Leakage Optimization Using Mixed-Vth Cells: Vth Swapping and Cell Relocation

Multiple threshold voltage (multi-Vth) optimization reduces leakage by replacing low-Vth cells with high-Vth cells but is limited by tight design constraints and timing violations on critical paths. This paper proposes a novel approach using mixed-Vth cells, where pull-up and pull-down networks are independently optimized for different Vth types. By selectively assigning higher Vth to only one of the networks, the proposed method achieves significant leakage reduction without violating timing constraints. The methodology ensures to satisfy the constraint of minimum implant width through localized cell relocation. Experimental results show a reduction in leakage power by 22% on average with no timing violation in practical runtime, while the conventional cell-based method reduces 10% of leakage.