A narrow-band terahertz bandpass filter and a method of manufacturing the same

Abstract

The application discloses a kind of narrow-band terahertz band-pass filters and preparation method thereof, the filter is composed of aluminum foil paper, there is repeated structure unit on aluminum foil paper, structure unit is composed of three slot holes, it is " Y " type, the distance between structure unit is 100-200 μm, the width of slot hole is 20-70 μm, length is 30-80 μm;Preparation method is as follows: (1) the lower surface of aluminum foil paper is bonded on substrate, then coating photoresist on its upper surface, then heat curing is carried out;(2) again, the aluminum foil paper after heat curing is exposed to light, and the photomask is placed on the photoresist on the upper surface of aluminum foil paper;(3) using developing solution to develop the photoresist after exposure;(4) the aluminum foil paper after development is placed in weak alkaline solution and etched;(5) the substrate on the lower surface of the aluminum foil paper after etching treatment is stripped, and the terahertz band-pass filter is obtained.The terahertz band-pass filter of the application has the advantages of low cost, simple preparation process and low loss compared with the prior art.

Description

Technical Field

[0001] This invention relates to filters and their fabrication methods, specifically to a narrowband terahertz bandpass filter and its fabrication method. Background Technology

[0002] Terahertz waves refer to electromagnetic waves with frequencies between 0.1 THz and 10 THz and wavelengths between 30 μm and 3 mm. They lie between the microwave and infrared bands and possess enormous application potential. Frequency-selective surfaces (FSS) are two-dimensional arrays composed of periodically arranged subwavelength unit structures. Their interaction with electromagnetic waves exhibits distinct band-pass or band-stop filtering characteristics. By adjusting the shape, size, and materials of the unit structures, FSS can control electromagnetic waves. Terahertz filters have significant application value in terahertz communication, security detection, and terahertz sensing. Currently, most existing terahertz filters have complex fabrication structures, high manufacturing costs, and increased terahertz losses due to the presence of a substrate, severely limiting their practical applications.

[0003] Patent CN105048028 discloses a terahertz filter and its fabrication method, comprising: a polymer material layer and a metal layer; the metal layer includes a sheet-like structure, the sheet-like structure including horizontal and vertical stripes; the sheet-like structure is periodically distributed within the polymer material layer. This invention expands the filtering range of the filter and is more beneficial for the application of terahertz filters in other systems. Patent CN107230816 discloses a terahertz filter and its processing method, comprising a core and a package shell. The core has a rectangular waveguide cavity filter structure fabricated based on microelectromechanical systems (MEMS) and deep reactive ion etching (DRIE) technology. The package shell has a core cavity with the same external dimensions as the core, completely enclosing the core. A straight guide hole is provided at each end of the core cavity; one end of the guide hole connects to the waveguide cavity of the core, and the other end opens onto the outer surface of the package shell. The guide hole and the waveguide cavity are aligned, and the radial cross-section of the guide hole is consistent with the radial cross-section of the waveguide cavity. The terahertz filter of this invention can guarantee filtering performance while also possessing excellent strength, representing a significant improvement over existing technologies. However, the aforementioned filter has a complex structure and involves numerous fabrication steps, resulting in very high manufacturing costs, and the substrate used increases terahertz losses. Summary of the Invention

[0004] Purpose of the invention: In order to solve the technical problems existing in the prior art, the present invention aims to provide a narrowband terahertz bandpass filter with low cost, simple process and low loss. Furthermore, the present invention also provides a method for fabricating the filter.

[0005] Technical solution: The narrowband terahertz bandpass filter of the present invention is composed of aluminum foil paper. The aluminum foil paper has repeating structural units. Each structural unit consists of three slots in a "Y" shape. The distance between the structural units is 100-700μm, the width of the slot is 20-70μm, the length is 30-300μm, and the depth is 5-20μm.

[0006] Furthermore, the included angle between the three slots is 120°, and the frequency of the terahertz bandpass filter is 0.1-10THz.

