Lifetime Reliability-Aware Digital Synthesis

Abstract

CMOS downscaling poses a growing concern for circuit lifetime reliability. Bias temperature instability (BTI) is a major source of transistor aging, causing a threshold voltage increase in CMOS devices, and affecting circuit timing. This paper presents an aging mitigation approach that can be incorporated into standard synthesis. We propose a technique to restructure the logic expressions for aging-critical gates and to reduce the BTI stress duty cycle. A new technology mapping strategy is demonstrated, including a forward pass to select the most suitable cells and implement the optimized logic, and a backward pass to validate remapped circuits by restricting the negative slacks. The negative slacks produced in the mapping stage are eliminated by gate-level optimization, which aims to optimize a circuit to improve lifetime reliability under timing and area constraints. It employs a sensitivity metric that can be adjusted according to the design specifications to pick the most favorable transformation in terms of timing, lifetime or both. Our results show a 59.1% lifetime improvement with 0.86% area overhead on average. Compared with conventional over-design, a 28.29% higher lifetime improvement is realized. In addition, our approach can optimize a circuit under each corner case, considering both process variations and input data.