JP2008139693A - Infrared cut filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an infrared cut filter which suppresses cutting off of light in a wavelength region which is set by allowing a desired reflection band to decrease by a factor of an integer. <P>SOLUTION: The infrared cut filter comprises: a substrate 1; and a multilayer film 2 composed of a high refractive index film H, a low refractive index film L and a middle refractive index film M which are formed on the substrate 1, wherein respective films are stacked with an (LMHM) period in the multilayer film 2 or the infrared cut filter has a part where the respective films are stacked with the (LMHM) period. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a multilayer laminated infrared cut filter used in an optical system of various optical devices.

  In imaging devices such as digital cameras, surveillance cameras, and video cameras, photoelectric conversion elements called solid-state imaging devices such as CCDs and CMOSs are generally used. Image sensors such as CCD and CMOS have a sensitivity different from that of human vision. In addition to the wavelength range that humans can perceive (visible range), it also supports infrared light that has a longer wavelength than the visible range. Even with sensitivity. For this reason, when these solid-state imaging devices are used for imaging in the visible range, a phenomenon occurs in which image information obtained from the imaging device is different from image information viewed by humans. In order to prevent such a phenomenon, in general, in an imaging apparatus using a solid-state imaging device, an infrared cut filter having a function of selectively blocking infrared light and transmitting visible light is provided on the front surface of the imaging device. It is arranged.

  As one of typical infrared cut filters, a dielectric laminated film type infrared cut filter can be cited. Dielectric laminated film type infrared cut filter is a laminate of dielectric films on a substrate, and selectively transmits infrared light using interference of light on each side of the laminated film. It has a function to shut off.

  In general, an infrared cut filter used in a solid-state imaging device for the visible range often transmits visible light having a wavelength of about 400 to 650 nm and blocks infrared light having a wavelength of about 650 to 1100 nm.

  A dielectric laminated film type infrared cut filter generally has a configuration in which a high refractive index film and a low refractive index film are alternately laminated on a substrate, and an optical film thickness nd of each laminated film. (The refractive index of each film is n, and the thickness of each film is d.) However, if the wavelength corresponding to the center wavelength of the wavelength band of the light to be blocked is the design wavelength λ, there is a relationship of nd = λ / 4. (For example, refer to Patent Document 1). A filter having such a configuration increases the reflectance of light in a certain wavelength band centered on the design wavelength λ most efficiently due to light interference on each surface of the laminated film. Can be cut off. In practice, a filter that blocks light of a specific wavelength by laminating a dielectric film as described above is basically composed of a film layer having an optical film thickness corresponding to nd = λ / 4, and the optical characteristics are optimized. For this reason, the thickness of each film is often finely adjusted.

  Here, since the above-described dielectric laminated film type infrared cut filter uses the interference effect of light in the multilayer film, in principle, a desired reflection band (band that blocks light of a desired wavelength). The interference effect appears remarkably even for light of a wavelength of 1 (in the case of a general infrared cut filter in which a film having a thickness of ¼ of the design wavelength λ is laminated), in particular. Tend. For this reason, not only the light in the target reflection band, but also the reflectance of light having a wavelength of an integral number of that increases. Therefore, a reflection band is also formed in the region of about 210 to 360 nm corresponding to 1/3 of the region of about 650 to 1100 nm, which is the wavelength band of infrared light, due to the interference effect. However, the region of about 210 to 360 nm corresponds to ultraviolet light, and it was an unused region in conventional imaging devices. Therefore, even if ultraviolet light is blocked by the formation of a reflection band, the infrared cut filter has characteristics. There was no particular problem in use.

  However, due to the recent expansion of the range of use of solid-state imaging devices such as CCD and CMOS, the conventional visible range is widely used in cameras, video cameras, surveillance cameras, microscopes, inspection devices, sensors, etc. used in the industrial and medical fields. In addition to the use in the field, the use of light having a wavelength in the ultraviolet region (receiving and imaging) is increasing. Therefore, a reflection band generated in the ultraviolet region also becomes a problem, and an infrared cut filter capable of suppressing the blocking of light having a wavelength of an integral number of the reflection region is desired.

