Patent Publication Number: US-2021167254-A1

Title: Terahertz device and production method for terahertz device

Description:
TECHNICAL FIELD 
     The present disclosure relates to a terahertz device and a method for manufacturing a terahertz device. 
     BACKGROUND ART 
     With recent miniaturization of electronic devices such as transistors to reduce their sizes to nano-scale, a phenomenon called quantum effect has become often observed. Ultra-high-speed devices or new-function devices that use such quantum effect are being developed. Under such circumstances, attempts are being made in particular to use the frequency range of 0.1 to 10 THz, called a terahertz band, to perform high-capacity communication, information processing, imaging or measurement, for example. This frequency range has the characteristics of both light and radio waves, and devices that operate in this frequency range, if realized, can be utilized for various applications including imaging, high-capacity communication or information processing described above as well as measurement in various fields such as physical properties, astronomy or biology. 
     As an element that radiates high-frequency electromagnetic waves with frequencies in the terahertz band, an element is known that has a resonant tunneling diode (RTD) and a fine slot antenna integrated therein. 
     TECHNICAL REFERENCE 
     Patent Document 
     Patent Document 1: JP-A-2009-80448 
     SUMMARY OF THE INVENTION 
     Problems to Be Solved By the Invention 
     An object of the present disclosure is to provide a terahertz device with a packaging structure suitable for modularization of a terahertz element. 
     Means for Solving the Problems 
     According to a first aspect of the present disclosure, there is provided a terahertz device comprising: a terahertz element configured to perform conversion between terahertz waves and electric energy and having an element front surface and an element back surface spaced apart from each other in a first direction; a sealing resin covering the terahertz element; a wiring layer electrically connected to the terahertz element; and a frame-shaped member made of a conductive material and arranged around the terahertz element as viewed in the first direction, where the frame-shaped member has a reflective surface capable of reflecting the terahertz waves. 
     According to a second aspect of the present disclosure, there is provided a method for manufacturing a terahertz device that comprises a terahertz element configured to perform conversion between terahertz waves and electric energy and having an element front surface and an element back surface spaced apart from each other in a first direction. The method comprises: a support board preparation step for preparing a support board having a support-board front surface and a support-board back surface facing away from each other in the first direction; a frame-shaped member forming step for forming a frame-shaped member from a conductive material on the support board; a wiring layer forming step for forming a wiring layer electrically connected to the terahertz element; an element mounting step for mounting the terahertz element on the support board such that the frame-shaped member is positioned around the terahertz element as viewed in the first direction; a sealing resin forming step for forming a sealing resin covering the terahertz element; and a grinding step for grinding the support board, where the frame-shaped member has a reflective surface capable of reflecting the terahertz waves. 
     Effects of the Invention 
     The terahertz device according to the present disclosure has a packaging structure that allows for modularization of a terahertz element. Also the method for manufacturing a terahertz device according to the present disclosure makes it possible to manufacture a terahertz element with a packaging structure that allows for modularization of a terahertz element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a terahertz device according to a first embodiment; 
         FIG. 2  is a bottom view of the terahertz device according to the first embodiment; 
         FIG. 3  is a sectional view taken along line III-III in  FIG. 1 ; 
         FIG. 4  is a schematic view showing an example of a pattern of the terahertz element as viewed in plan; 
         FIG. 5  is a schematic view showing a section of the terahertz element; 
         FIG. 6  is an enlarged view showing a part of  FIG. 5 ; 
         FIG. 7  is a sectional view showing a step of a method for manufacturing the terahertz device according to the first embodiment; 
         FIG. 8  is a sectional view showing a step of the method for manufacturing the terahertz device according to the first embodiment; 
         FIG. 9  is a sectional view showing a step of the method for manufacturing the terahertz device according to the first embodiment; 
         FIG. 10  is a sectional view showing a step of the method for manufacturing the terahertz device according to the first embodiment; 
         FIG. 11  is a plan view showing a step of the method for manufacturing the terahertz device according to the first embodiment; 
         FIG. 12  is a sectional view showing a step of the method for manufacturing the terahertz device according to the first embodiment; 
         FIG. 13  is a sectional view showing a step of the method for manufacturing the terahertz device according to the first embodiment; 
         FIG. 14  is a plan view showing a step of the method for manufacturing the terahertz device according to the first embodiment; 
         FIG. 15  is a sectional view showing a step of the method for manufacturing the terahertz device according to the first embodiment; 
         FIG. 16  is a sectional view showing a step of the method for manufacturing the terahertz device according to the first embodiment; 
         FIG. 17  is a sectional view showing a step of the method for manufacturing the terahertz device according to the first embodiment; 
         FIG. 18  is a sectional view showing a step of the method for manufacturing the terahertz device according to the first embodiment; 
         FIG. 19  is a sectional view showing a step of the method for manufacturing the terahertz device according to the first embodiment; 
         FIG. 20  is a sectional view showing through electrodes according to a variation; 
         FIG. 21  is a plan view showing another example of the configuration of a frame-shaped member; 
         FIG. 22  is a plan view showing another example of the configuration of the frame-shaped member; 
         FIG. 23  is a plan view showing another example of the configuration of the frame-shaped member; 
         FIG. 24  is a plan view showing another example of the configuration of the frame-shaped member; 
         FIG. 25  is a plan view showing another example of the configuration of the frame-shaped member; 
         FIG. 26  is a plan view showing another example of the configuration of the frame-shaped member; 
         FIG. 27  is a plan view showing another example of the configuration of the frame-shaped member; 
         FIG. 28  is a plan view showing another example of the configuration of the frame-shaped member; 
         FIG. 29  is a plan view showing another example of the configuration of the frame-shaped member; 
         FIG. 30  is a plan view showing another example of the configuration of the frame-shaped member; 
         FIG. 31  is a plan view showing another example of the configuration of the frame-shaped member; 
         FIG. 32  is a plan view showing another example of the configuration of the frame-shaped member; 
         FIG. 33  is a sectional view of a terahertz device according to a first variation of the first embodiment; 
         FIG. 34  is a sectional view of a terahertz device according to a second variation of the first embodiment; 
         FIG. 35  is a sectional view of a terahertz device according to a third variation of the first embodiment; 
         FIG. 36  is a sectional view of a terahertz device according to a fourth variation of the first embodiment; 
         FIG. 37  is a sectional view of a terahertz device according to a fifth variation of the first embodiment; 
         FIG. 38  is a sectional view of a terahertz device according to a sixth variation of the first embodiment; 
         FIG. 39  is a plan view of a terahertz device according to a second embodiment; 
         FIG. 40  is a sectional view taken along line XL-XL in  FIG. 39 ; 
         FIG. 41  is a sectional view of a terahertz device according to a variation of the second embodiment; 
         FIG. 42  is a sectional view of a terahertz device according to a third embodiment; 
         FIG. 43  is a sectional view showing a step of a method for manufacturing the terahertz device according to the third embodiment; 
         FIG. 44  is a sectional view showing a step of the method for manufacturing the terahertz device according to the third embodiment; 
         FIG. 45  is a sectional view showing a step of the method for manufacturing the terahertz device according to the third embodiment; 
         FIG. 46  is a sectional view showing a step of the method for manufacturing the terahertz device according to the third embodiment; 
         FIG. 47  is a sectional view showing a step of the method for manufacturing the terahertz device according to the third embodiment; 
         FIG. 48  is a sectional view showing a step of the method for manufacturing the terahertz device according to the third embodiment; 
         FIG. 49  is a sectional view showing a step of the method for manufacturing the terahertz device according to the third embodiment; 
         FIG. 50  is a sectional view showing a step of the method for manufacturing the terahertz device according to the third embodiment; 
         FIG. 51  is a sectional view showing a step of the method for manufacturing the terahertz device according to the third embodiment; 
         FIG. 52  is a sectional view of a terahertz device according to a variation of the third embodiment; 
         FIG. 53  is a plan view of a terahertz device according to a fourth embodiment; 
         FIG. 54  is a sectional view taken along line LIV-LIV in  FIG. 53 ; 
         FIG. 55  is a plan view of a terahertz device according to a variation of the fourth embodiment; 
         FIG. 56  is a sectional view taken along line LVI-LVI in  FIG. 55 ; 
         FIG. 57  is a plan view of a terahertz device according to a fifth embodiment; 
         FIG. 58  is a sectional view taken along line LVIII-LVIII in  FIG. 57 ; 
         FIG. 59  is a plan view of a terahertz device according to a first variation of the fifth embodiment; 
         FIG. 60  is a sectional view taken along line LX-LX in  FIG. 59 ; 
         FIG. 61  is a sectional view of a terahertz device according to a second variation of the fifth embodiment; 
         FIG. 62  is a plan view of a terahertz device according to a sixth embodiment; 
         FIG. 63  is a plan view of the terahertz device according to the sixth embodiment; 
         FIG. 64  is a bottom view of the terahertz device according to the sixth embodiment; 
         FIG. 65  is an enlarged sectional view showing a part of  FIG. 64 ; 
         FIG. 66  is a sectional view taken along line LXVI-LXVI in  FIG. 63 ; 
         FIG. 67  is an enlarged sectional view showing a part of  FIG. 66 ; 
         FIG. 68  is a bottom view showing a different embodiment of a recess in a support board according to the sixth embodiment; 
         FIG. 69  is a bottom view showing a different embodiment of the recess in the support board according to the sixth embodiment; 
         FIG. 70  is a plan view showing a different embodiment of through electrodes according to the sixth embodiment; 
         FIG. 71  is a plan view showing a different embodiment of the through electrodes according to the sixth embodiment; 
         FIG. 72  is a plan view showing a different embodiment of external electrodes according to the sixth embodiment; 
         FIG. 73  is a plan view showing a different embodiment of the external electrodes according to the sixth embodiment; 
         FIG. 74  is a plan view showing a different embodiment of the through electrodes according to the sixth embodiment; 
         FIG. 75  is a sectional view of a terahertz device according to a first variation of the sixth embodiment; 
         FIG. 76  is a sectional view showing another example of the terahertz device according to the first variation of the sixth embodiment; 
         FIG. 77  is a sectional view of a terahertz device according to a second variation of the sixth embodiment; 
         FIG. 78  is a sectional view showing another example of the terahertz device according to the second variation of the sixth embodiment; and 
         FIG. 79  is a sectional view showing another example of the terahertz device according to the second variation of the sixth embodiment. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Preferred embodiments of a terahertz device and a method for manufacturing a terahertz device according to the present disclosure are described below with reference to the accompanying drawings. 
       FIGS. 1-3  show a terahertz device A 1  according to a first embodiment of the present disclosure. As shown in these figures, the terahertz device A 1  of the first embodiment includes a terahertz element  1 , a support board  2 , internal electrodes  3 , external electrodes  4 , bonding layers  5 , a frame-shaped member  6  and a sealing resin  7 . Each internal electrode  3  includes a wiring layer  31  and a through electrode  32 . 
       FIG. 1  is a plan view of the terahertz device A 1 . In  FIG. 1 , the sealing resin  7  is indicated by imaginary lines (dash-double-dot lines).  FIG. 2  is a bottom view of the terahertz device A 1 .  FIG. 3  is a sectional view taken along line III-III in  FIG. 1 . For the convenience of understanding, the three directions that are orthogonal to each other are defined as x direction, y direction and z direction, respectively. The z direction is the thickness direction of the terahertz device A 1 . The x direction is the horizontal direction in plan view (see  FIG. 1 ) of the terahertz device A 1 . The y direction is the vertical direction in plan view (see  FIG. 1 ) of the terahertz device A 1 . For the convenience of understanding, one sense of the z direction (e.g. the upper side in  FIG. 3 ) may be referred to as “upper”, while the other sense of the z direction (e.g. the lower side in  FIG. 3 ) may be referred to as “lower”, but such description is not meant to limit the posture of the terahertz device A 1  in use or in other conditions. 
     The terahertz element  1  is an element that performs conversion between electromagnetic waves in the terahertz band and electric energy. Herein, the electromagnetic wave includes either or both of light and radio waves. The terahertz element  1  converts the inputted electric energy into electromagnetic waves in the terahertz band to radiate terahertz waves. Or conversely, the terahertz element  1  may receive terahertz waves and convert the received terahertz waves into electric energy. The terahertz element  1  may both radiate and receive terahertz waves. The terahertz element  1  is rectangular as viewed in the z direction (hereinafter also referred to as “as viewed in plan”). The shape of the terahertz element  1  as viewed in plan is not limited to a rectangle and may be a circle, an oval or a polygon. The terahertz element  1  is of a type for mounting by flip-chip bonding. The dimension of the terahertz element  1  in the z direction is determined in accordance with the frequency of the terahertz waves to be radiated. Specifically, the dimension of the terahertz element  1  in the z direction is an integral multiple of one half the wavelength λ of the terahertz waves (i.e., λ/2). At the interface between an element substrate  11  and air, free-end reflection of terahertz waves occurs. Accordingly, setting the dimension of the terahertz element  1  in the z direction as described above can cause standing waves with a constant phase to be excited within the terahertz element  1 . Note that the dimension of the terahertz element  1  in the z direction is made smaller for providing terahertz waves with higher frequencies and made larger for providing terahertz waves with lower frequencies. 
     The terahertz element  1  has an element front surface  101 , an element back surface  102  and a plurality of element side surfaces  103 . The element front surface  101  and the element back surface  102  are spaced apart and face away from each other in the z direction. The electrodes of the terahertz element  1  (portions of the first conductive layer  13  and second conductive layer  14  described later) are exposed from the element back surface  102 . Each of the element side surfaces  103  is located between and connected to the element front surface  101  and the element back surface  102 . Each element side surface  103  is connected to the element front surface  101  at one edge in the z direction (upper edge in  FIG. 3 ) and connected to the element back surface  102  at the other edge in the z direction (lower edge in  FIG. 3 ). Since the terahertz element  1  is rectangular as viewed in plan, it has four element side surfaces  103 , i.e. a pair of element side surfaces  103  spaced apart and facing away from each other in the x direction and a pair of element side surfaces  103  spaced apart and facing away from each other in the y direction. The element front surface  101  of the terahertz element  1  is an active surface, and radiation (and/or reception) of terahertz waves is performed in proximity to the active surface. 
     In the present embodiment, the radiation point of the terahertz waves in the terahertz element  1  is the center position P 1  (see  FIG. 1 ) of the terahertz element  1  as viewed in plan. Herein, the vertical distance x 1  between each element side surface  103  and the radiation point (the center position P 1 ) is represented as x 1 =(λ′ InP /2)+((λ′ InP /2)×N) (where N is an integer greater than or equal to 0: N=0, 1, 2, 3, . . . ). Here, λ′ InP  is the effective wavelength of the terahertz waves propagating within the terahertz element  1 . λ′ InP  is obtained by λ′ InP =(1/n1)×(c/f c ) where n1 is the index of refraction of the terahertz element  1  (the element substrate  11  described later), c is the speed of light, and f c  is the center frequency of terahertz waves. By setting the vertical distance x 1  as described above, free-end reflection of the terahertz waves radiated from the terahertz element  1  occurs at each element side surface  103 . In this way, the terahertz element  1  itself is designed as a resonator (primary resonator) of the terahertz device A 1 . The vertical distances x 1  from the respective element side surfaces  103  to the radiation point of the terahertz waves may differ from each other, supposing that each vertical distance x 1  has a value obtained by the above-described formula. Accordingly, the radiation point of the terahertz waves is not limited to the center position P 1  as viewed in plan. 
       FIGS. 4-6  show an example of detailed configuration of the terahertz element  1 .  FIG. 4  is a schematic view showing an example of a pattern of the terahertz element  1  as viewed in plan.  FIG. 5  is a schematic view showing a section of the terahertz element  1 .  FIG. 6  is an enlarged view showing a part of  FIG. 5 . The terahertz element  1  includes an element substrate  11 , an active element  12 , a first conductive layer  13  and a second conductive layer  14 . 
     The element substrate  11  is made of a semiconductor and is semi-insulating. For example, the element substrate  11  may be made of InP (indium phosphide) but may be made of other semiconductors. The element substrate  11 , when made of InP, has an index of refraction (absolute index of refraction) of about 3.4. 
     The active element  12  performs conversion between electromagnetic waves in the terahertz band and electric energy. The active element  12  is typically an RTD. The active element  12  may be a diode other than an RTD or a transistor. Examples of the active element  12  include a tunnel transit time (TUNNETT) diode, an impact ionization avalanche transit time (IMPATT) diode, a GaAs-based field effect transistor (FET), a GaN-based FET, a high electron mobility transistor (HEMT), and a heterojunction bipolar transistor (HBT). The active element  12  is formed on the element substrate  11 . The active element  12  is electrically connected to the first conductive layer  13  and the second conductive layer  14 . 
