Structure for reducing area of SQUID (superconducting quantum interference device) superconducting loop and preparation method thereof

Abstract

According to the structure for reducing the area of the SQUID superconducting loop and the preparation method thereof provided by the invention, the laminated structure is formed on the silicon substrate, and then the laminated structure is accurately etched, so that the 3D nano bridge junction is formed on the slope surface of the laminated structure and stretches across the insulating layer, and therefore, batch preparation of the structure for reducing the area of the SQUID superconducting loop can be realized; according to the SQUID probe, large-scale application of the SQUID probe is more facilitated, the plane of the 3D nanometer bridge junction is perpendicular to the plane where the SQUID superconducting loop is located, so that the width of the 3D nanometer bridge junction does not influence the effective loop area of the SQUID any more, the performance of the SQUID can be improved by independently regulating and controlling the thickness of the 3D nanometer bridge junction, the inhibition effect of a magnetic field on the superconducting characteristic of the 3D nanometer bridge junction is greatly weakened, and in addition, the SQUID probe can be applied to a large scale. The SQUID superconducting loop with the minimum line width of 10nm can be prepared by combining the electron beam lithography technology with higher precision, the area of the SQUID superconducting loop can be greatly reduced, and the spin sensitivity is improved, so that higher spatial resolution can be realized during scanning magnetic imaging.

Description

Technical Field

[0001] The present invention relates to the field of superconducting quantum interference devices (SQUIDs), and particularly to a structure for reducing the area of a SQUID superconducting loop and a preparation method thereof. Background Art

[0002] With the development of spintronics and superconducting electronics, studying the direct magnetic response of materials at the microscale can reveal many properties that cannot be detected by other methods, such as the observation of the magnetization relaxation process of nanoparticles, the flux imaging in nanowires, and the flux quantization and vortex detection of superconductors. The direct-current SQUID (Superconducting quantum interference devices) composed of two parallel Josephson Junctions (JJs) is one of the most sensitive known flux sensors, and its detection sensitivity can approach the quantum limit. In micro-magnetic imaging, the SQUID probe combined with the SSM (Scanning SQUID Microscopy) composed of a high-precision three-axis scanning platform can achieve sub-micron-level flux imaging with its high magnetic field sensitivity and non-destructive readout of weak magnetic coupling.

[0003] The sensitivity and resolution of the scanning SQUID microscope are directly related to the size of the SQUID superconducting loop. Compared with the traditional micron-level SQUID superconducting loop, the SQUID probe with a nanoscale superconducting loop has a smaller loop size, higher imaging resolution, smaller flux noise, and higher spin sensitivity.

[0004] Although the nano-SQUID based on a thin-film bridge Josephson junction can easily achieve a nano-scale SQUID superconducting loop structure, such as the SQUID on Tip structure fabricated on the tip of a quartz glass tube, a magnetic imaging resolution of about 50 nm can be achieved. However, due to the contact of large-area electrodes with the same thickness at both ends of its nano-bridge junction, the superconducting phase interference will spread to the electrode position, thereby weakening the Josephson effect at the connection between the nano-bridge junction and the large-area electrode and the voltage-flux modulation performance of the SQUID. Secondly, since the plane where the nano-bridge junction thin film is located is in the same plane as the SQUID superconducting loop, the magnetic field passing through the SQUID superconducting loop suppresses the superconductivity of the nano-bridge junction, thereby reducing the maximum operating magnetic field of the SQUID probe. In addition, in terms of process preparation, the SQUID on Tip structure on the quartz tube cannot be mass-produced, which is not conducive to large-scale applications. Additionally, for the nano-SQUID probe based on a nano-bridge junction that can be mass-produced on a silicon wafer, the plane where the SQUID superconducting loop is located and the plane where the superconducting nano-bridge junction thin film is located are in the same plane, and it also faces the suppression of the magnetic field on the superconducting thin film of the nano-bridge junction. Due to the influence of the penetration depth of the superconducting thin film, the effective loop diameter of a conventional SQUID superconducting loop is mostly above 600 nm, making the effective area for the SQUID superconducting loop to capture magnetic flux much larger than the physical geometric area, resulting in limited spatial resolution of the SQUID probe.

