Vanadium dioxide-based multi-frequency / ultra-wideband switchable terahertz metamaterial absorber and its fabrication method

Abstract

This invention discloses a vanadium dioxide-based multi-frequency / ultra-wideband switchable terahertz metamaterial absorber, comprising M×N multilayered multi-frequency / ultra-wideband switchable terahertz absorbing units. These M×N multilayered multi-frequency / ultra-wideband switchable terahertz absorbing units are distributed in an M×N two-dimensional pattern, where M and N are positive integers. Each multilayered multi-frequency / ultra-wideband switchable terahertz absorbing unit includes, from top to bottom, an upper patterned VO2 layer unit, an upper Topas material dielectric layer, a lower VO2 layer, a middle patterned gold layer unit, a lower Topas material dielectric layer, and a bottom gold layer. This terahertz absorber, utilizing a double-layer resonant design and the phase transition characteristics of VO2, achieves high absorption and flexible mode switching in both multi-frequency and ultra-wideband applications. This invention also provides a method for fabricating the vanadium dioxide-based multi-frequency / ultra-wideband switchable terahertz metamaterial absorber.

Description

Technical Field

[0001] This invention relates to the field of terahertz wave technology, specifically to a terahertz metamaterial absorber based on vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial, and also to a method for preparing the vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber. Background Technology

[0002] Terahertz (THz) waves typically refer to electromagnetic waves in the frequency band between microwaves and infrared light. This frequency band possesses characteristics such as strong penetration, low photon energy, and a rich spectrum, making it a characteristic absorption band for many biological macromolecules and chemical substances. It has significant application value in fields such as non-destructive testing, biosensing, and imaging. However, the development of high-performance control devices such as absorbers and filters faces challenges. Due to the lack of natural materials capable of achieving efficient electromagnetic coupling with this frequency band, traditional absorbers are mostly based on metal-dielectric periodic structures, achieving high absorption at specific frequencies through geometric resonance. However, because the operating frequency band is fixed and the bandwidth is narrow (e.g., single-peak or double-peak), it is difficult to adapt to the demands of dynamic electromagnetic environments.

[0003] Metamaterials are artificial composite structures that, through flexible design of subwavelength units, can flexibly control the amplitude, phase, and polarization of electromagnetic waves, effectively overcoming the functional limitations of natural materials in the terahertz band. In 2008, Landy et al. first proposed a perfect absorber based on metamaterials, sparking a research boom in terahertz metamaterial absorbers. Subsequently, researchers have successively achieved single-frequency, multi-frequency, and broadband absorption characteristics. However, once traditional metamaterial absorbers are fabricated, their structure is fixed, resulting in an inability to dynamically adjust absorption performance, severely limiting their applicability in flexible application scenarios.

[0004] In recent years, with the introduction of phase change materials (such as vanadium dioxide VO2) and graphene, significant progress has been made in the research of tunable terahertz metamaterial absorbers. VO2 undergoes an insulator-metal phase transition at approximately 340 K, and its conductivity can undergo abrupt changes of up to five orders of magnitude within the picosecond range, providing an ideal mechanism for dynamically controlling terahertz waves. Based on this characteristic, several studies have successively achieved tunable absorbers with different performances: In 2020, Huang et al. used a composite structure of VO2 and square metal rings to achieve an absorption rate of over 90% in the range of 1.85–4.3 THz; in 2021, Liu et al. achieved dual-mode tuning of narrowband and broadband absorption through a vanadium dioxide-graphene hybrid design; in 2022, Mou et al. used a ring-shaped vanadium dioxide structure for coupling to achieve broadband absorption of 0.398–1.356 THz; and in 2023, Hu et al. further achieved two broadband absorptions (0.73–1.53 THz and 3.03–3.64 THz) in the insulating state and a broadband high-efficiency absorption of 1.00–3.55 THz in the metallic state through the synergistic regulation of VO2 and graphene.

[0005] Although research has made some progress in tunable terahertz absorption, challenges remain, including limited absorption bandwidth and relatively limited modulation modes. In particular, achieving flexible and reliable switching between ultra-wideband absorption and multi-band absorption in a single device remains a key challenge in current terahertz absorber design. Therefore, it is necessary to propose a multi-frequency / ultra-wideband switchable terahertz absorber based on vanadium dioxide. This design employs a modular approach, cleverly integrating complementary broadband and multi-frequency absorption modules, which is expected to effectively overcome existing technological limitations and achieve high-performance, easily switchable dual-function terahertz absorption. Summary of the Invention

[0006] The first objective of this invention is to provide a terahertz metamaterial absorber based on vanadium dioxide with multi-frequency / ultra-wideband switchable characteristics, which achieves high absorption and flexible mode switching in both multi-frequency and ultra-wideband applications by means of a double-layer resonant design and the phase transition characteristics of VO2.

[0007] The second objective of this invention is to provide a method for preparing a terahertz metamaterial absorber based on vanadium dioxide multi-frequency / ultra-wideband switchable absorber.

[0008] The first technical solution adopted in this invention is a vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber, which includes M×N multi-layer structured multi-frequency / ultra-wideband switchable terahertz absorption units. The M×N multi-layer structured multi-frequency / ultra-wideband switchable terahertz absorption units are distributed in an M×N two-dimensional pattern, where M and N are both positive integers.

[0009] Each multi-layered multi-frequency / ultra-wideband switchable terahertz absorption unit includes, from top to bottom, an upper patterned VO2 layer unit, an upper Topas material dielectric layer, a lower VO2 layer, an intermediate patterned gold layer unit, a lower Topas material dielectric layer, and a bottom gold layer, with the six material layers bonded together.

[0010] The top Topas material dielectric layer, the bottom VO2 layer, the bottom Topas material dielectric layer, and the bottom gold layer are all square with equal side lengths.

[0011] The invention is further characterized in that:

[0012] The upper patterned VO2 layer unit includes one first patterned VO2 layer and four second patterned VO2 layers; the first patterned VO2 layer is an annular shape and is located at the center of the upper surface of the upper Topas material dielectric layer; the second patterned VO2 layer is a quarter circle and the four second patterned VO2 layers are respectively located at the four corners of the upper Topas material dielectric layer.

[0013] The outer radius r1 of the first patterned VO2 layer is 18μm-24μm, the annular width d1 of the first patterned VO2 layer is 4μm-6μm, the radius r2 of the circle containing the second patterned VO2 layer is 1.5μm-7.5μm, the thickness t1 of the first patterned VO2 layer is 0.02μm-0.2μm, and the thickness of the second patterned VO2 layer is the same as that of the first patterned VO2 layer.

[0014] The intermediate patterned gold layer unit includes one first patterned gold layer, four second patterned gold layers, and four third patterned gold layers;

[0015] The first patterned gold layer is a ring shape and is located at the center of the upper surface of the underlying Topas material dielectric layer.

[0016] The second patterned gold layer is a quarter circle, and four second patterned gold layers are respectively set at the four corners of the lower Topas material dielectric layer;

[0017] The third patterned gold layer is semi-circular, and a third patterned gold layer is set between every two second patterned gold layers; the center of each third patterned gold layer coincides with the midpoint of the side length of the underlying Topas material dielectric layer;

[0018] The outer radius r3 of the first patterned gold layer is 3.6μm-4.2μm, the annular width d2 of the first patterned gold layer is 4μm-6μm, the radius r4 of the circle containing the second patterned gold layer is 2.8μm-3.5μm, and the radius of the circle containing the third patterned gold layer is 2.6μm-3.2μm; the thickness t4 of the first patterned gold layer is 1μm-3μm; the thicknesses of the second and third patterned gold layers are the same as the thickness of the first patterned gold layer.

[0019] The thickness t2 of the upper Topas material dielectric layer is 4μm-8μm, the thickness t3 of the lower VO2 layer is 0.2μm-0.5μm, the thickness t5 of the lower Topas material dielectric layer is 4μm-8μm, and the thickness t6 of the bottom gold layer is 0.2μm-0.5μm; the side length of the upper Topas material dielectric layer is 32μm-35μm, and the side lengths of the lower VO2 layer, the lower Topas material dielectric layer (5), and the bottom gold layer are the same as the side length of the upper Topas material dielectric layer.

[0020] The conductivity of the first patterned VO2 layer, the second patterned VO2 layer, and the lower VO2 layer in the insulating phase is 20 S / m, and the conductivity in the metallic phase is 200,000 S / m.

[0021] The dielectric constant of the upper and lower Topas material dielectric layers is 1.93; the conductivity of the bottom gold layer, the first patterned gold layer, the second patterned gold layer, and the four third patterned gold layers is 4.56 × 10⁻⁶. 7 S / m.

[0022] The second technical solution adopted in this invention is a terahertz metamaterial absorber based on vanadium dioxide multi-frequency / ultra-wideband switchable technology, comprising the following steps:

[0023] Step 1: Preparation of the bottom gold layer;

[0024] Step 2: Deposition of the lower Topas material dielectric layer;

[0025] Step 3: Fabrication of patterned gold layer units in the intermediate layer;

[0026] Step 4: Preparation of the lower VO2 layer;

[0027] Step 5: Deposition of the upper Topas material dielectric layer;

[0028] Step 6: Fabrication of the upper patterned VO2 layer unit.

[0029] The invention is further characterized in that:

[0030] Step 1 is as follows:

[0031] Step 1.1, Substrate cleaning:

[0032] High-purity silicon was selected as the substrate and ultrasonically cleaned with acetone, ethanol and deionized water for 10 min-15 min in sequence to remove surface contaminants; after drying with nitrogen, it was dried in an oven at 110℃-120℃ for 30 min-40 min.

[0033] Step 1.2, Metal Thin Film Deposition:

[0034] Gold thin films were deposited using electron beam evaporation.

[0035] Step 1.3, Annealing treatment:

[0036] Annealing at 300℃-350℃ for 30min-40min improves the crystallinity and conductivity of the gold film, resulting in a bottom gold layer;

[0037] Step 2 is as follows:

[0038] Step 2.1, Spin-coating the polyimide dielectric layer:

[0039] A polyimide precursor solution is spin-coated onto a base gold film, and the desired dielectric layer thickness is obtained by precisely controlling the spin-coating speed and time.

[0040] Step 2.2, Curing treatment:

[0041] Curing at 150℃-160℃ for 1h-2h ensures the formation of a stable polyimide film. The curing process is strictly controlled to ensure that the film is flat, free of bubbles and stress cracks. The lower Topas material dielectric layer (5) is obtained on the bottom gold layer 6.

[0042] Step 3 specifically involves:

[0043] Step 3.1, Photolithographic Patterning:

[0044] The designed metal structure pattern is defined on the cured polyimide surface using electron beam lithography.

[0045] Step 3.2, Gold Thin Film Deposition:

[0046] A thin gold film is deposited using electron beam evaporation.

[0047] Step 3.3, Peeling and Shaping:

[0048] The photoresist and excess gold film on it are removed by stripping, leaving the designed gold micro-nano structure, and the metal patch is used as the intermediate patterned gold layer unit.

