Amorphous metal superconducting thin film and preparation method therefor, and amorphous metal superconducting nanowire single-photon detector and preparation method therefor

Abstract

The present disclosure belongs to the technical field of photon detection. Provided are an amorphous metal superconducting thin film and a preparation method therefor, and an amorphous metal superconducting nanowire single-photon detector and a preparation method therefor. The amorphous metal superconducting thin film is a nitrogen-doped amorphous metal superconducting thin film, the amorphous metal comprising amorphous molybdenum or amorphous tungsten.

Description

Amorphous metal superconducting thin films and their preparation methods; Amorphous metal superconducting nanowire single-photon detectors and their preparation methods. Technical Field

[0001] This disclosure relates to the field of photon detection technology, and in particular to an amorphous metal superconducting thin film and its preparation method, and an amorphous metal superconducting nanowire single-photon detector and its preparation method. Background Technology

[0002] Superconducting nanowires single-photon detectors (SNSPDs) can achieve single-photon detection in the ultraviolet to mid- and far-infrared wavelength range without requiring extremely low operating temperatures. The working principle of an SNSPD is based on the fact that when the energy carried by a single photon acts on a superconducting nanowire, it breaks the Cooper pairs within the nanowire, causing a non-superconducting hotspot region to form on the nanowire. The heat from this hotspot region then gradually relaxes into the substrate through electron-phonon transitions. Once the heat is completely transferred, the nanowire returns to its initial superconducting state. During this process, the transition from the non-superconducting to the superconducting state generates voltage pulses at its terminals. By accurately detecting and identifying these voltage pulses, effective detection of single photons can be achieved.

[0003] The main body of a superconducting nanowire detector (SNSPD) is made of ultrathin superconducting films, and its material properties directly affect detection efficiency, response speed, and low-temperature operating costs. In the development of high-speed, high-efficiency SNSPDs, currently widely used niobium-based superconducting materials (such as NbN and NbTiN) possess relatively high critical temperatures (T0). c While nanowires have a density of approximately 16K, their grain boundary defects result in low intrinsic absorption rates during photon absorption in the communication band. Higher absorption efficiency requires photonic crystal structures, but these structures introduce additional noise, leading to problems such as insufficient photon absorption efficiency and high dark count rates in practical applications. Amorphous materials such as WSi and MoSi have also attracted significant attention in SNSPD research. They exhibit high uniformity and robustness, their amorphous structure reduces grain boundary defects, and their smaller superconducting bandgap and lower carrier density allow for the generation of more quasiparticles during single-photon absorption, forming larger hotspot regions to improve internal efficiency. However, their poor stability makes SNSPD fabrication complex, and the nanowires inevitably degrade during use, preventing the detector from operating for extended periods.

[0004] Therefore, there is an urgent need to explore a new type of superconducting material that combines a high superconducting critical temperature with excellent stability. Summary of the Invention

[0005] In view of this, in order to at least partially solve the aforementioned technical problems, this disclosure provides an amorphous metal superconducting thin film and its preparation method, and an amorphous metal superconducting nanowire single-photon detector and its preparation method.

[0006] According to one aspect of the present disclosure, an amorphous metal superconducting thin film is provided, which is a nitrogen-doped amorphous metal superconducting thin film, and the amorphous metal includes: amorphous molybdenum or amorphous tungsten.

[0007] According to embodiments of this disclosure, the thickness of the amorphous molybdenum superconducting thin film is 3–30 nm; the thickness of the amorphous tungsten superconducting thin film is 2–20 nm.

[0008] According to embodiments of this disclosure, the superconducting transition temperature of the amorphous molybdenum superconducting thin film is 2–10 K, and the sheet resistance is 300–15 Ω / L. □ The superconducting transition temperature of amorphous tungsten superconducting thin films is 1–10 K, and the sheet resistance is 400–40 Ω / m². □

[0009] According to embodiments of this disclosure, in amorphous molybdenum superconducting thin films, the molar content of nitrogen doping is 5-17%; in amorphous tungsten superconducting thin films, the molar content of nitrogen doping is 8-12%.

[0010] According to another aspect of this disclosure, a method for preparing an amorphous metal superconducting thin film is provided, comprising: growing an amorphous metal superconducting thin film on a substrate by sputtering using a mixture of argon and nitrogen as the working gas; the amorphous metal includes amorphous molybdenum or amorphous tungsten.

[0011] According to embodiments of this disclosure, the sputtering current is 100–360 mA when growing amorphous tungsten superconducting thin films; and the sputtering current is 180–250 mA when growing amorphous molybdenum superconducting thin films.

[0012] According to embodiments of this disclosure, when growing amorphous tungsten superconducting thin films, the flow rate of argon in the mixed gas is 20-80 sccm, and the flow rate of nitrogen is 1-5 sccm; when growing amorphous molybdenum superconducting thin films, the flow rate of argon in the mixed gas is 30-60 sccm, and the flow rate of nitrogen is 5-9 sccm.

[0013] According to another embodiment of this disclosure, an amorphous metal superconducting nanowire single-photon detector is provided, comprising: a light-absorbing layer; the light-absorbing layer comprising nanowires formed from the above-described amorphous metal superconducting thin film or nanowires formed from the above-described preparation method of the amorphous metal superconducting thin film.

[0014] According to embodiments of this disclosure, when the amorphous metal superconducting thin film is an amorphous tungsten superconducting thin film, the width of the nanowire is 40–120 nm; when the amorphous metal superconducting thin film is an amorphous molybdenum superconducting thin film, the width of the nanowire is 30–100 nm.

[0015] According to embodiments of this disclosure, the nanowires are meandering nanowires.

[0016] According to another embodiment of this disclosure, a method for fabricating the above-mentioned amorphous metal superconducting nanowire single-photon detector is provided, comprising: sequentially exposing and etching an amorphous metal superconducting thin film to form a nanowire structure to obtain an amorphous metal superconducting nanowire; and assembling the amorphous metal superconducting nanowire as a light absorption layer to obtain an amorphous metal superconducting nanowire single-photon detector.

[0017] According to embodiments of this disclosure, the process of sequentially exposing and etching an amorphous metal superconducting thin film to form a nanowire structure and obtaining amorphous metal superconducting nanowires includes: spin-coating photoresist onto the surface of the amorphous metal superconducting thin film; sequentially exposing, developing, and fixing the photoresist using electron beam exposure to obtain an amorphous metal superconducting thin film with a nanowire shape; and etching the amorphous metal superconducting thin film with a nanowire shape using reactive ion beam etching to obtain amorphous metal superconducting nanowires.

[0018] According to embodiments of this disclosure, when the amorphous metal in the amorphous metal superconducting thin film with a nanowire structure is tungsten, the accelerating voltage for reactive ion beam etching is 180–260 V, the anode current is 4.5–6.2 A, the etching time is 1–5 min, and the electron beam exposure dose is set to 200–400 μC / cm. 2 When the amorphous metal in the amorphous metal superconducting thin film with nanowire structure is molybdenum, the accelerating voltage of reactive ion beam etching is 150–240 V, the anolyte current is 4.0–6.0 A, the etching time is 30–120 s, and the electron beam exposure dose is set to 180–300 μC / cm. 2 .

[0019] According to another embodiment of this disclosure, an amorphous tungsten superconducting nanowire single-photon detector is provided, including a photosensitive component, wherein the photosensitive component is an amorphous tungsten superconducting nanowire, and the amorphous tungsten superconducting nanowire is prepared by the following steps: (1) growing an amorphous tungsten thin film on a substrate; (2) etching the amorphous tungsten film into a meandering nanowire structure using electron beam exposure and reactive ion beam etching to obtain the amorphous tungsten superconducting nanowire.

[0020] According to the embodiments of this disclosure, step (2) specifically includes the following processes: (2.1) spin-coating photoresist on the surface of an amorphous tungsten film and exposing the photoresist to form nanowire patterns using electron beam exposure; (2.2) developing and fixing the photoresist after exposure to obtain an amorphous tungsten film with nanowire shapes; (2.3) etching the amorphous tungsten film using reactive ion beam etching to remove residual photoresist and obtain amorphous tungsten nanowires.

[0021] According to an embodiment of this disclosure, in step (2.1), the electron beam exposure dose is set to 200-400 μC / cm. 2 Image correction and dose correction are used to ensure uniform nanowire width.

[0022] According to an embodiment of this disclosure, in step (2.3), the operating parameters for reactive ion beam etching are: etching gas flow rate of 10-25 sccm; and operating gas pressure of 0.2-0.6 Pa.

[0023] According to the embodiments of this disclosure, in step (2.3), during reactive ion beam etching, the accelerating voltage is 180-260V, the anolyte current is 4.5-6.2A, and the etching time is 1-5min.

[0024] According to an embodiment of this disclosure, in step (2.1), the photoresist material is polymethyl methacrylate (PMMA) and / or hydrogen silsesquioxane (HSQ).

[0025] According to an embodiment of the present disclosure, in step (1), a nanoscale thick amorphous tungsten film is grown on a Si / SiO2 substrate by magnetron sputtering.

[0026] According to embodiments of this disclosure, the DC target power for magnetron sputtering is 40W-180W.

