JP2018092030A - Optical filter and imaging optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical filter and an image pickup element having stable light amount adjustment performance. SOLUTION: A multi-layer structure in which a light amount adjusting layer provided on at least one surface of a light transmitting substrate is formed between a first and second light absorbing layers and these first and second light absorbing layers. It is composed of an intermediate layer, and the extinction coefficient in the visible light wavelength region of the layer on the first light absorption layer side of the intermediate layer of the multilayer structure is the extinction coefficient in the visible light wavelength region of the layer on the second light absorption layer side. The structure is larger than that, and the film thickness of the layer on the first light absorption layer side is thinner than the film thickness of the layer on the second light absorption layer side. [Selection diagram] Fig. 1

Description

  The present invention relates to an optical filter and an imaging optical system having the optical filter.

  An imaging optical system such as a camera is equipped with an imaging element such as a CCD or CMOS, and an image is obtained by converting light incident on the imaging element into an electrical signal. The imaging optical system is provided with an aperture mechanism and an optical filter such as an ND filter that adjust the amount of light incident on the imaging element in accordance with the shooting situation.

  The light amount adjustment filter has a function of substantially uniformly attenuating the transmittance in the light wavelength band used for photographing, and can adjust the amount of light incident on the image sensor while maintaining color reproducibility. By using the optical adjustment filter, it is possible to reduce the hunting phenomenon that can be caused by the light amount adjustment only by the diaphragm mechanism and the deterioration of the image due to the diffraction of light, and to obtain a higher quality image.

  An optical filter mounted in an imaging optical system such as a camera has a substantially uniform transmittance in the target light wavelength region, that is, the flatness of the transmittance is regarded as important. In general, a laminated structure of a light absorption layer made of a metal or a metal compound and a dielectric layer made of a metal oxide is used.

Japanese Patent Laid-Open No. 2003-43211

  Here, in a conventional optical filter such as an ND filter, for example, the optical characteristics of the light absorption layer of the light absorption layer and the dielectric layer are not particularly stable, and the light quantity adjustment performance may not be stably obtained. there were.

  The present invention provides an optical filter and an image sensor having a stable light amount adjustment function.

  In order to solve the above-described problems, an optical filter according to the present invention includes an optical adjustment layer provided on at least one surface of a light-transmitting substrate, metal A, metal A oxide AO, and metal A nitride. First and second light absorption layers selected from the group consisting of AN, and an oxide BO or nitridation of metal B which is a metal element different from metal A formed between the first and second light absorption layers And the extinction coefficient in the visible light wavelength region of the layer on the first light absorption layer side of the intermediate layer of the multilayer structure is the second light absorption layer side. And the thickness of the layer on the first light absorption layer side constituting the intermediate layer is thinner than that on the second light absorption layer side.

  ADVANTAGE OF THE INVENTION According to this invention, the optical filter and imaging device which have the function of the stable light quantity adjustment are realizable.

The block diagram of the optical filter which concerns on this invention. 1 is a configuration diagram of an optical filter according to Embodiment 1. FIG. The figure which shows the spectral transmittance characteristic of the optical filter which concerns on the design examples 1-3. FIG. 6 is a configuration diagram of an optical filter according to a second embodiment. FIG. 6 is a diagram showing spectral transmittance characteristics of an optical filter according to design example 4; FIG. 6 is a configuration diagram of an optical filter according to a third embodiment. FIG. 10 is a diagram showing spectral transmittance characteristics of an optical filter according to design example 5. The figure which shows the transmittance | permeability characteristic of an infrared cut film. FIG. 10 is a configuration diagram illustrating a modification of the optical adjustment filter according to the third embodiment. FIG. 10 is a graph showing the transmittance characteristics of an infrared cut film in a modification of the optical adjustment filter of Example 3. The block diagram which shows the imaging optical system using the optical filter concerning this invention.

  Hereinafter, the structure of an optical filter according to an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a configuration diagram of an optical filter according to an embodiment of the present invention as an example.
In the optical filter of the present invention, an optical adjustment layer provided on at least one surface of a transparent substrate transparent at a desired light wavelength is formed of a metal A, a metal A oxide AO, and a metal A nitride AN. And a compound of oxide BO or nitride BN of metal B which is a metal element different from metal A formed between the first and second light absorption layers It is obtained by comprising with the intermediate layer of the multilayer structure formed by.

  In the present invention, among the intermediate layers having a multilayer structure, the layer on the first light absorption layer side has a larger extinction coefficient in the visible light wavelength region than the layer on the second light absorption layer side, and The film thickness is thin. Further preferably, an antireflection layer is formed on the outermost layer of the optical filter.

  Here, as described above, the optical adjustment layer in the present invention constitutes one optical adjustment layer with the first and second light absorption layers and the intermediate layer having a multilayer structure provided therebetween, For example, in the case where a plurality of optical adjustment layers are provided on a substrate, a light absorption layer and an intermediate layer may be alternately stacked, and one light absorption layer and an intermediate layer may be used as one optical adjustment layer. When a plurality of optical adjustment layers are provided, the intermediate layer may be a combination of a single layer structure and a multilayer structure (two or more layer structures).

  In the present invention, one or more optical adjustment layers may be provided on at least one surface of the substrate to constitute an optical filter. However, one or more optical adjustment layers are provided on both surfaces of the substrate, respectively. An optical filter may be configured. One or a plurality of optical adjustment layers and an antireflection layer are combined to form a light amount adjustment film.

The elements that constitute the optical filter of the present invention will be described below.
(Transparent substrate)
As the transparent substrate used in the present invention, any substrate can be used as long as it is a transparent substrate in a desired light wavelength region. For example, substrates made of inorganic materials such as glass and quartz, polyester, norbornene, polyether, acrylic, styrene, PET (polyethylene terephthalate), PES (polyethersulfone), polysulfone, PEN (polyethylene Various synthetic resin substrates such as phthalate), PC (polycarbonate), and polyimide can be used.

