A mid-infrared detection structure and a multi-band adjustable absorbing structure

Abstract

The present invention provides a mid-infrared detection structure, comprising a silicon layer, a gold layer, an aluminum oxide layer, and a gold array layer stacked in sequence from bottom to top. The gold array layer is provided with periodically distributed slits, which divide the gold array layer into a plurality of periodic arrays of rectangular gold array elements. Half a slit is provided at both ends of the gold array layer along the array direction. The slit is used to leak local energy generated by surface plasmon resonance excited by the gold array layer and the aluminum oxide layer to balance the absorptivity / radioactivity of the entire detection structure. The aluminum oxide layer acts as a capacitor, and the absorption peak is red-shifted by adjusting the thickness of the aluminum oxide layer and the array period of the rectangular gold array elements. The mid-infrared detection structure provided by the present invention has a small size, a thin thickness, a simple structure, can achieve more miniaturized processing, and is more conducive to integrated assembly in actual industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic wave absorption and radiation, and in particular relates to a mid-infrared detection structure and a multi-band adjustable wave absorbing structure. Background Art

[0002] Due to physical effects such as plasmon resonance and FP cavity resonance generated by micro-nanophotonic devices, the intrinsic emissivity of an object can be altered by changing the material, structure, and size of the micro-nanostructure. This allows for tunable infrared absorption and thermal radiation, and even allows for the integration of compatible camouflage in two different wavelength bands within the same device. For example, Kaikai Du et al. proposed a selective microbolometer based on a metamaterial absorber. This metamaterial absorber provides a new method for adjusting and monitoring the thermal distribution of microbolometers, showing promise in photothermal imaging systems. Therefore, micro-nanostructures have made significant contributions to infrared detection in specific wavelength regions of the mid- and far-infrared. Zhu H et al. used micro-nanostructures such as multilayer films (including ZnS / Ge) and metasurfaces (including Cu-ITO-Cu) to achieve multispectral camouflage, wavelength-selective emission, and microwave absorption, providing insights into multifunctional and compatible stealth.

[0003] However, the selective wavelengths of these studies all depend on the shape, size, and period of the corresponding micro-nanostructures. This means that once these micro-nanostructures are manufactured, their corresponding resonant wavelengths and absorption spectra are also determined and cannot be changed. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a mid-infrared detection structure with a simple structure, small size, thin thickness, and the ability to achieve more miniaturized processing, which is conducive to integrated assembly in actual industrial production.

[0005] In order to achieve the above-mentioned purpose, the technical solution of the present invention is as follows: a mid-infrared detection structure, comprising a silicon layer, a gold layer, an aluminum oxide layer and a gold array layer stacked in sequence from bottom to top, the gold array layer being provided with periodically distributed slits, the slits dividing the gold array layer into a plurality of periodic arrays of rectangular gold array elements, the gold array layer being provided with half a slit at both ends along the array direction, the slits being used to leak the local energy generated by the surface plasmon resonance excited by the gold array layer and the aluminum oxide layer to balance the absorptivity / radiation rate of the entire detection structure, the aluminum oxide layer being used as a capacitor, and the absorption peak being red-shifted by adjusting the thickness of the aluminum oxide layer and the array period of the rectangular gold array elements.

[0006] Preferably, the mid-infrared detection structure has an absorption peak at 3-5 μm and 8-12 μm respectively.

[0007] Preferably, the silicon layer and the aluminum oxide layer are obtained by radio frequency sputtering, and the gold layer is obtained by direct current sputtering.

[0008] Preferably, the thickness of the multilayer film structure in the first device is, from bottom to top, as follows: the thickness of the silicon layer is 100 nm, the thickness of the gold layer is 50 nm, the thickness of the aluminum oxide layer is 20 nm, the thickness of the gold array layer is 50 nm, the width of the rectangular gold array element is 2 μm, the array period of the rectangular gold array element is 2.1 μm, and the width of the slit is 100 nm.

[0009] The mid-infrared detection structure provided by the present invention has a rectangular gold array element with a simple structure, small size, and thin thickness, which can achieve more miniaturized processing and is more conducive to integrated assembly in actual industrial production.

[0010] A multi-band adjustable wave absorbing structure comprises the above-mentioned mid-infrared detection structure, wherein a phase change material layer is provided between the gold layer and the aluminum oxide layer.

[0011] Preferably, the phase change material layer is a Ge2Sb2Te5 thin film.

