JP6136661B2 - Near-infrared cut filter - Google Patents

Description

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

  A charge coupled device (CCD) image sensor, a complementary metal oxide semiconductor (CMOS) image sensor or the like (hereinafter referred to as a solid-state imaging device) is used for a digital camera, a digital video, or the like. However, the spectral characteristics of these solid-state imaging devices are more sensitive to infrared light than human visual sensitivity characteristics. Therefore, in digital cameras, digital videos, and the like, spectral correction is performed using a near-infrared cut filter.

As the near-infrared cut filter, for example, a near-infrared absorption type color glass filter such as fluorophosphate glass containing Cu ²⁺ ions as a coloring component has been used. However, since a color glass filter alone cannot sufficiently cut light in the near infrared region and ultraviolet region, at present, an optical multilayer film having a characteristic capable of cutting near infrared light is used in combination.

  The optical multilayer film is required not to cause a phenomenon in which the transmittance drops locally (hereinafter sometimes referred to as ripple) in the transmission band at 400 to 700 nm required for the solid-state imaging device. Techniques for suppressing ripples in optical multilayer films have been proposed in the past (see, for example, Patent Documents 1 and 2).

Japanese Patent No. 4672101 JP 2008-139893 A

  However, even if the ripple of light incident at a specific angle can be suppressed in the optical multilayer film, when the incident angle of light changes, a ripple may occur with the change. Although the techniques described in Patent Documents 1 and 2 can cope with the suppression of the ripple of light incident at a specific angle, the ripple generated due to the change of the incident angle of light is completely considered. Absent.

  Under these circumstances, in recent years, digital cameras, digital videos, and the like are further reduced in size and thickness, and lenses for digital cameras, digital videos, and the like have been widened. For this reason, for example, conventionally, a response to a case where the incident angle of light to the solid-state imaging device is 30 ° or less has been demanded, but in recent years, a response to an incident angle exceeding 30 ° has been strongly demanded. It is getting to be.

  The ripple described above increases the amount of decrease in transmittance as the incident angle of light is inclined. In the proposals disclosed in Patent Documents 1 and 2, since the suppression of the ripple accompanying the change in the incident angle is not considered, if the incident angle of the light to the solid-state imaging device is 30 ° or less, the ripple is extremely large. Although it does not increase, when the incident angle exceeds 30 °, there is a possibility that a ripple that may adversely affect the captured image may occur.

  This invention is made | formed in view of the said subject, and aims at providing the near-infrared cut off filter by which the ripple was suppressed.

The near-infrared cut filter according to the present invention includes a transparent substrate and first and second optical multilayer films respectively provided on the first and second main surfaces of the transparent substrate, and the first and second optical multilayer films are provided. Each of the optical multilayer films includes a high refractive index film having a refractive index of 2.0 or more at a wavelength of 500 nm and a low refractive index film having a refractive index of less than 1.6 at a wavelength of 500 nm, When the film is H and the low refractive index film is L, it has a repetitive laminated structure represented by repetition of (HL) ^ n (n is a natural number of 1 or more), and 0 ° incidence condition (optical multilayer film 12 In the wavelength range of 400 to 700 nm and the average transmittance of 85% or more in the wavelength range of 900 to 1200 nm. The width of the region where the average transmittance is 30% or less is 100 Having a stopband of ˜280 nm, and the wavelength indicating the local minimum where the transmittance generated with the change in the angle of incident light is locally reduced is the transmission band of the first optical multilayer film and the first Unlike each other in a transmission band according to a second optical multilayer film, by the second optical multilayer membrane and the transmission band the transmittance wavelength showing a minimum value of a portion reduced locally by the first optical multilayer membrane The transmission bands are separated from each other by 25 nm or more and less than 100 nm .

  According to the present invention, the ripple in the wavelength range of 400 to 700 nm caused by the first optical multilayer film and the second optical multilayer film is dispersed. For this reason, the near-infrared cut filter with which the ripple was suppressed can be provided.

It is sectional drawing of the near-infrared cut off filter which concerns on 1st Embodiment. It is sectional drawing of the 1st, 2nd optical multilayer film which concerns on 1st Embodiment. It is a spectral characteristic of IRCF which concerns on the comparative example 1. FIG. It is a spectral characteristic of IRCF which concerns on the comparative example 2. It is a spectral characteristic of IRCF which concerns on Example 1. FIG. 3 is a spectral characteristic of the RCF according to Example 2. It is a spectral characteristic of IRCF which concerns on the comparative example 3.

(First embodiment)
FIG. 1 is a cross-sectional view of a near-infrared cut filter 100 (hereinafter, IRCF 100) according to the first embodiment. FIG. 2 is a cross-sectional view of the first and second optical multilayer films 12A and 12B. Hereinafter, the configuration of the IRCF 100 will be described with reference to FIGS. 1 and 2.

