Terahertz wave signal enhanced glass and preparation method thereof

Abstract

The invention discloses terahertz wave signal enhanced glass and a preparation method thereof, the terahertz wave signal enhanced glass comprises a glass substrate and a multilayer film structure, the multilayer film structure is attached to the surface of the glass substrate, and the multilayer film structure is a refractive index gradient structure composed of multiple layers of low-loss media. The terahertz wave signal enhancement glass can improve terahertz wave signal transmission and reduce signal loss, and is widely applied to the fields of 6G communication, indoor and outdoor Internet of Things signal coverage and the like.

Description

Technical Field

[0001] This invention belongs to the field of 6G communication technology, specifically relating to a terahertz wave signal enhancement glass and its preparation method. Background Technology

[0002] 6G, the next-generation communication technology following 5G, will bring a series of revolutionary changes, significantly improving not only speed, capacity, and latency, but also profoundly impacting all sectors of society. Terahertz waves (0.1-3 THz), their non-ionizing properties, and their ability to penetrate non-conductive materials hold broad application potential in 6G communications, indoor wireless networks, terahertz imaging, and automotive radar.

[0003] As communication technology evolves towards 6G, its signal frequency expands into the terahertz band, ranging from 0.1 THz to 3 THz. Compared to millimeter-wave bands, terahertz waves offer higher bandwidth and transmission rates, but their penetration through dielectric materials is significantly reduced. The stability of network signals, upon which 6G relies, has become a major concern. Ordinary glass, due to its high interface reflectivity and material absorption losses, severely affects signal transmission. Moreover, as the terahertz frequency increases, the absorption and scattering effects of ordinary glass intensify significantly, resulting in very noticeable signal attenuation. Its terahertz wave transmittance is generally below 50%, and its insertion loss is as high as 5 dB or more, limiting its use in 6G applications (such as 6G communication windows and indoor / outdoor signal coverage). Commonly used energy-saving coated glass (such as heat-reflective coated glass) is primarily used in the visible and near-infrared bands, and it is difficult to function effectively in the terahertz band, similarly leading to signal attenuation and affecting communication quality.

[0004] Therefore, the future market urgently needs a terahertz signal enhancement glass that can achieve low loss and high transmittance on a glass substrate to meet the wide application requirements of 6G communication, Internet of Things, smart building rooms, terahertz imaging and other fields. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned technical problems by providing a glass that can effectively improve terahertz wave signal transmission and reduce terahertz wave signal loss. To achieve the above-mentioned objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a terahertz wave signal enhancement glass, comprising a glass substrate and a refractive index graded multilayer film structure, wherein the refractive index graded multilayer film structure is attached to the surface of the glass substrate and is composed of five low-loss dielectric layers, wherein a matching buffer layer, a high refractive index layer, a medium refractive index layer, a low refractive index layer and an impedance transition layer are stacked sequentially from the glass surface outward.

[0006] In a preferred embodiment, the refractive index of the matching buffer layer is 1.7-1.8.

[0007] In a preferred embodiment, the refractive index of the high refractive index layer is 2.1-2.2.

[0008] In a preferred embodiment, the refractive index of the intermediate refractive index layer is 1.65-1.75.

[0009] In a preferred embodiment, the refractive index of the low refractive index layer is 1.45-1.55.

[0010] In a preferred embodiment, the refractive index of the impedance transition layer is 1.35-1.40.

[0011] In a preferred embodiment, the refractive index gradient multilayer film structure has a dielectric loss factor (tanδ) of each film layer material in the terahertz band that is not greater than 0.01.

[0012] In a preferred embodiment, the material of the matching buffer layer is Al2O3.

[0013] In a preferred embodiment, the high refractive index layer is made of ZrO2.

[0014] In a preferred embodiment, the material of the intermediate refractive index layer is SiON or Si3N4.

[0015] In a preferred embodiment, the material of the intermediate refractive index layer is SiON.

[0016] In a preferred embodiment, the material of the low refractive index layer is SiON or SiO2.

[0017] In a preferred embodiment, the low-refractive-index layer is made of SiON.

[0018] In a preferred embodiment, the material of the impedance transition layer is YF3 or MgF2.

[0019] In a preferred embodiment, the impedance transition layer is made of YF3, which also serves to protect the film surface.

