JP6193553B2 - Terahertz wave detection sensor - Google Patents

Description

  The present invention relates to a terahertz wave detection sensor that detects a terahertz wave using a superconducting tunnel junction element (hereinafter referred to as “STJ element”).

  Conventionally, as this type of terahertz wave detection sensor, for example, a sensor described in Patent Document 1 is known. This sensor detects a terahertz wave with a well-known element such as a silicon bolometer. For example, the sensor emits a terahertz wave from a light source toward a predetermined inspection object, and detects the terahertz wave transmitted through the inspection object. Is. This sensor is used as a sensor of a so-called active type substance discriminating apparatus that discriminates an inspection object.

JP 2006-71412 A

  By the way, a small amount of terahertz waves showing a specific frequency spectrum corresponding to the type of the constituent material are naturally emitted from the inspection object. If this naturally radiated terahertz wave can be detected, it is advantageous in terms of sensor performance.

  However, since the terahertz wave detection sensor described in Patent Document 1 has a configuration in which a terahertz wave is simply detected by a known element such as a silicon bolometer, for example, a very small amount of terahertz wave that is naturally radiated from an inspection object. It is considered difficult to detect this due to the influence of noise or the like.

  Further, as described in Patent Document 1, when an element such as a silicon bolometer is used as a sensor of a substance discriminating apparatus that discriminates a substance based on a detection result of a terahertz wave, a light source that generates a terahertz wave is required. In addition to the optical system for receiving terahertz waves, an optical system for projecting is required.

  The present invention has been made paying attention to the above-described problems, and an object of the present invention is to provide a terahertz wave detection sensor capable of detecting a minute amount of terahertz waves that are naturally emitted from a substance.

A terahertz wave detection sensor according to the present invention includes a superconducting tunnel junction element cooled by a cooling device having a multilayer heat shield structure in a space where a magnetic field is demagnetized, and the outermost shield wall of the cooling device A phonon generated from a terahertz wave collected by a condensing device having a condensing lens provided in is detected by the superconducting tunnel junction element, and an electric signal corresponding to the terahertz wave is output. Yes.

According to the terahertz wave detection sensor, a superconducting tunnel junction element cooled by a cooling device having a multilayer heat shield structure is provided in a space where the magnetic field is demagnetized, and the outermost shield wall of the cooling device is provided. Detection of terahertz waves because phonons generated from terahertz waves collected by a condensing device having a condensing lens provided are detected by the superconducting tunnel junction element and an electric signal corresponding to the terahertz waves is output. Sensitivity can be improved. Thereby, a trace amount of terahertz waves that are naturally emitted from the substance can be detected.

  In addition, since a trace amount of terahertz waves naturally radiated from the inspection object can be detected, it is not necessary to separately facilitate a light source that generates terahertz waves when determining a substance based on the detection result of terahertz waves. Since the optical system for projecting terahertz waves is unnecessary, the configuration is simplified.

It is a block diagram which shows the structure of the terahertz wave detection sensor by embodiment of this invention. It is a figure which shows the schematic of the condensing apparatus, board | substrate absorption type STJ element, and cooling device which are used with the said terahertz wave detection sensor. It is a figure which shows the structure of the board | substrate absorption STJ element used with the said terahertz wave detection sensor. It is the elements on larger scale for demonstrating the modification of the said embodiment. It is the elements on larger scale for explaining another modification of the above-mentioned embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a block diagram showing a configuration of a terahertz wave detection sensor according to an embodiment of the present invention.
The terahertz wave detection sensor 1 according to the present embodiment is configured to be able to detect a terahertz wave and determine a substance S (for example, illegal drugs such as narcotics or dangerous substances such as explosives) existing in the detection region, As an example, a substrate absorption type STJ element 20 as a substrate absorption type superconducting tunnel junction (STJ) element including a condensing device 10 and an absorber substrate 21 that receives terahertz waves and generates phonons; A cooling device 30, a preamplifier 40 for amplifying the detection signal of the substrate absorption type STJ element 20, an A / D converter 50 for A / D converting the output of the preamplifier 40 and outputting it as digital data, and an A / D converter A substance discriminating device 60 that discriminates the substance S based on the output of 50.

  FIG. 2 is a schematic cross-sectional view of the light converging device 10, the substrate absorption type STJ element 20, and the cooling device 30. In FIG. 2, for the sake of simplification of the drawing, shield walls (36a to 36d), which will be described later, of the cooling device 30 are indicated by lines. Needless to say, each shield wall has a thickness.

