A method for depositing gold electrodes on the surface of BSCCO single crystal

Abstract

The present invention discloses a method for depositing gold electrodes on the surface of a BSCCO single crystal, belonging to the technical field of superconducting device preparation. The method comprises the following steps: S1, cleaning a sapphire substrate; S2, placing the sapphire substrate in a vacuum tube, fixing a PDMS film with a BSCCO single crystal adhered thereto on the sapphire substrate, and cleaving the BSCCO single crystal within the vacuum tube; S3, depositing a gold film on the surface of the BSCCO single crystal fixed on the sapphire substrate using magnetron sputtering; S4, photolithographically transferring a gold electrode pattern onto the surface of the BSCCO single crystal; S5, ion beam etching, removing the gold film outside the photolithographic pattern; S6, evaporating a silicon oxide film as a protective layer; and S7, removing the photoresist using an organic solvent. The method of the present invention completes all necessary steps for depositing the gold electrode on the BSCCO single crystal in a vacuum environment, effectively reducing the effects of organic reagents, water, and air on the BSCCO single crystal structure.

Description

Technical Field

[0001] The invention belongs to the technical field of superconducting device preparation, and particularly relates to a method for depositing a gold electrode on the surface of a BSCCO single crystal. Background Art

[0002] Superconducting nanowire single-photon detectors (SNSPDs) have important application value in quantum communication, quantum computing, and high-precision optical sensing due to their high quantum efficiency, low temporal jitter, and fast response speed. As a typical high-temperature superconducting material, single crystals are ideal for preparing high-temperature, high-performance SNSPDs due to their high superconducting transition temperature (Tc) and excellent physical properties. BSCCO's high-temperature superconductivity enables operation at liquid nitrogen temperatures, reducing refrigeration costs and complexity. Its anisotropic structure gives it unique advantages in low-dimensional superconductor research. Mechanical exfoliation techniques can be used to produce ultrathin single crystals with few defects, facilitating the study of low-dimensional superconducting properties and the fabrication of prototype superconducting electronics devices. However, research on BSCCO-based SNSPDs still faces challenges, such as complex preparation processes and a high superconducting gap voltage that could affect detection efficiency.

[0003] The main difficulties in depositing gold electrodes on BSCCO single crystals are:

[0004] (1) After the two-dimensional transfer, the surface of the BSCCO single crystal on the substrate will be exposed to the air for a period of time, causing the surface of the single crystal to lose oxygen and the superconducting properties to degrade;

[0005] (2) After photolithography, the electrode pattern is etched by ion beam. However, during the etching process, some argon ions will penetrate into the BSCCO single crystal and destroy its structure, resulting in degradation of superconducting properties.

[0006] (3) After the BSCCO single crystal is etched, a protective layer needs to be added to its surface. However, during the process of transferring the sample from the etching equipment to the protective layer evaporation equipment, the side wall of the single crystal is exposed to air and will cause degradation. Summary of the Invention

[0007] In response to the above-mentioned problems existing in the prior art, the technical problem to be solved by the present invention is to provide a method for depositing gold electrodes on the surface of BSCCO single crystals. This method has the advantages of greatly simplifying the steps of depositing gold electrodes on the surface of BSCCO single crystals, effectively reducing the effects of organic reagents, water and air on the BSCCO single crystal structure, and effectively improving the success rate and reliability of preparing superconducting nanowire single-photon detectors.

[0008] Technical solution: In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0009] A method for depositing a gold electrode on the surface of a BSCCO single crystal comprises the following steps:

[0010] S1. Cleaning the sapphire substrate;

[0011] S2. Place the sapphire substrate in a vacuum tube, fix the PDMS film with the BSCCO single crystal on the sapphire substrate, and cleave the BSCCO single crystal in the vacuum tube;

[0012] S3, using magnetron sputtering to deposit a gold film on the surface of the BSCCO single crystal fixed on the sapphire substrate;

[0013] S4, photolithographic transfer of gold electrode patterns onto the surface of the BSCCO single crystal;

[0014] S5, ion beam etching, to remove the gold film outside the photolithography pattern;

[0015] S6, transferring the sample in situ to an electron beam evaporation device and evaporating a silicon oxide film as a protective layer;

[0016] S7. Remove the photoresist using an organic solvent.

[0017] Preferably, the S1 cleaning step is: placing the sapphire substrate in an acetone solution and using ultrasonic cleaning for a cleaning time of T1, then using alcohol and deionized water to clean the residue, and blowing it dry with a nitrogen gun, and then baking it on a drying table, the drying table temperature is D1, and the sapphire substrate baking time is T2.

