JP2023026301A - waveguide element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waveguide element capable of ensuring excellent low propagation loss performance even when guiding an electromagnetic wave with a frequency of 30 GHz or more.

SOLUTION: A waveguide element 101 includes a waveguide member 11. The waveguide member 11 includes an inorganic material substrate 1 and a conductor layer provided on an upper part of the inorganic material substrate 1. A thickness t of the inorganic material substrate 1 satisfies the following equation (1). In the equation, t represents the thickness of the inorganic material substrate, 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 7

COPYRIGHT: (C)2023,JPO&INPIT

Description

The present invention relates to waveguide devices.

As one of devices for guiding millimeter waves to terahertz waves, waveguide devices are being developed. Waveguide devices are expected to be applied and developed in a wide range of fields such as optical waveguides, next-generation high-speed communication, sensors, laser processing, and photovoltaic power generation. An example of such a waveguide element is a microstrip antenna comprising a transparent substrate having a thickness of 2 mm, an antenna conductor provided on the transparent substrate, and a transparent conductive film provided on the opposite side of the transparent substrate to the antenna conductor. A technique using this technique has been proposed (Patent Document 1).
However, according to such a technique, there is a problem that propagation loss increases significantly when millimeter waves to terahertz waves are guided.

WO2019/107514

A main object of the present invention is to provide a waveguide element capable of ensuring excellent low propagation loss performance even when guiding high-frequency electromagnetic waves having a frequency of 30 GHz or higher.

（式中、ｔは、無機材料基板の厚みを表す。λは、導波部材に導波される電磁波の波長を表す。εは、無機材料基板の比誘電率を表す。ａは、３以上の数値を表す。）
１つの実施形態においては、上記式（１）において、ａが６以上の数値を表す。
１つの実施形態においては、上記無機材料基板の３００ＧＨｚにおける比誘電率εと誘電正接（誘電体損失）ｔａｎδは、それぞれ３．５以上１２．０以下、０．００３以下である。
１つの実施形態においては、上記無機材料基板は、石英ガラス基板である。
１つの実施形態においては、上記導体層は、コプレーナ型電極である。
１つの実施形態においては、上記導波部材を伝搬する電磁波の周波数が３０ＧＨｚ以上５ＴＨｚ以下において、上記無機材料基板の厚みは、１０μｍ以上である。
１つの実施形態においては、上記導波素子は、上記無機材料基板において、上記導体層が形成される面とは反対側の面に接地電極を備えている。
１つの実施形態においては、上記導体層は、マイクロストリップ型電極であって、上記導波素子は、上記無機材料基板において、上記導体層が形成される面とは反対側の面に接地電極を備えている。
１つの実施形態においては、上記導波素子は、上記導波部材の下部に設けられ、上記導波部材を支持する支持基板を備えている。 A waveguide element according to an embodiment of the present invention includes a waveguide member capable of guiding an electromagnetic wave 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 thickness t of the inorganic material substrate satisfies the following formula (1).

(Wherein, 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 dielectric constant of the inorganic material substrate, and a is 3 or more. represents the numerical value of
In one embodiment, a represents a numerical value of 6 or more in the above formula (1).
In one embodiment, the 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.
In one embodiment, the inorganic material substrate is a quartz glass substrate.
In one embodiment, the conductor layer is a coplanar electrode.
In one embodiment, 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.
In one embodiment, the waveguide element includes a ground electrode on the surface of the inorganic material substrate opposite to the surface on which the conductor layer is formed.
In one embodiment, the conductor layer is a microstrip electrode, and the waveguide element has a ground electrode on the surface of the inorganic material substrate opposite to the surface on which the conductor layer is formed. I have.
In one embodiment, the waveguide element includes a support substrate provided under the waveguide member and supporting the waveguide member.

According to the embodiments of the present invention, it is possible to realize a waveguide element that can ensure excellent low propagation loss performance even when guiding high-frequency electromagnetic waves having a frequency of 30 GHz or higher.

