A method for preparing a flexible wave-absorbing material based on nano-imprinting technology

Abstract

The application relates to the field of electromagnetic wave absorbers, and discloses a method for preparing a flexible wave-absorbing material based on a nano-imprinting technology, and aims to solve the problems of large weight, high thickness and complex process of traditional wave-absorbing materials. The method comprises the following steps: preparing a required micro-nano structure nano-imprinting template through electron beam lithography; spin-coating double-layer glue films on a silicon substrate and forming complementary imprinted patterns through imprinting; etching to form transition structures with recessed sidewalls; depositing a composite metal layer to optimize impedance matching and electromagnetic loss; removing residual photoresist by using a developing solution and a water jet cavitation bubble technology; and finally transferring the composite metal micro-nano structure to a flexible substrate through secondary imprinting. The application realizes controllable microstructure through the nano-imprinting technology, enhances the wave-absorbing performance by combining the composite metal layer design, and simultaneously endows the material with excellent mechanical adaptability due to the flexible substrate. The prepared wave-absorbing material has the characteristics of light weight, ultra-thin thickness and high flexibility.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave absorbers, and in particular to a method for preparing flexible wave-absorbing materials by nanoimprinting. Background Technology

[0002] With the rapid development of modern electronic and wireless communication technologies, problems such as electromagnetic interference (EMI) and radar detection are becoming increasingly prominent. Therefore, developing efficient, lightweight materials with excellent microwave absorption properties has become an important topic in scientific research and industrial applications. Traditional microwave absorbing materials mostly rely on metal powders or magnetic materials. While these materials can absorb electromagnetic waves to some extent, they often suffer from problems such as large weight, high thickness, and complex manufacturing processes, limiting their widespread application in practice.

[0003] In recent years, the development of nanotechnology has brought new opportunities for the research of microwave absorbing materials. Nanoimprint lithography (NIL), as an advanced micro / nano fabrication technology, has gradually become one of the ideal choices for preparing high-performance microwave absorbing materials due to its high resolution, low cost, and large-area fabrication capabilities. By precisely controlling the microstructure, the electromagnetic properties of materials can be optimized, thereby significantly improving microwave absorption performance.

[0004] However, existing methods for preparing microwave absorbing materials based on nanoimprint technology still face some challenges. On the one hand, achieving efficient microwave absorption while maintaining material flexibility remains a challenge; on the other hand, existing methods also have shortcomings in terms of reproducibility and cost-effectiveness in large-scale production. Therefore, there is an urgent need for a novel preparation method that can achieve efficient microwave absorption at the microscale while taking into account the material's flexibility and structural controllability, and is suitable for large-scale industrial production. Summary of the Invention

[0005] In order to solve the technical problems existing in the prior art, the purpose of this invention is to provide a method for preparing flexible microwave absorbing materials by nanoimprinting to solve the above-mentioned technical problems.

[0006] This invention provides a method for preparing flexible microwave absorbing materials using nanoimprint technology, aiming to solve the problems of existing microwave absorbing materials in terms of weight, thickness, and manufacturing process complexity. This method not only possesses strong structural controllability but also achieves high-efficiency microwave absorption performance at the microscale and is suitable for large-scale industrial production.

[0007] According to a first aspect of the present invention, the present invention provides a method for preparing flexible microwave absorbing materials by nanoimprinting, comprising the following steps: (1) Electron beam lithography was used to etch micro-nano structure patterns on the first silicon substrate, and an anti-adhesion layer was applied to obtain a nanoimprint template. (2) Photoresist and nanoimprint adhesive are spin-coated sequentially on the second silicon substrate and cured to form a double-layer adhesive film; (3) Press the nanoimprint template described in step (1) into the double-layer adhesive film described in step (2), cure, demold, and form an imprint pattern on the second silicon substrate that is complementary to the nanoimprint template described in step (1). Use plasma etching to remove the residual nanoimprint adhesive on the second silicon substrate, and use a developer to remove the exposed photoresist layer to form a silicon substrate with a transition structure of recessed sidewalls. (4) Deposit a composite metal layer on the silicon substrate with the transition structure with recessed sidewalls formed in step (3), and peel off the photoresist remaining on the silicon substrate to obtain a silicon substrate with a composite metal micro / nano structure ("composite structure of metal layer-oxide dielectric layer-metal layer"). (5) Coating photoresist on the surface of a flexible substrate as an adhesion layer, then imprinting it onto the silicon substrate with the composite metal micro-nano structure described in step (4), curing, peeling, and transferring the composite metal micro-nano structure to the flexible substrate (using the high adhesion between the photoresist and the metal layer to achieve complete peeling), to obtain a flexible microwave absorbing material.

