Element and terahertz camera system using the element

Abstract

To provide a favorable antenna array structure.SOLUTION: In an antenna array that includes a first antenna, a second antenna, a third antenna, a fourth antenna, and a fifth antenna, the second antenna, the first antenna, and the third antenna are arranged in this order in a first direction, and the fourth antenna, the first antenna, and the fifth antenna are arranged in this order in a second direction. A conductor layer of the second antenna is connected with a conductor layer of the first antenna via a first coupling line extending in the first direction. The conductor layer of the first antenna is connected with a conductor layer of the third antenna via a second coupling line extending in the first direction. A conductor layer of the fourth antenna is connected with the conductor layer of the first antenna via a third coupling line extending in the second direction. The conductor layer of the first antenna is connected with a conductor layer of the fifth antenna via a fourth coupling line extending in the second direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a device and a terahertz camera system using the device. [Background technology]

[0002] As a current injection type light source that generates terahertz waves, an oscillator that integrates an element with electromagnetic wave gain for terahertz waves and a resonator is known. Among these, an oscillator that integrates a resonant tunneling diode (RTD) and an antenna is expected to operate at room temperature in the frequency range around 1 THz.

[0003] Patent Document 1 discloses a terahertz wave antenna array in which multiple oscillators, each integrating an RTD and an antenna, are arranged on the same substrate. The antenna array in Patent Document 1 discloses a microstrip line, which is a coupling line for synchronizing and oscillating the multiple oscillators in phase with each other. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-200065 [Non-patent literature]

[0005] [Non-Patent Document 1] Jpn.J.Appl.Phys.,Vol.47,No.6(2008), pp.4375-4384 [Non-patent document 2] J.Appl.Phys.,Vol.103,124514(2008) Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Document 1, sufficient consideration has not been given to satisfying the phase matching conditions among a plurality of oscillators.

[0007] In view of the above problems, an object of the present invention is to provide a suitable antenna array structure. [Means for solving the problem]

[0008] One aspect of the present invention is an element including an antenna array in which a plurality of antennas are arranged, each antenna including a first conductor layer, a semiconductor layer electrically connected to the first conductor layer and configured to generate or detect terahertz waves, a second conductor layer electrically connected to the semiconductor layer and facing the first conductor layer via the semiconductor layer, and a dielectric layer located between the first conductor layer and the second conductor layer, wherein the antenna array includes a first antenna, a second antenna, a third antenna, a fourth antenna, and a fifth antenna, and the second antenna, the first antenna, and the third antenna are arranged in this order in a first direction, and a dielectric layer is arranged in a second direction intersecting the first direction. The fourth antenna, the first antenna, and the fifth antenna are arranged in this order, the second conductor layer of the second antenna is connected to the second conductor layer of the first antenna via a first coupling line extending in the first direction, the second conductor layer of the first antenna is connected to the second conductor layer of the third antenna via a second coupling line extending in the first direction, the second conductor layer of the fourth antenna is connected to the second conductor layer of the first antenna via a third coupling line extending in the second direction, and the second conductor layer of the first antenna is connected to the second conductor layer of the fifth antenna via a fourth coupling line extending in the second direction. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a suitable antenna array structure. [Brief explanation of the drawings]

[0010] [Figure 1]1(a) is a schematic top view showing the device 10 according to embodiment 1. FIG. 1(b) is a schematic top view showing a modified example of the device 10 according to embodiment 1. FIG. [Figure 2] 1 is a schematic diagram illustrating the configuration of a device 10 according to a first embodiment. [Figure 3] 1(a) is a schematic cross-sectional view illustrating the element 10 according to embodiment 1. FIG. 1(b) is a schematic cross-sectional view illustrating the element 10 according to embodiment 1. FIG. [Figure 4] 2 is a plan view of a second conductor layer included in the device 10 according to the first embodiment. FIG. [Figure 5] 1A and 1B are diagrams illustrating the effects of the element 10 according to the first embodiment. [Figure 6] FIG. 2 is a diagram showing an element 20 according to a second embodiment. [Figure 7] 1 is a cross-sectional view showing a device 20 according to a second embodiment. [Figure 8] FIG. 10 is a diagram showing an element 30 according to a third embodiment. [Figure 9] FIG. 10 is a diagram showing an element 40 according to a fourth embodiment. [Figure 10] FIG. 10 is a diagram showing a terahertz camera system according to a fifth embodiment. [Figure 11] (a) A schematic top view showing the element 50 according to embodiment 6. (b) A schematic top view showing the element 50 according to embodiment 6. (c) A schematic top view showing an enlarged view of the element 50 according to embodiment 6. (d) A schematic top view showing a modified example of the element 50 according to embodiment 6. [Figure 12] 10(a) to 10(c) are cross-sectional views showing a device 50 according to a sixth embodiment. [Figure 13] 10(a) is a schematic top view showing a device 60 according to embodiment 7. FIG. 10(b) is a schematic top view showing a device 70 according to embodiment 7. FIG. [Figure 14] 10(a) and 10(b) are schematic top views showing the element according to embodiment 8. FIG. [Figure 15] 10(a) and 10(b) are schematic top views showing the element according to embodiment 8. FIG. [Figure 16] 10(a) and 10(b) are schematic top views showing the element according to embodiment 8. FIG. [Figure 17] 10(a) and 10(b) are schematic top views showing the element according to embodiment 8. FIG. [Figure 18] 10(a) and 10(b) are schematic top views showing the element according to embodiment 8. FIG. [Figure 19] 10(a) and 10(b) are schematic top views showing the element according to embodiment 8. FIG. [Figure 20] 10(a) and 10(b) are schematic top views showing the element according to embodiment 8. FIG. [Figure 21] FIG. 10 is a schematic diagram illustrating an element according to an eighth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Each embodiment will be described with reference to the drawings. In the following description, the device 10 will be used as an oscillator, but the device 10 can also be used as a receiver. Here, terahertz waves refer to electromagnetic waves in a frequency range of 10 GHz to 100 THz, more preferably 30 GHz to 30 THz.

[0012] In the description of each embodiment, the description of the same configuration as in other embodiments may be omitted. The embodiments can be appropriately modified or combined with other embodiments.

[0013] (Embodiment 1) The element 10 according to this embodiment will be described with reference to FIG. 1(a) and FIGS. 2 to 5. The configuration of the element 10 will be described with reference to FIG. 1(a) and FIGS. 2 to 4. FIG. 1(a) is a schematic top view of the element 10. FIG. 1(a) can be said to show the element 10 when viewed from above. FIG. 1(a) shows the X, Y, and Z directions. The X and Y directions may intersect, but in FIG. 1(a) they are perpendicular. The X and Y directions are included in a single plane. The Z direction is perpendicular to the X and Y directions, and is also referred to as the upward direction. FIG. 2 is a perspective view schematically showing the appearance of the element 10. FIG. 3(a) is a schematic cross-sectional view of the element 10 taken along line A-A' in FIG. 1(a). FIG. 3(b) is a schematic cross-sectional view of the element 10 taken along line B-B' in FIG. 1(a). FIG. 4 is a schematic plan view showing the second conductor layer of the element 10.

[0014] 1(a) and 2 to 4, the length of each component in the stacking direction of each component, such as the substrate 113, the dielectric layer 104, and the semiconductor layer 115 of the element 10, is referred to as the "thickness" or "height." The direction in which the dielectric layer 104 or the semiconductor layer 115 exists relative to the substrate 113 is referred to as the "upper."

[0015] The element 10 will be described using FIG. 1(a). The element 10 is an element that oscillates or detects terahertz waves with a frequency of fTHz, and is made of a semiconductor material. The element 10 has a plurality of antennas arranged therein. In this embodiment, the element 10 has an antenna array in which nine antennas 100a, 100b, 100c, 100d, 100e, 100f, 100g, 100h, and 100i are arranged in a 3×3 matrix.

[0016] The configuration of the antennas will be described. Each of the antennas 100a to 100i has the same configuration. In the following description, the configuration of the antenna 100a will be described in detail, and detailed descriptions of the components of the other antennas 100b to 100i that are the same as those of the antenna 100a will be omitted. In addition, in the description, the reference numerals of the components of each of the antennas 100a to 100i will be followed by an alphabet corresponding to each antenna. For example, the components of the second conductor layer 103 that the antenna 100a has will be described in association with the second conductor layer 103a.

[0017] The antenna 100a functions as both a resonator that resonates with terahertz waves and a radiator that transmits or receives terahertz waves. The antennas can be arranged at a pitch equal to or less than the wavelength of the terahertz waves to be detected or generated, or at an integral multiple of the wavelength.

[0018] As shown in FIG. 3(a), a substrate 113, a first conductor layer 106, and a second conductor layer 103a are stacked in this order. Between the first conductor layer 106 and the second conductor layer 103a, a dielectric layer 1042 and a dielectric layer 1041 are arranged in this order from the first conductor layer 106 side. Similar to the antennas 100a to 100i, the second conductor layers 103a to 103i each have the same configuration. Between the second conductor layer 103a and the second conductor layer 103b, a third conductor layer 110ab is arranged. Similar to the antennas 100a to 100i, the third conductor layer 110ab includes a third conductor layer 110bc, a third conductor layer 110cf, etc. Between the second conductor layer 103b and the second conductor layer 103c, a third conductor layer 110bc is arranged. In the following description, for example, a conductor layer connecting the antenna 100x and the antenna 100y will be referred to as a conductor layer 110xy or a conductor layer 110yx, etc. This is not limited to conductor layers, but also applies to coupling layers and the like.

[0019] The antenna 100a includes at least a first conductor layer 106, a second conductor layer 103a, and a semiconductor layer 101a disposed therebetween. The semiconductor layer 101a is a resonant tunneling diode (RTD), which will be described in detail later, and is also referred to as the RTD 101a or active layer 101a. Hereinafter, the semiconductor layer 101a may also be referred to as the RTD 101a. The antenna 100a further includes a semiconductor layer 115a, an electrode 116a for forming an ohmic junction, and a conductor 117a for connecting the second conductor layer 103a and the RTD 101a. The bonded wire 109ab includes a third conductor layer 110ab. A bias line 111x2 is disposed between the third conductor layer 110ab and the first conductor layer 106. The bias line 111x2 is located between the dielectric layer 1042 and the dielectric layer 1041.

[0020] In FIG. 3(b), bias lines 111y2 and the like are arranged on the same layer as the bias line 111x2 shown in FIG. 3(a). The bias line 111y2 forms lines 108g1 and 108d2. The second conductor layer 103a is connected to the second conductor layer 103b via conductor 107g1, line 108g1, line 108d2, and conductor 107d2. The layer of the bias line 111y2 is electrically connected to the bias circuit 120, as shown in FIG. 2. The bias circuit 120 is also referred to as a power supply circuit. The first conductor layer 106 is grounded, as shown in FIG. 2. 3(a) and 3(b), the layer including the first conductor layer 106 can be referred to as the first wiring layer, the layer including the bias line 111 as the second wiring layer, and the layer including the second conductor layer 103 and the third conductor layer 110 as the third wiring layer. The conductors included in each wiring layer can be said to be located at the same height. The height refers to the height from the surface of the substrate 113.

[0021] 4 is a schematic diagram showing a pattern located at the same height including the second conductor layer 103 and the third conductor layer 110. Here, an element having a plurality of antennas 100 will be described.

[0022] Arranging multiple antennas 100 is considered in order to increase the antenna gain of the element 10. As described above, each antenna 100 is provided with an RTD 101, and mutual injection synchronization between the antennas 100 increases the antenna gain. To synchronize the multiple antennas 100, coupling lines are required to couple adjacent antennas. Here, the coupling lines are also called coupling lines.

[0023] Coupled lines have not been studied in detail until now. Specifically, when connecting adjacent antennas with coupled lines, it has been difficult to satisfy the phase matching condition in either the transverse direction (magnetic field direction, H direction) or the longitudinal direction (electric field direction, E direction), or both. As a result, as the number of antennas increases, injection locking in either the longitudinal or transverse direction becomes insufficient, reducing the gain increase. In addition, the improvement in directivity is less than expected. Therefore, efficient generation and detection of terahertz waves using antenna arrays has not been possible.

[0024] The coupling lines that couple multiple antennas 100 will be described using FIG. 4. First, the case where multiple antennas 100 are coupled in the X direction will be described. Antenna 100e is coupled to antenna 100f by coupling line 109ef. The coupling of antennas in the X direction will be described. Antenna 100e is coupled to antenna 100f via coupling line 109ef and to antenna 100d via coupling line 109de. Antenna 100h is coupled to antenna 100i via coupling line 109hi and to antenna 100g via coupling line 109gh. Antenna 100b is coupled to antenna 100c via coupling line 109bc and to antenna 100a via coupling line 109ab. In FIG. 4, each antenna is directly connected to each coupling line, but they may also be connected via capacitive coupling. Here, the X direction is the vertical direction mentioned above, which is the direction of the electric field, i.e., the E direction.

[0025] Next, a case where multiple antennas 100 are coupled in the Y direction will be described. The coupling of the antennas 100 in the Y direction is achieved by coupled line 109fi, coupled line 109cf, coupled line 1091he, coupled line 1091eb, coupled line 1092he, coupled line 1092eb, coupled line 109dg, and coupled line 109ad. The coupled line 1091he couples the coupled line 109hi to the coupled line 109ef, and the coupled line 1091eb couples the coupled line 109ef to the coupled line 109bc. The coupled line 1092he couples the coupled line 109gh to the coupled line 109de, and the coupled line 1092eb couples the coupled line 109de to the coupled line 109ab.

[0026] Focusing on antenna 100e, the following can be seen. Antennas 100f and 100d are arranged adjacent to antenna 100e on both sides of antenna 100e in a first direction (vertical direction). Antenna 100e is connected to antennas 100f and 100d by coupling lines 109ef and 109ed extending in the first direction (vertical direction). Similarly, antennas 100h and 100b are arranged adjacent to both sides of antenna 100e in a second direction (horizontal direction) intersecting the first direction. Here, in the case of the patch antenna used in this embodiment, the first direction is the resonance direction of the terahertz wave (propagation direction of the resonant electric field, electric field direction, E direction), and the second direction is a direction perpendicular to the first direction (magnetic field direction, H direction). Note that the present invention is applicable not only to antennas that radiate horizontally and vertically polarized waves as described above, but also to antennas that radiate circularly polarized waves.

[0027] Furthermore, focusing on antenna 100e, the following can be seen. In a first direction (vertical direction), antennas 100d, 100e, and 100f are arranged in this order. In a second direction (horizontal direction) intersecting the first direction, antennas 100h, 100e, and 100b are arranged in this order. Antennas 100e and 100f are coupled by a coupling line 109ef extending along the first direction, and antennas 100e and 100d are coupled by a coupling line 109de extending along the first direction. Antennas 100e and 100b are coupled by a coupling line 1091eb extending along the second direction, and antennas 100e and 100h are coupled by a coupling line 1091he extending along the second direction.

[0028] Here, the first antenna is antenna 100e, the second antenna is antenna 100f, the third antenna is antenna 100d, the fourth antenna is antenna 100h, and the fifth antenna is antenna 100b. If the first direction is the X direction and the second direction is the Y direction, this can be explained as follows. In the first direction, the second antenna, the first antenna, and the third antenna are arranged in this order. In the second direction, the fourth antenna, the first antenna, and the fifth antenna are arranged in this order. The second conductor layer of the second antenna is connected to the second conductor layer of the first antenna via a first coupling line extending in the first direction, and the second conductor layer of the first antenna is connected to the second conductor layer of the third antenna via a second coupling line extending in the first direction. The second conductor layer of the fourth antenna is connected to the second conductor layer of the first antenna via a third coupled line extending in the second direction, and the second conductor layer of the first antenna is connected to the second conductor layer of the fifth antenna via a fourth coupled line extending in the second direction. Here, the first coupled line is 109ef, the second coupled line is 109de, the third coupled line is 1091he or 1092he, and the fourth coupled line is 1091eb or 1092eb.

[0029] As shown in FIG. 4, the element 10 further includes bonded lines 1091he, 1092he, 1091eb, and 1092eb extending in a second direction (horizontal direction) intersecting the first direction (vertical direction). The bonded lines 1091he and 1091eb extending in the second direction are connected to the bonded lines 109hi, 109ef, and 109bc extending in the first direction. The bonded lines 1092he and 1092eb extending in the second direction are connected to the bonded lines 109gh, 109de, and 109ab extending in the first direction. This type of connection allows multiple antennas 100 to be coupled together. This connection also increases the antenna gain. When the bonded lines are connected to each other, the bonded lines may be formed of a continuous conductor, i.e., a single conductor.