     One implementation of the active element  12  is described below with reference to  FIG. 6 . As shown in the figure, a GaInAs layer  122   a  is disposed on a semiconductor layer  121   a  (made of e.g., GaInAs) and doped with an n-type impurity. A GaInAs layer  123   a  is disposed on the GaInAs layer  122   a  and undoped. An AlAs layer  124   a  is disposed on a GaInAs layer  123   a , an InGaAs layer  125  is disposed on the AlAs layer  124   a , and an AlAs layer  124   b  is on the InGaAs layer  125 . The AlAs layer  124   a , the InGaAs layer  125  and the AlAs layer  124   b  provide an RTD unit. A GaInAs layer  123   b  is disposed on the AlAs layer  124   b  and undoped. A GaInAs layer  122   b  is disposed on the GaInAs layer  123   b  and doped with an n-type impurity. A GaInAs layer  121   b  is disposed on the GaInAs layer  122   b  and doped with an n-type impurity at a high concentration. The first conductive layer  13  is on the GaInAs layer  121   b.    
     Though not illustrated, unlike the configuration shown in  FIG. 6 , a GaInAs layer doped with an n-type impurity at a high concentration may be interposed between the GaInAs layer  121   b  and the first conductive layer  13 . Such a configuration can enhance the contact between the first conductive layer  13  and the GaInAs layer  121   b . Note that the active element  12  may have any other configuration as long as it allows for radiation (and/or reception) of terahertz waves. 
     The first conductive layer  13  and the second conductive layer  14  are formed on the element substrate  11 . The first conductive layer  13  and the second conductive layer  14  are insulated from each other. Each of the first conductive layer  13  and the second conductive layer  14  is a laminate of metal layers. For example, each of the first conductive layer  13  and the second conductive layer  14  may be a laminate of Au (gold), Pd (palladium) and Ti (titanium). Alternatively, each of the first conductive layer  13  and the second conductive layer  14  may be a laminate of Au and Ti. The first conductive layer  13  and the second conductive layer  14  may be formed by vacuum deposition or sputtering, for example. The first conductive layer  13  and the second conductive layer  14  are exposed from the element back surface  102 . In the terahertz element  1 , portions of the first conductive layer  13  and the second conductive layer  14  provide an antenna integrated on the element front surface  101 . In the present embodiment, portions of the first conductive layer  13  and the second conductive layer  14  form a dipole antenna, as shown in  FIG. 4 . Note that the antenna is not limited to a dipole antenna and may be other types of antenna such as a slot antenna, a bow tie antenna or a ring antenna. 
     The configuration of the terahertz element  1  is not limited to that described above. For example, a back-surface reflective metal layer may be disposed on the opposite side of the element substrate  11  from the active element  12 . In this case, the electromagnetic waves (terahertz waves) radiated from the active element  12  are reflected by the back-surface reflective metal layer to form a surface-emission radiation pattern perpendicular to the element substrate  11  (the z direction). When such a back-surface reflective metal layer is present, fixed-end reflection of terahertz waves occurs at the interface between the element substrate  11  and the back-surface reflective metal layer, producing a phase shift of n. Thus, with such a configuration, the dimension of the terahertz element  1  in the z direction may be set to (λ/4)+(an integral multiple of λ/2), where λ is the wavelength of the terahertz waves. 
     The support board  2  is a support member on which the terahertz element  1  is mounted to thereby form the base of the terahertz device A 1 . The support board  2  is made of an insulating material. The support board  2  may be made of an intrinsic semiconductor such as single-crystal silicon (Si). The support board  2  may be rectangular as viewed in plan. The dimension of the support board  2  in the z direction may be about 50 to 200 μm, for example. 
     The support board  2  has a support-board front surface  201 , a support-board back surface  202  and a plurality of support-board side surfaces. The support-board front surface  201  and the support-board back surface  202  are spaced apart and face away from each other in the z direction. Each of the support-board side surfaces  203  is located between and connected to the support-board front surface  201  and the support-board back surface  202 . Each support-board side surface  203  is connected to the support-board front surface  201  at one edge in the z direction (upper edge in  FIG. 3 ) and connected to the support-board back surface  202  at the other edge in the z direction (lower edge in  FIG. 3 ). The support board  2  has four support-board side surfaces  203 , i.e. a pair of support-board side surfaces  203  spaced apart and facing away from each other in the x direction and a pair of support-board side surfaces  203  spaced apart and facing away from each other in the y direction. 
     The support board  2  is formed with through-holes  21 . The through-holes  21  penetrate from the support-board front surface  201  to the support-board back surface  202  in the z direction. The through-holes  21  are filled with through electrodes  32 . The through-holes  21  may be formed by reactive ion etching (RIE) and particularly by a technique called Bosch process. Thus, the inner wall of each through-hole  21  has a stepped profile with so-called scallop. 
     The internal electrodes  3  are disposed inside the terahertz device A 1  and electrically connect the terahertz element  1  and the external electrodes  4 . Each internal electrode  3  includes a wiring layer  31  and a through electrode  32 . 
     As shown in  FIG. 3 , the wiring layers  31  are formed on the support board  2  and electrically connected to the terahertz element  1 . As shown in  FIG. 3 , the wiring layers  31  are formed on the support-board front surface  201 . Each of the wiring layers  31  may be rectangular, as shown in  FIG. 3 . The configuration and arrangement of the wiring layers  31  are not limited to those illustrated in the figures, and may be varied as appropriate in accordance with the arrangement of the terahertz element  1 , the arrangement of the through electrodes  32  and the arrangement of the external electrodes  4 . 
     Each of the wiring layers  31  has a wiring-layer front surface  311  and a wiring-layer back surface  312 . The wiring-layer front surface  311  and the wiring-layer back surface  312  are spaced apart and face away from each other in the z direction. The wiring-layer front surface  311  faces in the direction in which the element front surface  101  faces, whereas the wiring-layer back surface  312  faces in the direction in which the element back surface  102  faces. 
     The through electrodes  32  are formed so as to penetrate the support board  2 . The through electrode  32  are formed in the respective through-holes  21  so as to fill the through-holes  21 . Since the inner wall of each through-hole  21  has a stepped profile with so-called scallop as described above, the side surface of each through electrode  32  also has a stepped profile. Each through electrode  32  is exposed from the support-board front surface  201  and the support-board back surface  202 . Each through electrode  32  is connected to a wiring layer  31  at one end exposed from the support-board front surface  201  and connected to an external electrode  4  at the other end exposed from the support-board back surface  202 . In this way, the through electrodes  32  electrically connect the wiring layers  31  and the external electrodes  4 . 
     Each of the through electrodes  32  has a wiring-layer contact surface  321  and an external-electrode contact surface  322 . The wiring-layer contact surface  321  is exposed from the support-board front surface  201  and in contact with the wiring layer  31 . The wiring-layer contact surface corresponds to the above-described one end exposed from the support-board front surface  201 . The external-electrode contact surface  322  is exposed from the support-board back surface  202  and in contact with the external electrode  4 . The external-electrode contact surface  322  corresponds to the above-described other end exposed from the support-board back surface  202 . Both of the wiring-layer contact surface  321  and the external-electrode contact surface  322  may be generally circular as viewed in plan. 
     The external electrodes  4  are exposed outside the terahertz device A 1  and electrically connected to the internal electrode  3 . The external electrodes  4  serve as terminals when the terahertz device A 1  is mounted to a circuit board of an electronic device, for example. The external electrodes  4  are formed on the support-board back surface  202  and cover the external-electrode contact surfaces  322  of the through electrodes  32 . The external electrodes  4  may be formed by electroless plating. Each external electrode  4  is a laminate of a Ni layer, a Pd layer and a Au layer. The Ni layer is in contact with the external-electrode contact surface  322 , and the Au layer is exposed to the outside. The Pd layer is interposed between the Ni layer and the Au layer. The dimension of each external electrode  4  in the z direction may be about 2 to 6 μm, for example. As shown in  FIGS. 1 and 3 , each external electrode  4  projects outward relative to the external-electrode contact surface  322  by an amount of about 1 to 5 μm, for example, in all directions perpendicular to the z direction. The thickness, material and forming method of the external electrodes  4  are not limited. For example, the above-described laminate may not include a Pd layer. Also, instead of electroless plating, the external electrodes may be formed by pattern formation through photolithography and electrolytic plating or by rewiring process. These techniques make it possible to freely design the size and arrangement of the external electrodes  4  as viewed in plan. Also, in the terahertz device A 1 , a solder bump may be formed so as to cover each external electrode  4  or may be formed instead of each external electrode  4 . 
     Bonding layers  5  bond and electrically connect the terahertz element  1  to the internal electrode  3  (wiring layer  31 ). The material for the bonding layers  5  may be solder, for example. The bonding layers are not limited to solder and may be any other bonding material that is electrically conductive. Examples of solder used in the present embodiment include Sn—Pb alloy and lead-free solders such as Sn—Sb alloy or Sn—Ag alloy. Ag paste may be used instead of solder. The bonding layers  5  are interposed between the first conductive layer  13  or the second conductive layer  14  of the terahertz element  1  and the wiring layers  31 . The bonding layers  5  are in contact with the first conductive layer  13  or the second conductive layer  14  of the terahertz element  1  and the wiring layers  31  to electrically connect these. Thus, with the bonding layers  5 , the terahertz element  1  is fixedly mounted to each wiring layer  31 , and electrical connection between the terahertz element  1  and the wiring layers  31  is secured. 
     The frame-shaped member  6  is arranged around the terahertz element  1  as viewed in plan. The frame-shaped member  6  is arranged on the outer side of the terahertz element  1  and surrounds the terahertz element  1 , as viewed in plan. The frame-shaped member  6  may have the shape of a rectangular ring as viewed in plan. Part of the sealing resin  7  is interposed between the frame-shaped member  6  and the terahertz element  1 . The frame-shaped member  6  is covered with the sealing resin  7 . The frame-shaped member  6  is made of an electrically conductive material. The material for the frame-shaped member  6  may be Cu, for example, but is not limited to this, and any material capable of reflecting terahertz waves may be used. The frame-shaped member  6  is formed on the support board  2  and stands on the support-board front surface  201 . The frame-shaped member  6  is spaced apart from the internal electrodes  3 . Parts of the frame-shaped member  6  overlap with the wiring layers  31  as viewed in the x direction, while other parts of the frame-shaped member  6  overlap with the wiring layers  31  as viewed in the y direction. As viewed in plan, the frame-shaped member  6  does not overlap the wiring layers  31 . The frame-shaped member  6  may be formed by electrolytic plating. 
     The frame-shaped member  6  has an inner peripheral surface  61 , an outer peripheral surface  62  and a top surface  63 . The inner peripheral surface  61  is defined by the inner periphery of the frame-shaped member  6  as viewed in plan. The outer peripheral surface  62  is defined by the outer periphery of the frame-shaped member  6  as viewed in plan. The inner peripheral surface  61  faces the element side surfaces  103  of the terahertz element  1 . The inner peripheral surface  61  is generally in parallel with each of the element side surfaces  103  of the terahertz element  1 . The top surface  63  faces upward in  FIG. 3 . The top surface  63  is exposed from the sealing resin  7 . The frame-shaped member  6  may be formed with a through-hole penetrating from the inner peripheral surface  61  to the outer peripheral surface  62 . 
     In the present embodiment, the distance x 2  between each of the element side surfaces  103  and a corresponding part of the inner peripheral surface  61  facing that element side surface is: x 2 =(λ′ Resin /4)+((λ′ Resin /2)×N) (where N is an integer greater than or equal to 0: N=0, 1, 2, 3, . . . ). Here, λ′ Resin  is the effective wavelength of the terahertz waves propagating within the sealing resin  7 . λ′ Resin  is obtained by λ′ Resin =(1/n2)×(c/f c ) where n2 is the index of refraction of the sealing resin  7 , c is the speed of light, and f c  is the center frequency of the terahertz waves. By setting the distance x 2  as described above, fixed-end reflection of the terahertz waves radiated from the terahertz element  1  occurs at the inner peripheral surface  61 . Thus, the inner peripheral surface  61  of the frame-shaped member  6  serves as a reflective surface that reflects the terahertz waves radiated from the terahertz element  1 . In particular, the inner peripheral surface  61  reflects the terahertz waves to produce resonance. In this way, the frame-shaped member  6  serves as a resonator (secondary resonator) that produces resonance of terahertz waves. In the present embodiment, the dimension of the frame-shaped member  6  in the z direction is not particularly limited, but it is desired that the dimension is set so as to make the inner peripheral surface  61  function as a reflective surface. The distance x 2  between each element side surface  103  and a corresponding part of the inner peripheral surface  61  facing that element side surface may differ among the pairs of an element side surface and a corresponding part of the inner peripheral surface, supposing that each distance x 2  is obtained by the formula described above. 
     The sealing resin  7  is formed on the support-board front surface  201  and covers the terahertz element  1 , the wiring layers  31 , the bonding layers  5  and the frame-shaped member  6 . The sealing resin  7  is made of an electrically insulating resin material. The resin material is, for example, a black epoxy resin. The index of refraction (absolute index of refraction) of the sealing resin  7  is about 1.55, for example. The index of refraction depends on the material for the sealing resin  7 . 
     The sealing resin  7  has a resin front surface  701 , a resin back surface  702  and a plurality of resin side surfaces  703 . The resin front surface  701  and the resin back surface  702  are spaced apart and face away from each other in the z direction. The resin front surface  701  faces in the direction in which the element front surface  101  faces, whereas the resin back surface  702  faces in the direction in which the element back surface  102  faces. The resin front surface  701  may be flat or made rougher than the resin back surface  702  by etching, for example. When the resin front surface  701  is a rough surface, the reflectivity at the interface between the resin front surface  701  and the outside air is reduced, which leads to an improved radiation efficiency of terahertz waves. However, since a large surface roughness of the resin front surface  701  influences the radiation pattern of the terahertz waves, it is desirable that the roughness is not larger than ¼ times the wavelength λ of terahertz waves (i.e., not larger than λ/4). The resin back surface  702  is in contact with the support board  2  (support-board front surface  201 ). Each of the resin side surfaces  703  is located between and connected to the resin front surface  701  and the resin back surface  702 . The sealing resin  7  has four resin side surfaces  703 , i.e. a pair of resin side surfaces  703  spaced apart and facing away from each other in the x direction and a pair of resin side surfaces  703  spaced apart and facing away from each other in the y direction. The resin side surfaces  703  facing away from each other in the x direction are flush with the support-board side surfaces  203  facing away from each other in the x direction, respectively. The resin side surfaces  703  facing away from each other in the y direction are flush with the support-board side surfaces  203  facing away from each other in the y direction, respectively. 
     The sealing resin  7  covers the element front surface  101 . Part of the sealing resin  7  is interposed between each element side surface  103  and the inner peripheral surface  61  of the frame-shaped member  6 . 
     An example of a method for manufacturing the terahertz device A 1  is described below with reference to  FIGS. 7-19 . Of  FIGS. 7-19 ,  FIGS. 12 and 15  are plan views showing steps of a method for manufacturing the terahertz device A 1 . Of  FIGS. 7-19 , the figures other than  FIGS. 12 and 15  are sectional views showing steps of the method for manufacturing the terahertz device A 1 . These sectional views correspond to the section shown in  FIG. 3 . 
     First, a support board  820  is prepared, and grooves  829  are formed in the prepared support board  820 , as shown in  FIG. 7 . The support board  820  will later become the support board  2  of the terahertz device A 1 , and the grooves  829  will later become the through-holes  21  of the terahertz device A 1 . In the step of preparing the support board  820  (the support board preparation step), a support board  820  made of single-crystal silicon (Si) as an intrinsic semiconductor is prepared. The support board  820  has a size capable of producing a plurality of support boards  2  of terahertz devices A 1 . Thus, the manufacturing method in the present disclosure uses a technique to collectively manufacture a plurality of terahertz devices A 1 . As shown in  FIG. 7 , the support board  820  has a support-board front surface  820   a  and a support-board back surface  820   b  facing away from each other in the z direction. The support-board front surface  820   a  will later become the support-board front surface  201 . In the subsequent step of forming grooves  829  (groove forming step), the grooves are formed by reactive ion etching, particularly by a technique called Bosch process. By forming the grooves  829  by Bosch process, the inner walls of the groove  829  have a stepped profile with so-called scallop. In the present embodiment, the grooves  829  with a depth of 50 μm or more from the support-board front surface  820   a  of the support board  820  are formed. The depth of the grooves  829  may be set as appropriate in accordance with the thickness of the support board  2  of the terahertz device A 1  to be manufactured. 
