Josephson probe working temperature control method and method for regulating Nb film thickness

Abstract

The application discloses a Josephson probe working temperature control method and a Nb film thickness regulation method, the working temperature of the probe is controlled by regulating the film thickness parameter, the working temperature of the Nb-based probe is increased to 7.2 K, and the highest record of the same kind of probe is created. The Nb film thickness regulation method of the application selects a four-slot quartz tube as a substrate, after ultrasonic cleaning, a nanometer needle tip is drawn by using a laser heating method, so that a needle tip structure with a clean surface and a controllable geometric structure is obtained; the prepared nanometer needle tip is horizontally fixed on a probe support, a niobium thin film is deposited by using a magnetron sputtering process, the Nb film thickness is controlled, and a Josephson probe is prepared. The application significantly reduces the dependence of the probe on an extremely low temperature environment, breaks the original process limitation, effectively widens the available film thickness range, significantly improves the preparation yield and performance consistency of the probe, and provides a reliable device basis for the practical development of near-field microwave imaging and quantum sensing technology.

Description

Technical Field

[0001] This invention belongs to the field of Josephson probe technology, specifically relating to a method for controlling the operating temperature of a Josephson probe and a method for regulating the thickness of an Nb film. Background Technology

[0002] Microwave technology, based on the precise generation, manipulation, and measurement of microwave signals, plays a crucial role in numerous fields such as microwave integrated circuits, circuit quantum electrodynamics, microwave photonics, and spintronics. Performance improvements in these devices often depend on in-depth exploration of nanoscale microwave materials and a deeper understanding of their working mechanisms. Simultaneously, with increasing integration density, planar microcircuits place higher demands on efficient microwave transmission, but electromagnetic compatibility issues and signal crosstalk also become more prominent. To optimize system performance, the need for precise detection of the near-field distribution of microwave devices is increasingly urgent. This will not only help reveal the physical mechanisms of microwave-material interactions but also provide crucial evidence for improving signal coupling efficiency.

[0003] Traditional on-chip Josephson junctions are difficult to get close to the device under test under extreme conditions, which limits their near-field detection capabilities.

[0004] A Josephson junction is a structure consisting of two superconductors separated by a thin insulator or a normal metal layer. As a core component in superconducting electronics, it forms a weakly coupled system, allowing Cooper pairs to tunnel across the potential barrier via quantum tunneling. This junction exhibits highly nonlinear current characteristics and can be used as a mixer, with sensitivity approaching the quantum noise limit. Furthermore, when operating at frequencies exceeding its characteristic frequency, the Josephson junction can be used as a calorimeter, exhibiting extremely high sensitivity to microwave signals, even capable of detecting single microwave photons.

[0005] Traditional methods for fabricating probes, such as directional electron beam evaporation or focused ion beam milling, are typically used to create nanoscale SQUIDs. Another approach involves a specially designed collimated sputtering system to fabricate MoRe alloy probes. In traditional probe fabrication processes, the probe needs to be removed from a vacuum environment and flipped, a process with the following key problems: First, when the probe is exposed to the atmosphere, its surface comes into contact with oxygen and forms an oxide layer; second, during manual flipping, the probe tip structure is extremely fragile, and even minor mechanical stress can cause it to break, leading to experimental failure. This oxide layer can not only affect the final performance of the probe but also hinder the formation of a Josephson junction at the tip during subsequent coating processes, thus severely impacting the probe's testing performance and experimental success rate. These process defects significantly limit the success rate of probe fabrication and the reproducibility of device performance. Summary of the Invention

[0006] The technical problem solved by this invention is to provide a method for controlling the operating temperature of a Josephson probe and a method for regulating the thickness of an Nb film.

[0007] Technical Solution: To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A method for controlling the operating temperature of a Josephson probe, which controls the operating temperature range of the Josephson probe by precisely adjusting the Nb film thickness.

