A wide-temperature-range stable dual-band infrared filter for extreme environment and a preparation method thereof

Abstract

The application relates to a wide-temperature-range stable dual-band infrared filter for extreme environments and a preparation method thereof, which comprises a front film system, a substrate and a back film system; the front film system and the back film system are both composed of alternately superimposed germanium layers and zinc sulfide film layers; the infrared filter has a drift amount of a passband center wavelength less than 0.05% in a temperature range of-120 DEG C to +85 DEG C. The application remarkably reduces the internal stress of the film layer through an optimized film system design, thereby realizing excellent stability of optical performance under extreme temperature environments, solving technical problems of some special infrared spectrum detection systems working in a wide temperature range, and providing a reliable solution for high-end aerospace infrared applications.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical filters, and particularly relates to a wide-temperature-range stable dual-band infrared filter for extreme environments and a preparation method thereof. BACKGROUND

[0002] In the field of aerospace and deep space exploration, infrared spectral detection systems need to accurately analyze specific gas components (such as carbon dioxide and water vapor). One of the core components of such systems is a dual-band infrared filter. However, existing dual-band filters face extreme low temperatures (about -120℃) on the surface of Mars, large day-night temperature differences, or dramatic internal temperature fluctuations (such as -55℃ to +85℃) in unmanned aerial vehicle systems. Due to the mismatch of the thermal expansion coefficients of the film layers and the substrate, a large thermal stress is generated, causing the central wavelength of the film layer to shift significantly, the transmittance to decrease, and even the film layer to crack and wrinkle, resulting in inaccurate detection data and shortened device lifespan. Currently, there is a lack of infrared filter products on the market that can maintain high optical performance stability in such a wide temperature range. Therefore, there is an urgent need for an infrared filter solution that can maintain high performance stability in extreme temperature environments. SUMMARY

[0003] The technical problem to be solved by the present application is to provide a wide-temperature-range stable dual-band infrared filter for extreme environments and a preparation method thereof, aiming to solve the key technical problems of excessive wavelength shift and film layer failure of existing infrared filter products in extreme temperature environments.

[0004] The present application provides a wide-temperature-range stable dual-band infrared filter for extreme environments, comprising a front film system, a substrate, and a back film system; the front film system and the back film system are both composed of alternating and superimposed germanium layers and zinc sulfide film layers; the infrared filter has a wavelength shift of less than 0.05% in the temperature range of -120℃ to +85℃.

[0005] Preferably, the substrate is a germanium substrate.

[0006] Preferably, the substrate has a diameter of 10-15mm and a thickness of 0.5-3mm.

[0007] Preferably, the film layer structure of the front film system is: Sub / 100.00H 97.90L... 135.64H 220.54L 358.95H / Air, wherein Sub represents the substrate, Air represents air, H represents a germanium film layer with physical thickness, and L represents a zinc sulfide film layer with physical thickness; the design wavelength of the film layer structure is 3360nm.

[0008] Preferably, the front film system has a total of 30-35 layers.

[0009] Preferably, the film layer structure of the back film system is: Sub / 100.00H 671.37L... 76.63H 477.68L / Air, wherein Sub represents the substrate, Air represents air, H represents a germanium film layer in physical thickness, and L represents a zinc sulfide film layer in physical thickness; and the design wavelength of the film layer structure is 5200nm.

[0010] Preferably, the total number of layers of the back film system is 60-65 layers.

[0011] The application also provides a preparation method of the wide-temperature-range stable dual-band infrared filter for extreme environments.

[0012] (1) ultrasonic cleaning and drying of the substrate;

[0013] (2) baking and heating of the substrate under vacuum conditions;

[0014] (3) treatment of the front surface of the substrate using a high-energy ion beam, followed by plating of a film system structure on the front surface of the substrate, and then annealing treatment, and after cooling to a specified temperature, first point release and then air introduction;

[0015] (4) repeating steps (1)-(3) to plate a film system structure on the back surface of the substrate to obtain the wide-temperature-range stable dual-band infrared filter.

[0016] Preferably, the plating process in steps (3) and (4) uses an electron beam with an 8-hole crucible and a 6-position evaporation plating machine.

[0017] Preferably, the annealing treatment is performed at 200℃ for 2 hours, then cooled to 60℃ at a rate of 0.5℃ / min, and then point release and air introduction are performed.

[0018] Preferably, the parameters for the treatment of the front surface of the substrate using a high-energy ion beam are: an anode voltage of 150V, an anode current of 3A, a cathode current of 18A, and a bombardment time of 20 minutes.

