Globalfoundries claims a breakthrough in 3D stacking of chips with the demonstration of functional 20nm silicon wafers with integrated through-silicon vias.
The technique allows chips to be stacked on top of each other with circuit interconnections provided by the through-silicon vias (TSVs).
TSVs are vertical vias etched in a silicon wafer that are filled with a conducting material, enabling communication between vertically stacked integrated circuits.
Source:
http://www.electronicsweekly.com/Articles/2013/04/02/55866/globalfoundries-claims-3d-chip-breakthrough-with-tsvs.htm