  The condensing device 10 collects the terahertz wave to be detected on the absorber substrate 21 (see FIG. 3) of the substrate absorption type STJ element 20. For example, as shown in FIG. And an optical filter 3 and a super hemispherical lens 4.

  The condensing lens 2 condenses the terahertz wave toward the light condensing surface 21a (see FIG. 3), which will be described later, of the absorber substrate 21, and is a general convex lens. For example, the condenser lens 2 is designed so that light is incident within a predetermined angle in the super hemispherical lens 4, and is fixed to a low-pass filter 3 a described later by bonding or the like.

  The optical filter 3 is provided between the condenser lens 2 and the super hemispherical lens 4, has a light transmission band including the frequency of the terahertz wave, and has the transmission band of the light transmitted through the condenser lens 2. The perimeter allows the light to pass through. Specifically, the optical filter 3 includes, for example, a low-pass filter 3a, intermediate filters 3b and 3c, and a band-pass filter 3d, and the light transmission band is within a range of approximately 0.7 THz to approximately 30 THz. is there.

  The low-pass filter 3a is, for example, a filter that passes light having a frequency of about 100 THz or less. For example, as shown in FIG. 2, the low-pass filter 3a is attached to the outer wall of the 300K shield 36a integrally with the condenser lens 2 so as to block a through hole formed in a peripheral wall of the 300K shield 36a described later. Yes.

  Each of the intermediate filters 3b and 3c is, for example, a filter that allows light having a frequency of about 50 THz or less to pass through, and as shown in FIG. Each is attached to block.

  The band pass filter 3d is, for example, a filter that allows light in a frequency range of about 0.7 THz to about 30 THz to pass therethrough. For example, as shown in FIG. 2, a through-hole opened in a peripheral wall of a 1K shield 36d described later Is attached to the outer wall of the 1K shield 36d integrally with the super hemisphere lens 3.

  The super hemispherical lens 4 is provided in close contact with the absorber substrate 21, and the terahertz wave that has passed through the condenser lens 2 and the optical filters (3 a to 3 d) is converted into the light condensing surface 21 a side on the absorber substrate 21. For example, as shown in FIG. 2, the band-pass filter is fixed to the band-pass filter 3d by adhesion or the like, and closes the through-hole opened in the peripheral wall of the 1K shield 36d. It is attached to the outer wall of the 1K shield 36d integrally with 3d.

3 shows the configuration of the substrate absorption type STJ element 20, FIG. 3 (a) is a plan view, and FIG. 2 (b) is a cross-sectional view taken along line AA of FIG. 3 (a).
As shown in FIG. 3, the substrate absorption type STJ element 20 includes, for example, an absorber substrate 21 and a surface 21b (hereinafter referred to as an upper surface 21b) opposite to the light condensing surface 21a of the absorber substrate 21. The STJ element 22 is provided.

The absorber substrate 21 receives terahertz waves to generate phonons, and is a single crystal substrate made of LiNbO ₃ (lithium niobate), LiTaO ₃ (lithium tantalate), or the like that easily absorbs terahertz waves that are detection targets. It is. In the following, the absorber substrate 21 is simply referred to as the substrate 21.

  The STJ element 22 detects a phonon generated from a terahertz wave and outputs an electric signal corresponding to the terahertz wave. For example, a single layer of a superconducting electrode material or an upper surface 21b of the substrate 21 From a lower electrode 22a composed of two layers of films having different superconducting energy gaps, a tunnel barrier (tunnel barrier) 22b composed of an insulating film, and a single layer of superconducting electrode material, or from two layers of films having different superconducting energy gaps This is an element having a structure in which upper electrodes 22c are sequentially stacked. Specifically, the STJ element 22 detects phonons generated in the substrate 21 and outputs an electric signal corresponding to the terahertz wave as a terahertz wave detection signal. As the superconducting electrode material, for example, an Al (aluminum) / niobium (Nb) bilayer film, and as an insulating film serving as a tunnel barrier, for example, AlOx (aluminum oxide) is used.

A wiring layer 23 is laminated on the upper surface 21 b of the substrate 21, and the STJ element 22 is provided on the wiring layer 23. As the material of the wiring layer 23, for example, the same material as that of the substrate 21 can be used. As an example, the wiring layer 23 is a crystal thin film (crystal substrate) formed of LiNbO ₃ (lithium niobate), sapphire, or the like, and is bonded to the upper surface 21b of the substrate 21 with an adhesive, for example.

  A ground layer (wiring) 24 is formed on the wiring layer 23, and the ground layer 24 is connected to the lower electrode 22a.

