Electromagnetic wave absorber

Abstract

An electromagnetic wave absorber (10) according to the present invention is provided to a substrate (14) and comprises a metamaterial layer (11), a spacer layer (12), and a reflective thin film (13), in this order. The electromagnetic wave absorber (10) absorbs and suppresses the resonance mode of electromagnetic waves in the substrate (14).　The present invention can thus provide a small electromagnetic wave absorber that does not require a complicated production process.

Description

[Technical field]

[0001] The present invention relates to an electromagnetic wave absorber that absorbs electromagnetic waves, and more particularly to an electromagnetic wave absorber used in high frequency integrated circuit technology. [Background technology]

[0002] In high-frequency integrated circuit (IC) technologies, two adverse effects appear when the operating speed exceeds 1 / 10 GHz. In the first effect, feedback circuits with parasitic inductance and capacitance induce vibrations and cause instability in the ground potential of high-frequency ICs, called ground bounce. Ground bounce generates peaks and dips in the signal response and degrades the group delay. The second effect is substrate resonance, which begins at the millimeter-wave bandwidth. When the wavelength of the signal propagating through the IC approaches the size of the chip, additional electromagnetic (EM) wave modes are easily radiated into the substrate, causing oscillations and degradation of the circuit operation due to the energy dispersion of the EM wave signal.

[0003] In order to minimize the effects of ground bounce and substrate resonance and ensure stable operation of high-speed ICs at sub-millimeter wavelengths, the substrate 51 is thinned and a high-density through-substrate via (TSV) system is formed on the backside of the IC chip 5, as shown in FIG. 12.

[0004] Ground bounce is suppressed by connecting the ground plane in the IC chip to the module ground 53 using vias 52 and bond wires. Substrate resonance is blocked by thinning the substrate and forming a high density of ground vias through the substrate. The thickness of the thinned substrate, the diameter of the TSVs and the density of the TSVs depend on the operating frequency of the IC circuit.

[0005] In commonly used metallized via systems, the resistivity per unit area between the front and back surfaces must be minimized to stabilize the ground potential of the IC chip. Smaller resistivity can be obtained by reducing the diameter of the vias, the spacing between the vias, and the thickness of the substrate. Smaller vias are also advantageous for improving the layout flexibility and packaging level of the IC.

[0006] In general, absorbing materials can be added to IC chips instead of high-density TSV systems to suppress the effects of ground bounce and substrate resonance and absorb EM wave modes propagating through the substrate of the IC chip. Absorbers can effectively absorb or remove unwanted electromagnetic radiation or scattering, and have potential in radar stealth technology, EM shielding, and energy harvesting.

[0007] However, conventional absorbers are thick and heavy, making it practically difficult to use them in small IC chips for high-frequency electronic devices.

[0008] As described above, in order to suppress the board resonance and ground bounce that occur in high-speed ICs, it is necessary to make the board thinner and create high-density TSVs on the back surface of the board. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] “Broadband metamaterial absorber at mid-infrared using multiplexed cross resonators,” Wei Ma, Yongzheng Wen, and Xiaomei Yu, Opt. Express 21, 30724-30730 (2013). [Non-Patent Document 2] “Broadband metamaterial microwave absorber based on asymmetric sectional resonator structures,” Yongzhi Cheng, Hui Luo and Fu Chen, J. Appl. Phys.127, 214902 (2020). [Non-Patent Document 3] “Experimental demonstration of terahertz metamaterial absorbers with a broad and flat high absorption band,” Li Huang, Dibakar Roy Chowdhury, Suchitra Ramani, Matthew T. Reiten, Sheng-Nian Luo, Antoinette J. Taylor, and Hou-Tong Chen, Opt. Lett. 37, 154-156 (2012). [Non-Patent Document 4] “Perfect Metamaterial Absorber,” NI Landy, S. Sajuyigbe, JJ Mock, DR Smith, and WJ Padilla, Phys. Rev. Lett. 100, 207402. [Non-Patent Document 5] “Wafer-level backside process technology for forming high-density vias and backside metal patterning for 50-μm-thick InP substrate,” Tsutsumi, Takuya & Kosugi, T. & Matsuzaki, H. (2013). 2013 International Conference on Compound Semiconductor Manufacturing Technology, CS MANTECH 2013. 55-58. Summary of the Invention [Problem to be solved by the invention]

[0010] However, thinning the substrate and forming the TSV system has the following problems with respect to manufacturing and designing the IC layout:

[0011] First, because the fabrication of TSV systems requires etching through the substrate, the design of the IC layout must take into account the implementation of TSVs on the backside of the IC chip. Because the size of individual electrical components on the chip is much smaller than the diameter of an individual TSV, this requires a significant increase in chip size and a simultaneous reduction in the packaging level of the IC chip.

[0012] Second, the fabrication of TSVs requires a multi-step process that includes mounting IC chips on a glass substrate using epoxy adhesive, thinning the substrate using polishing, forming vias using reactive ion etching, and metallizing the backside of the substrate and inside the vias. This complex multi-step process significantly increases the cost and time of fabricating high-speed IC chips.

