Waveguide element

Abstract

To provide a waveguide element capable of sufficiently reducing propagation loss even when guiding a high-frequency electromagnetic wave whose frequency is 30 GHz or more.SOLUTION: A waveguide element 101 includes an inorganic material substrate 1, a conductor layer 2 provided on an upper part of the inorganic material substrate 1, a support substrate 7 located on the opposite side of the conductor layer 2 with respect to the inorganic material substrate 1, a first metal layer 3 located between the inorganic material substrate 1 and the support substrate 7, a second metal layer 4 located on the opposite side of the inorganic material substrate 1 with respect to the support substrate 7, and a plurality of through-substrate vias 5 that electrically connects the first metal layer 3 and the second metal layer 4. The conductor layer 2 includes a signal electrode 21 constituting a transmission line capable of propagating an electromagnetic wave. The first metal layer 3, the second metal layer 4, and the plurality of through-substrate vias 5 constitute substrate-integrated waveguides capable of propagating electromagnetic waves.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a waveguide element. [Background technology]

[0002] Waveguide elements are being developed as one type of element that guides millimeter waves to terahertz waves. Waveguide elements are expected to be applied and developed in a wide range of fields, such as optical waveguides, next-generation high-speed communications, sensors, laser processing, and solar power generation. As an example of such a waveguide element, a technology has been proposed that uses a microstrip antenna including a transparent substrate with a thickness of 2 mm, an antenna conductor provided on the transparent substrate, and a transparent conductive film provided on the surface of the transparent substrate opposite to the antenna conductor (Patent Document 1). When using waveguide elements based on such technology in various industrial products, mounting the waveguide element on a supporting substrate such as an IC substrate or a printed circuit board is considered. However, when mounting a waveguide element on a supporting substrate and guiding millimeter waves to terahertz waves (especially electromagnetic waves of 300 GHz or higher), there is a problem in that the propagation loss increases significantly. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 107514 Summary of the Invention [Problem to be solved by the invention]

[0004] A primary object of the present invention is to provide a waveguide element capable of sufficiently reducing propagation loss even when guiding high-frequency electromagnetic waves having frequencies of 30 GHz or higher. [Means for solving the problem]

[0005] [1] A waveguide element according to an embodiment of the present invention is capable of guiding an electromagnetic wave having a frequency of 30 GHz or more and 20 THz or less. The waveguide element includes an inorganic material substrate; a conductor layer provided on the inorganic material substrate; a support substrate located on the inorganic material substrate opposite the conductor layer; a first metal layer located between the inorganic material substrate and the support substrate; a second metal layer located on the support substrate opposite the inorganic material substrate; and a plurality of through-substrate vias electrically connecting the first metal layer and the second metal layer. The conductor layer includes a signal electrode extending in a predetermined direction and constituting a transmission line capable of propagating the electromagnetic wave. The first metal layer, the second metal layer, and the plurality of through-substrate vias constitute a substrate integrated waveguide capable of propagating the electromagnetic wave. The thickness t of the inorganic material substrate satisfies the following formula (1).

number

[10] In the waveguide element described in any one of [1] to [9] above, there may be no organic adhesive between the inorganic material substrate and the supporting substrate, and the inorganic material substrate and the supporting substrate may be directly bonded via the first metal layer. Effect of the Invention

[0006] According to the embodiments of the present invention, it is possible to realize a director element that can sufficiently reduce propagation loss even when guiding high-frequency electromagnetic waves having frequencies of 30 GHz or higher. [Brief description of the drawings]

[0007] [Figure 1] 1 is a schematic perspective view of a waveguide element according to an embodiment of the present invention; [Diagram 2] 2 is a cross-sectional view of the waveguide element of FIG. 1 along line II-II'. [Diagram 3] FIG. 2 is an exploded perspective view of the waveguide element of FIG. [Figure 4] 3 is a schematic cross-sectional view of the conductive pin of FIG. 2 covered with an insulating material. [Diagram 5] FIG. 2 is a schematic perspective view of a waveguide element according to another embodiment of the present invention. [Figure 6] 6 is a cross-sectional view of the waveguide element of FIG. 5 along the line VI-VI'. [Figure 7] 11 is a schematic cross-sectional view of a waveguide element according to yet another embodiment of the present invention. [Figure 8]11 is a schematic cross-sectional view of a waveguide element according to yet another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments. A. Overall configuration of the waveguide element FIG. 1 is a schematic perspective view of a waveguide element according to an embodiment of the present invention; FIG. 2 is a cross-sectional view of the waveguide element of FIG. 1 taken along line II-II'; and FIG. 3 is an exploded perspective view of the waveguide element of FIG. The illustrated waveguide element 101 can guide electromagnetic waves having a frequency of 30 GHz or more and 20 THz or less, in other words, millimeter waves to terahertz waves. Note that millimeter waves are typically electromagnetic waves having a frequency of about 30 GHz to 300 GHz, and terahertz waves are typically electromagnetic waves having a frequency of about 300 GHz to 20 THz. In particular, the waveguide element 101 can guide electromagnetic waves having a frequency of 30 GHz to 2 THz or less (particularly electromagnetic waves having a frequency of 30 GHz to 1 THz or less) with excellent propagation loss.

