JP7326738B2 - Near-infrared cut filter - Google Patents

Description

The present invention relates to a near-infrared cut filter, and more particularly to a near-infrared cut filter having an optical multilayer film on a transparent substrate.

Charge Coupled Device (CCD) image sensors, Complementary Metal Oxide Semiconductor (CMOS) image sensors, etc. (hereinafter referred to as solid-state imaging devices) are used in digital cameras, digital videos, and the like. However, the spectral characteristics of these solid-state imaging devices have greater sensitivity to infrared light than human visibility characteristics. Therefore, in digital cameras, digital videos, etc., spectral correction is performed using a near-infrared cut filter.

In recent years, smartphones have come to be used as a substitute for digital cameras and digital videos, and the thickness of device housings in which solid-state imaging devices are mounted is becoming thinner. Furthermore, as smartphones become thinner and more compact, the thickness of device housings tends to become even thinner. For this reason, light has come to enter the solid-state imaging device provided in the housing from a wider angle (higher incident angle).

It is known that the above-described optical multilayer film shifts the light transmission characteristics to the short wavelength side as the incident angle of light increases (the angle of incident light with respect to the normal direction of the optical multilayer film increases). ing. In addition, in the light transmitted through the optical multilayer film, a phenomenon in which the transmittance of light at a high incident angle in the visible light region partially decreases (hereinafter referred to as "grazing incidence ripple" in the present specification) has also been observed. . In a normal solid-state imaging device, the incident angle of light should be considered from 0° to 35°. However, the incidence angle of light is becoming larger due to the thinning of the housing as described above, and it is required to provide desired optical characteristics even for light of such a high incidence angle. Therefore, there is a demand for an optical filter that provides desired optical characteristics at high incident angles.

Here, in the oblique incidence ripple described above, there is a problem that as the incident angle of light increases, the drop in transmittance also increases. In order to address such a problem, for example, a technique has been proposed for suppressing oblique incident ripples by means of an optical multilayer film even when the incident angle of light is large (see, for example, Patent Document 1).

Japanese Patent No. 6119747

However, in a configuration that achieves suppression of oblique incident ripple caused by light with a high incident angle, the total number of optical multilayer films tends to increase as the oblique incident ripple is suppressed with higher accuracy, which tends to impair productivity. was there.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and provides a near-infrared cut filter that uses an optical multilayer film with a relatively small number of layers and is capable of suppressing oblique incident ripple caused by light with a high incident angle. for the purpose.

A near-infrared cut filter of the present invention is a near-infrared cut filter comprising a transparent substrate and a first optical multilayer film provided on at least one main surface of the transparent substrate, wherein the first optical multilayer In the film, a medium refractive index film having a refractive index of 1.8 or more and 2.21 or less at a wavelength of 500 nm and a low refractive index film having a refractive index of 1.45 or more and 1.49 or less at a wavelength of 500 nm are alternately laminated. The number of combination units of the medium refractive index film and the low refractive index film is 5 or more and 35 or less, and the first optical multilayer film has a wavelength range in which transmission of light incident at 0° is restricted. has a central wavelength of 890 nm or more and 1200 nm or less, and a width of the wavelength range of 100 nm or more and 300 nm or less.

In the near-infrared cut filter of the present invention, the low refractive index film is at least one compound selected from silicon oxide, magnesium fluoride, calcium fluoride and yttrium fluoride, or a mixture containing at least one of these compounds. The medium refractive index film is preferably composed of one or more compounds selected from zirconium oxide, tantalum oxide, yttrium oxide, lanthanum titanate, zinc sulfide, titanium oxide, and aluminum oxide, or It preferably consists of a mixture containing one or more.

The near-infrared cut filter of the present invention comprises a second optical multilayer film on at least one main surface of the transparent substrate, and the second optical multilayer film has a refractive index exceeding 2.21 at a wavelength of 500 nm. .A high refractive index film of 8 or less and the low refractive index film are alternately laminated, and the number of combination units of the high refractive index film and the low refractive index film is 3 or more and 30 or less, It is preferable that the second optical multilayer film has a center wavelength of 700 nm or more and less than 890 nm in a wavelength range in which transmission of light incident at 0° is restricted, and a width of the wavelength range of 100 nm or more and 300 nm or less.

In the near-infrared cut filter of the present invention, the high refractive index film is preferably made of one or more compounds selected from tantalum oxide, titanium oxide and niobium oxide, or a mixture containing one or more of these compounds.

The near-infrared cut filter of the present invention preferably has a plurality of at least one of the first optical multilayer film and the second optical multilayer film.

In the near-infrared cut filter of the present invention, the transparent substrate is preferably made of one or more materials selected from glass, glass ceramics, crystal, resin and sapphire.

In the near-infrared cut filter of the present invention, the transparent substrate preferably has a property of absorbing light with wavelengths in the near-infrared region.

The near-infrared cut filter of the present invention has a transmission band that transmits light in the wavelength range of 430 nm to 600 nm with respect to light incident at 0 °, and a blocking that limits the transmission of light in the wavelength range of 750 nm to 1000 nm. The difference between the average transmittance of light incident at 0° and the average transmittance of light incident at 40° in the transmission band (average transmittance of light incident at 0° -40° The average light transmittance) is preferably 3% or less.

In the near-infrared cut filter of the present invention, the total number of layers of the first optical multilayer film and the second optical multilayer film is preferably 90 or less.

In this specification, the term "to" and the sign "to" represent a range from the numerical value on the left to the numerical value on the right. Further, near-infrared rays represent light having a wavelength in the range of 750 nm to 1300 nm, for example.

According to the present invention, it is possible to provide a near-infrared cut filter that can suppress oblique incident ripple caused by light with a high incident angle by using an optical multilayer film having a relatively small number of layers.

