Short-wave absorption cut-off film and preparation method thereof

Abstract

According to the short-wave absorption cut-off film and the preparation method thereof, by controlling the flow of reaction gas oxygen (O) and adjusting the stoichiometric ratio of tantalum oxide (Ta2O5-x), the optical absorption of the short-wave absorption cut-off film in a short-wave region (less than or equal to 1.0 mu m) is remarkably enhanced, and meanwhile, the stability of optical constants (refractive index and extinction coefficient) of the short-wave absorption cut-off film in an infrared band (greater than or equal to 2.0 mu m) is kept. According to the method, a reaction evaporation deposition technology is adopted, metal tantalum (Ta) is taken as a raw material, plasma is combined to assist in enhancing oxidation reaction, and the tantalum oxide film with the short-wave absorption characteristic is formed by controlling the oxygen flow (5-50 sccm) and deposition parameters (background vacuum is smaller than or equal to 5 * 10 <-4 > Pa, and the evaporation rate is 0.1-0.5 nm / s). The relation between the oxygenation amount and the extinction coefficient is established based on spectral test data fitting optical constants, and the short-wave high absorption (transmittance lt; 5%) and infrared band high transmission (transmittance gt; 90%). The method is high in process compatibility and suitable for optical systems such as infrared detectors and laser protection.

Description

Technical Field

[0001] The present invention relates to the field of optical thin film technology, specifically a short-wave absorption cutoff film and a preparation method thereof, which is suitable for the high-efficiency cutoff of short-wave infrared (≤1.0μm) and the high transmittance requirements of mid-infrared (≥2.0μm), and can be applied to laser protection, spectral filtering and infrared sensing systems. Background Art

[0002] Short-wave infrared absorption films play an indispensable and critical role in many cutting-edge fields, such as laser protection and optical filtering. With the rapid development of science and technology, the requirements for optical thin film performance are becoming increasingly stringent, and traditional absorption film technology has gradually exposed many limitations.

[0003] At present, there are two main methods for preparing traditional absorption films: metal doping and multilayer interference structure. Metal doping technology, such as CN118707641A, an ultra-thin optical functional film and its preparation method, changes its optical properties by introducing metal elements into the film. However, this method often requires the use of a variety of coating materials, which increases the difficulty of material selection and matching, and also makes the process more complicated. Multilayer interference structure technology, such as CN111609573A, uses solar selective absorption materials at the interface of multiple photon heterostructures to construct a multilayer film system to utilize the interference effect of light to achieve optical control of specific wavelengths. However, this technology requires the use of a variety of target materials, which not only increases the preparation cost, but also places higher requirements on the accuracy and stability of the coating equipment.

[0004] In addition, traditional absorption films also have the problem of poor environmental stability. Taking carbon-based films (such as diamond-like carbon films, DLC) as an example, although they have a high absorption rate, they have large internal stress and are prone to cracking during use, seriously affecting the performance and life of the film. Although the interference cutoff film can achieve selective transmission or cutoff of the band to a certain extent, its film thickness is relatively large, which not only increases the volume and weight of the film, but also limits the adjustment range of the bandwidth, making it difficult to meet some application scenarios that require thin films and high bandwidth flexibility.

[0005] Tantalum oxide is commonly used in optical thin film dielectric film materials due to its high refractive index (~2.1@2μm) and excellent comprehensive properties such as high resistance to laser damage and good environmental adaptability. However, when it is applied to the preparation of short-wave infrared absorption films, it also faces unique challenges. During the vacuum coating process, tantalum oxide shows a strong sensitivity to oxygen. Even a slight change in the oxygen flow rate will affect the tantalum oxide (Ta2O 5-x), which in turn changes its optical properties. It is not easy to precisely control the flow rate of the reactive gas oxygen (O2). On the one hand, the oxygen flow control accuracy of the coating equipment is limited, making it difficult to achieve the theoretically required level of accuracy. On the other hand, other factors in the coating process, such as vacuum degree, substrate temperature, evaporation rate, etc., will also interact with the oxygen flow rate, further increasing the difficulty of precise control.

