A stacked dual-band microwave metamaterial absorbing chip and its fabrication method

Abstract

This invention provides a stacked dual-band microwave metamaterial absorbing chip and its fabrication method, belonging to the field of microwave metamaterial technology. The stacked dual-band microwave metamaterial absorbing chip provided by this invention exhibits excellent absorption performance for K-band and Ka-band microwaves at two specific frequencies. One frequency band absorbs electromagnetic waves through a first metal resonant square ring, and the other frequency band absorbs electromagnetic waves through a third metal resonant square ring. By adjusting the size of the metal resonant square rings, the positions and absorptivity of the two absorption frequencies can be changed simultaneously, thereby flexibly achieving absorption at specific frequencies. Moreover, while ensuring high absorptivity across both frequency bands, the size of the absorbing chip is significantly reduced, resulting in an ultra-thin structure and flexible applications, showing great potential in radar stealth and counter-radar detection.

Description

Technical Field

[0001] This invention relates to the field of microwave metamaterials technology, and in particular to a stacked dual-band microwave metamaterial absorbing chip and its fabrication method. Background Technology

[0002] Microwaves typically refer to alternating current signals with frequencies between 300MHz and 300GHz, corresponding to wavelengths between 1m and 1mm. Microwaves offer excellent mobility, a wide operating bandwidth, and the ability to transmit more information, making them widely used in communications, satellites, and radar antennas. Electromagnetic microwave absorbers, due to their efficient absorption of microwave electromagnetic waves, have broad application prospects in fields such as 5G communications, phased array radar, and electromagnetic stealth.

[0003] Metamaterials refer to artificial composite materials or structures possessing extraordinary physical properties not found in natural materials. Through human design, metamaterials can be created from atomic or molecular designs, undergoing rigorous and complex artificial design and fabrication processes to form composite or hybrid material systems with periodic or aperiodic arrangements of artificial microstructure units, tailored to specific application needs. Metamaterial absorbers are constructed using resonant metamaterials, primarily utilizing the electromagnetic losses of the dielectric material within the metamaterial to convert incident electromagnetic waves into ohmic heat or other forms of energy, thus achieving absorption. Because metamaterial absorbers can achieve near-perfect absorption of incident electromagnetic waves in specific frequency bands through structural design of functional units, they have become a hot research area in electromagnetic metamaterials. Furthermore, due to their extraordinary physical properties, simple structure, polarization insensitivity, and perfect absorption characteristics, they have broad application prospects in fields such as antenna radar, electromagnetic stealth, sensing technology, thermal imaging, biological detection, and photovoltaic cells.

[0004] However, while existing metamaterial absorbers have high absorption rates, the large size of the absorbing chip limits their widespread application in radar stealth and counter-radar detection. Summary of the Invention

[0005] The purpose of this invention is to provide a stacked dual-band microwave metamaterial absorbing chip and its preparation method, which greatly reduces the chip size while ensuring high absorption rate, laying the foundation for radar stealth and counter-radar reconnaissance.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a stacked dual-band microwave metamaterial absorbing chip, which is composed of an electrically resonant chip and a metal reflective chip stacked together;

[0008] The metal reflective chip is disposed below the electrical resonant chip; the centers of the electrical resonant chip and the metal reflective chip coincide in the vertical direction.

[0009] The electric resonant chip is composed of a periodic array of several unit structures, each unit structure including a metal resonant layer and a dielectric layer; the metal resonant layer is grown below the dielectric layer.

[0010] The metal resonant layer is composed of a first metal resonant square ring, a second metal resonant square ring, and a third metal resonant square ring disposed on the same plane, nested together.

[0011] The first, second, and third metal resonant square rings are arranged concentrically, with the first metal resonant square ring located at the center, the second metal resonant square ring located outside the first metal resonant square ring, and the third metal resonant square ring located on the outermost side.

[0012] Preferably, the metal reflective chip is made of a silicon wafer covered with a metal, wherein the metal covered by the silicon wafer is gold; the electrical conductivity of gold is 4.1 × 10⁻⁶. 7 S / m.

