YBA2CU3O7 RAMP-TYPE JUNCTIONS AND SUPERCONDUCTING QUANTUM INTERFERENCE DEVICES WITH AN ULTRATHIN BARRIER OF NDGAO3

We have fabricated ramp-type Josephson junctions and SQUIDs (superconducting quantum interference devices) using an ultrathin barrier layer of NdGaO3 as weak contact between the YBa2Cu3O7 electrodes. The junctions operate up to 82 K, exhibiting current-voltage characteristics of the resistively-shunted-junction type. A normal-state resistance of up to 30 OMEGA at a junction width of 5 mum and a characteristic voltage in excess of 100 muV at 77 K are obtained. We find hysteretic behavior below 70 K and an intrinsic junction capacitance of about 0.15 muF/cm2 at 4 K. SQUIDs show a transfer function delta V/delta PHI of 50 muV/PHI0 at an inductance of 40 pH at 77 K. Thus we observe excellent Josephson properties at a thickness of the NdGaO3 barrier of 2 nm. (C) 1994 American Institute of Physics.