Design and preparation method of a random structure metal grid electromagnetic shielding film

Abstract

The present invention discloses a design and preparation method of a random structure metal grid electromagnetic shielding film, which generates a regular periodic lattice in a two-dimensional plane; randomly perturbs each point in the regular periodic lattice to obtain an irregular random lattice; divides the random lattice into a Delaunay triangulation, and divides it into Thiessen polygons to obtain a random structure metal grid pattern; checks whether the structural parameters of the random structure metal grid meet expected standards, including the degree of randomness of the mesh, optical transmittance, secondary diffraction distribution and electromagnetic shielding effectiveness; if the standards are not met, repeats the random perturbation and Thiessen polygon division of the regular periodic lattice until the expected standards are met; the present invention designs and prepares a random structure metal grid electromagnetic shielding film, which is easy to design and process, and can also perform targeted adjustment on the structural parameters of the random structure metal grid according to the specific requirements of the optical system for optical performance and electromagnetic shielding effectiveness, and can be applied to different working environments.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical films, and in particular relates to a design and preparation method of a random structure metal grid electromagnetic shielding film. Background Art

[0002] Optical windows are crucial components of various optoelectronic devices. With the advancement of modern technology and the expansion of communication frequency bands, the electromagnetic environment in space is becoming increasingly complex, placing a high demand on optical windows to provide electromagnetic shielding. Metal mesh electromagnetic shielding films are one of the primary methods for achieving both high optical transmittance and excellent electromagnetic shielding effectiveness in optical windows, and have recently garnered widespread attention in both civilian and military applications.

[0003] Currently, metal mesh structures are typically periodic structures formed by regular polygonal arrays. During use, high-order diffraction light is concentrated and distributed, creating stray light interference, which adversely affects the resolution and image quality of precision optical systems. Especially when detecting strong point light sources, high-order diffraction spots can create false targets, seriously affecting detection accuracy. Therefore, weakening and eliminating the concentrated distribution of high-order diffraction light is an urgent problem to be solved.

[0004] Researchers at home and abroad have conducted in-depth research on eliminating the concentrated distribution of secondary diffraction in metal grids. They have reduced the degree of concentrated distribution of high-order diffraction energy by using a variety of nested and interactive arrangements of circular rings or adopting multi-periodic composite structures. However, the grid structure as a whole is still a periodic arrangement, which cannot fundamentally suppress the phenomenon of secondary diffraction concentration.

[0005] CN 114727577 A achieves randomization of the grid structure by spraying silver nanowires on the surface of a regular metal grid. This patent has two drawbacks: first, the process is complex, requiring the regular metal grid to be prepared through photolithography and coating processes, and then spraying silver nanowires on top of the regular grid to form irregular grid lines, which increases manufacturing costs; second, the arrangement of the sprayed silver nanowires cannot be precisely controlled, resulting in poor process stability. If the structural parameters of the sprayed random grid do not meet the expected effect, the optical window must be repaired and reprocessed, which is not conducive to engineering manufacturing.

[0006] CN 110348100 A designs a metal grid structure with randomly distributed circular rings by constructing random basic circular rings, externally circumscribed circular rings, and inscribed subcircles in a two-dimensional plane. This structure deeply homogenizes higher-order diffraction, resulting in a uniform distribution of higher-order diffraction energy. The grid pore structure is relatively uniformly distributed, homogenizing the distribution of diffracted stray light while ensuring that its electromagnetic shielding capability is virtually unaffected. However, this patent suffers from the fact that the lines of the random grid pattern are all curved, and the spacing between two grid lines in the pattern is often too small. This requires high processing precision from the equipment and results in a narrow process window.

[0007] CN 109652774 A creates a randomly distributed network of cracks by cracking an oxide film coated on the surface of a light window. Subsequently, a random metal grid embedded in the cracks is fabricated through coating and plasma etching. The random grid fabrication method described in this patent suffers from poor structural repeatability of the cracks formed by cracking the oxide film, and places extremely strict demands on process control and environmental factors, making it unsuitable for industrial production. Summary of the Invention

[0008] The purpose of the present invention is to provide a design and preparation method for a random structure metal mesh electromagnetic shielding film, which can produce a random electromagnetic shielding metal mesh with good optical transmittance, optical diffraction characteristics and electromagnetic shielding efficiency, thereby improving the imaging quality of precision optical systems.

