阅读说明：本技术 偏光板及其制造方法、以及光学设备
(Polarizing plate, method for manufacturing same, and optical device
) 是由 大和田雅弘 于 2019-02-13 设计创作，主要内容包括：具有线栅构造的偏光板(1),其具有透明基板(10)和以比使用波段的光的波长短的间距在透明基板(10)上配置排列且沿预定方向延伸的格子状凸部(11),格子状凸部(11)从透明基板(10)侧起,依次具有反射层(13)、介电体层(14)、以及吸收层(15),反射层(13)的宽度(b)比介电体层(14)的宽度及吸收层(15)的宽度(栅格宽度(a))的任一个都小。由此,能够提供一种可更准确地控制吸收轴反射率的波长分散的偏光板。(A polarizing plate (1) having a wire grid structure, which comprises a transparent substrate (10) and grid-like projections (11) arranged on the transparent substrate (10) at a pitch shorter than the wavelength of light in a use wavelength band and extending in a predetermined direction, wherein the grid-like projections (11) have a reflective layer (13), a dielectric layer (14), and an absorbing layer (15) in this order from the transparent substrate (10) side, and the width (b) of the reflective layer (13) is smaller than either the width of the dielectric layer (14) or the width (grid width (a)) of the absorbing layer (15). Thus, a polarizing plate capable of controlling the wavelength dispersion of the absorption axis reflectance more accurately can be provided.)
1. A polarizing plate having a wire grid structure, comprising:
a transparent substrate; and
lattice-shaped projections arranged on the transparent substrate at a pitch shorter than the wavelength of light in a used wavelength band and extending in a predetermined direction,
the lattice-like projection has a reflective layer, a dielectric layer and an absorbing layer in this order from the transparent substrate side,
the maximum width of the reflective layer is smaller than either the maximum width of the dielectric layer or the maximum width of the absorption layer.
2. The polarizing plate according to claim 1,
the maximum width of the dielectric layer is substantially the same as the maximum width of the absorption layer.
3. The polarizing plate according to claim 1 or 2,
the thickness of the dielectric layer is 1 to 50 nm.
4. The polarizing plate according to any one of claims 1 to 3,
the thickness of the absorption layer is 10 to 50 nm.
5. The polarizing plate according to any one of claims 1 to 4,
the transparent substrate is transparent to the wavelength of light in the use wavelength band and is made of glass, crystal, or sapphire.
6. The polarizing plate according to any one of claims 1 to 5,
the reflective layer is made of aluminum or an aluminum alloy.
7. The polarizing plate according to any one of claims 1 to 6,
the dielectric layer is made of Si oxide.
8. The polarizing plate according to any one of claims 1 to 7,
the absorption layer is formed of Fe or Ta and Si.
9. The polarizing plate according to any one of claims 1 to 8,
the surface of the polarizing plate on which light is incident is covered with a protective film made of a dielectric material.
10. The polarizing plate according to any one of claims 1 to 9,
the surface of the polarizing plate on which light is incident is covered with an organic water-repellent film.
11. A method for manufacturing a polarizing plate having a wire grid structure,
the method for manufacturing a polarizing plate is characterized by comprising:
a reflective layer forming step of forming a reflective layer on a transparent substrate;
a dielectric layer forming step of forming a dielectric layer on the reflective layer;
an absorption layer forming step of forming an absorption layer on the dielectric layer; and
an etching step of selectively etching the formed laminate to form lattice-shaped projections arranged on the transparent substrate at a pitch shorter than the wavelength of light in the use wavelength band and extending in a predetermined direction,
in the etching step, the maximum width of the reflective layer is made smaller than the maximum width of the dielectric layer and the maximum width of the absorption layer.
12. The method for manufacturing a polarizing plate according to claim 11,
in the etching step, the maximum width of the reflective layer is adjusted so that the absorption axis reflectance in the wavelength range of the light in the use wavelength band is minimized.
13. An optical device comprising the polarizing plate according to any one of claims 1 to 10.
Technical Field
The invention relates to a polarizing plate, a method for manufacturing the same, and an optical apparatus.