Japanese Patent No. 3679268

  Accordingly, an object of the present invention is to provide an infrared cut filter that suppresses the blocking of light in a wavelength region of an integral number of a desired reflection band.

  As a result of earnest research in view of the above object, the present inventor provides a substrate with a high refractive index film, a low refractive index film and a medium refractive index film laminated at a predetermined cycle or provided with a portion laminated at a predetermined cycle. Thus, it has been found that the blocking of light by the reflection band formed in the wavelength region of 1 / integer of the desired reflection band can be suppressed, and the present invention has been conceived.

の関係をほぼ満たすことを特徴とする赤外カットフィルタ。
(9) 上記(7) に記載の赤外カットフィルタにおいて、（ＬＭＨＭ）周期における高屈折率膜Ｈの屈折率をｎ_Ｈとし、低屈折率膜Ｌの屈折率をｎ_Ｌとし、中屈折率膜Ｍの屈折率をｎ_Ｍとすると、下記式(2)

の関係をほぼ満たすことを特徴とする赤外カットフィルタ。
(10) 上記(1)〜(9) のいずれかに記載の赤外カットフィルタにおいて、赤外域で遮断特性を示すとともに、可視域及び紫外域で透過特性を示すことを特徴とする赤外カットフィルタ。
(11) 上記(4)〜(10) のいずれかに記載の赤外カットフィルタにおいて、設計波長λは650〜1100 nmであることを特徴とする赤外カットフィルタ。
(12) 上記(1)〜(11) のいずれかに記載の赤外カットフィルタにおいて、高屈折率膜ＨはZrO₂，HfO₂， Ta₂O₅，Nb₂O₅，TiO₂からなる群から選ばれた少なくとも一種からなることを特徴とする赤外カットフィルタ。
(13) 上記(1)〜(12) のいずれかに記載の赤外カットフィルタにおいて、低屈折率膜ＬはSiO₂，MgF₂からなる群から選ばれた少なくとも一種からなることを特徴とする赤外カットフィルタ。
(14) 上記(1)〜(13) のいずれかに記載の赤外カットフィルタにおいて、中屈折率膜Ｍは高屈折率膜Ｈの材料と低屈折率膜Ｌの材料との混合物からなることを特徴とする赤外カットフィルタ。
(15) 上記(1)〜(14) のいずれかに記載の赤外カットフィルタを備えた撮像装置。 That is, the present invention can be specifically achieved by the following means.
(1) A substrate and a laminated film formed on the substrate, which is composed of a high refractive index film H, a low refractive index film L, and a medium refractive index film M, and the laminated film is laminated with a (LMHM) period. Infrared cut filter characterized by being made.
(2) A substrate and a multilayer film formed on the substrate, which is composed of a high-refractive index film H, a low-refractive index film L, and a medium-refractive index film M, and has a portion laminated with a (LMHM) period. An infrared cut filter comprising:
(3) In the infrared cut filter according to (2), a part of the multilayer film is a multilayer film in which a high refractive index film A and a low refractive index film B are alternately laminated (AB). Infrared cut filter characterized by.
(4) The infrared cut filter according to (3), wherein the optical film thickness of each layer of the (AB) multilayer film is λ / 4, where λ is a design wavelength. .
(5) The infrared cut filter according to any one of (1) to (4) above, wherein the total optical film thickness in the (LMHM) period is λ / 2, where λ is the design wavelength. Infrared cut filter.
(6) In the infrared cut filter described in (5) above, the optical film thickness of the high refractive index film H and the medium refractive index film M in the (LMHM) period is λ / 10, and the optical characteristics of the low refractive index film L An infrared cut filter having a film thickness of λ / 5.
(7) In the infrared cut filter described in (5) above, the optical film thickness of the high refractive index film H and the low refractive index film L in the (LMHM) period is λ / 6, and the optical film of the medium refractive index film M An infrared cut filter having a film thickness of λ / 12.
(8) In the infrared cut filter described in (6) above, the refractive index of the high refractive index film H in the (LMHM) period is n _H , the refractive index of the low refractive index film L is n _L , and the medium refractive index When the refractive index of the film M is n _M , the following formula (1)

