Engineering high-Q superconducting tantalum microwave coplanar waveguide resonators for compact coherent quantum circuits

TL;DR

This paper demonstrates the fabrication of high-Q superconducting tantalum microwave resonators with engineered thickness-dependent properties, enabling compact, high-fidelity quantum circuits with enhanced coupling capabilities.

Contribution

It introduces a method to produce high-quality, high-kinetic-inductance tantalum resonators on silicon substrates, optimizing their performance for quantum computing applications.

Findings

Maximum internal quality factor Q_i of ~3.6 million at high power for 100 nm Ta

Achieved kinetic inductance of 0.6 pH/sq for 40 nm thick Ta films

Successful fabrication without substrate heating using Nb seed layer

Abstract

Tantalum (Ta) has recently received considerable attention in manufacturing robust superconducting quantum circuits. Ta offers low microwave loss, high kinetic inductance compared to aluminium (Al) and niobium (Nb), and good compatibility with complementary metal-oxide-semiconductor (CMOS) technology, which is essential for quantum computing applications. Here, we demonstrate the fabrication engineering of thickness-dependent high quality factor (high-Q_i) Ta superconducting microwave coplanar waveguide resonators. All films are deposited on high-resistivity silicon substrates at room temperature without additional substrate heating. Before Ta deposition, a niobium (Nb) seed layer is used to ensure a body-centred cubic lattice ({\alpha}-Ta) formation. We further engineer the kinetic inductance (L_K) resonators by varying Ta film thicknesses. High L_K is a key advantage for applications because it facilitates the realisation of high-impedance, compact quantum circuits with enhanced coupling to qubits. The maximum internal quality factor Q_i of ~ 3.6 * 10^6 is achieved at the high power regime for 100 nm Ta, while the highest kinetic inductance is obtained to be 0.6 pH/sq for the thinnest film, which is 40 nm. This combination of high Q_i and high L_K highlights the potential of Ta microwave circuits for high-fidelity operations of compact quantum circuits.