Background
The polarizing plate is an optical element that absorbs polarized light in the absorption axis direction and transmits polarized light in the transmission axis direction orthogonal to the absorption axis direction. In recent years, in optical devices such as liquid crystal projectors, which require heat resistance, wire grid type inorganic polarizing plates have been used in place of organic polarizing plates.
The inorganic polarizing plate comprises a reflective layer, a dielectric layer and an absorbing layer in this order from the transparent substrate side. These inorganic layers are formed by a physical film formation method or the like, and a line-grid type polarizer pattern is formed by a photo dry etching technique or the like.
However, liquid Crystal projectors may have different light source spectra and different channel wavelengths constituting the visible light range of 3lcd (liquid Crystal display) depending on manufacturers. Therefore, a polarizing plate having optimum optical characteristics in accordance with the channel wavelength of each manufacturer is required.
The absorption axis reflectance characteristic, which is a characteristic of the polarizing plate, is generally controlled by adjusting the thicknesses of the dielectric layer and the absorption layer to suppress wavelength dispersion of the absorption axis reflectance characteristic, thereby performing channel control in the visible light range. In this case, the thicknesses of the dielectric layer and the absorption layer are adjusted so that the absorption axis reflectance in the channel wavelength range to be selected is the lowest, and the optical design is exclusively designed.
Disclosure of Invention
Problems to be solved by the invention
Each of the inorganic layers constituting the inorganic polarizing plate is generally designed to have a rectangular cross section with a uniform dimension in the width direction, and is formed by the above-described physical etching technique. In this case, the absorption layer at the front end of the polarizer is etched by physical etching at all times, and the thickness and volume thereof fluctuate according to variations in the degree of vacuum and the air pressure control of the etching apparatus. As a result, the wavelength range in which the absorption axis reflectance characteristic is the lowest also fluctuates, and it is difficult to obtain the absorption axis reflectance characteristic optimal for the channel wavelength range of each manufacturer.
The present invention has been made in view of the above, and an object thereof is to provide a polarizing plate capable of controlling wavelength dispersion of absorption axis reflectance more accurately.
Means for solving the problems
In order to achieve the above object, the present invention provides a polarizing plate (for example, a polarizing plate 1 described later) having a wire grid structure, the polarizing plate including: a transparent substrate (e.g., a transparent substrate 10 described later); and lattice-shaped projections (for example, lattice-shaped projections 11 described later) arranged on the transparent substrate at a pitch shorter than the wavelength of light in the use wavelength band and extending in a predetermined direction, the lattice-shaped projections having, in order from the transparent substrate side, a reflective layer (for example, a reflective layer 13 described later), a dielectric layer (for example, a dielectric layer 14 described later), and an absorbing layer (for example, an absorbing layer 15 described later), the maximum width of the reflective layer (for example, the width b of the reflective layer described later) being smaller than any one of the maximum width of the dielectric layer (for example, the width b of the reflective layer described later) and the maximum width of the absorbing layer (for example, the grating width a described later).
The maximum width of the dielectric layer may be substantially the same as the maximum width of the absorber layer.
The thickness of the dielectric layer may be 1 to 50 nm.
The thickness of the absorption layer may be 10 to 50 nm.
The transparent substrate may be made of glass, crystal, or sapphire, and may be transparent to the wavelength of light in the use wavelength band.
The reflective layer may be made of aluminum or an aluminum alloy.
The dielectric layer may be made of an Si oxide.
The absorption layer may be formed of Fe or Ta and Si.
The surface of the polarizing plate on which light enters may be covered with a protective film made of a dielectric material (e.g., a dielectric protective film 20 described later).
The surface of the polarizing plate on which light is incident may be covered with an organic water-repellent film.
In addition, the present invention provides a method for manufacturing a polarizing plate having a wire grid structure, the method comprising: a reflective layer forming step of forming a reflective layer on a transparent substrate; a dielectric layer forming step of forming a dielectric layer on the reflective layer; an absorption layer forming step of forming an absorption layer on the dielectric layer; and an etching step of selectively etching the formed laminate to form lattice-shaped projections arranged on the transparent substrate at a pitch shorter than the wavelength of light in the use wavelength band and extending in a predetermined direction, wherein in the etching step, the maximum width of the reflective layer is made smaller than the maximum width of the dielectric layer and the maximum width of the absorption layer.