[0018] Preferably, in S2, a high-temperature vacuum tape is used to fix the sapphire substrate on a sample tray, the sample tray is fixed on a trolley in a vacuum pipe, and a PDMS film with a BSCCO single crystal adhered thereto is fixed on the sapphire substrate. One end of the PDMS film is connected by a second tape, and the other end of the second tape is fixed to the wall of the vacuum pipe cavity. By moving the trolley, the inertia of the trolley is utilized to cleave the BSCCO single crystal in the pipe.

[0019] Preferably, in S3, magnetron sputtering is used to deposit a 40 nm gold film at a rate of 8 nm / min.

[0020] Preferably, in S4, during the photolithography process, a BSCCO single crystal film with a thickness of 10 nm to 20 nm is screened for photolithography, and the steps of photolithography exposure and development are: spin-coating a layer of photoresist on the sample surface, and placing the sample on a heating platform for baking, the heating platform temperature is D2, the sample baking time is T3, then using a microscope of a UV exposure machine to observe the sample surface, placing an electrode pattern on the BSCCO single crystal film, and developing after the exposure is completed, the exposure time is T4, and the development time is T5.

[0021] Preferably, in S5, the sample is placed in a vacuum pipe and 300V ion beam etching is used to treat the sample for 60 seconds.

[0022] Preferably, in S6, the thickness of the silicon oxide film is 30 nm.

[0023] Preferably, after removing the photoresist in S7, the sample is cleaned with acetone, then rinsed with alcohol, and then blown dry with a nitrogen gun.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0025] 1. This method uses a pipe to cleave a BSCCO single crystal in a vacuum environment, deposits a 40 nm gold film using magnetron deposition, removes the gold-filmed BSCCO single crystal sample from the vacuum pipe, transfers the electrode pattern by UV exposure, and then uses a 300 V ion beam to etch. By controlling the etching time, the gold film is removed just outside the photolithographic pattern without over-etching. The sample is then transferred in situ to an electron beam evaporation system to deposit a 30 nm silicon oxide protective layer. Using metal mask technology, photolithography, electron beam evaporation, and magnetron sputtering, gold electrodes can be deposited while effectively protecting the BSCCO single crystal.

[0026] 2. Using a moving carriage within a vacuum tube to cleave BSCCO single crystals is simple and efficient, ensuring that the cleaved sample is only in contact with the vacuum environment before the gold film is evaporated, reducing degradation. After the subsequent etching step is completed, a silicon oxide protective layer is evaporated in situ, preventing the exposed single crystal sidewalls from coming into contact with air.

[0027] 3. This method completes all necessary steps for depositing gold electrodes on BSCCO single crystals in a vacuum environment. It is suitable for depositing gold electrodes on BSCCO single crystal thin films with a thickness of 10nm to 20nm. It has the advantages of greatly simplifying the steps for depositing gold electrodes on the BSCCO single crystal surface, effectively reducing the effects of organic reagents, water, and air on the BSCCO single crystal structure, and weakening the degradation of the BSCCO single crystal surface during the electrode preparation process. It improves the preparation success rate and performance of ultra-thin BSCCO single crystal samples, laying the foundation for the realization of superconducting nanodevices with higher operating temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a flow chart for preparing a gold electrode deposited on the surface of a BSCCO single crystal according to an embodiment of the present invention;

[0029] Figure 2 is a positive optical image of a sample prepared in the embodiment;

[0030] Figure 3 is a backlit optical image of a sample prepared in the embodiment;

[0031] Figure 4 1 is a resistance-temperature characteristic test diagram of the sample in the embodiment;

[0032] Figure 5 This is a diagram of the inertia decomposition method of the car. DETAILED DESCRIPTION

[0033] The present invention will be further illustrated below with reference to specific examples. The examples are implemented based on the technical solutions of the present invention. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0034] like Figure 1 As shown, the method of depositing a gold electrode on the surface of a BSCCO single crystal in this embodiment includes the following steps:

[0035] S1. Clean the sapphire substrate. Place the sapphire substrate in acetone and use 100 W ultrasonic cleaning for a cleaning time of T1. In this embodiment, T1 = 5 minutes. Then, use alcohol and deionized water to remove residues, blow dry with a nitrogen gun, and then bake on a drying table. The drying table temperature is D1, 90°C ≤ D1 ≤ 98°C, in this embodiment, D1 = 95°C. The sapphire substrate is baked for a time of T2, 3 minutes ≤ T2 ≤ 10 minutes. In this embodiment, T2 = 5 minutes.

[0036] S2. The sapphire substrate is placed in the vacuum pipe of the vacuum system. The vacuum zone of the pipe is , the PDMS film with BSCCO single crystal is attached to the sapphire substrate, and the BSCCO single crystal is cleaved in a vacuum tube. The specific process is as follows: Figure 5 As shown, in a vacuum pipe, a high-temperature vacuum tape (Teflon high-temperature tape) is used to fix the sapphire substrate to the sample tray, which is fixed to a trolley. A PDMS membrane with a BSCCO single crystal is attached to the sapphire substrate. One end of the PDMS membrane is connected by a second tape (the second tape is Scotch tape), and the other end of the second tape is fixed to the wall of the vacuum pipe cavity. By moving the trolley in the vacuum pipe, the second tape connecting the vacuum pipe cavity wall and the PDMS membrane will be straightened, and the PDMS membrane fixed to the sapphire substrate will be forced to fall off the sapphire substrate, and the BSCCO single crystal will remain on the sapphire substrate to form a sample.

