Polarizing plate and optical device

Abstract

To provide a polarizing plate and optical equipment having heat resistance and excellent in optical characteristics.SOLUTION: Disclosed is a polarizing plate having a wire grid structure which includes: a transparent substrate; a plurality of protrusions located on the transparent substrate and spaced apart from each other in a first direction at a pitch shorter than a wavelength of light in a used band; and a protective layer covering the plurality of protrusions and the transparent substrate. Each of the plurality of protrusions includes a first absorbing layer, a reflecting layer, and a second absorbing layer sequentially from the side closer to the transparent substrate. A width in the first direction of a first surface on the side closer to the first absorbing layer of the reflecting layer is larger than that of a second surface facing the first surface.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a polarizing plate and optical device to the device .

Background Art

[0002] A polarizing plate is an optical element that absorbs polarized light in one direction and transmits polarized light in a direction orthogonal thereto. In principle, a polarizing plate is required in a liquid crystal display device. In particular, in a liquid crystal display device that uses a light source with a large amount of light, such as a transmissive liquid crystal projector, since the polarizing plate receives strong radiation, excellent heat resistance and light resistance are required, and it has a size of about several centimeters, and high extinction ratio and reflectance characteristics are required. controlled. A wire grid type inorganic polarizing plate has been proposed to meet these requirements.

[0003] A wire grid type polarizing plate has a structure in which a large number of wires of conductors extending in one direction are arranged side by side on a substrate at a pitch (tens of nm to hundreds of nm) narrower than the band of the wavelength of the light to be used. When light is incident on this polarizing plate, polarized light (TE wave (S wave)) parallel to the extending direction of the wire cannot be transmitted, and polarized light (TM wave (P wave)) perpendicular to the extending direction of the wire is transmitted as it is.

[0004] For example, Patent Document 1 discloses a polarizing plate having sidebars that can assist each other on the sidewalls of a wire grid polarizer (polarizing plate). The sidebar improves the durability of the wire grid polarizer. On the other hand, if an attempt is made to improve the durability of a wire grid polarizer with a high aspect ratio only by sidebars, the sidebar width will naturally become thick, which will cause deterioration of polarization characteristics such as a decrease in transmittance and an increase in reflectance.

[0005] Patent Document 2 discloses a polarizing plate in which an overcoat layer is formed from the tip to the sidewall of a wire grid polarizer (polarizing plate). The overcoat layer prevents the wire grid polarizer from collapsing. However, when the overcoat layer is formed, the number of air interfaces increases, which causes deterioration of polarization characteristics such as a decrease in transmittance and an increase in reflectance.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] In recent years, lighting and display light sources have evolved from lamps to LEDs and then to lasers. Even in liquid crystal projectors, high luminous fluxes are achieved by using multiple semiconductor lasers (LDs), aiming to increase the brightness of liquid crystal projectors. Polarizing plates are required to have durability even in an environment of high-intensity light.

[0008] Coating the wire grid structure with a protective film is one way to enhance the durability of the polarizing plate. On the other hand, adding a protective film to the polarizing plate can cause a decrease in optical properties.

[0009] This invention has been made in view of the above problems, and an object thereof is to provide a polarizing plate, an optical device, and a method for manufacturing a polarizing plate, which have heat resistance and excellent optical properties.

Means for Solving the Problems

[0010] In order to solve the above problems, this invention proposes the following means.

[0011] (1) The polarizing plate according to the first aspect is a polarizing plate having a wire grid structure, and includes a transparent substrate, a plurality of convex portions, and a protective layer. The plurality of convex portions are on the transparent substrate. The plurality of convex portions are periodically arranged at a pitch shorter than the wavelength of light in the use band and spaced apart from each other in a first direction. Each of the plurality of convex portions has a first absorption layer, a reflection layer, and a second absorption layer in order from the side close to the transparent substrate. The width in the first direction of the first surface of the reflection layer on the side close to the first absorption layer is wider than the width in the first direction of the second surface facing the first surface.

[0012] (2) The polarizing plate according to the above aspect may further include a first dielectric layer between the first absorption layer and the reflection layer.

[0013] (3) The polarizing plate according to the above aspect may further include a second dielectric layer between the second absorption layer and the reflection layer.

[0014] (4) The polarizing plate according to the above aspect may further have an underlayer between the transparent substrate and the plurality of convex portions. The underlayer protrudes toward the plurality of convex portions and has a plurality of pedestal portions that serve as pedestals for the plurality of convex portions.

[0015] (5) In the polarizing plate according to the above aspect, the transparent substrate may be sapphire.

[0016] (6) The optical device according to the second aspect includes the polarizing plate according to the above aspect.

