Preparation method of controllable thickness bismuth strontium calcium copper oxide high-temperature superconducting single crystal microwire

Abstract

The application discloses a preparation method of a controllable-thickness BiSrCaCuO high-temperature superconducting single-crystal microwire, and belongs to the technical field of superconducting micro-nano electronic device preparation. The application obtains a fresh surface by cleaving a BSCCO single crystal through a Scotch tape under a high-vacuum environment and evaporates a gold film in situ, and after gold electrodes are prepared through photolithography and wet etching, secondary photolithography and argon ion beam etching are combined to define a line channel with a width of micrometer level to a preset depth; then, the sample is bonded and solidified with a second substrate through an Epoxy glue, and the substrate is separated to realize a turn-over transfer, and finally, residual bulk BSCCO single crystals are cleaved and removed to obtain a finished product. The application combines in-situ gold electrode technology, dry and wet etching technology and turn-over transfer and cleaving technology, realizes a good ohmic contact, and is precise in microwire thickness control, stable and repeatable in process, and provides a new way for the preparation of high-performance high-temperature superconducting devices.

Description

Technical Field

[0001] This invention belongs to the field of superconducting micro-nano electronic device technology, specifically relating to a method for preparing bismuth-strontium-calcium-copper-oxygen high-temperature superconducting single-crystal microwires with controllable thickness. Background Technology

[0002] BSCCO (such as Bi-2212), as a typical layered high-temperature superconducting material, has enormous application potential in cutting-edge fields such as single-photon detection, terahertz radiation sources and detectors, and qubits due to its naturally occurring intrinsic Josephson junction array. In the application of these devices, the critical current of superconducting microwires (…) The thickness of the micrometer wire determines the device's performance, and this parameter is related to the thickness of the micrometer wire. Directly related, its ideal relationship is: ( (Line width).

[0003] Especially in single-photon detector applications, to improve the hotspot effect and response sensitivity after photon absorption, superconducting microwires are typically required to be as thin as possible. However, due to factors such as material processing and environment, a "dead layer" that loses superconductivity often forms on the surface of BSCCO crystals. If the microwire thickness is too thin, the proportion of the dead layer will increase significantly, leading to degradation or even complete loss of the overall superconducting performance of the device. Therefore, precisely controlling the thickness of the microwire within a critical range that meets the requirements of ultra-thin detection while effectively overcoming the influence of the dead layer is a pressing problem that needs to be solved in current technology.

[0004] The existing BSCCO microwire fabrication technology has the following main drawbacks:

[0005] 1. Random initial film thickness leads to uncontrollable final micrometer line thickness: Current micro / nano fabrication methods often use polymers such as polydimethylsiloxane (PDMS) for mechanical exfoliation and dry transfer to obtain thin-layer BSCCO. However, due to the uncertainty of interlayer cleavage, the initial film thickness obtained by PDMS transfer has a high degree of randomness. If independent micrometer lines are fabricated directly on such randomly thick films, the final thickness of the micrometer lines cannot be precisely controlled, directly leading to the unpredictability of core parameters such as the critical current of the device.

[0006] 2. Independent microwires lack three-dimensional physical support, making them structurally fragile and prone to breakage: Using traditional top-down forward etching processes, microwires are typically exposed on the substrate surface as isolated steps. Due to the extremely strong natural cleavage tendency of BSCCO, this exposed structure, lacking lateral physical support, is extremely fragile. During subsequent testing or exposure to extremely low-temperature cycling (thermal expansion and contraction stress), interlayer slippage, peeling, or even direct open-circuit failure can easily occur.

[0007] 3. Damaged electrode contact interface and high ohmic contact resistance: Traditional processes generally employ a fabrication sequence of "first cleaving the single crystal, then transferring it to the coating equipment to deposit electrode material." This inevitably leads to the freshly cleaved BSCCO single crystal surface being exposed to air before gold film deposition, resulting in oxygen loss and degradation. The damaged interface makes it difficult to form an ideal low-resistance contact with the electrode, causing severe Joule heating during actual power-on operation and affecting device performance.

