WO2019189039A1

WO2019189039A1 - Optical filter

Info

Publication number: WO2019189039A1
Application number: PCT/JP2019/012619
Authority: WO
Inventors: 満幸舘村
Original assignee: Ａｇｃ株式会社
Priority date: 2018-03-30
Filing date: 2019-03-25
Publication date: 2019-10-03
Also published as: TWI798400B; JPWO2019189039A1; TW201942602A; CN111954833B; CN111954833A; JP7215476B2

Abstract

This invention pertains to an optical filter (1) comprising: a transparent substrate (10); and three or more thin-film laminated structures (11), (12) and (13) which respectively restrict the passage of light having predetermined wavelength ranges within the near-infrared wavelength region. Each of the thin-film laminated structures is laminated on one surface of the transparent substrate (10), and the wavelength ranges for which the passage of light is restricted are different to one another for at least two of the three or more thin-film laminated structures (11), (12) and (13). The wavelength ranges for which the passage of light is restricted by the three or more thin-film laminated structures (11), (12) and (13) are contiguous, and the wavelength regions for which the passage of light is restricted by the thin-film laminated structures (11) and (13) positioned on the same side of the transparent substrate (10) are not contiguous.

Description

Optical filter

The present invention relates to an optical filter. Specifically, the present invention relates to an optical filter that restricts transmission of light having a wavelength in the near infrared region.

In recent years, ambient light sensors have been used in devices such as smartphones, game machine bodies, and game machine controllers (see, for example, Patent Document 1). The ambient light sensor is provided inside the device, detects ambient light around the device, which is taken in through the window of the housing of the device, and controls the brightness of the display based on the detection result.

The ambient light sensor measures the intensity of visible light in the detected ambient light. Therefore, the ambient light sensor uses an optical filter such as a near-infrared cut filter that cuts extra wavelength components such as light in the near-infrared region.

Near-infrared cut filters are often used in solid-state imaging devices. For example, an optical multilayer film in which a high-refractive index film and a low-refractive index film are stacked with a predetermined film thickness and number of layers is formed on a substrate. Composed. The light incident on the near-infrared cut filter is cut at a wavelength in the near-infrared region by the optical multilayer film on the substrate, and only visible light is transmitted (see, for example, Patent Document 2).

With the progress of thinning of smartphones and game machines, the thickness of the device casing in which the ambient light sensor is provided has become very thin. For this reason, the distance from the window (opening) of the housing to the ambient light sensor is shortened, so that light is incident on the ambient light sensor from a wider angle (high incident angle).

The optical multilayer film described above has an incident angle dependency. Specifically, it is known that when the incident angle of light increases (the incident light angle increases with respect to the normal direction of the optical multilayer film surface), the light transmission characteristics shift to the short wavelength side. Yes. In addition, a phenomenon has been observed in which the transmittance in the visible light region of light having a high incident angle is partially reduced in the light transmitted through the optical multilayer film. In general, in a solid-state imaging device, it is only necessary to consider the incident angle of light from about 0 ° to about 35 °. However, as described above, the ambient light sensor needs to have desired optical characteristics with respect to light with a high incident angle, and at a higher incident angle than a near-infrared cut filter used in a conventional solid-state imaging device. In addition, there is a demand for an optical filter that can obtain desired optical characteristics, and improvement of optical characteristics is achieved by various methods (see, for example, Patent Documents 3 and 4).

Japanese Unexamined Patent Publication No. 2017-86922 Japanese Unexamined Patent Publication No. 2006-60014 Japanese Patent No. 6119747 Japanese Patent No. 6206410

An object of the present invention is to provide an optical filter having high visible light transmittance and low incidence angle dependency even for light incident at a wide angle.

The optical filter according to the present invention is an optical filter including a transparent substrate and three or more thin film laminated structures that limit transmission of light in a predetermined wavelength range in the near-infrared wavelength region, Each of the thin film stack structures is stacked on one surface of the transparent substrate, and at least two of the three or more thin film stack structures have a wavelength range that limits transmission. The wavelength ranges in which transmission is limited by the three or more thin film multilayer structures are different, and the thin film multilayer structure disposed on the same surface side of at least one of the transparent substrates is transparent. The limiting wavelength region is discontinuous.

According to the optical filter of the present invention, the visible light transmittance is high even for light incident at a wide angle, and the incident angle dependency can be reduced. Therefore, it can be suitably used not only as an environmental sensor but also as an optical filter for a solid-state imaging device.

FIG. 1 is a cross-sectional view illustrating an optical filter according to the first embodiment. FIG. 2 is a diagram illustrating optical characteristics of the optical filter according to the first embodiment. FIG. 3 is a diagram illustrating optical characteristics (wavelengths 850 to 1050 nm) of the optical filter according to the first embodiment. FIG. 4 is a diagram illustrating optical characteristics of the thin film laminated structure on one surface of the optical filter according to the first example. FIG. 5 is a diagram illustrating optical characteristics of the thin film laminated structure on the other surface of the optical filter according to the first embodiment. FIG. 6 is a diagram illustrating optical characteristics of the optical filter according to the second embodiment. FIG. 7 is a diagram illustrating optical characteristics (wavelengths 850 to 1050 nm) of the optical filter according to the second embodiment. FIG. 8 is a diagram illustrating optical characteristics of the thin film laminated structure on one surface of the optical filter according to the second embodiment. FIG. 9 is a diagram illustrating optical characteristics of the thin film laminated structure on the other surface of the optical filter according to the second embodiment. FIG. 10 is a diagram illustrating optical characteristics of the optical filter according to the third embodiment. FIG. 11 is a diagram illustrating optical characteristics (wavelength 850 to 1050 nm) of the optical filter according to the third embodiment. FIG. 12 is a diagram illustrating optical characteristics of the thin film laminated structure on one surface of the optical filter according to the third embodiment. FIG. 13 is a diagram illustrating optical characteristics of the thin film laminated structure on the other surface of the optical filter according to the third embodiment. FIG. 14 is a diagram illustrating the optical characteristics of the optical filter according to the first comparative example. FIG. 15 is a diagram showing the optical characteristics (wavelength 850 to 1050 nm) of the optical filter according to Comparative Example 1. FIG. 16 is a diagram showing optical characteristics of the thin film laminated structure on one surface of the optical filter according to Comparative Example 1. FIG. 17 is a diagram showing optical characteristics of the thin film laminated structure on the other surface of the optical filter according to Comparative Example 1. FIG. 18 is a diagram illustrating optical characteristics of the optical filter according to Comparative Example 2. FIG. 19 is a diagram showing the optical characteristics (wavelength 850 to 1050 nm) of the optical filter according to Comparative Example 2. FIG. 20 is a diagram illustrating optical characteristics of the thin film laminated structure on one surface of the optical filter according to Comparative Example 2.

