Superconducting tunnel junction based on liquid metal and preparation method and application thereof

Abstract

The invention relates to the field of superconducting electronic devices, in particular to a superconducting tunnel junction based on liquid metal and a preparation method and application thereof. The superconducting tunnel junction comprises a first gallium electrode, a tunneling barrier layer formed on the first gallium electrode, and a second gallium electrode formed on the tunneling barrier layer; and the tunneling barrier layer is a tunneling barrier layer containing a gallium compound. According to the novel gallium-based liquid metal tunnel junction structure, the superconducting critical temperature can be increased, stable work under the 4K condition is achieved, the preparation process is simple, and the novel gallium-based liquid metal tunnel junction structure has natural oxidation potential barriers and flexible device potential.

Description

Technical Field

[0001] This invention relates to the field of superconducting electronic devices, and more particularly to a superconducting tunnel junction based on liquid metal, its preparation method, and its application. Background Technology

[0002] Superconducting quantum technology is a crucial pathway for building superconducting quantum computers, and significant breakthroughs have been achieved in the field in recent years. This technology relies on macroscopic quantum effects in superconducting circuits and utilizes core components such as Josephson junctions to construct qubits. Compared to conventional computers, superconducting quantum computers exhibit significant speed advantages in specific applications, providing new solutions for complex system simulation, cryptography breaking, and optimized computation.

[0003] Josephson junctions are core components in superconducting electronics. Essentially, they involve introducing a "weakly connected" region between two superconductors, enabling superconducting current coupling through the tunneling effect. A typical structure is a "sandwich" type, with superconductors on both sides and a very thin insulating dielectric or normal metal layer in between. Depending on the intermediate layer, common structures include: superconductor-insulator-superconducting junction (SIS), superconductor-normal metal-superconducting junction (SNS), and superconductor-semiconductor-superconducting junction (S-Sm-S). Besides differences in the intermediate layer material, Josephson junctions can also be constructed geometrically. For example, "microbridge junctions" are created by fabricating narrow bridge regions on superconducting thin films using micro-nano fabrication techniques such as photolithography and electron beam lithography; "point contact junctions" are formed through mechanical contact between a superconducting tip and a planar superconductor. These structures have limitations in stability and controllability, making them difficult to meet the demands of large-scale commercial applications at present. From a material system perspective, Josephson junctions can be divided into high-temperature superconducting junctions and low-temperature superconducting junctions. High-temperature superconducting junctions are typically based on materials such as yttrium barium copper oxide (YBCO), but their superconducting coherence lengths are extremely short and their anisotropy is strong, making the fabrication of stable and controllable Josephson junctions extremely difficult. Even when using grain boundaries to achieve weak connections, there are still problems with controllability, consistency, and repeatability. Therefore, despite the high critical temperatures of high-temperature superconductors, achieving high-performance, highly uniform Josephson junctions based on them remains a significant challenge.

[0004] To date, the SIS structure remains the most widely used Josephson junction. Typical systems include Al / Al₂O₃ / Al and Nb / AlOx / Nb. The Al system relies on the natural oxidation of Al to form a high-quality Al₂O₃ barrier; the process is mature and reproducible. However, due to Al's critical temperature of only about 1.2 K, it requires cryogenic operation, making it difficult to meet the 4 K level application requirements. The Nb system has a higher critical temperature (9.3 K), but due to Nb's extremely high melting point (2468 ℃) and complex processing technology, its fabrication difficulty and cost are increased. Existing mainstream SIS junction systems have the following shortcomings: the Al / Al₂O₃ / Al system has too low a critical temperature, making it difficult to operate stably in the liquid helium temperature range and higher; the Nb / AlOx / Nb system has a high Nb melting point, making its fabrication process complex and difficult, hindering large-scale deployment. Currently, developing a novel material system with a simple fabrication process and stable operation in the liquid helium temperature range is an important direction in superconducting tunnel junction research. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a gallium-based liquid metal superconducting tunnel junction, its fabrication method, and its applications. The novel gallium-based liquid metal tunnel junction structure provided by this invention can increase the superconducting critical temperature, achieve stable operation at 4K, and has a simple fabrication process, while also possessing the potential of a natural oxide barrier and flexible device design.

