A method for preparing a high-temperature superconducting Josephson junction

Abstract

The present invention relates to the field of superconducting electronic technology, and in particular to a method for preparing a high-temperature superconducting Josephson junction. The preparation method provided by the present invention comprises the following steps: preparing a Tl2Ba2CaCu2O8 high-temperature superconducting precursor film on the surface of a substrate and then annealing it to obtain a beveled Tl2Ba2CaCu2O8 high-temperature superconducting film; the c-axis of the beveled Tl2Ba2CaCu2O8 high-temperature superconducting film is inclined to the surface of the substrate; a gold plating layer and a photoresist are sequentially prepared on the surface of the beveled Tl2Ba2CaCu2O8 high-temperature superconducting film; the photoresist is sequentially photoetched and removed, and then focused ion beam treatment is performed to obtain the high-temperature superconducting Josephson junction. The preparation method can overcome the problems of low junction formation rate and poor consistency in the preparation of step junctions, and can efficiently and stably prepare a high-temperature superconducting Josephson series junction with high consistency.

Description

Technical Field

[0001] The invention relates to the technical field of superconducting electronics, and in particular to a method for preparing a high-temperature superconducting Josephson junction. Background Art

[0002] Superconducting Josephson junctions play a vital role in ultra-sensitive electromagnetic sensors, quantum computing, terahertz detection, and many devices based on superconducting principles. In particular, high-temperature superconducting Josephson junctions prepared based on high-temperature superconducting films exhibit highly nonlinear voltage and current characteristics and relatively sensitive high-frequency response, which makes high-temperature superconducting Josephson junctions have outstanding application advantages in the fields of radio frequency and terahertz. In addition, high-temperature superconducting Josephson junctions have obvious advantages in increasing the operating temperature of superconducting electronic devices, which reduces the dependence of superconducting electronic devices on refrigeration conditions. At the same time, the preparation of high-performance high-temperature superconducting Josephson junctions is of great significance for promoting the practical application and diversified application of superconducting electronic devices.

[0003] In the 60 years since the Josephson effect was discovered and proved, Josephson junctions have been prepared on low-temperature superconductors and high-temperature superconductors. For high-temperature superconducting Josephson junctions, based on high-temperature superconducting films such as YBCO, high-temperature superconducting Josephson intrinsic junctions have been prepared on beveled substrates, step substrates and MESA structure substrates. High-temperature superconducting Josephson intrinsic junctions have been prepared on bicrystalline substrates and step substrates. These junctions are used to study the mechanism of high-temperature superconductivity on the one hand, and are widely used in the development of superconducting devices such as terahertz radiation sources, terahertz detectors, mixers, SQUIDs, etc. on the other hand. So far, there are very few studies on nano-sized high-temperature superconducting Josephson junctions, and there is a wide demand for efficient preparation of stable high-temperature superconducting Josephson junctions. The existing methods for preparing high-temperature superconducting Josephson junctions have more or less defects. For example, the preparation of step junctions generally has the problems of low junction formation rate and poor junction formation consistency. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a high-temperature superconducting Josephson junction, which can overcome the problems of low junction formation rate and poor consistency in step junction preparation, and can efficiently and stably prepare a high-temperature superconducting Josephson tandem junction with high consistency.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a high-temperature superconducting Josephson junction, comprising the following steps:

[0007] After preparing a Tl2Ba2CaCu2O8 high temperature superconducting precursor film on the surface of a substrate, annealing is performed to obtain a beveled Tl2Ba2CaCu2O8 high temperature superconducting film; the c-axis of the beveled Tl2Ba2CaCu2O8 high temperature superconducting film is inclined to the surface of the substrate;

[0008] Sequentially preparing a gold plating layer and a photolithography positive resist on the surface of the bevel-cut Tl2Ba2CaCu2O8 high-temperature superconducting thin film;

[0009] After the positive photoresist is subjected to photolithography and removed in sequence, it is subjected to focused ion beam treatment to obtain the high temperature superconducting Josephson junction.

