Analytical Modeling of Read Margin Probability Distribution Function of Static Random Access Memory Cells in Presence of Process Variations and Negative Bias Temperature Instability Effect

Abstract

In this work, we present an analytical model for calculating the read margin of static random access memory (SRAM) cells as a function of different transistors parameters. Using this model and assuming normal distribution for the threshold voltages of transistors in the presence of process variations, the probability distribution function (PDF) of the read margin is analytically derived. In addition, the time variation of the PDF due to the negative bias temperature instability (NBTI) effect is also considered in the model. The accuracy of the model is verified by comparing its results with those of HSPICE simulations in 45 and 32 nm technologies. The comparison demonstrates a very high level of accuracy for the proposed model.