  As shown in FIG. 1, the IRCF 100 includes a transparent substrate 11 and an optical multilayer film 12 provided on the transparent substrate 11. The optical multilayer film 12 includes a first optical multilayer film 12A provided on the surface (first main surface) of the transparent substrate 11, and a second optical layer 12 provided on the back surface (second main surface) of the transparent substrate 11. From the optical multilayer film 12B, the third optical multilayer film 12C provided on the surface of the first optical multilayer film 12A, and the fourth optical multilayer film 12D provided on the surface of the second optical multilayer film 12B Composed.

(Transparent substrate 11)
The material of the transparent substrate 11 is not particularly limited as long as it can transmit at least light in the visible wavelength region. Examples of the material for the transparent substrate 11 include crystals such as glass, quartz, lithium niobate, and sapphire, polyester resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), polyethylene, polypropylene, ethylene vinyl acetate copolymer, and the like. Polyolefin resins, norbornene resins, polyacrylates, polymethylmethacrylates and other acrylic resins, urethane resins, vinyl chloride resins, fluororesins, polycarbonate resins, polyvinyl butyral resins, polyvinyl alcohol resins, and the like.

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, an image quality close to human visibility characteristics can be obtained. Examples of the transparent substrate 11 that absorbs light in the near-infrared wavelength region include absorption glass in which Cu ²⁺ (ion) is added to fluorophosphate glass or phosphate glass. Moreover, you may use what added the absorber which absorbs near-infrared rays in the resin material. Examples of the absorbent include dyes, pigments, and metal complex compounds, and specifically include phthalocyanine compounds, naphthalocyanine compounds, and dithiol metal complex compounds.

(Optical multilayer film 12A, 12B)
FIG. 2 is a cross-sectional view of the first and second optical multilayer films 12A and 12B. The optical multilayer films 12A and 12B are first and second SWPFs (Short Wide Pass Filters) provided on the front surface (first main surface) and the back surface (second main surface) of the transparent substrate 11, respectively. When the high refractive index film having a refractive index of 2.0 or more at a wavelength of 500 nm is H and the low refractive index film having a refractive index of less than 1.6 at a wavelength of 500 nm is L, the following expression (1) is used. Has a structure.
(HL) ^ n (n is a natural number of 1 or more) (1)

  The value of n is preferably 3 or more and 20 or less. In the optical multilayer film, the greater the number of repetitions (HL) of the high refractive index film H and the low refractive index film L, the lower the transmittance in a predetermined wavelength range. By setting the value of n of the first and second optical multilayer films 12A and 12B to 3 or more, the spectral characteristics of both are overlapped, so that the average transmittance is 10% or less in the wavelength range of 900 to 1200 nm. Rate can be obtained. Further, by setting the value of n of the first and second optical multilayer films 12A and 12B to 20 or less, the spectral characteristics can be obtained with a small number of film layers, and the productivity is good and the cost is low. A cut filter can be manufactured.

  The first and second optical multilayer films 12A and 12B each have a spectral characteristic under an incident condition of 0 °, a transmission band having an average transmittance of 85% or more in a wavelength range of 400 to 700 nm, and a wavelength of 900 to 1200 nm. In the wavelength range, the width of the region where the average transmittance is 30% or less is 100 to 280 nm.

  When the average transmittance in the wavelength range of 400 to 700 nm in the transmission band is less than 85%, there is a risk that a captured image becomes dark when the near-infrared cut filter is used for a solid-state imaging device. The average transmittance in the wavelength range of 400 to 700 nm is preferably 87% or more, and more preferably 90% or more.

  If the average transmittance in the wavelength range of 900 to 1200 nm in the stop band exceeds 30%, there is a possibility that a defect may occur in the color tone of the captured image when the near-infrared cut filter is used for a solid-state image sensor. The average transmittance in the wavelength range of 900 to 1200 nm is preferably 25% or less, and more preferably 20% or less.

  When the width of the region where the average transmittance in the wavelength range of 900 to 1200 nm in the stopband is 30% is less than 100 nm, it is necessary to provide another optical multilayer film for forming the stopband, and the near-infrared cut The cost for manufacturing the filter may be high. On the other hand, if the width exceeds 280 nm, the design of the optical multilayer film may be complicated because the width of the blocking band is very wide.

(Third optical multilayer film 12C)
The third optical multilayer film 12C is a UV cut filter that cuts ultraviolet light (UV). The third optical multilayer film 12C may have any film configuration as long as it has spectral characteristics under 0 ° incidence conditions and cuts ultraviolet rays in a wavelength range of less than 400 nm with a predetermined wavelength width and transmittance. There may be. In the third optical multilayer film 12C, for example, a high refractive index film H having a refractive index of 2.0 or more at a wavelength of 500 nm and a low refractive index film L having a refractive index of less than 1.6 at a wavelength of 500 nm are laminated. It has a structure. In the present invention, the third optical multilayer film 12C has an arbitrary configuration.

  The third optical multilayer film 12C may be provided between the transparent substrate 11 and the first optical multilayer film 12A, and the front surface (between the transparent substrate 11) or the back surface of the second optical multilayer film 12B. May be provided. In addition, an adjustment layer for adjusting the spectral characteristics may be provided.

