Molybdenum silicide superconducting thin film applied to superconducting nanowire single-photon detector and preparation method of molybdenum silicide superconducting thin film

Abstract

The invention provides a molybdenum silicide superconducting thin film applied to a superconducting nanowire single-photon detector and a preparation method thereof, the molybdenum silicide superconducting thin film comprises three layers, the bottom layer is a substrate used for supporting the growth of a superconducting thin film, the middle layer is a molybdenum silicide superconducting thin film used for absorbing single photons and responding, and the top layer is a niobium hexanitrogen pentade protection layer used for absorbing single photons. The molybdenum silicide superconducting thin film is prevented from being oxidized; the molybdenum silicide superconducting thin film is prepared by adopting a direct-current magnetron sputtering method, and a mechanical pump and a molecular pump are used for vacuumizing, so that the vacuum degree of a cavity of a magnetron sputtering system reaches 2.5 * 10 <-5 > Pa; the surface cleanliness of the substrate and the adhesiveness of the superconducting thin film are improved by adopting ion milling; inert argon gas is introduced into a chamber of the magnetron sputtering system, air pressure is set, direct current is applied to the molybdenum silicide alloy target, ionized argon ions in the chamber bombard the molybdenum silicide alloy target, ions escaping from a target material grow on the surface of the substrate layer by layer, and finally the molybdenum silicide superconducting thin film is formed. And growing a niobium hexanitrogen pentaniobium protective layer on the surface of the molybdenum silicide superconducting thin film by adopting a radio frequency magnetron sputtering method. According to the preparation method, the molybdenum silicide superconducting thin film with high superconducting transition temperature and good uniformity can be obtained, the problem that a traditional crystal superconducting thin film depends on a substrate is solved, and the spectral response and process compatibility capacity of a superconducting nanowire single-photon detector is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-nano processing and thin film preparation, and in particular to a molybdenum silicide superconducting thin film used in a superconducting nanowire single-photon detector and a preparation method thereof. Background Art

[0002] Superconducting nanowire single-photon detectors (SNSPDs) have rapidly developed into a highly promising photon counting technology in the near-infrared region. Their excellent performance (such as high detection efficiency, low dark counts, and low temporal jitter) has led to their widespread application in cutting-edge fields such as quantum key distribution, Earth-Moon optical communications, and bioluminescence imaging. The first and most critical step in developing SNSPDs is to grow a superconducting thin film on a substrate. The material parameters of the superconducting film are closely related to the detector's performance. For example, the superconducting band gap and Cooper pair binding energy of the superconducting film affect the detector's photon detection sensitivity and efficiency, the superconducting transition temperature of the superconducting film affects the detector's operating temperature, and the optical constants of the superconducting film affect the detector's photon response band.

[0003] Currently, two types of superconducting films are used in the development of SNSPDs: crystalline and amorphous. As a crystalline film, niobium nitride (NbN) films exhibit high superconducting transition temperatures and critical current densities, making them a classic candidate for SNSPDs. However, they require a demanding preparation environment and are prone to significant lattice mismatch with the substrate. Their short coherence length significantly increases the process complexity and defect sensitivity of SNSPDs. Molybdenum silicide (MoSi) films, amorphous films, exhibit a smaller superconducting energy gap and lower carrier density than crystalline films. Given identical structural parameters, amorphous films are more likely to generate a higher number of quasiparticles per absorbed photon, enabling them to respond to longer-wavelength photons and achieve higher quantum detection efficiency. Furthermore, amorphous films lack a fixed crystal orientation and are less dependent on the substrate. The choice of substrate type does not significantly degrade the superconducting performance of the film, resulting in excellent process compatibility and the development of SNSPDs with large photosensitive areas. Precisely controlling the stoichiometric ratio of silicon to molybdenum in the development of MoSi superconducting films remains a key challenge that needs to be addressed. Summary of the Invention

[0004] Purpose of the invention: In order to solve the problems of poor uniformity and difficult stoichiometric ratio control of superconducting films used in superconducting nanowire single-photon detectors, the present invention proposes a molybdenum silicide superconducting film used in superconducting nanowire single-photon detectors and a preparation method thereof.

