Normal and Reverse Temperature Dependence in Variation-Tolerant Nanoscale Systems with High-k Dielectrics and Metal Gates

The delay dependence on temperature reverses at increasingly larger supply voltages as technology scales into the nanometer regime, causing delay to decrease as temperature increases. This reversal can be problematic for variation-tolerant systems using critical path replicas to determine delay guardbands, as delay may no longer indicate when the system is in danger of thermal runaway. Adaptive voltage scaling, commonly used in variation-tolerant systems, further complicates the temperature impact, as the range of voltages may intersect both temperature regions. In this paper, it is shown that use of high-k dielectrics and metal gates increases the supply voltage where this reversal occurs by 40% compared to low-k, poly gate technologies. 45, 32, and 22 nm models are examined, and the reversal voltage is shown to approach 90% of nominal voltage at 22 nm, making the effect important even for non-adaptive designs. Techniques to account for these complex temperature dependencies are proposed to ensure functionality under all conditions.