[0012] Preferably, the thickness of the silicon layer is 100 nm, the thickness of the gold layer is 50 nm, the thickness of the phase change material layer is 50 nm, the thickness of the aluminum oxide layer is 10 nm, the thickness of the gold array layer is 50 nm, the width of the rectangular gold array element is 2.7 μm, the array period of the rectangular gold array element is 2.8 μm, and the width of the slit is 100 nm.

[0013] The beneficial effects of the present invention are: 1. Innovatively introducing the non-volatile phase change material GST to adjust the electromagnetic wave absorption rate. Compared with traditional electromagnetic wave absorption methods, this method can achieve dynamic adjustment of the absorption rate without changing the device structure, and can realize multifunctional applications on one structure.

[0014] 2. The structure used is an innovative metal-dielectric-metal sandwich structure. The top layer is composed of a uniquely designed gold array and alternating slits. Through the mutual resonance with the nanolayers of Si layer, Au layer, Al2O3 layer and GST layer, multi-band electromagnetic wave absorption is achieved. The device is small in size, easy to manufacture, with a simplified structure and convenient processing. It can be integrated and can be used for large-scale actual industrial production and can serve multi-band and multi-functional application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the mid-infrared detection structure; Figure 1 (a) is a three-dimensional view of the periodic four-layer structure. Figure 1 (b) is a schematic diagram of the stacking. Figure 1 (c) is a schematic diagram of the dimensions.

[0016] Figure 2 (a) Absorption and reflection spectra of the mid-infrared detection structure in the infrared band; Figure 2 (b) is the electric field distribution at the first absorption peak; Figure 2 (d) is a schematic diagram of the magnetic field distribution at the first absorption peak; Figure 2 (c) is the electric field distribution at the second absorption peak; Figure 2 (e) Schematic diagram of the magnetic field distribution at the second absorption peak.

[0017] Figure 3 is the reflection spectrum of the mid-infrared detection structure in the infrared band; Figure 3 (a) is a schematic diagram of the reflectance spectrum in the infrared band at different polarization angles; Figure 3 (b) Schematic diagram of the reflection spectrum in the infrared band at different incident angles.

[0018] Figure 4 It is a structural schematic diagram of a multi-band adjustable absorbing structure; Figure 4 (a) is a three-dimensional view of the periodic four-layer structure. Figure 4 (b) is a schematic diagram of the stacking. Figure 4 (c) is a schematic diagram of the dimensions.

[0019] Figure 5 The absorptivity and reflectivity of the multi-band adjustable absorbing structure in the infrared-laser band; Figure 5 (a) is a schematic diagram of the absorptivity and reflectivity of the GST film in the infrared-laser band when it is in an amorphous state. Figure 5 (b) Schematic diagram of the absorptivity and reflectivity of the GST film in the infrared-laser band when it is in the crystalline state.

[0020] Figure 6 Schematic diagram of the electric and magnetic field distribution of the multi-band adjustable absorbing structure containing aGST film; Figure 6 (a) is a schematic diagram of the electric field distribution at the first absorption peak. Figure 6 (b) Schematic diagram of the magnetic field distribution at the first absorption peak, Figure 6 (c) is a schematic diagram of the electric field distribution at the second absorption peak. Figure 6 (d) is a schematic diagram of the magnetic field distribution at the second absorption peak. Figure 6 (e) is a schematic diagram of the electric field distribution at the third absorption peak. Figure 6 (f) Schematic diagram of the magnetic field distribution at the third absorption peak.

[0021] Figure 7 Schematic diagram of the electric and magnetic field distribution of the multi-band adjustable absorbing structure containing cGST film; Figure 7 (a) is a schematic diagram of the electric field distribution at the first absorption peak. Figure 7(b) Schematic diagram of the magnetic field distribution at the first absorption peak, Figure 7 (c) is a schematic diagram of the electric field distribution at the second absorption peak. Figure 7 (d) is a schematic diagram of the magnetic field distribution at the second absorption peak. Figure 7 (e) is a schematic diagram of the electric field distribution at the third absorption peak. Figure 7 (f) Schematic diagram of the magnetic field distribution at the third absorption peak.

