Ultra-wideband-multifrequency terahertz absorber based on patterned vanadium dioxide and method

Abstract

This invention discloses an ultra-wideband, multi-frequency terahertz absorber based on patterned vanadium dioxide, comprising M×N tunable wideband terahertz absorbing units of patterned vanadium dioxide. These M×N multilayered patterned vanadium dioxide tunable wideband terahertz absorbing units are distributed in an M×N two-dimensional pattern, where M and N are positive integers. Each patterned vanadium dioxide tunable wideband terahertz absorbing unit includes, from top to bottom, a composite resonant layer unit, a second dielectric layer, a vanadium dioxide resonant layer unit, a first dielectric layer, and a metal reflective layer. This terahertz absorber simultaneously achieves high absorption, ultra-wideband, and multi-frequency dynamic tunability over a wide frequency range. A method for fabricating the ultra-wideband, multi-frequency terahertz absorber based on patterned vanadium dioxide is also provided.

Description

Technical Field

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

[0002] Terahertz (THz) waves typically refer to electromagnetic waves with frequencies between 0.1 and 10 THz (corresponding to wavelengths of 30µm to 3mm). Located between microwave and infrared bands, they possess the unique advantages of both microwave and infrared radiation, demonstrating enormous application potential in fields such as high-speed communication, non-destructive testing, security inspection, and biomedical imaging. With the rapid development of terahertz technology, the manipulation and utilization of terahertz waves has become a core research focus. Terahertz absorbers, as key functional devices in terahertz systems, can achieve efficient absorption of terahertz waves in specific frequency bands, playing an irreplaceable role in scenarios such as terahertz stealth, sensing detection, and electromagnetic protection.

[0003] Traditional terahertz absorbers are mostly based on metallic superstructure designs, achieving narrowband absorption through electromagnetic resonance effects. However, their inherent limitations—narrow bandwidth, single function, and lack of tunability—make it difficult to meet the application requirements of modern terahertz systems for broadband, multi-frequency, and reconfigurable applications. To overcome this limitation, researchers have begun to explore tunable terahertz absorbers based on phase change materials. Vanadium dioxide (VO2) has become a research hotspot due to its unique metal-insulator phase transition (MIT) characteristics: near room temperature (approximately 68°C), vanadium dioxide can reversibly transform from an insulating state (high resistance) to a metallic state (low resistance). During the phase transition, the conductivity can undergo a sudden change of 3 to 5 orders of magnitude, with fast response and good reversibility, providing an ideal material basis for the dynamic control of terahertz absorbers.

[0004] However, existing vanadium dioxide-based terahertz absorbers still have many shortcomings: First, most vanadium dioxide-based absorbers can only achieve single-frequency or dual-frequency tunability, making it difficult to cover the entire terahertz band and meet the need for simultaneous multi-band control; second, some broadband absorbers rely on complex multi-layer structure designs, which are difficult and costly to manufacture and have poor structural stability; third, existing patterned vanadium dioxide absorbers mostly adopt simple periodic structures, and the optimization of the slot design is insufficient, making it difficult to balance key performance aspects such as absorption bandwidth, switching efficiency, and absorption intensity, and thus failing to achieve integrated control that is broadband, multi-frequency, and switchable.

[0005] Furthermore, in practical applications, terahertz systems often require absorbers to simultaneously possess the capabilities of broadband continuous absorption and multi-frequency selective switching. For example, in terahertz communication, broadband electromagnetic shielding and selective reception of signals in specific frequency bands must be achieved simultaneously; in sensing and detection, dynamic switching is required based on the characteristic absorption peaks of different analytes. In existing technologies, broadband absorption and multi-frequency switchability are usually mutually restrictive: broadband absorption relies on the coupling and superposition of multiple resonant peaks, while multi-frequency switching requires independently controllable resonant units. It is difficult to simultaneously achieve high-performance broadband absorption and multi-frequency switchability in a single structure, becoming a core bottleneck restricting the practical application of vanadium dioxide-based terahertz absorbers.

[0006] Meanwhile, existing methods for fabricating vanadium dioxide-based absorbers mostly employ micro-nano fabrication processes such as photolithography and electron beam lithography, which suffer from complex processes, long cycle times, and difficulty in large-area fabrication. Furthermore, the precision control of the grooved structure is challenging, leading to poor device performance consistency and failing to meet the demands of large-scale applications. Therefore, developing a vanadium dioxide-based terahertz absorber with a simple structure, convenient fabrication, and broadband, multi-frequency, and switchable characteristics, along with its fabrication method, has become a critical issue urgently needing to be addressed in the field of terahertz technology. Summary of the Invention

[0007] The first objective of this invention is to provide an ultrawideband multi-frequency terahertz absorber based on patterned vanadium dioxide, which simultaneously achieves high absorption, ultrawideband and multi-frequency dynamic tunability over a wide frequency range.

[0008] The second objective of this invention is to provide a method for preparing an ultrawideband multi-frequency switchable terahertz absorber based on patterned vanadium dioxide.

[0009] The first technical solution adopted in this invention is an ultra-wideband multi-frequency terahertz absorber based on patterned vanadium dioxide, which includes M×N tunable wideband terahertz absorption units of patterned vanadium dioxide. The M×N multilayer patterned vanadium dioxide tunable wideband terahertz absorption units are distributed in an M×N two-dimensional pattern, where M and N are both positive integers. Each patterned vanadium dioxide tunable broadband terahertz absorption unit includes, from top to bottom, a composite resonant layer unit, a second dielectric layer, a vanadium dioxide resonant layer unit, a first dielectric layer, and a metal reflective layer.

[0010] The invention is further characterized in that: The metal reflective layer, the first dielectric layer, and the second dielectric layer are all square; the side lengths of the metal reflective layer, the first dielectric layer, and the second dielectric layer are equal; the side length P of the metal reflective layer is 14µm-15µm. The thickness h1 of the metal reflective layer is 0.2µm-0.4µm; the thickness h2 of the first dielectric layer is 3µm-4µm; and the thickness h4 of the second dielectric layer is 3µm-4µm. The metallic reflective layer is made of gold, with an electrical conductivity of 4.52 × 10⁻⁶. 6 S / m; The first and second dielectric layers are made of silicon dioxide with a relative permittivity of 3.9.

[0011] The vanadium dioxide resonant layer unit includes a rectangular frame patch, the outer frame of which is rectangular and the inner frame is square. A cross-shaped patch is set in the center of the rectangular frame patch, which divides the rectangular frame patch into four identical blank areas. A first square patch is set in each blank area. The rectangular frame patch, the cross-shaped patch, and the four first square patches are all attached to the upper surface of the first dielectric layer; the rectangular frame patch, the cross-shaped patch, and the four first square patches are not connected to each other; The rectangular frame patch, the cross-shaped patch, and the four first square patches are all made of vanadium dioxide; the conductivity of vanadium dioxide in the nonmetallic phase is 200 S / m, and the conductivity in the metallic phase is 200000 S / m.

[0012] The rectangular frame patch, the cross-shaped patch, and the four first square patches all have the same thickness; the thickness h3 of the rectangular frame patch is 0.2µm. The rectangular patch has an outer frame width v of 11.6µm and an outer frame length n of 12µm. The inner frame is a square with a side length q of 8µm. The cross-shaped patch has a cross length m of 7.8µm and a width z of 1.4µm.

[0013] The side length t of the first square patch is 2.3µm. The horizontal and vertical spacing between the first square patch and the cross-shaped patch are equal, and the horizontal spacing u is 0.3µm.

[0014] The composite resonant layer unit includes a composite patch assembly disposed at the center of the upper surface of the second dielectric layer, and eight second square patches disposed around the composite patch assembly; except for the center position, the eight second square patches are arranged in a 3-2-3 array on the upper surface of the second dielectric layer; each second square patch has the same size; The second square patch is made of vanadium dioxide; the conductivity of vanadium dioxide in the nonmetallic phase is 200 S / m, and the conductivity in the metallic phase is 200000 S / m. The side length W of the second square patch is 0.8µm; the spacing d1 between two second square patches in adjacent columns is 4.2µm; the spacing d2 between two second square patches in adjacent rows is 4.2µm; spacing d1 and spacing d2 are equal.

[0015] The composite patch assembly includes, from the inside out, a circular patch, a first circular patch, a second circular patch, and an outer patch; The circular patch, the first annular patch, and the second annular patch are sequentially and tightly bonded together; The outer patch does not adhere to the second circular patch; The outer patch is a circular patch divided into six equal parts. The outer patch consists of six identical arc-shaped patches, and the spacing g between any two adjacent arc-shaped patches is the same, with a spacing g of 0.1µm. The circular patch, the second circular patch, and the outer patch are made of gold; The first annular patch is made of vanadium dioxide; The radius 'a' of the circular patch is 1µm; The inner radius of the first annular patch is equal to the radius a of the circular patch, and the outer radius b is 1.8µm; The inner radius of the second annular patch is equal to the outer radius b of the first annular patch, and the outer radius c of the second annular patch is 2.2µm; The inner radius e of the outer patch is 2.8µm, and the outer radius f of the outer patch is 3.2µm; The thicknesses of the second square patch, the circular patch, the first annular patch, the second annular patch, and the outer patch are all equal, and the thickness h5 of the second square patch is 0.2µm.