[0017] (7) The method for manufacturing a polarizing plate according to the third aspect includes a step of sequentially laminating at least a first absorption layer, a reflection layer, and a second absorption layer on a transparent substrate, forming a mask on the upper surface of the laminated body, performing etching through the mask, and forming a plurality of convex portions that are periodically arranged at a pitch shorter than the wavelength of light in the use band and spaced apart from each other in a first direction, and a step of forming a protective layer on the plurality of convex portions produced by etching, and performing the etching under conditions optimized in advance so that the side surfaces of the respective convex portions are inclined, or changing the etching conditions during the etching for forming the plurality of convex portions.

Advantages of the Invention

[0018] The polarizing plate and the optical device according to this embodiment have heat resistance and excellent optical properties.

Brief Description of the Drawings

[0019]

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Modes for Carrying Out the Invention

[0020] Hereinafter, this embodiment will be described in detail with appropriate reference to the drawings. The drawings used in the following description may show the characteristic parts enlarged for convenience in order to make the features of the present invention easier to understand, and the dimensional ratios of each component may be different from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto, and it can be appropriately modified and implemented within the range where the effects are achieved.

[0021] [Optical device] FIG. 1 is a schematic diagram of an optical device according to the first embodiment. The optical device shown in FIG. 1 is a transmissive liquid crystal projector 200. The transmissive liquid crystal projector 200 is an example of an optical device. The optical device is not limited to the transmissive liquid crystal projector 200 as long as it includes a polarizing plate. For example, a liquid crystal display, a head-up display, a vehicle headlight, etc. are also included in the optical device.

[0022] The transmissive liquid crystal projector 200 includes a light source 110, a polarizing beam splitter 120, a phosphor 130, a plurality of dichroic mirrors 140, a plurality of mirrors 150, a plurality of polarizing plates 100, a plurality of liquid crystal panels 160, a cross prism 170, and a projection lens 180.

[0023] The light source 110 is a laser light source. The light source 110 emits, for example, blue (wavelength 380 nm to 490 nm) light. The S wave of the light emitted from the light source 110 is reflected by the polarizing beam splitter 120 and enters the phosphor 130.

[0024] The phosphor 130 absorbs, for example, blue light and emits yellow light. The light emitted by the phosphor 130 merges with the blue light to become white light. The P wave of the white light passes through the light beam splitter 120 and is separated while being reflected by the plurality of dichroic mirrors 140 and mirrors 150, and is decomposed into blue light, green light, and red light. Each of the blue light, green light, and red light enters a different liquid crystal panel 160.

[0025] Polarizing plates 100 are disposed on the incident side and the exit side of the liquid crystal panel 160, respectively. The polarizing plate on the incident side and the polarizing plate 100 on the exit side are arranged in a cross Nicol state. When the liquid crystal in the liquid crystal panel 160 is aligned, the light transmitted through the polarizing plate 100 reaches the cross prism 170. The light color-combined by the cross prism 170 is emitted from the projection lens 180.

[0026] FIG. 2 is a perspective view of the polarizing plate 100 according to the first embodiment. FIG. 3 is a cross-sectional view of the polarizing plate 100 according to the first embodiment. Both the polarizing plate 100 on the incident side and the polarizing plate 100 on the exit side of the liquid crystal panel 160 may satisfy the configuration shown below, or only either one of them may satisfy the configuration shown below.

[0027] The polarizing plate 100 includes a transparent substrate 1, a plurality of convex portions 2, and a protective layer 3. Hereinafter, the plane on which the transparent substrate 1 extends is defined as the xy plane, the direction orthogonal to the transparent substrate 1 is defined as the z direction, and the direction in which the grid extends is defined as the y direction. The direction in which the grid extends is the same as the direction in which each convex portion 2 extends. The direction orthogonal to the y direction and the z direction is defined as the x direction.

[0028] A polarizing plate having a wire grid structure 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 due to optical anisotropy. In FIGS. 2 and 3, the y direction is the direction of the absorption axis of the polarizing plate, and the x direction is the direction of the transmission axis of the polarizing plate.

[0029] The transparent substrate 1 exhibits light transmittance with respect to the light in the use band. "Exhibiting light transmittance with respect to the light in the use band" does not mean that the transmittance of the light in the use band is 100%, but it suffices to exhibit light transmittance capable of maintaining the function as a polarizing plate. The light in the use band includes, for example, visible light having a wavelength of 380 nm or more and 810 nm or less. The main surface shape of the transparent substrate 1 is not particularly limited, and a shape according to the purpose (for example, a rectangular shape) is appropriately selected. The average thickness of the transparent substrate 1 is, for example, 0.3 mm or more and 1.0 mm or less.

[0030] The refractive index of the transparent substrate 1 is, for example, 1.1 or more and 2.2 or less. The transparent substrate 1 is, for example, glass, crystal, quartz, sapphire, etc. Glass, especially quartz glass (refractive index 1.46) or soda-lime glass (refractive index 1.51), is inexpensive and has high transmittance. Crystal or sapphire has excellent thermal conductivity. When crystal or sapphire is used for the transparent substrate 1, the light resistance of the polarizing plate 100 is enhanced. Crystal or sapphire is suitable for the polarizing plate for the optical engine of the transmissive liquid crystal projector 200 with a large amount of heat generation.

