Connecting Chips With More Than 100 GHz Bandwidth

Connecting chips within a module is a basic requirement in transforming MMIC performance to system functionality. More and more applications demand for operation at high mm-wave frequencies or with ultra-large bandwidth. While semiconductor devices have seen tremendous progress in terms of their frequency limits, the chip interconnects lag behind and often form the bottleneck in realizing such systems. This paper reviews the broadband potential of the most common interconnect types in use and their performance demonstrated so far, covering wirebonding, approaches with chips embedded in a substrate, and flip-chip. Additionally, as an intermediate solution between system-on-chip and system-in-a-package, semiconductor hetero-integration on the chip-level is included. As is discussed, bond wire interconnects are most limited in bandwidth among the four types and reach the 100 GHz band only at the expense of narrowband characteristics. Dedicated embedded-chip packaging techniques show significantly better performance, bandwidths in the order of 100 GHz have been shown in the literature. Flip-chip has clearly the highest potential, interconnects covering the range from DC to 500 GHz have been demonstrated and are presented in the paper. Hetero-integration on the chip proves to allow for very broadband interconnects between elements and circuits on the compound chip as well: For an InP-on-BiCMOS process 325 GHz bandwidth were achieved and even higher values seem to be feasible.