Efficient Transistor-Level Sizing Technique under Temporal Performance Degradation due to NBTI

Abstract

Temporal performance degradation in VLSI circuits due to Negative Bias Temperature Instability (NBTI) has emerged as a challenging design issue in nano-scale technology. In this paper, we analyze the impact of NBTI degradation in circuit performance in terms of timing, and show that under worst case scenario, one can expect more than a 10% degradation in the maximum circuit delay after 3 years (~ 108 seconds) operation time. Based on this observation, we propose an efficient transistor-level sizing algorithm based on a modified Lagrangian Relaxation (LR) technique to account for the temporal degradation of circuit and guarantee lifetime reliability of circuit under NBTI. The technique reformulates the sizing problem by considering the fact that only the rising (0 rarr 1) delays of CMOS logic gates are affected by the NBTI. Experimental results on several ISCAS'85 benchmarks have shown that our proposed transistor-level sizing approach can reduce the area overhead of conventional cell-level sizing method by an average of 43%.