CN114361021B - A two-dimensional material heterojunction device and its preparation method - Google Patents
A two-dimensional material heterojunction device and its preparation methodInfo
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- CN114361021B CN114361021B CN202111540061.3A CN202111540061A CN114361021B CN 114361021 B CN114361021 B CN 114361021B CN 202111540061 A CN202111540061 A CN 202111540061A CN 114361021 B CN114361021 B CN 114361021B
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Abstract
本发明涉及一种二维材料异质结器件及其制备方法，属于二维材料领域。所述制备方法通过反应离子刻蚀机刻蚀基底后加工包埋电极，保证电极与衬底高度基本一致从而有效提高了表面平整度，有利于避免在制备多层异质结结构时异质结结构出现破裂，有利于形成更多层数的异质结结构，极大提高了多层异质结器件的成功率与器件质量。所述制备方法还通过热胀冷缩来控制干法转移过程中的贴合速率以降低贴合过程中对材料造成的破坏，极大提高了利用多层异质结器件的成功率与器件质量。
The present invention relates to a two-dimensional material heterojunction device and a preparation method thereof, belonging to the field of two-dimensional materials. The preparation method etches a substrate with a reactive ion etcher and then processes an embedded electrode, ensuring that the electrode and substrate are substantially at the same height, thereby effectively improving surface flatness. This helps avoid cracking of the heterojunction structure during the preparation of a multi-layer heterojunction structure, facilitates the formation of heterojunction structures with a larger number of layers, and significantly improves the success rate and device quality of multi-layer heterojunction devices. The preparation method also controls the bonding rate during the dry transfer process by utilizing thermal expansion and contraction to reduce damage to the material during the bonding process, significantly improving the success rate and device quality of the multi-layer heterojunction device.
Description
Technical Field
The invention relates to the field of two-dimensional materials, in particular to a high-quality two-dimensional material heterojunction device prepared based on electrode embedding and a preparation method thereof.
Background
Two-dimensional materials can be easily cleaved into monolayers due to bonding between layers with van der waals forces, and van der waals heterojunction devices can be fabricated by combinatorial stacking of different materials. The device has excellent physical and chemical characteristics, and has great application prospect in the aspects of novel field effect transistors, photoelectricity, energy storage and flexible electronic devices. The preparation of such devices requires special transfer methods, typically wet and dry. Since wet transfer contaminates two-dimensional materials and is not suitable for water-oxygen sensitive materials such as transition metal chalcogenides (TMDS), black phosphorus, cadmium iodide, etc., device fabrication techniques based on dry transfer have recently been developed.
For van der waals heterojunction devices, the conventional electrode fabrication methods have a number of drawbacks. If the electrode is prepared after dry transfer, the two-dimensional material is exposed to air in the process, so that the oxidation and deterioration are caused, the quality of a device is affected, even if a special means is used for isolating water and oxygen, the electrode deposited by an evaporation method can damage a contact interface, the working performance of the thin film two-dimensional material can be greatly affected, and meanwhile, the structure can not be used for preparing a top gate and a field effect transistor based on a van der Waals heterojunction device because the electrode is arranged above the two-dimensional material. On the other hand, if the electrode is prepared on a silicon substrate (substrate or base) in advance and the two-dimensional material is transferred again, the thickness of the electrode is generally greater than 30nm due to the mechanical strength requirement of the electrode. For the target device, the thickness of the used two-dimensional material is generally smaller than 5nm, so that a relatively large height difference exists between the electrode and the substrate (base), and the material on the surface of the electrode can be fluctuated or even broken after the transfer is completed. On one hand, the success rate of preparing the van der Waals heterojunction device is greatly affected, and on the other hand, the interlayer bonding quality of the van der Waals heterojunction is reduced, so that the performance of the device is affected in the electrical test.
Therefore, a preparation method of a two-dimensional material heterojunction device with good integrity, high success rate and a large number of layers is needed to be searched.
Disclosure of Invention
In order to solve the problems, the invention provides a two-dimensional material heterojunction device and a preparation method thereof.
In a first aspect, the present invention provides a method of fabricating a two-dimensional material heterojunction device.
A method of fabricating a two-dimensional material heterojunction device, comprising:
(I) Dissociating the two-dimensional material;
Embedding an electrode on a substrate, namely spin-coating electron beam photoresist on the substrate, baking, exposing the substrate to light by electron beam lithography to obtain a pre-designed electrode shape, developing with a developing solution, putting the substrate into a reactive ion etching machine to etch the substrate, evaporating the electrode, and removing photoresist to obtain the substrate embedded with the electrode;
(III) transferring the dissociated two-dimensional material to a substrate embedded with electrodes;
(IV) repeating the steps (I) and (III) by taking at least one two-dimensional material which is the same or different to form a multi-layer heterojunction structure;
The steps (I) and (II) can be carried out in any order.