[0016] The second technical solution adopted in this invention is, The fabrication method of an ultrawideband multi-frequency terahertz absorber based on patterned vanadium dioxide specifically includes the following steps: Step 1: Fabrication of the bottom metal reflective layer; Step 2: Deposition of the first dielectric layer; Step 3: Fabrication of vanadium dioxide resonant layer units; Step 4: Preparation of the second dielectric layer; Step 5: Fabrication of composite resonant layer units.

[0017] The invention is further characterized in that: Step 1 is as follows: Step 1.1: Substrate cleaning: 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. Step 1.2: Metal Thin Film Deposition: Gold thin films were deposited using electron beam evaporation. Step 1.3: Annealing treatment: Annealing at 300℃-350℃ for 30min-40min improves the crystallinity and conductivity of the gold film, thus obtaining a metal reflective layer; Step 2 is as follows: Step 2.1: Deposition of the silica dielectric layer: A silicon dioxide precursor was deposited on the upper surface of the metal reflective layer using plasma-enhanced chemical vapor deposition to obtain the required dielectric layer thickness. Step 2.2: Curing treatment: The first dielectric layer was cured at a constant temperature of 200℃-250℃ for 1.5h-2.5h, and a qualified first dielectric layer was finally prepared on the surface of the metal reflective layer. Step 3 specifically involves: Step 3.1: Photolithography defines the vanadium dioxide region: The vanadium dioxide pattern area is defined in a pre-designed location using photolithography; Step 3.2: Vanadium dioxide thin film deposition: A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition. Step 3.3: Peeling and Shaping: The photoresist and excess vanadium dioxide film on it are removed by stripping, leaving the designed structure, to obtain the vanadium dioxide resonant layer unit. Step 4.1, Deposition of silica dielectric layer: On the upper surface of the vanadium dioxide resonant layer unit, a silicon dioxide precursor is deposited by plasma-enhanced chemical vapor deposition to obtain the required dielectric layer thickness. Step 4.2, Curing treatment: A qualified second dielectric layer was prepared on the upper surface of the vanadium dioxide resonant layer unit by curing at a constant temperature of 200℃-250℃ for 1.5h-2.5h. Step 5 specifically involves: Step 5.1: Photolithography defines the vanadium dioxide region: The vanadium dioxide pattern area is defined in a pre-designed location using photolithography; Step 5.2: Vanadium dioxide thin film deposition: A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition. Step 5.3: Photolithography defines the gold patch area: Photoresist is spin-coated onto the substrate surface of the prepared second dielectric layer, and the patterned area of ​​the gold patch is defined at a preset position by photolithography. Step 5.4: Gold thin film deposition: A gold thin film of a specified thickness is deposited in the area defined by photolithography using a magnetron sputtering process; Step 5.5: Peeling and Shaping The photoresist and excess vanadium dioxide and gold films on it are removed by a stripping method, leaving the designed structure to obtain the composite resonant layer unit.

[0018] The beneficial effects of this invention are: (1) The absorber of this invention, in order to broaden the absorption bandwidth, patterns the vanadium dioxide resonant layer to improve impedance matching. It consists of a vanadium dioxide resonant layer, an intermediate silicon dioxide dielectric layer, and a bottom gold reflective layer. Under normal incidence, the absorption rate reaches 90%-98% in the frequency range of 4.3-16 THz, with an absorption bandwidth of 11.7 THz, a center frequency of 9.85 THz, and a corresponding relative bandwidth of 145.2%. The absorber achieves an absorption rate of 90%-99% in multiple discrete high-frequency bands, including 14.5-15.2 THz, 16.0-17.0 THz, 18.5-19.5 THz, and 20.0-21.0 THz, with center frequencies of 14.8 THz, 16.5 THz, 19.0 THz, and 20.5 THz, respectively, and corresponding relative bandwidths of 4.7%, 6.1%, 5.3%, and 4.9%. This terahertz absorber achieves high absorption and dynamic tunability / switching across a wide frequency range.

[0019] (2) The absorber of the present invention can adjust the conductivity of vanadium dioxide from 200 S / m to 200000 S / m by changing the temperature, and achieve amplitude tuning of the absorption peak from 2.5% to 99% within the corresponding bandwidth.

[0020] (3) The absorber of the present invention is polarization insensitive and maintains excellent absorption performance under different polarization angles and wide incident angles. Attached Figure Description

[0021] Figure 1 This is the periodic structure of the ultrawideband-multi-frequency terahertz absorber based on patterned vanadium dioxide provided in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the structure of the patterned vanadium dioxide tunable broadband terahertz absorption unit of the absorber provided in Embodiment 1 of the present invention; Figure 3 This is a top view of the composite resonant layer unit of the absorber provided in Embodiment 1 of the present invention; Figure 4 This is a top view of the vanadium dioxide resonant layer unit of the absorber provided in Embodiment 1 of the present invention; Figure 5 This is a side view of the vanadium dioxide resonant layer unit of the absorber provided in Embodiment 1 of the present invention; Figure 6 This is a broadband absorption spectrum of the ultra-wideband multi-frequency terahertz absorber with patterned vanadium dioxide when vanadium dioxide is a metallic phase, provided in Embodiment 1 of the present invention. Figure 7 This is the multi-frequency absorption spectrum of the ultra-wideband multi-frequency terahertz absorber with patterned vanadium dioxide when vanadium dioxide is a non-metallic phase, provided in Embodiment 1 of the present invention. Figure 8 This is the absorption spectrum of an ultrawideband multi-frequency terahertz absorber with patterned vanadium dioxide under different electrical conductivity conditions provided in Embodiment 1 of the present invention. Figure 9 This is the multi-frequency electric field distribution of a patterned vanadium dioxide ultrawideband multi-frequency terahertz absorber with a conductivity of 200 S / m provided in Embodiment 1 of the present invention. Figure 10 This is the broadband electric field distribution of an ultrawideband multi-frequency terahertz absorber with patterned vanadium dioxide at a conductivity of 200,000 S / m, provided in Embodiment 1 of the present invention. Figure 11 This describes the absorption characteristics of the absorber provided in Embodiment 1 of the present invention at different polarization angles when electromagnetic waves are incident normally in a metallic phase. Figure 12 This is the absorption spectrum of the absorber provided in Embodiment 1 of the present invention under different incident angles in the metallic phase TE wave; Figure 13 This is the absorption spectrum of the absorber provided in Embodiment 1 of the present invention under different incident angles in the metallic phase TM wave.

[0022] Figure 14 This describes the absorption characteristics of the absorber provided in Embodiment 1 of the present invention under different polarization angles when electromagnetic waves are incident normally in a non-metallic phase. Figure 15 This is the absorption spectrum of the absorber provided in Embodiment 1 of the present invention under different incident angles in the nonmetallic phase TE wave; Figure 16 The absorption spectra of the absorber provided in Embodiment 1 of the present invention at different incident angles under non-metallic TM waves are shown.

[0023] In the figure, 1. Metal reflective layer, 2. First dielectric layer, 3. Vanadium dioxide resonant layer unit, 4. Second dielectric layer, 5. Composite resonant layer unit; 3-1. Rectangular patch, 3-2. Cross-shaped patch, 3-3. First square patch; 5-1. Second square patch, 5-2. Circular patch, 5-3. First annular patch, 5-4. Second annular patch, 5-5. Outer ring patch. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0025] This invention provides an ultrawideband multi-frequency terahertz absorber based on patterned vanadium dioxide, such as... Figure 1-5 As shown, it includes M×N patterned vanadium dioxide tunable broadband terahertz absorption units. The M×N multilayer patterned vanadium dioxide tunable broadband terahertz absorption units are distributed in an M×N two-dimensional pattern, where M and N are both positive integers. Each patterned vanadium dioxide tunable broadband terahertz absorption unit includes, from top to bottom, a composite resonant layer unit 5, a second dielectric layer 4, a vanadium dioxide resonant layer unit 3, a first dielectric layer 2, and a metal reflective layer 1, with the five layers bonded together.

[0026] Metal reflective layer 1, first dielectric layer 2 and second dielectric layer 4 are all square; the side lengths of metal reflective layer 1, first dielectric layer 2 and second dielectric layer 4 are equal; the side length P of metal reflective layer 1 is 14µm-15µm; The thickness h1 of the metal reflective layer 1 is 0.2µm-0.4µm; the thickness h2 of the first dielectric layer 2 is 3µm-4µm; and the thickness h4 of the second dielectric layer 4 is 3µm-4µm. The metal reflective layer 1 is made of gold with an electrical conductivity of 4.52 × 10⁻⁶. 6 S / m; The first dielectric layer 2 and the second dielectric layer 4 are made of silicon dioxide with a relative permittivity of 3.9.

[0027] Vanadium dioxide resonant layer unit 3 includes a rectangular frame patch 3-1, the outer frame of which is rectangular and the inner frame is square; A cross-shaped patch 3-2 is provided at the center of the rectangular frame patch 3-1. The cross-shaped patch 3-2 divides the rectangular frame patch 3-1 into four identical blank areas. A first square patch 3-3 is provided in each blank area. The rectangular frame patch 3-1, the cross-shaped patch 3-2, and the four first square patches 3-3 are all attached to the upper surface of the first dielectric layer 2; the rectangular frame patch 3-1, the cross-shaped patch 3-2, and the four first square patches 3-3 are not connected to each other; The rectangular frame patch 3-1, the cross-shaped patch 3-2, and the four first square patches 3-3 are all made of vanadium dioxide; the conductivity of vanadium dioxide in the non-metallic phase is 200 S / m, and the conductivity in the metallic phase is 200000 S / m.