The optical filter of the present invention includes a transparent substrate and three or more thin film laminated structures that restrict transmission of light in a predetermined wavelength range within the near infrared wavelength region, and each of the thin film laminated structures. Is laminated on one surface of the transparent substrate. In addition, at least two of the three or more thin-film stacked structures have different wavelength ranges for limiting transmission, and the wavelengths for which transmission is limited by the three or more thin-film stacked structures. The range is continuous. And the transmission limiting wavelength range by the thin film laminated structure arrange | positioned at the same surface side of at least one of a transparent substrate is discontinuous.

In a conventional optical filter using only a thin film laminated structure having a wide wavelength range of light for limiting transmission (hereinafter also referred to as “transmission-limited wavelength range”), when the incident angle of light increases, A phenomenon in which the transmittance partially decreases in a predetermined wavelength range (hereinafter referred to as “reflection ripple”) is likely to occur. On the other hand, a general method for suppressing the reflection ripple is to use a thin film laminated structure having a narrow transmission limiting wavelength range. When this is applied, the transmittance is partially in a predetermined wavelength range in the near infrared wavelength region. May occur (hereinafter referred to as “transmission ripple”). Therefore, in an optical filter using a conventional technique, it is very difficult to achieve both suppression of reflection ripples in the visible wavelength band and suppression of transmission ripples in the near infrared wavelength region.

Usually, the cause of the decrease in the transmittance in the red region of the optical filter is mostly glass absorption or the shift of the near-infrared region in the near-infrared region to the short wavelength side due to the change in incident angle. The amount of change is greatly influenced by the design of the optical system and can be expected. On the other hand, the main reason for the decrease in transmittance in the blue and green regions is the generation of huge reflection ripples caused by a shift in the design balance of the short-pass filter that forms the stopband in the near-infrared wavelength region. It is difficult to predict the amount of change. The green region is an important region that is frequently used in image processing, and the blue region is a region that requires a higher amount of light due to a problem such as low original susceptibility. Therefore, the optical filter in which the reflection ripples in the blue and green regions are suppressed (inhibition of the decrease in transmittance) can be suitably used as an image sensor such as a CCD or a CMOS or other optical sensor.

In the optical filter of the present invention, since transmission of light having a wavelength in the near-infrared region is restricted by three or more thin film laminated structures, even if a thin film laminated structure having a narrow transmission limited wavelength range is used. In addition, transmission ripples in the near-infrared wavelength region and reflection ripples in the visible wavelength region are unlikely to occur, and high transmission limiting performance can be maintained even when light is incident at a wide angle.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, the optical filter 1 according to the first embodiment includes a transparent substrate 10 and three thin film stacked

structures

11, 12, and 13. The thin film laminated

structures

11, 12, and 13 are each laminated on one surface of the transparent substrate 10. In FIG. 1, a thin film laminated structure 12 is laminated on one surface 10a of a transparent substrate 10, and a thin film laminated structure 11 and a thin film laminated structure 13 are laminated on the other surface 10b. In addition, the thin film laminated structure 12 may be provided on any surface of the transparent substrate 10, and in this case, the thin film laminated structure 11 and the thin film laminated structure 13 are the same as the thin film laminated structure 12 of the transparent substrate 10. It is provided on the surface opposite to the provided surface. For example, the thin film laminated structure 12 may be laminated on the surface 10b, and the thin film laminated structure 11 and the thin film laminated structure 13 may be laminated on the surface 10a.

The thin film laminated

structures

11, 12, and 13 each limit the transmission of light in a predetermined wavelength range within the near-infrared wavelength region. Specifically, the thin film laminated structure 11 restricts transmission of light in the first wavelength range included in the near-infrared wavelength region, for example. Similarly, the thin film stack structure 12 transmits light in the second wavelength range included in the near infrared wavelength region, and the thin film stack structure 13 transmits light in the third wavelength range included in the near infrared wavelength region. Limit each. In addition, as for each thin film laminated structure used by this invention, it is preferable that the wavelength range in which transmission of the light within a near-infrared wavelength range is restrict | limited is continuous. In other words, each thin-film laminated structure preferably has one light transmission limited wavelength range in the near infrared wavelength region (the light transmission limited wavelength range is not divided into two or more).

The wavelength ranges in which the thin film laminated

structures

11, 12, and 13 restrict transmission are different from each other. For example, the first wavelength range is a wavelength range including the range on the shortest wavelength side when the near-infrared wavelength region is divided into three ranges, and the third wavelength range is the range on the longest wavelength side. It is a wavelength range including. The second wavelength range is a wavelength range including an intermediate range between the first wavelength range and the third wavelength range. In this case, the center wavelengths of the first wavelength range, the second wavelength range, and the third wavelength range are the center wavelength of the first wavelength range and the center of the second wavelength range from the short wavelength side to the long wavelength side. Wavelength, in order of the center wavelength of the third wavelength range, or from the long wavelength side to the short wavelength side, the center wavelength of the first wavelength range, the center wavelength of the second wavelength range, and the center wavelength of the third wavelength range It is preferable to position in order.

In FIG. 1, the thin film laminated

structures

11 and 13 are arranged in the order of the thin film laminated structure 11 and the thin film laminated structure 13 from the glass substrate side. They may be arranged in order. Moreover, the main part of the thin film laminated structure 12 needs to be arrange | positioned on the surface different from the surface where the thin film laminated structure 11 and the thin film laminated structure 13 are arrange | positioned. That is, most of the light blocking amount that the optical filter 1 restricts transmission is preferably created by the thin film laminated structure 12 on the side opposite to the surface on which the thin film laminated structure 11 and the thin film laminated structure 13 are arranged. In addition, you may provide the thin film laminated structure which restrict | limits permeation | transmission of the light of an ultraviolet wavelength range, for example separately from said each thin film laminated structure. The thin film laminated structure for restricting the transmission of light in the ultraviolet wavelength region is generated in a portion where the transmission restricted wavelength ranges overlap with each other because the transmission restricted wavelength ranges are not continuous with the thin film laminated

structures

11, 12, and 13. It is because there is no influence of the transmission ripple which is easy to do.