FIG. 1 is a cross-sectional view showing a near-infrared cut filter according to an embodiment. FIG. 2 is a cross-sectional view of an optical multilayer film included in a near-infrared cut filter. FIG. 3 is a graph showing the optical characteristics of the near-infrared cut filter of Example 1 for 0° incident light and 40° incident light. FIG. 4 is a graph showing the optical characteristics of the near-infrared cut filter of Example 2 with respect to 0° incident light and 40° incident light. FIG. 5 is a graph showing the optical characteristics of the near-infrared cut filter of Example 3 with respect to 0° incident light and 40° incident light. FIG. 6 is a graph showing the optical characteristics of the near-infrared cut filter of the comparative example for 0° incident light and 40° incident light.

Hereinafter, embodiments will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a cross-sectional view of a near-infrared cut filter 10 according to the first embodiment. FIG. 2 is a cross-sectional view of the first optical multilayer film 12 included in the near-infrared cut filter 10. FIG. The near-infrared cut filter 10 limits transmission of near-infrared rays. Therefore, the near-infrared cut filter 10 preferably has an average transmittance of 5% or less for light incident at 0° in the near-infrared wavelength range. The configuration of the near-infrared cut filter 10 will be described below with reference to FIGS. 1 and 2. FIG.

As shown in FIG. 1 , the near-infrared cut filter 10 includes a transparent substrate 11 , a first optical multilayer film 12 and a second optical multilayer film 13 . The near-infrared cut filter 10 has a first optical multilayer film 12 on one main surface of a transparent substrate 11 and a second optical multilayer film 13 on the first optical multilayer film 12 . The configuration of the near-infrared cut filter is not limited to this. good. Also, the order of the first optical multilayer film 12 and the second optical multilayer film 13 is not limited. , or the second optical multilayer film 13 (not shown) may be placed on the transparent substrate 11 side.

Here, in general, the optical film thickness of a film having a thickness (physical film thickness) d is nd×cos θ (where θ is the incident angle of light with normal incidence at 0°, n is the refractive index of the film ). According to the above formula, the optical film thickness depends on the incident angle θ of light to the film, and decreases as θ increases. Here, the occurrence of a local decrease in transmittance in the visible light region due to the optical multilayer film (so-called oblique incidence ripple) is due to the degree of decrease in the optical film thickness due to an increase in the incident angle. It is thought that this is due to the difference in

For example, considering the high refractive index film H and the low refractive index film L, as described above, as the incident angle θ increases, the optical film thicknesses of the high refractive index film H and the low refractive index film L are proportional to cos θ. and decrease. At this time, since the smaller the refractive index n, the greater the effect of the decrease in the optical film thickness due to the increase in the incident angle θ, when the incident angle θ increases, the optical film thicknesses of the high-refractive-index film H and the low-refractive-index film L decrease. The ratio deviates greatly from the physical film thickness ratio designed at θ=0°. As a result, it is considered that an oblique incident ripple occurs due to a difference in the optical film thickness ratio between the high refractive index film H and the low refractive index film L. It has also been found that oblique incidence ripples are generated in the vicinity of half the central wavelength of the wavelength range in which the optical multilayer film limits the transmission of light, for example, at an incident angle of 0°.

Furthermore, the increase in the incident angle θ shifts the light transmission characteristics of the optical multilayer film to the short wavelength side, and the oblique incidence ripple generation region also increases with the incident angle θ of 0° (vertical incidence). It was found that the grazing incidence ripple generation region in λ shifts to the short wavelength side. Based on such findings, the near-infrared cut filter of the embodiment employs the configuration described below for the first optical multilayer film 12 and the second optical multilayer film 13 .

The first optical multilayer film 12 is configured to reduce the drop in the transmittance of oblique incident ripples in the visible light region, which generally has a wavelength of 440 nm to 650 nm, preferably 500 nm to 560 nm (G region). Therefore, the center wavelength of the wavelength range in which the transmission of light incident at 0° is limited (hereinafter referred to as “stopband”) is 890 nm to 1200 nm in the first optical multilayer film 12 .

The stopband formed by the first optical multilayer film 12 has a width of 100 nm to 300 nm. If the width of the stopband is less than 100 nm, it will be necessary to provide a large number of separate optical multilayer films for forming the stopband of the near-infrared cut filter, which may increase the cost of manufacturing the near-infrared cut filter. There is A stopband width of more than 300 nm is advantageous in designing an optical multilayer film. However, in the structure in which the medium refractive index films M and the low refractive index films L are alternately laminated in the first optical multilayer film 12, the stopband is essentially large because the refractive index difference between the two types of films is small. Hard to become. Therefore, if the single first optical multilayer film 12 is designed to form a stopband of more than 300 nm, it is difficult to design the medium refractive index film M and the low refractive index film L with desired refractive indices.

When the near-infrared cut filter has a plurality of first optical multilayer films 12, the width and center wavelength of the stopband formed by each of the plurality of first optical multilayer films 12 are all within the ranges described above. That is, in the case of a near-infrared cut filter having a stopband exceeding 300 nm in the infrared region, the width of each stopband is 100 nm to 300 nm, and the plurality of first optical multilayer films 12 having different center wavelengths cut near-infrared rays. It is preferable to configure the stopband of the cut filter 10 .

Here, the stopband is preferably a wavelength region in which the average transmittance of light incident at 0° is 5% or less, as described above. Since the average transmittance in the stopband is 5% or less, it is easy to obtain an image with a natural color tone when the near-infrared cut filter of the present embodiment is used in a solid-state imaging device. In the near-infrared cut filter 10, the center wavelength of the stopband and the width of the stopband of the first optical multilayer film 12 can be measured as follows. The same applies to the second optical multilayer film 13 to be described later.