An infrared cut filter characterized by substantially satisfying the above relationship.
(9) In the infrared cut filter described in (7) above, the refractive index of the high refractive index film H in the (LMHM) period is n _H , the refractive index of the low refractive index film L is n _L , and the medium refractive index When the refractive index of the film M is n _M , the following formula (2)

An infrared cut filter characterized by substantially satisfying the above relationship.
(10) The infrared cut filter according to any one of the above (1) to (9), wherein the infrared cut filter has a blocking characteristic in the infrared region and a transmission characteristic in the visible region and the ultraviolet region. filter.
(11) The infrared cut filter according to any one of (4) to (10), wherein the design wavelength λ is 650 to 1100 nm.
(12) In the infrared cut filter according to any one of (1) to (11), the high refractive index film H is a group consisting of ZrO ₂ , HfO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , and TiO _2. An infrared cut filter comprising at least one selected from the group consisting of:
(13) The infrared cut filter according to any one of (1) to (12), wherein the low refractive index film L is made of at least one selected from the group consisting of SiO ₂ and MgF _2. Infrared cut filter.
(14) In the infrared cut filter according to any one of (1) to (13), the medium refractive index film M is made of a mixture of a material of the high refractive index film H and a material of the low refractive index film L. Infrared cut filter characterized by.
(15) An imaging device including the infrared cut filter according to any one of (1) to (14).

  The infrared cut filter of the present invention can suppress light blocking in a wavelength region of an integral number of a desired reflection band, and can block light in the visible region and ultraviolet light while blocking light in the infrared region. It can be selectively transmitted.

[1] Infrared cut filter FIG. 1 shows an infrared cut filter according to an embodiment of the present invention. The infrared cut filter includes a substrate 1 and a multilayer film 2 formed on the substrate 1 and including a high refractive index film H, a low refractive index film L, and a medium refractive index film M. Are stacked with a (LMHM) period.

  The total of the optical film thicknesses nd of each film in the (LMHM) cycle of the multilayer film 2 (the refractive index of each film is n and each physical film thickness is d) is λ / 2 where λ is the design wavelength. Preferably there is. Here, the “design wavelength” means the wavelength at the center of the reflection band by the infrared cut filter of the present invention. In this way, by repeating the periodic structure with the total optical thickness nd of each film being λ / 2 (LMHM), in the reflection band formed around the design wavelength λ by the periodic structure and the light interference effect of each layer. Light can be blocked.

  In addition, since the (LMHM) configuration itself satisfies a condition (antireflection condition) for suppressing the generation of a reflection band at a fraction of an integer of the design wavelength λ, an integral part of the reflection band centered on the design wavelength λ. The generation of a reflection band is suppressed in one wavelength band of In this way, by providing an infrared cut filter having a multilayer film that repeats the (LMHM) periodic structure, not only has reflection characteristics in a certain wavelength band centered on the design wavelength λ, but also an integer of the design wavelength λ. Blocking light can be prevented by suppressing the generation of the reflection band in a fraction.

の関係をほぼ満たしているのが好ましい。ここで、ｎ_Ｈは高屈折率膜Ｈの屈折率であり、ｎ_Ｌは低屈折率膜Ｌの屈折率であり、ｎ_Ｍは中屈折率膜Ｍの屈折率である。このように各膜の屈折率及び厚さを設定することにより、赤外カットフィルタの遮断及び透過の効果をより高めることができ、特に設計波長λを中心とする反射帯域の１／２及び１／３の波長帯域における反射帯の発生を抑制することができる。 As for the optical film thickness of each film, the total thickness in the (LMHM) cycle can be set as appropriate, but the optical film thicknesses of the high refractive index film H and the medium refractive index film M are λ / 10, and the low refractive index. The optical film thickness of the film L is preferably λ / 5, and the optical film thickness of each film is preferably λ / 10. At this time, the refractive index of each film is expressed by the following formula (1)

It is preferable that the above relationship is substantially satisfied. Here, n _H is the refractive index of the high refractive index film H, n _L is the refractive index of the low refractive index film L, and n _M is the refractive index of the medium refractive index film M. By setting the refractive index and thickness of each film in this way, the effect of blocking and transmitting the infrared cut filter can be further enhanced, and in particular, 1/2 and 1 of the reflection band centered on the design wavelength λ. Generation of reflection bands in the / 3 wavelength band can be suppressed.