(Fourth optical multilayer film 12D)
The fourth optical multilayer film 12D has spectral characteristics under an incident condition of 0 °, and has a transmission band having an average transmittance of 85% or more in a wavelength range of 400 to 700 nm, and 750 to 950 nm on the near infrared side of the transmission band. In this wavelength range, the width of the region having an average transmittance of 10% or less is 100 to 200 nm. That is, the first and second optical multilayer films 12A and 12B form a stop band in the wavelength range of 900 to 1200 nm, whereas the fourth optical multilayer film 12D has a stop band in the wavelength range of 750 to 950 nm. Form. Therefore, by using the first and second optical multilayer films 12A and 12B and the fourth optical multilayer film 12D, a blocking band having an average transmittance of 10% or less can be formed in a wavelength range of 750 to 1200 nm.

  The fourth optical multilayer film 12D may have any film configuration. In the fourth optical multilayer film 12D, for example, a high refractive index film H having a refractive index of 2.0 or more at a wavelength of 500 nm and a low refractive index film L having a refractive index of less than 1.6 at a wavelength of 500 nm are laminated. It has a structure. In the present invention, the fourth optical multilayer film 12D has an arbitrary configuration.

  The fourth optical multilayer film 12D may be provided between the transparent substrate 11 and the second optical multilayer film 12B, and the front surface (between the transparent substrate 11) or the back surface of the first optical multilayer film 12A. May be provided. In addition, an adjustment layer for adjusting the spectral characteristics may be provided. The fourth optical multilayer film 12D may be provided only on one main surface of the transparent substrate 11, or may be provided separately on each of the first and second main surfaces of the transparent substrate 11.

The high refractive index films H of the first to fourth optical multilayer films 12A to 12D are not particularly limited as long as they are made of a material having a refractive index of 2.0 or more at a wavelength of 500 nm. Suitable examples of such a high refractive index material include titanium oxide (TiO ₂ ), niobium oxide (Nb ₂ O ₅ ), or a composite oxide thereof. Moreover, if a refractive index is 2.0 or more, you may contain the additive. A higher refractive index is advantageous for suppressing the wavelength shift at the time of oblique incidence, extending the stop band, and the like.

The low refractive index films L of the first to fourth optical multilayer films 12A to 12D are not particularly limited as long as they are made of a material having a refractive index of less than 1.6 at a wavelength of 500 nm. Suitable examples of such a low refractive index material include silicon oxide (SiO ₂ ). Moreover, if a refractive index is less than 1.6, you may contain the additive.

  The high-refractive index film H and the low-refractive index film L can be formed by a sputtering method, a vacuum evaporation method, an ion beam method, an ion plating method, or a CVD method, and in particular, formed by a sputtering method or a vacuum evaporation method. It is preferable. The transmission band is a wavelength band used for light reception by a solid-state imaging device such as a CCD or CMOS, and its film thickness accuracy is important. The sputtering method and the vacuum deposition method are excellent in controlling the film thickness when forming a thin film. For this reason, the film thickness accuracy of the high refractive index film H and the low refractive index film L can be increased.

  The IRCF 100 may be further provided with an adhesion strengthening layer for improving the adhesion between the transparent substrate 11 and the optical multilayer film in contact with the transparent substrate 11, an antistatic layer on the outermost surface layer (air side), and the like. Good.

(Spectral characteristics of the first optical multilayer film 12A and the second optical multilayer film 12B)
In a near-infrared cut filter using an optical multilayer film, the occurrence of a spot (ripple) in which the transmittance is locally reduced in the wavelength range of 400 to 700 nm due to fluctuations in the angle of incident light is prevented at 900 to 1200 nm. This is caused by an optical multilayer film (hereinafter referred to as an optical multilayer film _900-1200 ) for forming a band. Note that the optical multilayer film for forming the stop band at 750 to 950 nm generates a portion where the transmittance is locally reduced in the wavelength range of less than 400 nm as the angle of incident light varies.

As described above, when the optical multilayer film _900-1200 is formed only on one main surface of the transparent substrate 11, there is a portion where the transmittance is locally reduced in the wavelength range of 400 to 700 nm due to the change in the angle of the incident light. Occur. Therefore, even if the film structure of the optical multilayer film _900-1200 is divided in half and formed on each of the first and second main surfaces of the transparent substrate 11, the magnitude and position of the ripple caused by the formed optical multilayer film ( (Wavelength) is not significantly different from the case of forming only on one main surface of the transparent substrate 11. When verifying the optical multilayer film _900-1200 divided into two, the magnitude of the ripple due to each optical multilayer film becomes smaller when the film configuration is halved, but the position (wavelength) of the ripple does not change. Therefore, the spectral characteristics comprising both of the optical multilayer films divided into the first and second main surfaces of the transparent substrate 11 are not significantly different from the case where the optical multilayer films _900-1200 are formed only on one main surface. it is conceivable that.

From the above, when the film configuration of the optical multilayer film _900-1200 is divided in half and formed on each of the first and second main surfaces of the transparent substrate 11, the position (wavelength) of the ripple caused by each optical multilayer film Move. This suppresses the magnitude of ripples in the wavelength range of 400 to 700 nm accompanying the change in the angle of the incident light in the spectral characteristics composed of both the optical multilayer films on the first and second main surfaces of the transparent substrate 11. Can do.

