Josephson junction based on two-dimensional material and preparation method thereof
By combining top-down micro/nano fabrication and van der Waals dry transfer technology, Josephson junctions were fabricated in an ultra-high vacuum environment, solving the problem of poor integration of two-dimensional materials in traditional methods. This resulted in high-performance and consistent two-dimensional Josephson junctions, which are particularly suitable for superconducting qubits.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-23
- Publication Date
- 2026-04-07
AI Technical Summary
Traditional Josephson junctions suffer from poor barrier layer uniformity and interface clarity, making them difficult to integrate with two-dimensional materials with high quality. Furthermore, the fabrication process is prone to introducing contamination and damage, leading to inconsistent performance.
By combining top-down micro-nano fabrication technology with bottom-up van der Waals dry transfer technology, a high-vacuum integrated system is used to perform non-destructive transfer and electrode deposition of two-dimensional materials, ensuring clean and undamaged interfaces and avoiding polymer residues and atmospheric pollution.
This technology achieves atomically clean integration between superconducting electrodes and two-dimensional materials, improves the uniformity of the barrier layer and interface quality of the Josephson junction, ensures the high performance and consistency of the device, and is suitable for superconducting qubits with high coherence time.
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Figure CN121815953A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the field of superconducting quantum devices and micro-nano processing technology, and particularly relates to a Josephson junction based on a two-dimensional material and a preparation method thereof. BACKGROUND
[0002] A Josephson junction is a basic building block of core devices such as superconducting quantum computers, superconducting quantum interference devices (SQUIDs) and superconducting single-photon detectors. A traditional Josephson junction usually adopts a "sandwich" structure, that is, a very thin non-superconducting barrier layer (such as aluminum oxide) is deposited between two superconducting electrodes (such as aluminum) to achieve the purpose.
[0003] However, the traditional Josephson junction has the following inherent defects: 1. Poor barrier layer uniformity: The thickness and uniformity of the barrier layer formed by natural oxidation or plasma oxidation are difficult to accurately control, resulting in large fluctuations in performance (such as critical current) between junctions and poor repeatability; 2. Low interface clarity: The interface between the superconducting electrode and the barrier layer may have diffusion or defects, affecting the coherence characteristics of the junction; 3. Limited process compatibility: The preparation method is difficult to achieve clean and high-quality integration with emerging two-dimensional material systems.
[0004] In recent years, two-dimensional materials have been considered as ideal barrier materials for building high-quality Josephson junctions due to their atomically flat surfaces, no dangling bonds and excellent electrical properties. However, conventional two-dimensional material transfer techniques (such as wet transfer) are prone to introduce polymer residues and contamination. If the subsequent electrode deposition and patterning processes are carried out in an atmospheric environment, water, oxygen and impurities will be introduced, which will damage the interface quality, and thus the advantages of two-dimensional materials as ideal barrier layers cannot be fully utilized. SUMMARY
[0005] To solve the above technical problems, the application provides a Josephson junction based on a two-dimensional material and a preparation method thereof. The core of the application is to combine the "top-down" micro-nano processing technology with the "bottom-up" van der Waals dry transfer technology, and to complete all key steps in a fully automated, ultra-high vacuum cluster deposition and in-situ transfer integrated system to ensure that the sample is not exposed to the atmosphere throughout the process. The application realizes atomic-level clean and non-destructive van der Waals integration between the superconducting electrode and the two-dimensional material barrier layer, avoids interface contamination, material damage and performance inconsistency problems, and thus prepares a two-dimensional material Josephson junction with high performance and high consistency.
[0006] The application provides a Josephson junction based on a two-dimensional material and a preparation method thereof, which adopts the following technical scheme: In one aspect of the present application, a method for preparing a Josephson junction based on a two-dimensional material is provided, comprising the following steps: Step 1. Substrate preparation and lower electrode preparation: in an ultrahigh vacuum deposition and in-situ transfer integrated system, a clean surface insulating substrate is prepared; a patterned lower superconducting electrode is formed on the insulating substrate by using a molecular beam epitaxy technique, and the electrode has a clean surface, low defects and uniform thickness; Step 2. Dry transfer of two-dimensional material: in the ultrahigh vacuum deposition and in-situ transfer integrated system, a pre-set two-dimensional material sheet is accurately aligned and transferred to the target area of the lower superconducting electrode obtained in step 1 by using a dry transfer technique, and an atomic-level flat contact is formed by Van der Waals force, and the introduction of polymer solvents and organic residues is avoided throughout the process; Step 3. Upper electrode deposition: after the two-dimensional material is transferred in step 2, an upper superconducting electrode is deposited above the two-dimensional material by using a low-temperature electron beam evaporation technique in the same integrated system, thereby obtaining a "electrode / two-dimensional material / electrode" Josephson junction; Step 4. Pattern definition of junction area: in order to protect the two-dimensional material from damage, a specific energy electron beam exposure and dry etching process is used to pattern the Josephson junction obtained in step 3, and the effective area and critical dimension of the Josephson junction are accurately controlled.
