Nb-Based Superconducting Silicon Interconnect Fabric for Cryogenic Computing Applications

As the number of qubits goes beyond one million, the I/O count and the interconnect wiring within a limited area become problematic. In this paper, we present a simple integration method (an Au interlayer) with a fine interconnect pitch (10 um) and close lateral die spacing (60 um) that can overcome the large I/O and high wiring level requirements of very large scale of quantum circuits. A System-on-Wafer (SoW) Superconducting Silicon Interconnect Fabric (Superconducting-IF) is proposed with the help of the mentioned Au interlayer technology. Through three testing structures, the Au interlayer integration technology is demonstrated to be fine pitch (<= 10 um), Josephson-Junctioncompatible (<150 degrees C), mechanically robust (> 30 MPa) on various bonding areas, and electrically reliable at 2 K. It is one of the first demonstrations of the robust and reliable Au interlayer optimized for quantum applications. This work enables quantum computing to uncover its full strength through high-density (>10000 mm(2) I/O and dense wiring) heterogeneous integration.