JP2012042491A - Neutral density (nd) filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ND filter capable of more flattening the transmittance for light in a visible region than a conventional filter.SOLUTION: The ND Filter 1 comprises a substrate 10 and a layered film 20 formed on the surface of the substrate 10. The layered film 20 is constituted by sequentially stacking, from the substrate 10 side, a substrate side dielectric layer 30 having a dielectric film; a metal layer 40 comprising a metal film; and a dielectric layer 50 opposite to the substrate, having a high extinction coefficient in a visible light region than the substrate side dielectric layer 30 and comprising a dielectric film.

Description

  The present invention relates to an ND (Neutral Density) filter that adjusts the amount of light mainly in the visible light region.

  Conventionally, in an imaging apparatus such as a still camera or a video camera, the amount of light is adjusted by using a so-called stop and an ND filter together. When adjusting the amount of light only with the aperture, for example, when imaging a high-brightness scene such as clear weather, overexposure may occur even if the aperture of the aperture is minimized. Further, when the aperture of the diaphragm is minimized, the influence of the hunting phenomenon and light diffraction becomes large, so that the image quality may be deteriorated.

  For this reason, in a conventional imaging device, when an ND (Neutral Density) filter that adjusts the amount of transmitted light by extinguishing (absorbing) transmitted light is incorporated together with a diaphragm device, the luminance of the field is high. In addition, the aperture of the diaphragm can be enlarged.

  Since the ND filter used in this way adjusts the amount of light in place of the diaphragm, it is preferable that the light transmittance be as flat (uniform) as possible over the entire visible light region. Further, by flattening the transmittance, only light having a specific wavelength range is not emphasized, so that color reproducibility can be improved.

  For this reason, in recent years, ND filters in which light absorbing films (metal films) that absorb light and dielectric films that interfere with light are alternately laminated on the surface of a transparent substrate such as a resin film are widely used. (For example, see Patent Documents 1 to 3).

JP 2003-43211 A JP 2006-91694 A JP 2007-206136 A

  However, the conventional ND filters do not actually have a very high transmittance flatness in the visible light region, and few of them can satisfy market demands. Particularly in recent years, the sensitivity of image sensors such as CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor) has been remarkably improved. It has become sensitive to images, and further flattening of transmittance is desired.

  In view of such circumstances, the present invention intends to provide an ND filter capable of flattening the transmittance of light in the visible light region more than before.

  (1) The present invention comprises a substrate having light permeability and a laminated film formed on the surface of the substrate, and the laminated film has a dielectric layer on the substrate side having a dielectric film; A metal layer made of a metal film and an anti-base material-side dielectric layer having a higher extinction coefficient in the visible light region than the base material-side dielectric layer and having a dielectric film are stacked in order from the base material side. It is an ND filter characterized by comprising.

  (2) The present invention is also characterized in that the substrate-side dielectric layer has a plurality of the dielectric films and is laminated so that the dielectric films of different materials are adjacent to each other. The ND filter according to (1) above.

  (3) In the ND filter according to (1) or (2), the anti-base material-side dielectric layer includes a plurality of the dielectric films made of different materials. is there.

  (4) In the present invention, the anti-base material-side dielectric layer is a high extinction film made of a material having a higher extinction coefficient in the visible light region than the material contained in the base material-side dielectric layer. The ND filter according to any one of (1) to (3), wherein the ND filter is included.

  (5) The present invention is also the ND filter according to (4) above, wherein the high extinction film is made of metal nitride or metal oxide.

  (6) The present invention is also the ND filter according to (5), wherein the high extinction film is made of a metal nitride or oxide that forms the metal film.

  (7) The present invention is also characterized in that the material constituting the metal film is any one of titanium, chromium or nickel having a molar ratio of 50% or more. The ND filter according to any one of the above.

  (8) In the present invention, the substrate-side dielectric layer may include a substrate-side first dielectric film, a substrate-side second dielectric film, and a substrate-side third dielectric film. The anti-base material-side dielectric layer is formed by stacking the anti-base material side first dielectric film and the anti-base material side second dielectric film in order from the base material side. The ND filter according to any one of the above (1) to (7).

  (9) Further, in the present invention, the anti-base material-side dielectric layer is formed between the anti-base material side first dielectric film and the anti-base material side second dielectric film. The ND filter according to (8), wherein the ND filter has a high extinction film made of a material having a higher extinction coefficient in the visible light region than a material included in the material.

