| The second generation high temperature superconductor(HTS) wires, based on YBa2Cu3O7-δ(YBCO), have the following advantages: higher current carrying level,higher irreversible field, better magnetic properties, better mechanical properties, lower cost and so on. HTS wires have huge market prospect. Ion Beam Assisted Deposition(IBAD) is among preparation technology route of HTS wire’s. Based on IBAD route,LaMnO3(LMO) provides the growing surface for YBCO thin films and plays a decisive role in the performance of YBCO. Current carrying capacity of double-sided HTS wires is twice of the one-sided wires. So, double-sided HTS wires have much greater application prospect. Growth of double-sided YBCO films needs double-sided LMO films to provide the growth surface. Therefore, preparation of double-sided LMO film is the key issue. Taking double-sided homo-epitaxial MgO(homo-epi MgO) /IBAD-MgO/ Chemical solution deposition planarization( SDP)-Y2O3 / Hastelloy as substrate, we studied the preparation of double-sided LMO buffer layers by mid-frequency(MF) reactive magnetron sputtering. In more detail:The heating device of the deposition system has been improved. The power for heating the substrate, which is imported into the substrate by a direct-current(DC)current, can provide the required deposition temperature for the growth of the films.This heating device is very simple, good temperature uniformity of double sides and low cost. Furthermore, the preparation of the double-sided LMO films is much more effective.The characteristics of MF magnetron reactive sputtering have been studied, which include the properties of LMO films prepared by three kinds of power supply modes,the deposition rate, the composition and the roughness of LMO films. The following conclusions have been obtained: Firstly, there is obvious hysteresis effect in the sputtering with constant power mode or constant current mode. With the constant voltage mode, hysteresis effect does not exist so the operating point is very stable.Constant voltage mode meets needs of reactive sputtering deposition of LMO film.Secondly, deposition rate is higher by MF reactive sputtering than that of DC reactive sputtering and radio frequency(RF)reactive sputtering, which is up to 100 nm/min or more. Thirdly, the composition of LMO film does not change significantly with thevariation of deposition temperature. Finally, LMO films are very smooth, dense and crack-free.The texture and surface morphology of LMO film have been studied with different growth parameters, which include: sputtering voltage, oxygen flux, substrate temperature, gas(argon) pressure, substrate angle, and tape speed. Optimal growth process for the LMO films has been obtained. Double-sided LMO films prepared with optimal growth process have high uniformity and high quality. The root mean square surface roughness(RMS) is only 1.3 nm. The in-plane textures of double-sided LMO films are both about 4.7 °, while out-of-plane textures are both about 2.7 °. The in-plane texture of LMO film is 1-2°less and the out-of-plane texture is 0.8-1.2°less than the underline MgO. The critical current density of YBCO superconducting thin film prepared on MF-LMO is 3.2 MA/cm2, which indicates that MF-LMO has good practicability with YBCO deposition process.The rapid preparation of double-sided LMO film tape was also been studied. A 20 meter long LMO-buffered tape has been prepared. The uniformity of the texture and surface morphology of the long tape are very excellent. Preparation speed is up to as fast as 40 m/h(thickness about 45 nm). |
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