Terahertz metamaterial sensor with polyimide superposed on substrate

Abstract

The invention discloses a terahertz metamaterial sensor with a substrate superposed with polyimide, which comprises a high-resistance silicon substrate, polyimide superposed on the high-resistance silicon substrate and a two-dimensional array fixed on the surface of the polyimide, and each array unit comprises a circular ring metal structure and a square split ring metal structure. The center of the circular ring metal structure coincides with the center of the array unit, surrounds the square split ring metal structure and is not connected with the square split ring metal structure. The vertical bisector of the square split ring metal structure coincides with the circular ring metal structure and is located in a ring of the circular ring metal structure, and the opening is located in an upper arm of the square split ring metal structure and located in the center of the upper arm. A layer of polyimide is introduced on the high-resistance silicon substrate, so that the sensor has higher resonance intensity, sensitivity and quality factors, the manufacturing process is mature, and the sensor is particularly suitable for high-sensitivity sensing of trace biomolecules.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz sensors, and in particular to a terahertz metamaterial sensor with a polyimide substrate stacked thereon. Background Art

[0002] Terahertz waves have the advantages of strong penetration and good safety. They have been widely used in biomedicine, environmental monitoring, and material analysis. Terahertz metamaterial sensors have become an important tool for detecting weak signals and characterizing molecular characteristics in these fields. The operating frequency of terahertz metamaterial sensors can be selected by precisely designing the unit structure of the metamaterial, and a strong electromagnetic resonance can be formed at a specific terahertz frequency, thereby amplifying the signal and improving the sensing sensitivity. Existing terahertz metamaterial sensors mainly use a single metal, a single substrate or a two-dimensional material, and their sensitivity is generally low. They cannot meet the needs of trace molecule detection, which greatly limits the application of metamaterial terahertz sensors. Summary of the invention

[0003] The purpose of the present invention is to disclose a terahertz metamaterial sensor with a polyimide superimposed on a substrate, comprising a high-resistance silicon substrate, a polyimide superimposed on the high-resistance silicon substrate, and a two-dimensional array fixed on the surface of the polyimide, wherein each array unit comprises a circular ring metal structure and a square open ring metal structure. The two-dimensional array is symmetrical on both sides, and the circular ring metal structure and the square open ring metal structure in the same array unit are not connected. The present invention improves the quality factor Q (quality factor) and the sensing sensitivity S by superimposing a polyimide layer on the high-resistance silicon substrate. The present invention overcomes the defects of the existing single-substrate terahertz metamaterial sensors, which generally have low quality factors and low sensitivity, and achieves higher sensing sensitivity.

[0004] The present invention designs a terahertz metamaterial sensor with a polyimide superimposed on a substrate, comprising a high-resistance silicon substrate, a polyimide superimposed on the high-resistance silicon substrate, and a two-dimensional array fixed on the surface of the polyimide, wherein the side length of the two-dimensional array is 1.0 to 1.5 times the diameter of the incident terahertz beam. The length and width of the polyimide and the high-resistance silicon substrate are both greater than the length and width of the two-dimensional array. The polyimide is a high-temperature curable polyimide with a thickness of 5 to 10 microns. The terahertz wave is incident from above the two-dimensional array, passes through the two-dimensional array, the polyimide layer and the high-resistance silicon substrate in sequence, and then is emitted.

[0005] Each array unit of the two-dimensional array includes a circular ring metal structure and a square open ring metal structure.

[0006] The material of each metal structure is any one of gold, copper or aluminum.

[0007] The center of the circular ring metal structure coincides with the center of the array unit, and surrounds the square open ring metal structure without being connected.

[0008] The perpendicular bisector of the square open ring metal structure coincides with the circular ring metal structure and is located inside the circular ring metal structure. The opening is located on the upper arm of the square open ring metal structure and at the center of the upper arm.

[0009] When electromagnetic waves are incident vertically on a metal structure, the terahertz metamaterial sensor with polyimide superimposed on the substrate has stronger surface current resonance, higher sensitivity S and quality factor Q than the terahertz metamaterial sensor without polyimide.

[0010] The polyimide is a high temperature curable polyimide with a thickness of 500 to 800 microns.

[0011] The lateral width and longitudinal length of an array unit in the two-dimensional array are both 90 micrometers to 100 micrometers.