[0013] Preferably, the material of the dielectric layer is silicon nitride.

[0014] Preferably, the dielectric layer has a square structure with a side length of 2.8–3 mm and a thickness of 0.5–1 μm.

[0015] Preferably, the first, second, and third metal resonant square rings are made of gold; the electrical conductivity of gold is 4.1 × 10⁻⁶. 7 S / m.

[0016] Preferably, the first, second, and third metal resonant square rings are all square rings; the outer side length of the first metal resonant square ring is 0.8–1 mm, the inner side length is 0.4–0.7 mm, and the thickness is 0.5–1 μm; the outer side length of the second metal resonant square ring is 1.9–2.1 mm, the inner side length is 1.6–1.9 mm, and the thickness is 0.5–1 μm; the outer side length of the third metal resonant square ring is 2.5–2.8 mm, the inner side length is 2.2–2.5 mm, and the thickness is 0.5–1 μm.

[0017] Preferably, the distance between the metal resonant layer of the electric resonant chip and the metal surface of the metal reflective chip is 150–200 μm.

[0018] This invention provides a method for fabricating the stacked dual-band microwave metamaterial absorbing chip described in the above technical solution, comprising the following steps:

[0019] Using the material corresponding to the dielectric layer, low-pressure chemical vapor deposition is performed on both sides of the silicon wafer substrate, and photolithography is performed on one side of the formed dielectric layer film to form the dielectric layer with the desired pattern.

[0020] The dielectric layer is sequentially deposited with a metal film and photo-etched to form a metal resonant layer with the desired metal resonant square ring structure, thereby obtaining an electric resonant chip.

[0021] A cavity is formed by photolithography on a silicon wafer, and a metal film is deposited on the surface of the cavity to obtain a metal reflective chip;

[0022] The electric resonant chip and the metal reflective chip are bonded together to form a stacked chip;

[0023] The stacked chip is etched to remove excess silicon substrate from the electrically resonant chip, resulting in a stacked dual-band microwave metamaterial absorbing chip.

[0024] Preferably, the depth of the cavity is 150–200 μm.

[0025] Preferably, the thickness of the metal film on the metal reflective chip is 0.5 to 1 μm.

[0026] The stacked dual-band microwave metamaterial absorbing chip provided by this invention exhibits excellent absorption performance at two specific frequencies (28.35 GHz and 39.2 GHz), demonstrating perfect absorption at both frequencies in both TE and TM modes. One frequency band absorbs electromagnetic waves through a first metallic resonant square ring, while the other band absorbs electromagnetic waves through a third metallic resonant square ring. Adjusting the size of the first metallic resonant square ring changes the absorption frequency at the high-frequency end, and adjusting the size of the third metallic resonant square ring changes the absorption frequency at the low-frequency end. The second metallic resonant square ring forms a new resonant circuit with the first and third metallic resonant square rings. Adjusting the size of the second metallic resonant square ring accordingly affects the resonant parameters in the resonant circuit, thus influencing the absorption frequency. Therefore, this invention allows for flexible absorption at specific frequencies by simultaneously changing the position and absorptivity of both absorption frequencies by adjusting the size of the metallic resonant square rings.

[0027] This invention provides a stacked dual-band microwave metamaterial absorbing chip. A metal resonant square ring is grown on a dielectric layer, which serves as the first layer to receive electromagnetic waves. The metal resonant square ring then reduces the resonant loss, increasing the absorption rate. Furthermore, this invention stacks a substrate-free electric resonant chip with a metal reflective chip, allowing electromagnetic waves that would otherwise pass through the substrate-free electric resonant chip to be further reflected back to the electric resonant chip via the metal reflective chip, thereby improving the chip's absorption rate. Therefore, this invention minimizes the thickness of the absorbing chip, thus reducing its volume. Traditional sandwich absorbers rely primarily on the absorption from the dielectric layer's losses, requiring a relatively thick dielectric layer. Therefore, the absorbing chip provided by this invention significantly reduces its volume while maintaining high absorption rates across both frequency bands. Its ultra-thin structure allows for flexible applications, and due to the material's inherent ductility, it can be used as a stealth material, offering greater practicality in its coverage environment and demonstrating significant potential in radar stealth and counter-radar detection. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention;

[0029] Figure 2 This is a schematic diagram illustrating the fabrication process of the stacked dual-band microwave metamaterial absorbing chip of the present invention.