[0009] In order to achieve the above purpose, the technical solutions adopted are as follows:

[0010] A method for designing a random structure metal grid electromagnetic shielding film comprises the following steps:

[0011] (1) Generate a regular periodic lattice in a two-dimensional plane;

[0012] (2) Randomly perturb each point in the regular periodic lattice to obtain an irregular random lattice;

[0013] (3) dividing the random point matrix into Delaunay triangulation, and dividing the Delaunay triangulation into Thiessen polygons to obtain a random structure metal grid pattern;

[0014] (4) Check whether the structural parameters of the random structure metal mesh meet the expected standards, including the degree of mesh randomness, optical transmittance, secondary diffraction distribution and electromagnetic shielding effectiveness; if the structural parameters do not meet the standards, repeat the random perturbation of the regular periodic lattice and the Thiessen polygon division until the structural parameters meet the expected standards.

[0015] According to the above scheme, the regular periodic lattice in step 1 is a two-dimensional equilateral triangle lattice, a two-dimensional tetragonal lattice or a two-dimensional close-packed hexagonal lattice.

[0016] According to the above scheme, step 2 randomly assigns values ​​to the generated regular periodic lattice using the following formula:

[0017] (x rand_ ,y rand_ )=((x i +rand(1)),(y j +rand(1)))

[0018] Among them, x i 、yj is the initial coordinate of each point in the regular lattice, rand(1) is a function that randomly generates any value in the range of 0 to 1, (x rand_i ,y rand_j ) are the coordinates of each point after random assignment, and the regular periodic lattice is transformed into an irregular random lattice.

[0019] According to the above scheme, step 3 sets the width and length of all lines in the Thiessen polygon network according to specific technical requirements to obtain a random structure metal grid pattern.

[0020] According to the above scheme, if the mesh randomness, optical transmittance, secondary diffraction distribution and electromagnetic shielding effectiveness of the random structure metal grid in step 4 all meet the expected standards, then it is determined that its structural parameters meet the expected standards.

[0021] A method for preparing a random structure metal grid electromagnetic shielding film comprises the following steps:

[0022] (a) Cleaning the surface of optical components;

[0023] (b) spraying photoresist on the surface of the optical element and performing a pre-baking process on a constant temperature hot plate of the spraying equipment;

[0024] (c) exposing the random structure metal grid pattern meeting the desired standard on the optical element coated with photoresist using laser direct writing exposure or mask exposure technology and developing the pattern; cleaning the optical window with deionized water, drying the surface of the optical element with high-purity nitrogen gas, and post-baking the optical element on a constant temperature hot plate;

[0025] (d) A metal film is plated on the surface of the developed optical element, and the obtained optical window is immersed in an NMP solution and subjected to high-pressure jet treatment to obtain a random structure metal grid electromagnetic shielding film.

[0026] According to the above scheme, the temperature of the pre-baking and post-baking treatments is 95° C. to 105° C., and the time is 1 to 2 minutes.

[0027] According to the above scheme, the metal film coating on the surface of the optical element in step d includes the following steps:

[0028] The vacuum degree is better than 10 -4 Pa environment, a transition metal film layer and a main metal film layer are successively prepared on the surface of the optical element by thermal evaporation or magnetron sputtering to obtain a metal grid electromagnetic shielding film; wherein, the material of the transition metal film layer is tungsten and titanium, and the thickness is 5nm to 17nm; the material of the main metal film layer is any one of nickel, gold, and aluminum, wherein the thickness of nickel is 100nm to 150nm, and the thickness of gold or aluminum is 200nm to 400nm.

[0029] According to the above scheme, the optical window obtained in step d is immersed in the NMP solution at a temperature of 50°C to 60°C and a time of 60min to 180min; the jet pressure of the high-pressure jet treatment is 4 to 8MPa, and the nozzle diameter is 0.1mm to 0.5mm.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention generates a regular periodic lattice on a two-dimensional plane, randomly perturbs each point in the lattice, and then divides the random lattice into Delaunay triangulations and finally into Thiessen polygons to obtain a random polygonal metal grid. The resulting random polygonal metal grid is composed of interconnected irregular line segments, and the line segments do not intersect.