[0008] To address the aforementioned pain points, a novel process route is urgently needed that can achieve precise control over thickness to balance detection sensitivity and "dead layer" limitations, protect the fragile superconducting material interface, and simultaneously enable high-quality metal electrode extraction. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a method for preparing bismuth strontium calcium copper oxide high-temperature superconducting single crystal microwires with controllable thickness. The method achieves the preparation of high-quality BSCCO microwires with controllable thickness through in-situ gold evaporation, ion beam etching and flip-over transfer technology.

[0010] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0011] A method for preparing controllable thickness bismuth-strontium-calcium-copper-oxygen high-temperature superconducting single-crystal microwires includes the following steps:

[0012] 1) High-temperature superconducting BSCCO single crystals were fixed to the first substrate using Scotch tape in a high vacuum environment;

[0013] 2) Deposit a gold film on the surface of a BSCCO single crystal;

[0014] 3) Perform photolithography to position the electrode pattern on the gold film on the BSCCO single crystal surface;

[0015] 4) Wet etching is used to remove the gold film outside the electrode pattern, and then organic solvents are used to remove the photoresist;

[0016] 5) Perform a second photolithography to position a meandering line pattern on the micrometer scale between the gold electrodes on top of the BSCCO single crystal;

[0017] 6) Use ion beam etching to etch the required thickness of the micrometer line, and then use organic solvents to remove the photoresist;

[0018] 7) The top of the BSCCO microwire sample was connected to the second substrate using epoxy adhesive. After baking and curing, the two substrates were separated, and the gold electrode, BSCCO microwire and some residual bulk BSCCO single crystal were transferred to the second substrate.

[0019] 8) The residual bulk BSCCO single crystal above the BSCCO microwire on the second substrate was removed by Scotch tape cleaving to obtain a bismuth-strontium-calcium-copper-oxygen high-temperature superconducting single crystal microwire with controllable thickness.

[0020] Further, in step 1), the high-temperature superconducting BSCCO single crystal fixed on the first substrate is bonded with Scotch tape, and the other end of the tape is fixed to a baffle in the cavity of the thermal evaporation equipment. After the cavity is evacuated to a high vacuum, the baffle is opened and the high-temperature superconducting BSCCO single crystal fixed on the first substrate is dissected.

[0021] Further, in step 2), a gold film is deposited on the surface of a BSCCO single crystal using a thermal evaporation device. The gold film deposition rate is 2 nm / s, and a 100 nm gold film is deposited in 50 s.

[0022] Further, in step 3), an electrode pattern is prepared on the gold film on the surface of a BSCCO single crystal using ultraviolet lithography exposure and development technology: first, photoresist is spin-coated, then baking and pattern exposure are performed, and development is performed after exposure; the spin-coating process is as follows: first, rotate at a low speed of 600 rpm for 10 seconds, then rotate at a high speed of 3000 rpm for 60 seconds; the baking temperature is 95℃ and the time is 2 minutes; the exposure time is 15 seconds and the development time is 30 seconds.

[0023] Further, in step 4), a KI / I2 solution is used as an isotropic wet etchant, and the organic solvent for removing the photoresist is acetone and ethanol; the ratio of the KI / I2 solution is: KI:I2:H2O = 4g:1g:40mL.

[0024] Further, in step 5), a micron-line pattern is prepared between the gold electrodes on the top of the BSCCO single crystal using ultraviolet lithography exposure and development technology: first, photoresist is spin-coated, then baked and the pattern is exposed, and after exposure, development is performed; the spin-coating process is as follows: first, rotate at a low speed of 600 rpm for 10 seconds, then rotate at a high speed of 3000 rpm for 60 seconds; the baking temperature is 95℃ and the time is 2 minutes; the exposure time is 15 seconds and the development time is 30 seconds; the micron-line width is 2 μm.

[0025] Further, in step 6), the ion beam etching is argon ion beam physical dry etching, and the organic solvents for removing the photoresist are acetone and ethanol; the etching voltage is 500V, the etching rate of BSCCO single crystal is 1nm / s, the etching time is 20s, and the etching depth is 20nm.

