Method for regulating and controlling current density of superconducting micron wire

Abstract

According to the method for regulating and controlling the current density of the superconducting micron wire, the hole shape with a certain size is designed in the linear area of the winding superconducting micron wire, so that the current density of the superconducting micron wire is redistributed, the current density at the corner of the winding superconducting micron wire is reduced, and the current crowding effect of the superconducting micron wire is effectively relieved. According to the current density regulation and control method, the superconducting micron wire is allowed to work under higher overall bias current without causing too high dark counting, so that the photon counting rate upper limit of the detector is improved. According to the invention, the detection efficiency of the superconducting micron wire can be improved, dark counting and time jitter are reduced, the structure is simple, the current density is flexible to regulate and control, meanwhile, the device is easy to expand to the development of a large photosensitive area detector, and the device has a wide application prospect in the fields of quantum communication, bioluminescence imaging, dark substance detection and the like.

Description

Technical Field

[0001] This invention relates to the field of photoelectric detection technology, and more specifically to a method for controlling the current density of superconducting micrometer wires. Background Technology

[0002] Since their development in the early 21st century, superconducting nanowire single-photon detectors (SNSPDs) have become core devices for quantum communication, lidar, and deep space exploration due to their high detection efficiency (>90%), low dark count rate (<0.1Hz), and low timing jitter (~3ps) in the near-infrared band. Recent research has found that superconducting microwire single-photon detectors (SMSPDs) can achieve a larger photosensitive area (>1mm) while maintaining single-photon sensitivity response. 2 The characteristics of the superconducting microwire provide new pathways for low-background applications such as dark matter detection, biological fluorescence imaging, and astronomical spectroscopy. The ability of the SMSPD to detect single photons mainly relies on the superconducting microwire. When the bias current of the superconducting microwire approaches the critical current, the photon energy is incident on the superconducting microwire and absorbed by it, forming a hot spot on the superconducting microwire. This suppresses the local superconducting bandgap, and the current accumulates at the edge of the hot spot until it exceeds the critical current density, forming a resistive state and generating a transient voltage pulse, thereby realizing single-photon detection.

[0003] The geometry of SMSPDs is typically a meandering superconducting microwire. However, this structure exhibits uneven current density distribution. At the bends, the current density is higher due to different current paths, a phenomenon known as current congestion. This effect is more pronounced with large duty cycles in the superconducting microwire. Because of the higher current density at these bends, SMSPDs are prone to thermal or quantum fluctuations, triggering dark counting of non-photons. Simultaneously, in regions with lower current density, the superconducting microwire is less sensitive to photons, leading to a decrease in the overall detection efficiency of the SMSPD.

[0004] Therefore, how to alleviate the current congestion effect at the winding corners of superconducting microwires and achieve flexible control of the current density of superconducting microwires is one of the problems that urgently need to be solved by those skilled in the art. Summary of the Invention

[0005] Purpose of the invention: In order to solve the current congestion effect caused by the meandering superconducting microwire structure in SMSPD, and the problems of reduced detection efficiency and increased dark count caused by the current congestion effect, this invention proposes a method for controlling the current density of superconducting microwires.

[0006] Technical solution: To achieve the above objective, the present invention provides a method for controlling the current density of a superconducting microwire, characterized in that the superconducting microwire comprises two layers, the first layer being a substrate and the second layer being a superconducting thin film.

[0007] Furthermore, a meandering superconducting microwire structure is designed on the surface of the second superconducting thin film, and a hole shape of a certain size is designed in the straight region of the meandering superconducting microwire. The hole shapes are arranged in an array. Through micro-nano fabrication process, a meandering superconducting microwire structure with current density control function can be obtained.

[0008] Furthermore, the substrate provides a stable growth surface for the superconducting thin film, serving as a physical support.

[0009] Furthermore, the substrate includes one of a silicon oxide substrate, a magnesium oxide substrate, and a magnesium fluoride substrate.

[0010] Furthermore, the thickness of the substrate can be, but is not limited to, 300 μm to 800 μm.

[0011] Furthermore, the superconducting thin film, as a carrier of energy absorption and superconducting state destruction, can convert photon energy into quasiparticles, triggering the transition from the superconducting state to the normal state, and then outputting an electrical signal through a change in resistance.

[0012] Furthermore, the superconducting thin film includes one of NbN thin film, MoSi thin film, WSi thin film, Nb thin film, and NbTiN thin film.

[0013] Furthermore, the thickness of the superconducting thin film can be, but is not limited to, 2 nm to 20 nm.

[0014] Furthermore, the superconducting microwire is a meandering superconducting microwire with a certain linewidth and duty cycle designed on the surface of the superconducting thin film, and a hole shape with a certain size is designed in the straight area of ​​the superconducting microwire, and the hole shape is arranged in an array.

[0015] Furthermore, the micro / nano fabrication process includes electron beam lithography, reactive ion etching, and stripping processes.

