Waveguide device including a waveguide member in an inorganic material substrate attached to a support substrate and with a low-loss dielectric portion

1 . A waveguide device, comprising:

a waveguide member including an inorganic material substrate and coplanar electrodes arranged above the inorganic material substrate, the waveguide member being capable of guiding an electromagnetic wave having a frequency of 30 GHz or more and 20 THz or less;

a support substrate, which is arranged below the inorganic material substrate, and is configured to support the waveguide member; and

a low-dielectric constant portion, which is arranged below the inorganic material substrate, and has a dielectric constant smaller than a dielectric constant of the inorganic material substrate; and

wherein a thickness “t” of the inorganic material substrate satisfies the following formula (1):

t

<

λ

a

⁢

ε

(

1

)

where λ represents a wavelength of the electromagnetic wave guided by the waveguide member, ε represents a relative dielectric constant of the inorganic material substrate and “a” represents a numerical value of 2.

2 . The waveguide device according to claim 1 , wherein the inorganic material substrate has a relative dielectric constant ε of 3.5 or more and 12 or less, and a dielectric loss tangent tan δ of 0.003 or less at 300 GHz.

3 . The waveguide device according to claim 1 ,

wherein the support substrate has a recess,

wherein a lower surface of the inorganic material substrate and the recess of the support substrate define a cavity, and

wherein the cavity functions as the low-dielectric constant portion.

4 . The waveguide device according to claim 3 ,

wherein the coplanar electrodes include a signal electrode extending in a predetermined direction, and ground electrodes each positioned in a direction intersecting the predetermined direction at a distance from the signal electrode, and

wherein when a dimension of a respective gap between the signal electrode and each of the ground electrodes in the direction intersecting the predetermined direction is represented by “g”, a dimension of the cavity in a thickness direction of the inorganic material substrate is equal to or more than “g”.

5 . The waveguide device according to claim 1 , further comprising an earth electrode positioned between the inorganic material substrate and the support substrate; and

wherein the earth electrode is positioned between a lower surface of the low-dielectric constant portion and an upper surface of the support substrate.

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