[0026] Further, in step 7), uncured epoxy adhesive is covered over the micron line and electrode area, then the second substrate is gently pressed on top of it, and then placed on the baking table to bake, so that the epoxy adhesive is cured. Then the two substrates are separated, so that the gold electrode, BSCCO micron line and some residual bulk BSCCO single crystal are transferred to the second substrate; the baking table temperature is 105°C and the drying time is 3 hours.

[0027] Further, in step 8), the Scotch tape is cut into thin strips, lightly applied to the micron line pattern, and then cleaved.

[0028] Furthermore, the superconducting transition temperature of the controllable thickness bismuth-strontium-calcium-copper-oxygen high-temperature superconducting single-crystal micron wire is greater than 80K, the critical current is 2mA, and the voltage jump is 0.15V.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] (1) Thickness controllable and structurally stable: This invention creatively utilizes etching depth and flip-over cleavage to obtain micron lines of a defined thickness. When cleaving the residual bulk BSCCO single crystal after flipping, the epoxy resin used for transfer also plays a role in providing physical support for the micron line structure, ensuring that the micron lines of the preset thickness obtained by etching are well preserved.

[0031] (2) The present invention achieves perfect ohmic contact: gold film is deposited immediately when the material is freshest, avoiding the degradation of the BSCCO surface and solving the problem of high contact resistance. Attached Figure Description

[0032] Figure 1 A flowchart illustrating the fabrication of a bismuth-strontium-calcium-copper-oxygen high-temperature superconducting single-crystal microwire with controllable thickness for this application;

[0033] Figure 2 This is an orthophoto image of the sample prepared in the embodiments of this application;

[0034] Figure 3 This is a backlight image of the optical image of the sample prepared in the embodiments of this application;

[0035] Figure 4 This is a test graph showing the resistance-temperature characteristics of the sample in the embodiments of this application;

[0036] Figure 5 This is a test graph showing the current-voltage characteristics of the sample in the embodiments of this application. Detailed Implementation

[0037] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0038] Example 1

[0039] like Figure 1 As shown, this embodiment provides a method for preparing bismuth-strontium-calcium-copper-oxygen high-temperature superconducting single-crystal microwires with controllable thickness, including the following steps:

[0040] (1) The high-temperature superconducting BSCCO single crystal fixed on the first substrate is bonded with Scotch tape, and the other end of the tape is fixed to the baffle in the cavity of the thermal evaporation equipment. When the mechanical pump and the molecular pump pump the cavity to 1×10 -6 Torr uses the force of opening the baffle to pull the Scotch tape, cleaving the BSCCO single crystal, peeling off the surface oxide layer, and obtaining a smooth, fresh surface.

[0041] (2) A gold film is deposited on the BSCCO single crystal surface fixed on the substrate using a thermal evaporation device. The gold film deposition rate is 2nm / s, and a 100nm gold film is deposited in 50s.

[0042] (3) Take the sample out of the thermal evaporation equipment and perform photolithography exposure and development. The steps are as follows: spin-coat a layer of photoresist on the sample surface. The photoresist used is AZ5214 photoresist. First, rotate at a low speed of 600 rpm for 10 s, then rotate at a high speed of 3000 rpm for 60 s. Place the sample on a heating platform for baking. The heating platform temperature is 95℃ and the baking time is 2 min. Then, observe the sample surface using the microscope of the UV exposure machine and position the electrode pattern on the BSCCO single crystal covered with gold film. After the exposure is completed, perform development. The exposure time is 15 s and the development time is 30 s.

[0043] (4) The exposed gold film was etched isotropically using a KI / I2 solution with a ratio of KI:I2:H2O = 4g:1g:40mL. The surface photoresist was then washed away with acetone, rinsed with ethanol, and dried with a nitrogen gun.

[0044] (5) Spin-coating photoresist again for high-precision overlay alignment. The steps are as follows: Spin-coating a layer of photoresist on the sample surface. The photoresist used is AZ5214 photoresist. First, rotate at a low speed of 600 rpm for 10 s, then rotate at a high speed of 3000 rpm for 60 s. Place the sample on a heating platform for baking. The heating platform temperature is 95℃ and the baking time is 2 min. Then, observe the sample surface using a microscope of an ultraviolet exposure machine. Position the micron line pattern between the gold electrodes on the top of the BSCCO single crystal. The width of the micron line is 2 μm. After exposure, develop the sample. The exposure time is 15 s and the development time is 30 s.