[0032] The irregular line segments in the grid pattern of the present invention can effectively homogenize the distribution of diffracted light of various orders, avoid the concentrated distribution of high-order diffraction spots, greatly weaken the adverse effects of diffracted stray light on the image quality and resolution of complex precision optical systems, and at the same time ensure the imaging quality and excellent electromagnetic shielding effectiveness of the optical system.

[0033] The present invention designs a random structure metal grid electromagnetic shielding film and clarifies the manufacturing method. It is easy to design and process. The structural parameters of the random structure metal grid can be adjusted in a targeted manner according to the specific requirements of the optical system for optical performance and electromagnetic shielding effectiveness, and can be applied to different working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 : Design flow chart of the random structure metal mesh electromagnetic shielding film mesh of the present invention.

[0035] Figure 2 : Distribution diagram of secondary diffraction spots of periodic square metal grid.

[0036] Figure 3 : Distribution diagram of secondary diffraction spots of the random structure metal grid described in the present invention. DETAILED DESCRIPTION

[0037] The following examples further illustrate the technical solutions of the present invention, but are not intended to limit the scope of protection of the present invention. The technical solutions of the present invention are further described in detail below with reference to the accompanying drawings.

[0038] The specific embodiment provides a method for designing a random structure metal grid electromagnetic shielding film:

[0039] 1) Generate a regular periodic lattice on a two-dimensional plane, where the relative positions and spacings between adjacent points in the lattice are fixed, such as Figure 1 As shown in a.

[0040] 2) Randomly assign values ​​to the generated regular lattice using the following formula:

[0041] (x rand_ ,y rand_ )=((x i +rand(1)),(y j +rand(1)))

[0042] Among them, x i 、y j is the initial coordinate of each point in the regular lattice, rand(1) is a function that randomly generates any value in the range of 0 to 1, and x(rand_i) and y(rand_j) are the coordinates of each point after random assignment. The regular periodic lattice is transformed into a random lattice, such as Figure 1 As shown in b.

[0043] 3) Divide the random point matrix into Delaunay triangulation, such as Figure 1 As shown in c.

[0044] 4) Divide the Delaunay triangulation into a Thiessen polygon network, such as Figure 1 As shown in d.

[0045] 5) According to specific technical requirements, the width and length of all lines in the Thiessen polygon network are set to obtain a random structure metal grid pattern.

[0046] 6) Check whether the structural parameters of the random structure metal grid meet the expected standards. If the structural parameters do not meet the expected standards, repeat steps 1) to 5) until the structural parameters of the metal grid meet the expected standards.

[0047] In an embodiment of the present invention, the optical element can be a planar element, and a metal grid can be prepared on one side of the optical element or on both sides. The optical element material includes but is not limited to optical grade sapphire, optical grade single crystal silicon, single crystal germanium, optical glass, and zinc sulfide.

[0048] In this embodiment, the arrangement of the regular periodic dot matrix is ​​a regular hexagonal arrangement. In other embodiments, the arrangement of the regular periodic dot matrix can also be a triangle, a regular quadrilateral, etc.; the line width and length of the random structure metal grid can be set and scaled according to actual needs. For example, the line width can be 7μm, the shortest line length is set to 200μm, and the other line lengths are set proportionally based on the shortest line.

[0049] The structural parameters of the mesh include but are not limited to one or more of the following: mesh randomness, mesh line width, and average mesh area. When the line width and line length of the metal mesh change, the optical transmittance, secondary diffraction distribution, and electromagnetic shielding effectiveness of the metal mesh will also change. Therefore, the criteria for the random structure metal mesh structural parameters to meet the expected standards are:

[0050] If the optical transmittance, secondary diffraction distribution, and electromagnetic shielding effectiveness of the random structure metal mesh all meet the expected standards, it can be determined that the mesh structure parameters meet the expected standards.

[0051] In this embodiment, a random metal grid structure is generated by applying a Thiessen polygon transformation to a random lattice on a two-dimensional plane and setting the width and length of each line in the Thiessen polygon network. This grid, composed of several irregular meshes, effectively homogenizes higher-order diffracted light while maintaining good optical transmittance and electromagnetic shielding effectiveness, thereby improving the image quality and resolution of the optical system. Furthermore, the design and processing methods are flexible and convenient, offering promising prospects for engineering applications.