In the optical filter according to the present embodiment, “restrict light transmission” means that light having a predetermined wavelength has a light transmittance of less than 5% when incident at an incident angle of 0 degrees (normal incidence). Say something. Further, “transmission-limited wavelength range is discontinuous” means that the transmission-limited wavelength range is divided by the transmission ripple, and the degree of the transmission ripple is a state where the transmittance is 5% or more.

The wavelength range in which the transmission is limited by the thin film laminated

structures

11, 12, and 13 is continuous. That is, the range obtained by superimposing the first wavelength range, the second wavelength range, and the third wavelength range includes all the predetermined regions of the near infrared wavelength region.

It is preferable that the thin film laminated structure 12 and the thin film laminated structure 13 are thin film laminated structures having a characteristic that reflection ripple of oblique incidence described later is small. In particular, the thin film laminated structure 12 is more than the thin film laminated structure 13. It is preferable that all the thin films have a high average refractive index and a small amount of wavelength shift due to the oblique incidence dependence of incident light.

Thin-film multilayer structures with these characteristics often have narrower transmission-limited wavelength ranges than usual, but the number of layers of thin-film multilayer structures is increased due to the fundamentally small reflection ripple at oblique incidence. In this case, there is little problem of increase in reflection ripple due to oblique incidence, and it is easy to form a transmission limited wavelength range. Furthermore, since the thin film laminated structure 12 is disposed on a different surface from the others, the problem of transmission ripple caused by the overlapping of the thin film laminated structures is unlikely to occur.

Moreover, the thin film laminated structure 12 can maintain the transmission limiting performance in a specific wavelength region stably at a wide angle by making the wavelength shift amount at the time of oblique incidence very small. When the wavelength shift amount at the oblique incidence of the thin film multilayer structure 13 is sufficiently larger than the wavelength shift amount at the oblique incidence of the thin film multilayer structure 12, if the incident angle is large, the transmission limited wavelength in the thin film multilayer structure 13 The range moves to the wavelength band that the thin film laminated structure 12 has been responsible for. Accordingly, the transmission limited wavelength ranges formed by the respective thin film laminated structures always overlap each other, which is preferable because it is easy to maintain the light blocking performance at wavelengths of 800 to 1000 nm. Moreover, it is preferable that the transmittance | permeability of the optical filter which this invention comprises is 0.05% or less in the wavelength with the lowest transmittance | permeability within the wavelength range of the incident angle of 0 degree which the thin film laminated structure 12 has.

In the present invention, the light transmittance can be measured using a spectrophotometer, for example, a spectrophotometer U4100 manufactured by Hitachi High-Tech Science. Unless otherwise specified, the light transmittance refers to the transmittance at an incident angle of 0 °.

In addition, although the optical filter 1 which has the three thin film laminated

structures

11, 12, and 13 was demonstrated above, the number of thin film laminated structures may be four or more. When there are four or more thin film laminated structures, a thin film laminated structure in which the center wavelength in the wavelength range for limiting transmission is longer than the center wavelength of the thin film laminated

structures

11, 12, and 13 is additionally provided. be able to. That is, when there are four or more thin film laminated structures, the three thin film laminated

structures

11, 12, and 13 described above are thin film laminated structures having a central wavelength in the wavelength range that restricts transmission on the shortest wavelength side, 2 The third is the thin film laminated structure on the short wavelength side, and the third is the thin film laminated structure on the short wavelength side. The number of thin film laminated structures is preferably 3 or more and 7 or less, and particularly preferably 4 or more and 6 or less. In the case where the optical filter of the embodiment has four or more thin film laminated structures, the thin film laminated structure is formed so that the transmission limiting wavelengths of the thin film laminated structures laminated on the same surface of the transparent substrate are not continuous. Be placed. For example, four thin-film stacked structures can be alternately stacked on both surfaces of the transparent substrate 10 in order from the shortest central wavelength in the transmission-limited wavelength range. Alternatively, even if a thin film laminated structure having a second central wavelength in the wavelength range that restricts transmission of light in the near-infrared region is stacked on a different surface from the other thin film laminated structures. Good. By doing so, reflection ripples in the visible wavelength band can be suppressed.

Next, each configuration of the optical filter 1 of the present embodiment will be described.

The thin film laminated

structures

11, 12, and 13 are configured to limit transmission in a desired wavelength range by using, for example, a dielectric multilayer film. The dielectric multilayer film is selected from a low refractive index dielectric film (low refractive index film), a medium refractive index dielectric film (medium refractive index film) and a high refractive index dielectric film (high refractive index film). And a film having an optical function obtained by alternately laminating. By design, it is possible to develop a function of controlling the transmission of light in a specific wavelength region and the light transmission limitation using the interference of light. The low refractive index, the high refractive index, and the medium refractive index mean that the refractive index has a high refractive index, a low refractive index, and an intermediate refractive index relative to the refractive index of the adjacent layer.

In the optical filter of the present invention, an optical multilayer film (near-infrared cut filter) having the following configuration can be suitably used as the thin film laminated structure that can reduce the reflection ripple of oblique incidence.