[0031] When a crystal having optical activity such as crystal or sapphire is used for the transparent substrate 1, it is preferable that the extending direction of the convex portion 2 coincides with the parallel direction or the perpendicular direction with respect to the optical axis of the crystal. Thereby, the optical characteristics of the polarizing plate 100 are improved. Here, the optical axis is a direction axis in which the difference in refractive index between O (ordinary ray) and E (extraordinary ray) of light traveling in that direction is minimized.

[0032] Each of the plurality of convex portions 2 is on the transparent substrate 1. The plurality of convex portions 2 are periodically arranged at a pitch p shorter than the wavelength of the light in the used band and spaced apart from each other in the x direction. Each of the plurality of convex portions 2 extends in the y direction.

[0033] The pitch p of the plurality of convex portions 2 is, for example, 100 nm or more and 200 nm or less. The pitch p is the distance in the x direction between adjacent convex portions 2 and is the sum of the widths in the x direction of the space portion between the convex portions 2 and the line portion where the convex portion 2 is located and the adjacent convex portion 2. The pitch p can be measured with a scanning electron microscope or a transmission electron microscope. For example, the distances between any four adjacent convex portions 2 are measured, and the arithmetic mean thereof is taken as the pitch p.

[0034] The width of the convex portion 2 in the x direction is, for example, shorter than the wavelength of the light in the used band. The width of the convex portion 2 is, for example, shorter than the pitch p. The average width of the convex portion 2 in the x direction is, for example, 20% or more and 50% or less of the pitch p. The width of the convex portion 2 is, for example, 35 nm or more and 45 nm or less. The width of the convex portion 2 is the width at the center of the height of the convex portion 2 in the z direction and can be measured with an electron microscope or the like.

[0035] The convex portion 2 has, for example, a first absorption layer 20, a first dielectric layer 30, a reflection layer 40, a second dielectric layer 50, and a second absorption layer 60 in order from the side closer to the transparent substrate 1.

[0036] For example, an underlayer 10 may be provided between each convex portion 2 and the transparent substrate 1. The underlayer 10 is, for example, silicon oxide. The underlayer 10 may have a plurality of pedestal portions 11. Each of the plurality of pedestal portions 11 protrudes toward each of the convex portions 2 and serves as a pedestal for each convex portion 2.

[0037] The width of the pedestal portion 11 in the x direction increases as it approaches the transparent substrate 1. The pedestal portion 11 has a trapezoidal shape in the xz cross-section, for example, an isosceles trapezoid. The pedestal portion 11 can be formed by setting dry etching conditions and gradually changing the balance between isotropic etching and anisotropic etching. When the cross-sectional shape of the pedestal portion 11 is trapezoidal, the refractive index in the z direction changes stepwise, and light reflection can be prevented.

[0038] The first absorption layer 20 extends in a strip shape in the y direction, which is the absorption axis. The first absorption layer 20 has an absorption effect on the wavelength of light in the use band. The first absorption layer 20 absorbs, for example, 10% or more of the light incident on the first absorption layer 20, at least in visible light.

[0039] The first absorption layer 20 is composed of any one or more materials selected from the group consisting of metals, alloy materials, and semiconductor materials. The constituent material of the first absorption layer 20 is appropriately selected according to the wavelength range of the applied light.

[0040] The metal material used for the first absorption layer 20 is, for example, a single metal such as Ta, Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni, Fe, Sn, or an alloy containing one or more of these elements. The semiconductor material used for the first absorption layer 20 is, for example, Si, Ge, Te, ZnO, silicide materials (β-FeSi2, MgSi2, NiSi2, BaSi2, CrSi2, CoSi2, TaSi, etc.). The first absorption layer 20 preferably contains Fe or Ta and also contains Si. More preferably, the first absorption layer 20 contains 50 wt% or more of Si.

[0041] When a semiconductor material is used for the first absorption layer 20, the bandgap energy of the semiconductor is involved in the absorption effect. The semiconductor used for the first absorption layer 20 is required to have a bandgap energy below the used band. For example, when used with visible light, absorption at a wavelength of 400 nm or more, that is, a material with a bandgap of 3.1 eV or less is required.

[0042] The film thickness of the first absorption layer 20 is, for example, 10 nm or more and 100 nm or less. The film thickness of the first absorption layer 20 can be measured by, for example, an electron microscope. The first absorption layer 20 can be formed as a high-density film using, for example, vapor deposition or sputtering. The first absorption layer 20 may be composed of two or more layers with different constituent materials.

