Method for controlling the reflection characteristics of a micromirror array

Abstract

The application provides a micro-mirror array reflection characteristic regulation method, and belongs to the technical field of micro-mirror array optical screen design and preparation. Firstly, a micro-mirror array model with convex and concave types alternately is designed, wherein the convex mirror and the concave mirror both have quadratic curvature and continuously and smoothly transit, and the reflection characteristic of the micro-mirror array model is simulated and optimized; and then a micro-mirror array with convex and concave types alternately is prepared based on the optimized micro-mirror array model with convex and concave types alternately; and the reflection characteristic of the micro-mirror array can be flexibly regulated by adjusting the proportion of the convex mirror and the concave mirror in the micro-mirror array, so that the use scene of the micro-mirror array is expanded.

Description

Technical Field

[0001] This invention relates to the field of micromirror array optical screen design and fabrication technology, specifically to a method for controlling the reflection characteristics of a micromirror array. Background Technology

[0002] As a key component in a projection system that directly interacts with the human eye, the performance of the projection screen directly determines the final visual experience. Currently, the mainstream front projection screen technologies mainly include diffuse reflection screens and optical structure screens. Among them, diffuse reflection screens (such as white plastic screens), although having a wide viewing angle, scatter incident light uniformly in all directions on their surface, resulting in lower brightness (gain). Furthermore, under ambient light, the image appears washed out and the contrast drops sharply, severely affecting the viewing experience.

[0003] To overcome the shortcomings of diffuse reflection screens, optical microstructure screens, especially those based on microlens arrays, have gradually become a research and industrialization hotspot. However, existing microlens array projection screens still have significant limitations, mainly reflected in the lack of adjustable optical properties, the difficulty in fabricating complex micron-scale structures, which in turn limits their application scenarios and makes mass production difficult.

[0004] Therefore, there is an urgent need in this field for a microlens array design and fabrication method that can flexibly adjust its reflective properties, so that the projection screen can adapt to different application scenarios and is suitable for commercial production. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for controlling the reflectivity of a micromirror array and applies it to the design and fabrication of optical screens. This invention first designs a micromirror array with alternating convex and concave shapes of varying proportions, and then fabricates it using a series of processes including 3D photolithography. This results in a micromirror array with advantages such as low surface roughness, high design fidelity, and good uniformity. Furthermore, it allows for flexible adjustment of the gain and brightness of the micromirror array, expanding its application scenarios.

[0006] To achieve the above objectives, the specific technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for controlling the reflection characteristics of a micromirror array, comprising the following steps:

[0008] Design a micromirror array model with alternating convex and concave structures, wherein both the convex mirrors (convex micromirrors) and the concave mirrors (concave micromirrors) have quadratic curvature and a continuous and smooth transition;

[0009] The reflection characteristics of the micromirror array model with alternating convex and concave structures are simulated and optimized to obtain the optimized micromirror array model with alternating convex and concave structures.

[0010] Based on the optimized micromirror array model with alternating convex and concave structures, a micromirror array with alternating convex and concave structures is prepared.

[0011] The reflection characteristics of the micromirror array can be adjusted by changing the ratio of the convex and concave mirrors.

[0012] Furthermore, the reflection characteristics of the micromirror array model were analyzed and simulated using Zmax software.

[0013] Furthermore, the reflective properties include, but are not limited to, optical gain and wide field of view.

[0014] Furthermore, the simulation optimization of the reflection characteristics of the micromirror array model with alternating convex and concave structures includes:

[0015] (1) Preset the dimensions of the micromirror array unit structure;

[0016] (2) Import the geometric light source model;

[0017] (3) The micro-mirror array unit structure is optimized by using computational lithography algorithm to obtain the optimal morphology and size.

[0018] Furthermore, the preset dimensions of each micromirror satisfy the following: aperture of 60-80 μm, and height (convex) or depth (concave) of 2-12 μm. The reason for selecting this size range in this invention is that, considering the process window and visual effect of large-area transfer printing later, if the height / depth is too high, it will lead to excessive structural loss during template splicing and large-scale transfer printing, failing to achieve the designed effect; if the aperture is too large, exceeding the human eye resolution of 100 μm, it will result in poor visual effects. During the simulation optimization process, based on the preset dimensions, by minimizing the function value of the evaluation function, the optical system parameters (such as curvature, thickness, material, etc.) are iteratively adjusted to obtain the optimal morphology and dimensions.

