Terahertz device

Abstract

This terahertz device includes a substrate, an electroconductive layer formed on a portion of a surface of the substrate, and an annular slot formed in the electroconductive layer. A first active element and a second active element are provided in the slot. The electroconductive layer includes a first electrode partitioned by the slot, and a second electrode formed so as to surround the first electrode via the slot. The first active element and the second active element are disposed across the first electrode on a reference line passing through the center of the first electrode in plan view. A first distance between the first end and the second end of the second electrode on the reference line is less than a first substrate distance between the first substrate end and the second substrate end of the substrate on the reference line.

Description

Terahertz Device

[0001] The present disclosure relates to terahertz devices.

[0002] In recent years, as electronic devices such as transistors have become increasingly miniaturized and their size has reached nanoscale, a phenomenon known as the quantum effect has become observable. Development is underway to utilize this quantum effect to realize ultrafast devices and devices with new functions.

[0003] In such an environment, attempts are being made to utilize electromagnetic waves in the frequency range known as the terahertz band, which has a frequency of 0.1 THz to 10 THz, to perform high-capacity communication, information processing, imaging, measurement, etc. This frequency range combines the properties of both light and radio waves, and if devices operating in this frequency band can be realized, they could be used for a wide range of applications, including the aforementioned imaging, high-capacity communication, and information processing, as well as measurements in various fields such as physical analysis, astronomy, and biology.

[0004] As an element for emitting or receiving electromagnetic waves in the terahertz band, for example, a terahertz device having a structure in which a resonant tunneling diode and a fine antenna are integrated is known (see, for example, Patent Document 1).

[0005] Japanese Patent Application Laid-Open No. 2020-115500

[0006] Terahertz devices are used as light sources that output electromagnetic waves with frequencies in the terahertz band or as detectors that detect electromagnetic waves with frequencies in the terahertz band. Higher output and improved resolution are desirable for such terahertz devices. Therefore, adjustment of the impedance of the antenna is required.

[0007] A terahertz device according to one aspect of the present disclosure comprises a substrate having a front surface and a back surface, a conductive layer formed on a portion of the surface, a ring-shaped slot formed in the conductive layer, and first and second active elements provided within the slot for oscillating or detecting electromagnetic waves, wherein the conductive layer includes a first electrode partitioned by the slot and a second electrode formed to surround the first electrode via the slot, and the first active element and the second active element are arranged on either side of the first electrode on a reference line passing through the center of the first electrode in a planar view viewed from a direction perpendicular to the surface, and a first distance between both ends of the second electrode on the reference line is smaller than a first substrate distance between both ends of the substrate on the reference line.

[0008] According to the terahertz device according to one aspect of the present disclosure, it is possible to adjust the impedance.

[0009] FIG. 1 is a schematic plan view of an exemplary terahertz device according to the first embodiment. FIG. 2 is a schematic perspective view of the terahertz device of FIG. 1. FIG. 3 is a schematic cross-sectional view taken along line F3-F3 of FIG. 1. FIG. 4 is a schematic plan view of some components of the terahertz device of FIG. 1. FIG. 5 is a schematic plan view of an active element of the terahertz device of FIG. 1 and its periphery. FIG. 6 is a schematic plan view of an active element of the terahertz device of FIG. 1 and its periphery. FIG. 7 is a schematic cross-sectional view of the active element of FIGS. 5 and 6 and its periphery. FIG. 8 is a schematic plan view of a resistive element of FIG. 1 and its periphery. FIG. 9 is a schematic cross-sectional view of the resistive element of FIG. 8 and its periphery. FIG. 10 is a characteristics diagram showing the conductance of the terahertz device of FIG. 1. FIG. 11 is a characteristics diagram showing the conductance and output power of the terahertz device of FIG. 1. FIG. 12 is a characteristics diagram showing the conductance of the terahertz device of FIG. 1. FIG. 13 is a schematic plan view of a modified terahertz device. FIG. 14 is a schematic plan view showing a terahertz device of a modified example. FIG. 15 is a schematic plan view showing a terahertz device of a modified example. FIG. 16 is a schematic plan view showing a terahertz device of a modified example. FIG. 17 is a schematic plan view showing a terahertz device of a modified example. FIG. 18 is a schematic plan view showing a terahertz device of a modified example. FIG. 19 is a schematic plan view showing a terahertz device of a modified example. FIG. 20 is a schematic plan view showing a terahertz device of a modified example. FIG. 21 is a schematic plan view of an exemplary terahertz device according to a second embodiment. FIG. 22 is a schematic plan view showing an active element and its periphery of the terahertz device of FIG. 21. FIG. 23 is a schematic plan view showing the active element and its periphery of the terahertz device of FIG. 21. FIG. 24 is a schematic cross-sectional view showing the active element and its periphery of FIG. 22.

[0010] Hereinafter, several embodiments of the terahertz device of the present disclosure will be described with reference to the accompanying drawings. Note that for simplicity and clarity of explanation, components shown in the drawings are not necessarily drawn to scale. Also, for ease of understanding, hatching lines may be omitted in cross-sectional views. The accompanying drawings merely illustrate embodiments of the present disclosure and should not be construed as limiting the present disclosure. Terms such as "first," "second," and "third" in this disclosure are used merely to distinguish between objects and do not rank them. In this specification, "equal" includes not only cases where objects are exactly equal, but also cases where there are slight differences between compared objects due to dimensional tolerances, etc.

[0011] The following detailed description includes devices, systems, and methods embodying exemplary embodiments of the present disclosure. This detailed description is merely illustrative in nature and is not intended to limit the embodiments of the present disclosure or the application and uses of such embodiments.

[0012] The phrase "at least one" as used herein means "one or more" of the desired options. As an example, the phrase "at least one" as used herein means "only one option" or "both of two options" when the number of options is two. As another example, the phrase "at least one" as used herein means "only one option" or "any combination of two or more options" when the number of options is three or more.

[0013] First Embodiment A terahertz device 10 according to a first embodiment will be described with reference to FIGS. 1 to 12. (Schematic Configuration of Terahertz Device) FIG. 1 is a schematic plan view of an exemplary terahertz device 10 according to a first embodiment. FIG. 2 is a schematic perspective view of the terahertz device of FIG. 1. FIG. 3 is a schematic cross-sectional view taken along line F3-F3 in FIG. 1. FIG. 4 is a schematic plan view showing some components of the terahertz device 10 of FIG. 1, illustrating the arrangement of a first electrode 41, a second electrode 42, a first active element 60, a second active element 70, a first resistive element 81, and a second resistive element 82. Note that the term "planar view" used in this disclosure refers to viewing the terahertz device 10 in the Z-axis direction of the X, Y, and Z axes that are orthogonal to each other and shown in FIG. 1.

[0014] As shown in FIGS. 1 to 4 , the terahertz device 10 includes a substrate 20. The substrate 20 is formed in a flat plate shape. As shown in FIG. 1 , the substrate 20 is formed in a rectangular parallelepiped shape. The substrate 20 includes a front surface 21, a back surface 22, and multiple side surfaces 23, 24, 25, and 26. The front surface 21 and the back surface 22 of the substrate 20 face opposite each other in the Z-axis direction. Therefore, "planar view" refers to a view from a direction perpendicular to the front surface 21 of the substrate 20. Furthermore, "perpendicular" does not only refer to a strictly perpendicular view, but also includes a view that is approximately perpendicular within the scope of the effects of this embodiment. The side surfaces 23 to 26 of the substrate 20 face either the X-axis direction or the Y-axis direction. The side surfaces 23 and 24 extend along the XZ plane. The side surfaces 23 and 24 face opposite each other in the Y-axis direction. The side surfaces 25 and 26 extend along the YZ plane. The side surface 25 and the side surface 26 face in opposite directions in the X-axis direction.

[0015] The substrate 20 has a length Bx in the X-axis direction and a length By in the Y-axis direction. The length Bx in the X-axis direction can be 1 mm or less. In one example, the length Bx in the X-axis direction can be 500 μm. The length By in the Y-axis direction can be 1 mm or less. In one example, the length By in the Y-axis direction can be 500 μm.

[0016] 2 and 3, the substrate 20 includes a semiconductor substrate 31 and an insulating layer 32 on the semiconductor substrate 31. The semiconductor substrate 31 is formed in a flat plate shape. As shown in FIG. 1, the shape of the semiconductor substrate 31 in a planar view is rectangular. In one example, the shape of the semiconductor substrate 31 in a planar view is square. Note that the shape of the semiconductor substrate 31 in a planar view is not limited to a rectangular shape, and may be a circular shape, an elliptical shape, or a polygonal shape.

[0017] The semiconductor substrate 31 is formed of at least one semiconductor material selected from the group consisting of InP (indium phosphide), GaAs (gallium arsenide), AlGaAs (aluminum gallium arsenide), InGaAs (indium gallium arsenide), InGaAsP (indium gallium arsenide phosphide), Si (silicon), SiC (silicon carbide), GaN (gallium nitride), and single-crystal AlN (aluminum nitride). In one example, the semiconductor substrate 31 is formed of a material containing InP.

