A square-shaped heterostructure terahertz metamaterial sensor device and a preparation method thereof

Abstract

The application provides a square-shaped heterostructure terahertz metamaterial sensor device and a preparation method thereof. The device comprises a heterostructure sandwich structure which is formed by constructing a multilayer structure on a silicon material. The multilayer structure is composed of a top metal square array unit, a middle dielectric layer and a bottom metal reflection layer. The sensor device controls the full width at half maximum of the plasmonic resonance peak by adjusting the thickness of the dielectric layer to achieve wide resonance enhancement. The metal square array unit adopts two structure size parameters, and the overall architecture scaling realizes the spectral response of different wave bands. When the sensor device works, the terahertz wave is vertically incident on the heterostructure sandwich structure and induces the excitation of the plasmonic mode, so that the signal of the outgoing terahertz wave received by the terahertz receiver presents the super-wideband resonance characteristic. The application can control the spin coating speed of photoresist to customize the wide-spectrum resonance characteristic of the plasmon excited by the square-shaped heterostructure terahertz metamaterial under two different structure scales.

Description

Technical Field

[0001] This invention relates to the field of terahertz metamaterials technology, and in particular to a square heterogeneous terahertz metamaterial sensor and its fabrication method. Background Technology

[0002] Terahertz metamaterials, through artificial microstructures, enable flexible manipulation of electromagnetic waves at the subwavelength scale, showing broad application prospects in fields such as biomedical sensing, non-destructive testing, and high-speed communication. Among them, metal-dielectric-metal metamaterials based on surface plasmon resonance are widely used to enhance the terahertz fingerprint absorption of trace molecules due to their significant local field enhancement effect. However, the structural size of terahertz devices is uniquely on the micrometer scale: unlike infrared devices, whose film thickness can be precisely controlled through thin film techniques such as chemical vapor deposition or atomic layer deposition, and unlike microwave / RF devices, whose millimeter-scale thickness provides high relative error tolerance, terahertz devices can be perturbed by even micrometer-scale thickness variations, leading to shifts or distortions in the preset resonance peak.

[0003] Currently, traditional multi-resonance design strategies often employ the fabrication of numerous independent array units of varying sizes to achieve broad enhancement coverage. Correspondingly, terahertz device fabrication methods primarily utilize photolithography, femtosecond lasers, and other processes, using dielectrics such as silicon and quartz, or all-metal structures to excite plasmonic resonance. However, the bandwidth of a single resonant unit in these methods is extremely limited, necessitating a large number of units of different sizes to achieve broad spectral coverage. This results in complex device structures, high fabrication costs, and an inability to achieve effective broadband enhancement under a single resonance, often leading to device performance falling short of expectations. Summary of the Invention

[0004] This invention proposes a cubic heterogeneous terahertz metamaterial sensor and its fabrication method, which can customize the broadband resonance characteristics of the plasma excited by the cubic heterogeneous terahertz metamaterial at two different structural scales by controlling the photoresist spin coating speed.

[0005] The present invention adopts the following technical solution.

[0006] A square heterogeneous terahertz metamaterial sensor includes a heterogeneous sandwich structure for achieving ultra-wideband fingerprint enhancement in the terahertz band. The heterogeneous sandwich structure is formed by constructing a multilayer structure on a silicon material. The multilayer structure consists of a top layer of metal square array units (3), a middle dielectric layer (4), and a bottom layer of metal reflective layer (5).

[0007] The sensor device accurately controls the full width at half maximum (FWHM) of the plasma resonance peak by adjusting the thickness of the dielectric layer, thereby achieving wide resonance enhancement; the metal square array unit adopts two structural size parameters, and achieves spectral response in different bands through overall architecture scaling.

[0008] When the sensor is operational, terahertz waves are incident perpendicularly on the heterostructure and induce plasma mode excitation on its surface. This results in the signal received by the terahertz receiver after the terahertz waves exiting the structure exhibiting ultrawideband resonance characteristics. This invention, by controlling the photoresist spin-coating speed, customizes the broadband resonance characteristics of the plasma excited by the square heterostructure terahertz metamaterial at two structural scales.

[0009] The metal reflective layer is a Cr / Au composite layer, with a thickness corresponding to two different structural sizes of metal square array units, using parameters of 10 / 150 nm respectively;

[0010] The dielectric layer is formed by photoresist, and its thickness corresponds to the two structural sizes of the metal square array unit, which are 33 μm or 13 μm respectively.

[0011] The metal square array unit is a Cr / Au composite layer, with a thickness corresponding to two structural sizes of metal square array units, namely 10 / 150 nm.

[0012] In the two structural sizes of the metal square array unit, the period of the square unit is 90 μm and 36 μm, respectively; the 90 μm square structural unit corresponds to a photoresist thickness of 33 μm, and the 36 μm square structural unit corresponds to a photoresist thickness of 13 μm.

[0013] The dielectric layer is prepared using SU-8 photoresist, which has high loss characteristics in the terahertz band, so that the thickness of the dielectric layer can directly affect the intensity and broadening of the plasma resonance peak.

