Realization of inclined-sidewall stacked Josephson junction arrays with uniform critical current via barrier layer parameter optimization

Abstract

For the critical issue of wire layer cracking that tends to occur during the wire layer deposition of vertically stacked Josephson junction arrays, this paper proposes an inclined-side stack structure design. By optimizing the stack etching process parameters, inclined-side stacked Josephson junction array samples (containing two Josephson junctions per stack) were successfully fabricated. Focused ion beam cross sectioning and scanning electron microscopy characterization confirmed that this design eliminates the wire layer splitting phenomenon. Furthermore, through precise regulation of the barrier layer parameters of the upper and lower Josephson junctions in the stack, the inconsistency in junction areas caused by the inclined-side structure was effectively compensated, ultimately achieving an inclined stacked Josephson junction array with uniform critical current. Experimental results demonstrate that the fabricated inclined-side stacked devices exhibit excellent performance consistency in a 4.2 K cryogenic environment, and their maximum sustainable current is significantly enhanced compared to that of vertical-structure devices.