[0005] It should be noted that the above introduction of the technical background is only for the convenience of clearly and completely explaining the technical solutions of the present application and facilitating the understanding of those skilled in the art. It cannot be simply considered that the above technical solutions are well-known to those skilled in the art just because these solutions are described in the background art part of the present application. Summary of the Invention

[0006] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a structure for reducing the area of the SQUID superconducting loop and its preparation method, which is used to solve the problems in the prior art that the maximum operating magnetic field of the SQUID probe is reduced and the effective loop diameter of the conventional SQUID superconducting loop is mostly above 600 nm due to the influence of the magnetic field on the penetration depth of the superconducting thin film, making the effective area for the SQUID superconducting loop to capture magnetic flux much larger than the physical geometric area, resulting in limited spatial resolution of the SQUID probe.

[0007] To achieve the above object and other related objects, the present invention provides a structure for reducing the area of the SQUID superconducting loop, and the structure includes:

[0008] A silicon substrate, on which a silicon dioxide thin film is formed, and on which a laminated structure in the shape of an isosceles trapezoid is formed. The laminated structure includes a first superconducting thin film layer, an insulating layer, and a second superconducting thin film layer in sequence from bottom to top. Both side walls of the laminated structure form slopes with an inclination angle θ with the silicon substrate;

[0009] A third superconducting thin film layer, which is disposed on the silicon substrate near the laminated structure, on the slope, and is connected to the first superconducting thin film layer and the second superconducting thin film layer respectively;

[0010] A 3D nano-bridge junction, which is symmetrically disposed on the slope and spans across the insulating layer. The insulating layer between the 3D nano-bridge junctions forms a SQUID superconducting loop.

[0011] Optionally, the magnitude range of the inclination angle θ is 45° to 85°.

[0012] Optionally, the geometric height of the SQUID superconducting loop is 5 - 20 nm, which is the thickness of the insulating layer structure, and the geometric width is 10 - 100 nm, which is the width of the insulating layer structure.

[0013] Optionally, the plane where the 3D nano-bridge junction is located is perpendicular to the plane where the SQUID superconducting loop is located.

[0014] Optionally, the materials of the first superconducting thin film layer, the second superconducting thin film layer, and the third superconducting thin film layer are the same.

[0015] Optionally, the widths of the first superconducting thin film layer, the insulating layer, and the second superconducting thin film layer decrease in sequence.

[0016] Optionally, the thickness of the first superconducting thin film layer is 5 - 300 nm, the thickness of the second superconducting thin film layer is 5 - 300 nm, and the thickness of the third superconducting thin film layer is 5 - 30 nm.

[0017] Optionally, the material of the insulating layer is one of SiO 2 , MgO, AlN, Al 2 O 3 , and the thickness of the insulating layer is 5 - 20 nm.

[0018] The present invention also provides a preparation method for a structure that reduces the area of the SQUID superconducting loop, including the following steps:

[0019] Provide a silicon substrate, form a silicon dioxide thin film on the silicon substrate, and then form a laminated structure on the silicon dioxide thin film. The laminated structure includes a first superconducting thin film layer, an insulating layer, and a second superconducting thin film layer deposited in sequence;

[0020] The stacked structure is exposed and etched with a reactive ion beam so that the shape of the stacked structure is an isosceles trapezoid, and the two side walls of the stacked structure form slopes with an inclination angle θ with the silicon substrate;

[0021] A third superconducting thin film layer is deposited again on the slopes and the silicon substrate near the stacked structure, and electron beam lithography technology is performed on the third superconducting thin film layer. By controlling different exposure doses, 3D nano-bridge junctions are formed on the slopes of the insulating layer. The 3D nano-bridge junctions are symmetrically arranged on the two side slopes of the stacked structure.

[0022] Optionally, the materials of the first superconducting thin film layer, the second superconducting thin film layer, and the third superconducting thin film layer include one of Nb, NbN, Al, and Pb.