  A synthetic resin substrate is softer and lighter and has better workability than an inorganic substrate such as glass, but is prone to deformation due to film stress or thermal stress, and property change due to moisture. For this reason, when using a synthetic resin substrate, it is desirable to use a material having high heat resistance (high glass transition temperature Tg), high flexural modulus, and low water absorption. For example, a polyimide or PES system can be used as a high heat resistance substrate, a PET can be used as a substrate having a large flexural modulus, and a norbornene system can be used as a low water absorption base material. Further, if necessary, a substrate made of an organic-inorganic hybrid material, for example, a substrate having a silsesquioxane skeleton may be used.

  In the present invention, the transparent substrate is a substrate having light transmittance at least in the visible light wavelength. For example, a substrate having light absorption in the ultraviolet wavelength region or the infrared wavelength region may be used. Good. As such a substrate, for example, an ultraviolet absorbing substrate in which an ultraviolet absorber is kneaded into glass or resin, a dye or pigment having infrared absorbing performance, or a metal ion typified by copper is kneaded into glass or resin. Examples include an infrared absorption substrate.

  Further, the thickness of the substrate is preferably as thin as possible within a range in which rigidity can be maintained in consideration of reduction in size and weight, and specifically, about 20 μm to 1 mm and about 25 μm to 400 μm are preferable. In addition, when using the board | substrate which has light absorption other than the transmission band formed with an optical interference thin film laminated body, the base material thickness is determined also considering the light absorption characteristic of a board | substrate.

(First and second light absorption layers)
The first and second light absorption layers of the present invention include at least one light absorption selected from the group consisting of a metal A having a light absorption characteristic, a metal A oxide (AO), and a metal A nitride (AN). Specific examples of the light-absorbing material include metals A such as Ti, Ni, Cr, Fe, Nb, and Ta, alloys, oxides, and nitrides.

  The first light absorption layer and the second light absorption layer may be formed using the same light absorption material, but may be formed using different light absorption materials. When the metal A is used as the first and second light absorption layers, it is preferable that the plasma frequency is higher than the frequency of light in a wavelength region where light absorption is desired to be exhibited.

  Here, the plasma frequency refers to a limit frequency at which metal free electrons cause plasma oscillation. When the plasma frequency is greater than the light frequency, light is prevented from entering the metal and reflected. On the other hand, when the frequency of light is greater than the plasma frequency, the light enters the metal and is absorbed by the metal. For this reason, by selecting a material in which the plasma frequency of the metal A is larger than the frequency of light in the wavelength region where light absorption is desired to occur, an optical filter with higher transmittance flatness in a desired region can be obtained. .

  When the metal A oxide (AO) and the metal A nitride (AN) are used as the first and second light absorption layers, the extinction coefficients of the first and second light absorption layers are 0.5 or more. Is preferred. Here, the extinction coefficient indicates how much light is attenuated when light is incident on the material. The larger this value, the stronger the incident light is attenuated.

  Here, compared with metals and alloys, the extinction coefficient of the oxide (AO) of the metal A or the nitride (AN) of the metal A is small. In the first and second light absorption layers, if the extinction coefficient is too small, the number of layers and the film thickness necessary for attenuating the desired light amount are increased, which causes warping or cracking of the optical filter. is there. Further, the first and second light absorption layers are preferably layers made of metal A oxide (AO) or metal A nitride (AN). Since metal oxide or nitride has a smaller extinction coefficient than metal, the thickness of each layer can be kept to some extent.

  For this reason, the degree of freedom in film design is increased, the stability of the film thickness control of the light absorption layer is improved, and an optical filter having good spectral characteristics and good reproducibility of optical characteristics can be obtained. When the metal A oxide (AO) or the metal A nitride (AN) is used for the first and second absorption films, it is particularly preferable to use titanium oxide (TiOx 0 <x <2). is there. This is because TiOx has a relatively linear absorption characteristic in the visible region and can be an optical filter with a flatter transmittance characteristic.

  The first and second light absorption layers can be formed by various known techniques such as vacuum deposition, ion plating, and ion assist.

(Middle layer)
The intermediate layer of the present invention is formed from a compound of an oxide BO or nitride BN of a metal B, which is a metal element different from the metal A formed between the first and second light absorption layers, for example, Si, It is formed from oxides, nitrides or oxynitrides such as Al, Mg, La, Zr, Ti, Nb and Ta. In the present invention, when the intermediate layer is formed of a multilayer structure, for example, the first intermediate layer and the second intermediate layer, the first intermediate layer and the second intermediate layer may use the same material, Materials may be used.

  The intermediate layer has a multilayer structure. For example, when the intermediate layer is formed of two layers (first and second intermediate layers), the first intermediate layer is formed on the first light absorption layer, and the first intermediate layer is formed on the first intermediate layer. Two intermediate layers are formed. Then, one optical adjustment layer is formed by forming the second light absorption layer on the second intermediate layer.

  In this case, the first intermediate layer is provided so that the extinction coefficient of the first intermediate layer in the visible light wavelength region is larger than the extinction coefficient of the second intermediate layer in the visible light wavelength region. At this time, the magnitude relationship between the extinction coefficient of the compound forming the first intermediate layer and the extinction coefficient of the compound forming the second intermediate layer is defined at the same wavelength.

  Note that three or more intermediate layers may be provided. In that case, the compound forming each intermediate layer is made of a similar material, which is advantageous in reducing the difference in refractive index and improving the adhesion.

For example, when a first intermediate layer and a second intermediate layer are laminated with aluminum oxide on a first light absorption layer formed of a titanium oxide oxide (TiO _x ), the oxidation that forms the first intermediate layer It is formed so that the oxidation number of aluminum oxide (Al ₂ O _z ) forming the second intermediate layer is larger than the oxidation number of aluminum (Al ₂ O _y ), that is, y <z is satisfied. The second intermediate layer is preferably formed to be, for example, Al ₂ O ₃ so that the extinction coefficient at the visible light wavelength is as small as possible.

