Amorphous tungsten superconducting nanowire single-photon detector

Abstract

The invention discloses an amorphous tungsten superconducting nanowire single-photon detector, which comprises a photosensitive component, and is 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 film on a substrate; and (2) etching the amorphous tungsten film into a roundabout nanowire structure by using electron beam exposure and reactive ion etching methods to obtain the amorphous tungsten superconducting nanowire. According to the invention, the tungsten nanowire with good stability is used as the main body material of the SNSPD, so that the robustness of the SNSPD preparation process is improved, and the service life of the SNSPD device in practical application is prolonged.

Description

Technical Field

[0001] The 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 changing 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 small temperature change will occur, causing the resistance of the superconducting film to change. This tiny signal is amplified by 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 light to near-infrared band, but its extremely low operating temperature (<10mK) undoubtedly poses a great challenge to refrigeration technology.

[0003] Compared with the harsh operating conditions of TES, SNSPD can achieve single photon detection from ultraviolet band to mid-infrared band without extremely low operating temperature. The main body of SNSPD is a superconducting nanowire made of ultra-thin superconducting film. The working principle is to use the energy of a single photon to break up the Cooper pairs in the superconducting nanowire, thereby forming a non-superconducting hot spot area on the nanowire. After the heat in the hot spot area relaxes to the substrate through the electron-phonon effect, the nanowire will restore the initial superconducting state. The detection of single photons can be achieved by detecting and identifying the voltage pulses generated at both ends of the nanowire due to this transition.

[0004] SNSPD has the advantages of high detection efficiency, low dark count, low time jitter, and wide response spectrum. Therefore, it has been widely used in quantum information, astronomical detection, lidar, national defense and military fields, and has gradually become one of the most mainstream single-photon detectors. The detection mechanism of SNSPD determines that the superconducting energy gap of nanowires has a fundamental impact on the detectable band. Therefore, the current research and development of SNSPD for mid- and far-infrared bands mainly uses low-energy gap materials such as MoSi and WSi.

[0005] However, the stability of these two materials is poor, which makes the preparation process of SNSPD based on this type of amorphous silicide nanowires more complicated, and the nanowires will inevitably degrade during use, which makes the detector unable to work for a long time. In summary, exploring a superconducting nanowire with a low superconducting energy gap and better stability for the preparation of SNSPD has a very important research value 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 comprises a photosensitive component, wherein the photosensitive component 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 more than 10 minutes to remove impurities on the surface of the substrate. The substrate is preferably a Si / SiO2 substrate. An amorphous tungsten film with a nanometer thickness is grown on the pretreated Si / SiO2 substrate by magnetron sputtering.

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

[0014] (2.2) developing and fixing after exposure 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 when spin coating 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 developing 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 amorphous tungsten film will be exposed in the exposed area through the development process, while the unexposed area 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 area where the amorphous tungsten film is exposed after exposure is etched cleanly, while the amorphous tungsten film is preserved in the unexposed area due to the protection of the photoresist thereon.

[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 of amorphous tungsten superconducting nanowires for the first time, providing a new material for SNSPD detectors, making up for the shortcoming of poor stability of low-bandgap materials currently used in SNSPDs, and using tungsten nanowires with good stability as the main material of SNSPDs, thereby improving the robustness of the SNSPD preparation process and extending the service life of SNSPD devices in practical applications. (2) The amorphous tungsten superconducting nanowire single-photon detector of the present invention can realize single-photon detection in the 1064nm and 1550nm bands, and the quantum detection efficiency of single-photon detection reaches 100% in the temperature range of 0.3K to 1K, 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 present invention provides a method for preparing the amorphous tungsten superconducting nanowire single-photon detector;

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

[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 placed in air for different time periods;

[0028] Figure 5 This is a SEM comparison picture of the 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 the 1064nm band in Example 2;

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

[0032] Fig. 9 This is the PCR light response diagram of the amorphous tungsten superconducting nanowire single-photon detector prepared in Example 3 in the 1550nm band;

[0033] Fig.10 This is the 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, wherein 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 ultrasonically cleaned in acetone, ethanol, and deionized water in sequence, and finally dried with a nitrogen gun and placed in a drying cabinet to obtain a pretreated substrate.