[0013] Third, the fabrication of TSV systems requires precise control of the via hole diameter, which is important for the suppression of undesired EM wave modes, and therefore requires very high etch selectivity in the ion reactive etching process to precisely control the TSV diameter.

[0014] Fourth, the control of the substrate temperature during the ion reactive etching process is also essential and must be considered, because the adhesive commonly used to mount IC chips on glass deteriorates at high temperatures, which makes the thin IC chip difficult to remove from the glass after backside processing due to the deterioration of the adhesive, and makes it more susceptible to breakage due to mechanical stress.

[0015] Fifth, as the diameter of TSV decreases, the etching rate decreases due to the microloading effect, which is prominent at sub-mm wave. Therefore, with the increase in the operating frequency range, it becomes essential to adjust the etching parameters, which increases the overall fabrication time.

[0016] Sixth, after the formation of the TSVs, metallization is required on the backside of the substrate and inside the vias, typically by electroplating a few micrometers of metal and then reactive ion etching to remove any extraneous seed layer.

[0017] As described above, in order to suppress the substrate resonance and ground bounce that occur in high-speed ICs, there are problems in the layout design of the IC chip and in the fabrication of the TSVs in order to reduce the substrate thickness and fabricate high-density TSVs on the back surface of the substrate. [Means for solving the problem]

[0018] In order to solve the above-mentioned problems, the electromagnetic wave absorber according to the present invention is an electromagnetic wave absorber disposed on a substrate, which is provided with a metamaterial layer, a spacer layer, and a reflective thin film, in that order, and absorbs and suppresses the resonant mode of the electromagnetic wave in the substrate. The metamaterial layer includes a plurality of subwavelength structured metamaterial cells, the metamaterial cells are periodically arranged and designed to resonate at a predetermined frequency, and the structure and period of the metamaterial cells are determined by the wavelength of an incident electromagnetic wave. It is characterized by the above. In addition, the electromagnetic wave absorber according to the present invention is characterized in that the metamaterial cell is composed of a plurality of sections having different characteristic sizes, and the plurality of sections are arranged asymmetrically. Moreover, the electromagnetic wave absorber according to the present invention is an electromagnetic wave absorber arranged on a substrate, which comprises, in order, a metamaterial layer, a spacer layer, and a reflective thin film, and which absorbs and suppresses a resonance mode of an electromagnetic wave in the substrate, and is characterized in that the effective dielectric constant and permeability of the metamaterial layer are adjusted so as to match the impedance of the metamaterial layer to the impedance of the substrate and absorb the resonance mode of the electromagnetic wave. Moreover, the electromagnetic wave absorber according to the present invention is an electromagnetic wave absorber disposed on a substrate, which comprises, in order, a metamaterial layer, a spacer layer, and a reflective thin film, and which absorbs and suppresses a resonance mode of an electromagnetic wave within the substrate, and is characterized in that the difference between the relative dielectric constant of the spacer layer and the relative dielectric constant of the substrate is 2 or more and 11 or less. Moreover, the electromagnetic wave absorber according to the present invention is an electromagnetic wave absorber arranged on a substrate, which comprises, in order, a metamaterial layer, a spacer layer, and a reflective thin film, and which absorbs and suppresses a resonant mode of an electromagnetic wave within the substrate, the electromagnetic wave having a source within the substrate of a high-speed electronic circuit. Effect of the Invention

[0019] According to the present invention, it is possible to provide a small electromagnetic wave absorber that does not require a complicated manufacturing process. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic cross-sectional view of a semiconductor substrate for high-speed electronic circuits that includes an electromagnetic wave absorber according to a first embodiment of the present invention. [Figure 2A]FIG. 2A is a schematic top view showing the configuration of an electromagnetic wave absorber according to a first embodiment of the present invention. [Figure 2B] FIG. 2B is a schematic top view showing the configuration of the electromagnetic wave absorber according to the first embodiment of the present invention. [Figure 2C] FIG. 2C is a schematic top view showing the configuration of the electromagnetic wave absorber according to the first embodiment of the present invention. [Diagram 3] FIG. 3 is a perspective bird's-eye view showing the configuration of a semiconductor substrate for high-speed electronic circuits including an electromagnetic wave absorber according to a first embodiment of the present invention. [Figure 4A] FIG. 4A is a diagram for explaining characteristics of the electromagnetic wave absorber according to the first embodiment of the present invention. [Figure 4B] FIG. 4B is a diagram for explaining the characteristics of the electromagnetic wave absorber according to the first embodiment of the present invention. [Diagram 5] FIG. 5 is a bird's-eye perspective view showing the configuration of a coplanar waveguide including an electromagnetic wave absorber according to a first embodiment of the present invention. [Figure 6] FIG. 6 is a diagram for explaining the characteristics of the electromagnetic wave absorber according to the first embodiment of the present invention. [Figure 7] FIG. 7 is a diagram for explaining the characteristics of the electromagnetic wave absorber according to the first embodiment of the present invention. [Figure 8] FIG. 8 is a diagram for explaining the characteristics of the electromagnetic wave absorber according to the first embodiment of the present invention. [Figure 9] FIG. 9 is a diagram for explaining the characteristics of the electromagnetic wave absorber according to the first embodiment of the present invention. [Figure 10] FIG. 10 is a diagram for explaining the characteristics of the electromagnetic wave absorber according to the second embodiment of the present invention. [Figure 11] FIG. 11 is a bird's-eye perspective view showing the configuration of a coplanar waveguide including an electromagnetic wave absorber according to a third embodiment of the present invention. [Figure 12] FIG. 12 is a schematic cross-sectional view of a semiconductor substrate for a conventional high-speed electronic circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] <First embodiment> An electromagnetic wave absorber according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 8. FIG.

