Narrowband high-transmittance mid-infrared filter with multilayer superstructure surface and preparation method of narrow-band high-transmittance mid-infrared filter

Abstract

The invention relates to a narrow-band high-transmittance intermediate infrared filter with a multi-layer superstructure surface and a preparation method, the narrow-band high-transmittance intermediate infrared filter comprises a substrate and the multi-layer superstructure surface, the multi-layer superstructure surface is composed of composite units arranged periodically, each composite unit is of a cross-shaped structure, and each composite unit comprises a metal structure layer; a dielectric structure layer; and the transition layer is positioned between the metal structure layer and the dielectric structure layer. The mid-infrared filter has the beneficial effects that the filter has higher transmission efficiency, narrower half-peak width and higher quality factor, and the performance of the mid-infrared filter is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of mid-infrared ultra-narrowband filter technology, and particularly relates to a narrowband high-transmittance mid-infrared filter with a multilayer superstructure surface and its preparation method. Background Technology

[0002] Mid-infrared (MIR) spectral analysis has become an important research field due to its ability to detect molecular vibrational modes and chemical structural fingerprints. Mid-infrared spectroscopy is widely used in chemical substance detection, environmental monitoring, biomedical analysis, materials science, gas sensing, and remote sensing technologies. In particular, the transmission and reflection characteristics of the mid-infrared region (approximately 3-30 micrometers) provide crucial information about substances and play an irreplaceable role in many practical applications.

[0003] Traditional mid-infrared filters typically have wide bandwidths and low transmittance, limiting their application in high-precision sensing and spectroscopy. To improve spectral resolution and detection sensitivity, the development of mid-infrared filters with ultra-narrow bandwidths, low losses, and adjustable characteristics has become particularly important. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a narrowband high-transmittance mid-infrared filter with a multilayer metastructure surface and a method for its fabrication.

[0005] In a first aspect, a multi-layered superstructure surface is provided, consisting of periodically arranged composite units, each composite unit having a cross-shaped structure, and each composite unit comprising:

[0006] Metal structural layer;

[0007] Dielectric structure layer;

[0008] and a transition layer located between the metal structure layer and the dielectric structure layer;

[0009] The transition layer is used to enhance the connection between the metal structure layer and the dielectric structure layer, and to optimize the optical response of the composite unit in the mid-infrared band.

[0010] Preferably, the metal structure layer is made of gold, the dielectric structure layer is made of silicon, and the transition layer is made of TiO2.

[0011] In a second aspect, a narrowband high-transmittance mid-infrared filter is provided, comprising a substrate and the multilayer metastructure surface described in the first aspect; the multilayer metastructure surface is located on the substrate.

[0012] Preferably, the substrate is made of calcium fluoride material.

[0013] Thirdly, a method for fabricating a narrowband high-transmittance mid-infrared filter as described in the second aspect is provided, comprising:

[0014] Step 1: Provide a substrate and clean and heat-treat the substrate;

[0015] Step 2: Form a metal structure layer exposure pattern on the substrate to form a multilayer superstructure surface, and perform exposure, development and deposition to form the metal structure layer;

[0016] Step 3: Deposit a transition layer on the metal structure layer;

[0017] Step 4: Deposit a dielectric structure layer on the transition layer;

[0018] Step 5: Perform graphical processing on the medium structure layer to form a cross structure.

[0019] Preferably, between step 1 and step 2, the following is also included:

[0020] An adhesion layer is deposited on the substrate surface, the adhesion layer being made of magnesium oxide.

[0021] As a preferred option, it also includes:

[0022] Step 6: Use a Fourier spectrometer to test the transmission characteristics of the filter.

[0023] Preferably, step 2 includes:

[0024] Step 2.1: Coat the substrate with an electron beam lithography resist;

[0025] Step 2.2: Place the substrate coated with resist on a hot plate for baking;

[0026] Step 2.3: Place the substrate coated with resist into an electron beam lithography machine, define the metal structure layer and alignment marks using the exposure pattern, and perform exposure and development;

[0027] Step 2.4: Deposit a thin metal film on the exposed area using an electron beam evaporation device to form a metal structure layer.