[0014] During the preparation of the dielectric layer, the thickness of the dielectric layer can be precisely controlled by adjusting the spin coating speed of the photoresist, thereby regulating the full width at half maximum (FWHM) of the resonance peak and achieving broadband resonance enhancement.

[0015] The metal square array unit adopts two structural size parameters and achieves ultra-wide spectrum response of different bands by scaling the overall architecture. When the terahertz wave is perpendicularly incident on the heterostructure, it induces the excitation of the plasma mode on its surface. The terahertz wave (7) emitted after passing through the structure is received by the terahertz receiver (8), and the received signal exhibits ultra-wideband resonance characteristics.

[0016] A method for fabricating a cubic heterogeneous terahertz metamaterial sensor, used to fabricate the aforementioned cubic heterogeneous terahertz metamaterial sensor, wherein the method is used to fabricate a cubic heterostructure sandwich structure that generates broadband enhancement characteristics in two frequency windows, and the coupling conditions of the sensor to terahertz waves are controlled by adjusting the thickness of the intermediate layer, including the following steps:

[0017] Step S1: Deposit a bottom metal reflective layer on the surface of the silicon wafer;

[0018] Step S2: Prepare an intermediate dielectric layer on the bottom metal reflective layer, and form a dielectric layer with a preset thickness by photolithography.

[0019] Step S3: Fabricate a top-layer metal square array on the middle dielectric layer, and form square resonant units of different scaling scales through photolithography and lift-off processes;

[0020] Step S4: Cut the prepared silicon wafer into individual devices.

[0021] In step S1, the specific method is as follows:

[0022] Step A1: Select a 2-inch single-polished silicon wafer as the substrate, and ultrasonically clean it in acetone and isopropanol solutions for 5 minutes each to remove surface contaminants.

[0023] Step A2: Use a plasma desmearing machine at 400W power for 5 minutes to improve the surface activity of the substrate;

[0024] Step A3: Cr / Au metal layers are sequentially deposited on the silicon wafer surface using magnetron sputtering, with thicknesses of 10 nm and 150 nm, respectively. The sputtering power is 500 W and the deposition rate is 2.3 nm / s.

[0025] In step S2, the specific method is as follows:

[0026] Step B1: Spin-coat SU-8 photoresist onto the silicon wafer surface with deposited bottom metal, and control the thickness of the photoresist layer to be 33 μm or 13 μm through a spin coating process;

[0027] Step B2: Place the silicon wafer with photoresist spin-coated on a hot plate for pre-baking at 60℃ / 1min, and then increase the temperature to 95℃ / 5min.

[0028] Step B3: Expose the photoresist layer using a mask. The exposure time is set to 10s or 5s depending on the thickness of the photoresist.

[0029] Step B4: After exposure, the silicon wafer is post-baked at 60℃ for 1 min, and then the temperature is increased to 95℃ for 3 min.

[0030] Step B5: Immerse the silicon wafer in PGMEA developer solution for development. The development time is set to 1 minute or 30 seconds depending on the photoresist thickness. Remove the photoresist from the unexposed areas to form a dielectric layer pattern.

[0031] Step B6: Place the developed silicon wafer on a hot plate at 150°C and bake for 10 minutes to perform a hardening process.

[0032] In step S3, the specific method is as follows:

[0033] Step C1: Apply 7133 photoresist to the surface of the dielectric layer formed in step S2 using a spray coating process. The thickness of the photoresist layer is 4 μm.

[0034] Step C2: Expose the photoresist layer using a mask for 12 seconds;

[0035] Step C3: Immerse the silicon wafer in a 2.38% TMAH developer solution for 40 seconds to remove the photoresist in the exposed areas and form a pattern of the top metal structure.

[0036] Step C4: Deposit Cr / Au metal layers on the surface of the patterned photoresist layer using magnetron sputtering, with thicknesses of 10 nm and 150 nm, respectively. The sputtering power is 500 W and the deposition rate is 2.3 nm / s.

[0037] Step C5: Place the silicon wafer with the deposited metal layer into acetone and isopropanol solutions in turn and ultrasonically clean for 5 minutes each to remove the photoresist and the metal layer above it, while retaining the metal pattern that is in direct contact with the dielectric layer to form a top metal square array.

[0038] Step C6: Use a plasma stripper at 400W power for 5 minutes to remove residual photoresist and impurities.

[0039] In step S4, the prepared silicon wafer is cut into 15 mm × 15 mm individual devices using a DISCO dicing machine.

[0040] In the ultrasonic cleaning, the cleaning time for both acetone and isopropanol is 5 minutes; the plasma cleaning time is 5 minutes.

[0041] In the spin coating process, for SU-8 2025 photoresist with a thickness of 33 μm, the spin coating speed is 500 rpm / 10s and 2000 rpm / 30s; for SU-8 2015 photoresist with a thickness of 13 μm, the spin coating speed is 500 rpm / 10s and 5000 rpm / 30s; both the pre-baking and post-baking use hot plate heating; the developer is PGMEA; the hardening treatment temperature is 150℃ and the time is 10 minutes.

