Flexible graphene Hall device and preparation method thereof

Abstract

The invention discloses a flexible graphene Hall device and a preparation method thereof. The preparation method comprises the following steps: S1, carrying out pretreatment on a quartz plate; s2, spin-coating a quartz plate with the polyimide solution, and carrying out drying treatment to form a semi-dry PI film; s3, laminating the graphene surface of the copper foil on which the graphene grows with a PI film, and then performing hot pressing; s4, the quartz / PI / graphene / Cu composite film is placed in an etching solution to be etched, and a quartz / PI / graphene composite film is obtained; s5, printing by adopting a microelectronic printer to obtain a metal electrode and a graphene pattern protection layer; s6, etching the graphene which is not covered by the graphene pattern protection layer by adopting oxygen plasma; and S7, stripping the quartz plate from the PI film to obtain the flexible graphene Hall device. According to the preparation method disclosed by the invention, the graphene / PI composite layer can be directly subjected to micro-nano processing, the overall performance of the flexible graphene Hall device is remarkably improved, and the requirement of the ultrathin flexible graphene Hall device on an ultrathin structure can be met.

Description

Technical Field

[0001] The present invention belongs to the technical field of Hall elements, and in particular relates to a flexible graphene Hall device and a preparation method thereof. Background Art

[0002] Hall effect-based magnetic field sensors are widely used to measure physical quantities such as displacement, force, angular velocity, linear velocity, magnetic field, and current. Hall effect devices play an important role in automotive electronics, smartphones, medical devices, industrial control, and security equipment. However, traditional silicon-based Hall effect devices are limited by the inherent carrier mobility of the material, making it difficult to further improve their sensitivity and response speed. Therefore, researchers have begun exploring new semiconductor materials to enhance the performance of Hall effect devices. Graphene, a two-dimensional semiconductor nanomaterial, exhibits ultra-high carrier mobility, excellent mechanical flexibility, and thermal stability, making it an ideal candidate for Hall effect devices. Compared to traditional silicon-based materials, graphene's atomic-scale thickness and large surface area significantly improve sensor measurement accuracy while reducing device weight. Furthermore, graphene's flexibility makes it suitable for emerging applications such as wearable electronics and flexible electronics. Therefore, graphene-based Hall effect devices hold great promise for development.

[0003] However, the preparation of graphene Hall devices faces a key challenge: how to achieve efficient and lossless transfer of high-quality graphene. Currently, the commonly used graphene transfer methods mainly include the following: (1) coating PMMA as a support layer, corroding the metal substrate, transferring the graphene to an insulating substrate, and then dissolving the PMMA with acetone. This method can transfer the graphene completely to the insulating substrate, but PMMA is not easy to remove and can easily contaminate the graphene; (2) directly corroding the metal without coating PMMA, and using an insulating substrate to pick up the graphene in the solution. This process is simple, but the graphene film is easily broken during the picking process, making it difficult to transfer the graphene completely to the desired substrate; (3) directly using micromechanical peeling to peel the graphene onto the insulating substrate. This method can obtain high-quality graphene on the insulating substrate, but the size of the graphene will be greatly limited; (4) coating PDMS or other colloids on the substrate with graphene attached and curing it, and then directly using mechanical methods to peel the PDMS from the original substrate surface. This method is not efficient, and the graphene often tears or sticks to the original substrate instead of being transferred to the PDMS.

[0004] In summary, the existing preparation technology of graphene Hall devices is restricted by the common problems of contamination residue, transfer damage, and size limitation in graphene transfer technology, which restricts the performance optimization and practical application of graphene Hall devices. Summary of the Invention

