Multilayer metal wire grid structure thin film broadband terahertz polarizer and manufacturing method thereof

Abstract

This invention discloses a multilayer metal wire grid structure thin-film broadband terahertz polarizer and its manufacturing method. It includes a thin-film substrate (1), a thin-film capping layer (2) on top of the substrate (1), and multiple layers of metal wire grids (4) spaced apart by metal wires (3) within the capping layer (2), with adjacent metal wire grids (4) arranged intersectingly. This invention maintains a high extinction ratio in the broadband terahertz spectrum, making it well-suited for high-frequency terahertz wave applications. Furthermore, this invention eliminates reflection losses caused by different optical media, enhancing the overall mechanical strength and stability of the thin-film device.

Description

Technical Field

[0001] The invention relates to a polarizer and a manufacturing method thereof, in particular to a multilayer metal wire grid structure thin film broadband terahertz polarizer and a manufacturing method thereof, belonging to the field of terahertz polarizers. Background Art

[0002] Terahertz polarizers are devices used to study different polarization characteristics in terahertz waves. They can convert / filter terahertz wave signals with polarization components in all directions emitted by terahertz sources into linearly polarized waves that are (mainly) polarized in only one direction. The main parameters are: extinction ratio (the decibel ratio of the desired transmitted polarization mode and the cutoff polarization mode, the higher the better), (insertion) loss (the smaller the better), and effective operating frequency (determines whether it can be used in certain applications, the wider the effective operating spectrum, the better).

[0003] Existing polarizers for terahertz waves are divided into two categories:

[0004] One type is without substrate support, only metal wires or nanowires are wound around a hollow bracket to form selective reflection of different polarizations. The winding of metal wires in this type of polarizer was the first to be industrialized, but there are many process limitations for the poor control of the uniformity of the winding interval of the metal wire and the reduction of the winding interval period (to improve the extinction ratio) (the period is about 250μm, resulting in an extinction ratio of only about 30dB at 1THz).

[0005] The other type is supported by a substrate, but some substrates use silicon materials, which leads to large Fresnel reflection losses between interfaces (more than 3dB). On the other hand, thick substrates will cause additional multi-reflection interference in the terahertz time-domain spectrometer. Therefore, we have previously realized polarizers with two thin film substrates: using a silicon dioxide / silicon composite substrate as a substrate, and completely removing the silicon part of the bottom substrate by dry deep etching, and using micromachining methods to make single-layer and double-layer metal wire grid structures on the front. This can not only reduce multi-reflection interference signals, but also reduce overall losses (the refractive index of silicon dioxide and air is much closer to that of silicon, and the Fresnel reflection loss is large). Finally, the measured extinction ratio of a 1THz single-layer metal wire grid thin film polarizer is still 30dB, while the double-layer metal wire grid thin film polarizer has reached 50-60dB. However, with the gradual development of terahertz wave applications at higher frequencies (above 2THz), it is necessary to develop devices with better performance (high extinction ratio and low loss) in high frequency bands. At present, the extinction ratio of the single-layer wire grid thin film polarizer obtained by simulation of the same structure is below 20dB at 4THz and below 10dB at 10THz; while the extinction ratio of the double-layer wire grid thin film polarizer is about 45dB at 4THz and drops to 30dB at 10THz. This shows that the current terahertz polarizer is still very limited in its application in broadband terahertz waves. Summary of the invention

[0006] The object of the present invention is to provide a multilayer metal wire grid structure thin film broadband terahertz polarizer and a manufacturing method thereof. The present invention still has a high extinction ratio in the broadband terahertz spectrum and can be well applied to the application of high-frequency terahertz waves. In addition, the present invention eliminates the reflection loss caused by different optical media and enhances the overall mechanical strength and stability of the thin film device.

[0007] The technical solution of the present invention is a multi-layer metal wire grid structure thin film broadband terahertz polarizer, comprising a thin film substrate, a thin film covering layer is arranged above the thin film substrate, and a plurality of metal wire grids composed of metal wires arranged at intervals are arranged in the thin film covering layer, and the metal wire grids of adjacent layers are arranged crosswise.

[0008] In the above-mentioned multilayer metal wire grid structure thin film broadband terahertz polarizer, a copper sheet bracket is provided at the bottom of the film substrate, a light-transmitting circular hole is provided in the middle of the copper sheet bracket, and a film base is provided below the copper sheet bracket.

[0009] In the aforementioned multilayer metal wire grid structure thin film broadband terahertz polarizer, the metal wires are selected from aluminum wires, gold wires, silver wires or chromium wires.

[0010] In the aforementioned multi-layer metal wire grid structure thin film broadband terahertz polarizer, three layers of parallel metal wire grids are arranged in the thin film covering layer.

[0011] In the aforementioned multilayer metal wire grid structure thin film broadband terahertz polarizer, the thin film substrate, thin film cover layer and thin film base are thin film materials, and are Epocore thin film materials. The Epocore thin film material is a polymer negative photoresist material used for optical waveguide structures of printed integrated circuit PCB boards from German microresist technology GmbH. The advantages of using this material as a thin film material are: Epocore has good mechanical properties and thermal stability, can form a relatively stable suspended film (9 microns thick, 1 inch diameter circular area) with a thickness of less than 10 microns without (obviously) wrinkling on the surface, and has good anti-seismic properties.

