Metasurface device and metasurface device preparation method

Abstract

The invention provides a metasurface device of which the double-sided structure can be the same or different, a double-layer metasurface composed of a double-sided nano-column structure in a specific shape is designed, the design freedom degree of each point on the device can be increased by utilizing a double-layer metasurface composed of nano-columns in a specific size, and the length, width, height and rotation direction of the metasurface can be different at each point; the design freedom degree of the double-layer metasurface is further increased, compared with a traditional Powell beam expanding system and a complex surface type, the machining difficulty is increased, the freedom degree brought by the metasurface is avoided, and therefore the double-layer metasurface can achieve the better beam expanding effect by changing the length, width, height and rotation direction of the nanometer size.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a metasurface device and a method for preparing the metasurface device. Background Art

[0002] Laser beam expander is an optical device that can not only expand the diameter of the laser beam, but also reduce the divergence angle of the laser beam. Therefore, it is often used in long-distance lighting or projection, as well as focusing systems. The core component of traditional laser beam expanders is the Powell prism. The Powell lens is similar to a circular prism with a curved top. It is a laser line generator that stretches a narrow laser beam into a straight line with uniform illumination. However, due to its three-dimensional shape, it is difficult to integrate, and it is necessary to find suitable components to replace it in order to achieve the purpose of lightweighting.

[0003] Metasurface is an artificial layered material characterized by a thickness less than the wavelength and composed of subwavelength-sized units. Metasurfaces can manipulate light and electromagnetic waves at a microscopic scale, achieving flexible and effective control of the polarization, amplitude, phase, polarization mode, and propagation mode of electromagnetic waves. The arrangement of these subwavelength units can be precisely designed according to specific application requirements. By changing the geometric shape and spatial arrangement of these units, metasurfaces can control various parameters of the light field. Metasurfaces are arranged according to certain rules to form metasurface arrays.

[0004] At present, metasurfaces have shown potential application value in many fields, especially in optics and micro-nanoscale. They can significantly simplify the design of optical systems and improve the integration of systems. Therefore, metasurfaces can be used to replace Powell prisms in traditional beam expanders to achieve the purpose of integration and lightweight. However, how to design metasurface structures and optimize the preparation process of metasurfaces to achieve the best technical effect has become a technical problem in this field. Summary of the invention

[0005] In order to at least overcome the above-mentioned deficiencies in the prior art, the present application provides a metasurface device and a method for preparing a metasurface device.

[0006] In a first aspect, the present application provides a metasurface device, the metasurface device comprising:

[0007] substrate layer;

[0008] A first super surface layer located on one side of the substrate layer;

[0009] A second super surface layer located on a side of the substrate layer away from the first super surface layer;

[0010] The first super surface layer includes a plurality of first nanostructures distributed in a first shape;

[0011] The second super surface layer includes a plurality of second nanostructures distributed in a second shape;

[0012] The first shape and the second shape are selected from a nanostructure whose sidewall is perpendicular to the substrate layer or a nanostructure whose top cross-section length is shorter than or equal to that of the bottom cross-section length.

[0013] In a possible implementation manner, the first shape and the second shape may be the same or different.

[0014] In a possible implementation manner, the placement angles of the plurality of first nanostructures and the second nanostructures relative to the substrate layer are not completely the same.

[0015] In a possible implementation manner, the nanostructure whose sidewall is perpendicular to the substrate layer is selected from one or more of a rectangular parallelepiped structure and a cylindrical structure.

[0016] In a possible implementation, the nanostructure whose top cross-section length is shorter than or equal to that of the bottom cross-section length is selected from one or more of a trapezoidal structure and a zigzag structure.

[0017] In a possible implementation manner, the first nanostructure and the second nanostructure are cuboids.

[0018] In a possible implementation, the first nanostructure and the second nanostructure are arranged in an array to form a first supersurface layer and a second supersurface layer.

[0019] In a possible implementation manner, the material of the substrate layer is selected from one or more of quartz, silicon wafer, and sapphire.

[0020] Preferably, the material of the substrate layer is quartz.

[0021] In a possible implementation manner, the thickness of the substrate layer is 2 to 5 mm.

[0022] Preferably, the thickness of the substrate layer is 3 mm.

[0023] In a possible implementation manner, the material of the first nanostructure and the second nanostructure is selected from one or more of zinc oxide, silicon dioxide, titanium dioxide, and aluminum oxide.

[0024] Preferably, the material of the first nanostructure and the second nanostructure is titanium dioxide.

[0025] In a possible implementation manner, the height of the first nanostructure and the second nanostructure is 600-900 nm.

[0026] Preferably, the height of the first nanostructure and the second nanostructure is 800 nm.

[0027] In a possible implementation, a spacing between the first nanostructures in the first supersurface layer is 50 to 70 nm.

[0028] In a possible implementation, a spacing between the second nanostructures in the second supersurface layer is 50 to 70 nm.