[0022] <Configuration of electromagnetic wave absorber> The electromagnetic wave absorber according to the present embodiment uses a metamaterial to absorb a wide range of electromagnetic wave modes radiated from a high-speed electronic circuit to a substrate. Hereinafter, the principle and configuration of the present invention will be described in detail with reference to the drawings. This description provides some detailed examples of possible implementations of the present invention, but it should be noted that these details are illustrative and do not limit the scope of the present invention.

[0023] Metamaterials are artificial media that derive their properties from embedded subwavelength structures arranged together in configurations similar to atoms in ordinary materials, exhibiting desired values ​​of permittivity and permeability over a measured frequency range, and manipulate electromagnetic (EM) waves. The electromagnetic properties of metamaterials result from the dimensions, geometry, orientation, and arrangement of the circuit's periodic structures, as well as the materials from which those structures are composed.

[0024] With precise design, metamaterials can be applied as electromagnetic wave absorbers in a wide range of frequencies. Here, the absorption wavelength and bandwidth can be adjusted by changing the design of the metamaterial cells. A typical structure of an electromagnetic wave absorber consists of a three-layer structure, which has an array of metallic subwavelength structures on the front surface of a dielectric spacer and a metallic ground layer on the back surface. Here, the metamaterial periodic structure on the front surface is responsible for the electric resonant response of the metamaterial absorber 10, and the coupling of the metallic layer and the dielectric spacer layer on the back surface determines the magnetic resonant response. Hereinafter, the "electromagnetic wave absorber" is also referred to as the "metamaterial absorber".

[0025] 1 shows a cross section of a semiconductor substrate for high-speed electronic circuits including an electromagnetic wave absorber 10 according to this embodiment. The electromagnetic wave absorber 10 has a three-layer structure using a metamaterial, and includes a metamaterial layer 11 having subwavelength metamaterial cells 111 periodically arranged on the back surface of a high-speed IC chip substrate 14, an intermediate spacer layer 12, and a lower reflective thin film 13. Here, an electromagnetic wave source is provided within the substrate of the high-speed electronic circuit.

[0026] The subwavelength metamaterial cells 111 are designed to resonate at a predetermined frequency.

[0027] Metamaterial structures can be made from metals such as gold, copper and aluminum, as well as other highly conductive materials such as graphene or carbon nanotubes.

[0028] The intermediate dielectric spacer layer 12 can be any type of dielectric material, such as silicon-based dielectrics (silicon dioxide, silicon nitride), or polymers, such as polyimide or benzocyclobutene (BCB). The thickness of the dielectric spacer 12 is adjusted based on the dielectric constant (dielectric constant) to enhance the absorption of electromagnetic waves by the metamaterial absorber 10.

[0029] The lower reflective thin film 13 is made of metals, metal alloys, and compounds that are thicker than the skin depth of the target radiation (incident electromagnetic wave) to block the transmission of the incident electromagnetic wave. The minimum thickness of the reflective thin film 13 can be obtained by calculating the skin depth δ.

[0030]

number

[0031] ρ is the resistivity of the material used, μ0 is the transmittance of free space (μ0=4π 10 -7 ), μ r is the relative permeability of the material used (usually equal to 1), and f0 is the frequency of the EM wave. For example, ρ = 2.24 μΩ cm, μ rFor a gold thin film with a thickness of 1 at 300 GHz, the skin depth is 0.138 μm. Therefore, the underlying reflective thin film 13 must be thicker than this value.

[0032] 2A-C show examples of metamaterial cells (unit cells) in the electromagnetic wave absorber 10 according to the present embodiment. Generally, in the present embodiment, the metamaterial cell 111 is composed of one layer of a so-called asymmetric sectional resonator (ASR) structure of various shapes.

[0033] For example, the ASR is composed of four sections 112 with different characteristic sizes, denoted A1, A2, A3, and A4, which are combined to form a new metamaterial cell (unit cell) 111. Here, the characteristic size of each section 112 can be, for example, the width w, gap g, and perimeter length l of each section 112. i etc., which relate to the respective resonant frequencies.