[0020] In a preferred embodiment, the multilayer film structure comprises five layers, which are sequentially stacked: a matching buffer layer, a high refractive index film layer, a medium refractive index film layer, a low refractive index film layer, and an impedance transition layer.

[0021] In a preferred embodiment, the thickness of the matching buffer layer is 1.8 μm - 2.2 μm.

[0022] In a preferred embodiment, the thickness of the high refractive index layer is 1.2 μm - 1.8 μm.

[0023] In a preferred embodiment, the thickness of the intermediate refractive index layer is 0.8 μm - 1.2 μm.

[0024] In a preferred embodiment, the thickness of the low refractive index layer is 0.5 μm - 1.0 μm.

[0025] In a preferred embodiment, the thickness of the impedance transition layer is 0.8 μm - 1.2 μm.

[0026] In a preferred embodiment, the multilayer membrane structure comprises five membrane layers, arranged as follows: First layer: Matching buffer layer, with a thickness of 1.8μm - 2.2μm.

[0027] The second layer is a high refractive index layer with a thickness of 1.2 μm - 1.8 μm.

[0028] The third layer: a medium refractive index layer with a thickness of 0.8μm - 1.2μm.

[0029] Fourth layer: Low refractive index layer, with a thickness of 0.5μm - 1.0μm.

[0030] Fifth layer: Impedance transition layer, with a thickness of 0.8μm - 1.2μm.

[0031] In a preferred embodiment, the total thickness of the multilayer film structure is 5.1 μm - 6.8 μm.

[0032] In a preferred embodiment, the dielectric loss factor tanδ of the glass substrate is not higher than 0.01, and low-iron ultra-white glass or borosilicate glass can be selected, with a thickness of ≤5 mm.

[0033] Secondly, the present invention provides a method for preparing the high-frequency terahertz wave signal enhancement glass described herein, which involves depositing a five-layer anti-reflection film by dynamic multi-target magnetron sputtering and using closed-loop feedback to control the refractive index and thickness, and includes the following steps: S1. Glass substrate pretreatment: The glass substrate is cut, edge-ground and cleaned; S2. Deposition of matching buffer layer: A first layer of refractive index buffer material Al2O3 or MgO is magnetron sputtered onto the surface of the glass substrate using a radio frequency (RF) power supply. Ar is used as the sputtering gas, with a gas flow rate of 50-60 sccm (Ar:O2=15:1 to 10:1), a power of 150-300 W (Al2O3) or 100-250 W (MgO), and a deposition rate of 0.8-1.0 nm / s.

[0034] S3. Deposition of a high refractive index layer: A second high refractive index material, ZrO2, Nb2O5, or Ta2O5, is magnetron sputtered onto the first matching buffer layer using an RF (ceramic target) power supply. Ar and O2 are used as sputtering gases, with a gas flow rate of 55-70 sccm (Ar:O2=10:1 to 5:1), a power of 150-400 W (RF) or 200-600 W (DC), and a deposition rate of 0.9-1.2 nm / s.

[0035] S4. Deposition of the intermediate refractive index layer: A medium refractive index material SiON or Si3N4 layer is magnetron sputtered on the high refractive index layer. Sputtering is performed using an AC or DC power supply (silicon target), with Ar, N2, and O2 as sputtering gases. The refractive index of SiON is precisely controlled to about 1.65 by the N2:O2 ratio. The gas flow rate is 80-90 sccm (SiON, Ar:N2:O2=10:6:2; Si3N4, Ar:N2=10:6), the power is 200-500 W, and the deposition rate is 0.8-1.0 nm / s.

[0036] S5. Deposition of a low refractive index layer: Magnetron sputtering of low refractive index materials SiON or SiO2 onto the medium refractive index layer. Sputtering is performed using an AC or DC power supply with Ar, N2, and O2 as sputtering gases. The refractive index of SiON is precisely controlled to approximately 1.50 by adjusting the N2:O2 ratio. The gas flow rate is 80-90 sccm (SiON, Ar:N2:O2=10:1:7; SiO2, Ar:O2=10:2), the power is 200-500 W (SiON) or 100-300 W (SiO2), and the deposition rate is 0.8-1.0 nm / s.

