Patent Publication Number: US-2022236178-A1

Title: Terahertz device

Description:
TECHNICAL FIELD 
     The present disclosure relates to a terahertz device. 
     BACKGROUND ART 
     Recent advances in electronic devices such as transistors have reduced the size of electronic devices to nanoscale, so that there have been observations of a phenomenon called a quantum effect. The quantum effect is used to develop an ultra-speed processing device and a device having a new function. 
     In such environment, in particular, the range of frequencies of 0.1 THz to 10 THz, which is called a terahertz band, is used in attempts to perform high capacity communication, information processing, imaging, and measurements. The range of frequencies has characteristics of both light and radio waves. If a device operating in this frequency band is realized, the device may be used in many applications such as measurements in various fields such as physical field, astronomical filed, and biological field in addition to imaging, high capacity communication, and information processing, which are described above. 
     A known element that oscillates a high-frequency electromagnetic wave having a frequency in the terahertz band has a structure integrating a resonant tunneling diode and a fine slot antenna (refer to, for example, Patent Document 1). 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: Japanese Laid-Open Patent Publication No. 2016-111542 
     SUMMARY OF THE INVENTION 
     Problems that the Invention is to Solve 
     In a terahertz device including a terahertz element as described above, there may be a need to improve the gain. 
     It is an objective of the present disclosure to provide a terahertz device that improves gain. 
     Means for Solving the Problems 
     To achieve the above objective, a terahertz device includes a base member, a terahertz element mounted on the base member and configured to generate an electromagnetic wave, an antenna base located opposing the base member and including an antenna surface, and a reflection film formed on the antenna surface to reflect at least part of the electromagnetic wave generated by the terahertz element in one direction. With this structure, electromagnetic waves generated by the terahertz element are reflected by the reflection film in one direction. This increases the output of the electromagnetic waves emitted from the terahertz device. Thus, the gain of the terahertz device is improved. 
     To achieve the above objective, a terahertz device includes a terahertz element configured to generate an electromagnetic wave, a base member including a reflector located opposing the terahertz element to reflect at least part of the electromagnetic wave generated by the terahertz element, an antenna base located opposing the base member and including an antenna surface, and a reflection film formed on the antenna surface to reflect at least part of the electromagnetic wave reflected by the reflector in one direction. With this structure, electromagnetic waves generated by the terahertz element are reflected by the reflector, and the electromagnetic waves are further reflected by the reflection film in one direction. This increases the output of the electromagnetic waves emitted from the terahertz device. Thus, the gain of the terahertz device is improved. 
     To achieve the above objective, a terahertz device includes a base member, a terahertz element mounted on the base member and configured to receive an electromagnetic wave, an antenna base located opposing the base member and including an antenna surface, and a reflection film formed on the antenna surface to reflect an incident electromagnetic wave toward the terahertz element. With this structure, incident electromagnetic waves of the reflection film are reflected by the reflection film toward the terahertz element. This increases the reception strength of the terahertz device. Thus, the gain of the terahertz device is improved. 
     To achieve the above objective, a terahertz device includes a terahertz element configured to receive an electromagnetic wave, a base member including a reflector located opposing the terahertz element to reflect at least part of an incident electromagnetic wave toward the terahertz element, an antenna base located opposing the base member and including an antenna surface, and a reflection film formed on the antenna surface to reflect at least part of an incident electromagnetic wave toward the reflector. With this structure, incident electromagnetic waves of the reflection film is reflected toward the reflector, and the electromagnetic waves are further reflected by the reflector toward the terahertz element. This increases the reception strength of the terahertz device. Thus, the gain of the terahertz device is improved. 
     To achieve the above objective, a terahertz device includes a base member, a terahertz element mounted on the base member and configured to generate an electromagnetic wave, an antenna base opposed to the base member and including an antenna surface, a reflection film formed on the antenna surface to reflect at least part of the electromagnetic wave generated by the terahertz element in one direction, and an electrode used for electrical connection with an external device. The electrode projects sideward relative to the antenna base as viewed in an opposing direction of the base member and the antenna base. 
     With this structure, electromagnetic waves generated by the terahertz element are reflected by the reflection film in one direction. This increases the output of the electromagnetic waves emitted from the terahertz device. Thus, the gain of the terahertz device is improved. 
     In addition, since the electrode projects sideward relative to the antenna base, the terahertz device is mountable on a circuit substrate having a hole when the antenna base is inserted into the hole. Thus, when the terahertz device is mounted on the circuit substrate, the terahertz device has a low profile. 
     To achieve the above objective, a terahertz device includes a base member, a terahertz element mounted on the base member and configured to receive an electromagnetic wave, an antenna base located opposing the base member and including an antenna surface, a reflection film formed on the antenna surface to reflect an incident electromagnetic wave toward the terahertz element, and an electrode used for electrical connection with an external device. The electrode projects sideward relative to the antenna base as viewed in an opposing direction of the base member and the antenna base. 
     With this structure, incident electromagnetic waves of the reflection film are reflected by the reflection film toward the terahertz element. This increases the reception strength of the terahertz device. Thus, the gain of the terahertz device is improved. 
     In addition, since the electrode projects sideward relative to the antenna base, the terahertz device is mountable on a circuit substrate having a hole when the antenna base is inserted into the hole. Thus, when the terahertz device is mounted on the circuit substrate, the terahertz device has a low profile. 
     Effects of the Invention 
     The terahertz device described above improves gain. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a first embodiment of a terahertz device as viewed from above. 
         FIG. 2  is a perspective view of the terahertz device as viewed from below. 
         FIG. 3  is a top view of the terahertz device. 
         FIG. 4  is an end view taken along line  4 - 4  in  FIG. 3 . 
         FIG. 5  is a front view of a terahertz element and a lead frame. 
         FIG. 6  is a schematic end view of an active element and its surroundings. 
         FIG. 7  is an enlarged end view showing a cross-sectional structure of the active element. 
         FIG. 8  is an end view showing a step in a method for manufacturing the terahertz device in the first embodiment. 
         FIG. 9  is an end view showing a step in the method for manufacturing the terahertz device. 
         FIG. 10  is an end view showing a step in the method for manufacturing the terahertz device. 
         FIG. 11  is an end view showing a step in the method for manufacturing the terahertz device. 
         FIG. 12  is an end view showing a step in the method for manufacturing the terahertz device. 
         FIG. 13  is an end view showing a step in the method for manufacturing the terahertz device. 
         FIG. 14  is an end view showing a step in the method for manufacturing the terahertz device. 
         FIG. 15  is an end view showing a step in the method for manufacturing the terahertz device. 
         FIG. 16  is an end view showing a step in the method for manufacturing the terahertz device. 
         FIG. 17  is an end view showing a step in the method for manufacturing the terahertz device. 
         FIG. 18  is a plan view showing a step in the method for manufacturing the terahertz device. 
         FIG. 19  is a plan view showing a step in the method for manufacturing the terahertz device. 
         FIG. 20  is an end view of a modified example of the terahertz device of the first embodiment. 
         FIG. 21  is a circuit diagram showing the overview of a second embodiment of a terahertz device. 
         FIG. 22  is a front view of a terahertz element and a lead frame in the second embodiment. 
         FIG. 23  is an end view taken along line  23 - 23  in  FIG. 22 . 
         FIG. 24  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 25  is a front view showing a modified example of connectors. 
         FIG. 26  is a front view showing a modified example of connectors. 
         FIG. 27  is a front view showing a modified example of a lead frame. 
         FIG. 28  is an end view taken along line  28 - 28  in  FIG. 27 . 
         FIG. 29  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 30  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 31  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 32  is a front view showing a modified example of a lead frame. 
         FIG. 33  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 34  is a schematic plan view showing a modified example of a terahertz device. 
         FIG. 35  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 36  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 37  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 38  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 39  is a perspective view of a third embodiment of a terahertz device as viewed from above. 
         FIG. 40  is a perspective view of the terahertz device as viewed from below. 
         FIG. 41  is a top view of the terahertz device. 
         FIG. 42  is an end view taken along line  4 - 4  in  FIG. 41 . 
         FIG. 43  is a front view of a terahertz element and a lead frame. 
         FIG. 44  is a schematic end view of an active element and its surroundings. 
         FIG. 45  is an enlarged end view showing a cross-sectional structure of the active element. 
         FIG. 46  is an end view showing a step in a method for manufacturing the terahertz device in the third embodiment. 
         FIG. 47  is an end view showing a step in the method for manufacturing the terahertz device. 
         FIG. 48  is an end view showing a step in the method for manufacturing the terahertz device. 
         FIG. 49  is an end view showing a step in the method for manufacturing the terahertz device. 
         FIG. 50  is an end view showing a step in the method for manufacturing the terahertz device. 
         FIG. 51  is an end view showing a step in the method for manufacturing the terahertz device. 
         FIG. 52  is an end view showing a step in the method for manufacturing the terahertz device. 
         FIG. 53  is an end view showing a step in the method for manufacturing the terahertz device. 
         FIG. 54  is a plan view showing a step in the method for manufacturing the terahertz device. 
         FIG. 55  is a plan view showing a step in the method for manufacturing the terahertz device. 
         FIG. 56  is an end view showing an example of a mount mode of the terahertz device on a circuit substrate. 
         FIG. 57  is an end view of a modified example of the terahertz device of the third embodiment. 
         FIG. 58  is a circuit diagram showing the overview of a fourth embodiment of a terahertz device. 
         FIG. 59  is a front view of a terahertz element and a lead frame in the fourth embodiment. 
         FIG. 60  is an end view taken along line  22 - 22  in  FIG. 59 . 
         FIG. 61  is a schematic end view showing a fifth embodiment of a terahertz device. 
         FIG. 62  is an end view showing a step of the terahertz device in the fifth embodiment. 
         FIG. 63  is an end view of a modified example of the terahertz device of the fifth embodiment. 
         FIG. 64  is a schematic end view showing a sixth embodiment of a terahertz device. 
         FIG. 65  is an end view of a modified example of the terahertz device of the sixth embodiment. 
         FIG. 66  is an end view of a modified example of the terahertz device of the sixth embodiment. 
         FIG. 67  is a schematic end view showing a seventh embodiment of a terahertz device. 
         FIG. 68  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 69  is a front view showing a modified example of connectors. 
         FIG. 70  is a front view showing a modified example of connectors. 
         FIG. 71  is a front view showing a modified example of a lead frame. 
         FIG. 72  is an end view taken along line  34 - 34  in  FIG. 71 . 
         FIG. 73  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 74  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 75  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 76  is a front view showing a modified example of a lead frame. 
         FIG. 77  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 78  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 79  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 80  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 81  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 82  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 83  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 84  is a schematic end view showing a modified example of a terahertz device. 
         FIG. 85  is a schematic end view showing a modified example of a terahertz device. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     Embodiments of a terahertz device will now be described with reference to the drawings. The embodiments described below exemplify configurations and methods for embodying a technical concept and are not intended to limit the material, shape, structure, layout, dimensions, and the like of each component to those described below. The embodiments described below may undergo various modifications. Portions of the drawings are shown schematically. 
     First Embodiment 
       FIGS. 1 to 7  show a first embodiment of a terahertz device  10  according to the present disclosure. The terahertz device  10  of the first embodiment includes a mount plate  11 , which is used as a base member, a terahertz element  20  configured to generate an electromagnetic wave, an antenna base  50 , a reflection film  54 , and a lead frame  60 , which is used as an electrode and a conductive member. 
       FIGS. 1 and 2  are perspective views of the terahertz device  10 .  FIG. 3  is a top view of the terahertz device  10 .  FIG. 4  is an end view taken along line  4 - 4  in  FIG. 3 .  FIG. 5  is a lower view of the terahertz device  10  and a front view of the terahertz element  20  and the lead frame  60  with the antenna base  50  removed.  FIG. 5  shows electrodes  94  and  101  in a cut state for the sake of convenience. 
     The mount plate  11  is formed of a material transmissive to electromagnetic waves generated by the terahertz element  20 . In the present embodiment, the mount plate  11  is formed of a dielectric material, for example, a synthetic resin such as an epoxy resin or an intrinsic semiconductor such as a single crystal of silicon (Si). An example of the epoxy resin is a glass epoxy resin. However, the material of the mount plate  11  is not limited to those described above and may be any material, for example, Teflon (registered trademark) or glass. The mount plate  11  is insulative. 
     The mount plate  11  is, for example, rectangular. For the sake of brevity, the thickness-wise direction of the mount plate  11  is referred to as the z-direction. Two directions that are orthogonal to each other and the z-direction are referred to as the x-direction and the y-direction. 
     As shown in  FIGS. 3 and 4 , the mount plate  11  includes a mount main surface  12  and a mount back surface  13 , which are plate surfaces intersecting the thickness-wise direction of the mount plate  11 . The mount main surface  12  and the mount back surface  13  are flat and rectangular. The mount main surface  12  and the mount back surface  13  extend in the x-direction and the y-direction and are separate from each other in the z-direction. The shapes of the mount main surface  12  and the mount back surface  13  are not limited to a rectangle and may be a circle, an ellipse, or a polygon. For the sake of brevity, in the present embodiment, a direction extending away from the mount back surface  13  in the z-direction is referred to as “upward”, and a direction extending away from the mount main surface  12  in the z-direction is referred to as “downward”. 
     As shown in  FIG. 5 , in the present embodiment, the mount plate  11  includes two first plate side surfaces  14 , which are opposite end surfaces in the x-direction, and two second plate side surfaces  15 , which are opposite end surfaces in the y-direction. The first plate side surfaces  14  intersect the x-direction. In the present embodiment, the first plate side surfaces  14  are orthogonal to the x-direction. The second plate side surfaces  15  intersect the y-direction. In the present embodiment, the second plate side surfaces  15  are orthogonal to the y-direction. The first plate side surfaces  14  are orthogonal to the second plate side surfaces  15 . 
     The terahertz element  20  converts electromagnetic waves in the terahertz band and electrical energy to and from each other. It is considered that the electromagnetic wave includes concepts of one or both of light and radio waves. The terahertz element  20  converts received electrical energy into electromagnetic waves in the terahertz band. Thus, the terahertz element  20  oscillates the electromagnetic waves (i.e., terahertz waves). The frequency of the electromagnetic waves generated by the terahertz element  20  is, for example, 0.1 Thz to 10 Thz. 
     As shown in  FIG. 5 , the terahertz element  20  has the shape of a rectangular plate as viewed the z-direction (hereafter, also referred to as “in plan view”). In the present embodiment, the terahertz element  20  is square in plan view. The shape of the terahertz element  20  in plan view is not limited to a rectangle and may be a circle, an ellipse, or a polygon. 
     The terahertz element  20  includes an element main surface  21  and an element back surface  22 . The element main surface  21  and the element back surface  22  intersect the z-direction. In the present embodiment, the element main surface  21  and the element back surface  22  are orthogonal to the z-direction. The element main surface  21  and the element back surface  22  are rectangular, for example, square, as viewed in the z-direction. However, the shape of the element main surface  21  and the element back surface  22  is not limited to this and may be any shape. 
     As shown in  FIG. 4 , in the present embodiment, when the element back surface  22  is in contact with the mount main surface  12  or is opposed to the mount main surface  12  via an intermediate layer, the terahertz element  20  is attached to the mount plate  11 . That is, the mount plate  11  is configured to allow for attachment of the terahertz element  20 . The terahertz element  20  is mounted on the mount plate  11 . 
     The terahertz element  20  includes two first element side surfaces  23 , which are opposite end surfaces in the x-direction, and two second element side surfaces  24 , which are opposite end surfaces in the y-direction. The first element side surfaces  23  intersect the x-direction. In the present embodiment, the first element side surfaces  23  are orthogonal to the x-direction. The second element side surfaces  24  intersect the y-direction. In the present embodiment, the second element side surfaces  24  are orthogonal to the y-direction. The first element side surfaces  23  are orthogonal to the second element side surfaces  24 . 
       FIGS. 6 and 7  show an example of a detailed structure of the terahertz element  20 .  FIG. 6  is a schematic diagram showing an example of a cross section of the terahertz element  20 .  FIG. 7  is an enlarged partial view of  FIG. 6 . 
     As shown in  FIGS. 6 and 7 , the terahertz element  20  includes an element substrate  31 , an active element  32 , a first conductive layer  33 , and a second conductive layer  34 . 
     The element substrate  31  is formed of a semiconductor and is semi-insulating. The semiconductor forming the element substrate  31  is, for example, InP (indium phosphide) but may be a semiconductor other than InP. When the element substrate  31  is formed of InP, the refractive index (absolute refractive index) is approximately 3.4. In the present embodiment, the element substrate  31  is rectangular and is, for example, square in plan view. The element main surface  21  and the element back surface  22  are the main surface and the back surface of the element substrate  31 . The element side surfaces  23  and  24  are side surfaces of the element substrate  31 . 
     The active element  32  converts electromagnetic waves in the terahertz band and electrical energy to and from each other. The active element  32  is formed on the element substrate  31 . The active element  32  is typically a resonant tunneling diode (RTD). 
     The active element  32  may be, for example, a tunnel injection transit time (TUNNETT) diode, an impact ionization avalanche transit time (IMPATT) diode, a GaAs-base field effect transistor (FET), a GaN-base FET, a high electron mobility transistor (HEMT), or a heterojunction bipolar transistor (HBT). 
     An example of obtaining the active element  32  will be described. 
     A semiconductor layer  41   a  is formed on the element substrate  31 . The semiconductor layer  41   a  is formed of, for example, GaInAs. The semiconductor layer  41   a  is doped with an n-type impurity at a high concentration. 
     A GaInAs layer  42   a  is stacked on the semiconductor layer  41   a . The GaInAs layer  42   a  is doped with an n-type impurity. For example, the impurity concentration of the GaInAs layer  42   a  is lower than the impurity concentration of the semiconductor layer  41   a.    
     A GaInAs layer  43   a  is stacked on the GaInAs layer  42   a . The GaInAs layer  43   a  is not doped with impurities. 
     An AlAs layer  44   a  is stacked on the GaInAs layer  43   a . An InGaAs layer  45  is stacked on the AlAs layer  44   a . An AlAs layer  44   b  is stacked on the InGaAs layer  45 . The AlAs layer  44   a , the InGaAs layer  45 , and the AlAs layer  44   b  form an RTD unit. 
     A GaInAs layer  43   b  is not doped with impurities and is stacked on the AlAs layer  44   b . A GaInAs layer  42   b  is doped with an n-type impurity and is stacked on the GaInAs layer  43   b . A GaInAs layer  41   b  is stacked on the GaInAs layer  42   b . The GaInAs layer  41   b  is doped with an n-type impurity at a high concentration. For example, the impurity concentration of the GaInAs layer  41   b  is higher than the impurity concentration of the GaInAs layer  42   b.    
     The active element  32  may have any specific structure configured to generate electromagnetic waves (or receive electromagnetic waves or both generate and receive electromagnetic waves). In other words, the active element  32  may be configured to oscillate in electromagnetic waves of the terahertz band. 
     As shown in  FIG. 5 , the terahertz element  20  includes an oscillation point P 1  where oscillation of electromagnetic waves is performed. The oscillation point P 1  is formed on the element main surface  21 . The element main surface  21  that includes the oscillation point P 1  may be referred to as an active surface. Also, the oscillation point P 1  may refer to a position on which the active element  32  is disposed. 
     In the present embodiment, the oscillation point P 1  (the active element  32 ) is disposed at the center of the element main surface  21 . However, the position of the oscillation point P 1 , that is, the position of the active element  32  on the element main surface  21 , is not limited to the center of the element main surface  21  and may be any position. 
     In the present embodiment, it is preferred that a first perpendicular distance x 1  between the oscillation point P 1  and each first element side surface  23  is (λ′InP/2)+((λ′InP/2)×N) (N is an integer that is greater than or equal to 0: N=0, 1, 2, 3, . . . ). 
     λ′InP denotes an effective wavelength of an electromagnetic wave that transmits through the terahertz element  20 . When n1 denotes the refractive index of the terahertz element  20  (the element substrate  31 ), c denotes the speed of light, and fc denotes the center frequency of electromagnetic waves, λ′InP is (1/n1)×(c/fc). When the first perpendicular distance x 1  is set as described above, an electromagnetic wave oscillated by the terahertz element  20  performs a free end reflection on the first element side surface  23 . Thus, the terahertz element  20  itself is designed as a resonator (primary resonator/one-dimensional resonator) of the terahertz device  10 . 
     In the same manner, it is preferred that a second perpendicular distance y 1  between the oscillation point P 1  and each second element side surface  24  is (λ′InP/2)+((λ′InP/2)×N) (N is an integer that is greater than or equal to 0: N=0, 1, 2, 3, . . . ). 
     The perpendicular distances x 1  and y 1  may have different values for each of the element side surfaces  23  and  24  as long as the values are calculated by the above equation. Further, in  FIG. 5 , the first perpendicular distance x 1  from the oscillation point P 1  to the first element side surface  23  located at the right side may differ from the first perpendicular distance x 1  from the oscillation point P 1  to the first element side surface  23  located at the left side. Also, in  FIG. 5 , the second perpendicular distance y 1  from the oscillation point P 1  to the second element side surface  24  located at the upper side may differ from the second perpendicular distance y 1  from the oscillation point P 1  to the second element side surfaces  24  located at the lower side. 
     The dimension of the terahertz element  20  in the z-direction may be designed in accordance with, for example, the frequency of an oscillated electromagnetic wave. More specifically, the dimension of the terahertz element  20  in the z-direction is an integer multiple of ½ times a wavelength λ of the electromagnetic wave (i.e., λ/2). The electromagnetic wave performs free end reflection in the interface between the element substrate  31  and air. When the dimension of the terahertz element  20  in the z-direction is set as described above, standing waves having an aligned phase are excited in the terahertz element  20 . The dimension of the terahertz element  20  in the z-direction is decreased as the frequency of the electromagnetic wave becomes higher. The dimension in the z-direction is increased as the frequency of the electromagnetic wave becomes lower. 
     The structure of the terahertz element  20  is not limited to that described above. For example, a back reflector metal layer may be disposed on the element back surface  22 , which is located at the opposite side of the element substrate  31  from the element main surface  21  on which the active element  32  is disposed. In this case, the back reflector metal layer reflects an electromagnetic wave (electromagnetic wave) emitted from the active element  32 . 
     When the back reflector metal layer is arranged, the electromagnetic wave performs a fixed end reflection in the interface between the element substrate  31  and the back reflector metal layer. This results in a π phase shift. In this case, the dimension of the terahertz element  20  in the z-direction may be designed to be (λ/4)+(integer multiple of λ/2) using the wavelength λ of the electromagnetic wave. 
     In the present embodiment, electromagnetic waves generated from the oscillation point P 1  have directivity. As shown in  FIG. 4 , the electromagnetic waves generated from the oscillation point P 1  are radiated in the range of an opening angle θ. The opening angle θ is, for example, 120° to 180°. However, the opening angle θ is not limited to that described above and may be any angle. 
     The first conductive layer  33  and the second conductive layer  34  are formed on the element main surface  21 . The first conductive layer  33  and the second conductive layer  34  are insulated from each other. Each of the first conductive layer  33  and the second conductive layer  34  has a stacked structure of metals. The stacked structure of each of the first conductive layer  33  and the second conductive layer  34  is obtained by stacking, for example, gold (Au), palladium (Pd), and titanium (Ti). In another example, the stacked structure of each of the first conductive layer  33  and the second conductive layer  34  is obtained by stacking Au and Ti. The first conductive layer  33  and the second conductive layer  34  are formed through vacuum vapor deposition or sputtering. 
     As shown in  FIG. 6 , in the present embodiment, part of the first conductive layer  33  and part of the second conductive layer  34  are disposed at opposite sides of the active element  32  in the x-direction. The first conductive layer  33  includes a first connection region  33   a  overlapping the active element  32  in the z-direction. The first connection region  33   a  is disposed on the GaInAs layer  41   b  in contact with the GaInAs layer  41   b.    
     The semiconductor layer  41   a  extends further than other layers such as the GaInAs layer  42   a  toward the second conductive layer  34  in the x-direction. The second conductive layer  34  includes a second connection region  34   a  stacked on part of the semiconductor layer  41   a  where the GaInAs layer  42   a  and other layers are not stacked. Thus, the active element  32  is electrically connected to the first conductive layer  33  and the second conductive layer  34 . The second connection region  34   a  is spaced from the GaInAs layer  42   a  and other layers in the x-direction. 
     Although not shown in  FIG. 7 , alternatively, a GaInAs layer doped with an n-type impurity at a high concentration may be disposed between the GaInAs layer  41   b  and the first connection region  33   a . This may result in good contact of the first conductive layer  33  with the GaInAs layer  41   b.    
     As shown in  FIG. 5 , part of the first conductive layer  33  and part of the second conductive layer  34  form a dipole antenna. That is, in the terahertz element  20 , the antenna is integrated by part of the first conductive layer  33  and part of the second conductive layer  34  at the side of the element main surface  21 . Instead of a dipole antenna, another antenna such as a slot antenna, a biconical antenna, or a loop antenna may be used. Moreover, the antenna may be omitted. 
     In the present embodiment, the terahertz element  20  includes a metal insulator metal (MIM) reflector  35 . The MIM reflector  35  is formed by holding an insulator between part of the first conductive layer  33  and part of the second conductive layer  34  in the z-direction. The MIM reflector  35  is configured to short the part of the first conductive layer  33  and the part of the second conductive layer  34  at a high frequency. The MIM reflector  35  reflects a high-frequency electromagnetic wave. However, the MIM reflector  35  is not necessary and may be omitted. 
     As shown in  FIG. 5 , the first conductive layer  33  includes a first pad  33   b , and the second conductive layer  34  includes a second pad  34   b . The first pad  33   b  and the second pad  34   b  are spaced apart in the x-direction and insulated from each other. 
     As shown in  FIG. 2 , the antenna base  50  is, for example, rectangular-box-shaped as a whole. The antenna base  50  is formed of, for example, an insulative material. More specifically, the antenna base  50  is formed of a dielectric material, for example, a synthetic resin such as an epoxy resin. An example of the epoxy resin is a glass epoxy resin. However, the material of the antenna base  50  is not limited to this and may be any material, for example, Si, Teflon, or glass. 
     The antenna base  50  is disposed on the mount plate  11  at the mount main surface  12 , which is opposite the mount back surface  13 . The antenna base  50  is located opposing the mount plate  11 . Specifically, the antenna base  50  is opposed to the mount plate  11  via the lead frame  60  in the z-direction. The z-direction may be referred to as the opposing direction of the antenna base  50  and the mount plate  11 . 
     The antenna base  50  includes a base main surface  50   a  opposed to the mount main surface  12 , a base back surface  50   b  opposite the base main surface  50   a , and base side surfaces  51 . 
