A josephson probe, method of manufacture and superconducting josephson probe microscope

Abstract

This invention relates to a Josephson probe, its fabrication method, and a superconducting Josephson probe microscope. The fabrication method includes: providing a quartz nanotip with a first, second, third, and fourth groove sequentially and equidistantly arranged on its outer circumference; aligning the first groove of the quartz nanotip with a superconducting sputtering target, with the angle θ between the axis of the quartz nanotip and the horizontal direction, and depositing a first superconducting thin film by magnetron sputtering; symmetrically flipping the quartz nanotip so that the third groove is aligned with the superconducting sputtering target, and depositing a second superconducting thin film by magnetron sputtering, forming a Josephson junction at the tip of the quartz nanotip. This invention fabricates a high-quality, ultra-wideband Josephson probe through a two-step self-calibrating thin film deposition process, and achieves effective control of the detection frequency across the entire frequency band from microwave to millimeter wave, significantly expanding the application potential of the Josephson probe microscope in high-frequency integrated circuit characterization.

Description

Technical Field

[0001] This invention relates to the field of superconducting electronics technology, specifically to Josephson probes, and more particularly to a Josephson probe, its preparation method, and a superconducting Josephson probe microscope. Background Technology

[0002] Superconducting Josephson probe microscopy (JPM) is an interdisciplinary field combining superconducting electronics, scanning probe microscopy (SPM), and quantum sensing. Its fundamental principle is to utilize the DC and AC Josephson effects of a Josephson junction (JJ) to achieve highly sensitive detection of multiple physical quantities, including nanomagnetic imaging, nanothermal imaging, and microwave near-field imaging. For a Josephson junction, the frequency range in which coherent detection can be performed is determined by the junction's characteristic frequencies, where I... c R is the superconducting critical current of the junction. n The resistance is in the normal state, and e is the electron charge (e≈1.602×10). -19 C); h is Planck's constant (6.626 × 10⁻⁶). -34 Js), the coefficient h / 2e is called the Josephson frequency-voltage coefficient. When the frequency to be measured is much higher than the characteristic frequency, the Shapiro step cannot be measured on the current-voltage (IV) characteristic curve of the probe, that is, only the amplitude can be detected but the frequency and phase cannot be detected.

[0003] The Josephson probe is the core component of the superconducting Josephson probe microscope. Its key feature is the organic combination of the Josephson junction and the nanotip, achieving a dual guarantee of detection sensitivity and spatial resolution. Essentially, the Josephson probe is a weakly connected Josephson junction fabricated at the tip of a nanotip, which is then used to detect near-field electromagnetic waves. Probes with different characteristic frequencies can be fabricated to broaden the coherent detection frequency range of the system, which is of great significance for expanding the application of the Josephson probe microscope.

[0004] CN114152902A discloses a SQUID probe based on a thin-film bridge Josephson junction and its usage method. This invention utilizes a SQUID probe combined with deep silicon etching technology to position the probe end of the device fabricated on a silicon substrate at the tip of the silicon substrate. This allows for precise control of the distance between the first SQUID and the edge of the silicon wafer tip, thereby improving the magnetic coupling strength between the SQUID and the sample surface. Furthermore, during use, the SQUID probe structure can be combined with tuning fork resonance to achieve precise tip-sample distance control, thus significantly improving the spatial resolution of the SQUID probe on the silicon substrate. In addition, by combining the first and second feedback coils integrated on the silicon substrate, multifunctional measurement of the probe can be achieved.

[0005] CN116981341A discloses a method for fabricating a superconducting Josephson probe. The method involves surface treatment of a grooved quartz capillary; laser melting to draw a grooved quartz nanoneedle tip; DC magnetron sputtering to deposit superconducting thin films on the left and right sides of the grooved quartz nanoneedle tip, respectively, to obtain the left and right electrodes of the probe; and DC magnetron sputtering to deposit a superconducting thin film on the top of the nanoneedle tip, forming two parallel microbridge-type superconducting Josephson junctions, thus completing the fabrication of the superconducting Josephson probe. This invention effectively solves the problem of difficulty in fabricating high-melting-point superconducting materials such as niobium / niobium nitride-based Josephson probes using electron beam evaporation, overcomes the limitation of poor directionality in Josephson probe fabrication by DC magnetron sputtering, and effectively reduces the difficulty of fabricating Josephson probes by DC magnetron sputtering.

