An infrared broadband absorption metasurface structure
By utilizing the infrared broadband absorption metasurface of the MIM composite structure and enhancing multimode coupling with corner-deficient asymmetric subunits, the problems of broadband high-efficiency absorption and poor material stability in the prior art are solved, and a high-efficiency and stable infrared absorption effect is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUAZHONG UNIV OF SCI & TECH
- Filing Date
- 2025-04-30
- Publication Date
- 2026-07-03
AI Technical Summary
Existing infrared absorption structures have shortcomings in terms of broadband requirements, material stability, and process compatibility, making it difficult to achieve efficient and continuous broadband absorption.
An infrared broadband absorbing metasurface with a MIM composite structure enhances the multimode coupling effect and optimizes the supercell structure parameters by introducing asymmetric subunits with missing corners, thus forming a continuous broadband absorption response.
It achieves a high absorption rate of over 60% in the 8–13 μm atmospheric window band, and an absorption rate of less than 20% in the 5–8 μm and 13–20 μm bands. The material exhibits good stability and strong process compatibility.
Smart Images
Figure CN120405815B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of micro-nano photonics and infrared sensing, and more specifically, relates to an infrared broadband absorbing metasurface structure. Background Technology
[0002] Infrared absorbing materials have significant application value in infrared sensing, thermal radiation management, and spectral detection, especially in the 8–13 μm atmospheric window band, where their performance directly affects the ability to modulate the infrared signal characteristics of target objects. Traditional infrared absorbing structures are mostly based on metal thin films, semiconductor heterojunctions, or multilayer dielectric films, achieving selective absorption of specific wavelengths through plasmon resonance, exciton effects, or destructive interference mechanisms. However, each of these approaches has its own drawbacks. Metal thin films rely on surface plasmon resonance absorption, but their absorption peaks have narrow half-maximum widths (FWHM), making it difficult to cover broad spectral requirements. While multilayer dielectric films can extend bandwidth through thickness control, interlayer refractive index mismatch easily leads to interface scattering losses, resulting in low average absorptivity. Furthermore, existing structures face problems such as poor material thermal stability and low processing tolerance, severely restricting their engineering applications in complex environments.
[0003] Recent research has attempted to excite multimode resonances using asymmetric metasurfaces such as L-shaped and cross-shaped structures. However, the electromagnetic coupling effect between units is weak, and the absorption peaks still exhibit discretization characteristics after superposition. Furthermore, the high precision required for micro / nano fabrication and the use of non-traditional materials and processes make large-scale fabrication difficult. To address these issues, an innovative design that combines broad-spectrum, high-efficiency absorption, material stability, and process compatibility is urgently needed to overcome the current technological bottlenecks. Summary of the Invention
[0004] This invention proposes an infrared broadband absorbing metasurface structure, belonging to the MIM composite metasurface structure. By introducing an asymmetric structure with missing corner subunits, a multimode coupling effect is achieved, effectively enhancing the absorption capability of the resonant unit in different frequency bands. Furthermore, the parameters of the supercell structures constituting the infrared broadband absorbing metasurface structure are finely tuned, enhancing the coupling and superposition effect between the supercell structures and forming a continuous and smooth broadband absorption response. This solves the technical problems of broadband high-efficiency absorption, poor material stability, and poor process compatibility faced by existing technologies.
[0005] According to the present invention, an infrared broadband absorbing metasurface structure is provided. The infrared broadband absorbing metasurface structure is formed by a periodic arrangement of supercell structures. The supercell structure specifically includes: a bottom platinum metal layer, a dielectric layer covering the bottom platinum metal layer, and four sub-units a, b, c, and d arranged on the dielectric layer; wherein the material of the four sub-units a, b, c, and d is platinum, and the material of the dielectric layer is silicon; both the bottom platinum metal layer and the dielectric layer are square.
[0006] The four sub-units a, b, c, and d are arranged in a square array, with a located in the upper left corner, b in the upper right corner, c in the lower left corner, and d in the lower right corner; the distance between the centers of any two adjacent sub-units is equal.
[0007] Among the four sub-units a, b, c, and d, at least one sub-unit is a pentagon formed by a square with a missing corner, where the missing corner is cut off along the two adjacent sides of the square. The other sub-units are squares without missing corners. Let the side length of the side that is not cut off in the missing corner square sub-unit be the side length of the missing corner square sub-unit. Then at least two sub-units have different side lengths.