[0019] Advantages

[0020] The application significantly reduces the internal stress of the film layer by optimizing the film system design, thereby achieving excellent stability of optical performance in extreme temperature environments, solving the technical difficulties of some special infrared spectrum detection systems working in a wide temperature range, and providing a reliable solution for high-end aerospace infrared applications. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 FIG. 1 is a structural schematic diagram of the wide-temperature-range stable dual-band infrared filter for extreme environments according to the application; wherein 1 is the front film system, 2 is the substrate, and 3 is the back film system.

[0022] Figure 2 This is a graph showing the transmittance of the main peak (front) membrane system in Example 1.

[0023] Figure 3 This is a graph showing the permeability of the secondary peak (back side) membrane system in Example 1.

[0024] Figure 4 The transmittance curve of the wide-temperature-range stable dual-band infrared filter prepared for extreme environments in Example 1 is shown.

[0025] Figure 5 This is a schematic diagram of the process for preparing a wide-temperature-range stable dual-band infrared filter for extreme environments according to the present invention. Detailed Implementation

[0026] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0027] Example 1

[0028] Depend on Figure 1 As shown, this embodiment provides a wide-temperature-range stable dual-band infrared filter for extreme environments, comprising a front film system, a substrate, and a back film system; both the front and back film systems are composed of alternating layers of germanium and zinc sulfide; the substrate is a germanium substrate with a diameter of 12.7 mm (0.5 inches) and a thickness of 1.0 mm. The front film system has a total of 33 layers, and the back film system has a total of 62 layers.

[0029] Compared with the prior art, the advantages of the present invention are that, through specific film system design and preparation process, the passband center wavelength drift is less than 0.05% in a wide temperature range of -120℃ to +85℃, while maintaining high transmittance in two target wavelength bands of 2.70-2.74µm & 4.24-4.28µm, and depth cutoff of less than 0.5% in other wavelength bands.

[0030] Depend on Figure 5 As shown, this embodiment also provides a method for fabricating a wide-temperature-range stable dual-band infrared filter for extreme environments, comprising the following steps:

[0031] The optical film is prepared by using an electron beam with 8-hole crucible and a 6-position resistance evaporation coating machine. The germanium material is evaporated by electron beam evaporation, and the zinc sulfide material is evaporated by molybdenum boat thermal evaporation. The evaporation rate of the germanium film layer is 5-7 Å / s, and the evaporation rate of the zinc sulfide film layer is 10-12 Å / s.

[0032] The film layer is adjusted in real time by quartz crystal oscillator signal feedback to maintain the set evaporation rate by PID control of the evaporation source power, and the evaporation is automatically stopped after reaching the target thickness.

[0033] (1) The substrate is cleaned by full-automatic ultrasonic wave, and after cleaning, IPA is used for dehydration of the substrate.

[0034] (2) The substrate is placed on the umbrella disc in the vacuum chamber of the coating machine, vacuumizing and baking heating, and the baking temperature is set to 180℃, and the baking time is greater than 180min.

[0035] (3) After the vacuum reaches 3.0x10 -4 Pa, the front surface of the substrate is bombarded by low-energy argon ions, the bombardment time is 20min, and the bombardment parameters are anode voltage 150V, anode current 3A, and cathode current 18A.

[0036] (4) The main peak film system structure is coated on the front surface of the substrate, and the main peak film system structure includes: Sub / 100.00H97.90L 209.47H 534.14L 224.56H 276.90L 176.37H 276.74L 312.93H 343.02L161.28H 132.08L 598.49H 373.18L 207.40H 373.75L 207.16H 373.24L 206.71H371.64L 205.59H 366.31L 201.45H 352.67L 294.80H 333.53L 190.29H 536.92L251.74H 303.94L 135.64H 220.54L 358.95H / Air, wherein Sub represents the substrate, Air represents air, H represents the germanium film layer with physical thickness, L represents the zinc sulfide film layer with physical thickness, the numbers in the film system formula represent the physical thickness of the film layer, and the design wavelength is 3360nm. The obtained main peak film system structure is shown in Figure 2 , the transmittance in the wavelength band of 2850-4100nm is effectively suppressed, and the transmittance in the wavelength bands of 2600-2745nm and 4235-4400nm is effectively improved.

[0037] (5) After the main peak film system structure is plated, the infrared filter is annealed, the annealing temperature is 200℃, the constant temperature time is 2 hours, and the cooling speed is 0.5℃ / min.

[0038] (6) When the temperature drops to 60℃, manually point to release gas 8 times, and then continuously introduce air into the vacuum chamber, the point release requires 2 seconds to release and 10 seconds to stop.

[0039] (7) The plated substrate is cleaned with a full-automatic ultrasonic wave, and after cleaning, IPA is used to dehydrate the substrate.

