WO2022153388A1

WO2022153388A1 - Electromagnetic wave absorber

Info

Publication number: WO2022153388A1
Application number: PCT/JP2021/000805
Authority: WO
Inventors: アダムパンダー; 裕史濱田
Original assignee: 日本電信電話株式会社
Priority date: 2021-01-13
Filing date: 2021-01-13
Publication date: 2022-07-21
Also published as: JPWO2022153388A1

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

Electromagnetic wave absorber

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.

In high frequency integrated circuit (IC) technology, if the operating speed exceeds 1/10 GHz, two adverse effects will appear. In the first effect, the feedback circuit with parasitic inductance and capacitance induces vibration, causing instability of the ground potential of the high frequency IC called ground bounce. Grand bounce causes peaks and dips in the signal response, degrading group delay. The second effect is the substrate resonance starting at the millimeter wave bandwidth. When the wavelength of the signal propagating in the IC approaches the size of the chip, an additional electromagnetic (EM) wave mode is easily radiated to the substrate, causing oscillation and deterioration of circuit operation due to energy distribution of the EM wave signal.

In order to minimize the effects of ground bounce and substrate resonance and ensure stable operation of the high-speed IC at submillimeter wavelengths, as shown in FIG. 12, the substrate 51 is made thinner and the high-density substrate is placed on the back surface of the IC chip 5. A through-substrate via (TSV) system is formed.

The ground bounce is suppressed by connecting the ground plane in the IC chip to the ground 53 of the module using a via 52 or a bonding wire. Substrate resonance is blocked by thinning the substrate and forming high density ground vias through the substrate. The thickness of the thinned substrate, the diameter of the TSV, and the density of the TSV depend on the operating frequency of the IC circuit.

In a commonly used metallized via system, the resistivity per unit area between the front surface and the back surface must be minimized in order to stabilize the ground potential of the IC chip. A smaller resistivity can be obtained by reducing the diameter of the vias, reducing the spacing between the vias, and reducing the thickness of the substrate. Also, small vias are advantageous for improving the layout flexibility and packaging level of the IC.

In general, an absorbent material can be added to the IC chip instead of the high density TSV system in order to suppress the effects of ground bounce and substrate resonance and absorb the EM wave mode propagating through the substrate of the IC chip. Absorbers can effectively absorb or eliminate unwanted electromagnetic radiation or scattering and have potential in radar stealth techniques, EM shielding, and energy harvesting.

However, since the conventional absorber has a large thickness and weight, it is practically difficult to use it in a small IC chip for high-frequency electronic devices.

As described above, in order to suppress the substrate resonance and ground bounce generated in the high-speed IC, it is necessary to reduce the thickness of the substrate and prepare a high-density TSV on the back surface of the substrate.

However, the thinning of the substrate and the formation of the TSV system have the following problems with respect to the manufacture and design of the IC layout.

First, since the manufacture of the TSV system requires etching through the substrate, it is necessary to consider the mounting of the TSV on the back surface of the IC chip in the design of the IC layout. Since the size of the individual electrical components on the chip is much smaller than the diameter of the individual TSVs, the chip size must be significantly increased and at the same time the packaging level of the IC chip must be reduced.

Second, the production of TSV involves mounting an IC chip on a glass substrate using an epoxy adhesive, thinning the substrate using a polishing method, forming vias using reactive ion etching, and the back surface of the substrate. And requires a multi-step process that includes internal metallization of the via. This complex multi-step process significantly increases the cost and time of manufacturing high speed IC chips.

Third, precise control of the diameter of the via hole is required to fabricate the TSV system. This is important for suppressing unwanted EM wave modes. Here, in order to accurately control the TSV diameter, very high etching selectivity is required in the ion reactive etching process.

Fourth, since adhesives commonly used for mounting IC chips on glass deteriorate at high temperatures, it is essential to control the substrate temperature during the ion-reactive etching process, which must be taken into consideration. It doesn't become. In this case, the adhesive deteriorates, the thin IC chip after the back surface processing cannot be smoothly removed from the glass, and the thin IC chip is easily broken by mechanical stress.

