JP7255995B2 - Optical filter and imaging device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical filter used in an imaging device equipped with a solid-state imaging device such as a digital camera, video camera, surveillance camera, etc., and the transmission continuously changes over the transmission wavelength range and the non-transmission wavelength range. The present invention relates to an optical filter having a transmissive-non-transmissive transition wavelength region, and an imaging device equipped with the same.

2. Description of the Related Art Solid-state imaging devices used in imaging devices such as video cameras are often used in combination with filters that adjust optical characteristics such as spectral transmittance so as to correspond to the sensitivity characteristics of the human eye. Specifically, there are an ultraviolet cut filter (UV cut filter), a near infrared cut filter (IR cut filter), or a UVIR cut filter realized by one filter.

Such an edge filter type or bandpass filter type optical filter has a transmission wavelength range that transmits light, a non-transmission wavelength range that limits or blocks transmission, and transmission from the transmission wavelength range to the non-transmission wavelength range. a linearly varying transmissive-nontransmissive transition wavelength region. Among such filters, for example, a reflective type IR cut filter constructed by laminating a plurality of thin films by a vapor deposition method or the like is used in an imaging optical system such as a video camera. A portion of the wavelength corresponding to the region is reflected by the imaging device or the like after passing through the filter, and a portion of the wavelength re-enters the optical filter surface from the imaging device side. Then, part of this re-incident light is reflected again by the optical filter, and the reflected light reaches the imaging element again, which may deteriorate the image.

JP 2014-191346 A JP-A-2008-51985

Patent Document 1 proposes an IR cut filter in which an IR cut coat is applied on an absorption base material that absorbs light of near-infrared wavelengths. The intensity of unwanted light in the transmissive-non-transmissive transition wavelength region can be reduced. However, in the case of such a configuration, there is a problem that the influence of the absorption of the base material extends to the transmission band and even the amount of transmitted light in the transmission band is attenuated.

In addition, in the optical filter proposed in Patent Document 2, if the transmittance in the visible wavelength region is increased, the transition wavelength region that overlaps a part of the visible wavelength region, especially the near-infrared region formed of an inorganic thin film A large absorption cannot be obtained at the half-value wavelength, which is the wavelength at which the transmittance is 50%. Therefore, reflection in this wavelength region cannot be greatly reduced, and it is difficult to reduce the intensity of unnecessary light as described above.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to solve the above-described problems and to provide an optical filter with a new configuration that enables high precision. Another object of the present invention is to provide an image pickup apparatus that achieves high accuracy by using such an optical filter.

In order to solve the above problems, the optical filter of the present invention comprises a transmission wavelength region that transmits light in a predetermined wavelength region, a non-transmission wavelength region that blocks transmission of light in another predetermined wavelength region, and the transmission wavelength region. A functional film having a transition wavelength region in which transmission continuously decreases from the wavelength region to the non-transmitting wavelength region, and a transition wavelength absorption structure configured by dispersing fine metal particles in the predetermined range. Provided on a substrate having optical transparency in a wavelength region, the absorption peak of the transition wavelength absorption structure overlaps with a wavelength region having a transmittance of 5 to 95% in the transition wavelength region , and the outer shape of the metal fine particles is At least one of a cylindrical shape and a rod shape, and the absorption wavelength region in which the absorption rate of 5% or more with the absorption peak is continuous has a transmittance of 5 to 95% in the transition wavelength region. The wavelength region is narrower than the wavelength region .

According to the optical filter having a transmission-non-transmission transition wavelength region according to the present invention, in addition to the reflection function formed by the laminated thin film, the plasmon absorption effect by the metal fine particles is used together, and in addition to this, the laminated thin film is formed. By combining the absorption wavelength region due to plasmon with the transmission-non-transmission transition wavelength region, generation of unnecessary light due to reflection in the transition wavelength region can be reduced in the entire optical filter. Furthermore, by using the relatively steep absorption characteristics of the plasmon effect, it is possible to selectively absorb light only in the transition region, which reduces the attenuation of the amount of transmitted light in the transmission wavelength region due to the absorption layer, and supports high image quality. It is possible to

Further, by using such an optical filter in an imaging device, it is possible to obtain an imaging device capable of achieving high accuracy.

1 is a configuration diagram of an optical filter according to the first embodiment; FIG. Layout of metal fine particles in the transition wavelength absorbing structure in Example 1 Optical characteristic diagram of the optical filter in the first embodiment FIG. 4 is a configuration diagram of an optical filter in the second embodiment; Optical characteristic diagram of the optical filter in the present embodiment 2 FIG. 10 is a configuration example diagram of an optical filter in the present embodiment 3; Explanatory diagram of the imaging device in the present embodiment 4

The optical filter of this embodiment has an edge filter type or bandpass filter type functional film on a substrate that blocks transmission of light in a predetermined wavelength region and transmits light in an adjacent predetermined wavelength region. The optical filter further comprises a transition wavelength absorption layer having absorption due to the plasmon effect in the transmission/non-transmission transition wavelength region formed by the functional film in which fine metal particles are dispersed.

The substrate of such an optical filter is required to have optical transparency at least in the transmission wavelength region of the optical filter. A filter having optical transparency in the wavelength region is used, and an IR pass filter having optical transparency in the near-infrared wavelength region is used. Further, the substrate may be glass type, resin type, or organic/inorganic hybrid type, and a substrate having the strength and optical properties required for an optical filter substrate and capable of functioning as a substrate is used.

