Metasurface reflector, retina scanning display and manufacturing method of metasurface reflector

Abstract

The invention relates to a metasurface reflector, a retina scanning display and a manufacturing method of the metasurface reflector. Provided is a metasurface reflector or the like which has high process resistance and is not susceptible to deterioration in reflection characteristics. A nanostructure (11) is provided with a protective layer (8), a first metal layer (10) constituting a nanostructure, a dielectric layer (20), and a second metal layer (30), the protective layer (8) covers the first metal layer (10), the dielectric layer (20) is positioned between the first metal layer (10) and the second metal layer (30), and the nanostructure (11) contains Ag and Zn, or Ag and Sn.

Description

Technical Field

[0001] This application relates to metasurface reflectors, retinal scanning displays, and methods for manufacturing metasurface reflectors. Background Technology

[0002] Currently, glasses-type terminals are being researched in AR (Augmented Reality) and VR (Virtual Reality). In particular, retinal scanning displays, which allow users to perceive images by imaging scanned light onto their retina in recent years, have garnered significant attention. In retinal scanning displays, generally, visible light of three colors emitted from a light source such as an LD (Laser Diode) corresponding to each of the three colors (R, G, and B) is combined along an optical axis by a PLC (Planer Lightwave Circuit). The combined visible light of the three colors is scanned by a MEMS (Micro Electro Mechanical Systems) mirror and reflected by a semi-reflective mirror located in front of the user's eye, thus entering the user's pupil. This incident light is imaged on the user's retina, thereby allowing the user to perceive the image.

[0003] Metasurface reflectors are used as semi-reflective mirrors. Metasurface reflectors are thin films with nanoscale microstructures (nanostructures) that function as light reflectors.

[0004] Figure 13 (a) is a cross-sectional view showing the structure of an existing metasurface reflector (Prior Art 1). For example... Figure 13 As shown in (a), the outermost surface of the metasurface reflector of the prior art 1 has exposed metal of nanostructures (see, for example, Patent Documents 1 and 2).

[0005] in addition, Figure 13 (b) is a cross-sectional view showing the structure of an existing metasurface reflector (Prior Art 2). For example... Figure 13 As shown in (b), the metasurface reflector of the prior art 2 has a process protection layer formed only on the upper surface of the nanostructure.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: U.S. Patent Application Publication No. 2018 / 0113310

[0009] Patent Document 2: Japanese Patent Application Publication No. 2024-94887 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] like Figure 13 As shown in (a), the metasurface reflector of the prior art 1 has an Ag layer 130, a SiO2 layer 120, and an Ag layer 112 sequentially formed on a substrate 140. The upper Ag layer 112 is exposed.

[0012] In the metasurface reflector of prior art 1, the outermost nanostructure has exposed metal. Therefore, during the formation of the nanostructure, regardless of the stripping or polishing process, when the resist pattern is removed with an organic solvent (e.g., NMP (N-methyl-2-pyrrolidone)), the outermost metal layer (Ag layer 112) is exposed, resulting in corrosion damage as shown in corrosion section 119 due to the organic solvent. (No process resistance)

[0013] like Figure 13 As shown in (b), the metasurface reflector of prior art 2 has an Ag layer 130, a SiO2 layer 120, an Ag layer 112, and an Au layer 108 sequentially formed on a substrate 140. Only the upper surface of the upper Ag layer 112 is covered by the protective Au layer 108.

[0014] If, as in prior art 2, a protective Au layer 108 is formed only on the upper surface of the Ag layer 112, then even if there is no corrosion damage when the resist is removed, the sides of the Ag layer 112 will be exposed to air, resulting in the problem of intensified corrosion as shown in corrosion section 119 and deterioration of reflective properties. (No storage resistance)

[0015] This application was made in view of the above-mentioned problems, and its purpose is to provide a metasurface reflector with high process resistance and less prone to degradation of reflective properties, a retinal scanning display, and a method for manufacturing a metasurface reflector.

[0016] Solution for solving the problem

[0017] The metasurface reflector of the present invention comprises a protective layer, a first metal layer constituting a nanostructure, a dielectric layer and a second metal layer, wherein the protective layer covers the first metal layer, the dielectric layer is located between the first metal layer and the second metal layer, and the nanostructure comprises Ag and Zn, or comprises Ag and Sn.

[0018] The retinal scanning display of the present invention includes: an eyeglass frame, a lens mounted on the eyeglass frame, and a retinal projection device mounted on the eyeglass frame. The retinal projection device includes: a light source unit that emits a laser, a movable mirror that scans the laser, and a metasurface reflector that reflects the scanned laser. The metasurface reflector is disposed on the inner surface of the lens and has a protective layer, a first metal layer constituting a nanostructure, a dielectric layer, and a second metal layer. The protective layer covers the first metal layer, and the dielectric layer is located between the first metal layer and the second metal layer. The nanostructure comprises Ag and Zn, or comprises Ag and Sn.

