Impact of statistical variability and charge trapping on 14 nm SOI FinFET SRAM cell stability

Variability is a critical concern for the stability and yield of SRAM with minimized size. We present a study of a 14 nm node SOI FinFET SRAM cell under the influence of statistical variability and random charge trapping due to positive/negative bias temperature instability (P/NBTI). Low channel doping is believed to be one of the main advantages of FinFETs in reducing statistical variability, but fin and gate edge roughness and metal gate granularity can cause significant variability and affect SRAM stability. The noise margins are largely skewed, and read and write noise margins are decorrelated due to statistical variability. Under heavy stress conditions cell read noise margin can be degraded by 30mV on average due to charge trapping, and its 6σ-yield becomes even worse due to the enhanced variability in N/PBTI.