[0012] Each metal structure is a metal strip of any one of gold, copper or aluminum, with a thickness of 0.2 micrometer to 0.8 micrometer and a width of 9 micrometer to 11 micrometer.

[0013] In the circular metal structure, the outer ring diameter is 85 micrometers to 96 micrometers, and the ring line width is 10 micrometers to 11 micrometers.

[0014] In the square open ring metal structure, the lateral width and longitudinal length are both 34 microns to 38 microns, the metal arm line width is 10 microns to 11 microns; and the opening size is 4 microns to 6 microns.

[0015] Compared with the prior art, the terahertz metamaterial sensor with a polyimide superimposed on a substrate of the present invention has the following advantages: 1. By superimposing polyimide on the substrate, a stronger surface current resonance, higher sensitivity S and quality factor Q can be obtained than without polyimide, and trace molecules can be detected more effectively; 2. The thickness of the polyimide can be achieved by a simple spin coating and curing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A top view of an embodiment of a terahertz metamaterial sensor with a polyimide substrate stacked on a substrate according to the present invention;

[0017] Figure 2 for Figure 1 Schematic diagram of the AA section;

[0018] Figure 3 for Figure 1 A schematic diagram of an array unit structure;

[0019] Figure 4 3 is a schematic diagram of the BB section;

[0020] Figure 5 is a simulation diagram of the power transmission spectrum of the terahertz metamaterial sensor according to an embodiment of the present invention;

[0021] Figure 6 is a simulation diagram of the two-dimensional distribution of the surface current density of the terahertz metamaterial sensor in resonance according to an embodiment of the present invention;

[0022] Figure 7 is a simulation diagram of the two-dimensional distribution of the electric field amplitude of the terahertz metamaterial sensor in the embodiment of the present invention when in resonance;

[0023] Figure 8 It is a simulation diagram of the resonant frequency shift of the terahertz metamaterial sensor according to the embodiment of the present invention when analytes with different refractive indices are placed;

[0024] Fig. 9 This is a simulation diagram of the resonant frequency shift of the terahertz metamaterial sensor according to an embodiment of the present invention when analytes of different thicknesses are placed.

[0025] Numbers in the figure: 1. high-resistance silicon substrate, 2. polyimide, 3. two-dimensional array, 31. circular ring metal structure, 32. square open ring metal structure. DETAILED DESCRIPTION

[0026] A solution of a terahertz metamaterial sensor with a polyimide substrate stacked thereon according to the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0027] The schematic diagram of the embodiment of the terahertz metamaterial sensor with a polyimide substrate stacked on the substrate of the present invention is as follows Figure 1 and 2 As shown, it comprises a high-resistance silicon substrate 1, a polyimide layer 2 located on the high-resistance silicon substrate 1, and a two-dimensional array 3 fixed on the surface of the polyimide. In this example, the diameter of the normally incident terahertz beam is 500 microns.

[0028] In this example, the length and width of the polyimide layer 2 and the high-resistance silicon substrate 1 are greater than the length and width of the two-dimensional array 3. In this example, the polyimide layer 2 is a high-temperature curable polyimide with a thickness of 5 microns. In this example, the thickness of the high-resistance silicon substrate 1 is 50 microns. The terahertz wave incident normally from above the two-dimensional array 3 passes through the two-dimensional array 3 to obtain an absorption spectrum, and then passes through the polyimide layer 2 and the high-resistance silicon substrate 1 and then exits.

[0029] like Figure 3 and 4 As shown, each array unit of the two-dimensional array 3 in this example includes a circular ring metal structure 31 and a square open ring metal structure 32. The length and width of an array unit are both d=100 microns.

[0030] In this example, the circular ring metal structure 31 and the square open ring metal structure 32 are gold strips with a thickness of 0.2 microns and a width of 11 microns.

[0031] In this example, the outer ring diameter of the circular metal structure is r = 96 microns, and the ring line width is w = 11 microns.

[0032] In this example, the square open ring metal structure has a lateral width and a longitudinal length of x=y=38 microns, a metal arm line width of m=11 microns, and an opening size of g=6 microns.

