Year

2023

Season

Fall

Paper Type

Master's Thesis

College

College of Arts and Sciences

Degree Name

Master of Science in Material Science & Engineering (MS)

Department

Physics

NACO controlled Corporate Body

University of North Florida. Department of Physics

First Advisor

Daniel Santavicca

Second Advisor

Maitri Warusawithana

Third Advisor

Steve Stagon

Abstract

This thesis involves the fabrication and characterization of devices made from two different superconducting materials: yttrium barium copper oxide (YBCO), a high-TC complex oxide, and niobium nitride (NbN), a low-TC transition metal nitride. Both types of devices are fabricated on strontium titanate substrates, which provides a good lattice match to YBCO and also an extremely large permittivity at low temperature. We demonstrate that wet etching of YBCO thin films via bromine can be a viable microfrabriation technique for the material. Using approximately 35 nm thick epitaxially grown YBCO on an STO substrate, we were able to fabricate YBCO “microwires” with widths of 5 μm and 50 μm. These wires had a superconducting critical temperature (TC) of 86 K and a critical current density of 1 × 1011 A/m2 at low temperature, indicating that our fabrication process yields wires with electrical properties that are close to that of the bulk material. We have also developed impedance-matched lowloss microwave resonators using high kinetic inductance NbN nanowires on a substrate consisting of 100 nm of epitaxial STO on a 0.5 mm thick lanthanum aluminate (LAO) substrate. Comparing the measured transmission coefficient to numerical simulations, we were able to determine the dielectric constant of the STO film and determined it to be ϵ = 590 with an upper bound on the STO loss tangent of tan δ = 5 × 10−4 at 4.5 K. These devices demonstrate the potential for combining high-inductance superconducting nanowires with high-permittivity substrates to realize impedance-matched devices with dramatic spatial compression of the signal wavelength.

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