[0006] Studies have shown that Ta2O 5-x The stoichiometric ratio has a significant impact on its optical properties: in the absence of oxygen (such as Ta2O 5-x , x < 5), the short-wavelength region produces strong absorption due to the increase in defect states, while the mid-infrared optical constants change little. However, accurately controlling this specific stoichiometric ratio in the actual preparation process and achieving the coordinated optimization of short-wavelength absorption and mid-infrared transmission requires overcoming numerous technical obstacles. For example, how to establish a precise mathematical model between oxygen flow rate and stoichiometric ratio, how to monitor and provide feedback on the stoichiometric ratio and optical properties of the film in real time, and how to adjust process parameters in a timely manner based on the monitoring results are all urgent issues to be addressed. Summary of the Invention

[0007] In order to overcome the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing a short-wave absorption cutoff film. By controlling the oxygen flow rate during the reactive evaporation deposition process and combining thin film design and preparation technology, the synergistic optimization of short-wave absorption and mid-infrared transmission is achieved, forming high absorption in the short-wave region (≤1.0μm) while maintaining low-loss transmission in the infrared band (≥2.0μm).

[0008] The technical solutions provided by the present invention are as follows:

[0009] A method for preparing a short-wave absorption cutoff film is characterized in that it comprises the following steps:

[0010] Using metal tantalum (Ta) as the evaporation raw material, reactive evaporation deposition is carried out in a vacuum coating equipment;

[0011] Oxygen (O2) is introduced with an oxygen flow rate controlled at 5-50 sccm, and argon (Ar) plasma is used for assisted oxidation with an argon flow rate of 5-30 sccm;

[0012] By controlling the oxygen flow rate, the tantalum oxide film (Ta2O 5-x , x<5), the stoichiometric ratio of tantalum oxide film produces ≤80% absorption in the short-wave region (≤1.0μm) while maintaining stable optical constants in the infrared band (≥2.0μm);

[0013] Tantalum oxide is used as the high refractive index material H and silicon dioxide is used as the low refractive index material L. The multilayer film stack structure is obtained by optimizing the film system design software.

[0014] Furthermore, the background vacuum degree of the vacuum coating equipment is ≤5×10 -4 Pa, substrate temperature is 100-300°C, and the deposition rate of metal tantalum is 0.1-0.6nm / s.

[0015] Furthermore, the substrate material is K9 glass, fused quartz, CaF2 or Al2O3.

[0016] Furthermore, the plasma assist adopts a radio frequency ion source with an operating frequency of 13.56 MHz and a substrate bias voltage of -50 to -150 V.

[0017] Furthermore, the short-wave absorption cut-off film is made of Ta2O 5-x (high refractive index layer) and SiO (low refractive index layer) are stacked alternately, and the specific film layer thickness ratio is optimized by thin film design software.

[0018] Furthermore, when the oxygen flow rate is 12-20 sccm, the average transmittance of the film in the 0.4-1.0 μm band is less than 5%, and the average transmittance in the 2.0-4.0 μm band is greater than 90%.

[0019] Furthermore, the method further includes: after the prepared film is subjected to a humidity and heat test (85°C / 85% RH, 96h) and a salt spray test (5% NaCl, 48h), the film transmittance changes by less than 0.5% and the film layer does not fall off.

[0020] The present invention also provides a short-wave absorption cut-off film, which is characterized in that it is prepared by the above method and has a film layer structure of substrate / (Ta2O 5-x / SiO) n / Air, wherein n is an integer of 3-15, wherein the Ta2O 5-x The stoichiometric ratio x of the layer is less than 5, and the average transmittance in the 0.4-1.0 μm band is less than 5%, and the average transmittance in the 2.0-4.0 μm band is greater than 90%.

[0021] Compared with the prior art, the present invention has the following technical effects:

[0022] (1) Utilizing the sensitivity of tantalum oxide to oxygen, the reaction gas flow rate is precisely controlled to directly regulate the Ta2O 5-xThe stoichiometric ratio achieves shortwave absorption and transmission in the target infrared band without the need for doping or post-processing, simplifying the film structure. By inducing shortwave defect state absorption through oxygen-deficient states (x < 5), the film maintains stable infrared optical constants, achieving a synergistic "high absorption and high transmission" strategy. Average transmittance in the 400-1000nm band is <5% (down to 0.7%), and the extinction coefficient k@600nm is increased to 0.01-0.025, a 10-25x improvement over traditional tantalum oxide films (k ~ 0.001). Average transmittance in the 2.0-4.0μm band is >90% (up to 95.8%), and the infrared extinction coefficient k@2μm is stabilized below 0.001, addressing the high infrared loss issues of traditional absorber films.

[0023] (2) Using a single metal tantalum evaporation source, combined with plasma-assisted oxidation, compatible with conventional PVD equipment, reducing production costs;

[0024] (3) The film layer has high mechanical properties and strong environmental adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 :Ta2O under different oxygen flow rates 5-x Extinction coefficient change curve of the film.

