Amorphous tungsten superconducting nanowire single-photon detector

Abstract

The present invention discloses an amorphous tungsten superconducting nanowire single-photon detector (SNSPD), comprising a photosensitive component, which is an amorphous tungsten superconducting nanowire. The amorphous tungsten superconducting nanowire is prepared by the following steps: (1) growing an amorphous tungsten thin film on a substrate; and (2) etching the amorphous tungsten film into a circuitous nanowire structure using electron beam exposure and reactive ion etching to obtain the amorphous tungsten superconducting nanowire. The present invention uses tungsten nanowires with good stability as the main material of the SNSPD, thereby improving the robustness of the SNSPD preparation process and extending the service life of the SNSPD device in practical applications.

Description

Technical Field

[0001] The present invention relates to a single-photon detector, in particular to an amorphous tungsten superconducting nanowire single-photon detector. Background Art

[0002] Superconducting photon detectors mainly include superconducting critical temperature transition single photon detectors (TES) and superconducting nanowires single photon detectors (SNSPD). Both detectors use the process of superconducting materials transitioning from a superconducting state to a non-superconducting state to detect single photons. Among them, TES is usually composed of an ultra-thin superconducting film. After the photon is absorbed, a tiny temperature change will occur, causing the resistance of the superconducting film to change. This tiny signal is amplified using a superconducting quantum interference device to realize the signal readout of a single photon. The presence of the photon can be detected by using this resistance change, thereby realizing the detection of single photons. TES can achieve high detection efficiency in the visible to near-infrared range, but its extremely low operating temperature (<10mK) undoubtedly poses a great challenge to refrigeration technology.

[0003] Compared to the demanding operating conditions of TES, SNSPD can achieve single-photon detection from the ultraviolet to the mid- and far-infrared bands without requiring extremely low operating temperatures. The SNSPD's main body is a superconducting nanowire made from an ultrathin superconducting film. Its operating principle is to use the energy of a single photon to break up Cooper pairs in the superconducting nanowire, thereby forming a non-superconducting hotspot region on the nanowire. Once the heat from this hotspot relaxes to the substrate through electron-phonon interaction, the nanowire returns to its initial superconducting state. Single photon detection is achieved by detecting and discriminating the voltage pulse generated at both ends of the nanowire by this transition.

[0004] SNSPDs offer the advantages of high detection efficiency, low dark counts, low temporal jitter, and a wide response spectrum. Consequently, they have found widespread application in fields such as quantum information, astronomical detection, lidar, and defense, and have gradually become one of the most mainstream single-photon detectors. The SNSPD's detection mechanism fundamentally influences the detectable wavelength range due to the superconducting energy gap of the nanowire. Therefore, current SNSPD development targeting the mid- and far-infrared range primarily utilizes low-energy-gap materials such as MoSi and WSi.

[0005] However, the poor stability of these two materials complicates the fabrication process of SNSPDs based on these amorphous silicide nanowires. Furthermore, the nanowires inevitably degrade during use, preventing the detectors from functioning for extended periods. Therefore, exploring a superconducting nanowire with a low superconducting band gap and improved stability for use in SNSPD fabrication is of great importance for expanding single-photon detection in the mid- and far-infrared bands. Summary of the Invention

[0006] Purpose of the invention: The purpose of the present invention is to provide an amorphous tungsten superconducting nanowire single-photon detector with a low superconducting energy gap and better stability.

[0007] Technical solution: The amorphous tungsten superconducting nanowire single-photon detector of the present invention includes a photosensitive component, which is an amorphous tungsten superconducting nanowire; the amorphous tungsten superconducting nanowire is prepared by the following steps:

[0008] (1) growing an amorphous tungsten thin film on a substrate;

[0009] (2) The amorphous tungsten film is etched into a tortuous nanowire structure using electron beam exposure and reactive ion etching to obtain amorphous tungsten superconducting nanowires.

