SuperGaN: Synthesis of NbTiN/GaN/NbTiN Tunnel Junctions

Nb-based circuits have broad applications in quantum-limited photon detectors, low-noise parametric amplifiers, superconducting digital logic circuits, and low-loss circuits for quantum computing. The current state-of-the-art approach for superconductor-insulator-superconductor (SIS) junction material is the Gurvitch trilayer process based on magnetron sputtering of Nb electrodes with Al-Oxide or AlN tunnel barriers grown on an Al overlayer. However, a current limitation of elemental Nb-based circuits is the low-loss operation of THz circuits operating above the 670 GHz gap frequency of Nb and operation at higher temperatures for projects with a strict power budget, such as space-based applications. NbTiN is an alternative higher energy gap material and we have previously reported on the first NbTiN/AlN/NbTiN superconducting-insulating-superconducting (SIS) junctions with an epitaxially grown AlN tunnel barrier. One drawback of a directly grown tunnel barrier compared to thermal oxidation or plasma nitridation is control of the barrier thickness and uniformity across a substrate, leading to variations in current density (Jc). Semiconductor barriers with smaller barrier heights enable thicker tunnel barriers for a given Jc. GaN is an alternative semiconductor material with a closed-packed Wurtzite crystal structure similar to AlN and it can be epitaxially grown as a tunnel barrier using the Reactive Bias Target Ion Beam Deposition (RBTIBD) technique. This work presents the preliminary results of the first reported high-quality NbTiN/GaN/NbTiN heterojunctions with underdamped SIS I(V) characteristics.Comment: Presented at the 16th EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVIT

Dynamic Versus Static Oxidation of Nb/Al-AlOx_x/Nb Trilayer

High quality Nb-based superconductor-insulator-superconductor (SIS) junctions with Al oxide (AlO$_x$) tunnel barriers grown from Al overlayers are widely reported in the literature. However, the thin barriers required for high critical current density (J$_c$) junctions exhibit defects that result in significant subgap leakage current that is detrimental for many applications. High quality, high-J$_c$ junctions can be realized with AlN$_x$ barriers, but control of J$_c$ is more difficult than with AlO$_x$. It is therefore of interest to study the growth of thin AlO$_x$ barriers with the ultimate goal of achieving high quality, high-J$_c$ AlO$_x$ junctions. In this work, 100\%\ O$_2$ and 2\%\ O$_2$ in Ar gas mixtures are used both statically and dynamically to grow AlO$_x$ tunnel barriers over a large range of oxygen exposures. In situ ellipsometry is used for the first time to extensively measure AlO$_x$ tunnel barrier growth in real time, revealing a number of unexpected patterns. Finally, a set of test junction wafers was fabricated that exhibited the well-known dependence of J$_c$ on oxygen exposure (E) in order to further validate the experimental setup

Superconducting parametric amplifiers: The next big thing in (Sub)millimeter-wave receivers

We are developing a new superconducting amplifier technology for radio astronomy instruments called the Traveling-Wave Kinetic Inductance Parametric (TKIP) amplifier. Invented at Caltech/JPL, recent laboratory demonstrations have resulted in near quantum-limited noise performance over more than an octave of microwave bandwidth and operating temperatures as high as 3 Kelvin. These amplifiers have the potential to be used as front-end replacements for ALMA's mm/sub-mm SIS receivers and intermediate frequency (IF) amplifiers, and for multiplexing faint signals from focal-plane arrays of single-photon detectors on space telescopes such as NASA's Origins Space Telescope (OST). The enhanced observational capabilities that would be enabled by TKIP front-end amplifiers on ALMA would tremendously benefit ALMA science across all bands

Superconducting parametric amplifiers: The next big thing in (Sub)millimeter-wave receivers

We are developing a new superconducting amplifier technology for radio astronomy instruments called the Traveling-Wave Kinetic Inductance Parametric (TKIP) amplifier. Invented at Caltech/JPL, recent laboratory demonstrations have resulted in near quantum-limited noise performance over more than an octave of microwave bandwidth and operating temperatures as high as 3 Kelvin. These amplifiers have the potential to be used as front-end replacements for ALMA's mm/sub-mm SIS receivers and intermediate frequency (IF) amplifiers, and for multiplexing faint signals from focal-plane arrays of single-photon detectors on space telescopes such as NASA's Origins Space Telescope (OST). The enhanced observational capabilities that would be enabled by TKIP front-end amplifiers on ALMA would tremendously benefit ALMA science across all bands