  The presence of amorphous oxide layers can significantly affect the coherent
time of superconducting qubits due to their high dielectric loss. Typically,
the surface oxides of superconductor films exhibit lossy and unstable behavior
when exposed to air. To increase the coherence time, it is essential for qubits
to have stable and low dielectric loss oxides, either as barrier or passivation
layers. In this study, we highlight the robust and stable nature of an
amorphous tantalum oxide layer formed on {\alpha}-Ta (110) film by employing
chemical and structural analyses. Such kind of oxide layer forms in a
self-limiting process on the surface of {\alpha}-Ta (110) film in piranha
solution, yielding stable thickness and steady chemical composition. Quarter
wavelength coplanar waveguide resonators are made to study the loss of this
oxide. One resonator has a Qi of 3.0x10^6 in the single photon region. The Qi
of most devices are higher than 2.0x10^6. Moreover, most of them are still over
1x10^6 even after exposed to air for months. Based on these findings, we
propose an all-tantalum superconducting qubit utilizing such oxide as
passivation layers, which possess low dielectric loss and improved stability.
