Terahertz oscillation element, its manufacturing method, and terahertz oscillation device

Abstract

To provide a terahertz oscillation element using high-temperature superconducting whisker crystals, a method for manufacturing the same, and a terahertz oscillation device.SOLUTION: A terahertz oscillation element of the present invention has a first high-temperature superconducting whisker crystal and a second high-temperature superconducting whisker crystal, which are cross junctioned, and a current suppressor at both ends across the junction region of at least one of the first and second high-temperature superconducting whisker crystals. The high-temperature superconducting whisker crystals have at least one crystalline phase selected from a group consisting of the Bi-2212 phase, the Bi-2201 phase, and the Bi-2223 phase, respectively.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a terahertz oscillation element using high-temperature superconducting whisker crystals, a manufacturing method thereof, and a terahertz oscillation device using the same. [Background technology]

[0002] A terahertz oscillator using an intrinsic Josephson junction of a copper oxide high-temperature superconductor has been developed (see, for example, Non-Patent Document 1). According to Non-Patent Document 1, terahertz oscillation is reported by processing a Bi-based high-temperature superconducting single crystal Bi2Sr2CaCu2O8 into a mesa structure. Such a terahertz oscillator using an intrinsic Josephson junction is attracting attention as the third compact terahertz oscillation source after quantum cascade lasers and resonant tunneling diodes.

[0003] However, the high-temperature superconducting single crystal used in Non-Patent Document 1 requires the use of expensive single crystal growth equipment such as the floating zone (FZ) method, and the single crystal growth process is difficult. In addition, processing into a mesa structure requires fine processing such as photolithography and etching. This results in low yields and high costs.

[0004] Meanwhile, Josephson devices using high-temperature superconducting whiskers have been developed (see, for example, Patent Document 1 and Non-Patent Document 2). Patent Document 1 and Non-Patent Document 2 report that Josephson junctions are formed by crossing high-temperature superconducting whisker crystals and subjecting them to heat treatment. However, terahertz oscillation has not been confirmed in devices obtained in this way. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4092393 [Non-patent literature]

[0006] [Non-Patent Document 1] L. Ozyuzer et al., SCIENCE, VOL. 318, 23, NOVEMBER 2007 [Non-Patent Document 2] Takeshi Hatano et al., Journal of the Japan Institute of Metals, Vol. 66, No. 4, 2002, 247-253 Summary of the Invention [Problem to be solved by the invention]

[0007] In view of the above, an object of the present invention is to provide a terahertz oscillation element using high-temperature superconducting whisker crystals, a manufacturing method thereof, and a terahertz oscillation device. [Means for solving the problem]

[0008] The terahertz oscillation element according to the present invention comprises a first high-temperature superconducting whisker crystal and a second high-temperature superconducting whisker crystal joined in a cross shape, and is provided with current suppression sections on both ends of the joining region of at least one of the first high-temperature superconducting whisker crystal and the second high-temperature superconducting whisker crystal, thereby solving the above-mentioned problems. The first high temperature superconducting whisker crystal and the second high temperature superconducting whisker crystal may each have at least one crystal phase selected from the group consisting of a Bi-2212 phase, a Bi-2201 phase, and a Bi-2223 phase. The thickness direction of the first high temperature superconducting whisker crystal and the second high temperature superconducting whisker crystal may be the c-axis direction of the crystal phase. The current suppressing portion may be a notch and / or a modified crystal. The current suppression portion may be the notch, and the area formed by the thickness remaining by the notch out of the total thickness of either of the whisker crystals and the width of either of the whisker crystals may be 1 / 2000 or more of the area formed by the width of either of the whisker crystals in the short direction and the distance between the current suppression portions. The current suppressing portion may be the notch, and the length of the notch may be equal to or greater than half the overall width of the one of the whisker crystals. The modified crystal may be a region that does not exhibit superconductivity. In the cross junction, the first high temperature superconducting whisker crystal and the second high temperature superconducting whisker crystal may intersect so that the angle between the longitudinal direction of the first high temperature superconducting whisker crystal and the longitudinal direction of the second high temperature superconducting whisker crystal is in the range of greater than 0° and less than 90°. The method for manufacturing the above-mentioned terahertz oscillation element according to the present invention comprises crossing a first high-temperature superconducting whisker crystal and a second high-temperature superconducting whisker crystal, heat-treating them, and joining them, and forming current suppression portions on both ends of the joining region of at least one of the first high-temperature superconducting whisker crystal and the second high-temperature superconducting whisker crystal, thereby solving the above-mentioned problem. The current suppressing portion may be formed by using one or more processing methods selected from the group consisting of focused ion beam (FIB) processing, laser processing, micro electric discharge processing, and argon ion milling. Forming the current suppressing portion may involve reacting with water. The formation of the current suppressing portion may include performing a hydrogen annealing treatment. The forming of the current suppressing portion may be performed by reacting with an acid. The heat treatment and bonding may be performed by heating in an oxygen-containing atmosphere at a temperature in the range of 700° C. to 1000° C. for a time in the range of 5 minutes to 10 days. The heat treating and bonding may be performed on a substrate selected from the group consisting of a magnesium oxide (MgO) substrate, a sapphire substrate, an alumina substrate, a silicon carbide (SiC) substrate, and glass. A terahertz oscillation device according to the present invention includes the above-mentioned terahertz oscillation element and a power source that supplies a current to the junction region, thereby solving the above-mentioned problems. Effect of the Invention

