Process scaling has resulted in an exponential increase of the number of transistors available to designers. Meanwhile, global interconnect has not scaled nearly as well, because global wires scale only in one dimension instead of two, resulting in fewer, high-resistance routing tracks. This paper evaluates the use of three-dimensional (3D) integration to reduce global interconnect by adding multiple layers of silicon with vertical connections between them using through-silicon vias (TSVs). Because global interconnect can be millimeters long, and silicon layers tend to be only tens of microns thick in 3D stacked processes, the power and performance gains by using vertical interconnect can be substantial. To address the thermal issues that arise with 3D integration, this paper also evaluates the use of near-threshold computing—operating the system at a supply voltage just above the threshold voltage of the transistors.
Specifically, we will discuss the design and test of Centip3De, a large-scale 3D-stacked near-threshold chip multiprocessor. Centip3De uses Tezzaron's 3D stacking technology in conjunction with Global Foundries' 130 nm process. The Centip3De design comprises 128 ARM Cortex-M3 cores and 256MB of integrated DRAM. Silicon measurements are presented for a 64-core version of the design.
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