Diffusion sheet with deflection angle and preparation method thereof

Abstract

The invention discloses a diffusion sheet with a deflection angle and a preparation method thereof, and belongs to the technical field of optical elements. The diffusion sheet adopts the glass substrate and has the characteristics of high mechanical strength, high temperature resistance, yellowing resistance and warping resistance. The diffusion sheet comprises a double-sided microstructure, wherein one side is a prism microstructure which is arranged periodically and is used for enabling light spots to deflect; and the other surface is of a disorderly-arranged round hole microstructure and is used for homogenizing light. The manufacturing method is based on a wet etching process, a gradient aperture is designed through a mask plate, and the etching rate is controlled to form an inclined microstructure. The problems that an existing diffusion sheet is high in light spot fixed angle, high in process cost and poor in material stability are solved, the diffusion sheet is suitable for vehicle-mounted HUD and laser radar systems, and the imaging quality and reliability are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical element manufacturing, in particular to a light uniformizing plate with deflection function and a preparation method thereof. BACKGROUND

[0002] HUD is a display technology whose core principle is to project key information (such as navigation, speed, warning signals) to the front of the driver's or user's field of view through an optical system, so that the user can obtain information without lowering his head, thereby reducing the distraction caused by visual switching and improving safety and operational efficiency. HUD is usually based on optical reflection or refraction technology to superimpose virtual images on transparent glass or combiner, and is widely used in the fields of automobiles, aviation and consumer electronics. In the vehicle-mounted HUD system, the diffuser as a key optical element is responsible for adjusting the light distribution, and its performance directly affects the imaging quality and system reliability. For example, by optimizing the deflection angle of the diffuser, sunlight backflow (i.e. external strong light is reflected to the projection unit PGU, causing the element to overheat or be damaged) can be prevented, while the clarity and brightness uniformity of the image are improved. In the laser radar system, the diffuser is used to control the divergence angle of the laser beam to achieve uniform illumination of the target area, thereby improving the detection accuracy and efficiency.

[0003] However, the existing diffuser technology has significant limitations. First, the mainstream diffuser film uses plastic substrates (such as PMMA or PC), and the microstructure is usually made by nanoimprint or injection molding process, which can only produce fixed-angle light spots and cannot dynamically adjust the deflection angle, making it difficult to avoid the problem of sunlight backflow. Second, the high-precision nanoimprint process relies on complex equipment, has high cost and low production efficiency; the injection molding process requires customized molds, has a long design cycle and high initial investment. In addition, plastic substrates face serious challenges in vehicle-mounted environments: high temperatures (such as summer temperatures inside the car can reach more than 80℃) can cause yellowing and warping, affecting optical performance; long-term exposure to ultraviolet light and humidity environments accelerates material aging, shortening service life. In contrast, glass substrates have inherent high stability, but the microstructure of glass-based diffusers in existing technologies is difficult to manufacture, especially the integration of complex microstructures on both sides. SUMMARY

[0004] The purpose of the present application is to provide a diffuser with a deflection angle and a preparation method thereof to solve the problems raised in the background.

[0005] To achieve the above purpose, the present application provides the following technical solution: a diffuser with a deflection angle, comprising a glass substrate and a microstructure layer formed on at least one side of the glass substrate; the microstructure layer comprises at least one of prismatic microstructures for light spot deflection and circular hole microstructures for light spot uniformization.

[0006] Preferably, the glass substrate has a thickness of 0.5-1.0 mm, can withstand high temperatures up to 300℃, and is resistant to yellowing and warping.

[0007] Preferably, the prism microstructure is arranged periodically, with a period width of 10-60 μm, a depth of 4-10 μm, and an inclination angle of 3-15°.

[0008] Preferably, the circular hole microstructure is randomly arranged, with a pore diameter of 10-70 μm and a depth of 3-12 μm.

[0009] Preferably, the microstructure layer has a double-sided structure, with the prism microstructure on one side and the circular hole microstructure on the other side.

