SRAM Gauge: SRAM Health Monitoring via Cells Race

By shrinking transistors’ dimensions and, consequently, reducing the operating voltage in nano-scale CMOS technologies, the stability of SRAM cells has become a major reliability concern. SRAM cells’ robustness against undesirable bit-flips is commonly measured by Static Noise Margin (SNM). Degradation in SNM is mainly because of the gradual variations in transistors’ parameters due to aging. This work proposes a built-in SRAM health sensor capable of monitoring the SNM of individual SRAM cells in a memory block. The sensor is composed of extra non-operational sensor cells with different predefined SNMs. These sensor cells are put in a race with operational SRAM cells to determine their strength. The precision, sensing range, and robustness of the proposed sensor against process variation are adjustable at the cost of small area overhead. In our simulation setup, with the area overhead of 0.29%, the sensor monitors a wide range of SNMs from 275mV to 325mV, with a precision of 5mV.