Tantalum resonators on silicon with a niobium seed layer reach internal quality factors up to 3.6 million at high power and kinetic inductance up to 0.6 pH per square, with thinner films giving more inductance but lower quality.
Investigation of the deposition of $\alpha$-tantalum (110) films on a-plane sapphire substrate by molecular beam epitaxy for superconducting circuit
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abstract
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.
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Engineering high-Q superconducting tantalum microwave coplanar waveguide resonators for compact coherent quantum circuits
Tantalum resonators on silicon with a niobium seed layer reach internal quality factors up to 3.6 million at high power and kinetic inductance up to 0.6 pH per square, with thinner films giving more inductance but lower quality.