| Budget Amount *help |
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 2001: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2000: ¥2,600,000 (Direct Cost: ¥2,600,000)
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| Research Abstract |
The "123" high-Tc superconductors are very sensitive to oxygen content and are liable to cause oxygen deficiency. We attempted to establish the methods for recovery treatment of a degraded superconducting thin film and for prevention against degradation of or recovery treatment of a lower-layer superconducting thin film in insulator deposition. The initial plan was to use plasma induced by sputtering and plasma induced by microwaves in this investigation. Though satisfactory results were obtained by the former method, the results obtained by the latter method were not good. Activated oxygen plasma (AOP) through which EuBa_2Cu_3O_7(EBCO) thin films with Tc=90 K were synthesized by DC magnetoron sputtering using a high-quality sintered superconducting target was used as a treating plasma. The results are summarized as follows.
a) Recovery treatment for degraded EBCO thin films : When the degraded EBCO was indirectly exposed to AOP, the high-quality characteristics of the film were complet
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ely recovered. The appropriate AOP recovery conditions were annealing temperature of 450-700 ℃, plasma exposing time of more than 30 min and oxygen introducing pressures after annealing (Pox) of above 2 kPa. The AOP recovery treatment technology was newly developed for oxide superconductors.
b) Application to insulator/superconductor multi-layers and protective layer : SrTiO_2(STO) and CeO_2 thin films were deposited on as-grown EBCO, and the influence on the lower-layer EBCO was examined. STO caused marked deterioration of the EBCO thin films compared with CeO_2. By means of insertion of 50-Å-thick CeO_2 between EBCO and STO, the degradation of the lower-layer EBCO was mitigated. Though the AOP treatment was effective for recovery of the multi-layer, the degree of recovery depended on STO film thickness and Pox. On the other hand, CeO_2 films were deposited on EBCO films at 500-570 ℃ in AOP, but the lower-layer EBCO did not degenerate. When EBCO with 2000-Å-thick CeO_2 was exposed to the atmosphere with relative humidity of 70 %, the EBCO films exhibited high Tc values for 2 months. Less
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