Grain boundary Josephson devices by YBaCuO films and 77 K operations

Magnetron sputtering and screen printing methods were used to fabricate YBaCuO films with thicknesses of 5 to 30 μm. The annealing of the films at 1000°C gave abnormal grain growth. The grain size of the films was about 2 to 70 μm. With photolithography and razor cutting techniques, the films were formed into bridge-type Josephson junctions having a few grain boundaries in the bridge regions. In the devices, clear Shapiro steps and SQUID (superconducting quantum interference devices) patterns were observed at 77 K. The experiments showed that all currents flowing through grain boundaries are Josephson currents in YBaCuO polycrystalline films. Clear Josephson effects were observed in about 30% of the fabricated devices. Such devices may have high potential for high-frequency detectors and SQUID flux sensors operative at 77 K