[0028] The rectangular frame patch 3-1, the cross-shaped patch 3-2, and the four first square patches 3-3 are all of equal thickness; the thickness h3 of the rectangular frame patch 3-1 is 0.2µm. The rectangular patch 3-1 has an outer frame width v of 11.6µm and an outer frame length n of 12µm. The inner frame is a square with a side length q of 8µm. The cross-shaped patch 3-2 has a cross length m of 7.8µm and a width z of 1.4µm.

[0029] The side length t of the first square patch 3-3 is 2.3µm. The horizontal and vertical spacing between the first square patch 3-3 and the cross-shaped patch 3-2 are equal, and the horizontal spacing u is 0.3µm.

[0030] The composite resonant layer unit 5 includes a composite patch assembly disposed at the center of the upper surface of the second dielectric layer 4, and eight second square patches 5-1 disposed around the composite patch assembly; except for the center position, the eight second square patches 5-1 are arranged in a 3-2-3 array on the upper surface of the second dielectric layer 4; each second square patch 5-1 has the same size; The material of the second square patch 5-1 is vanadium dioxide; the conductivity of vanadium dioxide in the nonmetallic phase is 200 S / m, and the conductivity in the metallic phase is 200000 S / m; The side length W of the second square patch 5-1 is 0.8µm; the spacing d1 between two second square patches 5-1 in adjacent columns is 4.2µm; the spacing d2 between two second square patches 5-1 in adjacent rows is 4.2µm; the spacing d1 and the spacing d2 are equal.

[0031] The composite patch assembly includes, from the inside out, a circular patch 5-2, a first annular patch 5-3, a second annular patch 5-4, and an outer patch 5-5; The circular patch 5-2, the first annular patch 5-3, and the second annular patch 5-4 are sequentially and tightly bonded together; The outer patch 5-5 does not fit with the second annular patch 5-4; The outer patch 5-5 is a circular patch divided into six equal parts. The outer patch 5-5 is composed of six identical arc-shaped patches, and the spacing g between each pair of adjacent arc-shaped patches is the same, with a spacing g of 0.1µm. The circular patch 5-2, the second annular patch 5-4, and the outer patch 5-5 are made of gold; The material of the first annular patch 5-3 is vanadium dioxide; The radius 'a' of the circular patch 5-2 is 1µm; The inner radius of the first annular patch 5-3 is equal to the radius a of the circular patch 5-2, and the outer radius b is 1.8µm; The inner radius of the second annular patch 5-4 is equal to the outer radius b of the first annular patch 5-3, and the outer radius c of the second annular patch 5-4 is 2.2µm; The inner radius e of the outer patch 5-5 is 2.8µm, and the outer radius f of the outer patch 5-5 is 3.2µm; The thicknesses of the second square patch 5-1, the circular patch 5-2, the first annular patch 5-3, the second annular patch 5-4, and the outer patch 5-5 are all equal, and the thickness h5 of the second square patch 5-1 is 0.2µm.

[0032] This invention also provides a method for preparing an ultrawideband multi-frequency terahertz absorber based on patterned vanadium dioxide, specifically including the following steps: Step 1: Preparation of the bottom metal reflective layer 1; Step 1 is as follows: Step 1.1: Substrate cleaning: 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. Step 1.2: Metal Thin Film Deposition: Gold thin films were deposited using electron beam evaporation. Step 1.3: Annealing treatment: Annealing at 300℃-350℃ for 30min-40min improves the crystal quality and conductivity of the gold film, resulting in metal reflective layer 1; Step 2: Deposition of the first dielectric layer 2; Step 2 is as follows: Step 2.1: Deposition of the silica dielectric layer: A silica precursor, such as tetraethyl orthosilicate (Si(OC2H5)4), is deposited on the upper surface of the metal reflective layer 1 using plasma-enhanced chemical vapor deposition (PECVD). The required dielectric layer thickness is obtained by precisely controlling the deposition power (100W-150W), precursor flow rate (50sccm-80sccm), reaction pressure (10Pa-30Pa), and deposition time (30min-40min). Step 2.2: Curing treatment: Curing at a constant temperature of 200℃-250℃ for 1.5h-2.5h ensures that the silica precursor is fully cross-linked and cured, forming a stable and dense silica film. The silica precursor deposited by PECVD without additional annealing treatment can meet the requirements of density and flatness of the dielectric layer after curing. During the curing process, temperature uniformity must be strictly controlled to avoid local overheating or uneven temperature, ensuring that the film surface is flat, free of pinholes, cracks, and peeling. Finally, a qualified first dielectric layer 2 is prepared on the upper surface of the metal reflective layer 1. Step 3: Preparation of vanadium dioxide resonant layer unit 3; Step 3 specifically involves: Step 3.1: Photolithography defines the vanadium dioxide region: The vanadium dioxide pattern area is defined in a pre-designed location using photolithography; Step 3.2: Vanadium dioxide thin film deposition: A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition. Step 3.3: Peeling and Shaping: The photoresist and excess vanadium dioxide film on it were removed by stripping, leaving the designed structure, to obtain vanadium dioxide resonant layer unit 3. Step 4: Preparation of the second dielectric layer 4; Step 4.1, Deposition of silica dielectric layer: On the upper surface of vanadium dioxide resonant layer unit 3, a silica precursor, preferably tetraethyl orthosilicate Si(OC2H5)4, is deposited using plasma-enhanced chemical vapor deposition (PECVD). By precisely controlling the deposition power (100W-150W), precursor flow rate (50sccm-80sccm), reaction pressure (10Pa-30Pa), and deposition time (30min-40min), the thickness of the dielectric layer is precisely controlled to obtain the required dielectric layer thickness and ensure that the thickness uniformity meets the preparation requirements. Step 4.2, Curing treatment: Curing at a constant temperature of 200℃-250℃ for 1.5h-2.5h ensures that the silica precursor is fully cross-linked and cured, forming a stable and dense silica film. The silica precursor deposited by PECVD without additional annealing can meet the requirements for density and flatness of the dielectric layer after curing. During the curing process, temperature uniformity must be strictly controlled to avoid local overheating or temperature unevenness, ensuring that the film surface is flat, free of pinholes, cracks, and peeling. Finally, a qualified second dielectric layer 4 is prepared on the surface of the vanadium dioxide resonant layer unit 3. Step 5: Fabrication of composite resonant layer unit 5; Step 5 specifically involves: Step 5.1: Photolithography defines the vanadium dioxide region: The vanadium dioxide pattern area is defined in a pre-designed location using photolithography; Step 5.2: Vanadium dioxide thin film deposition: A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition. Step 5.3: Photolithography defines the gold patch area: Photoresist is spin-coated onto the substrate surface of the prepared second dielectric layer 4, and the pattern area of ​​the gold patch is defined at a preset position by photolithography. Step 5.4: Gold film deposition: A gold film of a specified thickness is deposited in the area defined by photolithography using magnetron sputtering (or electron beam evaporation / thermal evaporation). Step 5.5: Peeling and Shaping The photoresist and excess vanadium dioxide and gold films on it were removed by a stripping method, leaving the designed structure, to obtain the composite resonant layer unit 5.

[0033] Example 1 Ultra-wideband multi-frequency terahertz absorber based on patterned vanadium dioxide, such as Figure 1-5 As shown, it includes 3×4 patterned vanadium dioxide tunable broadband terahertz absorption units. The number of patterned vanadium dioxide ultra-wideband-multi-frequency terahertz absorption units does not affect the overall absorption performance. The 3×4 multilayer patterned vanadium dioxide tunable broadband terahertz absorption units are distributed in a 3×4 two-dimensional pattern. Each patterned vanadium dioxide tunable broadband terahertz absorption unit includes, from top to bottom, a composite resonant layer unit 5, a second dielectric layer 4, a vanadium dioxide resonant layer unit 3, a first dielectric layer 2, and a metal reflective layer 1.

[0034] Metal reflective layer 1, first dielectric layer 2 and second dielectric layer 4 are all square; the side lengths of metal reflective layer 1, first dielectric layer 2 and second dielectric layer 4 are equal; the side length P of metal reflective layer 1 is 14µm; The thickness h1 of the metal reflective layer 1 is 0.2µm; the thickness h2 of the first dielectric layer 2 is 3µm; and the thickness h4 of the second dielectric layer 4 is 3µm. The metal reflective layer 1 is made of gold with an electrical conductivity of 4.52 × 10⁻⁶. 6 S / m; much greater than the skin depth of metal in the terahertz band, ensuring the transmittance of the absorber T = 0.

[0035] The first dielectric layer 2 and the second dielectric layer 4 are made of silicon dioxide with a relative permittivity of 3.9.

