Waveguide element

Abstract

A waveguide element that ensures low propagation loss performance even at high frequencies of 30 GHz or higher is provided. [Solution] A waveguide element 100 includes a waveguide member 10 capable of guiding electromagnetic waves with a frequency of 30 GHz or more and 20 THz or less. The waveguide member includes an inorganic material substrate 1 and a conductor layer 6 provided on the inorganic material substrate. The thickness t of the inorganic material substrate satisfies the following formula (1): TIFF2023026414000006.tif42127 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 dielectric constant of the inorganic material substrate, and a represents a value of 3 or more.

Description

[Technical field]

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

[0002] Waveguide elements are being developed as one type of element that guides millimeter waves to terahertz waves. Waveguide elements are expected to be applied and developed in a wide range of fields, such as optical waveguides, next-generation high-speed communications, sensors, laser processing, and solar power generation. As an example of such a waveguide element, a technology has been proposed that uses a microstrip antenna including a transparent substrate with a thickness of 2 mm, an antenna conductor provided on the transparent substrate, and a transparent conductive film provided on the surface of the transparent substrate opposite to the antenna conductor (Patent Document 1). However, such technology has a problem in that propagation loss increases significantly when millimeter waves to terahertz waves are guided. [Prior art documents] [Patent documents]

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

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

[0005] A waveguide element according to an embodiment of the present invention includes a waveguide member capable of guiding electromagnetic waves having a frequency of 30 GHz or more and 20 THz or less. The waveguide member includes an inorganic material substrate and a conductor layer provided on the inorganic material substrate. The inorganic material substrate has a thickness t that satisfies the following formula (1).

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[0006] According to the embodiments of the present invention, it is possible to realize a director element that can ensure excellent low propagation loss performance even when guiding high frequency electromagnetic waves having frequencies of 30 GHz or more. [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 schematic perspective view of a waveguide element according to another embodiment of the present invention. [Figure 4] 4 is a cross-sectional view of the waveguide element of FIG. 3 along line IV-IV'. [Diagram 5] FIG. 13 is a schematic perspective view of a waveguide element according to yet another embodiment of the present invention. [Figure 6] 6 is a cross-sectional view of the waveguide element of FIG. 5 along the line VI-VI'. [Figure 7] FIG. 13 is a schematic perspective view of a waveguide element according to yet another embodiment of the present invention. [Figure 8] 8 is a cross-sectional view of the waveguide element of FIG. 7 along the line VIII-VIII'. 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 A-1. Overall configuration of the waveguide element 100 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 waveguide element 100 of the illustrated example includes a waveguide member 10. The waveguide member 10 is capable of guiding electromagnetic waves having a frequency of 30 GHz or more and 20 THz or less, in other words, electromagnetic waves from 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. The waveguide member 10 includes an inorganic material substrate 1 and a conductor layer 6 provided on the inorganic material substrate 1. The thickness of the inorganic material substrate 1 satisfies the following formula (1).

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[0009] 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.

[0010] The relative dielectric constant ε of the inorganic material substrate 1 at 300 GHz is typically 3.5 or more, and typically 12.0 or less, preferably 10.0 or less, and more preferably 5.0 or less. The dielectric tangent (dielectric loss) tan δ 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. 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.

[0011] 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 further 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 further preferably 100 μm or less. When the frequency of the electromagnetic wave 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. 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.

[0012] The illustrated waveguide member 10 constitutes a coplanar 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 is composed 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 disposed 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 first ground electrode 2b with respect to the signal electrode 2a in a direction perpendicular to the longitudinal direction of the signal electrode 2a, and is disposed 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 gap (slit) is, for example, 2 μm or more, preferably 5 μm or more, and for example, 100 μm or less, preferably 80 μm or less.

[0013] In such a coplanar 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, 2c. When the above-mentioned high-frequency electromagnetic wave is input to the waveguide element 100, it couples with the electric field generated between the signal electrode 2a and the ground electrodes 2b, 2c and propagates through the inorganic material substrate 1.

