JP2017005631A - Terahertz waveguide circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that a waveguide manufacturing technology for terahertz wave suitable for mass production does not exist yet, in particular, since a short side of a waveguide substantially becomes as long as several hundred μm in a terahertz wave domain in a frequency lower than 1 THz, a problem relating to a processing depth in forming the waveguide may be severe and become a considerable obstruction in realizing an integrated circuit for terahertz wave.SOLUTION: In a terahertz waveguide circuit, a waveguide of a hollow structure is formed by bonding two substrates, such that the depth of a groove required to be formed may become half of the prior arts. A processing displacement amount during groove formation can be suppressed by half. Thus, in a filter that is manufactured by utilizing the waveguide of the hollow structure, central wavelength displacement is suppressed by half and a waveguide circuit in which a reflection attenuation amount is suppressed can be realized. Further, a problem that the waveguide circuit s cracked by thermal shock during processing of the groove or vibration shock during use can also be avoided. An Si substrate or the like that is thinner and more inexpensive can be selected and a waveguide circuit for terahertz wave domain at a lower frequency side may also be realized.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a waveguide for guiding terahertz band electromagnetic waves and an integrated circuit using the waveguide.

  A terahertz wave is an electromagnetic wave in an intermediate region between radio waves (microwaves) and light, and is not clearly defined, but is known as an electromagnetic wave having a frequency in a range of approximately 0.1 THz to 10 THz. It is said to be an undeveloped electromagnetic wave that has not been fully utilized compared to radio waves and light. When terahertz waves are used, quantitative analysis and transmission image photographing of organic materials such as resin materials, pharmaceuticals, and living bodies are possible, and terahertz waves are increasingly applied in various fields. However, current terahertz wave application systems are limited to those based on transmittance and transmittance spectrum, that is, intensity measurement of terahertz waves. It has not yet been achieved for highly accurate measurement of permittivity utilizing terahertz wave coherency (coherence) and high-sensitivity transmission image acquisition using interference.

  In such a situation regarding the use of terahertz waves, it is difficult to generate and detect terahertz waves, and in recent years, generation and detection of terahertz waves has only been realized. Thus, although the use of terahertz waves is in an immature stage, the social needs of terahertz waves are quite high in a specific field, considering that, for example, transmission image capturing devices have been put into practical use. Can be seen. Application research on terahertz waves is expected to develop further in the future.

  Most measuring instruments that use terahertz waves at the present time have a simple configuration in which an object to be inspected is placed between a terahertz light source and a detector. In addition, various advanced systems with more complex configurations are also expected. For example, a configuration that uses a switch to switch the beam optical path of terahertz waves and continuously measure multiple points in a short time, or selects only a specific frequency from a broadband terahertz wave and irradiates the sample Has been.

  In order to further promote the application of such terahertz waves to advanced systems, it is necessary to further enhance basic technologies for manipulating the terahertz waves themselves, such as filtering and route switching. Even for the same electromagnetic wave, in the light and microwave regions, the functions of wavelength (frequency) filter, switch, etc. have already been realized with small size and high performance by the waveguide / waveguide technology, and more than one function on one substrate. In some cases, these are integrated. The integration technology on one substrate is not only a merit such as small size, low cost and excellent mass productivity, but also, for example, keeps the optical path lengths of the light to be measured and the reference light stable and completely eliminates the influence of vibration. It is also useful for dramatically improving the characteristics, such as realizing an interference-type measurement system that is not subject to interference.

G. Chattopadhyay, et al., “Submillimeter-Wave 90 ° polarization Twists for Integrated Waveguide Circuits”., The IEEE Microwave and Wireless Components Letters., Vol. 20 no. 1, pp. 592-594 (2010) CA Leal-Sevillano, et al., “Silicon Micromachined Canonical E-Plane and H-Plane Bandpass Filters at the Terahertz Band”., The IEEE Microwave and Wireless Components Letters., Vol. 23 no. 6, pp. 288-290 (2013) Y. Miura, et al., “A 60GHz Double-layer Waveguide Slot Array with more than 32dBi and 80% Efficiency over 5GHz Bandwidth Fabricated by Diffusion Bonding of Laminated Thin Metal Plates”., IEEE Antennas and Propagation Society International Symposium, pp. 1-4 (2010)