[0034] 2A and 2C, for example, a material (such as a metal) having a circumferential shape (ring, square, or rectangle) with a width w is divided into four sections 112, and each section 112 is arranged with a gap g between its end faces. In this case, the distance (perimeter length) l from the center of the metamaterial cell (hereinafter also referred to as the "ASR cell") 111 to the outer periphery of each section 112 is i (l1 to l4) are arranged so as to be different. Here, the width w and gap g of each section 112 are the same. Also, the center of the ASR cell 111 is the intersection of lines connecting the centers of the outer peripheries of the sections 112 facing each other in the cell 111.

[0035] In FIG. 2B, a material (such as a metal) having a circular shape (square or rectangle) with a width w is divided into four sections 112, and each section 112 is arranged with a gap g between its end faces. In this case, the distance (perimeter length) l from the approximate center line of the ASR cell 111 to the outer periphery of each section 112 is iThe ASR cells 111 are arranged so that their spacings (l1 to l4) are different. Here, the width w and gap g of each section 112 are the same. The approximate center line of the ASR cell 111 is a straight line that is parallel to any one outer periphery and passes through two opposing gaps g.

[0036] Thus, the circumferential length l of each section 112 i have a slight difference, forming an asymmetric ASR cell 111.

[0037] Here, the width w and the gap g do not have to be the same, and the number of sections does not have to be four, as long as there are multiple sections.

[0038] In addition, the outer circumferential length l of each section 112 i However, an asymmetric ASR cell 111 may be configured by a difference in width w and gap g of each section 112.

[0039] In this embodiment, metamaterial cell 111 is composed of multiple sections 112, and each section 112 is formed by dividing a material having a circular shape. Each section 112 has a characteristic size (width w, gap g, peripheral length l i ) to form the ASR cell 111, so that the resonant frequencies of the sections 112 of the ASR cell 111 may be slightly different.

[0040] Here, the size of the ASR cell 111 may be equal to or less than half the size of the target radiation (incident electromagnetic wave). The characteristic size of each section 112 and its difference may be set within a range that satisfies the size of this cell 111. For example, when the incident electromagnetic wave is a millimeter wave, it is desirable that the size of the ASR cell 111 is about 0.5 mm or less, and the difference in characteristic size is 0.001 mm or more and 0.1 mm or less.

[0041] The resonant frequencies of each section 112 of the ASR cell 111 have slightly different values ​​which, when combined, produce a broader band absorption characteristic that is highly advantageous for absorbing the various EM wave modes generated in high speed ICs.

[0042] First, adjust the shape, dimensions, period of the cells 111, and arrangement style of the ASR metamaterial cells 111 shown in Figures 2A-C to achieve the desired resonant frequency range. The resonant frequency f R can be expressed by equation (2).

[0043]

number

[0044] where L is the equivalent inductance and C is the equivalent capacitance of the metamaterial cell 111. The equivalent inductance L and capacitance C can be expressed by equations (3) and (4), respectively.

[0045]

number

[0046]

number

[0047] where w is the width of the resonant element, ε0 and μ0 are the permittivity and permeability of free space, and l i is the external dimension (length) of the section resonator, and a and b are numerical factors. ε r is the relative dielectric constant (dielectric constant) and h is the thickness of the dielectric spacer layer.

[0048] Once the material of the dielectric spacer 12 is selected, the gap between the sections 112 of the ASR structure and the width w of each section 112 are also determined from equations (2) to (4), and the resonant frequency of the ASR metamaterial is determined by the external length l of each section 112, as shown in equation (5). i is proportional to the size of the resonator.

[0049]

number

[0050] By varying the geometry of the ASR structure and the thickness of the dielectric spacer 12, the effective permittivity ε and permeability μ of the metamaterial absorber 10 can be independently tuned to impedance match the substrate 14 of the high speed electrical circuit. When EM radiation is incident on the ASR structure, the metamaterial absorber 10 absorbs the EM wave modes through coupled resonance. In the metamaterial absorber 10, the metamaterial layer 11 is a structure that strongly couples to the electric component of the EM wave, while the combination of the spacer layer 12 and reflective thin film 13 strongly couples to the magnetic component of the EM wave.

[0051] FIG. 3 shows an example of a metamaterial cell (unit cell) obtained by simulation in this embodiment. This metamaterial cell (unit cell) 111 is tuned to 300 GHz, and a circular ASR metamaterial cell is used. In addition, r1 12.4 and an indium phosphide (InP) substrate with a dielectric constant ε r2 A dielectric spacer layer with a diameter of 8 and a thickness of 12.5 μm is used.

[0052] 3, the metamaterial absorber 10 is positioned below a thick semiconductor substrate 14, allowing direct transmission of incident EM waves between the substrate 14 and the metamaterial absorber 10. Simulations of the metamaterial cell 111 used a time-domain solver with normal incidence and appropriate periodic boundary conditions, with the electric component of the EM wave along the x-axis.

