Multi-layer thin film structure, preparation method and application of multi-layer thin film structure

Abstract

The invention discloses a multi-layer thin film structure, a preparation method and application of the multi-layer thin film structure. The multi-layer thin film structure comprises a single crystal substrate, an aluminum thin film and a tantalum thin film. The preparation method comprises the following steps: processing the surface of a single crystal substrate; epitaxially growing an aluminum film on the surface of the single crystal substrate; a tantalum film is epitaxially grown over the aluminum film. According to the multilayer film structure, the preparation method and the superconducting quantum bit device provided by the invention, the preparation method of a tantalum film is expanded, uniform growth of a large-area alpha-phase tantalum film is realized, the interface quality of the multilayer film is high, and the superconducting critical temperature is 2-4K. Meanwhile, the superconducting quantum bit device designed by the invention is long in de-coherence time, and the manufactured resonant cavity circuit has a high quality factor and can be applied to the fields of superconducting quantum bit devices, superconducting quantum computers and the like.

Description

Technical Field

[0001] The present invention relates to the field of quantum computing, and in particular to a multilayer film structure, a preparation method and applications thereof in superconducting quantum bit devices and superconducting quantum computing chips. Background Art

[0002] Quantum computing has advantages far beyond classical computers and has become the most cutting-edge technology field in which countries around the world compete. Quantum computing has become a potential solution in accelerating the development of new drugs, accelerating the cracking of encryption algorithms, accelerating artificial intelligence, promoting the development of the digital economy, and exploring and developing new materials. In 2017, the University of Science and Technology of China built the world's first optical quantum computer prototype for multi-photon "Bose sampling" tasks ( Jianwei Pan, et al., High-efficiency multiphoton boson sampling, Nature Photonics, 11, 2017 In 2021, the team led by Academician Pan Jianwei successfully developed the "Zu Chongzhi II", which achieved a high-density integration of 66 bits and a processing speed more than 10 million times faster than the fastest supercomputer currently available ( Jianwei Pan, et al., Strong quantum computational advantage using a superconducting quantum processor, Physical Review Letters, 127, 2021 ). At the same time, Huawei, Tencent, Alibaba, Baidu, Origin Quantum, Guodun Quantum and other companies are ranked in the "first echelon" of international quantum computing in terms of quantum computer research and development. In 2022, Baidu released the world's first full-platform quantum hardware and software integrated superconducting quantum computer "Qianshi" ( https: / / quantum.baidu.com / ), Hefei Benyuan Quantum's 64-bit quantum computer "Wuyuan" third generation was developed in Hefei ( https: / / qcloud.originqc.com.cn / zh / ).

[0003] Superconducting quantum computers need to build large-scale superconducting quantum bits, that is, to increase the number of quantum bits as much as possible. However, the manufacturing properties of two-dimensional planar circuits, on the one hand, limit the increase in the number of superconducting bits. On the other hand, the design of introducing control lines from the four sides of the chip to the middle position gradually increases the density during the expansion process, and the crosstalk is serious. Therefore, the development of three-dimensional integration technology to solve these problems has become a focus. Sapphire has extremely low dielectric loss and is the most commonly used wafer substrate for superconducting quantum computing, but it is hard and difficult to process. Similarly, single-crystal silicon substrates also have low dielectric loss, and the manufacturing and processing technology (especially the three-dimensional interconnection technology of silicon chips) is mature. Therefore, the development of superconducting quantum chips on silicon substrates has broad application prospects.

[0004] Decoherence time is an important indicator for evaluating the quality of a quantum bit. In superconducting quantum circuits, dissipative channels may be introduced throughout the entire process, including structural design, material preparation, chip processing, and manufacturing environment, which will reduce the decoherence time and affect the manipulation and reading of its quantum state. At present, energy decoherence can be reduced by reducing parasitic capacitance through air bridge structures, adding magnetic shielding covers to reduce external magnetic field noise, and using filters to reduce infrared rays. However, material microstructures such as material defects, interface quality, impurity atoms, and amorphous oxide layer thickness are difficult to control. Ta grown on sapphire will be based on Transmon The quantum bit decoherence time is increased to 300 μs [ Andrew A. Houck et al., New material platform for superconducting transmon qubits with coherence times exceeding 0.3 milliseconds, Nature Communications, 12, 1779, 2021. ], which triggered a boom in the growth of Ta thin films. However, the process conditions of Ta thin films grown by magnetron sputtering are difficult to control, and the material interface is easily damaged. It is necessary to develop new preparation technologies to manufacture higher quality superconducting Ta thin films and achieve better quantum bit performance. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a multi-layer thin film structure, including a single crystal substrate, an aluminum thin film, and a tantalum thin film stacked in sequence.

[0006] Preferably, the multilayer thin film structure has superconducting transition properties, and the superconducting transition temperature ranges from 2 to 4K.

[0007] Preferably, the aluminum film is a single crystal structure.

