JP5854467B2 - Microwave dynamics inductance detection type terahertz wave sensor and terahertz wave detection system - Google Patents

Description

  The present invention relates to a microwave dynamic inductance detection type terahertz wave sensor (hereinafter referred to as “MKID”), and in particular, it is possible to achieve higher sensitivity and wider bandwidth with respect to terahertz (THz) waves, and further downsizing. The present invention relates to an MKID capable of achieving the above and a terahertz wave detection system using the same.

  The MKID is a terahertz wave detector having a superconducting microwave resonator as a basic component, and the incidence of terahertz waves is sensed by changing the resonance frequency of the microwave resonator (for example, a resonance frequency of about several GHz). For example, there is one described in Non-Patent Document 1. Non-Patent Document 2 describes a MKID in which a terahertz wave antenna is connected in addition to a microwave resonator in order to improve terahertz wave sensitivity. Further, Non-Patent Document 3 describes a terahertz wave antenna in a spiral shape in order to reduce the size of the terahertz wave antenna and increase the bandwidth.

Peter K. Day, Henry G. LeDuc, Benjamin A. Mazin, Anastasios Vayonakis & Jonas Zmuidzinas, “A broadband superconducting detector suitable for use in large arrays” NATURE, VOL 425, 817-821, 23 OCTOBER 2003 Andrey Baryshev, Jochem JA Baselmans, Angelo Freni, Senior Member, IEEE, Giampiero Gerini, Senior Member, IEEE, Henk Hoevers, Annalisa Iacono, Student Member, IEEE, and Andrea Neto, Senior Member, IEEE, ”Progress in Antenna Coupled Kinetic Inductance Detectors ”IEEE TRANSACTIONS ON TERAHERTZ SCIENCE AND TECHNOLOGY, VOL. 1, NO. 1, 112-123, SEPTEMBER 2011 E. R. Brown, A. W. M. Lee, B. S. Navi, and J. E. Bjarnason, ”CHARACTERIZATION OF A PLANAR SELF-COMPLEMENTARY SQUARESPIRAL ANTENNA IN THE THz REGION”, MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Vol. 48, 524-529, No. 3, March

  As shown in FIG. 8, the conventional MKID 30 described in Non-Patent Document 2 is a micro-resonant formed on a Si (silicon) substrate 33 by a superconductor Al (aluminum) at a frequency of several GHz. When the resonance frequency of the wave resonator 32 changes, the incidence of the terahertz wave is sensed through the terminals 1 and 2 connected to the micro waveguide 34. In Non-Patent Document 2, in addition to the microwave resonator 32, a terahertz wave antenna 31 for detecting a terahertz (THz) wave with high sensitivity is connected. For this reason, as described in Non-Patent Document 3, even if the terahertz wave antenna is reduced in size, the microwave resonator has a microwave wavelength (for example, 100 mm at 3 GHz) and a terahertz wave wavelength (for example, 100 mm). For example, when it is 3 THz, it is longer than 100 μm), and there is a restriction in reducing its size. Further, in order to achieve a wide band and high sensitivity, the microwave resonator 32 and the terahertz wave antenna 31 must be provided, and there is a problem that it is difficult to reduce the size of the entire MKID.

  The present invention has been made paying attention to such a problem. A microwave dynamics inductance detection type terahertz wave sensor and a terahertz wave detection system capable of detecting a broadband terahertz wave with high sensitivity and capable of further downsizing are provided. It is intended to provide.

In order to solve the above problems, a microwave dynamics inductance detection type terahertz wave sensor according to the present invention is a microwave dynamics inductance detection type terahertz wave sensor including a terahertz wave antenna, and the terahertz wave antenna is about a half wavelength of a microwave. It also has the function of a microwave resonator by having a line length of.
According to this feature, the terahertz wave antenna can be combined with the function of a microwave resonator by having a line length of about a half wavelength of the microwave, so the terahertz wave antenna and the microwave resonator are configured separately. Therefore, it is possible to reduce the size further. Even a terahertz wave antenna configured to function as a microwave resonator can detect a broadband terahertz wave as it is with high sensitivity.