[0009] The waveguide element 101 comprises an inorganic material substrate 1, a conductor layer 2 having a signal electrode 21, a support substrate 7, a first metal layer 3, a second metal layer 4, and a plurality of through-substrate vias 5. The conductor layer 2 is provided on the inorganic material substrate 1. The signal electrode 21 extends in a predetermined direction (waveguiding direction). The signal electrode 21 constitutes a transmission line capable of propagating the above-mentioned electromagnetic wave. The support substrate 7 is located on the opposite side of the inorganic material substrate 1 to the conductor layer 2. The first metal layer 3 is located between the inorganic material substrate 1 and the support substrate 7. The second metal layer 4 is located on the opposite side of the support substrate 7 to the first metal layer 3. Each of the multiple through-substrate vias 5 electrically connects the first metal layer 3 and the second metal layer 4. The first metal layer 3, the second metal layer 4, and the multiple through-substrate vias 5 constitute a substrate integrated waveguide (SIW) capable of propagating the electromagnetic wave. The thickness t of the inorganic material substrate 1 satisfies the following formula (1).

number

[0010] In one embodiment, in the above formula (1), a represents a numerical value of 6 or more. When the thickness of the inorganic material substrate satisfies formula (1) in which a represents a numerical value of 6 or more, it is possible to stably reduce the propagation loss when guiding the above-mentioned high-frequency electromagnetic wave. The thickness of the inorganic material substrate 1 satisfying the above formula (1) is specifically 1 μm or more, preferably 2 μm or more, more preferably 10 μm or more, even more preferably 20 μm or more, and particularly preferably 31 μm or more, and is, for example, 1700 μm or less, preferably 500 μm or less, more preferably 200 μm or less, and even more preferably 100 μm or less. When the frequency of the electromagnetic wave propagating through the waveguide element is 30 GHz or more and 5 THz or less, the thickness of the inorganic material substrate 1 is preferably 10 μm or more. If the thickness of the inorganic material substrate 1 falls below the lower limit, the thickness and width of the electrodes constituting the waveguide element will be reduced to about a few μm, resulting in increased propagation loss due to the skin effect and a significant decrease in the tolerance of line performance due to manufacturing variations. When the thickness of the inorganic material substrate 1 is equal to or less than the above upper limit, induction of slab mode and occurrence of substrate resonance are suppressed, and a waveguide element with small propagation loss over a wide frequency range (ie, wideband) can be realized.

[0011] The signal electrode 21 in the illustrated example, together with the first metal layer 3, constitutes a microstrip line as an example of a transmission line. That is, the signal electrode 21 and the first metal layer 3 are microstrip type electrodes. When the signal electrode and the first metal layer are microstrip type electrodes, the above-mentioned high-frequency electromagnetic wave is coupled with an electric field generated between the signal electrode 21 and the first metal layer 3 and propagates through the inorganic material substrate 1.

[0012] In one embodiment, the conductor layer 2 further includes a ground electrode 22 disposed at a distance from the signal electrode 21. In the illustrated example, the conductor layer 2 includes a first ground electrode 22a, a second ground electrode 22b, and a third ground electrode 22c. The first ground electrode 22a and the second ground electrode 22b are disposed at intervals from each other in a direction intersecting (preferably perpendicular to) the longitudinal direction of the signal electrode 21. One end of the signal electrode 21 is located between the first ground electrode 22a and the second ground electrode 22b. A predetermined gap is formed between the signal electrode 21 and each of the first ground electrode 22a and the second ground electrode 22b. The first ground electrode 22a and the second ground electrode 22b may be electrically connectable to an external element (not shown). The third ground electrode 22c is disposed at a predetermined interval from the other end of the signal electrode 21. A predetermined gap is formed between the signal electrode 21 and the third ground electrode 22c. The third ground electrode 22c has a substantially C-shape when viewed from the thickness direction of the inorganic material substrate 1, and surrounds the other end of the signal electrode 21. The conductor layer 2 does not need to include the third ground electrode 22c. Although not shown, the signal electrode 21 may form a coplanar electrode, which is an example of a transmission line, together with the first ground electrode 22a and the second ground electrode 22b.

[0013] In one embodiment, the director element 101 further includes vias 6 that electrically connect the ground electrode 22 and the first metal layer 3. This strengthens the ground and suppresses stray capacitance due to surrounding lines and elements. In the illustrated example, each of the first ground electrode 22a, the second ground electrode 22b, and the third ground electrode 22c is electrically connected to the first metal layer 3 by a plurality of vias 6.

