Investigation of the effect of thermal cycling on the device performance of YBa2Cu3O7-delta DC-SQUIDs


Avci I., Algul B. P. , Bozbey A., Akram R., Tepe M., Abukay D.

SUPERCONDUCTOR SCIENCE & TECHNOLOGY, vol.20, no.10, pp.944-949, 2007 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 20 Issue: 10
  • Publication Date: 2007
  • Doi Number: 10.1088/0953-2048/20/10/008
  • Title of Journal : SUPERCONDUCTOR SCIENCE & TECHNOLOGY
  • Page Numbers: pp.944-949

Abstract

We investigated the effect of thermal cycling on the operational performance of YBa2Cu3O7-delta (YBCO) direct current superconducting quantum interference devices (DC-SQUIDs) fabricated onto 24 degrees SrTiO3 (STO) bicrystal substrates. The devices under investigation consist of directly coupled DC-SQUID magnetometer configurations. Thin films having 200 nm thicknesses were deposited by dc-magnetron sputtering and device patterns were made by a standard lithography process and chemical etching. The SQUIDs having 4 mu m-wide grain boundary Josephson junctions (GBJJs) were characterized by means of critical currents, peak-to-peak output voltages and noise levels, depending on the thermal cycles. In order to achieve a protective layer for the junctions against the undesired effects of thermal cycles and ambient atmosphere during the room temperature storage, the devices were coated with a 400 nm thick YBCO layer at room temperature. Since the second layer of amorphous YBCO is completely electrically insulating, it does not affect the operation of the junctions and pick-up coils of magnetometers. This two-layered configuration ensures the protection of the junctions from ambient atmosphere as well as from the effect of water molecules interacting with the film structure during each thermal cycle.