Graphene tunable terahertz sensor and application

Abstract

The invention discloses a graphene tunable terahertz sensor and application, and belongs to the technical field of sensors. The graphene tunable terahertz sensor comprises a plurality of sensing units arranged in an array, each sensing unit comprises a metasurface, a dielectric layer is arranged below the metasurface, a reflecting layer is arranged below the dielectric layer, the metasurface is graphene of a regular hexagonal prism structure, and a through hole is formed in the center of the metasurface. The side length of the metasurface is 14.7 [mu] m to 15 [mu] m, and the radius of the through hole is 7.65 [mu] m to 8.55 [mu] m. The dielectric layer is a silicon dioxide layer, and the thickness of the dielectric layer is 9-15 microns. And the thickness of the reflecting layer is 5-7 [mu] m. The thickness of the graphene is 2 nm, and the Fermi level of the graphene changes between 0.6 eV and 1.1 eV. According to the graphene tunable terahertz sensor and the application thereof, the structure and parameters of the sensor are set, so that the local effect of an electromagnetic field is effectively enhanced, and the sensor has a double-resonance mode; the problems of low sensitivity and poor tuning capability of the sensor can be solved.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to a graphene tunable terahertz sensor and its applications. Background Technology

[0002] Terahertz (THz) waves typically refer to electromagnetic waves with frequencies ranging from 0.1 THz to 10 THz and wavelengths between 0.03 mm and 3 mm. Located between infrared and microwaves, terahertz waves combine the advantages of both: low photon energy, strong penetration, and a wide spectral bandwidth. Crucially, the rotational and vibrational energy levels of many biomolecules fall within the terahertz frequency band, generating a unique "fingerprint spectrum" that provides reliable evidence for material identification. This characteristic has directly driven the rapid development of terahertz sensing and detection, an emerging technology. In recent years, graphene, with its unique two-dimensional lattice structure and excellent electrical and optical properties, has become a core candidate for next-generation tunable electromagnetic functional materials. Its carrier concentration can be flexibly controlled through an external electric field or chemical doping, thereby achieving dynamic tuning of the absorption, reflection, and transmission characteristics in the terahertz band—an advantage not possessed by traditional metals or semiconductors. Furthermore, graphene possesses ultra-high electron mobility and strong surface plasmon resonance effect, enabling it to be deeply coupled with artificial metamaterial structures to generate multi-band, strongly localized field-enhanced resonant modes, providing a new design approach for high-sensitivity terahertz sensing.

[0003] However, existing metamaterial sensors can only function within a limited operating frequency band after they are made. Once the design is completed, their performance cannot be adjusted, which makes them lack sufficient flexibility in practical applications and difficult to adapt to different environments and detection needs. Summary of the Invention

[0004] The purpose of this invention is to provide a graphene-tunable terahertz sensor and its application. By setting the structure and parameters of the sensor, the local effect of the electromagnetic field is effectively enhanced, and the problems of low sensitivity and poor tuning capability of the sensor are solved.

[0005] To achieve the above objectives, the present invention provides a graphene tunable terahertz sensor, comprising a plurality of sensing units arranged in an array. Each sensing unit includes a metasurface, a dielectric layer disposed below the metasurface, and a reflective layer disposed below the dielectric layer. The metasurface is graphene with a regular hexagonal prism structure, and a through hole is disposed at the center of the metasurface.

[0006] Preferably, the metasurface, dielectric layer, and reflective layer are coaxially arranged, and one side length of the metasurface is parallel to one side length of both the dielectric layer and the reflective layer.

[0007] Preferably, the metasurface has a side length of 14.7 μm-15 μm and the through hole has a radius of 7.65 μm-8.55 μm.

[0008] Preferably, the dielectric layer is a silicon dioxide layer with a thickness of 9μm-15μm and a side length that is twice the side length of the metasurface.

[0009] Preferably, the reflective layer is made of gold, has a thickness of 5μm-7μm, and the side length of the reflective layer is equal to the side length of the dielectric layer.

[0010] Preferably, the metasurface is a single layer of graphene with a thickness of 2 nm and the Fermi level of the graphene varies between 0.6 eV and 1.1 eV.

[0011] Preferably, the sensor has an absorption rate of 95%-99.45% in the frequency range of 3.5THz-6.2THz.

[0012] Preferably, the sensor has an absorption rate greater than 95% in the frequency range of 1.2THz-1.4THz.