[0005] Technical solution: A molybdenum silicide superconducting film used in superconducting nanowire single-photon detectors. The molybdenum silicide superconducting film consists of three layers: the bottom layer is the substrate, the middle layer is the molybdenum silicide superconducting film, and the top layer is the hexanitrogen pentaniobium protective layer.

[0006] Furthermore, the substrate is used to support the growth of a molybdenum silicide superconducting thin film, and the substrate includes one of a silicon-based substrate, a sapphire substrate, a magnesium oxide substrate, and a magnesium fluoride substrate.

[0007] Furthermore, the molybdenum silicide superconducting film is an alloy material of silicon and molybdenum in a certain stoichiometric ratio.

[0008] The present invention also discloses a method for preparing a molybdenum silicide superconducting film for use in a superconducting nanowire single-photon detector, comprising the following steps:

[0009] Step 1: Clean the substrate surface by placing the substrate in an organic solution and ultrasonically cleaning it in an ultrasonic cleaning machine;

[0010] Step 2: Ion milling the substrate surface, ion milling the substrate in the sub-chamber of the magnetron sputtering equipment;

[0011] Step 3: Using a DC magnetron sputtering method, setting the gas and gas pressure in the main chamber of the magnetron sputtering equipment, setting the DC current, and growing a molybdenum silicide superconducting thin film on the substrate surface;

[0012] Step 4: Using the radio frequency magnetron sputtering method, set the gas and gas pressure in the main chamber of the magnetron sputtering equipment, set the radio frequency power, and in-situ grow the hexanitride pentaniobium protective layer on the surface of the molybdenum silicide superconducting film.

[0013] Furthermore, the organic solution includes acetone and ethanol.

[0014] Furthermore, the ion milling uses an ion beam to bombard impurities adsorbed on the surface of the stripped substrate, thereby enhancing surface activation and increasing the adhesion of the film.

[0015] Furthermore, the step (1) specifically includes:

[0016] Place the substrate in a beaker, first pour acetone solution into the beaker and ultrasonically clean it for 5 minutes, then pour ethanol into the beaker and ultrasonically clean it for 5 minutes, then pour deionized water into the beaker and ultrasonically clean it for 5 minutes, finally use a nitrogen gun to blow dry the substrate surface and set aside.

[0017] Furthermore, the step (2) specifically includes:

[0018] After pretreatment (cleaning and drying), the substrate is transferred to the sub-chamber of the magnetron sputtering system by a robot. High-purity argon (Ar, 99.999%) is used as the ion source gas, and parameters such as ion beam current, working gas pressure, acceleration voltage and ion milling time are set to perform ion milling on the substrate.

[0019] Furthermore, the step (3) specifically includes:

[0020] The ion-milled substrate was sent into the main chamber of the magnetron sputtering system by a robot. The position of the substrate was moved by a translation stage so that the substrate was under the molybdenum silicide alloy target. When the vacuum degree in the main chamber reached 2.5×10 -5 Pa and below, a certain flow rate of high-purity argon gas is introduced into the main chamber, and the working gas pressure and working current of the main chamber are set. When the gas flow rate, gas pressure and current are stable, the baffle under the molybdenum silicide alloy target is opened, and the molybdenum silicide superconducting film grows layer by layer on the substrate surface under the action of glow discharge.

[0021] Furthermore, the step (4) specifically includes:

[0022] In the main chamber, the grown molybdenum silicide superconducting film is moved to the bottom of the niobium target via a translation stage, and a certain flow rate of argon and nitrogen is introduced into the main chamber. The working gas pressure and radio frequency power of the main chamber are set. When the gas flow, pressure and power are stable, the baffle under the niobium target is opened, and a hexanitrogen pentaniobium protective layer grows on the surface of the molybdenum silicide superconducting film under the action of glow discharge.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) The present invention uses an alloy target to prepare a molybdenum silicide superconducting film, achieving the purpose of controlling the stoichiometric ratio of silicon to molybdenum. Compared with traditional niobium nitride superconducting films, molybdenum silicide superconducting films have low requirements on substrate materials, better uniformity, and high process compatibility, which is conducive to the application of molybdenum silicide superconducting films in the preparation of SNSPDs.

