Ion-beam etching of substrate steps: SNS compared to step-edge grain boundary Josephson-junctions

Abstract

For “SNS step and gap”, and for “step-edge grain boundary”, Josephson-junctions steep steps in the substrate are needed to get either a break in the YBa₂Cu₃O₇-film (SNS) or to induce grain boundaries in the growth of the YBa₂Cu₃O₇-film across the step (step-edge).

We report on the influence of the profiles of ion-beam etched substrate steps in MgO and SrTiO₃ on the growth of YBa₂Cu₃O₇-films at the step-edges and on the electrical properties of the different Josephson-junction types. On MgO we have fabricated Josephson-junctions of the SNS-type (using Ag as “N”), while for the step-edge junctions SrTiO₃ was used. Both types of junctions exhibit Josephson-effects at 77 K. For the steps we use photoresist AZ 5214 E with steep edges as the mask. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) analysis on differently fabricated steps are presented and compared to the electrical properties of patterned YBa₂Cu₃O₇-films grown on them. Especially the role of material redeposited at the edge of a step during ion-beam etching is discussed. The reproducible step edge profiles are reflected in reproducible electrical properties of the Josephson-junctions and dc-SQUIDs (on chip and chip to chip).