[0049] Step 4 is as follows:

[0050] A VO2 substrate was deposited on the patterned gold layer unit in the intermediate layer using pulsed laser deposition as the lower VO2 layer;

[0051] Step 5 specifically involves:

[0052] Step 5.1: Spin-coating the polyimide dielectric layer:

[0053] A polyimide precursor solution is spin-coated onto a base gold film, and the desired dielectric layer thickness is obtained by precisely controlling the spin-coating speed and time.

[0054] Step 5.2, Curing treatment:

[0055] Curing at 150℃-160℃ for 1-2 hours ensures the formation of a stable polyimide film. The curing process is strictly controlled to ensure that the film is flat, free of bubbles and stress cracks, and the upper Topas material dielectric layer is obtained on the lower VO2 layer.

[0056] Step 6 specifically involves:

[0057] Step 6.1, Photolithography defines the VO2 region:

[0058] After the top gold structure is fabricated, vanadium dioxide pattern areas are defined in pre-designed locations using photolithography.

[0059] Step 6.2, VO2 thin film deposition:

[0060] A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition.

[0061] Step 6.3, Peeling and Shaping:

[0062] The photoresist and excess vanadium dioxide film on it are removed using a stripping method, leaving the designed structure to obtain a vanadium dioxide patch.

[0063] The beneficial effects of this invention are:

[0064] (1) This invention is based on a vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber. The designed absorber can switch from multi-frequency absorption to ultra-wideband absorption by adjusting the conductivity of vanadium dioxide through temperature control. When the conductivity of vanadium dioxide is 20 S / m, the absorber exhibits multi-frequency absorption, with four absorption peaks above 90%, located at 8.05 THz, 9.65 THz, 10.42 THz, and 11.45 THz. When the conductivity of vanadium dioxide is 200,000 S / m, the absorber achieves an absorption rate of over 90% in the range of 5.87-17.95 THz, with an absorption bandwidth of 12.08 THz.

[0065] (2) The present invention is based on a vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber that is polarization insensitive and maintains excellent absorption performance under different polarization angles and a wide incident angle of 0°-60°.

[0066] (3) The present invention is based on a vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber, which can tune the position and absorption intensity of the absorption peak in the multi-frequency absorption mode to a certain extent by changing the structural parameters.

[0067] (4) The preparation method of the present invention is simple and easy to operate. Attached Figure Description

[0068] Figure 1 This is a schematic diagram of the structure of a vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber provided in Embodiment 1 of the present invention;

[0069] Figure 2 This is a schematic diagram of the structure of the multi-layered multi-frequency / ultra-wideband switchable terahertz absorption unit provided in Embodiment 1 of the present invention;

[0070] Figure 3 This is a side view of the multi-layered, multi-frequency / ultra-wideband switchable terahertz absorption unit provided in Embodiment 1 of the present invention.

[0071] Figure 4 This is a top view of the upper patterned VO2 layer unit in the multi-frequency / ultra-wideband switchable terahertz absorption unit with a multi-layer structure provided in Embodiment 1 of the present invention.

[0072] Figure 5 This is a top view of the patterned gold layer unit in the middle layer of the multi-frequency / ultra-wideband switchable terahertz absorption unit with a multi-layer structure provided in Embodiment 1 of the present invention.

[0073] Figure 6 The absorption spectrum of the vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber provided in Embodiment 1 of the present invention;

[0074] Figure 7 The absorption spectrum of the vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber provided in Embodiment 1 of the present invention;

[0075] Figure 8 The real and imaginary parts of the relative impedance of vanadium dioxide in the insulating phase in the vanadium dioxide-based multi-frequency / ultra-wideband switchable terahertz metamaterial absorber provided in Embodiment 1 of the present invention;

[0076] Figure 9 The real and imaginary parts of the relative impedance of vanadium dioxide in the metallic phase in the vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber provided in Embodiment 1 of the present invention;

[0077] Figure 10 The electric field distribution on the xoy surface of a multi-frequency / ultra-wideband switchable terahertz absorber with a frequency of 8.05 THz and a vanadium dioxide conductivity of 20 S / m provided in Embodiment 1 of the present invention;

[0078] Figure 11 The electric field distribution of the xoz surface of a multi-frequency / ultra-wideband switchable terahertz absorber with a frequency of 8.05 THz and a vanadium dioxide conductivity of 20 S / m provided in Embodiment 1 of the present invention;

[0079] Figure 12 The electric field distribution of the xoy surface of the multi-frequency / ultra-wideband switchable terahertz absorber with a frequency of 11.45 THz and a vanadium dioxide conductivity of 20 S / m provided in Embodiment 1 of the present invention.

[0080] Figure 13 The electric field distribution on the xoz surface of a multi-frequency / ultra-wideband switchable terahertz absorber with a frequency of 11.45 THz and a vanadium dioxide conductivity of 20 S / m provided in Embodiment 1 of the present invention;

[0081] Figure 14 The electric field distribution of a multi-frequency / ultra-wideband switchable terahertz absorber with a frequency of 4THz and a vanadium dioxide conductivity of 200,000S / m provided in Embodiment 1 of the present invention;

[0082] Figure 15 The electric field distribution of a multi-frequency / ultra-wideband switchable terahertz absorber with a frequency of 12.1 THz and a vanadium dioxide conductivity of 200,000 S / m provided in Embodiment 1 of the present invention;

[0083] Figure 16 The absorption spectra of the multi-frequency / ultrawideband switchable terahertz absorber with a vanadium dioxide conductivity of 20 S / m provided in Embodiment 1 of the present invention at different polarization angles;

[0084] Figure 17 The absorption spectra of the multi-frequency / ultra-wideband switchable terahertz absorber with a vanadium dioxide conductivity of 200,000 S / m provided in Embodiment 1 of the present invention at different polarization angles;

[0085] Figure 18 The absorption spectra of the vanadium dioxide multi-frequency / ultra-wideband switchable terahertz absorber with a conductivity of 200,000 S / m provided in Embodiment 1 of the present invention at different incident angles under TE waves.

[0086] The structure consists of: 1. Upper patterned VO2 layer unit; 2. Upper Topas material dielectric layer; 3. Lower VO2 layer; 4. Middle patterned gold layer unit; 5. Lower Topas material dielectric layer; 6. Bottom gold layer.

[0087] 1-1. First patterned VO2 layer; 1-2. Second patterned VO2 layer;

[0088] 4-1. First patterned gold layer, 4-2. Second patterned gold layer, 4-3. Third patterned gold layer. Detailed Implementation

[0089] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0090] This invention provides a terahertz metamaterial absorber based on vanadium dioxide with multi-frequency / ultra-wideband switchable structure, comprising M×N multi-layered multi-frequency / ultra-wideband switchable terahertz absorption units, wherein the M×N multi-layered multi-frequency / ultra-wideband switchable terahertz absorption units are distributed in an M×N two-dimensional pattern, where M and N are both positive integers.

[0091] Each multi-layer structure multi-frequency / ultra-wideband switchable terahertz absorption unit includes, from top to bottom, an upper patterned VO2 layer unit 1, an upper Topas material dielectric layer 2, a lower VO2 layer 3, an intermediate patterned gold layer unit 4, a lower Topas material dielectric layer 5, and a bottom gold layer 6, with the six material layers bonded together.

[0092] The upper Topas material dielectric layer 2, the lower VO2 layer 3, the lower Topas material dielectric layer 5, and the bottom gold layer 6 are all square with equal side lengths.

[0093] The upper patterned VO2 layer unit 1 includes one first patterned VO2 layer 1-1 and four second patterned VO2 layers 1-2; the first patterned VO2 layer 1-1 is an annular shape and is disposed at the center of the upper surface of the upper Topas material dielectric layer 2; the second patterned VO2 layer 1-2 is a quarter circle, and the four second patterned VO2 layers 1-2 are respectively disposed at the four apex corners of the upper Topas material dielectric layer 2;

[0094] The outer radius r1 of the first patterned VO2 layer 1-1 is 18μm-24μm, the annular width d1 of the first patterned VO2 layer 1-1 is 4μm-6μm, the radius r2 of the circle containing the second patterned VO2 layer 1-2 is 1.5μm-7.5μm, the thickness t1 of the first patterned VO2 layer 1-1 is 0.02μm-0.2μm, and the thickness of the second patterned VO2 layer 1-2 is the same as that of the first patterned VO2 layer 1-1.

[0095] The intermediate patterned gold layer unit 4 includes a first patterned gold layer 4-1, four second patterned gold layers 4-2, and four third patterned gold layers 4-3;

[0096] The first patterned gold layer 4-1 is an annular shape and is located at the center of the upper surface of the lower Topas material dielectric layer 5.

[0097] The second patterned gold layer 4-2 is a quarter circle, and the four second patterned gold layers 4-2 are respectively set at the four top corners of the lower Topas material dielectric layer 5;

[0098] The third patterned gold layer 4-3 is semi-circular, and a third patterned gold layer 4-3 is set between every two second patterned gold layers 4-2; the center of each third patterned gold layer 4-3 coincides with the midpoint of the side length of the lower Topas material dielectric layer 5;

[0099] The outer radius r3 of the first patterned gold layer 4-1 is 3.6μm-4.2μm, the annular width d2 of the first patterned gold layer 4-1 is 4μm-6μm, the radius r4 of the circle containing the second patterned gold layer 4-2 is 2.8μm-3.5μm, and the radius of the circle containing the third patterned gold layer 4-3 is 2.6μm-3.2μm; the thickness t4 of the first patterned gold layer 4-1 is 1μm-3μm; the thicknesses of the second patterned gold layer 4-2 and the third patterned gold layer 4-3 are the same as the thickness of the first patterned gold layer 4-1.

[0100] The thickness t2 of the upper Topas material dielectric layer 2 is 4μm-8μm, the thickness t3 of the lower VO2 layer 3 is 0.2μm-0.5μm, the thickness t5 of the lower Topas material dielectric layer 5 is 4μm-8μm, and the thickness t6 of the bottom gold layer 6 is 0.2μm-0.5μm. The side length of the upper Topas material dielectric layer 2 is 32μm-35μm, and the side lengths of the lower VO2 layer 3, the lower Topas material dielectric layer 5, and the bottom gold layer 6 are the same as the side length of the upper Topas material dielectric layer 2.

[0101] The conductivity of the first patterned VO2 layer 1-1, the second patterned VO2 layer 1-2, and the lower VO2 layer 3 in the insulating phase is 20 S / m, and the conductivity in the metallic phase is 200000 S / m.

[0102] The dielectric constants of the upper Topas material dielectric layer 2 and the lower Topas material dielectric layer 5 are 1.93; the bottom gold layer 6, the first patterned gold layer 4-1, the second patterned gold layer 4-2, and the four third patterned gold layers 4-3 are made of gold with a conductivity of 4.56 × 10⁻⁶. 7 S / m.

