Waveguide

Abstract

To provide a waveguide element capable of ensuring excellent low propagation loss performance even when guiding a high-frequency electromagnetic wave with a frequency of 30 GHz or more.SOLUTION: A waveguide element 100 includes a waveguide member 10 capable of guiding an electromagnetic wave whose frequency is 30 GHz or more and 20 THz or less. The waveguide member includes an inorganic material substrate 1 and a conductor layer 6, which is a coplanar electrode 2 provided on an upper part of the inorganic material substrate. A thickness t of the inorganic material substrate satisfies the following equation (1). In the equation, λ represents a wavelength of an electromagnetic wave guided in the waveguide member, 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.

Background Art

[0002] As one of the elements for guiding millimeter waves to terahertz waves, the development of waveguide elements has been promoted. Waveguide elements are expected to be applied and expanded in a wide range of fields such as optical waveguides, next-generation high-speed communication, sensors, laser processing, and solar power generation. As an example of such a waveguide element, a technique using 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 a surface of the transparent substrate opposite to the antenna conductor has been proposed (Patent Document 1). However, according to such a technique, there is a problem that when guiding millimeter waves to terahertz waves, the propagation loss significantly increases.

Prior Art Documents

Patent Documents

number

[10] The waveguide element described in [5] or [6] above comprises a support substrate provided below the waveguide member and supporting the waveguide member, and the support substrate may have a ground electrode on the side on which the waveguide member is formed.

[11] In the waveguide element described in any of [1] to [4] above, the conductor layer is a microstrip type electrode, the waveguide element is provided below the waveguide member and includes a support substrate that supports the waveguide member, and the support substrate may have a ground electrode on the side on which the waveguide member is formed.

[12] The waveguide element described in any of [9] to

[11] above may have a back surface conductor layer on the side of the support substrate opposite to the side on which the waveguide member is provided. [Effects of the Invention]

[0006] According to embodiments of the present invention, a waveguide element can be realized that can ensure excellent low propagation loss performance even when guiding high-frequency electromagnetic waves with a frequency of 30 GHz or higher. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic perspective view of a waveguide element according to an embodiment of the present invention. [Figure 2] Figure 2 is a cross-sectional view of the waveguide element in Figure 1, taken along line II-II'. [Figure 3] Figure 3 is a schematic perspective view of a waveguide element according to another embodiment of the present invention. [Figure 4] Figure 4 is a cross-sectional view of the waveguide element shown in Figure 3, taken along line IV-IV'. [Figure 5] Figure 5 is a schematic perspective view of a waveguide element according to yet another embodiment of the present invention. [Figure 6] Figure 6 is a cross-sectional view of the waveguide element shown in Figure 5, taken along the line VI-VI'. [Figure 7] Figure 7 is a schematic perspective view of a waveguide element according to yet another embodiment of the present invention. [Figure 8] Figure 8 is a cross-sectional view of the waveguide element in Figure 7, taken along the line VIII-VIII'. [Figure 9] Figure 9(a) is a schematic cross-sectional view of the waveguide element of Figure 1 with a junction. Figure 9(b) is a schematic cross-sectional view of the waveguide element of Figure 3 with a junction. [Figure 10] FIG. 10(a) is a schematic cross-sectional view of the waveguide element of FIG. 5 including a joint portion. FIG. 10(b) is a schematic cross-sectional view of the waveguide element of FIG. 7 including a joint portion in an embodiment. [Figure 11] FIG. 11(a) is a schematic cross-sectional view of the waveguide element of FIG. 3 in a mode where a joint portion is provided between an inorganic material substrate and a ground electrode. FIG. 11(b) is a schematic cross-sectional view of the waveguide element of FIG. 5 in a mode where a joint portion is provided between an inorganic material substrate and a ground electrode. FIG. 11(c) is a schematic cross-sectional view of the waveguide element of FIG. 7 in a mode where a joint portion is provided between an inorganic material substrate and a ground electrode.

Embodiments for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments. A. Overall Configuration of Waveguide Element A-1. Overall Configuration of Waveguide Element 100 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 taken along line II-II' of the waveguide element of FIG. 1. The illustrated waveguide element 100 includes a waveguide member 10. The waveguide member 10 can guide electromagnetic waves having a frequency of 30 GHz or more and 20 THz or less, that is, electromagnetic waves in the millimeter wave to terahertz wave range. Note that millimeter waves are typically electromagnetic waves having a frequency of about 30 GHz to 300 GHz; terahertz waves are typically electromagnetic waves having a frequency of about 300 GHz to 20 THz. The waveguide member 10 includes an inorganic material substrate 1 and a conductor layer 6 provided on the upper portion of the inorganic material substrate 1. The thickness of the inorganic material substrate 1 satisfies the following formula (1).

Equation

[0009] In one embodiment, in formula (1) above, a represents a numerical value of 6 or greater. When the thickness of the inorganic material substrate satisfies equation (1), where a is a value of 6 or greater, it is possible to stably reduce the propagation loss when guiding the high-frequency electromagnetic waves described above.

