A method for preparing ybco nanowires at low temperature and low pressure

Abstract

The application aims to provide a method for preparing YBCO nanowires at low temperature and low pressure, and belongs to the technical field of single photon detection. The method adopts inductively coupled plasma reactive ion etching (ICP-RIE) technology to prepare nanowires. The YBCO nanowires prepared by the method have a thickness of 5 nm and a width of 68 nm, and excellent morphology and electrical characteristics of the nanowires are ensured. By accurately adjusting the temperature and pressure parameters, the damage caused by the thermal effect in the etching process is effectively reduced, and a very small lateral etching damage width (about 15 nm) is obtained. At the same time, the switching current (I s ) coefficient of variation of the batch-prepared nanowires is less than 6%, and the coefficient of variation of the resistance-temperature (R-T) characteristics is less than 1%, which proves the excellent uniformity.

Description

Technical Field

[0001] This invention belongs to the field of single-photon detection technology, specifically relating to a method for preparing YBCO nanowires at low temperature and low pressure. Background Technology

[0002] Superconducting nanowire single-photon detectors (SNSPDs) are highly regarded for their superior performance (detection efficiency > 98%, count rate ≥ 1.5 GHz, dark count rate < 6 × 10⁻⁶). -6 With its fast response speed (<3 ps), wide bandwidth (from X-rays to 10.6 μm), and maximum array size of up to 400,000 pixels, SNSPDs (Superconducting Narrow-Range Devices) are gaining increasing attention and their applications are rapidly expanding. High-temperature superconductors (SNSPDs) promise to operate at liquid nitrogen temperatures, significantly simplifying cryogenic requirements compared to low-temperature SNSPDs that rely on liquid helium. Currently, SNSPDs based on Bi₂Sr₂CaCu₂O₃ are being studied. 8-δ The SNSPD has achieved single-photon response at 25K, but developing high-temperature superconducting SNSP Ds that operate at higher temperatures still faces challenges. (YBa2Cu3O) 7-δ (YBCO) is due to its high critical temperature (T) c With a temperature of 92K, large-area epitaxial growth (inch-scale), and a short electron-phonon relaxation time, it has become the preferred thin film material for preparing high-temperature SNSPDs.

[0003] The core step in high-temperature SNSPDs devices lies in the fabrication of high-quality YBCO nanowires. The sensitivity of YBCO superconducting films presents a significant challenge to the fabrication of high-quality, ultrathin, and ultranarrow nanowires. YBCO is chemically unstable; oxygen atoms readily migrate and diffuse along the Cu-O chain. Exposed YBCO films gradually lose optimal oxygen doping when exposed to air, leading to performance degradation. Furthermore, it exhibits extreme sensitivity to defects and disorder due to its very short coherence length and the d-type wave symmetry of the superconducting order parameter. Simultaneously, conventional etching methods struggle to remove its metallic components, resulting in slow etching rates. Therefore, YBCO thin-film nanowires are highly susceptible to failure during the patterning process due to thermal effects causing oxygen loss in the superconducting layer, as well as direct erosion by chemicals and ions. It is difficult to fabricate high-performance and uniform nanowires without significant film degradation.

[0004] Currently, the patterning processes for fabricating ultrathin YBCO nanowires mainly rely on methods such as focused ion beam (FIB), reactive ion etching (RIE), ion beam etching (IBE), and ion irradiation. Among these, FIB and IBE combined with electron beam lithography are the most common and successful techniques. However, FIB suffers from low efficiency and difficulty in arraying, while IBE is complex and lacks controllability. Furthermore, when using RIE for etching, the etching rate of YBCO is very slow, and the reaction products are difficult to volatilize and easily adsorb onto the YBCO surface, hindering etching and resulting in poor etching effects. In addition, there are novel patterning processes such as porous alumina templates, porous SrTiO3 (STO) insulating film templates, amorphous STO templates, atomic force microscopy contact lithography, and superlattice-nanowire pattern transfer, but their application efficiency is relatively low. In addition, atomic layer etching (ALE) and inductively coupled plasma reactive ion etching (ICP-RIE) have been widely used in the micro-nano fabrication of semiconductors and other materials, especially in the precise fabrication of ultrathin materials and nanostructures. These two techniques have significant advantages and were therefore considered for the fabrication of YBCO nanowires. However, the application of ALE in the fabrication of ultrathin YBCO nanowires is limited, mainly because it is usually performed at high temperatures (above 150°C), while YBCO films are extremely sensitive to temperature. Improper temperature control and excessively high oxygen partial pressure can lead to a decrease in superconducting properties. Furthermore, ALE relies on precise gas control, achieving atomic-level removal through alternating exposure to etching and removal gases, resulting in a slow etching rate. Each reaction cycle may introduce errors, affecting morphology and superconducting performance. As early as 2001, a study used ICP-RIE to etch 500 nm thick YBCO, but found the etching rate to be too fast for processing thin films. Research on ICP-RIE for YBCO nanowire fabrication has made no progress to date.