1 is a schematic perspective view of a waveguide element according to an embodiment of the invention; FIG. FIG. 2 is a cross-sectional view of the waveguide element of FIG. 1 taken along the line II-II'; FIG. 5 is a schematic perspective view of a waveguide element according to another embodiment of the invention; FIG. 4 is a cross-sectional view of the waveguide device of FIG. 3 taken along line IV-IV'; FIG. 5 is a schematic perspective view of a waveguide element according to yet another embodiment of the invention; FIG. 6 is a VI-VI′ cross-sectional view of the waveguide element of FIG. 5; FIG. 5 is a schematic perspective view of a waveguide element according to yet another embodiment of the invention; FIG. 8 is a cross-sectional view of the waveguide element of FIG. 7 taken along line VIII-VIII';

（式中、ｔは、無機材料基板の厚みを表す。λは、導波部材に導波される電磁波の波長を表す。εは、無機材料基板の比誘電率を表す。ａは、３以上の数値を表す。）
無機材料基板の厚みが上記式（１）を満足すると、導波部材が上記した高周波数の電磁波を導波する場合であっても、スラブモードの誘起を抑制でき、導波部材が支持基板に支持される構成では基板共振の発生を抑制できる。
そのため、上記導波素子は、上記した高周波数の電磁波を導波する場合であっても、伝搬損失が増大することを抑制でき、優れた低伝搬損失性能を確保できる。
また、導波素子は小型化の開発が進められており、将来的には回路の集積化が見込まれるため、導波部材（線路構造）もそれに伴う小型化が求められると予想される。上記の導波素子では、導波部材（線路構造）が備える無機材料基板の薄板化が図られているので、優れた低伝搬損失性能を確保しながら、小型化の要望にも対応することができる。 Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.
A. Overall Configuration of Waveguide Device A-1. Overall Configuration of Waveguide Device 100 FIG. 1 is a schematic perspective view of a waveguide device according to one embodiment of the present invention; FIG. 2 is a II-II' sectional view of the waveguide device of FIG.
A waveguide element 100 in the illustrated example 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, in other words, electromagnetic waves of millimeter waves to terahertz waves. Note that millimeter waves are typically electromagnetic waves with a frequency of about 30 GHz to 300 GHz; terahertz waves are typically electromagnetic waves with 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).

(Wherein, 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 dielectric constant of the inorganic material substrate, and a is 3 or more. represents the numerical value of
When the thickness of the inorganic material substrate satisfies the above formula (1), even when the waveguide member guides the above-described high-frequency electromagnetic wave, the induction of the slab mode can be suppressed, and the waveguide member can be attached to the support substrate. The supported configuration can suppress the occurrence of substrate resonance.
Therefore, even when the waveguide element guides the above-described high-frequency electromagnetic waves, it is possible to suppress an increase in propagation loss and to ensure excellent low propagation loss performance.
In addition, since waveguide devices are being developed for miniaturization, and it is expected that circuits will be integrated in the future, it is expected that waveguide members (line structures) will also be required to be miniaturized accordingly. In the above-mentioned waveguide element, the inorganic material substrate included in the waveguide member (line structure) is made thinner, so it is possible to meet the demand for miniaturization while ensuring excellent low propagation loss performance. can.

In one embodiment, a represents a numerical value of 6 or more in the above formula (1).
When the thickness of the inorganic material substrate satisfies the formula (1) expressing a numerical value in which a is 6 or more, it is possible to stably reduce the propagation loss when guiding the above-described high-frequency electromagnetic wave.

The dielectric constant ε of the inorganic material substrate 1 at 300 GHz is typically 3.5 or more, typically 12.0 or less, preferably 10.0 or less, more preferably 5.0 or less.
The dielectric loss 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, 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 further reduced when guiding the above-described high-frequency electromagnetic waves (especially electromagnetic waves of 300 GHz or higher). It can be stably planned. The dielectric constant ε and dielectric loss tangent (dielectric loss) tan δ can be measured by terahertz time domain spectroscopy. Moreover, in this specification, when there is no mention of the measurement frequency with respect to the dielectric constant and the dielectric loss tangent, it means the dielectric constant and the dielectric loss tangent at 300 GHz.

