Suspending superconducting qubits by silicon micromachining

We present a method for relieving aluminum 3D transmon qubits from a silicon substrate using micromachining. Our technique is a high yield, one-step deep reactive ion etch that requires no additional fabrication processes and results in the suspension of the junction area and edges of the aluminum film. The drastic change in the device geometry affects both the dielectric and the flux noise environment experienced by the qubit. In particular, the participation ratios of various dielectric interfaces are significantly modified, and suspended qubits exhibited longer T1's than non-suspended ones. We also find that the suspension increases the flux noise experienced by tunable SQUID-based qubits.