DC Sqiids made from YBa₂Cu₃O_y

Abstract

This paper reports on progress made at IBM in the fabrication of HiTc dc SQUIDs (Superconducting QUantum Interference Devices)1,2. We have fabricated SQUIDs from polycrystalline YBa2Cu3Oy samples on MgO substrates3 and from epitaxial films on SrTiO3 (100) substrates4. The films were patterned using either ion-implanting to selectively convert the superconductor into an insulator without actually removing any material1,5, laser ablation to pattern a loop into the film by removing material6, or a conventional ion milling process to selectively remove material using a photoresist mask. In the case of the polycrystalline films, the naturally occurring grain boundaries provide the weak link or Josephson junction behavior in a stripe that is much larger in size than the superconducting coherence length. We have measured the noise amplitude of one such SQUID made on MgO to be about1 × 10-5ΦO/Hz1/2 at 1000 Hz and 40 K. Loops formed from true epitaxial films containing many twin boudaries will not operate as dc SQUIDs unless the films are damaged across each link. A SQUID formed in this way operated in liquid nitrogen and had an estimated white noise performance of1 × 10-3Φ0/Hz1/2 at 74 K. © 1988, Elsevier Science Publishers B.V.. All rights reserved.