Reflection-type phase difference structure

Abstract

Provided is a reflection-type phase difference structure having uniform characteristics in a wide band.　A reflective phase difference structure 200 comprises a laminated structure including a metal reflective layer 210, a dielectric spacer layer 220, an anisotropic structure layer 230, and a dielectric protective layer 240. The anisotropic structure layer 230 includes a metal component 232. The present invention satisfies the relationships α ≥ 10%, h ≥ 10 µm, and −3.5α + 103.25 µm ≤ h ≤ −3.5α + 190.75 µm, where α is the duty ratio in a first direction of the metal component 232, and h is the height of the metal component 232.

Description

Reflective phase difference structure

[0001] This disclosure relates to a reflective phase difference structure.

[0002] In the field of optics, controlling the phase of light is an important technique. Waveplates such as quarter-wave plates and half-wave plates are widely used as optical components for controlling the phase of light.

[0003] By forming an anisotropic structure on the surface of an object through microfabrication, the function of a phase difference plate can be realized.

[0004] Conventionally, reflective phase difference structures have had the problem that their wavelength characteristics are determined by the materials used, making it difficult to obtain uniform characteristics over a wide bandwidth. The present inventors have proposed a reflective phase difference structure that can obtain uniform characteristics over a wide bandwidth (Patent Document 2). This reflective phase difference structure has a laminated structure consisting of a reflective layer, a dielectric spacer layer, and an anisotropic structure layer made of an aluminum-based metal.

[0005] Japanese Patent Publication No. 2015-210479 Japanese Patent Publication No. 2024-075471

[0006] This disclosure is made in the circumstances described herein, and one exemplary objective of a certain aspect thereof is to provide a reflective phase difference structure with improved properties.

[0007] A reflective phase difference structure according to one aspect of the present disclosure comprises a metal reflective layer, a dielectric spacer layer formed on the metal reflective layer, an anisotropic structure layer formed on the dielectric spacer layer and including a plurality of metal components and dielectric filling members that fill the gaps between the plurality of metal components, wherein the plurality of metal components are formed anisotropically with respect to a first direction and a second direction perpendicular to each other, and a dielectric protective layer formed on top of the anisotropic structure layer. When the duty cycle of the metal components in the first direction is α and the height is h, the following relationships are satisfied: α ≥ 10% h ≥ 10 μm -3.5α + 103.25 μm ≤ h ≤ -3.5α + 190.75 μm. The reflective phase difference structure controls and reflects the phase difference between a component having polarization in the first direction and a component having polarization in the second direction of light with a wavelength of 450 nm to 650 nm incident from the anisotropic structure layer side.

[0008] Furthermore, any combination of the above components, or any substitution of the components or expressions of this disclosure between methods, apparatus, systems, etc., are also valid forms of this disclosure.

[0009] According to one aspect of this disclosure, a reflective phase difference structure having good phase difference characteristics in the wavelength range of 450 nm to 650 nm can be provided.

[0010] This is a perspective view of a reflective phase difference structure according to an embodiment. This is a cross-sectional view of the reflective phase difference structure shown in Figure 1. This is a cross-sectional view illustrating the design parameters of the reflective phase difference structure. This is a contour plot of the phase difference characteristics (simulation results) of the reflective phase difference structure according to design condition 1. This is a contour plot of the phase difference characteristics (simulation results) of the reflective phase difference structure according to design conditions 1 to 4. This is a contour plot of the phase difference characteristics (simulation results) of the reflective phase difference structure according to design conditions 1, 5 to 7. This is a contour plot of the maximum phase difference values ​​for wavelengths of 450 nm, 550 nm, and 650 nm for each coordinate (h, α) under design conditions 1 to 7.

[0011] (Outline of Embodiments) An outline of some exemplary embodiments of this disclosure is provided below. This outline is intended to provide a basic understanding of the embodiments and to serve as a prelude to the detailed description that follows later. It simplifies some concepts of one or more embodiments and does not limit the scope of the invention or disclosure. Furthermore, this outline is not a comprehensive overview of all possible embodiments and does not limit the essential components of the embodiments. For convenience, “one embodiment” may be used to refer to one embodiment (example or variation) or more embodiments (example or variation) disclosed herein.