[0043] The first dielectric layer 30 is on the first absorption layer 20. The first dielectric layer 30 extends in a strip shape in the y direction, which is the absorption axis. The first dielectric layer 30 adjusts the phase between the polarized light incident from the transparent substrate 1 and reflected by the first absorption layer 20 and the polarized light reflected by the reflection layer 40.

[0044] The film thickness of the first dielectric layer 30 is set, for example, so that the phase of the polarized light reflected by the first absorption layer 20 and the polarized light reflected by the reflection layer 40 is shifted by half a wavelength. The film thickness of the first dielectric layer 30 is, for example, 1 nm or more and 500 nm or less. The film thickness of the first dielectric layer 30 can be measured by, for example, an electron microscope.

[0045] The material constituting the first dielectric layer 30 is, for example, a metal oxide, cryolite, germanium, titanium dioxide, silicon, magnesium fluoride (MgF2), boron nitride, carbon, or a combination thereof. The metal oxide is, for example, silicon oxide, aluminum oxide, beryllium oxide, bismuth oxide, boron oxide, tantalum oxide, etc. Among these, silicon oxide is preferably used for the first dielectric layer 30.

[0046] The refractive index of the first dielectric layer 30 is, for example, 1.0 or more and 2.5 or less. Since the optical properties of the reflective layer 40 are affected by the refractive index of the surroundings, the properties of the polarizing plate 100 can be improved by selecting the material of the first dielectric layer 30. The first dielectric layer 30 is not limited to a single layer and may be composed of a plurality of layers with different constituent materials.

[0047] The first absorption layer 20 and the first dielectric layer 30 attenuate the light incident on the polarizing plate 100 from the transparent substrate 1 side. Among the light that has passed through the first absorption layer 20 and the first dielectric layer 30, the TM wave (P wave) passes through the reflective layer 40, and the TE wave (S wave) is reflected by the reflective layer 40. The TE wave reflected by the reflective layer 40 is absorbed or attenuated by interference in the first dielectric layer 30 and the first absorption layer 20.

[0048] The reflective layer 40 is, for example, on the first dielectric layer 30. The reflective layer 40 extends in a strip shape in the y direction, which is the absorption axis.

[0049] The plurality of reflective layers 40 function as a wire grid polarizer. The plurality of reflective layers 40 attenuate the polarized light wave (TE wave (S wave)) having an electric field component in the direction parallel to the longitudinal direction of the reflective layer 40 and transmit the polarized light wave (TM wave (P wave)) having an electric field component in the direction perpendicular to the longitudinal direction of the reflective layer 40. The reflective layer 40 reflects, for example, 10% or more of the light incident on the reflective layer 40, at least in the visible light range.

[0050] The film thickness (thickness in the z direction) of the reflective layer 40 is not particularly limited, and for example, 100 nm to 300 nm is preferable. Note that the film thickness of the reflective layer 40 can be measured with, for example, an electron microscope.

[0051] The reflective layer 40 is composed of a material having reflectivity with respect to light in the used band. The reflective layer 40 is, for example, a single metal such as Al, Ag, Cu, Mo, Cr, Ti, Ni, W, Fe, Si, Ge, Te, Nd, or an alloy containing one or more of these elements. Aluminum or an aluminum alloy can suppress absorption loss in the wire grid in visible light to a small level and is also inexpensive. The reflective layer 40 contains, for example, 50 wt% or more of Al. In addition to these metal materials, the reflective layer 40 may also be an inorganic film or a resin film other than a metal formed with high surface reflectivity by, for example, coloring or the like.

[0052] The reflective layer 40 can be formed as a high-density film, for example, by using a vapor deposition method or a sputtering method. The reflective layer 40 may be composed of two or more layers having different constituent materials.

[0053] The reflective layer 40 has a first surface 41 and a second surface 42. The first surface 41 is the surface of the reflective layer 40 closer to the first absorption layer 20. The second surface 42 is the surface facing the first surface 41. The first surface 41 and the second surface 42 face each other in the z direction.

[0054] The width W in the x direction of the first surface 41 41 is wider than the width W in the x direction of the second surface 42 42 . The width of the reflective layer 40 in the x direction is, for example, wider from the second surface 42 toward the first surface 41. The side surface of the reflective layer 40 in the x direction is, for example, inclined with respect to the z direction. A metal oxide film may be formed on the side surface of the reflective layer 40.

[0055] The second dielectric layer 50 is, for example, on the reflective layer 40. The second dielectric layer 50 extends in a band shape in the y direction, which is the absorption axis.

[0056] The second dielectric layer 50 adjusts the phases of the polarized light incident from the side opposite to the transparent substrate 1 (the grid side) and reflected by the second absorption layer 60 and the polarized light reflected by the reflective layer 40.

