Power, Performance, and Thermal Trade-offs in M3D-enabled Manycore Chips.

Monolithic 3D (M3D) technology enables unprecedented degrees of integration on a single chip. The miniscule monolithic inter-tier vias (MIVs) in M3D are the key behind higher transistor density and more flexibility in designing circuits compared to conventional through silicon via (TSV)-based architectures. This results in significant performance and energyefficiency improvements in M3D-based systems. Moreover, the thin inter-layer dielectric (ILD) used in M3D provides better thermal conductivity compared to TSV-based solutions and eliminates the possibility of thermal hotspots. However, the fabrication of M3D circuits still suffers from several non-ideal effects. The thin ILD layer may cause electrostatic coupling between tiers. Furthermore, the low-temperature annealing degrades the top-tier transistors and bottom-tier interconnects. An NoC-based manycore design needs to consider all these M3D- process related non-idealities. In this paper, we discuss various design challenges for an M3D-enabled manycore chip. We present the power-performance-thermal trade-offs associated with these emerging manycore architectures.