Waveguide element and method for manufacturing the same

Abstract

To provide a waveguide element for guiding an electromagnetic wave of 30 GHz or more that sufficiently reduces the propagation loss and a manufacturing method for the same.SOLUTION: A waveguide element 100 includes an inorganic material substrate 1 that satisfies the equation (1), a conductor layer 2 on an upper part of the inorganic material substrate 1, a support substrate 7 located on the opposite surface of the conductor layer, a second ground electrode 3 between the inorganic material substrate and the support substrate, a third ground electrode 4 on the opposite surface of the second ground electrode, and a via 5 that connects first ground electrodes 2b, 2c provided on the conductor layer to the second ground electrode and the third ground electrode. In the equation, t represents a thickness of the inorganic material element, λ represents a wavelength of an electromagnetic wave guided in the waveguide element, ε represents the relative permittivity of the inorganic material substrate, and a represents a number equal to or greater than 3.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a waveguide element and a method for manufacturing 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 grounded coplanar waveguide that is composed of a glass substrate with a thickness of 300 μm, a coplanar conductor provided on the glass substrate, and a ground electrode provided on the surface of the glass substrate opposite to the coplanar 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] Special Publication No. 2021-509767 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, and a method for manufacturing the same. [Means for solving the problem]

[0005] A waveguide element according to an embodiment of the present invention can guide electromagnetic waves with 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, the conductor layer including a signal electrode extending in a predetermined direction and a first ground electrode spaced apart from the signal wiring in a direction intersecting the predetermined direction; a support substrate located on the opposite side of the conductor layer with respect to the inorganic material substrate; a second ground electrode located between the inorganic material substrate and the support substrate; a third ground electrode located on the opposite side of the support substrate from the second ground electrode; and a via that electrically connects the first ground electrode and the third ground electrode and is electrically connected to the second ground electrode. The thickness t of the inorganic material substrate satisfies the following formula (1).

number

[0006] According to the embodiment of the present invention, it is possible to realize a waveguide element that can sufficiently reduce propagation loss even when guiding a high-frequency electromagnetic wave having a frequency of 30 GHz or more. Also, according to the embodiment of another aspect of the present invention, it is possible to smoothly manufacture the above-mentioned waveguide element. [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 a cross-sectional view of a waveguide element according to another embodiment of the present invention taken along line II-II'. [Figure 4] FIG. 4 is a cross-sectional view of a waveguide element according to another embodiment of the present invention taken along line IV-IV'. [Diagram 5] FIG. 2 is a cross-sectional view taken along line II-II' of a waveguide element according to yet another embodiment of the present invention. [Figure 6] FIG. 2 is a cross-sectional view taken along line II-II' 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 one embodiment of the present invention; FIG. 2 is a cross-sectional view of the waveguide element of FIG. 1 taken along line II-II'. The illustrated waveguide element 100 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 100 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 100 comprises an inorganic material substrate 1; a conductor layer 2 including a signal electrode 2a and first ground electrodes 2b, 2c; a support substrate 7; a second ground electrode 3; a third ground electrode 4; and a via 5. The conductor layer 2 is provided on the inorganic material substrate 1. The signal electrode 2a extends in a predetermined direction (waveguiding direction). The first ground electrodes 2b, 2c are each disposed at a distance from the signal electrode 2a in a direction intersecting the predetermined direction in which the signal electrode 2a extends. The support substrate 7 is located on the opposite side of the inorganic material substrate 1 to the conductor layer 2. The second ground electrode 3 is located between the inorganic material substrate 1 and the support substrate 7. The third ground electrode 4 is located on the opposite side of the support substrate 7 to the second ground electrode 3. The via 5 electrically connects the first ground electrodes 2b, 2c and the third ground electrode 4, and is also electrically connected to the second ground electrode 3. 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 the formula (1) in which a is a numerical value of 6 or more, it is possible to stably reduce the propagation loss when guiding the above-mentioned high-frequency electromagnetic waves.

[0011] 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 and 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 in 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.

[0012] 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, and even more preferably 20 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.

