Infrared reflectance adjusting film, infrared reflection suppression film, and method for manufacturing an infrared reflectance adjusting film

Abstract

The objective is to ensure hardness while suppressing infrared reflection. [Solution] The infrared reflectance adjusting film 4 contains at least cerium oxide and aluminum nitride.

Description

Technical Field

[0001] The present disclosure relates to a surface coating for infrared transmission lenses used in infrared cameras, infrared sensors and the like, and window members used in housings of cameras, sensors and the like.

Background Art

[0002] Infrared transmission lenses used in infrared cameras, infrared sensors and the like are coated with an antireflective film in order to suppress reflection of incident light and improve the transmittance of incident light to the cameras, sensors and the like. For example, as disclosed in Patent Document 1, a fluoride film may be used as the antireflective film.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, fluoride films generally have low hardness, and the function of the antireflective film may be degraded by external factors such as external impact. Therefore, antireflective films are required to have improved mechanical strength against external impacts and the like.

[0005] The present disclosure aims to ensure hardness while suppressing reflection of infrared rays.

Means for Solving the Problems

[0006] To achieve the above object, an infrared reflectance adjusting film according to an embodiment of the present disclosure contains at least cerium oxide and aluminum nitride.

[0007] An infrared reflection suppression film according to one embodiment of the present disclosure comprises a layer made of the infrared reflectance adjusting film and a high refractive index layer having a refractive index higher than that of the infrared reflectance adjusting film.

[0008] In one embodiment of the present disclosure, a method for manufacturing an infrared reflectance adjusting film involves forming a film containing at least cerium oxide and aluminum nitride on a substrate by sputtering. [Brief explanation of the drawing]

[0009] [Figure 1] This diagram illustrates the structure of an infrared reflection suppression film. [Modes for carrying out the invention]

[0010] [Infrared reflection suppression coating] Optical devices equipped with lenses, such as cameras and sensors, have an anti-reflective coating on the lens surface to efficiently capture light into the device through the lens. This suppresses light reflection, allowing for efficient light capture into the device.

[0011] In infrared cameras and infrared sensors, it is necessary to sufficiently capture infrared light into the device, making the infrared reflection suppression coating highly important. In other words, it is preferable to coat the lenses of infrared cameras and infrared sensors, and the window materials provided in the housings that house and use these devices, with an infrared reflection suppression coating to suppress infrared reflection and increase infrared transmittance. Such an infrared reflection suppression coating is formed on the front and / or back surfaces of the lens and / or window material of the camera or sensor.

[0012] The configuration of the infrared reflection suppression film and the infrared reflectance adjustment film used in this embodiment will be described below with reference to Figure 1.

[0013] The infrared reflection suppression film has a configuration in which a low refractive index layer 4 and a high refractive index layer 6 are laminated on the surface of a substrate 2. The low refractive index layer 4 is the infrared reflectance adjustment film of this disclosure. The refractive index of the high refractive index layer 6 for infrared rays is higher than the refractive index of the low refractive index layer 4 for infrared rays. By laminating the low refractive index layer 4 and the high refractive index layer 6, infrared reflection can be suppressed and infrared rays can be transmitted efficiently. For example, by setting the refractive index of the high refractive index layer 6 for infrared rays with wavelengths of 8 μm to 12 μm to 3 or more, infrared rays with wavelengths of 8 μm to 12 μm can be effectively transmitted.

[0014] The infrared reflection suppression film may be laminated on at least one side (the first surface) of the substrate 2, but it may also be laminated on both sides (the first surface and the second surface, which is the back surface to the first surface). Laminating the infrared reflection suppression film on both sides of the substrate 2 is effective in improving transmittance because it also suppresses back surface reflection. Furthermore, it is preferable that the low refractive index layer 4 and the high refractive index layer 6 are laminated in this order.