[0030] The coupled wires are preferably connected as follows. The length is preferably such that the electrical length between the RTDs of adjacent antennas is an integer multiple of 2π. For example, when the X direction is taken as the first direction, the coupled wire 109de extending in the X direction has a length such that the electrical length between the RTDs 100e and 100d is 2π. Furthermore, when the Y direction is taken as the second direction, the coupled wire 1091eb or 1092eb extending in the Y direction has a length such that the electrical length between the RTDs 100e and 100b is 4π. Here, the electrical length refers to the wiring length that takes into account the propagation speed of high-frequency waves propagating through the coupled wire. This facilitates mutual injection locking with positive phase from the RTDs 101a to 101i of each antenna. The error in the length range is ±1 / 4π.

[0031] Next, coupling will be explained. Figures 5(a) and 5(b) are schematic diagrams for explaining the element 10 of this embodiment. Figures 5(a) and 5(b) are schematic diagrams showing the relationship between the antennas and coupling lines. Figure 5(c) is a graph showing the correlation between the number of antennas and the radiation angle of electromagnetic waves.

[0032] Figure 5(a) shows the configuration of element 10 coupled in the XY directions, while Figure 5(b) shows the configuration of element 10' coupled only in the X direction. Here, the "+" and "-" in the figure indicate the loops and polarities of the resonant electric field of frequency fTHz existing in the antenna array, and the "x" indicates the nodes of the resonant electric field. Element 10' lacks coupling lines connecting the central antenna 100e to the two adjacent antennas 100h in the Y direction or to antenna 100b, resulting in insufficient synchronization between the antennas in the Y direction. Antenna 100e of element 10 is connected to the adjacent antennas 100h and 100b in the Y direction by coupling lines, resulting in sufficient synchronization between the antennas in the Y direction. This increases the antenna gain.

[0033] Furthermore, to satisfy the phase matching condition between the antennas, the X-direction and Y-direction coupling lines are connected at a position shifted in the X direction from the axis of symmetry between adjacent antennas in the X direction. In other words, the X-direction and Y-direction coupling lines are connected at a position shifted in the X direction from the center between adjacent antennas in the X direction. For example, in the case of antennas 100e and 100d adjacent in the X direction, the following applies. If antennas 100e and 100d are symmetrical with respect to a line segment extending in the Y direction, the symmetry point is taken as the point where the line segment intersects with the X direction. The X-direction coupling line 109de and the Y-direction coupling line 1092he are connected at a position shifted in the X direction from the symmetry point. The X-direction coupling line 109de and the Y-direction coupling line 1092eb are connected at a position shifted in the X direction from the symmetry point. The shift amount is, for example, 30 μm. 1(a), the distance between the two antennas 100 in the X direction is defined as length LX1, and the distance between the two antennas 100 in the Y direction is defined as length LY1. Here, the connection between the coupled line 109ab and the coupled line 1092eb is shifted from the center of the length LX1 toward the antenna 100a. Here, the shift is also called an offset.

[0034] More preferably, the coupled lines in the X and Y directions are connected at a position other than the node of the resonant electric field standing on the coupled line at the frequency of the terahertz wave. In other words, it is preferable that the coupled lines in the X and Y directions are connected at a position shifted from the center of electrical symmetry between adjacent antennas in the X direction at the frequency of the terahertz wave fTHz. This is because if the two antennas are connected at the node of the resonant electric field standing on the coupled line at the frequency of the terahertz wave, the phase matching conditions between the vertical and horizontal antennas will be inconsistent. Therefore, mutual weakening of the outputs due to interference may occur. Furthermore, the directivity may be disrupted.

[0035] Figure 5(c) shows a graph showing the correlation between the number of antennas and the radiation angle. The straight and dashed lines on the graph represent calculated values (using ANSYS HFSS), and the dots represent measured data for 2x2, 4x4, 5x5, and 6x6 arrays. For element 10', which is coupled only vertically, it can be seen that horizontal synchronization becomes insufficient for antenna arrays of 3x3 or larger. It can also be seen that the effect of improving directivity saturates. Furthermore, for element 10's configuration, which couples antennas in both the vertical and horizontal directions, both calculations and measurements confirm that directivity improves and the radiation angle becomes sharper as the number of antennas increases in both the vertical and horizontal directions. Due to the effect of the connected horizontal coupling lines, sufficient synchronization between antennas is achieved in both the vertical and horizontal directions, even in antenna arrays of 3x3 or larger, such as antenna 100e, where the number of antennas surrounded by adjacent antennas increases. In other words, the phase matching condition between antennas is met. Therefore, with the element of this embodiment, even an antenna surrounded by adjacent antennas in an M × N array (M and N are natural numbers) can achieve both enhanced coupling and phase matching in at least the vertical direction and both the vertical and horizontal directions. Therefore, the element 10 shown in Figure 5(a) is expected to have stronger antenna output strength than the element 10' shown in Figure 5(b), which is synchronized only in the vertical direction. Also, improved directivity is expected.

[0036] The configuration in which one coupling line is arranged vertically and horizontally between each antenna is a suitable configuration in which the number of coupling lines is minimized to reduce loss in the terahertz waves due to coupling, but is not limited to this.

[0037] The detailed configuration of the antenna will be described below. As shown in FIGS. 3(a) and 3(b), the antenna 100a has a first conductor layer 106, a second conductor layer 103a, and a dielectric layer 104. The dielectric layer 104 is located between two conductor layers (wiring layers), the first conductor layer 106 and the second conductor layer 103a. Such a configuration of the antenna 100a is called a microstrip antenna that uses a microstrip line or the like of a finite length. In this embodiment, an example using a patch antenna, which is a microstrip resonator, will be described.

[0038] As shown in FIGS. 3(a) and 3(b), the second conductor layer 103a is a patch conductor of the antenna 100a, and is disposed so as to face the first conductor layer 106 with the dielectric layer 104 (semiconductor layer 115a) interposed therebetween. The second conductor layer 103a is electrically connected to the semiconductor layer 115a. The antenna 100a is configured to operate as a resonator with a width of λTHz / 2 in the A-A' direction (resonance direction) of the second conductor layer 103a. The first conductor layer 106 is a ground conductor that is electrically grounded. Note that λTHz is the effective wavelength in the dielectric layer 104 of the terahertz wave that resonates in the antenna 100a. λTHz is expressed as λ0 × εr-1 / 2, where λ0 is the wavelength of the terahertz wave in a vacuum and εr is the effective relative dielectric constant of the dielectric layer 104.

[0039] As shown in FIGS. 3(a) and 3(b), the antenna 100a has a semiconductor structure. The semiconductor structure is, for example, a mesa-type structure. The semiconductor structure includes a semiconductor layer 115a and a semiconductor layer 101a. The semiconductor structure further includes a third electrode 116a, which is an ohmic electrode. The semiconductor layer 115a is located inside the antenna 100a and is configured to emit or detect terahertz electromagnetic waves. Although FIG. 1(a) shows only the semiconductor layer 101a of the antenna 100a, the semiconductor layer 115a is also disposed between the semiconductor layer 101a and the second conductor layer 103a.

[0040] The semiconductor layer 101a will be described below. The semiconductor layer 101a is composed of a semiconductor layer having electromagnetic wave gain or nonlinearity for terahertz waves. A typical semiconductor layer having electromagnetic wave gain in the frequency band of terahertz waves is a resonant tunneling diode (RTD), which is also called an active layer. In this embodiment, an example in which an RTD is used as the semiconductor layer 101a will be described. In the following, the semiconductor layer 101a may also be called an RTD 101a.

[0041] The RTD 101a has a resonant tunneling structure layer including multiple tunnel barrier layers, with quantum well layers provided between the multiple tunnel barriers, and has a multiple quantum well structure that generates terahertz waves through intersubband transitions of carriers. The RTD 101a has electromagnetic wave gain in the terahertz wave frequency range based on the photon-assisted tunneling phenomenon in the negative differential resistance region of the current-voltage characteristics, and exhibits self-sustained oscillation in the negative differential resistance region.

[0042] Antenna 100a is an active antenna in which an RTD 101a, a semiconductor layer 115a, and a patch antenna are integrated. The frequency (fTHz) of the terahertz waves oscillated from antenna 100a alone is determined by the resonant frequency of a full-parallel resonant circuit that combines the reactance of the patch antenna and semiconductor layer 115a. Specifically, from the equivalent circuit of the oscillator described in Non-Patent Document 1, for a resonant circuit that combines the admittances of the RTD and antenna (YRTD and Yaa), the frequency that satisfies the amplitude condition in equation (1) and the phase condition in equation (2) is determined as the oscillation frequency (fTHz). Re[YRTD]+Re[Yaa]≦0 (1) Im[YRTD]+Im[Yaa]=0 (2)

[0043] Here, YRTD is the admittance of the semiconductor layer 115a, Re is the real part, and Im is the imaginary part. Since the semiconductor layer 115a includes the RTD 101a, which is a negative resistance element, Re[YRTD] has a negative value. Also, Yaa is the admittance of the entire structure of the patch antenna 100a as seen from the semiconductor layer 115a.

[0044] The semiconductor layer 101a may be a quantum cascade laser (QCL) structure having a multilayer structure of several hundred to several thousand semiconductor layers. In this case, the semiconductor layer 115a is a semiconductor layer including a QCL structure. The semiconductor layer 101a may be a negative resistance element such as a Gunn diode or an IMPATT diode, which are often used in the millimeter wave band. The semiconductor layer 101a may be a high-frequency element such as a transistor terminated at one terminal. Suitable transistors include a heterojunction bipolar transistor (HBT), a compound semiconductor layer-based FET, and a high electron mobility transistor (HEMT). The semiconductor layer 101a may be a Josephson device with a negative differential resistance using a superconductor layer.

[0045] The dielectric layer 104 is composed of two layers: a first dielectric layer 1041 and a second dielectric layer 1042. In microstrip resonators such as patch antennas, a thick dielectric layer 104 reduces conductor loss and improves radiation efficiency. The dielectric layer 104 must be able to be formed into a thick film (typically 3 μm or more), have low loss and a low dielectric constant in the terahertz band, and be easily microfabricated (e.g., planarized or etched). The thicker the dielectric layer 104, the higher the radiation efficiency; however, if it is too thick, multimode resonance may occur. Therefore, the thickness of the dielectric layer 104 is preferably designed to be no more than 1 / 10 of the oscillation wavelength. Meanwhile, increasing the frequency and output of oscillators requires miniaturization and high current density of diodes. Therefore, the dielectric layer 104, as an insulating structure for the diode, must also suppress leakage current and mitigate migration. In this embodiment, in order to achieve the above two objectives, the first dielectric layer 1041 and the second dielectric layer 1042 are made of two different materials.

[0046] Specific examples of materials that can be suitably used for the first dielectric layer 1041 include organic dielectric materials such as BCB (benzocyclobutene, manufactured by Dow Chemical Company, εr1=2), polytetrafluoroethylene, and polyimide. Here, εr1 is the relative dielectric constant of the first dielectric layer 1041. Alternatively, the first dielectric layer 1041 may be made of an inorganic dielectric material such as a TEOS oxide film or spin-on glass, which can be formed into a relatively thick film and has a low dielectric constant.

[0047] The second dielectric layer 1042 is required to have insulating properties (the ability to act as an insulator and high resistance material that does not conduct electricity when subjected to DC voltage), barrier properties (the ability to prevent the diffusion of metal materials used in the electrodes), and processability (the ability to be processed with submicron precision). Specific examples of materials that satisfy these requirements include inorganic insulating materials such as silicon oxide (εr2=4), silicon nitride (εr2=7), aluminum oxide, and aluminum nitride. εr2 is the relative dielectric constant of the second dielectric layer 1042.

[0048] Here, when the dielectric layer 104 has a two-layer structure as in this embodiment, the relative dielectric constant εr of the dielectric layer 104 is an effective relative dielectric constant determined by the thickness and relative dielectric constant εr1 of the first dielectric layer 1041 and the thickness and relative dielectric constant εr2 of the second dielectric layer 1042. From the viewpoint of impedance matching between the antenna and space, it is preferable that the difference in dielectric constant between the antenna and air is small. Therefore, it is preferable that the first dielectric layer 1041 is made of a material different from that of the second dielectric layer 1042 and that has a low relative dielectric constant (εr1<εr2). Note that in the element 10, the dielectric layer 104 does not need to have a two-layer structure, and may have a structure formed of only one layer of the above-mentioned materials.

[0049] The semiconductor layer 115a is disposed on a first conductor layer 106 formed on the substrate 113. The semiconductor layer 115a and the first conductor layer 106 are electrically connected. In order to reduce ohmic loss, the semiconductor layer 115a and the first conductor layer 106 are preferably connected with low resistance. An electrode 116a is disposed on the side of the semiconductor layer 115a opposite to the side on which the first conductor layer 106 is disposed, and the electrode 116a and the semiconductor layer 115a are electrically connected. The semiconductor layer 115a and the electrode 116a are embedded in a second dielectric layer 1042 and are surrounded by the second dielectric layer 1042.

[0050] If the electrode 116a is a conductor ohmically connected to the semiconductor layer 115a, it is suitable for reducing ohmic loss and RC delay due to series resistance. When the electrode 116a is used as an ohmic electrode, suitable materials include Ti / Pd / Au, Ti / Pt / Au, AuGe / Ni / Au, TiW, Mo, and ErAs. Furthermore, if the region of the semiconductor layer 115a in contact with the electrode 116a is a semiconductor highly doped with impurities, the contact resistance is further reduced, making it suitable for higher output and higher frequencies. Since the absolute value of negative resistance, which indicates the magnitude of the gain of the RTD 101a used in the terahertz wave band, is approximately 1 to 100 Ω, it is preferable to suppress the electromagnetic wave loss to 1% or less of that. Therefore, it is recommended that the contact resistance of the ohmic electrode be suppressed to 1 Ω or less as a guideline. Furthermore, to operate in the terahertz wave band, the width of semiconductor layer 115a (≈ electrode 116a) is typically about 0.1 to 5 μm, and therefore it is preferable to suppress the contact resistance to a range of 0.001 to several Ω, with the resistivity being 10 Ω·μm2 or less.

[0051] It is also possible to use a metal that forms a Schottky contact with the electrode 116a rather than an ohmic contact. In this case, the contact interface between the electrode 116a and the semiconductor layer 115a exhibits rectification, and the antenna 100a is suitable as a terahertz wave detector. In the following, in this embodiment, a configuration using an ohmic electrode as the electrode 116a will be described.

[0052] Inside the antenna 100a arranged above and below the RTD 101a, as shown in FIG. 3(a), a substrate 113, a first conductor layer 106, a semiconductor layer 115a, an electrode 116a, a conductor 117a, and a second conductor layer 103a are stacked in this order.

[0053] Conductor 117a is formed inside dielectric layer 104, and second conductor layer 103a and electrode 116a are electrically connected via conductor 117a. If conductor 117a is too wide, the resonance characteristics of patch antenna 100a will deteriorate and radiation efficiency will decrease due to increased parasitic capacitance. Therefore, the width of conductor 117a is preferably set to a size that does not interfere with the resonant electric field, typically, 1 / 10 or less of the effective wavelength λ of the terahertz waves with an oscillation frequency fTHz present in antenna 100a. Furthermore, the width of conductor 117a may be small enough not to increase series resistance; as a guideline, it can be reduced to approximately twice the skin depth. To minimize the series resistance to a level not exceeding 1 Ω, the width of conductor 117a is typically set to a range of 0.1 μm to 20 μm.

[0054] In FIG. 1(a), the second conductor layer 103a is electrically connected to the lines 108a1 and 108a2 via the conductors 107a1 and 107a2. The lines 108a1 and 108a2 are also drawn out and electrically connected to the bias circuit 120 via the bias line 111, a common wiring formed within the chip. The lines 108 are drawn out from each antenna. The bias circuit 120 is a power source for supplying a bias signal to the RTD 101a of the antenna 100a. Therefore, the bias line 111 is connected to the lines 108 drawn out from adjacent antennas, thereby supplying a bias signal to the semiconductor layer 115 of each antenna. The common bias line 111 ensures sufficient wiring width, reducing operating voltage variations between antennas due to variations in wiring resistance. This stabilizes synchronization even when the number of arrays is increased. Furthermore, the structure around the antennas can be made symmetrical, preventing the radiation pattern from collapsing.