[0008] When 1-3 of the four sub-units a, b, c, and d are notched squares with chamfered corners, the sides of the not-chamfered square sub-units and the sides of the other not-chamfered square sub-units are parallel or perpendicular to the sides of the bottom platinum metal layer.
[0009] When all four sub-units a, b, c, and d are notched squares, the sides of the not-cut-off square sub-units are parallel or perpendicular to the sides of the bottom platinum metal layer.
[0010] Preferably, when two or more of the four sub-units a, b, c, and d have a chamfer, each chamfer is located at the upper left corner of the sub-unit, or at the upper right corner of the sub-unit, or at the lower left corner of the sub-unit, or at the lower right corner of the sub-unit.
[0011] Preferably, the tangent is an isosceles right triangle.
[0012] Preferably, the leg length of the isosceles right triangle is less than or equal to 60% of the side length of the subunit containing the tangent angle.
[0013] Preferably, the side lengths of the four sub-units a, b, c, and d are each independently selected from 0.6-2 μm.
[0014] Preferably, the bottom platinum metal layer and dielectric layer are square with a side length of 2-5 μm.
[0015] Preferably, the thickness of the underlying platinum metal layer is 50-1000 nm.
[0016] Preferably, the thickness of the dielectric layer is 100-300 nm.
[0017] Preferably, the four sub-units a, b, c, and d have the same thickness, which is 50-300 nm.
[0018] Preferably, the infrared broadband absorbing metasurface structure has an average absorption rate of over 60% in the 8–13 μm atmospheric window band, and an average absorption rate of less than 20% in the 5–8 μm and 13–20 μm bands.
[0019] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:
[0020] (1) The infrared broadband absorption metasurface structure of the present invention has an average absorption rate of over 60% in the 8-13 μm atmospheric window band, and an average absorption rate of less than 20% in the 5-8 μm band and the 13-20 μm band.
[0021] (2) This invention achieves flexible optical control and application by adjusting the side length and chamfer, thereby regulating the resonant frequency and absorption bandwidth.
[0022] (3) The platinum metal and silicon dielectric material selected in this invention are both traditional process materials with mature processing technology; they have stable chemical properties, good oxidation resistance, and long-term stability; they are acid resistant, not easily corroded by etching agents during the process, and have good process compatibility; they have moderate hardness, which improves the mechanical stability of the system.
[0023] (4) The method described in this invention has a simple structure and low process difficulty. The bottom metal and dielectric layer are uniform material layers, and the top metal layer adopts a square chamfered structure. Attached Figure Description
[0024] Figure 1 This is a structural schematic diagram provided for the present invention.
[0025] Figure 2 The effect of the side length of the square on the sub-unit absorption rate when there are no chamfers.
[0026] Figure 3 The effect of different ratios of chamfer length to square side length on the sub-unit absorption rate.
[0027] Figure 4 The absorptivity of the metasurface is the absorptivity of near-infrared light when incident orthogonally.
[0028] Figure 5 The surface electric field corresponds to the resonant wavelength of the four units.
[0029] Wherein: 1-dielectric layer, 2-bottom platinum metal layer. Detailed Implementation
[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.
[0031] This invention discloses a mid-infrared broadband absorbing metasurface structure, wherein the infrared broadband absorbing metasurface structure is formed by a periodic arrangement of supercell structures. The supercell structure specifically includes: a bottom platinum metal layer, a dielectric layer covering the bottom platinum metal layer, and four sub-units a, b, c, and d arranged on the dielectric layer; wherein the material of the four sub-units a, b, c, and d is platinum, and the material of the dielectric layer is silicon.
[0032] The four sub-units a, b, c, and d are arranged in a square array, with a located in the upper left corner, b in the upper right corner, c in the lower left corner, and d in the lower right corner. The distance between the centers of any two adjacent sub-units is equal. The sides of the four sub-units a, b, c, and d are either parallel or perpendicular to each other.
[0033] The four sub-units a, b, c, and d are squares. At least two of the four sub-units have different side lengths, and at least one of the four sub-units a, b, c, and d has a chamfered corner that is cut off along the two adjacent sides of the square.
[0034] By simulating individual sub-units, adjusting the size of each sub-unit, the thickness of each layer, and the arrangement, the absorption spectrum of mid-infrared light under normal incidence is calculated under different conditions.
[0035] In some embodiments, the supercell structure is periodically arranged along the x and y directions, with a single period size of 3 μm, a bottom platinum layer thickness of 160 nm, a silicon layer thickness of 200 nm, and a top platinum layer thickness of 100 nm.