  For example, when forming the first intermediate layer, the first intermediate layer is formed by introducing the reactive gas without introducing a reactive gas, and forming the second intermediate layer while sufficiently introducing a reactive gas such as oxygen. The extinction coefficient in the visible light wavelength region of the second intermediate layer becomes larger than the extinction coefficient in the visible light wavelength region of the second intermediate layer, and the extinction coefficient in the visible light wavelength region of the second intermediate layer becomes close to zero. In addition, it can suppress that the extinction coefficient of a 1st absorption layer fluctuates at the time of intermediate layer film-forming by not introduce | transducing reactive gas at the time of 1st intermediate layer film-forming.

  Here, if the extinction coefficient of the first intermediate layer is set to be larger than that of the second intermediate layer, the light absorption rate of the first intermediate layer increases. However, in the present invention, the variation factor of the optical absorption characteristics of the optical filter In order to minimize the thickness of the first intermediate layer, the thickness of the first intermediate layer should be as thin as possible, preferably less than half that of the second intermediate layer, more preferably less than 1/4. .

  That is, the first intermediate layer is provided so as to have a larger extinction coefficient than that of the second intermediate layer, and the fluctuation of the extinction coefficient of the first light absorption layer due to the formation of the second intermediate layer is suppressed. By reducing the thickness of the layer as much as possible to minimize the influence on the light absorption characteristics of the optical filter, and further providing the second intermediate layer so that the extinction coefficient of the second intermediate layer is substantially zero, The light absorption characteristics can be determined by the first and second light absorption layers. That is, the first and second light absorption layers can provide a stable light amount adjustment function without being affected by the intermediate layer.

  The extinction coefficient of the first intermediate layer is preferably 0.1 or less. This is because if the extinction coefficient is larger than 0.1, the influence on the transmittance characteristics of the optical filter is increased, and the transmittance characteristics may be significantly deteriorated.

  Furthermore, as described above, the first intermediate layer is thinner than the second intermediate layer, and specifically, it is preferably 60 to 200 mm. If the film thickness is less than 60 mm, the first intermediate layer has a sea-island structure and there is a possibility that a sufficient layer may not be formed. The oxidation of the first light absorption layer by the reactive gas introduced during the formation of the second intermediate layer or the Nitriding may not be sufficiently prevented. On the other hand, if it is thicker than 200 mm, the minute light absorption characteristics in the visible light wavelength region of the first intermediate layer may adversely affect the transmittance flatness of the optical filter.

  The intermediate layer has a function for flattening the transmittance flatness of the optical filter. The extinction coefficient of the light absorption layer is not necessarily uniform in the visible light wavelength region. Therefore, in order to make the amount of light absorbed by the entire light absorption layer substantially uniform in the visible light wavelength region, light interference occurs at the interface between the light absorption layer and the intermediate layer, and light is transmitted or reflected under optimum conditions. There is a need.

  Depending on the material of the light absorption layer and the required flatness of transmittance, a film thickness of about 60 to 1500 mm is required as the intermediate layer to obtain the optimum optical interference at the interface between the light absorption layer and the intermediate layer. It becomes. As described above, since the first intermediate layer has a large extinction coefficient, when the thickness of the intermediate layer is greater than 200 mm, a multilayer structure of the first intermediate layer and the second intermediate layer is used. It is preferable to make it 200 or less.

  Here, the intermediate layer is a compound of an oxide BO or nitride BN of a metal B which is a metal element different from the metal A formed between the first and second light absorption layers. This is to effectively provide a difference in refractive index from the intermediate layer.

  As described above, in order to improve the transmittance flatness of the optical filter, it is necessary to use the light interference effect between the light absorption layer and the intermediate layer, but when the light absorption layer and the intermediate layer are made of the same metal element, This is because a sufficient difference in refractive index may not be obtained, and an effective optical interference function may not be obtained.

  Specifically, the first and second intermediate layers can be formed by various known methods such as vacuum deposition, ion plating, and ion assist. For example, the first and second intermediate layers are formed using metal B or metal oxide BO as a starting material, the first intermediate layer is formed without introducing a reactive gas such as oxygen, and the second intermediate layer has sufficient oxygen. Alternatively, the film is formed by introducing a reactive gas composed of nitrogen.

  The first and second intermediate layers are preferably a compound made of the same metal B and a metal oxide BO or metal nitride BN. By forming from the same metal, the difference in refractive index between the first and second intermediate layers can be made extremely small, and the transmittance characteristics of the optical filter are deteriorated due to optical interference with the first and second intermediate layers. Can be suppressed.

  Furthermore, the first and second intermediate layers can be made tight by closely bonding the first and second intermediate layers by using a metal oxide BO made of the same metal B or a compound made of metal nitride BN. It becomes.

(Antireflection layer)
An antireflection layer is preferably formed on the outermost layer of the optical filter of the present invention. The antireflection layer is made of a material having a small refractive index, such as SiO ₂ or MgF _2, and is formed so that the optical film thickness is about λ / 4, where λ is the central wavelength of the wavelength region for suppressing reflection. . Here, the optical film thickness is represented by the product of the refractive index and the physical film thickness. The antireflection layer can be formed by various known methods such as vacuum deposition, ion plating, and ion assist. The antireflection layer may be formed from a plurality of thin films having different refractive indexes as necessary. Also when formed from a plurality of thin films, the optical film thickness of the outermost layer is preferably about λ / 4. Here, about λ / 4 refers to a film thickness of about 0.7 to 1.3λ / 4.

<Example 1>
FIG. 2 shows a configuration diagram of an optical filter according to the present embodiment. The optical filter of the present embodiment has a configuration in which a light amount adjustment film 8 including a plurality of optical adjustment layers and an antireflection layer is formed on both surfaces of a transparent substrate. Table 1 shows a design example of the optical filter according to Example 1 as Design Example 1.