[0023] As described above, a structure for reducing the area of a SQUID superconducting loop and a preparation method thereof proposed by the present invention. Compared with the prior art, the SQUID probe is prepared based on a silicon substrate and can be mass-produced, which is more conducive to large-scale applications. The thickness of the third superconducting thin film at both ends of the 3D nano-bridge junction in the SQUID probe is greater than the thickness of the 3D nano-bridge junction, further improving the performance of the SQUID probe; the plane where the 3D nano-bridge junction is located is perpendicular to the plane where the SQUID superconducting loop is located, thereby reducing the area surrounded by the magnetic field entering the superconducting thin film and reducing the effective area of the SQUID superconducting loop; the width of the 3D nano-bridge junction is no longer a factor restricting the effective area of the SQUID superconducting loop, so that the area of the SQUID superconducting loop can be adjusted by adjusting the thickness of the insulating layer, and the performance of the SQUID probe can be optimized. In addition, this method combined with electron beam lithography technology with higher etching accuracy can prepare a SQUID superconducting loop with a minimum line width of 10 nm, greatly reducing the area of the SQUID superconducting loop and improving the spin sensitivity, so that a higher spatial resolution can be achieved during scanning magnetic imaging. Brief Description of the Drawings

[0024] Figure 1 It shows a schematic diagram of the structure for reducing the area of the SQUID superconducting loop of the present invention.

[0025] Figure 2 It shows a front view of the structure for reducing the area of the SQUID superconducting loop of the present invention.

[0026] Figure 3 It shows a schematic diagram of the SQUID superconducting loop formed in the structure for reducing the area of the SQUID superconducting loop of the present invention.

[0027] Figure 4 It shows a process flow chart of the preparation method of the structure for reducing the area of the SQUID superconducting loop of the present invention.

[0028] Figure 5 It shows a schematic structural diagram in the preparation method of the structure for reducing the area of the SQUID superconducting loop of the present invention.

[0029] Element label description

[0030] 101, silicon substrate; 102, first superconducting thin film layer; 103, insulating layer; 104, second superconducting thin film layer; 105, third superconducting thin film layer; 106, 3D nanobridge junction; 107, SQUID superconducting loop; S1 - S3, steps. Detailed implementation manners

[0031] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0032] It should be noted that the diagrams provided in this embodiment only illustrate the basic concept of the present invention in a schematic manner. Therefore, only the components related to the present invention are shown in the diagrams, rather than being drawn according to the number, shape, and size of the components in actual implementation. The types, quantities, and proportions of the components in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0033] Please refer to Figures 1 to 5 . It should be known that the structures, proportions, sizes, etc. shown in the diagrams of this specification are only used to cooperate with the content disclosed in the specification for those skilled in the art to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention. Therefore, they do not have technical essence. Any modification of the structure, change of the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope that can be covered by the technical content disclosed in the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle", "first", "second", etc. cited in this specification are only for the convenience of clear narration and are not used to limit the scope for the implementation of the present invention. The change or adjustment of their relative relationships, without substantial change in the technical content, should also be regarded as the scope within which the present invention can be implemented.

[0034] As Figures 1 to 3 shown, this embodiment provides a structure for reducing the area of the SQUID superconducting loop 107, and the structure includes:

[0035] A silicon substrate 101, on which a silicon dioxide thin film is formed, and on which a laminated structure in the shape of an isosceles trapezoid is formed. The laminated structure sequentially includes a first superconducting thin film layer 102, an insulating layer 103, and a second superconducting thin film layer 104 from bottom to top. Both side walls of the laminated structure form slopes with an inclination angle θ with the silicon substrate 101;

[0036] A third superconducting thin film layer 105, which is disposed on the silicon substrate 101 near the laminated structure, on the slopes, and is respectively connected to the first superconducting thin film layer 102 and the second superconducting thin film layer 104;

[0037] A 3D nano-bridge junction 106, which is symmetrically disposed on the slopes and spans across the insulating layer 103. The insulating layer 103 between the 3D nano-bridge junctions 106 constitutes a SQUID superconducting loop 107.

[0038] In addition, the structure for reducing the area of the SQUID superconducting loop 107 proposed in this embodiment can also etch away the silicon substrate 101 corresponding to the SQUID probe in combination with deep silicon etching technology, so as to achieve precise control of the distance between the SQUID probe and the edge of the silicon chip tip. This distance can be reduced from 2 μm in the prior art to about 300 nm, improving the coupling strength between the SQUID probe and the magnetic signal, and improving the intensity and spatial resolution of the scanning imaging signal.

