Metasurface reflector, projection device, near-eye wearable apparatus, and method for manufacturing metasurface reflector

Abstract

To suppress deterioration in reflection characteristics.SOLUTION: A metasurface reflector comprises: a first metal layer and a second metal layer stacked in a first direction; a dielectric layer provided between the first metal layer and the second metal layer in the first direction; and a protective layer covering the second metal layer. The dielectric layer has a main surface on which the second metal layer is provided. The metasurface reflector is divided into a plurality of unit regions arranged in a second direction along the main surface and in a third direction along the main surface and intersecting the second direction. The second metal layer includes metal units respectively provided in all or some of the plurality of unit regions. The protective layer is made of metal having a standard electrode potential higher than that of the metal constituting the second metal layer. The protective layer includes a first portion covering a top surface of each metal unit and a second portion covering a side surface of each metal unit.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a metasurface reflector, a projection device, a near-eye wearable device, and a method for manufacturing a metasurface reflector. [Background technology]

[0002] Reflectors using metasurface technology are known. For example, Patent Document 1 describes a near-eye display assembly including an image source and a combiner including a nanostructured surface optically coupled to the image source. A unit cell of the nanostructured surface is formed by stacking a base layer, a dielectric layer, and a meta-atom layer in that order. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2018 / 0113310 Summary of the Invention [Problem to be solved by the invention]

[0004] In the near-eye display assembly described in Patent Document 1, the meta-atomic layer is exposed. When a metal layer such as silver or aluminum is used as the meta-atomic layer, the metal layer may be oxidized or sulfurized when exposed to air. This may cause changes in optical properties and may degrade the reflective properties.

[0005] The present disclosure describes a metasurface reflector, a projection device, a near-eye wearable device, and a method for manufacturing a metasurface reflector that can suppress degradation of reflection properties. [Means for solving the problem]

[0006] A metasurface reflector according to one aspect of the present disclosure includes a first metal layer and a second metal layer stacked in a first direction, a dielectric layer disposed between the first metal layer and the second metal layer in the first direction, and a protective layer covering the second metal layer. The dielectric layer has a main surface on which the second metal layer is disposed. The metasurface reflector is divided into a plurality of unit areas arranged in a second direction along the main surface and a third direction along the main surface and intersecting the second direction. The second metal layer includes metal units disposed in all or some of the plurality of unit areas. The protective layer is composed of a metal having a higher standard electrode potential than the metal constituting the second metal layer. The metal units have a bottom surface facing the dielectric layer in the first direction, a top surface disposed on the opposite side of the bottom surface in the first direction, and a side surface connecting the top surface and the bottom surface. The protective layer includes a first portion covering the top surface and a second portion covering the side surface.

[0007] In this metasurface reflector, a protective layer covers the top and side surfaces of the metal unit. Therefore, the top and side surfaces of the metal unit are not exposed to air when the metasurface reflector is in use, reducing the possibility of the metal unit being oxidized and sulfurized. Furthermore, since the protective layer is made of a metal having a higher standard electrode potential than the metal constituting the second metal layer, the protective layer is less susceptible to oxidation and sulfurization than the second metal layer. Therefore, the optical properties of the metasurface reflector are less likely to change. As a result, it is possible to suppress deterioration of the reflection properties.

[0008] The thickness of the protective layer may be 20% or less of the sum of the length of the second metal layer in the first direction and the thickness of the protective layer. In this case, the protective layer can be provided while minimizing the effect on the reflection characteristics of the metasurface reflector. Therefore, it is possible to further suppress deterioration of the reflection characteristics.

[0009] The metal unit may be a metal body having a trapezoidal shape when viewed from the first direction. In this case, the structure of the metal unit can be simplified compared to when the metal unit is composed of multiple metal bodies. Therefore, it is possible to facilitate the manufacture of the metasurface reflector.

[0010] The length of the metal body in the second direction may be 500 nm or more and 2500 nm or less. The length of the metal body in the first direction may be 10 nm or more and 100 nm or less. The length of the short side of the metal body may be 10 nm or more and 200 nm or less. The length of the long side of the metal body may be longer than the length of the short side, and may be 100 nm or more and 500 nm or less. In this case, the reflection efficiency for visible light can be increased.

[0011] The protective layer may be made of a metal containing at least one element selected from the group consisting of gold, ruthenium, and iridium, which can suppress deterioration of the reflective properties compared to molybdenum, titanium, tungsten, etc.

[0012] The second metal layer may be made of a metal containing at least one element selected from the group consisting of silver, aluminum, and copper. In this case, the second metal layer has a relatively high reflectivity and a relatively high conductivity. Therefore, the electromagnetic resonance between the first metal layer and the second metal layer can be strengthened, and the reflection efficiency can be increased.

[0013] The dielectric layer may be made of a material that is transparent in the visible light region, in which case the absorption rate of visible light in the dielectric layer is reduced, thereby increasing the reflection efficiency of visible light.

[0014] The dielectric layer may be made of a compound selected from the group consisting of silicon oxide, titanium oxide, magnesium oxide, and aluminum oxide. In this case, a dielectric layer having a dielectric constant that does not inhibit electromagnetic interaction is obtained. This strengthens the electromagnetic resonance between the first metal layer and the second metal layer, thereby improving reflection efficiency.

[0015] The length of the dielectric layer in the first direction may be 10 nm or more and 100 nm or less. The length of the first metal layer in the first direction may be 50 nm or more and 1000 nm or less. In this case, the possibility that the dielectric layer will interfere with electromagnetic effects can be reduced, and the possibility that laser light will pass through the first metal layer can be reduced. Therefore, the reflection efficiency can be increased.

[0016] The thickness of the second portion may decrease in the first direction as it moves away from the dielectric layer. The thinner the thickness of the second portion, the higher the reflected electric field strength. This allows the protective layer to be provided while minimizing the impact on the reflection characteristics of the metasurface reflector. This further reduces the deterioration of the reflection characteristics.

[0017] According to another aspect of the present disclosure, there is provided a projection device mounted on a near-eye wearable device, the projection device including a light source that emits laser light, a movable mirror for scanning with the laser light, and the metasurface reflector that reflects the laser light that has passed through the movable mirror to allow a user wearing the near-eye wearable device to view an image. This projection device can also suppress deterioration of reflection characteristics.

[0018] According to another aspect of the present disclosure, there is provided a near-eye wearable device including the projection device and a lens provided with a metasurface reflector. This near-eye wearable device can also suppress deterioration of reflection characteristics.

[0019] A method for manufacturing a metasurface reflector according to another aspect of the present disclosure includes the steps of: preparing a stack in which a first metal layer, a dielectric layer, a second metal layer, and a third metal layer are stacked in this order in a first direction; forming a resist film on the third metal layer; forming a pattern on the resist film to form a metal unit constituting the metasurface reflector, the metal unit having a bottom surface facing the dielectric layer in the first direction, a top surface opposite the bottom surface in the first direction, and a side surface connecting the top surface and the bottom surface; milling the second metal layer and the third metal layer using the pattern to form the metal unit and to form a first protective film covering the top surface; and forming a second protective film covering the side surface of the metal unit. The first protective film and the second protective film are made of metals having a standard electrode potential higher than that of the metal constituting the second metal layer.

[0020] In this method for manufacturing a metasurface reflector, a pattern is formed on a resist film formed on the third metal layer of the laminate, and the second and third metal layers are milled using the pattern to form a metal unit and a first protective film covering the top surface of the metal unit. Furthermore, a second protective film is formed on the side surface of the metal unit. In a metasurface reflector manufactured in this manner, the top and side surfaces of the metal unit are not exposed to air during use, reducing the possibility of oxidation and sulfurization of the metal unit. Furthermore, since the first and second protective films are made of metals with a higher standard electrode potential than the metal constituting the second metal layer, the first and second protective films are less susceptible to oxidation and sulfurization than the second metal layer. Therefore, the optical properties of the metasurface reflector are less likely to change. As a result, deterioration of the reflection properties can be suppressed.

[0021] The step of forming the second protective film may include the steps of removing the resist film, forming a metal film on the surface of the structure obtained by removing the resist film, and forming the second protective film by removing a portion of the metal film formed on the main surface of the dielectric layer. In this case, the second protective film can be formed on the side surface of the metal unit by a relatively simple process.

[0022] In the step of forming the resist film, a multilayer resist film including a lower-layer resist film and an upper-layer resist film may be formed on the third metal layer. The step of forming the second protective film may include the steps of: forming a metal film on the surface of the structure obtained by the step of forming the first protective film; forming a second protective film by removing a portion of the metal film formed on the main surface of the dielectric layer; and removing the multilayer resist film after the second protective film is formed. In this case, the multilayer resist film is removed while the top surface of the metal unit is covered by the first protective film and the side surface of the metal unit is covered by the second protective film. Therefore, the top surface and side surface of the metal unit are not exposed to the solvent used to remove the multilayer resist film, reducing the possibility of corrosion of the metal unit. As a result, it is possible to further suppress deterioration of the reflection characteristics of the metasurface reflector.

