Numerical studies of interchip pulse transmission for complex RSFQ systems

As the complexity of superconducting digital systems increases, the necessity of a careful design of interconnecting structures becomes more and more evident. Especially in the communication between chips, discontinuities are inevitable. Deriving a high frequency characterization of critical regions is therefore a crucial step for a design-oriented microwave modeling. We employed the finite-difference time-domain technique based on the discretization of Maxwell's equations for the numerical analysis of typical interconnect components, e.g. flip chip connection pads, vias, and transmission line discontinuities. The peculiar properties of superconductors are taken into account by incorporation of the London equations and the two-fluid model into the numerical scheme. Computer simulations have been carried out for various arrangements. Their results show in the time-domain how the shape of a rapid single flux quantum (RSFQ) pulse is affected by passing a discontinuity in the interchip signal path. Furthermore, frequency domain characterizations are obtained in terms of scattering parameters providing information about the bandwidth of the structure under investigation.