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. MgB2​, known for its highest Tc​ (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 MgB2​
devices into the application base of superconducting electronics, despite
promising preliminary results for a number of applications. We have developed
smooth and uniform MgB2​ 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
104 at 4.5 K and tunable high kinetic inductance (5-50 pH/â–¡
readily achieved in a 40 nm film), opening up the path for development of high
frequency and high temperature MgB2​ microdevices