A method for preparing a gradient film layer achromatic optical film

Abstract

This application relates to the field of optical coating technology, specifically disclosing a method for preparing a gradient-coated achromatic optical thin film, comprising the following steps: S1, the substrate is pretreated by cleaning to obtain a pretreated substrate; S2, silicon dioxide and titanium dioxide layers are alternately deposited on the surface of the pretreated substrate, with a total deposition of 4-6 layers, to obtain coated glass; S3, the coated glass is polished by ion beam, with the edge thickness decreasing by 4-6 nm / μm, to obtain the finished optical thin film; eliminating the color difference between the screen and the bezel, while adapting to curved dials and irregularly shaped bezels.

Description

Technical Field

[0001] This application relates to the field of optical coating technology, and more specifically, it relates to a method for preparing achromatic optical thin films with gradient coating layers. Background Technology

[0002] In the field of optical thin films, with the rapid development of electronic devices, especially high-end smartwatches and medical device displays, people have put forward higher requirements for the aesthetics and display effects of display devices. The color difference between the screen and the bezel and how to adapt to curved dials and irregular bezels have become key factors restricting the further improvement of product appearance quality. Good color consistency and adaptability to complex shapes can not only enhance the visual aesthetics of products, but also enhance their competitiveness in the market and promote the development of related industries towards higher quality.

[0003] In the past, various methods were commonly used to solve the color difference problem between the screen and the bezel, as well as to adapt to complex-shaped dials and bezels. On the one hand, optical films with a single refractive index were used to try to reduce color difference, but this method often struggled to precisely control the refraction and interference of different wavelengths of light, making it impossible to effectively eliminate color difference over a wide range. On the other hand, for adapting to curved dials and irregularly shaped bezels, traditional methods often involved simple mechanical processing or bonding processes, but these methods were prone to problems such as film delamination and bubbles, affecting the optical performance and overall appearance of the film. In addition, some methods attempted to improve color difference and adaptability by adjusting the composition of materials, but due to a lack of effective control over key factors such as optical path difference, the results were not ideal.

[0004] These conventional methods in existing technologies have significant drawbacks. Optical films with a single refractive index cannot meet the requirements for high-precision color difference elimination, resulting in noticeable color differences between screen pixels and the bezel. Furthermore, simple machining and bonding processes cannot guarantee the uniformity and stability of the film layer on curved and irregularly shaped areas, making the film layer prone to delamination and severely affecting the product's appearance quality. Moreover, traditional methods do not fully consider optical principles such as optical path difference, failing to fundamentally solve the color difference problem between the screen and the bezel, as well as the adaptation challenges of complex shapes. Summary of the Invention

[0005] In order to eliminate the color difference between the screen and the bezel, and to adapt to curved dials and irregularly shaped bezels, this application provides a method for preparing a gradient achromatic optical thin film.

[0006] In a first aspect, this application provides a method for preparing a gradient achromatic optical thin film, employing the following technical solution:

[0007] A method for preparing a gradient achromatic optical thin film includes the following steps:

[0008] S1. The substrate is pretreated by cleaning to obtain a pretreated substrate;

[0009] S2. Alternately deposit silica and titanium dioxide layers on the pretreated substrate surface, with a total of 4-6 layers deposited to obtain coated glass;

[0010] S3. The coated glass is polished with an ion beam, and the thickness decreases by 4-6 nm / μm at the edge to obtain the finished optical thin film.

[0011] By adopting the above technical solution, the surface of the substrate after cleaning and pretreatment has a high degree of cleanliness, which facilitates the deposition of silicon dioxide. The refractive index of silicon dioxide is about 1.46, and the refractive index of titanium dioxide is about 2.4. By alternating the deposition of silicon dioxide layer and titanium dioxide layer, the optical performance is controlled by interference effect, so that the reflected light undergoes destructive interference at the interface, thereby reducing the overall reflectivity and reducing dispersion. Laying 4-6 layers can cover the visible light band and avoid color difference between the frame and the screen due to wavelength selective reflection as much as possible.

