Reliability improvement of logic and clock paths in power-efficient designs

Performance degradation due to transistor aging is a significant impediment to high-performance IC design due to increasing concerns of reliability mechanisms such as negative-bias-temperature-instability (NBTI). The concern only grows with technology scaling as the effects of positive bias temperature instability (PBTI) is becoming prominent in future technologies and compounding with the effects of NBTI. Although aging of transistor is inevitable and the magnitude of degradation due to aging varies depending upon the context. Specifically, in power-efficient systems designs, the logic and clock paths are susceptible to static stress resulting in peak degradation due to BTI occurrence when clock is gated. In this article, we present the reliability impact of making systems power efficient and propose a design-for-reliability methodology that can be used in conjunction with low-power design techniques to alleviate the stress conditions caused by rendering circuits in idle state. The technique—BTI-Refresh, is shown to be applicable to both logic and clock paths alike and focuses on preventing prolonged static stress using periodic refreshes to achieve alternating stress. The mechanism is shown to integrate seamlessly into the design at gate-level without requiring any architectural or RT-level changes. Using ISCAS benchmarks and Kogge-Stone-Adder circuits, it is shown to reduce the aging effect in logic path delay due to static stress by up to 50% with negligible area and power overhead. BTI-Refresh is extended to clock-paths to prevent pulse-width degradation due to static aging and with minimal clock-skew.