[0005] In general, while there are various methods for preparing YBCO nanowires, the processes are relatively complex and lack stability. During patterning, oxygen loss due to thermal effects and direct erosion by chemicals or ions can easily occur, leading to the failure of the superconducting layer. Therefore, in order to meet the high quality requirements of high-performance SNSPDs for superconducting nanowires, it is urgent to develop a nanowire preparation process that is efficient, low-damage, and has good stability. Summary of the Invention

[0006] To address the problems existing in the background technology, the present invention aims to provide a method for preparing YBCO nanowires at low temperature and low pressure. This method employs inductively coupled plasma reactive ion etching (ICP-RIE) technology. By precisely controlling the sample stage temperature and pressure conditions during etching, the etching selectivity is improved, thermal damage and non-ideal lateral etching effects during the etching process are reduced, and the electrical properties of the prepared ultrathin YBCO nanowires are significantly enhanced. This lays a solid foundation for the preparation of high-temperature SNSPDs and has important significance in the fields of superconducting devices, quantum computing, and nanoelectronics.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A method for preparing YBCO nanowires at low temperature and low pressure includes the following steps:

[0009] Step 1: Grow a YBCO thin film on the substrate surface;

[0010] Step 2: Attach an electrode pattern mask to the sample surface, and then prepare metal electrodes using electron beam evaporation. After the electrode preparation is completed, remove the mask and then grow a dense alumina protective layer using plasma-enhanced atomic layer deposition.

[0011] Step 3: YBCO microwire devices are fabricated using ultraviolet lithography combined with low-temperature, low-pressure inductively coupled plasma reactive ion etching, and the region to be fabricated for nanowires is located.

[0012] Step 4: The required nanowires are prepared by electron beam lithography combined with low-temperature, low-pressure inductively coupled plasma reactive ion etching.

[0013] Furthermore, in step 1, the growth substrate is preferably a strontium titanate, magnesium oxide, or lanthanum aluminate substrate.

[0014] Furthermore, in step 1, the preferred method for growing the YBCO thin film is DC magnetron sputtering.

[0015] Furthermore, in step 1, when the thickness of the YBCO thin film is 10 nm or less, an amorphous YBCO protective layer is grown in situ on the surface of the YBCO thin film. The thickness of the amorphous YBCO protective layer is 6-10 nm, which avoids the YBCO thin film from contacting the atmospheric environment and degrading during subsequent processing. The preferred growth method is DC magnetron sputtering.

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

[0017] Furthermore, in steps 3 and 4, the parameters for low-temperature, low-pressure inductively coupled plasma reactive ion etching are the same: the sample stage temperature is -20 to -10°C, the etching gas is a CHF3 / Ar mixed etching gas, the ICP power is 800-1200W, the RF power is 80-120W, and the etching pressure is 1-3 mTorr.

[0018] Furthermore, in step 4, the thicker the YBCO film, the longer the inductively coupled plasma reactive ion etching time; for a YBCO film with a thickness of 15 nm, the etching time of inductively coupled plasma reactive ion etching is 90 s to 135 s.

[0019] Furthermore, in step 3, the specific process of ultraviolet lithography is as follows: after cleaning the sample surface, spin-coating photoresist and heating the photoresist; then performing ultraviolet exposure and development to etch the micron region of the nanowire to be made connected to the electrode channel, and then removing the photoresist.