According to the invention, the evaporated electrode is embedded into the substrate etched by the reactive ion etcher, so that the height of the electrode is basically consistent with that of the substrate, and the surface flatness is effectively improved, so that the electrode and the two-dimensional material form an ultra-flat ohmic contact interface, the breaking of the two-dimensional material is avoided, the integrity of the heterojunction structure is greatly improved, and the success rate and the device quality of preparing a multi-layer van der Waals heterojunction device by using the water-oxygen sensitive material are greatly improved.
The etching depth can be 20nm-100nm deeper than the surface of the substrate, the thickness of the electrode can be 21nm-125nm, and the electrode is 1nm-25nm higher than the surface of the substrate.
In some embodiments, the step (IV) may be performed by repeating the step (III) with at least 1 different two-dimensional material to form a multi-layer heterojunction structure, thereby obtaining a two-dimensional material heterojunction device. In some embodiments, the step (IV) is to repeat the operation of the step (III) by taking 1 or 2 different two-dimensional materials to form a multi-layer heterojunction structure, thereby obtaining the two-dimensional material heterojunction device.
The step (III) may include transferring the dissociated two-dimensional material to a surface of PDMS, bringing the PDMS with the two-dimensional material adjacent to an electrode, heating to expand the PDMS and contact the substrate, turning off the heating, cooling the PDMS, and removing the PDMS. The PDMS is expanded and transferred to the two-dimensional material by heating, and the viscosity of the PDMS is lost under the high temperature condition, so that the two-dimensional material is transferred to the substrate, and then the PDMS is contracted and separated from the substrate by cooling, so that the complete transfer of the two-dimensional material is realized, and the success rate and the device quality of preparing a multi-layer van der Waals heterojunction device by using the water-oxygen sensitive material are greatly improved.
The multi-layer heterojunction structure in step (IV) may comprise a 2-4 layer heterojunction structure. In some embodiments, the multi-layer heterojunction structure in step (IV) comprises a2, 3, or 4-layer heterojunction structure.
The approaching the PDMS with the two-dimensional material to the electrode may be approaching the PDMS with the two-dimensional material to a distance of 10 μm-500 μm from the two-dimensional material to the electrode. In some embodiments, the approaching the PDMS with the two-dimensional material to the electrode may be approaching the PDMS with the two-dimensional material to a distance of 50 μm-400 μm from the two-dimensional material to the electrode. In some embodiments, the approaching the PDMS with the two-dimensional material to the electrode may be approaching the PDMS with the two-dimensional material to a distance of 50 μm-300 μm from the two-dimensional material to the electrode. In some embodiments, the approaching the PDMS with the two-dimensional material to the electrode may be approaching the PDMS with the two-dimensional material to a distance of 50 μm-200 μm from the two-dimensional material to the electrode. In some embodiments, the approaching the PDMS with the two-dimensional material to the electrode may be approaching the PDMS with the two-dimensional material to a distance of 50 μm-200 μm from the two-dimensional material to the electrode. In some embodiments, the approaching the PDMS with the two-dimensional material to the electrode may be approaching the PDMS with the two-dimensional material to a distance of 100 μm-200 μm from the two-dimensional material to the electrode. In some embodiments, the approaching the PDMS with the two-dimensional material to the electrode may be approaching the PDMS with the two-dimensional material to a distance of 100 μm-200 μm from the two-dimensional material to the electrode.
The approaching the PDMS with the two-dimensional material to the electrode can be the approaching of the PDMS with the two-dimensional material to the contact surface to generate interference fringes.
The thickness of the PDMS may be 500 μm to 2000 μm. In some embodiments, the PDMS has a thickness of 800 μm to 1500 μm. In some embodiments, the PDMS has a thickness of 800 μm to 1200 μm. In some embodiments, the PDMS has a thickness of 900 μm to 1100 μm.
The heating may be to 130-150 ℃. Based on PDMS with the thickness of 1000 mu m, in the process of gradually heating the PDMS to 150 ℃ at 90 ℃, the expansion rate of the PDMS gradually decreases to 1-2 mu m/DEG C from 20 mu m/DEG C, the PDMS is adopted to be heated to 130-150 ℃ after a certain distance exists between the PDMS and an electrode for expansion lamination, the higher expansion of the PDMS at 90-130 ℃ is consumed by a certain distance, and the low expansion of the PDMS at 130-150 ℃ is fully utilized, so that a sample can be laminated very slowly, and the integrity of a two-dimensional material heterojunction is improved.
The heating may be at a rate of 1 ℃ per second to 4 ℃ per second. In some embodiments, the heating is at a rate of 1 ℃ per second to 3 ℃ per second. In some embodiments, the heating is at a rate of 2 ℃ per second to 4 ℃ per second. In some embodiments, the heating is at a rate of 1 ℃,2 ℃,3 ℃, or 4 ℃.