[0010] Preferably, the method for preparing the Tl2Ba2CaCu2O8 high temperature superconducting precursor film comprises magnetron sputtering;

[0011] The discharge current of the magnetron sputtering is 50-100 mA, the voltage is 100-200 V, and the time is 90-150 min.

[0012] Preferably, the annealing temperature is 750-780° C. and the time is 60-120 min.

[0013] Preferably, the thickness of the Tl2Ba2CaCu2O8 high temperature superconducting precursor film and the beveled Tl2Ba2CaCu2O8 high temperature superconducting thin film is 400-500 nm.

[0014] Preferably, the thickness of the gold plating layer is 50-100 nm;

[0015] The preparation method of the photolithography positive resist is spin coating; the rotation speed of the spin coating is 7000-8000 rpm, and the time is 45-50 s.

[0016] Preferably, the photolithography comprises: firstly transferring the primary structure of the superconducting Josephson junction on the surface of the photoresist positive resist, then performing ultraviolet exposure, then performing development with a developer, and finally performing etching.

[0017] Preferably, the acceleration voltage of the focused ion beam treatment is 2.00-3.00 kV, and the ion beam is a gallium ion beam with a beam current intensity of 0.10-0.30 nA.

[0018] Preferably, the primary structure of the superconducting Josephson junction includes an antenna region, a junction region and two electrode regions;

[0019] The two electrode regions are respectively located at opposite sides of the junction region and the antenna region;

[0020] The two electrode areas each include two square electrodes with side lengths of 1.2mm×1.2mm~2.0mm×2.0mm; the distance between the two square electrodes with side lengths of 1.2mm×1.2mm~2.0mm×2.0mm is 0.7~1mm; the distance between the two electrode areas is 2.9~4mm.

[0021] Preferably, the antenna area is composed of a planar log-periodic antenna;

[0022] The opening angle of the branch feed line in the center of the planar log-periodic antenna is 45°, and the opening angle of the fan-shaped sawtooth dipole connected on both sides of the branch feed line of the planar log-periodic antenna is 45°;

[0023] The two sector antennas of the planar log-periodic antenna are respectively located at two sides of the junction area.

[0024] Preferably, the antenna region, the junction region and the two electrode regions are connected by connecting wires;

[0025] The connecting wire is composed of superconducting micron wires, and the superconducting micron wires are located on the central axis of the antenna area, the junction area and the two electrode areas;

[0026] The width of the superconducting micron wire is 0.1-0.2 mm.

[0027] The invention provides a method for preparing a high-temperature superconducting Josephson junction, comprising the following steps: preparing a Tl2Ba2CaCu2O8 high-temperature superconducting precursor film on the surface of a substrate and then annealing the film to obtain a beveled Tl2Ba2CaCu2O8 high-temperature superconducting film; the c-axis of the beveled Tl2Ba2CaCu2O8 high-temperature superconducting film is inclined to the surface of the substrate; a gold plating layer and a photoresist are sequentially prepared on the surface of the beveled Tl2Ba2CaCu2O8 high-temperature superconducting film; and after sequentially performing photolithography on the photoresist and removing the photoresist, a focused ion beam treatment is performed to obtain the high-temperature superconducting Josephson junction. The preparation method described in the present invention is the first to prepare a nano-sized Josephson junction on a Tl2Ba2CaCu2O8 high-temperature superconducting film. At the same time, the stability and consistency of the high-temperature superconducting Josephson junction depend on the growth quality of the high-temperature superconducting film and the size of the nanojunction. The use of a focused ion beam process with nano-machining precision based on high-quality high-temperature superconducting films can greatly improve the dimensional accuracy of the Josephson junction, thereby providing a new path for preparing high-consistency Josephson junctions based on high-quality high-temperature superconducting films. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the preparation process of the preparation method of the present invention;

[0029] Figure 2A schematic diagram of the structure of the primary structure of the high-temperature superconducting Josephson junction prepared by the present invention;

[0030] Figure 3 This is a SEM image of a high-temperature superconducting Josephson junction prepared in Example 1 of the present invention;

[0031] Figure 4 It is a schematic diagram of the structure of measuring the high-temperature superconducting Josephson junction by using the four-point method in Example 1 of the present invention;

[0032] Figure 5 The IV curve of a 1.5 μm-wide microbridge fabricated by conventional photolithography at 50 K.