[0019] The method for manufacturing a metasurface reflector involved in this invention includes: sequentially forming a second metal layer, a dielectric layer and a first metal layer on a substrate; forming a nanostructure on the first metal layer by photolithography and etching; and forming a protective layer to cover the upper surface and side surface of the nanostructure. The nanostructure contains Ag and Zn, or contains Ag and Sn.

[0020] The effects of the invention

[0021] According to this application, it is possible to provide metasurface reflectors with high process resistance and low susceptibility to deterioration of reflective properties. Attached Figure Description

[0022] Figure 1 This is a magnified view of the metasurface reflector of the first embodiment of the present invention, which is mounted on the lens of an eyeglass-type retinal scanning display.

[0023] Figure 2 It is a general representation Figure 1 A three-dimensional view of a unit region of a metasurface reflector.

[0024] Figure 3 It is along Figure 2 The cross-sectional view along line III-III shows the structure of the metasurface reflector of the first embodiment of this application.

[0025] Figure 4 yes Figure 2 Top view.

[0026] Figure 5 This diagram illustrates the reflection principle based on metasurface reflectors in an eyeglass-type retinal scanning display.

[0027] Figure 6 It is a graph representing the phase change of reflected light at a position along the x-axis of a metasurface reflector.

[0028] Figure 7This diagram illustrates how reflected light converges relative to incident light when metal units are arranged such that their length along the x-axis varies with their position along the x-axis.

[0029] Figure 8 (a) represents the relationship between the reflection angle and the incident angle when the metal unit length is 500 nm, (b) represents the relationship between the reflection angle and the incident angle when the metal unit length is 750 nm, and (c) represents the relationship between the reflection angle and the incident angle when the metal unit length is 1400 nm.

[0030] Figure 9 It is a diagram showing the deterioration of metal units with a trapezoidal pattern over the years.

[0031] Figure 10 It is a graph showing the change in the reflection angle relative to the length of the trapezoidal metal unit under the condition of annual deterioration of the metal unit.

[0032] Figure 11 This is a cross-sectional view showing the structure of the metasurface reflector according to the second embodiment of the present invention.

[0033] Figure 12 This is a cross-sectional view showing the structure of the metasurface reflector according to the third embodiment of the present invention.

[0034] Figure 13 (a) is a cross-sectional view showing the corrosion state in the case of prior art 1 without a protective layer, and (b) is a cross-sectional view showing the corrosion state in the case of prior art 2 with an Au protective layer.

[0035] Explanation of reference numerals in the attached figures

[0036] 1, 2, 3 Metasurface Reflectors

[0037] 5 unit areas

[0038] 8. Process protective layer (protective layer)

[0039] 10 First metal layer

[0040] 11 Nanostructures

[0041] 12 Ag layers

[0042] 13 Zn or Sn layers

[0043] 15 Ag-Zn alloy or Ag-Sn alloy

[0044] 18 Metal Units

[0045] 19 Corrosion Section

[0046] 20 Dielectric layer

[0047] 30 Second metal layer

[0048] 40 substrate

[0049] 50 Eyeglasses Frames

[0050] 51 Lenses

[0051] 51a Inner Surface

[0052] 52. Eyeglass frames

[0053] 53. Temples

[0054] 60 Retina projection device

[0055] 61 Light Source Units

[0056] 62 movable mirrors

[0057] E eyeball

[0058] PP pupil

[0059] RE retina

[0060] 100 Retina Scanning Displays Detailed Implementation

[0061] The embodiments of this application will now be described in detail with reference to the accompanying drawings. Furthermore, for ease of understanding, the scales of various parts in the drawings may sometimes differ from actual scales. In the xyz orthogonal coordinate system set in the drawings, the x-axis and y-axis directions are horizontal, and the z-axis direction is vertical. The positive z-axis direction is also referred to as the up direction, and the negative z-axis direction as the down direction, but this is independent of the direction of gravity. Deviations are permitted in parallel, right-angled, orthogonal, horizontal, vertical, up-down, left-right, and other directions, to a degree that does not impair the effectiveness of the embodiment. Additionally, the "~" indicating a numerical range refers to the values ​​described before and after it as the lower and upper limits.

[0062] [First Implementation Method]

[0063] First, the first embodiment of this application will be described. Hereinafter, the example described is the case where the metasurface reflector 1 of this embodiment is mounted as a semi-reflective mirror on the lens 51 of an eyeglass-type retinal scanning display 100, but the application is not limited to this.

[0064] (structure)

[0065] Figure 1 This is an enlarged view of the metasurface reflector 1 of the first embodiment of this application, which is mounted on the lens 51 of an eyeglass-type retinal scanning display 100. (See diagram below.) Figure 1As shown, the metasurface reflector 1 is divided into multiple unit regions 5. These unit regions 5 are disposed along the inner surface 51a of the lens 51. The multiple unit regions 5 are arranged in a two-dimensional array along the transverse (x-axis direction) and longitudinal (y-axis direction) directions of the lens 51. Each unit region 5 is a stack containing a first metal layer 10, a dielectric layer 20, and a second metal layer 30 sequentially along the z-axis direction.