[0010] A method for preparing a diffuser with a deflection angle includes the following steps: Provide glass substrates and clean them; Coat the substrate surface with photoresist; A pattern is formed by exposing and developing a photomask. Wet etching forms microstructures.

[0011] Preferably, the pattern of the mask is a gradient arrangement of square or round holes.

[0012] Preferably, the wet etching uses a hydrofluoric acid-based etching solution with a concentration of 5-10% and an etching time of 1-5 minutes.

[0013] Preferably, the exposure is yellow light exposure with a wavelength of 365nm and an exposure dose of 100-200mJ / cm².

[0014] Preferably, the microstructure layer is achieved by etching both sides separately, processing one side first and then flipping it over to process the other side.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention utilizes a glass substrate, completely overcoming the inherent defects of traditional plastic substrates. The glass substrate boasts a high-temperature resistance of up to 300℃, far exceeding the tolerance limit of plastic substrates, effectively resisting yellowing. Its coefficient of thermal expansion is less than 4 × 10⁻⁶. -6 / ℃, which basically eliminates the warping and deformation problem and ensures the long-term stability of the optical system.

[0016] The dual-sided microstructure design of this invention achieves perfect functional integration. The prism microstructure allows for a controllable deflection angle of 3-15° in the light spot, effectively preventing sunlight backflow. The circular aperture microstructure achieves excellent light uniformity, improving light spot uniformity and reducing brightness standard deviation. This integration of dual functions into a single component not only simplifies the optical system structure but also significantly improves imaging quality and visual experience.

[0017] Compared to traditional nanoimprint lithography, wet etching reduces equipment investment costs and increases production efficiency. The flexibility of mask design allows for rapid customization of microstructure parameters. The isotropic etching properties enable the formation of complex tilted microstructures in a single process, avoiding the cumulative errors of multiple processing steps.

[0018] This technology is not only applicable to automotive HUD systems, but can also be extended to multiple fields such as LiDAR, AR / VR devices, and projection displays. By adjusting the microstructure parameters, it can meet the specific needs of different application scenarios, achieving broad applicability and a promising market prospect. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of the diffuser sheet of the present invention; Figure 2 This is an enlarged schematic diagram of the microstructure; Figure 3 This is an enlarged view of the microstructure (structure 1); Figure 4 This is a magnified view of the microstructure. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention provides a technical solution: a diffuser with a deflection angle, comprising a glass substrate and a microstructure layer formed on at least one side of the glass substrate; the microstructure layer includes at least one of a prism microstructure for light spot deflection and a circular hole microstructure for light spot homogenization. The glass substrate is made of high borosilicate material, possessing excellent optical properties and mechanical stability. Its thickness is controlled between 0.5-1.0 mm, enabling a thinner and lighter device design while ensuring structural strength. The substrate can withstand temperatures up to 300℃ and maintains stable performance under long-term high-temperature environments. It exhibits good anti-yellowing properties, preventing a decrease in transmittance due to ultraviolet or thermal radiation, and also has strong anti-warping capabilities, ensuring surface flatness under temperature changes or mechanical stress.

[0022] The prism microstructures are periodically arranged using precision machining, with a period width of 10-60 μm and a structural depth of 4-10 μm. The tilt angle is precisely controlled within the range of 3-15°. This design can effectively control the exit direction of the incident light, achieving accurate light spot deflection. The circular aperture microstructures are arranged in a random, non-periodic pattern, with an aperture diameter ranging from 10-70 μm and a depth of 3-12 μm. Through light scattering and overlap, a homogenization effect is achieved, resulting in a more uniform energy distribution of the output light spot.

[0023] The microstructure layer has a double-sided structure. One side is provided with the prism microstructure for controlling the beam angle, and the other side is provided with the circular hole microstructure for optimizing the beam uniformity. The composite design of the double-sided microstructure significantly improves the overall performance and integration of the optical components.