[0033] Figure 6 The IV characteristic curve of the high temperature superconducting Josephson junction of the present invention measured at a temperature of 50K;

[0034] Figure 7 This is a TEM image of the oblique-cut Tl2Ba2CaCu2O8 high-temperature superconducting film of the present invention;

[0035] Figure 8 This is a selected area electron diffraction (SAED) pattern of the oblique-cut Tl2Ba2CaCu2O8 high-temperature superconducting film of the present invention;

[0036] Figure 1~2 and 4, 1-electrode, 2-antenna, 3-Josephson junction, 4-connecting line, 5-substrate, 6-Tl2Ba2CaCu2O8 high temperature superconducting precursor film, 7-Tl2Ba2CaCu2O8 high temperature superconducting thin film, 8-gold plating, 9-photolithography positive resist, 10-photolithography positive resist after exposure, 11-electrode connection, 12-indium pressure point. DETAILED DESCRIPTION

[0037] like Figure 1 As shown, the present invention provides a method for preparing a high-temperature superconducting Josephson junction, comprising the following steps:

[0038] After preparing a Tl2Ba2CaCu2O8 high temperature superconducting precursor film on the surface of a substrate, annealing is performed to obtain a beveled Tl2Ba2CaCu2O8 (Tl-2212) high temperature superconducting film; the c-axis of the beveled Tl2Ba2CaCu2O8 high temperature superconducting film is inclined to the surface of the substrate;

[0039] Sequentially preparing a gold plating layer and a photolithography positive resist on the surface of the bevel-cut Tl2Ba2CaCu2O8 high-temperature superconducting thin film;

[0040] After the positive photoresist is subjected to photolithography and removed in sequence, it is subjected to focused ion beam treatment to obtain the high temperature superconducting Josephson junction.

[0041] In the present invention, unless otherwise specified, all preparation raw materials are commercially available products well known to those skilled in the art.

[0042] The invention prepares a Tl2Ba2CaCu2O8 high temperature superconducting precursor film on the surface of a substrate and then performs annealing to obtain a beveled Tl2Ba2CaCu2O8 high temperature superconducting film.

[0043] In the present invention, the substrate is preferably a beveled substrate, the material of the beveled substrate is preferably lanthanum aluminate (LaAlO3), the size of the beveled substrate is preferably 10 mm×12 mm, the thickness of the beveled substrate is preferably 0.5 mm, and the bevel angle is preferably 20°; the bevel direction of the beveled substrate is parallel to the short side direction of the beveled substrate.

[0044] In the present invention, the method for preparing the Tl2Ba2CaCu2O8 high-temperature superconducting precursor film preferably includes magnetron sputtering; the discharge current of the magnetron sputtering is preferably 50~100mA, more preferably 80~100mA, and most preferably 100mA; the voltage is preferably 100~200V, more preferably 130~180V, and most preferably 150~160V; the time is preferably 90~150min, more preferably 90~130min, and most preferably 90~100min.

[0045] In the present invention, the thickness of the Tl2Ba2CaCu2O8 high temperature superconducting precursor film is preferably 400-500 nm, more preferably 420-480 nm, and most preferably 450-470 nm.

[0046] In the present invention, the annealing temperature is preferably 750-780° C., more preferably 760-770° C.; the annealing time is preferably 60-120 min, more preferably 90-100 min.

[0047] In the present invention, the purpose of the annealing is to promote the crystallization of the Tl2Ba2CaCu2O8 high temperature superconducting precursor film to produce a Tl2Ba2CaCu2O8 high temperature superconducting thin film with excellent performance.

[0048] In the present invention, the thickness of the bevel-cut Tl2Ba2CaCu2O8 high-temperature superconducting film is preferably 500 nm.

[0049] After obtaining the bevel-cut Tl2Ba2CaCu2O8 high-temperature superconducting film, the present invention sequentially prepares a gold plating layer and a photolithography positive resist on the surface of the bevel-cut Tl2Ba2CaCu2O8 high-temperature superconducting film.