In the etching step, the maximum width of the reflective layer may be adjusted so that the absorption axis reflectance in the wavelength range of the light in the use wavelength band is the lowest.
The present invention also provides an optical device including any one of the polarizing plates described above.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the present invention, it is possible to provide a polarizing plate capable of controlling the wavelength dispersion of the absorption axis reflectance more accurately.
Drawings
Fig. 1 is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention.
Fig. 2 is a graph showing the optical characteristics of the polarizing plate of example 1 in which the width of the reflective layer is 88% with respect to the width of the grid.
Fig. 3 is a diagram showing the optical characteristics of the polarizing plate of example 2 in which the width of the reflective layer is 56% with respect to the width of the grid.
Fig. 4 is a diagram showing the optical characteristics of the polarizing plate of comparative example 1 in which the width of the reflective layer is the same as the width of the grid.
Detailed Description
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[ polarizing plate ]
A polarizing plate according to an embodiment of the present invention is an inorganic polarizing plate having a wire grid structure, including: a transparent substrate; and lattice-shaped projections arranged on the transparent substrate at a pitch (period) shorter than the wavelength of light in the use wavelength band and extending in a predetermined direction. The lattice-shaped projection has a reflective layer, a dielectric layer, and an absorbing layer in this order from the transparent substrate side.
Fig. 1 is a schematic cross-sectional view of a polarizing plate 1 according to an embodiment of the present invention. As shown in fig. 1, the polarizing plate 1 includes a transparent substrate 10 transparent to light in a use wavelength band, and lattice-shaped protrusions 11 arranged on one surface of the transparent substrate 10 at a pitch shorter than the wavelength of light in the use wavelength band. The lattice-shaped projection 11 includes a base 12, a reflective layer 13, a dielectric layer 14, an absorption layer 15, and a dielectric layer 16 in this order from the transparent substrate 10 side. That is, the polarizing plate 1 has the following wire grid structure: the lattice-shaped projections 11 formed by sequentially laminating the base 12, the reflective layer 13, the dielectric layer 14, the absorber layer 15, and the dielectric layer 16 from the transparent substrate 10 side are arranged in a one-dimensional lattice shape on the transparent substrate 10.
Here, as shown in fig. 1, the direction (predetermined direction) in which the lattice-shaped projections 11 extend is referred to as the Y-axis direction. The direction perpendicular to the Y-axis direction and in which the lattice-shaped projections 11 are arranged along the main surface of the transparent substrate 10 is referred to as the X-axis direction. In this case, the light incident on the polarizing plate 1 is preferably incident from a direction orthogonal to the X-axis direction and the Y-axis direction on the side of the transparent substrate 10 where the lattice-shaped protrusions 11 are formed.
The polarizing plate 1 attenuates a polarized light wave (TE wave (S wave)) having an electric field component parallel to the Y-axis direction and transmits a polarized light wave (TM wave (P wave)) having an electric field component parallel to the X-axis direction by utilizing four actions of transmission, reflection, interference, and selective light absorption of the polarized light wave by optical anisotropy. Thus, the Y-axis direction is the direction of the absorption axis of the polarizing plate 1, and the X-axis direction is the direction of the transmission axis of the polarizing plate 1.
Light entering from the side of the polarizing plate 1 where the lattice-shaped protrusions 11 are formed is partially absorbed and attenuated when passing through the dielectric layer 16, the absorption layer 15, and the dielectric layer 14. The polarized light wave (TM wave (P wave)) of the light transmitted through the dielectric layers 16, 15, and 14 transmits the reflective layer 13 at a high transmittance. On the other hand, a polarized wave (TE wave (S wave)) of light transmitted through the dielectric layers 16, 15, and 14 is reflected by the reflective layer 13. When the TE wave reflected by the reflective layer 13 passes through the dielectric layer 16, the absorption layer 15 and the dielectric layer 14, a part of the TE wave is absorbed and a part of the TE wave is reflected and returns to the reflective layer 13. The TE wave reflected by the reflective layer 13 interferes with and attenuates when passing through the dielectric layer 16, the absorption layer 15, and the dielectric layer 14. As described above, the polarizing plate 1 can obtain desired polarization characteristics by selectively attenuating the TE wave.
