Fabrication and characterisation of YBCO single grain boundary step edge junctions

We use ion beam etching techniques to fabricate YBCO step edge junctions (S EJ) on MgO substrates, Argon ion-beam etching (IBE) of the substrate at ang les other than at normal incidence is used to define the step height and an gle. Thin (similar to 300 nm) magnetron sputtered YBCO films are deposited over the step and patterned using microlithography and cold substrate ion-b eam etching techniques. The critical current, I-c, of these SEJs can be con trolled by varying the angle of the step etched into the substrate. Fabrica tion techniques are described which produce one grain boundary at the top o f the step and include a smooth return path thereby avoiding a second grain boundary at the bottom of the step. At 77 K, the current-voltage (I-V) cha racteristics show resistively shunted junction behaviour. These junctions r outinely demonstrate reasonably large IcRN products (0.1-0.6 mV), making th em suitable for applications in high temperature SQUID devices.