JP2020126249A - Polarizer, method for manufacturing the same, and optical apparatus - Google Patents

Abstract

To provide a polarizer with a high transmission characteristic and suppressed reflection lights, a method for manufacturing the polarizer, and an optical apparatus having the polarizer.SOLUTION: There is provided a polarizer 100 with a wire grid structure including: a transparent substrate 1; lattice protrusions 20 arranged on the transparent substrate at smaller pitches than the wavelength of light in a used bandwidth, the protrusions 20 extending in a predetermined direction and having a reflection layer 3 and a dielectric layer 4, the reflection layer being closer to the transparent substrate 1 than the dielectric layer 4 is, the reflection layer 3 having at least one step on a side when viewed from the predetermined direction and the base on the transparent substrate 1 side having the largest width.SELECTED DRAWING: Figure 1

Description

The present invention relates to a polarizing plate, a method for manufacturing the same, and an optical device.

Conventionally, as a polarizing element, a metal grating having a pitch smaller than the wavelength of light in the used band is formed on a substrate, and a dielectric layer and an inorganic fine particle layer are formed on the metal grating to interfere with light reflected from the metal grating. An absorptive wire grid type polarizing element has been proposed which cancels out the effect and transmits the other polarized component.

With respect to such a polarizing element, the demand for lowering the reflectance is increasing more and more with the increase in brightness and definition of liquid crystal projectors in recent years. If the reflectance is high, it may cause a malfunction of the liquid crystal panel or may deteriorate the image quality due to stray light.

Here, the reflectance is determined by the interference between layers and the absorption in the layers that form the lattice structure. Then, a method of controlling the reflectance by using a material that meets the requirements for the dielectric layer or the like has been proposed (see Patent Document 1). However, in Patent Document 1, since each layer is designed as a rectangular shape, it is difficult to form a perfect rectangular shape at the nano level. Therefore, it is very difficult to design a material considering the shape.

Further, before forming the metal layer, a method of controlling the reflectance characteristic of the obtained polarizing element by forming a fine pattern on the resin substrate and controlling the reflectance and wavelength of the substrate is proposed. (See Patent Document 2). However, since the base material used in Patent Document 2 is made of resin, it is inferior in heat resistance and light resistance to a wire grid polarizing element made of an inorganic material, and is used for a long time in an environment of strong light. Is anxious.

Japanese Patent Publication No. 2010-530994 JP, 2005-212741, A

The present invention has been made in view of the above background art, and an object thereof is a polarizing plate excellent in control of reflectance characteristics and having excellent selective absorption, a manufacturing method thereof, and an optical device including the polarizing plate. Is to provide. More specifically, it is to provide a polarizing plate that suppresses reflection in the absorption axis direction, a method for manufacturing the polarizing plate, and an optical device including the polarizing plate.

The present inventors provide a polarizing plate having a wire grid structure, which includes a transparent substrate and lattice-shaped convex portions arranged on the transparent substrate at a pitch shorter than the wavelength of light in the use band and extending in a predetermined direction. , The lattice-shaped convex portion is provided with a reflective layer and a dielectric layer in this order from the transparent substrate side, and if the shape of the reflective layer when viewed from the predetermined direction is specified, excellent selective absorption is obtained. It was found that a polarizing plate having the above can be obtained, and the present invention has been completed.

That is, the present invention is a polarizing plate having a wire grid structure, which is arranged on a transparent substrate (for example, a transparent substrate 1 described later) and the transparent substrate at a pitch shorter than the wavelength of light in a used band, and has a predetermined direction. And a grid-shaped convex portion (for example, a grid-shaped convex portion 20 described later) that extends in the direction of, and the grid-shaped convex portion is, in order from the transparent substrate side, a reflective layer (for example, a reflective layer 3 described below). , A dielectric layer (for example, a dielectric layer 4 described later), and when viewed from the predetermined direction, the reflective layer has at least one step on its side and a transparent substrate. It is a polarizing plate (for example, a polarizing plate 10 described later) having the largest width of the bottom side.

The steps may be formed by straight lines and/or curved lines.

The transparent substrate is transparent to the wavelength of light in the used band and may be made of glass, crystal, or sapphire.

The reflective layer may be made of aluminum or an aluminum alloy.

The dielectric layer may be made of Si oxide.

The absorption layer may be configured to include Si as well as Fe or Ta.

The surface of the polarizing plate on which light is incident may be covered with a protective film made of a dielectric material.

The surface of the polarizing plate on which light is incident may be covered with an organic water repellent film.

Yet another aspect of the present invention is a method for manufacturing a polarizing plate having a wire grid structure, including a reflective layer forming step of forming a reflective layer on one surface of a transparent substrate, and a dielectric layer on a surface of the reflective layer opposite to the transparent substrate. A dielectric layer forming step of forming a body layer, an absorbing layer forming step of forming an absorbing layer on the surface of the dielectric layer opposite to the reflecting layer, and by selectively etching the formed laminate, An etching step of forming lattice-shaped convex portions arranged on the transparent substrate at a pitch shorter than the wavelength of light in the used band, and in the etching step, isotropic etching and anisotropic etching are combined. Thus, at least one step is formed on the side wall of the reflective layer, and the polarizing layer is formed so that the width of the reflective layer on the transparent substrate side is maximized.

Still another aspect of the present invention is an optical device including the polarizing plate.