Edge filter type and bandpass filter type functional films such as IR cut films and UVIR cut films formed on substrates are produced by laminating one or more thin films, and these thin films are physically or chemically processed. It may be formed by a conventional film forming method, or may be formed by a coating method such as spin coating. Among these film forming methods, from the viewpoint of reproducibility and environmental resistance of the film, a process capable of forming a film with relatively high energy, such as a sputtering method or a film forming method with some kind of assist, is preferable. More specifically, a sputtering method, an IAD method, an ion plating method, an IBS method, a cluster vapor deposition method, or the like can be applied, and the film thickness can be controlled relatively accurately, and a film with high reproducibility can be obtained. Any method may be used as long as it is a film method, and the optimum method may be selected in consideration of the properties, productivity, etc. required for the functional film.

The thin film disposed on the outermost layer of these functional films has a transmission band central wavelength, for example, a functional film having a transmission band of 400 to 600 nm, has a thickness of about 1.0 qw at a wavelength of 500 nm, which is the central wavelength of the transmission band. Preferably. Here, qw is a unit representing the film thickness, and one wavelength λ is used as a reference, and λ/4 is used as one unit. Expressed as 0qw.

In the transmission band of such a functional film, it is ideally desirable to transmit 100% in the entire range, but in practice it is very difficult to completely satisfy this. It is adjusted to obtain a transmittance as close to 100% as possible. In order to achieve such a transmittance, in this embodiment, the transmittance in the transmission band is maximized, and when another functional film such as an anti-reflection film is provided on the back surface of the substrate, other functions are performed. By maximizing the transmittance in the transmission band formed by the film and synthesizing these two transmission characteristics, the optical filter as a whole is configured to maximize the transmittance in the transmission band.

Here, as the wavelength continuously changes, the transmittance in the transmission band changes not a little in a wavy manner, and this is called a ripple in the transmission band (transmission ripple). , is likely to occur as the film becomes thicker. If this transmission ripple becomes large, for example, the color balance of a color image will be lost, and in a surveillance camera, the overall amount of light incident on the imaging device during nighttime photography will decrease, which may lead to deterioration in the image quality of night-vision images. Therefore, it is desirable that the ripple be as small as possible. Therefore, in order to reduce ripples in this transmission band, a transmission ripple adjustment layer for reducing ripples was inserted in the initial layer of the functional film arranged on the substrate side. When other functional films such as anti-reflection films are formed in addition to functional films such as bandpass, the transmission ripple of the optical filter as a whole is the transmission ripple in the transmission band of the functional film and the transmission ripple in other functional films. In the present invention, the functional film has flat transmission characteristics with less transmission ripple, and the other functional films also have flat transmission characteristics with less transmission ripple, which is determined by combination with ripple. By synthesizing these two flat transmission characteristics, the optical filter as a whole forms a flat transmission characteristic with little transmission ripple. Apart from this, for example, by adjusting the phase of the transmission ripple of another functional film with respect to the transmission ripple of the functional film so that the ripples are canceled on both sides, the optical filter as a whole can be made flat with little transmission ripple. However, if there is an error in the phase relationship, there is a risk that the transmission ripple will increase. Selected configuration.

In addition, if the insertion position of the transmission ripple adjustment layer is the position of the outermost layer of the functional film, the effect on the antireflection function in the transmission band at the outermost layer is increased, so the reflection in the transmission band is minimized, that is, It becomes difficult to simultaneously maximize transmission in the transmission band and reduce ripple. In addition, if it is inserted in the middle layer of the functional film, the arrangement will divide the functional film, hindering the maximization of reflection in the opaque band, and at the same time, it will be difficult to reduce the ripple. turn into. For the above reasons, the transmission ripple adjustment layer is arranged in the first layer of the functional film adjacent to the substrate, and priority is given to maximizing the transmission in the transmission band and minimizing the transmission in the non-transmission band. Optimized with a concept that prioritizes ripple reduction. Such a transmission ripple adjustment layer has the feature that the film thickness is the thinnest among the plurality of thin films forming the functional film. Two or more transmission ripple adjustment layers may be provided, but even in that case, all the transmission ripple adjustment layers are thinner than the plurality of thin films forming the functional film.

The transition wavelength region absorption structure in the optical filter of this embodiment is a structure in which a large number of fine metal particles with a size of several nanometers to several hundreds of nanometers are dispersed. Here, the resonant wavelength of the plasmon is determined by various factors such as the metal material, size, shape, inter-particle distance, periodicity, and fine particle arrangement of the dispersed fine metal particles. At this resonant wavelength, the plasmon effect exerts a light absorption effect. For example, in the case of Au particles of about 100 nm or less, a local absorption peak can be obtained at a wavelength in the vicinity of 500 to 700 nm. Thus, by appropriately setting the above parameters, it is possible to selectively obtain absorption in a desired wavelength region. In addition, if the particle concentration is increased by making the particle-to-particle distance too small, the reflection component increases and there is a risk that the required transmission may be reduced. It is necessary.

The minimum thickness of the transition wavelength region absorption structure is equal to or greater than the size of the fine metal particles, but it is possible to increase the thickness depending on the coating method. In addition, multi-layering is also possible depending on the formation method. Furthermore, it can be arranged on only one side of the substrate, or it can be arranged on both sides of the substrate.

