JP5909523B2 - ND filter, light quantity diaphragm device, and imaging device - Google Patents

Description

  The present invention relates to an ND filter, a light quantity diaphragm device, and an image pickup apparatus using the light quantity diaphragm device, particularly for use in cameras and the like.

  In some cases, an ND (Neutral Density) filter is used in a light amount diaphragm device such as a video camera or a digital still camera in order to reduce the influence of a hunting phenomenon or a diffraction phenomenon in a small diaphragm state.

  In recent years, the sensitivity of the image sensor has improved, and the density of the ND filter has been increased to further reduce the light transmittance. The device is designed to prevent the opening from becoming too small.

  In addition, transparent substrates such as glass are also used as substrates for ND filters, but in recent years, synthetic resin substrates have also become available due to demands for processability to arbitrary shapes, miniaturization, and weight reduction. It has been used. As a general method for manufacturing an ND filter, a multilayer film is formed on a transparent substrate made of synthetic resin or glass by a vacuum deposition method, a sputtering method, or the like.

  Further, in the spectral characteristics of the ND filter, there is an increasing demand for higher accuracy for reasons such as improving the photosensitivity of the CCD. Among them, the spectral characteristics are uniform in the entire visible light wavelength region from approximately λ = 400 to 700 nm. It is required to be. By designing these ND filters optimally, it is possible to obtain characteristics with uniform spectral characteristics over the entire visible light wavelength range. However, the ND filter has a problem that the spectral characteristics are changed due to oxidation of the metal / metal oxide used as the light attenuating film due to moisture or the like entering the light attenuating film from the atmosphere or the substrate.

As a countermeasure against this problem, the ND filter described in Patent Document 1 uses a lower metal nitride such as TiN _x , NbN _x , TaN _x , and AlN _x as the light attenuation film. Thus, it is disclosed that an oxide, which is an adjacent dielectric, is affected by the external environment and the light attenuating film is prevented from being oxidized, and an ND filter having stable spectral characteristics is obtained.

FIG. 10 shows a film configuration diagram of a conventional ND filter 1. On the transparent substrate 2, Al ₂ O ₃ films 3 are laminated alternately on the first, third, fifth, seventh and ninth layers, and Ti _x O _y films 4 are laminated alternately on the second, fourth, sixth, eighth and tenth layers. An ND film 6 having a total of 11 layers, in which an MgF ₂ film 5 is formed on the eleventh layer as the surface layer, is formed.

The ND film 6 is designed with sufficient consideration so that the spectral transmittance in the visible light wavelength region is uniform. Further, the design value of such layers of thicknesses different, an Al ₂ O ₃ film any number layers or all of the Al ₂ O ₃ film 3 of 3 may be replaced with the SiO ₂ film. Then, even if the Al ₂ O ₃ film 3 is replaced with the SiO ₂ film and the Ti _x O _y film 4 is laminated on each other, it is possible to produce the ND film 6 having substantially the same optical characteristics. It is.

The outermost MgF ₂ film 5 is an antireflection film configured for the purpose of reducing the reflectance of the surface of the ND film 6, and is selected so that the refractive index n is 1.5 or less in the visible light wavelength region. . Since the antireflection film is mainly intended to reduce the reflectance, any material having a low refractive index may be used. For example, even when an SiO ₂ film or the like is used, an almost similar ND film 6 can be produced. it can.

  FIG. 11 shows the change in transmittance in the visible light wavelength region before and after the environmental test in which an environmental load (60 ° C., 90%, 1000 h) was applied to the ND filter 1 shown in FIG. The transmittance is increased by about 1%.

JP 2003-322709 A

However, when a lower metal nitride such as TiN _x , NbN _x , TaN _x , or AlN _x is used as the light attenuating film, the extinction coefficient is relatively large, so the design film thickness needs to be reduced. Since the light amount attenuation rate of the ND filter greatly depends on the film thickness of the light attenuating film, if the designed film thickness is small, a film forming error is likely to occur, which causes a decrease in reproducibility.