[0042] In the photoresist spraying process, the photoresist type is 7133 and the photoresist layer thickness is 4 μm; the exposure time is 12 seconds; the developer is a 2.38% TMAH developer with a development time of 40 seconds; the magnetron sputtering power is 500 W and the deposition rate is 2.3 nm / s; in the stripping process, the cleaning time for both acetone and isopropanol is 5 minutes.

[0043] A testing method for a cubic heterogeneous terahertz metamaterial sensor is used to test the aforementioned cubic heterogeneous terahertz metamaterial sensor. In the testing method, multiple analytes with characteristic absorption at specific frequencies are used to experimentally test the sensor, and the enhanced molecular characteristic signals of the five analytes are obtained after modulation by the device. Since different substances have multiple characteristic absorption peaks and a large frequency range, it is impossible in practice for all plasma resonance peaks and molecular vibration absorption peaks to be in a state of perfect frequency matching.

[0044] The enhancement effect is strongest when the plasmonic resonance peak and the molecular vibrational absorption peak are frequency-matched. As detuning increases, the enhancement factor gradually decreases. Using 1 / e of the enhancement factor under matched conditions as the effective enhancement threshold, this method is used to evaluate the enhancement capability of the device under detuning conditions. The results show that the absorption intensities at all ten characteristic absorption frequencies of the five materials are higher than this threshold.

[0045] When absorbing specific frequency features, the structure corresponding to the two scales of the metal square array unit structure size parameters is mainly responsible for enhancing the feature absorption capability in the low-frequency region by the structure size parameters of the first scale of the metal square array unit, while the enhancement of the feature absorption capability in the high-frequency region is responsible for the structure size parameters of the second scale of the metal square array unit.

[0046] The square heterogeneous terahertz metamaterial device prepared by this invention has a stable structure, and the method can achieve micron-level controllable thickness of the intermediate dielectric layer to customize the expected plasma resonance.

[0047] The significant advantages of this invention also include:

[0048] (1) By combining multiple photolithography and deep silicon etching micromachining processes, we can make full use of their respective characteristics of accurate geometric pattern replication and high precision, high aspect ratio geometric structure etching to process relatively complex geometric patterns on silicon wafers, thus solving the problem of low processing accuracy of other methods on all-dielectric metamaterials.

[0049] (2) The silicon-based all-dielectric terahertz metamaterial prepared by the present invention uses double-sided polished silicon wafer as substrate material. It has a stable structure, a high quality factor of resonance frequency, and can support multiple resonance modes on the terahertz surface. It is very suitable for application in various high-performance terahertz functional devices.

[0050] This invention proposes a cubic heterogeneous terahertz metamaterial device with a heterostructure sandwich structure capable of achieving ultra-wideband fingerprint enhancement in the terahertz band. The heterostructure sandwich structure is constructed on a silicon substrate using multiple layers. These multiple layers consist of a top layer of cubic metal array units, an intermediate dielectric layer, and a bottom layer of metal reflective layer. The thickness of the dielectric layer can be precisely controlled to precisely measure the full width at half maximum (FWHM) of the plasmonic resonance peak, thereby achieving wide resonance enhancement. The cubic metal array units employ two different structural size parameters, and spectral responses in different bands are achieved through overall architecture scaling. When a terahertz wave is perpendicularly incident on this heterostructure sandwich structure, it induces plasmonic mode excitation on its surface. After passing through this structure, the emitted terahertz wave is received by a terahertz receiver, and the signal exhibits ultra-wideband resonance characteristics. Therefore, this invention can customize the broadband resonance characteristics of the plasmonic plasma excited by the cubic heterostructure terahertz metamaterial at two structural scales by controlling the photoresist spin coating speed. Attached Figure Description

[0051] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0052] Appendix Figure 1 This is a schematic diagram of a cross-sectional microscopic image of a square heterogeneous terahertz metamaterial device.

[0053] Appendix Figure 2 This is a top-down electron microscope view of a square heterogeneous terahertz metamaterial device;

[0054] Appendix Figure 3 This is a schematic diagram of the experimental test results of enhanced molecular characteristic signals of five analytes after modulation by the device.

[0055] Appendix Figure 4 This is a schematic diagram of the experimental absorption spectrum of a square heterogeneous terahertz metamaterial device with precisely controlled thicknesses of 34 μm and 14 μm.

[0056] Appendix Figure 5 This is a schematic diagram illustrating the experimental principle of the device;

[0057] In the diagram: 1-Terahertz wave emitter; 2-Incident terahertz wave; 3-Square array unit; 4-Dielectric layer (a photoresist dielectric layer of customized thickness); 5-Metal reflective layer; 6-Silicon substrate; 7-Outgoing terahertz wave; 8-Terahertz detector; 9-Signal analysis system. Detailed Implementation

[0058] As shown in the figure, a square heterogeneous terahertz metamaterial sensor includes a heterogeneous sandwich structure for achieving ultra-wideband fingerprint enhancement in the terahertz band. The heterogeneous sandwich structure is formed by constructing a multilayer structure on a silicon material. The multilayer structure consists of a top layer of metal square array units 3, a middle dielectric layer 4, and a bottom layer of metal reflective layer 5.

[0059] The sensor device accurately controls the full width at half maximum (FWHM) of the plasma resonance peak by adjusting the thickness of the dielectric layer, thereby achieving wide resonance enhancement; the metal square array unit adopts two structural size parameters, and achieves spectral response in different bands through overall architecture scaling.

