Abstract-Negative Bias Temperature Instability (NBTI) is an important lifetime reliability problem in microprocessors. SRAM-based structures within the processor are especially susceptible to NBTI since one of the PMOS devices in the memory cell always has an input of '0'. Previously proposed recovery techniques for SRAM cells aim to balance the degradation of the two PMOS devices by attempting to keep their inputs at a logic '0' exactly 50% of the time. However, one of the devices is always in the negative bias condition at any given time. In this paper, we propose a technique called Recovery Boosting that allows both PMOS devices in the memory cell to be put into the recovery mode by slightly modifying the design of conventional SRAM cells. We present the circuit-level design of an issue queue that uses such cells and perform SPICElevel simulations to verify its functionality and quantify area and power consumption. We then conduct an architecturelevel evaluation of the performance and reliability of using an area-neutral design of such an issue queue using the M5 simulator and the SPEC CPU2000 benchmark suite. We show that recovery boosting provides a 56% improvement in the static noise margin for the issue queue while having very little impact on power consumption and a negligible loss in performance.

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NBTI is one of the most important silicon reliability problems facing processor designers today. The impact of NBTI can be mitigated at both the circuit and microarchitecture levels. In this paper, we propose a multi-level optimization approach, combining techniques at the circuit and microarchitecture levels, for reducing the impact of NBTI on the functional units (FUs) of a highperformance processor core. We perform SPICE simulations to evaluate the impact of circuit-level design optimizations to reduce the NBTI guardband in terms of area, delay, and power. We then propose a set of NBTI-aware dynamic instruction scheduling policies at the microarchitecture level and quantify their impact on application performance and guardband reduction through executiondriven simulation. We show that carefully combining techniques at both these levels provides the most attractive solution to reducing the guardband while imposing the least overhead in terms of area, power, delay, and application performance.

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