  However, no effort has been made to realize an integrated circuit in which a waveguide circuit using a terahertz wave is formed on a surface substrate. The main reason is a limitation due to the wavelength value of the terahertz wave itself. As described above, the terahertz wave is said to be an electromagnetic wave in a range of approximately 0.1 THz to 10 THz. Therefore, when a typical frequency is 1 THz, the spatial wavelength is 300 μm. When a single-mode hollow waveguide similar to a microwave is manufactured in accordance with the wavelength of the terahertz wave, the dimensions in the tube are 270 μm × 135 μm. Although it is not impossible to cut such a hollow waveguide having a size of several hundreds of micrometers by machining, it is necessary to manufacture with high accuracy using a special end mill. Naturally, it is difficult to integrate a plurality of waveguide circuits, and there is no mass productivity (Non-patent Document 1).

  In addition, it is still difficult to produce a hollow waveguide of the above size by a processing method such as photolithography and dry etching used in the semiconductor industry. Photolithography and etching techniques are extremely excellent in accuracy and mass productivity in the production of patterns having a size of about micron to submicron. However, it is not suitable for processing deep grooves that require processing of several hundred μm in the depth direction, and processing for a long time is required (Problem 1). Further, when a substrate having a sufficient thickness with respect to the processing depth is not used, the substrate is cracked by a thermal shock during etching processing or a vibration shock during dicing (Problem 2). For deep groove processing, a BOSH method has been proposed in which an etching mode and a passivation mode are alternately repeated. Even with this method, when a groove having a width and depth of about 100 μm is processed, an error of several μm in the groove width and a sidewall inclination error of several degrees occur (Problem 3). As a result, in a waveguide type filter manufactured using photolithography and etching technology, integration such that the return loss is deteriorated by 10 dB and the center frequency is shifted from the design value by 20 to 30%. Problems with characteristics that make it difficult have been reported (Non-Patent Document 2).

  As a precedent example of the millimeter wave region having a frequency slightly lower than that of the terahertz wave, there is also a report that a hollow waveguide was produced by processing a metal plate having a thickness of about 0.3 mm and laminating and stacking several layers thereof (Non-Non-Patent Document) Patent Document 3). However, in order to apply this method of bonding to a waveguide in the terahertz wave region, a substrate material having a special performance is required, which is expensive and lacks mass productivity. Considering the availability of the substrate and the accumulation of mass production technology, it is preferable that a silicon wafer substrate or the like used for a general integrated circuit can also be used for terahertz waves. In the manufacturing method by the above-mentioned bonding, the area has a size enough to enclose a waveguide circuit to be integrated (condition 1), and is one to one digit thinner than a normal silicon substrate (for example, 500 μm) (condition 2). Furthermore, a special metal plate having strength and rigidity (Condition 3) that can withstand machining and bonding operations is required. Since the metal having high rigidity is limited in kind, even if a terahertz wave hollow waveguide by the bonding method can be realized, it will eventually become expensive.

  As described above, there is currently no terahertz waveguide manufacturing technique suitable for mass production. In particular, in the terahertz wave region having a frequency lower than 1 THz studied above, the short side of the waveguide becomes even longer to about several hundred μm, so the problem of the processing depth when forming the waveguide is more serious. Therefore, this is a major obstacle when realizing an integrated circuit for terahertz waves.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a waveguide circuit capable of realizing an integrated circuit including a terahertz wave waveguide at low cost with high productivity. is there.

  In order to achieve such an object, the present invention according to claim 1 has a first substrate on which a groove of a waveguide circuit pattern is formed, and a shape symmetrical to the waveguide circuit pattern. A second substrate on which a groove of the corresponding waveguide circuit pattern is formed, wherein the groove of the waveguide circuit pattern on the first substrate and the groove of the corresponding waveguide circuit pattern are opposed to each other. A second substrate that is superposed on the first substrate and has a hollow waveguide formed by the two grooves facing each other, and includes at least the first substrate and the second substrate In the waveguide circuit, a metal film is formed on a surface of the hollow waveguide formed on the substrate.

  The waveguide pattern on the first substrate and the corresponding waveguide pattern on the second substrate have a mirror-symmetric shape. Note that the mirror symmetry here refers to the relationship that when one mirror is placed on the symmetry line between two patterns, one pattern matches the mirror image of the other pattern in the mirror. Means.