[0006] In existing technologies, the three-step self-calibrating thin-film deposition process for superconducting Josephson probes makes it difficult to expand their characteristic frequencies. This is because the length and width of the weakly connected Josephson junction at the probe tip are entirely determined by the microbridges inherent in the resulting tip shape. Therefore, with unchanged coating materials and the drawing process, the probe's characteristic frequencies typically remain within a narrow range and are difficult to change significantly. Furthermore, although the characteristic frequencies can be altered by controlling the drawing process to change the size of the tip microbridges, this leads to a reduction in the probe's spatial resolution.

[0007] Therefore, there is an urgent need for a Josephson probe and its fabrication method that can achieve a wide range of characteristic frequency modulation, in order to meet the characterization requirements of integrated circuits in the millimeter-wave and even terahertz frequency bands and expand the high-frequency near-field detection applications of Josephson probe microscopes. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a Josephson probe, its fabrication method, and a superconducting Josephson probe microscope. This invention fabricates a high-quality, ultra-wideband Josephson probe through a two-step self-calibrating thin-film deposition process, achieving effective control of the detection frequency across the entire frequency band from microwave to millimeter wave, significantly expanding the application potential of the Josephson probe microscope in high-frequency integrated circuit characterization.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing a Josephson probe, the method comprising:

[0011] A quartz nanoneedle tip is provided with a first groove, a second groove, a third groove, and a fourth groove arranged equidistantly on its outer circumference along the axial direction. The first groove of the quartz nanoneedle tip is aligned with a superconducting sputtering target, and the angle between the axis of the quartz nanoneedle tip and the horizontal direction is set to θ. A first superconducting thin film is deposited by magnetron sputtering. The plane containing the surface of the superconducting sputtering target being bombarded is the horizontal direction. The nanoneedle tip is symmetrically flipped along a direction away from the superconducting sputtering target, with the midpoint of its axis as the center. A quartz nanoneedle tip is rotated so that the third trench is aligned with the superconducting sputtering target, and a second superconducting thin film is deposited by magnetron sputtering. Josephson junctions are formed at the tips of the first and second superconducting thin films at corresponding positions in the second and fourth trenches, respectively, to prepare the Josephson probe. The angle between the axis of the quartz nanoneedle tip and the horizontal direction is θ = -25° to 25°. The deposition thicknesses of the first and second superconducting thin films are each independently 20 nm to 80 nm.

[0012] This invention employs a two-step self-calibrating thin-film deposition process to fabricate a first superconducting thin film and a second superconducting thin film in the first and third trenches, respectively. The first and second superconducting thin films form a weakly connected Josephson junction at the narrowest point of the tips of the second and fourth trenches, thus producing a high-quality ultrawideband Josephson probe. By adjusting the thickness of the superconducting thin films on both sides of the Josephson probe, the tightness of the weak connection at the probe tip can be controlled, changing the size of the junction region and consequently altering the characteristic frequency of the Josephson probe. Ultimately, this achieves effective control of the Josephson probe's detection frequency across the entire frequency band from microwave to millimeter wave, significantly expanding the application potential of Josephson probe microscopy in high-frequency integrated circuit characterization.

[0013] The preparation method provided by this invention not only does not rely on an additional collimation device and does not require modification of the magnetron sputtering equipment to achieve directional plasma deposition, but also utilizes the characteristics of weak directionality and good coverage of magnetron sputtering, shortening the process flow and improving preparation efficiency.

[0014] Preferably, the tip diameter of the quartz nanoneedle is 50nm~200nm.