[0010] Furthermore, in step (1), the substrate is ultrasonically cleaned in acetone, ethanol, and deionized water for at least 10 minutes to remove impurities on the substrate surface. The substrate is preferably a Si / SiO2 substrate. An amorphous tungsten film having a nanometer-scale thickness is grown on the pretreated Si / SiO2 substrate by magnetron sputtering.

[0011] Furthermore, the amorphous tungsten film is grown by magnetron sputtering, and the process parameters of the magnetron sputtering are as follows: the magnetron sputtering target is metal tungsten; the sputtering gas is an Ar / N2 mixed gas atmosphere, the argon flow rate is 40-60 sccm, and the nitrogen flow rate is 2-5 sccm; the magnetron sputtering DC target power is 40W-180W; the working pressure is 4.9-6.1mTorr, the DC power supply current is 150-200mA, the deposition rate is 0.3-0.4nm / s, and the growth time is more than 20s. The amorphous tungsten film has a thickness of 2-20nm, a superconducting transition temperature of 1-10K, and a sheet resistance of 400Ω / □ -40Ω / □ .

[0012] Furthermore, step (2) specifically includes the following process:

[0013] (2.1) Spin-coating a photoresist on the surface of the amorphous tungsten film and performing nanowire patterning on the photoresist using electron beam exposure;

[0014] (2.2) After exposure, development and fixing are performed to obtain an amorphous tungsten film having a nanowire shape;

[0015] (2.3) The amorphous tungsten film is etched using reactive ion beam etching to remove residual photoresist and obtain amorphous tungsten nanowires.

[0016] Furthermore, in step (2.1), the rotation speed during spin coating of the photoresist is 3000-4000 rpm, the acceleration is 1000-1500 rpm / s, and the coating time is 60-90 s; the material of the photoresist is PMMA and / or HSQ.

[0017] Furthermore, in step (2.1), the electron beam exposure dose is set to 200-400 μC / cm 2 The electron beam exposure adopts image correction and dose correction to ensure uniform width of the nanowires.

[0018] Furthermore, in step (2.2), the development time is 10-30 seconds, and the fixing time in water is 10-25 seconds.

[0019] Furthermore, in step (2.2), after development and fixing, the exposed areas will expose the amorphous tungsten film through the development process, while the unexposed areas will be protected by PMMA, thereby obtaining a nanowire pattern of the photoresist.

[0020] Furthermore, in step (2.3), the working parameters of reactive ion beam etching are: the etching gas is preferably CHF3; the etching gas flow rate is 10-25sccm; the working gas pressure is 0.2-0.6Pa; the acceleration voltage is 180-260V, the anode current is 4.5-6.2A, and the etching time is 1-5min.

[0021] Furthermore, in step (2.3), the amorphous tungsten film is immersed in an organic solvent to remove residual photoresist; the organic solvent is preferably acetone and / or ethanol.

[0022] Furthermore, in step (2.3), after the reactive ion beam etching, the exposed area of ​​the amorphous tungsten film is etched cleanly, while the unexposed area is protected by the photoresist, so that the amorphous tungsten film is preserved.

[0023] Beneficial Effects: Compared with the prior art, the present invention has achieved the following significant effects: (1) The present invention realizes single-photon detection by amorphous tungsten superconducting nanowires for the first time, providing a new material for SNSPD detectors, making up for the poor stability of the low-bandgap materials currently used in SNSPDs. By using tungsten nanowires with good stability as the main material of SNSPDs, the robustness of the SNSPD preparation process is improved, and the service life of SNSPD devices in practical applications is extended. (2) The amorphous tungsten superconducting nanowire single-photon detector of the present invention can realize single-photon detection in the 1064nm and 1550nm bands. In the temperature range of 0.3K to 1K, the quantum detection efficiency of single-photon detection reaches 100%, which provides an excellent material for the development of SNSPDs in the mid- and foreign infrared bands. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The invention provides a method for preparing an amorphous tungsten superconducting nanowire single-photon detector;

[0025] Figure 2 The SEM and AFM images of the amorphous tungsten film prepared in Example 1 are shown;