[0006] In a first aspect, the present invention provides a superconducting tunnel junction based on liquid metal, characterized in that the superconducting tunnel junction includes a first gallium electrode, a tunneling barrier layer formed on the first gallium electrode, and a second gallium electrode formed on the tunneling barrier layer; the tunneling barrier layer is a gallium-containing compound tunneling barrier layer. The present invention utilizes the relatively high critical temperature of the Ga phase (Tc≈6.0 K) to construct a superconducting tunnel junction, which, compared to low-Tc materials such as Al, can operate stably in the liquid helium temperature range. The superconducting tunnel junction provided by the present invention not only increases the critical temperature but also forms a naturally stable tunneling barrier, which does not require a complex anodizing process and can expand the applications of flexible superconducting electronics and superconducting circuits.

[0007] Preferably, the tunneling barrier layer is a Ga2O3 tunneling barrier layer, a GaN tunneling barrier layer, a GaS tunneling barrier layer, or a GaP tunneling barrier layer. In this invention, the tunneling barrier layer can be formed on the Ga surface by oxidation, nitriding, sulfidation, or phosphating to form Ga2O3, GaN, GaS, or GaP as an insulating layer to obtain different bandgap characteristics and barrier heights, thereby optimizing the tunneling performance.

[0008] Preferably, the materials of the first gallium electrode and the second gallium electrode are gallium metal, gallium-based alloy, or a mixture of gallium-based alloys containing doped particles, in order to improve superconducting performance or process stability. The gallium-based alloy is preferably a gallium-based alloy containing indium, tin, or zinc, and the doped particles are preferably metal particles and / or metal oxide particles; the doped particles are selected from one or more of metal particles such as nickel, iron, and copper, or their metal oxide particles.

[0009] Further preferably, the tunneling barrier layer is a Ga2O3 tunneling barrier layer; and / or, the first gallium electrode and the second gallium electrode are gallium metal layers. The method for constructing the Ga / Ga2O3 / Ga sandwich structure provided by the present invention adopts a three-layer stacked structure of Ga electrode / Ga2O3 barrier / Ga electrode to form a superconducting tunnel junction.

[0010] Further preferably, the thickness of the tunneling barrier layer is 1~5 nm; and / or, the thickness of the first gallium electrode is 20~200 nm, and the thickness of the second gallium electrode is 20~200 nm.

[0011] Further preferably, the tunneling barrier layer is formed by in-situ oxidation of the surface of the first gallium electrode; and / or, the first gallium electrode and the second gallium electrode are obtained by transforming liquid gallium under cooling conditions, wherein the cooling temperature is preferably 0~10 °C.

[0012] In a second aspect, the method for fabricating the superconducting tunnel junction provided by the present invention includes: forming a first gallium electrode on a substrate, forming a tunneling barrier layer containing a gallium compound on the first gallium electrode, and forming a second gallium electrode on the tunneling barrier layer containing the gallium compound.

[0013] Preferably, the method for preparing the superconducting tunnel junction includes: 1) Liquid gallium is sputtered, printed or spin-coated on a substrate, and then cooled to obtain a first gallium electrode film.

[0014] 2) The surface of the first gallium electrode film is oxidized to form a Ga2O3 thin layer.

[0015] 3) Deposit a second gallium electrode film on the Ga2O3 thin layer; and optionally, maintain it at a low temperature. This method eliminates the need for a complex anodizing process, improving process simplicity and repeatability.

[0016] Further preferred, in step 1), the substrate is SiO2 / Si, sapphire, or a flexible polymer matrix.

[0017] Further preferably, in step 2), the oxidation is carried out under vacuum conditions by introducing oxygen or an argon-oxygen mixture, with an oxygen pressure of 5 × 10⁻⁶. -3 ~2×10 -2Torr, lasting 110–130 s; liquid Ga can spontaneously generate a dense Ga2O3 thin layer in air or controlled oxygen. Alternatively, radio frequency plasma oxidation can be used to obtain a Ga2O3 thin layer with a thickness of 1–5 nm.