[0028] Preferably, step 5 includes:

[0029] Step 5.1: Coat the dielectric structure layer with an electron beam lithography resist and use predefined alignment marks to perform electron beam exposure on the resist to define a cross structure on the dielectric structure layer;

[0030] Step 5.2: Develop the mixture to obtain a pattern of intersecting structures;

[0031] Step 5.3: Deposit an aluminum oxide layer on the developed substrate, which will serve as an etching mask;

[0032] Step 5.4: Deposit aluminum oxide using electron beam evaporation;

[0033] Step 5.5: Use deep reactive ion etching technology to etch the dielectric structure layer to form a cross structure.

[0034] The beneficial effects of this invention are:

[0035] 1. High transmittance and ultra-narrow bandwidth: The filter of this invention is designed to achieve higher transmittance efficiency, narrower half-width at half-maximum (FWHM), and higher quality factor at the target wavelength, significantly improving the performance of the mid-infrared filter.

[0036] 2. Flexible wavelength adjustment: By adjusting structural parameters (such as the width of the cross arm and the thickness of the metal layer), this invention can achieve wavelength adjustment of the filter in the mid-infrared region, making it adaptable to the needs of different gas detection and spectral applications.

[0037] 3. Simplified fabrication process: This invention uses electron beam exposure and sputtering deposition technology, which simplifies the traditional complex multilayer process of filters and is easy to mass-produce. Attached Figure Description

[0038] Figure 1 A three-dimensional schematic diagram of a narrowband high-transmittance mid-infrared filter;

[0039] Figure 2 This is a planar schematic diagram of a multilayer metastructure surface;

[0040] Figure 3 Transmission curves from CST simulation;

[0041] Figure 4 A comparison of transport curves for TiO2 with different thicknesses;

[0042] Figure 5 This is a flowchart of electron beam lithography;

[0043] Figure 6 This is a flowchart of the electron beam evaporation process;

[0044] Figure 7 This is a schematic diagram of the spectrum testing principle.

[0045] Explanation of reference numerals in the attached figures: 1. Substrate; 2. Metal structure layer; 3. Transition layer; 4. Dielectric structure layer. Detailed Implementation

[0046] The present invention will be further described below with reference to embodiments. The description of the embodiments below is only for the purpose of helping to understand the present invention. It should be noted that those skilled in the art can make several modifications to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0047] Example 1:

[0048] Existing mid-infrared filters have the following drawbacks:

[0049] Excessive bandwidth: Traditional filters have a wide bandwidth in the mid-infrared band, making it impossible to accurately distinguish multiple target absorption peaks, which affects high-precision gas sensing applications.

[0050] Low transmission efficiency: Due to the high absorption loss of metallic materials, traditional filters have low transmission efficiency, which affects detection sensitivity.

[0051] Complex design and manufacturing: Existing filters have complex multi-layer structure designs, require high-level manufacturing processes, and are costly, making large-scale production difficult.

[0052] To address the problems of existing technologies, this application provides a narrowband, high-transmittance mid-infrared filter with a multilayer metastructure surface, based on metamaterial technology. Metamaterials are artificially designed materials possessing unique properties not found in natural materials, such as negative refractive index, superlens effect, and surface plasmon resonances. These properties give metamaterials significant advantages in the mid-infrared region.

[0053] Specifically, Embodiment 1 of this application first provides a metal-dielectric composite multilayer metastructure surface. Through the innovative metal-dielectric composite metamaterial structure, a narrowband mid-infrared filter is obtained. This method has a simple manufacturing process, low cost, and significantly improves the transmittance, selectivity and bandwidth of the mid-infrared filter.

[0054] like Figure 1 As shown, the multilayer superstructure surface provided in Embodiment 1 of this application is composed of periodically arranged composite units. The composite unit is a cross-shaped structure, and each composite unit includes: a metal structure layer 2, a dielectric structure layer 4, and a transition layer 3 located between the metal structure layer 2 and the dielectric structure layer 4.