[0103] The dielectric constant of vanadium dioxide in the terahertz band is described using the Drude model:

[0104]

[0105] Where ω represents the incident frequency, ω p (σ) represents the plasma frequency, and its value is related to its own conductivity σ. The high-frequency dielectric constant ε of vanadium dioxide... ∞ =12, collision frequency γ=5.75×10 13 rad / s; plasma frequency ω p (σ) can be approximated as:

[0106]

[0107] Where σ0=3×10 5 S / m, ω p (σ0)=1.45×10 15 S -1 This is the initial value of the plasma frequency of VO2.

[0108] This invention also provides a method for fabricating a vanadium dioxide-based multi-frequency / ultra-wideband switchable terahertz metamaterial absorber, comprising the following steps:

[0109] Step 1: Preparation of the bottom gold layer 6;

[0110] Step 1 is as follows:

[0111] Step 1.1, Substrate cleaning:

[0112] High-purity silicon was selected as the substrate and ultrasonically cleaned with acetone, ethanol and deionized water for 10 min-15 min in sequence to remove surface contaminants; after drying with nitrogen, it was dried in an oven at 110℃-120℃ for 30 min-40 min.

[0113] Step 1.2, Metal Thin Film Deposition:

[0114] Gold thin films were deposited using electron beam evaporation.

[0115] Step 1.3, Annealing treatment:

[0116] Annealing at 300℃-350℃ for 30min-40min improves the crystal quality and conductivity of the gold film, resulting in the bottom gold layer 6;

[0117] Step 2: Deposition of the lower Topas material dielectric layer 5;

[0118] Step 2 is as follows:

[0119] Step 2.1, Spin-coating the polyimide dielectric layer:

[0120] A polyimide precursor solution is spin-coated onto a base gold film, and the desired dielectric layer thickness is obtained by precisely controlling the spin-coating speed and time.

[0121] Step 2.2, Curing treatment:

[0122] Curing at 150℃-160℃ for 1-2 hours ensures the formation of a stable polyimide film. The curing process is strictly controlled to ensure that the film is flat, free of bubbles and stress cracks, and the lower Topas material dielectric layer 5 is obtained on the bottom gold layer 6.

[0123] Step 3: Fabrication of the intermediate patterned gold layer unit 4;

[0124] Step 3 specifically involves:

[0125] Step 3.1, Photolithographic Patterning:

[0126] The designed metal structure pattern is defined on the cured polyimide surface using electron beam lithography.

[0127] Step 3.2, Gold Thin Film Deposition:

[0128] A thin gold film is deposited using electron beam evaporation.

[0129] Step 3.3, Peeling and Shaping:

[0130] The photoresist and excess gold film on it are removed by stripping, leaving the designed gold micro-nano structure, and the metal patch is used as the intermediate patterned gold layer unit 4.

[0131] Step 4: Preparation of the lower VO2 layer 3;

[0132] Step 4 is as follows:

[0133] A VO2 substrate was deposited on the patterned gold layer unit 4 of the intermediate layer using pulsed laser deposition as the lower VO2 layer 3;

[0134] Step 5: Deposition of the upper Topas material dielectric layer 2;

[0135] Step 5 specifically involves:

[0136] Step 5.1: Spin-coating the polyimide dielectric layer:

[0137] A polyimide precursor solution is spin-coated onto a base gold film, and the desired dielectric layer thickness is obtained by precisely controlling the spin-coating speed and time.

[0138] Step 5.2, Curing treatment:

[0139] Curing at 150℃-160℃ for 1-2 hours ensures the formation of a stable polyimide film. The curing process is strictly controlled to ensure that the film is flat, free of bubbles and stress cracks. The upper Topas material dielectric layer 2 is obtained on the lower VO2 layer 3.

[0140] Step 6: Fabrication of the upper patterned VO2 layer unit 1.

[0141] Step 6 specifically involves:

[0142] Step 6.1, Photolithography defines the VO2 region:

[0143] After the top gold structure is fabricated, vanadium dioxide pattern areas are defined in pre-designed locations using photolithography.

[0144] Step 6.2, VO2 thin film deposition:

[0145] A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition.

[0146] Step 6.3, Peeling and Shaping:

[0147] The photoresist and excess vanadium dioxide film on it are removed using a stripping method, leaving the designed structure to obtain a vanadium dioxide patch.

[0148] Example 1

[0149] This embodiment is based on a vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber, which includes M×N multi-layered multi-frequency / ultra-wideband switchable terahertz absorption units. The M×N multi-layered multi-frequency / ultra-wideband switchable terahertz absorption units are distributed in an M×N two-dimensional pattern, where M and N are both positive integers.

[0150] Each multi-layer structure multi-frequency / ultra-wideband switchable terahertz absorption unit includes, from top to bottom, an upper patterned VO2 layer unit 1, an upper Topas material dielectric layer 2, a lower VO2 layer 3, an intermediate patterned gold layer unit 4, a lower Topas material dielectric layer 5, and a bottom gold layer 6, with the six material layers bonded together.

[0151] The upper Topas material dielectric layer 2, the lower VO2 layer 3, the lower Topas material dielectric layer 5, and the bottom gold layer 6 are all square with equal side lengths.

[0152] The upper patterned VO2 layer unit 1 includes one first patterned VO2 layer 1-1 and four second patterned VO2 layers 1-2; the first patterned VO2 layer 1-1 is an annular shape and is disposed at the center of the upper surface of the upper Topas material dielectric layer 2; the second patterned VO2 layer 1-2 is a quarter circle, and the four second patterned VO2 layers 1-2 are respectively disposed at the four apex corners of the upper Topas material dielectric layer 2;

[0153] The outer radius r1 of the first patterned VO2 layer 1-1 is 22 μm, the annular width d1 of the first patterned VO2 layer 1-1 is 4 μm, the radius r2 of the circle containing the second patterned VO2 layer 1-2 is 7.5 μm, the thickness t1 of the first patterned VO2 layer 1-1 is 0.05 μm, and the thickness of the second patterned VO2 layer 1-2 is the same as the thickness of the first patterned VO2 layer 1-1.

[0154] The intermediate patterned gold layer unit 4 includes a first patterned gold layer 4-1, four second patterned gold layers 4-2, and four third patterned gold layers 4-3;

[0155] The first patterned gold layer 4-1 is an annular shape and is located at the center of the upper surface of the lower Topas material dielectric layer 5.

[0156] The second patterned gold layer 4-2 is a quarter circle, and the four second patterned gold layers 4-2 are respectively set at the four top corners of the lower Topas material dielectric layer 5;

[0157] The third patterned gold layer 4-3 is semi-circular, and a third patterned gold layer 4-3 is set between every two second patterned gold layers 4-2; the center of each third patterned gold layer 4-3 coincides with the midpoint of the side length of the lower Topas material dielectric layer 5;

[0158] The outer radius r3 of the first patterned gold layer 4-1 is 4.2 μm, the annular width d2 of the first patterned gold layer 4-1 is 4 μm, the radius r4 of the circle containing the second patterned gold layer 4-2 is 3.5 μm, and the radius r5 of the circle containing the third patterned gold layer 4-3 is 2.6 μm; the thickness t4 of the first patterned gold layer 4-1 is 2 μm; the thicknesses of the second patterned gold layer 4-2 and the third patterned gold layer 4-3 are the same as the thickness of the first patterned gold layer 4-1.

[0159] The thickness t2 of the upper Topas material dielectric layer 2 is 6 μm, the thickness t3 of the lower VO2 layer 3 is 0.2 μm, the thickness t5 of the lower Topas material dielectric layer 5 is 5 μm, and the thickness t6 of the bottom gold layer 6 is 0.2 μm. The side length of the upper Topas material dielectric layer 2 is 35 μm, and the side lengths of the lower VO2 layer 3, the lower Topas material dielectric layer 5, and the bottom gold layer 6 are the same as the side length of the upper Topas material dielectric layer 2.

[0160] The conductivity of the first patterned VO2 layer 1-1, the second patterned VO2 layer 1-2, and the lower VO2 layer 3 in the insulating phase is 20 S / m, and the conductivity in the metallic phase is 200000 S / m.

[0161] The dielectric constants of the upper Topas material dielectric layer 2 and the lower Topas material dielectric layer 5 are 1.93; the bottom gold layer 6, the first patterned gold layer 4-1, the second patterned gold layer 4-2, and the four third patterned gold layers 4-3 are made of gold with a conductivity of 4.56 × 10⁻⁶. 7 S / m.

[0162] The fabrication method of a vanadium dioxide-based multi-frequency / ultra-wideband switchable terahertz metamaterial absorber includes the following steps:

[0163] Step 1: Preparation of the bottom gold layer 6;

[0164] Step 2: Deposition of the lower Topas material dielectric layer 5;

[0165] Step 3: Fabrication of the intermediate patterned gold layer unit 4;

[0166] Step 4: Preparation of the lower VO2 layer 3;

[0167] Step 5: Deposition of the upper Topas material dielectric layer 2;

[0168] Step 6: Fabrication of the upper patterned VO2 layer unit 1.

[0169] Step 1 is as follows:

[0170] Step 1.1, Substrate cleaning:

[0171] High-purity silicon was selected as the substrate and ultrasonically cleaned with acetone, ethanol and deionized water for 10 min in sequence to remove surface contaminants; after drying with nitrogen, it was dried in an oven at 110℃ for 30 min.

[0172] Step 1.2, Metal Thin Film Deposition:

[0173] Gold thin films were deposited using electron beam evaporation.

[0174] Step 1.3, Annealing treatment:

[0175] Annealing at 300℃ for 30 min improves the crystal quality and conductivity of the gold film, resulting in the bottom gold layer 6;

[0176] Step 2 is as follows:

[0177] Step 2.1, Spin-coating the polyimide dielectric layer:

[0178] A polyimide precursor solution is spin-coated onto a base gold film, and the desired dielectric layer thickness is obtained by precisely controlling the spin-coating speed and time.

[0179] Step 2.2, Curing treatment:

[0180] Curing at 150℃ for 1 hour ensures the formation of a stable polyimide film. The curing process is strictly controlled to ensure that the film is flat, free of bubbles and stress cracks, and the lower Topas material dielectric layer 5 is obtained on the bottom gold layer 6.

[0181] Step 3 specifically involves:

[0182] Step 3.1, Photolithographic Patterning:

[0183] The designed metal structure pattern is defined on the cured polyimide surface using electron beam lithography.

[0184] Step 3.2, Gold Thin Film Deposition:

[0185] A thin gold film is deposited using electron beam evaporation.

[0186] Step 3.3, Peeling and Shaping:

[0187] The photoresist and excess gold film on it are removed by stripping, leaving the designed gold micro-nano structure, and the metal patch is used as the intermediate patterned gold layer unit 4.

[0188] Step 4 is as follows:

[0189] A VO2 substrate was deposited on the patterned gold layer unit 4 of the intermediate layer using pulsed laser deposition as the lower VO2 layer 3;

[0190] Step 5 specifically involves:

[0191] Step 5.1: Spin-coating the polyimide dielectric layer:

[0192] A polyimide precursor solution is spin-coated onto a base gold film, and the desired dielectric layer thickness is obtained by precisely controlling the spin-coating speed and time.