[0026] Figure 3 is the XRD pattern of the amorphous tungsten film prepared in Example 1;

[0027] Figure 4 RT diagrams of the amorphous tungsten film prepared in Example 1 after being placed in air for different times;

[0028] Figure 5 SEM comparison images of amorphous tungsten superconducting nanowires prepared in Example 1 and Comparative Example 3;

[0029] Figure 6 IV comparison diagrams of amorphous tungsten superconducting nanowires in Example 1, Comparative Example 1, and Comparative Example 2, respectively;

[0030] Figure 7 This is a single-photon response pulse diagram of the amorphous tungsten superconducting nanowire single-photon detector in Example 2 in the 1064nm band;

[0031] Figure 8 1064 nm DCR and PCR photoresponse diagrams of the amorphous tungsten superconducting nanowire single-photon detector in Example 2;

[0032] Figure 9 This is the PCR light response graph of the amorphous tungsten superconducting nanowire single-photon detector prepared in Example 3 at 1550 nm;

[0033] Figure 10 This is a time jitter diagram of the amorphous tungsten superconducting nanowire single-photon detector prepared in Example 3 in the 1550nm band. DETAILED DESCRIPTION

[0034] The present invention is described in further detail below.

[0035] Example 1

[0036] The present invention provides an amorphous tungsten superconducting nanowire single-photon detector, comprising a photosensitive component, the photosensitive component is an amorphous tungsten superconducting nanowire, such as Figure 1 As shown, the preparation method comprises the following steps:

[0037] (1) Si / SiO2 substrate treatment: A double-sided polished Si / SiO2 substrate with a horizontal size of two inches was taken and ultrasonically cleaned in acetone, ethanol, and deionized water in sequence. Finally, it was blown dry with a nitrogen gun and placed in a drying cabinet to obtain a pretreated substrate.

[0038] (2) Amorphous tungsten film growth: The Si / SiO2 substrate processed in step (1) was placed in the chamber of the magnetron sputtering system and vacuumed to 8×10 -4 The magnetron sputtering parameters are set as follows: argon flow rate of 50 sccm, nitrogen flow rate of 5 sccm, working pressure of 5.9 mTorr, DC power supply current of 200 mA, and growth time of 20 s. An amorphous tungsten film with a thickness of about 8 nm can be obtained. Figure 1 As shown in a in Figure 2 As shown in Figure 2, scanning electron microscopy and atomic force microscopy also revealed the smooth surface and nanometer-scale thickness of the grown amorphous tungsten film. Figure 3 As shown in FIG, in the measurement of X-ray diffraction pattern (XRD), the tungsten film does not show a crystal peak, indicating that the grown tungsten film is a standard amorphous material. Figure 4 As shown in the figure, after the prepared amorphous tungsten film was placed in the air for 360 hours and 720 hours respectively, the measurement results of its superconductivity were not significantly different from those of the newly prepared amorphous tungsten film, indicating that the amorphous tungsten film has high stability in the air.

[0039] (3) Electron beam exposure (EBL): PMMA was spin-coated on the tungsten film surface at a rotation speed of 4000 rpm, an acceleration of 1000 rpm / s, and a coating time of 60 s. The film was then exposed using an electron beam exposure system with an exposure dose of 300 μC / cm 2 The exposed amorphous tungsten film and PMMA were developed in a developer for 10 seconds and fixed in water for 15 seconds. The nanowire width in the layout was set to 100 nm. During this process, the exposed areas were exposed to the amorphous tungsten film, while the unexposed areas were protected by PMMA, resulting in a PMMA nanowire pattern.

[0040] (4) Reactive ion etching (RIE): The film with the nanowire pattern obtained in step (3) was placed in the RIE reaction chamber, and the process parameters were set as follows: acceleration voltage 250 V, anode current 5.5 A, etching gas CHF3, gas flow rate 7 sccm, working pressure 0.27 Pa, etching time 10 min, i.e. Figure 1 After RIE etching, the area where the amorphous tungsten film is exposed after exposure in step (3) is etched cleanly, while the unexposed area is protected by PMMA, so that the amorphous tungsten film is preserved.