[0014] The via 6 is made of a conductive material, typically made of the same metal (described later) as the conductive layer 2. The via 6 is disposed in the first via hole 8 (see FIG. 2). That is, the waveguide element 101 has a plurality of first via holes 8 corresponding to a plurality of vias 6. In the illustrated example, the first via hole 8 penetrates the ground electrode 22, the inorganic material substrate 1, and the first metal layer 3 all at once. The via 6 is typically a conductive film formed on the entire inner surface of the via hole 8. The first via hole may penetrate only the inorganic material substrate without penetrating the ground electrode and the first metal layer. In this case, the via is filled in the first via hole so as to contact the ground electrode and the first metal layer. The first via hole 8 may be filled with a conductive material throughout the hole. When the via 6 is formed of a conductive film, the inside of the via 6 may be filled with a conductive material. The conductive material may be the same metal as the via 6, or may be a different material such as a conductive paste.

[0015] Each of the plurality of through-substrate vias 5 penetrates the support substrate 7 in the thickness direction and is periodically arranged in the support substrate 7. Typically, the plurality of through-substrate vias 5 includes a first via row 5a and a second via row 5b. Each of the first via row 5a and the second via row 5b is composed of a plurality of through-substrate vias 5 arranged at intervals in a predetermined direction. The second via row 5b is located away from the first via row 5a in a direction perpendicular to the extension direction of the first via row 5a. In one embodiment, an area of ​​the support substrate 7 surrounded by the first metal layer 3, the second metal layer 4, the first via row 5a, and the second via row 5b functions as a SIW.

[0016] The through-substrate via 5 is made of a conductive material, typically made of the same metal (described later) as the conductive layer 2. The through-substrate via 5 is disposed in the second via hole 9 (see FIG. 2). That is, the waveguide element 101 has a plurality of second via holes 9 corresponding to the plurality of through-substrate vias 5. In the illustrated example, the second via hole 9 penetrates the first metal layer 3, the support substrate 7, and the second metal layer 4 all at once. The through-substrate via 5 is typically a conductive film formed on the entire inner surface of the second via hole 9. Note that the second via hole may penetrate only the support substrate without penetrating the first metal layer and the second metal layer. In this case, the through-substrate via is filled in the second via hole so as to contact the first metal layer and the second metal layer. In addition, when the through-substrate via 5 that electrically connects the first metal layer 3 and the second metal layer 4 is formed of a conductive film, the inside of the through-substrate via may be filled with a material such as a resin.

[0017] In the director element 101, the transmission line and the SIW formed by the signal electrode 21 may be independent of each other, or may be coupled so that electromagnetic waves can propagate through them. In one embodiment, as shown in FIG. 2, the transmission line (typically a microstrip transmission line) formed by the signal electrode 21 and the SIW are coupled by a conductor pin 25. This makes it possible to convert the propagation mode of the electromagnetic wave between a transmission line mode and a waveguide mode. For example, an electromagnetic wave (signal) in the transmission line mode propagating through an inorganic material substrate can be converted into an electromagnetic wave in the waveguide mode propagating through a support substrate via a conductor pin. The support substrate can function as an antenna that spatially radiates the electromagnetic wave propagating in the waveguide mode in the in-plane direction of the substrate.

[0018] The conductor pin 25 passes through the inorganic material substrate 1 from the signal electrode 21 and reaches the SIW in the support substrate 7. The conductor pin 25 can be a propagation medium for electromagnetic waves. The conductor pin 25 is made of a conductive material, and is typically made of the same metal (described later) as the conductor layer 2. In the illustrated example, the conductor pin 25 extends in the thickness direction of the inorganic material substrate 1. The conductor pin 25 may be a columnar shape, such as a cylindrical shape, or may be a cylindrical shape (hollow shape), such as a cylindrical shape. The base end of the conductor pin 25 is connected to the end of the signal electrode 21. The free end of the conductor pin 25 is inserted into a recess 71 formed in the support substrate 7 (see FIG. 3). The recess 71 is located between the first via row 5a and the second via row 5b. The portion of the conductor pin 25 between the base end and the free end is inserted into an opening 31 of the first metal layer 3. The conductor pin 25 is preferably insulated from the first metal layer 3. In one embodiment, as shown in FIG. 2, the opening 31 forms an air layer around the conductor pin 25. The opening 31 is larger than the outer shape of the conductor pin 25, and the entire periphery of the opening 31 is separated from the conductor pin 25. This makes it possible to insulate the conductor pin from the first metal layer, and in turn to stably insulate the signal electrode from the first metal layer. In addition, it is possible to further suppress substrate resonance caused by leakage of the electric field to the support substrate. Furthermore, it is possible to suppress the effect of dielectric loss compared to a structure in which the air layer is filled with resin.

[0019] 4, the conductor pin 25 may be covered with an insulating material 15. This also insulates the conductor pin from the first metal layer. Examples of insulating materials include resin and SiO2.

