Analysis of electrical characteristics and magnetic field dependences of YBCO step edge and bicrystal grain boundary junctions for rf-SQUID applications

The dc characteristics and magnetic field dependences of Y-Ba-Cu-O bicrystal grain boundary junctions (BGBJs) and step edge junctions (SEJs) were investigated for fabrication of rf-SQUIDs. Test junctions with up to 8 μm widths as well as the junctions of the two types of junction-based rf-SQUID were studied. The SEJs typically showed lower Jc and higher ρN as compared to the BGBJs, resulting in close IcRN products. All the BGBJs showed classical field dependent Ic following their junction width, resembling Fraunhofer patterns. The field sensitivity of the BGBJs' Uc led to low yield submicron BGBJ rf-SQUIDs partially impaired by the Earth's magnetic field. Two major behaviours of low and high field dependences of Ic were observed for the SEJs. Only the low field-sensitive SEJs resulted in micron size junction rf-SQUIDs not impaired by the Earth's magnetic field. The low field-sensitive SEJs led to low I/f noise magnetically stable rf-SQUIDs appropriate for applications in unshielded environments at 77 K.