Ge thin-films with tantalum diffusion-barriers for use in Nb-based superconductor technology

TL;DR

This study demonstrates that adding a tantalum diffusion barrier layer significantly reduces intermixing and microwave losses in germanium thin films used in superconducting devices, improving their performance.

Contribution

It introduces a Ta diffusion barrier layer in Ge/Nb structures, reducing intermixing and enhancing microwave resonator quality in superconductor technology.

Findings

Ta barrier reduces intermixing to less than 5 nm

Improved structural properties of Ge layers with Raman spectroscopy

Enhanced microwave resonator performance with lower losses

Abstract

Germanium thin films are an excellent candidate for use as a low-loss dielectric in superconducting microwave resonators, a low-loss inter-layer metal wiring dielectric, and passivation layers in microwave and Josephson junction devices. In Ge/Nb structures deposited at 400 {\deg}C, we observe intermixing over as much as 20 nm. The addition of a 10 nm Ta diffusion barrier layer reduces the superconductor/dielectric intermixing to less than 5 nm and enhances the structural properties of deposited a-Ge layers based on Raman spectroscopy. Additionally, superconducting microwave resonators fabricated at room-temperature on crystalline Ge substrates with a Ta barrier layer show marked improvement in total and power-dependent two-level system microwave losses.