Fine pitch Nb-Nb Direct Bonding for quantum applications

Hydrophilic direct bonding of Nb-Nb fine pitch pads has been demonstrated for the first time. Initially developed using full-sheet Nb layers, this process was successfully applied to bond 7 µm pitch patterned Nb pads surrounded by air. Surface and interface characterizations, including Atomic Force Microscopy, Scanning Acoustic Microscopy, Double Cantilever Beam method for adherence measurement and Transmission Electronic Microscopy have been carried on to qualify the bonding quality and strength in the case of Nb full sheet films bonding and in the case of Nb pads. Such interconnects offer new alternatives in term of three-dimensional integration to reach dense quantum and superconducting systems. The absence of dielectrics between the bonded Nb pads should be particularly advantageous for thermal decoupling and reduction of signal loss.