[0018] The semiconductor substrate 31 includes a substrate front surface 311 and a substrate back surface 312. The substrate front surface 311 and the substrate back surface 312 face in opposite directions. The substrate front surface 311 faces the same side as the front surface 21, and the substrate back surface 312 faces the same side as the back surface 22. The semiconductor substrate 31 has substrate side surfaces that form part of each of the side surfaces 23 to 26. Because the substrate front surface 311 faces the same side as the front surface 21, the Z-axis direction is perpendicular to the substrate front surface 311.

[0019] The terahertz device 10 includes an insulating layer 32 provided on a semiconductor substrate 31. A substrate surface 311 of the semiconductor substrate 31 is covered with the insulating layer 32. The insulating layer 32 is made of an insulating material. The insulating layer 32 is made of, for example, silicon oxide (SiO ２ In one example, the insulating layer 32 is formed over the entire substrate surface 311 of the semiconductor substrate 31 .

[0020] The insulating layer 32 has an insulating surface 321 and an insulating back surface 322 opposite to the insulating surface 321. The insulating surface 321 faces the same side as the substrate surface 311, and the insulating back surface 322 faces the same side as the substrate back surface 312. The insulating surface 321 constitutes the surface 21. The insulating back surface 322 is in contact with the substrate surface 311 of the semiconductor substrate 31. Note that another member such as an insulating layer may be interposed between the substrate surface 311 of the semiconductor substrate 31 and the insulating layer 32. The insulating layer 32 has insulating side surfaces that constitute part of each of the side surfaces 23 to 26.

[0021] The terahertz device 10 includes a conductive layer 40 formed on the surface 21 of the substrate 20. The conductive layer 40 is formed on a portion of the surface 21 of the substrate 20. The conductive layer 40 is formed of at least one metal material selected from the group consisting of gold (Au), silver (Ag), aluminum (Al), copper (Cu), titanium (Ti), titanium nitride (TiN), and platinum (Pt). It can also be said that the conductive layer 40 contains at least one of Au, Ag, Al, Cu, Ti, and Pt. In one example, the conductive layer 40 is formed of a material containing Au. The conductive layer 40 is formed by, for example, sputtering. The conductive layer 40 may also be formed of a stacked structure of multiple metal layers.

[0022] The terahertz device 10 includes a slot 40A formed in the conductive layer 40. The slot 40A is formed in an annular shape in a planar view. In one example, the slot 40A is formed in an annular shape in a planar view. Therefore, the terahertz device 10 includes the annular slot 40A.

[0023] The conductive layer 40 includes a first electrode 41 defined by a slot 40A and a second electrode 42 formed to surround the first electrode 41 via the slot 40A. In one example, the first electrode 41 is formed in a circular shape in a plan view. In one example, the first electrode 41 is disposed at the center of the substrate 20 in a plan view. In one example, the second electrode 42 is formed in a rectangular shape. The second electrode 42 includes a first side 421 and a second side 422 extending parallel to each other in a plan view, and a third side 423 and a fourth side 424 perpendicular to the first side 421 and the second side 422 in a plan view. In one example, the second electrode 42 is formed in a rectangular shape in which the lengths of the first side 421 and the second side 422 are greater than the lengths of the third side 423 and the fourth side 424. In one example, the second electrode 42 is disposed such that the first side 421 and the second side 422 extend in the X-axis direction in a plan view. The second electrode 42 may be square-shaped in which the lengths of the first side 421 and the second side 422 are equal to the lengths of the third side 423 and the fourth side 424. Alternatively, the second electrode 42 may be rectangular-shaped in which the lengths of the third side 423 and the fourth side 424 are greater than the lengths of the first side 421 and the second side 422.

[0024] The terahertz device 10 includes a first active element 60 and a second active element 70 provided in the slot 40A. The first active element 60 and the second active element 70 are disposed in the slot 40A in a plan view. Therefore, it can be said that the first active element 60 and the second active element 70 are disposed between the first electrode 41 and the second electrode 42.

[0025] The first active element 60 and the second active element 70 are elements that convert electromagnetic waves into electrical energy. Note that the term "electromagnetic waves" encompasses the concepts of either light or radio waves, or both. The first active element 60 and the second active element 70 are elements that emit electromagnetic waves (terahertz waves) in a predetermined frequency band, for example, the terahertz band. In this case, the first active element 60 and the second active element 70 can be considered as terahertz elements that emit terahertz waves. Furthermore, for example, the first active element 60 and the second active element 70 are elements that detect terahertz waves, which are electromagnetic waves in a predetermined frequency band, for example, the terahertz band. In this case, the first active element 60 and the second active element 70 can be considered as terahertz elements that receive terahertz waves. Here, the frequency band of the terahertz waves is, for example, 0.1 THz or more and 10 THz or less.

[0026] The first active element 60 and the second active element 70 convert the supplied electrical energy into electromagnetic waves by oscillating due to the supplied electrical energy. As a result, the first active element 60 and the second active element 70 oscillate electromagnetic waves in a desired frequency band. The first active element 60 and the second active element 70 also receive electromagnetic waves and convert the electromagnetic waves into electrical energy. As a result, the first active element 60 and the second active element 70 detect electromagnetic waves in a desired frequency band.

[0027] For example, the first active element 60 and the second active element 70 may be resonant tunneling diodes (RTDs). The first active element 60 and the second active element 70 may be diodes or transistors other than RTDs. Examples of other active elements include tunnel injection transit time (TUNNETT) diodes, impact ionization avalanche transit time (IMPATT) diodes, GaAs-based field effect transistors (FETs), GaN-based FETs, high electron mobility transistors (HEMTs), heterojunction bipolar transistors (HBTs), and complementary metal-oxide-semiconductor (CMOS) FETs.

[0028] The first active element 60 and the second active element 70 have a rectangular shape in plan view. Note that the shape of the first active element 60 and the second active element 70 in plan view is not limited to a rectangular shape and may be a circular shape, an elliptical shape, or a polygonal shape.

[0029] As shown in FIG. 4 , the first active element 60 and the second active element 70 are connected between the first electrode 41 and the second electrode 42. The first active element 60 and the second active element 70 are arranged on a reference line LM passing through the center 41C of the first electrode 41 in a plan view, with the first electrode 41 sandwiched between them. In the first embodiment, the reference line LM is set to extend in the X-axis direction. In the first embodiment, the reference line LM is parallel to the first side 421 of the second electrode 42 in a plan view. The reference line LM is also parallel to the side surfaces 23 and 24 of the substrate 20 in a plan view. Note that "parallel" does not only mean strictly parallel, but also includes roughly parallel states within a range in which the effects of this embodiment can be achieved.

[0030] The first active element 60 and the second active element 70 are connected to the first electrode 41 and the second electrode 42 so as to oscillate in a state where the phases are reversed (anti-phase) to each other. The first active element 60 and the second active element 70 are connected between the first electrode 41 and the second electrode 42 so as to be in parallel.

[0031] 1 , 3 , and 4 , the first active element 60 is connected between the second electrode 42 and the first electrode 41. The conductive layer 40 includes a connection portion 441 extending from the second electrode 42 toward the first electrode 41. The conductive layer 40 also includes a connection portion 431 extending from the first electrode 41 toward the second electrode 42. The first active element 60 is connected between the second electrode 42 and the first electrode 41 by the connection portion 441 and the connection portion 431.

[0032] 1 , 3 , and 4 , the second active element 70 is connected between the first electrode 41 and the second electrode 42. The conductive layer 40 includes a connection portion 432 extending from the first electrode 41 toward the second electrode 42. The conductive layer 40 includes a connection portion 442 extending from the second electrode 42 toward the first electrode 41. The second active element 70 is connected between the first electrode 41 and the second electrode 42 by the connection portion 432 and the connection portion 442.

[0033] 1 and 4 , the terahertz device 10 includes a first resistor element 81 and a second resistor element 82. The first resistor element 81 and the second resistor element 82 are provided outside the slot 40A. In one example, the first resistor element 81 and the second resistor element 82 are arranged at positions overlapping the second electrode 42 in a plan view. The first resistor element 81 and the second resistor element 82 are arranged with the first electrode 41 interposed therebetween. The first resistor element 81 and the second resistor element 82 are arranged at positions symmetrical with respect to the first electrode 41. In the terahertz device 10 of the first embodiment, the first resistor element 81 and the second resistor element 82 are arranged at positions point-symmetrical with respect to the center 41C of the first electrode 41.

[0034] The first resistive element 81 and the second resistive element 82 are electrically connected in parallel to the first active element 60 and the second active element 70. The first resistive element 81 and the second resistive element 82 suppress parasitic oscillation, thereby stabilizing oscillation in the terahertz device 10.