[0024] Substrate material: High borosilicate glass is used as the substrate. This material has excellent chemical stability and optical properties, and is widely used in high-end optical devices. The substrate thickness is controlled within the range of 0.5-1.0 mm to balance mechanical strength and weight requirements. Its coefficient of thermal expansion is low, only 3.2 × 10⁻⁶. -6 / ℃ ensures dimensional stability under temperature variations, with high temperature resistance up to 300℃, making it suitable for harsh environments. Light transmittance exceeds 91%, guaranteeing high optical efficiency, while high surface hardness effectively resists scratches and abrasion. During production, the substrate undergoes ultrasonic cleaning and plasma treatment to thoroughly remove surface contaminants and organic residues, significantly enhancing the adhesion of coatings or microstructures and ensuring long-term reliability.

[0025] Microstructure design: The diffuser contains double-sided microstructure layers, which respectively achieve precise deflection and homogenization functions to optimize light management. Structure 1 (Deflection Microstructure): Located on one side of the substrate, it consists of periodically arranged prism units with a period width of 10-60 μm, a depth of 4-10 μm, and a tilt angle designed within the range of 3-15°. Parameter optimization is performed using simulation optics software (such as LightTools), and the shape and arrangement of the prisms are precisely calculated to ensure controllable refraction and deflection of incident light. The deflection angle can be adjusted according to application requirements to achieve efficient light guidance.

[0026] Structure 2 (Uniform Light Microstructure): Located on the other side of the substrate, it consists of randomly arranged circular aperture units with aperture diameters ranging from 10-70 μm and depths from 3-12 μm. The aperture distribution density employs a gradient design, gradually adjusted from the center to the edge, to ensure that light undergoes multiple scattering and reflections as it passes through, thereby uniformly dispersing light intensity, completely eliminating hotspot phenomena, and improving illumination uniformity and visual comfort.

[0027] A method for preparing a diffuser with a deflection angle includes the following steps: Provide and clean the glass substrate; first, select a suitable glass substrate and thoroughly clean it using deionized water and an ultrasonic cleaner to remove surface contaminants, dust, and grease, ensuring that the substrate surface is clean and hydrophilic, in preparation for subsequent processes.

[0028] Photoresist is coated on the substrate surface; a layer of positive photoresist is uniformly coated on the substrate using spin coating, with the thickness of the photoresist layer controlled at 1-2 micrometers, and then a soft baking process is performed (e.g., baking at 90°C for 1 minute) to remove solvent and improve the adhesion and uniformity of the photoresist layer.

[0029] The pattern is formed by exposure and development using a photomask. A photomask with square or round holes arranged in a gradient pattern is used for exposure in a photoluminescence exposure machine at a wavelength of 365nm and an exposure dose of 100-200mJ / cm². The exposure time is automatically adjusted according to the light intensity. After exposure, an alkaline developer (such as 0.5% tetramethylammonium hydroxide solution) is used to develop the photoresist to remove the exposed areas and form a clear pattern. The development time is about 30-60 seconds. After that, the image is rinsed with deionized water and dried.

[0030] Microstructures are formed by wet etching; the developed substrate is immersed in a hydrofluoric acid-based etching solution with a concentration of 5-10%, the temperature of the etching solution is maintained at 20-25°C, the etching time is 1-5 minutes, and slight stirring is performed during the process to ensure uniform etching; isotropic etching is achieved by utilizing the gradual distribution of apertures on the mask, thereby controlling the depth, tilt and shape gradient of the microstructure.

[0031] The mask pattern consists of square or round holes arranged in a gradient, with the hole diameter gradually changing from the center to the edge or according to a specific pattern. The minimum hole diameter is in the micrometer range, and the maximum hole diameter is adjusted according to design requirements to produce continuous depth changes during the etching process.

[0032] The wet etching process uses a hydrofluoric acid-based etching solution with a concentration of 5-10%. Buffers such as ammonium fluoride are typically added to stabilize the etching rate. The etching time is 1-5 minutes. After etching, the reaction is immediately terminated with deionized water and the surface is cleaned.