Fifth, when the diameter of the TSV decreases, the etching rate decreases due to the microloading effect, which becomes remarkable in the submillimeter wave. Therefore, as the operating frequency range increases, it becomes essential to adjust the etching parameters, and the overall manufacturing time increases.

Sixth, after forming the TSV, it is necessary to metallize the back surface of the substrate and the inside of the via. Typically, electroplated metal with a thickness of a few micrometers is treated by reactive ion etching to remove unrelated seed layers.

As described above, in suppressing substrate resonance and ground bounce generated in high-speed ICs, problems in IC chip layout design and TSV fabrication are required for reducing the substrate thickness and producing high-density TSVs on the back surface of the substrate. There is.

In order to solve the above-mentioned problems, the electromagnetic wave absorber according to the present invention is an electromagnetic wave absorber arranged on a substrate, and is provided with a metamaterial layer, a spacer layer, and a reflective thin film in this order. It is characterized by absorbing and suppressing the resonance mode of electromagnetic waves in the substrate.

According to the present invention, it is possible to provide a small electromagnetic wave absorber that does not require a complicated manufacturing process.

FIG. 1 is a schematic cross-sectional view of a semiconductor substrate for a high-speed electronic circuit including an electromagnetic wave absorber according to the first embodiment of the present invention. FIG. 2A is a top view showing the configuration of the electromagnetic wave absorber according to the first embodiment of the present invention. FIG. 2B is a top schematic showing the configuration of the electromagnetic wave absorber according to the first embodiment of the present invention. FIG. 2C is a top view showing the configuration of the electromagnetic wave absorber according to the first embodiment of the present invention. FIG. 3 is a bird's-eye view showing the configuration of a semiconductor substrate for a high-speed electronic circuit including an electromagnetic wave absorber according to the first embodiment of the present invention. FIG. 4A is a diagram for explaining the characteristics of the electromagnetic wave absorber according to the first embodiment of the present invention. FIG. 4B is a diagram for explaining the characteristics of the electromagnetic wave absorber according to the first embodiment of the present invention. FIG. 5 is a bird's-eye view showing the configuration of the Coplanar waveguide provided with the electromagnetic wave absorber according to the first embodiment of the present invention. FIG. 6 is a diagram for explaining the characteristics of the electromagnetic wave absorber according to the first embodiment of the present invention. FIG. 7 is a diagram for explaining the characteristics of the electromagnetic wave absorber according to the first embodiment of the present invention. FIG. 8 is a diagram for explaining the characteristics of the electromagnetic wave absorber according to the first embodiment of the present invention. FIG. 9 is a diagram for explaining the characteristics of the electromagnetic wave absorber according to the first embodiment of the present invention. FIG. 10 is a diagram for explaining the characteristics of the electromagnetic wave absorber according to the second embodiment of the present invention. FIG. 11 is a bird's-eye view showing the configuration of the Coplanar waveguide provided with the electromagnetic wave absorber according to the third embodiment of the present invention. FIG. 12 is a schematic cross-sectional view of a conventional semiconductor substrate for a high-speed electronic circuit.

<First Embodiment>
The electromagnetic wave absorber according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 8.

<Structure 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. It should be noted that this description provides some detailed examples of possible implementations of the invention, but these details are exemplary and do not limit the scope of the invention.

Metamaterials are artificial media that obtain their properties from embedded sub-wavelength structures that are arranged together in the same arrangement as atoms in ordinary materials, and obtain the desired values of permittivity and permeability in the measured frequency range. Show and manipulate electromagnetic (EM) waves. The electromagnetic properties of metamaterials are due to the dimensions, geometry, orientation and arrangement of the periodic structures of the circuit, as well as the material consisting of those structures.

With accurate 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 cell. A typical structure of an electromagnetic wave absorber is a three-layer structure, the three-layer structure having an array of metal sub-wavelength structures on the front surface of a dielectric spacer and a metal grounding layer on the back surface. Here, the metamaterial periodic structure on the front surface is involved in the electrical resonance response of the metamaterial absorber 10, and the coupling between the metal layer and the dielectric spacer layer on the back surface determines the magnetic resonance response. Hereinafter, the "electromagnetic wave absorber" is also referred to as a "metamaterial absorber".