     The base main surface  50   a  and the base back surface  50   b  intersect the z-direction. In the present embodiment, the element main surface  21  and the element back surface  22  are orthogonal to the z-direction. The base main surface  50   a  and the base back surface  50   b  are, for example, rectangular (e.g., square). The base back surface  50   b  defines the bottom surface of the terahertz device  10 . 
     In the present embodiment, the base side surfaces  51  are surfaces of the terahertz device  10  (the antenna base  50 ) facing sideward. The base side surfaces  51  may be referred to as the end surfaces of the antenna base  50  facing in directions orthogonal to the opposing direction of the base main surface  50   a  and the base back surface  50   b . The base side surfaces  51  joins the base main surface  50   a  and the base back surface  50   b.    
     The present embodiment includes four base side surfaces  51 . Specifically, the base side surfaces  51  include a first base side surface  51   a  and a second base side surface  51   b , which are opposite end surfaces of the antenna base  50  in the x-direction, and a third base side surface  51   c  and a fourth base side surface  51   d , which are opposite end surfaces of the antenna base  50  in the y-direction. The first base side surface  51   a  and the second base side surface  51   b  intersect the x-direction. In the present embodiment, the first base side surface  51   a  and the second base side surface  51   b  are orthogonal to the x-direction. The third base side surface  51   c  and the fourth base side surface  51   d  intersect the y-direction. In the present embodiment, the third base side surface  51   c  and the fourth base side surface  51   d  are orthogonal to the y-direction. The first base side surface  51   a  and the second base side surface  51   b  are orthogonal to the third base side surface  51   c  and the fourth base side surface  51   d.    
     The antenna base  50  includes a recess  52  recessed with respect to the base main surface  50   a  in a direction away from the mount main surface  12 . The recess  52  is recessed from the base main surface  50   a  in a direction away from the mount main surface  12 , that is, downward. In the present embodiment, the recess  52  is semispherical as a whole. The recess  52  is filled with air. 
     The recess  52  is open upward. The opening of the recess  52  is circular as viewed in the z-direction. The opening of the recess  52  is closed by the mount plate  11 . In the present embodiment, the terahertz element  20  is accommodated in the recess  52 . 
     The recess  52  includes an antenna surface  53 . The antenna surface  53  is, for example, a curved surface projecting downward. The antenna surface  53  is formed in conformance with the shape of an antenna. For example, the antenna surface  53  is curved to be parabolic-antenna-shaped. The antenna surface  53  is circular as viewed from above. 
     As shown in  FIG. 4 , the reflection film  54  is formed on the antenna surface  53 . The reflection film  54  is formed of a material that reflects electromagnetic waves generated by the terahertz element  20 , for example, a metal such as Cu. In the present embodiment, the reflection film  54  is formed on the entire antenna surface  53 . The reflection film  54  is not formed on the base main surface  50   a.    
     The reflection film  54  is configured to reflect at least part of the electromagnetic waves received from the terahertz element  20  in one direction. In the present embodiment, the reflection film  54  reflects the electromagnetic waves received from the terahertz element  20  in the z-direction (specifically, upward). In other words, when electromagnetic waves are radiated in the range of the opening angle θ, the reflection film  54  is configured to guide the electromagnetic waves in one direction. 
     Specifically, the reflection film  54  is antenna-shaped. In the present embodiment, the antenna surface  53  is curved in conformance with the shape of an antenna. Accordingly, the reflection film  54  that is formed on the antenna surface  53  is shaped in conformance with the antenna. In the present embodiment, the reflection film  54  is parabolic-antenna-shaped. In other words, the reflection film  54  is a parabolic reflector. The reflection film  54  is circular as viewed in the z-direction. 
     The reflection film  54  and the mount plate  11  are opposed to each other in the z-direction. In other words, the mount plate  11  is located opposing the reflection film  54 . In the present embodiment, the mount plate  11  is located above the reflection film  54 . Thus, the electromagnetic waves reflected by the reflection film  54  are emitted upward transmitting through the mount plate  11 . 
     The reflection film  54  is not disposed at the side of the element back surface  22  but at the side of the element main surface  21 , where the oscillation point P 1  exists, and is opposed to the terahertz element  20  (in the present embodiment, the element main surface  21 ). The reflection film  54  is disposed, for example, so that the focal point of the reflection film  54  is the oscillation point P 1 . In the present embodiment, the reflection film  54  has a center point P 2  that coincides with the oscillation point P 1  as viewed in the z-direction. In the present embodiment, the center point P 2  is the center of the circular reflection film  54  as viewed in the z-direction. 
     It is preferred that the antenna surface  53  is curved so that the condition Z=(1/(4z 1 ))X 2  is satisfied when the perpendicular distance from the oscillation point P 1  to the reflection film  54  is referred to as a specified distance z 1 , the coordinate of the reflection film  54  in the z-direction is denoted by Z, and the position of the reflection film  54  in the x-direction is denoted by X. However, the curving aspect of the antenna surface  53  is not limited to this and may be any curving aspect. 
     The z-direction may be referred to as the opposing direction of the reflection film  54  and the terahertz element  20  (the element main surface  21 ) or the output direction of the electromagnetic waves of the terahertz device  10 . Further, the z-direction may be referred to as the opposing direction of the center point P 2  of the reflection film  54  and the oscillation point P 1 . The specified distance z 1  may be refer to as the distance between the oscillation point P 1  and the center point P 2 . 
     The reflection film  54  is disposed at a position corresponding to the frequency of electromagnetic waves generated from the terahertz element  20  so that the electromagnetic waves resonate. Specifically, the specified distance z 1  may be, for example, (λ′ A /4)+((λ′ A /2)×N) (N is an integer greater than or equal to 0) so that the resonance condition of the electromagnetic waves generated by the terahertz element  20  is satisfied. λ′ A  is (1/n A )(c/fc) (c: speed of light, fc: center frequency of oscillation) where n A  represents the refractive index of an object intervening between the oscillation point P 1  and the reflection film  54 . For example, when air is present between the oscillation point P 1  and the reflection film  54 , n A  is 1. fc may be a target frequency of the terahertz element  20  or the frequency having the maximum output among the electromagnetic waves generated from the terahertz element  20 . 
     As viewed in the z-direction, the distance between opposite ends of the reflection film  54  in the x-direction or the y-direction is referred to as the opening width of the reflection film  54 . In the present embodiment, since the reflection film  54  is formed on the entire antenna surface  53 , the opening width of the reflection film  54  is equal to the opening width of the recess  52 . The opening width of the recess  52  may be referred to as the diameter of the opening of the circular recess  52 . 
     The reflection film  54  is formed, for example, over an angle that is greater than or equal to the opening angle θ of the oscillation point P 1 . More specifically, when the oscillation point P 1  is the vertex, the antenna surface  53  is formed over an angle that is greater than or equal to the opening angle θ. As described above, in the present embodiment, the reflection film  54  is formed on the entire antenna surface  53 . In the present embodiment, the angle over which the reflection film  54  is formed with the oscillation point P 1  is greater than 180°. Therefore, in the present embodiment, the reflection film  54  reflects all of the electromagnetic waves emitted from the oscillation point P 1  within the range of the opening angle θ. 
     In the present embodiment, the dimension of the antenna base  50  in the z-direction is greater than the dimension of the mount plate  11  in the z-direction, that is, the thickness of the mount plate  11 . The dimension of the antenna base  50  in the x-direction is set to be equal to the dimension of the mount plate  11  in the x-direction. The dimension of the antenna base  50  in the y-direction is set to be equal to the dimension of the mount plate  11  in the y-direction. However, the antenna base  50  and the mount plate  11  may have any dimensional relationship. 
     As shown in  FIGS. 4 and 5 , the lead frame  60  is attached to the mount main surface  12  of the mount plate  11 . The lead frame  60  and the mount plate  11  are bonded to each other in tight contact and fixed so as not to be displaced from each other. 
     The lead frame  60  has the shape of, for example, a rectangular plate, the thickness-wise direction of which conforms to the z-direction. In the present embodiment, the lead frame  60  has a greater thickness than the mount plate  11 . In other words, in the present embodiment, the mount plate  11  has a smaller thickness than the lead frame  60 . 
     The lead frame  60  includes a first lead part  61  and a second lead part  71  that are insulated from each other. The first lead part  61  and the second lead part  71  are, for example, separated and opposed to each other in the x-direction and respectively include a first lead opposing surface  62  and a second lead opposing surface  72  that are separated and opposed to each other in the x-direction. In the present embodiment, the lead opposing surfaces  62  and  72  are orthogonal to the x-direction. In the present embodiment, the first lead part  61  and the second lead part  71  correspond to “first conductor” and “second conductor”. 
     As viewed in the z-direction, the first lead part  61  and the second lead part  71  extend sideward, in the present embodiment, in the x-direction, beyond the mount plate  11 . The dimension of the two lead parts  61  and  71  in the y-direction is set to be slightly less than the dimension of the mount plate  11  in the y-direction, for example, equal to the dimension of the antenna base  50  in the y-direction. In the present embodiment, the lead frame  60  is less likely to extend beyond the mount plate  11  in the y-direction. 
     The lead frame  60  is formed so as to avoid overlapping with the reflection film  54  (the recess  52 ) in the z-direction. More specifically, the lead frame  60  includes an opening  80  that overlaps at least a portion of the reflection film  54  as viewed in the z-direction. 
     The opening  80  includes, for example, a gap  81  extending between the two lead parts  61  and  71 , a first part opening  63  formed in the first lead part  61 , and a second part opening  73  formed in the second lead part  71 . 
     The gap  81  is slit-shaped and extends in the y-direction and includes a space between the lead opposing surfaces  62  and  72  and a space between the part openings  63  and  73 . 
     The first part opening  63  is formed in a portion of the first lead part  61  that overlaps the reflection film  54  as viewed in the z-direction. The second part opening  73  is formed in a portion of the second lead part  71  that overlaps the reflection film  54  in the z-direction. 
     The first part opening  63  and the second part opening  73  extend through in the z-direction to be continuous with the recess  52 . The first part opening  63  and the second part opening  73  are separated by the gap  81  and opposed to each other in the x-direction. The two part openings  63  and  73  are open in the x-direction. The first part opening  63  is open toward the second lead part  71 . The second part opening  73  is open toward the first lead part  61 . Thus, the two part openings  63  and  73  are continuous with the gap  81 . 
     Each of the first part opening  63  and the second part opening  73  is semicircular as viewed in the z-direction. The first part opening  63  and the second part opening  73  form a single circular hole. In other words, the terahertz element  20  is located in the center of the circle formed by the part openings  63  and  73 . The diameter of the circle formed by the part openings  63  and  73  may be, for example, greater than or equal to the opening width of the reflection film  54 . 
     The first lead part  61  includes a first inner surface  64 , which is the wall surface of the first part opening  63 . The first inner surface  64  is recessed from the first lead opposing surface  62  in a direction away from the second lead opposing surface  72 . 
     The second lead part  71  includes a second inner surface  74 , which is the wall surface of the second part opening  73 . The second inner surface  74  is recessed from the second lead opposing surface  72  in a direction away from the first lead opposing surface  62 . 
     The first inner surface  64  and the second inner surface  74  are curved to project away from each other. The two inner surfaces  64  and  74 , for example, extend along the outer side of an end  54   a  of the reflection film  54 , that is, the opening edge of the recess  52 , to avoid overlapping of the two lead parts  61  and  71  with the reflection film  54 . 
     As shown in  FIG. 5 , in the present embodiment, the first lead part  61  includes a first connector  65  configured to be electrically connected to the terahertz element  20 . In the present embodiment, the first connector  65  is a portion of the first lead part  61  that projects toward the terahertz element  20  from where the first lead part  61  does not overlap the recess  52  (i.e., the reflection film  54 ) as viewed in the z-direction. More specifically, the first connector  65  is a projection piece projecting from the first inner surface  64  toward the terahertz element  20 . The first connector  65  overlaps the reflection film  54  as viewed in the z-direction. The first connector  65  and the first pad  33   b  are connected by a first wire W 1 . Thus, the first lead part  61  is electrically connected to the terahertz element  20 . 
     In the present embodiment, the projection dimension of the first connector  65  from the first inner surface  64  is less than the length of the first wire W 1  as viewed in the z-direction. The projection dimension is, for example, less than ¼ of the opening width of the reflection film  54 . 
     In the same manner, in the present embodiment, the second lead part  71  includes a second connector  75  configured to be electrically connected to the terahertz element  20 . In the present embodiment, the second connector  75  is a portion of the second lead part  71  that projects toward the terahertz element  20  from where the second lead part  71  does not overlap the recess  52  (i.e., the reflection film  54 ) as viewed in the z-direction. More specifically, the second connector  75  is a projection piece projecting from the second inner surface  74  toward the terahertz element  20 . The second connector  75  overlaps the recess  52  (i.e., the reflection film  54 ) as viewed in the z-direction. The second connector  75  and the second pad  34   b  are connected by a second wire W 2 . Thus, the second lead part  71  is electrically connected to the terahertz element  20 . 
     In the present embodiment, the projection dimension of the second connector  75  from the second inner surface  74  is less than the length of the second wire W 2  as viewed in the z-direction. The projection dimension is, for example, less than ¼ of the opening width of the reflection film  54 . 
     In the present embodiment, the first connector  65  and the second connector  75  are opposed to each other at opposite sides of the terahertz element  20 . For example, the two connectors  65  and  75  are symmetrically arranged in the x-direction. In other words, the two connectors  65  and  75  are shifted 180° from each other as viewed in the z-direction. 
     As shown in  FIG. 4 , the terahertz device  10  includes an adhesive layer  90  that adheres the antenna base  50  to the lead frame  60 . The adhesive layer  90  is formed of, for example, an insulative material and includes, for example, a resin adhesive agent. The adhesive layer  90  is disposed between the base main surface  50   a  of the antenna base  50  and the lead frame  60 . The antenna base  50  is adhered to the lead frame  60  by the adhesive layer  90 . This unitizes the mount plate  11 , the lead frame  60 , and the antenna base  50 . More specifically, the mount plate  11 , that is, the base member, and the antenna base  50  are unitized so as not to be displaced from each other. Accordingly, the terahertz element  20 , which is mounted on the mount plate  11 , and the reflection film  54 , which is formed on the antenna base  50 , are unitized so as not to be displaced from each other. 
     The adhesive layer  90  is disposed between the reflection film  54  and the lead frame  60 . The adhesive layer  90  hinders electrical connection of the reflection film  54  with the lead frame  60 . As described above, the reflection film  54  is not electrically connected to the antenna base  50  and the lead frame  60  and is electrically isolated. 
     In particular, in the present embodiment, the inner peripheral end of the adhesive layer  90  extends inward (i.e., toward the terahertz element  20 ) beyond the reflection film  54 . Thus, the reflection film  54  is less likely to circumvent the adhesive layer  90  and contact the lead frame  60 . The inner peripheral end of the adhesive layer  90  may be referred to as the end of the adhesive layer  90  located close to the terahertz element  20 . The inner peripheral end of the adhesive layer  90  is, for example, circular in conformance with the recess  52  as viewed in the z-direction. However, the inner peripheral end of the adhesive layer  90  may have any shape and may be rectangular. 
     The terahertz element  20  and the reflection film  54  are accommodated in an accommodation space A 1  defined by the mount plate  11  and the recess  52 . In the present embodiment, the accommodation space A 1  is defined by the mount main surface  12  and the antenna surface  53 . In the present embodiment, the accommodation space A 1  is hermetically sealed by the adhesive layer  90  and other components. Air exists in the accommodation space A 1 . 
     As shown in  FIGS. 3 to 5 , the terahertz device  10  includes a first electrode  94  and a second electrode  101  used for electrical connection with an external device. In the present embodiment, the first electrode  94  and the second electrode  101  are obtained by bending the lead frame  60  along the antenna base  50 . 
     More specifically, the first lead part  61  extends from the first base side surface  51   a  to an outer side of the antenna base  50  and is bent along the antenna base  50  to reach the base back surface  50   b . The first electrode  94  is formed by the above-described bent portion of the first lead part  61 . 
     The first electrode  94  includes a first proximal portion  94   a , a first bent portion  94   b  (or curved portion), and a first distal portion  94   c . The first proximal portion  94   a  is bent toward the first base side surface  51   a  at the corner of the first base side surface  51   a  and the base main surface  50   a . The first bent portion  94   b  is bent at the corner of the first base side surface  51   a  and the base back surface  50   b . The first distal portion  94   c  is disposed on the base back surface  50   b . The first electrode  94  is L-shaped as viewed in the y-direction and extends over the first base side surface  51   a  and the base back surface  50   b.    
     The first electrode  94  includes a first side electrode  95  formed on the first base side surface  51   a  and a first back electrode  93  formed on the base back surface  50   b . The first side electrode  95  is part of the first electrode  94  extending from the first proximal portion  94   a  to the first bent portion  94   b  and is formed on the entire first base side surface  51   a . The first back electrode  93  is part of the first electrode  94  extending from the first bent portion  94   b  to the first distal portion  94   c.    
     In the same manner, the second lead part  71  extends from the second base side surface  51   b  to an outer side of the antenna base  50  and is bent along the antenna base  50  to reach the base back surface  50   b . The second electrode  101  is formed by the above-described bent portion of the second lead part  71 . 
     The second electrode  101  includes a second proximal portion  101   a , a second bent portion  101   b  (or curved portion), and a second distal portion  101   c . The second proximal portion  101   a  is bent toward the second base side surface  51   b  at the corner of the second base side surface  51   b  and the base main surface  50   a . The second bent portion  101   b  is bent at the corner of the second base side surface  51   b  and the base back surface  50   b . The second distal portion  101   c  is disposed on the base back surface  50   b . The second electrode  101  is L-shaped as viewed in the y-direction and extends over the second base side surface  51   b  and the base back surface  50   b.    
     The second electrode  101  includes a second side electrode  102  formed on the second base side surface  51   b  and a second back electrode  103  formed on the base back surface  50   b . The second side electrode  102  is part of the second electrode  101  extending from the second proximal portion  101   a  to the second bent portion  101   b  and is formed on the entire second base side surface  51   b . The second back electrode  103  is part of the second electrode  101  extending from the second bent portion  101   b  to the second distal portion  101   c.    
     In the present embodiment, the two electrodes  94  and  101  are symmetrically at the left side and the right side. The first distal portion  94   c  and the second distal portion  101   c  are separated in the x-direction. This ensures insulation between the electrodes  94  and  101 . 
     Each of the two electrodes  94  and  101  has a width in the y-direction that is set to be equal to the dimension of the antenna base  50  in the y-direction. However, the width of the two electrodes  94  and  101  is not limited to this and may be changed in any manner. For example, the width of the two electrodes  94  and  101  may be less than the dimension of the antenna base  50  in the y-direction. 
     As described above, the dimension of the antenna base  50  in the z-direction is greater than the thickness of the mount plate  11 . In addition, the dimension of the antenna base  50  in the z-direction is greater than the sum of the thickness of the mount plate  11  and the thickness of the lead frame  60 . The lead frame  60 , which is disposed between the antenna base  50  and the mount plate  11 , is disposed at an upper part of the terahertz device  10 . Thus, the first proximal portion  94   a  and the second proximal portion  101   a  are disposed at an upper part of the terahertz device  10 . 
     More specifically, when the z-direction is the thickness-wise direction of the terahertz device  10 , the first proximal portion  94   a  and the second proximal portion  101   a  are located upward from the center of the terahertz device  10  in the thickness-wise direction (in other words, toward the mount plate  11  or at the side where electromagnetic waves are output). 
     As shown in  FIG. 4 , the terahertz device  10  is mounted, for example, on a circuit substrate  113  on which a wiring pattern  114  is formed. More specifically, the terahertz device  10  is configured to be installed so that the base back surface  50   b  is opposed to the circuit substrate  113 . When the back electrodes  93  and  103  are bonded to the wiring pattern  114  by a conductive bonding member  115  such as solder, the terahertz device  10  is mounted on the circuit substrate  113 . 
     A method for manufacturing the terahertz device  10  of the present embodiment will now be described. To simplify the description, a method for manufacturing one terahertz device  10  will first be described. 
     As shown in  FIG. 8 , the method for manufacturing the terahertz device  10  includes a step of forming the lead frame  60 . In this step, the first lead part  61  including the first part opening  63  and the first connector  65  is formed, and the second lead part  71  including the second part opening  73  and the second connector  75  is formed. 
     As shown in  FIG. 9 , the method for manufacturing the terahertz device  10  includes a step of forming the mount plate  11 . In this step, the mount plate  11  is formed so as to extend over the two lead parts  61  and  71 . Any specific process for forming the mount plate  11  may be used. 
     As shown in  FIG. 10 , the method for manufacturing the terahertz device  10  subsequently includes a step of mounting the terahertz element  20  on the mount plate  11 . In this step, the terahertz element  20  is mounted on a surface of the mount plate  11  on which the lead frame  60  is formed. This unitizes the lead frame  60 , the mount plate  11 , and the terahertz element  20 . 
     As shown in  FIG. 11 , the method for manufacturing the terahertz device  10  includes a step of electrically connecting the terahertz element  20  and the two lead parts  61  and  71  using the two wires W 1  and W 2 . In this step, the first wire W 1  is bonded to the first pad  33   b  and the first lead part  61 , and the second wire W 2  is bonded to the second pad  34   b  and the second lead part  71 . The bonding order may be determined in any manner. 
     As shown in  FIG. 12 , the method for manufacturing the terahertz device  10  includes a step of forming the recess  52  in the antenna base  50 . In this step, molds that are formed in conformance with the antenna surface  53  are used to form the recess  52  having the antenna surface  53 . 
     As shown in  FIG. 13 , the method for manufacturing the terahertz device  10  includes a step of forming a metal film forming the reflection film  54 , which is performed after the recess  52  is formed. In this step, the metal layer is formed on both the base main surface  50   a  and the antenna surface  53 . 
     As shown in  FIG. 14 , the method for manufacturing the terahertz device  10  includes a step of removing the metal film from the base main surface  50   a . Any specific process for removing the metal film from the base main surface  50   a  may be used. For example, the metal film may be removed by patterning or an abrasive process. As a result, the metal film is formed on only the antenna surface  53  as the reflection film  54 . 
     The step of forming the metal film is not limited to the above-described steps. For example, the method for manufacturing the terahertz device  10  may include a step of masking the base main surface  50   a  and a step of forming a metal film on the antenna surface  53  by vapor deposition using electron beams. This case eliminates the need for the step of removing the metal film from the base main surface  50   a.    
     As shown in  FIG. 15 , the method for manufacturing the terahertz device  10  includes a step of coupling the unitized body of the lead frame  60 , the mount plate  11 , and the terahertz element  20  to the antenna base  50  on which the reflection film  54  is formed. In this step, the adhesive layer  90  is used to adhere the antenna base  50  and the lead frame  60 . 
     As shown in  FIG. 16 , the method for manufacturing the terahertz device  10  subsequently includes a first bending step of bending the lead frame  60 . In the first bending step, the lead frame  60  (the two lead parts  61  and  71 ), which projects sideward from the antenna base  50 , is bent at the corners of the antenna base  50  so as to extend along the base side surfaces  51   a  and  51   b  of the antenna base  50 . This forms the side electrodes  95  and  102 . 
     As shown in  FIG. 17 , the method for manufacturing the terahertz device  10  subsequently includes a second bending step of further bending the lead frame  60 . In the second bending step, the lead frame  60 , which projects upward from the antenna base  50 , is bent at the corners of the antenna base  50  so as to extend along the base back surface  50   b  of the antenna base  50 . This forms the bent portions  94   b  and  101   b  and the back electrodes  93  and  103 . As a result, the terahertz device  10  is formed. 
     To simplify the description, the method for manufacturing one terahertz device  10  has been described above. However, practically, a plurality of terahertz devices  10  may be simultaneously manufactured. 
     For example, as shown in  FIG. 18 , a metal plate  111 , including a plurality of lead frames  60  and including punched-out portions corresponding to the openings  80 , is prepared. A plurality of mount plates  11  and a plurality of terahertz elements  20  are mounted on the metal plate  111 . The metal plate  111  is punched out along the ends of the lead frames  60  in the y-direction to form first through holes  111   a . The first through holes  111   a  are, for example, slit-shaped and extend from opposite sides of the mount plate  11  in the x-direction by an amount corresponding to the two electrodes  94  and  101 . 
     Meanwhile, as shown in  FIG. 19 , a base body  112 , in which the recesses  52  and the reflection films  54  are formed, is prepared. Second through holes  112   a  are formed in portions of the base body  112  corresponding to where the lead frames  60  are exposed. The second through holes  112   a  are formed in portions opposed to the electrodes  94  and  101  when the metal plate  111  is adhered to the base body  112 . The metal plate  111 , which includes the mount plates  11  and the terahertz elements  20 , and the base body  112  are positioned and adhered to each other by an adhesive. Subsequently, the metal plate  111  and the base body  112  are cut by dicing. Then, the lead frames  60  are bent. This manufactures a plurality of terahertz devices  10 . 
     The metal plate  111  may include first positioning portions  111   b , and the base body  112  may include second positioning portions  112   b . When adhering the metal plate  111  to the base body  112 , the metal plate  111  and the base body  112  may be positioned so that the first positioning portions  111   b  overlap the second positioning portions  112   b.    
     Operation of the present embodiment will now be described. 
     When electromagnetic waves are generated from the oscillation point P 1  of the terahertz element  20 , the reflection film  54  reflects and emits the electromagnetic waves in one direction. 
     In addition, in the present embodiment, the two electrodes  94  and  101  are formed on the base back surface  50   b , which defines the bottom surface of the terahertz device  10 . This allows the terahertz device  10  to be mounted on the circuit substrate  113  with an orientation so that the base back surface  50   b  faces the circuit substrate  113 . Thus, the terahertz device  10  is readily mounted on the circuit substrate  113 . 
     The present embodiment, which has been described above, has the following advantages. 
     (1-1) The terahertz device  10  includes the mount plate  11  used as the base member, the terahertz element  20  mounted on the mount plate  11 , the antenna base  50  located opposing the mount plate  11  and including the antenna surface  53 , and the reflection film  54  formed on the antenna surface  53 . The reflection film  54  reflects at least part of electromagnetic waves generated by the terahertz element  20  in one direction (for example, upward). With this structure, electromagnetic waves generated by the terahertz element are emitted in one direction. This increases the output of the electromagnetic waves emitted from the terahertz device  10 . Thus, the gain of the terahertz device  10  is improved. 
     (1-2) The terahertz device  10  includes the electrodes  94  and  101  used for electrical connection with an external device. The electrodes  94  and  101  include the side electrodes  95  and  102 , which are formed on the base side surfaces  51   a  and  51   b , and the back electrodes  93  and  103 , which are formed on the base back surface  50   b . With this structure, the side electrodes  95  and  102  or the back electrodes  93  and  103  are electrically connected to the wiring pattern  114  of the circuit substrate  113  in a relatively easy manner. Thus, the terahertz device  10  is readily mounted on the circuit substrate  113 . 
