  We report on the fabrication and characterization of 50 Ohms, flux-tunable,
low-loss, SQUID-based transmission lines. The fabrication process relies on the
deposition of a thin dielectric layer (few tens of nanometers) via Atomic Layer
Deposition (ALD) on top of a SQUID array, the whole structure is then covered
by a non-superconducting metallic top ground plane. We present experimental
results from five different samples. We systematically characterize their
microscopic parameters by measuring the propagating phase in these structures.
We also investigate losses and discriminate conductor from dielectric losses.
This fabrication method offers several advantages. First, the SQUID array
fabrication does not rely on a Niobium tri-layer process but on a simpler
double angle evaporation technique. Second, ALD provides high quality
dielectric leading to low-loss devices. Further, the SQUID array fabrication is
based on a standard, all-aluminum process, allowing direct integration with
superconducting qubits. Moreover, our devices are in-situ flux tunable,
allowing mitigation of incertitude inherent to any fabrication process.
Finally, the unit cell being a single SQUID (no extra ground capacitance is
needed), it is straightforward to modulate the size of the unit cell
periodically, allowing band-engineering. This fabrication process can be
directly applied to traveling wave parametric amplifiers.
