Mechanical Stress Aware Optimization for Leakage Power Reduction

摘要

Process-induced mechanical stress is used to enhance carrier transport and achieve higher drive currents in current complementary metal-oxide—semiconductor technologies. This paper explores how to fully exploit the layout dependence of stress enhancement and proposes a circuit-level, block-based, stress-enhanced optimization algorithm that uses stress-optimized layouts in conjunction with dual-$V_{rm th}$ assignment to achieve optimal power-performance tradeoffs. We begin by studying how channel stress and drive current depend on layout parameters such as active area length and contact placement, while considering all layout-dependent sources of mechanical stress in a 65 nm industrial process. We then investigate the three main layout properties that impact mechanical stress in this process and discuss how to improve stress-based performance enhancement in standard cell libraries. While varying the stress-altering layout properties of a number of standard cells in a 65 nm industrial library, we show that “dual-stress” standard cell layouts (analogous to “dual-$V_{rm th}$”) can be designed to achieve drive current differences up to ${sim}{rm 14}%$ while incurring less than half the leakage penalty of dual-$V_{rm th}$. Therefore, when the flexibility of “dual-stress” assignment is combined with dual-$V_{rm th}$ assignment (within the proposed joint optimization framework), simulation results for a set of benchmark circuits show that leakage is reduced by ${sim}{rm 24}%$ on average, for iso-delay, when compa-nred to dual-$V_{rm th}$ assignment. Since mobility enhancement does not incur the exponential leakage penalty associated with $V_{rm th}$ assignment, our optimization technique is ideal for leakage power reduction. However, our framework can also be used to achieve higher performance circuits for iso-leakage and our joint optimization framework can be used to reduce delay on average by ${sim}{rm 5}%$. In both cases, the proposed method only incurs a small area penalty $({u0003C;}{rm 0.5}%)$.