[0012] A reflective phase difference structure according to one embodiment comprises a metal reflective layer, a dielectric spacer layer formed on the metal reflective layer, an anisotropic structure layer formed on the dielectric spacer layer and including a plurality of metal components and dielectric filling members that fill the gaps between the plurality of metal components, wherein the plurality of metal components are formed anisotropically with respect to a first direction and a second direction perpendicular to each other, and a dielectric protective layer formed on top of the anisotropic structure layer. When the duty cycle of the metal components in the first direction is α and the height is h, the following relationships are satisfied: α ≥ 10%, h ≥ 10 μm, and -3.5α + 103.25 μm ≤ h ≤ -3.5α + 190.75 μm. The reflective phase difference structure controls and reflects the phase difference between the component having polarization in the first direction and the component having polarization in the second direction of light with a wavelength of 450 nm to 650 nm incident from the anisotropic structure layer side.

[0013] In structures where an anisotropic structural layer is formed in contact with the metal reflective layer, i.e., structures without a dielectric spacer layer, it is difficult to obtain uniform characteristics over a wide wavelength range. In contrast, by inserting a dielectric spacer layer between the metal reflective layer and the anisotropic structural layer and optimizing its material and thickness, it is possible to achieve uniform characteristics over a wide bandwidth.

[0014] Furthermore, by optimizing the thickness of the dielectric protective layer, the dispersion of the phase difference can be adjusted, resulting in more uniform characteristics.

[0015] In this configuration, by determining the duty cycle α in the first direction and the height h of the metal component, which define the cross-sectional shape of the metal component, so as to satisfy the above relationship, good phase difference characteristics can be obtained in the wavelength range of 450 nm to 650 nm.

[0016] In one embodiment, the material of the metal reflective layer may be aluminum or silver. The materials of the dielectric filling member, dielectric spacer layer and dielectric protective layer are SiO ２ The gaps between multiple metal components may be solidly filled without any voids by dielectric filling material.

[0017] In one embodiment, the pitch of the multiple metal components in the first direction may be 210 nm or less. This makes it easier to obtain good phase difference characteristics in design conditions where the height of the multiple metal components is low and manufacturing is easy.

[0018] (Embodiments) Preferred embodiments will be described below with reference to the drawings. The same or equivalent components, members, and processes shown in each drawing will be denoted by the same reference numerals, and redundant descriptions will be omitted as appropriate. Furthermore, the embodiments are illustrative and not intended to limit the disclosure or the invention, and not all features or combinations thereof described in the embodiments are necessarily essential to the disclosure or the invention.

[0019] Furthermore, the dimensions (thickness, length, width, etc.) of each component shown in the drawing may be enlarged or reduced as appropriate for ease of understanding. Moreover, the dimensions of multiple components do not necessarily represent their relative sizes; even if component A is depicted as thicker than component B in the drawing, component A may actually be thinner than component B.

[0020] Figure 1 is a perspective view of a reflective phase difference structure 200 according to an embodiment. The reflective phase difference structure 200 is a laminated structure including a metal reflective layer 210, a dielectric spacer layer 220, an anisotropic structure layer 230, and a dielectric protective layer 240.

[0021] Suitable materials for the metal reflective layer 210 include Ag and Al in the visible range. When designing for the near-infrared range, Au and Cu can be used. If high reflectivity is not required, Cr, Ni, Fe, etc. may be used. The metal reflective layer 210 is formed on the surface of a substrate (not shown) or on the surface of another component that is to be given the function of a phase difference plate.

[0022] The anisotropic structural layer 230 has geometrically different structures with respect to a first direction (x-direction) and a second direction (y-direction) perpendicular to each other in the in-plane (x-y) of the reflective phase difference structure 200. The anisotropic structural layer 230 includes a plurality of metal components 232. In this embodiment, the anisotropic structural layer 230 has a wire grid structure (line and space structure), and the plurality of metal components 232 are a plurality of wire grids extending in the y-direction and adjacent in the x-direction.

[0023] The metal component 232 of the anisotropic structure layer 230 is made of an aluminum (Al)-based metal. An aluminum-based metal means a metal that contains at least aluminum, and may include not only pure aluminum, but also aluminum with impurities, or aluminum alloys in which aluminum is the main component. In short, an aluminum-based metal is a metal in which aluminum is the main component, and other materials may be included as long as they do not impair the optical properties of pure aluminum, or if optical properties equivalent to those of pure aluminum can be obtained.

[0024] The anisotropic structural layer 230 further includes dielectric filling members 234 that fill the spaces between the multiple metal components 232.