[0027] According to an embodiment of this disclosure, in step (2.3), the amorphous tungsten film is immersed in an organic solvent to remove residual photoresist.

[0028] According to embodiments of this disclosure, in step (1), the thickness of the amorphous tungsten film is 2-20 nm, the superconducting transition temperature is 1-10 K, and the sheet resistance is 400 Ω / □ -40Ω / □ .

[0029] According to embodiments of this disclosure, the lower sputtering power and nitrogen introduction result in less energy for the sputtered tungsten or molybdenum atoms. This leads to weaker migration ability upon reaching the substrate surface, hindering long-distance diffusion and causing them to randomly accumulate on the substrate surface. This suppresses the formation and growth of crystal nuclei, resulting in a random amorphous structure. Furthermore, the lower sputtering power generates less heat during the sputtering process, and the lower temperature further suppresses the thermal motion of tungsten or molybdenum atoms, helping to maintain the amorphous structure of the thin film. The introduction of nitrogen further disrupts the periodicity of the tungsten or molybdenum atom arrangement, increasing the difficulty of arranging atoms into an ordered lattice, thereby further promoting the formation of the amorphous structure.

[0030] According to embodiments of this disclosure, the electron scattering in the nitrogen-doped amorphous metallic superconducting thin film differs from that in a crystal structure, which facilitates the interaction between electrons to form Cooper pairs, thereby leading to superconductivity. Furthermore, the disorder in the amorphous structure can, to some extent, reduce the negative impact of impurities or defects on superconducting performance, further contributing to the maintenance and expression of superconducting properties.

[0031] According to embodiments of this disclosure, single-photon detection using amorphous tungsten superconducting nanowires and amorphous molybdenum superconducting nanowires is achieved, providing novel materials for SNSPD detectors. This overcomes the poor stability of low-bandgap materials currently used in SNSPDs. By employing more stable amorphous tungsten and / or amorphous molybdenum superconducting nanowires as the main materials for SNSPD detectors, the robustness of SNSPD detectors during fabrication and use (i.e., detection accuracy and stability in the face of complex and variable environments and interference factors) is improved, extending the lifespan of SNSPD detectors in practical applications. The amorphous tungsten superconducting nanowire single-photon detector of this disclosure can achieve single-photon detection in the 1064nm and 1550nm wavelength bands, and the quantum detection efficiency of single-photon detection reaches 100% in the temperature range of 0.3–1K. The amorphous molybdenum superconducting nanowire single-photon detector disclosed herein can achieve single-photon detection in the 1064nm band. The quantum detection efficiency of single-photon detection reaches 100% in the temperature range of 0.1 to 2.1K. Compared with the amorphous tungsten superconducting nanowire single-photon detector, the amorphous molybdenum superconducting nanowire single-photon detector has a wider temperature detection range. Attached Figure Description

[0032] The above and other objects, features and advantages of this disclosure will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0033] Figure 1 shows a schematic diagram of magnetron sputtering growth of amorphous metal superconducting thin films according to an embodiment of the present disclosure;

[0034] Figure 2 shows a schematic diagram of an amorphous metallic superconducting tortuous nanowire according to an embodiment of the present disclosure;

[0035] Figure 3 shows a flowchart of the fabrication method of an amorphous metallic superconducting nanowire single-photon detector according to an embodiment of the present disclosure;

[0036] Figure 4 shows a process flow diagram of the method for preparing amorphous metallic superconducting nanowires according to an embodiment of the present disclosure;

[0037] Figure 5 shows a scanning electron microscope (SEM) image and an atomic force microscope (AFM) image of the amorphous tungsten superconducting thin film of Embodiment 1 of this disclosure;

[0038] Figure 6 shows the X-ray diffraction pattern of the amorphous tungsten superconducting thin film of Embodiment 1 of this disclosure;

[0039] Figure 7 shows the X-ray photoelectron spectroscopy (XPS) spectrum of the amorphous tungsten superconducting thin film of Embodiment 1 of this disclosure;

[0040] Figure 8 shows the resistance of the amorphous tungsten superconducting thin film of Embodiment 1 of this disclosure as a function of time after being placed in air for different periods of time;

[0041] Figure 9 shows a statistical graph of the superconducting properties of the amorphous tungsten superconducting thin film obtained by deposition at different nitrogen flow rates in Embodiment 1 of this disclosure;

[0042] Figure 10 shows a comparison of XRD and RT of the amorphous tungsten superconducting thin film deposited in the presence and absence of nitrogen atmosphere according to Embodiment 1 of this disclosure;

[0043] Figure 11 shows the current versus voltage curves of amorphous tungsten superconducting nanowires in Embodiments 1, 2, and Comparative Example 2 of this disclosure;

[0044] Figure 12 shows scanning electron microscope (SEM) images of the amorphous tungsten superconducting nanowires prepared in Example 1 and Comparative Example 1 of this disclosure;

[0045] Figure 13 shows the single-photon response pulse diagram of the amorphous tungsten superconducting nanowire single-photon detector in the 1064 nm band of Application Example 1 of this disclosure;

[0046] Figure 14 shows the single-photon photoconductivity response of the amorphous tungsten superconducting nanowire single-photon detector in the 1064 nm band of Application Example 1 of this disclosure.

[0047] Figure 15 shows the single-photon photoconductivity response of the amorphous tungsten superconducting nanowire single-photon detector in the 1550 nm band of Application Example 2 of this disclosure.

[0048] Figure 16 shows the time jitter diagram of the amorphous tungsten superconducting nanowire single-photon detector in the 1550 nm band of Application Example 2 of this disclosure.

[0049] Figure 17 shows a graph of the resistance of the amorphous molybdenum superconducting thin film of Embodiment 5 of this disclosure as a function of temperature;

[0050] Figure 18 shows an atomic force microscopy (AFM) image of the amorphous molybdenum superconducting thin film of Embodiment 5 of this disclosure;

[0051] Figure 19 shows the X-ray photoelectron spectroscopy (XPS) spectrum of the amorphous molybdenum superconducting thin film of Embodiment 5 of this disclosure;

[0052] Figure 20 shows a transmission electron microscope (TEM) image and a corresponding selected area electron diffraction (SAED) pattern of the amorphous molybdenum superconducting thin film of Embodiment 5 of this disclosure;

[0053] Figure 21 shows the X-ray diffraction pattern of the amorphous molybdenum superconducting thin film prepared in Example 5 of this disclosure;

[0054] Figure 22 shows the XRD patterns and RT statistics of the amorphous molybdenum superconducting thin film obtained by deposition under different sputtering currents in Embodiment 5 of this disclosure;

[0055] Figure 23 shows a comparison of the light absorption efficiency of amorphous molybdenum superconducting nanowires of different thicknesses in finite-time domain (FDTD) simulations of Embodiment 5 of this disclosure;

[0056] Figure 24 shows a comparison of the light absorption efficiency of amorphous molybdenum superconducting nanowires with different duty cycles in FDTD simulation of Embodiment 5 of this disclosure;

[0057] Figure 25 shows the resistance curves of nitrogen-doped amorphous metal thin films prepared by Comparative Examples 2, 3, and 4 of this disclosure as a function of temperature.

[0058] Figure 26 shows the current versus voltage curves of the amorphous molybdenum superconducting nanowires in Embodiments 5, 6, 7 and 8 of this disclosure;

[0059] Figure 27 shows a graph of the resistance of the oxygen-doped amorphous molybdenum thin film prepared in Comparative Example 5 of this disclosure as a function of temperature.

[0060] Figure 28 shows SEM images of the amorphous molybdenum superconducting nanowires prepared in Examples 5 and 9 of this disclosure;

[0061] Figure 29 shows the current versus voltage curves of the SNSPD assembled in Application Examples 3 and 4 of this disclosure.

[0062] Figure 30 shows the response pulse diagram of the amorphous molybdenum superconducting nanowire single-photon detector assembled in Application Examples 3 and 4 of this disclosure in the 1064 nm band.

[0063] Figure 31 is a comparison of the light absorption efficiency of the amorphous molybdenum superconducting nanowire single-photon detectors assembled in Application Example 3 and Application Example 4 of this disclosure in the 1064 nm band. Detailed Implementation

[0064] To make the objectives, technical solutions and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0065] The endpoints and any values ​​of the ranges disclosed in this disclosure are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such 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 regarded as specifically disclosed in this disclosure.

[0066] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0067] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0068] It should be noted that, unless otherwise defined, the technical or scientific terms used in this disclosure should have the ordinary meaning understood by a person with ordinary skill in the art to which this disclosure pertains. Where the terms "first," "second," etc., are used throughout, they are used only to distinguish similar objects and should not be construed as indicating or implying their relative importance, order of precedence, or implicitly specifying the number of technical features indicated. It should be understood that the data described by "first," "second," etc., can be interchanged where appropriate.

[0069] Similarly, to simplify this disclosure and aid in understanding one or more of the various aspects of the disclosure, in the above description of exemplary embodiments of the present disclosure, various features of the present disclosure are sometimes grouped together in a single embodiment, figure, or description thereof. The use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refers to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present disclosure. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0070] Furthermore, the technical solutions of the various embodiments can be combined with each other, but only if they are based on the ability of a person skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed in this disclosure.