[0009] Furthermore, the probe's operating temperature range exhibits a clear film thickness dependence; by preparing probe samples with different film thicknesses and combining them with the system's electrical characterization, a quantitative relationship between film thickness and operating temperature range was established.

[0010] Furthermore, microwave signals of fixed frequency and different power are applied to the probe at different temperatures to determine whether the probe exhibits a Shapiro step and whether a weak junction is formed.

[0011] Furthermore, at temperatures below 4.7 K, the superconductivity of the barrier layer is too strong, hindering the formation of weak junctions and causing the probe to exhibit the characteristics of ordinary superconducting thin films; while at temperatures above 7.5 K, the superconductivity of the barrier layer weakens to the point of disappearing, and the probe instead exhibits resistive characteristics; the probe does not form weak junctions below 4.7 K and above 7.5 K.

[0012] Furthermore, the probe exhibits typical weak junction behavior within the temperature range of 4.4–6.0 K. I - V The Shapiro step appearing in the curve conforms to the AC Josephson effect; the highest operating temperature of the Nb-based Josephson probe reaches 7.2 K; under the condition of 7.2 K, when microwave signals of 5 GHz, -11 dBm and 5.5 GHz, 0 dBm are applied, the superconducting transition temperature of the Shapiro step tip junction region is clearly observed to be 7.2 K, while the overall superconducting transition temperature of the Nb film is 8.6 K.

[0013] Furthermore, the criterion for determining the probe's operating temperature range is: the lower limit is determined by the temperature variation. I - V The new voltage jump in the curve is determined, with the upper limit determined by the superconducting transition temperature of the needle-head junction. T c0 Decide.

[0014] A method for controlling the thickness of a Nb film includes:

[0015] S1: A four-groove quartz tube is selected as the substrate. After ultrasonic cleaning, the nano-needle tip is drawn by laser heating to obtain a needle tip structure with a clean surface and controllable geometry.

[0016] S2: The prepared nanoneedle tip is horizontally fixed on the probe holder, and a niobium thin film is deposited using a magnetron sputtering process.

[0017] Furthermore, after completing the deposition of one side electrode, the probe is transferred to the in-situ flipping system via a vacuum transfer system and flipped 180° in a vacuum environment. Then, the other side electrode is deposited with the same parameters to ensure the symmetry of the two electrodes.

[0018] Furthermore, the thickness of the Nb film was adjusted to be 40 nm-80 nm.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0020] (1) The performance of traditional Nb-based Josephson probes is limited by the thickness of the Nb film, and their maximum operating temperature has long been restricted to below 5K, making it difficult to meet the testing requirements of special samples. In order to promote the practical application of the device, this invention is committed to systematically studying the relationship between film thickness and operating temperature range, aiming to achieve a significant improvement in operating temperature and simultaneous optimization of process stability.

[0021] (2) By optimizing the film thickness parameters, this invention successfully raised the operating temperature of the Nb-based probe to 7.2K, setting a new record for similar probes. This breakthrough significantly reduced the probe's dependence on extremely low temperature environments, broke through the original process limitations, effectively broadened the range of usable film thicknesses, and significantly improved the probe's fabrication yield and performance consistency, providing a reliable device foundation for the practical development of near-field microwave imaging and quantum sensing technologies. Attached Figure Description

[0022] Figure 1 (a) is a flowchart of the two-step self-calibrated thin film deposition process for preparing Nb-based Josephson probes; (b) is an optical image of the Nb-based Josephson probe; and (c) is a SEM image of the Nb-based Josephson probe.

[0023] Figure 2 These are the transport characteristics of Nb-based Josephson probes with different film thicknesses.

[0024] Figure 3 These are the Shapiro step test results of an 80nm thick Nb-based Josephson probe at different temperatures.

[0025] Figure 4 This is the highest operating temperature Nb-based Josephson probe prepared, (a) is the resistance-temperature (T / T) curve. R - T (a) Curve measurement results; (b) is I - V Line graph.

[0026] Figure 5 This is the simulation result of the temperature distribution within 1000μm of the probe tip.

