JP2016114699A - Optical filter and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical filter and imaging apparatus capable of reducing a ripple without decreasing the transmissivity in a transmission band through which light passes.SOLUTION: The optical filter includes: a transparent substrate; and a light transmission restriction structure that is disposed on the transparent substrate via a thin film, and has an optical characteristic having a light transmission region and light transmission restriction region in a predetermined wavelength region. Between the transparent substrate and the light transmission restriction structure, a ripple reduction layer for reducing the ripple in the light transmission region of the light transmission restriction structure. The ripple reduction layer is thinner than the thin film constituting the light transmission restriction structure.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an optical filter used in an optical system such as a camera, and an imaging apparatus including the optical filter.

  As an optical filter mounted on an imaging device, it is known that when limiting light transmission in a predetermined wavelength range, so-called ripple (transmission ripple) is generated in which the transmittance is not stable in a transmission band through which light passes. (See Patent Document 1).

JP 2008-070827 A

  Here, various countermeasures against ripples in the transmission band have been proposed, but it is very difficult to effectively reduce the ripples without reducing the transmittance of the transmission band.

  The present invention provides an optical filter and an imaging apparatus capable of reducing ripples without reducing transmittance in a transmission band through which light passes.

The optical filter of the present invention is a transparent substrate and a light transmission limiting structure which is provided by laminating a thin film on the transparent substrate and has an optical characteristic having a light transmission region and a light transmission limitation region in a predetermined wavelength region. And a ripple reduction layer that reduces a ripple in the light transmission region of the light transmission restriction structure is provided only between the transparent substrate and the light transmission restriction structure.
According to this aspect of the present invention, the ripple can be effectively reduced without reducing the transmittance in the light transmission band by providing the ripple reduction layer only between the transparent substrate and the light transmission limiting structure.

Further, the optical filter of the present invention is provided with a transparent substrate and a light transmission restriction having an optical characteristic having a light transmission region and a light transmission restriction region in a predetermined wavelength range provided by laminating a thin film on the transparent substrate. A ripple reduction layer that reduces ripples in the light transmission region of the light transmission limiting structure with a thickness smaller than a thin film that forms the light transmission limiting structure, and the transparent substrate and the structure It is provided only between the light transmission restricting structures.
In such an aspect of the present invention, the ripple reduction layer is provided only between the transparent substrate and the light transmission limiting structure, and is provided with a thickness thinner than the thin film constituting the light transmission limiting structure, thereby providing a light transmission band. The ripple can be more effectively reduced without reducing the transmittance.

Moreover, the optical filter of the present invention is characterized in that the ripple reduction layer is composed of a plurality of multilayer films each laminated with a thickness thinner than a thin film constituting the light transmission limiting structure.
In such an aspect of the present invention, the ripple can be reduced more effectively without reducing the transmittance in the light transmission band by forming the ripple reduction layer with a plurality of multilayer films.

In the optical filter of the present invention, the light transmission restricting structure includes a first light transmission restricting structure provided by laminating a thin film on one surface side of the transparent substrate, and the other surface side of the transparent substrate. A second light transmission restricting structure provided by laminating a thin film on the first substrate, and the ripple reduction layer is provided between the transparent substrate and the first light transmission restricting structure. A first ripple reduction layer formed with a thickness thinner than a thin film constituting the restriction structure; and the second light transmission restriction structure provided between the transparent substrate and the second light transmission restriction structure. And a second ripple reduction layer formed with a thickness smaller than that of the constituent thin film.
In this aspect of the present invention, the light transmission restricting structure is divided and arranged on both sides of the transparent substrate to reduce the stress load of the entire filter to prevent warping, and to reduce ripple corresponding to each light transmission restricting structure. By providing the layer, the ripple in the light transmission band of each light transmission limiting structure can be effectively reduced.

Further, in the optical filter of the present invention, the thin film constituting the first light transmission restriction structure and the thin film constituting the second light transmission restriction structure are formed with different film thicknesses, respectively.
The first ripple reduction layer and the second ripple reduction layer are formed with different film thicknesses.
In this aspect of the present invention, the film thickness of the first ripple reduction layer is defined corresponding to the thin film constituting the first light transmission restriction structure, and the first film corresponding to the thin film constituting the second light transmission restriction structure. By defining the film thickness of the 2 ripple reduction layer, the ripple can be reduced more effectively.

The optical filter of the present invention is characterized in that an antireflection layer is provided on the light transmission limiting structure, and the ripple reduction layer is provided with a thickness smaller than that of the antireflection layer. To do.
In such an aspect of the present invention, the ripple can be reduced more effectively without reducing the transmittance in the light transmission band by providing the ripple reducing layer thinner than the antireflection layer.

Note that the present invention can be widely applied to an imaging apparatus including the above-described optical filter.
In this aspect of the present invention, the optical filter in which the ripple reduction layer is provided on the surface of the light transmission restriction structure with a thickness smaller than that of the light transmission restriction structure is mounted. Ripple can be effectively reduced without reducing the transmittance in the light transmission band, and imaging quality can be improved.

  The present invention can realize an optical filter and an imaging apparatus that can reduce ripples without reducing transmittance in a transmission band through which light passes.

The spectral transmission characteristic figure of the optical filter in one Embodiment. The spectral characteristic figure of the comparison explanation of the transmission ripple in one Embodiment. The block diagram of the comparative description of the transmission ripple in one Embodiment. Wavelength dispersion characteristic diagram of the refractive index of the TiO ₂ film and the SiO ₂ film in one embodiment. Explanatory drawing of the manufacturing method of an optical filter. Explanatory drawing of the thin film laminated structure in one Embodiment. Explanatory drawing of the other structure in one Embodiment. The spectral transmission characteristic figure of the optical filter in one Embodiment. Schematic of the imaging device in other embodiments. Schematic of the imaging device in other embodiments.

  Hereinafter, embodiments of the present invention will be described in detail.

  The optical filter of the present invention comprises a transparent substrate and a light transmission limiting structure provided by laminating a thin film on the transparent substrate, and is transparent on the surface side on the substrate provided with the light transmission limiting structure. It is characterized in that a ripple reduction layer is provided only between the substrate and the light transmission limiting structure. Although the details will be described later, the ripple can be effectively reduced without lowering the transmittance in the light transmission band of the light transmission limiting structure.