[0041] (5) Degumming: After etching, the PMMA pattern still remains on the surface of the amorphous tungsten nanowires. Therefore, the amorphous tungsten nanowires are immersed in acetone solution to clean the remaining PMMA pattern. Ultrasonic assistance is required in this process. The ultrasonic power is 60W and the ultrasonic time is 120s. At this point, the amorphous tungsten film is transformed into amorphous tungsten nanowires after the above steps. Figure 5 As shown in a in FIG, the IV curve of the nanowire is measured in a low-temperature electrical measurement system, that is, Figure 6 As shown in a in .

[0042] Comparative Example 1

[0043] This embodiment provides an amorphous tungsten superconducting nanowire single-photon detector, which is basically the same as that of embodiment 1, except that the exposure dose of the electron beam exposure in step (3) is set to 200 μC / cm 2 The IV curve of the nanowire was measured in a low-temperature electrical measurement system. Figure 6 As shown in middle b, the supercurrent of the nanowire is only 2.6 μA, which makes it difficult to support the nanowire to effectively detect single photons.

[0044] Comparative Example 2

[0045] This embodiment provides an amorphous tungsten superconducting nanowire single-photon detector, which is basically the same as that of embodiment 1, except that the exposure dose of the electron beam exposure in step (3) is set to 400 μC / cm 2 The IV curve of the nanowire was measured in a low-temperature electrical measurement system. Figure 6 As shown in Figure c, the supercurrent of the nanowire is only 1.5μA, which makes it difficult for the nanowire to effectively detect single photons.

[0046] Comparative Example 3

[0047] This embodiment provides an amorphous tungsten superconducting nanowire single photon detector, which is basically the same as that of Example 1, except that the etching gas for reactive ion etching in step (4) is set to SF6. The SEM image of the nanowire prepared in this comparative example is as follows: Figure 5As shown in b, the residual electron beam glue in the nanowire channel leads to an uneven morphology, and the width of the nanowire is also too thin, indicating that the nanowire prepared in Comparative Example 3 cannot be used for the next measurement.

[0048] Example 2

[0049] This embodiment provides a method for measuring an interface superconducting device with photon energy resolution. The measurement system primarily comprises 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 refrigerator system. The measurement method includes the following steps:

[0050] (H1) placing the optically aligned amorphous tungsten superconducting nanowire single-photon detector in a refrigerator, and connecting an optical fiber to the back of the detector so that the light spot is aligned with the center area of ​​the interface superconducting detector;

[0051] (H2) Utilizing a laser to output laser light, the light energy is then attenuated to a single-photon level via an attenuator, and is then coupled to an amorphous tungsten superconducting detector region via an optical fiber;

[0052] (H3) Use the readout module to collect data on the response of the amorphous tungsten superconducting nanowire single-photon detector to single photons.

[0053] The amorphous tungsten superconducting nanowire single-photon detector prepared in Example 1 was measured according to the above method. Figure 6 As can be seen in a, the superconducting critical current can reach 5.5μA, which meets the device's requirements for single-photon detection. In contrast, the superconducting critical currents of the amorphous tungsten superconducting nanowires obtained in Comparative Examples 1 and 2 are both low, and cannot meet the requirements for high-efficiency single-photon detection. The pulse diagram collected by the oscilloscope when the amorphous tungsten superconducting nanowire single-photon detector is working is shown in the figure. Figure 7 As shown, Figure 8 This is a graph showing the response characteristics of the amorphous tungsten superconducting nanowire single-photon detector prepared in Example 1 to photons in the 1064 nm band. Figure 8 As can be seen from figure b, in the 1064nm band, as the bias current increases, the light counting rate of the amorphous tungsten superconducting nanowire single-photon detector stabilizes at 220,000, which proves that the amorphous tungsten superconducting nanowire single-photon detector has a saturated quantum efficiency for single-photon detection at 1064nm.

