A method for screening application performance of superconducting material based on size regulation

Abstract

The application discloses a kind of based on size regulation's superconducting material application performance screening method, by in the design and development of superconducting nanowire single-photon detector, the geometric size of superconducting nanowire is closely associated with the application performance of device.This method carries out structural treatment to target superconducting film, then by comparing and analyzing the size effect and the physical mechanism behind in this process in detail, so that the size and application performance are multidimensional mapping, and then the application potential of target superconducting film is evaluated quickly, and the optimal size is selected for target application scene.

Description

Technical Field

[0001] This invention belongs to the field of superconducting material characterization and device application technology, specifically a method for screening the application performance of superconducting materials based on size control. Background Technology

[0002] Superconducting nanowire devices, especially superconducting nanowire single-photon detectors (SNSPDs), possess advantages such as a wide spectral operating range from ultraviolet to long-wave infrared, high count rates exceeding GHz, time jitter of 3 ps, and extremely low dark count rates. Therefore, they have wide applications in fields such as quantum communication, deep space exploration, and biological imaging.

[0003] The detection performance of SNSPDs is determined by the superconductivity of the superconducting nanowires. However, as the geometry of superconducting materials decreases (e.g., width and thickness), size effects become increasingly significant. For superconducting nanowires, length also becomes an important size dimension. Size effects lead to changes in the superconducting transition temperature (T0). c ), transformation current density (J) sw The optical response and other properties will change accordingly. The effect of size also varies among different superconducting thin films. This means that the superconducting properties of a superconducting thin film alone are insufficient to evaluate the application performance of superconducting devices fabricated from that material.

[0004] In existing technologies, the following methods are typically used to evaluate the application performance of a superconducting material:

[0005] Single-parameter characterization method: It only focuses on the intrinsic parameters of the material (such as the superconducting transition temperature), ignores the modulation effect of geometric dimensions on the actual device performance, and makes it difficult to accurately predict its performance in specific application scenarios.

[0006] Trial and error method: First, select the most commonly used size to fabricate the device, test its performance, and if it does not meet the requirements, readjust the size and fabricate again. This method has a long development cycle, high cost, and cannot systematically grasp the full picture of material properties.

[0007] Taking high-speed device design as an example, conventional high-speed devices typically employ a scheme of short nanowires connected in series with large inductors to avoid the latch-up effect of short wires. However, the optimal size for the device's high-speed response is masked by the large inductance. The same problem arises in the design of devices for high-sensitivity detection. To pursue higher wavelength sensitivity, small linewidths or thicknesses are used, which can lead to significant changes in superconducting performance and a substantial degradation of the device's signal-to-noise ratio, sensitivity, and other characteristics.

[0008] The methods described above can lead to two extremes: either wasting too much effort on unsuitable materials or failing to achieve the best performance due to inaccurate evaluations. Therefore, there is an urgent need in the field for a systematic and predictable method for screening the application performance of superconducting materials to quickly assess their potential and provide guidance for device design. Summary of the Invention

[0009] Purpose of the invention: To address the two extremes of existing methods, which may lead to excessive effort being invested in unsuitable materials and failure to achieve the best performance of materials due to inaccurate evaluation, this invention proposes a method for screening the application performance of superconducting materials based on size control. By establishing a multidimensional mapping relationship between size and application performance, the performance of superconducting materials can be quickly evaluated, and the optimal geometric structure parameters can be quickly selected for target application scenarios, thereby realizing rapid evaluation and targeted design of superconducting material applications.

[0010] Technical solution: In a first aspect, this invention proposes a method for screening the application performance of superconducting materials based on size control, comprising:

[0011] The target superconducting thin film was fabricated into two sets of nanowire test arrays with width and length gradients to obtain multiple samples of different sizes.

[0012] By testing the current-voltage curves of samples of different lengths, a length-critical transition current phase diagram was obtained.

[0013] Using the combination of the shortest nanowire and an inductor in series as a reference, the reference is illuminated with light of the target wavelength to obtain the bias current-quantum efficiency curve.

[0014] Based on the bias current-quantum efficiency curve, determine the bias current corresponding to the point where the quantum efficiency just saturates, and use this bias current as the threshold.

[0015] Based on the length-critical transition current phase diagram and the threshold, when the length increases and the critical transition current decreases to the threshold, the length value at this point is the longest length at which the nanowire can achieve quantum efficiency saturation.

[0016] Based on the longest length, the photosensitive surface of the superconducting nanowire single-photon detector fabricated from this nanowire is determined.