[0033] In the case of a terahertz metamaterial sensor without polyimide 3 on the substrate, in order to ensure that its resonant frequency is close to that of the sensor of the present invention and to facilitate the comparison of performance parameters, the unit structure size of the terahertz metamaterial sensor without polyimide 3 on the substrate is reduced to 0.9 times that of the sensor of the present invention in the simulation, and other parameters remain unchanged. When the electromagnetic wave is incident vertically on the metal structure, the structure has only one symmetrical resonance within the simulated frequency range of 0.1 to 1.1 THz, and the fundamental mode resonance frequency is 0.706 THz. This resonance has a large bandwidth and a low quality factor of 9.6 due to radiation loss.

[0034] When the terahertz metamaterial sensor with polyimide 3 superimposed on the substrate, the structure also has a symmetrical resonance in the simulated frequency range of 0.1 to 1.1 THz. The fundamental mode resonance frequency is 0.704 THz, and the quality factor is 15.2, which is higher than the quality factor of the terahertz metamaterial sensor without polyimide on the substrate. The relationship between the power transmittance of the two sensors and the frequency is obtained as follows: Figure 5 shown.

[0035] The current density distribution on the metal surface of the sensor in this example at the fundamental mode resonant frequency is as follows Figure 6 As shown, the left and right sides have currents of the same magnitude and opposite directions, and the current density is 1.5 times the current density of the terahertz metamaterial sensor without polyimide 3 at the corresponding resonance. Figure 7 The electric field amplitude distribution in the plane where the metal upper surface is located at the fundamental mode resonant frequency of the sensor of the present invention is shown in Figure 1. The electric field strength is mainly concentrated at the upper and lower ends of the circular metal structure, and is concentrated in a relatively small spatial range within the unit structure. The maximum electric field strength of this structure is 1.1 times the maximum electric field strength of the terahertz metamaterial sensor without polyimide at the corresponding resonance.

[0036] When analytes of different types and thicknesses are placed on the metamaterial metal surface, the resonant frequency of the metamaterial structure will red-shift, and the shift in the resonant frequency is related to the type and thickness of the analyte. Figure 8The shift change of the resonant frequency of the sensor of the present invention and the terahertz metamaterial sensor without polyimide was compared when different refractive index materials (n=1.2, 1.4, 1.6, 1.8 and 2.0) were placed on the metal surface, where the thickness of the analyte material was 20 microns. The slope of the straight line obtained by linear function fitting is the sensitivity of the sensor when the analyte thickness is 20 microns, and the values ​​are S=5.6GHz / RIU (sensor without polyimide terahertz metamaterial) and S=12.9GHz / RIU (sensor with superimide terahertz metamaterial), where RIU is the refractive index unit. Therefore, the sensitivity S of the sensor of the present invention is 2.3 times the sensitivity of the sensor without polyimide terahertz metamaterial. At the same time, it can be calculated that the sensing quality factors are 9.6 (without polyimide terahertz metamaterial sensor) and 15.2 (with superimide terahertz metamaterial sensor), respectively. Therefore, the quality factor of the sensor of the present invention is 1.58 times that of the sensor without polyimide terahertz metamaterial sensor.

[0037] Fig. 9The shift changes of the resonant frequency of the sensor of the present invention and the terahertz metamaterial sensor without polyimide were compared when materials of different thicknesses (0.5, 1, 2, 5, 10, 15, 20, 25 and 30 microns) were placed on the metal surface, wherein the analyte material was red blood cells infected with malaria, and the dielectric constant was 1.383. The resonant frequency shift is nonlinearly related to the thickness of the analyte. As the thickness of the analyte increases, the frequency shift first rises rapidly, then increases slowly, and finally tends to saturation. Since the electric field value of the sensor of the present invention is large when it resonates and the strong field is confined to a spatial region small from the interface between the metal and the substrate, when the thickness of the analyte material is small, the sensor of the present invention has a larger resonant frequency shift than the terahertz metamaterial sensor without polyimide, thereby having a higher sensitivity. When the thickness of the analyte is 1 micron, the resonant frequency of the terahertz metamaterial sensor without polyimide decreases by 1.5 GHz, while the resonant frequency of the sensor of the present invention decreases by 3.7 GHz, which is 2.5 times that of the terahertz metamaterial sensor without polyimide; when the thickness of the analyte is 5 microns, the resonant frequency of the terahertz metamaterial sensor without polyimide decreases by 4.1 GHz, while the resonant frequency of the sensor of the present invention decreases by 9.6 GHz, which is 2.3 times that of the terahertz metamaterial sensor without polyimide; when the thickness of the analyte is 10 microns, the resonant frequency of the terahertz metamaterial sensor without polyimide decreases by 5.5 GHz, while the resonant frequency of the sensor of the present invention decreases by 12.2 GHz, which is 2.2 times that of the terahertz metamaterial sensor without polyimide, and gradually tends to be stable. Therefore, the sensor of the present invention has a sensitivity far higher than that of a terahertz metamaterial sensor without polyimide when detecting extremely thin materials. The thinner the thickness, the more obvious the sensitivity improvement, especially for materials within 20 microns in thickness. Therefore, it is particularly suitable as a high-sensitivity sensor for detecting trace molecules.