[0009] The terahertz oscillation element of the present invention is provided with current suppression parts at both ends of the junction region of at least one of the pair of high-temperature superconducting whisker crystals joined in a cross-junction, so that when a current is passed through the cross-junction, a sufficient current flows in the thickness direction of the whisker crystal. As a result, an effective intrinsic Josephson junction is formed in the thickness direction of the whisker crystal between the current suppression parts, enabling terahertz oscillation. In addition, such a cross-junctioned whisker crystal functions as an antenna, and a directional terahertz oscillation element can be provided. If the terahertz oscillation element of the present invention is used together with a power source, a terahertz oscillation device can be provided. The terahertz oscillation device of the present invention is applicable to non-destructive testing, security applications, biomedical, environmental, material sensing, and the like.

[0010] The method for manufacturing a terahertz oscillation element of the present invention does not require a complicated processing process because it is only necessary to provide current suppression sections on both ends of a junction region of a pair of cross-junctioned high-temperature superconducting whisker crystals. In addition, since high-temperature superconducting whisker crystals are manufactured without requiring a special crystal growth device or special technology, the method of the present invention can provide a terahertz oscillation element with a high yield. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a perspective view showing a terahertz oscillation device of the present invention. [Diagram 2] FIG. 2 is a schematic diagram showing a cross section of the terahertz oscillation element of the present invention taken along the line AA in FIG. [Diagram 3] Schematic diagram showing an exemplary bismuth-based high-temperature superconducting phase [Figure 4] Schematic diagram of a current suppression unit [Diagram 5] Schematic diagram showing a terahertz oscillation device of the present invention. [Figure 6] A flowchart showing the steps of manufacturing the terahertz oscillation device of the present invention. [Figure 7] Diagram showing the appearance of whisker crystals of the Bi-2212 phase [Figure 8] Optical microscope image of the element in Example 1 [Figure 9]Secondary electron image of the element in Example 1 taken with a FIB device [Figure 10] 1 is a diagram showing the current-voltage characteristics of the element of Example 1 and the voltage dependence of the oscillation wave intensity. [Figure 11] FIG. 13 is a diagram showing bias points of the current-voltage characteristics in the frequency dependence shown in FIG. 12. [Figure 12] Graph showing frequency dependence of oscillation wave of element in Example 1 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that like elements are given like reference numerals and their description will be omitted.

[0013] FIG. 1 is a perspective view showing a terahertz oscillation device of the present invention. FIG. 2 is a schematic diagram showing a cross section of the terahertz oscillation device of the present invention taken along line AA in FIG.

[0014] The terahertz oscillation element 100 of the present invention comprises a cross-jointed first high temperature superconducting whisker crystal 110 and a second high temperature superconducting whisker crystal 120. "Cross-jointed" means that when the current-voltage characteristics of the joined first high temperature superconducting whisker crystal 110 and second high temperature superconducting whisker crystal 120 are measured, a voltage jump (gap voltage) of one or more is shown, and means that an intrinsic Josephson junction is formed by the cross junction.

[0015] The inventors of the present application have discovered that terahertz oscillation can be achieved by providing current suppression sections 140a, 140b on both ends of the junction region 130 of at least one of the cross-jointed first high temperature superconducting whisker crystal 110 and second high temperature superconducting whisker crystal 120 (first high temperature superconducting whisker crystal 110 in Figures 1 and 2).

[0016] As described in Patent Document 1 and Non-Patent Document 2, an intrinsic Josephson junction is formed only at the interface of the whisker crystal by the cross junction, but by providing the current suppression parts 140a and 140b, a current can flow perpendicular to the junction region 130 of the first and second high-temperature superconducting whisker crystals 110 and 120, so that an infinite number of intrinsic Josephson junctions are formed perpendicular to the surface of the first high-temperature superconducting whisker crystal 110 (a rectangular region formed by the distance D in FIG. 1 and the total width of the first high-temperature superconducting whisker crystal 110 in the short direction) that spans between the current suppression parts 140a and 140b including the junction region 130. When a voltage is applied to the infinitely formed intrinsic Josephson junctions 210 (FIG. 2) with an increase in current, electromagnetic waves are generated from the intrinsic Josephson junctions, but since there are an infinite number of intrinsic Josephson junctions, the phase of the electromagnetic waves is easily aligned, enabling terahertz oscillation. In this specification, the range of terahertz oscillation refers to a range of 300 GHz to 3 THz.