A high refractive index film having a refractive index of 2.0 or more at a wavelength of 500 nm, a medium refractive index film having a refractive index of 1.6 or more at a wavelength of 500 nm and less than the refractive index of the high refractive index film, and a refraction at a wavelength of 500 nm. A low refractive index film having a refractive index of less than 1.6, where the high refractive index film is H, the medium refractive index film is M, and the low refractive index film is L, (LMMHML) ^ n (n Is a repetitive laminated structure represented by repetition of a natural number of 1 or more, a transmission band having an average transmittance of 85% or more in a wavelength range of 400 to 700 nm, and an average transmittance in a wavelength range of 750 to 1100 nm. A band width of less than 5% is 100 to 280 nm, and a QWOT (Quater-wave Optical Thickness) of the high refractive index film of the optical multilayer film is T _H , and the medium refractive index When QWOT of the film is T _M and QWOT of the low refractive index film is T _L , the refractive index of the medium refractive index film is intermediate between the refractive index of the high refractive index film and the refractive index of the low refractive index film. When the value is greater than or equal to the value, the optical multilayer film has 2T _L / (T _H + 2T _M) where there is no portion where the transmittance is locally reduced by 5% or more in the wavelength range of 400 to 700 nm in the spectral characteristics under normal incidence conditions. ) Is set to 100% and the minimum value is set to 0%, 2T _L / (T _H + 2T _M ) is in the range of 100% to 70%, and the refractive index of the medium refractive index film is high. When the refractive index is less than the intermediate value between the refractive index of the refractive index film and the refractive index of the low refractive index film, the optical multilayer film has a local transmittance within a wavelength range of 400 to 700 nm in terms of spectral characteristics under normal incidence conditions. most of the no portion to lower than _{_{5% (2T L + 2T M}} ) / T H 100% value, if the minimum value was set to _{_{0%, (2T L + 2T}} M) / T H so is in the range of from 100% to 70%, the high-refractive-index film, the intermediate refractive index layer and It is a near infrared cut filter in which the low refractive index film is laminated. This is described in detail in Patent Document 3.

The optical multilayer film includes alternating medium refractive index films having a refractive index of 1.8 to 2.23 at a wavelength of 500 nm and low refractive index films having a refractive index of 1.45 to 1.49 at a wavelength of 500 nm. A wavelength range in which the combination unit of the medium refractive index film and the low refractive index film has a number of 5 or more and 35 or less, and light incident on the optical multilayer film at 0 ° is limited in transmission Is a near-infrared cut filter having a width of 100 nm to 300 nm. This is described in detail in Japanese Patent Application No. 2017-253468 by the applicant. However, the wavelength range in which the light incident on the optical multilayer film at 0 ° is limited in transmission is not limited to the range described therein.

The optical multilayer film is composed of 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 wavelength of 1.6 or less, and the optical multilayer film has a wavelength of the high refractive index film. the QWOT at 500nm _{Q H,} when a QWOT at a wavelength 500nm for the low refractive index film was _{_{_{_{Q L, (a n Q H}}}} , b n Q L, c n Q H, d n Q L) basic units n of in pieces stacked repeating structure _(where, a _n, b _n, c n, _{d n} is the physical thickness of the membrane in each basic unit is a coefficient indicating how many times the QWOT, and n is 1 This is a near-infrared cut filter having the above natural number). This is described in detail in Patent Document 4. However, since the characteristic of ultraviolet cut is not an essential component, the coefficient is not limited.

As another aspect, the constituent material of the high refractive index film is preferably a material having a refractive index of 2 or more, more preferably 2.2 to 2.7. Examples of such a constituent material include TiO ₂ , Nb ₂ O ₅ (refractive index: 2.38), Ta ₂ O ₅ , and composite oxides thereof.

At this time, the constituent material of the medium refractive index film preferably has a refractive index of more than 1.6 and less than 2, and more preferably 1.62 to 1.92. As such a constituent material, for example, Al ₂ O ₃ , Y ₂ O ₃ (refractive index: 1.81), or a composite oxide thereof, a mixture film of Al ₂ O ₃ and ZrO ₂ (refractive index: 1). .67) and the like. The medium refractive index film may be replaced with an equivalent film in which a high refractive index film and a low refractive index film are combined.

The constituent material of the low refractive index film preferably has a refractive index of 1.3 to 1.6, for example. Examples of such a constituent material include SiO ₂ , SiO _x N _y , and MgF _2.

When the dielectric multilayer film (thin film laminated structure) is configured by alternately laminating thin films having different refractive indexes, the number of layers depends on the optical characteristics of the dielectric multilayer film, 50 to 150 layers are preferred. If the total number of laminated layers is less than 50, the blocking performance at a wavelength of 800 nm to 1000 nm may not be sufficient. On the other hand, if the total number of laminated layers exceeds 150, the tact time during the production of the optical filter becomes long, and the warp of the optical filter due to the dielectric multilayer film occurs, which is not preferable.

As the film thickness of the dielectric multilayer film (thin film laminated structure), the thinner one is preferable from the viewpoint of reducing the thickness of the optical filter 1 while satisfying the preferable number of laminated layers. However, in order to obtain desired optical characteristics, it is preferably 5 μm or more. In consideration of the warp of the optical filter caused by the dielectric multilayer film, the thickness is preferably 15 μm or less.

Further, in the optical filter 1 including three thin film laminated structures, it is preferable that the total film thicknesses of the thin film laminated structures arranged on both surfaces of the transparent substrate 10 are as close as possible to each other. In the optical filter 1 used for the ambient light sensor, since the optical filter 1 is formed extremely thin, the transparent substrate 10 is also extremely thin. Therefore, when the physical film thickness of the thin film laminated structure on both surfaces of the transparent substrate 10 is greatly different, the optical filter 1 may have a convex warp on the side of the thin film laminated structure having a small physical film thickness.

Therefore, in the optical filter 1 including three thin film laminated structures, the transmission limiting wavelength range is located on the second short wavelength side among the three thin film laminated structures, and is laminated alone on the surface of the transparent substrate 10. It is preferable that the physical film thickness of the thin film laminated structure 12 is larger than the other two thin film laminated

structures

11 and 13. That is, the physical film thickness of the thin film laminated structure 12 having the center wavelength located at the second shortest wavelength among the central wavelengths in the transmission limited wavelength range of the three thin film laminated

structures

11, 12, 13 is other than that It is preferably thicker than the physical film thickness of the two thin film laminated structures 11 and the thin film laminated structure 13. Thereby, the difference of the thickness of the whole thin film laminated structure in the both surfaces of the transparent substrate 10 when laminated | stacked on the transparent substrate 10 can be made small, and the curvature of the optical filter 1 can be suppressed.

In forming the dielectric multilayer film (thin film laminated structure), for example, dry film formation processes such as IAD (Ion Assisted Deposition) deposition method, CVD method, sputtering method, vacuum deposition method, spray method, dipping method, etc. A wet film formation process such as can be used.

The transparent substrate 10 is a material that transmits visible light. For example, glass, glass ceramics, crystal such as crystal, sapphire, resin (polyester resin such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyolefin resin such as polyethylene, polypropylene, ethylene vinyl acetate copolymer, norbornene resin Acrylic resins such as polyacrylate and polymethyl methacrylate, urethane resins, vinyl chloride resins, fluororesins, polycarbonate resins, polyvinyl butyral resins, polyvinyl alcohol resins, etc.).