According to the present invention, it is possible to provide a polarizing plate having an excellent selective absorption property, a method for manufacturing the same, and an optical device including the polarizing plate. More specifically, it is possible to provide a polarizing plate that suppresses reflection in the absorption axis direction, a method for manufacturing the polarizing plate, and an optical device including the polarizing plate. Therefore, according to the present invention, it is possible to provide a polarizing plate having a high transmittance characteristic and a low reflectance, a manufacturing method thereof, and an optical device including the polarizing plate.
Further, according to the present invention, since it is possible to form a polarizing plate having a grid having a thickest bottom, it is possible to improve the mechanical strength of the polarizing plate.
Furthermore, since the optical characteristics can be controlled by adjusting the number of steps and the shape of the reflective layer, for example, it is possible to create an optimal polarizing plate at a required wavelength and increase the degree of freedom in design. ..

It is a cross-sectional schematic diagram which shows the polarizing plate which concerns on one Embodiment of this invention. It is a cross-sectional schematic diagram which shows the polarizing plate which concerns on one Embodiment of a conventional structure. It is a cross-sectional schematic diagram which shows the polarizing plate which concerns on one Embodiment of this invention. It is a cross-sectional schematic diagram which shows the polarizing plate which concerns on one Embodiment of this invention. It is a cross-sectional schematic diagram which shows the polarizing plate which concerns on one Embodiment of this invention. It is a cross-sectional schematic diagram which shows the polarizing plate which concerns on one Embodiment of this invention. It is a cross-sectional schematic diagram which shows the polarizing plate of step angle 87 degrees. It is a cross-sectional schematic diagram which shows the polarizing plate of step angle 45 degrees. It is a cross-sectional schematic diagram which shows the polarizing plate of step angle 4 degrees. 5 is a graph showing the results of verifying the relationship between wavelength and absorption axis transmittance for the polarizing plates of Examples 1, 2, and 5 and Comparative Example 1. 5 is a graph showing the results of verifying the relationship between wavelength and absorption axis reflectance for the polarizing plates of Examples 1, 2, and 5 and Comparative Example 1. It is a graph which shows the relationship between the step angle in wavelength 520-590 nm, and absorption axis reflectance (Rs) about the polarizing plate of Examples 1-5 and Comparative Example 1.

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

[Polarizer]
The polarizing plate of the present invention is a polarizing plate having a wire grid structure, which is arranged on the transparent substrate at a pitch (cycle) shorter than the wavelength of light in the used band and extends in a predetermined direction. And a convex portion. The lattice-shaped convex portion has at least a reflective layer and a dielectric layer in this order from the transparent substrate side. The polarizing plate of the present invention may have layers other than the transparent substrate, the reflective layer, and the dielectric layer as long as the effects of the present invention are exhibited.

FIG. 1 is a schematic sectional view showing a polarizing plate 100 according to an embodiment of the present invention. As shown in FIG. 1, a polarizing plate 100 includes a transparent substrate 1 that is transparent to light in a use band, and a grid-like convex array arranged on one surface of the transparent substrate 1 at a pitch shorter than the wavelength of light in the use band. And a unit 20. The lattice-shaped convex portion 20 has a second dielectric layer 2, a reflective layer 3, a dielectric layer 4, an absorption layer 5, and a third dielectric layer 6 in order from the transparent substrate 1 side. .. That is, in the polarizing plate 100, the grid-shaped convex portions 20 formed by laminating the reflective layer 3 and the dielectric layer 4 in this order from the transparent substrate 1 side are arranged in a one-dimensional grid on the transparent substrate 1. Has a wire grid structure.

Here, the direction (predetermined direction) in which the grid-shaped convex portions 20 extend as shown in FIG. 1 is referred to as the Y-axis direction. Further, a direction orthogonal to the Y-axis direction and in which the lattice-shaped convex portions 20 are arranged along the main surface of the transparent substrate 1 is referred to as an X-axis direction. In this case, the light that enters the polarizing plate 100 preferably enters from the direction orthogonal to the X-axis direction and the Y-axis direction on the side of the transparent substrate 1 where the lattice-shaped convex portions 20 are formed.

A polarizing plate having a wire grid structure utilizes four effects of transmission, reflection, interference, and selective light absorption of a polarized wave due to optical anisotropy, so that a polarized wave having an electric field component parallel to the Y-axis direction ( TE waves (S waves) are attenuated and polarized waves (TM waves (P waves)) having an electric field component parallel to the X-axis direction are transmitted. Therefore, in FIG. 1, the Y-axis direction is the absorption axis direction of the polarizing plate, and the X-axis direction is the transmission axis direction of the polarizing plate.

The light L incident from the side of the polarizing plate 100 shown in FIG. 1 on which the grid-shaped convex portions 20 are formed is partially absorbed and attenuated when passing through the absorption layer 5 and the dielectric layer 4. Of the light transmitted through the absorption layer 5 and the dielectric layer 4, the polarized wave (TM wave (P wave)) passes through the reflective layer 3 with high transmittance. On the other hand, of the light transmitted through the absorption layer 5 and the dielectric layer 4, the polarized wave (TE wave (S wave)) is reflected by the reflective layer 3. The TE wave reflected by the reflection layer 3 is partially absorbed when passing through the absorption layer 5 and the dielectric layer 4, and partly reflected and returned to the reflection layer 3. The TE wave reflected by the reflection layer 3 interferes with and attenuates when passing through the absorption layer 5 and the dielectric layer 4. By performing the TE wave selective attenuation as described above, the polarizing plate 100 can obtain desired polarization characteristics.