In addition to Au, Ag, Cu, Al, etc., metal materials for such metal fine particles include Mg, Ti, Nb, Zr, Ni, Fe, Cr, Pt, W, Mo, Ta, etc., and alloys thereof. There are no particular restrictions, and various materials can be used. Furthermore, the outer shape of the fine metal particles may be appropriately selected from a wide variety of shapes such as spheres, cylinders, rods, triangular pyramids, and squares. Among them, in the case of optical filters having a transition wavelength region from visible wavelengths to near-infrared wavelengths, such as IR cut filters, UVIR cut filters, IR pass filters, etc., they have resonance wavelengths in the required wavelength region and are relatively available. A spherical, cylindrical, or rod-shaped Au is particularly desirable because it is easy to form.

In the optical filter of this embodiment, two transition wavelength region absorption structures having different sizes, metal materials, etc. may be arranged as long as the transmission in the transmission band of the optical filter is not impaired. It is also possible to form one transition wavelength region absorption structure by mixing two kinds of metal fine particles with different values. Furthermore, for example, by using rod-shaped or rectangular-shaped metal fine particles having two plasmon resonance wavelengths on the major axis side and the minor axis side, one transition wavelength region absorption structure has two different absorption peaks. It may be configured.

As the method of forming the transition wavelength region absorption structure, in addition to the method using photolithography, the method using anodic oxidation and nanoimprinting, the dipping method and spin coating method using a binder or solvent, screen printing, etc. Various methods such as a printing method such as gravure printing can be used, and the optimum manufacturing method may be appropriately selected in consideration of the properties and productivity required for the structure.

As an absorption structure that absorbs a predetermined wavelength region, there is an absorption structure that uses a dye, but since the dye is very weak against ultraviolet rays and the like, it has a problem of remarkably inferior environmental resistance. Compared to these structures, the structure utilizing the absorption by the plasmon effect of the fine metal particles of the present invention can provide excellent environmental performance, and is required to have particularly severe environmental resistance, for example, in surveillance cameras. It is also possible to suitably use an optical filter used in an optical device that is used.

The functional film constituting the edge filter type or bandpass filter type optical filter of this embodiment has a transmission-non-transmission transition wavelength region in which the transmission continuously decreases from the transmission band to the non-transmission band. A wavelength with a transmittance of 50% in this transmission-non-transmission transition wavelength region is called a half-value wavelength. For example, an IR cut filter or a UVIR cut filter has a half-value wavelength in the transmission-non-transmission transition wavelength range between the visible wavelength range and the near-infrared wavelength range.

Of the incident light, after passing through the optical filter, it is reflected by the image sensor or the like, and part of it re-enters the optical filter surface from the image sensor side. The intensity of unnecessary light that re-arrives at the element and is generated is simply a value calculated by (spectral transmittance of functional film)×(spectral reflectance of functional film). Therefore, the intensity of unnecessary light is extremely small in the transmission band and the non-transmission band where either transmission or reflection is extremely small. On the other hand, assuming an ideal state in which absorption does not occur in the functional film, the intensity of unnecessary light at the half-value wavelength is maximum, with a transmittance of 50% and a reflectance of 50% to 25%. If the functional film has absorption, by assuming that the half-value wavelength is about half the average value of the transmittance in the transmission band, the unwanted light intensity near the half-value wavelength similarly becomes the maximum value. As described above, the intensity of unnecessary light in the functional film is maximized at the half-value wavelength. Therefore, by adjusting the absorption peak due to the plasmon effect of the transition wavelength region absorption structure to around the half-value wavelength, the above-mentioned unnecessary light intensity can be reduced. It is possible to reduce it significantly. Conversely, in the case of a configuration in which sufficient absorption cannot be obtained near the half-value wavelength, it is extremely difficult to sufficiently reduce the intensity of unnecessary light.

In addition, if the absorption spectrum of the transition wavelength region absorption structure has a broad characteristic, the absorption spectrum of the absorption structure is near the half-value wavelength because it also absorbs a large amount of light in the originally required transmission wavelength region. A steep spectrum with a narrow absorption wavelength region having an absorption peak at . Furthermore, for the same reason, it may be preferable to arrange the absorption amount on the non-transmissive wavelength region side more than on the transmissive wavelength region side. From the above, in order to increase the Q value at the resonance wavelength of plasmons in the transition wavelength region absorption structure, it is more desirable to have a structure in which the size of the metal fine particles is constant and the periodicity is high.

For the above reasons, the absorption spectrum of the transition wavelength region absorbing structure in the transmissive-non-transmissive transition wavelength region preferably has an absorption band in a narrower wavelength region than the transmissive-non-transmissive transition wavelength region. In addition, when the absorption spectrum of the transition wavelength region absorbing structure in the transmission-non-transmission transition wavelength region is wider than the transmission-non-transmission transition wavelength region, the absorption peak wavelength is shifted to the non-transmission region side, and the transmission of the transmission band It is desirable to have a configuration that can maximize In this way, by reducing the attenuation of the amount of transmitted light in the transmission wavelength range by the absorption layer, it is possible to achieve high image quality.

By using the optical filter of the present invention as described above in a photographing device such as a surveillance camera, it is possible to achieve high accuracy.

Hereinafter, the optical filter and imaging device of the present invention will be specifically described in detail based on examples.