[0007] The method for fabricating the narrowband terahertz bandpass filter of the present invention comprises the following steps:

[0008] (1) The lower surface of the aluminum foil is bonded to the substrate, and AZ1500 photoresist is evenly coated on the upper surface of the aluminum foil using a spin coater, and then heat-cured.

[0009] (2) The aluminum foil paper after heat curing is exposed using a photolithography machine, and a photomask with repeating structural unit "Y" is placed on the photoresist on the upper surface of the aluminum foil paper.

[0010] (3) The exposed photoresist was developed using ZJ-100 developer;

[0011] (4) Place the developed aluminum foil paper in a weakly alkaline solution for etching treatment;

[0012] (5) The substrate on the lower surface of the etched aluminum foil is peeled off to obtain a terahertz bandpass filter.

[0013] Further, in step (1), the bonding method is as follows: the aluminum foil can be firmly fixed on the substrate by photoresist or adhesive, which is conducive to the stable progress of subsequent reactions; the coating process is as follows: first, the adhesive is uniformly coated at a low speed of 500-600 r / min for 6-10s, and then the speed is directly increased to a high speed of 4000-4500 r / min for spinning, and maintained for 40-60s; the heating curing conditions are as follows: the temperature is 90-100℃ and the time is 3-5min.

[0014] Further, in step (4), the etching process takes 10-20 hours; the weakly alkaline solution is ammonia or an alkaline developing solution.

[0015] Further, in steps (1) and (5), when the substrate is plexiglass, the method of bonding the plexiglass to the lower surface of the aluminum foil is as follows: AZ1500 photoresist is uniformly coated on the upper surface of the plexiglass using a spin coater, and then the lower surface of the aluminum foil is attached to the plexiglass substrate coated with photoresist. Another clean substrate is used to align and press the aluminum foil firmly to the plexiglass substrate. Then, it is placed on a heating table for heating. During heating, continuous pressing should be maintained to avoid the generation of air bubbles. The coating process is as follows: first, spin coating is performed at a low speed of 500-600 r / min, and after maintaining for 4-6 seconds, the speed is directly increased to a high speed of 2500-3000 r / min for spin coating, and maintained for 40-60 seconds. The heating parameters are: temperature of 80-90℃, time of 2-2.5 min. The peeling process is as follows: the etched aluminum foil is immersed in N-methylpyrrolidone at 30-50℃ for 2-4 hours.

[0016] Invention principle: The frequency selective surface is a two-dimensional periodic array structure that interacts with electromagnetic waves and exhibits obvious bandpass or bandstop characteristics. By rationally designing the unit structure, bandpass filtering of different center frequencies can be achieved.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0018] (1) The terahertz bandpass filter prepared by the present invention uses aluminum foil paper as the substrate, which has simple raw materials, low cost and low terahertz loss, and at the same time has a pass rate of more than 90% for frequencies of 0.1-10THz.

[0019] (2) The preparation method used in this invention can achieve etching of the surface of aluminum foil by combining photolithography and wet etching technology. The process is simple and controllable. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the photomask template with repeating structural unit "Y" used in Embodiment 1 of the present invention;

[0021] Figure 2 An experimental photograph of the terahertz bandpass filter prepared in Embodiment 1 of the present invention;

[0022] Figure 3 A micrograph of the terahertz bandpass filter prepared in Embodiment 1 of the present invention;

[0023] Figure 4 The filtering characteristics of the terahertz bandpass filter obtained in Embodiment 1 of the present invention in the 0-3THz band are shown.

[0024] Figure 5 A micrograph of the terahertz bandpass filter prepared in Embodiment 2 of the present invention;

[0025] Figure 6 The image shows the filtering characteristics of the terahertz bandpass filter obtained in Embodiment 2 of the present invention in the 0-3THz band. Detailed Implementation

[0026] The present invention will now be further described in conjunction with specific embodiments and accompanying drawings.