[0010] The relative permittivity ε of the inorganic material substrate 1 at 300 GHz is typically 3.5 or higher, typically 12.0 or lower, preferably 10.0 or lower, and more preferably 5.0 or lower. The dielectric loss tangent (dielectric loss) tanδ of the inorganic material substrate 1 at 300 GHz is typically 0.0030 or less, preferably 0.0020 or less, and more preferably 0.0015 or less. If the relative permittivity ε and dielectric loss tangent (dielectric loss) tanδ of the inorganic material substrate are within the above range, the propagation loss when guiding the high-frequency electromagnetic waves (especially electromagnetic waves above 300 GHz) can be reduced more stably. The relative permittivity ε and dielectric loss tangent (dielectric loss) tanδ can be measured by terahertz time-domain spectroscopy. In this specification, unless otherwise specified regarding the measurement frequency of relative permittivity and dielectric loss tangent, it refers to the relative permittivity and dielectric loss tangent at 300 GHz.

[0011] The thickness of the inorganic material substrate 1 that satisfies 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, 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. From the viewpoint of miniaturization by reducing the size of the electrodes, the thickness of the inorganic material substrate 1 is preferably 80 μm or less, and even more preferably 60 μm or less. Also, when the frequency of the electromagnetic waves propagating through the waveguide member is 30 GHz or more and 5 THz or less, the thickness of the inorganic material substrate 1 is preferably 10 μm or more. To ensure strength, the thickness of the inorganic material substrate 1 is preferably 30 μm or more, and even more preferably 40 μm or more. When the thickness of the inorganic material substrate 1 falls below the above lower limit, the thickness and width of the electrodes constituting the waveguide element become smaller, down to about a few micrometers. This increases propagation loss due to the skin effect, and also significantly reduces the tolerance of the transmission line performance due to manufacturing variations. If the thickness of the inorganic material substrate 1 is below the above upper limit, the induction of slab modes and the occurrence of substrate resonance are suppressed, making it possible to realize a waveguide element with low propagation loss over a wide frequency range (i.e., broadband).

[0012] The waveguide member 10 in the illustrated example constitutes a coplanar transmission line. That is, the conductor layer 6 of the waveguide member 10 is a coplanar electrode 2. The coplanar electrode 2 is provided on the upper surface of the inorganic material substrate 1. The coplanar electrode 2 consists of a signal electrode 2a, a first ground electrode 2b, and a second ground electrode 2c. The signal electrode 2a has a linear shape extending in a predetermined direction. The width w of the signal electrode 2a is, for example, 2 μm or more, preferably 20 μm or more, for example 200 μm or less, preferably 150 μm or less. The first ground electrode 2b is positioned at a distance from the signal electrode 2a in a direction perpendicular to the longitudinal direction of the signal electrode 2a. The second ground electrode 2c is located on the opposite side of the signal electrode 2a from the first ground electrode 2b in a direction perpendicular to the longitudinal direction of the signal electrode 2a, and is positioned at a distance from the signal electrode 2a. As a result, a gap (slit) extending in the longitudinal direction of the signal electrode 2a is formed between the signal electrode 2a and the ground electrodes 2b and 2c. The width g of the void (slit) is, for example, 2 μm or more, preferably 5 μm or more, for example 100 μm or less, preferably 80 μm or less.

[0013] In such a coplanar transmission line, when a voltage is applied to the coplanar electrode 2, an electric field is generated between the signal electrode 2a and the ground electrodes 2b and 2c. When the high-frequency electromagnetic waves described above are input to the director element 100, they couple with the electric field generated between the signal electrode 2a and the ground electrodes 2b and 2c and propagate through the inorganic material substrate 1.

[0014] The illustrated waveguide element 100 is provided below the waveguide member 10 and further comprises a support substrate 20 that supports the waveguide member 10. While the mechanical strength of a waveguide element can be increased by providing a support substrate, when the waveguide member guides the aforementioned high-frequency electromagnetic waves, substrate resonance may occur at the thickness including the substrate, potentially increasing propagation loss. However, in the above configuration, the thickness of the inorganic material substrate satisfies equation (1) above, and the dielectric constants of the support substrate and the waveguide member are different, so even when the waveguide member guides the high-frequency electromagnetic waves described above, the occurrence of substrate resonance can be suppressed. Therefore, even when the waveguide element is equipped with a support substrate and guides the high-frequency electromagnetic waves described above, an increase in propagation loss can be suppressed. From this perspective, a larger difference in dielectric constant between the waveguide member and the support substrate is desirable, and furthermore, the dielectric constant of the support substrate should be smaller than that of the waveguide member. If the dielectric constant of the support substrate is larger than that of the waveguide member, a layer with a lower dielectric constant may be provided between the waveguide member and the support substrate. Furthermore, to completely suppress substrate resonance, grounded coplanar lines or microstrip lines can be used, as described later.

[0015] In the illustrated example of the waveguide element 100, a support substrate is provided to support the waveguide member, but the waveguide element of the present invention does not require a support substrate. In other words, the waveguide element may consist only of the waveguide member. The same applies to the waveguide elements 101 and 102 described later.

