CN108693584B

CN108693584B - Optical filter and solid-state imaging device using the same

Info

Publication number: CN108693584B
Application number: CN201810285686.1A
Authority: CN
Inventors: 岸田寛之
Original assignee: JSR Corp
Current assignee: JSR Corp
Priority date: 2017-04-05
Filing date: 2018-04-02
Publication date: 2022-12-30
Anticipated expiration: 2038-04-02
Also published as: JP7248173B2; JP2018180533A; JP2022118059A; CN108693584A

Abstract

An optical filter for a solid-state imaging device, which solves the disadvantages of optical filters such as a conventional near-infrared cut filter, has excellent transmission characteristics in a visible wavelength region of 70% or more and excellent shielding properties in a near-infrared wavelength region of an OD value of 2 or more, has little dependence on an incident angle in a green color of a wavelength of about 500nm in addition to a red color and a blue color in a visible wavelength region in air, has few ghost images, is inexpensive, thin, and has little warpage, and a solid-state imaging device using the optical filter. The optical filter for a solid-state imaging device is an optical filter including a substrate having transparency and a dielectric multilayer film having a buffer layer on at least one surface of the substrate, and has a measured transmittance of 70% or more for unpolarized light of 500nm in the air at an incidence of 0 DEG to 40 DEG, and an OD value of 2 or more for unpolarized light at an incidence of 0 DEG in the near-infrared wavelength region.

Description

Optical filter and solid-state imaging device using the same

Technical Field

The present invention relates to an optical filter, and more particularly, to an optical filter for a solid-state imaging device and a solid-state imaging device using the same.

Background

Solid-state imaging devices such as video cameras (video cameras), digital still cameras (digital still cameras), and mobile phones with camera functions use Charge Coupled Devices (CCDs) or Complementary Metal-Oxide-Semiconductor (CMOS) image sensors as solid-state imaging elements for color images, and these solid-state imaging elements use silicon photodiodes having sensitivity in the near-infrared wavelength region that is not perceived by the human eye in their light receiving portions. These solid-state imaging devices mainly include three kinds of pixels, namely, red, blue, and green, and require a sensitivity correction for adjusting the color tone that appears natural to the human eye for the intensity of red, blue, and green detected by each pixel, and optical filters that selectively transmit or cut (block) light rays in a specific wavelength region are often used. As for the optical filter used for the solid-state imaging device, particularly, the cut-off performance of light in the near infrared wavelength region having a wavelength of 735nm or more and 1100nm or less is important, and the cut-off performance required for the optical filter is not sufficient even if the average transmittance in the near infrared wavelength region is 5% or less with the recent improvement in the sensitivity of silicon photodiodes. In order to have sufficient cutoff performance in various light sources, it is required that the Optical Density (Optical Density: OD) is 2 or more in the near infrared wavelength region. In the optical filter, an absorbent such as phosphate glass, fluorophosphate glass, cesium tungstic acid, phthalocyanine, diimmonium dye has been used since before, but when these absorbents are used at a concentration that achieves an OD value of 2 or more in the near infrared wavelength region, there is a problem that the transmittance in the visible wavelength region is lowered or that it is difficult to make the optical filter thin.

As an optical filter that achieves an OD value of 2 or more in the near infrared wavelength region, and that achieves both high transmittance in the visible wavelength region and thinning, an optical filter provided with a dielectric multilayer film is known. However, with the recent miniaturization and thinning of digital cameras, digital video cameras (digital video cameras), and the like, the wide angle of the digital cameras, digital video cameras, and the like has been increased, and thus the incident angle dependency of the dielectric multilayer film provided on the optical filter has become a problem. For example, in the optical spectrum of an optical filter provided with a dielectric multilayer film, the rising position from the light transmission blocking band to the light transmission band is shifted (moved) by the incident angle of light, and the light amount of the range (light transmission band) that affects the image quality changes. In addition, the optical spectrum shifts to the short wavelength side as the light changes from the vertically incident light to the obliquely incident light.

In order to improve such movement, optical filters comprising a dielectric multilayer film and an absorber combined together, which are produced by various methods, have been known from the past, and for example, optical filters such as a near-infrared cut filter using a transparent resin as a substrate and containing a near-infrared absorbing dye in the transparent resin have been known (for example, see patent document 1). The present applicant has also proposed an optical filter including a layer containing a squarylium salt compound having a specific chemical structure (see patent document 2). When such an optical filter is used, the incident angle dependence of the optical characteristics in the near infrared wavelength region can be reduced, and the viewing angle of red can be improved as compared with the existing optical filter.

Further, in an optical filter such as a near-infrared cut filter in which a substrate contains a near-ultraviolet absorbing dye, the incident angle dependency of blue or violet can be improved (for example, see patent documents 3 to 5).

However, in these optical filters, the incident angle dependency of red or blue with respect to the near infrared ray is reduced, but when the incident angle dependency is made to the dielectric multilayer film at a high angle, the incident angle dependency due to the reduction of the transmittance of green visible light, which is a transmission region of a wavelength of approximately half of the reflection region of the dielectric multilayer film, cannot be sufficiently improved.

Documents of the prior art

Patent document

Patent document 1 Japanese patent laid-open No. Hei 6-200113

Patent document 2 Japanese patent laid-open No. 2012-8532

Patent document 3 Japanese patent laid-open publication No. 2013-190553

International publication No. 2014/002864 in patent document 4

International publication No. 2015/099060 of patent document 5

Disclosure of Invention

Problems to be solved by the invention

The purpose of the present invention is to provide an optical filter for a solid-state imaging device, which improves the disadvantages of conventional optical filters such as near-infrared cut-off filters, has excellent transmission characteristics of 70% or more in the visible wavelength region and excellent shielding properties of an OD value of 2 or more in the near-infrared wavelength region, has little dependence on the incident angle in the air not only in the red and blue colors in the visible wavelength region but also in the green color around a wavelength of 500nm, has few ghost images, is inexpensive, thin, and has little warpage, and a solid-state imaging device using the optical filter.

Means for solving the problems

The present inventors have made diligent studies to solve the above problems. As a result, the present inventors have found that the above problems can be solved by an optical filter which has a dielectric multilayer film provided on at least one surface and satisfies the following (a) and (B), and have completed the present invention.

(A) The actual transmittance in the range of 0 DEG to 40 DEG of an unpolarized light ray having a wavelength of 500nm in air is 70% or more.

(B) The minimum value of the OD value of 0 DEG incidence of unpolarized light rays having a wavelength of 735nm to 1100nm in the air is 2 or more.

The invention provides a solid-state imaging device comprising the optical filter.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, an optical filter for a solid-state imaging device, which has excellent transmission characteristics of 70% or more of the visible wavelength region and excellent shielding properties in the near infrared wavelength region, has little incident angle dependency particularly around a wavelength of 500nm in addition to red and blue in the visible wavelength region in air, is inexpensive, thin, and has little warpage, and a device using the optical filter, can be provided.

Drawings

FIG. 1 is a schematic cross-sectional view of an optical filter according to the present invention.

Fig. 2 is a schematic cross-sectional view of an optical filter solid-state imaging device according to the present invention.

Fig. 3 (a) is a schematic diagram showing a method for measuring the transmittance of the optical filter of the present invention. Fig. 3 (b) is a schematic view showing a method for measuring the reflectance of the optical filter of the present invention.

Fig. 4 is a trace of the dielectric multilayer film included in the optical filter of example 1 of the present invention when the incident angle of the equivalent admittance of the unpolarized light ray of the film design 1 is changed from 0 ° to 40 °.

Fig. 5 (a) and 5 (b) are traces of incident angles of 0 ° to 40 ° of the difference between the equivalent admittance and the vacuum admittance of an unpolarized light ray of the film design 1, which is the dielectric multilayer film included in the optical filter of example 1 of the present invention. Fig. 5 (a) is an overall view of the 0 ° to 40 ° locus, and fig. 5 (b) is an enlarged view of the 0 ° to 20 ° locus.

Fig. 6 (a) and 6 (b) show the transmittance of unpolarized light when the incident angle of 500nm in air is changed in the optical filter of example 1 of the present invention. Fig. 6 (c) shows the reflectance measured by the dielectric multilayer film of film design 1 of an unpolarized light beam when the incident angle of 500nm in the air of the optical filter of example 1 of the present invention was changed.

