Avci I.Algul, B.P.Bozbey, A.Akram, R.Tepe, M.Abukay, D.2016-02-082016-02-0820070953-2048http://hdl.handle.net/11693/23362We investigated the effect of thermal cycling on the operational performance of YBa2Cu3O7-δ (YBCO) direct current superconducting quantum interference devices (DC-SQUIDs) fabricated onto 24°SrTiO3 (STO) bicrystal substrates. The devices under investigation consist of directly coupled DC-SQUID magnetometer configurations. Thin films having 200nm thicknesses were deposited by dc-magnetron sputtering and device patterns were made by a standard lithography process and chemical etching. The SQUIDs having 4νm-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 400nm 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. © IOP Publishing Ltd.EnglishCritical currentsEtchingLithographyMagnetron sputteringMolecular interactionsSQUIDsSubstratesThermal cyclingDC-magnetron sputteringProtective layersYttrium barium copper oxidesArticle10.1088/0953-2048/20/10/008