  (10) In the present invention, the base material side first dielectric film, the base material side third dielectric film, and the anti-base material side second dielectric film are made of a first material, The substrate-side second dielectric film and the anti-substrate-side first dielectric film are made of a second material different from the first material, as described in (9) above It is an ND filter.

  (11) In the present invention, the refractive index in the visible light region of the first material is not more than the refractive index in the visible light region of the second material. It is an ND filter.

  (12) In the present invention, the first material is a material having a refractive index of 1.38 to 2.0 at a wavelength of 550 nm, and the second material has a refractive index of 1 at a wavelength of 550 nm. The ND filter according to (11), wherein the ND filter is made of any one of .38 to 2.4.

  (13) The present invention is also characterized in that the difference between the refractive index of the first material at a wavelength of 550 nm and the refractive index of the second material at a wavelength of 550 nm is 0.5 or less. The ND filter according to 11) or (12).

  (14) The present invention is also characterized in that the first material and the second material are different metal compounds in which different elements are bonded to a common metal. The ND filter according to any one of the above.

  (15) The present invention is also characterized in that the material constituting the high extinction film and the second material are different metal compounds in which a common element is bonded to different metals. The ND filter according to any one of (14) to (14).

  (16) In the present invention described in any one of (10) to (15), the first material is silicon dioxide, and the second material is silicon nitride. ND filter.

  (17) The present invention is also characterized in that the material constituting the metal film is titanium and the material constituting the high extinction film is titanium nitride. The ND filter according to any one of the above.

  According to the ND filter of the present invention, it is possible to achieve an excellent effect that the light transmittance in the visible light region can be flattened more than ever.

It is the schematic which showed the structure of the ND filter which concerns on embodiment of this invention. (A) It is the graph which showed the extinction coefficient k and refractive index n in the visible light area | region of Ti. (B) It is the graph which showed the extinction coefficient k and refractive index n in visible region at the time of forming TiN in the thin film. (C) is a graph showing the extinction coefficient k and refractive index n in the visible light region when TiN is formed in a thick film. (A) is a graph showing the extinction coefficient k and refractive index n in the visible light region of the SiO _2. (B) It is the graph which showed the extinction coefficient k and refractive index n in the visible light area | region of SiN. It is the graph which showed the example of the simulation result of the transmittance | permeability T and the reflectance R of ND filter at the time of changing a refractive index. It is the graph which showed the example of the simulation result of the transmittance | permeability T and the reflectance R of ND filter at the time of changing a refractive index. It is the graph which showed the example of the simulation result of the transmittance | permeability T and the reflectance R of ND filter at the time of changing a refractive index. It is the graph which showed the example of the simulation result of the transmittance | permeability T and the reflectance R of ND filter at the time of changing a refractive index. It is the graph which showed the example of the simulation result of the transmittance | permeability T and the reflectance R of ND filter at the time of changing a refractive index. It is the table | surface which showed the structure of the ND filter of the Example of this invention. (A) It is the graph which showed the simulation result of the transmittance | permeability T and the reflectance R of the ND filter of the Example of this invention. (B) It is the graph which showed the actual measurement result of the transmittance | permeability T and the reflectance R of the ND filter of the Example of this invention.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic diagram illustrating a configuration of an ND filter 1 according to the present embodiment. As shown in the figure, the ND filter 1 includes a base material 10 made of a material that transmits light, such as transparent resin and glass, and a laminated film 20 formed on the surface of the base material 10. Yes.

  Although the material which comprises the base material 10 will not be specifically limited if it is the material which permeate | transmits the light of the wavelength according to the use of the ND filter 1, In this embodiment, a PET (PolyEthylene Terephthalate) sheet is used. ing.

  The laminated film 20 is a thin film for extinction of light in the visible light region (wavelength in the range of about 400 to 700 nm) transmitted through the ND filter 1 substantially flatly. It is configured by stacking. Specifically, the laminated film 20 is configured by laminating a base material side dielectric layer 30, a metal layer 40 made of a metal film, and an anti-base material side dielectric layer 50 in order from the base material 10 side. Has been. That is, the laminated film 20 has a configuration in which the metal layer 40 is sandwiched between the base-side electric layer 30 and the anti-base-side dielectric layer 50.

  The laminated film 20 is formed on the surface of the substrate 10 by a dry process such as vacuum deposition, ion beam assist, ion plating, and sputtering. Then, explanation is omitted.

