A method for building low loss multi-layer wiring for superconducting microwave devices

• Published in: Applied physics letters 2018-02, Vol.112 (6)
• Main Authors: Dunsworth, A., Barends, R., Chen, Yu, Chen, Zijun, Chiaro, B., Fowler, A., Foxen, B., Jeffrey, E., Kelly, J., Klimov, P. V., Lucero, E., Mutus, J. Y., Neeley, M., Neill, C., Quintana, C., Roushan, P., Sank, D., Vainsencher, A., Wenner, J., White, T. C., Neven, H., Martinis, John M., Megrant, A.
• Format: Article
• Language: English
• Subjects: Aluminum; Applied physics; Coplanar waveguides; Crossovers; Dielectrics; Energy dissipation; Integrated circuits; Jumpers; Metal oxides; Multilayers; Resonators; Superconductivity; Wiring
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.5014033

Complex integrated circuits require multiple wiring layers. In complementary metal-oxide-semiconductor processing, these layers are robustly separated by amorphous dielectrics. These dielectrics would dominate energy loss in superconducting integrated circuits. Here, we describe a procedure that capitalizes on the structural benefits of inter-layer dielectrics during fabrication and mitigates the added loss. We use a deposited inter-layer dielectric throughout fabrication and then etch it away post-fabrication. This technique is compatible with foundry level processing and can be generalized to make many different forms of low-loss wiring. We use this technique to create freestanding aluminum vacuum gap crossovers (airbridges). We characterize the added capacitive loss of these airbridges by connecting ground planes over microwave frequency λ/4 coplanar waveguide resonators and measuring resonator loss. We measure a low power resonator loss of ∼3.9 × 10−8 per bridge, which is 100 times lower than that of dielectric supported bridges. We further characterize these airbridges as crossovers, control line jumpers, and as part of a coupling network in gmon and fluxmon qubits. We measure qubit characteristic lifetimes (T1s) in excess of 30 μs in gmon devices.