As shown in FIG. 1, the lattice-shaped convex portions of the polarizing plate of the present invention are the same as the reflection layer 3 when viewed from the extending direction (predetermined direction) of each one-dimensional lattice, that is, in a cross-sectional view orthogonal to the predetermined direction. , And the dielectric layer 4.

Here, dimensions in this specification will be described with reference to FIGS. The height means the dimension in the direction perpendicular to the main surface of the transparent substrate 1 in FIG. The width W means a dimension in the X-axis direction orthogonal to the height direction when viewed from the Y-axis direction along the extending direction of the grid-shaped convex portions 20. Further, when the polarizing plate 100 is viewed from the Y-axis direction along the extending direction of the grid-shaped convex portions 20, the repeating interval of the grid-shaped convex portions 20 in the X-axis direction is referred to as a pitch P.

In the polarizing plate of the present invention, the pitch P of the lattice-shaped convex portions is not particularly limited as long as it is shorter than the wavelength of light in the used band. From the viewpoint of ease of production and stability, the pitch P of the lattice-shaped convex portions is preferably 100 nm to 200 nm, for example. The pitch P of the lattice-shaped convex portions can be measured by observing with a scanning electron microscope or a transmission electron microscope. For example, using a scanning electron microscope or a transmission electron microscope, the pitch P can be measured at any four points, and the arithmetic mean value thereof can be used as the pitch P of the grid-shaped convex portions. Hereinafter, this measuring method is referred to as an electron microscope method.

In the polarizing plate of the present invention, the reflective layer has at least one step on its side when viewed from the direction in which the lattice-shaped convex portions extend (predetermined direction: Y-axis direction), and the transparent substrate. It is characterized by the largest width of the bottom side. Accordingly, it is possible to realize a polarizing plate having excellent control of reflectance characteristics and excellent selective absorption, specifically, a polarizing plate in which reflection in the absorption axis direction is suppressed.

The step of forming the reflective layer means that the width of the reflective layer changes stepwise or continuously when the reflective layer is viewed from the extending direction of the lattice-shaped convex portions (predetermined direction: Y-axis direction). Means the shape. Therefore, the steps in the present invention are not limited to those formed by a straight line, and may be formed by a curved line, for example. Moreover, the number of steps is not limited to one, and may be a multi-step including two or more steps.

As described above, the polarizing plate having the wire grid structure attenuates a polarized wave (TE wave (S wave)) having an electric field component parallel to the extending direction (Y-axis direction) of the lattice-shaped convex portion, and the X-axis. A polarized wave (TM wave (P wave)) having an electric field component parallel to the direction is transmitted. That is, it is required that the polarized wave (TE wave (S wave)) having the electric field component parallel to the extending direction of the lattice-shaped convex portions (Y-axis direction) is not transmitted and reflected, and the reduction of the reflectance is required. It becomes an important required characteristic.

Here, since the polarizing plate of the present invention has the step formed in the reflective layer, it has an electric field component that is vertically incident on the transparent substrate and is parallel to the extending direction of the lattice-shaped convex portions (Y-axis direction). The polarized wave (TE wave (S wave)) is partially reflected by the reflection layer and then bent by steps and scattered. The scattered polarized wave (TE wave (S wave)) having an electric field component parallel to the extending direction of the lattice-shaped convex portion (Y axis direction) does not contribute to the reflection, and as a result, in the absorption axis direction. Reflection can be suppressed.

(Transparent substrate)
The transparent substrate (transparent substrate 1 in FIG. 1) is not particularly limited as long as it is a substrate that transmits light in the used band, and can be appropriately selected according to the purpose. The phrase "shows translucency with respect to the light in the used band" does not mean that the light transmittance in the used band is 100%, but does not mean that the function as a polarizing plate can be maintained. Just show it. Examples of the light in the used band include visible light having a wavelength of about 380 nm to 810 nm.

The shape of the main surface of the transparent substrate is not particularly limited, and a shape (for example, rectangular shape) suitable for the purpose is appropriately selected. The average thickness of the transparent substrate is preferably 0.3 mm to 1 mm, for example.

As a constituent material of the transparent substrate, a material having a refractive index of 1.1 to 2.2 is preferable, and glass, crystal, sapphire and the like can be mentioned. From the viewpoint of cost and light transmittance, it is preferable to use glass, particularly quartz glass (refractive index 1.46) or soda lime glass (refractive index 1.51). The component composition of the glass material is not particularly limited, and for example, an inexpensive glass material such as silicate glass widely distributed as optical glass can be used.

From the viewpoint of thermal conductivity, it is preferable to use quartz or sapphire, which have high thermal conductivity. Thereby, high light resistance to strong light is obtained, and it is preferably used as a polarizing plate for an optical engine of a projector which generates a large amount of heat.

When using a transparent substrate made of an optically active crystal such as quartz, it is preferable to dispose the lattice-shaped convex portions 20 in a direction parallel or perpendicular to the optical axis of the crystal. Thereby, excellent optical characteristics can be obtained. Here, the optical axis is a directional axis that minimizes the difference in refractive index between O (ordinary ray) and E (extraordinary ray) of light traveling in that direction.