[0007] Preferably, in step 1, the ultrahigh vacuum deposition and in-situ transfer integrated system comprises a sample inlet chamber, a vacuum hub, a molecular beam epitaxy chamber, a two-dimensional material processing chamber and an electron beam evaporation chamber; the sample inlet chamber, the molecular beam epitaxy chamber, the two-dimensional material processing chamber and the electron beam evaporation chamber are connected by the vacuum hub; wherein the two-dimensional material processing chamber comprises a precision manipulator, an optical microscope and a heating stage.
[0008] Preferably, in step 1, the ultrahigh vacuum deposition and in-situ transfer integrated system further comprises a surface treatment chamber and an analysis chamber; wherein the analysis chamber comprises a scanning tunneling microscope (STM) and / or an X-ray photoelectron spectrometer (XPS).
[0009] Preferably, in step 1, the material of the insulating substrate is sapphire; the material of the lower superconducting electrode is aluminum, tantalum, niobium or an alloy thereof.
[0010] Preferably, in step 2, the dry transfer technique is a PC / PDMS film assisted Van der Waals force transfer method; the two-dimensional material is graphene, hexagonal boron nitride or a graphene / hexagonal boron nitride stacked heterojunction structure.
[0011] Preferably, in step 3, the material of the upper superconducting electrode is aluminum, tantalum, niobium or an alloy thereof.
[0012] Preferably, in step 4, the electron beam exposure dose is 10-100 μC / cm. 2 The power of dry etching is 10-30W.
[0013] In another aspect, the present invention provides a Josephson junction based on two-dimensional materials obtained by the above preparation method.
[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention is particularly suitable for fabricating quantum devices such as superconducting qubits, which require extremely high coherence time and parameter consistency. 1. Extremely high interface quality: Since the entire preparation process, especially electrode deposition and two-dimensional material transfer, is completed in ultra-high vacuum, the influence of atmospheric water, oxygen and organic pollutants on the interface is completely eliminated, resulting in an atomically clean superconducting / two-dimensional material interface.
[0015] 2. Good junction uniformity: Dry transfer technology avoids polymer residues and, combined with atomically flat two-dimensional materials, significantly improves the uniformity of the barrier layer of the Josephson junction, effectively improving the uniformity and repeatability of junction parameters (such as critical current).
[0016] 3. Intrinsic properties of the material are preserved: Low-energy subsequent patterning processes and low-temperature superconducting electrode deposition minimize damage to the lattice structure and electrical properties of the two-dimensional material, ensuring the intrinsic high quality of the device.
[0017] 4. High process integration and flexibility: The ultra-high vacuum deposition and in-situ transfer integrated system realizes full-process automation and seamless vacuum connection from electrode preparation to two-dimensional material stacking, providing a powerful platform support for the preparation of complex multilayer two-dimensional material quantum devices. Attached Figure Description
[0018] Figure 1 This invention provides a schematic diagram of the integrated system structure for ultra-high vacuum deposition and in-situ transfer; Figure 2 This invention provides a flowchart of a method for preparing Josephson junctions based on two-dimensional materials. Detailed Implementation
[0019] To make the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings.
[0020] This invention provides a Josephson junction based on two-dimensional materials and its fabrication method. The process involves substrate preparation and lower electrode fabrication, dry transfer of the two-dimensional material, and upper electrode deposition within an ultra-high vacuum deposition and in-situ transfer integrated system. Finally, the junction region is patterned to obtain a patterned Josephson junction. This invention achieves atomically clean and lossless van der Waals integration between the superconducting electrode and the two-dimensional material barrier layer, avoiding interface contamination, material damage, and performance inconsistencies. This results in a high-performance, highly consistent two-dimensional Josephson junction, particularly suitable for fabricating quantum devices such as superconducting qubits with extremely high requirements for coherence time and parameter consistency.