[0013] In one embodiment, the director element comprises a coplanar line, i.e., the conductor layer of the director element is a coplanar electrode. In one embodiment, the conductor layer 2 is a coplanar electrode. When the conductor layer 2 is a coplanar electrode as shown in Fig. 2, the high-frequency electromagnetic wave is coupled with an electric field generated between the signal electrode 2a and the first ground electrodes 2b and 2c, and propagates through the inorganic material substrate 1. When the conductor layer 2 is a coplanar electrode, the signal electrode 2a has a linear shape extending in a predetermined direction (waveguiding direction). The first ground electrode 2b is arranged so as to form a predetermined gap between the signal electrode 2a and the first ground electrode 2b in a direction intersecting (preferably perpendicular) with the longitudinal direction of the signal electrode 2a. The first ground electrode 2c is located on the opposite side of the first ground electrode 2b with respect to the signal electrode 2a in a direction intersecting (preferably perpendicular) with the longitudinal direction of the signal electrode 2a, and is arranged so as to form a predetermined gap between the first ground electrode 2c and the signal electrode 2a. The gap extends in the longitudinal direction of the signal electrode 2a. The width (dimension in a direction perpendicular to the longitudinal direction) w of the signal electrode 2a of the coplanar electrode is, for example, 2 μm or more, preferably 20 μm or more, for example, 200 μm or less, preferably 150 μm or less. The width (dimension in a direction intersecting the longitudinal direction) g of the above-mentioned gap is, for example, 2 μm or more, preferably 5 μm or more, and for example, 100 μm or less, preferably 80 μm or less.

[0014] In one embodiment, the director element comprises a microstrip line, i.e., the conductor layer of the director element and the second ground electrode are microstrip type electrodes. In one embodiment, the conductor layer 2 and the second ground electrode 3 are microstrip type electrodes. In the case of the microstrip type electrodes, the high-frequency electromagnetic wave described above is coupled with an electric field generated between the signal electrode 2a and the second ground electrode 3 and propagates through the inorganic material substrate 1, as shown in FIG. When the conductor layer 2 is a microstrip electrode, the signal electrode 2a has a flat belt shape extending in a predetermined direction (waveguiding direction). The second ground electrode 3 is arranged so as to form a predetermined gap (thickness of the inorganic material substrate) between the signal electrode 2a and the second ground electrode 3 in a direction intersecting (preferably perpendicular) the longitudinal direction of the signal electrode 2a. The gap extends in the longitudinal direction of the signal electrode 2a. On the other hand, the first ground electrodes 2b and 2c can also be installed in the same manner as the coplanar electrode, and the first ground electrodes 2b and 2c are located away from the signal electrode 2a in a direction intersecting (preferably perpendicular) the longitudinal direction of the signal electrode 2a by a distance greater than the width g of the gap of the coplanar electrode described above. The width (dimension in a direction perpendicular to the longitudinal direction) w of the signal electrode 2a of the microstrip electrode is, for example, 100 μm or more, preferably 300 μm or more, for example, 800 μm or less, preferably 500 μm or less.

[0015] In the illustrated example, whether the conductor layer 2 is a coplanar electrode or a microstrip electrode, the signal electrode 2a extends over the entire waveguide element 100, but the longitudinal dimension of the signal electrode 2a may be any appropriate dimension as long as it is equal to or smaller than the dimension of the waveguide element in the waveguide direction. In addition, a plurality of signal electrodes may be provided in the waveguide element so as to be aligned in the waveguide direction.

[0016] 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. Hereinafter, the specific configuration of each component of the waveguide element will be described in Sections B to G. Also, a method for manufacturing the waveguide element will be described in Section H.

[0017] B. Inorganic material substrate As shown in FIGS. 1 and 2, the inorganic material substrate 1 has an upper surface on which a conductor layer 2 is provided, and a lower surface located within the composite substrate. 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.

[0018] 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.

[0019] 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, so that the pore diameter and pore period are stable, and a waveguide element with small characteristic changes 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.

[0020] 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.

[0021] 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 100 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.

[0022] 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 100. 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.

[0023] 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 pore size of 1 μm or more. If the porosity is within such a range, densification is possible, and further, due to the synergistic effect with the effect of setting the pore size within a predetermined range, a stable waveguide element can be realized in terms of both mechanical strength and long-term reliability. Furthermore, since the particle size can be made small, there is an advantage that the shape of the via hole described later can be made uniform without variation. Note that if the porosity exceeds 3000 ppm, the propagation loss in the waveguide may become large. It is difficult to make the porosity less than 0.5 ppm with the technology using the inorganic material substrate.

[0024] 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).

[0025] C. Conductive layer The conductor layer 2 is located on the opposite side of the inorganic material substrate 1 to the second ground electrode 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 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.