The center wavelength of the stopband is calculated as the average value of the center wavelengths of the optical film thicknesses of the layers of the optical multilayer film forming the stopband. An optical multilayer film (repeated structure of optical films with different refractive indices) having a stopband with a central wavelength λ is represented by the formula d=λ/(4×n) cos θ. Here, d is the physical film thickness, n is the refractive index of the film, and θ is the incident angle of light. As described above, the oblique incidence ripple occurs in the vicinity of half the central wavelength of the wavelength range in which the optical multilayer film limits the transmission of light at an incident angle of 0°. It is assumed that there is However, the refractive index of the film actually changes with the wavelength (has wavelength dependence). Specifically, the refractive index of the film is greater when the wavelength of light is short than when the wavelength of light is high. Therefore, the oblique-incidence ripple occurs at a wavelength slightly longer than half the central wavelength of the wavelength range in which the optical multilayer film limits the transmission of light at an incident angle of 0°.

Because of this technical background, the center wavelength of the stopband of the optical multilayer film is not calculated only from the optical properties of light, but is calculated from the physical film thickness and refractive index of the film using the above formula. In addition, the width of the stop band is the maximum wavelength and the shortest wavelength at which the transmittance of light incident at 0° is 30% in the respective optical characteristics of the first optical multilayer film 12 or the second optical multilayer film 13. It means the difference between

In order to realize the stopband, the first optical multilayer film 12 includes a medium refractive index film M having a refractive index of 1.8 to 2.21 at a wavelength of 500 nm and a refractive index of 1.45 to 1 at a wavelength of 500 nm. It is a structure in which low refractive index films L of .49 are alternately laminated. The first optical multilayer film 12 has one or a plurality of combination units of the middle refractive index film M and the low refractive index film L. An optical multilayer film having such a configuration is represented by [ML]^ ^k , where M is a medium refractive index film, L is a low refractive index film, ML is a combination unit thereof, and k is the number of repetitions of the combination unit. The repetition number k is preferably 5-35. When the repetition number k of the combination unit (ML) of the medium refractive index film M and the low refractive index film L is more than 35, the transmittance in a predetermined wavelength range can be lowered, but if it is too large, the productivity is impaired. There is Moreover, when the repetition number k is less than 5, it is difficult to form a stopband with a sufficiently low transmittance. Therefore, k is preferably 5 to 34, more preferably 5 to 33.

Here, the reason why the refractive index of the medium refractive index film M constituting the first optical multilayer film 12 at a wavelength of 500 nm is set to 1.8 to 2.21 will be explained. The optical characteristics of the optical multilayer film having the structure of (ML)^ ^k , in which the center wavelength of the stopband of light incident at 0° is 940 nm, were verified using simulation software (TF-Calc). Here, the medium refractive index film M has a refractive index of 1.8, 2.0, 2.21, 2.3, and 2.5 at a wavelength of 500 nm, and the low refractive index film L has a refractive index of 500 nm. was set to 1.48 and k was set to 15. That is, through the above verification, changes in optical characteristics (especially occurrence of oblique incidence ripple) were confirmed when the refractive index of the medium refractive index film M was changed. As a result, the minimum transmittance at a wavelength of 400 to 450 nm for light incident on the optical multilayer film at 50° was 87.5% when the refractive index of the medium refractive index film M was 1.8, and 71% when the refractive index was 2.0. .9%, 52.1% at 2.21, 41.6% at a refractive index of 2.3, and 28.3% at a refractive index of 2.5. From these, there is a correlation between the refractive index of the medium refractive index film and the minimum transmittance at a wavelength of 400 to 450 nm. The upper limit of the refractive index of the medium refractive index film M of the first optical multilayer film 12 was defined as a refractive index of 2.21 at which the rate of decrease (100-minimum transmittance) was 67% or less. When the refractive index is 1.8, the minimum transmittance is high, but when the refractive index is less than 1.8, the width of the stopband becomes narrow. 12, the lower limit of the refractive index of the medium refractive index film M.

In the first optical multilayer film 12, since the refractive indices of the low refractive index film L and the medium refractive index film M are within the ranges described above, it is possible to suppress oblique incidence ripples in the G region. From the viewpoint of suppressing oblique incident ripples, the refractive index of the medium refractive index film M constituting the first optical multilayer film 12 is preferably 1.9 to 2.1, and most preferably about 2.0.

The low refractive index film L is not particularly limited as long as it is made of a material having a refractive index of 1.45 to 1.49 at a wavelength of 500 nm. Silicon oxide ( _SiO2, etc.), magnesium fluoride ( _MgF2, etc.), calcium fluoride ( _CaF2, etc.), yttrium fluoride (YF3 _, etc.), etc. are used as materials for such a low refractive index film L. can do. These compounds may be used individually by 1 type, and may use 2 or more types together. Also, as the material of the low refractive index film L, a mixture containing one or more of these compounds may be used. Such mixtures include mixtures of the above compounds with other metal oxides, such as mixtures of silicon oxide and aluminum oxide. The mixture in this case may be a mixture of two or more metal oxides, or a composite oxide of two or more metals. For example, a mixture of silicon oxide and aluminum oxide may be a mixed oxide of Si and Al in any ratio, or a mixture of silicon oxide and aluminum oxide in any ratio. Further, the low refractive index film L may contain additives as long as the refractive index is 1.45 to 1.49.