[0027] Figure 6 This is a diagram of the external structure of the in-situ flipping system.

[0028] Figure 7 This is a schematic diagram of an in-situ flipping system omitting the vacuum pipes.

[0029] Figure 8 This is a schematic diagram of the flipping and rotating frame and the external knob structure.

[0030] Figure 9 This is a schematic diagram of the probe mounting bracket structure. Detailed Implementation

[0031] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. Example 1

[0032] This embodiment provides a method for controlling the thickness of a Nb film, employing a two-step self-correcting in-situ flipping deposition process. A dedicated in-situ flipping system is used to precisely form a weakly connected squiid structure at the needle tip through two Nb film deposition processes. The specific implementation steps are as follows:

[0033] S1: A four-groove quartz tube is selected as the substrate. The quartz tube is ultrasonically cleaned to remove surface impurities. Then, a nano-needle tip is drawn by laser heating to obtain a needle tip structure with a clean surface and controllable geometry.

[0034] The laser needle pulling device used in the experiment was a Sutter P-2000 microelectrode pulling device. Its working principle is to use laser to locally heat the hollow quartz tube. After it melts, it is stretched outward by the clamping devices on both sides, so that the heated area forms a needle tip under tension.

[0035] S2: The prepared nanoneedle tip is horizontally fixed on the probe holder, and a niobium thin film is deposited using a magnetron sputtering process.

[0036] To ensure the successful drawing of quartz tubes into qualified probes, their morphology needs to be preliminarily screened before magnetron sputtering coating. The specific operation is as follows: First, the morphology of the drawn probes is observed using an optical microscope. After confirming that the probe tip meets the basic requirements of being sharp and structurally intact, it is then transferred to the subsequent magnetron sputtering process for coating treatment.

[0037] The geometric dimensions of quartz nanoneedles directly determine the spatial resolution of probe microscopy. Furthermore, whether the quartz capillary can maintain its intended structural morphology after laser heating and melting is a crucial factor in the successful fabrication of Josephson junctions. Therefore, precise characterization of the microstructure of nanoneedles, especially their tip regions, is essential. Since the tip size is typically in the tens to hundreds of nanometers range, ordinary optical microscopes are insufficient for observation. Therefore, this invention employs field emission scanning electron microscopy (ZEISS, MERLIN Compact SEM) to systematically observe a series of fabricated nanoneedles.

[0038] In the electrode deposition step of the magnetron sputtering process, the deposition of a single-sided electrode is completed first. The specific sputtering parameters are as follows: sputtering power of 200W, chamber height h = 50mm, initial argon flow rate of 5sccm, adjusted to 2.5sccm after stabilization, and deposition gas pressure of 1.9 × 10⁻⁶. -3 Torr.

[0039] After depositing one side of the electrode, the probe is transferred to an in-situ flipping system via a vacuum transfer system and rotated 180° in a vacuum environment. Then, the other side of the electrode is deposited using the same process parameters as the completed single-sided electrode. This process effectively ensures the symmetry of the two electrodes in terms of thickness, morphology, and performance. Based on this process, superconducting Josephson junctions can be precisely fabricated on nanoneedle tips and further assembled to form superconducting quantum interference devices (SQUIDs).

[0040] In this embodiment, the magnetron sputtering process is completed by the cooperation of a magnetron sputtering system and an in-situ flipping system, such as... Figures 6-9 As shown, the in-situ flipping system includes a vacuum chamber 1, a magnetically controlled sample inlet baffle 2, a sample transfer platform 3, a transfer rod 4, a flipping rotation frame 5, a probe fixing bracket 6, an external knob 7, a vacuum pipe 8, and a linear slide rail 9. The sample transfer platform 3 and the linear slide rail 9 are located inside the vacuum pipe 8, the probe fixing bracket 6 and the flipping rotation frame 5 are located inside the vacuum chamber 1, and the magnetically controlled sample inlet baffle 2 is located at the end of the vacuum pipe 8.

