Development of cryopackaging and I/O technologies for high-speed superconductive digital systems

A cryocooled system with I/O interface circuits, which enables high-speed system operation of superconductive single-flux-quantum (SFQ) circuits at over 40 GHz, and the demonstration of a 47-Gbps SFQ 2 x 2 switch system are presented. The cryocooled system has 32 I/Os and cools an SFQ multi-chip module (MCM) to 4 K with a two-stage I W Gifford-McMahon cryocooler. An SFQ 4:1 multiplexer (MUX) and an SFQ 1:4 demultiplexer (DEMUX) have been designed to interface the speed gap between the I/O (similar to 10 Gbps/ch) and SFQ circuits (> 40 GHz). An SFQ 2x2 switch chip, in which the MUX/DEMUX and an SFQ 2x2 switch are integrated, and an 8-channel superconductive voltage driver (SVD) chip have been designed with an advanced cell library for a junction critical current density of 10 kA/cm(2). An SFQ 2 x 2 switch MCM has been made by flip-chip bonding the switch chip and SVD chip on a superconductive MCM carrier with phi 50-mu m InSn solder bumps. An SFQ 2 x 2 switch system, which is the switch MCM packaged in the cryocooled system, has been demonstrated up to a port speed of 47 Gbps for the first time.