[0038] (2) Growth of amorphous tungsten film: The Si / SiO2 substrate treated in step (1) was placed in the chamber of a magnetron sputtering system and evacuated to 8×10 -4 Pa. The magnetron sputtering parameters are set as follows: the flow rate of argon is 50sccm, the flow rate of nitrogen is 5sccm, the working pressure is 5.9mTorr, the current of the DC power supply is 200mA, and the growth time is 20s. An amorphous tungsten film with a thickness of about 8nm 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. 1 , in the measurement of the 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, after the prepared amorphous tungsten film was placed in the air for 360h and 720h respectively, the measurement results of its superconductivity were not significantly different from those of the just prepared amorphous tungsten film, indicating that the amorphous tungsten film has high stability in the air.

[0039] (3) Electron beam lithography (EBL): PMMA was spin-coated on the surface of the tungsten film 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 lithography 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 width of the nanowires in the layout was set to 100 nm. During this process, the amorphous tungsten film was exposed in the exposed area after the development process, while the unexposed area was protected by PMMA, thus obtaining 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 gas pressure 0.27 Pa, etching time 10 min, that is, Figure 1 After RIE etching, the area where the amorphous tungsten film is exposed after exposure in step (3) is etched cleanly, while the amorphous tungsten film is preserved in the unexposed area due to the protection of PMMA.

[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 an 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, namely Figure 6 As shown in middle b, the supercurrent of the nanowire is only 2.6 μA, which makes it difficult for 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, namely Figure 6 As shown in 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 embodiment 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 step of measurement.

[0048] Example 2

[0049] This embodiment provides a method for measuring an interface superconducting device with photon energy resolution, wherein the measuring system mainly comprises an optical system, a cryogenic system and a circuit system. The optical system comprises a laser and an attenuator connected in sequence. The cryogenic system is a dilution refrigerator system. The measuring method comprises 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 to the central area of ​​the interface superconducting detector;

[0051] (H2) using a laser to output laser light, then attenuating the light energy to a single photon level via an attenuator, and coupling it 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 It can be seen from a in the figure that 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 Figure 1. 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 basically the same as that of Embodiment 1, except that the width of the nanowire in the layout exposed by the electron beam in step (3) is set to 70 nm. The amorphous tungsten superconducting nanowire obtained by the method of this embodiment has a smaller width, which brings higher single-photon detection sensitivity to the nanowire because it can respond to single photons in the 1550 nm band. Fig. 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 eventually 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] Fig.10 The time jitter diagram of the single photon detection of the amorphous tungsten superconducting nanowire single photon detector prepared in Example 3 in the 1550nm band, the half-peak width of the curve obtained by Gaussian fitting is 167ps, indicating that the time jitter of the single photon detection of the amorphous tungsten superconducting nanowire single photon detector in the 1550nm band is only 167ps. The above characterizations all prove that the amorphous tungsten superconducting nanowire single photon detector has excellent single photon detection performance.

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 using electron beam exposure and reactive ion etching to obtain amorphous tungsten superconducting nanowires.

2. The amorphous tungsten superconducting nanowire single-photon detector according to claim 1, characterized in that: Step (2) specifically includes the following process: (2.1) spin coating a photoresist on the surface of the amorphous tungsten film, and performing nanowire patterning exposure on the photoresist using electron beam exposure; (2.2) developing and fixing after exposure 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, characterized in that: 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 width of the nanowires.

4. 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.

5. 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 180-260V, the anode current is 4.5-6.2A, and the etching time is 1-5min.

6. 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.

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

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

9. 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.

10. 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 400 Ω / □ -40Ω / □ .

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