[0016] A-2. Overall configuration of the director element 101 Figure 3 is a schematic perspective view of a waveguide element according to another embodiment of the present invention; Figure 4 is a cross-sectional view of the waveguide element of Figure 3 along the line IV-IV'. In the illustrated waveguide element 101, the waveguide member 11 constitutes a grounded coplanar line and comprises a coplanar electrode 2, an inorganic material substrate 1, and a ground electrode 3. The ground electrode 3 is located on the opposite side of the inorganic material substrate 1 from the coplanar electrode 2. In one embodiment, the ground electrode 3 is provided on the inorganic material substrate 1 on the side opposite to the surface on which the coplanar electrode 2 (conductor layer 6) is formed. In the illustrated waveguide element 101, the ground electrode 3 is located between the inorganic material substrate 1 and the support substrate 20. If the waveguide member 11 is equipped with a ground electrode 3, the electric field generated between the signal electrode 2a and the ground electrodes 2b and 2c will not leak from the inorganic material substrate 1 to the support substrate 20, thereby suppressing propagation loss due to substrate resonance and stray capacitance generation. The width w of the signal electrode 2a is, for example, 2 μm or more, preferably 20 μm or more, for example 300 μm or less, preferably 250 μm or less. The width g of the void (slit) is, for example 2 μm or more, preferably 5 μm or more, for example 200 μm or less, preferably 150 μm or less.

[0017] Furthermore, as shown in Figures 7 and 8, the ground electrodes 2b and 2c may be electrically connected to the ground electrode 3. When the ground electrodes 2b and 2c are electrically connected to the ground electrode 3, the ground can be strengthened and stray capacitance caused by surrounding lines and elements can be suppressed. In the illustrated example, multiple via holes are formed in the inorganic material substrate 1, and vias 5 located within each via hole short-circuit the first ground electrode 2b and ground electrode 3, and the second ground electrode 2c and ground electrode 3, respectively. The vias 5 that short-circuit the first ground electrode 2b and ground electrode 3 and the vias 5 that short-circuit the second ground electrode 2c and ground electrode 3 are spaced apart from each other in a direction intersecting the longitudinal direction of the signal electrode 2a. The vias 5 are typically conductive films. The arrangement of the multiple via holes is not particularly limited, but in the illustrated example, the multiple via holes are aligned in the longitudinal direction of the signal electrode 2a.

[0018] A-3. Overall configuration of director element 102 Figure 5 is a schematic perspective view of a waveguide element according to yet another embodiment of the present invention; Figure 6 is a cross-sectional view of the waveguide element of Figure 5 along the line VI-VI'. In the illustrated example of the waveguide element 102, the waveguide member 12 constitutes a microstrip line and comprises a microstrip-type electrode 4 as a conductor layer 6, an inorganic material substrate 1, and a ground electrode 3. The microstrip electrode 4 has a flat strip shape extending in a predetermined direction. The width w of the microstrip electrode 4 is, for example, 100 μm or more, preferably 300 μm or more, for example 800 μm or less, preferably 500 μm or less. The ground electrode 3 is located on the opposite side of the inorganic material substrate 1 from the microstrip electrode 4. In one embodiment, the ground electrode 3 is provided on the inorganic material substrate 1 on the side opposite to the side on which the microstrip electrode 4 (conductor layer 6) is formed. In the illustrated waveguide element 102, the ground electrode 3 is located between the inorganic material substrate 1 and the support substrate 20.

[0019] In such a microstrip line, when a voltage is applied to the microstrip electrode 4 and the ground electrode 3, an electric field is generated between the microstrip electrode 4 and the ground electrode 3. When the high-frequency electromagnetic waves described above are input to the director element 102, they couple with the electric field generated between the microstrip electrode 4 and the ground electrode 3 and propagate through the inorganic material substrate 1.

[0020] In this specification, "waveguide element" includes 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.

[0021] B. Inorganic material substrate The inorganic material substrate 1 has an upper surface on which a conductive layer 6 is provided, and a lower surface located within the composite substrate. The inorganic material substrate 1 is composed of an inorganic material. Any suitable material can be used as the inorganic material, as long as the effects according to the embodiments of the present invention are obtained. Typical examples of such materials include single crystal quartz (relative permittivity 4.5, dielectric loss tangent 0.0013), amorphous quartz (quartz glass, relative permittivity 3.8, dielectric loss tangent 0.0010), spinel (relative permittivity 8.3, dielectric loss tangent 0.0020), AlN (relative permittivity 8.5, dielectric loss tangent 0.0015), sapphire (relative permittivity 9.4, dielectric loss tangent 0.0030), SiC (relative permittivity 9.8, dielectric loss tangent 0.0022), magnesium oxide (relative permittivity 10.0, dielectric loss tangent 0.0012), and silicon (relative permittivity 11.7, dielectric loss tangent 0.0016) (the relative permittivity and dielectric loss tangent in parentheses are values ​​at a frequency of 300 GHz). The inorganic material substrate 1 is preferably a quartz glass substrate composed of amorphous quartz. If the inorganic material substrate 1 is a quartz glass substrate, the increase in propagation loss can be suppressed even more stably, even when guiding the high-frequency electromagnetic waves mentioned above. Furthermore, because it has a higher dielectric constant compared to resin-based substrates, the substrate size can be reduced, and because it has a relatively low dielectric constant among inorganic materials, it is advantageous for reducing latency. Furthermore, quartz glass has low dielectric loss (tanδ), and unlike resin-based substrates, it has the advantage of allowing the formation of a conductor layer (metal layer) for the transmission line without roughening or surface treatment. Therefore, propagation loss can be further reduced.