[0066] Figure 2 It is a three-dimensional diagram that roughly represents the unit area 5. Figure 3 It is along Figure 2 The cross-sectional view along line III-III shows the configuration of the metasurface reflector 1 according to the first embodiment of this application. Figure 2 and Figure 3 As shown, the metasurface reflector 1 has, along the z-axis, a second metal layer 30, a dielectric layer 20, a first metal layer 10 constituting the nanostructure 11, and a protective layer (process protection layer) 8 on a substrate 40. The protective layer 8 covers the first metal layer 10. The dielectric layer 20 is located between the first metal layer 10 and the second metal layer 30. The first metal layer 10 contains Ag and Zn, or contains Ag and Sn.

[0067] To improve adhesion, a chromium (Cr) layer can be provided between the first metal layer 10 and the dielectric layer 20. For the same purpose, Cr layers can also be provided between the dielectric layer 20 and the second metal layer 30, and between the second metal layer 30 and the substrate 40. The thickness of the Cr layer is, for example, 3 nm. The first metal layer 10 can also be constructed by arranging multiple nanostructures 11 one-dimensionally or two-dimensionally on the dielectric layer 20. Light incident on the metasurface reflector 1 from the protective layer 8 side is reflected at a predetermined angle according to the wavelength, incident angle, and shape of the nanostructures 11. The metasurface reflector 1 can be, for example, a thin plate or film, and can also be rectangular, square, polygonal, circular, etc. when viewed from above.

[0068] The term "light" as used in this specification is assumed to refer to visible light, but is not limited to visible light. It can also refer to infrared light with a wavelength longer than visible light, or ultraviolet light with a wavelength shorter than visible light. For example, the wavelength of visible light is 380 nm or more and less than 800 nm. The wavelength of infrared light is, for example, 800 nm or more and less than 1 mm. The wavelength of ultraviolet light is, for example, 200 nm or more and less than 380 nm.

[0069] The following is an explanation of each component.

[0070] <Substrate>

[0071] The substrate 40 is made of, for example, sapphire. The substrate 40 may be, for example, a flexible sheet or a quartz substrate. In the case of a spectacle-type retinal scanning display 100, the metasurface reflector 1 may not have a substrate 40, and the metasurface reflector 1 may be mounted on the inner surface 51a of the lens 51.

[0072] <Second Metal Layer>

[0073] The second metal layer 30 is the substrate layer. The second metal layer 30 is, for example, composed of a metal containing at least one element selected from gold (Au), copper (Cu), silver (Ag), iridium (Ir), ruthenium (Ru), rhodium (Rh), titanium (Ti), tantalum (Ta), tungsten (W), cobalt (Co), iron (Fe), and nickel (Ni). The second metal layer 30 is preferably mainly composed of silver (Ag). The length (thickness) of the second metal layer 30 in the z-axis direction is sufficient to allow the resonant current to flow and the light to be reflected when light is incident; for example, it is 1 nm to 1000 nm, or for example, 200 nm.

[0074] <Dielectric Layer>

[0075] The dielectric layer 20 functions as a spacer. The dielectric layer 20 is disposed on the second metal layer 30. The dielectric layer 20 has a dielectric constant that does not impede the electromagnetic interaction between the first metal layer 10 and the second metal layer 30. To achieve high reflectivity, the dielectric layer 20 may also be made of a material with a high dielectric constant. The dielectric layer 20 is, for example, made of at least 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) of the dielectric layer 20 in the z-axis direction is, for example, 1 nm to 1000 nm, and may be, for example, 40 nm.

[0076] <First Metal Layer>

[0077] The first metal layer 10 is formed of metal, constituting a nanostructure 11 as a nanoscale structure. The first metal layer 10 is a layer that, together with the second metal layer 30, induces electromagnetic resonance. Specifically, the incident electric field of light, which is an electromagnetic wave incident on the first metal layer 10, resonates through the dielectric layer 20, generating a reverse electric field in the second metal layer 30. A magnetic field opposite to the incident magnetic field is generated in the dielectric layer 20. As a result, the direction of travel of the light, which is an electromagnetic wave, is reversed.

[0078] The first metal layer 10 is provided on the main surface of the dielectric layer 20 on the side opposite to the second metal layer 30. Similar to the second metal layer 30, the first metal layer 10 is made of a metal mainly containing at least one element selected from the group consisting of Au, Cu, Ag, Ir, Ru, Rh, Ti, Ta, W, Co, Fe, and Ni. In the present embodiment, the first metal layer 10 is mainly made of Ag.

[0079] Specifically, the nanostructure 11 is, for example, a multilayer structure of an Ag layer and a Zn (zinc) layer, or a multilayer structure of an Ag layer and a Sn (tin) layer.

[0080] In the case of the multilayer structure of the Ag layer 12 and the Zn layer 13, for example, it is a multilayer structure of an Ag layer with a specified thickness, a Zn layer 13 with a thickness of 5.4 Å, an Ag layer with a specified thickness, a Zn layer 13 with a thickness of 5.4 Å, and an Ag layer with a specified thickness. In the case of the multilayer structure of the Ag layer and the Sn layer, for example, it is a multilayer structure of an Ag layer with a specified thickness, a Sn layer with a thickness of 9.4 Å, an Ag layer with a specified thickness, a Sn layer with a thickness of 9.4 Å, and an Ag layer with a specified thickness. However, in each multilayer structure, the total film thickness of the Ag layer is 40 nm.

