SRAM On-Chip Monitoring Methodology for High Yield and Energy Efficient Memory Operation at Near Threshold Voltage

Low power design by near-threshold voltage (NTV) operation is very attractive since it affords to considerably mitigate the sharp increase of power dissipation. However, one key barrier for the use of NTV operation is the significant increase of the SRAM failure. In this work, we propose an on-chip SRAM monitoring methodology that is able to accurately predict the minimum voltage, Vddmin, on each die that does not cause SRAM failure under a target confidence level. Precisely, we propose an SRAM monitor, from which we measure a maximum voltage, Vfail that causes functional failure on that SRAM monitor. Then, we propose a novel methodology of inferring SRAM Vddmin on each die from the measured Vfail of SRAM monitor on the same die where Vfail-Vddmin correlation table is built-up in design infra development phase, and Vddmin can be directly derived from the measured Vfail referencing the correlation table in silicon production phase. Through experiments, we confirm that our proposed methodology is able to save leakage power by 7.43%, read energy by 3.98%, and write energy by 4.06% in SRAM bitcell array over that by applying a uniform minimum voltage for all dies while meeting the same yield constraint.