[0022] C. Conductor layer and ground electrode In one embodiment, the conductive layer 6 is formed on the surface (one side in the thickness direction) of the inorganic material substrate 1 and is in direct contact with the inorganic material substrate 1. The conductive layer 6 is typically composed of a metal. Examples of metals include chromium (Cr), nickel (Ni), copper (Cu), and gold (Au). The metals can be used individually or in combination. The conductive layer 6 may be a single layer or may be formed by laminating two or more layers. The conductive layer 6 is formed on the inorganic material substrate 1, for example, by sputtering. The thickness of the conductive layer 6 is, for example, 1 μm or more, preferably 4 μm or more, and for example, 20 μm or less, preferably 10 μm or less. In one embodiment, the ground electrode 3 is formed on the back surface (the other surface in the thickness direction) of the inorganic material substrate 1 and is in direct contact with the inorganic material substrate 1. Furthermore, the ground electrode 3 is made of the same metal as the conductive layer 6, and the thickness range of the ground electrode 3 is the same as the thickness range of the conductive layer 6. The ground electrode 3 is formed on the inorganic material substrate 1, for example, by sputtering. The arrangement of the ground electrode 3 is not particularly limited, as long as it is located on the side of the inorganic material substrate 1 opposite to the conductive layer 6. In one embodiment, the ground electrode 3 is formed on the surface of the support substrate 20 and is in direct contact with the support substrate 20. That is, the waveguide element (specifically waveguide element 101 or waveguide element 102) may have the ground electrode 3 on the side of the support substrate 20 on which the waveguide member is formed. In this case, the ground electrode 3 is formed on the support substrate 20, for example, by sputtering.

[0023] D. Support substrate The support substrate 20 has an upper surface located within the composite substrate and a lower surface exposed to the outside. The support substrate 20 is provided to increase the strength of the composite substrate, thereby making it possible to reduce the thickness of the inorganic material substrate to satisfy the above formula (1). Any suitable configuration can be adopted for the support substrate 20. Specific examples of materials constituting the support substrate 20 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 20 is preferably composed of at least one selected from the group consisting of indium phosphide, silicon, aluminum nitride, silicon carbide, and silicon nitride, and more preferably of silicon. When active elements such as oscillators and receivers are mounted on the waveguide element 100, the inorganic material substrate may heat up, potentially degrading the characteristics of other active elements and mounted components. To prevent this, a material with high thermal conductivity can be used for the support substrate. In this case, the thermal conductivity is preferably 150 W / Km or higher, and from this viewpoint, examples of support substrates 20 include silicon (Si), aluminum nitride (AlN), gallium nitride (GaN), silicon carbide (SiC), and silicon nitride (Si3N4). Furthermore, it is preferable that the coefficient of thermal expansion of the material constituting the support substrate 20 is close to the coefficient of thermal expansion of the material constituting the inorganic material substrate 1. With such a configuration, thermal deformation (typically warping) of the composite substrate can be suppressed. Preferably, the coefficient of thermal expansion of the material constituting the support substrate 20 is in the range of 50% to 150% of the coefficient of thermal expansion of the material constituting the inorganic material substrate 1. Furthermore, in coplanar transmission lines, it is preferable that the dielectric loss tangent of the material constituting the support substrate 20 be small. In the case of coplanar transmission lines, if the thickness of the waveguide member is small, the propagating electromagnetic waves may seep into the support substrate, and propagation loss can be suppressed by reducing the dielectric loss tangent. From this viewpoint, it is preferable that the dielectric loss tangent is 0.07 or less.