[0012] Alternating layers of silicon dioxide and titanium dioxide form different film layers on the pretreated substrate surface. Combined with ion beam polishing, this creates a nanoscale textured surface on the optical thin film, further dispersing the direction of reflected light, reducing local color shift, and suppressing dispersion caused by high-angle incident light. This reduces color difference and improves visual consistency. Furthermore, ion beam polishing repairs the interfacial stress and microscopic defects of the alternating silicon dioxide and titanium dioxide layers, reducing optical interference anomalies caused by abrupt changes in interface refractive index, further reducing color difference and improving the quality of the optical thin film. Simultaneously, the edge thickness decreases by 4-6 nm / μm, compensating for the optical path difference caused by changes in the incident angle of the curved surface through a gradient refractive index distribution. This allows the interference effect to still achieve broadband antireflection in the curved area, reducing color difference between the curved screen and the bezel.

[0013] Ion beam polishing reduces the edge thickness by 4-6 nm / μm. By limiting the decreasing size, a gradient refractive index distribution is formed to compensate for the optical path difference caused by the change in the incident angle of the curved surface. This ensures that the interference effect can still achieve broadband anti-reflection in the curved surface area, thus adapting to curved surfaces and irregularly shaped frames.

[0014] Preferably, the specific steps of the cleaning pretreatment are as follows:

[0015] The tubes are sequentially ultrasonically cleaned, rinsed with deionized water, dehydrated with ethanol, and dried with nitrogen.

[0016] By adopting the above technical solution, ultrasonic cleaning combined with deionized water rinsing can remove surface impurities and contaminants, ensure the deposition stability of the silica layer, prevent peeling problems, and guarantee the adhesion effect.

[0017] Preferably, the substrate is either optical glass or sapphire cover plate.

[0018] By adopting the above technical solution, silicon dioxide and titanium dioxide layers are alternately deposited on the surface of optical glass or sapphire cover plate. By utilizing the complementary characteristics of high refractive index titanium dioxide layer and low refractive index silicon dioxide layer, the phase difference of light of different wavelengths can be dispersed and the dispersion effect can be suppressed.

[0019] Preferably, the sputtering frequency of the silicon dioxide layer is 140-160W, the sputtering time is 25-35min, and the sputtering pressure is 0.4-0.6Pa.

[0020] Preferably, the sputtering frequency of the titanium dioxide layer is 110-130W, the sputtering time is 12-16min, and the sputtering pressure is 0.4-0.6Pa.

[0021] By adopting the above technical solutions, the sputtering frequency is limited to ensure a moderate plasma density, thereby ensuring the compactness of the magnetron sputtered film and reducing scattering. The time limitation can better control the film thickness, achieving interference achromatic aberration. The gas pressure limitation increases the mean free path of particles and improves the uniformity of the film, thus giving the optical thin film the advantages of small chromatic aberration and high quality.

[0022] Preferably, the deposition thickness of each silicon dioxide layer is 90-110 nm, and the deposition thickness of each titanium dioxide layer is 40-60 nm.

[0023] By adopting the above technical solution, the silicon dioxide layer has a high deposition thickness, close to the refractive index of optical glass, while the titanium dioxide layer has a low thickness. The overlapping and progressive effect of the refractive index can further compensate for dispersion and enhance long-wavelength suppression, thereby reducing interface scattering, promoting destructive interference, and reducing chromatic aberration.

[0024] Preferably, in the magnetron sputtering process of the silicon dioxide layer, the silicon dioxide composite target is made of silicon dioxide and alumina-coated cerium oxide in a mass ratio of 8-10:1.

[0025] By adopting the above technical solution, the refractive index of silicon dioxide is about 1.46, the refractive index of aluminum oxide is about 1.62, and the refractive index of cerium oxide is about 2.2. Aluminum oxide is used as a transition between silicon dioxide and cerium oxide to form a gradual step refractive index structure, which reduces chromatic aberration. The refractive index and variable valence state of cerium oxide are used to adjust the absorption and reflection of ultraviolet-visible light of the optical film. Combined with aluminum oxide to reduce light interference fringes, the aluminum oxide-coated cerium oxide can cover the chromatic aberration compensation in the 400-700nm wavelength band.

[0026] Alumina has high hardness and low refractive index. The uniform distribution of cerium oxide in the alumina coating, combined with the flexible substrate of silicon dioxide, ensures that the optical film remains uniform on curved or irregularly shaped frames, avoiding local refractive index changes caused by local stress and reducing color difference. At the same time, the stable refractive index of silicon dioxide and glass substrate further eliminates the color difference between the screen and the frame, making it suitable for curved surfaces and irregularly shaped frames.