The medium refractive index film M is not particularly limited as long as it is made of a material having a refractive index of 1.8 to 2.21 at a wavelength of 500 nm. Such medium refractive index materials include _zirconium oxide (such as _ZrO2 ) _, tantalum oxide ₍ such as _Ta2O5 ) _, yttrium oxide (such as _Y2O3 ), lanthanum titanate ( _La2Ti2O7 etc.), zinc sulfide ₍ ZnS etc.), titanium oxide ( _Ti4O7 , _Ti2O3 , _TiO , _{TiO2 etc.} ), aluminum oxide ( _Al2O3 etc.) and the like can be used. These compounds may be used individually by 1 type, and may use 2 or more types together. Moreover, as the material of the medium refractive index film M, a mixture containing one or more of these compounds may be used. Examples of such mixtures include mixtures of the above compounds and other metal oxides, such as mixtures of zirconium oxide and tantalum oxide, and mixtures of zirconium oxide and titanium oxide. The mixture in this case may be a mixture of two or more metal oxides, or a composite oxide of two or more metals. For example, a mixture of zirconium oxide and tantalum oxide may be a mixed oxide of Zr and Ta in any ratio, or a mixture of zirconium oxide and tantalum oxide in any ratio. Similarly, the mixture of zirconium oxide and titanium oxide may be a mixed oxide of Zr and Ti in any ratio, or may be a mixture of zirconium oxide and titanium oxide in any ratio. The medium refractive index film M may contain additives as long as the refractive index is 1.8 to 2.21.

In the first optical multilayer film 12, the film arranged closest to the transparent substrate 11 may be either the medium refractive index film M or the low refractive index film L.

The physical thickness of each layer of the medium refractive index film M and the low refractive index film L constituting the first optical multilayer film 12 is basically determined by the refractive index of each film and the center of the first optical multilayer film 12. It is determined by the wavelength and further adjusted appropriately for the purpose of waveform adjustment, etc., and the total physical thickness of the medium refractive index film M and the low refractive index film L (physical thickness of the first optical multilayer film 12) is, for example, 1 μm to 20 μm. The total number of layers of the medium refractive index film M and the low refractive index film L constituting the first optical multilayer film 12 is preferably 70 layers or less, more preferably 50 layers, from the viewpoint of increasing the productivity of the near-infrared cut filter. layer or less, particularly preferably 10 to 45 layers. Note that the plurality of medium refractive index films M and low refractive index films L constituting the first optical multilayer film 12 may have different physical thicknesses and may have the same refractive index. Also, the medium refractive index film M may be composed of an equivalent film. Specifically, the equivalent film is a film formed by alternately laminating a high refractive index film H and a low refractive index film L so as to have a refractive index within the range of the medium refractive index film M. For example, one medium refractive index film M can be replaced with a three-layer structure of high refractive index film H/low refractive index film L/high refractive index film H.

The second optical multilayer film 13 is configured to suppress the occurrence of oblique incidence ripples in the visible light region, which generally has a wavelength of 400 nm to 500 nm, preferably 440 nm to 480 nm (B region). Therefore, the central wavelength of the stopband of the second optical multilayer film 13 is 700 nm or more and less than 890 nm.

The second optical multilayer film 13 has a stopband width of 100 nm to 300 nm. If the width of the stopband is too small, it becomes necessary to provide a separate optical multilayer film for forming the stopband of the near-infrared cut filter, which may increase the cost of manufacturing the near-infrared cut filter. Also, if the width of the stopband is too large, there is a risk that there will be almost no choice between the high refractive index film H and the low refractive index film L that can be used in manufacturing.

In order to realize the stopband, the second optical multilayer film 13 is composed of a high refractive index film H having a refractive index of more than 2.21 and not more than 2.8 at a wavelength of 500 nm and a low refractive index film L alternately. It is a laminated structure. It has one or a plurality of combination units (HL) of the high refractive index film H and the low refractive index film L. An optical multilayer film having such a structure is represented by [HL]^ ^m , where H is a high refractive index film, L is a low refractive index film, HL is a combination unit thereof, and m is the number of repetitions of the combination unit. The number of repetitions m is preferably 3-30. When the repetition number m of the combination unit (HL) of the high refractive index film H and the low refractive index film L is more than 30, the transmittance in a predetermined wavelength range can be lowered, but the productivity may be impaired. Moreover, when the repetition number m is less than 3, it is difficult to form a stopband with a sufficiently low transmittance. Therefore, m is preferably 3-29, more preferably 3-28.

A combination of the high refractive index film H and the low refractive index film L, which have a relatively large difference in refractive index, tends to increase the oblique incidence ripple value. Therefore, by setting the center wavelength and width of the stopband of the second optical multilayer film 13 to the range described above, the oblique incident ripple caused by the second optical multilayer film 13 is reduced to the short wavelength side of the visible light region (for example, (wavelength range of 400 nm or more and less than 440 nm), or to a shorter wavelength side than the visible light region (for example, wavelength range of less than 400 nm). Therefore, oblique incident ripples in the visible light region can be suppressed. When the near-infrared cut filter has a plurality of second optical multilayer films 13, the width and center wavelength of the stopband formed by each of the plurality of second optical multilayer films 13 are all within the ranges described above.

The high refractive index film H is not particularly limited as long as it is made of a material having a refractive index of more than 2.21 and less than or equal to 2.8 at a wavelength of 500 nm. Materials for such a high refractive index film H include tantalum oxide (Ta ₂ O ₅ etc.), titanium oxide (Ti ₄ O ₇ , Ti ₂ O ₃ , TiO, TiO ₂ etc.), niobium oxide (Nb ₂ O ₅ etc.) can be used. As a material for the high refractive index film H, a mixture containing one or more of these compounds may be used. Further, the high refractive index film H may be composed of only one kind of material described above, or may be composed of two or more kinds of materials. Also, if the refractive index exceeds 2.21 and is 2.8 or less, it may contain an additive.