  Here, the ripple reduction layer in the present invention is formed only between the light transmission limiting structure and the transparent substrate on the surface side on the substrate on which the light transmission limiting structure is provided. While realizing this, it is possible to reduce the transmission ripple. Furthermore, by forming such a ripple-reducing layer thin, that is, thinner than the thin film constituting the light transmission limiting structure, the ripple reduction effect in the light transmission limiting structure can be further enhanced. Can do.

  The material for forming the ripple reduction layer is a material similar to the material of the thin film adjacent to the ripple reduction layer in the light transmission limiting structure described above, for example, the ripple if the thin film of the light transmission limiting structure is an oxide film. The reduction layer is also preferably a similar oxide film. Thereby, it is possible to increase the adhesion between the ripple reduction layer and the light transmission limiting structure.

  In addition, such a ripple reduction layer is formed by making the thickness smaller than that based on the thin film having the smallest thickness among the plurality of thin films constituting the light transmission limiting structure formed thereon. It is desirable to do. It is also effective to form the ripple reduction layer thinner than that corresponding to the thickness of the thin film formed immediately above the ripple reduction layer. That is, the ripple reduction layer is preferably formed thinner than the thin film constituting the light transmission restriction structure at the interface between the transparent substrate and the light transmission restriction structure.

  Further, the ripple reduction layer may have a single layer structure, but may also have a multilayer structure. In this case, on the surface side on the substrate on which the light transmission limiting structure is provided, only at a position between the substrate and the light transmission limiting structure, for example, is thinner than the thin film constituting the light transmission limiting structure. And a plurality of multilayer films laminated respectively. As a result, it is possible to effectively reduce only the ripple while suppressing a decrease in the transmittance in the filter transmission band.

  Here, in the present invention, when the light transmission restriction structure is provided only on one surface of the transparent substrate, as described above, a structure in which a ripple reduction layer is provided between the transparent substrate and the light transmission restriction structure, However, the present invention can also be applied to the case where the light transmission limiting structures are provided on both surfaces of the transparent substrate.

  For example, the first light transmission restriction structure may be provided on one surface of the transparent substrate, and the second light transmission restriction structure may be provided on the other surface of the transparent substrate. In this case, a first ripple reduction layer is provided between one surface of the transparent substrate and the first light transmission restriction structure, and a second ripple is provided between the other surface of the transparent substrate and the second light transmission restriction structure. A reduction layer is provided. That is, the first ripple reduction layer corresponds to the first light transmission restriction structure, and the second ripple reduction layer corresponds to the second light transmission restriction structure.

  At this time, the first ripple reduction layer is formed thinner than the film thickness of the thin film constituting the first light transmission restriction structure, and the second ripple reduction layer is a thin film film constituting the second light transmission restriction structure. It is formed thinner than the thickness.

  Further, in the present invention, when the thin film constituting the first light transmission restriction structure and the thin film constituting the second light transmission restriction structure are formed with different film thicknesses, the first ripple corresponding to this is formed. The reduction layer and the second ripple reduction layer are preferably formed with different film thicknesses.

  For example, it is preferable to provide the first ripple reduction layer thinner than the thin film constituting the first light transmission restriction structure and to provide the second ripple reduction layer thinner than the thin film constituting the second light transmission restriction structure. That is, the film thickness of the first ripple reduction layer is defined corresponding to the thin film constituting the first light transmission restriction structure, and the second ripple reduction layer is designated corresponding to the thin film constituting the second light transmission restriction structure. The film thickness should be specified. As a result, the ripple corresponding to each transmission band of the first light transmission limiting structure and the second light transmission limiting structure can be individually reduced, and the ripple of the entire filter is also reduced without causing a decrease in transmittance. can do.

As described above, if one light transmission restriction structure is divided and arranged on both surfaces of the transparent substrate,
In addition to reducing the stress load on the entire filter to prevent warping, it is possible to take ripple reduction measures individually.

  Here, the form of the optical filter of the present invention will be specifically described. The optical filter of the present embodiment is, for example, a bandpass filter that restricts transmission of light in a predetermined wavelength region in the near infrared light region and ultraviolet light region and transmits light in a predetermined wavelength region in the visible light region. A certain UVIR cut filter or an IR cut filter that is an edge filter that restricts transmission of a predetermined light beam in the near-infrared light region and transmits a light beam in a predetermined wavelength region in the visible light region.

  These filters are produced by laminating a plurality of thin films on a substrate, and this thin film may be formed by a physical or chemical film formation method or by a coating method such as spin coating. It may be formed.

  In the case of such an optical filter, a glass substrate is often used. However, due to the recent demand for miniaturization and weight reduction of optical devices, further space saving is required in the optical system, and further thinning is required. Is required.

  For example, when the glass substrate is thinned, the mechanical strength becomes extremely low, and the possibility of breakage may be remarkably increased. Therefore, the glass substrate is not suitable for mass production. In such a case, if a plastic substrate having high flexibility is used, the substrate itself can be prevented from cracking even if it is thin.

  Here, for example, when a plastic substrate is used as the base material of the optical filter, it is preferable to consider thermal stress in the film forming process. Use a plastic substrate with an extremely low glass transition temperature compared to the glass substrate, irregular warpage of the substrate due to the difference in coefficient of linear expansion between the substrate and the film, and wrinkles on the surface of the deposited film accompanying this warpage. The occurrence of cracks is considered.

  Therefore, it is preferable to take measures against heat generated during film formation. For example, a method of selecting a substrate material having a high heat-resistant temperature or performing a low-temperature process during film formation is effective. In the present embodiment using a plastic substrate, for example, a method of giving a heat absorption mechanism to the film forming apparatus and forcibly removing heat generated on the substrate during film formation is used. At this time, it is desirable to measure in advance the maximum temperature on the substrate that can be reached in the film formation process, and to select a substrate that can withstand that temperature. For example, in the present embodiment, considering the stability of the film forming process, a certain allowable value is added to the highest temperature reached in advance, and the glass transition temperature is used as a parameter for determining the suitability. A material with temperature was used.