  In the present embodiment, the light reflectivity R is reduced by sandwiching the metal layer 40 made of a metal film and extinguishing light between the base-side dielectric layer 30 and the anti-base dielectric layer 50 that interfere with light. However, the light transmittance T can be made substantially flat over substantially the entire visible light region.

  In particular, the base-side dielectric layer 30 and the anti-base-side dielectric layer 50 are each composed of a plurality of dielectric films made of different materials, and the light extinction coefficient of the anti-base-side dielectric layer 50 ( By setting the light extinction capability higher than that of the base-side dielectric layer 30, it is possible to flatten the transmittance T in the visible light region more than before.

  The substrate-side dielectric layer 30 is formed by laminating a substrate-side first dielectric film 31, a substrate-side second dielectric film 32, and a substrate-side third dielectric film 33 in order from the substrate 10 side. It is configured. Thus, by laminating films made of three dielectrics and disposing the metal layer 40 on the substrate 10 side, the transmittance T in the visible light region can be flattened more than ever.

The material constituting the substrate-side first dielectric film 31, the substrate-side second dielectric film 32, and the substrate-side third dielectric film 33 is not particularly limited, and SiO ₂ (silicon dioxide, Silica), SiN (silicon nitride), AL ₂ O ₃ (aluminum oxide, alumina), MgF ₂ (magnesium fluoride), TiO ₂ (titanium dioxide), and other materials conventionally used as dielectric films are used. be able to.

  In order to appropriately adjust the light transmittance T and the reflectance R in the laminated film 20, it is preferable to laminate the adjacent dielectric films in the base-side dielectric layer 30 so as to be made of different materials. . Further, in order to flatten the transmittance T in the visible light region more than before, it is preferable that the dielectric films whose refractive index difference is within a predetermined range are adjacent to each other.

Accordingly, in the present embodiment, the first dielectric film 31 and the substrate-side third dielectric film 33 substrate side consist of SiO _2, it constitutes a substrate-side second dielectric layer 32 from SiN. In addition, from the different metal compounds in which different elements (O, N) are bonded to the common metal (Si), the substrate-side first dielectric film 31, the substrate-side second dielectric film 32, and the substrate By forming the side third dielectric film 33, it is possible to efficiently perform film formation by a dry process. That is, when forming a film by sputtering, for example, all the dielectric films constituting the base-side dielectric layer 30 can be formed by changing the reaction gas without changing the target.

  The metal layer 40 is composed of a metal film. The visible light transmittance T in the ND filter 1 can be adjusted by appropriately adjusting the film thickness of the metal layer 40. The material which comprises the metal layer 40 is not specifically limited, Ti (titanium), Cr (chromium), Ni (nickel), etc. are conventionally used as a light absorption film (light extinction film) Can be used.

  In order to stabilize the extinction of light, the material constituting the metal layer 40 is preferably any one of Ti, Cr or Ni having a molar ratio of 50% or more. In the present embodiment, the metal layer 40 is composed of a single metal film made of Ti. However, a plurality of types of metal films may be laminated to form the metal layer 40.

  The anti-base material-side dielectric layer 50 is configured by laminating an anti-base material first dielectric film 51, a high extinction film 52, and an anti-base material side second dielectric film 53 in order from the base material 10 side. ing. Among these, the anti-base material first dielectric film 51 and the anti-base material side second dielectric film 53 are films made of a dielectric, and the high extinction film 52 is included in the base material side dielectric layer 30. It is a film made of a material having a higher extinction coefficient k in the visible light region than the material. In addition, the high extinction film | membrane 52 may be comprised from a dielectric material and may be comprised from a metal.

  In the present embodiment, by disposing the anti-base material side dielectric layer 50 sandwiching the high extinction film 52 between the two dielectric films 51 and 53 in this manner on the anti-base material 10 side of the metal layer 40, the metal The extinction of visible light by the layer 40 is appropriately complemented, and the visible light transmittance T in the ND filter 1 can be flattened. That is, the flatness of the transmittance T in the visible light region can be improved more than before by using the metal layer 40 and the high extinction film 52 having different optical characteristics in combination as appropriate.