Here, tantalum oxide and titanium oxide can be adjusted to have a refractive index of 1.8 to 2.21 at a wavelength of 500 nm by appropriately adjusting the film forming conditions and film forming method. It can be more than 21 and less than or equal to 2.8

In the second optical multilayer film 13, either the high refractive index film H or the low refractive index film L may be the film arranged closest to the transparent substrate 11 side.

The physical thickness of each layer of the high refractive index film H and the low refractive index film L constituting the second optical multilayer film 13 is basically determined by the refractive index of each film and the center of the second optical multilayer film 13 The total physical thickness of the high refractive index film H and the low refractive index film L (physical film of the second optical multilayer film 13 thickness) is, for example, 2 μm to 10 μm. The physical film thickness of the second optical multilayer film 13 is preferably thin from the viewpoint of thinning the near-infrared cut filter. The total number of layers of the high refractive index film H and the low refractive index film L constituting the second optical multilayer film 13 is preferably 60 layers or less, more preferably 50 layers, from the viewpoint of increasing the productivity of the near-infrared cut filter. layer or less, particularly preferably 6 to 45 layers. The physical thickness and refractive index of the plurality of high refractive index films H and low refractive index films L constituting the second optical multilayer film 13 may be different from each other or may be the same.

When the first optical multilayer film 12 and the second optical multilayer film 13 are respectively arranged on both surfaces of the transparent substrate 11, the total physical film thickness of the first optical multilayer film 12 on both surfaces and the second It is preferable that the total physical film thicknesses of the optical multilayer film 13 are as close to each other as possible. When the transparent substrate 11 is made extremely thin in order to make the near-infrared cut filter thinner, the physical film thicknesses of the first optical multilayer film 12 and the second optical multilayer film 13 on both surfaces of the transparent substrate 11 are greatly different. This is because the near-infrared cut filter 10 may be warped in such a manner that the optical multilayer optical film side having a smaller physical film thickness becomes convex.

From the viewpoint of increasing the productivity of the near-infrared cut filter 10, the total number of layers of the first optical multilayer film 12 and the second optical multilayer film 13 is preferably 90 or less, more preferably 60 or more and 85 or less. It is more preferable to have

The near-infrared cut filter 10 may have a plurality of first optical multilayer films 12 and second optical multilayer films 13, respectively. In particular, it is preferable to have two or more first optical multilayer films 12 . As described above, the first optical multilayer film 12 has a relatively narrow stopband width, but the near-infrared cut filter 10 includes a plurality of the first optical multilayer films 12, so that light in a wider wavelength range can be emitted. Permeation can be limited.

Furthermore, when a plurality of first optical multilayer films 12 and second optical multilayer films 13 are provided, each optical multilayer film has Forming stopbands having different center wavelengths is particularly preferable because a higher effect of suppressing oblique incident ripples in the visible wavelength range can be obtained.
In addition, when the near-infrared cut filter 10 has a plurality of first optical multilayer films 12, the plurality of first optical multilayer films 12 may be on the same main surface of the transparent substrate 11, They may be on different major surfaces.

The high refractive index film H, the medium refractive index film M, and the low refractive index film L constituting the first optical multilayer film 12 and the second optical multilayer film 13 are formed by, for example, a sputtering method, a vacuum deposition method, an ion beam method, an ion Although it can be formed by a plating method or a CVD method, it is particularly preferably formed by a sputtering method or a vacuum deposition method. The transmission band is a wavelength band used for light reception by solid-state imaging devices such as CCD and CMOS, and the accuracy of the physical film thickness is important. The sputtering method and the vacuum deposition method are excellent in physical film thickness control when forming a thin film. Therefore, the accuracy of the physical thickness of the high refractive index film H, the medium refractive index film M, and the low refractive index film L constituting the first optical multilayer film 12 and the second optical multilayer film 13 can be improved. As a result, oblique incidence ripple can be suppressed.

In addition, the first optical multilayer film 12 and the second optical multilayer film 13 include layers other than the layers constituting the optical multilayer film, such as the adhesion strength layer and the antistatic layer on the outermost surface layer (air side). It may be In addition to the first optical multilayer film 12 and the second optical multilayer film 13, an adjustment layer may be provided. The adjustment layer is between the first optical multilayer film 12 and the second optical multilayer film 13 and the transparent substrate 11, or on the air side of the first optical multilayer film 12 and the second optical multilayer film 13, or It is appropriately provided between the first optical multilayer film 12 and the second optical multilayer film 13 . The adjustment layer suppresses periodic fluctuations (referred to as ripples) in optical characteristics (transmittance) caused by stacking layers with different refractive indices. This ripple is clearly different from the above-described oblique incidence ripple, and does not have angular dependence due to oblique incidence of light. By using the adjustment layer, the transmission band of the optical characteristics of the near-infrared cut filter can be made flatter, except for those caused by oblique incident ripples.

The transparent substrate 11 is not particularly limited as long as it can transmit at least light in the visible wavelength range. Examples of materials for the transparent substrate 11 include glass, glass ceramics, crystal, lithium niobate, crystals such as sapphire, resins (polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and other polyester resins, polyethylene, polypropylene, ethylene acetate, etc.). polyolefin resins such as vinyl copolymers, acrylic resins such as norbornene resins, polyacrylates and polymethyl methacrylates, urethane resins, vinyl chloride resins, fluororesins, polycarbonate resins, polyvinyl butyral resins, polyvinyl alcohol resins, etc.). Also, the transparent substrate 11 may be a composite made of two or more of the above materials.

As the transparent substrate 11, a substrate that absorbs light in the near-infrared wavelength region is particularly preferable. This is because by using the transparent substrate 11 that absorbs light in the near-infrared wavelength region, it is possible to obtain an image quality that is close to the visibility characteristics of humans. As the transparent substrate 11 that absorbs light in the near-infrared wavelength region, for example, fluorophosphate glass, CuO-containing fluorophosphate glass in which Cu ²⁺ (ions) are added to phosphate-based glass, or CuO-containing Phosphate glass (hereinafter collectively referred to as "CuO-containing glass") may be mentioned.