[0017] Furthermore, the statement that when the length increases causing the critical switching current to decrease to a threshold value, the length at which the nanowire can achieve quantum efficiency saturation includes:

[0018] If the threshold is not covered in the length-critical transition current phase diagram, the following model is used for prediction, with the mathematical expression as follows:

[0019] I SW≈ I0 - α(ln(L')) 0.5 - βln(L')

[0020] Among them, I SW For the switching current, I0 is approximately the critical current, L' ≈ L / w, where L is the nanowire length, w is the nanowire width, and α and β are fitting factors.

[0021] The above model reflects the combined effect of size inhomogeneity fluctuations and the linear superposition of conversion rates. The relationship between conversion current and nanowire length is fitted using the above formula to obtain α and β; then, let I... SW The longest length can be obtained by fitting the current threshold.

[0022] Secondly, this invention proposes a method for screening the application performance of superconducting materials based on size control, comprising:

[0023] The target superconducting thin film was fabricated into two sets of nanowire test arrays with width and length gradients to obtain multiple samples of different sizes.

[0024] By testing the current-voltage curves of samples of different lengths, a length-critical transition current phase diagram was obtained; by irradiating the samples with light of the target wavelength, bias current-quantum efficiency curves of nanowires of different lengths were obtained.

[0025] The optimal length is defined as the length at which the dynamic inductance of the nanowire does not affect the critical switching current or the trend of the quantum efficiency curve. The optimal length corresponds to the shortest length of the target superconducting thin film under the current conditions. The shortest length determines the maximum detection rate of the target superconducting thin film.

[0026] Thirdly, this invention proposes a method for screening the application performance of superconducting materials based on size control, including:

[0027] The target superconducting thin film was fabricated into two sets of nanowire test arrays with width and length gradients to obtain multiple samples of different sizes.

[0028] Current-voltage curves of samples with different widths were obtained from the test;

[0029] The width-transition current density phase diagram and the width-critical transition current phase diagram were extracted from the current-voltage curves of samples with different widths.

[0030] Based on the test conditions, the width at which the pulse signal can just be identified is defined as the minimum width;

[0031] The width corresponding to the inflection point in the width-transition current density phase diagram is defined as the maximum width.

[0032] With a width of [W] min W max The nanowires within the film were subjected to light response tests at corresponding wavelengths. Based on the light response test results, the size of the target superconducting thin film for achieving the highest wavelength sensitivity detection was selected.

[0033] Beneficial Effects: This invention closely links the geometric dimensions of superconducting nanowires with the application performance of the device during the design and fabrication of superconducting nanowire single-photon detectors. This method involves structuring the target superconducting thin film, then conducting a detailed comparative analysis of the size effects and underlying physical mechanisms during this process. This allows for a multi-dimensional mapping between size and application performance, enabling rapid evaluation of the application potential of the target superconducting thin film and selection of the optimal size for the target application scenario. Compared with existing technologies, this invention has the following advantages:

[0034] (1) This invention, through systematic size gradient design, fully reveals the physical laws of the evolution of superconducting material properties with geometric size, overcoming the limitations of the traditional single-point trial and error method;

[0035] (2) The method of the present invention does not depend on a specific superconducting material and is applicable to any superconducting thin film system with size effect, including but not limited to nitride, silicide, oxide and iron-based superconducting materials.

[0036] (3) The multidimensional correlation map established by the present invention has a predictive function, which can provide a direct design basis for the subsequent application development of the same material system, significantly shorten the research and development cycle and reduce the research and development cost.

[0037] (4) This invention directly links the basic performance parameters with the needs of specific application scenarios, realizing a seamless connection from "material characterization" to "device design", and has strong engineering practical value. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the structured processing of the present invention;

[0039] Figure 2 This is a schematic diagram of the RT curve;

[0040] Figure 3 For I sw A schematic diagram of the curves showing the change of L and a schematic diagram of the bias current-quantum efficiency curves obtained based on the shortest nanowire + inductor combination.

[0041] Figure 4 For WJ sw Schematic diagram of the curve;

[0042] Figure 5 For example, I in Example 1 swCurves showing the change in length and quantum efficiency curves for nanowires of different lengths;

[0043] Figure 6 This is a graph showing the relationship between the time constant and length in Example 1;

[0044] Figure 7 The diagram shows the electrical and response characteristics of nanowires with different widths in Example 2;

[0045] Figure 8 The graph shows the relationship between the switching current and length of nitrogen-doped amorphous molybdenum nanowires in Example 3, and the normalized count rate curves of 1550 nm light for nanowires of different lengths.