The optical filter 11 of the design example 1 includes a transparent substrate made of a PET substrate having a thickness of 75 μm, first and second light absorption layers made of TiO _x (0 <x <2), and Al ₂ O _y (first oxide). ) And a _second intermediate layer made of Al ₂ O _z (second oxide).

Here, y <z, and the extinction coefficient of Al ₂ O _{y at} the visible light wavelength is larger than the extinction coefficient of Al ₂ O _{z at} the visible light wavelength. Further, an antireflection layer made of MgF2 is formed on the outermost layer.

In the light amount adjustment film 8 of the present embodiment, the light absorption layers of all the optical adjustment layers are TiO _x , the first intermediate layer is the first compound Al ₂ O _y , and the second intermediate film is the second compound Al ₂ O _z. ing. FIG. 3 shows the spectral transmittance characteristics of the optical filter of design example 1.

A method for manufacturing the optical filter of this example will be described. The optical filter of Example 1 was produced by a vacuum deposition method. First, the PET substrate is set on a film forming jig, and is attached to the vapor deposition dome so that the film forming surface of the PET substrate faces the vapor deposition material. The vapor deposition dome is put into the vapor deposition chamber and exhausted. When the inside of the vapor deposition chamber reaches a desired degree of vacuum, for example, about 1.0 × 10 ⁻³ Pa, film formation of the first light absorption layer is started.

The first light absorption layer uses titanium oxide as a starting material, and heats the titanium oxide stored in the crucible with an electron beam, and deposits it on the PET substrate. Titanium oxide is deposited on the PET substrate as a TiO _x film. In this embodiment, no reactive gas such as oxygen was introduced when forming the first light absorption layer, but it may be introduced as needed.

  Subsequently, after the first light absorption layer is formed with a desired film thickness, the first intermediate layer is formed next. The first intermediate layer uses aluminum oxide as a starting material. Aluminum oxide, which is a starting material filled in the crucible, is heated with an electron beam and evaporated without introducing oxygen gas.

  When the film is formed without introducing oxygen gas, the oxygen vacancies of aluminum oxide, which is a starting material generated by the energy of the electron beam, are formed without being sufficiently supplemented before reaching the PET substrate. By not introducing oxygen gas during the formation of the first intermediate layer, it is possible to suppress the fluctuation of the extinction coefficient of the first absorption layer and form the intermediate layer.

Further, when the first intermediate layer is formed, the second intermediate layer is formed. Similar to the first intermediate layer, the second intermediate layer uses aluminum oxide as a starting material. The second intermediate layer is formed by heating aluminum oxide, which is a starting material, by an electron beam and introducing oxygen gas so that the pressure in the chamber becomes 3.0 × 10 ⁻³ Pa.

  By forming the film in this manner, a layer in which oxygen deficiency of the starting aluminum oxide generated by the energy of the electron beam is sufficiently supplemented by oxygen introduced into the chamber can be obtained.

In this embodiment, the pressure at the time of forming the second intermediate layer is set to 3.0 × 10 ⁻³ Pa. However, the pressure is not limited to this, and an optimal oxygen gas is used depending on the film formation rate and the pressure at the start of film formation. The amount introduced may be used. Here, the first intermediate layer is configured to be thinner than the second intermediate layer.

  Both the first intermediate layer and the second intermediate layer are oxides of aluminum, but the first intermediate layer is in a state where oxygen vacancies are generated and has a weak absorption in the visible light wavelength region. This is because if the layer is thick, the transmittance flatness of the light amount adjusting film may be deteriorated.

Subsequently, when the film formation of the second intermediate layer is finished, TiO _x that is the second absorption layer is formed. The second absorption layer can be formed in the same manner as the first absorption layer. The light absorption layer and the intermediate layer are sequentially formed as described above, and when the ninth layer is formed, an antireflection layer is formed. Such an antireflection layer may not be provided.

In this example, MgF ₂ was deposited as an antireflection layer. As the antireflection layer, a crucible filled with magnesium fluoride as a starting material is heated by an electron beam to form a MgF ₂ film with a desired thickness. When film formation of the antireflection layer is completed, venting is performed, the pressure in the vapor deposition chamber is set to normal pressure, and the PET substrate is taken out. Further, a light amount adjustment film comprising a light absorption layer, an intermediate layer and an antireflection layer is also formed on the opposite surface of the PET substrate.

  In particular, when a resin substrate or the like is used as the transparent substrate as in this embodiment, it is preferable to provide a light amount adjustment film on both surfaces of the transparent substrate, and the light amount adjustment films provided on both surfaces of the substrate are designed to be substantially the same. More preferably. With such a configuration, even when a resin substrate having relatively low rigidity is used as the transparent substrate, an optical filter with small warpage and undulation can be obtained.

  In the present embodiment, the optical filter in which the light amount adjusting film of the same design is formed on both surfaces of the transparent substrate is used. However, the light amount adjusting film may be formed only on one side of the transparent substrate, or different films on each surface. It is good also as a design light quantity adjustment film | membrane. Further, a light amount adjustment film may be formed only on one surface of the substrate.

Moreover, you may provide a base layer in the interface of a transparent substrate and a light quantity adjustment film | membrane. Preferably oxides of metals as the base layer, for example SiO ₂ or _Al 2 _O 3, etc. TiO ₂ is preferred. The underlayer preferably does not affect the transmittance flatness of the light amount adjusting film, and preferably has low light absorption in the visible light wavelength region.

  Specifically, it is preferable that the oxidation number is the same as that of the second intermediate layer, that is, it is a metal oxide that is almost completely oxidized. By providing these base layers, the adhesion between the transparent substrate and the light amount adjusting film can be improved. Furthermore, when a transparent substrate made of a resin having a large water absorption rate is used as in this embodiment, water vapor and oxygen move from the transparent substrate to the first layer. The effect which suppresses this can also be expected.