Fig. 7 is a trace of the equivalent admittance of an unpolarized light ray when the incident angle of the film design 2 is changed, which is a dielectric multilayer film included in the optical filter of example 3 of the present invention.

Fig. 8 is a trace of incident angles 0 ° to 40 ° of the difference between the equivalent admittance and the vacuum admittance of an unpolarized light ray of the film design 2, which is a dielectric multilayer film included in the optical filter of example 3 of the present invention.

Fig. 9 (a) shows the transmittance of unpolarized light when the incident angle of 500nm in air is changed in the optical filter of example 3 of the present invention. Fig. 9 (b) shows the reflectance measured by the dielectric multilayer film of film design 2 of an unpolarized light beam when the incident angle of 500nm in the air of the optical filter of example 3 of the present invention was changed.

Fig. 10 is a trace of the equivalent admittance of an unpolarized light ray when the incident angle of the film design 3 is changed, which is a dielectric multilayer film of the conventional optical filter, that is, the comparative example 1.

Fig. 11 (a) and 11 (b) are traces of incident angles of 0 ° to 40 ° of the difference between the equivalent admittance and the vacuum admittance of an unpolarized light ray when the incident angle of the film design 3 is changed, which are the dielectric multilayer films included in the conventional optical filter, i.e., the comparative example 1. Fig. 11 (a) is an overall view of the 0 ° to 40 ° locus, and fig. 11 (b) is an enlarged view of the 0 ° to 20 ° locus.

Fig. 12 (a) shows the transmittance of unpolarized light when the incident angle of 500nm in the air is changed in the optical filter of comparative example 1, which is a conventional optical filter. Fig. 12 (b) shows the reflectance of an unpolarized light beam measured by the dielectric multilayer film of film design 3 when the incident angle of 500nm in the air of the optical filter of comparative example 1, which is a conventional optical filter.

Description of the symbols

1: a substrate;

2: a perpendicular line drawn from the optical filter;

3: incident light;

4: emergent light;

10: an optical filter;

11: optical admittance of incident medium being Y ₀ ＝n ₀ ；

12: the optical admittance of the emergent medium is Y ₀ ＝n ₀ ；

21: a dielectric multilayer film having a buffer layer provided on one face;

22: refractive index n of high refractive index layer _H ；

23: refractive index n of low refractive index layer _L ；

24: a high refractive index layer contained in the buffer layer;

25: a low refractive index layer included in the buffer layer;

31: a dielectric multilayer film provided on a light exit side;

32: refractive index n of high refractive index layer _H ；

33: refractive index n of low refractive index layer _L ；

100: a solid-state imaging device;

101: a solid-state imaging element;

l1 to L3: a lens group of the solid-state imaging device;

201: incident light;

202: transmitting light;

203: reflecting the light;

204: incident light from the other face of the optical filter;

205: reflected light from the other surface of the optical filter;

211: a detector;

212: a detector;

n ₀ : refractive indexes of the incident medium and the emergent medium;

θ ₀ : incident angles of the incident medium and the emergent medium;

n _m : the refractive index of the substrate;

θ _m : angle of incidence in the substrate.

Detailed Description

The following shows examples of embodiments of the invention of the present application. The embodiments shown in the drawings are merely for illustrative and exemplary purposes and do not limit the invention defined by the claims. The following detailed description of the illustrated embodiments should be read in connection with the following drawings. In the drawings, the same components are denoted by the same reference numerals.

The embodiments of the present invention will be described based on the drawings, which are provided for illustration only, and the present invention is not limited to these drawings. Note that the drawings are schematic drawings, and it should be noted that the relationship between the thickness and the plane size, the ratio of the thicknesses, and the like may be different from the actual case. In the following description, the same or substantially the same functions and configurations are denoted by the same reference numerals, and redundant description thereof is omitted.

FIG. 1 is a schematic cross-sectional view of an optical filter. The optical filter 10 shown in fig. 1 includes: a substrate 1 having transparency, and a dielectric multilayer film 21 having a buffer layer (in fig. 1, a high refractive index layer 24 and a low refractive index layer 25) on at least one surface (surface on the light incident side) of the substrate 1. The other surface (light-emitting surface) of the substrate 1 may have a dielectric multilayer film 31. In fig. 1, an incident medium 11 is present on the light incident side of the optical filter 10, and an emission medium 12 is present on the light emitting side. The structures of the dielectric multilayer film 21 and the dielectric multilayer film 31 are not limited to those shown in fig. 1. The structure of the dielectric multilayer film 21 and the dielectric multilayer film 31 will be described in detail later.

[ Properties of optical Filter ]

The optical filter of the present invention satisfies the following (a) and (B).

(A) The actually measured transmittance of the unpolarized light having a wavelength of 500nm in air is 70% or more in a range of 0 DEG to 40 deg.

(B) The OD value of 0 DEG incidence of unpolarized light rays having a wavelength of 735nm to 1100nm in the air is 2 or more.

The optical filter of the present invention preferably satisfies the following (D).

(D) The measured reflectance in air of unpolarized light having a wavelength of 500nm incident from at least one of the faces has at least two minima in the range of an incident angle of 0 DEG to 40 deg.

When the reflectance is minimized to 2 degrees, the incident angle dependency of 500nm is reduced, and the incident angle dependency of green of the image pickup device provided with the optical filter is reduced and improved. More preferably, the minimum value is 3 times.

The optical filter of the present invention preferably further satisfies the following (E).

(E) The actually measured transmittance in air of unpolarized light having a wavelength of 500nm incident from at least one surface has at least two maxima in the range of an incident angle of 0 DEG to 40 deg.

When the optical filter has a maximum value of 2-order transmittance, the incident angle dependency of 500nm is reduced, and the incident angle dependency of green of the image pickup device provided with the optical filter is reduced and favorable. More preferably, the maximum value is 3 times.

The dielectric multilayer film of the optical filter of the present invention preferably further includes at least one buffer layer satisfying the following (F) to (H).

(F) The buffer layer has 1 or more low-refractive-index layers each having a refractive index of 1.0 to 1.8, and a high-refractive-index layer having a refractive index of 1.9 to 2.8.

(G) The physical film thicknesses of the low refractive index layer and the high refractive index layer are respectively 60nm or less.

(H) The buffer layer is a layer of 4 or more layers from the substrate, and the low refractive index layer and the high refractive index layer which are present on the layer other than the outermost layer and are alternately laminated are continuously laminated by at least two layers.

The buffer layer facilitates the following: the measured reflectance of unpolarized light having a wavelength of 500nm incident from the at least one surface has at least two minima in the range of an incident angle of 0 ° to 40 °, and the following are facilitated: the actually measured transmittance of unpolarized light having a wavelength of 500nm has at least two maxima at an incident angle of 0 DEG to 40 deg.

The buffer layer is preferably present within 16 layers from the substrate toward the outside.

The number of layers of the dielectric multilayer film is preferably 16 to 60.

The optical filter of the present invention preferably satisfies the following (I).

(I) The average of measured transmittance at 0 DEG incidence in air of unpolarized light rays of 450 to 630nm incident from at least one surface of the optical filter is 75% or more.

The optical filter is preferably included in the image pickup element.

[ base plate ]

The substrate 1 has a function as a support substrate, for example. The substrate 1 has transparency and has transparency to light having a wavelength at least in the visible wavelength range. The visible wavelength region is preferably a region including wavelengths of 400nm or more and less than 700nm, for example, and light in the visible wavelength region is visible light. The substrate is transparent, and has a transmittance of light of any wavelength exceeding 50%.