[0039] As Figure 2 shown, as an example, the magnitude range of the inclination angle θ is 45° to 85°. The silicon substrate 101 includes a front surface and a back surface that are oppositely disposed. A silicon dioxide thin film is formed on the front surface of the silicon substrate 101, and a laminated structure is provided on the silicon dioxide thin film. The laminated structure sequentially includes a first superconducting thin film layer 102, an insulating layer 103, and a second superconducting thin film layer 104 from bottom to top, and the widths of the first superconducting thin film layer 102, the insulating layer 103, and the second superconducting thin film layer 104 decrease in sequence, such that the laminated structure is in the shape of an isosceles trapezoid. When preparing the laminated structure, by adjusting the ratio of oxygen (O 2 ) and carbon tetrafluoride (CF 4 ) during the etching process, the inclination angle θ formed by both sides of the laminated structure with the silicon substrate 101 is ensured to meet the target requirements.

[0040] As Figure 2 and Figure 3As shown, by way of example, the geometric height of the SQUID superconducting loop 107 is 5 to 20 nm, and the geometric width is 10 to 100 nm. The 3D nanobridge junction 106 is symmetrically disposed on the slope surface and distributed across the insulating layer 103, such that the insulating layer 103 between the 3D nanobridge junctions 106 on both side walls forms the SQUID superconducting loop 107. The minimum area of the SQUID superconducting loop 107 mainly depends on the slope surface area of the insulating layer 103 under the 3D nanobridge junction 106 and the effective magnetic field penetration depth λ. Specifically, the width of the SQUID superconducting loop 107 depends on the thickness of the insulating layer 103, i.e., it is between 5 and 20 nm, and the length of the SQUID superconducting loop 107 depends on the length of the insulating layer 103, i.e., it is between 10 and 100 nm. Compared with the conventional micron-scale SQUID superconducting loop, the SQUID superconducting loop 107 formed in the present invention is at the nanoscale, greatly reducing the effective area of the SQUID superconducting loop 107, thereby improving the spin sensitivity and spatial resolution.

[0041] As Figure 1 and Figure 2 As shown, by way of example, the materials of the first superconducting thin film layer 102, the second superconducting thin film layer 104, and the third superconducting thin film layer 105 are the same. A third superconducting thin film layer 105 is also formed on the slope surfaces of both side walls of the stacked structure and on the silicon substrate 101 near the stacked structure. A 3D nanobridge junction 106 is formed in the middle of the third superconducting thin film layer 105 on the slope surface. Both ends of the 3D nanobridge junction 106 are respectively connected to the third superconducting thin film layer 105. The third superconducting thin film layer 105 on the slope surface has good electrical connection with the slope surfaces of the first superconducting thin film layer 102 and the second superconducting thin film layer 104. Specifically, the materials of the first superconducting thin film layer 102, the second superconducting thin film layer 104, and the third superconducting thin film layer 105 are selected from one of Nb, NbN, Al, and Pb. Among them, NbN has a relatively high superconducting transition temperature and critical magnetic field. The superconducting critical temperature of NbN is 10.5 to 13.2 K, and the superconducting critical temperature of Nb is 7.5 to 9.3 K. Of course, on the premise of meeting the structural performance of reducing the area of the SQUID superconducting loop 107, the materials of the first superconducting thin film layer 102, the second superconducting thin film layer 104, and the third superconducting thin film layer 105 can be selected according to actual situations, and are not limited herein.

[0042] As Figure 2As shown, by way of example, the plane where the 3D nanobridge junction 106 is located is perpendicular to the plane where the SQUID superconducting loop is located. Specifically, when the structure for reducing the area of the SQUID superconducting loop 107 is in the working mode, based on the superconducting Josephson effect and the flux quantization effect, the measurement of the changing magnetic field (stray magnetic field on the sample surface) can be realized according to its magnetic field response curve, and a plane rectangular coordinate system as shown in Figure 2 is established. During the test, the magnetic field applied to the SQUID superconducting loop 107 is distributed along the y-axis, that is, the direction of the applied magnetic field is parallel to the plane where the 3D nanobridge junction 106 is located, so that the applied magnetic field no longer perpendicularly penetrates the plane of the 3D nanobridge junction 106, which can weaken the inhibitory effect of the magnetic field on the superconducting properties of the 3D nanobridge junction 106, making it possible for this structure to work under a magnetic field above 1T.

[0043] As shown in Figure 1 and Figure 2 by way of example, the thickness of the first superconducting thin film layer 102 is 5 - 300 nm, the thickness of the second superconducting thin film layer 104 is 5 - 300 nm, and the thickness of the third superconducting thin film layer 105 is 5 - 30 nm. The thickness of the third superconducting thin film at both ends of the 3D nanobridge junction 106 in the structure for reducing the area of the SQUID superconducting loop 107 is greater than the thickness of the 3D nanobridge junction 106, which can obtain a superconducting current phase relationship closer to the sine function, thereby further improving the performance of the structure for reducing the area of the SQUID superconducting loop 107.

