Method and device for preparing non-destructive metal electrode on surface of YBCO (Yttrium Barium Copper Oxide) film

Abstract

The invention provides a method and a device for preparing a nondestructive metal electrode on the surface of a YBCO (Yttrium Barium Copper Oxide) film, and belongs to the technical field of electrode preparation. According to the method, a low-temperature evaporation electrode is innovatively adopted, and direct contact between a YBCO film and a chemical reagent in a traditional electrode preparation method is avoided; meanwhile, the evaporation device is independently designed and modified, the device controls the temperature of the substrate table by controlling the liquid nitrogen flow and the heating power in the evaporation process, low-temperature evaporation is achieved, and therefore accumulation of the heat effect in the YBCO film in the electrode evaporation process is reduced, and the YBCO film still has very excellent superconducting performance after metal electrode preparation is completed.

Description

Technical Field

[0001] The invention belongs to the technical field of electrode preparation, and in particular relates to a method and a device for preparing a damage-free metal electrode on the surface of a YBCO film. Background Art

[0002] Since the discovery of superconductivity by Dutch physicists in 1911, superconducting materials have shown rich application prospects. Compared with low-temperature superconductors, high-temperature superconductors have a wider range of applications due to their higher operating temperature, stronger anti-magnetism and greater current carrying capacity. In addition to the above characteristics, YBCO film has better processability and scalability than other high-temperature superconductors, and can meet the needs of various complex applications. It shows great application potential in power transmission, superconducting magnets, quantum computing and magnetic levitation. These advantages make YBCO film one of the key materials for the development of modern superconducting technology and devices.

[0003] The key step in preparing superconducting devices using YBCO thin films is to prepare metal electrodes on the thin films. The quality of the metal electrode preparation process is determined by the size of the contact resistance between the prepared electrode and the thin film. The traditional method of preparing metal electrodes uses photolithography to accurately pattern the required electrode structure on the surface of the thin film, and then the electrode is prepared by evaporating the required metal material and stripping technology. However, the chemical properties of the YBCO thin film itself are very sensitive, and the above preparation method will cause great damage to the YBCO thin film. First, during the photolithography process, the YBCO thin film will inevitably come into contact with the atmospheric environment, resulting in performance degradation; secondly, during the photolithography and stripping process, the film needs to be in direct contact with chemical reagents, which will also cause serious degradation of superconducting performance; finally, the accumulation of thermal effects generated during the room temperature evaporation process will also cause YBCO to degrade; therefore, the traditional method of preparing metal electrodes is not suitable for preparing metal electrodes on the surface of YBCO thin films.

[0004] Therefore, how to prepare metal electrodes with good contact without affecting the superconducting properties of YBCO thin films is an important problem that needs to be solved urgently in the preparation of YBCO-based single-photon detectors. Summary of the invention

[0005] In view of the problems existing in the background technology, the purpose of the present invention is to provide a method and device for preparing a non-damaged metal electrode on the surface of a YBCO film. The method innovatively adopts low-temperature evaporation electrode to avoid direct contact between the YBCO film and chemical reagents in the traditional electrode preparation method; at the same time, the evaporation device is independently designed and modified. During the evaporation process, the device controls the temperature of the substrate stage by controlling the liquid nitrogen flow rate and the heating power to achieve low-temperature evaporation, thereby reducing the accumulation of thermal effects in the YBCO film during the electrode evaporation process, so that the YBCO film still has very excellent superconducting properties after the preparation of the metal electrode is completed.

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

[0007] A method for preparing a damage-free metal electrode on a YBCO film surface comprises the following steps:

[0008] Step 1. Prepare a YBCO thin film on the substrate surface;

[0009] Step 2. Preparing an amorphous YBCO protective layer on the surface of the YBCO film can effectively prevent YBCO from being degraded by contact with the atmospheric environment during processing;

[0010] Step 3. Fixing a mask plate on the surface of the YBCO film using a high temperature tape, wherein the mask plate has a desired electrode structure pattern;

[0011] Step 4: Use electron beam evaporation to evaporate metal electrodes at low temperature. The specific evaporation process parameters are: vacuum degree is not higher than 5×10 -4 Pa, and the substrate stage temperature during the evaporation process is -30℃ to -60℃, and the electrode growth rate is

[0012] Furthermore, in step 1, the substrate includes but is not limited to magnesium oxide, lanthanum aluminate or strontium titanate substrate.

[0013] Furthermore, in step 1, the thickness of the YBCO film is in the range of 3-10 nm.

