Multispectral coating method for linear gradient filter and linear gradient filter

Abstract

The application provides a multispectral coating method of a linear gradient filter and the linear gradient filter, and the method comprises the following steps: S1, placing optical glass into a cleaning agent for ultrasonic cleaning to obtain a substrate of the linear gradient filter to be coated; S2, placing the substrate into a reaction cavity of a radio frequency magnetron, closing the reaction cavity, and setting environmental parameters for multispectral coating; S3, under the environmental parameters, using a double-target radio frequency magnetron to sputter and deposit target materials on the surface of the substrate, wherein SiO2 and Si are used as the target materials of the double-target, and the power interval of the radio frequency magnetron is adjusted to switch the sputtering and deposition of the target materials of different target positions alternately; and S4, closing the radio frequency magnetron, keeping the reaction cavity airtight, naturally cooling the reaction cavity to a preset cooling temperature, opening the reaction cavity, and taking out the substrate with the coating as the linear gradient filter. The application has a simple process, good infrared spectral performance of the filter product, and is suitable for various scenes.

Description

Technical Field

[0001] This invention relates to the field of optical coating technology, and particularly to a multispectral coating method for a linear gradient filter and the linear gradient filter itself. Background Technology

[0002] As a core spectroscopic element in multispectral detection, the coating performance of a linear graded filter (LVF) directly determines its spectral resolution, transmittance, and environmental adaptability. The coating of a LVF is primarily achieved by physically controlling the deposition time or particle flux to change linearly in a single direction, ultimately resulting in a linear gradient in film thickness. This film thickness directly determines its optical properties, thus achieving the linearly graded filtering effect.

[0003] However, existing linear graded filter coating methods have the following problems:

[0004] First, there is the issue of the material system. Traditional linear gradient filters often use heterogeneous material combinations such as TiO2 / Al2O3 and Nb2O5 / SiO2. This means that the manufacturing of the filter requires the purchase of a variety of high-purity target materials. The thermal expansion coefficients of different materials vary greatly, which can easily lead to film cracking or spectral drift.

[0005] Secondly, the manufacturing process is complicated. Existing coating methods require switching between multiple machines to complete the deposition of different material films. For example, a high refractive index layer is first deposited by electron beam evaporation, and then a low refractive index layer is deposited by magnetron sputtering. The time spent on transfer between processes accounts for more than 30%, and each machine needs to be calibrated separately, which has a significant impact on production capacity.

[0006] Third, the short-wave infrared adaptability of the final linear gradient filter is poor. The 900nm~1700nm infrared band has extremely high requirements for the uniformity of the filter film system. The peak transmittance of the film system made by the existing coating method is generally less than 75% in this band, and the cutoff band transmittance is more than 2%, which cannot meet the requirements of multispectral detection for signal-to-noise ratio.

[0007] Therefore, it is necessary to propose a new multispectral coating method for linear gradient filters to solve the above problems. Summary of the Invention

[0008] This invention provides a multispectral coating method for a linear gradient filter and a linear gradient filter, aiming to solve the technical problems of high material cost, numerous process steps, and poor short-wave infrared performance of the finished product in existing processes.

[0009] To address the aforementioned technical problems, in a first aspect, the present invention provides a multispectral coating method for a linear gradient filter, comprising the following steps:

[0010] S1. The optical glass is placed in a cleaning agent and ultrasonically cleaned to obtain the substrate of the linear gradient filter to be coated.

[0011] S2. Place the substrate into the reaction chamber of the radio frequency magnetron and set the environmental parameters for multispectral coating;

[0012] S3. Under the environmental parameters, the target material is sputtered and deposited on the surface of the substrate by the dual target positions of the radio frequency magnetron. The dual target positions use SiO2 and Si as target materials respectively, and different target materials are sputtered and deposited alternately by switching between different target positions.

[0013] S4. Turn off the radio frequency magnetron, keep the reaction chamber sealed and allow it to cool naturally to the preset cooling temperature, then open the reaction chamber and remove the coated substrate as the linear gradient filter.