[0008] In some embodiments, the first silicon substrate in step (1) is a single-sided polished silicon substrate; the micro-nano structure pattern is formed by multiple cross patterns uniformly distributed on the polished surface of the silicon substrate, the arrangement interval of each cross pattern is 100nm-400nm, and the height of each cross pattern is 100-400nm.

[0009] In some embodiments, the micro-nano structure pattern in step (1) is formed by multiple cross patterns uniformly distributed on the polished surface of the silicon substrate, with an arrangement interval of 150 nm between each cross pattern and a height of 200 nm for each cross pattern.

[0010] In some embodiments, the anti-sticking layer treatment in step (1) includes: placing the first silicon substrate after etching the micro-nano structure pattern in a vacuum environment, introducing 1,1,2,2H-perfluorooctyltrichlorosilane (DDTS) vapor, and reacting at a temperature of 100-150°C for 20-40 min.

[0011] In some embodiments, the anti-sticking layer treatment in step (1) includes: placing the first silicon substrate after etching the micro-nano structure pattern in a vacuum environment, introducing 1,1,2,2H-perfluorooctyltrichlorosilane (DDTS) vapor, and reacting at a temperature of 120°C for 30 min.

[0012] In some embodiments, the photoresist in step (2) is a positive photoresist or a negative photoresist, and the thickness of the photoresist coating is 100-500 nm; the nanoimprint adhesive is a UV-curable photoresist, and the thickness of the nanoimprint adhesive coating is 100-500 nm. The photoresist serves as the inner layer of the bilayer adhesive film, and the nanoimprint adhesive serves as the outer layer of the bilayer adhesive film.

[0013] In some embodiments, the photoresist in step (2) is a negative photoresist, specifically AZ-5214E ​​(manufactured by AZ Electronic Materials, Inc., USA), and the thickness of the photoresist coating is 200 nm.

[0014] In some embodiments, the nanoimprint adhesive in step (2) is a thermosetting, photosetting, or other imprint adhesive.

[0015] In some embodiments, the nanoimprint adhesive in step (2) is UV-curable photoresist ZEP520A (Zeon Corporation of Japan), and the thickness of the nanoimprint adhesive coating is 200 nm.

[0016] In some implementations, the second silicon substrate in step (2) is a single-sided polished silicon substrate.

[0017] In some embodiments, the curing method in step (3) is UV light curing, and the method for removing the residual nanoimprint adhesive on the second silicon substrate is plasma etching; the developer in step (3) is MIF300 (AZ Electronic Materials, USA), and the concentration of the developer is 0.1-5 wt%.

[0018] In some embodiments, the composite metal layer in step (4) includes a first metal layer, an oxide dielectric layer, and a second metal layer; the first metal layer is made of Ag or Au, and the oxide dielectric layer is made of... MgO or The material of the second metal layer is Ag or Au; the thickness of the first metal layer is 30-100 nm, the thickness of the oxide medium layer is 40-150 nm, and the thickness of the second metal layer is 30-100 nm.

[0019] In some embodiments, the composite metal layer in step (4) includes a first metal layer, a first adhesion layer, an oxide medium layer, a second adhesion layer, and a second metal layer; the thickness of the first adhesion layer and the second adhesion layer is 2-10 nm; and the material of the first adhesion layer and the second adhesion layer is Ti.

[0020] In some embodiments, the composite metal layer in step (4) includes a first metal layer, a first adhesion layer, an oxide medium layer, a second adhesion layer, and a second metal layer; the first metal layer is made of Ag, the first adhesion layer is made of Ti, the oxide medium layer is made of Al2O3, the second adhesion layer is made of Ti, and the second metal layer is made of Ag, wherein the thickness of the first metal layer and the second metal layer is 30-100 nm, the thickness of the first adhesion layer and the second adhesion layer is 2-10 nm, and the thickness of the oxide medium layer is 40-150 nm.

