Investigation of tantalum films growth for coplanar resonators with internal quality factors above ten million

Abstract

Alpha-tantalum on silicon is a promising platform for high-coherence superconducting quantum circuits. However, the growth mechanism of alpha-tantalum on silicon remains poorly understood. We present a comprehensive study on alpha-tantalum films growth on various substrate. The decisive role of a substrate material Debye temperature on phase selection mechanism in tantalum films growth is experimentally confirmed, contradicting the prior assumptions on substrate temperature influence. Crucially, we confirm that alpha-tantalum starts growing only after a 7-10 nm thick beta-tantalum underlayer. It results in ranging the critical temperature of α-Ta films from 3.77 K to 4.39 K for the total thickness from 20 to 150 nm, respectively. Finally, we compared high-quality Al and Ta coplanar resonators on silicon, demonstrating compact tantalum resonators (4/10.5/4 um) with an internal quality factor exceeding 10 million at single-photon excitation powers.

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in E. V. Zikiy et al., Appl. Phys. Rev. 1 June 2026; 13 (2): 021418. and may be found at https://doi.org/10.1063/5.0308010