Josephson junction, manufacturing method and quantum equipment

Abstract

The invention discloses a Josephson junction, a manufacturing method and quantum equipment, and belongs to the field of quantum chip manufacturing. Wherein the Josephson junction comprises a first superconducting film, a barrier layer and a second superconducting film which are stacked in sequence. The method comprises the following steps of: performing oxidation reaction under the condition that the reaction atmosphere is updated to realize that the oxygen pressure in the reaction atmosphere is in dynamic balance, so as to manufacture an oxide layer as the barrier layer. According to the mode, the consistency of the barrier layer in the manufactured Josephson junction can be higher, so that the performance or parameters, associated with the consistency, of the Josephson junction and derivative equipment of the Josephson junction can be improved.

Description

Technical Field

[0001] The present application belongs to the field of quantum information, especially the field of quantum chip manufacturing. In particular, the present application relates to a Josephson junction and a manufacturing method and a quantum device. Background Art

[0002] The Josephson junction is an important superconducting electronic component that plays a key role in quantum computing, quantum information processing, precision measurement, and basic research. This structure is known for its unique electrical properties and is a key component in the field of superconductors.

[0003] Therefore, when manufacturing superconducting quantum chips, ensuring the manufacturing quality of the Josephson junction has an important impact on the performance of the superconducting quantum chip. Summary of the invention

[0004] The examples of the present application provide a Josephson junction and a manufacturing method and a quantum device, which can be used to manufacture quantum devices such as Josephson junctions with higher barrier consistency, thereby improving the performance of quantum devices associated with the consistency, such as the constant temperature resistance of the Josephson junction.

[0005] The solution of this application example is implemented through the following contents.

[0006] In a first aspect, examples of the present application propose a method of manufacturing a Josephson junction for improving fluctuations in critical current in a superconducting state of the Josephson junction.

[0007] The Josephson junction comprises a first superconducting film, a barrier layer and a second superconducting film stacked in sequence, and the method comprises the step of manufacturing the barrier layer in the following manner: the superconducting film undergoes an oxidation reaction under the condition of updating the reaction atmosphere to achieve a dynamic equilibrium of the oxygen pressure in the reaction atmosphere, so as to manufacture an oxide layer as the barrier layer.

[0008] According to some examples of the present application, the oxidation reaction is carried out in a container, and the method of updating the reaction atmosphere includes:

[0009] Oxygen is introduced into the container and simultaneously exhausted from the container, so that the container is continuously in a constant pressure state of oxygen flow during the oxidation reaction.

[0010] According to some examples of the present application, the container is connected to a pressure gauge and a valve;

[0011] The pressure gauge is configured to measure the oxygen pressure in the container, and the valve is configured to be controlled to be linked to perform opening or closing or adjust the opening degree depending on the pressure value reflected by the pressure gauge.

[0012] In a second aspect, an example of the present application provides a method for manufacturing a Josephson junction. The Josephson junction includes a first superconducting film, a barrier layer, and a second superconducting film stacked in sequence. The method includes:

[0013] Manufacturing or providing a substrate with a pattern layer, the pattern layer having a deposition window;

[0014] Depositing in the deposition window to manufacture the first superconducting film;

[0015] Oxidizing the first superconducting film to form a barrier layer, and the oxygen for oxidizing the first superconducting film is provided by an oxygen-containing reaction atmosphere that flows relative to the first superconducting film and generates a constant pressure; and

[0016] Depositing in the deposition window to manufacture the second superconducting film, thereby forming a Josephson junction in a region where the first superconducting film, the barrier layer, and the second superconducting film are stacked in sequence.

[0017] According to some examples of the present application, the pattern layer is a photoresist layer, and the photoresist layer forms a suspended resist structure at the deposition window;

[0018] And / or, the pattern layer is a photoresist layer, and the photoresist layer is a bilayer resist;

[0019] And / or, the method for manufacturing a Josephson junction further includes: removing the pattern layer after the Josephson junction is formed.

[0020] According to some examples of the present application, the deposition window includes a first sub-window and a second sub-window, and the first sub-window and the second sub-window cross each other;

[0021] And / or, the deposition process for manufacturing one or both of the first superconducting film and the second superconducting film is implemented by inclined evaporation.

[0022] According to some examples of the present application, in the step of oxidizing the first superconducting film to manufacture the barrier layer, the oxidation operation is performed in-situ;

[0023] Optionally, the method for in-situ oxidizing the first superconducting film includes the step of providing an oxygen-containing reaction atmosphere. The supply mode of the reaction atmosphere is: in a non-closed chamber where the substrate is placed, after manufacturing the first superconducting film, the substrate does not leave the chamber, and gas is dynamically supplied to the chamber and simultaneously pumped out of the chamber so that the oxygen pressure in the chamber is constant.

[0024] According to some examples of the present application, the pattern layer is a photoresist layer and is manufactured by a photolithography process;

[0025] The photolithography process includes: removing the residual resist generated during the development process by directionally etching through a reactive ion etching device after development.

[0026] According to some examples of the present application, the photolithography process further includes: an operation of etching the substrate surface to enhance the bonding strength between the manufactured first superconducting film and the substrate; and the etching of the substrate is achieved by performing reactive ion etching directed in the deposition window.