(Example 1)
A transition wavelength region absorption structure in which fine metal particles are dispersed and arranged on one side of a transparent substrate, and a near-infrared shielding film composed of multilayer thin films are formed on one side, and a reflection composed of multilayer thin films is formed on the other side. An example of fabricating the optical filter shown in FIG. 1 with a protective film is described in detail below.

FIG. 1 shows a configuration diagram of an optical filter 14 of Example 1 that functions as an IR cut filter that limits transmission of at least light in the near-infrared wavelength region. For the substrate 10 of the optical filter 14 of Example 1, B270i glass having a thickness of 0.4 mm and having transparency at least in the visible wavelength range of 400 to 700 nm was used. Here, although B270i glass was used in the first embodiment, there is no particular limitation as long as it has transparency in the transmission wavelength region as an optical filter, and other glass materials can also be used. However, it is also possible to use a resin-based substrate or an inorganic-organic hybrid substrate. In the case of resin substrates, olefins, polyimides, PET, PEN, polyesters, acrylics, aramids, PC (polycarbonate), acetate, polyvinyl chloride, PVA (polyvinyl alcohol), etc. are also suitable materials. be. Furthermore, it is also possible to use various resin films having a thickness of 100 μm or less.

First, a transition wavelength region absorption structure 11 in which fine metal particles are dispersed is formed on one surface of a substrate 10 which has been thoroughly washed and dried. Cylindrical Au fine particles with a diameter of 100 nm were used as the metal fine particles, and the fine particles were arranged in a dispersed manner within the absorption structure. A photolithography method was used as a method for fabricating this transition wavelength region absorption structure.

First, an Au thin film was vapor-deposited on the substrate 10 with a constant thickness of about 100 nm. After that, a resist solution for lithography was applied by spin coating, and the solvent in the resist was removed by once baking. Next, the previously applied resist film was subjected to exposure processing, and patterning was performed so as to have a shape opposite to the circular array with a diameter of 100 nm. Then, after ion milling is performed to remove the bare Au thin film, etching is performed with a chemical agent to remove the resist film, and the metal fine particles 15 are periodically dispersed as shown in FIG. An arranged transition wavelength region absorbing structure 11 was formed. As shown in FIG. 2, in the first embodiment, the metal fine particles 15 are arranged in a three-way (hexagonal) arrangement so as to obtain an isotropic effect in all directions. can be

In Example 1, the transition wavelength region absorption structure 11 was formed by such a process, but substantially the same structure can be obtained by the so-called lift-off process described below, for example. First, a resist solution for lithography is applied by spin coating onto the substrate 10 which has been thoroughly washed and dried, and then baked. Next, the applied resist film is subjected to exposure processing, patterning is performed to form a circular array with a diameter of 100 nm, which is the opposite of the previous process, and part of the resist film is removed. Then, after depositing an Au thin film with a constant thickness of about 100 nm by vapor deposition or sputtering on the Au thin film, an etching treatment using chemicals is performed to remove the resist film. It is possible to form substantially the same transition wavelength region absorption structure 11 by the lift-off process as described above.

As another method, it is also possible to use a nanoimprint method together. For example, in the manufacturing process of the transition wavelength region absorption structure 11 in the first embodiment described above, after forming the previous resist film by photo-nanoimprinting, ashing treatment is performed, and the remaining film in nanoimprinting is treated by metal Expose the thin film. After that, the exposed metal thin film portion is removed by ion milling, and finally the resist is removed by a chemical solution or the like. By using nanoimprinting in combination in this way, although the number of steps increases, the efficiency of the patterning process can be greatly improved, and productivity can be improved.

In addition, in Example 1, since the Q value of the absorption peak in the transition wavelength region absorption structure 11 was emphasized, the photolithography method, which has high reproducibility of the shape and arrangement periodicity of the fine particles, was used. It is also possible to select not only these but a wet process. As an example, a method of preparing a mixed solution in which Au nanoparticles are dispersed in an organic solvent or a binder material, spin-coating this on the substrate 10, or a method of coating by a printing method such as screen printing or gravure printing. is mentioned.

Next, a near-infrared shielding film 12 was formed on this transition wavelength region absorption structure 11 by the IAD method. After that, the front and back of the substrate 10 were changed, and an antireflection film 13 was similarly formed by the IAD method.

The near-infrared shielding film 12 of Example 1 formed on the substrate 10, as shown in FIG. It has a transmission band in which most of the components other than the components reflected on the back side of the substrate are transmitted, and an opaque band in which light in the wavelength range of about 700 to 1050 nm from visible wavelengths to the near-infrared wavelength region is blocked. In addition, the wavelength region of about 550 to 650 nm sandwiched between the transmission band and the non-transmission band has a transmission-non-transmission transition wavelength region in which the transmission continuously changes from the transmission band to the non-transmission band. Furthermore, the wavelength at which the transmittance is 50% in the transmission-non-transmission transition wavelength region is defined as the IR half-value wavelength, and this value is set to 580 nm. The near-infrared shielding film 12 in Example 1 is formed by alternately laminating TiO2, which is a high refractive index material, and SiO2, which is a low refractive index material. A transmission ripple adjusting layer having a transmission ripple reduction function is arranged in the first layer of , and has the smallest film thickness among all the film thicknesses constituting the near-infrared shielding film 12 . Furthermore, the outermost SiO2 layer has a thickness of about 1.0 qw at 400 to 600 nm, which is the center wavelength of the antireflection wavelength region.

