Development of planar first order gradiometer coupled to HTS SQUID sensor

The HTS SQUID sensors coupled to an on-chip integrated planar gradiometric pick-up loop were fabricated using highly reliable advanced micro-fabrication techniques such as deposition of superconducting thin films by Pulsed Laser Deposition (PLD), UV photolithography and RF ion beam etching. It may be noted that use of wire wound gradiometers and approaches based on electronic subtraction of sensor outputs to realize synthetic gradiometers have not been entirely satisfactory. We have designed a first order planar gradiometer with two planar loops in opposition with the Josephson weak links in the form of microbridges located at the centre. Bicrystal SrTiO₃ substrates with a 24° misorientation angle were used for realizing the Josephson weak links using YBCO thin films, as well as HTS planar gradiometer coupled to a HTS SQUID sensor. The performance of these devices are evaluated.