In the design example 1, all the intermediate layers have a multilayer structure. However, for example, as shown in the design example 2 in Table 2, a configuration in which a part of the intermediate layers is composed of one layer may be used. In design example 2, the intermediate layer existing between the fourth and sixth light absorption layers is only Al ₃ O _y .

  In design example 2, the film thickness required for the fifth intermediate layer is sufficiently small, and the light absorption due to oxygen vacancies in the fifth intermediate layer does not affect the flatness of the light amount adjustment film. This is because it is thick. FIG. 3 shows the spectral transmittance characteristics of the optical filter of design example 2.

In design example 1, both the first intermediate layer and the second intermediate layer are made of metal oxide (Al ₂ O _y or Al ₂ O _z ). However, as shown in design example 3, for example, the first intermediate layer is made of the first compound SiO 2. _n , the second intermediate layer may be a second compound Si ₃ N _m , one may be a metal oxide (first oxide), and the other may be a metal nitride (second nitride). Also in this case, the extinction coefficient in the visible light wavelength region of the first intermediate layer is larger than the extinction coefficient in the visible light wavelength region of the second intermediate layer, and the first intermediate layer is thinner than the second intermediate layer. It is a layer.

The Si ₃ N _m of the second intermediate layer is preferably formed in a sufficiently nitrided state, that is, Si ₃ N _4, and the extinction coefficient in the visible light wavelength region is preferably substantially zero. Here, SiO _n is obtained by heating silicon oxide with an electron beam using silicon oxide as a starting material and forming a film without introducing a reactive gas, and nitride film SiN _m is obtained by using silicon as a starting material. It is obtained by heating silicon as a starting material with a beam and introducing nitrogen gas so that the pressure in the chamber becomes 8.0 × 10 ⁻³ Pa.

  By forming the film in this way, the fluctuation of the extinction coefficient of the first light absorption layer due to the intermediate layer film formation can be suppressed, and an optical adjustment film having stable optical characteristics can be obtained. FIG. 3 shows the spectral transmittance characteristics of the optical filter of Design Example 3 (Table 3).

  The light amount adjustment film may have a region where the transmittance changes stepwise or continuously in the surface direction. Optical filters having different transmittance densities in stages can be produced, for example, by using a plurality of film formation masks having different openings when forming an optical adjustment film.

  The film formation mask determines the range of the vapor deposition film formed on the transparent substrate, and the opening of the film formation mask becomes a film formation region on the transparent substrate. By using a plurality of film formation masks with different openings and performing vapor deposition a plurality of times, the regions where the film is formed in the respective vapor deposition processes are different. .

  An optical filter whose transmittance changes continuously is, for example, that the thickness of the light absorption layer, which mainly determines the transmittance of the light amount adjustment film, changes continuously in the plane direction, or the light absorption layer is formed. It can be produced by adjusting the amount of reactive gas introduced at the time and changing the oxidation number or nitridation number continuously low in the surface direction.

  When the transmittance changes stepwise or continuously, it is preferable that a region where the light absorption layer is not formed, that is, a substantially transparent region exists in the optical filter. The light amount adjusting film whose transmittance changes stepwise or continuously is not limited to the above-described method, and can be manufactured by various known methods.

<Example 2>
FIG. 4 shows a configuration diagram of an optical filter according to the present embodiment. The optical filter of this embodiment has a configuration in which the light amount adjusting film 8 is formed on one surface of the transparent substrate 1 and the antireflection film 9 is formed on the other surface. Table 4 shows a design example of the optical adjustment filter according to Example 2 as Design Example 4.

  In the optical filter of this example, an optical adjustment layer composed of a light absorption layer and an intermediate layer is formed on one surface of a transparent substrate 400 μm thick glass substrate (B270i: manufactured by Schott). It has a configuration in which an antireflection film comprising a plurality of layers is formed on the surface. The optical filter of design example 4 has spectral transmittance characteristics as shown in FIG. 5, and the spectral transmittance in the visible light wavelength region is substantially uniform.

The optical adjustment film of design example 4 uses TiO _x and Ti as the light absorption layer. In design example 4, the light amount adjustment film is required to attenuate light only on one side of the transparent substrate. For this reason, in the design example 4, Ti which is a metal film is used for a part of the light absorption layer. Ti has a larger extinction coefficient than TiO _x, and the use of Ti can reduce the total thickness of the light absorption layer.

Ti is formed by using metal titanium as an evaporation material, irradiating a crucible filled with metal titanium with an electron beam, and forming a film without introducing a reactive gas such as oxygen gas during film formation. The other light absorbing layers, TiO _x and the first and second intermediate layers, were formed under the same conditions as in Example 1.

  In Design Example 4, only a part of the light absorption layer is a metal film. However, all layers of the light absorption layer may be a metal film, or the metal film may not be used. Moreover, the metal element which forms a 1st absorption layer and a 2nd absorption layer may differ.

Here, the antireflection film will be described. In design example 4, the antireflection film is provided to suppress surface reflection of the surface of the transparent substrate on which the light amount adjustment film is not formed. The antireflection film is formed by laminating a plurality of thin films having different refractive indexes. In the design example 4, four layers of TiO ₂ and SiO ₂ are alternately laminated.

In design example 4, TiO ₂ and SiO ₂ are used, but not limited thereto, MgF ₂ , SiO, Si ₃ H ₄ , Al ₂ O ₃ , MgO, LaTiO ₃ , ZrO ₂ , Nb ₂ O ₅ , Ta ₂ O Various materials such as ₅ can be used in any combination.

The outermost layer of the antireflection film is preferably a low refractive index material, although the SiO ₂ In Example 4, MgF ₂ can be preferably used. In this embodiment, the reason why the antireflection film is composed of a plurality of layers is to prevent the transmittance flatness of the light amount adjustment film from being affected as much as possible.