[0030] Figure 3 This is a schematic diagram of the structure of Comparative Example 1 of the present invention;

[0031] Figure 4 This is a simulation result of the absorption rate of Embodiment 1 of the present invention;

[0032] Figure 5 The figure shows the simulation results of the absorption rate of Comparative Example 1 of this invention. Detailed Implementation

[0033] like Figure 1 As shown, the present invention provides a stacked dual-band microwave metamaterial absorbing chip, which is composed of an electrically resonant chip and a metal reflective chip stacked together;

[0034] The metal reflective chip is disposed below the electrical resonant chip; the centers of the electrical resonant chip and the metal reflective chip coincide in the vertical direction.

[0035] The electric resonant chip is composed of a periodic array of several unit structures, each unit structure including a metal resonant layer and a dielectric layer; the metal resonant layer is grown below the dielectric layer.

[0036] The metal resonant layer is composed of a first metal resonant square ring, a second metal resonant square ring, and a third metal resonant square ring disposed on the same plane, nested together.

[0037] The first, second, and third metal resonant square rings are arranged concentrically, with the first metal resonant square ring located at the center, the second metal resonant square ring located outside the first metal resonant square ring, and the third metal resonant square ring located on the outermost side.

[0038] In this invention, the metal reflective chip is preferably made of a silicon wafer covered with a metal, and the metal covered by the silicon wafer is preferably gold; the conductivity of the gold is preferably 4.1 × 10⁻⁶. 7 S / m; the thickness of the silicon wafer is preferably 0.1 mm. The present invention does not impose any special limitations on the fabrication process of the metal reflective chip; a metal reflective chip of the required size can be obtained by coating a silicon wafer with gold according to methods well known in the art.

[0039] In this invention, the distance between the metal resonant layer of the electric resonant chip and the metal surface of the metal reflective chip is preferably 150-200 μm.

[0040] In this invention, the electric resonant chip is composed of a periodic array of several unit structures; this invention does not have a special limitation on the number of unit structures, which can be adjusted according to actual needs; this invention does not have a special limitation on the manner of the periodic array, which can be arranged into an array of any shape according to actual needs.

[0041] In this invention, the unit structure includes a metal resonant layer and a dielectric layer; the metal resonant layer is grown below the dielectric layer.

[0042] In this invention, the first, second, and third metal resonant square rings are preferably made of gold; the electrical conductivity of gold is preferably 4.1 × 10⁻⁶. 7 S / m.

[0043] In this invention, the first, second, and third metal resonant square rings are all preferably square rings; the outer side length of the first metal resonant square ring is preferably 0.8–1 mm, the inner side length is preferably 0.4–0.7 mm, more preferably 0.5 mm, and the thickness is preferably 0.5–1 μm; the outer side length of the second metal resonant square ring is preferably 1.9–2.1 mm, the inner side length is preferably 1.6–1.9 mm, more preferably 1.7 mm, and the thickness is preferably 0.5–1 μm; the outer side length of the third metal resonant square ring is preferably 2.5–2.8 mm, the inner side length is preferably 2.2–2.5 mm, more preferably 2.3 mm, and the thickness is preferably 0.5–1 μm.

[0044] In this invention, the material of the dielectric layer is preferably silicon nitride, which has almost no absorption effect on electromagnetic waves; the dielectric layer is preferably a square structure, the side length of the square structure is preferably 2.8 to 3 mm, and the thickness of the dielectric layer is preferably 0.5 to 1 μm.

[0045] In this invention, both the metal resonant chip and the metal reflective chip are made of gold, and the two chips are stacked by bonding gold to gold.