[0016] Furthermore, the linewidth of the meandering superconducting micrometer wire can be, but is not limited to, 1 μm to 10 μm, and the duty cycle can be, but is not limited to, 0.3 to 0.8.

[0017] Furthermore, the shape of the hole includes one of the following: a round hole, an elliptical hole, and a teardrop hole.

[0018] Furthermore, the lateral width of the hole shape is 0.05 to 0.8 times the width of the superconducting micron line.

[0019] Furthermore, the hole shapes are arranged in an array, wherein the array length can be, but is not limited to, 1μm to 500μm, and the array width can be, but is not limited to, 0.2μm to 6μm.

[0020] As described above, the method for controlling the current density of superconducting microwires according to the present invention has the following advantages. Results: First, it effectively suppresses the current congestion effect. By designing the shape of holes in the meandering superconducting microwire, the current accumulation at the bends of the superconducting microwire is directionally diverted, significantly reducing its current density and eliminating non-photon dark counting triggered by thermal or quantum fluctuations. Second, it eliminates the low-photon response blind zone through spatial redistribution of current density, improving the uniformity of photon detection by the superconducting microwire and thus increasing the overall detection efficiency of the detector. Third, this current density modulation method is compatible with existing micro-nano processes, applicable to various superconducting thin films, and has a high yield. It is easy to extend to large-area superconducting microwire single-photon detectors, providing reliable technical support for low-noise single-photon detection applications. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structural framework for superconducting microwire current density modulation provided by the present invention; Figure 2 Is Figure 1 A magnified schematic diagram of superconducting microwires arranged in an array with circular holes, based on the original design. Figure 3 This is a current density distribution diagram of a non-porous superconducting microwire simulated using COMSOL finite element software. Figure 4 This is a current density distribution diagram of a superconducting microwire with a circular hole diameter of 100 nm simulated using COMSOL finite element software. Figure 5 This is a current density distribution diagram of a meandering superconducting microwire with a circular hole diameter of 200 nm simulated using COMSOL finite element software. Figure 6 This is a current density distribution diagram of a meandering superconducting microwire with a circular hole diameter of 300 nm simulated using COMSOL finite element software. Figure 7 This is a current density distribution diagram of a meandering superconducting microwire with a circular hole diameter of 400 nm simulated using COMSOL finite element software. Figure 8 This is a current density distribution diagram of a meandering superconducting microwire with a circular hole diameter of 500 nm, simulated using COMSOL finite element software. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0023] This invention discloses a method for controlling the current density of a superconducting microwire. The superconducting microwire comprises two layers: a first layer is a substrate 1, and a second layer is a superconducting thin film 2, as shown below. Figure 1 As shown; wherein, a meandering superconducting microwire structure 3 is designed on the surface of the second superconducting thin film 2, and a hole shape 4 of a certain size is designed in the straight region of the meandering superconducting microwire. The hole shapes are arranged in an array, such as... Figure 2 As shown, a meandering superconducting microwire structure with current density control function can be obtained through micro-nano fabrication processes.

[0024] As an example, substrate 1 can be, but is not limited to, one of silicon oxide substrate, magnesium oxide substrate, and magnesium fluoride substrate; the thickness of substrate 1 can be, but is not limited to, 300μm to 800μm, and can be selected according to requirements. Preferably, in this embodiment, the substrate 1 is a commonly used silicon oxide substrate, and the thickness of substrate 1 is 500μm.

[0025] As an example, the superconducting thin film 2 can be, but is not limited to, one of NbN thin film, MoSi thin film, WSi thin film, Nb thin film, and NbTiN thin film, and the specific type can be selected according to the preparation process. The thickness of the superconducting thin film 2 can be, but is not limited to, 2 nm to 10 nm, and can be determined according to the actual design requirements. Preferably, in this embodiment, the superconducting thin film 2 is a MoSi thin film, and the thickness of the superconducting thin film 2 is 6 nm.

[0026] As an example, the linewidth of the meandering superconducting microwire can be, but is not limited to, 1 μm to 10 μm, and the duty cycle of the meandering superconducting microwire can be, but is not limited to, 0.3 to 0.8. Specifically, in this embodiment, the linewidth of the meandering superconducting microwire is 1 μm, and the duty cycle of the meandering superconducting microwire is 0.5.

[0027] As an example, the hole shape can be, but is not limited to, one of a circular hole, an elliptical hole, or a teardrop hole. Designing a hole shape of a certain size in the straight area of ​​the meandering superconducting micrometer wire mainly serves to redistribute the current density and alleviate the current congestion effect at the bends. Specifically, in this embodiment, the hole shape is a circular hole.

[0028] As an example, the lateral width of the hole shape can be, but is not limited to, 0.05 to 0.8 times the width of the superconducting micrometer line. Specifically, in this embodiment, the diameter of the circular hole shape is selected as 100 nm to 600 nm.