[0052] As a possible implementation method, preparing a regular polygonal metal grid on the surface of the optical window can be detailed as the following steps:

[0053] The random structure metal grid electromagnetic shielding film designed by the present invention can be prepared by the following steps:

[0054] 1) Clean the optical component surface. Place the component to be cleaned in a cleaning basket and then place it in a multi-tank ultrasonic cleaning machine. Ultrasonic cleaning is performed using a dedicated optical component cleaning agent and DI water. Finally, DI spraying, rinsing, slow pull drying, and warm air drying are used. Inspect the component surface with a metallographic microscope. If there are no impurities or watermarks, proceed to the next step.

[0055] 2) Spray positive photoresist on the surface of the optical element at a spraying temperature of 95°C to 105°C. After spraying, continue to place it on the spraying table for baking at a baking temperature of 95°C to 105°C for 1 to 2 minutes.

[0056] 3) Use UV mask exposure technology to expose a random structure metal grid pattern on the photoresist surface and develop it. The exposure parameters are: light source wavelength 365nm, power density 6-10mW / cm 2 Exposure time: 30-50 seconds. Develop the exposed photoresist with a 2.38% TMAH solution for 60-90 seconds. After development, rinse with deionized water overflow for 90-120 seconds. After rinsing, blow dry the component with high-purity nitrogen at 60-70°C.

[0057] 4) Place the dried optical component on a constant temperature hot plate and bake it at a temperature of 95°C to 105°C for 1 to 2 minutes.

[0058] 5) A metal film is deposited on the developed optical element. In this step, the metal film is deposited using ion-assisted electron beam evaporation, and the background vacuum during the deposition is better than 10 -4 Pa, the coating temperature is room temperature. First, an ion beam is used to clean the surface of the coating component. During cleaning, the ion source bias is 110-150V, the discharge current is 50A, and the cleaning time is 3-5min; then an ion source is used to assist in the plating of transition metal film layers (tungsten and titanium) and main metal film layers (nickel and gold). When plating the transition metal film layer, the ion source bias is 90-110V, the discharge current is 50A, and the evaporation rate is 0.1-0.3nm. The thickness of the tungsten film layer is 3-5nm, and the thickness of the titanium film layer is 2-12nm. When plating the main metal film layer, no ion source is used, and the evaporation rate is 0.6-1.2nm. The thickness of the nickel film layer is 100nm-150nm, and the thickness of the gold film layer is 200nm-400nm.

[0059] 6) Soaking the metal film-coated component in NMP at a temperature of 50-60° C. for 60-180 minutes. After soaking, rinse the component surface with a high-pressure NMP jet at a pressure of 4-8 MPa and a nozzle diameter of 0.1-0.5 mm to remove excess photoresist and metal film. After rinsing, rinse the component with deionized water overflow for 90-120 seconds. After rinsing, dry the component with high-purity nitrogen at 60-70° C. to obtain a random structure metal grid electromagnetic shielding film.

[0060] After the random structure metal grid electromagnetic shielding film is prepared, it is necessary to coat the surface of the optical element with an anti-reflection film to improve the optical transmittance of the optical element. Taking K9 optical glass material as an example, the K9 material optical element coated with the random structure metal grid electromagnetic shielding film is placed in a vacuum coating machine. The background vacuum during coating is better than 10 -4 Pa, baking temperature is 200℃, and the coating film materials are SiO2 and Ta2O5.

[0061] Figure 2 is the secondary diffraction distribution diagram of the periodic square metal grid, Figure 3 This is the secondary diffraction distribution diagram of the random-structure metal grid prepared in the present invention. The secondary diffraction light of a periodic square metal grid is concentrated in the X- and Y-axis directions. This diffracted light will exist as stray light in the optical imaging system, seriously affecting the image quality and resolution of the optical imaging system. The secondary diffraction light of the random-structure metal grid prepared in this embodiment is evenly distributed around the zero-order diffraction, without concentrated distribution. This can significantly reduce the interference of diffracted stray light on the optical imaging system, improving the image quality and resolution of the optical imaging system.