[0036] Vanadium dioxide resonant layer unit 3 includes a rectangular frame patch 3-1, the outer frame of which is rectangular and the inner frame is square; A cross-shaped patch 3-2 is provided at the center of the rectangular frame patch 3-1. The cross-shaped patch 3-2 divides the rectangular frame patch 3-1 into four identical blank areas. A first square patch 3-3 is provided in each blank area. The rectangular frame patch 3-1, the cross-shaped patch 3-2, and the four first square patches 3-3 are all attached to the upper surface of the first dielectric layer 2; the rectangular frame patch 3-1, the cross-shaped patch 3-2, and the four first square patches 3-3 are not connected to each other; The rectangular frame patch 3-1, the cross-shaped patch 3-2, and the four first square patches 3-3 are all made of vanadium dioxide; the conductivity of vanadium dioxide in the non-metallic phase is 200 S / m, and the conductivity in the metallic phase is 200000 S / m.

[0037] The rectangular frame patch 3-1, the cross-shaped patch 3-2, and the four first square patches 3-3 are all of equal thickness; the thickness h3 of the rectangular frame patch 3-1 is 0.2µm. The rectangular patch 3-1 has an outer frame width v of 11.6µm and an outer frame length n of 12µm. The inner frame is a square with a side length q of 8µm. The cross-shaped patch 3-2 has a cross length m of 7.8µm and a width z of 1.4µm.

[0038] The side length t of the first square patch 3-3 is 2.3µm. The horizontal and vertical spacing between the first square patch 3-3 and the cross-shaped patch 3-2 are equal, and the horizontal spacing u is 0.3µm.

[0039] The composite resonant layer unit 5 includes a composite patch assembly disposed at the center of the upper surface of the second dielectric layer 4, and eight second square patches 5-1 disposed around the composite patch assembly; except for the center position, the eight second square patches 5-1 are arranged in an array of 3-2-3 first row number-second row number-third row number on the upper surface of the second dielectric layer 4; the size of each second square patch 5-1 is the same. The material of the second square patch 5-1 is vanadium dioxide; the conductivity of vanadium dioxide in the nonmetallic phase is 200 S / m, and the conductivity in the metallic phase is 200000 S / m; The side length W of the second square patch 5-1 is 0.8µm; the spacing d1 between two second square patches 5-1 in adjacent columns is 4.2µm; the spacing d2 between two second square patches 5-1 in adjacent rows is 4.2µm; the spacing d1 and the spacing d2 are equal.

[0040] The composite patch assembly includes, from the inside out, a circular patch 5-2, a first annular patch 5-3, a second annular patch 5-4, and an outer patch 5-5; The circular patch 5-2, the first annular patch 5-3, and the second annular patch 5-4 are sequentially and tightly bonded together; The outer patch 5-5 does not fit with the second annular patch 5-4; The outer patch 5-5 is a circular patch divided into six equal parts. The outer patch 5-5 is composed of six identical arc-shaped patches, and the spacing g between each pair of adjacent arc-shaped patches is the same, with a spacing g of 0.1µm. The circular patch 5-2, the second annular patch 5-4, and the outer patch 5-5 are made of gold; The material of the first annular patch 5-3 is vanadium dioxide; The radius 'a' of the circular patch 5-2 is 1µm; The inner radius of the first annular patch 5-3 is equal to the radius a of the circular patch 5-2, and the outer radius b is 1.8µm; The inner radius of the second annular patch 5-4 is equal to the outer radius b of the first annular patch 5-3, and the outer radius c of the second annular patch 5-4 is 2.2µm; The inner radius e of the outer patch 5-5 is 2.8µm, and the outer radius f of the outer patch 5-5 is 3.2µm; The thicknesses of the second square patch 5-1, the circular patch 5-2, the first annular patch 5-3, the second annular patch 5-4, and the outer patch 5-5 are all equal, and the thickness h5 of the second square patch 5-1 is 0.2µm.

[0041] Absorption spectrum as shown Figures 6-7 As shown, the absorption rate exceeds 90% in the frequency range of 4.3-16 THz, with an absorption bandwidth reaching 11.7 THz. Within multiple discrete high-frequency bands, including 14.5-15.2 THz, 16.0-17.0 THz, 18.5-19.5 THz, and 20.0-21.0 THz, the absorption rate reaches 90%-99%, achieving excellent absorption performance. The absorption spectra of vanadium dioxide at different conductivities are shown in the figure. Figure 8 As shown, when vanadium dioxide is in the insulating phase with a conductivity of 200 S / m, its absorption rate reaches 90%~99% in multiple discrete high-frequency bands, achieving good absorption performance. When vanadium dioxide is in the metallic phase with a conductivity of 200,000 S / m, it achieves absorption performance with an absorption rate higher than 90% in the 1.5-4.2 THz frequency band, reaching a fully absorbed state and achieving tunable performance. The electric field distribution diagrams under different conductivity are shown below. Figures 9-10 As shown, Figure 9The electric field energy in the insulating state is highly localized within the internal region of the ring resonant structure, forming a concentric ring-shaped field strength distribution centered on the ring's core. The central region within the ring exhibits a low field strength, with multiple layers of high-field-strength rings appearing radially outwards, ultimately reaching a peak field strength at the inner edge of the ring structure. The square pad region shows no significant electric field accumulation, forming only a uniform background field around the structure. This distribution is a typical characteristic of metamaterial geometric electromagnetic resonance modes: the non-metallic vanadium dioxide phase exhibits dielectric-like properties. The incident terahertz wave excites multiple standing wave resonances within the ring structure, confining the electric field within the structure. This corresponds to sharp discrete absorption peaks in the multi-frequency absorption curves, with each absorption peak corresponding to an independent internal resonance mode. The field strength exhibits a distinct layered standing wave morphology with extremely strong localization, forming an effective field distribution only within the resonant structure. The field strength outside the structure is uniform and relatively low, perfectly demonstrating the characteristics of "geometric resonance dominance and multi-frequency narrowband absorption."

[0042] When the conductivity is high, as vanadium dioxide gradually transforms into metallic properties, the charge is mainly distributed at the outer edge of the patterned vanadium dioxide. When the conductivity is 200,000 S / m, the electric field distribution location remains unchanged, but the electric field strength increases significantly, generating localized surface plasmon resonance at the silica / vanadium dioxide interface. The influence of the resonant layer and the reflective layer on terahertz waves is enhanced, further improving the absorption performance and increasing the absorption rate.

[0043] When vanadium dioxide is in the metallic phase, the absorber achieves an absorption rate of 90%-98% in the frequency range of 4.3-16 THz, with an absorption bandwidth of 11.7 THz, a center frequency of 9.85 THz, and a corresponding relative bandwidth of 145.2%. When vanadium dioxide is in the nonmetallic phase, the absorber achieves an absorption rate of 90%-99% in multiple discrete high-frequency bands, including 14.5-15.2 THz, 16.0-17.0 THz, 18.5-19.5 THz, and 20.0-21.0 THz, with center frequencies of 14.8 THz, 16.5 THz, 19.0 THz, and 20.5 THz, and corresponding relative bandwidths of 4.7%, 6.1%, 5.3%, and 4.9%, respectively. By changing the conductivity of vanadium dioxide, the absorption peak can be approximately tuned from 2.5% to 99%.

[0044] Based on the basic structure and metal phase absorption characteristics of Example 1, the absorption characteristics of the absorber under different polarization angles and different incident angles (TE wave, TM wave) in the metal phase (vanadium dioxide conductivity = 200000 S / m) were tested and analyzed to verify the stability and practicality of ultra-wideband absorption in the metal phase.

[0045] Figure 11This embodiment describes the absorption characteristics of the ultra-wideband multi-frequency terahertz absorber based on patterned vanadium dioxide under different polarization angles when electromagnetic waves are incident normally in a metallic phase. Figure 11 It can be seen that, within a polarization angle of 0°-50°, the ultra-wideband high absorption characteristics of the absorber are basically maintained in the 90%-99% absorption range, with small fluctuations in absorption rate. The absorption rate decreases when the angle is too large, indicating that the absorber has good polarization insensitivity and can still maintain ultra-wideband absorption characteristics within a certain polarization angle range when in the metallic phase, thus broadening its practical application scenarios.

[0046] Figure 12 This embodiment presents the absorption spectra of an ultrawideband multi-frequency terahertz absorber based on patterned vanadium dioxide under metallic phase TE waves at different incident angles. The incident angle adjustment range is 0°-80°, with a test point set every 20°, covering the common incident angle range in practical applications. Figure 12 It can be seen that as the incident angle of the TE wave gradually increases, the ultra-wideband absorption plateau of the absorber remains basically stable. Within the incident angle range of 0°-80°, the absorption rate is consistently maintained above 90% without significant attenuation, thus maintaining a high absorption efficiency. This test result proves that the absorber has good absorption stability under different incident angles of the TE wave in the metallic phase. The synergistic design of its layered structure and patterned resonant layer can effectively suppress electromagnetic coupling losses caused by changes in the incident angle, ensuring efficient terahertz wave absorption even in non-normal incident scenarios.