[0013] The aforementioned graphene-tunable terahertz sensor has applications in biomolecular detection, medical diagnosis, and environmental monitoring.

[0014] The advantages and positive effects of the graphene tunable terahertz sensor and its application described in this invention are as follows: 1. The sensor described in this invention comprises a hexagonal metasurface of monolayer graphene, a silicon dioxide dielectric layer, and a metal reflective substrate, and the metasurface has a through hole at its center. It not only has a simple structure and low processing cost, but also effectively improves the absorption efficiency by designing the structural parameters.

[0015] 2. The sensor described in this invention has dual-mode tunable absorption characteristics, with complementary absorption peaks in the low-frequency and high-frequency bands. It can achieve dual-mode integration in a single device, effectively reducing system complexity and improving the flexibility and applicability of terahertz devices.

[0016] 3. This invention achieves high absorption and low reflection performance through graphene-metal hybrid resonance and standing wave destructive interference effect, and has good frequency tunability and polarization insensitivity characteristics, making it suitable for fields such as biomolecular detection, portable sensing, environmental monitoring and intelligent medical diagnosis.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 This is a three-dimensional structural diagram of Embodiment 1 of the present invention; Figure 2 This is a top view of the structure of Embodiment 1 of the present invention; Figure 3This is an absorption curve diagram of different silica dielectric layer thicknesses in the sensor of Embodiment 1 of the present invention; Figure 4 This is a low-frequency amplified absorption curve of the sensor with different silica dielectric layer thicknesses in Embodiment 1 of the present invention; Figure 5 This is a high-frequency amplified absorption curve of the sensor with different silica dielectric layer thicknesses in Embodiment 1 of the present invention; Figure 6 This is an absorption curve diagram of different media refractive indices in the sensor of Embodiment 1 of the present invention; Figure 7 This is a low-frequency absorption curve of graphene at different Fermi levels in the sensor of Embodiment 1 of the present invention; Figure 8 This is a high-frequency absorption curve of graphene at different Fermi levels in the sensor of Embodiment 1 of the present invention; Figure 9 This is a low-frequency absorption curve of different Fermi levels of the hexagonal prism structure graphene without through holes in the sensor of Comparative Example 1 of this invention. Figure 10 This is a high-frequency absorption curve of different Fermi levels of the hexagonal prism graphene without through holes in the sensor of Comparative Example 1 of this invention.

[0019] Figure Labels 1. Metasurface; 2. Dielectric layer; 3. Reflective layer; 4. Through-hole. Detailed Implementation

[0020] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use. They are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," and "connect" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0021] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0022] Example 1 like Figure 1 , Figure 2As shown, a graphene-tunable terahertz sensor includes several sensing units arranged in a periodic array on the xy plane. Each sensing unit includes a metasurface 1, a dielectric layer 2 disposed below the metasurface 1, and a reflective layer 3 disposed below the dielectric layer 2. The metasurface 1, dielectric layer 2, and reflective layer 3 are coaxially arranged, with one side length of the metasurface 1 parallel to one side length of both the dielectric layer 2 and the reflective layer 3.

[0023] Metasurface 1 is a hexagonal prism graphene structure with a central via 4. The hexagonal prism structure of metasurface 1 exhibits multi-order rotational symmetry, which can excite multiple plasmonic hybrid resonances to enhance terahertz wave absorption. The side length of metasurface 1 is 14.7 μm–15 μm, and the radius of via 4 is 7.65 μm–8.55 μm. Metasurface 1 is a single layer of graphene with a thickness of 2 nm. The Fermi level of the graphene can be varied between 0.6 eV and 1.1 eV by changing the external voltage, pressure, or temperature applied to metasurface 1.

[0024] The dielectric layer 2 is a silicon dioxide layer with a thickness of 9μm-15μm and a side length twice that of the metasurface 1. When the Fermi level of graphene is tuned by applying an external electric field, if the dielectric layer is conductive, the electric field cannot be effectively established, and the charge will leak directly. However, silicon dioxide, as an excellent insulator, can withstand high electric fields without breakdown, thus ensuring that the gate voltage can be efficiently applied to the graphene, ensuring the stability and reliability of its dynamic tuning. Simultaneously, silicon dioxide is the cornerstone of the silicon-based semiconductor industry. The processes for thermally growing or chemically vapor-depositing high-quality, uniformly thick silicon dioxide films on silicon wafers are now extremely mature, controllable, and inexpensive. This significantly lowers the manufacturing threshold and cost of this sensor. Furthermore, its chemically stable and inert nature means it is not easily degraded or reacts with the surrounding environment during subsequent processing and use, ensuring the reliability of the device.