[0035] The first resistor element 81 and the second resistor element 82 are electrically connected to the first electrode 41 at virtual short-circuit points 45A and 45B. It can be said that the first resistor element 81 and the second resistor element 82 are connected to both ends of the first electrode 41 on an auxiliary line LS that passes through the center 41C of the first electrode 41.

[0036] The virtual short points 45A and 45B are portions where the electric field strength of the terahertz waves generated by the first active element 60 and the second active element 70, which oscillate in opposite phases, is relatively low, and can be referred to as pseudo short points. The virtual short points 45A and 45B may be set in a range where the electric field strength of the terahertz waves is relatively low. The electric fields generated by the first active element 60 and the second active element 70, which oscillate in opposite phases, are added together in opposite phases. As a result, a portion where the electric field strength is relatively low occurs near the center between the first active element 60 and the second active element 70. Therefore, the area where the electric field strength is relatively low occurs equidistant from the first active element 60 and the second active element 70. As shown in FIG. 4 , the area where the electric field strength is relatively low occurs along an auxiliary line LS that is perpendicular to a reference line LM passing through the first active element 60 and the second active element 70 and passes through the center 41C of the first electrode 41.

[0037] (Details of the first active element and the second active element) Fig. 5 is a schematic plan view enlarging a portion of the terahertz device 10 in Fig. 1, showing the arrangement of the first active element 60. Fig. 6 is a schematic plan view enlarging a portion of the terahertz device 10 in Fig. 1, showing the arrangement of the second active element 70. Fig. 7 is a schematic cross-sectional view showing the first active element 60, the second active element 70, and their surroundings.

[0038] Next, a description will be given of an example of a configuration for realizing the first active element 60. As shown in Figures 5 and 7, the first active element 60 is provided between the second electrode 42 and the semiconductor substrate 31 in the Z-axis direction.

[0039] As shown in FIG. 7 , a semiconductor layer 61a is provided on a substrate surface 311 of a semiconductor substrate 31. In one example, the semiconductor layer 61a has a rectangular shape in a plan view. The semiconductor layer 61a is formed of, for example, GaInAs. The semiconductor layer 61a is heavily doped with n-type impurities. A GaInAs layer 62a is stacked on the semiconductor layer 61a. The GaInAs layer 62a is doped with n-type impurities. The n-type impurity concentration of the GaInAs layer 62a is lower than the n-type impurity concentration of the semiconductor layer 61a. A GaInAs layer 63a is stacked on the GaInAs layer 62a. The GaInAs layer 63a is not doped with impurities.

[0040] An AlAs layer 64a is stacked on the GaInAs layer 63a. An InGaAs layer 65 is stacked on the AlAs layer 64a. The InGaAs layer 65 is not doped with impurities. An AlAs layer 64b is stacked on the InGaAs layer 65. The AlAs layer 64a, the InGaAs layer 65, and the AlAs layer 64b form a resonant tunneling section.

[0041] An undoped GaInAs layer 63b is stacked on the AlAs layer 64b. An n-type impurity-doped GaInAs layer 62b is stacked on the GaInAs layer 63b. A highly doped GaInAs layer 61b is stacked on the GaInAs layer 62b. Therefore, the n-type impurity concentration of the GaInAs layer 61b is higher than that of the GaInAs layer 62b.

[0042] The specific configuration of the first active element 60 can be changed as desired as long as it can generate (or detect, or both) electromagnetic waves. In other words, the first active element 60 may be anything that performs at least one of oscillation and detection of electromagnetic waves in the terahertz band.

[0043] The connection portion 441 extending from the second electrode 42 extends toward the semiconductor layer 61 a and is electrically connected to the semiconductor layer 61 a. The connection portion 431 extending from the first electrode 41 contacts the upper surface of the GaInAs layer 61 b ​​and is electrically connected to the GaInAs layer 61 b. In this manner, the first active element 60 is connected between the second electrode 42 and the first electrode 41.

[0044] Next, a description will be given of an example of a configuration for realizing the second active element 70. As shown in Figures 6 and 7, the second active element 70 is provided between the first electrode 41 and the semiconductor substrate 31 in the Z-axis direction.

[0045] As shown in FIG. 7 , a semiconductor layer 71a is provided on the substrate surface 311 of the semiconductor substrate 31. In one example, the shape of the semiconductor layer 71a is rectangular in a plan view. The semiconductor layer 71a is formed of, for example, GaInAs. The semiconductor layer 71a is heavily doped with n-type impurities. A GaInAs layer 72a is stacked on the semiconductor layer 71a. The GaInAs layer 72a is doped with n-type impurities. The n-type impurity concentration of the GaInAs layer 72a is lower than the n-type impurity concentration of the semiconductor layer 71a. A GaInAs layer 73a is stacked on the GaInAs layer 72a. The GaInAs layer 73a is not doped with impurities.

[0046] An AlAs layer 74a is stacked on the GaInAs layer 73a. An InGaAs layer 75 is stacked on the AlAs layer 74a. The InGaAs layer 75 is not doped with impurities. An AlAs layer 74b is stacked on the InGaAs layer 75. The AlAs layer 74a, the InGaAs layer 75, and the AlAs layer 74b form a resonant tunneling section.

[0047] An undoped GaInAs layer 73b is stacked on the AlAs layer 74b. An n-type impurity-doped GaInAs layer 72b is stacked on the GaInAs layer 73b. A highly doped GaInAs layer 71b is stacked on the GaInAs layer 72b. Therefore, the n-type impurity concentration of the GaInAs layer 71b is higher than that of the GaInAs layer 72b.

[0048] The specific configuration of the second active element 70 can be changed as desired as long as it can generate (or detect, or both) electromagnetic waves. In other words, the second active element 70 may be any element that can perform at least one of oscillation and detection of electromagnetic waves in the terahertz band.

[0049] The connecting portion 432 extending from the first electrode 41 contacts the upper surface of the GaInAs layer 71 b and is electrically connected to the GaInAs layer 71 b. The connecting portion 442 extending from the second electrode 42 extends toward the semiconductor layer 71 a and is electrically connected to the semiconductor layer 71 a. In this manner, the second active element 70 is connected between the first electrode 41 and the second electrode 42.

[0050] (Details of Resistance Element) Fig. 8 is a schematic plan view enlarging a part of the terahertz device 10 of Fig. 1, showing the arrangement of the first resistance element 81. Fig. 9 is a schematic cross-sectional view showing the first resistance element 81 of Fig. 8 and its periphery.

[0051] 9 , the first resistor element 81 is provided between the semiconductor substrate 31 and the second electrode 42. The first resistor element 81 is provided on the substrate surface 311 of the semiconductor substrate 31. In one example, the first resistor element 81 has a rectangular shape in a plan view. The first resistor element 81 is configured of a semiconductor layer doped with a high concentration of n-type impurities. In one example, the semiconductor layer may be GaInAs.

[0052] The first resistor element 81 includes a first end 811 and a second end 812 opposite the first end. The first end 811 is electrically connected to the second electrode 42 by a via 83A formed on the first resistor element 81. The via 83A is formed of at least one metal material selected from the group consisting of Au, Ag, Al, Cu, Ti, TiN, and Pt. It can also be said that the via 83A includes at least one of Au, Ag, Al, Cu, Ti, and Pt. In one example, the via 83A is formed of a material including Au.

[0053] The lower wiring 84A is electrically connected to the second end 812 of the first resistor element 81. The lower wiring 84A is disposed within the insulating layer 32 in the Z-axis direction. It can be said that the lower wiring 84A is disposed between the insulating front surface 321 and the insulating back surface 322 in the Z-axis direction. In one example, the insulating layer 32 may include a first insulating film formed on the semiconductor substrate 31 and a second insulating film formed on the first insulating film. The first insulating film may be formed to the same thickness as the first resistor element 81. The lower wiring 84A may be formed on the first insulating film. The insulating layer 32 may include three or more insulating films. The lower wiring 84A is formed of at least one metal material selected from the group consisting of Au, Ag, Al, Cu, Ti, TiN, and Pt. It can also be said that the lower wiring 84A includes at least one of Au, Ag, Al, Cu, Ti, and Pt. In one example, the lower wiring 84A is formed of a material containing Au.

[0054] As shown in FIGS. 4 and 8 , the lower wiring 84A extends toward the first electrode 41. It can be said that the lower wiring 84A extends so as to intersect with the slot 40A between the second electrode 42 and the first electrode 41. The lower wiring 84A is electrically connected to the first electrode 41 by a via 85A. As shown in FIG. 4 , the via 85A electrically connecting the lower wiring 84A and the first electrode 41 is located at the virtual short point 45A. The via 85A is formed of at least one metal material selected from the group consisting of Au, Ag, Al, Cu, Ti, TiN, and Pt. It can also be said that the via 85A includes at least one of Au, Ag, Al, Cu, Ti, and Pt. In one example, the via 85A is formed of a material including Au.