     (1-3) The electrodes  94  and  101  are obtained by bending the lead frame  60  along the antenna base  50 . In this structure, the lead frame  60 , which is relatively easy to bend, is used as the electrodes  94  and  101 . Thus, the side electrodes  95  and  102  and the back electrodes  93  and  103  are readily formed. In addition, the bending of the lead frame  60  along the antenna base  50  limits sideward projection of the lead frame  60 . As a result, the terahertz device  10  is reduced in size in the x-direction. 
     (1-4) The first electrode  94  includes the first proximal portion  94   a , the first bent portion  94   b , and the first distal portion  94   c . The first proximal portion  94   a  is bent toward the first base side surface  51   a  at the corner of the first base side surface  51   a  and the base main surface  50   a . The first bent portion  94   b  is bent at the corner of the first base side surface  51   a  and the base back surface  50   b . The first distal portion  94   c  is disposed on the base back surface  50   b . The first side electrode  95  extends from the first proximal portion  94   a  to the first bent portion  94   b . The first back electrode  93  extends from the first bent portion  94   b  to the first distal portion  94   c.    
     In the same manner, the second electrode  101  includes the second proximal portion  101   a , the second bent portion  101   b , and the second distal portion  101   c . The second proximal portion  101   a  is bent toward the second base side surface  51   b  at the corner of the second base side surface  51   b  and the base main surface  50   a . The second bent portion  101   b  is bent at the corner of the second base side surface  51   b  and the base back surface  50   b . The second distal portion  101   c  is disposed on the base back surface  50   b . The second side electrode  102  extends from the second proximal portion  101   a  to the second bent portion  101   b . The second back electrode  103  extends from the second bent portion  101   b  to the second distal portion  101   c.    
     With this structure, the side electrodes  95  and  102  and the back electrodes  93  and  103  are obtained by bending the lead frame  60  at each corner of the antenna base  50  used as a support point. Thus, the side electrodes  95  and  102  and the back electrodes  93  and  103  are relatively easily formed. 
     (1-5) The two distal portions  94   c  and  101   c  are separate from each other in the x-direction. This structure ensures insulation of the two electrodes  94  and  101 . 
     (1-6) The terahertz element  20  includes the element main surface  21 , which includes the oscillation point P 1  configured to generate electromagnetic waves, and the element back surface  22 , which is opposite the element main surface  21 . The reflection film  54  is disposed at the side of the element main surface  21 , not at the side of the element back surface  22 . In this structure, electromagnetic waves readily reach the reflection film  54 . Thus, the reflection film  54  is appropriately used to reflect electromagnetic waves generated from the oscillation point P 1 . 
     (1-7) The terahertz element  20  radiates electromagnetic waves from the oscillation point P 1  in the range of the opening angle θ. The reflection film  54  is formed over an angle that is greater than or equal to the opening angle θ of the oscillation point P 1 . With this structure, the electromagnetic waves radiated from the oscillation point P 1  in the range of the opening angle θ are reflected by the reflection film  54 . This reduces electromagnetic waves that are not reflected by the reflection film  54 , thereby improving the gain. 
     (1-8) The reflection film  54  is parabolic-antenna-shaped. With this structure, electromagnetic waves are appropriately reflected in one direction. 
     (1-9) The reflection film  54  is disposed so that the focal point of the reflection film  54  is located at the oscillation point P 1 . With this structure, electromagnetic waves generated from the oscillation point P 1  are guided in one direction by the reflection film  54 . This reduces electromagnetic waves that are not reflected in one direction by the reflection film  54 , thereby improving the gain. 
     (1-10) The reflection film  54  is disposed at a position corresponding to the frequency of electromagnetic waves generated by the terahertz element  20  so that the electromagnetic waves resonate. In an example, the specified distance z 1 , which is the perpendicular distance from the oscillation point P 1  toward the reflection film  54 , is set to satisfy the resonance condition of the electromagnetic waves, for example, (λ′ A /4)+((λ′ A /2)×N). This structure improves the gain of the terahertz device  10 . 
     (1-11) The reflection film  54  is electrically isolated. This structure obviates disadvantages such as absorption of electromagnetic waves by the reflection film  54 . 
     (1-12) The antenna base  50  is formed of an insulative material. This structure limits electrical connection of the reflection film  54  with another member via the antenna base  50 . 
     (1-13) The mount plate  11 , which is used as the base member, includes the mount main surface  12  on which the terahertz element  20  is mounted. The antenna base  50  includes the base main surface  50   a , which is opposed to the mount main surface  12 , and the recess  52 , which is recessed from the base main surface  50   a  and includes the antenna surface  53 . The terahertz element  20  and the reflection film  54  are disposed in the accommodation space A 1  defined by the mount main surface  12  and the antenna surface  53 . This structure reduces external effects on the terahertz element  20  and the reflection film  54 . 
     (1-14) The reflection film  54  is formed on the antenna surface  53  but is not formed on the base main surface  50   a . This structure obviates reflection of electromagnetic waves by the reflection film  54  formed on the base main surface  50   a . Thus, disadvantages caused by unwanted reflection waves, for example, the occurrence of standing waves, are limited. 
     (1-15) The lead frame  60 , which is used as a conductive member, is disposed on the mount main surface  12 . The antenna base  50  is adhered to the lead frame  60  by the adhesive layer  90 . The adhesive layer  90  is formed from an insulative material and is disposed between the reflection film  54  and the lead frame  60 . In this structure, the adhesive layer  90  restricts contact of the reflection film  54  with the lead frame  60 . Thus, electrical connection of the reflection film  54  with the lead frame  60  is hindered. 
     (1-16) The lead frame  60  includes the opening  80  overlapping at least a portion of the reflection film  54  as viewed in the z-direction. In this structure, electromagnetic waves reflected by the reflection film  54  are output through the opening  80 . This limits interruption of electromagnetic waves by the lead frame  60 . 
     (1-17) The lead frame  60  includes the first lead part  61  and the second lead part  71 , which are separated and opposed to each other. The opening  80  includes the gap  81  between the two lead parts  61  and  71 . This structure limits interruption (blocking) of electromagnetic waves by the lead frame  60  while ensuring the insulation properties of the two lead parts  61  and  71 . 
     (1-18) The opening  80  includes the first part opening  63  formed in a portion of the first lead part  61  that overlaps the reflection film  54  as viewed in the z-direction and is continuous with the gap  81 . The opening  80  includes the second part opening  73  formed in a portion of the second lead part  71  that overlaps the reflection film  54  as viewed in the z-direction and is continuous with the gap  81 . In this structure, the interruption of electromagnetic waves by the lead frame  60  is further limited. 
     (1-19) The first lead part  61  includes the first connector  65  configured to be electrically connected to the terahertz element  20 . The first connector  65  projects from the first inner surface  64 , which is the wall surface of the first part opening  63 , toward the terahertz element  20  and overlaps the reflection film  54  as viewed in the z-direction. The second lead part  71  includes the second connector  75  configured to be electrically connected to the terahertz element  20 . The second connector  75  projects from the second inner surface  74 , which is the wall surface of the second part opening  73 , toward the terahertz element  20  and overlaps the reflection film  54  as viewed in the z-direction. In this structure, while limiting interruption of electromagnetic waves by the lead frame  60 , the two lead parts  61  and  71  are electrically connected to the terahertz element  20 . 
     (1-20) The terahertz device  10  includes the first wire W 1  and the second wire W 2 . The first wire W 1  connects the first connector  65  to the first pad  33   b  formed on the terahertz element  20 , The second wire W 2  connects the second connector  75  to the second pad  34   b  formed on the terahertz element  20 . As viewed in the z-direction, the projection dimension of the first connector  65  from the first inner surface  64  is less than the length of the first wire W 1 . With this structure, interruption of electromagnetic waves by the first connector  65  is limited as the projection dimension of the first connector  65  is decreased. In the same manner, as viewed in the z-direction, the projection dimension of the second connector  75  from the second inner surface  74  may be less than the length of the second wire W 2 . 
     (1-21) The two connectors  65  and  75  are opposed to each other at opposite sides of the terahertz element  20 . In this structure, the two wires W 1  and W 2  are less likely to interfere with each other. Thus, contact of the two wires W 1  and W 2  is avoided. 
     Modified Example of First Embodiment 
     As shown in  FIG. 20 , the terahertz device  10  may include a reflection reduction film  120  formed on the mount back surface  13 . The reflection reduction film  120  may refer to a reflection prevention film or an anti-reflection (AR) coating film. 
     For example, the reflection reduction film  120  may be formed on at least a portion of the part of the mount back surface  13  overlapping the lead frame  60  as viewed in the z-direction. In an example, the reflection reduction film  120  is formed on the entirety of the part of the mount back surface  13  overlapping the lead frame  60  as viewed in the z-direction. This limits the occurrence of standing waves caused by reflection of electromagnetic waves at the lead frame  60 . Any specific structure of the reflection reduction film  120  may be used as long as reflection of electromagnetic waves in at least the terahertz band is reduced. 
     Second Embodiment 
     As shown in  FIG. 21 , the present embodiment of a terahertz device  10  includes protection diodes  131  and  132 , which are an example of a specific element that is electrically connected to the terahertz element  20 . The protection diodes  131  and  132  are electrically connected to the terahertz element  20 . In the present embodiment, the protection diodes  131  and  132  are connected to the terahertz element  20  in parallel. The two protection diodes  131  and  132  are connected to the terahertz element  20  in opposite directions. The protection diodes  131  and  132  may be general diodes or Zener diodes, Schottky diodes, or light emitting diodes. 
     The specific element is not limited to the protection diodes  131  and  132  and may be a control integrated circuit (IC) (e.g., application-specific integrated circuit (ASIC)). The control IC may be configured to, for example, detect current flowing to the terahertz element  20 , serve as an amplifier, supply power to the terahertz element  20 , or process signals. The specific element may be connected to the terahertz element  20  in any mode and may be, for example, connected in series. 
     As shown in  FIGS. 22 and 23 , the two protection diodes  131  and  132  are opposed to each other at opposite sides of the terahertz element  20 . The two protection diodes  131  and  132  are mounted on the lead frame  60 . 
     More specifically, the first protection diode  131  is disposed on the first lead part  61  and electrically connected to the first lead part  61 . The first protection diode  131  is disposed, for example, near the first part opening  63  on the first lead part  61 . In the present embodiment, the first protection diode  131  is disposed in a region surrounded by the first inner surface  64 , the first lead opposing surface  62 , and the end surface of the first lead part  61  in the y-direction. 
     The first protection diode  131  and the second lead part  71  are electrically connected by a first diode wire W 3 . Thus, the first protection diode  131  is electrically connected to the two electrodes  94  and  101 . 
     The first diode wire W 3  is bonded to the second lead part  71  at a position close to the first protection diode  131 , that is, a region defined by the second inner surface  74 , the second lead opposing surface  72 , and the end surface of the second lead part  71  in the y-direction. This reduces the length of the first diode wire W 3 . 
     In the same manner, the second protection diode  132  is disposed on the second lead part  71  and electrically connected to the second lead part  71 . The second protection diode  132  is disposed, for example, near the second part opening  73  on the second lead part  71 . In the present embodiment, the second protection diode  132  is disposed in a region surrounded by the second inner surface  74 , the second lead opposing surface  72 , and the end surface of the second lead part  71  in the y-direction. 
     The second protection diode  132  and the first lead part  61  are electrically connected by a second diode wire W 4 . Thus, the second protection diode  132  is electrically connected to the two electrodes  94  and  101 . 
     The second diode wire W 4  is bonded to the first lead part  61  at a position closet to the second protection diode  132 , that is, a region surrounded by the first inner surface  64 , the first lead opposing surface  62 , and the end surface of the first lead part  61  in the y-direction. This reduces the length of the second diode wire W 4 . 
     As shown in  FIG. 23 , in the present embodiment, the antenna base  50  includes receptacles  141  and  142  that are recessed from the base main surface  50   a . The protection diodes  131  and  132  are accommodated in the receptacles  141  and  142 . The receptacles  141  and  142  are formed around the recess  52  so as not to be continuous with the recess  52 . That is, the receptacles  141  and  142  are arranged separately from the recess  52  to accommodate the specific elements. As shown in  FIG. 23 , the adhesive layer  90  is not formed on locations corresponding to the receptacles  141  and  142 . 
     The present embodiment, which has been described above, has the following operational advantages. 
     (2-1) The terahertz device  10  includes the protection diodes  131  and  132  connected to the terahertz element  20  in parallel. With this structure, for example, when static electricity causes to a high voltage to be applied to opposite ends of the terahertz element  20 , current flows through the protection diodes  131  and  132 . Thus, an excessive current flowing to the terahertz element  20  is limited, so that the terahertz element  20  is protected. 
     (2-2) The two protection diodes  131  and  132  are connected to the terahertz element  20  in opposite directions. With this structure, the terahertz element  20  is protected from a high voltage produced in each direction. 
     (2-3) The antenna base  50  includes the receptacles  141  and  142  recessed from the base main surface  50   a . The protection diodes  131  and  132  are accommodated in the receptacles  141  and  142 . This structure limits increases in the size of the terahertz device  10  caused by arrangement of the protection diodes  131  and  132 . 
     Modified Examples 
     In each embodiment, the terahertz device  10  may be modified, for example, as follows. The modified examples described below may be combined with one another as long as there is no technical inconsistency. For the sake of convenience, the following modified examples will be basically described using the first embodiment. However, other embodiments may be used as long as there is no technical inconsistency. 
     As shown in  FIG. 24 , the terahertz device  10  may include a spacer  200  that is different from the adhesive layer  90  to insulate the reflection film  54  from the lead frame  60 . The spacer  200  is insulative. The spacer  200  is also disposed between the reflection film  54  and the lead frame  60 . In  FIG. 24 , the spacer  200  is disposed between the lead frame  60  and the adhesive layer  90 . However, alternatively, the spacer  200  may be disposed between the antenna base  50  and the adhesive layer  90 . 
     In this configuration, contact of the reflection film  54  with the lead frame  60  is restricted by the spacer  200  and the adhesive layer  90 . Thus, the contact of the reflection film  54  with the lead frame  60  is further restricted. 
     As shown in  FIG. 25 , the first connector  65  and the second connector  75  may extend to the vicinity of the terahertz element  20 . For example, the distal portion of the first connector  65  may be located closer to the terahertz element  20  than to the first inner surface  64 , and the distal portion of the second connector  75  may be located closer to the terahertz element  20  than to the second inner surface  74 . In other words, the projection dimension of each of the two connectors  65  and  75  may be greater than ¼ of the opening width of the reflection film  54 . 
     In addition, as viewed in the z-direction, the length of the first wire W 1  may be less than the projection dimension of the first connector  65  from the first inner surface  64 . In the same manner, the length of the second wire W 2  may be less than the projection dimension of the second connector  75  from the second inner surface  74 . In this structure, the length of the wires W 1  and W 2  is decreased, thereby limiting adverse effects on the responsiveness caused by the wires W 1  and W 2 . 
     As shown in  FIG. 26 , the first connector  65  and the second connector  75  may be arranged parallel to each other. This structure improves the responsiveness of the terahertz device  10 . 
     The first connector  65  and the second connector  75  may be omitted. 
     As shown in  FIGS. 27 and 28 , the lead frame  60  may be used as the base member on which the terahertz element  20  is mounted. Specifically, the lead frame  60  may include a mount base  210  on which the terahertz element  20  is mounted, a first connector  211  joined to the mount base  210 , and a second connector  212  insulated from the first connector  211 . The first connector  211  is electrically connected to the first pad  33   b  by the first wire W 1 . The second connector  212  is electrically connected to the second pad  34   b  by the second wire W 2 . 
     In addition, the lead frame  60  may include a first curved portion  213  extending from the first connector  211  along the outer side of the opening edge of the recess  52  and a second curved portion  214  extending from the second connector  212  along the outer side of the opening edge of the recess  52 . 
     In this modified example, as shown in  FIG. 28 , the terahertz device  10  may include a cover member  215  covering the mount base  210  and the two connectors  211  and  212  from above. The cover member  215  may be formed of a material transmissive to electromagnetic waves, for example, a dielectric. 
     As shown in  FIG. 29 , the recess  52  may include a large diameter surface  221  having a larger diameter than the antenna surface  53  and a stepped surface  222  formed between the antenna surface  53  and the large diameter surface  221 . The stepped surface  222  intersects the z-direction. In this structure, a reflection film  223  may be formed over the antenna surface  53  and the stepped surface  222 . In this case, the reflection film  223  and the lead frame  60  are separate in the z-direction and thus are not likely to contact each other. 
     As shown in  FIG. 30 , a reflection film  224  may be formed on a portion of the antenna surface  53 . For example, the reflection film  224  may be formed on a portion located below the oscillation point P 1 . The reflection film  224  may be formed over an angle that is less than the opening angle θ of the oscillation point P 1 . Any reflection film that reflects at least part of electromagnetic waves generated by the terahertz element  20  in one direction may be used. 
     The shape of the reflection film may be changed. For example, the reflection film is not limited to a single film and may include a plurality of separate parts. For example, a slit and/or a hole may be formed in the reflection film. 
     As shown in  FIG. 31 , the antenna base  50  may be configured to be disposed at the side of the mount back surface  13 . In this case, the mount plate  11  is disposed between the lead frame  60  and the reflection film  54 , so that contact of the reflection film  54  with the lead frame  60  is avoided. However, considering the point that the terahertz element  20  is accommodated in the accommodation space A 1 , it is more preferred that the antenna base  50  is disposed at the side of the mount main surface  12 . 
     As shown in  FIG. 32 , the lead opposing surfaces  62  and  72  may be inclined from the y-direction. In this case, the gap  81  diagonally extend with respect to the y-direction. 
     In this structure, when the protection diodes  131  and  132  are arranged as in the second embodiment, at least a portion of the first protection diode  131  may be disposed between the first inner surface  64  and the first lead opposing surface  62 . Also, at least a portion of the second protection diode  132  may be disposed between the second inner surface  74  and the second lead opposing surface  72 . 
     As shown in  FIG. 33 , the terahertz element  20  may be disposed so that the oscillation point P 1  is located at a position separate from the center point P 2  of the reflection film  54  as viewed from above. That is, the focal point of the reflection film  54  does not have to coincide with oscillation point P 1 . 
     As shown in  FIG. 34 , the terahertz device  10  may be of a multi-reflector type including a reflector  300  disposed separately from the reflection film  54 . 
     Specifically, the terahertz device  10  includes the reflector  300  in addition to the reflection film  54 . More specifically, the mount main surface  12  includes a reflection protrusion  301 , and a metal film is formed on the surface of the reflection protrusion  301  to form the reflector  300 . In accordance with the curve of the reflection protrusion  301  protruding toward the reflection film  54 , the reflector  300  is curved to protrude toward the reflection film  54 . The reflector  300  and the reflection film  54  are radially opposed to each other. Electromagnetic waves reflected by the reflector  300  are emitted toward the reflection film  54 . 
     In the present modified example, the terahertz element  20  is located opposing the reflector  300 . In other words, the mount plate  11 , which is used as the base member including the reflector  300 , is located opposing the terahertz element  20 . 
     The terahertz device  10  includes, for example, mount poles  302  and  303 . The mount poles  302  and  303  are formed of, for example, a conductive material. The mount poles  302  and  303  extend through the antenna base  50  and the reflection film  54  from below and enter the accommodation space A 1 . The terahertz element  20  is mounted on the mount poles  302  and  303 . The terahertz element  20  is electrically connected to the mount poles  302  and  303 . 
     The terahertz element  20  may be bonded to the mount poles  302  and  303  directly or by a conductive bonding member. In addition, to avoid contact of the mount poles  302  and  303  with the reflection film  54 , an insulator (e.g., insulation coating) may be disposed on side surfaces of the mount poles  302  and  303 . In this modified example, the mount poles  302  and  303  are two. However, the number of mount poles  302  and  303  may be any number. 
     In this modified example, the terahertz device  10  includes electrodes  304  and  305  electrically connected to the mount poles  302  and  303 . The electrodes  304  and  305  are formed on the base back surface  50   b , which is a side of the antenna base  50  opposite from the base main surface  50   a , and are joined to the mount poles  302  and  303 . 
     In this modified example, when a voltage is applied from the both electrodes  304  and  305 , electromagnetic waves are generated by the terahertz element  20 . The electromagnetic waves are reflected by the reflector  300  and then further reflected by the reflection film  54  and are emitted upward, which corresponds to one direction. That is, the electromagnetic waves generated by the terahertz element  20  are emitted to the reflection film  54  via the reflector  300  and further reflected by the reflection film  54 . 
     More specifically, the reflector  300  is configured to receive electromagnetic waves generated by the terahertz element  20  and reflect at least part of the electromagnetic waves. The reflection film  54  is configured to receive the electromagnetic waves reflected by the reflector  300  and reflect at least part of the electromagnetic waves in one direction (upward). 
     In this modified example, the lead frame  60  and the two wires W 1  and W 2  are not formed on the mount plate  11 . The reflector  300  may be disposed, for example, within a projection range of the terahertz element  20  as viewed from above. This limits interruption (blocking) of the electromagnetic waves. 
     As shown in  FIG. 34 , the reflection film  54  includes through holes  306 , through which the mount poles  302  and  303  are inserted. The through holes  306  may be greater in size than the mount poles  302  and  303  to avoid contact of the reflection film  54  with the mount poles  302  and  303 . The portion of the reflection film  54  located between the mount poles  302  and  303  may be omitted. That is, as viewed from above, the reflection film  54  may be annular with the central portion removed. The reflector  300  may be recessed with respect to the terahertz element  20 . Specifically, the reflector  300  may be shaped as an antenna that is recessed in the opposite direction of the reflection film  54  (i.e., upward). More specifically, the reflector  300  may be a Cassegrain type or a Gregorian type. 
     The shape of the antenna base  50  may be changed. For example, as shown in  FIG. 35 , the antenna base  50  may be chamfered and dome-shaped. Specifically, in this modified example, the antenna base  50  may include inclined surfaces  311  and  312  formed between the base back surface  50   b  and the base side surfaces  51   a  and  51   b . The first inclined surface  311  intersects both the first base side surface  51   a  and the base back surface  50   b . The second inclined surface  312  intersects both the second base side surface  51   b  and the base back surface  50   b.    
     In this case, the first electrode  94  may be formed along the first base side surface  51   a , the first inclined surface  311 , and the base back surface  50   b . The second electrode  101  may be formed along the second base side surface  51   b , the second inclined surface  312 , and the base back surface  50   b.    
     As shown in  FIG. 36 , the inner peripheral end of the adhesive layer  90  may be flush with the surface of the reflection film  54 . That is, the adhesive layer  90  may be configured not to extend inward (in other words, toward the terahertz element  20 ) beyond the reflection film  54 . 
     As shown in  FIGS. 37 and 38 , the inner peripheral end of the adhesive layer  90  may be located outward from the surface of the reflection film  54  (in other words, toward the base side surfaces  51 ) in the x-direction and the y-direction. For example, as shown in  FIG. 37 , the inner peripheral end of the adhesive layer  90  may be flush with the antenna surface  53 . Alternatively, as shown in  FIG. 38 , the inner peripheral end of the adhesive layer  90  may be located outward from the antenna surface  53  in the x-direction and the y-direction. In this case, the adhesive layer  90  is not disposed between the end  54   a  of the reflection film  54  and the lead frame  60 . In other words, the adhesive layer  90  does not necessarily have to be disposed between the reflection film  54  and the lead frame  60 . Even in this case, the reflection film  54  is separated from the lead frame  60  by the height of the adhesive layer  90 , so that contact of the reflection film  54  with the lead frame  60  is limited. 
     When the terahertz device  10  is electrically connected to the wiring pattern  114  using the side electrodes  95  and  102 , the terahertz device  10  may be mounted on the circuit substrate  113 . Specifically, the conductive bonding member  115  may be arranged to connect the side electrodes  95  and  102  to the wiring pattern  114 . 
     The electrodes  94  and  101  may be formed using a conductive member other than the lead frame  60 . 
     Inclined surfaces may be arranged between the base main surface  50   a  and the base side surfaces  51   a  and  51   b . In this case, the inclined surfaces correspond to the corners between the base main surface  50   a  and the base side surfaces  51   a  and  51   b.    
     The terahertz element  20  may be disposed so that the element back surface  22  faces the reflection film  54 . That is, the reflection film  54  may be disposed at the side of the element back surface  22  of the terahertz element  20 , not at the side of the element main surface  21 . 
     The reflection film  54  does not have to be electrically isolated. 
     The reflection film  54  may be formed on the base main surface  50   a . In this case, for example, a reflection reduction film may be located opposing the base main surface  50   a.    
     The gas existing in the accommodation space A 1  is not limited to air and may be changed in any manner. Moreover, the accommodation space A 1  may be vacuum. 
     The antenna base  50  and the lead frame  60  may be unitized by a process other than adhesion. 
     The shape of the opening  80  may be changed in any manner. For example, one of the part openings  63  and  73  may be omitted. The part openings  63  and  73  may be smaller than the reflection film  54 . 
     The mount plate  11 , which is used as the base member, may have any shape. For example, the mount plate  11  may have a greater thickness than the lead frame  60 . 
     The electrodes  94  and  101  may extend from the proximity of the center of the terahertz device  10  in the z-direction or may extend from below the center of the terahertz device  10 . The side electrodes  95  and  102  are not limited to the disposition on the first base side surface  51   a  and the second base side surface  51   b  and may be disposed on the third base side surface  51   c  and the fourth base side surface  51   d.    
     In other words, the two electrodes  94  and  101  may be disposed on opposite sides of the antenna base  50  in the x-direction or the y-direction. The first electrode  94  may be formed over the first base side surface  51   a  and the third base side surface  51   c . The second electrode  101  may be formed in the same manner. 
     The specific structure of the terahertz element  20  may be changed. For example, the position and size of the two pads  33   b  and  34   b  may be changed. The oscillation point P 1  may be located at a position other than the center. 
     The terahertz element  20  may be configured to receive electromagnetic waves and convert the received electromagnetic waves into electrical energy. Specifically, the terahertz element  20  receives electromagnetic waves, for example, in the range of the opening angle θ of the oscillation point P 1 . In this case, the oscillation point P 1  may be referred to as a reception point that receives electromagnetic waves. 
     In this structure, the reflection film may reflect the incident electromagnetic waves toward the terahertz element  20  (preferably, the reception point). This increases the reception strength of the terahertz device  10 , thereby improving the gain related to reception. 
     Moreover, the terahertz element  20  may be configured to oscillate and receive electromagnetic waves. That is, the oscillation point P 1  may perform at least one of oscillation and reception of electromagnetic waves. 
     When the terahertz element  20  is configured to receive electromagnetic waves, the reflector  300  of the modified example reflects electromagnetic waves reflected by the reflection film  54  toward the terahertz element  20 . In this structure, the electromagnetic waves reflected by the reflection film  54  are emitted via the reflector  300  to the terahertz element  20 . More specifically, the reflection film  54  is configured to reflect at least part of the incident electromagnetic waves toward the reflector  300 . The reflector  300  is configured to receive the electromagnetic waves reflected by the reflection film  54  and emit at least part of the electromagnetic waves toward the terahertz element  20 . 
