CeO2 insulating films for application to high-temperature superconducting digital devices

CeO2 thin films as insulating layers for high-temperature superconducting digital devices were studied. The dependence on substrate temperature and oxygen pressure of the surface morphology and crystallinity of CeO2 thin films prepared by pulsed laser deposition were investigated. CeO2 thin films with a flat and closely grained surface were obtained at a relatively low oxygen pressure of 3.6 Pa, whereas higher oxygen pressure led to CeO2 thin films with a rough surface and columnar grains. The recovery of oxygen content in superconducting layers was examined for multilayer structures with CeO2 thin films. Enough oxygen was supplied to the upper and lower superconducting layers when the multilayer was cooled slowly in 3 × 10−4 Pa oxygen pressure after deposition. Resistively shunted junction type I-V characteristics were confirmed for interface-engineered ramp-edge junctions in a multilayer structure including four superconducting layers with CeO2 thin films.