[0020] B. Alternative Embodiments of the Waveguide Element Fig. 5 is a schematic perspective view of a director element according to another embodiment of the present invention, and Fig. 6 is a cross-sectional view taken along line VI-VI' of the director element of Fig. 5. Note that, for convenience, ground electrodes and vias are omitted in Fig. 5. The above-mentioned director element 101 includes one signal electrode 21, but the number of signal electrodes 21 is not particularly limited. The director element 102 includes a plurality of signal electrodes 21 located apart from each other. Therefore, the director element 102 includes a plurality of transmission lines corresponding to the signal electrodes. In the illustrated example, the director element 102 includes a conductor layer 2 including a first signal electrode 21a and a second signal electrode 21b; a first conductor pin 25a; and a second conductor pin 25b. The first signal electrode 21a constitutes a first transmission line together with the first metal layer 3, and the second signal electrode 21b constitutes a second transmission line together with the first metal layer 3. The first conductor pin 25a couples the first transmission line to the SIW including the first metal layer 3, the second metal layer 4, and the plurality of through-substrate vias 5. The second conductive pin 25b couples the SIW, which is composed of the first metal layer 3, the second metal layer 4, and the plurality of through-substrate vias 5, to the second transmission line. As a result, in one embodiment, an electromagnetic wave (signal) in a transmission line mode propagating through the inorganic material substrate can be converted to a SIW mode via the first conductor pin, then propagated through the support substrate in the SIW mode, and then converted again to a transmission line mode propagating through the inorganic material substrate via the second conductor pin. In this embodiment, the electromagnetic wave propagated through the inorganic material substrate can be emitted from an antenna element provided on the inorganic material substrate.

[0021] C. Further Embodiments of Waveguide Elements 7 and 8 are each a schematic cross-sectional view of a waveguide element according to yet another embodiment of the present invention. The above-mentioned waveguide element 101 and waveguide element 102 each include one support substrate 7, but the number of support substrates 7 is not particularly limited. In the waveguide element 103 and the waveguide element 104, a plurality of support substrates 7 are arranged at intervals from each other in the thickness direction of the inorganic material substrate 1, and each of the plurality of support substrates 7 is provided with a substrate integrated waveguide (SIW). With this configuration, the antenna portion that radiates electromagnetic waves in SIW mode can be arrayed in the thickness direction. Therefore, such a waveguide element can be used as a phased array antenna in wireless communication. Note that, when a plurality of substrates that transmit signals (electromagnetic waves) are integrated, heat generation from the waveguide element may become a problem. However, in the above embodiment, since the through-substrate vias that penetrate the support substrate are connected to the metal layer, heat can be smoothly dissipated from the waveguide element.

[0022] 7, in the waveguide element 103, a second metal layer 4 is disposed between adjacent ones of a plurality of support substrates 7. As a result, the SIW provided on each support substrate 7 is composed of metal layers (i.e., a first metal layer 3 and a second metal layer 4, or two second metal layers 4) disposed on both sides of the support substrate 7, and a plurality of through-substrate vias 5 penetrating the support substrate 7.

[0023] 8, in the waveguide element 104, a plurality of waveguide units 12 including SIW are arranged at intervals from one another in the thickness direction of the inorganic material substrate 1. Each of the plurality of waveguide units 12 includes a first metal layer 3, a support substrate 7, a second metal layer 4, and a plurality of through-substrate vias 5. A spacer substrate 13 may be provided between adjacent ones of the plurality of support substrates 7. In one embodiment, the spacer substrate 13 is disposed between adjacent waveguide units 12. By providing the spacer substrate, the interval between the antenna portions of the plurality of support substrates can be adjusted. In particular, by adjusting the interval between the plurality of antenna portions to λ / 2, the radiation angle of the electromagnetic wave can be sufficiently scanned. Representative materials for the spacer substrate include inorganic materials (described later) similar to those for the inorganic material substrate.

[0024] Moreover, a waveguide element having a plurality of SIWs preferably has the same number of signal electrodes 21 and conductor pins 25 as the number of SIWs. Each conductor pin 25 couples a transmission path constituted by each signal electrode 21 with a corresponding SIW. The conductor pin 25 passes from the corresponding signal electrode 21 through the inorganic material substrate 1, is inserted into an opening 31 of the first metal layer 3, and further passes through the support substrate 7, the second metal layer 4, and the spacer substrate 13 as necessary to reach the corresponding support substrate 7. With such a configuration, it is relatively easy to manufacture, and a signal (electromagnetic wave) from an external signal source X placed on the inorganic material substrate can be easily propagated to the SIW of each support substrate.

[0025] In this specification, the term "waveguide element" encompasses both a wafer on which at least one waveguide element is formed (waveguide element wafer) and a chip obtained by cutting the waveguide element wafer. The specific configuration of each component of the waveguide element will be described below in Sections D to H.

