Superconducting Electronics: High-Transition-Temperature Superconducting Quantum Interference Devices
EY Cho, MK Ma, C Huynh, K Pratt, DN Paulson, VN Glyantsev, RC Dynes SA Cybart
Applied Physics Letters 106 (0), 000000
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 4x1016 ions/cm2 had metallic barrier junctions that exhibited nearly ideal electrical transport characteristics at 50 K and a flux noise of 20 μΦ0 at 10 Hz. At higher irradiation doses, the SQUIDs had insulating barrier Josephson junctions with a quasi particle energy gap edge at 20 meV.
SA Cybart, EY Cho, TJ Wong, VN Glyantsev, JU Huh, CS Yung, BH Moeckly, JW Beeman, E Ulin-Avila, SM Wu, RC Dynes
Applied Physics Letters 104 (6), 062601
We have fabricated and tested two-dimensional arrays of YBa2 Cu 3O7− δ superconducting
quantum interference devices. The arrays contain over 36 000 nano Josephson junctions
fabricated from ion irradiation of YBa2Cu3O7-δ through narrow slits in a resist-mask that
was patterned with electron beam lithography and reactive ion etching. Measurements of
current-biased arrays in magnetic field exhibit large voltage modulations as high as 30 mV.
SA Cybart, SM Anton, SM Wu, J Clarke, RC Dynes
Nano letters 9 (10), 3581-3585
Very large scale integration of Josephson junctions in a two-dimensional series−parallel array has been achieved by ion irradiating a YBa2Cu3O7-δ film through slits in a nanofabricated mask created with electron beam lithography and reactive ion etching. The mask consisted of 15820 high aspect ratio (20:1), 35 nm wide slits that restricted the irradiation in the film below to form Josephson junctions. Characterizing each parallel segment k, containing 28 junctions, with a single critical current Ick we found a standard deviation in Ick of about 16%.
SA Cybart, SM Wu, SM Anton, I Siddiqi, J Clarke, RC Dynes
Applied Physics Letters 93 (18), 182502-182502-3
We have fabricated a series array of 280 superconducting quantum interference devices(SQUIDs) using YBa2Cu3O7−δ thin film ion damage Josephson junctions. The SQUID loop areas were tapered exponentially so that the response of the current-biased array to magnetic field is a single voltage spike at zero field. We fitted the current-voltage characteristics of the array to a model in which we summed the voltages across the SQUIDs assuming a resistively shunted junction model with a normal distribution of SQUID critical currents. At 75 K the standard deviation of these critical currents was 12%.
Superconducting Electronics: Josephson Junctions
S Cybart, P Roediger, K Chen, J Parker, E Cho, T Wong, R Dynes
IEEE
We investigate the temporal stability of YBa2Cu3O7 Josephson junctions created by ion irradiation through a nano-scale 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 weaklink from diffusion of defects. Shapiro step measurements performed 8 years after fabrication reveal that device uniformity is maintained and is strong evidence that these devices have excellent temporal stability for applications.
SA Cybart, K Chen, RC Dynes
Applied Superconductivity, IEEE Transactions on 15 (2), 241-244
Reproducible low resistance lumped element Josephson junction arrays are desired for many microwave applications. Using our established process of electron beam lithography and ion damage, we have fabricated and demonstrated high quality YBa2Cu3O7-δ superconductor-normal superconductor-superconductor (SS'S) in-plane Josephson junctions. Single junctions and multiple junction arrays with as many as 50 junctions in series have been investigated. These junctions are in close proximity and offer several possible applications. Current-voltage characteristics for single junctions are consistent with the resistively shunted junction model. Junction in pairs have been fabricated which show nearly identical characteristics. Rounding near the critical current occurs for larger number arrays which we attribute to junction nonuniformity. Microwave measurements reveal sharp giant Shapiro steps for junction pairs and 10 junction arrays, rounded steps appear for larger arrays.
K Chen, SA Cybart, RC Dynes
Applied Superconductivity, IEEE Transactions on 15 (2), 149-152
Using electron beam lithography and ion damage, high quality YBa2Cu3O7-δ superconductor-normal metal-superconductor in-plane Josephson junction pairs have been fabricated. These junctions operate at temperatures between 60 and 85 K and have spacing ranging between 150 nm and 800 nm. Central electrodes connecting to the area between the two junctions were made, allowing for simultaneous measurements of the individual junctions as well as the series. Josephson junction pairs with 150 nm spacing were found to have extraordinary properties under microwave radiation with different power. At low power the structure functioned as two independent Josephson junctions in series, while at high power it behaved as one single Josephson junction. A possible origin of this behavior could be that the applied microwave radiation induces weak link behavior in the YBa2Cu3O7-δ between the two junctions.