FIG. 1 shows a cross section of a semiconductor substrate for a high-speed electronic circuit including the electromagnetic wave absorber 10 according to the present embodiment. The electromagnetic wave absorber 10 has a three-layer structure using a metamaterial, and has a metamaterial layer 11 having a sub-wavelength metamaterial cell 111 periodically arranged on the back surface of a high-speed IC chip substrate 14, and an intermediate spacer layer 12. And the reflective thin film 13 of the lower layer. Here, the electromagnetic wave generation source is provided in the substrate of the high-speed electronic circuit.

The sub-wavelength metamaterial cell 111 is designed to resonate at a predetermined frequency.

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.

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 with reference to the relative permittivity (dielectric constant) in order to enhance the absorption of electromagnetic waves by the metamaterial absorber 10.

The lower reflective thin film 13 is composed of a metal, a metal alloy, and a compound thicker than the skin depth of the target radiation (incident electromagnetic wave) in order to block the transmission of the incident electromagnetic wave. The minimum thickness of the reflective thin film 13 can be obtained from the calculation of the epidermis depth δ.

ρ is the resistivity of the material used, μ ₀ is the transmittance in free space (μ ₀ = 4π ・^10-7 ), μ _r is the relative transmittance of the material used (usually equal to 1), and f ₀ is the EM wave. Frequency. For example, when a gold thin film having ρ = 2.24 μΩ · cm and μ _r = 1 is used at a frequency of 300 GHz, the skin depth is 0.138 μm. Therefore, the underlying reflective thin film 13 must be thicker than this value.

FIG. 2A-C shows an example of a metamaterial cell (unit cell) in the electromagnetic wave absorber 10 according to the present embodiment. Generally, in this embodiment, the metamaterial cell 111 is composed of one layer of so-called asymmetric sectional resonator (ASR) structures having various shapes.

For example, the ASR is composed of four sections 112 with different characteristic sizes indicated by A1, A2, A3, and A4, and these sections 112 are combined to form a new metamaterial cell (unit cell) 111. .. Here, the characteristic size of each section 112 is, for example, the width w, the gap _g , the outer peripheral length li, etc. of each section 112, and is related to the respective resonance frequencies.

For example, in FIGS. 2A and 2C, a material (metal or the like) having a circular shape (ring or square or rectangle) having a width w is divided into four sections 112, and each section 112 has a gap (gap) g between its end faces. Placed in. At this time, the distances (outer circumference lengths) li ( _l ₁ to l ₄ ) from the center of the metamaterial cell (hereinafter, also referred to as “ASR cell”) 111 to the outer circumference of each section 112 are arranged so as to be different. Here, the width w and the gap g of each section 112 are the same. Further, the center of the ASR cell 111 is an intersection of lines connecting the centers of the outer circumferences of the sections 112 facing each other in the cell 111.

Further, in FIG. 2B, a material (metal or the like) having a circular shape (square or rectangle) having a width w is divided into four sections 112, and each section 112 is arranged at a gap (gap) g between the end faces thereof. .. At this time, the distances (outer circumference lengths) li ( _l ₁ to l ₄ ) from the substantially center line of the ASR cell 111 to the outer circumference of each section 112 are arranged so as to be different. Here, the width w and the gap g of each section 112 are the same. Further, the substantially center line of the ASR cell 111 is a straight line parallel to any one outer circumference and passing through two opposing distances g.

As described above, the outer peripheral length _li of each section 112 has a slight difference, forming an asymmetric ASR cell 111.

Here, the width w and the gap g do not have to be the same. Further, it does not have to be four sections, but may be a plurality of sections.

Further, although an example in which the asymmetric ASR cell 111 is formed by the difference in the outer peripheral length li of each section 112 is shown, the asymmetric ASR cell 111 may be formed by the difference in the width _w and the gap g of each section 112. good.