As a method of shifting the position (wavelength) of the ripple caused by each optical multilayer film (the first optical multilayer film 12A and the second optical multilayer film 12B), the purpose is to form only on one main surface of the transparent substrate 11. The optical multilayer film _900-1200 designed in the above is divided in half, and one of the optical multilayer films (for example, the first optical multilayer film 12A provided on the first main surface) is a physical film of all the films. There is a method to increase or decrease the thickness at a uniform rate. Moreover, each optical multilayer film is comprised by the film | membrane structure or film | membrane material from which the width | variety of the area | region whose average transmittance | permeability is 30% or less in the wavelength range of 900-1200 nm differs in the stop band which is 100-280 nm, The position (wavelength) of the ripple caused by the optical multilayer film can be shifted.

  The wavelength that shows the minimum value of the ripple in the wavelength range of 400 to 700 nm accompanying the change in the angle of incident light is 25 nm between the transmission band of the first optical multilayer film 12A and the transmission band of the second optical multilayer film 12B. It is preferable that they are separated from each other. If the wavelengths showing the minimum value of the ripple are less than 25 nm, the ripples caused by the respective optical multilayer films may be combined into one and become a large ripple. The wavelengths that show the minimum value of the ripple are preferably 28 nm or more apart from each other, more preferably 30 nm or more, and still more preferably 33 nm or more.

  In addition, when the wavelength indicating the minimum value of the ripple is 100 nm or more away from each other, the stop band of the first optical multilayer film 12A and the stop band of the second optical multilayer film 12B in the wavelength range of 900 to 1200 nm are obtained. There is a great difference, and there is a possibility that the average transmittance cannot be lowered. The wavelengths showing the minimum value of the ripple are preferably separated from each other by less than 100 nm, more preferably separated by less than 80 nm, and further preferably separated by less than 60 nm.

  The individual spectral characteristics of the first optical multilayer film 12A and the second optical multilayer film 12B are such that the transmittance is locally within a wavelength range of 400 to 700 nm when the angle of incident light is 0 ° to 45 °. It is preferable that there is no portion where the temperature decreases by 15% or more. By doing in this way, the near-infrared cut filter provided with the first optical multilayer film 12A and the second optical multilayer film 12B has a small ripple generated in the wavelength range of 400 to 700 nm, and the solid-state imaging device Spectral characteristics suitable for the application can be provided. The spectral characteristics of the first optical multilayer film 12A and the second optical multilayer film 12B are such that the transmittance is locally within a wavelength range of 400 to 700 nm when the angle of incident light is 0 ° to 45 °. It is more preferable that there is no portion that decreases by 13% or more, and it is further preferable that there is no portion that decreases by 10% or more.

  The stop bands in the spectral characteristics of the first optical multilayer film 12A and the second optical multilayer film 12B are such that the width of the region where the average transmittance is 30% or less in the wavelength range of 900 to 1200 nm is 100 to 280 nm. is there. Therefore, the transmittance of the blocking band is not sufficiently low with only one of the optical multilayer films, and there is a possibility that the blocking band required for the solid-state imaging device application cannot be formed. However, by using both the first optical multilayer film 12A and the second optical multilayer film 12B, the average transmittance can be lowered in the wavelength range of 900 to 1200 nm. Characteristics can be provided.

(Spectral characteristics of the fourth optical multilayer film 12D)
As described above, the fourth optical multilayer film 12D has a transmission band in which the average transmittance is 85% or more in the wavelength range of 400 to 700 nm, and a region in which the average transmittance is 10% or less in the wavelength range of 750 to 950 nm. And a stop band having a width of 100 to 200 nm. A near-infrared cut filter for use in a solid-state imaging device is required to have a sharply small transmittance in a wavelength range near 700 to 750 nm. In the case of such an application, it is preferable to provide the fourth optical multilayer film 12D only on one main surface of the transparent substrate 11. On the other hand, as described above, when the transmittance in the wavelength range near 700 to 750 nm does not need to be sharply decreased, the fourth optical multilayer film 12D is divided into the first and second main surfaces, respectively. It may be provided.

(Spectral characteristics of the third optical multilayer film 12C)
The third optical multilayer film 12C cuts ultraviolet rays having a wavelength range of less than 400 nm. As described above, since the fourth optical multilayer film 12D has a stop band at 750 to 950 nm, a portion where the transmittance is locally reduced in accordance with a change in the angle of incident light is generated in a wavelength range of less than 400 nm. Therefore, by providing the third optical multilayer film 12C, it is possible to suppress ripples caused by the fourth optical multilayer film 12D.

(Spectral characteristics of optical multilayer film 12)
Next, preferable spectral characteristics of the entire optical multilayer film 12 used for a solid-state imaging device composed of the optical multilayer films 12A to 12D will be described.