[0020] Further, in step 4, the specific process of electron beam lithography is as follows: after cleaning the sample surface, spin-coating photoresist and heating to bake the photoresist; then spin-coating conductive adhesive and heating to bake the photoresist again; then electron beam lithography is performed to prepare nanowire patterns, followed by development and etching, and finally photoresist removal.

[0021] The mechanism of this invention is as follows:

[0022] In the etching process of YBCO thin films, temperature and pressure conditions have a crucial impact on superconducting performance and etching efficiency. Firstly, low temperatures help slow down heat accumulation and prevent changes in the oxygen content of the YBCO film, thus ensuring optimal oxygen doping throughout the etching process and maintaining stable superconducting performance. (YBa₂Cu₃O) 7-δThe superconductivity of YBCO is extremely sensitive to oxygen content, and the optimal superconducting performance corresponds to a relatively small range of δ values. Excessively high temperatures can lead to oxygen loss (deoxidation), resulting in degradation of superconducting properties. Simultaneously, lower ion energy and slower reaction rates at low temperatures reduce excessive etching of the film sidewalls, helping to mitigate damage to the nanowire edges. Secondly, at low pressures, the molecular free path is longer, the plasma density is lower, and the ion beam energy is more concentrated. High-energy plasma bombardment enhances the directionality and longitudinal etching effects, which not only helps remove byproducts from the YBCO film surface (because these byproducts are complex in composition and have low saturated vapor pressure, the passivations they form on the surface hinder the continued etching process), improving the etching rate and uniformity, but also, combined with the low-temperature conditions, more effectively reduces damage caused by lateral etching. Furthermore, high-energy plasma bombardment at low pressures generates a large amount of heat, thus necessitating low-temperature conditions to avoid thermal damage. The etching technique using a combination of low temperature and low pressure significantly optimizes the etching effect of YBCO nanowires by slowing down heat accumulation, efficiently removing byproducts, improving etching precision, and stabilizing superconducting properties. This enables high-precision and highly selective nanowire fabrication while ensuring the consistency and stability of electrical properties.

[0023] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0024] The method of this invention enhances the controllability and consistency of the etching process, ensuring the uniformity of the nanowire's morphology and electrical properties. By precisely controlling temperature and pressure parameters, damage caused by thermal effects during etching is effectively reduced, resulting in an extremely small lateral etching damage width (approximately 15 nm). This improves the maximum processing size of the nanowires, because if the damage width is too large, it is impossible to prepare nanowires with small linewidths. The nanowires prepared using this method have a thickness as low as 5 nm and a width as narrow as 68 nm, while ensuring excellent morphology and electrical properties. Simultaneously, the switching current (I) of the nanowires prepared in batches can be increased. s The coefficient of variation is less than 6% and the coefficient of variation of the resistance-temperature (RT) characteristics is less than 1%, demonstrating its excellent uniformity. Attached Figure Description

[0025] Figure 1 The nanowire switching current (I) under different etching time conditions at 4K obtained in Example 1 is... s The relationship between the actual etched damage width and the etching time is shown in Figure (a) and Figure (b) obtained by linear fitting.

[0026] Figure 2 Here are schematic diagrams and actual SEM images of the nanowire structure prepared in Example 2;

[0027] Figure 3The nanowire switching current (I) under different etching time conditions at 4K obtained in Example 2 is... s The relationship between the actual etched damage width and the etching time is shown in Figure (a) and Figure (b) obtained by linear fitting.