[0193] Step 5.2, Curing treatment:

[0194] Curing at 150℃ for 1 hour ensures the formation of a stable polyimide film. The curing process is strictly controlled to ensure that the film is flat, free of bubbles and stress cracks. The upper Topas material dielectric layer 2 is obtained on the lower VO2 layer 33.

[0195] Step 6 specifically involves:

[0196] Step 6.1, Photolithography defines the VO2 region:

[0197] After the top gold structure is fabricated, vanadium dioxide pattern areas are defined in pre-designed locations using photolithography.

[0198] Step 6.2, VO2 thin film deposition:

[0199] A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition.

[0200] Step 6.3, Peeling and Shaping:

[0201] The photoresist and excess vanadium dioxide film on it are removed using a stripping method, leaving the designed structure to obtain a vanadium dioxide patch.

[0202] The periodic structure of the absorber in this embodiment is as follows: Figure 1 As shown, the unit structure diagram is as follows: Figure 2 As shown, each multi-layer structure multi-frequency / ultra-wideband switchable terahertz absorption unit includes, from top to bottom, an upper patterned VO2 layer unit 1, an upper Topas material dielectric layer 2, a lower VO2 layer 3, a middle patterned gold layer unit 4, a lower Topas material dielectric layer 5, and a bottom gold layer 6, with the six material layers bonded together.

[0203] Side view of the unit structure as shown Figure 3 As shown, the thickness t1 of the upper patterned VO2 layer unit 1 is 0.05 μm, the thickness t2 of the upper Topas material dielectric layer 2 is 6 μm, the thickness t3 of the lower VO2 layer 3 is 0.2 μm, the thickness t4 of the middle patterned gold layer unit 4 is 2 μm, the thickness t5 of the lower Topas material dielectric layer 5 is 5 μm, and the thickness t6 of the bottom gold layer 6 is 0.2 μm.

[0204] The top view of the upper patterned VO2 layer unit 1 is as follows Figure 4As shown, the upper patterned VO2 layer unit 1 includes one first patterned VO2 layer 1-1 and four second patterned VO2 layers 1-2. The first patterned VO2 layer 1-1 is annular and is disposed at the center of the upper surface of the upper Topas material dielectric layer 2. The two second patterned VO2 layers 1-2 are quarter-circles, and the four second patterned VO2 layers 1-2 are respectively disposed at the four vertices of the upper Topas material dielectric layer 2. The radius r1 of the first patterned VO2 layer 1-1 is 22 μm, the width d1 of the annulus is 4 μm, and the radius r2 of the second patterned VO2 layer 1-2 is 7.5 μm.

[0205] Top view of intermediate patterned gold layer unit 4 as shown Figure 5 As shown, the intermediate patterned gold layer unit 4 includes a first patterned gold layer 4-1, four second patterned gold layers 4-2 and four third patterned gold layers 4-3.

[0206] The first patterned gold layer 4-1 is an annular shape and is located at the center of the upper surface of the lower Topas material dielectric layer 5.

[0207] The second patterned gold layer 4-2 is a quarter circle, and the four second patterned gold layers 4-2 are respectively set at the four top corners of the lower Topas material dielectric layer 5;

[0208] The third patterned gold layer 4-3 is semi-circular, and a third patterned gold layer 4-3 is set between every two second patterned gold layers 4-2; the center of each third patterned gold layer 4-3 coincides with the midpoint of the side length of the lower Topas material dielectric layer 5;

[0209] The outer radius r3 of the first patterned gold layer 4-1 is 4.2 μm, the annular width d1 of the first patterned gold layer 4-1 is 4 μm, the radius r4 of the circle containing the second patterned gold layer 4-2 is 3.5 μm, and the radius of the circle containing the third patterned gold layer 4-3 is 2.6 μm; the thickness t4 of the first patterned gold layer 4-1 is 2 μm; the thicknesses of the second patterned gold layer 4-2 and the third patterned gold layer 4-3 are the same as the thickness of the first patterned gold layer 4-1.

[0210] The absorption spectrum of vanadium dioxide in the insulating phase absorber is as follows: Figure 6 As shown, when VO2 is in the insulating phase (conductivity 20 S / m), the structure exhibits multi-frequency absorption, with four absorption peaks above 90%, located at 92% at 8.05 THz, 96% at 9.65 THz, 99% at 10.42 THz, and 94% at 11.45 THz.

[0211] The absorption spectrum of vanadium dioxide in a metallic phase absorber is as follows: Figure 7As shown, when VO2 is in the metallic phase (with an electrical conductivity of 200,000 S / m), this structure exhibits ultra-wideband absorption, with an absorption rate of over 90% in the range of 5.87-17.95 THz and an absorption bandwidth of 12.08 THz.

[0212] The real and imaginary parts of the relative impedance of the absorber under the insulating phase of vanadium dioxide are as follows: Figure 8 As shown, when the conductivity of VO2 is 20 S / m, the real part Re(z) of the equivalent impedance at the frequency corresponding to the absorption peak is close to 1, and the imaginary part Im(z) is close to 0. The absorber has achieved the impedance matching condition, thus realizing a discrete perfect absorption peak in the frequency domain.

[0213] The real and imaginary parts of the relative impedance of vanadium dioxide absorbers in the metallic phase are as follows: Figure 9 As shown, when the conductivity of VO2 is 200000 S / m, it can be seen that in the corresponding high absorption frequency range, the solid line represents the real part of the impedance Re(z) approaching 1, and the dashed line represents the imaginary part of the impedance Im(z) approaching 0, which makes the absorber exhibit good matching with free space in the broadband absorption frequency range.

[0214] The electric field distribution on the xoy surface of the absorber at a frequency of 8.05 THz and a vanadium dioxide conductivity of 20 S / m is as follows: Figure 10 As shown, the electric field is concentrated at the edge of the metal patch. The rings and cylinders are similar to different resonators, and the absorption peak appears due to the coupling between the two or all three. This phenomenon indicates that adjacent rings and cylinders with similar but unequal sizes will couple.

[0215] The electric field distribution on the xoz surface of the absorber at a frequency of 8.05 THz and a vanadium dioxide conductivity of 20 S / m is as follows: Figure 11 As shown, the electric field is distributed at the edges of the three resonators. Observing the electric field distribution in different layers of the xoz surface, it can be found that there are higher electric field hotspots in the upper dielectric layer cavity, which indicates that the electromagnetic wave at this absorption peak excites an electric dipole resonance.

[0216] The electric field distribution on the xoy surface of the absorber at a frequency of 11.45 THz and a vanadium dioxide conductivity of 20 S / m is as follows: Figure 12 As shown, the electric field is mainly concentrated at the edges of the metal patch ring and cylinder, indicating that a coupling effect occurs between adjacent resonators of similar but different sizes, which jointly excite the absorption peak.

[0217] The electric field distribution on the xoz surface of the absorber at a frequency of 11.45 THz and a vanadium dioxide conductivity of 20 S / m is as follows: Figure 13As shown, the strong electric field is highly concentrated in the extremely narrow gap between the three metal resonators. This indicates that the absorption peaks differ due to the coupling between adjacent resonators.

[0218] The electric field distribution of the absorber at a frequency of 4 THz and a vanadium dioxide conductivity of 200,000 S / m is as follows: Figure 14 As shown, the electric field distribution mainly occurs at the edges of the annular and circular patches. Coupling not only occurs between adjacent cells of the same patch, but also between different patches. Due to their similar size and moderate distance, this coupling method is more stable.

[0219] The cross-sectional electric field distribution of an absorber at a frequency of 12.1 THz and a vanadium dioxide conductivity of 200,000 S / m. For example... Figure 15 As shown, the absorption characteristics of the model are an ultrawide flat absorption peak within the broadband absorption range. This characteristic is similar to that of a typical Fabry-Pérot resonator. The bottom gold layer acts like a reflective mirror, concentrating the electric field in the dielectric cavity and absorbing energy through internal heat loss.

[0220] When the VO2 conductivity is 20 S / m, the polarization sensitivity of the absorber at different polarization angles is as follows: Figure 16 As shown, the proposed structures all possess good symmetry, and the absorbers exhibit excellent polarization stability.

[0221] When the VO2 conductivity is 200000 S / m, the polarization sensitivity of the absorber at different polarization angles is as follows: Figure 17 As shown, when the polarization angle increases from 0° to 90°, the absorption spectra of both remain unchanged, indicating that the absorber has polarization insensitivity in broadband mode.

[0222] When the conductivity of VO2 is 200000 S / m, the effect of the incident angle on the absorptivity is as follows: Figure 18 As shown, perfect absorption is achieved at an incident angle of less than 60°, indicating that the absorber has a good wide incident angle, and the designed terahertz absorber has excellent wide-angle absorption characteristics.

[0223] In summary, this invention presents a vanadium dioxide-based terahertz metamaterial absorber with switchable multi-frequency / ultra-wideband absorption. The designed absorber can switch between multi-frequency and ultra-wideband absorption by adjusting the conductivity of vanadium dioxide through temperature control. When the conductivity of vanadium dioxide is 20 S / m, the absorber exhibits multi-frequency absorption with four absorption peaks above 90%, located at 8.05 THz, 9.65 THz, 10.42 THz, and 11.45 THz. When the conductivity of vanadium dioxide is 200,000 S / m, the absorber achieves an absorption rate of over 90% in the range of 5.87–17.95 THz, with an absorption bandwidth of 12.08 THz. This vanadium dioxide-based terahertz metamaterial absorber exhibits polarization insensitivity and maintains excellent absorption performance under different polarization angles and a wide incident angle range of 0°–60°. The preparation method of this invention is simple and easy to operate.

[0224] Example 2

[0225] This embodiment is based on a vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber, which includes M×N multi-layered multi-frequency / ultra-wideband switchable terahertz absorption units. The M×N multi-layered multi-frequency / ultra-wideband switchable terahertz absorption units are distributed in an M×N two-dimensional pattern, where M and N are both positive integers.

[0226] Each multi-layer structure multi-frequency / ultra-wideband switchable terahertz absorption unit includes, from top to bottom, an upper patterned VO2 layer unit 1, an upper Topas material dielectric layer 2, a lower VO2 layer 3, an intermediate patterned gold layer unit 4, a lower Topas material dielectric layer 5, and a bottom gold layer 6, with the six material layers bonded together.

[0227] The upper Topas material dielectric layer 2, the lower VO2 layer 3, the lower Topas material dielectric layer 5, and the bottom gold layer 6 are all square with equal side lengths.

[0228] The upper patterned VO2 layer unit 1 includes one first patterned VO2 layer 1-1 and four second patterned VO2 layers 1-2; the first patterned VO2 layer 1-1 is an annular shape and is disposed at the center of the upper surface of the upper Topas material dielectric layer 2; the second patterned VO2 layer 1-2 is a quarter circle, and the four second patterned VO2 layers 1-2 are respectively disposed at the four apex corners of the upper Topas material dielectric layer 2;

[0229] The outer radius r1 of the first patterned VO2 layer 1-1 is 18 μm, the annular width d1 of the first patterned VO2 layer 1-1 is 6 μm, the radius r2 of the circle containing the second patterned VO2 layer 1-2 is 6.0 μm, the thickness t1 of the first patterned VO2 layer 1-1 is 0.08 μm, and the thickness of the second patterned VO2 layer 1-2 is the same as the thickness of the first patterned VO2 layer 1-1.