[0033] The exposure is yellow light exposure with a wavelength of 365nm and an exposure dose of 100-200mJ / cm². The exposure machine needs to be calibrated to ensure uniform energy. After exposure, check whether the pattern resolution meets the requirements.

[0034] The microstructure layer is achieved by etching both sides separately, processing one side first and then flipping to process the other side; first, photolithography, development and etching steps are completed on one side of the substrate, then the substrate is thoroughly cleaned and dried, and the same process is repeated on the other side after flipping to ensure the alignment and consistency of the microstructure on both sides.

[0035] Mask design: Use CAD software (such as AutoCAD or professional lithography software) to draw a gradient aperture pattern. The pattern type is a square hole or a round hole. The aperture size gradually changes linearly or non-linearly from the starting value to the ending value. When designing, consider etching selectivity, pattern density and minimum feature size to precisely control the etching rate and microstructure morphology.

[0036] Photolithography and etching: After coating the photoresist and soft baking, the pattern is formed by exposure and development with yellow light. The quality of the pattern is checked after development. Then, isotropic etching is performed using a hydrofluoric acid-based etching solution. Surfactants can be added to the etching solution to improve wettability. The etching rate is controlled locally by utilizing the difference in aperture, thereby forming the preset microstructure depth and tilt. The etching solution is cleaned and neutralized immediately after etching.

[0037] Post-processing: After etching, residual photoresist is removed using an organic solvent (such as acetone) or a plasma stripper. Then, annealing is performed by heating at 300°C in an inert atmosphere (such as nitrogen) for 1 hour to release internal stresses generated during etching and the thermal process, improving the mechanical stability, surface quality, and long-term reliability of the microstructure. Finally, final cleaning, drying, and optical or microscopic inspection are conducted to ensure the microstructure meets specifications.

[0038] Example 1: Preparation of a single-sided prism microstructure diffuser sheet Substrate pretreatment stage Borosilicate glass substrates with a thickness of 0.5mm-1.5mm are selected. This material has good thermal stability and chemical corrosion resistance, and is suitable for the fabrication of micro-patterns.

[0039] A three-stage cleaning process is performed to ensure the substrate surface is clean: Level 1: Use acetone for ultrasonic cleaning at a frequency of 40kHz for 5-20 minutes to effectively remove surface organic contaminants and grease; Second stage: Use ethanol for ultrasonic cleaning for 5-20 minutes to thoroughly remove residual acetone and other organic matter; Third stage: Rinse with 18 MΩ·cm ultrapure deionized water for 5-20 minutes to thoroughly remove ionic contaminants and particles; Plasma treatment is then performed: the substrate is treated with 200W radio frequency power for 5-20 minutes in an oxygen atmosphere, which significantly improves the hydrophilicity and adhesion of the substrate surface.

[0040] Photoresist coating process Positive photoresist (model AZ 5214) was selected, which has good photosensitivity and contrast.

[0041] A two-step spin coating process is adopted: the first stage is to spin at a low speed of 300-700 rpm for 5-20 seconds to allow the photoresist to spread initially; the second stage is to increase the speed to 3000 rpm for 30 seconds to achieve uniform coverage.

[0042] Pre-baking is performed on a hot plate at 100℃ for 30-60 seconds to promote solvent evaporation and enhance film adhesion. The final adhesive layer thickness was controlled within the range of 3.0±0.2μm-5.0±0.2um, and the thickness was verified by ellipsometry. Next, the mask alignment and exposure process is performed: A chromium mask with a square aperture array is used, with the aperture size designed in a gradient distribution of 5-50 μm; Achieving alignment accuracy within ±1μm using a high-precision lithography machine; The exposure light source was i-line ultraviolet light (wavelength 365nm), the exposure dose was set to 150mJ / cm², and the corresponding exposure time was about 30 seconds.

