A method for preparing a flexible spin valve device

Abstract

The present invention discloses a method for preparing a flexible spin valve, belonging to the field of magnetoelectronics. The method utilizes PI as a carrier, magnetic particles or diamagnetic particles as dopants, and a laser-induced graphene process to layer-by-layer prepare flexible ferromagnetic or antiferromagnetic thin films, thereby constructing a flexible spin valve device. Because the prepared thin films are all made of flexible materials, their bending resistance is significantly improved. This method allows for the large-scale production of spin valves, providing a new approach to the preparation of magnetic electronic devices.

Description

Technical Field

[0001] The invention relates to the technical field of magnetoelectronics, in particular to a method for preparing a flexible spin valve device. Background Art

[0002] With the development of the Internet of Things (IoT), wearable devices, and biomimetic robotics, flexible electronic devices have garnered widespread attention. Among them, flexible magnetoelectronic devices based on magnetic films have significant application prospects, as they can be integrated into smart wearable devices as sensors and memory cells. There are two main methods for preparing flexible metal magnetic films: one is to obtain a free-standing magnetic film through a sacrificial layer method and then transfer it to a flexible substrate; the other is to deposit the magnetic film directly on the flexible substrate. Common flexible substrates include polyvinylidene fluoride (PVDF), polyimide (PI), polydimethylsiloxane (PDMS), and polyethylene terephthalate (PET). PET and PI can be used to directly grow flat magnetic films. However, due to the magnetoelastic anisotropy of flexible materials, the performance of flexible materials is affected when stretched or compressed, which is detrimental to device stability. Therefore, it is necessary to explore methods to stabilize the magnetic anisotropy of flexible magnetic films under strain.

[0003] Spin valves are a key device in the field of spintronics. They use electron spin rather than charge to manipulate current, enabling more efficient magnetic storage and sensing devices. Flexible spin valves are a type of spintronic device that can be bent and stretched. With the rise of flexible electronics around 2000, researchers began exploring the integration of flexible materials and spin, focusing primarily on flexible magnetic materials. Preliminary experiments in 2006 demonstrated the feasibility of depositing magnetic films on flexible substrates, laying the foundation for subsequent research on flexible spin valves. In 2010, flexible spin valves were successfully fabricated. These thin films, typically deposited on flexible substrates such as polyimide (PI) or parylene, maintain their giant magnetoresistance (GMR) or tunnel magnetoresistance (TMR) effects when bent. By 2025, researchers began using two-dimensional materials and one-dimensional nanowires to fabricate flexible spin valves, significantly improving their performance. Since then, research on flexible spin valves has focused on their reliability and applications.

[0004] PI is a high-performance polymer material widely used in many fields due to its excellent thermal stability, mechanical strength, and chemical resistance. Laser-induced graphene (LIG) technology is an innovative method that directly converts certain carbon-containing materials into graphene through laser processing. This technology is fast, efficient, controllable, and low-cost, and has shown broad application prospects in various fields. Materials that respond to magnetic fields in some way are called magnetic materials. Depending on the strength of their response to an external magnetic field, they can be classified as diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic, and ferrimagnetic. For magnetic materials, magnetization curves and hysteresis loops are characteristic curves that reflect their basic magnetic properties. Ferromagnetic materials are generally Co, Fe, Ni and their alloys, rare earth elements and their alloys, and some Mn compounds. Magnetic materials are a typical class of functional materials. Their unique electromagnetic properties make them widely used in magnetic sensing, information processing, and magnetic storage. Summary of the Invention

[0005] The present invention proposes a method for preparing a flexible spin valve, which uses PI as a carrier, antiferromagnetic particles and magnetic particles as dopants to prepare a multilayer PI film, and combines the laser-induced graphene (LIG) process to prepare a flexible spin valve device.

[0006] The technical solutions provided by the present invention are as follows:

[0007] A method for preparing a flexible spin valve device, comprising the steps of:

[0008] 1) Preparation of bottom electrode: PI tape is pasted on the substrate, and a graphene bottom electrode is formed on the PI tape using a laser direct writing induced graphene process;

[0009] 2) Preparation of the antiferromagnetic pinning layer, specifically including the following steps:

[0010] 2-1) Evenly mix the antiferromagnetic particles into the PI liquid;

[0011] 2-2) The above substrate is placed on a coating machine, and the PI liquid obtained in step 2-1) is dropped on the central area of ​​the substrate, spin-coated, and cured to form a PI film on the graphene bottom electrode.