[0029] As an example, the holes are arranged in an array, wherein the array length can be, but is not limited to, 1μm to 500μm, and the array width can be, but is not limited to, 0.2μm to 6μm. Specifically, in this embodiment, the array length is 300μm and the array width is 2μm.

[0030] To fully illustrate the superior performance of this embodiment, a superconducting microwire electromagnetic-thermal coupling model was established using COMSOL finite element software to analyze the current density distribution of the superconducting microwire. Figure 3 The image shows the current density distribution of a hole-free, meandering superconducting microwire simulated using COMSOL finite element software. Significant current accumulation occurs at the bends, with a peak current density reaching 2.14 × 10⁻⁶. 11 A / m 2 This confirms that the spatial inhomogeneity of superconducting microwires is caused by their geometric structure. Figures 4-8 The figures show the current density distribution of meandering superconducting microwires with apertures of 100 nm, 200 nm, 300 nm, 400 nm, and 500 nm, respectively. It can be observed that the increase in aperture size is negatively correlated with the current density at the bends, indicating that the introduction of a circular aperture shape into the meandering superconducting microwire can alleviate the current density aggregation at the bends. Figure 7 and Figure 8 As shown, when the aperture is greater than or equal to 400 nm, the extreme point of current density shifts from the bend to the edge of the circular hole. This phenomenon will cause the risk of local bandgap suppression in superconducting microwires. Therefore, 300 nm is defined as the aperture design threshold. The establishment of this critical value provides a theoretical basis for the optimization of the core parameters of this invention.

[0031] In summary, this invention utilizes the shape of the aperture to flexibly control the current density of superconducting microwires. Different aperture shapes and corresponding sizes can be designed according to specific application requirements to alleviate the current congestion effect caused by the meandering geometry of superconducting microwires. The method of controlling the current density of superconducting microwires in this invention is ingenious and easy to fabricate using micro-nano technology, providing new ideas for developing new structures and functions of superconducting microwire single-photon detectors.

[0032] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Those skilled in the art will understand that implementing all or part of the processes of the above embodiments, and making equivalent changes according to the claims of this application, still falls within the scope of this application.

Claims

1. A method for controlling the current density of a superconducting micron-wire, characterized in that, The superconducting microwire consists of two layers: a substrate and a superconducting thin film. A meandering superconducting microwire structure is designed on the surface of the second superconducting thin film, and holes of a certain size are designed in the straight regions of the meandering superconducting microwire. The holes are arranged in an array. Through micro-nano fabrication processes, a meandering superconducting microwire structure with current density control function can be obtained.

2. The method for controlling the current density of a superconducting microwire according to claim 1, characterized in that, The substrate provides a stable growth surface for the superconducting thin film and plays a physical support role. The substrate includes one of silicon oxide substrate, magnesium oxide substrate and magnesium fluoride substrate, and the thickness of the substrate can be, but is not limited to, 300μm to 800μm.

3. The method for controlling the current density of a superconducting microwire according to claim 1, characterized in that, The superconducting thin film, acting as a carrier for energy absorption and superconducting state destruction, can convert photon energy into quasiparticles, triggering the transition from the superconducting state to the normal state, and then outputting an electrical signal through a change in resistance.

4. The method for controlling the current density of a superconducting microwire according to claim 1, characterized in that, The superconducting thin film includes one of NbN thin film, MoSi thin film, WSi thin film, Nb thin film, and NbTiN thin film, and the thickness of the superconducting thin film can be, but is not limited to, 2 nm to 20 nm mm.

5. The method for controlling the current density of a superconducting microwire according to claim 1, characterized in that, The superconducting microwires are meandering superconducting microwires with a certain linewidth and duty cycle designed on the surface of a superconducting thin film, and holes of a certain size are designed in the straight regions of the superconducting microwires, with the holes arranged in an array.

6. The method for controlling the current density of a superconducting microwire according to claim 1, characterized in that, The micro / nano fabrication process includes electron beam lithography, reactive ion etching, and stripping.

7. The method for controlling the current density of a superconducting microwire according to claim 5, characterized in that, The linewidth of the meandering superconducting microwire can be, but is not limited to, 1 μm to 10 μm, and the duty cycle can be, but is not limited to, 0.3 to 0.

8.

8. The method for controlling the current density of a superconducting micron-wire according to claim 5, characterized in that, The hole shape includes one of the following: round hole, elliptical hole, and teardrop hole.

9. The method for controlling the current density of a superconducting microwire according to claim 5, characterized in that, The lateral width of the hole shape is 0.05 to 0.8 times the width of the superconducting micrometer line.

10. The method for controlling the current density of a superconducting microwire according to claim 5, characterized in that, The holes are arranged in an array, wherein the array length can be, but is not limited to, 1μm to 500μm, and the array width can be, but is not limited to, 0.2μm to 6μm.

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