[0014] Furthermore, in step 2, the thickness of the amorphous YBCO protective layer is not less than 8 nm, and the growth method is room temperature DC magnetron sputtering.

[0015] Furthermore, in step 3, the sticking of the high temperature tape will not have a shielding effect on the electrode structure. The function of the high temperature tape is only to make the stainless steel mask and the YBCO film fit closely to prevent the mask from falling off during the evaporation process.

[0016] The present invention also provides a device used in the above-mentioned preparation method, including an evaporation chamber, a liquid nitrogen cooling system, an evaporation crucible, a crystal oscillator, a substrate stage and a temperature control system;

[0017] The liquid nitrogen cooling system comprises a self-pressurizing liquid nitrogen tank, a liquid nitrogen delivery pipeline, a liquid nitrogen flow control valve and a cooling chamber;

[0018] The temperature control system includes a data converter, a heating control module and a low temperature sensor;

[0019] The evaporation crucible is arranged at the bottom of the evaporation chamber, and the evaporated metal is placed in it; the crystal oscillator and the substrate stage are arranged at the top of the evaporation chamber, and the center of the evaporation crucible is opposite to the center of the substrate stage; the crystal oscillator and the substrate stage are flush with each other, and are used to detect the evaporation rate and the thickness of the evaporated metal film;

[0020] The sample to be evaporated is arranged on the lower surface of the substrate stage, opposite to the evaporation crucible, and the cooling chamber is arranged on the upper surface of the substrate stage; a heating control module and a low-temperature temperature sensor are arranged on the substrate stage, and a data converter is arranged outside the evaporation chamber and connected to the heating control module and the low-temperature temperature sensor;

[0021] The cooling chamber cools the substrate stage by flowing liquid nitrogen, thereby ensuring that the heat accumulated on the sample can be effectively released in a timely manner through the substrate stage; the cooling chamber is connected to an external self-pressurized liquid nitrogen tank through a liquid nitrogen delivery pipeline; the liquid nitrogen flow control valve is used to control the flow rate of liquid nitrogen flowing through the cooling chamber, thereby controlling the cooling efficiency of the cooling chamber on the substrate stage.

[0022] The low temperature sensor is used to realize real-time monitoring of the temperature of the substrate stage and transmit the monitoring data to the data converter; the data converter is used to determine whether to turn on the heating control module; the heating control module is used to heat the substrate stage.

[0023] Furthermore, the data converter is used to compare the monitoring data with a set threshold value, and if the real-time temperature is lower than the set threshold value, the heating control module is turned on.

[0024] Furthermore, the threshold is set according to demand, preferably -40°C to -60°C.

[0025] The mechanism of the present invention is: the thinner the YBCO film is, the more sensitive it is to damage and defects generated during the processing, which means that it is more likely to degrade and lose its superconducting properties during the processing, making it more difficult to prepare a metal electrode with good contact on an ultra-thin YBCO film. The present invention designs an evaporation device, controls the liquid nitrogen flow rate and the heating power of the heating module by the system during the evaporation process, and simultaneously realizes the control of the cooling amount and the heat amount, so that the substrate stage reaches a dynamic thermal equilibrium state, and the sample stage temperature is maintained at the required sub-zero temperature. While ensuring the stability of the evaporation environment, the heat accumulated on the YBCO film during the evaporation process can be efficiently released through heat conduction, thereby ensuring that the YBCO film obtained after the electrode preparation still has excellent superconducting properties.

[0026] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0027] (1) The use of the evaporation method can effectively avoid the direct contact between the YBCO film and the chemical reagents in the process of preparing electrodes by conventional photolithography, thereby effectively avoiding the degradation of the YBCO film caused by the chemical reagents; compared with the traditional photolithography method of preparing electrodes, the process steps of preparing the electrode structure using a stainless steel mask are simpler, which can effectively avoid the degradation of the YBCO film when it is exposed to the atmospheric environment during the photolithography process.

[0028] (3) The use of low-temperature evaporation technology can timely release the heat accumulated on the surface of the YBCO film during the evaporation process, effectively avoiding the degradation of the YBCO film caused by thermal damage; at the same time, the present invention controls the temperature of the substrate stage at a relatively low temperature by controlling the liquid nitrogen flow rate and the heating power, thereby achieving low-temperature evaporation while maintaining the stability of the evaporation environment and ensuring the quality of the evaporated metal film. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a structural diagram of the device for preparing damage-free metal electrodes according to the present invention.