[0038] The above embodiments are only specific examples for further describing the purpose, technical solutions and beneficial effects of the present invention, and the present invention is not limited thereto. Any modification, equivalent replacement, improvement, etc. made within the scope of the disclosure of the present invention are included in the protection scope of the present invention.

Claims

1. A terahertz metamaterial sensor with a polyimide superimposed on a substrate, comprising a high-resistance silicon substrate (1), a polyimide (2) superimposed on the high-resistance silicon substrate, and a two-dimensional array (3) fixed on the surface of the polyimide, wherein the side length of the two-dimensional array (3) is 1.0 to 1.5 times the diameter of the incident terahertz wave beam. The length and width of the polyimide (2) and the high-resistance silicon substrate (1) are both greater than the length and width of the two-dimensional array (3). The polyimide (2) is a high-temperature curable polyimide with a thickness of 5 to 10 microns. The terahertz wave is incident from above the two-dimensional array (3), passes through the two-dimensional array (3) to obtain an absorption spectrum, and passes through the polyimide (2) and the high-resistance silicon substrate (1) before being emitted; characterized in that: Each array unit of the two-dimensional array (3) comprises a circular ring metal structure (31) and a square open ring metal structure (32); The center of the circular ring metal structure (31) coincides with the center of the array unit, and surrounds the square open ring metal structure (32) without being connected. The perpendicular bisector of the square open ring metal structure (32) coincides with the circular ring metal structure (31) and is located inside the circular ring metal structure (31); the opening is located on the upper arm of the square open ring metal structure (32) and at the center of the upper arm. When electromagnetic waves are incident vertically on a metal structure, a terahertz metamaterial sensor having polyimide (3) stacked on a substrate has stronger surface current resonance, higher sensitivity S and quality factor Q when resonating than a terahertz metamaterial sensor without polyimide.

2. The terahertz metamaterial sensor with a substrate stacked with polyimide according to claim 1, characterized in that: The polyimide is a high temperature curable polyimide with a dielectric constant of 3.2 or 3.4 and a thickness of 500 to 800 microns.

3. The terahertz metamaterial sensor with a substrate stacked with polyimide according to claim 1, characterized in that: The lateral width and longitudinal length of an array unit in the two-dimensional array are both 90 micrometers to 100 micrometers.

4. The terahertz metamaterial sensor with a substrate stacked with polyimide according to claim 1, characterized in that: The material of the circular ring metal structure (31) and the square open ring metal structure (32) is any one of gold, copper or aluminum.

5. The terahertz metamaterial sensor with a substrate stacked with polyimide according to claim 1, characterized in that: The circular ring metal structure (31) and the square open ring metal structure (32) have a thickness of 0.2 micrometer to 0.8 micrometer and a width of 9 micrometer to 11 micrometer.

6. The terahertz metamaterial sensor with a substrate stacked with polyimide according to claim 1, characterized in that: In the circular metal structure (31), the outer ring diameter is 85 micrometers to 96 micrometers, and the ring line width is 10 micrometers to 11 micrometers.

7. The terahertz metamaterial sensor with a substrate stacked with polyimide according to claim 1, characterized in that: In the square open ring metal structure (32), the lateral width and longitudinal length are both 34 microns to 38 microns, the metal arm line width is 10 microns to 11 microns; and the opening size is 4 microns to 6 microns.

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