     Next, a base layer  830   a  is formed, as shown in  FIG. 8 . Parts of the base layer  830   a  that are formed on the support board front surface  820   a  will later become parts of the wiring layers  31  of the terahertz device A 1 , and parts of the base layer  830   a  that are formed on the support board front surface  820   a  will later become parts of the frame-shaped member  6  of the terahertz device A 1 . Also, parts of the base layer  830   a  that are formed on the inner walls of the grooves  829  will later become parts of the through electrodes  32  of the terahertz device A 1 . The step of forming the base layer  830   a  (base layer forming step) may be performed by sputtering. The base layer  830   a  of the present embodiment is a laminate of a Ti layer and a Cu layer and about 200 to 800 nm in thickness. In the base layer forming step, a Ti layer is formed to cover the support board front surface  820   a  and all of the inner walls of the grooves  829 , and then a Cu layer is formed in contact with the Ti layer. 
     Next, a first plating layer  830   b  is formed, as shown in  FIG. 9 . Parts of the first plating layer  830   b  will later become parts of the wiring layer  31  of the terahertz device A 1 , and other parts of the first plating layer  830   b  will later become parts of the through electrode  32  of the terahertz device A 1 . The formation of the first plating layer  830   b  may be performed by pattern formation through photolithography and electrolytic plating. Specifically, in the step of forming the first plating layer  830   b  (first plating layer forming step), a resist (not shown) with a predetermined pattern for forming the first plating layer  830  is formed by photolithography. In this resist patterning process, a photoresist is first applied by spin coating to cover the entirety of the base layer  830   a . Next, the photoresist is formed into a predetermined pattern by exposure to light and development. In this way, a resist having a pattern is obtained. In this state, part of the base layer  830   a  is exposed from the resist. The part exposed from the resist is the region on which the first plating layer  830   b  is to be formed. Next, electrolytic plating is performed using the base layer  830   a  as a conduction path to form the first plating layer  830   b . The first plating layer  830   b  is deposited on the part of the base layer  830   a  that is exposed from the resist. The first plating layer  830   b  is made of Cu, for example. Thereafter, the unnecessary resist is removed, whereby the first plating layer  830   b  shown in  FIG. 9  is obtained. As shown in  FIG. 9 , the first plating layer  830   b  includes parts covering parts of the support board front surface  820   a  and parts filling the grooves  829 . 
     Next, a bonding layer  850  is formed, as shown in  FIG. 10 . The bonding layer  850  corresponds to the bonding layers  5  of the terahertz device A 1 . The formation of the bonding layer  850  may be performed by pattern formation by photolithography and electrolytic plating. Specifically, in the step of forming the bonding layer  850  (bonding layer forming step), a resist (not shown) for forming the bonding layer  850  is formed to have a predetermined pattern by photolithography. When a resist having a pattern is formed in this way, part of the first plating layer  830   b  is exposed from the resist. The part exposed from the resist is the region on which the bonding layer  850  is to be formed. Next, electrolytic plating is performed using the base layer  830 a and the first plating layer  830   b  as a conduction path to form the bonding layer  850 . The bonding layer  850  is deposited on the first plating layer  830   b  exposed from the resist. The bonding layer  850  may be solder, for example. Thereafter, the unnecessary resist is removed, whereby the bonding layer  850  shown in  FIG. 10  is obtained. 
     Next, a second plating layer  830   c  is formed, as shown in  FIGS. 11 and 12 . Part of the second plating layer  830   c  will later become the frame-shaped member  6  of the terahertz device A 1 . The formation of the second plating layer  830   c  may be performed by pattern formation by photolithography and electrolytic plating. Specifically, in the step of forming the second plating layer  830   c  (second plating layer forming step), a resist (not shown) for forming the second plating layer  830   c  is formed to have a predetermined pattern by photolithography. When a resist having a pattern is formed in this way, part of the base layer  830   a  is exposed from the resist. The part exposed from the resist is the region on which the second plating layer  830   c  is to be formed. Next, electrolytic plating is performed using the base layer  830   a  as a conduction path to form the second plating layer  830   c . The second plating layer  830   c  is deposited on the part of the base layer  830   a  that is exposed from the resist. The second plating layer  830   c  is made of Cu, for example. Thereafter, the unnecessary resist is removed, whereby the second plating layer  830   c  shown in  FIGS. 11 and 12  is obtained. As shown in  FIG. 12 , the second plating layer  830   c  formed in this way has the shape of a rectangular ring as viewed in plan. In this state, the first plating layer  830   b  and the bonding layer  850  are surrounded by the second plating layer  830   c , as viewed in plan. 
     Next, as shown in  FIG. 13 , unnecessary parts of the base layer  830   a  on the support-board front surface  820   a  that are not covered with the first plating layer  830   b  or the second plating layer  830   c  are removed. The removal of the unnecessary parts of the base layer  830   a  may be performed by wet etching. The wet etching may use a mixed solution of H 2 SO 4  (sulfuric acid) and H 2 O 2  (hydrogen peroxide), for example. By the step of removing parts of the base layer  830   a  (base layer removal step), the support-board front surface  820   a  is exposed at the region where the base layer  830   a  has been removed. In this way, the base layer  830   a  is separated into the parts covered with the first plating layer  830   b  and the parts covered with the second plating layer  830   c . Through these steps, wiring layers  831  are obtained that are made up of the base layer  830   a  covering parts of the support-board front surface  820   a  and the first plating layer  830   b  formed on the base layer  830   a . Also, through electrodes  832  are formed that are made up of the base layer  830   a  covering the inner walls of the grooves  829  and the first plating layer  830   b  formed on the base layer  830   a . The frame-shaped member  860  is also formed that is made up of the base layer  830   a  covering parts of the support-board front surface  820   a  and the second plating layer  830   c  formed on the base layer  830   a . The frame-shaped member  860  formed in this way has the shape of a rectangular ring as viewed in plan. Note that, in each of the wiring layers  831  and the through electrodes  832 , the base layer  830   a  and the first plating layer  830   b  are integral with each other. Thus,  FIGS. 14-19  do not individually illustrate the base layer  830   a  and the first plating layer  830   b  but illustrate collectively as the wiring layer  831  or the through electrode  832 . Likewise, in the frame-shaped member  860 , the base layer  830   a  and the second plating layer  830   c  are integral with each other. Thus,  FIGS. 14-19  do not individually illustrate the base layer  830   a  and the second plating layer  830   c  but illustrate collectively as the frame-shaped member  860 . 
     Next, as shown in  FIGS. 14 and 15 , a terahertz element  810  is mounted on the wiring layers  831 . The terahertz element  810  corresponds to the terahertz element  1  of the terahertz device A 1 . The step of mounting the terahertz element  810  (element mounting step) is performed by FCB (flip chip bonding). Specifically, flux is applied to the first conductive layer  813  and the second conductive layer  814  exposed from the element back surface  810   b  of the terahertz element  810 . Thereafter, with the element back surface  810   b  facing the support-board front surface  820   a , the terahertz element  810  is temporarily attached to the bonding layers  850  using a flip chip bonder. In this state, the bonding layers  850  are sandwiched between the wiring layers  831  and the terahertz element  810 . Next, the bonding layers  850  are melted by ref lowing and then solidified by cooling, whereby mounting of the terahertz element  810  is completed. In the state after the element mounting step, the terahertz element  810  is surrounded by the frame-shaped member  860 , as shown in  FIG. 15 . The inner peripheral surface of the frame-shaped member  860  faces the element side surfaces  810   c  of the terahertz element  810 . 
     Next, as shown in  FIGS. 16 and 17 , a sealing resin  870  is formed to cover the terahertz element  810 , the wiring layers  831 , the bonding layers  850  and the frame-shaped member  860 . The sealing resin  870  will later become the sealing resin  7  of the terahertz device A 1 . The sealing resin  870  is a synthetic resin containing, for example, black epoxy resin as the main ingredient. In the step of forming the sealing resin  870  (sealing resin forming step), the sealing resin  870  is formed on the support-board front surface  820   a  of the support board  820  so as to cover all of the terahertz element  810 , the wiring layers  831 , the bonding layers  850  and the frame-shaped member  860 , as shown in  FIG. 16 . In this state, as shown in  FIG. 16 , the resin front surface  870   a  of the sealing resin  870  is located above the upper surface of the frame-shaped member  860 . Next, as shown in  FIG. 17 , the sealing resin  870  is ground from the resin front surface  870   a  toward the resin back surface  870   b . In this process, the grinding is performed until the frame-shaped member  860  is exposed. The grinding of the sealing resin  870  may be permed by machine grinding. This process makes the top surface of the frame-shaped member  860  and the resin front surface  870   a  flush with each other, with the top surface of the frame-shaped member  860  exposed from the sealing resin  870 . After the sealing resin  870  is ground, the resin front surface  870   a  may be roughened by etching. 
     Next, as shown in  FIG. 18 , the support board  820  is ground from the support board back surface  820   b . The grinding of the support board  820  may be performed by machine grinding, as with the grinding of the sealing resin  870 . In the step of grinding the support board  820  (support board grinding step), the support board  820  is ground from the support-board back surface  820   b  so that the through electrodes  832  are exposed from the support-board back surface  820   b . By the support board grinding step, the grooves  829  become the through-holes  821  penetrating the support board  820  in the z direction. The through-holes  821  correspond to the through-holes  21  of the terahertz device A 1 . 
     Next, external electrodes  840  are formed, as shown in  FIG. 19 . The external electrodes  840  will later become the external electrodes  4  of the terahertz device A 1 . The formation of the external electrodes  840  is performed by electroless plating. In the process of forming the external electrodes  84  (external electrode forming step), a Ni layer, a Pd layer and a Au layer are successively deposited by electroless plating. Specifically, by electroless plating, a Ni layer is formed to be into contact with and cover the exposed surfaces  832   b  of the through electrodes  832 , a Pd layer is then formed on the Ni layer, and an Au layer is then formed on the Pd layer, whereby the external electrodes  840  are formed. The external electrodes  840  may be about 2 to 6 μm in thickness. The external electrode forming step is not limited to the above and may be varied as appropriate in accordance with the composition of the external electrodes  4 . For example, when the external electrodes  4  are a laminate of a Ni layer and a Au layer, depositing a Pd layer is not required in the electrode forming step. 
     Next, the sealing resin  870  and the support board  820  are cut into individual pieces for terahertz elements  810 . The cutting may be performed by blade dicing, for example. Specifically, in the step of cutting the sealing resin  870  and the support board  820  (cutting step), blade dicing is performed to cut the sealing resin  870  and the support board  820  along the x direction and along the y direction as well. The cutting line CL 1  shown in  FIG. 19  is an example of a cut position along the y direction. 
     By going through the above-described steps, the terahertz device A 1  shown in  FIGS. 1-3  is obtained. 
     The advantages of the terahertz device A 1  according to the first embodiment are described below. 
     In the terahertz device A 1 , the terahertz element  1  is covered with the sealing resin  7 . Thus, the terahertz element  1  is not exposed to the outside. When the terahertz element in a terahertz device is exposed to the outside or the outside air unlike the terahertz device A 1 , malfunctions may occur. Such malfunctions may be caused by the influence of moisture or dust in the air, or the influence of vibration or impact, for example. Covering the terahertz element  1  with the sealing resin  7  protects the terahertz element  1  from such influences from the outside. In this way, the terahertz device A 1  has a packaging structure that allows for modularization of the terahertz element  1  with improved reliability. 
     In the terahertz device A 1 , the frame-shaped member  6  is arranged so as to surround the terahertz element  1 . The frame-shaped member  6  is made of an electrically conductive material. With such an arrangement, the frame-shaped member  6  functions as an electromagnetic shield, so that the terahertz device A 1  can reduce problems such as disturbance noise or crosstalk. In this way, the terahertz device A 1  has a packaging structure that allows for modularization of the terahertz element  1  with improved emission or reception quality of terahertz waves. 
     In the terahertz device A 1 , the terahertz waves radiated from the terahertz element  1  are reflected by the frame-shaped member  6  (inner peripheral surface  61 ) to produce resonance and thereby radiated in the z direction. With such an arrangement, the terahertz device A 1  can radiate terahertz waves with reduced noise components. Also, the terahertz device A 1  can radiate terahertz waves with an increased gain due to resonant reflection. In this way, the terahertz device A 1  has a packaging structure that allows for modularization of the terahertz element  1  with improved emission or reception quality of terahertz waves. 
     In the terahertz device A 1 , the frame-shaped member  6  has the shape of a rectangular ring as viewed in plan. Thus, the inner peripheral surface  61  (reflective surface) can be made generally parallel with each of the element side surfaces  103  of the terahertz element  1 . Thus, when the antenna structure integrated in the terahertz element  1  is an antenna with a fixed polarization direction such as a dipole antenna, a slot antenna or a bow tie antenna, the inner peripheral surface  61  reflects the terahertz waves from the terahertz element  1  in the vertical direction. In this way, the terahertz device A 1  has a packaging structure that allows for modularization of the terahertz element  1  with improved emission or reception quality of terahertz waves. 
     In the terahertz device A 1 , the terahertz element  1  is flip-chip mounted with the bonding layers  5  on the support board  2  on which the wiring layers  31  are formed. In this way, electrical connection of the terahertz element  1  with the wiring layers  31  does not use wires. This shortens the length of the wiring path in the terahertz device A 1 , so that the impedance and the inductance are reduced. In this way, the terahertz device A 1  has a packaging structure that allows for modularization of the terahertz element  1  in a manner suitable for driving at high frequencies. Moreover, flip-chip mounting uses a smaller mount area than wire bonding. Thus, the terahertz device A 1  has a packaging structure that allows for modularization of the terahertz element  1  while achieving size reduction. 
     In the process of manufacturing the terahertz device A 1 , the sealing resin  870  is ground from the resin front surface  870   a , as shown in  FIGS. 16 and 17 . This reduces the thickness of the sealing resin  7  in the terahertz device A 1 . Thus, the distance between the element front surface  101  of the terahertz element  1  and the resin front surface  701  of the sealing resin  7  is reduced, which reduces absorption loss of terahertz waves due to the sealing resin  7 . The terahertz device A 1  having such a packaging structure allows for modularization of the terahertz element  1  while securing efficient emission of the terahertz waves from the terahertz element  1 . 
     In the terahertz device A 1 , the dimension of the support board  2  in the z direction is about 50 to 200 μm. This reduces problems such as cracking or distortion of the support board  2 . In this way, the terahertz device A 1  has a packaging structure that allows for modularization of the terahertz element  1  while securing robustness of the support board  2 . 
     Though the through electrodes  32  are formed to fill the through-holes  21  in the first embodiment, the present disclosure is not limited to this. For example, depending on the deposition amount of the first plating layer  830  in the first plating layer forming step (see  FIG. 9 ), the through electrodes  32  may be formed to such a degree as to cover the inner walls of the through-holes  21 .  FIG. 20  shows an example in which the through electrodes  32  do not completely fill the through-holes  21 . Each of the through electrodes  32  is formed to have the shape of a bottomed cylinder, and the hollow portion of each through electrode  32  is filled with the sealing resin  7 . Such an arrangement also provides the same advantages as the first embodiment. 
     In the first embodiment, the above-described cutting step performs division into individual pieces for terahertz elements. However, the present disclosure is not limited to this, and division into blocks each including a plurality of terahertz elements  1  may be performed. In this case, the division may be performed such that each block includes a plurality of terahertz elements  1  arranged in a straight line or arranged in a matrix. 
     Though the first embodiment shows an example in which the frame-shaped member  6  has the shape of a rectangular ring as viewed in plan, the shape of the frame-shaped member  6  as viewed in plan is not particularly limited and may be any shape as long as the inner peripheral surface  61  of the frame-shaped member  6  functions as a resonant surface.  FIGS. 21-32  show other shapes of the frame-shaped member  6  that can be employed in the terahertz device of the present disclosure. Note that the shapes of the frame-shaped member  6  shown in these figures are merely examples and the present disclosure is not limited to these. 
       FIG. 21  shows an example in which the frame-shaped member  6  has the shape of a circular ring as viewed in plan. In this variation, the radius r of the inner peripheral surface  61  of the frame-shaped member  6  as viewed in plan is an integral multiple of ¼times the wavelength λ of the terahertz waves, i.e. λ/4. Such a fame-shaped member  6  having the shape of a circular ring as viewed in plan also functions as an electromagnetic shield, and hence, improves resistance to disturbance noise and reduces crosstalk. Moreover, when the antenna structure integrated in the terahertz element  1  is an antenna that does not rely on waves polarized in a particular direction, configuring the frame-shaped member  6  into the shape of a circular ring as viewed in plan assures that electromagnetic waves are efficiently received from every direction. Note that the frame-shaped member  6  may not have the shape of a circular ring as shown in  FIG. 21  but may have the shape of an oval ring. 