[0027] Optionally, in the photolithography process of manufacturing the photoresist layer, there are steps implemented to improve the linewidth consistency and controllability of the deposition window, and these steps include controlling the temperature of the developer to delay the development speed and also performing ultrasonic treatment simultaneously.

[0028] In a third aspect, an example of the present application proposes a Josephson junction manufactured by implementing a method for manufacturing a Josephson junction.

[0029] In a fourth aspect, an example of the present application proposes a quantum device. The quantum device is, for example, a qubit, a quantum interferometer, a quantum chip, a quantum memory, or a quantum computer, and the quantum device has the aforementioned Josephson junction.

[0030] In the above implementation process, when multiple Josephson junctions need to be manufactured simultaneously or in batches, through the method in the examples of the present application, the barrier layers (or described as tunneling layers, etc.) in these Josephson junctions can have more consistent or identical performance, and for the overall Josephson junction, consistent performance can also be obtained due to this solution. That is to say, the above solution not only makes the difference in the barrier layers between different Josephson junctions small, thereby improving the related performance of the Josephson junction based on the barrier layer, such as the normal temperature resistance and the corresponding critical current. Description of the Drawings

[0031] For a clearer illustration, the drawings required for use in the description will be briefly introduced below.

[0032] Figure 1 It is a comparative schematic diagram of the resistance of the Josephson junction when manufacturing the barrier layer in multiple Josephson junctions in two ways of static oxidation and dynamic oxidation in the examples of the present application;

[0033] Figure 2 It is a process flow schematic diagram of manufacturing a Josephson junction by dynamic oxidation in the examples of the present application;

[0034] Figure 3 It is a structural comparative schematic diagram of two forms of deposition windows in the photoresist layer formed on the substrate surface in the examples of the present application;

[0035] Figure 4 records Figure 3 It is a structural schematic diagram of the suspended photoresist of the photoresist layer with a bilayer resist structure;

[0036] Figure 5A structural comparison diagram showing two structural forms of Josephson junctions in the examples of this application. Detailed implementation

[0037] A Josephson Junction (JJ for short) is an important superconducting electronics component. It plays a crucial role in quantum computing, quantum information processing, precision measurement, and basic research. It forms a key component in the field of superconducting quantum computers due to its unique electrical properties.

[0038] The following elaborates on multiple aspects of the Josephson junction.

[0039] 1. Structure and principle:

[0040] A Josephson junction consists of a non-superconducting tunnel or insulating layer between two superconducting electrodes. In a superconductor, electrons form Cooper pairs and flow with zero resistance. When the non-superconductor in the Josephson junction is very thin, electrons can cross the tunnel by quantum tunneling. Such a quantum tunneling method leads to the Josephson effect.

[0041] 2. Josephson effect:

[0042] A Josephson junction can exhibit some amazing electrical properties. The most well-known are the DC Josephson effect and the AC Josephson effect.

[0043] DC Josephson Effect: At zero voltage, the current on both sides of the superconductor is quantized and can be described by the following relationship: I = I0sin(φ). Where I is the current, I0 is the critical current, and φ is the phase difference.

[0044] AC Josephson Effect: When the voltage on both sides of the superconductor is not zero, an alternating voltage will be generated. This effect is widely used in frequency standards (such as atomic clocks) and voltage standards (such as superconducting voltage standards).

[0045] 3. Application fields:

[0046] Josephson junctions have important applications in quantum computing and quantum information processing and can be used as components of quantum bits. In addition, Josephson junctions can also be used in the field of precision measurement, such as voltage standards, frequency standards, and magnetic field measurement.

[0047] 4. Stability:

[0048] The stability of Josephson junctions is crucial for realizing high-performance qubits. To improve the stability of Josephson junctions, factors such as temperature, magnetic field, and current can be precisely controlled, and materials and fabrication processes can be optimized.

[0049] Some structural examples of Josephson junctions:

[0050] In superconducting qubits (Quantum Bit, qubit), Josephson junctions have various different structural types.

[0051] For example, Josephson junctions include cross junctions (Manhattan junctions), Dolan bridges, anisotropic junctions, etc. In addition, there are some other variants and derivative structures of Josephson junctions to meet different quantum computing requirements.

[0052] The following is a brief description of these main structures, as well as some other possible Josephson junction structures.

[0053] Cross junction:

[0054] A cross junction is a special-shaped Josephson junction, usually formed by the intersection of two superconducting electrodes. Cross junctions can be used to realize charge qubits, phase qubits, and hybrid qubits.

[0055] Dolan bridge:

[0056] The Josephson junction structure in the form of a Dolan bridge includes a Josephson junction and an inductive element connected to it. Dolan bridges are usually used for the realization of flux qubits.

[0057] Anisotropic junction:

[0058] An anisotropic junction is a Josephson junction with non-uniform superconductivity characteristics. Its superconducting properties have different characteristics in different directions and are usually used to realize some special qubits.

[0059] Crossed Josephson Junction:

[0060] A crossed Josephson junction is a structure in which multiple Josephson junctions cross each other in a superconducting circuit and is used to realize complex qubit layouts.

[0061] It can be known that with the continuous development of quantum technology, other new structural forms of Josephson junction structures and variants may emerge to meet the quantum computing and information processing needs in different fields. These different types of Josephson junction structures provide more flexibility and choices for the design and performance of qubits.