[0015] While silicon (Si) is used as an example for substrate 2, it is not particularly limited and is not limited as long as it satisfies various conditions such as adhesion to the infrared reflection suppression film of this disclosure and infrared transmission performance. For example, substrate 2 can be germanium (Ge), silicon (Si), chalcogenide glass, or diamond. Among these, germanium and silicon are preferred because they have high refractive indices for infrared rays with wavelengths of around 10 μm, and when combined with the infrared reflectance adjusting film of this disclosure, a reflection suppression effect can be obtained.

[0016] While the high refractive index layer 6 is exemplified by a germanium (Ge) layer, it is not particularly limited as long as it has high adhesion to the low refractive index layer 4 of this disclosure and improves the overall transmittance. For example, the high refractive index layer 6 can be germanium (Ge), silicon (Si), gallium arsenide (GaAs), lead telluride (PbTe), or tellurium (Te), with germanium (Ge) or silicon (Si) being preferred from the viewpoint of handling. Among these, it is especially preferable that the high refractive index layer 6 be germanium (Ge) with a high refractive index. The thickness of the high refractive index layer 6 is about 50 to 300 nm, and the refractive index is about 3 to 4.5.

[0017] The composition ratio of cerium oxide and aluminum nitride in the low refractive index layer 4 is not particularly limited as long as both compounds are present, however, it is preferable that the aluminum nitride is contained in an amount of 1 at% (atomic%) to 15 at% in terms of metal atom ratio. In other words, it is preferable that the ratio of the amount of cerium oxide (moles) to the sum of the amount of cerium oxide (moles) and the amount of aluminum nitride (moles) contained in the low refractive index layer 4 be 1% to 15%. This makes it possible to obtain a reflectivity-adjusting film with high hardness in infrared light with a wavelength of about 8 to 12 μm.

[0018] The thickness (physical film thickness) of the low refractive index layer 4 is not particularly limited, but is approximately 250 to 2000 nm, and more preferably between 500 nm and 1000 nm. A thickness greater than 2000 nm is undesirable because it reduces infrared transmittance, and a thickness less than 250 nm is undesirable because it reduces durability.

[0019] The elemental composition in the film or layer can be analyzed, for example, by EDS (Energy Dispersive X-ray Spectroscopy) attached to a scanning electron microscope. This apparatus can obtain information on the surface composition by irradiating a sample with X-rays and measuring the energy of photoelectrons emitted from the sample, whereby the atomic content in the film can be measured. In the present disclosure, the content in the film or layer may be measured by a method other than the above measurement method.

[0020] The refractive indices of the high-refractive-index layer 6 and the low-refractive-index layer 4 are preferably set according to the light to be transmitted. For example, the low-refractive-index layer 4 can have a refractive index of 1.7 or more and 2.5 or less, more preferably 1.8 or more and 2.45 or less, and still more preferably 2.0 or more and 2.4 or less for infrared rays having a wavelength of 10 μm. Thereby, the low-refractive-index layer 4 can efficiently transmit infrared rays.

[0021] [Method for producing infrared reflection suppressing film] Next, an example of a method for producing an infrared reflection suppressing film will be described with reference to FIG. 1.

[0022] First, cerium oxide and aluminum nitride are deposited by sputtering on the surface (first surface) of a silicon substrate 2. The deposited film is the low-refractive-index layer 4. Thereby, the infrared reflectance adjusting film is formed.

[0023] Next, the high-refractive-index layer 6 made of germanium is formed on the low-refractive-index layer 4 (on the surface on the back side of the low-refractive-index layer 4 relative to the substrate 2 side).

[0024] Finally, the low-refractive-index layer 4 and the high-refractive-index layer 6 are similarly laminated on the back surface (second surface) of the substrate 2.

[0025] The infrared reflection suppression film may be configured such that the low refractive index layer 4 and the high refractive index layer 6 are laminated on both sides (first surface and second surface) of the substrate 2, or it may be configured such that the low refractive index layer 4 and the high refractive index layer 6 are laminated only on the surface (first surface) of the substrate 2. It has been found that the infrared reflection suppression film, when the low refractive index layer 4 and the high refractive index layer 6 are laminated on both sides (first surface and second surface) of the substrate 2, prevents back surface reflection and further improves transmittance.

