A method for improving IV characteristics of YBCO nanowires

Abstract

The present invention provides a method for improving the IV characteristics of YBCO nanowires, belonging to the field of single-photon detection technology. The method is used to improve the IV characteristics of YBCO nanowires by combining controllable heat treatment and voltage-driven enhancement treatment. The YBCO nanowires obtained by the method of the present invention can not only increase the critical current I c , improve the critical current density J c , J c Can be increased to 1.86MA·cm ‑2 It can also widen the hysteresis window, making the superconducting state more stable and having a sharp voltage jump; in addition, it can also make the nanowire device with degraded superconducting performance change from the original flux flow state to an obvious hysteresis state, improve the superconducting properties, and thus restore the ability of light detection, greatly improving the detection sensitivity, time resolution and environmental stability of the detector, and providing strong support for the future realization and application expansion of SNSPD based on YBCO nanowires.

Description

Technical Field

[0001] The present invention belongs to the technical field of single-photon detection, and in particular relates to a method for improving the IV characteristics of YBCO nanowires. Background Art

[0002] The realization of superconducting nanowire single photon detectors (SNSPDs) with operating temperatures above liquid helium is a research hotspot at home and abroad. High-temperature SNSPDs greatly reduce system operating costs and bring great hope for the application of superconducting technology, so they have extremely broad potential applicability. c =92K), large-area epitaxial growth, and shorter electron-phonon relaxation time. 7-x YBCO stands out among various high-temperature superconducting materials as a leading candidate for practical SNSPD applications.

[0003] In the preparation, evaluation and practical application of SNSPD, the current-voltage (IV) characteristic is one of the most basic and important characteristics of the device. When SNSPD absorbs a single photon, it generates a voltage pulse, which is a metastable state generated under current bias. This metastable state is essential for the operation of the detector, and is manifested as a hysteretic IV characteristic. It is the result of the competition between the current-induced Joule self-heating and the electron cooling process of the nanowire in the resistance state. It determines whether the nanowire device can generate a measurable voltage signal after absorbing a single photon, which is crucial to the application of SNSPD. For IV characteristics, the hysteresis window is an important condition for the nanowire device to be capable of light detection. Under the condition of the same nanowire size, the critical current (I c ) is larger, which means the critical current density (J c ) indicates better nanowire quality; a sharper voltage jump indicates a higher resistance when the nanowire becomes resistive, resulting in a more pronounced voltage signal and a larger optical detection signal amplitude; and a larger hysteresis window indicates a more stable superconducting state in the nanowire. Therefore, research on SNSPDs focuses on preparing YBCO nanowires with higher critical current density, sharper voltage jumps, and improved hysteresis windows.

[0004] YBCO thin films are sensitive and their superconducting properties are easily degraded. After being processed into very narrow nanowires, the IV characteristics are poor, and the hysteresis is weak or even disappears completely. Some researchers (Andersson E, Arpaia R, Trabaldo E, et al. Fabrication and electrical transport characterization of high quality underdoped YBa2Cu3O7-δ nanowires[J]. Superconductor Science and Technology, 2020, 33(6): 064002.) have successfully prepared narrow nanowires (200nm) using underdoped YBCO thin films, giving them hysteresis IV characteristics. However, there are great challenges in terms of doping uniformity, repeatability of hysteresis phenomena, and long-term stability. Because the underdoping process is difficult to achieve in a controllable manner, this method is more suitable as a technical means to study specific physical phenomena (such as quantum phase slip, nonlinear transport, etc.), rather than an ideal process for large-scale application. Meanwhile, researchers (Baghdadi R, Arpaia R, Charpentier S, et al. Fabricating nanogaps in YBa2Cu3O7-δ for hybrid proximity-based Josephson junctions [J]. Physical Review Applied, 2015, 4(1): 014022.) have successfully improved the IV characteristics of YBCO nanowires through in-situ ozone treatment, turning resistive nanowires into superconductors, but IV hysteresis has not yet been achieved. Therefore, how to improve the IV characteristics of YBCO nanowire devices in order to realize SNSPD based on YBCO nanowires has become a key issue that needs to be addressed urgently. Summary of the Invention