  The optical multilayer film 12 has an average transmittance of 85% or more in a wavelength range of 400 to 700 nm under a 0 ° incident condition (a condition in which light is incident perpendicularly (0 °) to the main surface of the optical multilayer film 12). And a stop band on the near infrared side of the transmission band. The stop band has a width of 100 to 280 nm in a region where the average transmittance is 10% or less in a wavelength range of 750 to 1200 nm. The difference between the half-value wavelength on the ultraviolet side and the half-value wavelength on the near infrared side of the transmission band of the optical multilayer film 12 is 200 nm or more. Further, the difference in half-value wavelength of the transmission band of the optical multilayer film 12 under the 0 ° incident condition and the 30 ° incident condition (conditions in which light is incident on the main surface of the optical multilayer film 12 with a tilt of 30 ° from the vertical). Is less than 10 nm on the ultraviolet side and less than 22 nm on the near infrared side.

  Note that the optical multilayer film 12 preferably further satisfies the following requirements in terms of spectral characteristics under 0 ° incidence conditions. Specifically, the difference between the ultraviolet half-value wavelength and the near-infrared half-value wavelength of the transmission band of the optical multilayer film 12 is preferably 350 nm or less, and more preferably 300 nm or less. The half-wavelength on the ultraviolet side is preferably in the range of 390 to 430 nm, and the half-value wavelength on the near infrared side is preferably in the range of 640 to 720 nm. Further, the width of the stop band on the ultraviolet side is preferably 30 nm or more, and the width of the stop band on the near infrared side is preferably 200 nm or more.

  Here, the range of the transmission band of the optical multilayer film 12 (the range for obtaining the average transmittance) is the wavelength at which the transmittance starts to decrease from the transmission band toward the ultraviolet-side stop band (the base point on the ultraviolet side). ) To the wavelength (base point on the near infrared side) when the transmittance starts to decrease from the transmission band toward the stop band on the near infrared side.

  Further, the range of the stop band of the optical multilayer film 12 (the range for obtaining the average transmittance and width) is that the stop band on the ultraviolet side of the optical multilayer film 12 is transmitted from the stop band on the ultraviolet side toward the transmission band. From the wavelength when the rate starts to rise (base point on the transmission band side) to the wavelength when the rate when the transmittance first reaches 40% toward the ultraviolet side (base point on the ultraviolet side) To do.

  Further, the near-infrared side stop band of the optical multilayer film 12 has its near red color from the wavelength (base point on the transmission band side) when the transmittance starts to increase from the near-infrared side stop band toward the transmission band. Up to the wavelength (base point on the near infrared side) at which the rise starts when the transmittance first reaches 40% toward the outside.

  In the present invention, the amount of local decrease in transmittance means a local transmittance loss amount due to ripple. Specifically, in the spectral characteristics of the transmission band, it is formed by ripples from the flat part of the transmission band or a continuous transmittance fluctuation part similar thereto (for example, the transmission band has a gentle mountain shape in the case of absorption glass or the like). The transmittance at the first inflection point toward the minimum value is (A), the minimum value of the transmittance due to the ripple is (B), and the transmittance increases from the minimum value of the ripple to the transmission band flat part. Of the absolute value of (A)-(B), (C)-(B), where (C) is the transmittance of the first inflection point that is the end of Say.

(Spectral characteristics of the combination of the transparent substrate 11 that absorbs light in the near infrared wavelength region and the optical multilayer film)
When the transparent substrate 11 that absorbs light in the near-infrared wavelength region is used, even if the average transmittance in the blocking band of the first and second optical multilayer films 12A and 12B is somewhat large, , The transmittance in the wavelength range of 900 to 1200 nm is low, and a stop band suitable for solid-state imaging device applications can be formed. Therefore, the first and second optical multilayer films 12A and 12B can be configured with a small number of film layers, and a near-infrared cut filter can be manufactured with high productivity and low cost. In addition, the transparent substrate 11 that absorbs light in the near-infrared wavelength region can create spectral characteristics close to human visibility characteristics, particularly in the wavelength range of around 700 nm. By using it for an image sensor, a captured image with a natural color tone can be obtained.

(Other embodiments)
As described above, the present invention has been described in detail based on the above specific examples. However, the present invention is not limited to the above specific examples, and various modifications and changes can be made without departing from the scope of the present invention. is there.

  The IRCF 100 described with reference to FIGS. 1 and 2 is used, for example, as a visibility correction filter in an imaging device such as a digital still camera, a digital video camera, a surveillance camera, an in-vehicle camera, a web camera, or an automatic exposure meter. . In an imaging apparatus such as a digital still camera, a digital video camera, a surveillance camera, an in-vehicle camera, or a web camera, for example, it is disposed between an imaging lens and a solid-state imaging device. In the automatic exposure meter, for example, it is arranged in front of the light receiving element.

  In the imaging apparatus, the IRCF 100 may be disposed at a position away from the front surface of the solid-state imaging device, or may be directly attached to the solid-state imaging device or the package of the solid-state imaging device, or a cover that protects the solid-state imaging device. May be IRCF100. Alternatively, it may be directly attached to a low-pass filter using a crystal such as quartz or lithium niobate for suppressing moire or false color. By applying IRCF100 to the cover glass, lens group, etc. of the imaging device, it is possible to suppress the incident angle dependency (ripple generation) of the spectral characteristics caused by the near-infrared cut filter, so that a captured image with a natural color tone can be obtained. Can do.

