Reduction of charge offset drift using plasma oxidized aluminum in SETs

Abstract

Aluminum oxide ({text {AlO}}_x)-based single-electron transistors (SETs) fabricated in ultra-high vacuum (UHV) chambers using in situ plasma oxidation show excellent stabilities over more than a week, enabling applications as tunnel barriers, capacitor dielectrics or gate insulators in close proximity to qubit devices. Historically, {text {AlO}}_x-based SETs exhibit time instabilities due to charge defect rearrangements and defects in {text {AlO}}_x often dominate the loss mechanisms in superconducting quantum computation. To characterize the charge offset stability of our {text {AlO}}_x-based devices, we fabricate SETs with sub-1 e charge sensitivity and utilize charge offset drift measurements (measuring voltage shifts in the SET control curve). The charge offset drift (Delta {Q_0}) measured from the plasma oxidized {text {AlO}}_x SETs in this work is remarkably reduced (best Delta {Q_0}=0.13 , hbox {e} , pm , 0.01 , hbox {e} over approx 7.6 days and no observation of Delta {Q_0} exceeding 1, hbox {e}), compared to the results of conventionally fabricated {text {AlO}}_x tunnel barriers in previous studies (best Delta {Q_0}=0.43 , hbox {e} , pm , 0.007 , hbox {e} over approx 9 days and most Delta {Q_0}ge 1, hbox {e} within one day). We attribute this improvement primarily to using plasma oxidation, which forms the tunnel barrier with fewer two-level system (TLS) defects, and secondarily to fabricating the devices entirely within a UHV system.