[0062] The above embodiments are merely illustrative of the principles and effects of the present invention, as well as some embodiments of its application. A person skilled in the art may make several modifications and improvements without departing from the inventive concept of the present invention, and all of these modifications and improvements fall within the scope of protection of the present invention.

Claims

1. A method for designing a random structure metal grid electromagnetic shielding film, characterized in that The following steps are involved: (1) generating a regular periodic lattice in a two-dimensional plane; the regular periodic lattice is a two-dimensional equilateral triangle lattice, a two-dimensional tetragonal lattice, or a two-dimensional close-packed hexagonal lattice; (2) Randomly perturb each point in the regular periodic lattice to obtain an irregular random lattice; the random perturbation method is: randomly assign values ​​to the generated regular periodic lattice using the following formula: Among them, x i 、y j is the initial coordinate of each point in the regular lattice, rand (1) is a function that randomly generates any value in the range of 0 to 1, (x rand_i ,y rand_j ) are the coordinates of each point after random assignment, and the regular periodic lattice is transformed into an irregular random lattice; (3) Divide the random point matrix into Delaunay triangulation, and divide the Delaunay triangulation into Thiessen polygons to obtain a random structure metal grid pattern; (4) Check whether the structural parameters of the random structure metal mesh meet the expected standards, including the degree of mesh randomness, optical transmittance, secondary diffraction distribution and electromagnetic shielding effectiveness; if the structural parameters do not meet the standards, repeat the random perturbation of the regular periodic lattice and the Thiessen polygon division until the structural parameters meet the expected standards.

2. The method for designing a random structure metal grid electromagnetic shielding film according to claim 1, wherein Step 3: According to specific technical requirements, the width and length of all lines in the Thiessen polygon network are set to obtain a random structure metal grid pattern.

3. The method for designing a random structure metal grid electromagnetic shielding film according to claim 1, wherein If the mesh randomness, optical transmittance, secondary diffraction distribution and electromagnetic shielding effectiveness of the random structure metal grid in step 4 all meet the expected standards, then it is determined that its structural parameters meet the expected standards.

4. A method for preparing a random structure metal grid electromagnetic shielding film, characterized in that The following steps are involved: (a) Cleaning the surface of optical components; (b) spraying photoresist on the surface of the optical element and performing a pre-baking process on a constant temperature hot plate of the spraying equipment; (c) using laser direct writing exposure or mask exposure technology to expose the random structure metal grid pattern of claim 1 that meets the expected standards on the optical element sprayed with photoresist and develop it; using deionized water to clean the optical window, using high-purity nitrogen to blow dry the surface of the optical element, and placing it on a constant temperature hot plate for post-baking; (d) A metal film is plated on the surface of the developed optical element, and the resulting optical window is immersed in an NMP solution and treated with a high-pressure jet to obtain a random structure metal grid electromagnetic shielding film.

5. The method for preparing the random structure metal grid electromagnetic shielding film according to claim 4, characterized in that The temperature of the pre-baking and post-baking treatments is 95° C. to 105° C., and the time is 1 to 2 minutes.

6. The method for preparing the random structure metal grid electromagnetic shielding film according to claim 4, characterized in that The step d of coating the metal film on the surface of the optical element comprises the following steps: The vacuum degree is better than 10 -4 Pa environment, a transition metal film layer and a main metal film layer are successively prepared on the surface of the optical element by thermal evaporation or magnetron sputtering to obtain a metal grid electromagnetic shielding film; wherein, the material of the transition metal film layer is tungsten and titanium, and the thickness is 5nm to 17nm; the material of the main metal film layer is any one of nickel, gold, and aluminum, wherein the thickness of nickel is 100nm to 150nm, and the thickness of gold or aluminum is 200nm to 400nm.

7. The method for preparing the random structure metal grid electromagnetic shielding film according to claim 4, characterized in that The optical window obtained in step d is immersed in the NMP solution at a temperature of 50° C. to 60° C. for a time of 60 min to 180 min. The jet pressure of the high-pressure jet treatment is 4 to 8 MPa, and the nozzle diameter is 0.1 mm to 0.5 mm.

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