In the present embodiment, the metamaterial cell 111 is composed of a plurality of sections 112, and the material having a shape in which each section 112 orbits is divided, and the characteristic size (width w, gap g,) of each section 112 is divided. The ASR cell 111 may be configured by the difference in the outer peripheral length _li ), and as a result, the resonance frequency of each section 112 of the ASR cell 111 may be slightly different.

Here, the size of the ASR cell 111 may be 1/2 or less of the target radiation (incident electromagnetic wave). The characteristic size of each section 112 and the difference thereof may be set within a range satisfying the size of the 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.

The resonance frequencies of each section 112 of the ASR cell 111 have slightly different values, and when combined, a wider band absorption characteristic is generated, which is very advantageous for absorption of various EM wave modes generated by a high-speed IC.

First, the shape, dimensions, period of the cells 111, and placement style of the ASR metamaterial cells 111 shown in FIGS. 2A-C are adjusted to achieve the desired resonance frequency range. The resonance frequency f _R of the metamaterial can be expressed by the equation (2).

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

Here, w is the width of the resonant element, ε ₀ and μ ₀ are the permittivity and magnetic permeability of the free space, _li is the external dimension (length) of the section resonator, and a and b are numerical values. It is a factor. ε _r is the relative permittivity (permittivity), and h is the thickness of the dielectric spacer layer.

When the material of the dielectric spacer 12 is selected, the gap between the section 112 of the ASR structure and the width w of each section 112 is also determined from the equations (2) to (4), and the resonance frequency of the ASR metamaterial is determined. Is proportional to the size of the section resonator associated with the outer length _li of each section 112, as shown in equation (5).

By changing the geometric shape of the ASR structure and the thickness of the dielectric spacer 12, the effective permittivity ε and magnetic permeability μ of the metamaterial absorber 10 can be adjusted independently, and the impedance matches with the substrate 14 of the high-speed electric circuit. do. When the EM radiation enters the ASR structure, the metamaterial absorber 10 absorbs the EM wave mode due to coupling resonance. In the metamaterial absorber 10, the metamaterial layer 11 has a structure that is strongly bonded to the electric component of the EM wave, but the combination of the spacer layer 12 and the reflective thin film 13 is strongly bonded to the magnetic component of the EM wave.

FIG. 3 shows an example of a metamaterial cell (unit cell) obtained by simulation in the present embodiment. The metamaterial cell (unit cell) 111 is adjusted to 300 GHz, and a circular ASR metamaterial cell is used. Further, an indium phosphide (InP) substrate having a thick dielectric constant ε _r1 of 12.4 and a dielectric spacer layer having a dielectric constant ε _r2 of 8 and a thickness of 12.5 μm are used.

In FIG. 3, the metamaterial absorber 10 is placed beneath the thick semiconductor substrate 14 to allow direct transmission of incident EM waves between the substrate 14 and the metamaterial absorber 10. In the simulation of the metamaterial cell 111, a time domain solver was used with vertical incidence and appropriate periodic boundary conditions, and the electrical component of the EM wave along the x-axis was used.

The reflection R (ω) and transmission T (ω) of the metamaterial cell 111 can be calculated by Eqs. (6) and (7), respectively, from the S parameters depending on the extraction frequency.

Here, S ₁₁ (ω) is a reflection coefficient, and S ₂₁ (ω) is a transmission coefficient.

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

Since the transmission is removed by the reflective thin film 13 thicker than the skin depth δ shown in the formula (1) and the transmission value in the entire measured frequency range is 0, the formula (8) representing absorption is the formula (9). ) Simplifies.

FIG. 4A shows an example of simulation of the absorption spectrum of the metamaterial absorber 10 at a frequency of 300 GHz. Here, the absorption was calculated according to the equation (9) from the extraction reflectance coefficient S ₁₁ (ω) obtained from the simulation shown in FIG.

The optimized absorber has a wideband absorption of 30 GHz and is observed between 285 GHz and 315 GHz. Here, the wideband absorption width (30 GHz) was measured as a bandwidth for absorption of 90% or more, similarly to a normal wideband absorber. Moreover, due to the nearly symmetrical design of the ASR cell 111, the absorption obtained by the simulation showed similar absorption for both the lateral electrical (TE) 102 and the lateral magnetic (TM) 101 polarization modes.