[0041] Vacuum chamber 1 is connected to an adjacent vacuum chamber via vacuum pipe 8. The rotating shaft of the flipping rotating frame 5 is led out of vacuum chamber 1 via a vacuum dynamic sealing flange and connected to an external knob 7. By rotating this external knob 7, the flipping rotating frame 5 can be driven to complete a 180° directional flip while maintaining a vacuum.

[0042] The movement of the conveyor rod 4 is achieved through an external magnetic coupling mechanism: the external magnetic handle 41 and its own pickup 42 form a non-contact magnetic coupling pair. Moving the magnetic handle 41 outside the vacuum pipe 8 will cause the pickup 42 of the conveyor rod 4 to extend or retract axially. The conveyor rod 4 is connected to the vacuum pipe 8 via a metal bellows compensator flange 43. This structure ensures a vacuum seal while allowing the conveyor rod 4 to move up and down within a certain range.

[0043] The sample transfer platform 3 is mounted on a linear slide rail 9 inside the vacuum pipe 8. It can be driven non-contactly by another set of external magnets, thereby achieving precise positioning and smooth movement of the sample within the vacuum pipe 8. The probe fixing bracket 6 engages with the positioning groove on the sample transfer platform 3 through its base, forming a stable mechanical fit, thus ensuring reliable fixation during movement and preventing it from falling off. The flipping and rotating frame 5 is a U-shaped structure with one open end, and a storage slot 51 is provided on the U-shaped structure. The probe fixing bracket 6 is movably disposed within the storage slot 51.

[0044] During the in-situ flipping operation, the sample transfer platform 3 carrying the probe holder 6 is first moved along the linear slide rail to the front of the flipping rotation frame 5. Then, the manipulator rod 4 is lowered and picked up; the rod 4 integrates a grooved picker 42, whose groove design matches the geometry of the probe holder 6. This design achieves reliable gripping and fixation through shape interlocking. The probe holder 6 is then smoothly transferred to the bearing surface of the flipping rotation frame 5. After confirming positioning, the external knob 7 is rotated to drive the flipping rotation frame 5 to complete a 180° rotation, thus achieving in-situ flipping of the probe. An observation window is also provided on the vacuum chamber 1 for easy observation of the internal conditions.

[0045] Through the above process, superconducting Josephson junctions can be precisely fabricated on nanoneedle tips and further formed into SQUIDs.

[0046] This embodiment provides a method for controlling the thickness of Nb films. Through a vacuum interconnect design, the probe can complete spatial pose transformation under conditions of complete atmospheric isolation. More importantly, the system can maintain 10 -7 The high vacuum environment at the Torr level effectively inhibits the formation of oxide layers.

[0047] This invention connects the magnetron sputtering system to the in-situ flipping system via a vacuum pipeline. After the probe holder 6 is fed into the flipping rotating frame 5 via the sample transfer platform 3, the in-situ flipping operation of the probe can be achieved in a vacuum environment by rotating the external knob 7. This method can effectively avoid probe breakage caused by micro-stress, and at the same time, the formation of the oxide layer is isolated by the vacuum interconnection system, thereby significantly improving the success rate of probe preparation and the repeatability of device performance.

[0048] like Figure 1 As shown, Figure 1 (a) is a flowchart of a two-step self-calibrating thin film deposition process for preparing Nb-based Josephson probes. Figure 1 (b) is an optical image of an Nb-based Josephson probe. Figure 1 (c) is an SEM image of the Nb-based Josephson probe. Example 2

[0049] This embodiment provides a method for controlling the operating temperature of a Josephson probe, which controls the operating temperature range of the Josephson probe by precisely adjusting the Nb film thickness.

[0050] For precise thickness control, a probe with a Nb film of a specific thickness and an undeposited probe are first prepared. The tip dimensions of the two probes are measured using a scanning electron microscope (SEM), and half the difference between the two measurements represents the thickness of the deposited Nb film. Based on this measurement, by adjusting the deposition parameters of the film thickness gauge in the magnetron sputtering system, the deposition rate of the Nb film on the tip (40 nm / min) can be calibrated and precisely controlled, thereby achieving precise control of the film thickness.