The transparent substrate 10 preferably has a property of absorbing light having a wavelength in the near infrared region. For example, when the optical filter 1 of the present invention is used as a near-infrared cut filter for a solid-state imaging device, the transparent substrate 10 has a property of absorbing light in the near-infrared wavelength region, so that the color is close to human visibility characteristics. Correction is possible. Since the thin-

film multilayer structures

11, 12, and 13 can provide spectral characteristics with low incident angle dependency, the thin-film multilayer structure is provided on the transparent substrate 10 having the property of absorbing light having a wavelength in the near infrared region. Thus, an excellent spectral characteristic that restricts transmission of light having a wavelength in the near infrared region can be obtained. Therefore, it becomes possible to obtain the optical filter 1 having good characteristics as a near-infrared cut filter for a solid-state imaging device.

The transparent substrate 10 having the property of absorbing light having a wavelength in the near infrared region is a glass having the ability to transmit light in the visible light region and absorb light in the near infrared region, such as CuO-containing fluorophosphate glass. Alternatively, it is preferably composed of a CuO-containing phosphate glass (hereinafter collectively referred to as “CuO-containing glass”).

The transparent substrate 10 is composed of CuO-containing glass, so that it has a high transmittance for visible light and a high transmission limiting property for light having a wavelength in the near infrared region. The “phosphate glass” includes silicic acid phosphate glass in which a part of the glass skeleton is composed of SiO ₂ .

The CuO-containing glass substrate has a feature that absorption of light having a wavelength of 400 to 450 nm is slight, and an absorptance ratio of light having a wavelength of 400 to 450 nm with respect to light having a wavelength of 775 to 900 nm is low. As a result, even if the CuO-containing glass substrate increases the absorption rate by increasing the CuO content so as to sufficiently limit the transmission of light having a wavelength of 775 to 900 nm by absorption, the visible light transmittance does not decrease significantly. Because it is useful.

As the transparent substrate 10 having the property of absorbing light having a wavelength in the near infrared region, as a material other than the CuO-containing glass, the transparent resin has a near resin that absorbs light having a wavelength in a specific range in the near infrared region. A near-infrared absorbing substrate containing an infrared-absorbing dye is also included.

Moreover, in order to improve the near-infrared light absorption performance of the optical filter, a near-infrared absorbing layer containing a near-infrared absorbing dye and a transparent resin on the surface of the transparent substrate 10 using the same material as the above-mentioned near-infrared absorbing substrate. May be formed. In this case, the near-infrared absorbing layer is formed between the transparent substrate 10 and the thin film laminated structure 11 or the thin film laminated structure 12. Further, the near infrared absorption layer may be formed on at least one surface of the transparent substrate 10.

The near-infrared absorbing dye is not particularly limited as long as it is a near-infrared absorbing dye having the ability to transmit light in the visible light region and absorb light in the near infrared region. The dye in the present invention may be a pigment, that is, a state in which molecules are aggregated.

As near-infrared absorbing dyes, cyanine compounds, phthalocyanine compounds, naphthalocyanine compounds, dithiol metal complex compounds, diimonium compounds, polymethine compounds, phthalide compounds, naphthoquinone compounds, anthraquinone compounds, indophenol compounds, Examples include squarylium compounds.

Of these, squarylium compounds, cyanine compounds and phthalocyanine compounds are more preferred, and squarylium compounds are particularly preferred. A near-infrared absorbing dye made of a squarylium compound is preferred because its absorption spectrum has little absorption of visible light and high storage stability and stability to light. A near-infrared absorbing dye made of a cyanine compound is preferable because of its low absorption of visible light in its absorption spectrum and high light absorption on the long wavelength side in the near-infrared region. In addition, it is known that cyanine compounds are low-cost, and long-term stability can be secured by salt formation. Near-infrared absorbing dyes composed of phthalocyanine compounds are preferred because they are excellent in heat resistance and weather resistance.

As the near-infrared absorbing dye, one of the above compounds may be used alone, or two or more of them may be used in combination.

As the transparent resin, a transparent resin having a refractive index of 1.45 or more is preferable. The refractive index is more preferably 1.5 or more, and particularly preferably 1.6 or more. The upper limit of the refractive index of the transparent resin is not particularly limited, but is preferably about 1.72 in view of availability. In the present specification, the refractive index means a refractive index at a wavelength of 500 nm unless otherwise specified.

Transparent resins include acrylic resin, epoxy resin, ene / thiol resin, polycarbonate resin, polyether resin, polyarylate resin, polysulfone resin, polyethersulfone resin, polyparaphenylene resin, polyarylene ether phosphine oxide resin, polyimide Examples include resins, polyamideimide resins, polyolefin resins, cyclic olefin resins, and polyester resins. As transparent resin, 1 type may be used individually from these resin, and 2 or more types may be mixed and used for it.

Among the above, from the viewpoint of solubility of the near-infrared absorbing dye in the transparent resin, the transparent resin is at least one selected from acrylic resins, polyester resins, polycarbonate resins, ene / thiol resins, epoxy resins, and cyclic olefin resins. preferable. Further, the transparent resin is more preferably at least one selected from an acrylic resin, a polyester resin, a polycarbonate resin, and a cyclic olefin resin. As the polyester resin, polyethylene terephthalate resin, polyethylene naphthalate resin and the like are preferable.

The near-infrared absorbing layer is, for example, a transparent coating liquid prepared by dissolving or dispersing a near-infrared absorbing dye and a transparent resin or a transparent resin raw material component, and optionally an ultraviolet absorber in a solvent or dispersion medium. It can be produced by coating on the substrate 10, drying, and further curing as necessary.

The near-infrared absorbing layer may contain other optional components as required, as long as the effects of the present invention are not impaired, in addition to the near-infrared absorbing dye, the transparent resin, and the optional ultraviolet absorber. As other optional components, specifically, near infrared rays or infrared absorbers, color tone correction dyes, ultraviolet absorbers, leveling agents, antistatic agents, heat stabilizers, light stabilizers, antioxidants, dispersants, flame retardants , Lubricants, plasticizers and the like. Moreover, the component added to the coating liquid used when forming the near-infrared absorption layer mentioned later, for example, the component derived from a silane coupling agent, a heat | fever or photoinitiator, a polymerization catalyst, etc. are mentioned.