[0055] The metal structure layer 2 is made of gold (Au), which has low MIR loss and is stable and resistant to oxidation in the MIR region. The combination of the gold sheet and the silicon cross structure generates various electric dipole, magnetic dipole, and higher-order quadrupole resonance modes through the coupling of surface plasmon resonances and dielectric Mie resonances.

[0056] The dielectric structure layer 4 is made of silicon (Si) material. Silicon has a high refractive index and low absorption loss in the mid-infrared band, which can effectively enhance the local field intensity of light and improve the optical performance of the filter.

[0057] The combination of metal-dielectric composite materials optimizes the interaction between light and matter, achieving higher spectral selectivity and ultra-narrow bandwidth spectral response.

[0058] The transition layer 3 is made of TiO2 material. The thickness of the transition layer 3 is 0.2 micrometers, and its size is the same as the surface structure, serving to optimize the connection between the metal and silicon. This multilayer superstructure surface composite structure design utilizes the plasmon resonance effect of the metal and the dielectric resonance effect of silicon, significantly improving the optical response of the metal-dielectric composite structure in the mid-infrared region and reducing system losses. Furthermore, a narrowband filter with a specific wavelength can be obtained by adjusting the period size.

[0059] Furthermore, the specific functions of transition layer 3 are as follows:

[0060] Improved adhesion: TiO2, as a transition layer, helps the adhesion between the metal and silicon cross structure, enhances the interlayer bonding force, and avoids the delamination problem between the metal and silicon layers.

[0061] Optimizing optical performance: The TiO2 layer, as a dielectric layer, can improve the optical performance of the metal-dielectric composite structure, especially in the mid-infrared band, thereby enhancing the transmission efficiency and bandwidth selectivity of the filter.

[0062] Reduced loss: The TiO2 layer can effectively reduce the absorption loss of metal materials and improve the optical transmission efficiency of the system.

[0063] Improved stability: TiO2 has good thermal and chemical stability, which can improve the stability of filters under high temperature or environmental changes.

[0064] For example, the plane of a multilayer metastructure surface is as follows: Figure 2 As shown, Px and Py are the periods of the unit in the x and y directions, W and L are the width and length of the cross, and L is also the side length of the metal patch. d is the distance between the metal patch and the unit boundary. Px = Py = 2.5 micrometers, W = 0.3 micrometers, L = 2.2 micrometers, and d = 0.15 micrometers.

[0065] like Figure 3 The graph shows the simulation results of the multilayer metasurface structure in CST simulation software, displaying the change in transmittance of this metasurface structure in the wavelength range of 3.5-7 micrometers. Figure 4 The graph compares the transmittance effect after changing the thickness of the transition layer. It can be seen that the transmittance is high and the filtering effect is good when the thickness of the transition layer is 0.2 micrometers.

[0066] Example 2:

[0067] Based on Example 1, Example 2 of this application provides a narrowband high-transmittance mid-infrared filter. Please refer to [link / reference needed]. Figure 1 It includes a substrate 1 and a multilayer superstructure surface; the multilayer superstructure surface is located on the substrate 1.

[0068] The substrate 1 is made of calcium fluoride (CaF2) material, which is suitable for the mid-infrared region due to its good optical transparency and low loss.

[0069] Furthermore, Embodiment 2 of this application also provides a method for fabricating a narrowband high-transmittance mid-infrared filter, such as... Figure 5 and Figure 6 As shown, it includes:

[0070] Step 1: Provide a substrate and clean and heat-treat the substrate.

[0071] Specifically, in step 1, the CaF2 substrate is immersed in acetone and isopropanol solutions using an ultrasonic cleaning device for 10 minutes each to remove impurities and organic matter from the substrate. After cleaning, the substrate is heat-treated to remove surface stress and ensure structural stability. For example, the substrate is dried with a nitrogen gun and placed on lint-free paper to ensure complete drying.

[0072] Step 2: Form a metal structure layer exposure pattern on the substrate to form a multilayer superstructure surface, and perform exposure, development and deposition to form a metal structure layer.

[0073] In steps 2 through 5, electron beam lithography (EBL) is employed to ensure pattern accuracy by precisely controlling the thickness and exposure dose of the photoresist. Using both ultraviolet and electron beam lithography equipment, the substrate is exposed twice according to the designed pattern to achieve high-precision alignment of the metal-silicon cross-structure.

