Reflective phase-shift structure

Abstract

Provided is a reflective phase-shift structure with uniform characteristics through a broad spectrum.　A reflective phase-shift structure 200 includes a dielectric spacer layer 220, an anisotropic structure layer 230, and a dielectric protective layer 240. The anisotropic structure layer 230 includes a plurality of metal components 232 and dielectric filling members 234 that fill the gaps between the plurality of metal components 232. The dielectric spacer layer 220 is sandwiched between a metal reflection layer and the anisotropic structure layer 230. When a cross-section of the metal components 232 is observed, assuming that the length of the top side is x, the length of the bottom side is y, and the width at half height is w, the following relationships are established: 0.6 ≦ (x / w) ≦ 1.3; 1.8×w ≦ (x+y) ≦ 2.2×w.

Description

Reflective phase difference structure

[0001] The present disclosure relates to a reflective retardation structure.

[0002] In the field of optics, controlling the phase of light is an important technology. Wave plates 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 by microfabrication, the function of a retardation plate can be realized.

[0004] JP 2015-210479 A

[0005] Conventionally, a reflective retardation structure has a problem in that it is difficult to obtain uniform characteristics over a wide band because the wavelength characteristics are determined by the material used.

[0006] The present disclosure has been made in view of the above-mentioned problems, and one exemplary purpose of an embodiment thereof is to provide a reflective retardation structure having uniform characteristics over a wide band.

[0007] A reflective retardation structure according to an embodiment of the present disclosure includes a metal reflective layer, an anisotropic structure layer including a plurality of metal components and a dielectric filling member that fills gaps between the plurality of metal components, a dielectric spacer layer sandwiched between the metal reflective layer and the anisotropic structure layer, and a dielectric protection layer formed on the anisotropic structure layer. When viewed in cross section, the metal components satisfy the following relationships: 0.6≦x / w≦1.3, 1.8×w≦x+y≦2.2×w, where x is the length of the top side, y is the length of the bottom side, and w is the width at half the height.

[0008] Any combination of the above components, or mutual substitution of the components or expressions of the present disclosure between methods, devices, systems, etc., are also valid aspects of the present disclosure.

[0009] According to an aspect of the present disclosure, a reflective retardation structure having uniform characteristics over a wide band can be provided.

[0010] FIG. 1 is a perspective view of a reflective retardation structure according to an embodiment; FIG. 2 is a cross-sectional view of the reflective retardation structure of FIG. 1; FIG. 3 is a cross-sectional view of a metal component; FIG. 4 is a diagram showing the dependency of the TE reflectivity and TM reflectivity of a reflective retardation structure on the top duty ratio x / w; FIG. 5 is a diagram showing the dependency of the retardation characteristics of a reflective retardation structure on the top duty ratio x / w; FIG. 6 is a diagram showing the dependency of the retardation characteristics of a reflective retardation structure on the top duty ratio x / w; FIG. 7 is a diagram explaining a margin for manufacturing variations in a reflective retardation structure; FIG. 8 is a perspective view of a reflective retardation structure according to Modification 1; FIG. 9 is a plan view explaining design parameters of an anisotropic structure layer according to Modification 1;

[0011] (Summary of the Embodiments) A summary of some exemplary embodiments of the present disclosure will be provided. This summary is intended to provide a basic understanding of one or more embodiments as a prelude to the detailed description that follows, and is not intended to limit the scope of the invention or disclosure. Furthermore, this summary is not intended to be a comprehensive overview of all possible embodiments, nor does it limit essential elements of the embodiments. For convenience, the term "one embodiment" may refer to one embodiment (example or variant) or multiple embodiments (examples or variants) disclosed herein.

[0012] A reflective retardation structure according to an embodiment of the present disclosure includes a metal reflective layer, an anisotropic structure layer including a plurality of metal components and a dielectric filling member that fills gaps between the plurality of metal components, a dielectric spacer layer sandwiched between the metal reflective layer and the anisotropic structure layer, and a dielectric protection layer formed on the anisotropic structure layer. When viewed in cross section, the metal components satisfy the following relationships: 0.6≦x / w≦1.3, 1.8×w≦x+y≦2.2×w, where x is the length of the top side, y is the length of the bottom side, and w is the width at half the height.

[0013] In a structure in which an anisotropic structure layer is formed in contact with a metal reflective layer, i.e., a structure 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 structure layer and optimizing its material and thickness, it is possible to uniformize characteristics over a wide band.

[0014] The retardation structure can be evaluated based on its retardation characteristics and reflectance characteristics. Ideally, it is desirable for the retardation structure to have uniform retardation characteristics and uniform reflectance characteristics. However, depending on the application, the uniformity of one of the two characteristics may be required preferentially.

[0015] Adding a dielectric filler can reduce the dispersion of the phase difference.

[0016] Furthermore, by adding a dielectric protection layer and optimizing its thickness, the dispersion of the phase difference can be adjusted to obtain more uniform characteristics.