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, still more preferably 20 μm or more, for example 1700 μm or less, preferably 500 μm or less, It is more preferably 200 μm or less, still more preferably 100 μm or less. Moreover, 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 is less than the above lower limit, the thickness and width of the electrodes constituting the waveguide element are reduced to about several μm, and the propagation loss increases due to the skin effect. Performance tolerance is significantly reduced.
When the thickness of the inorganic material substrate 1 is equal to or less than the above upper limit, the induction of slab mode and the occurrence of substrate resonance are suppressed, and a waveguide element with small propagation loss over a wide frequency range (that is, broadband) can be realized.

The waveguide member 10 in the illustrated example constitutes a coplanar line. That is, the conductor layer 6 of the waveguide member 10 is the coplanar electrode 2 .
A 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, and for example, 200 μm or less, preferably 150 μm or less. The first ground electrode 2b is spaced apart from the signal electrode 2a in a direction orthogonal to the longitudinal direction of the signal electrode 2a. The second ground electrode 2c is located on the side opposite to the first ground electrode 2b with respect to the signal electrode 2a in the direction orthogonal to the longitudinal direction of the signal electrode 2a, and is spaced apart from the signal electrode 2a. there is Thus, 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.

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 and 2c. When the above-described high-frequency electromagnetic wave is input to the waveguide element 100, it is coupled with the electric field generated between the signal electrode 2a and the ground electrodes 2b and 2c and propagates through the inorganic material substrate 1. FIG.

The waveguide element 100 of the illustrated example further includes a support substrate 20 that is provided under the waveguide member 10 and supports the waveguide member 10 .
If the waveguide element is provided with a support substrate, the mechanical strength of the waveguide element can be increased. On the other hand, when the waveguide member guides the above-described high-frequency electromagnetic wave, substrate resonance occurs in the thickness including the substrate. may occur and increase propagation loss.
However, in the above configuration, the thickness of the inorganic material substrate satisfies the above formula (1), and the dielectric constants of the support substrate and the waveguide member are different. , the occurrence of substrate resonance can also be suppressed. Therefore, even when the waveguide element has a support substrate and guides the high-frequency electromagnetic wave, it is possible to suppress an increase in propagation loss.
From this point of view, the larger the difference between the dielectric constants of the waveguide member and the support substrate, the better, and the lower the dielectric constant of the support substrate, the better. Further, when the dielectric constant of the support substrate is higher than that of the waveguide member, a layer with a small dielectric constant may be provided between the waveguide member and the support substrate.
Furthermore, in order to completely suppress substrate resonance, a grounded coplanar line or microstrip line can be employed as described later.

Although the waveguide element 100 of the illustrated example includes a support substrate for supporting the waveguide member, the waveguide element of the present invention may not include a support substrate. In other words, the waveguide element may consist only of the waveguide member. The same applies to waveguide element 101 and waveguide element 102, which will be described later.

A-2. Overall Configuration of Waveguide 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 IV-IV' sectional view of the waveguide element of FIG.
In the illustrated waveguide element 101 , the waveguide member 11 constitutes a grounded coplanar line 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 waveguide element 101 of the illustrated example, the ground electrode 3 is positioned between the inorganic material substrate 1 and the support substrate 20 .
When the waveguide member 11 has the ground electrode 3, the electric field generated between the signal electrode 2a and the ground electrodes 2b and 2c is suppressed from leaking from the inorganic material substrate 1 to the support substrate 20, and substrate resonance and Reduction in propagation loss due to floating capacitance generation can be suppressed.
The width w of the signal electrode 2a is, for example, 2 μm or more, preferably 20 μm or more, and 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, and for example, 200 μm or less, preferably 150 μm or less.

Further, as shown in FIGS. 7 and 8, the ground electrodes 2b, 2c and the ground electrode 3 may be electrically connected. When the ground electrodes 2b, 2c and the ground electrode 3 are electrically connected, the ground can be strengthened and the stray capacitance due to the 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 connected by the vias 5 located in each via hole. Each is shorted. The via 5 that short-circuits the first ground electrode 2b and the ground electrode 3 and the via 5 that short-circuits the second ground electrode 2c and the ground electrode 3 are spaced apart from each other in the direction crossing the longitudinal direction of the signal electrode 2a. It is The via 5 is typically a conductive film. The arrangement of the plurality of via holes is not particularly limited, but in the illustrated example, the plurality of via holes are arranged in the longitudinal direction of the signal electrode 2a.