[0055] Conductors 107a1 and 107a2 are connectors for electrically and mechanically connecting lines 108a1 and 108a2 to second conductor layer 103a. Structures that electrically connect upper and lower layers, such as conductor 117a and conductors 107a1 and 107a2, are called vias. First conductor layer 106 and second conductor layer 103a not only serve as components of the patch antenna, but also function as electrodes for injecting current into RTD 101a when connected to these vias. Conductor 117a and conductors 107a1 and 107a2, which are vias, are preferably made of materials with a resistivity of 1×10-6 Ω·m or less. Specifically, metals and metal compounds such as Ag, Au, Cu, W, Ni, Cr, Ti, Al, AuIn alloys, and TiN are preferably used as materials.

[0056] The widths of conductors 107a1 and 107a2 are smaller than the width of second conductor layer 103a. The widths shown here refer to the widths in the electromagnetic wave resonance direction (= A-A' direction) within antenna 100a. The width of the portion (connection portion) of line 108a1 (line 108a2) connected to conductor 107a1 (conductor 107a2) is smaller (thinner) than the width of second conductor layer 103a (antenna 100a). These widths are preferably 1 / 10 or less of the effective wavelength λ (λ / 10 or less) of the terahertz wave with an oscillation frequency fTHz standing in antenna 100a. This is because, in order to improve radiation efficiency, it is preferable to arrange conductors 107a1 and 107a2 and lines 108a1 and 108a2 in dimensions and positions that do not interfere with the resonant electric field within antenna 100a.

[0057] Furthermore, conductors 107a1 and 107a2 are preferably positioned at nodes of the electric field of terahertz waves with an oscillation frequency of fTHz standing in antenna 100a. In this case, conductors 107a1 and 107a2 and lines 108a1 and 108a2 are configured to have impedances sufficiently higher than the absolute value of the negative differential resistance of RTD 101a in a frequency band near the oscillation frequency of fTHz. In other words, lines 108a1 and 108a2 are connected to antennas other than antenna 100a so as to present high impedance to the RTD at the oscillation frequency of fTHz. In this case, the other antennas and antenna 100a are isolated from each other through the path via bias line 111 at the frequency of fTHz. This prevents the current with an oscillation frequency of fTHz induced in each antenna via bias line 111 and bias circuit 120 from affecting adjacent antennas. Furthermore, interference between the electric field of the oscillation frequency fTHz standing within the antenna 100a and these power supply members is suppressed. The other antennas 100b to 100i in the element 10 are similar to the antenna 100a.

[0058] The bias line 111 is a common bias wiring (wiring layer) for the antennas 100a to 100i. The antennas 100a to 100i are connected to the bias line 111 via lines 108a1, 108a2, and lines 108i1 and 108i2 connected to them, respectively. Of the bias lines 111, the lines in the A-A' direction (resonance direction) are shown as 111x1 to 111x4, and the lines in the B-B' direction are shown as 111y1 to 111y4 in FIGS. 3(a) and 3(b). In this description, the bias common wiring for the element 10 is referred to as the bias line 111 as a whole.

[0059] 2, the bias circuit 120 is a power supply arranged outside the chip to supply bias signals to the RTDs 101a to 101i. The bias circuit 120 includes shunt resistors 121 connected in parallel with the RTDs 101a to 101i, wiring 122, a power supply 123, and a capacitor 124 connected in parallel with the shunt resistors 121.

[0060] The wiring 122 is shown as an inductance in FIG. 2 because it necessarily has a parasitic inductance component. The power supply 123 supplies the current required to drive each of the RTDs 101a-101i and adjusts the bias voltage applied to each of the RTDs 101a-101i. The bias voltage is typically selected from voltages in the negative differential resistance region of the RTDs used for the RTDs 101a-101i. The bias circuit 120 is connected to a bias line 111, which is an in-chip wiring. In the case of the antenna 100a, the bias voltage from the bias circuit 120 is supplied to the RTD 101a in the antenna 100a via lines 108a1 and 108a2. The same applies to the other antennas 100b-100i.

[0061] The shunt resistor 121 and the capacitor 124 have the role of suppressing parasitic oscillation of a relatively low resonant frequency (typically a frequency band from DC (Direct Current) to 10 GHz) caused by the bias circuit 120. The value of the shunt resistor 121 is selected to be equal to or slightly smaller than the absolute value of the combined negative differential resistance of the RTDs 101a to 101i connected in parallel. Like the shunt resistor 121, the capacitor 124 is also set so that the impedance of the element is equal to or slightly lower than the absolute value of the combined negative differential resistance of the RTDs 101a to 101i connected in parallel. In other words, the bias circuit 120 is set, due to these shunt structures, to have an impedance lower than the absolute value of the combined negative resistance corresponding to the gain in the frequency band from DC to 10 GHz. Generally, the capacitor 124 is preferably larger within the above-mentioned range, and in the example of this embodiment, the capacitance is about several tens of pF. The capacitor 124 is a decoupling capacitor, and may have, for example, a MIM (Metal-Insulator-Metal) structure in which the antenna 100a and the substrate are the same.

[0062] Element 10 is an antenna array having nine antennas 100a, 100b, 100c, 100d, 100e, 100f, 100g, 100h, and 100i arranged in a 3x3 matrix. Each of antennas 100a to 100i independently emits terahertz waves at a frequency of fTHz. Adjacent antennas are coupled to each other by coupling wires 109, and are mutually injection locked (mutually synchronized) at the terahertz wave oscillation frequency of fTHz.

[0063] Mutual injection locking refers to the mutual synchronization of multiple self-excited oscillators through mutual interaction. For example, antennas 100a and 100b are mutually coupled by coupling line 109ab, and antennas 100a and 100d are mutually coupled by coupling line 109ad. The same applies to other adjacent antennas. Note that "mutually coupled" refers to the phenomenon in which a current induced in one antenna acts on another adjacent antenna, changing their transmission and reception characteristics. By synchronizing mutually coupled antennas in phase or opposite phase, the mutual injection locking phenomenon causes mutual strengthening or weakening of the electromagnetic fields between the antennas. This allows for adjustment of antenna gain. Note that in this description, the entire coupling line connecting the antennas of element 10 is referred to as coupling line 109. Furthermore, the coupling lines connecting each antenna that make up coupling line 109 are referred to using the alphabet corresponding to each antenna. For example, the coupling line that couples the antenna 100a and the antenna 100b is represented as coupling line 109ab.

[0064] The oscillation conditions of element 10 are determined by the conditions for mutual injection locking in a configuration in which two or more individual RTD oscillators are coupled, as disclosed in J. Appl. Phys., Vol. 103, 124514 (2008) (Non-Patent Document 2). Specifically, consider the oscillation conditions of an antenna array in which antennas 100a and 100b are coupled by coupling wire 109ab. In this case, two oscillation modes occur: positive-phase mutual injection locking and anti-phase mutual injection locking. The oscillation conditions for the positive-phase mutual injection locking oscillation mode (even mode) are expressed by equations (4) and (5), and the oscillation conditions for the anti-phase mutual injection locking oscillation mode (odd mode) are expressed by equations (6) and (7). Positive phase (even mode): Frequency f=feven Yeven=Yaa+Yab+YRTD Re(Yeven)≦0 (4) Im(Yeven)=0 (5) Out of phase (odd mode): frequency f=fodd Yodd=Yaa+Yab+YRTD Re(Yodd)≦0 (6) Im(Yodd)=0 (7)

[0065] Here, Yab is the mutual admittance between antenna 100a and antenna 100b. Yab is proportional to the coupling constant that represents the strength of coupling between the antennas, and ideally, the real part of -Yab is large and the imaginary part is zero. The element 10 of this embodiment is coupled under the condition of mutual injection locking in positive phase, and the oscillation frequency fTHz≈feven. Similarly, the other antennas are coupled to each other at coupling line 109 so as to satisfy the above-mentioned condition of mutual injection locking in positive phase.

[0066] The coupled wire 109 is a microstrip line in which the dielectric layer 104 is sandwiched between the third conductor layer 110 and the first conductor layer 106. For example, as shown in FIG. 3( a), the coupled wire 109ab has a structure in which the dielectric layer 104 is sandwiched between the third conductor layer 110ab and the first conductor layer 106. Similarly, the dielectric layer 104 is sandwiched between the first conductor layer 106 by the third conductor layer 110bc of the coupled wire 109bc, the third conductor layer 110ad of the coupled wire 109ad, and the third conductor layer 110cf of the coupled wire 109cf.

[0067] In FIG. 4, the antennas of element 10 are DC-coupled. A third conductor layer 110ab, which is an upper conductor layer of a coupling wire 109ab that couples antennas 100a and 100b, is directly connected to the second conductor layers 103a and 103b. As shown in FIGS. 3 and 4, in element 10, the third conductor layer 110ab and the second conductor layers 103a and 103b are formed on the same layer. Similarly, a third conductor layer 110ae, which is an upper conductor layer of a coupling wire 109ae that couples antennas 100a and 100e, is directly connected to the second conductor layers 103a and 103e. The third conductor layer 110ae and the second conductor layers 103a and 103e are formed on the same layer.

[0068] With this structure, antennas 100b and 100e are mutually coupled to antenna 100a, and operate in synchronization with each other at the frequency of the oscillating terahertz waves (fTHz). Such an antenna array synchronized by DC coupling can synchronize adjacent antennas with strong coupling, making it easy to synchronize by pulling and resistant to variations in frequency and phase among the antennas.

[0069] In the element 10, the bonded wire 109 and the bias line 111 are arranged on different layers. For example, as shown in FIG. 3(a), the third conductor layer 110ab constituting the bonded wire 109ab coupling the antennas 100a and 100b is arranged on a different layer from the fourth conductor layer 111x2 constituting the bias line 111. Also, the third conductor layer 110ad constituting the bonded wire 109ad coupling the antennas 100a and 100d is arranged on a different layer from the fourth conductor layer 111x1 constituting the bias line 111. In other words, the wiring layer in which the bonded wire 109 has a portion extending in the in-plane direction of the substrate 113 (a direction perpendicular to the stacking direction) and the wiring layer in which the bias line 111 has a portion extending in the in-plane direction of the substrate 113 are arranged on different layers. Here, the wiring layers in which the bond wire 109 has a portion extending in the in-plane direction are the third conductor layer 110 and the first conductor layer 106. On the other hand, the wiring layer in which the bias line 111 has a portion extending in the in-plane direction is the fourth conductor layer 111. In this embodiment, all of the third conductor layers 110 and first conductor layers 106 in all of the antennas are arranged on a layer different from any of the fourth conductor layers 111.

[0070] In this way, the coupled line 109 that transmits a high frequency (fTHz) and the bias line 111 that transmits a low frequency (DC to several tens of GHz) are arranged on different layers, which allows the layout of the transmission line, such as its width, length, and routing, to be freely set within each layer.

[0071] In addition, in the element 10, the substrate 113, the first conductor layer 106, and the second conductor layer 103a are stacked in this order from the substrate 113 side. At least one of the bond wire 109 and the bias line 111 is disposed on a layer between the first conductor layer 106 and the second conductor layer 103. For example, as shown in FIG. 3(a), the fourth conductor layers 111x2 and 111x1 are disposed on a layer between the first conductor layer 106 and the second conductor layer 103.

[0072] Furthermore, as shown in FIG. 1(a), when viewed from above (in a plan view), the bond line 109 and the bias line 111 intersect with each other. For example, in a plan view, the third conductor layer 110ab and the fourth conductor layer 111x2 intersect with each other, and the third conductor layer 110ad and the fourth conductor layer 111y3 intersect with each other. As shown in FIGS. 3(a) and 3(b), the intersecting conductor layers are located at different heights.

[0073] In this way, by laying the coupling lines 109 and the bias lines 111 so that they cross each other, a more layout-saving configuration can be realized. Therefore, with this configuration, the number of antennas can be increased even in an antenna array in which antennas are arranged in an m×n (m≧2, n≧2) matrix. According to this embodiment, even if the number of antennas is increased, physical interference between the coupling lines (coupling lines 109) for synchronizing the antennas and the feed lines (bias lines 111) for supplying bias to each RTD 101 can be suppressed. Therefore, the upper limit on the number of antennas that can be arranged in the element 10 is suppressed, and significant improvements in directivity and front intensity can be expected as the number of antennas in the array increases.

[0074] Furthermore, by arranging at least one of the coupled wire 109 and the bias line 111 in a layer between two conductor layers that constitute the antenna, a layout-saving configuration can be achieved. Specifically, the coupled wire 109 and / or the bias line 111 are embedded in the surplus area other than the antennas in the dielectric layer 104 that constitutes the antennas 100a to 100i. This allows multiple transmission lines to be arranged in the relatively small space between adjacent antennas that are arranged at a pitch of about the wavelength, which can adequately accommodate an increase in the number of lines that accompanies an increase in the number of antennas.

[0075] In the terahertz band, resistance due to the skin effect increases, making conductor loss associated with high-frequency transmission between antennas non-negligible. As the current density between conductor layers increases, conductor loss per unit length (dB / mm) increases. In the case of a microstrip line, conductor loss per unit length (dB / mm) is inversely proportional to the square of the dielectric thickness. Therefore, to increase the radiation efficiency of the antenna array, it is preferable to reduce conductor loss by thickening not only the antenna but also the dielectric constituting the coupling line 109. In contrast, the element 10 according to this embodiment has a configuration in which the bias line 111 is disposed on the first conductor layer 106 side of the first dielectric layer 1041, and the third conductor layer 110, through which a high-frequency wave with a frequency of fTHz is transmitted, is disposed above the dielectric layer 104. This configuration can suppress the reduction in radiation efficiency of the antenna array associated with conductor loss in the terahertz band. In this case, in the antenna 100a, the substrate 113, the first conductor layer 106, the fourth conductor layers 111x1 and 111x2, the second conductor layer 103a, and the third conductor layers 110ad and 110ab are laminated in this order from the substrate 113 side. The same applies to the relationship between the coupling wires 109 and bias lines 111 that couple the other antennas.

[0076] From the viewpoint of conductor loss, the thickness of the dielectric constituting the bonded wire 109 is preferably 1 μm or more, and more preferably 2 μm or more. This reduces conductor loss in the terahertz band to approximately 20%. Similarly, from the viewpoint of conductor loss, a wider thickness-wise gap between the third conductor layer 110 constituting the bonded wire 109 and the first conductor layer 106 is preferable. Furthermore, a wider thickness-wise gap between the third conductor layer 110 constituting the bonded wire 109 and the fourth conductor layer 111 constituting the bias line 111 is preferable. For the bias line 111, setting the dielectric thickness to 2 μm or less, preferably 1 μm or less, allows the bias line 111 to function as a low-impedance line up to the gigahertz band. Even when the dielectric thickness is set to 2 μm or more, a shunt component can be connected to the bias line, as in the device 30, to allow the bias line 111 to function as a low-impedance line.

[0077] Furthermore, in the element 10 according to this embodiment, adjacent antennas are fed by a common bias line 111 disposed between the antennas. For example, as shown in FIG. 3(b), the antenna 100a is connected to the bias line 111y3 via the conductor 107a2 and the line 108a2, and the antenna 100d is connected to the bias line 111y3 via the conductor 107d1 and the line 108d1. Similarly, since the antennas 100a and 100b are adjacent to each other, a bias signal is fed by connecting them to the common bias line 111x2 disposed between the two antennas. The same applies to the bias lines 111 of the other antennas 100b to 100i. In this way, by sharing the bias line 111, which is the wiring within the chip, between each antenna, driving on the same channel becomes possible, simplifying the driving method. Furthermore, the number of wirings is reduced, allowing each wiring to be thicker, thereby suppressing the increase in wiring resistance that occurs with an increase in the number of arrays and the resulting operating point misalignment between antennas. This reduces the frequency and phase shifts between the antennas that occur when the number of arrays is increased, making it easier to achieve a synchronization effect using the arrays.

[0078] Note that sharing the bias line 111 is not a required configuration. For example, multiple bias lines 111 may be provided for each antenna through multilayering or miniaturization, allowing for individual power supply. In this case, isolation between each antenna via the bias line 111 is strengthened, reducing the risk of low-frequency parasitic oscillation. Furthermore, in the element 10, the lines 108a1, 108a2 to the lines 108i1, 108i2 and the bias line 111 preferably have lower impedance than the negative resistance of the RTDs 101a to 101i in the low-frequency band below the oscillation frequency fTHz. More preferably, the impedance should be equal to or slightly smaller than the absolute value of the combined negative differential resistance of the parallel-connected RTDs 101a to 101i. This makes it possible to suppress low-frequency multimode oscillation.