[0053] The reflection R(ω) and transmission T(ω) of the metamaterial cell 111 can be calculated from the S parameters that depend on the extraction frequency using equations (6) and (7), respectively.

[0054]

number

[0055]

number

[0056] Here, S 11 (ω) is the reflection coefficient, S 21 (ω) is the transmission coefficient.

[0057] The absorption A(ω) of the EM wave passing through the absorber is calculated by equation (8).

[0058]

number

[0059] Since the transmission is eliminated by the reflective thin film 13, which is thicker than the skin depth δ in equation (1), and the transmission value is zero over the entire frequency range measured, equation (8) for absorption can be simplified to equation (9).

[0060]

number

[0061] FIG. 4A shows an example of a simulated absorption spectrum of the metamaterial absorber 10 at a frequency of 300 GHz, where the absorption is calculated using the extracted reflection coefficient S obtained from the simulation shown in FIG. 11 (ω) was calculated according to equation (9).

[0062] The optimized absorber has a broadband absorption of 30 GHz, observed between 285 GHz and 315 GHz. Here, the broadband absorption width (30 GHz) is measured as the bandwidth for more than 90% absorption, similar to that of a conventional broadband absorber. Furthermore, due to the nearly symmetrical design of the ASR cell 111, the simulated absorption shows similar absorption for both the transverse electric (TE) 102 and transverse magnetic (TM) 101 polarization modes.

[0063] As shown in FIG. 4B, very high absorption was achieved by impedance matching between the metamaterial absorber structure and the semiconductor substrate 14 of the high-speed circuit. The effective impedance is calculated by the extracted reflection coefficient S 11 Based on (ω), S 21 It is calculated according to equation (10) with (ω)=0.

[0064]

number

[0065] In FIG. 4B, on average, the real part Re(z) 103 of the relative impedance is about 1 and the imaginary part Im(z) 104 is about 0 in the broadband frequency range observed in FIG. 4A. When a good impedance match is obtained, Z in (ω)=Z S = 1, the input impedance (Z in ) is the impedance (Z S ) Therefore, the absorptance of the metamaterial absorber 10 according to the present embodiment is nearly 100%.

[0066] As shown in FIG. 5, a coplanar waveguide 20 with a metamaterial absorber 10 on its back surface is used to evaluate the optimized metamaterial cell shown in FIG. 3 in a more practical setting.

[0067] Typically, the structure of the coplanar waveguide 2 has wave ports 25, 26 at one end and the other end of the waveguide 20, respectively, and is composed of a surface metal layer and a bottom surface layer. In the coplanar waveguide 2, the propagation direction of the electromagnetic radiation is different compared to the simulation of the metamaterial cell 111, since it is from the first waveguide port 25 to the second waveguide port 26. To test the metamaterial absorber 10, the bottom surface layer of the coplanar waveguide 20 is replaced with the metamaterial absorber 20 designed as described above. The metamaterial layer 21 is added to the back surface of the substrate 24 together with the dielectric spacer layer 22. Furthermore, a reflective thin film 23 is added to the back surface (the bottom layer of the coplanar waveguide 20). The reflective thin film 23 also serves as the ground layer of the coplanar waveguide 20.

[0068] <Characteristics of electromagnetic wave absorbers> Figure 6 shows the frequency-dependent transmission coefficient S 21 (ω) is shown. In the first case 201, the coplanar waveguide 2 has an optimized structure of the metamaterial absorber 20. In the second case 202, the metamaterial layer 21 is removed from the absorber 20, leaving only the spacer dielectric layer 22 and the reflective thin film 23. In the third case 203, the material of the spacer dielectric layer 22 is replaced with the same material as the substrate 24 to simulate the inclusion of the metamaterial layer 21 in the semiconductor substrate 24.

[0069] In the first case 201, a high intensity resonance peak was observed, and it was confirmed that the electromagnetic wave transmitted through the waveguide was absorbed in a certain frequency range.

[0070] In the second case 202, the absorber without the metamaterial layer does not affect the transmission of the EM wave modes, and therefore typical coplanar waveguide transmission of EM waves occurs with minimal loss.

[0071] In the third case 203, flat transmission characteristics were observed in the measured frequency range, so that the metamaterial absorber in which the dielectric spacer layer 22 is replaced with the same material as the substrate 24 (InP in this embodiment) does not absorb EM wave modes.

[0072] The effects on the operation of the optimized metamaterial absorber structure are discussed below.

[0073] In the coplanar waveguide 2, the orientation of the electric field towards the metamaterial cell 211 is different from that of the simulated single metamaterial cell 111 shown in Fig. 3. In the single metamaterial cell 111 shown in Fig. 3, the electric field vector E is parallel to the surface of the metamaterial absorber 10, so that LC resonance is easily induced in the gap of the ASR structure.

[0074] On the other hand, in a coplanar waveguide, the electric field vector E is oriented perpendicular to the surface due to the structure of the waveguide and its operating principle.