[0019] Furthermore, the geometric light source model includes, but is not limited to: point light source, elliptical light source, rectangular light source, Gaussian light source, or diode light source. In the specific implementation of this invention, the geometric light source used is a point light source.

[0020] Secondly, the present invention provides a method for fabricating a micromirror array with alternating convex and concave structures, comprising the following steps:

[0021] A micro-mirror array model with a certain ratio of convex to concave mirrors was designed and optimized according to the control method described above.

[0022] The optimized micro-mirror array model is offset according to a certain rule to form a unit structure, and then fabricated on the photoresist layer using 3D laser direct writing lithography technology to obtain a photoresist template;

[0023] A nickel plate with convex and concave structures is prepared by electroplating and demolding based on the photoresist template;

[0024] The structural features of the nickel plate are transferred onto a PUA-type flexible UV adhesive via plate-to-plate nanoimprinting to obtain a flexible substrate with alternating convex and concave structures.

[0025] A silver reflective layer is prepared on the surface of the flexible substrate with alternating convex and concave structures to obtain a micromirror array with alternating convex and concave structures.

[0026] Furthermore, the photoresist template meets the following accuracy requirements: feature size less than 250 nm, and accuracy error less than 0.8 nm.

[0027] Furthermore, the side length of each micromirror array is 1.8-2 mm; each micromirror is uniformly distributed along the entire glass substrate with an edge spacing of 8-10 μm.

[0028] Furthermore, the steps for preparing photoresist templates using 3D laser direct-write lithography include:

[0029] (1) Take out a two-inch glass plate and put it into a plasma cleaner to clean it, improve its surface cleanliness and adhesion, and clean for 15 minutes.

[0030] (2) Apply photoresist covering 4 / 5 of the area to the plasma-cleaned glass plate;

[0031] (3) Place the glass plate into the spin coater for spin coating. The operating parameters of the spin coater are: rotation speed 400-1000 rpm, spin coating for 10-30 s;

[0032] (4) Place the glass plate with the glue evenly on the heating plate and bake at 80-120℃ for 5-10 min. After removing it, cool it for 20-40 min.

[0033] (5) Import the optimized micro-mirror array model into the laser direct writing lithography machine, and place the cooled glass plate into it for lithography;

[0034] (6) After photolithography is completed, the glass plate is removed, cleaned and dried, and then placed in the developing solution for development to obtain the photoresist template.

[0035] Furthermore, the step of preparing a nickel plate based on the photoresist template includes:

[0036] (1) Use plasma cleaning or chemical solvents to thoroughly remove organic matter and particulate contaminants from the surface of the photoresist template;

[0037] (2) Place the dried photoresist template into the cavity of the magnetron sputtering instrument. Turn on the instrument and bombard the high-purity nickel target with high-energy particles in a high vacuum environment to deposit nickel atoms in the form of a thin film on the surface of the photoresist template. The thickness of the seed layer is about 50~100 nm and must completely and uniformly cover the sidewalls and bottom of all the nano-deep pits without any breaks.

[0038] (3) Use a photoresist template with a thin film seed layer as the cathode and connect it to the negative terminal of the power supply; use a high-purity nickel block as the anode and connect it to the positive terminal of the power supply; immerse both in a nickel sulfamate electroplating solution with a specific formula, turn on the DC power supply, and electroplating starts from the seed layer and fills each nano-pattern on the master plate from the inside out; after the pattern is completely filled, nickel atoms will continue to accumulate and form a dense nickel plate on the surface of the template; control the current and time so that the final thickness of the nickel plate reaches about 300 micrometers.

[0039] (4) Remove the photoresist template with nickel plate from the electroforming solution, rinse it thoroughly with deionized water and dry it;

[0040] (5) Using a precision wedge cutter or a special demolding device, the nickel plate is peeled off from the photoresist template to obtain a nickel plate with the opposite texture to the photoresist template pattern;

[0041] Further, the step of transferring the structural features of the nickel plate onto a PUA-type flexible UV substrate to obtain a flexible substrate with alternating convex and concave structures includes:

[0042] (1) Use a plasma cleaner to treat the nickel plate with a power of 100-200 W for 30-50 s to activate the surface, and then put it into a vacuum tower with fluorosilane and let it stand for 10-30 min to form an anti-stick self-assembled monolayer on the surface of the nickel plate.

