YBaCuO BICRYSTAL JUNCTIONS AND DC SUPERCONDUCTING QUANTUM INTERFERENCE DEVICES

We have prepared yttria-stabilized-zirconia bicrystal substrates using a simple hot-pressing method. The grain-boundary junctions have been fabricated with YBa2Cu3O7 thin films grown epitaxially on the bicrystals. The patterns are defined by conventional photolithography. The dc and microwave characteristics of the junctions and the dc superconducting quantum interference devices (SQUIDs) have been intensively studied. The current-voltage curves are bridge-typed with noise rounding near the critical current. Resistive tail has been observed in the resistance versus temperature curves. The results are compared with the theoretical prediction for classical Josephson junctions. It is found that the behavior of bicrystal junctions can be described in the frame of classical theory. The deviations are attributed to the nonuniformity of the junctions. The small loop dc SQUIDs demonstrate diffraction and interference effects with regard to the applied magnetic field. A large square-washer with a new configuration has been designed to enhance the effective area of dc SQUID as a magnetometer. It has achieved a magnetic field resolution down to 1 pT/Hz(at 10 Hz) at 77 K.