[0027] Example 1: The narrowband terahertz bandpass filter of the present invention is composed of aluminum foil paper. The aluminum foil paper has repeating structural units. Each structural unit consists of three slots in a "Y" shape. The distance between the structural units is 120.83 μm, the width of the slot is 32.27 μm, the length is 47.62 μm, and the depth is 15 μm.

[0028] The fabrication method of the above-mentioned terahertz bandpass filter is specifically as follows:

[0029] (1) Prepare several clean, round acrylic substrates, a roll of clean, wrinkle-free aluminum foil, and a photomask template with a repeating structural unit "Y", such as... Figure 1 As shown;

[0030] (2) Cut the aluminum foil to the size of a circular acrylic substrate, keeping the aluminum foil flat.

[0031] (3) Take a clean acrylic substrate and coat it with a layer of AZ1500 photoresist using a spin coater. The parameters are: first, spin coat at a low speed of 600 r / min and maintain for 6 seconds, then directly increase the speed to a high speed of 3000 r / min and spin coat for 40 seconds.

[0032] (4) Place the bottom surface of the cut circular aluminum foil onto the photoresist-coated acrylic substrate, align and press it with another clean substrate to firmly adhere the aluminum foil to the acrylic substrate, place it on a heating table and heat it with the heating parameters of 90℃ for 2 min 30 s. Press continuously during heating to avoid the formation of air bubbles.

[0033] (5) Remove the substrate used for pressing, and apply a layer of AZ1500 photoresist to the upper surface of the aluminum foil paper attached to the plexiglass substrate. The parameters are: first, perform uniform coating at a low speed of 600r / min, maintain for 6s, and then directly increase the speed to a high speed of 4000r / min for spin coating, maintain for 40s.

[0034] (6) Place the coated aluminum foil on the heating table and heat it at 90℃ for 3 minutes;

[0035] (7) Expose with a photolithography machine, and place a photomask with repeating structural unit "Y" on the photoresist on the upper surface of aluminum foil;

[0036] (8) Develop the exposed photoresist with ZJ-100 developer;

[0037] (9) Place the developed aluminum foil in a weak alkaline solution for etching for 12 hours;

[0038] (10) Remove the aluminum foil and observe the etching progress under light. After etching is complete, place the aluminum foil with the substrate into a beaker containing N-methylpyrrolidone and heat in a water bath for 2 hours. Then peel the aluminum foil off the substrate to obtain the terahertz bandpass filter. Figure 2 As shown.

[0039] The fabricated terahertz bandpass filter was observed under a microscope and its performance was tested, such as... Figure 3 and Figure 4 As shown. Figure 3 The structural dimensions of the medium-sized filter basically conform to the simulation results of a 1.6THz bandpass filter, and the test results of the filter are as follows: Figure 4 As shown, the transmittance exceeds 90% near 1.6THz. Figure 3 The rounded edges of the "Y"-shaped structure are a processing error caused by the etching process. This error can be reduced by strictly controlling the process conditions and improving the etching uniformity.

[0040] Example 2: The narrowband terahertz bandpass filter of the present invention is composed of aluminum foil paper. The aluminum foil paper has repeating structural units. Each structural unit consists of three slots in a "Y" shape. The distance between the structural units is 500.02 μm, the width of the slot is 34.61 μm, the length is 201.53 μm, and the depth is 15 μm.

[0041] The fabrication method of the above-mentioned terahertz bandpass filter is specifically as follows:

[0042] (1) Prepare several clean, round acrylic substrates, a roll of clean, wrinkle-free aluminum foil, and a photomask template with a repeating structural unit "Y", such as... Figure 1 As shown;

[0043] (2) Cut the aluminum foil to the size of a circular acrylic substrate, keeping the aluminum foil flat.

[0044] (3) Take a clean acrylic substrate and coat it with a layer of AZ1500 photoresist using a spin coater. The parameters are: first, spin coat at a low speed of 600 r / min and maintain for 6 seconds, then directly increase the speed to a high speed of 3000 r / min and spin coat for 40 seconds.

