1/f frequency fluctuations due to kinetic inductance in CoSi₂ microwave cavities

Cobalt disilicide provides a promising nearly-epitaxial superconducting material on silicon, which is compatible with high-density integrated circuit technology. We have characterized CoSi₂ superconducting microwave cavities around 5.5 GHz for resonance frequency fluctuations at temperatures 10 - 200 mK. We found relatively weak fluctuations (δ f/f)² following the spectral density A/fγ, with A 6 × 10⁻¹⁶ and γ slightly below 1 at an average number of photons of 10⁴; the noise decreased with measurement power as 1/P1/2. We identify the noise as arising from kinetic inductance fluctuations and discuss possible origins of such fluctuations.