Low-loss, ultra-thin AlOx films with specific resistances from (10² – 10¹⁰) Ω∙um²

Using an oxygen plasma technique, we have demonstrated extremely low charge noise using single electron transistors and have now extended the process to produce films with a very wide range of specific resistances. Ultra-thin AlOx films are essential for the Josephson tunnel junctions (~ 100 Ω∙um²) used for various superconducting qubits and could enable significant size reductions for shunt capacitors (>10⁷ Ω∙um²) if the loss is sufficiently low. By tuning the plasma oxidation time from 0.1 s to 1200 s, we produced films with specific resistances from 100 Ω∙um² to 10¹⁰ Ω∙um², spanning the desired range. Using WKB model fitting to extract the barrier thickness, we find an approximately logarithmic relationship between the thickness and the oxidation time, suggesting a diffusion limited growth process. Further, in the high oxidation regime (> 300 sec), we find that the specific capacitance is ~20 fF/um², in agreement with the estimated thickness. Finally, progress toward incorporating this process to produce capacitors in superconducting LC circuits will be discussed.