の関係をほぼ満たしているのが好ましい。このように各膜の屈折率及び厚さを設定することにより、赤外カットフィルタの遮断及び透過の効果をより高めることができ、特に設計波長λを中心とする反射帯域の１／２、１／３及び１／４の波長帯域における反射帯の発生を抑制することができる。 In the (LMHM) cycle, the optical film thickness of the high refractive index film H and the low refractive index film L is preferably λ / 6, and the optical film thickness of the medium refractive index film M is preferably λ / 12. At this time, the refractive index of each film is expressed by the following formula (2)

It is preferable that the above relationship is substantially satisfied. By setting the refractive index and thickness of each film in this way, the effect of blocking and transmitting the infrared cut filter can be further enhanced, and in particular, 1/2 of the reflection band centered around the design wavelength λ, 1 Generation of reflection bands in the / 3 and ¼ wavelength bands can be suppressed.

  The design wavelength λ in the infrared cut filter of the present invention is preferably 650 to 1100 nm. By setting the design wavelength λ in this way, the infrared light for near infrared light that selectively blocks near infrared light and at the same time functions as a filter that selectively transmits light in the visible region and ultraviolet region. A cut filter is obtained.

  The substrate 1 is not particularly limited as long as it is a material that can be used for an infrared cut filter and has little absorption in the transmission band, but glass, crystal, ceramics, resin, and the like are preferable, and quartz glass is particularly preferable.

The high refractive index film H is not particularly limited as long as it satisfies a desired refractive index, but ZrO ₂ , HfO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , TiO _{2 and the} like are preferable, and ZrO ₂ is particularly preferable. The low refractive index film L is not particularly limited as long as it satisfies a desired refractive index, but SiO ₂ , MgF _{2 and the} like are preferable, and SiO ₂ is particularly preferable.

The medium refractive index film M is not particularly limited as long as it satisfies a desired refractive index, but a single material may be used, or a mixture of a high refractive index material and a low refractive index material may be used. In the case of a single material, Al ₂ O ₅ and MgO are preferable, and in the case of a mixture of a high refractive index material and a low refractive index material, a mixture of SiO ₂ and ZrO ₂ is preferable.

  The optical film thickness in the above-described infrared cut filter of the present invention is such as ripple removal according to each light incident angle, film material, substrate material, and surrounding environment (incident medium) of the infrared cut filter. Therefore, optimization such as fine adjustment of the optical film thickness of each film or appropriate correction of the film configuration near the substrate or the surface may be performed.

  In the above example, the design wavelength λ is set substantially at the center of the reflection band. However, the present invention is not limited to this, and a plurality of different design wavelengths λ are provided in the reflection band to correspond to each design wavelength λ (LMHM). A multilayer film may be laminated on the substrate. As a result, a cutoff characteristic can be obtained in a certain wavelength band centered on each design wavelength λ, and generation of a reflection band can be suppressed in a wavelength band centered on a wavelength of an integer of each design wavelength λ. it can.

  In the infrared cut filter shown in FIG. 1, the multilayer film 2 is entirely composed of (LMHM) cycles. However, the infrared cut filter of the present invention is not limited to this, and within the range where desired characteristics can be obtained (LMHM). ) The structure of the period may be provided as appropriate in a part of the multilayer film 2. For example, the multilayer film 2 is composed of a (LMHM) multilayer film having a (LMHM) cycle, and a multilayer film (AB) formed by alternately stacking a high refractive index film A and a low refractive index film B. Also good.