[0046] Figure 9 The graph shows the relationship between the conversion current and length of niobium nitride nanowires in Example 3, and the normalized count rate curves of 1064 nm light for nanowires of different lengths. Detailed Implementation

[0047] This invention discloses a method for screening the application performance of superconducting materials based on size control, comprising the following steps:

[0048] Step 1: The target superconducting thin film is structured, and the size of the sample is measured using size as the independent variable. c Curve graph, dimensions - I sw Phase diagram and bias current-quantum efficiency curve; T c I represents the superconducting transition temperature. sw This represents the critical transition current.

[0049] In this step, the structuring process involves fabricating the target superconducting thin film (thickness approximately equal to the coherence length) into two sets of nanowire test arrays with width and length gradients. The width W is distributed between 50 nm and 500 nm, and the length L is distributed between 100 nm and 10 mm.

[0050] The fabricated superconducting nanowires were installed in a physical property measurement system (PPMS or CPMS) to measure the temperature-resistance curves of samples of different sizes, thereby obtaining the critical transition temperature T for each sample. c , build size - T c Line graph.

[0051] The fabricated superconducting nanowires were installed in a refrigerator at a temperature lower than half the critical transition temperature of the superconducting thin film. Current-voltage curves of samples of different sizes were measured to obtain the critical transition current I for each sample. sw , build size - I swPhase diagram; based on this, the target detection wavelength is selected, and the bias current-quantum efficiency curves of samples of different sizes are measured respectively.

[0052] For the nanowires described above, for samples with low dynamic inductance (<100 nH), to avoid premature superconducting phase transitions caused by high-frequency noise in the testing environment, a large inductor (>500 nH) made of the same material is connected in series at the front of the sample. When evaluating high-speed response characteristics, nanowires with low dynamic inductance do not require a series inductor.

[0053] Step 2: By comparing and analyzing the size effect of sample performance and the underlying physical mechanism, obtain the mapping relationship between size and application performance, and then judge the application potential of the target superconducting thin film in the development of SNSPD.

[0054] The target application scenarios for evaluating the SNSPD application potential of the superconducting thin film fabrication include, but are not limited to, large photosensitive surface detection, high-speed detection, and high-wavelength sensitivity detection. The specific evaluation methods are as follows:

[0055] (1) Large photosensitive surface detection. First, IV curves of samples of different lengths were obtained by testing, and LI curves were obtained by processing. sw Curve. Next, using the combination of the shortest nanowire and a series inductor as a benchmark, the bias current I was measured by illuminating the benchmark sample with light of the target wavelength. b - Quantum efficiency curve. Then, define I. b0 The bias current corresponding to the point where the quantum efficiency just saturates is given by I. b0 As a threshold. Finally, based on the LI obtained from the test. sw Phase diagram combined with I b0 An evaluation is performed. When the length increases, I... sw Reduce to I b0 When the optimal length is defined as the length at that point, the nanowire is considered to have the longest possible length under the current conditions to achieve quantum efficiency saturation. This determines the maximum size that the photosensitive surface of the SNSPD fabricated from the nanowire can be extended.

[0056] If LI sw Phase diagram not covered I b0 If the value is obtained, formula I can be used. SW ≈ I0 - α(ln(L')) 0.5 - βln(L') is used for fitting and prediction. Where, I SW Let I0 be the transition current, approximating the critical current, and L' ≈ L / w, where L is the nanowire length, w is the nanowire width, and α and β are fitting factors. This formula reflects the dual effects of size inhomogeneity and the linear superposition of the transition rate. Based on LI swA phase diagram can be fitted to obtain the values ​​of α and β, and thus predict when I... sw Reduce to I b0 When, the optimal length value.

[0057] (2) High-speed detection. First, without series inductor, LI is measured and acquired. sw Phase diagram and L-quantum efficiency curve. Then, increasing the nanowire length until the dynamic inductance does not affect the switching current I. sw The length L0 that does not affect the trend of the quantum efficiency curve is defined as the optimal length. This length corresponds to the shortest length of the target thin film under the current conditions and determines its maximum detection rate.

[0058] (3) High wavelength sensitivity detection. IV curves of samples with different widths were obtained, and the width W and the switching current density J were extracted. sw Phase diagram and WI sw Phase diagram. Based on laboratory testing conditions, the minimum width W is defined as the width at which the pulse signal can just be extracted and identified. min WJ sw The width corresponding to the inflection point of the curve is defined as the maximum width W. max The optimal width for achieving the highest wavelength sensitivity detection falls within the range [W]. min W max Finally, nanowires with widths within this range are used to perform light response tests at corresponding wavelengths, and final size selection is conducted to meet specific application requirements.