[0047] Figure 13 This embodiment presents the absorption spectra of the ultrawideband multi-frequency terahertz absorber based on patterned vanadium dioxide under metallic TM waves at different incident angles. The incident angle adjustment range is consistent with that of TE waves (0°-80°), ensuring the uniformity and comparability of the test conditions. Similar to the TE wave test results, the absorber can still stably maintain ultrawideband high absorption characteristics under different incident angles of TM waves. Within the 0°-80° incident angle range, the absorption rate is consistently maintained above 90%, and the absorption plateau is stable without significant fluctuations. This result further verifies the angular stability of the absorber under metallic phase. The optimized matching of its patterned vanadium dioxide resonant layer with the reflective layer and dielectric layer can effectively adapt to both TE and TM wave polarization modes, and achieve stable absorption within a wide incident angle range. This ensures that in practical applications, it can achieve efficient capture and absorption of terahertz electromagnetic waves with different incident directions and polarization modes, further improving the practicality and adaptability of the device.

[0048] Based on the basic structure of the ultra-wideband multi-frequency terahertz absorber based on patterned vanadium dioxide provided in Example 1, and combined with the previously verified multi-frequency narrowband absorption characteristics of the non-metallic phase (vanadium dioxide conductivity = 200 S / m), further targeted performance tests and mechanism analyses are conducted. The focus is on testing and analyzing the absorption characteristics of the absorber under different polarization angles and different incident angles (for TE wave and TM wave polarization modes, respectively) in the non-metallic phase state. The core objective is to verify the stability and practical applicability of the multi-frequency absorption characteristics of the non-metallic phase, supplement and improve the bidirectional tunable characteristics of the present invention of "metallic phase ultra-wideband, non-metallic phase multi-frequency", and ensure that the absorber can meet the needs of practical application scenarios in both working modes, providing sufficient experimental support for the technical feature of "tunable and stable terahertz absorption" in the claims.

[0049] Figure 14 This embodiment presents test graphs of the absorption characteristics of an ultra-wideband multi-frequency terahertz absorber based on patterned vanadium dioxide under different polarization angles when electromagnetic waves are incident normally (incident angle of 0°) in a non-metallic phase. During the test, the polarization angle was adjusted from 0° to 80°, with test nodes set at 20° intervals to comprehensively cover all possible polarization directions, ensuring the comprehensiveness, objectivity, and accuracy of the test data. Figure 14 The absorption spectrum curves show that under different polarization angles, the absorption characteristics of the four peak frequencies of the absorber remain basically stable. The center frequency positions of each discrete absorption peak show no significant shift, and the fluctuation range of the peak absorptivity is controlled within 3%. This fluctuation range is within the normal test error range and will not affect the actual performance of the device. This test result fully demonstrates that the absorber also has good polarization insensitivity in the non-metallic phase, which complements the polarization stability characteristics in the metallic phase in Example 3. This achieves polarization stability of the absorber in all phases (metallic and non-metallic phases), eliminating the need for additional polarization adjustment components. It can adapt to terahertz electromagnetic waves with different polarization directions, further broadening the application scenarios of the device in terahertz multi-frequency detection, multi-frequency communication, and other fields.

[0050] Figure 15 This is the absorption spectrum of the ultrawideband multi-frequency terahertz absorber based on patterned vanadium dioxide provided in this embodiment, under nonmetallic phase with TE wave incident. Figure 15 It can be seen that within the incident angle range of 0° to about 50°, the multi-frequency absorption characteristics of the absorber exhibit excellent stability, the center frequency position of each major absorption peak remains basically constant, and the peak absorptivity remains at a high level.

[0051] When the incident angle is further increased to a wide range of 60°-80°, although the main absorption peak in the low-frequency band still maintains a good frequency position, slight perturbations in the absorption mode and the excitation of new resonant modes are observed in the high-frequency band (above approximately 20 THz), which is manifested as a new absorption band in the high-frequency region of the figure, resulting in slightly more complex spectral characteristics. Compared with TM waves, TE waves exhibit more significant absorption frequency stability over a wide angle range, proving that the structure has good wide-angle absorption characteristics for TE-polarized waves.

[0052] Figure 16 This is the absorption spectrum of the ultrawideband multi-frequency terahertz absorber based on patterned vanadium dioxide provided in this embodiment under nonmetallic phase with TM wave incident. Unlike TE waves, this absorber exhibits significant sensitivity to the incident angle of TM waves. As the incident angle increases, the absorption peak shows a significant frequency blue shift (movement to higher frequencies), and the original multi-frequency absorption peak positions shift considerably, with the absorption intensity also fluctuating accordingly.

[0053] The absorber exhibits significant polarization anisotropy in the nonmetallic phase: it has wide-angle frequency stability for TE waves, making it suitable for TE wave absorption scenarios that require adaptation to different incident angles; while for TM waves, it exhibits angle-dependent frequency tuning characteristics.

[0054] In summary, the technical solution and effects of this invention are fully presented from four dimensions: basic structure, core absorption performance, angular polarization characteristics of the metallic phase, and angular polarization characteristics of the non-metallic phase. The various embodiments support each other and progress step by step, clearly verifying the core inventive point of this invention: achieving ultra-wideband, multi-frequency tunable terahertz absorption through patterned vanadium dioxide phase state modulation. It also demonstrates the stability and practicality of the absorber, providing sufficient support for the claims. This terahertz absorber simultaneously achieves high absorption, ultra-wideband performance, and multi-frequency dynamic tunability over a wide frequency range.

[0055] Example 2 Ultra-wideband multi-frequency terahertz absorber based on patterned vanadium dioxide, such as Figure 1-5 As shown, it includes 3×3 patterned vanadium dioxide tunable broadband terahertz absorption units. The 3×3 multilayer patterned vanadium dioxide tunable broadband terahertz absorption units are distributed in a 3×3 two-dimensional pattern, where 3×3 are all positive integers. Each patterned vanadium dioxide tunable broadband terahertz absorption unit includes, from top to bottom, a composite resonant layer unit 5, a second dielectric layer 4, a vanadium dioxide resonant layer unit 3, a first dielectric layer 2, and a metal reflective layer 1.

[0056] Metal reflective layer 1, first dielectric layer 2 and second dielectric layer 4 are all square; the side lengths of metal reflective layer 1, first dielectric layer 2 and second dielectric layer 4 are equal; the side length P of metal reflective layer 1 is 14µm-15µm; The thickness h1 of the metal reflective layer 1 is 0.4µm; the thickness h2 of the first dielectric layer 2 is 4µm; and the thickness h4 of the second dielectric layer 4 is 4µm. The metal reflective layer 1 is made of gold with an electrical conductivity of 4.52 × 10⁻⁶. 6 S / m; The first dielectric layer 2 and the second dielectric layer 4 are made of silicon dioxide with a relative permittivity of 3.9.

[0057] Vanadium dioxide resonant layer unit 3 includes a rectangular frame patch 3-1, the outer frame of which is rectangular and the inner frame is square; A cross-shaped patch 3-2 is provided at the center of the rectangular frame patch 3-1. The cross-shaped patch 3-2 divides the rectangular frame patch 3-1 into four identical blank areas. A first square patch 3-3 is provided in each blank area. The rectangular frame patch 3-1, the cross-shaped patch 3-2, and the four first square patches 3-3 are all attached to the upper surface of the first dielectric layer 2; the rectangular frame patch 3-1, the cross-shaped patch 3-2, and the four first square patches 3-3 are not connected to each other; The rectangular frame patch 3-1, the cross-shaped patch 3-2, and the four first square patches 3-3 are all made of vanadium dioxide; the conductivity of vanadium dioxide in the non-metallic phase is 200 S / m, and the conductivity in the metallic phase is 200000 S / m.

[0058] The rectangular frame patch 3-1, the cross-shaped patch 3-2, and the four first square patches 3-3 are all of equal thickness; the thickness h3 of the rectangular frame patch 3-1 is 0.2µm. The rectangular patch 3-1 has an outer frame width v of 11.6µm and an outer frame length n of 12µm. The inner frame is a square with a side length q of 8µm. The cross-shaped patch 3-2 has a cross length m of 7.8µm and a width z of 1.4µm.

[0059] The side length t of the first square patch 3-3 is 2.3µm. The horizontal and vertical spacing between the first square patch 3-3 and the cross-shaped patch 3-2 are equal, and the horizontal spacing u is 0.3µm.

[0060] The composite resonant layer unit 5 includes a composite patch assembly disposed at the center of the upper surface of the second dielectric layer 4, and eight second square patches 5-1 disposed around the composite patch assembly; except for the center position, the eight second square patches 5-1 are arranged in a 3-2-3 array on the upper surface of the second dielectric layer 4; each second square patch 5-1 has the same size; The material of the second square patch 5-1 is vanadium dioxide; the conductivity of vanadium dioxide in the nonmetallic phase is 200 S / m, and the conductivity in the metallic phase is 200000 S / m; The side length W of the second square patch 5-1 is 0.8µm; the spacing d1 between two second square patches 5-1 in adjacent columns is 4.2µm; the spacing d2 between two second square patches 5-1 in adjacent rows is 4.2µm; the spacing d1 and the spacing d2 are equal.