[0062] It should be noted that in the following text of this application, the optimization of the cross junction is mainly discussed and elaborated, but this does not limit that the solutions of the examples of this application can only be applied to the cross junction.

[0063] The manufacturing process of the existing Josephson junctions can refer to the following content:

[0064] The process steps for preparing a cross-shaped Josephson junction can be briefly summarized as using a resist pattern mask and in-situ evaporation and oxidation to form a stacked Al / AlOx / Al JJ structure, and it can be mainly implemented through the following specific steps.

[0065] The following multiple operations are involved in the above process.

[0066] Patterning: Use a bilayer resist (PMMA+MMA; polymethyl methacrylate+methyl methacrylate) to form a cross pattern on the substrate through electron beam lithography (abbreviated as EBL).

[0067] Oblique evaporation: Evaporate a 36.6 nm thick aluminum (Al) layer for the first time (E-beam; electron beam evaporation); evaporate at an oblique angle of 45° to hide the line pattern perpendicular to the evaporation direction. Since the nominal film thickness is calibrated at an incident angle of 0°, the actual film thickness depends on the evaporation angle.

[0068] Oxidation: Introduce pure oxygen at 1.0 Torr for 10 minutes, and the surface of the first aluminum film is oxidized into an alumina surface (this oxidation is insufficient oxidation) to form the AlOx barrier / barrier layer of the JJ. The typical barrier layer thickness is 1.4 - 1.9 nm.

[0069] Oblique evaporation: Evaporate for the second time (E-beam) after the wafer is rotated 90°, and evaporate at an oblique angle of 45°. The thickness of the second aluminum is 96.7 nm.

[0070] Lift-off: Clean the substrate with an organic solution to obtain one or more required Josephson junctions.

[0071] In order to investigate various characteristics and performances of the Josephson junction, etc., the inventors determined in practice that it can be evaluated through some characteristics described below.

[0072] I. Josephson junction stability

[0073] The inventors believe that to improve the uniform stability of Josephson junctions in quantum chips, the following key factors and methods need to be considered.

[0074] A. Material selection:

[0075] The performance of Josephson junctions highly depends on the superconducting materials used. Selecting high-quality and uniform superconducting materials is crucial. For example, aluminum and silver are both commonly used superconducting materials. Ensure that the material preparation process is strictly controlled to reduce non-uniformity.

[0076] B. Fabrication process:

[0077] When fabricating Josephson junctions, precise process control should be used to ensure the uniformity and stability of the structure. This includes depositing thin films of superconducting materials, defining the size and shape of Josephson junctions, and controlling the interface quality of the materials.

[0078] C. Temperature control:

[0079] The operating temperature of superconducting materials usually needs to be maintained in the superconducting state, which is typically a very low temperature. The stability and uniformity of temperature are key factors in ensuring the stable performance of Josephson junctions. Use high-quality cooling systems and temperature control devices to reduce temperature gradients and fluctuations.

[0080] D. Stability of the current source:

[0081] Josephson junctions are usually manipulated by applying a current to them. Use a highly stable current source to ensure the uniformity and stability of the current, which is very important for obtaining consistent quantum operations.

[0082] E. Magnetic field shielding:

[0083] Magnetic fields have a great impact on the performance of Josephson junctions. In a laboratory environment, use magnetic field shielding devices to reduce the influence of external magnetic fields on the junctions.

[0084] F. Noise control:

[0085] Noise is a key issue in quantum computing. Reduce the influence of external electromagnetic noise and thermal noise on Josephson junctions through appropriate design and shielding.

[0086] G. Stability of the experimental setup:

[0087] Ensure the stability of the mechanical and electronic components of the experimental setup to reduce the influence of any vibrations or electronic noise on Josephson junctions.

[0088] H. Monitoring and feedback:

[0089] Monitor the performance of the Josephson junction in real time and perform feedback control as needed to maintain its stability and uniformity.

[0090] In short, in order to improve the uniformity and stability of the Josephson junction, careful design and control can be considered in multiple aspects such as material selection, preparation process, temperature control, current source, magnetic field shielding, noise control, and experimental setup. And this is crucial for realizing high-performance quantum computing and quantum information processing. The solution in the examples of this application mainly optimizes the stability of the Josephson junction from the perspective of the preparation process.

[0091] II. Normal Temperature Resistance of Josephson Junction

[0092] The normal temperature resistance refers to the resistance characteristics exhibited by the Josephson junction at normal temperature (usually referring to room temperature, i.e., about 20 degrees Celsius or 293 Kelvin). At normal temperature, the Josephson junction is usually no longer in the superconducting state, so it will exhibit a finite resistance, and this resistance value is the normal temperature resistance of the Josephson junction.

[0093] The normal temperature resistance of the Josephson junction is usually expressed in ohms (Ω). It represents the voltage drop generated by the current passing through the junction at normal temperature. The normal temperature resistance is one of the electrical characteristics of the Josephson junction and is used to describe the resistance properties of the junction in the non-superconducting state. However, this value may vary due to specific Josephson junction types, preparation processes, and material differences.

[0094] The normal temperature resistance usually corresponds to the key parameters of the Josephson junction at low temperature, mainly the critical current, critical voltage, and energy gap of the Josephson junction, etc.

