Flux Noise Reduction of HTS-SQUIDs via Introduction of Antidots

High-
T
_C
superconducting quantum interference devices (HTS-SQUID), which can be used at near liquid nitrogen temperature, allow for reduction of the SQUID equipment both size and operating costs. However, the noise of HTS-SQUID, which consists of white and 1/f noise is higher than that of low-
T
_C
SQUID. The 1/f noise, particularly prominent in HTS devices, is generated by fluctuations of the critical current in the Josephson junction and by the motion of the magnetic flux trapped in the superconducting thin film. Presence of low-frequency noise is a problem especially in HTS-SQUID applications such as bioinstrumentation, environmental measurement, and magnetic contamination inspection. Nanoscale holes (antidots) in HTS films are known to attract and pin magnetic flux. In this study, we investigate the effect of artificially introduced nanoscale antidots near the junction boundaries on the noise characteristics of bicrystal SQUIDs. We used focused ion beam irradiation to create in YBa
₂
Cu
₃
O
_7-
δ
(YBCO) thin film holes of about 90 nm in diameter. As a result of the antidots introduction, the 1/f noise of the bicrystal SQUID in a magnetic field of 66 μT at 77 K was significantly reduced.