A non-destructive transfer method for graphene films

Abstract

This invention discloses a non-destructive transfer method for graphene films. A polymer composite film is sequentially spin-coated onto a graphene / metal substrate, and a heat-release tape (TRT) is then bonded to it. The graphene film is separated from the metal substrate by mechanical peeling and then bonded to the target substrate. After low-temperature cooling, the TRT and polymer composite film are directly removed, achieving the transfer of the graphene film. The procedure is simple, uses only water as the solvent (no organic solvents involved), is safe and environmentally friendly, and yields graphene with a complete structure, which is beneficial for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of carbon materials, and specifically relates to a non-destructive transfer method for graphene films. Background Technology

[0002] Currently, there are many methods for transferring graphene. The most common one is the chemical etching substrate transfer method, which sacrifices the growth substrate. In this method, a graphene wafer coated with a polymer film is placed in an etching solution for tens of hours to completely etch the copper and separate the graphene from the copper wafer.

[0003] Another commonly used method is the bubbling method. This method utilizes the hydrogen bubbles generated between the growth substrate and the graphene after energizing, thereby decoupling the graphene from the growth substrate and achieving complete separation.

[0004] The existing graphene film transfer methods described above are cumbersome and difficult to scale up; the organic waste liquid or strong alkaline solutions are difficult to treat and pose a significant environmental hazard. Furthermore, the use of organic solvents for degumming is unsuitable for industrial production and results in difficult waste liquid treatment, causing severe environmental pollution. Summary of the Invention

[0005] To address the problems in the prior art, this invention provides a method for transferring graphene films, specifically comprising the following steps:

[0006] S1. A polymer composite film is spin-coated onto the surface of a graphene film grown directly on a metal substrate to form a polymer composite film / graphene film / metal substrate composite structure.

[0007] S2. Heat-release tape (TRT) is laminated onto the polymer composite film to form a composite structure of TRT / polymer composite film / graphene film / metal substrate.

[0008] S3. Separate the TRT / polymer composite film / graphene film from the metal substrate;

[0009] S4. The TRT / polymer composite film / graphene film is bonded to the target substrate to obtain the TRT / polymer composite film / graphene film / target substrate composite structure.

[0010] S5. Cool the TRT / polymer composite film / graphene film / target substrate composite structure to below 0°C;

[0011] S6. Directly remove the heat-release tape (TRT) and the polymer composite film to obtain the graphene film / target substrate composite structure.

[0012] According to a specific embodiment of the present invention, the polymer composite film comprises an organic polymer that is highly soluble in water and an organic small molecule that is highly soluble in water. The organic polymer is one or more of polyvinyl alcohol (PVA), polyacrylic acid, polymethacrylic acid, polyacrylamide, polymethacrylamide, polymethacrylate, polyacrylate, polyvinylpyrrolidone, and copolymers, preferably polyvinyl alcohol (PVA). The organic small molecule is one or more of sorbitol, hydroxyl-containing volatile small molecule silicone oil, and glycerol, preferably sorbitol.

[0013] The role of adding small organic molecules (such as sorbitol) to polymer films is to increase the number of hydroxyl groups in the polymer film, which is more conducive to the bonding of hydroxyl groups at low temperatures and reduces the viscosity of the polymer at low temperatures.

[0014] According to a specific embodiment of the present invention, the mass ratio of organic polymer to small molecule is 1:100 to 100:1, preferably 1:1.

[0015] According to a specific embodiment of the present invention, step S1 specifically includes: dissolving an organic polymer in water to obtain an organic polymer solution; then adding small molecules to it to obtain a mixed solution of organic polymer and small molecules; and using a spin coater to uniformly cover the surface of a graphene film with the mixed solution of organic polymer and small molecules to obtain a polymer composite film / graphene film / metal substrate composite structure.

[0016] The rotation speed is 500-5000 rpm, the temperature is room temperature, and the number of spin coatings is 1.

[0017] The organic polymer solution has a mass concentration of 3wt% to 20wt%, preferably 8wt%; the small molecules in the mixed solution have a mass concentration of 3wt% to 20wt%, preferably 8wt%.

[0018] According to a specific embodiment of the present invention, before step S1, the method further includes: pre-oxidizing the graphene film / metal substrate composite structure in an alcohol / aqueous solution. The alcohol is a commonly used alcohol in the art, preferably one or more of methanol and ethanol.

[0019] This invention reduces the adhesion between graphene films and metal substrates by pre-oxidizing graphene films.

[0020] According to a specific embodiment of the present invention, the volume ratio of alcohol to water in the alcohol / water solution is 1:1.