[0075] Normally, when the electric field vector E is oriented perpendicular to the surface of the metamaterial, no resonance occurs because the perpendicular electric field E (electric field with electric field vector E) cannot couple into the metamaterial gap. However, a small additional frequency shift can be observed to cause resonance to occur, as shown in Figure 6.

[0076] Moreover, in the above-described third case, although the same metamaterial layer 21 is included, the material of the dielectric spacer 22 is made the same as that of the substrate 24, thereby suppressing the occurrence of resonance.

[0077] Thus, in the coplanar waveguide 2 of this embodiment, the occurrence of resonance in the metamaterial absorber 20 is influenced by additional factors.

[0078] From equations (3) and (4), the resonant frequency is given by the relative dielectric constant ε r Since the dielectric constant of the dielectric constant r is proportional to the dielectric constant of the substrate 24, the shift of the resonance peak for various substrates 24 having different dielectric constant values ​​can be clearly obtained.

[0079] FIG. 7 shows the relationship between the position of the resonance peak of the metamaterial layer 21 and the relative dielectric constant ε of the dielectric spacer layer 12 in two different high-speed IC semiconductor substrates 24. r2 The results of calculations regarding the relationship between the change in the dielectric constant ε of the semiconductor substrate 24 are shown below. r1 When is 12.4, the dielectric constant ε r1 The calculation was performed for 205 when the dielectric constant ε of the dielectric spacer layer 22 was 6. r2 By increasing the value of , a shift of the resonance peak position to lower frequencies is observed. The shift change is proportional to the relative dielectric constant ε r1 The smaller the value of the substrate, the larger the

[0080] 6, no resonant peaks are observed upon removal of metamaterial layer 21 or replacement of the material of spacer layer 22 with the material of substrate 24. Thus, metamaterial layer 21 and spacer layer 22 are necessary for the generation of the resonant peaks and absorption of the transmitted EM waves.

[0081] The shift in the resonance peak shown in FIG. 7 is due to the transmission of an electric field E through a waveguide having a metamaterial layer 21 disposed at the interface of two dielectric materials with different dielectric constants.

[0082] To explain the shift of the resonant peak, first consider the interface between two dissimilar dielectric materials under an electric field. For an EM wave propagating in a waveguide, the electric field E is oriented perpendicular to the upper and lower metal layers, generating an electric flux density D. The electric flux density vector D is defined by equation (11).

[0083]

number

[0084] Here, ε is the relative dielectric constant (dielectric constant) of the dielectric film, and E is the electric field vector.

[0085] When the interface between the substrate 24 and the spacer layer 22 is composed of two materials with different dielectric constants, a change in the electric field E occurs at the transmission across the dielectric boundary.

[0086] The electric flux vector D at normal incidence is continuous across the dielectric boundary, resulting in a discontinuity in the resultant electric field E related to the dielectric constant. The resultant electric field E is a continuous tangential electric field (E T ) field mode and the vertical component of the electric field E(E N ) can be separated into

[0087] Electric field E T Since the direction of is in the plane of the metamaterial cell 211, resonance is induced in the metamaterial gap.

[0088] Furthermore, the tangential electric field E T Since the occurrence of modes of ε strongly depends on the change in dielectric constant and the propagation of the electric field E in these dielectrics, r1 and ε r2 A resonance shift due to the difference between

[0089] It is also observed that the larger the difference in the dielectric constants, the larger the difference in the electric field propagation and the larger the change in the direction of the electric field vector E, resulting in a stronger tangential electric field component. This results in an increase in the intensity of the resonance peak and stronger absorption.

[0090] In Fig. 8, r1 The relative dielectric constant (ε r2 ) dependence of the dielectric constant ε r2 is about 12.4, that is, the relative dielectric constant ε r1 In other words, when the relative dielectric constant ε of the substrate 24 is approximately equal to r1 and the relative dielectric constant ε of the spacer layer 22 r2 The larger the difference, the higher the observed peak intensity.

[0091] For example, the relative dielectric constant ε r1is 12.4, while the relative dielectric constant ε r2 is about 1 to 10 or about 15 to 20, and the peak intensity is high. r1 and the relative dielectric constant ε of the spacer layer 22 r2 When the difference between these is between 2 and 11, the resonance peak strength is high.

[0092] Thus, when the materials of the substrate 24 and the spacer layer 22 are the same or similar, the occurrence of tangential electric modes is limited and resonances in the metamaterial layer 21 are not induced due to the lack of a well-established dielectric interface.

[0093] Thus, by designing the dielectric interfaces, the shift of the resonance peak in the coplanar waveguide 2 can be predicted and additional tuning of the metamaterial absorber 20 can be easily performed to exhibit broadband absorption in the required frequency range.

[0094] <First Example> As a first embodiment of the present invention, an example in which the metamaterial absorber 10 according to the first embodiment is applied to an InP substrate coplanar waveguide intended for a high-speed IC will be described.