  The object of the present invention is to eliminate the above-mentioned problems, reduce the film formation error, and suppress the change in the spectral characteristics due to the oxidation of the metal / metal oxide used as the light attenuation film. An object of the present invention is to provide a stabilized ND filter, a light quantity diaphragm device, and an imaging device.

In order to achieve the above object, an ND filter according to the present invention includes a transparent resin substrate having a higher moisture content than a glass substrate, and a dielectric layer and a light absorption layer stacked on the transparent resin substrate. A light attenuating film, and the light absorbing layer included in the light attenuating film is sandwiched between a water vapor barrier layer and another water vapor barrier layer provided together on the transparent resin substrate. And

  According to the ND filter of the present invention, the light absorption layer of the light attenuation film that is affected by moisture or oxygen that enters the light attenuation film is provided between the plurality of water vapor barrier layers to suppress the change in spectral characteristics. Can do.

It is a block diagram of the imaging optical system of a reference example. It is a film | membrane block diagram of the ND filter of a reference example. It is a graph of the transmittance | permeability change before and after the environmental test of a reference example. 2 is a film configuration diagram of an ND filter according to Embodiment 1. FIG. 2 is a film configuration diagram of an ND filter according to Embodiment 1. FIG. 2 is a graph of transmittance change before and after an environmental test of Example 1. FIG. 6 is a film configuration diagram of an ND filter of Example 2. FIG. 6 is a film configuration diagram of an ND filter of Example 2. FIG. 6 is a graph showing a change in transmittance before and after an environmental test of Example 2. FIG. It is a film | membrane structural view of the conventional ND filter. It is a graph of the transmittance | permeability change before and behind the environmental test of the conventional ND filter.

  FIG. 1 is a configuration diagram of a photographing optical system, in which a solid photographing element 17 including a lens 11, a light amount diaphragm 12, lenses 13 to 15, a low-pass filter 16, a CCD, and the like are sequentially arranged. In the light quantity diaphragm device 12, a pair of diaphragm blades 19 a and 19 b are movably attached to the diaphragm blade support plate 18. An ND filter 20 is bonded to the diaphragm blade 19a for the purpose of reducing the amount of light passing through the opening formed by the diaphragm blades 19a and 19b.

  FIG. 2 shows a film configuration diagram of the ND filter 20 in the reference example. The transparent substrate 21 made of the transparent synthetic resin material of the ND filter 20 has a 200 μm thick Arton (made by JSR Corporation, trade name), which is a norbornene-based resin that is excellent in heat resistance, flexibility, and cost as a substrate material. ) Film is selected.

  In this reference example, Arton (trade name) manufactured by JSR was selected as the material of the transparent substrate 21, but is not limited thereto, and other norbornene resins such as Zeonex and Zeonor (trade name, manufactured by Nippon Zeon Co., Ltd.). May be used. In addition, various transparent synthetic resin substrates such as PMMA, polycarbonate, PET, PEN, PC, and polyimide resin other than norbornene resin can be used.

  Generally, as a material of the transparent substrate 21 used as the ND filter 20 as in this reference example, the heat resistance (glass transition point Tg) is high, the bending elasticity is high, and further, it is transparent in the visible light wavelength region. A material having high properties and low water absorption is more preferable.

  In the case where an ND film is formed on a thin film-like transparent substrate 21 as in this reference example, in consideration of the above-mentioned heat resistance, bending elasticity, cost factors, etc., norbornene resin, polyimide A series resin is one of the most suitable materials.

In this reference example, the first, _third , fifth, seventh, and ninth layers on the transparent substrate 21 are vacuum-deposited on the first, _third , fifth, seventh, and ninth layers of the Al ₂ O ₃ film 22 that is a dielectric layer, and the _second , fourth, sixth, eighth, and tenth layers. Further, Ti _x O _y films 23 as light absorption layers are alternately laminated to form a light attenuating film. Then, an Si ₃ N ₄ film 24 functioning as a water vapor barrier layer is laminated as an eleventh layer on the tenth Ti _x O _y film 23 which is the uppermost layer of the light attenuation film, and an antireflection film is further formed on the outermost layer. forming a MgF ₂ film 25 is, and forming a ND film 26 consisting of a total of 12 layers.