[0026] D. Inorganic material substrate The inorganic material substrate 1 has an upper surface on which the conductor layer 2 is provided, and a lower surface located within the composite substrate. The dielectric constant of the inorganic material substrate 1 at 100 GHz to 10 THz is, for example, 10.0 or less, preferably 3.7 or more and 10.0 or less, and more preferably 3.8 or more and 9.0 or less. When the frequency used is 300 GHz, the relative dielectric constant ε of the inorganic material substrate 1 is typically 3.5 or more, typically 12.0 or less, preferably 10.0 or less, and more preferably 5.0 or less. If the dielectric constant of the inorganic material substrate is within such a range, the delay of the propagating electromagnetic wave can be suppressed. The dielectric loss tangent (tan δ) of the inorganic material substrate is preferably 0.01 or less at the frequency used, more preferably 0.008 or less, even more preferably 0.006 or less, and particularly preferably 0.004 or less. When the frequency used is 300 GHz, the dielectric loss tangent tan δ of the inorganic material substrate 1 is preferably 0.0030 or less, more preferably 0.0020 or less, and even more preferably 0.0015 or less. If the dielectric loss tangent is in this range, the propagation loss in the waveguide can be reduced. The smaller the dielectric loss tangent, the more preferable it is. The dielectric loss tangent can be, for example, 0.001 or more. When the dielectric constant ε and the dielectric loss tangent (dielectric loss) tan δ of the inorganic material substrate are within the above ranges, the propagation loss can be reduced more stably when guiding the above-mentioned high-frequency electromagnetic waves (particularly electromagnetic waves of 300 GHz or higher). The dielectric constant ε and the dielectric loss tangent (dielectric loss) tan δ can be measured by terahertz time-domain spectroscopy. In this specification, when there is no mention of the measurement frequency for the dielectric constant and the dielectric loss tangent, the dielectric constant and the dielectric loss tangent at 300 GHz are meant.

[0027] The inorganic material substrate 1 is made of an inorganic material. Any appropriate material can be used as the inorganic material as long as the effect of the embodiment of the present invention can be obtained. Representative examples of such materials include single crystal quartz (relative dielectric constant 4.5, dielectric loss tangent 0.0013), amorphous quartz (quartz glass, relative dielectric constant 3.8, dielectric loss tangent 0.0010), spinel (relative dielectric constant 8.3, dielectric loss tangent 0.0020), AlN (relative dielectric constant 8.5, dielectric loss tangent 0.0015), sapphire (relative dielectric constant 9.4, dielectric loss tangent 0.0030), SiC (relative dielectric constant 9.8, dielectric loss tangent 0.0022), magnesium oxide (relative dielectric constant 10.0, dielectric loss tangent 0.0012), and silicon (relative dielectric constant 11.7, dielectric loss tangent 0.0016). The inorganic material substrate 1 is preferably a quartz glass substrate made of amorphous quartz. If the inorganic material substrate is a quartz glass substrate, the increase in propagation loss can be more stably suppressed even when guiding the above-mentioned high-frequency electromagnetic waves. Furthermore, since the dielectric constant is larger than that of resin-based substrates, the substrate size can be made smaller, and since the dielectric constant is relatively small among inorganic materials, it is advantageous in terms of reducing delay.

[0028] The resistivity of the inorganic material substrate 1 is, for example, 100 kΩ·cm or more, preferably 300 kΩ·cm or more, more preferably 500 kΩ·cm or more, and even more preferably 700 kΩ·cm or more. If the resistivity is in such a range, the electromagnetic wave can propagate through the material with low loss without affecting the electronic conduction. Although the details of this phenomenon are not clear, it can be presumed that if the resistivity is low, the electromagnetic wave binds with the electrons and the energy of the electromagnetic wave is taken away by the electronic conduction, resulting in loss. From this viewpoint, the higher the resistivity, the more preferable it is. The resistivity can be, for example, 3000 kΩ (3 MΩ)·cm or less.

[0029] The flexural strength of the inorganic material substrate 1 is, for example, 50 MPa or more, and preferably 60 MPa or more. If the flexural strength is in this range, the substrate is less likely to deform, and a waveguide element with small changes in characteristics can be realized. The higher the flexural strength, the more preferable it is. The flexural strength can be, for example, 700 MPa or less. The flexural strength can be measured in accordance with JIS standard R1601.

[0030] The thermal expansion coefficient (linear expansion coefficient) of the inorganic material substrate 1 is, for example, 10×10 -6 / K or less, preferably 8×10 -6 / K or less. If the thermal expansion coefficient is in this range, thermal deformation (typically, warpage) of the substrate can be effectively suppressed. The thermal expansion coefficient can be measured in accordance with JIS standard R1618.