[0012] 2-3) Performing a laser direct writing operation to obtain a graphene layer containing antiferromagnetic particles, which serves as an antiferromagnetic pinning layer. Because the graphene layer contains antiferromagnetic particles, the antiferromagnetic pinning layer can fix the magnetic moment direction of the fixed ferromagnetic electrode.

[0013] 3) Preparation of fixed ferromagnetic electrodes, specifically including the following steps:

[0014] 3-1) Evenly mix the ferromagnetic particles into the PI liquid;

[0015] 3-2) The substrate is placed on a spin coater, and the PI liquid obtained in step 3-1) is dropped onto the center area of ​​the substrate, spin-coated, and cured to form a PI film on the antiferromagnetic pinning layer. The thickness of the film is less than that of the PI film prepared in step 2-2);

[0016] 3-3) performing a laser direct writing operation to obtain a graphene layer containing ferromagnetic particles as a fixed ferromagnetic layer;

[0017] 4) Preparation of the tunnel barrier layer: A pure PI liquid or a PI liquid doped with non-magnetic insulating particles is selected. The substrate is then placed on a spin coater. The pure PI liquid or the PI liquid doped with non-magnetic insulating particles is dropped onto the center of the substrate. The solution is spin-coated and cured to form a PI film on the fixed ferromagnetic layer. This PI film serves as the tunnel barrier layer.

[0018] 5) Preparation of a free ferromagnetic electrode: Using steps 3-1) to 3-3), obtain a graphene layer containing ferromagnetic particles, which serves as a free ferromagnetic electrode layer. The thickness of the free ferromagnetic layer can be different from or the same as that of the fixed ferromagnetic layer, and the type of magnetic particles doped in the free ferromagnetic layer can be the same as or different from that of the fixed ferromagnetic layer.

[0019] 6) Preparation of the top electrode: A layer of PI liquid is coated on the surface of the substrate and cured to form a PI film on the free ferromagnetic layer. A laser direct writing process is then used to obtain a graphene top electrode, thereby forming the device structure.

[0020] 7) Spin valve device packaging: PI tape is evenly adhered to the outer surface of the device structure. At the same time, the bottom layer of PI tape is separated from the rigid substrate. The bottom and top electrodes are exposed using a laser direct writing process to obtain a flexible spin valve device.

[0021] Furthermore, the substrate in step 1) is glass, mica or silicon wafer.

[0022] Furthermore, the antiferromagnetic particles are CoFeB, CoO, MnAu, CrSb, Mn2As, NiMn, MnO, FeO, CoO, NiO, MnS, α-Fe2O3, FeS, FeCl2 or MnF2 particles.

[0023] Furthermore, the ferromagnetic particles are Fe, Co, Ni, FeCo, FeNi or CoFeB particles.

[0024] Furthermore, the non-magnetic insulating particles are MgO, Al2O3, AlN, TiO2 or ZnO particles.

[0025] Furthermore, in step 2-1), the ratio of antiferromagnetic particles to PI liquid is 0.1 g / mL to 0.3 g / mL, and in step 3-1), the ratio of ferromagnetic particles to PI liquid is 0.1 g / mL to 0.3 g / mL. The antiferromagnetic particles or ferromagnetic particles are uniformly mixed into the PI liquid by first dissolving the antiferromagnetic particles or magnetic particles in an organic solvent as a dispersant. The organic solvent is then mixed with the PI liquid and sonicated in an ultrasonic chamber to obtain a PI liquid uniformly doped with the antiferromagnetic particles or magnetic particles. The organic solvent is selected from dimethylformamide, dimethylacetamide, or N-methylpyrrolidone.

[0026] Furthermore, the spin coating in step 2-2), step 3-2) or step 4) is specifically as follows: firstly, a low rotation speed is set to spread the PI liquid evenly, and then a high rotation speed is set to evenly distribute the PI liquid.

[0027] Furthermore, the curing in step 2-2), step 3-2) or step 4) is specifically divided into three stages, namely, the first stage: 60°C-100°C, maintaining for 20min-30min; the second stage: 150°C-200°C, maintaining for 40min-60min; the third stage: 260°C-300°C, maintaining for 30min-60min.

[0028] The beneficial effects of the present invention are as follows:

[0029] The present invention prepares a flexible spin valve device. Since each layer of the thin film is made of flexible material, its bending resistance is significantly improved. The present invention uses laser-induced graphene technology to directly write electrodes. The operation is simple and maskless, which effectively prevents the wafer from being contaminated. The spin valve preparation process of the present invention is simple and can be prepared on a large scale, providing new ideas for the preparation of magnetic electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a flow chart for preparing a spin valve according to a specific embodiment of the present invention.