[0024] The support substrate 20 typically supports the waveguide members (waveguide members 10, 11, 12) by directly bonding them to the waveguide members. In other words, the waveguide members and the support substrate are directly bonded. In this specification, "direct bonding" means that two layers or substrates are bonded without the interposition of an adhesive (typically an organic adhesive). The form of direct bonding can be appropriately set according to the configuration of the layers or substrates to be bonded to each other. Furthermore, the interface bonded by direct bonding is typically amorphous. Therefore, it is possible to dramatically reduce the thermal resistance of the bonding interface compared to resin bonding. As a result, when active elements such as oscillators and receivers are mounted on the waveguide element, even if heat generated from the active elements is transferred to the inorganic material substrate, such heat can be smoothly dissipated from the inorganic material substrate to the package via the support substrate. As a result, heating of the inorganic material substrate can be suppressed, and degradation of the characteristics of other active elements and mounted components can be suppressed. By integrating them through direct bonding, delamination in the waveguide element can be effectively suppressed, and as a result, damage to the inorganic material substrate (e.g., cracks) caused by such delamination can be effectively suppressed. Each of the waveguide elements (100, 101, and 102) may further include a joint 30 provided between the waveguide member (10, 11, and 12) and the support substrate 20, which joins the waveguide member 10 and the support substrate 20. Specifically, in the waveguide element 100 shown in Figures 1 and 2, as shown in Figure 9(a), the joint 30 may be located between the inorganic material substrate 1 and the support substrate 20, and they may be integrated. In such a configuration, only the inorganic material substrate 1 and the joint 30 may be provided between the conductor layer 6 and the support substrate 20. It is preferable that no resin material such as an organic material-based adhesive or a resin material substrate is interposed between the conductor layer 6 and the support substrate 20 (i.e., it is composed of inorganic materials (including the inorganic material substrate 1)). This makes it possible to reduce the thermal resistance at the interface between the inorganic material substrate 1 and the support substrate 20, and suppress the degradation of the characteristics of the active element and mounted components. A structure without interposed resin material can be obtained by directly joining the inorganic material substrate 1 and the support substrate 20. Furthermore, in the waveguide element 101 shown in Figures 3 and 4, as shown in Figure 9(b), the junction 30 may be located between the ground electrode 3 and the support substrate 20 and integrated with them, or as shown in Figure 11(a), the junction 30 may be located between the ground electrode 3 and the inorganic material substrate 1 and integrated with them. Furthermore, in the waveguide element 102 shown in Figures 5 and 6, as shown in Figure 10(a), the junction 30 may be located between the ground electrode 3 and the support substrate 20 and integrated with them, or as shown in Figure 11(b), the junction 30 may be located between the ground electrode 3 and the inorganic material substrate 1 and integrated with them. In these configurations, only the inorganic material substrate 1, the ground electrode 3, and the junction 30 may be provided between the conductor layer 6 and the support substrate 20. Furthermore, in the waveguide element 101 shown in Figures 7 and 8, as shown in Figure 10(b), the junction 30 may be located between the ground electrode 3 and the support substrate 20 and integrated with them, or as shown in Figure 11(c), the junction 30 may be located between the ground electrode 3 and the inorganic material substrate 1 and integrated with them. In these configurations, only the inorganic material substrate 1 including the vias 5, the ground electrode 3, and the junction 30 may be provided between the conductor layer 6 and the support substrate 20. It is preferable that no resin material, such as an organic adhesive or a resin substrate, is interposed between the conductive layer 6 and the support substrate 20 (i.e., it is composed of inorganic materials (including the inorganic material substrate 1)). This reduces the thermal resistance at the interface between the inorganic material substrate 1 and the support substrate 20, thereby suppressing the degradation of the characteristics of active elements and mounted components. A structure without interposed resin material can be obtained by directly joining the inorganic material substrate 1 and the support substrate 20 (with a ground electrode 3 formed on either the inorganic material substrate 1 or the support substrate 20, or both).

[0025] Furthermore, although not shown in the figures, a back conductor layer may be provided on the side of the support substrate 20 opposite to the side on which the waveguide member is provided. Typically, the back conductor layer is located on the side of the support substrate 20 opposite to the ground electrode 3. The back conductor layer may be formed on the back surface (the other side in the thickness direction) of the support substrate 20 and be in direct contact with the support substrate 20. The back conductor layer is made of the same metal as the conductor layer 6, and the thickness range of the back conductor layer is the same as the thickness range of the conductor layer 6. The back conductor layer is formed on the support substrate 20, for example, by sputtering.

[0026] The joint may consist of a single layer or two or more layers stacked together. Typically, the joint is composed of an inorganic material. Examples of joints include an SiO2 layer, an amorphous silicon layer, and a tantalum oxide layer. Since the ground electrode is metal, the joint may also be made of a metal selected from gold (Au), titanium (Ti), platinum (Pt), chromium (Cr), copper (Cu), tin (Sn), or a combination (alloy) of these. Among these joints, an amorphous silicon layer is preferred. The thickness of the joint is, for example, 0.001 μm to 10 μm, and preferably 0.1 μm to 3 μm.

[0027] Furthermore, when the waveguide member and the support substrate are directly joined without providing a joint, only an inorganic material substrate may be provided between the conductor layer and the support substrate.

[0028] Direct bonding can be achieved, for example, by the following procedure: in a high vacuum chamber (e.g., 1 × 10⁻⁶) -6 At a pressure of approximately Pa, a neutralizing beam is irradiated onto each bonding surface of the components to be joined (layers or substrates). 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, 100N to 20000N. In one embodiment, when performing surface activation with a neutralizing beam, an inert gas is introduced into a chamber, and a high voltage is applied from a DC power supply to electrodes placed in the chamber. In such a configuration, electrons move due to the electric field generated between the electrode (positive electrode) and the chamber (negative electrode), generating a beam of atoms and ions from the inert gas. Of the beam that reaches the grid, the ion beam is neutralized at the grid, so a beam of neutral atoms is emitted from the high-speed atomic beam source. The atomic species constituting the beam are preferably inert gas elements (e.g., argon (Ar), nitrogen (N)). The voltage during activation by beam irradiation is, for example, 0.5kV to 2.0kV, and the current is, for example, 50mA to 200mA. Furthermore, the direct bonding method is not limited to this; other methods such as FAB (Fast Atom Beam), surface activation methods using ion guns, atomic diffusion methods, and plasma bonding methods can also be applied. [Examples]

[0029] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0030] <Example 1> 1-1. Fabrication of waveguide elements (coplanar transmission lines) The waveguide elements shown in Figures 1 and 2 were fabricated.

[0031] A 0.5 mm thick quartz glass wafer (quartz glass substrate, inorganic material substrate) was prepared, and a 0.2 μm amorphous silicon film was formed on the quartz glass wafer by sputtering. After film formation, the amorphous silicon film was polished and planarized. At this point, the arithmetic mean roughness of a 10 μm square area (a region of 10 μm on each side; the same applies below) on the surface of the amorphous silicon film was measured using an atomic force microscope and was found to be 0.2 nm.

