Role of atomic oxygen produced by an electron cyclotron resonance plasma in the oxidation of YBa2Cu3O7-x thin films studied by in situ resistivity measurement
ABSTRACT In situ resistivity measurements have been performed to monitor the effect of activated oxygen (atomic oxygen, oxygen ions) on films subjected to an electron cyclotron resonance (ECR) oxygen plasma. The resistivity of c‐axis and mixed a+c oriented YBa 2 Cu 3 O 7-x films, which were deposited in situ by 90° off‐axis magnetron sputtering, was measured as a function of time in an ECR oxygen plasma. The resistivity of a film in the plasma corresponds to that found in the same film subjected to higher oxygen pressure when no plasma is present. The resistivity is shown to be determined by the flux of atomic oxygen. The steady‐state concentration in the film is found to depend on the kinetics of oxygen dissociation at the film surface. From the temperature dependence of the activity of atomic oxygen, we determined the activation energy for the decomposition of O 2 at the surface of films with mixed a+c axis orientation and c‐axis orientation to be ∼1.3 eV and ∼2.1 eV, respectively. It is proposed that in the presence of atomic oxygen, the phase diagram of oxygen content versus temperature of YBa 2 Cu 3 O 7-x is changed in a way that depends on the atomic oxygen flux.
- [Show abstract] [Hide abstract]
ABSTRACT: The issue of oxygen diffusion through insulating layers to buried superconductor films is common to any multilayer structure based on YBCO. Our earliest technique for obtaining fully oxidized underlayers on a practical time scale used reduced growth temperatures for strontium titanate insulating films to introduce defects which enabled oxygen diffusion while maintaining the integrity of electrical isolation. Since this approach did not work well with Sr-Al-Ta-O (SAT) and Sr-Al-Nb-O (SAN) insulators which have more desirable dielectric properties, a plasma oxidation process was introduced. For digital circuits based on HTS Josephson junctions where buried groundplanes must be fully oxidized, plasma oxidation had profound effects on the properties of cobalt or calcium-doped YBCO films used for N-layers in SNS edge junctions, increasing function critical currents by a factor of five. These experiments offer some insight into the role of oxygen in determining both individual junction properties and junction reproducibility. A third approach to oxidation of buried films relies on “oxygen vias” patterned in the insulating layer to permit oxygen to diffuse in the a-b plane of YBCO films instead of diffusing through the insulating layer. We designed and measured test structures which set a practical limit of 20-30 micrometers for via sparingIEEE Transactions on Applied Superconductivity 07/1999; · 1.32 Impact Factor