[0230] The intermediate patterned gold layer unit 4 includes a first patterned gold layer 4-1, four second patterned gold layers 4-2, and four third patterned gold layers 4-3;

[0231] The first patterned gold layer 4-1 is an annular shape and is located at the center of the upper surface of the lower Topas material dielectric layer 5.

[0232] The second patterned gold layer 4-2 is a quarter circle, and the four second patterned gold layers 4-2 are respectively set at the four top corners of the lower Topas material dielectric layer 5;

[0233] The third patterned gold layer 4-3 is semi-circular, and a third patterned gold layer 4-3 is set between every two second patterned gold layers 4-2; the center of each third patterned gold layer 4-3 coincides with the midpoint of the side length of the lower Topas material dielectric layer 5;

[0234] The outer radius r3 of the first patterned gold layer 4-1 is 4.0 μm, the annular width d2 of the first patterned gold layer 4-1 is 6 μm, the radius r4 of the circle containing the second patterned gold layer 4-2 is 3.3 μm, and the radius of the circle containing the third patterned gold layer 4-3 is 2.9 μm; the thickness t4 of the first patterned gold layer 4-1 is 1.5 μm; the thicknesses of the second patterned gold layer 4-2 and the third patterned gold layer 4-3 are the same as the thickness of the first patterned gold layer 4-1.

[0235] The thickness t2 of the upper Topas material dielectric layer 2 is 4 μm, the thickness t3 of the lower VO2 layer 3 is 0.5 μm, the thickness t5 of the lower Topas material dielectric layer 5 is 4 μm, and the thickness t6 of the bottom gold layer 6 is 0.5 μm. The side length of the upper Topas material dielectric layer 2 is 32 μm, and the side lengths of the lower VO2 layer 3, the lower Topas material dielectric layer 5, and the bottom gold layer 6 are the same as the side length of the upper Topas material dielectric layer 2.

[0236] The conductivity of the first patterned VO2 layer 1-1, the second patterned VO2 layer 1-2, and the lower VO2 layer 3 in the insulating phase is 20 S / m, and the conductivity in the metallic phase is 200000 S / m.

[0237] The dielectric constants of the upper Topas material dielectric layer 2 and the lower Topas material dielectric layer 5 are 1.93; the bottom gold layer 6, the first patterned gold layer 4-1, the second patterned gold layer 4-2, and the four third patterned gold layers 4-3 are made of gold with a conductivity of 4.56 × 10⁻⁶. 7 S / m.

[0238] The fabrication method of a vanadium dioxide-based multi-frequency / ultra-wideband switchable terahertz metamaterial absorber includes the following steps:

[0239] Step 1: Preparation of the bottom gold layer 6; Step 2: Deposition of the lower Topas material dielectric layer 5; Step 3: Preparation of the intermediate patterned gold layer unit 4; Step 4: Preparation of the lower VO2 layer 3; Step 5: Deposition of the upper Topas material dielectric layer 2; Step 6: Preparation of the upper patterned VO2 layer unit 1.

[0240] Step 1 is as follows:

[0241] Step 1.1, Substrate Cleaning: High-purity silicon was selected as the substrate and ultrasonically cleaned sequentially with acetone, ethanol, and deionized water for 15 min to remove surface contaminants; after drying with nitrogen, it was dried in an oven at 120℃ for 40 min; Step 1.2, Metal Thin Film Deposition: Gold thin film was deposited using electron beam evaporation; Step 1.3, Annealing Treatment: Annealing was performed at 350℃ for 40 min to improve the crystallinity and conductivity of the gold thin film, resulting in the bottom gold layer 6;

[0242] Step 2 is as follows:

[0243] Step 2.1, Spin-coating of polyimide dielectric layer: Spin-coating of polyimide precursor solution onto the bottom gold film. By precisely controlling the spin-coating speed and time, the required dielectric layer thickness is obtained. Step 2.2, Curing treatment: Curing at 160℃ for 2 hours to ensure the formation of a stable polyimide film. The curing process is strictly controlled to ensure that the film is flat, free of bubbles and stress cracks, and the lower Topas material dielectric layer 5 is obtained on the bottom gold layer 6.

[0244] Step 3 specifically involves:

[0245] Step 3.1, Photolithography Patterning: The designed metal structure pattern is defined on the cured polyimide surface using electron beam lithography. Step 3.2, Gold Thin Film Deposition: A thin gold film is deposited using electron beam evaporation. Step 3.3, Lift-off Forming: The photoresist and excess gold film on it are removed using a lift-off method, leaving the designed gold micro / nano structure, resulting in a metal patch as the intermediate patterned gold layer unit 4.

[0246] Step 4 is as follows:

[0247] A VO2 substrate was deposited on the patterned gold layer unit 4 of the intermediate layer using pulsed laser deposition as the lower VO2 layer 3;

[0248] Step 5 specifically involves:

[0249] Step 5.1, Spin-coating of polyimide dielectric layer: Spin-coating of polyimide precursor solution onto the underlying gold film. By precisely controlling the spin-coating speed and time, the required dielectric layer thickness is obtained. Step 5.2, Curing treatment: Curing at 160℃ for 2 hours to ensure the formation of a stable polyimide film. The curing process is strictly controlled to ensure that the film is flat, free of bubbles and stress cracks. The upper Topas material dielectric layer 2 is obtained on the lower VO2 layer 33.

[0250] Step 6 specifically involves:

[0251] Step 6.1, Photolithography to define the VO2 region: After the top gold structure is prepared, the vanadium dioxide pattern region is defined in the pre-designed position by photolithography; Step 6.2, VO2 thin film deposition: A vanadium dioxide thin film is deposited in the designated area using pulsed laser deposition; Step 6.3, Lifting and shaping: The photoresist and the excess vanadium dioxide thin film on it are removed by the lift-off method, leaving the designed structure, and a vanadium dioxide patch is obtained.

[0252] Example 3

[0253] This embodiment is based on a vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber, which includes M×N multi-layered multi-frequency / ultra-wideband switchable terahertz absorption units. The M×N multi-layered multi-frequency / ultra-wideband switchable terahertz absorption units are distributed in an M×N two-dimensional pattern, where M and N are both positive integers.

[0254] Each multi-layer structure multi-frequency / ultra-wideband switchable terahertz absorption unit includes, from top to bottom, an upper patterned VO2 layer unit 1, an upper Topas material dielectric layer 2, a lower VO2 layer 3, an intermediate patterned gold layer unit 4, a lower Topas material dielectric layer 5, and a bottom gold layer 6, with the six material layers bonded together.

[0255] The upper Topas material dielectric layer 2, the lower VO2 layer 3, the lower Topas material dielectric layer 5, and the bottom gold layer 6 are all square with equal side lengths.

[0256] The upper patterned VO2 layer unit 1 includes one first patterned VO2 layer 1-1 and four second patterned VO2 layers 1-2; the first patterned VO2 layer 1-1 is an annular shape and is disposed at the center of the upper surface of the upper Topas material dielectric layer 2; the second patterned VO2 layer 1-2 is a quarter circle, and the four second patterned VO2 layers 1-2 are respectively disposed at the four apex corners of the upper Topas material dielectric layer 2;

[0257] The outer radius r1 of the first patterned VO2 layer 1-1 is 24 μm, the annular width d1 of the first patterned VO2 layer 1-1 is 5 μm, the radius r2 of the circle containing the second patterned VO2 layer 1-2 is 4.5 μm, the thickness t1 of the first patterned VO2 layer 1-1 is 0.12 μm, and the thickness of the second patterned VO2 layer 1-2 is the same as the thickness of the first patterned VO2 layer 1-1.

[0258] The intermediate patterned gold layer unit 4 includes a first patterned gold layer 4-1, four second patterned gold layers 4-2, and four third patterned gold layers 4-3;

[0259] The first patterned gold layer 4-1 is an annular shape and is located at the center of the upper surface of the lower Topas material dielectric layer 5.

[0260] The second patterned gold layer 4-2 is a quarter circle, and the four second patterned gold layers 4-2 are respectively set at the four top corners of the lower Topas material dielectric layer 5;

[0261] The third patterned gold layer 4-3 is semi-circular, and a third patterned gold layer 4-3 is set between every two second patterned gold layers 4-2; the center of each third patterned gold layer 4-3 coincides with the midpoint of the side length of the lower Topas material dielectric layer 5;

[0262] The outer radius r3 of the first patterned gold layer 4-1 is 3.9 μm, the annular width d2 of the first patterned gold layer 4-1 is 5 μm, the radius r4 of the circle containing the second patterned gold layer 4-2 is 3.2 μm, and the radius of the circle containing the third patterned gold layer 4-3 is 3.0 μm; the thickness t4 of the first patterned gold layer 4-1 is 1.0 μm; the thicknesses of the second patterned gold layer 4-2 and the third patterned gold layer 4-3 are the same as the thickness of the first patterned gold layer 4-1.

[0263] The thickness t2 of the upper Topas material dielectric layer 2 is 8 μm, the thickness t3 of the lower VO2 layer 3 is 0.4 μm, the thickness t5 of the lower Topas material dielectric layer 5 is 6 μm, and the thickness t6 of the bottom gold layer 6 is 0.3 μm. The side length of the upper Topas material dielectric layer 2 is 33 μm, and the side lengths of the lower VO2 layer 3, the lower Topas material dielectric layer 5, and the bottom gold layer 6 are the same as the side length of the upper Topas material dielectric layer 2.

[0264] The conductivity of the first patterned VO2 layer 1-1, the second patterned VO2 layer 1-2, and the lower VO2 layer 3 in the insulating phase is 20 S / m, and the conductivity in the metallic phase is 200000 S / m.

[0265] The dielectric constants of the upper Topas material dielectric layer 2 and the lower Topas material dielectric layer 5 are 1.93; the bottom gold layer 6, the first patterned gold layer 4-1, the second patterned gold layer 4-2, and the four third patterned gold layers 4-3 are made of gold with a conductivity of 4.56 × 10⁻⁶. 7 S / m.

[0266] The fabrication method of a vanadium dioxide-based multi-frequency / ultra-wideband switchable terahertz metamaterial absorber includes the following steps:

[0267] Step 1: Preparation of the bottom gold layer 6; Step 2: Deposition of the lower Topas material dielectric layer 5; Step 3: Preparation of the intermediate patterned gold layer unit 4; Step 4: Preparation of the lower VO2 layer 3; Step 5: Deposition of the upper Topas material dielectric layer 2; Step 6: Preparation of the upper patterned VO2 layer unit 1.