[0044] As shown in Figure 2 , the material of the insulating layer 103103 is one of SiO 2 , MgO, AlN or Al 2 O 3 , and the thickness of the insulating layer 103 is 5 - 20 nm. Among them, materials such as SiO 2 and MgO have the advantages of good insulation and good sidewall wrapping performance, so as to be able to reduce the penetration of superconducting materials and further reduce the effective area of the SQUID superconducting loop 107.

[0045] As shown in Figure 4 and Figure 5 by way of another example, the present invention further provides a preparation method for a structure for reducing the area of the SQUID superconducting loop 107, including the following steps:

[0046] S1: Provide a silicon substrate 101, form a silicon dioxide thin film on the silicon substrate 101, and then form a stacked structure on the silicon dioxide thin film, and the stacked structure includes a first superconducting thin film layer 102, an insulating layer 103, and a second superconducting thin film layer 104 deposited in sequence;

[0047] S2: Expose and perform reactive ion beam etching on the stacked structure so that the shape of the stacked structure is an isosceles trapezoid, and both side walls of the stacked structure form slopes with an inclination angle θ with the silicon substrate 101;

[0048] S3: Deposit and form a third superconducting thin film layer 105 again on the slopes and the silicon substrate 101 near the stacked structure, perform electron beam lithography technology on the third superconducting thin film layer 105, and form 3D nanobridge junctions 106 on the slopes of the insulating layer 103 by controlling different exposure doses. The 3D nanobridge junctions 106 are symmetrically arranged on the two side slopes of the stacked structure.

[0049] Specifically, as Figure 5 shown in a, first, a silicon dioxide thin film (not shown in the figure) is formed on the silicon substrate 101 by a deposition process, and then a first superconducting thin film layer 102 with a certain thickness is deposited on the silicon dioxide thin film. As Figure 5 shown in b and Figure 5 c, then an insulating layer 103 and a second superconducting thin film layer 104 are sequentially deposited on the first superconducting thin film layer 102 to obtain a stacked structure. The deposition process can effectively control the thickness of each thin film layer, thereby realizing the control of the effective area of the SQUID superconducting loop 107. As Figure 5 shown in d, expose and perform reactive ion beam etching on the stacked structure. By controlling the ratio of oxygen (O 2 ) and carbon tetrafluoride (CF 4 ) during the reactive ion beam etching process, the etching area on both sides of the stacked structure can be changed, so that both sides of the stacked structure can form slopes with an inclination angle θ with the silicon substrate 101.

[0050] As Figure 5 shown in e, a third superconducting thin film layer 105 is deposited and formed again on the slopes and the silicon substrate 101 by a deposition process. The third superconducting thin film layer 105 has good electrical connection with the slopes of the first superconducting thin film layer 102 and the second superconducting thin film layer 104. Then, an electron beam lithography technology with higher etching precision is used. By controlling the exposure dose, the third superconducting thin film layer 105 forms 3D nanobridge junctions 106 on the slopes of the insulating layer 103. The formed 3D nanobridge junctions 106 are symmetrically distributed on the two side slopes of the stacked structure.

[0051] As an example, the materials of the first superconducting thin film layer 102, the second superconducting thin film layer 104, and the third superconducting thin film layer 105 include one of Nb, NbN, Al, and Pb. Among them, the niobium nitride material has a relatively high superconducting transition temperature and critical magnetic field. The superconducting critical temperature of the niobium nitride material is 10.5 - 13.2 K, and the superconducting critical temperature of the niobium material is 7.5 - 9.3 K. Of course, when the structural performance of reducing the area of the SQUID superconducting loop 107 is satisfied, the materials of the first superconducting thin film layer 102, the second superconducting thin film layer 104, and the third superconducting thin film layer 105 can be selected according to the actual situation, and no limitation is made here.