[0054] Example 3

[0055] This embodiment provides an amorphous tungsten superconducting nanowire single-photon detector, which is substantially the same as that of embodiment 1, except that the width of the nanowire in the electron beam exposure pattern in step (3) is set to 70 nm. The amorphous tungsten superconducting nanowire produced using the method of this embodiment has a smaller width, which provides the nanowire with higher single-photon detection sensitivity because it can respond to single photons in the 1550 nm band. Figure 9 This is a graph showing the photon response characteristics of the amorphous tungsten superconducting nanowire single-photon detector prepared in Example 3 for the 1550nm band. As the bias current increases, the light counting rate finally stabilizes at 280,000, indicating that the amorphous tungsten superconducting nanowire single-photon detector also has a saturated quantum efficiency for single-photon detection at 1550nm.

[0056] Figure 10 This is a graph showing the timing jitter of the amorphous tungsten superconducting nanowire single-photon detector prepared in Example 3 for single-photon detection in the 1550nm band. The full width at half maximum of the curve, obtained through Gaussian fitting, is 167 ps, indicating that the timing jitter of the amorphous tungsten superconducting nanowire single-photon detector for single-photon detection in the 1550nm band is only 167 ps. These characteristics demonstrate the excellent single-photon detection performance of the amorphous tungsten superconducting nanowire single-photon detector.

Claims

1. An amorphous tungsten superconducting nanowire single-photon detector, comprising a photosensitive component, characterized in that: The photosensitive component is an amorphous tungsten superconducting nanowire; the amorphous tungsten superconducting nanowire is prepared by the following steps: (1) Growing an amorphous tungsten thin film on a substrate; (2) The amorphous tungsten film is etched into a tortuous nanowire structure by electron beam exposure and reactive ion etching to obtain an amorphous tungsten superconducting nanowire; the electron beam exposure dose is set to 200-400 μC / cm 2 , image correction and dose correction are used to ensure uniform width of nanowires.

2. The amorphous tungsten superconducting nanowire single-photon detector according to claim 1, characterized in that: Step (2) specifically includes the following processes: (2.1) Spin-coating a photoresist on the surface of the amorphous tungsten film and patterning the photoresist into nanowires using electron beam lithography; (2.2) After exposure, development and fixing are performed to obtain an amorphous tungsten film having a nanowire shape; (2.3) The amorphous tungsten film is etched using reactive ion beam etching to remove residual photoresist and obtain amorphous tungsten nanowires.

3. The amorphous tungsten superconducting nanowire single-photon detector according to claim 2 is characterized in that: In step (2.3), the working parameters of reactive ion beam etching are: etching gas flow rate is 10-25 sccm; working gas pressure is 0.2-0.6 Pa.

4. The amorphous tungsten superconducting nanowire single-photon detector according to claim 2, characterized in that: In step (2.3), during reactive ion beam etching, the acceleration voltage is 180-260 V, the anode current is 4.5-6.2 A, and the etching time is 1-5 min.

5. The amorphous tungsten superconducting nanowire single-photon detector according to claim 2, characterized in that: In step (2.1), the material of the photoresist is PMMA and / or HSQ.

6. The amorphous tungsten superconducting nanowire single-photon detector according to claim 1, characterized in that: In step (1), an amorphous tungsten film with a nanometer thickness is grown on a Si / SiO2 substrate by magnetron sputtering.

7. The amorphous tungsten superconducting nanowire single-photon detector according to claim 6, characterized in that: The DC target power of magnetron sputtering is 40 W-180 W.

8. The amorphous tungsten superconducting nanowire single-photon detector according to claim 2, characterized in that: In step (2.3), the amorphous tungsten film is immersed in an organic solvent to remove residual photoresist.

9. The amorphous tungsten superconducting nanowire single-photon detector according to claim 1, characterized in that: In step (1), the amorphous tungsten film has a thickness of 2-20 nm, a superconducting transition temperature of 1-10 K, and a sheet resistance of 400Ω / □ -40Ω / □ .

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