The microwave dynamics inductance detection type terahertz wave sensor according to the present invention is characterized in that the terahertz wave antenna is formed in a spiral shape with a substantially half portion of the line length as a center.
According to this feature, the terahertz wave antenna, which also functions as a microwave resonator, is formed in a spiral shape around the half of the line length, so that it is folded and wound from half the line length. Therefore, further downsizing can be achieved.

The microwave dynamics inductance detection type terahertz wave sensor according to the present invention is characterized in that the terahertz wave antenna is disposed in proximity to one or two microwave waveguides at a predetermined interval. .
According to this feature, the terahertz antenna is microwave-coupled by being arranged close to the one or two microwave waveguides at a predetermined interval, and is connected to the microwave waveguide. Through this, the resonance of the microwave can be detected. For example, when the terahertz wave antenna is disposed close to one microwave waveguide, an absorption type MKID can be configured by connecting terminals to both sides of the microwave waveguide. Further, when the terahertz wave antenna is disposed close to two opposing microwave waveguides, a transmission type MKID can be configured by connecting a terminal to each of the two microwave waveguides. .

The microwave dynamics inductance detection type terahertz wave sensor of the present invention includes a microwave resonator in which a resonance frequency in the microwave changes when a terahertz wave is incident, and a predetermined interval with respect to the microwave resonator. One or two microwave waveguides arranged in close proximity to each other, and the microwave resonator has a spiral line, a line length of about a half wavelength of the microwave, and a line that operates as a broadband terahertz wave antenna And a line spacing.
According to this feature, the microwave resonator includes a line having a spiral type and a line length of about a half wavelength of the microwave, a width of the line operating as a broadband terahertz antenna, and an interval between the lines. Since the resonator can also function as a broadband terahertz wave antenna, it is not necessary to separately configure the terahertz wave antenna and the microwave resonator, and thus the size can be further reduced. Further, even with the terahertz wave antenna configured as described above, a broadband terahertz wave can be detected with high sensitivity as it is.

A terahertz wave detection system of the present invention includes a plurality of the microwave dynamic inductance detection type terahertz wave sensors, and the plurality of microwave dynamic inductance detection type terahertz wave sensors have a predetermined interval with respect to a common microwave waveguide. It is characterized by being arranged in an array in close proximity to each other.
According to this feature, the microwave dynamics inductance detection type terahertz wave sensor is small, so the terahertz wave detection system in which these are arranged in an array with a predetermined interval close to the common microwave waveguide can be downsized. Can be planned.

(A), (b) It is a block diagram of MKID in an Example. (A), (b) It is the equivalent circuit of MKID in an Example. It is a figure which shows the microwave transmission characteristic of MKID in an Example. It is a figure which shows the measurement microwave power dependence of the microwave transmission characteristic of MKID in an Example. It is a figure which shows the return loss frequency dependence by a 100 time dimension model. It is a figure which shows the electromagnetic field analysis of the return loss frequency dependence of MKID in an Example. It is explanatory drawing which shows the creation process of MKID in an Example. It is a block diagram of MKID in a prior art.

  A mode for carrying out a microwave dynamic inductance detection type terahertz wave sensor (hereinafter referred to as MKID) according to the present invention will be described below based on examples.

  The embodiment will be described with reference to FIGS. 1 to 7. 1A and 1B show a configuration diagram of the MKID in the embodiment, and FIGS. 2A and 2B show an electrical equivalent circuit of the MKID in the embodiment. In particular, FIGS. 1 (a) and 2 (a) show a configuration diagram of an absorption type MKID and its equivalent circuit, and FIGS. 1 (b) and 2 (b) show a configuration diagram of a transmission type MKID. The equivalent circuit is shown.

  The present invention is an MKID including a microwave resonator using a superconducting material whose inductance is changed by photon energy when a photon of a terahertz wave is incident. The microwave resonator has a line made of a superconducting material. It is formed in a spiral shape, and has a line length of about a half wavelength of the microwave, a width of a line that operates as a broadband terahertz wave antenna, and an interval between lines. In this embodiment, as shown in FIG. 1, a superconducting spiral 5 is provided which is a microwave resonator and functions as a broadband terahertz wave antenna. The total length of the line length of the superconducting spiral 5 is not based on the wavelength of the terahertz wave as in Non-Patent Document 3, but is set to a predetermined length of about a half wavelength (half wavelength) of the microwave. It will be confirmed later that it can also operate as a resonator having a resonance frequency unique to microwaves, and it will be described later that a broadband terahertz wave can be detected with high sensitivity without impairing the performance of the terahertz wave antenna at all. Confirmed by experiment. With such a configuration, the spiral broadband terahertz antenna can be configured to serve as a microwave resonator by providing a line length of about a half wavelength (half wavelength) of the microwave. Thus, the incidence of terahertz waves is sensed by changing the resonance frequency of the microwave resonator so that a broadband terahertz wave can be detected with high sensitivity.