  In this case, since the temperature during film formation is lower than that of normal film formation, it is necessary to add some assistance, or to select a process in which film density is increased by film formation with relatively high energy such as sputtering. Is more preferable. More specifically, for example, a film forming method capable of relatively accurately controlling the film thickness and obtaining a highly reproducible film, such as sputtering, IAD, ion plating, IBS, and cluster deposition. What is necessary is just to select the optimal method from the property of the film | membrane required, the constraint conditions of each material including a board | substrate, etc.

  As described above, it is desirable to appropriately select an optimal base material from glass, plastic, etc., taking into account the specifications of the final product, the manufacturing process thereof, and the like.

  Here, for example, a UVIR cut filter or an IR cut filter has a relatively large number of films to be laminated, and is likely to cause a problem of warping due to film stress, which is particularly noticeable in the case of a thin glass substrate or resin substrate. Therefore, the film stress can be reduced most when the same material and the same film thickness are laminated on both surfaces of the substrate.

  On the other hand, in order to provide desired optical characteristics, it may be difficult to design a film so that the number of stacked layers is the same as that in the case of designing on one side of the substrate in the structural design of the laminated thin film. Further, in order to satisfy the relaxation of the optical characteristics and the film stress at the same time, the number of stacked layers increases, which may increase the man-hours for manufacturing the optical filter. Therefore, it is desirable to divide and arrange the thin film laminated structure having a predetermined blocking wavelength region on both sides of the substrate. The warping of the filter can be alleviated without increasing the number and without sacrificing the optical characteristics.

  Here, with reference to FIGS. 1 to 3, a UVIR cut filter is taken as an example to describe a thin film laminated structure. FIG. 1 shows spectral transmission characteristics of an optical filter according to an embodiment of the present invention. FIG. 2 is a spectral characteristic diagram for comparison and explanation of transmission ripples of an optical filter according to an embodiment of the present invention. FIG. 3 is a schematic configuration diagram for comparison and explanation of transmission ripples of an optical filter according to an embodiment of the present invention.

  When a UVIR cut filter having a spectral transmission characteristic as shown in FIG. 1 is formed by a plurality of thin film laminated structures having a predetermined blocking wavelength region, the first blocking is performed in a desired wavelength region from a visible wavelength to an ultraviolet wavelength. A second stop band in the desired wavelength range from the visible wavelength to the near infrared wavelength, and a third stop zone in the desired wavelength range from the second stop wavelength range to the near infrared wavelength, It is constituted by three blocking wavelength regions.

  When the thin film laminated structure constituting one blocking wavelength region is considered as one block, it is formed by three blocks forming the first to third blocking regions described above. These are defined as a first stack, a second stack, and a third stack, respectively. Each of these three stacks has a different central wavelength, and when this is λ, it is based on a structure in which high refractive index materials and low refractive index materials are alternately laminated in λ / 4 layers, etc. In order to obtain characteristics, the layers are laminated by adding a fine adjustment of about 0.7 to 1.3 times to the thickness of each layer.

  In addition, as a method of expressing such a film thickness, there is a method of expressing λ / 4 as one unit, for example, 2.0 qw when the film thickness is 2.0 × λ / 4. Thus, if the center wavelength in the previous three stacks is replaced with one reference wavelength λ, the thickness of each stack can be expressed using this λ in common.

  Next, a method for reducing ripple in the transmission band will be described.

  FIG. 2 (a) is optimized with the same design concept, which consists of 450 nm to 650 nm transmission band, 750 nm to 950 nm blocking band, and 18 TiO2 and SiO2 films stacked alternately. It is an example of the spectral transmission characteristic of four types of IR cut filters. FIG. 2B is an enlarged view of the transmission band of FIG.

  Here, as shown in FIG. 3, these four types are for reducing ripples with respect to the thin-film laminated structure 32 as a base and the antireflection structure 33 for reducing reflection disposed on the outermost layer. The ripple reduction layers 31 are inserted at different positions. FIG. 3A shows between the substrate 30 and the thin film laminated structure 32, and FIG. 3B shows the thin film laminated structure 32 and the antireflection structure 33. 3C shows an example in which the thin film laminated structure 32 is inserted in the vicinity of the central layer, and FIG. 3D shows an example in which the ripple reducing layer 31 is not inserted.

  These four types of filters shown in FIG. 3 were optimized based on the concept of giving priority to maximizing transmission in the transmission band, minimizing transmission in the stop band, and then giving priority to reducing transmission ripple. FIG. 4 shows the wavelength dispersion characteristics of the refractive indexes of the TiO 2 film and the SiO 2 film used in this embodiment.

  Here, the ripple reduction layer 31 has a characteristic that the film thickness is very thin as compared with the plurality of thin films forming the thin film laminated structure 32 and the antireflection structure 33. More specifically, in the case of the thin-film laminated structure 32 shown in FIG. 3 that constitutes the above-described stop zone, the thickness is approximately 1.5 to 2.0 qw (λ: 500 nm), and the antireflection structure 33 is 1.0 qw. It is around (λ: 500 nm). On the other hand, the ripple reduction layer 31 has a film thickness of about 0.1 to 0.4 qw (λ: 500 nm).

  Thus, in the optical filter of the present embodiment, the ripple reduction layer 31 described above is the thinnest layer among all the layers. Further, there may be two or more ripple reduction layers. In this case, each thin film constituting all the ripple reduction layers 31 is a layer (thin film) forming the thin film laminated structure 32 or the antireflection structure 33. It is better to make it thinner.

  Here, as shown in FIG. 2, among the four types of filters, FIG. 3A shows the smallest ripple in the transmission band. In order to compare each condition as a numerical value, the transmittance in the transmission band is linearly approximated as an evaluation value of the ripple, and the absolute value of the difference between the approximate value and the actual transmittance is calculated at a 1 nm pitch and transmitted. The value added for the entire band was divided by the wavelength region, and the amount of deviation from the transmittance approximate line per 1 nm in the transmission region was calculated. It can be evaluated that the smaller the obtained value, the smaller the ripple. In the example of FIG. 3, this evaluation value is 0.227 in FIG. 3A, 0.466 in FIG. 3B, 0.518 in FIG. 3C, and 0.417 in FIG. Thus, FIG. 3A shows the smallest value.