[0026] D.Second ground electrode In one embodiment, the second ground electrode 3 is provided on the surface of the inorganic material substrate 1 opposite to the conductor layer 2. The second ground electrode 3 is disposed at a distance from the signal electrode 2a in the thickness direction of the inorganic material substrate 1. The second ground electrode 3 is typically in direct contact with the inorganic material substrate 1. The second ground electrode 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 second ground electrode 3 needs to ensure an adhesion strength that makes it easy to flatten the bonding surface, and the metal of the second ground electrode 3 may be different from the metal of the conductor layer 2. The thickness range of the second ground electrode 3 is the same as the thickness range of the conductor layer 2. The second ground electrode 3 is formed on the inorganic material substrate 1 typically by sputtering or plating.

[0027] E. 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, crystal, 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. When active elements such as an oscillator or a receiver are mounted on the waveguide element 100, 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).

[0028] 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. In the case of a coplanar line, when the thickness of the director element is small, the propagating electromagnetic waves may seep into the support substrate, and the propagation loss can be suppressed by reducing the dielectric loss tangent. From this viewpoint, it is preferable that the dielectric loss tangent of the support substrate 7 is 0.07 or less.

[0029] The thickness of the support substrate 7 is, for example, 50 μm or more, preferably 100 μm or more, more preferably 150 μm or more, and, for example, 3000 μm or less, preferably 2000 μm or less, more preferably 300 μm or less. In one embodiment, the thickness of the support substrate 7 is greater than the thickness of the inorganic material substrate. If 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, the slab mode propagation can be suppressed, the waveguide element can be made thinner (the mechanical strength of the waveguide element can be maintained), and the substrate resonance can be suppressed.

[0030] The support substrate 7 supports the conductor layer 2, the inorganic material substrate 1, and the second ground electrode 3. More specifically, the support substrate 7 may be directly bonded to the inorganic material substrate 1 only via the second ground electrode 3, or may be directly bonded to the inorganic material substrate 1 via the second ground electrode 3 and a bonding portion (not shown). In this specification, the term "direct bonding" means that two layers or substrates are bonded together without the use of an adhesive. The form of direct bonding can be appropriately set depending on the configuration of the layers or substrates to be bonded together. By integrating them by direct bonding, peeling in the waveguide element can be effectively suppressed, and as a result, damage (e.g., cracks) to the inorganic material substrate caused by such peeling can be effectively suppressed. Details of direct bonding will be described in Section H below. When the supporting substrate 7 is joined to the inorganic material substrate 1 only via the second ground electrode 3, the second ground electrode 3 functions as a joining part joining the inorganic material substrate 1 and the supporting substrate 7, and the supporting substrate 7 is in direct contact with the second ground electrode 3. When the support substrate 7 is joined to the inorganic material substrate 1 via the second ground electrode 3 and the joint, the joint is provided between the second ground electrode 3 and the support substrate 7. The joint may be a single layer, or may be a laminate of two or more layers. Examples of the joint include a SiO2 layer, an amorphous silicon layer, and a tantalum oxide layer. In addition, 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 second ground electrode or between the support substrate and the second ground electrode. The thickness of the joint is, for example, 0.01 μm or more and 3 μm or less.

[0031] F. Third ground electrode In one embodiment, the third ground electrode 4 is provided on the surface of the support substrate 7 opposite to the second ground electrode 3. The third ground electrode 4 is disposed at a distance from the second ground electrode 3 in the thickness direction of the inorganic material substrate 1. The third ground electrode 4 is typically in direct contact with the support substrate 7. The third ground electrode 4 is made of the same metal as the conductor layer 2, and the thickness range of the third ground electrode 4 is the same as the thickness range of the conductor layer 2. The third ground electrode 4 is formed on the support substrate 7 by, for example, sputtering or plating. The third ground electrode 4 does not necessarily have to be formed on the entire surface of the support substrate 7 opposite to the second ground electrode.

[0032] G.Beer In the director element 100, the vias 5 are provided on both sides of the signal electrode 2a in a direction intersecting (preferably perpendicular to) the longitudinal direction of the signal electrode 2a. In the following, the vias electrically connecting the first ground electrode 2b and the third ground electrode 4 may be referred to as vias 5a, and the vias electrically connecting the first ground electrode 2c and the third ground electrode 4 may be referred to as vias 5b, and may be distinguished from each other. The vias 5a are in contact with the first ground electrode 2b and the third ground electrode 4, and extend continuously between the first ground electrode 2b and the third ground electrode 4. The vias 5b are in contact with the first ground electrode 2c and the third ground electrode 4, and extend continuously between the first ground electrode 2c and the third ground electrode 4. Each of the vias 5a and 5b penetrates the second ground electrode 3 and is in contact with the second ground electrode 3. The director element may include only one of the vias 5a and 5b.