[0017] For this reason, the current suppressing portions 140a, 140b suppress the flow of current in the in-plane direction of the junction region 130 of the cross-junctioned first high-temperature superconducting whisker crystal 110 and second high-temperature superconducting whisker crystal 120, and act to allow the current to flow in the thickness direction. The current suppressing portions 140a, 140b only need to suppress the flow of current, and do not include portions that completely stop the flow of current, such as a state in which the current suppressing portion is essentially cut when it is a notch as described below, or a state in which the crystallinity is broken or the current suppressing portion is non-superconductive throughout the entire thickness direction when it is a crystal that has been modified as described below.

[0018] Therefore, the current suppressing portions 140a, 140b may be provided on at least one of the whiskers, but may also be provided on both of the whiskers, allowing more current to flow in the thickness direction of the junction region .

[0019] In the cross junction, the first and second high-temperature superconducting whisker crystals 110, 120 are not limited in the manner of joining as long as they are joined parallel to each other, but they cross so that the angle between the longitudinal direction of the first high-temperature superconducting whisker crystal 110 and the longitudinal direction of the second high-temperature superconducting whisker crystal 120 is greater than 0° and less than 90°. The Josephson characteristic can also be controlled by the crossing angle. For example, the first and second high-temperature superconducting whisker crystals 110, 120 cross so that the angle between the longitudinal direction of the first high-temperature superconducting whisker crystal 110 and the longitudinal direction of the second high-temperature superconducting whisker crystal 120 is greater than 45° and less than 90°.

[0020] There are no particular limitations on the first high temperature superconducting whisker crystals 110 and the second high temperature whisker crystals 120 as long as they exhibit high temperature superconductivity and have a fibrous shape with a large aspect ratio, but an example is a bismuth-based high temperature superconductor.

[0021] FIG. 3 is a schematic diagram showing an exemplary bismuth-based high-temperature superconducting phase.

[0022] The bismuth-based high-temperature superconductor is preferably a B-2201 phase represented by Bi2Sr2CuO6, a B-2212 phase represented by Bi2Sr2CaCu2O8, or a B-2213 phase represented by Bi2Sr2Ca2Cu3O 10 The first high-temperature superconducting whisker crystal 110 and the second high-temperature superconducting whisker crystal 120 have at least one crystal phase selected from the group consisting of B-2223 phases represented by. As shown in Fig. 3, these bismuth-based high-temperature superconductors have a structure in which a BiO layer exhibiting insulating properties is positioned between a pair of CuO2 layers exhibiting superconductivity, stacked in the c-axis direction, and since this structure itself has an intrinsic Josephson junction at the atomic level, it is advantageous for terahertz oscillation. The first high-temperature superconducting whisker crystal 110 and the second high-temperature superconducting whisker crystal 120 may be different bismuth-based high-temperature superconducting phases or may be the same.

[0023] The above-mentioned B-2201 phase, B-2212 phase, and B-2223 phase also include those in which the strontium (Sr) site is replaced with calcium (Ca), barium (Ba), scandium (Sc), yttrium (Y), rare earth elements (RE), etc., the bismuth (Bi) site is replaced with lead (Pb), tellurium (Te), etc., and the copper (Cu) site is replaced with iron (Fe), cobalt (Co), nickel (Ni), etc., to the extent that the crystal structure is not destroyed.

[0024] From this viewpoint, when the first and second high-temperature superconducting whisker crystals 110, 120 are the above-mentioned bismuth-based high-temperature superconductors, the thickness direction of the whisker crystals is preferably the c-axis direction of the above-mentioned crystal phase. This allows efficient oscillation of terahertz waves. The plane formed by the longitudinal and lateral directions of the first and second high-temperature superconducting whisker crystals 110, 120 is preferably the ab-plane of the above-mentioned crystal phase.

[0025] There is no particular restriction on the size of the first and second high-temperature superconducting whisker crystals 110, 120, but, for example, they may be plate-shaped with a length in the range of 100 μm or more and 30 mm or less in the longitudinal direction, a length in the range of 1 μm or more and 100 μm or less in the lateral direction, and a length in the range of 0.1 μm or more and 100 μm or less in the thickness direction.

[0026] More preferably, the first and second high temperature superconducting whisker crystals 110, 120 may be plate-shaped with a length in the range of 1 mm to 10 mm in the longitudinal direction, a length in the range of 10 μm to 70 μm in the lateral direction, and a length in the range of 0.5 μm to 30 μm in the thickness direction.

[0027] Whisker crystals made of bismuth-based high-temperature superconductors having such sizes can be synthesized and produced, for example, by the methods described in M. Nagao et al., Appl. Phys. Lett., 79, 2001, 2612; M. Nagao et al., Physica C, 377, 2002, 260; and M. Nagao et al., Jpn. J. Appl. Phys., 41, 2002, L43.

