Preparation of multilayer films for integrated high-Tc SQUIDs with ramp-edge Josephson junctions

Abstract We proposed a novel multilayer structure having a new combination of oxides for integrated high- T c SQUID with ramp-edge Josephson junctions. La 0.1 Er 0.95 Ba 1.95 Cu 3 O y (L1ErBCO) and SmBa 2 Cu 3 O y (SmBCO) were used as counter- and base-electrodes, respectively. An SrSnO 3 (SSO) layer was deposited as an insulating layer. Prior to deposition of SmBCO, Pr 1.4 Ba 1.6 Cu 2.6 Ga 0.4 O y (P4G4) and SSO were deposited on MgO (100) substrate in order to improve film quality of L1ErBCO/SSO/SmBCO layers. The black-colored P4G4 layer was expected to work as a temperature homogenizer over a whole substrate area during deposition of the upper layers. All the layers except L1ErBCO were deposited by an off-axis magnetron sputtering. An L1ErBCO layer was deposited by a pulsed laser deposition method. A thin Cu-poor L1ErBCO layer was initially deposited to form an adequate barrier on the ramp-edge of SmBCO. Gradiometer arrays having multilayered feedback coils and pickup loops were made in a chip and their proper operation at 77 K was confirmed. The present multilayer structure is promising for application to SQUIDs with more complicated designs.