Method for producing multilayer metasurface structure, and multilayer metasurface structure

Abstract

The present invention addresses the problem of providing a production method that makes it possible to produce a multilayer metasurface structure with excellent position precision between metasurface structures. A production method according to the present invention comprises: a step 1 for disposing a spacer part including a polymerizable compound in a pattern on a first metasurface structure which includes a first substrate and a first structure layer that is provided to at least one surface side of the first substrate and that is obtained by disposing a plurality of first metallic microstructures in the in-plane direction; a step 2 for affixing, to the spacer part, a second metasurface structure which includes a second substrate and a second structure layer that is provided to at least one surface side of the second substrate and that is obtained by disposing a plurality of second metallic microstructures in the in-plane direction, so as to obtain a laminate including the first metasurface structure, the spacer part, and the second metasurface structure; and a step 3 for polymerizing the polymerizable compound.

Description

Method for manufacturing a multilayer metasurface structure and a multilayer metasurface structure

[0001] The present invention relates to a method for manufacturing a multilayer metasurface structure formed by stacking multiple metasurface structures, and to a multilayer metasurface structure.

[0002] In recent years, attention has been focused on artificial materials that are fabricated from metals, dielectrics, magnetic materials, etc. into structures smaller than the wavelength of electromagnetic waves, exhibiting behaviors not found in natural materials, such as a negative refractive index for electromagnetic waves. Among these artificial materials, so-called metasurface structures, which are flat-plate elements in which metal microstructures made of metal or other materials are arranged on a substrate, are known.

[0003] A metasurface structure can bend electromagnetic waves in a desired direction by, for example, imparting a phase difference to the electromagnetic waves passing through it using metal microstructures arranged on a substrate. Therefore, metasurface structures are expected to be applied to various elements such as convex lenses (condensing lenses) and deflection elements.

[0004] In particular, high-frequency electromagnetic waves, such as millimeter waves and terahertz waves (THz waves), used in high-capacity wireless communications, tend to propagate in a straight line. Therefore, there is a need to control the directivity of these waves toward communication devices. Therefore, there is a strong need to collimate (convert into a plane wave) the electromagnetic waves emitted from a wave source by refracting them with a phase difference using an element having a convex lens effect.

[0005] Here, as described above, the metasurface structure refracts electromagnetic waves by imparting a phase difference to the electromagnetic waves using the arranged metal microstructures. Such metasurface structures are flat and do not require the thickness of a typical optical refractive lens, nor do they require the formation of concaves and convexes with steep grooves like a diffractive lens (Fresnel lens). In other words, by using a metasurface structure, elements such as very thin flat convex lenses can be realized.

[0006] However, conventional metasurface structures are often unable to provide sufficient phase difference or obtain sufficient refractive index, particularly for electromagnetic waves in the high frequency band such as terahertz waves, limiting the range of applications as optical elements that can be realized in the terahertz region. To solve these problems of conventional technology, it is thought that stacking metasurface structures can improve their properties.

[0007] In response to such demands, for example, Patent Document 1 describes a multilayer metasurface structure (laminated metamaterial film) that transmits various electromagnetic waves by stacking multiple metasurface structures.

[0008] Japanese Patent Application Laid-Open No. 2017-175201

[0009] As described in Patent Document 1, by stacking multiple metasurface structures, a metasurface structure that can respond to various electromagnetic waves can be obtained. Furthermore, by stacking multiple metasurface structures, it is thought that it will be possible to impart a larger phase difference to electromagnetic waves.

[0010] Here, in a multilayer metasurface structure in which multiple metasurface structures are stacked, it is important that the stacked metasurface structures are properly aligned to each other in order to obtain the desired performance. However, in conventional manufacturing of a multilayer metasurface structure in which multiple metasurface structures are stacked, it is difficult to align the metasurface structures with each other, and the positional accuracy of the metasurface structures with each other is often insufficient.

[0011] The object of the present invention is to solve the problems of the conventional technology and to provide a manufacturing method that can suitably align metasurface structures with each other in the manufacture of a multilayer metasurface structure in which multiple metasurface structures are stacked, thereby manufacturing a multilayer metasurface structure with excellent positional accuracy between the metasurface structures, and to provide a multilayer metasurface structure manufactured by this manufacturing method that has excellent positional accuracy between the metasurface structures.

[0012] In order to solve this problem, the present invention has the following configuration: [1] A method for manufacturing a multilayer metasurface structure, including: Step 1: arranging spacer portions containing a polymerizable compound in a pattern on a first metasurface structure including a first substrate and a first structure layer provided on at least one surface of the first substrate and including a plurality of first metal microstructures arranged in an in-plane direction; Step 2: bonding a second metasurface structure including a second substrate and a second structure layer provided on at least one surface of the second substrate and including a plurality of second metal microstructures arranged in an in-plane direction to the spacer portions to obtain a laminate including the first metasurface structure, the spacer portions, and the second metasurface structure; and Step 3: polymerizing the polymerizable compound. [2] The method for manufacturing a multilayer metasurface structure according to [1], wherein step 1 comprises: step A: forming a photosensitive layer containing a polymerizable compound on a first metasurface structure including a first substrate and a first structure layer arranged on the first substrate and having a plurality of first metal microstructures arranged in an in-plane direction; step B: exposing the photosensitive layer to light in a pattern; and step C: developing the exposed photosensitive layer to form spacer portions. [3] The method for manufacturing a multilayer metasurface structure according to [1], wherein step 1 comprises: forming a spacer portion by laminating a patterned photosensitive layer containing a polymerizable compound on a first metasurface structure including a first substrate and a first structure layer arranged on the first substrate and having a plurality of first metal microstructures arranged in an in-plane direction. [4] The method for manufacturing a multilayer metasurface structure according to [1], wherein step 1 comprises: forming a spacer portion by laminating a patterned photosensitive layer containing a polymerizable compound on a first metasurface structure including a first substrate and a first structure layer arranged on the first substrate and having a plurality of first metal microstructures arranged in an in-plane direction. 5 Pa s or more, and the melt viscosity at 80°C is 1.0 × 10 5 [5] A multilayer metasurface structure manufactured by the method for manufacturing a multilayer metasurface structure according to any one of [1] to [4]. [6] The multilayer metasurface structure according to [5], which is a transmission element. [7] The multilayer metasurface structure according to [5], which is a sheet-type metalens.

[0013] According to the present invention, in manufacturing a multilayer metasurface structure in which multiple metasurface structures are stacked, a multilayer metasurface structure having excellent positional accuracy between the metasurface structures can be obtained.

[0014] FIG. 1 is a diagram conceptually showing an example of a metasurface structure manufactured by the manufacturing method of the present invention. FIG. 2 is a diagram conceptually showing another example of a metasurface structure manufactured by the manufacturing method of the present invention. FIG. 3 is a diagram conceptually showing another example of a metasurface structure manufactured by the manufacturing method of the present invention. FIG. 4 is a conceptual diagram for explaining the manufacturing method of the present invention. FIG. 5 is a conceptual diagram for explaining an embodiment of the present invention. FIG. 6 is a conceptual diagram for explaining an embodiment of the present invention.

[0015] Below, a method for manufacturing a multilayer metasurface structure will be described in detail based on a preferred embodiment shown in the accompanying drawings.

[0016] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In this specification, "the same" includes a margin of error generally accepted in the technical field.

[0017] The following figures are conceptual diagrams for explaining the multilayer metasurface structure. Therefore, the shape, size, thickness, spacing, and in-plane positional relationships of each component do not necessarily correspond to the actual ones.

[0018] An example of a multilayer metasurface structure is conceptually shown in Figure 1. The multilayer metasurface structure 10 shown in Figure 1 includes a first substrate 12, a second substrate 14, a first structural layer 16, a second structural layer 18, a third structural layer 20, a fourth structural layer 24, and a spacer 26 disposed between the first substrate 12 and the second substrate 14. Note that Figure 1 (Figures 2 and 3) conceptually show a cut of the multilayer metasurface structure cut in the thickness direction, i.e., the stacking direction of the first structural layer 16 to the fourth structural layer 24, and in the longitudinal direction of the first metal microstructure 16a to the fourth metal microstructure 24a described below. However, hatching has been omitted in all figures to clearly show the configuration of the multilayer metasurface structure.

[0019] The first structure layer 16 is formed using one surface (top surface in the figure) of the first substrate 12, and is formed by arranging (disposing) a plurality of first metal microstructures 16a on the surface of the first substrate 12. The second structure layer 18 is formed using one surface (bottom surface in the figure) of the second substrate 14, and is formed by arranging (disposing) a plurality of second metal microstructures 18a on the surface of the first substrate 12. The third structure layer 20 is formed using the other surface (bottom surface in the figure) of the first substrate 12, and is formed by arranging (disposing) a plurality of third metal microstructures 20a on the surface of the first substrate 12. The fourth structure layer 24 is formed using the other surface (top surface in the figure) of the second substrate 14, and is formed by arranging (disposing) a plurality of fourth metal microstructures 24a on the surface of the second substrate 14.