[0074] Specifically, step 2 includes:

[0075] Step 2.1: Coat the substrate with an electron beam lithography resist.

[0076] In this process, an electron beam lithography (EBL) resist is coated onto the CaF2 substrate. For example, SML resist is used because it is adaptable to high aspect ratio patterns and can meet the requirements of precision patterns. For instance, the resist is uniformly coated onto the substrate using a spin coating method, ensuring that the resist thickness is moderate (typically 200-300 nm) during the coating process.

[0077] Step 2.2: Place the substrate coated with resist on a hot plate for baking.

[0078] The purpose of this step is to remove the solvent. The heating temperature is usually 90°C and the baking time is 1 minute.

[0079] Step 2.3: Place the substrate coated with resist into an electron beam lithography (EBL) machine, define the metal structure layer and alignment marks using the exposure pattern, and perform exposure and development.

[0080] This step requires setting the exposure dose to ensure high precision of the exposed pattern (typically 20 keV). After exposure, development is performed immediately.

[0081] Step 2.4: Deposit a thin metal film on the exposed area using an electron beam evaporation device to form a metal structure layer.

[0082] For example, an electron beam evaporation (E-beam evaporation) apparatus is used to deposit a thin film of gold (Au) onto the exposed area. The gold film thickness is set to 0.1 μm to optimize the effects of surface plasmon resonance. After deposition, a stripping step is performed to remove unwanted metal layers. Unused metal is removed using solvents and ultrasonic cleaning equipment to ensure the gold patch structure is clear and intact.

[0083] Step 3: Deposit a transition layer on the metal structure layer.

[0084] Specifically, an electron beam evaporation (E-beam evaporation) technique was used to deposit a TiO2 layer to optimize the bonding between the metal and silicon layers and improve the overall optical response of the structure. Deposition was performed in a vacuum environment using an electron beam evaporation system. The deposition rate was adjusted to... / s, controlling the uniformity of the deposition process. A film thickness sensor is used to ensure the deposited layer thickness is 0.2 micrometers.

[0085] Step 4: Deposit a medium structure layer on the transition layer.

[0086] Specifically, a 1.55 μm thick silicon layer was deposited on a gold (Au) patch using plasma-enhanced chemical vapor deposition (PECVD). Silicon was chosen as the dielectric material because of its high refractive index and low absorption loss, making it particularly suitable for the mid-infrared region.

[0087] Step 5: Perform graphical processing on the medium structure layer to form a cross structure.

[0088] Step 5 includes:

[0089] Step 5.1: Coat the dielectric structure layer with an electron beam lithography resist and use predefined alignment marks to perform electron beam exposure on the resist to define a cross structure on the dielectric structure layer.

[0090] This step involves a second resist coating and electron beam exposure. Specifically, an electron beam lithography resist is spin-coated to uniformly cover the silicon layer, and a second electron beam exposure is performed using predefined alignment marks to precisely define the cross structures on the silicon layer.

[0091] Step 5.2: Develop the second layer of photoresist to obtain the pattern of the silicon cross structure.

[0092] Step 5.3: Deposit an aluminum oxide (Al2O3) layer on the developed substrate. The aluminum oxide layer will serve as an etching mask to protect areas that do not need to be etched.

[0093] Specifically, a 25nm thick aluminum oxide layer is deposited on the developed substrate.

[0094] Step 5.4: Deposit aluminum oxide using electron beam evaporation to ensure uniform and smooth deposition.

[0095] Step 5.5: Use deep reactive ion etching (RIE) technology to etch the dielectric structure layer to form a cross structure.

[0096] In step 5.5, appropriate RIE parameters are set to ensure the accuracy of the silicon cross structure while keeping the gold (Au) patch undamaged.

[0097] Example 3:

[0098] Based on Example 2, Example 3 of this application provides another method for a narrowband high-transmittance mid-infrared filter, including:

[0099] Step 1: Provide a substrate and clean and heat-treat the substrate.

[0100] Step 2: Deposit an adhesion layer on the substrate surface, wherein the adhesion layer is made of magnesium oxide.