(Second dielectric layer)
The second dielectric layer (second dielectric layer 2 in FIG. 1) is an optional layer in the present invention. It is formed on a transparent substrate and is formed between the reflective layer and the transparent substrate in the present invention.

The second dielectric layer 2 in the polarizing plate 100 according to the embodiment of the present invention shown in FIG. 1 is laminated on the transparent substrate 1, and the portion of the dug amount H dug by etching is A part of the grid-shaped convex portion 20 is formed.

The material forming the second dielectric layer may be the same as or different from the dielectric layer to be described later, and may be, for example, a Si oxide such as SiO ₂ , Al ₂ O ₃ , or beryllium oxide. , Metal oxides such as bismuth oxide, MgF ₂ , cryolite, germanium, titanium dioxide, silicon, magnesium fluoride, boron nitride, boron oxide, tantalum oxide, carbon, or a general material such as a combination thereof. Can be mentioned. Above all, the second dielectric layer is preferably composed of Si oxide.

The refractive index of the second dielectric layer is preferably more than 1.0 and 2.5 or less. Since the optical characteristics of the reflective layer are affected by the refractive index of the surroundings, the polarizing plate characteristics can be controlled by selecting the material of the dielectric layer.

The film thickness of the second dielectric layer is not particularly limited and is preferably 10 nm to 100 nm, for example. The film thickness of the second dielectric layer can be measured, for example, by the electron microscope method described above.

(Reflective layer)
The reflective layer (reflective layer 3 in FIG. 1) is formed on one side surface of the transparent substrate and has a strip-shaped metal film arranged in the Y-axis direction which is the absorption axis. In the present invention, another layer such as the second dielectric layer may be present between the transparent substrate and the reflective layer, as in the polarizing plate 100 shown in FIG. 1 described above. ..

The reflective layer contributes to the function as a wire grid type polarizer and attenuates a polarized wave (TE wave (S wave)) having an electric field component in a direction parallel to the extending direction (longitudinal direction) of the reflective layer. Then, a polarized wave (TM wave (P wave)) having an electric field component is transmitted in a direction orthogonal to the extending direction (longitudinal direction) of the reflective layer.

The reflective layer in the polarizing plate of the present invention extends substantially perpendicular to the surface direction of the transparent substrate, and when viewed from the direction in which the lattice-shaped convex portions extend (predetermined direction: Y-axis direction), that is, the predetermined direction. It is characterized in that it has at least one or more steps on the side and has the largest width of the bottom side on the transparent substrate side in a cross-sectional view orthogonal to. In the present invention, this makes it possible to realize a polarizing plate having excellent control of reflectance characteristics, and a polarizing plate having excellent selective absorption, specifically, a polarizing plate in which reflection in the absorption axis direction is suppressed. Obtainable.

The constituent material of the reflective layer is not particularly limited as long as it is a material having reflectivity for light in the used band, and examples thereof include Al, Ag, Cu, Mo, Cr, Ti, Ni, W, Fe, Si, Examples include simple elements such as Ge and Te, and alloys containing one or more of these elements. Above all, the reflective layer is preferably made of aluminum or an aluminum alloy. In addition to these metal materials, for example, an inorganic film or a resin film other than a metal whose surface has a high reflectance due to coloring or the like may be used.

The film thickness of the reflective layer (8 in FIG. 1) is not particularly limited and is preferably 100 nm to 300 nm, for example. The film thickness of the reflective layer can be measured, for example, by the electron microscope method described above.

The width of the bottom side on the transparent substrate side, which is the largest width of the reflective layer of the polarizing plate of the present invention, depends on the relationship with the pitch P of the grid-shaped convex portions, but for example, the ratio to the pitch P is 20. It is preferably ˜50%. Note that these widths can be measured by, for example, the electron microscope method described above.

In the polarizing plate 100 according to the embodiment of the present invention shown in FIG. 1, the reflection layer 3 is viewed from the extending direction (predetermined direction: Y-axis direction) of the grid-shaped convex portions 20, that is, the predetermined direction. In a cross-sectional view orthogonal to, each side has one step 10, and the bottom side on the transparent substrate 1 side has the largest width. More specifically, the reflection layer 3 of the polarizing plate 100 has a shape in which a substantially isosceles trapezoid is combined with a substantially rectangular shape in a cross-sectional view orthogonal to a predetermined direction, and the length of the lower base of the trapezoidal portion is the rectangular shape. The width of the trapezoidal portion is smaller than that of the transparent substrate 1.

In the polarizing plate 100 according to the embodiment of the present invention shown in FIG. 1, the step angle of the reflective layer 3 represented by θs may be in the range of 0°<θs<90°, but in the range of 15°. It is preferably in the range of <θs<90°.

As a method of providing at least one step on the side of the reflective layer and maximizing the width of the bottom side on the transparent substrate side, for example, a combination of isotropic etching and anisotropic etching is used. , There is a method of changing the balance.

(Dielectric layer)
The dielectric layer (dielectric layer 4 in FIG. 1) is formed on the reflective layer and has dielectric films arranged in a strip shape arranged in the Y-axis direction which is the absorption axis. In the present invention, another layer may exist between the reflective layer and the dielectric layer.