  FIG. 2 shows an infrared cut filter according to another embodiment of the present invention. The infrared cut filter includes a multilayer film (AB) formed by alternately laminating a high refractive index film A and a low refractive index film B formed on the substrate 1 and the high refractive index film H, It consists of a low refractive index film L and a medium refractive index film M, and each film consists of a (LMHM) multilayer film laminated with a (LMHM) period.

  By combining the (AB) multilayer film and the (LMHM) multilayer film, visible light and ultraviolet light can be selectively transmitted while blocking infrared light. In addition, since the number of layers in one cycle is smaller in the (AB) multilayer film than in the (LMHM) multilayer film, the number of layers in the entire multilayer film can be reduced as compared with the case of being composed of only the (LMHM) multilayer film. it can.

  The total of the optical film thicknesses nd of each film in one cycle of the multilayer film (AB) in which the high refractive index film A and the low refractive index film B are alternately laminated is preferably λ / 2. Each of the optical film thicknesses nd is preferably λ / 4.

  In FIG. 2, the (AB) multilayer film is provided on the substrate 1, and the (LMHM) multilayer film is provided thereon. However, the (LMHM) multilayer film is provided on the substrate 1, and the (AB) multilayer film is provided thereon. A configuration may be employed in which a film is provided.

  The infrared cut filter of the present invention can be used in various imaging apparatuses, and examples thereof include a digital camera, a surveillance camera, and a video camera.

[2] Infrared Cut Filter Manufacturing Method As an example of the formation process of the multilayer film 2 on the substrate 1 in the manufacture of the infrared cut filter of the present invention, a method of forming using the sputtering method is shown in FIG. This will be described below using a membrane device.

  In the example shown in FIG. 3, on the side surface of the vacuum chamber 10, an exhaust device 11 for evacuating the vacuum chamber 10, a target 13 made of a material of a high refractive index film H, and a film material are scattered from the target 13. There are provided a sputtering power source 14 for sputtering, a target 15 made of the material of the low refractive index film L, and a sputtering power source 16 for scattering the film material from the target 15, and a plurality of substrates 1 are provided in the vacuum chamber 10. And a rotatable cylindrical substrate holder 12 is provided, and the substrate holder 12 is connected to the rotation mechanism 17 on the upper surface.

  First, the inside of the vacuum chamber 10 is exhausted by the exhaust device 11. When the high refractive index film H is formed on the substrate 1, the material of the high refractive index film H is operated by operating the sputtering power source 14 and supplying power to the target 13 while driving the rotating mechanism 17 to rotate the substrate holder 12. Are scattered and attached to the substrate 1. At that time, since the sputtering power source 16 for supplying power to the target 15 is not operated and the material of the low refractive index film L is not scattered, only the material of the high refractive index film H can be formed.

  When the low refractive index film L is formed on the substrate 1, the material of the low refractive index film L is scattered by operating the sputtering power source 16 and applying power to the target 15 while rotating the cylindrical substrate holder 12. Adhere to the substrate 1. At this time, since the sputtering power source 14 for supplying power to the target 13 is not operated and the material of the high refractive index film H is not scattered, only the material of the low refractive index film L can be formed.

  When the medium refractive index film M is formed on the substrate 1, the sputtering power source 14 and the sputtering power source 16 are operated while rotating the cylindrical substrate holder 12, and power is supplied to both the target 13 and the target 15. The material of the refractive index film H and the material of the low refractive index film L are simultaneously scattered and deposited on the surface of the substrate 1 placed on the substrate holder 12 rotated at a high speed, so that the high refractive index film H and the low refractive index film H are deposited. A film in which the material of the rate film L is mixed adheres to the substrate 1. A medium refractive index film M having a mixing ratio of materials having a desired refractive index by adjusting the amount of scattering of the materials of the high refractive index film H and the low refractive index film L by the outputs of the sputtering power source 14 and the sputtering power source 16, respectively. Is obtained.

  In this way, depending on the type of film to be formed, the high refractive index film H and the low refractive index can be obtained by scattering the film material from the target 13 which is a high refractive index material source and the target 15 which is a low refractive index material source. The multilayer film 2 composed of the index film L and the medium refractive index film M can be formed on the substrate 1.

