Effect of ultra-thin SrTiO{sub}3 seed layer on the microwave surface resistance of YBa{sub}2Cu{sub}3O{sub}7 films deposited on (1 0 0) MgO

摘要

RHEED control led ultra-thin buffer layers of SrTiO{sub}3 have been deposited on (100) MgO by pulsed laser deposition to grow YRa{sub}2Cu{sub}3O{sub}7 films for microwave applications. A buffer layer with a thickness from 5 to 40 unit cells of SrTiOv3 is sufficient to expand to more than 60℃ the range of deposition temperatures for which a low microwave surface resistance [Rs(10GHz, 77 K) <0.5 mΩ] is obtained. The Rs values are as low as those obtained on LaAlO{sub}3 substrates, furthermore they present a slightly lower magnetic field dependency. The XRD Φ-scans show that the SrTiO{sub}3 seed layer induces an oriented epitaxial growth with the [100] axis of YBCO parallel to the one of MgO over this broadened range of deposition temperatures. This seed layer promoting effect is not observed with other oxides such as Ba{sub}0.15Sr{sub}0.85TiO{sub}3, CeO{sub}2, Ce{sub}(1-x)La{sub}xO{sub}2.