[0022] In the figure, 1, silicon layer; 2, gold layer; 3, aluminum oxide layer; 4, gold array layer; 41, slit; 42, rectangular gold array element; 5, phase change material layer. DETAILED DESCRIPTION

[0023] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0024] Example 1

[0025] Please also refer to Figure 1-3 The mid-infrared detection structure provided in this embodiment includes a silicon layer 1, a gold layer 2, an aluminum oxide layer 3, and a gold array layer 4 stacked in sequence from bottom to top. The gold array layer 4 is provided with periodically distributed slits 42, and the slits 42 divide the gold array layer 4 into a plurality of periodic arrays of rectangular gold array elements 41. The rectangular gold array elements 41 are provided with half a slit at both ends along the array direction. The half slits of two adjacent rectangular gold array elements 41 form a positive slit 42. The slit 42 is used to leak local energy generated by surface plasmon resonance excited by the gold array layer 4 and the aluminum oxide layer 3 to balance the absorptivity / radiation rate of the entire detection structure, mainly the absorptivity / radiation rate of the aluminum oxide layer 3. The aluminum oxide layer 3 acts as a capacitor, and the absorption peak is redshifted by adjusting the thickness of the aluminum oxide layer 3 and the array period of the rectangular gold array elements 41.

[0026] The thickness of the multilayer film structure from bottom to top is: T1 = 100nm, T2 = 50nm, T3 = 20nm, T4 = 50nm. Since the device is a simple multilayer film structure and the top layer is a simple rectangular gold array, the top layer gold array has a simple structure and is more conducive to mass production in actual industry.

[0027] The main function of the mid-infrared detection structure is to achieve wide-angle, polarization-insensitive dual-band infrared detection. Figure 2It can be seen that the device proposed in this application has a clear absorption peak in two atmospheric windows (3-5μm and 8-12μm), with an absorption rate of 73% at λ=3.6μm and an absorption rate of 83% at λ=8.5μm. This shows that this structure has a strong detection capability for the target's infrared radiation and can be regarded as a mid-infrared detector. Because this application innovatively introduces narrow slits and nano-gap Al2O3 layers on the MIM structure; they provide an important channel for controlling absorption behavior. The former helps local energy leak out of the slits to stay away from the resonant unit, thereby balancing the absorption of the material and the leakage rate of radiation, maintaining perfect absorption of the structure. The latter acts as a capacitor, and the absorption peak can be redshifted by adjusting the thickness and period.

[0028] Figure 3 (a) shows the absorption rate of the device at different incident angles. As the incident angle increases, the absorption rate does not decrease significantly. Even at a large incident angle of about 60 degrees, the device can still maintain an absorption rate of more than 50% in both bands, indicating that it has good wide-angle absorption. In addition, since the designed structure is a highly symmetrical gold array and multi-layer thin film structure, it is theoretically insensitive to the polarization angle. Through simulation calculations, we can see that Figure 3 (b) The effect of polarization angle on the structure is shown, verifying the polarization-insensitive nature of the device. Therefore, the designed four-layer structure has wide-angle absorption and polarization insensitivity, which is beneficial for practical applications in infrared detection.

[0029] First, the mid-infrared detection structure we proposed with dual-band infrared detection capabilities consists of four layers. Using magnetron sputtering and then physical deposition, a multilayer film can be obtained: the base silicon and dielectric layer aluminum oxide films are obtained by radio frequency sputtering (RF sputtering), and the gold film is obtained by direct current sputtering (DC sputtering). Figure 1 As shown in (a), from bottom to top, they are Si, Au, Al2O3 and Au respectively. The top layer is composed of alternating gold arrays and slits, which, combined with the middle dielectric layer Al2O3, produces nanogap resonance and plasmon resonance to achieve high absorption of the corresponding wavelength. In order to simulate the absorption spectrum of nanogap resonance, we studied the electromagnetic response of the structure. After simulation and numerical calculation of the physical field using commercial software (Lumerical, FDTD Solutions), we obtained the optimal parameters after modeling and optimization of the structure. Figure 1 As shown in (b), the width of the single rectangular gold element at the top of the four-layer unit structure is W1 = 2μm, the width of the half-slits on both sides is Ws = 50nm, and the single period of the top periodic structure is P1 = 2.1μm. The thicknesses of the multilayer film structure from bottom to top are: T1 = 100nm, T2 = 50nm, T3 = 20nm, and T4 = 50nm.

[0030] Example 2

[0031] Please also refer to Figure 4-7 The multi-band adjustable absorbing structure provided in this embodiment includes the above-mentioned mid-infrared detection structure, and a phase change material layer is provided between the gold layer and the aluminum oxide layer, which is a five-layer thin film structure.

[0032] The phase change material layer is a phase change material Ge2Sb2Te5 (GST) thin film obtained by three-target co-sputtering method. The GST thin film obtained by coating is in an amorphous state at room temperature. After annealing at 160°C (433.15K), the amorphous GST (aGST) will be transformed into crystalline GST (cGST). After undergoing rapid annealing at 640°C (913.15K), cGST returns to the amorphous state. Since GST is non-volatile, once the phase change is completed, it can maintain the corresponding state for a long time at room temperature, so our research is carried out at room temperature. At the same time, since Si, Au and Al2O3 all have high melting points and boiling points, the annealing process of GST does not affect the final research results. With the addition of the phase change material layer, the designed structure can realize different functions in different states and different bands, completing multifunctional applications.