[0029] In a second aspect, the present application provides a method for preparing a metasurface device as described in the first aspect of the present application, comprising the following steps:

[0030] Step S1: pre-treating the substrate layer;

[0031] Step S2: coating photoresist on the surface of the substrate layer;

[0032] Step S3: making a reverse pattern opposite to the first super surface layer pattern on the imprint template, and aligning the imprint template with the substrate layer coated with photoresist in step S2;

[0033] Step S4: making the reverse pattern on the imprint template contact the photoresist on the substrate layer, and forming a first super surface layer pattern on the surface of the photoresist by using nanoimprint technology;

[0034] Step S5: using atomic layer deposition technology, depositing a first nanostructure on the surface of the photoresist obtained in step S4 to obtain a first metasurface device, wherein the first metasurface device includes a first nanostructure arranged from top to bottom, a photoresist having the same shape as the first nanostructure, and a substrate layer;

[0035] Step S6: removing the photoresist under the first nanostructure in the first metasurface device, and coating the photoresist on the surface of the first nanostructure again;

[0036] Step S7: turning over the first metasurface device, and coating the photoresist again on the side of the substrate layer away from the first nanostructure;

[0037] Step S8: making a reverse pattern opposite to the second super surface layer pattern on the imprint template, and aligning the imprint template with the substrate layer coated with the photoresist;

[0038] Step S9: making the reverse pattern on the imprint template contact the photoresist on the substrate layer, and forming a second super surface layer pattern on the surface of the photoresist by using nanoimprint technology;

[0039] Step S10: using atomic layer deposition technology, depositing a second nanostructure on the surface of the photoresist obtained in step S9 to obtain a second metasurface device, wherein the second metasurface device includes a second nanostructure arranged from top to bottom, a photoresist having the same shape as the second nanostructure, a substrate layer, a first nanostructure, and a photoresist coated on the surface of the first nanostructure;

[0040] Step S11: removing the photoresist under the second nanostructure in the second metasurface device and the photoresist coated on the surface of the first nanostructure to obtain a final metasurface device.

[0041] In a possible implementation, in step S2, step S6, and step S7, the thickness of the applied photoresist is in micrometer order.

[0042] In a possible implementation, in step S3, the material of the imprint template is selected from one of silicon, graphite, and metal.

[0043] In a possible implementation, in step S5, the thickness of the photoresist having the same shape as the first nanostructure is 4-6 nm.

[0044] Preferably, the thickness of the photoresist having the same shape as the first nanostructure is 5 nm.

[0045] In a possible implementation, in steps S5 and S10, the material of the first nanostructure and the second nanostructure is titanium dioxide.

[0046] In one possible implementation, in steps S5 and S10, the parameters of the atomic layer deposition technology are: the atomic layer deposition technology uses a standard dual circulation system of water and TDMAT precursor, the water pulse is 0.2s, the delay is 7s, the TDMAT pulse is 0.4s, the delay is 10s, and the overall standard dual circulation system is maintained at a continuous 20cm 3 The whole process was maintained at 90°C under N2 carrier gas flow rate of 1 / min. The deposition rate of each cycle was ∼0.7 nm.

[0047] In a possible implementation, steps S4 and S9 may be repeated multiple times.

[0048] Preferably, steps S4 and S9 are repeated 1 to 20 times.

[0049] In a possible implementation, in step S6, the method for removing the residual photoresist under the first nanostructure in the first metasurface device is reactive ion etching (RIE), and the method for removing the photoresist when developing the first deposition of TiO2 is solvent (acetone) removal. The method for removing the residual photoresist under the second nanostructure in the second metasurface device is reactive ion etching (RIE), and the method for removing the photoresist when removing the protective photoresist of the first layer of metasurface and developing the second deposition of TiO2 is solvent (acetone) removal.

[0050] Technical advantages of this application:

[0051] 1. The present application prepares a metasurface device whose double-sided structures can be the same or different. By designing a double-sided nanopillar structure of a specific shape, a double-layer metasurface composed of nanopillars of a specific size can increase the design freedom of each point on the device, because its length, width, height and rotation direction can be different at each point, and the double layer further increases its design freedom. Compared with the traditional Powell beam expansion system, the complex surface shape increases the difficulty of processing, and there is no degree of freedom brought by the metasurface. Therefore, the double-layer metasurface can achieve a better beam expansion effect by changing the length, width, height, and rotation direction of the nanometer size;

[0052] 2. The layouts of the two sides of the metasurface device prepared in this application can be different, which effectively increases the design freedom of the metasurface device. The length, width, height and rotation direction of the nanocolumns at each point on the layout can be fine-tuned according to the design requirements of optical density uniformity, stability and linearity, which greatly increases the freedom of the device and has greater application value;

[0053] 3. This application adopts nanoimprint technology, and the production process is simple. By performing graphical preparation of the metasurface, devices can be prepared on a large scale. In actual production, for the preparation of planar beam expansion devices, it can save time, improve efficiency, reduce design costs, and save energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0055] Figure 1 A metasurface device provided in one embodiment of the present application;

[0056] Figure 2A metasurface device provided in one embodiment of the present application;

[0057] Figure 3 A metasurface device provided in one embodiment of the present application;

[0058] Figure 4 A metasurface device provided in one embodiment of the present application;

[0059] Figure 5 The SEM images of the surface of the metasurface device obtained after embossing 1 time, 10 times, and 20 times in one embodiment of the present application;

[0060] Figure 6 A method for preparing a metasurface device provided in one embodiment of the present application;

[0061] Figure 7 A scan diagram of a supersurface unit structure provided in one embodiment of the present application;

[0062] Figure 8 A metasurface angle-dependent phase diagram provided in one embodiment of the present application;

[0063] Fig. 9 A diagram of the angle-dependent transmission efficiency of a metasurface provided in one embodiment of the present application;

[0064] Fig.10 A spatial intensity distribution diagram of laser beam expansion before incident provided in one embodiment of the present application;

[0065] Fig.11 This is a diagram showing the intensity distribution of the central focus line of the laser beam expansion provided in one embodiment of the present application along the x-direction.