[0060] When the sensor is operational, terahertz waves are incident perpendicularly on the heterostructure and induce plasma mode excitation on its surface. This results in the signal received by the terahertz receiver after the terahertz waves exiting the structure exhibiting ultrawideband resonance characteristics. This invention, by controlling the photoresist spin-coating speed, customizes the broadband resonance characteristics of the plasma excited by the square heterostructure terahertz metamaterial at two structural scales.

[0061] The metal reflective layer is a Cr / Au composite layer, with a thickness corresponding to two different structural sizes of metal square array units, using parameters of 10 / 150 nm respectively;

[0062] The dielectric layer is formed by photoresist, and its thickness corresponds to the two structural sizes of the metal square array unit, which are 33 μm or 13 μm respectively.

[0063] The metal square array unit is a Cr / Au composite layer, with a thickness corresponding to two structural sizes of metal square array units, namely 10 / 150 nm.

[0064] In the two structural sizes of the metal square array unit, the period of the square unit is 90 μm and 36 μm, respectively; the 90 μm square structural unit corresponds to a photoresist thickness of 33 μm, and the 36 μm square structural unit corresponds to a photoresist thickness of 13 μm.

[0065] The dielectric layer is prepared using SU-8 photoresist, which has high loss characteristics in the terahertz band, so that the thickness of the dielectric layer can directly affect the intensity and broadening of the plasma resonance peak.

[0066] During the preparation of the dielectric layer, the thickness of the dielectric layer can be precisely controlled by adjusting the spin coating speed of the photoresist, thereby regulating the full width at half maximum (FWHM) of the resonance peak and achieving broadband resonance enhancement.

[0067] The metal square array unit adopts two structural size parameters and achieves ultra-wide spectrum response of different bands by scaling the overall architecture. When the terahertz wave is perpendicularly incident on the heterostructure, it induces the excitation of the plasma mode on its surface. The terahertz wave (7) emitted after passing through the structure is received by the terahertz receiver (8), and the received signal exhibits ultra-wideband resonance characteristics.

[0068] A method for fabricating a cubic heterogeneous terahertz metamaterial sensor, used to fabricate the aforementioned cubic heterogeneous terahertz metamaterial sensor, wherein the method is used to fabricate a cubic heterostructure sandwich structure that generates broadband enhancement characteristics in two frequency windows, and the coupling conditions of the sensor to terahertz waves are controlled by adjusting the thickness of the intermediate layer, including the following steps:

[0069] Step S1: Deposit a bottom metal reflective layer on the surface of the silicon wafer;

[0070] Step S2: Prepare an intermediate dielectric layer on the bottom metal reflective layer, and form a dielectric layer with a preset thickness by photolithography.

[0071] Step S3: Fabricate a top-layer metal square array on the middle dielectric layer, and form square resonant units of different scaling scales through photolithography and lift-off processes;

[0072] Step S4: Cut the prepared silicon wafer into individual devices.

[0073] In step S1, the specific method is as follows:

[0074] Step A1: Select a 2-inch single-polished silicon wafer as the substrate, and ultrasonically clean it in acetone and isopropanol solutions for 5 minutes each to remove surface contaminants.

[0075] Step A2: Use a plasma desmearing machine at 400W power for 5 minutes to improve the surface activity of the substrate;

[0076] Step A3: Cr / Au metal layers are sequentially deposited on the silicon wafer surface using magnetron sputtering, with thicknesses of 10 nm and 150 nm, respectively. The sputtering power is 500 W and the deposition rate is 2.3 nm / s.

[0077] In step S2, the specific method is as follows:

[0078] Step B1: Spin-coat SU-8 photoresist onto the silicon wafer surface with deposited bottom metal, and control the thickness of the photoresist layer to be 33 μm or 13 μm through a spin coating process;

[0079] Step B2: Place the silicon wafer with photoresist spin-coated on a hot plate for pre-baking at 60℃ / 1min, and then increase the temperature to 95℃ / 5min.

[0080] Step B3: Expose the photoresist layer using a mask. The exposure time is set to 10s or 5s depending on the thickness of the photoresist.

[0081] Step B4: After exposure, the silicon wafer is post-baked at 60℃ for 1 min, and then the temperature is increased to 95℃ for 3 min.

[0082] Step B5: Immerse the silicon wafer in PGMEA developer solution for development. The development time is set to 1 minute or 30 seconds depending on the photoresist thickness. Remove the photoresist from the unexposed areas to form a dielectric layer pattern.

[0083] Step B6: Place the developed silicon wafer on a hot plate at 150°C and bake for 10 minutes to perform a hardening process.

[0084] In step S3, the specific method is as follows:

[0085] Step C1: Apply 7133 photoresist to the surface of the dielectric layer formed in step S2 using a spray coating process. The thickness of the photoresist layer is 4 μm.

[0086] Step C2: Expose the photoresist layer using a mask for 12 seconds;

[0087] Step C3: Immerse the silicon wafer in a 2.38% TMAH developer solution for 40 seconds to remove the photoresist in the exposed areas and form a pattern of the top metal structure.