[0033] exist Figure 4 (b) and Figure 4 In (c), after the addition of the GST layer, the thicknesses of the layers from bottom to top are: t1 = 100 nm, t2 = 50 nm, t3 = 50 nm, t4 = 10 nm, and t5 = 50 nm. The width of the single rectangular gold element at the top of the five-layer unit structure is W = 2.7 μm, and the period P = 2.8 μm.

[0034] In traditional devices, for opaque materials, the sum of the absorptivity and reflectivity is 1. Therefore, achieving compatible stealth in the infrared bands (3-5 and 8-12μm) and the lidar band (10.6μm) presents a natural conflict: the goal requires both low absorptivity (i.e., low emissivity) at 8-12μm to achieve infrared stealth, and high absorptivity (i.e., low reflectivity) at 10.6μm, located between 8-12μm, to achieve lidar stealth. Therefore, achieving compatible camouflage in the infrared and laser bands presents significant contradictions and remains a highly challenging task.

[0035] In response to the above practical needs, we have studied and designed a multifunctional device, such as Figure 4 As shown, it has a simple structure, yet it can integrate multiple functions in a fixed structure. Based on the four-layer structure, we innovatively introduced the non-volatile phase change material GST, and used the change in its dielectric constant before and after the phase change to dynamically adjust the absorption rate of the device, thereby realizing multifunctional applications. Figure 5It was observed that after the addition of the GST film, the position and number of the main absorption peaks of the device changed. This was because the resonant frequency and loss changed, and the position and intensity of the resonant wavelength also changed accordingly. Figure 5 (a) Shows the absorptivity and reflectivity of the designed five-layer structure in the infrared-laser band. There are distinct absorption peaks in two atmospheric windows (3-5 μm and 8-12 μm) and a non-atmospheric window (5-8 μm). The two absorption peaks within the atmospheric window achieve absorptivity of 95% and 55%, respectively, maintaining good infrared detection capabilities.

[0036] At the same time, by simply changing the temperature and annealing the GST film at 160℃ (433.15K), we obtained a five-layer structure containing cGST film ( Figure 5 (b) thumbnail). From Figure 5 (b) It can be observed that the device's absorption rate in the atmospheric window is significantly reduced, especially in the 3-5μm range, where the maximum absorption rate drops significantly from 95% to 22%, and the average absorption rate also drops to around 15%. This makes it possible to transform the device from infrared detection to infrared stealth.

[0037] In order to study the reasons for the phenomenon in this application, we simulated and analyzed the electromagnetic field distribution of the device in two phases. Figure 6 (a), (b) and Figure 7 In the comparison between (a) and (b), it can be found that with the phase change of GST, the electromagnetic field intensity of the device at the first absorption peak decreases. When the GST film is in an amorphous state, the upper surface of the bottom metal and the contact surface of GST produce plasmon resonance, and the contact surface between the top gold array and the nano-spaced Al2O3 layer also excites the same resonance phenomenon. In addition, since the thickness of the dielectric layer changes from 20nm in the four-layer structure to a narrower 10nm, a stronger nano-gap resonance is excited, causing the resonance wavelength to be slightly red-shifted than before, and the peak value becomes larger. When the GST film phase changes to a crystalline state, the various resonance effects weaken, resulting in a transition of the device from high infrared absorption to low absorption. Similarly, through Figure 6 (c), (d) and Figure 7Comparing (c) and (d), we can observe that the electric field energy in the GST layer is significantly weakened, causing the absorption rate in the non-atmospheric window to decrease, and the absorption peak at λ = 6.6μm drops from 66% to 34%. However, since the magnetic field distribution is mainly concentrated in the slits, as well as the connection area between the inner surface of the gold array and the thick gold layer, the change in magnetic field intensity is not large, and the effect of MR on the absorption spectrum is small. Although the average emissivity of the device in the non-atmospheric window has decreased at this time, it still maintains a certain radiation cooling effect. Interestingly, although the first two absorption peaks have changed significantly, the absorption peak in LWIR is exactly at λ = 10.6μm, and is in a higher absorption state before and after the phase change. The position of the resonant wavelength is exactly the detection wavelength of LiDAR, which can achieve better laser stealth function. Combined with Figure 6 and Figure 7 Overall, whether in the aGST or cGST state, high-order resonances are excited at short wavelengths. As the wavelength increases, the resonance order gradually decreases, which is consistent with the characteristics of nanogap resonance. Because gap plasma resonance generates electric dipoles between parallel metal plates, smaller gap sizes lead to lower energy states. In summary, from Figure 5 As shown in (b), the device's average absorptivity / emissivity in both atmospheric windows is around 20%. In particular, while maintaining high absorption in the 10.6μm band, the average emissivity in the 8-14μm band remains relatively low. This demonstrates that our designed five-layer structure can achieve both good infrared and laser stealth capabilities and a moderate radiative cooling effect, enabling multifunctional applications.