[0028] Figure 4 The resistance-temperature (R / R) ratio of the 400 nm wide nanowire prepared in Example 1 and the 30 μm wide microwire prepared in Comparative Example 1 is shown. 300K -T) Characteristic Comparison Chart;

[0029] Figure 5 The nanowire switching current (I) at 4K obtained in Example 1 and Comparative Example 2 is... s The relationship between the width and the actual etching damage width obtained by linear fitting;

[0030] Figure 6 The nanowire switching current (I) obtained at 4K in Comparative Example 3 s A diagram showing the relationship between width and height;

[0031] Figure 7 The nanowire switching current (I) at 4K obtained in Example 1 and Comparative Example 4 is... s A diagram showing the relationship between width and height;

[0032] Figure 8 The nanowire switching current (I) at 4K obtained in Example 3 is... s Uniformity analysis of resistance-temperature (RT) characteristics. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0034] Example 1

[0035] A method for preparing YBCO nanowires at low temperature and low pressure includes the following steps:

[0036] Step 1: Prepare a YBCO thin film on the substrate surface:

[0037] Strontium titanate substrates were selected and cleaned (acetone megasonic 5 min, isoacetone megasonic 5 min, isopropanol rinsing, and drying with a nitrogen gun); a 15 nm thick YBCO thin film was grown on the substrate surface using DC magnetron sputtering. The cavity contained an O2:Ar = 1:3 mixed gas at a pressure of 30 Pa, a sputtering power of 125 W, and a substrate temperature of 802 °C; after sputtering, heating was turned off, and the sample was removed after cooling to room temperature.

[0038] Step 2: Attach a stainless steel mask with electrode patterns to the surface of the YBCO thin film on the sample, and then fabricate metal electrodes (Ag / Au: 20nm / 20nm) using electron beam evaporation, with a cavity vacuum level below 5×10⁻⁶. -6 mbar, evaporation rate is

[0039] After the electrode fabrication is completed, the mask is removed, and then a dense 10 nm alumina protective layer is grown on the entire device surface using plasma-enhanced atomic layer deposition to prevent the YBCO thin film from degrading due to contact with the atmospheric environment during subsequent processing.

[0040] Step 3: Perform UV lithography on the sample obtained in Step 2: First, clean the surface of the sample obtained in Step 2; then place it on a 110℃ hot plate for pre-baking for 1 min; spin-coat AZ5214 photoresist (6000 rpm, 60 s); bake the photoresist on a 110℃ hot plate for 1 min; after UV exposure, develop with ZX238 for 45 s to locate the micron region to be formed for the nanowire connected to the electrode channel; use low-temperature, low-pressure inductively coupled plasma reactive ion etching to obtain a micron line with a width of 30 μm: using a mixed etching gas (CHF3 / Ar: 10 / 10 sccm), ICP power of 1000 W, RF power of 100 W, etching pressure of 1 mTorr, and maintaining the sample stage temperature at -20℃ to prevent thermal damage during the etching process; after etching, remove the UV photoresist by soaking in acetone for 10 min, megasonic etching for 20 min, rinsing with isopropanol, and then drying with a nitrogen gun.

[0041] Step 4: Perform electron beam lithography on the sample obtained in Step 3: First, clean the surface of the sample obtained in Step 3, then pre-bake it on a 180℃ hot plate for 1 min; spin-coat ZEP-520A electron beam photoresist (7000 rpm, 60 s), and bake it on a 180℃ hot plate for 3 min; spin-coat conductive carbon adhesive (4000 rpm, 60 s), and bake it on a 110℃ hot plate for 2 min; use electron beam lithography at an accelerating voltage of 20 kV and an exposure dose of 30 μC / cm. 2 In this case, nanowires of multiple widths (1 μm in length and 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 600 nm, 700 nm, 750 nm, 800 nm, 900 nm, 1 μm, 1.1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, and 6 μm) were patterned; the conductive carbon adhesive was removed by rinsing with deionized water, dried with a nitrogen gun, and then developed with ZED-N50 developer at room temperature for 3 min. Subsequently, the nanowires were immersed in isopropanol for 15 s, rinsed with deionized water, and dried with a nitrogen gun.

[0042] The exposed samples were subjected to low-temperature (-20℃) low-pressure (1mTorr) inductively coupled plasma reactive ion etching for etching times of 90s, 105s, 120s, and 135s, yielding single nanowires with lengths of 1μm and widths of 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 600nm, 700nm, 750nm, 800nm, 900nm, 1μm, 1.1μm, 1.5μm, 2μm, 2.5μm, 3μm, and 6μm. The resist removal process consisted of UV light treatment for 5 min, acetone immersion for 10 min, megasonic treatment for 20 min, isopropanol rinsing, and drying with a nitrogen gun.