[0088] Step C4: Deposit Cr / Au metal layers on the surface of the patterned photoresist layer using magnetron sputtering, with thicknesses of 10 nm and 150 nm, respectively. The sputtering power is 500 W and the deposition rate is 2.3 nm / s.

[0089] Step C5: Place the silicon wafer with the deposited metal layer into acetone and isopropanol solutions in turn and ultrasonically clean for 5 minutes each to remove the photoresist and the metal layer above it, while retaining the metal pattern that is in direct contact with the dielectric layer to form a top metal square array.

[0090] Step C6: Use a plasma stripper at 400W power for 5 minutes to remove residual photoresist and impurities.

[0091] In step S4, the prepared silicon wafer is cut into 15 mm × 15 mm individual devices using a DISCO dicing machine.

[0092] In the ultrasonic cleaning, the cleaning time for both acetone and isopropanol is 5 minutes; the plasma cleaning time is 5 minutes.

[0093] In the spin coating process, for SU-8 2025 photoresist with a thickness of 33 μm, the spin coating speed is 500 rpm / 10s and 2000 rpm / 30s; for SU-8 2015 photoresist with a thickness of 13 μm, the spin coating speed is 500 rpm / 10s and 5000 rpm / 30s; both the pre-baking and post-baking use hot plate heating; the developer is PGMEA; the hardening treatment temperature is 150℃ and the time is 10 minutes.

[0094] In the photoresist spraying process, the photoresist type is 7133 and the photoresist layer thickness is 4 μm; the exposure time is 12 seconds; the developer is a 2.38% TMAH developer with a development time of 40 seconds; the magnetron sputtering power is 500 W and the deposition rate is 2.3 nm / s; in the stripping process, the cleaning time for both acetone and isopropanol is 5 minutes.

[0095] A testing method for a cubic heterogeneous terahertz metamaterial sensor is used to test the aforementioned cubic heterogeneous terahertz metamaterial sensor. In the testing method, multiple analytes with characteristic absorption at specific frequencies are used to experimentally test the sensor, and the enhanced molecular characteristic signals of the five analytes are obtained after modulation by the device. Since different substances have multiple characteristic absorption peaks and a large frequency range, it is impossible in practice for all plasma resonance peaks and molecular vibration absorption peaks to be in a state of perfect frequency matching.

[0096] The enhancement effect is strongest when the plasmonic resonance peak and the molecular vibrational absorption peak are frequency-matched. As detuning increases, the enhancement factor gradually decreases. Using 1 / e of the enhancement factor under matched conditions as the effective enhancement threshold, this method is used to evaluate the enhancement capability of the device under detuning conditions. The results show that the absorption intensities at all ten characteristic absorption frequencies of the five materials are higher than this threshold.

[0097] When absorbing specific frequency features, the structure corresponding to the two scales of the metal square array unit structure size parameters is mainly responsible for enhancing the feature absorption capability in the low-frequency region by the structure size parameters of the first scale of the metal square array unit, while the enhancement of the feature absorption capability in the high-frequency region is responsible for the structure size parameters of the second scale of the metal square array unit.

[0098] Example:

[0099] As shown in the figure, a square heterogeneous terahertz metamaterial device has a heterostructure sandwiched in the terahertz band that enables ultra-wideband fingerprint enhancement. The heterostructure sandwiched in the terahertz band is constructed on a silicon substrate 6, comprising a top layer of square metal array units 3, an intermediate dielectric layer 4, and a bottom layer of metal reflective layer 5. The intermediate dielectric layer uses SU-8 photoresist, which exhibits high loss characteristics in the terahertz band. The thickness of this dielectric layer directly affects the intensity and broadening of the plasmon resonance peak. By adjusting the spin-coating speed of the photoresist, the thickness of the dielectric layer can be precisely controlled, thereby modulating the resonance peak. The full width at half maximum (FWHM) of the top-layer square array unit achieves broadband resonance enhancement. Simultaneously, the geometric dimensions of the top-layer square array unit determine the excitation frequency of the plasma resonance peak. To achieve broadband coverage, utilizing the full width at half maximum (FWHM) characteristic of a single resonance peak, the metal square array unit employs two structural size parameters (specifically as follows). By scaling the overall architecture, ultra-wideband spectral responses in different bands can be achieved. When terahertz waves 1-2 are perpendicularly incident on this heterostructure, they induce plasma mode excitation on its surface. After passing through this structure, the emitted terahertz waves 7 are received by the terahertz receiver 8, and the signal exhibits ultra-wideband resonance characteristics.

[0100] The bottom metal reflective layer is a Cr / Au composite layer with a thickness of 10 / 150 nm; the intermediate dielectric layer is a high-loss SU-8 photoresist with a thickness of 33 μm or 13 μm. The top metal square array is a Cr / Au composite layer with a thickness of 10 / 150 nm. The square units have periods of 90 μm and 36 μm, respectively; the 90 μm square unit corresponds to a photoresist thickness of 33 μm and a square side length of 70 μm; the 36 μm square unit corresponds to a photoresist thickness of 13 μm and a square side length of 28 μm.