[0268] Step 1 is as follows:

[0269] Step 1.1, Substrate Cleaning: High-purity silicon was selected as the substrate and ultrasonically cleaned with acetone, ethanol and deionized water for 12 min in sequence to remove surface contaminants; after drying with nitrogen, it was dried in an oven at 115℃ for 35 min; Step 1.2, Metal Thin Film Deposition: Gold thin film was deposited using electron beam evaporation; Step 1.3, Annealing Treatment: Annealing was performed at 320℃ for 35 min to improve the crystallinity and conductivity of the gold thin film, resulting in the bottom gold layer 6;

[0270] Step 2 is as follows:

[0271] Step 2.1, Spin-coating of polyimide dielectric layer: Spin-coating of polyimide precursor solution onto the bottom gold film, obtaining the required dielectric layer thickness by precisely controlling the spin-coating speed and time; Step 2.2, Curing treatment: Curing at 155℃ for 1.5h to ensure the formation of a stable polyimide film, strictly controlling the curing process to ensure the film is flat, free of bubbles and stress cracks, thus obtaining the lower Topas material dielectric layer 5 on the bottom gold layer 6;

[0272] Step 3 specifically involves:

[0273] Step 3.1, Photolithography Patterning: The designed metal structure pattern is defined on the cured polyimide surface using electron beam lithography. Step 3.2, Gold Thin Film Deposition: A thin gold film is deposited using electron beam evaporation. Step 3.3, Lift-off Forming: The photoresist and excess gold film on it are removed using a lift-off method, leaving the designed gold micro / nano structure, resulting in a metal patch as the intermediate patterned gold layer unit 4.

[0274] Step 4 is as follows:

[0275] A VO2 substrate was deposited on the patterned gold layer unit 4 of the intermediate layer using pulsed laser deposition as the lower VO2 layer 3;

[0276] Step 5 specifically involves:

[0277] Step 5.1, Spin-coating of polyimide dielectric layer: Spin-coating of polyimide precursor solution onto the underlying gold film. By precisely controlling the spin-coating speed and time, the required dielectric layer thickness is obtained. Step 5.2, Curing treatment: Curing at 155℃ for 1.5h to ensure the formation of a stable polyimide film. Strict control of the curing process to ensure that the film is flat, free of bubbles and stress cracks. The upper Topas material dielectric layer 2 is obtained on the lower VO2 layer 3.

[0278] Step 6 specifically involves:

[0279] Step 6.1, Photolithography to define the VO2 region: After the top gold structure is prepared, the vanadium dioxide pattern region is defined in the pre-designed position by photolithography; Step 6.2, VO2 thin film deposition: A vanadium dioxide thin film is deposited in the designated area using pulsed laser deposition; Step 6.3, Lifting and shaping: The photoresist and the excess vanadium dioxide thin film on it are removed by the lift-off method, leaving the designed structure, and a vanadium dioxide patch is obtained.

[0280] Example 4

[0281] This embodiment is based on a vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber, which includes M×N multi-layered multi-frequency / ultra-wideband switchable terahertz absorption units. The M×N multi-layered multi-frequency / ultra-wideband switchable terahertz absorption units are distributed in an M×N two-dimensional pattern, where M and N are both positive integers.

[0282] Each multi-layer structure multi-frequency / ultra-wideband switchable terahertz absorption unit includes, from top to bottom, an upper patterned VO2 layer unit 1, an upper Topas material dielectric layer 2, a lower VO2 layer 3, an intermediate patterned gold layer unit 4, a lower Topas material dielectric layer 5, and a bottom gold layer 6, with the six material layers bonded together.

[0283] The upper Topas material dielectric layer 2, the lower VO2 layer 3, the lower Topas material dielectric layer 5, and the bottom gold layer 6 are all square with equal side lengths.

[0284] The upper patterned VO2 layer unit 1 includes one first patterned VO2 layer 1-1 and four second patterned VO2 layers 1-2; the first patterned VO2 layer 1-1 is an annular shape and is disposed at the center of the upper surface of the upper Topas material dielectric layer 2; the second patterned VO2 layer 1-2 is a quarter circle, and the four second patterned VO2 layers 1-2 are respectively disposed at the four apex corners of the upper Topas material dielectric layer 2;

[0285] The outer radius r1 of the first patterned VO2 layer 1-1 is 23 μm, the annular width d1 of the first patterned VO2 layer 1-1 is 4 μm, the radius r2 of the circle containing the second patterned VO2 layer 1-2 is 3.0 μm, the thickness t1 of the first patterned VO2 layer 1-1 is 0.16 μm, and the thickness of the second patterned VO2 layer 1-2 is the same as the thickness of the first patterned VO2 layer 1-1.

[0286] The intermediate patterned gold layer unit 4 includes a first patterned gold layer 4-1, four second patterned gold layers 4-2, and four third patterned gold layers 4-3;

[0287] The first patterned gold layer 4-1 is an annular shape and is located at the center of the upper surface of the lower Topas material dielectric layer 5.

[0288] The second patterned gold layer 4-2 is a quarter circle, and the four second patterned gold layers 4-2 are respectively set at the four top corners of the lower Topas material dielectric layer 5;

[0289] The third patterned gold layer 4-3 is semi-circular, and a third patterned gold layer 4-3 is set between every two second patterned gold layers 4-2; the center of each third patterned gold layer 4-3 coincides with the midpoint of the side length of the lower Topas material dielectric layer 5;

[0290] The outer radius r3 of the first patterned gold layer 4-1 is 3.6 μm, the annular width d2 of the first patterned gold layer 4-1 is 4 μm, the radius r4 of the circle containing the second patterned gold layer 4-2 is 3.0 μm, and the radius of the circle containing the third patterned gold layer 4-3 is 3.1 μm; the thickness t4 of the first patterned gold layer 4-1 is 2.5 μm; the thicknesses of the second patterned gold layer 4-2 and the third patterned gold layer 4-3 are the same as the thickness of the first patterned gold layer 4-1.

[0291] The thickness t2 of the upper Topas material dielectric layer 2 is 4 μm, the thickness t3 of the lower VO2 layer 3 is 0.5 μm, the thickness t5 of the lower Topas material dielectric layer 5 is 8 μm, and the thickness t6 of the bottom gold layer 6 is 0.5 μm. The side length of the upper Topas material dielectric layer 2 is 35 μm, and the side lengths of the lower VO2 layer 3, the lower Topas material dielectric layer 5, and the bottom gold layer 6 are the same as the side length of the upper Topas material dielectric layer 2.

[0292] The conductivity of the first patterned VO2 layer 1-1, the second patterned VO2 layer 1-2, and the lower VO2 layer 3 in the insulating phase is 20 S / m, and the conductivity in the metallic phase is 200000 S / m.

[0293] The dielectric constants of the upper Topas material dielectric layer 2 and the lower Topas material dielectric layer 5 are 1.93; the bottom gold layer 6, the first patterned gold layer 4-1, the second patterned gold layer 4-2, and the four third patterned gold layers 4-3 are made of gold with a conductivity of 4.56 × 10⁻⁶. 7 S / m.

[0294] The fabrication method of a vanadium dioxide-based multi-frequency / ultra-wideband switchable terahertz metamaterial absorber includes the following steps:

[0295] Step 1: Preparation of the bottom gold layer 6; Step 2: Deposition of the lower Topas material dielectric layer 5; Step 3: Preparation of the intermediate patterned gold layer unit 4; Step 4: Preparation of the lower VO2 layer 3; Step 5: Deposition of the upper Topas material dielectric layer 2; Step 6: Preparation of the upper patterned VO2 layer unit 1.

[0296] Step 1 is as follows:

[0297] Step 1.1, Substrate Cleaning: High-purity silicon was selected as the substrate and ultrasonically cleaned sequentially with acetone, ethanol, and deionized water for 15 min to remove surface contaminants; after drying with nitrogen, it was dried in an oven at 110℃ for 40 min; Step 1.2, Metal Thin Film Deposition: Gold thin film was deposited using electron beam evaporation; Step 1.3, Annealing Treatment: Annealing was performed at 300℃ for 30 min to improve the crystallinity and conductivity of the gold thin film, resulting in the bottom gold layer 6;

[0298] Step 2 is as follows:

[0299] Step 2.1, Spin-coating of polyimide dielectric layer: Spin-coating of polyimide precursor solution onto the bottom gold film. By precisely controlling the spin-coating speed and time, the required dielectric layer thickness is obtained. Step 2.2, Curing treatment: Curing at 160℃ for 2 hours to ensure the formation of a stable polyimide film. The curing process is strictly controlled to ensure that the film is flat, free of bubbles and stress cracks, and the lower Topas material dielectric layer 5 is obtained on the bottom gold layer 6.

[0300] Step 3 specifically includes: Step 3.1, Photolithography Patterning: The designed metal structure pattern is defined on the cured polyimide surface using electron beam lithography; Step 3.2, Gold Thin Film Deposition: A thin gold film is deposited using electron beam evaporation; Step 3.3, Lift-off Forming: The photoresist and excess gold film on it are removed using a lift-off method, leaving the designed gold micro / nano structure, resulting in a metal patch as the intermediate patterned gold layer unit 4;

[0301] Step 4 specifically involves: depositing a VO2 substrate as the lower VO2 layer 3 on the patterned gold layer unit 4 of the intermediate layer using pulsed laser deposition;

[0302] Step 5 specifically involves:

[0303] Step 5.1, Spin-coating of polyimide dielectric layer: Spin-coating of polyimide precursor solution onto the underlying gold film. By precisely controlling the spin-coating speed and time, the required dielectric layer thickness is obtained. Step 5.2, Curing treatment: Curing at 150℃ for 1 hour to ensure the formation of a stable polyimide film. Strict control of the curing process to ensure that the film is flat, free of bubbles and stress cracks. The upper Topas material dielectric layer 2 is obtained on the lower VO2 layer 3.

[0304] Step 6 specifically includes: Step 6.1, Photolithography to define the VO2 region: After the top gold structure is prepared, the vanadium dioxide pattern region is defined in the pre-designed position by photolithography; Step 6.2, VO2 thin film deposition: A vanadium dioxide thin film is deposited in the designated area using pulsed laser deposition; Step 6.3, Lifting and shaping: The photoresist and the excess vanadium dioxide thin film on it are removed by the lift-off method, leaving the designed structure to obtain the vanadium dioxide patch.

[0305] Example 5

[0306] This embodiment is based on a vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber, which includes M×N multi-layered multi-frequency / ultra-wideband switchable terahertz absorption units. The M×N multi-layered multi-frequency / ultra-wideband switchable terahertz absorption units are distributed in an M×N two-dimensional pattern, where M and N are both positive integers.

[0307] Each multi-layer structure multi-frequency / ultra-wideband switchable terahertz absorption unit includes, from top to bottom, an upper patterned VO2 layer unit 1, an upper Topas material dielectric layer 2, a lower VO2 layer 3, an intermediate patterned gold layer unit 4, a lower Topas material dielectric layer 5, and a bottom gold layer 6, with the six material layers bonded together.

[0308] The upper Topas material dielectric layer 2, the lower VO2 layer 3, the lower Topas material dielectric layer 5, and the bottom gold layer 6 are all square with equal side lengths.