[0017] In this configuration, by setting x / w in the range of 0.6 to 1.3, the phase difference can be kept within the range of 180±20 degrees over a wide wavelength band.

[0018] Within the above range, the wavelength band where the phase difference is flat (180±20 degrees) is narrowest when x / w=1, and the flat wavelength band becomes wider as the value moves away from x / w=1. Therefore, 0.6≦x / w≦0.8 or 1.1≦x / w≦1.3 may be satisfied.

[0019] In one embodiment, the working wavelength of the reflective retardation structure may be in the wavelength range of 400 to 1200 nm.

[0020] In one embodiment, the dielectric spacer layer and the dielectric fill member may be the same material.

[0021] In one embodiment, the dielectric fill member and the dielectric protection layer may be the same material.

[0022] In one embodiment, the material of the metal component may be an aluminum-based metal, which, rather than the common metasurface materials Au or Ag, allows for uniform properties across a wide wavelength range in the visible range.

[0023] (Embodiments) Preferred embodiments will be described below with reference to the drawings. The same or equivalent components, parts, and processes shown in each drawing will be given the same reference numerals, and redundant explanations will be omitted as appropriate. Furthermore, the embodiments are illustrative and do not limit the disclosure or invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the disclosure or invention.

[0024] In addition, the dimensions (thickness, length, width, etc.) of each member shown in the drawings may be enlarged or reduced as appropriate for ease of understanding. Furthermore, the dimensions of multiple members do not necessarily represent the relative size of each other, and even if a member A is depicted as being thicker than another member B in the drawings, member A may actually be thinner than member B.

[0025] 1 is a perspective view of a reflective retardation structure 200 according to an embodiment. The reflective retardation structure 200 has a layered structure including a metal reflective layer 210, a dielectric spacer layer 220, an anisotropic structure layer 230, and a dielectric protection layer 240.

[0026] As materials for the metal reflective layer 210, Ag, Al, etc. are suitable in the visible range. When designing assuming near-infrared, Au, Cu, etc. can be used. When high reflectivity is not required, Cr, Ni, Fe, etc. may also be used. The metal reflective layer 210 is formed on the surface of a substrate (not shown) or on the surface of another member that is to function as a retardation plate.

[0027] The anisotropic structure layer 230 has different structures in a first direction (x direction) and a second direction (y direction) that are perpendicular to each other in the plane (xy) of the reflective retardation structure 200. The anisotropic structure layer 230 includes a plurality of metal components 232. In this embodiment, the anisotropic structure layer 230 has a wire grid structure (line and space structure), and the plurality of metal components 232 are a plurality of wire grids that extend in the y direction and are adjacent to each other in the x direction.

[0028] The material of the metal components 232 of the anisotropic structure layer 230 can be selected depending on the wavelength used in the reflective retardation structure 200 .

[0029] For example, when the reflective retardation structure 200 is to be used in the visible range, an aluminum (Al)-based metal can be used as the material. An aluminum-based metal means a metal containing at least aluminum, and can include not only pure aluminum, but also aluminum containing impurities and aluminum alloys containing aluminum as the main component. In short, an aluminum-based metal contains aluminum as the main component and can contain other materials as long as they do not impair the optical properties of pure aluminum or can obtain optical properties equivalent to those of pure aluminum.

[0030] The anisotropic structure layer 230 further includes a dielectric filler member 234 that fills the spaces between the plurality of metal components 232 .

[0031] The dielectric spacer layer 220 is sandwiched between the metal reflective layer 210 and the anisotropic structure layer 230. A dielectric protection layer 240 is formed on the anisotropic structure layer 230. In other words, the reflective retardation structure 200 has a layered structure in which the metal reflective layer 210, the dielectric spacer layer 220, the anisotropic structure layer 230, and the dielectric protection layer 240 are stacked in this order.

[0032] The dielectric spacer layer 220, the dielectric filling member 234, and the dielectric protection 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 protection 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 etc. can be used.

[0033] 2 is a cross-sectional view of the reflective retardation structure 200 of FIG. 1. The reflective retardation structure 200 has a thickness d １ and material, the structure and size (height d ２ and line width Wl, space width Ws), the material of the dielectric filling member 234, the thickness d of the dielectric protection layer 240３ The optical properties can be designed using the parameters of the material.

[0034] 3 is a cross-sectional view of the metal component 232. The shape of the metal component 232 is assumed to be rectangular. When the metal component 232 is viewed in cross section along the y axis, the length of the top side is defined as x, the length of the bottom side as y, and the width at half the height as w. Here, x / w is defined as the top duty ratio. The following describes the results of verifying the influence of the top duty ratio x / w on the optical characteristics of the reflective retardation structure 200 by simulation. The horizontal axis represents wavelength, and the vertical axis represents the top duty ratio x / w.

[0035] First, the design was optimized assuming use in the wavelength band of 400 to 800 nm.

