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IEEE Transactions on Applied Superconductivity

Tuning Y–Ba–Cu–O Focused Helium Ion Beam Josephson Junctions for Use as THz Mixers

Anthony Cortez, Ethan Y. Cho, Hao Li, Daniel Cunnane, Boris S. Karasik, Shane A. Cybart

Published Mar 18, 2019• 12 citations
Publisher

Abstract

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.

DOI
10.1109/tasc.2019.2905166

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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.
We have fabricated spiral THz antennas containing embedded high TCYBa2Cu3O7 (YBCO) focused helium ion beam Josephson junctions (JJ) for characterization of their high frequency characteristics. The values of the resistance and critical current of the junctions are controlled through the irradiation dose and geometry of the junction. We observe several orders of Shapiro steps in the current voltage characteristics of the device when irradiated with 0.6 THz and a single step when irradiated at 2.52 THz.
YBa2_22​Cu3_33​O7_77​ nano-constriction Josephson junctions and SQUIDs fabricated by focused helium-ion-beam irradiation
By focused 30 keV30\,\mathrm{keV}30keV He ion beam irradiation, epitaxially grown YBa2_22​Cu3_33​O7_77​ (YBCO) thin films can be driven from the superconducting to the insulating state with increasing irradiation dose. A properly chosen dose suppresses superconductivity down to 4 K4\,\mathrm{K}4K, while crystallinity is still preserved. With this approach we create areas of normal-conducting YBCO that can be used to define resistively shunted constriction-type Josephson junctions (cJJs) on the nanometer scale. We also demonstrate that the fabricated cJJs can be incorporated in direct current superconducting quantum interference devices and can be used as detector junctions in THz antennas.
Ion-irradiated YBa2_22​Cu3_33​O7_77​ Josephson arrays
We designed, fabricated and tested short one dimensional arrays of masked ion-irradiated YBa2_22​Cu3_33​O7_77​ Josephson junctions (JJ) embedded into log-periodic spiral antennas. Our arrays consist of 4 or 8 junctions separated either by 960~nm or 80~nm long areas of undamaged YBCO. Samples with distanced junctions and with closely spaced junctions showed qualitatively different behaviors. Well separated arrays demonstrated giant Shapiro steps in the hundreds-GHz band at 66K and were tested as Josephson mixers with improved impedance matching. All closely spaced arrays behaved as one junction with a lower superconducting transition temperature, hence forming a single weak link on distances up to 880~nm. Such design opens a new way to increase the Ic_{c}c​RN_{N}N​ product of ion-irradiated junctions and we speculate that the phenomena and physics behind it might be similar to the so-called "giant" Josephson coupling observed in cuprates.
Using focused helium-ion beam irradiation, we fabricated in-plane, high-Tc YBa2Cu3O7−δ Josephson junctions. By varying the dose of the irradiation, we tune the junction barriers from metallic to insulating and investigate how this transition affects microwave-driven dynamics. As the barrier transitions from metallic to insulating, the oscillatory response of the Shapiro steps to the RF power changes dramatically. On either side of the metal–insulator transition, the devices exhibit clean integer Shapiro steps without half-integer features, demonstrating that the current–phase relation is dominated by the first harmonic and that the excess current is minimal. The current–voltage response is well described by the resistively, capacitively shunted junction model assuming a single-harmonic current–phase relation. This behavior indicates well-controlled junction properties suitable for a wide range of superconducting electronics, including detectors, mixers, and high-density integrated circuits.
Abstract We designed, fabricated and measured short one-dimensional arrays of masked ion-irradiated YBa 2 Cu 3 O 7 Josephson junctions embedded into log-periodic spiral antennas. They consist of four or eight junctions separated either by 960 nm or 80 nm long areas of pristine material. Large spacing arrays show ‘giant’ Shapiro steps in the hundreds-GHz band at 66 K and are tested as Josephson mixers with improved impedance matching. On the contrary, small spacing arrays behave as one junction with a lower superconducting transition temperature, hence forming a single weak link on distances up to 880 nm. Such design opens a new way to increase the I c R n product of the devices, and therefore the efficiency of Josephson mixers. Hints on the origin of the observed long range proximity effect are proposed.
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.