[0095] In the simulated device, the dielectric constant of the InP substrate 14 is ε r1 = 12.4, and the thickness of the substrate 14 is t s = 55 μm. The InP substrate parameters and its thickness are based on values ​​used in real InP high-speed ICs. The top layer of the coplanar waveguide is a 2 μm thick gold film. The dimensions of the waveguide are determined by the total size of the metamaterial absorber 10 (3 × 7 cells) placed on the backside of the substrate 14, and are equal to 1.89 mm in length and 0.81 mm in width.

[0096] The metamaterial absorber 10 is disposed on the backside of an InP substrate 14. The metamaterial layer 11 is made of a 200 nm thick gold thin film. The parameters of the ASR cell 111 are the radius of each section 112: l1=0.126 mm, l2=0.116 mm, l3=0.129 mm, and l4=0.119 mm. The width w=0.045 mm, gap size g=0.018 mm, and cell period size a=0.27 mm. The parameters are adjusted to obtain broadband absorption at 300 GHz. The spacer layer 12 has a ε r2 A silicon nitride film of 100 nm thickness is formed on the bottom surface of the spacer layer 12. The thickness of the material is sufficient to block all transmission for electromagnetic waves with frequencies above 150 GHz.

[0097] The effects of this embodiment will be described below. Fig. 9 shows the results of calculations of the electromagnetic wave modes propagating through the coplanar waveguide in this embodiment for an InP / SiN waveguide 301 without a metamaterial layer, an InP / SiN waveguide 302 with a metamaterial layer 11, and an InP / InP waveguide 303 with a metamaterial layer 11. The left side of the figure shows the electric field mode, and the right side shows the magnetic field mode.

[0098] 9, the electromagnetic wave mode propagating through the coplanar waveguide 302 in this embodiment is largely absorbed. The electromagnetic wave passes through the coplanar waveguide having the metamaterial absorber 10 on the back surface and is gradually absorbed. No absorption of the electromagnetic wave mode is observed in the case where there is no metamaterial layer 301 or in the case where the same dielectric material is used for the spacer layer 12 303.

[0099] According to this embodiment, the trade-off between good suppression of substrate resonance and ground bounce on the one hand and complex multi-step processing and smaller packaging of IC circuit elements on the other hand can be mitigated.

[0100] In this way, according to this embodiment, good suppression of electromagnetic wave modes can be achieved through a simple process without forming TSVs, so that the mechanical strength of the substrate is increased and higher cost-effectiveness is achieved. In addition, since TSVs are not required, the layout design is simplified and the mounting level of high-speed ICs can be significantly improved.

[0101] Moreover, different parts of the metamaterial absorber 10 can be freely tuned by varying the materials in each layer, the design of the metamaterial cells, and the thickness of each layer, so that it can be tailored for various frequency ranges and different material-based high-speed IC circuits.

[0102] <Second Example> In the electromagnetic wave absorber according to the second embodiment of the present invention, an active metamaterial absorber is used as the metamaterial absorber, instead of the passive absorber used in the first embodiment.

[0103] Resonance occurs when the electric field E of an incident electromagnetic wave is localized parallel to the gap of a metamaterial cell, and the gap acts as an equivalent capacitance according to equation (2).

[0104] Therefore, by adding a variable capacitor diode (varactor) or transistor as a controllable variable capacitance in the gap region between the sections of the metamaterial cell, the resonant frequency of the metamaterial can be changed and actively tuned.

[0105] As shown in Fig. 10, in the metamaterial absorber according to this embodiment, the high absorption of the electromagnetic wave mode is shifted towards different frequency ranges. The change of the lumped capacitance value C in the metamaterial absorber from 0fF to 5fF shifts the broadband absorption peak to lower frequencies. The center frequency of the metamaterial cell shifts from 300 GHz when C is 0fF to 265 GHz when C is 5fF.

[0106] Furthermore, the absorption band for 90% or more absorption is reduced from 30 GHz when C is 0 fF to about 20 GHz when C is 5 fF. In this embodiment, since the absorption peak can only be shifted to a lower frequency, once the maximum operating frequency is determined for the passive metamaterial absorber structure, the resonant frequency can be actively adjusted in the frequency range below the maximum operating frequency.

[0107] Active control of the absorption characteristics is achieved by controlling the bias voltage applied to the active components, so that when high-speed ICs are capable of operating at a wide range of frequencies over a wide bandwidth, the active metamaterial absorber can be tuned to suppress the resonant substrate modes that arise.

[0108] This embodiment provides similar advantages to the first embodiment, while increasing the degree of freedom of operation through application of a single design, and improving the cost-effectiveness of manufacturing a single IC and metamaterial absorber that operates over a wider frequency range.

[0109] <Third Example> In the electromagnetic wave absorber according to the third embodiment of the present invention, the metamaterial absorber is modified to increase the absorption of substrate resonant modes in an IC chip. A single cell of the metamaterial absorber can absorb up to 100% of the EM incident radiation of a certain wavelength, depending on the geometry of the resonant metamaterial cell. Thus, the broadband properties of the metamaterial absorber are increased by the combination of ASR cells (unit cells) of different sizes.

