Noise in NbTiN, Al, and Ta Superconducting Resonators on Silicon and Sapphire Substrates

We present measurements of the frequency noise and resonance frequency temperature dependence in planar superconducting resonators on both silicon and sapphire substrates. We show, by covering the resonators with sputtered SiO
_x
layers of different thicknesses, that the temperature dependence of the resonance frequency scales linearly with thickness, whereas the observed increase in noise is independent of thickness. The frequency noise decreases when increasing the width of the coplanar waveguide in NbTiN on hydrogen passivated silicon devices, most effectively by widening the gap. We find up to an order of magnitude more noise when using sapphire instead of silicon as substrate. The complete set of data points towards the noise being strongly affected by superconductor-dielectric interfaces.