[0043] Development process The developer was prepared by diluting AZ 400K with deionized water at a volume ratio of 1:(2.5-4.7). The development time should be controlled between 40 and 70 seconds. Immersion development should be used, accompanied by gentle shaking 30 times per minute to ensure uniform development. Immediately after development, rinse with deionized water for 30 seconds as a stop solution to prevent over-development.

[0044] wet etching process The etching solution was prepared by mixing hydrofluoric acid and deionized water at a volume ratio of 1:(7-10) and carried out in a polytetrafluoroethylene tank. The etching environment temperature is maintained at (20-40) ±1℃, and temperature control is achieved through a water bath circulation system; The etching time is set to within 5 minutes. During the process, the magnetic stirrer is kept at a constant speed of 200 rpm to ensure uniform etching. The etching rate was controlled at approximately 2 μm / min, and the rate was calibrated using a cross-sectional scanning electron microscope.

[0045] Post-processing Photoresist removal is performed using oxygen plasma ashing, which is carried out at 300W power for 30 minutes to completely remove residual colloid. Then, annealing is performed: annealing at 300°C for 60 minutes in air to eliminate processing stress and enhance structural stability; Finally, the substrate is ultrasonically cleaned with deionized water for 5 minutes and then dried with high-purity nitrogen to ensure that there is no residual moisture or particles.

[0046] Example 2: Complete fabrication process of double-sided microstructured diffuser sheet Double-sided pretreatment of substrate The substrate material is aluminosilicate glass with a thickness of 1.0 mm. This material has good thermal stability and mechanical strength, and is suitable for microstructure processing.

[0047] The double-sided simultaneous cleaning process includes the following steps: Ultrasonic cleaning in an alkaline cleaning solution (pH = 10) for 15 minutes effectively removes organic matter and particulate contaminants from the surface; Rinse repeatedly with deionized water until the water resistivity is greater than 18 MΩ·cm to ensure that the surface is clean and free of ion residue. The infrared drying stage is set at 80℃ for 30 minutes to completely remove moisture and prevent bubbles or poor adhesion in subsequent processes.

[0048] Detailed description of the first side (structure 2) Photoresist coating process: Using thick adhesive AZ 4620, the thickness was controlled to 8 μm through spin coating process; The softening conditions were set to 90°C for 120 seconds to remove solvent and enhance film adhesion.

[0049] Mask design specifications: The diameter of the circular hole ranges from 10 to 70 μm; The staggered arrangement density is designed to be 1000–5000 pieces / mm² to meet the functional distribution requirements of the structure.

[0050] Exposure parameter settings: The exposure dose is 200 mJ / cm²; The focusing accuracy is controlled within ±0.5 μm to ensure the accuracy of image transfer and edge sharpness.

[0051] Development process control: The development time must be strictly controlled within 90 seconds; The development level is monitored in real time using a microscope to avoid underdevelopment or overdevelopment.

[0052] The etching process uses buffered hydrofluoric acid (BHF) as the etching solution, and the etching time is set to 4 minutes. The depth control target is 5 ± 0.5 μm, and the etching endpoint is accurately determined through intermittent measurements.

[0053] Substrate flipping and alignment operations: A precision flipping fixture is used, achieving a mechanical positioning accuracy of ±2 μm; The substrate is fixed by vacuum adsorption, which effectively prevents displacement or vibration during the processing. A high-resolution optical alignment system is used for calibration to achieve an alignment accuracy of ±1 μm, ensuring the accuracy of the relative position of the double-sided pattern.

[0054] Detailed description of the second side (structure 1) The photoresist used is AZ 5214, and the thickness is controlled at 3 μm. The mask is designed with square holes, with a side length ranging from 5 to 50 μm, arranged periodically, and the spacing is controlled between 10 and 60 μm.

[0055] The exposure uses grayscale exposure technology: The dose gradient was set in the range of 100–200 mJ / cm² to adjust the characteristics of the morphological transition region.

[0056] The etching process uses a hydrofluoric acid mixture (HF:H2O = 1:8), and the etching time is controlled at 2.5 minutes. By controlling the etching rate and time, a tilted structure of 8–12° is formed.