[0008] Preferably, the thickness of the aluminum thin film is 1 to 50 nm.

[0009] Preferably, the aluminum thin film and the tantalum thin film are grown on the single crystal substrate by epitaxial method.

[0010] Preferably, the thickness of the tantalum film is 1 to 500 nm.

[0011] Preferably, the tantalum film is in an alpha phase.

[0012] Preferably, the single crystal substrate is a silicon, gallium arsenide or sapphire wafer.

[0013] The present invention also provides a method for preparing a multilayer film, comprising the following steps: treating the surface of a single crystal substrate; epitaxially growing an aluminum film on the surface of the single crystal substrate; and epitaxially growing a tantalum film on the aluminum film.

[0014] Preferably, the growth temperature of the aluminum thin film is 0 to 100°C, and the growth temperature of the tantalum thin film is 0 to 300°C.

[0015] Preferably, the growth rate of the aluminum thin film and the tantalum thin film is 0.01 to 1 nm / sec.

[0016] The present invention also provides the application of the multilayer film structure in superconducting quantum bit devices and superconducting quantum computing chips.

[0017] The present invention provides a new superconducting multilayer film structure which can be obtained by epitaxial method, has higher interface quality, and has a higher and adjustable critical superconducting temperature. T c 2 to 4 K. The superconducting quantum bit device designed with a multilayer film structure according to the present invention has a high interface quality, few microwave loss channels, and the tantalum film is located at the top layer, and its surface oxide layer is dense, and the loss of the two-level defect is lower, so it has a long decoherence time and a high quality factor of the resonant cavity, and can be used to prepare superconducting quantum bit devices and superconducting quantum computing chips. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solution of the present invention, the accompanying drawings required for use in the following embodiments are shown. It should be understood that the accompanying drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 Schematic diagram of the multilayer film structure of the present invention.

[0020] Figure 2 This is an XRD spectrum of a multilayer thin film structure in Example 1 of the present invention.

[0021] Figure 3 This is a low-temperature resistance spectrum of a multilayer thin film structure in Example 1 of the present invention.

[0022] Figure 4 This is an XRD spectrum of a multilayer thin film structure in Example 2 of the present invention.

[0023] Figure 5 This is a low-temperature resistance spectrum of a multilayer thin film structure in Example 2 of the present invention. Implementation

[0024] The following is an explanation of the embodiments of the present invention through the accompanying drawings and specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0025] The present invention provides a multilayer film structure such as Figure 1As shown, it includes a single crystal substrate 01, an aluminum film 02, and a tantalum film 03 from bottom to top. In a superconducting quantum computing chip, the superconducting aluminum film and tantalum film have stable and excellent quantum bit performance. The multilayer film structure of the present invention has superconducting transition performance. Due to the characteristics of the film structure, the superconducting transition temperature is adjustable within a certain range, and the superconducting transition temperature range is 2-4 K. The present invention introduces a high-quality aluminum film into the single crystal substrate 01 and the tantalum film 03 to ensure a high-quality interface between the substrate and the film. At the same time, the tantalum film is located on the top layer, and the naturally generated Ta2O5 on its surface is dense, and the loss of the double-level defect is lower. The multilayer structure of the present invention reduces the defect channel of the growth interface and the microwave photon loss of the surface oxide layer. When applied to superconducting quantum bit devices and superconducting quantum computing chips, it can increase the decoherence time and improve the quality factor of the resonant cavity. The single crystal substrate 01 is preferably a silicon, sapphire, or gallium arsenide wafer substrate, which has low microwave dielectric loss, is commercially mature and can be processed in large sizes, and is conducive to the large-area growth of epitaxial films.

[0026] The aluminum film 02 and the tantalum film 03 can be prepared using molecular beam epitaxy technology. In the present invention, the aluminum film preferably has a single crystal structure, with regular atomic arrangement, and maintains a highly ordered alignment with the substrate atoms, while ensuring the epitaxial growth of the upper tantalum film. The thickness of the aluminum film is generally 1-50 nm, which can ensure good crystal quality of the film and is conducive to the subsequent micro-nano processing of quantum bit devices. The tantalum film is preferably alpha phase, and the spacing between the (110) plane of α-Ta and the (111) plane of aluminum is equal, which provides convenient conditions for the high-quality epitaxial growth of α-Ta. The thickness of the tantalum film can be selected according to the later application, preferably 1-500 nm.

[0027] The present invention also provides a method for preparing a multilayer thin film structure, comprising the following steps: treating the surface of a single crystal substrate; epitaxially growing an aluminum film on the surface of the single crystal substrate; and epitaxially growing a tantalum film on the aluminum film. Since the melting point of tantalum is as high as 3000°C, the surface will be damaged to a certain extent during the epitaxial growth on the substrate, affecting the interface quality and introducing additional defects. The present invention first epitaxies a layer of aluminum film on the substrate to ensure a high-quality interface between the substrate and the film. In the present invention, the growth temperature of the aluminum film is 0-100°C, and the growth temperature of the tantalum film is 0-300°C. The growth rates of the aluminum film and the tantalum film are 0.01-1 nm / sec.