[0071] Superconducting photon detectors mainly include transition edges detectors (TES) and superconducting nanowire single-photon detectors (SNSPD). Both types of detectors utilize the process of a superconducting material transitioning from a superconducting state to a non-superconducting state to detect a single photon. TES typically consists of an ultrathin superconducting film. When a photon is absorbed, a tiny temperature change occurs, causing a change in the resistance of the superconducting film. This tiny signal is amplified using a superconducting quantum interference device (SQU) to read out the single photon signal. This resistance change is then used to detect the presence of the photon, thus achieving single-photon detection. TES can achieve high detection efficiency in the visible to near-infrared wavelength range, but its operating temperature (<10 mK) is extremely low, and conventional cooling processes struggle to achieve such low operating temperatures.

[0072] Single-photon detectors (SNSPDs) utilize the energy carried by a single photon to break Cooper pairs in a superconducting nanowire, creating a hotspot region of non-superconducting state on the nanowire. After heat transfer, the nanowire returns to its initial superconducting state. This unique working mechanism endows SNSPDs with advantages such as high detection rate, high detection efficiency, low dark count, and low time jitter. Therefore, they have irreplaceable application value in quantum key distribution, quantum computing, astronomical observation, and other applications requiring high-precision photon counting, and are gradually becoming one of the mainstream single-photon detectors.

[0073] Currently, commonly used superconducting thin films for single-photon detectors (SNSPDs) employ materials such as niobium-based superconductors or amorphous materials like WSi and MoSi. However, niobium-based materials suffer from insufficient photon absorption efficiency and high dark count rates; while amorphous materials exhibit poor stability, causing nanowires to degrade during use and hindering the sustainable operation of single-photon detectors.

[0074] In the process of realizing this disclosure, it was discovered that the amorphous metallic superconducting thin film provided by this disclosure, due to its amorphous disordered structure and the disordered dispersion of the doped nitrogen element, increases the mean free path of electrons, which facilitates electron pairing to form Cooper pairs and promotes superconductivity. Furthermore, the disorder of the amorphous metallic superconducting thin film of this disclosure can suppress the adverse effects of impurities or defects on superconducting performance. Based on the disordered atomic arrangement in the nitrogen-doped amorphous metallic superconducting thin film, the amorphous metallic superconducting thin film exhibits superconducting properties, which is beneficial for its subsequent application as nanowires in single-photon detectors. Moreover, the amorphous metallic superconducting thin film of this disclosure possesses both a high superconducting critical temperature and excellent stability, ensuring stable and reliable operation during long-term use.

[0075] Specifically, according to one aspect of the present disclosure, an amorphous metal superconducting thin film is provided. The amorphous metal superconducting thin film is a nitrogen-doped amorphous metal superconducting thin film, and the amorphous metal includes: amorphous molybdenum or amorphous tungsten.

[0076] According to embodiments of this disclosure, nitrogen doping helps induce superconductivity in amorphous metallic superconducting thin films. Based on the amorphous state and nitrogen doping, molybdenum and tungsten atoms are placed in a disordered, dispersed amorphous state. The electron scattering in the amorphous metallic superconducting thin film of this disclosure differs from that in crystalline structures, facilitating the formation of Cooper pairs through electron interactions, thus exhibiting superconducting properties. Furthermore, the disorder of the amorphous structure and the effect of nitrogen doping help reduce the negative impact of impurities or defects on superconducting performance, enhancing the stability of the amorphous metallic superconducting thin film and improving its robustness in subsequent applications in SNSPD detectors. The amorphous metallic superconducting thin film of this disclosure provides a novel material for SNSPD detectors, overcoming the difficulty in balancing stability and superconducting critical temperature in currently used materials.

[0077] The disclosed amorphous metallic superconducting thin film possesses a high superconducting critical temperature, enabling it to withstand relatively high operating temperatures and reducing cooling costs and complexity. Simultaneously, it exhibits excellent stability, ensuring stable and reliable performance during long-term use. This facilitates the fabrication of superconducting nanowires with fast photon response speeds and high photon absorption efficiencies. When subsequently applied to superconducting single-photon detectors, the combination of high response speed and high absorption efficiency is of great significance for advancing the development of high-speed superconducting single-photon detectors.

[0078] According to embodiments of this disclosure, the thickness of the amorphous molybdenum superconducting thin film is 3–30 nm; the thickness of the amorphous tungsten superconducting thin film is 2–20 nm. Within the above thickness range, the microstructure and electronic morphology of the amorphous metal superconducting thin film can reach a relatively suitable state, utilizing the cooperative motion of electrons to promote the formation of Cooper pairs, thereby exhibiting good superconducting properties.

[0079] Optionally, the thickness of the amorphous molybdenum superconducting thin film can be 3nm, 6nm, 9nm, 12nm, 14nm, 18nm, 20nm, 25nm or 30nm, or a range consisting of any two of the above values.

[0080] Optionally, the thickness of the amorphous tungsten superconducting thin film can be 2nm, 5nm, 8nm, 10nm, 12nm, 14nm, 16nm, 18nm or 20nm, or a range consisting of any two of the above values.

[0081] According to embodiments of this disclosure, the superconducting transition temperature of the amorphous molybdenum superconducting thin film is 2–10 K, for example, it can be 2 K, 4 K, 6 K, or 10 K, or a range consisting of any two of the above values. Preferably, the superconducting transition temperature of the amorphous molybdenum superconducting thin film is 6–8 K; the sheet resistance is 300–15 Ω / □ The superconducting transition temperature of the amorphous tungsten superconducting thin film is 1–10 K, for example, it can be 1 K, 2 K, 4 K, 6 K, 8 K, or 10 K, or a range consisting of any two of the above values. Preferably, the superconducting transition temperature of the amorphous tungsten superconducting thin film is 4–6 K, and the sheet resistance is 400–40 Ω / L. □ .

[0082] It should be noted that the superconducting transition temperature of amorphous molybdenum superconducting films is higher than that of amorphous tungsten superconducting films. This makes amorphous molybdenum superconducting films easier to achieve and maintain in cryogenic cooling processes, resulting in lower maintenance costs. Compared to amorphous tungsten superconducting films, amorphous molybdenum superconducting films can achieve stable operation at relatively higher temperatures, making them more adaptable.

[0083] According to embodiments of this disclosure, in amorphous molybdenum superconducting thin films, the molar content of doped nitrogen is 5% to 17%, for example, 5%, 10%, 13%, 16%, or 17%. In amorphous tungsten superconducting thin films, the molar content of doped nitrogen is 8% to 12%, for example, 8%, 9%, 10%, 11%, or 12%. During experiments related to this disclosure, it was found that this configuration allows for further increases in the superconducting critical temperature of both materials by adjusting the molar content of nitrogen doping, thereby expanding the temperature detection range for subsequent SNSPD detectors.

[0084] According to another aspect of this disclosure, a method for preparing an amorphous metal superconducting thin film is provided, comprising: growing an amorphous metal superconducting thin film on a substrate by sputtering using a mixture of argon and nitrogen as the working gas; wherein the amorphous metal includes amorphous molybdenum or amorphous tungsten.

[0085] According to embodiments of this disclosure, nitrogen gas is introduced during the preparation of amorphous metal superconducting thin films. The nitrogen gas collides with sputtered amorphous metal atoms to form nitrogen-doped amorphous metal superconducting thin films. The introduction of nitrogen atoms further increases the disorder of the amorphous metal superconducting thin films and promotes their formation.

[0086] Figure 1 shows a schematic diagram of magnetron sputtering growth of amorphous metal superconducting thin films according to an embodiment of the present disclosure. As shown in Figure 1, the introduction of nitrogen atoms further increases the disorder of the amorphous metal superconducting thin film.

[0087] According to embodiments of this disclosure, the sputtering current is 100–360 mA when growing amorphous tungsten superconducting thin films, and 180–250 mA when growing amorphous molybdenum superconducting thin films. This setting, with a lower sputtering current (corresponding to lower power), results in sputtered tungsten or molybdenum atoms possessing relatively less energy. When these atoms reach the substrate surface, their migration ability is weakened, making long-distance diffusion difficult and hindering their ability to find suitable positions to form a regular crystal structure. Furthermore, the lower energy of these atoms makes them more prone to randomly accumulating on the substrate, thus suppressing the formation and growth of crystal nuclei and promoting the generation of amorphous structures. Simultaneously, the lower sputtering current means less heat generation and a lower substrate temperature, further suppressing atomic thermal motion and making it difficult for atoms to adjust their positions through thermal activation to form a regular crystal arrangement, thereby maintaining the amorphous state of the amorphous metal superconducting thin film.

[0088] According to embodiments of this disclosure, the sputtering method may be, for example, magnetron sputtering or ion beam sputtering, and this disclosure does not particularly limit it.

[0089] During the experiments related to this disclosure, adjusting the nitrogen flow rate and keeping the sputtering power or current within a lower range increased the disorder in the formed thin film structure, which facilitated the formation of amorphous superconducting thin films. This further improved the robustness of the SNSPD detector during fabrication and use, extending its lifespan.