[0012] The manufacturing method of the aforementioned multilayer metal wire grid structure thin film broadband terahertz polarizer specifically comprises the following steps:

[0013] a. Take a copper sheet, spin-coat a thin film on the surface of the copper sheet, and then deposit a layer of aluminum wire grid on the thin film;

[0014] b. Continue to spin-coat a layer of thin film, and then deposit a layer of metal wire grid parallel to the previous layer of metal wire grid on the thin film, and the layer of metal wire grid and the previous layer of metal wire grid are arranged in a cross pattern; repeat this step to deposit multiple layers of metal wire grid;

[0015] c. Finally, spin-coat a thin film to encapsulate the multi-layer metal wire grid structure;

[0016] d. Spin-coat a thin film on the bottom surface of the pure copper sheet, soft-dry the film, and then open a circular hole in the center of the film using photolithography technology;

[0017] e. Place it in a ferric chloride solution, heat it to 70-80 degrees Celsius, corrode the exposed copper sheet, and obtain the finished product.

[0018] In the above-mentioned method for manufacturing a multi-layer metal wire grid structure thin film broadband terahertz polarizer, in step a, a layer of aluminum wire grid pattern is deposited on the thin film using microlithography technology and wet etching technology.

[0019] In the aforementioned method for manufacturing the multilayer metal wire grid structure thin film broadband terahertz polarizer, in step e, after the exposed copper sheet is corroded away, it is washed with deionized water and dried, and then attached to the angle rotating seat to obtain the finished product.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention includes a thin film substrate, a thin film covering layer is provided above the thin film substrate, and multiple layers of metal wire grids composed of metal wires arranged at intervals are provided in the thin film covering layer, and the metal wire grids of adjacent layers are arranged crosswise. After the improvement, under the signal-to-noise ratio limitation of the existing terahertz time-domain spectrum system, the average extinction ratio at 0.5-1.8THz is measured to be above 60dB, and the theoretical extinction ratio simulated by the actual prepared sample will reach 75dB at 4THz, and the theoretical extinction ratio at 10THz is not less than 50dB. It can be seen that the present invention still has a high extinction ratio in the broadband terahertz spectrum and can be well applied to the application of high-frequency terahertz waves.

[0022] (2) The present invention adopts a thin film substrate, eliminating the optical reflection loss between the different material layers of the silicon dioxide substrate and the polymer cover layer. At the same time, the thin film substrate and the thin film cover layer are both made of Epocore polymer material. Epocore has good mechanical properties and thermal stability. It can form a relatively stable suspended film (9 microns thick, 1 inch diameter circular area) with a thickness of less than 10 microns without (obvious) wrinkling on the surface and good anti-seismic properties. Therefore, the above improvements enhance the overall mechanical strength and stability of the thin film device.

[0023] (3) A copper sheet bracket is provided at the bottom of the film substrate, a light-transmitting circular hole is provided in the middle of the copper sheet bracket, and a film base is provided below the copper sheet bracket. The copper sheet bracket can effectively protect the film and strengthen the entire polarizer, and can also make it easier to use the polarizer (the metal copper sheet part can be conveniently attached directly to the angle rotation seat to achieve the angle rotation of the polarization direction). At the same time, the copper sheet bracket can effectively filter out the noise residual wave around the polarizer (the copper sheet reflects all the residual waves around it).

[0024] (4) The present invention also optimizes and improves the manufacturing method. First, a multi-layer precisely aligned metal wire grid is prepared on one side of the metal copper sheet using micromachining technology, and then the center of the copper sheet is completely etched through on the other side of the copper sheet using a chemical mask etching method. Therefore, the processes on both sides of the product are independently separated and do not interfere with each other, which reduces the difficulty of preparation and reduces production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the structure of the present invention;

[0026] Figure 2 is a schematic diagram of the structure of a metal wire grid;

[0027] Figure 3 is a structural diagram of step 1 in Example 2;

[0028] Figure 4 is a structural diagram of step 2 in Example 2;

[0029] Figure 5 is a structural diagram of step 2 in Example 2;

[0030] Figure 6 is a structural diagram of step 3 in Example 2;

[0031] Figure 7 is a structural diagram of step 4 in Example 2; DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with the embodiments, but they are not intended to limit the present invention.

[0033] Embodiment 1: A multi-layer metal wire grid structure thin film broadband terahertz polarizer, taking a three-layer metal wire grid structure as an example, Figure 1 As shown, the film substrate 1 includes an Epocore material, a film cover layer 2 is provided on the film substrate 1, and three layers of parallel metal wire grids 4 are provided in the film cover layer 2. Figure 2As shown, each layer of metal wire grid 4 is composed of a number of metal wires 3 arranged at periodic intervals, and two adjacent layers of metal wire grid 4 are arranged crosswise, and the metal wires are preferably aluminum wires. A copper sheet bracket 5 is provided at the bottom of the film substrate 1, a light-through circular hole 6 is provided in the middle of the copper sheet bracket 5, and a film base 7 is provided at the bottom of the copper sheet bracket 5. The film cover layer 2 has a three-layer aluminum wire grid structure, which can be expanded to a four-layer or five-layer aluminum wire grid structure.