[0023] In the process of forming the metal film, the metal film may be formed using oblique incidence sputtering. In this case, the metal film is easily formed on the side surface of the metal unit. Therefore, it is possible to shorten the time required to manufacture the metasurface reflector. [Effects of the Invention]

[0024] According to each aspect and embodiment of the present disclosure, deterioration of reflection characteristics can be suppressed. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a perspective view showing the appearance of a near-eye wearable device to which a metasurface reflector according to one embodiment is applied. [Figure 2] FIG. 2 is a schematic diagram illustrating the configuration of the projection device shown in FIG. [Figure 3] FIG. 3 is an enlarged view of the metasurface reflector shown in FIG. 2. [Figure 4] FIG. 4 is a perspective view schematically illustrating the unit area shown in FIG. [Figure 5] FIG. 5 is a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is a diagram for explaining the principle of reflection by the metasurface reflector shown in FIG. [Figure 7] FIG. 7 is a diagram showing the amount of phase change of reflected light at different positions in the X-axis direction of the metasurface reflector. [Figure 8] FIG. 8 is a diagram for explaining the relationship between the position in the X-axis direction and the length of the metal unit in the X-axis direction. [Figure 9] FIG. 9 is a diagram showing the relationship between the ratio of the protective layer and the reflected electric field strength. [Figure 10] FIG. 10 is a process diagram showing an example of a method for manufacturing a metasurface reflector. [Figure 11] FIG. 11 is a diagram for explaining the resist film forming step shown in FIG. [Figure 12] FIG. 12 is a diagram for explaining the pattern forming step shown in FIG. [Figure 13] FIG. 13 is a diagram for explaining the first protective film forming step shown in FIG. [Figure 14] FIG. 14 is a view for explaining the resist film removing step shown in FIG. [Figure 15] FIG. 15 is a diagram for explaining the metal film forming step shown in FIG. [Figure 16] FIG. 16 is a diagram for explaining the metal film removing step shown in FIG. [Figure 17] Figure 17 is a process diagram showing another example of a method for manufacturing a metasurface reflector. [Figure 18]FIG. 18 is a diagram for explaining the resist film forming step shown in FIG. [Figure 19] FIG. 19 is a diagram for explaining the pattern forming step shown in FIG. [Figure 20] FIG. 20 is a diagram for explaining the first protective film forming step shown in FIG. [Figure 21] FIG. 21 is a diagram for explaining the metal film forming step shown in FIG. [Figure 22] FIG. 22 is a diagram for explaining the metal film removing step shown in FIG. [Figure 23] FIG. 23 is a view for explaining the resist film removing step shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the description of the drawings, the same elements are given the same symbols, and duplicate explanations will be omitted. An XYZ coordinate system may be shown in each drawing. The Y-axis direction (third direction) is a direction that intersects (e.g., is perpendicular to) the X-axis direction (second direction) and the Z-axis direction (first direction). The Z-axis direction is a direction that intersects (e.g., is perpendicular to) the X-axis direction and the Y-axis direction. In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values ​​written before and after "to" as the minimum and maximum values, respectively. Individually written upper and lower limit values ​​can be combined in any way.

[0027] A near-eye wearable device to which a metasurface reflector according to one embodiment is applied will be described with reference to FIG. 1. FIG. 1 is a perspective view showing the appearance of a near-eye wearable device to which a metasurface reflector according to one embodiment is applied. The near-eye wearable device 1 shown in FIG. 1 is a device that overlays an image on a field of view of the real world. The near-eye wearable device 1 is, for example, a head-mounted device, and can take the form of glasses, goggles, a hat, a helmet, or the like. Examples of the near-eye wearable device 1 include smart glasses such as AR (Augmented Reality) glasses and MR (Mixed Reality) glasses. The near-eye wearable device 1 includes a frame 2, a lens 3, and a projection device 10.

[0028] The frame 2 includes a pair of rims 2a, a bridge 2b, and a pair of temples 2c. The rims 2a are portions that hold the lenses 3. The bridge 2b is a portion that connects the pair of rims 2a. The temples 2c extend from the rims 2a and are portions that are hung on the user's ears. The frame 2 may be a rimless frame. The lenses 3 have an inner surface 3a (see FIG. 2) that faces the eyeball E (see FIG. 6) of the user wearing the near-eye wearable device 1.

[0029] In this embodiment, the projection device 10 is a device that directly projects (draws) an image onto the retina RE (see FIG. 6) of a user wearing the near-eye wearable device 1. The projection device 10 is mounted on the near-eye wearable device 1. In this embodiment, the near-eye wearable device 1 includes two projection devices 10 in order to project images onto both the left and right retinas RE, but may include only one of the projection devices 10.

[0030] Next, the projection device 10 will be described in detail with reference to Fig. 2. Fig. 2 is a schematic diagram illustrating the configuration of the projection device shown in Fig. 1. As shown in Fig. 2, the projection device 10 includes an optical engine 20 and a metasurface reflector 30.

[0031] The optical engine 20 is a device that generates laser light Ls of a color and intensity corresponding to the pixels of an image to be projected onto the retina RE, and emits the laser light Ls to the metasurface reflector 30. The optical engine 20 is mounted on each temple 2c. The optical engine 20 includes a light source unit 21 (light source), optical components 22, a movable mirror 23, a laser driver 24, a mirror driver 25, and a controller 26.

[0032] The light source unit 21 emits laser light. For example, a full-color laser module is used as the light source unit 21. The light source unit 21 includes a red laser diode, a green laser diode, a blue laser diode, and a multiplexing section that multiplexes the laser light emitted from each laser diode into one laser light. The light source unit 21 emits the multiplexed laser light. The multiplexed laser light includes a component having a red wavelength (red component), a component having a green wavelength (green component), and a component having a blue wavelength (blue component). The light source unit 21 emits laser light of a color and intensity corresponding to the pixels of the image to be projected onto the retina RE.

[0033] The optical component 22 is a component that optically processes the laser light emitted from the light source unit 21. In this embodiment, the optical component 22 includes a collimator lens 22a, a slit 22b, and a neutral density filter 22c. The collimator lens 22a, the slit 22b, and the neutral density filter 22c are arranged in this order along the optical path of the laser light. The optical component 22 may have other configurations.

[0034] The movable mirror 23 is an optical component for performing scanning with the laser light Ls. The movable mirror 23 is provided in the emission direction of the laser light processed by the optical component 22. The movable mirror 23 is configured to be swingable, for example, around an axis extending in the horizontal direction (X-axis direction) of the lens 3 and an axis extending in the vertical direction (Y-axis direction) of the lens 3, and reflects the laser light by changing the angle in the X-axis direction and the Y-axis direction. For example, a MEMS (Micro Electro Mechanical Systems) mirror is used as the movable mirror 23.

[0035] The laser driver 24 is a drive circuit that drives the light source unit 21. The laser driver 24 drives the light source unit 21 based on, for example, the intensity of the laser light and the temperature of the light source unit 21. The mirror driver 25 is a drive circuit that drives the movable mirror 23. The mirror driver 25 oscillates the movable mirror 23 within a predetermined angle range and at a predetermined timing. The controller 26 is a device that controls the laser driver 24 and the mirror driver 25.

[0036] In the optical engine 20, laser light of a color and intensity corresponding to the pixels of the image to be projected onto the retina RE is emitted from the light source unit 21, passes through the optical component 22, and is reflected by the movable mirror 23. The laser light reflected by the movable mirror 23 is emitted to the metasurface reflector 30 as laser light Ls.

[0037] The metasurface reflector 30 is an optical component that reflects the laser light Ls that has passed through the movable mirror 23, allowing a user wearing the near-eye wearable device 1 to view an image. No image is displayed on the metasurface reflector 30. The metasurface reflector 30 is provided on the inner surface 3a of the lens 3.

[0038] Next, the configuration of the metasurface reflector 30 will be described with reference to Figs. 3 to 5. Fig. 3 is an enlarged view of the metasurface reflector shown in Fig. 2. Fig. 4 is a perspective view schematically showing a unit area shown in Fig. 3. Fig. 5 is a cross-sectional view taken along line VV in Fig. 4.

[0039] 3, the metasurface reflector 30 is divided into a plurality of unit areas 31. The plurality of unit areas 31 are provided along the inner surface 3a of the lens 3. The plurality of unit areas 31 are arranged in a two-dimensional array in the horizontal direction (X-axis direction) and vertical direction (Y-axis direction) of the lens 3.

[0040] As shown in Figures 4 and 5, the metasurface reflector 30 includes, in the Z-axis direction, a metal layer 41 (first metal layer), a dielectric layer 42, a metal layer 43 (second metal layer), and a protective layer 44, in that order.