[0095] Critical Current:

[0096] The critical current is the maximum current that can pass through the Josephson junction in the superconducting state. At low temperature, when the Josephson junction is in the superconducting state, it can pass a non-zero current without generating a voltage. The resistance at normal temperature corresponds to the situation of the critical current of the Josephson junction at low temperature. That is, when the current is greater than the critical current, the Josephson junction will deviate from the superconducting state and a voltage drop will occur.

[0097] Critical Voltage:

[0098] The critical voltage is the voltage that appears when the Josephson junction deviates from the superconducting state. When the current of the Josephson junction exceeds the critical current, it will cause the critical voltage, thereby bringing it into the normal state and the resistance becomes a finite value.

[0099] Energy Gap:

[0100] The energy gap of a superconductor refers to the minimum energy required for electrons to transition to an excited state in the superconducting state. The energy gap is usually related to the critical current and critical voltage because it is closely related to the stability of the superconducting state.

[0101] Josephson frequency:

[0102] An important property exhibited by a Josephson junction in the superconducting state is the Josephson frequency. The Josephson frequency is related to the energy gap of the Josephson junction and can be expressed by the following formula: F j = 2eV / h. Where, F j is the Josephson frequency, e is the electron charge, V is the voltage of the Josephson junction, and h is the Planck constant. The Josephson frequency is related to the energy gap of the Josephson junction in the superconducting state.

[0103] Quantum bit frequency:

[0104] The frequency of a quantum bit refers to the energy difference between energy levels in its energy level structure, usually measured in Hertz (Hz). The frequency of a quantum bit can be affected by an external magnetic field, microwave excitation, and Josephson junctions. In some quantum bit systems, Josephson junctions are used as components of the quantum bit.

[0105] It should be noted that the above parameters of the Josephson junction can typically achieve their typical superconducting electronics characteristics only at low temperatures. In the superconducting state, current can flow without resistance, and below the critical current, the Josephson junction exhibits zero resistance. At room temperature, due to thermal excitation and other factors, the Josephson junction will exhibit finite resistance.

[0106] Therefore, there is a close connection between the room temperature resistance and the critical current, critical voltage, and energy gap at low temperatures. These parameters all play important roles in the research and application of the superconducting properties of the Josephson junction.

[0107] The main purpose of the examples of this application is to provide a method for reducing the non-uniformity of the room temperature resistance of Josephson junctions generated in the manufacturing process - especially the non-uniformity of the associated critical current. Moreover, through the solution of the examples of this application, the overall uniformity of the room temperature resistance of the Josephson junction can be made within 5%, thereby improving the quality of the Josephson junction.

[0108] The non-uniformity, for example, is manifested as obvious and significant fluctuations in performance parameters such as the normal temperature resistance and critical current of Josephson junctions manufactured in batches, with each batch manufacturing one or more Josephson junctions. For example, the normal temperature resistance value is 12% measured by relative standard deviation (RSD). The solution exemplified in this application can achieve controlling the RSD to below 7%, such as 5% as described above.

[0109] Through the analysis of relevant data in the experiment and physical products, the inventor found that one of the important factors causing the above-mentioned normal temperature resistance fluctuations in Josephson junctions lies in the structure of its barrier layer.

[0110] The inventor is familiar with the fact that in superconducting Josephson junctions, the change in the thickness of the AlOx layer (referred to as the barrier layer) of the AlOx tunnel barrier and structural defects form noise sources, thus restricting the application of various components and devices based on it. For example, when there are defects caused by the barrier layer in a superconducting Josephson junction, it will cause a decrease in the detection sensitivity of superconducting interference devices constructed based on it and a shortening of the coherence time of qubits.

[0111] Analyzing the existing manufacturing scheme of Josephson junctions, the applicant found that the current scheme is to manufacture the barrier layer of Josephson junctions by static oxidation. In other words, oxidation is carried out to manufacture the barrier layer under a fixed O2 partial pressure.

[0112] That is, the oxidation chamber used to manufacture the barrier layer by oxidation is first pumped to a certain air pressure and then sealed to form a sealed cavity. Then, oxygen is introduced into the cavity until the set oxidation air pressure is reached, and then the ventilation is stopped. Maintaining the low-pressure oxygen atmosphere in the cavity, the holding pressure time is set for oxidation. During this oxidation process, it mainly involves controlling the oxidation air pressure and oxidation time, and accordingly achieving the control of the thickness of AlOx.

[0113] However, the results show that the actual effect of the above-mentioned static oxidation scheme is not ideal, and there are often large fluctuations in the normal temperature resistance between different Josephson junctions, thus seriously affecting their performance and normal use.

[0114] For aluminum junctions - aluminum-based Josephson junctions, in the form of Al / AlOx / Al - its oxidation process is a self-limiting process. That is to say, in the initial stage, aluminum undergoes rapid oxidation, and then the oxide layer grows to saturation, and the oxidation rate decreases to zero.

[0115] The specific oxidation process is as follows:

[0116] During the oxidation process, first, oxygen molecules are adsorbed on the aluminum surface through physical action (van der Waals force). At this time, no covalent or ionic bonds are formed between the oxygen molecules and the atoms or lattice on the aluminum surface. Then, the oxygen molecules dissociate into oxygen atoms (the oxygen-oxygen bond breaks), and the dissociated oxygen atoms diffuse and sink on the aluminum surface to find reaction sites. When the oxygen atoms diffuse to a suitable position, they react with aluminum atoms - aluminum loses electrons to form aluminum oxide. Finally, as an aluminum oxide film is formed on the aluminum surface through oxidation, it will prevent the continuous diffusion of oxygen atoms, thereby protecting the further oxidation of the aluminum layer. In this process, the oxidation reaction of aluminum is spontaneous, that is, the Gibbs free energy ΔG = ΔH - TΔS > 0 for the reaction of aluminum with oxygen.