Next, it demonstrates concretely with reference to an Example.
The inventors create near-infrared cut filters (IRCFs) according to Examples 1 and 2 and Comparative Examples 1 to 3 described below, and light is incident on the 0 ° incident condition (the main surface of the optical multilayer film 12). Spectral characteristics were examined under conditions of normal (0 °) incidence and 45 ° incidence conditions (conditions where light is incident on the main surface of the optical multilayer film 12 at an angle of 45 ° from the vertical (0 °)). . In the following description, QWOT (Quarter-wave Optical Thickness) of the high refractive index film H at a wavelength of 500 nm is Q _H , and QWOT of the low refractive index film L at a wavelength of 500 nm is Q _L.

In addition, titanium oxide (TiO ₂ ) was used as the material for the high refractive index film, and silicon oxide (SiO ₂ ) was used as the material for the low refractive index film. Spectral characteristics were verified using optical thin film simulation software (TFCalc, manufactured by Software Spectra). In the present application, the refractive index of each film at a wavelength of 500 nm is used as a representative value, but simulation was performed in consideration of the wavelength dependence of the refractive index in the simulation. In the simulation, the refractive index at a wavelength of 500 nm of the high refractive index film H (TiO ₂ ) is set to 2.47 in Example 1, Comparative Example 1 and Comparative Example, and 2.421 in Example 2 and Comparative Example 3. The refractive index of the low refractive index film L (SiO ₂ ) at a wavelength of 500 nm was 1.48 in Example 1, Comparative Example 1 and Comparative Example, and 1.456 in Example 2 and Comparative Example 3.

  The refractive index has a wavelength dependency called dispersion. For example, in the wavelength range of 300 to 1300 nm, in the film substance or the like targeted by the present application, the refractive index tends to increase as the wavelength decreases, and the refractive index tends to decrease as the wavelength increases. These wavelength-refractive index relationships are not linear, and are generally expressed using approximate equations such as Hartmann and Sellmeier. Further, the refractive index (dispersion) of the film substance varies depending on various film forming conditions. Therefore, a film was actually formed by a vapor deposition method, an ion-assisted vapor deposition method, a sputtering method, or the like, and the obtained dispersion data of the refractive index of each film was used in the following simulation.

  In Example 1, Comparative Example 1 and Comparative Example 2, a transparent substrate having no absorption in the visible wavelength range was used. Further, an optical multilayer film (near-infrared cut filter) constituting a stop band having an average transmittance of 30% or less in a wavelength range of 950 to 1200 nm at 0 ° incidence condition and having a width of 100 to 280 nm was formed. . Spectral characteristics of each example as IRCF (spectral characteristics of combinations of optical multilayer films and transparent substrates) were calculated by simulation. In addition, in the film | membrane structure of an Example and a comparative example below, it is an optical thin film in which the number 1 layer side was formed in the transparent substrate side.

(Comparative Example 1)
In Comparative Example 1, an optical multilayer film (near infrared cut filter) shown in Table 1 was provided on the first main surface, and an antireflection film (AR) consisting of six layers shown in Table 2 was provided on the second main surface. .

Table 1 shows the film conditions of the optical multilayer film (near infrared cut filter) formed on the first main surface of Comparative Example 1. Table 2 shows the film conditions of the antireflection film (AR) formed on the second main surface of Comparative Example 1. The film thickness is a physical film thickness.

As shown in Table 1, in the optical multilayer film of Comparative Example 1, the basic unit (1.33Q _H , 1.39Q _L ) was repeatedly laminated 6 times (n = 6), and the adjustment layer (1 .33Q _H , 0.67Q _L ) are stacked. The film laminated on the transparent substrate has 20 layers including AR.

  FIG. 3 is a simulation result of the spectral characteristics of the IRCF according to Comparative Example 1. In FIG. 3, the vertical axis represents transmittance and the horizontal axis represents wavelength. FIG. 3 shows simulation results under 0 ° incidence conditions and 45 ° incidence conditions. As a result of the simulation, in the IRCF according to Comparative Example 1, almost no ripple is generated under the 0 ° incident condition, but the ripple under the 45 ° incident condition is the minimum value of the transmittance (70.0%) at the wavelength of 495 nm. The amount of local decrease in transmittance is as high as 25.9%.

(Comparative Example 2)
In Comparative Example 2, the optical multilayer film (excluding the near-infrared cut filter and adjustment layer) formed on the first main surface of Comparative Example 1 is divided into two, and the basic units (1.33Q _H , 1.39Q _L ) Is repeatedly provided three times (n = 3), and an optical multilayer film (near infrared cut filter) is provided on each of the first main surface and the second main surface.

The film conditions of the optical multilayer film (near infrared cut filter) formed on the first main surface of Comparative Example 2 and the film conditions of the optical multilayer film (near infrared cut filter) formed on the second main surface of Comparative Example 2 Table 3 shows. As shown in Table 3, the film conditions of the optical multilayer film formed on the first main surface of Comparative Example 2 and the optical multilayer film formed on the second main surface are the same. The film thickness is a physical film thickness.