[0025] The dielectric spacer layer 220 is sandwiched between the metal reflective layer 210 and the anisotropic structure layer 230. A dielectric protective layer 240 is formed on top of the anisotropic structure layer 230. In other words, the reflective phase difference structure 200 has a laminated structure in which the metal reflective layer 210, dielectric spacer layer 220, anisotropic structure layer 230, and dielectric protective layer 240 are stacked in that order.

[0026] FIG. 2 is a cross-sectional view of the reflective retardation structure 200 of FIG. 1. The dielectric spacer layer 220, the dielectric filling member 234, and the dielectric protective layer 240 may be made of the same material or different materials. Examples of materials for the dielectric spacer layer 220, the dielectric filling member 234, and the dielectric protective layer 240 include SiO ２ , TiO ２ , MgF ２ , Al ２ O ３ , MgO, Y ２ O ３ , HfO ２ , ZrO ２ , Ta ２ O ５ , or the like can be used.

[0027] The metal component 232 has a sub-wavelength structure. The laminated structure of the metal component 232, the transparent dielectric spacer layer 220 covering the upper and lower sides of the metal component 232, and the dielectric protective layer 240 can balance the birefringent structure and the provided retardation amount, so that the function as a retardation plate can be obtained in a wide band.

[0028] FIG. 3 is a cross-sectional view for explaining design parameters of the reflective retardation structure 200. The optical characteristics of the reflective retardation structure 200 can be designed using the thickness u and material of the dielectric spacer layer 220, the thickness of the anisotropic structure layer 230 (the height of the metal component 232) h, the material of the dielectric filling member 234, and the thickness t and material of the dielectric protective layer 240 as parameters.

[0029] The reflective retardation structure 200 has various applications such as color compensation and viewing angle improvement films for liquid crystal display devices. In these applications, it is required to function as a quarter-wave plate, and therefore the target value of the retardation φ is 180°.

[0030] Ideally, a retardation φ of 180° is required. In practice, however, an error of ±40° may be allowed, and it can be said that the characteristics are flatter if the retardation falls within the range of 180°±20°.

[0031] The present inventors have found that, in order to achieve a retardation characteristic of 180°±40°, and further a retardation characteristic of 180°±20°, the shape of the metal component 232, specifically the height h thereof and the duty ratio α in the x-direction, are important parameters. The duty ratio α in the x-direction refers to the line width W of the metal component 232 with respect to the pitch (period) Λ of the metal component 232 in the x-direction Ｌ , which is a ratio expressed by the following formula. The pitch Λ is the line width W Ｌ and the space width W Ｓ of the sum. α=W Ｌ / Λ

[0032] Under several design conditions, with the height h and the duty ratio α of the metal component 232 varied as parameters, the retardation characteristics of the polarization component in the first direction (x-direction) and the polarization component in the second direction (y-direction) were calculated by simulation.

[0033] • Common conditions: Material of the metal component 232 and the metal reflective layer 210: Al; Thickness u of the dielectric spacer layer 220: 50 nm

[0034] • Design condition 1: Assumed incident angle θ=0°; Thickness t of the dielectric protective layer 240: 60 nm; Pitch (period) of the metal component 232: 180 nm

[0035] • Design condition 2: Assumed incident angle θ=0°; Thickness t of the dielectric protective layer 240: 60 nm; Pitch (period) of the metal component 232: 150 nm

[0036] • Design condition 3: Assumed incident angle θ=0°; Thickness t of the dielectric protective layer 240: 60 nm; Pitch (period) of the metal component 232: 210 nm

[0037] • Design condition 4: Assumed incident angle θ=0°; Thickness t of the dielectric protective layer 240: 60 nm; Pitch (period) of the metal component 232: 240 nm

[0038] • Design condition 5: Assumed incident angle θ=30°; Thickness t of the dielectric protective layer 240: 60 nm; Pitch (period) of the metal component 232: 180 nm

[0039] ・Design condition 6: Assumed incident angle θ=0°, thickness t of dielectric protective layer 240: 30 nm, pitch (period) of metal component 232: 180 nm

[0040] ・Design condition 7: Assumed incident angle θ=30°, thickness t of dielectric protective layer 240: 30 nm, pitch (period) of metal component 232: 180 nm

[0041] Fig. 4 is a contour diagram of the phase difference characteristics (simulation results) of the reflective phase difference structure 200 according to Design condition 1. The vertical axis represents the height h of the metal component 232, and the horizontal axis represents the duty ratio α. Fig. 4 shows the phase difference φ at wavelengths of 450 nm, 550 nm, and 650 nm. The contour lines are plotted for the value φ' obtained by converting the phase difference φ based on the following relational expression: φ'=φ (0°≦φ≦180°) φ'=360−φ (180°≦φ) That is, the contour diagram is plotted with 180° as the maximum value, and the range of φ'=160° to 180° represents the range where optimal phase difference characteristics (180°±20°) can be obtained.