  The material constituting the high extinction film 52 is not particularly limited, and metals such as Ti, Cr, and Ni, and metal compounds such as oxides or nitrides of these metals can be used. However, the material constituting the high extinction film 52 is a material (material having different optical characteristics) different from the material constituting the metal layer 40 as described above in order to appropriately adjust the transmittance T. It is preferable. Furthermore, if the material constituting the high extinction film 52 is a metal nitride or oxide constituting the metal layer 40, the film can be formed efficiently. Therefore, in the present embodiment, the high extinction film 52 is made of TiN (titanium nitride).

The material constituting the anti-base material-side first dielectric film 51 and the anti-base material-side second dielectric film 53 is not particularly limited. Like the base material-side dielectric layer 30, SiO ₂ , SiN A material conventionally used as a dielectric film, such as AL ₂ O ₃ , MgF ₂ , and TiO ₂ , can be used. However, in order to improve the flatness of the transmittance T in the visible light region, it is preferable that the anti-base material side first dielectric film 51 and the anti base material side second dielectric film 53 are made of different materials. Furthermore, in order to perform film formation efficiently, the anti-base material side first dielectric film 51 and the anti-base material side second dielectric film 53 are made of a material common to the base material side dielectric layer 30. It is preferable. Therefore, in this embodiment, the non-base material side first dielectric film 51 is made of SiN, and the anti-base material side second dielectric film 53 is made of SiO ₂ .

  FIG. 2A is a graph showing the extinction coefficient k and refractive index n of Ti in the visible light region, and FIG. 2B shows the extinction coefficient in the visible light region when TiN is formed in a thin film. FIG. 5C is a graph showing the extinction coefficient k and the refractive index n in the visible light region when TiN is formed in a thick film.

  As shown in these figures, Ti and TiN have different optical characteristics (extinction coefficient k, refractive index n), respectively. Further, with respect to TiN, the refractive index characteristics are greatly changed by changing the film thickness. In the present embodiment, based on such characteristics, two different light extinction films (the metal layer 40 and the high extinction film 52) are used in combination, and the film thickness of both is appropriately adjusted, so that the visible light region It is possible to flatten the transmittance T at a level higher than that of the prior art.

  The film thickness of the metal layer 40 and the high extinction film 52 is not particularly limited, and depends on the required average transmittance and the characteristics of the material constituting the metal layer 40 and the high extinction film 52. Can be set appropriately. Further, if the film thickness is appropriately set together with the matching of the optical characteristics, the same effect can be obtained even by a combination of other materials.

FIG. 3A is a graph showing the extinction coefficient k and refractive index n in the visible light region of SiO ₂ , and FIG. 3B shows the extinction coefficient k and refractive index n in the visible light region of SiN. It is the graph which showed. As shown in these figures, SiO ₂ and SiN have a light extinction coefficient of approximately 0 in the visible light region.

  Therefore, in this embodiment, the visible light region extinction coefficient k of the base material side dielectric layer 30 as a whole is substantially 0, and the base material side dielectric layer 30 hardly attenuates (absorbs) visible light. ) Is configured as follows. Further, the extinction coefficient k in the visible light region of the entire anti-substrate-side dielectric layer 50 is substantially the same as the extinction coefficient k in the visible light region of the high extinction film 52.

  That is, in the present embodiment, the base-side dielectric layer 30 having a low extinction coefficient k in the visible light region (substantially 0), the metal layer 40 having a high extinction coefficient k in the visible light region, and the visible light region (of The laminated film 20 is formed by sequentially laminating an anti-base material side dielectric layer 50 having an extinction coefficient k at the same wavelength) higher than that of the base material side dielectric layer 30 and lower than that of the metal layer 40 from the base material 10 side. Thus, the flatness of the transmittance T in the visible light region can be improved.

  Furthermore, in the present embodiment, the laminated film 20 is roughly divided into a three-layer configuration of the base-side dielectric layer 30, the metal layer 40, and the anti-base-side dielectric layer 50, specifically, the base-side dielectric layer 30 and the anti-base-side dielectric layer 30. In the case where the substrate-side dielectric layer 50 has a seven-layer configuration in which three layers are configured, the substrate-side first dielectric film 31 (first layer) and the substrate-side second dielectric film 32 (second layer) ) And the base material side third dielectric film 33 (third layer), and the anti-base material side first dielectric film 51 (fifth layer) and the anti base material side second dielectric film 53 (seventh layer). By setting the refractive index appropriately, the flatness of the transmittance T in the visible light region is further enhanced.