[0021] According to a specific embodiment of the present invention, the metal substrate is one of Cu, Ni, Pt, Ru or an alloy thereof; or, the metal substrate is a composite structure of one of Cu, Ni, Pt, Ru or an alloy thereof and sapphire.

[0022] According to a specific embodiment of the present invention, in step S3, the separation method is mechanical peeling, and the mechanical peeling speed is 0.1 cm / s-10 cm / s.

[0023] According to a specific embodiment of the present invention, in step S4, the bonding method is static pressure, roll pressing or vacuum bonding.

[0024] The bonding process ensures that there are no air bubbles in the bonding gaps.

[0025] According to a specific embodiment of the present invention, step S4 includes: bonding a TRT / polymer composite film / graphene film to a target substrate, and then holding it under heat and pressure in a static press to achieve better conformal contact, thereby obtaining a TRT / polymer composite film / graphene film / target substrate composite structure; wherein the heat holding and pressure conditions are: pressure of 0.1 MPa to 1 MPa, temperature control of 10℃ to 200℃, and holding time of 1 min to 600 min. Preferably, the holding temperature is 40℃, the pressure is 0.5 MPa, and the time is 60 min.

[0026] This invention achieves a tighter bond between graphene and the target substrate by maintaining heat and pressure and controlling the conditions, thereby enabling the graphene to be completely transferred to the target substrate.

[0027] According to a specific embodiment of the present invention, in step S5, the cooling temperature is -100℃ to 0℃, preferably -100℃ to -40℃; specifically, it can be -10℃, -20℃, -30℃, -40℃, -50℃, -60℃, -70℃, -80℃, or -90℃.

[0028] The cooling method in step S5 is a common cooling method in the art, such as placing it in a refrigerator to cool it down.

[0029] This invention utilizes low-temperature cooling to reduce the adhesion between graphene and the polymer film. The low-temperature treatment has no effect on the adhesion between the polymer film and the heat-release tape, allowing both the heat-release tape and the polymer film to be removed simultaneously, resulting in intact, residue-free graphene. This eliminates the need for separate removal of the heat-release tape, reducing the number of steps and thus minimizing damage to the graphene structure, thereby improving the integrity of the transferred graphene.

[0030] According to a specific embodiment of the present invention, the thickness of the polymer film is 50 nm to 10 μm; preferably 100 nm to 1 μm.

[0031] According to a specific embodiment of the present invention, the size of the graphene film is 2 to 10 inches, preferably 2 to 8 inches. Examples include 2 inches, 4 inches, 6 inches, and 8 inches.

[0032] According to a specific embodiment of the present invention, the graphene film has 1 to 100 layers.

[0033] According to a specific embodiment of the present invention, the target substrate is a conventional target substrate in the art, such as a silicon wafer.

[0034] Beneficial effects:

[0035] This invention provides a rapid and non-destructive transfer method for single-crystal graphene wafer films. By pre-treating the single-crystal graphene wafer with oxidation to reduce its adhesion to the growth substrate, the polymer film can completely peel off the graphene. Subsequent heat and pressure treatment further strengthens the bond between the graphene and the target substrate, enabling complete transfer of the graphene. Low-temperature treatment of the composite structure reduces the adhesion between the graphene and the polymer film, allowing for the simultaneous removal of the heat-release tape and the polymer film, resulting in intact, residue-free graphene. The technical solution of this invention is simple, uses only water as the solvent (no organic solvents involved), is safe and environmentally friendly, and yields graphene with a complete structure, which is beneficial for industrial production. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the graphene film transfer process of the present invention;

[0037] Figure 2 This is a SEM image of the graphene film after transfer in Example 1;

[0038] Figure 3 This is a photograph of the graphene film after transfer in Example 1;

[0039] Figure 4 This is a SEM image of the graphene film after transfer in Comparative Example 1.

[0040] Figure 5 This is a SEM image of the graphene film after transfer in Comparative Example 2. Detailed Implementation

[0041] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention fall within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0042] Example 1

[0043] like Figure 1As shown, the graphene film / copper / sapphire wafer was first oxidized in an ethanol-water solution for 5 hours, then removed and gently dried with high-purity nitrogen. Polyvinyl alcohol (molecular weight 31K) was dissolved in water at a concentration of 8 wt%, and sorbitol (molecular weight 182.18) was also dissolved at a concentration of 8 wt%. A spin coater was used to uniformly coat the 4-inch graphene film / copper / sapphire wafer surface with the polyvinyl alcohol (PVA) and sorbitol mixture at 2000 rpm and room temperature, with one spin coat. The polymer film thickness was 150 nm. Then, thermal release tape (TRT) was applied to the polymer film using a roller press to obtain the "TRT / polymer film / graphene wafer film / copper / sapphire" composite structure. This was fixed on a flat plate, and the "TRT / polymer film / graphene wafer film" composite structure was slowly peeled off from the "copper / sapphire" growth substrate using tweezers. The copper / sapphire growth substrate was cleaned with a small amount of deionized water and dried with high-purity nitrogen gas, and then used for subsequent re-growth of high-quality graphene wafer films. The resulting TRT / polymer film / graphene wafer film composite layer was roll-pressed onto a silicon wafer containing a 285 nm thick oxide layer, and then held at temperature and pressure in a static press to achieve better conformal contact. The temperature and pressure holding conditions were: pressure 0.5 MPa, temperature 40℃, and time 60 min. Afterward, it was placed in a -80℃ freezer for 15 min, and then the heat release tape and polymer film were directly removed, finally obtaining a 4-inch graphene wafer film transferred onto the silicon wafer.