[0026] [Examples] The following describes embodiments of this disclosure. However, this disclosure is not limited to the following embodiments.

[0027] (Example 1) As substrate 2, a double-sided polished silicon (Si) plate (refractive index 3.4 at a wavelength of 10 μm, thickness 1 mm) was used to deposit the first layer on one side of the plate using a sputtering apparatus (ULVAC: QAM-4-ST) under an argon (Ar) and nitrogen (N2) atmosphere, with a target mixture of 98.5 at% cerium oxide (CeO2) and 1.5 at% aluminum nitride (AlN) (low refractive index layer 4: physical film thickness 782 nm). Next, using the same apparatus, a second layer was deposited on top of this layer under an argon (Ar) atmosphere, with germanium (Ge) as the target (high refractive index layer 6: physical film thickness 91 nm). An infrared reflection suppression film was also fabricated on the back side of substrate 2 in the same manner, with two layers laminated in the same way. The composition ratio of cerium oxide and aluminum nitride was confirmed to be approximately the same as that of the target composition and the film composition by the aforementioned EDS analysis.

[0028] (Example 2) An infrared reflection suppression film similar to that in Example 1 was fabricated, except that the first layer (low refractive index layer 4) consisted of 93.6 at% cerium oxide (CeO2) and 6.4 at% aluminum nitride (AlN).

[0029] (Example 3) An infrared reflection suppression film similar to that in Example 1 was prepared, except that the first layer (low refractive index layer 4) consisted of 91.5 at% cerium oxide (CeO2) and 8.5 at% aluminum nitride (AlN).

[0030] (Example 4) An infrared reflection suppression film similar to that in Example 1 was prepared, except that the first layer (low refractive index layer 4) consisted of 87.2 at% cerium oxide (CeO2) and 12.8 at% aluminum nitride (AlN).

[0031] (Comparative Example 1) An infrared reflection suppression film similar to that in Example 1 was prepared, except that aluminum nitride (AlN) was not used and cerium oxide (CeO2) was used in a proportion of 100 at%.

[0032] (Comparative Example 2) An infrared reflection suppression film similar to that in Example 1 was prepared, except that cerium oxide (CeO2) was not used and aluminum nitride (AlN) was used in a proportion of 100 at%.

[0033] (Comparative Example 3) The same evaluation as in the example was performed using only substrate 2.

[0034] (Comparative Example 4) A Si window manufactured by IR System Co., Ltd. (8-14 μm band double-sided AR coated product, with a Si substrate laminated with three YbF layers (corresponding to low refractive index layer 4), etc., 1 mm thick) was evaluated in the same manner as in the examples.

[0035] 〔evaluation〕 The above examples and comparative examples were evaluated as follows. The results are shown in Table 1.

[0036] (Hardness (Indentation Strength)) The indentation strength (hardness) of the infrared anti-reflective coating in each case was measured using a nanoindenter (ELIONIX Corporation, ENT-1100a). A Berkovich indenter was used as the indenter, and the nanoindentation hardness (hardness) was measured when indented with a maximum load of 1.5 mN. Specifically, first, the indenter was pressed into the sample while applying a constant load until the maximum load was reached. Next, the load was removed at a constant rate until the load became 0, and the indenter was pulled away. The displacement of the indenter during loading and unloading was recorded, and the maximum load was determined. Furthermore, the contact projection area (base area of ​​the cone) of the contact portion when the indenter was pressed was determined, and the nanoindentation hardness was calculated by dividing the maximum load by the contact projection area.

[0037] (Refractive index) Using a spectroscopic ellipsometer (GES5E, manufactured by Nippon Semilab Co., Ltd.), the optical constants of each layer were measured, and the refractive index and other parameters for each wavelength in the infrared range of 8 to 12 μm were calculated.