[0005] To address the challenges presented by the prior art, the present invention provides a method for enhancing the IV characteristics of YBCO nanowires. This method combines controlled thermal treatment with voltage-driven enhancement to produce nanowires with superior hysteresis IV characteristics, maintaining a more stable superconducting state and significantly improving the device's potential for photodetection.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A method for improving the IV characteristics of YBCO nanowires, comprising the following steps:

[0008] Step 1: Grow a YBCO thin film on the substrate surface, and then in-situ grow an amorphous YBCO protective layer on the surface of the YBCO film to prevent the YBCO film from being degraded by contact with the atmospheric environment during subsequent processing;

[0009] Step 2: Attach an electrode pattern mask to the amorphous YBCO protective layer, then use electron beam evaporation to form a metal electrode. After the electrode preparation is completed, remove the mask, and then use plasma-enhanced atomic layer deposition to grow a dense aluminum oxide protective layer;

[0010] Step 3: Prepare YBCO microwire devices using UV lithography combined with low-temperature inductively coupled plasma reactive ion etching to locate the area where the nanowires are to be made;

[0011] Step 4: Prepare the desired nanowire device using electron beam lithography combined with low-temperature inductively coupled plasma reactive ion etching;

[0012] Step 5: placing the nanowire device obtained in step 4 in a chamber of a plasma-enhanced atomic layer deposition system and performing a heat treatment under a specific working atmosphere. After the reaction is completed, the device is naturally cooled and taken out after cooling to room temperature.

[0013] Step 6: Place the nanowire device obtained in step 5 on a temperature-controlled DC probe station and process the nanowire using a voltage-driven enhancement method. The processing process is as follows: at a low temperature of 4K, increase the external electric field control voltage value in a certain voltage step until the critical voltage threshold. Perform an IV hysteresis curve test at each external electric field control voltage value. After the test, the required YBCO nanowire with good IV characteristics can be obtained.

[0014] Furthermore, in step 1, the growth substrate may be a strontium titanate, magnesium oxide or lanthanum aluminate substrate;

[0015] Furthermore, in step 1, the thickness of the YBCO film is not less than 5 nm; the thickness of the amorphous YBCO protective layer is not less than 8 nm; and the growth method is preferably DC magnetron sputtering.

[0016] Furthermore, in step 2, the vacuum degree of the electron beam evaporation system cavity is lower than 5×10 -6 mbar, the evaporation rate is

[0017] Furthermore, in steps 3 and 4, the sample stage temperature of low-temperature inductively coupled plasma reactive ion etching is -20°C--10°C, the etching gas is Ar / Cl2 mixed etching gas, the ICP power is 800-1200W, the RF power is 80-120W, and the etching pressure is 1mTorr.

[0018] Furthermore, the specific working atmosphere in step 5 is preferably pure Ar, N2, pure oxygen or air; the heat treatment temperature is 150-200°C, and the treatment time is not less than 1 hour.

[0019] Furthermore, in step 6, the critical voltage threshold is positively correlated with the size of the YBCO nanowires. The thinner the nanowires, the smaller the critical voltage threshold; preferably, it is 8-20V.

[0020] Furthermore, the voltage step value is preferably 1-3V.

[0021] The mechanism of the present invention is:

[0022] Controlled heat treatment promotes the diffusion of oxygen atoms within YBCO nanowires, resulting in a more uniform distribution of oxygen doping. This effect is manifested in two ways: First, it effectively reduces the defect density of the superconducting nanowires, weakening localized inhomogeneities caused by defects and thus reducing the formation of localized hotspots. Furthermore, the uniform oxygen distribution makes the superconducting current more evenly distributed across the nanowires, minimizing localized current density reductions caused by factors such as poor contact and significantly reducing the randomness of the critical current. Second, oxygen diffusion to the nanowire edges repairs edge oxygen loss caused by etching, expanding the effective superconducting wire width and thus optimizing the nanowire's IV characteristics.

[0023] Voltage-driven enhancement can generate a strong electric field within the material, inducing the migration of oxygen ions or oxygen vacancies, enabling localized control of the oxygen doping concentration, thereby altering the charge carrier density of YBCO and adjusting its superconducting properties. High electric fields enhance the stability of the dynamic transition from the superconducting state to the normal state, reducing the inhomogeneous transport caused by defects or localized oxygen misdistribution. Furthermore, the combined effects of thermal effects and high voltages introduce nonlinear dynamic effects, which help eliminate nonideal responses in weakly connected regions and improve measurement repeatability, playing a key role in optimizing the IV characteristics of nanowires.