[0043] Example 2

[0044] YBCO nanowires were prepared according to the steps in Example 1, with step 1 modified as follows: an 8 nm thick YBCO thin film was grown on the substrate surface using DC magnetron sputtering; after the film growth was completed, the cavity was allowed to cool to room temperature, and then a 10 nm thick amorphous YBCO protective layer was grown on the YBCO thin film under the same gas conditions and sputtering power to avoid degradation of the ultrathin YBCO thin film due to contact with the atmospheric environment during subsequent processing.

[0045] Step 4 was adjusted to: Inductively coupled plasma reactive ion etching was performed on the electron beam lithography sample, the sample stage temperature was -20℃, the chamber pressure was 1mTorr, and the etching times were 110s, 115s and 120s, respectively, to obtain single nanowires with widths of 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm and 500nm.

[0046] Example 3

[0047] YBCO nanowires were prepared according to the steps in Example 1;

[0048] Only step 1 is adjusted to: a 10 nm thick YBCO film is grown on the substrate surface using DC magnetron sputtering; after the film growth is completed, the cavity is allowed to cool to room temperature, and then a 10 nm thick amorphous YBCO protective layer is grown on the YBCO film under the same gas conditions and sputtering power to avoid degradation of the ultrathin YBCO film due to contact with the atmospheric environment during subsequent processing.

[0049] Only step 4 is adjusted to: 15 single nanowires with widths of 400 nm, 600 nm, 800 nm and 1 μm are prepared on the same sample.

[0050] Example 4

[0051] YBCO nanowires were prepared according to the steps in Example 1, except that the etching gas pressure of the inductively coupled plasma reactive ion etching in step 4 was adjusted to 3 mTorr, while the other steps remained unchanged.

[0052] This embodiment can also achieve the fabrication of nanowires.

[0053] Comparative Example 1

[0054] YBCO microwires were prepared according to the steps in Example 1, except that step 4 was omitted, while the other steps remained unchanged.

[0055] Comparative Example 2

[0056] YBCO nanowires were prepared according to the steps in Example 1, except that step 4 was adjusted to have an inductively coupled plasma reactive ion etching temperature of 20°C, resulting in single nanowires with widths of 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm and 600 nm.

[0057] Comparative Example 3

[0058] YBCO nanowires were prepared according to the steps in Example 1, except that step 4 was adjusted as follows: the inductively coupled plasma reactive ion etching pressure was 5 mTorr, and the etching time was increased from 120 s to 300 s, and then increased by 30 s in each step, to prepare single nanowires with widths of 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm and 600 nm.

[0059] Comparative Example 4

[0060] YBCO nanowires were prepared according to the steps in Example 1, except that step 4 was adjusted to: the inductively coupled plasma reactive ion etching pressure was 0.6 mTorr, and single nanowires with widths of 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm and 600 nm were prepared.

[0061] Example 1 demonstrates the superiority of this invention in the efficient fabrication of high-quality YBCO nanowires by fabricating nanowires on a 15 nm thick YBCO film without an in-situ amorphous YBCO protective layer. To evaluate the superconducting properties of the nanowires, the current-voltage (IV) characteristics under different conditions were measured, and the key switching current (I0) was extracted. s ) value, J c =I s / wd, where w is the nanowire width and d is the nanowire thickness, J c The higher the value, the better the quality of the nanowires, therefore I s This indicator directly reflects the quality and uniformity of the nanowires. Figure 1(a) shows the I at 4K under different etching times. s The linear relationship between I and nanowire width, ranging from 300 nm to 6 μm, under different etching times. s The results remain almost unchanged, consistent with the linear relationship to the nanowire width, indicating that the superconducting current is uniformly distributed along the nanowire, which also indicates good uniformity of the nanowire. The fitted extrapolated curve for each etching time intersects the positive X-axis at almost the same point (this intersection value is defined as the nanowire edge damage width, which quantifies the nanowire edge damage caused by etching), which is very close to zero, indicating that in Figure 1 (a) shows a small edge damage width during the etching process. Figure 1 (b) It can be seen that as the etching time increases, I s The value remained relatively stable, while the edge damage width increased slightly (from 20 nm to approximately 60 nm), indicating that controlling the etching time can fine-tune the edge damage width. The longer the etching time, the wider the edge damage, and the narrower the actual effective width of the nanowire.