[0037] S6. Deposition of impedance transition layer: YF3 or MgF2 impedance transition layer material is magnetron sputtered on the low refractive index layer. Radio frequency (RF) power supply sputtering is used with Ar as sputtering gas. The gas flow rate is 50-55 sccm (Ar, or Ar:F2=25:1), the power is 100-250W, and the deposition rate is 0.8-0.9 nm / s.

[0038] In a preferred embodiment, the materials for the intermediate and low refractive index layers are silicon oxynitride (SiON). The refractive index of SiON is precisely controlled by adjusting the nitrogen to oxygen flow ratio during reactive sputtering, with nitrogen to oxygen flow ratios of 6:2 and 1:7, respectively, thereby achieving a smooth transition of refractive index.

[0039] In a preferred embodiment, the dielectric loss factor of each film material is no greater than 0.01 in the 0.1THz-3THz frequency band, which meets the requirements for low-loss wave transmission.

[0040] In a preferred embodiment, the structure has a transmittance of greater than 85% and an insertion loss of less than 0.6 dB in the 0.1THz-3THz frequency band.

[0041] As a preferred implementation, the transmittance changes by less than 0.5% after testing according to international standards for properties such as thermal cycling, salt spray, and UV resistance.

[0042] The structure and process of this invention incorporate a stress matching mechanism, select materials with a thermal expansion coefficient similar to that of the glass substrate, achieve compatible control of the thermal expansion coefficient, and provide a dynamic multi-target magnetron sputtering process to ensure film uniformity, which helps to reduce stress gradient, avoid film cracking or warping, and improve overall thermal stability and adhesion.

[0043] The preferred materials for the medium and low refractive index layers are silicon oxynitride. The refractive index of SiON is precisely controlled by adjusting the flow ratio of nitrogen (N2) to oxygen (O2) in reactive sputtering, with nitrogen to oxygen flow ratios of 6:2 and 1:7, respectively, thereby achieving a smooth transition of refractive index.

[0044] The present invention has the following advantages: 1. Multilayer Low-Loss Dielectric Constructing a Gradual Refractive Index Structure: The terahertz wave signal enhancement glass of this invention utilizes a multilayer low-loss dielectric to construct a gradual refractive index structure. The multilayer dielectric has low dielectric loss, with a dielectric loss factor not exceeding 0.01, meeting the low-loss transmission requirements and increasing the penetration capability of terahertz waves with minimal attenuation. The unique multilayer refractive index gradient design achieves a smooth transition with progressively decreasing refractive indices, significantly reducing interfacial reflections between the glass and air, as well as multiple reflection losses caused by interfacial discontinuities, thereby improving the transmittance of terahertz signals. This results in a low-reflection, low-absorption, broadband transmission structure, achieving enhanced transmission of terahertz signals.

[0045] 2. The present invention provides a method for preparing terahertz wave signal enhancement glass. By dynamically switching the target material and adjusting the atmosphere, dynamic multi-target magnetron sputtering is used to deposit a refractive index gradient film, thereby achieving adjustable film refractive index and ensuring deposition quality, interface cleanliness and process stability.

[0046] 3. The terahertz wave signal enhancement glass provided by the present invention is a 6G signal enhancement glass. By coating the glass surface, it can effectively improve the transmission of terahertz wave signals, reduce terahertz wave signal loss, and improve anti-interference ability. It can achieve a terahertz wave signal power transmittance of more than 85% and an insertion loss of less than 0.6 dB in the 0.1THz-3THz frequency band, which is far superior to ordinary soda-lime silicon glass.

[0047] 4. The multilayer film structure of this invention incorporates a stress matching mechanism: materials with thermal expansion coefficients similar to those of the substrate (such as Al2O3, SiON, Si3N) are selected.4、 YF3 (and other materials) helps reduce the difference in thermal expansion coefficients between the film and the glass, regulates the thermal strain between the film system and the glass substrate, alleviates stress concentration at the interface caused by thermal cycling, and effectively disperses the internal stress gradient of the film. Simultaneously, the dynamic multi-target magnetron sputtering process ensures film uniformity and also helps reduce stress gradients. This prevents film cracking or warping, and improves the overall thermal stability and adhesion of the film.