The cooling is to cool to PDMS release substrate or to 50-70 ℃.
The two-dimensional material may include at least one selected from the group consisting of transition metal chalcogenides, graphene, boron nitride, black phosphorus, and chromium triiodide.
The transition metal chalcogenide compound comprises at least one selected from molybdenum disulfide, molybdenum ditelluride, tungsten diselenide, niobium diselenide and indium diselenide.
The substrate may comprise a silicon wafer selected from the group consisting of silicon dioxide, silicon wafers having a silicon dioxide layer on the surface, silicon wafers, mica, sapphire, or flexible materials. In some embodiments, the substrate is silicon dioxide, a silicon wafer with a silicon dioxide layer on the surface, silicon wafer, mica, sapphire, or a flexible material.
The flexible material comprises at least one selected from polyimide, polyvinyl alcohol, polyester and polyethylene terephthalate.
The step (I) may comprise stripping by mechanical stripping.
The step (I) can comprise the steps of sticking the two-dimensional material by using the adhesive tape, tearing after sticking the new adhesive tape and the adhesive tape stuck with the two-dimensional material, repeating the steps for 3-4 times, and tearing after sticking the new adhesive tape and the adhesive tape stuck with the two-dimensional material, so as to obtain the adhesive tape containing single-layer or less-layer two-dimensional material.
Transferring the dissociated two-dimensional material to the PDMS surface may include bonding a tape comprising a single layer or a few layers of two-dimensional material to the PDMS and tearing.
The electron beam photoresist may include a material selected from polymethyl methacrylate (PMMA).
The developing solution may include a mixed solution selected from methyl isobutyl ketone and isopropyl alcohol.
The volume ratio of methyl isobutyl ketone to isopropyl alcohol may be 9:1 to 1:9. In some embodiments, the volume ratio of methyl isobutyl ketone to isopropyl alcohol is from 6:1 to 1:6. In some embodiments, the volume ratio of methyl isobutyl ketone to isopropyl alcohol is 3:1 to 1:6. In some embodiments, the volume ratio of methyl isobutyl ketone to isopropyl alcohol is 1:1 to 1:6. In some embodiments, the volume ratio of methyl isobutyl ketone to isopropyl alcohol is 1:1 to 1:4. In some embodiments, the volume ratio of methyl isobutyl ketone to isopropyl alcohol is from 1:1 to 1:3. In some embodiments, the volume ratio of methyl isobutyl ketone to isopropyl alcohol is 1:3.
The etching may be etching with a trifluoromethane gas.
In the step (II), the step may include washing with at least one solvent selected from water, acetone, and isopropyl alcohol before evaporating the electrode after etching the substrate in the reactive ion etcher. In some embodiments, in step (II), after etching the substrate in the reactive ion etcher, and before evaporating the electrode, ultrasonic cleaning is performed with a solvent including at least one selected from the group consisting of water, acetone, and isopropyl alcohol. In some embodiments, in the step (II), after etching the substrate in the reactive ion etcher, before evaporating the electrode, the substrate is ultrasonically cleaned with at least one solvent selected from the group consisting of water, acetone, and isopropyl alcohol for 1 minute to 15 minutes, respectively. In some embodiments, step (II) comprises ultrasonic cleaning with water, acetone and isopropanol, respectively, for 1 minute to 15 minutes after etching the substrate in the reactive ion etcher, before evaporating the electrode.
The photoresist removal can comprise the steps of soaking the photoresist with acetone, or the photoresist removal comprises the steps of soaking the photoresist with acetone and cleaning the photoresist with isopropanol.
The method may further comprise, after step (III), performing a plasma cleaning with hydrogen, argon or a mixture thereof.
In the mixed gas of the hydrogen and the argon, the volume ratio of the hydrogen to the argon is 100:1-1:100. In some embodiments, the volume ratio of hydrogen to argon in the mixed gas of hydrogen and argon is 50:1-1:50. In some embodiments, the volume ratio of the hydrogen to the argon in the mixed gas of the hydrogen and the argon is 20:1-1:20. In some embodiments, the volume ratio of the hydrogen to the argon in the mixed gas of the hydrogen and the argon is 10:1-1:10. In some embodiments, the volume ratio of hydrogen to argon in the mixed gas of hydrogen and argon is 5:1-1:5.
The plasma cleaning time may be 20s to 120s. In some embodiments, the plasma cleaning time may be 30s-100s. In some embodiments, the plasma cleaning time may be 30s-60s.