[0081] When Ag is alloyed with Zn or Sn, the initial reflectivity decreases, but compared with pure Ag, sulfurization can be inhibited, and deterioration of the reflectivity can be suppressed. If the content of Zn or Sn is gradually increased from pure Ag, the deterioration of the reflectivity is minimized when the content is about 3 at%. Based on this insight, a multilayer structure of an Ag layer and a Zn layer or a Sn layer having the same performance as an Ag-Zn alloy (Zn: 3 at%) or an Ag-Sn alloy (Sn: 3 at%) is considered, and the film thickness of the Zn layer or the Sn layer that can inhibit sulfurization and suppress deterioration of the reflectivity is calculated as follows.

[0082] <Thickness of the Zn layer>

[0083] When the nanostructure 11 has a multilayer structure of an Ag layer and a Zn layer, the film thickness d1 of the Zn layer is obtained by the following formula.

[0084] d1 = (S1 / (S1 + N)) × D

[0085] Where,

[0086] S1 = (mass% of Zn) / (density of Zn) [volume%]

[0087] N = (mass% of Ag) / (density of Ag) [volume%]

[0088] D: Film thickness of the Ag layer

[0089] When the content of Zn is 3 at%, S1 = 0.258 [vol%] and N = 9.357 [vol%]. Therefore, for example, when the film thickness D of the Ag layer is 40 nm, the film thickness d1 of the Zn layer is (0.258 / (0.258 + 9.357)) × 40 [nm] = 1.07 [nm] = 10.7 [Å]. Thus, when the nanostructure 11 includes two Zn layers, the film thickness of one Zn layer is 10.7 / 2 = 5.35 [Å].

[0090] <Film thickness of the Sn layer>

[0091] In the case where the nanostructure 11 has a multilayer structure of an Ag layer and an Sn layer, the film thickness d2 of the Sn layer is obtained by the following formula in the same manner as above.

[0092] d2 = (S2 / (S2 + N)) × D

[0093] Where

[0094] S2 = (mass% of Sn) / (density of Sn) [vol%]

[0095] N = (mass% of Ag) / (density of Ag) [vol%]

[0096] D: Film thickness of the Ag layer

[0097] When the content of Sn is 3 at%, S2 = 0.453 [vol%] and N = 9.219 [vol%]. Therefore, for example, when the film thickness D of the Ag layer is 40 nm, the film thickness d2 of the Sn layer is (0.453 / (0.453 + 9.219)) × 40 [nm] = 1.87 [nm] = 18.7 [Å]. Thus, in the case where the nanostructure 11 includes two Sn layers, the film thickness of one Zn layer is 18.7 / 2 = 9.35 [Å].

[0098] As Figure 2 and Figure 4 shown, the first metal layer 10 constituting the nanostructure 11 includes, for example, metal units 18 having a trapezoidal shape in a plan view when viewed along the negative z-axis direction.

[0099] The length L of the trapezoidal metal unit 18 in the direction perpendicular to both the short and long sides parallel to the trapezoidal shape, i.e., the x-axis direction (hereinafter referred to as the "length direction"), is, for example, 500 nm or more and 2500 nm or less. The thickness d of the metal unit 18 in the z-axis direction is, for example, 10 nm or more and 100 nm or less. Among the parallel short and long sides of the trapezoidal shape of the metal unit 18, the length W1 of the short side is, for example, 10 nm or more and 200 nm or less, and the length W2 of the long side is greater than the length W1 of the short side, for example, 100 nm or more and 500 nm or less. In this case, the reflectivity of visible light can be improved.

[0100] The first metal layer 10 may also include multiple metal units 18 arranged in two dimensions in the x-axis and y-axis directions (see reference). Figure 1 , Figure 7 The spacing between two adjacent metal units 18 in the x-axis direction is set in a manner that ensures the wavefront continuity of the reflected light. This spacing only needs to be such that the two metal units 18 do not touch, for example, it can be set to less than half the wavelength of the incident light (laser Ls). For example, the spacing is approximately 20 nm. Multiple metal units 18 are formed, for example, by photolithography.

[0101] <Protective Layer>

[0102] The process protective layer 8 covers the upper surface and sides of the first metal layer 10. The process protective layer 8 is, for example, made of at least one material selected from the group consisting of Au, Ru, Ir, and TiN. The film thickness of the process protective layer 8 is, for example, 10 nm. The film thickness of the process protective layer 8 is, for example, less than 20% of the film thickness of the first metal layer 10.

[0103] (Reflection based on metasurface reflectors)

[0104] Next, the light reflection principle of the metasurface reflector 1 based on this embodiment will be explained.