[0052] In summary, for a structure for reducing the area of a SQUID superconducting loop and a preparation method thereof according to the present invention, compared with the prior art, based on forming a stacked structure on a silicon substrate, a 3D nanobridge junction can be formed on the slope of the stacked structure and span the insulating layer, thereby realizing the batch preparation of the structure for reducing the area of the SQUID superconducting loop, which is more conducive to the large-scale application of SQUID probes. In addition, the superconducting thin film thickness at both ends of the 3D nanobridge junction in the structure for reducing the area of the SQUID superconducting loop is greater than that of the 3D nanobridge junction, further improving the performance of the SQUID. The plane where the 3D nanobridge junction is located is perpendicular to the plane where the SQUID superconducting loop is located, thereby reducing the area surrounded by the magnetic field entering the superconducting thin film and reducing the effective area of the SQUID superconducting loop; the width of the 3D nanobridge junction is no longer a factor limiting the effective area of the SQUID superconducting loop, so that the area of the SQUID superconducting loop can be adjusted by adjusting the thickness of the insulating layer, realizing the optimization of the performance of the SQUID probe. In addition, combined with an electron beam lithography technology with higher precision, a SQUID superconducting loop with a minimum line width of 10 nm can be prepared, greatly reducing the area of the SQUID superconducting loop and improving the spin sensitivity, so that a higher spatial resolution can be achieved during scanning magnetic imaging.

[0053] The above embodiments merely illustrate the principles and effects of the present invention, rather than limiting the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A structure for reducing the area of ​​a SQUID superconducting loop, characterized in that: The structure comprises: A silicon substrate, a silicon dioxide film is formed on the silicon substrate, a stacked structure in an isosceles trapezoidal shape is formed on the silicon dioxide film, the stacked structure includes a first superconducting film layer, an insulating layer and a second superconducting film layer in order from bottom to top, and both side walls of the stacked structure form a slope with an inclination angle θ with the silicon substrate; a third superconducting thin film layer, the third superconducting thin film layer being disposed on the silicon substrate near the stacked structure and on the slope surface and being connected to the first superconducting thin film layer and the second superconducting thin film layer respectively; 3D nano-bridge junctions, wherein the 3D nano-bridge junctions are symmetrically arranged on the slope surface and distributed across the insulating layer, and the insulating layer between the 3D nano-bridge junctions constitutes a SQUID superconducting loop.

2. The structure according to claim 1, characterized in that: The inclination angle θ ranges from 45° to 85°.

3. The structure according to claim 1, characterized in that: The geometric height of the SQUID superconducting loop is 5 to 20 nm, and the geometric width is 10 to 100 nm.

4. The structure according to claim 1, characterized in that: The plane where the 3D nanobridge is located is perpendicular to the plane where the SQUID superconducting loop is located.

5. The structure according to claim 1, characterized in that: The first superconducting thin film layer, the second superconducting thin film layer and the third superconducting thin film layer are made of the same material.

6. The structure according to claim 1, characterized in that: The widths of the first superconducting thin film layer, the insulating layer, and the second superconducting thin film layer decrease in sequence.

7. The structure according to claim 1, characterized in that: The thickness of the first superconducting thin film layer is 5 to 300 nm, the thickness of the second superconducting thin film layer is 5 to 300 nm, and the thickness of the third superconducting thin film layer is 5 to 30 nm.

8. The structure according to any one of claims 1 to 7, characterized in that: The material of the insulating layer is one of SiO2, MgO, AlN or Al2O3, and the thickness of the insulating layer is 5 to 20 nm.

9. A method for preparing a SQUID superconducting loop area structure, characterized in that: The following steps are involved: Providing a silicon substrate, forming a silicon dioxide film on the silicon substrate, and then forming a stacked structure on the silicon dioxide film, wherein the stacked structure includes a first superconducting film layer, an insulating layer, and a second superconducting film layer deposited in sequence; Expose and perform reactive ion beam etching on the stacked structure, so that the stacked structure has an isosceles trapezoidal shape, and both side walls of the stacked structure form slopes with an inclination angle θ with the silicon substrate; A third superconducting film layer is deposited again on the slope and the silicon substrate near the stacked structure, and the third superconducting film layer is subjected to electron beam lithography technology. By controlling the difference in exposure dose, a 3D nanobridge is formed on the slope of the insulating layer. The 3D nanobridge is symmetrically arranged on the slopes on both sides of the stacked structure.

10. The preparation method according to claim 9, characterized in that: The material of the first superconducting thin film layer, the second superconducting thin film layer and the third superconducting thin film layer includes one of Nb, NbN, Al and Pb.

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