After step (IV), the two-dimensional material heterojunction device may be placed in a vacuum condition to remove air from the interlayer. The two-dimensional material heterojunction device is placed in a vacuum condition, so that air in an interlayer between the two-dimensional material and the electrode and the substrate is removed, oxidation of the two-dimensional material by the interlayer air is avoided, binding force of the two-dimensional material and the substrate is improved, and electrical test performance is improved.
The time of placing under vacuum may be 1-3 hours. In some embodiments, the time placed under vacuum conditions is 1 hour, 2 hours, or 3 hours.
Spin coating the substrate with the electron beam resist may include uniformly spreading the electron beam resist on the substrate with a bench type resist homogenizer at a rotational speed of 3000 rpm-6000rpm for 1-2 minutes.
The baking temperature may be 120-180 ℃.
The baking time may be 1 minute to 2 minutes.
The steps (I) and/or (III) are carried out in a glove box.
In a second aspect, the present invention provides a two-dimensional material heterojunction device prepared according to the method of the first aspect.
A two-dimensional material heterojunction device prepared according to the method of the first aspect.
Advantageous effects
Compared with the prior art, the invention has at least one of the following beneficial technical effects:
(1) The invention adopts embedding the evaporated electrode into the substrate etched by the reactive ion etcher (trifluoromethane), ensures the height of the electrode and the substrate to be basically consistent, thereby effectively improving the surface flatness, leading the electrode and the two-dimensional material to form an ultra-flat ohmic contact interface, being beneficial to avoiding the occurrence of cracking of the heterojunction structure when preparing a multi-layer heterojunction structure, being beneficial to forming heterojunction structures with more layers, being capable of forming at least 2 layers of morphological complete heterojunction structures and greatly improving the success rate and the device quality of the multi-layer van der Waals heterojunction device.
(2) The invention also improves the two-dimensional material dry transfer technology, controls the bonding rate in the dry transfer process through thermal expansion and cold contraction to reduce the damage to the material in the bonding process, expands and transfers the two-dimensional material through heating, and the PDMS loses viscosity under the high temperature condition, thereby being beneficial to transferring the two-dimensional material onto a substrate, and then contracts and leaves the substrate through cooling, realizing the complete transfer of the two-dimensional material, and greatly improving the success rate and the device quality of preparing the multi-layer van der Waals heterojunction device by utilizing the water-oxygen sensitive material.
(3) When the two-dimensional material is transferred to the substrate, the heating speed is 1-4 ℃ per second, the integrity of the heterojunction structure of the two-dimensional material is improved, the two-dimensional material is prevented from being broken, and when the heating speed is more than or equal to 5 ℃ per second, the heating speed is too high, so that the two-dimensional material is easily broken.
(4) When transferring the two-dimensional material to the substrate, the two-dimensional material is transferred by heating to 130-150 ℃, based on PDMS with the thickness of 1000 mu m, the expansion rate of the PDMS is gradually reduced to 1-2 mu m/DEG C from 20 mu m/DEG C in the process of gradually heating to 150℃ at 90℃, the PDMS is heated to 130-150 ℃ for expansion lamination after a certain distance exists between the PDMS and the electrode, the higher expansion of the PDMS at 90-130 ℃ is consumed by a certain distance, and the low expansion of the PDMS at 130-150 ℃ is fully utilized, so that the sample can be laminated very slowly, the integrity of the heterojunction structure of the two-dimensional material is improved, and the rupture of the two-dimensional material is avoided.
(5) And placing the two-dimensional material heterojunction device in a vacuum condition to remove air in the interlayer. The two-dimensional material heterojunction device is placed in a vacuum condition, so that air in an interlayer between the two-dimensional material and the electrode and the substrate is removed, oxidation of the two-dimensional material by the interlayer air is avoided, binding force of the two-dimensional material and the substrate is improved, and electrical test performance is improved.
Drawings
Fig. 1 is an enlarged view of a heterojunction structure obtained in example 1.
Fig. 2 is an enlarged view of the heterojunction structure obtained in example 2.
Fig. 3 is an enlarged view of the heterojunction structure obtained in example 3.
Fig. 4 is an enlarged view of the heterojunction structure obtained in example 4.
Fig. 5 is an enlarged view of the heterojunction structure obtained in example 5.
Fig. 6 is an enlarged view of the heterojunction structure obtained in example 6.
Definition of terms:
In the context of the present invention, all numbers disclosed herein are approximations, whether or not the word "about" or "about" is used. Based on the numbers disclosed, there is a possibility that the values of each number may differ by less than + -10% or a reasonable difference as recognized by those skilled in the art, such as + -1%, + -2%, + -3%, + -4%, or + -5%.
The term "PDMS" refers to polydimethylsiloxane.
The term "PMMA" means polymethyl methacrylate.
The term "and/or" is understood to mean any one of the selectable items or a combination of any two or more of the selectable items.