[0062] Example 2 further verified the effectiveness of the present invention in preparing high-quality ultrathin YBCO nanowires by patterning nanowires on an 8nm thick YBCO thin film with an in-situ amorphous YBCO protective layer. Figure 2 (a) shows the fabricated nanowire structure with a straight length of 1 μm. The transition regions between the nanowires and the electrodes are designed with rounded corners to minimize current crowding effects, which would otherwise reduce Ig. s . Figure 2 (b) shows a scanning electron microscope (SEM) image of a YBCO nanowire with a width of 300 nm and provides a magnified view of the white rectangular area where the clearly defined etch profile along the edge of the nanowire demonstrates the high precision of the patterning process, ensuring the ideal geometry and structure of the YBCO nanowire.

[0063] Figure 3 (a) This demonstrates the relationship between nanowire width (from 150 nm to 500 nm) and I at different etching times. s The linear relationship between them shows that... Figure 2 A similar trend is shown in (a), and Figure 3 (b) shows that the edge damage of the nanowires is relatively stable under different etching times, with the smallest edge-damaged nanowire width being only about 15 nm. Unlike Example 1, the 8 nm thick YBCO ultrafilm in Example 2 is covered with a 10 nm thick amorphous YBCO protective layer, which effectively avoids damage caused during the nanowire fabrication process. The results of Example 2 and Comparative Example 1 are as follows... Figure 4 As shown, the R / R ratio of 30μm wide micrometer lines and 400nm nanometer lines on an 8nm thick YBCO ultrathin film. 300K-T characteristics are almost identical, critical temperature (T) c0 The decrease was only slight, and the superconducting transition width showed a negligible increase, demonstrating that the YBCO ultrafilm maintained excellent electrical properties even after the preparation of narrow linewidth nanowires.

[0064] Figure 5 The results of Example 1 and Comparative Example 2 are shown in comparison. At a low temperature of -20°C, nanowire I s The linear relationship with width is clear and consistent, yielding nanowires with widths as low as 150 nm and damage as low as 22 nm; however, at 20 °C, it is difficult to prepare nanowires with widths below 300 nm, the edge damage width increases to 248 nm, and the nanowire yield is low. s The linear relationship with width also becomes poorer. This result demonstrates that low-temperature conditions can effectively reduce thermal damage and material degradation that may occur during etching, and can enhance the selectivity of the etching process, thereby improving the etching accuracy and ensuring low-loss and high-efficiency fabrication of ultrathin nanowires.

[0065] Figure 6 The results of Comparative Example 3 show that when the etching gas pressure was increased to 5 mTorr, the etching effect failed to meet expectations, such as the etching of a 15 nm thick and 300 nm wide YBCO nanowire under normal conditions. s It should be around 1.5mA, but at this point the nanowire I... s The etching pressure remained stable at 8 mA, unaffected by the nanowire width, indicating minimal etching effect. This meant the YBCO film in the exposed area during nanowire patterning was not fully etched through, and adjusting the etching time did not improve the problem. Reducing the gas pressure to 0.6 mTorr... Figure 7 The comparison results of Example 1 and Comparative Example 4 are shown, where low gas pressure leads to nanowires I under the same conditions. s Nanowires with a width less than 600 nm will be damaged due to reduced Ig. This indicates that etching pressure has a decisive impact on etching performance. Higher pressure leads to increased collisions between etching gas molecules, reducing the directionality and orientation of ions, making etching more diffuse and difficult to precisely etch nanowires. Simultaneously, ions experience greater energy loss during transport, resulting in reduced etching efficiency. While lower pressure helps improve ion directionality and energy control, excessively low pressure can lead to excessively high ion energy, causing over-etching and damage. Under low pressure, the ion beam may become too concentrated, easily causing nanowire breakage or the formation of uneven etching edges, thus affecting the electrical properties of the nanowires and reducing Ig. s .