[0066] Among them, 1-substrate layer; 2-first super surface layer; 21-first nanostructure; 3-second super surface layer; 31-second nanostructure. DETAILED DESCRIPTION

[0067] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0068] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0069] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0070] In the description of this application, it should be noted that the terms "upper", "lower", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the application is usually placed when in use, which is only for the convenience of describing this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0071] In addition, the terms "horizontal", "vertical", "overhanging" and the like do not mean that the components are required to be absolutely horizontal or overhanging, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0072] In the description of this application, it should also be noted that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0073] It should be noted that, in the absence of conflict, different features in the embodiments of the present application may be combined with each other.

[0074] See also Figure 1 , Figure 1 A metasurface device is provided in one embodiment of the present application, and the metasurface device includes:

[0075] Substrate layer 1;

[0076] In this embodiment, the material of the substrate layer 1 has a variety of options, and illustratively, silicon, quartz, polymer or engineering plastic can be used, and the selection is made according to the actual working conditions; the thickness, size and shape of the substrate layer 1 can also be adjusted according to the actual situation to adapt to different application scenarios;

[0077] A first super surface layer 2 located on one side of the substrate layer 1;

[0078] A second super surface layer 3 located on a side of the substrate layer 1 away from the first super surface layer 2;

[0079] In this embodiment, the substrate layer 1 mainly plays a supporting role, supporting the first super surface layer 2 and the second super surface layer 3, and the first super surface layer 2 and the second super surface layer 3 form a structure arranged oppositely;

[0080] The first super surface layer 2 includes a plurality of first nanostructures 21 distributed in a first shape;

[0081] The second super surface layer 3 includes a plurality of second nanostructures 31 distributed in a second shape;

[0082] The first supersurface layer 2 and the second supersurface layer 3 described in this embodiment are surface layers with a thickness less than the wavelength and a sub-wavelength microstructure, and are composed of a number of nano-pillars. The supersurface can realize the regulation of the light beam.

[0083] In this embodiment, the first super surface layer 2 is composed of a plurality of first nanostructures 21 having a first shape. Here, the first shape and the second shape in the first super surface layer 2 and the second super surface layer 3 can be the same shape. For example, see Figure 1 , the first shape and the second shape are both rectangular; different shapes can also be selected, for example, see Figure 2 , the first shape in the first supersurface layer 2 and the second shape in the second supersurface are selected from cylindrical and rectangular.

[0084] Therefore, the shapes of the plurality of first nanostructures 21 may be the same or different; the first supersurface layer 2 is composed of a plurality of first nanostructures 21 having a first shape, and the shape of the first nanostructure 21 corresponds to the first shape, specifically, if the first shape is a rectangle, the first nanostructure 21 is a rectangular column; if the first shape is a cylinder, the first nanostructure 21 is a cylinder; if the first shape is a triangle, the first nanostructure 21 is a pyramid; if the first shape is a trapezoid, the first nanostructure 21 is a trapezoidal column; if the first shape is a cylinder and a rectangle, the first nanostructure 21 includes a cylinder and a cuboid. The relationship between the second nanostructure 31 and the second shape is similar.

[0085] It should be explained that the first shape and the second shape are the cross-sectional shapes of the first nanostructure 21 and the second nanostructure 31 , but since the cross-sections of the rectangular column and the cylindrical shape are both rectangular, they are distinguished in terms of expression.

[0086] The shapes of the first nanostructures 21 and the second nanostructures 31 can be the same or different; the shapes of the first nanostructure 21 and the second nanostructure 31 can be the same or different. This flexibility in the design structure provides more design freedom. The first shape and the second shape can be designed according to actual control needs, and then the first nanostructure 21 and the second nanostructure 31 can be determined. In actual working conditions, the technical effect can be achieved by processing different imprint templates. The shape and arrangement of the first nanostructure 21 and the second nanostructure 31 can be designed according to actual needs to achieve specific functions, such as light absorption, reflection, refraction, polarization, etc., to achieve better technical effects.

[0087] The metasurface device provided in the present application is different from the traditional Powell prism. The top of the traditional Powell prism is a complex two-dimensional aspherical surface, so it has a higher processing cost, a large volume, and a long effective distance. The metasurface device provided in the present application has a higher degree of freedom in light field control. Considering that the double-layer metasurface can be processed, its degree of freedom is further increased. The nanoimprint processing method reduces the processing cost.

[0088] In one embodiment, see Figure 4 The first nanostructure 21 and the second nanostructure 31 are completely identical structures, both of which are cuboid nanocolumns. At this time, only one nanoimprint template is used to achieve the purpose of preparing a double-sided pattern, and the preparation process is simple.

[0089] The first shape and the second shape are selected from nanostructures whose sidewalls are perpendicular to the substrate layer 1;

[0090] and / or,

[0091] A nanostructure whose top cross-sectional length is shorter than or equal to the bottom cross-sectional length.