[0025] (2) The present invention optimizes film preparation conditions by using DC magnetron sputtering technology, focusing on regulating the sputtering gas pressure and sputtering current. The superconducting transition temperature of a 200nm thick molybdenum silicide superconducting film prepared on a silicon-based substrate can reach 7.8K, and the superconducting transition temperature of an 8nm thick molybdenum silicide superconducting film can reach 5.4K. These values ​​are comparable to the research level abroad, breaking through the technical bottleneck of high-performance superconducting film development.

[0026] (3) The molybdenum silicide superconducting film prepared by the present invention has the advantages of controllable stoichiometric ratio, good uniformity, and high superconducting transition temperature, which is of great benefit to the preparation of SNSPDs. It can enable SNSPDs to achieve both large photosensitivity and wide-spectrum photon response capabilities, and further improve the operating temperature of SNSPDs (for example, the operating temperature of SNSPDs prepared with 8 nm thick molybdenum silicide superconducting film is greater than 2.4K). BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a cross-sectional schematic diagram of a silicon-based substrate used in the present invention;

[0028] Figure 2 is Figure 1 Schematic diagram of the molybdenum silicide superconducting film grown on the basis;

[0029] Figure 3 is Figure 2 Schematic diagram of the hexanitride pentaniobium protective layer grown on the base;

[0030] Figure 4 The surface roughness distribution of MoSi superconducting thin films was characterized using atomic force microscopy;

[0031] Figure 5 The cross-sectional morphology of a MoSi superconducting film was characterized using a transmission electron microscope.

[0032] Figure 6 It is a graph of optical constants of MoSi superconducting films at different wavelengths using spectroscopic ellipsometry.

[0033] Figure 7 The figure is a graph showing the relationship between resistance and temperature of an 8 nm thick molybdenum silicide superconducting film prepared by the present invention.

[0034] Figure 8 The figure is a graph showing the relationship between resistance and temperature of a 200 nm thick molybdenum silicide superconducting film prepared by the present invention. DETAILED DESCRIPTION

[0035] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present invention and are not intended to limit the present invention.

[0036] The present invention relates to a molybdenum silicide superconducting film for use in a superconducting nanowire single-photon detector, which specifically comprises a substrate 1 as a bottom layer, a molybdenum silicide superconducting film 2 as an intermediate layer, and a hexanitrogen pentaniobium protective layer 3 as a top layer. Figure 3 As shown;

[0037] A method for preparing a molybdenum silicide superconducting thin film for use in a superconducting nanowire single-photon detector of the present invention comprises the following steps:

[0038] Step 1:

[0039] The substrate was placed in a beaker and ultrasonically cleaned in an ultrasonic cleaner using acetone, ethanol, and deionized water for 5 minutes respectively, and then the substrate was blown dry using a nitrogen gun;

[0040] The substrate 1 used is a silicon-based thermally oxidized SiO2 substrate with a thickness of 500 μm and a size of 20 μm×20 μm. Figure 1 shown.

[0041] Step 2:

[0042] The thermally oxidized SiO2 substrate is transferred to the sub-chamber of the magnetron sputtering system by a robot, and the surface of the thermally oxidized SiO2 substrate is further cleaned by ion milling;

[0043] Turn on the ion milling power switch, set the argon gas flow rate to 3.5 sccm, the ion beam current to 30 mA, the working gas pressure to 0.03 Pa, the acceleration voltage to 208 V, and the ion milling time to 2 min.

[0044] Step 3:

[0045] The thermally oxidized SiO2 substrate after ion milling was sent into the main chamber of the magnetron sputtering system by a robot. The position of the thermally oxidized SiO2 substrate was moved by a translation stage so that it was under the molybdenum silicide alloy target. The stoichiometric ratio of silicon to molybdenum in the molybdenum silicide alloy target was 0.2:0.8.