[0079] As described above, according to this embodiment, synchronization of the antenna array allows oscillation or detection to be performed more efficiently than before.

[0080] The specific configuration of the element 10 that oscillates terahertz waves according to the first embodiment will be described with reference to Fig. 1(a) and Fig. 2. The element 10 is a semiconductor device capable of single-mode oscillation in the frequency band of 0.45 to 0.50 THz. The substrate 113 is an InP substrate. The RTDs 101a to 101i are configured with a multiple quantum well structure made of InGaAs / AlAs lattice-matched to the substrate 113, and in this embodiment, RTDs with a double-barrier structure are used. This is also called an RTD semiconductor layer heterostructure.

[0081] The current-voltage characteristics of the RTDs 101a to 101i are measured to have a peak current density of 9 mA / μm2 and a negative differential conductance per unit area of 10 mS / μm2. The antenna 100a has a mesa structure formed from a semiconductor layer 115a including the RTD 101a and a third electrode 116a, which is an ohmic electrode. In this embodiment, the mesa structure is circular with a diameter of 2 μm. The magnitude of the negative differential resistance of the RTD 101a is approximately -30 Ω per diode. In this case, the negative differential conductance (GRTD) of the semiconductor layer 115a including the RTD 101a is estimated to be approximately 30 mS, and the diode capacitance (CRTD) of the RTD 101a is estimated to be approximately 10 fF.

[0082] The antenna 100a is a patch antenna having a structure in which a dielectric layer 104 is sandwiched between a second conductor layer 103a, which is a patch conductor, and a first conductor layer 106, which is a ground conductor. A semiconductor layer 115a including an RTD 101a is integrated inside the antenna 100a. The antenna 100a is a square patch antenna in which the second conductor layer 103a has a side length of 150 μm, and the resonator length (L) of the antenna is 150 μm.

[0083] The second conductor layer 103a, which is a patch conductor, and the first conductor layer 106, which is a ground conductor, are made of metal layers primarily composed of a thin Au film with low resistivity. The second conductor layer 103a is made of a metal containing Ti / Au (=5 / 300 nm). A dielectric layer 104 is disposed between the second conductor layer 103a and the first conductor layer 106. The dielectric layer 104 is made of two layers: a first dielectric layer 1041 made of BCB (benzocyclobutene, manufactured by Dow Chemical Company, εr1=2) with a thickness of 5 μm, and a second dielectric layer 1042 made of SiO2 (plasma CVD, εr2=4) with a thickness of 2 μm.

[0084] The first conductor layer 106 is composed of a Ti / Pd / Au layer (20 / 20 / 200 nm) and a semiconductor layer made of an n+-InGaAs layer (100 nm) with an electron concentration of 1×1018 cm-3 or more, and the metal and semiconductor layer are connected by low-resistance ohmic contact.

[0085] The electrode 116a is an ohmic electrode made of Ti / Pd / Au layers (20 / 20 / 200 nm) and is connected through low-resistance ohmic contact to a semiconductor layer made of an n+-InGaAs layer (100 nm) with an electron concentration of 1×1018 cm-3 or more formed on the semiconductor layer 115a.

[0086] Around the RTD 101a, the following layers are stacked and electrically connected in order from the substrate 113 side: substrate 113, first conductor layer 106, semiconductor layer 115a, electrode 116a, conductor 117a composed of a conductor containing Cu, and second conductor layer 103a. RTD 101a is positioned 40% (60 μm) off one side of second conductor layer 103a from the center of gravity of second conductor layer 103a in the resonance direction (direction AA′). The position of RTD 101a within antenna 100a determines the input impedance when feeding high-frequency power from the RTD to the patch antenna. Second conductor layer 103a is connected to lines 108a1 and 108a2 arranged in the underlying layer via conductors 107a1 and 107a2, which are vias formed of Cu.

[0087] The lines 108a1 and 108a2 are formed of a metal layer containing Ti / Au (=5 / 300 nm) laminated on the second dielectric layer 1042. The lines 108a1 and 108a2 are connected to the bias circuit 120 via a bias line 111, which is a common wiring formed within the chip. The bias line 111 is formed of a metal layer containing Ti / Au (=5 / 300 nm) laminated on the second dielectric layer 1042. The antenna 100a is designed to obtain an oscillation power of 0.2 mW at a frequency fTHz=0.5 THz by setting a bias in the negative resistance region of the RTD 101a.

[0088] Conductors 107a1 and 107a2 have a cylindrical structure with a diameter of 10 μm. Lines 108a1 and 108a2 are configured as patterns formed from a metal layer containing Ti / Au (=5 / 300 nm) with a width of 10 μm and a length of 75 μm in the resonance direction (=A-A' direction). Conductors 107a1 and 107a2 are connected to second conductor layer 103a at their centers in the resonance direction (=A-A' direction) and their ends in the B-B' direction. This connection position corresponds to a node of the electric field of the fTHz terahertz wave standing in antenna 100a.

[0089] The element 10 is an antenna array in which nine antennas 100a-100i are arranged in a 3x3 matrix. Each antenna is designed to emit terahertz waves at a frequency of fTHz and is arranged at a pitch (spacing) of 340 μm in both the A-A' and B-B' directions. Adjacent antennas are coupled to each other by coupling lines 109 including a third conductor layer 110 made of Ti / Au (=5 / 300 nm). For example, antennas 100a and 100b are coupled to each other by coupling line 109ab. Furthermore, the central antenna 100e is connected to antennas 100f and 100d, respectively, by coupling lines 109ef and 109ed extending in the first direction (vertical direction). Similarly, antenna 100e is connected to adjacent antennas 100h and 100b by coupling lines 1091he, 1092he, 1091eb, and 1092eb extending in the second direction (horizontal direction). In the case of antennas 100e and 100d, vertical coupling line 109de and horizontal coupling lines 1092he and 1092eb are connected at a position shifted 30 μm in the A direction from the center of symmetry between antennas 100e and 100d in the vertical direction. In other words, the connection is made at a point other than the center of the line connecting antennas 100e and 100d. Second conductor layer 103a and second conductor layer 103b are directly connected by third conductor layer 110ab, which is 5 μm wide and 190 μm long and formed on the same layer. Antennas 100a and 100d are also coupled to each other by coupling line 109ad. The second conductor layers 103a and 103d are directly connected by a third conductor layer 110ad, which is formed on the same layer and has a width of 5 μm and a length of 440 μm. The same is true for the other antennas. The antennas 100a to 100i oscillate in mutual injection locking with each other in phase (positive phase) at an oscillation frequency of fTHz=0.5 THz.

[0090] A bias line 111, which is a common wiring formed within the chip, is a bias wiring common to each antenna, and is connected to the lines 108a1, 108a2 to 108i1, 108i2 connected to each of the antennas 100a to 100i.

[0091] In element 10, bonded wire 109 and bias line 111 are arranged on different layers, as shown by the relationship between bonded wire 109ab on third conductor layer 110ab and bias line 111 on fourth conductor layer 111x1. Furthermore, element 10 is stacked in the order of substrate 113, first conductor layer 106, and second conductor layer 103a, from the substrate 113 side. Furthermore, as shown by the third conductor layer 110ab and fourth conductor layer 111x1, bias line 111 is arranged on a layer between first conductor layer 106 and second conductor layer 103. Furthermore, bonded wire 109 and bias line 111 cross each other. The same applies to the relationship between bonded wire 109 and bias line 111 that couples the other antennas 100b to 100i. This configuration reduces physical interference between the coupling lines (coupling lines 109) for synchronizing the antennas and the feed lines (bias lines 111) for supplying bias to each RTD 101. Therefore, the upper limit on the number of antennas that can be arranged increases, and significant improvements in directivity and frontal intensity can be expected as the number of arrays increases.

[0092] (About the manufacturing method of the element) Next, a method for manufacturing (fabrication) the device 10 of this embodiment will be described.

[0093] (1) First, an InGaAs / AlAs-based semiconductor multilayer structure constituting semiconductor layers 115a-115i including RTDs 101a-101i is formed by epitaxial growth on an InP substrate 113. This is done by molecular beam epitaxy (MBE), metalorganic vapor phase epitaxy (MOVPE), or the like.

[0094] (2) On the semiconductor layers 115a to 115i, Ti / Pd / Au layers (20 / 20 / 200 nm) constituting the electrodes 116a to 116i, which are ohmic electrodes, are formed by sputtering.

[0095] (3) The electrodes 116a-116i and the semiconductor layers 115a-115i are formed into a circular mesa shape with a diameter of 2 μm, thereby forming a mesa structure. Here, the mesa shape is formed by photolithography and dry etching using ICP (inductively coupled plasma).

[0096] (4) After the first conductor layer 106 is formed on the substrate 113 by the lift-off method on the etched surface, a silicon oxide film having a thickness of 2 μm is formed by the plasma CVD method to become the second dielectric layer 1042.

[0097] (5) On the second dielectric layer 1042, a Ti / Au layer (=5 / 300 nm) is formed as the fourth conductor layer 111 that constitutes the lines 108a1 to i2 and the bias line 111.

[0098] (6) Spin coating and dry etching are used to fill and planarize the first dielectric layer 1041 with BCB to a thickness of 5 μm.

[0099] (7) Photolithography and dry etching are used to remove the BCB and silicon oxide from the portions where conductors 117a-117i and 107a1-107i2 will be formed, thereby forming via holes (contact holes). At this time, if photolithography including grayscale exposure is used, the taper angles of the via holes for forming first dielectric layer 1041, second dielectric layer 1042, and bond line 109 can be controlled as desired.

[0100] (8) Conductors 117a to 117i and 107a1 to 107i2, which are vias, are formed in the via holes by using a conductor containing Cu. To form the conductors 117a to 117i and 107a1 to 107i2, the via holes are filled with Cu and planarized using sputtering, electroplating, or chemical mechanical polishing.

[0101] (9) An electrode Ti / Au layer (=5 / 300 nm) that will become the third conductor layer 110 that constitutes the second conductor layers 103a to 103i and the bonded wires 109 of each antenna is deposited by sputtering.

[0102] (10) The second conductor layers 103a to 103i and the third conductor layer 110 that constitutes the bond wires 109 are patterned by photolithography and dry etching using ICP (inductively coupled plasma).

[0103] (11) Finally, the shunt resistor 121 and the capacitor 124 are formed and connected to the wiring 122 and the power supply 123 by wire bonding or the like, thereby completing the element 10. The capacitor 124 is, for example, a MIM (Metal Insulator Metal) capacitor.

[0104] Power is supplied to the element 10 from a bias circuit 120, and when a bias voltage that is normally in the negative differential resistance region is applied and a bias current is supplied, the element 10 operates as an oscillator.

[0105] The element 10 of this embodiment has a suitable antenna array, which makes it possible to provide an antenna array that achieves at least one of improved antenna gain and improved directivity.

[0106] Each of the antennas 100 of the element 10 can also be modified as shown in FIG. 1(b). FIG. 1(b) is a schematic top view showing a modified example of the antenna 100a of the element 10 of FIG. 1(a). In FIG. 1(b), the antenna 100a has at least two semiconductor layers, namely, a semiconductor layer 101a1 and a semiconductor layer 101a2. The semiconductor layer 101a1 and the semiconductor layer 101a2 have the same configuration as the semiconductor layer 101. This configuration further improves the antenna gain.

[0107] The antenna 100a is a square patch antenna. In FIG. 1(b), the line segment connecting the centers of two opposing sides of the patch antenna is indicated by a dotted line. The intersection of the dotted lines is the center of the patch antenna. The conductor 107a1 and the conductor 107a2 are each located at the center of two sides of the patch antenna extending along the X direction. The semiconductor layer 101a1 and the semiconductor layer 101a2 are located on the dotted line connecting the centers of two sides of the patch antenna extending along the Y direction. The semiconductor layer 101a1 and the semiconductor layer 101a2 are also located equidistant from the center of the patch antenna. This configuration stabilizes the operation of the antenna.

[0108] (Embodiment 2) The configuration and cross-sectional schematic diagrams of element 20 according to embodiment 2 are shown in Figures 6(a), 6(b), 7(a), and 7(b). The configuration and structure of element 20 other than those described below are the same as those of element 10 according to embodiment 1, and therefore detailed description thereof will be omitted. Figure 6(a) corresponds to Figure 4 of embodiment 1, and Figure 6(b) corresponds to Figure 5(a) of embodiment 1, and redundant description will be omitted. Figure 6(b) is a schematic diagram illustrating the positions of the nodes and antinodes of the resonant electric field in the configuration of Figure 6(a). Figures 7(a) and 7(b) correspond to Figures 3(a) and 3(b) of embodiment 1, and redundant description will be omitted.

[0109] The element 20 is an antenna array in which nine antennas 200a to 200i are arranged in a 3 × 3 matrix. Unlike the first embodiment, the antenna 200a includes two semiconductor layers having electromagnetic wave gain or nonlinearity for terahertz waves. Specifically, as shown in FIG. 7(a), the antenna 200a includes a semiconductor layer 215a1 including an RTD 201a1 and a semiconductor layer 215a2 including an RTD 201a2.

[0110] 7(a), electrodes 216a1 and 216a2 are arranged on the side of semiconductor layers 215a1 and 215a2 opposite to the side on which first conductor layer 206 is arranged. Semiconductor layer 215a1 is arranged between first conductor layer 206 and electrode 216a1, and semiconductor layer 215a2 is arranged between first conductor layer 206 and electrode 216a2. Electrode 216a1 and semiconductor layer 215a1 are electrically connected, and electrode 216a2 and semiconductor layer 215a2 are electrically connected. A bias signal is supplied from bias circuit 120 to two RTDs 201a1 and 201a2 via conductors 217a1 and 217a2, which are vias connected between electrodes 216a1 and 216a2 and second conductor layer 203a.

[0111] As shown in FIG. 6(a), the RTD 201a1 is disposed at a position shifted 40% of the length of one side of the second conductor layer 203a from the center of gravity of the second conductor layer 203a in the resonance direction (i.e., the AA′ direction). On the other hand, the RTD 201a2 is disposed at a position shifted −40% of the length of one side of the second conductor layer 203a from the center of gravity of the second conductor layer 203a in the resonance direction (i.e., the AA′ direction). That is, the RTD 201a1 and the RTD 201a2 are disposed at positions that are line-symmetrical with respect to a line (center line) that passes through the center of gravity of the second conductor layer 203a and is perpendicular to the resonance direction and the stacking direction. In this case, the RTD 201a1 and the RTD 201a2 oscillate by mutual injection locking with their phases reversed (antiphase). In this way, a configuration in which the RTDs are disposed symmetrically in the left-right and top-bottom directions within the antenna is a configuration that more easily achieves improvements in directivity and frontal intensity as the number of arrays increases.

[0112] The coupled line 209 is composed of a microstrip line in which the dielectric layer 204 and the dielectric layer 218 are sandwiched between the fifth conductor layer 210 and the first conductor layer 206, which are stacked on the dielectric layer 218 stacked on the dielectric layer 204. For example, as shown in FIG. 7(a), the coupled line 209ab has a structure in which the dielectric layer 204 and the dielectric layer 218 are sandwiched between the fifth conductor layer 210ab and the first conductor layer 206.

[0113] Similarly, bonded wire 209bc has fifth conductor layer 210bc as its upper conductor layer, and bonded wire 209ad has fifth conductor layer 210ad as its upper conductor layer, and has a structure in which dielectric layer 204 and dielectric layer 218 are sandwiched between first conductor layer 206 and bonded wire 209bc.

[0114] The element 20 is an antenna array in which the antennas are coupled by AC coupling (capacitive coupling). For example, the fifth conductor layer 210ab, which is the upper conductor layer of the coupling line 209ab that couples the antennas 200a and 200b, overlaps the second conductor layers 203a and 203b by 5 μm near the radiation ends in a plan view. The same applies to the coupling between the other antennas 200b to 200i.

[0115] In the overlapping portion of the conductor layers, second conductor layers 203a and 203b, dielectric layer 218, and fifth conductor layer 210ab are stacked in this order, forming a metal-insulator-metal (MIM) capacitance structure. In this case, the space between second conductor layer 203a and second conductor layer 203b is open at DC, and in the low-frequency region below fTHz, the magnitude of coupling is small, ensuring isolation between elements. Meanwhile, in the fTHz oscillation frequency band, the magnitude of coupling between antennas can be adjusted by capacitance. This structure significantly weakens the coupling between antennas, which also reduces transmission loss between antennas and is expected to improve the radiation efficiency of the antenna array.