As shown in fig. 1, when viewed from the direction in which each primary cell extends (hereinafter, the predetermined direction), that is, when viewed in a cross section orthogonal to the predetermined direction, the lattice-shaped projection 11 has a rectangular pedestal 12, a rectangular lattice leg 17, and a rectangular lattice tip 18. However, the shapes of the base 12, the grid leg 17, and the grid tip 18 are not limited to rectangular shapes, and may be any shapes. For example, the corners of the grid tips 18 of the grid-like projections 11 may be rounded or tapered by etching.
The grid leg 17 is formed extending vertically from the pedestal 12. The grid leg 17 is formed of the reflective layer 13. That is, the boundary between the grid leg 17 and the grid tip 18 is located at the boundary between the reflective layer 13 and the dielectric layer 14.
As shown in fig. 1, the grid tip portion 18 of the present embodiment has a rectangular shape when viewed from a predetermined direction. The grid tip 18 is composed of the dielectric layer 14, the absorber layer 15, and the dielectric layer 16.
However, the dielectric layer 16 is not essential, and the grid tip 18 may be composed of the dielectric layer 14 and the absorber layer 15.
In the following description, the height direction is a direction perpendicular to the main surface of the transparent substrate 10, and the width is a dimension in the X-axis direction perpendicular to the height direction when viewed from the Y-axis direction along the direction in which the lattice-shaped projections 11 extend. When the polarizing plate 1 is viewed from the Y-axis direction along the direction in which the lattice-shaped protrusions 11 extend, the repeating interval of the lattice-shaped protrusions 11 in the X-axis direction is referred to as a pitch P.
The pitch P of the lattice-shaped projections 11 is not particularly limited as long as it is shorter than the wavelength of light in the use wavelength band. The pitch P of the lattice-shaped projections 11 is preferably, for example, 100nm to 200nm from the viewpoint of ease of production and stability. The pitch P of the lattice-shaped convex portions 11 can be measured by observation with a scanning electron microscope or a transmission electron microscope. For example, the pitch P can be measured for any four positions using a scanning electron microscope or a transmission electron microscope, and the arithmetic average thereof can be taken as the pitch P of the lattice-shaped convex portion 11. Hereinafter, this measurement method is referred to as electron microscopy.
As shown in fig. 1, the width of the grid tip 18 of the grid-like projection 11 in the X-axis direction is referred to as a grid width a. The grid width a is the same as the width of the dielectric layer 14, the absorber layer 15, and the dielectric layer 16 in the X-axis direction. Specifically, the grid width a is preferably 35 to 45 nm. The grid width a can be measured by the electron microscopy method described above, for example.
Here, in the present invention, when the shape of the reflective layer 13 constituting the grid leg 17, the shapes of the dielectric layers 14, the absorber layer 15, and the dielectric layer 16 constituting the grid tip portion 18, and the shape of the pedestal 12 described later are not rectangular and the widths thereof in the height direction are varied, the width of each layer in the X axis direction means the maximum width of each layer in the X axis direction. In this case, the grid width "a" refers to the maximum width of the grid tip 18 in the X-axis direction.
In particular, the shapes of the dielectric layer 14 and the absorption layer 15 may be any shapes that can satisfy the optical characteristics described above in a shape with a reduced volume, as compared with a rectangular shape having a design structure that satisfies the desired optical characteristics.
The transparent substrate 10 is not particularly limited as long as it has translucency to light in the use wavelength band, and can be appropriately selected according to the purpose. The phrase "light transmittance with respect to light in the use wavelength band" does not mean that the transmittance of light in the use wavelength band is 100%, and it is sufficient that the light transmittance is exhibited so that the function of the polarizing plate can be maintained. The light in the wavelength band used may be, for example, visible light having a wavelength of about 380nm to 810 nm.
The shape of the main surface of the transparent substrate 10 is not particularly limited, and the shape (for example, rectangular shape) can be appropriately selected according to the purpose. The average thickness of the transparent substrate 10 is preferably 0.3mm to 1mm, for example.
The material constituting the transparent substrate 10 is preferably a material having a refractive index of 1.1 to 2.2, and examples thereof include glass, crystal, sapphire and the like. From the viewpoint of cost and light transmittance, glass, particularly quartz glass (refractive index 1.46) and soda-lime glass (refractive index 1.51) are preferably used. The composition of the glass material is not particularly limited, and for example, an inexpensive glass material such as silicate glass widely used as optical glass can be used.