[0048] 5. The terahertz wave signal enhancement glass provided by this invention exhibits good thermal cycling, salt spray, and UV resistance properties, with a transmittance change of <0.5% after testing. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the structure of the terahertz wave signal enhancement glass of the present invention. Detailed Implementation

[0050] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. Unless otherwise specified, the instruments or reagents used in the embodiments are all conventional instruments or reagents in the art and are conventional products that can be purchased from the market. Unless otherwise specified, the specific experimental operations involved in the text are all understandable or known to those skilled in the art based on their common knowledge or conventional technical means, and will not be described in detail here.

[0051] like Figure 1 As shown, the terahertz wave signal enhancement glass of the present invention includes a glass substrate 1 and a multilayer film structure with a graded refractive index. The multilayer film structure is attached to the surface of the glass substrate 1 and is composed of multiple low-loss dielectrics, wherein a matching buffer layer 2, a high refractive index layer 3, a medium refractive index layer 4, a low refractive index layer 5, and an impedance transition layer 6 are stacked sequentially from the glass surface outward.

[0052] As an example, Figure 1 A multilayer membrane structure comprising five membrane layers is shown.

[0053] The refractive index of the matching buffer layer 2 is 1.7-1.8, the refractive index of the high refractive index layer 3 is 2.1-2.2, the refractive index of the medium refractive index layer 4 is 1.65-1.75, the refractive index of the low refractive index layer 5 is 1.45-1.55, and the refractive index of the impedance transition layer 6 is 1.35-1.40.

[0054] The matching buffer layer is made of Al2O3 or MgO, the high refractive index layer is made of ZrO2, Nb2O5 or Ta2O5, the medium refractive index layer is made of SiON or Si3N4, the low refractive index layer is made of SiON or SiO2, and the impedance transition layer is made of YF3 or MgF2. Table 1 shows the relevant data on the dielectric material, refractive index and dielectric loss factor of different films.

[0055] Table 1. Dielectric loss factor of each film layer material

[0056] The matching buffer layer has a thickness of 1.8 μm - 2.2 μm, more preferably 2.0 μm. The high refractive index layer has a thickness of 1.2 μm - 1.8 μm, more preferably 1.5 μm. The medium refractive index layer has a thickness of 0.8 μm - 1.2 μm, more preferably 1.0 μm. The low refractive index layer has a thickness of 0.5 μm - 1.0 μm, more preferably 0.8 μm. The impedance transition layer has a thickness of 0.8 μm - 1.2 μm, more preferably 1.0 μm.

[0057] The total thickness of the multilayer film structure is 5.1 μm - 6.8 μm. The thickness of glass substrate 1 is less than 4 mm.

[0058] In a preferred embodiment, the multilayer film structure comprises five layers, which are sequentially stacked as a matching transition layer, a high refractive index layer, a medium refractive index layer, a low refractive index layer, and an impedance transition layer.

[0059] The terahertz wave signal enhancement glass of the present invention can be prepared by the following steps: (1) Pretreatment of glass substrate 1: Cut, grind and clean the glass substrate 1 according to the required size; (2) Deposit matching buffer layer 2: The glass substrate 1 is fed into a vacuum magnetron sputtering equipment, and a buffer layer material is deposited on the surface of the glass substrate 1 using the appropriate target material and protective gas to form the first matching buffer layer 2. The thickness is controlled between 1.8 μm and 2.2 μm, preferably 2.0 μm; (3) Deposition of high refractive index layer 3: Using appropriate target material and protective gas in the coating chamber, high refractive index layer material is deposited on the matching buffer layer 2 to form a second high refractive index layer 3 with a thickness controlled between 1.2 μm and 1.8 μm, preferably 1.5 μm; (4) Deposition of intermediate refractive index layer 4: Using appropriate target material and protective gas in the coating chamber, intermediate refractive index layer material is deposited on high refractive index layer 3 to form third intermediate refractive index layer 4, with thickness controlled between 0.8μm and 1.2μm, preferably 1.0μm; (5) Deposit low refractive index layer 5: In the coating chamber, a corresponding target material and protective gas are used to deposit a low refractive index layer material on the medium refractive index layer 4 to form a fourth low refractive index layer 5 with a thickness controlled between 0.5 μm and 1.0 μm, preferably 0.8 μm; (6) Deposition of impedance transition layer 6: Using appropriate target material and protective gas in the coating chamber, an impedance transition material is deposited on the low refractive index layer to form the fifth impedance transition layer 6, with the thickness controlled between 0.8μm and 1.2μm, 1.0μm.