[0033] The via 5 is typically a conductive film. The via 5 is made of a conductive material, typically made of the same metal as the conductive layer 2. The shape of the via 5 corresponds to the shape of the via hole 8 in which it is arranged. That is, the waveguide element 100 has a via hole 8. In the illustrated example, the via hole in which the via 5a is arranged may be referred to as the via hole 8a, and the via hole in which the via 5b is arranged may be referred to as the via hole 8b, to be distinguished from each other. The via hole 8 penetrates the inorganic material substrate 1, the second ground electrode 3, and the support substrate 7. The via hole 8 typically has a circular shape when viewed from the surface (upper surface) direction of the inorganic material substrate 1. When the via hole has a circular shape, the inner diameter of the via hole is, for example, 10 μm or more, preferably 20 μm or more, and, for example, 200 μm or less, preferably 100 μm or less, more preferably 80 μm or less. 2, via hole 8 has a circular shape when viewed from the surface (top) direction of inorganic material substrate 1, and penetrates inorganic material substrate 1, second ground electrode 3, and supporting substrate 7 linearly along the thickness direction of inorganic material substrate 1. When the via hole is circular and linear, via 5 has a columnar or cylindrical shape extending along the thickness direction of inorganic material substrate 1. In this case, the range of the outer diameter of via 5 is the same as the range of the inner diameter of the above-mentioned via hole. 3, the via hole 8 may have a circular shape when viewed from the surface (upper) direction of the inorganic material substrate 1, and may have a tapered shape with a smaller diameter toward the second ground electrode 3. Although not shown, the via hole 8 may have a circular shape when viewed from the surface (upper) direction of the inorganic material substrate 1, and may have a tapered shape with a larger diameter toward the second ground electrode 3. When the via hole has a tapered shape, it is possible to provide the following features: it is easy to form a conductive layer in the via, and it is easy to ensure the strength of the substrate. Furthermore, the via may be formed so that the conductive material is embedded in the via hole. When the via hole is circular and tapered, the structure of the via 5 is not particularly limited, but the via 5 preferably has an hourglass shape in which the diameter is small at the contact portion with the second ground electrode 3 and the diameter becomes larger as it moves away from the second ground electrode 3. In other words, the via 5 preferably has a shape in which the apexes of two cones are connected to each other. In this case, the maximum outer diameter of the via 5 falls within the above range. In one embodiment, the outer diameter of one end of the via 5 that contacts the first ground electrodes 2b and 2c is smaller than the outer diameter of the other end of the via 5 that contacts the third ground electrode 4. In the via 5, the taper angle on the conductor layer 2 side with respect to the second ground electrode is smaller than the taper angle on the third ground electrode side with respect to the second ground electrode. In the illustrated example, the first ground electrode and the third ground electrode are each formed to block the via hole, but the configuration of the first ground electrode and the third ground electrode is not limited to this. Each of the first ground electrode and the third ground electrode only needs to be electrically connected to the via, and may be open without blocking the via hole.

[0034] 1, 4, and 5, the waveguide element 100 preferably includes a plurality of vias 5a. As shown in FIGS. 1 and 4, the plurality of vias 5a may be arranged at intervals in the longitudinal direction of the signal electrode 2a. As shown in FIG. 5, the plurality of vias 5a may be arranged at intervals in a direction intersecting (preferably perpendicular) the longitudinal direction of the signal electrode 2a. In other words, the waveguide element 100 may have a plurality of rows of vias 5a arranged in the longitudinal direction of the signal electrode 2a in a direction intersecting (preferably perpendicular) the longitudinal direction of the signal electrode 2a. The pitch P of the multiple vias 5a (the distance between the centers of adjacent vias 5a) is, for example, 20 μm or more, preferably 30 μm or more, and for example, 300 μm or less, preferably 200 μm or less, more preferably 100 μm or less. Similarly to the via 5a, the waveguide element 100 may also include a plurality of vias 5b.

[0035] H. Method of manufacturing waveguide elements Next, a method for manufacturing the waveguide element 100 will be described with reference to Figures 1 and 2. In one embodiment, the method for manufacturing the waveguide element 100 includes the steps of: preparing a laminate 11 including, in this order, an inorganic material substrate 1, a second ground electrode 3, and a support substrate 7, and having a via hole 8 penetrating the inorganic material substrate 1, the second ground electrode 3, and the support substrate 7; and forming a conductor layer 2 on the upper part of the inorganic material substrate 1, forming a via 5 in the via hole 8, and forming a third ground electrode 4 on the lower part of the support substrate 7.

