High T/sub c/ bi-epitaxial junctions and dc SQUIDs structured by focused ion beam etching

Focused ion beam etching has been used to pattern dc SQUIDs into previously characterised template bi-epitaxial grain boundary junctions. Using this technique the screening parameter /spl beta//sub L/ can be optimised for a chosen temperature (in our case 30 K). Electrical characteristics, including noise measurements, are presented. A minimal white noise level of 22 /spl mu//spl phi//sub 0//spl middot/Hz/sup -1/2/ (1.8/spl middot/10/sup -29/ J/spl middot/Hz/sup -1/) has been obtained at 20 K. Using bias current modulation the 1/f noise could almost completely be suppressed down to 1 Hz in the entire temperature range (10-65 K).<>