[0040] (8) The substrate is placed on the umbrella disc in the vacuum chamber of the plating machine, vacuumizing and baking heating, the baking temperature is set to 180℃, and the baking time is greater than 180min.

[0041] (9) After the vacuum reaches 3.0x10 -4 Pa, the back surface sub-peak film system structure is plated on the other side of the substrate, including: Sub / 100.00H 671.37L 283.90H 46.79L 51.85H 575.89L 384.13H 435.88L 270.36H 553.89L 376.60H 623.56L 307.86H 590.03L 221.37H 672.36L 261.66H 721.09L 209.46H 145.51L 26.68H 618.98L 390.26H 362.25L 88.59H 318.43L 253.82H 761.04L 401.55H 364.91L 106.41H 128.21L 531.62H 376.34L 545.05H 560.10L 608.52H 719.25L 543.85H 752.27L 371.45H 766.23L 381.64H 839.75L 100.13H 188.68L 119.23H 198.32L 92.41H 275.50L 142.59H 182.50L 95.75H 225.16L 121.07H 700.70L 36.51H 587.11L 85.63H 212.00L 76.63H 477.68L / Air, wherein Sub represents the substrate, Air represents air, H represents a germanium film layer with physical thickness, and L represents a zinc sulfide film layer with physical thickness, the numbers in the film system formula represent the physical thickness of the film layer, and the design wavelength is 5200nm. The obtained sub-peak film system structure is composed of Figure 3As shown, the transmittance in the 1650-2650 nm and 4400-7000 nm wavebands is effectively inhibited, and the transmittance in the 2695-2850 nm and 4100-4285 nm wavebands is effectively improved.

[0042] (10) After the back film system structure is plated, the infrared filter is annealed, the annealing temperature is 200°C, the constant temperature time is 2 hours, and the cooling rate is 0.5°C / min.

[0043] (11) When the temperature drops to 60°C, manually point to release air 8 times, and then continue to introduce air into the vacuum chamber, and the point release requires 2 seconds to release and 10 seconds to stop.

[0044] By Figure 4 As shown, the substrate in the embodiment satisfies the technical requirements that T≥90%, Tavg≥94% at 23°C and an incident angle of 0° in the 2.70-2.74 µm & 4.24-4.28 µm wavebands, and T≤0.5% in the 1.0-2.5 µm & 3.0-4.0 µm & 4.5-7 µm wavebands. At the same time, the center wavelength drift of the passband of the filter is less than 0.05% in the temperature range of -120°C to +85°C, and the center wavelength drift is less than 0.1% in the incident angle range of 0-10°, and is recorded as sample A.

[0045] Comparative Example 1

[0046] Preparation of a conventional process filter:

[0047] To verify the superiority of the process of the present application, a comparative filter is prepared. The only difference between it and Example 1 is in the following key process parameters, and the rest of the conditions are the same: baking temperature: 160°C; ion bombardment parameters: anode voltage 180V, anode current 4A, cathode current 21A; annealing temperature: 180°C; annealing cooling rate: 1.0°C / min; annealing point release operation: none. This comparative sample is marked as sample B.

[0048] Performance test and comparative analysis: sample A (the present application) and sample B (the comparative example) are tested as follows at the same time:

[0049] 1. Initial performance test: under the conditions of 23°C and an incident angle of 0°, the spectral curve is measured using a Fourier transform infrared spectrometer. The results show that both samples basically meet the initial optical indicators: T≥90%, Tavg≥94% in the 2.70-2.74 µm & 4.24-4.28 µm wavebands.

[0050] 2. Environmental reliability test: two samples were placed in a high-low temperature test chamber, and temperature cycle test from -120°C to +85°C was carried out, and the cycle number was 100 times. The temperature change rate was set to 10°C / min, and each high and low temperature was kept for 30 minutes.

[0051] 3. Final performance test: after the temperature cycle, the spectral curve of the two samples was measured again under the same conditions.

[0052] The test results are shown in the following table:

[0053]

[0054] From the above table data, it can be seen that:

[0055] 1. The sample A prepared by the process of the application has a center wavelength drift of less than 0.05% in both passbands after severe temperature cycle test, showing extremely excellent spectral stability, fully meeting the design requirements.

[0056] 2. The center wavelength drift of sample B prepared by the conventional process is close to 0.5%, which is more than one order of magnitude higher than that of the sample of the application. This means that in actual detection, it will cause the detection channel to deviate from the target gas absorption peak seriously, resulting in inaccurate data.

[0057] 3. In terms of film layer reliability, the process of the application (sample A) effectively suppresses film layer cracking, while the conventional process (sample B) has shown signs of failure.