[0036] 4 is a diagram showing the dependence of the TE reflectivity and TM reflectivity of the reflective retardation structure 200 on the top duty ratio x / w. In the simulation, w is fixed, and y is changed according to a change in x, assuming that the relationship 2×w=x+y holds. The cross-sectional shape of the metal component 232 is a triangle with an upper vertex when x / y=0, a rectangle when x / y=1, and an inverted triangle with an upper vertex when x / y=2.

[0037] FIG. 5 is a diagram showing the dependency of the phase difference characteristic of the reflective phase difference structure 200 on the top duty ratio x / w.

[0038] In the figure, a flatness of 180±20 degrees is ensured within the range enclosed by the rectangle. Focusing on the vertical axis of this rectangle, it can be seen that a flatness of 180±20 degrees can be ensured if the top duty ratio x / w is within the following range: 0.6≦x / w≦1.3

[0039] Here, when focusing on the contour line of a phase difference of 160 degrees, the wavelength band is narrow when x / y is around 0.8 to 1.1, and the wavelength band where flatness is ensured becomes wider as the distance from this point increases. Therefore, x / y may be designed to satisfy 0.6≦x / w≦0.8 or 1.1≦x / w≦1.3. This can further improve flatness.

[0040] In this simulation, it was assumed that 2×w=x+y holds true, but in an actual manufacturing process, depending on the etching method, processing conditions, and dimensional tolerances, the cross-sectional shape may not necessarily be a trapezoid as shown in Figure 3, and 2×w=x / w may not strictly hold true. If an error of 10% is allowed, it is sufficient that 1.8×w≦x+y≦2.2×w holds true.

[0041] Next, the optimal dimensional parameters (specifically, width w, height h, grid spacing, etc.) obtained assuming use in the wavelength range of 400 to 800 nm were scaled to assume use in the wavelength range of 800 to 1200 nm, and a simulation was performed.

[0042] 6 is a diagram showing the dependency of the phase difference characteristics of the reflective retardation structure 200 on the top duty ratio x / w. A flatness of 180±20 degrees is ensured within the range enclosed by the rectangle. Focusing on the vertical axis of this rectangle, it can be seen that a flatness of 180±20 degrees can be ensured if the top duty ratio x / w is within the following range: 0.6≦x / w≦1.3 This is the same as the case of an optimal design for 400 to 800 nm, and this supports the idea that the optimal range of the top duty ratio can be generalized even if the operating wavelength changes.

[0043] 7 is a diagram illustrating the margin for manufacturing variations in the reflective retardation structure 200. Fig. 7 shows characteristics for wavelengths of 400 nm, 450 nm, 550 nm, 650 nm, and 700 nm, with the horizontal axis representing the top duty ratio and the vertical axis representing the reflectance and retardation. At a wavelength of 450 nm, the retardation margin for variations in the top duty ratio is the largest.

[0044] Next, a modified example of the anisotropic structure layer 230 will be described.

[0045] 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.

[0046] Furthermore, the anisotropic structure layer 230 is not limited to a collection of wire grids.

[0047] 8 is a perspective view of a reflective retardation structure 200F according to Modification 1. In this modification, a plurality of metal components 232F are a set of a plurality of blocks adjacent to each other in the x and y directions. The anisotropic structure layer 230F may include a dielectric filling member 234, and a dielectric protection layer 240 may be formed on the anisotropic structure layer 230F.

[0048] 9 is a plan view illustrating design parameters of an anisotropic structure layer 230F according to Modification 1. The anisotropic structure layer 230F has a metal component 232F having a length Δx in the x direction, a length Δy in the y direction, and a space d in the x direction. ｘ , y-direction space d ｙ In order for the anisotropic structure layer 230F to be said to have an anisotropic structure, Δx≠Δy, d ｘ ≠d ｙ At least one of the above conditions must be satisfied.

[0049] 200 Reflection type retardation structure 210 Metal reflection layer 220 Dielectric spacer layer 230 Anisotropic structure layer 232 Metal component 234 Dielectric filling member 240 Dielectric protection layer

Claims

1. A reflective phase difference structure comprising: a metal reflective layer; an anisotropic structure layer including a plurality of metal components and a dielectric filling member that fills gaps between the plurality of metal components; a dielectric spacer layer sandwiched between the metal reflective layer and the anisotropic structure layer; and a dielectric protection layer formed on the anisotropic structure layer, wherein, when the metal components are viewed in cross section, the length of the top side is x, the length of the bottom side is y, and the width at half the height is w, the following relationships are satisfied: 0.6≦x / w≦1.3 1.8×w≦x+y≦2.2×w 2. The reflective retardation structure according to claim 1, characterized in that the wavelength used is within the wavelength range of 400 to 1200 nm.

3. The reflective phase difference structure according to claim 1 or 2, wherein the dielectric spacer layer and the dielectric filling member are made of the same material.

4. The reflective phase difference structure according to claim 1 or 2, wherein the dielectric filling member and the dielectric protection layer are made of the same material.

5. The reflective phase difference structure according to claim 1 or 2, wherein the material of the metal component is an aluminum-based metal.

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