[0092] In one embodiment, the sidewalls of the nanostructures are perpendicular to the substrate layer 1, that is, the outer sidewalls of the nanostructures are perpendicular to the surface of the substrate layer 1. For example, the nanostructures can be selected from one or more of a cube, a cylinder, and a cuboid. The design of this vertical structure can ensure the optical stability and consistency of the nanostructure, because the vertical sidewalls allow the nanostructures to form an ordered array in space, which can more effectively regulate the parameters of light. In addition, the vertical sidewalls also help to increase the surface area of ​​the nanostructure, which may enhance the interaction with light and improve the regulation effect of the device.

[0093] In one embodiment, the nanostructure whose top cross section length is shorter than or equal to the bottom cross section length is a geometric feature similar to a "cone" or "pyramid", wherein the size of the top is smaller than the size of the bottom. Exemplarily, the nanostructure can be selected from one or more of a pyramid, a cone, a tetrahedron, and a trapezoidal column. The design of this shape can make the nanostructure produce a special resonance effect during the propagation of light. When light interacts with a nanostructure of this shape, due to multiple reflections and refractions of the structure, specific regulation of the light is achieved.

[0094] It should be noted that in one embodiment of the present application, the two shapes are not mutually exclusive, the first shape and the second shape can include both of the above shapes, and can be combined and optimized according to actual needs. In one super surface layer, nanostructures with different shapes can coexist to achieve more complex functions and performances. In addition, the above two shapes also have the technical advantage of easy demoulding.

[0095] In one embodiment, the first shape and the second shape may be the same or different. Due to the reasons explained above, the first shape and the second shape are designed according to actual control needs.

[0096] In one embodiment, the placement angles of the plurality of first nanostructures 21 and second nanostructures 31 relative to the substrate layer 1 are not completely the same. Specifically, each first nanostructure 21 and second nanostructure 31 has a different rotation angle on the substrate layer 1, and the substrate layer 1 is taken as the x-axis, and the placement angle, i.e., the angle between the cross section of the nanocolumn and the x-axis, ranges from 0° to 90°.

[0097] Exemplarily, the placement angle can be 0° (i.e. parallel to the midline of the substrate layer 1), 30°, 60°, 90° (i.e. perpendicular to the midline of the substrate layer 1). It should be noted that, in one embodiment of the present application, the first nanostructure 21 and the second nanostructure 31 are not neatly arranged on the substrate layer 1, but present a diversified distribution state. Nanostructures at different placement angles have different optical properties, which can better regulate the effect of the metasurface; on the other hand, the placement angle of the nanostructure can also be adjusted to regulate the scattering path of the light, thereby achieving regulation of the light path.

[0098] In one embodiment, the nanostructures whose sidewalls are perpendicular to the substrate layer 1 are selected from one or more of a rectangular parallelepiped structure and a cylindrical structure. The rectangular parallelepiped structure and the cylindrical structure are very stable structural forms, which enable them to maintain good shape and stability at the nanoscale, thereby ensuring the stability of the overall supersurface structure. In addition, the volumes occupied by these two shapes in space are relatively regular, and the space utilization rate is high. More nanostructures can be arranged on a supersurface of a specific size. In addition, the nanoimprint templates of these two shapes are relatively simple to manufacture, which reduces the manufacturing cost.

[0099] In one embodiment, the nanostructure with a top cross-section length shorter than or equal to a bottom cross-section length is selected from one or more of a ladder column structure and a pyramid structure. Nanoimprint templates of these two shapes are relatively simple to manufacture, which reduces the manufacturing cost.

[0100] Preferably, the first nanostructure 21 and the second nanostructure 31 are cuboids. The cuboid-shaped nanostructures can be arranged most compactly and provide the most nanostructures.

[0101] In one embodiment, the first nanostructure 21 and the second nanostructure 31 are arranged in an array to form a first supersurface layer 2 and a second supersurface layer 3. Exemplarily, the array arrangement includes a circular array arrangement, a hexagonal array, a rectangular array, and a grid array. The array arrangement can maximize the space utilization of the supersurface.

[0102] In one embodiment, the material of the substrate layer 1 is selected from one or more of quartz, silicon wafer, and sapphire. These three materials have high hardness, high infrared, ultraviolet and visible light transmittance, mature processing technology and low cost.

[0103] Specifically, the material of the substrate layer 1 is quartz.

[0104] In one embodiment, the thickness of the substrate layer 1 is 2-5 mm, and illustratively, 2, 3, 4, or 5 mm can be selected.

[0105] Preferably, the thickness of the substrate layer 1 is 3 mm.

[0106] In a possible implementation, the material of the first nanostructure 21 and the second nanostructure 31 is selected from one or more of zinc oxide, silicon dioxide, titanium dioxide, and aluminum oxide. The above materials have stable chemical properties and excellent photoelectric properties and are often used in various optoelectronic devices.

[0107] Preferably, the material of the first nanostructure 21 and the second nanostructure 31 is titanium dioxide. The preparation process of the titanium dioxide deposition layer is mature and is easy to promote in industrial application.

[0108] In one embodiment, the height of the first nanostructure 21 and the second nanostructure 31 is 600-900 nm.

[0109] Preferably, the height of the first nanostructure 21 and the second nanostructure 31 is 800 nm.

[0110] In one embodiment, the spacing between the first nanostructures 21 in the first supersurface layer 2 is 50-100 nm.