[0024] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0025] The method of the present invention is used to improve the IV characteristics of YBCO nanowires by combining controlled thermal treatment and voltage-driven enhancement treatment. The YBCO nanowires obtained by the method of the present invention can not only increase the critical current (I c ), improve the critical current density J c , J c Can be increased to 1.86MA·cm -2It can also widen the hysteresis window, making the superconducting state more stable and having a sharp voltage jump; in addition, it can also make the nanowire device with degraded superconducting performance change from the original flux flow state to an obvious hysteresis state, improve the superconducting properties, and thus restore the ability of light detection, greatly improving the detection sensitivity, time resolution and environmental stability of the detector, and providing strong support for the future realization and application expansion of SNSPD based on YBCO nanowires. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a comparison chart of the IV characteristics of YBCO nanowires with a line width of 400 nm obtained in Example 1 and Comparative Examples 1 and 2.

[0027] Figure 2 This is a comparison chart of the IV characteristics of YBCO nanowires with a line width of 600 nm obtained in Example 1 and Comparative Examples 1 and 2.

[0028] Figure 3 YBCO nanowires 1 obtained in Example 1, Comparative Example 1 and Comparative Example 2 c Statistical comparison chart.

[0029] Figure 4 Schematic diagram of IV characteristics of YBCO nanowires damaged by high voltage obtained in Comparative Example 3.

[0030] Figure 5 This is the optical display image of the YBCO meandering nanowires obtained in Example 2.

[0031] Figure 6 This is a comparison chart of the IV characteristics of the YBCO meandering nanowires obtained in Example 2, Comparative Examples 4 and 5. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the implementation methods and drawings.

[0033] Example 1

[0034] A method for improving the IV characteristics of YBCO nanowires, comprising the following steps:

[0035] Step 1: Select a strontium titanate substrate and clean it. A 6nm thick YBCO film is grown on the substrate surface using a DC magnetron sputtering method. The chamber contains a 1:3 O2:Ar mixed gas, the pressure is 30Pa, the sputtering power is 125W, and the chamber temperature is 802°C. After the film growth is completed, wait for the chamber to cool to room temperature, and then grow a 10nm thick amorphous YBCO protective layer on the YBCO film using the same gas conditions and sputtering power.

[0036] Step 2: Attach the electrode pattern stainless steel mask to the amorphous YBCO protective layer, and then use electron beam evaporation to prepare the metal electrode (Ag / Au: 20nm / 20nm). The vacuum degree of the cavity is less than 5×10 -6 mbar, the evaporation rate is

[0037] After the electrode preparation is completed, the mask is removed, and then a 10nm dense aluminum oxide protective layer is grown on the entire surface of the device using plasma-enhanced atomic layer deposition to further isolate the nanowires from damage by air;

[0038] Step 3: UV photolithography of the sample obtained in step 2: first, clean the surface of the sample obtained in step 2 (acetone megasonic for 5 minutes, isopropyl alcohol megasonic for 5 minutes, rinse with isopropyl alcohol, and blow dry with N2); then, pre-bake on a 110°C hot plate for 1 minute; spin-coat AZ5214 photoresist (6000 rpm, 60 seconds); bake the resist on a 110°C hot plate for 1 minute; after UV exposure, develop with ZX238 for 45 seconds to locate the micron area of ​​the nanowire to be connected to the electrode channel; use inductively coupled plasma reactive ion etching on the sample after UV photolithography to obtain a 30μm micron wire device: use a mixed etching gas (Ar / Cl2: 18 / 2sccm), an ICP power of 1000W, an RF power of 100W, an etching pressure of 1mTorr, and maintain the sample stage temperature at -20°C to prevent thermal damage caused by the etching process; the degumming process is acetone soaking for 10 minutes, megasonic for 20 minutes, isopropyl alcohol rinsing, and N2 blow dry;