[0041] The metal layer 41 is a base layer. The metal layer 41 is provided on the inner surface 3a of the lens 3. The metal layer 41 is made of a metal that has high reflectivity in the visible light region. The metal layer 41 is made of a metal that includes at least one element selected from the group consisting of gold (Au), copper (Cu), silver (Ag), and aluminum (Al), for example. The length (thickness d1) of the metal layer 41 in the Z-axis direction may be any length that allows the metal layer 41 to pass a resonant current and reflect light, and is, for example, 50 nm to 1000 nm.

[0042] The dielectric layer 42 functions as a spacer. The dielectric layer 42 is provided between the metal layer 41 and the metal layer 43 in the Z-axis direction. In this embodiment, the dielectric layer 42 is provided on the metal layer 41. The dielectric layer 42 has a main surface 42a on which the metal layer 43 is provided. The dielectric layer 42 has a dielectric constant that does not inhibit the electromagnetic interaction between the metal layer 41 and the metal layer 43. The dielectric layer 42 is made of a material that is transparent in the visible light range. The dielectric layer 42 may be made of a material with a high dielectric constant to achieve high reflection characteristics. The dielectric layer 42 is made of, for example, one compound selected from the group consisting of silicon oxide (e.g., SiO2), titanium oxide (e.g., TiO2), magnesium oxide (e.g., MgO), and aluminum oxide (e.g., Al2O3). The length (thickness d2) of the dielectric layer 42 in the Z-axis direction is, for example, 10 nm to 100 nm.

[0043] The metal layer 43 is a layer that excites electromagnetic resonance together with the metal layer 41. The metal layer 41 and the metal layer 43 are stacked in the Z-axis direction via the dielectric layer 42. In this embodiment, the metal layer 43 is provided on the main surface 42a of the dielectric layer 42. The metal layer 43 is made of a metal that has high reflectivity in the visible light range. The metal layer 43 is made of a metal that includes at least one element selected from the group consisting of silver (Ag), aluminum (Al), and copper (Cu), for example.

[0044] The metal layer 43 includes a plurality of metal units 45. The metal units 45 are provided in each of the plurality of unit regions 31. Each metal unit 45 is configured such that the phase change amount φ of the reflected light Lr by the metal unit 45 changes linearly from one end 31a (first end) to the other end 31b (second end) in the X-axis direction of the unit region 31 in which the metal unit 45 is provided. Furthermore, each metal unit 45 is configured such that the phase change amount φ of the reflected light Lr changes substantially by 360° (2π radians) from one end 31a to the other end 31b. The phase change amount φ of the reflected light Lr is the amount of phase change of the reflected light Lr when the length of the metal unit 45 in the Y-axis direction is changed, with the phase of the reflected light Lr at a certain length in the Y-axis direction of the metal unit 45 as a reference. Hereinafter, the length in the Y-axis direction may be referred to as the "width."

[0045] In this embodiment, each metal unit 45 is a single metal body having a trapezoidal shape when viewed from the Z-axis direction. The length (thickness d3) of each metal unit 45 in the Z-axis direction is, for example, 10 nm to 100 nm. The length of each metal unit 45 in the X-axis direction is the same as or slightly shorter than the length Lx of the unit region 31 in the X-axis direction. The length of each metal unit 45 in the X-axis direction is, for example, 500 nm to 2500 nm.

[0046] The length of the short side (width W1) of each metal unit 45 is set, for example, near the resolution of an exposure device used when forming the metal unit 45. The width W1 is, for example, 10 nm to 200 nm. The length of the long side (width W2) of each metal unit 45 is set to be greater than the width W1 and to a length that provides a phase difference of substantially 360° (2π radians) from the phase of the reflected light Lr at the width W1. The width W2 is, for example, 100 nm to 500 nm. Each metal unit 45 is formed, for example, by photolithography.

[0047] The metal unit 45 includes a top surface 45a, a bottom surface 45b, and a side surface 45c. The bottom surface 45b faces the dielectric layer 42 in the Z-axis direction. The top surface 45a is located on the opposite side of the bottom surface 45b in the Z-axis direction. The side surface 45c connects the top surface 45a and the bottom surface 45b. The side surface 45c connects the entire periphery of the top surface 45a to the entire periphery of the bottom surface 45b.

[0048] The protective layer 44 is a layer that protects the metal layer 43 (metal units 45). The protective layer 44 is provided so as to cover the entire metal units 45. In other words, the metal units 45 are not exposed. The protective layer 44 is made of a metal that is less susceptible to oxidation and sulfurization than the metal layer 43 and has high corrosion resistance. In other words, the protective layer 44 is made of a metal that has a higher standard electrode potential than the metal that constitutes the metal layer 43. The protective layer 44 is made of a metal that includes at least one element selected from the group consisting of gold (Au), ruthenium (Ru), and iridium (Ir), for example. When these metals are combined with the metal (e.g., silver) that constitutes the metal layer 43, attenuation of near-field light is small.

[0049] In this embodiment, the protective layer 44 includes a plurality of metal bodies respectively covering the plurality of metal units 45. The thickness d4 of the protective layer 44 (metal bodies) is 20% or less of the thickness d5, which is the sum of the thickness d3 and the thickness d4. The thickness d4 is, for example, 2.5 nm to 25 nm. The thickness d4 of the protective layer 44 is not limited to the length in the Z-axis direction, but refers to the length (layer thickness) from the surface of the metal unit 45 to the surface of the protective layer 44.

[0050] The protective layer 44 includes a first portion 44a and a second portion 44b. The first portion 44a is a portion that covers the top surface 45a of the metal unit 45. The second portion 44b is a portion that covers the side surface 45c of the metal unit 45. The thickness of the second portion 44b may decrease with increasing distance from the dielectric layer 42 in the Z-axis direction.

[0051] An adhesion layer 46 (see FIG. 11) may be provided between the inner surface 3a of the lens 3 and the metal layer 41. An adhesion layer 47 (see FIG. 11) may be provided between the metal layer 41 and the dielectric layer 42. An adhesion layer 48 (see FIG. 16) may be provided between the dielectric layer 42 and the metal layer 43. Each of the adhesion layers 46 to 48 is a layer for improving adhesion between the two layers. Each of the adhesion layers 46 to 48 is made of, for example, chromium (Cr). The length (film thickness) of each of the adhesion layers 46 to 48 in the Z-axis direction is about 3 nm.

[0052] Next, the principle of reflection by the metasurface reflector 30 and a method for determining the length Lx will be described with reference to Figs. 5 to 8. Fig. 6 is a diagram for explaining the principle of reflection by the metasurface reflector shown in Fig. 2. Fig. 7 is a diagram showing the amount of phase change of reflected light at a position in the X-axis direction of the metasurface reflector. Fig. 8 is a diagram for explaining the relationship between the position in the X-axis direction and the length of the metal unit in the X-axis direction.

[0053] As shown in FIGS. 5 and 6, each unit area 31 is illuminated at an incident angle θ i When the laser light Ls is incident at the unit area 31, the reflection angle θ r The nanostructure is configured to reflect the laser light Ls at a reflection angle θ of each unit area 31 so that the laser light Ls (reflected light Lr) reflected by each unit area 31 passes through the center of the pupil PP. r is set. Therefore, the incident angle θ i and reflection angle θ ris determined depending on the position where the unit area 31 is provided. The incident angle θ according to the position where the unit area 31 is provided i and reflection angle θ r The unit area 31 is configured so that:

[0054] Here, the incident angle θ i is the angle between the normal to the surface onto which the laser light Ls is irradiated and the incident direction of the laser light Ls. r is the angle between the normal to the surface onto which the laser light Ls is irradiated and the direction of the reflected light Lr. In a plane including the laser light Ls and the reflected light Lr, when the reflected light Lr is emitted on the opposite side of the normal to the incident light (laser light Ls), the reflection angle θ r is expressed as a positive value, and when the reflected light Lr is emitted on the same side as the incident light (laser light Ls) with the normal as the boundary, the reflection angle θ r is expressed as a negative value.

[0055] For example, as shown in Fig. 6, when the user's pupil PP faces forward, the unit area 31 provided from position Pa to position Pc in the X-axis direction is used. The laser light Ls reflected by the unit area 31 provided at position Pa corresponds to the pixel on the right edge of the image. Position Pb is located midway between positions Pa and Pc, and the laser light Ls reflected by the unit area 31 provided at position Pb corresponds to the pixel in the center of the image. The laser light Ls reflected by the unit area 31 provided at position Pc corresponds to the pixel on the left edge of the image.