[0038] Theoretical analysis shows that high absorptivity at the infrared atmospheric windows (3-5μm and 8-12μm) can achieve infrared detection, while low emissivity can achieve infrared stealth. High absorptivity at the lidar band (10.6μm) can achieve lidar stealth. High emissivity at the non-atmospheric windows (5-8μm) can achieve radiative cooling.

[0039] So by Figure 2 and Figure 3As can be seen, based on the dynamic changes in the device's absorptivity under different GST states, we can leverage the significantly lower first absorption peak to achieve a transition from atmospheric window infrared detection to infrared stealth. We can also leverage the second absorption peak's favorable absorptivity / emissivity to maintain excellent radiative cooling. The nearly constant third absorption peak enables stable laser stealth. Furthermore, based on the continuous changes in the GST phase transition, we can achieve infrared-LiDAR compatible camouflage based on the actual background emissivity, dynamically aligning the device's infrared emissivity with the background, thus achieving dynamic, continuous infrared stealth and stable laser stealth. Furthermore, the entire dynamic adjustment process requires only simple temperature changes. The device also maintains a certain level of radiative cooling during temperature changes, preventing internal heat accumulation and thus better meeting the requirements of practical applications. In summary, our device achieves complex multi-band, multi-scenario, and multi-functional applications within a fixed, minimalist structure, providing important insights and references for electromagnetic shielding, perfect absorption, thermal management, and infrared stealth.

[0040] This application utilizes changes in external temperature to achieve a phase transition in GST, and then achieves multifunctional applications by changing the device's absorptivity. Before and after the GST phase transition, the device's absorption peak does not shift significantly, but the peak absorptivity does change significantly.

[0041] In this invention, in response to the shortcomings of existing research, we considered combining phase change materials and metasurfaces to study and design a multifunctional metal-dielectric-metal (MIM) sandwich structure. Complex multifunctional effects are realized on a very simple micro-nano structure. At the same time, without changing the structure and size, the absorption / radiation intensity is controlled only by temperature changes, thereby achieving different practical applications. Compared with previous work, our design overcomes the shortcomings of non-tunability, single function and difficulty in integration. It can achieve better tunable infrared detection, radiation cooling and infrared-lidar compatible camouflage and other functions in a simple fixed structure. This will greatly contribute to the development of optical communications, radiation cooling, adjustable electromagnetic wave control and various thermal camouflage technologies for military purposes, and has good practical application value.

[0042] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A mid-infrared detection structure, characterized in that: The device comprises a silicon layer, a gold layer, an aluminum oxide layer, and a gold array layer stacked sequentially from bottom to top. The gold array layer is provided with periodically distributed slits, which divide the gold array layer into a plurality of periodic arrays of rectangular gold array elements. Half a slit is provided at both ends of the gold array layer along the array direction. The slit is used to leak the local energy generated by the surface plasmon resonance excited by the gold array layer and the aluminum oxide layer to balance the absorptivity / radioactivity of the entire detection structure. The aluminum oxide layer acts as a capacitor, and the absorption peak is red-shifted by adjusting the thickness of the aluminum oxide layer and the array period of the rectangular gold array elements. There is an absorption peak at 3-5μm and 8-12μm respectively; The silicon layer and the aluminum oxide layer are obtained by radio frequency sputtering, and the gold layer is obtained by direct current sputtering; From bottom to top, the thickness of the silicon layer is 100nm, the thickness of the gold layer is 50nm, the thickness of the aluminum oxide layer is 20nm, the thickness of the gold array layer is 50nm, the width of the rectangular gold array element is 2μm, the array period of the rectangular gold array element is 2.1μm, and the width of the slit is 100nm.

2. A multi-band adjustable absorbing structure, characterized by: The mid-infrared detection structure according to claim 1 is provided with a phase change material layer between the gold layer and the aluminum oxide layer.

3. The multi-band adjustable absorbing structure according to claim 2, characterized in that: The phase change material layer is a Ge2Sb2Te5 thin film.

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