In addition, from the viewpoint of thermal conductivity, crystal or sapphire having high thermal conductivity is preferably used. Thus, high light resistance can be obtained for strong light, and the polarizing plate is preferably used as a polarizing plate for an optical engine of a projector which generates a large amount of heat.
When a transparent substrate made of an optically active crystal such as quartz is used, the lattice-shaped projections 11 are preferably arranged in a direction parallel to or perpendicular to the optical axis of the crystal. Thereby, excellent optical characteristics can be obtained. Here, the optical axis is a direction axis in which the difference between refractive indexes of O (normal light) and E (extraordinary light) of light traveling in the direction is smallest.
The shape of the transparent substrate 10 is not particularly limited, and may be, for example, a wafer shape of 6 inches or 8 inches. When the transparent substrate 10 is formed in a wafer shape, the lattice-shaped projections 11 are formed and then cut out to an arbitrary size by a scribing apparatus or the like, whereby the rectangular polarizing plate 1 can be obtained, for example.
As shown in fig. 1, the pedestal 12 of the present embodiment has a rectangular shape when viewed from the direction (predetermined direction) in which each primary cell extends, that is, in a cross-sectional view orthogonal to the predetermined direction.
The width of the pedestal 12 in the X-axis direction is preferably equal to or greater than the width of the reflective layer 13. These widths can be measured, for example, by the electron microscopy described above.
The film thickness of the pedestal 12 is not particularly limited, and is preferably 10nm to 100nm, for example. The film thickness of the pedestal 12 can be measured by, for example, the electron microscopy described above.
The base 12 is formed by arranging dielectric films extending in a band shape in the Y-axis direction as the absorption axis on the transparent substrate 10. The material constituting the pedestal 12 is limited to a material which is transparent to light in the use wavelength band and has a refractive index smaller than that of the transparent substrate 10, and among these, SiO is preferable2And the like.
The pedestal 12 can be formed by, for example, changing the balance between isotropic etching and anisotropic etching by dry etching in a stepwise manner with respect to the base layer 19 made of the dielectric material formed on the transparent substrate 10. In this case, as shown in fig. 1, the pedestal 12 is disposed on a base layer 19 formed on the transparent substrate 10.
The reflective layer 13 is formed on the base 12, and is formed by arranging and arranging a metal film extending in a band shape in the Y-axis direction as the absorption axis. More specifically, as shown in fig. 1, the reflective layer 13 of the present embodiment extends perpendicularly from the pedestal 12 and has a rectangular shape when viewed from the predetermined direction, that is, in a cross-sectional view orthogonal to the predetermined direction. The reflective layer 13 has a function as a wire grid polarizer, and attenuates a polarized wave (TE wave (S wave)) having an electric field component in a direction parallel to the longitudinal direction of the reflective layer 13, and transmits a polarized wave (TM wave (P wave)) having an electric field component in a direction orthogonal to the longitudinal direction of the reflective layer 13.
The material constituting the reflective layer 13 is not particularly limited as long as it is a material having reflectivity for light of a wavelength band to be used, and examples thereof include elemental materials such as Al, Ag, Cu, Mo, Cr, Ti, Ni, W, Fe, Si, Ge, and Te, and alloys containing one or more of these elements. Among them, the reflective layer 13 is preferably made of aluminum or an aluminum alloy. In addition to these metal materials, the reflective layer 13 may be formed of an inorganic film or a resin film other than a metal whose surface reflectance is high by coloring or the like, for example.
The film thickness of the reflective layer 13 is not particularly limited, and is preferably 100nm to 300nm, for example. The film thickness of the reflective layer 13 can be measured, for example, by the electron microscopy described above.
The width b of the reflective layer 13 in the X-axis direction is preferably equal to or less than the width of the pedestal 12. The width b of the reflective layer 13 is designed to be smaller than the grid width a (the width of the dielectric layer 14, the width of the absorption layer 15). The width b of the reflective layer 13 can be measured by, for example, the electron microscopy method described above.