  In FIG. 1A, an absorption type MKID 100a is disposed close to a superconducting spiral 5 in which a line is formed in a spiral shape with a superconducting material, with a predetermined interval on one side of the superconducting spiral 5. One superconducting microwave waveguide 3, a surrounding portion 8 in which a line is formed so as to surround the superconducting spiral 5, and a line 11 disposed close to the outside of the superconducting microwave waveguide 3. It is configured as such a pattern.

  In this embodiment, the superconducting spiral 5 is set to a line length of about half a wavelength so that the resonance frequency is about 3.3 GHz, and is wound around a half of the line length. The vertical width 6 and the horizontal width 7 of one side of the outermost periphery of the rectangular shape have a length of about 0.5 mm, and the number of turns depends on the set line length. Is set. The line length is preferably set to be equal to or less than a half wavelength of the set resonance frequency. Further, the width of the line and the distance between the lines that operate as a broadband terahertz wave antenna are provided. In this embodiment, the width of the line and the distance between the lines are provided so as to have a terahertz wave reception sensitivity up to about 2 THz. Are set to approximately the same 10-15 μm. In addition, the distance between one side of the outermost circumference of the rectangular shape of the superconducting spiral 5 and the thin wire of the surrounding portion 8 and the distance between the thin wire of the surrounding portion 8 and the superconducting microwave waveguide 3 are also set in advance to about 10 to 15 μm. doing. Moreover, the line width of the thin line of the enclosure 8 is also set in advance to about 10 to 15 μm, and the line width of the superconducting microwave waveguide 3 is set to about 50 to 60 μm in advance.

Further, the superconducting microwave waveguide 3 is formed with a line made of a superconducting material and is disposed close to one side of the outermost periphery of the superconducting spiral 5, thereby forming the microwave coupling portion 4. By connecting the terminals 1 and 2 to both sides of the superconducting microwave waveguide 3, respectively, an absorption type MKID as shown in FIG. In the equivalent circuit of FIG. 2A, a superconducting spiral 5 equivalent to the LC series resonance circuit 12 is coupled to a superconducting microwave waveguide 3 to which terminals 1 and 2 are connected via a microwave coupling portion 4. . The resonance frequency f ₀ is expressed by f ₀ = 1 / (2π√LC). When a terahertz photon is incident on the superconducting spiral 5, the inductance L changes due to the photon energy, and the resonance frequency f ₀ changes. To do.

  Further, as shown in FIG. 1A, a surrounding portion 8 and a line 11 are provided, and ground lines are formed by grounding them, and by adjusting the area of the surrounding portion 8, noise or the like is caused. The influence can be prevented more. In this embodiment, the vertical width 9 on one side of the inner periphery of the enclosure 8 is set to about 0.6 mm, and the horizontal width 7 is set to about 0.7 mm.

  With such a configuration, the MKID in this embodiment has a resonance frequency of the microwave at the terminals 1 and 2 because the resonance frequency of the microwave is lowered by increasing the superconducting inductance of the superconducting spiral 5 due to the incidence of the terahertz wave. It is possible to detect the incidence of terahertz waves.

  Further, when a transmissive MKID as shown in FIG. 2B is configured, the pattern is configured as shown in FIG.

  In FIG. 1B, an absorption type MKID 100b includes a superconducting spiral 5 in which a line is formed in a spiral shape with a superconducting material, and two superconducting micros disposed in the vicinity of one side of the superconducting spiral 5. A pattern comprising wave waveguides 3 a and 3 b, a surrounding portion 8 a in which a line is formed so as to surround the superconducting spiral 5, and lines 11 a and 11 b disposed close to the outside of the superconducting microwave waveguide 3. It is configured as.