[0028] FIG. 4 is a diagram illustrating a schematic diagram of a current suppressing unit.

[0029] There are no particular limitations on the shape of the current suppression portions 140a, 140b as long as they suppress the flow of current in the in-plane direction of the first high-temperature superconducting whisker crystal 110, but preferably they may be notched as shown in Figures 4(A) to (C) and / or modified crystals as shown in Figures 4(D) to (E).

[0030] The notch is formed by physically milling the whisker crystal. There is no particular limitation on the shape of the notch, and it may be U-shaped as shown in Fig. 4(A), V-shaped as shown in Fig. 4(B), or U-shaped as shown in Fig. 4(C). Fig. 4 is merely an example, and is not limited thereto.

[0031] In the notch, the area formed by the thickness remaining due to the notch out of the total thickness of the whisker crystal and the width of the whisker crystal in the short side direction is preferably 1 / 2000 (0.0005) or more of the area formed by the width of the whisker crystal in the short side direction and the distance D between the current suppression parts 140a and 140b (area of ​​the Josephson junction). This makes it possible to maintain conductivity while suppressing the current flow in the in-plane direction of the whisker crystal by the notch. There is no particular limit on the upper limit since it is not related to the critical current and cannot be expressed as a ratio to the area of ​​the Josephson junction.

[0032] In the notch, more preferably, the area formed by the thickness remaining due to the notch out of the total thickness of the whisker crystal and the width in the short direction of the whisker crystal is preferably 0.001 or more of the area formed by the width in the short direction of the whisker crystal and the distance D between the current suppression parts 140a and 140b. This makes it possible to efficiently suppress the superconducting critical current of the part remaining due to the notch from being exceeded and the superconducting current being destroyed. In particular, since it is known that the ratio of the critical current in the c-axis direction to the critical current in the ab-axis direction of the above-mentioned bismuth-based high-temperature superconductor is about 1 / 1000, it is reasonable to set the lower limit at 0.001.

[0033] The notch does not need to span the entire width of the whisker in the short direction, and preferably should be at least half the entire width of the whisker. This makes it possible to efficiently suppress current flow in the in-plane direction of the whisker through the notch.

[0034] The modified crystal is a region where a part of the whisker crystal does not exhibit superconductivity. For example, as shown in FIG. 4(D), it may be a region where the crystallinity of a part of the whisker crystal is broken (disordered) (the region indicated by diagonal lines in the figure), or as shown in FIG. 4(E), it may be a part of the whisker crystal that is a non-superconducting layer (the region indicated by dots in the figure). This makes it possible to suppress the flow of current in the in-plane direction of the whisker crystal. In this case, too, the modified crystal region can be set to the same length and depth as the notch. It is also possible to employ both the notch and the modified crystal region.

[0035] The positions of the current suppressing parts 140a and 140b are not particularly limited, but for example, they are each located at a distance of 0 μm or more and 500 μm or less from the junction region 130. This makes it possible to suppress the flow of current in the in-plane direction of the whisker crystal. More preferably, they are each located at a distance of 0 μm or more and 50 μm or less from the junction region 130. If they are within this range, the terahertz oscillation element of the present invention can be provided with good yield.

[0036] Since the second high temperature superconducting crystal whiskers 120 also function as electrodes, electrodes using metal conductors are not required, so that little heat is generated and terahertz waves can be oscillated stably.

[0037] Although not shown, the terahertz oscillation element 100 of the present invention may be located on a substrate. This improves the manufacturing yield and promotes heat dissipation, allowing stable oscillation of terahertz waves. Such a substrate is illustratively selected from the group consisting of a magnesium oxide (MgO) substrate, a sapphire substrate, an alumina substrate, a silicon carbide (SiC) substrate, and glass.

[0038] Moreover, one or more of the terahertz oscillation elements 100 of the present invention may be integrated on a substrate, thereby increasing the oscillation intensity of the terahertz wave.

[0039] Next, an oscillation device using the thus obtained terahertz oscillation element of the present invention will be described. FIG. 5 is a schematic diagram showing a terahertz oscillation device of the present invention.

[0040] The terahertz oscillation device 500 of the present invention includes the above-mentioned terahertz oscillation element 100 of the present invention, and a power supply 510 that supplies a current to the junction region 130.

[0041] The current supplied from the power source 510 flows vertically from the second high-temperature superconducting whisker crystal 120 to the first high-temperature superconducting whisker crystal 110 with respect to the junction region 130, since the first high-temperature superconducting whisker crystal 110 has current suppression parts 140a, 140b at both ends thereof. As a result, a voltage is applied vertically to the junction region 130, so that countless intrinsic Josephson junctions are formed in the thickness direction of the first high-temperature superconducting whisker crystal 110 between the current suppression parts 140a, 140b. Resonance occurs between the countless intrinsic Josephson junctions, and the oscillating current flows coherently with the same phase, so that terahertz waves 520 are oscillated to the outside.

