paper

A Superconducting Phase Shifter and Traveling Wave Kinetic Inductance Parametric Amplifier for W-Band Astronomy

arXiv:1710.11335

Abstract

The W-Band ( $75 - 110 GHz$ ) sky contains a plethora of information about star formation, galaxy evolution and the cosmic microwave background. We have designed and fabricated a dual-purpose superconducting circuit to facilitate the next generation of astronomical observations in this regime by providing proof-of-concept for both a millimeter-wave low-loss phase shifter, which can operate as an on-chip Fourier transform spectrometer (FTS) and a traveling wave kinetic inductance parametric amplifier (TKIP). Superconducting transmission lines have a propagation speed that depends on the inductance in the line which is a combination of geometric inductance and kinetic inductance in the superconductor. The kinetic inductance has a non-linear component with a characteristic current, $I_{*}$ , and can be modulated by applying a DC current, changing the propagation speed and effective path length. Our test circuit is designed to measure the path length difference or phase shift, $I^ I ¨ $ , between two symmetric transmission lines when one line is biased with a DC current. To provide a measurement of $I^ I ¨ $ , a key parameter for optimizing a high gain W-Band TKIP, and modulate signal path length in FTS operation, our $3.6 \times 2.5 cm$ chip employs a pair of $503 mm$ long NbTiN inverted microstrip lines coupled to circular waveguide ports through radial probes. For a line of width $3 I^¼ m$ and film thickness $20 nm$ , we predict $I^ I ¨ \approx 1767 rad$ at $90 GHz$ when biased at close to $I_{*}$ . We have fabricated a prototype with $200 nm$ thick Nb film and the same line length and width. The predicted phase shift for our prototype is $I^ I ¨ \approx 30 rad$ at $90 GHz$ when biased at close to $I_{*}$ for Nb.

8 pages, 3 figures, submitted to Journal of Low Temperature Physics