The term "multilayer" means at least two or more layers.
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.
Detailed Description
In order to better understand the technical solution of the present invention, some non-limiting examples are further disclosed below to further describe the present invention in detail.
The reagents used in the present invention are all commercially available or can be prepared by the methods described herein.
In the present invention, "sccm" means standard milliliters per minute, "s" means seconds, "nm" means nanometers, "μm" means micrometers, "mm" means millimeters, "rpm" means rotations per minute, and "° C/s" means degrees Celsius per second.
Reagent and consumable:
PDMS polydimethylsiloxane film (MKNANO, thickness about 1000 μm), blue tape (USI, ULTRON SYSTEMS, inc.), acetone, methanol and isopropanol (available from alfa group), silicon wafer. PMMA 950A4 gel, methyl isobutyl ketone and isopropyl alcohol mixed solution (volume ratio 1:3) (from MicroChem);
Instrument:
Glove box, optical microscope, two-dimensional material transfer platform, plasma descaling machine, desk-top even machine, electron beam exposure system, electron beam coating by vaporization appearance.
Example 1 preparation of two-dimensional Material heterojunction device (3-layer boron nitride-niobium diselenide-tungsten ditelluride heterojunction)
(1) A silicon wafer (Si) having 300nm silicon dioxide (SiO 2) on the surface was cut into a size of 5mm by 5mm, PMMA 950A4 gel was used, and the gel was spread on the silicon wafer uniformly by a bench type gel machine at 4000rpm for 1 minute. And then baked on a hot plate at 120 ℃ for 1 minute.
(2) The electrode pattern designed in advance is exposed on an electron beam exposure system, and a mixed solution of methyl isobutyl ketone and isopropanol (volume ratio is 1:3) is used for developing for 1 minute. Thereafter, a Reactive Ion Etcher (RIE) is used to etch 60nm silicon dioxide using a gas of trifluoromethane (CHF 3). And then the treated silicon wafer is put into water, acetone and isopropanol to be respectively ultrasonically treated for 10 minutes for cleaning. And then using an electron beam coating machine to plate a 65nm gold film as an electrode. After removal, the photoresist is removed by soaking in acetone for half an hour, and finally washed with isopropanol.
(3) And (3) carrying out two-dimensional material dissociation in a glove box, uniformly spreading WTE 2 (tungsten telluride) crystals which are obtained from main growth on a blue adhesive tape, taking another piece of blue adhesive tape to be close to the two-dimensional material, tearing the adhesive tape for thinning, repeatedly repeating the steps for 3-4 times, and tearing after the new adhesive tape is oppositely adhered with the adhesive tape with the two-dimensional material, so as to obtain the adhesive tape with single-layer or less-layer two-dimensional material.
(4) Cutting PDMS into a proper size, removing an outer protective film, adhering the soft film surface to a two-dimensional material area of the adhesive tape containing a single layer or less layers of two-dimensional materials, slightly adhering the PDMS to the adhesive tape to remove middle gas, standing for about 5 minutes, and rapidly tearing off the PMDS from the adhesive tape by using tweezers. After being placed on a glass slide, the slide is subjected to optical microscopy to find a suitable thin layer for marking, and simultaneously the PDMS block with the two-dimensional material area is cut to a suitable size.
(5) The treated PDMS block is precisely placed on a special transfer slide, and a raised area in the middle of the slide is used for jacking up the PDMS of the two-dimensional material part, so that the PDMS is conveniently contacted with a substrate. The transfer slide is then assembled with the two-dimensional material transfer platform and adjusted to center the two-dimensional material in the field of view of the mirror.
(6) The electrode is placed on the transfer platform, the center of the electrode is aligned with the two-dimensional material, the cantilever beam is controlled slowly to be close to the electrode, heating is turned on when the electrode is in close contact (after interference fringes appear), the two-dimensional material is slowly contacted with the electrode by using PDMS thermal expansion, and the damage to the two-dimensional material can be reduced by using a thermal expansion method with a slow contact rate.
(7) After the heating table was stabilized to 80 ℃, the temperature rise was started. After a part of PDMS in a microscope window is found to be attached to a silicon wafer in the two-dimensional material transferring process, the operation of the stepper is stopped, the operation is changed into a heating transfer platform, the temperature rising rate is controlled to be about 3.6 ℃ per second (the temperature rising rate is changed along with the temperature rising to approximately obtain the average value), the PDMS is slowly heated to 150 ℃, in the process, the PDMS is heated and expanded, the PDMS is slowly and gradually attached to the surface of the silicon wafer, and the smooth attachment is realized by matching with a leveling electrode. After the bonding is completed, heating is stopped, the object stage is cooled and retracted, the object stage is slightly moved, the two-dimensional material is separated from the PDMS, and the cantilever beam is slowly lifted, so that the two-dimensional material is left on the surface of the electrode.