[0043] (2) Spin-coating a PUA-type flexible UV adhesive onto a flexible substrate;

[0044] (3) Align the flexible substrate coated with PUA adhesive with the nickel plate in a vacuum environment, press the nickel plate into the PUA adhesive layer at a speed of 0.1-1 mm / s, and maintain the pressure for 10-30 s to allow the adhesive to fully fill the nickel plate structure.

[0045] (4) Maintain the imprinting pressure and irradiate the back of the substrate with a UV lamp for 60-120 seconds to allow the PUA adhesive to fully cure.

[0046] (5) Remove the film to obtain a flexible substrate with alternating convex and concave structures.

[0047] Furthermore, an extremely thin silver reflective layer is prepared on the surface of the flexible substrate with alternating convex and concave structures by magnetron sputtering silver plating.

[0048] Furthermore, the thickness of the silver reflective layer is less than 100 nm.

[0049] Furthermore, the magnetron sputtering silver plating step includes:

[0050] (1) Place the flexible substrate with alternating convex and concave structures into the magnetron sputtering apparatus and align it;

[0051] (2) Clean the metallic silver material and place it in the corresponding position of the magnetron sputtering instrument;

[0052] (3) Power on the magnetron sputtering instrument to evaporate the metallic silver and form a metal thin film on a flexible substrate with alternating convex and concave phase structures;

[0053] (4) Adjust the instrument evaporation settings to perform secondary evaporation on the flexible substrate with alternating convex and concave phase structures to form a thinner silver reflective layer of less than 100 nm;

[0054] (5) Take out the flexible substrate with alternating convex and concave structures after silver plating and let it stand for 3 h to obtain a micro-mirror array with alternating convex and concave structures.

[0055] Thirdly, the present invention provides a micromirror array with alternating convex and concave structures prepared by the aforementioned preparation method.

[0056] Fourthly, this aspect provides the application of the micromirror array with alternating convex and concave structures in curtains (for indoor or outdoor use) or retroreflective signs.

[0057] Compared with the prior art, the advantages of the present invention are:

[0058] This invention designs a micromirror array with alternating convex and concave structures. Furthermore, by changing the ratio of the convex and concave micromirrors, micromirror arrays with different reflection characteristics can be obtained. This invention further successfully fabricates the aforementioned micromirror array with alternating convex and concave structures on a flexible material substrate. The method provided by this invention allows for flexible adjustment of reflection characteristics, and the fabricated micromirror arrays exhibit high precision, making them applicable to various optical screen applications and suitable for commercial production.

[0059] Furthermore, the micromirror array fabrication method provided by this invention produces a structure with alternating convex and concave sections exhibiting quadratic curvature and a smooth transition. Specifically, firstly, laser direct-write 3D lithography is used to fabricate the structural features of the micromirror array onto photoresist in a single lithographic exposure. During the lithography process, the exposure parameters obtained by calculating the optical imaging inversion model of the lithography can control the error of the structural features within a small range. Then, the structure on the photoresist is transferred with high precision to a nickel plate through electroplating. The nanostructure features of the nickel plate are then transferred onto a PUA-type flexible UV adhesive layer to obtain a flexible substrate with alternating convex and concave structures. Finally, a silver film of a predetermined thickness is deposited on the surface of the PUA-type flexible UV substrate using a magnetron sputtering instrument, thereby fabricating a micromirror array with alternating convex and concave structures. Attached Figure Description

[0060] Figure 1 Models of micromirror arrays with alternating convex and concave structures and different duty cycles are given; (a) is a micromirror array model with convex / concave ratios of 20% and 80% respectively; (b) is a micromirror array model with convex / concave ratios of 40% and 60% respectively; and (c) is a micromirror array model with convex / concave ratios of 90% and 10% respectively.

[0061] Figure 2 The simulation results of the reflection characteristics of the micromirror array models with convex and concave alternating structures with different duty cycles in Example 1 are shown. Among them, (a)-(k) are the simulation results of the reflection characteristics of different micromirror array models with the proportion of convex micromirrors decreasing from 100% to 0% and the proportion of concave micromirrors increasing from 0% to 100%, respectively.

[0062] Figure 3 The reflection characteristics of the micromirror array vary with different proportions of convex / concave micromirrors.