[0105] Figure 3 This indicates the case where laser Ls is incident on metasurface reflector 1 at an incident angle θi, and the reflected light Lr is reflected at a reflection angle θr. For example... Figure 3 As shown, the incident angle θi is the angle between the normal to the surface illuminated by the laser Ls and the incident direction of the laser Ls. The reflection angle θr is the angle between the normal to the surface illuminated by the laser Ls and the exit direction of the reflected light Lr. In the plane containing both the laser Ls and the reflected light Lr, when the reflected light Lr is emitted towards the opposite side of the incident light (laser Ls) with the normal as the boundary, the reflection angle θr is represented by a positive value; when the reflected light Lr is emitted towards the same side of the incident light (laser Ls) with the normal as the boundary, the reflection angle θr is represented by a negative value.

[0106] like Figure 1As shown, the metasurface reflector 1 has multiple unit regions 5. Each unit region 5 has a metal element 18, which is configured such that when a laser Ls is incident at an incident angle θi corresponding to the position where the unit region 5 is located, the laser Ls is reflected at a reflection angle θr corresponding to the position where the unit region 5 is located. Figure 2 For example, as described later, the reflection angle θr of each unit region 5 is set such that the laser Ls (i.e., reflected light Lr) reflected by each unit region 5 passes through the center of the pupil PP of the user's eyeball E. Therefore, the incident angle θi and the reflection angle θr are determined by the position where the unit region 5 is set. The unit region 5 is configured in such a way that the incident angle θi and the reflection angle θr corresponding to the position where the unit region 5 is set can be obtained.

[0107] Figure 5 This diagram illustrates the reflection principle of the metasurface reflector 1 in a glasses-type retinal scanning display 100. (See diagram for example.) Figure 5 As shown, for example, when the user's pupil PP is facing forward, a unit region 5 is used, positioned at positions Pa to Pc along the x-axis. The laser Ls reflected by the unit region 5 at position Pa corresponds to the pixel at the right end of the image projected onto the retina RE. Position Pb is located between positions Pa and Pc, and the laser Ls reflected by the unit region 5 at position Pb corresponds to the pixel at the center of the image. The laser Ls reflected by the unit region 5 at position Pc corresponds to the pixel at the left end of the image.

[0108] Specifically, in unit region 5 located at position Pa, laser Ls is incident at an angle of incidence θi of 30°, and is reflected at a reflection angle θr of 5°, exiting as reflected light Lr. In unit region 5 located at position Pb, laser Ls is incident at an angle of incidence θi of 40°, and is reflected at a reflection angle θr of -5°, exiting as reflected light Lr. In unit region 5 located at position Pc, laser Ls is incident at an angle of incidence θi of 50°, and is reflected at a reflection angle θr of -10°, exiting as reflected light Lr.

[0109] Figure 6 This is a graph representing the phase change of the reflected light Lr at a position along the x-axis of the metasurface reflector 1. For example... Figure 6As shown, along the x-axis, the width of the metal element 18 increases from width W1 to width W2. The phase change at each position of the metal element 18 along the x-axis is substantially the same as the phase change caused by a square metal body (shown by dashed lines) with sides of the same length as the width at that position when viewed from above. The larger the area of ​​the square metal body when viewed from above, the greater the phase change (phase delay) at that position. Thus, the laser Ls is reflected with different phase changes depending on the position along the x-axis, and a wavefront is formed through interference between the reflected light. That is, a plane wave is generated that propagates along the direction determined by the relationship between the position and the phase change along the x-axis. The reflection angle varies depending on the length (pattern length) of the metal element 18 along the x-axis.

[0110] Figure 4 The length Lx of each unit region 5 shown is determined by the wavelength λ of the reflecting object and the incident angle θi and reflection angle θr corresponding to the position where the unit region 5 is located. The length L of the metal unit 18 in the x-axis direction is the same as or slightly shorter than the length Lx of the unit region 5 in the x-axis direction. Therefore, the length L of the metal unit 18 in the x-axis direction is determined by the wavelength λ of the reflecting object and the incident angle θi and reflection angle θr corresponding to the position where the unit region 5 of the metal unit 18 is located.

[0111] In this embodiment, the lengths Lx of the unit regions 5 contained in the same arrangement in the x-axis direction are different from each other, and the lengths L of the metal units 18 contained in the same arrangement in the x-axis direction are also different from each other in the x-axis direction.

[0112] Furthermore, the length Ly of each unit region 5 is a predetermined fixed value. The length Ly is slightly larger than the width W2. The length Ly can be the length obtained by adding the resolution of the exposure apparatus used to form the metal unit 18 (e.g., 100 nm) to the width W2, for example, set to 600 nm. The widths W1 and W2 of each metal unit 18 are predetermined fixed values. As described above, the width W1 is set to be near the resolution of the exposure apparatus used to form the metal unit 18 (e.g., 100 nm). The width W2 is set to a length (e.g., 350 nm) that can obtain a phase difference of substantially 360° (2π radians) based on the phase of the reflected light Lr at the width W1.

