 Laminated 22 steps 24,26 Conductor 30 Laminated 32 holes

Claims (8)

A flat or curved layered material containing a conductive layer having electrical conductivity in the plane direction is laminated so as to have a step.
The steps expose at least a portion of the top and sides of the conductive layer of each layered material.
A laminate of transition metal chalcogenides. In claim 1 ,
A laminate in which the transition metal chalcogenide is MoS ₂ . In claim 1 ,
A laminate in which the transition metal chalcogenide is WSe ₂ . In any of claims 1 to 3 ,
A laminate in which a part of the upper surface and the side surface of the conductive layer are exposed by the step. In any of claims 1 to 4 ,
A laminate in which the electrical conductivity in the stacking direction is smaller than the electrical conductivity in the plane direction of the layered material. In any of claims 1 to 5 ,
A laminate having holes and having the steps on the sides of the holes. The laminate according to any one of claims 1 to 6 , which has the steps at both ends in the plane direction.
Conductors provided on the steps at both ends and
Parts with. A method for manufacturing a laminate according to any one of claims 1 to 6 .
A method for producing a laminated body, which comprises a step of inducing the plasma in a direction away from the surface while bringing a plasma of a processing gas into contact with the surface of the laminated material to form the step on the layered material.

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