[0015] Preferably, the vertical distance between the axis of the quartz nanoneedle tip and the superconducting sputtering target is 40mm~60mm.

[0016] Preferably, the gas pressure of the magnetron sputtering is 1.6 mTor to 2.2 mTor.

[0017] Preferably, the magnetron sputtering power is 180W~220W.

[0018] Preferably, the deposition rates of the first and second superconducting films are each independently 0.5 nm / s to 1 nm / s.

[0019] Preferably, the superconducting sputtering target is made of any one of niobium, niobium nitride, aluminum, or lead.

[0020] Preferably, the purity of the superconducting sputtering target is above 99.99%.

[0021] Preferably, the method for preparing the quartz nanoneedle tip includes: performing laser local heating on a quartz capillary tube with four grooves evenly distributed on its outer circumference, and then pulling it apart to obtain the quartz nanoneedle tip.

[0022] Preferably, the outer diameter of the quartz capillary is 1 mm to 1.5 mm.

[0023] Preferably, the inner diameter of the quartz capillary is 0.3mm to 0.5mm.

[0024] Preferably, the depth of the trench is 0.2mm to 0.3mm.

[0025] Preferably, the width of the groove is 0.08mm to 0.12mm.

[0026] In a second aspect, the present invention provides a Josephson probe, which is prepared by the preparation method described in the first aspect.

[0027] Thirdly, the present invention provides a superconducting Josephson probe microscope, the superconducting Josephson probe microscope comprising the Josephson probe as described in the second aspect.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] This invention prepares a high-quality ultrawideband Josephson probe through a two-step self-calibrating thin film deposition process. By adjusting the thickness of the superconducting thin film on both sides of the Josephson probe, the tightness of the weak connection at the tip can be controlled, the size of the junction region can be changed, and the characteristic frequency of the Josephson probe can be changed. Ultimately, the detection frequency of the Josephson probe is effectively controlled across the entire frequency band from microwave to millimeter wave, which greatly expands the application potential of Josephson probe microscopy in high-frequency integrated circuit characterization. Attached Figure Description

[0030] Figure 1 This is a cross-sectional view of the quartz nanoneedle tip in the circumferential direction provided in Embodiment 1 of the present invention.

[0031] Figure 2 This is a process flow diagram of the preparation method of the Josephson probe provided in Embodiment 1 of the present invention.

[0032] Figure 3 This is a SEM image of the Josephson probe prepared in Example 1 of this invention.

[0033] Figure 4 This is a diagram showing the power transfer characteristics of the Josephson probe prepared in Example 1 of this invention.

[0034] Figure 5 This is a diagram showing the power transfer characteristics of the Josephson probe prepared in Example 2 of this invention.

[0035] Figure 6 This is a diagram showing the power transfer characteristics of the Josephson probe prepared in Example 3 of this invention.

[0036] Wherein, 1-first trench; 2-second trench; 3-third trench; 4-fourth trench; 5-first niobium film; 6-second niobium film. Detailed Implementation

[0037] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0038] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0039] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0040] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0041] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0042] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0043] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0044] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0045] In this invention, the terms "first aspect," "second aspect," "third aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0046] In this invention, "optional" means that something is optional, that is, it refers to either "with" or "without". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0047] In this invention, unless otherwise specified, it is assumed that the experiments are conducted at room temperature or a temperature conventionally set in the art. "Room temperature" generally refers to 4°C to 35°C, and may refer to 20°C ± 5°C. In some embodiments of this invention, room temperature refers to 20°C to 30°C.