[0111] In one embodiment, the spacing between the second nanostructures 31 in the second super surface layer 3 is 50-100 nm. In this embodiment, since the template and the photoresist need to be well demolded in the nanoimprinting step to ensure the accuracy of the shape after nanoimprinting, the nanostructures need to have a certain spacing, for example, 50, 55, 60, 65, 70 nm can be selected.

[0112] In a second aspect, the present application provides a method for preparing a metasurface device as described in the first aspect of the present application, comprising the following steps:

[0113] Step S1: pre-treat the substrate layer 1. The pre-treatment can achieve the purpose of cleaning the substrate layer 1 and increasing the adhesion between the substrate layer 1 and the photoresist. The pre-treatment may include four steps: 1. Cleaning to remove pollutants on the substrate surface, which may be removed by an organic solvent or deionized water; 2. Drying, which may be done by hot air, vacuum drying, inert gas purging, etc.; 3. Pre-baking. This step is not a necessary step. The substrate may be pre-baked to a certain temperature (such as 100-200°C), which helps to enhance the adhesion between the photoresist and the substrate; pre-baking may be done by heating on a hot plate or using an oven; 4. Adhesion enhancement treatment. For hydrophilic substrates, an adhesion enhancer is required to increase the adhesion between the substrate and the photoresist. The adhesion enhancer will form a thin film on the substrate to enhance the adhesion between the photoresist and the substrate.

[0114] Exemplarily, the pretreatment method used in this embodiment is: a 3 mm thick quartz substrate is cleaned with acetone, alcohol, and deionized water respectively, and then the substrate is blown dry with nitrogen to obtain a pretreated substrate layer 1;

[0115] Step S2: coating photoresist on the surface of substrate layer 1;

[0116] In this step, the photoresist coated on the substrate layer 1 is the base layer of the subsequent step. Exemplarily, the coating method can be a spin coating method, a polishing method, a spray coating method, or a dip coating method. Different coating methods are suitable for different process requirements. The thickness of the photoresist coating can be controlled at the micron level, and the photoresist is controlled to form a uniform and flat film on the substrate surface. In one embodiment of the present application, the coating method is a spin coating method;

[0117] Step S3: making a reverse pattern opposite to the pattern of the first super surface layer 2 on the imprint template, and aligning the imprint template with the substrate layer 1 coated with the photoresist in step S2;

[0118] The imprint template described in this embodiment is a template with a reverse pattern prepared in advance according to the target pattern, that is, a template that is exactly complementary to the first nanostructure 21; when the imprint template contacts the photoresist for imprinting, the pattern of the first nanostructure 21 can be left on the photoresist.

[0119] The preparation of imprint templates is a mature existing technology. Common template materials include glass sheets, silicon sheets, graphite sheets, etc. For example, the template material used in this embodiment is a silicon sheet. There are many methods for processing imprint templates, for example, electron beam etching, laser beam exposure, indirect writing method, etc. In this embodiment, it is necessary to determine the imprint pattern first, and then prepare the template;

[0120] Step S4: making the reverse pattern on the imprint template contact the photoresist on the substrate layer 1, and using nanoimprint technology to form a first super surface layer 2 pattern on the surface of the photoresist;

[0121] In this embodiment, the imprint template has a reverse first super surface layer 2 pattern. After the imprint template contacts the photoresist, by applying appropriate pressure, the surface of the photoresist gradually forms a first super surface layer 2 pattern consistent with the reverse pattern on the template, and the imprint process is repeatedly applied to squeeze the excess photoresist out of the nano template. Finally, after nanoimprinting, the thickness of the photoresist base glue is controlled to be about 5nm. The thickness of the photoresist should not be too thick because the photoresist needs to be removed later.

[0122] Step S5: using atomic layer deposition technology, depositing a first nanostructure 21 on the surface of the photoresist obtained in step S4 to obtain a first supersurface device, wherein the first supersurface device includes the first nanostructure 21 arranged from top to bottom, the photoresist having the same shape as the first nanostructure 21, and a substrate layer 1;

[0123] Atomic layer deposition technology ALD is a mature existing technology that can accurately control the growth of thin film layers at the atomic level. The thickness of the first nanostructure 21 can be effectively controlled by adjusting the deposition temperature, reaction gas concentration, reaction time, and deposition cycle number of ALD. When the first nanostructure 21 is deposited again on the photoresist base having the shape of the first nanostructure 21 formed in step S4, a first nanostructure 21 with the same shape as the first super surface will naturally be formed.

[0124] The type of the first nanostructure 21 is obtained by controlling the type of the ALD reaction gas. Exemplarily, the material of the first nanostructure 21 is selected from one of zinc oxide, silicon dioxide, titanium dioxide, and aluminum oxide.

[0125] After step S5, an incomplete metasurface device is preliminarily obtained, including a first nanostructure 21 arranged from top to bottom, wherein the first nanostructure 21 is formed through an ALD process; a photoresist having the same shape as the first nanostructure 21, i.e., the photoresist obtained after nanoimprinting in step S4; and a substrate layer 1, which plays a supporting role.