[0038] (Average infrared transmittance) Using optical simulation software (TOHO TSUSHO INC., ThinFilmView), we calculated the simulated values ​​of the average transmittance in the infrared range (wavelength: 8 μm to 12 μm).

[0039] (result) As shown in Table 1 below, in the embodiments of this disclosure, the average infrared transmittance at wavelengths of 8 to 12 μm is high enough for practical use, and the hardness is also high at 15 GPa or more. Therefore, it can be seen that the present invention is effective as a coating for lenses of infrared cameras and sensors that require strength, and for window materials provided in housings that house and use these devices. [Table 1]

[0040] In particular, in Examples 1 to 4, where the low refractive index layer 4 contains both cerium oxide and aluminum nitride, Examples 2 and 3, where the refractive index of the low refractive index layer 4 for infrared rays with wavelengths of 8 μm to 12 μm is between 2.0 and 2.5, show a higher average infrared transmittance compared to Examples 1 and 4. This indicates that in infrared reflection suppression films where the low refractive index layer 4 contains both cerium oxide and aluminum nitride, the infrared transmittance can be further improved by setting the refractive index of the low refractive index layer 4 to between 2.0 and 2.4.

[0041] [Another embodiment] In the above embodiment, the infrared reflection suppression film and the infrared reflectance adjusting film are not limited to being manufactured by the method described above, but may be manufactured by any other method.

[0042] In each of the embodiments described above, the method for forming the low refractive index layer 4 and the high refractive index layer 6, which are infrared reflectance adjusting films of this disclosure, is not particularly limited and existing techniques can be used. For example, this can be done by vacuum deposition, sputtering, ion plating, or ion beam deposition, which are classified as physical vapor deposition, or by atomic layer deposition or plasma CVD, which are classified as chemical vapor deposition. Vapor deposition tends to result in films with a fast formation rate but low hardness. Sputtering tends to result in films with a slow formation rate but high hardness. Therefore, from the viewpoint of hardness, it is preferable in the present invention to form the low refractive index layer 4 and the high refractive index layer 6 by sputtering, respectively.

[0043] In each of the above embodiments, the infrared reflection suppression film is laminated on the substrate 2 in the order of low refractive index layer 4 and high refractive index layer 6, but it may also be configured in which the low refractive index layer 4 is laminated on the high refractive index layer 6. Furthermore, the infrared reflection suppression film may include other functional layers in addition to the low refractive index layer 4 and high refractive index layer 6. This makes it possible to easily configure the infrared reflection suppression film to exhibit the required functions and performance.

[0044] In each of the above embodiments, depending on the application, the low refractive index layer 4 or the high refractive index layer 6 may be further mixed with an oxide such as zirconium oxide (ZrO2) to the extent that it does not degrade the performance of the infrared reflection suppression film. This can improve acid resistance.

[0045] [Summary of the above embodiment] The following describes the infrared reflectance adjusting film, infrared reflection suppression film, and method for manufacturing the infrared reflectance adjusting film as described in the above embodiments.

[0046] <1> One embodiment of the infrared reflectance adjusting film contains at least cerium oxide and aluminum nitride.

[0047] This configuration allows for the suppression of infrared reflection with wavelengths between 8 μm and 12 μm, thereby ensuring transmittance while maintaining a predetermined hardness.

[0048] <2> the above <1> In the infrared reflectance adjusting film described above, the aluminum nitride may be contained in an amount of 1 at% to 15 at%.

[0049] This configuration allows for the precise securing of the required hardness while suppressing the reflection of infrared rays with wavelengths between 8 μm and 12 μm to ensure transmittance.

[0050] <3> the above <1> or <2> In the infrared reflectance adjusting film described above, the refractive index for infrared radiation with a wavelength of 10 μm may be 1.7 or more and 2.5 or less.

[0051] This configuration allows for precise suppression of infrared reflection with wavelengths between 8 μm and 12 μm, ensuring transmittance while maintaining a predetermined hardness.