  Also, in order to confirm reproducibility, the same design concept and the same film design were repeated, and the magnitude of the ripple was compared in the same way. The design in which the ripple reduction layer 31 is inserted at the position always has the smallest ripple, and FIG. 3C always results in the largest ripple. Further, FIG. 3B and FIG. 3D have similar values, and the result is that the order of evaluation values of ripples is switched depending on the case. From the above, it was only the configuration of FIG. 3A that the transmission ripple was reliably reduced as compared with FIG. 3D in which the ripple reduction layer 31 was not inserted.

  This is because, when the number of stacked layers is constant, the influence on the antireflection structure 33 arranged on the surface layer becomes large at the position shown in FIG. 3B, so that the reflection of the transmission band is minimized, that is, the transmission band. It becomes difficult to satisfy both the maximization of transmission and the ripple reduction at the same time. In the case of the position shown in FIG. 3C, the thin film laminated structure 32 is divided so that the influence on the thin film laminated structure is increased, and as a result, the maximum reflection in the blocking region by the thin film laminated structure is obtained. It will inhibit the conversion. From these, it is considered that it is difficult to reduce the ripple at the same time.

  Further, as shown in FIG. 2 (a), there is another problem that the possibility that a large ripple is generated in the transmission blocking area is significantly increased only in the case of the divided configuration as shown in FIG. 3 (c). As described above, this is because the thin-film laminated structure 32 is divided so as to adversely affect the maximization of reflection in the transmission blocking wavelength region by the thin-film laminated structure. Therefore, even if the adjustment layer is inserted at the position of FIG. 3A and another ripple reduction layer 31 is inserted at the position of FIG. 3C, FIG. 3C in FIG. Such as the spectral transmission characteristics of the product, causing large ripples in the stop band, reducing the transmittance, and increasing the number of layers to cope with this. Another problem will occur. The same applies to the case where there are a plurality of thin film laminated structures, and one thin film laminated structure has a large central wavelength, such as an ultrathin ripple reducing layer or another thin film laminated structure. It is not preferable to adopt a structure in which different single-layer films and a plurality of layers are inserted, and it is desirable not to take such a divided arrangement but to have an integrated arrangement. As described above, the ripple reduction layer 31 serving as the adjustment layer for reducing the transmission ripple is disposed only between the substrate 30 and the thin film multilayer structure 32 on the surface side on which the thin film multilayer structure is provided on the substrate 30. Further, it is desirable that the film be thinned in order to enhance the ripple reduction effect. In addition to this configuration, the same applies when another thin film laminated structure 32 is provided on the other surface side of the substrate 30. On the surface side of the substrate 30 on which the thin film laminated structure 32 is provided, the substrate 30 is provided. The ripple reducing layer 31 serving as an adjustment layer for reducing ripples is disposed only between the thin film laminated structure 32 and the other surface on the substrate 30 on which the other thin film laminated structure 32 is provided. Even on the side, if the ripple reduction layer 31 serving as another adjustment layer for reducing the ripple is disposed only between the substrate 30 and the other thin film laminated structure 32, the same effect can be obtained.

  Here, the more specific film thickness of the ripple reduction layer 31 in FIG. 3A in this embodiment is 0.143 qw (λ: 500 nm), and the physical film thickness at this time is 7.35 nm. . Further, when λ was 600 nm, it was 0.116 qw, and when λ was 700 nm, it was 0.097 qw.

  Further, in the case of the same insertion position as that in FIG. 3A, the film thickness of the TiO2 film of the adjustment layer that is the first layer is 0.233 qw or less when λ is 500 nm. When λ was 600 nm, it was 0.189 qw or less, and when λ was 700 nm, it was 0.159 qw or less, which was 3% or less of the visible wavelength (400 nm), and the physical film thickness was 12 nm or less.

  Similarly, in the case of the same insertion position as in FIG. 3A, the film thickness of the adjustment layer TiO 2 film as the first layer is 0.078 qw or more when λ is 500 nm in the convergence solution in all the film designs described above. When λ is 600 nm, 0.063 qw or more, and when λ is 700 nm, 0.053 qw or more, and 1% or more of the visible wavelength (400 nm), and the physical film thickness is 4 nm or more.

  Further, such a configuration can be applied not only to the UVIR cut filter and the IR cut filter, but also to various bandpass filters having a transmission band and a stop band, an edge filter, and the like. Can be obtained.

  Furthermore, by using such an optical filter of this embodiment in a photographing apparatus such as a video camera, it is possible to obtain an imaging apparatus with little image degradation due to transmission ripple. Further, when a plastic substrate is used, the damage or the like when the optical filter is incorporated into the apparatus is less than that of a conventional optical filter using glass, and the apparatus can be easily assembled.

  Here, the antireflection structure is composed of a single-layer thin film. However, the present invention is not limited to this, and may be formed of a plurality of layers, or a microstructure having an antireflection effect having a pitch of a visible light wavelength or less. Or a complex of these.

  In the case of a fine structure, the configuration and shape thereof are not particularly limited as long as the reflection reduction effect can be obtained. For example, a concavo-convex structure periodically provided at a predetermined pitch can be used. As such a concavo-convex structure, the projections or recesses of the concavo-convex structure finely formed in a staircase shape, such as protrusions such as needle-like bodies and columnar bodies formed randomly or regularly, and the adjacent medium The thing etc. which reduced the refractive index difference can be mentioned, What was arbitrarily selected according to the objective can be used. Specific examples of such a fine structure include a structure in which a large number of protrusions are two-dimensionally arranged, such as a bell-shaped moth-eye shape having a height of 400 nm and a period of 250 nm. For example, if the microstructure is composed of a large number of protrusions and uneven structures arranged with a period shorter than the wavelength of visible light, for example, the thermal nanoimprint method and the optical nanoimprint method can be used with good reproducibility. Furthermore, it can be manufactured with high productivity. Further, from the viewpoint of rigidity and the like, it is particularly desirable that the aspect ratio obtained by dividing the aforementioned height by the period is in the range of 0.8 to 2.0. Furthermore, regarding the arrangement of the protrusions, a square arrangement, a three-way (hexagonal) arrangement, and the like are conceivable. However, the three-way arrangement can increase the reflection reduction effect because the exposed surface of the substrate side surface is less. .