[0026] Figure 2 : Schematic diagram of the film structure of Example 1.

[0027] Figure 3 : Transmittance spectrum curve of Example 1.

[0028] Figure 4 : Schematic diagram of the structure of the film S1 mask system of Example 2.

[0029] Figure 5 : Schematic diagram of the structure of the film S2 mask system of Example 2.

[0030] Figure 6 : Transmittance spectrum curve of Example 2. DETAILED DESCRIPTION

[0031] The specific examples of the present invention are described in detail below with reference to the accompanying drawings.

[0032] 1. Materials and Process: Using high-purity tantalum as the evaporation source, oxygen (O) is introduced into the reactive evaporation deposition, combined with argon plasma assistance to enhance the oxidation reaction of tantalum. The oxygen flow rate is controlled at 5-50sccm, and the formation of Ta2O is induced by reducing the oxygen supply. 5-x The non-stoichiometric structure (x<5) increases short-wave (≤1.0μm) absorption.

[0033] 2. Optical Performance Control: Film transmittance was measured using a UV / visible / near-infrared spectrophotometer, and optical constants were fitted by constructing an appropriate dispersion model. Experimental results showed that when the oxygen flow rate was reduced from 50 sccm to 20 sccm, the shortwave extinction coefficient k@1μm increased from 0.0001 to 0.01, while the infrared extinction coefficient k@2μm remained essentially unchanged.

[0034] 3. Film system design: Ta2O 5-x (x<5) and SiO2 are used as high-refractive-index materials and low-refractive-index materials, respectively. According to the spectral characteristics of the cutoff band and the target transmission band, and based on the obtained optical constants and the corresponding relationship between different oxygen flow rates and the extinction coefficient of the tantalum oxide film, the appropriate oxygen flow rate is selected and the film system structure is optimized using thin film design software (TFCalc, EssentialMacleod or Optilayer, etc.) to meet the transmittance requirements of the short-wave cutoff and infrared bands.

[0035] Example 1: Laser protection window

[0036] Index requirements: short wave (0.4-1.0μm) transmittance <5%, infrared band (2.0-2.5μm) transmittance >90%, substrate is fused quartz.

[0037] The specific steps are as follows:

[0038] (1) Film structure design: Based on the corresponding relationship between different oxygen flow rates and the extinction coefficient of tantalum oxide film ( Figure 1 As shown), the oxygen flow rate is determined to be 20 sccm. Under this oxygen flow condition, tantalum oxide is selected as the high refractive index material H, silicon dioxide is selected as the low refractive index material L, and the single-sided film system structure is designed, specifically: Sub / 0.17H0.14L0.17H0.06L0.44H0.14L0.34H0.14L0.20H0.16L0.16H0.19L0.18H0.15L0.18H0.20L0.14H / Air, where Sub represents the substrate (fused silica) and Air represents air. Figure 2 shown.

[0039] (2) Coating process: Background vacuum 5×10 -4 Pa, substrate temperature 150℃, high refractive index material preparation, using metal tantalum as raw material, by evaporating metal Ta for deposition, the deposition rate is 0.1nm / s, filling O2 during the evaporation process, the flow rate is 20sccm, and using Ar plasma assistance, the Ar flow rate is 10sccm, and finally depositing (1) film system on the surface of the quartz substrate.

[0040] (3) Performance test: The transmittance of the film was tested using a UV / visible / near-infrared spectrophotometer. The results showed that the average transmittance in the short wave band was 1.8%, and the average transmittance in the infrared band was 92.6%. The spectral curve is as follows: Figure 3 shown.

[0041] (4) Environmental test: Refer to GJB150-2009 and conduct environmental tests such as humidity and heat test and salt spray test. After the test, the film layer does not fall off and the transmittance change is <0.5%.

[0042] Example 2: CaF2 lens filter film

[0043] Index requirements: short-wave cutoff 0.7-1μm transmittance <1%, infrared band (2.0-4.0μm) transmittance >95%.

[0044] The specific steps are as follows:

[0045] (1) Combined with the index requirements and the corresponding relationship between different oxygen flow rates and the extinction coefficient of tantalum oxide films ( Figure 1 As shown), the oxygen flow rate can be selected as 12sccm. At this flow rate, tantalum oxide is used as the high refractive index material H, and silicon dioxide is used as the low refractive index material L to design a double-sided film system structure: the S1 surface has both short-wave filter cutoff and target infrared band anti-reflection function, and the S2 surface only has the target infrared band anti-reflection function. The S1 mask system structure is: Sub / 0.24L0.07H0.39L0.11H0.24L0.13H0.32L0.15H0.25L0.10H0.23L0.16H0.17L0.19H0.17L0.19H0.11L0.15H0.62L / Air, the S1 mask system structure is: Sub / 0.36L0.16H0.32L0.25H0.69L / Air, where Sub represents the substrate and Air represents air. The schematic diagrams of the S1 and S2 mask system structures are shown as follows: Figure 4 、 Figure 5 shown.