[0005] In the prior art, a hot pressing process is also used to combine a flexible polyethylene terephthalate (PET) film with a graphene / copper foil composite structure to prepare a Cu / graphene / PET composite film, and then the copper foil is removed by etching to finally obtain a transparent PET / graphene film. Although this method avoids the problems of impurity contamination, size limitation, transfer damage, etc. that may be introduced in the traditional solution etching process, the inventors of this application found that due to the characteristics of the PET material itself, the obtained transparent PET / graphene film lacks sufficient mechanical support strength and is difficult to directly perform micro-nano processing such as printing and etching to prepare functional devices. Moreover, the thickness of conventional dry PET film is usually in the range of 25~250μm, which is difficult to meet the ultra-thin requirements of modern electronic devices. Performance requirements of the structure; although ultra-thin PET films of 6~25μm can be prepared through special processes, such ultra-thin PET films are very easy to break during the hot pressing transfer process, which seriously affects the success rate of the transfer and the yield of the device; in addition, the prepared PET / graphene composite film also has the problem of interface instability. Specifically, the dry PET film and graphene are only physically adsorbed and bonded by hot pressing. This physical adsorption is not stable. In the subsequent micro-nano processing process, due to the lack of strong interfacial chemical bonding, when subjected to the thermal stress of plasma etching or the swelling effect of etching solution treatment, the PET / graphene interface is very easy to be locally peeled off. At the same time, the mechanical stress or temperature change during the operation of the device will significantly reduce the interface stability of the two, thereby affecting the overall performance of the device.

[0006] Based on the above problems, the purpose of the present invention is to provide a flexible graphene Hall device and a preparation method thereof. The preparation method not only avoids problems such as contamination, size limitation, transfer damage, etc., but also enables the graphene / PI composite layer to be directly micro-nano processed, and significantly improves the overall performance of the flexible graphene Hall device and can meet the requirements of ultra-thin flexible graphene Hall devices for ultra-thin structures.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a flexible graphene Hall device, comprising the following steps: S1, pre-treating a quartz sheet; S2, spin-coating a polyimide solution on the quartz sheet, and drying the sheet to form a semi-dry PI film; S3, laminating the graphene surface of a copper foil with graphene grown thereon to the PI film and then hot-pressing the laminate to obtain a quartz / PI / graphene / Cu composite film; S4, placing the quartz / PI / graphene / Cu composite film in an etching solution and etching it until the copper foil is completely removed to obtain a quartz / PI / graphene composite film; S5, using a microelectronic printer to print on the graphene surface of the quartz / PI / graphene composite film to obtain a metal electrode and a graphene pattern protective layer; S6, using oxygen plasma to etch away the graphene not covered by the graphene pattern protective layer; S7, peeling the quartz sheet from the PI film to obtain a flexible graphene Hall device.

[0008] Compared with the existing technology, the present invention uses a quartz plate as the supporting substrate. Its high thermal stability and chemical inertness can withstand subsequent hot pressing and etching processes. The PI solution is applied to the surface of the quartz plate through a spin coating process. Specifically, the thickness of the PI film can be precisely controlled to a few microns by adjusting the rotation speed, meeting the needs of ultra-thin flexible devices. The semi-dry PI film formed on the quartz plate retains a certain molecular chain activity to promote interfacial adhesion and has sufficient mechanical strength to support graphene transfer. The graphene grown on the copper foil is directly hot-pressed on the surface of the semi-dry PI film. The viscoelastic properties of the semi-dry PI are used to achieve stable adsorption of the graphene and the PI film, achieving high-quality graphene transfer, thereby significantly improving the overall performance of the flexible graphene Hall device. After etching away the copper foil, the graphene / PI composite layer remains firmly attached to the quartz substrate and can directly enter micro-nano processing processes such as printing and etching without the need for secondary transfer. Therefore, the present invention can form an ultra-thin semi-dry PI film by spin-coating a polyimide solution on a quartz wafer, and utilize the unique viscoelastic properties of the PI film to achieve high-quality and stable transfer of graphene. At the same time, with the help of the rigid support of the quartz substrate, the graphene / PI composite layer can be directly micro-nano processed, thereby significantly improving the overall performance of the flexible graphene Hall device while meeting the thickness requirements of the ultra-thin flexible device.

[0009] Furthermore, the pretreatment in step S1 of the present invention includes: ultrasonic cleaning using acetone, isopropyl alcohol, ethanol and ultrapure water in sequence; and then surface treatment using a plasma cleaning machine.

[0010] Furthermore, the drying process in step S2 of the present invention includes: heating from room temperature to 100° C. and maintaining the temperature for 60 minutes.

[0011] Furthermore, the thickness of the PI film of the present invention is 5-10 μm.

[0012] Furthermore, step S3 of the present invention includes growing graphene on the surface of the copper foil using a chemical vapor deposition process to obtain the copper foil grown with graphene.

[0013] Furthermore, step S3 of the present invention includes: S31, laminating the graphene surface of the copper foil on which graphene is grown to the PI film; S32, placing silicone rubber on the copper foil surface on which graphene is grown and then hot pressing.