[0014] Furthermore, the cleaning agent includes a neutral cleaning solution, deionized water, and isopropanol. In step S1, the optical glass is sequentially immersed in the neutral cleaning solution, the deionized water, and the isopropanol for ultrasonic cleaning.

[0015] Furthermore, the optical glass is K9 glass.

[0016] Furthermore, step S1 also includes:

[0017] After ultrasonic cleaning, the substrate is dried using nitrogen gas with a purity of 99.99%.

[0018] Furthermore, the environmental parameters in step S2 include:

[0019] Vacuum level, set to 1×10 -6 ~3×10 -6 torr;

[0020] The atmosphere was set to maintain an intracavitary pressure of 1 mtorr by 18-20 sccm of argon gas with a purity of 99.999%.

[0021] Set the temperature to 110~120℃.

[0022] Furthermore, in step S3, the two target sites are a SiO2 target with a purity of 99.99% and a Si target with a purity of 99.999%.

[0023] Furthermore, in step S3, during the step of alternating sputtering deposition of different target materials at different target sites, a lower reflective layer, a resonant cavity layer, an upper reflective layer, and a long-wavelength pass layer are successively deposited on the surface of the substrate. Switching between different target sites for alternating sputtering deposition of different target materials is achieved by adjusting the power range of the RF magnetron.

[0024] The lower reflective layer is obtained by alternating deposition of SiO2 layer and Si layer four times;

[0025] The resonant cavity layer is obtained by alternating deposition of SiO2 layer and Si layer 6 to 8 times;

[0026] The upper reflective layer is obtained by alternating deposition of SiO2 layer and Si layer four times;

[0027] The long-wavelength pass-through layer is obtained by alternating deposition of SiO2 and Si layers five times.

[0028] Furthermore, the single-layer thickness of the SiO2 layer in the lower reflective layer is 50-80 nm, and the single-layer thickness of the Si layer is 30-50 nm;

[0029] The thickness of the single layer of SiO2 in the resonant cavity layer is 60-100nm, and the thickness of the single layer of Si is 40-70nm.

[0030] The single-layer thickness of the SiO2 layer in the upper reflective layer is 50-80 nm, and the single-layer thickness of the Si layer is 30-50 nm.

[0031] The single-layer thickness of the SiO2 layer in the long-wavelength pass layer is 40-60 nm, and the single-layer thickness of the Si layer is 20-40 nm.

[0032] Furthermore, the preset cooling temperature in step S4 is 50°C.

[0033] Secondly, the present invention also provides a linear gradient filter, which is prepared by the multispectral coating method for linear gradient filters described above.

[0034] The beneficial effects achieved by this invention lie in proposing a multispectral coating method for linear gradient filters. This method uses Si / SiO2 as the target material for coating, which is lower in cost than existing materials. Moreover, this method can complete the entire coating process with a single radio frequency magnetron sputtering instrument without the need for equipment switching, thus simplifying the process. The Si / SiO2 material coating also gives the finished filter better optical performance in the infrared spectrum, making it suitable for various scenarios such as multispectral detection, plastic sorting, plant identification, and tobacco virus detection. Attached Figure Description

[0035] The present invention will now be described in detail with reference to the accompanying drawings. The above and other aspects of the present invention will become clearer and more readily understood through the detailed description following the accompanying drawings. In the drawings:

[0036] Figure 1 This is a flowchart of the steps of the multispectral coating method for a linear gradient filter provided in the embodiments of the present invention;

[0037] Figure 2 This is a schematic diagram of the complete steps of the multispectral coating method for a linear gradient filter provided in the embodiments of the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0039] Please refer to Figure 1 , Figure 1 This is a flowchart illustrating the steps of a multispectral coating method for a linear graded filter provided in this invention. The multispectral coating method includes the following steps:

[0040] S1. The optical glass is placed in a cleaning agent and ultrasonically cleaned to obtain the substrate of the linear gradient filter to be coated.