[0018] Thirdly, this invention provides applications of the superconducting tunnel junction in superconducting quantum bits, superconducting detectors, terahertz radiation sources, flexible superconducting electronic devices, and superconducting functional circuits constructed by combining the junction with capacitors and inductors written in liquid metal; the superconducting functional circuit is preferably an LC oscillating circuit. The tunnel junction of this invention can not only be used in single devices, but can also be combined with capacitors and inductors directly written in liquid metal to construct LC oscillating circuits, further expanding its application in superconducting quantum electronics.

[0019] The beneficial effects of this invention are at least as follows: 1. Increase the critical temperature. The superconducting critical temperature of β-Ga (Tc≈6.0 K) is significantly higher than that of Al (Tc≈1.2 K), which enables the prepared tunnel junction to operate stably in the liquid helium temperature range (4.2 K) and reduces the cooling requirements.

[0020] 2. Formation of a naturally stable tunneling barrier. Liquid Ga can generate dense thin layers such as Ga2O3, with a thickness controllable between 1 and 5 nm. As a tunneling barrier, it eliminates the need for complex anodic oxidation processes, thus improving process simplicity and repeatability.

[0021] 3. Expanding applications of flexible superconducting electronics. Ga has a low melting point and ductility, and can be fabricated on flexible substrates through spraying, sputtering, transfer printing, and other methods to obtain bendable and stretchable tunnel junction devices, providing new avenues for flexible superconducting quantum devices and portable detectors.

[0022] 4. Expanding the applications of superconducting circuits. By combining the gallium-based liquid metal-based superconducting tunnel junction of this invention with capacitors and inductors directly written in liquid metal, LC oscillating circuits can be further constructed, exhibiting the nonlinear and oscillating characteristics of superconducting circuits, thus expanding the application space of this tunnel junction in quantum devices, signal processing, and superconducting electronics. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1This is a schematic diagram illustrating the fabrication method of a gallium-based liquid metal-based superconducting tunnel junction provided in an embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram of an LC oscillation circuit in which the tunnel junction is coupled to a liquid metal writing capacitor and an inductor, as provided in an embodiment of the present invention.

[0026] In the diagram, 1-substrate; 2-Ga first electrode; 3-Ga2O3 tunneling barrier layer; 4-Ga second electrode; C-liquid metal writing capacitor; L-liquid metal writing inductor; J-Ga / Ga2O3 / Ga tunnel junction; C g - Gate capacitor; C J Junction capacitance. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0028] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0029] Unless otherwise specified, the techniques or conditions described in the embodiments of this invention shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Devices, instruments, reagents, etc., without specified manufacturers, are all conventional products that can be purchased through legitimate channels. All experimental reagents and raw materials involved are commercially available products, and all reagents are analytical grade products.

[0030] Example 1: Tunnel Knot Preparation This embodiment provides a superconducting tunnel junction based on gallium-based liquid metal and its fabrication method, such as... Figure 1 As shown, the electrode includes a Ga first electrode 1 formed on a substrate 1; a Ga2O3 tunneling barrier layer formed on the Ga first electrode 1; and a Ga second electrode 4 formed on the Ga2O3 tunneling barrier layer. The fabrication method provided in this embodiment includes the following steps: 1) Liquid gallium is deposited on a Si substrate, rapidly cooled at 0°C and held for a certain time to obtain a Ga thin film, which serves as the first electrode. Figure 1 As shown in (a).

[0031] 2) In-situ controlled oxidation was performed on the Ga thin film surface using radio frequency plasma oxidation to obtain a Ga2O3 tunneling barrier layer with a thickness of 1-5 nm, such as... Figure 1 As shown in (b).

[0032] 3) Liquid gallium is deposited on top of the Ga2O3 layer, rapidly cooled at 0°C and held for a certain time to obtain a second Ga thin film, which serves as the second electrode. Figure 1 As shown in (c), a Ga / Ga2O3 / Ga tunnel junction structure is formed.

[0033] 4) Keep the device below the critical temperature of Ga to obtain a tunnel junction with the Josephson effect, i.e., a Josephson junction.