[0042] Although not shown, the terahertz oscillation element 100 may be placed in a refrigerator and cooled. This allows efficient oscillation of terahertz waves. The cooling temperature during operation is in the range of 4K to 80K, more preferably 30K to 60K. This allows oscillation of terahertz waves with high intensity.

[0043] If such a terahertz oscillator 500 is used together with, for example, a spectrometer, it is possible to identify polymers, enzymes, proteins, etc. In addition to material identification, the terahertz oscillator of the present invention is also applicable to non-destructive testing, security applications, biomedical, environmental, material sensing, etc.

[0044] Next, a method for producing the terahertz oscillation device of the present invention will be described. FIG. 6 is a flow chart showing the steps of manufacturing the terahertz oscillation device of the present invention.

[0045] Step S610: The first high temperature superconducting whisker crystal and the second high temperature superconducting whisker crystal are intersected, heat treated, and bonded. Step S620: Current suppressing portions are formed on both ends of a junction region of at least one of the first high temperature superconducting whisker crystal and the second high temperature superconducting whisker crystal. In this way, the terahertz oscillation element of the present invention does not require complicated processing since it is only necessary to provide current suppression sections on both ends of a junction region in a pair of cross-junctioned high-temperature superconducting whisker crystals.

[0046] Each step will be described in detail. In step S610, the first high-temperature superconducting whisker crystal and the second high-temperature superconducting whisker crystal are as described with reference to Fig. 1, and therefore the description will be omitted. Note that the bismuth-based high-temperature superconducting whisker crystal may be a commercially available product or may be synthesized by the above-mentioned method.

[0047] In step S610, the first high temperature superconducting whisker crystal and the second high temperature superconducting whisker crystal are intersected so that the angle between the longitudinal direction of the first high temperature superconducting whisker crystal and the longitudinal direction of the second high temperature superconducting whisker crystal is greater than 0° and less than 90°.

[0048] In step S610, the crossed first and second high-temperature superconducting whisker crystals are heated in an oxygen-containing atmosphere at a temperature range of 700°C to 1000°C for 5 minutes or more. There is no upper limit to the heating time, but even if the heating is performed for 10 days or more, there is no change in the bonding, so the upper limit is 10 days. An exemplary oxygen partial pressure is in the range of 20% to 100%. This range promotes bonding.

[0049] In step S610, the crossed first and second high-temperature superconducting whisker crystals may be heat-treated on the substrate to bond them together. Heat treatment on the substrate promotes bonding. The substrate may be one selected from the group consisting of the magnesium oxide (MgO) substrate, sapphire substrate, alumina substrate, silicon carbide (SiC) substrate, and glass substrate.

[0050] Whether or not an intrinsic Josephson junction is formed in the junction region in step S610 can be determined by whether or not one or more voltage jumps (gap voltages) are observed when the current-voltage characteristics are measured by four-terminal measurement.

[0051] In step S620, when the current suppressing portions 140a and 140b are notches, they are formed by one or more processing methods selected from the group consisting of focused ion beam (FIB) processing, laser processing, micro-electric discharge processing, and argon ion milling. These methods allow the high-temperature superconducting whisker crystals to be physically milled to form the notches. The FIB processing method is preferable. This allows the size of the notches to be highly controlled.

[0052] In step S620, when the current suppression parts 140a and 140b are regions where the crystallinity of the whisker crystal is broken (disordered), the whisker crystal can be reacted with an acid. As a result, the crystal structure of the whisker crystal in the region reacted with the acid is physically broken or disordered, and it functions as a current suppression part. For such an acid, an inorganic acid such as hydrochloric acid, sulfuric acid, nitric acid, or hydrofluoric acid can be used.

[0053] In step S620, when the current suppression units 140a, 140b are part of a whisker crystal that is a non-superconducting layer, the whisker crystal may be reacted with water. This forms a non-superconducting layer on the surface of the whisker crystal in the area that reacted with water, and functions as a current suppression unit. Alternatively, hydrogen annealing may be performed. In this case, a non-superconducting layer is also formed on the surface of the whisker crystal in the area that reacted with hydrogen. The hydrogen annealing may be performed by, for example, heat treatment in a temperature range of 300°C to 1000°C in a 100% hydrogen gas atmosphere.

[0054] In forming the current suppressing portions 140a and 140b, if necessary, a mask exposing the region where the current suppressing portions of the whisker crystals are to be formed may be applied, and any processing or treatment may be performed.

[0055] 6, the method for manufacturing the terahertz oscillation element of the present invention has been described by performing step S610 and step S620 in this order, but step S610 may be performed after step S620. That is, first, two current suppression parts are formed in at least one of the first and second high-temperature superconducting whisker crystals (corresponding to step S620), and then the first and second high-temperature superconducting whisker crystals are crossed so that a junction region is formed in the region sandwiched between the two current suppression parts, and heat-treated (corresponding to step S610) to form a cross junction. In this manner, the terahertz oscillation element 100 of the present invention can also be manufactured.