The film thickness of the near-infrared absorbing layer is appropriately determined according to the arrangement space in the apparatus to be used and the required absorption characteristics. The film thickness is preferably 0.1 to 100 μm. If the film thickness is less than 0.1 μm, the near-infrared absorbing ability may not be sufficiently exhibited. On the other hand, if the film thickness exceeds 100 μm, the flatness of the film is lowered, and there is a possibility that the absorption rate varies. The film thickness is more preferably 0.5 to 50 μm. If it exists in this range, sufficient near-infrared absorptivity and flatness of a film thickness can be compatible.

According to the optical filter of the present invention described above, three or more thin film laminated structures having different transmission limiting wavelength ranges are laminated on the surface of the transparent substrate so that the transmission limiting wavelength ranges on the same surface are not continuous. As a result, it is possible to obtain spectral characteristics having high visible light transmittance and high blocking performance in the near infrared region even for light incident at a wide angle.

The optical filter of the present invention preferably has a transmittance of 1% or less for light in the near-infrared wavelength region, for example, a wavelength of 800 nm to 1000 nm. Further, it is preferable that the wavelength range in which the light transmittance is less than 0.05% at a wavelength of 800 nm to 1000 nm is 100 nm or more. Further, according to the optical filter of the present invention, it is possible to greatly reduce the decrease in transmittance due to the optical multilayer film in the wavelength range that transmits light having an incident angle of 0 to 50 °. This feature makes it suitable for use as an optical filter for imaging devices such as CCD and CMOS, and other optical sensor applications that can provide images with little flare and ghosting even in environments where near-infrared radiation is frequently used. can do.

The optical filter of the present invention can effectively suppress a decrease in transmittance in the visible light region, particularly in the blue and green regions having a wavelength of 430 nm to 560 nm, within a wide angle range where the incident angle of light is 0 to 50 °. . Therefore, the average transmittance in the wavelength range can be 85% or more in a wide range of light incident angles.

Moreover, in the optical filter of the present invention, the transmission of light in the near-infrared wavelength range is surely limited by using a transparent substrate having near-infrared absorption or by providing a near-infrared absorption layer on the surface of the transparent substrate. Therefore, it is possible to obtain an optical filter having more excellent optical characteristics that enables color correction close to human visibility characteristics.

Example 1
The optical filter (near-infrared cut filter) according to this example includes a transparent substrate (near-infrared absorbing glass, plate thickness: 0.3 mm, trade name: NF-50T, manufactured by AGC Techno Glass), and one surface of the transparent substrate. And a total of five thin film laminated structures provided on the other surface. Each of the thin film laminated structures has a structure in which a high refractive index film and a low refractive index film are sequentially laminated from the transparent substrate surface side.

Four thin film laminated structures are disposed on one surface of the transparent substrate. The four thin-film stacked structures are a repetition of a high refractive index film (titanium oxide (TiO ₂ )) and a low refractive index film (silicon oxide (SiO ₂ )) having a total of four, 32 layers and a physical film thickness of 3796.98 nm. This is a laminated structure (1-1 thin film laminated structure). That is, the transparent substrate has a first-first thin film laminated structure composed of four thin film laminated structures on one surface.

One thin film laminated structure is disposed on the other surface of the transparent substrate. This thin film laminated structure is a repetitive laminated structure of a total of 52 layers of a high refractive index film (titanium oxide (TiO ₂ )) and a low refractive index film (silicon oxide (SiO ₂ )) and a physical film thickness of 3093.23 nm. (1-2 thin film laminated structure).

Table 1 shows the configuration of the thin film laminated structure (1-1 thin film laminated structure) provided on one surface of the transparent substrate of the optical filter. Table 2 shows the configuration of the thin film laminated structure (1-2 thin film laminated structure) provided on the other surface of the transparent substrate of the optical filter. In Tables 1 and 2, the number of film layers is the ordinal number of layers from the transparent substrate side, and the film thickness indicates the physical film thickness.

The optical characteristics of the optical filter at incident angles of 0 °, 40 °, and 50 ° were verified using optical thin film simulation software (TFCalc, manufactured by Spectra, Inc.). The results are shown in FIGS. 2 and 3 (enlarged views in the wavelength region of 850 nm to 1050 nm).

Also, incident angles of 0 °, 40 ° and 50 ° only on the thin film laminated structure (1-1 thin film laminated structure) provided on one surface of the transparent substrate (excluding the influence of light absorption by the transparent substrate). The optical characteristics at 0 ° were verified using the optical thin film simulation software. The results are shown in FIG. Also, incident angles of 0 °, 40 ° and 50 ° only for the thin film laminated structure (1-2 thin film laminated structure) provided on the other surface of the transparent substrate (excluding the influence of light absorption by the transparent substrate). The optical characteristics at 0 ° were verified using the optical thin film simulation software. The results are shown in FIG.

As shown in FIG. 4, in the optical filter of Example 1 of the present invention, in the optical characteristics of the thin film laminated structure disposed on the same surface side of the transparent substrate, the wavelength is 970 nm, 1070 nm, and around 1190 nm at 0 ° incidence. Have a portion with a transmittance of 5% or more, and the wavelength region in which the thin film laminated structure restricts transmission is discontinuous. Since only the thin film laminated structure that restricts transmission in a specific near-infrared region is formed on the other surface, the width of the transmission restricted wavelength range of the thin film laminated structure on the other surface is narrow. Even when the incident angle of the thin film is increased, it is possible to provide a thin film laminated structure in which reflection ripples hardly occur in the visible region.

(Example 2)
The optical filter (near-infrared cut filter) according to this example includes a transparent substrate similar to that used in Example 1, and a thin film laminated structure provided on one surface and the other surface of the transparent substrate. Prepare. Each of the thin film laminated structures has a structure in which films having different refractive indexes are sequentially laminated from the transparent substrate surface side.