The antireflection film 13 of the present embodiment 1 formed on the other surface of the substrate 10 reflects light in the wavelength range of about 400 to 700 nm from the visible wavelength to the near-infrared wavelength range on the back side of the substrate. It has an optical characteristic of having a transmission band that blocks most of the reflection except for the component, that is, transmits most of the light (not shown). As described above, at 580 nm, which is the IR half-value wavelength of the near-infrared shielding film 12, the antireflection film 13 arranged to face the back surface of the substrate forms a transmission band. Even if the optical properties of the shielding film 12 are shifted, for example, by 10 nm to the short wavelength side or the long wavelength side, the antireflection film 13 can maintain the transmission band at the IR half-value wavelength. Therefore, even if the optical characteristics of the antireflection film 13 change due to a film formation error during the formation of the antireflection film 13, the IR of the optical filter 14 formed including the substrate 10 can be detected by the configuration design as described above. The effect on the half-value wavelength is extremely small, and the transmissive-non-transmissive transition wavelength region of the optical filter 14 is determined only by the error of the near-infrared shielding film 12, so the reproducibility can be further improved, and the optical filter as a whole has high accuracy. can be realized.

Further, the antireflection film 13 in Example 1 is formed by alternately laminating TiO2, which is a high refractive index material, and SiO2, which is a low refractive index material. The layer has a film thickness of about 1.0 qw at 500 to 600 nm, which is the central wavelength of the wavelength band that forms the antireflection band.

The transmission characteristics of the transmission band produced by the single near-infrared shielding film 12 formed on the substrate 10 are flat with little transmission ripple and have substantially constant transmission characteristics. It has the characteristic of transmitting most of the light except for the component. Similarly, the transmission characteristics of the transmission band produced by the single antireflection film 13 formed on the substrate 10 are flat with little transmission ripple, and have substantially constant transmission characteristics. It has the characteristic of transmitting most of the light except for the reflected component. The respective transmission characteristics in the transmission bands produced by these two functional films have characteristics that can be regarded as substantially the same. Then, by synthesizing the transmission characteristics of these two functional films, which are flat with little transmission ripple and have high transmission, as shown in FIG. , which produces flat, high-transmission characteristics with little transmission ripple. Similarly, in the opaque band of the optical filter 14, the transmission characteristics are determined by synthesizing the transmission characteristics produced by the two functional films. Therefore, the transmission characteristics of the optical filter 14 as a whole are determined by synthesizing the transmission characteristics produced by the two functional films of the near-infrared shielding film 12 and the antireflection film 13 .

In the near-infrared shielding film 12 and the antireflection film 13 in the first embodiment, in addition to TiO2, which is a high refractive index material and SiO2, which is a low refractive index material, which are formed as vapor deposition films, Nb2O5 is used as a high refractive index material. , ZrO2, Ta2O5, etc. can be used, and MgF2, etc. can be used as a low refractive index material. In addition, for reasons of design and film formation, it is possible to use an intermediate refractive index material such as Al2O3 in some layers. Metal compounds such as Ti, Si, Nb, Zr, Pt, In, W, Mo, Ta, Cu, Ag, and Au may be used, and an optimum combination of materials may be selected depending on the situation.

As shown in FIG. It is adjusted to overlap with the wavelength around the half-value wavelength in the transmissive-non-transmissive transition wavelength region formed by the infrared shielding film 12 . Furthermore, as shown in FIGS. 3A and 3B, the absorption spectrum of the transition wavelength region absorption structure 11 absorbs a narrower wavelength region than the transmission-non-transmission transition wavelength region of the near-infrared shielding film 12. It was configured as a wavelength region. Here, considering the conditions under which the effect of absorption is actually exhibited, the absorption wavelength region in this embodiment is defined as a wavelength region in which the absorptance is continuously 5% or more. As a result, it is possible to selectively greatly reduce only unnecessary light in the vicinity of the half-value wavelength in the transmission-non-transmission transition wavelength region, where the intensity of unnecessary light is theoretically maximized, while absorption loss in the transmission band is reduced. can be suppressed. More specifically, when compared with a simple reference value for the unnecessary light intensity calculated by (spectral transmittance of the functional film) x (spectral reflectance of the functional film), the theoretical value of the near-infrared shielding film 12 alone is While the maximum intensity is 25%, in this case the maximum value is obtained when the transmission is about 28% and the reflection is about 28%, and the value is less than 8%, which is a reduction of more than one-third. was made.

In addition, compared to structures that obtain absorption from organic components such as pigments, it is also resistant to deterioration due to ultraviolet rays. Since the optical characteristics of the optical filter as a whole are obtained mainly from two characteristics, changes in the absorption characteristics due to the surrounding environment such as temperature, humidity, and ultraviolet rays are extremely small, and an optical filter with excellent environmental resistance can be obtained. .

The spectral transmission characteristics of the optical filter 14 manufactured as described above were close to the design values shown in FIG. 3(c). As a result, it was possible to obtain an optical filter that reduces the intensity of unnecessary light while maintaining high transmission in the transmission band, achieves high precision, and has excellent environmental resistance.

(Example 2)
A transition wavelength region absorption structure in which fine metal particles are dispersed and a near-infrared shielding film composed of multilayer thin films are formed on one side of a transparent substrate, and fine metal particles are dispersed on the other side. An example of fabricating the optical filter shown in FIG. 4, in which the disposed transition wavelength region absorption structure and the antireflection film composed of the multilayer thin films are formed, will be described in detail below.