[0036] In some embodiments, subunits a, b, c, and d are all square in shape, and a corner of subunits a, c, and d is cut off in the same direction, with the two sides of the cut corner having the same length.
[0037] In some embodiments, the square side length of subunit a is 1.45 μm, and the ratio of the chamfer length to the square side length is 0.4;
[0038] Subunit b has a square side length of 0.9 μm and no chamfered corners;
[0039] The square side length of subunit c is 1μm, and the ratio of the chamfer length to the square side length is 0.3;
[0040] The square side length of subunit d is 1.15 μm, and the ratio of the chamfer length to the square side length is 0.4.
[0041] In some embodiments, the absorptivity of the four sub-units a, b, c, and d at their respective resonant wavelengths is greater than 80%, and the average absorptivity of the metasurface for 8–13 μm light is greater than 60%.
[0042] According to the fundamental laws of electromagnetic wave propagation, when a beam of light is incident on a subunit structure, the energy is divided into three parts: transmitted light, reflected light, and light absorbed by the structure. According to the law of conservation of energy, the sum of the structure's absorptivity A(ω), reflectivity R(ω), and transmittance T(ω) is 1. Therefore, the structure's absorptivity A(ω) is:
[0043] A(ω)=1-R(ω)-T(ω)
[0044] The thickness of the underlying platinum metal in this invention is 160 nm, which is much greater than the skin depth of platinum in the mid-infrared band, and the transmittance T(ω) is zero. The above formula can be simplified to:
[0045] A(ω)=1-R(ω)
[0046] To maximize the absorption rate of the structure, the reflectivity R(ω) should be reduced. This can be achieved by optimizing the dimensions and materials of the unit structure to match the impedance at the incident interface with the impedance of free space.
[0047] The present invention uses platinum, which has a small real part of dielectric constant and a large imaginary part of dielectric constant, thereby reducing the reflectivity of incident light and attenuating the electromagnetic waves incident into the material.
[0048] The square subunit structure can achieve high absorption rate in a narrow band through single-mode resonance and interference effects. By cutting off one corner of the square and breaking the C4 symmetry, multimode absorption can be formed in a subunit. Although the absorption rate will decrease slightly, the absorption peak can be broadened to cover a wider absorption range.
[0049] The absorption spectrum of the scanning unit cell structure is adjusted according to different dimensions, including side length, chamfer size, and layer thickness, requiring each sub-unit to have an absorption rate greater than 80% at its corresponding resonant frequency. Unit cell structures of different sizes are combined by combining the absorption spectra of each unit cell size to achieve coverage of broadband absorption. Four sub-units are selected to form a periodic supercell. Simultaneously, the electromagnetic coupling between units is used to enhance the overall absorption intensity. The parameters of each unit cell are fine-tuned to cause partial misalignment and superposition of their absorption peaks within the target spectral range, thereby forming a continuous and efficient broadband response.
[0050] The finite-difference time-domain (FDTD) method was used to simulate the sub-unit structure and metasurface. The incident light was defined as a plane wave of 5-20 μm with normal incidence. The horizontal boundary conditions were all set to periodicity, and the vertical boundary conditions were set to a perfectly matched layer to simulate the absorption of the metasurface when electromagnetic waves were normally incident.
[0051] By optimizing the structural design, a metasurface with broadband absorption in the infrared band was obtained, with an average absorption rate of less than 20% in the 5-8μm and 13-20μm ranges and an average absorption rate of more than 60% in the 8-13μm range.
[0052] The following are specific embodiments.
[0053] Example 1
[0054] like Figure 1 As shown, the infrared broadband absorbing metasurface structure is formed by a periodic arrangement of supercell structures. The supercell structure specifically includes: a bottom platinum metal layer 2, a dielectric layer 1 covering the bottom platinum metal layer, and four sub-units a, b, c, and d arranged on the dielectric layer; and the material of the four sub-units a, b, c, and d is platinum, and the material of the dielectric layer is silicon.
