SRAM Supply Voltage Scaling: a Reliability Perspective

SRAM leakage power is a significan fraction of the total power consumption on a chip. Various system level techniques have been proposed to reduce this leakage-power by reducing (scaling) the supply voltage. SRAM supply voltage scaling reduces the leakage-power, but it increases stored-data failure rate due to commonly known failure mechanisms, for example, soft-errors. This work studies SRAM leakage-power reduction using system level design techniques, with a data-reliability constraint. A statistical or probabilistic setup is used to model failure mechanisms like soft-errors or process-variations, and error-probability is used as a metric for reliability. Error models which combine various SRAM cell failure mechanisms are developed. In a probabilistic setup, the bit-error probability increases due to supply voltage reduction, but it can be compensated by suitable choices of error-correction code and data-refresh (scrubbing) rate. The trade-offs between leakage-power, supply voltage reduction, data-refresh rate, error-correction code, and decoding error probability are studied. The leakage-power - including redundancy overhead, coding power, and data-refresh power is set as the cost-function and an error-probability target is set as the constraint. The cost-function is minimized subject to the constraint, over the choices of data-refresh rate, error-correction code, and supply voltage. Using this optimization procedure, simulation results and circuit-level leakage-power reduction estimates are presented.