Thermocompression bonding technology for multilayer superconducting quantum circuits

Extensible quantum computing architectures require a large array of quantum bits operating with low error rates. A quantum processor based on superconducting devices can be scaled up by stacking microchips that perform wiring, shielding, and computational functionalities. In this article, we demonstrate a vacuum thermocompression bonding technology that utilizes thin indium films as a welding agent to attach pairs of lithographically patterned chips. At 10 mK, we find a specific dc bond resistance of 49.2 μΩ cm2. We show good transmission up to 6.8 GHz in a tunnel-capped, bonded device as compared to a similar uncapped device. Finally, we fabricate and measure a set of tunnel-capped superconducting resonators, demonstrating that our bonding technology can be used in quantum computing applications.