Junction fabrication by shadow evaporation without a suspended bridge

Abstract

We present a novel shadow evaporation technique for the realization of junctions and capacitors. The design by e-beam lithography of strongly asymmetric undercuts on a bilayer resist enables in situ fabrication of junctions and capacitors without the use of the well-known suspended bridge (Dolan 1977 Appl. Phys. Lett. 31 337-9). The absence of bridges increases the mechanical robustness of the resist mask as well as the accessible range of the junction size, from 10(-2) µm(2) to more than 10(4) µm(2). We have fabricated Al/AlO(x)/Al Josephson junctions, phase qubit and capacitors using a 100 kV e-beam writer. Although this high voltage enables a precise control of the undercut, implementation using a conventional 20 kV e-beam is also discussed. The phase qubit coherence times, extracted from spectroscopy resonance width, Rabi and Ramsey oscillation decays and energy relaxation measurements, are longer than the ones obtained in our previous samples realized by standard techniques. These results demonstrate the high quality of the junction obtained by this bridge-free technique.

Kerr coefficients of plasma resonances in Josephson junction chains

“…Junctions and transmission lines are fabricated in the same fabrication step by shadow evaporation of aluminum on a silicon substrate. We use 100 keV electron beam lithography with an asymmetric undercut in the two-layer resist (PMMA/MAA, PMMA) to deposit all unwanted structures on the resist walls 21,22 . The sample parameters are summarized in Table I.…”

Microwave Characterization of Josephson Junction Arrays: Implementing a Low Loss Superinductance

“…1. We fabricated the junctions by e-beam lithography and double angle evaporation of aluminum using the bridge-free technique of [20,21]. Prior to aluminum deposition, the substrate is cleaned of resist residues using an oxygen plasma [22].…”

Demonstrating a Driven Reset Protocol for a Superconducting Qubit

“…The ratio =À up determines the fidelity of the ground state preparation and must therefore be much greater than 1. The measurements presented here were performed in a standard circuit QED setup on an aluminum transmon qubit, fabricated using a bridgeless double-angle evaporation technique [17,18], inside a three-dimensional copper cavity, thermally anchored to the mixing chamber of a dilution refrigerator with a base temperature of 17 mK. The cavity was mounted inside a copper shield coated with infraredabsorbing material on the inside.…”