As shown in Table 3, the optical multilayer film formed on the first main surface and the second main surface of Comparative Example 2 has three basic units (1.33Q _H , 1.39Q _L ) (n = 3) It has a structure in which (1.33Q _H , 0.67Q _L ) is stacked as an adjustment layer after being repeatedly stacked.

  FIG. 4 is a simulation result of the spectral characteristics of the IRCF according to Comparative Example 2. In FIG. 4, the vertical axis represents transmittance and the horizontal axis represents wavelength. FIG. 4 shows simulation results under 0 ° incident conditions and 45 ° incident conditions. As a result of the simulation, in the IRCF according to Comparative Example 2, almost no ripple is generated under the 0 ° incidence condition, but the ripple under the 45 ° incidence condition is the minimum value of the transmittance (75.3%) at the wavelength of 490 nm. The amount that the transmittance is locally reduced is as large as 20.5%.

Example 1
In Example 1, the physical film thickness of the optical multilayer film (near infrared cut filter) provided on the first main surface of Comparative Example 2 was uniformly increased by 0.95. Further, the physical film thickness of the optical multilayer film (near infrared cut filter) provided on the second main surface of Comparative Example 2 was uniformly increased 1.05 times.

Table 4 shows the film conditions of the optical multilayer film (near infrared cut filter) formed on the first main surface of Example 1. Table 5 shows the film conditions of the optical multilayer film (near infrared cut filter) formed on the second main surface of Example 1. The film thickness is a physical film thickness.

As shown in Tables 4 and 5, the optical multilayer film formed on the first main surface and the second main surface of Example 1 has three basic units (1.33Q _H , 1.39Q _L ). (N = 3) It has a structure in which (1.33Q _H , 0.67Q _L ) is stacked as an adjustment layer after being repeatedly stacked.

  FIG. 5 is a simulation result of the spectral characteristics of the IRCF according to the first embodiment. In FIG. 5, the vertical axis represents transmittance and the horizontal axis represents wavelength. FIG. 5 shows simulation results under 0 ° incident conditions and 45 ° incident conditions. As a result of the simulation, in the IRCF according to Example 1, almost no ripple occurs under the 0 ° incidence condition. Further, the ripple under the 45 ° incidence condition has a minimum transmittance value (87.6%) at a wavelength of 467 nm, and the amount of the local decrease in the transmittance is 12.0%, which is the comparison example 1 and the comparison. Compared to Example 2, it is very small. Further, as can be seen from the spectral characteristics of the IRCF according to Example 1 in FIG. 5, in the visible wavelength region, two portions (467 nm and 515 nm) where the transmittance is locally decreased are dispersed.

  From the results of Example 1, Comparative Example 1 and Comparative Example 2, since Comparative Example 1 and Comparative Example 2 have one position (wavelength) where a ripple in the visible wavelength region occurs, the magnitude of the ripple is sufficiently large. It cannot be suppressed. On the other hand, in Example 1, the positions (wavelengths) where the ripples in the visible wavelength region occur are dispersed in two, and the magnitude of the ripples is sufficiently suppressed.

  Next, Example 2 and Comparative Example 3 using a transparent substrate that absorbs light in the near-infrared wavelength region will be described. As a transparent substrate that absorbs light in the near-infrared wavelength region, near-infrared cut filter glass (manufactured by AGC Techno Glass, NF-50, plate thickness: 0.3 mm) was used.

(Example 2)
In Example 2, an optical multilayer film (near infrared cut filter) was provided on the first main surface and the second main surface. The total number of layers of the optical multilayer films on both sides was 44, and the total film thickness was 4.67 μm.

Table 6 shows the film conditions of the optical multilayer film (near-infrared cut filter) formed on the first main surface of Example 2. Table 7 shows the film conditions of the antireflection film formed on the second main surface of Example 2. The film thickness is a physical film thickness.

  The optical multilayer film formed on the first main surface of Example 2 shown in Table 6 is an infrared ray that cuts infrared rays in the wavelength range of 1 to 5 and 900 to 1200 nm constituting the ultraviolet cut filter (UVCF). It has a structure in which 6 to 16 layers constituting the cut filter (IRCF) and 17 to 32 infrared cut filter (IRCF) layers for cutting infrared rays in the wavelength range of 750 to 950 nm are laminated.

  In addition, the optical multilayer film formed on the second main surface of Example 2 shown in Table 7 has 1 to 12 layers constituting an infrared cut filter (IRCF) that cuts infrared rays in the wavelength range of 900 to 1200 nm. Have a laminated structure. Therefore, the wavelength range of 900 to 1200 nm is obtained by both the infrared cut filter having 6 to 16 layers formed on the first main surface and the infrared cut filter having 1 to 12 layers formed on the second main surface. Infrared cut in.