[0046] like Figure 2 As shown, the present invention provides a method for fabricating the stacked dual-band microwave metamaterial absorbing chip described in the above technical solution, comprising the following steps:

[0047] Using the material corresponding to the dielectric layer, low-pressure chemical vapor deposition is performed on both sides of the silicon wafer substrate, and photolithography is performed on one side of the formed dielectric layer film to form the dielectric layer with the desired pattern.

[0048] The dielectric layer is sequentially deposited with a metal film and photo-etched to form a metal resonant layer with the desired metal resonant square ring structure, thereby obtaining an electric resonant chip.

[0049] A cavity is formed by photolithography on a silicon wafer, and a metal film is deposited on the surface of the cavity to obtain a metal reflective chip;

[0050] The electric resonant chip and the metal reflective chip are bonded together to form a stacked chip;

[0051] The stacked chip is etched to remove excess silicon substrate from the electrically resonant chip, resulting in a stacked dual-band microwave metamaterial absorbing chip.

[0052] In this invention, the silicon substrate is preferably a silicon wafer with a thickness of 300 μm, which can reduce etching time and improve etching uniformity; the present invention preferably polishes the silicon substrate on both sides before deposition to ensure the uniformity of silicon etching on the back side.

[0053] The present invention does not impose any particular limitation on the specific process of the low-pressure chemical vapor deposition (LPCVD), and can be carried out according to the process known in the art; the thickness of the dielectric layer film is preferably 0.5 to 1 μm.

[0054] This invention does not impose any particular limitation on the photolithography; the desired patterned structure can be obtained by following a process well-known in the art. During the formation of the desired patterned dielectric layer by photolithography, the dielectric film on the back side of the silicon wafer is simultaneously etched away.

[0055] The present invention does not impose any special limitations on the process of depositing the metal film; the desired thickness of the metal film can be obtained by following a process well known in the art.

[0056] In this invention, the depth of the cavity is preferably 150-200 μm, corresponding to the spacing between the electric resonant chip and the metal reflective chip.

[0057] In this invention, the thickness of the metal film on the metal reflective chip is 0.5 to 1 μm.

[0058] The present invention does not impose any special limitations on the specific bonding process; the bonding of the electric resonant chip and the metal reflective chip can be achieved by following a process well known in the art.

[0059] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0060] Example 1

[0061] like Figures 1-2 As shown, the stacked dual-band microwave metamaterial absorbing chip provided in this embodiment is composed of an electric resonant chip and a metal reflective chip stacked together, which are composed of a periodic array of several unit structures; the periodic arrangement of 40*40 units forms a rectangular array with 40 units in length and width, for a total of 1600 units.

[0062] The metal resonant layer and the dielectric layer constitute an electric resonant chip, with the metal resonant layer located below the dielectric layer.

[0063] The metal reflective chip is located below the electric resonant chip; the two chips are stacked together by gold-to-gold bonding, and the centers of the two chips coincide in the vertical direction.

[0064] The metal resonant layer of the electric resonant chip is composed of nested metal resonant square rings C1, C2, and C3. Metal resonant square ring C1 is a square ring made of a material with an electrical conductivity of 4.1 × 10⁻⁶. 7 The S / m gold resonant square ring C1 has an outer side length of 0.8 mm, an inner side length of 0.5 mm, and a thickness of 0.5 μm; the metal resonant square ring C2 is a square ring, and the material used is gold with a conductivity of 4.1 × 10⁻⁶ m. 7 The S / m gold resonant square ring C2 has an outer side length of 1.9 mm, an inner side length of 1.7 mm, and a thickness of 0.5 μm; the metal resonant square ring C3 is a square ring, and the material used is gold with a conductivity of 4.1 × 10⁻⁶ m. 7 The S / m gold metal resonant square ring C3 has an outer side length of 2.5mm, an inner side length of 2.3mm, and a thickness of 0.5μm.

[0065] The dielectric layer is made of silicon nitride, has a square unit structure with a side length of 3 mm and a thickness of 0.5 μm;

[0066] The reflective chip is made of a silicon wafer covered with a metal, the metal of which has an electrical conductivity of 4.1 × 10⁻⁶. 7 Gold with a strength of S / m, silicon wafer size of 0.1mm;

[0067] The distance between the metal resonant layer of the electric resonant chip and the metal surface of the reflective chip is 200 μm.