The film thickness of the dielectric layer (9 in FIG. 1) is formed within a range in which the phase of the polarized light reflected by the absorbing layer and transmitted by the absorbing layer and reflected by the reflecting layer is shifted by a half wavelength. Specifically, the film thickness of the dielectric layer is appropriately set within a range of 1 to 500 nm capable of adjusting the phase of polarized light to enhance the interference effect. The film thickness of this dielectric layer can be measured, for example, by the electron microscope method described above.

Materials for forming the dielectric layer include Si oxides such as SiO ₂ , metal oxides such as Al ₂ O ₃ , beryllium oxide and bismuth oxide, MgF ₂ , cryolite, germanium, titanium dioxide, silicon and fluorine. Typical materials include magnesium chloride, boron nitride, boron oxide, tantalum oxide, carbon, or a combination thereof. Above all, the dielectric layer 4 is preferably made of Si oxide.

The refractive index of the dielectric layer is preferably more than 1.0 and 2.5 or less. Since the optical characteristics of the reflective layer are affected by the refractive index of the surroundings, the polarization characteristics can be controlled by selecting the material of the dielectric layer.

Further, by appropriately adjusting the film thickness and the refractive index of the dielectric layer, it is possible to partially reflect the TE wave reflected by the reflective layer when returning through the absorption layer and return it to the reflective layer. The light passing through can be attenuated by interference. By selectively attenuating the TE wave in this manner, desired polarization characteristics can be obtained.

In the polarizing plate of the present invention, the width of the dielectric layer is not particularly limited, and there is no problem if it is larger or smaller than the width of the reflective layer positioned as the lower layer. The width of the dielectric layer depends on the relationship with the pitch P of the grid-shaped convex portions, but the ratio to the pitch P is preferably 20 to 50%, for example. Note that these widths can be measured by, for example, the electron microscope method described above.

The dielectric layer 4 of the polarizing plate 100 according to the embodiment of the present invention shown in FIG. 1 is laminated on the reflective layer 4 perpendicularly to the surface direction of the transparent substrate 1, and has a lattice-shaped convex portion. It has a rectangular shape when viewed from the extending direction (predetermined direction: Y-axis direction), that is, in a cross-sectional view orthogonal to the predetermined direction. The width of the dielectric layer 4 is substantially the same as the width of the rectangular portion of the reflective layer 4 located below.

(Absorption layer)
The absorption layer (absorption layer 5 in FIG. 1) is formed on the dielectric layer and is arranged so as to extend in a band shape in the Y-axis direction which is the absorption axis. The absorption layer forms a part of the grid-shaped convex portion 20.

Examples of the constituent material of the absorption layer include one or more kinds of substances having a light absorption effect, such as a metal material and a semiconductor material, having an extinction constant of optical constants which is not zero, and are appropriately selected according to the wavelength range of the applied light. It Examples of the metal material include simple elements such as Ta, Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni, Fe, and Sn, or alloys containing one or more of these elements. Examples of the semiconductor material include Si, Ge, Te, ZnO, and silicide materials (β-FeSi ₂ , MgSi ₂ , NiSi ₂ , BaSi ₂ , CrSi ₂ , CoSi ₂ , TaSi, etc.). By using these materials, the polarizing plate 100 can obtain a high extinction ratio in the visible light range to which it is applied. Above all, it is preferable that the absorption layer contains Si in addition to Fe or Ta.

When a semiconductor material is used for the absorption layer, the bandgap energy of the semiconductor is involved in the absorption action, so the bandgap energy needs to be within the usable band. For example, when used in visible light, it is necessary to use a material having absorption at a wavelength of 400 nm or more, that is, a band gap of 3.1 ev or less.

The thickness of the absorption layer (10 in FIG. 1) is not particularly limited, and is preferably 10 nm to 100 nm, for example. The film thickness of the absorption layer 5 can be measured, for example, by the electron microscope method described above.

Note that the absorption layer can be formed as a high-density film by an evaporation method or a sputtering method. Further, the absorption layer may be composed of two or more layers having different constituent materials.

The width of the absorption layer depends on the relationship with the pitch P of the grid-shaped convex portions, but the ratio to the pitch P is preferably 20 to 50%. Note that these widths can be measured by, for example, the electron microscope method described above.

The absorption layer 5 of the polarizing plate 100 according to the embodiment of the present invention shown in FIG. 1 is laminated on the dielectric layer 4 perpendicularly to the surface direction of the transparent substrate 1 and has a lattice-shaped convex portion. It has a rectangular shape when viewed from the extending direction (predetermined direction: Y-axis direction), that is, in a cross-sectional view orthogonal to the predetermined direction. The width of the absorption layer 5 is substantially the same as the width of the rectangular portion of the reflection layer 4 located below and the width of the dielectric layer 5.

(Third dielectric layer)
The third dielectric layer (dielectric layer 2 in FIG. 1) is an optional layer in the present invention. It is formed on a transparent substrate, and is formed as an upper layer of the dielectric layer in addition to the dielectric layer of the present invention.

The third dielectric layer 6 in the polarizing plate 100 according to the embodiment of the present invention shown in FIG. 1 is laminated on the absorption layer 5 and forms a part of the grid-shaped convex portion 20.

The material forming the third dielectric layer may be the same as or different from the above-mentioned dielectric layer and, if present, the second dielectric layer. For example, SiO ₂ Si oxides such as, metal oxides such as Al ₂ O ₃ , beryllium oxide and bismuth oxide, MgF ₂ , cryolite, germanium, titanium dioxide, silicon, magnesium fluoride, boron nitride, boron oxide, tantalum oxide, Common materials such as carbon, or a combination thereof, may be mentioned. Above all, the second dielectric layer is preferably composed of Si oxide.

