Wafer-scale magnesium diboride thin films and devices with tunable high kinetic inductance

Kavli Affiliate: Nathan Lewis

| First 5 Authors: Changsub Kim, Christina Bell, Jake Evans, Jonathan Greenfield, Nathan Lewis

| Summary:

Progress in superconducting device and detector technologies over the past
decade have realized practical applications in quantum computers, detectors for
far-IR telescopes, and optical communications. Superconducting thin film
materials, however, have remained largely unchanged, with aluminum still being
the material of choice for superconducting qubits, and Nb compounds for higher
frequency devices. $mathrm{MgB}_2$, known for its highest $mathrm{T}_c$ (39
K) among metallic superconductors, is a viable material for higher frequency
superconducting devices moving towards THz frequencies. However, difficulty in
synthesizing thin films have prevented implementation of $mathrm{MgB}_2$
devices into the application base of superconducting electronics, despite
promising preliminary results for a number of applications. We have developed
smooth and uniform $mathrm{MgB}_2$ films on 4-inch Si wafers by depositing
uniform Mg-B co-sputtered film, capping the film in situ to create a closed
environment, followed by an optimized post-annealing step. We further report
mature device fabrication processes and demonstrate test structures to measure
properties of the films. This includes resonators with internal Q factor over
$mathrm{10}^4$ at 4.5 K and tunable high kinetic inductance (5-50 pH/$square$
readily achieved in a 40 nm film), opening up the path for development of high
frequency and high temperature $mathrm{MgB}_2$ microdevices.

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