| Tl2Ba2Ca2Cu30io (T1-2223) film owns the highest critical temperature in Tl based high temperature superconductor family. Up to now, it is also the superconductor of the highest critical temperature in the world except Hg based high temperature superconductor. T1-2223films are attractive in the worldwide for its high critical current density, low microwave surface resistance (Rs), good stability in moisture. However, because of the hypertoxicity and low melting point for Tl2O, the loss of Tl is very serious during the preparation. Therefore, the growth of high quality T1-2223film, which is suitable for microwave passive device applications, is difficult relatively. In this Ph.d. dissertation, the process condition of Tl-2223film will be researched systemically. An inter-phase based technique is proposed by using the Tl2Ba2CaCu2O8(T1-2212) to convert to T1-2223phase. Utilizing the different ratios of O2/Ar to reduce the annealing temperature and improve the superconducting property of Tl-2223film. Finally, a high temperature superconducting filter operating below108K is fabricated on the double-sided T1-2223thin films. The main contents are as follows:1. The precursor film is deposited on the (00l) LaA103substrates by dc magnetron sputtering. The growth condition of the inter-phase T1-2212in the argon is researched to obtain the optimal process which can make T1-2212convert to T1-2223phase completely.2. Combined with the annealing condition of T1-2212, the annealing process of T1-2223film in the argon is studied in this paper. In the optimal condition, the T1-2223film crystallizes compactly and orderly, with good lattice-periodicity and typical features of obvious layer growth. The film orients with the c-axis and owns epitaxial structure with substrate. The critical temperature is about115K. The critical current density is about0.03MA/cm2.3. The influence of oxygen on T1-2223film is researched in the first place. Secondly, the process of T1-2223film annealed in different ratios of O2/Ar is studied, In addition, the result of the precursor film annealed in the flowing oxygen directly is also discussed. The result shows that Tl-2223film annealed in the low ratio of O2/Ar (1%-5%) owns the high crystal quality. Furthermore, the crystallization of the film is uniform and dense. The film owns high purity of Tl-2223phase and orients with the c-axis. In addition, the critical current density can raise an order of magnitude compare to the result annealing in the argon. It is up to the105A/cm2. As for the result of the precursor film annealing in the flowing oxygen, the critical current density can reach to1MA/cm2. The critical temperature is only about115K.4. The influence of third annealing process in the flowing oxygen on Tl-2223film is researched. The Tl-2223films which prepared in Ar and O2/Ar (1%) are annealed in the third process in the flowing oxygen. The result shows that the highest critical temperature of the films reached120K and the critical current density of the films exceeded2MA/cm. In addtion, the Tl-2212phase appeared after the third annealing. Utilizing inter-phase based technique, double-sided Tl-2223films are fabricated on the10mm×10mm LaAlO3substrate. After the third annealing in the flowing oxygen, the films of two sides crystallize uniformly and compactly. Both sides are homogeneous. The critical temperature of the two sides is about120±1K. The critical current density of the films is4.2MA/cm2on the upside and3.9MA/cm2on the downside at77K. The microwave surface resistance Rs is346μΩ (77K,10GHz). This result has met the standard of preparation of superconducting filter.5. A3-pole Chebyshev filter is fabricated on the10mm×10mm double sided Tl-2223thin films with4%relative bandwidth and a center frequency of4.0GHz. The measurements of the filter have shown that the insertion loss in the passband is0.088dB and0.27dB when the filter works at77K and102K, respectively. Different characteristics of the filter have been tested by varying the operating temperature. Performance analysis shows that the designed filter can work stably at the temperatures around102K. Furthermore, its maximum operating temperature can be up to108K. Considering the high performance of the Tl-2223superconducting filter at a temperature above100K, it is promising for applications in satellites and deep space communications. |
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