[0025] The reflective layer 3 is made of gold, with a thickness of 5μm-7μm, and its side length is equal to that of the dielectric layer 2. The reflective layer 3 is used to reflect incident terahertz waves and enhance the local electromagnetic field coupling effect. One of the core principles of the sensor is that the underlying material must have the ability to completely reflect terahertz waves to ensure that they do not escape. Only when the reflected wave interferes with the incident wave can a significant absorption effect be produced. Metallic materials, especially gold, behave as near-perfect conductors in the terahertz frequency band, similar to an extremely smooth mirror, capable of reflecting almost all the energy of the incident terahertz waves back.

[0026] If other materials, such as silicon, are used, their reflection efficiency for terahertz waves is far lower than that of gold, and some waves will pass through or be absorbed, resulting in energy loss. This makes it difficult for the sensor to achieve an absorption rate of over 95%. Furthermore, gold possesses excellent chemical stability, maintaining its physical and chemical properties in air and various biological sample environments for a long period. It is not easily oxidized or sulfided, avoiding interface degradation caused by the formation of surface compounds. From a process integration perspective, gold films can achieve uniform and dense coverage on silicon dioxide substrates through mature evaporation or sputtering processes, with flatness and adhesion meeting the requirements of micro-nano fabrication.

[0027] This invention relates to a terahertz sensor employing a geometric structure with a through-hole in the center of a regular hexagonal prism, aiming to enhance sensor performance through symmetry and multi-scale coupling. When a terahertz wave is incident, surface plasmons excited at the edges of the hexagonal prism form two resonance modes with different coupling strengths: weak edge coupling generates a low-frequency resonance peak, while strong edge coupling forms a hybrid propagation mode with the metal substrate, generating a high-frequency resonance peak. When the refractive index of the measured medium changes, the change in the local electromagnetic environment causes a shift in the position of the resonance peak, thus achieving refractive index detection. Simultaneously, by adjusting the Fermi level of graphene, its surface conductivity can be dynamically adjusted, causing a significant blue shift or red shift in the resonance peak, thereby achieving active electrically tunable terahertz sensing without altering the structure.

[0028] The performance of the sensor described in this invention was tested. The effect of different heights of the silicon dioxide dielectric layer 2 on the absorption of the resonance peak was analyzed. At this point, the height of the reflective layer 3 was 5 μm, and the Fermi level of graphene was 0.7 eV. The edge length of the metasurface was 15 μm, and the radius of the via was 8.1 μm. The effect of different silicon dioxide layer heights on the absorption of the resonance peak is as follows: Figure 3 , Figure 4 , Figure 5 As shown, different silica heights have different effects on the absorption of the resonance peak. The sensor with a silica dielectric layer height of 11 μm has the best absorption effect and maintains stable low reflection characteristics over a wide frequency range, making it suitable for terahertz waveguides and biosensing applications.

[0029] The influence of the refractive index of different media on the absorption of the resonance peak was analyzed. In this case, the height of the reflective layer 3 was 5 μm, the Fermi level of graphene was 0.7 eV, the height of the silicon dioxide dielectric layer was 11 μm, the edge length of the metasurface was 15 μm, and the radius of the via was 8.1 μm. To analyze the influence of the refractive index of different media, the sensor was placed in the liquid medium to be measured, and the refractive index of the medium was changed by altering the liquid medium. Figure 6The absorption response characteristics of graphene metamaterials in the terahertz band are shown under conditions where the refractive index n = 1.0 to 1.5. In the low-frequency range (around 1 THz), the absorption peak intensity remains close to 99% with a narrow bandwidth, indicating that this resonant mode is highly sensitive to changes in refractive index, making it suitable as a high-resolution refractive index sensing window. In the high-frequency range (around 4–6 THz), the increase in refractive index leads to a more significant overall shift in the absorption peak, and the peak value shows a slight attenuation, indicating that the localized distribution of the electromagnetic field in the structure is closely related to the optical constants of dielectric layer 2.