[0046] (2) Coating process: Background vacuum 5×10 -4 Pa, substrate temperature 300 ° C, high refractive index metal tantalum is used as raw material, the evaporation metal Ta deposition rate is 0.1nm / s, the O2 flow rate during the evaporation process is 12sccm, Ar plasma assistance is used, and its flow rate is 5sccm. Finally, the S1 surface and S2 surface film system are deposited on both sides of the CaF2 substrate respectively.

[0047] (3) Performance test: The transmittance of the film was tested using a UV / visible / near-infrared spectrophotometer. The results showed that the average transmittance in the short wave band was 0.7%, and the average transmittance in the infrared band was 95.8%. The spectral curve is as follows: Figure 6 shown.

[0048] (4) Environmental test: Refer to GJB150-2009 and conduct environmental tests such as humidity and heat test and salt spray test. After the test, the film layer does not fall off and the transmittance change is <0.5%.

[0049] Through collaborative innovation in "materials-processes-structures", this invention achieves a performance balance between short-wave absorption and infrared transmission, resolving core contradictions in existing technologies such as "high absorption must sacrifice transmittance" and "complex processes in exchange for performance", providing a reliable solution for the new generation of optical systems.

[0050] The above description is only a preferred example of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a short-wave absorbing cutoff film, characterized in that: The steps include: Using metal tantalum (Ta) as the evaporation raw material, reactive evaporation deposition is carried out in a vacuum coating equipment; Oxygen (O2) is introduced with an oxygen flow rate controlled at 5-50 sccm, and argon (Ar) plasma is used for assisted oxidation with an argon flow rate of 5-30 sccm; By controlling the oxygen flow rate, the tantalum oxide film (Ta2O 5-x , x<5), the stoichiometric ratio of tantalum oxide film produces ≤80% absorption in the short-wave region (≤1.0μm) while maintaining stable optical constants in the infrared band (≥2.0μm); Tantalum oxide is used as the high refractive index material H and silicon dioxide is used as the low refractive index material L. The multilayer film stack structure is obtained by optimizing the film system design software.

2. The method for preparing a short-wave absorbing cutoff film according to claim 1, wherein: The background vacuum degree of the vacuum coating equipment is ≤5×10 -4 Pa, substrate temperature is 100-300°C, and the deposition rate of metal tantalum is 0.1-0.6nm / s.

3. The method for preparing a short-wave absorbing cutoff film according to claim 1, wherein: The substrate material is K9 glass, fused quartz, CaF2 or Al2O3.

4. The method for preparing a short-wave absorbing cutoff film according to claim 1, wherein: The plasma assist adopts a radio frequency ion source with an operating frequency of 13.56 MHz and a substrate bias voltage of -50 to -150 V.

5. The method for preparing a short-wave absorbing cutoff film according to claim 1, wherein: The short-wave absorption cut-off film adopts Ta2O 5-x (high refractive index layer) and SiO (low refractive index layer) are stacked alternately, and the specific film layer thickness ratio is optimized by thin film design software.

6. The method for preparing a short-wave absorbing cutoff film according to claim 1, wherein: When the oxygen flow rate is 12-20 sccm, the average transmittance of the film in the 0.4-1.0 μm band is less than 5%, and the average transmittance in the 2.0-4.0 μm band is greater than 90%.

7. The method for preparing a short-wave absorbing cutoff film according to any one of claims 1 to 6, characterized in that: Also includes: After the prepared film was subjected to a humidity and heat test (85°C / 85% RH, 96h) and a salt spray test (5% NaCl, 48h), the film transmittance changed by less than 0.5% and the film layer did not fall off.

8. A short-wave absorption cut-off film, characterized in that Prepared by the method according to any one of claims 1 to 7, the film structure is substrate / (Ta2O 5-x / SiO) n / Air, wherein n is an integer of 3-15, wherein the Ta2O 5-x The stoichiometric ratio x of the layer is less than 5, and the average transmittance in the 0.4-1.0 μm band is less than 5%, and the average transmittance in the 2.0-4.0 μm band is greater than 90%.

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