[0050] In the present invention, the method for preparing the gold plating layer is preferably magnetron sputtering; the present invention has no special limitation on the process of magnetron sputtering, and the process well known to those skilled in the art can be used.

[0051] In the present invention, the thickness of the gold plating layer is preferably 50-100 nm, more preferably 60-90 nm, and most preferably 70-80 nm.

[0052] In the present invention, the gold plating layer can better protect the superconducting Josephson junction from the influence of environmental humidity.

[0053] In the present invention, the photoresist positive photoresist is preferably AZP4620 photoresist positive photoresist. In the present invention, the preparation method of the photoresist positive photoresist is preferably spin coating; the rotation speed of the spin coating is preferably 7000-8000rpm, more preferably 7200-7800rpm, and most preferably 740-760rpm; the time is preferably 45-50s, more preferably 46-49s, and most preferably 47-48s. After the spin coating is completed, the present invention also preferably includes drying, the drying temperature is preferably 89°C, the time is preferably 100s; the drying is preferably carried out in an oven.

[0054] After the gold plating layer and the photoresist are prepared, the present invention sequentially performs photolithography on the photoresist and removes the photoresist, and then performs focused ion beam treatment to obtain the high-temperature superconducting Josephson junction.

[0055] In the present invention, the photolithography preferably comprises: firstly transferring the primary structure of the superconducting Josephson junction on the surface of the photoresist positive resist, then performing ultraviolet exposure, then performing development with a developer, and finally performing etching.

[0056] In the present invention, the primary structure of the superconducting Josephson junction preferably includes an antenna region, a junction region and two electrode regions;

[0057] The two electrode regions are preferably located at opposite sides of the junction region and the antenna region;

[0058] The two electrode areas preferably include two square electrodes with side lengths of 1.2mm×1.2mm~2.0mm×2.0mm; the distance between the two square electrodes with side lengths of 1.2mm×1.2mm~2.0mm×2.0mm is preferably 0.7~1mm; the distance between the two electrode areas is preferably 2.9~4mm.

[0059] In the present invention, the antenna area is preferably composed of a planar log-periodic antenna;

[0060] The opening angle of the branch feed line in the center of the planar log-periodic antenna is preferably 45°, and the opening angle of the fan-shaped sawtooth dipole connected on both sides of the branch feed line of the planar log-periodic antenna is preferably 45°;

[0061] The two sector antennas of the planar log-periodic antenna are preferably located at two sides of the junction area.

[0062] In the present invention, the antenna region, the junction region and the two electrode regions are preferably connected by connecting wires;

[0063] The connecting wire is preferably composed of superconducting micron wires, and the superconducting micron wires are preferably located on the central axis of the antenna area, the junction area and the two electrode areas;

[0064] The width of the superconducting microwire is preferably 0.1-0.2 mm.

[0065] In the present invention, the junction region is located at the center of the planar log-periodic antenna, and the junction region includes a three-level linear structure, the line widths of the first two poles are 4 μm and 2 μm respectively, and the narrowest size is 500 nm×300 nm (such as Figure 3 as shown).

[0066] In the present invention, the exposure is preferably ultraviolet exposure, and the ultraviolet exposure time is preferably 7s.

[0067] In the present invention, the development is preferably performed by rinsing the sample obtained after the exposure in a positive photoresist developer for 27 seconds and then quickly rinsing it twice in distilled water.

[0068] In the present invention, the etching is preferably performed in a pure argon environment. The present invention does not have any special limitation on the etching process, and the etching can be performed using a process well known to those skilled in the art.

[0069] In the present invention, the etching can remove the superconducting film on the surface of the specific high-temperature superconducting film that is not covered by the positive photoresist. After the etching is completed, acetone needs to be used to erase the residual positive photoresist on the surface of the specific high-temperature superconducting film. The etching can prepare a primary structure on the surface of the specific high-temperature superconducting film.

[0070] In the present invention, the acceleration voltage of the focused ion beam treatment is preferably 2.00~3.00kV, more preferably 2.2~2.8kV, and most preferably 2.5~2.6kV; the ion beam is a gallium ion beam with a beam current intensity of preferably 0.10~0.30nA, and more preferably 0.15~0.25nA.