  The STJ element 22 and the ground layer 24 are covered with an interlayer insulating film 25 made of SiO 2 (silicon dioxide) or the like, so that electrical insulation between the lower electrode 22a and the upper electrode 22c of the STJ element 22 is reduced. It has been.

  Further, a wiring 26 connected to the upper electrode 22c is formed on the STJ element 22 through a contact hole 25a formed in the interlayer insulating film 25. This wiring 26 is connected to a signal detecting PAD 26a. The The PAD 26a is connected to the preamplifier 40 by wiring.

  The cooling device 30 can cool the substrate absorption STJ element 20 to about 0.3K. Specifically, as shown in FIG. 2, the cooling device 30 includes a small mechanical refrigerator 31, a 4K pot 32, a 1K pot 33, a 3He pot 34, and a gas handling unit 35. It is a typical cryogenic refrigerator. As shown in FIG. 2, the cooling device 30 has a four-layer structure of, for example, a 300K shield 36a, a 50K shield 36b, a 4K shield 36c, and a 1K shield 36d, and keeps the temperature in each shield at a low temperature for a long time. Formed possible. Each shield 36a-36d is formed in a cylindrical shape with copper etc., for example.

  The small mechanical refrigerator 31 is a general regenerative refrigerator that can generate a low temperature of about 4.2K, for example, and includes a first cooling stage 31a, a second cooling stage 31b, and a cooling head 31c. Composed. The first cooling stage 31a is a high temperature side cooling stage of about 50K, and the second cooling stage 31b is connected to the lower surface of the first cooling stage 31a and reaches the low temperature side of about 4.2K. It is a cooling stage. The cooling head 31c is connected to the lower surface of the second cooling stage 31b. Although not shown, the small mechanical refrigerator 31 is connected to a cooling compressor.

  The 4K pot 32 is formed in a cylindrical shape and is connected to a cooling head 31c cooled to about 4.2K. Although not shown, a coil is wound around the outer periphery of the 4K pot 32. The magnetic field in the 4K pot 32 is demagnetized by this coil, and the detection sensitivity of the terahertz wave in the STJ element 22 is improved. The 1K pot 33 is connected to the bottom of the 4K pot 32 via a low thermal conductivity communicating portion (not shown). That is, the 1K pot 33 is connected to the 4K pot 32 in an internal communication state. The 3He pot 34 is connected to the bottom of the 1K pot 33 via a connection portion (not shown). Each pot 32-34 is formed with high heat conductive materials, such as oxygen-free copper, for example. And the heat conduction jig 34a formed in plate shape with high heat conductive materials, such as oxygen-free copper, is connected to the bottom part of 3He pot 34, for example. The substrate absorption type STJ element 20 is attached to the heat conducting jig 34.

  The gas handling unit 35 appropriately supplies liquid 4He, 4He gas, and 3He gas to the pots 32 to 34, and forcibly exhausts the gases from the pots 32 to 34. Although not shown, a gas supply / exhaust pipe is connected between the gas handling unit 35 and each of the pots 32 to 34. By the gas supply / exhaust control by the gas handling unit 35, the 3He pot 34 is finally cooled to about 0.3K.

  The substance discriminating apparatus 60 discriminates a substance S that emits a terahertz wave based on an electrical signal (detection signal) output from the STJ element 22. For example, the substrate absorbing STJ amplified by the preamplifier 40 is used. Based on the data obtained by digitally converting the detection signal of the element 20 through the A / D converter 50, the type of the substance S is discriminated.

  Here, the operation of the terahertz wave detection sensor 1 according to the present embodiment will be described with reference to FIGS. 1 and 2. In the following description, the case where the terahertz wave detection sensor 1 is installed facing the envelope will be described as an example.

  First, the substrate absorption type STJ element 20 is cooled to about 0.3K by the cooling device 30, and the terahertz wave detection sensor 1 is installed by the operator or the like so that the condenser lens 2 faces the envelope, and preparation for detection is performed. Complete.

  Here, the terahertz wave naturally radiated from the substance S enclosed in the envelope is transmitted to the outside through the envelope. The condensing lens 2 and the super hemispherical lens 4 condense the naturally radiated terahertz wave at a predetermined light receiving point on the light condensing surface 21 a of the substrate 21. At this time, the optical filter 3 provided between the condenser lens 2 and the super hemispherical lens 4 transmits light in a frequency range of about 0.7 THz to about 30 THz among the light collected by the condenser lens 2.

  When the terahertz wave is condensed at a predetermined light receiving point of the light condensing surface 21a, the substrate 21 absorbs the terahertz wave (that is, photon energy), and phonons are generated in the substrate 21 by the absorption of the terahertz wave. To do. The phonon group generated in the substrate 21 propagates in the substrate 21, and part of the phonon group reaches the lower electrode 22 a of the STJ element 22 through the wiring layer 23.