[0021] In some embodiments, the composite metal layer in step (4) includes a first metal layer, a first adhesion layer, an oxide medium layer, a second adhesion layer, and a second metal layer; the first metal layer is made of Ag, the first adhesion layer is made of Ti, the oxide medium layer is made of Al2O3, the second adhesion layer is made of Ti, and the second metal layer is made of Ag, wherein the thickness of the first metal layer and the second metal layer is 40 nm, the thickness of the first adhesion layer and the second adhesion layer is 3 nm, and the thickness of the oxide medium layer is 50 nm.

[0022] In some embodiments, step (4) of stripping the residual photoresist on the silicon substrate includes: immersing the silicon substrate after depositing the composite metal layer in a developer solution, generating cavitation bubbles through water jet, and lifting the residual photoresist layer with the bubbles (gently removing the residual photoresist and avoiding damage to the composite metal micro / nano structure), rinsing, drying, and completing the stripping of the residual photoresist on the silicon substrate.

[0023] In some embodiments, the developing solution used in step (4) to remove the residual photoresist on the silicon substrate is a corresponding negative photoresist developing solution.

[0024] In some embodiments, the flexible substrate in step (5) is a flexible polyimide film (PI), the spin-coating thickness of the photoresist is 100-500 nm, and the photoresist is polyurethane acrylate (PUA). Polyurethane acrylate is selected as the photoresist because it has good adhesion to the composite metal layer. After curing, the photoresist can separate from the silicon substrate along with the deposited composite metal layer, thereby transferring the micro / nano structured composite metal layer to the flexible substrate.

[0025] According to a second aspect of the present invention, a flexible microwave absorbing material prepared by the above-described method is provided. The surface of the flexible microwave absorbing material has periodically arranged cross-shaped composite metal micro / nano structures, and said structures are attached to a flexible substrate.

[0026] This invention proposes a method for preparing flexible wave-absorbing materials via nanoimprinting. This method not only offers good structural controllability but also achieves highly efficient wave absorption performance at the microscale. By introducing a flexible substrate and innovative nanostructure design, the wave-absorbing material prepared by this invention exhibits excellent wave absorption characteristics and good mechanical flexibility, making it suitable for various applications such as aerospace, military stealth, and electronic product protection, demonstrating broad application prospects. Furthermore, this method is easily scalable to industrial-scale production, possessing high economic value and technical feasibility.

[0027] Compared with the prior art, the present invention has the following beneficial effects and advantages: (1) The method provided by the present invention uses nanoimprint technology, which can flexibly design and control the shape and size of nanostructures, and achieve high-efficiency wave absorption performance at the microscale.

[0028] (2) The flexible absorbing material prepared by the method provided by the present invention has a composite metal layer structure that can significantly enhance the absorbing performance.

[0029] (3) The method provided by the present invention, the flexible substrate transfer technology breaks through the limitations of traditional rigid absorbing materials and can be adapted to complex curved surface application scenarios.

[0030] (4) The method provided by the present invention is easy to be extended to industrial-scale production and has high economic value and technical feasibility.

[0031] (5) The flexible absorbing material prepared by the present invention has both high flexibility and excellent electromagnetic wave absorption characteristics, and has broad application prospects in aerospace, stealth technology and electronic equipment protection. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the nanoimprint template structure unit used in this invention; Figure 2 Flowchart for the preparation of microwave absorbing materials using nanoimprinting process; Figure 3 This is a schematic diagram of the microwave absorbing material obtained in an embodiment of the present invention; Among them, 1 is a silicon substrate; 2 is a negative photoresist; 3 is a UV-curable photoresist; 4 is a metal deposition layer; 5 is a polyurethane acrylate (PUA) photoresist; and 6 is a flexible polyimide (PI) film.

[0034] Figure 4 The transmission spectrum is shown in the example. Detailed Implementation

[0035] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0036] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0037] The AZ-5214E ​​and MIF300 used in the following examples were manufactured by AZ Electronic Materials, Inc. of the United States, and the ZEP520A was manufactured by Zeon Corporation of Japan.

[0038] The flexible absorbing materials prepared in the following examples were subjected to transmission spectrum measurements using an optical microscope (Hyperion 1000). A ×10–×10, 0.1 numerical aperture objective lens was used, connected to a Fourier transform infrared spectrometer (Vertex70) with a spatial aperture of 3.75 mm. The transmission spectra were normalized relative to the exposed substrate.