[0021] Example 1 This invention provides a method for preparing Josephson knots based on two-dimensional materials, comprising the following steps: 1. Substrate preparation and lower electrode fabrication: In the ultra-high vacuum deposition and in-situ transfer integrated system, a clean sapphire insulating substrate is prepared; on the substrate, a patterned lower superconducting aluminum electrode is deposited using molecular beam epitaxy, which has a clean surface, low defects, and uniform thickness. 2. Dry transfer of two-dimensional materials: In the integrated system of ultra-high vacuum deposition and in-situ transfer, the van der Waals force dry transfer technology assisted by PC / PDMS thin film is used to precisely align and transfer the pre-set graphene two-dimensional material sheet to the target area of the lower superconducting aluminum electrode. The atomic-level flat contact is formed by relying on van der Waals force, and the introduction of polymer solvents and organic residues is avoided throughout the process. 3. Top electrode deposition: In the ultra-high vacuum deposition and in-situ transfer integrated system, after the two-dimensional material transfer is completed, a top superconducting aluminum electrode is deposited directly on the two-dimensional material using low-temperature electron beam evaporation technology within the same integrated system, thereby obtaining a Josephson junction of "electrode / two-dimensional material / electrode"; 4. Patterning and Defining the Junction Region: The Josephson junction is patterned using electron beam lithography and dry etching processes to precisely control its effective area and critical dimensions. After removing the Josephson junction obtained in step 3, PMMA photoresist is spin-coated onto it, and then it is placed in an electron beam lithography chamber for patterning. The electron beam lithography dose is 50 μC / cm. 2 After development, the Josephson junction was placed in a reactive ion beam etching chamber, and the aluminum and graphene outside the target junction region were etched using Cl2 (15 sccm) / BCl3 (15 sccm) / O2 (5 sccm) / Ar (10 sccm) at a pressure of 20 mTorr and a power of 10 W. After etching, the sample was cleaned with an organic solution to obtain the target patterned Josephson junction.
[0022] like Figure 1As shown, the ultra-high vacuum deposition and in-situ transfer integrated system includes a sample introduction chamber, a vacuum hub, a molecular beam epitaxy chamber, a two-dimensional material processing chamber, and an electron beam evaporation chamber; Electron beam evaporation chamber and molecular beam epitaxy chamber: used for depositing superconducting electrode thin films; Two-dimensional material handling chamber: Equipped with a precision robotic arm, optical microscope and heating stage, for performing mechanical peeling, picking and dry stacking of two-dimensional materials; Sample introduction chamber: As an "airlock", it is used to introduce substrates and materials without disrupting the vacuum of the main system.
[0023] Optional auxiliary modules include, but are not limited to, surface treatment and analysis compartments: Surface treatment chamber: used for cleaning sample surfaces; Analysis Chamber: Integrates scanning tunneling microscope (STM) and X-ray photoelectron spectroscopy (XPS) for in-situ characterization and quality monitoring during the process.
[0024] The preparation system adopts Figure 1 The ultra-high vacuum deposition and in-situ transfer integrated system shown connects three preparation chambers—a molecular beam epitaxy chamber, a two-dimensional material processing chamber, and an electron beam evaporation chamber—through a vacuum hub. Samples are introduced through the sample inlet chamber, and the outlet ensures that the device fabrication process does not involve external transfer, thereby avoiding unnecessary contamination.
[0025] like Figure 2 The diagram illustrates a typical process for fabricating Josephson junctions in this integrated system.
[0026] Example 2 This invention provides a method for preparing Josephson knots based on two-dimensional materials, similar to Example 1, except that it includes the following steps: 1. Substrate preparation and lower electrode fabrication: In the ultra-high vacuum deposition and in-situ transfer integrated system, a clean sapphire insulating substrate is prepared; on the substrate, a patterned lower superconducting tantalum electrode is deposited using molecular beam epitaxy, which has a clean surface, low defects, and uniform thickness. 2. Dry transfer of two-dimensional materials: In the integrated system of ultra-high vacuum deposition and in-situ transfer, the van der Waals force dry transfer technology assisted by PC / PDMS thin film is used to precisely align and transfer the pre-set hexagonal boron nitride two-dimensional material sheet to the target area of the lower superconducting aluminum electrode. The atomic-level flat contact is formed by relying on van der Waals force, and the introduction of polymer solvents and organic residues is avoided throughout the process. 3. Top electrode deposition: In the ultra-high vacuum deposition and in-situ transfer integrated system, after the two-dimensional material transfer is completed, a superconducting tantalum electrode is deposited on top of the two-dimensional material directly in the same integrated system using low-temperature electron beam evaporation technology, thereby obtaining a Josephson junction of "electrode / two-dimensional material / electrode"; 4. Patterning and Defining the Junction Region: The Josephson junction is patterned using electron beam lithography and dry etching processes to precisely control its effective area and critical dimensions. After removing the Josephson junction obtained in step 3, PMMA photoresist is spin-coated onto it, and then it is placed in an electron beam lithography chamber for patterning. The electron beam lithography dose is 100 μC / cm². 2 After development, the Josephson junction is placed in a reactive ion beam etching chamber and etched using CF4 (30 sccm) / O2 (5 sccm) / Ar (10 sccm) at a pressure of 20 mTorr and a power of 20 W to tantalum and hexagonal boron nitride outside the target junction region. After etching, the sample is cleaned with an organic solution to obtain the target patterned Josephson junction.