[0044] pass Figure 2 and Figure 3 It can be seen that the graphene film obtained by the transfer method of the present invention has a complete structure.

[0045] Comparative Example 1

[0046] Other conditions were the same as in Example 1. The difference was that sorbitol was not added. The SEM images of the transferred graphene are shown below. Figure 4 As shown. By Figure 4 It can be seen that the structure of the transferred graphene film is damaged.

[0047] Comparative Example 2

[0048] Other conditions were the same as in Example 1. The difference was that no heat and pressure were applied. The SEM images of the transferred graphene are shown below. Figure 5 As shown. By Figure 5 It can be seen that the structure of the transferred graphene film is damaged.

[0049] Unless otherwise specified, the terms used in this invention have the meanings commonly understood by those skilled in the art.

[0050] The embodiments described in this invention are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Those skilled in the art can make various other substitutions, changes and improvements within the scope of this invention. Therefore, this invention is not limited to the above embodiments, but is only defined by the claims.

Claims

1. A method for transferring graphene wafer thin films, characterized in that, Specifically, the following steps are included: S1. A polymer composite film is spin-coated onto the surface of a graphene wafer film grown directly on a metal substrate to form a polymer composite film / graphene wafer film / metal substrate composite structure. S2. Heat-release tape (TRT) is bonded onto the polymer composite film to form a TRT / polymer composite film / graphene wafer film / metal substrate composite structure. S3. Separate the TRT / polymer composite film / graphene wafer film from the metal substrate; S4. The TRT / polymer composite film / graphene wafer film is bonded to the target substrate to obtain the TRT / polymer composite film / graphene wafer film / target substrate composite structure. S5. Cool the TRT / polymer composite film / graphene wafer film / target substrate composite structure to below 0°C; S6. Directly remove the heat-release tape (TRT) and the polymer composite film to obtain the graphene wafer film / target substrate composite structure. Specifically, step S1 includes: dissolving an organic polymer in water to obtain an organic polymer solution; then adding small organic molecules to it to obtain a mixed solution of the organic polymer and the small organic molecules; and using a spin coater to uniformly cover the surface of the graphene wafer film with the mixed solution to obtain the polymer composite film / graphene wafer film / metal substrate composite structure. The organic polymer is one or more of polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polyacrylamide, polymethacrylamide, polymethacrylate, polyacrylate, and polyvinylpyrrolidone; the organic small molecule is one or more of sorbitol, silicone oil, and glycerol.

2. The transfer method according to claim 1, characterized in that, The metal substrate is one of Cu, Ni, Pt, Ru or an alloy thereof.

3. The transfer method according to claim 1, characterized in that, The metal substrate is a composite structure of sapphire and one of Cu, Ni, Pt, Ru or an alloy thereof.

4. The transfer method according to claim 1, characterized in that, In step S3, the separation method is mechanical peeling, and the mechanical peeling speed is 0.1 cm / s-10 cm / s.

5. The transfer method according to claim 1, characterized in that, Step S4 includes: bonding the TRT / polymer composite film / graphene wafer film to the target substrate, and then holding it under heat and pressure in a static press to achieve better conformal contact, thereby obtaining a TRT / polymer composite film / graphene wafer film / target substrate composite structure; wherein the heat and pressure holding conditions are: pressure of 0.1 MPa~1 MPa, temperature control of 10℃~200℃, and holding time of 1 min~600 min.

6. The transfer method according to claim 1, characterized in that, In step S5, the cooling temperature is -100℃ to 0℃.

7. The transfer method according to claim 6, characterized in that, The cooling temperature is -100℃ to -40℃.

8. The transfer method according to claim 1, characterized in that, The thickness of the polymer composite film is 50 nm to 10 μm.

9. The transfer method according to claim 8, characterized in that, The thickness of the polymer composite film is 100 nm to 1 μm.

10. The transfer method according to claim 1, characterized in that, The graphene wafer film has 1 to 100 layers.

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