[0090] According to embodiments of this disclosure, during the growth of amorphous tungsten superconducting thin films, the flow rate of argon in the mixed gas is 40–60 sccm, for example, 40 sccm, 45 sccm, 50 sccm, 55 sccm, or 60 sccm, or any combination of two of the above values, preferably 50 sccm; the flow rate of nitrogen is 1–5 sccm, for example, 1 sccm, 3 sccm, 4 sccm, or 5 sccm, or any combination of two of the above values, preferably 5 sccm. This configuration allows for further improvement of the superconducting critical temperature of the amorphous tungsten superconducting thin film by optimizing the flow rates of nitrogen and argon.

[0091] According to embodiments of this disclosure, during the growth of amorphous molybdenum superconducting thin films, the flow rate of argon in the mixed gas is 30–60 sccm, for example, 30 sccm, 40 sccm, 50 sccm, or 60 sccm, or any combination of two of the above values, preferably 40 sccm. The flow rate of nitrogen is 5–9 sccm, for example, 5 sccm, 6 sccm, 7 sccm, 8 sccm, or 9 sccm, or any combination of two of the above values, preferably 7 sccm. This configuration allows for further improvement of the superconducting critical temperature of the amorphous molybdenum superconducting thin film by optimizing the flow rates of nitrogen and argon.

[0092] According to embodiments of this disclosure, the substrate may be, for example, a silicon substrate or a silicon oxide substrate, or a combination of both, and this disclosure does not particularly limit it.

[0093] The following detailed description uses the preparation of nitrogen-doped amorphous molybdenum superconducting thin films as an example.

[0094] A stack of monocrystalline silicon and silicon oxide was selected as the substrate, with silicon oxide on the top layer and monocrystalline silicon on the bottom layer. The substrate was then placed in acetone, ethanol, and deionized water in sequence and subjected to ultrasonic cleaning for more than 5 minutes each to achieve cleaning of the substrate surface.

[0095] A nitrogen-doped amorphous molybdenum superconducting thin films with a thickness of 7–15 nm were prepared by magnetron sputtering using a molybdenum target and a mixed gas of argon and nitrogen, with an argon flow rate of 30–60 sccm and a nitrogen flow rate of 5–9 sccm. The magnetron sputtering power was 50–100 W, the working gas pressure was 4.5–5.8 mTorr, the DC power supply output current was 180–250 mA, the deposition rate was stable at 0.3–0.4 nm / s, and the growth time was ≥20 s.

[0096] The following detailed description uses the preparation of nitrogen-doped amorphous tungsten superconducting thin films as an example.

[0097] A stack of monocrystalline silicon and silicon oxide was selected as the substrate, with silicon oxide on the top layer and monocrystalline silicon on the bottom layer. The substrate was then placed in acetone, ethanol, and deionized water in sequence and ultrasonically cleaned for more than 10 minutes each to remove impurities from the substrate surface.

[0098] Using magnetron sputtering, a tungsten target was used as the target material. The sputtering working gas was a mixture of argon and nitrogen, with an argon flow rate of 40–60 sccm and a nitrogen flow rate of 1–5 sccm. The magnetron sputtering power was 40–180 W, the working gas pressure was 4.9–6.1 mTorr, the DC power supply output current was 100–360 mA, the deposition rate was stable at 0.3–0.4 nm / s, and the growth time was ≥20 s, thus obtaining nitrogen-doped amorphous molybdenum superconducting thin films with a thickness of 2–20 nm.

[0099] According to another aspect of this disclosure, an amorphous metal superconducting nanowire single-photon detector is provided, comprising: a light-absorbing layer; the light-absorbing layer comprising nanowires formed from the above-described amorphous metal superconducting thin film or nanowires formed from the above-described preparation method of the amorphous metal superconducting thin film.

[0100] According to embodiments of this disclosure, nanowires formed using the aforementioned amorphous molybdenum superconducting thin film exhibit a faster photon response rate, reducing the recovery time of single-photon detectors using amorphous molybdenum superconducting nanowires and improving the detection rate of SNSPD detectors in practical applications. Furthermore, the stability of nanowires formed using amorphous molybdenum superconducting thin films is better than that of WSi and MoSi in related technologies, extending the lifespan of SNSPD detectors in practical applications. Nanowires formed using the aforementioned amorphous tungsten superconducting thin film also demonstrate good stability, improving the robustness of SNSPD fabrication and detection processes and extending the lifespan of SNSPD detectors in practical applications.

[0101] According to embodiments of this disclosure, when the amorphous metal superconducting thin film is an amorphous tungsten superconducting thin film, the width of the nanowires is 40–120 nm; when the amorphous metal superconducting thin film is an amorphous molybdenum superconducting thin film, the width of the nanowires is 30–100 nm. This configuration further helps the aforementioned amorphous metal superconducting thin films to exert their superconducting properties.

[0102] For example, the nanowire width in an amorphous tungsten superconducting thin film can be, for example, 40 nm, 60 nm, 80 nm, 100 nm, or 120 nm, or a range consisting of any two of the above values, preferably 100 nm. The nanowire width in an amorphous molybdenum superconducting thin film can be, for example, 30 nm, 50 nm, 70 nm, 80 nm / 90 nm, or 100 nm, or a range consisting of any two of the above values, preferably 70 nm.

[0103] According to embodiments of this disclosure, the nanowires are meandering nanowires. Figure 2 shows a schematic diagram of an amorphous metallic superconducting meandering nanowire according to an embodiment of this disclosure. As shown in Figure 2, a meandering nanowire can be understood as having connecting portions perpendicular to the extension direction of the nanowires at the ends of the parallel, spaced nanowires, to connect at least two adjacent nanowires to each other. This configuration helps to improve the absorption efficiency of photons and further enhance the photon response rate.

[0104] According to another embodiment of the present disclosure, a method for fabricating the above-described amorphous metal superconducting nanowire single-photon detector is provided. FIG3 shows a flowchart of the method for fabricating the amorphous metal superconducting nanowire single-photon detector according to an embodiment of the present disclosure. As shown in FIG3, the fabrication method includes operations S301 to S302.

[0105] In operation S301, the amorphous metal superconducting thin film is sequentially exposed and etched to form a nanowire structure, thus obtaining amorphous metal superconducting nanowires.

[0106] In operation S302, amorphous metal superconducting nanowires were assembled as light absorption layers to obtain an amorphous metal superconducting nanowire single-photon detector.

[0107] According to embodiments of this disclosure, amorphous metal superconducting thin films can be fabricated into nanowire structures through exposure and etching. This method allows for precise control of the shape, size, and layout of the nanowires, facilitating the optimization of nanowire performance to meet the requirements of different application scenarios. Using the fabricated amorphous metal superconducting nanowires as a light-absorbing layer, their unique nanowire structure and material properties enable efficient absorption of photons, facilitating single-photon level detection. Upon photon absorption, the electronic states within the nanowires change, potentially disrupting the superconducting state and generating a detectable electrical signal. The superconducting material of this disclosure exhibits extremely low resistance and high sensitivity, enabling rapid and accurate conversion of optical signals into electrical signals, improving detector response speed and detection accuracy, reducing noise levels, and achieving efficient, low-noise detection of single photons.

[0108] According to an embodiment of this disclosure, operation S301 includes sub-operations S3011 to S3012.

[0109] In sub-operation S3011, photoresist is spin-coated onto the surface of an amorphous metal superconducting thin film. The photoresist is then subjected to nanowire patterning exposure, development, and fixing processes using electron beam exposure to obtain an amorphous metal superconducting thin film with nanowire shapes.

[0110] In sub-operation S3012, reactive ion beam etching is used to etch amorphous metal superconducting thin films with nanowire shapes to obtain amorphous metal superconducting nanowires.

[0111] Figure 4 shows a process flow diagram of the fabrication method of amorphous metal superconducting nanowires according to an embodiment of this disclosure. As shown in Figure 4, an amorphous metal thin film is grown on the substrate surface. Photoresist is spin-coated to uniformly cover the surface of the amorphous metal thin film, and then patterning exposure is performed by electron beam exposure. Further, the amorphous metal superconducting thin film not covered by photoresist is etched away by reactive ion beam etching (reactive ion beam etching in Figure 4), and then the photoresist is removed to obtain amorphous metal superconducting nanowires with superconducting properties.

[0112] According to embodiments of this disclosure, the photoresist may be, for example, polymethyl methacrylate (PMMA) and / or hydrogen silsesquioxane (HSQ). The aforementioned photoresist exhibits good performance and is suitable for high-precision reactive ion beam etching used in the fabrication of nanostructures.

[0113] According to embodiments of this disclosure, when the amorphous metal in the amorphous metal superconducting thin film with a nanowire structure is tungsten, the accelerating voltage for reactive ion beam etching is 180–260 V, for example, 180 V, 200 V, 220 V, 240 V, or 260 V, or a range consisting of any two of the above values. The anode current is 4.5–6.2 A, for example, 4.5 A, 5.0 A, 5.5 A, 6.0 A, or 6.2 A, or a range consisting of any two of the above values. The etching time is 1–5 min, for example, 1 min, 2 min, 3 min, 4 min, or 5 min, or a range consisting of any two of the above values. This configuration allows for more thorough etching of the amorphous tungsten superconducting thin film outside the photoresist coverage area.