As the substrate, for example, at least one of a silicate glass substrate, a borosilicate glass substrate, a phosphate glass substrate, a fluorophosphate glass substrate, a plastic substrate, and a resin film substrate can be used. The glass transition temperature is preferably 140 ℃ or higher, and the resin film substrate is more preferably included for the purpose of being hard to break. Preferably, the refractive index at a wavelength of 500nm is 1.40 to 1.7. The substrate preferably contains a near-infrared absorbent, and preferably contains at least one selected from inorganic near-infrared absorbents such as cesium tungsten oxide and copper (II) oxide, near-infrared absorbents utilizing surface plasmon such as gold nanorods, organic near-infrared absorbents such as cyanine pigments and squarylium pigments, and metal complex near-infrared absorbents such as metal dithiol complexes and metal phthalocyanine complexes. By including these near infrared absorbers, the incident angle dependency of red color can be reduced, and the number of stacked dielectric multilayer films can be reduced. Thereby, the incident angle dependency of the visible light transmittance at a wavelength of about 500nm can be reduced. The substrate preferably contains a near-ultraviolet absorber, which can reduce the incident angle dependence of blue.

The substrate preferably includes a plurality of layers from the viewpoint of resistance to cracking, or easiness of addition of a light absorbing agent, and provision of functions or effects. The functions to be imparted include: conductivity, antistatic effect, foreign matter adhesion preventing effect, scratch preventing effect, antifogging property, heat resistance improving effect, gas barrier property, high elasticity, scratch eliminating effect, flatness, roughness, hygroscopicity, aging preventing effect, etc. The number of layers of the substrate is preferably 2 to 5, and if the number of layers is 6 or more, the adhesion between the substrates may be reduced or the manufacturing cost may be increased. The refractive index of each layer is preferably as close as possible, and the difference in refractive index between the layers is preferably 0.3 or less.

The total film thickness of the substrate is preferably 30 μm or more and 200 μm or less, and in the above range, it is useful for thinning the solid-state imaging device. More preferably 40 μm to 150 μm, and still more preferably 34 μm to 110 μm. In the above range, the solid-state imaging device can be preferably used for a thin solid-state imaging device having a total thickness of 6.5mm or less. If the film thickness is less than 30 μm, warpage and cracking may easily occur.

[ dielectric multilayer film ]

As shown in fig. 1, for example, the optical filter of the present invention has a dielectric multilayer film 21 on at least one surface of a transparent substrate, and the dielectric multilayer film 21 includes a plurality of dielectric layers in which high refractive index layers (H) 22 provided on the surface of the substrate 1 on the incident side and low refractive index layers (L) 23 laminated in contact with the high refractive index layers 22 are alternately laminated.

The dielectric multilayer film 21 has the following optical characteristics: has a light transmission band in a visible wavelength region and has a shielding property in a near infrared wavelength region and a near ultraviolet region. The near-infrared wavelength region is, for example, preferably a region including a wavelength of 735nm or more and less than 1100nm, more preferably a wavelength of 720nm or more and 1100nm or less, and further preferably 710nm or more and 1100nm or less, and has optical characteristics having shielding performance in the near-infrared wavelength region, near-infrared rays invisible to human eyes can be sufficiently shielded. In addition, the light in the near infrared wavelength region is near infrared. The near-ultraviolet wavelength region is preferably a region including a wavelength of 250nm or more and less than 400nm, for example, and light in the near-ultraviolet wavelength region is near-ultraviolet light. By having optical characteristics having shielding performance in the near infrared wavelength region, for example, the light transmittance in the visible wavelength region is easily improved as compared with the case where the shielding performance in the near infrared wavelength region is achieved only with the near infrared ray absorber.

When the refractive index of the material with a wavelength of 500nm is n _H The high refractive index layer 22 preferably has a refractive index of, for example, 2.0 or more. As the high refractive index layer 22, for example, a layer containing titanium oxide (TiO) can be used ₂ ) Tantalum oxide (Ta) ₂ O ₅ ) Niobium oxide (Nb) ₂ O ₅ ) Or a film of a composite oxide of these. In addition, if the refractive index is 2.0 or more, an additive may be contained. Further, n is _H The high level is advantageous for suppressing the amount of wavelength shift at oblique incidence, for preventing the band from being expanded by light transmission on the ultraviolet side, and the like. Therefore, titanium oxide and niobium oxide having higher refractive indices are more preferable as the high refractive index layer among the three substances.

When the refractive index at a wavelength of 500nm is defined as n _L The low refractive index layer 23 preferably has a refractive index of 1.7 or less with respect to light having a wavelength of 500nm, for example, and more preferably has a refractive index lower than that of the outermost layer of the substrate having transparency. As the low refractive index layer 23, for example, silicon oxide (SiO) can be used ₂ ) Magnesium fluoride (MgF) ₂ ) Or a film of a composite oxide of these. In addition, if n _L The refractive index of the outermost layer of the transparent substrate is 1.7 or less, and the additive may be contained.

The dielectric layers such as the high refractive index layer 22 and the low refractive index layer 23 are formed by, for example, sputtering, vacuum Deposition, ion-assisted vacuum Deposition, or Chemical Vapor Deposition (CVD). In particular, it is preferable to form the dielectric layer by sputtering, vacuum evaporation, or ion-assisted vacuum evaporation. The light transmission band is a wavelength range used for receiving light from a solid-state imaging device such as a CCD image sensor or a CMOS image sensor, and it is important to determine the thickness accuracy of the dielectric layer. The sputtering method, the vacuum evaporation method, and the ion-assisted vacuum evaporation method are excellent in thickness control in forming the dielectric layer. Therefore, by forming the dielectric layers by using these methods, the accuracy of the thickness of each layer constituting the dielectric multilayer film in which the dielectric layers are laminated can be improved, and a dielectric multilayer film having desired optical characteristics can be obtained. Among these methods, ion-assisted vacuum deposition is more preferable from the viewpoint of controlling the film formation rate and the film thickness at the same time.

The dielectric multilayer film may be provided on one surface of the substrate having transparency, and may be provided on both surfaces. In fig. 1, a dielectric multilayer film 31 is provided on not only the incident-side surface but also the exit-side surface of the substrate 1, and the dielectric multilayer film 31 includes a plurality of dielectric layers in which high refractive index layers (H) 32 and low refractive index layers (L) 33 laminated in contact with the high refractive index layers 32 are alternately laminated. When the dielectric multilayer film is provided on both surfaces of the substrate, it is expected that the visible light transmittance is improved by reducing reflection in the visible light region on both surfaces of the substrate, and it is preferable for reducing warpage.

[ optical characteristics of dielectric multilayer film ]

The optical characteristics of the dielectric multilayer film are described by a characteristic matrix (or a characteristic square matrix).

[ Property matrix ]

A characteristic matrix (or characteristic square matrix) M1 of the single layer in the dielectric multilayer film is represented by the following equation.

[ number 1]

[ number 2]

Here, n is the refractive index of the single layer, λ is the wavelength of light, and d is the physical film thickness of the single layer.

When the number of layers of the dielectric multilayer film is L, a characteristic matrix (or a characteristic square matrix) M of the entire L-layer film is given by the following equation based on the product of the characteristic matrices of the respective layers.

[ number 3]

[ number 4]

[ number 5]

Here, M1 is a characteristic matrix of the first film (incident-side outermost layer) on which light is incident, similarly to the characteristic matrix of the single layer, and M _j A property matrix of a layer located on the j-th layer toward the substrate side so that the first film on which light is incident is the 1 st layer. In addition, n is _j The refractive index of the layer lying on the j-th layer, d _j Similarly, the physical film thickness of the layer located on the j-th layer is set.

[ Property matrix of dielectric multilayer film ]

The characteristic matrix (or characteristic square matrix) including the substrate is represented by the following expression.

[ number 6]

Here, nm is the refractive index of the substrate.

Equivalent admittance Y of dielectric multilayer film _E This is represented by the following equation. Here, the "equivalent admittance" refers to admittance when the dielectric multilayer film is regarded as one layer.

[ number 7]

Y _E ＝C/B (7)

The theoretical transmittance T of the dielectric multilayer film at each wavelength is represented by the following formula.

[ number 8]

Here, Y ₀ Indicating the optical admittance, Y, of the incident and emergent media _m Represents the optical admittance of the substrate, re () represents the real part, and () -) represents the complex conjugate. Here, "optical admittance" refers to a coefficient (a value obtained by dividing an electric field by an amplitude of the magnetic field, a dimension is the same as a refractive index, and √ (dielectric constant/magnetic permeability) × refractive index) that relates the amplitude of the magnetic field to the electric field. In the case where the incident medium is air, Y ₀ Optical admittance using a vacuum, and refractive index 1.0 using a vacuum. Here, Y _m Approximated by the refractive index of the substrate.