A-3. Overall Configuration of Waveguide 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 VI-VI' sectional view of the waveguide element of FIG.
In the illustrated 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, for example 800 μm or less, preferably 500 μm or less.
The ground electrode 3 is provided on the surface of the inorganic material substrate 1 opposite to the surface on which the microstrip electrode 4 (conductor layer 6) is formed. In the illustrated waveguide element 102 , the ground electrode 3 is positioned between the inorganic material substrate 1 and the support substrate 20 .

In such a microstrip line, an electric field is generated between the microstrip electrode 4 and the ground electrode 3 when a voltage is applied to the microstrip electrode 4 and the ground electrode 3 . When the above-described high-frequency electromagnetic wave is input to waveguide element 102 , it is coupled with the electric field generated between microstrip electrode 4 and ground electrode 3 and propagates through inorganic material substrate 1 .

As used herein, the term "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.

B. Inorganic Material Substrate The inorganic material substrate 1 has an upper surface on which the 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 effects of the embodiments of the present invention can be obtained. Typical examples of such materials include single crystal quartz (dielectric constant 4.5, dielectric loss tangent 0.0013), amorphous quartz (quartz glass, 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 ( 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). be done. 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, it is possible to more stably suppress an increase in propagation loss even when the above-described high-frequency electromagnetic wave is guided. In addition, since the dielectric constant is larger than that of a resin-based substrate, the size of the substrate can be reduced, and since the dielectric constant is relatively small among inorganic materials, it is advantageous in reducing the delay.

C. Conductor Layer and Ground Electrode Conductor layer 6 is typically made of metal. Examples of metal include chromium (Cr), nickel (Ni), and copper (Cu). 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 sputtering, for example.
The thickness of the conductor layer 6 is, for example, 1 μm or more, preferably 4 μm or more, and is, for example, 20 μm or less, preferably 10 μm or less.
The ground electrode 3 is made of the same metal as the conductor layer 6 , and the thickness range of the ground electrode 3 is the same as the thickness range of the conductor layer 6 .

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 so as to satisfy the above formula (1). Any appropriate configuration can be adopted as 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). _{2O3.3SiO2 )} , 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 ) can be mentioned.
Support substrate 20 preferably comprises at least one selected from the group consisting of indium phosphide, silicon, aluminum nitride, silicon carbide and silicon nitride, and more preferably comprises silicon.
When an active element such as an oscillator or a receiver is mounted on the waveguide element 100, the inorganic material substrate may be heated, degrading the characteristics of other active elements and mounted parts. 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 more, and from this point of view, the support substrate 20 is composed of silicon (Si), aluminum nitride (AlN), gallium nitride (GaN), silicon carbide (SiC), silicon night Ride (Si ₃ N ₄ ) can be mentioned.
It is preferable that the coefficient of linear expansion of the material forming the support substrate 20 is closer to the coefficient of linear expansion of the material forming the inorganic material substrate 1 . With such a configuration, thermal deformation (typically, warpage) of the composite substrate can be suppressed. Preferably, the coefficient of linear expansion of the material forming the support substrate 20 is in the range of 50% to 150% of the coefficient of linear expansion of the material forming the inorganic material substrate 1 .
Further, in the coplanar line, it is preferable that the dielectric loss tangent of the material forming the support substrate 20 is small. In the case of a coplanar line, when the thickness of the waveguide member is reduced, propagating electromagnetic waves may seep into the supporting substrate, and propagation loss can be suppressed by reducing the dielectric loss tangent. From this point of view, the dielectric loss tangent is preferably 0.07 or less.