[0117] Moreover, the aluminum oxide grown in this way is an unsaturated and amorphous AlOx layer. In specific practice, electron beam evaporation can be used to achieve the static preparation of the aluminum layer in a deposition system under high vacuum (HV) conditions.

[0118] As described above, static oxidation is carried out at a fixed oxygen partial pressure, and at a certain pressure and fixed oxygen flow rate. The oxidation process is a self-limiting process. It oxidizes rapidly in the initial stage, then the growth of the oxide layer saturates, and the oxidation rate decreases to zero. The growth of self-limiting oxides is conducive to rapid and batch preparation of the barrier layer in Josephson junctions. That is to say, this growth mode of self-limiting oxides is conducive to the AlOx-tunnel barrier in the Josephson junctions fabricated based on it, because it provides a high degree of reproducibility, thus providing the necessary conditions for large-scale manufacturing.

[0119] Continuing from the above, after studying the barrier layer of Josephson junctions fabricated using static oxidation, the inventors are convinced that the above problems existing in the static oxidation scheme can be attributed to the inaccurate control of the background vacuum during the oxidation process, the amount of oxygen introduced, the pressure retention of the cavity, and the leak rate, etc.

[0120] In addition, the inventors also know that the oxidation conditions of the barrier layer in Josephson junctions can be related to the critical current at low temperatures. Therefore, during the static oxidation process, the critical current is affected by temperature, oxidation pressure, and oxidation time.

[0121] Previously, the change in the critical current was attributed to the change in the thickness of the oxide layer (and the thickness is related to the normal temperature resistance corresponding to normal temperature).

[0122] However, according to the analysis of the above-mentioned static oxidation process of aluminum, the thickness of the AlOx tunnel barrier in the aluminum junction is basically fixed. Through repeated experiments, the inventors found that the change in the composition of the AlOx barrier layer and the change in the Al-O coordination - that is, the average number of bonds between Al and O - will also affect the resistivity of the tunnel barrier, and this can be verified and confirmed through atomic-scale analysis of the AlOx composition and relevant tests of normal temperature resistance.

[0123] Based on the above discussions and analyses, the inventors believe that the conclusion can be drawn that the quality of the Josephson junction (the composition of AlOx) is highly related to the initial oxidation conditions, yet it is very difficult to control with the existing static oxidation method.

[0124] In view of this, in the examples of this application, the inventors proposed a dynamic oxidation scheme for manufacturing the barrier layer. That is, a constant MFC (Mass Flow Controller) is used to control the flow of O2, but the cavity is not closed during the oxidation process. The molecular pump valve is connected to a vacuum gauge, and the opening degree of the molecular pump valve is controlled in real time to keep the cavity at a constant pressure state. And during this process, the overall cavity is also kept in a balanced state of ventilation and pumping. In such a flowing O2 gas environment, the uniformity of oxidation can be further ensured.

[0125] Technically speaking, compared with the factors such as the background vacuum, oxygen flow rate, pressure retention and leakage rate of the cavity during the static oxidation process, which are difficult to accurately and stably control, the dynamic oxidation in this application can better and more easily control the oxygen flow rate and the pressure in the cavity, thus ensuring the process repeatability between batches and further improving the stability of the Josephson junction.

[0126] Figure 1 A comparison chart of the normal temperature resistance of two groups (25 in each group, and the junctions in the same group have the same manufacturing raw materials and design structures) of Josephson junctions under different oxidation processes (dynamic oxidation and static oxidation) conditions is given. According to Figure 1 As can be seen from the figure, by using the dynamic oxidation method, higher normal temperature resistance stability can be achieved, that is, the fluctuation of the normal temperature resistance is small.

[0127] In one aspect, this application proposes a method for manufacturing a Josephson junction to improve the fluctuation of the critical current in the superconducting state of the Josephson junction.

[0128] The Josephson junction therein, for example, is a tunnel junction, which includes a three-layer structure. In the examples of this application, the three-layer structure is a first superconducting film, a barrier layer, and a second superconducting film. And, the three-layer structure is stacked in sequence, that is, the barrier layer is clamped by the first superconducting film and the second superconducting film. When specifically applied to quantum devices, the Josephson junction is formed on the surface of the substrate, or further can be surrounded by other structural layers (such as a ground plane) on the surface of the substrate, etc. And, the Josephson junction can be attached to the surface of the substrate with the first superconducting film layer therein; or, it can also be selected to make the Josephson junction attached to the surface of the substrate with the second superconducting film layer therein.

[0129] Based on the above Josephson junction, in some examples of the present application, a Josephson junction manufacturing method capable of reducing the critical current fluctuation of the manufactured Josephson junction includes the step of manufacturing a barrier layer by the following method: under the condition of updating the reaction atmosphere to achieve a dynamic equilibrium of the oxygen pressure in the reaction atmosphere, the superconducting film undergoes an oxidation reaction to manufacture an oxide layer as the barrier layer.

