arXiv subjects

Yanfu Wu

Publications and source records attributed to Yanfu Wu.

4 recordsLinked to original sources

arXiv2023

Investigation of the deposition of $\alpha$-tantalum (110) films on a-plane sapphire substrate by molecular beam epitaxy for superconducting circuit

Polycrystalline {\alpha}-tantalum (110) films deposited on c-plane sapphire substrate by sputtering are used in superconducting qubits nowadays. However, these films always occasionally form other structures, such as {\alpha}-tantalum (111) grains and \b{eta}-tantalum grains. To improve the film quality, we investigate the growth of {\alpha}-tantalum (110) films on a-plane sapphire substrate under varying conditions by molecular beam epitaxy technology. The optimized {\alpha}-tantalum (110) film is single crystal, with a smooth surface and atomically flat metal-substrate interface. The film with thickness of 30 nm shows a Tc of 4.12K and a high residual resistance ratio of 9.53. The quarter wavelength coplanar waveguide resonators fabricated with the 150 nm optimized {\alpha}-tantalum (110) film, exhibits intrinsic quality factor of over one million under single photon excitation at millikelvin temperature.

physics.app-ph↗

arXiv2023

Epitaxial {\alpha}-Ta (110) film on a-plane sapphire substrate for superconducting qubits on wafer scale

Realization of practical superconducting quantum computing requires many qubits of long coherence time. Compared to the commonly used Ta deposited on c-plane sapphire, which occasionally form {\alpha}-Ta (111) grains and \b{eta}-tantalum grains, high quality Ta (110) film can grow epitaxial on a-plane sapphire because of the atomic relationships at the interface. Well-ordered {\alpha}-Ta (110) film on wafer-scale a-plane sapphire has been prepared. The film exhibits high residual resistance ratio. Transmon qubits fabricated using these film shows relaxation times exceeding 150 {\mu}s. The results suggest Ta film on a-plane sapphire is a promising choice for long coherence time qubit on wafer scale.

quant-ph↗

arXiv2023

Stable and low loss oxide layer on {\alpha}-Ta (110) film for superconducting qubits

The presence of amorphous oxide layers can significantly affect the coherent time of superconducting qubits due to their high dielectric loss. Typically, the surface oxides of superconductor films exhibit lossy and unstable behavior when exposed to air. To increase the coherence time, it is essential for qubits to have stable and low dielectric loss oxides, either as barrier or passivation layers. In this study, we highlight the robust and stable nature of an amorphous tantalum oxide layer formed on {\alpha}-Ta (110) film by employing chemical and structural analyses. Such kind of oxide layer forms in a self-limiting process on the surface of {\alpha}-Ta (110) film in piranha solution, yielding stable thickness and steady chemical composition. Quarter wavelength coplanar waveguide resonators are made to study the loss of this oxide. One resonator has a Qi of 3.0x10^6 in the single photon region. The Qi of most devices are higher than 2.0x10^6. Moreover, most of them are still over 1x10^6 even after exposed to air for months. Based on these findings, we propose an all-tantalum superconducting qubit utilizing such oxide as passivation layers, which possess low dielectric loss and improved stability.

cond-mat.mtrl-sci↗

arXiv2023

High-quality superconducting {\alpha}-Ta film sputtered on heated silicon substrate

Intrigued by the discovery of the long lifetime in the {\alpha}-Ta/Al2O3-based Transmon qubit, researchers recently found {\alpha}-Ta film is a promising platform for fabricating multi-qubits with long coherence time. To meet the requirements for integrating superconducting quantum circuits, the ideal method is to grow {\alpha}-Ta film on a silicon substrate compatible with industrial manufacturing. Here we report the {\alpha}-Ta film sputter-grown on Si (100) with a low-loss superconducting TiNx buffer layer. The {\alpha}-Ta film with a large growth temperature window has a good crystalline character. The superconducting critical transition temperature (Tc) and residual resistivity ratio (RRR) in the {\alpha}-Ta film grown at 500 {\deg}C are higher than that in the {\alpha}-Ta film grown at room temperature (RT). These results provide crucial experimental clues toward understanding the connection between the superconductivity and the materials' properties in the {\alpha}-Ta film and open a new route for producing a high-quality {\alpha}-Ta film on silicon substrate for future industrial superconducting quantum computers.

cond-mat.supr-con↗