  4 to 8 show the substrate-side first dielectric film 31 (first layer), the substrate-side third dielectric film 33 (third layer), and the anti-substrate-side second dielectric film 53 of the laminated film 20. When the refractive index of the (seventh layer) and the refractive index of the substrate-side second dielectric film 32 (second layer) and the non-substrate-side first dielectric film 51 (fifth layer) are changed, respectively. 5 is a graph showing an example of simulation results of transmittance T and reflectance R of the ND filter 1.

  In these examples, the refractive index n of the first, third, and seventh layers and the refractive index n of the second and fifth layers are assumed to be constant regardless of the wavelength. Further, the extinction coefficients k of the first, third, seventh and second, fifth layers are all assumed to be zero. The metal layer (fourth layer) is made of Ti, and the high extinction film (sixth layer) is made of TiN.

From these simulation results, in the laminated film 20 having the seven-layer structure of the present embodiment, the refractive index n of the first, third, and seventh layers is set to any value within the range of 1.38 to 2.0. By setting the refractive index n of the second and fifth layers to any value within the range of 1.38 to 2.4, the flatness of the transmittance T in the visible light region can be made within 30%. It turns out that it is possible. That is, it can be seen that the flatness of the transmittance T in the visible light region T _flat = (T _max −T _min ) / T _ave ≦ 0.3. Here, T _max is the maximum value of the transmittance T in the visible light region, T _min is the minimum value of the transmittance T in the visible light region, and T _ave is the average value of the transmittance T in the visible light region.

  When an actual material is applied to each layer, it is considered that a material having a representative refractive index (refractive index at a wavelength of 550 nm) n in the visible light region within the above range may be applied to each layer.

  Also, from these simulation results, the value of the refractive index (representative refractive index) n of the first, third, and seventh layers is less than the value of the refractive index (representative refractive index) n of the second and fifth layers. It can be seen that the flatness of the transmittance T tends to be high. Furthermore, in this case, the difference between the refractive index (representative refractive index) n of the first, third and seventh layers and the refractive index (representative refractive index) n of the second and fifth layers is about 0.5 or less. More preferably, if it is within the range of 0.2 to 0.5, the flatness of the transmittance T tends to be further increased.

  For the reflectance R, the value of the refractive index (representative refractive index) n of the first, third and seventh layers is set to 1.9 or less (that is, larger than the refractive index 1.0 of vacuum and 1.9 or less). For example, the reflectance R in the visible light region can be 2% or less, and the reflectance R in the visible light region decreases as the refractive index (representative refractive index) n of the first, third, and seventh layers decreases. It can be seen that there is a tendency to decrease.

In the present embodiment, based on such consideration, the base material side first dielectric film 31 (first layer), the base material side third dielectric film 33 (third layer), and the anti-base material of the laminated film 20 are used. The material constituting the side second dielectric film 53 (seventh layer) is SiO ₂ , and the base material side second dielectric film 32 (second layer) and the non-base material side first dielectric film 51 (fifth layer) ) Is SiN. By selecting the material in this way, it is possible to obtain an unprecedented flatness of the transmittance T in the visible light region.

  As described above, the ND filter 1 according to the present embodiment includes the base material 10 having optical transparency and the laminated film 20 formed on the surface of the base material 10, and the laminated film 20 is a dielectric. The substrate-side dielectric layer 30 having a film, the metal layer 40 made of a metal film, and the anti-base material having a higher extinction coefficient k in the visible light region than the substrate-side dielectric layer 30 and having a dielectric film The side dielectric layer 50 is laminated in order from the base material 10 side.

  With such a configuration, the extinction of light in the metal layer 40 can be appropriately adjusted by the base-side dielectric layer 30 and the anti-base-side dielectric layer 50, so that in the visible light region The transmittance T can be flattened more than before.

  The substrate-side dielectric layer 30 includes a plurality of dielectric films, and is laminated so that dielectric films made of different materials are adjacent to each other. Further, the non-base material side dielectric layer 50 has a plurality of dielectric films made of different materials. By doing in this way, since it becomes possible to adjust the transmittance | permeability T and the reflectance R more finely, the transmittance | permeability T can be planarized more than before, reducing the reflectance R. FIG.

  A dielectric film included in the base material side dielectric layer 30 (in the present embodiment, the base material side first dielectric film 31, the base material side second dielectric film 32, and the base material side third dielectric film 33). ) (Thickness) may be set as appropriate according to required characteristics, dielectric material, and the like, and is not particularly limited. The thickness of the side dielectric layer 30 is preferably set to approximately ½ wavelength (λ = 550 nm).