[0057] The film thickness of the second dielectric layer 50 is set, for example, such that the phases of the polarized light reflected by the second absorption layer 60 and the polarized light reflected by the reflection layer 40 are shifted by half a wavelength. The film thickness of the second dielectric layer 50 is, for example, 1 nm or more and 500 nm or less. The film thickness of the second dielectric layer 50 can be measured with, for example, an electron microscope.

[0058] The same material as that of the first dielectric layer 30 can be used for the second dielectric layer 50. If the materials of the second dielectric layer 50 and the first dielectric layer 30 are the same, the etching conditions during manufacturing can be made the same, facilitating the manufacture of the polarizing plate 100. Also, the performance of the first dielectric layer 30 and the second dielectric layer 50 can be matched.

[0059] The refractive index of the second dielectric layer 50 is, for example, 1.0 or more and 2.5 or less. Since the optical characteristics of the reflection layer 40 are affected by the surrounding refractive index, the characteristics of the polarizing plate 100 can be improved by selecting the material of the second dielectric layer 50. The second dielectric layer 50 is not limited to a single layer and may be composed of a plurality of layers with different constituent materials.

[0060] The second absorption layer 60 extends in a strip shape in the y direction, which is the absorption axis. The second absorption layer 60 has an absorption effect on the wavelength of light in the used band. The second absorption layer 60 absorbs, for example, 10% or more of the light incident on the second absorption layer 60, at least in visible light.

[0061] The same material as that of the first absorption layer 20 can be used for the second absorption layer 60. The second absorption layer 60 and the first absorption layer 20 are preferably composed of the same material.

[0062] The film thickness of the second absorption layer 60 is, for example, 10 nm or more and 100 nm or less. The film thickness of the second absorption layer 60 can be measured with, for example, an electron microscope. The second absorption layer 60 can be formed as a high-density film using, for example, vapor deposition or sputtering. The second absorption layer 60 may be composed of two or more layers with different constituent materials.

[0063] The second dielectric layer 50 and the second absorption layer 60 attenuate light incident from the side opposite to the transparent substrate 1 (grid side) with respect to the polarizing plate 100. Among the light that has passed through the second absorption layer 60 and the second dielectric layer 50, the TM wave (P wave) passes through the reflection layer 40, and the TE wave (S wave) is reflected by the reflection layer 40. The TE wave reflected by the reflection layer 40 is absorbed or attenuated by interference in the second dielectric layer 50 and the second absorption layer 60.

[0064] The film thickness of the second absorption layer 60 is preferably substantially the same as the film thickness of the first absorption layer 20. Also, the film thickness of the second dielectric layer 50 is preferably substantially the same as the film thickness of the first dielectric layer 30. When the film thickness of the first absorption layer 20 is t1 (nm), the film thickness of the second absorption layer 60 is preferably 0.80t1 or more and 1.20t1 or less, and more preferably 0.90t1 or more and 1.10t1 or less. When the film thickness of the first dielectric layer 30 is t2 (nm), the film thickness of the second dielectric layer 50 is preferably 0.80t2 or more and 1.20t2 or less, and more preferably 0.90t2 or more and 1.10t2 or less.

[0065] The side surfaces of the second dielectric layer 50 and the second absorption layer 60 in the x direction are, for example, inclined with respect to the z direction. The surface (upper surface) of the second dielectric layer 50 on the reflection layer 40 side is wider in the x direction than the surface (lower surface) of the second absorption layer 60 on the side farther from the reflection layer 40. The width of the second dielectric layer 50 and the second absorption layer 60 in the x direction becomes wider, for example, as it approaches the surface (lower surface) of the second dielectric layer 50 on the reflection layer 40 side from the surface (upper surface) of the second absorption layer 60 on the side farther from the reflection layer 40.

[0066] The width of the lower surface of the second dielectric layer 50 in the x direction is, for example, wider than the width W in the x direction of the second surface 42 of the reflection layer 40. 42 There is, for example, a step between the second dielectric layer 50 and the reflection layer 40.

[0067] The protective layer 3 covers the transparent substrate 1 and the plurality of convex portions 2. The protective layer 3 covers, for example, the upper surface of the underlayer 10 and the periphery of the convex portions 2.

[0068] The protective layer 3 is, for example, a metal oxide or a metal nitride. The protective layer 3 is, for example, aluminum oxide. The protective layer 3 may have a two-layer structure of, for example, aluminum oxide and silicon oxide. By making the outermost surface of the protective layer 3 silicon oxide, the adhesion between the protective layer 3 and the water-repellent layer is improved. The protective layer 3 can be formed, for example, by an ALD (atomic layer deposition) method or a CVD (chemical vapor deposition) method. Further, the protective layer 3 may fill the spaces between the plurality of convex portions 2.

[0069] The thickness of the protective layer 3 is, for example, 1 nm or more and 50 nm or less. The thickness of the protective layer 3 is preferably 25 nm or less, and more preferably 10 nm or less.