[0063] Figure 4 The images are SEM cross-sectional views of the photoresist templates; (a) is an SEM cross-sectional view of the photoresist template with a convex / concave ratio of 50% and 50% respectively; (b) is an SEM cross-sectional view of the photoresist template with a convex / concave ratio of 66.7% and 33.3% respectively. Detailed Implementation

[0064] To enable those skilled in the art to clearly and completely understand the technical solution of the present invention, the present invention will be further described in detail below with reference to embodiments. Obviously, the embodiments described herein are only for explaining the present invention and are not intended to limit the scope 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.

[0065] This invention provides a method for controlling the reflection characteristics of a micromirror array, comprising the following steps:

[0066] The inventors designed a micromirror array model with alternating convex and concave structures, where both the convex mirrors (convex micromirrors) and the concave mirrors (concave micromirrors) have quadratic curvature and a continuous, smooth transition. Their research revealed that if there are geometric discontinuities (such as steps, cusps, or fracture surfaces) between the convex and concave micromirrors, it can lead to increased scattering loss, wavefront distortion, and local hot spots / dark areas, ultimately resulting in poor color gamut, chromatic aberration, and imaging quality.

[0067] The reflection characteristics of the micromirror array model with alternating convex and concave structures are simulated and optimized to obtain the optimized micromirror array model with alternating convex and concave structures.

[0068] Based on the optimized micromirror array model with alternating convex and concave structures, a micromirror array with alternating convex and concave structures is prepared.

[0069] The reflection characteristics of the micromirror array can be adjusted by changing the ratio of the convex and concave mirrors.

[0070] In one implementation, the reflection characteristics of the micromirror array model are analyzed and simulated using Zmax software.

[0071] In one embodiment, the reflective properties include, but are not limited to, optical gain and wide field of view.

[0072] In one embodiment, the operation of simulating and optimizing the reflection characteristics of the micromirror array model with alternating convex and concave structures includes:

[0073] (1) Preset the dimensions of the micromirror array unit structure;

[0074] (2) Import the geometric light source model;

[0075] (3) The micro-mirror array unit structure is optimized by using computational lithography algorithm to obtain the optimal morphology and size.

[0076] In one implementation, each micromirror has a preset size that satisfies the following: aperture of 60-80 μm and height (convex) or depth (concave) of 2-12 μm. This size range is chosen because, considering the process window and visual effect of large-area transfer printing, excessive height / depth would lead to excessive structural loss during template splicing and large-scale transfer printing, failing to achieve the designed effect; excessive aperture, exceeding the human eye resolution of 100 μm, would result in poor visual effects. During simulation optimization, based on the preset size, the optical system parameters (such as curvature, thickness, and material) are iteratively adjusted by minimizing the function value of the evaluation function to obtain the optimal morphology and size.

[0077] In one embodiment, the geometric light source model includes, but is not limited to, a point light source, an elliptical light source, a rectangular light source, a Gaussian light source, or a diode light source. The geometric light source used in this specific embodiment of the invention is a point light source.

[0078] This invention also provides a method for fabricating a micromirror array with alternating convex and concave structures, comprising the following steps:

[0079] A micro-mirror array model with a certain ratio of convex to concave mirrors was designed and optimized according to the control method described above.

[0080] The optimized micro-mirror array model is offset according to a certain rule to form a unit structure, and then fabricated on the photoresist layer using 3D laser direct writing lithography technology to obtain a photoresist template;

[0081] A nickel plate with convex and concave structures is prepared by electroplating and demolding based on the photoresist template;

[0082] The structural features of the nickel plate are transferred to a PUA-type flexible UV substrate by plate-to-plate nanoimprinting to obtain a flexible substrate with alternating convex and concave structures.

[0083] A silver reflective layer is prepared on the surface of the flexible substrate with alternating convex and concave structures to obtain a micromirror array with alternating convex and concave structures.

[0084] In one embodiment, the photoresist template has the following accuracy requirements: feature size less than 250 nm and accuracy error less than 0.8 nm.

[0085] In one embodiment, each micromirror array has a side length of 1.8-2 mm; each micromirror is uniformly distributed along the entire glass substrate with an edge spacing of 8-10 μm.