[0027] In summary, this invention achieves atomically clean and non-destructive van der Waals integration between the superconducting electrode and the two-dimensional material barrier layer, avoiding interface contamination, material damage, and performance inconsistencies. This results in a high-performance, highly consistent two-dimensional Josephson junction, which is particularly suitable for fabricating quantum devices such as superconducting qubits with extremely high requirements for coherence time and parameter consistency.
[0028] It should be noted that those skilled in the art can make various improvements and additions without departing from the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention. Any modifications, alterations, and variations made by those skilled in the art without departing from the spirit and scope of the present invention, based on the disclosed technical content, are equivalent embodiments of the present invention; furthermore, any modifications, alterations, and variations made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.
Claims
1. A method for preparing a Josephson junction based on two-dimensional materials, characterized in that, Includes the following steps: Step 1. Substrate preparation and lower electrode fabrication: In the ultra-high vacuum deposition and in-situ transfer integrated system, a clean insulating substrate is prepared; on the insulating substrate, a patterned lower superconducting electrode is deposited using molecular beam epitaxy, which has a clean surface, low defects, and uniform thickness. Step 2. Dry transfer of two-dimensional materials: In the integrated system of ultra-high vacuum deposition and in-situ transfer, dry transfer technology is used to precisely align and transfer the preset two-dimensional material sheet to the target area of the lower superconducting electrode obtained in Step 1. Atomic-level flat contact is formed by relying on van der Waals forces, and the introduction of polymer solvents and organic residues is avoided throughout the process. Step 3. Upper electrode deposition: In the ultra-high vacuum deposition and in-situ transfer integrated system, after the two-dimensional material transfer in step 2, a superconducting electrode is deposited on top of the two-dimensional material directly in the same integrated system using low-temperature electron beam evaporation technology, thereby obtaining a Josephson junction of "electrode / two-dimensional material / electrode"; Step 4. Patterning the junction region: To protect the two-dimensional material from damage, electron beam exposure and dry etching processes with specific energies are used to pattern the Josephson junction obtained in Step 3, precisely controlling the effective area and critical dimensions of the Josephson junction.
2. The preparation method according to claim 1, characterized in that: In step 1, the ultra-high vacuum deposition and in-situ transfer integrated system includes a sample introduction chamber, a vacuum hub, a molecular beam epitaxy chamber, a two-dimensional material processing chamber, and an electron beam evaporation chamber; the sample introduction chamber, the molecular beam epitaxy chamber, the two-dimensional material processing chamber, and the electron beam evaporation chamber are connected through the vacuum hub; wherein, the two-dimensional material processing chamber includes a precision robotic arm, an optical microscope, and a heating stage.
3. The preparation method according to claim 2, characterized in that: In step 1, the integrated system of ultra-high vacuum deposition and in-situ transfer further includes a surface treatment chamber and an analysis chamber; wherein, the analysis chamber includes a scanning tunneling microscope and / or an X-ray photoelectron spectroscopy instrument.
4. The preparation method according to claim 1, characterized in that: In step 1, the insulating substrate is made of sapphire; the lower superconducting electrode is made of aluminum, tantalum, niobium or their alloys.
5. The preparation method according to claim 1, characterized in that: In step 2, the dry transfer is a van der Waals force transfer method assisted by PC / PDMS thin film; the two-dimensional material is graphene, hexagonal boron nitride, or a graphene / hexagonal boron nitride stacked heterojunction structure.
6. The preparation method according to claim 1, characterized in that: In step 3, the material of the upper superconducting electrode is aluminum, tantalum, niobium or their alloys.
7. The preparation method according to claim 1, characterized in that: In step 4, the electron beam exposure dose is 10-100 μC / cm. 2 The power of dry etching is 10-30W.
8. A Josephson junction based on two-dimensional materials obtained by the preparation method according to any one of claims 1-7.