     Third Embodiment 
       FIGS. 39 to 45  show a third embodiment of a terahertz device  10  according to the present disclosure. The terahertz device  10  of the third embodiment includes a mount plate  11  used as a base member, a terahertz element  20  configured to generate an electromagnetic wave, an antenna base  50 , a reflection film  54 , and a lead frame  60  used as an electrode and a conductive member. 
       FIGS. 39 and 40  are perspective views of the terahertz device  10 .  FIG. 41  is a top view of the terahertz device  10 .  FIG. 42  is an end view taken along line  4 - 4  in  FIG. 41 .  FIG. 43  is a lower view of the terahertz device  10  and a front view of the terahertz element  20  and the lead frame  60  with the antenna base  50  removed. 
     The mount plate  11  is formed of a material transmissive to electromagnetic waves generated by the terahertz element  20 . In the present embodiment, the mount plate  11  is formed of a dielectric material, for example, a synthetic resin such as an epoxy resin or an intrinsic semiconductor such as a single crystal of silicon (Si). An example of the epoxy resin is a glass epoxy resin. However, the material of the mount plate  11  is not limited to those described above and may be any material, for example, Teflon (registered trademark) or glass. The mount plate  11  is insulative. 
     The mount plate  11  is, for example, rectangular. For the sake of brevity, the thickness-wise direction of the mount plate  11  is referred to as the z-direction. Two directions that are orthogonal to each other and the z-direction are referred to as the x-direction and the y-direction. 
     As shown in  FIGS. 41 and 42 , the mount plate  11  includes a mount main surface  12  and a mount back surface  13 , which are plate surfaces intersecting the thickness-wise direction of the mount plate  11 . The mount main surface  12  and the mount back surface  13  are flat and rectangular. The mount main surface  12  and the mount back surface  13  extend in the x-direction and the y-direction and are separate from each other in the z-direction. The shapes of the mount main surface  12  and the mount back surface  13  are not limited to a rectangle and may be a circle, an ellipse, or a polygon. For the sake of brevity, in the present embodiment, a direction extending away from the mount back surface  13  in the z-direction is referred to as “upward”, and a direction extending away from the mount main surface  12  in the z-direction is referred to as “downward”. 
     As shown in  FIG. 43 , in the present embodiment, the mount plate  11  includes two first plate side surfaces  14 , which are opposite end surfaces in the x-direction, and two second plate side surfaces  15 , which are opposite end surfaces in the y-direction. The first plate side surfaces  14  intersect the x-direction. In the present embodiment, the first plate side surfaces  14  are orthogonal to the x-direction. The second plate side surfaces  15  intersect the y-direction. In the present embodiment, the second plate side surfaces  15  are orthogonal to the y-direction. The first plate side surfaces  14  are orthogonal to the second plate side surfaces  15 . 
     The terahertz element  20  converts electromagnetic waves in the terahertz band and electrical energy to and from each other. It is considered that the electromagnetic wave includes concepts of one or both of light and radio waves. The terahertz element  20  converts received electrical energy into electromagnetic waves in the terahertz band. Thus, the terahertz element  20  oscillates the electromagnetic waves (i.e., terahertz waves). The frequency of the electromagnetic waves generated by the terahertz element  20  is, for example, 0.1 Thz to 10 Thz. 
     As shown in  FIG. 43 , the terahertz element  20  has the shape of a rectangular plate as viewed the z-direction (hereafter, also referred to as “in plan view”). In the present embodiment, the terahertz element  20  is square in plan view. The shape of the terahertz element  20  in plan view is not limited to a rectangle and may be a circle, an ellipse, or a polygon. 
     The terahertz element  20  includes an element main surface  21  and an element back surface  22 . The element main surface  21  and the element back surface  22  intersect the z-direction. In the present embodiment, the element main surface  21  and the element back surface  22  are orthogonal to the z-direction. The element main surface  21  and the element back surface  22  are rectangular, for example, square, as viewed in the z-direction. However, the shape of the element main surface  21  and the element back surface  22  is not limited to this and may be any shape. 
     As shown in  FIG. 42 , in the present embodiment, when the element back surface  22  is in contact with the mount main surface  12  or is opposed to the mount main surface  12  via an intermediate layer, the terahertz element  20  is attached to the mount plate  11 . That is, the mount plate  11  is configured to allow for attachment of the terahertz element  20 . The terahertz element  20  is mounted on the mount plate  11 . 
     The terahertz element  20  includes two first element side surfaces  23 , which are opposite end surfaces in the x-direction, and two second element side surfaces  24 , which are opposite end surfaces in the y-direction. The first element side surfaces  23  intersect the x-direction. In the present embodiment, the first element side surfaces  23  are orthogonal to the x-direction. The second element side surfaces  24  intersect the y-direction. In the present embodiment, the second element side surfaces  24  are orthogonal to the y-direction. The first element side surfaces  23  are orthogonal to the second element side surfaces  24 . 
       FIGS. 44 and 45  show an example of a detailed structure of the terahertz element  20 .  FIG. 44  is a schematic diagram showing an example of a cross section of the terahertz element  20 .  FIG. 45  is an enlarged partial view of  FIG. 44 . 
     As shown in  FIGS. 44 and 45 , the terahertz element  20  includes an element substrate  31 , an active element  32 , a first conductive layer  33 , and a second conductive layer  34 . 
     The element substrate  31  is formed of a semiconductor and is semi-insulating. The semiconductor forming the element substrate  31  is, for example, InP (indium phosphide) but may be a semiconductor other than InP. When the element substrate  31  is formed of InP, the refractive index (absolute refractive index) is approximately 3.4. In the present embodiment, the element substrate  31  is rectangular and is, for example, square in plan view. The element main surface  21  and the element back surface  22  are the main surface and the back surface of the element substrate  31 . The element side surfaces  23  and  24  are side surfaces of the element substrate  31 . 
     The active element  32  converts electromagnetic waves in the terahertz band and electrical energy to and from each other. The active element  32  is formed on the element substrate  31 . The active element  32  is typically a resonant tunneling diode (RTD). 
     The active element  32  may be, for example, a tunnel injection transit time (TUNNETT) diode, an impact ionization avalanche transit time (IMPATT) diode, a GaAs-base field effect transistor (FET), a GaN-base FET, a high electron mobility transistor (HEMT), or a heterojunction bipolar transistor (HBT). 
     An example of obtaining the active element  32  will be described. A semiconductor layer  41   a  is formed on the element substrate  31 . The semiconductor layer  41   a  is formed of, for example, GaInAs. The semiconductor layer  41   a  is doped with an n-type impurity at a high concentration. 
     A GaInAs layer  42   a  is stacked on the semiconductor layer  41   a . The GaInAs layer  42   a  is doped with an n-type impurity. For example, the impurity concentration of the GaInAs layer  42   a  is lower than the impurity concentration of the semiconductor layer  41   a.    
     A GaInAs layer  43   a  is stacked on the GaInAs layer  42   a . The GaInAs layer  43   a  is not doped with impurities. 
     An AlAs layer  44   a  is stacked on the GaInAs layer  43   a . An InGaAs layer  45  is stacked on the AlAs layer  44   a . An AlAs layer  44   b  is stacked on the InGaAs layer  45 . The AlAs layer  44   a , the InGaAs layer  45 , and the AlAs layer  44   b  form an RTD unit. 
     A GaInAs layer  43   b  is not doped with impurities and is stacked on the AlAs layer  44   b . A GaInAs layer  42   b  is doped with an n-type impurity and is stacked on the GaInAs layer  43   b . A GaInAs layer  41   b  is stacked on the GaInAs layer  42   b . The GaInAs layer  41   b  is doped with an n-type impurity at a high concentration. For example, the impurity concentration of the GaInAs layer  41   b  is higher than the impurity concentration of the GaInAs layer  42   b.    
     The active element  32  may have any specific structure configured to generate electromagnetic waves (or receive electromagnetic waves or both generate and receive electromagnetic waves). In other words, the active element  32  may be configured to oscillate in electromagnetic waves of the terahertz band. 
     As shown in  FIG. 43 , the terahertz element  20  includes an oscillation point P 1  where oscillation of electromagnetic waves is performed. The oscillation point P 1  is formed on the element main surface  21 . The element main surface  21  that includes the oscillation point P 1  may be referred to as an active surface. Also, the oscillation point P 1  may refer to a position on which the active element  32  is disposed. 
     In the present embodiment, the oscillation point P 1  (the active element  32 ) is disposed at the center of the element main surface  21 . However, the position of the oscillation point P 1 , that is, the position of the active element  32  on the element main surface  21 , is not limited to the center of the element main surface  21  and may be any position. 
     In the present embodiment, it is preferred that a first perpendicular distance x 1  between the oscillation point P 1  and each first element side surface  23  is (λ′InP/2)+((λ′InP/2)×N) (N is an integer that is greater than or equal to 0: N=0, 1, 2, 3, . . . ). 
     λ′InP denotes an effective wavelength of an electromagnetic wave that transmits through the terahertz element  20 . When n1 denotes the refractive index of the terahertz element  20  (the element substrate  31 ), c denotes the speed of light, and fc denotes the center frequency of electromagnetic waves, λ′InP is (1/n1)×(c/fc). When the first perpendicular distance x 1  is set as described above, an electromagnetic wave oscillated by the terahertz element  20  performs a free end reflection on the first element side surface  23 . Thus, the terahertz element  20  itself is designed as a resonator (primary resonator/one-dimensional resonator) of the terahertz device  10 . 
     In the same manner, it is preferred that a second perpendicular distance y 1  between the oscillation point P 1  and each second element side surface  24  is (λ′InP/2)+((λ′InP/2)×N) (N is an integer that is greater than or equal to 0: N=0, 1, 2, 3, . . . ). 
     The perpendicular distances x 1  and y 1  may have different values for each of the element side surfaces  23  and  24  as long as the values are calculated by the above equation. Further, in  FIG. 43 , the first perpendicular distance x 1  from the oscillation point P 1  to the first element side surface  23  located at the right side may differ from the first perpendicular distance x 1  from the oscillation point P 1  to the first element side surface  23  located at the left side. Also, in  FIG. 43 , the second perpendicular distance y 1  from the oscillation point P 1  to the second element side surface  24  located at the upper side may differ from the second perpendicular distance y 1  from the oscillation point P 1  to the second element side surfaces  24  located at the lower side. 
     The dimension of the terahertz element  20  in the z-direction may be designed in accordance with, for example, the frequency of an oscillated electromagnetic wave. More specifically, the dimension of the terahertz element  20  in the z-direction is an integer multiple of ½ times a wavelength λ of the electromagnetic wave (i.e., λ/2). The electromagnetic wave performs free end reflection in the interface between the element substrate  31  and air. When the dimension of the terahertz element  20  in the z-direction is set as described above, standing waves having an aligned phase are excited in the terahertz element  20 . The dimension of the terahertz element  20  in the z-direction is decreased as the frequency of the electromagnetic wave becomes higher. The dimension in the z-direction is increased as the frequency of the electromagnetic wave becomes lower. 
     The structure of the terahertz element  20  is not limited to that described above. For example, a back reflector metal layer may be disposed on the element back surface  22 , which is located at the opposite side of the element substrate  31  from the element main surface  21  on which the active element  32  is disposed. In this case, the back reflector metal layer reflects an electromagnetic wave (electromagnetic wave) emitted from the active element  32 . 
     When the back reflector metal layer is arranged, the electromagnetic wave performs a fixed end reflection in the interface between the element substrate  31  and the back reflector metal layer. This results in a π phase shift. In this case, the dimension of the terahertz element  20  in the z-direction may be designed to be (λ/4)+(integer multiple of λ/2) using the wavelength λ of the electromagnetic wave. 
     In the present embodiment, electromagnetic waves generated from the oscillation point P 1  have directivity. As shown in  FIG. 42 , the electromagnetic waves generated from the oscillation point P 1  are radiated in the range of an opening angle θ. The opening angle θ is, for example, 120° to 180°. However, the opening angle θ is not limited to that described above and may be any angle. 
     The first conductive layer  33  and the second conductive layer  34  are formed on the element main surface  21 . The first conductive layer  33  and the second conductive layer  34  are insulated from each other. Each of the first conductive layer  33  and the second conductive layer  34  has a stacked structure of metals. The stacked structure of each of the first conductive layer  33  and the second conductive layer  34  is obtained by stacking, for example, gold (Au), palladium (Pd), and titanium (Ti). In another example, the stacked structure of each of the first conductive layer  33  and the second conductive layer  34  is obtained by stacking Au and Ti. The first conductive layer  33  and the second conductive layer  34  are formed through vacuum vapor deposition or sputtering. 
     As shown in  FIG. 44 , in the present embodiment, part of the first conductive layer  33  and part of the second conductive layer  34  are disposed at opposite sides of the active element  32  in the x-direction. The first conductive layer  33  includes a first connection region  33   a  overlapping the active element  32  in the z-direction. The first connection region  33   a  is disposed on the GaInAs layer  41   b  in contact with the GaInAs layer  41   b.    
     The semiconductor layer  41   a  extends further than other layers such as the GaInAs layer  42   a  toward the second conductive layer  34  in the x-direction. The second conductive layer  34  includes a second connection region  34   a  stacked on part of the semiconductor layer  41   a  where the GaInAs layer  42   a  and other layers are not stacked. Thus, the active element  32  is electrically connected to the first conductive layer  33  and the second conductive layer  34 . The second connection region  34   a  is spaced from the GaInAs layer  42   a  and other layers in the x-direction. 
     Although not shown in  FIG. 45 , alternatively, a GaInAs layer doped with an n-type impurity at a high concentration may be disposed between the GaInAs layer  41   b  and the first connection region  33   a . This may result in good contact of the first conductive layer  33  with the GaInAs layer  41   b.    
     As shown in  FIG. 43 , part of the first conductive layer  33  and part of the second conductive layer  34  form a dipole antenna. That is, in the terahertz element  20 , the antenna is integrated by part of the first conductive layer  33  and part of the second conductive layer  34  at the side of the element main surface  21 . Instead of a dipole antenna, another antenna such as a slot antenna, a biconical antenna, or a loop antenna may be used. Moreover, the antenna may be omitted. 
     In the present embodiment, the terahertz element  20  includes a metal insulator metal (MIM) reflector  35 . The MIM reflector  35  is formed by holding an insulator between part of the first conductive layer  33  and part of the second conductive layer  34  in the z-direction. The MIM reflector  35  is configured to short the part of the first conductive layer  33  and the part of the second conductive layer  34  at a high frequency. The MIM reflector  35  reflects a high-frequency electromagnetic wave. However, the MIM reflector  35  is not necessary and may be omitted. 
     As shown in  FIG. 43 , the first conductive layer  33  includes a first pad  33   b , and the second conductive layer  34  includes a second pad  34   b . The first pad  33   b  and the second pad  34   b  are spaced apart in the x-direction and insulated from each other. 
     As shown in  FIG. 40 , the antenna base  50  is, for example, rectangular-box-shaped as a whole. The antenna base  50  is formed of, for example, an insulative material. More specifically, the antenna base  50  is formed of a dielectric material, for example, a synthetic resin such as an epoxy resin. An example of the epoxy resin is a glass epoxy resin. However, the material of the antenna base  50  is not limited to this and may be any material, for example, Si, Teflon, or glass. 
     The antenna base  50  is disposed on the mount plate  11  at the mount main surface  12 , which is opposite the mount back surface  13 . The antenna base  50  is located opposing the mount plate  11 . Specifically, the antenna base  50  is opposed to the mount plate  11  via the lead frame  60  in the z-direction. The z-direction may be referred to as the opposing direction of the antenna base  50  and the mount plate  11 . 
     The antenna base  50  includes a base main surface  50   a  opposed to the mount main surface  12 , a base back surface  50   b  opposite the base main surface  50   a , and base side surfaces  51 . 
     The base main surface  50   a  and the base back surface  50   b  intersect the z-direction. In the present embodiment, the element main surface  21  and the element back surface  22  are orthogonal to the z-direction. The base main surface  50   a  and the base back surface  50   b  are, for example, rectangular (e.g., square). The base back surface  50   b  defines the bottom surface of the terahertz device  10 . 
     In the present embodiment, the base side surfaces  51  are surfaces of the terahertz device  10  (the antenna base  50 ) facing sideward. The base side surfaces  51  may be referred to as the end surfaces of the antenna base  50  facing in directions orthogonal to the opposing direction of the base main surface  50   a  and the base back surface  50   b . The base side surfaces  51  joins the base main surface  50   a  and the base back surface  50   b.    
     The present embodiment includes four base side surfaces  51 . Specifically, the base side surfaces  51  include a first base side surface  51   a  and a second base side surface  51   b , which are opposite end surfaces of the antenna base  50  in the x-direction, and a third base side surface  51   c  and a fourth base side surface  51   d , which are opposite end surfaces of the antenna base  50  in the y-direction. The first base side surface  51   a  and the second base side surface  51   b  intersect the x-direction. In the present embodiment, the first base side surface  51   a  and the second base side surface  51   b  are orthogonal to the x-direction. The third base side surface  51   c  and the fourth base side surface  51   d  intersect the y-direction. In the present embodiment, the third base side surface  51   c  and the fourth base side surface  51   d  are orthogonal to the y-direction. The first base side surface  51   a  and the second base side surface  51   b  are orthogonal to the third base side surface  51   c  and the fourth base side surface  51   d.    
     The antenna base  50  includes a recess  52  recessed with respect to the base main surface  50   a  in a direction away from the mount main surface  12 . The recess  52  is recessed from the base main surface  50   a  in a direction away from the mount main surface  12 , that is, downward. In the present embodiment, the recess  52  is semispherical as a whole. The recess  52  is filled with air. 
     The recess  52  is open upward. The opening of the recess  52  is circular as viewed in the z-direction. The opening of the recess  52  is closed by the mount plate  11 . In the present embodiment, the terahertz element  20  is accommodated in the recess  52 . 
     The recess  52  includes an antenna surface  53 . The antenna surface  53  is, for example, a curved surface projecting downward. The antenna surface  53  is formed in conformance with the shape of an antenna. For example, the antenna surface  53  is curved to be parabolic-antenna-shaped. The antenna surface  53  is circular as viewed from above. 
     As shown in  FIG. 42 , the reflection film  54  is formed on the antenna surface  53 . The reflection film  54  is formed of a material that reflects electromagnetic waves generated by the terahertz element  20 , for example, a metal such as Cu. In the present embodiment, the reflection film  54  is formed on the entire antenna surface  53 . The reflection film  54  is not formed on the base main surface  50   a.    
     The reflection film  54  is configured to reflect at least part of the electromagnetic waves received from the terahertz element  20  in one direction. In the present embodiment, the reflection film  54  reflects the electromagnetic waves received from the terahertz element  20  in the z-direction (specifically, upward). In other words, when electromagnetic waves are radiated in the range of the opening angle θ, the reflection film  54  is configured to guide the electromagnetic waves in one direction. 
     Specifically, the reflection film  54  is antenna-shaped. In the present embodiment, the antenna surface  53  is curved in conformance with the shape of an antenna. Accordingly, the reflection film  54  that is formed on the antenna surface  53  is shaped in conformance with the antenna. In the present embodiment, the reflection film  54  is parabolic-antenna-shaped. In other words, the reflection film  54  is a parabolic reflector. The reflection film  54  is circular as viewed in the z-direction. 
     The reflection film  54  and the mount plate  11  are opposed to each other in the z-direction. In other words, the mount plate  11  is located opposing the reflection film  54 . In the present embodiment, the mount plate  11  is located above the reflection film  54 . Thus, the electromagnetic waves reflected by the reflection film  54  are emitted upward transmitting through the mount plate  11 . 
     The reflection film  54  is not disposed at the side of the element back surface  22  but at the side of the element main surface  21 , where the oscillation point P 1  exists, and is opposed to the terahertz element  20  (in the present embodiment, the element main surface  21 ). The reflection film  54  is disposed, for example, so that the focal point of the reflection film  54  is the oscillation point P 1 . In the present embodiment, the reflection film  54  has a center point P 2  that coincides with the oscillation point P 1  as viewed in the z-direction. In the present embodiment, the center point P 2  is the center of the circular reflection film  54  as viewed in the z-direction. 
     It is preferred that the antenna surface  53  is curved so that the condition Z=(1/(4z 1 ))X 2  is satisfied when the perpendicular distance from the oscillation point P 1  to the reflection film  54  is referred to as a specified distance z 1 , the coordinate of the reflection film  54  in the z-direction is denoted by Z, and the position of the reflection film  54  in the x-direction is denoted by X. However, the curving aspect of the antenna surface  53  is not limited to this and may be any curving aspect. 
     The z-direction may be referred to as the opposing direction of the reflection film  54  and the terahertz element  20  (the element main surface  21 ) or the output direction of the electromagnetic waves of the terahertz device  10 . Further, the z-direction may be referred to as the opposing direction of the center point P 2  of the reflection film  54  and the oscillation point P 1 . The specified distance z 1  may be refer to as the distance between the oscillation point P 1  and the center point P 2 . 
     The reflection film  54  is disposed at a position corresponding to the frequency of electromagnetic waves generated from the terahertz element  20  so that the electromagnetic waves resonate. Specifically, the specified distance z 1  may be, for example, (λ′ A /4)+((λ′ A /2)×N) (N is an integer greater than or equal to 0) so that the resonance condition of the electromagnetic waves generated by the terahertz element  20  is satisfied. λ′ A  is (1/n A )(c/fc) (c: speed of light, fc: center frequency of oscillation) where n A  represents the refractive index of an object intervening between the oscillation point P 1  and the reflection film  54 . For example, when air is present between the oscillation point P 1  and the reflection film  54 , n A  is 1. fc may be a target frequency of the terahertz element  20  or the frequency having the maximum output among the electromagnetic waves generated from the terahertz element  20 . 
     As viewed in the z-direction, the distance between opposite ends of the reflection film  54  in the x-direction or the y-direction is referred to as the opening width of the reflection film  54 . In the present embodiment, since the reflection film  54  is formed on the entire antenna surface  53 , the opening width of the reflection film  54  is equal to the opening width of the recess  52 . The opening width of the recess  52  may be referred to as the diameter of the opening of the circular recess  52 . 
     The reflection film  54  is formed, for example, over an angle that is greater than or equal to the opening angle θ of the oscillation point P 1 . More specifically, when the oscillation point P 1  is the vertex, the antenna surface  53  is formed over an angle that is greater than or equal to the opening angle θ. As described above, in the present embodiment, the reflection film  54  is formed on the entire antenna surface  53 . In the present embodiment, the angle over which the reflection film  54  is formed with the oscillation point P 1  is greater than 180°. Therefore, in the present embodiment, the reflection film  54  reflects all of the electromagnetic waves emitted from the oscillation point P 1  within the range of the opening angle θ. 
     In the present embodiment, the dimension of the antenna base  50  in the z-direction is greater than the dimension of the mount plate  11  in the z-direction, that is, the thickness of the mount plate  11 . The dimension of the antenna base  50  in the x-direction is set to be equal to the dimension of the mount plate  11  in the x-direction. The dimension of the antenna base  50  in the y-direction is set to be equal to the dimension of the mount plate  11  in the y-direction. However, the antenna base  50  and the mount plate  11  may have any dimensional relationship. 
     As shown in  FIGS. 42 and 43 , the lead frame  60  is attached to the mount main surface  12  of the mount plate  11 . The lead frame  60  and the mount plate  11  are bonded to each other in tight contact and fixed so as not to be displaced from each other. 
     The lead frame  60  has the shape of, for example, a rectangular plate, the thickness-wise direction of which conforms to the z-direction. In the present embodiment, the lead frame  60  has a greater thickness than the mount plate  11 . In other words, in the present embodiment, the mount plate  11  has a smaller thickness than the lead frame  60 . 
     The lead frame  60  includes a first lead part  61  and a second lead part  71  that are insulated from each other. The first lead part  61  and the second lead part  71  are, for example, separated and opposed to each other in the x-direction and respectively include a first lead opposing surface  62  and a second lead opposing surface  72  that are separated and opposed to each other in the x-direction. In the present embodiment, the lead opposing surfaces  62  and  72  are orthogonal to the x-direction. In the present embodiment, the first lead part  61  and the second lead part  71  correspond to “first conductor” and “second conductor”. 
     As viewed in the z-direction, the first lead part  61  and the second lead part  71  extend sideward, in the present embodiment, in the x-direction, beyond the mount plate  11 . The dimension of the two lead parts  61  and  71  in the y-direction is set to be slightly less than the dimension of the mount plate  11  in the y-direction, for example, equal to the dimension of the antenna base  50  in the y-direction. In the present embodiment, the lead frame  60  is less likely to extend beyond the mount plate  11  in the y-direction. 
     The lead frame  60  is formed so as to avoid overlapping with the reflection film  54  (the recess  52 ) in the z-direction. More specifically, the lead frame  60  includes an opening  80  that overlaps at least a portion of the reflection film  54  as viewed in the z-direction. 
     The opening  80  includes, for example, a gap  81  extending between the two lead parts  61  and  71 , a first part opening  63  formed in the first lead part  61 , and a second part opening  73  formed in the second lead part  71 . 
     The gap  81  is slit-shaped and extends in the y-direction and includes a space between the lead opposing surfaces  62  and  72  and a space between the part openings  63  and  73 . 
     The first part opening  63  is formed in a portion of the first lead part  61  that overlaps the reflection film  54  as viewed in the z-direction. The second part opening  73  is formed in a portion of the second lead part  71  that overlaps the reflection film  54  in the z-direction. 
     The first part opening  63  and the second part opening  73  extend through in the z-direction to be continuous with the recess  52 . The first part opening  63  and the second part opening  73  are separated by the gap  81  and opposed to each other in the x-direction. The two part openings  63  and  73  are open in the x-direction. The first part opening  63  is open toward the second lead part  71 . The second part opening  73  is open toward the first lead part  61 . Thus, the two part openings  63  and  73  are continuous with the gap  81 . 
     Each of the first part opening  63  and the second part opening  73  is semicircular as viewed in the z-direction. The first part opening  63  and the second part opening  73  form a single circular hole. In other words, the terahertz element  20  is located in the center of the circle formed by the part openings  63  and  73 . The diameter of the circle formed by the part openings  63  and  73  may be, for example, greater than or equal to the opening width of the reflection film  54 . 
     The first lead part  61  includes a first inner surface  64 , which is the wall surface of the first part opening  63 . The first inner surface  64  is recessed from the first lead opposing surface  62  in a direction away from the second lead opposing surface  72 . 
     The second lead part  71  includes a second inner surface  74 , which is the wall surface of the second part opening  73 . The second inner surface  74  is recessed from the second lead opposing surface  72  in a direction away from the first lead opposing surface  62 . 
     The first inner surface  64  and the second inner surface  74  are curved to project away from each other. The two inner surfaces  64  and  74 , for example, extend along the outer side of an end  54   a  of the reflection film  54 , that is, the opening edge of the recess  52 , to avoid overlapping of the two lead parts  61  and  71  with the reflection film  54 . 
     As shown in  FIG. 43 , in the present embodiment, the first lead part  61  includes a first connector  65  configured to be electrically connected to the terahertz element  20 . In the present embodiment, the first connector  65  is a portion of the first lead part  61  that projects toward the terahertz element  20  from where the first lead part  61  does not overlap the recess  52  (i.e., the reflection film  54 ) as viewed in the z-direction. More specifically, the first connector  65  is a projection piece projecting from the first inner surface  64  toward the terahertz element  20 . The first connector  65  overlaps the reflection film  54  as viewed in the z-direction. The first connector  65  and the first pad  33   b  are connected by a first wire W 1 . Thus, the first lead part  61  is electrically connected to the terahertz element  20 . 