[0086] In one embodiment, the step of preparing a photoresist template using 3D laser direct-write lithography technology includes:

[0087] (1) Take out a two-inch glass plate and put it into a plasma cleaner to clean it, improve its surface cleanliness and adhesion, and clean for 15 minutes.

[0088] (2) Apply photoresist covering 4 / 5 of the area to the plasma-cleaned glass plate;

[0089] (3) Place the glass plate into the spin coater for spin coating. The operating parameters of the spin coater are: rotation speed 400-1000 rpm, spin coating for 10-30 s;

[0090] (4) Place the glass plate with the glue evenly on the heating plate and bake at 80-120℃ for 5-10 min. After removing it, cool it for 20-40 min.

[0091] (5) Import the optimized micro-mirror array model into the laser direct writing lithography machine, and place the cooled glass plate into it for lithography;

[0092] (6) After photolithography is completed, the glass plate is removed, cleaned and dried, and then placed in the developing solution for development to obtain the photoresist template.

[0093] In one embodiment, the step of preparing a nickel plate based on the photoresist template includes:

[0094] (1) Use plasma cleaning or chemical solvents to thoroughly remove organic matter and particulate contaminants from the surface of the photoresist template;

[0095] (2) Place the dry photoresist template into the cavity of the magnetron sputtering instrument; turn on the instrument and bombard the high-purity nickel target with high-energy particles in a high vacuum environment to deposit nickel atoms in the form of a thin film on the surface of the photoresist template; the thickness of the thin film seed layer is about 50~100 nm and must completely and uniformly cover the sidewalls and bottom of all the nano-deep pits without any breaks.

[0096] (3) A photoresist template with a thin-film seed layer is used as the cathode and connected to the negative terminal of the power supply; a high-purity nickel block is used as the anode and connected to the positive terminal of the power supply; both are immersed in a nickel sulfamate electroplating solution with a specific formula, and the DC power supply is turned on. Electroplating starts from the seed layer and fills each nano-pattern on the master plate from the inside out; after the pattern is completely filled, nickel atoms will continue to accumulate and form a dense nickel plate on the surface of the template. The current and time are controlled so that the final thickness of the nickel plate reaches about 300 micrometers;

[0097] (4) Remove the photoresist template with nickel plate from the electroforming solution, rinse it thoroughly with deionized water and dry it;

[0098] (5) Using a precision wedge cutter or a special demolding device, the nickel plate is peeled off from the photoresist template to obtain a nickel plate with the opposite texture to the photoresist template pattern;

[0099] In one embodiment, the step of transferring the structural features of the nickel plate onto a PUA-type flexible UV substrate to obtain a flexible substrate with alternating convex and concave structures includes:

[0100] (1) Use a plasma cleaner to treat the nickel plate with a power of 100-200 W for 30-50 s to activate the surface, and then put it into a vacuum tower with fluorosilane and let it stand for 10-30 min to form an anti-stick self-assembled monolayer on the surface of the nickel plate.

[0101] (2) Spin-coating a PUA-type flexible UV adhesive onto a flexible substrate;

[0102] (3) Align the flexible substrate coated with PUA adhesive with the nickel plate in a vacuum environment, press the nickel plate into the PUA adhesive layer at a speed of 0.1-1 mm / s, and maintain the pressure for 10-30 s to allow the adhesive to fully fill the nickel plate structure.

[0103] (4) Maintain the imprinting pressure and irradiate the back of the substrate with a UV lamp for 60-120 seconds to allow the PUA adhesive to fully cure.

[0104] (5) Remove the film to obtain a flexible substrate with alternating convex and concave structures.

[0105] In one embodiment, an extremely thin silver reflective layer is prepared on the surface of a flexible substrate with alternating convex and concave structures by magnetron sputtering.

[0106] Furthermore, the thickness of the silver reflective layer is less than 100 nm.

[0107] Furthermore, the magnetron sputtering silver plating step includes:

[0108] (1) Place the flexible substrate with alternating convex and concave structures into the magnetron sputtering apparatus and align it;

[0109] (2) Clean the metallic silver material and place it in the corresponding position of the magnetron sputtering instrument;

[0110] (3) Power on the magnetron sputtering instrument to evaporate the metallic silver and form a metal thin film on a flexible substrate with alternating convex and concave phase structures;

[0111] (4) Adjust the instrument evaporation settings to perform secondary evaporation on the flexible substrate with alternating convex and concave phase structures to form a thinner silver reflective layer of less than 100 nm;

[0112] (5) Take out the flexible substrate with alternating convex and concave structures after silver plating and let it stand for 3 h to obtain a micro-mirror array with alternating convex and concave structures.