The refractive index of the third dielectric layer is preferably more than 1.0 and 2.5 or less. Since the optical characteristics of the reflective layer are affected by the refractive index of the surroundings, the polarizing plate characteristics can be controlled by selecting the material of the dielectric layer.

The film thickness of the third dielectric layer (11 in FIG. 1) is not particularly limited and is preferably 10 nm to 100 nm, for example. The film thickness of the third dielectric layer can be measured, for example, by the electron microscope method described above.

(Diffusion barrier layer)
The polarizing plate of the present invention may have a diffusion barrier layer between the dielectric layer and the absorption layer. By having the diffusion barrier layer, diffusion of light in the absorption layer is prevented. The diffusion barrier layer can be composed of a metal film of Ta, W, Nb, Ti or the like.

(Protective film)
Further, in the polarizing plate of the present invention, the surface on the light incident side may be covered with a protective film made of a dielectric material as long as the change in optical characteristics is not affected. The protective film is made of a dielectric film and can be formed, for example, on the surface of the polarizing plate (the surface on which the wire grid is formed) by using CVD (Chemical Vapor Deposition) or ALD (Atomic Layer Deposition). .. As a result, it is possible to suppress unnecessary oxidation reaction with respect to the metal film.

(Organic water repellent film)
Furthermore, in the polarizing plate of the present invention, the surface on the light incident side may be covered with an organic water repellent film. The organic water-repellent film is made of, for example, a fluorine-based silane compound such as perfluorodecyltriethoxysilane (FDTS), and can be formed by using the above-mentioned CVD or ALD, for example. Thereby, the reliability of the polarizing plate such as the moisture resistance can be improved.

The present invention is not limited to the above-described embodiment shown in FIG. 1, and modifications and improvements within the range in which the object of the present invention can be achieved are included in the present invention.

FIG. 3 is a schematic sectional view showing a polarizing plate 300 according to one embodiment of the present invention. The polarizing plate 300 shown in FIG. 3 includes the grid-shaped convex portions 20 on the transparent substrate 1. As the lattice-shaped convex portion 20, the reflective layer 3 is formed directly on the transparent substrate 1, the dielectric layer 4 is formed on the reflective layer 3, and the absorption layer 5 is formed thereon. That is, the polarizing plate 300 shown in FIG. 3 is a polarizing plate that does not include the second dielectric layer 2 and the third dielectric layer 6 that are present in the polarizing plate 100 shown in FIG.

In the embodiment shown in FIG. 3, as in FIG. 1, when viewed from the extending direction of the lattice-shaped convex portions 20 (predetermined direction: Y-axis direction), that is, in a cross-sectional view orthogonal to the predetermined direction, both sides Each side has one step, and the bottom side on the transparent substrate 1 side has the largest width. More specifically, the reflective layer 3 of the polarizing plate 300 has a shape in which a substantially isosceles trapezoid is combined with a substantially rectangular shape in a cross-sectional view orthogonal to a predetermined direction, and the length of the lower bottom of the trapezoidal portion is the rectangular shape. The width of the trapezoidal portion is smaller than that of the transparent substrate 1.

FIG. 4 is a schematic sectional view showing a polarizing plate 400 according to another embodiment of the present invention. In the polarizing plate 400 shown in FIG. 4, the reflective layer 3 is directly formed on the transparent substrate 1 as the grid-shaped convex portions 20, the dielectric layer 4 is formed on the reflective layer 3, and the absorption layer 5 is formed on the dielectric layer 4. Are formed.

In the embodiment shown in FIG. 4, when viewed from the extending direction of the grid-shaped convex portions 20 (predetermined direction: Y-axis direction), that is, in a cross-sectional view orthogonal to the predetermined direction, four steps are provided on each side. And the width of the bottom side on the transparent substrate 1 side is the largest.

FIG. 5 is a schematic sectional view showing a polarizing plate 500 according to still another embodiment of the present invention. In the polarizing plate 500 shown in FIG. 5, the reflective layer 3 is directly formed on the transparent substrate 1 as the grid-shaped convex portions 20, the dielectric layer 4 is formed on the reflective layer 3, and the absorbing layer 5 is formed on the dielectric layer 4. Are formed.

In the embodiment shown in FIG. 5, when viewed from the extending direction of the lattice-shaped convex portions 20 (predetermined direction: Y-axis direction), that is, in a cross-sectional view orthogonal to the predetermined direction, two substantially orthogonal steps are performed. The width of the bottom side which is on both sides and is on the transparent substrate 1 side is the largest.

FIG. 6 is a schematic sectional view showing a polarizing plate 600 according to another embodiment of the present invention. In the polarizing plate 600 shown in FIG. 6, the reflective layer 3 is directly formed on the transparent substrate 1 as the grid-shaped convex portions 20, the dielectric layer 4 is provided on the reflective layer 3, and the absorbing layer 5 is provided thereon. Are formed.

In the embodiment shown in FIG. 6, when viewed from the extending direction of the lattice-shaped convex portions 20 (predetermined direction: Y-axis direction), that is, in a cross-sectional view orthogonal to the predetermined direction, steps formed by curves are performed. There is one on each side, and the width of the bottom on the transparent substrate 1 side is the largest. The region formed by the curved line has a tapered shape in which the region becomes smaller as it gets closer to the dielectric layer 4 (the side opposite to the transparent substrate 1), and the width becomes narrower.