[0048] In one specific embodiment, the present invention provides a method for preparing a Josephson probe, the method comprising:

[0049] A quartz nanoneedle tip is provided with a first groove, a second groove, a third groove, and a fourth groove equidistantly arranged on its outer circumference along the axial direction. The first groove of the quartz nanoneedle tip is aligned with a superconducting sputtering target, and the angle between the axis of the quartz nanoneedle tip and the horizontal direction is set to θ. A first superconducting thin film is deposited by magnetron sputtering. The plane containing the surface of the superconducting sputtering target being bombarded is the horizontal direction. The quartz nanoneedle tip is symmetrically rotated around the midpoint of its axis, away from the superconducting sputtering target, so that the third groove is aligned with the superconducting sputtering target. A second superconducting thin film is deposited by magnetron sputtering. The first and second superconducting thin films are located at the tip of the quartz nanoneedle tip. Josephson junctions are formed at corresponding positions in the second and fourth trenches, respectively, to prepare the Josephson probe; the angle between the axis of the quartz nanoneedle tip and the horizontal direction is θ = -25°~25°, for example, it can be -25°, -20°, -15°, -10°, -5°, 0°, 5°, 10°, 15°, 20° or 25°; the deposition thickness of the first superconducting film and the second superconducting film are each independently 20nm~80nm, for example, it can be 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm or 80nm.

[0050] This invention prepares a high-quality ultrawideband Josephson probe through a two-step self-calibrating thin film deposition process. By adjusting the thickness of the superconducting thin film on both sides of the Josephson probe, the tightness of the weak connection at the tip can be controlled, the size of the junction region can be changed, and the characteristic frequency of the Josephson probe can be changed. Ultimately, the detection frequency of the Josephson probe is effectively controlled across the entire frequency band from microwave to millimeter wave, which greatly expands the application potential of Josephson probe microscopy in high-frequency integrated circuit characterization.

[0051] In this invention, the type of plasma used in the magnetron sputtering is not particularly limited; for example, argon plasma can be used to bombard the superconducting sputtering target.

[0052] In some embodiments, the tip diameter of the quartz nanoneedle is 50nm to 200nm, for example, it can be 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 120nm, 140nm, 160nm, 180nm or 200nm.

[0053] In some embodiments, the vertical distance between the axis of the quartz nanoneedle tip and the superconducting sputtering target is 40mm to 60mm, for example, it can be 40mm, 45mm, 50mm, 55mm or 60mm.

[0054] In some embodiments, the gas pressure of the magnetron sputtering is 1.6 mTor to 2.2 mTor, for example, it can be 1.6 mTor, 1.7 mTor, 1.8 mTor, 1.9 mTor, 2 mTor, 2.1 mTor or 2.2 mTor.

[0055] In some embodiments, the magnetron sputtering power is 180W to 220W, for example, it can be 180W, 190W, 200W, 210W or 220W.

[0056] In some embodiments, the deposition rates of the first and second superconducting thin films are each independently 0.5 nm / s to 1 nm / s, for example, 0.5 nm / s, 0.6 nm / s, 0.7 nm / s, 0.8 nm / s, 0.9 nm / s or 1 nm / s.

[0057] In this invention, the characteristic frequency of forming a Josephson junction can be controlled by adjusting the deposition thickness of the superconducting thin film.

[0058] In some embodiments, the superconducting sputtering target is made of any one of niobium, niobium nitride, aluminum, or lead.

[0059] In some embodiments, the purity of the superconducting sputtering target is above 99.99%.

[0060] In some embodiments, the method for preparing the quartz nanoneedle tip includes: locally heating a quartz capillary with four grooves evenly distributed on its outer circumference using laser, and then breaking it to obtain the quartz nanoneedle tip.

[0061] In some embodiments, the outer diameter of the quartz capillary is 1 mm to 1.5 mm, for example, it can be 1 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm or 1.5 mm.

[0062] In some embodiments, the inner diameter of the quartz capillary is 0.3 mm to 0.5 mm, for example, it can be 0.3 mm, 0.35 mm, 0.4 mm, 0.45 mm or 0.5 mm.

[0063] In some embodiments, the depth of the trench is 0.2mm to 0.3mm, for example, it can be 0.2mm, 0.22mm, 0.24mm, 0.26mm, 0.28mm, or 0.3mm.