[0114] According to embodiments of this disclosure, in the subsequent preparation of two types of amorphous metal superconducting nanowires, the uniformity of the nanowire linewidth is ensured by correcting the etched pattern (which can be understood as a template) or compensating for the etching measurement.

[0115] According to embodiments of this disclosure, when the amorphous metal in the amorphous metal superconducting thin film with a nanowire structure is tungsten, the electron beam exposure dose is set to 200–400 μC / cm. 2 For example, it could be 200 μC / cm 2 300μC / cm 2 Or 400μC / cm 2 Or a range consisting of any two of the above values. When the amorphous metal in the amorphous metallic superconducting thin film with a nanowire structure is molybdenum, the electron beam exposure dose is set to 180–300 μC / cm. 2 For example, it could be 180 μC / cm 2 200μC / cm 2 250μC / cm 2Or 300μC / cm 2 Or a range consisting of any two of the above values. This setting ensures the uniformity of the nanowire width through image correction and dose correction, further improving the quality of exposure.

[0116] According to embodiments of this disclosure, after etching, the amorphous metal superconducting nanowires are immersed in an organic solution to remove residual photoresist. The organic solvent may be, for example, acetone, ethanol, etc., and this disclosure does not impose any particular limitation on it.

[0117] According to embodiments of this disclosure, when the amorphous metal in the amorphous metal superconducting thin film with a nanowire structure is molybdenum, the accelerating voltage for reactive ion beam etching is 150–240 V, for example, 150 V, 180 V, 200 V, 220 V, or 240 V, or a range consisting of any two of the above values. The anode current is 4.0–6.0 A, for example, 4.0 A, 4.5 A, 5.0 A, 5.5 A, or 6.0 A, or a range consisting of any two of the above values. The etching time is 30–120 s, for example, 30 s, 60 s, 90 s, or 120 s, or a range consisting of any two of the above values. This configuration allows for more thorough etching of the amorphous molybdenum superconducting thin film outside the photoresist coverage area.

[0118] According to embodiments of this disclosure, the etching gas for reactive ion beam etching is preferably CHF3.

[0119] According to embodiments of this disclosure, the novel materials possess high superconducting critical temperatures, particularly the amorphous molybdenum superconducting thin film, which exhibits a relatively higher superconducting critical temperature, enabling it to withstand relatively high operating temperatures and reducing cooling costs and complexity. Simultaneously, both the amorphous molybdenum and amorphous tungsten superconducting thin films possess excellent stability, ensuring stable and reliable performance during long-term use. This allows for the subsequent fabrication of superconducting nanowires with fast photon response speeds and high photon absorption efficiencies. These nanowires possess high response speeds and high absorption efficiencies, helping to reduce the recovery time of photons detected by SNSPD detectors and improving the detection rate of SNSPD detectors in practical applications. This has extremely important research value and practical significance for promoting the development of novel high-speed superconducting single-photon detectors.

[0120] The following details the preparation process using the example of amorphous molybdenum superconducting nanowires.

[0121] Photoresist was spin-coated onto the surface of an amorphous molybdenum superconducting thin film. The spin-coating speed was 3000-5000 rpm, the acceleration was 900-1500 rpm / s, and the spin-coating time was 40-80 s. The photoresist material was PMMA and / or HSQ. Nanowire patterning of the photoresist was performed using electron beam lithography, with the electron beam exposure dose set to 180-300 μC / cm. 2 Electron beam exposure employs image correction and dose correction to ensure uniform nanowire width. The width of the nanowire pattern is set to 30-100 nm. After exposure, development is performed for 10-30 seconds, followed by fixing in water for 10-25 seconds. This process dissolves the photoresist in the exposed areas, revealing the underlying amorphous molybdenum superconducting film; while the unexposed areas are protected by photoresist (such as PMMA), thus forming a photoresist pattern with nanowire shapes.

[0122] Amorphous molybdenum superconducting thin films were etched using reactive ion beam etching (RIE). The operating parameters for RIE were as follows: the preferred etching gas was CHF3; the etching gas flow rate was 10-25 sccm; the operating pressure was 0.2-0.6 Pa; the accelerating voltage was 180-260 V; the anolyte current was 4.5-6.2 A; and the etching time was 1-5 min. After RIE, the areas of the exposed amorphous molybdenum superconducting film were completely etched away, while the unexposed areas retained the film due to the protection of photoresist. The amorphous molybdenum superconducting film was then immersed in an organic solvent to remove residual photoresist, yielding amorphous molybdenum superconducting nanowires.

[0123] The following details the preparation process using the preparation of amorphous tungsten superconducting nanowires as an example.

[0124] Photoresist was spin-coated onto the surface of an amorphous tungsten superconducting thin film. The spin-coating speed was 3000-4000 rpm, the acceleration was 1000-1500 rpm / s, and the spin-coating time was 60-90 s. The photoresist material was PMMA and / or HSQ. Nanowire patterning of the photoresist was performed using electron beam lithography, with the electron beam exposure dose set to 200-400 μC / cm. 2 Electron beam exposure employs image correction and dose correction to ensure uniform nanowire width. The width of the nanowire pattern is set to 40-120 nm. After exposure, development is performed for 10–30 s, followed by fixing in water for 10–25 s. This process dissolves the photoresist in the exposed areas, revealing the underlying amorphous tungsten superconducting film; while the unexposed areas are protected by photoresist (such as PMMA), thus forming a photoresist pattern with nanowire shapes.

[0125] Amorphous tungsten superconducting thin films were etched using reactive ion beam etching (RIE). The operating parameters for RIE were as follows: the preferred etching gas was CHF3; the etching gas flow rate was 10-25 sccm; the operating pressure was 0.2-0.6 Pa; the accelerating voltage was 180-260 V; the anolyte current was 4.5-6.2 A; and the etching time was 1-5 min. After RIE, the areas of the exposed amorphous tungsten superconducting film were completely etched away, while the unexposed areas retained the film due to the protection of photoresist. The amorphous tungsten superconducting film was then immersed in an organic solvent to remove residual photoresist, yielding amorphous tungsten superconducting nanowires.

[0126] The present disclosure is further illustrated below through embodiments and related test experiments and results. In the following detailed description, numerous specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Moreover, the details in the following embodiments can be arbitrarily combined to form other feasible embodiments without conflict.

[0127] It should be noted that the specific embodiments described below are merely illustrative examples, and the scope of protection of this disclosure is not limited thereto. The chemicals and raw materials used in the following embodiments are all commercially available or prepared using recognized processing methods.

[0128] Example 1:

[0129] The preparation process of the amorphous tungsten superconducting nanowires in Example 1 is shown below.

[0130] Monocrystalline silicon / silicon oxide stacked substrate treatment: Take a two-inch double-sided polished monocrystalline silicon / silicon oxide stacked substrate, with monocrystalline silicon on the bottom layer and silicon oxide on the top layer. After ultrasonic cleaning in acetone, ethanol and deionized water in sequence, it is dried with a nitrogen gun to obtain a pre-treated substrate with a clean surface.

[0131] Amorphous tungsten superconducting thin film growth: A clean substrate is placed in the chamber of a magnetron sputtering system and evacuated to 8 × 10⁻⁶ ppm. -4Pa. The magnetron sputtering parameters were set as follows: argon flow rate of 50 sccm, nitrogen flow rate of 5 sccm, working pressure of 5.9 mTorr, tungsten target for the DC target, DC power supply current of 200 mA, and growth time of 20 s. This yielded an amorphous tungsten superconducting thin film with a thickness of approximately 8 nm. Figure 5 shows the scanning electron microscope (SEM) and atomic force microscope (AFM) images of the amorphous tungsten superconducting thin film of Embodiment 1 of this disclosure, where a is the SEM image of the amorphous tungsten superconducting thin film; b is the AFM image of the thickness of the amorphous molybdenum superconducting thin film. As shown in Figure 5a, the grown amorphous tungsten superconducting thin film has a smooth surface; as shown in Figure 5b, the thickness of the amorphous tungsten superconducting thin film was obtained through pattern imaging and measurement, resulting in a thickness of approximately 8 nm. Figure 6 shows the X-ray diffraction (XRD) pattern of the amorphous tungsten superconducting thin film of Embodiment 1 of this disclosure. As shown in Figure 6, in the XRD measurement, apart from the crystallization peak formed on the silicon substrate, no crystallization peak appeared on the prepared tungsten superconducting thin film, indicating that the grown tungsten superconducting thin film is a standard amorphous material. Figure 7 shows the X-ray photoelectron spectroscopy (XPS) pattern of the amorphous tungsten superconducting thin film of Embodiment 1 of this disclosure. As shown in Figure 7, the XPS pattern clearly shows the presence of nitrogen element. The nitrogen element content was calculated to be 15% based on the peak area, proving the doping of nitrogen element in the amorphous tungsten superconducting thin film.

