Analytical Modeling of Read Margin Probability Distribution Function of SRAM Cells in Presence of Process Variations and NBTI Effect

Abstract— In this work, we present an analytical model for calculating the Read Margin of 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 NBTI (negative bias temperature instability) 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 nm and 32 nm technologies. The comparison demonstrates a very high level of accuracy for the proposed model.