Revealing the Origin and Nature of the Buried Metal-Substrate Interface Layer in Ta/Sapphire Superconducting Films

Abstract

Despite constituting a smaller fraction of the qubits electromagnetic mode, surfaces and interfaces can exert significant influence as sources of high-loss tangents, which brings forward the need to reveal properties of these extended defects and identify routes to their control. Here, we examine the structure and composition of the metal-substrate interfacial layer that exists in Ta/sapphire-based superconducting films. Synchrotron-based X-ray reflectivity measurements of Ta films, commonly used in these qubits, reveal an unexplored interface layer at the metal-substrate interface. Scanning transmission electron microscopy and core-level electron energy loss spectroscopy identified an approximately 0.65 \ \text{nm} \pm 0.05 \ \text{nm} thick intermixing layer at the metal-substrate interface containing Al, O, and Ta atoms. Density functional theory (DFT) modeling reveals that the structure and properties of the Ta/sapphire heterojunctions are determined by the oxygen content on the sapphire surface prior to Ta deposition, as discussed for the limiting cases of Ta films on the O-rich versus Al-rich Al2O3 (0001) surface. By using a multimodal approach, integrating various material characterization techniques and DFT modeling, we have gained deeper insights into the interface layer between the metal and substrate. This intermixing at the metal-substrate interface influences their thermodynamic stability and electronic behavior, which may affect qubit performance.

References in corpus (12)

• Supplementary information for "Quantum supremacy using a programmable superconducting processor"
• Transmon qubit with relaxation time exceeding 0.5 milliseconds
• Systematic Improvements in Transmon Qubit Coherence Enabled by Niobium Surface Encapsulation
• Moving beyond the transmon: Noise-protected superconducting quantum circuits
• Enhanced coherence of all-nitride superconducting qubits epitaxially grown on silicon substrate
• Chemical profiles of the oxides on tantalum in state of the art superconducting circuits
• Precision measurement of the microwave dielectric loss of sapphire in the quantum regime with parts-per-billion sensitivity
• Modelling dielectric loss in superconducting resonators: Evidence for interacting atomic two-level systems at the Nb/oxide interface
• High-quality superconducting α-Ta film sputtered on heated silicon substrate
• Revealing the Origin and Nature of the Buried Metal-Substrate Interface Layer in Ta/Sapphire Superconducting Films
• Stable and low loss oxide layer on α-Ta (110) film for superconducting qubits
• Methods to achieve near-millisecond energy relaxation and dephasing times for a superconducting transmon qubit

Cited by in corpus (1)

• Revealing the Origin and Nature of the Buried Metal-Substrate Interface Layer in Ta/Sapphire Superconducting Films