[0068] Preparation method:

[0069] Low-pressure chemical vapor deposition is performed on both sides of a silicon wafer substrate. One side of the resulting silicon nitride film is photolithographically etched, while the silicon nitride on the back side is etched away to form a dielectric layer with the desired pattern.

[0070] The dielectric layer is sequentially deposited with a metal film and photo-etched to form a metal resonant layer with the desired metal resonant square ring structure, thereby obtaining an electric resonant chip.

[0071] A silicon wafer is photolithographically etched to form a cavity with a depth of 200 μm. After depositing a metal film on the surface of the cavity, a metal reflective chip is obtained.

[0072] The electric resonant chip and the metal reflective chip are bonded together to form a stacked chip;

[0073] The stacked chip is etched to remove excess silicon substrate from the electrically resonant chip, resulting in a stacked dual-band microwave metamaterial absorbing chip.

[0074] Comparative Example

[0075] like Figure 3 As shown, the conventional sandwich dual-band absorber provided in this comparative example is manufactured as a whole. The dimensions of all metal resonant square rings are the same as those in Example 1. Compared with Example 1, this absorber uses a conventional sandwich structure. The first layer is a resonant metal square ring with a thickness of 0.01 mm. The second layer is a Rogers 5880 substrate (dielectric layer with a thickness of 0.15 mm). The third layer is a metal substrate (gold) with a thickness of 0.01 mm.

[0076] Performance testing

[0077] The absorption performance of the stacked dual-band microwave metamaterial absorbing chip described in this invention is represented by the absorption coefficient A(ω), which can be derived from the reflectivity R(ω) and transmittance T(ω) as follows: A(ω)=1-R(ω)-T(ω), where R(ω) and T(ω) can be represented by scattering parameters (S-parameters), R(ω)=|S 11 | 2 T(ω)=|S 21 | 2Since electromagnetic waves cannot penetrate from the bottom layer to the outside due to the fully covered metal, T(ω) is considered to be 0. Therefore, the absorptivity A(ω) can be simplified to A(ω) = 1 - R(ω) = 1 - |S 11 | 2 .

[0078] Simulations were performed using CST software, and the absorption spectra of the microwave dual-band metamaterial absorbing chip of Embodiment 1 of this invention in TE and TM modes are as follows: Figure 4 As shown, it has two highly efficient absorption peaks in the 20-45GHz band, with absorption frequencies of 28.35GHz and 39.2GHz, respectively, and the absorption rate reaches 100%. Furthermore, in the absorbing chip of this invention, the thickness of the electrically resonant chip is only 1μm, which is only 1 / 8000 of the wavelength of the absorption band.

[0079] The comparative example's absorption spectrum in TE mode is as follows: Figure 5 As shown, it has two highly efficient absorption peaks in the 20-45GHz band, with absorption frequencies of 23.6GHz and 32.8GHz, respectively, and an absorption rate of 80% for both. The thickness of the comparative absorbing chip (0.17mm) is 1 / 40 of the wavelength in the absorption band.

[0080] pass Figure 4 and Figure 5 It is evident that, with the same metal resonant structure parameters, Example 1 has a higher absorption rate and a smaller structural thickness compared to the comparative example.

[0081] In summary, the stacked dual-band microwave metamaterial absorbing chip provided by this invention significantly reduces the size of the absorbing chip while ensuring high absorption rate, laying the foundation for applications such as radar stealth and counter-radar reconnaissance.

