Surface Passivation of Niobium and Aluminum Superconducting Thin-Films using Self-Assembled Monolayers to Suppress the Growth of Oxides

In the development and optimization of superconducting quantum circuits, post-fabrication surface passivation of superconducting thin films is pivotal [1,2]. This research directs a spotlight on harnessing self-assembled monolayers (SAMs) as a means to achieve enhanced surface passivation, countering the deleterious effects of two-level-system (TLS) defects from metal oxides, which are notorious for significantly precipitating decoherence and impeding the optimal functioning of quantum devices. Traditional methods of mitigating these defects, such as employing an inorganic passivating layer, are discounted due to their propensity to further deteriorate interface conditions. The deployment of SAMs in this context has been explored to effectively forestall defect regrowth post-etching processes, resulting a significant improvement in the quality factor of the superconducting co-planar waveguide (CPW) resonators. The main focus is placed on materials analysis, with techniques such as Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and X-ray Photoelectron Spectroscopy (XPS) being employed to validate the efficacy of SAMs in both inhibiting oxide regrowth and steadily enhancing superconducting quantum circuit performance. This detailed analysis underscores the pivotal role of SAMs in realizing and maintaining improved surface passivation for Niobium and Aluminum superconducting thin films in cQED applications.