In this manner, the Si ₃ N ₄ film 24 is formed between the MgF ₂ film 25 that is the outermost layer of the ND film 26 and the tenth Ti _x O _y film 23 that is the uppermost layer of the light attenuation film. Thus, intrusion of water vapor or the like from the atmosphere can be prevented. Thereby, deterioration of the Ti _x O _y film 23 that is a light absorption layer can be prevented, and a change in spectral characteristics can be suppressed.

Since the MgF ₂ film 25 is an antireflection film, it is preferably positioned on the outermost layer of the ND film 26. However, the Si ₃ N ₄ film 24, which is a water vapor barrier layer, is used as the outermost layer on the MgF ₂ film 25. It may be formed.

  FIG. 3 shows the experimental results of the change in transmittance in the visible light wavelength region before and after the environmental test (60 ° C., 90%, 1000 h) for the ND filter 20 of this reference example. The change in transmittance before and after the environmental test is approximately 0.6%, which is a significant improvement compared to the transmittance of the conventional ND filter 1 shown in FIG. 11 in which no water vapor barrier layer is provided.

  In this reference example, the vacuum deposition method was used for the formation of the ND film 26. However, in the deposition method such as the sputtering method, the IAD method (ion assist film formation), the IBS method, the ion plating method, and the cluster deposition method. Film formation is possible. In addition, the most appropriate film forming method may be selected as the vapor deposition method in consideration of the purpose and conditions.

In FIG. 4, in addition to the film configuration of the ND film 26 of the reference example, the Si ₃ N ₄ film 24 that is a water vapor barrier layer is formed on the first layer that is the surface of the transparent substrate 21 on which the light attenuation film is formed. By doing so, a total 13-layer film configuration is obtained. That is, the Si ₃ N ₄ film 24 that is a water vapor barrier layer is formed between the Al ₂ O ₃ film 22 closest to the transparent substrate 21.

In particular, when a synthetic resin material is used for the transparent substrate 21, there are advantages such as processability to an arbitrary shape and reduction in size and weight. However, the moisture content of the synthetic resin substrate is higher than that of a glass substrate. As a result, there is a concern that the spectral characteristics of the light attenuating film may change. However, with such a configuration, the moisture of the transparent substrate 21 is prevented from entering the upper layer of the Si ₃ N ₄ film 24, and the change in the spectral characteristics of the light attenuation film due to the moisture from the transparent substrate 21 is prevented. Can be reduced.

In this case, the adhesion between the Si ₃ N ₄ film 24 and the transparent substrate 21 may be a problem. At that time, as shown in FIG. 5, a SiO ₂ film 31 or a SiO film having a relatively high adhesion and a low water absorption rate is formed as the first layer, and a Si ₃ N ₄ film is formed as a water vapor barrier layer thereon. It can be improved by depositing 24 and forming a total of 14 layers.

  FIG. 6 shows the experimental results of the change in transmittance in the visible light wavelength region before and after the environmental test (60 ° C., 90%, 1000 h) for the ND filter 20 in the first embodiment. The change in transmittance before and after the environmental test was approximately 0.4%.

FIG. 7 shows a film configuration diagram in the second embodiment. In the second embodiment, a Si ₃ N ₄ film 24 that is a water vapor barrier layer is formed between all the Al ₂ O ₃ films 22 and the Ti _x O _y film 23. At the same time, by forming the Si ₃ N ₄ film 24 between the outermost MgF ₂ film 25 and the 20th Ti _x O _y film 23 of the optical attenuation film, a total of 22 film structures are formed. It is said. The Si ₃ N ₄ film 24 inserted between the Al ₂ O ₃ film 22 and the Ti _x O _y film 23, the transmission of preventing the optical attenuation film oxidation of Ti _x O _y film 23 by the Al ₂ O ₃ film 22 Further reduce the rate change.

