Transmission of single-flux-quantum pulse between superconductor chips

Single-flux-quantum (SFQ) pulse transmission between superconductor chips mounted on a passive microstrip carrier is reported. In contrast to the earlier work based on a double-flux-quantum (DFQ) driver, we used an SFQ driver; that is, the simplest driver. To deal with transmission loss at solder-bump bonds, we improved the receiver’s sensitivity by reducing its critical current, and optimized the SFQ driver to have as large an output amplitude as possible with a sufficient bias margin. Chip-to-chip transmission on a passive microstrip carrier with 50μm solder-bump bonds up to 60Gbps has been achieved at a junction critical current density of 2.5KA∕cm2.