[0020] The first substrate 12 and the first structural layer 16 constitute the first metasurface structure of the present invention. The second substrate 14 and the second structural layer 18 constitute the second metasurface structure of the present invention. Furthermore, in a preferred embodiment, the multilayer metasurface structure 10 shown in Figure 1 has a third metasurface structure constituted by the first substrate 12 and the third structural layer 20, and a fourth metasurface structure constituted by the second substrate 14 and the fourth structural layer 24. Note that in the present invention, a metasurface refers to a structure in which a plurality of metal microstructures smaller than the optical wavelength corresponding to the design frequency, i.e., the frequency of the corresponding electromagnetic wave, are arranged on the surface of a dielectric film, and a macroscopic response to incident electromagnetic waves is utilized.

[0021] The first substrate 12 and the second substrate 14 are stacked and fixed with the first structural layer 16 and the second structural layer 18 facing each other, sandwiching a spacer 26. In the illustrated example, the multilayer metasurface structure 10 is stacked with the first substrate 12 and the second substrate 14 sandwiching the spacer 26, thereby separating the first structural layer 16 and the second structural layer 18 from each other. The first substrate 12 and the second substrate 14 are attached by the spacer 26. This will be described in more detail later. The first structural layer 16 and the third structural layer 20 are stacked with a space between them by the first substrate 12, and the second structural layer 18 and the fourth structural layer 24 are stacked with a space between them by the second substrate 14.

[0022] The illustrated multilayer metasurface structure has four structural layers, from the first structural layer 16 to the fourth structural layer 24. However, as long as the multilayer metasurface structure of the invention has the first structural layer 16 and the second structural layer 18, it may have only two structural layers as shown in FIG. 3, or it may have three structural layers, or even five or more structural layers. However, it is preferable that at least one of the first substrate 12 and the second substrate 14 has structural layers on both sides, and it is more preferable that both the first substrate 12 and the second substrate 14 have structural layers on both sides, as shown in the illustrated example. The following explanation also applies to multilayer metasurface structures having two to three structural layers, or five or more structural layers.

[0023] In a preferred embodiment, the multilayer metasurface structure 10 manufactured by the manufacturing method of the present invention is one that acts on electromagnetic waves with a frequency of 10 THz or less, i.e., electromagnetic waves with a wavelength of 30 μm or more. In other words, the design electromagnetic wave of the multilayer metasurface structure 10 is preferably 10 THz or less. Specifically, a multilayer metasurface structure that acts on electromagnetic waves with a frequency of 10 THz or less means that when electromagnetic waves of a certain frequency of 10 THz or less are incident on the multilayer metasurface structure, the multilayer metasurface structure functions as a body with a high refractive index against the electromagnetic waves, in other words, the multilayer metasurface structure functions as a structure that can obtain a high diffraction angle.

[0024] Although there is no lower limit to the frequency of the electromagnetic waves that the multilayer metasurface structure 10 acts on, it is preferable that the multilayer metasurface structure 10 acts on electromagnetic waves with a frequency of 10 GHz or higher, i.e., a wavelength of 30 mm or less. More preferably, the multilayer metasurface structure 10 acts on electromagnetic waves with a frequency of 100 GHz or higher, i.e., a wavelength of 3 mm or less. In other words, it is preferable that the multilayer metasurface structure 10 acts on electromagnetic waves with a frequency of 10 GHz to 10 THz, so-called terahertz waves (THz waves).

[0025] As described above, the multilayer metasurface structure 10 is formed by stacking a first substrate 12 having a first structural layer 16 on one side and a third structural layer 20 on the other side, and a second substrate 14 having a second structural layer 18 on one side and a fourth structural layer 24 on the other side, via a spacer 26. The spacer 26 is a patterned (not solid) spacer that separates and stacks the first substrate 12 and the second substrate 14. The pattern shape preferably satisfies the following requirements: - Not contacting the second metal microstructures 18a - Not contacting the first metal microstructures 16a - Having a size sufficient to ensure the strength to support and separate the first substrate 12 and the second substrate 14 Specifically, the spacer 26 may be a frame-shaped spacer that surrounds the arrangement of the first metal microstructures 16a of the first structure layer 16 and the arrangement of the second metal microstructures 18a of the second structure layer 18 in the in-plane direction of the first substrate 12 and the second substrate 14. When the spacer 26 is frame-shaped, a portion of it may be cut out. For example, from the viewpoint of ensuring the strength to support and space the first substrate 12 and the second substrate 14, it is preferable that the spacers 26 be provided in an area corresponding to 50% or more of the outer circumferential length of the frame body that surrounds the arrangement of the first metal microstructures 16a of the first structural layer 16 and the arrangement of the second metal microstructures 18a of the second structural layer 18 in the in-plane direction of the first substrate 12 and the second substrate 14, it is more preferable that the spacers 26 be provided in an area corresponding to 75% or more, and it is even more preferable that the spacers 26 be provided in an area corresponding to 90% or more.

[0026] In the multilayer metasurface structure 10, the first substrate 12 and the second substrate 14 are both substrates made of a dielectric material. That is, in the illustrated multilayer metasurface structure 10, the first substrate 12 acts as a dielectric layer provided between the first structural layer 16 and the third structural layer 20, and the second substrate 14 acts as a dielectric layer provided between the second structural layer 18 and the fourth structural layer 24. In addition, the spacer 26 forms an air layer between the first structural layer 16 and the second structural layer 18, acting as a dielectric layer.

[0027] The illustrated multilayer metasurface structure 10 is not limited to a structure in which metal microstructures are provided on both sides of a single substrate and two such substrates are stacked at a distance from each other, thereby stacking the first to fourth structural layers at a distance from each other. For example, the multilayer metasurface structure may be a structure in which four substrates are used: a substrate having a first structural layer on one side, a substrate having a second structural layer on one side, a substrate having a third structural layer on one side, and a substrate having a fourth structural layer on one side, with the structural layers facing the substrates, thereby stacking the first to fourth structural layers at a distance from each other. Furthermore, other layers (e.g., adhesive layers) may be disposed between the first substrate 12 and the first structural layer 16, between the first substrate 12 and the third structural layer 20, between the second substrate 14 and the second structural layer 18, and between the second substrate 14 and the fourth structural layer 24.

[0028] The first substrate 12 and the second substrate 14 are dielectric resin films. A dielectric resin film refers to one or more dielectric substrates that can be handled independently and on which a metal pattern can be formed. The dielectric substrate may have a single-layer structure or a laminated structure. Examples of preferred dielectric substrates include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyethylene (PE), polypropylene (PP), polystyrene, ethylene vinyl acetate (EVA), polyolefins such as cycloolefin polymer (COP) and cycloolefin copolymer (COC), vinyl resins, polycarbonate (PC), polyamide, polyimide, acrylic resin, and triacetyl cellulose (TAC). Among these, substrates made of cycloolefin polymer (COP) and cycloolefin copolymer (COC) are particularly suitable.

[0029] There are no limitations on the thickness of the first substrate 12 and the second substrate 14. A thickness that exhibits sufficient dielectric properties and can support the metal microstructures described below can be appropriately set depending on the forming material, etc. The thickness of the first substrate 12 and the second substrate 14 is preferably 5 to 100 μm, more preferably 10 to 80 μm, and even more preferably 15 to 50 μm. Furthermore, the first substrate 12 and the second substrate 14 preferably have high transmittance for the target electromagnetic waves. Specifically, the transmittance for the target electromagnetic waves of the first substrate 12 and the second substrate 14 is preferably 75% or more, more preferably 85% or more, and even more preferably 95% or more. There is no particular upper limit to the electromagnetic wave transmittance, and it is often less than 100%. When the first substrate 12 and the second substrate 14 are at or above a predetermined thickness, they are easy to handle. Furthermore, when the first substrate 12 and the second substrate 14 are at or below a predetermined thickness and / or when their transmittance is at or above a predetermined value, they are more likely to function as metamaterials.

[0030] The first substrate 12 and the second substrate 14 are usually made of the same material, but may be made of different materials. The first substrate 12 and the second substrate 14 are usually made of the same thickness, but may be made of different materials.

