Preparation and characterization of planar YBa/sub 2/Cu/sub 3/O/sub x/ flux transformers

Planar magnetometer and gradiometer flux transformers, which can be used for high-temperature superconductor superconducting quantum interference devices (SQUIDs), were fabricated from epitaxial, excimer-laser-deposited YBa/sub 2/Cu/sub 3/O/sub x/ three-layer stacks. The first YBa/sub 2/Cu/sub 3/O/sub x/ layer and the SrTiO/sub 3/ insulator layer were deposited through silicon shadow masks. As the edges of these layers are very smooth, a second YBa/sub 2/Cu/sub 3/O/sub x/ film can grow epitaxially onto the device without forming grain boundaries. It was subsequently patterned by argon ion milling to magnetomer and gradiometer flux transformers with up to 12 turns and 25- mu m 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.<>