[0064] In some embodiments, the width of the groove is 0.08mm to 0.12mm, for example, it can be 0.08mm, 0.09mm, 0.1mm, 0.11mm or 0.12mm.

[0065] In another specific embodiment, the present invention provides a Josephson probe, which is prepared by the preparation method described in one of the preceding specific embodiments.

[0066] In yet another embodiment, the present invention provides a superconducting Josephson probe microscope, the superconducting Josephson probe microscope comprising the Josephson probe as described in another preceding embodiment.

[0067] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0068] Example 1

[0069] This embodiment provides a method for preparing a Josephson probe, the method comprising:

[0070] (1) A quartz capillary with an outer diameter of 1.2 mm, an inner diameter of 0.4 mm, and four grooves of 0.25 mm depth and 0.1 mm width evenly distributed along the axial direction on its outer circumference is subjected to laser local heating and rapid breakage to obtain a quartz nanoneedle tip with a tip diameter of 100 nm. Figure 1 A cross-sectional view of the quartz nanoneedle tip in the circumferential direction shows that the outer circumference of the quartz nanoneedle tip is provided with a first groove 1, a second groove 2, a third groove and a fourth groove 4 at equal intervals.

[0071] We provide niobium targets with a purity of 99.99%.

[0072] (2) such as Figure 2 The flowchart shown illustrates the following steps: with the plane containing the surface of the niobium target being bombarded as the horizontal direction, the first groove 1 of the quartz nanoneedle tip is aligned with the niobium target, and the angle between the axis of the quartz nanoneedle tip and the horizontal direction is 0°. The vertical distance between the axis of the quartz nanoneedle tip and the niobium target is adjusted to 50 mm. The magnetron sputtering pressure is set to 1.9 mTor, the magnetron sputtering power is set to 200 W, and the first niobium film 5 is deposited by magnetron sputtering at a deposition rate of 0.7 nm / s and a deposition thickness of 40 nm.

[0073] (3) With the midpoint of the axis of the quartz nanoneedle tip as the center, symmetrically flip the quartz nanoneedle tip away from the niobium target so that the third groove 3 is directly opposite the niobium target. Use the same process as in step (2) to magnetron sputter and deposit a second niobium film 6 with a thickness of 30 nm. The first niobium film 5 and the second niobium film 6 form Josephson junctions at the tip of the quartz nanoneedle tip at the corresponding positions of the second groove 2 and the fourth groove 4, respectively, to prepare the Josephson probe. Figure 3 This is a SEM image of the Josephson probe.

[0074] Example 2

[0075] This embodiment provides a method for preparing a Josephson probe, the method comprising:

[0076] (1) A quartz capillary with an outer diameter of 1 mm, an inner diameter of 0.3 mm, and four grooves with a depth of 0.2 mm and a width of 0.08 mm are equidistantly distributed along the axial direction on the outer circumference. The capillary is subjected to laser local heating and rapid breakage to obtain a quartz nanoneedle tip with a tip diameter of 50 nm and four grooves (first, second, third, and fourth) equidistantly arranged on the outer circumference.

[0077] We provide lead and palladium with a purity of 99.99%.

[0078] (2) With the plane where the lead-palladium surface is bombarded as the horizontal direction, the first groove of the quartz nanoneedle tip is aligned with the lead-palladium, and the angle between the axis of the quartz nanoneedle tip and the horizontal direction is -10°. The vertical distance between the axis of the quartz nanoneedle tip and the lead-palladium is adjusted to 40 mm. The gas pressure of magnetron sputtering is set to 1.6 mTor, the power of magnetron sputtering is 180 W, and the first lead film is deposited by magnetron sputtering at a deposition rate of 0.5 nm / s and a deposition thickness of 20 nm.