[0055] 1 and 4 , the second resistor element 82 is electrically connected to the first electrode 41 and the second electrode 42, similar to the first resistor element 81. Although not shown, the second resistor element 82 is provided on the substrate surface 311 of the semiconductor substrate 31. In one example, the second resistor element 82 has a rectangular shape in a plan view. The second resistor element 82 is configured from a semiconductor layer doped with a high concentration of n-type impurities. In one example, the semiconductor layer may be GaInAs.

[0056] The second resistor element 82 includes a first end 821 and a second end 822 opposite the first end. The first end 821 is electrically connected to the second electrode 42 by a via 83B formed on the second resistor element 82. The via 83B is formed of at least one metal material selected from the group consisting of Au, Ag, Al, Cu, Ti, TiN, and Pt. It can also be said that the via 83B includes at least one of Au, Ag, Al, Cu, Ti, and Pt. In one example, the via 83B is formed of a material including Au.

[0057] The lower wiring 84B is electrically connected to the second end 822 of the second resistor element 82. The lower wiring 84B is disposed within the insulating layer 32 in the Z-axis direction. It can be said that the lower wiring 84B is disposed between the insulating front surface 321 and the insulating back surface 322 in the Z-axis direction. In one example, the insulating layer 32 may include a first insulating film formed on the semiconductor substrate 31 and a second insulating film formed on the first insulating film. The first insulating film may be formed to the same thickness as the second resistor element 82, for example. The lower wiring 84B may be formed on the first insulating film. The insulating layer 32 may include three or more insulating films. The lower wiring 84B is formed of at least one metal material selected from the group consisting of Au, Ag, Al, Cu, Ti, TiN, and Pt. It can also be said that the lower wiring 84B includes at least one of Au, Ag, Al, Cu, Ti, and Pt. In one example, the lower wiring 84B is formed of a material containing Au.

[0058] As shown in FIGS. 4 and 8 , the lower wiring 84B extends toward the first electrode 41. In a plan view, the lower wiring 84B can be said to extend so as to intersect with the slot 40A between the second electrode 42 and the first electrode 41. The lower wiring 84B is electrically connected to the first electrode 41 by a via 85B. As shown in FIG. 4 , the via 85B electrically connecting the lower wiring 84B and the first electrode 41 is located at the virtual short point 45B. The via 85B is formed of at least one metal material selected from the group consisting of Au, Ag, Al, Cu, Ti, TiN, and Pt. The via 85B can also be said to include at least one of Au, Ag, Al, Cu, Ti, and Pt. In one example, the via 85B is formed of a material containing Au.

[0059] (First Electrode Pad, Second Electrode Pad) As shown in FIGS. 1 and 2 , the terahertz device 10 includes a first electrode pad 51 and a second electrode pad 52 provided on the surface 21 of the substrate 20. The first electrode pad 51 and the second electrode pad 52 are arranged at the edge of the substrate 20. In one example, the first electrode pad 51 and the second electrode pad 52 are arranged along the side surface 24 on the surface 21 of the substrate 20. In the first embodiment, the first electrode pad 51 is arranged at a corner 21A formed by the side surface 24 and the side surface 26 on the surface 21 of the substrate 20. The second electrode pad 52 is arranged at a corner 21B formed by the side surface 24 and the side surface 25 on the surface 21 of the substrate 20.

[0060] The terahertz device 10 also includes a first connection wiring 53 that connects the first electrode pad 51 and the first electrode 41. The first connection wiring 53 electrically connects the first electrode pad 51 and the first electrode 41. The first connection wiring 53 is preferably connected to the first electrode 41 at a virtual short-circuit point 45B. By connecting the first connection wiring 53 to the first electrode 41 at the virtual short-circuit point 45B in this manner, leakage of electromagnetic waves to the first connection wiring 53 can be suppressed.

[0061] In one example, the first connection wiring 53 includes a first wiring 531, a second wiring 532, a lower wiring 533, and a via 534. The first wiring 531 extends from the first electrode pad 51 in the X-axis direction. The second wiring 532 extends from the tip of the first wiring 531 in the Y-axis direction. The via 534 is connected to the tip of the second wiring 532. The lower wiring 533 is connected to the second wiring 532 by the via 534 and is also electrically connected to the lower wiring 84B. As a result, the first connection wiring 53 electrically connects the first electrode pad 51 and the first electrode 41 via the lower wiring 84B and the via 85B. In this way, the first connection wiring 53 connects the first electrode pad 51 to the virtual short point 45B of the first electrode 41. Note that the lower wiring 533 of the first connection wiring 53 may be arranged on a path different from that of the lower wiring 84B and connected to the first electrode 41.

[0062] The terahertz device 10 includes a second connection wiring 54 connecting the second electrode pad 52 and the second electrode 42. The second connection wiring 54 electrically connects the second electrode pad 52 and the second electrode 42. The second connection wiring 54 is preferably connected to the second electrode 42 at a virtual short point. In one example, the second connection wiring 54 includes a first wiring 541 and a second wiring 542. The first wiring 541 extends from the second electrode pad 52 in the X-axis direction. The second wiring 542 extends from the tip of the first wiring 541 in the Y-axis direction. The second wiring 542 extends from the tip of the first wiring 541 toward the second electrode 42 and is electrically connected to the second electrode 42. In the terahertz device 10 of the first embodiment, the second electrode pad 52 is connected to the second electrode 42 by the second connection wiring 54 near the auxiliary line LS, which is the virtual short point. In this way, by connecting the second connection wiring 54 near the virtual short-circuit point, leakage of electromagnetic waves to the second connection wiring 54 can be suppressed.

[0063] (Reflective Layer) The terahertz device 10 includes a reflective layer 33 provided on the rear surface 22 of the substrate 20. The reflective layer 33 is in contact with the rear surface 22 of the substrate 20. The reflective layer 33 includes a reflective surface 331 and a reflective rear surface 332 opposite the reflective surface 331. The reflective surface 331 faces the same direction as the substrate surface 311. The reflective rear surface 332 faces the same direction as the substrate rear surface 312. The reflective layer 33 has a thickness that allows it to reflect electromagnetic waves generated or detected by the first active element 60 and the second active element 70.

[0064] The reflective layer 33 is composed of a metal layer provided on the rear surface 22 of the substrate 20. The reflective layer 33 is formed of at least one metal material selected from the group consisting of Au, Ag, Al, Cu, Ti, TiN, and Pt. It can also be said that the reflective layer 33 contains at least one of Au, Ag, Al, Cu, Ti, and Pt. In one example, the reflective layer 33 is formed of a material containing Au. The reflective layer 33 may be formed of the same material as the conductive layer 40. The reflective layer 33 is formed, for example, by sputtering. The reflective layer 33 may also be formed of a laminate structure of multiple metal layers.

[0065] (Operation) Next, the operation of the terahertz device 10 of the first embodiment will be described. The terahertz device 10 includes a substrate 20, a conductive layer 40, a slot 40A, a first active element 60, and a second active element 70. The substrate 20 includes a front surface 21 and a back surface 22, and the conductive layer 40 is formed in a portion of the front surface 21. The slot 40A is formed in the conductive layer 40. The slot 40A is formed in an annular shape. The first active element 60 and the second active element 70 are provided within the slot 40A. The conductive layer 40 includes a first electrode 41 defined by the slot 40A and a second electrode 42 formed to surround the first electrode 41 via the slot 40A. The end face of the conductive layer 40 (first electrode 41, second electrode 42) facing the annular slot 40A constitutes a ring slot antenna 40R.

[0066] As shown in FIG. 4 , the distance L12 between the first active element 60 and the second active element 70 in the circumferential direction of the slot 40A is equal to half the effective wavelength λg of the terahertz waves generated by the first active element 60 and the second active element 70. In this disclosure, "equal" refers not only to exact equality but also to slight differences between the compared elements due to dimensional tolerances and the like. The effective wavelength λg is the wavelength of the terahertz waves propagating inside the terahertz device 10. The size (radius) of the slot 40A is set corresponding to the distance L12 between the first active element 60 and the second active element 70. In one example, the radius of the slot 40A may be 30 μm.

[0067] The first active element 60 and the second active element 70 are arranged on a reference line LM that passes through the center 41C of the first electrode 41. This terahertz device 10 can be said to include two oscillators, each consisting of two semicircular slots 40A1 and 40A2 and the first active element 60 and the second active element 70 arranged in each semicircular slot 40A1 and 40A2. The first electrode 41 and the second electrode 42 facing the semicircular slots 40A1 and 40A2 in which the first active element 60 and the second active element 70 are arranged respectively constitute slot antennas. The polarization direction of the terahertz waves generated by the slot antennas of the terahertz device 10 coincides with the direction of extension of the reference line LM on which the first active element 60 and the second active element 70 are arranged.

[0068] The second electrode 42 includes a first end P21 and a second end P22, which are opposite ends on the reference line LM in a plan view. The second electrode 42 has a first distance Lx between the first end P21 and the second end P22. The first distance Lx can be considered to be the electrode size of the second electrode 42 in the polarization direction (the direction along the reference line LM).