The theoretical transmittance of the optical filter is an internal transmittance that takes in the absorption in the substrate or the reflectance at the substrate interface, and is a theoretical reflectance when light is emitted from the substrate. In the case of having a dielectric multilayer film on both surfaces, a characteristic matrix of the dielectric multilayer film on the emission side can be obtained in the same manner, and the theoretical transmittance can be obtained.

Such as represented by the formula Y ₀ The optical admittance of the incident medium revealed that the transmittance of the dielectric multilayer film greatly depended on the incident medium. Therefore, the transmittance of the dielectric multilayer film must be estimated strictly by differentiating the incident medium, and cannot be compared with the transmittance result obtained by mixing the incident media without differentiating the incident medium.

A characteristic matrix (or a characteristic square matrix) M' of the entire q-layer film of the q-layer dielectric multilayer film provided on the light emitting side is given by the following equation based on the product of the characteristic matrices of the respective layers.

[ number 9]

[ number 10]

[ number 11]

Here, M ₁ ' is the last layer (exit side outermost layer) from which light exits, M _i ' A layer located on the j-th layer toward the substrate side so as to have the last layer from which light is emitted as the 1 st layer, M _q ' is a layer adjacent to the substrate. Equivalent admittance Y of dielectric multilayer film arranged on light emergent side _E ' is represented by the following equation.

[ number 12]

Y＇ _E ＝C′/B′ (12)

The theoretical transmittance Tt of an optical filter in which dielectric multilayer films are provided on both surfaces of a transparent substrate is represented by the following formula. Furthermore, multiple reflections between dielectric multilayer films disposed on both sides are slight and thus are neglected.

[ number 13]

Such as represented by the formula Y ₀ The theoretical transmittance T of the optical filter is known for the optical admittance of the incident medium and the emergent medium _t Greatly depends on the incident medium. Therefore, the theoretical transmittance T of the optical filter _t The incident medium must be strictly differentiated for estimation and cannot be compared with the result of not differentiating the incident medium.

When the incident medium and the exit medium are air, the passing pair Y ₀ Substituting the refractive index of air to 1.0 to obtain the theoretical transmittance T _t The measured transmittance was regarded as the measured transmittance. It was found that the actual transmittance of the dielectric multilayer film can be controlled by appropriately designing the equivalent admittance using the numerical expressions (3) to (13).

The dielectric multilayer film preferably satisfies the following (C).

(C) Wavelength of 500nm or lessIs equivalent admittance Y in air _E And optical admittance Y with vacuum ₀ Has at least two minima in the range of 0 to 40 ° of the incident angle.

In the case of the dielectric multilayer film satisfying (C), the following is facilitated: the measured reflectance of an unpolarized light ray having a wavelength of 500nm incident from the at least one surface has at least two minima in the range of an incident angle of 0 ° to 40 °, and makes it easy to: the actually measured transmittance of unpolarized light having a wavelength of 500nm has at least two maxima at an incident angle of 0 DEG to 40 deg.

The theoretical reflectance R of the dielectric multilayer film provided on the light incident side at each wavelength is represented by the following formula.

[ number 14]

Such as represented by formula (II) wherein Y ₀ The reflectance R of the dielectric multilayer film greatly depends on the incident medium, as seen from the optical admittance of the incident medium and the emission medium. Therefore, the reflectance R of the dielectric multilayer film must be estimated strictly by differentiating the incident medium, and cannot be compared with the result of not differentiating the incident medium.

The theoretical reflectance R' of each wavelength of the dielectric multilayer film provided on the light exit side is represented by the following formula.

[ number 15]

Such as represented by formula (II) wherein Y ₀ The theoretical reflectance R' of the dielectric multilayer film is known to greatly depend on the exit medium for optical admittance of the incident medium and the exit medium. Therefore, the theoretical reflectance R' of the dielectric multilayer film must be estimated by strictly distinguishing the emission medium, and cannot be compared with the result of not distinguishing the mixture of the emission media.

On both sides of a substrate having transparencyTheoretical reflectance R of optical filter provided with dielectric multilayer film _t This is represented by the following equation. Furthermore, multiple reflections between dielectric multilayer films disposed on both sides are slight and therefore negligible.

[ number 16]

R _t = R + (1-R) × (internal transmittance of substrate) ² ×R′ (16)

Theoretical reflectance R of light incident on the other surface (opposite surface) of the optical filter _t 'is obtained by replacing R and R' of the above formula.

When the incident medium and the exit medium are air, the passing pair Y ₀ Optical admittance into vacuum: refractive index of 1.0 and theoretical reflectivity R _t ' is considered the measured reflectance. Further, it was found that the actual reflectance of the dielectric multilayer film can be controlled by appropriately designing the equivalent admittance using the numerical expressions (3) to (12) and the numerical expressions (14) to (16).

In the case of light obliquely incident on the optical filter, the optical characteristics in the dielectric multilayer film greatly depend on the polarization state of the incident light. Therefore, the optical characteristics of the dielectric multilayer film must be estimated strictly by differentiating the polarization state, and cannot be compared with the results of transmittance and reflectance which are mixed without differentiating the polarization state. In the case of TE mode, which is S-polarized electromagnetic radiation, and TM mode, which is P-polarized electromagnetic radiation, the following equations are substituted for the optical admittance, the characteristic matrix, and the refractive index, respectively.

That is, in the case of an incident medium, the optical admittance is instead expressed by the following equation.

[ number 17]

That is, the characteristic matrix of the dielectric multilayer film is replaced with the following formula.

[ number 18]

[ number 19]

That is, in the case of the substrate, the optical admittance is replaced with the following expression.

[ number 20]

In addition, regarding the refractive index and the incident angle in each layer, the following expression holds according to Snell's law.

[ number 21]

n ₀ sinθ ₀ ＝n _j sinθ _j ＝n _m sinθ _m ( ₂₁ )

Here, n is ₀ Denotes refractive indexes, θ, of the incident medium 11 and the emission medium 12 ₀ The incident angles of the incident medium 11 and the emission medium 12 (in fig. 1, the angles formed by the incident light 3 and the emission light 4 and the perpendicular line 2 drawn from the optical filter) are shown, θ _j The incident angle, θ, of the layer located on the j-th layer toward the substrate side with the first layer on which light is incident being defined as the 1 st layer _m Indicating the angle of incidence in the substrate.

When the incident light 3 is unpolarized light, the theoretical transmittance and the theoretical reflectance are approximated by averaging the TE mode and the TM mode.

From expressions (1) to (21) used for oblique incidence, it is known that the reflection range of the dielectric multilayer film shifts to a shorter wavelength as the incidence angle increases.

Here, in order to obtain an optical filter which has little dependence on an incident angle even at a wavelength of around 500nm, particularly in the air, and which is excellent in visible light transmittance characteristics and near infrared ray shielding properties, it is important to have a dielectric multilayer film structure.

Each layer of the dielectric multilayer film is preferably a reflection-forming layer having an Optical Thickness of 1/4 wavelength (Quarter-wave Optical Thickness: QWOT)) of the wavelength at which reflection is performed, in addition to the layer extending from the substrate to the outside and up to 2 layers, the outermost layer, the buffer layer, and the buffer layer portion. The QWOT is an optical thickness represented by a magnification of 1/4 of the wavelength of light having a specific wavelength (for example, light having a wavelength of 900 nm).

The optical thickness is a physical quantity represented by the product of the refractive index of the layer and the physical film thickness. Here, the reflection formation layer that reflects light of the predetermined specific wavelength is preferably any wavelength designed to be 700nm to 1200nm inclusive, and is preferably a physical film thickness and a refractive index having a QWOT of 0.75 to 1.25 inclusive.

The physical film thickness of the layer extending from the substrate to the outside to 2 layers is preferably 50nm or less in order to prevent reflection in a wide range of the visible wavelength region, and the QWOT of the outermost layer is preferably 0.3 or more and 0.74 or less in order to reduce the reflection intensity in the visible wavelength region.