  The superconducting spiral 5 in FIG. 1 (b) is configured in the same manner as the superconducting spiral 5 described in FIG. 1 (a), and has a line length of about half a wavelength so that the resonance frequency is about 3.3 GHz. It is formed in a rectangular spiral shape so that it is wound around about half the length of the line length, and the vertical width 6 and the horizontal width 7 on one side of the outermost periphery of the rectangular shape are about 0. 0. It has a length of about 5 mm, and the number of turns is set according to the set line length. Further, the width of the line and the distance between the lines that operate as a broadband terahertz wave antenna are provided. In this embodiment, the width of the line and the distance between the lines are provided so as to have a terahertz wave reception sensitivity up to about 2 THz. Is set to about 10 to 15 μm, which is substantially the same. Further, the distance between one side of the outermost periphery of the superconducting spiral 5 and the fine line of the surrounding part 8 and the distance between the fine line of the surrounding part 8 and the superconducting microwave waveguide 3a or 3b are also about 10 to 15 μm. It is set in advance. Moreover, the line width of the thin line of the enclosure 8 is also set in advance to about 10 to 15 μm, and the line width of the superconducting microwave waveguide 3 is set to about 50 to 60 μm in advance.

Also, the superconducting microwave waveguides 3a and 3b are formed by a superconducting material and are arranged close to a side of the outermost periphery of the superconducting spiral 5 with a predetermined interval therebetween, thereby coupling microwaves. Part 4 is formed. By connecting the terminals 1 and 2 to the superconducting microwave waveguides 3a and 3b, a transmission type MKID as shown in FIG. 2B is formed. In the equivalent circuit of FIG. 2B, the superconducting spiral 5 equivalent to the LC series resonance circuit 12 is coupled to the superconducting microwave waveguide 3a to which the terminal 1 is connected via the microwave coupling portion 4a. A transmission type microwave resonator is formed. The resonance frequency f ₀ is expressed by f ₀ = 1 / (2π√LC). When a terahertz photon is incident on the superconducting spiral 5, the inductance L changes due to the photon energy, and the resonance frequency f ₀ changes. To do.

  Further, as shown in FIG. 1B, a surrounding portion 8a and lines 11a and 11b are provided and grounded to form a ground line, and the area of the surrounding portion 8a is adjusted to reduce noise and the like. Can be prevented more effectively. In the present embodiment, the vertical width 9a on one side of the inner periphery of the surrounding portion 8a is set to about 0.52 mm, and the horizontal width 7 is set to about 0.7 mm.

  With such a configuration, the MKID in this embodiment has a resonance frequency of the microwave at the terminals 1 and 2 because the resonance frequency of the microwave is lowered by increasing the superconducting inductance of the superconducting spiral 5 due to the incidence of the terahertz wave. It is possible to detect the incidence of terahertz waves.

  Next, a method for creating an MKID in this embodiment will be described with reference to FIG. FIG. 7 shows an MKID creation process in the embodiment.

  Basically, the MKID having the above-mentioned pattern can be created by using various known superconducting thin film pattern forming techniques. As an example, in this embodiment, direct current (DC) by a vacuum deposition apparatus is used. A superconducting thin film 24 is formed on the substrate 25 by a sputtering method, masked with the photomask 28 having the pattern as shown in FIGS. The case of creating the will be described.

  In FIG. 7A, first, a substrate 25 such as sapphire is placed on a sample stage in the vacuum vapor deposition apparatus 20, and exhausted from the exhaust port 26 so as to become a vacuum, and an inert gas 21 such as Ar (argon) and the like. A high voltage is applied while introducing nitrogen gas 22. As the glow discharge is generated by this high voltage, the inert gas 21 and the nitrogen gas 22 are turned into plasma, and positively charged ions collide with the target 23 made of metal such as niobium as the cathode, and the surface of the target 23 The niobium nitride (NbN) thin film 27a as shown in FIG. 7B is formed by repelling the atoms and the like and depositing them on the substrate 25. Next, after removing dust and the like on the surface of the niobium nitride (NbN) thin film 27a, a photosensitive resist is uniformly applied as shown in FIG. 7C, and the niobium nitride (NbN) thin film coated with the photosensitive resist is applied. 27b is created. The thickness of the thin film can be about several nm to several tens of nm. Next, a photomask 28 (FIG. 7 (d)) having a pattern as shown in FIG. 1 (a) or (b) prepared in advance is exposed to light as shown in FIG. 7 (e). As shown in FIG. 7 (f), the resist is applied to a niobium nitride (NbN) thin film 27b coated with a resist 27b and exposed to ultraviolet light, and the resist is developed in a developing solution to develop the pattern. An etching process is performed (FIG. 7G), and a resist stripping process is performed (FIG. 7H).