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 according to the equation (10) with S ₂₁ (ω) = 0 based on the extraction reflectance coefficient S ₁₁ (ω) obtained from the simulation of FIG.

In FIG. 4B, the real part Re (z) 103 of the relative impedance is about 1 and the imaginary part Im (z) 104 is about 0 on average in the broadband frequency range observed in FIG. 4A. When good impedance matching is obtained, Z _in (ω) = Z _S = 1, so that the input impedance (Z _in ) of the metamaterial absorber 10 according to the present embodiment is the substrate 14 in the wide band frequency range. It almost matches the impedance (Z _S ) of. Therefore, the absorption rate of the metamaterial absorber 10 according to the present embodiment is approximately 100%.

As shown in FIG. 5, the Coplanar waveguide 20 having the metamaterial absorber 10 on the back surface is used to evaluate the optimized metamaterial cell shown in FIG. 3 in a more practical state.

Typically, the structure of the coplanar waveguide 2 has

waveguide ports

25 and 26 at one end and the other end of the waveguide 20, respectively, from the surface metal layer and the bottom ground layer. It is composed. In the Coplanar waveguide 2, the propagation direction of the electromagnetic radiation is different from the simulation of the metamaterial cell 111 because it is from the first waveguide port 25 to the second waveguide port 26. To test the metamaterial absorber 10, the bottom ground 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. Further, a reflective thin film 23 is added to the back surface (the lowest layer of the Coplanar waveguide 20). The reflective thin film 23 also serves as a grounding layer for the Coplanar waveguide 20.

<Characteristics of electromagnetic wave absorber>
FIG. 6 shows the frequency dependent transmission coefficient S ₂₁ (ω) in three different Coplanar waveguide structures. In the first case 201, the Coplanar waveguide 2 comprises an optimized structure of the metamaterial absorber 20. In the second case 202, the metamaterial layer 21 is removed from the absorber 20 and has 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, and the case where the metamaterial layer 21 is included in the semiconductor substrate 24 is simulated.

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 region.

In the second case 202, the absorber without the metamaterial layer does not affect the transmission of the EM wave mode. Therefore, typical EM wave Coplanar waveguide transmission occurs with minimal loss.

In the third case 203, since the flat transmission characteristics were observed in the measured frequency range, the metamaterial absorber in which the dielectric spacer layer 22 was replaced with the same material as the substrate 24 (InP in the present embodiment) was used. Does not absorb EM wave mode.

The effects on the operation of the optimized metamaterial absorber structure will be explained below.

In the Coplanar waveguide 2, the orientation of the electric field toward the metamaterial cell 211 is different from the simulated single metamaterial cell 111 shown in FIG. In the single metamaterial cell 111 shown in FIG. 3, since the electric field vector E is parallel to the surface of the metamaterial absorber 10, LC resonance is easily induced in the gap of the ASR structure.

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

Normally, when the electric field vector E is oriented vertically toward the surface of the metamaterial, the vertical electric field E (the electric field having the electric field vector E) cannot be coupled to the metamaterial gap, so that resonance does not occur. However, as shown in FIG. 6, the occurrence of resonance is observed due to a small additional frequency shift.

Further, in the above-mentioned third case, the occurrence of resonance is suppressed by using the same material as the substrate 24 for the dielectric spacer 22 even though the same metamaterial layer 21 is included.

As described above, in the Coplanar waveguide 2 in the present embodiment, the occurrence of resonance of the metamaterial absorber 20 is affected by additional factors.

From equations (3) and (4), since the resonance frequency is proportional to the relative permittivity ε _r of the substrate 24, it is possible to clearly obtain the shift of the resonance peak in various substrates 24 having different relative permittivity values. can.