[0014] Furthermore, the hot pressing conditions in step S3 of the present invention include: a pressure of 350-450 psi, a temperature of 130-150° C., and a time of 12-18 min.

[0015] Furthermore, the etching solution of the present invention is an aqueous solution of ammonium persulfate.

[0016] Furthermore, step S5 of the present invention includes: S51, using a microelectronic printer to print conductive silver paste on the graphene surface of the quartz / PI / graphene composite film to obtain a metal electrode; S52, using a microelectronic printer to print organic silicone on the graphene surface of the quartz / PI / graphene composite film to obtain a graphene graphic protective layer.

[0017] Accordingly, a second aspect of the present invention provides a flexible graphene Hall device, which is manufactured using the above-mentioned method for manufacturing a flexible graphene Hall device. The flexible graphene Hall device has good overall performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The figure is a process flow chart of the flexible graphene Hall device and its preparation method of the present invention.

[0019] Figure 2 Schematic diagram of the relationship between the output Hall voltage and magnetic field size of the flexible graphene Hall device provided in Example 1.

[0020] Figure 3 Schematic diagram of the relationship between current sensitivity and input current of the flexible graphene Hall device provided in Example 1.

[0021] Figure 4 Schematic diagram of the relationship between the voltage sensitivity and input voltage of the flexible graphene Hall device provided in Example 1.

[0022] Figure 5 This is a current sensitivity histogram of the flexible graphene Hall device provided in Example 1.

[0023] Figure 6 This is a voltage sensitivity histogram of the flexible graphene Hall device provided in Example 1. DETAILED DESCRIPTION

[0024] In order to solve the problems of impurity contamination, size limitation, transfer damage and other problems that may be introduced in the traditional solution etching process in the existing technology, please refer to Figure 1 The present invention provides a flexible graphene Hall device and a preparation method thereof, the steps comprising:

[0025] S1, pre-treating the quartz plate;

[0026] S2, spin-coating a polyimide (PI) solution on a quartz wafer and drying it to form a semi-dry PI film;

[0027] S31, the graphene surface of the copper foil with graphene grown thereon is bonded to the PI film;

[0028] S32, placing silicone rubber on the copper foil surface where graphene is grown and hot pressing to obtain a quartz / PI / graphene / Cu composite film;

[0029] S4, placing the quartz / PI / graphene / Cu composite film in an etching solution and etching until the copper foil is completely removed to obtain a quartz / PI / graphene composite film;

[0030] S51, using a microelectronic printer to print a conductive silver paste on the graphene surface of the quartz / PI / graphene composite film to obtain a metal electrode;

[0031] S52. Printing organic silica gel on the graphene surface of the quartz / PI / graphene composite film using a microelectronic printer to obtain a graphene graphic protection layer.

[0032] S6, etching away the graphene not covered by the graphene pattern protection layer using oxygen plasma;

[0033] S7. Peel the quartz sheet off the PI film to obtain a flexible graphene Hall device.

[0034] The pretreatment in step S1 includes ultrasonic cleaning using acetone, isopropyl alcohol, ethanol, and ultrapure water in sequence, followed by surface treatment using a plasma cleaner. More specifically, the quartz wafer is cleaned in an ultrasonic cleaner using acetone, isopropyl alcohol, ethanol, and ultrapure water for 10 to 20 minutes, dried with nitrogen, and then placed in a plasma cleaner for surface treatment at a power of 80 to 120 watts for 3 to 6 minutes. This surface treatment further increases the surface energy of the quartz wafer and enhances its adhesion to the polyimide film.

[0035] In step S2 , a polyimide solution is spin-coated on a quartz wafer at a spin-coating speed of 1000-3000 rpm and a spin-coating time of 30-60 s. The thickness of the PI film is precisely controlled by adjusting the spin speed and time. Specifically, the polyimide is PI-2610.

[0036] The thickness of the PI film is 5-10 μm. Specifically, the thickness of the PI film can be, but is not limited to, 5 μm, 6 μm, 8 μm, 9 μm, or 10 μm.

[0037] Among them, the drying treatment in step S2 includes: heating from room temperature to 100°C and maintaining it for 60 minutes; the maximum temperature during the drying treatment process of this application does not exceed 100°C, which is much lower than the 300°C required for complete curing of the polyimide solution. Therefore, the drying treatment of this application can obtain a semi-dry PI film.