[0014] The waveguide element 100 in the illustrated example further includes a support substrate 20 that is provided below the waveguide member 10 and supports the waveguide member 10 . When a waveguide element is provided with a supporting substrate, the mechanical strength of the waveguide element can be increased. However, when the waveguide member guides the above-mentioned high-frequency electromagnetic waves, substrate resonance may occur in the thickness including the substrate, resulting in increased propagation loss. However, in the above configuration, since the thickness of the inorganic material substrate satisfies the above formula (1) and the dielectric constants of the support substrate and the waveguide are different, the occurrence of substrate resonance can be suppressed even when the waveguide guides the above-mentioned high-frequency electromagnetic waves. Therefore, even when the above-mentioned director element includes a support substrate and guides the above-mentioned high-frequency electromagnetic waves, an increase in propagation loss can be suppressed. From this viewpoint, the greater the difference in dielectric constant between the waveguide and the support substrate, the better, and the dielectric constant of the support substrate should be smaller than that of the waveguide. If the dielectric constant of the support substrate is larger than that of the waveguide, a layer with a smaller dielectric constant may be provided between the waveguide and the support substrate. Furthermore, in order to completely suppress substrate resonance, a grounded coplanar line or a microstrip line can be adopted as described below.

[0015] Although the illustrated waveguide element 100 includes a support substrate that supports the waveguide member, the waveguide element of the present invention does not need to include a support substrate. In other words, the waveguide element may be composed of only a waveguide member. The same applies to the waveguide elements 101 and 102 described below.

[0016] A-2. Overall configuration of the director element 101 FIG. 3 is a schematic perspective view of a waveguide element according to another embodiment of the present invention; FIG. 4 is a cross-sectional view of the waveguide element of FIG. 3 taken along line IV-IV'. In the illustrated waveguide element 101, the waveguide member 11 forms a coplanar line with a ground, and includes a coplanar electrode 2, an inorganic material substrate 1, and a ground electrode 3. The ground electrode 3 is provided on the surface of the inorganic material substrate 1 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. When the waveguide member 11 is provided with the ground electrode 3, the electric field generated between the signal electrode 2a and the ground electrodes 2b, 2c is prevented from leaking from the inorganic material substrate 1 to the supporting substrate 20, thereby suppressing the reduction in propagation loss due to substrate resonance and the generation of stray capacitance. 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 gap (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] 7 and 8, the ground electrodes 2b, 2c may be electrically connected to the ground electrode 3. When the ground electrodes 2b, 2c are electrically connected to the ground electrode 3, the ground can be strengthened and stray capacitance due to surrounding lines and elements can be suppressed. In the illustrated example, a plurality of via holes are formed in the inorganic material substrate 1, and the first ground electrode 2b and the ground electrode 3, and the second ground electrode 2c and the ground electrode 3 are short-circuited by the vias 5 located in each via hole. The vias 5 shorting the first ground electrode 2b and the ground electrode 3, and the vias 5 shorting the second ground electrode 2c and the ground electrode 3 are arranged at intervals in a direction intersecting the longitudinal direction of the signal electrode 2a. The vias 5 are typically conductive films. The arrangement of the plurality of via holes is not particularly limited, but in the illustrated example, the plurality of via holes are lined up in the longitudinal direction of the signal electrode 2a.

[0018] A-3. Overall configuration of the director element 102 FIG. 5 is a schematic perspective view of a waveguide element according to yet another embodiment of the present invention; FIG. 6 is a cross-sectional view of the waveguide element of FIG. 5 taken along line VI-VI'. In the illustrated example of the waveguide element 102 , the waveguide member 12 constitutes a microstrip line, and includes a microstrip electrode 4 as a conductor layer 6 , an inorganic material substrate 1 , and a ground electrode 3 . The microstrip electrode 4 has a flat belt 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, and is, for example, 800 μm or less, preferably 500 μm or less. 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 supporting 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 above-mentioned high-frequency electromagnetic wave is input to the director element 102, it couples with the electric field generated between the microstrip electrode 4 and the ground electrode 3 and propagates through the inorganic material substrate 1.

[0020] 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.

[0021] B. Inorganic material substrate The inorganic material substrate 1 has an upper surface on which a conductor layer 6 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 1 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.

[0022] C. Conductor Layer and Ground Electrode The conductor layer 6 is typically made of a metal. Examples of metals include chromium (Cr), nickel (Ni), and copper (Cu). The metals can be used alone or in combination. The conductor layer 6 may be a single layer, or may be formed by laminating two or more layers. The conductor layer 6 is formed on the inorganic material substrate 1 by, for example, sputtering. The thickness of the conductor 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. Moreover, the ground electrode 3 is made of the same metal as the conductor layer 6, and the range of the thickness of the ground electrode 3 is the same as the range of the thickness of the conductor layer 6.