[0101] A method for fabricating a cubic heterostructure terahertz metamaterial device, used to generate a cubic heterostructure sandwich structure with broadband enhancement characteristics in two frequency windows, wherein the thickness of the intermediate layer can be adjusted to control the coupling condition of the device with terahertz waves, includes the following steps:

[0102] Step S1: Deposit a bottom metal reflective layer 5 on the surface of silicon wafer 6;

[0103] Step S2: Prepare an intermediate dielectric layer on the bottom metal reflective layer 5, and form a dielectric layer 4 with a preset thickness by photolithography.

[0104] Step S3: Fabricate a top-layer metal square array 3 on the intermediate dielectric layer, and form square resonant units of different scaling scales through photolithography and lift-off processes.

[0105] Step S4: Cut the prepared silicon wafer into individual devices.

[0106] In step S1, the specific method is as follows:

[0107] Step A1: Select a 2-inch single-polished silicon wafer as the substrate, and ultrasonically clean it in acetone and isopropanol solutions for 5 minutes each to remove surface contaminants.

[0108] Step A2: Use a plasma desmearing machine at 400W power for 5 minutes to improve the surface activity of the substrate;

[0109] Step A3: Cr / Au metal layers with thicknesses of 10 nm and 150 nm are sequentially deposited on the silicon wafer surface using magnetron sputtering, with a sputtering power of 500 W and a deposition rate of 2.3 nm / s.

[0110] In step S2, the specific method is as follows:

[0111] Step B1: Spin-coat SU-8 photoresist onto the silicon wafer surface with the deposited underlying metal, controlling the photoresist layer thickness to be 33 μm or 13 μm using a spin coating process. Figure 1 As shown;

[0112] Step B2: Place the silicon wafer with photoresist spin-coated on a hot plate for pre-baking at 60℃ / 1min, and then increase the temperature to 95℃ / 5min.

[0113] Step B3: Expose the photoresist layer using a mask. The exposure time is set to 10s or 5s depending on the thickness of the photoresist.

[0114] Step B4: After exposure, the silicon wafer is post-baked at 60℃ for 1 min, and then the temperature is increased to 95℃ for 3 min.

[0115] Step B5: Immerse the silicon wafer in PGMEA developer solution for development. The development time is set to 1 minute or 30 seconds depending on the photoresist thickness. Remove the photoresist from the unexposed areas to form a dielectric layer pattern.

[0116] Step B6: Place the developed silicon wafer on a hot plate at 150°C and bake for 10 minutes to perform a hardening process.

[0117] In step S3, the specific method is as follows:

[0118] Step C1: Apply 7133 photoresist to the surface of the dielectric layer formed in step S2 using a spray coating process. The thickness of the photoresist layer is 4 μm.

[0119] Step C2: Expose the photoresist layer using a mask for 12 seconds;

[0120] Step C3: Immerse the silicon wafer in a 2.38% TMAH developer solution for 40 seconds to remove the photoresist in the exposed areas and form a pattern of the top metal structure.

[0121] Step C4: Deposit Cr / Au metal layers on the surface of the patterned photoresist layer using magnetron sputtering, with thicknesses of 10 nm and 150 nm, respectively. The sputtering power is 500 W and the deposition rate is 2.3 nm / s.

[0122] Step C5: The silicon wafer with the deposited metal layer is sequentially immersed in acetone and isopropanol solutions for ultrasonic cleaning for 5 minutes each, removing the photoresist and the metal layer above it, retaining the metal pattern in direct contact with the dielectric layer, forming a top-layer metal square array. The microscopic imaging results are as follows: Figure 2 As shown;

[0123] Step C6: Use a plasma stripper at 400W power for 5 minutes to remove residual photoresist and impurities.

[0124] In step S4, the prepared silicon wafer is cut into 15 mm × 15 mm individual devices using a DISCO dicing machine.

[0125] In the ultrasonic cleaning, the cleaning time for both acetone and isopropanol is 5 minutes; the plasma cleaning time is 5 minutes.

[0126] In the spin coating process, for SU-8 2025 photoresist with a thickness of 33 μm, the spin coating speed is 500 rpm / 10s and 2000 rpm / 30s; for SU-8 2015 photoresist with a thickness of 13 μm, the spin coating speed is 500 rpm / 10s and 5000 rpm / 30s; both the pre-baking and post-baking are done using hot plates; the developer is PGMEA; the hardening treatment temperature is 150℃ and the time is 10 minutes.

[0127] In the photoresist spraying process, the photoresist type is 7133 and the photoresist layer thickness is 4 μm; the exposure time is 12 seconds; the developer is a 2.38% TMAH developer with a development time of 40 seconds; the magnetron sputtering power is 500 W and the deposition rate is 2.3 nm / s; in the stripping process, the cleaning time for both acetone and isopropanol is 5 minutes.

[0128] In this example, two square heterogeneous terahertz metamaterial devices with different structural scales are evaluated in a terahertz time-domain spectroscopy system. Specifically, the terahertz metamaterial device is fixed in the reflection spectrum measurement region of the system, and the terahertz wave is incident perpendicularly on the surface of the device. The square metal array structure on the surface will cause the incident wave to couple into a surface plasmon mode. After being modulated by the metamaterial, the reflected terahertz wave is received by the terahertz receiver.