[0037] S3. Use magnetron sputtering to deposit a gold film on the surface of the BSCCO single crystal fixed on the sapphire substrate. The magnetron power is 150W, the gold film evaporation rate is 8 nm / min, and the evaporation time is 5 minutes to deposit a 40 nm gold film. Figure 1 The gold film is deposited as shown in (1).

[0038] S4, photolithography transfer gold electrode pattern on the surface of BSCCO single crystal, take the sample out of the vacuum pipe and perform photolithography. During the photolithography process, since the backlight image of the BSCCO single crystal film can distinguish the thickness according to the color of BSCCO, the colors from thin to thick are white-yellow-orange-black, select light yellow BSCCO single crystal, the thickness of which is expected to be 10nm~20nm, screen out (light yellow, thickness range 10nm~20nm, thin BSCCO single crystal film has better heat dissipation, which is more conducive to making superconducting nanowires) BSCCO single crystal film for photolithography, the steps of photolithography exposure and development are: spin-coat a layer of photoresist on the sample surface, AZ5214 photoresist is selected as the photoresist, first rotate at a low speed of 600rpm for 10s, then rotate at a high speed of 3000rpm for 60s, and place the sample on a heating platform for baking, the heating platform temperature is D2, 90℃≤D2≤98℃, in this embodiment D2=95℃, the sample baking time is T3, 1 min≤T3≤5 min, in this embodiment T3=2 minutes, then use the microscope of the UV exposure machine to observe the sample surface, place the electrode pattern on the photoresist layer, and develop after the exposure. The exposure time is T4, 5 s≤T4≤10 s, in this embodiment T4=7 s, and the development time is T5, 20 s≤T5≤30 s, in this embodiment T5=22 s, Figure 1 (2) is shown in the photolithography development of the uniform resist.

[0039] S5, ion beam etching, remove the gold film outside the photolithography pattern, send the sample into the vacuum pipe, use 300V (the existing technology generally uses 500V ion beam voltage, the speed and density of argon ion beam are higher than 300V, and argon ion beam is easy to damage deep BSCCO single crystal) ion beam etching to treat the sample for 60 seconds to expose the fresh surface. Figure 1 As shown in (3) 300V ion beam etching, if you look from the top down at the actual image, part of the BSCCO single crystal is under the gold film, and part is exposed. The average velocity of the argon ion beam in this step is lower than that of conventional 500V ion beam etching. Controlling the etching time can avoid over-etching.

[0040] S6. Transfer the sample in situ to an electron beam evaporation device, and evaporate a silicon oxide film as a protective layer. The thickness of the protective layer is greater than or equal to 20 nm. In this embodiment, the thickness of the silicon oxide film is 30 nm. Figure 1 (4) shows a 30 nm silicon oxide protective layer evaporated.

[0041] S7: Remove the photoresist using an organic solvent, such as acetone or ethanol. After removing the photoresist, clean the sample for 10 seconds, rinse with alcohol, and then blow dry with a nitrogen gun. (The photoresist dissolves in acetone, and the corresponding silicon oxide will fall off after the photoresist disappears.) Figure 1As shown in (5), the photoresist is removed using an organic solvent.

[0042] The performance of the prepared BSCCO single crystal film samples was tested as follows:

[0043] Use an optical microscope to obtain an optical image of the entire film sample, such as Figure 2 and Figure 3 As shown, Figure 2 and Figure 3 The magnification is 50 times, and ion milling can fully etch away the gold film on the surface of the sapphire substrate without causing obvious damage to the surface of the BSCCO single crystal.

[0044] The current source KEITHLEY 6221 and the voltmeter KEITHLEY 2182A were used to test the current-voltage characteristics of the BSCCO single crystal. The results are as follows: Figure 4 As shown, Figure 4 The vertical axis R represents resistance in ohms, and the horizontal axis T represents temperature in Kelvin. The test results show that the RT of the BSCCO single crystal is normal, and the superconducting transition temperature is around 80K, which meets the standard for preparing high-temperature superconducting single-photon detectors.