[0031] As described above, the multilayer metasurface structure 10 is formed by stacking the first substrate 12 and the second substrate 14 via the spacer 26. The spacer 26 is formed in a pattern. In the illustrated example, as described above, the spacer 26 is a frame-like structure that surrounds the arrangement of the first metal microstructures 16a of the first structure layer 16 and the arrangement of the second metal microstructures 18a of the second structure layer 18 in the in-plane direction of the first substrate 12 and the second substrate 14.

[0032] Note that the spacer 26 is not limited to having a frame-shaped pattern surrounding the arrangement of the first metal microstructures 16 a and the second metal microstructures 18 a, and various patterns can be used depending on the arrangement of the metal microstructures, such as a pattern consisting of a rectangular frame and its diagonal lines, a pattern consisting of a circular frame and lines crossing the circle in the diameter direction, and a pattern consisting of a rectangular frame and lines parallel to the frame.

[0033] However, when spacers are arranged in the array of metal microstructures, there is a possibility that inconveniences may arise, such as high difficulty in patterning the spacers, etc. In consideration of this point, as in the illustrated example, spacers 26 having a frame-shaped pattern that surrounds the array of first metal microstructures 16 a and second metal microstructures 18 a are preferably used.

[0034] The distance between the first substrate 12 and the second substrate 14, i.e., the thickness of the spacer 26, is not limited; it can be set appropriately as long as it provides an air gap thick enough to function as a dielectric layer. If the thickness of the spacer 26 is sufficiently thinner than the wavelength of the electromagnetic wave of interest, the proximity (bonding) between the first metal microstructures 16a and the second metal microstructures 18a may change the resonance structure and distort the resonance peak. However, this effect can be actively utilized. However, when using the resonance due to the proximity between the first metal microstructures 16a and the second metal microstructures 18a by thinning the spacer 26, care must be taken to ensure that alignment errors that occur during stacking do not affect the transmitted electromagnetic wave. Conversely, the thickness of the spacer 26 can be set sufficiently far enough so that the resonance between the first metal microstructures 16a and the second metal microstructures 18a is negligible and so that alignment errors that occur during stacking do not affect the transmitted electromagnetic wave.

[0035] The spacers 26 will be described in detail later. As will be described later, the spacers 26 contain at least a polymer (cured product) of a polymerizable compound.

[0036] As described above, in the multilayer metasurface structure 10, the first structure layer 16 is formed by arranging a plurality of first metal microstructures 16a at a distance from one another on one surface (top surface in the figure) of the first substrate 12. The first structure layer 16 is basically composed of an arrangement of unit cells formed by one first metal microstructure 16a and the space surrounding the first metal microstructure 16a. The second structure layer 18 is formed by arranging a plurality of second metal microstructures 18a at a distance from one another on one surface (bottom surface in the figure) of the second substrate 14. The second structure layer 18 is basically composed of an arrangement of unit cells formed by one second metal microstructure 18a and the space surrounding the second metal microstructure 18a. The third structure layer 20 is formed by arranging a plurality of third metal microstructures 20a at a distance from one another on the other surface (bottom surface in the figure) of the first substrate 12. The third structure layer 20 is basically composed of an arrangement of unit cells formed by one third metal microstructure 20a and the space surrounding the third metal microstructure 20a. The fourth structure layer 24 is composed of a plurality of fourth metal microstructures 24a arranged at a distance from each other on the other surface (the lower surface in the figure) of the second substrate 14. The fourth structure layer 24 is basically composed of an arrangement of unit cells formed by one fourth metal microstructure 24a and the space surrounding the fourth metal microstructure 24a.

[0037] As described above, in the multilayer metasurface structure 10, the first structure layer 16 to the fourth structure layer 24 all use the surface of a corresponding substrate, and have the same basic structure in which the first metal microstructures 16a to the fourth metal microstructures 24a are arranged on this surface. Therefore, in the following description, when there is no need to distinguish between the first structure layer 16 to the fourth structure layer 24, they will also be collectively referred to as structure layers. Similarly, when there is no need to distinguish between the first metal microstructures 16a to the fourth metal microstructures 24a, they will also be collectively referred to as metal microstructures.

[0038] In the multilayer metasurface structure 10, the structure layer has a configuration similar to that of a typical metasurface structure (metamaterial), in which metal microstructures (unit cells) are arranged on one surface of a substrate. Therefore, there are no limitations on the shape of the metal microstructures, the arrangement of the metal microstructures, or the spacing (pitch) of the metal microstructures.

[0039] In the multilayer metasurface structure 10, the metal microstructures are made of metal. As described above, the multilayer metasurface structure 10 preferably acts on electromagnetic waves with frequencies of 10 THz or less. Metals have high conductivity and transmittance for electromagnetic waves with frequencies of 10 THz or less. Therefore, by using metal microstructures, the multilayer metasurface structure 10 can efficiently refract electromagnetic waves with frequencies of 10 THz or less.

[0040] The material for forming the metal microstructure is not particularly limited as long as it contains a metal in part and causes resonance when a specific electromagnetic wave is incident thereon, and the metal microstructure may contain a dielectric material, a magnetic material, etc. in addition to the metal. The metal microstructure may also contain a conductive material such as a conductive polymer in part. Preferred examples of the metal include gold, silver, platinum, copper, aluminum, and alloys containing one or more of these, with silver and copper being more preferred examples.

[0041] Similarly, the shape of the metal microstructures that make up the structure layer is not limited, and various shapes used as metal microstructures (resonators) in known metasurface structures can be used. When electromagnetic waves are incident on the metal microstructures, the interaction between the electric field and magnetic field of the incident electromagnetic waves simultaneously generates electric and magnetic resonance, and the effective permittivity and permeability can be simultaneously controlled. Examples of the shape of the metal microstructures include cut metal wires, cross and swastika shapes formed by crossing metal cut wires, C-shapes, U-shapes, double ring shapes, V-shapes, L-shapes, H-shapes, lattice shapes, spiral shapes, square shapes, and circles. Other shapes that can be used include solids with a base shape such as that shown in Figure 5 of "Appl. Sci. 2018, 8(9), 1689; https: / / doi.org / 10.3390 / app8091689."

[0042] Among these, metal cut wires (metal rods) are preferably used. There are no limitations on the cross-sectional shape of the metal cut wire, and various columnar shapes such as a quadrangular prism, a triangular prism, and a cylindrical shape can be used. For a quadrangular prism, the cross section in the direction perpendicular to the longitudinal direction can be various shapes such as a square, a rectangle, a parallelogram, and a trapezoid. Similarly, for a triangular prism, various shapes such as an equilateral triangle and an isosceles triangle can be used, and for a cylindrical shape, not only a circle but also an ellipse can be used.

[0043] In one structure layer, only one type of metal microstructure may be used, or multiple types may be used in combination. The metal microstructures in each structure layer may be the same or different from each other.

[0044] In the multilayer metasurface structure 10, there is no limit to the size of the metal microstructures, but as with ordinary metasurface structures (metamaterials), the size is equal to or less than the wavelength of the electromagnetic wave of interest, preferably equal to or less than 1.0 times the wavelength, and more preferably equal to or less than 0.5 times the wavelength. For example, in the case of electromagnetic waves with a frequency of 0.1 to 10 THz (terahertz waves), the size (major axis) of the metal microstructures is preferably 1 to 3,000 μm, and more preferably 5 to 1,000 μm.

[0045] In the multilayer metasurface structure 10 shown in Figure 1, the first metal microstructure 16a, the second metal microstructure 18a, the third metal microstructure 20a, and the fourth metal microstructure 24a are arranged offset from each other in the in-plane direction of the first substrate 12 and the second substrate 14. In other words, when viewed from the normal direction of the substrates, the first metal microstructure 16a, the second metal microstructure 18a, the third metal microstructure 20a, and the fourth metal microstructure 24a do not completely overlap.

[0046] The normal direction is the direction perpendicular to the main surface of the sheet-like material, and in the multilayer metasurface structure 10, it is the thickness direction, i.e., the stacking direction of the structure layers, i.e., the stacking direction of the first substrate 12, the spacer 26, and the second substrate 14. The main surface is the largest surface of the sheet-like material, and is usually both sides in the thickness direction.

[0047] The multilayer metasurface structure manufactured by the manufacturing method of the present invention is not limited to this, and as conceptually shown in Figure 2, the first metal microstructure 16a, the second metal microstructure 18a, the third metal microstructure 20a, and the fourth metal microstructure 24a may be arranged so that they are aligned with each other in the in-plane direction of the first substrate 12 and the second substrate 14. In other words, when viewed from the normal direction of the substrates, the multilayer metasurface structure may be such that the first metal microstructure 16a, the second metal microstructure 18a, the third metal microstructure 20a, and the fourth metal microstructure 24a completely overlap.

