Complex integrated circuits require multiple wiring layers. In complementarymetal-oxide-semiconductor (CMOS) processing, these layers are robustlyseparated by amorphous dielectrics. These dielectrics would dominate energyloss in superconducting integrated circuits. Here we demonstrate a procedurethat capitalizes on the structural benefits of inter-layer dielectrics duringfabrication and mitigates the added loss. We separate and support multiplewiring layers throughout fabrication using SiO$_2$ scaffolding, then remove itpost-fabrication. This technique is compatible with foundry level processingand the can be generalized to make many different forms of low-loss multi-layerwiring. We use this technique to create freestanding aluminum vacuum gapcrossovers (airbridges). We characterize the added capacitive loss of theseairbridges by connecting ground planes over microwave frequency $\lambda/4$coplanar waveguide resonators and measuring resonator loss. We measure a lowpower resonator loss of $\sim 3.9 \times 10^{-8}$ per bridge, which is 100times lower than dielectric supported bridges. We further characterize theseairbridges as crossovers, control line jumpers, and as part of a couplingnetwork in gmon and fuxmon qubits. We measure qubit characteristic lifetimes($T_1$'s) in excess of 30 $\mu$s in gmon devices.
展开▼