[0113] Figure 7 This diagram illustrates a mirror based on a metal unit 18, which is a nanostructure. The length of the multiple metal units 18 arranged along the x-axis changes according to their position in the x-axis direction. For example, even through... Figure 5The movable mirror 62 is used to change the position of the incident laser Ls along the x-axis, and the reflected light Lr will also converge. In this way, the pattern that changes the length (metal unit length) of the metal unit 18 in the longitudinal direction can be integrated to form multiple reflection angles across the positive and negative directions.

[0114] Figure 8 (a) represents the relationship between the reflection angle and the incident angle when the metal unit length is 500 nm. Figure 8 (b) represents the relationship between the reflection angle and the incident angle when the metal unit length is 750 nm. Figure 8 (c) represents the relationship between the reflection angle and the incident angle when the metal unit length is 1400 nm. From Figure 8 From (a), it can be seen that when the laser Ls is incident on... Figure 7 In the case of the right end of the reflector, if the metal element length is 500 nm, the incident angle is 47° and the reflection angle is -20°. From Figure 8 From (b), it can be seen that when the laser Ls is incident on... Figure 7 In the case of the center of the reflector, if the length of the metal element is 750 nm, the angle of incidence is 45° and the angle of reflection is 0°. From Figure 8 From (c), it can be seen that when the laser Ls is incident on... Figure 7 In the case of the left end of the reflector, if the metal element length is 1400 nm, the incident angle is 44° and the reflection angle is +20°. Thus, with multiple metal elements arranged in a manner where the metal element length varies along the x-axis... Figure 7 In the mirror, reflected light generated at positive and negative angles is converged. Figure 5 In the retinal scanning display 100 shown, laser Ls can also be incident obliquely onto the metasurface reflector 1, and the reflected light Lr can be focused on the pupil PP on the front.

[0115] (The effects of corrosion on nanostructures)

[0116] Figure 9 This diagram illustrates the deterioration of the trapezoidal metal unit 18 over time. It shows the state where the trapezoidal metal unit 18, due to accelerated corrosion over the years, shrinks in area from its original trapezoidal shape to metal unit 18'. If the shape of the metal unit 18 changes from its original trapezoidal shape due to deterioration over time, the reflection angle will deviate, or the intensity of the reflected light will decrease.

[0117] Figure 10This is a graph showing the change in the reflection angle relative to the length of the trapezoidal metal unit 18 under conditions of annual degradation. The solid line represents the theoretical curve of metal unit length versus reflection angle. As the shape of the trapezoidal metal unit 18 changes due to annual degradation, the metal unit length versus reflection angle relationship shifts, for example, from the solid line to the dashed line above or below, or varies between the dashed lines above and below.

[0118] The metasurface reflector 1 of this embodiment, by including Zn or Sn in Ag within the nanostructure 11, can suppress the sulfidation of the first metal layer 10 itself, which is the nanostructure 11, thereby achieving high process resistance. Furthermore, since the process protection layer 8 also includes a side layer that covers the first metal layer 10 internally, corrosion damage to the outermost first metal layer 10 can be avoided when removing the resist pattern using organic solvents. Therefore, degradation of reflective properties is less likely to occur.

[0119] (Manufacturing process)

[0120] The metasurface reflector 1 is obtained by sequentially fabricating a second metal layer 30, a dielectric layer 20, a first metal layer 10, and a process protection layer 8 on a substrate 40 using methods such as sputtering and photolithography. The substrate 40 can be a sapphire substrate, a flexible sheet, or a quartz substrate, etc.

[0121] Specifically, a second metal layer 30 is formed on a substrate 40 by vacuum deposition, for example, using methods such as DC (Direct Current) sputtering. In forming the second metal layer 30, a metallic material is used, consisting of any metal selected from the group consisting of Au, Cu, Ag, Ir, Ru, Rh, Ti, Ta, W, Co, Fe, and Ni, or a metallic alloy containing at least one element selected from the above group. The second metal layer 30 is formed, for example, with a film thickness of 1 nm to 1000 nm. When silver is used as the metallic material, the film thickness of the second metal layer 30 is, for example, 200 nm.

[0122] Next, a dielectric layer 20 is formed on the second metal layer 30. Specifically, the dielectric layer 20 is formed by vacuum deposition using methods such as RF (Radio Frequency) sputtering. The dielectric layer 20 is formed using dielectric materials such as silicon dioxide (SiO2), titanium dioxide (TiO2), magnesium oxide (MgO), or aluminum oxide (Al2O3), which can be formed using semiconductor processes. The dielectric layer 20 is formed with a film thickness of, for example, 1 nm to 1000 nm. When silicon dioxide is used as the dielectric material, the film thickness of the dielectric layer 20 is, for example, 40 nm.

[0123] Next, a metal layer (hereinafter referred to as the "outermost metal layer") that forms the basis of the first metal layer 10 is formed on the dielectric layer 20. The outermost metal layer may be, for example, a multilayer structure of Ag and Zn layers, and is formed by sputtering or other methods in the same manner as the second metal layer 30. The outermost metal layer is formed, for example, with a film thickness of 1 nm to 1000 nm. The film thickness of the outermost metal layer is, for example, 40 nm.