[0079] (3) Taking the midpoint of the axis of the quartz nanoneedle tip as the center, symmetrically flip the quartz nanoneedle tip in the direction away from the superconducting sputtering target so that the third groove is directly opposite the superconducting sputtering target. The same process as step (2) is used to magnetron sputter and deposit a second lead film with a thickness of 20 nm. The first lead film and the second lead film form Josephson junctions at the tip of the quartz nanoneedle tip at the corresponding positions of the second groove 2 and the fourth groove 4, respectively, to prepare the Josephson probe.

[0080] Example 3

[0081] This embodiment provides a method for preparing a Josephson probe, the method comprising:

[0082] (1) A quartz capillary with an outer diameter of 1.5 mm, an inner diameter of 0.5 mm, and four grooves with a depth of 0.3 mm and a width of 0.12 mm are equidistantly distributed along the axial direction on the outer circumference. The capillary is subjected to laser local heating and rapid breakage to obtain a quartz nanoneedle tip with a tip diameter of 200 nm and four grooves (first, second, third, and fourth) equidistantly arranged on the outer circumference.

[0083] We provide niobium nitride targets with a purity of 99.99%.

[0084] (2) With the plane of the niobium nitride target being bombarded as the horizontal direction, the first groove of the quartz nanoneedle tip is aligned with the niobium nitride target, and the angle between the axis of the quartz nanoneedle tip and the horizontal direction is 25°. The vertical distance between the axis of the quartz nanoneedle tip and the niobium nitride target is adjusted to 60 mm. The gas pressure of magnetron sputtering is set to 2.2 mTor, the power of magnetron sputtering is set to 220 W, and the first niobium nitride film is deposited by magnetron sputtering at a deposition rate of 1 nm / s and a deposition thickness of 80 nm.

[0085] (3) With the midpoint of the axis of the quartz nanoneedle tip as the center, the quartz nanoneedle tip is symmetrically flipped in the direction away from the niobium nitride target so that the third groove is facing the niobium nitride target. The same process as step (2) is used to magnetron sputter and deposit a second niobium nitride film with a thickness of 80 nm. The first niobium nitride film and the second niobium nitride film form Josephson junctions at the tip of the quartz nanoneedle tip at the corresponding positions of the second groove 2 and the fourth groove 4, respectively, to prepare the Josephson probe.

[0086] Comparative Example 1

[0087] This comparative example provides a method for preparing a Josephson probe, the method comprising:

[0088] (1) Same as step (1) in Example 1.

[0089] (2) Except for adjusting the axis of the quartz nanoneedle tip prepared in step (1) to be at a 30° angle with the horizontal direction, the rest are the same as in Example 1;

[0090] (3) Same as step (3) in Example 1;

[0091] (4) With the tip of the quartz nanoneedle obtained in step (3) facing the superconducting sputtering target, a superconducting thin film with a thickness of 20 nm is sputtered on the tip using the same magnetron sputtering process as in steps (2) and (3) to prepare the Josephson probe.

[0092] Comparative Example 2

[0093] This comparative example provides a method for preparing a Josephson probe. Except for the deposition thickness of the first niobium film and the second niobium film in steps (2) and (3) being 15 nm, the preparation method is the same as in Example 1.

[0094] Comparative Example 3

[0095] This comparison provides a method for preparing a Josephson probe. Except for the deposition thickness of the first niobium film and the second niobium film in steps (2) and (3) being 85 nm, the preparation method is the same as in Example 1.

[0096] Performance testing:

[0097] The IV curves of the Josephson probes prepared in all the above embodiments and comparative examples were tested. The critical current, normal-state resistance, and characteristic frequency were measured. The test results are shown in Table 1. The transport characteristic diagrams of the Josephson probes prepared in Examples 1 to 3 are shown in Table 1. Figure 4 , Figure 5 and Figure 6 As shown.

[0098] Table 1

[0099]

[0100] In summary, this invention prepares a high-quality ultrawideband Josephson probe through a two-step self-calibrating thin film deposition process. By adjusting the thickness of the superconducting thin film on both sides of the Josephson probe, the tightness of the weak connection at the probe tip can be controlled, the size of the junction region can be changed, and thus the characteristic frequency of the Josephson probe can be changed. Ultimately, the detection frequency of the Josephson probe is effectively controlled across the entire frequency band from microwave to millimeter wave, greatly expanding the application potential of Josephson probe microscopy in high-frequency integrated circuit characterization.