     In the present embodiment, the projection dimension of the first connector  65  from the first inner surface  64  is less than the length of the first wire W 1  as viewed in the z-direction. The projection dimension is, for example, less than ¼ of the opening width of the reflection film  54 . 
     In the same manner, in the present embodiment, the second lead part  71  includes a second connector  75  configured to be electrically connected to the terahertz element  20 . In the present embodiment, the second connector  75  is a portion of the second lead part  71  that projects toward the terahertz element  20  from where the second lead part  71  does not overlap the recess  52  (i.e., the reflection film  54 ) as viewed in the z-direction. More specifically, the second connector  75  is a projection piece projecting from the second inner surface  74  toward the terahertz element  20 . The second connector  75  overlaps the recess  52  (i.e., the reflection film  54 ) as viewed in the z-direction. The second connector  75  and the second pad  34   b  are connected by a second wire W 2 . Thus, the second lead part  71  is electrically connected to the terahertz element  20 . 
     In the present embodiment, the projection dimension of the second connector  75  from the second inner surface  74  is less than the length of the second wire W 2  as viewed in the z-direction. The projection dimension is, for example, less than ¼ of the opening width of the reflection film  54 . 
     In the present embodiment, the first connector  65  and the second connector  75  are opposed to each other at opposite sides of the terahertz element  20 . For example, the two connectors  65  and  75  are symmetrically arranged in the x-direction. In other words, the two connectors  65  and  75  are shifted 180° from each other as viewed in the z-direction. 
     As shown in  FIG. 42 , the terahertz device  10  includes an adhesive layer  90  that adheres the antenna base  50  to the lead frame  60 . The adhesive layer  90  is formed of, for example, an insulative material and includes, for example, a resin adhesive agent. The adhesive layer  90  is disposed between the base main surface  50   a  of the antenna base  50  and the lead frame  60 . The antenna base  50  is adhered to the lead frame  60  by the adhesive layer  90 . This unitizes the mount plate  11 , the lead frame  60 , and the antenna base  50 . More specifically, the mount plate  11 , that is, the base member, and the antenna base  50  are unitized so as not to be displaced from each other. Accordingly, the terahertz element  20 , which is mounted on the mount plate  11 , and the reflection film  54 , which is formed on the antenna base  50 , are unitized so as not to be displaced from each other. 
     The adhesive layer  90  is disposed between the reflection film  54  and the lead frame  60 . The adhesive layer  90  hinders electrical connection of the reflection film  54  with the lead frame  60 . As described above, the reflection film  54  is not electrically connected to the antenna base  50  and the lead frame  60  and is electrically isolated. 
     In particular, in the present embodiment, the inner peripheral end of the adhesive layer  90  extends inward (i.e., toward the terahertz element  20 ) beyond the reflection film  54 . Thus, the reflection film  54  is less likely to avoid/circumvent/evade the adhesive layer  90  and contact the lead frame  60 . The inner peripheral end of the adhesive layer  90  may be referred to as the end of the adhesive layer  90  located close to the terahertz element  20 . The inner peripheral end of the adhesive layer  90  is, for example, circular in conformance with the recess  52  as viewed in the z-direction. However, the inner peripheral end of the adhesive layer  90  may have any shape and may be rectangular. 
     The terahertz element  20  and the reflection film  54  are accommodated in an accommodation space A 1  defined by the mount plate  11  and the recess  52 . In the present embodiment, the accommodation space A 1  is defined by the mount main surface  12  and the antenna surface  53 . In the present embodiment, the accommodation space A 1  is hermetically sealed by the adhesive layer  90  and other components. Air exists in the accommodation space A 1 . 
     As shown in  FIGS. 41 to 43 , the terahertz device  10  includes a first electrode  91  and a second electrode  92  used for electrical connection with an external device. In the present embodiment, the lead frame  60  includes the first electrode  91  and the second electrode  92 . 
     More specifically, in the present embodiment, part of the first lead part  61  and part of the second lead part  71  project sideward relative to the antenna base  50 . The first electrode  91  is formed by a portion of the first lead part  61  projecting sideward relative to the antenna base  50 . The first electrode  91  projects from the first base side surface  51   a.    
     In the same manner, the second electrode  92  is formed by a portion of the second lead part  71  projecting sideward relative to the antenna base  50 . The second electrode  92  projects from the second base side surface  51   b.    
     In the present embodiment, the first electrode  91  and the second electrode  92  are separate from each other in the x-direction. The first electrode  91  and the second electrode  92  extend in opposite directions from the antenna base  50 . In the present embodiment, the first electrode  91  and the second electrode  92  extend in the x-direction. The first electrode  91  and the second electrode  92  are orthogonal to the z-direction. In other words, the first electrode  91  and the second electrode  92  are flat plates extending horizontally. 
     As described above, the dimension of the antenna base  50  in the z-direction is greater than the thickness of the mount plate  11 . In addition, the dimension of the antenna base  50  in the z-direction is greater than the sum of the thickness of the mount plate  11  and the thickness of the lead frame  60 . The lead frame  60 , which is disposed between the antenna base  50  and the mount plate  11 , is disposed at an upper part of the terahertz device  10 . Thus, the first electrode  91  and the second electrode  92 , which are formed of part of the lead frame  60 , are disposed at an upper side of the terahertz device  10 . 
     More specifically, when the z-direction is the thickness-wise direction of the terahertz device  10 , the first electrode  91  and the second electrode  92  are located upward from the center of the terahertz device  10  in the thickness-wise direction (in other words, toward the mount plate  11  or at the side where electromagnetic waves are output). In other words, the electrodes  91  and  92  project sideward from portions of the base side surfaces  51   a  and  51   b  located toward the base main surface  50   a  from the center. The projection direction is not limited to the direction orthogonal to the base side surfaces  51   a  and  51   b  and may be inclined from the direction orthogonal to the base side surfaces  51   a  and  51   b.    
     A method for manufacturing the terahertz device  10  of the present embodiment will now be described. To simplify the description, a method for manufacturing one terahertz device  10  will first be described. 
     As shown in  FIG. 46 , the method for manufacturing the terahertz device  10  includes a step of forming the lead frame  60 . In this step, the first lead part  61  including the first part opening  63  and the first connector  65  is formed, and the second lead part  71  including the second part opening  73  and the second connector  75  is formed. 
     As shown in  FIG. 47 , the method for manufacturing the terahertz device  10  includes a step of forming the mount plate  11 . In this step, the mount plate  11  is formed so as to extend over the two lead parts  61  and  71 . Any specific process for forming the mount plate  11  may be used. 
     As shown in  FIG. 48 , the method for manufacturing the terahertz device  10  subsequently includes a step of mounting the terahertz element  20  on the mount plate  11 . In this step, the terahertz element  20  is mounted on a surface of the mount plate  11  on which the lead frame  60  is formed. This unitizes the lead frame  60 , the mount plate  11 , and the terahertz element  20 . 
     As shown in  FIG. 49 , the method for manufacturing the terahertz device  10  includes a step of electrically connecting the terahertz element  20  and the two lead parts  61  and  71  using the two wires W 1  and W 2 . In this step, the first wire W 1  is bonded to the first pad  33   b  and the first lead part  61 , and the second wire W 2  is bonded to the second pad  34   b  and the second lead part  71 . The bonding order may be determined in any manner. 
     As shown in  FIG. 50 , the method for manufacturing the terahertz device  10  includes a step of forming the recess  52  in the antenna base  50 . In this step, molds that are formed in conformance with the antenna surface  53  are used to form the recess  52  having the antenna surface  53 . 
     As shown in  FIG. 51 , the method for manufacturing the terahertz device  10  includes a step of forming a metal film forming the reflection film  54 , which is performed after the recess  52  is formed. In this step, the metal layer is formed on both the base main surface  50   a  and the antenna surface  53 . 
     As shown in  FIG. 52 , the method for manufacturing the terahertz device  10  includes a step of removing the metal film from the base main surface  50   a . Any specific process for removing the metal film from the base main surface  50   a  may be used. For example, the metal film may be removed by patterning or an abrasive process. As a result, the metal film is formed on only the antenna surface  53  as the reflection film  54 . 
     The step of forming the metal film is not limited to the above-described steps. For example, the method for manufacturing the terahertz device  10  may include a step of masking the base main surface  50   a  and a step of forming a metal film on the antenna surface  53  by vapor deposition using electron beams. This case eliminates the need for the step of removing the metal film from the base main surface  50   a.    
     As shown in  FIG. 53 , the method for manufacturing the terahertz device  10  includes a step of coupling the unitized body of the lead frame  60 , the mount plate  11 , and the terahertz element  20  to the antenna base  50  on which the reflection film  54  is formed. In this step, the adhesive layer  90  is used to adhere the antenna base  50  and the lead frame  60 . As a result, the terahertz device  10  is formed. 
     To simplify the description, the method for manufacturing one terahertz device  10  has been described above. However, practically, a plurality of terahertz devices  10  may be simultaneously manufactured. 
     For example, as shown in  FIG. 54 , a metal plate  104  including a plurality of lead frames  60  and including punched-out portions corresponding to the openings  80  is prepared. A plurality of mount plates  11  and a plurality of terahertz elements  20  are mounted on the metal plate  104 . The metal plate  104  is punched out along the ends of the lead frames  60  in the y-direction to form first through holes  104   a . The first through holes  104   a  are, for example, slit-shaped and extend from opposite sides of the mount plate  11  in the x-direction by an amount corresponding to the two electrodes  91  and  92 . 
     Meanwhile, as shown in  FIG. 55 , a base body  105  in which the recesses  52  and the reflection films  54  are formed is prepared. Second through holes  105   a  are formed in portions of the base body  105  corresponding to where the lead frames  60  are exposed. The second through holes  105   a  are formed in portions faced toward the electrodes  91  and  92  when the metal plate  104  is adhered to the base body  105 . The metal plate  104 , which includes the mount plates  11  and the terahertz elements  20 , and the base body  105  are positioned and adhered to each other by an adhesive. Subsequently, the metal plate  104  and the base body  105  are cut by dicing. This manufactures a plurality of terahertz devices  10 . 
     The metal plate  104  may include first positioning portions  104   b , and the base body  105  may include second positioning portions  105   b . When adhering the metal plate  104  to the base body  105 , the metal plate  104  and the base body  105  may be positioned so that the first positioning portions  104   b  overlap the second positioning portions  105   b.    
     Operation of the present embodiment will now be described. 
     When electromagnetic waves are generated from the oscillation point P 1  of the terahertz element  20 , the reflection film  54  reflects and emits the electromagnetic waves in one direction. 
     The two electrodes  91  and  92  of the terahertz device  10  project sideward relative to the antenna base  50  as viewed in the z-direction. As shown in  FIG. 56 , the terahertz device  10  may be mounted on a circuit substrate  110  having a hole  116  when the antenna base  50  is inserted into the hole  116  of the circuit substrate  110 . In this case, for example, a conductive bonding member  117  such as solder may be used to bond the electrodes  91  and  92  to the circuit substrate  110 . 
     The present embodiment, which has been described above, has the following advantages. 
     (3-1) The terahertz device  10  includes the mount plate  11  used as the base member, the terahertz element  20  mounted on the mount plate  11 , the antenna base  50  located opposing the mount plate  11  and including the antenna surface  53 , and the reflection film  54  formed on the antenna surface  53 . The reflection film  54  reflects at least part of electromagnetic waves generated by the terahertz element  20  in one direction (for example, upward). With this structure, electromagnetic waves generated by the terahertz element are emitted in one direction. This increases the output of the electromagnetic waves emitted from the terahertz device  10 . Thus, the gain of the terahertz device  10  is improved. 
     (3-2) The terahertz device  10  includes the first electrode  91  and the second electrode  92  as electrodes used for electrical connection with an external device. The electrodes  91  and  92  project sideward relative to the antenna base  50  as viewed in the z-direction, that is, the opposing direction of the mount plate  11  and the antenna base  50 . This structure allows for the mounting on the circuit substrate  110  when the antenna base  50  is inserted into the hole  116  of the circuit substrate  110 . Thus, when the terahertz device  10  is mounted on the circuit substrate  110 , the projection of the terahertz device  10  from the circuit substrate  110  in the z-direction is limited, thereby achieving a low profile structure. 
     More specifically, when the terahertz device  10  includes the antenna base  50  including the reflection film  54 , the terahertz device  10  is increased in size in the z-direction corresponding to the antenna base  50 , while improving the gain. This may be a disadvantage such that the terahertz device  10  interferes with the mounting on the circuit substrate  110 . 
     In this regard, when the electrodes  91  and  92  project sideward, the terahertz device  10  may be mounted on the circuit substrate  110  with the antenna base  50  inserted into the hole  116  as described above. More specifically, the antenna base  50  may be inserted into the hole  116  to a position where the electrodes  91  and  92  contact the circuit substrate  110 . This reduces the amount of projection of the terahertz device  10  from the circuit substrate  110 , thereby reducing the disadvantage of including the antenna base  50 . 
     (3-3) The electrodes  91  and  92  are located toward the mount plate  11  from the center of the terahertz device  10  in the z-direction. This structure allows for an increase in the size of the antenna base  50 , which is inserted into the hole  116 , thereby achieving a further low profile structure. 
     (3-4) The electrodes  91  and  92  extend in a direction (the x-direction) orthogonal to the thickness-wise direction of the terahertz device  10  (the z-direction). In this structure, the length of the electrodes  91  and  92  are decreased as compared to in a structure in which the electrodes  91  and  92  are bent. Accordingly, inductance of the electrodes  91  and  92  is decreased. In addition, adverse effects produced by the bending of the electrodes  91  and  92  on high frequency response are limited. 
     (3-5) The electrodes  91  and  92  are separated and face each other. In this structure, contact of the electrodes  91  and  92  is avoided. The two electrodes  91  and  92  support the terahertz device  10  on the circuit substrate  110 . 
     (3-6) The terahertz element  20  includes the element main surface  21 , which includes the oscillation point P 1  configured to generate electromagnetic waves, and the element back surface  22 , which is opposite the element main surface  21 . The reflection film  54  is disposed at the side of the element main surface  21 , not at the side of the element back surface  22 . In this structure, electromagnetic waves readily reach the reflection film  54 . Thus, the reflection film  54  is appropriately used to reflect electromagnetic waves generated from the oscillation point P 1 . 
     (3-7) The terahertz element  20  radiates electromagnetic waves from the oscillation point P 1  in the range of the opening angle θ. The reflection film  54  is formed over an angle that is greater than or equal to the opening angle θ of the oscillation point P 1 . With this structure, the electromagnetic waves radiated from the oscillation point P 1  in the range of the opening angle θ are reflected by the reflection film  54 . This reduces electromagnetic waves that are not reflected by the reflection film  54 , thereby improving the gain. 
     (3-8) The reflection film  54  is parabolic-antenna-shaped. With this structure, electromagnetic waves are appropriately reflected in one direction. 
     (3-9) The reflection film  54  is disposed so that the focal point of the reflection film  54  is located at the oscillation point P 1 . With this structure, electromagnetic waves generated from the oscillation point P 1  are guided in one direction by the reflection film  54 . This reduces electromagnetic waves that are not reflected in one direction by the reflection film  54 , thereby improving the gain. 
     (3-10) The reflection film  54  is disposed at a position corresponding to the frequency of electromagnetic waves generated from the terahertz element  20  so that the electromagnetic waves resonate. In an example, the specified distance z 1 , which is the perpendicular distance from the oscillation point P 1  toward the reflection film  54 , is set to satisfy the resonance condition of the electromagnetic waves, for example, (λ′ A /4)+((λ′ A /2)×N). This structure improves the gain of the terahertz device  10 . 
     (3-11) The reflection film  54  is electrically isolated. This structure obviates disadvantages such as absorption of electromagnetic waves by the reflection film  54 . 
     (3-12) The antenna base  50  is formed of an insulative material. This structure limits electrical connection of the reflection film  54  with another member via the antenna base  50 . 
     (3-13) The mount plate  11 , which is used as the base member, includes the mount main surface  12  on which the terahertz element  20  is mounted. The antenna base  50  includes the base main surface  50   a , which is opposed to the mount main surface  12 , and the recess  52 , which is recessed from the base main surface  50   a  and includes the antenna surface  53 . The terahertz element  20  and the reflection film  54  are disposed in the accommodation space A 1  defined by the mount main surface  12  and the antenna surface  53 . This structure reduces external effects on the terahertz element  20  and the reflection film  54 . 
     (3-14) The reflection film  54  is formed on the antenna surface  53  but is not formed on the base main surface  50   a . This structure obviates reflection of electromagnetic waves by the reflection film  54  formed on the base main surface  50   a . Thus, disadvantages caused by unwanted reflection waves, for example, occurrence of standing waves, are limited. 
     (3-15) The lead frame  60 , which is used as a conductive member, is disposed on the mount main surface  12 . The antenna base  50  is adhered to the lead frame  60  by the adhesive layer  90 . The adhesive layer  90  is formed from an insulative material and is disposed between the reflection film  54  and the lead frame  60 . In this structure, the adhesive layer  90  restricts contact of the reflection film  54  with the lead frame  60 . Thus, electrical connection of the reflection film  54  with the lead frame  60  is hindered. 
     (3-16) The lead frame  60  includes the opening  80  overlapping at least a portion of the reflection film  54  as viewed in the z-direction. In this structure, electromagnetic waves reflected by the reflection film  54  are output through the opening  80 . This limits interruption of electromagnetic waves by the lead frame  60 . 
     (3-17) The lead frame  60  includes the first lead part  61  and the second lead part  71 , which are separated and opposed to each other. The opening  80  includes the gap  81  between the two lead parts  61  and  71 . This structure limits interruption (blocking) of electromagnetic waves by the lead frame  60  while ensuring the insulation properties of the two lead parts  61  and  71 . 
     (3-18) The opening  80  includes the first part opening  63  formed in a portion of the first lead part  61  that overlaps the reflection film  54  as viewed in the z-direction and is continuous with the gap  81 . The opening  80  includes the second part opening  73  formed in a portion of the second lead part  71  that overlaps the reflection film  54  as viewed in the z-direction and is continuous with the gap  81  In this structure, the interruption of electromagnetic waves by the lead frame  60  is further limited. 
     (3-19) The first lead part  61  includes the first connector  65  configured to be electrically connected to the terahertz element  20 . The first connector  65  projects from the first inner surface  64 , which is the wall surface of the first part opening  63 , toward the terahertz element  20  and overlaps the reflection film  54  as viewed in the z-direction. The second lead part  71  includes the second connector  75  configured to be electrically connected to the terahertz element  20 . The second connector  75  projects from the second inner surface  74 , which is the wall surface of the second part opening  73 , toward the terahertz element  20  and overlaps the reflection film  54  as viewed in the z-direction. In this structure, while limiting interruption of electromagnetic waves by the lead frame  60 , the two lead parts  61  and  71  are electrically connected to the terahertz element  20 . 
     (3-20) The terahertz device  10  includes the first wire W 1  and the second wire W 2 . The first wire W 1  connects the first connector  65  to the first pad  33   b  formed on the terahertz element  20 , The second wire W 2  connects the second connector  75  to the second pad  34   b  formed on the terahertz element  20 . As viewed in the z-direction, the projection dimension of the first connector  65  from the first inner surface  64  is less than the length of the first wire W 1 . With this structure, interruption of electromagnetic waves by the first connector  65  is limited as the projection dimension of the first connector  65  is decreased. In the same manner, as viewed in the z-direction, the projection dimension of the second connector  75  from the second inner surface  74  may be less than the length of the second wire W 2 . 
     (3-21) The two connectors  65  and  75  are opposed to each other at opposite sides of the terahertz element  20 . In this structure, the two wires W 1  and W 2  are less likely to interfere with each other. Thus, contact of the two wires W 1  and W 2  is avoided. 
     Modified Example of Third Embodiment 
     As shown in  FIG. 57 , the terahertz device  10  may include a reflection reduction film  120  formed on the mount back surface  13 . The reflection reduction film  120  may refer to a reflection prevention film or an anti-reflection (AR) coating film. 
     For example, the reflection reduction film  120  may be formed on at least a portion of the part of the mount back surface  13  overlapping the lead frame  60  as viewed in the z-direction. In an example, the reflection reduction film  120  is formed on the entirety of the part of the mount back surface  13  overlapping the lead frame  60  as viewed in the z-direction. This limits occurrence of standing waves caused by reflection of electromagnetic waves at the lead frame  60 . Any specific structure of the reflection reduction film  120  may be used as long as reflection of electromagnetic waves in at least the terahertz band is reduced. 
     Fourth Embodiment 
     As shown in  FIG. 58 , the present embodiment of a terahertz device  10  includes protection diodes  131  and  132 , which are an example of a specific element that is electrically connected to the terahertz element  20 . The protection diodes  131  and  132  are electrically connected to the terahertz element  20 . In the present embodiment, the protection diodes  131  and  132  are connected to the terahertz element  20  in parallel. The two protection diodes  131  and  132  are connected to the terahertz element  20  in opposite directions. The protection diodes  131  and  132  may be general diodes or Zener diodes, Schottky diodes, or light emitting diodes. 
     The specific element is not limited to the protection diodes  131  and  132  and may be a control integrated circuit (IC) (e.g., application-specific integrated circuit (ASIC)). The control IC may be configured to, for example, detect current flowing to the terahertz element  20 , serve as an amplifier, supply power to the terahertz element  20 , or process signals. The specific element may be connected to the terahertz element  20  in any mode and may be, for example, connected in series. 
     As shown in  FIGS. 59 and 60 , the two protection diodes  131  and  132  are opposed to each other at opposite sides of the terahertz element  20 . The two protection diodes  131  and  132  are mounted on the lead frame  60 . 
     More specifically, the first protection diode  131  is disposed on the first lead part  61  and electrically connected to the first lead part  61 . The first protection diode  131  is disposed, for example, near the first part opening  63  on the first lead part  61 . In the present embodiment, the first protection diode  131  is disposed in a region surrounded by the first inner surface  64 , the first lead opposing surface  62 , and the end surface of the first lead part  61  in the y-direction. 
     The first protection diode  131  and the second lead part  71  are electrically connected by a first diode wire W 3 . Thus, the first protection diode  131  is electrically connected to the two electrodes  91  and  92 . 
     The first diode wire W 3  is bonded to the second lead part  71  at a position close to the first protection diode  131 , that is, a region defined by the second inner surface  74 , the second lead opposing surface  72 , and the end surface of the second lead part  71  in the y-direction. This reduces the length of the first diode wire W 3 . 
     In the same manner, the second protection diode  132  is disposed on the second lead part  71  and electrically connected to the second lead part  71 . The second protection diode  132  is disposed, for example, near the second part opening  73  on the second lead part  71 . In the present embodiment, the second protection diode  132  is disposed in a region surrounded by the second inner surface  74 , the second lead opposing surface  72 , and the end surface of the second lead part  71  in the y-direction. 
     The second protection diode  132  and the first lead part  61  are electrically connected by a second diode wire W 4 . Thus, the second protection diode  132  is electrically connected to the two electrodes  91  and  92 . 
     The second diode wire W 4  is bonded to the first lead part  61  at a position closet to the second protection diode  132 , that is, a region surrounded by the first inner surface  64 , the first lead opposing surface  62 , and the end surface of the first lead part  61  in the y-direction. This reduces the length of the second diode wire W 4 . 
     As shown in  FIG. 60 , in the present embodiment, the antenna base  50  includes receptacles  141  and  142  that are recessed from the base main surface  50   a . The protection diodes  131  and  132  are accommodated in the receptacles  141  and  142 . The receptacles  141  and  142  are formed around the recess  52  so as not to be continuous with the recess  52 . That is, the receptacles  141  and  142  are arranged separately from the recess  52  to accommodate the specific elements. As shown in  FIG. 60 , the adhesive layer  90  is not formed on locations corresponding to the receptacles  141  and  142 . 
     The present embodiment, which has been described above, has the following operational advantages. 
     (4-1) The terahertz device  10  includes the protection diodes  131  and  132  connected to the terahertz element  20  in parallel. With this structure, for example, when static electricity causes to a high voltage to be applied to opposite ends of the terahertz element  20 , current flows through the protection diodes  131  and  132 . Thus, an excessive current flowing to the terahertz element  20  is limited, so that the terahertz element  20  is protected. 
     (4-2) The two protection diodes  131  and  132  are connected to the terahertz element  20  in opposite directions. With this structure, the terahertz element  20  is protected from a high voltage produced in each direction. 
     (4-3) The antenna base  50  includes the receptacles  141  and  142  recessed from the base main surface  50   a . The protection diodes  131  and  132  are accommodated in the receptacles  141  and  142 . This structure limits increases in the size of the terahertz device  10  caused by arrangement of the protection diodes  131  and  132 . 
     Fifth Embodiment 
     As shown in  FIG. 61 , the terahertz device  10  includes a support substrate  150  as a base member. The support substrate  150  is formed of, for example, a material transmissive to electromagnetic waves. In an example, the support substrate  150  is formed of a dielectric. 
     The support substrate  150  is plate-shaped and, in the present embodiment, is rectangular-plate-shaped. The support substrate  150  includes a first extension  151  and a second extension  152  that are longer than the antenna base  50  in a predetermined direction as viewed in the z-direction and extend sideward (e.g., the x-direction) beyond the antenna base  50  as viewed in the z-direction. The two extensions  151  and  152  are separated and opposed to each other in the x-direction. 
     The support substrate  150  includes plate surfaces defining a mount main surface  153  and a mount back surface  154 . The mount main surface  153  and the mount back surface  154  intersect the z-direction and, in an example, are orthogonal to the z-direction. The terahertz element  20  is mounted on the mount main surface  153 . The mount main surface  153  and the reflection film  54  are opposed to each other. 
     The terahertz device  10  includes a wiring pattern  160  and an adhesive layer  170 . The wiring pattern  160  is formed on the mount main surface  153  and used as a conductive member and an electrode. The adhesive layer  170  adheres the wiring pattern  160  to the antenna base  50 . 
     The wiring pattern  160  is a conductive layer formed on the mount main surface  153  and is formed of, for example, Cu. The thickness of the support substrate  150 , that is, the dimension of the support substrate  150  in the z-direction, is greater than the thickness of the wiring pattern  160 . The wiring pattern  160  includes a first pattern  161  and a second pattern  162 . The specific layout of the first pattern  161  and the second pattern  162  is basically the same as that of the first lead part  61  and the second lead part  71 . In the present embodiment, the first pattern  161  and the second pattern  162  correspond to “first conductor” and “second conductor”. 
     The adhesive layer  170  is formed of an insulative material. The adhesive layer  170  is disposed between the base main surface  50   a  and the wiring pattern  160  and between the reflection film  54  and the wiring pattern  160 . 
     In the present embodiment, the wiring pattern  160  includes electrodes  171  and  172 . For example, the electrodes  171  and  172  are formed of the wiring pattern  160  that is formed on the extensions  151  and  152  of the support substrate  150 . The first electrode  171  is formed of a portion of the first pattern  161  extending from the antenna base  50  (the first base side surface  51   a ) in the x-direction. The second electrode  172  is formed of a portion of the second pattern  162  extending from the antenna base  50  (the second base side surface  51   b ) in the x-direction. Thus, in the same manner as the third embodiment, the electrodes  171  and  172  project sideward relative to the antenna base  50 . In other words, the support substrate  150  supports the electrodes  171  and  172 . 