[0039] Step 4: Electron beam lithography was performed on the sample obtained in step 3: the sample surface obtained in step 3 was cleaned first, and then placed on a 180°C hot plate for pre-baking for 1 min; ZEP-520A electron beam photoresist was spin-coated (7000 rpm, 60 s), and the glue was baked on a 180°C hot plate for 3 min; conductive carbon glue was spin-coated (4000 rpm, 60 s), and the glue was baked on a 110°C hot plate for 2 min; the sample surface was cleaned first, and the sample surface was pre-baked on a 180°C hot plate for 1 min; ...10°C hot plate for 2 min; the sample surface was 2The nanowires were patterned by electron beam exposure under the condition of ; the conductive carbon glue was rinsed with deionized water to remove it, and after drying with N2, it was developed with ZED-N50 developer at room temperature for 3 minutes, then immersed in isopropyl alcohol for 15 seconds, rinsed with deionized water and dried with a nitrogen gun; the samples after electron beam lithography were subjected to inductively coupled plasma reactive ion etching to obtain single nanowire devices with line widths of 400nm, 600nm, 800nm, 1μm and 2μm; the debonding process was UV treatment for 5min, acetone soaking for 10min, megasonic treatment for 20min, isopropyl alcohol rinsing and drying with N2; all nanowire devices were placed in a temperature-controlled DC probe station and IV hysteresis curve tests were performed at a low temperature of 4K, with a maximum limiting voltage of 4V;

[0040] Step 5: The nanowire device obtained in step 4 is placed in a chamber of a plasma-enhanced atomic layer deposition system and subjected to heat treatment in an N2 atmosphere at a temperature of 200°C for 1 hour. After the reaction is completed, the device is cooled at a rate of approximately 27°C / minute and then removed from the chamber after cooling to room temperature.

[0041] Step 6: Place the nanowire device obtained in step 5 into a temperature-controlled DC probe station and process the nanowire using a voltage-driven enhancement method. The processing process is as follows: at a low temperature of 4K, the initial external electric field control voltage is 4V, and the external electric field control voltage value is increased in 2V voltage steps until it reaches 8V. An IV hysteresis curve test is performed at each external electric field control voltage value. After the test, the required YBCO nanowire with good IV characteristics can be obtained.

[0042] Example 2

[0043] YBCO meandering nanowires were prepared according to the steps of Example 1, except that step 4 was adjusted as follows: the nanowire size structure was a meandering nanowire with a line width of 400 nm.

[0044] The optical microscope image of the YBCO meandering nanowires prepared in this example is shown in FIG. Figure 5 As shown in the figure, it can be seen that the width of the nanowires is uniform.

[0045] Comparative Example 1

[0046] YBCO nanowires were prepared according to the steps of Example 1, except that Step 5 and Step 6 were omitted and the remaining steps remained unchanged.

[0047] Comparative Example 2

[0048] YBCO nanowires were prepared according to the steps of Example 1, except that step 6 was omitted and the remaining steps remained unchanged.

[0049] Comparative Example 3

[0050] YBCO nanowires were prepared according to the steps of Example 1, except that step 6 was adjusted as follows: an IV hysteresis curve test was performed at a low temperature of 4K, and the external electric field control voltage was gradually increased to 22V in steps of 2V.

[0051] Comparative Example 4

[0052] YBCO meandering nanowires were prepared according to the steps of Example 2, except that Step 5 and Step 6 were omitted and the remaining steps remained unchanged.

[0053] Comparative Example 5

[0054] YBCO meandering nanowires were prepared according to the steps of Example 2, except that step 6 was omitted and the remaining steps remained unchanged.

[0055] The comparison diagrams of IV characteristics of YBCO nanowires with line widths of 400nm and 600nm obtained in Example 1, Comparative Example 1 and Comparative Example 2 are shown as follows: Figure 1 and Figure 2 As shown. Figure 1 It can be seen that the 400nm nanowire device prepared in Comparative Example 1 has no IV hysteresis (magnetic flux flow state), while the nanowire device prepared in Comparative Example 2 becomes an obvious hysteresis state. c Significantly increased, the IV characteristics in Example 1 were further optimized, I c Increases significantly, and the hysteresis window becomes wider. Figure 2 As can be seen from the figure, the 600nm nanowire device I c The hysteresis window becomes wider and the voltage jump becomes larger.

[0056] Figure 3 YBCO nanowires 1 obtained in Example 1, Comparative Example 1 and Comparative Example 2 c Statistical comparison chart. Figure 3 As shown, the I c Statistical analysis shows that nanowire devices I c and J c Therefore, it can be confirmed that the IV characteristics of the nanowire device prepared by the present invention are significantly improved after being processed in steps 5 and 6.