[0045] In this embodiment, trolley cleavage in a vacuum tube replaces the existing cumbersome thermal evaporation vacuum cleavage steps or transparent tape cleavage (manual cleavage is not possible in a vacuum tube). All important steps (S2, S3, and S5) are completed in a vacuum environment, eliminating the time required to enter and exit the vacuum system, preventing degradation of the BSCCO single crystal due to contact with air, and being suitable for gold electrode deposition on BSCCO single crystal films with a thickness of 10 nm to 20 nm (BSCCO single crystals of approximately 10 nm will begin to degrade once exposed to air), thus ensuring the quality of the BSCCO single crystal (which will later be used in the production of single-photon detectors, which have high requirements for the heat dissipation of the sample, so the thickness of the BSCCO single crystal film must be between 10 nm and 20 nm).

[0046] Existing gold films are typically deposited using vacuum thermal evaporation, but the thermally evaporated gold film has a weak attraction to the substrate. For the electrodes in this embodiment, removing the photoresist from extremely fine areas requires repeated acetone cleaning, and the thermally evaporated gold film easily falls off. In this embodiment, the gold film is deposited using magnetron sputtering, achieving a contact resistance of approximately 50Ω, meeting experimental requirements. Furthermore, the magnetron sputtered gold electrode remains intact during resist removal.

[0047] This method performs all the steps of gold electrode deposition in a vacuum system, improving the success rate and performance of ultrathin BSCCO single crystal sample preparation. It also enables higher operating temperatures after superconducting nanowire fabrication (the superconducting transition temperature in this embodiment exceeds 80K, compared to 50K in prior art). The relatively simple process (replacing the previously cumbersome thermal evaporation vacuum cleavage step, all steps are completed within the vacuum system, eliminating time spent entering and exiting the vacuum system, preventing degradation of the BSCCO single crystals due to contact with air, and ensuring high quality) allows for mass production.

[0048] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for depositing a gold electrode on the surface of a BSCCO single crystal, characterized in that: The following steps are involved: S1. Cleaning the sapphire substrate; S2. Place the sapphire substrate in a vacuum tube, fix the PDMS film with the BSCCO single crystal on the sapphire substrate, and cleave the BSCCO single crystal in the vacuum tube; S3, using magnetron sputtering to deposit a gold film on the surface of the BSCCO single crystal fixed on the sapphire substrate; S4, photolithographic transfer of gold electrode patterns onto the surface of the BSCCO single crystal; S5, ion beam etching, to remove the gold film outside the photolithography pattern; S6, transferring the sample in situ to an electron beam evaporation device and evaporating a silicon oxide film as a protective layer; S7, removing the photoresist with an organic solvent; In S2, a first tape is used to fix the sapphire substrate to a sample tray, which is fixed to a trolley in a vacuum pipe. A PDMS film with a BSCCO single crystal adhered thereto is fixed to the sapphire substrate. One end of the PDMS film is connected by a second tape, and the other end of the second tape is fixed to the wall of the vacuum pipe. The BSCCO single crystal is cleaved in the pipe by moving the trolley and utilizing its inertia.

2. The method for depositing a gold electrode on the surface of a BSCCO single crystal according to claim 1, characterized in that: The step S1 is as follows: placing the sapphire substrate in an acetone solution and performing ultrasonic cleaning for a cleaning time of T1, then using alcohol and deionized water to clean the residue, blowing it dry with a nitrogen gun, and then baking it on a drying table at a drying table temperature of D1 and a baking time of T2.

3. The method for depositing a gold electrode on a BSCCO single crystal surface according to claim 1, characterized in that: The first adhesive tape is a high-temperature vacuum adhesive tape.

4. The method for depositing a gold electrode on a BSCCO single crystal surface according to claim 1, wherein: In S3, a 40 nm gold film is deposited by magnetron sputtering at a rate of 8 nm / min.

5. The method for depositing a gold electrode on the surface of a BSCCO single crystal according to claim 1, characterized in that: In the S4, during the photolithography process, a BSCCO single crystal film with a thickness of 10 nm to 20 nm is selected for photolithography. The steps of photolithography exposure and development are as follows: a layer of photoresist is spin-coated on the sample surface, and the sample is placed on a heating platform for baking. The heating platform temperature is D2, and the sample baking time is T3. Then, the sample surface is observed using a microscope of a UV exposure machine, and an electrode pattern is placed on the BSCCO single crystal film. After the exposure is completed, development is performed. The exposure time is T4, and the development time is T5.

6. The method for depositing a gold electrode on a BSCCO single crystal surface according to claim 1, characterized in that: In S5, the sample is placed in a vacuum pipe and ion beam etching is performed at 300 V for 60 seconds.

7. The method for depositing a gold electrode on a BSCCO single crystal surface according to claim 1, characterized in that: In the above-mentioned S6, the thickness of the silicon oxide film is 30 nm.

8. The method for depositing a gold electrode on a BSCCO single crystal surface according to claim 1, characterized in that: After removing the photoresist in S7, the sample is cleaned with acetone, rinsed with alcohol, and then blown dry with a nitrogen gun.

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