Analytical model for SRAM dynamic write-ability degradation due to gate oxide breakdown

Progressive gate oxide breakdown is emerging as one of the most important source of stability degradation in nanoscale SRAMs, especially at lower supply voltages. Low voltage operation of SRAM arrays is critical in reducing the power consumption of embedded microprocessors, thus necessitating the lowering of V_min. However, the oxide breakdown undesirably increases F_min due to increase in dynamic write failures and eventually static write failures as the supply voltage decreases. In this work, we describe an analytical model based on the Kohlrausch-William-Watts (KWW) function to predict the degradation in the WL_crit as the oxide breakdown increases. The KWW model also accurately predicts the efficacy of the word-line boosting and Vdd lowering write-assist techniques in reducing WL_crit. Simulation results from an industrial low-power 32nm SRAM show that model is accurate to within 1% of SPICE across range of supply voltages and severity of oxide breakdown with orders of improvement in runtime.