[0034] Example 2: LC oscillator circuit diagram with coupled Josephson junction This embodiment provides an application scheme for a superconducting tunnel junction based on gallium-based liquid metal. The tunnel junction, combined with capacitors and inductors written in liquid metal, forms an LC oscillating circuit, the schematic diagram of which is shown below. Figure 2 As shown.

[0035] The LC oscillation circuit structure consists of a Josephson junction and a capacitor connected in parallel, forming the core unit of the superconducting quantum bit. This superconducting quantum bit is coupled to another LC oscillation circuit via the capacitor, enabling quantum interaction and information exchange. In the LC oscillation circuit, the capacitor C is a liquid metal writing capacitor, the inductor L is a liquid metal writing inductor, and the Josephson junction J is a Ga / Ga₂O₃ / Ga tunnel junction. g The gate capacitance C is coupled to the superconductor at one end of the Josephson junction. g C J The junction capacitance C that constitutes a superconducting quantum bit J .

[0036] An external driving field is injected into the circuit through a capacitor or current bias coupled to the Josephson junction, thereby modulating the phase dynamics of the Josephson junction and thus enabling the excitation and manipulation of the superconducting quantum bit energy level.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A liquid-metal-based superconducting tunnel junction, comprising: The superconducting tunnel junction comprises a first gallium electrode, a tunnel barrier layer formed on the first gallium electrode, and a second gallium electrode formed on the tunnel barrier layer; the tunnel barrier layer is a tunnel barrier layer of gallium-containing compound.

2. The superconducting tunnel junction of claim 1, wherein, The tunnel barrier layer is a Ga2O3 tunnel barrier layer, a GaN tunnel barrier layer, a GaS tunnel barrier layer, or a GaP tunnel barrier layer. The material of the first gallium electrode and the second gallium electrode is gallium metal, gallium-based alloy, or gallium-based alloy mixture containing doped particles; the gallium-based alloy is preferably gallium-based alloy containing indium, tin, or zinc.

3. The superconducting tunnel junction of claim 2, wherein, The tunnel barrier layer is a Ga2O3 tunnel barrier layer; and / or the first gallium electrode and the second gallium electrode are gallium metal layers.

4. The superconducting tunnel junction of any of claims 1-3, wherein, The thickness of the tunnel barrier layer is 1-5 nm.

5. The superconducting tunnel junction of any of claims 1-4, wherein, The tunnel barrier layer is formed by in-situ oxidation of the surface of the first gallium electrode; and / or the first gallium electrode and the second gallium electrode are obtained by transformation of liquid gallium under cooling conditions.

6. The method of producing a superconducting tunnel junction according to any of claims 1-5, characterized in that, The application comprises: forming a first gallium electrode on a substrate, forming a tunnel barrier layer of gallium-containing compound on the first gallium electrode, and forming a second gallium electrode on the tunnel barrier layer of gallium-containing compound.

7. The preparation method according to claim 6, characterized in that, The application comprises: 1) sputtering, printing, or spin-coating liquid gallium on a substrate to obtain a first gallium electrode film after cooling; 2) oxidizing the surface of the first gallium electrode film to form a Ga2O3 thin layer; 3) depositing a second gallium electrode film on the Ga2O3 thin layer; and optionally, maintaining in a low-temperature environment.

8. The preparation method according to claim 7, characterized in that, In step 1), the substrate is SiO2 / Si, sapphire, or a flexible polymer matrix.

9. The production method according to claim 7 or 8, characterized by, In step 2), the oxidation is carried out by passing oxygen or argon-oxygen mixed gas under vacuum condition, with oxygen pressure of 5x10 -3 -2 Torr for 110-130 s; or by using radio frequency plasma oxidation, to obtain a Ga2O3 thin layer with thickness of 1-5 nm.​ 10. Use of a superconducting tunnel junction according to any one of claims 1 to 5 or a superconducting tunnel junction obtained by a method according to any one of claims 6 to 9, characterized in that, The application is used in any of the following: superconducting quantum bits, superconducting detectors, terahertz radiation sources, flexible superconducting electronic devices, and superconducting functional circuits constructed by combining capacitances and inductances written with liquid metal; the superconducting functional circuit is preferably an LC oscillation circuit.

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