[0061] The composite patch assembly includes, from the inside out, a circular patch 5-2, a first annular patch 5-3, a second annular patch 5-4, and an outer patch 5-5; The circular patch 5-2, the first annular patch 5-3, and the second annular patch 5-4 are sequentially and tightly bonded together; The outer patch 5-5 does not fit with the second annular patch 5-4; The outer patch 5-5 is a circular patch divided into six equal parts. The outer patch 5-5 is composed of six identical arc-shaped patches, and the spacing g between each pair of adjacent arc-shaped patches is the same, with a spacing g of 0.1µm. The circular patch 5-2, the second annular patch 5-4, and the outer patch 5-5 are made of gold; The material of the first annular patch 5-3 is vanadium dioxide; The radius 'a' of the circular patch 5-2 is 1µm; The inner radius of the first annular patch 5-3 is equal to the radius a of the circular patch 5-2, and the outer radius b is 1.8µm; The inner radius of the second annular patch 5-4 is equal to the outer radius b of the first annular patch 5-3, and the outer radius c of the second annular patch 5-4 is 2.2µm; The inner radius e of the outer patch 5-5 is 2.8µm, and the outer radius f of the outer patch 5-5 is 3.2µm; the thicknesses of the second square patch 5-1, the circular patch 5-2, the first annular patch 5-3, the second annular patch 5-4, and the outer patch 5-5 are all equal, and the thickness h5 of the second square patch 5-1 is 0.2µm.

[0062] Example 3 Ultra-wideband multi-frequency terahertz absorber based on patterned vanadium dioxide, such as Figure 1-5As shown, it includes 5×5 patterned vanadium dioxide tunable broadband terahertz absorption units. The 5×5 multilayer patterned vanadium dioxide tunable broadband terahertz absorption units are distributed in a 5×5 two-dimensional pattern, where M and N are both positive integers. Each patterned vanadium dioxide tunable broadband terahertz absorption unit includes, from top to bottom, a composite resonant layer unit 5, a second dielectric layer 4, a vanadium dioxide resonant layer unit 3, a first dielectric layer 2, and a metal reflective layer 1.

[0063] Metal reflective layer 1, first dielectric layer 2 and second dielectric layer 4 are all square; the side lengths of metal reflective layer 1, first dielectric layer 2 and second dielectric layer 4 are equal; the side length P of metal reflective layer 1 is 14µm-15µm; The thickness h1 of the metal reflective layer 1 is 0.3µm; the thickness h2 of the first dielectric layer 2 is 3.5µm; and the thickness h4 of the second dielectric layer 4 is 3.5µm. The metal reflective layer 1 is made of gold with an electrical conductivity of 4.52 × 10⁻⁶. 6 S / m; The first dielectric layer 2 and the second dielectric layer 4 are made of silicon dioxide with a relative permittivity of 3.9.

[0064] Vanadium dioxide resonant layer unit 3 includes a rectangular frame patch 3-1, the outer frame of which is rectangular and the inner frame is square; A cross-shaped patch 3-2 is provided at the center of the rectangular frame patch 3-1. The cross-shaped patch 3-2 divides the rectangular frame patch 3-1 into four identical blank areas. A first square patch 3-3 is provided in each blank area. The rectangular frame patch 3-1, the cross-shaped patch 3-2, and the four first square patches 3-3 are all attached to the upper surface of the first dielectric layer 2; the rectangular frame patch 3-1, the cross-shaped patch 3-2, and the four first square patches 3-3 are not connected to each other; The rectangular frame patch 3-1, the cross-shaped patch 3-2, and the four first square patches 3-3 are all made of vanadium dioxide; the conductivity of vanadium dioxide in the non-metallic phase is 200 S / m, and the conductivity in the metallic phase is 200000 S / m.

[0065] The rectangular frame patch 3-1, the cross-shaped patch 3-2, and the four first square patches 3-3 are all of equal thickness; the thickness h3 of the rectangular frame patch 3-1 is 0.2µm. The rectangular patch 3-1 has an outer frame width v of 11.6µm and an outer frame length n of 12µm. The inner frame is a square with a side length q of 8µm. The cross-shaped patch 3-2 has a cross length m of 7.8µm and a width z of 1.4µm.

[0066] The side length t of the first square patch 3-3 is 2.3µm. The horizontal and vertical spacing between the first square patch 3-3 and the cross-shaped patch 3-2 are equal, and the horizontal spacing u is 0.3µm.

[0067] The composite resonant layer unit 5 includes a composite patch assembly disposed at the center of the upper surface of the second dielectric layer 4, and eight second square patches 5-1 disposed around the composite patch assembly; except for the center position, the eight second square patches 5-1 are arranged in a 3-2-3 array on the upper surface of the second dielectric layer 4; each second square patch 5-1 has the same size; The material of the second square patch 5-1 is vanadium dioxide; the conductivity of vanadium dioxide in the nonmetallic phase is 200 S / m, and the conductivity in the metallic phase is 200000 S / m; The side length W of the second square patch 5-1 is 0.8µm; the spacing d1 between two second square patches 5-1 in adjacent columns is 4.2µm; the spacing d2 between two second square patches 5-1 in adjacent rows is 4.2µm; the spacing d1 and the spacing d2 are equal.

[0068] The composite patch assembly includes, from the inside out, a circular patch 5-2, a first annular patch 5-3, a second annular patch 5-4, and an outer patch 5-5; The circular patch 5-2, the first annular patch 5-3, and the second annular patch 5-4 are sequentially and tightly bonded together; The outer patch 5-5 does not fit with the second annular patch 5-4; The outer patch 5-5 is a circular patch divided into six equal parts. The outer patch 5-5 is composed of six identical arc-shaped patches, and the spacing g between each pair of adjacent arc-shaped patches is the same, with a spacing g of 0.1µm. The circular patch 5-2, the second annular patch 5-4, and the outer patch 5-5 are made of gold; The material of the first annular patch 5-3 is vanadium dioxide; The radius 'a' of the circular patch 5-2 is 1µm; The inner radius of the first annular patch 5-3 is equal to the radius a of the circular patch 5-2, and the outer radius b is 1.8µm; The inner radius of the second annular patch 5-4 is equal to the outer radius b of the first annular patch 5-3, and the outer radius c of the second annular patch 5-4 is 2.2µm; The inner radius e of the outer patch 5-5 is 2.8µm, and the outer radius f of the outer patch 5-5 is 3.2µm; the thicknesses of the second square patch 5-1, the circular patch 5-2, the first annular patch 5-3, the second annular patch 5-4, and the outer patch 5-5 are all equal, and the thickness h5 of the second square patch 5-1 is 0.2µm.

[0069] Example 4 The fabrication method of an ultrawideband multi-frequency terahertz absorber based on patterned vanadium dioxide specifically includes the following steps: Step 1: Preparation of the bottom metal reflective layer 1; Step 1 is as follows: Step 1.1: Substrate cleaning: 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. Step 1.2: Metal Thin Film Deposition: Gold thin films were deposited using electron beam evaporation. Step 1.3: Annealing treatment: Annealing at 300℃ for 30 min improves the crystal quality and conductivity of the gold film, resulting in metal reflective layer 1; Step 2: Deposition of the first dielectric layer 2; Step 2 is as follows: Step 2.1: Deposition of the silica dielectric layer: A silica precursor, such as tetraethyl orthosilicate Si(OC2H5)4, was deposited on the upper surface of the metal reflective layer 1 using plasma-enhanced chemical vapor deposition (PECVD). The required dielectric layer thickness was obtained by precisely controlling the deposition power of 100W, the precursor flow rate of 50sccm, the reaction pressure of 10Pa, and the deposition time of 30min. Step 2.2: Curing treatment: Curing at a constant temperature of 200℃ for 1.5 hours ensures that the silica precursor is fully cross-linked and cured, forming a stable and dense silica film. The silica precursor deposited by PECVD without additional annealing treatment can meet the requirements for density and flatness of the dielectric layer after curing. During the curing process, temperature uniformity must be strictly controlled to avoid local overheating or uneven temperature, ensuring that the film surface is flat, free of pinholes, cracks, and peeling. Finally, a qualified first dielectric layer 2 is prepared on the upper surface of the metal reflective layer 1. Step 3: Preparation of vanadium dioxide resonant layer unit 3; Step 3 specifically involves: Step 3.1: Photolithography defines the vanadium dioxide region: The vanadium dioxide pattern area is defined in a pre-designed location using photolithography; Step 3.2: Vanadium dioxide thin film deposition: A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition. Step 3.3: Peeling and Shaping: The photoresist and excess vanadium dioxide film on it were removed by stripping, leaving the designed structure, to obtain vanadium dioxide resonant layer unit 3. Step 4: Preparation of the second dielectric layer 4; Step 4.1, Deposition of silica dielectric layer: On the upper surface of vanadium dioxide resonant layer unit 3, a silicon dioxide precursor, preferably tetraethyl orthosilicate Si(OC2H5)4, is deposited using plasma-enhanced chemical vapor deposition (PECVD). By precisely controlling the deposition power of 100W, the precursor flow rate of 50sccm, the reaction pressure of 10Pa, and the deposition time of 30min, the thickness of the dielectric layer is precisely controlled to obtain the required dielectric layer thickness and ensure that the thickness uniformity meets the preparation requirements. Step 4.2, Curing treatment: Curing at a constant temperature of 200℃ for 1.5 hours ensures that the silica precursor is fully cross-linked and cured, forming a stable and dense silica film. The silica precursor deposited by PECVD without additional annealing can meet the requirements for density and flatness of the dielectric layer after curing. During the curing process, temperature uniformity must be strictly controlled to avoid local overheating or temperature unevenness, ensuring that the film surface is flat, free of pinholes, cracks, and peeling. Finally, a qualified second dielectric layer 4 is prepared on the upper surface of the vanadium dioxide resonant layer unit 3. Step 5: Fabrication of composite resonant layer unit 5; Step 5 specifically involves: Step 5.1: Photolithography defines the vanadium dioxide region: The vanadium dioxide pattern area is defined in a pre-designed location using photolithography; Step 5.2: Vanadium dioxide thin film deposition: A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition. Step 5.3: Photolithography defines the gold patch area: Photoresist is spin-coated onto the substrate surface of the prepared second dielectric layer 4, and the pattern area of ​​the gold patch is defined at a preset position by photolithography. Step 5.4: Gold thin film deposition: A gold thin film of a specified thickness is deposited in the area defined by photolithography using a magnetron sputtering process; Step 5.5: Peeling and Shaping The photoresist and excess vanadium dioxide and gold films on it were removed by a stripping method, leaving the designed structure, to obtain the composite resonant layer unit 5.