[0048] Furthermore, the multilayer metasurface structure manufactured by the manufacturing method of the present invention may have only two structural layers, a first structural layer 16 and a second structural layer 18, as conceptually shown in Figure 3.

[0049] The multilayer metasurface structure manufactured by the manufacturing method of the present invention, i.e., the multilayer metasurface structure of the present invention, may focus, diffuse, or refract electromagnetic waves in one direction. Furthermore, the multilayer metasurface structure may be either transmissive or reflective, but is preferably transmissive. Therefore, the multilayer metasurface structure can be used in various known elements, such as metalenses such as convex and concave lenses, and deflection elements that bend electromagnetic waves. Here, the multilayer metasurface structure can be fabricated into a sheet-type element by providing a refractive index distribution structure in the structure layer, utilizing the characteristic optical response exhibited by the metal microstructure in the structure layer. Therefore, the multilayer metasurface structure is preferably a sheet-type metalense such as a convex or concave lens.

[0050] The method for manufacturing such a multilayer metasurface structure of the present invention will be described in detail below. The multilayer metasurface structure of the present invention is a multilayer metasurface structure manufactured by the manufacturing method of the present invention, which includes the following steps 1 to 3.

[0051] As conceptually shown in the upper part of Figure 4, a first metasurface structure is prepared, in which a first structure layer 16 having first metal microstructures 16a arranged on one surface of a first substrate 12 is provided. Note that in this example, a third metasurface structure is provided, in which a third structure layer 20 having third metal microstructures 20a arranged on the other surface of the first substrate 12 is provided. Similarly, a second metasurface structure is prepared, in which a second structure layer 18 having second metal microstructures 18a arranged on one surface of a second substrate 14 is provided. As before, in this example, a fourth metasurface structure is provided, in which a fourth structure layer 24 having fourth metal microstructures 24a arranged on the other surface of the second substrate 14 is provided.

[0052] Furthermore, how the multilayer metasurface structure reacts to electromagnetic waves with frequencies of 10 THz or less can be set by appropriately selecting and combining the shape and forming material of the metal microstructures in each structure layer, the arrangement of the metal microstructures, and the spacing between the metal microstructures.

[0053] In a multilayer metasurface structure, the metal microstructures used and the arrangement of the metal microstructures in each structure layer can be set using known methods to obtain the desired characteristics of the multilayer metasurface structure. For example, if the metasurface structure is a sheet-type lens (convex lens), the arrangement density of the metal microstructures can be gradually decreased from the center to the periphery so that the phase difference imparted to the transmitted electromagnetic wave gradually decreases from the center to the periphery. For example, these designs can be performed by calculating the amplitude and phase of the electromagnetic wave transmitted through the metal microstructures using commercially available simulation software, and then setting the arrangement of the metal microstructures so that the desired phase difference (phase modulation amount (refractive index)) distribution is obtained.

[0054] There are no limitations on the method for forming the structure layer in which the metal microstructures are arranged, and various known manufacturing methods used in manufacturing metasurface structures can be used. As an example, a metal layer can be formed on both sides (or one side) of a substrate by a known film formation method such as sputtering, and a structure layer in which the metal microstructures are arranged can be formed on this metal layer using photolithography technology.

[0055] In the manufacturing method of the multilayer metasurface structure of the present invention, first, in step 1, as conceptually shown in the middle of Figure 4, spacer portions 26a that become frame-shaped spacers 26 are formed in a pattern on the first metasurface structure (i.e., on the surface of the first substrate 12 on which the first structure layer 16 is formed) so as to surround the array of first metal microstructures 16a that constitute the first structure layer 16 in the substrate surface direction. Next, in step 2, as conceptually shown in the bottom of Figure 4, the spacer portions 26a and the second metasurface structure, i.e., the surface of the second substrate 14 on which the second structure layer 18 is formed, are bonded together to obtain a laminate including the first metasurface structure, spacer portions 26a, and second metasurface structure.

[0056] Here, the spacer portion 26a contains a polymerizable compound and has some adhesiveness until it is polymerized in the subsequent step 3. Therefore, even after the spacer portion 26a and the second metasurface structure (i.e., the surface of the second substrate 14 on which the second structure layer 18 is formed) are laminated and bonded in step 2, they can be easily peeled off and reattached. Moreover, in the manufacturing method of the present invention, the spacer portion 26a is arranged in a pattern, so the first metasurface structure and the second metasurface structure are not bonded entirely. In the illustrated example, a preferred embodiment has a frame-shaped pattern. This makes it easier to peel off the laminated and bonded spacer portion 26a and the second metasurface structure. Note that when step 3, described below, is performed, the polymerizable compound in the spacer portion 26a polymerizes, improving the adhesion between the first metasurface structure and the second metasurface structure. The manufacturing method of the present invention for a laminated metasurface structure thereby enables the production of a laminated metasurface structure with high positional accuracy relative to the metasurface structures.

[0057] As described above, a multilayer metasurface structure, which is composed of multiple stacked metasurface structures, can impart a larger phase shift to incident electromagnetic waves than a conventional single-layer metasurface structure. To achieve the desired performance, the metasurface structures must be precisely aligned and stacked and attached. However, the microstructures that form the metasurface structure are very small. For example, when using electromagnetic waves with a frequency of 0.1 to 10 THz as described above, the size of the microstructures is typically 1 to 3,000 μm. Therefore, stacking metasurface structures in the correct positional relationship requires extremely high precision, and it is rare to achieve the correct positional relationship in a single operation.

[0058] If the relative positions of the metasurface structures are incorrect when stacked, the metasurface structures must be peeled off, realigned, and re-stacked. However, in conventional manufacturing of multilayer metasurface structures, the stacked metasurface structures are adhered with an adhesive. Therefore, even if the relative positions of the stacked metasurface structures are incorrect, it is very difficult to peel off the metasurface structures once they have been stacked.

[0059] In contrast, with the manufacturing method of the present invention, as described above, the second metasurface structure can be easily peeled off even after the spacer portion 26a and the second metasurface structure are stacked to form a stack including the first metasurface structure, the spacer portion 26a, and the second metasurface structure. Therefore, even if the positional relationship between the first metasurface structure and the second metasurface structure is improper when the spacer portion 26a and the second metasurface structure are stacked, the second metasurface structure can be easily peeled off, the positions can be realigned, and the spacer portion 26a and the second metasurface structure can be stacked. As a result, with the manufacturing method of the present invention, the metasurface structures can be appropriately aligned with each other, and a multilayer metasurface structure with excellent positional accuracy between the metasurface structures can be manufactured.

[0060] The procedures of steps 1 to 3 of the manufacturing method of the present invention will be described in more detail below. Step 1 of the manufacturing method of the present invention is a step of arranging spacer portions containing a polymerizable compound in a pattern on a first metasurface structure including a first substrate and a first structure layer provided on at least one surface side of the first substrate and including a plurality of first metal microstructures arranged in the in-plane direction. The first metasurface structure including the first structure layer used in this step is as described above.

[0061] The spacer portion used in this step contains a polymerizable compound. As described above, the spacer portion contains a polymerizable compound, which causes some adhesiveness. Furthermore, during the polymerization treatment in step 3 described below, polymerization of the polymerizable compound progresses, improving the adhesion between the first metasurface structure and the second metasurface structure.

[0062] The type of polymerizable compound contained in the spacer portion is not particularly limited, and any known polymerizable compound can be used. The polymerizable compound means a compound different from the resin described below.

[0063] The polymerizable group of the polymerizable compound may be any group that is involved in a polymerization reaction, and examples thereof include groups having an ethylenically unsaturated group such as a vinyl group, an acryloyl group, a methacryloyl group, a styryl group, and a maleimide group; and groups having a cationic polymerizable group such as an epoxy group and an oxetane group. Among these, the polymerizable group is preferably a group having an ethylenically unsaturated group, and more preferably an acryloyl group or a methacryloyl group.

[0064] The polymerizable compound is preferably a compound having one or more ethylenically unsaturated groups, more preferably a compound having two or more ethylenically unsaturated groups in the molecule. In terms of superior polymerizability, the number of ethylenically unsaturated groups in the ethylenically unsaturated compound molecule is preferably 1 to 6, more preferably 1 to 3, even more preferably 2 to 3, and particularly preferably 3.

[0065] The polymerizable compound may have an alkyleneoxy group. The alkyleneoxy group is preferably an ethyleneoxy group or a propyleneoxy group, and more preferably an ethyleneoxy group in terms of achieving better effects of the present invention. The number of alkyleneoxy groups contained in the polymerizable compound is preferably 2 to 30, more preferably 2 to 20, per molecule.