FIG. 4 shows a configuration diagram of the optical filter 24 of Example 2 that functions as an IR cut filter that limits transmission of at least light in the near-infrared wavelength region. For the substrate 20 of the optical filter 24 of Example 2, B270i glass having a thickness of 0.4 mm and having transparency at least in the visible wavelength range of 400 to 700 nm was used. Here, although B270i glass was used in the second embodiment, there is no particular limitation as long as it has transparency in the transmission wavelength region of the optical filter.

First, a transition wavelength region absorption structure 21 in which fine metal particles are dispersed is formed on one surface of a substrate 20 that has been thoroughly washed and dried. Spherical Au microparticles with a diameter of 100 nm were used as the metal microparticles, and these microparticles were arranged in a dispersed manner within the transition wavelength absorption structure. A dipping method was used as a method for fabricating this transition wavelength region absorption structure 21 . The dispersion liquid and formation process were adjusted so that the film thickness of the transition wavelength region absorption structure 21 corresponded to the diameter size of the metal fine particles.

First, a dispersion containing a large number of Au metal fine particles having a spherical shape of 100 nm size was prepared. Next, after immersing the entire substrate 20 in this dispersion liquid, the substrate 20 was lifted out of the liquid under predetermined conditions and held for a certain period of time, followed by a drying process to fabricate the transition wavelength region absorption structure 21 . With such a dipping process, the transition wavelength region absorbing structures 21 can be fabricated on both sides of the substrate 20 simultaneously. Here, depending on the binder and solvent to be mixed, it is possible to produce an ultra-thin film, it is also possible to correspond to a thick film, and it is also possible to arrange the metal fine particles relatively regularly and periodically. Furthermore, other than the manufacturing method by such a dipping process, according to the shape and size of the metal fine particles, a manufacturing method such as a photolithography method described in Example 1, a lift-off process, or a process using a nanoimprint method in combination is selected. Is possible. In addition, it is also possible to select other wet processes such as spin coating and printing.

Next, a near-infrared shielding film 22 was formed on this transition wavelength region absorption structure 21 by the IAD method. After that, the substrate 20 was turned over, and an antireflection film 23 was similarly formed on the transition wavelength region absorption structure 21 by the IAD method.

The near-infrared shielding film 22 of Example 2 formed on the substrate 20, as shown in FIG. It has a transmission band in which most of the components other than the components reflected on the back side of the substrate are transmitted, and an opaque band in which light in the wavelength range of about 700 to 1050 nm from visible wavelengths to the near-infrared wavelength region is blocked. In addition, the wavelength region of about 550 to 650 nm sandwiched between the transmission band and the non-transmission band has a transmission-non-transmission transition wavelength region in which the transmission continuously changes from the transmission band to the non-transmission band. Furthermore, the IR half-value wavelength was set to 580 nm. Further, the near-infrared shielding film 22 in Example 2 is configured by alternately laminating TiO2, which is a high refractive index material, and SiO2, which is a low refractive index material. A transmission ripple adjusting layer having a transmission ripple reduction function is arranged in the first layer of , and has the smallest film thickness among all the film thicknesses constituting the near-infrared shielding film 22 . Furthermore, the outermost SiO2 layer has a film thickness of about 1.0 qw at the center wavelength of the wavelength range of 400 to 600 nm, which is the antireflection band.

The antireflection film 23 of the present embodiment 2 formed on the other surface of the substrate 20 has a wavelength range of about 400 to 700 nm from the visible wavelength to the near-infrared wavelength range. It has an optical characteristic of having a transmission band that blocks most of the reflection except the reflection component, that is, transmits most of the light (not shown). In this manner, the antireflection film 23 arranged to face the rear surface of the substrate forms a transmission band at 580 nm, which is the IR half-value wavelength of the near-infrared shielding film 22 . Therefore, even if the optical characteristics of the antireflection film 23 change due to film formation errors, the effect on the IR half-value wavelength of the optical filter 24 formed including the substrate 20 is extremely small, and only the error of the near-infrared shielding film 22 Since the transmission-non-transmission transition wavelength region of the optical filter 24 is determined, the reproducibility can be improved, and the accuracy of the optical filter as a whole can be improved.

In addition, the antireflection film 23 in the second embodiment is formed by alternately laminating TiO2, which is a high refractive index material, and SiO2, which is a low refractive index material. The layer has a film thickness of about 1.0 qw at 500 to 600 nm, which is the central wavelength of the wavelength band that forms the antireflection band.

The transmission characteristics of the transmission band produced by the single near-infrared shielding film 22 formed on the substrate 20 are flat with little transmission ripple and have substantially constant transmission characteristics. It has the characteristic of transmitting most of the light except for the component. Similarly, the transmission characteristics of the transmission band produced by the single antireflection film 23 formed on the substrate 20 are flat with little transmission ripple and have substantially constant transmission characteristics. It has the characteristic of transmitting most of the light except for the reflected component. The respective transmission characteristics in the transmission bands produced by these two functional films have characteristics that can be regarded as substantially the same. Then, by synthesizing the transmission characteristics of these two functional films, which are flat with little transmission ripple and have high transmission, as shown in FIG. , which produces flat, high-transmission characteristics with little transmission ripple. Similarly, in the opaque band of the optical filter 24, the transmission characteristics are determined by synthesizing the transmission characteristics produced by the two functional films. Therefore, the transmission characteristics of the optical filter 24 as a whole are determined by synthesizing the transmission characteristics produced by the two functional films of the near-infrared shielding film 22 and the antireflection film 23 .