[Production method of polarizing plate]
The method for manufacturing a polarizing plate of the present invention includes a reflective layer forming step, a dielectric layer forming step, an absorbing layer forming step, and an etching step.

In the reflective layer forming step, a reflective layer is formed on one surface of the transparent substrate. In the dielectric layer forming step, a dielectric layer is formed on the reflecting layer formed in the reflecting layer forming step. In the absorbing layer forming step, the absorbing layer is formed on the dielectric layer formed in the dielectric layer forming step. In each of these layer forming steps, each layer can be formed by, for example, a sputtering method or a vapor deposition method.

In the etching step, by selectively etching the laminated body formed through each of the above-described layer forming steps, the grid-shaped convex portions arranged on the transparent substrate at a pitch shorter than the wavelength of light in the used band are formed. .. Specifically, for example, a one-dimensional lattice-shaped mask pattern is formed by a photolithography method or a nanoimprint method. Then, by selectively etching the laminated body, lattice-shaped convex portions arranged on the transparent substrate at a pitch shorter than the wavelength of light in the used band are formed. Examples of the etching method include a dry etching method using an etching gas corresponding to the etching target.

In particular, in the present invention, at least one step is formed on the side wall of the reflective layer by changing the balance by combining isotropic etching and anisotropic etching, and at the same time, the width of the reflective layer on the transparent substrate side is formed. Is the largest.

The polarizing plate manufacturing method of the present invention may include a step of coating the surface thereof with a protective film made of a dielectric material. Further, the method for producing a polarizing plate of the present invention may have a step of coating the surface thereof with an organic water repellent film.

[Optical equipment]
The optical device of the present invention includes the polarizing plate of the present invention described above. Examples of the optical device include a liquid crystal projector, a head-up display, a digital camera and the like. The polarizing plate according to the present invention can be used for various purposes as a polarizing plate having a high transmittance of polarized light in the transmission axis direction. Further, since it is an inorganic polarizing plate having excellent heat resistance as compared with an organic polarizing plate made of an organic material, it is particularly suitable for applications such as liquid crystal projectors and head-up displays that require heat resistance.

When the optical device according to the present invention includes a plurality of polarizing plates, at least one of the plurality of polarizing plates may be the polarizing plate according to the present invention. For example, when the optical device according to the present embodiment is a liquid crystal projector, at least one of the polarizing plates arranged on the incident side and the emitting side of the liquid crystal panel may be the polarizing plate according to the present invention.

According to the polarizing plate, the method for manufacturing the same, and the optical device of the present invention described above, the following effects are achieved.

The polarizing plate according to the present invention is a polarizing plate having excellent selective absorption properties, and specifically, a polarizing plate in which reflection in the absorption axis direction is suppressed. Therefore, according to the present invention, it is possible to provide a polarizing plate having a high transmittance characteristic and a low reflectance, a manufacturing method thereof, and an optical device including the polarizing plate.
Further, according to the present invention, since it is possible to form a polarizing plate having a grid having a thickest bottom, it is possible to improve the mechanical strength of the polarizing plate.
Furthermore, since it is possible to control the optical characteristics by adjusting the number of steps and the shape of the reflective layer, it is possible to create a polarizing plate that excels in the control of reflectance characteristics and is optimal for the required wavelength. , The freedom of design increases.

Next, examples of the present invention will be described, but the present invention is not limited to these examples.

<Examples 1 to 5 and Comparative Example 1>
[Creation of polarizing plate]
In Examples 1 to 5, the polarizing plate 100 having the structure shown in FIG. 1 is used, in which the step angle θs of the reflective layer 3 is 87°, 45°, 21°, 8°, and 4°, respectively. Therefore, it was subjected to a simulation.
Further, as Comparative Example 1, a polarizing plate 200 having a different structure of the absorbing layer 3 from the polarizing plate 100 of Example 1 was prepared and subjected to simulation. The polarizing plate 200 serving as Comparative Example 1 has the structure shown in FIG. 2, and is a cross-sectional view when viewed from the direction (predetermined direction: Y-axis direction) in which the grid-shaped convex portions 20 extend, that is, orthogonal to the predetermined direction. Then, the reflection layer 3 has a rectangular shape and has no step (step angle θs=0°).

The step angle θs of the polarizing plate 100 is calculated by the following equation 1.
[Formula 1]
θs=arctan{Hs/(W−Ws)/2}
Here, as shown in FIG. 1, Hs is the height of step 10, W is the width of the lattice-shaped convex portion 20, and Ws is the width of the apex of the reflective layer 3.

FIG. 7 is a schematic cross-sectional view of a polarizing plate 700 in which the step angle θs of the reflective layer 3 is 87° according to Example 1, and FIG. 9 is a schematic sectional view of a polarizing plate 800, and FIG. 9 is a schematic sectional view of a polarizing plate 900 having a step angle θs of the reflection layer 3 of 4° as Example 5.

[Simulation method]
The optical characteristics of the polarizing plates of Examples 1 to 3 and Comparative Example 1 were verified by electromagnetic field simulation by the RCWA (Rigrous Coupled Wave Analysis) method. For the simulation, a grating simulator Gsolver V51 manufactured by Grating Solver Development was used.