  FIG. 6 is a simulation result of the spectral characteristics of the IRCF according to the second embodiment. In FIG. 6, the vertical axis represents transmittance and the horizontal axis represents wavelength. FIG. 6 shows simulation results under 0 ° incident conditions and 45 ° incident conditions. As a result of the simulation, in the IRCF according to Example 2, almost no ripple occurs under the 0 ° incidence condition. The ripple under the 45 ° incidence condition has a minimum transmittance (86.6%) at the wavelength of 488 nm, and the amount of local decrease in the transmittance is 5.3%, which will be described later in Comparative Example 3. Is very small compared to Further, as can be seen from the spectral characteristics of the IRCF according to Example 2 in FIG. 6, there are a plurality of locations where the transmittance is locally reduced in the visible wavelength range, and the transmittance is reduced on average. .

(Comparative Example 3)
In Comparative Example 3, an optical multilayer film (near infrared cut filter) was provided on the first main surface, and an antireflection film (AR) was provided on the second main surface. The total number of layers of the optical multilayer films on both sides was 43, and the total film thickness was 5.24 μm.

Table 8 shows the film conditions of the optical multilayer film (near infrared cut filter) formed on the first main surface of Comparative Example 3. Also, Table 9 shows the film formation conditions of the antireflection film formed on the second major surface of Comparative Example 3 (AR). The film thickness is a physical film thickness.

  As shown in Table 8 and Table 9, the optical multilayer film formed on the first main surface of Comparative Example 3 is an ultraviolet cut filter (UVCF), an infrared cut filter that cuts infrared rays in the wavelength range of 900 to 1200 nm ( IRCF), an infrared cut filter (IRCF) that cuts infrared rays in the wavelength range of 750 to 950 nm is laminated. As shown in Table 9, the optical multilayer film formed on the second main surface of Comparative Example 3 has a structure in which an antireflection film (AR) is laminated. Therefore, Comparative Example 3 has a configuration in which a near-infrared cut filter is formed on one main surface of the transparent substrate and an antireflection film is formed on the other main surface, as in Comparative Example 1.

  FIG. 7 is a simulation result of the spectral characteristics of the IRCF according to Comparative Example 3. In FIG. 7, the vertical axis represents transmittance and the horizontal axis represents wavelength. FIG. 7 shows simulation results under 0 ° incident conditions and 45 ° incident conditions. As a result of the simulation, in the IRCF according to Comparative Example 3, almost no ripple is generated under the 0 ° incidence condition, but the ripple under the 45 ° incidence condition is the minimum value of the transmittance (72.3%) at the wavelength of 499 nm. The amount of local decrease in transmittance is 20.2%, which is very large compared to Example 2. In addition, as can be seen from the spectral characteristics of IRCF according to Comparative Example 3 in FIG. 7, in the visible wavelength region, a portion where the transmittance is locally reduced exists in the vicinity of the wavelength of 500 nm. When such an IRCF is used for a solid-state imaging device, a captured image having a desired color tone may not be obtained.

  From the above, it can be seen that the near-infrared cut filter of the present invention can very efficiently suppress the ripple generated with the change in the angle of incident light, particularly in the wavelength range of 400 to 700 nm.

  The near-infrared cut filter of the present invention can suppress the ripple of the transmission band depending on the incident angle of light. Therefore, it can be suitably used for spectral correction of a solid-state imaging device (for example, a CCD image sensor or a CMOS image sensor) such as a digital camera or a digital video.

  DESCRIPTION OF SYMBOLS 100 ... Near-infrared cut filter, 11 ... Transparent substrate, 12 ... Optical multilayer film.

Claims (4)

A transparent substrate, and first and second optical multilayer films respectively provided on the first and second main surfaces of the transparent substrate,
The first and second optical multilayer films are respectively
A high refractive index film having a refractive index of 2.0 or more at a wavelength of 500 nm and a low refractive index film having a refractive index of less than 1.6 at a wavelength of 500 nm, wherein the high refractive index film is H, and the low refractive index is When the film is L, it has a repeated laminated structure represented by repeating (HL) ^ n (n is a natural number of 1 or more),
With spectral characteristics under 0 ° incidence conditions, the width of the transmission band in which the average transmittance is 85% or more in the wavelength range of 400 to 700 nm and the width of the region in which the average transmittance is 30% or less in the wavelength range of 900 to 1200 nm is 100. A stopband that is ˜280 nm,
Wavelengths indicating local minimum values at locations where the transmittance generated locally with a change in the angle of incident light is reduced are different from each other in the transmission band formed by the first optical multilayer film and the transmission band formed by the second optical multilayer film. different Ri,
The wavelength showing the local minimum value where the transmittance is locally reduced is that the transmission band formed by the first optical multilayer film and the transmission band formed by the second optical multilayer film are separated from each other by 25 nm or more and less than 100 nm. A featured near-infrared cut filter. The near-infrared cut filter according to claim 1 , wherein the value of n is 3 or more and 20 or less. The transparent substrate is, near-infrared cut filter of claim 1 or claim 2, you characterized in that it comprises optical properties having an absorption in the near infrared wavelength region. The first and second optical multilayer films are characterized in that there is no portion where the transmittance is locally reduced by 15% or more in a wavelength range of 400 to 700 nm in terms of spectral characteristics under an incident condition of 0 ° to 45 °. The near-infrared cut filter according to any one of claims 1 to 3 .

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