[0041] S2. Place the substrate into the reaction chamber of the radio frequency magnetron and set the environmental parameters for multispectral coating;

[0042] S3. Under the environmental parameters, the target material is sputtered and deposited on the surface of the substrate by the dual target positions of the radio frequency magnetron. The dual target positions use SiO2 and Si as target materials respectively, and different target materials are sputtered and deposited alternately by switching between different target positions.

[0043] S4. Turn off the radio frequency magnetron, keep the reaction chamber sealed and allow it to cool naturally to the preset cooling temperature, then open the reaction chamber and remove the coated substrate as the linear gradient filter.

[0044] In this embodiment of the invention, the optical glass is K9 glass, which is an optical borosilicate glass with silicon dioxide (SiO2), boron oxide (B2O3), and barium oxide (BaO) as the main components. In this embodiment of the invention, SiO2 and Si are used as coating components, so the selection of substrate material is also particularly important.

[0045] The cleaning agent includes a neutral cleaning solution, deionized water, and isopropanol. In step S1, the optical glass is sequentially immersed in the neutral cleaning solution, the deionized water, and the isopropanol for ultrasonic cleaning. Preferably, the neutral cleaning solution is prepared by mixing deionized water and ethanol in a 3:1 ratio. During the ultrasonic cleaning process, the K9 glass is immersed in the neutral cleaning solution for 5 minutes of ultrasonic cleaning, then in deionized water for 5 minutes of ultrasonic cleaning, and finally in isopropanol for 3 minutes of ultrasonic cleaning.

[0046] Step S1 also includes:

[0047] After ultrasonic cleaning, the substrate is dried using nitrogen gas with a purity of 99.99%. Upon completion of step S1, ensure that the number of particles on the substrate surface is less than or equal to 1 per cm², the water residue rate is 0, and that the substrate is clean and dry.

[0048] Furthermore, the environmental parameters in step S2 include:

[0049] Vacuum level, set to 1×10 -6 ~3×10 -6 torr;

[0050] The atmosphere was set to maintain an intracavitary pressure of 1 mtorr by 18-20 sccm of argon gas with a purity of 99.999%.

[0051] Set the temperature to 110~120℃.

[0052] During implementation, the vacuum level is first controlled by a mechanical pump to 2×10⁻⁶. -2 torr, then pumped to 1×10 -6 ~3×10 -6 Torr helps reduce the adsorption of impurities.

[0053] The temperature setting is matched to the thermal expansion coefficient of Si / SiO2 to avoid film stress.

[0054] During the process, after the substrate is placed into the reaction chamber, the environmental parameters are adjusted to keep the reaction chamber sealed.

[0055] Specifically, in this embodiment of the invention, an alternating film design is achieved using a Si / SiO2 material system, and a magnetron sputtering process is implemented using a single device. In step S3, the dual targets are a SiO2 (silicon dioxide) target with a purity of 99.99% and a Si (high-purity silicon) target with a purity of 99.999%. SiO2 serves as a low-refractive-index layer with a refractive index of 1.46 at 1550 nm, while Si serves as a high-refractive-index layer with a refractive index of 3.42 at 1550 nm. The Si / SiO2 material system is approximately 30% cheaper than heterogeneous material combinations such as TiO2 / Al2O3 and Nb2O5 / SiO2, and the difference in thermal expansion coefficients between the two systems is smaller, which helps reduce cracking or spectral drift in the finished film.

[0056] During implementation, step S3, switching between different target sites for alternating sputtering deposition of different target materials, is achieved by adjusting the power range of the RF magnetron. For example, the RF power of the SiO2 target is controlled at 180~200W, the deposition rate is 0.5nm / s, and the film thickness error is monitored in real time to be ≤2nm; the RF power of the Si target is controlled at 220~250W, the deposition rate is 0.3nm / s, and the transition region at the interface with the SiO2 layer is ≤5nm. Target site switching through simple power control simplifies the process flow.

