A FinFET SRAM cell design with BTI robustness at high supply voltages and high yield at low supply voltages

Abstract

Summary In this paper, a SRAM cell structure which uses pMOS access transistors and predischarged bitlines is presented. By using the strained pMOS transistor technology, the degradation of the read static noise margin (SNM) at high supply voltages due to the aging, especially in the presence of symmetric stress, is suppressed. In contrast to conventional cell, the write margin of the proposed cell does not degrade considerably at low supply voltages. To assess the efficacy, the proposed cell is compared with conventional cell for two cases of unstrained and strained pMOS. A comparative study is performed using mixed mode device/circuit simulations for a gate length of 22 nm. The results show that the read SNM degradation due to the symmetric aging at the supply voltage of 1 V is about 6% after three years for the proposed strained structure, while degradations are 14%, 12%, and 11% for the unstrained proposed structure, unstrained, and strained conventional structures, respectively. In addition, the proposed cell has both read and write cell sigma yields higher than six for supply voltages ranging from 1 V down to 0.5 V while the other structures have read or write yields less than six at the minimum supply voltage. Through some work function tuning, the cell sigma yields of the other structures reach above six for both read and write while being still lower than those of the proposed structure. Copyright © 2015 John Wiley & Sons, Ltd.

DPCS

“…Second, by allowing for per-block power gating, both power rails must be routed in the wordline direction. Unfortunately, this is not a common approach in industry, where a thin-cell SRAM cell is preferred for above-threshold operation (e.g., as seen by layouts in Sinangil et al [2011] and Ebrahimi et al [2015]). However, others have used wordline-oriented rails successfully in a variety of low-voltage design scenarios [Calhoun and Chandrakasan 2006;Verma and Chandrakasan 2008;Singh et al 2008;Cheng et al 2014;Chang et al 2015].…”

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