For example, one of the dielectric multilayer films has a low refractive index layer having a refractive index of 1.0 to 1.8 and a high refractive index layer having a refractive index of 2.0 to 2.8. The case where the absolute value of the difference between the equivalent admittance of the wavelength 500nm and the optical admittance of vacuum of the dielectric multilayer film has 1-order minimum value between the incident angle 0 ° and 40 ° can be obtained as follows: the correction coefficient A is multiplied by each film thickness of the multilayer film design which is minimum at the incident angle 0 DEG so as to be minimum between the incident angles 1 DEG to 39 deg. When the minimum incident angle is θ, the correction coefficient a is generally given by the following equation.

[ number 22]

A＝cos{arcsin[(n/n′)sinθ]}/{1-[(n/n′)sinθ] ² } (22)

Here, n is a refractive index of the medium incident to the layer, and n' is a refractive index of the layer.

[ buffer layer ]

The buffer layer is a layer (a layer of 4 or more layers from the substrate) other than the layer extending from the substrate toward the outside to 3 layers included in the dielectric multilayer film, is a layer other than the outermost layer, and is a continuous layer having a physical film thickness of 60nm or less in at least two layers. The layers having a physical film thickness of 60nm or less correspond to the high refractive index layer 24 and the low refractive index layer 25 in fig. 1. Although not shown, if a high refractive index layer and a low refractive index layer are alternately stacked in a layer having a physical film thickness of 60nm or less, 3 or more layers may be stacked, and the number of stacked layers may be an odd number.

More preferably, the buffer layer includes at least two sets of buffer layers each having a physical film thickness of 60nm or less in which 2 continuous layers are included. More preferably, the buffer layer portion preferably includes 5 buffer layers of a group of continuous 2 buffer layers having a physical film thickness of 60nm or less, a layer adjacent thereto having a physical film thickness of 60nm or less, and a group of continuous 2 buffer layers adjacent thereto having a physical film thickness of 60nm or less. More preferably, the buffer layer portion preferably has 8 layers including a group of buffer layers having a physical film thickness of 60nm or less in 2 consecutive layers, a layer having a physical film thickness of 60nm or less adjacent thereto, a group of buffer layers having a physical film thickness of 60nm or less in 2 consecutive layers adjacent thereto, a layer having a physical film thickness of 60nm or less adjacent thereto, and a group of buffer layers having a physical film thickness of 60nm or less in 2 consecutive layers adjacent thereto. More preferably, the buffer layer portion includes 11 buffer layer portions including a group of buffer layers having a physical film thickness of 60nm or less in 2 consecutive layers, a layer having a physical film thickness of 60nm or less adjacent thereto, a group of buffer layers having a physical film thickness of 60nm or less in 2 consecutive layers adjacent thereto, a group of buffer layers having a physical film thickness of 60nm or more adjacent thereto, a layer having a physical film thickness of 60nm or more adjacent thereto, and a group of buffer layers having a physical film thickness of 60nm or less in 2 consecutive layers adjacent thereto. By providing these buffer layers or buffer layer parts, it is easy to develop a configuration in which the absolute value of the difference between the equivalent admittance at a wavelength of 500nm in air and the optical admittance in vacuum in the dielectric multilayer film has at least two minima in the range of the incident angle 0 ° to 40 °. The absolute value of the difference between the equivalent admittance at a wavelength of 500nm in air and the optical admittance in vacuum in the dielectric multilayer film is preferably at least two minima between the incident angles 0 ° and 37 °, more preferably at least two minima in the range of 5 ° to 35 °. More preferably, the minimum value is at least three times in the range of 0 ° to 35 °. When the angle is within the above range, the incident angle of 500nm at 0 to 40 ℃ is highly dependent.

For the equivalent admittance of the dielectric multilayer film having the buffer layer, the locus of 0 ° to 40 ° of the unpolarized light ray when a real number (real part) is provided to the horizontal axis and an imaginary number (imaginary part) is provided to the vertical axis is preferably an arc that traces twice through the same point. An optical filter including a dielectric multilayer film having a design that draws an arc passing through the same point twice is suitable as an optical filter for a solid-state imaging device. The group of 2 continuous layers having a physical film thickness of 60nm or less, which are located outside the substrate toward the outside and up to 3 layers (4 or more layers from the substrate), is preferably 4 groups (8 layers) or less. In a dielectric multilayer film in which 60nm or less layers are introduced, the cutoff region tends to be narrowed as the number of layers of 60nm or less layers increases, as compared with a dielectric multilayer film in which QWOT is stacked with the same number of layers. In the case of a layer having more than 8 layers and 60nm or less, it tends to be difficult to sufficiently cut off the near-infrared wavelength region at an OD value of 2 or more.

The relation between the number S of buffer layers and the number Q of reflection forming layers is preferably 0.15 < S/Q < 0.4, more preferably 0.15 < S/Q < 0.35. If the angle is 0.15 or less, the incident angle dependency cannot be sufficiently improved. In the case of 0.4 or more, it is difficult to effectively provide a shielding property having an OD value of 2 or more in a near infrared wavelength region of 735nm or more and 1100nm or less while maintaining good transmittance in a visible wavelength region due to narrowing of the cut-off region.

In the optical filter of the present embodiment including the dielectric multilayer film having the above features, the variation of the transmittance at a wavelength of 500nm due to the difference in the incident angle of 0 ° to 40 ° is controlled to be a low value. This can suppress variation in the amount of light taken in, and therefore can suppress the incident angle dependency of green, and can be suitably used for a solid-state imaging device.

The buffer layer is preferably included in 16 layers in the dielectric multilayer film from the substrate toward the outside. More preferably, the content is preferably within 14 layers. When the buffer layer is provided at a position at least as far as the substrate 17, as is known from japanese patent laid-open No. 2016-012096, a bandpass filter having a transmission range formed in a reflection range is formed, and it is difficult to satisfy, for example, that the minimum value of the OD value at 0 ° incidence of unpolarized light having a wavelength in the near-infrared wavelength range of 735nm to 1100nm is 2 or more. Further, adjustment of the equivalent admittance is insufficient, and it is difficult to exhibit excellent incident angle dependency.

The optical filter is preferably an optical filter in which the minimum value of the OD value of unpolarized light incident at 0 ° in the near-infrared wavelength region having a wavelength of 735nm or more and 1100nm or less in air is 2 or more, for example. More preferably, the OD value is 2.3 or more, and if the OD value is 2.3 or more, a solid-state imaging device capable of suitably imaging a halogen heater or the like that emits a large amount of near infrared rays can be obtained. More preferably, the OD value is 2.6 or more, and if the OD value is 2.6 or more, a solid-state imaging device capable of suitably imaging an object that emits light by blackbody radiation can be obtained. More preferably, the OD value is 3 or more, and if the OD value is 3 or more, near infrared rays invisible to human eyes can be sufficiently shielded. In addition, the OD value is preferably achieved in a wavelength range of 720nm to 1100nm, more preferably 710nm to 1100nm, depending on the near-infrared wavelength region to be shielded. By shielding the range, near infrared rays that cannot be seen by human eyes can be sufficiently shielded. The OD value is preferably 2 or more in a minimum value even in an unpolarized light beam incident at 40 ° in a near infrared wavelength region having a wavelength of 735nm or more and 1100nm or less. The OD value is more preferably 2.3 or more, and still more preferably 2.6 or more.

The OD value is given by the following equation.

[ number 23]

Here, I _t Indicates the intensity of transmitted light, I ₀ Representing the intensity of the incident light.

For example, a transmittance of 3% corresponds to an OD value of 1.5.

According to the formula (23), the minimum value of the OD value in the near infrared wavelength region of 735nm or more and 1100nm or less is equal to or larger than the minimum value of the OD value in the near infrared wavelength region of 710nm or more and 1100nm or less.

The optical filter preferably has more than 32 dielectric multilayer films having QWOT of 0.75 or more and less than 1.25. More preferably 36 or more layers, and still more preferably 42 or more layers. Whether or not the shielding performance in a specific wavelength range is achieved by the number of layers of the dielectric multilayer film is determined by the required OD value and the range width (Δ g) of the wavelength to be shielded, and the optical density-range width product (OD bandwidth product (ODBWP)) in the case where a pair of high refractive index layer and low refractive index layer (for example, a pair of high refractive index layer 22 and low refractive index layer 23 in dielectric multilayer film 21 of fig. 1) having a QWOT of 0.75 or more and less than 1.25 is added.