  Similarly, the thickness (film thickness) of the dielectric films (in this embodiment, the anti-base material side first dielectric film 51 and the anti-base material side second dielectric film 53) included in the anti-base material side dielectric layer 50. ) Is not particularly limited, but in order to reduce the reflectance R, the thickness of the outermost dielectric film (in this embodiment, the second dielectric film 53 on the side opposite to the base material) is set to about 1. It is preferable to set to / 4 wavelength (λ = 550 nm).

  Further, in the present embodiment, the base material side dielectric layer 30 has a three-layer configuration of the base material side first dielectric film 31, the base material side second dielectric film 32, and the base material side third dielectric film 33. However, the present invention is not limited to this, and the substrate-side dielectric layer 30 may be composed of one layer or may be composed of four or more layers. In other words, the number of dielectric film layers constituting the substrate-side dielectric layer 30 may be appropriately set according to required characteristics, dielectric material, and the like.

  Similarly, the anti-base-side dielectric layer 50 may have a layer configuration other than the layer configuration shown in the present embodiment, and the anti-base-side dielectric layer 50 is configured only from the high extinction film 52. It may be.

  The anti-base material-side dielectric layer 50 includes a high extinction film 52 made of a material having a higher extinction coefficient k in the visible light region than the material contained in the base material side dielectric layer 30. By doing in this way, since the metal layer 40 and the high extinction film | membrane 52 function synergistically, the transmittance | permeability T can be planarized more than before.

  The high extinction film 52 is preferably composed of metal nitride or metal oxide. By doing in this way, the high extinction film | membrane 52 of the characteristic different from the metal layer 40 can be combined suitably.

  The high extinction film 52 is more preferably composed of a metal nitride or oxide constituting the metal film (metal layer) 40. By doing in this way, it becomes possible to form the metal layer 40 and the high extinction film | membrane 52 by sputtering using the same target, for example, and film-forming can be performed efficiently and at low cost.

  Moreover, it is preferable that the material which comprises the metal film (metal layer) 40 is either titanium, chromium, or nickel which becomes 50% or more by molar ratio. By doing so, visible light can be stably extinguished.

  The substrate-side dielectric layer 30 is formed by laminating a substrate-side first dielectric film 31, a substrate-side second dielectric film 32, and a substrate-side third dielectric film 33 in order from the substrate 10 side. The anti-base material side dielectric layer 50 is configured by laminating an anti-base material side first dielectric film 51 and an anti-base material side second dielectric film 53 in order from the base material 10 side. ing. By doing in this way, the transmittance | permeability T in visible region can be planarized more than before with the minimum required structure, without increasing the number of layers (number of films) of the laminated film 20.

  Further, the anti-base material-side dielectric layer 50 is located between the anti-base material side first dielectric film 51 and the anti-base material side second dielectric film 53 than the material contained in the base material side dielectric layer 30. It has a high extinction film 52 made of a material having a high extinction coefficient k in the visible light region. By doing in this way, the high extinction film | membrane 52 which complements the metal layer 40 can be arrange | positioned appropriately.

Moreover, the base material side first dielectric film 31, the base material side third dielectric film 33, and the anti-base material side second dielectric film 53 are composed of a first material (in this embodiment, SiO ₂ ). The base-material-side second dielectric film 32 and the non-base-material-side first dielectric film 51 are made of a second material (SiN in this embodiment) different from the first material. By doing so, the transmittance T in the visible light region can be flattened with the minimum number of materials. That is, it is possible to realize the ND filter 1 having optical characteristics that are higher than conventional ones at low cost.

  At this time, the refractive index n in the visible light region of the first material is preferably less than or equal to the refractive index n in the visible light region of the second material.

  The first material has a refractive index of 1.38 to 2.0 at a wavelength of 550 nm, and the second material has a refractive index of 1.38 to 2.4 at a wavelength of 550 nm. It is preferable that the material is any one.

  The difference between the refractive index of the first material at a wavelength of 550 nm and the refractive index of the second material at a wavelength of 550 nm is preferably 0.5 or less.

  Thus, by using the first material and the second material having an appropriate refractive index, the transmittance T in the visible light region can be flattened more than ever.

  Further, the first material and the second material are preferably different metal compounds in which different elements are bonded to a common metal. By doing in this way, film-forming can be performed efficiently.