The support substrate 20 typically supports the waveguide members (waveguide members 10, 11 and 12) by directly bonding to the waveguide members (waveguide members 10, 11 and 12). As used herein, "direct bonding" means that two layers or substrates are bonded without an intervening adhesive. The form of direct bonding can be appropriately set according to the configuration of the layers or substrates to be bonded together.
By integrating them by direct bonding, delamination in the waveguide element can be suppressed satisfactorily, and as a result, damage (for example, cracks) to the inorganic material substrate caused by such delamination can be satisfactorily suppressed. be able to.
Although not shown, the waveguide elements (waveguide elements 100, 101, and 102, respectively) are provided between the waveguide members (waveguide members 10, 11, and 12) and the support substrate 20. and the support substrate 20 may be further provided.
Specifically, in the waveguide device 100 shown in FIGS. 1 and 2, the junction may be positioned between the inorganic material substrate 1 and the support substrate 20 to integrate them. Moreover, in the waveguide element 101 shown in FIGS. 3 and 4, the junction may be positioned between the ground electrode 3 and the support substrate 20, and they may be integrated. Moreover, in the waveguide element 102 shown in FIGS. 5 and 6, the junction may be positioned between the ground electrode 3 and the support substrate 20 to integrate them.

The joint portion may be one layer, or two or more layers may be laminated. The junction includes, for example, a _SiO2 layer, an amorphous silicon layer, and a tantalum oxide layer. The thickness of the joint portion is, for example, 0.1 μm or more and 3 μm or less.

Direct bonding can be realized, for example, by the following procedure. In a high-vacuum chamber (eg, about 1×10 ⁻⁶ Pa), a neutralizing beam is applied to each bonding surface of the components (layers or substrates) to be bonded. Thereby, each joint surface is activated. Next, in a vacuum atmosphere, the activated bonding surfaces are brought into contact with each other and bonded at room temperature. The load during this joining may be, for example, 100N to 20000N. In one embodiment, when performing surface activation with a neutralizing beam, an inert gas is introduced into the chamber, and a high voltage is applied from a DC power supply to the electrodes arranged in the chamber. With such a configuration, electrons move due to the 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, so that a beam of neutral atoms is emitted from the fast atom beam source. The atomic species that make up the beam are preferably inert gas elements (eg, 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 FAB (Fast Atom Beam), a surface activation method using an ion gun, an atomic diffusion method, a plasma bonding method, or the like can also be applied.

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

<Example 1>
1-1. Fabrication of Waveguide Device (Coplanar Line) The waveguide device shown in FIGS. 1 and 2 was fabricated.

A quartz glass wafer (quartz glass substrate, inorganic material substrate) having a thickness of 0.5 mm was prepared, and an amorphous silicon film having a thickness of 0.2 μm was formed on the quartz glass wafer by sputtering. After the film formation, the amorphous silicon film was polished and planarized. Using an atomic force microscope, the arithmetic average roughness of the surface of the amorphous silicon film of square 10 μm was measured to be 0.2 nm.

Also, a silicon wafer (supporting substrate) having a thickness of 525 μm was prepared. Using an atomic force microscope, the arithmetic mean roughness of the surface of the silicon wafer with a square of 10 μm was measured and found to be 0.2 nm.

The amorphous silicon surface of the quartz glass wafer and the silicon wafer were directly bonded as follows. First, a quartz glass wafer and a silicon wafer are placed in a vacuum chamber, and a high-speed Ar neutral atom beam is applied to both bonding surfaces (amorphous silicon surface of the quartz glass wafer and the surface of the silicon wafer) in a vacuum of the order of 10 ⁻⁶ Pa. (accelerating voltage of 1 kV, Ar flow rate of 60 sccm) was applied for 70 seconds. After the irradiation, the quartz glass wafer and the silicon wafer were allowed to stand for 10 minutes to cool. The quartz glass wafer and the silicon wafer were bonded by pressing for 2 minutes. After bonding, the quartz glass wafer was polished to a thickness of 150 μm to form a composite wafer. In the resulting quartz glass/silicon composite substrate, no defect such as peeling was observed at the bonded interface.

Next, a resist was applied to the surface (polished surface) of the quartz glass wafer on the side opposite to the silicon wafer, and patterning was performed by photolithography so as to expose the portion where the coplanar electrode pattern was to be formed. Thereafter, a Cr film of 50 nm thickness and a Ni film of 100 nm thickness were formed by sputtering on the upper surface of the quartz glass wafer exposed from the resist to form a base electrode. Furthermore, a coplanar electrode pattern was formed by depositing a copper film on the base electrode by electroplating. The length of the signal electrode in the waveguide direction was 10 mm.
As described above, a waveguide element including a waveguide member including coplanar electrodes and an inorganic material substrate, and a support substrate was obtained.