[0031] As described above, the dielectric loss tangent tanδ of the inorganic material substrate 1 is preferably as small as possible. A method for reducing the dielectric loss tangent (tanδ) of the inorganic material substrate 1 in the 300 GHz band is to reduce the concentration of OH groups contained in the inorganic material substrate. When the waveguide element 101 guides electromagnetic waves with frequencies of 250 GHz to 350 GHz, the concentration of OH groups in the inorganic material substrate is, for example, 100 wtppm or less, preferably 15 wtppm or less, and more preferably 10 wtppm or less. The concentration of OH groups in the inorganic material substrate can typically be 0 wtppm or more. The concentration of OH groups can be measured by FTIR (Fourier transform infrared spectroscopy), Raman scattering spectroscopy, or the Karl Fischer method.

[0032] The dielectric loss of the inorganic material substrate 1 can be evaluated by the FQ value, which is calculated by multiplying the inverse of the dielectric tangent (tan δ) by the frequency of the electromagnetic wave guided by the director element 101. When the OH group concentration of the inorganic material substrate 1 is 100 wtppm or less, if the frequency of the electromagnetic wave is 150 GHz or more and less than 250 GHz, the FQ value is preferably 45,000 GHz or more, and if the frequency of the electromagnetic wave is 250 GHz or more and less than 350 GHz, the FQ value is preferably 75,000 GHz or more. Furthermore, when the OH group concentration of the inorganic material substrate 1 is 15 wtppm or less, if the frequency of the electromagnetic wave is 150 GHz or more and less than 250 GHz, the FQ value is preferably 75,000 GHz or more, and if the frequency of the electromagnetic wave is 250 GHz or more and less than 350 GHz, the FQ value is preferably 105,000 GHz or more. Furthermore, when the OH group concentration of the inorganic material substrate 1 is 10 wtppm or less, if the frequency of the electromagnetic wave is 150 GHz or more and less than 250 GHz, the FQ value is preferably 150,000 GHz or more and typically 270,000 GHz or less, and if the frequency of the electromagnetic wave is 250 GHz or more and less than 350 GHz, the FQ value is preferably 250,000 GHz or more and typically 390,000 GHz or less.

[0033] The porosity of the inorganic material substrate 1 is, for example, 0.5 ppm to 3000 ppm, preferably 0.5 ppm to 1000 ppm, more preferably 0.5 ppm to 100 ppm, for pores with a size of 1 μm or more. If the porosity is within such a range, densification is possible, and a stable waveguide element can be realized in terms of both mechanical strength and long-term reliability. If the porosity exceeds 3000 ppm, the propagation loss in the waveguide may increase. It is difficult to achieve a porosity of less than 0.5 ppm using a technology that uses an inorganic material substrate.

[0034] The size of the pores refers to the diameter when the pores are approximately spherical, the diameter when viewed from above when the pores are approximately cylindrical, and the diameter of a circle inscribed in the pores when the pores have other shapes. The presence or absence of pores can be confirmed, for example, by optical CT (Computed Tomography) or a transmittance meter. The size of the pores can be measured, for example, by a scanning electron microscope (SEM).

[0035] E. Conductive layer The conductor layer 2 is located on the opposite side of the inorganic material substrate 1 to the first metal layer 3, and is provided on the surface of the inorganic material substrate 1. The conductor layer 2 is typically in direct contact with the inorganic material substrate 1. The conductor layer 2 is typically made of a metal. Examples of metals include chromium (Cr), nickel (Ni), copper (Cu), gold (Au), silver (Ag), palladium (Pd), and titanium (Ti). The metals can be used alone or in combination. The conductor layer 2 may be a single layer, or may be formed by laminating two or more layers. The conductor layer 2 is formed on the inorganic material substrate 1 by, for example, plating, sputtering, vapor deposition, or printing. The conductor layer 2 includes at least a signal electrode 21. The width (dimension in a direction perpendicular to the longitudinal direction) of the signal electrode 21 is, for example, 2 μm or more, preferably 100 μm or more, and more preferably 300 μm or more, and is, for example, 800 μm or less, preferably 500 μm or less. The longitudinal dimension of the signal electrode 21 can be any appropriate dimension. The thickness of the conductor layer 2 is, for example, 1 μm or more, preferably 4 μm or more, and, for example, 20 μm or less, preferably 10 μm or less.

[0036] F. 1st metal layer In one embodiment, the first metal layer 3 is provided on the surface of the inorganic material substrate 1 opposite to the conductor layer 2. The first metal layer 3 is disposed at a distance from the signal electrode 21 in the thickness direction of the inorganic material substrate 1. The first metal layer 3 is typically in direct contact with the inorganic material substrate 1. The first metal layer 3 can be made of the same metal as the conductor layer 2. From the viewpoint of bonding the inorganic material substrate 1 and the support substrate 7, the first metal layer 3 needs to ensure an adhesive strength that makes it easy to flatten the bonding surface, and the metal of the first metal layer 3 may be different from the metal of the conductor layer 2. The thickness range of the first metal layer 3 is the same as the thickness range of the conductor layer 2. The first metal layer 3 is typically formed on the inorganic material substrate 1 by sputtering or plating.

