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This paper studies read stability and write ability of various dual-Vt configurations of an SRAM cell in an array considering the process-induced intra-die threshold voltage Vt variations using N-curve metrics. The effects of process induced intra-die Vt variations in 11 different dual-Vt cell combinations are evaluated and compared. In this work, N-curve metrics are adopted for the analysis as information about read stability and write ability can be obtained using a single curve. The statistical parameters like mean, standard deviation, average deviation for each of the metrics is found for all the 11 dual -Vt configurations using Monte-Carlo simulations. The effects of intra-die variations are considered as they are prominent at nanometer technologies. The comparisons are made with the help of power noise margins which are obtained by finding the product of mean of voltage noise margins and mean of current noise margins. The variances and percentage variances from the mean, of voltage and current margins for all combinations are tabulated and analyzed. Comparisons are also made based on rive different yield values. Thus given a range of a metric and the yield value one can choose the type of configuration of SRAM cell.
Date of Conference: 24-27 March 2008