[0056] In the unit area 31 provided at the position Pa, the incident angle θ i The laser beam Ls is incident at a reflection angle of 5° θ r The laser beam Ls is reflected by the unit area 31 at the position Pb and emitted as reflected light Lr. i The laser beam Ls is incident at a reflection angle of -5°. r The laser beam Ls is reflected by the unit area 31 at the position Pc and emitted as reflected light Lr. iThe laser beam Ls is incident at a reflection angle of -10°. r The laser light Ls is reflected by the reflector 11 and emitted as reflected light Lr.

[0057] As shown in FIG. 7, the width of the metal unit 45 increases from width W1 to width W2 as it moves from one end 31a to the other end 31b. The phase change amount φ at each position in the X-axis direction of the metal unit 45 is substantially the same as the phase change amount φ of a square metal body having sides of the same length as the width at that position in a planar view. The larger the area of ​​the square metal body in a planar view, the larger the phase change amount φ (phase delay amount) at that position. Therefore, the laser light Ls is reflected with different phase change amounts φ depending on the position in the X-axis direction, and a wavefront is formed due to interference between the reflected lights. That is, a plane wave is generated whose wave vector Φ is the slope of a function φ(x) that indicates the relationship between the position x in the X-axis direction and the phase change amount φ.

[0058] As shown in FIG. 5, Snell's law can be generalized as follows: i , reflection angle θ r and the wave vector Φ, as expressed by equation (1).

number

[0059] The wave vector k0 is expressed as 2π / λ using the wavelength λ of the laser light Ls. The wave vector Φ is expressed as 2π / Lx using the length Lx in the X-axis direction of the unit area 31. By transforming equation (1) using these relationships, equation (2) is obtained.

number

[0060] Equation (2) is expressed by the wavelength λ of the laser light Ls and the incident angle θ of the laser light Ls according to the position where the unit region 31 is provided. i and reflection angle θ rBy substituting the above, the length Lx of the unit area 31 can be obtained. The laser light Ls contains red, green, and blue components, and the length Lx is determined, for example, by using the wavelength λ of the green component to which the human eye is most sensitive.

[0061] When the length Lx is a positive value, the shape of the metal unit 45 is set to a trapezoidal shape in which the width of the metal unit 45 increases from one end 31 a toward the other end 31 b. When the length Lx is a negative value, the shape of the metal unit 45 is set to a trapezoidal shape in which the width of the metal unit 45 decreases from one end 31 a toward the other end 31 b.

[0062] As described above, the length Lx of each unit area 31 is determined by the wavelength λ of the light to be reflected and the incident angle θ corresponding to the position where the unit area 31 is provided. i and reflection angle θ r The length of the metal unit 45 in the X-axis direction is equal to or slightly shorter than the length Lx of the unit area 31 in the X-axis direction. Therefore, the length of the metal unit 45 in the X-axis direction is determined by the wavelength λ of the reflection target and the angle of incidence θ i and reflection angle θ r and is determined from.

[0063] reflection angle θ r is the angle of incidence θ i If the incident angle θ is less than θ, the length Lx will be a negative value. i and reflection angle θ r 8, in the near-eye wearable device 1, the reflection angle θ r becomes smaller, and the incident angle θ i and reflection angle θ r As the difference between the lengths Lx and Lx increases, the length Lx also decreases. Therefore, the unit regions 31 included in the same array in the X-axis direction have different lengths Lx, and the metal units 45 included in the same array in the X-axis direction also have different lengths in the X-axis direction.

[0064] The length Ly of each unit region 31 is a predetermined fixed value. The length Ly is slightly larger than the width W2. The length Ly may be a length obtained by adding the resolution (e.g., 100 nm) of the exposure device used to form the metal unit 45 to the width W2, and is set to, for example, 600 nm. The widths W1 and W2 of each metal unit 45 are predetermined fixed values. As described above, the width W1 is set to a value close to the resolution (e.g., 100 nm) of the exposure device used to form the metal unit 45. The width W2 is set to a length (e.g., 350 nm) that provides a phase difference of substantially 360° (2π radians) from the phase of the reflected light Lr at the width W1.

[0065] Next, the effect of the protective layer 44 on the intensity of the reflected light Lr will be described with reference to FIG. 9. FIG. 9 is a diagram showing the relationship between the proportion of the protective layer and the reflected electric field strength. The horizontal axis of FIG. 9 represents the proportion of the protective layer 44 (unit: %). The proportion of the protective layer 44 is expressed as the ratio of thickness d4 to thickness d5. The vertical axis of FIG. 9 represents the reflected electric field strength normalized with the reflected electric field strength when the protective layer 44 is not provided being 1.0.

[0066] The characteristics shown in Fig. 9 were obtained by calculation. Specifically, silver was used as the constituent material of metal layer 41 and metal layer 43 (metal unit 45), and SiO2 was used as the constituent material of dielectric layer 42. Thickness d1 was set to 200 nm, thickness d2 was set to 40 nm, and thickness d3 was set to 40 nm. Width W1 was set to 120 nm, and width W2 was set to 300 nm. The length of metal unit 45 in the X-axis direction was set to 2250 nm. Gold, ruthenium, and iridium were used as the constituent materials of protective layer 44, and the thickness of protective layer 44 was changed for each constituent material, and the reflected electric field strength at each thickness was calculated.

[0067] As shown in Figure 9, for all constituent materials, the reflected electric field strength decreases as the proportion of protective layer 44 increases. When the proportion of protective layer 44 is 20% or less, the reflected electric field strength hardly decreases from the reflected electric field strength when protective layer 44 is not provided, and remains at 90% or more. On the other hand, when the proportion of protective layer 44 exceeds 20%, the reflected electric field strength decreases sharply, and when the proportion of protective layer 44 is about 30% to 40% or more, the reflected electric field strength becomes almost zero. From the above, it can be said that the intensity of reflected light Lr can be maintained if the proportion of protective layer 44 is 20% or less.

[0068] Next, an example of a manufacturing method for the near-eye wearable device 1 will be described with reference to FIGS. 10 to 16. FIG. 10 is a process diagram showing an example of a manufacturing method for a metasurface reflector. FIG. 11 is a diagram for explaining a resist film forming process shown in FIG. 10. FIG. 12 is a diagram for explaining a pattern forming process shown in FIG. 10. FIG. 13 is a diagram for explaining a first protective film forming process shown in FIG. 10. FIG. 14 is a diagram for explaining a resist film removing process shown in FIG. 10. FIG. 15 is a diagram for explaining a metal film forming process shown in FIG. 10. FIG. 16 is a diagram for explaining a metal film removing process shown in FIG. 10.

[0069] 10 is a method for manufacturing a metasurface reflector 30. The method M1 includes a preparation step S11, a resist film formation step S12, a pattern formation step S13, a first protective film formation step S14, and a second protective film formation step S15.

[0070] <Preparation process S11> The preparation step S11 is a step of preparing the laminate 40. The laminate 40 is formed by sequentially stacking a substrate 50, a metal layer 41, a dielectric layer 42, a metal layer 143 (second metal layer) that will become the metal layer 43, and a metal layer 144 (third metal layer) that will become the first portion 44a of the protective layer 44 in the Z-axis direction. Here, an example will be described in which the metasurface reflector 30 is formed on the substrate 50 instead of the lens 3.

[0071] In the preparation step S11, first, a substrate 50 is prepared and set in a vacuum film-forming apparatus. An example of the substrate 50 is a sapphire substrate. A flexible sheet may also be used as the substrate 50. Then, a metal layer 41 is formed on a surface 50a of the substrate 50. Specifically, the metal layer 41 is formed by vacuum film-forming using a method such as DC (Direct Current) sputtering. The metal layer 41 is formed using a metal material selected from the group consisting of gold (Au), copper (Cu), silver (Ag), and aluminum (Al), or a metal alloy containing at least one element selected from the group. Here, silver is an example of a constituent material of the metal layer 41. The thickness d1 of the metal layer 41 is, for example, 200 nm.

[0072] In order to improve adhesion between the surface 50a of the substrate 50 and the metal layer 41, an adhesion layer 46 may be formed on the surface 50a, and the metal layer 41 may be formed on the adhesion layer 46. The adhesion layer 46 may be formed by, for example, sputtering or vapor deposition. Chromium (Cr) may be used to form the adhesion layer 46. The length (film thickness) of the adhesion layer 46 in the Z-axis direction is, for example, 3 nm.

[0073] Subsequently, a dielectric layer 42 is formed on the metal layer 41. Specifically, the dielectric layer 42 is formed by vacuum film formation using a technique such as RF (Radio Frequency) sputtering. The dielectric layer 42 is formed from a dielectric material that can be formed by a semiconductor process, such as silicon dioxide (SiO2), titanium oxide (TiO2), magnesium oxide (MgO), or aluminum oxide (Al2O3). Here, silicon dioxide is exemplified as a constituent material of the dielectric layer 42. The thickness d2 of the dielectric layer 42 is, for example, 40 nm.