[0057] Double-sided structure integrated processing The synchronous annealing process parameters are as follows: The heating rate is controlled at 5℃ / minute, the holding temperature is 300℃ for 2 hours, and then it is naturally cooled to room temperature to release internal stress and improve structural stability.

[0058] Preparation of anti-reflective coating: The material was MgF2, which was deposited using vacuum evaporation with a thickness of 100 nm. The evaporation rate was controlled at 0.5 nm / second to ensure the density and uniformity of the film.

[0059] Example 3: Special process of variant example Large-size substrate processing Substrate size: 300mm×300mm, suitable for high-capacity semiconductor and display panel manufacturing; Special coating equipment: Employs a high-precision slot coater to achieve uniform film deposition with a thickness deviation of less than ±2%; Zoned exposure strategy: Utilizing 9-grid zoned exposure technology to effectively reduce edge distortion and improve pattern alignment accuracy; Etching uniformity control: Through real-time monitoring and feedback adjustment of multi-point temperature, the etching rate is kept consistent, with deviation controlled within ±1.5%. Special structural variations: Supports the processing of curved and irregularly shaped substrates, adapting to the application requirements of flexible electronics and micro-optical components; Hybrid microstructure design: By combining the arrangement of prisms and circular holes, light transmission and mechanical stability are optimized; A gradient depth variation design is introduced to achieve a continuous transition between aperture and depth, enhancing functionality; Multi-layer structure fabrication: A double-stage photolithography process was used to complete the stacking of high aspect ratio structures; Depth control accuracy reaches ±0.1μm, ensuring the consistency and repeatability of microstructure morphology.

[0060] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative and not exhaustive. All modifications within the scope of this invention or its equivalents are included in this invention.

Claims

1. A diffuser sheet with a deflection angle, characterized by: The application relates to a glass substrate and a microstructure layer formed on at least one side of the glass substrate; the microstructure layer comprises at least one of prismatic microstructure for light spot deflection and round hole microstructure for light spot homogenization.

2. A diffuser sheet with a deflection angle according to claim 1, characterized in that: The thickness of the glass substrate is 0.5-1.0 mm, the high-temperature resistance reaches 300 DEG C, and the glass substrate is resistant to yellowing and warping.

3. A diffuser sheet with a deflection angle according to claim 1, characterized in that: The prismatic microstructure is periodically arranged, the period width is 10-60 mu m, the depth is 4-10 mu m, and the inclination angle is 3-15 DEG.

4. The diffuser of claim 1, wherein: The round hole microstructure is randomly arranged, the hole diameter is 10-70 mu m, and the depth is 3-12 mu m.

5. The diffuser of claim 1, wherein: The microstructure layer is a double-sided structure, one side is provided with the prismatic microstructure, and the other side is provided with the round hole microstructure.

6. A method of producing a diffuser sheet with a deflection angle, characterized by: The application further discloses a preparation method of the glass substrate. The glass substrate is provided and cleaned; Photoresist is coated on the surface of the substrate; Exposure and development are carried out through a mask plate to form a pattern; Wet etching is carried out to form a microstructure.

7. The method of claim 6, wherein the diffusion sheet having a deflection angle is prepared by the steps of: The pattern of the mask plate is a square hole or a round hole in a gradually changed square arrangement. ​ 8. The method of claim 6, wherein the diffusion sheet having a deflection angle is prepared by the steps of: The wet etching adopts a hydrofluoric acid etching solution with a concentration of 5-10%, and the etching time is 1-5 minutes. ​ 9. The method of claim 6, wherein the diffusion sheet having a deflection angle is prepared by the steps of: The exposure is yellow light exposure, the wavelength is 365 nm, and the exposure amount is 100-200 mJ / cm2. ​ 10. The method of claim 6, wherein the diffusion sheet having a deflection angle is prepared by the steps of: The microstructure layer is realized by double-sided etching, one side is processed first, and then the other side is processed after being turned over. ​

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