[0039] Example 1 This embodiment provides a method for preparing flexible microwave absorbing materials via nanoimprinting. The specific steps are as follows (refer to...). Figure 2 (as shown) (1) Fabrication of nanoimprint template: A cross-shaped micro / nano structure was etched on a single-sided polished silicon substrate 1 using electron beam lithography to form a nanoimprint template. The cross pattern was spaced 200 nm apart and had a height of 200 nm. Figure 1 As shown.

[0040] (2) Apply an anti-sticking layer to the template: Place the template in a vacuum chamber and introduce 1,1,2,2H-perfluorooctyltrichlorosilane (DDTS) vapor. React at 120°C for 30 min to form a low surface energy anti-sticking layer.

[0041] (3) Spin coating of the double-layer photoresist: After cleaning the silicon substrate, spin coat negative photoresist 2 (AZ-5214E) at 3000 rpm with a thickness of 200 nm, and then bake on a hot plate at 130℃ for 4 min to complete pre-curing. Spin coat UV-curable photoresist 3 (ZEP520A) on the negative photoresist surface at 2500 rpm with a thickness of 200 nm, and then bake on a hot plate at 100℃ for 5 min to form a double-layer film with a total thickness of about 400 nm.

[0042] (4) Nanoimprinting: After aligning the template with the silicon substrate, press the UV photoresist layer into the template at a pressure of 5 MPa and a temperature of 80℃ to ensure the photoresist fully fills the micro-nano structures within the template. The photoresist is cured by UV irradiation, followed by demolding, forming a cross-shaped imprint pattern on the substrate surface that complements the template, such as... Figure 2 As shown in (a).

[0043] (5) Residual photoresist removal: Residual nanoimprint resist is removed using plasma etching technology, followed by removal of the exposed photoresist layer using 1 wt% MIF300 developer, forming a sidewall recessed structure, such as... Figure 2 As shown in (b). This recessed structure facilitates subsequent stripping operations.

[0044] (6) Metal film deposition: Using electron beam evaporation technology, 40 nm Ag, 3 nm Ti, 50 nm Al2O3, 3 nm Ti and 40 nm Ag were deposited sequentially on the substrate of step (4) in a vacuum to ensure that the metal deposition layer 4 (Ag-Ti-Al2O3-Ti-Ag) uniformly covers the substrate surface. The deposited sample is as follows. Figure 2 As shown in (c),

[0045] (7) Photoresist Removal: The sample is immersed in a negative photoresist developer, and cavitation bubbles are generated by water jetting and directed to the sample surface. The bubbles lift the residual photoresist layer. The sample is then rinsed with deionized water and dried with nitrogen gas, thereby obtaining independent metal micro / nano structures on the substrate, such as... Figure 2 As shown in (d).

[0046] (8) Preparation of flexible substrate: A 200 nm layer of polyurethane acrylate (PUA) photoresist 5 was spin-coated onto the surface of a flexible polyimide (PI) film 6. After pre-curing, it was bonded to the metal micro / nano structure silicon substrate obtained in step 5, and then cured with ultraviolet light, such as... Figure 2 As shown in (e) and (f).

[0047] (9) Peeling: The flexible substrate is separated from the silicon substrate by mechanical peeling, and the metal micro / nano structure is transferred intact to the flexible substrate, such as... Figure 2 As shown in (g), flexible absorbing materials (such as...) are thus obtained. Figure 3 (As shown). The obtained absorbing material is flexible and can be used for non-planar wave absorption needs, showing good application prospects.

[0048] Example 2 In Example 2, in step (1), electron beam lithography is used to etch a cross-shaped micro-nano structure on a single-sided polished silicon substrate to form a nanoimprint template. The cross pattern is spaced 100 nm apart and has a height of 200 nm. The remaining steps are the same as in Example 1.

[0049] Example 3 In Example 3, in step (1), electron beam lithography is used to etch a cross-shaped micro-nano structure on a single-sided polished silicon substrate to form a nanoimprint template. The cross pattern is spaced 400 nm apart and has a height of 200 nm. The remaining steps are the same as in Example 1.

[0050] Example 4 In Example 4, Ag in the metal deposition layer was replaced with Au and Al2O3 was replaced with MgO in step (6), and the remaining steps were the same as in Example 1.