[0031] Figure 2 These are characterization diagrams of graphene generated in a specific embodiment of the present invention, in which: (a) is an optical microscope image of graphene generated by laser direct writing of pure PI; (b) is an optical microscope image of graphene generated by spin coating and solidification of PI liquid doped with ferromagnetic particles and then laser direct writing. DETAILED DESCRIPTION

[0032] The present invention is further illustrated below by fabricating a flexible CoFeB-MgO-CoFeB-IrMn spin valve. It should be noted that the examples disclosed are intended to facilitate a deeper understanding of the present invention. However, those skilled in the art will appreciate that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the disclosure of the examples; the scope of protection claimed by the present invention shall be determined by the scope defined in the claims.

[0033] like Figure 1 As shown, the method for preparing a flexible spin valve device of the present invention comprises the following steps:

[0034] (1) Preparation of bottom electrode: Select a glass sheet of 5cm×5cm size, stick the PI tape flatly on the glass sheet, set the electrode shape to 50um*50um, and directly pattern the PI tape to generate a graphene electrode, such as Figure 2 (a).

[0035] (2) Preparation of pinning layer: First, an organic solvent such as dimethylformamide (DMF), dimethylacetamide (DMAC), or N-methylpyrrolidone (NMP) is used as a dispersant. IrMn antiferromagnetic particles are dissolved in the organic solvent and then mixed with PI. The mixture is placed in an ultrasonic chamber and ultrasonicated for 30 minutes to obtain a PI liquid uniformly doped with antiferromagnetic particles. The ratio of IrMn antiferromagnetic particles to PI is 0.6g / 4ml. The PI liquid is spin-coated on the center area of ​​the glass slide in two steps. First, a low speed is set to spread the PI liquid evenly, and then a high speed is set to evenly distribute the PI liquid. Then, vacuum heating is used for curing. The temperature is raised to 100°C and kept constant for 30 minutes. Then, the temperature is raised to 150°C and kept constant for 40 minutes. The temperature is further raised to 300°C and kept constant for 30 minutes to 1 hour. The PI film is cured and the cured PI film is subjected to laser direct writing to prepare IrMn-containing graphene as an antiferromagnetic pinning layer.

[0036] (3) Preparation of a fixed ferromagnetic layer: Using the same method as step (2), the anti-ferromagnetic particles IrMn are replaced with magnetic particles CoFeB to obtain a PI liquid doped with magnetic particles CoFeB. Here, the thickness of the layer can be controlled to 1 / 4 of the thickness of the anti-ferromagnetic pinned layer by setting the speed of the slurry roller. Then, a curing treatment is performed to prepare a PI film containing ferromagnetic particles. The PI film is subjected to a laser direct writing operation to obtain a graphene layer containing ferromagnetic particles as a fixed ferromagnetic layer, such as Figure 2 (b)

[0037] (4) Preparation of tunnel barrier layer: Place the glass sheet on a coating machine and drop the PI liquid doped with non-magnetic particles MgO on the center area of ​​the glass sheet. Here, the thickness of the layer can be controlled to be equivalent to the thickness of the fixed ferromagnetic layer by setting the speed of the coating machine.

[0038] (5) Preparation of a free ferromagnetic layer: The same method as step 3 is used to obtain a PI liquid doped with magnetic particles CoFeB. Here, the thickness of the layer can be controlled to be the same as the thickness of the fixed ferromagnetic layer by setting the speed of the glue spreader. Then, a laser direct writing operation is performed to obtain a graphene layer containing ferromagnetic particles. The graphene layer serves as a free ferromagnetic layer.

[0039] (6) Preparation of graphene top electrode: A layer of PI liquid is coated on the upper surface of the free ferromagnetic layer and solidified, and then a laser direct writing operation is performed to prepare the graphene top electrode. The two-terminal electrode structure provided by the present invention can increase the number of pad uses and the device utilization rate.

[0040] (7) Making the encapsulation layer: Finally, PI tape is used as the encapsulation layer, and the PI tape is evenly pasted on the outer surface of the device structure, and the bottom layer of PI tape is separated from the rigid substrate, and the PI tape is subjected to laser direct writing. The purpose of the laser direct writing process of this layer is only to expose the bottom electrode and the top electrode to the outside, and the other parts are protected by the PI film. After the preparation is completed, the electrode part and the 1um*1um width of the PI layer are laser cut to separate them into many individual spin valve devices, so as to realize the mass production of the device. The flexible spin valve is obtained by using the present invention. The structure can be used for magnetic storage and can also be used to measure magnetic variables.