[0082] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A stacked dual-band microwave metamaterial absorbing chip, characterized in that, It is composed of stacked electrical resonant chips and metal reflective chips; The metal reflective chip is disposed below the electrical resonant chip; the centers of the electrical resonant chip and the metal reflective chip coincide in the vertical direction. The electric resonant chip is composed of a periodic array of several unit structures, each unit structure including a metal resonant layer and a dielectric layer; the metal resonant layer is grown below the dielectric layer. The metal resonant layer is composed of a first metal resonant square ring, a second metal resonant square ring, and a third metal resonant square ring disposed on the same plane, nested together. The first metal resonant square ring, the second metal resonant square ring, and the third metal resonant square ring are arranged concentrically, with the first metal resonant square ring located at the center, the second metal resonant square ring located outside the first metal resonant square ring, and the third metal resonant square ring located on the outermost side. The fabrication method of the stacked dual-band microwave metamaterial absorbing chip includes the following steps: Using the material corresponding to the dielectric layer, low-pressure chemical vapor deposition is performed on both sides of the silicon wafer substrate, and photolithography is performed on one side of the formed dielectric layer film to form the dielectric layer with the desired pattern. The dielectric layer is sequentially deposited with a metal film and photo-etched to form a metal resonant layer with the desired metal resonant square ring structure, thereby obtaining an electric resonant chip. A cavity is formed by photolithography on a silicon wafer, and a metal film is deposited on the surface of the cavity to obtain a metal reflective chip; The electric resonant chip and the metal reflective chip are bonded together to form a stacked chip; The stacked chip is etched to remove excess silicon substrate from the electrically resonant chip, resulting in a stacked dual-band microwave metamaterial absorbing chip.

2. The stacked dual-band microwave metamaterial absorbing chip according to claim 1, characterized in that, The metal reflective chip is made of a silicon wafer covered with a metal, namely gold; the electrical conductivity of gold is 4.1 × 10⁻⁶. 7 S / m .

3. The stacked dual-band microwave metamaterial absorbing chip according to claim 1, characterized in that, The dielectric layer is made of silicon nitride.

4. The stacked dual-band microwave metamaterial absorbing chip according to claim 1 or 3, characterized in that, The dielectric layer has a square structure with a side length of 2.8~3mm and a thickness of 0.5~1μm.

5. The stacked dual-band microwave metamaterial absorbing chip according to claim 1, characterized in that, The first, second, and third metal resonant square rings are made of gold; the electrical conductivity of gold is 4.1 × 10⁻⁶. 7 S / m .

6. The stacked dual-band microwave metamaterial absorbing chip according to claim 1 or 5, characterized in that, The first, second, and third metal resonant square rings are all square rings; the outer side length of the first metal resonant square ring is 0.8~1mm, the inner side length is 0.4~0.7mm, and the thickness is 0.5~1μm; the outer side length of the second metal resonant square ring is 1.9~2.1mm, the inner side length is 1.6~1.9mm, and the thickness is 0.5~1μm; the outer side length of the third metal resonant square ring is 2.5~2.8mm, the inner side length is 2.2~2.5mm, and the thickness is 0.5~1μm.

7. The stacked dual-band microwave metamaterial absorbing chip according to claim 2, characterized in that, The distance between the metal resonant layer of the electric resonant chip and the metal surface of the metal reflective chip is 150~200μm.

8. The method for fabricating the stacked dual-band microwave metamaterial absorbing chip according to any one of claims 1 to 7, characterized in that, Includes the following steps: Using the material corresponding to the dielectric layer, low-pressure chemical vapor deposition is performed on both sides of the silicon wafer substrate, and photolithography is performed on one side of the formed dielectric layer film to form the dielectric layer with the desired pattern. The dielectric layer is sequentially deposited with a metal film and photo-etched to form a metal resonant layer with the desired metal resonant square ring structure, thereby obtaining an electric resonant chip. A cavity is formed by photolithography on a silicon wafer, and a metal film is deposited on the surface of the cavity to obtain a metal reflective chip; The electric resonant chip and the metal reflective chip are bonded together to form a stacked chip; The stacked chip is etched to remove excess silicon substrate from the electrically resonant chip, resulting in a stacked dual-band microwave metamaterial absorbing chip.

9. The preparation method according to claim 8, characterized in that, The depth of the cavity is 150~200μm.

10. The preparation method according to claim 8, characterized in that, The thickness of the metal film on the metal reflective chip is 0.5~1μm.

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