[0056] The present invention will now be described in detail with reference to specific examples, but it should be noted that the present invention is not limited to these examples. EXAMPLES

[0057] [Production of high-temperature superconducting whisker crystals] As high-temperature superconducting whisker crystals, whisker crystals of the Bi-2212 phase, which is a bismuth-based high-temperature superconductor, were produced as follows.

[0058] Bismuth (III) oxide (Wako Pure Chemical Industries, Ltd.), strontium carbonate (Kojundo Chemical Laboratory Co., Ltd.), calcium carbonate (Kojundo Chemical Laboratory Co., Ltd.), copper (II) oxide (Furuuchi Chemical Co., Ltd.), and tellurium oxide (Wako Pure Chemical Industries, Ltd.) were weighed and mixed to a molar ratio of Bi:Sr:Ca:Cu:Te = 2:2:2:2:0.5, and pre-fired three times at 760°C, 790°C, and 820°C. The pre-fire time at each temperature was 10 hours. The sample was molded into a φ10 pellet using a hydraulic press and heat-treated at 840°C for 50 hours under oxygen flow to obtain whisker crystals.

[0059] The whisker crystals thus obtained were identified as being of the Bi-2212 phase, with the thickness direction being the c-axis direction and the in-plane direction (the plane formed by the longitudinal and lateral directions) being the ab-plane, using an X-ray diffraction device (MiniFlex600, manufactured by Rigaku Corporation). The appearance of the whisker crystals made of the Bi-2212 phase obtained is shown in Figure 7.

[0060] FIG. 7 is a diagram showing the appearance of whisker crystals of the Bi-2212 phase.

[0061] Figure 7(A) shows the growth of whisker crystals from a pellet. Figure 7(B) is an optical microscope photograph of one whisker crystal. The size of each whisker crystal was 500μm to 5mm in the longitudinal direction, 10μm to 40μm in the lateral direction, and 0.5μm to 1.5μm in the thickness direction.

[0062] [Example 1] In Example 1, a terahertz oscillation device was manufactured according to the method shown in FIG.

[0063] A pair of whisker crystals was crossed at 90° on a magnesium oxide (MgO) substrate (2 mm x 2 mm x 0.5 mm, manufactured by Furuuchi Chemical Co., Ltd.), heat-treated, and bonded (step S610 in FIG. 6). The whisker crystals were cut to 1 mm in the longitudinal direction, one measuring 3 mm in the longitudinal direction, 30 μm in the lateral direction, and 1 μm in the thickness direction, and the other measuring 3 mm in the longitudinal direction, 33 μm in the lateral direction, and 1 μm in the thickness direction. The heat treatment conditions were 850°C for 30 minutes in an oxygen flow (oxygen partial pressure 100%). It was confirmed by current-voltage measurement using a four-terminal measurement method that an intrinsic Josephson junction was formed in the junction region.

[0064] Next, current suppression parts were formed on both ends of the junction region of the lower (substrate side) whisker crystal (short side length 30 μm) of the pair of cross-junctioned whisker crystals obtained (step S620 in FIG. 6). The current suppression parts were notches made using a focused ion beam (Seiko Instruments Inc., SMI9800SE). The focused ion beam was irradiated under the following conditions: a gallium (Ga) source was used, the acceleration voltage was 30 kV, and the current density was 320 pA / cm. 2 The resulting notch was U-shaped as shown in FIG. 4(A), had a depth of 0.9 μm, spanned the entire width of the whisker crystal, and was spaced 27.5 μm from the junction region. The element thus obtained is referred to as the element of Example 1.

[0065] The element of Example 1 was observed using an optical microscope (Nikon Corporation, SMZ745T) and an electron microscope. The observation results are shown in Figures 8 and 9. The electron microscope observation was performed using the secondary electron photography function of the above-mentioned FIB device.

[0066] A DC power supply was connected to the element of Example 1 as shown in FIG. 5, and the element was placed in a windowed pulse tube refrigerator and cooled to 30K to 60K. The current-voltage characteristics were measured by a four-terminal measurement method. Next, a Fourier transform infrared spectrometer (JASCO Corporation, FARIS-1) and an InSb hot electron bolometer were placed outside the refrigerator via a polyethylene lens, and the frequency of the oscillation wave from the element was measured. The results are shown in FIG. 10 to FIG. 12.

[0067] [Example 2] In Example 2, two whisker crystals, one measuring 2 mm in the longitudinal direction, 32 μm in the lateral direction, and 0.7 μm in the thickness direction, and the other measuring 2 mm in the longitudinal direction, 32 μm in the lateral direction, and 0.66 μm in the thickness direction, were used, and an element was obtained in the same manner as in Example 1, except that no current suppression section was formed. The element obtained in this manner is called the element of Example 2. As in Example 1, the element of Example 2 was observed, the current-voltage characteristics were measured, and the oscillation intensity from the element was measured. The results are shown in Table 2.

[0068] [Example 3] In Example 3, a terahertz oscillation element was manufactured according to the method described in FIG. 6. In Example 3, a notch was formed as a current suppression part in one whisker crystal (length in the short direction: 30 μm) of the element of Example 2. Under the same FIB conditions as in Example 1, a notch having a depth of 0.4 μm and spaced 26.5 μm from the junction region was formed over the entire width of the whisker crystal. The element obtained in this manner is called the element of Example 3. As in Example 1, the element of Example 3 was observed, the current-voltage characteristics were measured, and the oscillation intensity and oscillation frequency from the element were measured. The results are shown in Table 2.

[0069] [Example 4] In Example 4, a terahertz oscillation element was manufactured according to the method described in FIG. 6. In Example 4, the notch of the element of Example 3 was further processed by FIB to a depth of 0.52 μm. The element obtained in this manner is called the element of Example 4. As in Example 1, the element of Example 4 was observed, the current-voltage characteristics were measured, and the oscillation intensity and oscillation frequency from the element were measured. The results are shown in Table 2.

[0070] For simplicity, the structures of the elements of Examples 1 to 4 are shown in Table 1, and the above results are summarized and explained.

[0071] [Table 1]

[0072] FIG. 8 is an optical microscope photograph of the device of Example 1. FIG. 9 is a secondary electron image of the element of Example 1 taken by an FIB device.

[0073] Fig. 8 shows that in the element of Example 1, a pair of whisker crystals are cross-joined, and silver paste is applied to the ends of the whisker crystals. Fig. 9 shows that notches are formed on both ends of the bonding region of the element of Example 1. The notches were spaced 27.5 μm from the bonding region. Although not shown, the elements of Examples 3 and 4 also showed a similar appearance.

[0074] FIG. 10 is a graph showing the current-voltage characteristics of the element of Example 1 and the voltage dependence of the oscillating wave intensity.

[0075] Fig. 10 shows the current-voltage characteristics when the element of Example 1 was cooled to 45K. According to the current-voltage characteristics of Fig. 10, a gap voltage of 1 or more was confirmed, and it was found that an intrinsic Josephson junction was formed in the element of Example 1. Although not shown, according to the current-voltage characteristics of the elements of Examples 3 and 4, the number of gap voltages of the elements increased as the depth of the notch increased, and it was shown that the notch functioned as a current suppressing portion, causing the current to flow perpendicular to the junction region of the pair of whisker crystals, and that an infinite number of intrinsic Josephson junctions were formed in the thickness direction of the whisker crystals between the current suppressing portions.

[0076] Furthermore, when focusing on the change in the oscillating wave intensity in Fig. 10, a remarkable increase in the oscillating wave intensity from the element of Example 1 was confirmed during the return current of the current sweep. This tendency was confirmed for the element of Example 1 over the entire range of 30K to 60K, and the greatest intensity was confirmed especially when cooled to 35K to 45K.

[0077] [Table 2]

[0078] Table 2 shows a list of the signal intensities of the bolometers of the elements of Examples 2 to 4. The elements of Examples 2 to 4 were measured under the same measurement conditions with the same pair of cross-jointed whisker crystals with different cutting depths, so that the signal intensities can be compared. As shown in Table 2, the elements of Examples 3 and 4 showed intensities of 0.1 mV and 0.22 mV, respectively, when cooled to 40 K. On the other hand, the element of Example 2 showed a current-voltage characteristic with a gap voltage, but no increase in the oscillation wave intensity was observed. In addition, although not shown, the elements of Examples 3 and 4 were confirmed in the entire range of 30 K to 60 K, similar to the element of Example 1, and the largest intensity was confirmed especially when cooled to 35 K to 45 K.

[0079] According to Table 2, it was found that the oscillation intensity increased as the notch became deeper. This is because the voltage jump increased as the notch became deeper. Furthermore, these results suggest that the intrinsic Josephson junction formed in the perpendicular direction (thickness direction of the whisker crystal) to the rectangular area formed by the width of the whisker crystal in the short direction and the distance between the notches contributes to the oscillation.

[0080] FIG. 11 is a diagram showing bias points of the current-voltage characteristics in the frequency dependence shown in FIG. FIG. 12 is a diagram showing the frequency dependence of the oscillation wave of the element of Example 1.

[0081] The element of Example 1 oscillated at a bias point of 0.72 V in Fig. 11, and according to Fig. 12, the frequency of the oscillation wave confirmed in Fig. 10 was found to be 650 GHz. This demonstrated that the element of Example 1 functions as a terahertz oscillation element. The elements of Examples 3 and 4 also oscillated in the range of 300 GHz to 3 THz.

[0082] From Table 1 and the results of terahertz oscillation of the elements of Examples 1, 3 and 4, it was found that the ratio of the area formed by the thickness remaining due to the notches and the area formed by the width of the whisker crystal in the short direction to the area formed by the width of the whisker crystal in the short direction and the distance between the notches is 0.001 or more. As for the upper limit, since it is not related to the critical current, it cannot be expressed as a ratio to the area of ​​the Josephson junction, and no particular limit is set, but it has been experimentally confirmed that from the viewpoint of the depth of the notches, it should be 0.3 μm or more.

[0083] As explained above, it has been shown that terahertz oscillation can be achieved by providing a current suppression portion such as a notch on both ends of the junction region of at least one of the whisker crystals in a pair of high-temperature superconducting whisker crystals joined in a cross shape, and it has been found that a terahertz oscillation element and a device using the same can be provided. [Industrial Applicability]

[0084] The terahertz oscillation element of the present invention is applicable to non-destructive testing, security applications, biomedical, environmental, and material sensing, and the like. [Explanation of symbols]

[0085] 100 Terahertz oscillator 110 The first high-temperature superconducting whisker crystal 120 Second high-temperature superconducting whisker crystal 130 Joint area 140a, 140b current suppressor 210 Intrinsic Josephson Junction 500 Terahertz Oscillator 510 Power supply

Claims

1. a first high temperature superconducting whisker crystal and a second high temperature superconducting whisker crystal, the first high temperature superconducting whisker crystal and the second high temperature superconducting whisker crystal being cross-joined; a current suppressing portion provided on both ends of a junction region of at least one of the first high-temperature superconducting whisker crystal and the second high-temperature superconducting whisker crystal; each of the first high temperature superconducting whisker crystal and the second high temperature superconducting whisker crystal has at least one crystal phase selected from the group consisting of a Bi-2212 phase, a Bi-2201 phase, and a Bi-2223 phase; A terahertz oscillation element in which the current suppression portion is a crystal having at least one of a notch, a region in which the crystallinity of a part of the whisker crystal is broken (disordered), or a region in which a part of the whisker crystal does not exhibit superconductivity, and does not include anything that causes current to completely stop flowing.

2. 2. The terahertz oscillation element according to claim 1, wherein the thickness direction of the first high temperature superconducting whisker crystal and the thickness direction of the second high temperature superconducting whisker crystal are the c-axis direction of the crystal phase.

3. the current suppressing portion is the notch, 2. The terahertz oscillation element described in claim 1, wherein the area formed by the thickness remaining by the notch out of the total thickness of either one of the whisker crystals and the width of either one of the whisker crystals is 1 / 2000 or more of the area formed by the width of either one of the whisker crystals in the short direction and the distance between the current suppression portions.

4. the current suppressing portion is the notch, The length of the notch is equal to or greater than half the overall width of the whisker crystal. The terahertz oscillation device according to claim 1 .

5. A terahertz oscillation element as described in any one of claims 1 to 4, wherein in the cross junction, the first high temperature superconducting whisker crystal and the second high temperature superconducting whisker crystal cross each other so that an angle between the longitudinal direction of the first high temperature superconducting whisker crystal and the longitudinal direction of the second high temperature superconducting whisker crystal is in the range of more than 0° and not more than 90°.

6. intersecting the first high temperature superconducting whisker crystal with the second high temperature superconducting whisker crystal, heat treating and bonding the first high temperature superconducting whisker crystal and the second high temperature superconducting whisker crystal; forming current suppressing portions on both ends of a junction region of at least one of the first high temperature superconducting whisker crystal and the second high temperature superconducting whisker crystal; The method for producing a terahertz oscillation element according to any one of claims 1 to 5, comprising:

7. The method of claim 6 , wherein forming the current suppressing portion uses at least one processing method selected from the group consisting of focused ion beam (FIB) processing, laser processing, micro-electric discharge processing, and argon ion milling.

8. The method of claim 6 , wherein forming the current suppressing portion comprises reacting with water.

9. The method of claim 6 , wherein forming the current suppressing portion comprises a hydrogen annealing process.

10. The method of claim 6 , wherein forming the current suppressing portion comprises reacting with an acid.

11. The method according to any one of claims 6 to 10, wherein the heat treatment and bonding is performed by heating in an oxygen-containing atmosphere at a temperature in the range of 700°C to 1000°C for a time in the range of 5 minutes to 10 days.

12. 12. The method according to claim 6, wherein the heat treating and bonding is performed on a substrate selected from the group consisting of a magnesium oxide (MgO) substrate, a sapphire substrate, an alumina substrate, a silicon carbide (SiC) substrate, and glass.

13. A terahertz oscillation element according to any one of claims 1 to 5, A power source that applies current to the junction area; A terahertz oscillator comprising:

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