[0041] The embodiments described above are not intended to limit the present invention. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention is defined by the scope of the claims.

Claims

1. A method for preparing a flexible spin valve device, comprising the steps of: 1) Preparation of bottom electrode: PI tape is pasted on the substrate, and a graphene bottom electrode is formed on the PI tape using a laser direct writing induced graphene process; 2) Preparation of the antiferromagnetic pinning layer, specifically including the following steps: 2-1) Evenly mix the antiferromagnetic particles into the PI liquid; 2-2) The above substrate is placed on a spin coater, and the PI liquid obtained in step 2-1) is dropped on the central area of ​​the substrate, spin-coated, and cured to form a PI film on the graphene bottom electrode. 2-3) performing a laser direct writing operation to obtain a graphene layer containing antiferromagnetic particles as an antiferromagnetic pinning layer; 3) Preparation of fixed ferromagnetic electrodes, specifically including the following steps: 3-1) Evenly mix the ferromagnetic particles into the PI liquid; 3-2) The substrate is placed on a spin coater, and the PI liquid obtained in step 3-1) is dropped onto the center area of ​​the substrate, spin-coated, and cured to form a PI film on the antiferromagnetic pinning layer. The thickness of the film is less than that of the PI film prepared in step 2-2); 3-3) performing a laser direct writing operation to obtain a graphene layer containing ferromagnetic particles as a fixed ferromagnetic layer; 4) Preparation of the tunnel barrier layer: A pure PI liquid or a PI liquid doped with non-magnetic insulating particles is selected. The substrate is then placed on a spin coater. The pure PI liquid or the PI liquid doped with non-magnetic insulating particles is dropped onto the center of the substrate. The solution is spin-coated and cured to form a PI film on the fixed ferromagnetic layer. This PI film serves as the tunnel barrier layer. 5) Preparation of a free ferromagnetic layer: Using steps 3-1) to 3-3), a graphene layer containing ferromagnetic particles is obtained, and the graphene layer serves as the free ferromagnetic layer; 6) Preparation of the top electrode: A layer of PI liquid is coated on the surface of the substrate and cured to form a PI film on the free ferromagnetic layer. A laser direct writing process is then used to obtain a graphene top electrode, thereby forming the device structure. 7) Spin valve device packaging: PI tape is evenly adhered to the outer surface of the device structure. At the same time, the bottom layer of PI tape is separated from the rigid substrate. The bottom and top electrodes are exposed using a laser direct writing process to obtain a flexible spin valve device.

2. The method according to claim 1, wherein The substrate in step 1) is glass, mica or silicon wafer.

3. The method according to claim 1, wherein The antiferromagnetic particles are CoFeB, CoO, MnAu, CrSb, Mn2As, NiMn, MnO, FeO, CoO, NiO, MnS, α-Fe2O3, FeS, FeCl2 or MnF2 particles.

4. The method according to claim 1, wherein The ferromagnetic particles are Fe, Co, Ni, FeCo, FeNi or CoFeB particles.

5. The method according to claim 1, wherein The non-magnetic insulating particles are MgO, Al2O3, AlN, TiO2 or ZnO particles.

6. The method according to claim 1, wherein The ratio of antiferromagnetic particles to PI liquid in step 2-1) is 0.1 g / mL to 0.3 g / m, and the ratio of ferromagnetic particles to PI liquid in step 3-1) is 0.1 g / mL to 0.3 g / m.

7. The method according to claim 1, wherein The specific operation of uniformly mixing antiferromagnetic particles or ferromagnetic particles into PI liquid is as follows: first, an organic solvent is used as a dispersant, the antiferromagnetic particles or magnetic particles are dissolved in the organic solvent, and then mixed with the PI liquid, and placed in an ultrasonic container for ultrasonication to obtain a PI liquid uniformly doped with antiferromagnetic particles or ferromagnetic particles, wherein the organic solvent is selected from one of dimethylformamide, dimethylacetamide or N-methylpyrrolidone.

8. The method according to claim 1, wherein The spin coating in step 2-2), step 3-2) or step 4) is specifically as follows: first, set a low rotation speed to spread the PI liquid evenly, and then set a high rotation speed to evenly distribute the PI liquid.

9. The method according to claim 1, wherein The curing in step 2-2), step 3-2) or step 4) is specifically divided into three stages, namely, the first stage: 60°C-100°C, maintaining for 20min-30min; the second stage: 150°C-200°C, maintaining for 40min-60min; The third stage: 260℃-300℃, maintain for 30min-60min.

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