[0113] Example 1

[0114] A method for controlling and fabricating the reflection properties of a micromirror array with alternating convex and concave structures, comprising the following specific steps:

[0115] S1. Design a micromirror array model with alternating convex and concave mirrors. The convex and concave mirrors have quadratic curvature that changes continuously. Establish micromirror array models with convex micromirror proportions of 0%, 10%, 20%, ..., 90%, 100%, and corresponding concave micromirror proportions of 100%, 90%, 80%, ..., 10%, 0%. For example, a micromirror array model with convex / concave proportions of 20% and 80% is shown below. Figure 1 As shown in (a); the micromirror array model with convex / concave ratios of 40% and 60% is as follows. Figure 1 As shown in (b); the micromirror array model with convex / concave ratios of 90% and 10% is as follows. Figure 1 As shown in (c).

[0116] S2. Simulation and Optimization of Reflection Characteristics. The Zmax software was used to analyze the reflection characteristics of the micromirror array model, including optical gain and wide field of view. For example... Figure 2 As shown, as the proportion of convex micromirrors decreases, the reflective diameter of the micromirror array gradually decreases, indicating that its field of view is also gradually decreasing; as the proportion of concave micromirrors increases, the gain value of the micromirror array gradually increases, indicating that the overall brightness of its reflected light is gradually increasing. Figure 3 The diagram shows the reflection characteristics of micromirror arrays with different proportions of convex and concave micromirrors. When the proportions of convex and concave micromirrors are similar, the performance is relatively balanced. Here, a micromirror array model with 50% convex and 50% concave micromirror proportions is used to fabricate a micromirror array with alternating convex and concave structures, which can be used for home theater screens.

[0117] S3. Preparation of photoresist template. (1) Take out a two-inch glass plate and put it into a plasma cleaner to clean it, improve its surface cleanliness and adhesion. The cleaning time is 15 min. (2) Drop 4 / 5 of the area of ​​photoresist (AZ4562 photoresist) onto the glass plate after plasma cleaning. (3) Put the glass plate into a spin coater for spin coating. The spin coater operating parameters are: first spin coating at 500 rpm for 10 s, then spin coating at 1000 rpm for 30 s. (4) Place the glass plate with the photoresist coating flat on a heating plate and bake it at 100 ℃ for 5 min. After removing it, cool it for 30 min. (5) Import the model optimized by calculation into a laser direct writing lithography machine and put the cooled glass plate into it for photolithography. (6) After the photolithography is completed, take out the glass plate, clean and dry it, put it into the developer for development, and finally obtain the unit structure prepared by photoresist. Figure 4(a) shows a SEM cross-sectional view of a unit structure prepared by photoresist with a convex / concave ratio of 50% and 50%, respectively.

[0118] S4. Preparation of nickel plate. (1) Use plasma cleaning or chemical solvent to thoroughly remove organic matter and particulate contaminants from the surface of the photoresist template; (2) Place the dried photoresist template into the cavity of the magnetron sputtering instrument; turn on the equipment and bombard the high-purity nickel target with high-energy particles in a high vacuum environment to deposit nickel atoms in the form of a thin film on the surface of the photoresist template; the thickness of the thin film seed layer is about 75 nm and must completely and uniformly cover the sidewalls and bottom of all nano pits without any breaks; (3) Use the photoresist template with the thin film seed layer as the cathode and connect it to the negative terminal of the power supply; use the high-purity nickel block as the anode and connect it to the positive terminal of the power supply; immerse both in a nickel sulfamate electroplating solution with a specific formula, turn on the DC power supply, and electroplating starts from the seed layer and fills each nano pattern on the master plate from the inside out; after the pattern is completely filled, nickel atoms will continue to accumulate and form a dense nickel plate on the surface of the template. (3) Control the current and time to make the final thickness of the nickel plate reach about 300 micrometers; (4) Take out the photoresist template with the nickel plate from the electroforming solution, rinse it thoroughly with deionized water and dry it; (5) Use a precision wedge cutter or special demolding equipment to peel the nickel plate off from the photoresist template to obtain a nickel plate with the opposite concave and convex patterns to the photoresist template.