As the transparent substrate 11 that absorbs light in the near-infrared wavelength range, a resin material that forms a transparent resin to which an absorber that absorbs near-infrared rays is added may be used. Examples of absorbents include dyes, pigments, and metal complex compounds, and specific examples include phthalocyanine compounds, naphthalocyanine compounds, and dithiol metal complex compounds.

In addition, in order to enhance the near-infrared light absorption performance of the near-infrared cut filter 10, a material similar to that of the near-infrared absorbing substrate is used on the surface of the transparent substrate 11, and a near-infrared absorbing pigment and a transparent resin containing a near-infrared absorbing pigment and a transparent resin are used. An infrared absorbing layer may be formed. In this case, the near-infrared absorbing layer is formed between the transparent substrate 11 and the first optical multilayer film 12 or between the transparent substrate 11 and the second optical multilayer film 13 . Also, the near-infrared absorption layer may be formed on at least one main surface of the transparent substrate 11, or may be formed on both main surfaces.

The near-infrared cut filter 10 preferably has a transmission band in the wavelength range of 430 nm to 600 nm and a stop band in the wavelength range of 750 nm to 1000 nm. Furthermore, the difference (0 The average transmittance of .degree. incident light-average transmittance of 40.degree. incident light) is preferably 3% or less. When the difference in average transmittance is 3% or less, it is possible to reduce the difference in optical characteristics between the case of transmitting light with a high incident angle and the case of transmitting light with an incident angle of 0°. It is possible to obtain a captured image with desired color representation by the solid-state imaging device. Note that the transmission band refers to a wavelength region in which the average transmittance of light incident at 0° is 85% or more.

The near-infrared cut filter 10 also measures the difference between the minimum transmittance at 0° incidence and the minimum transmittance at 40° incidence (minimum transmittance at 0° incidence −40° The minimum transmittance at the time of incidence) is preferably 5% or less. As a result, it is possible to significantly suppress the occurrence of oblique incidence ripples when light is incident at a high incident angle.

The average transmittance and minimum transmittance of light incident at the incident angle θ can be calculated, for example, by measuring the spectral transmittance of the near-infrared cut filter 10 using a spectrophotometer. Specifically, the average transmittance can be calculated as the arithmetic mean of the transmittance measurements over a given wavelength range. Also, the minimum transmittance can be measured as the minimum value of transmittance in a predetermined wavelength range.

According to the near-infrared cut filter of the embodiment described above, it is possible to suppress the oblique incident ripple caused by light with a high incident angle with a relatively small number of optical multilayer films.

Next, specific description will be given with reference to examples. Note that the refractive index of each substance described below refers to the refractive index at a wavelength of 500 nm.

(Example 1)
The near-infrared cut filter according to this example was provided on a transparent substrate (near-infrared absorbing glass, plate thickness 0.3 mm, trade name: NF-50, manufactured by AGC Techno Glass Co., Ltd.) and one surface of the transparent substrate. and an optical multilayer film. This optical multilayer film has a structure in which an optical multilayer film having a structure of [ML] ^̂k1 and an optical multilayer film having a structure of [H ₁ L] ^̂m1 are laminated in this order from the transparent substrate surface side. Also, an optical multilayer film (antireflection film) made of [H ₂ L] ^̂m2 is provided on the other surface of the transparent substrate. The first layer, the second layer, and the 57th to 60th layers from the transparent substrate surface side may be either a film having a structure of [ML] ^̂k1 or a film having a structure of [H ₁ L] ^̂m1 . It is a coordination layer that does not belong to.
The center wavelength of the stopband formed by each optical multilayer film is the average value of the center wavelength of the stopband of each layer.
The width of the stopband formed by each optical multilayer film is the difference between the maximum wavelength and the minimum wavelength at which the transmittance is 30%.

In [ML]^ ^k1 , the medium refractive index film M is zirconium oxide (ZrO ₂ , refractive index: 2.058), the low refractive index film L is silicon oxide (SiO ₂ , refractive index: 1.483), and k1 is a repeated laminated structure of 18 layers, totaling 36 layers. The center wavelength of the stopband of [ML]^ ^k1 is 1038.6 nm and the width of the stopband is in the range of 100 nm to 300 nm.

In [H ₁ L] ^m1 , the high refractive index film H ₁ is tantalum oxide (Ta ₂ O ₅ , refractive index: 2.211), and the low refractive index film L is silicon oxide (SiO ₂ , refractive index: 1.483 ), m1 is 9, and a total of 18 layers are repeatedly laminated. The center wavelength of the stopband of [H ₁ L] ^m1 is 815.7 nm and the width of the stopband is in the range of 100 nm to 300 nm.

In the optical multilayer film ([H ₂ L]^ ^{m 2} ) provided on the other surface, the high refractive index film H ₂ is titanium oxide (TiO ₂ , refractive index: 2.467), and the low refractive index film L is silicon oxide. (SiO ₂ , refractive index: 1.483), m2 is 3, and a total of 6 layers are repeatedly stacked.

Table 1 shows the configuration of the optical multilayer films ([ML] ^̂k1 and [ _H1L ] ^̂m1 ) provided on one side of the transparent substrate of the near-infrared cut filter. Table 2 shows the configuration of the optical multilayer film ([H ₂ L] ^̂m2 ) provided on the other surface of the transparent substrate of the near-infrared cut filter. In Tables 1 and 2, the film layer number is the ordinal number of layers from the transparent substrate side, and the film thickness indicates the physical film thickness. Also, the central wavelength of each layer was calculated using the formula λ=4×nd×cos θ (λ: central wavelength, n: refractive index, d: physical film thickness, θ: incident angle of light).
For this near-infrared cut filter, the optical characteristics of light incident from the optical multilayer film ([ML] ^ ^k1 and [H ₁ L] ^ ^m1 ) sides at incident angles of 0° and 40° were measured using optical thin film simulation software (TFCalc , Software Spectra). The results are shown in FIG.

