When is 3D 2B?

A key facet of "More than Moore" scaling comes under the heading of "3D"—the stacking of multiple integrated-circuit dies using through-silicon vias (TSVs). Stacked-die products reached the marketplace decades ago, but with peripheral I/O on individual dies and interchip interconnect on the "side" of the stack. TSVs are a game changer, as this column explains.