[0129] like Figure 3Absorption spectral signals were acquired from both devices. Experimental tests were conducted using various analytes exhibiting characteristic absorption at specific frequencies to obtain enhanced molecular characteristic signals of five analytes modulated by the devices. Since different substances possess multiple characteristic absorption peaks with a wide frequency range, it is practically impossible for all plasmonic resonance peaks and molecular vibrational absorption peaks to be in a state of perfect frequency matching. The enhancement effect is strongest when the frequencies are matched, and the enhancement factor gradually decreases as detuning increases. Therefore, using 1 / e of the enhancement factor under matched conditions as the effective enhancement threshold criterion allows for an objective assessment of the device's enhancement capability under detuning conditions. The results show that the absorption intensity at all ten characteristic absorption frequency points of the five substances is higher than this threshold. The characteristic absorption in the low-frequency region is mainly enhanced by the scale-one structure, while the high-frequency region is enhanced by the scale-two structure. Test results show that the resonant effective enhancement bandwidth of the scale-one structure covers 0.5 THz to 1 THz, while the resonant effective enhancement bandwidth of the scale-two structure covers 1 THz to 1.6 THz. Ultra-wideband fingerprint enhancement absorption coverage (0.5-1.6 THz) can be customized using only these two array structures. Figure 4 As shown, this is achieved through the ingenious use of photoresist as part of the terahertz metamaterial device, and by precisely controlling the thickness of the SU-8 photoresist by adjusting the spin coating speed, thus ensuring a stable full width at half maximum (FWHM) for the terahertz metamaterial device within a preset working window. Simultaneously, the precise deposition of the Cr / Au metal layer using magnetron sputtering ensures the dimensional accuracy of the top array and the uniformity of the bottom reflective layer. Furthermore, the organic combination of two photolithography and lift-off processes allows for the integration of square arrays of different scaling scales on the same chip, avoiding the large number of independent array units required by traditional pixelated or gradient metamaterials. This results in ultra-wideband coverage with fewer process steps and a more compact structure. The above fabrication method not only simplifies the processing flow but also significantly improves the detection efficiency and spectral efficiency of the device, demonstrating the superior process of this invention.

[0130] Although the present invention has been described in detail through specific embodiments, those skilled in the art should understand that any changes in form and detail made on this basis without exceeding the scope of protection of the claims are within the scope of protection of the present invention.

Claims

1. A square-shaped heterogeneous terahertz metamaterial sensor, characterized in that: This includes a heterojunction sandwich structure for achieving ultra-wideband fingerprint enhancement in the terahertz band. The heterojunction sandwich structure is formed by constructing a multilayer structure on silicon material. The multilayer structure consists of a top layer of metal square array units (3), a middle dielectric layer (4), and a bottom layer of metal reflective layer (5). The sensor device achieves wide resonance enhancement by controlling the full width at half maximum (FWHM) of the plasma resonance peak by adjusting the thickness of the dielectric layer; the metal square array unit adopts two structural size parameters and achieves spectral response in different bands by scaling the overall architecture. When the sensor is working, terahertz waves are incident perpendicularly on the heterostructure and induce plasma mode excitation on its surface, causing the signal received by the terahertz receiver to exhibit ultra-wideband resonance characteristics.

2. The square heterogeneous terahertz metamaterial sensor device according to claim 1, characterized in that: The metal reflective layer is a Cr / Au composite layer, with a thickness corresponding to two different structural sizes of metal square array units, using parameters of 10 / 150 nm respectively; The dielectric layer is formed by photoresist, and its thickness corresponds to the two structural sizes of the metal square array unit, which are 33 μm or 13 μm respectively. The metal square array unit is a Cr / Au composite layer, with a thickness corresponding to two structural sizes of metal square array units, namely 10 / 150 nm. In the two structural sizes of the metal square array unit, the period of the square unit is 90 μm and 36 μm, respectively; the 90 μm square structural unit corresponds to a photoresist thickness of 33 μm, and the 36 μm square structural unit corresponds to a photoresist thickness of 13 μm.

3. The square heterogeneous terahertz metamaterial sensor device according to claim 1, characterized in that: The dielectric layer is prepared using SU-8 photoresist, which has high loss characteristics in the terahertz band, so that the thickness of the dielectric layer can affect the intensity and broadening of the plasmonic resonance peak. During the preparation of the dielectric layer, the thickness of the dielectric layer can be precisely controlled by adjusting the spin coating speed of the photoresist, thereby regulating the full width at half maximum (FWHM) of the resonance peak and achieving broadband resonance enhancement.

4. The square heterogeneous terahertz metamaterial sensor device according to claim 1, characterized in that: The metal square array unit achieves ultra-wide spectrum response in different bands through overall architecture scaling; when the terahertz wave is perpendicularly incident on the heterostructure, it induces the excitation of the plasma mode on its surface. The terahertz wave (7) emitted after passing through the structure is received by the terahertz receiver (8), and the received signal exhibits ultra-wideband resonance characteristics.