[0070] The upper surface of the protective layer 3 may be coated with a water-repellent film. The water-repellent film is, for example, a fluorine-based silane compound. For example, tridecafluorooctyltrichlorosilane (FOTS) is an example of the water-repellent film. The water-repellent film can be formed by an ALD method, a CVD method, or the like. The water-repellent film improves the moisture resistance of the polarizing plate 100.

[0071] The polarizing plate 100 may further include an antireflection layer on the transparent substrate 1 side. The antireflection layer may have, for example, a moth-eye structure, an antiglare structure, or an antireflector structure. The antireflection layer may be, for example, a laminate in which a high refractive index layer and a low refractive index layer are alternately laminated. The outer surface of the antireflection layer is coated with, for example, the protective layer 3.

[0072] The polarizing plate can be manufactured by sequentially performing a lamination process of a laminate, a processing process of the laminate, and a coating process of a protective layer. Hereinafter, the manufacturing method of the polarizing plate will be described using the polarizing plate 100 shown in FIG. 1 as an example.

[0073] First, a base layer 10, a first absorption layer 20, a first dielectric layer 30, a reflection layer 40, a second dielectric layer 50, and a second absorption layer 60 are sequentially formed on the transparent substrate 1 to form a laminate. Each layer can be formed by a sputtering method, a vapor deposition method, or the like.

[0074] Next, the laminate is processed. The laminate can be produced by a photolithography method, a nanoimprint method, or the like. For example, a grid-shaped resist mask is formed on the upper surface of the laminate, and selective etching is performed through the mask. The etching is performed, for example, by dry etching. At this time, as etching conditions, two or more types of gas ratios, gas flow rates, gas pressures, powers, substrate cooling temperatures, etc. are optimized, or the conditions are switched during formation, whereby the side surface of the processed region to be etched can be inclined with respect to the lamination direction. The side surface of the processed region to be etched corresponds to the side surface of the convex portion 2 after production. The optimization of the etching conditions is performed by conducting a preliminary study of processing the laminate produced under the same conditions while changing the etching conditions. The etching conditions to be changed are, for example, if it is a gas ratio, from a ratio with high etching reactivity to a ratio with low etching reactivity, if it is a gas flow rate, from a low flow rate to a high flow rate, if it is a gas pressure, from a high pressure to a low pressure, if it is a power, from a low power to a high power, if it is the substrate cooling temperature, from a high temperature to a low temperature, etc. By using one condition or a plurality of conditions and switching the conditions during formation, a desired shape can be formed.

[0075] For example, a mask film is formed on the laminate. The mask film is selectively etched with a resist mask. Then, the laminate is selectively etched using the mask film remaining after the selective etching. The mask film may be composed of two or more layers having different constituent materials.

[0076] Next, a protective layer 3 is formed so as to cover the plurality of convex portions 2 obtained by processing the laminate. The protective layer 3 can be formed, for example, by an ALD method, a CVD method, etc. as described above.

[0077] The polarizing plate 100 according to the first embodiment is excellent in heat resistance. For example, the polarizing plate 100 used in a liquid crystal projector 200 or the like is likely to generate heat because it is irradiated with laser light. When the polarizing plate 100 generates heat, the reflective layer 40 or the like undergoes thermal oxidation, and the optical characteristics of the polarizing plate 100 deteriorate. Further, when the polarizing plate 100 has the first absorption layer 20 and the second absorption layer 60 and absorbs light from both the transparent substrate 1 side and the side opposite to the transparent substrate 1 (grid side), the polarizing plate 100 is particularly likely to generate heat.

[0078] In the polarizing plate 100 according to the first embodiment, a plurality of convex portions 2 are covered with the protective layer 3, and even when the polarizing plate 100 generates heat, thermal oxidation of the reflective layer 40 or the like can be prevented. Further, when the transparent substrate 1 is made of sapphire having excellent heat dissipation properties, the amount of heat generated by the polarizing plate 100 can be reduced.

[0079] On the other hand, the protective layer 3 is a cause for adding a reflection interface. Simply adding the protective layer 3 reduces the transmittance of the polarizing plate, and sufficient optical characteristics cannot be obtained. In contrast, in the polarizing plate 100 according to the first embodiment, the width W of the first surface 41 of the reflective layer 40 41 is wider than the width W of the second surface 42 42 and a high transmittance can be realized even when the protective layer 3 is provided.

[0080] Further, the polarizing plate 100 according to the first embodiment includes the first dielectric layer 30 and the second dielectric layer 50, so that a higher transmittance can be realized even when the protective layer 3 is provided. Further, when the polarizing plate 100 has the first dielectric layer 30 and the second dielectric layer 50, the thicknesses of the first absorption layer 20 and the second absorption layer 60 can be reduced, and the heat generation of the polarizing plate 100 can be reduced.