[0066] Finally, in Example 3, 15 nanowires of four different widths were prepared on a 10 nm thick YBCO film with an in-situ protective layer, further verifying the high efficiency and excellent uniformity of YBCO nanowire preparation in this invention. Figure 8 As shown in (a), the on-chip uniformity of nanowires with widths of 400 nm, 600 nm, 800 nm, and 1 μm is excellent. s The mean values ​​were 0.9, 1.48, 2.1 and 2.7 mA, respectively, with coefficients of variation less than 6%. Figure 8 The coefficient of variation of the resistance-temperature (RT) characteristics of the 800 nm wide nanowires presented in (b) is less than 1%, which proves their excellent uniformity. The large-scale fabrication of highly uniform nanowires is a solid foundation for the fabrication of array devices and the expansion of applications.

[0067] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A method for preparing YBCO nanowires at low temperature and low pressure, characterized in that, Includes the following steps: Step 1: Grow a YBCO thin film on the substrate surface; Step 2: Attach an electrode pattern mask to the sample surface, and then prepare metal electrodes using electron beam evaporation. After the electrode preparation is completed, remove the mask and then grow a dense alumina protective layer using plasma-enhanced atomic layer deposition. Step 3: YBCO microwire devices are fabricated using ultraviolet lithography combined with low-temperature, low-pressure inductively coupled plasma reactive ion etching, and the region to be fabricated for nanowires is located. Step 4: Fabricate the required nanowires using electron beam lithography combined with low-temperature, low-pressure inductively coupled plasma reactive ion etching (ICP-IR). In steps 3 and 4, the parameters for low-temperature, low-pressure ICP-IR are the same: the stage temperature is -20 to -10°C, the etching gas is a CHF3 / Ar mixed etching gas with a CHF3 to Ar flow ratio of 1:1, the ICP power is 800-1200W, the RF power is 80-120W, and the etching pressure is 1-3 mTorr.

2. The method for preparing YBCO nanowires at low temperature and low pressure as described in claim 1, characterized in that, In step 1, the growth substrate is a strontium titanate, magnesium oxide, or lanthanum aluminate substrate.

3. The method for preparing YBCO nanowires at low temperature and low pressure as described in claim 1, characterized in that, In step 1, the YBCO thin film is grown using DC magnetron sputtering.

4. The method for preparing YBCO nanowires at low temperature and low pressure as described in claim 1, characterized in that, In step 1, when the thickness of the YBCO thin film is 10 nm or less, an amorphous YBCO protective layer is grown in situ on the surface of the YBCO thin film. The thickness of the amorphous YBCO protective layer is 6-10 nm, and the growth method is DC magnetron sputtering.

5. The method for preparing YBCO nanowires at low temperature and low pressure as described in claim 1, characterized in that, In step 2, the vacuum level of the electron beam evaporation system cavity is lower than 5 × 10⁻⁶. -6 mbar, evaporation rate of 0.5-2 Å / s.

6. The method for preparing YBCO nanowires at low temperature and low pressure as described in claim 1, characterized in that, In step 4, the thicker the YBCO film, the longer the inductively coupled plasma reactive ion etching time; for a YBCO film with a thickness of 15 nm, the etching time for inductively coupled plasma reactive ion etching is 90 s to 135 s.

7. The method for preparing YBCO nanowires at low temperature and low pressure as described in claim 1, characterized in that, In step 3, The specific process of ultraviolet lithography is as follows: after cleaning the sample surface, spin-coating photoresist and heating the photoresist; then ultraviolet exposure and development are performed to etch the micron region of the nanowire to be made connected to the electrode channel, and then the photoresist is removed.

8. The method for preparing YBCO nanowires at low temperature and low pressure as described in claim 1, characterized in that, In step 4, the specific process of electron beam lithography is as follows: after cleaning the sample surface, spin-coating photoresist and heating to bake the photoresist; then spin-coating conductive adhesive and heating to bake the photoresist again; then electron beam lithography is performed to prepare nanowire patterns, followed by development and etching, and finally photoresist removal.

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