The invention according to claim 2 is the waveguide circuit according to claim 1, wherein the depth of the groove of the waveguide circuit pattern on the first substrate and the corresponding waveguide on the second substrate. The groove depth of the circuit pattern is substantially equal, and the depth direction of the groove is the short side direction of the hollow waveguide.
The invention according to claim 3 is the waveguide circuit according to claim 1 or 2, wherein the hollow waveguide has a size capable of propagating a signal in a terahertz wave region, and the first substrate and the waveguide The second substrate is a silicon substrate, and the groove is formed by photolithography and dry etching.

  Invention of Claim 4 is the waveguide circuit in any one of Claims 1 thru | or 3, Comprising: In the waveguide of the said hollow structure of the end surface vicinity of the said 1st board | substrate and the said 2nd board | substrate which were overlapped, An opening structure that gradually widens the width of the waveguide inside the waveguide circuit is provided.

  A fifth aspect of the present invention is the waveguide circuit according to any one of the first to third aspects, wherein the waveguide of the hollow conducting structure is in the vicinity of the end surfaces of the first substrate and the second substrate that are overlaid. And an inclined wall structure that reflects and scatters the reflected light of the input signal from the outside or the output signal to the outside to the outside of the substrate, adjacent to the opening of the end. .

  The invention according to claim 6 is the waveguide circuit according to any one of claims 1 to 3, wherein the waveguide having the hollow structure in the vicinity of the end surfaces of the first substrate and the second substrate that are overlaid. At the end, adjacent to the opening of the end, the hollow structure has a depth length that is a quarter of the operating wavelength of the waveguide circuit corresponding to the cross-sectional structure of the waveguide of the hollow structure. It further comprises one or more cavities extending along the direction of the waveguide.

  According to the terahertz wave waveguide circuit of the present invention, the processing error of the structure of the waveguide or the like is suppressed by half compared to the prior art, and as a result, the center wavelength shift of the filter and the increase of the return loss are suppressed. A waveguide circuit capable of Furthermore, the waveguide circuit can be prevented from being damaged by thermal shock during processing or vibration shock during use of the waveguide circuit, so that a thinner and cheaper substrate can be selected. A waveguide circuit for a terahertz wave region on a lower frequency side with a larger waveguide size can also be realized.

1 is a diagram illustrating a configuration of a terahertz wave waveguide circuit according to a first embodiment of the present invention. FIG. 2 is a view showing a more detailed structure of two substrates constituting the waveguide circuit of the present invention. FIG. 3 is a diagram illustrating the configuration of the terahertz wave waveguide circuit according to the second embodiment of the present invention.

  According to the terahertz wave waveguide circuit of the present invention, by forming the hollow waveguide by bonding the two substrates, the depth of the groove that needs to be formed can be halved. Therefore, the amount of processing shift when forming the groove can be reduced to half. As a result, it is possible to realize a waveguide circuit in which the center wavelength shift of a filter manufactured using a waveguide having a hollow structure is suppressed to half and the return loss is suppressed. Furthermore, it is possible to avoid the problem that the waveguide circuit is broken due to thermal shock during processing of the groove or vibration shock during use of the waveguide circuit. A thinner and cheaper substrate can be selected, and a waveguide circuit for the terahertz wave region on the lower frequency side can be realized. In the following description, a circuit including a waveguide having a hollow structure is called a “waveguide circuit” in order to propagate a terahertz wave in an intermediate region between light and radio waves, but it has the same meaning as “waveguide circuit”. I use it.

  Hereinafter, embodiments of the terahertz wave waveguide circuit of the present invention will be described in detail with reference to the drawings.

[Example 1]
1 is a diagram illustrating a configuration of a terahertz wave waveguide circuit according to a first embodiment of the present invention. FIG. 1A is a perspective view of the entire waveguide circuit 10, and FIG. 1B is a view of a cross section of the waveguide passing through the line AA ′. As shown in FIG. 1A, the waveguide 1 is a hollow waveguide, and its size (inner dimension) is 280 μm wide and 140 μm high. This value is assumed assuming that the frequency of the terahertz wave used in the waveguide circuit 10 is 1 THz. It is necessary to change the cross-sectional size of the waveguide according to the frequency to be used, as in the microwave waveguide. As can be seen from the cross-sectional view of FIG. 1B, the hollow waveguide 1 includes a first groove formed on the lower substrate 2 and a corresponding second groove formed on the upper substrate 3. This is realized by superimposing them facing each other. A metal film 4 is formed on the surface where the lower substrate 2 and the upper substrate 3 face each other. The detailed configuration of the metal film 4 will be described later.