  As described above, a spiral type MKID 29 made of a niobium nitride (NbN) thin film can be formed by the processing described above.

  In the above-described production method, niobium (Nb) is used for the target 23, but a superconducting thin film may be formed using other metals such as aluminum (Al) and titanium (Ti). Other known substrates may also be used for the substrate. Alternatively, the pattern may be formed of a material other than the superconducting material as long as it has a material whose inductance or resistance changes due to incidence of photons of terahertz waves.

  An experiment for evaluating the performance of the absorption type MKID having the pattern shown in FIG. 1A in the present embodiment formed by the above-described production method is performed, and the results will be described with reference to FIGS.

  FIG. 3 is a diagram showing the microwave transfer characteristics of the absorption type MKID having the pattern shown in FIG. 1A in this embodiment, and FIG. 4 is the absorption type having the pattern shown in FIG. 1A in the embodiment. It is a figure which shows the measurement microwave power dependence of the microwave transfer characteristic of MKID of.

  FIG. 3 shows the transfer characteristics when the frequency is changed by inputting a microwave between the two terminals of the absorption type MKID having the pattern shown in FIG. The portion indicates the actual measurement value, and the alternate long and short dash line portion indicates the polynomial approximation curve. As shown in FIG. 3, a high resonance performance index Q (Quality Factor) is shown at a natural microwave resonance frequency (about 3.3 GHz) which is one of the characteristic elements that determine the sensitivity of the terahertz wave. It can be seen that the absorption type MKID in the examples has high sensitivity. In FIG. 3, when the output is about 3.3 GHz, the output drops by −7 dB, and the resonance performance index Q value is about 200,000, which indicates that a highly sensitive resonance circuit is formed.

  FIG. 4 shows the measured power dependence of the microwave transfer characteristics at a temperature of 0.3K. When the applied power is -70 dBm (0.1 nW) and -60 dBm (1 nW) (similar to the microwave transfer characteristics shown in FIG. 3), the microwave resonance frequency and the microwave resonance frequency are compared. A value different from the transmittance is shown. When the power is increased from -70 dBm (0.1 nW) to -60 dBm (1 nW), the superconducting inductance increases due to the power difference (thermal energy difference) absorbed by the superconducting spiral 5 and the resonance frequency decreases. Is shown. This feature is considered to be equivalent to the case where the superconducting inductance increases and the resonance frequency decreases when terahertz photons are incident. Therefore, it can be seen that the absorption type MKID in this example operates as a microwave resonator.

  FIG. 5 shows a copper foil spiral antenna in which the spiral dimension of MKID is increased to 100 times the dimension shown in FIG. 1A, and the return loss frequency dependency was measured using the copper foil spiral antenna. Results are shown. Although the frequency range of the antenna is reduced to 1/100 by enlarging the spiral dimension, the return loss can be regarded as equivalent to the return loss in the MKID having the dimension in the above-described embodiment. From the measured values shown in FIG. 5, it was confirmed that the return loss was low over a wide band from 1 GHz to the upper limit of 20 GHz of measurable frequency. Therefore, it can be seen that the MKID having the dimensions in the above-described embodiment operates as an antenna over a wide frequency range from 0.1 THz to 2 THz, which is 100 times the frequency range of the antenna.

  FIG. 6 shows a three-dimensional electromagnetic field analysis result by simulation of the return loss frequency dependency in the MKID shown in FIG. As shown in FIG. 6, the result of analysis also indicates that the antenna operates over a wide band region from 0.1 THz to 2 THz or more.