[0052] <4> One embodiment of the infrared reflection suppression film is characterized by the lamination of a layer (4) made of the infrared reflectance adjusting film and a high refractive index layer (6) having a refractive index higher than that of the layer (4) made of the infrared reflectance adjusting film.

[0053] This configuration allows for the suppression of infrared reflection with wavelengths between 8 μm and 12 μm, thereby ensuring transmittance while maintaining a predetermined hardness.

[0054] <5> the above <4> In the infrared reflection suppression film described above, the refractive index of the high refractive index layer (6) may be 3 or more.

[0055] This configuration allows for precise suppression of infrared reflection with wavelengths between 8 μm and 12 μm, ensuring transmittance while maintaining a predetermined hardness.

[0056] <6> the above <4> or <5> In the infrared reflection suppression film described above, the high refractive index layer (6) may contain germanium.

[0057] This configuration allows for precise suppression of infrared reflection with wavelengths between 8 μm and 12 μm, ensuring transmittance while maintaining a predetermined hardness.

[0058] <7> the above <4> from <6> An infrared reflection suppression film according to any of the above, comprising a substrate (2), a layer (4) made of the infrared reflectance adjusting film and a high refractive index layer (6) laminated on the substrate (2), wherein the layer (4) made of the infrared reflectance adjusting film and the high refractive index layer (6) are laminated in this order on a first surface of the substrate (2), and the layer (4) made of the infrared reflectance adjusting film and the high refractive index layer (6) are laminated in this order on a second surface which is the back surface of the substrate (2) relative to the first surface.

[0059] This configuration allows for the suppression of back-surface reflection, accurately suppressing the reflection of infrared rays with wavelengths between 8 μm and 12 μm, thereby ensuring transmittance while maintaining a predetermined hardness.

[0060] <8> One embodiment of a method for manufacturing an infrared reflectance adjustment film is to form a film containing at least cerium oxide and aluminum nitride on a substrate (2) by sputtering.

[0061] This configuration makes it possible to easily manufacture infrared reflectivity adjustment films that suppress the reflection of infrared rays with wavelengths of 8 μm to 12 μm while ensuring transmittance, and that maintain a predetermined hardness. [Industrial applicability]

[0062] This disclosure can be applied to infrared reflection suppression films that suppress the reflection of infrared rays, and infrared reflectance adjusting films used in infrared reflection suppression films. [Explanation of Symbols]

[0063] 2 Base material 4. Low refractive index layer (film for adjusting infrared reflectivity) 6. High refractive index layer

Claims

1. A film for adjusting infrared reflectivity, containing at least cerium oxide and aluminum nitride.

2. The infrared reflectance adjusting film according to claim 1, wherein the aluminum nitride is contained in an amount of 1 at% to 15 at%.

3. An infrared reflectance adjusting film according to claim 1 or 2, wherein the refractive index for infrared radiation with a wavelength of 10 μm is 1.7 or more and 2.5 or less.

4. An infrared reflection suppression film comprising a layer made of an infrared reflectance adjusting film according to any one of claims 1 to 3, and a high refractive index layer having a refractive index higher than that of the infrared reflectance adjusting film.

5. The infrared reflection suppression film according to claim 4, wherein the refractive index of the high refractive index layer is 3 or more.

6. The infrared reflection suppression film according to claim 4 or 5, wherein the high refractive index layer comprises germanium.

7. The system comprises a substrate, a layer consisting of the infrared reflectance adjusting film laminated on the substrate, and the high refractive index layer, A layer consisting of the infrared reflectance adjusting film and the high refractive index layer are laminated on the first surface of the substrate in this order. The infrared reflection suppression film according to any one of claims 4 to 6, wherein a layer consisting of the infrared reflectance adjusting film and the high refractive index layer are laminated in this order on a second surface which is the back surface of the substrate relative to the first surface.

8. A method for manufacturing an infrared reflectance adjusting film, wherein a film containing at least cerium oxide and aluminum nitride is formed on a substrate by sputtering.

Images