  Therefore, the terahertz wave waveguide circuit of the present invention includes a first substrate (2) on which a groove (5a) of the waveguide circuit pattern is formed, and a corresponding waveguide circuit having a shape symmetrical to the waveguide circuit pattern. A second substrate (3) having a pattern groove (5b) formed thereon, wherein the groove of the waveguide circuit pattern on the first substrate faces the groove of the corresponding waveguide circuit pattern. A second substrate that is superposed on the first substrate and has a hollow waveguide formed by the two grooves facing each other, and includes at least the first substrate and the second substrate It can be implemented on the assumption that a metal film (4) is formed on the surface of the hollow waveguide formed on the substrate.

  The waveguide pattern on the first substrate 2 and the corresponding waveguide pattern on the second substrate 3 have a mirror-symmetric shape. Note that the mirror symmetry here refers to the relationship that when one mirror is placed on the symmetry line between two patterns, one pattern matches the mirror image of the other pattern in the mirror. Means. For example, when a mirror is placed between the substrate 2 in FIG. 2C and the substrate 3 in FIG. 2D and the substrate 2 is copied, the pattern of the substrate 3 becomes a mirror image of the pattern of the substrate 2. Is in a relationship.

  FIG. 2 is a view showing a more detailed structure of two substrates constituting the waveguide circuit of the present invention. FIGS. 2C and 2D are views of the surfaces of the lower substrate 2 and the upper substrate 3 on which grooves are formed, respectively. FIGS. 2A and 2B are views of the lower substrate 2. It is sectional drawing containing an AA 'line and the BB' line of the upper board | substrate 3. FIG. As can be seen from FIGS. 2 (c) and 2 (d), if a folding line is virtually placed between the two substrates 2 and 3, and the left and right sides are opposed to each other, the grooves 5a on the two substrate surfaces are arranged. 5b are completely overlapped to form a mirror-symmetric wave guide circuit pattern. The depths of the grooves 5a and 5b are both 70 μm, and the two substrates 2 and 3 are bonded to each other so that the height of the hollow portion in the substrate thickness direction (short side direction) is 140 μm.

  Therefore, in the terahertz wave waveguide circuit of the present invention, the depth of the groove of the waveguide circuit pattern on the first substrate is substantially equal to the depth of the groove of the corresponding waveguide circuit pattern on the second substrate, The depth direction of the groove is the short side direction of the hollow waveguide. In the configuration of FIG. 2, the grooves 5a and 5b in the two substrates have been described as having the same depth. However, as long as there is no significant difference, the groove depths may be different depending on other needs.

  The two substrates 2 and 3 are made of silicon, which is generally used in the semiconductor industry, and the substrate thickness is 525 μm, which is inexpensive. Photolithography and dry etching were used to form the grooves 5a and 5b having a depth of 70 μm. Under the etching conditions used, an etching time of about 3.5 hours was required to process a groove having a depth of 70 μm. According to the configuration of the waveguide circuit of the present invention, the depth of the groove to be formed can be halved as compared with the case where the deep grooves on one substrate are formed all at once in the prior art. For this reason, it is possible to realize a process of finishing the processing within one day even if a pretreatment time such as chamber cleaning is included, and the process management in the actual manufacturing process is simplified. In order to use photolithography, two photomasks that are mirror-symmetrical with respect to the two substrates are required. If the pattern design of one (lower substrate 2) photomask for the first substrate is made using CAD or the like, the other (upper substrate 3) photomask for the second substrate is designed. In this case, it is only necessary to reverse the pattern on the electronic data of CAD, and there is no increase in labor and cost in the actual design process.

  Further, gold was vapor-deposited as the metal film 4 on the substrate surface including the portions of the grooves 5 a and 5 b of the two substrates 2 and 3. In addition to the function of confining electromagnetic waves in the hollow by making the inner wall of the hollow waveguide / waveguide a metal, the metal film 4 also functions as an adhesive layer when the lower substrate 2 and the upper substrate 3 are thermocompression bonded. . In the first embodiment shown in FIGS. 1 and 2, the metal film is deposited on the entire surface of the substrate. However, when it is desired to reduce the metal material cost, the inside of the grooves 5a and 5b and the grooves 5a and 5b are used. Alternatively, gold may be vapor-deposited only in the vicinity of and the two substrates may be bonded to each other on the remaining substrate surface using an adhesive.