5. A method for fabricating a cubic heterogeneous terahertz metamaterial sensor, used to fabricate the cubic heterogeneous terahertz metamaterial sensor according to any one of claims 1, 2, 3, and 4, characterized in that: The fabrication method is used to prepare a square heterostructure with broadband enhancement characteristics across two frequency windows, and to control the coupling conditions of the sensor to terahertz waves by adjusting the thickness of the intermediate layer. The method includes the following steps: Step S1: Deposit a bottom metal reflective layer on the surface of the silicon wafer; Step S2: Prepare an intermediate dielectric layer on the bottom metal reflective layer, and form a dielectric layer with a preset thickness by photolithography. Step S3: Fabricate a top-layer metal square array on the middle dielectric layer, and form square resonant units of different scaling scales through photolithography and lift-off processes; Step S4: Cut the prepared silicon wafer into individual devices.

6. The method for fabricating the square heterogeneous terahertz metamaterial sensor according to claim 5, characterized in that: In step S1, the specific method is as follows: Step A1: Select a single-layer polished silicon wafer as the substrate, and ultrasonically clean it in acetone and isopropanol solutions in sequence to remove surface contaminants; Step A2: Use a plasma stripper to treat the substrate surface to improve its activity; Step A3: Cr / Au metal layers are sequentially deposited on the silicon wafer surface using magnetron sputtering.

7. The method for fabricating the square heterogeneous terahertz metamaterial sensor according to claim 5, characterized in that: In step S2, the specific method is as follows: Step B1: Spin-coat SU-8 photoresist onto the silicon wafer surface with deposited underlying metal, and control the thickness of the photoresist layer through a spin coating process. Step B2: Place the silicon wafer with photoresist spin-coated on a hot plate for pre-baking, and then heat it up; Step B3: Expose the photoresist layer using a photomask. The exposure time is set according to the photoresist thickness. Step B4: Post-bake the exposed silicon wafer; Step B5: Immerse the silicon wafer in PGMEA developer to develop and remove the photoresist in the unexposed areas to form a dielectric layer pattern; Step B6: Perform hardening treatment on the developed silicon wafer.

8. The method for fabricating the square heterogeneous terahertz metamaterial sensor according to claim 5, characterized in that: In step S3, the specific method is as follows: Step C1: Photoresist is sprayed onto the surface of the dielectric layer formed in step S2 using a spray coating process; Step C2: Expose the photoresist layer using a photomask; Step C3: Immerse the silicon wafer in the developing solution to develop and remove the photoresist in the exposed areas, forming a pattern of the top metal structure; Step C4: Deposit two thicknesses of Cr / Au metal layers on the surface of the patterned photoresist layer using magnetron sputtering. Step C5: Place the silicon wafer with the deposited metal layer into acetone and isopropanol solutions in sequence for ultrasonic cleaning to remove the photoresist and the metal layer above it, while retaining the metal pattern that is in direct contact with the dielectric layer to form a top metal square array. Step C6: Use a plasma stripper to remove residual photoresist and impurities.

9. The method for fabricating the square heterogeneous terahertz metamaterial sensor according to claim 5, characterized in that: In step S4, the prepared silicon wafer is cut into 15 mm × 15 mm individual devices using a DISCO dicing machine. In the ultrasonic cleaning, the cleaning time for both acetone and isopropanol is 5 minutes; the plasma cleaning time is 5 minutes. In the spin coating process, for SU-8 2025 photoresist with a thickness of 33 μm, the spin coating speed is 500 rpm / 10s and 2000 rpm / 30s; for SU-8 2015 photoresist with a thickness of 13 μm, the spin coating speed is 500 rpm / 10s and 5000 rpm / 30s; both the pre-baking and post-baking use hot plate heating; the developer is PGMEA; the hardening treatment temperature is 150℃ and the time is 10 minutes. In the photoresist spraying process, the photoresist type is 7133 and the photoresist layer thickness is 4 μm; the exposure time is 12 seconds; the developer is a 2.38% TMAH developer with a development time of 40 seconds; the magnetron sputtering power is 500 W and the deposition rate is 2.3 nm / s; in the stripping process, the cleaning time for both acetone and isopropanol is 5 minutes.

10. A testing method for a cubic heterogeneous terahertz metamaterial sensor, used to test the cubic heterogeneous terahertz metamaterial sensor according to any one of claims 1, 2, 3, and 4, characterized in that: In the testing method, various analytes with characteristic absorption at specific frequencies are used to conduct experimental tests on the sensor device to obtain the enhanced molecular characteristic signal information of the analyte after modulation by the device; The enhancement effect is strongest when the frequencies of the plasmonic resonance peak and the molecular vibrational absorption peak are matched. As the detuning increases, the enhancement factor gradually decreases. Using 1 / e of the enhancement factor under matched conditions as the effective enhancement threshold criterion, this method is used to evaluate the enhancement capability of the device under detuning conditions. When absorbing specific frequency features, the structure corresponding to the two scales of the metal square array unit structure size parameters is mainly responsible for enhancing the feature absorption capability in the low-frequency region by the structure size parameters of the first scale of the metal square array unit, while the enhancement of the feature absorption capability in the high-frequency region is responsible for the structure size parameters of the second scale of the metal square array unit.

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