As a method for making the width b of the reflective layer 13 smaller than the width of the pedestal 12 and the grid width a, for example, isotropic etching by wet etching or additional processing by wet etching may be mentioned as will be described later in detail. As described above, although the reflective layer 13 reflects light, the area of the reflective layer 13 viewed from the light incidence direction can be changed by controlling the width b of the reflective layer 13, and the amount of light reflected by the reflective layer 13 can be changed. Thus, by controlling the ratio of the width b of the reflective layer 13 to the grid width a, the light transmission characteristics of the polarizing plate 1 can be controlled.
Further, by making the width b of the reflective layer 13 smaller than the grating width a (the width of the dielectric layer 14, the width of the absorption layer 15), the wavelength dispersion of the absorption axis reflectance Rs can be shifted to the longer wavelength side.
Here, the absorption axis reflectance Rs is a reflectance of polarized light in the absorption axis direction (Y axis direction) incident to the polarizing plate 1. The absorption axis reflectance Rs has a characteristic of being the lowest in a wavelength range in the visible light range. That is, a curve obtained by plotting the absorption axis reflectance Rs with respect to the wavelength has a very small peak that is convex downward (see fig. 2 to 4 described later).
That is, in the present embodiment, by making the width b of the reflection layer 13 smaller than the grid width a (the width of the dielectric layer 14, the width of the absorption layer 15), the wavelength range in which the absorption axis reflectance Rs is the lowest can be shifted to the longer wavelength side, and the absorption axis reflectance Rs of the polarizing plate 1 can be accurately controlled.
The dielectric layer 14 is formed on the reflective layer 13 and arranged by a dielectric film extending in a stripe shape in the Y-axis direction as the absorption axis. The dielectric layer 14 is formed to have a thickness that shifts the phase of the polarized light reflected by the absorbing layer 15 by a half wavelength with respect to the polarized light transmitted by the absorbing layer 15 and reflected by the reflecting layer 13. Specifically, the film thickness of the dielectric layer 14 is set to be within a range of 1 to 500nm, which can adjust the phase of polarized light and improve the interference effect. More preferably, the film thickness is in the range of 1 to 50 nm. The film thickness of the dielectric layer 14 can be measured by, for example, the electron microscopy described above.
As a material constituting the dielectric layer 14, SiO can be mentioned2isoSi oxide, Al2O3Metal oxides such as beryllium oxide and bismuth oxide, MgF2Cryolite, germanium, titanium dioxide, silicon, magnesium fluoride, boron nitride, boron oxide, tantalum oxide, carbon, or a combination thereof. Among them, the dielectric layer 14 is preferably made of Si oxide.
The refractive index of the dielectric layer 14 is preferably larger than 1.0 and 2.5 or less. Since the optical characteristics of the reflective layer 13 are also affected by the refractive index of the surroundings, the polarizing plate characteristics can be controlled by selecting the material of the dielectric layer 14.
Further, by appropriately adjusting the film thickness and refractive index of the dielectric layer 14, the TE wave reflected by the reflective layer 13 can be partially reflected and returned to the reflective layer 13 while passing through the absorption layer 15, and the light passing through the absorption layer 15 can be attenuated by interference. By selectively attenuating the TE wave in this manner, desired polarization characteristics can be obtained.
The absorption layer 15 is formed on the dielectric layer 14, and is arranged to extend in a band shape along the Y-axis direction as an absorption axis. The material constituting the absorption layer 15 may be one or more substances having an optical absorption function and an extinction constant different from zero, such as a metal material and a semiconductor material, and is appropriately selected according to the wavelength range of light to be applied. Examples of the metal material include a single element such as Ta, Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni, Fe, and Sn, and an alloy containing one or more of these elements. In addition, as a semiconductor material,examples thereof include Si, Ge, Te, ZnO and silicide material (β -FeSi)2、MgSi2、NiSi2、BaSi2、CrSi2、CoSi2TaSi, etc.). By using these materials, the polarizing plate 1 can obtain a high extinction ratio with respect to the visible light range of application. Among them, the absorption layer 15 is preferably composed of Fe or Ta and Si.
When a semiconductor material is used as the absorption layer 15, the band gap energy of the semiconductor is related to the absorption action, and therefore the band gap energy is required to be equal to or less than the use wavelength band. For example, when used under visible light, it is necessary to use a material of 3.1eV or less as an absorption, i.e., a band gap, having a wavelength of 400nm or more.