  When the (AB) multilayer film composed of the high refractive index film A and the low refractive index film B is formed on the substrate 1, the material of the high refractive index film A is used as the target 13 and the high refractive index film B is used as the target 15. (AB) A multilayer film is obtained by alternately laminating using the above materials.

  In the sputtering film forming apparatus shown in FIG. 3, the medium refractive index film M is formed by mixing the materials of the high refractive index film H and the low refractive index film L. The method for forming the infrared cut filter of the present invention For example, a medium refractive index material source including the material of the medium refractive index film M may be provided separately.

  The method of forming each film on the substrate 1 is not limited to the sputtering method, and any method capable of forming a desired film may be used, and a vacuum deposition method, an ion plating method, an ion assist method, a CVD method, or the like may be used. .

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1
First, 20 layers of (AB) multilayer films composed of a high refractive index film A and a low refractive index film B were laminated on the substrate 1 in the configuration shown in FIGS. 4 (a) and 4 (b). Quartz glass as the substrate 1, ZrO ₂ as a high refractive index film A, SiO ₂ was used as a low refractive index film B. The design wavelength lambda ₁ and 760 nm, the high refractive index film A and the optical thickness of the low refractive index film B was lambda _1/4, respectively. The refractive index of ZrO ₂ was 2.344, and the refractive index of SiO ₂ was 1.478. Quartz glass has a refractive index of 1.46 and air has a refractive index of 1.00.

On top of that, a (LMHM) multilayer film in which a high refractive index film H, a low refractive index film L, and a medium refractive index film M are laminated in a (LMHM) cycle is shown in FIGS. 4 (a) and 4 (b). Layer formation. ZrO ₂ was used as the high refractive index film H, SiO ₂ was used as the low refractive index film L, and a mixed material of ZrO ₂ and SiO ₂ was used as the middle refractive index film M. The design wavelength lambda ₂ and 960 nm, the optical thickness of the high refractive index film H and the medium refractive index layer M and lambda _2/10, the optical thickness of the low refractive index film L was lambda _2/5. The refractive index n _H of ZrO ₂ is 2.344, the refractive index n _L of SiO ₂ is 1.478, and the refractive index n _M of the medium refractive index film M is set to 1.964 from the equation (1). The sputtering apparatus shown in FIG. 3 was used for laminating each film.

The spectral transmittance in the air of the obtained infrared cut filter was measured. The obtained results are shown in FIG. As can be seen from FIG. 5, infrared light of 650 to 1150 nm was blocked, and the transmission region also included the ultraviolet region of 300 to 650 nm. From this, it can be seen that the formation of the reflection band in the wavelength region (region near the wavelength of 320 nm) corresponding to 1/3 of the cutoff region centered on the design wavelength λ ₂ = 960 nm is suppressed. Thus, an infrared cut filter having a cutoff characteristic in the infrared region and selectively transmitting light in the visible region and the ultraviolet region was obtained.

Example 2
First, 40 layers of the high refractive index film H, the low refractive index film L, and the middle refractive index film M were formed on the substrate 1 with the (LMHM) period and the configuration shown in FIGS. The substrate 1 and each film were the same as those in Example 1. The design wavelength lambda ₁ and 760 nm, the optical thickness of the high refractive index film H and the medium refractive index layer M and λ _1/10, the optical thickness of the low refractive index film L was lambda _1/5.

In addition, the design wavelength is changed to λ ₂ = 960 nm, and the high refractive index film H, the low refractive index film L, and the middle refractive index film M are formed with (LMHM) period in FIGS. 41 layers were formed with the structure shown in FIG. The optical thickness of the high refractive index film H and the medium refractive index layer M and λ _1/10, the optical thickness of the low refractive index film L was lambda _1/5. The sputtering apparatus shown in FIG. 3 was used for laminating each film.