[0030] Figure 2 This is a flow chart for preparing a damage-free metal electrode according to Example 1 of the present invention.

[0031] Figure 3 This is a stainless steel mask pattern with an electrode structure and a YBCO thin film pattern with an electrode structure according to Example 1 of the present invention.

[0032] Figure 4 RT characteristic diagrams of Example 1 and Example 2 of the present invention after metal electrodes are prepared on YBCO films of different thicknesses.

[0033] Figure 5 This is a comparison chart of the RT characteristics of the YBCO thin films obtained in Example 1 of the present invention and Comparative Example 1.

[0034] Figure 6 This is a RT characteristic diagram of the YBCO thin film obtained in Comparative Example 2 of the present invention.

[0035] Figure numerals: 1 is a liquid nitrogen delivery pipeline; 2 is a liquid nitrogen flow control valve; 3 is a crystal oscillator; 4 is a self-pressurized liquid nitrogen tank; 5 is an infusion port; 6 is a liquid outlet; 7 is a data converter; 8 is a cooling chamber; 9 is a low-temperature temperature sensor; 10 is a heating control module; 11 is a substrate stage; 12 is an evaporation chamber; 13 is a crucible device. DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the implementation modes and the accompanying drawings.

[0037] The structure diagram of the device for preparing the damage-free metal electrode of the present invention is as follows Figure 1 As shown, it includes an evaporation chamber 12, a liquid nitrogen cooling system, an evaporation crucible 13, a crystal oscillator 3, a substrate stage 11 and a temperature control system;

[0038] The liquid nitrogen cooling system includes a self-pressurizing liquid nitrogen tank 4, a liquid nitrogen delivery pipeline 1, a liquid nitrogen flow control valve 2 and a cooling chamber 8; the temperature control system includes a data converter 7, a cryogenic temperature sensor 9 and a heating control module 10;

[0039] The evaporation crucible is arranged at the bottom of the evaporation chamber, and the evaporated metal is placed in it; the crystal oscillator and the substrate stage are arranged at the top of the evaporation chamber, and the center of the evaporation crucible is opposite to the center of the substrate stage; the crystal oscillator is flush with the height of the substrate stage; the cooling chamber is arranged on the upper surface of the substrate stage, and the sample to be evaporated is arranged on the lower surface of the substrate stage, opposite to the evaporation crucible; a heating control module and a low-temperature temperature sensor are arranged on the substrate stage, and a data converter is arranged outside the evaporation chamber and connected to the heating control module and the low-temperature temperature sensor.

[0040] During evaporation, the YBCO film will be adhered to the lower surface of the substrate stage 11, the vacuum system will be turned on to evacuate the evaporation chamber 12, the liquid nitrogen flow control valve 2 will be opened, and the liquid nitrogen stored in the liquid nitrogen booster tank 4 will be transported to the liquid outlet 6 through the infusion port 5 and the liquid nitrogen delivery pipe 1 and enter the cooling chamber 8. The substrate stage 11 will be cooled by heat exchange. After the liquid nitrogen enters the cooling chamber through the liquid inlet, it will remain in the chamber until it is evaporated.

[0041] The data converter 7 and the temperature sensor 9 are activated through the operation panel of the evaporation equipment to monitor the temperature of the substrate stage. When the temperature is close to -40°C, the heating control module 10 starts to work, and the data converter 7 automatically adjusts the heating power according to the temperature of the substrate stage to ensure that the temperature of the substrate stage remains stable. During the cooling period, the size of the valve 2 can be controlled to control the flow of liquid nitrogen. After the temperature of the substrate stage stabilizes at -50°C, the evaporation of the metal electrode begins. A certain current is applied to the crucible device 13 through the control panel of the evaporation equipment to heat the metal material to a gaseous state so that it is deposited on the YBCO film. The crystal oscillator 3 next to the substrate stage 11 will monitor the evaporation rate and film thickness of the metal in real time.