       FIGS. 22-29  show examples in which the frame-shaped member  6  is not continuous as viewed in plan but formed with one or more slits  69 , and in particular, the one or more slits are arranged symmetrically with respect to the radiation point of the terahertz waves, i.e. the center position P 1  of the terahertz element.  FIGS. 22, 24, 26 and 28  show examples in which one or more slits  69  are formed in the frame-shaped member  6  having the shape of a rectangular ring as viewed in plan, whereas  FIGS. 23, 25, 27 and 29  show examples in which one or more slits  69  are formed in the frame-shaped member  6  having the shape of a circular ring as viewed in plan.  FIGS. 22 and 23  show examples in which two slits  69  are formed. In  FIGS. 22 and 23 , two slits  69  are aligned in the y direction. However, the present disclosure is not limited to this, and the two slits  69  may be aligned in the x direction.  FIGS. 24 and 25  show examples in which four slits  69  are formed at locations facing the respective element side surfaces  103  of the terahertz element  1 .  FIGS. 26 and 27  show examples in which four slits  69  are formed on diagonal lines of the terahertz element  1  as viewed plan.  FIGS. 28 and 29  show examples in which eight slits  69  are formed. 
     In these cases again, the terahertz waves radiated from the terahertz element  1  are reflected by the inner peripheral surface  61  of the frame-shaped member  6  to produce resonance, which leads to noise reduction and gain improvement of the terahertz waves emitted from the terahertz device A 1  according to the present variation. 
       FIG. 30  shows an example in which the frame-shaped member  6  is formed with one or more slits  69  as with the examples shown in  FIGS. 22-29 , but unlike the examples shown in  FIGS. 22-29 , the slits in this example are not arranged symmetrically with respect to the radiation point of the terahertz waves. In this variation shown in  FIG. 30 , the frame-shaped member  6  includes a plurality of metal pieces  601  separated from each other by the slits  69 . The metal pieces  601  are not limited to those of a particular configuration, but may be configured such that the terahertz waves from the terahertz element  1  are stationarily reflected by the inner peripheral surface  61  of the frame-shaped member  6 . That is, it is only required that the metal pieces  601  are arranged such that the frame-shaped member  6  stationarily functions as a resonator that produces resonance of terahertz waves from the terahertz element  1 . In the present variation, to make the frame-shaped member  6  function as a resonator, the metal pieces  601  may be configured as follows. 
     First, for each of the metal pieces  601 , assume that there is a rectangle that surrounds the metal piece  601  as viewed in the z direction with the smallest area, as shown in  FIG. 30  (see the thinner dot lines in the figure). The length of the longer side of each imaginary rectangle is defined as length L i  of the relevant metal piece  601 . Herein, i is a positive integer (i=1, 2, . . . n), and n is the number of the metal pieces  601 . Since there are four metal pieces  601  in  FIG. 30 , i=1, 2, 3, 4. The minimum distance between two metal pieces  601  on opposite sides of a slit  69  is defined as distance S i . To determine the distance S i , consider an imaginary closed loop surrounding the terahertz element  1  and extending along the metal pieces  601  to connect the metal pieces  601  to each other. Specifically, consider a closed loop with the shortest length that does not traverse the terahertz element  1 . In the example shown in  FIG. 30 , the closed loop takes the route indicated by thicker dot lines. The above-described distance S i  between two metal pieces  601  is the distance measured along the closed loop. With the length L i  of each metal piece  601  and the distance S i  between metal pieces  601  are defined as described above, the metal pieces  601  are arranged so as to satisfy S 0 /L 0 &lt;1, where L 0 =ΣL i =L 1 +L 2 + . . . +L i + . . . +L n  and S 0 =ΣS i =S 1 +S 2 + . . . +S i + . . . +S n . That is, the metal pieces  601  are configured such that the sum of the respective lengths L i  of the metal pieces  601  is greater than the sum of the respective distances S i . This arrangement allows the terahertz waves radiated from the terahertz element  1  to be reflected by the inner peripheral surface  61  of the frame-shaped member  6  to produce resonance, which leads to noise reduction and gain improvement of the terahertz waves emitted from the terahertz device A 1  according to the present variation. Thus, even when the frame-shaped member  6  has the shape shown in  FIG. 31  as viewed in plan, for example, as long as the metal pieces  601  are configured to satisfy the above-described condition, noise reduction and gain improvement of the terahertz waves from the terahertz device A 1  is achieved as with the case where no slits  69  are formed. 
       FIG. 32  shows an example in which a plurality of small metal pieces  601  having generally the same shape are arranged to form a rectangular ring as a frame-shaped member  6 . Note that the metal pieces may be arranged to form a circular ring rather than a rectangular ring. In the example shown in  FIG. 32 , the metal pieces  601  are arranged such that the length L i  of each metal piece  601  satisfies L i &lt;λ/8 (where λ is the wavelength of the terahertz waves) and the distance S i  between metal pieces  601  satisfies S i ≤2L i . Such a configuration of the metal pieces  601  allows the terahertz waves to be reflected by the inner peripheral surface  61  of the frame-shaped member  6  to produce resonance, i.e. allows the frame-shaped member  6  to stationarily function as a resonator. This leads to noise reduction and gain improvement of the terahertz waves emitted from the terahertz device A 1  according to the present variation. Though the metal pieces  601  form a rectangular shape as viewed in plan in  FIG. 32 , the shape as viewed in plan may be any shape as long as it satisfies the condition described above. 
       FIGS. 33-38  show variations of the terahertz device A 1  according to the first embodiment. In the variations described below, the elements that are identical or similar to those of the terahertz device A 1  described above are denoted by the same reference signs as those used for the terahertz device A 1 , and the description thereof is omitted. 
       FIG. 33  shows a terahertz device A 2  according to a first variation of the first embodiment.  FIG. 33  is a sectional view of the terahertz device A 2  and corresponds to the section of the terahertz device A 1  shown in  FIG. 3 . The terahertz device A 2  of the first variation differs from the terahertz device A 1  in that the element front surface  101  of the terahertz element  1  is exposed from the sealing resin  7 . 
     In the terahertz device A 2 , the element front surface  101  of the terahertz element  1 , which is exposed from the sealing resin  7  as described above, is flush with the resin front surface  701  and the top surface  63  of the frame-shaped member  6 . The terahertz device A 2  having such a configuration may be obtained by, after forming the sealing resin  870  in the sealing resin forming step (see  FIGS. 16 and 17 ), grinding the sealing resin  870  from the resin front surface  870   a  until the element front surface  101  is exposed. 
     In the terahertz device A 2 , the element front surface  101  of the terahertz element  1  is exposed. That is, the element front surface  101  is not covered with the sealing resin  7 . With such an arrangement, the absorption loss of terahertz waves due to the sealing resin  7  is reduced. 
       FIG. 34  shows a terahertz device A 3  according to a second variation of the first embodiment.  FIG. 34  is a sectional view of the terahertz device A 3  and corresponds to the section of the terahertz device A 1  shown in  FIG. 3 . The terahertz device A 3  of the second variation differs from the terahertz device A 1  in that the upper surface (top surface  63 ) of the frame-shaped member  6  is covered with the sealing resin  7 . 
     In the terahertz device A 3 , the top surface  63  of the frame-shaped member  6  is covered with the sealing resin  7 , as described above. The terahertz device A 2  having such a configuration may be obtained by, after forming the sealing resin  870  in the sealing resin forming step (see  FIGS. 16 and 17 ), not grinding the sealing resin  870  at all or grinding the sealing resin from the resin front surface  870   a  to such a degree that the top surface of the frame-shaped member  860  is not exposed. 
       FIG. 35  shows a terahertz device A 4  according to a third variation of the first embodiment.  FIG. 35  is a sectional view of the terahertz device A 4  and corresponds to the section of the terahertz device A 1  shown in  FIG. 3 . The terahertz device A 4  of the third variation differs from the terahertz device A 1  in shape of the through-holes  21 . 
     In the terahertz device A 4 , the inner wall of each through-hole  21  is inclined such that the cross section of the through-hole orthogonal to the z direction becomes smaller as progressing from the support-board front surface  201  toward the support-board back surface  202  of the support board  2 . The through-holes  21  may be formed by e.g. anisotropic etching, and the inclination angle of the inner walls with respect to the support-board back surface  202  is about 54.7°. Since the through electrodes  32  are formed so as to fill the through-holes  21 , the shape of the through electrodes  32  of the terahertz device A 4  also differs from the shape of the through electrodes  32  of the terahertz device A 1 . 
       FIG. 36  shows a terahertz device A 5  according to a fourth variation of the first embodiment.  FIG. 36  is a sectional view of the terahertz device A 5  and corresponds to the section of the terahertz device A 1  shown in  FIG. 3 . The terahertz device A 6  of the fourth variation differs from the terahertz device A 1  in that the outer peripheral surface  62  of the frame-shaped member  6  is exposed from the sealing resin  7 . In the terahertz device A 5 , the sealing resin  7  is formed on the inner side of the frame-shaped member  6  and is not formed on the outer side of the frame-shaped member. With such an arrangement, the size of the terahertz device A 5  in plan view is reduced. That is, the terahertz device A 5  can be made compact. 
       FIG. 37  shows a terahertz device A 6  according to a fifth variation of the first embodiment.  FIG. 37  is a sectional view of the terahertz device A 6  and corresponds to the section of the terahertz device A 1  shown in  FIG. 3 . The terahertz device A 6  of the fifth variation differs from the terahertz device A 1  in that the frame-shaped member  6  is formed in contact with the element side surfaces  103 . In the terahertz device A 6 , the frame-shaped member  6  is in contact with the element side surfaces  103  of the terahertz element  1 . Thus, as viewed in plan, the inner periphery of the frame-shaped member  6  and the outer periphery of the terahertz element  1  generally correspond to each other. 
       FIG. 38  shows a terahertz device A 7  according to a sixth variation of the first embodiment.  FIG. 38  is a sectional view of the terahertz device A 7  and corresponds to the section of the terahertz device A 1  shown in  FIG. 3 . The terahertz device A 7  of the sixth variation differs from the terahertz device A 1  in that terahertz device A 7  does not include the frame-shaped member  6 . 
     In all terahertz devices A 2 -A 7  of the first through the sixth variations of the first embodiment, at least part of the terahertz element  1  is covered with the sealing resin  7 . Thus, as with the first embodiment, malfunctions due to influences from the outside are reduced. Also, since the terahertz devices A 2 -A 6  of the first through the fifth variations are provided with frame-shaped members, disturbance noise and crosstalk are reduced. Moreover, in the terahertz devices A 2 -A 5  according to the first through the fourth variations, terahertz waves are reflected by the inner peripheral surface  61  of the frame-shaped member  6  to produce resonance, which leads to noise reduction and gain improvement of the terahertz waves emitted from the terahertz devices A 2 -A 5 . 
       FIGS. 39 and 40  show a terahertz device B 1  according to a second embodiment. In the embodiments described below, the elements that are identical or similar to those of the terahertz device A 1  described above are denoted by the same reference signs as those used for the terahertz device A 1 , and the description thereof is omitted. As the difference from the terahertz device A 1 , the support board  2  of the terahertz device B 1  of the second embodiment is formed with a depression, in which the terahertz element  1  is housed. The depression corresponds to a recess  22  described later. 
       FIG. 39  is a plan view of the terahertz element B 1 . Note that the illustration of the sealing resin  7  is omitted in  FIG. 39 .  FIG. 40  is a sectional view taken along line XL-XL in  FIG. 39 . 
     As shown in  FIG. 40 , the support board  2  has a recess  22 . The recess  22  is formed so as to dent from the support-board front surface  201  toward the support-board back surface  202 . The recess  22  does not penetrate the support board  2  in the z direction. The recess  22  may be formed by e.g. anisotropic etching. The recess  22  houses at least part of the terahertz element  1 . In the present embodiment, the recess  22  houses the entirety of the terahertz element  1 , as shown in  FIGS. 39 and 40 . That is, the depth of the recess  22  (dimension in the z direction) is larger than the dimension of the terahertz element  1  in the z direction. The shape of the recess  22  as viewed in plan is rectangular in the example shown in  FIG. 39 , but is not limited to this and may be circular, for example. The recess  22  has a bottom surface  221  and a connecting surface  222 . 
     The bottom surface  221  is the surface on which the terahertz element  1  is mounted. The bottom surface  221  is orthogonal to the z direction. The bottom surface  221  is flat. The bottom surface  221  faces the element back surface  102 . In the present embodiment, the wiring layers  31  are formed on the bottom surface  221 . 
     The connecting surface  222  is connected to the support-board front surface  201  and the bottom surface  221 , as shown in  FIG. 40 . The connecting surface  222  is connected to the support-board front surface  201  at one edge in the z direction (upper edge in  FIG. 40 ) and connected to the bottom surface  221  at the other edge in the z direction (lower edge in  FIG. 40 ). The connecting surface  222  is inclined with respect to the bottom surface  221 . The support-board front surface  201  is a (100) surface, so that the connecting surface  222  is a (111) surface. Accordingly, the connecting surface  222  has an inclination angle of about 54.7° with respect to the bottom surface  221 . 
     As shown in  FIG. 40 , the frame-shaped member  6  is formed so as to cover the connecting surface  222 . The frame-shaped member  6  is inclined with respect to the z direction. The inner peripheral surface  61  of the frame-shaped member  6  is also inclined with respect to the z direction. The frame-shaped member  6  is connected to and formed integrally with the wiring layers  31 . In an example, in the first plating layer forming step described above, the wiring layers  31  are formed, and the frame-shaped member  6  is also formed at the same time. 
     Since the terahertz element  1  of the terahertz device B 1  is covered with the sealing resin  7  as with the first embodiment, the terahertz element  1  is protected from influences from the outside. In this way, the terahertz device B 1  has a packaging structure that allows for modularization of the terahertz element  1  with improved reliability. 
     In the terahertz device B 1 , the frame-shaped member  6  is arranged so as to surround the terahertz element  1 , as with the first embodiment. With such an arrangement, the frame-shaped member  6  functions as an electromagnetic shield, so that the terahertz device B 1  can reduce problems such as disturbance noise or crosstalk. In this way, the terahertz device B 1  has a packaging structure that allows for modularization of the terahertz element  1  with improved emission or reception quality of terahertz waves. 
     In the terahertz device B 1 , the inner peripheral surface  61  of the frame-shaped member  6  is inclined with respect to the z direction. Thus, the frame-shaped member  6  cannot cause resonance of the terahertz waves from the terahertz element  1 . That is, the frame-shaped member  6  cannot function as a resonator. However, the frame-shaped member  6  can function as a horn antenna by using the inclination of the inner peripheral surface  61 . 
       FIG. 41  shows a variation of the terahertz device B 1  according to the second embodiment.  FIG. 41  is a sectional view of a terahertz device B 2  according to a variation of the second embodiment, and corresponds to the section of the terahertz device B 1  shown in  FIG. 40 . The terahertz device B 2  of this variation differs from the terahertz device B 1  in that the terahertz device B 2  does not include the through electrodes  32 . 
     In the terahertz device B 2 , the external electrodes  4  are in contact with the wiring-layer back surfaces  312  of the wiring layers  31  and electrically connected to the wiring layers  31  directly. As shown in  FIG. 41 , the wiring-layer back surfaces  312  are exposed from the support board  2 , so that an insulating film  49  is provided to prevent undesired short circuit between conductors or deterioration of the wiring layers  31 . The insulating film  49  covers the support-board back surface  202  and the wiring-layer back surfaces  312 . 
     The terahertz device B 2  provides the same advantages as those of the terahertz device B 1 . Moreover, the terahertz device B 2  can reduce the dimension of the support board  2  in the z direction as compared with the terahertz device B 1 . Thus, the terahertz device B 2  can be made thinner than the terahertz device B 1 . 
       FIG. 42  shows a terahertz device C 1  according to a third embodiment.  FIG. 42  is a sectional view of the terahertz device C 1  and corresponds to the section of the terahertz device A 1  shown in  FIG. 3 . The terahertz device C 1  of the third embodiment differs from the terahertz device A 1  mainly in that the support board  2  is arranged in proximity to the element front surface  101  as shown in  FIG. 42 . When the terahertz device C 1  is mounted on e.g. a circuit board, the upper side in  FIG. 42  faces the circuit board. 
     In the terahertz device C 1 , the terahertz element  1  is bonded to the support board  2 , with the element front surface  101  facing the support-board front surface  201  of the support board  2 . 
     The support board  2  is formed with grooves  23 . The grooves  23  may serve as a mark showing the mount position for use in mounting the terahertz element  1  or prevent the bonding layers  5  from unduly spreading. Note that the grooves  23  are not necessarily required and may be provided as appropriate. 
     As shown in  FIG. 42 , the bonding layer  5  is interposed between the element front surface  101  of the terahertz element  1  and the support-board front surface  201  of the support board  2  to bond the terahertz element  1  to the support board  2 . In the present embodiment, unlike the first embodiment, the bonding layer  5  does not need to be a material capable of providing electrical connection, and may be any material capable of bonding the terahertz element  1  to the support board  2 . Examples of such a material include DAF (Die Attach Film), Ag paste and solder paste. When DAF is used as the bonding layer  5 , the grooves  23  may not be formed. 
     As shown in  FIG. 42 , the wiring layers  31  are formed on the resin front surface  701  rather than on the support-board front surface  201  of the support board  2 . The terahertz device C 1  includes an insulating film  49  covering the wiring layers  31 . The insulating film  49  is formed with openings to expose parts of the wiring layers  31 , and the external electrodes  4  are formed in the openings. As shown in  FIG. 42 , in the openings of the insulating film  49 , the external electrodes  4  are in contact with the wiring layers  31  and hence electrically connected to the wiring layers  31  directly. 