  Here, when it is necessary to improve the adhesion between the fine structure and the underlying layer, it is possible to perform primer treatment and provide an adhesion layer at the interface between them. Furthermore, if the primer layer is in a range that does not have any adverse effects, hydrophilic treatment with UV ozone or the like may be performed before the primer solution coating in order to more uniformly apply the primer solution. In addition, when performing coating by such a process, it is also possible to limit the coating area by, for example, performing masking or changing the process to an inkjet method, a gravure method, a micro contact printing method, or the like. is there.

Example 1
The production of the UVIR cut filter will be described in detail below.
Thick Zeonor (product name / registered trademark made by Nippon Zeon Co., Ltd.) film is used for the substrate on which the UVIR cut film is formed, and transmission of a part of the desired ultraviolet wavelength region and near infrared wavelength region is restricted and sandwiched between them. 1 was designed so as to have a spectral transmittance characteristic as shown in FIG.

  The Zeonor film was selected because it has a relatively high glass transition temperature of 100 ° C. or higher and can reduce the waviness of the substrate. In this embodiment, Zeonor, which is a norbornene-based material, is used. In addition, Arton (product name / registered trademark, manufactured by JSR), a polyimide-based resin film, and the like are also suitable substrates. Moreover, it is not limited to these, and may be PET, PEN, PC, PES, PMMA, or the like.

  One film has a square shape of 100 mm both vertically and horizontally, and a mask is formed on the film so that the film formation area is as shown in FIG. 5, thereby forming a 10 mm square range in several places on the same film. Films were formed and cut out after film formation as shown in FIG. Similarly, a similar filter can be produced by a method of forming a film on the entire surface of the substrate and processing the film surface into a desired shape without using a mask for determining the outer shape.

In addition, TiO ₂ is used for the high refractive index material and SiO ₂ is used for the low refractive index material as the vapor deposition material for forming the vapor deposition film, and the film configuration is alternating between SiO ₂ and TiO ₂ as shown in FIG. In order to reduce warpage and undulation, the layers are composed on both sides of the substrate, and 29/21 layers on both sides of the substrate are laminated to form a 50-layer film on both sides. The 29-layer film has a physical film thickness of about 2500 nm and the 21-layer film has a thickness of about 2700 nm so that the both surfaces have substantially the same film thickness. Further, the two layers immediately above the substrate on each surface were used as adjustment layers for reducing ripples. Here, the TiO ₂ film and the SiO ₂ film used in Example 1 have wavelength dispersion characteristics of a refractive index as shown in FIG.

In addition, Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ or the like is used as the high refractive index material, and MgF ₂ or the like may be used for the low refractive index material. In some cases, Al ₂ O ₃ or the like, which is an intermediate refractive index material, may be used in some layers for reasons of design or film formation, and an optimal combination of materials may be selected from time to time.

  Like the design value of the spectral transmission characteristic shown in FIG. 1, the UVIR cut filter produced in this example has a first blocking wavelength region in the wavelength region of about 300 to 400 nm from the visible wavelength to the ultraviolet wavelength. 3 having a second blocking wavelength region in the wavelength region of about 700 to 900 nm from the visible wavelength region to the near infrared wavelength region, and a third blocking wavelength region in the wavelength region of about 900 to 1100 nm. It consists of two stop wavelength regions. In addition, a wavelength region of about 450 to 630 nm, which is a part of a visible wavelength region of about 400 to 700 nm sandwiched between the first and second blocking wavelength regions, is a transmission band, and this region is as high as possible. The transmission and the low transmission ripple are configured.

  As a film forming method in this embodiment, the DC pulse superposition type RF ion plating method is used because the stress caused by the film can be controlled to a relatively small value as compared with other film forming methods to which assistance is added. Using.

  During film formation, vapor deposition was performed while cooling the rear surface of the film formation substrate in all layers from the start of film formation to the end of film formation. Water was used as the cooling refrigerant and the temperature was controlled at 10 ° C.

  In the film-forming process, first, a 21-layer film was formed on the surface of the substrate, then the front and back of the Zeonor film were changed, a mask was applied in the same manner as the front surface, and a 29-layer film was formed on the back surface. Here, an adjustment layer for reducing ripples was arranged on the first layer formed immediately above the substrate on both sides. In the 21-layer film, the outermost antireflection layer as the antireflection structure is about 1.0 qw (λ = 500 nm), and the thin film laminated structure forming the third blocking wavelength region is about 2.1 qw (λ = The adjustment layer was about 0.1 qw (λ = 500 nm).

  More specifically, the film thickness of the adjustment layer of the SiO2 film, which is the first of the 21-layer films in Example 1, is 0.118 qw (λ: 500 nm), and the physical film thickness at this time is 10.17 nm. It became. Further, when λ is 600 nm, it becomes 0.098 qw, and when λ is 700 nm, it becomes 0.084 qw. Similarly, the thickness of the adjustment layer of the TiO2 film which is the second layer of the 21-layer film was 0.131 qw (λ: 500 nm), and the physical film thickness at this time was 6.74 nm. Further, when λ was 600 nm, it was 0.106 qw, and when λ was 700 nm, it was 0.089 qw.

  Similarly, in the 29-layer film, the outermost antireflection layer which is an antireflection structure is about 1.0 qw (λ = 500 nm), and the thin film laminated structure forming the first blocking wavelength region is 0.00. Around 6qw (λ = 500 nm), the thin film laminated structure forming the second blocking wavelength region is around 1.7 qw (λ = 500 nm), whereas the adjustment layer is about 0.1 qw (λ = 500 nm). It was before and after. More specifically, the thickness of the adjustment layer of the SiO 2 film that is the first layer of the 29-layer film in Example 1 is 0.096 qw (λ: 500 nm), and the physical film thickness at this time is 8.27 nm. It became. Further, when λ is 600 nm, it becomes 0.080 qw, and when λ is 700 nm, it becomes 0.068 qw. Similarly, the film thickness of the adjustment layer of the TiO2 film, which is the second layer of the 29-layer film, was 0.125qw (λ: 500 nm), and the physical film thickness at this time was 6.43 nm. Further, when λ was 600 nm, it was 0.101 qw, and when λ was 700 nm, it was 0.085 qw. As described above, the adjustment layer has the thinnest thickness among all the layers.