  The single-layer antireflection film has the lowest reflectance at the center wavelength, and the reflectance gradually increases as the distance from the center wavelength increases. That is, in the case of an antireflection film formed from a single layer, as the distance from the center wavelength of the antireflection film increases, the transmittance of the optical filter decreases due to the influence of the antireflection film, and the flatness of the transmittance may be deteriorated. . On the other hand, when the antireflection film has a laminated structure composed of a plurality of layers, reflection can be suppressed in a wider wavelength range than a single-layer antireflection film, and the transmittance flatness of the optical filter is significantly deteriorated. This can be suppressed.

  In this embodiment, metal oxides are used for the first intermediate layer and the second intermediate layer. However, a single intermediate layer may be included as in Design Example 2, or the first intermediate layer may be included as in Design Example 3. A metal oxide may be used for the intermediate layer, and a metal nitride may be used for the second intermediate layer. As in the first embodiment, the light amount adjustment film in this embodiment may have a region where the transmittance changes stepwise or continuously.

<Example 3>
FIG. 6 shows a configuration diagram of an optical filter according to the present embodiment. The optical filter of this example has a structure in which a light amount adjusting film is formed on one surface of a transparent substrate and an infrared cut film is formed on the other surface. Table 5 shows a design example of the optical filter according to Example 3 as Design Example 5.

  The optical filter of this example uses an infrared absorbing glass (NF50T: manufactured by Asahi Glass Co., Ltd.) having a thickness of 400 μm that substantially transmits visible light and has an absorption function in the infrared wavelength region as a transparent substrate 1, and an infrared absorbing glass. The light quantity adjustment film 8 having the optical adjustment layer composed of the light absorption layer and the intermediate layer is formed on one surface of the infrared ray cut film, and the other surface is an infrared cut film made of a laminate of a plurality of thin films having different refractive indexes. 10 is formed. The spectral characteristics of the optical filter of design example 5 are shown in FIG.

  In the optical filter of design example 5, the transmittance in the visible light wavelength region is attenuated substantially uniformly by the light amount adjusting film, and at the same time, the transmission of light in the near infrared wavelength region is shielded by the infrared cut film.

  A method for manufacturing the optical filter of this example will be described. The infrared absorbing glass is set on a film forming jig, and a light amount adjusting film is formed on one surface of the infrared absorbing glass in the same manner as in the first embodiment. Next, an infrared cut film is formed on the surface opposite to the surface on which the light amount adjustment film of the infrared absorption glass is formed.

Here, the infrared cut film will be described. The infrared cut film is a plurality of thin film laminated structures having different refractive indexes. The thin film is laminated so as to reflect the light in the infrared wavelength region by expressing optical interference using the difference in refractive index of the thin film. _The thin film material _may be used _{MgF 2, SiO 2, SiO,} Si 3 H 4, Al 2 O 3, MgO, etc. _{LaTiO 3, ZrO 2, TiO 2} , Nb 2 O 5, Ta 2 O 5.

  The infrared cut film is a refraction having an optical film thickness of about λ / 4, specifically about 0.7 to 1.3λ / 4, where λ is the center wavelength in the cut wavelength region formed by the infrared cut film. The basic structure is a structure in which a plurality of inorganic thin films having different rates are stacked. However, in order to reduce the ripple in the transmission band, a layer greatly separated from λ / 4 may be provided. In particular, it is effective to form a plurality of layers that reduce ripples at the interface with the transparent substrate.

  The infrared cut film has a spectral characteristic as shown in FIG. 8 and has a transition wavelength region that transitions from the transmission region to the cut region, and a red light with a transmittance of 50% in this transition wavelength region. There is an outer half-value wavelength. Although the infrared absorption glass used in this example also has an infrared half-value wavelength, the infrared half-value wavelength formed by the infrared cut film is longer than the infrared half-value wavelength of the infrared absorption glass. It is preferable to be present on the side.

  Compared with the infrared cut film, the infrared half-value wavelength of the infrared absorbing glass is less likely to vary in the manufacturing method. For this reason, it can be set as the optical filter with which the infrared half value wavelength was stabilized by setting it as the structure which an infrared half value wavelength mainly determines with infrared absorption glass.

In the infrared cut film, the larger the refractive index difference of the thin film, the fewer the number of layers necessary for obtaining the desired spectral characteristics, so it is preferable that the combination has a large refractive index difference as much as possible. An infrared cut film was formed of SiO ₂ and TiO ₂ . The reason for this combination is that the combination has the largest refractive index difference.

The infrared cut film is produced as follows. The surface opposite to the surface on which the optical adjustment layer of the infrared absorption glass is formed is set in the vapor deposition dome so as to correspond to the vapor deposition material, and exhausted until the pressure in the vapor deposition chamber becomes 1.0 × 10 ⁻³ Pa. I do. When the pressure in the chamber reaches 1.0 × 10 ⁻³ Pa, silicon oxide, which is a starting material for the SiO ₂ layer filled in the crucible, is heated by an electron beam and evaporated.

At this time, plasma is generated in the vapor deposition chamber, and the film is formed so that the vapor deposition component reaches the infrared absorption glass through the plasma atmosphere. When the SiO ₂ layer has a predetermined thickness, a TiO ₂ layer is formed next. Titanium oxide is used as the starting material for the TiO ₂ layer, and the titanium oxide filled in the crucible is heated with an electron beam to generate plasma in the vapor deposition chamber and pass through the plasma atmosphere in the same manner as when forming the SiO ₂ layer. The film is deposited so that the deposited components reach the infrared absorbing glass. In this way, the desired number of layers SiO ₂ layers and TiO ₂ layers are alternately stacked.