[0051] Figure 4 The images show the transmission spectra of the flexible absorbing materials obtained in each embodiment. Figure 4 As shown, the flexible absorbing material ("cross" absorbing material) obtained in this embodiment exhibits significant electromagnetic wave absorption characteristics in the near-infrared band. This material possesses wide-bandwidth and high-intensity absorption performance within the aforementioned bands.

[0052] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for preparing flexible microwave absorbing materials by nanoimprinting, characterized in that, Includes the following steps: (1) A micro-nano structure pattern is etched on the first silicon substrate, and an anti-adhesion layer is applied to obtain a nanoimprint template; (2) Photoresist and nanoimprint adhesive are spin-coated sequentially on the second silicon substrate and cured to form a double-layer adhesive film; (3) Press the nanoimprint template described in step (1) into the double-layer adhesive film described in step (2), cure, demold, form an imprint pattern on the second silicon substrate that is complementary to the nanoimprint template described in step (1), remove the residual nanoimprint adhesive on the second silicon substrate, use a developer to remove the exposed photoresist layer, and form a silicon substrate with a transition structure having recessed sidewalls. (4) Deposit a composite metal layer on the silicon substrate with the transition structure with recessed sidewalls formed in step (3), and peel off the photoresist remaining on the silicon substrate to obtain a silicon substrate with a composite metal micro / nano structure. (5) Coating photoresist on the surface of a flexible substrate, then imprinting it onto the silicon substrate with the composite metal micro-nano structure described in step (4), curing, peeling, and transferring the composite metal micro-nano structure onto the flexible substrate to obtain a flexible microwave absorbing material; The first silicon substrate in step (1) is a single-sided polished silicon substrate; the micro-nano structure pattern is formed by a number of cross patterns evenly distributed on the polished surface of the silicon substrate, the arrangement interval of each cross pattern is 100 nm-400 nm, and the height of each cross pattern is 100-400 nm. The composite metal layer in step (4) includes a first metal layer, a first adhesion layer, an oxide medium layer, a second adhesion layer, and a second metal layer; the material of the first metal layer is Ag or Au, the material of the oxide medium layer is Al2O3, MgO, Fe2O3, or TiO2, and the material of the second metal layer is Ag or Au; the thickness of the first metal layer is 30-100 nm, the thickness of the oxide medium layer is 40-150 nm, and the thickness of the second metal layer is 30-100 nm; the thickness of the first adhesion layer and the second adhesion layer is 2-10 nm; and the material of the first adhesion layer and the second adhesion layer is Ti.

2. The method for preparing flexible microwave absorbing materials by nanoimprinting according to claim 1, characterized in that, The anti-sticking layer treatment in step (1) includes: placing the first silicon substrate after etching the micro-nano structure pattern in a vacuum environment, introducing 1,1,2,2H-perfluorooctyltrichlorosilane vapor, and reacting at a temperature of 100-150℃ for 20-40 min.

3. The method for preparing flexible microwave absorbing materials by nanoimprinting according to claim 1, characterized in that, The photoresist in step (2) is either a positive photoresist or a negative photoresist, and the thickness of the photoresist coating is 100-500 nm; the nanoimprint adhesive is a UV-curable photoresist, and the thickness of the nanoimprint adhesive coating is 100-500 nm.

4. The method for preparing flexible microwave absorbing materials by nanoimprinting according to claim 1, characterized in that, The curing method in step (3) is UV light curing, and the method for removing the residual nanoimprint adhesive on the second silicon substrate is plasma etching; the developer in step (3) is MIF300, and the concentration of the developer is 0.1-5 wt%.

5. The method for preparing flexible microwave absorbing materials by nanoimprinting according to claim 1, characterized in that, Step (4) involves stripping the residual photoresist on the silicon substrate, which includes immersing the silicon substrate after depositing the composite metal layer in a developer solution, generating cavitation bubbles through water jets, lifting the residual photoresist layer with the bubbles, rinsing, drying, and completing the stripping of the residual photoresist on the silicon substrate.

6. The method for preparing flexible microwave absorbing materials by nanoimprinting according to claim 1, characterized in that, In step (5), the flexible substrate is a flexible polyimide film, the spin-coating thickness of the photoresist is 100-500 nm, and the photoresist is polyurethane acrylate.

7. A flexible microwave absorbing material prepared by the method according to any one of claims 1-6.

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