[0119] S5. Preparation of flexible substrate. (1) Use a plasma cleaner to treat the nickel plate with a power of 150 W for 30-50 s to activate the surface, and then put it into a vacuum tower with fluorosilane and let it stand for 20 min to form an anti-stick self-assembled monolayer on the surface of the nickel plate; (2) Spin coat the flexible substrate with PUA-type flexible UV adhesive; (3) Align the flexible substrate coated with PUA adhesive with the nickel plate in a vacuum environment, press the nickel plate into the PUA adhesive layer at a speed of 0.5 mm / s, and maintain the pressure for 20 s to allow the adhesive to fully fill the nickel plate structure; (4) Maintain the pressing pressure and irradiate the back of the substrate with a UV lamp for 90 s to allow the PUA adhesive to fully cure; (5) Peel off the film to obtain a flexible substrate with a convex and concave alternating structure.

[0120] S6. Preparation of silver reflective layer. (1) Place the flexible substrate with alternating convex and concave structures into the magnetron sputtering instrument and align it; (2) Clean the metallic silver material and place it in the corresponding position of the magnetron sputtering instrument; (3) Power on the magnetron sputtering instrument and evaporate the metallic silver to form a metal film on the flexible substrate with alternating convex and concave structures; (4) Adjust the instrument evaporation settings and perform secondary evaporation on the flexible substrate with alternating convex and concave structures to form a thinner silver metal film of less than 100 nm; (5) Take out the silver-plated flexible substrate with alternating convex and concave structures and let it stand for 3 h to obtain a micro-reflective mirror array with alternating convex and concave structures.

[0121] Example 2

[0122] The difference between this embodiment and Embodiment 1 is that the proportions of convex and concave micromirrors are 66.7% and 33.3%, respectively. When the proportion of convex micromirrors is larger, the micromirror array with alternating convex and concave structures is suitable for conference room environments, resulting in a wider field of view for the reflected image, a larger audience, and preventing viewers on the side from not being able to see the image. Figure 4 (b) shows the SEM cross-section of the photoresist template when the proportions of convex / concave micromirrors are 66.7% and 33.3%, respectively.

[0123] Example 3

[0124] The difference between this embodiment and Embodiment 1 is that the proportions of convex and concave micromirrors are 33.3% and 66.7%, respectively. When the proportion of concave micromirrors is larger, the micromirror array with alternating convex and concave structures obtained is suitable for outdoor scenarios or for retroreflective marking, avoiding interference light being stronger than reflected light, which would cause image distortion.

[0125] Example 4

[0126] This embodiment compares the impact of different optical screens and their processing methods (see Table 1) on imaging quality.

[0127] Table 1: Comparison of different optical screens and their processing methods

[0128]

[0129] To further evaluate the imaging quality of microstructure array optical screens fabricated using photolithography and Fresnel optical screens obtained through precision machining, this embodiment employs an objective evaluation method for quantitative analysis. Four different image quality evaluation indicators are used to evaluate the imaging quality at different viewing angles and time periods. The average evaluation results are shown in Table 2. Edge Intensity (EI) describes the image edge contour information. It calculates the gradient direction within a pixel region, calculates the difference excitation values ​​in the vertical and horizontal directions within the region, and sums them. High-quality images have sharper edges and larger gradient values. Average Gradient (AG) refers to the difference in grayscale values ​​on both sides of an image boundary or shadow line, representing the magnitude of the grayscale change rate. It reflects the subtle detail contrast and texture changes in the image, and measures image sharpness by evaluating edge clarity and contrast. Information Entropy (EN) represents the average amount of information contained in an image; a larger value indicates more information. Difference Mean Score (DMOS) is the mean of the subjective score difference between the original image and the screen reflection image. A larger DMOS value indicates a greater score difference between the original image and the screen reflection image, and a lower quality screen reflection image.