  When the phonon reaches the lower electrode 22a, the Cooper pair in the lower electrode 22a is destroyed and quasiparticles are generated. The substrate absorption type STJ element 20 outputs a tunnel current that flows when the quasiparticle generated in the lower electrode 22a tunnels through the tunnel barrier 22b as a detection signal via the upper electrode 22c, the wiring 26, and the PAD 26a.

  The detection signal (tunnel current value) output from the PAD 26 a is amplified by the preamplifier 40. The amplified detection signal is converted into digital data by the A / D converter 50 and output to the substance determination device 60. The substance discriminating device 60 discriminates the type of the substance S in the envelope based on the input digital data. For example, when the substance S is an illegal drug such as a narcotic or a dangerous substance such as an explosive, the substance discriminating device 60 displays the alarm on the display or the like provided separately with the type of illegal drug or explosive. Note that the type and warning can be displayed on a display or the like without generating an alarm sound.

  According to the terahertz wave detection sensor 1 of this embodiment, the phonon generated from the terahertz wave is detected by the STJ element 22 in the cooled state, and an electric signal corresponding to the terahertz wave is output. Detection efficiency can be improved. Thereby, a trace amount of terahertz waves that are naturally emitted from the substance can be detected.

  In addition, the terahertz wave detection sensor 1 of the present embodiment can detect a minute amount of terahertz waves naturally radiated from a substance, and distinguishes the substance based on the detection signal, so-called passive substance discrimination sensor. Therefore, the light source for generating the terahertz wave and the light collecting device for projecting the terahertz wave, which are necessary in the conventional active type material discrimination sensor, are not required, and the configuration is simplified.

  Further, by using a substrate absorption type STJ20 element in which the substrate 21 is a terahertz wave energy absorber as in this embodiment, the detection efficiency of terahertz waves can be further improved.

  Here, the terahertz wave in the frequency range of about 0.7 THz to about 30 THz sufficiently passes through clothing, paper, and the like. Therefore, as exemplified in this embodiment, the type of the substance S enclosed in the envelope can be determined in an unopened state. Further, the substance S is not limited to being in the envelope, but may be present in clothes, cardboard, or the like, and may be covered with any material that can transmit terahertz waves. Needless to say, when the substance S is placed alone, the terahertz wave can be detected with higher accuracy.

  In the present embodiment, the small mechanical refrigerator 31 of the cooling device 30 has been described as including the first cooling stage 31a, the second cooling stage 31b, the cooling head 31c, and the compressor. Not limited to this, a cryostud type that does not require a compressor may be used.

  In the present embodiment, the cooling device 30 has been described in the case of cooling the substrate absorption type STJ element 20 to about 0.3K. However, the present invention is not limited to this, and it is only necessary to be able to cool to about 4.2K. The lower the cooling temperature of the substrate absorption STJ element 20, the more the terahertz wave detection sensitivity is improved. However, if the substrate absorption STJ element 20 can be cooled to at least approximately 4.2K, terahertz waves naturally radiated from the substance S can be reduced. This is because sufficient detection is possible. In this case, the cooling device 30 need only be a small mechanical refrigerator 31 capable of cooling to about 4.2K.

  In the present embodiment, the terahertz wave detection sensor 1 has been described as including the cooling device 30. However, the present invention is not limited to this, and the cooling device 30 may not be provided as long as the STJ element 22 is in the cooling state. . That is, it is only necessary that the STJ element 22 is sufficiently cooled (for example, approximately 4.2 K), and the cooling facility (refrigeration apparatus) does not necessarily have to be accompanied when the sensor is activated.

FIG. 4 is a partially enlarged view for explaining a modification of the embodiment.
As shown in FIG. 4, this modification is configured with a one-dimensional galvanometer mirror 70 as a region switching device for switching the inspection region D (inside the dotted line in FIG. 4) of the sensor. The one-dimensional galvanometer mirror 70 is, for example, a general galvanometer mirror formed by using a semiconductor manufacturing technique, and is installed outside the condenser lens 2. Thereby, the location of the inspection region D of the terahertz wave incident on the condenser lens 2 can be moved one-dimensionally and sensed linearly. In this case, a detection signal may be output in each inspection region D during scanning, and the type of the substance S may be determined based on each detection signal. Further, not only the one-dimensional galvanometer mirror but also a two-dimensional galvanometer mirror may be used. In this case, the location of the inspection region D can be moved two-dimensionally to sense in a planar shape. In this case, based on each detection signal during scanning, the shape of the substance S may be displayed on a display or the like, and the type of the substance S may be determined. Note that the galvanometer mirror is not limited to the outside of the condenser lens 2 and may be configured to be arranged inside the 300K shield 36a, for example. Further, as described above, the area switching device is not an optical means such as a galvanometer mirror, but may be a mechanical means for rotating the entire sensor body surrounded by the 300K shield 36a in an intended direction, for example. Good.