[0046] When the vacuum degree in the main chamber reaches 2.5×10 -5 Pa and below, a certain flow rate of high-purity argon gas is introduced into the main chamber, and the argon gas flow rate of the main chamber is set to 22 sccm, the working pressure is 0.2 Pa, and the working current is 0.5 A;

[0047] When the gas flow, working pressure and working current are stable, the baffle under the molybdenum silicide alloy target is opened, and under the action of glow discharge, 8nm and 200nm thick molybdenum silicide superconducting films are grown on the surface of the thermally oxidized SiO2 substrate, as shown in FIG. Figure 2 shown.

[0048] Step 4:

[0049] Since the silicon element in the MoSi superconducting film is unstable in the air, in order to prevent the film from being oxidized, a protective layer of hexanitrogen pentaniobium is in situ grown on the surface of the MoSi superconducting film by radio frequency magnetron sputtering. Figure 3 As shown;

[0050] In the main chamber of the magnetron sputtering system, the grown molybdenum silicide superconducting film was moved to the bottom of the niobium target via a translation stage. Argon and nitrogen were introduced into the main chamber at a certain flow rate (118 sccm and 29 sccm, respectively). The operating pressure was 2.66 Pa, and the RF power was 400 W.

[0051] When the gas flow, working gas pressure and radio frequency current are stable, the baffle under the niobium target is opened, and under the action of glow discharge, a 4nm thick hexanitrogen pentaniobium protective layer is grown on the surface of the molybdenum silicide superconducting film.

[0052] The above implementation steps are the result of optimizing the method for preparing a molybdenum silicide superconducting thin film according to the present invention. To fully illustrate the excellent effect of this embodiment, the film properties and superconducting properties of the molybdenum silicide superconducting thin film are characterized using thin film characterization technology.

[0053] Figure 4 The surface roughness of an 8nm thick molybdenum silicide superconducting film was characterized using an atomic force microscope, and the root mean square value of the surface roughness of the film was calculated using software to be 0.4nm. This value indicates that the prepared molybdenum silicide superconducting film has good uniformity and high flatness.

[0054] Figure 5 The surface morphology of the molybdenum silicide superconducting film was characterized using a transmission electron microscope. It can be seen that the thickness of the molybdenum silicide superconducting film is 8nm. It can also be clearly seen that the prepared molybdenum silicide superconducting film is an amorphous structure with anisotropy, and a 4nm thick hexanitrogen pentaniobium protective layer is grown on the surface of the molybdenum silicide superconducting film.

[0055] Figure 6 The optical constants of MoSi superconducting films, namely the absorption coefficient n and the extinction coefficient k, were characterized using spectral ellipsometer. It was found that within the measured spectral range, the absorption coefficient n and the extinction coefficient k of MoSi superconducting films increased with increasing wavelength, which means that MoSi superconducting films have obvious advantages in absorbing wide-spectrum photons.

[0056] Figure 7 The resistance-temperature curve of an 8nm thick molybdenum silicide superconducting film was measured using a liquid helium cryogenic system and a four-terminal method. The superconducting transition temperature of the film is defined as the temperature at which the film resistance disappears. The resistance-temperature curve shows that the superconducting critical transition temperature of the 8nm thick molybdenum silicide superconducting film is 5.4K.

[0057] Figure 8 The resistance-temperature curve of a 200nm thick MoSi superconducting film was measured using a liquid helium cryogenic system and a four-terminal method. The resistance-temperature curve shows that the superconducting critical transition temperature of the 200nm thick MoSi superconducting film is 7.8K.

Claims

1. A molybdenum silicide superconducting film used in a superconducting nanowire single-photon detector, characterized in that: The molybdenum silicide superconducting film consists of three layers: the bottom layer is the substrate, the middle layer is the molybdenum silicide superconducting film, and the top layer is the hexanitrogen pentaniobium protective layer.

2. The molybdenum silicide superconducting film for use in superconducting nanowire single-photon detectors according to claim 1, characterized in that: The substrate is used to support the growth of a molybdenum silicide superconducting thin film, and the substrate comprises one of a silicon-based substrate, a sapphire substrate, a magnesium oxide substrate and a magnesium fluoride substrate.