[0130] Table 2: Quantitative Analysis Results

[0131]

[0132] In the test results for the square chessboard image, the EI values ​​of convex and concave micromirror arrays were slightly larger than those of Fresnel, indicating that the microstructure-based mirror arrays achieved or even slightly exceeded the Fresnel level in edge intensity. The AG value of the convex micromirror array was comparable to that of Fresnel, while the AG value of the concave micromirror array was slightly smaller, indicating that the average gradient of the microstructure-based mirror array reached the Fresnel level. The EN value of the concave micromirror array was the largest, followed by the convex micromirror array, with the Fresnel array having the smallest EN value. The DMOS value of the Fresnel array was the largest, followed by the concave micromirror array, with the convex micromirror array having the smallest, indicating that Fresnel reflection image quality was the lowest, and convex micromirror array was the best. This is because the brightness gain of the convex micromirror array varied within a relatively flat range, had a larger operating range, and excellent color reproduction capabilities, resulting in higher overall image quality. Concave micromirror arrays offer excellent color reproduction and high brightness gain, but the gain change is steeper, and their working range is smaller compared to convex micromirror arrays, resulting in slightly lower overall image quality. Fresnel arrays, due to their structure which partially blocks light and their smaller working range, exhibit the worst overall image quality.

[0133] In the test results for circular array images, convex MMA had the highest EI value, followed by concave MMA, with Fresnel in the middle; the AG value followed a similar pattern. However, concave MMA had the highest EN value, followed by convex MMA, with a very small difference between the two, while Fresnel had the lowest. Fresnel also had the highest DMOS value, followed by concave MMA, and then convex MMA. Overall, in the circular array test, convex MMA performed better in all indicators, followed by concave MMA, and Fresnel performed the worst.

[0134] The above detailed embodiments describe the implementation of the present invention; however, the present invention is not limited to the specific details described in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A method for controlling the reflection characteristics of a micromirror array, characterized in that, Includes the following steps: Design a micromirror array model with alternating convex and concave structures, wherein the convex and concave mirrors have quadratic curvature and a continuous and smooth transition; The reflection characteristics of the micromirror array model with alternating convex and concave structures are simulated and optimized to obtain the optimized micromirror array model with alternating convex and concave structures. Based on the optimized micromirror array model with alternating convex and concave structures, a micromirror array with alternating convex and concave structures is prepared. The reflection characteristics of the micromirror array can be adjusted by changing the ratio of the convex and concave mirrors.

2. The method for controlling the reflection characteristics of a micromirror array according to claim 1, characterized in that, The reflection characteristics of the micromirror array model were analyzed and simulated using Zmax software.

3. The method for controlling the reflection characteristics of a micromirror array according to claim 2, characterized in that, The reflective properties include, but are not limited to, optical gain and wide field of view.

4. The method for controlling the reflection characteristics of a micromirror array according to claim 2, characterized in that, The simulation optimization of the reflection characteristics of the micromirror array model with alternating convex and concave structures includes: (1) Preset the dimensions of the micromirror array unit structure; (2) Import the geometric light source model; (3) The micro-mirror array unit structure is optimized by using computational lithography algorithm to obtain the optimal morphology and size.

5. The method for controlling the reflection characteristics of a micromirror array according to claim 4, characterized in that, Each micromirror has the following preset dimensions: aperture of 60-80 μm and height or depth of 2-12 μm.

6. The method for controlling the reflection characteristics of a micromirror array according to claim 4, characterized in that, The geometric light source model includes, but is not limited to: point light source, elliptical light source, rectangular light source, Gaussian light source or diode light source.

7. A method for fabricating a micromirror array with alternating convex and concave structures, characterized in that, Includes the following steps: A micro-mirror array model with a certain convex mirror / concave mirror ratio is designed and optimized according to the control method described in any one of claims 1-6. The optimized micro-mirror array model is offset according to a certain rule to form a unit structure, and then fabricated on the photoresist layer using 3D laser direct writing lithography technology to obtain a photoresist template; A nickel plate with convex and concave structures is prepared by electroplating and demolding based on the photoresist template; The structural features of the nickel plate are transferred to a PUA-type flexible UV substrate by plate-to-plate nanoimprinting to obtain a flexible substrate with alternating convex and concave structures. A silver reflective layer is prepared on the surface of the flexible substrate with alternating convex and concave structures to obtain a micromirror array with alternating convex and concave structures.

8. The method for fabricating a micromirror array with alternating convex and concave structures according to claim 7, characterized in that, The precision requirements of the photoresist template are: feature size less than 250 nm and precision error less than 0.8 nm.

9. A micromirror array with alternating convex and concave structures prepared by the preparation method described in claim 7.

10. The application of the micromirror array with alternating convex and concave structures as described in claim 9 in curtains or retroreflective markings.

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