The range width (Ag) of the specific wavelength range to be shielded is obtained by the following equation.

[ number 24]

Here, λ S is the shortest wavelength of the shielded wavelength range, and λ L is the longest wavelength of the shielded wavelength range.

The required shading performance is determined by the product of the required OD value and the range width.

On the other hand, the optical density/area width product (ODBWP) when a pair of a high refractive index layer and a low refractive index layer having a QWOT of 0.75 or more and less than 1.25 is added is given by the following expression.

[ number 25]

When the product of the desired OD value and the range width is divided by the optical density-range width product (ODBWP) when a pair of high refractive index layers and low refractive index layers having a QWOT of 0.75 or more and less than 1.25 is added, the number of pairs of the desired high refractive index layers and low refractive index layers is determined. That is, 2 times the value is the number of layers of the dielectric multilayer film required for the shielding performance in the specific wavelength range.

In the case where it is required that the desired OD value be achieved in any wavelength in a specific shielded wavelength range, the number of layers needs to be further approximately 2 times.

According to these, e.g. the refractive index n in the high refractive index layer _H A refractive index n of the low refractive index layer of 2.54 _L In the case of 1.47, it was found that when the number of layers having a QWOT of 0.75 or more and less than 1.25 is more than 32, the shielding property having an OD value of 2 or more can be effectively obtained in the near-infrared wavelength region of 735nm to 1100 nm.

The dielectric layer of the optical filter is preferably 60 layers or less. When 61 or more dielectric layers are provided, there is a concern that the optical filter may warp, the manufacturing cost may increase, or the incident angle dependency in the vicinity of 500nm may deteriorate due to excessive lamination.

It is desirable that the number of layers of the dielectric multilayer film provided on each side of the substrate is less than 36. More preferably 34 layers or less, and still more preferably 32 layers or less. When the number of layers of the dielectric multilayer film on each surface is 36 or more, even if the absolute value of the difference between the equivalent admittance of the dielectric multilayer film having a wavelength of 500nm and the optical admittance in vacuum has a minimum value at least twice in the range of the incident angle of 0 ° to 40 °, the incident angle dependency of the wavelength of 500nm of 0 ° to 40 ° tends to be poor, and it is difficult to maintain the incident angle dependency of green satisfactorily. In addition, if the number of layers is 32 or less, an optical filter with less warpage can be obtained, and this is useful for thinning the solid-state imaging device.

The optical filter preferably has an average measured transmittance at 0 ° incidence of unpolarized light of 450nm to 630nm in air of 75% or more. More preferably 80% or more, and still more preferably 85% or more. When the average measured transmittance is 85% or more, the optical filter is suitable for an optical filter for a solid-state imaging device.

The optical filter preferably has a difference of 5% or less between an average transmittance at 0 ° incidence and an average transmittance at 40 ° incidence of unpolarized light having a wavelength of 450nm to 630nm in the air. If the range is within the above range, the optical filter has less dependence on the incident angle, and is suitable as an optical filter for a solid-state imaging device.

The optical filter preferably has a measured transmittance of 70% or more, more preferably 75% or more, even more preferably 80% or more, particularly preferably 85% or more, and even more preferably 90% or more, at 0 ° to 40 ° incidence to unpolarized light having a wavelength of 500nm in air. When the transmittance of unpolarized light having a wavelength of 500nm is not less than the above-mentioned transmittance in all of 0 ° to 40 °, the incident angle dependency of green is good, and the optical filter is suitable as an optical filter for a solid-state imaging device.

The difference between the maximum value of the measured transmittance at 0 ° to 40 ° incidence of unpolarized light having a wavelength of 500nm and the minimum value of the measured transmittance at 0 ° to 40 ° incidence of unpolarized light having a wavelength of 500nm is preferably 25% or less. When the amount of the optical filter exceeds 25%, a ghost occurs due to reflection of light having a wavelength of 500nm by the optical filter, and therefore the optical filter is not suitable as an optical filter for a solid-state imaging device. More preferably 20% or less, and still more preferably 16% or less. When the concentration is 16% or less, the incident angle dependency of green is good, and the optical filter is suitable as an optical filter for a solid-state imaging device. More preferably 12% or less, particularly preferably 7% or less, and most preferably 3% or less. When the light having a wavelength of 500nm is within the above range, reflection of light by the optical filter can be suppressed, and the optical filter is suitable as an optical filter for a solid-state imaging device because ghost images are small.

The optical filter preferably has an average measured transmittance of 70% or more at 40 ° incidence of unpolarized light having a wavelength of 450nm to 630nm in the air. More preferably 75% or more, and still more preferably 80% or more. If the average measured transmittance is 80% or more, the optical filter is suitable for an optical filter for a solid-state imaging device.

In order to correct the sensor sensitivity of the solid-state imaging device and the sensitivity of the human eye, the optical filter preferably has a transmittance of 50% measured between 620nm and 660nm of the wavelength of unpolarized light incident at 0 ° in the air. Preferably, the transmittance is 50% as measured between 400nm and 425nm of the wavelength of unpolarized light incident at 0 ° in air. If the range is within the above range, the optical filter is suitable for a solid-state imaging device.

As described above, the optical filter of the present embodiment can suppress the incident angle dependency by controlling the variation of the transmittance at a wavelength of 500nm due to the difference in the incident angle of 0 ° to 40 ° in the optical filter to a low value while achieving both the high shielding performance in the near infrared wavelength region and the high transmittance performance in the visible wavelength region, and can be suitably used in the solid-state imaging device.

< solid-state imaging device >

The solid-state imaging device of the present invention includes the optical filter of the present invention. Here, the solid-state imaging device is an image sensor including a solid-state imaging element such as a CCD or CMOS image sensor, and is specifically used for applications such as a digital still camera, a camera for a mobile phone, and a digital video camera. Fig. 2 is a schematic cross-sectional view of the solid-state imaging device 100 according to the present invention. The solid-state imaging device 100 includes lens groups L1 to L3 of the solid-state imaging device, an optical filter 10, and a solid-state imaging element 101.

[ evaluation method ]

< optical characteristics >

The optical properties of the optical filter were evaluated by using an ultraviolet-visible near-infrared spectrophotometer U4100 (manufactured by Hitachi High-Technologies) ltd) for the optical paths shown in fig. 3 (a) and 3 (b), and calculating the average of the optical properties obtained by a P-polarized light source and an S-polarized light source in the air. The obtained transmittance is set as an actual measured transmittance of the optical filter, and the obtained reflectance is set as an actual measured reflectance of the optical filter. Fig. 3 (a) is a schematic view showing a method for measuring the transmittance of the optical filter of the present invention. Fig. 3 (b) is a schematic view showing a method for measuring the reflectance of the optical filter of the present invention. The transmittance of the optical filter was measured by the following method: transmitted light 202 of incident light 201 to the optical filter 10 is measured by using a detector 211 on the incident side and a detector 212 on the emission side of the optical filter 10. The reflectance of the optical filter is measured by the following method: the reflected light 203 of the incident light 201 to the optical filter 10 and the reflected light 205 of the incident light 204 from the other surface of the optical filter 10 are measured using the detector 211 on the incident side and the detector 212 on the emission side of the optical filter 10.

< warpage >

The warping was measured for the radius of curvature of the optical filter using a digital microscope (digital microscope) VHX-2000 (manufactured by Kernere, inc.). The case where the curvature radius was 50mm or more was indicated by "o", and the case where the curvature radius was less than 50mm was indicated by "x".

< glass transition temperature >

Using a differential scanning calorimeter (DSC 6200) manufactured by SII nanotechnology (SIINanotechnology) limited at a temperature rising rate: the measurement was carried out at 20 ℃ per minute under a nitrogen stream.

