Using Surface Engineering to Modulate Superconducting Coplanar Microwave Resonator Performance

Superconducting microwave resonators are important components of superconducting quantum information and astronomy detector systems. In this paper, we show how to modify the microwave resonator performance after fabrication through surface engineering. In particular, we focus on titanium nitride (TiN)/silicon (Si) resonators because they have shown potential for achieving high-quality factors (Q(i)s). Depending on the type of surface treatment, chemical-or plasma-based, we found Q(i)s that vary by approximately a factor of 18. We used inductively coupled plasma (ICP) combined with reactive ion etching (RIE) for the plasma surface treatment. We found that the microwave resonator performance depends on the type of plasma environment, such as single gas (oxygen) or gas mixtures [argon/hydrogen (Ar/H-2), argon/octafluorocyclobutane (Ar/C4F8), and argon/sulfur hexafluoride (Ar/SF6)], and the plasma processing conditions, such as treatment time, ICP power, and RIE power. Of the plasma surface treatments, the Ar/SF6 environments with no or low ICP power showed the highest potential to improve Q(i). The processing conditions determined the chemistry and roughness of the Si and TiN surfaces, TiN film thickness, and the overall TiN/Si resonator structure (edge and sidewall). Our results can be used as a guideline for optimizing the microwave resonator performance using surface treatments.