  Furthermore, the film design was repeated many times so as to obtain substantially the same optical characteristics. In all the design examples, the thickness of the SiO 2 film of the adjustment layer which is the first layer on both sides is 0.00 when λ is 500 nm. 163qw or less, 0.135qw or less when λ is 600nm, 0.116qw or less when λ is 700nm, and 14nm or less in physical film thickness. Similarly, the thickness of the adjustment layer TiO2 film, which is the second layer on both sides, is 0.233qw or less when λ is 500nm, 0.189qw or less when λ is 600nm, and 0.159qw or less when λ is 700nm. The physical film thickness was 12 nm or less, which was 3% or less of (400 nm).

  Similarly, in all design examples, the SiO2 film thickness of the adjustment layer which is the first layer on both sides is 0.070 qw or more when λ is 500 nm, 0.058 qw or more when λ is 600 nm, and λ is 700 nm. The time was 0.050 qw or more, and the physical film thickness was 6 nm or more. Similarly, the film thickness of the adjustment layer TiO2 film, which is the second layer on both sides, is 0.078 qw or more when λ is 500 nm, 0.063 qw or more when λ is 600 nm, and 0.051 qw or more when λ is 700 nm. The physical film thickness was 4 nm or more, which was 1% or more of (400 nm).

  The maximum temperature during film formation was 60 ° C. or lower on both sides, and was about 50 ° C. or less. This is the result of measurement from a vacuum-only thermolabel that was previously set on the substrate surface. The value was sufficiently lower than the transition temperature of the Zeonor film as the substrate.

  Moreover, the high temperature, high humidity environmental test was done with the some sample produced by the said method. After 1000 hours, the change in transmittance at the half-value wavelength on the IR side compared to before the start of the environmental test, the average shift amount was 0.5 nm or less. In consideration of the error of the measuring instrument, a film quality close to the so-called non-shift with almost no change was obtained.

  The appearance of the filter was also good, and no warpage, unevenness, wrinkles or cracks were generated, and no wrinkles or cracks were observed after the environmental test.

  Further, another sample produced in the same manner was subjected to a high-temperature test in a dry environment, but no occurrence of wrinkles or cracks was observed even after 1000 hours.

  Furthermore, although the thermal shock test was implemented, generation | occurrence | production of a wrinkle, a crack, etc. was not confirmed even after 1000 cycles progress.

  The UVIR cut filter manufactured as described above was able to obtain spectral transmittance characteristics substantially the same as the design values shown in FIG.

  Here, the ripple of the transmission band was evaluated for the manufactured UVIR cut filter using the above-described calculation formula. In this example, when the amount of deviation from the transmittance approximate line in the transmission region per 1 nm in the wavelength region of the transmission band 450 nm to 630 nm was calculated, the value was 0.258, which was also transmitted compared to the above example. The ripple could be controlled to a very small value.

  In this embodiment, as a UVIR cut filter, a part of the ultraviolet wavelength region and the near-infrared wavelength region is divided into three, ie, a first stop region A to a third stop region C, thereby stacking three thin films. Although the structure using the structure is used, the structure incorporating the thin film laminated structure is not limited to this, and various structures can be adopted. For example, as shown in the schematic diagrams of FIGS. 6A and 6B, a configuration in which three stop zones are provided only in the IR region, or a total of four stop zones in one UV region and three IR regions are configured. It is also possible to divide them appropriately on both sides of the substrate.

In the present embodiment, the first layer on the substrate is the SiO ₂ film, but the first layer can be a TiO ₂ film. In this case, even if the adjustment layer is constituted by only the first layer, In some cases, it is possible to achieve transmission ripple reduction of the same level as in this embodiment. This is due to the difference in the refractive index with the substrate, and the refractive index of the material forming the adjacent ultra-thin adjustment layer with respect to the substrate having a refractive index of about 1.55 as in the present example. The larger the difference is, the easier it is to reduce the transmission ripple, and the TiO ₂ film having a refractive index of 2.3 or more reduces the transmission ripple more efficiently than the SiO ₂ film having a refractive index of about 1.46. it can. For the same reason, conversely, when the first layer is an SiO ₂ film and the adjustment layer is composed of only the first layer, it may be difficult to reduce the transmission ripple to the same level as in this embodiment. Therefore, when a transparent substrate having a refractive index of about 1.45 to 1.65 used for an IR cut filter, a UVIR cut filter, or the like is used, the gap between the transparent substrate and the thin film laminated structure is approximately 1.80 or more. having a refractive index, by disposing e.g. ZrO ₂ and _{Nb2O 5, Ta 2 O 5,} TiO 2 , etc. the main component was 1 or more layers be less adjustment layer of ultrathin constituted by the high refractive index material, Transmission ripple can be greatly reduced.

Furthermore, when the first layer is a thin film having a small difference in refractive index with the substrate, in this embodiment an SiO ₂ film, the layer is thickened and the second layer has a large difference in refractive index with the substrate. In the case of this embodiment, a TiO ₂ film or the like is used, and the second layer is an ultra-thin adjustment layer, so that transmission ripple can be reduced. It is also possible to arrange an extremely thin layer as the adjustment layer. In this way, an ultra-thin adjustment layer having a refractive index of approximately 1.80 or more, which has a large refractive index difference with the substrate, between the substrate and the thin film laminated structure disposed at a position closest to the substrate. By arranging it, it is possible to greatly reduce transmission ripple in an IR cut filter or the like.

(Example 2)
The production of the IR cut filter will be described in detail below.
BK7 glass with a thickness of 0.4 mm is used for the substrate on which the IR cut film is formed, and a part of the desired ultraviolet wavelength region and near-infrared wavelength region is restricted, and the wavelength region is sandwiched between them. Design was performed so as to have spectral transmittance characteristics as shown in FIG. 8 with a part of the visible wavelength region as a transmission band.

  Similarly to Example 1, a mask was formed on the substrate to form a 10 mm square area in several places on the same substrate, and each was cut out after the film formation as shown in FIG.

