CROWNE: current ratio outliers with neighbor estimator

Increased leakage and process variations make distinction between fault-free and faulty chips by I_DDQ test difficult. Earlier, the concept of current ratios (CR) was proposed to screen defective (outlier) chips. However, it is not capable of catching certain defects. Neighboring chips on a wafer have similar fault-free parameters that are correlated through the underlying fabrication process. Based on this observation, an alternative test metric called neighbor current ratio (NCR) was proposed. NCR screens outlier chips based on their nonconformance to local variation in I_DDQ. In this paper, we explore the correlation between different vectors that yield CR and NCR values. The effectiveness of NCR along with additional test parameters to screen outlier chips is evaluated using industrial test data.