Ultralow Power Circuit Design With Subthreshold/Near-Threshold 3-D IC Technologies

The requirement of ultralow power and energy efficient systems is becoming more and more important with the increase in the use of miniaturized portable devices and unsupervised remote sensor systems. 3-D integration is an emerging technology that helps in reducing footprint as well as power. In this paper, we study in detail the combined benefits of 3-D ICs and low-voltage supply designs to obtain maximum energy efficiency. We implement different types of circuits in conventional 2-D and through-silicon-via-based 3-D designs at different supply voltages varying from nominal to subthreshold voltages. The impact of 3-D integration on these different types of circuits is analyzed. Our study is based on power and energy comparison of full GDSII layouts. Our study confirms that subthreshold/near-threshold circuits indeed offer a few orders of magnitude power versus performance tradeoff with further improvement due to 3-D implementation. In addition, 3-D designs reduce the footprint area up to 78% and wirelength up to 33% compared with the 2-D counterpart for individual design benchmarks. Our studies also show that thermal and IR drop issues are negligible in subthreshold 3-D implementation due to its extreme low-power operation. Finally, we demonstrate the low-power and high-memory bandwidth advantages of many-core 3-D subthreshold circuits.