[0116] The element 20 of this embodiment is an example in which two coupled lines extending in the second direction (horizontal direction) are arranged between the centrally arranged antenna 200e and an antenna adjacent to it in the second direction (horizontal direction). Specifically, coupled lines 2091he, 2092fi, 2092cf, and 2091eb extending in the second direction (horizontal direction) are arranged between the antennas 200e and 200f and connected to coupled line 209ef extending in the first direction. Furthermore, coupled lines 2092he, 2091dg, 2091ad, and 2092eb extending in the second direction (horizontal direction) are arranged between the antennas 200e and 200d and connected to coupled line 209de extending in the first direction.

[0117] The coupled lines in element 20 are arranged in a ladder shape between the row in which antennas 200i, 200f, and 200c are arranged and the row in which antennas 200h, 200e, and 200b are arranged. Coupled lines 209bc, 209hi, and 209ef are arranged between these rows along the X direction. Coupled lines 2092fi, 2092cf, 2091he, and 2091eb are arranged between these rows along the Y direction. Coupled lines 2092fi and 2092cf are connected to coupled lines 209bc and 209hi. Coupled lines 2092fi and 2092cf are connected by coupled line 209ef. Coupled lines 2091he and 2091eb are connected to coupled lines 209bc and 209hi. The coupled wires 2091he and 2091eb are connected by a coupled wire 209ef. Each coupled wire may be formed from a single conductor. The antenna 200 and the coupled wire are connected by AC coupling.

[0118] Furthermore, coupled lines are arranged in a ladder shape between the row in which antennas 200h, 200e, and 200b are arranged and the row in which antennas 200g, 200d, and 200a are arranged. Coupled lines 209gh, 209de, and 209ab are arranged between these rows along the X direction. Coupled lines 2092he, 2092eb, 2091dg, and 2091ad are arranged between these rows along the Y direction. Coupled lines 2092he and 2092eb connect to coupled lines 209gh and 209ab. Coupled lines 2092he and 2092eb are connected by coupled line 209de. Coupled lines 2091dg and 2091ad connect to coupled lines 209gh and 209ad. The coupled wires 2091dg and 2091ad are connected by the coupled wire 209de. Each coupled wire may be formed from a single conductor. The antenna 200 and the coupled wire are connected by AC coupling.

[0119] To satisfy the phase matching condition between the antennas, the coupling line extending in the second direction (horizontal direction) is connected to the coupling line in the first direction at a position shifted a predetermined distance in the first direction from the center of symmetry between adjacent antennas in the first direction. In this embodiment, the coupling lines in the first and second directions are connected at positions shifted 30 μm upward and downward from the nodes of the resonant electric field standing in the coupling line at the frequency of the terahertz wave. This configuration, in which two coupling lines in the second direction are arranged, strengthens the coupling between the antennas in the horizontal direction, resulting in a stronger mutual injection locking effect. This improves the antenna gain. Furthermore, the symmetry of the connection between the coupling line and the antenna is improved compared to when a single coupling line is used, which is expected to result in a more uniform radiation pattern.

[0120] (Embodiment 3) 8(a) and 8(b) are diagrams illustrating the configuration of element 30 of this embodiment. Element 30 is an antenna array in which nine antennas 300a to 300i are arranged in a 3 x 3 matrix. Like element 10 according to embodiment 1, each of antennas 300a to 300i includes a semiconductor layer having gain or nonlinearity for electromagnetic waves with respect to terahertz waves. FIG. 8(a) corresponds to FIG. 4 of embodiment 1, and FIG. 8(b) corresponds to FIG. 5(a) of embodiment 1, and redundant explanations will be omitted.

[0121] The element 30 has a configuration in which the coupling lines of the antennas arranged at the ends of the array extend outward. For example, the four corner antennas 300a, 300c, 300g, and 300i are connected to lines 3091a, 3092a, 3091c, 3092c, 3091g, 3092g, 3091i, and 3092i in the horizontal direction, and the coupling lines extend outward. Similarly, the four corner antennas 300b, 300d, 300f, and 300h are connected to lines 3093d and 3093f in the vertical direction and lines 3091b, 3092b, 3091h, and 3092h in the horizontal direction, and the coupling lines extend outward. With this configuration, even at the ends of the array, the antennas and at least one of the coupled lines arranged vertically and the coupled lines arranged horizontally are in the same relationship. In other words, the relationship between the antenna 300e and the coupled lines is uniform in layout with the relationships between the other antennas 300 and the coupled lines. This reduces unwanted reflections and phase mismatches due to the effects of the ends, which is expected to enhance phase synchronization and improve the uniformity of the radiation pattern. Additionally, the antennas and coupled lines for each unit antenna are symmetrical in both the vertical and horizontal directions, which simplifies and simplifies the design of the antenna array. While this embodiment ensures symmetry between the coupled lines in the X direction and the antenna, and between the coupled lines in the Y direction and the antenna, it is also possible to improve the symmetry of only one of them.

[0122] Furthermore, a configuration such as element 30 is advantageous for strengthening phase synchronization and adjusting the radiation pattern, since it can further reduce unwanted reflections and phase mismatches caused by the effects of the ends of the single antenna or array by electrically terminating the coupled wires at the ends of the array.

[0123] (Embodiment 4) Figures 9(a) and 9(b) are diagrams illustrating the configuration of element 40 of this embodiment. Figure 9(a) corresponds to Figure 4 of embodiment 1, and Figure 9(b) corresponds to Figure 5(a) of embodiment 1, and redundant explanations will be omitted.

[0124] The element 40 has a configuration in which independent coupled lines are drawn from the unit antennas in the vertical and horizontal directions. For example, coupled lines 409ef and 409de are drawn vertically from antenna 400e and connected to antennas 400f and 400d. Coupled lines 4091he, 4092he, 4091eb, and 4092eb are drawn horizontally and connected to antennas 400h and 400b. The coupled lines are adjusted to a length such that the electrical length between the oscillators of adjacent antennas is an integer multiple of 2π to mutually injection lock the RTDs 401a to 401i, which are the oscillators of each antenna, in positive phase. In other words, when the electrical length between the semiconductor layers of the two antennas is L1, the length L2 of the coupled line should be set to satisfy the equation L1 = 2π × k (k is an integer). The length of the coupled line 409de in the first direction (vertical direction) is adjusted so that the electrical length between the RTDs 401e and 401d is 2π. The coupled lines 4091eb and 4092eb extending in the second direction are adjusted so that the electrical length between the RTDs 401e and 401b is 4π. In the case of coupled lines branching in three directions (top, right, and left) like element 40, the length of each coupled line can be adjusted individually to adjust the electrical length between the antennas. This configuration allows for individual design of the vertical and horizontal coupled lines, improving design flexibility. Furthermore, a configuration like element 40 is advantageous for enhancing phase synchronization and adjusting the radiation pattern because it further reduces unwanted reflections and phase mismatches due to edge effects by electrically terminating the coupled lines at the ends of a single antenna or array.

[0125] (Embodiment 5) In this embodiment, a case where the element of any one of Embodiments 1 to 4 is applied to a terahertz camera system will be described. The following description will be made with reference to FIG. 10. The terahertz camera system 1100 has a transmitter 1101 that emits terahertz waves and a receiver 1102 that detects the terahertz waves. The terahertz camera system 1100 further has a controller 1103 that controls the operation of the transmitter 1101 and the receiver 1102 based on an external signal, and processes an image based on the detected terahertz waves or outputs it to the outside. The element of each embodiment may be the transmitter 1101 or the receiver 1102.

[0126] Terahertz waves from transmitter 1101 are reflected by subject 1105 and detected by receiver 1102. A camera system having such transmitter 1101 and receiver 1102 is also called an active camera system. Note that in a passive camera system without transmitter 1101, the elements of each embodiment can be used as a receiver.

[0127] Therefore, a camera system using the element of each embodiment having a high antenna gain can obtain high detection sensitivity and high-quality images.

[0128] (Embodiment 6) The configuration of the element 50 of this embodiment will be described with reference to FIGS. 11(a) to 12(c). FIGS. 11(a) and 11(b) are schematic top views of the element 50. FIG. 11(c) is a schematic top view enlarging the main part of one antenna of the element 50. FIG. 11(d) shows a modified example of the main part of one antenna of the element 50. FIGS. 12(a), 12(b), and 12(c) are schematic cross-sectional views of the element 50 corresponding to FIG. 11(a). The configuration and structure of the element 50 other than those described below are the same as those of the semiconductor element 100 according to the first embodiment, and therefore detailed description thereof will be omitted.

[0129] 11(a), element 50 is an antenna array in which nine antennas 500a to 500i are arranged in a 3 x 3 matrix. Element 50 is an antenna array in which antenna 500a is a unit antenna and the unit antennas are arranged at a pitch of 0.6 wavelengths.

[0130] The element 50 has capacitors 530 arranged along the Y direction. Twelve capacitors 530 are shown in the element 50. The capacitors 530 arranged between two antennas along the Y direction are indicated as capacitor 530ad, etc., using the symbols of the two antennas, and six of them are shown in FIG. 11(a). The capacitors 530 arranged on the periphery of the antenna array along the Y direction are indicated as capacitor 530a, etc., using the symbols of the adjacent antennas, and six of them are shown in FIG. 11(a).

[0131] The element 50 has capacitors 531 and 532 arranged along the X direction. Capacitor 531 is arranged between antennas 500a to 500i, and capacitor 532 is arranged around antennas 500a to 500i. Capacitor 531 is located between two antennas and is indicated as capacitor 531ab, etc. using the symbols of the two antennas. Six capacitors 531 are shown in element 50. Capacitor 521 is located on the periphery of the antenna array and is indicated as capacitor 532a, etc. using the symbol of the adjacent antenna. Six capacitors 521 are shown in element 50.

[0132] The antenna 500a includes multiple coupled lines, which are transmission lines for transmitting power between adjacent antennas in the X and Y directions at an oscillation frequency of fTHz. The coupled lines are also referred to as coupling lines. At least one antenna includes multiple coupled lines. At least one antenna is connected to at least three or more coupled lines. At least one antenna is connected to at least four or more different antennas via coupled lines. Here, when a coupled line is said to be coupled to an antenna, this includes cases where the antenna and coupled line are electrically connected via capacitance, cases where the antenna and coupled line are directly connected, and cases where the antenna and coupled line are made of a single conductor. The coupled line has a microstrip line structure. The microstrip line structure includes one conductor layer, a dielectric, and another conductor layer. In the following description, for ease of understanding, the same reference numeral may be used to refer to one conductor layer and one coupled line.

[0133] In the first row of the antenna array, antenna 500i, antenna 500f, and antenna 500c are arranged in this order along the Y direction. In the second row of the antenna array, antenna 500h, antenna 500e, and antenna 500b are arranged in this order along the Y direction. In the third row of the antenna array, antenna 500g, antenna 500d, and antenna 500a are arranged in this order along the Y direction. If the X direction is the upward direction, the antennas in the second row are arranged above the third row, and the antennas in the first row are arranged above the second row.

[0134] The coupling lines will now be described. First, the plurality of conductor layers 5091, the plurality of conductor layers 509, and the plurality of conductor layers 5092 shown in FIG. 11(a) can each function as a coupling line. For simplicity, focusing on the second row, the antennas 500h, 500e, and 500b in the second row are provided with conductor layers 5091 and 509 between them and the antennas in the first row. Furthermore, the antennas 500h, 500e, and 500b in the second row are provided with conductor layers 5092 and 509 between them and the antennas in the third row. Here, the conductor layers coupling the two antennas are given the symbols of the two antennas. For example, focusing on the antenna 500e, the antennas 500h and 500e are coupled by conductor layers 5091he and 5092he. Antennas 500e and 500b are coupled by conductor layers 5091eb and 5092eb. Antennas 500e and 500f are coupled by conductor layers 509ef. Antennas 500e and 500d are coupled by conductor layer 509de.

[0135] In other words, the antenna 500h is coupled to the conductor layer 5091he and to the conductor layer 5092he. The antenna 500e is coupled to the conductor layer 5091he and to the conductor layer 5092he. The antenna 500e is coupled to the antenna 500h via the conductor layers 5091he and 5092he. The antenna 500e is coupled to the conductor layer 5091eb and to the conductor layer 5092eb. The antenna 500b is coupled to the conductor layer 5091eb and to the conductor layer 5092eb. The antenna 500e is coupled to the antenna 500b via the conductor layers 5091eb and 5092eb. The antenna 500e is coupled to the conductor layer 509ef. The antenna 500f is coupled to the conductor layer 509ef. The antenna 500e is coupled to the antenna 500f through the conductor layer 509ef. The antenna 500e is coupled to the conductor layer 509de. The antenna 500d is coupled to the conductor layer 509de. The antenna 500e is coupled to the antenna 500d through the conductor layer 509de.

[0136] When the symbol for the antenna in FIG. 11(a) is xy, x ≠ y ≠ z, and x, y, and z are a to i. Conductor layer 5091xy is positioned above the antenna and provides coupling in the Y direction. Conductor layer 5092xy is positioned below the antenna and provides coupling in the Y direction. Conductor layer 509xz is also disposed between conductor layers 5091xy and 5092xy. Here, "upper" and "lower" refer to positions along the X direction, and refer to the top and bottom of the paper on which FIG. 11(a) is drawn.

[0137] The end of the antenna array will now be described. In the antenna array shown in FIG. 11(a), the antennas at the end are not shown, and are therefore indicated as 5091h and 5091i, for example. However, similar conductor layers may be arranged for the other antennas. Furthermore, for example, when focusing on antenna 500d, conductor layer 5093d coupled to antenna 500d is not coupled to other antennas. Conductor layer 5093d may be coupled to capacitor 532d. Conductor layer 5093d can also be said to be terminated.

[0138] The arrangement of the conductor layers is similar to that of antenna 500e. That is, with this configuration, the arrangement of the antennas and conductor layers at the ends of the antenna array is equivalent to the arrangement of the antennas and conductor layers at the interior of the antenna array. In other words, it can be said that antenna 500a is repeatedly arranged as a unit cell in antennas 500b to 500i. With this configuration, the symmetry of the antenna array can be improved.

[0139] The relationship between the antenna and capacitance will now be explained. Capacitors 530, 531, and 532 can function as shunt elements. The multiple capacitors 531 and 532 arranged in the X direction are coupled to the conductor layer above the antenna via the conductor layer, which is a coupling line. The multiple capacitors 530 arranged along the Y direction are coupled to the conductor layer above the antenna. This configuration can reduce parasitic oscillation in the coupling line. In this specification, coupling can include capacitive coupling and direct connection.

[0140] The capacitor 531 can be coupled to multiple conductor layers. That is, one capacitor 531 can be shared by multiple conductor layers. For example, a description will be given using the capacitor 531ab. The capacitor 531ab is coupled to the conductor layer 509ab, the conductor layer 5091a, the conductor layer 5091ad, the conductor layer 5092b, and the conductor layer 5092eb. The same applies to the capacitor 532; one capacitor 531 can be shared by multiple conductor layers. For example, the capacitor 532a is coupled to the conductor layer 5092a, the conductor layer 5092ad, and the coupling wire 5093a. This configuration makes it possible to reduce the element area by sharing the element. Furthermore, the capacitor 530 can be coupled to multiple antennas. That is, one capacitor 530 can be shared by multiple antennas. For example, a description will be given using the capacitor 530ad. The capacitor 530ad is coupled to the conductor layer of the antenna 500a and the conductor layer of the antenna 500d. The capacitors connected to the respective antennas can be shared, which enables a reduction in the element area. The capacitors 530 to 532 and the configuration of the connections between the conductor layers and the capacitors will be described later with reference to Figures 12(a) to 12(c).

[0141] The antenna 500a has an RTD 501a1 and an RTD 501a2 that constitute an oscillation element. The antenna 500b has an RTD 501b1 and an RTD 501b2. The antenna 500d has an RTD 501d1 and an RTD 501d2. The same applies to the other antennas.