The spectral transmittance in the air of the obtained infrared cut filter was measured. The obtained results are shown in FIG. As can be seen from FIG. 7, infrared light of 650 to 1150 nm was blocked, and the transmission region included 250 to 650 nm and the ultraviolet region. This suppresses the formation of a reflection band in a wavelength region (region near the wavelength of 250 nm) corresponding to 1/3 of the cutoff region centered on the design wavelength λ ₂ = 760 nm, and the design wavelength λ ₂ = 960. It can be seen that the formation of a reflection band in the wavelength region corresponding to 1/3 of the cutoff region centered on nm (region near the wavelength of 320 nm) is suppressed.

Example 3
First, 40 layers of a high refractive index film H, a low refractive index film L, and a middle refractive index film M were formed on the substrate 1 with the (LMHM) period and the configuration shown in FIGS. The substrate 1 and each film were the same as those in Example 1. The design wavelength λ ₁ was 760 nm, the optical film thickness of the high refractive index film H and the low refractive index film L was λ / 6, and the optical film thickness of the medium refractive index film M was λ / 12.

In addition, the design wavelength is changed to λ ₂ = 960 nm, and the high refractive index film H, the low refractive index film L, and the middle refractive index film M are formed with (LMHM) period as shown in FIGS. 41 layers were formed with the structure shown in FIG. The optical film thickness of the high refractive index film H and the low refractive index film L was λ / 6, and the optical film thickness of the medium refractive index film M was λ / 12. The sputtering apparatus shown in FIG. 3 was used for laminating each film.

The spectral transmittance in the air of the obtained infrared cut filter was measured. The obtained result is shown in FIG. As can be seen from FIG. 9, infrared light of 650 to 1150 nm was blocked, and the transmission region included 200 to 650 nm and the ultraviolet region. Therefore, a wavelength region corresponding to 1/3 of the cutoff region centered around the design wavelength λ ₂ = 760 nm (region near wavelength 250 nm) and a wavelength region equivalent to 1/4 (region near wavelength 190 nm) ) Is suppressed, and a wavelength region corresponding to 1/3 of a cutoff region centered around the design wavelength λ ₂ = 960 nm (region near 320 nm wavelength) and a wavelength region corresponding to 1/4 It can be seen that the formation of a reflection band in the region (wavelength around 240 nm) is suppressed.

Comparative Example 1
20 layers of (AB) multilayer films composed of a high refractive index film A and a low refractive index film B were laminated on the substrate 1 in the configuration shown in FIGS. 10 (a) and 10 (b). The substrate 1 and the films A and B were the same as those in Example 1. The design wavelength lambda ₁ and 760 nm, the high refractive index film A and the optical thickness of the low refractive index film B was lambda _1/4, respectively.

In addition, the design wavelength is changed to λ ₂ = 960 nm, and the (AB) multilayer film composed of the high refractive index film A and the low refractive index film B is configured as shown in FIGS. 10 (a) and 10 (b). 21 layers were formed. High refractive index film A and the optical thickness of the low refractive index film B was lambda _1/4, respectively. The sputtering apparatus shown in FIG. 3 was used for laminating each film.

The spectral transmittance in the air of the obtained infrared cut filter was measured. The obtained results are shown in FIG. As can be seen from FIG. 11, infrared light of 650 to 1150 nm is blocked and the transmission region is in the visible region of 350 to 650 nm, but a reflection band is formed in the ultraviolet region of 250 to 350 nm. It was. Thus, a reflection band in a wavelength region (region near the wavelength of 320 nm) corresponding to 1/3 of the cutoff region centered on the design wavelength λ ₂ = 960 nm was formed, and the ultraviolet light was blocked.

