Superconductive multi-chip module process for high speed digital applications

We report on the development of a superconducting multi-chip module (MCM) process for high speed digital packaging applications, which allows superconducting microstrip connections of superconducting chips with impedances up to 50 /spl Omega/. The MCM process uses a low temperature polymer, benzocyclobutene (BCB) dielectric, which has excellent planarization properties (>90%). The six mask MCM process uses three Nb wire layers, two BCB layers, and Ti/Pd/Au for the pad metallization. To maximize yield of 32 mm square MCM die, we optimized Nb deposition and BCB curing parameters to minimize stress-induced failures and reduce defect density. Current-carrying capabilities of signal lines and vias (5 /spl mu/m minimum design rule) are in excess of 20 mA//spl mu/m linewidth. We discuss successful packaging of superconducting chips, demonstrating error-free operation up to 5 Gbit/s, and other process improvements, such as the use of NbN wiring for 10 K operation.