[0027] Preferably, the alumina-coated cerium oxide is obtained by depositing a 3-5 nm alumina film on the surface of cerium oxide.

[0028] By employing the above technical solutions, the high refractive index of cerium oxide and the low refractive index of aluminum oxide can modulate the optical interference effect of the thin film, compensating for the optical path difference at the edges of curved surfaces. A 2-5nm aluminum oxide film layer, acting as a transition layer, reduces the lattice mismatch stress between cerium oxide and silicon dioxide, improving film adhesion and enhancing the quality and stability of the optical thin film. Furthermore, the nanoscale deposition of aluminum oxide (2-5nm) fills microscopic defects on the cerium oxide surface, reducing light scattering, improving film uniformity, and minimizing local color shift caused by surface curvature. Simultaneously, the high hardness of aluminum oxide combined with the toughness of cerium oxide ensures a uniform film thickness on curved surfaces, minimizing stress concentration caused by curvature, making it suitable for curved screens. The high sputtering rate of the cerium oxide target and the stability of aluminum oxide work synergistically to ensure consistent film deposition at irregular bezel edges, making the optical thin film suitable for irregular bezels and extending its lifespan.

[0029] Preferably, in the magnetron sputtering of the titanium dioxide layer, the titanium dioxide composite target is made of titanium dioxide, yttrium oxide and alumina-coated boron nitride in a mass ratio of 100:5-13:2-5.

[0030] By adopting the above technical solution, the refractive index of titanium dioxide is about 2.4, the refractive index of yttrium oxide is about 1.8-1.9, and the refractive index of aluminum oxide is about 1.76. The three form a refractive index gradient hierarchy, which compensates for the optical path difference at the edge of the curved surface through the interference destructive effect, thereby reducing color difference. The refractive index of the aluminum oxide coating layer is about 1.76, and the refractive index of boron nitride is about 2.0, forming a gradient refractive index structure, which can compensate for abrupt changes in refractive index and reduce dispersion caused by interface reflection, thereby further reducing the color difference between the screen and the bezel.

[0031] Yttrium oxide can refine crack propagation units and improve the toughness of titanium dioxide films. Aluminum oxide can form a dispersed phase in the titanium dioxide film layer, further controlling crack propagation. Combined with the layered structure of boron nitride, it forms a stepped transition, improving the interfacial bonding strength while controlling stress concentration, maintaining the uniformity of refractive index distribution, avoiding optical path difference caused by stress gradient, and improving optical uniformity. At the same time, in magnetron sputtering, the high sputtering rate of yttrium oxide target and the deposition of boron nitride ensure the uniformity of film layers on curved dials and irregularly shaped frames, and control color difference.

[0032] Preferably, the alumina-coated boron nitride is prepared by depositing a 2-4 nm alumina film on the surface of boron nitride.

[0033] By adopting the above technical solution, boron nitride can disperse local stress and alleviate stress concentration in irregularly shaped frames. At the same time, the layered structure of boron nitride provides uniform nucleation sites for alumina deposition, improving film adhesion. Meanwhile, the alumina film, through precise deposition coverage, reduces lattice mismatch between boron nitride and titanium dioxide and silicon dioxide films, reduces interface defects, improves the stability of thin film deposition, indirectly reduces color difference, and ensures the quality of optical thin films.

[0034] In summary, this application has the following beneficial effects:

[0035] 1. By depositing a multi-layer gradient film of silicon dioxide and titanium dioxide on the surface of glass or sapphire cover plate, combined with optical path difference compensation technology, the color difference between the screen and the bezel is eliminated, and the edge thickness decreases by 4-6nm / μm. This ensures the adaptability of the film on curved dials and irregularly shaped bezels, and also has good optical performance and adaptability, meeting the usage requirements of high-end smartwatches and medical device displays.

[0036] 2. Through optical path difference compensation technology, the color difference (ΔE) between screen pixels and the frame is reduced to less than 0.5, which is far lower than that of traditional coating technology (ΔE>3), significantly improving the appearance quality and high-end feel of the product, and has the advantage of significantly reducing color difference.

[0037] 3. When the screen is off, the RGB three-color consistency (color gamut matching degree) is greater than 98%, ensuring that the screen and the bezel have a high degree of color consistency when the screen is off, which improves the overall aesthetics of the product.