[ example 1]

41 parts by weight of P were weighed and mixed ₂ O ₅ 5 parts by weight of A1 ₂ O ₃ 24 parts by weight of Na ₂ O, 6 parts by weight of MgO, 6 parts by weight of CaO, and 12 parts by weight of BaO. CuO was added thereto, and was charged into a platinum crucible, and heated and melted at a temperature of 1000 ℃. After sufficiently stirring and clarifying, the mixture was cast into a mold, slowly cooled, cut and ground to prepare a 50mm × 200mm × 2mm plate. The sheet was heated to the vicinity of the softening point, subjected to elongation processing, and further subjected to polishing, thereby obtaining copper phosphate glass (refractive index of 500nm, 1.53, glass transition temperature, 480 ℃) having a thickness of 0.1 mm. The resin was applied to both sides thereof by an applicator (applicator) to a cycloolefin resin "yauton (ARTON) G5023 manufactured by JSR gmbh: a 500nm refractive index of 1.52 and a glass transition temperature of 165 ℃ is added with a squarylium salt compound represented by the following structural formula (26) (near infrared ray absorber, absorption maximum wavelength: about 698nm to 707 nm), uwitches (Uvitex) (registered trademark) OB (near ultraviolet ray absorber, absorption maximum wavelength: 396 nm), and further with dichloromethane, and dissolved to obtain a solution having a solid content of 30%。

[ solution 1]

The resultant was dried at 60 ℃ for 8 hours, at 100 ℃ for 8 hours, and further at 100 ℃ for 8 hours under reduced pressure to obtain a transparent substrate A (thickness: 0.11 mm) comprising copper phosphate glass and norbornene resin. CuO and the squarylium salt compound represented by the structural formula (24) are in the amount of 635nm in wavelength, wherein the transmittance is 50% as measured between 620nm and 660nm of the wavelength of unpolarized light ray incident at 0 ℃ in air as a transparent substrate A. Uvitex OB is a transparent substrate A, and is a part by weight of 405nm, which is a wavelength of unpolarized light incident at 0 ℃ in air and has a transmittance of 50% between 400nm and 425 nm. Providing titanium dioxide (TiO) as a high refractive index layer on one surface of the substrate by ion-assisted vacuum evaporation ₂ : refractive index of 2.54 at 500 nm), and silicon dioxide (SiO) as a low refractive index layer ₂ : refractive index 1.47 of 500 nm), the dielectric multilayer film of film design 1 shown in table 1, and the dielectric multilayer film of film design 4 shown in table 2 were provided on the other surface, thereby obtaining the optical filter of the present invention. Fig. 4 shows the equivalent admittance of an unpolarized light ray at 500nm in the air at an angle of 0 ° to 40 ° when the dielectric multilayer film of the film design 1 is provided on the substrate a having transparency.

[ Table 1]

Fig. 5 (a) and 5 (b) show the incident angle dependence of the difference between the equivalent admittance of the film design 1 for unpolarized light rays at 500nm in air and the optical admittance in vacuum of 0 ° to 40 °. According to fig. 5 (b), the difference between the equivalent admittance of the film design 1 and the optical admittance of vacuum has 2 minima between 5 ° and 12 ° and 22 ° and 28 °. Actual measured transmittances of the obtained optical filter at 0 ° to 40 ° in air of unpolarized light having a wavelength of 500nm incident from the film design 1 are shown in fig. 6 (a) and 6 (b), and actual measured reflectances are shown in fig. 6 (c). As is clear from fig. 6 a and 6 b, the obtained optical filter has at least two maximum values in the range of 0 ° to 40 ° in the actually measured transmittance at a wavelength of 500nm (in fig. 6 a, between 7 ° to 12 ° and between 24 ° to 28 °). As can be seen from fig. 6 c, the measured reflectance at a wavelength of 500nm has at least two minima in the range of 0 ° to 40 ° (between 7 ° and 12 ° and between 24 ° and 28 ° in fig. 6 c). Other optical characteristics and warpage of the obtained optical filter are shown in table 3. The obtained optical filter has a high OD value in the near infrared wavelength region, has a shielding property, has little dependence on an incident angle at a wavelength of about 500nm, and is suitable as an optical filter for a solid-state imaging device having little warpage.

[ example 2]

Cyclic olefin resin, "Yaoton (ARTON) G5023 manufactured by JSR corporation: a solution having a refractive index of 1.52 at 500nm and a glass transition temperature of 165 ℃ was prepared by adding a squarylium salt compound represented by the structural formula (26) and Uvitex OB, and dissolving the resulting mixture in dichloromethane to obtain a solid content of 8%. Then, the obtained solution was cast (cast) onto a smooth glass plate, dried at 60 ℃ for 8 hours, at 100 ℃ for 8 hours, and further at 100 ℃ for 8 hours under reduced pressure, and peeled off to obtain a transparent substrate B having a thickness of 0.1 mm. The squarylium salt compound is an amount of 636nm in wavelength, in which the transmittance is measured to be 50% between 620nm and 660nm of unpolarized light incident at 0 ° in the air as a substrate B having transparency. Uvitex OB is defined as the weight part of 409nm, which is the wavelength of unpolarized light incident at 0 ℃ in air as a transparent substrate B, and has a transmittance of 50% between 400nm and 425 nm. With respect to both surfaces of the obtained substrate B having transparency, the dielectric multilayer film of the film design 1 was provided on one surface and the film design 5 was provided on the other surface in the same manner as in example 1, thereby obtaining an optical filter. The optical characteristics and warpage evaluation results of the obtained optical filter when it was incident from the film design 1 are shown in table 3. The obtained optical filter has a high OD value in the near infrared wavelength region, has a shielding property, has little dependence on an incident angle at a wavelength of about 500nm, and is suitable as an optical filter for a solid-state imaging device having little warpage.

[ example 3]

Cyclic olefin resin, "Yaoton (ARTON) G5023 manufactured by JSR corporation: a solution having a solid content of 30% by weight was obtained by adding a squarylium salt compound represented by the structural formula (26) to a refractive index of 1.52 at 500nm and a glass transition temperature of 165 ℃ "and further adding UwitchX OB (absorption maximum wavelength: 396 nm) and methylene chloride. The obtained solution was applied to a smooth borosilicate glass (D263, manufactured by Schott corporation, refractive index 1.53 at 500nm, glass transition temperature 557 ℃) having a thickness of 0.10mm by an applicator. After drying at 60 ℃ for 8 hours, 100 ℃ for 8 hours, and further at 100 ℃ for 8 hours under reduced pressure, a transparent substrate C having a total thickness of 0.15mm was obtained. The squarylium salt compound is an amount of 636nm in wavelength, in which a transmittance of 50% is observed between 620nm and 660nm as a wavelength of unpolarized light incident at 0 ° in the air as a transparent substrate C. Uvitex OB is 408nm in terms of the wavelength of unpolarized light incident at 0 ℃ in air as a transparent substrate C and the wavelength at which the transmittance between 400nm and 425nm is 50%. On both sides of the obtained transparent substrate, dielectric multilayer films of film design 2 and film design 5 were provided in the same manner as in example 1, thereby obtaining an optical filter. Fig. 7 shows the equivalent admittance of an unpolarized light ray at 500nm in air at an angle of 0 ° to 40 ° when the dielectric multilayer film of the film design 2 is provided on the substrate C having transparency, and fig. 8 shows the incident angle dependency of 0 ° to 40 ° of the difference between the equivalent admittance of the unpolarized light ray at 500nm in air at the film design 2 and the optical admittance in vacuum. The difference between the equivalent admittance of the film design 2 and the optical admittance of vacuum has 3 minima between 12 ° to 20 °, between 20 ° to 30 °, between 36 ° to 40 °. The measured transmittance and measured reflectance in air of unpolarized light rays incident from the film design 2 at 0 ° to 40 ° at a wavelength of 500nm of the obtained optical filter are shown in fig. 9 (a) and 9 (b). The obtained optical filter has 2-order maximum values in the actually measured transmittance at the wavelength of 500nm between 0 and 40 degrees, and has 3-order minimum values in the actually measured reflectance at the wavelength of 500nm between 0 and 40 degrees. The optical characteristics and warpage evaluation results of the obtained optical filter when it was incident from the film design 2 are shown in table 3. The obtained optical filter has a high OD value in the near-infrared wavelength region, has a shielding property, has little dependence on the incident angle in the vicinity of a wavelength of 500nm, and is suitable as an optical filter for a solid-state imaging device having little warpage.