[0069] In a plan view, the substrate 20 includes a first substrate end P11 and a second substrate end P12, which are opposite ends on the reference line LM. The substrate 20 has a first substrate distance Cx between the first substrate end P11 and the second substrate end P12. The first substrate distance Cx can be considered to be the substrate size of the substrate 20 in the polarization direction (the direction along the reference line LM).

[0070] The first distance Lx of the second electrode 42 is smaller than the first substrate distance Cx of the substrate 20. It can be said that the terahertz device 10 includes the second electrode 42 with the first distance Lx (electrode size) smaller than the first substrate distance Cx of the substrate 20. This changes the standing wave distribution in the second electrode 42. The standing wave distribution affects the impedance at the locations where the first active element 60 and the second active element 70 are disposed. Therefore, the impedance can be adjusted by changing the standing wave distribution, that is, by changing the first distance Lx of the second electrode 42.

[0071] FIG. 10 shows an example of the overall conductance of the terahertz device 10 versus the first distance Lx at the resonant frequency. In FIG. 10, the horizontal axis represents the first distance Lx, and the vertical axis represents the conductance (S). The characteristics shown in FIG. 10 are for a case where the radius of the slot 40A is 30 μm. By adjusting the first distance Lx, the overall conductance of the terahertz device 10 can be adjusted. Therefore, the impedance of the ring slot antenna 40R, which includes the first active element 60, the second active element 70, and the annular slot 40A, can be adjusted.

[0072] As shown in Fig. 10, it can be seen that the overall conductance decreases significantly as the first distance Lx decreases. The first distance Lx is preferably smaller than the effective wavelength λg of the terahertz wave. The first distance Lx is preferably equal to or smaller than ½ of the effective wavelength λg (= λg / 2) of the terahertz wave. The first distance Lx may be smaller than ½ of the effective wavelength λg.

[0073] Furthermore, in a plan view, the second electrode 42 includes a third end P23 and a fourth end P24 on an auxiliary line LS that is perpendicular to the reference line LM and passes through the center 41C of the first electrode 41. The second electrode 42 has a second distance Ly between the third end P23 and the fourth end P24. The second distance Ly can be considered to be the electrode size of the second electrode 42 in a direction perpendicular to the polarization direction (the direction along the auxiliary line LS). The second distance Ly may be the same as the first distance Lx. Furthermore, the second distance Ly may be smaller or larger than the first distance Lx.

[0074] In a plan view, the substrate 20 includes a third substrate end P13 and a fourth substrate end P14, which are opposite ends on the auxiliary line LS. The substrate 20 has a second substrate distance Cy between the third substrate end P13 and the fourth substrate end P14. The second substrate distance Cy can be considered to be the substrate size of the substrate 20 in a direction perpendicular to the polarization direction (the direction along the auxiliary line LS).

[0075] The second distance Ly of the second electrode 42 is smaller than the second substrate distance Cy of the substrate 20. It can be said that the terahertz device 10 includes the second electrode 42 with the second distance Ly (electrode size) smaller than the second substrate distance Cy of the substrate 20. This changes the standing wave distribution in the second electrode 42. The standing wave distribution affects the impedance at the locations where the first active element 60 and the second active element 70 are disposed. Therefore, the impedance can be adjusted by changing the standing wave distribution, that is, by changing the second distance Ly of the second electrode 42.

[0076] FIG. 12 shows an example of the calculation results of the overall conductance of the terahertz device 10 with respect to the first distance Lx when the second distance Ly is changed at the resonant frequency. In FIG. 12, the horizontal axis represents the first distance Lx, and the vertical axis represents the conductance (S). The characteristics shown in FIG. 12 are for a case where the radius of the slot 40A is 30 μm. In FIG. 12, the solid line, dashed line, and dashed-dotted line represent the conductance at different second distances Ly. In FIG. 12, the second distance Ly increases in the order of solid line, dashed line, and dashed-dotted line. In one example, the solid line represents the case where the second distance Ly = 100 μm, the dashed line represents the case where the second distance Ly = 150 μm, and the dashed-dotted line represents the case where the second distance Ly = 200 μm. By adjusting the second distance Ly, the overall conductance of the terahertz device 10 can be adjusted. Therefore, it is possible to adjust the impedance of the ring slot antenna 40R including the first active element 60, the second active element 70 and the annular slot 40A.

[0077] Fig. 11 shows an example of the overall conductance of the terahertz device 10 and the power of the terahertz waves generated by the terahertz device 10 when the first distance Lx is changed at the resonant frequency. In Fig. 11, the horizontal axis represents the first distance Lx, and the vertical axis represents the conductance and the power of the terahertz waves. Note that the characteristics shown in Fig. 11 are obtained when the second distance Ly is 100 µm. In Fig. 11, the solid line represents the conductance, and the dashed line represents the power. By changing the first distance Lx, the overall conductance and the power of the terahertz waves can be adjusted.

[0078] As described above, the first embodiment provides the following advantages. (1-1) The terahertz device 10 includes a substrate 20, a conductive layer 40, a slot 40A, a first active element 60, and a second active element 70. The substrate 20 includes a front surface 21 and a back surface 22, and the conductive layer 40 is formed in a portion of the front surface 21. The slot 40A is formed in the conductive layer 40. The slot 40A is formed in an annular shape. The first active element 60 and the second active element 70 are provided within the slot 40A. The conductive layer 40 includes a first electrode 41 defined by the slot 40A and a second electrode 42 formed to surround the first electrode 41 via the slot 40A. The first active element 60 and the second active element 70 are arranged on either side of the first electrode 41 on a reference line LM that passes through a center 41C of the first electrode 41 in a planar view. The first distance Lx between the first end P21 and the second end P22 of the second electrode 42 on the reference line LM is smaller than the first substrate distance Cx between the first substrate end P11 and the second substrate end P12 of the substrate 20 on the reference line LM.

[0079] In the terahertz device 10, the standing wave distribution in the second electrode 42 changes. The standing wave distribution affects the impedance at the locations where the first active element 60 and the second active element 70 are disposed. As a result, the impedance can be adjusted. Adjusting the impedance can improve the output power (output electric power) of the terahertz device 10, that is, increase the output power.

[0080] (1-2) In a plan view, a second distance Ly between the third end P23 and the fourth end P24 of the second electrode 42 on an auxiliary line LS that passes through the center 41C of the first electrode 41 and is perpendicular to the reference line LM is smaller than a second substrate distance Cy between the third substrate end P13 and the fourth substrate end P14 of the substrate 20 on the auxiliary line LS. In the terahertz device 10, the standing wave distribution in the second electrode 42 changes. The standing wave distribution affects the impedance at the locations where the first active element 60 and the second active element 70 are disposed. As a result, the impedance can be adjusted.

[0081] (1-3) The first active element 60 and the second active element 70 are connected in parallel. Therefore, by causing the first active element 60 and the second active element 70 to oscillate in opposite phases, the output power (output electric power) of the terahertz device 10 can be improved.

[0082] (1-4) The terahertz device 10 includes a first resistive element 81 and a second resistive element 82 connected in parallel to the first active element 60 and the second active element 70. This allows the oscillation to be stabilized in the terahertz device 10.

[0083] (1-5) The terahertz device 10 includes a reflective layer 33 provided on the rear surface 312 of the semiconductor substrate 31. The reflective layer 33 reflects electromagnetic waves radiated from the ring slot antenna 40R toward the semiconductor substrate 31. Therefore, the terahertz device 10 can radiate electromagnetic waves in the direction in which the front surface 311 of the substrate 20 faces.

[0084] (1-6) The first electrode pad 51 and the second electrode pad 52 may be disposed at the corners 21A and 21B of the substrate 20. This configuration can prevent the first electrode pad 51 and the second electrode pad 52 from blocking the electromagnetic waves reflected by the reflective layer 33 and heading toward the surface 21.

[0085] (1-7) The first electrode pad 51 is connected to the first electrode 41 by a first connection wiring 53. The first connection wiring 53 is connected to a virtual short-circuit point 45B of the first electrode 41. By connecting the first connection wiring 53 to the virtual short-circuit point 45B, leakage of electromagnetic waves to the first connection wiring 53 can be suppressed.

[0086] (1-8) The second electrode pad 52 is connected to the second electrode 42 by a second connection wiring 54. The second connection wiring 54 is connected to the second electrode 42 near the auxiliary line LS, which is a virtual short-circuit point. By connecting the second connection wiring 54 to the second electrode 42 near the virtual short-circuit point, leakage of electromagnetic waves to the second connection wiring 54 can be suppressed.

[0087] (Modifications of the First Embodiment) The first embodiment can be modified, for example, as follows. The first embodiment and the following modifications can be combined with each other as long as no technical contradiction occurs. In the following modifications, parts that are common to the first embodiment are assigned the same reference numerals as in the first embodiment, and descriptions thereof will be omitted.

