Characterizations of Indium Interconnects for 3D Quantum Assemblies

Large-scale integration of quantum bits and quantum technologies relies on multi-chip assemblies. In that context, we focus on indium microbumps to connect chips made from different materials and technological nodes. We have fabricated two test vehicles, comprising GaAs and Si chips stacked by die-to-die process on a Si-based substrate. GaAs on Si and Si on Si daisy chains were compared to evaluate the impact of thermal expansion coefficient mismatch on the chip connection. Electrical measurements in a cryostat from 300 K to 2 K, as well as morphological and mechanical characterizations were used to support this study and qualify In interconnect technology for heterogeneous quantum assemblies.