     An example of a method for manufacturing the method for manufacturing the terahertz device  10  of the present embodiment will now be described. 
     As shown in  FIG. 62 , the method for manufacturing the terahertz device  10  includes a step of forming the wiring pattern  160  on the support substrate  150 . In this step, the wiring pattern  160  is patterned on the mount main surface  153  of the support substrate  150 . This forms the two patterns  161  and  162 . The subsequent steps such as the step of mounting the terahertz element  20  are the same as those of the third embodiment and will not be described in detail. 
     The present embodiment, which has been described above, has the following operational advantages. 
     (5-1) The terahertz device  10  includes the support substrate  150 , which is used as the base member, and the wiring pattern  160 , which is used the conductive members. In this structure, instead of the lead frame  60 , the wiring pattern  160  is used as the conductive members. Thus, micromachining may be performed and readily form a signal path corresponding to high-speed signal transmission. 
     (5-2) The support substrate  150  includes the first extension  151  and the second extension  152  extending sideward relative to the antenna base  50  as viewed in the z-direction. The two electrodes  171  and  172  are formed of the wiring pattern  160  that is formed on the two extensions  151  and  152 . In this structure, the electrodes  171  and  172  project sideward relative to the antenna base  50 , and the advantage (3-2) is obtained. 
     Modified Example of Fifth Embodiment 
     As shown in  FIG. 63 , a reflection reduction film  180  is formed on at least a portion of the part of the mount back surface  154  overlapping the wiring pattern  160  as viewed in the z-direction. The reflection reduction film  180  may be formed on, for example, portions overlapping the electrodes  171  and  172 , that is, the extensions  151  and  152 . 
     Sixth Embodiment 
     In the present embodiment, as shown in  FIG. 64 , the terahertz device  10  includes a first connection pattern  191  and a first electrode  192  that are formed on the mount main surface  153 , a first back pattern  193  formed on the mount back surface  154 , and first through vias  194  and  195  that electrically connect the first connection pattern  191  and the first electrode  192  to the first back pattern  193 . 
     The first connection pattern  191  is obtained by forming a wiring pattern on the mount main surface  153 . The first connection pattern  191  is formed on a portion of the mount main surface  153  faced toward the recess  52 . The first connection pattern  191  is disposed in the accommodation space A 1 . The first connection pattern  191  is separate from the end  54   a  of the reflection film  54 , so that the first connection pattern  191  does not contact the reflection film  54 . The first wire W 1  is bonded to the first connection pattern  191 . 
     The first electrode  192  is obtained by forming a wiring pattern on the mount main surface  153 . The first electrode  192  is disposed outside the accommodation space A 1 . The first electrode  192  is formed on a portion of the mount main surface  153  corresponding to the first extension  151  and projects sideward relative to the antenna base  50 . 
     The first back pattern  193  is obtained by forming a wiring pattern on the mount back surface  154 . The first back pattern  193  extends over the first connection pattern  191  and the first electrode  192  and overlaps the first connection pattern  191  and the first electrode  192  as viewed in the z-direction. 
     The first through vias  194  and  195  extend through the support substrate  150  in the thickness-wise direction. One of the first through vias denoted by  194  connects the first connection pattern  191  to the first back pattern  193 . The other one of the first through vias denoted by  195  connects the first electrode  192  to the first back pattern  193 . Thus, the first electrode  192  is electrically connected to the terahertz element  20 . 
     The terahertz device  10  includes, for example, a second connection pattern  201  and a second electrode  202  that are formed on the mount main surface  153 , a second back pattern  203  formed on the mount back surface  154 , and second through vias  204  and  205  that electrically connect the second connection pattern  201  and the second electrode  202  to the second back pattern  203 . The second connection pattern  201 , the second electrode  202 , the second back pattern  203 , and the second through vias  204  and  205  are the same as the first connection pattern  191 , the first electrode  192 , the first back pattern  193 , and the first through vias  194  and  195  except being symmetrical with respect to the x-direction and thus will not be described in detail. In the present embodiment, the first connection pattern  191  corresponds to “first connector”. The second connection pattern  201  corresponds to “second connector”. 
     In the present embodiment, the antenna base  50  is attached to the mount main surface  153  by the adhesive layer  170 . In this case, the connection patterns  191  and  201  are disposed toward the terahertz element  20  from the end  54   a  of the reflection film  54 . In contrast, the electrodes  192  and  202  are disposed sideward relative to the end  54   a  of the reflection film  54 . That is, as viewed in the z-direction, the end  54   a  of the reflection film  54  (and the base main surface  50   a ) is disposed between the connection patterns  191  and  201  and the electrodes  192  and  202  and separated from the connection patterns  191  and  201  and the electrodes  192  and  202 . This ensures the insulation of the reflection film  54  from the electrodes  192  and  202  and the insulation of the reflection film  54  from the connection patterns  191  and  201 . 
     The present embodiment, which has been described above, has the following operational advantages. 
     (6-1) The terahertz device  10  includes the support substrate  150  as a base member including the mount main surface  153  and the mount back surface  154 , the connection patterns  191  and  201  and the electrodes  192  and  202  formed on the mount main surface  153  of the support substrate  150 , the back patterns  193  and  203  formed on the mount back surface  154 , and the through vias  194 ,  195 ,  204 , and  205 . The connection patterns  191  and  201  are connected to the terahertz element  20  by the wires W 1  and W 2 . The through vias  194 ,  195 ,  204 , and  205  extend through the circuit substrate  110  to connect the connection patterns  191  and  201  and the electrodes  192  and  202  to the back patterns  193  and  203 . The end  54   a  of the reflection film  54  is disposed between the connection patterns  191  and  201  and the electrodes  192  and  202  and separated from the connection patterns  191  and  201  and the electrodes  192  and  202 . In this structure, while avoiding contact of the connection patterns  191  and  201  and the electrodes  192  and  202  with the reflection film  54 , the electrodes  192  and  202  are electrically connected to the terahertz element  20 . 
     Modified Example of Sixth Embodiment 
     As shown in  FIG. 65 , the terahertz device  10  may include specific elements  216  and  217  mounted on the mount back surface  154  (in the present embodiment, the back patterns  193  and  203 ). Thus, the specific elements  216  and  217  are electrically connected to the terahertz element  20  in a relatively easy manner. The specific elements  216  and  217  may be, for example, protection diodes. Thus, an excessive current flowing to the terahertz element  20  is limited. 
     However, the specific elements  216  and  217  are not limited to those described above and may be changed in any manner. For example, each of the specific elements  216  and  217  may be a control IC (e.g., ASIC). The control IC may be configured to, for example, detect current flowing to the terahertz element  20 , serve as an amplifier, supply power to the terahertz element  20 , or process signals. 
     For example, when the specific elements  216  and  217  are electrically connected to the terahertz element  20 , the specific elements  216  and  217  may be mounted on the mount back surface  154 . For example, the specific elements  216  and  217  are not limited to being mounted on the back patterns  193  and  203  as described above and may be mounted on a portion of the mount back surface  154  where the back patterns  193  and  203  are not formed. In this case, the specific elements  216  and  217  may be electrically connected to the back patterns  193  and  203  by conductors. 
     As shown in  FIG. 66 , the terahertz device  10  may include a reflection reduction film  220  formed on the support substrate  150  to overlap wiring patterns as viewed in the z-direction. The reflection reduction film  220  is formed, for example, on the back patterns  193  and  203 . In an example, the reflection reduction film  220  may overlap the back patterns  193  and  203  and the electrodes  192  and  202 . 
     Seventh Embodiment 
     As shown in  FIG. 67 , an antenna base  230  may be convex-lens-shaped. For example, the antenna base  230  is disposed on the support substrate  150  at the side of the mount back surface  154 . The antenna base  230  includes an antenna surface  231  and a flange surface  232 . The antenna surface  231  is curved to project in a direction away from the terahertz element  20  disposed on the mount main surface  153 . The flange surface  232  projects sideward beyond the proximal end of the antenna surface  231 . The antenna surface  231  is curved in conformance with the lens surface of the antenna base  230 . The antenna surface  231  and the terahertz element  20  are opposed to each other in the z-direction. 
     In the present embodiment, a reflection film  233  is formed on at least the antenna surface  231 . In an example, the reflection film  233  is formed over the antenna surface  231  and the flange surface  232 . In the present embodiment, the support substrate  150  and the antenna base  230  are disposed between the terahertz element  20  and the reflection film  233 . 
     In the present embodiment, it is preferred that the support substrate  150  and the antenna base  230  are formed of a material transmissive to electromagnetic waves generated by the terahertz element  20  and may be formed of, for example, a dielectric. The dielectric may be, for example, Si, resin, Teflon, or glass. The support substrate  150  and the antenna base  230  may be formed of the same material or different materials. For example, when the support substrate  150  and the antenna base  230  are formed of the same material, the refractive index is less likely change, so that reflection in the interface between the support substrate  150  and the antenna base  230  is reduced. 
     The support substrate  150  and the antenna base  230  may be adhered to each other or may be formed integrally. 
     In the present embodiment, the terahertz device  10  includes a first connection pattern  241  formed on the mount main surface  153 , a first electrode  242  formed on the mount back surface  154 , and a first through via  243  connecting the first connection pattern  241  to the first electrode  242 . The first electrode  242  is disposed at a position projecting sideward (e.g., the x-direction) relative to the antenna base  230  as viewed in the z-direction. The first electrode  242  and the reflection film  233  are separate in the x-direction. 
     The terahertz device  10  includes a second connection pattern  251  formed on the mount main surface  153 , a second electrode  252  formed on the mount back surface  154 , and a second through via  253  connecting the second connection pattern  251  to the second electrode  252 . The second electrode  252  is disposed at a position projecting sideward (e.g., the x-direction) relative to the antenna base  230  as viewed in the z-direction. The second electrode  252  and the reflection film  233  are separate in the x-direction. 
     In the present embodiment, the terahertz element  20  is disposed so that the element main surface  21  faces the reflection film  233 . More specifically, when the element main surface  21  is faced toward the mount main surface  153 , the terahertz element  20  is mounted on the support substrate  150 . In this case, conductive bonding members  244  and  245  such as solder may be used to electrically connect the two pads  33   b  and  34   b  to the connection patterns  241  and  251 . The shape and positional relationship of the antenna surface  231  with respect to the oscillation point P 1  is the same as those of the third embodiment. 
     In the present embodiment, the terahertz device  10  is mounted on the circuit substrate  110  from the mount back surface  154 . As a result, at least a portion of the antenna base  230  is inserted into the hole  116 . The electrodes  242  and  252  are faced toward the circuit substrate  110  and thus are electrically connected by the conductive bonding member  117 . 
     The present embodiment, which has been described above, has the following operational advantages. 
     (7-1) The terahertz device  10  includes the antenna base  230 , which is convex-lens-shaped and curved to project in a direction away from the terahertz element  20 . The antenna surface  231  corresponds to the lens surface of the antenna base  230 . With this structure, for example, the advantage (3-1) is obtained. 
     (7-2) The antenna base  230  is disposed at the side of the mount back surface  154 . The terahertz element  20  and the reflection film  233  are opposed to each other at opposite sides of the support substrate  150  and the antenna base  230 . This structure eliminates the need for forming a recess accommodating the terahertz element  20  in the antenna base  230 , thereby simplifying the structure of the antenna base  230 . 
     Modified Examples 
     In each embodiment, the terahertz device  10  may be modified, for example, as follows. The modified examples described below may be combined with one another as long as there is no technical inconsistency. For the sake of convenience, the following modified examples will be basically described using the third embodiment. However, other embodiments may be used as long as there is no technical inconsistency. 
     As shown in  FIG. 68 , the terahertz device  10  may include a spacer  260  that is different from the adhesive layer  90  to insulate the reflection film  54  from the lead frame  60 . The spacer  260  is insulative. The spacer  260  is also disposed between the reflection film  54  and the lead frame  60 . In  FIG. 68 , the spacer  260  is disposed between the lead frame  60  and the adhesive layer  90 . However, alternatively, the spacer  260  may be disposed between the antenna base  50  and the adhesive layer  90 . 
     In this configuration, contact of the reflection film  54  with the lead frame  60  is restricted by the spacer  260  and the adhesive layer  90 . Thus, the contact of the reflection film  54  with the lead frame  60  is further restricted. 
     As shown in  FIG. 69 , the first connector  65  and the second connector  75  may extend to the vicinity of the terahertz element  20 . For example, the distal portion of the first connector  65  may be located closer to the terahertz element  20  than to the first inner surface  64 , and the distal portion of the second connector  75  may be located closer to the terahertz element  20  than to the second inner surface  74 . In other words, the projection dimension of each of the two connectors  65  and  75  may be greater than ¼ of the opening width of the reflection film  54 . 
     In addition, as viewed in the z-direction, the length of the first wire W 1  may be less than the projection dimension of the first connector  65  from the first inner surface  64 . In the same manner, the length of the second wire W 2  may be less than the projection dimension of the second connector  75  from the second inner surface  74 . In this structure, the length of the wires W 1  and W 2  is decreased, thereby limiting adverse effects on the responsiveness caused by the wires W 1  and W 2 . 
     As shown in  FIG. 70 , the first connector  65  and the second connector  75  may be arranged parallel to each other. This structure improves the responsiveness of the terahertz device  10 . 
     The first connector  65  and the second connector  75  may be omitted. 
     As shown in  FIGS. 71 and 72 , the lead frame  60  may be used as the base member on which the terahertz element  20  is mounted. Specifically, the lead frame  60  may include a mount base  270  on which the terahertz element  20  is mounted, a first connector  271  joined to the mount base  270 , and a second connector  272  insulated from the first connector  271 . The first connector  271  is electrically connected to the first pad  33   b  by the first wire W 1 . The second connector  272  is electrically connected to the second pad  34   b  by the second wire W 2 . 
     In addition, the lead frame  60  may include a first curved portion  273  extending from the first connector  271  along the outer side of the opening edge of the recess  52  and a second curved portion  274  extending from the second connector  272  along the outer side of the opening edge of the recess  52 . 
     In this modified example, as shown in  FIG. 72 , the terahertz device  10  may include a cover member  275  covering the mount base  270  and the two connectors  271  and  272  from above. The cover member  275  may be formed of a material transmissive to electromagnetic waves, for example, a dielectric. 
     As shown in  FIG. 73 , the recess  52  may include a large diameter surface  281  having a larger diameter than the antenna surface  53  and a stepped surface  282  formed between the antenna surface  53  and the large diameter surface  281 . The stepped surface  282  intersects the z-direction. In this structure, a reflection film  283  may be formed over the antenna surface  53  and the stepped surface  282 . In this case, the reflection film  283  and the lead frame  60  are separate in the z-direction and thus are not likely to contact each other. 
     As shown in  FIG. 74 , a reflection film  290  may be formed on a portion of the antenna surface  53 . For example, the reflection film  290  may be formed on a portion located below the oscillation point P 1 . The reflection film  290  may be formed over an angle that is less than the opening angle θ of the oscillation point P 1 . Any reflection film that reflects at least part of electromagnetic waves generated by the terahertz element  20  in one direction may be used. 
     The shape of the reflection film may be changed. For example, the reflection film is not limited to a single film and may include a plurality of separate parts. For example, a slit and/or a hole may be formed in the reflection film. 
     As shown in  FIG. 75 , the antenna base  50  may be configured to be disposed at the side of the mount back surface  13 . In this case, the mount plate  11  is disposed between the lead frame  60  and the reflection film  54 , so that contact of the reflection film  54  with the lead frame  60  is avoided. However, considering the point that the terahertz element  20  is accommodated in the accommodation space A 1 , it is more preferred that the antenna base  50  is disposed at the side of the mount main surface  12 . 
     As shown in  FIG. 76 , the lead opposing surfaces  62  and  72  may be inclined from the y-direction. In this case, the gap  81  diagonally extend with respect to the y-direction. 
     In this structure, when the protection diodes  131  and  132  are arranged as in the fourth embodiment, at least a portion of the first protection diode  131  may be disposed between the first inner surface  64  and the first lead opposing surface  62 . Also, at least a portion of the second protection diode  132  may be disposed between the second inner surface  74  and the second lead opposing surface  72 . 
     As shown in  FIG. 77 , the terahertz element  20  may be disposed so that the oscillation point P 1  is located at a position separate from the center point P 2  of the reflection film  54  as viewed from above. That is, the focal point of the reflection film  54  does not have to coincide with oscillation point P 1 . 
     As shown in  FIG. 78 , the terahertz device  10  may be of a multi-reflector type including a reflector  300  disposed separately from the reflection film  54 . 
     Specifically, the terahertz device  10  includes the reflector  300  in addition to the reflection film  54 . More specifically, the mount main surface  12  includes a reflection protrusion  301 , and a metal film is formed on the surface of the reflection protrusion  301  to form the reflector  300 . In accordance with the curve of the reflection protrusion  301  protruding toward the reflection film  54 , the reflector  300  is curved to protrude toward the reflection film  54 . The reflector  300  and the reflection film  54  are radially faced to each other. Electromagnetic waves reflected by the reflector  300  are emitted toward the reflection film  54 . 
     In the present modified example, the terahertz element  20  is located opposing the reflector  300 . In other words, the mount plate  11 , which is used as the base member including the reflector  300 , is located opposing the terahertz element  20 . 
     The terahertz device  10  includes, for example, mount poles  302  and  303 . The mount poles  302  and  303  are formed of, for example, a conductive material. The mount poles  302  and  303  extend through the antenna base  50  and the reflection film  54  from below and enter the accommodation space A 1 . The terahertz element  20  is mounted on the mount poles  302  and  303 . The terahertz element  20  is electrically connected to the mount poles  302  and  303 . 
     The terahertz element  20  may be bonded to the mount poles  302  and  303  directly or by a conductive bonding member. In addition, to avoid contact of the mount poles  302  and  303  with the reflection film  54 , an insulator (e.g., insulation coating) may be disposed on side surfaces of the mount poles  302  and  303 . In this modified example, the mount poles  302  and  303  are two. However, the number of mount poles  302  and  303  may be any number. 
     In this modified example, the terahertz device  10  includes electrodes  304  and  305  electrically connected to the mount poles  302  and  303 . The electrodes  304  and  305  are formed on the base back surface  50   b , which is a side of the antenna base  50  opposite from the base main surface  50   a , and are joined to the mount poles  302  and  303 . 
     In this modified example, when a voltage is applied from the both electrodes  304  and  305 , electromagnetic waves are generated by the terahertz element  20 . The electromagnetic waves are reflected by the reflector  300  and then further reflected by the reflection film  54  and are emitted upward, which corresponds to one direction. That is, the electromagnetic waves generated by the terahertz element  20  are emitted to the reflection film  54  via the reflector  300  and further reflected by the reflection film  54 . 
     More specifically, the reflector  300  is configured to receive electromagnetic waves generated by the terahertz element  20  and reflect at least part of the electromagnetic waves. The reflection film  54  is configured to receive the electromagnetic waves reflected by the reflector  300  and reflect at least part of the electromagnetic waves in one direction (upward). 
     In this modified example, the lead frame  60  and the two wires W 1  and W 2  are not formed on the mount plate  11 . The reflector  300  may be disposed, for example, within a projection range of the terahertz element  20  as viewed from above. This limits interruption (blocking) of the electromagnetic waves. 
     As shown in  FIG. 78 , the reflection film  54  includes through holes  306 , through which the mount poles  302  and  303  are inserted. The through holes  306  may be greater in size than the mount poles  302  and  303  to avoid contact of the reflection film  54  with the mount poles  302  and  303 . The portion of the reflection film  54  located between the mount poles  302  and  303  may be omitted. That is, as viewed from above, the reflection film  54  may be annular with the central portion removed. The reflector  300  may be recessed with respect to the terahertz element  20 . Specifically, the reflector  300  may be shaped as an antenna that is recessed in the opposite direction of the reflection film  54  (i.e., upward). More specifically, the reflector  300  may be a Cassegrain type or a Gregorian type. 
     The shape of the antenna base  50  may be changed. For example, as shown in  FIG. 79 , the antenna base  50  may be chamfered and dome-shaped. As shown in  FIG. 80 , the antenna base  50  may include a cutaway portion  313 . 
     As shown in  FIG. 81 , the antenna base  50  may be circular as viewed in the z-direction. More specifically, the antenna base  50  may have the shape of a cylinder, the axis of which extends in the z-direction. In this case, exposure regions  321  are formed around the antenna base  50  to expose the lead frame  60 . In this modified example, for example, the exposure regions  321  may be used to mount the terahertz device  10  on the circuit substrate  110 . More specifically, the diameter of the hole  116  formed in the circuit substrate  110  is equal to or slightly greater than the diameter of the contour of the antenna base  50  In this case, when the antenna base  50  is inserted into the hole  116 , the exposure regions  321  contact the circuit substrate  110 . Therefore, the conductive bonding members  117  are disposed on the exposure regions  321 , so that the terahertz device  10  is electrically connected and mounted on the circuit substrate  110 . As a result, the terahertz device  10  is further reduced in size. 
     As shown in  FIG. 82 , the electrodes  91  and  92  may include inclined portions  91   a  and  92   a  inclined in a direction away from the mount plate  11 , more specifically, downward, as the inclined portions  91   a  and  92   a  extend away from the antenna base  50 . For example, the first electrode  91  may be crank-shaped and include a first proximal portion  91   b  extending from the antenna base  50  (the first base side surface  51   a ) in the x-direction, a first distal portion  91   c  disposed sideward and downward relative to the first proximal portion  91   b , and a first inclined portion  91   a  joined to the first proximal portion  91   b  and the first distal portion  91   c.    
     In the same manner, the second electrode  92  may be crank-shaped and include a second proximal portion  92   b  extending from the antenna base  50  (the second base side surface  51   b ) in the x-direction, a second distal portion  92   c  located sideward and downward relative to the second proximal portion  92   b , and a second inclined portion  92   a  joined to the second proximal portion  92   b  and the second distal portion  92   c.    
     In this structure, when part of the antenna base  50  is inserted in the hole  116 , the two distal portions  91   c  and  92   c  may be bonded to the circuit substrate  110  by the conductive bonding member  117  so that the terahertz device  10  is mounted on the circuit substrate  110 . This limits downward projection of the terahertz device  10  from the circuit substrate  110  even when the circuit substrate  110  has a smaller thickness than the terahertz device  10 . The first proximal portion  91   b  and the second proximal portion  92   b  may be omitted. 
     As shown in  FIG. 83 , the inner peripheral end of the adhesive layer  90  may be flush with the surface of the reflection film  54 . That is, the adhesive layer  90  may be configured not to extend inward (in other words, toward the terahertz element  20 ) beyond the reflection film  54 . 
     As shown in  FIGS. 84 and 85 , the inner peripheral end of the adhesive layer  90  may be located outward from the surface of the reflection film  54  (in other words, toward the base side surfaces  51 ) in the x-direction and the y-direction. For example, as shown in  FIG. 84 , the inner peripheral end of the adhesive layer  90  may be flush with the antenna surface  53 . Alternatively, as shown in  FIG. 85 , the inner peripheral end of the adhesive layer  90  may be located outward from the antenna surface  53  in the x-direction and the y-direction. In this case, the adhesive layer  90  is not disposed between the end  54   a  of the reflection film  54  and the lead frame  60 . In other words, the adhesive layer  90  does not necessarily have to be disposed between the reflection film  54  and the lead frame  60 . Even in this case, the reflection film  54  is separated from the lead frame  60  by the height of the adhesive layer  90 , so that contact of the reflection film  54  with the lead frame  60  is limited. 
     The electrodes  91  and  92  may project in the y-direction instead of the x-direction. The electrodes  91  and  92  may project in both the x-direction and the y-direction. 
     The terahertz element  20  may be disposed so that the element back surface  22  faces the reflection film  54 . That is, the reflection film  54  may be disposed at the side of the element back surface  22  of the terahertz element  20 , not at the side of the element main surface  21 . 
     The reflection film  54  does not have to be electrically isolated. 
     The reflection film  54  may be formed on the base main surface  50   a . In this case, for example, a reflection reduction film may be located opposing the base main surface  50   a.    
     The gas existing in the accommodation space A 1  is not limited to air and may be changed in any manner. Moreover, the accommodation space A 1  may be vacuum. 
     The antenna base  50  and the lead frame  60  may be unitized by a process other than adhesion. 
     The shape of the opening  80  may be changed in any manner. For example, one of the part openings  63  and  73  may be omitted. The part openings  63  and  73  may be smaller than the reflection film  54 . 
     The mount plate  11  and the support substrate  150 , which are used as the base member, may have any shape. For example, the mount plate  11  may have a greater thickness than the lead frame  60 . 
     The electrodes  91  and  92  may be disposed in the proximity of the center of the terahertz device  10  in the z-direction or disposed downward from the center. 
     The specific structure of the terahertz element  20  may be changed. For example, the position and size of the two pads  33   b  and  34   b  may be changed. The oscillation point P 1  may be located at a position other than the center. 
     The terahertz element  20  may be configured to receive electromagnetic waves and convert the received electromagnetic waves into electrical energy. Specifically, the terahertz element  20  receives electromagnetic waves, for example, in the range of the opening angle θ of the oscillation point P 1 . In this case, the oscillation point P 1  may be referred to as a reception point that receives electromagnetic waves. 
     In this structure, the reflection film may reflect the incident electromagnetic waves toward the terahertz element  20  (preferably, the reception point). This increases the reception strength of the terahertz device  10 , thereby improving the gain related to reception. 
     Moreover, the terahertz element  20  may be configured to oscillate and receive electromagnetic waves. That is, the oscillation point P 1  may perform at least one of oscillation and reception of electromagnetic waves. 
     When the terahertz element  20  is configured to receive electromagnetic waves, the reflector  300  of the modified example reflects electromagnetic waves reflected by the reflection film  54  toward the terahertz element  20 . In this structure, the electromagnetic waves reflected by the reflection film  54  are emitted via the reflector  300  to the terahertz element  20 . More specifically, the reflection film  54  is configured to reflect at least part of the incident electromagnetic waves toward the reflector  300 . The reflector  300  is configured to receive the electromagnetic waves reflected by the reflection film  54  and emit at least part of the electromagnetic waves toward the terahertz element  20 . 
     CLAUSES 
     The technical aspects will be described below based on the embodiments and the modified examples described above. 
     1. A terahertz device, including: 
     a base member; 
     a terahertz element mounted on the base member and configured to generate an electromagnetic wave; 
     an antenna base located opposing the base member and including an antenna surface; and 
     a reflection film formed on the antenna surface to reflect at least part of the electromagnetic wave generated by the terahertz element in one direction. 
     2. The terahertz device according to clause 1, in which 
     the antenna base includes
         a base main surface faced to the base member,   a base back surface opposite the base main surface, and   a base side surface facing sideward,       

