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Applied Physics Letters

YBa2Cu3O7− δ superconducting quantum interference devices with metallic to insulating barriers written with a focused helium ion beam

Ethan Y. Cho, M. K., Chuong Huynh, Kevin Pratt, Douglas N. Paulson, V. N. Glyantsev, R. C. Dynes, Shane A. Cybart

Published Jun 22, 2015• 69 citations
Publisher

Abstract

In this work, we demonstrate the ability to fabricate superconducting quantum interference devices (SQUIDs) by directly writing Josephson junctions into the plane of YBa2Cu3O7−δ thin films with a focused helium ion beam. This technique allows for the control of the Josephson barrier transport properties through the single parameter, ion dose. SQUIDs written with a dose of 4 × 1016 ions/cm2 had metallic barrier junctions that exhibited nearly ideal electrical transport characteristics at 50 K and a flux noise of 20 μΦ0/Hz at 10 Hz. At higher irradiation doses, the SQUIDs had insulating barrier Josephson junctions with a quasi particle energy gap edge at 20 meV.

DOI
10.1063/1.4922640

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In this work, we demonstrate the ability to fabricate superconducting quantum interference devices (SQUIDs) by directly writing Josephson junctions into the plane of YBa2Cu3O7−δ thin films with a focused helium ion beam. This technique allows for the control of the Josephson barrier transport properties through the single parameter, ion dose. SQUIDs written with a dose of 4 × 1016 ions/cm2 had metallic barrier junctions that exhibited nearly ideal electrical transport characteristics at 50 K and a flux noise of 20 μΦ0/Hz at 10 Hz. At higher irradiation doses, the SQUIDs had insulating barrier Josephson junctions with a quasi particle energy gap edge at 20 meV.
In this work, we present nanoscale superconducting quantum interference devices (SQUIDs) with dimensions as small as 10 nm from the high-transition-temperature superconductor YBa2Cu3O7−δ (YBCO). The SQUID features and Josephson junctions are directly written into a 35-nm thick YBCO film with a focused helium ion beam. We integrate these nano-SQUIDs with directly written nano-isolated inductively coupled control lines to demonstrate a low power superconducting output driver capable of transimpedance conversion over a very wide temperature range of 4–50 K.
Abstract The reliable fabrication of high-sensitivity superconducting quantum interference devices (SQUIDs) with high critical transition temperature (high- T c ) is crucial for many practical applications such as weak magnetic sensing. In this work, we report the first realization of the YBa 2 Cu 3 O 7− δ (YBCO) radio frequency SQUIDs (rf SQUIDs) based on focused helium ion beam (FHIB) technique. A series of YBCO rf SQUIDs with high consistency were fabricated using a 30 keV FHIB with different helium ion (He + ) dose. The dose-dependent characteristics of the fabricated devices were systematically investigated at a temperature of 77 K. The experimental results verify that the variation in He + dose can effectively modulate the junction parameters and thereby the device noise performance. A non-monotonic white noise trend with increasing He + dose was observed, which could be primarily attributed to the transition of operational working regime of the fabricated rf SQUIDs. Based upon the dose optimization, a flux noise of 58 μ Φ 0 / H z 1 / 2 , corresponding to a field sensitivity of 185 f T / H z 1 / 2 , was achieved with our current device configuration. Approaches to further optimize the overall device performance are also discussed. Our work demonstrates FHIB-based high- T c SQUIDs with high junction parameter consistency a promising candidate for the implementation of multi-channel weak magnetic field detection systems and might hopefully serve as a platform for validating the theoretical models of high- T c SQUIDs.
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.
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.
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 demonstrate a direct writing method for the fabrication of planar Josephson junctions from high-quality superconducting niobium titanium nitride (NbTiN) thin films, by creating local disorder using focused He ion beam irradiation. We control the suppression of superconductivity in NbTiN as a function of the helium ion beam fluence, enabling us to successfully fabricate Josephson junctions with highly tunable weak links ranging from the metallic to the insulating phase, utilizing the continuous nature of the disorder-induced superconductor-insulator transition. We demonstrate the successful fabrication of both superconductor-normal metal-superconductor (SNS) and superconductor-insulator-superconductor (SIS) type of devices, and show that we can achieve an exceptionally wide range ( ∼ 5 orders of magnitude) of critical current densities and junction resistances. The SNS-type junctions follow closely the ideal resistively and capacitively shunted junction behavior, have high characteristic voltages up to ∼ 1.5 mV , and show Shapiro steps up to very high orders, while the SIS junctions also follow established theories well. The results suggest that the junctions are suitable for a wide range of applications in superconducting electronics because of the excellent mechanical, electrical, and microwave properties of NbTiN. In particular, as NbTiN has previously been used to fabricate high-quality factor microwave resonators, we see the method as a promising and simple way to realize high-frequency superconducting qubits and other quantum devices using only a single superconducting film.