[0051] like Figure 2 The figure shows the transport characteristics of Nb-based Josephson probes with different film thicknesses. Experimental results indicate that the probe's operating temperature range exhibits a significant film thickness dependence. The lower limit of the operating temperature range is defined as the temperature-dependent range. I - V The curve first shows the temperature point where the new voltage transition occurs, while the upper limit is determined by... R - T In the curve T c01 The determined temperature (i.e., the superconducting transition temperature at the tip) is shown in the data. Data shows that as the coating thickness increases from 40 nm to 80 nm, the operating temperature range of the probe is significantly widened, with the upper limit temperature increasing by about 1.3 K, demonstrating the important regulatory role of film thickness on the operating temperature range.

[0052] This invention establishes, for the first time, a quantitative relationship between film thickness and operating temperature range by preparing probe samples with different film thicknesses and combining them with the electrical characterization of the system.

[0053] like Figure 3 The figure shows the Shapiro step test results of an 80nm thick Nb-based Josephson probe at different temperatures. To verify that the probe did not form a weakly connected Josephson junction under both low and high temperature environments, microwave signals of fixed frequency and different powers were applied to the probe at different temperatures. The experimental results show that no Shapiro steps appeared on the probe in the temperature range below 4.7K and above 7.5K, indicating that the probe did not form a weakly connected Josephson junction within this temperature range, but rather has a unique operating temperature range.

[0054] This phenomenon stems from the structural characteristics of the fabricated Josephson probe: its barrier layer is a weak superconductor, and its superconducting properties change significantly with ambient temperature. At excessively low temperatures, the superconductivity of the barrier layer is too strong, hindering the formation of weak connections and causing the probe to exhibit the characteristics of ordinary superconducting thin films; while at excessively high temperatures, the superconductivity of the barrier layer weakens or disappears, and the probe instead exhibits resistive characteristics.

[0055] like Figure 4 As shown, Figure 4 (a) in the figure represents the highest operating temperature Nb-based Josephson probe prepared to date, which is a resistance-temperature (RTT) probe. R - T Curve measurement results; Figure 4 (b) is I - V Line graph;

[0056] This invention, based on the adjustable film thickness Nb-based probe, significantly improves both its maximum operating temperature and fabrication success rate. Experimental studies show that the maximum operating temperature of this Nb-based Josephson probe can reach 7.2 K. As shown in the figure, even at 7.2 K, the Shapiro step can still be clearly observed when microwave signals of 5 GHz, -11 dBm and 5.5 GHz, 0 dBm are applied. Further analysis using resistance-temperature (RTT)... R - T Curve measurements show that the superconducting transition temperature of the tip junction region is 7.2 K, while the overall superconducting transition temperature of the Nb film is 8.6 K. Using this process route, the actual operating temperature limit of the Nb-based probe is further increased, gradually approaching the theoretical superconducting transition temperature of bulk Nb material (9.25 K).

[0057] According to the probe R - T The curve test results show that the superconducting transition temperature of its Nb film ( T c The superconducting transition temperature of the needle-head junction is 8.6 K, while the superconducting transition temperature of the needle-head junction is... T c0 Up to 7.2K. T c0 The value matches the highest operating temperature obtained in microwave testing, indicating that the prepared Nb-based probe achieved an operating temperature of 7.2 K. This value surpasses all previously reported Nb-based probes of the same type, demonstrating a significant advantage. This work successfully raises the operating temperature of Nb-based probes to a new level, making an important contribution to the development of high-performance low-temperature near-field microwave detection technology.