(8) The electrodes were placed in a plasma cleaning machine and the two-dimensional material was treated with a hydrogen argon mixture (hydrogen 5sccm, argon 25 sccm) for 30 seconds to remove surface impurities and organics and further facilitate bonding in later operating steps.
(9) And (3) respectively taking two-dimensional materials of niobium diselenide and boron nitride, repeating the steps (1) - (8), and stacking sequentially to form a heterojunction with 3 layers, wherein the two-dimensional materials placed in the prior art can not be lifted during extraction due to the fact that the viscosity is lost when the PDMS is heated.
(10) And after stacking, placing the substrate stacked with the two-dimensional material in a vacuum environment for 1 hour to empty the gas in the interlayer, so as to obtain the two-dimensional material heterojunction device.
(11) The heterojunction morphology of the obtained two-dimensional material heterojunction device is observed by an optical microscope, and the result is shown in fig. 1. As can be seen from fig. 1, by adopting the technical scheme of the present embodiment, a 3-layer two-dimensional material heterojunction with complete structure and no breakage can be obtained.
Example 2 preparation of two-dimensional Material heterojunction device (3 layers boron nitride-molybdenum ditelluride-tungsten ditelluride heterojunction)
Steps (1) - (8) are the same as in example 1.
(9) And (3) respectively taking two-dimensional materials of boron nitride and molybdenum telluride, repeating the steps (1) - (8), and stacking in sequence to form a special heterojunction, wherein the two-dimensional materials placed in the prior art are not lifted during extraction due to the fact that the viscosity is lost when the PDMS is heated.
Step (10) is the same as in example 1.
(11) The heterojunction morphology of the obtained two-dimensional material heterojunction device is observed by an optical microscope, and the result is shown in fig. 2. As can be seen from fig. 2, by adopting the technical scheme of the present embodiment, a 3-layer two-dimensional material heterojunction with complete structure and no breakage can be obtained.
Example 3 preparation of two-dimensional Material heterojunction device (etching without reactive ion etcher)
Step (1) is the same as in example 1.
(2) The electrode pattern designed in advance is exposed on an electron beam exposure system, and a mixed solution of methyl isobutyl ketone and isopropanol (volume ratio is 1:3) is used for developing for 1 minute. And then the treated silicon wafer is put into water, acetone and isopropanol to be respectively ultrasonically treated for 10 minutes for cleaning. And then plating a 65nm gold film by using an electron beam plating machine. After removal, the photoresist is removed by soaking in acetone for half an hour, and finally washed with isopropanol.
Steps (3) - (10) are the same as in example 1.
(11) The morphology of the resulting two-dimensional material device was observed by an optical microscope, and the result is shown in fig. 3. As can be seen from fig. 3, if the two-dimensional material is transferred using a substrate in which electrodes are embedded after etching the substrate without using a reactive ion etcher, breakage and unevenness of the resulting two-dimensional material device may occur. Since the bottommost material has been broken, thereby affecting device testing, subsequent stacking of the top layer material is no longer performed.
Example 4 preparation of two-dimensional Material heterojunction device (transfer of two-dimensional Material without thermal expansion and Cold shrinkage)
Steps (1) - (5) are the same as in example 1.
(6) And placing the electrode on a transfer platform, aligning the center of the electrode with the two-dimensional material, slowly controlling the cantilever beam to be close to the electrode, continuously reducing the PDMS carrying the two-dimensional material to be attached to the substrate, slowly lifting the PDMS carrying the two-dimensional material, and retaining the two-dimensional material on the substrate.
(7) The electrodes were placed in a plasma cleaning machine and the two-dimensional material was treated with a hydrogen argon mixture (hydrogen 5sccm, argon 25 sccm) for 30 seconds to remove surface impurities and organics.
(8) The morphology of the obtained two-dimensional material device is observed by an optical microscope, the result is shown in fig. 4, and as can be seen from fig. 4, the two-dimensional material is transferred by adopting a mode of directly transferring the two-dimensional material, and the obtained two-dimensional material is damaged and uneven. Since the bottommost material has been broken, thereby affecting device testing, subsequent stacking of the top layer material is no longer performed.
Example 5 preparation of two-dimensional Material heterojunction device (heating Rate investigation)
Steps (1) - (6) are the same as in example 1.
(7) After the heating table was stabilized to 80 ℃, the temperature rise was started. After a part of PDMS in a microscope window is found to be attached to a silicon wafer in the two-dimensional material transferring process, the operation of the stepper is stopped, the operation is changed into a heating transfer platform, the temperature rising rate is controlled to be about 5 ℃ per second (the temperature rising rate is changed along with the temperature rising to approximately obtain the average value), the PDMS is slowly heated to 150 ℃, in the process, the PDMS is heated and expanded, the PDMS is slowly and gradually attached to the surface of the silicon wafer, and the smooth electrode is matched to achieve close attachment. After the bonding is completed, heating is stopped, the object stage is cooled and retracted, the object stage is slightly moved, the two-dimensional material is separated from the PDMS, and the cantilever beam is slowly lifted, so that the two-dimensional material is left on the surface of the electrode.