[0066] The polymerizable compound preferably includes a polymerizable compound X. The polymerizable compound X is a bifunctional ethylenically unsaturated compound having one or more aromatic rings in the molecule, among the above polymerizable compounds.

[0067] Examples of the aromatic ring contained in the polymerizable compound X include aromatic hydrocarbon rings such as a benzene ring, a naphthalene ring, and an anthracene ring; aromatic heterocycles such as a thiophene ring, a furan ring, a pyrrole ring, an imidazole ring, a triazole ring, and a pyridine ring; and condensed rings thereof. An aromatic hydrocarbon ring is preferred, and a benzene ring is more preferred. The aromatic ring may have a substituent. The polymerizable compound X may have two or more aromatic rings.

[0068] The polymerizable compound X preferably has a bisphenol structure, since this suppresses swelling of the photosensitive layer due to a developer, thereby improving resolution. Examples of the bisphenol structure include a bisphenol A structure derived from bisphenol A (2,2-bis(4-hydroxyphenyl)propane), a bisphenol F structure derived from bisphenol F (2,2-bis(4-hydroxyphenyl)methane), and a bisphenol B structure derived from bisphenol B (2,2-bis(4-hydroxyphenyl)butane), with the bisphenol A structure being preferred.

[0069] Examples of the polymerizable compound X having a bisphenol structure include a compound having a bisphenol structure and two polymerizable groups (preferably (meth)acryloyl groups) bonded to both ends of the bisphenol structure. The two polymerizable groups may be bonded directly to both ends of the bisphenol structure, or may be bonded via one or more alkyleneoxy groups. The alkyleneoxy groups added to both ends of the bisphenol structure are preferably ethyleneoxy groups or propyleneoxy groups, and more preferably ethyleneoxy groups. The number of alkyleneoxy groups (preferably ethyleneoxy groups) added to the bisphenol structure is preferably 2 to 30, more preferably 2 to 20, per molecule.

[0070] Examples of the polymerizable compound include bifunctional ethylenically unsaturated compounds having no aromatic ring and trifunctional or higher ethylenically unsaturated compounds. Examples of bifunctional ethylenically unsaturated compounds having no aromatic ring include alkylene glycol di(meth)acrylate, polyalkylene glycol di(meth)acrylate, urethane di(meth)acrylate, and trimethylolpropane diacrylate.

[0071] The molecular weight of the polymerizable compound is preferably from 200 to 3,000, more preferably from 280 to 2,200, and even more preferably from 300 to 2,200.

[0072] The content of the polymerizable group in the polymerizable compound is preferably 1.0 mmol / g or more, more preferably 2.0 mmol / g or more. The upper limit is preferably 10.0 mmol / g or less. When the spacer portion contains multiple polymerizable compounds, the content of the polymerizable group in all of the contained polymerizable compounds is preferably the preferred embodiment described above. The "content of the polymerizable group" means the equivalent (mol) of the polymerizable group contained per 1 g of the polymerizable compound.

[0073] The polymerizable compound may be used alone or in combination of two or more. The content of the polymerizable compound is preferably 5 to 70% by mass, more preferably 10 to 60% by mass, based on the total mass of the spacer portion.

[0074] The spacer portion may contain components other than the polymerizable compound. Examples of the other components include resins. The resin is preferably a (meth)acrylic resin. The (meth)acrylic resin is a resin having structural units derived from a (meth)acrylic compound, and examples of the (meth)acrylic compound include (meth)acrylic acid, (meth)acrylic acid esters, (meth)acrylamide, and (meth)acrylonitrile. In the (meth)acrylic resin, the content of structural units derived from the (meth)acrylic compound is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, based on the total structural units of the resin. Furthermore, the (meth)acrylic resin preferably contains, for example, a structural unit having an aromatic ring structure (for example, a structural unit derived from styrene and a structural unit derived from benzyl (meth)acrylate), a structural unit having an aliphatic hydrocarbon ring structure (for example, a structural unit having an aliphatic hydrocarbon ring structure such as a tricyclodecane ring, a cyclohexane ring, a cyclopentane ring, a norbornane ring, an isoborone ring, or a tetrahydrodicyclopentadiene ring), a structural unit having an acid group (examples of the acid group include a carboxy group, a sulfo group, a phosphonic acid group, and a phosphate group), and a structural unit having a reactive group (for example, a polymerizable group).

[0075] When the (meth)acrylic resin contains a structural unit having an aromatic ring structure, the content of the structural unit having an aromatic ring structure is preferably 10 to 90% by mass, and more preferably 20 to 80% by mass, based on all structural units of the (meth)acrylic resin. When the (meth)acrylic resin contains a structural unit having an acid group, the content of the structural unit having an acid group is preferably 5 to 50% by mass, and more preferably 5 to 40% by mass, based on all structural units of the (meth)acrylic resin. When the (meth)acrylic resin contains a structural unit having a reactive group, the content of the structural unit having a reactive group is preferably 5 to 70% by mass, and more preferably 10 to 50% by mass, based on all structural units of the (meth)acrylic resin.

[0076] The weight average molecular weight of the resin is preferably 5,000 to 500,000, more preferably 10,000 to 100,000, and even more preferably 10,000 to 60,000. The Tg of the resin is preferably 60 to 135°C, and more preferably 70 to 120°C.

[0077] The resin content is preferably 10 to 85% by mass, more preferably 20 to 75% by mass, based on the total mass of the spacer portion.

[0078] The spacer portion may contain other components such as a surfactant, a polymerization initiator, a sensitizer, a color former, and a rust inhibitor.

[0079] The thickness of the spacer portion is preferably 1 to 5000 μm, more preferably 10 to 1000 μm.

[0080] The spacer portions are arranged in a pattern. The shape of the pattern is not particularly limited, and they are arranged so as to form the above-mentioned spacer pattern. For example, as described above, they are arranged so as to obtain a spacer having a frame-shaped pattern that surrounds the array of the first metal microstructures and the second metal microstructures. That is, in step 1, frame-shaped spacer portions may be arranged on the first metasurface structure so as to surround the array of the first metal microstructures.

[0081] The melt viscosity of the spacer portion is not particularly limited, but the melt viscosity at 23°C is preferably 1.0 x 10 5 Pa s or more, and the melt viscosity at 80°C is 1.0 × 10 5 When the melt viscosity of the spacer portion satisfies the above-mentioned characteristics, the second metasurface structure can be more easily peeled off after being bonded to the spacer portion, improving the productivity of the multilayer metasurface structure. The melt viscosity of the spacer portion at 23°C is preferably 1.0 × 10 １０ The melt viscosity of the spacer portion at 80°C is preferably 1.0 x 10 １Preferably, it is Pa s or more. The melt viscosity ηc of the spacer portion at 23°C and 80°C is measured as follows: After preparing a spacer portion with a thickness of approximately 0.5 mm, measurements are made using a rheometer DHR-2 manufactured by T.A. Instruments (using a 20 mmΦ parallel plate and a Peltier plate (gap: approximately 0.5 mm)) at a set temperature of 20-125°C, a heating rate of 5°C / min, a frequency of 1 Hz, and a strain of 0.5%, and the melt viscosity at each temperature is calculated from the measured values ​​at 23°C and 80°C.

[0082] The procedure for arranging the spacer portions in a pattern is not particularly limited, and known methods can be used. In particular, one preferred embodiment of step 1 includes step A: forming a photosensitive layer containing a polymerizable compound on a first metasurface structure including a first structure layer having a first substrate and a plurality of first metal microstructures arranged in the in-plane direction on the first substrate; step B: exposing the photosensitive layer to light in a pattern; and step C: developing the exposed photosensitive layer to form spacer portions. In steps A to C, after forming a photosensitive layer on the first metasurface structure, unnecessary portions are removed to form patterned spacer portions. Steps A to C are described in detail below.

[0083] In step A, the method for forming the photosensitive layer is not particularly limited as long as it can form a photosensitive layer containing a polymerizable compound on the first metasurface structure, but examples include a method using a transfer film and a method of applying a photosensitive composition. A preferred method for using a transfer film is to prepare a transfer film containing a temporary support and a photosensitive layer, and then attach the transfer film to the first metasurface structure so that the photosensitive layer side of the transfer film faces the first structure layer. A preferred method for applying a photosensitive composition is to apply a photosensitive composition to the first structure layer of the first metasurface structure to form a photosensitive layer. Of these, a method using a transfer film is preferred.