     the terahertz device further comprises an electrode used for electrical connection with an external device, and 
     the electrode includes
         a side electrode formed on the base side surface, and   a back electrode formed on the base back surface.       

     3. The terahertz device according to clause 2, in which the electrode includes a lead frame bent along the antenna base. 
     4. The terahertz device according to clause 3, in which 
     the electrode includes
         a proximal portion that is bent at a corner between the base side surface and the base main surface toward the base side surface,   a bent portion that is bent at a corner between the base side surface and the base back surface, and   a distal portion disposed on the base back surface,       

     the side electrode is a portion of the electrode from the proximal portion to the bent portion, and 
     the back electrode is a portion of the electrode from the bent portion to the distal portion. 
     5. The terahertz device according to any one of clauses 1 to 4, in which 
     the terahertz element includes
         an element main surface including an oscillation point on which an electromagnetic wave is generated, and   an element back surface opposite the element main surface, and       

     the reflection film is disposed closer to the element main surface than to the element back surface. 
     6. The terahertz device according to clause 5, in which 
     the terahertz element is configured to radiate an electromagnetic wave from the oscillation point in a range of an opening angle, and 
     the reflection film is formed over an angle that is greater than or equal to the opening angle of the oscillation point. 
     7. The terahertz device according to clause 5 or 6, in which the reflection film is parabolic-antenna-shaped. 
     8. The terahertz device according to clause 7, in which the reflection film is disposed so that a focal point of the reflection film is located on the oscillation point. 
     9. The terahertz device according to clause 7, in which a center point of the reflection film coincides with the oscillation point as viewed in an opposing direction of the base member and the antenna base. 
     10. The terahertz device according to any one of clauses 7 to 9, in which the reflection film is disposed at a position corresponding to a frequency of an electromagnetic wave generated by the terahertz element so that the electromagnetic wave resonates. 
     11. The terahertz device according to clause 7, in which the terahertz element is disposed at a position so that a center point of the reflection film and the oscillation point are located at different positions as viewed in an opposing direction of the base member and the antenna base. 
     12. The terahertz device according to any one of clauses 1 to 11, in which the reflection film is electrically isolated. 
     13. The terahertz device according to any one of clauses 1 to 12, in which the antenna base is formed of an insulative material. 
     14. The terahertz device according to any one of clauses 1 to 13, in which the base member is located opposing the reflection film and is formed of a material transmissive to an electromagnetic wave. 
     15. The terahertz device according to clause 14, in which the base member is formed of a dielectric. 
     16. The terahertz device according to any one of clauses 1 to 15, in which 
     the base member includes a mount main surface on which the terahertz element is mounted, 
     the antenna base includes
         a base main surface opposed to the mount main surface, and   a recess recessed from the base main surface and including the antenna surface, and       

     the terahertz element and the reflection film are disposed in an accommodation space defined by the mount main surface and the antenna surface. 
     17. The terahertz device according to clause 16, in which the reflection film is formed on the antenna surface and is not formed on the base main surface. 
     18. The terahertz device according to clause 16 or 17, in which 
     the antenna base includes a receptacle, disposed separately from the recess, to accommodate a protection diode, and 
     the protection diode is connected in parallel to the terahertz element. 
     19. The terahertz device according to any one of clauses 16 to 18, further including: 
     a conductive member disposed on the mount main surface and connected to the terahertz element; and 
     an adhesive layer disposed between the antenna base and the conductive member to adhere the antenna base to the conductive member, 
     in which the adhesive layer is formed of an insulative material and is disposed between the reflection film and the conductive member. 
     20. The terahertz device according to clause 19, further including an insulative spacer disposed between the reflection film and the conductive member, in which the spacer is different from the adhesive layer. 
     21. The terahertz device according to clause 19 or 20, in which 
     the recess includes a large diameter surface having a diameter larger than that of the antenna surface and a stepped surface formed between the antenna surface and the large diameter surface, and 
     the reflection film is formed over the antenna surface and the stepped surface. 
     22. The terahertz device according to any one of clauses 19 to 21, in which 
     the base member includes a mount back surface opposite the mount main surface, 
     the terahertz device further includes a reflection reduction film formed on at least a portion of a part of the mount back surface, the part of the mount back surface overlapping the conductive member as viewed in an opposing direction of the base member and the antenna base, and 
     the reflection reduction film reduces reflection of an electromagnetic wave. 
     23. The terahertz device according to any one of clauses 1 to 22, in which 
     the base member includes a conductive member connected to the terahertz element, and 
     the conductive member includes an opening that overlaps at least a portion of the reflection film as viewed in an opposing direction of the base member and the antenna base. 
     24. The terahertz device according to clause 23, in which 
     the conductive member includes a first conductor and a second conductor that are separated and opposed to each other, and 
     the opening includes a gap between the first conductor and the second conductor. 
     25. The terahertz device according to clause 24, in which 
     the opening includes a first part opening formed in a part of the first conductor overlapping the reflection film as viewed in the opposing direction, the first part opening being continuous with the gap, and 
     the opening includes a second part opening formed in a part of the second conductor overlapping the reflection film as viewed in the opposing direction, the second part opening being continuous with the gap. 
     26. The terahertz device according to clause 25, in which 
     the first conductor includes a first connector configured to be electrically connected to the terahertz element, 
     the first connector projects toward the terahertz element from a first wall surface that is a wall surface defining the first part opening, 
     the second conductor includes a second connector configured to be electrically connected to the terahertz element, and 
     the second connector projects toward the terahertz element from a second wall surface that is a wall surface defining the second part opening. 
     27. The terahertz device according to clause 26, further including a first wire connecting the first connector to a first pad formed on the terahertz element, in which as viewed in the opposing direction, a projection dimension of the first connector from the first wall surface is less than a length of the first wire. 
     28. The terahertz device according to clause 27, further including a second wire connecting the second connector to a second pad formed on the terahertz element, in which as viewed in the opposing direction, a projection dimension of the second connector from the second wall surface is less than a length of the second wire. 
     29. The terahertz device according to clause 26, further including a first wire connecting the first connector to a first pad formed on the terahertz element, in which as viewed in the opposing direction, a length of the first wire is less than a projection dimension of the first connector from the first wall surface. 
     30. The terahertz device according to clause 29, further including a second wire connecting the second connector to a second pad formed on the terahertz element, in which as viewed in the opposing direction, a length of the second wire is less than a projection dimension of the second connector from the second wall surface. 
     31. The terahertz device according to any one of clauses 26 to 30, in which the first connector and the second connector are opposed to each other at opposite sides of the terahertz element. 
     32. The terahertz device according to any one of clauses 26 to 30, in which the first connector and the second connector are disposed parallel to each other. 
     33. The terahertz device according to any one of clauses 23 to 32, in which 
     the conductive member is formed of a lead frame, and 
     the base member is mounted on the lead frame. 
     34. The terahertz device according to clause 33, in which the base member is plate-shaped and has a thickness that is less than a thickness of the lead frame. 
     35. The terahertz device according to clause 1, further including a lead frame as the base member, in which the lead frame includes 
     a mount base on which the terahertz element is mounted, 
     a first connector joined to the mount base, the first connector being electrically connected to a first pad formed on the terahertz element by a first wire, and 
     a second connector insulated from the first connector, the second connector being electrically connected to a second pad formed on the terahertz element by a second wire. 
     36. The terahertz device according to clause 1, in which 
     the base member includes
         a mount main surface on which the terahertz element is mounted, and   a mount back surface opposite the mount main surface,       

     the antenna base is disposed at the mount back surface, and 
     the terahertz element and the reflection film are opposed to each other at opposite sides of the base member. 
     37. A terahertz device, including: 
     a terahertz element configured to generate an electromagnetic wave; 
     a base member including a reflector, the reflector being located opposing the terahertz element to reflect at least part of the electromagnetic wave generated by the terahertz element; 
     an antenna base located opposing the base member and including an antenna surface; and 
     a reflection film formed on the antenna surface to reflect at least part of the electromagnetic wave reflected by the reflector in one direction. 
     38. A terahertz device, including: 
     a base member; 
     a terahertz element mounted on the base member and configured to receive an electromagnetic wave; 
     an antenna base located opposing the base member and including an antenna surface; and 
     a reflection film formed on the antenna surface to reflect an incident electromagnetic wave toward the terahertz element. 
     39. The terahertz device according to clause 38, in which 
     the antenna base includes
         a base main surface opposed to the base member,   a base back surface opposite the base main surface, and   a base side surface facing sideward,       

     the terahertz device further comprises an electrode used for electrical connection with an external device, and 
     the electrode includes
         a side electrode formed on the base side surface, and   a back electrode formed on the base back surface.       

     40. The terahertz device according to clause 39, in which the electrode includes a lead frame bent along the antenna base. 
     41. The terahertz device according to clause 40, in which 
     the electrode includes
         a proximal portion that is bent at a corner between the base side surface and the base main surface toward the base side surface,   a bent portion that is bent at a corner between the base side surface and the base back surface, and   a distal portion disposed on the base back surface,       

     the side electrode is a portion of the electrode from the proximal portion to the bent portion, and 
     the back electrode is a portion of the electrode from the bent portion to the distal portion. 
     42. The terahertz device according to any one of clauses 38 to 41, in which 
     the terahertz element includes
         an element main surface including a reception point that receives an electromagnetic wave, and   an element back surface opposite the element main surface, and       

     the reflection film is disposed closer to the element main surface than to the element back surface. 
     43. The terahertz device according to clause 42, in which 
     the terahertz element is configured to receive an electromagnetic wave in a range of an opening angle with the reception point, and 
     the reflection film is formed over an angle that is greater than or equal to the opening angle with the reception point. 
     44. The terahertz device according to clause 42 or 43, in which the reflection film is parabolic-antenna-shaped. 
     45. The terahertz device according to clause 44, in which the reflection film is disposed so that a focal point of the reflection film is located on the reception point. 
     46. The terahertz device according to clause 44, in which a center point of the reflection film coincides with the reception point as viewed in an opposing direction of the base member and the antenna base. 
     47. The terahertz device according to any one of clauses 44 to 46, in which the reflection film is disposed at a position corresponding to a frequency of an electromagnetic wave received by the terahertz element so that the electromagnetic wave resonates. 
     48. The terahertz device according to clause 44, in which the terahertz element is disposed at a position so that a center point of the reflection film and the reception point are located at different positions as viewed in an opposing direction of the base member and the antenna base. 
     49. The terahertz device according to any one of clauses 38 to 48, in which the reflection film is electrically isolated. 
     50. The terahertz device according to any one of clauses 38 to 49, in which the antenna base is formed of an insulative material. 
     51. The terahertz device according to any one of clauses 38 to 50, in which the base member is located opposing the reflection film and is formed of a material transmissive to an electromagnetic wave. 
     52. The terahertz device according to clause 51, in which the base member is formed of a dielectric. 
     53. The terahertz device according to any one of clauses 38 to 52, in which 
     the base member includes a mount main surface on which the terahertz element is mounted, 
     the antenna base includes
         a base main surface opposed to the mount main surface, and   a recess recessed from the base main surface and including the antenna surface, and       

     the terahertz element and the reflection film are disposed in an accommodation space defined by the mount main surface and the antenna surface. 
     54. The terahertz device according to clause 53, in which the reflection film is formed on the antenna surface and is not formed on the base main surface. 
     55. The terahertz device according to clause 53 or 54, in which 
     the antenna base includes a receptacle disposed separately from the recess to accommodate a protection diode, and 
     the protection diode is connected in parallel to the terahertz element. 
     56. The terahertz device according to any one of clauses 53 to 55, further including: 
     a conductive member disposed on the mount main surface and connected to the terahertz element; and 
     an adhesive layer disposed between the antenna base and the conductive member to adhere the antenna base to the conductive member, 
     in which the adhesive layer is formed of an insulative material and is disposed between the reflection film and the conductive member. 
     57. The terahertz device according to clause 56, further including an insulative spacer disposed between the reflection film and the conductive member, in which the spacer is different from the adhesive layer. 
     58. The terahertz device according to clause 56 or 57, in which 
     the recess includes a large diameter surface having a diameter larger than that of the antenna surface and a stepped surface formed between the antenna surface and the large diameter surface, and 
     the reflection film is formed over the antenna surface and the stepped surface. 
     59. The terahertz device according to any one of clauses 56 to 58, in which 
     the base member includes a mount back surface opposite the mount main surface, 
     the terahertz device further comprises a reflection reduction film formed on at least a portion of a part of the mount back surface, the part of the mount back surface overlapping the conductive member as viewed in an opposing direction of the base member and the antenna base, and 
     the reflection reduction film reduces reflection of an electromagnetic wave. 
     60. The terahertz device according to any one of clauses 38 to 59, in which 
     the base member includes a conductive member connected to the terahertz element, and 
     the conductive member includes an opening that overlaps at least a portion of the reflection film as viewed in an opposing direction of the base member and the antenna base. 
     61. The terahertz device according to clause 60, in which 
     the conductive member includes a first conductor and a second conductor that are separated and opposed to each other, and 
     the opening includes a gap between the first conductor and the second conductor. 
     62. The terahertz device according to clause 61, in which 
     the opening includes a first part opening formed in a part of the first conductor overlapping the reflection film as viewed in the opposing direction, the first part opening being continuous with the gap, and 
     the opening includes a second part opening formed in a part of the second conductor overlapping the reflection film as viewed in the opposing direction, the second part opening being continuous with the gap. 
     63. The terahertz device according to clause 62, in which 
     the first conductor includes a first connector configured to be electrically connected to the terahertz element, 
     the first connector projects toward the terahertz element from a first wall surface that is a wall surface defining the first part opening, 
     the second conductor includes a second connector configured to be electrically connected to the terahertz element, and 
     the second connector projects toward the terahertz element from a second wall surface that is a wall surface defining the second part opening. 
     64. The terahertz device according to clause 63, further including a first wire connecting the first connector to a first pad formed on the terahertz element, in which as viewed in the opposing direction, a projection dimension of the first connector from the first wall surface is less than a length of the first wire. 
     65. The terahertz device according to clause 64, further including a second wire connecting the second connector to a second pad formed on the terahertz element, in which as viewed in the opposing direction, a projection dimension of the second connector from the second wall surface is less than a length of the second wire. 
     66. The terahertz device according to clause 63, further including a first wire connecting the first connector to a first pad formed on the terahertz element, in which as viewed in the opposing direction, a length of the first wire is less than a projection dimension of the first connector from the first wall surface. 
     67. The terahertz device according to clause 66, further including a second wire connecting the second connector to a second pad formed on the terahertz element, in which as viewed in the opposing direction, a length of the second wire is less than a projection dimension of the second connector from the second wall surface. 
     68. The terahertz device according to any one of clauses 63 to 67, in which the first connector and the second connector are opposed to each other at opposite sides of the terahertz element. 
     69. The terahertz device according to any one of clauses 63 to 67, in which the first connector and the second connector are disposed parallel to each other. 
     70. The terahertz device according to any one of clauses 60 to 69, in which 
     the conductive member is formed of a lead frame, and 
     the base member is mounted on the lead frame. 
     71. The terahertz device according to clause 70, in which the base member is plate-shaped and has a thickness that is less than that of the lead frame. 
     72. The terahertz device according to clause 38, further including a lead frame as the base member, in which the lead frame includes 
     a mount base on which the terahertz element is mounted, 
     a first connector joined to the mount base, the first connector being electrically connected to a first pad formed on the terahertz element by a first wire, and 
     a second connector insulated from the first connector, the second connector being electrically connected to a second pad formed on the terahertz element by a second wire. 
     73. The terahertz device according to clause 38, in which 
     the base member includes
         a mount main surface on which the terahertz element is mounted, and   a mount back surface opposite the mount main surface,       

