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IEEE Transactions on Applied Superconductivity

Temporal Stability of Y–Ba–Cu–O Nano Josephson Junctions from Ion Irradiation

Shane A. Cybart, Peter Roediger, Ke Chen, James M. Parker, Ethan Y. Cho, Travis J. Wong, R. C. Dynes

Published Nov 21, 2012• 22 citations
Publisher

Abstract

We investigate the temporal stability of YBa2Cu3O7-δJosephson junctions created by ion irradiation through a nanoscale implant mask fabricated using electron beam lithography and reactive ion etching. A comparison of current-voltage characteristics measured for junctions after fabrication and eight years of storage at room temperature show a slight decrease in critical current and increase in normal state resistance consistent with broadening of the weak link from diffusion of defects. Shapiro step measurements performed eight years after fabrication reveal that device uniformity is maintained and is strong evidence that these devices have excellent temporal stability for applications.

DOI
10.1109/tasc.2012.2227646

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We present Josephson junctions fabricated from high transition temperature superconductor YBa2Cu3O7coupled to spiral THz antennas. The fabrication process involves creating a Josephson junction at the center of a superconducting bridge embedded into a THz spiral antenna using irradiation from a focused helium ion beam. For low doses of helium irradiation, the junctions have metallic barriers and operate at temperatures as high as 67 K. For higher doses of irradiation, insulator barriers are created. These devices have higher resistance but require cooling to lower temperatures (~10 K) due to smaller critical currents. Through optimization of the dose and by trimming the width of the junctions, we have created high resistance devices to improve the impedance match to a spiral antenna. Under 90-GHz radiation, we observe up to 17 Shapiro steps in the I-V curve out to approximately 3 mV at a temperature of 10 K.
Ion-irradiated YBa2_22​Cu3_33​O7_77​ Josephson arrays
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Abstract The Josephson junction (JJ) is the corner stone of superconducting electronics and quantum information processing. While the technology for fabricating low T c JJ is mature and delivers quantum circuits able to reach the “quantum supremacy”, the fabrication of reproducible and low-noise high- T c JJ is still a challenge to be taken up. Here we report on noise properties at RF frequencies of recently introduced high- T c Josephson nano-junctions fabricated by mean of a Helium ion beam focused at sub-nanometer scale on a YBa 2 Cu 3 O 7 thin film. We show that their current-voltage characteristics follow the standard Resistively-Shunted-Junction (RSJ) circuit model, and that their characteristic frequency f c = (2 e / h ) I c R n reaches ~300 GHz at low temperature. Using the “detector response” method, we evidence that the Josephson oscillation linewidth is only limited by the thermal noise in the RSJ model for temperature ranging from T ~ 20 K to 75 K. At lower temperature and for the highest He irradiation dose, the shot noise contribution must also be taken into account when approaching the tunneling regime. We conclude that these Josephson nano-junctions present the lowest noise level possible, which makes them very promising for future applications in the microwave and terahertz regimes.