[0088] As shown in FIG. 13 , the terahertz device 10A of the modified example includes an elliptical second electrode 42. The second electrode 42 includes a first end P21 and a second end P22 on a reference line LM. The second electrode 42 also includes a third end P23 and a fourth end P24 on an auxiliary line LS. The second electrode 42 has an elliptical shape in which a first distance Lx between the first end P21 and the second end P22 is greater than a second distance Ly between the third end P23 and the fourth end P24. Unlike the second electrode 42 of the first embodiment, the second electrode 42 of this terahertz device 10A does not have any corners. Therefore, this terahertz device 10A can suppress radiation from the outer peripheral edge of the second electrode 42, improving the radiation pattern.

[0089] The second electrode 42 may have a circular shape in which the first distance Lx and the second distance Ly are equal to each other. Alternatively, the second electrode 42 may have an elliptical shape in which the first distance Lx is smaller than the second distance Ly. The shape of the second electrode 42 may be any shape other than an ellipse, such as a polygon, a rhombus, a trapezoid, or an oval.

[0090] 14 , the terahertz device 10B of the modified example differs from the first embodiment in the arrangement of the first active element 60 and the second active element 70. In the terahertz device 10B of the modified example, a reference line LM passing through a center 41C of the first electrode 41 is inclined with respect to a first side 421 and a second side 422 of the second electrode 42 in a plan view. The first side 421 and the second side 422 of the second electrode 42 are parallel to the side surface 23 and the side surface 24 of the substrate 20. The first active element 60 and the second active element 70 are arranged on the reference line LM with the first electrode 41 sandwiched therebetween. The first active element 60 and the second active element 70 are arranged at positions rotated in the X-axis direction and the Y-axis direction around the center 41C of the first electrode 41.

[0091] The terahertz device 10B of this modified example can adjust the first distance Lx and the second distance Ly by changing the rotation angle of the first active element 60 and the second active element 70, that is, the angle of the reference line LM with respect to the first side 421 and the second side 422 of the second electrode 42. In this way, the terahertz device 10B of the modified example can adjust the impedance by changing the slope of the reference line LM that indicates the polarization direction by the first active element 60 and the second active element 70, without changing the size of the second electrode 42.

[0092] 15 , a modified terahertz device 10C includes a rectangular second electrode 42. A first side 421 and a second side 422 of the second electrode 42 are inclined with respect to the side surfaces 23 and 24 of the substrate 20. The reference line LM is parallel to the first side 421 of the second electrode 42. In this manner, the second electrode 42 may be inclined with respect to the substrate 20 in a planar view. The terahertz device 10C of this modified example can change the first substrate distance Cx between the first substrate end P11 and the second substrate end P12, which are both ends of the substrate 20, by changing the angle of the second electrode 42, i.e., the angle of the reference line LM.

[0093] As shown in FIG. 16 , a terahertz device 10D of a modified example includes a rectangular second electrode 42. A first side 421 and a second side 422 of the second electrode 42 are parallel to the side surfaces 23 and 24 of the substrate 20. The second electrode 42 is disposed closer to the side surfaces 23 and 26 of the substrate 20. The second electrode 42 includes a first end P21 and a second end P22 on the reference line LM. A distance LC1 from the center 41C of the first electrode 41 to the first end P21 is smaller than a distance LC2 from the center 41C of the first electrode 41 to the second end P22. The second electrode 42 also includes a third end P23 and a fourth end P24 on the auxiliary line LS. A distance LC3 from the center 41C of the first electrode 41 to the third end P23 is larger than a distance LC4 from the center 41C of the first electrode 41 to the fourth end P24. It can be said that the second electrode 42 is disposed asymmetrically with respect to the center 41C of the first electrode 41. In the terahertz device 10D of this modified example, the admittances of the first active element 60 and the second active element 70 are asymmetrical. The terahertz device 10D of this modified example can perform impedance matching for each of the active elements having different mesa sizes.

[0094] 17 , in a terahertz device 10E of the modified example, the first resistor element 81 and the second resistor element 82 are disposed outside the second electrode 42. The first resistor element 81 is disposed so as to extend along the first side 421 of the second electrode 42, and the second resistor element 82 is disposed so as to extend along the second side 422 of the second electrode 42. It can be said that the first resistor element 81 and the second resistor element 82 are disposed at positions that do not overlap with the second electrode 42. The second electrode 42 includes resistance connecting portions 461 and 462 that protrude in the Y-axis direction from the first side 421 and the second side 422. The first resistor element 81 and the second resistor element 82 are electrically connected to the second electrode 42 by vias 83A and 83B and the resistance connecting portions 461 and 462. As in the terahertz device 10E of this modified example, by arranging the first resistive element 81 and the second resistive element 82 outside the second electrode 42, the second distance Ly of the second electrode 42 can be made smaller.

[0095] 18 , in a modified terahertz device 10F, the first resistor element 81 and the second resistor element 82 are disposed at an angle with respect to the first side 421 and the second side 422 of the second electrode 42. The first resistor element 81 and the second resistor element 82 are disposed so that they partially overlap the second electrode 42. It can be said that the first resistor element 81 and the second resistor element 82 are disposed so that they partially lie outside the second electrode 42. The first resistor element 81 and the second resistor element 82 are electrically connected to the second electrode 42 by vias 83A and 83B disposed at positions overlapping the second electrode 42. By disposing the first resistor element 81 and the second resistor element 82 so that they partially overlap the second electrode 42, as in the modified terahertz device 10F, the second distance Ly of the second electrode 42 can be further reduced.

[0096] As shown in FIG. 19 , a modified terahertz device 10G includes an upper wiring 55 arranged to straddle the slot 40A. More specifically, the modified terahertz device 10G includes a first connection wiring 53 that electrically connects the first electrode pad 51 and the first electrode 41. The first connection wiring 53 includes a first wiring 531, a second wiring 532, an upper wiring 55, and vias 561 and 562. The terahertz device 10G includes an insulating layer 57 formed on the conductive layer 40. The upper wiring 55 is formed on the insulating layer 57. The upper wiring 55 is electrically connected to the second wiring 532 by a via 561 that penetrates the insulating layer 57. The upper wiring 55 is then electrically connected to the first electrode 41 by a via 562 that penetrates the insulating layer 57. The via 562 may be disposed at the virtual short point 45B.

[0097] In a modified terahertz device 10E shown in Fig. 17, the first resistor element 81 and the second resistor element 82 may be electrically connected to the first electrode 41 by a configuration similar to that of the upper wiring 55 shown in Fig. 19. In a modified terahertz device 10F shown in Fig. 18, the first resistor element 81 and the second resistor element 82 may be electrically connected to the first electrode 41 by a configuration similar to that of the upper wiring 55 shown in Fig. 19.

[0098] 20 , a terahertz device 10H according to a modified example includes a second electrode pad 52 disposed diagonally to the first electrode pad 51. The second electrode pad 52 is disposed on the surface 21 of the substrate 20 at a corner 21C defined by the side surface 23 and the side surface 25.

[0099] The second electrode pad 52 is located on the opposite side of the center 41C of the first electrode 41 from the virtual short-circuit point 45B of the first electrode 41 to which the first electrode pad 51 is connected, and is electrically connected to the second electrode 42 at the virtual short-circuit point 45C of the second electrode 42. The second electrode pad 52 is electrically connected to the first side 421 of the second electrode 42 by the second connection wiring 54. By connecting the second connection wiring 54 to the second electrode 42 at the virtual short-circuit point 45C in this manner, it is possible to further reduce leakage of electromagnetic waves to the second connection wiring 54. Note that the second electrode pad 52 may be located at a corner 21D formed by the side surface 23 and the side surface 26 on the surface 21 of the substrate 20, as shown by the dashed dotted line in FIG. 20 .

[0100] Second Embodiment A terahertz device 100 according to a second embodiment will be described with reference to FIGS.

[0101] In the second embodiment, parts common to the first embodiment are denoted by the same reference numerals as in the first embodiment, and descriptions thereof will be omitted. Fig. 21 is a schematic plan view of an exemplary terahertz device 100 according to the second embodiment. Fig. 22 is a schematic plan view showing some components of the terahertz device 100 of Fig. 21, illustrating a first active element 60 and a first resistor element 81. Fig. 23 is a schematic plan view showing some components of the terahertz device 100 of Fig. 21, illustrating a second active element 70 and a second resistor element 82. Fig. 24 is a schematic cross-sectional view showing the first active element 60 and the first resistor element 81 of Fig. 21.

[0102] 21 , the terahertz device 100 of the second embodiment includes a first resistive element 81 and a second resistive element 82 that are arranged to overlap with the first active element 60 and the second active element 70 in a plan view. The first resistive element 81 is connected in parallel to the first active element 60. The second resistive element 82 is connected in parallel to the second active element 70.