[0034] Embodiment 2: The manufacturing method of the present invention comprises the following steps:

[0035] 1. Spin-coat a layer of Epocore thin film substrate 1 on one side of a 0.2-0.5 mm thick pure copper sheet (i.e., copper sheet bracket 5), and then use microlithography and wet etching technology to make a layer of aluminum metal wire grid 4 on it, such as Figure 3 As shown;

[0036] 2. Continue to spin-coat a certain thickness (2-3 μm) of the first thin film spacer layer 8 of the Epocore material, such as the attached Figure 4 As shown, the overlay technique is then used to align with the bottom metal wire grid, and an aluminum metal wire grid is prepared in parallel with the bottom metal wire grid, with the metal wires and gaps arranged in a position that are just crossed and spaced up and down; the second thin film spacer layer 9 of the same thickness of Epocore material is spin-coated, and a third aluminum metal wire grid structure is prepared; as shown Figure 5 As shown;

[0037] 3. Spin-coat a layer of Epocore material on the top layer 10 to encapsulate the multi-layer wire grid structure, such as Figure 6 As shown, the first thin film spacer layer 8, the second thin film spacer layer 9 and the thin film top layer 10 form an integral structure, namely the thin film cover layer 2;

[0038] 4. Spin-coat a layer of Epocore thin film substrate 7 on the other side of the copper sheet and perform soft-baking, and remove the Epocore material in the center by photolithography and development technology to form a circular hole with a diameter of about 2.5 cm, i.e., a light-transmitting circular hole 6 (the size can be adjusted according to actual needs, which determines the maximum size of the polarizer). Figure 7 As shown;

[0039] 5. Place the copper sheet with Epocore films on both sides into a ferric chloride solution and heat it to 70-80 degrees Celsius to completely corrode the exposed copper sheet to obtain a transparent thin film polarizer with a circular hole in the center. Figure 1 As shown;

[0040] 6. Finally, the polarizer obtained in step 5 is cleaned with deionized water and dried, and attached to a rotation holder to obtain the finished product.

[0041] The above embodiments are only preferred technical solutions of the present invention and should not be regarded as limiting the present invention. The protection scope of the present invention shall be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. Multilayer metal wire grid structure thin film broadband terahertz polarizer, characterized by: The invention comprises a thin film substrate (1), a thin film covering layer (2) is arranged above the thin film substrate (1), and a plurality of metal wire grids (4) composed of metal wires (3) arranged at periodic intervals are arranged in the thin film covering layer (2), and the metal wire grids (4) of adjacent layers are arranged crosswise; a copper sheet bracket (5) is arranged at the bottom of the thin film substrate (1), a light-transmitting circular hole (6) is arranged in the middle of the copper sheet bracket (5), and a thin film base (7) is arranged below the copper sheet bracket (5); three layers of metal wire grids (4) arranged in parallel are arranged in the thin film covering layer (2); The method for manufacturing the multilayer metal wire grid structure thin film broadband terahertz polarizer specifically comprises the following steps: a. Take a copper sheet, spin-coat a thin film on the surface of the copper sheet, and then deposit a layer of aluminum wire grid on the thin film; b. Continue to spin-coat a layer of thin film, and then deposit a layer of metal wire grid parallel to the previous layer of metal wire grid on the thin film, and the layer of metal wire grid and the previous layer of metal wire grid are arranged in a cross pattern; repeat this step to deposit multiple layers of metal wire grid; c. Finally, spin-coat a thin film to encapsulate the multi-layer metal wire grid structure; d. Spin-coat a thin film on the bottom surface of the pure copper sheet, soft-dry the film, and then open a circular hole in the center of the film using photolithography technology; e. Place it in a ferric chloride solution, heat it to 70-80 degrees Celsius, corrode the exposed copper sheet, and obtain the finished product.

2. The multilayer metal wire grid structure thin film broadband terahertz polarizer according to claim 1, characterized in that: The metal wire (3) is selected from aluminum wire, gold wire, silver wire or chromium wire.

3. The multilayer metal wire grid structure thin film broadband terahertz polarizer according to claim 1, characterized in that: The film substrate, film covering layer and film base are film materials, and are Epocore film materials.

4. The multilayer metal wire grid structure thin film broadband terahertz polarizer according to claim 1, characterized in that: In step a, a layer of aluminum wire grid is deposited on the film using microlithography and wet etching techniques.

5. The multilayer metal wire grid structure thin film broadband terahertz polarizer according to claim 1, characterized in that: In step e, after the exposed copper sheet is corroded away, it is washed with deionized water and dried, and then attached to the angle rotating seat to obtain the finished product.

Images