As can be seen from FIG. 3, the near-infrared cut filter of this example has a transmission band in which the average transmittance is 85% or more in the wavelength range of 430 to 600 nm with respect to light incident at 0°, and a transmission band near the transmission band. It is calculated to have a stopband in the region of an average transmittance of 5% or less in the wavelength range of 750 to 1000 nm in the infrared region.

(Example 2)
A near-infrared cut filter according to this example includes a transparent substrate similar to that used in Example 1, and an optical multilayer film provided on one surface of the transparent substrate. The optical multilayer film has a structure in which a film having a structure of [ML] ^̂k2 and a film having a structure of [H ₂ L] ^̂m3 are laminated in order from the transparent substrate surface side. The first layer, second layer, 57th layer, and 58th layer from the surface side of the transparent substrate may be either a film having a structure of [ML] ^̂k2 or a film having a structure of [H ₂ L] ^̂m3 . It is a coordination layer that does not belong to. Table 3 shows the configuration of the optical multilayer film provided on one surface of the transparent substrate of the near-infrared cut filter. Further, the other surface of the transparent substrate is provided with the same optical multilayer film (anti-reflection film made of [H ₂ L]̂m ² ) as used in Example 1. For this near-infrared cut filter, the optical characteristics of light incident from the optical multilayer film ([ML] ^ ^k2 and [[H ₂ L] ^ ^m3 ) sides at incident angles of 0° and 40° were calculated using optical thin film simulation software ( It was measured by verification using TFCalc, manufactured by Software Spectra). The results are shown in FIG. 4, respectively.

In [ML]^ ^k2 , the medium refractive index film M is zirconium oxide (ZrO ₂ , refractive index: 2.058), the low refractive index film L is silicon oxide (SiO ₂ , refractive index: 1.483), and k2 is 19, which is a repeated laminated structure of 38 layers in total. The center wavelength of the stopband of [ML]^ ^k2 is 1064.3 nm and the width of the stopband is in the range of 100 nm to 300 nm.

[H ₂ L]^ ^m3 is composed of titanium oxide (TiO ₂ , refractive index: 2.467) as the high refractive index film H ₂ and silicon oxide (SiO ₂ , refractive index: 1.483) as the low refractive index film L. m3 is 8, a total of 16 layers of repeated laminated structure. The center wavelength of the stopband of [H ₂ L] ^m3 is 800.1 nm, and the width of the stopband is in the range of 100 nm to 300 nm.

As can be seen from FIG. 4, the near-infrared cut filter of this example has a transmission band in which the average transmittance is 85% or more in the wavelength range of 430 to 600 nm with respect to light incident at 0°, and a transmission band near the transmission band. It is calculated to have a stopband in the region of an average transmittance of 5% or less in the wavelength range of 750 to 1000 nm in the infrared region.

(Example 3)
The near-infrared cut filter according to this example includes a transparent substrate similar to that used in Example 1, an optical multilayer film having a structure of [H ₂ L]^ ^m4 on one surface of the transparent substrate, and equipped with an ultraviolet cut filter. Note that the first to sixth layers from the substrate surface side on one surface of the transparent substrate are adjustment layers that do not belong to the film having the structure of [H ₂ L] ^̂m4 . Also, an optical multilayer film having a structure of [ML] ^̂k3 is provided on the other surface. Note that the 1st to 6th layers and the 43rd to 46th layers from the substrate surface side on the other surface of the transparent substrate are adjustment layers that do not belong to the film having the structure of [ML]^ ^k3 . Table 4 shows the configuration of the optical multilayer film ([H ₂ L]^ ^m4 ) provided on one side of the transparent substrate of the near-infrared cut filter, and the optical multilayer film ([ML] ^ ^k3 ) is shown in Table 5. For this near-infrared cut filter, the optical characteristics of light incident from the optical multilayer film ([H ₂ L]^ ^{m 4} ) side at incident angles of 0° and 40° were measured using optical thin film simulation software (TFCalc, manufactured by Software Spectra). was measured by verification using The results are shown in FIG. 5, respectively.

In [H ₂ L] ^m4 , the high refractive index film H is made of titanium oxide (TiO ₂ , refractive index: 2.467), and the low refractive index film L is made of silicon oxide (SiO ₂ , refractive index: 1.483). , m4 is 8, and a total of 16 layers are repeatedly laminated. The center wavelength of the stopband of [H ₂ L] ^m4 is 795.3 nm and the width of the stopband is 255 nm. The center wavelength of the blocking band of the ultraviolet cut filter is 330.6 nm.

In [ML]^ ^k3 , the medium refractive index film M is zirconium oxide (ZrO ₂ , refractive index: 2.058), the low refractive index film L is silicon oxide (SiO ₂ , refractive index: 1.483), and k3 is a repeated laminated structure of 18 layers, totaling 36 layers. The center wavelength of the stopband of [ML]^ ^k3 is 1039.7 nm and the width of the stopband is in the range of 100 nm to 300 nm.

As can be seen from FIG. 5, the near-infrared cut filter of this example has a transmission band in which the average transmittance is 85% or more in the wavelength range of 430 to 600 nm with respect to light incident at 0°, and a transmission band near the transmission band. It is calculated to have a stopband in the region of an average transmittance of 5% or less in the wavelength range of 750 to 1000 nm in the infrared region.