In the near-infrared shielding film 22 and the antireflection film 23 in Example 2, the material is not limited to TiO2, which is a high refractive index material, and SiO2, which is a low refractive index material, which are formed as vapor deposition films. A combination of materials should be selected.

Here, the local absorption peak wavelength in the transition wavelength region absorption structure 21 described above, that is, the plasmon resonance wavelength in the transition wavelength region absorption structure 21 is near-infrared as shown in FIG. It is adjusted to overlap with the wavelength around the half-value wavelength in the transmissive-non-transmissive transition wavelength region formed by the shielding film 22 . Furthermore, as shown in FIGS. 5A and 5B, the absorption spectrum of the transition wavelength region absorption structure 21 absorbs a wavelength region narrower than the transmission-non-transmission transition wavelength region of the near-infrared shielding film 22. It was configured as a wavelength region. As a result, when compared with a simple reference value for the unnecessary light intensity calculated by (spectral transmittance of the functional film)×(spectral reflectance of the functional film), the theoretical maximum of the near-infrared shielding film 22 is 25. %, whereas in this example , the maximum value was obtained when the transmission was about 19% and the reflection was about 19%, and the value was a little less than 4%, which was able to be reduced by more than one-fifth. .

The spectral transmission characteristics of the optical filter 24 manufactured as described above were close to the design values shown in FIG. 5(c). As a result, it was possible to obtain an optical filter that reduces the intensity of unnecessary light while maintaining high transmission in the transmission band, achieves high precision, and has excellent environmental resistance.

(Example 3)
Another configuration example of an edge filter type or bandpass filter type optical filter having a transmission-non-transmission transition wavelength region, such as those manufactured in Examples 1 and 2, will be described.

The optical filter of the present invention can also be configured as shown in FIGS. 6(a) to 6(d). Further, each optical filter in the following description has an absorption peak near the half-value wavelength in the transmissive/non-transmissive transition wavelength region due to the plasmon effect of the transition wavelength region absorption structure configured by dispersing and arranging fine metal particles. is assumed. In addition, the functional film 32 and the second functional film 33 described below may be appropriately selected from a near-infrared shielding film, an ultraviolet shielding film, an ultraviolet-near-infrared shielding film, a near-infrared shielding film, a near-infrared transmitting film, and an antireflection film in some cases. is possible.

FIG. 6(a) shows a transition wavelength region absorbing structure 31 or a transition wavelength region absorbing structure 31 and a second transition wavelength region absorbing structure 35 arranged on both sides of a substrate 30, followed by a transition wavelength region absorbing structure. A configuration example belonging to the second embodiment, in which a functional film 32 is formed on a structure 31, and a second functional film 33 is formed on the other transition wavelength region absorption structure 31 or transition wavelength region absorption structure 35. is. Although a near-infrared shielding film and an antireflection film are used as the functional film 32 and the second functional film 33 in the second embodiment, it is also possible to dispose a near-infrared shielding film and an ultraviolet shielding film, for example. It is possible to arrange an infrared shielding film and a near-infrared shielding film, or to arrange two types of near-infrared shielding films having different stopbands. It is also possible to disperse and arrange two or more different types of fine metal particles having different absorption peaks due to plasmon resonance in one layer of the transition wavelength region absorption structure 31 .

FIG. 6B shows a functional film 32 and a transition wavelength region absorption structure 31 arranged on one surface of a substrate 30, and a second functional film 33 and a second transition wavelength region on the other surface of the substrate 30. FIG. This is an example in which the area absorption structure 35 is arranged. Also, although not shown, one of the two transition wavelength region absorption structures 31 can be replaced with a second transition wavelength region absorption structure 35 having a different absorption wavelength region.

FIG. 6(c) is a configuration in which one transition wavelength region absorbing structure 41 in FIG. 6(b) is removed. Moreover, although not shown, it is also possible to further form another functional film such as an antireflection film on the transition wavelength region absorption structure 31 .

FIG. 6D shows a transition wavelength region absorption structure 31 arranged on a functional film 32 formed on one side of a substrate 30 and a second transition wavelength region absorption structure on the other side of the substrate 30 . This is an example in which a structure 36 is arranged and a second functional film 33 is arranged thereon. Here, although not shown, it is possible to change the functional film 32 to the second functional film 33, and to change the second transition wavelength region absorption structure 35 to the transition wavelength region absorption structure 31. It is also possible to arrange and configure It is also possible to further form other functional films such as an antireflection film on the transition wavelength region absorption structure 31 .

With the configuration and arrangement as described above, an IR cut filter, a UV cut filter, a UVIR cut filter, an IR pass filter, a color filter, and a fluorescent It is possible to form a wide variety of optical filters, such as filters, which are highly accurate and have excellent environmental resistance.

(Example 4)
An example in which the optical filter manufactured in Examples 1 to 3 is applied to an imaging device such as a video camera will be described with reference to FIG.