[0058] like Figure 5The figure shows a simulation of the temperature distribution within 1000 μm of the probe tip. To evaluate the effect of temperature on the superconducting performance of the Nb-based probe, the temperature distribution at the probe tip was first analyzed through simulation. The boundary conditions set for the simulation are as follows: the probe is cooled by a 4K cold source, and the external space is considered as a 30K aluminum-shell blackbody radiation environment. The simulation results show that the temperature on the probe structure exhibits a gradient distribution, with a temperature difference of approximately 0.5K within a 1000 μm range from the tip. For the Nb-based probe, this temperature distribution will cause the Nb film on the probe wall to enter the superconducting state first.

[0059] This invention systematically elucidates the operating temperature characteristics and regulation mechanism of Nb-based Josephson probes. High-performance Nb-based probes are prepared through an in-situ flipping process, solving the oxidation and mechanical damage problems encountered in traditional processes. The criteria for determining the probe's operating temperature range are clearly defined: the lower limit is determined by temperature variation. I - V The new voltage jump in the curve is determined, with the upper limit determined by the superconducting transition temperature of the needle-head junction region ( T c0 The experiment found that film thickness is a key parameter for controlling the operating temperature range, and increasing the film thickness can significantly increase the upper limit of the temperature range.

[0060] Microwave response testing showed that the probe exhibited typical weak junction behavior in the 4.4–6.0 K temperature range. I - V The Shapiro step observed in the curve conforms to the AC Josephson effect. It was also confirmed that the probe does not form a weak junction below 4.7K or above 7.5K, which stems from the temperature sensitivity of its barrier layer as a weak superconductor: at low temperatures, the excessive superconductivity of the barrier layer suppresses weak coupling, while at high temperatures, the disappearance of superconductivity causes the junction region to revert to a normal resistive state.

[0061] This invention ultimately achieved a record high operating temperature of 7.2K for Nb-based probes. This breakthrough significantly reduces the probe's dependence on extremely low temperatures. This understanding breaks through previous process limitations, effectively broadens the usable film thickness range, and significantly improves the probe's fabrication yield and performance consistency, laying the device foundation for practical applications in near-field microwave imaging and quantum sensing. The improved operating temperature is attributed to the improved junction interface quality resulting from process innovation, pointing the way to further approaching the theoretical transition temperature limit of Nb. Example 3

[0062] This embodiment provides a novel Josephson microscope that directly integrates a Josephson junction onto the tip of a nanoprobe, thereby achieving highly sensitive near-field microwave characterization of samples at low temperatures. Probe performance is a key factor determining image quality. Through process optimization, a superconducting Josephson probe capable of exhibiting the Shapiro step pattern under temperature-controlled conditions was successfully fabricated. This fabrication method significantly improves the probe's yield and operational stability, providing a reliable device foundation for near-field microwave imaging technology based on Josephson junctions.

[0063] This invention can precisely control the thickness of Nb films, and probes prepared in the traditional "ultra-thick" range still have a usable operating temperature range.

[0064] First, in terms of performance, by precisely controlling the Nb film thickness (40–80 nm), the highest operating temperature of the Josephson probe was successfully increased to about 7 K, significantly expanding the applicability of the probe in higher temperature regions.

[0065] Secondly, at the process level, traditional methods require the film thickness to be strictly within the narrow window of weak junction formation, resulting in high fabrication difficulty and low yield. This invention innovatively discovers that probes fabricated even within the traditional "ultra-thick" range still possess a usable operating temperature range. This understanding breaks through existing process limitations, effectively broadens the usable film thickness range, and significantly improves the probe fabrication yield and performance consistency.