[0038] 4. It adopts an asymmetric film thickness gradient distribution design, with the edge thickness decreasing by 4-6nm / μm, which can be well adapted to curved dials and irregularly shaped frames, solving the problem of layering in complex shapes by traditional coatings.

[0039] 5. This optical film is particularly suitable for high-end smartwatches, medical device displays, and other applications where aesthetics and display effects are highly important, and it has significant application value and market prospects. Detailed Implementation

[0040] The present application will be further described in detail below with reference to the embodiments.

[0041] All of the following ingredients are commercially available.

[0042] Example of preparation of silica composite target material

[0043] Preparation Example 1: Silica composite target material was prepared using the following method:

[0044] Cerium oxide microparticles were plasma-cleaned for 3 minutes and then dried to obtain cerium oxide; the average particle size of cerium oxide was 50 nm.

[0045] Using trimethylaluminum as the aluminum source and ozone as the oxygen source, alternating pulses were applied at 120°C. The pulses were first applied for 3 seconds, followed by argon purging, then water pulses for 5 seconds, and purging was repeated. This cycle was repeated to form an aluminum oxide film with an average thickness of 4 nm on the surface of cerium oxide. The purity of the cerium oxide was 99.99%, resulting in the finished product, aluminum oxide-coated cerium oxide.

[0046] 10g of alumina-coated cerium oxide was mixed with 90g of 99.99% pure silica to obtain a powder mixture. 80g of polyvinyl alcohol binder was added to the powder mixture and ball-milled for 6 hours. After drying, the mixture was vacuum hot-pressed and sintered at 1300℃ to obtain a silica composite target material. The polyvinyl alcohol binder was a 2% (w / w) aqueous solution of polyvinyl alcohol.

[0047] Preparation Example 2: The difference between this preparation example and Preparation Example 1 is that:

[0048] Using trimethylaluminum as the aluminum source and ozone as the oxygen source, alternating pulses were applied at 120°C. The pulses were first applied for 3 seconds, followed by argon purging, then water pulses for 5 seconds, and purging was repeated. This cycle was repeated to form an aluminum oxide film with an average thickness of 3 nm on the surface of cerium oxide, resulting in the finished product, aluminum oxide-coated cerium oxide.

[0049] 10g of alumina-coated cerium oxide was mixed with 80g of 99.99% pure silica to obtain a powder mixture. 80g of polyvinyl alcohol binder was added to the powder mixture and ball-milled for 6 hours. After drying, the mixture was vacuum hot-pressed and sintered at 1300℃ to obtain a silica composite target material. The polyvinyl alcohol binder was a 2% (w / w) aqueous solution of polyvinyl alcohol.

[0050] Preparation Example 3: The difference between this preparation example and Preparation Example 1 is that:

[0051] Using trimethylaluminum as the aluminum source and ozone as the oxygen source, alternating pulses were applied at 120°C. The pulses were first applied for 3 seconds, followed by argon purging, then water pulses for 5 seconds, and purging was repeated. This cycle was repeated to form an aluminum oxide film with an average thickness of 5 nm on the surface of cerium oxide, resulting in the finished product, aluminum oxide-coated cerium oxide.

[0052] 10g of alumina-coated cerium oxide was mixed with 100g of 99.99% pure silica to obtain a mixed powder. 80g of polyvinyl alcohol binder was added to the mixed powder and ball-milled for 6 hours. After drying, it was vacuum hot-pressed and sintered at 1300℃ to obtain a silica composite target. The polyvinyl alcohol binder was a 2% (w / w) aqueous solution of polyvinyl alcohol.

[0053] Example of preparation of titanium dioxide composite target material

[0054] Preparation Example 4: Titanium dioxide composite target material was prepared using the following method:

[0055] Using trimethylaluminum as the aluminum source and ozone as the oxygen source, alternating pulses were applied at 120°C. The pulses were first applied for 3 seconds, followed by argon purging, then water pulses for 5 seconds, and purging was repeated. This cycle was repeated to form an aluminum oxide film with an average thickness of 3 nm on the surface of boron nitride, thus obtaining alumina-coated boron nitride.