[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, and thereby allows the thickness of the inorganic material substrate to be thinned so as to satisfy the above formula (1). Any appropriate configuration may be adopted for the support substrate 20. Specific examples of materials constituting the support substrate 20 include indium phosphide (InP), silicon (Si), glass, sialon (Si 3 N 4 -Al 2 O 3 ), Mullite (3Al 2 O 3 2SiO 2 ,2Al 2 O 3 3SiO 2 ), aluminum nitride (AlN), magnesium oxide (MgO), aluminum oxide (Al 2 O 3 ), Spinel (MgAl 2 O 4 ), sapphire, quartz, crystal, gallium nitride (GaN), silicon carbide (SiC), silicon nitride (Si 3 N 4 ), gallium oxide (Ga 2 O 3 ) are mentioned. The support substrate 20 is preferably made of at least one selected from the group consisting of indium phosphide, silicon, aluminum nitride, silicon carbide, and silicon nitride, and more preferably made of silicon. When active elements such as an oscillator or receiver are mounted on the waveguide element 100, the inorganic material substrate may heat up, deteriorating the characteristics of the 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. From this perspective, the support substrate 20 may be made of silicon (Si), aluminum nitride (AlN), gallium nitride (GaN), silicon carbide (SiC), silicon nitride (SiN), or other suitable materials. 3 N 4 ) are mentioned. The linear expansion coefficient of the material constituting the support substrate 20 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. Preferably, the linear expansion coefficient of the material constituting the support substrate 20 is within a range of 50% to 150% of the linear expansion coefficient of the material constituting the inorganic material substrate 1. In addition, in a coplanar line, it is preferable that the dielectric tangent of the material constituting the support substrate 20 is small. In the case of a coplanar line, if the thickness of the waveguide member is small, the propagating electromagnetic waves may seep into the support substrate, and by making the dielectric tangent small, the propagation loss can be suppressed. From this viewpoint, it is preferable that the dielectric tangent is 0.07 or less.

[0024] The support substrate 20 typically supports the waveguide members (waveguide members 10, 11, 12) by directly bonding to the waveguide members (waveguide members 10, 11, 12). In this specification, "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 (for example, cracks) to the inorganic material substrate caused by such peeling can be effectively suppressed. Although not shown, the waveguide elements (respectively, the waveguide elements 100, 101, and 102) may further include a joint provided between the waveguide member (the waveguide member 10, 11, and 12) and the supporting substrate 20 to join the waveguide member 10 and the supporting substrate 20. Specifically, in the waveguide element 100 shown in Figures 1 and 2, the joint may be located between the inorganic material substrate 1 and the support substrate 20, and they may be integrated together. In the waveguide element 101 shown in Figures 3 and 4, the joint may be located between the ground electrode 3 and the support substrate 20, and they may be integrated together. In the waveguide element 102 shown in Figures 5 and 6, the joint may be located between the ground electrode 3 and the support substrate 20, and they may be integrated together.

[0025] The bonding portion may be a single layer, or may be a laminate of two or more layers. 2 Examples of the layer include an amorphous silicon layer, an amorphous silicon layer, and a tantalum oxide layer. The thickness of the junction is, for example, 0.1 μm or more and 3 μm or less.

[0026] Direct bonding can be achieved, for example, by the following procedure: In a high vacuum chamber (for example, 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. EXAMPLES

[0027] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0028] <Example 1> 1-1. Fabrication of waveguide elements (coplanar lines) The waveguide element shown in Figures 1 and 2 was fabricated.

[0029] 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.

[0030] 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.

[0031] 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 -6 In 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.

[0032] 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 waveguide member having a coplanar electrode and an inorganic material substrate, and a supporting substrate was obtained.

[0033] 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 waveguide member by a probe, and an electromagnetic wave was coupled to an RF signal receiver installed on the output side of the waveguide member by 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 caused the electromagnetic waves to propagate 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 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

[0034] <Example 2> 2-1. Fabrication of a waveguide element (coplanar line with ground) The waveguide element shown in Figures 3 and 4 was fabricated.

[0035] 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 ground electrode. Next, a 0.2 μm thick amorphous silicon film was formed on the 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.

[0036] A silicon wafer (support substrate) having 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.

[0037] 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 Example 1. In the obtained quartz glass / 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.

