Modeling of superconducting MCM contact for high speed RSFQ circuit

Conference poster, 2005

This work discusses modeling of Multi-Chip-Module's (MCM) contact for superconducting RSFQ circuits. At MCM contact bumps are formed between chips and carriers' pads to make electrical contacts and the SFQ pulse propagation depends on the impedance matching and contact resistance at bump contacts. Without careful optimization, desired SFQ pulse transmission through the contact bump cannot be achieved. Modeling is an important step towards the design and optimization of MCM contact bump. Studies have been done on the bumps and contact pad structures and an empirical model has been proposed. The p representation of this model has been estimated from the simulated scattering matrix for a wide frequency band, I-V data with proper mathematical model of bump shape. The model contains the following parameters: contact pads' capacitance to ground, bump inductances, contact resistance, mutual inductance between signal and ground bumps and other parasitic corresponding to the layout of the contact pad structure. This model has been used for optimization of the MCM contact structures to achieve return losses of less than -20 dB for more than 210 GHz, the SFQ pulse's bandwidth. The Optimized MCM contact provides SFQ driver, SMSL receiver datalink to work at 30 Gbit/s with 30% perational margin and can work up to 113 Gbit/s of operational speed. Several test chips have been designed with contact bumps for fabrication in Hypres 4.5 kA/cm2 process to verify the simulation results of scattering matrix data and corresponding operational margin.