[0126] Step S6: removing the photoresist under the first nanostructure 21 in the first metasurface device, and coating the photoresist on the surface of the first nanostructure 21 again;

[0127] In this embodiment, the technical solutions for removing the photoresist include wet degumming, such as organic solvent degumming, and the organic solvent that can be used is acetone; inorganic solvent degumming, such as using strong acid and strong oxidant; dry degumming can also be used, such as reactive ion etching RIE (Reactive Ion Etch) technology. For example, RIE technology is used in this embodiment, which has a better degumming effect. The choice of degumming depends on whether all the glue is to be removed. The role of RIE is to remove the residual glue, while solvent degumming will remove all the glue.

[0128] In this embodiment, the RIE technology is first used to remove the photoresist under the first nanostructure 21 in the first metasurface device. At this time, the metasurface device only includes the first nanostructure 21 and the substrate layer 1. The photoresist is coated on the surface of the first nanostructure 21 again. The coating method of the photoresist is as described in step S2, and the coating thickness is micrometer level. The photoresist coated in this step mainly protects the first nanostructure 21 from being damaged in the subsequent operation process and exists as a protective layer.

[0129] The choice of glue removal depends on whether all the glue needs to be removed. RIE removes residual glue, while solvent removal removes all the glue.

[0130] Step S7: turning over the first metasurface device, and coating the photoresist again on the surface of the substrate layer 1 away from the first nanostructure 21;

[0131] Step S8: making a reverse pattern opposite to the pattern of the second super surface layer 3 on the imprint template, and aligning the imprint template with the substrate layer 1 coated with the photoresist;

[0132] In this embodiment, the pattern of the first supersurface layer 2 and the pattern of the second supersurface layer 3 can be the same or different. When the patterns are the same, the same template can be used; when the patterns are different, different layouts need to be designed and different templates need to be prepared. Different patterns can be prepared by different imprinting templates, which increases the design freedom of the double-layer supersurface and has greater application value.

[0133] Step S9: making the reverse pattern on the imprint template contact the photoresist on the substrate layer 1, and forming a second super surface layer 3 pattern on the surface of the photoresist by using nanoimprint technology;

[0134] Step S10: using atomic layer deposition technology, depositing a second nanostructure 31 on the surface of the photoresist obtained in step S9 to obtain a second metasurface device, wherein the second metasurface device includes the second nanostructure 31 arranged from top to bottom, the photoresist having the same shape as the second nanostructure 31, the substrate layer 1, the first nanostructure 21, and the photoresist coated on the surface of the first nanostructure 21;

[0135] In this embodiment, the technical principles of steps S7 to S10 are the same as those of steps S2 to S5.

[0136] Step S11: remove the photoresist under the second nanostructure 31 in the second metasurface device and the photoresist coated on the surface of the first nanostructure 21 to obtain the final metasurface device. At this time, the composition of the metasurface device is the first nanostructure 21, the substrate layer 1, and the second nanostructure 31 arranged in sequence from top to bottom, that is, the final metasurface device.

[0137] In one embodiment of the present application, in the steps S2, S6, and S7, the thickness of the photoresist applied is in the micrometer range. The function of applying the photoresist in step S6 is to protect the first nanostructure 21 from being damaged, so a certain coating thickness is required; the function of applying the photoresist in steps S2 and S7 is to act as a nanoimprint primer, and in the later nanoimprint process, the excess photoresist will be squeezed out, so a coating thickness in the micrometer range is also required.

[0138] In one embodiment of the present application, in step S3, the material of the imprint template is selected from one of silicon, graphite, and metal. Preferably, the material of the imprint template is silicon, which has a moderate thermal expansion coefficient, which helps to reduce the impact of temperature changes on thermal deformation of the template and substrate, thereby reducing the risk of distortion and distortion of the imprinted pattern, making silicon have significant advantages when used as a high-precision photolithography imprint template. In addition, silicon materials have high hardness and tensile strength, good chemical stability, and low production costs.

[0139] In one embodiment of the present application, in step S5, the thickness of the photoresist having the same shape as the first nanostructure 21 is 4 to 6 nm. Preferably, the thickness of the photoresist having the same shape as the first nanostructure 21 is 5 nm. That is, in the first metasurface device, the thickness of the photoresist is 4 to 6 nm, and illustratively, it can be 4, 5, or 6 mm. The thickness of the photoresist should not be too thick, because the photoresist needs to be removed later; nor should it be too thin, because the photoresist is too thin and cannot support the deposition of subsequent surface nanostructures.

[0140] In one embodiment of the present application, in the steps S5 and S10, the material of the first nanostructure 21 and the second nanostructure 31 is titanium dioxide, that is, the material of the nanostructure deposited by ALD is titanium dioxide nanostructure, and the preparation of titanium dioxide thin film by ALD method is a mature technology with clear preparation process and preparation parameters. Titanium dioxide has a high refractive index, which can reach 2.6678 (532nm) in visible light, so it has a high application value in visible light.

[0141] In one embodiment of the present application, in steps S5 and S10, the parameters of the atomic layer deposition technology are: the atomic layer deposition technology uses a standard dual circulation system of water and TDMAT precursor, the water pulse is 0.2s, the delay is 7s, the TDMAT pulse is 0.4s, the delay is 10s, and the overall standard dual circulation system is maintained at a continuous 20cm 3 The whole process was maintained at 90° C. under N2 carrier gas with a flow rate of / min. The deposition rate of each cycle was ~0.7nm, and the height of the prepared titanium dioxide supersurface was about 800nm.

