Preparation and Characterization of Planar YBa2Cu3Ox Flux Transformers

Planar magnetometer and gradiometer flux transformers, which can be used for HTSC-SQUIDs, were fabricated from epitaxial, excimer laser deposited YBa2Cu3Ox-SrTiO3-YBa2Cu3Ox three-layer stacks. The first YBa2Cu3Ox layer and the SrTiO3 insulator layer were deposited through silicon shadow masks. As the edges of these layers are very smooth, a second YBa2Cu3Ox film can grow epitaxially onto the device without forming grain boundaries. It was subsequently patterned by argon ion milling to magnetometer and gradiometer flux transformers with up to 12 turns and 25 gm linewidth. The flux transformers were characterized by resistance and persistent current measurements, using a conventional SQUID magnetometer. At 77 K a persistent current of about 1 mA was measured in the flux transformer with 50 mu m linewidth.