As the vapor deposition material for forming the vapor deposition film, TiO ₂ is used for the high refractive index material, and SiO ₂ is used for the low refractive index material, and the film structure is composed of alternating layers of SiO ₂ and TiO ₂ as shown in FIG. Although it is configured on both sides of the substrate, 19 layers / 21 layers on both sides of the substrate are laminated, and 40 layers are configured on both sides, and a relatively rigid glass substrate is used, but the purpose is to reduce warping and undulation as much as possible The 19-layer film was adjusted to have the same film thickness as much as possible on both surfaces, and the physical film thickness was about 2600 nm, and the 21-layer film was about 2000 nm. Further, the two layers immediately above the substrate on each surface were used as adjustment layers for reducing ripples. Here, the TiO ₂ film and the SiO ₂ film used in Example 2 have a wavelength dispersion characteristic of a refractive index as shown in FIG.

  Like the design value of the spectral transmission characteristic shown in FIG. 8, the IR cut filter produced in this example has a first blocking wavelength in the wavelength region of about 700 to 900 nm from the visible wavelength region to the near infrared wavelength region. The region is constituted by two stop wavelength regions having a second stop wavelength region in a wavelength region of about 900 to 1100 nm. Further, the wavelength region of about 450 to 630 nm, which is a part of the visible wavelength region of about 400 to 700 nm adjacent to the first blocking wavelength region, is a transmission band, and in this region, the transmission is as high as possible and low. It is comprised so that it may become a transmission ripple.

  As a film forming method in this example, a DC pulse superposition type RF ion plating method was used.

  During film formation, vapor deposition was performed while cooling the rear surface of the film formation substrate in all layers from the start of film formation to the end of film formation. Water was used as the cooling refrigerant and the temperature was controlled at 10 ° C.

  In the film forming process, first, a 21-layer film was formed on the substrate surface, then the front and back of the substrate were changed, a mask was applied in the same manner as the front surface, and a 19-layer film was formed on the back surface. Here, an adjustment layer for reducing ripples was arranged on the first layer formed immediately above the substrate on both sides. In the 21-layer film, the outermost antireflection layer as the antireflection structure is about 1.0 qw (λ = 500 nm), and the thin film laminated structure forming the first blocking wavelength region is around 1.7 qw (λ = The adjustment layer was about 0.1 qw (λ = 500 nm). More specifically, the thickness of the adjustment layer of the SiO 2 film, which is the first layer of the 21-layer film in Example 2, is 0.094 qw (λ: 500 nm), and the physical thickness at this time is 8. It became 10 nm. Further, when λ was 600 nm, it was 0.078 qw, and when λ was 700 nm, it was 0.067 qw. Similarly, the thickness of the adjustment layer of the TiO2 film that is the second layer of the 21-layer film was 0.163 qw (λ: 500 nm), and the physical film thickness at this time was 8.38 nm. Further, when λ was 600 nm, it was 0.132 qw, and when λ was 700 nm, it was 0.111 qw.

  Similarly, in the 19-layer film, the outermost antireflection layer as the antireflection structure is about 1.0 qw (λ = 500 nm), and the thin film laminated structure forming the second blocking wavelength region is 2. The adjustment layer was about 0.1 qw (λ = 500 nm) while it was around 0 qw (λ = 500 nm). More specifically, the thickness of the adjustment layer of the SiO 2 film, which is the first layer of the 19-layer film in Example 2, is 0.103 qw (λ: 500 nm), and the physical film thickness at this time is 8. It became 88 nm. Further, when λ was 600 nm, it was 0.086 qw, and when λ was 700 nm, it was 0.073 qw. Similarly, the thickness of the adjustment layer of the TiO 2 film, which is the second layer of the 19-layer film, was 0.157 qw (λ: 500 nm), and the physical film thickness at this time was 8.07 nm. Further, when λ was 600 nm, it was 0.127 qw, and when λ was 700 nm, it was 0.107 qw. As described above, the adjustment layer has the thinnest thickness among all the layers.

  Furthermore, the film design was repeated many times so as to obtain substantially the same optical characteristics. In all the design examples, the thickness of the SiO 2 film of the adjustment layer which is the first layer on both sides is 0.00 when λ is 500 nm. 163qw or less, 0.135qw or less when λ is 600nm, 0.116qw or less when λ is 700nm, and 14nm or less in physical film thickness. Similarly, the thickness of the adjustment layer TiO2 film, which is the second layer on both sides, is 0.233qw or less when λ is 500nm, 0.189qw or less when λ is 600nm, and 0.159qw or less when λ is 700nm. The physical film thickness was 12 nm or less, which was 3% or less of (400 nm).

  Similarly, in all design examples, the SiO2 film thickness of the adjustment layer which is the first layer on both sides is 0.070 qw or more when λ is 500 nm, 0.058 qw or more when λ is 600 nm, and λ is 700 nm. The time was 0.050 qw or more, and the physical film thickness was 6 nm or more. Similarly, the film thickness of the adjustment layer TiO2 film, which is the second layer on both sides, is 0.078 qw or more when λ is 500 nm, 0.063 qw or more when λ is 600 nm, and 0.051 qw or more when λ is 700 nm. The physical film thickness was 4 nm or more, which was 1% or more of (400 nm).

  The maximum temperature during film formation was 60 ° C. or lower on both sides, and was about 50 ° C. or less. This is the result of measurement from a vacuum-only thermolabel that was previously set on the substrate surface. The value was sufficiently lower than the glass transition temperature of BK7 glass as the substrate.

  Moreover, the high temperature, high humidity environmental test was done with the some sample produced by the said method. After 1000 hours, the change in transmittance at the half-value wavelength on the IR side compared to before the start of the environmental test, the average shift amount was 0.5 nm or less. In consideration of the error of the measuring instrument, a film quality close to the so-called non-shift with almost no change was obtained.

  The appearance of the filter was also good, and no warpage, unevenness, wrinkles or cracks were generated, and no wrinkles or cracks were observed after the environmental test.

  Further, another sample produced in the same manner was subjected to a high-temperature test in a dry environment, but no occurrence of wrinkles or cracks was observed even after 1000 hours. Furthermore, although the thermal shock test was implemented, generation | occurrence | production of a wrinkle, a crack, etc. was not confirmed even after 1000 cycles progress.

  The IR cut filter manufactured as described above was able to obtain spectral transmittance characteristics substantially the same as the design values shown in FIG.