[0142] In one embodiment of the present application, the steps S4 and S9 can be repeated multiple times, that is, the number of nanoimprinting can be multiple times, see Figure 5 , respectively describe the SEM images of the surface of the metasurface device finally obtained after 1, 10, and 20 times of imprinting. The reason for repeating the nanoimprinting step in this embodiment is that nanoimprinting technology is a high-precision manufacturing technology, which has very high requirements for the accuracy and consistency of the pattern. A single imprinting may not be able to achieve the ideal accuracy and consistency. Therefore, through multiple imprinting, the pattern can be gradually corrected and optimized to improve the imprinting accuracy. Specifically, the steps S4 and S9 are repeated 1 to 20 times. Exemplarily, it can be 1 time, 5 times, 10 times, and 20 times. Through multiple imprinting, large-area processing can be achieved. Examples of processing effects are shown below. Figure 5 shown. Specific embodiments

[0144] See also Figure 6 , Figure 6An exemplary method for preparing a metasurface device in the present application is given. A quartz substrate layer of suitable size is prepared, and the quartz substrate layer is cleaned, and a layer of photoresist with a thickness of micrometers is spin-coated on the surface of the quartz substrate layer by spin coating. A silicon template with a pre-designed imprint pattern is prepared. In this embodiment, one side of the designed pattern is a regularly arranged rectangular parallelepiped structure. The nanoimprint plate is contacted with the photoresist, and a pattern that is exactly complementary to the silicon template used is prepared by ultraviolet nanoimprint technology, that is, the shape of the imprinted photoresist is a regularly arranged rectangular parallelepiped. The imprinting is repeated 5 times, and finally the thickness of the imprinted photoresist is controlled within 5nm. The excess primer is removed by RIE method to obtain a metasurface device structure with rectangular parallelepiped photoresist on the quartz substrate.

[0145] After the imprinting was completed, the titanium dioxide deposition layer was deposited on the photoresist structure by ALD method. The deposition parameters were as follows: a standard double circulation system of water and TDMAT precursor was used, with a water pulse of 0.2s and a delay of 7s, a TDMAT pulse of 0.4s and a delay of 10s, and the overall standard double circulation system was maintained at a continuous 20cm 3 The whole process was maintained at 90° C. under N2 carrier gas with a flow rate of 1 / min. The deposition rate of each cycle was 0.7 nm, and the thickness of the deposited titanium dioxide layer was 800 nm.

[0146] The structure obtained above is peeled off, and acetone is used to remove the photoresist under the titanium dioxide deposition layer to obtain a structure with the titanium dioxide deposition layer directly attached to the quartz substrate layer. Spin coating is performed again to coat micrometer-level photoresist on the titanium dioxide layer as a protective layer.

[0147] The whole device is turned over, and the steps in the above embodiment are repeated. A layer of photoresist with a thickness of micrometers is spin-coated on the other side of the substrate again, and a silicon template with a pre-designed embossing pattern is prepared. In this embodiment, please refer to Figure 6 The other side of the designed pattern is an irregularly arranged rectangular structure. The nanoimprint plate is brought into contact with the photoresist, and the ultraviolet nanoimprint technology is used to prepare a pattern that is exactly complementary to the silicon template used, that is, the shape of the imprinted photoresist is irregularly arranged rectangular blocks. The imprinting is repeated 5 times, and the excess primer is removed by RIE method. Finally, the thickness of the imprinted photoresist is controlled within 5nm, and a metasurface device structure is obtained in which one side of the quartz substrate is a regular titanium dioxide layer coated with a photoresist protective layer, and the other side has an irregular rectangular photoresist.

[0148] A titanium dioxide deposition layer was again deposited on the irregular rectangular photoresist surface by the ALD method, and the deposition parameters were as described in the above embodiment. The thickness of the deposited titanium dioxide deposition layer was 800 nm. Acetone was used to remove the photoresist under the titanium dioxide deposition layer and the photoresist protective layer on the other side to obtain a metasurface device. The unit period of the obtained metasurface device was 320 nm, and the height of the nanostructure was 800 nm.

[0149] The obtained metasurface device was characterized.

[0150] See also Figure 7 to Figure 9 , respectively, are the metasurface unit structure scanning diagram, metasurface angle-dependent phase diagram, and metasurface angle-dependent transmission efficiency diagram; Figure 7 The relationship between the transmittance, phase and diameter of the unit structure is shown. The blue line is the efficiency of the device at different radii. The transmission efficiency is greater than 90% when the unit diameter is between 50 nanometers and 250 nanometers. The red line is the phase of the device at different radii. When the unit diameter changes from 50 nanometers to 300 nanometers, the phase change covers 2π. Figure 8 The metasurface angle-dependent phase diagram is shown, and the phase control from 0 to 2π can be achieved when the unit diameter ranges from 50 nanometers to 300 nanometers and the incident angle ranges from -30° to 30°. Fig. 9 The results show that the transmission efficiency is greater than 90% when the unit diameter ranges from 50 nanometers to 230 nanometers and the incident angle ranges from -30° to 30°, proving that the selected meta-atoms with a diameter of 50 nanometers to 230 nanometers can achieve phase and amplitude regulation.

[0151] Then, laser was used to irradiate from the top to test the beam expansion capability of the metasurface device. Fig.10 This is the spatial intensity distribution diagram of the beam expansion before laser incidence (the display screen is 15 mm away from the metasurface); Fig.11 This is the intensity distribution diagram of the center focus line of the laser beam expansion along the x-direction (the display screen is 15 mm away from the metasurface).

