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Near/sub-threshold operation is promising to achieve energy minimization when high performance is not required. The device sizing in sub-threshold region is different from super-threshold region due to significantly different IV characteristics and impact of parasitic effects in these two regions. We have investigated the impact of the inverse narrow width effect (INWE) on transistor drain current in the near/sub-threshold region at three different technology nodes (90 nm, 65 nm, and 40 nm) and proposed an INWE-aware sub-threshold device sizing method to mitigate the impact of INWE to reduce delay, power consumption and area. We applied the proposed device sizing method to designing an INWE-aware standard cell library and achieved up to 20% less delay, 34% less power consumption and 47% less area, compared with the sub-threshold library designed using conventional sizing method. For further optimization, we proposed a dual-width library by combining the INWE-aware library and the minimum sized library. A near-threshold baseband processor designed with the dual width library achieved a total power consumption of ~ 4 μW with 6 MHz at 0.5 V, which is 30% better than the counterpart design.