(Comparative example)
The near-infrared cut filter according to the comparative example includes a transparent substrate similar to that used in Example 1, an optical multilayer film having a structure of [H ₂ L] ^ ^x on one surface of the transparent substrate, and An optical multilayer film (antireflection film) having a structure of [H ₂ L] ^̂z is provided. In the optical multilayer films on both sides, the materials of the high refractive index film _H2 and the low refractive index film L constituting the films are the same, but the total number of films is different. Table 6 shows the structure of the optical multilayer film provided on one surface of the transparent substrate of the near-infrared cut filter, and Table 7 shows the structure of the optical multilayer film provided on the other surface. For this near-infrared cut filter, the optical characteristics of light incident from the optical multilayer film ([H ₂ L]^ ^x ) side at incident angles of 0° and 40° were measured using optical thin film simulation software (TFCalc, manufactured by Software Spectra). was measured by verification using The results are shown in FIG. 6, respectively.

[H ₂ L]^ ^x is composed of titanium oxide (TiO ₂ , refractive index: 2.467) for the high refractive index film H ₂ and silicon oxide (SiO ₂ , refractive index: 1.483) for the low refractive index film L. , x is 19, and a total of 38 layers are repeatedly stacked.

[H ₂ L] ^̂z is a repeated laminated structure with z being 3 and a total of 6 layers.

Table 8 shows the optical properties of the near-infrared cut filters of Examples 1 to 3 and Comparative Example. As an optical characteristic, the difference between the average transmittance at 0° incidence and the average transmittance at 40° incidence of light with a wavelength of 430 nm to 600 nm (average transmittance at 0° incidence - average transmittance at 40° incidence ), the difference between the minimum transmittance at 0° incidence and the minimum transmittance at 40° incidence of light at a wavelength of 430 nm to 600 nm (minimum transmittance at 0° incidence - minimum transmittance at 40° incidence). .

As shown in Table 8, the near-infrared cut filter of this example has a difference in average transmittance between 0° incident light and 40° incident light in the visible light transmission band, compared to the near-infrared cut filter of the comparative example. is extremely small, and an optical multilayer film having a relatively small number of layers can be used to suppress oblique incident ripples due to light at a high incident angle.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on Japanese Patent Application No. 2017-253468 filed on December 28, 2017, the contents of which are incorporated herein by reference.

DESCRIPTION OF SYMBOLS 10... Near-infrared cut filter, 11... Transparent substrate, 12... First optical multilayer film, 13... Second optical multilayer film, L... Low refractive index film, M... Medium refractive index film.

Claims (8)

A near-infrared cut filter comprising a transparent substrate and a first optical multilayer film provided on at least one main surface of the transparent substrate,
The first optical multilayer film is
A medium refractive index film having a refractive index of 1.8 to 2.21 at a wavelength of 500 nm and a low refractive index film having a refractive index of 1.45 to 1.49 at a wavelength of 500 nm are alternately laminated,
having a combination unit of the medium refractive index film and the low refractive index film in a number of 5 or more and 35 or less,
In the first optical multilayer film, the center wavelength of the wavelength range in which the transmission of light incident at 0° is restricted is 890 nm or more and 1200 nm or less, and the width of the wavelength range is 100 nm or more and 300 nm or less;
The near-infrared cut filter comprises a second optical multilayer film on at least one main surface of the transparent substrate,
The second optical multilayer film is formed by alternately laminating a high refractive index film having a refractive index of more than 2.21 and 2.8 or less at a wavelength of 500 nm and the low refractive index film,
Having a combination unit of the high refractive index film and the low refractive index film in a number of 3 or more and 30 or less,
In the second optical multilayer film, the center wavelength of the wavelength range in which the transmission of light incident at 0° is restricted is 700 nm or more and less than 890 nm, and the width of the wavelength range is 100 nm or more and 300 nm or less,
The near-infrared cut filter has a transmission band that transmits light in a wavelength range of 430 nm to 600 nm for light incident at 0°, and a stop band that limits light transmission in a wavelength range of 750 nm to 1000 nm. have
The difference between the average transmittance of light incident at 0° and the average transmittance of light incident at 40° in the transmission band that transmits light in the wavelength range of 430 nm to 600 nm (average transmittance of light incident at 0° The average transmittance of light incident at -40°) is 3% or less,
A near-infrared cut filter characterized by: 2. The near-infrared cut filter according to claim 1, wherein the transmission band for transmitting light in the wavelength range of 430 nm to 600 nm has an average transmittance of 85% or more for light incident at 0°. The low refractive index film is made of one or more compounds selected from silicon oxide, magnesium fluoride, calcium fluoride and yttrium fluoride, or a mixture containing one or more of these compounds, and the medium refractive index film is , zirconium oxide, tantalum oxide, yttrium oxide, lanthanum titanate, zinc sulfide, titanium oxide and aluminum oxide, or a mixture containing one or more of these compounds. Item 3. The near-infrared cut filter according to item 2. 3. The near-infrared cut filter according to claim 1, wherein the high refractive index film comprises one or more compounds selected from tantalum oxide, titanium oxide and niobium oxide, or a mixture containing one or more of these compounds. . The near-infrared cut filter according to any one of claims 1 to 4, comprising a plurality of at least one of the first optical multilayer film and the second optical multilayer film. The near-infrared cut filter according to any one of claims 1 to 5, wherein the transparent substrate is made of one or more materials selected from glass, glass ceramics, crystal, resin and sapphire. The near-infrared cut filter according to any one of claims 1 to 6, wherein the transparent substrate has a property of absorbing light with a wavelength in the near-infrared region. 8. The near-infrared cut filter according to claim 1 , wherein the total number of layers of said first optical multilayer film and said second optical multilayer film is 90 layers or less.

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