[0152] In summary, the present application provides a metasurface device whose double-sided structures can be the same or different. By designing a double-sided nanocolumn structure of a specific shape, a better beam expansion effect can be achieved. Since the layouts of the two sides of the metasurface device prepared in the application can be different, the design freedom of the metasurface device is effectively increased. The device of the present application is prepared using nanoimprinting technology, and the production process is simple. Devices can be prepared on a large scale. In actual production, time can be saved, efficiency can be improved, design costs can be reduced, and energy consumption can be saved.

[0153] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0154] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A metasurface device, comprising: substrate layer; A first super surface layer located on one side of the substrate layer; A second super surface layer located on a side of the substrate layer away from the first super surface layer; The first super surface layer includes a plurality of first nanostructures distributed in a first shape; The second super surface layer includes a plurality of second nanostructures distributed in a second shape; The first shape and the second shape are selected from nanostructures whose sidewalls are perpendicular to the substrate layer; and / or, A nanostructure whose top cross-sectional length is shorter than or equal to the bottom cross-sectional length.

2. The metasurface device according to claim 1, characterized in that: The first shape and the second shape may be the same or different.

3. The metasurface device according to claim 2, characterized in that: The placement angles of the plurality of first nanostructures and the second nanostructures relative to the substrate layer are not completely the same.

4. The metasurface device according to claim 2, characterized in that: The nanostructures with side walls perpendicular to the substrate layer are selected from one or more of a rectangular parallelepiped structure and a cylindrical structure.

5. The metasurface device according to claim 1, characterized in that: The nanostructure whose top cross-section length is shorter than or equal to that of the bottom cross-section length is selected from one or more of a trapezoidal structure and a zigzag structure.

6. The metasurface device according to claim 1, characterized in that: The first nanostructure and the second nanostructure are arranged in an array to form a first supersurface layer and a second supersurface layer.

7. The metasurface device according to claim 1, characterized in that: The material of the substrate layer is selected from one or more of quartz, silicon wafer, and sapphire.

8. The metasurface device according to claim 7, characterized in that: The thickness of the substrate layer is 2-5 mm.

9. The metasurface device according to claim 1, characterized in that: The material of the first nanostructure and the second nanostructure is selected from one or more of zinc oxide, silicon dioxide, titanium dioxide, and aluminum oxide.

10. The metasurface device according to claim 9, characterized in that: The materials of the first nanostructure and the second nanostructure are titanium dioxide.

11. The metasurface device according to claim 1, characterized in that: The height of the first nanostructure and the second nanostructure is 600-900 nm.

12. The metasurface device according to claim 1, characterized in that: The spacing between the first nanostructures in the first super surface layer is 50 to 70 nm; the spacing between the second nanostructures in the second super surface layer is 50 to 70 nm.

13. The method for preparing a metasurface device according to any one of claims 1 to 12, comprising the following steps: Step S1: pre-treating the substrate layer; Step S2: coating photoresist on the surface of the substrate layer; Step S3: making a reverse pattern opposite to the first super surface layer pattern on the imprint template, and aligning the imprint template with the substrate layer coated with photoresist in step S2; Step S4: making the reverse pattern on the imprint template contact the photoresist on the substrate layer, and forming a first super surface layer pattern on the surface of the photoresist by using nanoimprint technology; Step S5: using atomic layer deposition technology, depositing a first nanostructure on the surface of the photoresist obtained in step S4 to obtain a first metasurface device, wherein the first metasurface device includes a first nanostructure arranged from top to bottom, a photoresist having the same shape as the first nanostructure, and a substrate layer; Step S6: removing the photoresist under the first nanostructure in the first metasurface device, and coating the photoresist on the surface of the first nanostructure again; Step S7: turning over the first metasurface device, and coating the photoresist again on the side of the substrate layer away from the first nanostructure; Step S8: making a reverse pattern opposite to the second super surface layer pattern on the imprint template, and aligning the imprint template with the substrate layer coated with the photoresist; Step S9: making the reverse pattern on the imprint template contact the photoresist on the substrate layer, and forming a second super surface layer pattern on the surface of the photoresist by using nanoimprint technology; Step S10: using atomic layer deposition technology, depositing a second nanostructure on the surface of the photoresist obtained in step S9 to obtain a second metasurface device, wherein the second metasurface device includes a second nanostructure arranged from top to bottom, a photoresist having the same shape as the second nanostructure, a substrate layer, a first nanostructure, and a photoresist coated on the surface of the first nanostructure; Step S11: removing the photoresist under the second nanostructure in the second metasurface device and the photoresist coated on the surface of the first nanostructure to obtain a final metasurface device.

14. The preparation method according to claim 13, characterized in that: In the steps S2, S6 and S7, the thickness of the applied photoresist is in micrometer order.

15. The preparation method according to claim 13, characterized in that: In the step S3, the material of the imprint template is selected from silicon, graphite, and metal.

16. The preparation method according to claim 15, characterized in that: In the step S5, the thickness of the photoresist having the same shape as the first nanostructure is 4-6 nm.

17. The preparation method according to claim 13, characterized in that: The steps S4 and S9 may be repeated multiple times.

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