     The terahertz device C 1  includes columnar electrodes  33  electrically connecting one of the wiring layers  31  with the first conductive layer  13  of the terahertz element  1 , and the other one of the wiring layers  31  with the second conductive layer  14  of the terahertz element  1 , respectively. The columnar electrodes  33  are made of a conductive material such as Cu. The columnar electrodes  33  are formed on the terahertz element  1  before the terahertz element  1  is mounted on the support board  2 . 
     In the terahertz device C 1 , the terahertz waves radiated from the terahertz element  1  are emitted through the support board  2 . Loss of terahertz waves can be prevented by making the support board  2  from a high-resistance material with an electrical resistivity of about 5000 Ω·cm or more. 
     An example of a method for manufacturing the terahertz device C 1  is described below with reference to  FIGS. 43-51 .  FIGS. 43-51  are sectional views showing the steps of a method for manufacturing the terahertz device C 1 . These sectional views correspond to the section shown in  FIG. 42 . 
     First, a support board  820  is prepared, and grooves  823  are formed in the prepared support board  820 , as shown in  FIG. 43 . The grooves  823  will later become the grooves  23  of the terahertz device C 1 . The support board  820  prepared in this step is the same as the support board  820  prepared in the support board preparation step according to the first embodiment. In the subsequent step of forming the grooves  823  (groove forming step), after a silicon oxide film is formed on the entirety of the support-board front surface  820   a , a resist is formed to have a predetermined pattern by photolithography. In this state, part of the silicon oxide film is exposed from the patterned resist. The part of the silicone oxide film exposed from the resist is removed by reactive ion etching. As a result, part of the support board  820  is exposed from the silicon oxide film. The part of the support board  820  exposed from the silicon oxide film is etched away by using KOH (potassium hydroxide) or THAM (tetramethyl ammonium hydroxide), whereby the grooves  823  are formed. Thereafter, the resist and the silicon oxide film are removed. The removal of the silicon oxide film may be performed by wet etching, for example. As the etching solution for wet etching, use may be made of a mixed solution, called BHF, of hydrofluoric acid and ammonium fluoride. 
     Next, a frame-shaped member  860  is formed, as shown in  FIG. 44 . In the step of forming the frame-shaped member  860  (frame-shaped member forming step) shown in  FIG. 44 , a base layer (not shown) is formed by sputtering on the entire surface of the support-board front surface  820   a  of the support board  820  and the grooves  823 . The base layer is a laminate of a Ti layer and a Cu layer. Next, a resist (not shown) for forming the frame-shaped member  860  is formed to have a predetermined pattern by photolithography. When a resist having a pattern is formed in this way, part of the base layer is exposed from the resist. The part exposed from the resist is the region on which the frame-shaped member  860  is to be formed. Next, electrolytic plating is performed using the base layer as a conduction path to form a plating layer. The plating layer is deposited on the part of the base layer that is exposed from the resist. The plating layer is made of Cu, for example. Thereafter, the unnecessary resist is removed, whereby the frame-shaped member  860  made up of the base layer and the plating layer is obtained. 
     Next, as shown in  FIG. 45 , a terahertz element  810  is mounted on the support board  820  by using the bonding layer  850 . In the step of mounting the terahertz element  810  (element mounting step) shown in  FIG. 45 , the terahertz element  810  is mounted on the support board  820 , with the element front surface  810   a  facing the support-board front surface  820   a . In this state, the bonding layers  850  are sandwiched between the element front surface  810   a  and the support-board front surface  820 a. In this element mounting step, DAF is used as the bonding layers  850 . Note that the terahertz element  810  mounted in the element mounting step has columnar electrodes  833  on the first conductive layer  813  and the second conductive layer  814 . That is, as a preparation for the element mounting step, columnar electrodes  833  are formed on the first conductive layer  813  and the second conductive layer  814  of the terahertz element  810 . 
     Next, as shown in  FIGS. 46 and 47 , a sealing resin  870  is formed to cover the terahertz element  810  and the frame-shaped member  860 . In the present embodiment, in the step of forming the sealing resin  870  (sealing resin forming step), the sealing resin  870  is applied on the support-board front surface  820   a  of the support board  820  so as to cover all of the columnar electrodes  833  of the terahertz element  810  and the frame-shaped member  860 , as shown in  FIG. 46 . Next, as shown in  FIG. 47 , the sealing resin  870  is ground from the resin front surface  870   a  toward the resin back surface  870   b  until the columnar electrodes  833  are exposed. The technique for grinding the sealing resin  870  is the same as the first embodiment. This grinding makes the upper surfaces of the columnar electrodes  833  and the resin front surface  870   a  flush with each other, while also exposing the upper surfaces of the columnar electrodes  833  from the sealing resin  870 . 
     Next, wiring layers  831  are formed, as shown in  FIG. 48 . The step of forming the wiring layers  831  (wiring layer forming step) is performed generally in the same manner as the frame-shaped member forming step. Specifically, in the wiring layer forming step, a base layer is first formed so as to cover all of the resin front surface  870   a  and the upper surfaces of the columnar electrodes  833 . Next, after a resist having a predetermined pattern is formed on the base layer, electrolytic plating by using the base layer as a conduction path is performed to deposit a plating layer on the part of the base layer that is exposed from the resist. Thereafter, the unnecessary resist is removed, whereby the wiring layers  831  made up of the base layer and the plating layer is obtained. 
     Next, an insulating layer  849  is formed, as shown in  FIG. 49 . In the step of forming the insulating layer  849  (insulating layer forming step), the insulating layer  849  is first applied so as to cover the entirety of the wiring layers  831 . Next, to later form the external electrodes  840 , part of the insulating layer  849  is removed to expose the wiring layers  831  from the removed part. Such removal of the insulating layer  849  may be performed by etching, for example. As the material for the insulating layer  849 , polymer-based resin may be used, for example. 
     Next, the external electrodes  840  are formed, as shown in  FIG. 50 . The step of forming the external electrodes  840  (external electrode forming step) is performed by electroless plating, as with the external electrode forming step of the first embodiment. Specifically, a Ni layer, a Pd layer and a Au layer are successively deposited on the parts of the wiring layers  831  that are exposed from the insulating layer  849 . The technique for forming the external electrodes  840  is not limited to this. For example, as the external electrodes  840 , solder bumps may be formed on the parts of the wiring layers  831  that are exposed from the insulating layer  849 . 
     Next, as shown in  FIG. 51 , the support board  820  is ground from the support-board back surface  820   b . The step of grinding the support board  820  (support board grinding step) is performed by machine grinding, as with the support board grinding step of the first embodiment. 
     Next, the sealing resin  870  and the support board  820  are cut into individual pieces for terahertz elements  810  similarly to the cutting step of the first embodiment. In the present embodiment, cutting may be performed along the cutting line CL 2  shown in  FIG. 51 , for example. 
     By going through the above-described steps, the terahertz device C 1  shown in  FIGS. 42  is obtained. 
     Since the terahertz element  1  of the terahertz device C 1  is covered with the sealing resin  7  as with the first embodiment, the terahertz element  1  is protected from influences from the outside. In this way, the terahertz device C 1  has a packaging structure that allows for modularization of the terahertz element  1  with improved reliability. 
     The terahertz device C 1  includes the frame-shaped member  6 , as with the first embodiment. Thus, the terahertz device C 1  achieves reduction of problems such as disturbance noise or crosstalk, as well as reduction of noise components and gain improvement due to resonant reflection. In this way, the terahertz device C 1  has a packaging structure that allows for modularization of the terahertz element  1  with improved emission or reception quality of terahertz waves. 
       FIG. 52  shows a variation of the terahertz device C 1  according to the third embodiment.  FIG. 52  is a sectional view of a terahertz device C 2  according to a variation of the third embodiment, and corresponds to the section of the terahertz device C 1  shown in  FIG. 42 . The terahertz device C 2  of this variation differs from the terahertz device C 1  mainly in that the terahertz device C 2  does not include the support board  2 . 
     As mentioned above, the terahertz device C 2  does not include the support board  2 . Thus, the element front surface  101  of the terahertz element  1  and the resin back surface  702  of the sealing resin  7  are exposed to the outside of the terahertz device C 2 . 
     Such a terahertz device C 2  may be obtained by grinding away the entirety of the support board  820  in the support board grinding step described above with reference to  FIG. 51 . 
     The terahertz device C 2  provides the same advantages as those of the terahertz device C 1 . Moreover, since the terahertz device C 2  does not include the support board  2 , the terahertz device C 2  can be made thinner than the terahertz device C 1 . 
       FIGS. 53 and 54  show a terahertz device D 1  according to a fourth embodiment.  FIG. 53  is a plan view of the terahertz device D 1 . Note that the illustration of the sealing resin  7  is omitted in  FIG. 53 .  FIG. 54  is a sectional view taken along line LIV-LIV in  FIG. 53 . The terahertz device D 1  of the fourth embodiment differs from the terahertz device A 1  of the first embodiment in that the terahertz device D 1  includes semiconductor elements  1 ′ in addition to the terahertz element  1 . 
     As mentioned above, as compared with the terahertz device A 1 , the terahertz device D 1  additionally includes a plurality of semiconductor elements  1 ′. As shown in  FIGS. 53 and 54 , the terahertz device D 1  includes two semiconductor elements  1 ′. Each semiconductor element  1 ′ is an electronic circuit element made of a semiconductor material. For example, each semiconductor element  1 ′ may be a diode, a transistor or a resistor. Examples of the diode include a Zener diode and a TVS (transistor voltage suppressor) diode. As shown in  FIG. 53 , each semiconductor element  1 ′ is disposed on the inner side of the frame-shaped member  6  as viewed in plan. That is, the frame-shaped member  6  surrounds the terahertz element  1  and the semiconductor elements  1 ′. The terahertz element  1  and the semiconductor elements  1 ′ are aligned in the x direction on the inner side of the frame-shaped member  6 . 
     Since the terahertz element  1  of the terahertz device D 1  is covered with the sealing resin  7  as with the first embodiment, the terahertz element  1  is protected from influences from the outside. In this way, the terahertz device D 1  has a packaging structure that allows for modularization of the terahertz element  1  with improved reliability. 
     The terahertz device D 1  includes the frame-shaped member  6 , as with the first embodiment. Thus, the terahertz device D 1  achieves reduction of problems such as disturbance noise or crosstalk, as well as reduction of noise components and gain improvement due to resonant reflection. In this way, the terahertz device D 1  has a packaging structure that allows for modularization of the terahertz element  1  with improved emission or reception quality of terahertz waves. 
     The terahertz device D 1  includes semiconductor elements  1 ′ other than the terahertz element  1 . Thus, the terahertz device D 1  can be configured as a multi-chip package with an additional function of the semiconductor elements  1 ′. For example, when a Zener diode or a TVS (transistor voltage suppressor) is used as the semiconductor elements  1 ′, surge protection function can be added to the terahertz device D 1 . Moreover, since the terahertz element  1  and the semiconductor elements  1 ′ are built in a single package, the mounting area on e.g. a circuit board can be reduced as compared with the case where they are individually packaged. 
       FIGS. 55 and 56  show a variation of the terahertz device D 1  according to the fourth embodiment. The terahertz device D 2  of this variation differs from the terahertz device D 1  in that the semiconductor elements  1 ′ are arranged on the outer side of the frame-shaped member  6  as viewed in plan.  FIG. 55  is a plan view of the terahertz device D 2 . Note that the illustration of the sealing resin  7  is omitted in  FIG. 55 .  FIG. 56  is a sectional view taken along line LVI-LVI in  FIG. 55 . 
     In the terahertz device D 2 , the semiconductor elements  1 ′ are arranged on the outer side of the frame-shaped member  6  unlike the terahertz device D 1 , as shown in  FIG. 55 . The terahertz element  1  and the semiconductor elements  1 ′ are aligned in the x direction. 
     In the prevent embodiment, unlike the terahertz device D 1 , the frame-shaped member  6  is interposed between the terahertz element  1  and the semiconductor elements  1 ′. Thus, it is difficult to electrically connect the terahertz element  1  and the semiconductor elements  1 ′ directly by the wiring layers  31 . For this reason, the terahertz device D 2  has a re-distribution layer  34  on the support-board back surface  820   b . The terahertz element  1  and the semiconductor elements  1 ′ are both electrically connected to the re-distribution layer  34  via the through electrode  32 , so that the terahertz element  1  and the semiconductor elements  1 ′ are electrically connected. 
     The terahertz device D 2  provides the same advantages as those of the terahertz device D 1  of the fourth embodiment. 
       FIGS. 57 and 58  show a terahertz device E 1  according to a fifth embodiment.  FIG. 57  is a plan view of the terahertz device E 1 .  FIG. 58  is a sectional view taken along line LVIII-LVIII in  FIG. 57 . The terahertz device E 1  according to the fifth embodiment differs from the terahertz device A 1  according to the first embodiment in that the terahertz device E 1  has, on the surface from which the terahertz waves are emitted (i.e., the resin front surface  701 ), an emission controlling member for controlling emission of the terahertz waves. As the emission control in the present disclosure, polarization control, frequency control, directivity control, dispersion control or resonance control may be performed to the terahertz waves radiated from the terahertz element  1 . Also, the emission controlling member may be configured to perform near-field control of the terahertz waves emitted from the terahertz device E 1 . The fifth embodiment shows the example in which the emission controlling member is added to the terahertz device A 1 , but the emission controlling member may be added to other terahertz devices described above, i.e. the terahertz devices A 2 -A 7 , B 1 , B 2 , C 1 , C 2 , D 1  or D 2 . 
     As mentioned above, as compared with the terahertz device A 1 , the terahertz device E 1  additionally includes the emission controlling member  91  on the resin front surface  701 . The terahertz device E 1  integrates a metamaterial structure as the emission controlling member  91 . The emission controlling member  91  overlaps with the element front surface  101  of the terahertz element  1 , as viewed in plan. As shown in  FIGS. 57 and 58 , the emission controlling member  91 , i.e. the metamaterial structure includes a patterned layer  911  and a protective layer  912 . 
     The patterned layer  911  is formed on the resin front surface  701 . As shown in  FIG. 57 , the patterned layer  911  overlaps with the terahertz element  1  as viewed in plan. As shown in  FIG. 57 , the patterned layer  911  overlaps with the region surrounded by the frame-shaped member  6  as viewed in plan. The patterned layer  911  includes a plurality of metal segments  911   a . Each of the metal segments  911   a  is in the form of a strip extending in the y direction, as viewed in plan. The metal segments  911   a  are arranged side by side in the x direction. In this way, the patterned layer  911  is made up of a plurality of strip-shaped metal segments  911   a  arranged in the shape of a louver. The protective layer  912  is formed so as to cover the patterned layer  911 . The protective layer  912  is made of an insulating material such as an epoxy resin, a polymer-based resin, a silicon oxide film (e.g., SiO 2 ) or a silicon nitride film (e.g., SiN). The front surface of the protective layer  912  (the upper surface in  FIG. 58 ) has irregularities in the example shown in  FIG. 58 , but may be a flat surface. In the protective layer  912 , protruding parts (projections) of the front surface overlap with the metal segment  911   a  as viewed in plan, whereas dented parts (recesses) of the front surface do not overlap with the metal segment  911   a  a as viewed in plan. 
     Since the terahertz element  1  of the terahertz device E 1  is covered with the sealing resin  7  as with the first embodiment, the terahertz element  1  is protected from influences from the outside. In this way, the terahertz device E 1  has a packaging structure that allows for modularization of the terahertz element  1  with improved reliability. 
     The terahertz device E 1  includes the frame-shaped member  6 , as with the first embodiment. Thus, the terahertz device E 1  achieves reduction of problems such as disturbance noise or crosstalk, as well as reduction of noise components and gain improvement due to resonant reflection. In this way, the terahertz device A 1  has a packaging structure that allows for modularization of the terahertz element  1  with improved emission or reception quality of terahertz waves. 
     In the terahertz device E 1 , the emission controlling member  91  is formed on the resin front surface  701  of the sealing resin  7 . Thus, terahertz waves from the terahertz element  1  are emitted to the outside through the emission controlling member  91 . Alternatively, terahertz waves from the outside may become incident on the terahertz element  1  through the emission controlling member  91 . Thus, in the terahertz device E 1 , emission or reception of terahertz waves can be controlled by the emission controlling member  91 . 
     In the terahertz device E 1 , the emission controlling member  91  includes the patterned layer  911 , and the patterned layer  911  includes a plurality of metal segments  911   a  arranged in the shape of a louver (see  FIGS. 57 and 58 ). With such an arrangement, the emission controlling member  91  functions as a polarization filter, so that the terahertz waves radiated from the terahertz element  1  is polarized by the emission controlling member  91  before emission. 