[0084] The temporary support contained in the transfer film is preferably a film, more preferably a resin film. Examples of resin films include polyethylene terephthalate films (e.g., biaxially oriented polyethylene terephthalate films), polymethyl methacrylate films, cellulose triacetate films, polystyrene films, polyimide films, and polycarbonate films. The thickness of the temporary support is preferably 5 μm or more, more preferably 6 μm or more. The upper limit is preferably 200 μm or less, and from the viewpoint of ease of handling and versatility, more preferably 150 μm or less, even more preferably 50 μm or less. In order to improve the adhesion between the temporary support and the photosensitive layer, the surface of the temporary support that contacts the photosensitive layer may be surface-modified. Examples of surface-modification treatments include treatments using UV irradiation, corona discharge, plasma, etc.

[0085] The photosensitive layer preferably contains the above-mentioned polymerizable compound, and more preferably contains the above-mentioned polymerizable compound and resin. The content of the polymerizable compound is preferably 5 to 70% by mass, and more preferably 15 to 60% by mass, based on the total mass of the photosensitive layer. The content of the resin is preferably 10 to 85% by mass, and more preferably 20 to 75% by mass, based on the total mass of the photosensitive layer.

[0086] The photosensitive layer may contain components other than the polymerizable compound and resin. Examples of such components include a polymerization initiator. Known polymerization initiators can be used depending on the type of polymerization reaction. The polymerization initiator may be either a radical polymerization initiator or a cationic polymerization initiator, with radical polymerization initiators being preferred. Examples of radical polymerization initiators include polymerization initiators having an oxime ester structure, polymerization initiators having an α-aminoalkylphenone structure, polymerization initiators having an α-hydroxyalkylphenone structure, polymerization initiators having an acylphosphine oxide structure, and polymerization initiators having an N-phenylglycine structure. From the viewpoints of photosensitivity, visibility of exposed and unexposed areas, and resolution, the radical polymerization initiator preferably includes at least one selected from the group consisting of 2,4,5-triarylimidazole dimer and its derivatives. The content of the polymerization initiator is preferably 0.1 to 20% by mass, more preferably 0.5 to 10% by mass, based on the total mass of the photosensitive layer.

[0087] The photosensitive layer may contain, in addition to the above-mentioned components, a polymerization inhibitor, a surfactant, a sensitizer, a color former, a rust inhibitor, and the like.

[0088] The method for attaching the transfer film to the first metasurface structure is not particularly limited, but a method of thermocompression bonding using a roll or the like is preferred.

[0089] After the above step A, step B is carried out, in which the photosensitive layer is exposed in a pattern. The exposed portions of the photosensitive layer remain as spacer portions, as described below. It is preferable to set the exposure conditions during exposure so that a portion of the polymerizable compound contained in the photosensitive layer remains after exposure. Known exposure methods can be used. For example, a method using a photomask can be used. By placing a photomask between the photosensitive layer and the exposure light source, the photosensitive layer can be pattern-exposed through the photomask. Examples of exposure light sources include various lasers, light-emitting diodes (LEDs), ultra-high pressure mercury lamps, high-pressure mercury lamps, and metal halide lamps. The exposure dose is 5 to 200 mJ / cm. 2 is preferred, and 10 to 200 mJ / cm 2The exposure dose is determined by the illuminance of the light source and the exposure time. The exposure dose may be measured using a known actinometer. In the exposure, the photosensitive layer may be exposed using a direct imaging device without using a photomask.

[0090] After the above step B, step C is carried out, in which the exposed photosensitive layer is subjected to a development treatment to form spacer portions. By carrying out this step, the unexposed portions are removed, and a pattern of spacer portions is formed. As a development treatment method, a known method using a developer can be used. Examples include puddle development, shower development, spin development, and dip development. As the developer, an alkaline aqueous solution is preferred. Examples of alkaline compounds contained in the alkaline aqueous solution (compounds that dissolve in water and have a pH of greater than 7.0) include sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate.

[0091] Another preferred embodiment of Step 1 is a step of forming a spacer portion by laminating a photosensitive layer containing a patterned polymerizable compound on a first metasurface structure including a first substrate and a first structure layer formed on the first substrate and including a plurality of first metal microstructures arranged in the in-plane direction. In this step, a photosensitive layer containing a patterned polymerizable compound is laminated directly on the first metasurface structure. This patterned photosensitive layer corresponds to the spacer portion. A preferred procedure for the step involves using a transfer film including a temporary support and a photosensitive layer containing a patterned polymerizable compound arranged on the temporary support. Specifically, a transfer film including a temporary support and a photosensitive layer containing a patterned polymerizable compound is prepared, and the transfer film is attached to the first metasurface structure so that the photosensitive layer side of the transfer film faces the first structure layer. The configurations of the temporary support and photosensitive layer that constitute the transfer film are as described above. The method for forming the patterned photosensitive layer containing the polymerizable compound is not particularly limited, and examples thereof include a method of cutting out unnecessary portions of the photosensitive layer in the transfer film. In the above process, the method for laminating the transfer film to the first metasurface structure is not particularly limited, but a method of thermocompression bonding using a roll or the like is preferred.

[0092] In the manufacturing method of the present invention, after performing step 1 above, step 2 is performed in which a second metasurface structure including a second substrate and a second structure layer formed on at least one surface side of the second substrate and including a plurality of second metal microstructures arranged in the in-plane direction is bonded to a spacer portion to obtain a laminate including the first metasurface structure, the spacer portion, and the second metasurface structure. The method for bonding the spacer portion and the second metasurface structure is not particularly limited, and known methods can be used. As described above, in the manufacturing method of the present invention, after bonding the spacer portion and the second metasurface structure, the second metasurface structure can be easily peeled off, allowing the second metasurface structure to be stacked on the spacer portion with high positional accuracy.

[0093] In the manufacturing method of the present invention, after performing step 2, step 3 is performed to polymerize the polymerizable compound. In other words, step 3 is a step of curing the polymerizable compound. By performing this step, polymerization of the polymerizable compound in the spacer portion proceeds, improving adhesion between the first metasurface structure and the second metasurface structure. By performing this step, for example, the spacer 26 described in FIG. 1 is formed. The method for polymerizing the polymerizable compound is not particularly limited, and examples include heat treatment and light irradiation treatment. From the viewpoint of polymerization, heat treatment is preferred. The conditions for the heat treatment are not particularly limited, and optimal conditions are selected depending on the type of polymerizable compound used. In particular, the heating temperature during the heat treatment is preferably 80 to 250°C, more preferably 90 to 160°C. Furthermore, the heating time during the heat treatment is preferably 1 to 180 minutes, more preferably 5 to 60 minutes.

[0094] Before or simultaneously with the heat treatment, the laminate may be subjected to an exposure treatment (hereinafter also referred to as a post-exposure treatment) as necessary. Examples of exposure light sources in the post-exposure treatment include various lasers, light-emitting diodes (LEDs), ultra-high pressure mercury lamps, high pressure mercury lamps, and metal halide lamps. The exposure dose in the post-exposure treatment is 100 to 5000 mJ / cm. 2 is preferred, and 200 to 3000 mJ / cm 2 is more preferred.

[0095] The above provides a detailed description of the manufacturing method for the multilayer metasurface structure and the multilayer metasurface structure of the present invention, but the present invention is not limited to the above examples, and of course various improvements and modifications may be made within the scope of the gist of the present invention.

[0096] The features of the present invention will be described in more detail below with reference to examples. Note that the examples shown below are merely examples of the present invention. Therefore, the present invention should not be construed as being limited by the specific examples shown below.

[0097] [Preparation of Composition and Transfer Film] <Synthesis of Resin A1> Propylene glycol monomethyl ether (67 g) was placed in a flask and heated to 90°C under a nitrogen stream. A solution of styrene (47.7 g), methyl methacrylate (1.3 g), methacrylic acid (19 g), and polymerization initiator V-601 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (4 g) dissolved in propylene glycol monomethyl ether (33 g) was added dropwise to this solution over a period of 3 hours. After completion of the dropwise addition, 1 g of V-601 was added three times, every hour. The resulting reaction solution was then allowed to react for an additional 3 hours. After the reaction, the reaction solution was diluted with propylene glycol monomethyl ether acetate (33 g) and propylene glycol monomethyl ether (100 g). The diluted reaction solution was heated to 100°C under an air stream, and tetraethylammonium bromide (0.53 g) and p-methoxyphenol (0.26 g) were added. To this solution, glycidyl methacrylate (Blemmer G, manufactured by NOF Corporation) (32 g) was added dropwise over 20 minutes. The resulting reaction solution was reacted at 100°C for 7 hours, and then diluted with propylene glycol monomethyl ether acetate to obtain a solution of Resin A1 with a solids concentration of 30%. The amount of residual monomer measured using gas chromatography was less than 0.1% by mass relative to the polymer solids for all monomers.

[0098] Using a similar method, resins A2 to A3 shown in Table 1 were synthesized. The amount of residual monomer in each resin measured by gas chromatography was less than 0.1% by mass based on the polymer solid content for all monomers.