[0074] In order to improve the adhesion between the metal layer 41 and the dielectric layer 42, an adhesion layer 47 may be formed on the metal layer 41, and the dielectric layer 42 may be formed on the adhesion layer 47. The method for forming the adhesion layer 47 is the same as the method for forming the adhesion layer 46, and therefore a detailed description thereof will be omitted. For example, chromium (Cr) is used to form the adhesion layer 47. The length (film thickness) of the adhesion layer 47 in the Z-axis direction is, for example, 3 nm.

[0075] Next, a metal layer 143 is formed on the dielectric layer 42. The method for forming the metal layer 143 is the same as that for the metal layer 41, and therefore a detailed description thereof will be omitted. The metal layer 143 is formed using a metal material made of a metal selected from the group consisting of copper (Cu), silver (Ag), and aluminum (Al), or a metal alloy containing at least one element selected from the above group. Here, silver is exemplified as a constituent material of the metal layer 143. The length (thickness d3) of the metal layer 143 in the Z-axis direction is, for example, 40 nm.

[0076] In order to improve the adhesion between the dielectric layer 42 and the metal layer 143, an adhesion layer 148 may be formed on the dielectric layer 42, and the metal layer 143 may be formed on the adhesion layer 148. The method for forming the adhesion layer 148 is similar to the method for forming the adhesion layer 46, and therefore a detailed description thereof will be omitted. The adhesion layer 148 is formed using, for example, chromium (Cr).

[0077] Next, a metal layer 144 is formed on the metal layer 143. The method for forming the metal layer 144 is the same as that for the metal layer 41, and therefore a detailed description thereof will be omitted. The metal layer 144 is formed using a metal material made of a metal selected from the group consisting of gold (Au), ruthenium (Ru), and iridium (Ir), or a metal alloy containing at least one element selected from the group. Here, gold is exemplified as a material for the metal layer 144. The length of the metal layer 144 in the Z-axis direction is, for example, 10 nm. In this manner, the stack 40 is obtained.

[0078] <Resist film forming step S12> Following the preparation step S11, a resist film formation step S12 is performed. The resist film formation step S12 is a step of forming a resist film 51 (photoresist) on the metal layer 144. As shown in Fig. 11, in the resist film formation step S12, a liquid resist is applied onto the metal layer 144 using a spin coater or the like, and the applied liquid resist is dried to form the resist film 51. The thickness of the resist film 51 is, for example, 230 nm.

[0079] <Pattern formation step S13> Following the resist film formation process S12, a pattern formation process S13 is performed. The pattern formation process S13 is a process of forming a pattern 51p for forming the metal units 45 that constitute the metasurface reflector 30 on the resist film 51. As shown in FIG. 12, in the pattern formation process S13, an exposure device such as a KrF exposure device or an electron beam lithography device is used to transfer the pattern 51p corresponding to the metal units 45 onto the resist film 51. Then, a developing device is used to develop the pattern 51p transferred onto the resist film 51.

[0080] <First protective film formation step S14> Following the pattern formation step S13, a first protective film formation step S14 is performed. In the first protective film formation step S14, the metal layer 143 and the metal layer 144 are milled using the pattern 51p to form metal units 45 in the metal layer 143 and to form first portions 44a (first protective film) in the metal layer 144 that cover the top surfaces 45a of the metal units 45. As shown in FIG. 13 , in the first protective film formation step S14, an ion beam is irradiated by ion milling until the dielectric layer 42 is exposed. As a result, portions of the metal layer 144, the metal layer 143, and the adhesion layer 148 that are not covered by the pattern 51p are removed, and the first portions 44a, the metal units 45, and the adhesion layer 48 are formed.

[0081] <Second protective film formation step S15> Following the first protective film forming step S14, a second protective film forming step S15 is performed. The second protective film forming step S15 is a step of forming a second portion 44b (second protective film) on the side surface 45c of the metal unit 45. The second protective film forming step S15 includes a resist film removing step S16, a metal film forming step S17, and a metal film removing step S18.

[0082] <Resist film removal step S16> The resist film removal step S16 is a step of removing the resist film 51. As shown in Fig. 14, the resist film 51 is removed with an organic solvent (NMP). As a result, a structure 130 is obtained.

[0083] <Metal film formation process S17> Following the resist film removal step S16, a metal film formation step S17 is performed. The metal film formation step S17 is a step of forming a metal film 52 on the surface 130a of the structure 130. The surface 130a includes the upper surface of the first portion 44a, the side surface of the first portion 44a, the side surface 45c of the metal unit 45, and the portion of the main surface 42a of the dielectric layer 42 that is not covered with the metal unit 45.

[0084] In the metal film formation process S17, a metal film 52 is formed by vacuum film deposition using oblique incidence sputtering. As shown in FIG. 15, the rotation axis AX of the structure 130 is set to the normal direction to the main surface 42a of the dielectric layer 42. The target T is positioned so that metal particles emitted from the target T are incident at an incident angle α. In other words, the angle formed by the normal direction to the main surface Ta of the target T and the normal direction (rotation axis AX) to the main surface 42a of the dielectric layer 42 is set to the incident angle α. The main surface Ta is the surface from which the metal particles are emitted. The incident angle α is, for example, 67°. Then, sputtering is performed while the structure 130 is rotated about the rotation axis AX. As a result, the metal particles enter between two adjacent metal units 45, and a metal film 52 is formed to cover the entire surface 130a.

[0085] The metal film 52 is formed using a metal material selected from the group consisting of gold (Au), ruthenium (Ru), and iridium (Ir), or a metal alloy containing at least one element selected from the group. Here, gold is exemplified as a constituent material of the metal film 52. The thickness of the metal film 52 is, for example, 10 nm.

[0086] <Metal film removal process S18> Following the metal film forming step S17, a metal film removing step S18 is performed. The metal film removing step S18 is a step of removing the metal film 52 covering the main surface 42a between two adjacent metal units 45. As shown in FIG. 16, anisotropic etching (etching back) is performed in the normal direction of the main surface 42a. The entire surface of the metal film 52 is etched until the main surface 42a between the two adjacent metal units 45 is exposed. As a result, the metal film 52 covering the top surface of the first portion 44a and the metal film 52 covering the main surface 42a between the two adjacent metal units 45 are removed, leaving a portion of the metal film 52 covering the side surface of the first portion 44a and the side surface 45c of the metal unit 45, thereby forming the second portion 44b. As a result of the etchback, the thickness of the second portion 44b becomes thinner as it moves away from the dielectric layer 42 in the Z-axis direction.

[0087] As a result of the above, the metasurface reflector 30 is formed on the surface 50a of the substrate 50.

[0088] Next, another example of a method for manufacturing a near-eye wearable device 1 will be described with reference to FIGS. 17 to 23. FIG. 17 is a process diagram showing another example of a method for manufacturing a metasurface reflector. FIG. 18 is a diagram for explaining a resist film formation process shown in FIG. 10. FIG. 19 is a diagram for explaining a pattern formation process shown in FIG. 17. FIG. 20 is a diagram for explaining a first protective film formation process shown in FIG. 17. FIG. 21 is a diagram for explaining a metal film formation process shown in FIG. 17. FIG. 22 is a diagram for explaining a metal film removal process shown in FIG. 17. FIG. 23 is a diagram for explaining a resist film removal process shown in FIG. 17.

[0089] 17 is a method for manufacturing a metasurface reflector 30. The method M2 includes a preparation step S21, a resist film formation step S22, a pattern formation step S23, a first protective film formation step S24, and a second protective film formation step S25.

[0090] <Preparation process S21> The preparation step S21 is a step of preparing the laminate 40. The preparation step S21 is the same as the preparation step S11, and therefore a detailed description thereof will be omitted.

[0091] <Resist film forming step S22> Following the preparation step S21, a resist film formation step S22 is performed. The resist film formation step S22 is a step of forming a multi-layer resist film 55 including a lower-layer resist film 53 and an upper-layer resist film 54 on the metal layer 144. As shown in FIG. 18 , in the resist film formation step S22, a liquid resist is applied to the metal layer 144 using a spin coater or the like, and the applied liquid resist is dried to form the lower-layer resist film 53. The film thickness of the lower-layer resist film 53 is, for example, 38 nm. Furthermore, a liquid resist is applied to the lower-layer resist film 53 using a spin coater or the like, and the applied liquid resist is dried to form the upper-layer resist film 54. The film thickness of the upper-layer resist film 54 is, for example, 250 nm.