[0070] Example 5 The fabrication method of an ultrawideband multi-frequency terahertz absorber based on patterned vanadium dioxide specifically includes the following steps: Step 1: Preparation of the bottom metal reflective layer 1; Step 1 is as follows: Step 1.1: Substrate cleaning: High-purity silicon was selected as the substrate and ultrasonically cleaned with acetone, ethanol and deionized water for 15 minutes in sequence to remove surface contaminants; after being dried with nitrogen, it was dried in an oven at 120℃ for 40 minutes. Step 1.2: Metal Thin Film Deposition: Gold thin films were deposited using electron beam evaporation. Step 1.3: Annealing treatment: Annealing at 350℃ for 40 min improves the crystallinity and conductivity of the gold film, resulting in metal reflective layer 1; Step 2: Deposition of the first dielectric layer 2; Step 2 is as follows: Step 2.1: Deposition of the silica dielectric layer: A silicon dioxide precursor, such as tetraethyl orthosilicate Si(OC2H5)4, was deposited on the upper surface of the metal reflective layer 1 using plasma-enhanced chemical vapor deposition (PECVD). The required dielectric layer thickness was obtained by precisely controlling the deposition power of 150W, the precursor flow rate of 80sccm, the reaction pressure of 30Pa, and the deposition time of 40min. Step 2.2: Curing treatment: Curing at a constant temperature of 250℃ for 2.5 hours ensures that the silica precursor is fully cross-linked and cured, forming a stable and dense silica film. The silica precursor deposited by PECVD without additional annealing treatment can meet the requirements for density and flatness of the dielectric layer after curing. During the curing process, temperature uniformity must be strictly controlled to avoid local overheating or uneven temperature, ensuring that the film surface is flat, free of pinholes, cracks, and peeling. Finally, a qualified first dielectric layer 2 is prepared on the upper surface of the metal reflective layer 1. Step 3: Preparation of vanadium dioxide resonant layer unit 3; Step 3 specifically involves: Step 3.1: Photolithography defines the vanadium dioxide region: The vanadium dioxide pattern area is defined in a pre-designed location using photolithography; Step 3.2: Vanadium dioxide thin film deposition: A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition. Step 3.3: Peeling and Shaping: The photoresist and excess vanadium dioxide film on it were removed by stripping, leaving the designed structure, to obtain vanadium dioxide resonant layer unit 3. Step 4: Preparation of the second dielectric layer 4; Step 4.1, Deposition of silica dielectric layer: On the upper surface of vanadium dioxide resonant layer unit 3, a silica precursor, preferably tetraethyl orthosilicate Si(OC2H5)4, is deposited using plasma-enhanced chemical vapor deposition (PECVD). By precisely controlling the deposition power of 150W, the precursor flow rate of 80sccm, the reaction pressure of 30Pa, and the deposition time of 40min, the thickness of the dielectric layer is precisely controlled to obtain the required dielectric layer thickness and ensure that the thickness uniformity meets the preparation requirements. Step 4.2, Curing treatment: Curing at a constant temperature of 250℃ for 2.5 hours ensures that the silica precursor is fully cross-linked and cured, forming a stable and dense silica film. The silica precursor deposited by PECVD without additional annealing can meet the requirements for density and flatness of the dielectric layer after curing. During the curing process, temperature uniformity must be strictly controlled to avoid local overheating or temperature unevenness, ensuring that the film surface is flat, free of pinholes, cracks, and peeling. Finally, a qualified second dielectric layer 4 is prepared on the surface of the vanadium dioxide resonant layer unit 3. Step 5: Fabrication of composite resonant layer unit 5; Step 5 specifically involves: Step 5.1: Photolithography defines the vanadium dioxide region: The vanadium dioxide pattern area is defined in a pre-designed location using photolithography; Step 5.2: Vanadium dioxide thin film deposition: A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition. Step 5.3: Photolithography defines the gold patch area: Photoresist is spin-coated onto the substrate surface of the prepared second dielectric layer 4, and the pattern area of ​​the gold patch is defined at a preset position by photolithography. Step 5.4: Gold film deposition: A gold film of a specified thickness is deposited in the area defined by photolithography using magnetron sputtering (or electron beam evaporation / thermal evaporation). Step 5.5: Peeling and Shaping The photoresist and excess vanadium dioxide and gold films on it were removed by a stripping method, leaving the designed structure, to obtain the composite resonant layer unit 5.

[0071] Example 6 The fabrication method of an ultrawideband multi-frequency terahertz absorber based on patterned vanadium dioxide specifically includes the following steps: Step 1: Preparation of the bottom metal reflective layer 1; Step 1 is as follows: Step 1.1: Substrate cleaning: High-purity silicon was selected as the substrate and ultrasonically cleaned with acetone, ethanol and deionized water for 12 minutes in sequence to remove surface contaminants; after drying with nitrogen, it was dried in an oven at 115℃ for 35 minutes. Step 1.2: Metal Thin Film Deposition: Gold thin films were deposited using electron beam evaporation. Step 1.3: Annealing treatment: Annealing at 320℃ for 35 min improves the crystallinity and conductivity of the gold film, resulting in metal reflective layer 1; Step 2: Deposition of the first dielectric layer 2; Step 2 is as follows: Step 2.1: Deposition of the silica dielectric layer: A silica precursor, such as tetraethyl orthosilicate Si(OC2H5)4, was deposited on the upper surface of the metal reflective layer 1 using plasma-enhanced chemical vapor deposition (PECVD). The required dielectric layer thickness was obtained by precisely controlling the deposition power of 120W, the precursor flow rate of 60sccm, the reaction pressure of 20Pa, and the deposition time of 35min. Step 2.2: Curing treatment: Curing at a constant temperature of 220℃ for 2 hours ensures that the silica precursor is fully cross-linked and cured, forming a stable and dense silica film. The silica precursor deposited by PECVD without additional annealing treatment can meet the requirements for density and flatness of the dielectric layer after curing. During the curing process, temperature uniformity must be strictly controlled to avoid local overheating or uneven temperature, ensuring that the film surface is flat, free of pinholes, cracks, and peeling. Finally, a qualified first dielectric layer 2 is prepared on the upper surface of the metal reflective layer 1. Step 3: Preparation of vanadium dioxide resonant layer unit 3; Step 3 specifically involves: Step 3.1: Photolithography defines the vanadium dioxide region: The vanadium dioxide pattern area is defined in a pre-designed location using photolithography; Step 3.2: Vanadium dioxide thin film deposition: A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition. Step 3.3: Peeling and Shaping: The photoresist and excess vanadium dioxide film on it were removed by stripping, leaving the designed structure, to obtain vanadium dioxide resonant layer unit 3. Step 4: Preparation of the second dielectric layer 4; Step 4.1, Deposition of silica dielectric layer: On the upper surface of vanadium dioxide resonant layer unit 3, a silicon dioxide precursor, preferably tetraethyl orthosilicate Si(OC2H5)4, is deposited using plasma-enhanced chemical vapor deposition (PECVD). By precisely controlling the deposition power of 120W, the precursor flow rate of 60sccm, the reaction pressure of 20Pa, and the deposition time of 35min, the thickness of the dielectric layer is precisely controlled to obtain the required dielectric layer thickness and ensure that the thickness uniformity meets the preparation requirements. Step 4.2, Curing treatment: Curing at a constant temperature of 220℃ for 2 hours ensures that the silica precursor is fully cross-linked and cured, forming a stable and dense silica film. The silica precursor deposited by PECVD without additional annealing can meet the requirements for density and flatness of the dielectric layer after curing. During the curing process, temperature uniformity must be strictly controlled to avoid local overheating or temperature unevenness, ensuring that the film surface is flat, free of pinholes, cracks, and peeling. Finally, a qualified second dielectric layer 4 is prepared on the upper surface of the vanadium dioxide resonant layer unit 3. Step 5: Fabrication of composite resonant layer unit 5; Step 5 specifically involves: Step 5.1: Photolithography defines the vanadium dioxide region: The vanadium dioxide pattern area is defined in a pre-designed location using photolithography; Step 5.2: Vanadium dioxide thin film deposition: A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition. Step 5.3: Photolithography defines the gold patch area: Photoresist is spin-coated onto the substrate surface of the prepared second dielectric layer 4, and the pattern area of ​​the gold patch is defined at a preset position by photolithography. Step 5.4: Gold film deposition: A gold film of a specified thickness is deposited in the area defined by photolithography using magnetron sputtering (or electron beam evaporation / thermal evaporation). Step 5.5: Peeling and Shaping The photoresist and excess vanadium dioxide and gold films on it were removed by a stripping method, leaving the designed structure, to obtain the composite resonant layer unit 5.

