DC Sqiids made from YBa 2Cu 3O 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 YBa 2Cu 3O y samples on MgO substrates 3 and from epitaxial films on SrTiO 3 (100) substrates 4. The films were patterned using either ion-implanting to selectively convert the superconductor into an insulator without actually removing any material 1,5, laser ablation to pattern a loop into the film by removing material 6, 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 -5Φ O/Hz 1/2 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 -3Φ 0/Hz 1/2 at 74 K.