[0059] like Figure 1 The diagram shown illustrates the structuring process of the target superconducting thin film. It includes dimensional gradient processing in two dimensions: width W and length L.

[0060] Figure 2 This is a schematic diagram of the RT curves for the samples. RT curve data for different sizes, size-T c The phase diagram can be extracted, thereby determining the subsequent test temperature of this invention. c It is usually defined as the midpoint of the jump interval in the RT curve, which can be taken as the median temperature corresponding to 90% and 10% of the sample resistance value at 20 K.

[0061] like Figure 3 As shown, this is I. sw A schematic diagram showing the curve of the change of current with L, and a schematic diagram showing the bias current-quantum efficiency curve obtained by testing the shortest nanowire + inductor combination as a benchmark. If of the superconducting nanowire. sw It is highly sensitive to defects; as L increases, the probability of a fatal defect increases, therefore I... swThe conversion rate continues to decline. Simultaneously, due to phase fluctuations, the conversion rate also increases with increasing L, leading to even greater decline. However, the quantum efficiency curve is unaffected by length, so quantum efficiency curves for different lengths almost overlap. But because I... sw The decay of the quantum efficiency curve leads to a compression of the quantum efficiency saturation plateau in long nanowires. The bias current at which the quantum efficiency curve just reaches saturation is defined as the threshold current I. b0 Then it can be done through LI sw The optimal length is determined by the phase diagram.

[0062] like Figure 4 As shown, this is WJ sw Schematic diagram of the curve. When the width decreases to a certain extent, the switching current density drops sharply due to the non-uniformity and the surge in the switching rate; when the width increases to a threshold, the current is no longer uniformly distributed in this nanowire due to the change in vortex motion characteristics, and the switching current density also decreases.

[0063] To make the objectives, technical solutions, and advantages of the present invention clearer, the design method proposed in this invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0064] Example 1:

[0065] The screening method proposed in this invention is applied to determine the optimal length of nanowires in high-speed detection scenarios, including:

[0066] NbN thin films were grown using magnetron sputtering. The growth parameters were Ar:N₂ = 100:4, total gas pressure 4.5 mTorr, sputtering current 0.5 A, and growth time 35 s. The sheet resistance of the film was 489 Ω. Nanowires with a width of 90 nm and lengths of 30 μm, 70 μm, 110 μm, and 410 μm were prepared using electron beam lithography and reactive ion etching. Testing was conducted at an operating temperature of 2.16 K and a test wavelength of 1064 nm. The response characteristics of the nanowires were tested as follows: Figure 5 As shown.

[0067] Depend on Figure 5 It can be seen that when the nanowire length is greater than 70 nm, the length no longer affects the quantum efficiency curve, and the latch-up effect caused by the small inductance is also eliminated. Therefore, 70 nm can be defined as the optimal length. Based on the response pulse, the time constant is extracted, such as... Figure 6 As shown in the figure. Therefore, the maximum count rate can be calculated to be approximately 1 / (3τ)≈87 MHz.

[0068] Example 2:

[0069] The screening method proposed in this invention is used to evaluate the switching current density characteristics and photoresponse characteristics of high-resistivity NbN with different widths for high-sensitivity detection scenarios. This includes:

[0070] NbN thin films were still grown using magnetron sputtering. The growth parameters were Ar:N₂ = 100:4, total gas pressure 4.5 mTorr, sputtering current 0.5 A, and growth time adjusted to 25 s. Nanowires with a length of 70 μm and widths of 85 nm, 190 nm, and 390 nm were prepared using electron beam lithography and reactive ion etching. Testing was conducted at an operating temperature of 0.36 K and a test wavelength of 2.2 μm. The test results for the nanowires are as follows: Figure 7 As shown.

[0071] Depend on Figure 7 As shown in (a), the nanowire width corresponding to the inflection point is approximately 170 nm. However, the switching current of an 85 nm wide nanowire is only 0.4 μA, which is less than the current that can be measured in the laboratory. Figure 7 As shown in (b) above. Therefore, the optimal operating width range is approximately [130 nm, 170 nm]. Figure 7 As shown in (c)-(d), under these conditions, the target thin film can achieve light saturation of at least 2.2 μm.