[0092] <Pattern formation step S23> Following the resist film formation process S22, a pattern formation process S23 is performed. The pattern formation process S23 is a process of forming a pattern 55p for forming the metal units 45 that constitute the metasurface reflector 30 in the multilayer resist film 55. As shown in FIG. 19 , in the pattern formation process S23, a pattern 55p corresponding to the metal units 45 is transferred to the upper-layer resist film 54 using an exposure device such as a KrF exposure device or an electron beam lithography device. Then, the pattern 55p transferred to the upper-layer resist film 54 is developed using a developing device. At this time, the lower-layer resist film 53 is isotropically dissolved without causing a photoreaction, forming an overhang in which the lower-layer resist film 53 is slightly smaller than the upper-layer resist film 54 when viewed from the stacking direction. In other words, the edge of the lower-layer resist film 53 is located inside the side surface of the upper-layer resist film 54. The position of the edge of the lower-layer resist film 53 is adjusted by the time of the development process.

[0093] <First protective film formation step S24> Following the pattern formation step S23, a first protective film formation step S24 is performed. In the first protective film formation step S24, the metal layer 143 and the metal layer 144 are milled using the pattern 55p to form metal units 45 in the metal layer 143 and to form first portions 44a (first protective film) in the metal layer 144 that cover the top surfaces 45a of the metal units 45. As shown in FIG. 20 , in the first protective film formation step S24, an ion beam is irradiated by ion milling until the dielectric layer 42 is exposed. As a result, portions of the metal layer 144, the metal layer 143, and the adhesion layer 148 that are not covered by the pattern 55p are removed, and the first portions 44a, the metal units 45, and the adhesion layer 48 are formed. This results in a structure 230.

[0094] <Second protective film formation step S25> Following the first protective film forming step S24, a second protective film forming step S25 is performed. The second protective film forming step S25 is a step of forming a second portion 44b (second protective film) on the side surface 45c of the metal unit 45. The second protective film forming step S25 includes a metal film forming step S26, a metal film removing step S27, and a resist film removing step S28.

[0095] <Metal film formation process S26> The metal film forming step S26 is a step of forming a metal film 56 on the surface 230a of the structure 230. The surface 230a includes the upper surface of the upper-layer resist film 54, the side surfaces of the upper-layer resist film 54, the side surfaces of the first portions 44a, the side surfaces 45c of the metal units 45, and the portions of the main surface 42a of the dielectric layer 42 that are not covered with the metal units 45.

[0096] In the metal film forming process S26, a metal film 56 is formed by vacuum film deposition using oblique incidence sputtering. As shown in FIG. 21, the rotation axis AX of the structure 230 is set in the normal direction to the main surface 42a of the dielectric layer 42. The target T is positioned so that metal particles emitted from the target T are incident at an incident angle β. In other words, the angle formed by the normal direction to the main surface Ta of the target T and the normal direction (rotation axis AX) to the main surface 42a of the dielectric layer 42 is set to be the incident angle β. The incident angle β is, for example, 0° to 28°. Then, sputtering is performed while the structure 230 is rotated around the rotation axis AX. As a result, the metal particles enter between two adjacent metal units 45.

[0097] Because the edge of the lower-layer resist film 53 is located inside the side surface of the upper-layer resist film 54, the metal film 56 is not formed on the edge of the lower-layer resist film 53. Therefore, the metal film 56 is formed on the top surface and side surface of the upper-layer resist film 54, the side surface of the first portion 44a, the side surface 45c of the metal unit 45, and the portion of the main surface 42a of the dielectric layer 42 that is not covered by the metal unit 45. A gap 56a is formed in the metal film 56 along the edge of the lower-layer resist film 53.

[0098] The metal film 56 is formed using a metal material selected from the group consisting of gold (Au), ruthenium (Ru), and iridium (Ir), or a metal alloy containing at least one element selected from the group. Here, gold is exemplified as a constituent material of the metal film 56. The thickness of the metal film 56 is, for example, 10 nm.

[0099] <Metal film removal process S27> Following the metal film forming step S26, a metal film removing step S27 is performed. The metal film removing step S27 is a step of removing the metal film 56 covering the main surface 42a between two adjacent metal units 45. As shown in FIG. 22 , in the metal film removing step S27, an ion beam is irradiated onto the entire surface of the metal film 56 by ion milling until the main surface 42a between the two adjacent metal units 45 is exposed. This removes the metal film 56 covering the top surface of the upper resist film 54 and the metal film 56 covering the main surface 42a between the two adjacent metal units 45, leaving the metal film 56 covering the side surface of the first portion 44a and the side surface 45c of the metal unit 45, thereby forming the second portion 44b. Note that the metal film 56 covering the side surface of the upper resist film 54 also remains.

[0100] <Resist film removal step S28> Following the metal film removing step S27, a resist film removing step S28 is performed. The resist film removing step S28 is a step of removing the multilayer resist film 55. As shown in FIG. 23, the organic solvent (NMP) enters the gap 56a and reaches the edge of the lower resist film 53, thereby dissolving the lower resist film 53. As a result, the multilayer resist film 55 is removed together with the metal film 56 covering the side surface of the upper resist film 54.

[0101] As a result of the above, the metasurface reflector 30 is formed on the surface 50a of the substrate 50.

[0102] By the above-mentioned method M1 or method M2, multiple metasurface reflectors 30 are formed on one substrate 50. Therefore, by cutting the substrate 50, a portion including one metasurface reflector 30 is obtained. Then, by attaching the substrate 50 of that portion to a predetermined region on the inner surface 3a of the lens 3, the metasurface reflector 30 is formed on the inner surface 3a of the lens 3.

[0103] Next, a frame 2 equipped with an optical engine 20 is prepared, and a lens 3 having a metasurface reflector 30 formed thereon is attached to the rim 2a of the frame 2. In this manner, the near-eye wearable device 1 is manufactured.

[0104] The metasurface reflector 30 may be formed directly on the inner surface 3a of the lens 3. The method for forming the metasurface reflector 30 on the inner surface 3a of the lens 3 is the same as the method for forming the metasurface reflector 30 on the surface 50a of the substrate 50. In this case, the metasurface reflector 30 is formed in a desired area on the inner surface 3a.

[0105] In the near-eye wearable device 1, projection device 10, and metasurface reflector 30 described above, the metasurface reflector 30 is divided into a plurality of unit areas 31 arranged in the X-axis direction along the main surface 42a and the Y-axis direction along the main surface 42a and intersecting (perpendicular to) the X-axis direction. Each unit area 31 is provided with a metal unit 45, and a protective layer 44 covers the top surface 45a and side surface 45c of the metal unit 45. Therefore, when the near-eye wearable device 1, projection device 10, and metasurface reflector 30 are in use, the top surface 45a and side surface 45c of the metal unit 45 are not exposed to air, reducing the possibility of the metal unit 45 being oxidized and sulfurized. Furthermore, since the protective layer 44 is made of a metal having a higher standard electrode potential than the metal constituting the metal layer 43, the protective layer 44 is less susceptible to oxidation and sulfurization than the metal layer 43. Therefore, the optical properties of the near-eye wearable device 1, projection device 10, and metasurface reflector 30 are less likely to change. As a result, it is possible to suppress deterioration of the reflection characteristics.

[0106] As the ratio of thickness d4 to thickness d5 increases, the influence of the protective layer 44 on the reflection characteristics of the metasurface reflector 30 increases. For example, gold (Au) reflects red light but tends to absorb green and blue light. Ruthenium and iridium tend to absorb light in the visible light range. Therefore, as the ratio of thickness d4 to thickness d5 increases, the reflection characteristics of the metasurface reflector 30 may deteriorate. In contrast, in the metasurface reflector 30, thickness d4 is 20% or less of thickness d5. Therefore, the protective layer 44 can be provided while suppressing the influence of the protective layer 44 on the reflection characteristics of the metasurface reflector 30. This makes it possible to further suppress deterioration of the reflection characteristics.

[0107] Metals such as molybdenum, titanium, and tungsten are also resistant to oxidation and sulfurization and have high corrosion resistance, but they have a large absorption coefficient in the visible light range. Therefore, if the protective layer 44 is made of these metals, the reflection characteristics of the metasurface reflector 30 may be degraded. The absorption coefficients of gold, ruthenium, and iridium in the visible light range are smaller than the absorption coefficients of metals such as molybdenum, titanium, and tungsten in the visible light range. Therefore, if the protective layer 44 is made of a metal containing at least one element selected from the group consisting of gold, ruthenium, and iridium, the degradation of the reflection characteristics of the metasurface reflector 30 can be further suppressed.

[0108] The metal unit 45 is a metal body having a trapezoidal shape when viewed from the Z-axis direction. Therefore, the structure of the metal unit 45 can be simplified compared to when the metal unit is composed of multiple metal bodies. This makes it possible to facilitate the manufacture of the metasurface reflector 30.