[0101] Based on the test results of Example 1 and Comparative Example 1, compared with the traditional three-step preparation process, the preparation method provided by the present invention can form a Josephson junction in only two steps, and can also effectively control the detection frequency of the Josephson probe across the entire frequency band from microwave to millimeter wave.

[0102] According to the test results of Example 1, Comparative Examples 2 and 3, if the thickness of the first superconducting film and the second superconducting film is too small, the wave functions of the superconductors on both sides cannot generate a superposition region, which leads to the superconducting Cooper pair being difficult to tunnel through and only exhibiting ordinary resistance characteristics without a characteristic frequency; if the thickness of the first superconducting film and the second superconducting film is too large, due to the excessively strong superconducting characteristics of the tip microbridge, a Josephson junction in the form of a weak connection cannot be formed, and there is also no characteristic frequency.

[0103] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a Josephson probe, characterized in that, The preparation method includes: A quartz nanoneedle tip is provided with a first groove, a second groove, a third groove and a fourth groove arranged at equal intervals on the outer circumference along the axial direction; The first groove of the quartz nanoneedle tip is aligned with the superconducting sputtering target, and the angle between the axis of the quartz nanoneedle tip and the horizontal direction is set to θ. The first superconducting thin film is deposited by magnetron sputtering. The plane on which the surface of the superconducting sputtering target is bombarded is the horizontal direction. Centered on the midpoint of the axis of the quartz nanoneedle tip, the quartz nanoneedle tip is symmetrically flipped in a direction away from the superconducting sputtering target so that the third groove is directly opposite the superconducting sputtering target, and the second superconducting thin film is deposited by magnetron sputtering. Josephson junctions are formed at the tips of the first and second superconducting films at the corresponding positions of the second and fourth trenches, respectively, to prepare the Josephson probe. The angle between the axis of the quartz nanoneedle tip and the horizontal direction is θ = -25°~25°; The deposition thickness of the first superconducting thin film and the second superconducting thin film are each independently 20 nm to 80 nm.

2. The preparation method according to claim 1, characterized in that, The tip diameter of the quartz nanoneedle is 50nm~200nm.

3. The preparation method according to claim 1, characterized in that, The vertical distance between the axis of the quartz nanoneedle tip and the superconducting sputtering target is 40mm~60mm.

4. The preparation method according to claim 1, characterized in that, The gas pressure for the magnetron sputtering is 1.6 mTor to 2.2 mTor; And / or, the power of the magnetron sputtering is 180W~220W.

5. The preparation method according to claim 1, characterized in that, The deposition rates of the first and second superconducting films are each independently 0.5 nm / s to 1 nm / s.

6. The preparation method according to claim 1, characterized in that, The superconducting sputtering target is made of any one of niobium, niobium nitride, aluminum, or lead. And / or, the purity of the superconducting sputtering target is above 99.99%.

7. The preparation method according to claim 1, characterized in that, The method for preparing the quartz nanoneedle tip includes: A quartz capillary with four grooves evenly distributed on its outer circumference is locally heated by laser and pulled apart to obtain the quartz nanoneedle tip.

8. The preparation method according to claim 7, characterized in that, The outer diameter of the quartz capillary is 1mm to 1.5mm; And / or, the inner diameter of the quartz capillary is 0.3mm~0.5mm; And / or, the depth of the trench is 0.2mm~0.3mm; And / or, the width of the groove is 0.08mm to 0.12mm.

9. A Josephson probe, characterized in that, The Josephson probe is prepared by the preparation method according to any one of claims 1 to 8.

10. A superconducting Josephson probe microscope, characterized in that, The superconducting Josephson probe microscope includes the Josephson probe as described in claim 9.

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