Metallurgy, Surface Preparation and Bonding for Cryogenic and Superconducting Hybrid Applications
Hybrid chip interconnect utilizing Indium is well-known in the production of hybrid chip assemblies that must operate at cryogenic temperatures. This technology has been used for decades in the Infrared Focalplane industry. Recent developments in Quantum Computing technology have now shown that Indium is also an excellent candidate for hybrid chip assemblies that operate at superconducting temperatures in the milli-Kelvin temperature range.
This Paper by the Quantum Computing groups at Google and UCSB describes the materials and processes (including SET hybrid bonders and Ontos Atmospheric Plasma) which are now routinely used to produce leading-edge quantum computing components operating at superconducting temperatures.