  Niobium films are a key component in modern two-dimensional superconducting
qubits, yet their contribution to the total qubit decay rate is not fully
understood. The presence of different layers of materials and interfaces makes
it difficult to identify the dominant loss channels in present two-dimensional
qubit designs. In this paper we present the first study which directly
correlates measurements of RF losses in such films to material parameters by
investigating a high-power impulse magnetron sputtered (HiPIMS) film atop a
three-dimensional niobium superconducting radiofrequency (SRF) resonator. By
using a 3D SRF structure, we are able to isolate the niobium film loss from
other contributions. Our findings indicate that microwave dissipation in the
HiPIMS-prepared niobium films, within the quantum regime, resembles that of
record-high intrinsic quality factor of bulk niobium SRF cavities, with
lifetimes extending into seconds. Microstructure and impurity level of the
niobium film do not significantly affect the losses. These results set the
scale of microwave losses in niobium films and show that niobium losses do not
dominate the observed coherence times in present two-dimensional
superconducting qubit designs, instead highlighting the dominant role of the
dielectric oxide in limiting the performance. We can also set a bound for when
niobium film losses will become a limitation for qubit lifetimes.