[0038] Furthermore, step S3 of the present invention includes growing graphene on the surface of the copper foil using a chemical vapor deposition process to obtain the graphene-grown copper foil. This chemical vapor deposition process is well known to those skilled in the art and will not be described in detail here. More specifically, reference may be made to the prior art method for preparing graphene-grown copper foil disclosed in CN117383551A.

[0039] Furthermore, step S3 of the present invention includes: S31, laminating the graphene surface of the copper foil on which graphene is grown to the PI film; S32, placing silicone rubber on the copper foil surface on which graphene is grown and then hot pressing. The placement of the silicone rubber ensures that the graphene is evenly stressed during the transfer process, thereby further improving the transfer quality and uniformity.

[0040] Furthermore, the hot pressing conditions in step S3 of the present invention include: a pressure of 350-450 psi, a temperature of 130-150°C, and a time of 12-18 minutes. Specifically, the pressure may be, but is not limited to, 350 psi, 380 psi, 400 psi, 420 psi, or 450 psi; the temperature may be, but is not limited to, 130°C, 135°C, 140°C, 145°C, or 150°C; and the time may be, but is not limited to, 12 minutes, 15 minutes, 16 minutes, or 18 minutes.

[0041] Furthermore, in step S4 of the present invention, the etching solution is an aqueous solution of ammonium persulfate. Specifically, the aqueous solution of ammonium persulfate is prepared by mixing ammonium persulfate and deionized water in a volume ratio of 0.8-1.2:0.8-1.2. The etching process is performed at 45-55°C for 1-2 hours until the copper foil is completely removed. The film is then rinsed in deionized water for 15-25 minutes to completely remove any residual etching solution, ultimately obtaining a clean quartz / PI / graphene composite film.

[0042] Furthermore, step S5 of the present invention includes: S51, using a microelectronic printer to print conductive silver paste on the graphene surface of the quartz / PI / graphene composite film to obtain a metal electrode; S52, using a microelectronic printer to print organic silicone on the graphene surface of the quartz / PI / graphene composite film to obtain a graphene graphic protective layer.

[0043] Furthermore, the oxygen plasma etching technology in step S6 of the present invention is also well known to those skilled in the art, and will not be described in detail here.

[0044] In order to better illustrate the purpose, technical solutions and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the following implementation method is a further explanation of the present invention and should not be used as a limitation of the present invention.

[0045] Example 1

[0046] This embodiment provides a flexible graphene Hall device, and the steps of the preparation method thereof include:

[0047] S1. Clean the quartz wafer in an ultrasonic cleaner using acetone, isopropyl alcohol, ethanol, and ultrapure water for 10 min in sequence, blow dry with nitrogen, and then place it in a plasma cleaner for surface treatment. The power of the plasma cleaner is 100 W and the cleaning time is 5 min.

[0048] S2. Spin-coat a polyimide PI-2610 solution (purchased from Hitachi Chemical DuPont MicroSystems) onto a quartz wafer. After spin coating, heat the wafer to 100°C at room temperature, maintain the temperature for 60 minutes, and then cool the wafer naturally to room temperature to obtain a semi-dry PI film. The spin speed is 1000 rpm, the spin time is 30 seconds, and the thickness of the PI film is 10 μm.

[0049] S31, the graphene surface of the copper foil with graphene grown thereon is bonded to the PI film;

[0050] S32, placing silicone rubber on the copper foil surface where graphene is grown, and then placing the silicone rubber on a hot press to obtain a quartz / PI / graphene / Cu composite film; wherein the hot pressing pressure is 400 psi, the temperature is 130° C., and the time is 15 minutes;

[0051] S4, placing the quartz / PI / graphene / Cu composite film in an etching solution and etching at 50° C. for 1 to 2 hours until the copper foil is completely removed, and then washing in deionized water for 20 minutes to obtain a quartz / PI / graphene composite film; wherein the etching solution is an aqueous solution of ammonium persulfate consisting of an ammonium persulfate solution and deionized water in a volume ratio of 1:1;

[0052] S51, using a microelectronic printer to print a conductive silver paste on the graphene surface of the quartz / PI / graphene composite film to obtain a metal electrode;

[0053] S52. Printing organic silica gel on the graphene surface of the quartz / PI / graphene composite film using a microelectronic printer to obtain a graphene graphic protection layer.