[0081] As described above, the embodiments of the present invention have been described. However, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

[0082] For example, FIG. 4 is a cross-sectional view of the polarizing plate 101 of the first modified example. FIG. 4 is an xz cross-section of the polarizing plate 101. The polarizing plate 101 is different from the polarizing plate 100 in that the base layer 10 does not have the pedestal portion 11. In the polarizing plate 101, the same components as those in the polarizing plate 100 are denoted by the same reference numerals, and the description thereof is omitted.

[0083] Also, for example, FIG. 5 is a cross-sectional view of the polarizing plate 102 of the second modified example. FIG. 5 is an xz cross-section of the polarizing plate 102. The polarizing plate 102 is different from the polarizing plate 100 in that it does not have the first dielectric layer 30 and the second dielectric layer 50. In the polarizing plate 102, the same components as those in the polarizing plate 100 are denoted by the same reference numerals, and the description thereof is omitted.

[0084] Also, for example, FIG. 6 is a cross-sectional view of the polarizing plate 103 of the third modified example. FIG. 6 is an xz cross-section of the polarizing plate 103. The polarizing plate 103 is different from the polarizing plate 100 in that it does not have a base layer and the transparent substrate 1 has a pedestal portion 1A. In the polarizing plate 103, the same components as those in the polarizing plate 100 are denoted by the same reference numerals, and the description thereof is omitted.

Example

[0085] <Optical property test> 「Example 1」 In Example 1, the structure was the same as that of the polarizing plate 100 shown in FIGS. 2 and 3, and the optical properties were measured by simulation. The optical measurement was performed by electromagnetic field simulation using the RCWA (Rigorous Coupled Wave Analysis) method. For the simulation, the grating simulator Gsolver of Grating Solver Development was used.

[0086] The configuration of each layer was as follows. Transparent substrate 1: Sapphire Convex portion 2: Pitch 141 nm, width 35 nm, height 345 nm (including pedestal portion 11) Base layer 10: Thickness 85 nm, SiO2 Pedestal portion 11: Thickness 20 nm, SiO2 First absorption layer 20: thickness 30 nm, FeSi First dielectric layer 30: thickness 5 nm, SiO2 Reflection layer 40: thickness 250 nm, Al, inclination angle 89° with respect to the xy plane of the side surface Second dielectric layer 50: thickness 5 nm, SiO2, inclination angle 80° with respect to the xy plane of the side surface Second absorption layer 60: thickness 30 nm, FeSi, inclination angle 80° with respect to the xy plane of the side surface Protection layer 3: thickness 5 nm

[0087] "Example 2" Example 2 had the same structure as that shown in the polarizing plate 102 shown in Fig. 5. Example 2 did not have the first dielectric layer 30 and the second dielectric layer 50, and the thicknesses of the first absorption layer 20 and the second absorption layer 60 were different from those in Example 1.

[0088] The composition of each layer in Example 2 is as follows. Transparent substrate 1: sapphire Convex portion 2: pitch 141 nm, width 35 nm, height 345 nm (including pedestal portion 11) Underlayer 10: thickness 85 nm, SiO2 Pedestal portion 11: thickness 20 nm, SiO2 First absorption layer 20: thickness 35 nm, FeSi Reflection layer 40: thickness 250 nm, Al, inclination angle 89° with respect to the xy plane of the side surface Second absorption layer 60: thickness 35 nm, FeSi, inclination angle 80° with respect to the xy plane of the side surface Protection layer 3: thickness 5 nm

[0089] "Example 3" Example 3 had the same structure as that shown in the polarizing plate 104 shown in Fig. 7. Example 3 was different from Example 2 in that it did not have the underlayer 10 and the transparent substrate 1 had the pedestal portion 1A.

[0090] The composition of each layer in Example 3 was as follows. Transparent substrate 1: sapphire Pedestal portion 1A: thickness 20 nm, sapphire Convex portion 2: pitch 141 nm, width 35 nm, height 345 nm (including pedestal portion 11) First absorption layer 20: thickness 35 nm, FeSi Reflection layer 40: thickness 250 nm, Al, inclination angle 89° with respect to the xy plane of the side surface Second absorption layer 60: thickness 35 nm, FeSi, inclination angle 80° with respect to the xy plane of the side surface Protection layer 3: thickness 5 nm

[0091] "Example 4" Example 4 had the same structure as that shown in the polarizing plate 105 shown in FIG. 8. Example 4 differed from Example 3 in that it did not have the pedestal portion 1A.

[0092] The composition of each layer of Example 4 was as follows. Transparent substrate 1: sapphire Convex portion 2: pitch 141 nm, width 35 nm, height 325 nm First absorption layer 20: thickness 35 nm, FeSi Reflection layer 40: thickness 250 nm, Al, inclination angle 89° with respect to the xy plane of the side surface Second absorption layer 60: thickness 35 nm, FeSi, inclination angle 80° with respect to the xy plane of the side surface Protection layer 3: thickness 5 nm

[0093] "Comparative Example 1" Comparative Example 1 had the same structure as that shown in the polarizing plate 106 shown in FIG. 9. Comparative Example 1 differed from Example 4 in that the side surfaces of the reflection layer 40 and the second absorption layer 60 were not inclined.