[0037] G.Support board The support substrate 7 can provide the waveguide element with excellent mechanical strength. This allows the thickness t of the inorganic material substrate to be thinned so as to satisfy the above formula (1). Any appropriate configuration can be adopted for the support substrate 7. Specific examples of materials constituting the support substrate 7 include indium phosphide (InP), silicon (Si), glass, sialon (Si3N4-Al2O3), mullite (3Al2O3·2SiO2, 2Al2O3·3SiO2), aluminum nitride (AlN), magnesium oxide (MgO), aluminum oxide (Al2O3), spinel (MgAl2O4), sapphire, quartz (single crystal quartz, amorphous quartz, etc.), quartz, gallium nitride (GaN), silicon carbide (SiC), silicon nitride (Si3N4), and gallium oxide (Ga2O3). The support substrate 7 is preferably made of at least one material selected from indium phosphide, silicon, aluminum nitride, silicon carbide, and silicon nitride, and more preferably made of silicon. In the present application, since the SIW is formed on the support substrate 7, a material with a small dielectric loss tan δ is preferred in order to reduce the loss of the electromagnetic wave propagating through the SIW. From this viewpoint, examples of the material include single crystal quartz, amorphous quartz, spinel, AlN, sapphire, aluminum oxide, SiC, magnesium oxide, and silicon. When active elements such as an oscillator or a receiver are mounted on the waveguide element 101, the inorganic material substrate may heat up, deteriorating the characteristics of other active elements and mounted components. To prevent this, a material with high thermal conductivity may be used for the support substrate. In this case, the thermal conductivity is preferably 150 W / Km or more, and from this viewpoint, examples of materials constituting the support substrate 7 include silicon (Si), aluminum nitride (AlN), gallium nitride (GaN), silicon carbide (SiC), and silicon nitride (Si3N4).

[0038] The linear expansion coefficient of the material constituting the support substrate 7 is preferably as close as possible to the linear expansion coefficient of the material constituting the inorganic material substrate 1. With such a configuration, thermal deformation (typically, warpage) of the composite substrate can be suppressed. The linear expansion coefficient of the material constituting the support substrate 7 is preferably within a range of 50% to 150% of the linear expansion coefficient of the material constituting the inorganic material substrate 1. Furthermore, it is preferable that the dielectric loss tangent of the material constituting the support substrate 7 is small. By making the dielectric loss tangent small, it is possible to suppress propagation loss. From this viewpoint, the dielectric loss tangent of the support substrate 7 is preferably 0.07 or less.

[0039] The thickness of the support substrate 7 is determined by setting the relative dielectric constant of the support substrate 7 to ε b If the wavelength of the electromagnetic wave guided by the waveguide element is λ, then, for example, λ / 4√ε b or more, preferably λ / 2√ε b For example, 2λ / √ε b Below 3λ / 2√ε, preferably b More preferably, λ / √ε bIf the thickness of the support substrate is equal to or greater than the lower limit, the mechanical strength of the waveguide element can be stably improved. If the thickness of the support substrate is equal to or less than the upper limit, slab mode propagation can be suppressed, the waveguide element can be made thinner (maintaining the mechanical strength of the waveguide element), and substrate resonance can be suppressed. When multiple support substrates 7 are arranged at intervals in the thickness direction of the inorganic material substrate 1, if the substrate is to be used as a phased array antenna, it is desirable that the interval between adjacent support substrates 7 be approximately λ / 2, which is suitable for the antenna pitch. However, if the thickness of the support substrate 7 is less than this interval, a suitable antenna pitch can be ensured by providing a spacer substrate 13 between adjacent support substrates.

[0040] The support substrate 7 supports the conductor layer 2, the inorganic material substrate 1, the first metal layer 3, and the second metal layer 4. More specifically, there is no organic adhesive (e.g., an adhesive such as a resin) between the inorganic material substrate 1 and the support substrate 7, and the inorganic material substrate 1 and the support substrate 7 are directly bonded via the first metal layer 3. In this specification, "direct bonding" means that two layers or substrates are bonded without the intermediation of an organic adhesive. The form of direct bonding can be appropriately set depending on the configuration of the layers or substrates to be bonded to each other. By integrating them by direct bonding, peeling in the waveguide element can be effectively suppressed, and as a result, damage (for example, cracks) to the inorganic material substrate caused by such peeling can be effectively suppressed. Furthermore, the interface bonded by direct bonding can be made amorphous, dramatically improving the thermal resistance of the bonded interface compared to resin bonding. This allows heat to be dissipated to the package without heating the inorganic material substrate when active elements such as oscillators and receivers are mounted on the waveguide element, suppressing deterioration of the characteristics of other active elements and mounted components. In the illustrated example, the support substrate 7 is directly bonded to the inorganic material substrate 1 only via the first metal layer 3. When the support substrate 7 is bonded to the inorganic material substrate 1 only via the first metal layer 3, the first metal layer 3 functions as a bonding portion bonding the inorganic material substrate 1 and the support substrate 7, and the support substrate 7 is in direct contact with the first metal layer 3. Furthermore, the support substrate 7 may be directly bonded to the inorganic material substrate 1 via the first metal layer 3 and a bonding portion (not shown). When the support substrate 7 is bonded to the inorganic material substrate 1 via the first metal layer 3 and a bonding portion, the bonding portion may be provided between the inorganic material substrate 1 and the first metal layer 3, or may be provided between the first metal layer 3 and the support substrate 7. In other words, the bonding portion is provided between the inorganic material substrate and the first metal layer and / or between the first metal layer and the support substrate. The bonding portion may be a single layer, or may be a laminate of two or more layers. Examples of the bonding portion include a SiO2 layer, an amorphous silicon layer, and a tantalum oxide layer. From the viewpoint of ensuring adhesion strength and preventing migration, a metal film of Ti, Cr, Ni, Pt, or Pd may be formed as an intermediate layer between the inorganic material substrate and the first metal layer, or between the support substrate and the first metal layer. The thickness of the bonding portion is, for example, 0.01 μm or more and 3 μm or less.