  Here, with respect to the manufactured IR cut filter, the ripple in the transmission band was evaluated using the above-described calculation formula. In the present embodiment, when the amount of deviation from the transmittance approximate line in the transmission region per 1 nm in the wavelength region of the transmission band 450 nm to 630 nm is calculated, the value is 0.137, which is a transmission even compared with the above example. The ripple could be controlled to a very small value.

In the present embodiment, the first layer on the substrate is the SiO ₂ film, but the first layer may be a TiO ₂ film. In this case, the adjustment layer may be composed of only the first layer. In some cases, it is possible to achieve transmission ripple reduction of the same level as in this embodiment.

Further, when the first layer is a SiO ₂ film having a small refractive index difference with the substrate, this layer is thickened, and the second layer is formed with a TiO ₂ film having a large refractive index difference with the substrate. By using a very thin adjustment layer, it is possible to reduce the transmission ripple, and similarly, a plurality of layers after the second layer can be used as the adjustment layer.

<Other embodiments>
As mentioned above, although this invention was demonstrated in detail based on one Embodiment, this invention is not limited to one Embodiment mentioned above.

  For example, the form applied to the light quantity diaphragm apparatus provided with the optical filter produced by one Embodiment mentioned above is demonstrated using FIG. FIG. 9 shows a light quantity stop device. A diaphragm of a light amount diaphragm device suitable for use in a photographing system such as a video camera or a digital still camera is provided for controlling the amount of light incident on a solid-state imaging device such as a CCD or CMOS sensor. As the field of view becomes brighter, the diaphragm blades 80 are controlled so as to be further narrowed down. At this time, an ND (Neutral Density) filter 83 is disposed in the vicinity of the stop as a countermeasure against the deterioration of the image performance that occurs in the small stop state, and the aperture of the stop is further increased even when the brightness of the object field is the same. The structure can be enlarged. Incident light passes through the light amount diaphragm 82 and reaches a solid-state image sensor (not shown), so that it is converted into an electrical signal to form an image.

  In the aperture device 82, the UVIR cut filter or the IR cut filter produced in the first or second embodiment is disposed. These optical filters can be arranged in place of the ND filter at the position of the ND filter 80, or can be arranged so as to be fixed to the diaphragm blade support plate 81. In this case, although it depends on the position where the optical filter is arranged and the mechanical mechanism of the diaphragm device 82, the required shape may be different from the filter produced in this embodiment. It is only necessary to change the shape of the mask jig used at the time of film formation by the same film design and film formation process as in Examples 1 and 2, and the same filter can be manufactured.

  By arranging the light quantity diaphragm device 82 thus produced in the imaging optical system, higher accuracy can be realized.

  In addition, an example in which the present invention is applied to an imaging apparatus including the optical filter manufactured in the above-described embodiment will be described with reference to FIG.

  FIG. 10 shows an image pickup apparatus such as a video camera. Light beams transmitted through the image pickup optical system 91 including the diaphragm blades 93 are limited by the optical filter 90 according to the characteristics of the solid-state image pickup element 92, and an appropriate image is obtained. To get. A UVIR cut filter and an IR cut filter are disposed in the optical filter 90 part.

  It is also possible to drive these filters in and out freely. More specifically, the amount of light that has passed through the imaging optical system 91 and is imaged on the imaging element 92 is determined, and the optical filter 90 is driven. When the amount of incident light is sufficient for normal shooting, the optical filter 90 is moved so as to cover the solid-state image sensor 92. When the amount of light is insufficient, the solid-state image sensor 92 is retracted out of the optical path so as not to be applied. Depending on the presence or absence of the optical filter 90, an optical path difference may occur in the light beam to be imaged, and the image may deteriorate. In such a case, a base material made of the same material as the base material of the optical filter is used as a dummy. As a result, it is possible to sufficiently reduce image degradation.

  The imaging device thus manufactured can improve image degradation due to the transmission ripple of the filter and achieve higher accuracy.

  As described above, the present invention is not limited to the above, and even in other optical apparatuses, image degradation caused by ripples and the like can be achieved by using an optical filter with reduced transmission ripple as produced in one embodiment. Can be reduced.

Claims (7)

A transparent substrate;
A light transmission limiting structure provided by laminating a thin film on the transparent substrate, and having an optical characteristic having a light transmission region and a light transmission limitation region in a predetermined wavelength range, and
An optical filter, wherein a ripple reduction layer for reducing a ripple in the light transmission region of the light transmission restriction structure is provided only between the transparent substrate and the light transmission restriction structure. A transparent substrate;
A light transmission limiting structure provided by laminating a thin film on the transparent substrate, and having an optical characteristic having a light transmission region and a light transmission limitation region in a predetermined wavelength range, and
The ripple reduction layer for reducing the ripple in the light transmission region of the light transmission restriction structure is thinner than the thin film constituting the light transmission restriction structure, and the transparent substrate and the light transmission restriction structure An optical filter characterized by being provided only between.   3. The optical filter according to claim 1, wherein the ripple reduction layer is formed of a plurality of multilayer films each having a thickness thinner than a thin film constituting the light transmission limiting structure. The light transmission limiting structure includes a first light transmission limiting structure provided by laminating a thin film on one surface side of the transparent substrate, and a first light transmission limiting structure provided by laminating a thin film on the other surface side of the transparent substrate. Two light transmission limiting structures,
The ripple reduction layer is a first ripple reduction layer formed between the transparent substrate and the first light transmission restriction structure and having a thickness smaller than a thin film constituting the first light transmission restriction structure. And a second ripple reduction layer formed between the transparent substrate and the second light transmission restriction structure and having a thickness smaller than a thin film constituting the second light transmission restriction structure. The optical filter according to any one of claims 1 to 3, wherein: The thin film constituting the first light transmission restriction structure and the thin film constituting the second light transmission restriction structure are formed with different film thicknesses, respectively.
The optical filter according to claim 4, wherein the first ripple reduction layer and the second ripple reduction layer are formed with different film thicknesses. An antireflection layer is provided on the light transmission limiting structure,
The optical filter according to claim 1, wherein the ripple reduction layer is provided with a thickness smaller than that of the antireflection layer. An imaging apparatus comprising the optical filter according to claim 1.

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