  In addition, since the wavelength of the terahertz wave is shorter than that of the millimeter wave, it is possible to perform sensing with higher positional accuracy than a general millimeter wave image display sensor. Therefore, the shape and position of a relatively small substance S present in clothes, packages, etc. can be detected with high accuracy.

FIG. 5 is a partially enlarged view for explaining another modification of the embodiment.
As shown in FIG. 5, this another modification is configured to include a plurality of superconducting tunnel junction elements 22 provided so as to be able to generate electrical signals corresponding to terahertz waves having different propagation paths. Yes. Specifically, for example, a plurality of light receiving portions 80 each including the light collecting device 10 and the substrate absorption type STJ element 20 are arranged in a single-row array. Thereby, linear sensing can be performed at a time based on the detection result from each light receiving unit 80. In addition, the shape of the substance S can be detected at a time, not only in a single line but also in a two-dimensional matrix. In addition, the configuration of this modification may be applied to a configuration including an area switching device that switches the inspection area D of the sensor shown in FIG.

  In the above description, the terahertz wave detection sensor 1 as the substance discrimination sensor that discriminates the substance S based on the detection signal of the terahertz wave has been described, but the present invention is not limited to this, and without substance discrimination, It may simply be a sensor that detects terahertz waves. In this case, the terahertz wave detection sensor 1 that does not have this substance discrimination function may be used as a sensor unit of a conventional active substance discrimination sensor.

DESCRIPTION OF SYMBOLS 1 ... Terahertz wave detection sensor 2 ... Condensing lens 3 ... Optical filter 4 ... Super hemispherical lens 10 ... Condensing device 21 ...・ Substrate (absorber substrate)
22 ... STJ element (superconducting tunnel junction element)
30 ... Cooling device 60 ... Substance discrimination device 70 ... One-dimensional galvanometer mirror (region switching device)
S ･ ･ ･ Material D, D '・ ・ ・ Inspection area

Claims (10)

In the space where the magnetic field is demagnetized, a superconducting tunnel junction element cooled by a cooling device having a multilayer heat shield structure is provided,
A phonon generated from a terahertz wave collected by a condensing device having a condensing lens provided on a shield wall of the outermost layer of the cooling device is detected by the superconducting tunnel junction element, and an electric power corresponding to the terahertz wave is detected. A terahertz wave detection sensor that outputs signals. An absorber substrate that receives the terahertz wave and generates phonons,
The terahertz wave detection sensor according to claim 1, wherein the superconducting tunnel junction element detects phonons generated in the substrate.   The terahertz wave detection sensor according to claim 1 or 2, wherein the superconducting tunnel junction element has a temperature of approximately 4.2K or lower. The cooling device includes a cylindrical pot that cools the superconducting tunnel junction element to a temperature of approximately 4.2K or less,
The terahertz wave detection sensor according to claim 2 , wherein a coil for demagnetizing a magnetic field in the cylindrical pot is wound around the outer periphery of the cylindrical pot. The light collecting device is:
The condenser lens;
A super hemispherical lens that is provided in close contact with the substrate and collects the terahertz wave that has passed through the condenser lens at a predetermined light receiving point on the substrate;
An optical filter provided between the condenser lens and the super hemisphere lens and having a light transmission band including the frequency of the terahertz wave;
The terahertz wave detection sensor according to claim 2 or 4 , comprising: The terahertz wave detection sensor according to claim 5 , wherein the light transmission band is in a range of approximately 0.7 THz to approximately 30 THz. Comprising a material discrimination device for discriminating a substance that emits the terahertz wave on the basis of the electrical signal, the terahertz wave detection sensor according to any one of claims 1-6. The terahertz wave detection sensor according to claim 7 , comprising a plurality of the superconducting tunnel junction elements provided so as to be able to generate electrical signals corresponding to terahertz waves having different propagation paths. The terahertz wave detection sensor according to claim 8 , wherein the plurality of superconducting tunnel junction elements are arranged in an array. The terahertz wave detection sensor according to claim 8 or 9 , comprising a region switching device that switches an inspection region of the sensor.