Note that it is not necessary to form the Si ₃ N ₄ film 24 which is a water vapor barrier layer between all the Al ₂ O ₃ films 22 and the Ti _x O _y film 23, and as shown in FIG. A water vapor barrier layer may be interposed. In particular, it is preferable to form the upper and lower surfaces of the thinnest Ti _x O _y film 23 that is most susceptible to the influence of oxygen and moisture with a water vapor barrier layer.

  FIG. 9 shows the experimental results of the change in transmittance in the visible light wavelength region before and after the environmental test (60 ° C., 90%, 1000 h) for the ND filter 20 in the second embodiment. The change in transmittance before and after the environmental test was approximately 0.3%.

The film thickness of the Si ₃ N ₄ film 24 which is a water vapor barrier layer has a predetermined light amount attenuation rate, that is, a predetermined transmittance in the use band of the ND filter 20, for example, in the normal visible light wavelength region of about λ = 400 to 700 nm. . The film thickness of the Si ₃ N ₄ film 24 is determined in advance together with the film thicknesses of the Al ₂ O ₃ film 22 and the Ti _x O _y film 23.

In the above-described embodiment, the Si ₃ N ₄ film 24 is used as the water vapor barrier layer, but substantially the same effect can be obtained even if SiO _x N _y is used. Since Si ₃ N ₄ and SiO _x N _y have a relatively small extinction coefficient, there is little influence of light absorption by Si ₃ N ₄ and SiO _x N _y , and the degree of design freedom can be expanded. That is, the water vapor barrier layer may be one or more of Si ₃ N ₄ and SiO _x N _y , and the film thickness may be set to an arbitrary thickness so as to satisfy desired optical characteristics.

Si ₃ N ₄ and SiO _x N _y can be formed by reacting in an Ar · N ₂ atmosphere and an Ar · N ₂ · O ₂ atmosphere, respectively, using Si as an evaporation source. Since Si ₃ N ₄ and SiO _x N _y have poor adhesion compared to Al ₂ O ₃ and Ti _x O _y , a finer film can be formed by assisting with an IAD method or an ion plating method. It becomes a film | membrane and the effect of a water vapor | steam barrier can be improved.

  The ND filter 20 manufactured in this way is applied to an imaging apparatus such as a video camera or a digital still camera, so that a light quantity diaphragm apparatus having good performance over a long period can be obtained.

20 ND filter 21 Transparent substrate 22 Al ₂ O ₃ film 23 Ti _x O _y film 24 Si ₃ N ₄ film 25 MgF ₂ film 26 ND film 31 SiO ₂ film

Claims (8)

A transparent resin substrate having a large moisture content compared to a glass substrate ;
A light attenuation film provided by laminating a dielectric layer and a light absorption layer on the transparent resin substrate,
The light absorbing layer included in the optical attenuation film, ND filter, characterized in that interposed between said transparent resin water vapor barrier layer together provided on the substrate and another water vapor barrier layer.   The ND filter according to claim 1, wherein the water vapor barrier layer is formed on the transparent resin substrate through a film having higher adhesion to the transparent resin substrate than the water vapor barrier layer. The other water vapor barrier layer is formed between an antireflection film that forms an outermost surface as an ND filter on the light attenuation film and a light absorption layer that is an uppermost layer of the light attenuation film. The ND filter according to claim 1 or 2.   The ND filter according to claim 1, wherein the other water vapor barrier layer and the water vapor barrier layer are formed on upper and lower surfaces of the light absorption layer.   The ND filter according to any one of claims 1 to 4, wherein the transparent resin substrate is a synthetic resin of a norbornene-based resin. The ND filter according to claim 1, wherein the water vapor barrier layer is made of Si ₃ N ₄ or SiO _x N _y .   A light quantity diaphragming device comprising the ND filter according to claim 1.   An imaging device using the light quantity diaphragm device according to claim 7.

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