[0045] (6) Argon ion beam physical dry etching was used. The etching voltage was 500V. The calculated etching rate of BSCCO single crystal was 1nm / s, the etching time was 20s, and the etching depth was 20nm. Then, the surface photoresist was washed away with the organic solvent acetone, rinsed with ethanol, and then dried with a nitrogen gun.

[0046] (7) Cover the micron line and electrode area with uncured epoxy adhesive, then press the second substrate lightly on top of it, and then place it on the drying table. The drying table temperature is 105°C and the drying time is 3h to cure the epoxy adhesive. Then separate the two substrates. The fracture surface naturally occurs at the bottom of the etching depth. The BSCCO micron line, gold electrode and some residual bulk BSCCO single crystal are transferred to the second substrate.

[0047] (8) Cut Scotch tape into thin strips and gently attach them to the microwire and gold electrode pattern. Then, remove the residual bulk BSCCO single crystal above the second substrate BSCCO microwire to obtain a BSCCO microwire supported by epoxy adhesive, with high-quality gold electrodes at both ends and controllable thickness.

[0048] The performance of the prepared micron-sized wire samples with controllable thickness using BSCCO was tested, as detailed below:

[0049] Optical images of BSCCO microwire samples were obtained using an optical microscope, such as... Figure 2 and Figure 3 As shown, the optical microscope has a magnification of 500x, and the BSCCO superconducting microwires are located between the electrodes.

[0050] The RT and current-voltage characteristics of the BSCCO superconducting microwire were tested using a Keithley 6221 current source and a Keithley 2182A voltmeter. The RT characteristic results are as follows: Figure 4 As shown, Figure 4 The vertical axis represents resistance in ohms, and the horizontal axis represents temperature in Kelvin. Test results show that the resistance (RT) of the BSCCO superconducting microwire is normal, and the superconducting transition temperature is around 81K. Current-voltage characteristics are as follows: Figure 5 As shown, Figure 5 The vertical axis represents current in milliamperes (mA), and the horizontal axis represents voltage in volts (V). The test results show that the critical current of the BSCCO superconducting microwire is 2 mA, and the voltage jump reaches 0.15 V, demonstrating excellent electrical transport characteristics. This provides a high-performance experimental sample for the subsequent application of BSCCO microwires in single-photon detection research.

[0051] This method improves the success rate and performance of superconducting microwire samples, and enables high operating temperatures (over 80K in this embodiment) after micro-nano fabrication, making it suitable for the fabrication of high-temperature superconducting microwires with various complex patterns.

[0052] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing bismuth-strontium-calcium-copper-oxygen high-temperature superconducting single-crystal microwires with controllable thickness, characterized in that: Includes the following steps: 1) High-temperature superconducting BSCCO single crystals were fixed to the first substrate using Scotch tape in a high vacuum environment; 2) Deposit a gold film on the surface of a BSCCO single crystal; 3) Perform photolithography to position the electrode pattern on the gold film on the BSCCO single crystal surface; 4) Wet etching is used to remove the gold film outside the electrode pattern, and then organic solvents are used to remove the photoresist; 5) Perform a second photolithography to position a meandering line pattern on the micrometer scale between the gold electrodes on top of the BSCCO single crystal; 6) Use ion beam etching to etch the required thickness of the micrometer line, and then use organic solvents to remove the photoresist; 7) The top of the BSCCO microwire sample was connected to the second substrate using epoxy adhesive. After baking and curing, the two substrates were separated, and the gold electrode, BSCCO microwire and some residual bulk BSCCO single crystal were transferred to the second substrate. 8) The residual bulk BSCCO single crystal above the BSCCO microwire on the second substrate was removed by Scotch tape cleaving to obtain a bismuth-strontium-calcium-copper-oxygen high-temperature superconducting single crystal microwire with controllable thickness.