[0042] In each of the contour diagrams for incident wavelengths of 450 nm, 550 nm, and 650 nm, a parallelogram X with the same position and the same size is shown. At any wavelength, the inside of this parallelogram is generally in the range of φ'=160° to 180°, and optimal phase difference characteristics (180°±20°) can be obtained over a wide range. Therefore, the range and position where good phase difference characteristics can be obtained are generally consistent for 450 nm, 550 nm, and 650 nm. That is, when the incident wavelength is in the range of 450 nm to 650 nm, it can be said that the wavelength has almost no influence on the phase difference, and wavelength uniformity can be achieved.

[0043] Fig. 5 is a contour diagram of the phase difference characteristics (simulation results) of the reflective phase difference structure 200 according to Design conditions 1 to 4. The vertical axis represents the height h of the metal component 232, and the horizontal axis represents the duty ratio α. Design conditions 1 to 4 differ in the pitch (period) Λ of the metal component 232, which are 150 nm, 180 nm, 210 nm, and 240 nm respectively. The wavelength is 450 nm.

[0044] Even when the pitch (period) Λ of the metal component 232 is different, the range φ' = 160° to 180° exists over a wide area within the parallelogram X described above, and it can be seen that optimal phase difference characteristics (180° ± 20°) can be obtained over a wide area. On the other hand, as the pitch Λ increases, the phase difference performance deteriorates in areas where the height h of the metal component 232 is low and under design conditions that are easy to manufacture, and the range in which optimal phase difference characteristics can be obtained tends to narrow. Specifically, it can be seen that the phase difference characteristics deteriorate relatively when the pitch Λ is 240 nm. Therefore, Λ = 240 nm is unsuitable, and the preferred range for pitch Λ is 210 nm or less. By setting the pitch Λ within this range, it becomes easier to obtain good phase difference characteristics under design conditions that are easy to manufacture.

[0045] Figure 6 is a contour plot of the phase difference characteristics (simulation results) of the reflective phase difference structure 200 under design conditions 1, 5 to 7. The vertical axis represents the height h of the metal component 232, and the horizontal axis represents the duty cycle α. Under design conditions 1 and 5, the thickness t of the anisotropic structure layer 230 is 60 nm, and under design conditions 6 and 7, the thickness t of the anisotropic structure layer 230 is 30 nm. Also, under design conditions 1 and 6, the incident angle θ = 0°, and under design conditions 5 and 7, the incident angle θ = 30°.

[0046] Comparing design conditions 1 and 5, and also design conditions 6 and 7, it can be seen that the phase difference characteristics hardly change when the incident angle θ is 0° and 30°.

[0047] Furthermore, under design condition 6, the φ' within the frame of parallelogram Y is in the range of 160° to 180° over a wide area, satisfying the optimal phase difference range (180° ± 20°) over a wide range. Within the frame of parallelogram X, in areas where the duty cycle α is large and the height h of the metal component 232 is low, φ' does not fall within the range of 160° to 180°, and thus falls outside the optimal phase difference range (180° ± 20°). As will be explained in more detail later, it can be seen that the optimal phase difference range changes slightly as the thickness of the dielectric protective layer changes.

[0048] Even under design condition 7, similar to design condition 6, within the frame of parallelogram X, in the range where the duty cycle α is large and the height h of the metal component 232 is low, φ' does not fall within the range of 160° to 180°, and falls outside the optimal phase difference range (180° ± 20°). In other words, although the difference in the incident angle θ has almost no effect, it can be seen that the optimal phase difference range changes slightly when the thickness of the dielectric protective layer changes.

