Approximate Yield Estimation of Correlated Failure Events for Near-threshold SRAM

Abstract

Abstract In advanced manufacturing technology, SRAM yield estimation with correlation is a significant challenge due to process variations and structures especially at low voltage. In this paper, Double Asymptotic Probability Approximation (DAPA) method with Subset Analytical Model (SAM) is proposed to effectively estimate the probability of correlated failure event. SAM models SRAM failure events based on simulation of subsets of the equivalent circuit. DAPA obtains the recursive function of partial failure rate. The key idea is to approximate the failure rate of the entire system based on a linear combination of partial failure rates by decoupling failure correlation. Under TSMC 28 nm process, (M=N=8) SRAM failure rate is estimated at 500 mV with an error of less than 5% by the proposed method. Besides 2.5 hours of modeling consumption, the calculation can be completed in 7 seconds, which greatly reduces SRAM failure estimation time, compared with Monte Carlo method.