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 produced in the same manner as described above.
Next, an RF signal generator was coupled with a probe to the input side of the waveguide member, and a probe was installed at the output side of the waveguide member to couple electromagnetic waves to the RF signal receiver.
Then, a voltage was applied to the RF signal generator to cause the RF signal generator to transmit electromagnetic waves of the frequencies shown in Table 1. Electromagnetic waves were thereby propagated to the coplanar line (waveguiding member). An RF signal receiver measured the RF power of the electromagnetic waves output from the coplanar line. Propagation loss (dB/cm) was calculated from the measurement results of three waveguide elements having different signal electrode lengths and evaluated according to the following criteria. Table 1 shows the results.
◎: Less than 0.5 dB/cm ○: 0.5 dB/cm or more and less than 1 dB/cm △: 1 dB/cm or more and less than 2 dB/cm ×: 2 dB/cm or more

<Example 2>
2-1. Fabrication of Waveguide Device (Coplanar Line with Ground) The waveguide device shown in FIGS. 3 and 4 was fabricated.

A quartz glass wafer (quartz glass substrate, inorganic material substrate) having a thickness of 0.5 mm was prepared, and a Cr film of 50 nm thickness and a Ni film of 100 nm thickness were formed on the quartz glass wafer by sputtering to form a base electrode. . Further, a copper film was formed on the base electrode by electroplating to form a ground electrode. Next, an amorphous silicon film of 0.2 μm was formed on the ground electrode by sputtering. After the film formation, the amorphous silicon film was polished and planarized. Using an atomic force microscope, the arithmetic average roughness of the surface of the amorphous silicon film of square 10 μm was measured to be 0.2 nm.

Also, a silicon wafer (supporting substrate) having a thickness of 525 μm was prepared. Using an atomic force microscope, the arithmetic mean roughness of the surface of the silicon wafer with a square of 10 μm was measured and found to be 0.2 nm.

After that, the amorphous silicon surface formed on the ground electrode was directly bonded to the silicon wafer. Direct bonding was carried out as in Example 1. In the resulting quartz glass/ground electrode/silicon composite substrate, no defect such as peeling was observed at the bonding interface.
The quartz glass wafer was then polished to a thickness of 150 μm.

Then, in the same manner as in Example 1, a coplanar electrode pattern was formed on the surface (polished surface) of the quartz glass wafer opposite to the silicon wafer. The length of the signal electrode in the waveguide direction was 10 mm.
As described above, a waveguide element including a waveguide member including a coplanar electrode, an inorganic material substrate, and a ground electrode, and a support substrate was obtained.

2-2. Calculation of Propagation Loss Also, in order 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 produced in the same manner as described above. Then, as in Example 1, the RF signal receiver was used to measure the RF power of the electromagnetic wave output from the coplanar line. The propagation loss of the waveguide element of Example 2 was evaluated in the same manner as in Example 1. Table 1 shows the results.

<Example 3>
3-1. Fabrication of Waveguide Device (Mylostrip Line) The waveguide device shown in FIGS. 5 and 6 was fabricated.

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 on the side opposite to the silicon wafer, and patterning was performed by photolithography so as to expose the portions where the microstrip electrodes were to be formed. Thereafter, a Cr film of 50 nm thickness and a Ni film of 100 nm thickness were formed by sputtering on the upper surface of the quartz glass wafer exposed from the resist to form a base electrode. Further, a copper film was formed on the base electrode by electroplating to form a microstrip electrode. The length of the microstrip electrodes in the waveguide direction was 10 mm.
As described above, a waveguide element including a waveguide member including a microstrip electrode and an inorganic material substrate, and a support substrate was obtained.

3-2. Calculation of Propagation Loss In order to measure the propagation loss of the waveguide element, 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 signal receiver was used to measure the RF power of the electromagnetic wave output from the coplanar line. The propagation loss of the waveguide element of Example 3 was evaluated in the same manner as in Example 1. Table 1 shows the results.