It is explanatory drawing which shows the infrared cut filter by one Example of this invention. It is explanatory drawing which shows the infrared cut filter by another Example of this invention. It is a top view which shows a sputtering device. It is a side view which shows a sputtering device. 3 is an explanatory diagram illustrating an infrared cut filter according to Embodiment 1. FIG. 3 is a diagram illustrating a configuration of a multilayer film of an infrared cut filter according to Example 1. FIG. 6 is a graph showing the spectral transmittance characteristics of the infrared cut filter of Example 1. 6 is an explanatory diagram illustrating an infrared cut filter according to Embodiment 2. FIG. It is a figure which shows the structure of the multilayer film of the infrared cut filter of Example 2. FIG. 6 is a graph showing the spectral transmittance characteristics of the infrared cut filter of Example 2. 6 is an explanatory diagram illustrating an infrared cut filter according to Example 3. FIG. 6 is a diagram illustrating a configuration of a multilayer film of an infrared cut filter of Example 3. FIG. 10 is a graph showing the spectral transmittance characteristics of the infrared cut filter of Example 3. 6 is an explanatory diagram showing an infrared cut filter of Comparative Example 1. FIG. 6 is a diagram illustrating a configuration of a multilayer film of an infrared cut filter of Comparative Example 1. FIG. 6 is a graph showing spectral transmittance characteristics of an infrared cut filter of Comparative Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Board | substrate 2 ... Multilayer film
10 ... Vacuum chamber
11 ... Exhaust device
12 ... Board holder
13, 15 ... Target
14, 16 ... Sputtering power supply
17 ... Rotation mechanism A, H ... High refractive index film B, L ... Low refractive index film
M ・ ・ ・ Medium refractive index film

Claims (15)

A substrate and a laminated film formed on the substrate and made of a high-refractive index film H, a low-refractive index film L, and a medium-refractive index film M, and the laminated films are laminated in a (LMHM) cycle. An infrared cut filter characterized by that. A substrate, and a multilayer film formed of the high refractive index film H, the low refractive index film L, and the medium refractive index film M on the substrate and having a portion laminated with a (LMHM) period. A featured infrared cut filter. 3. The infrared cut filter according to claim 2, wherein a part of the multilayer film is a multilayer film (AB) formed by alternately laminating a high refractive index film A and a low refractive index film B. Infrared cut filter. 4. The infrared cut filter according to claim 3, wherein an optical film thickness of each layer of the (AB) multilayer film is λ / 4, where λ is a design wavelength. 5. The infrared cut filter according to claim 1, wherein the total optical film thickness in the (LMHM) period is λ / 2, where λ is a design wavelength. 6. The infrared cut filter according to claim 5, wherein the optical film thickness of the high refractive index film H and the medium refractive index film M in the (LMHM) period is λ / 10, and the optical film thickness of the low refractive index film L is λ. IR cut filter characterized by being / 5. 6. The infrared cut filter according to claim 5, wherein the optical film thickness of the high refractive index film H and the low refractive index film L in the (LMHM) period is λ / 6, and the optical film thickness of the medium refractive index film M is λ. Infrared cut filter characterized by being / 12. In the infrared cut filter of claim 6, (LMHM) the refractive index of the high refractive index film H and n _H in period, the refractive index of the low refractive index film L and n _L, refraction of the medium refractive index layer M When the rate is n _M , the following formula (1)

An infrared cut filter characterized by substantially satisfying the above relationship. In the infrared cut filter of claim 7, (LMHM) the refractive index of the high refractive index film H and n _H in period, the refractive index of the low refractive index film L and n _L, refraction of the medium refractive index layer M When the rate is n _M , the following formula (2)

An infrared cut filter characterized by substantially satisfying the above relationship. The infrared cut filter according to claim 1, wherein the infrared cut filter exhibits a blocking characteristic in the infrared region and a transmission characteristic in the visible region and the ultraviolet region. The infrared cut filter according to any one of claims 4 to 10, wherein the design wavelength λ is 650 to 1100 nm. 12. The infrared cut filter according to claim 1, wherein the high refractive index film H is at least one selected from the group consisting of ZrO ₂ , HfO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , and TiO _2. An infrared cut filter comprising: The infrared cut filter according to any one of claims 1 to 12, wherein the low refractive index film L is made of at least one selected from the group consisting of SiO ₂ and MgF ₂ . 14. The infrared cut filter according to claim 1, wherein the medium refractive index film M is made of a mixture of a material of the high refractive index film H and a material of the low refractive index film L. Cut filter. An imaging device comprising the infrared cut filter according to claim 1.

Images