[0058] Conclusion:

[0059] The above comparative experiments fully prove that the specific process parameter combination provided by the application (including but not limited to higher baking and annealing temperature, slower cooling rate, mild ion bombardment and point gas operation) is not a routine selection or simple optimization of those skilled in the art. The combination produces a synergistic effect, unexpectedly and significantly improves the spectral stability and structural reliability of the optical filter in an extremely wide temperature range environment, and solves the long-standing technical problem in the field. Therefore, the application has significant progress and inventiveness.

[0060] The film layer reliability was verified by constant temperature and humidity test at a temperature of 85°C and a relative humidity of 85% (referring to JESD22-A101 or related standards), and no film layer peeling phenomenon was found.

[0061] The sample was tested by three times of pulling force test using 3M 600 adhesive tape meeting the requirements of ASTM D3359 standard, and no film layer peeling phenomenon was found, indicating that the adhesion of the filter film layer is firm.

[0062] It should be understood that the embodiments disclosed herein are merely for the purpose of illustration and the details thereof should not be construed as limiting the scope of the present application. Modifications, substitutions or variations of the described embodiments, such as equivalent replacements in the film system structure, process parameters, etc., which can achieve the same wide temperature range stability objective, should be considered as falling within the scope of the present application as defined by the claims.

Claims

1. A wide temperature stable dual band infrared filter for extreme environments, characterized in that, The infrared filter comprises a front film system, a substrate and a back film system; the front film system and the back film system are both composed of alternately stacked germanium layers and zinc sulfide film layers; the infrared filter has a drift of less than 0.05% in the passband center wavelength in the temperature range of-120℃ to +85℃; The film layer structure of the front film system is: Sub / 100.00H 97.90L 209.47H 534.14L 224.56H 276.90L 176.37H 276.74L 312.93H 343.02L 161.28H 132.08L 598.49H 373.18L 207.40H 373.75L 207.16H 373.24L 206.71H 371.64L 205.59H 366.31L 201.45H 352.67L 294.80H 333.53L 190.29H 536.92L 251.74H 303.94L 135.64H 220.54L 358.95H / Air, wherein Sub represents the substrate, Air represents air, H represents a germanium film layer in physical thickness, L represents a zinc sulfide film layer in physical thickness, the numbers in the film system structure formula represent the physical thickness of the film layer, and the design wavelength of the film layer structure is 3360nm; The film layer structure of the back film system is: Sub / 100.00H 671.37L 283.90H 46.79L 51.85H 575.89L 384.13H 435.88L 270.36H 553.89L 376.60H 623.56L 307.86H 590.03L 221.37H 672.36L 261.66H 721.09L 209.46H 145.51L 26.68H 618.98L 390.26H 362.25L 88.59H 318.43L 253.82H 761.04L 401.55H 364.91L 106.41H 128.21L 531.62H 376.34L 545.05H 560.10L 608.52H 719.25L 543.85H 752.27L 371.45H 766.23L 381.64H 839.75L 100.13H 188.68L 119.23H 198.32L 92.41H 275.50L 142.59H 182.50L 95.75H 225.16L 121.07H 700.70L 36.51H 587.11L 85.63H 212.00L 76.63H 477.68L / Air, wherein Sub represents a substrate, Air represents air, H represents a germanium film layer in physical thickness, L represents a zinc sulfide film layer in physical thickness, the numbers in the film system structure formula represent the physical thickness of the film layer, and the design wavelength of the film layer structure is 5200nm.

2. The wide temperature stable dual band infrared filter according to claim 1, wherein, The substrate is a germanium substrate.

3. The dual-band infrared filter of claim 1, wherein the first and second infrared passbands are centered at 3.7 μm and 4.8 μm, respectively. The substrate has a diameter of 10-15mm and a thickness of 0.5-3mm.

4. A method for preparing the wide temperature range stable dual-band infrared filter for extreme environments according to any one of claims 1 to 3, characterized in that, The method comprises the following steps: (1) ultrasonic cleaning and drying the substrate; (2) baking and heating the substrate under vacuum; (3) treating the front surface of the substrate using low-energy argon ions, then plating the film system structure on the front surface of the substrate, and then performing annealing treatment, and after cooling to a specified temperature, first spot placing and then introducing air; (4) repeating steps (1)-(3) to plate the film system structure on the back surface of the substrate to obtain a wide-temperature-range stable dual-band infrared filter.

5. The preparation method according to claim 4, characterized in that, The plating process in steps (3) and (4) uses an electron beam with an 8-hole crucible and a 6-position evaporation plating machine.

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