[0060] (7) The total thickness of the film layer is controlled between 5.1 μm and 6.8 μm.

[0061] (8) The process control of each film layer is shown in Table 1 below.

[0062] Table 1

[0063] Table 2 below lists the glass film structure and related data for Examples 1-5.

[0064] Table 2

[0065] Note: Power transmittance was tested using an Advantest TAS7500SP terahertz time-domain spectrometer (0.05-3 THz, vertical incidence, air background calibration). Thermal cycling, salt spray, and UV resistance tests were performed according to IEC60068 / ISO 9227 / ISO4892-3 standards.

[0066] Terahertz waves are prone to reflection and absorption losses at dielectric interfaces. Direct application using traditional media such as glass presents two key problems: high interface reflection loss and large transmission loss. The abrupt change in the refractive index of glass (n≈1.52) compared to air (n=1.00) causes strong reflection of terahertz waves upon incidence, with total reflection losses reaching over 8%. Ordinary glass exhibits dielectric absorption of terahertz waves; improper film design can also lead to multi-interface interference reflections, further reducing the main transmission peak. This invention effectively solves these problems.

[0067] The low-iron ultra-clear glass used in this invention has a low iron content (iron content ≤0.01%, light transmittance ≥91%), which reduces absorption in the terahertz band (0.1-3 THz) and increases transmittance compared to ordinary soda-lime silica glass, thus enhancing signal transmission. The dielectric loss factor (tanδ = 0.005) of low-iron glass is significantly lower than that of ordinary float glass (tanδ = 0.02), reducing terahertz wave energy loss and making it suitable for high-performance communication. The visible light transmittance of low-iron ultra-clear glass reaches over 90%, which is more conducive to building lighting. Similar to low-iron ultra-clear glass, borosilicate glass's low-loss characteristics reduce terahertz wave energy absorption and ensure high transmittance, making it suitable for use as a glass substrate.

[0068] The film materials used in this invention (such as Al2O3, ZrO) 2、Materials such as SiON, SiO2, and YF3 are all low-dielectric-loss dielectrics with a dielectric loss factor tanδ < 0.01, which can greatly reduce incident and reflection losses, enabling high-efficiency transmission of terahertz signals. When a terahertz signal is incident from a low-refractive-index medium (air) onto a high-refractive-index medium (glass), impedance mismatch causes partial wave reflection. Constructing a dielectric film system with a continuous transition from high to low refractive index on the glass surface can form an effective electromagnetic impedance matching channel during the terahertz signal's passage through the glass / air interface, avoiding large-scale reflection echoes caused by abrupt changes in refractive index. This achieves a broadband wave transmission structure with high transmission, low reflection, low absorption, and low loss, thus enhancing the terahertz signal.

[0069] This invention can more effectively improve the transmission of high-frequency terahertz wave signals, reduce signal loss and signal dead zones, improve communication quality and stability, provide seamless high-speed data transmission for indoor and outdoor communication, support large-scale Internet of Things applications, multi-device interconnection in smart homes, autonomous driving and vehicle-to-everything (V2X) applications, and has positive significance for promoting the development of future high-frequency communication technologies. Furthermore, by improving the performance of 6G communication systems, construction and maintenance costs can be reduced, improving economic efficiency.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A terahertz wave signal enhancement glass, comprising a glass substrate and a multilayer film structure with graded refractive index, characterized in that, The multilayer film structure is attached to the surface of the glass substrate and is a refractive index gradient structure composed of multiple low-loss media, with a matching buffer layer, a high refractive index layer, a medium refractive index layer, a low refractive index layer and an impedance transition layer stacked sequentially from the glass surface outwards.

2. The terahertz wave signal enhancement glass according to claim 1, characterized in that, The glass substrate is ultra-white low-iron glass or borosilicate glass, with a dielectric loss factor tanδ not higher than 0.01 and a thickness ≤ 5mm.

3. The terahertz wave signal enhancement glass according to claim 1, characterized in that, The refractive index of the matching buffer layer is 1.7-1.