[0032] Furthermore, a silicon wafer (support substrate) with a thickness of 525 μm was prepared. Using an atomic force microscope, the arithmetic mean roughness of a 10 μm square area on the surface of the silicon wafer was measured and found to be 0.2 nm.

[0033] The amorphous silicon surface of a quartz glass wafer and a silicon wafer were directly bonded as follows: First, the quartz glass wafer and the silicon wafer were placed in a vacuum chamber, and 10 -6 In a vacuum of Pa, 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 (acceleration voltage 1kV, Ar flow rate 60 sccm) for 70 seconds. After irradiation, the quartz glass wafer and silicon wafer were allowed to cool for 10 minutes. Then, the bonding surfaces of the quartz glass wafer and silicon wafer (the surface of the quartz glass wafer and the surface of the silicon wafer that was irradiated with the beam) were brought into contact and pressed with 4.90kN for 2 minutes to bond the quartz glass wafer and silicon wafer. In other words, the quartz glass wafer and silicon wafer were directly bonded via the amorphous silicon layer (bonding surface). After bonding, the quartz glass wafer was polished until its thickness reached 150 μm to form a composite wafer. No defects such as delamination at the bonding interface were observed in the obtained quartz glass / silicon composite substrate.

[0034] Next, a resist was applied to the surface (polished surface) of the quartz glass wafer opposite to the silicon wafer, and the area for forming the coplanar electrode pattern was patterned using photolithography to expose it. Subsequently, a 50nm thick Cr film and a 100nm thick Ni film were deposited on the upper surface of the quartz glass wafer exposed from the resist by sputtering to form the base electrode. Furthermore, copper was deposited on the base electrode by electroplating to form the coplanar electrode pattern. The length of the signal electrode in the waveguide direction was 10mm. Based on the above, a waveguide element comprising a coplanar electrode and an inorganic material substrate, and a support substrate was obtained.

[0035] 1-2. Calculation of propagation loss To measure the propagation loss of the waveguide element, three waveguide elements with signal electrode lengths of 30 mm, 40 mm, and 50 mm were fabricated in the same manner as described above. Next, an RF signal generator was coupled to the input side of the waveguide member using a probe, and electromagnetic waves were coupled to an RF signal receiver, which was connected to the output side of the waveguide member using a probe. Next, a voltage was applied to the RF signal generator, causing it to transmit electromagnetic waves at the frequencies shown in Table 1. This propagated the electromagnetic waves through the coplanar transmission line (waveguide). The RF signal receiver measured the RF power of the electromagnetic waves output from the coplanar transmission line. The propagation loss (dB / cm) was calculated from the measurement results of three waveguide elements with different signal electrode lengths and evaluated according to the following criteria. The results are shown in Table 1. ◎: Less than 0.5 dB / cm ○: 0.5 dB / cm or higher, less than 1 dB / cm △: 1 dB / cm or more and less than 2 dB / cm ×: 2dB / cm or more

[0036] <Example 2> 2-1. Fabrication of a waveguide element (coplanar transmission line with ground) The waveguide elements shown in Figures 3 and 4 were fabricated.

[0037] 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 deposited on the quartz glass wafer by sputtering to form a base electrode. Furthermore, a copper film was deposited on the base electrode by electroplating to form a ground electrode. Next, a 0.2 μm amorphous silicon film was formed on the ground electrode by sputtering. After film formation, the amorphous silicon film was polished and planarized. At this point, the arithmetic mean roughness of a 10 μm square on the surface of the amorphous silicon film was measured using an atomic force microscope and was found to be 0.2 nm.

[0038] Furthermore, a silicon wafer (support substrate) with a thickness of 525 μm was prepared. Using an atomic force microscope, the arithmetic mean roughness of a 10 μm square area on the surface of the silicon wafer was measured and found to be 0.2 nm.

[0039] Subsequently, the amorphous silicon surface formed on the ground electrode and the silicon wafer were directly bonded. The direct bonding was carried out in the same manner as in Example 1. That is, the ground electrode and the silicon wafer were directly bonded via the amorphous silicon layer (bonding portion). No defects such as peeling were observed at the bonding interface in the obtained quartz glass / ground electrode / silicon composite substrate. Next, the quartz glass wafer was polished to a thickness of 150 μm.

[0040] 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 Example 1. The length of the signal electrode in the waveguide direction was 10 mm. Based on the above, a waveguide element was obtained comprising a waveguide member having a coplanar electrode, an inorganic material substrate, and a ground electrode, and a support substrate.

[0041] 2-2. Calculation of propagation loss Furthermore, in order to measure the propagation loss of the waveguide elements, three waveguide elements with signal electrode lengths of 30 mm, 40 mm, and 50 mm were fabricated in the same manner as described above. Then, as in Example 1, the RF power of the electromagnetic waves output from the coplanar transmission line was measured using an RF signal receiver. The propagation loss of the waveguide elements in Example 2 was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0042] <Example 3> 3-1. Fabrication of waveguide elements (microstrip lines) The waveguide elements shown in Figures 5 and 6 were fabricated.