Two thin film laminated structures are disposed on one surface of the transparent substrate. The two thin film laminated structures have a total of 50 layers and a physical film thickness of 5930.11 nm. The two thin-film laminated structures have a total of 30 layers of a high refractive index film (zirconium oxide (ZrO ₂ )) and a low refractive index film (silicon oxide (SiO ₂ )) provided on the transparent substrate side. High refractive index film (titanium oxide (TiO ₂ )) and medium refractive index provided on the laminated structure (2-1 thin film laminated structure) and the 2-1 thin film laminated structure (air side) It consists of a total of 20 layers of repeated lamination structure (second thin film laminated structure) with a film (aluminum oxide (Al ₂ O ₃ )).

One thin film laminated structure is disposed on the other surface of the transparent substrate. This thin film laminated structure is a repetitive laminated structure having a total of 60 layers of a high refractive index film (titanium oxide (TiO ₂ )) and a low refractive index film (silicon oxide (SiO ₂ )) and a physical film thickness of 3570.77 nm. (2-3 thin film laminated structure).

Table 3 shows the structures of the thin film laminated structures (2-1 thin film laminated structure and 2-2 thin film laminated structure) provided on one surface of the transparent substrate of the optical filter. Table 4 shows the configuration of the thin film laminated structure (second-3 thin film laminated structure) provided on the other surface of the transparent substrate of the optical filter. In Tables 3 and 4, the number of film layers is the ordinal number of layers from the transparent substrate side, and the film thickness indicates the physical film thickness.

The optical characteristics of the optical filter at incident angles of 0 °, 40 °, and 50 ° were verified using optical thin film simulation software (TFCalc, manufactured by Spectra, Inc.). The results are shown in FIGS. 6 and 7 (enlarged views in the wavelength region of 850 nm to 1050 nm).

Further, only the thin film laminated structure (the 2-1 thin film laminated structure and the 2-2 thin film laminated structure) provided on one surface of the transparent substrate (excluding the influence of light absorption by the transparent substrate) ) Was verified using the optical thin film simulation software. The results are shown in FIG. In addition, incident angles of 0 °, 40 °, and 50 ° only for the thin film laminated structure (the second and third thin film laminated structures) provided on the other surface of the transparent substrate (excluding the influence of light absorption by the transparent substrate). The optical characteristics at 0 ° were verified using the optical thin film simulation software. The results are shown in FIG.

Example 3
The optical filter (near-infrared cut filter) according to this example includes a transparent substrate similar to that used in Example 1, and a thin film laminated structure provided on one surface and the other surface of the transparent substrate. Prepare. Each of the thin film laminated structures has a structure in which films having different refractive indexes are sequentially laminated from the transparent substrate surface side.

Two thin film laminated structures are disposed on one surface of the transparent substrate. The two thin film laminated structures have a total of 44 layers and a physical film thickness of 5738.57 nm. The two thin-film laminated structures have a total of 16 layers of a high refractive index film (zirconium oxide (ZrO ₂ )) and a low refractive index film (silicon oxide (SiO ₂ )) provided on the transparent substrate side. High refractive index film (titanium oxide (TiO ₂ )) and medium refractive index provided on the laminated structure (3-1 thin film laminated structure) and the 3-1 thin film laminated structure (air side) It consists of a total of 28 layers (3-2 thin film layered structure) with a film (silicon oxide (SiO ₂ )).

One thin film laminated structure is disposed on the other surface of the transparent substrate. This thin film laminated structure is a repetitive laminated structure having a total of 30 layers of a high refractive index film (zirconium oxide (ZrO ₂ )) and a low refractive index film (silicon oxide (SiO ₂ )) and a physical film thickness of 3656.75 nm. (3-3 Thin Film Laminated Structure)

Table 5 shows the configuration of the thin film laminated structure (3-1 thin film laminated structure and 3-2 thin film laminated structure) provided on one surface of the transparent substrate of the optical filter. Table 6 shows the configuration of the thin film stack structure (3-3 thin film stack structure) provided on the other surface of the transparent substrate of the optical filter. In Tables 5 and 6, the number of film layers is the ordinal number of layers from the transparent substrate side, and the film thickness indicates the physical film thickness.

The optical characteristics of the optical filter at incident angles of 0 °, 40 °, and 50 ° were verified using optical thin film simulation software (TFCalc, manufactured by Spectra, Inc.). The results are shown in FIGS. 10 and 11 (enlarged views in the wavelength region of 850 nm to 1050 nm).

Also, only the thin film laminated structure (3-1 thin film laminated structure and 3-2 thin film laminated structure) provided on one surface of the transparent substrate (excluding the influence of light absorption by the transparent substrate) The optical characteristics at 0 °, 40 ° and 50 ° of the incident angle were verified using optical thin film simulation software. The results are shown in FIG. Also, incident angles of 0 °, 40 ° and 50 ° only on the thin film laminated structure (3-3 thin film laminated structure) provided on the other surface of the transparent substrate (excluding the influence of light absorption by the transparent substrate). The optical characteristics at ° were verified using optical thin film simulation software. The results are shown in FIG.

(Comparative Example 1)
The optical filter (near infrared cut filter) according to this comparative example includes the same transparent substrate as that used in Example 1. A plurality of thin film laminated structures are provided on only one surface of the transparent substrate. This thin film laminated structure has a structure in which a high refractive index film and a low refractive index film are sequentially laminated from the transparent substrate surface side.

Five thin film laminated structures are disposed on one surface of the transparent substrate. This thin film laminated structure is a repetitive laminated structure having a total of 40 layers of a high refractive index film (titanium oxide (TiO ₂ )) and a low refractive index film (silicon oxide (SiO ₂ )) and a physical film thickness of 5151.58 nm. is there. That is, five thin film laminated structures having the same configuration are laminated on one surface of the transparent substrate.

The optical multilayer film provided on the other surface of the transparent substrate is an antireflection film. Each of the optical multilayer films has a high-refractive index film of titanium oxide (TiO ₂ ) and a low-refractive index film of silicon oxide (SiO ₂ ). is there.

Table 3 shows the configuration of the thin film laminated structure provided on one surface of the transparent substrate of the optical filter. Table 4 shows the configuration of the optical multilayer film provided on the other surface of the transparent substrate of the optical filter. In Tables 7 and 8, the number of film layers is the ordinal number of layers from the transparent substrate side, and the film thickness indicates the physical film thickness.