[0132] Figure 8 shows the resistance (RT) curves of the amorphous tungsten superconducting thin film of Embodiment 1 of this disclosure after being placed in air for different periods of time. In Figure 8, a represents the newly deposited amorphous tungsten superconducting thin film; b represents the amorphous tungsten superconducting thin film after one week of exposure to air; and c represents the amorphous tungsten superconducting thin film after two weeks of exposure to air. As shown in Figures 8(a-c), the measured superconducting transition temperature of the prepared amorphous tungsten superconducting thin film after one and two weeks of exposure to air is not significantly different from that of the newly prepared amorphous tungsten superconducting thin film, both being 4.2 K. This indicates that the amorphous tungsten superconducting thin film has high stability in air, which can improve its stable use as a photosensitive component in a single-photon detector.

[0133] The nitrogen flow rate was further adjusted, and the nitrogen doping amount in the amorphous tungsten superconducting thin film in Example 1 was calculated using XPS peak area. Figure 9 shows the superconducting performance statistics of the amorphous tungsten superconducting thin film deposited under different nitrogen flow rates in Example 1 of this disclosure. The nitrogen flow rates were 1 sccm, 2 sccm, 3 sccm, 4 sccm, and 5 sccm. Among them, the superconducting transition temperature was the highest and the superconducting transition width was the lowest when the nitrogen flow rate was 3 sccm, which is the optimal condition for the amorphous tungsten superconducting thin film.

[0134] Figure 10 shows the XRD and RT comparison images of the amorphous tungsten superconducting thin film deposited in the presence and absence of nitrogen atmosphere according to Embodiment 1 of this disclosure, where a is the XRD pattern and b is the RT comparison image. As shown in Figures 10a and 10b, when a nitrogen atmosphere of 3 sccm is introduced, the deposited film is amorphous and becomes a superconductor at low temperatures below 4K. When no nitrogen atmosphere is introduced, the deposited film is crystalline and does not transform into a superconductor at a low temperature of 2K, demonstrating the important role of nitrogen doping in superconducting tungsten films.

[0135] Electron beam lithography (EBL): PMMA was spin-coated onto the surface of an amorphous tungsten superconducting thin film at a spin speed of 4000 rpm, an acceleration of 1000 rpm / s, and a spin coating time of 60 s. Electron beam lithography was then performed, with an exposure dose set to 300 μC / cm². 2 The exposed amorphous tungsten superconducting film and PMMA were developed in a developer solution for 10 seconds and fixed in water for 15 seconds. The width of the nanowires in the pattern was set to 100 nm. During this process, the exposed areas would expose the amorphous tungsten superconducting film after the development process, while the unexposed areas would be protected by PMMA. This resulted in an amorphous tungsten superconducting film with a nanowire pattern of PMMA.

[0136] Reactive ion beam etching (RIE): An amorphous tungsten superconducting thin film with a PMMA nanowire pattern is placed in the RIE reaction chamber. The process parameters are set as follows: accelerating voltage 250V, anode current 5.5A, etching gas CHF3, gas flow rate 7 sccm, working pressure 0.27 Pa, and etching time 10 min. After RIE etching, the areas of the exposed amorphous tungsten superconducting thin film are completely etched away, while the unexposed areas retain the amorphous tungsten superconducting thin film due to the protection of the PMMA, thus obtaining amorphous tungsten superconducting nanowires.

[0137] Photoresist Removal: After etching, PMMA patterns remain on the surface of the amorphous tungsten superconducting nanowires. Therefore, the amorphous tungsten nanowires are immersed in acetone solution to clean the residual PMMA patterns. This process requires ultrasonic assistance, with an ultrasonic power of 60 W and an ultrasonic time of 120 s, resulting in clean amorphous tungsten superconducting nanowires. The current versus voltage (IV) curve of the nanowires is measured using a low-temperature electrical measurement system. Figure 11 shows the current versus voltage curves of the amorphous tungsten superconducting nanowires in Examples 1, 2, and 3 of this disclosure, where a is the curve for Example 1, b is the curve for Example 2, and c is the curve for Example 3. As shown in Figure 11a, the superconducting current of the nanowire is 5.5 μA, which supports effective detection of single photons.

[0138] Example 2:

[0139] The preparation process of Example 2 is basically the same as that of Example 1, except that the exposure dose of electron beam exposure is set to 200 μC / cm. 2 The IV curve of the nanowire was measured in a low-temperature electrical measurement system, as shown in Figure 11b. The superconducting current of the nanowire was 2.6 μA. Compared with Example 1, its support performance was poor and its stability was weak, making it difficult to support the effective detection of single photons by the nanowire.

[0140] Example 3:

[0141] The preparation process of Example 3 is basically the same as that of Example 1, except that the exposure dose of electron beam exposure is set to 400 μC / cm. 2 The IV curve of the nanowire was measured in a low-temperature electrical measurement system, as shown in Figure 11c. The superconducting current of the nanowire was only 1.5 μA. Compared with Example 1, its support performance was poor and its stability was weak, making it difficult to support the effective detection of single photons by the nanowire.

[0142] It should be noted that the exposure dose for further adjustments to electron beam exposure is less than 200 μC / cm. 2 and greater than 400 μC / cm 2 It was found that the superconducting current of the prepared nanowires was lower than that of Examples 2 and 3, and therefore could not be applied to the field of single-photon detection.

[0143] Comparative Example 1:

[0144] The preparation process of Comparative Example 1 is basically the same as that of Example 1, except that the etching gas used for reactive ion beam etching is SF6.

[0145] Figure 12 shows scanning electron microscope (SEM) images of the amorphous tungsten superconducting nanowires prepared in Example 1 and Comparative Example 1 of this disclosure, where a is an SEM image of the amorphous tungsten superconducting nanowires prepared in Example 1; and b is an SEM image of the amorphous tungsten superconducting nanowires prepared in Comparative Example 1. Comparing a and b in Figure 12, it can be seen that the residual electron beam binder in the nanowire channel of Comparative Example 1 results in an uneven morphology, and the width of the nanowire is also too thin, indicating that the nanowires prepared in Comparative Example 1 cannot be further measured.

[0146] Application Example 1:

[0147] Application Example 1 uses the amorphous tungsten superconducting nanowires prepared in Example 1 to assemble an amorphous tungsten superconducting nanowire single-photon detector. The measurement system formed by this detector mainly includes an optical system, a cryogenic system, and a circuit system. The optical system includes a laser and an attenuator connected in sequence. The cryogenic system is a dilution cryostat system. The measurement process includes the following steps:

[0148] An amorphous tungsten superconducting nanowire single-photon detector (SNSPD) with optical focusing completed was placed in a cryostat, and an optical fiber was connected to the back of the amorphous tungsten SNSPD so that the light spot was aligned with the central region of the interface amorphous tungsten SNSPD. A laser was used to output laser light, which was then attenuated to the single-photon level by an attenuator and coupled to the amorphous tungsten SNSPD region through an optical fiber. The single-photon response data of the SNSPD was acquired using a readout module.

[0149] Continuing with Figure 11a, it can be seen that the superconducting critical current can reach 5.5 μA, which meets the requirements of the device for single-photon detection. However, the superconducting critical currents of the amorphous tungsten superconducting nanowires obtained in Examples 2 and 3 are relatively low, resulting in lower efficiency of single-photon detection.

[0150] Figure 13 shows the single-photon response pulse diagram of the amorphous tungsten superconducting nanowire single-photon detector in the 1064 nm band of Application Example 1 of this disclosure; Figure 14 shows the single-photon photoconductivity response diagram of the amorphous tungsten superconducting nanowire single-photon detector in the 1064 nm band of Application Example 1 of this disclosure, where a is the response diagram based on dark counts; b is the response diagram based on light counts. As shown in Figure 13, the amorphous tungsten superconducting nanowire single-photon detector can respond to single photons relatively quickly. As shown in Figure 14a, the lower the dark count rate, the higher the detection accuracy and reliability of the amorphous tungsten superconducting nanowire single-photon detector for weak light signals, and the more accurately it can distinguish the real photon signal, reducing misjudgment and noise interference. As shown in Figure 14b, at the 1064nm wavelength, the photocount rate of the amorphous tungsten superconducting nanowire single-photon detector stabilizes at 220,000 as the bias current increases. This proves that the amorphous tungsten superconducting nanowire single-photon detector has saturated quantum efficiency for single-photon detection at 1064nm.

[0151] Example 4:

[0152] The preparation process of Example 4 is basically the same as that of Example 1, except that the width of the nanowires in the electron beam exposure pattern is set to 70 nm. The amorphous tungsten superconducting nanowires prepared by the method of Example 4 have a smaller width, which brings higher single-photon detection sensitivity to the nanowires, enabling them to respond to single photons in the 1550 nm band.

[0153] Application Example 2:

[0154] The method of this application example 2 is basically the same as that of application example 1, except that the amorphous tungsten superconducting nanowires prepared in example 4 are assembled to form an amorphous tungsten superconducting nanowire single-photon detector.

[0155] Figure 15 shows the single-photon photoconductivity response of the amorphous tungsten superconducting nanowire single-photon detector in the 1550 nm band of Application Example 2 of this disclosure. As shown in Figure 15, the photocount rate eventually stabilizes at 280,000 as the bias current increases, indicating that the amorphous tungsten superconducting nanowire single-photon detector also has saturated quantum efficiency for single-photon detection at 1550 nm.