[0045] (4) Place the bottom surface of the cut circular aluminum foil onto the photoresist-coated acrylic substrate, align and press it with another clean substrate to firmly adhere the aluminum foil to the acrylic substrate, place it on a heating table and heat it with the heating parameters of 90℃ for 2 min 30 s. Press continuously during heating to avoid the formation of air bubbles.

[0046] (5) Remove the substrate used for pressing, and apply a layer of AZ1500 photoresist to the upper surface of the aluminum foil paper attached to the plexiglass substrate. The parameters are: first, perform uniform coating at a low speed of 600r / min, maintain for 6s, and then directly increase the speed to a high speed of 4000r / min for spin coating, maintain for 40s.

[0047] (6) Place the coated aluminum foil on the heating table and heat it at 90℃ for 3 minutes;

[0048] (7) Expose with a photolithography machine, and place a photomask with repeating structural unit "Y" on the photoresist on the upper surface of aluminum foil;

[0049] (8) Develop the exposed photoresist with ZJ-100 developer;

[0050] (9) Place the developed aluminum foil in a weak alkaline solution for etching for 12 hours;

[0051] (10) Take out the aluminum foil and observe the etching progress under the light. After the etching is completed, put the aluminum foil with the substrate into a beaker containing N-methylpyrrolidone and heat it in a water bath for 2 hours. Then peel the aluminum foil off the substrate to obtain the terahertz bandpass filter.

[0052] The fabricated terahertz bandpass filter was observed under a microscope and its performance was tested, such as... Figure 5 and Figure 6 As shown. Figure 5 The structural dimensions of the medium-sized filter basically conform to the simulation results of a 0.35THz bandpass filter, and the test results of the filter are as follows: Figure 6 As shown, the transmittance is close to 90% near 0.35THz.

Claims

1. A narrowband terahertz bandpass filter, characterized in that, The terahertz bandpass filter is composed of aluminum foil paper with repeating structural units. Each structural unit consists of three slots arranged in a "Y" shape. The distance between the structural units is 100-700 μm, the width of the slots is 20-70 μm, the length is 30-300 μm, and the depth is 5-20 μm. The included angle between the three slots is 120°. The fabrication method of the narrowband terahertz bandpass filter is as follows: (1) The lower surface of the aluminum foil is bonded to the substrate, and AZ1500 photoresist is evenly coated on the upper surface of the aluminum foil using a spin coater, and then heat-cured. (2) The aluminum foil paper after heat curing is exposed using a photolithography machine, and a photomask with repeating structural unit "Y" is placed on the photoresist on the upper surface of the aluminum foil paper; (3) The exposed photoresist was developed using ZJ-100 developer; (4) Place the developed aluminum foil paper in a weakly alkaline solution for etching treatment; (5) The substrate on the lower surface of the etched aluminum foil is peeled off to obtain a terahertz bandpass filter.

2. The terahertz bandpass filter according to claim 1, characterized in that, The frequency of the terahertz bandpass filter is 0.1-10THz.

3. The terahertz bandpass filter according to claim 1, characterized in that, In step (1), the bonding method is: through photoresist or adhesive.

4. The terahertz bandpass filter according to claim 1, characterized in that, In step (1), the coating process is as follows: first, the adhesive is uniformly coated at a low speed of 500-600 r / min for 6-10 seconds, and then the speed is directly increased to a high speed of 4000-4500 r / min for spinning and maintained for 40-60 seconds.

5. The terahertz bandpass filter according to claim 1, characterized in that, In step (1), the conditions for heating and curing are: temperature of 90-100℃ and time of 3-5min.

6. The terahertz bandpass filter according to claim 1, characterized in that, In step (4), the etching process takes 10-20 hours.

7. The terahertz bandpass filter according to claim 1, characterized in that, In step (4), the weakly alkaline solution is ammonia or an alkaline developing solution.

8. The terahertz bandpass filter according to claim 1, characterized in that, In steps (1) and (5), when the substrate is plexiglass, the peeling process is as follows: the etched aluminum foil is immersed in N-methylpyrrolidone at 30-50°C for 2-4 hours.

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