<Examples 4 to 6>
A waveguide element was produced 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. Table 1 shows the results.

<Example 7>
In the same manner as in Example 1, except that the quartz glass wafer as the inorganic material substrate was changed to a single crystal silicon wafer, and the thickness of the silicon wafer after polishing was changed to the value shown in Table 1, a waveguide was obtained. A device was produced.
The propagation loss of the obtained waveguide element was calculated and evaluated in the same manner as in Example 1. Table 1 shows the results.

<Example 8>
A waveguide element was manufactured in the same manner as in Example 1, except that the quartz glass wafer as the inorganic material substrate was changed to a sapphire wafer, and the thickness of the sapphire wafer after polishing was changed to the value shown in Table 1. made.
The propagation loss of the obtained waveguide element was calculated and evaluated in the same manner as in Example 1. Table 1 shows the results.

<Example 9>
In the same manner as in Example 1, except that the quartz glass wafer as the inorganic material substrate was changed to a polycrystalline AlN wafer, and the thickness of the AlN wafer after polishing was changed to the value shown in Table 1, waveguides were obtained. A device was produced.
The propagation loss of the obtained waveguide element was calculated and evaluated in the same manner as in Example 1. Table 1 shows the results.

<Example 10>
A waveguide element was produced 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. Table 1 shows the results.

<Examples 11 to 14>
A waveguide element was produced 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. Table 1 shows the results.

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

As is clear from Table 1, when the thickness of the inorganic material substrate satisfies the above formula (1), even if a high frequency electromagnetic wave exceeding 30 GHz is guided, the propagation loss is small, and excellent low propagation loss performance is secured. I know you can.

The waveguide device 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 waveguides for millimeter waves to terahertz waves. can be Such waveguide elements can be used, for example, in antennas, bandpass filters, couplers, delay lines (phase shifters), or isolators.

REFERENCE SIGNS LIST 1 inorganic material substrate 2 coplanar electrode 3 ground electrode 4 microstrip electrode 10 waveguide member 11 waveguide member 12 waveguide member 100 waveguide element 101 waveguide element 102 waveguide element

Claims (8)

A waveguide element comprising a waveguide member capable of guiding an electromagnetic wave having a frequency of 30 GHz or more and 20 THz or less,
The waveguide member comprises an inorganic material substrate and a conductor layer provided on the inorganic material substrate,
The conductor layer is
a center electrode extending in a predetermined direction;
a first ground electrode spaced apart from the center electrode in a direction orthogonal to the longitudinal direction of the center electrode;
a second ground electrode located on the opposite side of the first ground electrode with respect to the center electrode, the second ground electrode being spaced from the center electrode;
The waveguide element is
a support substrate provided under the waveguide member, the support substrate supporting the waveguide member;
a third ground electrode located on the opposite side of the conductor layer with respect to the inorganic material substrate;
a first via that short-circuits the first ground electrode and the third ground electrode;
a second via that short-circuits the second ground electrode and the third ground electrode;
A waveguide element, wherein the thickness t of the inorganic material substrate satisfies the following formula (1).

(Wherein, 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 dielectric constant of the inorganic material substrate, and a is 3 or more. represents the numerical value of 2. The waveguide device according to claim 1, wherein a represents a numerical value of 6 or more in said formula (1). 3. The waveguide device according to claim 1, wherein the dielectric constant ε and the dielectric loss tangent (dielectric loss) tan δ at 300 GHz of the inorganic material substrate are 3.5 or more and 12.0 or less and 0.003 or less, respectively. . 4. The waveguide device according to claim 3, wherein said inorganic material substrate is a quartz glass substrate. 5. The waveguide device according to claim 1, wherein said conductor layer is a coplanar electrode. 6. The waveguide element according to claim 5, wherein the inorganic material substrate has a thickness of 10 [mu]m or more when the frequency of the electromagnetic wave propagating through the waveguide member is 30 GHz or more and 5 THz or less. 5. The waveguide element according to claim 1, wherein said conductor layer is a microstrip electrode. 8. The waveguide device according to claim 1, wherein said inorganic material substrate has a thickness of 100 [mu]m or less.

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