[0130] Therefore, it should be understood that the first superconducting film and the second superconducting film in the Josephson junction can be selected and manufactured by various processes known to those skilled in the art, and specific limitations are not made in the present application.

[0131] In other words, in the case of manufacturing the first superconducting film and the second superconducting film by using the existing scheme (such as the aforementioned inclined evaporation; and it can be understood that in other examples, it can also be direct evaporation), the improvement of the critical current performance of the Josephson junction can be achieved only by the manufacturing process of the barrier layer proposed in the examples of the present application.

[0132] Correspondingly, if combined with the improvement of the manufacturing process of the first superconducting film and the second superconducting film, the manufactured Josephson junction can have a better performance surface, such as a longer coherence time and smaller critical current fluctuation. For the first superconducting film and the second superconducting film, the improved manufacturing process is, for example, to change the single inclined evaporation of the existing first superconducting film or second superconducting film to two symmetric inclined evaporations; and the two inclined evaporations are symmetric to form a thickness supplement, so that the thickness of the superconducting film is more uniform. This is because, during inclined evaporation, there will be a thickness difference in one evaporation according to the distance from the evaporation source, and through the compensation of the other evaporation, the thickness of the two layers can be complementary - the thick part and the thin part cooperate up and down - to improve the stability and consistency of the overall thickness of the film.

[0133] Subsequently, the manufacturing process proposed by the inventors of the present application for the barrier layer will be mainly described.

[0134] For the barrier layer, its manufacturing method is: under the condition of updating the reaction atmosphere to achieve a dynamic equilibrium of the oxygen pressure in the reaction atmosphere, the superconducting film undergoes an oxidation reaction to manufacture an oxide layer as the barrier layer.

[0135] In the above method, the barrier layer is fabricated by the oxidation reaction of the first superconducting film (in an aluminum junction, it is a metal aluminum film layer). And in this step, the oxidation reaction is carried out in a container, and the way to update the reaction atmosphere includes: introducing oxygen into the container and simultaneously discharging oxygen out of the container, so that the container is continuously in a constant-pressure state of oxygen flow during the oxidation reaction.

[0136] For example, a roughly rectangular cavity may be provided with an air inlet and an air outlet on two opposite side walls thereof. The air inlet is used to inject pure oxygen into the container, or a mixture of oxygen and other gases if necessary. The air outlet is used to allow the gas in the container to be discharged outside the container; the power for the discharge may come from the input airflow of the air inlet, or by providing an additional exhaust device or a suction device.

[0137] In order to more accurately control the pressure balance in the container so as to realize the oxidation reaction of the superconducting film in a constant oxygen environment, the container can be connected with a pressure gauge and a valve. The valves can be an inlet valve and an exhaust valve, respectively. The pressure gauge is configured to measure the oxygen pressure in the container, and the valve is configured to be controlled to be linked to perform opening or closing or adjust the opening depending on the pressure value reflected by the pressure gauge.

[0138] In the automation control scheme, control devices can also be configured, such as central processing unit (CPU), micro control unit (MCU), programmable logic controller (PLC), programmable automation controller (PAC), industrial control computer (IPC), field programmable gate array (Field-Programmable Gate Array, FPGA), application-specific integrated circuit chip (ASIC chip, Application Specific Integrated Circuit), etc.

[0139] The pressure gauge and valve are electronic devices, so they can be connected to the control device in a communication manner. Specifically, the pressure gauge and valve can be connected to the control device in a wired manner. Or they can be connected wirelessly by infrared, Bluetooth, or near-field communication. The control device can obtain the measurement results of the pressure gauge and valve, and control the opening, closing, and opening size of the valve according to the pre-set operation process, mode, or manual operation.

[0140] The above method can realize the manufacture of high-quality barrier layers more easily and efficiently.

[0141] The reason why this solution is easy to implement and more efficient (completion of junction manufacturing in a shorter time) is that in this solution, in order to control the quality of the manufactured Josephson junction, the factors that can be controlled include controlling the flow rate of oxygen and the pressure in the cavity. However, in the existing static oxidation process, the control factors for obtaining a high-quality Josephson junction are the background vacuum, the amount of oxygen introduced, the pressure retention of the cavity, and the leakage rate. By comparison, it can be seen that the solution of the example of this application has a relatively small number of control factors and a relatively small control difficulty, so it can be implemented with less difficulty and thus obtain a high-quality junction.

[0142] In an example of the present application, another method for manufacturing a Josephson junction including a first superconducting film, a barrier layer, and a second superconducting film stacked in sequence is also proposed.

[0143] Refer to Figure 2 , the method for the Josephson junction includes the following steps:

[0144] Step S601, manufacturing or providing a substrate with a pattern layer, the pattern layer having a deposition window;

[0145] Step S602, depositing in the deposition window to manufacture the first superconducting film;

[0146] Step S603, oxidizing the first superconducting film to form a barrier layer, and the oxygen for oxidizing the first superconducting film is provided by an oxygen-containing reaction atmosphere flowing relative to the first superconducting film and generating a constant pressure;

[0147] Step S604, depositing in the deposition window to manufacture the second superconducting film, so as to form a Josephson junction in the region where the first superconducting film, the barrier layer, and the second superconducting film are stacked in sequence.

