Aluminum air bridges for superconducting quantum devices realized using a single step e-beam process*

Superconducting quantum devices typically rely on co-planar waveguides (CPWs) for qubit readout and information storage. CPWs break up the ground plane and introduce decoherence through mode mixing. These issues can be mitigated through the use of air bridges. These bridges act as an interconnect to improve uniformity of the ground plane, reduce slot line modes in resonators, and enable a greater design space for planar devices by allowing crossing of signal lines. We present our results on the development of a process for fabricating superconducting aluminum air bridges that rely on the use of a single electron-beam lithography (EBL) grayscale exposure step followed by aluminum deposition and liftoff. Besides the convenience of implementation in a single lithography step, this method offers flexibility with regards to design changes and positioning of the bridges. This process produces high-yield air bridges of various lengths, ranging from 10 micrometers to 100 micrometers. The air bridges are tested on superconducting resonators and are found to have little effect on the internal quality factor. We also discuss the integration of these bridges in flux-type superconducting devices for improved design capabilities, device density, and coherence.