[0071] In the present invention, the focused ion beam treatment is preferably carried out in a FEI-Helios NanolLab460HP focused ion beam-electron beam dual beam device produced by FEI Company.

[0072] The preparation method of the high temperature superconducting Josephson junction provided by the present invention is described in detail below in conjunction with the embodiments, but they should not be understood as limiting the protection scope of the present invention.

[0073] Example 1

[0074] The high-temperature superconducting Josephson junction of the present invention comprises four electrodes, a planar logarithmic periodic antenna, a Josephson junction and a superconducting micron connecting wire;

[0075] according to Figure 1 The preparation process comprises: preparing a 500nm thick Tl2Ba2CaCu2O8 high temperature superconducting precursor film on the surface of a LaAlO3 beveled substrate (10mm×12mm in size, 0.5mm in thickness, bevel angle of 20°, bevel direction parallel to the short side of the substrate) by magnetron sputtering (sputtering conditions: 100mA, 150V, 90min), and then annealing the Tl2Ba2CaCu2O8 high temperature superconducting precursor film (760°C, 90min) to obtain a Tl2Ba2CaCu2O8 high temperature superconducting thin film;

[0076] A 100 nm thick gold coating is magnetron sputtered on the surface of the Tl2Ba2CaCu2O8 high temperature superconducting film, and the surface of the gold coating is spun at 7000 rpm for 45 seconds to obtain an AZP4620 positive photoresist. After ultraviolet exposure for 7 seconds, the primary structure of the high temperature superconducting Josephson junction is transferred to the film. The positive photoresist exposed by ultraviolet light will be washed away by the positive photoresist developer during development, and the remaining part of the positive photoresist protects the covered area from argon ion etching during etching to obtain a primary structure. The residual positive photoresist is then erased with acetone to obtain a complete primary structure of the high temperature superconducting Josephson junction. The primary structure includes Figure 2 The electrode 1, the antenna 2, and the connecting wire 4 are processed at the nanoscale by using a focused ion beam (the acceleration voltage is 2.00 kV, and the ion beam is a gallium ion beam with a beam current intensity of 0.10 nA) to obtain the high-temperature superconducting Josephson junction;

[0077] The high temperature superconducting Josephson junction was subjected to SEM testing. The test results are as follows: Figure 3 As shown by Figure 3 It can be seen that the junction region includes a three-level linear structure, the line widths of the first two poles are 4μm and 2μm respectively, and the narrowest size is 500nm×300nm;

[0078] Figure 7 TEM image of the oblique-cut Tl2Ba2CaCu2O8 high-temperature superconducting film of the present invention; Figure 7It can be seen that the c-axis direction of the LaAlO3 substrate forms an angle of 20° with the substrate surface. The Tl-2212 film grows along the c-axis direction of the substrate. The periodic arrangement of the elements in the Tl-2212 crystal indicates that the high-quality Tl-2212 film is epitaxially grown on the beveled LaAlO3 substrate;

[0079] Figure 8 is the selected area electron diffraction (SAED) pattern of the oblique-cut Tl2Ba2CaCu2O8 high-temperature superconducting film of the present invention; Figure 8 It can be seen that the neat arrangement and clear spots of the film lattice diffraction spots indicate that the elements of the film have good periodicity, high phase purity, and strong consistency of lattice arrangement;

[0080] like Figure 4 As shown in the figure, the four-point method is used to connect four electrode cords through four indium pressure points to characterize the transmission characteristics of the high-temperature superconducting Josephson junction under different temperature conditions. The characterization results are shown in Figures 5 and 6 As shown, Figure 5 IV curve of a microbridge with a width of 1.5 μm prepared by conventional photolithography (compared with Example 1, the difference is that the conventional process does not use FIB nanofabrication, the length and width of the bridge are still relatively large, the characteristics of each Josephson junction connected in series in the microbridge are still different, and the consistency of these series junctions cannot be guaranteed) measured at a temperature of 50K; Figure 6 is the IV characteristic curve of the high temperature superconducting Josephson junction of the present invention measured at a temperature of 50K; Figures 5 and 6 It can be seen that the IV curve of the micron bridge has a large number of branches, indicating that the consistency of the series superconducting junction is poor; after the high-temperature superconducting Josephson junction is treated with a focused ion beam, the IV characteristic curve of the nano-sized superconducting junction no longer has branches, and the series superconducting junction shows extremely high consistency;