     Although the fifth embodiment shows the example in which a single layer is arranged in the z direction as the patterned layer  911 , the present disclosure is not limited to this, and a plurality of patterned layers may be laminated. Also, the fifth embodiment shows the example in which the metal segments  911   a  forming the patterned layer  911  are arranged in the shape of a louver, but the present disclosure is not limited to this. For example, a plurality of metal segments  911   a  each having the shape of a circular ring may be arranged concentrically. In such a case, the metal segments  911   a  differ from each other in inner diameter, and the outer diameter of each metal segment  911   a  is smaller than the inner diameters of the metal segments  911   a  arranged on the outer side of that metal segment  911   a . As another example, a plurality of metal segments  911   a  each having the shape of a small circle as viewed in plan may be arranged regularly (e.g., in a manner similar to the photonic crystal structure described below). 
       FIGS. 59-61  show variations of the terahertz device E 1  according to the fifth embodiment. 
       FIGS. 59 and 60  show a terahertz device E 2  according to a first variation of the fifth embodiment.  FIG. 59  is a plan view of the terahertz device E 2 .  FIG. 60  is a sectional view taken along line LX-LX in  FIG. 59 . The terahertz device E 2  according to the first variation differs from the terahertz device E 1  in that the terahertz device E 2  includes an emission controlling member  92  instead of the emission controlling member  91 . 
     Specifically, the terahertz device E 2  includes an integrated photonic crystal structure as the emission controlling member  92 . A photonic crystal refers to a structure made up of at least two types of optical materials (or one type of material and air) arranged periodically. 
     The terahertz device E 2  is formed with a dielectric member  921  on the resin front surface  701  of the sealing resin  7 . The dielectric member  921  may be e.g. a silicon oxide film, but is not limited to this. The dielectric member  921  has a plurality of depressions  921   a  arranged in e.g. a dot pattern on its front surface (i.e., the upper surface in the z direction that faces in the direction in which the resin front surface  701  faces). The arrangement of the depressions  921   a  is not limited to a dot pattern. It is only required that the depressions  921   a  are arranged such that the emission controlling member  92  is configured as a photonic crystal structure. As shown in  FIG. 59 , some of the depressions  921   a  arranged in a dot pattern overlap with the terahertz element  1  as viewed in plan. Also, as shown in  FIG. 59 , some of the depressions  921   a  arranged in a dot pattern overlap with the region surrounded by the frame-shaped member  6  as viewed in plan. 
     In the terahertz device E 2 , the depressions  921   a  are arranged such that the emission controlling member  92  functions as a frequency filter. The depressions  921   a  are not limited to such an arrangement and may be arranged such that the emission controlling member  92  functions as a resonator with a high quality factor or a component that performs distributed control. For example, in the arrangement shown in  FIG. 59 , the emission controlling member can function as a resonator with a high quality factor when 1 to 3 depressions  921   a  near the center are eliminated and function as a distributed control component when the cycle is gradually changed (the distance between adjacent depressions  921   a  is gradually changed). 
     The terahertz device E 2  provides the same advantages as those of the terahertz device E 1 . As described above, the emission controlling member  92  includes the dielectric member  921  having a plurality of depressions  921   a  arranged in a predetermined pattern (see  FIGS. 59 and 60 ). With such an arrangement, the emission controlling member  92  functions as a frequency filter, so that the frequency of the terahertz waves from the terahertz element  1  is controlled before emission. 
     This variation shows the example in which the emission controlling member  92  has the depressions as the photonic crystal structure formed in the dielectric member  921 . However, the depressions as the photonic crystal structure may be directly formed on the resin front surface  701 . In such a case again, the same advantages as those of the terahertz device E 2  are obtained. 
       FIG. 61  shows a terahertz device E 3  according to a second variation of the fifth embodiment.  FIG. 61  is a sectional view of the terahertz device E 3  and corresponds to the section of the terahertz device E 1  shown in  FIG. 58 . The terahertz device E 3  according to the second variation differs from the terahertz device E 1  in that the terahertz device E 3  includes an emission controlling member  93  instead of the emission controlling member  91 . 
     The terahertz device E 3  includes, as the emission controlling member  93 , an integrated laminate of a plurality of thin films that differ from each other in index of refraction. As shown in  FIG. 61 , the emission controlling member  93  has a first thin film  931 , a second thin film  932  laminated on the first thin film, and a third thin film  933  laminated on the second thin film  932 . The first thin film  931 , the second thin film  932  and the third thin film  933  overlap with the terahertz element  1  as viewed in plan. The first thin film  931 , the second thin film  932  and the third thin film  933  overlap with the region surrounded by the frame-shaped member  6  as viewed in plan.  FIG. 61  shows the example in which three thin films are formed, but the number of the thin films is not limited to three and may be smaller or larger than three. Provided that the index of refraction of the sealing resin  7  is n 7 , the indexes of refraction of the first thin film  931 , the second thin film  932  and the third thin film  933  are n 931 , n 932  and n 933 , respectively. By making the indexes of refraction of the thin films different from each other in this way, the emission controlling member  93  can control the terahertz waves radiated from the terahertz element  1  and emitted from the terahertz device E 3 . The index of refraction of each thin film may be varied as appropriate such that desired terahertz waves are emitted. 
     The terahertz device E 3  provides the same advantages as those of the terahertz device E 1 . 
       FIGS. 62-67  show a terahertz device F 1  according to a sixth embodiment.  FIG. 62  is a plan view of the terahertz device F 1 .  FIG. 63  is a plan view corresponding to  FIG. 62 , with the sealing resin  7  and the external electrodes  4  indicated by imaginary lines.  FIG. 64  is a bottom view of the terahertz device F 1 .  FIG. 65  is an enlarged view showing a part (region LXV) of  FIG. 64 .  FIG. 66  is a sectional view taken along line LXVI-LXVI in  FIG. 63 .  FIG. 67  is an enlarged sectional view of a part of  FIG. 66 . The terahertz device F 1  of the sixth embodiment differs from the terahertz device A 1  mainly in that the support board  2  has a depression and the external electrodes  4  are formed on the resin front surface  701 . 
     In the terahertz element  1  of the present embodiment, the active element  12  is arranged in proximity to the element back surface  102  in the z direction. Thus, the element back surface  102  is the active surface. In the present embodiment again, as viewed in plan, the functional part (radiation point) overlaps with the center position P 1  of the terahertz element  1 . 
     The terahertz element  1  further includes a reflective metal  15 . As shown in  FIG. 66 , the reflective metal  15  covers the element front surface  101 . The material for the reflective metal  15  may be Cu, for example. Other materials may be used as long as they are capable of reflecting terahertz waves. The terahertz waves radiated from the active element  12  is reflected by the reflective metal  15  and directed downward in the z direction. 
     As shown in  FIGS. 64 and 66 , the support board  2  has a recess  24 . The recess  24  is formed so as to dent from the support-board back surface  202  toward the support-board front surface  201 . The recess  24  does not penetrate the support board  2  in the z direction. The recess  24  has the shape of a truncated cone. The recess  24  is generally circular in cross section orthogonal to the z direction. The recess  24  is tapered. Because of such tapering, the cross section orthogonal to the z direction becomes smaller as progressing from the lower side toward the upper side in the z direction. The recess  24  may be formed by e.g. anisotropic etching. The anisotropic etching is performed using an alkaline solution such as KOH or TMAH described above. The support-board back surface  202  of the support board  2  has an opening due to the presence of the recess  24 . As shown in  FIGS. 64 and 66 , the recess  24  has a bottom surface  241  and a connecting surface  242 . 
     The bottom surface  241  is orthogonal to the z direction. The bottom surface  241  is flat. The bottom surface  241  faces in the z direction and faces in the direction in which the element back surface  102  faces. The bottom surface  241  is generally circular as viewed in plan. 
     The connecting surface  242  is connected to the support-board front surface  201  and the bottom surface  241 . The connecting surface  242  is connected to the support-board front surface  201  at one edge in the z direction (lower edge in  FIG. 66 ) and connected to the bottom surface  241  at the other edge in the z direction (upper edge in  FIG. 66 ). The connecting surface  242  is flat. The connecting surface  242  is inclined with respect to the bottom surface  241 . The support-board back surface  202  is a (100) surface in accordance with Miller index, so that the connecting surface  242  is a (111) surface in accordance with Miller index. The connecting surface  242  has an inclination angle θ (see  FIG. 66 ) of about 54.7°±0.5° with respect to the bottom surface  241 . 
     As shown in  FIG. 65 , in the recess  24 , the boundary  24   a  between the connecting surface  242  and the support-board back surface  202  is made up of edges extending in the x direction and edges extending in the y direction that are alternately arranged and connected to each other. Macroscopically, the boundary  24   a  looks like a circle in plan view, as shown in  FIG. 64 , since the length of each of the edges forming the boundary  24   a  is small. 
     Each internal electrode  3  includes a wiring layer  31  and a through electrode  35 . That is, as compared with the internal electrodes  3  of the first embodiment, each internal electrode  3  of this embodiment includes a through electrode  35  instead of the through electrode  32 . 
     The through electrodes  35  are formed so as to penetrate the sealing resin  7 . The through electrodes  35  electrically connect the wiring layers  31  and the external electrodes  4 . The through electrodes  35  are formed on the wiring-layer front surface  311  of the wiring layers  31 . The through electrodes  35  extend in the z direction from the wiring-layer front surfaces  311  to be exposed from the resin front surface  701  of the sealing resin  7 . Each of the through electrodes  35  is in the form of a strip extending in the y direction, as viewed in plan. The through electrodes  35  are arranged on each side of the terahertz element  1  in the x direction. As viewed in the x direction, the terahertz element  1  completely overlaps with the through electrodes  35 . As viewed in plan, each through electrode  35  has opposite edges in the y direction, and these ends do not overlap with the terahertz element  1  as viewed in the x direction. 
     Each through electrode  35  has a first end surface  351  and a second end surface  352 . The first end surface  351  and the second end surface  352  are spaced apart and face away from each other in the z direction. The first end surface  351  is in contact with the wiring layer  31 . Thus, the through electrode  35  and the wiring layer  31  are electrically connected to each other. The second end surface  352  is exposed from the resin front surface  701  of the sealing resin  7 . The second end surface  352  is covered with an external electrode  4  and in contact with the external electrode  4 . Thus, the through electrode  35  and the external electrode  4  are electrically connected to each other. 
     The external electrodes  4  are formed above the resin front surface  701  in the z direction and exposed from the sealing resin  7 . The external electrodes  4  cover the second end surfaces  352 . 
     The connecting surface  242  is covered with a metal film  65 . The metal film  65  is not in contact with the bottom surface  241 . The material for the metal film  65  may be Cu, for example. The material for the metal film  65  is not limited to Cu, and other materials may be used as long as they are capable of reflecting terahertz waves. The metal film  65  may be formed by sputtering or vacuum deposition, for example. The technique for forming the metal film  65  is not limited to this and may be electroplating. 
     The metal film  65  is arranged around the center position P 1  of the terahertz element  1  as viewed in plan. Since the center position P 1  generally corresponds to the functional part (radiation point) of the terahertz waves, the metal film  65  is positioned around the functional part (radiation point) of the terahertz waves. 
     As shown in  FIG. 67 , the metal film  65  has a first surface  651 , a second surface  652  and a third surface  653 . The first surface  651  is in contact with the connecting surface  242  of the recess  24 , covering the connecting surface. The second surface  652  is generally parallel to the first surface  651 . The second surface  652  may be curved. The area of the second surface  652  is smaller than that of the first surface  651 . The third surface  653  is connected to the first surface  651  and the second surface  652 . The third surface  653  is curved. The boundary between the first surface  651  and the third surface  653  generally corresponds to the boundary between the bottom surface  241  and the connecting surface  242 . The boundary between the first surface  651  and the third surface  653  may be on the connecting surface  242 . 
     In the terahertz device F 1 , the distance T 1  between the element back surface  102  of the terahertz element  1  and the support-board front surface  201  of the support board  2  in the z direction and the distance T 2  between the bottom surface  241  of the recess  24  and the support-board front surface  201  of the support board  2  in the z direction are designed to satisfy the following conditions: The distance T 1  and the distance T 2  are both smaller than the half-wavelength of the terahertz waves, or the distance T 1  and the distance T 2  each are a positive integer multiple of the half-wavelength of the terahertz waves. Herein, the “half-wavelength” refers to one half the wavelength λ of the terahertz waves (i.e., λ/2). 
     In the terahertz device F 1 , the thickness T 3  of the support board  2  (i.e., the distance between the support-board front surface  201  and the support-board back surface  202  in the z direction) is about 725 μm. The thickness T 3  of the support board  2  is not limited to such a value, and a larger thickness T 3  of the support board  2  provides a larger gain of emitted terahertz waves. However, increasing the thickness T 3  of the support board  2  results in an increased dimension of the terahertz device F 1  in the z direction. Thus, the thickness T 3  of the support board  2  may be determined as appropriate in accordance with the required product specifications (e.g., the gain of terahertz waves and the dimension of the terahertz device F 1  in the z direction). 
     In the terahertz device F 1 , the diameter R 1  of the bottom surface  241  is set to not less than λ/2 and not more than λ. Such an arrangement allows for single-mode excitation of the radiated terahertz waves. Note that the diameter R 2  of the lower edge of the recess  24  in the z direction (the diameter of the opening of the recess  24  in the support-board back surface  202 ) is calculated by R 2 =R 1 +2×((T 3 −T 2 )×tan(90−θ)). 
     Since the terahertz element  1  of the terahertz device F 1  is covered with the sealing resin  7  as with the first embodiment, the terahertz element  1  is protected from influences from the outside. In this way, the terahertz device F 1  has a packaging structure that allows for modularization of the terahertz element  1  with improved reliability. 
     In the terahertz device F 1 , the support board  2  is formed with the recess  24 . The recess  24  includes a connecting surface  242  covered with the metal film  65 . As viewed in plan, the metal film  65  has the shape of a circular ring and surrounds the functional part (radiation point) of the terahertz element. With such an arrangement, the terahertz waves radiated from the terahertz element  1  are reflected by the metal film  65  before emission. At this time, the recess  24  functions as a horn antenna, so that the gain, directivity and polarization, for example, of emitting or receiving terahertz waves can be controlled in accordance with the shape and size of the recess  24 . Thus, the terahertz device F 1  can be described as having an integrated horn antenna. Note that since the recess  24  in the terahertz device F 1  generally has the shape of a truncated cone, vibration in normal mode TE 11  occurs. 
     In the terahertz device F 1 , as viewed in the x direction, each through electrode  35  overlaps with the terahertz element  1  and projects relative to the terahertz element  1  in each side in the y direction. With such an arrangement, the through electrodes  35  reflect the terahertz waves radiated in the x direction from the terahertz element  1  to produce resonance. Thus, the terahertz device F 1  can radiate terahertz waves with reduced noise components. Also, the terahertz device F 1  can radiate terahertz waves with an increased gain due to resonant reflection. Moreover, the through electrodes  35  block other electromagnetic waves from the x direction. That is, the through electrodes  35  function as an electromagnetic shield that blocks interfering electromagnetic waves from the x direction. Thus, the terahertz device F 1  reduces problems such as disturbance noise or crosstalk. In this way, the terahertz device A 1  has a packaging structure that allows for modularization of the terahertz element  1  with improved emission or reception quality of terahertz waves. 
     In the terahertz device F 1 , the terahertz element  1  includes a reflective metal  15  covering the element front surface  101 . With such an arrangement, in the terahertz element  1 , the terahertz waves radiated from the active element  12  and propagating upward in the z direction is reflected by the reflective metal  15  downward in the z direction. As a result, the terahertz waves travel downward in the z direction, so that the gain of the terahertz waves emitted downward in the z direction is improved. Moreover, since emission of terahertz waves upward in the z direction is prevented, adverse effects (such as noise) on a circuit board on which the terahertz device F 1  is mounted are prevented. 
     The sixth embodiment shows the example in which the recess  24  has the shape of a truncated cone, but the present disclosure is not limited to this.  FIGS. 68 and 69  show other embodiments of the recess  24  that can be incorporated in the terahertz device F 1  according to the sixth embodiment. Note that the shapes of the recess  24  shown in these figures are merely examples and the present disclosure is not limited to these. 
       FIGS. 68 and 69  each are a bottom view of a terahertz device F 1  in which the recess  24  has the shape of a truncated pyramid.  FIG. 68  shows an example in which the recess  24  has the shape of a truncated rectangular pyramid and is generally square in cross section in the z direction. In the embodiment shown in  FIG. 68 , the two diagonal lines of the generally square cross section of the recess  24  described above extend along the x direction and the y direction, respectively. Note however that the recess  24  may be formed such that the sides of the generally square cross section described above extend in parallel to the sides of the terahertz element  1 , respectively.  FIG. 69  shows an example in which the recess  24  has the shape of a truncated rectangular pyramid and is generally in the form of an elongated rectangle in cross section in the z direction. In the embodiment shown in  FIG. 69 , the longer sides of the elongated rectangle of the cross section of the recess  24  extend along the y direction. Note however that the recess  24  may be formed such that the longer sides of the elongated rectangle of the cross section extend along the x direction. 