  In this embodiment, for simplicity, the waveguide circuit pattern has only one U-shaped waveguide on the substrate surface. However, the present invention is not limited to this. Using the waveguide circuit of the present invention having a hollow waveguide formed by superimposing grooves of corresponding waveguide circuit patterns formed in mirror symmetry on the two substrate surfaces of the present invention, the waveguide circuit of the present invention comprises a number of waveguides. It goes without saying that various terahertz wave guide circuits having a waveguide circuit pattern, such as a Mach-Zehnder interferometer type or an arrayed waveguide diffraction grating type frequency filter, can be realized.

  Although not drawn in the perspective view of FIG. 1A, for example, it is desirable that a metal film be applied to the substrate end faces 6a and 6b shown in FIGS. 2C and 2D. The terahertz wave is input from one of the entrances of the waveguide, for example, the openings of the end faces 6a and 6b on the upper side in FIGS. This is because when the substrate material is high-resistance silicon, the absorption of the terahertz wave is low, and the terahertz wave is prevented from propagating through the substrate when the terahertz wave enters from a portion other than the waveguide entrance.

  As described above, according to the waveguide circuit of the present invention configured by superimposing the grooves of the corresponding waveguide circuit pattern formed symmetrically on the two substrates, it is deep at once as in the prior art. Compared with the case of forming the groove, the depth of the groove that needs to be processed is halved. Therefore, half the etching time required for forming the deep groove is sufficient. Furthermore, since the groove depth is only half, the possibility of cracking due to thermal shock during etching or vibration shock during dicing can be suppressed, and a thinner substrate can be used. Furthermore, it is possible to halve an error of several μm in the groove width and a sidewall inclination error of several degrees, which still occur when etching is performed using the BOSH method or the like.

  In the deep etching technique such as the BOSH method in which the groove processing and the side surface reinforcement of the groove are alternately performed, an error of the mask gap when the etching processing of the groove progresses, an error of the groove width caused by the sidewall inclination angle, etc. Is generally proportional to the depth of the groove to be machined. Therefore, if the depth of the groove can be halved, the maximum error generated in the groove of one substrate can be halved. The maximum error in the width of the waveguide obtained by superimposing the two substrates can also be suppressed to approximately half.

  In this embodiment, the description has focused on the basic structure and manufacturing method of a waveguide circuit. However, in the next embodiment, a structure that reduces the influence of reflection of a terahertz wave signal introduced into the waveguide circuit is described. Present.

[Example 2]
FIG. 3 is a diagram illustrating the configuration of the terahertz wave waveguide circuit according to the second embodiment of the present invention. 3A to 3C each show a waveguide circuit in which a signal reflection preventing structure for a signal generator is provided in the vicinity of the waveguide entrance of the waveguide circuit. Each figure shows a waveguide circuit pattern in the vicinity of the waveguide entrance at the periphery of the substrate on the surface where the groove of the waveguide is formed for one of the two substrates. In general, a terahertz wave generated from a signal generator spreads on a spherical surface. Therefore, a collimated wave (hereinafter referred to as a beam) having a flat wavefront using a lens (for example, a high-density polyethylene lens) before being input into a waveguide circuit. To do. Referring to (a) of FIG. 3, when the diameter of the beam 25 (referring to a width whose intensity decreases to e ^{1/2 of the} central peak) does not match the width of the waveguide 21, the power of the terahertz wave is A part of the light does not enter the internal waveguide 21 from the opening of the substrate and is reflected by the substrate end face 20. Reflection occurs in the same manner when the beam input position is shifted. Such a reflected beam returns to a signal generator (not shown). Since the return beam is an undesirable factor in the operation of the signal generator and is not desirable, it is necessary to provide a structure for preventing reflection to the signal generator in the vicinity of the waveguide entrance. As in the case of the waveguide input side described above, on the output side of the terahertz wave waveguide circuit, the return signal (beam) from the subsequent device may affect the operation of the waveguide circuit.