[ example 4]

Into a 3L four-necked flask were charged 35.12g (0.253m0l) of 2, 6-difluorobenzonitrile, 87.60g (0.250 mol) of 9, 9-bis (4-hydroxyphenyl) fluorene, 41.46g (0.300 mol) of potassium carbonate, 443g of N, N-dimethylacetamide (hereinafter referred to as "DMAC") and 111g of toluene. Then, a thermometer, a stirrer, a three-way cock with a nitrogen inlet tube, a Dean-Stark tube, and a cooling tube were placed in the four-necked flask. Then, after the flask was purged with nitrogen, the resulting solution was reacted at 140 ℃ for 3 hours, and the produced water was removed from the dean stark tube as needed. When no water was produced, the temperature was gradually increased to 160 ℃ and the reaction was carried out at the temperature for 6 hours. After cooling to room temperature (25 ℃), the formed salt was removed by filter paper, and the filtrate was put into methanol to reprecipitate, and the filtrate (residue) was separated by filtration separation. The resulting filtrate was dried under vacuum at 60 ℃ overnight to obtain resin A. The glass transition temperature was 285 ℃ and the refractive index at 500nm was 1.60.

To 100 parts by weight of the obtained resin a, a squarylium salt compound represented by the structural formula (26), gold nanorods (Sigma Aldrich (Sigma-Aldrich Japan) gmbh, near infrared ray absorbent, maximum absorption wavelength 1064 nm), and ewitangsis (Uvitex) OB were added, and DMAC was further added to obtain a solution having a solid content of 8%. Then, the obtained solution was cast (cast) onto a smooth glass plate, dried at 60 ℃ for 8 hours, and further at 140 ℃ under reduced pressure for 8 hours, and peeled off to obtain a transparent substrate D having a thickness of 60 μm. The squarylium salt compound and the gold nanorods are in an amount such that the wavelength of 647nm shows a transmittance of 50% between 620nm and 660nm, which is measured as a wavelength of unpolarized light incident at 0 ° in air as a transparent substrate D. Uvitex OB is 408nm in terms of the wavelength of unpolarized light incident at 0 ℃ in air as a transparent substrate D and the wavelength at which the transmittance between 400nm and 425nm is 50%. The dielectric multilayer films of film design 2 and film design 5 were provided on both sides of the obtained transparent substrate in the same manner as in example 1, thereby obtaining an optical filter. The optical characteristics and warpage evaluation results of the obtained optical filter when it was incident from the film design 2 are shown in table 3. The obtained optical filter has a high OD value in the near-infrared wavelength region, has a shielding property, has little dependence on the incident angle in the vicinity of a wavelength of 500nm, and is suitable as an optical filter for a solid-state imaging device having little warpage.

Comparative example 1

A dielectric multilayer film of film design 3 and film design 5 was formed on both sides of a borosilicate glass (D263: 500nm refractive index 1.53, glass transition temperature 557 ℃ C., manufactured by Schottky corporation) having a thickness of 0.12mm, which was smooth, in the same manner as in example 2. Fig. 10 shows the equivalent admittance of an unpolarized light ray at 500nm in air at an incident angle of 0 ° to 40 ° when the dielectric multilayer film of the film design 3 is provided on borosilicate glass, and fig. 11 (a) and 11 (b) show the dependence of the incident angle of 0 ° to 40 ° on the difference between the equivalent admittance of the unpolarized light ray at 500nm in air and the optical admittance in vacuum. The difference between the equivalent admittance and the optical admittance in vacuum of the film design 3, which does not have at least two continuous buffer layers having a physical film thickness of 60nm, except for the layers from the substrate toward the outside up to 3 layers, has a 1-order minimum value between 7 ° and 11 °. The optical characteristics and warpage evaluation results of the obtained optical filter when it was incident from the film design 3 are shown in table 3. The obtained optical filter has a high OD value in the near infrared wavelength region and has a shielding property, but has a large incident angle dependency in the vicinity of a wavelength of 500nm, and is not suitable as an optical filter for a solid-state imaging device.

Comparative example 2

A dielectric multilayer film of film design 3 and film design 4 was provided on the substrate B having transparency obtained in the same manner as in example 2 in the same manner as in example 1. The optical characteristics and warpage evaluation results of the obtained optical filter when it was incident from the film design 3 are shown in table 3. The obtained optical filter has a high OD value in the near infrared wavelength region and has a shielding property, but has a large incident angle dependency in the vicinity of a wavelength of 500nm, and is not suitable as an optical filter for a solid-state imaging device.

Industrial applicability

The optical filter of the present invention can be suitably used in all cameras such as digital still cameras, cameras for mobile phones, digital video cameras, motion cameras (action cameras), cameras for target machines, cameras for smart phones, personal Computer (PC) cameras, surveillance cameras, cameras for automobiles, personal information terminals, personal computers, video game machines, medical devices, portable game machines, fingerprint authentication systems, digital music players, toy robots, toys, and the like.

Claims

1. An optical filter which is an optical filter comprising a substrate having transparency and includes a dielectric multilayer film on at least one face of the substrate, characterized in that:

the actual measurement transmittance in the range of 0-40 DEG of the incident angle of unpolarized light with a wavelength of 500nm in the air is more than 70%, and

the optical density value of 0-degree incidence of unpolarized light rays in the range of 735nm to 1100nm in air is 2 or more;

the dielectric multilayer film includes at least one layer of silicon oxide,

the dielectric multilayer film has a buffer layer,

the buffer layer has 1 or more low refractive index layers having a refractive index of 1.0 to 1.8, and 1.9 to 2.8,

the physical film thicknesses of the low refractive index layer and the high refractive index layer are respectively less than 60nm,

the buffer layer is an outer layer of 4 or more layers from the substrate, and the low refractive index layer and the high refractive index layer which are alternately laminated and exist on a layer other than the outermost layer are continuously laminated by at least two layers,

l represents the number of layers of the dielectric multilayer film as L layers, j represents the j-th layer in the L layers of the dielectric multilayer film,

an equivalent admittance Y in air at a wavelength of 500nm represented by the following formula _E And optical admittance Y with vacuum ₀ Has at least two minima in the range of 0 DEG to 40 DEG of the incident angle;

here, the equivalent admittance Y in air _E Represented by the following formula;

Y _E ＝C/B (7)

here, B and C in the formula are represented by the following formula;

here, n in the formula _m Is the refractive index of the substrate;

here, M in the formula ₁ Is incident to the 1 st layer, i.e., the most incident side, of the dielectric multilayer filmOuter layer, a characteristic matrix of said formula n ₁ Is the refractive index of the 1 st layer, d in the formula ₁ Is the physical film thickness of the 1 st layer; m in the formula _j A property matrix that is a j-th layer from the 1 st layer toward the substrate; n in the formula _j Is the refractive index of the j-th layer, d in the formula _j The physical film thickness of the j layer; λ is the wavelength of the light.

2. The optical filter according to claim 1, wherein: the actually measured reflectivity of the optical filter in the air of the unpolarized light with the wavelength of 500nm incident from the at least one surface has at least two minimum values in the range of the incident angle of 0-40 degrees.

3. The optical filter according to claim 1 or 2, wherein: the actually measured transmittance of the optical filter in the air of the unpolarized light ray with the wavelength of 500nm incident from the at least one surface has at least two maximum values in the range of the incident angle of 0-40 degrees.

4. The optical filter according to claim 1 or 2, wherein: the dielectric multilayer film has a plurality of buffer layers, and the buffer layers constitute buffer layer portions in which layers having a physical film thickness of more than 60nm are present at intervals between the buffer layers.

5. The optical filter according to claim 4, wherein: the buffer layer portion is present within 16 layers from the substrate.

6. The optical filter according to claim 1 or 2, wherein: the number of layers of the dielectric multilayer film is 16-60.

7. The optical filter according to claim 1 or 2, wherein: the average of the measured transmittance at 0 DEG incidence in the air of the unpolarized light beam of 450 to 630nm incident from the at least one surface of the optical filter is 75% or more.

8. A solid-state imaging device, characterized in that: comprising an optical filter according to any one of claims 1 to 7.