  Moreover, it is preferable that the material which comprises the high extinction film | membrane 52, and a 2nd material are mutually different metal compounds which the common element couple | bonded with the different metal. By doing in this way, film-forming can be performed efficiently.

The first material is preferably silicon dioxide (SiO ₂ ), and the second material is preferably silicon nitride (SiN). By doing so, it is possible to increase the efficiency of film formation and reduce the cost while selecting an optimal combination of materials for flattening the transmittance T.

  The material constituting the metal film (metal layer) 40 is preferably titanium (Ti), and the material constituting the high extinction film 52 is preferably titanium nitride (TiN). By doing so, it is possible to increase the efficiency of film formation and reduce the cost while selecting an optimal combination of materials for flattening the transmittance T.

  Note that the ND filter of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.

  Next, examples of the present invention will be described.

FIG. 9 is a table showing the configuration of the ND filter 1 according to the embodiment of the present invention. In this embodiment, as shown in the figure, the substrate-side first dielectric film 31 of the substrate-side dielectric layer 30 is SiO ₂ , the substrate-side second dielectric film 32 is SiN, 3 The dielectric film 33 is made of SiN, the metal layer 40 is made of Ti, the anti-base material side first dielectric film 51 of the anti-base material side dielectric layer 50 is SiN, the high extinction film 52 is TiN, and the anti base material side. A laminated film 20 in which the second dielectric film 53 was made of SiO ₂ was formed on the base material 10 of a PET sheet having a thickness of 100 μm.

  The thickness (film thickness) of the laminated film 20 is 0.568 for the base-side first dielectric film 31, 0.2187 for the base-side second dielectric film 32, and 0 for the base-side third dielectric film 33. 2683, metal layer 40 is 0.062, anti-base material side first dielectric film 51 is 0.1456, high extinction film 52 is 0.0602, and anti-base material side second dielectric film is 0.2042. (All optical film thickness (λ = 550 nm)).

For the film formation, carousel type DC-PULSE magnetron sputtering was used. The target is a 30 inch × 4 inch Si target and a Ti target. Ar (argon) gas is introduced to form a Ti film, and Ar + N ₂ (nitrogen) gas is introduced to form a TiN film and a SiN film. Then, Ar + O ₂ (oxygen) gas was introduced to form the SiO ₂ film. The introduction amount of each gas, 150SCCM of Ar gas, _{N 2} gas and _{O 2} gas was 120 SCCM, film forming pressure is, Ti film 4E-2 Pa in the formation of, 5E-2 Pa in the formation of the SiO ₂ film, SiN film and In the formation of the TiN film, the pressure was 6E-2 Pa.

  FIG. 10A is a graph showing a simulation result of the transmittance T and the reflectance R of the ND filter 1 of the present embodiment, and FIG. 10B is a graph showing the transmittance T of the ND filter 1 of the present embodiment. It is the graph which showed the actual measurement result of reflectance R. As shown in these drawings, according to the configuration of the present example, it was confirmed that the flatness of the transmittance T can be improved more than before in both the simulation result and the actual measurement result. Moreover, it was confirmed that the reflectance R can be reduced more than before.

  The ND filter of the present invention can be used in the field of various optical devices that use visible light in addition to the field of various imaging devices such as analog cameras, digital cameras, and video cameras.

DESCRIPTION OF SYMBOLS 1 ND filter 10 Base material 20 Laminated film 30 Base material side dielectric layer 31 Base material side 1st dielectric film 32 Base material side 2nd dielectric film 33 Base material side 3rd dielectric film 40 Metal layer 50 Anti-base material Side dielectric layer 51 Anti-base material side first dielectric film 52 High extinction film 53 Anti-base material side second dielectric film

(1) The present invention includes a light-transmitting base material and a laminated film formed on the surface of the base material, and the laminated film is composed of a plurality of dielectric films, and dielectric materials made of different materials. A base material-side dielectric layer formed by stacking so that the body films are adjacent to each other , a metal layer made of a metal film, and an extinction coefficient in the visible light region than the material included in the base material-side dielectric layer A high extinction film made of a high metal compound and an anti-base material-side dielectric layer constituted by alternately laminating dielectric films, and laminated in order from the base material side. The ND filter.

(2) The present invention is also characterized in that the anti-base material-side dielectric layer is configured such that a dielectric film made of nitride is adjacent to the metal layer. It is an ND filter.