[0094] The composition of each layer of Comparative Example 1 was as follows. Transparent substrate 1: sapphire Convex portion 2: pitch 141 nm, width 35 nm, height 325 nm First absorption layer 20: thickness 35 nm, FeSi Reflection layer 40: thickness 250 nm, Al Second absorption layer 60: thickness 35 nm, FeSi Protection layer 3: thickness 5 nm

[0095] "Comparative Example 2" Comparative Example 2 had the same structure as that shown in the polarizing plate 107 shown in FIG. 10. Comparative Example 2 differed from Comparative Example 2 in that the side surface of the second absorption layer 60 was inclined.

[0096] The composition of each layer of Comparative Example 2 was as follows. Transparent substrate 1: Sapphire Convex portion 2: Pitch 141 nm, width 35 nm, height 325 nm First absorption layer 20: Thickness 35 nm, FeSi Reflection layer 40: Thickness 250 nm, Al Second absorption layer 60: Thickness 35 nm, FeSi, inclination angle 80° with respect to the xy plane of the side surface Protective layer 3: Thickness 5 nm

[0097] FIG. 11 shows the simulation results of the optical characteristics of the polarizing plates of Examples 1 to 4 and Comparative Examples 1 and 2. The vertical axis in FIG. 11 is the transmittance, and the horizontal axis is the wavelength.

[0098] <Heat resistance test> A heat resistance test was conducted on the polarizing plates of Example 1, Example 5, and Comparative Example 3. Example 5 and Comparative Example 3 had the following configurations. The heat resistance test was performed at 250 °C, 300 °C, and 350 °C, respectively. The polarizing plate was placed in a thermostatic bath, and the contrast change rate of the polarizing plate after a predetermined time had elapsed was determined. The contrast was obtained by dividing the transmittance of the TM wave (P wave) by the transmittance of the TE wave (S wave). The contrast change rate is the change rate with respect to the contrast of the sample before the heat resistance test.

[0099] "Example 5" Example 5 differed from Example 1 in that the thickness of the protective layer 3 was 10 nm.

[0100] "Comparative Example 3" Example 3 differed from Example 1 in that it did not have the protective layer 3.

[0101] FIG. 12 shows the heat resistance test results at 250 °C. FIG. 13 shows the heat resistance test results at 300 °C. FIG. 14 shows the heat resistance test results at 350 °C.

[0102] As shown in FIGS. 12 to 14, the heat resistance is improved because the polarizing plate has a protective layer.

Explanation of Reference Numerals

[0103] 1…transparent substrate, 1A, 11…pedestal portion, 2…protrusion, 3…protective layer, 10…underlayer, 20…first absorption layer, 30…first dielectric layer, 40…reflective layer, 41…first surface, 42…second surface, 50…second dielectric layer, 60…second absorption layer, 100, 101, 102, 103, 104, 105, 106, 107…polarizing plate, 110…light source, 120…polarizing beam splitter, 130…phosphor, 140…dichroic mirror, 150…mirror, 160…liquid crystal panel, 170…cross prism, 180…projection lens, 200…liquid crystal projector, W 41 ,W 42 …width

Claims

1. A polarizing plate having a wire grid structure, comprising: a transparent substrate; a plurality of convex portions disposed on the transparent substrate, periodically arranged at a pitch shorter than the wavelength of light in the used band and spaced apart from each other in a first direction; a protective layer covering the plurality of convex portions and the transparent substrate; each of the plurality of convex portions has, in order from the side closer to the transparent substrate, a first absorption layer, a reflection layer, and a second absorption layer; the width in the first direction of the first surface of the reflection layer closer to the first absorption layer is wider than the width in the first direction of the second surface facing the first surface; the width of the reflection layer in the first direction becomes wider from the second surface toward the first surface, and the side surface of the reflection layer is inclined; a side surface of the reflection layer is formed with a metal oxide film, the polarizing plate.

2. The polarizing plate according to claim 1, further comprising a first dielectric layer between the first absorption layer and the reflection layer.

3. The polarizing plate according to claim 1 or 2, further comprising a second dielectric layer between the second absorption layer and the reflection layer.

4. further having an underlayer between the transparent substrate and the plurality of convex portions, the underlayer protrudes toward the plurality of convex portions and has a plurality of pedestal portions that serve as pedestals for the plurality of convex portions, the polarizing plate according to any one of claims 1 to 3.

5. The polarizing plate according to any one of claims 1 to 4, wherein the transparent substrate is sapphire.

6. An optical device comprising the polarizing plate according to any one of claims 1 to 5.

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