[0042] Example 1

[0043] A method for preparing a metal electrode on a YBCO film without damage, the flow chart of the preparation method is as follows Figure 2 As shown, the following steps are included:

[0044] Step 1: A 500 μm thick strontium titanate substrate is cleaned with acetone, ethanol and deionized water, and then dried with a nitrogen gun to remove water vapor on the substrate surface and ensure that there are no other impurities on the substrate surface;

[0045] Step 2: A YBCO film with a thickness of 10 nm is grown on the surface of the strontium titanate substrate cleaned in step 1 by using a DC magnetron sputtering method. 2 :Ar=1:3 mixed gas, gas pressure is 30Pa, sputtering power is 125W, chamber temperature is 802℃, film growth rate is calibrated to be 0.33nm / min, and 10nm ultra-thin single crystal YBCO film is obtained after deposition for 30min;

[0046] After the film growth is completed, wait for the chamber temperature to drop to room temperature, and grow a 10nm thick amorphous YBCO protective layer on the YBCO film under the same gas conditions and sputtering power while keeping the chamber temperature basically unchanged, and then take out the sample;

[0047] Step 3: Use high-temperature tape to attach the stainless steel mask with the electrode structure pattern to the surface of the sample obtained in step 2, and then place the sample on the substrate stage of the electron beam evaporation equipment;

[0048] Step 4: Electron beam evaporation was used to deposit metal electrodes (Ag / Au: 20nm / 20nm) onto the surface of the YBCO film. The vacuum degree of the chamber during evaporation was 5×10 -4 Pa, first evaporate a layer of Ag, then evaporate a layer of Au; the Ag evaporation rate is The Au evaporation rate is

[0049] First, evaporate the metal. During the evaporation process, control the liquid nitrogen flow and the heating power of the substrate stage. When the temperature of the substrate stage stabilizes at around -50°C, open the baffle on the sample surface and start depositing the electrode on the sample. Low temperature assists the rapid relaxation of heat to prevent excessive heat from being generated during the evaporation process, thereby causing irreversible thermal damage to YBCO. After the electrode preparation is completed, the substrate stage is raised to room temperature and the sample can be taken out. After removing the stainless steel mask, a YBCO film with an electrode structure can be obtained.

[0050] Figure 3 The stainless steel mask pattern with an electrode structure and the YBCO thin film pattern with an electrode structure in Example 1 of the present invention are shown in FIG. Figure 3 a is a picture of the stainless steel mask designed and processed according to actual needs. Figure 3 b is a photo of the YBCO thin film with electrode structure obtained after evaporation. It can be seen from the figure that the electrode structure obtained by evaporation is consistent with the initial structure of the design.

[0051] Example 2

[0052] A metal electrode structure was prepared on the YBCO film according to the steps of Example 1, except that the thickness of the YBCO film in step 2 was adjusted to 6 nm, 5 nm, and 4 nm, and the other steps remained unchanged.

[0053] In this embodiment, the electrode structure prepared on the YBCO thin films with different thicknesses still has excellent superconducting properties.

[0054] Example 3

[0055] YBCO nanowires were prepared according to the steps of Example 1, except that the temperature of the substrate stage in step 4 was adjusted to -40°C, -60°C and -70°C, and the remaining steps were unchanged to prepare YBCO nanowires.

[0056] Comparative Example 1

[0057] A metal electrode structure is prepared on the surface of the YBCO film according to the steps of Example 1, except that the substrate stage is not subjected to temperature reduction and temperature control during the evaporation process in step 4, and the remaining steps remain unchanged.

[0058] Comparative Example 2

[0059] A metal electrode structure was prepared on the YBCO film according to conventional photolithography, evaporation and stripping methods. On the basis of step 2 of Example 1, AZ MIR-703 photoresist was spin-coated on the surface of the YBCO film. After baking on a heating table at 100° C. for one minute, the electrode structure was patterned by photolithography. After development, the sample was placed in an evaporation chamber and the electrode material was grown by a room temperature evaporation method according to the parameters of step 4 of Example 1. The evaporated sample was then immersed in an acetone solution to remove the photoresist, and finally a YBCO film with an electrode structure was obtained.

[0060] The RT characteristics test results of Example 1 and Example 2 after preparing metal electrodes on YBCO with different thicknesses are as follows Figure 4 As shown. Critical temperature (T C0 ) refers to the highest temperature point required for a superconductor to enter the superconducting state. For high-temperature superconductors, T C0 The higher the value, the better the superconducting performance is. C0 They are 79K (10nm), 76K (6nm), 73K (5nm) and 65K (4nm) respectively, all of which are maintained above 60K, indicating that the low-temperature evaporation of the present invention can effectively ensure that the superconducting properties of the YBCO film will not be greatly affected after the metal electrode is prepared on the YBCO film.