[0148] Furthermore, the method for manufacturing a Josephson junction may further include an operation of removing the pattern layer after the Josephson junction is formed, so as to form a desired Josephson junction on the substrate surface.

[0149] In the above steps, in step S601, the substrate can be selected as sapphire or high-resistance silicon, and through thinning, surface planarization treatment, etc. The pattern layer can be selected as a hard mask (single layer or multiple layers), or can also be selected as a photoresist layer.

[0150] Taking the photoresist layer as an example, after the substrate is processed, a photoresist coating film is formed on the surface of the substrate by spin coating, and then a mask plate is used and various photolithography processes such as exposure, development, and fixing are performed to remove the photoresist in some areas to form a deposition window with a designed pattern.

[0151] Furthermore, according to different forms of the deposition window selected to be implemented, it can have different shapes. For example, from the cross section, refer to Figure 3 , the deposition window can include an undercut structure, and if necessary, it can also be implemented as a topcut structure. In such an example, the top edge and the bottom edge of the photoresist layer at the deposition window are in an inclined structure.

[0152] Or, in some other examples, the deposition window of the photoresist layer can also be a vertical hole relative to the substrate. Therefore, in such an example, the top edge and the bottom edge of the photoresist layer at the deposition window are in a vertical structure.

[0153] In still other examples, the photoresist layer is implemented as a bilayer resist structure, i.e., two stacked photoresist films. Further, for the undercut structure, the bilayer resist structure can form a suspended resist structure at the deposition window, as Figure 4 shown.

[0154] In addition to the limitation of the deposition window in the longitudinal structure, its specific composition can also be investigated.

[0155] For example, for a one-dimensional Josephson junction (abbreviated as a one-junction), the deposition window can be a single through hole perpendicular to the substrate formed on the photoresist layer.

[0156] Or, for a cross-shaped Josephson junction (abbreviated as a cross-junction), the deposition window can be two through holes that cross each other and are perpendicular to the substrate formed on the photoresist layer. That is, the deposition window includes a first sub-window and a second sub-window, and the first sub-window and the second sub-window cross each other.

[0157] Among them, the structures of the one-junction and the cross-junction are as Figure 5 shown. It should be noted that in Figure 5 only two layers of superconducting films (represented by different rectangular filled areas) of the two types of junctions are shown, while the barrier layer therebetween is omitted.

[0158] In the examples of this application, the specific structure of the Josephson junction is not specifically limited, and the form of the deposition window corresponding to the structure of the Josephson junction is selected according to actual manufacturing needs.

[0159] From a process perspective, the pattern layer with a deposition window can be formed by wet etching or dry etching. And these etching operations are implemented as one or more steps of the lithography process. In particular, in the lithography process, after development, the residual resist generated in the development process is etched away by directional etching using a reactive ion etching device. Directional etching will help avoid etching other parts that are not desired to be etched, thus ensuring the accuracy of the deposition window pattern, such as sharper and clearer edges, etc.

[0160] After development in the above manner, the lithography process for manufacturing the pattern layer can also include: an operation of etching the substrate surface to improve the bonding strength between the fabricated first superconducting film and the substrate. The operation of etching the substrate is, for example, achieved by performing reactive ion etching directed in the deposition window. Through such etching, the substrate surface can be impurity-free and smoother, which is more conducive to the attachment of the first superconducting film to the substrate.

[0161] Further, as a beneficial attempt and option, the lithography process for manufacturing the photoresist layer may further include steps implemented to improve the linewidth consistency and controllability of the deposition window. And this step includes controlling the temperature of the developer to delay the development speed and simultaneously performing ultrasonic treatment.

[0162] The consistency among them, for example, is that the sizes of the deposition windows are the same or closer in different batch processes. For example, for a rectangular deposition window, the above process can make the difference between the length and width dimensions of the rectangular structures of the deposition windows in different batches smaller.

[0163] The controllability among them, for example, is that the deposition window can be made to match the designed pattern better. Because a slower development speed can enable the photoresist to be etched more accurately. For example, for the top-down view angle relative to the substrate, the deposition window is a rectangular structure rather than a trapezoidal structure.

[0164] The above mainly discussed the related content of the photoresist layer. Next, turn to the discussion of step S603.

[0165] As described above, the barrier layer is formed by oxidizing the first superconducting film, and it is mentioned in the above analysis that the component composition of the barrier layer will have a considerable impact on the performance of the junction. Therefore, in some examples of the present application, the oxidation operation in the step of controlling the oxidation of the first superconducting film to manufacture the barrier layer is carried out in-situ. That is, after depositing and manufacturing the first superconducting film in a closed chamber, the substrate is not taken out, but the first superconducting film is directly oxidized in the chamber to form an oxide layer, which can be used as the barrier layer.

[0166] In some alternative examples, the method for in-situ oxidation of the first superconducting film includes the step of providing an oxygen-containing reaction atmosphere. And the supply mode of this reaction atmosphere is: in a non-closed chamber where the substrate is left, after manufacturing the first superconducting film, the substrate does not leave the chamber and gas is dynamically supplied to the chamber and simultaneously pumped out from the chamber so that the oxygen pressure in the chamber is constant. The constant pressure mode is achieved by a pressure monitoring device or system in combination with an exhaust system and a gas supply system. And it can be achieved by existing technologies, which are not elaborated in the present application.