[0028] The following examples use the United States Veeco The company's GENxplor Ⅱ molecular beam epitaxy system has a basic vacuum of 10 -11 torr. Equipped with American Telemark The company's TT-10 electron beam system has a deflection voltage of 10 kV.

[0029] Embodiment 1: The silicon (111) wafer substrate was placed in a diluted HF acid solution and soaked for 60 seconds to remove the oxide layer on the surface. It was then placed in a molecular beam epitaxy system and transferred to the growth chamber after baking. In the first step, a 5 to 10 nm aluminum film was epitaxially grown at a substrate temperature of room temperature with a growth rate of 0.01 nm / sec, serving as a seed layer for the growth of Ta films. The spacing between the (111) plane of aluminum and the (110) plane of α-Ta was equal, which was 0.2338 nm. In the second step, a 10 nm tantalum film was epitaxially grown at the same substrate temperature with a growth rate of 0.02 nm / sec.

[0030] like Figure 2 The figure shows the X-ray diffraction pattern of the product prepared in this example (characterizing the crystal structure of the product), in which the diffraction signals of the silicon substrate, aluminum (111) and α-Ta (110) can be clearly seen, wherein Al (111) and α-Ta (110) have the same diffraction peak position.

[0031] like Figure 3 The results of the low temperature resistance test of the product prepared in this embodiment are shown, showing that the critical superconducting temperature is T c =2.1 K, which can meet the application requirements of superconducting quantum chips.

[0032] Embodiment 2: The silicon (111) wafer substrate was placed in a diluted HF acid solution and soaked for 60 seconds to remove the oxide layer on the surface. It was then placed in a molecular beam epitaxy system and transferred to the growth chamber after baking. In the first step, a 10 to 20 nm aluminum film was epitaxially grown at a substrate temperature of room temperature with a growth rate of 0.01 nm / sec, serving as a seed layer for the growth of Ta films. The spacing between the (111) plane of aluminum and the (110) plane of α-Ta was equal, which was 0.2338 nm. In the second step, a 40 to 50 nm tantalum film was epitaxially grown at a substrate temperature of 100 °C with a growth rate of 0.04 nm / sec.

[0033] like Figure 4 The X-ray diffraction pattern of the product prepared in this example (characterizing the crystal structure of the product) is shown, and the diffraction signals of the silicon substrate, aluminum (111), α-Ta (110) and β-Ta (002) can be clearly seen. like Figure 5 The results of the low temperature resistance test of the product prepared in this embodiment are shown, showing a high critical superconducting temperature. T c =3.8 K.

[0034] The superconducting quantum device designed by the present invention has a structure in which tantalum is placed on the top layer, and its surface oxide layer has lower loss. In addition, the high-quality epitaxial interface has fewer loss channels, so the device has the advantages of a long decoherence time and a high quality factor of the resonant cavity, and can be applied to superconducting quantum computing chips.

[0035] Unless otherwise specified, the technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs. The embodiments of the present invention are illustrated in the non-limiting examples. Based on the above disclosed embodiments, various modifications that can be thought of by those skilled in the art should also be regarded as the protection scope of the present invention.

Claims

1. A multilayer film structure, characterized in that: The invention comprises a single crystal substrate, an aluminum film, and a tantalum film which are stacked in sequence.

2. The multilayer film structure according to claim 1, characterized in that: The multilayer film structure has superconducting transition properties, and the superconducting transition temperature range is 2-4 K.

3. The multilayer film structure according to claim 1, characterized in that: The aluminum film is a single crystal structure.

4. The multilayer film structure according to claim 1, characterized in that: The thickness of the aluminum film is 1-50 nm.

5. The multilayer film structure according to claim 1, characterized in that: The aluminum thin film and the tantalum thin film are grown on the single crystal substrate by epitaxial method.

6. The multilayer film structure according to claim 1, characterized in that: The tantalum film is an alpha phase.

7. The multilayer film structure according to claim 1, characterized in that: The thickness of the tantalum film is 1-500 nm.

8. The multilayer film structure according to claim 1, characterized in that: The single crystal substrate includes silicon, gallium arsenide and sapphire.

9. A method for preparing a multilayer thin film structure, characterized in that: include: Processing the surface of the single crystal substrate; epitaxially growing an aluminum thin film on the surface of the single crystal substrate; A tantalum film is epitaxially grown on the aluminum film.

10. The preparation method according to claim 9, characterized in that: The growth temperature of the aluminum film is 0 to 100°C, and the growth temperature of the tantalum film is 0 to 300°C.

11. The preparation method according to claim 9, characterized in that: The growth rates of the aluminum film and the tantalum film are 0.01-1 nm / sec.

12. Application of the multilayer thin film structure according to any one of claims 1 to 8 in superconducting quantum bit devices and superconducting quantum computing chips.

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