[0099] The amount of structural units, weight average molecular weight, double bond content, and glass transition temperature (Tg) of each synthesized resin are shown in Table 1. In Table 1, the abbreviations are as follows: st: styrene MMA: structural unit derived from methyl methacrylate MAA: structural unit derived from methacrylic acid GMA-MAA: structural unit obtained by adding glycidyl methacrylate to a structural unit derived from methacrylic acid BzMA: structural unit derived from benzyl methacrylate

[0100]

[0101] Next, compositions 1 to 3 were prepared according to the formulations shown in Table 2. The numerical values ​​for each component in Table 2 represent parts by mass. The abbreviations shown in Table 2 are as follows. (Polymerizable compounds) BPE-100: ethoxylated bisphenol A dimethacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd. (double bond content: 4.30 mmol / g) M-270: Aronix M-270, polypropylene glycol diacrylate (n≈12), manufactured by Toagosei Co., Ltd. (double bond content: 2.50 mmol / g) BPE-500: ethoxylated bisphenol A dimethacrylate, manufactured by Shin-Nakamura Chemical Co., Ltd. (double bond content: 2.49 mmol / g)

[0102] (Photopolymerization initiator) B-IMD: 2-(o-chlorophenyl)-4,5-diphenylimidazole dimer

[0103] (Sensitizer) EAB-F: 4,4'-bis(diethylamino)benzophenone

[0104] (Polymerization inhibitor) Phenothiazine Phenidone: Phenidone 1% methyl ethyl ketone (MEK) solution

[0105] (Chain transfer agent) Compound A: N-phenylcarbamoylmethyl-N-carboxymethylaniline (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0106] (Coloring agent) LCV: Leuco Crystal Violet: manufactured by Tokyo Chemical Industry Co., Ltd.

[0107] (Rust inhibitor) CBT-1: Carboxybenzotriazole, manufactured by Johoku Chemical Co., Ltd.

[0108] (Surfactant) F-552: Megafac F-552, manufactured by DIC Corporation

[0109] (Solvent) MMPGAc: 1-methoxy-2-propyl acetate MEK: methyl ethyl ketone MFG: propylene glycol monomethyl ether

[0110]

[0111] Next, a transfer film was prepared using the above composition. The specific procedure is as follows. First, Composition 1 was applied to the surface of a temporary support (a polyethylene terephthalate film (E5001, manufactured by Toyobo Co., Ltd.) having a thickness of 100 μm with a bar coater to form a coating film with a dry thickness of approximately 20 μm. Next, the coating film was dried at 90°C using an oven. This operation was repeated five times to form a film with a total photosensitive layer thickness of 100 μm, and then a polypropylene film (E-201F, manufactured by Oji F-Tex Co., Ltd.) was laminated thereon as a protective film to prepare Transfer Film 1. Transfer Film 2 was prepared according to the same procedure as above, except that Composition 1 was changed to Composition 2. Transfer Film 3 was prepared according to the same procedure as above, except that Composition 1 was changed to Composition 3 and the total thickness of the photosensitive layer was set to 20 μm. Further, a transfer film 4 was prepared in the same manner as above, except that composition 1 was changed to composition 4 and the total thickness of the photosensitive layer was set to 20 μm.

[0112] [Example 1] <Fabrication of metasurface structure> A cycloolefin polymer film (COP film) (40 μm thick) was fabricated as the first and second substrates using the method described in Japanese Patent No. 4991170. The first substrate was cut into a 10 × 10 cm size, and the surface was subjected to ultrasonic cleaning (45 kHz). The cut-out first substrate was then placed inside a sputtering device. After reducing the pressure inside the device, argon gas was introduced, and sputtering was performed using copper as the target. The sputtering conditions were Ar gas pressure: 2 mTorr (0.27 Pa), supplied power: 3.3 W / cm. 2 This sputtering was carried out on each side of the first substrate in turn, to form copper layers with a thickness of 100 nm on both sides of the first substrate.

[0113] On a temporary support (PET film, average thickness 30 μm, haze 0.19%), a negative resist layer forming composition was applied using a slit nozzle so that the dry film thickness was 3 μm and the application width was 1 m. Note that as the negative resist layer forming composition, negative resist layer forming composition 1B described in paragraph 0562 of JP 2020-204757 A was used.

[0114] The temporary support coated with the composition for forming a negative resist layer was passed through a drying zone at 80°C for 40 seconds, and then a protective film (polyethylene film, manufactured by Tredegar, OSM-N) was pressed onto the temporary support to prepare a negative transfer material. The prepared negative transfer material had a temporary support, a negative resist layer, and a protective film in this order.

[0115] The prepared negative transfer material was cut into a size of 9 x 9 cm, and the protective film was peeled off from the negative transfer material. The negative transfer material was bonded to a first substrate so that the negative resist layer surface exposed by peeling off the protective film was in contact with the copper layer. The negative transfer material was bonded to both sides of the first substrate, one side at a time, to obtain a laminate. This bonding was performed under conditions of a roll temperature of 100°C, a linear pressure of 1.0 MPa, and a linear speed of 4.0 m / min. Next, a photomask having a pattern complementary to the metal microstructure (metal cut wire) was laminated on the temporary support side of the negative transfer material on both sides of the obtained laminate. Thereafter, an ultra-high pressure mercury lamp (manufactured by Dai Nippon Kaken Co., Ltd., MAP-1200L, dominant exposure wavelength: 365 nm) was used to light the negative transfer material at 100 mJ / cm through this photomask. 2The negative resist layer of the negative transfer material was exposed by irradiation. The photomask pattern was formed only in a central 1 × 1 cm region within the substrate surface. The patterns were different on both sides of the first substrate, with one side having a design corresponding to the pattern of the first structural layer described below, and the other side having a design corresponding to the pattern of the third structural layer described below. The temporary supports of the negative transfer material on both sides were peeled off from the exposed laminate. Thereafter, the laminate was subjected to shower development for 30 seconds using a 1.0% aqueous sodium carbonate solution at a liquid temperature of 25°C, forming resist patterns on the copper layers on both sides. Next, the copper layer of the obtained laminate was etched for 30 seconds at 23°C using a copper etching solution (Cu-02, manufactured by Kanto Chemical Co., Ltd.). Furthermore, the resist pattern was peeled off using propylene glycol monomethyl ether acetate.

[0116] In this manner, a first structure layer (first metasurface structure) was formed in a central 1 × 1 cm region on one surface of the first substrate. The first metal microstructures (metal cut wires) had a length L of 0.4 mm and a width W of 0.05 mm, and were arranged in a grid pattern with a longitudinal spacing g of 0.02 mm and a lateral spacing y of 0.09 mm, as conceptually shown in Figures 5 and 6 . Furthermore, a third structure layer (third metasurface structure) in which third metal microstructures were similarly arranged was formed on the other surface of the first substrate. However, the third structure layer was formed so that the longitudinal offset a between the first and third metal microstructures was 0.28 mm. Furthermore, a second structure layer (second metasurface structure) and a fourth structure layer (fourth metasurface structure) were formed on the second substrate in exactly the same manner as the first structure layer and the third structure layer.

[0117] <Fabrication of Spacer Portion and Multilayer Metasurface Structure> Next, a 1 × 1 cm area was die-cut from the transfer film 1. Next, one side (the side facing the first structure layer) of the first substrate (COP film) on both sides of which the metal microstructures prepared above were formed was bonded to the surface of the photosensitive layer exposed by peeling the protective film from the transfer film 1 so that they were in contact with each other, thereby obtaining a laminate. At this time, alignment was performed visually so that the area on the first substrate where the first structure layer was located coincided with the cut-out area of ​​the transfer film 1. Through this procedure, the spacer portion was positioned so as to surround the area on the first substrate where the first structure layer was located. The bonding was performed under conditions of a roll temperature of 100°C, a linear pressure of 1.0 MPa, and a linear speed of 1.0 m / min.

[0118] Next, the photosensitive layer exposed by peeling off the temporary support of the transfer film 1 of the obtained laminate was bonded to one side (the side on the second structure layer side) of a second substrate (COP film) on both sides of which another metal microstructure was formed. The bonding was performed by adhering and peeling while observing with an optical microscope so that the area where the second structure layer was located on the second substrate coincided with the hollowed-out area of ​​the photosensitive layer, and so that the arrangement of the metal microstructures was in the positional relationship shown in FIG. 5. After that, the laminate was bonded under the conditions of a roll temperature of 100 ° C., a linear pressure of 1.0 MPa, and a linear speed of 1.0 m / min. The above alignment was performed by smoothly adhering and peeling while observing with an optical microscope, so that the arrangement of the metal microstructures was in the positional relationship shown in FIG. 5. The positional deviation from the design of the metal microstructures was within 10 μm, and the rotational deviation was within 3 °. The resulting laminate was then heated at 100°C for 5 minutes to polymerize the polymerizable compound in the spacer portion, producing a multilayer metasurface structure. Furthermore, a second structure layer formed on a second substrate was laminated so that the misalignment amount b between the first metal microstructure and the second metal microstructure was 0.07 mm. This resulted in the production of a multilayer metasurface structure with four structure layers, from the first structure layer to the fourth structure layer, as shown in Figure 5.