Claims

1. An ultrawideband multi-frequency terahertz absorber based on patterned vanadium dioxide, characterized in that, It includes M×N patterned vanadium dioxide tunable broadband terahertz absorption units, and the M×N multilayer patterned vanadium dioxide tunable broadband terahertz absorption units are distributed in an M×N two-dimensional pattern, where M and N are both positive integers. Each patterned vanadium dioxide tunable broadband terahertz absorption unit includes, from top to bottom, a composite resonant layer unit (5), a second dielectric layer (4), a vanadium dioxide resonant layer unit (3), a first dielectric layer (2), and a metal reflective layer (1).

2. The ultra-wideband multi-frequency terahertz absorber based on patterned vanadium dioxide according to claim 1, characterized in that, The metal reflective layer (1), the first dielectric layer (2) and the second dielectric layer (4) are all square; the side lengths of the metal reflective layer (1), the first dielectric layer (2) and the second dielectric layer (4) are equal; the side length P of the metal reflective layer (1) is 14µm-15µm; The thickness h1 of the metal reflective layer (1) is 0.2µm-0.4µm; the thickness h2 of the first dielectric layer (2) is 3µm-4µm; and the thickness h4 of the second dielectric layer (4) is 3µm-4µm.

3. The ultra-wideband multi-frequency terahertz absorber based on patterned vanadium dioxide according to claim 2, characterized in that, The metal reflective layer (1) is made of gold and has an electrical conductivity of 4.52 × 10⁻⁶. 6 S / m; The first dielectric layer (2) and the second dielectric layer (4) are made of silicon dioxide with a relative permittivity of 3.

9.

4. The ultra-wideband multi-frequency terahertz absorber based on patterned vanadium dioxide according to claim 1, characterized in that, The vanadium dioxide resonant layer unit (3) includes a rectangular frame patch (3-1), the outer frame of the rectangular frame patch (3-1) is rectangular, and the inner frame is square; A cross-shaped patch (3-2) is provided at the center of the rectangular frame patch (3-1). The cross-shaped patch (3-2) divides the rectangular frame patch (3-1) into four identical blank areas. A first square patch (3-3) is provided in each blank area. The rectangular frame patch (3-1), the cross-shaped patch (3-2), and the four first square patches (3-3) are all attached to the upper surface of the first dielectric layer (2); the rectangular frame patch (3-1), the cross-shaped patch (3-2), and the four first square patches (3-3) are not connected to each other; The rectangular frame patch (3-1), the cross-shaped patch (3-2), and the four first square patches (3-3) are all made of vanadium dioxide; the conductivity of vanadium dioxide in the non-metallic phase is 200 S / m, and the conductivity in the metallic phase is 200000 S / m.

5. The ultra-wideband multi-frequency terahertz absorber based on patterned vanadium dioxide according to claim 4, characterized in that, The rectangular frame patch (3-1), the cross-shaped patch (3-2), and the four first square patches (3-3) are all of equal thickness; the thickness h3 of the rectangular frame patch (3-1) is 0.2µm. The rectangular frame patch (3-1) has an outer frame width v of 11.6µm, an outer frame length n of 12µm, and an inner frame that is a square with a side length q of 8µm. The cross-shaped patch (3-2) has a cross length m of 7.8µm and a width z of 1.4µm; The side length t of the first square patch (3-3) is 2.3µm. The horizontal and vertical spacing between the first square patch (3-3) and the cross-shaped patch (3-2) are equal, and the horizontal spacing u is 0.3µm.

6. The ultra-wideband multi-frequency terahertz absorber based on patterned vanadium dioxide according to claim 1, characterized in that, The composite resonant layer unit (5) includes a composite patch assembly disposed at the center of the upper surface of the second dielectric layer (4), and eight second square patches (5-1) are disposed around the composite patch assembly; except for the center position, the eight second square patches (5-1) are arranged in a 3-2-3 array on the upper surface of the second dielectric layer (4); each second square patch (5-1) has the same size; The material of the second square patch (5-1) is vanadium dioxide; the conductivity of vanadium dioxide in the nonmetallic phase is 200 S / m, and the conductivity in the metallic phase is 200000 S / m; The side length W of the second square patch (5-1) is 0.8µm; the spacing d1 between two second square patches (5-1) in adjacent columns is 4.2µm; the spacing d2 between two second square patches (5-1) in adjacent rows is 4.2µm; the spacing d1 and the spacing d2 are equal.

7. The ultra-wideband multi-frequency terahertz absorber based on patterned vanadium dioxide according to claim 6, characterized in that, The composite patch assembly includes, from the inside out, a circular patch (5-2), a first annular patch (5-3), a second annular patch (5-4), and an outer patch (5-5). The circular patch (5-2), the first annular patch (5-3), and the second annular patch (5-4) are sequentially and tightly bonded together; The outer patch (5-5) and the second ring patch (5-4) are not attached; The outer patch (5-5) is a circular patch divided into six equal parts. The outer patch (5-5) consists of six identical arc-shaped patches, and the spacing g between each pair of adjacent arc-shaped patches is the same, with a spacing g of 0.1µm. The circular patch (5-2), the second annular patch (5-4), and the outer patch (5-5) are made of gold; The first annular patch (5-3) is made of vanadium dioxide; The radius a of the circular patch (5-2) is 1µm; The inner radius of the first annular patch (5-3) is equal to the radius a of the circular patch (5-2), and the outer radius b is 1.8µm; The inner radius of the second annular patch (5-4) is equal to the outer radius b of the first annular patch (5-3), and the outer radius c of the second annular patch (5-4) is 2.2µm; The inner radius e of the outer patch (5-5) is 2.8µm, and the outer radius f of the outer patch (5-5) is 3.2µm; The thicknesses of the second square patch (5-1), the circular patch (5-2), the first annular patch (5-3), the second annular patch (5-4), and the outer patch (5-5) are all equal, and the thickness h5 of the second square patch (5-1) is 0.2µm.

8. The method for preparing an ultrawideband multi-frequency terahertz absorber based on patterned vanadium dioxide according to any one of claims 1-7, characterized in that, Specifically, the following steps are included: Step 1: Preparation of the bottom metal reflective layer (1); Step 2: Deposition of the first dielectric layer (2); Step 3: Preparation of vanadium dioxide resonant layer unit (3); Step 4: Preparation of the second dielectric layer (4); Step 5: Fabrication of the composite resonant layer unit (5).

9. The method for preparing an ultrawideband multi-frequency terahertz absorber based on patterned vanadium dioxide according to claim 8, characterized in that, Step 1 is as follows: Step 1.1: Substrate cleaning: 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. Step 1.2: Metal Thin Film Deposition: Gold thin films were deposited using electron beam evaporation. Step 1.3: Annealing treatment: Annealing at 300℃-350℃ for 30min-40min improves the crystal quality and conductivity of the gold film, resulting in a metal reflective layer (1). Step 2 is as follows: Step 2.1: Deposition of silica dielectric layer: A silicon dioxide precursor was deposited on the upper surface of the metal reflective layer (1) using plasma-enhanced chemical vapor deposition to obtain the required dielectric layer thickness; Step 2.2: Curing treatment: Curing was carried out at a constant temperature of 200℃-250℃ for 1.5h-2.5h, and finally a qualified first dielectric layer (2) was prepared on the upper surface of the metal reflective layer (1). Step 3 specifically involves: Step 3.1: Photolithography defines the vanadium dioxide region: The vanadium dioxide pattern area is defined in a pre-designed location using photolithography; Step 3.2: Vanadium dioxide thin film deposition: A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition. Step 3.3: Peeling and Shaping: The photoresist and excess vanadium dioxide film on it are removed by stripping, leaving the designed structure, and the vanadium dioxide resonant layer unit is obtained (3). Step 4.1, Deposition of silica dielectric layer: On the upper surface of the vanadium dioxide resonant layer unit (3), a silicon dioxide precursor is deposited by plasma-enhanced chemical vapor deposition to obtain the required dielectric layer thickness. Step 4.2, Curing treatment: A qualified second dielectric layer (4) was prepared on the upper surface of the vanadium dioxide resonant layer unit (3) by curing at a constant temperature of 200℃-250℃ for 1.5h-2.5h. Step 5 specifically involves: Step 5.1: Photolithography defines the vanadium dioxide region: The vanadium dioxide pattern area is defined in a pre-designed location using photolithography; Step 5.2: Vanadium dioxide thin film deposition: A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition. Step 5.3: Photolithography defines the gold patch area: Photoresist is spin-coated onto the substrate surface of the prepared second dielectric layer (4), and the pattern area of ​​the gold patch is defined at a preset position by photolithography. Step 5.4: Gold thin film deposition: A gold thin film of a specified thickness is deposited in the area defined by photolithography using a magnetron sputtering process; Step 5.5: Peeling and Shaping The photoresist and the excess vanadium dioxide and gold films on it are removed by stripping, leaving the designed structure, and the composite resonant layer unit (5) is obtained.

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