[0056] 100g of 99.99% pure titanium dioxide, 10g of 99.99% pure yttrium oxide, and 4g of alumina-coated boron nitride were mixed evenly to obtain a mixture. 90g of polyvinyl alcohol binder was added to the mixture and ball-milled for 6 hours. After drying, the mixture was vacuum hot-pressed and sintered at 1550℃ to obtain a titanium dioxide composite target. The polyvinyl alcohol binder was a 2% (w / w) aqueous solution of polyvinyl alcohol.

[0057] Preparation Example 5: The difference between this preparation example and Preparation Example 4 is that:

[0058] Using trimethylaluminum as the aluminum source and ozone as the oxygen source, alternating pulses were applied at 120°C. The pulses were first applied for 3 seconds, followed by argon purging, then water pulses for 5 seconds, and purging was repeated. This cycle was repeated to form an aluminum oxide film with an average thickness of 2 nm on the surface of boron nitride, thus obtaining alumina-coated boron nitride.

[0059] 100g of titanium dioxide with a purity of 99.99%, 5g of yttrium oxide with a purity of 99.99%, and 5g of alumina-coated boron nitride were mixed evenly to obtain a mixture. 90g of polyvinyl alcohol binder was added to the mixture and ball-milled for 6 hours. After drying, the mixture was vacuum hot-pressed and sintered at 1550℃ to obtain a titanium dioxide composite target. The polyvinyl alcohol binder was a 2% (w / w) aqueous solution of polyvinyl alcohol.

[0060] Preparation Example 6: The difference between this preparation example and Preparation Example 4 is that:

[0061] Using trimethylaluminum as the aluminum source and ozone as the oxygen source, alternating pulses were applied at 120°C. The pulses were first applied for 3 seconds, followed by argon purging, then water pulses for 5 seconds, and purging was repeated. This cycle was repeated to form an aluminum oxide film with an average thickness of 4 nm on the surface of boron nitride, thus obtaining alumina-coated boron nitride.

[0062] 100g of 99.99% pure titanium dioxide, 13g of 99.99% pure yttrium oxide, and 2g of alumina-coated boron nitride were mixed evenly to obtain a mixture. 90g of polyvinyl alcohol binder was added to the mixture and ball-milled for 6 hours. After drying, the mixture was vacuum hot-pressed and sintered at 1550℃ to obtain a titanium dioxide composite target. The polyvinyl alcohol binder was a 2% (w / w) aqueous solution of polyvinyl alcohol.

[0063] Example 1: A method for preparing a gradient achromatic optical thin film:

[0064] S1. Select optical glass with a thickness of 1.1mm as the substrate. The optical glass substrate is first ultrasonically cleaned, then rinsed with deionized water, dehydrated with ethanol, and dried with nitrogen to complete the cleaning pretreatment and obtain the pretreated substrate.

[0065] S2. The pretreated substrate is placed in a vacuum magnetron sputtering apparatus with a vacuum level of 5×10⁻⁶. -4 First, a silica target with a purity of 99.99% was magnetron sputtered to deposit a silica layer on the surface of the optical glass. The magnetron sputtering frequency was 150 W, the sputtering time was 30 min, the sputtering gas was argon, and the sputtering pressure was 0.5 Pa. The average thickness of the silica layer was 100 nm. Then, a titanium dioxide target with a purity of 99.99% was magnetron sputtered to form a titanium dioxide layer with an average thickness of 50 nm on the surface of the silica layer. The sputtering power was 120 W, the sputtering time was 15 min, the sputtering gas was argon, and the gas pressure was maintained at 0.5 Pa. The magnetron sputtering was repeated, alternating between silica and titanium dioxide layers, for a total of 5 layers, to obtain the coated glass.

[0066] S3. Place the coated glass in an ion beam polishing device for ion beam polishing, with the edge thickness decreasing by 5nm / μm to obtain the finished optical thin film.

[0067] Example 2: The difference between this example and Example 1 is that:

[0068] S1. Take a sapphire cover plate with a thickness of 0.5mm as the substrate. The sapphire cover plate substrate is first ultrasonically cleaned, then rinsed with deionized water, dehydrated with ethanol, and dried with nitrogen to complete the cleaning pretreatment and obtain the pretreated substrate.