[0054] S6, etching away the graphene not covered by the graphene pattern protection layer using oxygen plasma;

[0055] S7. Peel the quartz sheet off the PI film to obtain a flexible graphene Hall device.

[0056] The performance of the flexible graphene Hall device prepared in Example 1 was tested by the following test method. The test results are as follows: Figures 2 to 6 shown.

[0057] Detection method: During testing, a Helmholtz coil is used to generate a magnetic field, a Keithley 2280S is used to provide bias current or voltage, and the Hall voltage is measured. The magnetic field is reset to zero after each measurement to reduce drift.

[0058] Depend on Figure 2 It can be seen that the Hall voltage of the flexible graphene Hall device of Example 1 changes linearly with the magnetic field, which confirms that the device of Example 1 has typical Hall effect characteristics.

[0059] Depend on Figure 3 and Figure 4 It can be seen that the flexible graphene Hall device of Example 1 has good current sensitivity and voltage sensitivity. Therefore, the flexible graphene Hall device of the present application has better performance than the graphene Hall device prepared by the traditional wet method.

[0060] Figure 5 and 6 The current and voltage sensitivities of 18 different devices tested at different locations are given by Figure 5 and Figure 6 It can be seen that the 18 different devices tested at different positions all showed good current and voltage sensitivity, which proves that the flexible graphene Hall device prepared by the preparation method of the present application has good integrity.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it is not limited to the embodiments. Those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a flexible graphene Hall device, characterized in that the steps include: S1, pre-treating the quartz plate; S2, spin-coating the polyimide solution on the quartz plate, and drying it to form a semi-dry PI film; S3, laminating the graphene surface of the copper foil on which graphene is grown to the PI film and then hot-pressing the laminate to obtain a quartz / PI / graphene / Cu composite film; S4, placing the quartz / PI / graphene / Cu composite film in an etching solution and etching until the copper foil is completely removed to obtain a quartz / PI / graphene composite film; S5, using a microelectronic printer to print on the graphene surface of the quartz / PI / graphene composite film to obtain a metal electrode and a graphene graphic protection layer; S6, etching away the graphene not covered by the graphene pattern protection layer using oxygen plasma; S7. Peeling the quartz sheet off the PI film to obtain a flexible graphene Hall device.

2. The method for preparing a flexible graphene Hall device according to claim 1, wherein: The pretreatment in step S1 includes: ultrasonic cleaning using acetone, isopropyl alcohol, ethanol and ultrapure water in sequence; and then surface treatment using a plasma cleaning machine.

3. The method for preparing the flexible graphene Hall device according to claim 1, wherein: The drying process in step S2 includes: heating from room temperature to 100° C. and then maintaining the temperature for 60 minutes.

4. The method for preparing a flexible graphene Hall device according to claim 1, wherein: The thickness of the PI film is 5-10 μm.

5. The method for preparing the flexible graphene Hall device according to claim 1, wherein: Step S3 includes growing graphene on the surface of the copper foil using a chemical vapor deposition process to obtain the copper foil grown with graphene.

6. The method for preparing a flexible graphene Hall device according to claim 1, wherein: Step S3 includes: S31, laminating the graphene surface of the copper foil with graphene grown thereon to the PI film; S32, placing silicone rubber on the copper foil surface of the copper foil with graphene grown thereon and then hot pressing.

7. The method for preparing a flexible graphene Hall device according to claim 1, wherein: The hot pressing conditions in step S3 include: pressure of 350-450 psi, temperature of 130-150° C., and time of 12-18 min.

8. The method for preparing a flexible graphene Hall device according to claim 1, wherein: The etching solution is an aqueous solution of ammonium persulfate.

9. The method for preparing a flexible graphene Hall device according to claim 1, wherein: Step S5 includes: S51, using a microelectronic printer to print conductive silver paste on the graphene surface of the quartz / PI / graphene composite film to obtain the metal electrode; S52, using a microelectronic printer to print organic silica gel on the graphene surface of the quartz / PI / graphene composite film to obtain the graphene graphic protective layer.

10. A flexible graphene Hall device, characterized in that: The flexible graphene Hall device is prepared by the preparation method according to any one of claims 1 to 9.

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