(3) The present invention is also the ND filter according to the above (1) or (2), wherein the anti-substrate-side dielectric layer has a plurality of dielectric films made of different materials. .

(4) The present invention is also the ND filter according to any one of (1) to (3) , wherein the high extinction film is made of metal nitride or metal oxide.

(5) The present invention is also the ND filter according to (4) , wherein the high extinction film is made of a metal nitride or an oxide constituting the metal film.

(6) The present invention is also characterized in that the material constituting the metal film is any one of titanium, chromium or nickel having a molar ratio of 50% or more. The ND filter according to any one of the above.

(7) The present invention is also characterized in that the material constituting the metal film is titanium and the material constituting the high extinction film is titanium nitride. The ND filter according to any one of the above.

(8) In the present invention, the substrate-side dielectric layer is configured by laminating a silicon dioxide film, a silicon nitride film, and a silicon dioxide film in order from the substrate side, and the metal layer includes: The anti-base material-side dielectric layer is formed by laminating a silicon nitride film, a titanium nitride film, and a silicon dioxide film in order from the base material side. The ND filter according to any one of (1) to (7).

(9) In the present invention, the substrate-side dielectric layer may include a substrate-side first dielectric film, a substrate-side second dielectric film, and a substrate-side third dielectric film. The anti-base material-side dielectric layer is formed by laminating the anti-base material-side first dielectric film, the high extinction film, and the anti-base material-side second dielectric film to the base material side. The ND filter according to any one of the above (1) to (7), wherein the ND filter is configured by laminating sequentially.

Claims (17)

A substrate having light permeability, and a laminated film formed on the surface of the substrate,
The laminated film includes a base material-side dielectric layer having a dielectric film, a metal layer made of a metal film, a higher extinction coefficient in the visible light region than the base material-side dielectric layer, and a dielectric film. The anti-base material-side dielectric layer having, and characterized by being laminated in order from the base material side,
ND filter. The base material-side dielectric layer has a plurality of the dielectric films, and is configured such that the dielectric films made of different materials are adjacent to each other.
The ND filter according to claim 1. The anti-substrate-side dielectric layer has a plurality of the dielectric films made of different materials,
The ND filter according to claim 1. The anti-base material-side dielectric layer includes a high extinction film composed of a material having a higher extinction coefficient in the visible light region than the material contained in the base material-side dielectric layer.
The ND filter according to claim 1. The high extinction film is composed of a metal nitride or a metal oxide,
The ND filter according to claim 4. The high extinction film is made of a metal nitride or oxide constituting the metal film,
The ND filter according to claim 5. The material constituting the metal film is any one of titanium, chromium or nickel having a molar ratio of 50% or more,
The ND filter according to claim 1. The base material side dielectric layer is configured by laminating a base material side first dielectric film, a base material side second dielectric film, and a base material side third dielectric film in order from the base material side,
The anti-base material-side dielectric layer is formed by laminating an anti-base material side first dielectric film and an anti-base material side second dielectric film in order from the base material side,
The ND filter according to claim 1. The anti-base material side dielectric layer is more visible than the material contained in the base material side dielectric layer between the anti base material side first dielectric film and the anti base material side second dielectric film. It has a high extinction film composed of a material having a high extinction coefficient in the region,
The ND filter according to claim 8. The base material side first dielectric film, the base material side third dielectric film, and the anti-base material side second dielectric film are made of a first material,
The base material side second dielectric film and the anti-base material side first dielectric film are made of a second material different from the first material,
The ND filter according to claim 9. The refractive index in the visible light region of the first material is not more than the refractive index in the visible light region of the second material,
The ND filter according to claim 10. The first material is a material having a refractive index of 1.38 to 2.0 at a wavelength of 550 nm,
The second material is a material having a refractive index of 1.38 to 2.4 at a wavelength of 550 nm,
The ND filter according to claim 11. The difference between the refractive index of the first material at a wavelength of 550 nm and the refractive index of the second material at a wavelength of 550 nm is 0.5 or less,
The ND filter according to claim 11 or 12. The first material and the second material are different metal compounds in which different elements are bonded to a common metal,
The ND filter according to claim 10. The material constituting the high extinction film and the second material are different metal compounds in which a common element is bonded to different metals,
The ND filter according to claim 10. The first material is silicon dioxide;
The second material is silicon nitride,
The ND filter according to claim 10. The material constituting the metal film is titanium,
The material constituting the high extinction film is titanium nitride,
The ND filter according to claim 10.

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