(8) The heterojunction morphology of the obtained two-dimensional material device was observed by an optical microscope, and as a result, as seen in fig. 5, breakage and unevenness of the obtained two-dimensional material were generated when PDMS was heated at a temperature rising rate of 5 ℃. Since the bottommost material has been broken, thereby affecting device testing, subsequent stacking of the top layer material is no longer performed.
Example 6 preparation of two-dimensional Material heterojunction device (heating Rate investigation)
Steps (1) - (6) are the same as in example 1.
(7) After the heating table was stabilized to 80 ℃, the temperature rise was started. After a part of PDMS in a microscope window is found to be attached to a silicon wafer in the two-dimensional material transferring process, the operation of the stepper is stopped, the operation is changed into a heating transfer platform, the temperature rising rate is controlled to be about 2 ℃ per second (the temperature rising rate is changed along with the temperature rising to approximately obtain the average value), the PDMS is slowly heated to 150 ℃, in the process, the PDMS is heated and expanded, the PDMS is slowly and gradually attached to the surface of the silicon wafer, and the smooth electrode is matched to achieve close attachment. After the bonding is completed, heating is stopped, the object stage is cooled and retracted, the object stage is slightly moved, the two-dimensional material is separated from the PDMS, and the cantilever beam is slowly lifted, so that the two-dimensional material is left on the surface of the electrode.
Step (8) is the same as in example 1.
(9) And placing the substrate containing the two-dimensional material in a vacuum environment for 1 hour to evacuate the gas in the interlayer, so as to obtain the two-dimensional material device.
(10) The morphology of the obtained two-dimensional material device was observed by an optical microscope, and as a result, fig. 6 shows that the transferred single layer of tungsten ditelluride was extremely high in bonding rate requirement and extremely easy to damage, and as can be seen from fig. 6, the two-dimensional material was transferred by heating PDMS at a temperature rising rate of 2 ℃ per second, and the obtained two-dimensional material was flat and free from breakage.
Conclusion from the results of the above examples, it can be seen that:
(1) The substrate is etched by the reactive ion etching machine to embed the electrode, so that the integrity of the heterojunction structure of the two-dimensional material is improved, the breakage of the two-dimensional material is avoided, and the number of layers of the heterojunction structure of the two-dimensional material can be improved.
(2) The two-dimensional material is transferred to the substrate in a heat expansion and cold contraction mode, so that the integrity of the heterojunction structure of the two-dimensional material is improved, the cracking of the two-dimensional material is avoided, and the number of layers of the heterojunction structure of the two-dimensional material can be improved.
(3) When the two-dimensional material is transferred to the substrate, the heating speed is 1-4 ℃ per second, the integrity of the heterojunction structure of the two-dimensional material is improved, the two-dimensional material is prevented from being broken, and when the heating speed is more than or equal to 5 ℃ per second, the heating speed is too high, so that the two-dimensional material is easily broken.
(4) When the two-dimensional material is transferred to the substrate, the two-dimensional material is transferred by heating to 130-150 ℃, so that the integrity of the heterojunction structure of the two-dimensional material is improved, and the two-dimensional material is prevented from being broken.
While the methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations and combinations of the methods and applications described herein can be made and applied within the spirit and scope of the invention. Those skilled in the art can, with the benefit of this disclosure, suitably modify the process parameters to achieve this. It is expressly noted that all such similar substitutions and modifications will be apparent to those skilled in the art, and are deemed to be included within the present invention.