3. The molybdenum silicide superconducting film for use in superconducting nanowire single-photon detectors according to claim 1, characterized in that: The molybdenum silicide superconducting film is an alloy material of silicon and molybdenum in a certain stoichiometric ratio.

4. A method for preparing a molybdenum silicide superconducting film for use in superconducting nanowire single-photon detectors, characterized in that: The steps include: Step 1: Clean the substrate surface by placing the substrate in an organic solution and ultrasonically cleaning it in an ultrasonic cleaning machine; Step 2: Ion milling the substrate surface, ion milling the substrate in the sub-chamber of the magnetron sputtering equipment; Step 3: Using a DC magnetron sputtering method, setting the gas and gas pressure in the main chamber of the magnetron sputtering equipment, setting the DC current, and growing a molybdenum silicide superconducting thin film on the substrate surface; Step 4: Using the radio frequency magnetron sputtering method, set the gas and gas pressure in the main chamber of the magnetron sputtering equipment, set the radio frequency power, and in-situ grow the hexanitride pentaniobium protective layer on the surface of the molybdenum silicide superconducting film.

5. The method for preparing a molybdenum silicide superconducting thin film for use in superconducting nanowire single-photon detectors according to claim 4, characterized in that: The organic solution includes acetone and ethanol.

6. The method for preparing a molybdenum silicide superconducting thin film for use in superconducting nanowire single-photon detectors according to claim 4, characterized in that: The ion milling uses an ion beam to bombard impurities adsorbed on the surface of the strippable substrate, thereby enhancing surface activation and increasing the adhesion of the film.

7. The method for preparing a molybdenum silicide superconducting thin film for use in superconducting nanowire single-photon detectors according to claim 4, characterized in that: The implementation process of step (1) is as follows: Place the substrate in a beaker, first pour acetone solution into the beaker and ultrasonically clean it for 5 minutes, then pour ethanol into the beaker and ultrasonically clean it for 5 minutes, then pour deionized water into the beaker and ultrasonically clean it for 5 minutes, finally use a nitrogen gun to blow dry the substrate surface and set aside.

8. The method for preparing a molybdenum silicide superconducting thin film for use in superconducting nanowire single-photon detectors according to claim 4, characterized in that: The implementation process of step (2) is as follows: After pretreatment (cleaning and drying), the substrate is transferred to the sub-chamber of the magnetron sputtering system by a robot. High-purity argon (Ar, 99.999%) is used as the ion source gas, and parameters such as ion beam current, working gas pressure, acceleration voltage and ion milling time are set to perform ion milling on the substrate surface.

9. The method for preparing a molybdenum silicide superconducting thin film for use in superconducting nanowire single-photon detectors according to claim 4, characterized in that: The implementation process of step (3) is as follows: The ion milled substrate is sent into the main chamber of the magnetron sputtering system by a robot. The position of the substrate is moved by a translation stage so that the substrate is under the molybdenum silicide alloy target. When the vacuum degree in the main chamber reaches 2.5×10- 5 Pa and below, a certain flow rate of high-purity argon gas is introduced into the main chamber, and the working gas pressure and working current of the main chamber are set. When the gas flow rate, gas pressure and current are stable, the baffle under the molybdenum silicide alloy target is opened, and the molybdenum silicide superconducting film grows layer by layer on the substrate surface under the action of glow discharge.

10. The method for preparing a large photosensitive area structured superconducting micro-ribbon single-photon detector according to claim 4, characterized in that: The implementation process of step (4) is as follows: In the main chamber, the grown molybdenum silicide superconducting film is moved to the bottom of the niobium target via a translation stage, and a certain flow rate of argon and nitrogen is introduced into the main chamber. The working gas pressure and radio frequency power of the main chamber are set. When the gas flow, pressure and power are stable, the baffle under the niobium target is opened, and a hexanitrogen pentaniobium protective layer grows on the surface of the molybdenum silicide superconducting film under the action of glow discharge.

Images