[0142] FIG. 11(b) is a top view of antenna 500a, a unit antenna of the antenna array of FIG. 11(a). Antenna 500a is a patch antenna. Antenna 500a has at least conductor layer 503a. Conductor layer 503a is supplied with a bias and is located at the top in a cross section along the Z direction, so it can also be called the upper conductor layer. Antenna 500a has at least one active layer therein that has electromagnetic wave gain or nonlinearity for terahertz waves. Specifically, antenna 500a has two active layers: semiconductor layer 515a1 including RTD 501a1 and semiconductor layer 515a2 including RTD 501a2. Antenna 500a is designed to oscillate at an oscillation frequency of fTHz even when used alone. 11(b), it is desirable that the RTD 501a1, the RTD 501a2, the conductor layer 503a, the bias line 511a, and the conductor layer 509a are configured to be symmetrical left and right and up and down with respect to the center of the antenna 500a. Here, left and right and up and down refer to the X direction (direction AA') and the Y direction (direction BB') in FIGS. 11(a) and 11(b).

[0143] Capacitor 530a includes resistor 5212, conductor layer 5224 constituting the MIM capacitor, line 508a2, and conductor layer 507a2. Capacitor 530ad includes resistor 5211, conductor layer 5223 constituting the MIM capacitor, line 508a1, and via 507a1. Opening 505a and opening 505ad are openings disposed in the conductor layer. The conductor layer includes bias line 511a, line 508a1, and line 508a2. Hereinafter, the line and via may also be referred to as conductor layers.

[0144] Capacitor 532a has conductor layer 5221, conductor layer 5071, resistor 5191, resistor 5192, and conductor layer 5072. Capacitor 531ab has at least conductor layer 5222, resistor 5193, and resistor 5194. Here, conductor layer 5071 and conductor layer 5082 can also be called vias.

[0145] 11(b), a portion of the conductor layer 5091ad is shown. The conductor layer 5091ad has a resistor 5511 and a resistor 5233. The conductor layer 5091ad further has other portions. The other portions are configured such that the portion shown in the figure is arranged on the antenna 500d side in line symmetry with respect to the resistor 5511. The conductor layer 5091a has a resistor 5512 and a resistor 5234. The conductor layer 5091ad is coupled to the capacitor 531ab via the resistor 5233, and the conductor layer 5091a is coupled to the capacitor 531ab via the resistor 5234.

[0146] Similarly, in Figure 11 (b), only a portion of the conductor layer 5092ad is shown. The conductor layer 5092ad has a resistor 5513 and a resistor 5231. The conductor layer 5092ad further has other portions. The other portions are configured such that the portion shown in the figure is arranged on the antenna 500d side in line symmetry with respect to the resistor 5513. The conductor layer 5092a has a resistor 5514 and a resistor 5232. The conductor layer 5092ad is coupled to the capacitor 532a via the resistor 5231, and the conductor layer 5092a is coupled to the capacitor 532a via the resistor 5232.

[0147] 11(b), the arrangement of the elements of the antenna 500a is highly symmetrical. Furthermore, the arrangement of each element coupled to the antenna 500a is also highly symmetrical. This configuration can suppress a decrease in radiation power.

[0148] FIG. 11(c) is an enlarged view of the coupling lines and capacitance of the antenna 500a shown in FIG. 11(b). A portion of the conductor layer 509ab, a conductor layer 5091a, and a portion of the conductor layer 5091ad are shown. A portion of the conductor layer 5093a, a conductor layer 5092a, and a portion of the conductor layer 5092ad are shown. The length of the portion of the conductor layer 509ab is equal to the length of the conductor layer 5093a, the length of the conductor layer 5091a is equal to the length of a portion of the conductor layer 5091ad, and the length of the conductor layer 5092a is equal to the length of a portion of the conductor layer 5092ad. Furthermore, the length of the conductor layer 5091a is equal to the length of the conductor layer 5092a, and the length of the portion of the conductor layer 5091ad is equal to the length of a portion of the conductor layer 5092ad. This configuration improves the symmetry of the antenna 500a.

[0149] The cross-sectional structure corresponding to Fig. 11(b) will be described using Fig. 12(a) to Fig. 12(c). Fig. 12(a) is a schematic cross-sectional view corresponding to line A-A' in Fig. 11(b). Fig. 12(b) is a schematic cross-sectional view corresponding to line B-B' in Fig. 11(b). Fig. 12(c) is a schematic cross-sectional view corresponding to line CC' in Fig. 11(b).

[0150] As shown in FIG. 12(a), element 50 includes substrate 513, conductor layer 506, conductor layer 5222, conductor layer 5221, conductor layer 503a, conductor layer 509ab, and conductor layer 5093a. Element 50 includes semiconductor layer 515a1 including RTD 501a1, semiconductor layer 515a2 including RTD 501a2, conductor layer 516a1, conductor layer 516a2, conductor layer 517a1, conductor layer 517a2, and conductor layer 514. Element 50 includes dielectric 5043, dielectric 5042, dielectric 501, and dielectric 5044. Conductor layer 517a1, conductor layer 517a2, and conductor layer 514 can also be referred to as vias or plugs. Conductor layer 506 supplies, for example, a ground voltage.

[0151] Conductor layer 509ab forms a coupling line with conductor layer 506 and the dielectric between conductor layer 509ab and conductor layer 506. Conductor layer 5093a forms a coupling line with conductor layer 506 and the dielectric between conductor layer 5093a and conductor layer 506. Conductor layer 503a functions as a resonator with conductor layer 506, the dielectric between conductor layer 503a and conductor layer 506, RTD 501a1, and RTD 501a2. Conductor layer 5222 forms capacitance 531ab with conductor layer 506 and the dielectric between conductor layer 5222 and conductor layer 506. Conductor layer 5221 forms capacitance 532a with conductor layer 506 and the dielectric between conductor layer 5221 and conductor layer 506. Conductor layer 509ab and conductor layer 503a are arranged to overlap in the Z direction, and the overlapping portion has a length L1. Conductor layer 5093a and conductor layer 503a are arranged to overlap in the Z direction, and the overlapping portion has a length of L2. In other words, two coupling lines are coupled to one antenna. Conductor layer 509ab is connected to capacitor 531ab, and conductor layer 5093a is connected to capacitor 532a.

[0152] The connections will be described using FIG. 12(c). In the configuration of FIG. 12(c), the same components as those in FIG. 12(a) are denoted by the same reference numerals, and their description will be omitted. As shown in FIG. 12(c), the element 50 has a resistor 5191, a resistor 5192, a conductor layer 5071, a conductor layer 5072, a conductor layer 514, and a conductor layer 5093a. The conductor layer 5093a is connected to the capacitor 532a via the conductor 514. The conductor layer 5093a is connected in series with the conductor layer 514, the resistor 5191, the conductor 5071, and the conductor layer 5221. The conductor layer 5093a is connected in series with the conductor layer 514, the resistor 5192, the conductor 5072, and the conductor layer 5221. The conductor layers 5071, 5072, and conductor layer 514 are also referred to as vias, plugs, etc.

[0153] In the configuration of FIG. 12(b), the same components as those in FIGS. 12(a) and 12(c) are designated by the same reference numerals, and their description will be omitted. Element 50 includes conductor layers 507a1, 507a2, 508a1, 508a2, 511a, 512, 5223, and 5224. Element 50 includes resistors 5211 and 5212. Conductor layers 507a1, 507a2, and 512 are also referred to as vias or plugs. Conductor layer 503a is connected to conductor layer 5223 via conductor layers 507a1, 508a1, resistor 5211, and 512. In other words, conductor layer 503a is connected to capacitor 530ad. Furthermore, conductor layer 503a is connected to conductor layer 5224 via conductor layer 507a2, conductor layer 508a2, resistor 5212, and conductor layer 512. That is, conductor layer 503a is connected to capacitor 530a. Here, conductor layer 511 is spaced apart from conductor layer 512 at two locations. Conductor layer 511a is connected to at least one of conductor layers 508a1 and 508a2 at least one of the front and rear of the paper. The front and rear of the paper refer to positions in the X direction. In other words, in a cross section including the Y and Z directions, conductor layer 511a has openings 505ad and 505a.

[0154] The above-mentioned multiple conductor layers are configured to have different distances from the upper surface of substrate 513. For example, the main parts of FIGS. 12(a) to 12(c) are configured as follows: The first layer includes conductor layer 506; the second layer includes conductor layers 5221, 5222, 5223, and 5224; the third layer includes conductor layers 512, 5071, and 5072; the fourth layer includes conductor layers 508a1, 508a2, 5191, 5192, and 511a; and the fifth layer includes conductor layers 508a1, 508a2, 5191, 5192, and 511a. The sixth layer includes conductor layer 507a1 and conductor layer 507a2, the seventh layer includes conductor layer 503a, and the eighth layer includes conductor layer 514, and the eighth layer includes conductor layer 509ab and conductor layer 5093a. The position of each component can be changed by selecting an arbitrary manufacturing method.

[0155] 12(a) to 12(c), the conductor layer 506 is provided in common to each component such as the capacitor and the coupling wire. The conductor layer 506 is an integrated conductor layer capacitor disposed over the entire surface of the element 50. Such a conductor layer 506 can reduce fluctuations in the supplied voltage.

[0156] The structure of the element 50 will be further described with reference to FIGS. 11(a) to 12(c). As described above, the multiple coupled lines have a microstrip structure. The coupled lines are composed of one conductor layer, a dielectric, and another conductor layer. For example, a microstrip line is formed by sandwiching a dielectric 504 and a dielectric 5044 between conductor layers 509a, 509ab, 5093a, 5091ad, 5091a, 5092ad, and 5092a, and conductor layers 506 and 511a. The conductor layer 511a can also be considered a bias line, operating as a ground conductor at fTHz. The antenna 500a is composed of a patch antenna and a microstrip line connected to the patch antenna, and is designed to oscillate at an oscillation frequency of fTHz even with a single antenna. The conductor layer 506 can also be considered a first conductor layer.

[0157] The patch antenna of the antenna 500a is AC-coupled (capacitively coupled) to the conductor layer 509a. For example, as shown in FIGS. 11(b) and 12(a), the conductor layers 503a and 509ab of the antenna 500a overlap near the radiation end of the antenna 500a, sandwiching an insulator between them, in a plan view. The overlap length is L1. Length L1 is, for example, 5 μm. The overlapping portion of the conductor layers forms a metal-insulator-metal (MIM) capacitance structure in which the conductor layer 503a, the dielectric layer 5044, and the conductor layer 509ab are stacked in this order. The capacitance value is, for example, 20 fF. The conductor layers 503a and 509ab are open in the DC and low-frequency range (up to 10 GHz) below fTHz, ensuring isolation between the antennas. Meanwhile, in the fTHz oscillation frequency band, the impedance is adjusted by capacitance to adjust the strength of the coupling between the antennas. The same applies to the other conductor layers 5091ad, 5091a, 5092ad, 5092a, and 5093a.

[0158] As shown in Figure 11(b), the antenna 500a has coupling lines branching in three directions (upper, lower, right, and left) at each radiation end, each of which is independently connected to six conductor layers. The six conductor layers are conductor layer 5091ad, conductor layer 5091a, conductor layer 5092ad, conductor layer 5092a, conductor layer 509ab, and conductor layer 5093a. Therefore, two antennas and one coupling line are connected in a 2:1:1 relationship. This configuration allows the length and width of each pair of two antennas and one coupling line to be adjusted independently, making it ideal for individually adjusting the electrical length and impedance between each antenna in an antenna array. Therefore, the vertical and horizontal coupling lines can be adjusted independently, improving design flexibility. As shown in Figure 11(c), a configuration is also possible in which the connection portion of the conductor layer 509a at the antenna's radiation end is connected at a single point by multiple coupling lines joining together, or a configuration in which the area of the connection portion within the antenna is increased to increase the coupling amount. These configurations can be selected appropriately depending on the application.

[0159] The width of the conductor layer 509a is an adjustment parameter for the impedance of the microstrip line and is designed from the perspective of matching with the antenna 500a and reducing transmission loss. The length of the conductor layer 509a is preferably designed so that the electrical length between the RTDs at the same position in adjacent antennas is an integer multiple of 2π. In the case of the antenna 500a, the conductor layer 509ab extending in the X direction has a length such that the electrical length between the RTDs 501a1 and 501b1 is 2π. Therefore, a portion of the conductor layer 509ab shown in FIG. 11(c) is set to a length that is half the length of the conductor layer 509ab (electrical length π). Furthermore, a portion of the conductor layer 509ab and the conductor layer 5093a are set to the same length. Similarly, the length of a portion of conductor layer 5091ad extending in the Y direction and conductor layer 5092ad is set to half the length that is 4π of the electrical length between RTD 501a1 and RTD 501d1 and between RTD 501a2 and RTD 501d2, i.e., an electrical length of 2π. Furthermore, conductor layer 5091a can be set to a length that is at least half the length of conductor layer 5091ad or half the length of conductor layer 5092ad. Furthermore, conductor layer 5092a can be set to a length that is at least half the length of conductor layer 5091ad or half the length of conductor layer 5092ad.

[0160] Conductor layer 509a includes a shunt component connected to a node of the resonant electric field of the oscillation frequency fTHz for mode stabilization. As shown in FIG. 11(c), conductor layer 509a and the shunt component are connected through via 514. The shunt component has a resistance and a capacitance. The shunt component is, for example, a snubber circuit. Resistors 5191, 5192, 5231, 5232, and capacitor 532a are connected in series. Resistors 5193, 5194, 5233, 5234, and capacitor 531ab are connected in series. The resistance is, for example, 20 Ω and is made of a thin film such as TiW. The capacitance is, for example, 20 pF and is an MIM capacitance. Capacitor 532a has a capacitance structure in which dielectric 5043 is sandwiched between conductor layer 5221 and conductor layer 506. Capacitor 531ab has a capacitance structure in which dielectric 5043 is sandwiched between conductor layer 5222 and conductor layer 506. This allows high frequencies other than the oscillation frequency fTHz to be AC shorted and impedance reduced, thereby suppressing multi-mode oscillation in the antenna array. Furthermore, conductor layer 509a has resistors 5511, 5512, 5513, and 5514 connected to the antinode positions of the resonant electric field of the oscillation frequency fTHz. These resistors have a resistance value of, for example, 20 Ω and are made of TiW thin film. This allows loss of frequencies other than the oscillation frequency fTHz and phase shift components, thereby stabilizing the mode.

[0161] These components, located at the nodes and antinodes of the resonant electric field of the fTHz oscillation frequency, also serve as electrical terminations at the ends of the conductor layer 509a of the antenna 500a, which is a unit antenna. For example, let us consider a case where no antennas are connected above or below the antenna 500a (in the X direction). The end of the conductor layer 509ab not connected to the conductor layer 503a is an open end. Similarly, the end of the conductor layer 5093a not connected to the conductor layer 503a is an open end. The presence of open ends can affect the resonance characteristics. By terminating the AC short circuit with a shunt component connected to the node of the fTHz resonant electric field, as in the case of the antenna 501a, unwanted reflections and phase mismatches are reduced, stabilizing the fTHz resonance. The same applies when no antennas are connected to the left or right (in the Y direction). Resistors connected to the ends of the conductor layers 5091ad, 5091a, 5092ad, and 5092a serve as terminations to adjust the impedance. The resistors are located at the antinodes of the resonant electric field of the fTHz oscillation frequency. This embodiment can be a suitable configuration for at least one of stabilizing oscillation, strengthening phase synchronization, and adjusting the radiation pattern by electrically terminating the coupling lines at the ends of a single antenna or array to reduce the effects of the ends.

[0162] Next, the bias lines for supplying power to RTDs 501a1 and 501a2 will be described. The bias lines are conductor layer 511. In antenna 501a, the bias lines are also configured symmetrically in the vertical and horizontal directions relative to the center (center of gravity) of antenna 500a. The vertical and horizontal directions refer to the X and Y directions, which can also be referred to as the A-A' and B-B' directions. Conductor layers 507a1 and 507a2, which are connected at the nodes of the resonant electric field at fTHz in conductor layer 503a, are connected to conductor layer 511a, which serves as a common wiring, via lines 508a1 and 508a2. Lines 508a1 and 508a2 have a tapered pencil shape, with the wiring widths of lines 508a1 and 508a2 narrow at the connection points with conductor layers 507a1 and 507a2 and increasing as they approach conductor layer 511a, which serves as a common wiring. The narrow portion of the wiring width is λTHz / 10 or less. The narrow connection width between conductor layer 507a1 and conductor layer 507a2 suppresses interference and loss between the bias line and the fTHz resonant electric field within the antenna. Furthermore, the gradually increasing wiring width reduces wiring resistance from DC to low frequency bands (<100 MHz), thereby suppressing variations in operating voltage among the antennas. This wiring structure is suitable for stable operation of mutual injection locking of the antenna array, since it simultaneously suppresses operating voltage variations by reducing wiring resistance in the low frequency band and interference and loss within the antenna at fTHz. Furthermore, line 508a1 and line 508a2 are connected to a snubber circuit. The snubber circuit is configured by connecting resistor 5211 and conductor layer 5223 of capacitor 530a in series. The snubber circuit is configured by connecting resistor 5212 and conductor layer 5224 of capacitor 530ad in series. Resistors 5211 and 5212 are, for example, 15 Ω and are made of thin TiW films. Capacitor 530ad is formed by conductor layer 5223, conductor layer 506, and dielectric 5043 therebetween. Capacitor 530a is formed by conductor layer 5224, conductor layer 506, and dielectric 5043 therebetween. Capacitor 530a and capacitor 530ad have capacitance values of, for example, 10 pF. The snubber circuit AC-shortes conductor layer 511a, line 508a1, and line 508a2 near the RTD in a frequency band of 100 GHz or less, thereby reducing impedance.Therefore, parasitic oscillations below 100 GHz caused by the inductance of the bias line can be reduced.