[0049] Figure 7 is a contour plot showing the coordinates (h, α) that yield the maximum phase difference from all data at wavelengths of 450 nm, 550 nm, and 650 nm under design conditions 1 to 7. This contour plot indicates that the range of coordinates (h, α) where the value of φ' is between 160° and 180° is likely to yield the optimal phase difference range (180° ± 20°) at any of the wavelengths of 450 nm, 550 nm, or 650 nm.

[0050] Figure 7 shows four straight lines (i) to (iv): (i) α ≥ 10% (ii) h ≥ 10 μm (iii) h = -3.5α + 103.25 μm (iv) h = -3.5α + 190.75 μm

[0051] Within the range enclosed by these four lines, the plotted φ' falls within the range of 160° to 180°, indicating that the optimal phase difference range (180° ± 20°) can be obtained at any of the wavelengths of 450 nm, 550 nm, or 650 nm. In other words, the anisotropic structure layer 230 should be designed within the range of trapezoidal Z enclosed by these four lines (i) to (iv).

[0052] In Figure 6, the dielectric protective layer thickness is 60 nm for design conditions 1 to 5, but 30 nm for design conditions 6 and 7. It can be seen that the optimal phase difference range changes slightly depending on the thickness of the dielectric protective layer. However, in the manufacturing process of reflective phase difference structures, the dielectric protective layer is added in the final step, and the thickness of the dielectric protective layer can be adjusted as appropriate according to the desired phase difference characteristics. In other words, by designing the metal components of the reflective phase difference structure to fall within the range of the four straight lines (i) to (iv) shown in Figure 7, it is possible to obtain a reflective phase difference structure with relatively superior phase difference characteristics. Furthermore, by adjusting the thickness of the dielectric protective layer, it is possible to obtain a reflective phase difference structure that satisfies an even more optimal phase difference range (180° ± 20°).

[0053] It is not obvious that a plot with duty cycle α and height h as variables can be used, nor that the range exhibiting good phase difference characteristics on this plot can be defined by a straight line. Before conducting detailed studies, the inventors believed that, considering that the cross-sectional area of ​​the metal component 232 is proportional to the product of height h and duty cycle α, the boundary of the range exhibiting good phase characteristics would be defined by an inversely proportional curve. However, contrary to this expectation, the range in which good phase difference characteristics can be obtained can be defined by a straight line, which is not easily derived from the common technical knowledge of those skilled in the art.

[0054] Next, we will explain a modified example of the anisotropic structure layer 230.

[0055] In this embodiment, the cross-section of the metal component 232 of the anisotropic structure layer 230 was rectangular, but it is not limited to this. The cross-section of the metal component 232 may be triangular or trapezoidal. If the cross-section of the metal component 232 is not rectangular, the duty cycle α may be defined using its cross-sectional area S as follows: α = S / (h × Λ)

[0056] Furthermore, the anisotropic structure layer 230 may have a double patterning structure in which pairs of two wire grids adjacent to each other in the x-direction are repeatedly formed in the x-direction.

[0057] 200 Reflective phase difference structure 210 Metal reflective layer 220 Dielectric spacer layer 230 Anisotropic structure layer 232 Metal component 234 Dielectric filling member 240 Dielectric protective layer

Claims

1. A reflective phase difference structure comprising: a metal reflective layer; a dielectric spacer layer formed on the metal reflective layer; an anisotropic structural layer formed on the dielectric spacer layer and comprising a plurality of metal components and dielectric filling members that fill the gaps between the plurality of metal components, wherein the plurality of metal components are formed anisotropically with respect to a first direction and a second direction perpendicular to each other; and a dielectric protective layer formed on the upper layer of the anisotropic structural layer, wherein when the duty cycle of the metal components in the first direction is α and the height is h, the following relationships are satisfied: α ≥ 10%, h ≥ 10 μm, and -3.5α + 103.25 μm ≤ h ≤ -3.5α + 190.75 μm, and the structure controls and reflects the phase difference between a component having polarization in the first direction and a component having polarization in the second direction of light with a wavelength of 450 nm to 650 nm incident from the anisotropic structural layer side.

2. The material of the metal reflective layer is aluminum or silver, and the materials of the dielectric filling member, the dielectric spacer layer and the dielectric protective layer are SiO ２ The reflective phase difference structure according to claim 1, wherein the gaps between the plurality of metal components are solidly filled without voids by the dielectric filling member.

3. The reflective phase difference structure according to claim 1 or 2, characterized in that the pitch of the plurality of metal components in the first direction is 210 nm or less.

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