[0069] S2. The pretreated substrate is placed in a vacuum magnetron sputtering apparatus with a vacuum level of 3×10⁻⁶. -4 For the pre-treatment substrate, a silica target with a purity of 99.99% was first magnetron sputtered onto the sapphire cover plate substrate to deposit a silica layer. The magnetron sputtering frequency was 130W, the sputtering time was 25min, the sputtering gas was argon, and the sputtering pressure was 0.4Pa. The average thickness of the silica layer was 80nm. Then, a titanium dioxide target with a purity of 99.99% was magnetron sputtered onto the sapphire cover plate substrate to form a titanium dioxide layer with an average thickness of 40nm. The sputtering power was 110W, the sputtering time was 12min, the sputtering gas was argon, and the gas pressure was maintained at 0.4Pa. The magnetron sputtering was repeated, alternating between silica and titanium dioxide layers, for a total of 4 layers, to obtain the coated glass.

[0070] S3. Place the coated glass in an ion beam polishing device for ion beam polishing, with the edge thickness decreasing by 5nm / μm to obtain the finished optical thin film.

[0071] Example 3: The difference between this example and Example 1 is that:

[0072] S1. The optical glass is first ultrasonically cleaned, then rinsed with deionized water, dehydrated with ethanol, and dried with nitrogen to complete the cleaning pretreatment and obtain the pretreated substrate.

[0073] S2. Pre-treatment of the substrate: First, the silica composite target prepared in Example 1 is prepared by magnetron sputtering. A silica layer is deposited on the surface of the optical glass. The magnetron sputtering frequency is 150W, the sputtering time is 30min, the sputtering gas is argon, and the sputtering pressure is 0.5Pa. The average thickness of the silica layer is 100nm. Then, the titanium dioxide composite target prepared in Example 4 is prepared by magnetron sputtering. A titanium dioxide layer with an average thickness of 50nm is formed on the surface of the silica layer. The sputtering power is 120W, the sputtering time is 15min, the sputtering gas is argon, and the gas pressure is maintained at 0.5Pa. The magnetron sputtering is repeated, and silica and titanium dioxide layers are deposited alternately for a total of 5 layers to obtain the coated glass.

[0074] S3. Place the coated glass in an ion beam polishing device for ion beam polishing, with the edge thickness decreasing by 5nm / μm to obtain the finished optical thin film.

[0075] Example 4: The difference between this example and Example 3 is that:

[0076] S1. The optical glass is first ultrasonically cleaned, then rinsed with deionized water, dehydrated with ethanol, and dried with nitrogen to complete the cleaning pretreatment and obtain the pretreated substrate.

[0077] S2. Pre-treatment of the substrate: First, the silica composite target prepared in Example 2 is prepared by magnetron sputtering. A silica layer is deposited on the surface of the optical glass. The magnetron sputtering frequency is 140W, the sputtering time is 35min, the sputtering gas is argon, and the sputtering pressure is 0.4Pa. The average thickness of the silica layer is 90nm. Then, the titanium dioxide composite target prepared in Example 5 is prepared by magnetron sputtering. A titanium dioxide layer with an average thickness of 40nm is formed on the surface of the silica layer. The sputtering power is 110W, the sputtering time is 16min, the sputtering gas is argon, and the gas pressure is maintained at 0.4Pa. The magnetron sputtering is repeated, and silica and titanium dioxide layers are deposited alternately for a total of 4 layers to obtain the coated glass.

[0078] S3. Place the coated glass in an ion beam polishing device for ion beam polishing, with the edge thickness decreasing by 4nm / μm to obtain the finished optical thin film.

[0079] Example 5: The difference between this example and Example 3 is that:

[0080] S1. The sapphire cover plate is first ultrasonically cleaned, then rinsed with deionized water, dehydrated with ethanol, and dried with nitrogen to complete the cleaning pretreatment and obtain the pretreated substrate.

[0081] S2. Pre-treatment of the substrate: First, the silica composite target prepared in Example 3 is prepared by magnetron sputtering. A silica layer is deposited on the surface of the optical glass. The magnetron sputtering frequency is 160W, the sputtering time is 25min, the sputtering gas is argon, and the sputtering pressure is 0.6Pa. The average thickness of the silica layer is 110nm. Then, the titanium dioxide composite target prepared in Example 6 is prepared by magnetron sputtering. A titanium dioxide layer with an average thickness of 60nm is formed on the surface of the silica layer. The sputtering power is 130W, the sputtering time is 12min, the sputtering gas is argon, and the gas pressure is maintained at 0.6Pa. The magnetron sputtering is repeated, and silica and titanium dioxide layers are deposited alternately for a total of 6 layers to obtain the coated glass.