  A terahertz wave detection system can be configured by providing a plurality of MKIDs in this embodiment and arranging them in a two-dimensional array in close proximity to a common microwave waveguide at a predetermined interval. Surface detection can be performed in units of pixels such as (coupled device). In particular, since the MKID in this embodiment can be reduced in size, even if it is arranged in an array, it can be configured in a small space, and a large-scale array can be configured.

  The MKID in the present embodiment can be used in various fields. For example, it can be used not only for detection of terahertz waves in the field of astronomy, but also for transmission imaging using terahertz waves, medical field using terahertz spectroscopy, and application to physical property research.

  As described above, according to this embodiment, by setting the line length of the superconducting spiral 5 of the MKID to a line length of about a half wavelength of the microwave, the function of the microwave resonator and the terahertz wave antenna can be combined. Therefore, it is not necessary to separately configure the terahertz wave antenna and the microwave resonator, so that the space can be saved with a simpler configuration and the size can be further reduced. Even a terahertz wave antenna configured to function as a microwave resonator can detect a broadband terahertz wave as it is with high sensitivity.

  In the embodiment described above, the pattern of the superconducting spiral 5 has a rectangular spiral configuration, but it may be a polygonal, circular, or other spiral configuration. In addition, since it is formed in a spiral shape with the half of the line length as the center, it is folded and wound from the half of the line length, and the size can be further reduced. In addition, it has been confirmed that a spiral antenna having a shape wound around one end of the line and having the other end on the outside cannot have a function of a microwave resonator.

  In addition, the dimensions of the superconducting spiral 5 in the above-described embodiment are merely examples. If the superconducting spiral 5 has a function of a terahertz wave antenna, the line width, the interval between the lines, and the outermost circumference of the rectangular shape may be used. The dimensions such as the vertical width 6 and the horizontal width 7 on one side can be appropriately selected. Furthermore, the distance between the superconducting spiral 5 and the superconducting microwave waveguide 3 can be set to an optimum distance for microwave coupling.

  As described above, the microwave dynamics inductance detection type terahertz wave sensor of the present invention has been described based on the embodiment. However, the present invention is not limited to this embodiment, and various modifications can be made without departing from the gist of the present invention. Those subjected to are also included in the scope of the present invention.

100a Absorption type MKID
100b Transmission type MKID
1 and 2 Terminal 3 Superconducting microwave waveguide 4 Microwave coupling part 5 Superconducting spiral 6 Superconducting spiral length 7 Superconducting spiral width 8 Enclosure 9 Enclosure inner circumference length 10 Enclosure inner circumference Width 11 line 12 LC series resonance circuit 20 vacuum deposition device 21 argon gas 22 nitrogen gas 23 niobium target 24 niobium nitride thin film 25 sapphire substrate 26 vacuum exhaust ports 27a to 27d niobium nitride thin film 28 photomask 29 NbN spiral type MKID
30 Conventional MKID
31 Terahertz wave antenna 32 Microwave resonator 33 Substrate 34 Coplanar waveguide

Claims (5)

In microwave dynamics inductance detection type terahertz wave sensor with terahertz wave antenna,
The terahertz wave antenna is a microwave dynamic inductance detection type terahertz wave sensor characterized in that the terahertz wave antenna also has a function of a microwave resonator by having a line length of about a half wavelength of the microwave.   2. The microwave dynamic inductance detection type terahertz wave sensor according to claim 1, wherein the terahertz wave antenna is formed in a spiral shape with a substantially half portion of the line length as a center.   3. The microwave dynamic inductance detection type according to claim 1, wherein the terahertz wave antenna is disposed adjacent to one or two microwave waveguides at a predetermined interval. Terahertz wave sensor. A microwave resonator in which the resonant frequency of the microwave changes when a terahertz wave is incident;
One or two microwave waveguides disposed close to the microwave resonator at a predetermined interval;
The microwave resonator includes a spiral type line having a line length of about a half wavelength of the microwave, a line width operating as a broadband terahertz wave antenna, and an interval between lines. Type terahertz wave sensor. A plurality of microwave dynamic inductance detection type terahertz wave sensors according to any one of claims 1 to 4,
A terahertz wave detection system, wherein a plurality of microwave dynamics inductance detection type terahertz wave sensors are arranged in an array with a predetermined interval close to a common microwave waveguide.

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