Reducing TLS loss in tantalum CPW resonators using titanium sacrificial layers

TL;DR

This paper presents a method using ultrathin titanium sacrificial layers to chemically modify tantalum oxide surfaces, significantly reducing two-level system loss in tantalum CPW resonators and enhancing their quality factors.

Contribution

The study introduces a novel surface treatment involving titanium sacrificial layers and annealing to improve superconducting resonator coherence by reducing oxide-related losses.

Findings

Internal quality factors exceeding 1.5 million in the single-photon regime

Threefold increase in quality factor compared to untreated devices

Effective surface chemistry modification enhances superconducting device performance

Abstract

We demonstrate a substantial reduction in two-level system loss in tantalum coplanar waveguide resonators fabricated on high-resistivity silicon substrates through the use of an ultrathin titanium sacrificial layer. A 0.2nm titanium film, deposited atop pre-sputtered {\alpha}-tantalum, acts as a solid-state oxygen getter that chemically modifies the native Ta oxide at the metal-air interface. After device fabrication, the titanium layer is removed using buffered oxide etchant, leaving behind a chemically reduced Ta oxide surface. Subsequent high-vacuum annealing further suppresses two-level system loss. Resonators treated with this process exhibit internal quality factors Qi exceeding an average of 1.5 million in the single-photon regime across ten devices, over three times higher than otherwise identical devices lacking the titanium layer. These results highlight the critical role of interfacial oxide chemistry in superconducting loss and reinforce atomic-scale surface engineering as an effective approach to improving coherence in tantalum-based quantum circuits. The method is compatible with existing fabrication workflows applicable to tantalum films, offering a practical route to further extending T1 lifetimes in superconducting qubits.