The thickness of the absorption layer 15 is not particularly limited, and is preferably 10nm to 100nm, for example. More preferably, the film thickness is in the range of 10 to 50 nm. The film thickness of the absorption layer 15 can be measured by, for example, the electron microscopy described above.
The absorption layer 15 can be formed as a high-density film by a vapor deposition method or a sputtering method. The absorption layer 15 may be formed of two or more layers of different materials.
The dielectric layer 16 is made of a dielectric film. The dielectric layer 16 can be formed as a high-density film by vapor deposition or sputtering, similarly to the absorber layer 15.
The polarizing plate 1 of the present embodiment having the above-described structure may have a diffusion barrier layer between the dielectric layer 14 and the absorber layer 15. That is, in this case, the lattice-shaped projection 11 includes a base 12, a reflective layer 13, a dielectric layer 14, a diffusion barrier layer, an absorber layer 15, and a dielectric layer 16 in this order from the transparent substrate 10 side. By having the diffusion barrier layer, the diffusion of light of the absorption layer 15 can be prevented. The diffusion barrier layer is composed of a metal film of Ta, W, Nb, Ti, or the like.
As shown in fig. 1, the polarizing plate 1 of the present embodiment may have a surface on the light incidence side covered with a dielectric protective film 20. The dielectric protective film 20 can be formed on the surface (the surface on which the wire grid is formed) of the polarizing plate 1 by, for example, cvd (chemical Vapor deposition) or ald (atomic Layer deposition). This can suppress an excessive oxidation reaction to the metal film.
Further, the surface of the polarizing plate 1 of the present embodiment on the light incidence side may be covered with an organic water-repellent film (not shown). The organic water-repellent film can be formed by CVD or ALD, for example. This can improve reliability such as moisture resistance of the polarizing plate 1.
The thicknesses of the dielectric protective film 20 and the organic water-repellent film are extremely small compared with the thicknesses of the reflective layer 13, the dielectric layer 14, the absorber layer 15, and the like. Therefore, when the dielectric protective film 20 and the organic water repellent film are provided, the grid width "a" does not include the film thickness of the dielectric protective film 20 and the film thickness of the organic water repellent film.
[ method for producing polarizing plate ]
The method for manufacturing the polarizing plate 1 of the present embodiment includes a base layer forming step, a reflective layer forming step, a dielectric layer forming step, an absorbing layer forming step, and an etching step.
In the base layer forming step, a base layer is formed on the transparent substrate 10. In the reflective layer forming step, a reflective layer is formed on the base layer formed in the base layer forming step. In the dielectric layer forming step, a dielectric layer is formed on the reflective layer formed in the reflective layer forming step. In the absorber layer forming step, an absorber layer is formed on the dielectric layer formed in the dielectric layer forming step. In the step of forming each layer, each layer can be formed by, for example, a sputtering method or a vapor deposition method.
In the dielectric layer forming step, the film thickness of the dielectric layer 14 is set so that the position of the extremely small peak of the absorption axis reflectance Rs is on the shorter wavelength side than the visible light range (hereinafter referred to as channel) to be selected.
Similarly, in the absorption layer forming step, the film thickness of the absorption layer 15 is set so that the position of the extremely small peak of the absorption axis reflectance Rs is on the shorter wavelength side than the visible light range (hereinafter referred to as channel) to be selected.
This is because the wavelength dispersion of the absorption axis reflectance Rs can be shifted to the longer wavelength side by selectively etching the width b of the reflective layer 13 to be smaller than the grating width a in the etching step described later.
In the etching step, the stacked body formed in the above-described layer forming step is selectively etched, thereby forming lattice-shaped projections 11 arranged on the transparent substrate 10 at a pitch shorter than the wavelength of light in the wavelength band used. Specifically, a mask pattern in a primary cell lattice shape is formed by, for example, a photolithography method or a nanoimprint method.
Then, the stacked body is selectively etched to form lattice-shaped projections 11 arranged on the transparent substrate 10 at a pitch shorter than the wavelength of light in the use wavelength band. As the etching method, for example, a dry etching method using an etching gas corresponding to an etching target can be cited.