FIG. 7 shows the calculation results regarding the relationship between the position of the resonance peak of the metamaterial layer 21 and the change in the relative permittivity ε _r2 of the dielectric spacer layer 12 in the two different high-speed IC semiconductor substrates 24. Calculations were made for 204 when the dielectric constant ε _r1 of the semiconductor substrate 24 was 12.4 and 205 when the dielectric constant ε _r1 was 6. In the case of both of the two substrates, a shift of the resonance peak position to a lower frequency is observed by increasing the value of the relative permittivity ε _r2 of the dielectric spacer layer 22. The shift change is larger as the value of the relative permittivity ε _r1 is smaller.

In the results shown in FIG. 6, no resonance peak is observed due to the removal of the metamaterial layer 21 or the replacement of the spacer layer 22 with the substrate 24 material. Therefore, the metamaterial layer 21 and the spacer layer 22 are required for the generation of the resonance peak and the absorption of the transmitted EM wave.

The shift of the resonance peak shown in FIG. 7 is caused by the electric field E passing through the waveguide having the metamaterial layer 21 arranged at the interface between the two dielectric materials having different dielectric constants.

To explain the shift of the resonance peak, first consider the interface between two different dielectrics under an electric field. For the EM wave propagating in the waveguide, the electric field E is oriented perpendicular to the upper and lower metal layers to generate the electric flux density D. The electric flux density vector D is defined by the equation (11).

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

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

Since the electrical flux vector D at vertical incidence is continuous across the dielectric boundary, there is a discontinuity in the combined electric field E related to the permittivity, and the combined electric field E is parallel to the horizontal plane or interface of the waveguide. It can be separated into an electric ( _ET ) field mode of continuous tangential components and an electric field E ( _EN ) of vertical components.

Since the direction of the electric field _ET is in the plane of the metamaterial cell 211, resonance in the metamaterial gap is induced.

Further, since the generation of the mode of the electric field _ET in the tangential direction strongly depends on the change of the permittivity and the propagation of the electric field E in these dielectrics, the resonance shift due to the difference between ε _r1 and ε _r2 is observed.

It is also observed that the larger the difference in permittivity, the larger the difference in electric field propagation, and the larger the change in the direction of the electric field vector E, and the stronger the electric field component in the tangential direction is generated. As a result, the intensity of the resonance peak increases and the absorption becomes stronger.

FIG. 8 shows the relative permittivity (ε _r2 ) dependence of the spacer layer 22 of the resonance peak intensity on the substrate (ε _r1 = 12.4) 24. When the relative permittivity ε _r2 of the spacer layer 22 is about 12.4, that is, about the same as the relative permittivity ε _r1 of the substrate 24, the resonance peak intensity shows the minimum value. In other words, the larger the difference between the relative permittivity ε _r1 of the substrate 24 and the relative permittivity ε _r2 of the spacer layer 22, the higher the peak intensity is observed.

For example, the relative permittivity ε _r1 of the substrate 24 is 12.4, while the relative permittivity ε _r2 of the spacer layer 22 is about 1 to 10 or about 15 to 20, and the peak intensity is high. In other words, the difference between the relative permittivity ε _r1 of the substrate 24 and the relative permittivity ε _r2 of the spacer layer 22 is about 2 or more and 11 or less, and the resonance peak intensity is high.

Thus, when the materials of the substrate 24 and the spacer layer 22 are the same or similar, the occurrence of the tangential electrical mode is limited and resonance in the metamaterial layer 21 is induced because there is no well-established dielectric interface. Not done.

As described above, by designing the dielectric interface, the shift of the resonance peak in the Coplanar waveguide 2 can be predicted, and additional adjustment of the metamaterial absorber 20 is facilitated in order to exhibit wideband absorption in the required frequency range. Can be done.

<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 the InP substrate Coplanar waveguide assuming a high-speed IC will be described.

In the simulated device, the relative permittivity of the InP substrate 14 is ε _r1 = 12.4, and the thickness of the substrate 14 is _ts = 55 μm. The InP substrate parameters and their thickness are based on the values used in the actual InP high speed IC. The top layer of the Coplanar waveguide is a 2 μm thick gold thin film. The dimensions of the waveguide are determined by the total size of the metamaterial absorber 10 (3 x 7 cells) arranged on the back surface of the substrate 14, and are equal to 1.89 mm in length and 0.81 mm in width.