[0081] Similar to the Josephson junction preparation method of this specific embodiment, a large amount of test data shows that the high-consistency high-temperature superconducting Josephson tandem junction preparation emphasized by the present invention relies on both the high performance of the c-axis tilted growth Tl-2212 superconducting thin film sample and the superiority of the FIB nanoprocess. In other words, the high-quality c-axis tilted growth Tl-2212 superconducting thin film sample and FIB process described in the present invention are two necessary conditions for preparing high-consistency high-temperature superconducting Josephson tandem junctions.

[0082] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a high temperature superconducting Josephson junction, characterized in that: The following steps are involved: After preparing a Tl2Ba2CaCu2O8 high temperature superconducting precursor film on the surface of a substrate, annealing is performed to obtain a beveled Tl2Ba2CaCu2O8 high temperature superconducting film; the c-axis of the beveled Tl2Ba2CaCu2O8 high temperature superconducting film is inclined to the surface of the substrate; Sequentially preparing a gold plating layer and a photolithography positive resist on the surface of the bevel-cut Tl2Ba2CaCu2O8 high-temperature superconducting film; After sequentially performing photolithography on the photoresist and removing the photoresist, a focused ion beam treatment is performed to obtain the high temperature superconducting Josephson junction; The acceleration voltage of the focused ion beam treatment is 2.00~3.00kV, and the ion beam is a gallium ion beam with a beam current intensity of 0.10~0.30nA; The Josephson junction is an intrinsic Josephson series junction; The photolithography comprises: firstly transferring the primary structure of the superconducting Josephson junction on the surface of the photoresist, then performing ultraviolet exposure, then performing development with a developer, and finally performing etching; The primary structure of the superconducting Josephson junction includes an antenna region, a junction region and two electrode regions; The two electrode regions are respectively located at two opposite sides of the junction region and the antenna region.

2. The preparation method according to claim 1, characterized in that The method for preparing the Tl2Ba2CaCu2O8 high temperature superconducting precursor film comprises magnetron sputtering; The discharge current of the magnetron sputtering is 50-100 mA, the voltage is 100-200 V, and the time is 90-150 min.

3. The preparation method according to claim 1, characterized in that: The annealing temperature is 750-780° C. and the annealing time is 60-120 min.

4. The preparation method according to claim 1, 2 or 3, characterized in that: The thickness of the Tl2Ba2CaCu2O8 high temperature superconducting precursor film and the beveled Tl2Ba2CaCu2O8 high temperature superconducting thin film is 400-500nm.

5. The preparation method according to claim 1, characterized in that: The thickness of the gold plating layer is 50-100 nm; The preparation method of the photolithography positive resist is spin coating; the rotation speed of the spin coating is 7000-8000 r / min, and the time is 45-50 s.

6. The preparation method according to claim 1, characterized in that: The two electrode areas each include two square electrodes with side lengths of 1.2mm×1.2mm~2.0mm×2.0mm; the distance between the two square electrodes with side lengths of 1.2mm×1.2mm~2.0mm×2.0mm is 0.7~1mm; the distance between the two electrode areas is 2.9~4mm.

7. The preparation method according to claim 6, characterized in that: The antenna area is composed of a planar log-periodic antenna; The opening angle of the branch feed line in the center of the planar logarithmic periodic antenna is 45°, and the opening angle of the fan-shaped sawtooth dipole connected on both sides of the branch feed line of the planar logarithmic periodic antenna is 45°; The two sector antennas of the planar log-periodic antenna are respectively located at two sides of the junction area.

8. The preparation method according to claim 6, characterized in that: The antenna region, the junction region and the two electrode regions are connected by connecting wires; The connecting wire is composed of superconducting micron wires, and the superconducting micron wires are located on the central axis of the antenna area, the junction area and the two electrode areas; The width of the superconducting micron wire is 0.1-0.2 mm.

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