[0309] The upper patterned VO2 layer unit 1 includes one first patterned VO2 layer 1-1 and four second patterned VO2 layers 1-2; the first patterned VO2 layer 1-1 is an annular shape and is disposed at the center of the upper surface of the upper Topas material dielectric layer 2; the second patterned VO2 layer 1-2 is a quarter circle, and the four second patterned VO2 layers 1-2 are respectively disposed at the four apex corners of the upper Topas material dielectric layer 2;

[0310] The outer radius r1 of the first patterned VO2 layer 1-1 is 20 μm, the annular width d1 of the first patterned VO2 layer 1-1 is 6 μm, the radius r2 of the circle containing the second patterned VO2 layer 1-2 is 1.5 μm, the thickness t1 of the first patterned VO2 layer 1-1 is 0.20 μm, and the thickness of the second patterned VO2 layer 1-2 is the same as the thickness of the first patterned VO2 layer 1-1.

[0311] The intermediate patterned gold layer unit 4 includes a first patterned gold layer 4-1, four second patterned gold layers 4-2, and four third patterned gold layers 4-3;

[0312] The first patterned gold layer 4-1 is an annular shape and is located at the center of the upper surface of the lower Topas material dielectric layer 5.

[0313] The second patterned gold layer 4-2 is a quarter circle, and the four second patterned gold layers 4-2 are respectively set at the four top corners of the lower Topas material dielectric layer 5;

[0314] The third patterned gold layer 4-3 is semi-circular, and a third patterned gold layer 4-3 is set between every two second patterned gold layers 4-2; the center of each third patterned gold layer 4-3 coincides with the midpoint of the side length of the lower Topas material dielectric layer 5;

[0315] The outer radius r3 of the first patterned gold layer 4-1 is 4.0 μm, the annular width d2 of the first patterned gold layer 4-1 is 6 μm, the radius r4 of the circle containing the second patterned gold layer 4-2 is 2.8 μm, and the radius of the circle containing the third patterned gold layer 4-3 is 3.2 μm; the thickness t4 of the first patterned gold layer 4-1 is 3.0 μm; the thicknesses of the second patterned gold layer 4-2 and the third patterned gold layer 4-3 are the same as the thickness of the first patterned gold layer 4-1.

[0316] The thickness t2 of the upper Topas material dielectric layer 2 is 6 μm, the thickness t3 of the lower VO2 layer 3 is 0.2 μm, the thickness t5 of the lower Topas material dielectric layer 5 is 6 μm, and the thickness t6 of the bottom gold layer 6 is 0.5 μm. The side length of the upper Topas material dielectric layer 2 is 3 μm, and the side lengths of the lower VO2 layer 3, the lower Topas material dielectric layer 5, and the bottom gold layer 6 are the same as the side length of the upper Topas material dielectric layer 2.

[0317] The conductivity of the first patterned VO2 layer 1-1, the second patterned VO2 layer 1-2, and the lower VO2 layer 3 in the insulating phase is 20 S / m, and the conductivity in the metallic phase is 200000 S / m.

[0318] The dielectric constants of the upper Topas material dielectric layer 2 and the lower Topas material dielectric layer 5 are 1.93; the bottom gold layer 6, the first patterned gold layer 4-1, the second patterned gold layer 4-2, and the four third patterned gold layers 4-3 are made of gold with a conductivity of 4.56 × 10⁻⁶. 7 S / m.

[0319] The fabrication method of a vanadium dioxide-based multi-frequency / ultra-wideband switchable terahertz metamaterial absorber includes the following steps:

[0320] Step 1: Preparation of the bottom gold layer 6; Step 2: Deposition of the lower Topas material dielectric layer 5; Step 3: Preparation of the intermediate patterned gold layer unit 4; Step 4: Preparation of the lower VO2 layer 3; Step 5: Deposition of the upper Topas material dielectric layer 2; Step 6: Preparation of the upper patterned VO2 layer unit 1.

[0321] Step 1 is as follows: Step 1.1, Substrate cleaning: High-purity silicon is selected as the substrate, and it is ultrasonically cleaned with acetone, ethanol and deionized water for 10 min in sequence to remove surface contaminants; after drying with nitrogen, it is dried in an oven at 110℃ for 40 min; Step 1.2, Metal film deposition: Gold film is deposited using electron beam evaporation; Step 1.3, Annealing treatment: Annealing is performed at 300℃ for 40 min to improve the crystal quality and conductivity of the gold film, resulting in the bottom gold layer 6;

[0322] Step 2 specifically includes: Step 2.1, spin coating of polyimide dielectric layer: spin coating of polyimide precursor solution onto the bottom gold film, obtaining the required dielectric layer thickness by precisely controlling the spin coating speed and time; Step 2.2, curing treatment: curing at 150℃ for 2 hours to ensure the formation of a stable polyimide film, strictly controlling the curing process to ensure that the film is flat, free of bubbles and stress cracks, and obtaining the lower Topas material dielectric layer 5 on the bottom gold layer 6;

[0323] Step 3 specifically includes: Step 3.1, Photolithography Patterning: The designed metal structure pattern is defined on the cured polyimide surface using electron beam lithography; Step 3.2, Gold Thin Film Deposition: A thin gold film is deposited using electron beam evaporation; Step 3.3, Lift-off Forming: The photoresist and excess gold film on it are removed using a lift-off method, leaving the designed gold micro / nano structure, resulting in a metal patch as the intermediate patterned gold layer unit 4;

[0324] Step 4 specifically involves: depositing a VO2 substrate as the lower VO2 layer 3 on the patterned gold layer unit 4 of the intermediate layer using pulsed laser deposition;

[0325] Step 5 specifically includes: Step 5.1, spin coating of polyimide dielectric layer: spin coating of polyimide precursor solution onto the bottom gold film, obtaining the required dielectric layer thickness by precisely controlling the spin coating speed and time; Step 5.2, curing treatment: curing at 150℃ for 2 hours to ensure the formation of a stable polyimide film, strictly controlling the curing process to ensure that the film is flat, free of bubbles and stress cracks, and obtaining the upper Topas material dielectric layer 2 on the lower VO2 layer 3;

[0326] Step 6 specifically includes: Step 6.1, Photolithography to define the VO2 region: After the top gold structure is prepared, the vanadium dioxide pattern region is defined in the pre-designed position by photolithography; Step 6.2, VO2 thin film deposition: A vanadium dioxide thin film is deposited in the designated area using pulsed laser deposition; Step 6.3, Lifting and shaping: The photoresist and the excess vanadium dioxide thin film on it are removed by the lift-off method, leaving the designed structure to obtain the vanadium dioxide patch.

[0327] Example 6

[0328] This embodiment is based on a vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber, which includes M×N multi-layered multi-frequency / ultra-wideband switchable terahertz absorption units. The M×N multi-layered multi-frequency / ultra-wideband switchable terahertz absorption units are distributed in an M×N two-dimensional pattern, where M and N are both positive integers.

[0329] Each multi-layer structure multi-frequency / ultra-wideband switchable terahertz absorption unit includes, from top to bottom, an upper patterned VO2 layer unit 1, an upper Topas material dielectric layer 2, a lower VO2 layer 3, an intermediate patterned gold layer unit 4, a lower Topas material dielectric layer 5, and a bottom gold layer 6, with the six material layers bonded together.

[0330] The upper Topas material dielectric layer 2, the lower VO2 layer 3, the lower Topas material dielectric layer 5, and the bottom gold layer 6 are all square with equal side lengths.

[0331] The upper patterned VO2 layer unit 1 includes one first patterned VO2 layer 1-1 and four second patterned VO2 layers 1-2; the first patterned VO2 layer 1-1 is an annular shape and is disposed at the center of the upper surface of the upper Topas material dielectric layer 2; the second patterned VO2 layer 1-2 is a quarter circle, and the four second patterned VO2 layers 1-2 are respectively disposed at the four apex corners of the upper Topas material dielectric layer 2;

[0332] The outer radius r1 of the first patterned VO2 layer 1-1 is 22 μm, the annular width d1 of the first patterned VO2 layer 1-1 is 5 μm, the radius r2 of the circle containing the second patterned VO2 layer 1-2 is 7.5 μm, the thickness t1 of the first patterned VO2 layer 1-1 is 0.05 μm, and the thickness of the second patterned VO2 layer 1-2 is the same as the thickness of the first patterned VO2 layer 1-1.

[0333] The intermediate patterned gold layer unit 4 includes a first patterned gold layer 4-1, four second patterned gold layers 4-2, and four third patterned gold layers 4-3;

[0334] The first patterned gold layer 4-1 is an annular shape and is located at the center of the upper surface of the lower Topas material dielectric layer 5.

[0335] The second patterned gold layer 4-2 is a quarter circle, and the four second patterned gold layers 4-2 are respectively set at the four top corners of the lower Topas material dielectric layer 5;

[0336] The third patterned gold layer 4-3 is semi-circular, and a third patterned gold layer 4-3 is disposed between every two second patterned gold layers 4-2; the center of each third patterned gold layer 4-3 coincides with the midpoint of the side length of the underlying Topas material dielectric layer 5; the outer radius r3 of the first patterned gold layer 4-1 is 4.0 μm, the annular width d2 of the first patterned gold layer 4-1 is 6 μm, the radius r4 of the circle containing the second patterned gold layer 4-2 is 2.8 μm, and the radius of the circle containing the third patterned gold layer 4-3 is 3.0 μm; the thickness t4 of the first patterned gold layer 4-1 is 2.0 μm; the thicknesses of the second patterned gold layer 4-2 and the third patterned gold layer 4-3 are the same as the thickness of the first patterned gold layer 4-1. The thickness t2 of the upper Topas material dielectric layer 2 is 6 μm, the thickness t3 of the lower VO2 layer 3 is 0.2 μm, the thickness t5 of the lower Topas material dielectric layer 5 is 6 μm, and the thickness t6 of the bottom gold layer 6 is 0.5 μm. The side length of the upper Topas material dielectric layer 2 is 35 μm, and the side lengths of the lower VO2 layer 3, the lower Topas material dielectric layer 5, and the bottom gold layer 6 are the same as the side length of the upper Topas material dielectric layer 2. The conductivity of the first patterned VO2 layer 1-1, the second patterned VO2 layer 1-2, and the lower VO2 layer 3 in the insulating phase is 20 S / m, and the conductivity in the metallic phase is 200000 S / m. The dielectric constants of the upper Topas material dielectric layer 2 and the lower Topas material dielectric layer 5 are 1.93; the bottom gold layer 6, the first patterned gold layer 4-1, the second patterned gold layer 4-2, and the four third patterned gold layers 4-3 are made of gold with a conductivity of 4.56 × 10⁻⁶. 7 S / m.

[0337] The fabrication method of a vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber includes the following steps: Step 1, fabrication of the bottom gold layer 6; Step 2, deposition of the lower Topas material dielectric layer 5; Step 3, fabrication of the intermediate patterned gold layer unit 4; Step 4, fabrication of the lower VO2 layer 3; Step 5, deposition of the upper Topas material dielectric layer 2; Step 6, fabrication of the upper patterned VO2 layer unit 1.