The metamaterial absorber 10 is arranged on the back surface of the InP substrate 14. The metamaterial layer 11 is composed of a gold thin film having a thickness of 200 nm. In the parameters of the ASR cell 111, the radii of each section 112 are l ₁ = 0.126 mm, l ₂ = 0.116 mm, l ₃ = 0.129 mm, l ₄ = 0.119 mm. The width w = 0.045 mm, the gap size g = 0.018 mm, and the cell cycle size a = 0.27 mm. The parameters are adjusted to obtain wideband absorption at 300 GHz. The spacer layer 12 is a silicon nitride film having ε _r2 = 8 and has a thickness of 12.5 μm. Finally, a gold thin film having a thickness of 200 nm is formed on the bottom surface of the spacer layer 12. The material is thick enough to block all transmissions for electromagnetic waves with frequencies above 150 GHz.

The effects of this embodiment will be described below. FIG. 9 shows the electromagnetic wave mode propagating in the Coplanar waveguide in this embodiment with the InP / SiN waveguide 301 having no metamaterial layer, the InP / SiN waveguide 302 having the metamaterial layer 11, and the metamaterial layer 11. The result of calculation for the included InP / InP waveguide 303 is shown. The electric field mode is shown on the left and the magnetic field mode is shown on the right.

As shown in FIG. 9, the electromagnetic wave mode propagating through the Coplanar waveguide 302 in this embodiment is largely absorbed. The electromagnetic waves pass through the Coplanar waveguide having the metamaterial absorber 10 on the back surface and are gradually absorbed. In the case where there is no metamaterial layer 301 and when the same dielectric material is used for the spacer layer 12, the absorption of the electromagnetic wave mode is not observed.

According to this embodiment, the trade-off between good suppression of substrate resonance and ground bounce and complex multi-step process of IC circuit elements and smaller packaging can be mitigated.

As described above, according to this embodiment, good suppression of the electromagnetic wave mode can be achieved by a simple process without forming a TSV, so that the mechanical strength of the substrate is increased and higher cost effectiveness is achieved. Further, since TSV is not required, the layout design becomes easy and the mounting level of the high-speed IC can be significantly increased.

Furthermore, different parts of the metamaterial absorber 10 can be freely adjusted by changing the material in each layer, designing the metamaterial cell, and the thickness of each layer, so that it can be used for various frequency ranges and different material-based high-speed IC circuits. Can be adjusted.

<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.

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

Therefore, by adding a variable capacitor diode (varicap) or a transistor as a controllable variable capacitance to the gap region between sections in the metamaterial cell, the resonance frequency of the metamaterial can be changed and actively adjusted.

As shown in FIG. 10, in the metamaterial absorber according to this embodiment, the high absorption of the electromagnetic wave mode is shifted toward a different frequency range. A change in the centralized capacitance value C from 0fF to 5fF in the material absorber shifts the wideband absorption peak to a lower frequency. The center frequency of the metamaterial cell shifts from 300 GHz when C is 0 fF to 265 GHz when C is 5 fF.

Furthermore, the absorption band for an absorption rate of 90% or more decreases from 30 GHz when C is 0 fF to about 20 GHz when C is 5 fF. In this embodiment, the absorption peak can be shifted only to a low frequency, so if the maximum operating frequency is determined for the passive metamaterial absorber structure, the resonance frequency is actively adjusted in the frequency range below the maximum operating frequency. can.

Since the active control of the absorption characteristics is achieved by the bias voltage control applied to the active component, when the high-speed IC can operate at various frequencies in a wide band, the active metamaterial absorber is adjusted to generate the resonance. The substrate mode can be suppressed.

According to this embodiment, a single IC and metamaterial absorber that operates in a wider frequency range while achieving the same effect as in the first embodiment and increasing the degree of freedom of operation by applying a single design. Improve the cost-effectiveness of manufacturing.

<Third Example>
In the electromagnetic wave absorber according to the third embodiment of the present invention, the metamaterial absorber is changed so as to increase the absorption of the substrate resonance mode in the IC chip. A single cell of a metamaterial absorber can absorb up to 100% of EM incident radiation of a wavelength, depending on the geometry of the resonant metamaterial cell. Therefore, the broadband properties of metamaterial absorbers are increased by the combination of different sized ASR cells (unit cells).