[0101] Step 3: Form a metal structure layer exposure pattern on the substrate to form a multilayer superstructure surface, and perform exposure, development and deposition to form a metal structure layer.

[0102] Step 4: Deposit a transition layer on the metal structure layer.

[0103] Step 5: Deposit a medium structure layer on the transition layer.

[0104] Step 6: Perform graphical processing on the medium structure layer to form a cross structure.

[0105] Step 7: Use a Fourier spectrometer to test the transmission characteristics of the filter.

[0106] Specifically, such as Figure 7As shown, the transmission characteristics of the filter were tested using a Fourier spectrometer to ensure that the filter has high transmission efficiency and ultra-narrow bandwidth within the target wavelength range. The wavelength and full width at half maximum (FWHM) of the transmission peak were precisely adjusted by modifying the geometric parameters of the unit structure (such as the width of the cross arms and the size of the metal sheet).

[0107] It should be noted that the parts in this embodiment that are the same as or similar to those in Embodiment 2 can be referred to each other, and will not be repeated in this application.

Claims

1. A multilayered metastructure surface, characterized in that, It is composed of periodically arranged composite units, each composite unit having a cross-shaped structure, and each composite unit includes: Metal structural layer; Dielectric structure layer; and a transition layer located between the metal structure layer and the dielectric structure layer; The transition layer is used to enhance the connection between the metal structure layer and the dielectric structure layer, and to optimize the optical response of the composite unit in the mid-infrared band.

2. The multilayer metastructure surface according to claim 1, characterized in that, The metal structure layer is made of gold, the dielectric structure layer is made of silicon, and the transition layer is made of TiO2.

3. A narrowband high-transmittance mid-infrared filter, characterized in that, include: The substrate and the multilayer superstructure surface according to claim 1 or 2; the multilayer superstructure surface is located on the substrate.

4. The narrowband high transmittance mid-infrared filter according to claim 3, characterized in that, The substrate is made of calcium fluoride.

5. A method for preparing a narrowband high-transmittance mid-infrared filter as described in claim 3 or 4, characterized in that, include: Step 1: Provide a substrate and clean and heat-treat the substrate; Step 2: Form a metal structure layer exposure pattern on the substrate to form a multilayer superstructure surface, and perform exposure, development and deposition to form the metal structure layer; Step 3: Deposit a transition layer on the metal structure layer; Step 4: Deposit a dielectric structure layer on the transition layer; Step 5: Perform graphical processing on the medium structure layer to form a cross structure.

6. The method for a narrowband high-transmittance mid-infrared filter according to claim 5, characterized in that, Between step 1 and step 2, the following is also included: An adhesion layer is deposited on the substrate surface, the adhesion layer being made of magnesium oxide.

7. The method for a narrowband high-transmittance mid-infrared filter according to claim 6, characterized in that, Also includes: Step 6: Use a Fourier spectrometer to test the transmission characteristics of the filter.

8. The method for a narrowband high-transmittance mid-infrared filter according to claim 7, characterized in that, Step 2 includes: Step 2.1: Coat the substrate with an electron beam lithography resist; Step 2.2: Place the substrate coated with resist on a hot plate for baking; Step 2.3: Place the substrate coated with resist into an electron beam lithography machine, define the metal structure layer and alignment marks using the exposure pattern, and perform exposure and development; Step 2.4: Deposit a thin metal film on the exposed area using an electron beam evaporation device to form a metal structure layer.

9. The method for a narrowband high-transmittance mid-infrared filter according to claim 8, characterized in that, Step 5 includes: Step 5.1: Coat the dielectric structure layer with an electron beam lithography resist and use predefined alignment marks to perform electron beam exposure on the resist to define a cross structure on the dielectric structure layer; Step 5.2: Develop the mixture to obtain a pattern of intersecting structures; Step 5.3: Deposit an aluminum oxide layer on the developed substrate, which will serve as an etching mask; Step 5.4: Deposit aluminum oxide using electron beam evaporation; Step 5.5: Use deep reactive ion etching technology to etch the dielectric structure layer to form a cross structure.

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