[0124] Next, a first metal layer 10 (multiple nanostructures 11) is formed using photolithography and etching processes. Specifically, a liquid resist is applied to the outermost metal layer using a spin coater or similar equipment, and the applied liquid resist is dried to form a resist film (photoresist). Then, a pattern corresponding to the nanostructures 11 is transferred onto the resist film using an exposure apparatus such as a KrF exposure machine or an electron beam lithography device. Then, the pattern transferred onto the resist film is developed using a developing machine. Then, the portions of the outermost metal layer not covered by the pattern are removed by ion polishing, and then the resist film is removed. Thus, the first metal layer 10 is formed. The widths W1 and W2 and the length L of each metal unit 18 are, for example, 10 nm to 1000 nm.

[0125] Next, a process protection layer 8 is formed by sputtering or other methods, including covering the first metal layer 10 on its sides. At this time, the portions where the process protection layer 8 will not be formed are pre-masked. In summary, a metasurface reflector 1 is formed.

[0126] The metasurface reflector 1 can also be formed directly on the lens of eyeglasses or a translucent mirror instead of on the substrate 40, depending on the application. The formation method is the same as that for forming the metasurface reflector 1 on the substrate 40.

[0127] <Second Implementation Method>

[0128] Next, the second embodiment of this application will be described. Figure 11 This is a cross-sectional view showing the structure of the metasurface reflector 2 according to the second embodiment of this application. The structure of the first metal layer 10 in the second embodiment differs from that in the first embodiment. Other structures are the same as in the first embodiment, and the same reference numerals are used to label the same structural elements, with appropriate omissions in description.

[0129] The first metal layer 10 constituting the nanostructure 11 is an alloy structure of Ag and Zn or an alloy structure of Ag and Sn.

[0130] In the case of an Ag-Zn alloy structure, it is preferable that the amount of Zn added to Ag is 3 at%. In the case of an Ag-Sn alloy structure, it is preferable that the amount of Sn added to Ag is 3 at.

[0131] As mentioned above, although alloying Ag with Zn and Sn reduces the initial reflectivity, it can suppress sulfidation and corrosion-induced reflectivity degradation compared to pure Ag. If the Zn or Sn content is gradually increased from pure Ag, the reflectivity degradation is minimized at a content of approximately 3 at%.

[0132] Furthermore, the principle of light reflection based on the metasurface reflector 2 is that the nanostructure 11 and the second metal layer 30 resonate through the dielectric layer 20, thereby enhancing reflection. Although there is a decrease in initial reflectivity, the layer that undergoes structural modification as a corrosion countermeasure is only the first metal layer 10. Considering the resonance principle of the metasurface reflector 2, the impact of the degradation of reflection intensity caused by alloying can be considered minimal.

[0133] By making the first metal layer 10 constituting the nanostructure 11 an alloy structure of Ag and Zn or an alloy structure of Ag and Sn, the sulfidation of the nanostructure 11 itself can be suppressed, resulting in high process resistance. Therefore, the deterioration of reflective properties is less likely to occur.

[0134] [Third Implementation Method]

[0135] Next, the third embodiment of this application will be described. Figure 12 This is a cross-sectional view showing the structure of the metasurface reflector 3 according to the third embodiment of the present invention. The structure of the first metal layer 10 in the third embodiment differs from that in the first embodiment. Other structures are the same as in the first embodiment, and the same reference numerals are used to label the same structural elements, with appropriate omissions in description.

[0136] The first metal layer 10 constituting the nanostructure 11 is a multilayer structure of Ag-Zn alloy layer 15 and Zn layer 13, or a multilayer structure of Ag-Sn alloy layer and Sn layer.

[0137] By making the first metal layer 10 constituting the nanostructure 11 a multilayer structure of Ag-Zn alloy layer and Zn layer or Ag-Sn alloy layer and Sn layer, the sulfidation of the nanostructure 11 itself can be further suppressed, resulting in higher process resistance. Therefore, the deterioration of reflective properties is less likely to occur.

[0138] [Application Example]

[0139] The metasurface reflectors 1, 2, and 3 of the embodiments of this application can be applied, for example, to a retinal projection device 60 and a retinal scanning display (near-eye wearable device) 100 equipped with a retinal projection device 60.

[0140] Figure 5The retinal scanning display 100 shown is a device that superimposes an image onto the real-world field of view. The retinal scanning display 100 can be, for example, a head-mounted device (head-mounted device); in this example, it is an eyeglass-type device, but it can also take the form of goggles, hats, helmets, etc. Examples of retinal scanning displays 100 include smart glasses such as AR glasses and Mixed Reality (MR) glasses. Figure 5 The retinal scanning display 100 includes an eyeglass frame 50, a lens 51 mounted on the frame 52, and a retinal projection device 60 mounted on the temple 53.

[0141] Figure 5 The retinal projection device 60 shown is a device for directly projecting (drawing) images onto the retina (RE) of a user wearing a retinal scanning display 100. The retinal projection device 60 is mounted on the retinal scanning display 100. The retinal projection device 60 includes a light source unit 61, a movable mirror 62, and a metasurface reflector 1, 2, or 3.

