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ABSTRACT3D stacked wafer integration has the potential to improve multiprocessor system-on-chip (MPSoC) integration density, performance, and power efficiency. However, the power density of 3D MPSoCs increases with the number of active layers, resulting in high chip temperatures. This can reduce system reliability, reduce performance, and increase cooling cost. Thermal optimization for 3D MPSoCs imposes numerous challenges. It is difficult to manage assignment and scheduling of heterogeneous workloads to maintain thermal safety. In addition, the thermal characteristics of 3D MPSoCs differ from those of 2D MPSoCs because each stacked layer has a different thermal resistance to the ambient and verticallyadjacent processors have strong temperature correlation.We propose a 3D MPSoC thermal optimization algorithm that conducts task assignment, scheduling, and voltage scaling. A power balancing algorithm is initially used to distribute tasks among cores and active layers. Detailed thermal analysis is used to guide a hotspot mitigation algorithm that incrementally reduces the peak MPSoC temperature by appropriately adjusting task execution times and voltage levels. The proposed algorithm considers leakage power consumption and adapts to inter-layer thermal heterogeneity. Performance evaluation on a set of multiprogrammed and multithreaded benchmarks indicates that the proposed techniques can optimize 3D MPSoC power consumption, power profile, and chip peak temperature.

The effect of lattice mismatch on the chemical ordering of epitaxial FePt films was studied. The results showed that the lattice constant (c) of the FePt films decreased with increasing lattice mismatch ε from about 2.23% to 6.33%. Upon further increase of ε to about 8.8%, c increased. On the other hand, the variation of the lattice constant (a) of the FePt films showed a reversal behavior to that of c with the increased lattice mismatch. The ratio c∕a of the FePt films held a minimum of about 0.9466, while the chemical ordering degree and magnetic anisotropy constant held maximum values for ε around 6.33%. These results indicated that the strain from the lattice mismatch favored the ordering of the FePt films.