     In each terahertz device F 1  shown in  FIGS. 68 and 69  again, the recess  24  and the metal film  65  function as a horn antenna, as with the terahertz device F 1 . In this way, the terahertz device A 1  has a packaging structure that allows for modularization of the terahertz element  1  while integrating a horn antenna. Note that the embodiment shown in  FIG. 68 , in which the recess  24  functions as a horn antenna called diagonal horn, is applicable to a multi-mode. On the other hand, in the embodiment shown in  FIG. 69 , the recess  24  has the shape of an elongated rectangle, so that vibration in normal mode TE 01  occurs. 
     The shape of the through electrodes  35  as viewed in plan in the sixth embodiment is not limited to that shown in  FIG. 62 .  FIGS. 70 and 71  show other embodiments of the through electrodes  35  that can be incorporated in the terahertz device F 1  according to the sixth embodiment.  FIGS. 70 and 71  are both plan views showing the terahertz device F 1  according to such variations. Note that the shapes of the through electrodes  35  shown in these figures are merely examples. 
     In the terahertz device F 1  shown in  FIG. 70 , the through electrodes  35  are formed so as to surround the terahertz element  1 . More specifically, two L-shaped through electrodes  35  are arranged with a space therebetween so that the terahertz element  1  is not completely surrounded. In the terahertz device F 1  shown in  FIG. 70 , the through electrodes  35  are configured similarly to a frame-shaped member  6  with slits  69 . Accordingly, the through electrodes  35  function as an electromagnetic shield, so that problems such as disturbance noise or crosstalk are reduced. Also, terahertz waves are reflected by the through electrodes  35  to produce resonance, so that noise reduction and gain improvement of the terahertz waves from the terahertz device F 1  is achieved. 
     In the terahertz device F 1  shown in  FIG. 71 , each through electrode  35  is columnar. Each through electrode  35  is smaller than the terahertz element  1  as viewed in the x direction, and opposite edges in the y direction overlap with the terahertz element  1  as viewed in the x direction. 
     In each terahertz device F 1  shown in  FIGS. 70 and 71 , the external electrodes  4  have a shape adapted for the shape in plan view of the second end surfaces  352  of the through electrodes  35 . 
     In the sixth embodiment, the formation area of the external electrodes  4  is not limited to the area shown in  FIG. 62 .  FIGS. 72-74  show other embodiments of the external electrodes  4  that can be incorporated in the terahertz device F 1  according to the sixth embodiment. Note that the formation areas of the external electrodes  4  shown in these figures are merely examples. 
       FIG. 72  is a plan view of the terahertz device F 1  in an example in which the formation area of the external electrodes  4  is changed from that in the terahertz device F 1  shown in  FIG. 62 .  FIG. 73  is a plan view of the terahertz device F 1  in an example in which the formation area of the external electrodes  4  is changed from that in the terahertz device F 1  shown in  FIG. 70 .  FIG. 74  is a plan view of the terahertz device F 1  in an example in which the formation area of the external electrodes  4  is changed from that in the terahertz device F 1  shown in  FIG. 71 . 
     In each of the embodiments shown in  FIGS. 72-74 , each external electrode  4  is formed to continuously extend over the second end surface  352  of a through electrode  35  and the resin front surface  701  of the sealing resin  7 . Note that, in the terahertz device F 1  shown in  FIG. 73 , part of the second end surface  352  of each through electrode  35  is exposed from the sealing resin  7 . Thus, an insulating protective film may be formed at least on the part of the second end surface  352  that is exposed from the sealing resin  7  to prevent undesired short circuit. 
     The arrangement of the terahertz device F 1  shown in  FIG. 72  can make the area of the external electrodes  4  as viewed in plan larger than that in the terahertz device F 1  shown in  FIG. 62 . Similarly, the arrangement of the terahertz device F 1  shown in  FIG. 73  can make the area of the external electrodes  4  as viewed in plan larger than that in the terahertz device F 1  shown in  FIG. 70 , and the arrangement of the terahertz device F 1  shown in  FIG. 74  can make the area of the external electrodes  4  as viewed in plan larger than that in the terahertz device F 1  shown in  FIG. 71 . Thus, the terahertz devices F 1  shown in  FIGS. 72-74 , in which the area of the external electrodes  4  that can be used for mounting on e.g. a circuit board is increased, can provide improved bonding strength or conduction efficiency with the circuit board. 
     In each terahertz device F 1  shown in  FIGS. 72 and 74 , the external electrodes  4  overlap with part of the terahertz element  1  as viewed in plan. With such an arrangement, the external electrodes  4  function as an electromagnetic shield that reflect the electromagnetic waves from the upper side in the z direction. Thus, the terahertz devices F 1  shown in  FIGS. 72 and 74  reduce problems such as disturbance noise or crosstalk. 
       FIG. 75  shows a terahertz device F 2  according to a first variation of the sixth embodiment.  FIG. 75  is a sectional view of the terahertz device F 2 . The sectional view shown in  FIG. 75  corresponds to the section shown in  FIG. 66 . The terahertz device F 2  differs from the terahertz device F 1  in shape of the support board  2 . 
     As compared with the support board  2  of the terahertz device F 1 , the support board  2  of the terahertz device F 2  additionally includes two raised parts  25  and  26 . 
     The raised part  25  rises from the bottom surface  241  of the recess  24  in the z direction. The raised part  25  has the shape of a truncated cone. The shape of the raised part  25  is not limited to a truncated cone and may be a truncated pyramid, a cone or a pyramid, for example. Also, the raised part  25  may have the shape of a column or a prism. As viewed in plan, the center of the raised part  25  overlaps with the center of the bottom surface  241 . Also, as viewed in plan, the functional part of the terahertz element  1  (radiation point of terahertz waves) overlaps with the center of the raised part  25 . Note however that the functional part of the terahertz element  1  may not overlap with the raised part  25  at its center, but overlap with the raised part  25  at any other location. Because of the presence of the raised part  25 , the bottom surface  241  has the shape of a circular ring as viewed in plan. The raised part  25  has a top surface  251  and a connecting surface  252 . 
     The top surface  251  is orthogonal to the z direction. The top surface  251  is flat. The top surface  251  faces downward in the z direction. The top surface  251  is generally circular as viewed in plan. When the raised part  25  has the shape of a truncated pyramid, the top surface  251  is polygonal as viewed in plan. As viewed in plan, the area of the top surface  251  is smaller than that of the bottom surface  241 . 
     The connecting surface  252  is connected to the bottom surface  241  and the top surface  251 . The connecting surface  252  is connected to the bottom surface  241  at one edge in the z direction (upper edge in  FIG. 75 ) and connected to the top surface  251  at the other edge in the z direction (lower edge in  FIG. 75 ). The connecting surface  252  is inclined with respect to the bottom surface  241 . The inclination angle is 54.7±0.5°. With such a connecting surface  252 , the raised part  25  is tapered. Because of such tapering, the cross section orthogonal to the z direction of the raised part  25  becomes smaller as progressing from the upper side toward the lower side in the z direction. 
     The raised part  26  rises from the support-board front surface  201  in the z direction. The shape of the raised part  26  may be any of a truncated cone, a truncated pyramid, a cone and a pyramid. Thus, the raised part  26  is tapered. Because of such tapering, the cross section orthogonal to the z direction of the raised part  26  becomes smaller as progressing from the lower side toward the upper side in the z direction. The raised part  26  overlaps with the terahertz element  1  as viewed in plan. The raised part  26  is formed below the terahertz element  1  in the z direction. The raised part  26  is covered with the sealing resin  7 . As viewed in plan, the center of the raised part  26  overlaps with both the center of the raised part  25  and the center of the bottom surface  241 . Also, as viewed in plan, the functional part of the terahertz element  1  (radiation point of terahertz waves) overlaps with the center of the raised part  26 . 
     The terahertz device F 2  provides the same advantages as those of the terahertz device F 1 . 
     In the terahertz device F 2 , the support board  2  has the raised part  25  rising from the bottom surface  241  of the recess  24 . The raised part  25  includes the top surface  251  and the connecting surface  252 . The connecting surface  252  is inclined with respect to the bottom surface  241 . Thus, the raised part  26  is tapered. With such an arrangement, the area of the surfaces in the recess  24  that are orthogonal to the z direction (hereinafter referred to as “first orthogonal surfaces”) is smaller, as compared with the terahertz device F 1 . In the terahertz device F 2 , the first orthogonal surfaces are the bottom surface  241  and the top surface  251 . Phenomenon such as refraction or reflection occurs when terahertz waves become incident on the interface between two substances with different dielectric constants. Thus, the terahertz waves traveling downward in the z direction are reflected vertically at the first orthogonal surfaces described above. Since the area of the first orthogonal surfaces is made smaller, the vertical reflection by the first orthogonal surface is reduced. Thus, the terahertz device F 2  improves the gain of the terahertz waves emitted downward in the z direction. 
     In the terahertz device F 2 , the support board  2  has the raised part  26 . The raised part  26  rises from the support-board front surface  201  of the support board  2 . The raised part  26  is tapered, as with the raised part  25 . With such an arrangement, the area of the surface of the support board  2  that is orthogonal to the z direction (hereinafter referred to as “second orthogonal surface”) is smaller, as compared with the terahertz device F 1 . In the terahertz device F 2 , the second orthogonal surface is the support-board front surface  201 . Since the area of the second orthogonal surface is made smaller, the vertical reflection by the second orthogonal surface is reduced. Thus, the terahertz device F 2  improves the gain of the terahertz waves emitted downward in the z direction. 
     In the terahertz device F 2 , the shape of the raised part  25  and the raised part  26  is not limited to that shown in  FIG. 75 .  FIG. 76  shows another embodiment of the raised parts  25 ,  26  that can be incorporated in the terahertz device F 2 . Note that the shape of the raised parts  25  and  26  shown in  FIG. 76  is merely an example. 
       FIG. 76  is a sectional view of the terahertz device F 2  in which the raised parts  25  and  26  are both conical (or generally pyramidal). The sectional view shown in  FIG. 76  corresponds to the section shown in  FIG. 75 . 
     In the terahertz device F 2  shown in  FIG. 76 , the raised part  25  is conical. Thus, the raised part does not have the top surface  251  but has an apex  253 . The apex  253  is the lower end of the raised part  25  in the z direction. The apex  253  is at the same position as the support-board back surface  202  in the z direction. Note however that the apex  253  may be at an upper position in the z direction than the support-board back surface  202 . The inclination angle of the connecting surface  252  in  FIG. 76  is larger than that of the connecting surface  252  in  FIG. 75 . 
     In the terahertz device F 2  shown in  FIG. 76 , the raised part  26  has the shape of a cone. The raised part  26  has an apex  261 . 
     In the terahertz device F 2  shown in  FIG. 76 , the support board  2  has the raised part  25  and the raised part  26 . Thus, the terahertz device improves the gain of the terahertz waves emitted downward in the z direction, as with the terahertz device F 2  shown in  FIG. 75 . 
     In the terahertz device F 2  shown in  FIG. 76 , the raised parts  25  and  26  are both conical. This makes the first and the second orthogonal surfaces described above further smaller as compared with those in the terahertz device F 2  shown in  FIG. 75 . Thus, the gain of the terahertz waves emitted downward in the z direction is improved. 
     In the terahertz devices F 2  shown in  FIGS. 75 and 76 , the support board  2  has both the raised part  25  and the raised part  26 , but the present disclosure is not limited to such an arrangement. In the terahertz devices F 2  shown in  FIGS. 75 and 76 , the support board  2  may include only one of the raised part  25  and the raised part  26 . 
     In the terahertz devices F 2  shown in  FIGS. 75 and 76 , the raised part  25  and the raised part  26  are formed on the support board  2 , but the present disclosure is not limited to such an arrangement. For example, either one or both of the raised part  25  and the raised part  26  may be made as a separate part from the support board  2  and bonded to the support board  2 . 
       FIG. 77  shows a terahertz device F 3  according to a second variation of the sixth embodiment.  FIG. 77  is a sectional view of the terahertz device F 3 . The sectional view shown in  FIG. 77  corresponds to the section shown in  FIG. 66 . As compared with the terahertz device F 1 , the terahertz device F 3  is additionally provided with an emission controlling member  94 . 
     As with the emission controlling members  91 - 93  described above, the emission controlling member  94  performs polarization control, frequency control, directivity control, dispersion control or resonance control of the terahertz waves radiated from the terahertz element  1 . As with the emission controlling member  91 , the emission controlling member  94  is a metamaterial structure. The emission controlling member  94  includes a resin layer  941  and a patterned layer  942 . 
     The resin layer  941  is formed so as to cover the support-board back surface  202  while filling the recess  24  of the support board  2 . The resin layer  941  has an exposed surface  941   a  facing downward in the z direction. The exposed surfaces  941   a  is exposed to the outside of the terahertz device F 3 . 
     The patterned layer  942  is formed on the exposed surfaces  941   a  of the resin layer  941 . The patterned layer  942  is configured similarly to the patterned layer  911  described above. The patterned layer  942  includes a plurality of metal segments  942   a . As viewed in plan, the metal segments  942   a , each of which is in the form of a strip extending in the y direction, are arranged side by side in the x direction. Thus, the patterned layer  942  is made up of a plurality of strip-shaped metal segments  942   a  arranged in the shape of a louver. The patterned layer  942  may be covered with a protective layer, as with the emission controlling member  91  described above. That is, the terahertz device F 3  may be provided with the emission controlling member  91  instead of the emission controlling member  94 . 
     The terahertz device F 3  provides the same advantages as those of the terahertz device F 1 . Moreover, the terahertz device F 3  is provided with the emission controlling member  94 . Thus, the terahertz device F 3  can control emission or reception of terahertz waves with the emission controlling member  94 . 
     In the second variation of the sixth embodiment, the configuration of the emission controlling member  94  is not limited to that shown in  FIG. 77 .  FIGS. 78 and 79  show other embodiments of the emission controlling member  94  that can be incorporated in the terahertz device F 3  according to the second variation of the sixth embodiment.  FIGS. 78 and 79  are both sectional views showing the terahertz device F 3  according to such variations. The sectional views shown in  FIGS. 78 and 79  each correspond to the section shown in  FIG. 66 . Note that the configurations of the emission controlling member  94  shown in these figures are merely examples. 
     In the terahertz device F 3  shown in  FIG. 78 , the patterned layer  942  is embedded in the resin layer  941 . The patterned layer  942  is arranged in proximity to the exposed surfaces  941   a  of the resin layer  941  in the x direction. In  FIG. 78 , the surfaces facing downward in the z direction of the metal segments  942   a  of the patterned layer  942  are exposed from the exposed surfaces  941   a  of the resin layer  941 , but these surfaces may be covered with the resin layer  941 . That is, the patterned layer  942  may be completely embedded in the resin layer  941 .  FIG. 78  shows an example in which the emission controlling member  9  includes a single patterned layer  942 . However, a plurality of patterned layers  942  may be laminated. In such a case, the plurality of patterned layers  942  are laminated in the z direction, with a resin layer  941  interposed between adjacent ones of the patterned layers  942 . When the emission controlling member  9  includes a plurality of patterned layers  942 , the patterned layer  942  at the lowest position in the z direction may be formed on the exposed surface  941   a  of the resin layer  941  or partially or entirely covered with the resin layer  941 . 
     In the terahertz device F 3  shown in  FIG. 79 , the emission controlling member  94  includes a dielectric layer  943  instead of the resin layer  941 . The dielectric layer  943  covers the patterned layer  942 . The dielectric layer  943  may be a dielectric sheet or a dielectric substrate. The material for the dielectric layer  943  is the same as that for the dielectric member  921  described before. The dielectric layer  943  is formed so as to cover the support-board back surface  202  while closing the opening of the recess  24 . Thus, the recess  24  is hollow.  FIG. 79  shows an example in which the emission controlling member  9  includes a single patterned layer  942 . However, a plurality of patterned layers  942  may be laminated. In such a case, the plurality of patterned layers  942  are laminated in the z direction, with a dielectric layer  943  interposed between adjacent ones of the patterned layers  942 . 
     The terahertz devices F 3  shown in  FIGS. 78 and 79  also provide the same advantages as those of the terahertz device F 3  shown in  FIG. 77 . 
       FIGS. 77-79  show examples in which the emission controlling member  94  is the metamaterial structure similar to the emission controlling member  91  (see  FIGS. 57 and 58 ), the present disclosure is not limited to this. Instead of the emission controlling members  94  shown in  FIGS. 77 and 79 , the terahertz device F 3  may be provided with a photonic crystal structure similar to the emission controlling member  92  (see  FIGS. 59 and 60 ) or a laminate of a plurality of thin films with different index of refraction similar to the emission controlling member  93  (see  FIG. 61 ). 
     The terahertz device and the manufacturing method according to the present disclosure are not limited to the foregoing embodiments. The specific configuration of each part of the terahertz device and the specific process in each step of the method for manufacturing the terahertz device according to the present disclosure may be varied in design in many ways. 
     The terahertz device and the method for manufacturing the terahertz device according to the present disclosure include the embodiments related to the following clauses.
     [Clause 1]   