[0057] When the external test voltage increases to 22V, the IV characteristics of the YBCO nanowire damaged by high voltage are shown in the figure below. Figure 4 As shown in the figure, due to the excessively high voltage, the nanowire device is instantly damaged to an insulating state; therefore, the external test voltage threshold of the present invention needs to be within a specific range to be improved, otherwise the excessively high voltage will cause irreversible damage to the nanowire.

[0058] The comparison of IV characteristics of YBCO meandering nanowires with a line width of 400 nm obtained in Example 2, Comparative Example 4 and Comparative Example 5 is shown in FIG. Figure 6 As shown; the IV characteristics of the meandering nanowires prepared in Comparative Example 4 have no hysteresis and are close to a resistive state. Comparative Example 5 becomes a clear superconducting state after heating, but still has no IV hysteresis; the meandering nanowires prepared in Example 2 have a clear IV hysteresis window, I c It significantly increases to 164 μA, and the voltage jump is sharp; therefore, the present invention has obvious and universal effects on improving the superconducting performance and optimizing the IV characteristics of YBCO nanowires.

[0059] The above description is only a specific embodiment of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes; all disclosed features, or all steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A method for improving the IV characteristics of YBCO nanowires, characterized in that: The following steps are involved: Step 1: Grow a YBCO thin film on the substrate surface, and then in-situ grow an amorphous YBCO protective layer on the surface of the YBCO film to prevent the YBCO film from being degraded by contact with the atmospheric environment during subsequent processing; Step 2: Attach an electrode pattern mask to the amorphous YBCO protective layer, then use electron beam evaporation to form a metal electrode. After the electrode preparation is completed, remove the mask, and then use plasma-enhanced atomic layer deposition to grow an aluminum oxide protective layer; Step 3: Prepare YBCO micron wires using UV lithography combined with low-temperature inductively coupled plasma reactive ion etching; Step 4: Prepare YBCO nanowires using electron beam lithography combined with low-temperature inductively coupled plasma reactive ion etching; Step 5: The YBCO nanowires obtained in step 4 are placed in a chamber of a plasma-enhanced atomic layer deposition system and subjected to heat treatment under a specific working atmosphere. After the reaction is completed, the nanowires are naturally cooled and taken out after cooling to room temperature. Step 6: Place the YBCO nanowire obtained in step 5 on a temperature-controlled DC probe station and process the nanowire using a voltage-driven enhancement method. The processing process is as follows: at a low temperature of 4K, increase the external electric field control voltage value in a certain voltage step until the critical voltage threshold is reached. Perform an IV hysteresis curve test at each external electric field control voltage value. After the test, the desired YBCO nanowire with good IV characteristics can be obtained; wherein the critical voltage threshold is 8-20V and the voltage step value is 1-3V.

2. The method for improving IV characteristics of YBCO nanowires according to claim 1, wherein: In step 1, the growth substrate is a strontium titanate, magnesium oxide or lanthanum aluminate substrate.

3. The method for improving IV characteristics of YBCO nanowires according to claim 1, wherein: In step 1, the thickness of the YBCO film is not less than 5 nm; the thickness of the amorphous YBCO protective layer is not less than 8 nm; and the growth method is DC magnetron sputtering.

4. The method for improving IV characteristics of YBCO nanowires according to claim 1, wherein: In step 2, the vacuum degree of the electron beam evaporation system chamber is lower than 5×10 -6 mbar, the evaporation rate is 5. The method for improving IV characteristics of YBCO nanowires according to claim 1, wherein: In steps 3 and 4, the sample stage temperature of low-temperature inductively coupled plasma reactive ion etching is -20°C to -10°C, the etching gas is Ar / Cl2 mixed etching gas, the ICP power is 800-1200W, the RF power is 80-120W, and the etching pressure is 1mTorr.

6. The method for improving IV characteristics of YBCO nanowires according to claim 1, wherein: The specific working atmosphere in step 5 is pure Ar, N2, pure oxygen or air; the heat treatment temperature is 150-200°C, and the treatment time is not less than 1 hour.

7. The method for improving IV characteristics of YBCO nanowires according to claim 1, wherein: In step 6, the critical voltage threshold is positively correlated with the size of the YBCO nanowire. The thinner the nanowire, the smaller the critical voltage threshold.

Images