[0061] The RT characteristics test results of Example 1 and Comparative Example 1 after preparing metal electrodes on YBCO are as follows: Figure 5 As shown in the figure, the blue line represents the RT characteristic curve of the YBCO film after the metal electrode is evaporated at room temperature. C0 The yellow line represents the RT characteristic curve of the YBCO film after low-temperature evaporation of the metal electrode. C0 The comparison result clearly shows that the present invention adopts low-temperature evaporation method to prepare electrodes, which can reduce the influence on the superconducting properties of YBCO thin film during the electrode preparation process. It shows that maintaining the substrate stage at a relatively low temperature can release the heat accumulated on the YBCO thin film during the evaporation process in an efficient heat conduction manner, thereby ensuring the superconducting properties of the YBCO thin film.

[0062] Comparative Example 2 The RT characteristics test results after preparing the metal electrode on YBCO are as follows Figure 6 As shown in the figure, the prepared sample is in an insulating state and the superconducting performance is completely degraded. This shows that the use of traditional photolithography plus evaporation electrode method to prepare electrodes on the surface of YBCO thin film will lead to film quenching.

[0063] The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all the disclosed features, or all the steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A method for preparing a damage-free metal electrode on the surface of a YBCO film, characterized in that: The following steps are involved: Step 1. Prepare a YBCO thin film on the substrate surface; Step 2. Preparing an amorphous YBCO protective layer on the surface of the YBCO film; Step 3. Fixing a mask on the surface of the YBCO film, wherein the mask has a pattern of the electrode structure to be prepared; Step 4: Use electron beam evaporation to evaporate metal electrodes at low temperature. The specific evaporation process parameters are: vacuum degree is not higher than 5×10 -4 Pa, and the substrate stage temperature during the evaporation process is -30℃ to -60℃, and the electrode growth rate is 2. The method for preparing a damage-free metal electrode on the surface of a YBCO film according to claim 1, characterized in that: In step 1, the substrate is a magnesium oxide, lanthanum aluminate or strontium titanate substrate.

3. The method for preparing a damage-free metal electrode on the surface of a YBCO film according to claim 1, characterized in that: In step 1, the thickness of the YBCO film ranges from 3 to 10 nm.

4. The method for preparing a damage-free metal electrode on the surface of a YBCO film according to claim 1, characterized in that: In step 2, the thickness of the amorphous YBCO protective layer is not less than 8 nm, and the growth method is room temperature DC magnetron sputtering.

5. A device used in the method for preparing a damage-free metal electrode on the surface of a YBCO film as claimed in any one of claims 1 to 4, characterized in that: It includes an evaporation chamber, a liquid nitrogen cooling system, an evaporation crucible, a crystal oscillator, a substrate stage and a temperature control system; The liquid nitrogen cooling system comprises a self-pressurizing liquid nitrogen tank, a liquid nitrogen delivery pipeline, a liquid nitrogen flow control valve and a cooling chamber; The temperature control system includes a data converter, a heating control module and a low temperature sensor; The evaporation crucible is arranged at the bottom of the evaporation chamber, and the evaporated metal is placed in it; the crystal oscillator and the substrate stage are arranged at the top of the evaporation chamber, and the center of the evaporation crucible is opposite to the center of the substrate stage; The crystal oscillator is flush with the substrate stage, which is used to detect the evaporation rate and the thickness of the evaporated metal film; The sample to be evaporated is arranged on the lower surface of the substrate stage, opposite to the evaporation crucible, and the cooling chamber is arranged on the upper surface of the substrate stage; a heating control module and a low-temperature temperature sensor are arranged on the substrate stage, and a data converter is arranged outside the evaporation chamber and connected to the heating control module and the low-temperature temperature sensor; The cooling chamber cools the substrate stage by flowing liquid nitrogen, thereby ensuring that the heat accumulated on the sample can be effectively released in a timely manner through the substrate stage; the cooling chamber is connected to an external self-pressurized liquid nitrogen tank through a liquid nitrogen delivery pipeline; the liquid nitrogen flow control valve is used to control the flow rate of liquid nitrogen flowing through the cooling chamber, thereby controlling the cooling efficiency of the cooling chamber on the substrate stage. The low temperature sensor is used to realize real-time monitoring of the temperature of the substrate stage and transmit the monitoring data to the data converter; the data converter is used to determine whether to turn on the heating control module; the heating control module is used to heat the substrate stage.

6. The device according to claim 5, characterized in that The data converter is used to compare the monitoring data with the set threshold. If the real-time temperature is lower than the set threshold, the heating control module is turned on.

7. The device according to claim 6, characterized in that The threshold is set according to the requirements.

8. The device according to claim 7, characterized in that The threshold is set between -40℃ and -60℃.

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