[0036] When the inorganic material substrate 1 and the support substrate 7 are joined via the second ground electrode 3, in order to prepare such a laminate 11, first, the metal constituting the second ground electrode 3 is sputtered onto the surface of the inorganic material substrate 1 to form a first metal thin film as a first joint. Furthermore, the metal constituting the second ground electrode 3 is sputtered onto the surface of the support substrate 7 to form a second metal thin film as a second joint. In addition, in terms of ensuring adhesion strength and preventing migration, when forming the first metal thin film and the second metal thin film, a metal film of Ti, Cr, Ni, Pt, or Pd may be formed as an intermediate layer. Then, in a high vacuum chamber (e.g., 1×10 -6 A neutralizing beam is irradiated to each of the bonding surfaces of the components (layers or substrates) to be bonded at a pressure of about 100 Pa. This activates each bonding surface. Next, the activated bonding surfaces are brought into contact with each other in a vacuum atmosphere and bonded at room temperature. The load during this bonding can be, for example, 100 N to 20,000 N. In one embodiment, when performing surface activation using the neutralizing beam, an inert gas is introduced into the chamber, and a high voltage is applied from a DC power source to an electrode placed in the chamber. With this configuration, electrons are moved by an electric field generated between the electrode (positive electrode) and the chamber (negative electrode), and a beam of atoms and ions is generated by the inert gas. Of the beams that reach the grid, the ion beam is neutralized by the grid, and a beam of neutral atoms is emitted from the high-speed atom beam source. The atomic species that constitute the beam is preferably an inert gas element (for example, argon (Ar), nitrogen (N)). The voltage during activation by beam irradiation is, for example, 0.5 kV to 2.0 kV, and the current is, for example, 50 mA to 200 mA. The direct bonding method is not limited to this, and surface activation methods using FAB (Fast Atom Beam) or an ion gun, atomic diffusion methods, plasma bonding methods, etc. can also be used. In this manner, the first metal thin film as the first bonding portion and the second metal thin film as the second bonding portion are directly bonded and integrated to form the second ground electrode 3. This results in a laminate 11 having a configuration of inorganic material substrate 1 / second ground electrode 3 / support substrate 7.

[0037] Furthermore, when the inorganic material substrate 1 and the support substrate 7 are joined via the second ground electrode 3 and a joint, in order to prepare such a laminate 11, the above-mentioned second ground electrode 3 is formed on the surface of the above-mentioned inorganic material substrate 1 by sputtering. Next, the above-mentioned joint is formed on the second ground electrode 3 (more specifically, a Cr thin film having a thickness of 0.02 μm and an amorphous silicon layer having a thickness of 0.1 μm are formed in that order). After the film formation, a flattening process is performed, for example, by CMP polishing. Furthermore, if necessary, a joint is also formed on the support substrate in the same manner as described above. Next, the inorganic material substrate and the support substrate are directly bonded in the same manner as above, thereby obtaining a laminate 11 having a structure of inorganic material substrate 1 / second ground electrode 3 / joint portion / support substrate 7.

[0038] Thereafter, via holes 8a and 8b penetrating inorganic material substrate 1, second ground electrode 3 and supporting substrate 7 all at once are formed by, for example, laser processing (more specifically, processing with a laser having a wavelength of 515 nm and a pulse width of 10 ps). Next, a thin metal film (more specifically, a thin Ti film having a thickness of 0.15 μm and a thin palladium film having a thickness of 0.04 μm are sequentially formed) is deposited on the sidewall portions of the via holes 8a and 8b, the front surface of the inorganic material substrate 1, and the rear surface of the support substrate 7, for example, by an ICP (inductively coupled plasma) sputtering device, and then a thin metal film (for example, a thin copper film having a thickness of 1.5 μm) is formed on the front surface by, for example, plating (more specifically, electrolytic plating). Thereafter, a resist is applied to the surface of the inorganic material substrate 1, and the resist is patterned by photolithography so as to expose the portions that form the gaps in the conductor layer 2 and mask the other portions. Thereafter, the conductor layer 2 (coplanar electrodes or microstrip electrodes) is formed by, for example, wet etching (more specifically, ferric chloride water). As a result, a conductor layer is formed on the upper part of the inorganic material substrate 1, a via 5 is formed in the via hole 8, and a third ground electrode 4 is formed on the lower part of the support substrate 7. Therefore, compared with the case where the conductor layer, the via, and the third ground electrode are formed separately, the waveguide element can be manufactured smoothly. Thereafter, the resist is removed. Note that, in the above embodiment, after the via 5 and the third ground electrode 4 are formed, the conductor layer 2 is formed by etching, but the present invention is not limited to this. The via 5, the third ground electrode 4, and the conductor layer 2 can also be formed simultaneously. In this manner, the director element 100 can be manufactured. In the above, the process of forming a laminate and then forming a via hole to prepare a laminate having a via hole has been described in detail, but the process of preparing a laminate is not limited to this. After forming holes in each of the inorganic material substrate, the second ground electrode, and the support substrate, the inorganic material substrate, the second ground electrode, and the support substrate can also be bonded so that the holes communicate with each other to form a via hole. EXAMPLES