  In the design example 5, the infrared cut film is laminated on one surface, but as shown in FIG. 9A, the infrared cut film 10a and the infrared cut film 10b are divided into the respective surfaces of the transparent substrate 1 and divided. A film may be formed. When the infrared cut film 10 is divided and formed, as shown in FIG. 10, the cut wavelengths of the infrared cut films 10a and 10b formed on the respective surfaces of the transparent substrate are different, and at least a part of them is formed. It is preferable to have overlapping optical characteristics. By forming in this way, it becomes possible to cut the infrared light wavelength efficiently, and it is possible to eliminate the region where the cut function is insufficient in the infrared wavelength region.

  Furthermore, in Design Example 5, the light amount adjustment film is formed on one surface of the transparent substrate. However, as shown in FIG. 9B, the light amount adjustment film 8a and the light amount adjustment film 8b may be formed on both surfaces of the transparent substrate. . At this time, the light amount adjusting films formed on both surfaces of the transparent substrate are combined so that a desired light amount can be attenuated.

In the case where the infrared cut film and the light amount adjustment film are provided on the same surface of the substrate, an optical filter having an antistatic function can be obtained by forming the light amount adjustment film on the infrared cut film. The light amount adjustment film has a conductive light absorption layer (metal or metal oxide or nitride), and even if it has an antireflection layer, the surface resistivity is about 10 × 10 ¹⁰ Ω / □ or less. This is because it has a sufficient antistatic function. For this reason, it can be set as the optical filter which a foreign material etc. cannot adhere easily.

  On the other hand, by forming an infrared cut film on the light amount adjustment film, the optical characteristics can be stabilized for a long time. The light amount adjustment film is a light absorption layer made of metal or metal oxide or nitride, and is in contact with oxygen or water vapor in the atmosphere, so that oxidation is accelerated and transmittance may increase over time. By forming the cut film on the light amount adjustment film, the first layer is prevented from coming into contact with oxygen or water vapor, and the transmittance change is less likely to occur.

  Furthermore, it is preferable that the infrared cut film including the end face is covered with the light amount adjusting film, or the light quantity adjusting film including the end face is covered with the infrared cut film. By doing in this way, the above-mentioned antistatic function or long-term stability of optical characteristics can be further improved.

  The stress direction may be different between the light amount adjusting film and the infrared cut film depending on the forming method. For this reason, when the light quantity adjustment film and the infrared cut film are formed on the same surface of the transparent substrate, the adhesion at the interface between the light quantity adjustment film and the infrared cut film may be a problem. In such a case, an adhesion layer may be provided at the interface between the light amount adjustment film and the infrared cut film. As the adhesion layer, a stress relaxation layer that relaxes the stress difference between the light amount adjusting film and the infrared cut film is optimal, and a layer in which stress continuously changes is preferable.

  Examples of such a stress relaxation layer include a layer in which the oxidation number changes continuously in the film thickness direction and a layer in which the film density changes continuously. The layer whose oxidation number continuously changes in the film thickness direction can be obtained, for example, by simultaneously forming a plurality of vapor deposition materials and changing the mixing ratio. Further, the layer in which the film density continuously changes can be obtained, for example, by continuously changing the pressure in the vapor deposition chamber during film formation. Furthermore, the stress relaxation layer may be a metal film.

  The metal film is a film made of a metal bond and has excellent ductility and can be deformed relatively freely as compared with a film made of a covalent bond or an ionic bond. For this reason, by arranging a metal film between the light amount adjustment film and the infrared cut film with different stress directions, the stress energy of the light amount adjustment film and the infrared cut film is used for the deformation of the metal film, and the light amount adjustment Peeling at the interface between the film and the infrared cut film can be suppressed.

  Further, when the light amount adjustment film and the infrared cut film are provided on the same surface of the transparent substrate, an interference adjustment layer may be introduced between the light amount adjustment film and the infrared cut film. The interference adjustment layer is a layer for adjusting the interference condition between the light quantity adjustment film and the infrared cut film, and adjusts the ripple generated by stacking the light quantity adjustment film and the infrared cut film.

For example, TiO ₂ can be suitably used as the interference adjustment film, but besides this, MgF ₂ , SiO ₂ , SiO, Si ₃ H ₄ , Al ₂ O ₃ , MgO, LaTiO ₃ , ZrO ₂ , Nb ₂ O ₅ , Ta ₂ O _{5 and the} like can also be suitably used, and any structure of a single layer or a laminate may be used.

  The infrared cut film may have a function of cutting transmission in the ultraviolet region. The UV cut function is achieved by an UV cut film obtained by laminating thin films with different refractive indexes so that the optical film thickness of each layer is approximately λ / 4, where λ is the wavelength of the ultraviolet region to be cut. Brought about.

The ultraviolet cut film can use the same material as the infrared cut film, and the larger the refractive index difference between the thin films, the smaller the number of layers. For example, a combination of a SiO ₂ layer and a TiO ₂ layer is preferable because it is a combination having the largest refractive index difference.

  In this embodiment, a metal oxide is used for the first intermediate layer and the second intermediate layer of the light amount adjustment film. However, a single-layer intermediate layer may be included as in Design Example 2, or as in Design Example 3. Alternatively, a metal oxide may be used for the first intermediate layer, and a metal nitride may be used for the second intermediate layer. Note that, similarly to the first embodiment, the light amount adjustment film may have a region where the transmittance changes stepwise or continuously with respect to the surface direction of the substrate.

  FIG. 11 shows an imaging optical system such as a camera. Incident light passes through a light amount adjusting device 20 formed of lenses 12, 15 to 17, aperture blades 13a and 13b, an optical filter 11, and the like, and enters an image sensor 18 composed of a CCD or CMOS sensor and is converted into an electrical signal. Visualized.

  The position information of the diaphragm blades 13a and 13b is transmitted to the light amount control unit 19, and the light amount control unit 19 uses the light amount information from the image sensor 18 and the position information of the diaphragm blades 13a and 13b so as to obtain an optimum aperture. , 13b are driven.

