Grain boundary Josephson devices by YBaCuO films and 77K operations

Magnetron sputtering and screen printing methods were used to fabricate YBaCuO films with thickness of 5 to 30 mu m. With photolithography and razor cutting techniques, the films were formed to bridge type Josephson junctions having a few grain boundaries in the bridge regions. In the devices, clear Shapiro steps and SQUID patterns were observed at 77K. The experiments show 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.