SUPERCONDUCTIVE MULTICHIP-MODULE PROCESS FOR HIGH-SPEED DIGITAL APPLICATIONS

We report on the development of a superconducting multi-chip module (M CM) process for high speed digital packaging applications, which allow s superconducting microstrip connections of superconducting chips with impedances up to 50 Omega. The MCM process uses a low temperature pol ymer, benzocyclobutene (BCB) dielectric, which has excellent planariza tion properties (>90%). The six mask MCM process uses three Nb wire la yers, two BCB layers, and Ti/Pd/Au for the pad metallization. To maxim ize yield of 32 mm square MCM die, we optimized Nb deposition and BCB curing parameters to minimize stress-induced failures and reduce defec t density. Current-carrying capabilities of signal lines and vias (5 m u m minimum design rule) are in excess of 20 mA/mu m line width. We di scuss successful packaging of superconducting chips, demonstrating err or-free operation up to 5 Gbit/s, and other process improvements, such as the use of NbN wiring for 10 K operation.