  FIG. 3A shows a first configuration example of the structure for preventing signal reflection, in which the width of the waveguide opening 22 in the vicinity of the waveguide entrance is compared with the width W of the waveguide 21 inside the waveguide circuit. It has a structure in which the width of the opening 22 of the waveguide is surely made larger than the diameter of the beam 25 by expanding in a tapered shape. Specifically, in the case of the 1 THz terahertz wave of Example 1, the depth of the openings 22 of the two substrates is set to 70 μm, which is the same as the waveguide, the maximum width of the openings 22 is 1500 μm, and the width changes in a tapered shape. The length of the portion in the waveguide direction can be 1300 μm. Each dimension can be determined by optimizing the shape of the tapered portion 22 and minimizing the return loss. The depth of the opening 22 may be 70 μm or more.

  The shape of the opening 22 is not limited to a tapered shape spreading toward the periphery of the substrate, and any shape that can guide the terahertz wave from the signal generator into the waveguide 21 may be used. Accordingly, in the waveguide circuit of the present invention, in the waveguide having a hollow structure in the vicinity of the end surfaces of the first substrate 2 and the second substrate 3 that are superimposed, the waveguide width is gradually larger than the waveguide width inside the waveguide circuit. It is preferable to have a wide opening structure (22).

  FIG. 3B is a second configuration example of the structure for preventing signal reflection, and the direction in which the terahertz wave that protrudes from the range of the waveguide opening in the vicinity of the waveguide entrance deviates from the signal generator. The reflection wall structures 23a and 23b are provided so as not to be scattered and reflected to return to the signal generator. By the oblique walls 23a and 23b installed in the vicinity of the waveguide entrance, the protruding portion of the beam 25 of the incident terahertz wave signal can be repelled as scattered signals 29a and 29b in the left and right oblique directions. Since the direction of the scattered signal deviates from the direction of arrival of the beam 25, it does not return to the signal generator and does not destabilize the operation of the signal generator.

  More specifically, the angle of inclination of the reflecting wall structures 23a and 23b can be a structure inclined by about 40 ° from the direction of the waveguide. In consideration of the opening angle of the waveguide to be formed, the inclination angle for reducing the level of the return beam may be determined. Therefore, in the waveguide circuit of the present invention, the end portion of the waveguide having the hollow guide structure adjacent to the end surfaces of the first substrate and the second substrate that are overlaid is adjacent to the opening of the end portion. In addition, it is possible to have an inclined wall structure (23a, 23b) that reflects and scatters the reflected light of the input signal from the outside or the output signal to the outside to the outside of the substrate.

  FIG. 3C shows a third configuration example of the signal reflection preventing structure, in which one or more cavities 24a to 24f are provided along the substrate end face on both sides of the opening near the waveguide entrance. With structure. Each of these cavities 24 a to 24 f has a length D that is a quarter of the operating wavelength in the same direction as the direction in which the waveguide 21 is formed. A part of the beam 25 from the signal generator returns as a reflected wave 27 at the end face of the substrate beside the opening, but the beam guided into the cavity is reflected at the back of the cavity, and the reflected beam 28 is within the cavity. , The traveling distance is longer by ½ wavelength than the reflected wave 27. The phase between the two reflected waves 27 and 28 is 180 degrees out of phase, and the reflected waves do not return to the signal generator because they interfere with each other and disappear due to interference. Therefore, the cavity length D may be determined in accordance with the frequency (wavelength) of the terahertz wave to be used. In addition, although the distance is an extremely short distance of ½ wavelength, the beam guided to the cavities 24a to 24f needs to propagate in the cavity, so the width of the cavity is approximately the same as that of the waveguide (70% ) It is desirable that there is a width above. The number of cavities may be one on each side or two or more depending on the generation state of the reflected beam.

  Specifically, considering the distinction between the waveguide and the cavity, the width of the cavities 24a to 24f is 250 μm, the distance between adjacent cavities is 20 μm, and the repetition distance is 270 μm. Therefore, in the waveguide circuit of the present invention, the hollow portion is adjacent to the opening of the end portion at the end portion of the waveguide having the hollow structure in the vicinity of the end surfaces of the superimposed first substrate and second substrate. One or more cavities (24a-24f) extending along the direction of the waveguide of the hollow structure having a depth length that is one-fourth of the operating wavelength of the waveguide circuit corresponding to the cross-sectional structure of the waveguide of the structure ) Can also be provided.