[0039] The present invention will be specifically described below with reference to Reference Examples, but the present invention is not limited to these Reference Examples.

[0040] <Reference example 1> 1-1. Fabrication of waveguide elements (coplanar lines) A 0.5 mm thick quartz glass wafer (quartz glass substrate, inorganic material substrate) was prepared, and a 0.2 μm thick amorphous silicon film was formed on the quartz glass wafer by sputtering. After film formation, the amorphous silicon film was polished and flattened. Here, the arithmetic mean roughness of the surface of the amorphous silicon film over a 10 μm square was measured using an atomic force microscope, and was found to be 0.2 nm.

[0041] A silicon wafer (support substrate) with a thickness of 525 μm was also prepared. The arithmetic mean roughness of the surface of the silicon wafer, measured over a 10 μm square area, was 0.2 nm using an atomic force microscope.

[0042] The amorphous silicon surface of the quartz glass wafer and the silicon wafer were directly bonded as follows. First, the quartz glass wafer and the silicon wafer were placed in a vacuum chamber and heated for 10 -6In a vacuum of the Pa range, both bonding surfaces (the amorphous silicon surface of the quartz glass wafer and the surface of the silicon wafer) were irradiated with a high-speed Ar neutral atomic beam (accelerating voltage 1 kV, Ar flow rate 60 sccm) for 70 seconds. After irradiation, the quartz glass wafer and silicon wafer were left to cool for 10 minutes, and then the bonding surfaces of the quartz glass wafer and silicon wafer (the beam-irradiated surfaces of the quartz glass wafer and silicon wafer) were brought into contact and pressed at 4.90 kN for 2 minutes to bond the quartz glass wafer and silicon wafer. After bonding, the quartz glass wafer was polished to a thickness of 150 μm to form a composite wafer. No defects such as peeling were observed at the bonding interface in the obtained quartz glass / silicon composite substrate.

[0043] Next, a resist was applied to the surface (polished surface) of the quartz glass wafer opposite the silicon wafer, and photolithography was used to pattern the surface so as to expose the area where the coplanar electrode pattern was to be formed. After that, a 50 nm thick Cr film and a 100 nm thick Ni film were formed by sputtering on the upper surface of the quartz glass wafer exposed from the resist to form a base electrode. Furthermore, a copper film was formed by electrolytic plating on the base electrode to form a coplanar electrode pattern. The length of the signal electrode in the waveguiding direction was 10 mm. In this manner, a waveguide element including a coplanar electrode, an inorganic material substrate, and a supporting substrate was obtained.

[0044] 1-2. Calculating propagation loss In order to measure the propagation loss of the director elements, three director elements with signal electrodes having lengths of 30 mm, 40 mm, and 50 mm were fabricated in the same manner as above. Next, an RF signal generator was coupled to the input side of the director element by a probe, and an electromagnetic wave was coupled to an RF signal receiver by installing a probe on the output side of the director element. Next, a voltage was applied to the RF signal generator, causing it to transmit electromagnetic waves at the frequencies shown in Table 1. This caused the electromagnetic waves to propagate through the coplanar line (waveguide element). The RF signal receiver measured the RF power of the electromagnetic waves output from the coplanar line. From the measurement results of three waveguide elements with different signal electrode lengths, the propagation loss (dB / cm) was calculated and evaluated according to the following criteria. The results are shown in Table 1. ◎: Less than 0.5dB / cm ○: 0.5dB / cm or more and less than 1dB / cm △: 1dB / cm or more and less than 2dB / cm ×: 2dB / cm or more

[0045] <Reference example 2> 2-1. Fabrication of a waveguide element (coplanar line with ground) A 0.5 mm thick quartz glass wafer (quartz glass substrate, inorganic material substrate) was prepared, and a 50 nm thick Cr film and a 100 nm thick Ni film were formed on the quartz glass wafer by sputtering to form a base electrode. Furthermore, a copper film was formed on the base electrode by electrolytic plating to form a second ground electrode. Next, a 0.2 μm thick amorphous silicon film was formed on the second ground electrode by sputtering. After film formation, the amorphous silicon film was polished and flattened. Here, the arithmetic mean roughness of the surface of the amorphous silicon film over 10 μm square was measured using an atomic force microscope, and was found to be 0.2 nm.

[0046] A silicon wafer (support substrate) with a thickness of 525 μm was also prepared. The arithmetic mean roughness of the surface of the silicon wafer, measured over a 10 μm square area, was 0.2 nm using an atomic force microscope.

[0047] Thereafter, the amorphous silicon surface formed on the ground electrode was directly bonded to the silicon wafer. The direct bonding was performed in the same manner as in Reference Example 1. In the obtained quartz glass / second ground electrode / silicon composite substrate, no defects such as peeling were observed at the bonding interface. The quartz glass wafer was then polished to a thickness of 150 μm.

[0048] Next, a coplanar electrode pattern was formed on the surface (polished surface) of the quartz glass wafer opposite to the silicon wafer in the same manner as in Reference Example 1. The length of the signal electrode in the waveguiding direction was 10 mm. In this manner, a waveguide element including the coplanar electrode, the inorganic material substrate, the second ground electrode, and the supporting substrate was obtained.

[0049] 2-2. Calculating propagation loss In addition, in order to measure the propagation loss of the director element, three director elements with signal electrode lengths of 30 mm, 40 mm, and 50 mm were fabricated in the same manner as described above. Then, the RF power of the electromagnetic wave output from the coplanar line was measured by an RF signal receiver in the same manner as in Reference Example 1. The propagation loss of the director element of Reference Example 2 was evaluated in the same manner as in Reference Example 1. The results are shown in Table 1.

[0050] <Reference example 3> 3-1. Fabrication of waveguide element (microstrip line) In the same manner as in Reference Example 2, a quartz glass / second ground electrode / silicon composite substrate was obtained. Next, a resist was applied to the surface (polished surface) of the quartz glass wafer opposite the silicon wafer, and patterned by photolithography to expose the portion where the microstrip electrode was to be formed. After that, a 50 nm thick Cr film and a 100 nm thick Ni film were formed by sputtering on the upper surface of the quartz glass wafer exposed from the resist to form a base electrode. Furthermore, a copper film was formed by electrolytic plating on the base electrode to form a microstrip electrode. The length of the microstrip electrode in the waveguiding direction was 10 mm. In this manner, a waveguide element including a microstrip electrode, an inorganic material substrate, and a supporting substrate was obtained.

[0051] 3-2. Calculating propagation loss In addition, in order to measure the propagation loss of the director element, three director elements with microstrip electrodes of lengths of 30 mm, 40 mm, and 50 mm were fabricated in the same manner as described above. Then, the RF power of the electromagnetic waves output from the coplanar line was measured by an RF signal receiver in the same manner as in Reference Example 1. The propagation loss of the director element of Reference Example 3 was evaluated in the same manner as in Reference Example 1. The results are shown in Table 1.

[0052] <Reference examples 4~6> Except for changing the thickness of the polished quartz glass wafer (inorganic material substrate) to the value shown in Table 1, waveguide elements were fabricated in the same manner as in each of Reference Examples 1 to 3. For the obtained waveguide element, the propagation loss was calculated and evaluated in the same manner as in Reference Example 1. The results are shown in Table 1.

[0053] <Reference example 7> A waveguide element was fabricated in the same manner as in Reference Example 1, except that the quartz glass wafer used as the inorganic material substrate was changed to a single crystal silicon wafer, and the thickness of the polished silicon wafer was changed to the value shown in Table 1. For the obtained waveguide element, the propagation loss was calculated and evaluated in the same manner as in Reference Example 1. The results are shown in Table 1.

[0054] <Reference example 8> A waveguide element was fabricated in the same manner as in Reference Example 1, except that the quartz glass wafer used as the inorganic material substrate was changed to a sapphire wafer, and the thickness of the polished sapphire wafer was changed to the value shown in Table 1. For the obtained waveguide element, the propagation loss was calculated and evaluated in the same manner as in Reference Example 1. The results are shown in Table 1.

[0055] <Reference example 9> A waveguide element was fabricated in the same manner as in Reference Example 1, except that the quartz glass wafer used as the inorganic material substrate was changed to a polycrystalline AlN wafer, and the thickness of the polished AlN wafer was changed to the value shown in Table 1. For the obtained waveguide element, the propagation loss was calculated and evaluated in the same manner as in Reference Example 1. The results are shown in Table 1.

[0056] <Reference example 10> A waveguide element was fabricated in the same manner as in Reference Example 1, except that the thickness of the polished quartz glass wafer (inorganic material substrate) was changed to the value shown in Table 1. For the obtained waveguide element, the propagation loss was calculated and evaluated in the same manner as in Reference Example 1. The results are shown in Table 1.

[0057] <Reference examples 11~14> A waveguide element was fabricated in the same manner as in Reference Example 3, except that the thickness of the polished quartz glass wafer (inorganic material substrate) was changed to the value shown in Table 1. For the obtained waveguide element, the propagation loss was calculated and evaluated in the same manner as in Reference Example 1. The results are shown in Table 1.

[0058] <Reference example 15> A waveguide element was fabricated in the same manner as in Reference Example 2, except that the thickness of the polished quartz glass wafer was changed to 300 μm. For the obtained waveguide element, the propagation loss was calculated and evaluated in the same manner as in Reference Example 1. The results are shown in Table 1.

[0059] <Reference example 16> A quartz glass wafer (quartz glass plate, inorganic material substrate) having a thickness of 2100 μm was prepared, and a waveguide element was fabricated in the same manner as in Reference Example 3, except that the thickness of the polished quartz glass wafer was changed to 2000 μm. For the obtained waveguide element, the propagation loss was calculated and evaluated in the same manner as in Reference Example 1. The results are shown in Table 1.

[0060] [Table 1]

[0061] As is clear from Table 1, when the thickness of the inorganic material substrate satisfies the above formula (1), the propagation loss when a high-frequency electromagnetic wave exceeding 30 GHz is guided is relatively small. [Industrial Applicability]

[0062] 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]

[0063] 1 Inorganic material substrate 2 Conductor layer 2a signal electrode 2b,2c 1st ground electrode 3 Second ground electrode 4 Third ground electrode 5 Via 8 Beer Hall 11 Laminate

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 an upper portion of the inorganic material substrate, the conductor layer including a signal electrode extending in a predetermined direction and a first ground electrode disposed at an interval from the signal electrode in a direction intersecting the predetermined direction; a support substrate located on the opposite side of the inorganic material substrate from the conductor layer; a second ground electrode located between the inorganic material substrate and the support substrate; a third ground electrode located on the opposite side of the support substrate from the second ground electrode; a via that electrically connects the first ground electrode and the third ground electrode and is also electrically connected to the second ground electrode; 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. The waveguide element according to claim 1 , wherein in the formula (1), a is a numerical value of 6 or more.

3. 3. The waveguide element according to claim 1, wherein the relative dielectric constant ε and the dielectric loss tangent tan δ of the inorganic material substrate at 300 GHz are 3.5 to 12.0 and 0.003 or less, respectively.

4. The waveguide element according to claim 3 , wherein the inorganic material substrate is a quartz glass substrate.

5. 5. The waveguide element according to claim 1, wherein the conductor layer is a coplanar electrode.

6. 5. The waveguide element according to claim 1, wherein the conductor layer and the second ground electrode are microstrip type electrodes.

7. 7. The waveguide element according to claim 5, wherein the inorganic material substrate has a thickness of 10 [mu]m or more when the frequency of the electromagnetic wave propagating through the waveguide element is 30 GHz or more and 5 THz or less.

8. 8. The waveguide element according to claim 1, further comprising a via hole in which the via is disposed, the via hole penetrating the inorganic material substrate, the second ground electrode and the support substrate.

9. 9. The waveguide element according to claim 8, wherein the via hole has a circular shape when viewed from the surface (upper surface) direction of the inorganic material substrate, and has a tapered shape whose diameter decreases toward the second ground electrode.

10. 9. The waveguide element according to claim 8, wherein the via hole has a circular shape when viewed from the surface (upper surface) direction of the inorganic material substrate, and has a tapered shape whose diameter increases as it approaches the second ground electrode.

11. A method for producing a waveguide element according to any one of claims 8 to 10, comprising the steps of: preparing a laminate including the inorganic material substrate, the second ground electrode, and the support substrate in this order, the laminate having a via hole penetrating all of the substrates; forming the via in the via hole, forming the third ground electrode on the lower part of the support substrate, and forming the conductor layer on the upper part of the inorganic material substrate.

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