K Chen, SA Cybart, RC Dynes
Applied physics letters 85 (14), 2863-2865
We have fabricated in-plane high-Tc Josephson junction pairs and series arrays using our established nanolithography and ion damage process. Junctions in a pair showed nearly identical electrical properties. The ten-junction array exhibited current–voltage characteristics that can be described by the resistively shunted junction model at 78K. Flat giant Shapiro steps were observed in both cases. We believe that the ion-damaged high-TcsuperconductingJosephson junction is a good candidate to form large numbers of junctions in series arrays that can function above 77K for quantum voltage standards and other applications.
Superconducting Electronics: Magnesium Diboride
SA Cybart, TJ Wong, EY Cho, JW Beeman, CS Yung, BH Moeckly, RC Dynes
Applied Physics Letters 104 (18), 182604
Magnetic field sensors based on two-dimensional arrays of superconducting quantum
interference devices were constructed from magnesium diboride thin films. Each array
contained over 30 000 Josephson junctions fabricated by ion damage of 30 nm weak links
through an implant mask defined by nano-lithography. Current-biased devices exhibited
very large voltage modulation as a function of magnetic field, with amplitudes as high as 8
mV.
SA Cybart, K Chen, Y Cui, Q Li, XX Xi, RC Dynes
Applied physics letters 88, 012509
We have fabricated planar thin-film MgB2Josephson junctions and 20-junction series arrays using 200-keV ion implantation and electron-beam lithography. Resistively shunted junctionI-V characteristics were observed in the temperature range of 34–38K. The ac Josephson effect was observed and flat giant Shapiro steps in arrays suggest good junction uniformity with a small spread in junction parameters. The temperature dependence of the critical current suggests that the nature of the interface between the superconductor and normal region can be described using a soft boundary proximity effect coupling model. We believe that the higher operating temperature and close spacing of these junctions make them promising candidates for quantum voltage standards and other devices.
Superconducting Electronics: Simulations
TN Dalichaouch, SA Cybart, RC Dynes
Superconductor Science and Technology 27 (6), 065006
A model is developed to investigate the effects of mutual inductance on the voltage–
field (V− B) characteristics of two-dimensional arrays of Josephson junctions. The V− B
characteristics were numerically simulated for arrays with and without mutual inductance
contributions. We find mutual inductances can have a strong impact on the voltage response
of SQUID arrays and mutual inductance contributions from nearest neighboring SQUIDs
only do not represent a good approximation.
S Wu, S Cybart, S Anton, R Dynes
IEEE
The voltage as a function of applied magnetic field (V-B) was calculated for arrays of superconducting quantum interference devices (SQUIDs) connected in series. Comparisons were made between arrays of equal area SQUIDs and superconducting quantum interference filters (SQIFs). The areas for the SQIFs were varied exponentially, so that the V-B had a sharp minimum at zero field. We used equations for the dc SQUID based on resistively shunted junctions, with typical parameters for YBa2Cu3O7 - δ ion damage Josephson junctions. The maximum transfer coefficient of the central minimum VB = (∂V/∂B)max of the SQIF decreases as the area range increases. We find that the equal area array is more robust to the effects of non-uniform junction critical currents than the SQIF, for the junction parameters and SQUID area distributions chosen. Furthermore, we find that slight variations (~5%) to the area due to fabrication irregularities have little effect on the central minimum of V-B for either device.
SA Cybart, TN Dalichaouch, SM Wu, SM Anton, JA Drisko, JM Parker, BD Harteneck, RC Dynes
Journal of Applied Physics 112 (6), 063911-063911-6
We have fabricated series-parallel (two-dimensional) arrays of incommensurate superconducting quantum interference devices(SQUIDs) using YBa2Cu3O7−δ thin film ion damage Josephson junctions. The arrays initially consisted of a grid of Josephson junctions with 28 junctions in parallel and 565 junctions in series, for a total of 15 255 SQUIDs. The 28 junctions in the parallel direction were sequentially decreased by removing them with photolithography and ion milling to allow comparisons of voltage–magnetic field (V–B) characteristics for different parallel dimensions and area distributions. Comparisons of measurements for these different configurations reveal that the maximum voltage modulation with magnetic field is significantly reduced by both the self inductances of the SQUIDs and the mutual inductances between them. Based on these results, we develop a computer simulation model from first principles which simultaneously solves the differential equations of the junctions in the array while considering the effects of self inductance, mutual inductance, and non-uniformity of junctioncritical currents. We find that our model can accurately predict V–B for all of the array geometries studied. A second experiment is performed where we use photolithography and ion milling to split another 28 × 565 junction array into 6 decoupled arrays to further investigate mutual interactions between adjacent SQUIDs. This work conclusively shows that the magnetic fields generated by self currents in an incommensurate array severely reduce its performance by reducing the maximum obtainable modulation voltage.