[0082] S3. Place the coated glass in an ion beam polishing device for ion beam polishing, with the edge thickness decreasing by 6 nm / μm to obtain the finished optical thin film.

[0083] Example 6: The difference between this example and Example 3 is that:

[0084] In the preparation of silica composite targets, cerium oxide of equal mass is used to replace cerium oxide coated with alumina.

[0085] Example 7: The difference between this example and Example 3 is that:

[0086] In the preparation of silica composite targets, cerium oxide coated with alumina is replaced with alumina of equal mass.

[0087] Example 8: The difference between this example and Example 3 is that:

[0088] In the preparation of titanium dioxide composite targets, yttrium oxide is replaced with titanium dioxide of equal mass.

[0089] Example 9: The difference between this example and Example 3 is that:

[0090] In the preparation of titanium dioxide composite targets, boron nitride coated with aluminum oxide is replaced with an equal mass of aluminum oxide.

[0091] Comparative Example

[0092] Comparative Example 1: The difference between this comparative example and Example 1 is that:

[0093] S2 is entirely filled with deposited titanium dioxide layers.

[0094] Comparative Example 2: This comparative example differs from Example 1 in that:

[0095] S3 does not perform edge thickness reduction.

[0096] Performance testing

[0097] 1. Color difference detection

[0098] Optical thin films were prepared using the methods of Examples 1-9 and Comparative Examples 1-2, respectively. The color difference ΔE between the center pixel of the screen and the frame was detected using a microspectrophotometer. The ΔE data was recorded at the curved surface of the frame.

[0099] 2. Color gamut matching test

[0100] Optical films were prepared using the methods described in Examples 1-5, respectively. The optical films were used as displays for medical devices. The consistency of the RGB three colors was measured when the screen was off, and the color gamut coverage was calculated.

[0101] Table 1 Performance Test Table (In the table, " / " indicates that the corresponding embodiment and comparative example did not test this item and no data is displayed)

[0102]

[0103] As can be seen from Examples 1-2 and Table 1, the optical film prepared in this application has low color difference between the screen and the frame, is suitable for curved dials and irregularly shaped frames, and has a high color gamut coverage, indicating that it has good quality.

[0104] As can be seen from Examples 1 and 3-5 and Table 1, the limitation of the silica composite target and the titanium dioxide composite target forms a gradual step refractive index structure, reducing color difference.

[0105] Combining Examples 3 and 6-9 with Table 1, it can be seen that in the preparation process of the silica composite target in Example 6, when cerium oxide was replaced with aluminum oxide coating of the same mass, the color difference in Example 6 was greater than that in Example 3. This indicates that the nanoscale deposition of aluminum oxide can fill the microscopic defects on the surface of cerium oxide, reduce light scattering, improve the uniformity of the film layer, and reduce local color deviation caused by the curvature of the curved surface. At the same time, the high hardness of aluminum oxide and the toughness of cerium oxide combine to maintain a uniform thickness of the film layer on the curved surface, and minimize stress concentration caused by curvature. This is suitable for curved surface screens, reduces the color difference between the screen and the frame, and is suitable for curved surfaces and irregular frames.

[0106] In Example 7, during the preparation of the silica composite target, aluminum oxide was used to replace cerium oxide coated with aluminum oxide of the same mass. Compared with Example 3, the color difference in Example 7 was greater than that in Example 3. This indicates that by using the refractive index and variable valence state of cerium oxide to adjust the absorption and reflection of ultraviolet-visible light in the optical film, and in combination with aluminum oxide to reduce light interference fringes, the aluminum oxide coated cerium oxide can cover the color difference compensation in the 400-700nm wavelength band, thereby reducing the color difference between the screen and the frame, and making it suitable for curved surfaces and irregular frames.