FIG. 11 shows the Coplanar waveguide 40 including the electromagnetic wave absorber according to the present embodiment. In the electromagnetic wave absorber according to the present embodiment, an aggregate (group) 41 of metamaterial cells adjusted to slightly different resonance frequencies is connected. Since the metamaterial absorber 10 is formed on the entire back surface of the chip, the propagating EM wave is almost completely absorbed in a certain optimized frequency range. By gradually changing the size of the geometric shape of the metamaterials of each group (groups 1 to n) 41_1 to 41_n (characteristic sizes, eg, g, w, l ₁ to l ₄ in FIG. 2A). , A small shift of resonance frequency f _Ri (i = 1 to n) is obtained. As a result, wideband absorption characteristics can be obtained.

As described above, in this embodiment, aggregates of metamaterial cells having different characteristic sizes are arranged, and adjacent lines of metamaterial aggregates having shifted resonance frequencies are formed. This configuration increases the absorption bandwidth because the propagating EM wave mode is absorbed over a wide frequency range (one or more frequencies).

The metamaterial absorber according to this embodiment has the same effect as that of the first embodiment and can operate in a wider frequency range.

<Fourth Example>
The electromagnetic wave absorber according to the fourth embodiment of the present invention includes an ASR structure having different resonance frequencies, and has a multi-layered laminated structure including a symmetric metamaterial cell.

With this configuration, the absorption characteristics of each metamaterial cell or aggregate of metamaterial cells are combined, and the bandwidth of the absorption characteristics increases. That is, the wideband absorption of the substrate resonance mode in the IC is improved.

The metamaterial absorber realizes further wideband absorption by the synergistic effect of the characteristics of the ASR structure and the characteristics of the multi-layer structure of the metamaterial cell.

In the embodiment of the present invention, examples of the structure, dimensions, materials, etc. of each component are shown in the structure of the absorber, the manufacturing method, and the like, but the present invention is not limited to this. Anything that exerts the function of the absorber and exerts an effect may be used.

The present invention can be applied to high frequency integrated circuits.

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

Claims

An electromagnetic wave absorber placed on a substrate
A metamaterial layer, a spacer layer, and a reflective thin film are provided in this order.
An electromagnetic wave absorber that absorbs and suppresses the resonance mode of electromagnetic waves in the substrate.
The metamaterial layer includes metamaterial cells having a plurality of sub-wavelength structures.
The metamaterial cells are arranged periodically and designed to resonate at a predetermined frequency.
The electromagnetic wave absorber according to claim 1, wherein the structure and period of the metamaterial cell are determined by the wavelength of the incident electromagnetic wave.
The metamaterial cell is composed of a plurality of sections having different characteristic sizes.
The electromagnetic wave absorber according to claim 2, wherein the plurality of sections are arranged asymmetrically.
From claim 1, the effective dielectric constant and magnetic permeability of the metamaterial layer are adjusted so as to match the impedance of the metamaterial layer with the impedance of the substrate and absorb the resonance mode of the electromagnetic wave. The electromagnetic wave absorber according to any one of claim 3.
The metamaterial layer binds to the electrical component of the electromagnetic wave and
The electromagnetic wave absorber according to any one of claims 1 to 4, wherein the spacer layer and the reflective thin film are bonded to a magnetic component of the electromagnetic wave.
The electromagnetic wave absorber according to any one of claims 1 to 5, wherein the difference between the relative permittivity of the spacer layer and the relative permittivity of the substrate is 2 or more and 11 or less.
The electromagnetic wave absorber according to any one of claims 1 to 6, wherein the reflective thin film is thicker than the skin depth of the electromagnetic wave.
The electromagnetic wave absorber according to any one of claims 1 to 7, wherein the electromagnetic wave has a source in a substrate of a high-speed electronic circuit.
A high-speed electronic circuit comprising the electromagnetic wave absorber according to any one of claims 1 to 8.