[0055] This mid-infrared broadband absorbing metasurface structure is a supercell metasurface composed of four sub-units (a, b, c, and d) of different sizes arranged in a planar array. The distance between the centers of the sub-units is 1.5 μm. The supercells are periodically arranged along the x and y directions. In one supercell structure, the side length of the bottom metal layer and dielectric layer is 3 μm. The thickness of the four sub-units (a, b, c, and d) is 100 nm, the thickness of the bottom metal layer is 160 nm, and the thickness of the middle dielectric layer is 200 nm. The specific parameters of its single-period structure are shown in the table below:
[0056] Table 1 Single-period structural parameters
[0057]
[0058] This method uses the finite-time difference method (FDTD) to simulate sub-units and supercells. The incident light is defined as a plane wave of 5-20 μm with normal incidence. The horizontal boundary conditions are all set to periodicity, and the vertical boundary conditions are set to a perfectly matched layer to simulate the absorption of the metasurface when electromagnetic waves are normally incident.
[0059] Figure 2 The absorption rate curves are for different sub-unit side lengths when the square has no chamfer. The absorption peaks show a red shift trend as the side length of the square increases. In this method, four sub-units with different side lengths are selected to cover the entire 8-13 μm absorption range.
[0060] Figure 3The absorption rate curves are shown for different ratios of chamfer length to square side length when the subunit side length is 1.2 μm. As the chamfer angle increases, the absorption peak decreases while broadening. In this method, the absorption curves are flattened by adjusting the chamfer angles of the four subunits, ensuring that the absorption rate in the 8-13 μm wavelength range is consistently above 60%. The final metasurface absorption rate is shown below. Figure 4 As shown.
[0061] Figure 5 The image shows the electric field profile of the metasurface's upper surface when light of the corresponding resonant wavelengths is incident on the four sub-units, with the incident light energy normalized. At the resonant wavelength corresponding to each sub-unit, the electric field energy is concentrated around that sub-unit, enhancing the silicon layer's resistance to the electric field loss and thus achieving a high absorption rate.
[0062] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. An infrared broadband absorption metasurface structure, characterized in that, The infrared broadband absorbing metasurface structure is formed by a periodic arrangement of supercell structures. The supercell structure specifically includes: a bottom platinum metal layer, a dielectric layer covering the bottom platinum metal layer, and four sub-units a, b, c, and d arranged on the dielectric layer; the material of the four sub-units a, b, c, and d is platinum, and the material of the dielectric layer is silicon; both the bottom platinum metal layer and the dielectric layer are square. The four sub-units a, b, c, and d are arranged in a square array, with a located in the upper left corner, b in the upper right corner, c in the lower left corner, and d in the lower right corner; the distance between the centers of any two adjacent sub-units is equal. Among the four sub-units a, b, c, and d, at least one sub-unit is a pentagon formed by a square with a missing corner, where the missing corner is cut off along the two adjacent sides of the square. The other sub-units are squares without missing corners. Let the side length of the side that is not cut off in the missing corner square sub-unit be the side length of the missing corner square sub-unit. Then at least two sub-units have different side lengths. When 1-3 of the four sub-units a, b, c, and d are notched squares with chamfered corners, the sides of the not-chamfered square sub-units and the sides of the other not-chamfered square sub-units are parallel or perpendicular to the sides of the bottom platinum metal layer. When all four sub-units a, b, c, and d are notched squares, the sides of the not-cut-off square sub-units are parallel or perpendicular to the sides of the bottom platinum metal layer. When two or more of the four sub-units a, b, c, and d have a chamfer, each chamfer is located at the upper left corner of its respective sub-unit, or at the upper right corner of its respective sub-unit, or at the lower left corner of its respective sub-unit, or at the lower right corner of its respective sub-unit.
2. The infrared broadband absorbing metasurface structure as described in claim 1, characterized in that, The shape of the chamfer is an isosceles right triangle.
3. The infrared broadband absorbing metasurface structure as described in claim 2, characterized in that, The leg length of the isosceles right triangle is less than or equal to 60% of the side length of the subunit containing the tangent angle.
4. The infrared broadband absorbing metasurface structure as described in claim 1, characterized in that, The side lengths of the four sub-units a, b, c, and d are each independently selected from 0.6-2 μm.
5. The infrared broadband absorbing metasurface structure as described in claim 1, characterized in that, The underlying platinum metal layer and dielectric layer are square with a side length of 2-5 μm.
6. The infrared broadband absorbing metasurface structure as described in claim 1, characterized in that, The thickness of the underlying platinum metal layer is 50-1000 nm.
7. The infrared broadband absorbing metasurface structure as described in claim 1, characterized in that, The thickness of the dielectric layer is 100-300 nm.
8. The infrared broadband absorbing metasurface structure as described in claim 1, characterized in that, The four sub-units a, b, c, and d have the same thickness, ranging from 50 to 300 nm.