Structure, transport, and microwave properties of superconducting tantalum films with in situ deposited oxides

The surface of superconducting quantum circuits is typically covered with native oxides, which contribute to dielectric losses at low temperatures and under microwave excitation. These superconducting resonators have shown changes in performance over time because oxide regrowth and environmental contamination degrade the heterostructures, particularly at the metal-air and metal-substrate interfaces. We replaced native oxides with deposited Al₂O₃, allowing precise control over film thickness and interfacial properties. We demonstrated that superconducting resonators fabricated with deposited Al₂O₃ on Ta films exhibit exceptional resistance to aging.  In this work, we investigated other oxides and different growth methods, studying the influence on the structure of the Ta films and their interfaces, characterized using XRD and XPS. Electrical transport measurements were performed to examine the superconducting properties. We quantified the performance of the deposited oxides/Ta films grown directly on sapphire substrates using the internal quality factor of microwave resonators at millikelvin temperatures, linking the observed structure and electrical transport properties to device performance. The in situ deposited oxides on superconducting films are applicable not only to superconducting supportive circuits but also to Josephson junctions.