FIG. 7 shows an image pickup apparatus such as a video camera, in which light rays transmitted through an image pickup optical system 43 composed of aperture blades 45 and the like are adjusted to the characteristics of a solid-state image pickup device 44 by an optical filter placed at an optical filter insertion position 40. It is configured so that the correct image can be obtained by adjusting the

For example, in the configuration of FIG. 7, the optical filter 41 having the function of an IR cut filter produced in Examples 1 to 3 is placed at a predetermined position in the imaging device, and the optical filter is placed at the optical filter insertion position 40. By moving 41, it is possible to select an appropriate filter according to the shooting situation and perform shooting. In the configuration of FIG. 7, the optical filter 41 is used to determine the amount of light transmitted through the imaging optical system 43 and imaged on the solid-state imaging device 44, and the optical filter 41 is placed at the optical filter insertion position 40, or the phase difference is adjusted. One of the filter regions of the AR filter 42, which is a dummy filter for doing so, is arranged. When the amount of incident light is sufficient for normal photography, the optical filter 41 is arranged at the optical filter insertion position 40 to form a color image. Conversely, when the amount of light is insufficient, the AR filter 42 is removed. It is arranged at the optical filter insertion position 40 . By adopting such a configuration, it is possible to form a night-vision image, for example, in the case of photographing at night. In the image pickup device manufactured in this manner, the reflection component of the optical filter 41, particularly the unnecessary light intensity due to the transmission-non-transmission transition wavelength region, is reduced. It is possible to suppress the occurrence of the red ghost, and the image quality of the captured image can be further improved. In addition, since the absorption component of such an optical filter is expressed by an inorganic metal material, it is possible to obtain an imaging device excellent in environmental resistance in which optical characteristics change little due to the surrounding environment.

In addition, the optical filter 41 in FIG. 7 transmits a predetermined near-infrared wavelength region, for example, 800 to 900 nm, which has absorption due to the plasmon effect of the metal fine particles in the two transmission-non-transmission transition wavelength regions, In the case of an IR pass filter that blocks transmission of 400 to 700 nm and 1000 to 1200 nm, by changing the AR filter 52 to an IR cut filter, when the amount of incident light is sufficient for normal photography, the IR cut filter is used. A color image can be formed by arranging it at the optical filter insertion position 50 , and conversely, when the amount of light is insufficient, an IR pass filter can be arranged at the optical filter insertion position 50 . By arranging such an IR pass filter, the unnecessary light intensity due to the transmissive/non-transmissive transition wavelength region is reduced, so the image quality of the night vision image is further improved, and the imaging with excellent environmental resistance is achieved. You can get the device.

Here, if the transition wavelength absorbing structure constituting the optical filter 41 is arranged only on one surface of the substrate, the reflection on the two surfaces on the substrate will be different. Therefore, it is more desirable to arrange a surface with low reflection in the wavelength region of unnecessary light on the imaging element side. This is because such an arrangement can further reduce the intensity of unnecessary light incident on the imaging device after repeated multiple reflections. Therefore, in the present embodiment, the surface of the optical filter 41 with low reflection in the transmissive-non-transmissive transition wavelength region formed by the functional film is arranged on the image sensor side.

Further, not only the optical device of this embodiment, but also other optical devices may be edge filter types having a transmissive-non-transmissive transition wavelength region, such as IR cut filters produced in Examples 1 to 3, or By using a band-pass filter type optical filter, it is possible to realize an imaging apparatus that can achieve high image quality and has excellent environmental resistance.

10, 20, 30. Substrates 11, 21, 31 . Transition wavelength region absorption layers 12, 22 . Near-infrared shielding films 13, 23 . Antireflection films 14, 24, 34. optical filter 15 . fine metal particles 32 . functional membrane 33 . Second functional film 35 . Second transition wavelength region absorbing structure

40. Optical filter insertion position 41 . optical filter 42 . AR filter 43 . imaging optical system 44 . Solid-state imaging device 45 . Aperture blade

Claims (8)

a transmission wavelength region that transmits light in a predetermined wavelength region;
an opaque wavelength region that blocks transmission of light in other predetermined wavelength regions;
a functional film having a transition wavelength region in which transmission continuously decreases from the transmission wavelength region to the non-transmission wavelength region;
a transition wavelength absorbing structure configured by dispersing and arranging fine metal particles,
Provided on a substrate having optical transparency in the predetermined wavelength region,
An absorption peak of the transition wavelength absorbing structure overlaps a wavelength region having a transmittance of 5 to 95% in the transition wavelength region ,
The outer shape of the fine metal particles is at least one of a columnar shape and a rod shape, and the absorption wavelength region in which the absorption rate of 5% or more with the absorption peak is continuous is the transition wavelength region. An optical filter characterized by a wavelength region narrower than a wavelength region having a transmittance of 5 to 95% . 2. The optical filter according to claim 1 , wherein said fine metal particles are periodically dispersed. 3. The optical filter according to claim 1 , wherein said fine metal particles are dispersed in a resin binder. Also on the other side of the substrate different from the side on which the transition wavelength absorbing structure is formed,
The optical filter according to any one of claims 1 to 3 , characterized in that said transition wavelength absorbing structure is formed. The optical system according to any one of claims 1 to 4 , characterized in that another functional film is formed on the other surface of the substrate different from the surface on which the functional film is formed. filter. the functional film or the other functional film,
The optical filter according to any one of claims 1 to 5 , characterized by having at least either a near-infrared shielding function or an ultraviolet shielding function. the functional film or the other functional film,
7. The optical filter according to any one of claims 1 to 6 , characterized by having a visible light blocking function and a near infrared transmitting function. An imaging apparatus comprising: the optical filter according to any one of claims 1 to 7 ; and an imaging element for imaging light transmitted through the optical filter.

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