[0103] 22 , the first resistor element 81 is disposed so as to overlap the first active element 60 in a plan view. The first resistor element 81 includes a first end 811 and a second end 812. The second end 812 of the first resistor element 81 is electrically connected to the first active element 60. The first end 811 of the first resistor element 81 is disposed so as to overlap the first electrode 41. The first end 811 of the first resistor element 81 is electrically connected to the first electrode 41 by a via 83A.

[0104] 23 , the second resistor element 82 is disposed so as to overlap the second active element 70 in a plan view. The second resistor element 82 includes a first end 821 and a second end 822. The second end 822 of the second resistor element 82 is electrically connected to the second active element 70. The first end 821 of the second resistor element 82 is disposed so as to overlap the first electrode 41. The first end 821 of the second resistor element 82 is electrically connected to the first electrode 41 by a via 83B.

[0105] 24 , the first resistor element 81 is formed on the substrate surface 311 of the semiconductor substrate 31. The first resistor element 81 is disposed adjacent to the semiconductor layer 61 a of the first active element 60. The GaInAs layer 62 a of the first active element 60 is disposed so as to overlap both the semiconductor layer 61 a and the first resistor element 81.

[0106] The semiconductor layer 61a and the first resistor element 81 may be made of the same material. In one example, the semiconductor layer 61a and the first resistor element 81 are made of GaInAs. The semiconductor layer 61a and the first resistor element 81 may be heavily doped with n-type impurities. The first resistor element 81 may be formed integrally with the semiconductor layer 61a. In FIG. 24 , the boundary between the semiconductor layer 61a and the first resistor element 81 is indicated by a dashed line, but this dashed line does not necessarily mean that there is an actually observable boundary. Although not shown, the second resistor element 82 is configured similarly to the first resistor element 81.

[0107] The terahertz device 100 of the second embodiment functions as a detector that detects terahertz waves. As shown in Figures 21 to 23, the first resistor element 81 is electrically connected in parallel with the first active element 60. The second resistor element 82 is electrically connected in parallel with the second active element 70. The first resistor element 81 and the second resistor element 82 of the second embodiment can suppress oscillation of the first active element 60 and the second active element 70.

[0108] As described above, the second embodiment provides the following advantages in addition to the advantages of the first embodiment. (2-1) Like the terahertz device 10 of the first embodiment, the terahertz device 100 of the second embodiment includes a first active element 60 and a second active element 70 arranged on either side of the first electrode 41, and is capable of adjusting impedance. The terahertz device 100 of the second embodiment detects terahertz waves using the first active element 60 and the second active element 70. Therefore, the terahertz device 100 of the second embodiment can improve resolution.

[0109] (2-2) The terahertz device 100 of the second embodiment includes a first resistor element 81 arranged to overlap the first active element 60, and a second resistor element 82 arranged to overlap the second active element 70. The first resistor element 81 and the second resistor element 82 suppress oscillation of the first active element 60 and the second active element 70. Therefore, the terahertz device 100 of the second embodiment can suppress oscillation of the first active element 60 and the second active element 70.

[0110] (Modifications) The above embodiment can be modified, for example, as follows. The above embodiment and each of the following modifications can be combined with each other as long as no technical contradiction occurs. In the following modifications, parts that are common to the above embodiment will be assigned the same reference numerals as in the above embodiment, and their description will be omitted.

[0111] The reflective layer 33 may be omitted. The semiconductor substrate 31 may be composed of multiple laminated substrates. The term "on" as used in this disclosure includes both the meanings of "on" and "above," unless the context clearly indicates otherwise. Thus, the expression "a first layer is formed on a second layer" is intended to mean that in some embodiments, the first layer may be in contact with the second layer and disposed directly on the second layer, while in other embodiments, the first layer may be disposed above the second layer without contacting the second layer. In other words, the term "on" does not exclude a structure in which another layer is formed between the first layer and the second layer.

[0112] The Z-axis direction used in this disclosure does not necessarily have to be the vertical direction, nor does it have to completely coincide with the vertical direction. Therefore, various structures according to this disclosure (for example, the structure shown in FIG. 1 ) are not limited to the "up" and "down" in the Z-axis direction described herein being "up" and "down" in the vertical direction. For example, the X-axis direction may be the vertical direction, or the Y-axis direction may be the vertical direction.

[0113] The term "annular" as used in this disclosure may refer to any structure that forms a loop, i.e., a continuous shape with no ends. "Annular" shapes include, but are not limited to, circles, ellipses, and polygons with sharp or rounded corners.

[0114] (Supplementary Notes) The technical ideas that can be understood from the present disclosure are described below. Note that, for the purpose of aiding understanding and not intending to be limiting, the components described in the Supplementary Notes are given the reference symbols of the corresponding components in the embodiments. The reference symbols are shown as examples to aid understanding, and the components described in each Supplementary Note should not be limited to the components indicated by the reference symbols.

[0115] (Supplementary Note 1) A substrate (20) including a front surface (21) and a back surface (22), a conductive layer (40) formed on a part of the front surface (21), an annular slot (40A) formed in the conductive layer (40), and a first active element (60) and a second active element (70) provided in the slot (40A) for oscillating or detecting electromagnetic waves, wherein the conductive layer (40) includes a first electrode (41) partitioned by the slot (40A), and a second electrode (42) formed so as to surround the first electrode (41) via the slot (40A), and the first active element (60) and the second active element (70) are arranged on a reference line (LM) passing through the center of the first electrode (41) in a plan view seen from a direction perpendicular to the front surface (21), with the first electrode (41) sandwiched therebetween, A terahertz device, wherein a first distance (Lx) between both ends (P21, P22) of the second electrode (42) on the reference line (LM) is smaller than a first substrate distance (Cx) between both ends (P11, P12) of the substrate on the reference line (LM).

[0116] (Supplementary Note 2) The terahertz device according to Supplementary Note 1, wherein the first distance (Lx) is shorter than an effective wavelength (λg) of the electromagnetic wave.

[0117] (Supplementary Note 3) The terahertz device according to Supplementary Note 2, wherein the first distance (Lx) is equal to or less than half of the effective wavelength (λg) of the electromagnetic wave.

[0118] (Supplementary Note 4) The terahertz device according to any one of Supplementary Note 1 to Supplementary Note 3, wherein, in the planar view, a second distance (Ly) between both ends (P23, P24) of the second electrode (42) on an auxiliary line (LS) that passes through the center of the first electrode (41) and is perpendicular to the reference line (LM) is smaller than a second substrate distance (Cy) between both ends (P13, P14) of the substrate on the auxiliary line (LS).

[0119] (Supplementary Note 5) The terahertz device according to Supplementary Note 4, wherein the second distance (Ly) is shorter than an effective wavelength (λg) of the electromagnetic wave.

[0120] (Supplementary Note 6) The terahertz device according to Supplementary Note 5, wherein the second distance (Ly) is equal to or less than half of the effective wavelength (λg) of the electromagnetic wave.

[0121] (Supplementary Note 7) The terahertz device according to any one of Supplementary Note 4 to Supplementary Note 6, wherein the second distance (Ly) is smaller than the first distance (Lx).

[0122] (Supplementary Note 8) The terahertz device according to any one of Supplementary Note 4 to Supplementary Note 7, wherein, in the plan view, the slot (40A) has an annular shape, and the first electrode (41) has a circular shape.

[0123] (Supplementary Note 9) The terahertz device according to any one of Supplementary Notes 4 to 8, wherein the first active element (60) and the second active element (70) are connected in parallel.

[0124] (Supplementary Note 10) The terahertz device according to any one of Supplementary Note 4 to Supplementary Note 9, including a first resistive element (81) and a second resistive element (82) electrically connected in parallel to the first active element (60) and the second active element (70).

[0125] (Supplementary Note 11) The terahertz device according to Supplementary Note 10, wherein the first resistive element (81) and the second resistive element (82) are arranged at symmetrical positions with the first electrode (41) interposed therebetween.

[0126] (Supplementary Note 12) The terahertz device according to Supplementary Note 10 or Supplementary Note 11, wherein the first resistor element (81) and the second resistor element (82) are electrically connected to the first electrode (41) at a virtual short point (45A, 45B).

[0127] (Supplementary Note 13) The terahertz device according to Supplementary Note 10 or Supplementary Note 11, wherein the first resistor element (81) and the second resistor element (82) are electrically connected to both ends of the first electrode (41) on the auxiliary straight line (LS).

[0128] (Supplementary Note 14) The terahertz device according to Supplementary Note 10 or Supplementary Note 11, wherein, in the planar view, the first resistive element (81) is arranged to overlap the first active element (60), and the second resistive element (82) is arranged to overlap the second active element (70).

[0129] (Supplementary Note 15) The terahertz device according to any one of Supplementary Note 4 to Supplementary Note 14, further comprising a reflective layer (33) provided on the rear surface (22) of the substrate and reflecting the electromagnetic wave, the reflective layer (33) being arranged to overlap with the slot (40A) in the planar view.