8.

4. The terahertz wave signal enhancement glass according to claim 1, characterized in that, The refractive index of the high refractive index layer is 2.1-2.

2.

5. The terahertz wave signal enhancement glass according to claim 1, characterized in that, The refractive index of the intermediate refractive index layer is 1.65-1.

75.

6. The terahertz wave signal enhancement glass according to claim 1, characterized in that, The refractive index of the low-refractive-index layer is 1.45-1.

55.

7. The terahertz wave signal enhancement glass according to claim 1, characterized in that, The refractive index of the impedance transition layer is 1.35-1.

40.

8. The terahertz wave signal enhancement glass according to claim 1, characterized in that, The material of the matching buffer layer is Al2O3 or MgO.

9. The terahertz wave signal enhancement glass according to claim 1, characterized in that, The material of the high refractive index layer is ZrO2, Nb2O5 or Ta2O5; Preferably, the material of the intermediate refractive index layer is SiON or Si3N4; Preferably, the material of the low refractive index layer is SiON or SiO2; Preferably, the material of the impedance transition layer is YF3 or MgF2; Preferably, the thickness of the matching buffer layer is 1.8 μm - 2.2 μm; Preferably, the thickness of the high refractive index layer is 1.2 μm - 1.8 μm; Preferably, the thickness of the intermediate refractive index layer is 0.8 μm - 1.2 μm; Preferably, the thickness of the low refractive index layer is 0.5 μm - 1.0 μm; Preferably, the thickness of the impedance transition layer is 0.8 μm - 1.2 μm.

10. A method for preparing terahertz wave signal enhancement glass as described in any one of claims 1 to 18, characterized in that, The method involves depositing a five-layer antireflective film via dynamic multi-target magnetron sputtering, using closed-loop feedback to control the refractive index and thickness. The method includes the following steps: S1. Glass substrate pretreatment: The glass substrate is cut, edge-ground and cleaned; S2. Deposition of matching buffer layer: A first layer of refractive index buffer material Al2O3 or MgO is magnetron sputtered onto the surface of the glass substrate using an RF power supply. Ar is used as the sputtering gas, with a gas flow rate of 50-60 sccm, Ar:O2 = 15:1 to 10:1, power of 150-300 W for Al2O3 or 100-250 W for MgO, and a deposition rate of 0.8-1.0 nm / s. S3. Deposition of a high refractive index layer: A second high refractive index material, ZrO2, Nb2O5, or Ta2O5, is magnetron sputtered onto the first matching buffer layer using an RF power supply. Ar and O2 are used as sputtering gases, with a gas flow rate of 55-70 sccm, Ar:O2 = 10:1 to 5:1, power of 150-400 W for RF or 200-600 W for DC, and a deposition rate of 0.9-1.2 nm / s. S4. Deposition of the intermediate refractive index layer: A medium refractive index material SiON or Si3N4 layer is magnetron sputtered on the high refractive index layer. Sputtering is performed using AC or DC power supply, with Ar, N2, and O2 as sputtering gases. The refractive index of SiON is precisely controlled to about 1.65 by the N2:O2 ratio, and the gas flow rate is 80-90 sccm; SiON, Ar:N2:O2=10:6:2; Si3N4, Ar:N2=10:6; power 200-500 W, deposition rate 0.8-1.0 nm / s; S5. Deposition of a low refractive index layer: Magnetron sputtering of low refractive index material SiON or SiO2 onto the medium refractive index layer. Sputtering is performed using AC or DC power, with Ar, N2, and O2 as sputtering gases. The refractive index of SiON is precisely controlled to approximately 1.50 by the N2:O2 ratio, and the gas flow rate is 80-90 sccm; SiON, Ar:N2:O2 = 10:1:7; SiO2, Ar:O2 = 10:2; Power: SiON, 200-500 W; or SiO2, 100-300 W; deposition rate 0.8-1.0 nm / s. S6. Deposition of impedance transition layer: On the low refractive index layer, magnetron sputtering of impedance transition layer material YF3 or MgF2 is performed using RF power supply sputtering with Ar as sputtering gas at a flow rate of 50-55 sccm. The gas is Ar or Ar:F2=25:1, the power is 100-250 W, and the deposition rate is 0.8-0.9 nm / s.

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