  The optical filter 11 is inserted into the optical path by the optical filter driving unit 14 when the diaphragm blades 13a and 13b are below a certain opening, and suppresses harmful effects such as flare caused by the apertures of the diaphragm blades 13a and 13b becoming too small. .

  The optical filter produced in Examples 1 to 3 is inserted into the optical filter 11 and is appropriately inserted into the optical path according to the amount of light at the time of photographing.

  Here, when using the optical filter of Example 3, it is preferable to arrange | position so that a light quantity adjustment film may exist between the infrared cut film which has an infrared half value wavelength, and an image pick-up element. By arranging in this way, the occurrence of ghost can be suppressed.

  Note that the ghost is generated by multiple reflection of light in the imaging optical system, and the equation for simply obtaining the ghost intensity due to the optical filter is (transmittance of the optical filter) × (reflectance of the optical filter) × ( (Sensitivity of imaging device). In the vicinity of the infrared half-value wavelength of the infrared cut film, it is a region where the transmittance and reflectance are large in the infrared region, and includes a wavelength in a limit region that can be recognized by the human eye.

  If a light amount adjustment film is arranged between the infrared cut film and the image sensor, the light transmitted through the infrared cut film is attenuated by the light amount adjustment film, and further reenters the light amount adjustment film reflected by the image sensor, etc. This is because after the light is attenuated by the light amount adjusting film, it reaches the infrared cut film, so that reflection caused by the infrared cut film can be efficiently attenuated.

  Furthermore, it is preferable to use an infrared absorbing glass for the transparent substrate and to provide the infrared absorbing glass between the infrared cut film having an infrared half-value wavelength and the imaging device. The infrared absorption glass has a light absorption function in the infrared half-value wavelength region of the infrared cut film, and can effectively attenuate light that causes ghost in the vicinity of the half-value wavelength of the infrared cut film.

  Since the optical filter according to the present invention has good transmittance flatness, the amount of light reaching the image sensor can be appropriately attenuated without losing the color balance of the subject.

DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 1st and 2nd light absorption layer 3 1st intermediate layer 4 2nd intermediate layer 5 Intermediate layer 6 Optical adjustment layer 7 Antireflection layer 8, 8a, 8b Light quantity adjustment film 9 Antireflection film 10, 10a, 10b Infrared cut film

DESCRIPTION OF SYMBOLS 11 Optical filter 12, 15-17 Lens 13a, 13b Diaphragm blade 14 Optical filter drive part 18 Image pick-up element 19 Light quantity control part 20 Light quantity adjustment apparatus

Claims (10)

A substrate having optical transparency;
An optical adjustment layer provided on at least one surface of the substrate,
The optical adjustment layer is formed of at least one light absorbing material selected from the group consisting of a metal A having light absorption characteristics, an oxide AO of the metal A, and a nitride AN of the metal A. An absorption layer; and an intermediate layer formed between a compound of an oxide BO or nitride BN of a metal B which is provided between the first and second light absorption layers and is a metal element different from the metal A ,
The intermediate layer includes a first intermediate layer provided on the first light absorption layer, and a second intermediate layer provided between the first intermediate layer and the second light absorption layer,
The extinction coefficient of the first compound forming the first intermediate layer at a visible wavelength is larger than the extinction coefficient of the second compound forming the second intermediate layer at a visible wavelength, and the first intermediate layer is An optical filter, wherein the optical filter is provided thinner than a thickness of the second intermediate layer. The first compound forming the first intermediate layer is a first oxide BOy (y is an oxidation number) which is an oxide of the metal B;
The second compound forming the second intermediate layer is a second oxide BOz (z is an oxidation number) which is an oxide of the metal B,
2. The optical filter according to claim 1, wherein the first oxide BOy and the second oxide BOz satisfy a condition of a relational expression y <z. The first compound forming the first intermediate layer is a first oxide BO which is an oxide of the metal B,
2. The optical filter according to claim 1, wherein the second compound forming the second intermediate layer is a second nitride BN that is a nitride of the metal B. 3. A substrate having optical transparency;
An optical adjustment layer provided on at least one surface of the substrate,
The optical adjustment layer is formed of at least one light absorbing material selected from the group consisting of a metal A having light absorption characteristics, an oxide AO of the metal A, and a nitride AN of the metal A. An absorption layer, and an intermediate layer formed between the first and second light absorption layers and an oxide BO of metal B, which is a metal element different from metal A,
The intermediate layer includes a first intermediate layer provided on the first light absorption layer, and a second intermediate layer provided between the first intermediate layer and the second light absorption layer,
The first intermediate layer is provided thinner than the thickness of the second intermediate layer,
The first oxide BOy (y represents the oxidation number) forming the first intermediate layer and the second oxide BOz (z represents the oxidation number) forming the second intermediate layer are expressed by the relation y < An optical filter characterized by satisfying a condition of z.   The metal A is Ti, Ni, Cr, Fe, Nb, Ta, and the metal B is Si, Al, Mg, La, Zr, Ti, Nb, Ta. The optical filter according to any one of 5. The optical adjustment layer is provided in a plurality of layers on one surface of the substrate,
7. The intermediate layer formed of an oxide BO of metal B is provided between the optical adjustment layers composed of a plurality of layers. Optical filter.   The said optical adjustment layer has a 1st optical adjustment layer provided on the one surface of the said board | substrate, and a 2nd optical adjustment layer provided on the other surface of the said board | substrate, The 1st thru | or 5 characterized by the above-mentioned. The optical filter according to any one of the above. On one surface of the substrate, an underlayer formed of the metal B oxide BO is provided,
The optical filter according to claim 1, wherein the optical adjustment layer is laminated on the base layer.   The optical filter according to claim 1, wherein an infrared cut film is formed on at least one surface of the substrate.   An imaging apparatus comprising the optical filter according to claim 1.

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