Reducing quantum-regime dielectric loss of silicon nitride for superconducting quantum circuits

摘要

The loss of amorphous hydrogenated silicon nitride (a-SiN_x:H) is measured at 30 mK and 5 GHz using a superconducting LC resonator down to energies where a single-photon is stored, and analyzed with an independent two-level system defect model. Each a-SiN_x: H film was deposited with different concentrations of hydrogen impurities. We find that quantum-regime dielectric loss tangent tan δ_0 in a-SiN_x: H is strongly correlated with N-H impurities, including NH_2. By slightly reducing x we are able to reduce tan δ_0 by approximately a factor of 50, where the best films show tan δ_0 approx= 3 × 10~(-5).