[0030] The influence of different Fermi levels of graphene on the absorption of the resonance peak was analyzed. At this time, the height of the reflective layer 3 was 5 μm, the height of the dielectric layer silicon dioxide was 11 μm, the side length of the metasurface was 15 μm, and the radius of the via was 8.1 μm. Figure 7 The graphs show the low-frequency absorption curves of graphene at different Fermi levels, illustrating the influence of the Fermi level on the absorbance in the low-frequency range (0.8 THz–1.8 THz). As the Fermi level gradually increases from 0.6 eV to 0.7 eV, the absorption intensity of the low-frequency resonance peak significantly increases; however, when the Fermi level exceeds the critical value of 0.7 eV, the resonance peak intensity shows a nonlinear weakening trend due to the carrier concentration tending to saturate and the enhanced electron scattering effect.

[0031] Figure 8 The graph shows the high-frequency absorption curves of graphene at different Fermi levels. This structure exhibits significant tunable absorption characteristics in the frequency range of 3.5–6.2 THz. As the Fermi level of graphene gradually increases from 0.6 eV to 1.1 eV, the main absorption peak shifts significantly towards higher frequencies, while the absorption rate remains consistently between 95% and 99.45%. Furthermore, the resonance intensity significantly increases with increasing Fermi level, indicating that the increase in free carrier density in graphene enhances the plasmon coupling effect. However, when the Fermi level further increases (above 0.9 eV), the absorption peak intensity weakens, exhibiting a nonlinear tuning law of "increase followed by decrease." This is manifested in the increased electron scattering loss at high carrier concentrations, which weakens the resonance absorption capability.

[0032] Comparative Example 1 The difference between this comparative example and Example 1 is that the hexagonal prism graphene sensor in this comparative example does not have through holes. Other parameters are the same as those analyzed in Example 1 regarding the influence of different Fermi levels on the absorption of the resonance peak. The low-frequency and high-frequency absorption curves of Comparative Example 1 were analyzed, and the results are as follows: Figure 9 , Figure 10 As shown. According to Figure 9 , Figure 10 absorption waveform and Figure 7 , Figure 8The comparison shows that the presence of through-holes significantly improves the sensor's tuning capability and absorption rate. This indicates that through-holes play a crucial role in enhancing the local effect of the electromagnetic field, improving sensitivity, and increasing absorption efficiency. It is by optimizing this structure that the sensor's high-efficiency performance in the terahertz band is ensured, further improving the sensor's overall performance and application applicability. This invention uses monolayer graphene as the metasurface material, with a thickness of 2 nm. This not only simplifies the structure but also enables the sensor to operate at a microscale, further enhancing its tuning capability in the high-frequency band.

[0033] Therefore, by using the graphene tunable terahertz sensor and its application described in this invention, the local electromagnetic field effect can be effectively enhanced by setting the structure and parameters of the sensor, and it has a dual resonant mode; this can solve the problems of low sensor sensitivity and poor tuning capability.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A graphene tunable terahertz sensor, characterized by: The sensor comprises a plurality of arrayed sensing units, the sensing unit comprises a metasurface, a dielectric layer is arranged below the metasurface, and a reflective layer is arranged below the dielectric layer, the metasurface is graphene with a regular hexagonal prism structure, and a through hole is arranged at the center of the metasurface.

2. The graphene tunable terahertz sensor according to claim 1, wherein: The metasurface, the dielectric layer and the reflective layer are coaxially arranged, and one side length of the metasurface is parallel to one side length of the dielectric layer and the reflective layer.

3. The graphene tunable terahertz sensor according to claim 1, wherein: The side length of the metasurface is 14.7-15 mu m, and the radius of the through hole is 7.65-8.55 mu m.

4. The graphene tunable terahertz sensor according to claim 1, wherein: The dielectric layer is a silicon dioxide layer, the thickness of the dielectric layer is 9-15 mu m, and the side length of the dielectric layer is twice the side length of the metasurface.

5. The graphene tunable terahertz sensor according to claim 1, wherein: The reflective layer is gold, the thickness of the reflective layer is 5-7 mu m, and the side length of the reflective layer is equal to the side length of the dielectric layer.

6. The graphene tunable terahertz sensor according to claim 1, wherein: The metasurface is single-layer graphene, the thickness of the graphene is 2 nm, and the Fermi energy level of the graphene changes between 0.6 eV and 1.1 eV.

7. The graphene tunable terahertz sensor according to claim 1, wherein: The sensor has an absorption rate of 95%-99.45% in a frequency range of 3.5-6.2 THz. 8.The graphene tunable terahertz sensor of claim 1, wherein: The sensor has an absorption rate of more than 95% in a frequency range of 1.2-1.4 THz.

9. Application of a graphene tunable terahertz sensor in biomolecule detection, medical diagnosis and environmental monitoring.

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