[0156] Figure 16 shows the time jitter of the amorphous tungsten superconducting nanowire single-photon detector in the 1550 nm band in Application Example 2 of this disclosure. As shown in Figure 16, the full width at half maximum (FWHM) of the curve obtained by Gaussian fitting is 167 ps, indicating that the time jitter of the amorphous tungsten superconducting nanowire single-photon detector in the 1550 nm band is only 167 ps. These characteristics demonstrate that the amorphous tungsten superconducting nanowire single-photon detector possesses excellent single-photon detection performance.

[0157] Example 5:

[0158] The preparation process of the amorphous molybdenum superconducting nanowires in Example 5 is shown below.

[0159] Monocrystalline silicon / silicon oxide stacked substrate treatment: Take a two-inch double-sided polished monocrystalline silicon / silicon oxide stacked substrate, with monocrystalline silicon on the bottom layer and silicon oxide on the top layer. After ultrasonic cleaning in acetone, ethanol and deionized water in sequence, it is dried with a nitrogen gun to obtain a pre-treated substrate with a clean surface.

[0160] Amorphous molybdenum superconducting thin film growth: A clean substrate is placed in the chamber of a magnetron sputtering system and evacuated to 8 × 10⁻⁶ ppm. -4 Pa. The magnetron sputtering parameters were set as follows: argon flow rate of 40 sccm, nitrogen flow rate of 7 sccm, working pressure of 6.2 mTorr, target material of molybdenum target, DC power supply current of 240 mA, and growth time of 32 s. This yielded an amorphous molybdenum superconducting thin film with a thickness of 14.1 nm.

[0161] Figure 17 shows the resistance curve of the amorphous molybdenum superconducting thin film of Embodiment 5 of this disclosure as a function of temperature. As shown in Figure 17, superconductivity measurements show that the amorphous molybdenum superconducting thin film has a superconducting transition temperature of approximately 5.9 K, which is higher than that of the amorphous tungsten superconducting thin film, laying a good foundation for the subsequent fabrication of single-photon detectors.

[0162] Figure 18 shows an atomic force microscopy (AFM) image of the amorphous molybdenum superconducting thin film of Embodiment 5 of this disclosure, where a is an AFM image of the surface of the amorphous molybdenum superconducting thin film; b is an AFM image of the thickness of the amorphous molybdenum superconducting thin film. As shown in Figure 13a, the atomic force microscopy reveals that the grown amorphous molybdenum thin film has a smooth surface. As shown in Figure 18b, the thickness of the amorphous molybdenum superconducting thin film is a nanometer-scale thickness of 14.1 nm. Figure 19 shows an X-ray photoelectron spectroscopy (XPS) image of the amorphous molybdenum superconducting thin film of Embodiment 5 of this disclosure. As shown in Figure 19, the XPS image clearly shows the presence of nitrogen (N) element. The N element content is calculated to be 11% based on the peak area, proving the doping of N element in the Mo film.

[0163] Figure 20 shows the transmission electron microscope (TEM) image and the corresponding selected area electron diffraction (SAED) pattern of the amorphous molybdenum superconducting thin film of Embodiment 5 of this disclosure, where a is the TEM image of the amorphous molybdenum superconducting thin film; and b is the SAED pattern of the amorphous molybdenum superconducting thin film. As shown in Figures 20a and b, both the TEM image in a and the selected area diffraction (SAED) pattern in the corresponding region in b demonstrate that the amorphous molybdenum superconducting thin film does not exhibit significant crystallinity.

[0164] Figure 21 shows the X-ray diffraction pattern of the amorphous molybdenum superconducting thin film prepared in Example 5 of this disclosure. As shown in Figure 21, no obvious molybdenum and molybdenum nitride crystallization peaks appeared in the XRD, indicating that the grown amorphous molybdenum superconducting thin film is a standard amorphous material. Figure 22 shows the XRD patterns and RT statistics of the amorphous molybdenum superconducting thin film deposited under different sputtering currents in Example 5 of this disclosure, where a is the XRD pattern under different sputtering currents and b is the RT statistics. As shown in Figures 22a and 22b, the sputtering currents were 180mA, 190mA, 200mA, 220mA, 240mA, and 250mA, respectively. Among them, the sputtering current of 240mA has a relatively higher superconducting transition temperature and a relatively lower superconducting transition width, which are the optimal conditions for amorphous molybdenum superconducting films, proving that the sputtering current plays an important role in the deposition process of amorphous molybdenum films.

[0165] Electron beam lithography (EBL): PMMA was spin-coated onto the surface of an amorphous molybdenum superconducting thin film at a spin speed of 3000 rpm, an acceleration of 1000 rpm / s, and a spin coating time of 45 s. Subsequently, exposure was performed using an electron beam lithography system with an exposure dose set to 200 μC / cm². 2 The exposed amorphous molybdenum superconducting thin film and PMMA were developed in a developer solution for 15 seconds and fixed in water for 15 seconds. The absorption efficiency of amorphous molybdenum superconducting nanowires with different thicknesses and linewidths was simulated using FDTD to obtain the thickness and linewidth of nanowires with relatively good absorption efficiency.

[0166] Figure 23 shows a comparison of the light absorption efficiency of amorphous molybdenum superconducting nanowires of different thicknesses in finite-time domain (FDTD) simulation of Embodiment 5 of this disclosure; Figure 24 shows a comparison of the light absorption efficiency of amorphous molybdenum superconducting nanowires of different duty cycles in FDTD simulation of Embodiment 5 of this disclosure. As shown in Figures 23 and 24, the width of the nanowires in the pattern is set to 75 nm according to the simulation results. During this process, the exposed areas will expose the amorphous molybdenum superconducting film after the development process, while the unexposed areas will be protected by PMMA, thus obtaining an amorphous molybdenum superconducting film with a nanowire pattern of PMMA.

[0167] Reactive ion beam etching (RIE): An amorphous molybdenum superconducting thin film with PMMA nanowire patterning is placed in the RIE reaction chamber. The process parameters are set as follows: accelerating voltage 250V, anode current 5.5A, etching gas CHF3, gas flow rate 7sccm, working pressure 0.27Pa, and etching time 10min. After RIE etching, the areas of the exposed amorphous molybdenum superconducting thin film are completely etched away, while the unexposed areas retain the amorphous molybdenum film due to the protection of PMMA, thus obtaining amorphous molybdenum superconducting nanowires.

[0168] Photoresist removal: After etching, PMMA patterns remain on the surface of the amorphous molybdenum superconducting nanowires. Therefore, the amorphous molybdenum superconducting nanowires are immersed in acetone solution to clean the residual PMMA patterns. Ultrasonic assistance is required in this process. The ultrasonic power is 60W and the ultrasonic time is 120s to prepare clean amorphous molybdenum superconducting nanowires.

[0169] Comparative Example 2:

[0170] The preparation process of Comparative Example 2 is basically the same as that of Example 5, except that the target material of the DC target site is replaced with platinum (Pt). The RT curve of the nitrogen-doped metal thin film is measured in a low-temperature electrical measurement system. Figure 25 shows the resistance curves of nitrogen-doped amorphous metal thin films prepared by Comparative Examples 2, 3, and 4 of this disclosure as a function of temperature, where a is the curve of nitrogen-doped platinum; b is the curve of nitrogen-doped titanium; and c is the curve of nitrogen-doped niobium. As shown in Figure 25a, the nitrogen-doped Pt thin film does not exhibit zero-resistance superconducting properties at a low temperature of 2K.

[0171] Comparative Example 3:

[0172] The preparation process of Comparative Example 3 is basically the same as that of Example 5, except that the target material of the DC target site is replaced with metallic titanium (Ti). The RT curve of the nitrogen-doped metal film was measured in a low-temperature electrical measurement system. As shown in Figure 25b, the nitrogen-doped Ti film did not exhibit zero-resistance superconducting properties at a low temperature of 2K.

[0173] Comparative Example 4:

[0174] The preparation process of Comparative Example 4 is basically the same as that of Example 5, except that the target material of the DC target site is replaced with niobium (Nb). The RT curve of the nitrogen-doped metal film was measured in a low-temperature electrical measurement system. As shown in Figure 25c, the nitrogen-doped Ti film did not exhibit zero-resistance superconductivity at a low temperature of 2K.

[0175] Example 6:

[0176] The preparation process of Example 6 is basically the same as that of Example 5, except that the nitrogen flow rate is set to 5 sccm. The nitrogen-doped amorphous molybdenum superconducting thin film is used to prepare amorphous molybdenum superconducting nanowires, and the IV curve is measured in a low-temperature electrical measurement system. Figure 26 shows the current versus voltage curves of the amorphous molybdenum superconducting nanowires in Examples 5, 6, 7, and 8 of this disclosure, where a is the curve for Example 6; b is the curve for Example 7; c is the curve for Example 5; and d is the curve for Example 8. As shown in Figure 26a, the superconducting critical current of this amorphous molybdenum superconducting nanowire is 2.4 μA, and the supercurrent hysteresis ratio is 2.8.

[0177] Example 7:

[0178] The preparation process of Example 7 is basically the same as that of Example 5, except that the nitrogen flow rate is set to 6 sccm. This nitrogen-doped amorphous molybdenum superconducting thin film was used to prepare amorphous molybdenum superconducting nanowires, and the IV curve was measured using a low-temperature electrical measurement system. As shown in Figure 26b, the superconducting critical current of this amorphous molybdenum superconducting nanowire is 7.7 μA, and the supercurrent hysteresis ratio is 5.9.