[0043] A quartz glass / ground electrode / silicon composite substrate was obtained in the same manner as in Example 2. Next, a resist was applied to the surface (polished surface) of the quartz glass wafer opposite to the silicon wafer, and the area for forming the microstrip electrode was patterned using photolithography to expose it. Then, a 50nm thick Cr film and a 100nm thick Ni film were deposited on the upper surface of the quartz glass wafer exposed from the resist by sputtering to form the base electrode. Furthermore, copper was deposited on the base electrode by electroplating to form the microstrip electrode. The length of the microstrip electrode in the waveguide direction was 10mm. Based on the above, a waveguide element was obtained comprising a waveguide member having a microstrip-type electrode and an inorganic material substrate, and a support substrate.

[0044] 3-2. Calculation of propagation loss Furthermore, in order to measure the propagation loss of the waveguide elements, three waveguide elements with microstrip electrode lengths of 30 mm, 40 mm, and 50 mm were fabricated in the same manner as described above. Then, as in Example 1, the RF power of the electromagnetic waves output from the coplanar transmission line was measured using an RF signal receiver. The propagation loss of the waveguide elements in Example 3 was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0045] <Examples 4-6> The waveguide elements were fabricated in the same manner as in Examples 1 to 3, except that the thickness of the polished quartz glass wafer (inorganic material substrate) was changed to the value shown in Table 1. The propagation loss of the obtained waveguide element was calculated and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0046] <Example 7> A waveguide element was fabricated in the same manner as in 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. The propagation loss of the obtained waveguide element was calculated and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0047] <Example 8> A waveguide element was fabricated in the same manner as in 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. The propagation loss of the obtained waveguide element was calculated and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0048] <Example 9> A waveguide element was fabricated in the same manner as in 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. The propagation loss of the obtained waveguide element was calculated and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0049] <Example 10> A waveguide element was fabricated in the same manner as in Example 1, except that the thickness of the polished quartz glass wafer (inorganic material substrate) was changed to the value shown in Table 1. The propagation loss of the obtained waveguide element was calculated and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0050] <Examples 11-14> A waveguide element was fabricated in the same manner as in Example 3, except that the thickness of the polished quartz glass wafer (inorganic material substrate) was changed to the value shown in Table 1. The propagation loss of the obtained waveguide element was calculated and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0051] <Example 15> 15-1. Fabrication of a waveguide element (coplanar transmission line with ground) The waveguide element was fabricated in the same manner as in Example 2, except that gold was deposited instead of copper to form the ground electrode, and the thickness of the polished quartz glass wafer (inorganic material substrate) was changed to 100 μm. The coplanar electrode pattern was designed to achieve 50 Ω impedance matching with the RF signal generator / receiver. 15-2. Calculation of propagation loss Next, an RF signal generator was coupled to the input side of the waveguide member using a probe, and an RF signal receiver was connected to the output side of the waveguide member using a probe to couple the electromagnetic waves. Then, a voltage was applied to the RF signal generator, causing it to transmit electromagnetic waves at a frequency of 300 GHz. As a result, the electromagnetic waves propagated through the coplanar line (waveguide member). The RF signal receiver measured the RF power of the electromagnetic waves output from the coplanar line. From the measurement results, the propagation loss (dB / cm) was calculated to be 0.4 dB / cm (evaluation: ◎).

[0052] 15-3. Evaluation of heat dissipation performance Thermal conduction analysis was performed on the waveguide element of Example 15 using the finite element method (FEMTET, manufactured by Murata Software Co., Ltd.). In the thermal conduction analysis, the thermal conductivity of quartz glass (inorganic material substrate) was set to 2 W / mK, the thermal conductivity of silicon (support substrate) to 150 W / mK, and the thermal conductivity of gold (ground electrode) to 300 W / mK. In Example 15, the waveguide member and the support substrate are directly joined, and the joining interface is amorphous, so the thermal interfacial resistance of the interface was set to zero. As a result of this analysis, the thermal resistance of the waveguide element was 70 K / W. This confirmed the improvement in heat dissipation due to direct joining.

[0053] <Example 16> A waveguide element was fabricated in the same manner as in Example 15, except that solder (AuSn: thermal conductivity 50 W / mK) was used to directly bond the ground electrode to the silicon wafer instead of an amorphous silicon layer. The thermal resistance of the obtained waveguide element was analyzed in the same manner as the heat dissipation performance evaluation described above. As a result, the thermal resistance of the waveguide element was 90 K / W.

[0054] <Comparative Example 1> A quartz glass wafer (quartz glass plate, inorganic material substrate) with a thickness of 2100 μm was prepared, and a waveguide element was fabricated in the same manner as in Example 3, except that the thickness of the polished quartz glass wafer was changed to 2000 μm. The propagation loss of the obtained waveguide element was calculated and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0055] <Comparative Example 2> A 100 μm thick polyimide substrate (manufactured by Mitsubishi Gas Chemical Company, THERPIM) was prepared, and a ground electrode was formed on the polyimide substrate in the same manner as in Example 15. A 525 μm thick silicon wafer (support substrate) was also prepared. Next, the polyimide substrate with the ground electrode formed on it and the silicon wafer were bonded together with a resin (organic adhesive). Then, a quartz glass wafer was polished to a thickness of 100 μm. After that, a coplanar electrode pattern was formed on the surface of the polyimide substrate opposite to the silicon wafer (polished surface) in the same manner as in Example 15. Based on the above, a waveguide element was obtained comprising a waveguide member having a coplanar electrode, a polyimide substrate, and a ground electrode, and a support substrate. The propagation loss of the obtained waveguide element was calculated in the same manner as in Example 1. As a result, the propagation loss was 2.5 dB / cm. Furthermore, the thermal resistance of the obtained waveguide element was analyzed in the same manner as in Example 15. As a result, the thermal resistance of the waveguide element was 130 K / W. In the analysis, the thermal conductivity of polyimide was assumed to be 0.2 W / mK.