Claims (23)
1. A method of fabricating a two-dimensional material heterojunction device, comprising:
(I) Dissociating the two-dimensional material;
Embedding an electrode on a substrate, namely spin-coating electron beam photoresist on the substrate, baking, exposing the substrate to light by electron beam lithography to obtain a pre-designed electrode shape, developing with a developing solution, putting the substrate into a reactive ion etching machine to etch the substrate, evaporating the electrode, and removing photoresist to obtain the substrate embedded with the electrode;
(III) transferring the dissociated two-dimensional material to a substrate embedded with an electrode, wherein the step (III) comprises transferring the dissociated two-dimensional material to the surface of PDMS, approaching the electrode to the PDMS with the two-dimensional material, heating to expand the PDMS and contact with the substrate, closing the heating, cooling the PDMS, and removing the PDMS, the approaching electrode to the PDMS with the two-dimensional material is formed by approaching the electrode to the PDMS with the two-dimensional material to the distance between the two-dimensional material and the electrode from 10 mu m to 500 mu m, or approaching the PDMS with the two-dimensional material to the contact surface, the thickness of the PDMS is 500 mu m to 2000 mu m, the heating is performed to 130 ℃ to 150 ℃, and the heating is performed at a speed of 1 ℃ to 4 ℃ per second;
(IV) repeating the steps (I) and (III) by taking at least one two-dimensional material which is the same or different to form a multi-layer heterojunction structure;
The steps (I) and (II) can be carried out in any order;
the two-dimensional material is selected from at least one of transition metal chalcogenide, graphene, boron nitride, black phosphorus and chromium triiodide;
the transition metal chalcogenide is at least one selected from molybdenum disulfide, molybdenum ditelluride, tungsten diselenide, niobium diselenide and indium diselenide;
The substrate is selected from silicon dioxide, silicon wafer with a silicon dioxide layer on the surface, silicon wafer, mica, sapphire or flexible material, wherein the flexible material is selected from at least one of polyimide, polyvinyl alcohol, polyester and polyethylene terephthalate.
2. The method of claim 1, wherein the etching depth is 20nm-100nm deeper than the substrate surface, the electrode thickness is 21nm-125nm, and the electrode is 1nm-25nm higher than the substrate surface.
3. The method according to any one of claim 1 to 2,
And (3) repeating the steps (I) and (III) for at least one different two-dimensional material to form a multi-layer heterojunction structure, thereby obtaining the two-dimensional material heterojunction device.
4. The method of any one of claims 1-2, wherein the multi-layer heterojunction structure in step (IV) is a 2-4 layer heterojunction structure.
5. The method of any one of claims 1-2, wherein step (I) comprises stripping using a mechanical stripping process.
6. The method according to any one of claims 1-2, wherein the step (I) comprises adhering the two-dimensional material with an adhesive tape, tearing after adhering the new adhesive tape to the adhesive tape adhered with the two-dimensional material, repeating the step of tearing after adhering the new adhesive tape to the adhesive tape adhered with the two-dimensional material 3-4 times, and obtaining the adhesive tape containing a single layer or less of the two-dimensional material.
7. The method of any of claims 1-2, the transferring the dissociated two-dimensional material to the PDMS surface comprising bonding a tape comprising a single layer or a few layers of two-dimensional material to the PDMS, tearing.
8. The method of any of claims 1-2, the electron beam photoresist comprising PMMA.
9. The method of any of claims 1-2, the developing solution comprising a mixed solution of methyl isobutyl ketone and isopropyl alcohol.
10. The method of claim 9, wherein the volume ratio of methyl isobutyl ketone to isopropyl alcohol is 9:1-1:9.
11. The method of any of claims 1-2, wherein the etching is etching with a trifluoromethane gas.
12. The method of any one of claims 1-2, the photoresist stripping comprising immersing the photoresist with acetone.
13. The method of any one of claims 1-2, wherein the stripping comprises immersing the stripping in acetone and rinsing with isopropyl alcohol.
14. The method of any one of claims 1-2, further comprising, after step (III), plasma cleaning with hydrogen, argon, or a mixture thereof.
15. The method according to claim 14, wherein the volume ratio of the hydrogen to the argon in the mixed gas of the hydrogen and the argon is 100:1-1:100.
16. The method of claim 14, wherein the plasma cleaning is for a period of 20s to 120s.
17. The method of any one of claims 1-2, wherein after step (IV), the two-dimensional material heterojunction device is placed in a vacuum condition to remove air from the interlayer.
18. The method of claim 17, wherein the time period of exposure to vacuum is 1 hour to 3 hours.
19. The method of any of claims 1-2, wherein spin coating the substrate with the electron beam resist comprises uniformly spreading the electron beam resist on the substrate with a bench-top resist coater at a speed of 3000 rpm-6000 rpm for 1-2 minutes.
20. The method of any one of claims 1-2, wherein the baking temperature is 120 ℃ to 180 ℃.
21. The method of any one of claims 1-2, wherein the baking time is 1 minute to 2 minutes.
22. The process according to any one of claims 1-2, wherein steps (I) and/or (III) are performed in a glove box.
23. A two-dimensional material heterojunction device prepared according to the method of any one of claims 1-22.
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| CN107833940A (en) * | 2017-10-20 | 2018-03-23 | 浙江大学 | A kind of opto-electronic device based on two-dimentional molybdenum disulfide rhenium disulfide hetero-junctions, preparation method and application |
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| CN107833940A (en) * | 2017-10-20 | 2018-03-23 | 浙江大学 | A kind of opto-electronic device based on two-dimentional molybdenum disulfide rhenium disulfide hetero-junctions, preparation method and application |
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