[0110] FIG. 11 shows a coplanar waveguide 40 equipped with an electromagnetic wave absorber according to this embodiment. In the electromagnetic wave absorber according to this embodiment, an assembly (group) 41 of metamaterial cells tuned to slightly different resonant frequencies is connected. Since the metamaterial absorber 10 is formed on the entire back surface of the chip, the propagating EM waves are almost completely absorbed in a certain optimized frequency range. By gradually changing the size (characteristic size, e.g., g, w, l1 to l4 in FIG. 2A) of the geometric shape of the metamaterial of each group (first group to nth group) 41_1 to 41_n, the resonant frequency f RiSmall shifts of (i = 1 to n) are obtained, resulting in broadband absorption characteristics.

[0111] Thus, in this embodiment, an ensemble of metamaterial cells with different characteristic sizes is arranged to form adjacent lines of metamaterial ensembles with shifted resonant frequencies, which increases the absorption bandwidth since the propagating EM wave mode is absorbed over a broad frequency range (one or more frequencies).

[0112] The metamaterial absorber according to this embodiment has the same effects as the first embodiment, and can operate in a wider frequency range.

[0113] <Fourth Example> An electromagnetic wave absorber according to a fourth embodiment of the present invention includes an ASR structure having different resonant frequencies, and has a multi-layer laminate structure including symmetric metamaterial cells.

[0114] This configuration combines the absorption characteristics of each metamaterial cell or collection of metamaterial cells to increase the bandwidth of the absorption characteristics, i.e., improves broadband absorption of substrate resonant modes in the IC.

[0115] The metamaterial absorber achieves even broader bandwidth absorption through the synergistic effect of the characteristics of the ASR structure and the multilayer structure of the metamaterial cells.

[0116] The metamaterial absorber according to this embodiment has the same effects as the first embodiment, and can operate in a wider frequency range.

[0117] In the embodiment of the present invention, the structure, dimensions, materials, etc. of each component in the configuration of the absorbent body and the manufacturing method thereof are shown as examples, but the present invention is not limited to these. Anything that can exert the function and effect of the absorbent body may be used. [Industrial Applicability]

[0118] The present invention can be applied to high frequency integrated circuits. [Explanation of symbols]

[0119] 10 Electromagnetic wave absorber 11 Metamaterial layer 12 Spacer layer 13 Reflective thin film 14 Substrate

Claims

1. An electromagnetic wave absorber disposed on a substrate, a metamaterial layer, a spacer layer, and a reflective thin film, Absorbing and suppressing resonant modes of electromagnetic waves within the substrate; The metamaterial layer comprises a plurality of subwavelength structure metamaterial cells; the metamaterial cells are arranged periodically and designed to resonate at a predetermined frequency; An electromagnetic wave absorber, characterized in that the structure and period of the metamaterial cells are determined by the wavelength of the incident electromagnetic wave.

2. the metamaterial cell is composed of a plurality of sections having different characteristic sizes; The plurality of sections are asymmetrically arranged 2. The electromagnetic wave absorber according to claim 1 .

3. An electromagnetic wave absorber disposed on a substrate, comprising: a metamaterial layer, a spacer layer, and a reflective thin film, Absorbing and suppressing resonant modes of electromagnetic waves within the substrate; The effective permittivity and permeability of the metamaterial layer are adjusted to match the impedance of the metamaterial layer to the impedance of the substrate and to absorb resonant modes of the electromagnetic wave. Electromagnetic wave absorber characterized by:

4. An electromagnetic wave absorber disposed on a substrate, comprising: a metamaterial layer, a spacer layer, and a reflective thin film, Absorbing and suppressing resonant modes of electromagnetic waves within the substrate; The difference between the dielectric constant of the spacer layer and the dielectric constant of the substrate is 2 or more and 11 or less. Electromagnetic wave absorber characterized by:

5. An electromagnetic wave absorber disposed on a substrate, comprising: a metamaterial layer, a spacer layer, and a reflective thin film, Absorbing and suppressing resonant modes of electromagnetic waves within the substrate; The electromagnetic waves originate from within the substrate of a high-speed electronic circuit. Electromagnetic wave absorber characterized by:

6. the metamaterial layer couples to an electric component of the electromagnetic wave; The spacer layer and the reflective thin film couple to the magnetic component of the electromagnetic wave.

6. The electromagnetic wave absorber according to claim 1, wherein the first and second electrodes are made of a material selected from the group consisting of fluororesin and fluororesin.

7. The reflective film is thicker than the skin depth of the electromagnetic wave.

7. The electromagnetic wave absorber according to claim 1, wherein the first and second electrodes are made of a material selected from the group consisting of fluororesin and fluororesin.

8. The electromagnetic wave absorber according to any one of claims 1 to 7. A high speed electronic circuit comprising:

Images