Globalfoundries has demonstrated a working 20nm chip using through-silicon vias (TSV). Glofo has been looking at TSV as a method of stacking chips and TSMC and Nvidia have also dabbled with stacked designs.
Glofo claims it can use copper as the TSV fill material and that TSVs could be used in the transition from 28nm to 20nm. Of course, AMD will be the top client for Glofo’s 20nm process, but it is still unclear whether Glofo will be able to start producing TSVs at 20nm.
It is still unclear when the 20nm TSV process will be ready for volume production, and it might take a while. Globalfoundries believes that the promise of 3D chip stacking will soon be a reality, but then again we’ve heard this before.
However, the fact that it already has working silicon is a very encouraging sign.