[0109] When the length of the metal unit 45 in the X-axis direction is 500 nm or more and 2500 nm or less, reflected light Lr corresponding to a viewing angle of 40° to 60° can be obtained. When the thickness d3 is 10 nm or more and 100 nm or less, electromagnetic resonance with the metal layer 41 via the dielectric layer 42 is effectively generated, resulting in reflected light Lr with strong electric field intensity. When the width W1 is 10 nm or more and 200 nm or less and the width W2 is 100 nm or more and 500 nm or less, the phase difference between the phase of the reflected light Lr at width W1 and the phase of the reflected light Lr at width W2 can be set to 360° (2π radians) for visible laser light Ls. From the above, by setting each dimension of the metal unit 45 within the above-mentioned ranges, the reflection efficiency for visible light can be improved.

[0110] The metal layer 43 is made of a metal containing at least one element selected from the group consisting of silver, aluminum, and copper. This allows the metal layer 43 to have a relatively high reflectance in the visible light range and a relatively high electrical conductivity. This makes it possible to strengthen the electromagnetic resonance between the metal layer 41 and the metal layer 43, thereby increasing the reflection efficiency.

[0111] The dielectric layer 42 is made of a material that is transparent in the visible light region, which reduces the absorption rate of visible light in the dielectric layer 42, thereby increasing the reflection efficiency of visible light.

[0112] The dielectric layer 42 is made of, for example, one compound selected from the group consisting of silicon oxide, titanium oxide, magnesium oxide, and aluminum oxide. In this case, the dielectric layer 42 has a dielectric constant that does not inhibit electromagnetic action. Therefore, the electromagnetic resonance between the metal layer 41 and the metal layer 43 can be strengthened, and the reflection efficiency can be increased.

[0113] The thickness d1 is, for example, not less than 50 nm and not more than 1000 nm. The thickness d2 is, for example, not less than 10 nm and not more than 100 nm. In this case, it is possible to reduce the possibility that the dielectric layer 42 will inhibit the electromagnetic action, and it is possible to reduce the possibility that the laser light Ls will transmit through the metal layer 41. Therefore, it is possible to increase the reflection efficiency.

[0114] The thinner the second portion 44b, the higher the reflected electric field strength. Therefore, if the protective layer 44 is configured so that the thickness of the second portion 44b becomes thinner with increasing distance from the dielectric layer 42 in the Z-axis direction, the protective layer 44 can be provided while suppressing the influence on the reflection characteristics of the metasurface reflector 30. Therefore, it is possible to further suppress the deterioration of the reflection characteristics.

[0115] In method M1 for manufacturing the metasurface reflector 30, a pattern 51p is formed in a resist film 51 formed on the metal layer 144 of the laminate 40, and the pattern 51p is used to mill the metal layers 143 and 144, thereby forming the metal unit 45 and a first portion 44a covering the top surface 45a of the metal unit 45. In method M2 for manufacturing the metasurface reflector 30, a pattern 55p is formed in a multilayer resist film 55 formed on the metal layer 144 of the laminate 40, and the pattern 55p is used to mill the metal layers 143 and 144, thereby forming the metal unit 45 and a first portion 44a covering the top surface 45a of the metal unit 45. Furthermore, a second portion 44b is formed on the side surface 45c of the metal unit 45. In the metasurface reflector 30 manufactured in this manner, the top surface 45a and the side surface 45c of the metal unit 45 are not exposed to air during use, reducing the possibility of the metal unit 45 being oxidized and sulfurized. Furthermore, since the protective layer 44 is made of a metal having a higher standard electrode potential than the metal constituting the metal layer 43, the protective layer 44 is less susceptible to oxidation and sulfurization than the metal layer 43. Therefore, the optical properties of the metasurface reflector 30 are less likely to change. As a result, it is possible to suppress deterioration of the reflection properties.

[0116] As described above, in the manufacturing process of the metasurface reflector 30, the resist film is removed with an organic solvent (NMP). At this time, if the metal layer 43 (metal unit 45) is exposed, the organic solvent may corrode the metal layer 43. In contrast, in methods M1 and M2, the resist films 51 and 55 are removed while the top surface 45a of the metal unit 45 is covered with the first portion 44a of the protective layer 44. Because the first portion 44a is made of a metal having a higher standard electrode potential than the metal constituting the metal layer 43, the first portion 44a is less susceptible to corrosion than the metal layer 43. Therefore, in the manufacturing process of the metasurface reflector 30, the possibility of corrosion of the metal layer 43 (metal unit 45) can be reduced, and corrosion resistance can be improved.

[0117] In method M1, metal film 52 is formed on surface 130a of structure 130 obtained by removing resist film 51, and second portion 44b is formed by removing the portion of metal film 52 that is formed on main surface 42a of dielectric layer 42. In this manner, second portion 44b can be formed on side surface 45c of metal unit 45 by a relatively simple process.

[0118] In method M2, the multilayer resist film 55 is removed in a state in which the top surface 45a of the metal unit 45 is covered by the first portion 44a and the side surface 45c of the metal unit 45 is covered by the second portion 44b. Therefore, the top surface 45a and the side surface 45c of the metal unit 45 are not exposed to the organic solvent used to remove the metal unit 45, reducing the possibility of corrosion of the metal unit 45. As a result, it is possible to further suppress deterioration of the reflection characteristics of the metasurface reflector 30.

[0119] In the metal film formation process S17, the metal film 52 is formed using oblique incidence sputtering. This allows metal particles to enter between two adjacent metal units 45, making it easier to form the metal film 52 on the side surfaces 45c of the metal units 45. Similarly, in the metal film formation process S26, the metal film 56 is formed using oblique incidence sputtering. This allows metal particles to enter between two adjacent metal units 45, making it easier to form the metal film 56 on the side surfaces 45c of the metal units 45. Therefore, it is possible to shorten the time required to manufacture the metasurface reflector 30.

[0120] It should be noted that the metasurface reflector, projection device, near-eye wearable device, and method for manufacturing a metasurface reflector according to the present disclosure are not limited to the above embodiments.

[0121] The near-eye wearable device 1 may be a pair of VR (Virtual Reality) glasses.

[0122] In the above embodiment, the projection device 10 projects (draws) an image directly onto the retina RE of the user of the near-eye wearable device 1, but the image may also be projected onto the metasurface reflector 30.

[0123] The metasurface reflector 30 may be applied to devices other than the projection device 10. For example, the metasurface reflector 30 may be applied to a general image projection surface such as a video screen.

[0124] The plurality of unit areas 31 may include a unit area 31 for a red component, a unit area 31 for a green component, and a unit area 31 for a blue component. In the X-axis direction, the unit areas 31 for the red component, the unit areas 31 for the green component, and the unit areas 31 for the blue component may be repeatedly arranged in that order. In the Y-axis direction, the unit areas 31 for the red component, the unit areas 31 for the green component, and the unit areas 31 for the blue component may also be repeatedly arranged in that order.

[0125] In the above embodiment, the metal unit 45 is provided in each of all of the unit areas 31 among the plurality of unit areas 31, but the metal unit 45 may also be provided in each of some of the unit areas 31 among the plurality of unit areas 31.

[0126] The method for determining the length Lx is not limited to the method described in the above embodiment. For example, the lengths Lx of the unit regions 31 located at both ends of the metasurface reflector 30 in the X-axis direction may be determined by the above-described method, and the lengths Lx of the unit regions 31 located therebetween may be determined so as to gradually change from the length Lx of the unit region 31 located at one end of the metasurface reflector 30 in the X-axis direction to the length Lx of the unit region 31 located at the other end.

[0127] The metal unit 45 is not limited to a single trapezoidal metal body, but may be configured by a plurality of metal bodies arranged in the X-axis direction, for example.

[0128] (Addendum) [Article 1] A metasurface reflector, a first metal layer and a second metal layer stacked in a first direction; a dielectric layer provided between the first metal layer and the second metal layer in the first direction; a protective layer covering the second metal layer; Equipped with the dielectric layer has a main surface on which the second metal layer is provided, The metasurface reflector is divided into a plurality of unit areas arranged in a second direction along the main surface and a third direction along the main surface and intersecting the second direction, the second metal layer includes metal units provided in all or some of the unit areas, the protective layer is made of a metal having a standard electrode potential greater than that of a metal constituting the second metal layer; the metal unit has a bottom surface facing the dielectric layer in the first direction, a top surface provided on the opposite side to the bottom surface in the first direction, and a side surface connecting the top surface and the bottom surface, A metasurface reflector, wherein the protective layer includes a first portion covering the top surface and a second portion covering the side surface.

[0129] [Clause 2] The metasurface reflector described in clause 1, wherein the thickness of the protective layer is less than 20% of the sum of the length of the second metal layer in the first direction and the thickness of the protective layer.

[0130] [Article 3] The metasurface reflector described in clause 1 or clause 2, wherein the metal unit is a metal body having a trapezoidal shape when viewed from the first direction.

[0131] [Article 4] The length of the metal body in the second direction is 500 nm or more and 2500 nm or less, the length of the metal body in the first direction is 10 nm or more and 100 nm or less; The length of the short side of the metal body is 10 nm or more and 200 nm or less, The metasurface reflector described in clause 3, wherein the length of the long side of the metal body is greater than the length of the short side and is 100 nm or more and 500 nm or less.

