Optimal technology selection for minimizing energy and variability in low voltage applications

Ultra Low voltage operation has recently drawn significant attention due to its large potential energy savings. However, typical design practices used for super-threshold operation are not necessarily compatible with the low voltage regime. Here, radically different guidelines may be needed since existing process technologies have been optimized for super-threshold operation. We therefore study the selection of the optimal technology in ultra low voltage designs to achieve minimum energy and minimum variability which are among foremost concerns. We investigate five industrial technologies, from 250 nm to 65 nm. We demonstrate that mature technologies are often the best choice in very low voltage applications, saving as much as ~1800X in total energy consumption compared to a poorly selected technology. In parallel, the effect of technology choice on variability is investigated, when operating at the energy optimal design point. The results show up to a 4X improvement in delay variation due to global process shift and mismatch when using the most advanced technologies despite their large variability at nominal V_dd.