[0142] The light source unit 61 emits laser light of a color and intensity corresponding to the pixels of the image projected onto the retina RE. For example, a panchromatic laser module can be used as the light source unit 61. The light source unit 61 includes, for example, a red laser diode, a green laser diode, a blue laser diode, a near-infrared laser diode, and a combiner that combines the laser light emitted from each laser diode into a single laser beam. The light source unit 61 emits the combined laser beam.

[0143] The movable mirror 62 is a component used for laser-based scanning (Ls).

[0144] Metasurface reflectors 1, 2, and 3 are components that reflect laser light Ls transmitted through movable mirror 62 and illuminate the reflected light Lr onto the retina RE of a user wearing a retinal scanning display 100, thereby projecting an image onto the retina RE. Metasurface reflectors 1, 2, and 3 do not display images.

[0145] Furthermore, the metasurface reflector of this application is not limited to the above-described embodiments.

[0146] In the above embodiments, when the nanostructure 11 is a multilayer structure consisting of an Ag layer and a Zn layer or a Sn layer, the Zn layer or Sn layer is set to two layers. However, as long as the desired film thickness can be achieved, it can also be one or three layers, for example. The film thickness of the Zn layer or Sn layer is determined, for example, by making the content of the Zn layer or Sn layer in the entire nanostructure 11 the most suitable value for sulfur resistance, for example, about 3 at%.

[0147] In addition, when the nanostructure 11 is a multilayer structure of Ag-Zn alloy layer and Zn layer or Ag-Sn alloy layer and Sn layer, the thickness of each film of Ag-Zn alloy layer and Zn layer is determined, for example, by making the content of Zn layer or Sn layer in the nanostructure 11 the most suitable value for sulfur resistance, for example, about 3 at%.

[0148] As described above, this application has the advantages of high process tolerance and low susceptibility to deterioration of reflective properties, which is useful for the overall metasurface reflector.

Claims

1. A metasurface reflector comprising a protective layer, a first metal layer constituting a nanostructure, a dielectric layer and a second metal layer, wherein the protective layer covers the first metal layer, the dielectric layer is located between the first metal layer and the second metal layer, and the nanostructure comprises Ag and Zn, or comprises Ag and Sn.

2. The metasurface reflector according to claim 1, wherein, The nanostructure is a multilayer structure of Ag and Zn layers, a multilayer structure of Ag and Sn layers, an alloy structure of Ag and Zn, an alloy structure of Ag and Sn, a multilayer structure of Ag-Zn alloy layer and Zn layer, or a multilayer structure of Ag-Sn alloy layer and Sn layer.

3. The metasurface reflector according to claim 1, wherein, The nanostructure has the following structure: The structure consists of an Ag layer, a 5.4 Å thick Zn layer, an Ag layer, a 5.4 Å thick Zn layer, and an Ag layer, with a total Ag layer thickness of 40 nm. The structure consists of an Ag layer, a 9.4 Å thick Sn layer, an Ag layer, a 9.4 Å thick Sn layer, and an Ag layer, with a total Ag layer thickness of 40 nm. The amount of Zn added to Ag is 3 at% in an alloy structure of Ag and Zn; or The amount of Sn added to Ag is 3 at% of the alloy structure of Ag and Sn.

4. The metasurface reflector according to claim 1, wherein, The nanostructure comprises metallic units that appear trapezoidal when viewed from above.

5. The metasurface reflector according to claim 4, wherein, The length of the metal unit in the longitudinal direction is between 500 nm and 2500 nm. The thickness of the metal unit is between 10 nm and 100 nm. In the trapezoidal shape of the metal unit, among the mutually parallel short and long sides, the length of the short side is 10 nm or more and 200 nm or less, and the length of the long side is greater than the length of the short side and is 100 nm or more and 500 nm or less.

6. The metasurface reflector according to claim 1, wherein, The dielectric layer is composed of at least one compound material selected from SiO2, TiO2, MgO, and Al2O3.

7. The metasurface reflector according to claim 1, wherein, The protective layer covers the upper surface and sides of the first metal layer.

8. The metasurface reflector according to claim 1, wherein, The protective layer is composed of at least one material selected from Au, Ru, Ir, and TiN.

9. A retinal scanning display comprising: an eyeglass frame, lenses mounted on the eyeglass frame, and a retinal projection device mounted on the eyeglass frame. The retinal projection device includes: A light source unit that emits laser light; A movable mirror that scans the laser; and A metasurface reflector that reflects the scanning laser. The metasurface reflector is disposed on the inner surface of the lens and has a protective layer, a first metal layer constituting a nanostructure, a dielectric layer and a second metal layer. The protective layer covers the first metal layer, and the dielectric layer is located between the first metal layer and the second metal layer. The nanostructure contains Ag and Zn, or contains Ag and Sn.

10. A method for manufacturing a metasurface reflector, comprising: A second metal layer, a dielectric layer, and a first metal layer are sequentially formed on the substrate. Nanostructures are formed on the first metal layer by photolithography and etching. A protective layer is formed by covering the upper surface and sides of the nanostructure. The nanostructure contains Ag and Zn, or contains Ag and Sn.

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