[0057] Specifically, in step S3, where different target materials are sputtered and deposited alternately at different target sites, a lower reflective layer, a resonant cavity layer, an upper reflective layer, and a long-wavelength pass layer are successively deposited on the surface of the substrate, wherein:

[0058] The lower reflective layer is obtained by alternating SiO2 and Si layers four times; the lower reflective layer is used to construct the basic reflective cavity and suppress stray light.

[0059] The resonant cavity layer is obtained by alternating deposition of SiO2 layer and Si layer 6 to 8 times; the resonant cavity layer is used to achieve linear spectral splitting of 900~1700nm and half-width ≤15nm;

[0060] The upper reflective layer is obtained by alternating deposition of SiO2 layer and Si layer four times; the upper reflective layer is used to form resonance with the lower reflective layer to improve the peak transmittance.

[0061] The long-wavelength pass-through layer is obtained by alternating deposition of SiO2 and Si layers five times; the long-wavelength pass-through layer is used to cut off short wavelengths below 900nm, and the transmittance is ≤0.1%.

[0062] Preferably, the single-layer thickness of the SiO2 layer in the lower reflective layer is 50-80 nm, and the single-layer thickness of the Si layer is 30-50 nm.

[0063] The thickness of the single layer of SiO2 in the resonant cavity layer is 60-100nm, and the thickness of the single layer of Si is 40-70nm.

[0064] The single-layer thickness of the SiO2 layer in the upper reflective layer is 50-80 nm, and the single-layer thickness of the Si layer is 30-50 nm.

[0065] The single-layer thickness of the SiO2 layer in the long-wavelength pass layer is 40-60 nm, and the single-layer thickness of the Si layer is 20-40 nm.

[0066] The coatings achieved within the aforementioned thickness range exhibit good optical performance in the infrared spectral band. Based on the specific thickness of the aforementioned film layer, the complete process steps of the coating method proposed in this embodiment of the invention are as follows: Figure 2 As shown.

[0067] Specifically, as an implementation example, the membrane parameters of a linear gradient filter adapted for tobacco virus detection can be set as follows:

[0068] Lower reflective layer: [SiO2 (60nm) - Si (40nm)] × 4, total thickness 400nm;

[0069] Resonant cavity layer: [SiO2 (80nm) - Si (50nm)]×7, total thickness 910nm (achieving linear beam splitting of 1000~1700nm, half-width 12nm);

[0070] Upper reflective layer: [SiO2 (60nm) - Si (40nm)] × 4, consistent with the lower reflective layer, with a total thickness of 400nm;

[0071] Long-wavelength through-layer: [SiO2 (50nm) - Si (30nm)] × 5, total thickness 400nm.

[0072] The remaining process parameters are set as follows:

[0073] Vacuum degree: 2×10 -6 torr;

[0074] Argon flow rate: 19 sccm;

[0075] Deposition temperature: 115℃.

[0076] Deposition power 190W, deposition rate 0.5nm / s;

[0077] Si deposition power 230W, rate 0.3nm / s.

[0078] This configuration allows the finished linear gradient filter to have better optical performance in the infrared spectrum and better results in collecting the optical characteristics of tobacco viruses.

[0079] The coating method achieved by the above parameters can be automated and controlled by a single RF magnetron, and the deposition time for a single batch is less than 2 hours, which is much shorter than the time required by existing processes.

[0080] Furthermore, the preset cooling temperature in step S4 is 50°C. It is understood that the reaction chamber remains closed until cooling is complete; natural cooling avoids membrane cracking caused by rapid cooling.

[0081] The beneficial effects achieved by this invention lie in proposing a multispectral coating method for linear gradient filters. This method uses Si / SiO2 as the target material for coating, which is lower in cost than existing materials. Moreover, this method can complete the entire coating process with a single radio frequency magnetron sputtering instrument without the need for equipment switching, thus simplifying the process. The Si / SiO2 material coating also gives the finished filter better optical performance in the infrared spectrum, making it suitable for various scenarios such as multispectral detection, plastic sorting, plant identification, and tobacco virus detection.

