They determined electrical characterizations at cryogenic temperatures of chip assemblies made with 3D interconnects such as SnAg microbumps and direct Cu bonded pads from Cu/SiO2 hybrid bonding process. SnAg microbumps have the advantage of being widely used in the 3D IC community, and the processes to fabricate them are well known at CEA-Leti with a state-of-the-art pitch as low as 20µm. The motivation to study Cu/SiO2 hybrid bonding lies in its high-resolution potential with a pitch as low as 1µm demonstrated at the institute with a wafer-to-wafer process.

Silicon-spin qubits have a small size and are compatible with CMOS technology. This work could achieve qubits of near term 20 micron sizes with tens of thousands of qubits and eventually one micron sizes with millions of qubits.