[0179] Example 8:

[0180] The preparation process of Example 8 is basically the same as that of Example 5, except that the nitrogen flow rate is set to 9 sccm. This nitrogen-doped amorphous molybdenum superconducting thin film was used to prepare amorphous molybdenum superconducting nanowires, and the IV curve was measured using a low-temperature electrical measurement system. As shown in Figure 26d, the superconducting critical current of this amorphous molybdenum nanowire is 4.0 μA, and the supercurrent hysteresis ratio is 3.8.

[0181] Comparing the superconducting critical currents in Examples 5 to 8, it can be seen that the amorphous molybdenum superconducting nanowires prepared in Example 5 have relatively better performance.

[0182] Comparative Example 5:

[0183] The preparation process of Comparative Example 5 is basically the same as that of Example 5, except that the sputtering atmosphere is set to a mixture of argon and oxygen, and the oxygen flow rate is set to 7 sccm. The RT curve of the oxygen-doped molybdenum film was measured in a low-temperature electrical measurement system. Figure 27 shows the resistance curve of the oxygen-doped amorphous molybdenum film prepared in Comparative Example 5 as a function of temperature. As shown in Figure 27, it is confirmed that the oxygen-doped molybdenum film does not exhibit zero-resistance superconductivity at a low temperature of 2K.

[0184] Application Example 3:

[0185] Application Example 3 uses the amorphous molybdenum superconducting nanowires prepared in Example 5 to assemble an amorphous molybdenum superconducting nanowire single-photon detector. The measurement system formed by this detector mainly includes an optical system, a cryogenic system, and a circuit system. The optical system consists of a laser and an attenuator connected in sequence; the cryogenic system uses a GM cryostat system. The measurement process includes the following steps:

[0186] An amorphous molybdenum SNSPD, having undergone optical manipulation, is placed inside a cryostat. An optical fiber is connected to the back of the amorphous molybdenum SNSPD to ensure precise alignment of the light spot with the central region of the interface amorphous molybdenum SNSPD. A laser outputs light, which is attenuated to the single-photon level by an attenuator before being transmitted to the amorphous molybdenum SNSPD region via fiber coupling. A readout module is used to collect the response data of the amorphous molybdenum SNSPD to the single photon.

[0187] Example 9:

[0188] The preparation process of Example 9 is basically the same as that of Example 5, except that the width of the nanowires in the electron beam exposure pattern is set to 53 nm. The amorphous molybdenum superconducting nanowires obtained using the method of Example 9 have a smaller width.

[0189] Figure 28 shows SEM images of the amorphous molybdenum superconducting nanowires prepared in Examples 5 and 9 of this disclosure, where a is the SEM image of Example 5 and b is the SEM image of Example 9. As shown in Figures 28a and b, it can be seen that the nanowires are relatively uniformly distributed in both cases.

[0190] Application Example 4:

[0191] The method of this application example 4 is basically the same as that of application example 3, except that the amorphous molybdenum superconducting nanowires prepared in example 9 are assembled to form an amorphous tungsten superconducting nanowire single-photon detector.

[0192] The amorphous molybdenum superconducting nanowire single-photon detectors prepared in Application Examples 3 and 4 were measured according to the above method. Figure 29 shows the current versus voltage curves of the SNSPDs assembled in Application Examples 3 and 4 of this disclosure. Here, 75 nm represents the SNSPD of Application Example 3, and 53 nm represents the SNSPD of Application Example 4. As shown in Figure 29, it can be seen that the superconducting critical current can reach 15.7 μA, and the supercurrent hysteresis ratio can reach 8.5, meeting the requirements of the device for single-photon detection. In comparison, the superconducting critical current of the amorphous molybdenum superconducting nanowires obtained in Examples 5 to 8 is lower than that in Examples 5 and 9, resulting in lower single-photon detection efficiency.

[0193] Figure 30 shows the response pulse diagrams of the amorphous molybdenum superconducting nanowire single-photon detectors assembled in Application Examples 3 and 4 of this disclosure in the 1064 nm band. As shown in Figure 30, it can be seen that the SNSPD prepared in Application Example 3 has a shorter recovery time for photon response, representing a higher photon response rate, which is beneficial for the development and preparation of high-speed SNSPDs.

[0194] Figure 31 shows a comparison of the light absorption efficiency of the amorphous molybdenum superconducting nanowire single-photon detectors assembled in Application Examples 3 and 4 of this disclosure in the 1064 nm band. As shown in Figure 31, in the 1064 nm band, with the increase of bias current, the photocount rate of the amorphous molybdenum superconducting nanowire single-photon detector gradually stabilizes. This indicates that the amorphous molybdenum SNSPD has a saturated quantum efficiency for single-photon detection at 1064 nm, thus proving that nitrogen-doped amorphous molybdenum can achieve efficient and stable detection of single photons in the 1064 nm band.

[0195] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. An amorphous metal superconducting thin film, wherein, The amorphous metal superconducting thin film is a nitrogen-doped amorphous metal superconducting thin film, and the amorphous metal includes: amorphous molybdenum or amorphous tungsten.

2. The amorphous metal superconducting thin film of claim 1, wherein, The thickness of amorphous molybdenum superconducting films is 3–30 nm; the thickness of amorphous tungsten superconducting films is 2–20 nm.

3. The amorphous metal superconducting thin film of claim 1, wherein, The superconducting transition temperature of the amorphous molybdenum superconducting film is 2-10K, and the square resistance is 300-15Ω □ ; The superconducting transition temperature of the amorphous tungsten superconducting thin film is 1-10 K, and the square resistance is 400-40 Ω □ .

4. The amorphous metal superconducting thin film of any one of claims 1-3, wherein, In amorphous molybdenum superconducting thin films, the molar content of doped nitrogen is 5–17%; In amorphous tungsten superconducting thin films, the molar content of nitrogen doping is 8–12%.

5. A method of making an amorphous metal superconducting thin film, wherein, The preparation method includes: Amorphous metal superconducting thin films were grown on a substrate by sputtering using a mixture of argon and nitrogen as the working gas. Among them, amorphous metals include: amorphous molybdenum or amorphous tungsten.

6. The production method according to claim 5, wherein When growing amorphous tungsten superconducting thin films, the sputtering current is 100–360 mA; The sputtering current is 180–250 mA when growing amorphous molybdenum superconducting thin films.

7. The production method according to claim 5, wherein When growing amorphous tungsten superconducting thin films, the flow rate of argon in the mixed gas is 40-60 sccm, and the flow rate of nitrogen is 1-5 sccm. During the growth of amorphous molybdenum superconducting thin films, the flow rate of argon in the mixed gas is 30–60 sccm, and the flow rate of nitrogen is 5–9 sccm.

8. An amorphous metal superconducting nanowire single-photon detector, comprising: Light absorption layer; The light-absorbing layer comprises nanowires formed from amorphous metal superconducting thin films according to any one of claims 1 to 4, or nanowires formed from amorphous metal superconducting thin films prepared by the preparation method according to any one of claims 5 to 7.

9. The amorphous metal superconducting nanowire single-photon detector of claim 8, wherein, When the amorphous metal superconducting thin film is an amorphous tungsten superconducting thin film, the width of the nanowire is 40–120 nm; When the amorphous metal superconducting thin film is an amorphous molybdenum superconducting thin film, the width of the nanowire is 30–100 nm.

10. The amorphous metal superconducting nanowire single-photon detector of claim 8, wherein, The nanowires are meandering nanowires.

11. A method for fabricating an amorphous metallic superconducting nanowire single-photon detector according to any one of claims 8 to 10, comprising: Amorphous metal superconducting thin films are sequentially exposed and etched to form nanowire structures, thus obtaining amorphous metal superconducting nanowires. The amorphous metal superconducting nanowires were assembled as a light absorption layer to obtain the amorphous metal superconducting nanowire single-photon detector.

12. The method of making according to claim 11, wherein, The process of sequentially exposing and etching an amorphous metal superconducting thin film to form a nanowire structure to obtain amorphous metal superconducting nanowires includes: Photoresist is spin-coated onto the surface of the amorphous metal superconducting thin film. The photoresist is then subjected to nanowire patterning exposure, development, and fixing processes using electron beam exposure to obtain an amorphous metal superconducting thin film with nanowire shapes. The amorphous metal superconducting thin film with nanowire shape was etched using reactive ion beam etching to obtain amorphous metal superconducting nanowires.

13. The method of making according to claim 12, wherein, When the amorphous metal in the nanowire-structured amorphous metal superconducting thin film is tungsten, the accelerating voltage of the reactive ion beam etching is 180–260 V, the anode current is 4.5–6.2 A, the etching time is 1–5 min, and the electron beam exposure dose is set to 200–400 μC / cm. 2 ; When the amorphous metal in the amorphous metal superconducting thin film with nanowire structure is molybdenum, the acceleration voltage of the reactive ion beam etching is 150-240V, the anode current is 4.0-6.0A, the etching time is 30-120s, and the dose setting of the electron beam exposure is 180-300μC / cm 2 .

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