Clock Tree Design Considerations in The Presence of Asymmetric Transistor Aging

Reliability is critical for integrated circuits (ICs) to ensure accurate operation over their lifetimes. With the rise of mission-critical systems, reliability continues to be ever more essential. However, recent advancements in semiconductors have revealed that ICs are vulnerable to reliability issues, particularly those stemming from transistor aging. Transistor aging refers to the gradual deterioration of a transistor’s performance over time and depends mainly on the bias-temperature instability (BTI). The BTI severely affects IC reliability, degrading performance and causing critical circuit failures due to timing violations. Additionally, asymmetric aging occurs when the degradation is unevenly distributed, intensifying timing violations and reliability concerns. This paper examines how asymmetric transistor aging affects clock tree design and highlights the role of useful skew, clock gates, and asymmetry between clock buffer delays and net delays in amplifying reliability concerns. Furthermore, we propose new design flow guidelines to address asymmetric-aging-related violations in clock trees.