In verifying the relationship between the wavelength and the absorption axis transmittance, a polarized wave (TE wave (S wave)) having an electric field component was made incident in a direction parallel to the extending direction (longitudinal direction) of the lattice-shaped convex portion. The transmittance at that time was verified. Further, in verifying the relationship between the wavelength and the absorption axis reflectance, a polarized wave (TE wave (S wave)) having an electric field component in a direction parallel to the extending direction (longitudinal direction) of the lattice-shaped convex portion, The reflectance when the light was incident at an incident angle of 5° was verified.

[simulation result]
FIG. 10 shows the results of verifying the relationship between the wavelength and the absorption axis transmittance for the polarizing plates of Examples 1, 2, and 5 and Comparative Example 1.
FIG. 11 shows the results of verifying the relationship between the wavelength and the absorption axis reflectance of the polarizing plates of Examples 1, 2, and 5 and Comparative Example 1.
FIG. 12 shows the relationship between the step angle and the absorption axis reflectance (Rs) at wavelengths of 520 to 590 nm for the polarizing plates of Examples 1 to 5 and Comparative Example 1.

In FIG. 10, the horizontal axis represents wavelength λ (nm) and the vertical axis represents absorption axis transmittance (%). Here, the absorption axis transmittance means the transmittance of polarized light (TE wave) in the absorption axis direction (Y-axis direction) incident on the polarizing plate. In FIG. 10, the graph indicated by the broken line represents the result of the polarizing plate 100 of the present invention as the example, and the graph (Ref) indicated by the solid line represents the result of the polarizing plate 200 as the comparative example. ing.

In FIG. 11, the horizontal axis represents the wavelength λ (nm), and the vertical axis represents the absorption axis reflectance (%). Here, the absorption axis reflectance means the reflectance of polarized light (TE wave) in the absorption axis direction (Y-axis direction) incident on the polarizing plate. In FIG. 11, a graph shown by a broken line shows the result of the polarizing plate 100 of the present invention as an example, and a graph (Ref) shown by a solid line shows the result of the polarizing plate 200 as a comparative example. ing.

As shown in FIG. 11, in the polarizing plate 100 having the structure shown in FIG. 1, when the step angle θs is decreased from 87°, the absorption axis reflectance in the entire visible region tends to decrease ( When the step angle θs is further reduced, the transmission axis reflectance at wavelengths of 650 nm or less tends to increase.

As shown in FIG. 12, the absorption axis reflectance (Rs) is 3.5 when the step angle θ is 90°, and the range in which the absorption axis reflectance (Rs) is less than 3.5 is 15 It can be seen that the range is °<θ<90°. Therefore, the step angle θ in the polarizing plate of the present invention is preferably in the range of 15°<θ<90°.

100, 200, 300, 400, 500, 600, 700, 800, 900 Polarizing plate 1 Transparent substrate 2 Second dielectric layer 3 Reflective layer 4 Dielectric layer 5 Absorption layer 6 Third dielectric layer 7 Second Film thickness of dielectric layer 8 Film thickness of reflective layer 9 Film thickness of dielectric layer 10 Film thickness of absorbing layer 11 Film thickness of third dielectric layer 10 Step 20 Lattice convex portion L Incident light P Lattice convex portion Pitch W Line width S Space width H Excavation amount Hs Step height Ws Metal layer vertex width

Claims (10)

A polarizing plate having a wire grid structure,
A transparent substrate,
Arranged on the transparent substrate at a pitch shorter than the wavelength of light in the band of use, comprising a lattice-shaped convex portion extending in a predetermined direction,
The lattice-shaped convex portion has, in order from the transparent substrate side, a reflective layer and a dielectric layer,
When viewed from the predetermined direction, the reflective layer is a polarizing plate having at least one step on its side and having the largest width of the bottom side on the transparent substrate side. The polarizing plate according to claim 1, wherein the step is formed by a straight line and/or a curved line. The polarizing plate according to claim 1 or 2, wherein the transparent substrate is transparent to a wavelength of light in a use band and is made of glass, crystal, or sapphire. The polarizing plate according to claim 1, wherein the reflective layer is made of aluminum or an aluminum alloy. The polarizing plate according to claim 1, wherein the dielectric layer is made of Si oxide. The polarizing plate according to any one of claims 1 to 5, wherein the absorption layer contains Si or Si while containing Fe or Ta. 7. The polarizing plate according to claim 1, wherein the surface of the polarizing plate on which light is incident is covered with a protective film made of a dielectric material. The polarizing plate according to claim 1, wherein a surface of the polarizing plate on which light is incident is covered with an organic water repellent film. A method for manufacturing a polarizing plate having a wire grid structure,
A reflective layer forming step of forming a reflective layer on one surface of the transparent substrate,
A dielectric layer forming step of forming a dielectric layer on the surface of the reflective layer opposite to the transparent substrate;
An absorption layer forming step of forming an absorption layer on the surface of the dielectric layer opposite to the reflection layer;
By selectively etching the formed laminate, an etching step of forming lattice-shaped convex portions arranged on the transparent substrate at a pitch shorter than the wavelength of light in the used band, and
In the etching process, isotropic etching and anisotropic etching are combined to form at least one step on the side wall of the reflective layer and to maximize the width of the reflective layer on the transparent substrate side. A method for manufacturing a polarizing plate to be formed. An optical device comprising the polarizing plate according to claim 1.

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