     the antenna base is disposed at the mount back surface, and 
     the terahertz element and the reflection film are opposed to each other at opposite sides of the base member. 
     74. A terahertz device, including: 
     a terahertz element configured to receive an electromagnetic wave; 
     a base member including a reflector, the reflector being located opposing the terahertz element to reflect at least part of an incident electromagnetic wave toward the terahertz element; 
     an antenna base located opposing the base member and including an antenna surface; and 
     a reflection film formed on the antenna surface to reflect at least part of an incident electromagnetic wave toward the reflector. 
     75. A terahertz device, including: 
     a base member; 
     a terahertz element mounted on the base member and configured to generate an electromagnetic wave; 
     an antenna base opposed to the base member and including an antenna surface; 
     a reflection film formed on the antenna surface to reflect at least part of the electromagnetic wave generated by the terahertz element in one direction; and 
     an electrode used for electrical connection with an external device, in which the electrode projects sideward relative to the antenna base as viewed in an opposing direction of the base member and the antenna base. 
     76. The terahertz device according to clause 75, in which the electrode is located toward the base member from a central portion of the terahertz device in the opposing direction. 
     77. The terahertz device according to clause 75 or 76, in which the electrode is formed of a lead frame. 
     78. The terahertz device according to clause 77, in which the electrode includes an inclined portion inclined in a direction away from the base member as the electrode extends away from the antenna base. 
     79. The terahertz device according to clause 77 or 78, in which the electrode is crank-shaped. 
     80. The terahertz device according to clause 75 or 76, in which 
     the base member includes a support substrate, 
     the support substrate includes an extension extending sideward beyond the antenna base as viewed in the opposing direction, and 
     the electrode includes a wiring pattern formed on the extension. 
     81. The terahertz device according to clause 80, in which 
     the base member includes a mount main surface on which the terahertz element is mounted and a mount back surface opposite the mount main surface, 
     the terahertz device further comprises:
         a connection pattern that is a wiring pattern formed on the mount main surface at a position separate from the electrode, the connection pattern being connected to the terahertz element;   a back pattern that is a wiring pattern formed on the mount back surface; and   a through via extending through the support substrate and connecting the connection pattern and the electrode to the back pattern, and       

     the reflection film includes an end disposed between the connection pattern and the electrode and separated from the connection pattern and the electrode as viewed in the opposing direction. 
     82. The terahertz device according to any one of clauses 75 to 81, in which 
     the terahertz element includes
         an element main surface including an oscillation point on which an electromagnetic wave is generated, and   an element back surface opposite the element main surface, and       

     the reflection film is disposed closer to the element main surface than to the element back surface. 
     83. The terahertz device according to clause 82, in which 
     the terahertz element is configured to radiate an electromagnetic wave from the oscillation point in a range of an opening angle, and 
     the reflection film is formed over an angle that is greater than or equal to the opening angle of the oscillation point. 
     84. The terahertz device according to clause 82 or 83, in which the reflection film is parabolic-antenna-shaped. 
     85. The terahertz device according to clause 84, in which the reflection film is disposed so that a focal point of the reflection film is located on the oscillation point. 
     86. The terahertz device according to clause 84, in which a center point of the reflection film coincides with the oscillation point as viewed in an opposing direction of the base member and the antenna base. 
     87. The terahertz device according to any one of clauses 84 to 86, in which the reflection film is disposed at a position corresponding to a frequency of an electromagnetic wave generated by the terahertz element so that the electromagnetic wave resonates. 
     88. The terahertz device according to clause 84, in which the terahertz element is disposed at a position so that a center point of the reflection film and the oscillation point are located at different positions as viewed in an opposing direction of the base member and the antenna base. 
     89. The terahertz device according to any one of clauses 75 to 88, in which the reflection film is electrically isolated. 
     90. The terahertz device according to any one of clauses 75 to 89, in which the antenna base is formed of an insulative material. 
     91. The terahertz device according to any one of clauses 75 to 90, in which the base member is located opposing the reflection film and is formed of a material transmissive to an electromagnetic wave. 
     92. The terahertz device according to clause 91, in which the base member is formed of a dielectric. 
     93. The terahertz device according to any one of clauses 75 to 92, in which 
     the base member includes a mount main surface on which the terahertz element is mounted, 
     the antenna base includes
         a base main surface faced to the mount main surface, and   a recess recessed from the base main surface and including the antenna surface, and       

     the terahertz element and the reflection film are disposed in an accommodation space defined by the mount main surface and the antenna surface. 
     94. The terahertz device according to clause 93, in which the reflection film is formed on the antenna surface and is not formed on the base main surface. 
     95. The terahertz device according to clause 93 or 94, in which 
     the antenna base includes a receptacle disposed separately from the recess to accommodate a protection diode, and 
     the protection diode is connected in parallel to the terahertz element. 
     96. The terahertz device according to any one of clauses 93 to 95, further including: 
     a conductive member disposed on the mount main surface and connected to the terahertz element; and 
     an adhesive layer disposed between the antenna base and the conductive member to adhere the antenna base to the conductive member, 
     in which the adhesive layer is formed of an insulative material and is disposed between the reflection film and the conductive member. 
     97. The terahertz device according to clause 96, further including an insulative spacer disposed between the reflection film and the conductive member, in which the spacer is different from the adhesive layer. 
     98. The terahertz device according to clause 96 or 97, in which 
     the recess includes a large diameter surface having a diameter larger than that of the antenna surface and a stepped surface formed between the antenna surface and the large diameter surface, and 
     the reflection film is formed over the antenna surface and the stepped surface. 
     99. The terahertz device according to any one of clauses 96 to 98, in which 
     the base member includes a mount back surface opposite the mount main surface, 
     the terahertz device further comprises a reflection reduction film formed on at least a portion of a part of the mount back surface, the part of the mount back surface overlapping the conductive member as viewed in an opposing direction of the base member and the antenna base, and 
     the reflection reduction film reduces reflection of an electromagnetic wave. 
     100. The terahertz device according to any one of clauses 65 to 99, in which 
     the base member includes a conductive member connected to the terahertz element, and 
     the conductive member includes an opening that overlaps at least a portion of the reflection film as viewed in an opposing direction of the base member and the antenna base. 
     101. The terahertz device according to clause 100, in which 
     the conductive member includes a first conductor and a second conductor that are separated and faced to each other, and 
     the opening includes a gap between the first conductor and the second conductor. 
     102. The terahertz device according to clause 101, in which 
     the opening includes a first part opening formed in a part of the first conductor overlapping the reflection film as viewed in the opposing direction, the first part opening being continuous with the gap, and 
     the opening includes a second part opening formed in a part of the second conductor overlapping the reflection film as viewed in the opposing direction, the second part opening being continuous with the gap. 
     103. The terahertz device according to clause 102, in which 
     the first conductor includes a first connector configured to be electrically connected to the terahertz element, 
     the first connector projects toward the terahertz element from a first wall surface that is a wall surface defining the first part opening, 
     the second conductor includes a second connector configured to be electrically connected to the terahertz element, and 
     the second connector projects toward the terahertz element from a second wall surface that is a wall surface defining the second part opening. 
     104. The terahertz device according to clause 103, further including a first wire connecting the first connector to a first pad formed on the terahertz element, in which as viewed in the opposing direction, a projection dimension of the first connector from the first wall surface is less than a length of the first wire. 
     105. The terahertz device according to clause 104, further including a second wire connecting the second connector to a second pad formed on the terahertz element, in which as viewed in the opposing direction, a projection dimension of the second connector from the second wall surface is less than a length of the second wire. 
     106. The terahertz device according to clause 103, further including a first wire connecting the first connector to a first pad formed on the terahertz element, in which as viewed in the opposing direction, a length of the first wire is less than a projection dimension of the first connector from the first wall surface. 
     107. The terahertz device according to clause 106, further including a second wire connecting the second connector to a second pad formed on the terahertz element, in which as viewed in the opposing direction, a length of the second wire is less than a projection dimension of the second connector from the second wall surface. 
     108. The terahertz device according to any one of clauses 103 to 107, in which the first connector and the second connector are faced to each other at opposite sides of the terahertz element. 
     109. The terahertz device according to any one of clauses 103 to 107, in which the first connector and the second connector are disposed parallel to each other. 
     110. The terahertz device according to any one of clauses 96 to 109, in which 
     the conductive member is formed of a lead frame, and 
     the base member is mounted on the lead frame. 
     111. The terahertz device according to clause 110, in which the base member is plate-shaped and has a thickness that is less than that of the lead frame. 
     112. The terahertz device according to any one of clauses 96 to 109, in which 
     the base member includes a support substrate, and 
     the conductive member includes a wiring pattern formed on the support substrate. 
     113. The terahertz device according to clause 75, further including a lead frame as the base member, in which the lead frame includes 
     a mount base on which the terahertz element is mounted, 
     a first connector joined to the mount base, the first connector being electrically connected to a first pad formed on the terahertz element by a first wire, and 
     a second connector insulated from the first connector, the second connector being electrically connected to a second pad formed on the terahertz element by a second wire. 
     114. The terahertz device according to clause 75, in which 
     the base member includes
         a mount main surface on which the terahertz element is mounted, and   a mount back surface opposite the mount main surface,       

     the antenna base is disposed at the mount back surface, and 
     the terahertz element and the reflection film are faced to each other at opposite sides of the base member. 
     115. The terahertz device according to clause 75, in which 
     the antenna base is convex-lens-shaped and is curved to project in a direction away from the terahertz element, and 
     the antenna surface corresponds to a lens surface of the antenna base. 
     116. The terahertz device according to clause 115, in which 
     the base member includes
         a mount main surface on which the terahertz element is mounted, and   a mount back surface opposite the mount main surface,       

     the antenna base is disposed at the mount back surface of the base member, and 
     the terahertz element and the reflection film are opposed to each other at opposite sides of the base member and the antenna base. 
     117. A terahertz device, including: 
     a base member; 
     a terahertz element mounted on the base member and configured to receive an electromagnetic wave; 
     an antenna base located opposing the base member and including an antenna surface; 
     a reflection film formed on the antenna surface to reflect an incident electromagnetic wave toward the terahertz element; and 
     an electrode used for electrical connection with an external device, in which the electrode projects sideward relative to the antenna base as viewed in an opposing direction of the base member and the antenna base. 
     118. The terahertz device according to clause 117, in which the electrode is located toward the base member from a central portion of the terahertz device in the opposing direction. 
     119. The terahertz device according to clause 117 or 118, in which the electrode is formed of a lead frame. 
     120. The terahertz device according to clause 119, in which the electrode includes an inclined portion inclined in a direction away from the base member as the electrode extends away from the antenna base. 
     121. The terahertz device according to clause 119 or 120, in which the electrode is crank-shaped. 
     122. The terahertz device according to clause 117 or 118, in which 
     the base member includes a support substrate, 
     the support substrate includes an extension extending sideward beyond the antenna base as viewed in the opposing direction, and 
     the electrode includes a wiring pattern formed on the extension. 
     123. The terahertz device according to clause 122, in which 
     the base member includes a mount main surface on which the terahertz element is mounted and a mount back surface opposite the mount main surface, 
     the terahertz device further comprises:
         a connection pattern that is a wiring pattern formed on the mount main surface at a position separate from the electrode, the connection pattern being connected to the terahertz element;   a back pattern that is a wiring pattern formed on the mount back surface; and   a through via extending through the support substrate and connecting the connection pattern and the electrode to the back pattern, and       

     the reflection film includes an end disposed between the connection pattern and the electrode and separated from the connection pattern and the electrode as viewed in the opposing direction. 
     124. The terahertz device according to any one of clauses 117 to 123, in which 
     the terahertz element includes
         an element main surface including a reception point that receives an electromagnetic wave, and   an element back surface opposite the element main surface, and       

     the reflection film is disposed closer to the element main surface than to the element back surface. 
     125. The terahertz device according to clause 124, in which 
     the terahertz element is configured to receive an electromagnetic wave in a range of an opening angle with the reception point, and 
     the reflection film is formed over an angle that is greater than or equal to the opening angle with the reception point. 
     126. The terahertz device according to clause 124 or 125, in which the reflection film is parabolic-antenna-shaped. 
     127. The terahertz device according to clause 126, in which the reflection film is disposed so that a focal point of the reflection film is located on the reception point. 
     128. The terahertz device according to clause 126, in which a center point of the reflection film coincides with the reception point as viewed in an opposing direction of the base member and the antenna base. 
     129. The terahertz device according to any one of clauses 126 to 128, in which the reflection film is disposed at a position corresponding to a frequency of an electromagnetic wave received by the terahertz element so that the electromagnetic wave resonates. 
     130. The terahertz device according to clause 126, in which the terahertz element is disposed at a position so that a center point of the reflection film and the reception point are located at different positions as viewed in an opposing direction of the base member and the antenna base. 
     131. The terahertz device according to any one of clauses 117 to 130, in which the reflection film is electrically isolated. 
     132. The terahertz device according to any one of clauses 117 to 131, in which the antenna base is formed of an insulative material. 
     133. The terahertz device according to any one of clauses 117 to 132, in which the base member is located opposing the reflection film and is formed of a material transmissive to an electromagnetic wave. 
     134. The terahertz device according to clause 133, in which the base member is formed of a dielectric. 
     135. The terahertz device according to any one of clauses 117 to 134, in which 
     the base member includes a mount main surface on which the terahertz element is mounted, 
     the antenna base includes
         a base main surface faced to the mount main surface, and   a recess recessed from the base main surface and including the antenna surface, and       

     the terahertz element and the reflection film are disposed in an accommodation space defined by the mount main surface and the antenna surface. 
     136. The terahertz device according to clause 135, in which the reflection film is formed on the antenna surface and is not formed on the base main surface. 
     137. The terahertz device according to clause 135 or 136, in which 
     the antenna base includes a receptacle disposed separately from the recess to accommodate a protection diode, and 
     the protection diode is connected in parallel to the terahertz element. 
     138. The terahertz device according to any one of clauses 135 to 137, further including: 
     a conductive member disposed on the mount main surface and connected to the terahertz element; and 
     an adhesive layer disposed between the antenna base and the conductive member to adhere the antenna base to the conductive member, 
     in which the adhesive layer is formed of an insulative material and is disposed between the reflection film and the conductive member. 
     139. The terahertz device according to clause 138, further including an insulative spacer disposed between the reflection film and the conductive member, in which the spacer is different from the adhesive layer. 
     140. The terahertz device according to clause 138 or 139, in which 
     the recess includes a large diameter surface having a diameter larger than that of the antenna surface and a stepped surface formed between the antenna surface and the large diameter surface, and 
     the reflection film is formed over the antenna surface and the stepped surface. 
     141. The terahertz device according to any one of clauses 138 to 140, in which 
     the base member includes a mount back surface opposite the mount main surface, 
     the terahertz device further comprises a reflection reduction film formed on at least a portion of a part of the mount back surface, the part of the mount back surface overlapping the conductive member as viewed in an opposing direction of the base member and the antenna base, and 
     the reflection reduction film reduces reflection of an electromagnetic wave. 
     142. The terahertz device according to any one of clauses 117 to 141, in which 
     the base member includes a conductive member connected to the terahertz element, and 
     the conductive member includes an opening that overlaps at least a portion of the reflection film as viewed in an opposing direction of the base member and the antenna base. 
     143. The terahertz device according to clause 142, in which 
     the conductive member includes a first conductor and a second conductor that are separated and faced to each other, and 
     the opening includes a gap between the first conductor and the second conductor. 
     144. The terahertz device according to clause 143, in which 
     the opening includes a first part opening formed in a part of the first conductor overlapping the reflection film as viewed in the opposing direction, the first part opening being continuous with the gap, and 
     the opening includes a second part opening formed in a part of the second conductor overlapping the reflection film as viewed in the opposing direction, the second part opening being continuous with the gap. 
     145. The terahertz device according to clause 144, in which 
     the first conductor includes a first connector configured to be electrically connected to the terahertz element, 
     the first connector projects toward the terahertz element from a first wall surface that is a wall surface defining the first part opening, 
     the second conductor includes a second connector configured to be electrically connected to the terahertz element, and 
     the second connector projects toward the terahertz element from a second wall surface that is a wall surface defining the second part opening. 
     146. The terahertz device according to clause 145, further including a first wire connecting the first connector to a first pad formed on the terahertz element, in which as viewed in the opposing direction, a projection dimension of the first connector from the first wall surface is less than a length of the first wire. 
     147. The terahertz device according to clause 146, further including a second wire connecting the second connector to a second pad formed on the terahertz element, in which as viewed in the opposing direction, a projection dimension of the second connector from the second wall surface is less than a length of the second wire. 
     148. The terahertz device according to clause 145, further including a first wire connecting the first connector to a first pad formed on the terahertz element, in which as viewed in the opposing direction, a length of the first wire is less than a projection dimension of the first connector from the first wall surface. 
     149. The terahertz device according to clause 148, further including a second wire connecting the second connector to a second pad formed on the terahertz element, in which as viewed in the opposing direction, a length of the second wire is less than a projection dimension of the second connector from the second wall surface. 
     150. The terahertz device according to any one of clauses 145 to 149, in which the first connector and the second connector are faced to each other at opposite sides of the terahertz element. 
     151. The terahertz device according to any one of clauses 145 to 149, in which the first connector and the second connector are disposed parallel to each other. 
     152. The terahertz device according to any one of clauses 138 to 151, in which 
     the conductive member is formed of a lead frame, and 
     the base member is mounted on the lead frame. 
     153. The terahertz device according to clause 152, in which the base member is plate-shaped and has a thickness that is less than that of the lead frame. 
     154. The terahertz device according to any one of clauses 138 to 151, in which 
     the base member includes a support substrate, and 
     the conductive member includes a wiring pattern formed on the support substrate. 
     155. The terahertz device according to clause 117, further including a lead frame as the base member, in which the lead frame includes 
     a mount base on which the terahertz element is mounted, 
     a first connector joined to the mount base, the first connector being electrically connected to a first pad formed on the terahertz element by a first wire, and 
     a second connector insulated from the first connector, the second connector being electrically connected to a second pad formed on the terahertz element by a second wire. 
     156. The terahertz device according to clause 117, in which 
     the base member includes
         a mount main surface on which the terahertz element is mounted, and   a mount back surface opposite the mount main surface,       

     the antenna base is disposed at the mount back surface, and 
     the terahertz element and the reflection film are faced to each other at opposite sides of the base member. 
     157. The terahertz device according to clause 117, in which 
     the antenna base is convex-lens-shaped and is curved to project in a direction away from the terahertz element, and 
     the antenna surface corresponds to a lens surface of the antenna base. 
     158. The terahertz device according to clause 157, in which 
     the base member includes
         a mount main surface on which the terahertz element is mounted, and   a mount back surface opposite the mount main surface,       

     the antenna base is disposed at the mount back surface of the base member, and 
     the terahertz element and the reflection film are opposed to each other at opposite sides of the base member and the antenna base. 
     159. The antenna base may include a receptacle arranged separately from the recess to accommodate a specific element, the specific element being electrically connected to the terahertz element. 
     160. The specific element may be an integrated circuit (IC). 
     161. A terahertz device, including: 
     a base member; 
     a terahertz element mounted on the base member and configured to generate an electromagnetic wave; 
     an antenna base located opposing the base member and including an antenna surface; and 
     a reflection film formed on the antenna surface to reflect at least part of the electromagnetic wave generated by the terahertz element in one direction. 
     162. A terahertz device, including: 
     a base member; 
     a terahertz element mounted on the base member and configured to receive an electromagnetic wave; 
     an antenna base located opposing the base member and including an antenna surface; and 
     a reflection film formed on the antenna surface to reflect an incident electromagnetic wave toward the terahertz element. 
     163. A terahertz device, including: 
     a terahertz element configured to generate an electromagnetic wave; 
     a base member including a reflector, the reflector being located opposing the terahertz element to reflect at least part of the electromagnetic wave generated by the terahertz element; 
     an antenna base located opposing the base member and including an antenna surface; and 
     a reflection film formed on the antenna surface to reflect at least part of the electromagnetic wave reflected by the reflector in one direction. 
     164. A terahertz device, including: 
     a terahertz element configured to receive an electromagnetic wave; 
     a base member including a reflector, the reflector being located opposing the terahertz element to reflect at least part of an incident electromagnetic wave toward the terahertz element; 
     an antenna base located opposing the base member and including an antenna surface; and 
     a reflection film formed on the antenna surface to reflect at least part of an incident electromagnetic wave toward the reflector. 
     165. The antenna base may include a receptacle arranged separately from the recess to accommodate a specific element, the specific element being electrically connected to the terahertz element. 
     166. A specific element that is mounted on the mount back surface when the specific element is electrically connected to the terahertz element may be included. 
     167. The specific element may be an IC. 
     DESCRIPTION OF THE REFERENCE NUMERALS 
       10 ) terahertz device;  11 ) mount plate (base member);  12 ) mount main surface;  13 ) mount back surface;  20 ) terahertz element;  21 ) element main surface;  22 ) element back surface;  33   b ) first pad;  34   b ) second pad;  50 ) antenna base;  50   a ) base main surface;  50   b ) base back surface;  51   a ) first base side surface;  51   b ) second base side surface;  52 ) recess;  53 ) antenna surface;  54 ,  223 ,  224 ) reflection film;  54   a ) end of reflection film;  60 ) lead frame;  61 ) first lead part;  63 ) first part opening;  64 ) first inner surface;  65 ,  211 ) first connector;  71 ) second lead part;  73 ) second part opening;  74 ) second inner surface;  75 ,  212 ) second connector;  80 ) opening;  81 ) gap;  90 ) adhesive layer;  94 ,  101 ,  304 ,  305 ) electrode;  94   a ,  101   a ) proximal portion;  94   b ,  101   b ) bent portion;  94   c ,  101   c ) distal portion;  95 ,  102 ) side electrode;  93 ,  103 ) back electrode;  110 ) circuit substrate;  120 ) reflection reduction film;  131 ,  132 ) protection diode;  141 ,  142 ) receptacle;  200 ) spacer;  210 ) mount base;  221 ) large diameter surface;  222 ) stepped surface;  300 ) reflector;  301 ) reflection protrusion; A 1 ) accommodation space; P 1 ) oscillation point; P 2 ) center point of reflection film; W 1 ) first wire; W 2 ) second wire; θ) opening angle;  153 ) mount main surface;  154 ) mount back surface;  230 ) antenna base;  231 ) antenna surface;  233 ,  283 ,  290 ) reflection film;  170 ) adhesive layer;  91 ,  171 ,  192 ,  242 ) first electrode (electrode);  92 ,  172 ,  202 ,  252 ) second electrode (electrode);  91   a ,  92   a ) inclined portion;  116 ) hole;  180 ,  220 ) reflection reduction film;  150 ) support substrate (base member);  151 ,  152 ) extension;  160 ) wiring pattern;  191 ,  201 ,  241 ,  251 ) connection pattern;  193 ,  203 ) back pattern;  194 ,  195 ,  204 ,  205 ) through via;  260 ) spacer;  270 ) mount base;  281 ) large diameter surface;  282 ) stepped surface