2. The method for preparing controllable thickness bismuth-strontium-calcium-copper-oxygen high-temperature superconducting single-crystal microwires according to claim 1, characterized in that: In step 1), the high-temperature superconducting BSCCO single crystal fixed on the first substrate is bonded with Scotch tape, and the other end of the tape is fixed to a baffle in the cavity of the thermal evaporation equipment. After the cavity is evacuated to a high vacuum, the baffle is opened and the high-temperature superconducting BSCCO single crystal fixed on the first substrate is cleaved.

3. The method for preparing controllable thickness bismuth-strontium-calcium-copper-oxygen high-temperature superconducting single-crystal microwires according to claim 1, characterized in that: In step 2), a gold film is deposited on the surface of a BSCCO single crystal using a thermal evaporation device. The gold film deposition rate is 2 nm / s, and a 100 nm gold film is deposited in 50 s.

4. The method for preparing controllable thickness bismuth-strontium-calcium-copper-oxygen high-temperature superconducting single-crystal microwires according to claim 1, characterized in that: In step 3), an electrode pattern is prepared on the gold film on the surface of a BSCCO single crystal using ultraviolet lithography exposure and development technology: first, photoresist is spin-coated, then baking and pattern exposure are performed, and development is performed after exposure; the spin-coating process is as follows: first, rotate at a low speed of 600 rpm for 10 seconds, then rotate at a high speed of 3000 rpm for 60 seconds; the baking temperature is 95℃ and the time is 2 minutes; the exposure time is 15 seconds and the development time is 30 seconds.

5. The method for preparing controllable thickness bismuth-strontium-calcium-copper-oxygen high-temperature superconducting single-crystal microwires according to claim 1, characterized in that: In step 4), a KI / I2 solution is used as an isotropic wet etchant, and the organic solvents for removing the photoresist are acetone and ethanol; the ratio of the KI / I2 solution is KI:I2:H2O = 4g:1g:40mL.

6. The method for preparing controllable thickness bismuth-strontium-calcium-copper-oxygen high-temperature superconducting single-crystal microwires according to claim 1, characterized in that: In step 5), a micron-line pattern is prepared between the gold electrodes on the top of the BSCCO single crystal using ultraviolet lithography exposure and development technology: first, photoresist is spin-coated, then baked and the pattern is exposed, and after exposure, development is performed; the spin-coating process is as follows: first, rotate at a low speed of 600 rpm for 10 seconds, then rotate at a high speed of 3000 rpm for 60 seconds; the baking temperature is 95℃ and the time is 2 minutes; the exposure time is 15 seconds and the development time is 30 seconds; the micron-line width is 2 μm.

7. The method for preparing controllable thickness bismuth-strontium-calcium-copper-oxygen high-temperature superconducting single-crystal microwires according to claim 1, characterized in that: In step 6), the ion beam etching is a physical dry etching method using argon ion beams. The organic solvents for removing the photoresist are acetone and ethanol. The etching voltage is 500V, the etching rate of the BSCCO single crystal is 1nm / s, the etching time is 20s, and the etching depth is 20nm.

8. The method for preparing controllable thickness bismuth-strontium-calcium-copper-oxygen high-temperature superconducting single-crystal microwires according to claim 1, characterized in that: In step 7), uncured epoxy adhesive is covered over the micrometer wire and electrode area. Then, the second substrate is gently pressed on top of it and placed on a baking tray to bake, so that the epoxy adhesive is cured. Then, the two substrates are separated, so that the gold electrode, BSCCO micrometer wire and some residual bulk BSCCO single crystal are transferred to the second substrate. The baking tray temperature is 105°C and the drying time is 3 hours.

9. The method for preparing controllable thickness bismuth-strontium-calcium-copper-oxygen high-temperature superconducting single-crystal microwires according to claim 1, characterized in that: In step 8), cut the Scotch tape into thin strips, gently apply them to the micron line pattern, and then peel it off.

10. The method for preparing controllable thickness bismuth-strontium-calcium-copper-oxygen high-temperature superconducting single-crystal microwires according to claim 1, characterized in that: The superconducting transition temperature of the controllable thickness bismuth-strontium-calcium-copper-oxygen high-temperature superconducting single-crystal micron wire is greater than 80K, the critical current is 2mA, and the voltage jump is 0.15V.

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