[0167] In terms of the manufacturing process, for steps S602 and S604, the deposition process of manufacturing one or both of the first superconducting film and the second superconducting film can be implemented by direct evaporation, or by oblique evaporation, or by a combination of the two in any order. Considering the advantages of oblique evaporation, it can be used as a better option.

[0168] By implementing the above solutions, a Josephson junction with higher quality and more stable performance can be manufactured and formed in the present application.

[0169] Furthermore, a quantum device can be proposed based on this arrangement. The quantum device includes a qubit, a quantum interferometer, a quantum chip, a quantum memory, or a quantum computer, and one or more Josephson junctions are provided in the quantum device.

[0170] The structure, features, and effects of the present application have been described in detail based on the embodiments shown in the drawings. The above are only the preferred embodiments of the present application, but the present application is not limited to the scope of implementation shown in the drawings. Any changes made according to the concept of the present application, or equivalent embodiments modified to equivalent changes, should still be within the protection scope of the present application as long as they do not exceed the spirit covered by the description and the drawings.

Claims

1. A method for manufacturing a Josephson junction, which is used to improve the fluctuation of the critical current in the superconducting state of the Josephson junction. The Josephson junction includes a first superconducting film, a barrier layer, and a second superconducting film stacked in sequence, and is characterized in that, The method comprises the steps of manufacturing the barrier layer by: The superconducting film undergoes an oxidation reaction under the condition that the reaction atmosphere is updated to achieve a dynamic equilibrium of the oxygen pressure in the reaction atmosphere, so as to produce an oxide layer as the barrier layer.

2. The method for manufacturing a Josephson junction according to claim 1, characterized in that, The oxidation reaction is carried out in a container, and the method of updating the reaction atmosphere includes: Oxygen is introduced into the container and simultaneously exhausted from the container, so that the container is continuously in a constant pressure state of oxygen flow during the oxidation reaction.

3. The method for manufacturing a Josephson junction according to claim 2, characterized in that, The container is connected to a pressure gauge and a valve; The pressure gauge is configured to measure the oxygen pressure in the container, and the valve is configured to be controlled to be linked to open or close or adjust the opening degree depending on the pressure value reflected by the pressure gauge.

4. A method for manufacturing a Josephson junction, the Josephson junction comprising a first superconducting film, a barrier layer, and a second superconducting film stacked in sequence, characterized in that, The method comprises: Manufacturing or providing a substrate having a patterned layer, wherein the patterned layer has a deposition window; Deposition in a deposition window to produce a first superconducting film; oxidizing the first superconducting film to form a barrier layer, and oxygen for oxidizing the first superconducting film is provided by flowing relative to the first superconducting film and generating a constant pressure of an oxygen-containing reaction atmosphere; and Deposition is performed in the deposition window to manufacture a second superconducting film, thereby forming a Josephson junction in a region where the first superconducting film, the barrier layer, and the second superconducting film are sequentially stacked.

5. The method for manufacturing a Josephson junction according to claim 4, characterized in that, The graphic layer is a photoresist layer, and the photoresist layer forms a suspended gel structure at the deposition window; And / or, the graphic layer is a photoresist layer, and the photoresist layer is a double-layer photoresist; And / or, the method for manufacturing a Josephson junction further includes: removing the pattern layer after forming the Josephson junction.

6. The method for manufacturing a Josephson junction according to claim 4 or 5, characterized in that, The deposition window includes a first sub-window and a second sub-window, and the first sub-window and the second sub-window intersect each other; And / or, the deposition process of manufacturing one or both of the first superconducting film and the second superconducting film is performed by oblique evaporation.

7. The method for manufacturing a Josephson junction according to claim 4, characterized in that, In the step of oxidizing the first superconducting film to produce the barrier layer, the oxidation operation is performed in situ; Optionally, the method for in-situ oxidation of the first superconducting film includes the step of providing an oxygen-containing reaction atmosphere, wherein the reaction atmosphere is supplied in the following manner: in a non-enclosed cavity where the substrate is retained, after the first superconducting film is manufactured, the substrate does not leave the cavity and gas is dynamically supplied into the cavity and gas is simultaneously extracted from the cavity so that the oxygen pressure in the cavity is constant.

8. The method for manufacturing a Josephson junction according to claim 4, wherein The graphic layer is a photoresist layer and is manufactured by a photolithography process; The photolithography process includes: after development, using a reactive ion etching device to directional etch away the residual glue generated during the development process.

9. The method for manufacturing a Josephson junction according to claim 8, wherein The photolithography process also includes: etching the surface of the substrate to enhance the bonding strength between the manufactured first superconducting film and the substrate; and etching the substrate is achieved by performing reactive ion etching directed in the deposition window; Optionally, the photolithography process for manufacturing the photoresist layer includes: a step implemented to improve the line width consistency and controllability of the deposition window, and the step includes controlling the temperature of the developer to slow down the development speed, and also performing ultrasonic treatment at the same time.

10. A Josephson junction manufactured by implementing the method for manufacturing a Josephson junction according to any one of claims 1 to 9.

11. A quantum device, characterized in that, The quantum device is a qubit, a quantum interferometer, a quantum chip, a quantum memory, or a quantum computer, and the quantum device has a Josephson junction as described in claim 10.

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