[0072] Example 3:

[0073] The screening method proposed in this invention is used to evaluate the photoresponse characteristics of nanowires of different lengths in large photosensitive surface detection scenarios. This includes:

[0074] Nitrogen-doped amorphous molybdenum (NAM) films were grown using magnetron sputtering. NAM films were deposited in an Ar (100 sccm) / N2 (2 sccm) gas atmosphere at a total pressure of 0.5 Pa, with the Mo target powered by an 80 W DC power supply. The sputtering time was set to 18 s. The film thickness was approximately 8 nm. Nanowires with widths of 80 nm and lengths of 5 μm, 20 μm, 80 μm, 320 μm, 1280 μm, and 5120 μm were prepared using electron beam lithography and reactive ion etching. Testing was conducted at an operating temperature of 0.79 K. The test results are as follows: Figure 8 As shown in the figure, for a 1550 nm optical signal, the optimal length of the target superconducting thin film under this condition is 2667 μm.

[0075] Niobium nitride films were grown using telemetry-controlled sputtering. The growth parameters were Ar:N₂ = 100:6, total gas pressure 4.25 mTorr, sputtering current 0.3 A, and growth time adjusted to 80 s. Nanowires with widths of 170 nm and lengths of 5 μm, 80 μm, 320 μm, and 1280 μm were prepared using electron beam lithography and reactive ion etching. Testing was conducted at an operating temperature of 2.3 K, and the results are as follows: Figure 9 As shown. Figure 9 The blue discrete points in (a) are LI sw The measured data, with the red dashed line representing the fitting result using the above formula, yielded α≈0.3 and β≈0.2. For a 1064 nm optical signal, according to... Figure 9 (b) I can be extracted b0 =7.2μA, binding Figure 9 The fitted curve in (a) can predict that the optimal length of the target superconducting film under this condition is 7561 μm.

Claims

1. A method for screening the application performance of superconducting materials based on size control, characterized in that: include: The target superconducting thin film was fabricated into two sets of nanowire test arrays with width and length gradients to obtain multiple samples of different sizes. By testing the current-voltage curves of samples of different lengths, a length-critical transition current phase diagram was obtained. Using the combination of the shortest nanowire and an inductor in series as a reference, the reference is illuminated with light of the target wavelength to obtain the bias current-quantum efficiency curve. Based on the bias current-quantum efficiency curve, determine the bias current corresponding to the point where the quantum efficiency just saturates, and use this bias current as the threshold. Based on the length-critical transition current phase diagram and the threshold, when the length increases and the critical transition current decreases to the threshold, the length value at this point is the longest length at which the nanowire can achieve quantum efficiency saturation. Based on the longest length, the photosensitive surface of the superconducting nanowire single-photon detector fabricated from this nanowire is determined.

2. The method for screening the application performance of superconducting materials based on size control according to claim 1, characterized in that: The statement that when the increase in length causes the critical switching current to decrease to a threshold value, the length at which the nanowire can achieve quantum efficiency saturation includes: If the threshold is not covered in the length-critical transition current phase diagram, the transition current-nanowire length is fitted according to the following formula to obtain fitting factors α and β: I SW ≈ I0- α(ln(L')) 0.5 - βln(L'); Among them, I SW For the switching current, I0 is approximately the critical current, L' ≈ L / w, where L is the nanowire length, w is the nanowire width, and α and β are fitting factors; Let I SW Equal to the current threshold, predict when I sw Reduce to I b0 At that time, the longest length at which nanowires can achieve quantum efficiency saturation is reached.

3. A method for screening the application performance of superconducting materials based on size control, characterized in that: include: The target superconducting thin film was fabricated into two sets of nanowire test arrays with width and length gradients to obtain multiple samples of different sizes. By testing the current-voltage curves of samples of different lengths, a length-critical transition current phase diagram was obtained; by irradiating the samples with light of the target wavelength, bias current-quantum efficiency curves of nanowires of different lengths were obtained. The optimal length is defined as the length at which the dynamic inductance of the nanowire does not affect the critical switching current or the trend of the quantum efficiency curve. The optimal length corresponds to the shortest length of the target superconducting thin film under the current conditions. The shortest length determines the maximum detection rate of the target superconducting thin film.

4. A method for screening the application performance of superconducting materials based on size control, characterized in that: include: The target superconducting thin film was fabricated into two sets of nanowire test arrays with width and length gradients to obtain multiple samples of different sizes. Current-voltage curves of samples with different widths were obtained from the test; The width-transition current density phase diagram and the width-critical transition current phase diagram were extracted from the current-voltage curves of samples with different widths. Based on the test conditions, the width at which the pulse signal can just be identified is defined as the minimum width; The width corresponding to the inflection point in the width-transition current density phase diagram is defined as the maximum width. With a width of [W] min W max The nanowires within the film were subjected to light response tests at corresponding wavelengths. Based on the light response test results, the size of the target superconducting thin film for achieving the highest wavelength sensitivity detection was selected.

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