[0041] H. Second metal layer In one embodiment, the second metal layer 4 is provided on the surface of the support substrate 7 opposite to the first metal layer 3. The second metal layer 4 is disposed at a distance from the first metal layer 3 in the thickness direction of the inorganic material substrate 1. The second metal layer 4 is typically in direct contact with the support substrate 7. The second metal layer 4 is made of the same metal as the conductor layer 2, and the thickness range of the second metal layer 4 is the same as the thickness range of the conductor layer 2. The second metal layer 4 is formed on the support substrate 7 by, for example, sputtering or plating. The second metal layer 4 does not necessarily have to be formed on the entire surface of the support substrate 7 opposite to the first metal layer. [Industrial Applicability]

[0042] The waveguide element according to the embodiment of the present invention can be used in a wide range of fields such as a waveguide, next-generation high-speed communication, a sensor, laser processing, and solar power generation, and can be particularly suitably used as a waveguide for millimeter waves to terahertz waves. Such a waveguide element can be used, for example, in an antenna, a bandpass filter, a coupler, a delay line (phase shifter), or an isolator. [Explanation of symbols]

[0043] 1 Inorganic material substrate 2 Conductor layer 21 Signal electrode 22 Ground electrode 3 1st metal layer 4 Second metal layer 5 Through-substrate vias 6 Via 7 Support substrate

Claims

1. A waveguide element capable of guiding an electromagnetic wave having a frequency of 30 GHz or more and 20 THz or less, An inorganic material substrate; A conductor layer provided on the inorganic material substrate; a support substrate located on the opposite side of the inorganic material substrate from the conductor layer; a first metal layer located between the inorganic material substrate and the support substrate; a second metal layer located on the opposite side of the support substrate from the inorganic material substrate; a plurality of through-substrate vias electrically connecting the first metal layer and the second metal layer; the conductor layer includes a signal electrode extending in a predetermined direction and constituting a transmission line capable of propagating the electromagnetic wave; the first metal layer, the second metal layer, and the plurality of through-substrate vias constitute a substrate integrated waveguide capable of propagating an electromagnetic wave; a waveguide element, wherein the thickness t of the inorganic material substrate satisfies the following formula (1): [0010] (In the formula, t represents the thickness of the inorganic material substrate; λ represents the wavelength of the electromagnetic wave guided by the waveguide element; ε represents the relative dielectric constant of the inorganic material substrate; and a represents a value of 3 or more).

2. 2. The waveguide element according to claim 1, wherein the inorganic material substrate has a thickness of 100 [mu]m or less.

3. 2. The waveguide element according to claim 1, wherein the inorganic material substrate has a thickness of 31 [mu]m or more.

4. 4. The waveguide element according to claim 1, wherein the conductor layer further comprises a ground electrode spaced apart from the signal electrode.

5. The waveguide element of claim 4 , further comprising a via electrically connecting the ground electrode and the first metal layer.

6. a conductor pin that couples the transmission line and the substrate integrated waveguide so that the electromagnetic wave can propagate; 4. The waveguide element according to claim 1, wherein the conductor pin extends from the signal electrode through the inorganic material substrate to reach the substrate integrated waveguide in the support substrate.

7. 7. The waveguide element according to claim 6, wherein the first metal layer has an opening through which the conductive pin is inserted and which forms an air layer around the conductive pin.

8. The waveguide element according to any one of claims 1 to 3, wherein the support substrates are arranged at intervals from each other in the thickness direction of the inorganic material substrate, and each of the support substrates is provided with a substrate integrated waveguide.

9. The waveguide element according to claim 8 , further comprising a spacer substrate provided between adjacent ones of the plurality of supporting substrates.

10. The waveguide element according to any one of claims 1 to 3, wherein there is no organic adhesive between the inorganic material substrate and the support substrate, and the inorganic material substrate and the support substrate are directly bonded via the first metal layer.

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