     A terahertz device comprising: 
     a terahertz element configured to perform conversion between terahertz waves and electric energy and having an element front surface and an element back surface spaced apart from each other in a first direction; 
     a sealing resin covering the terahertz element; 
     a wiring layer electrically connected to the terahertz element; and 
     a frame-shaped member made of a conductive material and arranged around the terahertz element as viewed in the first direction, 
     wherein the frame-shaped member has a reflective surface capable of reflecting the terahertz waves.
     [Clause 2]   

     The terahertz device according to clause 1, wherein the terahertz element further includes an element side surface located between and connected to the element front surface and the element back surface, and 
     part of the sealing resin is interposed between the element side surface and the frame-shaped member.
     [Clause 3]   

     The terahertz device according to clause 2, wherein the frame-shaped member is spaced apart from the wiring layer.
     [Clause 4]   

     The terahertz device according to clause 3, wherein the frame-shaped member has a shape of a ring surrounding the terahertz element as viewed in the first direction.
     [Clause 5]   

     The terahertz device according to clause 4, wherein the frame-shaped member has an inner peripheral surface functioning as the reflective surface and an outer peripheral surface, and 
     the frame-shaped member is formed with a slit extending from the inner peripheral surface to the outer peripheral surface as viewed in the first direction.
     [Clause 6]   

     The terahertz device according to clause 5, wherein the frame-shaped member includes a plurality of metal pieces separated from each other by the slit as viewed in the first direction, and 
     a sum of lengths of the metal pieces in respective longitudinal directions is smaller than a sum of respective distances between two adjacent ones of the metal pieces flanking the slit.
     [Clause 7]   

     The terahertz device according to any of clauses 1-6, further comprising a support board supporting the terahertz element, the support board having a support-board front surface facing the element back surface and a support-board back surface facing away from the support-board front surface.
     [Clause 8]   

     The terahertz device according to clause 7, further comprising an external electrode electrically connected to the wiring layer and exposed from the sealing resin.
     [Clause 9]   

     The terahertz device according to clause 8, further comprising a through electrode penetrating the support board and electrically connecting the wiring layer and the external electrode.
     [Clause 10]   

     The terahertz device according to clause 9, wherein the support board is formed with a through-hole extending from the support-board front surface to the support-board back surface, and 
     the through electrode fills the through-hole.
     [Clause 11]   

     The terahertz device according to any of clauses 7-10, wherein the wiring layer is formed on the support board, and 
     the terahertz device further comprises a bonding layer interposed between the terahertz element and the wiring layer, the bonding layer electrically connecting and bonding the terahertz element and the wiring layer.
     [Clause 12]   

     The terahertz device according to any of clauses 7-11, wherein the frame-shaped member stands on the support-board front surface.
     [Clause 13]   

     The terahertz device according to clause 12, wherein the element front surface overlaps with the frame-shaped member as viewed in a second direction orthogonal to the first direction.
     [Clause 14]   

     The terahertz device according to any of clauses 1-13, further comprising a semiconductor element different from the terahertz element, 
     wherein the frame-shaped member surrounds the terahertz element and the semiconductor element as viewed in the first direction.
     [Clause 15]   

     The terahertz device according to any of clauses 1-13, further comprising a semiconductor element different from the terahertz element, 
     wherein the semiconductor element is arranged outside the frame-shaped member as viewed in the first direction.
     [Clause 16]   

     The terahertz device according to any of clauses 1-15, further comprising an emission controlling member that controls emission of the terahertz waves, the emission controlling member overlapping the element front surface as viewed in the first direction.
     [Clause 17]   

     The terahertz device according to any of clauses 1-16, wherein the sealing resin has a resin front surface facing in a direction in which the element front surface faces and a resin back surface facing away from the resin front surface in the first direction, 
     the resin front surface is rougher than the resin back surface.
     [Clause 18]   

     The terahertz device according to any of clauses 1-17, wherein the element front surface is exposed from the sealing resin.
     [Clause 19]   

     A method for manufacturing a terahertz device comprising a terahertz element configured to perform conversion between terahertz waves and electric energy and having an element front surface and an element back surface spaced apart from each other in a first direction, the method comprising: 
     a support board preparation step for preparing a support board having a support-board front surface and a support-board back surface facing away from each other in the first direction; 
     a frame-shaped member forming step for forming a frame-shaped member from a conductive material on the support board; 
     a wiring layer forming step for forming a wiring layer electrically connected to the terahertz element; 
     an element mounting step for mounting the terahertz element on the support board such that the frame-shaped member is positioned around the terahertz element as viewed in the first direction; 
     a sealing resin forming step for forming a sealing resin covering the terahertz element; and 
     a grinding step for grinding the support board, 
     wherein the frame-shaped member has a reflective surface capable of reflecting the terahertz waves.
     [Clause 20]   

     The method for manufacturing a terahertz device according to clause 19, further comprising: 
     an external electrode forming step for forming an external electrode electrically connected to the wiring layer; and 
     a through electrode forming step for forming a through electrode extending through the support board and electrically connecting the wiring layer and the external electrode, 
     wherein the wiring layer forming step comprises forming the wiring layer on the support-board front surface, 
     the grinding step comprises grinding the support board from the support-board back surface until the through electrode is exposed from the support-board back surface, and 
     the external electrode forming step comprises forming the external electrode on a surface of the through electrode that is exposed from the support-board back surface.