[0163] Figure 11(b) shows an antenna array in which 3 x 3 unit antennas 500a are arranged at equal intervals of 0.6 wavelengths, with adjacent antennas connected by coupling lines. By connecting the coupling lines, the RTDs 501a1 and 501i2 of each antenna are mutually injection-locked in positive phase. The conductor layers 511a are also connected to the common conductor layer 511, i.e., a common bias line, between adjacent antennas. The common bias line allows bias signals to be supplied from a common power source to the RTDs of each antenna. In this case, it is preferable to connect the snubber circuits of adjacent antennas to maintain symmetry. For example, a snubber circuit 530ad is connected between antennas 500a and 500d to improve symmetry. The snubber circuit 530ad consists of a resistor and an MIM capacitor. The snubber circuit 530ad is connected to each antenna and connected to the common conductor layer 511. The snubber circuit 530ad is arranged between adjacent antennas. To increase integration by reducing the component layout, as in the case of snubber circuit 530ad, capacitance may be shared between adjacent antennas. A snubber circuit, including snubber circuit 530ad, is placed for each antenna to AC short-circuit the common conductor layer 511 of the antenna array in the frequency band below 100 GHz, thereby reducing impedance and suppressing low-frequency oscillation between the antennas. In other words, at least one snubber circuit is connected to multiple antennas.

[0164] Antenna 500e is connected to four different antennas, 500f, 500d, 500h, and 500b, above, below, and to the left and right of antenna 500e via coupling lines. Antennas 500f and 500d, which are arranged above and below antenna 500e, are each connected in a 1:1 ratio by a single independent coupling line. Antennas 500h and 500b, which are arranged left and right of antenna 500e, are each connected in a 1:1 ratio by two independent coupling lines. In other words, antenna 500e is connected to a total of six coupling lines. One coupling line 5091eb extending from antenna 500e does not branch out and is connected to an adjacent antenna 500b. In this way, an antenna array in which unit antennas with symmetrically arranged antenna components and coupling lines are regularly arranged makes it possible to accurately and efficiently design a large-scale M × N array (M and N are the number of antennas and are natural numbers) by approximation based on the impedance of the unit antennas. Furthermore, since the coupling lines can be routed in both the vertical (X) and horizontal (Y) directions, mutual injection locking between adjacent antennas is strengthened, making it easier to control the directivity by synchronizing the antenna array.

[0165] FIG. 11(d) is a schematic plan view showing a modified example of this embodiment. Element 51 and element 52 show the upper portion of antenna 500a in FIG. 11(b) in the X direction. That is, they show the coupling portions between conductor layer 503a, coupled line 5091ad, coupled line 509ab, and coupled line 5091a. While the ends of the three coupled lines are spaced apart in FIG. 11(b), the ends of the three coupled lines in element 51 are integrated. In other words, one coupled line coupled to antenna 500a branches into two or more, for example, three. Furthermore, in element 52, the three-pronged branch portions are spaced apart from element 51. In other words, the ends of the three coupled lines in FIG. 11(b) are connected by another conductor layer extending in the Y direction.

[0166] In plan view, element 51 and element 52 can be considered to be one coupled line inside the outer edge of the coupled antenna, which branches into three coupled lines outside the outer edge. Furthermore, the configuration of element 51 and element 52 can be considered, for example, as a connection point between the antenna and the three coupled lines. Furthermore, in FIG. 11(b), in plan view, there are three coupled lines inside the outer edge of the coupled antenna, and each coupled line is spaced apart. In other words, in FIG. 11(b), the antenna and the three coupled lines can be considered to be connected at three coupled points. Here, the "connection point" may be a coupling point, and the "connection" may be a coupling. This configuration allows synchronization between the three coupled lines.

[0167] Regarding the arrangement of the antenna array in FIG. 11(a), M×N is not limited to 3×3, and can be expanded to an antenna array such as 4×4 or 5×5.

[0168] (Embodiment 7) Fig. 13(a) is a top view of an element 60 which is a modification of embodiment 6. Except for the components designated by the reference numerals, the configuration is the same as that shown in Fig. 11(a).

[0169] In FIG. 13(a), the antenna 600e at the center of the antenna array has two or more adjacent antennas connectable to it on the top and bottom (X direction) and two or more on the left and right (Y direction), so it is connected to the adjacent antennas by coupling lines 609e extending left and right and up and down. The configuration of the antenna 600e is similar to that of the antenna 500e shown in FIG. 11(a). On the other hand, the antennas 600a-600d and 600f-600i at the ends of the array do not have coupling lines extending in directions away from adjacent antennas. The length and impedance of each coupling line of the element 60 can be adjusted to ensure stable synchronization of the oscillation frequency fTHz even without the coupling lines at the nodes and antinodes described above. Therefore, fluctuations in the resonance characteristics of the frequency fTHz can be reduced even if the number of coupling lines in each antenna is reduced. For example, at the top and bottom of the antenna, the element 60 is connected to two adjacent antennas in a 1:1:1 relationship by coupling lines, and the two antennas are connected separately and independently. The top and bottom ends of the antenna refer to the ends of the antenna in the X direction. Therefore, it is possible to thin out unnecessary coupling lines without changing the fTHz resonance characteristics. Element 60 connects two adjacent antennas at the left and right ends of the antenna with coupling lines in a 1:2:1 relationship. The left and right ends of the antenna are the antenna ends in the Y direction.

[0170] For antennas arranged on the periphery of the antenna array, by not arranging coupling lines on the outer periphery of the antenna array, the ends of the coupling lines are coupled to one of the nine antennas. In a microstrip line structure in the THz band, conductor loss due to the skin effect and dielectric loss due to an increase in tan δ occur, which can increase losses associated with power transmission. Therefore, as the amount of power transmitted for coupling increases, losses also increase, resulting in a trade-off between synchronization and loss. With a configuration like this embodiment, coupling lines that do not contribute to coupling can be eliminated, thereby reducing losses. Directivity control through injection locking and increased front gain due to reduced transmission loss are both possible. Furthermore, by eliminating the open ends of the coupling lines, the integration of the aforementioned termination components is unnecessary. This reduces characteristic variations due to manufacturing errors and manufacturing costs.

[0171] Figure 13(b) is a schematic top view of element 70, which is an antenna array of elements 60 expanded to a 4x4 array. Figure 13(b) shows only the conductor layers that make up the antenna in Figure 13(a) and the conductor layers that make up the coupling lines. By using unit antennas consisting of highly symmetric antennas and coupling lines as in Figure 13(a), it is possible to expand to an MxN array (M and N are natural numbers) regardless of odd or even numbers using the same design rules as for lower-order antenna arrays. Here, the center of gravity of the antenna array is tentatively indicated by point O.

[0172] 13(b), element 70 has antennas 700a to 700p. In element 70, the multiple antennas are coupled by coupled lines 709, 7091, and 7092, as shown in FIG. 13(a). With this configuration, it is possible to reduce loss while synchronizing the antennas.

[0173] (Embodiment 8) This embodiment shows a modified example of element 70, which is a modification of embodiment 7. Figures 14(a) to 20(b) show modified examples of the coupling lines of element 70 shown in Figure 13(b). Similar to Figure 13(b), Figures 14(a) to 20(b) only show the conductor layers that make up the antenna and the conductor layers that make up the coupling lines.

[0174] 14(a) to 15(b) show configurations in which the number of coupling lines provided along the Y direction for the element 70 is changed. Such a configuration makes it possible to achieve injection locking due to coupling between antennas and reduce transmission loss. Reducing transmission loss can increase radiation power.

[0175] FIG. 14(a) is a schematic top view showing the element 71. Compared to the element 70, six bond lines extending in the Y direction have been removed. Specifically, the bond lines 7092dh, 7092hl, 7092lp, 7091ae, 7091ei, and 7091im of the element 70 are not arranged in the element 71. If the unit array is a 2×2 array, the unit array UA1 includes antennas 700d, 700c, 700g, and 700h. The antennas 700d, 700c, 700g, and 700h are circularly coupled by the bond lines 7091dh, 709cd, 7092cg, and 709gh. Furthermore, the antennas 700c and 700g are circularly coupled by the bond line 7091cg. The unit array UA2 includes antennas 700a, 700b, 700e, and 700f. Antennas 700a, 700b, 700e, and 700f are coupled in a circular pattern by coupled lines 7091bf, 709ab, 7092ae, and 709ef. Furthermore, antennas 700f and 700b are coupled in a circular pattern by coupled line 7092bf. The arrangements of the antennas and coupled lines of the unit array UA1 and the unit array UA2 can be said to be mirror-symmetric. The same is true for the other unit arrays, allowing the antenna array to have a high degree of symmetry.

[0176] FIG. 14(b) is a schematic top view showing element 72. Six bond lines extending in the Y direction have been further reduced from element 71. Specifically, bond lines 7092bf, 7092fj, 7092jn, 7091cg, 7091gk, and 7091ko of element 71 are not arranged in element 72. If the unit array is a 2×2 array, unit array UA1 includes antennas 700d, 700c, 700g, and 700h. Antennas 700d, 700c, 700g, and 700h are coupled in a circular pattern by bond lines. Antennas 700h, 700g, 700k, and 700l are coupled in a circular pattern by bond lines. Antennas 700l, 700k, 700o, and 700p are coupled in a circular pattern by bond lines. The same applies to the other unit arrays, and the antenna array can have high symmetry.

[0177] FIG. 15(a) is a schematic top view showing the element 73. Six bond lines extending in the Y direction have been further reduced from those of the element 71. Specifically, the bond lines 7092cg, 7092gk, 7092ko, 7091bf, 7091fj, and 7091jn of the element 71 are not arranged in the element 73. If the unit array is a 2×2 array, the unit array UA1 includes antennas 700d, 700c, 700g, and 700h. Antennas 700d and 700c are coupled by a bond line 709cd, and antennas 700g and 700h are coupled by a bond line 709fh. Antennas 700c and 700g are coupled by a bond line 7091cg, and antennas 700h and 700d are coupled by a bond line 7091dh. The unit array UA2 includes antennas 700a, 700b, 700e, and 700f. Antennas 700a and 700b are coupled by a coupling line 709ab, and antennas 700e and 700f are coupled by a coupling line 709ef. Antennas 700a and 700e are coupled by a coupling line 7092ae, and antennas 700b and 700f are coupled by a coupling line 7092bf. The arrangements of the antennas and coupling lines of the unit array UA1 and unit array UA2 can be said to be mirror-symmetric. The same is true for the other unit arrays, and the antenna array can have a high degree of symmetry.

[0178] FIG. 15(b) is a schematic top view showing element 74. Six bond lines extending in the Y direction have been further reduced from element 73. Specifically, bond lines 7092bf, 7092fj, 7092jn, 7091cg, 7091gk, and 7091ko of element 73 are not arranged in element 74. As with the other examples, element 74 can also be configured as a unit array. The arrangements of the antennas and bond lines of unit array UA1 and unit array UA2 can be said to be mirror-symmetric. The same is true for the other unit arrays, allowing for a high degree of symmetry as an antenna array.

[0179] For example, in Fig. 15(a), the same number of coupling lines are arranged in the X and Y directions, one each, and the difference in the number of coupling lines connected to the antennas at the ends and the center of the antenna array is reduced, resulting in an arrangement that balances synchronization and loss. Also, in Fig. 14(a) to Fig. 15(b), when the center of gravity of the antenna array is taken, the antenna array and the coupling lines can be arranged symmetrically.

[0180] Figures 16(a) to 18(a) show further modified examples. This can be realized by extending the design rules for the unit array to an M × N array (both M and N are even numbers). Among the modified examples, there are configurations in which one antenna is responsible for coupling between the unit arrays, such as those shown in Figures 16(a), 17(a), and 18(a). This configuration makes it possible to reduce the number of coupling lines that contribute to coupling, thereby reducing variations in synchronization between the edges and center of the array.

[0181] FIG. 16(a) is a schematic top view showing the element 75. Compared to the element 70, the number of coupling lines extending in the X and Y directions has been reduced. The element 75 includes four unit arrays UA1 to UA4. The unit array UA1 includes antennas 700c, 700d, 700g, and 700h. The unit array UA2 includes antennas 700a, 700b, 700e, and 700f. The unit array UA3 includes antennas 700i, 700j, 700m, and 700n. The unit array UA4 includes antennas 700k, 700l, 700o, and 700p. The unit arrays UA1 to UA4 each include one coupling line 7091, one coupling line 7092, and two coupling lines 709. For example, the unit array UA1 will be described. Antennas 700c and 700d are coupled by a coupling line 709cd, and antennas 700d and 700h are coupled by a coupling line 7091dh. Antennas 700h and 700g are coupled by a coupling line 709gh, and antennas 700g and 700c are coupled by a coupling line 7092cg. In other words, the four antennas are coupled in a circular pattern by four coupling lines. The same applies to the other unit arrays UA2 to UA4. One antenna in each unit array is coupled in a circular pattern. Specifically, antennas 700g and 700f are coupled by a coupling line 709fg, and antennas 700f and 700j are coupled by a coupling line 7092fj. Antennas 700j and 700k are coupled by a coupling line 709jk, and antennas 700k and 700g are coupled by a coupling line 7091gk.

[0182] FIG. 16(b) is a schematic top view showing element 76. Compared to element 70, the number of bond lines extending in the X and Y directions has been reduced. Specifically, bond lines 7091hl, 7092hl, 7091ei, and 7091ei of element 70 are not arranged in element 76. In element 76, the unit array is 1×2 (1 row and 2 columns), and two antennas are coupled in a circular manner by bond lines. Unit array UA1 includes antennas 700d and 700h. Antennas 700d and 700h are coupled in a circular manner by bond lines 7091dh and 7092dh. Unit array UA2 includes antennas 700c and 700g. Antennas 700c and 700g are coupled in a circular manner by bond lines 7091cg and 7092cg. Antennas 700d and 700c are coupled by a coupling line 709cd, and antennas 700g and 700h are coupled by a coupling line 709gh. The connection relationships for the other 1×2 unit arrays and the 2×2 unit arrays are similar. As in FIG. 16(a), one antenna in each unit array is coupled in a circular pattern. Specifically, antennas 700g and 700f are coupled by a coupling line 709fg, and antennas 700f and 700j are coupled by a coupling line 7092fj. Antennas 700j and 700k are coupled by a coupling line 709jk, and antennas 700k and 700g are coupled by a coupling line 7091gk. Furthermore, antennas 700g and 700k are coupled by a coupling line 7092gk, and antennas 700f and 700j are coupled by a coupling line 7091fj. With this configuration, the 1×2 unit arrays can be connected together while maintaining the symmetry of the unit arrays.

[0183] FIG. 17(a) is a schematic top view showing element 77. Compared to element 70, the number of coupling lines extending in the X and Y directions has been reduced. In element 77, the unit array is 1×2, and two antennas are coupled in a circular manner by coupling lines. Unit array UA1 includes antennas 700d and 700h. Antennas 700d and 700h are coupled in a circular manner by coupling lines 7091dh and 7092dh. Unit array UA2 includes antennas 700c and 700g. Antennas 700c and 700g are coupled in a circular manner by coupling lines 7091cg and 7092cg. Antennas 700g and 700h are coupled by coupling line 709gh, but antennas 700d and 700c are not coupled by coupling line 709cd. The connection relationships of the other 1×2 unit arrays and the 2×2 unit arrays are similar. One antenna of each unit array is coupled to another in a ring shape. Specifically, antenna 700g and antenna 700f are coupled by coupling line 709fg, and antenna 700f and antenna 700j are coupled by coupling line 7092fj. Antenna 700j and antenna 700k are coupled by coupling line 709jk, and antenna 700k and antenna 700g are coupled by coupling line 7091gk. Furthermore, antenna 700g and antenna 700k are coupled by coupling line 7092gk, and antenna 700f and antenna 700j are coupled by coupling line 7091fj. The arrangement of the antennas and coupling lines of the antenna array can be point-symmetrical with respect to the center of gravity of the antenna array.