[0066] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for controlling the operating temperature of a Josephson probe, characterized in that: By precisely controlling the Nb film thickness, the operating temperature range of the Josephson probe is determined. The operating temperature range exhibits a clear film thickness dependence. By preparing probe samples with different film thicknesses and combining this with systematic electrical characterization, a quantitative relationship between film thickness and operating temperature is established. Microwave signals of fixed frequency and different powers are applied to the probe at different temperatures to determine whether a Shapiro step occurs and whether a weak junction is formed. Specifically, this includes: By adjusting the deposition parameters of the film thickness gauge in the magnetron sputtering system, the deposition rate of Nb thin film on the tip is calibrated and precisely controlled, thereby achieving precise control of film thickness from 40nm to 80nm. The electrical characterization of the system includes resistance-temperature testing, current-voltage testing, and microwave response testing at different temperatures. Resistance-temperature testing is used to determine the superconducting transition temperature of the probe, current-voltage testing is used to confirm the stable operating temperature range of the probe under actual bias conditions, and microwave response testing at different temperatures is used to verify whether the probe exhibits a Shapiro step within the operating temperature range, thereby determining whether it forms an effective weak junction. When the coating thickness is 40nm, the probe's operating temperature range is 4.0K~5.8K; when the coating thickness is 60nm, the probe's operating temperature range is 4.0K~6.5K; and when the coating thickness is 80nm, the probe's operating temperature range is 5.5K~7.1K.

2. The method for controlling the operating temperature of the Josephson probe according to claim 1, characterized in that: Below 4.7K, the superconductivity of the barrier layer is too strong, which hinders the formation of weak junctions and causes the probe to exhibit the characteristics of ordinary superconducting thin films. However, above 7.5K, the superconductivity of the barrier layer weakens to the point of disappearing, and the probe exhibits resistive characteristics. The probe does not form weak junctions below 4.7K and above 7.5K.

3. The method for controlling the operating temperature of the Josephson probe according to claim 2, characterized in that: The probe exhibits typical weak junction behavior in the temperature range of 4.4-6.0K. I - V The Shapiro step appearing in the curve conforms to the AC Josephson effect; the highest operating temperature of the Nb-based Josephson probe reaches 7.2K; under 7.2K conditions, when microwave signals of 5GHz, -11dBm and 5.5GHz, 0dBm are applied, the superconducting transition temperature of the Shapiro step tip junction region is 7.2K, while the overall superconducting transition temperature of the Nb film is 8.6K.

4. The method for controlling the operating temperature of the Josephson probe according to claim 1, characterized in that: The criterion for determining the probe's operating temperature range is: the lower limit is determined by the temperature variation. I - V The new voltage jump in the curve is determined, with the upper limit determined by the superconducting transition temperature of the needle-head junction. T c0 Decide.

5. A method for controlling the thickness of a Nb film, characterized in that, include: S1: A four-groove quartz tube is selected as the substrate. After ultrasonic cleaning, the nano-needle tip is drawn by laser heating to obtain a needle tip structure with a clean surface and controllable geometry. S2: The prepared nanoneedle tip is horizontally fixed on the probe holder, and a niobium film is deposited by magnetron sputtering to adjust the thickness of the Nb film to 40nm-80nm. In step S2, after the deposition of one side electrode is completed, the probe is transferred to the in-situ flipping system through the vacuum transfer system and flipped 180° in a vacuum environment. Then the other side electrode is deposited with the same parameters to ensure the symmetry of the two electrodes. The in-situ flipping system includes a vacuum chamber (1), a magnetically controlled sample inlet baffle (2), a sample transfer platform (3), a transfer rod (4), a flipping rotation frame (5), a probe fixing bracket (6), an external knob (7), a vacuum pipe (8), and a linear slide rail (9). The sample transfer platform (3) and the linear slide rail (9) are located inside the vacuum pipe (8). The probe fixing bracket (6) and the flipping rotation frame (5) are located inside the vacuum chamber (1). The magnetically controlled sample inlet baffle (2) is located at the end of the vacuum pipe (8). The transfer rod (4) is connected to the vacuum pipe (8) via a metal bellows compensator flange (43). The vacuum chamber (1) is connected to the adjacent vacuum chamber through the vacuum pipe (8). The rotating shaft of the flipping rotating frame (5) is led out to the outside of the vacuum chamber (1) through the vacuum dynamic sealing flange and connected to the external knob (7). By rotating the external knob (7), the flipping rotating frame (5) can be driven to complete a 180° directional flip under the condition of maintaining vacuum.

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