[0132] [Article 5] The metasurface reflector of any one of clauses 1 to 4, wherein the protective layer is made of a metal containing at least one element selected from the group consisting of gold, ruthenium, and iridium.

[0133] [Article 6] The metasurface reflector of any one of clauses 1 to 5, wherein the second metal layer is composed of a metal containing at least one element selected from the group consisting of silver, aluminum, and copper.

[0134] [Article 7] The metasurface reflector according to any one of clauses 1 to 6, wherein the dielectric layer is made of a material that is transparent in the visible light region.

[0135] [Article 8] 8. The metasurface reflector of claim 7, wherein the dielectric layer is composed of one compound selected from the group consisting of silicon oxide, titanium oxide, magnesium oxide, and aluminum oxide.

[0136] [Article 9] the length of the dielectric layer in the first direction is 10 nm or more and 100 nm or less; The metasurface reflector of any one of clauses 1 to 8, wherein the length of the first metal layer in the first direction is 50 nm or more and 1000 nm or less.

[0137] [Article 10] The metasurface reflector of any one of clauses 1 to 9, wherein the thickness of the second portion decreases in the first direction as it moves away from the dielectric layer.

[0138] [Article 11] A projection device mounted on a near-eye wearable device, a light source that emits laser light; a movable mirror for scanning with the laser light; The metasurface reflector according to any one of clauses 1 to 10, which reflects the laser light passing through the movable mirror and allows a user wearing the near-eye wearable device to view an image; A projection device comprising:

[0139] [Article 12] a projection device according to clause 11; A lens provided with the metasurface reflector; A near-eye wearable device comprising:

[0140] [Article 13] preparing a laminate in which a first metal layer, a dielectric layer, a second metal layer, and a third metal layer are laminated in this order in a first direction; forming a resist film on the third metal layer; forming a pattern on the resist film to form a metal unit constituting a metasurface reflector, the metal unit having a bottom surface facing the dielectric layer in the first direction, a top surface provided on the opposite side of the bottom surface in the first direction, and a side surface connecting the top surface and the bottom surface; milling the second metal layer and the third metal layer using the pattern to form the metal unit and a first protective film covering the top surface; forming a second protective film that covers the side surface of the metal unit; Including, A method for manufacturing a metasurface reflector, wherein the first protective film and the second protective film are made of a metal having a higher standard electrode potential than the metal constituting the second metal layer.

[0141] [Article 14] The step of forming the second protective film includes: removing the resist film; forming a metal film on the surface of the structure obtained by removing the resist film; forming the second protective film by removing a portion of the metal film formed on the main surface of the dielectric layer; 14. A method for manufacturing a metasurface reflector according to claim 13, comprising:

[0142] [Article 15] In the step of forming the resist film, a multi-layer resist film including a lower-layer resist film and an upper-layer resist film is formed on the third metal layer, The step of forming the second protective film includes: forming a metal film on the surface of the structure obtained by the step of forming the first protective film; forming the second protective film by removing a portion of the metal film formed on the main surface of the dielectric layer; removing the multilayer resist film after the second protective film is formed; 14. A method for manufacturing a metasurface reflector according to claim 13, comprising:

[0143] [Article 16] 16. The method for manufacturing a metasurface reflector according to claim 14 or 15, wherein in the step of forming the metal film, the metal film is formed using oblique incidence sputtering. [Explanation of symbols]

[0144] 1...Near eyewear device, 3...Lens, 10...Projection device, 21...Light source unit (light source), 23...Moveable mirror, 30...Metasurface reflector, 31...Unit area, 40...Laminate, 41...Metal layer (first metal layer), 42...Dielectric layer, 42a...Main surface, 43...Metal layer (second metal layer), 44...Protective layer, 44a...First portion (first protective film), 44b...Second portion (second protective film), 45 ...metal unit, 45a...top surface, 45b...bottom surface, 45c...side surface, 51...resist film, 51p...pattern, 52...metal film, 53...lower layer resist film, 54...upper layer resist film, 55...multilayer resist film, 55p...pattern, 56...metal film, 130...structure, 130a...surface, 143...metal layer (second metal layer), 144...metal layer (third metal layer), 230...structure, 230a...surface.

Claims

1. A metasurface reflector, a first metal layer and a second metal layer stacked in a first direction; a dielectric layer provided between the first metal layer and the second metal layer in the first direction; a protective layer covering the second metal layer; Equipped with the dielectric layer has a main surface on which the second metal layer is provided, The metasurface reflector is divided into a plurality of unit areas arranged in a second direction along the main surface and a third direction along the main surface and intersecting the second direction, the second metal layer includes metal units provided in all or some of the unit areas, the protective layer is made of a metal having a standard electrode potential greater than that of a metal constituting the second metal layer; the metal unit has a bottom surface facing the dielectric layer in the first direction, a top surface provided on the opposite side to the bottom surface in the first direction, and a side surface connecting the top surface and the bottom surface, A metasurface reflector, wherein the protective layer includes a first portion covering the top surface and a second portion covering the side surface.

2. The metasurface reflector of claim 1 , wherein the thickness of the protective layer is 20% or less of the sum of the length of the second metal layer in the first direction and the thickness of the protective layer.

3. The metasurface reflector according to claim 1 or 2, wherein the metal unit is a metal body having a trapezoidal shape when viewed from the first direction.

4. The length of the metal body in the second direction is 500 nm or more and 2500 nm or less, the length of the metal body in the first direction is 10 nm or more and 100 nm or less; The length of the short side of the metal body is 10 nm or more and 200 nm or less, The metasurface reflector of claim 3 , wherein the length of the long side of the metal body is greater than the length of the short side and is 100 nm or more and 500 nm or less.

5. The metasurface reflector of claim 1 or claim 2, wherein the protective layer is composed of a metal containing at least one element selected from the group consisting of gold, ruthenium, and iridium.

6. The metasurface reflector of claim 1 or claim 2, wherein the second metal layer is composed of a metal including at least one element selected from the group consisting of silver, aluminum, and copper.

7. The metasurface reflector according to claim 1 or claim 2, wherein the dielectric layer is made of a material that is transparent in the visible light region.

8. The metasurface reflector of claim 7 , wherein the dielectric layer is composed of a compound selected from the group consisting of silicon oxide, titanium oxide, magnesium oxide, and aluminum oxide.

9. the length of the dielectric layer in the first direction is 10 nm or more and 100 nm or less; The metasurface reflector of claim 1 or 2, wherein the length of the first metal layer in the first direction is 50 nm or more and 1000 nm or less.

10. The metasurface reflector of claim 1 or claim 2, wherein the thickness of the second portion decreases in the first direction with increasing distance from the dielectric layer.

11. A projection device mounted on a near-eye wearable device, a light source that emits laser light; a movable mirror for scanning with the laser light; 3. The metasurface reflector according to claim 1 or 2, wherein the metasurface reflector reflects the laser light passing through the movable mirror to allow a user wearing the near-eye wearable device to view an image; A projection device comprising:

12. A projection device according to claim 11; A lens provided with the metasurface reflector; A near-eye wearable device comprising:

13. preparing a stacked body in which a first metal layer, a dielectric layer, a second metal layer, and a third metal layer are stacked in this order in a first direction; forming a resist film on the third metal layer; forming a pattern on the resist film to form a metal unit constituting a metasurface reflector, the metal unit having a bottom surface facing the dielectric layer in the first direction, a top surface provided on the opposite side of the bottom surface in the first direction, and a side surface connecting the top surface and the bottom surface; forming the metal unit by milling the second metal layer and the third metal layer using the pattern, and forming a first protective film covering the top surface; forming a second protective film covering the side surface of the metal unit; Including, A method for manufacturing a metasurface reflector, wherein the first protective film and the second protective film are made of a metal having a higher standard electrode potential than the metal constituting the second metal layer.

14. The step of forming the second protective film includes: removing the resist film; forming a metal film on the surface of the structure obtained by removing the resist film; forming the second protective film by removing a portion of the metal film formed on the main surface of the dielectric layer; The method for manufacturing the metasurface reflector of claim 13, comprising:

15. In the step of forming the resist film, a multi-layer resist film including a lower-layer resist film and an upper-layer resist film is formed on the third metal layer, The step of forming the second protective film includes: forming a metal film on the surface of the structure obtained by the step of forming the first protective film; forming the second protective film by removing a portion of the metal film formed on the main surface of the dielectric layer; removing the multilayer resist film after the second protective film is formed; The method for manufacturing the metasurface reflector of claim 13, comprising:

16. The method for manufacturing a metasurface reflector according to claim 14 or 15, wherein in the step of forming the metal film, the metal film is formed using oblique incidence sputtering.

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