15 research outputs found
Dynamic Versus Static Oxidation of Nb/Al-AlO/Nb Trilayer
High quality Nb-based superconductor-insulator-superconductor (SIS) junctions
with Al oxide (AlO) tunnel barriers grown from Al overlayers are widely
reported in the literature. However, the thin barriers required for high
critical current density (J) junctions exhibit defects that result in
significant subgap leakage current that is detrimental for many applications.
High quality, high-J junctions can be realized with AlN barriers, but
control of J is more difficult than with AlO. It is therefore of
interest to study the growth of thin AlO barriers with the ultimate goal of
achieving high quality, high-J AlO junctions. In this work, 100\%\
O and 2\%\ O in Ar gas mixtures are used both statically and
dynamically to grow AlO tunnel barriers over a large range of oxygen
exposures. In situ ellipsometry is used for the first time to extensively
measure AlO 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 on oxygen exposure (E) in order to
further validate the experimental setup
Ultra-Thin Silicon Beam Lead Chips for Superconducting Terahertz Circuits
Abstract. We present a process for fabricating THz superconducting circuits on ultra-thin (4um and less) silicon chips. The chips feature gold beam-leads, and are designed to accommodate RF filter structures, and either SIS junctions or hot-electron bolometers as the non-linear circuit element. The beam leads provide electrical connections, thermal contact, and physical support for the chip within a waveguide. Our approach begins by fabricating the superconducting circuit and beam leads atop the device layer of a silicon-on-insulator (SOI) substrate. The chip is then mounted, device side down, atop a quartz carrier wafer. A combination of mechanical lapping and chemical etching removes the handle silicon. Using backside photolithographic alignment through the quartz carrier, a thick photoresist is patterned on the exposed device silicon. The individual chips are then defined in a reactive ion etch of the device silicon, which is terminated after the quartz carrier and gold beam leads are exposed. The combination of superconducting mixers technology and silicon-micromachining techniques promises to open up the THz regime to large format spectroscopic imaging arrays. The potential for such systems are multiple; examples include atmospheric research, astrophysics, and security systems
Legendre Fit to the Reflection Coefficient of a Radiating Rectangular Waveguide Aperture
We accurately calculate the reflection coefficient and normalized admittance of radiating open-ended rectangular waveguides and fit our results with a linear combination of Legendre polynomials. We verify the expression to an accuracy of 0.005 with other calculations and examine the impact of flanges and burrs on the accuracy to which the reflection coefficient can be approximated in practice
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