The optical characteristics of the optical filter at incident angles of 0 °, 40 °, and 50 ° were verified using optical thin film simulation software (TFCalc, manufactured by Spectra, Inc.). The results are shown in FIGS. 14 and 15 (enlarged views in the wavelength region of 850 nm to 1050 nm). Further, the optical thin film simulation software described above shows the optical characteristics at the incident angles of 0 °, 40 ° and 50 ° of only the thin film laminated structure (excluding the influence of light absorption by the transparent substrate) provided on one surface of the transparent substrate. It verified using. The results are shown in FIG. In addition, the optical thin film simulation software described above shows the optical characteristics at the incident angles of 0 °, 40 ° and 50 ° of only the optical multilayer film provided on the other surface of the transparent substrate (excluding the influence of light absorption by the transparent substrate). Used to verify. The results are shown in FIG.

(Comparative Example 2)
The optical filter (near-infrared cut filter) according to this comparative example includes a transparent substrate similar to that used in Example 1, and includes a thin film laminated structure only on one surface of the transparent substrate. This thin film laminated structure has a structure in which a high refractive index film and a low refractive index film are sequentially laminated from the transparent substrate surface side.

Five thin film laminated structures are disposed on one surface of the transparent substrate. Each of the five thin film laminated structures has a medium refractive index film (zirconium titanium (ZrO ₂ )), a low refractive index film (silicon oxide (SiO ₂ )), and a high refractive index film (titanium oxide (TiO ₂ )). A repetitive laminated structure having a total thickness of 56 and a physical film thickness of 7647.11 nm (third thin film laminated structure). In the third thin film laminated structure, the first layer to the twentieth layer have a repeated laminated structure in which the medium refractive index film and the low refractive index film are alternately laminated from the transparent substrate side. Up to the 56th layer is a repeated laminated structure in which high refractive index films and low refractive index films are alternately laminated. That is, this optical filter has five thin film laminated structures on one surface of a transparent substrate.

The optical multilayer film provided on the other surface of the transparent substrate is an antireflection film. This optical multilayer film is the same optical multilayer film as used in Comparative Example 1. Therefore, description of the film configuration and spectral characteristics is omitted.

Table 9 shows the configuration of the thin film laminated structure (third thin film laminated structure) provided on one surface of the transparent substrate of the optical filter. In Table 9, the number of film layers is the ordinal number of layers from the transparent substrate side, and the film thickness indicates the physical film thickness. About this optical filter, the optical characteristic in incident angles 0 degree, 40 degrees, and 50 degrees was verified using optical thin film simulation software (TFCalc, product made by Software Spectra). The results are shown in FIGS. 18 and 19 (enlarged views in the wavelength region of 850 nm to 1050 nm). Further, the optical thin film simulation software described above shows the optical characteristics at the incident angles of 0 °, 40 ° and 50 ° of only the thin film laminated structure (excluding the influence of light absorption by the transparent substrate) provided on one surface of the transparent substrate. It verified using. The results are shown in FIG.

From the above, for example, the optical filter of Example 1 has a transmittance of 850 nm to 990 nm in the near infrared region of 0.1% or less in the near infrared region even when the incident angle of light is 40 ° and 50 °, and the transmission ripple Is suppressed. Similarly, the transmittance in the visible region (450 nm to 550 nm) is 92% or more at the minimum even when the incident angle of light is 40 °, and the transmittance in the visible region is equal even when the incident angle of light is 50 °. The minimum value is 81% or more, and the reflection ripple is suppressed. Further, it has a transmittance of 0.0001% or less at wavelengths of 898 nm to 955 nm, and has a high near infrared absorption ability.

On the other hand, the optical filter of Comparative Example 1 has a minimum transmittance of 80% or less in the visible region (450 nm to 550 nm) at a light incident angle of 50 °, and the reflection ripple cannot be suppressed. The optical filter of Comparative Example 2 has a minimum transmittance of 80% or less in the visible region (450 nm to 550 nm) at a light incident angle of 50 °, and the reflection ripple cannot be suppressed. Further, even when the incident angle of light is 0 °, 40 °, and 50 °, the transmittance in the near infrared region (850 nm to 990 nm) is 0.1% or more, and the transmission ripple cannot be suppressed.

The reason why the reflection ripple in the visible region is not suppressed when the incident angle of light in Comparative Examples 1 and 2 is 50 ° is that the thin film laminated structure that restricts the transmission in the near infrared region is formed only on one surface. This is thought to be due to the fact that

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. 2018-067598 filed on Mar. 30, 2018, the contents of which are incorporated herein by reference.

DESCRIPTION OF SYMBOLS 1 ... Optical filter, 2 ... Transparent substrate, 11, 12, 13 ... Thin-film laminated structure, 10a, 10b ... Surface.

Claims

An optical filter comprising a transparent substrate and three or more thin film laminate structures that limit transmission of light in a predetermined wavelength range in the near-infrared wavelength region,
Each of the thin film laminated structures is laminated on one surface of the transparent substrate,
Of the three or more thin film laminated structures, at least two thin film laminated structures have different wavelength ranges for limiting transmission, respectively.
The wavelength range in which transmission is limited by the three or more thin film laminated structures is continuous,
An optical filter in which a wavelength region in which transmission of the thin film laminated structure disposed on the same surface side of at least one of the transparent substrates restricts transmission is discontinuous.
Among the three or more thin film laminated structures, the thin film laminated structure in which the center wavelength in the wavelength range that restricts the transmission of light having a wavelength in the near infrared region is the second shortest wavelength side is the other thin film laminated structure. 2. The optical filter according to claim 1, wherein the optical filter is laminated on a surface different from the body and has a physical film thickness that is larger than each of the other physical film thicknesses of the thin film laminated structure.
In the transmission limiting wavelength range of the thin film laminated structure, the wavelength having the center wavelength of the wavelength range that limits the transmission of light in the near-infrared region wavelength is the second shortest wavelength, the wavelength having the lowest transmittance within the wavelength range The optical filter according to claim 2, wherein the transmittance is 0.05% or less.
The optical filter according to any one of claims 1 to 3, wherein the transparent substrate is made of at least one selected from glass, glass ceramics, crystal, resin, and sapphire.
The optical filter according to claim 1, wherein the transparent substrate has a property of absorbing light having a wavelength in a near infrared region.
6. The optical filter according to claim 1, further comprising a near-infrared absorbing layer including a component that absorbs light having a wavelength in the near-infrared region on at least one surface of the transparent substrate.