[0082] This invention also provides a linear graded filter, which is fabricated using the multispectral coating method for linear graded filters described in the above embodiments. It is understood that the linear graded filter fabricated using the multispectral coating method for linear graded filters proposed in this invention uses Si / SiO2 as the target material, which has lower cost and smaller difference in thermal expansion coefficients compared to heterogeneous material combinations. This provides advantages in addressing issues such as film cracking or spectral drift, and the finished filter exhibits better optical performance in the infrared spectrum.

[0083] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0084] The embodiments of the present invention have been described above with reference to the accompanying drawings. The disclosed embodiments are merely preferred embodiments of the present invention. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many equivalent changes in form under the guidance of the present invention without departing from the spirit and scope of the claims. All such changes are within the protection scope of the present invention.

Claims

1. A multi-spectral coating method for a linearly graded filter, characterized in that, The method comprises the following steps: S1, placing the optical glass into a cleaning agent for ultrasonic cleaning to obtain a substrate of the linearly variable filter to be coated; S2, placing the substrate into a reaction chamber of a radio frequency magnetron and setting environmental parameters for multi-spectrum coating; S3, under the environmental parameters, sputtering and depositing target materials on the surface of the substrate by double target positions of the radio frequency magnetron, wherein the double target positions use SiO2 and Si as target materials respectively, and the sputtering and deposition of different target materials are alternately performed by switching different target positions; S4, closing the radio frequency magnetron, keeping the reaction chamber airtight and naturally cooling to a preset cooling temperature, then opening the reaction chamber and taking out the substrate with completed coating as the linearly variable filter; The optical glass is K9 glass; The cleaning agent comprises a neutral cleaning liquid, deionized water and isopropyl alcohol, and in step S1, the optical glass is sequentially placed into the neutral cleaning liquid, the deionized water and the isopropyl alcohol for ultrasonic cleaning; The environmental parameters in step S2 comprise: Vacuum, set to 1 x 10 -6 -3 x 10 -6 torr; Atmosphere: the pressure in the chamber is maintained at 1mtorr by 18-20sccm of argon gas with a purity of 99.999%; Temperature: 110-120℃; In step S3, the double target positions are SiO2 target with a purity of 99.99% and Si target with a purity of 99.999%; In step S3, in the step of alternately performing sputtering and deposition of different target materials by switching different target positions, a lower reflection layer, a resonant cavity layer, an upper reflection layer and a long-wave pass layer are deposited on the surface of the substrate in sequence, and the switching of different target positions to alternately perform sputtering and deposition of different target materials is realized by adjusting the power range of the radio frequency magnetron, wherein: The lower reflection layer is obtained by alternately depositing SiO2 layer and Si layer 4 times; The resonant cavity layer is obtained by alternately depositing SiO2 layer and Si layer 6-8 times; The upper reflection layer is obtained by alternately depositing SiO2 layer and Si layer 4 times; The long-wave pass layer is obtained by alternately depositing SiO2 layer and Si layer 5 times.

2. The multi-spectral coating method for a linearly-varying filter according to claim 1, wherein, Step S1 further comprises: After ultrasonic cleaning, the substrate is subjected to blow-drying treatment by nitrogen gas with a purity of 99.99%.

3. The multi-spectral coating method for a linearly-varying filter according to claim 1, wherein, The single-layer thickness of the SiO2 layer in the lower reflection layer is 50-80nm, and the single-layer thickness of the Si layer is 30-50nm; The single-layer thickness of the SiO2 layer in the resonant cavity layer is 60-100nm, and the single-layer thickness of the Si layer is 40-70nm; The single-layer thickness of the SiO2 layer in the upper reflection layer is 50-80nm, and the single-layer thickness of the Si layer is 30-50nm; The single-layer thickness of the SiO2 layer in the long-wave pass layer is 40-60nm, and the single-layer thickness of the Si layer is 20-40nm.

4. The multi-spectral coating method for a linearly-varying filter according to claim 1, wherein, The preset cooling temperature in step S4 is 50℃.

5. A linearly graduated filter, characterized in that The linearly variable filter is prepared by the multi-spectrum coating method of the linearly variable filter according to any one of claims 1-4.

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