[0119] [Example 2] In the same manner as in Example 1, a first substrate on which a first structural layer and a third structural layer were arranged, and a second substrate on which a second structural layer and a fourth structural layer were arranged were produced. Next, one surface (the surface on the first structural layer side) of the first substrate on both sides of which metal microstructures were formed was bonded to the surface of the photosensitive layer exposed by peeling off the protective film of the transfer film 2 so that they were in contact with each other, thereby obtaining a laminate. Next, on the temporary support of the obtained laminate, a mask was placed that shielded the 1 × 1 cm region on which the first structural layer was formed and did not shield the other portions, and an ultra-high pressure mercury lamp (exposure dominant wavelength: 365 nm) was used to illuminate the first substrate at 100 mJ / cm. 2 The photosensitive layer was exposed to light by irradiation, resulting in a pattern exposure. The temporary support was then peeled off, and the laminate was subjected to shower development for 30 seconds using a 1.0% by mass aqueous sodium carbonate solution at a liquid temperature of 25°C, forming a spacer portion. Through this procedure, the spacer portion was arranged so as to surround the area where the first structural layer was located on the first substrate. The spacer portion contained a polymerizable compound. The content of the polymerizable compound in the spacer portion was 10% by mass relative to the total mass of the spacer portion. The spacer portion was then bonded to one side (the side facing the second structural layer) of a second substrate (COP film) having metal microstructures formed on both sides thereof, while visually aligning the opening (1 x 1 cm area) of the spacer portion with the area where the second structural layer was located on the second substrate. The lamination was performed by affixing and peeling the metal microstructures while observing with an optical microscope so that the area of ​​the second structure layer on the second substrate coincided with the opening of the spacer portion and the metal microstructures were positioned as shown in Figure 5. The lamination was then performed under conditions of a roll temperature of 100°C, a linear pressure of 1.0 MPa, and a linear speed of 1.0 m / min. The alignment was achieved by smoothly affixing and peeling the metal microstructures while observing with an optical microscope, resulting in the metal microstructures being positioned as shown in Figure 5. The positional deviation from the design of the metal microstructures was within 10 μm, and the rotational deviation was within 3°. The resulting laminate was then heat-treated at 145°C for 30 minutes to produce a metasurface laminate.

[0120] Example 3 A multilayer metasurface structure was fabricated following the same procedure as in Example 1, except that transfer film 3 was used instead of transfer film 1. As in Example 1, the second substrate was aligned by smoothly attaching and peeling it while observing with an optical microscope, and the metal microstructures were bonded together so that the arrangement was in the positional relationship shown in Figure 5. The positional deviation from the design of the metal microstructures was within 10 μm, and the rotational deviation was within 3°.

[0121] Example 4 A multilayer metasurface structure was fabricated following the same procedure as in Example 1, except that transfer film 4 was used instead of transfer film 1. Regarding the alignment of the second substrate, more force was required to peel the second substrate from the spacer portion than in Examples 1 to 3, and peeling noise was generated, so the process had to be performed more carefully. The positional deviation of the metal microstructure from the design was within 10 μm, and the rotational deviation was within 3°.

[0122] [Comparative Example 1] An attempt was made to fabricate a multilayer metasurface structure following the same procedure as in Example 1, except that the transfer film 1 was not die-cut. In this Comparative Example 1, a photosensitive layer was disposed over the entire surface of the first substrate. When an attempt was made to align the second substrate by attaching and peeling it off onto this photosensitive layer, as in Example 1, the second metal microstructures on the second substrate were damaged, and it was not possible to fabricate a multilayer metasurface structure.

[0123] The results of Examples 1 to 4 and Comparative Example 1 are summarized below. The "Spacer portion" column indicates the shape of the spacer portion, with "patterned" meaning that the spacer portion is arranged so as to surround the structure layer and "solid" meaning that the spacer portion is arranged over the entire surface of the substrate. The "Melt viscosity" column indicates the melt viscosity characteristics of the spacer portion used in each Example, with "A" indicating that the melt viscosity of the spacer portion at 23°C is 1.0 x 10 5 Pa s or more, and the melt viscosity at 80°C is 1.0 × 10 5"B" means that the requirement of "A" is not satisfied. The melt viscosity ηc of the spacer portion at 23°C and 80°C was measured as follows. The method for measuring the melt viscosity of the spacer portion in Examples 1, 3, and 4 was as follows: First, the spacer portion was laminated and adjusted to a thickness of about 0.5 mm to prepare an evaluation sample, and then the melt viscosity was measured using a rheometer DHR-2 manufactured by TA Instruments (20 mmΦ parallel plates and Peltier plate (Gap: about 0.5 mm used)) at a set temperature of 20-125°C, a heating rate of 5°C / min, a frequency of 1 Hz, and a strain of 0.5%, and the melt viscosity at each temperature was calculated from the measured values ​​at 23°C and 80°C. The melt viscosity of the spacer portion in Example 2 was measured by laminating the photosensitive layer in the transfer film 2 to a thickness of about 0.5 mm, and then irradiating the resulting laminate with an ultra-high pressure mercury lamp (dominant wavelength of exposure: 365 nm) at 100 mJ / cm as an exposure dose equivalent to pattern exposure. 2 The obtained evaluation sample was subjected to measurement using the above-mentioned rheometer DHR-2 manufactured by TA Instruments (20 mmφ parallel plate and Peltier plate (Gap: approximately 0.5 mm)).

[0124]

[0125] From the above results, the effects of the present invention are clear.

[0126] The present invention can be suitably used in communication systems that use terahertz waves.

[0127] 10 Multilayer metasurface structure 12 First substrate 14 Second substrate 16 First structure layer 16a First metal microstructure 18 Second structure layer 18a Second metal microstructure 20 Third structure layer 20a Third metal microstructure 24 Fourth structure layer 24a Fourth metal microstructure 26 Spacer 26a Spacer portion

Claims

1. A step 1 of arranging spacer portions containing a polymerizable compound in a pattern on a first metasurface structure including a first substrate and a first structure layer having a plurality of first metal microstructures arranged in an in-plane direction and provided on at least one surface side of the first substrate; a step 2 of bonding a second metasurface structure including a second substrate and a second structure layer including a plurality of second metal microstructures arranged in an in-plane direction and provided on at least one surface side of the second substrate to the spacer portion to obtain a laminate including the first metasurface structure, the spacer portion, and the second metasurface structure; A method for manufacturing a multilayer metasurface structure, comprising: a step 3 of polymerizing the polymerizable compound.

2. The first metal microstructure is provided on at least one surface of the first substrate, The method of claim 1 , wherein the second metal microstructure is provided on at least one surface of the second substrate.

3. The step 1 includes a step A of forming a photosensitive layer including a polymerizable compound on a first metasurface structure including the first substrate and a first structure layer including a plurality of the first metal microstructures arranged in an in-plane direction on the first substrate; A step B of patternwise exposing the photosensitive layer; The method for manufacturing the multilayer metasurface structure described in claim 1, further comprising a step C of developing the exposed photosensitive layer to form the spacer portion.

4. The method for manufacturing a multilayer metasurface structure as described in claim 1, wherein step 1 is a step of forming the spacer portion by laminating a photosensitive layer containing a patterned polymerizable compound on a first metasurface structure including the first substrate and a first structure layer having a plurality of first metal microstructures arranged in an in-plane direction on the first substrate.

5. The melt viscosity of the spacer portion at 23° C. is 1.0×10 5 Pa s or more, and the melt viscosity at 80°C is 1.0 x 10 5 The method of claim 1 , wherein the multilayer metasurface structure has a viscosity of less than Pa·s.

6. A method for manufacturing a multilayer metasurface structure as described in claim 1, wherein an air layer is formed between the first structure layer and the second structure layer.

7. A multilayer metasurface structure manufactured by the method for manufacturing a multilayer metasurface structure according to any one of claims 1 to 6.

8. 10. The multilayer metasurface structure of claim 7, which is a transmission type element.

9. 8. The multilayer metasurface structure of claim 7, which is a sheet-type metalens.