[0038] 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 waveguiding direction was 10 mm. In this manner, a waveguide element was obtained that included a waveguide member including a coplanar electrode, an inorganic material substrate, and a ground electrode, and a supporting substrate.

[0039] 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 Example 1. The propagation loss of the director element of Example 2 was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0040] <Example 3> 3-1. Fabrication of waveguide element (microstrip line) The waveguide element shown in Figures 5 and 6 was fabricated.

[0041] In the same manner as in Example 2, a quartz glass / 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 was obtained that included a waveguide member having a microstrip electrode and an inorganic material substrate, and a supporting substrate.

[0042] 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 Example 1. The propagation loss of the director element of Example 3 was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0043] <Examples 4 to 6> Except for changing the thickness of the polished quartz glass wafer (inorganic material substrate) to the value shown in Table 1, the same procedures as in Examples 1 to 3 were carried out to fabricate waveguide elements. For the obtained waveguide element, the propagation loss was calculated and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0044] <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. For the obtained waveguide element, the propagation loss was calculated and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0045] <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. For the obtained waveguide element, the propagation loss was calculated and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0046] <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. For the obtained waveguide element, the propagation loss was calculated and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0047] <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. For the obtained waveguide element, the propagation loss was calculated and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0048] <Examples 11 to 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. For the obtained waveguide element, the propagation loss was calculated and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0049] <Comparative Example 1> 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 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 Example 1. The results are shown in Table 1.

[0050] [Table 1]

[0051] As is clear from Table 1, when the thickness of the inorganic material substrate satisfies the above formula (1), even when guiding high-frequency electromagnetic waves exceeding 30 GHz, the propagation loss is small and excellent low propagation loss performance can be ensured. [Industrial Applicability]

[0052] 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]

[0053] 1 Inorganic material substrate 2 Coplanar electrode 3 Ground electrode 4. Microstrip electrodes 10 Waveguide member 11 Waveguide member 12 Waveguide member 100 Waveguide element 101 Waveguide element 102 Waveguide element

Claims

1. A waveguide member capable of guiding an electromagnetic wave having a frequency of 30 GHz or more and 20 THz or less, wherein the waveguide member comprises an inorganic material substrate, a coplanar waveguide electrode provided on the upper surface of the inorganic material substrate, and a ground electrode provided on a surface of the inorganic material substrate opposite to the surface on which the coplanar waveguide electrode is formed, wherein the thickness t of the inorganic material substrate satisfies the following formula (1), wherein the coplanar waveguide electrode includes a signal electrode extending in a predetermined direction, a first ground electrode disposed at a distance from the signal electrode in a direction orthogonal to the longitudinal direction of the signal electrode, and a second ground electrode located on the opposite side of the first ground electrode with respect to the signal electrode and disposed at a distance from the signal electrode in a direction orthogonal to the longitudinal direction of the signal electrode, wherein the width of the signal electrode is 20 μm or more and 250 μm or less, and the width of the gap formed between each of the first ground electrode and the second ground electrode and the signal electrode is 5 μm or more and 150 μm or less, a waveguide element. 【Number 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 dielectric constant of the inorganic material substrate. a represents a numerical value of 3 or more.)

2. A waveguide member capable of guiding an electromagnetic wave having a frequency of 30 GHz or more and 20 THz or less, wherein the waveguide member comprises an inorganic material substrate, a microstrip electrode provided on the upper surface of the inorganic material substrate, and a ground electrode provided on a surface of the inorganic material substrate opposite to the surface on which the microstrip electrode is formed, wherein the thickness t of the inorganic material substrate is 500 μm or less and satisfies the following formula (1), wherein the microstrip electrode extends in a predetermined direction, and the width of the microstrip electrode is 100 μm or more and 500 μm or less, a waveguide element. 【Number 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 dielectric constant of the inorganic material substrate. a represents a numerical value of 3 or more.)

3. The waveguide element according to claim 1 or 2, wherein in the formula (1), a represents a numerical value of 6 or more.

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

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

6. The waveguide element according to claim 1, wherein the thickness of the inorganic material substrate is 10 μm or more when the frequency of the electromagnetic wave propagating through the waveguide member is 30 GHz or more and 5 THz or less.

7. The waveguide element according to any one of claims 1 to 6, further comprising a support substrate provided below the waveguide member and supporting the waveguide member.

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