High T c bi-epitaxial dc SQUIDs structured by focused ion beam etching from single junctions: β L optimisation

Abstract

Focused ion beam etching has been used to pattern dc SQUIDs into previously characterised template bi-epitaxial grain boundary junctions. In this way, the screening parameter β 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 μφ 0·Hz 1 2 (1.8·10 -29 J·Hz -1) has been obtained at 20 K. Using bias current modulation the 1/f noise could be almost completely suppressed down to 1 Hz in the entire temperature range (10–65 K).