[0107] In Example 8, during the preparation of the titanium dioxide composite target, yttrium oxide was replaced with titanium dioxide of the same mass. Compared with Example 3, the color difference in Example 8 was greater than that in Example 3, indicating that the refractive index of yttrium oxide is between that of titanium dioxide, aluminum oxide, and silicon dioxide, forming a refractive index gradient hierarchy. This reduces the color difference by compensating for the optical path difference at the edge of the curved surface through the interference cancellation effect. The high sputtering rate of the yttrium oxide target and the deposition of boron nitride ensure the uniformity of the film layer on the curved dial and the irregular frame, thus controlling the color difference.

[0108] In Example 9, during the preparation of the titanium dioxide composite target, boron nitride coated with alumina was replaced with an equal mass of alumina. Compared with Example 3, the color difference in Example 9 was greater than that in Example 3, indicating that the addition of boron nitride can control the abrupt change in refractive index and reduce the dispersion of interfacial reflection. Boron nitride can also suppress the blue light region color shift caused by band gap absorption of the titanium dioxide film. Moreover, the dispersion of boron nitride can improve the sputtering stability of the target, reduce film thickness fluctuations, and control internal stress, thereby reducing the color difference between the screen and the frame, making it suitable for circular panels or irregularly shaped frames.

[0109] Combining Example 1 and Comparative Examples 1-2 with Table 1, it can be seen that Comparative Example 1 has a large color difference in all deposited titanium dioxide layers, indicating that the refractive index of the interface between the titanium dioxide film and the substrate changes a lot, resulting in strong Fresnel reflection and interference dispersion, thus increasing the color difference.

[0110] Comparative Example 2 did not undergo edge thickness reduction. Compared to Example 1, the color difference was greater, indicating that edge thickness reduction can well adapt to curved dials and irregularly shaped frames. It controls the color difference between screen pixels and curved frames, solving the layering problem of traditional coatings on complex shapes. It is suitable for high-end smartwatches and medical device displays.

[0111] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a gradient achromatic optical thin film, characterized in that, Includes the following steps: S1. The substrate is pretreated by cleaning to obtain a pretreated substrate; S2. Alternately deposit silica and titanium dioxide layers on the pretreated substrate surface, with a total of 4-6 layers deposited to obtain coated glass; S3. The coated glass is polished with an ion beam, and the thickness decreases by 4-6 nm / μm at the edge to obtain the finished optical thin film.

2. The method for preparing a gradient achromatic optical thin film according to claim 1, characterized in that: The specific steps of the cleaning pretreatment are as follows: The tubes are sequentially ultrasonically cleaned, rinsed with deionized water, dehydrated with ethanol, and dried with nitrogen.

3. The method for preparing a gradient achromatic optical thin film according to claim 1, characterized in that, The substrate is either optical glass or sapphire cover plate.

4. The method for preparing a gradient achromatic optical thin film according to claim 1, characterized in that, The sputtering frequency of the silicon dioxide layer is 140-160W, and the sputtering pressure is 0.4-0.6Pa.

5. The method for preparing a gradient achromatic optical thin film according to claim 1, characterized in that, The sputtering frequency of the titanium dioxide layer deposited by magnetron sputtering is 110-130W, and the sputtering pressure is 0.4-0.6Pa.

6. The method for preparing a gradient achromatic optical thin film according to claim 1, characterized in that, The silicon dioxide layer has a deposition thickness of 90-110 nm per layer, and the titanium dioxide layer has a deposition thickness of 40-60 nm per layer.

7. The method for preparing a gradient achromatic optical thin film according to claim 5, characterized in that, The silicon dioxide layer is a silicon dioxide composite layer. During the magnetron sputtering process, the silicon dioxide composite target is made of silicon dioxide and cerium oxide coated with aluminum oxide in a mass ratio of 8-10:

1.

8. The method for preparing a gradient achromatic optical thin film according to claim 7, characterized in that, The alumina-coated cerium oxide is obtained by depositing a 3-5 nm alumina film on the surface of cerium oxide.

9. The method for preparing a gradient achromatic optical thin film according to claim 6, characterized in that, The titanium dioxide layer is a titanium dioxide composite layer. During the magnetron sputtering process, the titanium dioxide composite target is made of titanium dioxide, yttrium oxide and alumina coated boron nitride in a mass ratio of 100:5-13:2-5.

10. The method for preparing a gradient achromatic optical thin film according to claim 9, characterized in that, The alumina-coated boron nitride is prepared by depositing a 2-4 nm alumina film on the surface of boron nitride.

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