In particular, in this embodiment, by optimizing the etching conditions (gas flow rate, gas pressure, output, and cooling temperature of the transparent substrate), the width b of the reflective layer 13 can be made smaller than the grid width a (width of the dielectric layer 14 and width of the absorber layer 15). Specifically, the control of the width b of the reflective layer 13 can be performed by, for example, reactive etching (isotropic etching) in which the etching gas ratio corresponding to dry etching of the reflective layer 13 is increased. Alternatively, the etching may be performed by a method suitable for wet etching of the reflective layer 13 by additional processing.
Specifically, for example, in the case of the reflective layer 13 made of Al as a main material, the reflective layer 13 can be selectively etched to be fine due to a difference in etching rate from other inorganic layers by immersing an etching solution containing hydrofluoric acid as a main component.
The base layer 19 is etched by a dry etching method using an etching gas corresponding to the etching target, and forms, for example, a rectangular pedestal 12 when viewed from the extending direction of the lattice-shaped projections 11.
The method of manufacturing the polarizing plate 1 according to the present embodiment may further include a step of coating the surface on the light incidence side with the dielectric protective film 20. Further, the method for manufacturing the polarizing plate 1 of the present embodiment may further include a step of coating the dielectric protective film 20 with an organic water-repellent film. These dielectric protective film 20 and organic water-repellent film are formed by CVD, ALD, or the like as described above.
As described above, the polarizing plate 1 of the present embodiment is manufactured.
[ optical apparatus ]
The optical device of the present embodiment includes the polarizing plate 1 of the present embodiment described above. As the optical device, a liquid crystal projector, a head-up display, a digital camera, and the like can be cited. The polarizing plate 1 of the present embodiment is an inorganic polarizing plate having excellent heat resistance as compared with an organic polarizing plate, and is therefore suitable for applications such as a liquid crystal projector and a head-up display, which require heat resistance.
When the optical device of the present embodiment includes a plurality of polarizing plates, at least one of the plurality of polarizing plates may be the polarizing plate 1 of the present embodiment. For example, when the optical device of the present embodiment is a liquid crystal projector, at least one of the polarizing plates disposed on the incident side and the emission side of the liquid crystal panel may be the polarizing plate 1 of the present embodiment.
The polarizing plate 1, the method for manufacturing the same, and the optical device described above have the following effects.
In the present embodiment, in the polarizing plate 1 having the wire grid structure including the grid-like projections 11 having the reflective layer 13, the dielectric layer 14, and the absorber layer 15 in this order from the transparent substrate 10 side, the width b of the reflective layer 13 is made smaller than the grid width a (the width of the dielectric layer 14, the width of the absorber layer 15).
This enables more accurate control of the wavelength dispersion of the absorption axis reflectance Rs. More specifically, the wavelength dispersion of the absorption axis reflectance Rs can be shifted to the long wavelength side, and the wavelength range in which the absorption axis reflectance Rs is the lowest can be shifted to the long wavelength side. As a result, the polarizing plate 1 that can be controlled so that the absorption axis reflectance Rs becomes the lowest can be obtained more reliably.
Further, since the wavelength dispersion of the absorption axis reflectance Rs can be accurately controlled by making the width b of the reflective layer 13 smaller than the grid width a by etching, the film thicknesses of the dielectric layer 14 and the absorption layer 15 can be set with a degree of freedom as long as they are located on the shorter wavelength side than the channel wavelength range of each manufacturer of the liquid crystal projector. Therefore, according to the present embodiment, the optimum reflection characteristics can be obtained regardless of variations in film thickness, shape, and the like of the dielectric layer 14 and the absorption layer 15 during the manufacturing process without being limited to the exclusive design of each manufacturer of the liquid crystal projector. Further, it is possible to provide a polarizing plate having optimum optical characteristics for light source spectra different from manufacturer to manufacturer of liquid crystal projectors. In addition, a polarizing plate having improved transmission axis transmittance Tp and improved projection luminance of a liquid crystal projector can be provided at the same time for a basic design configuration in which the width of the reflective layer is the same as the grid width.
The present invention is not limited to the above-described embodiments, and variations and modifications within a range that can achieve the object of the present invention are also included in the present invention.
For example, the polarizing plate of the present embodiment can be used for various applications, not limited to a liquid crystal projector.
