| In recent years, with the rapid development of microelements and high-density integrated circuit products, thin film materials have been more and more widely used. At the same time, superconducting thin film is becoming a new material of superconducting electronic devices due to the advantages such as fast response in the superconducting state, high sensitivity and fast processing speed of superconducting processors, etc. Its critical state can identify weak signals; its feeble surface resistance can be used in making electronic devices. To ensure the high performance of electronic devices, the preparation of high-quality oxide superconducting thin films is especially important. Bi line (Bi-Sr-Ca-Cu-O) high-temperature superconductor has unparalleled advantages compared with other superconductors:Bi-based superconductor does not contain rare-earth or toxic elements; it has short coherence length, high anisotropy ratio and strong two-dimensional characteristics; its multi-layer structure can form intrinsic Josephson junction. Some of these characteristics have been used for the corresponding superconducting devices. Bi-based superconductor complex structure belongs to perovskite-type multi-layer structure of crystals. The preparation of Bi-based thin films is difficult because of the oxygen non-chemical content dose ratio, incommensurate modulation structure, the cation disorder distribution, and many defects. Therefore, the preparation of high-quality Bi-2212 thin film has a very important research and application value. In this paper, molecular beam epitaxy has been used to prepare BSCCO series film at different growth conditions and different oxide substrates, and a study has been carried out in searching for the optimum growth conditions and improving the film quality.First of all, the in-situ reflection high-energy electron diffraction (RHEED) was used to observe the states of oxide substrate before the thin film growth and the initial state of thin film growth, and then the thin films were prepared under different growth conditions. It was found that the phase purity is highest and the crystalline quality is better when Bi-2212 thin film epitaxial growth was conducted on the MgO (100) single crystal substrate under the conditions of substrate temperature at 699℃, ozone partial pressure at 2.2×104 Pa. Lowering substrate temperature can be in favor of raising nucleation rates of thin film, which is conducive to the formation of small-core and dense continuous film. At the same time, on the conditions of constant partial pressure of oxygen film composition, Bi-2212 phase has the trend to be transformed to Bi-2223 phase with the increase of substrate temperature, and decreasing the temperature, Bi-2223 phase has the trend to be transformed to Bi-2212 phase. Among all of this, Bi-2212 phase has the highest stability. Bi-2212 and Bi-2223 phase are all metastable. The STO (100) single crystal substrate for the growth of Bi-2212 thin film on the conditions of substrate temperature 699℃, ozone partial pressure at 2.2×104Pa, was chosen to compared with Bi-2212 film prepared on the MgO substrate. It was found that the phase purity and crystallization quality of film was improved when the mismatch decreases.Bi-2212 thin film has a high anisotropy coefficient, anisotropy ratioξab(0)/ξc(0)=30～60. For the latter study of Seebeck effect, we prepared Bi-2212 films on the LaAlO3 substrates.In this paper, the study to the growth conditions of Bi-2212 and the analysis for the growth mechanism can be the basis of preparing higher-quality Bi-2212 film, and provide high-quality films for the application of Bi-2212 in the future. |
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