Low Frequency Noise Characteristic in HTS Step-Edge Junction Rf SQUID

Rf SQUIDs have been fabricated on MgO substrate using step-edge YBCO junction. Ion beam etching as a post fabrication trimming process is routinely used to reduce (trim) the critical current of the junction for noise optimization. The white noise of SQUIDs with inductance,
L
_s
= 157 pH can be reduced to 55
μ
Φ
_o
Hz
^−1/2
after the trimming process. However, 1/f noise at low frequency has been found to be degraded after the trimming. Rf SQUIDs with
L
_s
= 130 pH were fabricated and measured. A similar noise performance was achieved in these SQUIDs down to 5 Hz without the need of trimming. The 1/f noise was found to be better than that of the trimmed SQUIDs.