  By using the antireflection structure for the signal generator according to the second embodiment together with the terahertz wave waveguide circuit according to the first embodiment, reflection of the terahertz wave at the entrance or the exit of the waveguide circuit can be prevented. For this reason, it is possible to realize a waveguide circuit having good characteristics including the return loss characteristic. Although described as an antireflection structure on the signal entrance side of the above-described waveguide circuit, it is desirable to provide a similar structure on the waveguide exit side as described above. A terahertz wave waveguide circuit is often connected to a subsequent device that further manipulates the terahertz wave. For this reason, if there is no antireflection structure on the output side of the waveguide circuit, the terahertz wave may reciprocate between the device at the rear stage such as a terahertz detector and the end face of the waveguide, and a standing wave may be generated. Because there is.

  Each antireflection structure of the second embodiment shown in each drawing of FIG. 3 has a mirror-symmetric pattern corresponding to each of the surfaces of the two substrates, like the hollow waveguides in the two substrates described in the first embodiment. Can be formed simultaneously with the hollow waveguide by overlapping the two substrates facing each other. Therefore, as in the first embodiment, the depth of each part of the antireflection structure that needs to be processed is halved. The etching time required for forming a deep groove or the like can be halved, and the possibility that the substrate is cracked by thermal shock during etching or vibration shock during dicing is reduced. It is also possible to use a thinner substrate, and it is possible to halve errors of several μm in groove width and several degrees of side wall tilt errors, which are generated when etching is performed using the BOSH method or the like.

  As described above, the terahertz wave waveguide circuit of the present invention can reduce the processing error of a structure such as a waveguide to half as compared with the prior art. As a result, a waveguide circuit is realized in which the center wavelength shift of the filter and the increase in return loss are suppressed. A substrate that is thinner and less expensive can be selected while avoiding damage to the substrate during processing or use of the waveguide. By providing a configuration of a terahertz wave waveguide circuit excellent in integration and mass productivity, it can be used for more advanced terahertz wave applications.

  The present invention is generally applicable to measurement and analysis systems using electromagnetic interference. In particular, it can be used for communication systems, quantitative analysis systems, transmission image capturing systems, and the like.

1, 21 Waveguide 2, 3 Substrate 4, 4a, 4b Metal film 5a, 5b Groove 10 Waveguide circuit 20 Substrate end face 22 Opening 23a, 23b Reflection wall 24a-24f Cavity 25 Input beam 27, 28, 29a, 29b Reflection beam

Claims (6)

A first substrate (2) on which a groove (5a) of a waveguide circuit pattern is formed;
A second substrate (3) having a corresponding waveguide circuit pattern groove (5b) having a shape symmetrical to the waveguide circuit pattern, the waveguide circuit pattern on the first substrate. And a groove of the corresponding waveguide circuit pattern are overlapped with the first substrate so that a hollow waveguide is formed by the two facing grooves. A board and
A waveguide circuit, wherein a metal film (4) is formed on at least the surface of the hollow waveguide formed on the first substrate and the second substrate.   The groove depth of the waveguide circuit pattern on the first substrate is substantially equal to the groove depth of the corresponding waveguide circuit pattern on the second substrate, and the depth direction of the groove is the The waveguide circuit according to claim 1, wherein the waveguide circuit is in a short side direction of the hollow waveguide.   The hollow waveguide has a size capable of propagating a terahertz wave signal, the first substrate and the second substrate are silicon substrates, and the groove is formed by photolithography and dry etching. The waveguide circuit according to claim 1, wherein the waveguide circuit is provided.   In the waveguide having the hollow structure in the vicinity of the end surfaces of the superimposed first substrate and the second substrate, an opening structure (22) that gradually widens beyond the waveguide width inside the waveguide circuit is further provided. The waveguide circuit according to claim 1, further comprising a waveguide circuit.   At the end of the waveguide of the hollow waveguide structure in the vicinity of the end faces of the first and second substrates that are overlaid, adjacent to the opening of the end, an input signal from the outside or to the outside 4. The waveguide circuit according to claim 1, wherein the waveguide circuit has an inclined wall structure (23 a, 23 b) that reflects and scatters the reflected light of the output signal to the outside of the substrate. 5.   The cross-sectional structure of the hollow waveguide in the end portion of the waveguide having the hollow structure in the vicinity of the end surfaces of the first substrate and the second substrate that are superimposed, adjacent to the opening of the end portion. And one or more cavities (24a to 24f) extending along the direction of the waveguide of the hollow structure having a depth length that is a quarter of the operating wavelength of the waveguide circuit corresponding to 4. The waveguide circuit according to claim 1, wherein the waveguide circuit is characterized in that: