Superconducting strip detector and method for manufacturing superconducting strip therefor

Abstract

A superconducting tape detector is provided with a superconducting tape disposed in a detection region of a detection object having significant energy, and detects the detection object in the detection region by causing the superconducting tape to be in a superconducting state and flowing a bias current into the superconducting tape from a predetermined bias current path. The superconducting strip includes a wiring portion in which a critical current value per unit length in the line width direction is larger in both end portions in the line width direction than in the center portion in the line width direction.

Description

Technical Field

[0001] The present invention relates to a superconducting strip detector and a method for manufacturing a superconducting strip used therefor. Background Art

[0002] For example, superconducting strip detectors are known that detect photons, electrons, molecules, radiation, etc. For example, superconducting single photon detectors (SSPDs) that detect single photons are highly sensitive, low-noise, and high-speed single photon detectors that are expected to be used in various fields such as quantum information communication and quantum optics (for example, refer to non-patent literature 1 and 2). As a detection element for detecting single photons in SSPD, a wiring-shaped light-receiving portion (hereinafter referred to as a superconducting strip) arranged in a specified detection area is used. The superconducting strip is called a nanostrip or nanowire, and is known to be formed by a niobium nitride wiring composed of, for example, niobium nitride (NbN) with a line width of about 100nm, and is used in a superconducting state. SSPDs using such nanostrips are also called SNSPDs (Superconducting Nanostrip Single Photon Detectors). Systems developed using SNSPDs have performance that exceeds that of semiconductor detectors, and are therefore being promoted to various cutting-edge technology fields such as quantum cryptography key distribution experiments or demonstration experiments of various quantum information technologies, and biomedical applications.

[0003] In addition, in recent years, it has been discovered that superconducting strips (called microstrips, microwires, or microbridges) with a line width exceeding 1 μm can be used instead of nanostrips to detect single photons (for example, refer to non-patent document 3). The SSPD using such microstrips is called SMSPD (Superconducting Microstrip Single Photon Detector). Compared with SNSPD, which requires electron beam lithography to form superconducting strips, SMSPD can form superconducting strips by optical lithography, which can greatly improve the uniformity and mass production of component performance. In addition, if the line width can be sufficiently larger than the focused spot diameter of the incident photon, such as more than 10 μm, the filling factor of the light receiving area relative to the focused spot diameter can be 100%, so it is expected to achieve high quantum efficiency.

[0004] Therefore, with the improvement of system performance and scale, the realization of quantum networks, quantum Internet, or quantum computers is expected to require a large number of high-performance photon detectors, and SMSPD has attracted worldwide attention as a highly important technology.

[0005] Prior art documents: Non-patent documents: Non-patent document 1: M. Sasaki, M. Fujiwara, H. Ishizuka, W. Klaus, K. Wakui, M. Takeoka, S. Miki, T. Yamashita, Z. Wang, A. Tanaka, K. Yoshino, Y. Nambu, S. Takahashi, A. Tajima, A. Tomita, T. Domeki, T. Hasegawa, Y. Sakai, H. Kobayashi, T. Asai, K. Shimizu, T. Tokura, T. Tsurumaru, M. Matsui, T. Honjo, K. Tamaki, H. Takesue, Y. Tokura, J. F. Dynes, A. R. Dixon, A. W. Sharpe, Z. L. Yuan, A. J. Shields, S. Uchikoga, M. Legre, S. Robyr, P. Trinkler, L. Monat, J. B. Page, G. Ribordy, A. Poppe, A. Allacher, O. Maurhart, T. Langer, M. Peev, and A. Zeilinger, "Field test of quantum key distribution in the Tokyo QKD Network", Opt Express 19, 10387 (2011); Non-patent document 2: T. Kobayashi, R. Ikuta, S. Yasui, S. Miki, T. Yamashita, H. Terai, T. Yamamoto, M. Koashi, and N. Imoto, "Frequency-domain Hong-Ou-Mandel interference", Nature Photonics 10, 441 (2016); Non-patent document 3: Y. P. Korneeva, D. Yu. Vodolazov, A. V. Semenov, I. N. Florya, N. Simonov, E. Baeva, A. A. Korneev, G. N. Goltsman, T. M. Klapwijk, "Optical Single-Photon Detection in Micrometer-Scale NbN Bridges", Phys. Rev. Applied 9, 064037 (2018). Summary of the invention

[0006] Problems to be solved by the invention: Since the line width of the superconducting strip in SNSPD is about 100nm, in order to form a light-receiving surface of a specified area such as 15μm×15μm, the nanostrip needs to be made into a specified shape such as a meander shape and spread over the detection area of ​​the specified area. Therefore, in order to realize SNSPD, advanced nano patterning technology is indispensable.

[0007] On the other hand, since the line width is wider in SMSPD, a light-receiving surface of a specified area can be formed without complicating the shape of the superconducting strip. However, there is a problem that dark counts, which output signals even when no photons are incident, increase as the line width of the superconducting strip becomes wider. In addition, the occurrence of dark counts in SNSPD is relatively rare, but the problem of dark counts may also occur in SNSPD. Moreover, for example, in other superconducting strip detectors used to detect detection objects other than single photons such as multiphotons, electrons, molecules, neutrals, and radiation, the problem of dark counts may also occur.

[0008] The present invention has been made to solve such a problem, and an object of the present invention is to provide a superconducting stripe detector capable of reducing the occurrence of dark counts and a method for manufacturing a superconducting stripe used in the superconducting stripe detector.

[0009] Means of solving the problem: A superconducting strip detector in one aspect of the present invention is a superconducting strip detector having a superconducting strip arranged in a detection area of ​​a detection object having significant energy, wherein the superconducting strip is put into a superconducting state, and a bias current is passed into the superconducting strip from a prescribed bias current path, thereby detecting the detection object in the detection area. The superconducting strip includes wiring portions at both ends in the line width direction in which the critical current value per unit length in the line width direction is larger than that in the central portion in the line width direction.

[0010] In addition, a method for manufacturing a superconducting strip used in a superconducting strip detector according to another aspect of the present invention is a method for manufacturing a superconducting strip used in a superconducting strip detector, the superconducting strip detector comprising a superconducting strip disposed in a detection region of a detection target having significant energy, the superconducting strip being in a superconducting state, a bias current flowing from a predetermined bias current path into the superconducting strip, thereby detecting the detection target in the detection region, The superconducting strip is formed to include wiring portions in which critical current values ​​per unit length in the line width direction are larger at both end portions in the line width direction than at a center portion in the line width direction.

[0011] Effect of the invention: According to the present invention, the occurrence of dark counts can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a plan view schematically showing a configuration example of a superconducting strip detector in one embodiment of the present invention; Figure 2 It is shown Figure 1 A diagram showing the distribution of critical current values ​​in the line width direction of the superconducting strip shown; Figure 3 is a diagram showing a first example of a method for manufacturing a superconducting strip in the present embodiment; Figure 4 is a diagram showing a second example of the method for manufacturing a superconducting strip in the present embodiment; Figure 5 is a diagram showing a third example of the method for manufacturing a superconducting strip in the present embodiment; Figure 6 is a diagram showing a fourth example of the method for manufacturing a superconducting strip in the present embodiment; Figure 7 is a diagram showing a fifth example of the method for manufacturing a superconducting strip in the present embodiment; Figure 8 is a diagram showing the distribution of critical current values ​​in the line width direction of a superconducting strip having a conventional structure; Fig. 9 This is a diagram illustrating a superconducting stripe state that causes dark counts. Fig. 9 A is a diagram showing a state in which the edge of the superconducting strip is notched in a cross-sectional view of the superconducting strip. Fig. 9 B is a diagram showing a state in which the side surface shape of the superconducting strip is rough in the cross-sectional view of the superconducting strip. Fig. 9 C is a diagram showing a state in which the line width of the superconducting strip becomes non-uniform in a plan view of the superconducting strip. DETAILED DESCRIPTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, in all the drawings, the same reference numerals are given to the same or corresponding components, and the repeated description of such components may be omitted below.

[0014] In addition, the present invention is not limited to the following embodiments. That is, the following specific description is only an example of the features of the "superconducting strip probe" of the present invention. Therefore, when the following specific examples are described by attaching appropriate reference symbols to the terms corresponding to the constituent elements that identify the "superconducting strip probe" of the present invention, the specific device is an example of the constituent element of the "superconducting strip probe" of the present invention corresponding thereto.

[0015] Figure 1 FIG. 1 is a plan view schematically showing a configuration example of a superconducting strip detector in one embodiment of the present invention. Figure 1 In the example of the embodiment, as an example of a superconducting strip detector, an example of a superconducting single photon detector for detecting single photons is shown. The superconducting single photon detector (SSPD) 1 in this embodiment has: a substrate 2; and a superconducting strip 3, which is arranged in a predetermined detection area A on the substrate 2 and is used in a superconducting state. The plane size of the detection area A is determined in accordance with the purpose of use of the superconducting single photon detector 1. For example, it is determined to be a square with a side of 15μm to 50μm.

[0016] In the present embodiment, the superconducting strip 3 is formed in a straight line in the detection region A. Therefore, for example, when the plane size of the detection region A is 15 μm on one side, the superconducting strip 3 has a wiring portion 3A whose line width in the detection region A has a range of, for example, 10 μm to 15 μm in order to cover the entire detection region A or a region close thereto.

[0017] The superconducting strip 3 is cooled by using an appropriate cooling means (e.g., a Gifford-McMahon refrigerator) and used in a superconducting state. The superconducting strip 3 is formed of, for example, niobium nitride (NbN). The thickness of the superconducting strip 3 is, for example, not less than 5 nm and not more than 10 nm. In addition, the substrate 2 is, for example, a silicon (Si) substrate.

[0018] The superconducting strip 3 is connected to electrodes 4 and 5 outside the detection area A. The first electrode 4 is connected to the transmission path 6, and the second electrode 5 is grounded. The superconducting strip 3 is connected to the bias current source 7 via the transmission path 6, and is configured so that a prescribed bias current Ib lower than the superconducting critical current flows from the bias current source 7 to the superconducting strip 3. In addition, a shunt resistor 13 is connected between the electrodes 4 and 5. However, the shunt resistor 13 may not be present. In addition, the electrodes 4, 5 and the transmission path 6 are preferably made of the same material as the superconducting strip 3 to prevent the superconducting state from being destroyed at the connection with the superconducting strip 3.

[0019] When a photon (single photon) P is incident on the light-receiving surface of the superconducting strip 3 (wiring portion 3A in the detection area A), the energy brought by the photon P exceeds the gap energy, thereby causing a resistance change or an inductance change on the superconducting strip 3 through several physical processes. The resistance change or the inductance change is detected through the transmission path 6.

[0020] Therefore, in the present embodiment, the SSPD 1 is connected with a bias tee 8 between the transmission path 6 and the bias current source 7. Generally, the bias tee 8 includes an inductor 9 and a capacitor 10. The bias tee 8 is connected to the bias current source 7 via the inductor 9 at the first end of a T-shaped wiring having three ends, is connected to the transmission path 6 at the second end, and is connected to the output loop 11 at the third end via the capacitor 10. The output loop 11 includes an amplifier 12, and the voltage signal in the transmission path 6 is amplified by the amplifier 12 and outputted. However, there is a case where the amplifier 12 is not used.

[0021] Figure 2 It is shown Figure 1 The graph shows the distribution of critical current values ​​in the line width direction of the superconducting strip. Figure 2 The distribution of critical current value in the line width direction and the cross section Figure 1 As shown, the cross-sectional view is orthogonal to the direction of the bias current Ib flowing in the wiring portion 3A of the superconducting strip 3. In this example, the direction of the bias current Ib flowing in the wiring portion 3A is equivalent to the length direction of the wiring portion 3A. In this embodiment, the wiring portion 3A includes wiring portions in both ends in the line width direction where the critical current value per unit length in the line width direction is larger than that in the central portion in the line width direction. In this embodiment, the wiring portion 3A of the superconducting strip 3 includes: a central band 31 whose critical current value per unit length in the line width direction is a first value; and a side band 32 whose critical current value per unit length in the line width direction is a second value larger than the first value.

[0022] In order to explain the structure of the wiring portion 3A of the superconducting strip 3 in the present embodiment, first, the problem of a superconducting strip having a uniform critical current value per unit length in the line width direction will be explained. Figure 8 : is a graph showing the distribution of critical current values ​​in the line width direction of a superconducting strip of a conventional structure. Fig. 9 This is a diagram illustrating a superconducting stripe state that causes dark counts.

[0023] Figure 8 The figure shows a cross-sectional view orthogonal to the length direction (the direction in which the bias current Ib flows) of a superconducting strip 50 of a conventional structure, and a graph showing the bias current distribution Jbo relative to the line width direction distance L from the center position in the line width direction of the superconducting strip 50. The superconducting strip 50 of the conventional structure is formed of a uniform material (a material with the same critical current density) with a constant film thickness. Therefore, in the line width direction of the superconducting strip 50, the critical current value Jco per unit length in the line width direction is constant regardless of the line width direction distance L.

[0024] If bias current Ib flows through superconducting strip 50 of such conventional structure, it is predicted that current distribution Jbo will be formed in which bias current Ib is concentrated at both ends of superconducting strip 50 in the line width direction. The degree of such current distribution Jbo (the degree of concentration of bias current at both ends in the line width direction) is more significant as the line width of superconducting strip 50 is wider and the amount of bias current is larger. Therefore, if the amount of bias current supplied to superconducting strip 50 increases, the amount of bias current flowing at both ends in the line width direction of superconducting strip 50 approaches critical current value Jco per unit length in the line width direction. Therefore, the amount of bias current flowing at both ends in the line width direction of superconducting strip 50 is more likely to approach critical current value Jco per unit length in the line width direction than the amount of bias current flowing in the center portion in the line width direction. That is, Jbo / Jco is more likely to approach 1. The closer the bias current flowing in the two ends of the superconducting strip 50 in the line width direction is to the critical current value Jco per unit length in the line width direction, the weaker the superconductivity of the two ends in the line width direction. In addition, magnetic flux (called eddy current or vortex filament) easily invades from the edge portion. Therefore, dark counts are likely to occur at the edge portion of the superconducting strip 50. This is considered to be one of the reasons why dark counts are more likely to occur as the line width of the superconducting strip 50 is wider. In addition, the bias current amount in the two ends in the line width direction (the value of the two ends in the line width direction in the bias current distribution Jbo) is larger than the bias current amount in the central portion in the line width direction (the value of the central portion in the line width direction in the bias current distribution Jbo), so it is difficult to apply sufficient bias current to the central portion in the line width direction, and thus the detection efficiency is also limited.

[0025] In addition, if Fig. 9 As shown, the edge portion of the superconducting strip 50 may have a non-uniform shape due to the manufacturing process of the element. Fig. 9 A shows a state in which the edge of the superconducting strip 50 is notched in the cross-sectional view of the superconducting strip 50. Due to such an edge notch, the film thickness of the superconducting strip 50 is uneven. In addition, Fig. 9 B shows a state where the side shape of the superconducting strip 50 is thick in the cross-sectional view of the superconducting strip 50. In addition, Fig. 9 C shows a state in which the line width of superconducting strip 50 becomes non-uniform in a plan view of superconducting strip 50 .

[0026] These states in the superconducting strip 50 become the main factors that weaken the superconductivity at both ends in the line width direction. Since the edge portion of the superconducting strip 50 has these shapes, magnetic flux (called eddy current) easily enters from the edge portion. The bias current flows, and the magnetic flux crosses the superconducting strip 50, and the superconducting state is destroyed. As a result, dark counts occur. In this way, the non-uniformity of the shape in the edge portion of the superconducting strip 50 is also considered to be one of the causes of the occurrence of dark counts.

[0027] Based on the analysis of the bias current distribution in the line width direction and the cause of dark counts, the inventors conducted in-depth research and realized that if the superconductivity of the edge portion of the wiring portion 3A of the superconducting strip 3 is weakened relative to the superconductivity of the central portion and dark counts are likely to occur, then by configuring the wiring portion 3A of the superconducting strip 3 to include wiring portions at both ends in the line width direction where the critical current value per unit length in the line width direction is larger than that of the central portion in the line width direction, the effect of weakening the superconductivity of the edge portion (both ends in the line width direction) can be reduced, and dark counts can be reduced and detection efficiency can be improved.

[0028] Figure 2 , a cross-sectional view of the wiring portion 3A of the superconducting strip 3 in the present embodiment and a graph showing the critical current value Jc per unit length in the line width direction at a distance L in the line width direction from the center position (L=0) in the line width direction in the wiring portion 3A are shown. In the present embodiment, the critical current value per unit length in the line width direction in the central band 31 is a first value Jcc, and the critical current value per unit length in the line width direction in the side band 32 is a second value Jce greater than the first value Jcc.

[0029] According to the present embodiment, the critical current value per unit length in the line width direction in the side band 32 of the wiring portion 3A is larger than the critical current value per unit length in the line width direction in the central band 31. That is, the superconductivity in the side band 32 is stronger than the superconductivity in the central band 31. Therefore, when the bias current Ib flows in the superconducting strip 3, even if the amount of bias current in the edge portion (i.e., the side band 32) of the wiring portion 3A is larger than that in the central band 31, it is difficult to cause the destruction of the superconducting state. In addition, the superconductivity in the side band 32 is strengthened, thereby suppressing the reduction of the superconductivity in the edge portion of the wiring portion 3A. In addition, the superconductivity in the side band 32 is strengthened, thereby suppressing the reduction of the superconductivity caused by the shape unevenness of the edge portion of the wiring portion 3A.

[0030] Thus, by suppressing the decrease of superconductivity in the edge portion, the occurrence of dark counts can be reduced. The reduction of dark counts can increase the line width of the wiring portion 3A or improve the temperature environment without reducing the detection performance.

[0031] Furthermore, it is possible to supply bias current Ib having a higher current value than bias current Ib supplied to superconducting strip 50 in the existing structure to central strip 31 of wiring portion 3A. Figure 2As shown, the critical current value per unit length in the line width direction in the central band 31 of the wiring portion 3A (first value Jcc) is equal to the critical current value per unit length in the line width direction of the superconducting strip 50 in the conventional structure, and the critical current value per unit length in the line width direction in the side band 32 of the wiring portion 3A (second value Jce) is configured to be a value higher than the critical current value per unit length in the line width direction of the superconducting strip 50 in the conventional structure.

[0032] At this time, Figure 2 In the graph of FIG. 1 , as indicated by the upward block arrow, when bias current Ib flows in superconducting strip 50 of the conventional structure, even if bias current Ib having a current value higher than bias current Ib (bias current having current distribution Jbo) in which dark counts are considered to be prone to occur flows, Figure 2 In the side band 32, the bias current value is unlikely to exceed the critical current value Jc per unit length in the line width direction. As a result, the bias current value in the central band 31 can be made closer to the critical current value (first value Jcc) per unit length in the line width direction compared to the conventional structure.

[0033] Since the bias current value in the central band 31 can be made close to the critical current value (first value Jcc) per unit length in the line width direction, the detection efficiency and jitter characteristics (temporal resolution) of the photons P when the photons P enter the central band 31 can be improved.

[0034] Hereinafter, a method for manufacturing superconducting strip 3 in the present embodiment will be described by way of example. Figure 3 It is a diagram showing a first example of the method for producing a superconducting strip in this embodiment. Figure 3 Each step of the present invention shows a cross-sectional view perpendicular to the direction in which the bias current flows in the formed superconducting strip 3. First, in step 1a, a wiring layer 30 having a predetermined wiring shape is formed on the substrate 2. The wiring layer 30 is formed with a uniform material to a certain film thickness. The wiring layer 30 formed in this step 1a has the same structure as the superconducting strip 50 of the conventional structure described above.

[0035] Next, in step 2a, a photomask 33 such as a photoresist is formed on both ends of the wiring portion 3Aa of the wiring layer 30 in the line width direction, and etching is performed. Etching may be either dry etching or wet etching. In step 3a, the photomask 33 is removed to form the wiring portion 3Aa of the superconducting strip 3. The portion whose film thickness is reduced by etching becomes the central strip 31, and the portion that is not etched (film thickness is not changed) by the photomask 33 becomes the side strip 32.

[0036] The wiring portion 3Aa manufactured in this way includes: a central band 31 having a first thickness D1; ​​and side bands 32 having a second thickness D2 thicker than the first thickness D1 at both ends of the central band 31 in the line width direction. The critical current density of the wiring portion 3Aa in this example is equal in both the central band 31 and the side band 32. However, the thickness of the side band 32 is greater than that of the central band 31, and thus the critical current value per unit length in the line width direction of the side band 32 is greater than that of the central band 31. That is, the superconductivity of the side band 32 is stronger than that of the central band 31.

[0037] Figure 4 It is a diagram showing a second example of the method for producing a superconducting strip in this embodiment. Figure 4 Each step of FIG. 1 also shows a cross-sectional view perpendicular to the direction in which the bias current flows in the formed superconducting strip 3. First, in step 1b, a wiring layer 30 having a predetermined wiring shape is formed on the substrate 2 in the same manner as in the first example.

[0038] Next, in step 2b, a photomask 34 such as a photoresist is formed on the central portion in the line width direction of the portion corresponding to the wiring portion 3Ab of the wiring layer 30 and on the substrate 2, and an additional layer 35 made of the same material as the wiring layer 30 is formed again thereon. In step 3b, the photomask 34 is removed to form the wiring portion 3Ab of the superconducting strip 3. The wiring portion 3Ab has the additional layer 35 remaining at both ends in the line width direction of the wiring layer 30 not covered by the photomask 34, so that the portion where the film thickness becomes thicker becomes the side band 32, and the portion where the additional layer 35 does not remain becomes the central band 31.

[0039] Similar to the first example, the wiring portion 3Aa manufactured in this example includes: a central band 31 having a first thickness D1; ​​and side bands 32 having a second thickness D2 thicker than the first thickness D1 at both ends of the central band 31 in the line width direction. The critical current density of the wiring portion 3Ab in this example is equal in both the central band 31 and the side band 32. However, the thickness of the side band 32 is greater than that of the central band 31, and thus the critical current value per unit length in the line width direction of the side band 32 is greater than that of the central band 31. That is, the superconductivity of the side band 32 is stronger than that of the central band 31.

[0040] In addition, Figure 4 In the example, the edge portion of the wiring layer 30 is formed so as not to be covered by the photomask 34. Therefore, outside the two end portions of the wiring layer 30 in the line width direction, there is a region where the additional layer 35 is formed on the substrate 2. Therefore, the side band 32 of the wiring portion 3Ab obtained by removing the photomask 34 has a region that is thinner than the second thickness D2. However, the side band 32 is formed as a whole to be thicker than the first thickness D1. By forming the additional layer 35 outside the two end portions of the wiring layer 30 in the line width direction, it is possible to suppress the Fig. 9 A to Fig. 9The degradation of superconductivity caused by the shape unevenness in the edge portion described in C.

[0041] Alternatively, the additional layer 35 may not be formed on the substrate 2 outside both ends in the line width direction of the wiring layer 30. In this case, since no step is generated on the formed side band 32, the thickness of the side band 32 can be uniformly set to the second thickness D2.

[0042] In this example, the additional layer 35 is made of the same material as the wiring layer 30, but the additional layer 35 may be made of a material having a different superconductivity from that of the wiring layer 30. In this example, the additional layer 35 is formed in contact with the wiring layer 30, but other layers such as an insulator layer may be provided between the wiring layer 30 and the additional layer 35. That is, the side band 32 may include: a first superconducting material layer having the same thickness as the central band 31; and a second superconducting material layer disposed close to the first superconducting material layer. In this case, the film thickness of the other layer between the first superconducting material layer and the second superconducting material layer is not particularly limited as long as the tunnel current flows between the first superconducting material layer and the second superconducting material layer.

[0043] Figure 5 It is a diagram showing a third example of the method for producing a superconducting strip in the present embodiment. Figure 5 Each step of the present invention also shows a cross-sectional view perpendicular to the direction in which the bias current flows in the formed superconducting strip 3. First, in step 1c, similarly to the first example, a wiring layer 30 having a predetermined wiring shape is formed on the substrate 2. In addition, the line width of the portion corresponding to the wiring portion 3Ac of the wiring layer 30 is formed to be shorter than the line width of the final wiring portion 3Ac (the line width of the central band 31).

[0044] Next, in step 2c, the portion corresponding to the side band 32 of the wiring portion 3Ac on the substrate 2 is removed to form a photomask 36, and a second material layer 37 is formed thereon. The second material layer 37 is composed of a second material having a higher critical current density than the first material constituting the wiring layer 30. In this example, the film thickness of the second material layer 37 is the same thickness as the thickness of the wiring layer 30.

[0045] In step 3c, the wiring portion 3Ac of the superconducting strip 3 is formed by removing the photomask 36. Thus, the wiring portion 3Ac in this example includes: a central band 31, which uses a first material having a first critical current density; and a side band 32, which uses a second material having a second critical current density higher than the first critical current density at both ends of the central band 31 in the line width direction. Therefore, even if the central band 31 and the side band 32 have the same film thickness, the critical current value per unit length in the line width direction is different in the central band 31 and the side band 32 due to the different critical current densities between the central band 31 and the side band 32. More specifically, the critical current value per unit length in the line width direction of the side band 32 is larger than that of the central band 31. That is, the superconductivity of the side band 32 is stronger than that of the central band 31.

[0046] The method for manufacturing the superconducting strip 3 having different critical current densities in the central band 31 and the side band 32 is not limited to the third example described above. For example, as shown in the fourth example described below, by irradiating the central portion of the wiring layer 30 in the line width direction with an ion beam or an electron beam, the wiring portion irradiated with the ion beam or the electron beam can form a central band 31 with a lower critical current density than the side band 32 not irradiated with the ion beam or the electron beam.

[0047] Figure 6 It is a diagram showing a fourth example of the method for producing a superconducting strip in the present embodiment. Figure 6 Each step of the present invention also shows a cross-sectional view perpendicular to the direction in which the bias current flows in the formed superconducting strip 3. First, in step 1d, similarly to the first example, a wiring layer 30 having a predetermined wiring shape is formed on the substrate 2. In this example, the wiring layer 30 is formed of a material whose critical current density is reduced by irradiation with an ion beam or an electron beam compared to before irradiation.

[0048] Next, in step 2d, a photomask 38 such as a photoresist is formed on both ends of the portion corresponding to the wiring portion 3Ad of the wiring layer 30 in the line width direction, and an ion beam or an electron beam is irradiated toward the surface of the wiring layer 30. In step 3d, the photomask 38 is removed to form the wiring portion 3Ad of the superconducting strip 3. The portion where the critical current density decreases due to the irradiation of the ion beam or the electron beam becomes the central band 31, and the portion that is not irradiated by the ion beam or the electron beam (the physical property is not changed) due to the photomask 33 becomes the side band 32.

[0049] The wiring portion 3Ad in this example includes: a central band 31 having a first critical current density; and side bands 32 having a second critical current density higher than the first critical current density at both ends in the line width direction of the central band 31. Thus, even if the central band 31 and the side band 32 have the same film thickness, the critical current value per unit length in the line width direction of the side band 32 is larger than that of the central band 31. That is, the superconductivity of the side band 32 is stronger than that of the central band 31.

[0050] In addition, there are also some superconducting materials used as wiring layer 30, which have a higher critical current density than before irradiation by irradiation with ion beam or electron beam. In this case, the wiring portion can also be irradiated with ion beam or electron beam at both ends in the line width direction, thereby forming side bands 32 having a critical current density different from that of the central band 31 in the central part in the line width direction that is not irradiated with ion beam or electron beam.

[0051] Furthermore, depending on the superconducting material, the critical current density of the superconducting material can be changed compared to before the irradiation by irradiating with radiation such as X-rays, alpha rays, or gamma rays.

[0052] Figure 7 It is a diagram showing a fifth example of the method for producing a superconducting strip in the present embodiment. Figure 7 Each step of FIG. 1 also shows a cross-sectional view perpendicular to the direction in which the bias current flows in the formed superconducting strip 3. First, in step 1e, a wiring layer 30 having a predetermined wiring shape is formed on the substrate 2 in the same manner as in the first example.

[0053] Next, in step 2e, a portion of the central band 31 corresponding to the wiring portion 3Ae on the wiring layer 30 is removed to form a photomask 39, and a dissimilar material layer 40 made of a non-superconducting material such as a metal or a superconducting material having a lower superconductivity than the wiring layer 30 is formed thereon. The dissimilar material layer 40 in this example is disposed in contact with or close to the wiring layer 30, and the wiring portion (central band 31) of the wiring layer 30 in contact with or close to the dissimilar material layer 40 can be made of a material having a smaller critical current value per unit length in the line width direction than the other portions (side bands 32).

[0054] In step 3e, by removing the photomask 39, the wiring portion 3Ae of the superconducting strip 3 is formed. The portion on the wiring layer 30 where the different material layer 40 is formed becomes the central band 31, and the portion where the different material layer 40 is not formed due to the photomask 39 becomes the side band 32. In the wiring portion 3Ae of this example, the central band 31 is in contact with the side band 32 through the different material layer 40, so that the critical current density is smaller than that of the side band 32. That is, the superconductivity of the side band 32 is stronger than that of the central band 31.

[0055] In addition, another layer may be formed between the different material layer 40 and the superconducting strip 3. That is, the different material layer 40 and the superconducting strip 3 may be arranged close to each other without being in contact.

[0056] Alternatively, a photomask 39 may be formed by removing the portion of the side band 32 corresponding to the wiring portion 3Ae on the wiring layer 30, and a different material layer composed of a superconducting material having a higher superconductivity than the wiring layer 30 may be formed thereon, instead of the above step 2e. In this case, the different material layer and the superconducting strip may be in contact, or another layer may be formed between the two. In this case, the different material layer is arranged in contact with or close to the wiring layer 30, and the wiring portion (side band 32) of the wiring layer 30 in contact with or close to the different material layer may be made of a material having a larger critical current value per unit length in the line width direction than the other portion (central band 31).

[0057] In this way, the wiring portion 3A of the superconducting strip 3 in which the superconductivity of the side strips 32 is higher than that of the central strip 31 can be formed by various manufacturing methods.

[0058] As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, Various improvements, changes, and corrections can be made within the range which does not deviate from the summary.

[0059] For example, in the above-mentioned embodiment, an example is shown in which the superconducting strip 3 (between the electrodes 4 and 5) is formed in a straight line, but the superconducting strip 3 may have various shapes such as a straight line, a meandering shape, and a spiral shape. For example, when the superconducting strip 3 is formed in a meandering shape, the straight line portion thereof may be configured as a wiring portion 3A including a central band 31 and a side band 32, or both the straight line portion and the curved line portion may be configured as a wiring portion 3A including a central band 31 and a side band 32. In addition, the line width of the wiring portion 3A of the superconducting strip 3 may not be constant. For example, the wiring portion 3A may have a larger line width as it approaches the electrodes 4 and 5, or may have a smaller line width as it approaches the center position between the electrodes 4 and 5. For example, the positions of both ends in the line width direction may also be formed in an arc shape.

[0060] In addition, in the above embodiment, the case where the line width of the wiring portion 3A is 10 μm or more and 15 μm or less is assumed, but it can also be applied to the wiring portion 3A having a line width of 10 μm or less or 15 μm or more, and the same effect as described in the above embodiment is achieved. Moreover, the structure of the wiring portion 3A described in the above embodiment is not limited to the SMSPD having a line width of 1 μm or more, and it can also be applied to the SNSPD having a line width of less than 1 μm, and the same effect as described in the above embodiment is achieved.

[0061] In addition, in the above-mentioned embodiment, the critical current value per unit length in the line width direction is discretely (for example, stepwise) changed at the boundary between the central band 31 and the side band 32, but the present invention is not limited thereto. For example, in the wiring portion 3A, the critical current value per unit length in the line width direction may be continuously changed from the first value Jcc to the second value Jce as it moves from the central position in the line width direction to the two end positions in the line width direction. For example, the wiring portion 3A may also have: a central band 31, whose critical current value per unit length in the line width direction is the first value Jcc; a side band 32, whose critical current value per unit length in the line width direction is the second value Jce; and a boundary portion between the central band 31 and the side band 32, where the critical current value per unit length in the line width direction approaches the second value Jce from the first value Jcc as it moves toward the outside of the line width direction. In the boundary portion, the critical current value per unit length in the line width direction may be changed in a stepwise manner or may be changed continuously.

[0062] In addition, there may be no clear boundary between the central band 31 and the side band 32. In the wiring portion 3A, the critical current value per unit length in the line width direction may be a minimum value, i.e., a first value Jcc, near the center of the line width direction, and a maximum value, i.e., a second value Jce, near both ends of the line width direction.

[0063] In addition, in the above-mentioned embodiment, as a method for manufacturing the wiring portion 3A, the first to fifth examples are shown, but these examples may be appropriately combined. For example, the central band 31 and the side bands 32 may be made of materials having different critical current densities, and the film thickness of the central band 31 and the film thickness of the side bands 32 may be different film thicknesses. In this case, as long as the critical current value per unit length in the line width direction of the side bands 32 is greater than that of the central band 31, the film thickness of the central band 31 may be greater than or less than that of the side band 32. In addition, as long as the critical current value per unit length in the line width direction of the side bands 32 is greater than that of the central band 31, the critical current density of the central band 31 may be higher than or lower than that of the side band 32.

[0064] In addition, the materials of the superconducting strip 3 and the substrate 2 are not limited to the above-mentioned embodiment, and various materials can be applied. In addition, there may be another layer or layers between the superconducting strip 3 and the substrate 2, and there may also be a structure made of the same or different material as the substrate 2.

[0065] In the above embodiment, as a superconducting strip detector applicable to the present invention, the SSPD 1 whose detection object is a single photon is exemplified, but the superconducting strip detector applicable to the present invention is not limited thereto. The structure of the superconducting strip 3 in the present invention can be applied to various superconducting strip detectors for detecting various detection objects with significant energy. The detection object includes, for example, particles such as photons (single photons, multi-photons), electrons, molecules, neutrons, and radiation, or electromagnetic waves. Radiation includes, for example, X-rays, gamma rays, alpha rays, etc.

[0066] [Public Summary] The following items disclose preferred embodiments.

[0067] [Project 1] A superconducting strip detector is a superconducting strip arranged in a detection area of ​​a detection object with significant energy. The superconducting strip is put into a superconducting state, and a bias current is passed into the superconducting strip from a specified bias current path, thereby detecting the detection object in the detection area. The superconducting strip includes a wiring portion at both ends in the line width direction, wherein the critical current value per unit length in the line width direction is larger than that in the central portion in the line width direction.

[0068] [Project 2] The superconducting strip probe according to item 1, wherein the wiring portion includes: a central strip having a first thickness; and side strips having a second thickness thicker than the first thickness at both ends of the central strip in the line width direction.

[0069] [Item 3] A superconducting strip probe according to item 1 or 2, wherein the wiring portion includes: a central strip having a first critical current density; and side strips having a second critical current density different from the first critical current density at both ends of the central strip in the line width direction.

[0070] [Item 4] The superconducting strip detector according to item 3, wherein the central strip is made of a first material having the first critical current density, and the side strips are made of a second material having the second critical current density higher than the first critical current density.

[0071] [Item 5] The superconducting strip probe according to Item 3, wherein the wiring portion is a portion irradiated with an ion beam or an electron beam in a center portion in a line width direction or at both ends in a line width direction.

[0072] [Item 6] The superconducting strip detector according to any one of items 1 to 5, wherein: The wiring portion includes: a wiring layer; and a heterogeneous material layer, which is arranged in contact with or close to the central part of the wiring layer in the line width direction and is composed of a non-superconducting material or a superconducting material with weaker superconductivity than the wiring layer; or a heterogeneous material layer is arranged in contact with or close to both end parts in the line width direction of the wiring layer and is composed of a superconducting material with stronger superconductivity than the wiring layer.

[0073] [Item 7] A manufacturing method is a manufacturing method for a superconducting strip for a superconducting strip detector, the superconducting strip detector comprising a superconducting strip arranged in a detection area of ​​a detection object having significant energy, the superconducting strip being put into a superconducting state, a bias current flowing into the superconducting strip from a prescribed bias current path, thereby detecting the detection object in the detection area, and the superconducting strip being formed into a wiring portion including a critical current value per unit length in the line width direction at both end portions in the line width direction being larger than that in the central portion in the line width direction.

[0074] Explanation of symbols: 1: Superconducting single photon detector (superconducting strip detector); 3: Superconducting strip; 3A, 3Aa, 3Ab, 3Ac, 3Ad, 3Ae: wiring part; 30: wiring layer; 31: Central belt; 32: side straps; 40: heterogeneous material layer; A: Detection area.

Claims

1. A superconducting strip detector, comprising a superconducting strip disposed in a detection region of a detection object having significant energy, wherein the superconducting strip is in a superconducting state, and a bias current is passed through the superconducting strip from a predetermined bias current path, thereby detecting the detection object in the detection region, wherein: The superconducting strip includes wiring portions at both ends in the line width direction, where the critical current value per unit length in the line width direction is larger than that in the center portion in the line width direction.

2. The superconducting strip detector according to claim 1, characterized in that: The wiring portion includes: a central band having a first thickness; and side bands having a second thickness thicker than the first thickness at both ends of the central band in a line width direction.

3. The superconducting strip detector according to claim 1 or 2, characterized in that: The wiring portion includes: a central zone having a first critical current density; and side zones having a second critical current density different from the first critical current density at both ends of the central zone in a line width direction.

4. The superconducting strip detector according to claim 3, characterized in that: The central band is formed of a first material having the first critical current density, and the side bands are formed of a second material having a second critical current density higher than the first critical current density.

5. The superconducting strip detector according to claim 3, characterized in that: The wiring portion is a portion irradiated with an ion beam or an electron beam at a center portion in a line width direction or at both ends in a line width direction.

6. The superconducting strip detector according to claim 1 or 2, characterized in that: The wiring part includes: a wiring layer; and A heterogeneous material layer, which is arranged in contact with or close to the central part of the wiring layer in the line width direction and is composed of a non-superconducting material or a superconducting material with weaker superconductivity than the wiring layer; or a heterogeneous material layer which is arranged in contact with or close to the two end parts in the line width direction of the wiring layer and is composed of a superconducting material with stronger superconductivity than the wiring layer.

7. A manufacturing method, a method for manufacturing a superconducting strip for a superconducting strip detector, the superconducting strip detector comprising a superconducting strip disposed in a detection region of a detection object having significant energy, the superconducting strip being in a superconducting state, and a bias current flowing from a predetermined bias current path into the superconducting strip, thereby detecting the detection object in the detection region, characterized in that: The superconducting strip is formed to include wiring portions in which critical current values ​​per unit length in the line width direction are larger at both end portions in the line width direction than at a center portion in the line width direction.

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