[0056] <Comparative Example 3> A waveguide element was obtained in the same manner as in Comparative Example 2, except that the following laminated substrate was used instead of a 100 μm thick polyimide substrate. The laminated substrate consisted of a quartz glass wafer (100 μm thick) and polyimide layers (15 μm thick, manufactured by Mitsubishi Gas Chemical, THERPIM) provided on both sides of the quartz glass wafer in the thickness direction. Based on the above, a waveguide element was obtained comprising a waveguide member having a coplanar electrode, a laminated substrate (polyimide layer / quartz glass wafer / polyimide layer), and a ground electrode, and a support substrate. The thermal resistance of the obtained waveguide element was analyzed in the same manner as in Example 15. As a result, the thermal resistance of the waveguide element was 150 K / W. In the analysis, the thermal conductivity of polyimide was assumed to be 0.2 W / mK.

[0057] [Table 1]

[0058] As is clear from Table 1, when the thickness of the inorganic material substrate satisfies equation (1) above, even when guiding electromagnetic waves of high frequencies exceeding 30 GHz, the propagation loss is small, and excellent low propagation loss performance can be ensured. [Industrial applicability]

[0059] The waveguide element according to the embodiment of the present invention can be used in a wide range of fields such as waveguides, next-generation high-speed communications, sensors, laser processing, and solar power generation, and is particularly suitable for use as a waveguide for millimeter-wave to terahertz waves. Such a waveguide element can be used, for example, in antennas, bandpass filters, couplers, delay lines (phase shifters), or isolators. [Explanation of Symbols]

[0060] 1 Inorganic material substrate 2 Coplanar electrodes 3 Ground electrode 4 Microstrip electrodes 10 Waveguide Member 11 Waveguide Member 12 Waveguide Members 100 Waveguide Elements 101 Waveguide 102 Waveguide element

Claims

1. It is equipped with a waveguide member capable of guiding electromagnetic waves with a frequency of 30 GHz or more and 20 THz or less. The aforementioned guiding member is Inorganic material substrate and The inorganic material substrate comprises a conductive layer provided on the upper part of the inorganic material substrate, The thickness t of the inorganic material substrate satisfies the following equation (1) for the waveguide element. [Math 1] (In the formula, t represents the thickness of the inorganic material substrate. λ represents the wavelength of the electromagnetic wave guided by the waveguide member. ε represents the relative permittivity of the inorganic material substrate. a represents a value of 6 or greater.)

2. The waveguide element according to claim 1, wherein the relative permittivity ε and dielectric loss tangent (dielectric loss) tanδ of the inorganic material substrate at 300 GHz are 3.5 or more and 12.0 or less, and 0.003 or less, respectively.

3. The waveguide element according to claim 2, wherein the inorganic material substrate is a quartz glass substrate.

4. The waveguide element according to claim 1 or 2, wherein the conductor layer is a coplanar electrode.

5. The waveguide element according to claim 4, wherein the frequency of the electromagnetic wave propagating through the waveguide member is 30 GHz or more and 5 THz or less, and the thickness of the inorganic material substrate is 10 μm or more.

6. A waveguide element comprising a waveguide member capable of guiding electromagnetic waves with a frequency of 30 GHz or more and 20 THz or less, The aforementioned guiding member is Inorganic material substrate and The inorganic material substrate comprises a conductive layer provided on the upper part of the inorganic material substrate, The aforementioned conductor layer is a coplanar electrode, The waveguide element is provided with a ground electrode on the inorganic material substrate on the side opposite to the side on which the conductor layer is formed. The thickness t of the inorganic material substrate satisfies the following equation (1) for the waveguide element. [Math 1] (In the formula, t represents the thickness of the inorganic material substrate. λ represents the wavelength of the electromagnetic wave guided by the waveguide member. ε represents the relative permittivity of the inorganic material substrate. a represents a value of 3 or greater.)

7. A waveguide element comprising a waveguide member capable of guiding electromagnetic waves with a frequency of 30 GHz or more and 20 THz or less, The aforementioned guiding member is Inorganic material substrate and The inorganic material substrate comprises a conductive layer provided on the upper part of the inorganic material substrate, The aforementioned conductive layer is a microstrip type electrode, The waveguide element is provided with a ground electrode on the inorganic material substrate on the side opposite to the side on which the conductor layer is formed. The thickness t of the inorganic material substrate satisfies the following equation (1) for the waveguide element. [Math 1] (In the formula, t represents the thickness of the inorganic material substrate. λ represents the wavelength of the electromagnetic wave guided by the waveguide member. ε represents the relative permittivity of the inorganic material substrate. a represents a value of 3 or greater.)

8. A waveguide element according to claim 1 or 2, comprising a support substrate provided at the lower part of the waveguide member and supporting the waveguide member.

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