[0184] 17(b) is a schematic top view showing element 78. Element 78 has a 2x2 unit array, similar to element 75 in FIG. 16(a), and four antennas are coupled in a circular pattern by coupling lines. Antennas 700g, 700f, 700j, and 700k are coupled by coupling lines 7091gk, 709fg, 709jk, and 7092fj, respectively, shown in element 75. Furthermore, antennas 700g, 700f, 700j, and 700k are coupled by coupling lines 7092gk and 7091fj.

[0185] FIG. 18(a) is a schematic top view showing an element 79. Like the element 75 in FIG. 16(a), the element 79 has a 2×2 unit array, with four antennas coupled in a ring shape by coupling lines. Also, like the element 75, the antennas 700g, 700f, 700j, and 700k of each unit array are coupled by coupling lines. The difference from the element 75 is that the coupling lines 7091 and 7092 are swapped in each of the unit arrays UA1 to UA4. Specifically, in the unit array UA1, antennas d and h are coupled by a coupling line 7092dh, and antennas c and g are coupled by a coupling line 7091cg. Antennas 700g and 700k are coupled by a coupling line 7092gk, and antennas 700j and 700f are coupled by a coupling line 7091fj. Even in this configuration, it is possible to provide an antenna array with high symmetry.

[0186] In Figures 17(a) and 17(b), the variation in coupling between the end and center of the antenna array can be reduced by changing the number of coupling lines coupled to any one antenna located at the end or center.

[0187] 18(b) to 20(b) show further modified examples. The inventors' investigations revealed that the following three conditions are important: 1) to make the number of coupling lines connected in the X and Y directions as close to the same as possible; 2) to reduce the difference in the number of coupling lines connected to the antenna at the edge and center of the antenna array; and 3) to reduce the difference in the number of coupling lines connected to the two radiation ends within the antenna. These configurations achieve a balanced vertical and horizontal coupling and reduce synchronization variations between the edge and center of the antenna array. For example, FIGS. 18(b), 19(a), and 19(b) show configurations that prioritize symmetry in the X and Y directions to improve directivity, while FIGS. 20(a) and 20(b) show configurations that prioritize loss reduction by reducing the number of coupling lines.

[0188] 18(b) is a schematic top view showing the element 80. The element 80 has a 1x2 unit array. The antenna array includes unit arrays UA1 to UA12. In the element 80, the antennas included in the unit arrays include antennas of adjacent unit arrays, and multiple unit arrays are arranged so as to overlap. The unit array UA1 includes antennas 700d and 700h, the unit array UA2 includes antennas 700c and 700g, the unit array UA3 includes antennas 700b and 700f, and the unit array UA4 includes antennas 700a and 700e. The unit array UA5 includes antennas 700h and 700l, the unit array UA6 includes antennas 700g and 700k, the unit array UA7 includes antennas 700f and 700j, and the unit array UA8 includes antennas 700e and 700i. The unit array UA9 includes antennas 700l and 700p, and the unit array UA10 includes antennas 700k and 700o. The unit array UA11 includes antennas 700j and 700n, and the unit array UA12 includes antennas 700i and 700m. The unit arrays UA2, UA3, UA6, UA7, UA10, and UA11 are coupled to each other by two coupling lines 709, 7091, and 7092 coupled to the top and bottom of each antenna. This configuration is the same as that shown in Figure 13(b). However, the unit arrays UA1, UA5, and UA9 are coupled to each other by a single coupling line 709 coupled to the bottom end of each antenna and a coupling line 7092 coupled to an adjacent antenna. The unit array UA4, unit array UA8, and unit array UA12 are coupled to one coupled line 709 coupled to the upper end of the antenna and to a coupled line 7091 coupled to the adjacent antenna.

[0189] FIG. 19(a) is a schematic top view showing element 81. Like element 80 shown in FIG. 18(b), element 81 has a 1×2 unit array. The antenna array includes unit arrays UA1 to UA12 similar to element 80. In element 81, each antenna is coupled in the X direction by a coupling line 709. The antennas are coupled in the Y direction by either a coupling line 7091 or a coupling line 7092. In other words, either a coupling line 7091 or a coupling line 7092 is disposed between antennas adjacent in the Y direction. Even with this configuration, a highly symmetrical antenna array can be provided.

[0190] 19(b) is a schematic top view showing element 82. Like element 81 in FIG. 19(a), element 82 has a 1×2 unit array, and the antennas are coupled in the Y direction by either coupling line 7091 or coupling line 7092.

[0191] 20(a) is a schematic top view showing element 83. Like element 81 in FIG. 19(a), element 83 has a 1×2 unit array, and the antennas are coupled in the Y direction by either coupling line 7091 or coupling line 7092.

[0192] 20(b) is a schematic top view showing element 84. Like element 81 in FIG. 19(a), element 84 has a 1×2 unit array, and each antenna is coupled in the Y direction by either a coupling line 7091 or a coupling line 7092. However, the coupling lines coupling the antennas in the Y direction are thinned out. For example, in unit arrays UA2, UA4, UA5, UA7, UA10, and UA12, the two antennas arranged in the Y direction are coupled by a coupling line 7091 or a coupling line 7092. However, in unit arrays UA1, UA3, UA6, UA8, UA9, and UA11, the two antennas arranged in the Y direction are not coupled.

[0193] Figure 21 is a schematic diagram showing the correlation between the degree of synchronization between antennas and the radiation power per antenna for the 4x4 antenna array described above. The "degree of synchronization" on the horizontal axis represents the power of the number of antennas to which the front gain of the antenna array increases proportionally. The "radiation power / antenna" on the vertical axis represents the magnitude of the oscillation power radiated in all directions from one antenna. For example, in the case of an ideal antenna array with lossless coupling lines, mutual injection synchronization can be achieved without loss, so that both the maximum radiation power per antenna and the front gain enhancement (square law) due to sharpened directivity are achieved. For example, the radiation power is 0.3 mW. This is shown as Comparative Example 2.

[0194] In reality, power transmission losses occur in microstrip lines, and these losses are particularly pronounced in the THz band. Therefore, increasing the number of coupled lines, as in Connection Examples 4, 5, and 1, increases transmission losses. The radiation power per antenna tends to decrease by the amount of the losses. On the other hand, increasing the number of coupled lines strengthens the coupling between antennas, resulting in sharper directivity due to mutual injection locking of the antenna array. Therefore, increasing the number of coupled lines can approximate the tendency for the front gain to increase in proportion to the square law of the number of antennas. A comparison example without coupled lines is shown as Comparative Example 1. In this case, there is no loss of power transmitted between antennas via the coupled lines, and thus the radiation power per antenna is maximized. However, because the coupling between antennas is weak and mutual injection locking does not occur, sharper directivity does not occur. Therefore, the increase in front gain is proportional to the number of antennas, and the "degree of synchronization" follows a linear law. The antenna array described above can achieve both the desired radiation power and directivity by adjusting the number of coupled lines in the X and Y directions. In addition, the front gain can be increased. Here, connection example 1 is the configuration in Fig. 13(a), connection example 4 is the configuration in Fig. 15(b), and connection example 5 is the configuration in Fig. 15(a).

[0195] (Other embodiments) Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention.

[0196] For example, in the above-described embodiment, the carriers are assumed to be electrons, but the present invention is not limited to this and may be implemented using holes. Furthermore, the materials for the substrate and dielectric may be selected depending on the application, and semiconductor layers such as silicon, gallium arsenide, indium arsenide, and gallium phosphide, and resins such as glass, ceramic, polytetrafluoroethylene, and polyethylene terephthalate may be used.

[0197] Furthermore, although the above-described embodiment uses a square patch antenna as a terahertz wave resonator, the shape of the resonator is not limited to this. For example, a resonator having a structure using a patch conductor of a polygonal shape such as a rectangle or a triangle, or a circle or an ellipse may be used.

[0198] Furthermore, the number of negative differential resistance elements integrated in the element is not limited to one, and a resonator having a plurality of negative differential resistance elements may be used. The number of lines is also not limited to one, and a configuration having a plurality of lines may be used. Terahertz waves can be generated and detected using the elements described in the above embodiments.

[0199] In addition, in each of the above-described embodiments, the RTD has been described as a double-barrier RTD made of InGaAs / AlAs grown on an InP substrate. However, the present invention is not limited to these structures and material systems, and other structures and material combinations can also be used to provide the device. For example, an RTD with a triple-barrier quantum well structure or an RTD with four or more multi-barrier quantum wells may also be used.

[0200] Furthermore, the following combinations may be used as materials for the RTD. GaAs / AlGaAs, GaAs / AlAs, InGaAs / GaAs / AlAs formed on GaAs substrate InGaAs / InAlAs, InGaAs / AlAs, InGaAs / AlGaAsSb formed on InP substrate InAs / AlAsSb and InAs / AlSb grown on InAs substrates ·SiGe / SiGe formed on a Si substrate

[0201] The above-mentioned structure and materials may be selected appropriately depending on the desired frequency and the like.

[0202] The configuration of the present embodiment described above eliminates the upper limit on the number of antennas that can be arranged in the antenna array, and has the effect of significantly improving the directivity and front intensity as the number of arrays increases. Therefore, the configuration of the above embodiment can provide a suitable element that can realize more efficient generation and detection of terahertz waves.

Claims

1. a first conductor layer; a semiconductor layer electrically connected to the first conductor layer and configured to generate or detect terahertz waves; a second conductor layer electrically connected to the semiconductor layer and facing the first conductor layer with the semiconductor layer interposed therebetween; an antenna array including a plurality of antennas, each of the antennas including a dielectric layer located between the first conductor layer and the second conductor layer, the antenna array includes a first antenna, a second antenna, a third antenna, a fourth antenna, and a fifth antenna; the second antenna, the first antenna, and the third antenna are arranged in this order in a first direction; the fourth antenna, the first antenna, and the fifth antenna are arranged in this order in a second direction intersecting the first direction; the second conductor layer of the second antenna is connected to the second conductor layer of the first antenna via a first coupling line extending in the first direction; the second conductor layer of the first antenna is connected to the second conductor layer of the third antenna via a second coupling line extending in the first direction; the second conductor layer of the fourth antenna is connected to the second conductor layer of the first antenna via a third coupling line extending in the second direction; An element characterized in that the second conductor layer of the first antenna is connected to the second conductor layer of the fifth antenna via a fourth coupling line extending in the second direction.

2. 2. The element according to claim 1, wherein the first coupled line and the third coupled line are connected at a position shifted from the center position of a line segment connecting the first antenna and the second antenna.

3. the first antenna and the second antenna are injection-locked at a frequency of the terahertz wave by the first coupled line; 3. The element according to claim 1, wherein the first antenna and the fourth antenna are injection-locked at the frequency of the terahertz wave by the third coupling line.

4. 4. The element according to claim 1, wherein the first bonded wire and the third bonded wire are made of an integral conductor.

5. 5. The element according to claim 1, wherein the first coupled line and the third coupled line are connected at a position other than a node of a resonant electric field standing in the coupled line at the frequency of the terahertz wave.

6. 6. The element according to claim 1, wherein the first coupled line and the third coupled line are connected at positions that satisfy a phase matching condition with an adjacent antenna at the frequency of the terahertz wave.

7. the third coupled line and a fifth coupled line extending along the second direction are disposed between the first antenna and the fourth antenna; the first coupled line and the third coupled line are connected at a position other than a node of a resonant electric field standing at a frequency of the terahertz wave, and the first coupled line and the fifth coupled line are connected at a position other than a node of a resonant electric field standing at a frequency of the terahertz wave, 7. The element according to claim 1, wherein a node of a resonant electric field standing at a frequency of the terahertz wave is located between a position where the first coupled line and the third coupled line are connected and a position where the first coupled line and the fifth coupled line are connected.

8. 8. The element according to claim 1, wherein the first direction is a resonance direction of a resonance electric field that exists at a frequency of the terahertz wave.

9. 9. The element according to claim 1, wherein the second direction is a direction perpendicular to the first direction.

10. 10. The element according to claim 1, wherein the second direction is a magnetic field direction induced by a resonant electric field standing at a frequency of the terahertz wave.

11. 11. An element according to any one of the preceding claims, characterized in that the antenna radiates circularly polarized waves.

12. 12. The element according to claim 1, further comprising a bias line for connecting a bias circuit for supplying a bias signal to the semiconductor layer and the second conductor layer.

13. 13. The device of claim 12, wherein the bias line is disposed in a layer between the first conductor layer and the second conductor layer.

14. the antenna array is disposed on a substrate; the first bonded wire and the third bonded wire are formed by a third conductor layer; the bias line is formed by a fourth conductor layer, 14. The element according to claim 12, wherein the third conductor layer and the fourth conductor layer are disposed at different layers from the surface of the substrate.

15. 15. The element according to claim 14, wherein the substrate, the first conductor layer, the fourth conductor layer, and the third conductor layer are stacked in this order.

16. 15. The element according to claim 14, wherein the substrate, the first conductor layer, the third conductor layer, and the fourth conductor layer are stacked in this order.

17. 17. The element according to claim 12, wherein the bias line has a lower impedance than the impedance of the semiconductor layer in a frequency band lower than the frequency of the terahertz wave.

18. 18. The element according to claim 1, wherein the antenna array comprises antennas arranged in an mxn matrix (m and n are integers, m≧2, n≧2).

19. 19. The element according to claim 18, wherein the antennas of the antenna array are arranged at a pitch equal to or less than the wavelength of the terahertz wave.

20. 20. An element according to any one of claims 1 to 19, wherein the antenna is a patch antenna.

21. 21. The device according to claim 1, wherein the semiconductor layer includes a negative resistance element.

22. 22. The device of claim 21, wherein the negative resistance device is a resonant tunneling diode.

23. An element described in any one of claims 1 to 22, characterized in that when the electrical length between the semiconductor layer of the first antenna and the semiconductor layer of the second antenna is L1, L1 = 2π × k (k: integer).

24. 24. An element according to any preceding claim, wherein each antenna comprises a second semiconductor layer operating in anti-phase with the semiconductor layer.

25. a transmitter having the element according to any one of claims 1 to 24 and radiating terahertz waves; a receiving unit that detects the terahertz waves.

26. An element including an antenna array provided with a plurality of antennas, each of which includes a first conductor layer, a semiconductor layer electrically connected to the first conductor layer and configured to generate or detect terahertz waves, a second conductor layer electrically connected to the semiconductor layer and facing the first conductor layer via the semiconductor layer, and a dielectric layer located between the first conductor layer and the second conductor layer, the antenna array includes coupling lines for connecting adjacent antennas and transmitting the terahertz waves; An element characterized in that at least one antenna of the antenna array is connected to at least three or more of the coupled lines.

27. 27. The element of claim 26, wherein the three or more bonded wires are connected to the antenna at one connection point.

28. 27. The element of claim 26, wherein the three or more bonded wires are respectively connected to the antenna at three or more separate connection points.

29. 27. The element of claim 26, wherein the three or more bonded wires each connect to an antenna at a separate connection point.

30. the first antenna and the at least two antennas are connected by the coupling wire; 27. The element according to claim 26, wherein the first antenna and the at least two antennas are connected by separate bonded wires, respectively.

31. 27. The element of claim 26, wherein two or more of said coupled wires are connected to each radiating end of at least one antenna of said antenna array.

32. The element according to claim 26, wherein the at least three or more coupled wires are, in a plan view, one wire inside the outer edge of the antenna and branched into two or more wires outside the outer edge.

33. 27. The element according to claim 26, wherein the at least three or more coupled wires are arranged apart from each other outside the outer edge of the antenna in a plan view.

34. 27. The device of claim 26, wherein the ends of the coupled wires are electrically terminated at a terahertz wave frequency.

35. 27. The element of claim 26, wherein the antennas at the ends of the antenna array have no coupling wires on the outer edge side of the antenna array.

36. 27. The element according to claim 26, wherein the coupling wire is connected to the antenna symmetrically with respect to the center of gravity of the antenna.

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