[0338] Step 1 specifically includes: Step 1.1, Substrate cleaning: High-purity silicon is selected as the substrate, and it is ultrasonically cleaned with acetone, ethanol and deionized water for 15 minutes in sequence to remove surface contaminants; after drying with nitrogen, it is dried in an oven at 110℃ for 30 minutes; Step 1.2, Metal thin film deposition: Gold thin film is deposited using electron beam evaporation; Step 1.3, Annealing treatment: Annealing is performed at 350℃ for 40 minutes to improve the crystal quality and conductivity of the gold thin film, resulting in the bottom gold layer 6;

[0339] Step 2 specifically includes: Step 2.1, spin coating of polyimide dielectric layer: spin coating of polyimide precursor solution onto the bottom gold film, obtaining the required dielectric layer thickness by precisely controlling the spin coating speed and time; Step 2.2, curing treatment: curing at 150℃ for 1 hour to ensure the formation of a stable polyimide film, strictly controlling the curing process to ensure that the film is flat, free of bubbles and stress cracks, and obtaining the lower Topas material dielectric layer 5 on the bottom gold layer 6;

[0340] Step 3 specifically includes: Step 3.1, Photolithography Patterning: The designed metal structure pattern is defined on the cured polyimide surface using electron beam lithography; Step 3.2, Gold Thin Film Deposition: A thin gold film is deposited using electron beam evaporation; Step 3.3, Lift-off Forming: The photoresist and excess gold film on it are removed using a lift-off method, leaving the designed gold micro / nano structure, resulting in a metal patch as the intermediate patterned gold layer unit 4;

[0341] Step 4 specifically involves: depositing a VO2 substrate as the lower VO2 layer 3 on the patterned gold layer unit 4 of the intermediate layer using pulsed laser deposition;

[0342] Step 5 specifically includes: Step 5.1, spin coating of polyimide dielectric layer: spin coating of polyimide precursor solution onto the bottom gold film, obtaining the required dielectric layer thickness by precisely controlling the spin coating speed and time; Step 5.2, curing treatment: curing at 150℃ for 2 hours to ensure the formation of a stable polyimide film, strictly controlling the curing process to ensure that the film is flat, free of bubbles and stress cracks, and obtaining the upper Topas material dielectric layer 2 on the lower VO2 layer 3;

[0343] Step 6 specifically includes: Step 6.1, Photolithography to define the VO2 region: After the top gold structure is prepared, the vanadium dioxide pattern region is defined in the pre-designed position by photolithography; Step 6.2, VO2 thin film deposition: A vanadium dioxide thin film is deposited in the designated area using pulsed laser deposition; Step 6.3, Lifting and shaping: The photoresist and the excess vanadium dioxide thin film on it are removed by the lift-off method, leaving the designed structure to obtain the vanadium dioxide patch.

[0344] This invention utilizes the insulating-to-metallic phase transition properties of VO2, based on a vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber. By controlling the temperature to regulate the conductivity of VO2, the absorption behavior of the absorber can be dynamically adjusted, enabling it to switch between ultra-wideband and multi-frequency absorption. This invention allows for flexible switching between multi-frequency and ultra-wideband terahertz absorption modes, overcoming the limitations of traditional terahertz sensors, such as fixed structures, limited functionality, and difficulty in dynamic reconfiguration. This absorber combines excellent absorption characteristics with flexible multi-frequency / ultra-wideband switching, demonstrating significant application potential in terahertz detection and sensing.

Claims

1. A vanadium dioxide based multi-frequency / ultra-wideband switchable terahertz metamaterial absorber, characterized in that, The application discloses a multi-frequency / ultra-wideband switchable terahertz absorption unit comprising M*N multi-layer structures, wherein M and N are positive integers. Each multi-frequency / ultra-wideband switchable terahertz absorption unit comprises, from top to bottom, an upper patterned VO2 layer unit (1), an upper Topas material dielectric layer (2), a lower VO2 layer (3), an intermediate patterned gold layer unit (4), a lower Topas material dielectric layer (5) and a bottom gold layer (6). The upper Topas material dielectric layer (2), the lower VO2 layer (3), the lower Topas material dielectric layer (5) and the bottom gold layer (6) are all square-shaped and have equal side lengths. The upper patterned VO2 layer unit (1) comprises a first patterned VO2 layer (1-1) and four second patterned VO2 layers (1-2); the first patterned VO2 layer (1-1) is circular annular and is arranged at the center of the upper surface of the upper Topas material dielectric layer (2); the second patterned VO2 layers (1-2) are all quarter circular, and the four second patterned VO2 layers (1-2) are arranged at the four corners of the upper Topas material dielectric layer (2) respectively. The outer circle radius r1 of the first patterned VO2 layer (1-1) is 18-24 mu m, the circular annular width d1 of the first patterned VO2 layer (1-1) is 4-6 mu m, the radius r2 of the circle where the second patterned VO2 layer (1-2) is located is 1.5-7.5 mu m; the thickness t1 of the first patterned VO2 layer (1-1) is 0.02-0.2 mu m; the thickness of the second patterned VO2 layer (1-2) is the same as that of the first patterned VO2 layer (1-1). The intermediate patterned gold layer unit (4) comprises a first patterned gold layer (4-1), four second patterned gold layers (4-2) and four third patterned gold layers (4-3). The first patterned gold layer (4-1) is circular annular and is arranged at the center of the upper surface of the lower Topas material dielectric layer (5). The second patterned gold layers (4-2) are all quarter circular, and the four second patterned gold layers (4-2) are arranged at the four corners of the lower Topas material dielectric layer (5) respectively. The third patterned gold layers (4-3) are all semicircular, and one third patterned gold layer (4-3) is arranged between every two second patterned gold layers (4-2); the center of each third patterned gold layer (4-3) coincides with the midpoint of the side length of the lower Topas material dielectric layer (5). The outer circle radius r3 of the first patterned gold layer (4-1) is 3.6-4.2 μm, the circular ring width d2 of the first patterned gold layer (4-1) is 4-6 μm, the radius r4 of the circle where the second patterned gold layer (4-2) is located is 2.8-3.5 μm, and the radius of the circle where the third patterned gold layer (4-3) is located is 2.6-3.2 μm; the thickness t4 of the first patterned gold layer (4-1) is 1-3 μm; the thicknesses of the second patterned gold layer (4-2) and the third patterned gold layer (4-3) are the same as that of the first patterned gold layer (4-1).

2. The vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber according to claim 1, characterized in that, The thickness t2 of the upper Topas material dielectric layer (2) is 4-8 μm, the thickness t3 of the lower VO2 layer (3) is 0.2-0.5 μm, the thickness t5 of the lower Topas material dielectric layer (5) is 4-8 μm, and the thickness t6 of the bottom gold layer (6) is 0.2-0.5 μm; the side length of the upper Topas material dielectric layer (2) is 32-35 μm, and the side lengths of the lower VO2 layer (3), the lower Topas material dielectric layer (5), and the bottom gold layer (6) are consistent with that of the upper Topas material dielectric layer (2). 3.The vanadium dioxide based multi-frequency / ultra-wideband switchable terahertz metamaterial absorber according to claim 1, wherein, The conductivity of the first patterned VO2 layer (1-1), the second patterned VO2 layer (1-2), and the lower VO2 layer (3) in the insulating phase is 20 S / m, and the conductivity in the metallic phase is 200000 S / m. 4.The vanadium dioxide based multi-frequency / ultra-wideband switchable terahertz metamaterial absorber of claim 1, wherein, The dielectric constant of the upper Topas material dielectric layer (2) and the lower Topas material dielectric layer (5) is 1.93; the conductivity of the bottom gold layer (6), the first patterned gold layer (4-1), the second patterned gold layer (4-2), and the four third patterned gold layers (4-3) is 4.56 x 10 7 S / m.

5. The vanadium dioxide multi-frequency / ultra-wideband switchable terahertz metamaterial absorber according to any one of claims 1-4, characterized in that, The method comprises the following steps: Step 1, preparation of the bottom gold layer (6); Step 2, deposition of the lower Topas material dielectric layer (5); Step 3, preparation of the middle layer patterned gold layer unit (4); Step 4, preparation of the lower VO2 layer (3); Step 5, deposition of the upper Topas material dielectric layer (2); Step 6, preparation of the upper patterned VO2 layer unit (1). 6.The vanadium dioxide based multi-frequency / ultra-wideband switchable terahertz metamaterial absorber according to claim 5, wherein, Step 1 is specifically: Step 1.1, substrate cleaning: High-purity silicon is selected as the substrate, and the surface contaminants are removed by ultrasonic cleaning with acetone, ethanol, and deionized water for 10-15 min; after nitrogen blowing and drying, the substrate is dried in an oven at 110-120 °C for 30-40 min; Step 1.2, metal thin film deposition: Gold thin film is deposited by electron beam evaporation method; Step 1.3, annealing treatment: Annealing at 300-350 °C for 30-40 min to improve the crystalline quality and conductivity of the gold thin film, thereby obtaining the bottom gold layer (6); Step 2 is specifically: Step 2.1, polyimide dielectric layer spin coating: A polyimide precursor solution is spin-coated on the bottom gold film, and the desired dielectric layer thickness is obtained by precisely controlling the spin-coating speed and time; Step 2.2, curing treatment: Curing at 150-160 °C for 1-2 h to ensure the formation of a stable polyimide film, and the curing process is strictly controlled to ensure that the film is flat, bubble-free, and stress-free, thereby obtaining the lower Topas material dielectric layer (5) on the bottom gold layer (6); Step 3 is specifically: Step 3.1, photolithography patterning: On the cured polyimide surface, the designed metal structure pattern is defined using electron beam lithography technology; Step 3.2, gold thin film deposition: A thin gold film is deposited using electron beam evaporation; Step 3.3, stripping and shaping: The photoresist and the excess gold film on it are removed using stripping method, leaving the designed gold micro-nano structure, obtaining the metal patch as the intermediate layer patterned gold layer unit (4); Step 4 is specifically: A layer of VO2 substrate is deposited on the intermediate layer patterned gold layer unit (4) using pulsed laser deposition as the lower VO2 layer (3); Step 5 is specifically: Step 5.1, polyimide dielectric layer spin coating: Spin-coat a polyimide precursor solution on the lower VO2 layer (3), and obtain the required dielectric layer thickness by precisely controlling the spin-coating speed and time; Step 5.2, curing treatment: Cure at 150-160°C for 1-2h to ensure the formation of a stable polyimide film, and strictly control the curing process to ensure the film is flat, bubble-free and stress-free, obtaining the upper Topas material dielectric layer (2) on the lower VO2 layer (3); Step 6 is specifically: Step 6.1, lithography defines VO2 area: After the top layer gold structure is prepared, the VO2 pattern area is defined at the designed position by lithography; Step 6.2, VO2 thin film deposition: A layer of vanadium dioxide thin film is deposited in the specified area using pulsed laser deposition; Step 6.3, stripping and shaping: The photoresist and the excess vanadium dioxide thin film on it are removed using stripping method, leaving the designed structure, obtaining the vanadium dioxide patch.

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