[0130] (Supplementary Note 16) A terahertz device according to any one of Supplementary Note 4 to Supplementary Note 15, comprising: a first electrode pad (51) and a second electrode pad (52) provided on the surface (21) of the substrate; a first connection wiring (53) connecting the first electrode pad (51) and the first electrode (41); and a second connection wiring (54) connecting the second electrode pad (52) and the second electrode (42).

[0131] (Supplementary Note 17) The terahertz device according to Supplementary Note 16, wherein the first electrode pad (51) and the second electrode pad (52) are arranged at an end (corner portion) of the substrate.

[0132] (Supplementary Note 18) The terahertz device according to Supplementary Note 16 or Supplementary Note 17, wherein the first connection wiring (53) and the second connection wiring (54) are electrically connected to the first electrode (41) and the second electrode (42) at a virtual short-circuit point.

[0133] (Supplementary Note 19) The terahertz device according to any one of Supplementary Notes 16 to 18, wherein the first connection wiring (53) and the second connection wiring (54) are electrically connected to ends of the first electrode (41) and the second electrode (42) on the auxiliary straight line (LS).

[0134] (Supplementary Note 20) The terahertz device according to any one of Supplementary Note 1 to Supplementary Note 19, wherein the first and second active elements (60, 70) are any of a resonant tunneling diode, a Tannett diode, an IMPATT diode, a GaAs-based field effect transistor, a GaN-based FET, a high electron mobility transistor, a heterojunction bipolar transistor, and a CMOSFET.

[0135] (Supplementary Note 21) The terahertz device according to any one of Supplementary Notes 1 to 20, wherein the substrate (20) is rectangular in the planar view and includes a first side surface (23) and a second side surface (24) facing opposite each other in a first direction in the planar view, and the reference line (LM) is parallel to the first side surface (23) in the planar view.

[0136] (Supplementary Note 22) The terahertz device according to any one of Supplementary Notes 1 to 20, wherein the substrate (20) is rectangular in the planar view and includes a first side surface (23) and a second side surface (24) facing opposite each other in a first direction in the planar view, and the reference line (LM) is inclined with respect to the first side surface (23) in the planar view.

[0137] (Supplementary Note 23) The terahertz device according to Supplementary Note 21 or Supplementary Note 22, wherein the second electrode (42) is rectangular in the planar view and includes a first side (421) and a second side (422) that are parallel to each other, and the reference line (LM) is parallel to the first side (421) in the planar view.

[0138] (Supplementary Note 24) The terahertz device according to Supplementary Note 21 or Supplementary Note 22, wherein the second electrode (42) is rectangular in the planar view and includes a first side (421) and a second side (422) that are parallel to each other, and the reference line (LM) is inclined with respect to the first side (421) in the planar view.

[0139] (Supplementary Note 25) The terahertz device described in any one of Supplementary Note 1 to Supplementary Note 24, wherein the second electrode (42) includes a first end (P21) and a second end (P22) on the reference line (LM), the first distance (Lx) is a distance between the first end (P21) and the second end (P22), and a distance (LC1) from a center (41C) of the first electrode (41) to the first end (P21) is different from a distance (LC2) from the center (41C) of the first electrode (41) to the second end (P22).

[0140] (Supplementary Note 26) The terahertz device described in any one of Supplementary Notes 4 to 19, wherein the second electrode (42) includes a third end (P23) and a fourth end (P24) on the auxiliary straight line (LS), the second distance (Ly) is a distance between the third end (P23) and the fourth end (P24), and a distance (LC3) from a center (41C) of the first electrode (41) to the third end (P23) is different from a distance (LC4) from the center (41C) of the first electrode (41) to the fourth end (P24).

[0141] (Supplementary Note 27) The terahertz device according to any one of Supplementary Note 1 to Supplementary Note 20, wherein the second electrode (42) has an elliptical shape in a planar view.

[0142] (Supplementary Note 28) The terahertz device according to any one of Supplementary Note 1 to Supplementary Note 27, wherein the first electrode (41) is disposed at the center of the substrate (20) in a plan view.

[0143] The above description is merely illustrative. Those skilled in the art will recognize that many more possible combinations and permutations are possible other than the components and methods (manufacturing processes) listed for the purpose of illustrating the technology of the present disclosure. The present disclosure is intended to embrace all alternatives, modifications, and variations that fall within the scope of the present disclosure, including the claims.

[0144] 10, 10A to 10H, 100 Terahertz device 20 Substrate 21 Front surface 21A to 21D Corner portions 22 Back surface 23 to 26 Side surfaces 31 Semiconductor substrate 311 Substrate front surface 312 Substrate back surface 32 Insulating layer 321 Insulating front surface 322 Insulating back surface 33 Reflecting layer 331 Reflecting front surface 332 Reflecting back surface 40 Conductive layer 40A Slot 40A1 Semicircular slot 40A2 Semicircular slot 40R Ring slot antenna 41 First electrode 41C Center 42 Second electrode 45A to 45C Virtual short point 51 First electrode pad 52 Second electrode pad 53 First connecting wiring 54 Second connecting wiring 55 Upper wiring 57 Insulating layer 60 First active element 70 Second active element 81 First resistor element 811, 812 First end, second end 82 Second resistor element 821, 822 First end, second end 83A, 83B Vias 84A, 84B Lower wiring 85A, 85B Vias 421 to 424 First side to fourth side 431, 432 Connection portion 441, 442 Connection portion 461, 462 Resistor connection portion 531, 532 First wiring, second wiring 533 Lower wiring 534 Vias 541, 542 First wiring, second wiring 561, 562 Vias λg Effective wavelength Bx, By Length Cx First substrate distance Cy Second substrate distance L12 Distances LC1 to LC4 Distances LM Reference line LS Auxiliary line Lx First distance Ly Second distance P11 to P14 1st board end - 4th board end P21 - P24 1st end - 4th end

Claims

1. A substrate including the front and back surfaces, A conductive layer formed on a part of the surface, An annular slot formed in the conductive layer, A first active element and a second active element are provided within the aforementioned slot for oscillating or detecting electromagnetic waves, Equipped with, The conductive layer is The first electrode partitioned by the aforementioned slot, A second electrode formed so as to surround the first electrode via the aforementioned slot, Includes, The first active element and the second active element are arranged on a reference line passing through the center of the first electrode in a plan view taken from a direction perpendicular to the surface, with the first electrode in between. The first distance between the two ends of the second electrode on the reference straight line is smaller than the first substrate distance between the two ends of the substrate on the reference straight line. Terahertz device.

2. The first distance is smaller than the effective wavelength of the electromagnetic wave. The terahertz device according to claim 1.

3. The first distance is less than or equal to half the effective wavelength of the electromagnetic wave. The terahertz device according to claim 2.

4. In the plan view, the second distance between the ends of the second electrode on an auxiliary line passing through the center of the first electrode and perpendicular to the reference line is smaller than the second substrate distance between the ends of the substrate on the auxiliary line. The terahertz device according to claim 1.

5. The second distance is smaller than the effective wavelength of the electromagnetic wave. The terahertz device according to claim 4.

6. The second distance is less than or equal to half the effective wavelength of the electromagnetic wave. The terahertz device according to claim 5.

7. The second distance is smaller than the first distance. The terahertz device according to claim 4.

8. In the plan view, the slot is annular, and the first electrode is circular. The terahertz device according to claim 4.

9. The first active element and the second active element are connected in parallel. The terahertz device according to claim 4.

10. The first active element and the second active element include a first resistive element and a second resistive element electrically connected in parallel to the first active element and the second active element, The terahertz device according to claim 4.

11. The first resistive element and the second resistive element are arranged symmetrically with respect to the first electrode. The terahertz device according to claim 10.

12. The first resistive element and the second resistive element are electrically connected to both ends of the first electrode on the auxiliary straight line. The terahertz device according to claim 10.

13. In the plan view, the first resistive element is arranged to overlap with the first active element, and the second resistive element is arranged to overlap with the second active element. The terahertz device according to claim 10.

14. The substrate is provided on the back surface and includes a reflective layer that reflects electromagnetic waves, The reflective layer is arranged so as to overlap with the slot in the plan view. The terahertz device according to claim 4.

15. A first electrode pad and a second electrode pad provided on the surface of the substrate, A first connecting wire connecting the first electrode pad and the first electrode, A second connecting wire connecting the second electrode pad and the second electrode, including, The terahertz device according to claim 4.

16. The first electrode pad and the second electrode pad are located at the edge of the substrate. The terahertz device according to claim 15.

17. The first connecting wire and the second connecting wire are electrically connected to the ends of the first electrode and the second electrode on the auxiliary straight line. The terahertz device according to claim 15.

18. The first and second active elements are any of the following: a resonant tunnel diode, a tannet diode, an INPAT diode, a GaAs-based field-effect transistor, a GaN-based FET, a high electron-mobility transistor, a heterojunction bipolar transistor, or a CMOSFET. A terahertz device according to any one of claims 1 to 17.