Sensitivity of static noise margins to random doping variations in 6T SRAM cells

SRAM bitcells are most negatively affected by random fluctuations of the doping concentration. The Static Noise Margins (SNM) of these circuits fluctuate from one cell to another because of random doping variations, mismatch, and inaccuracies during the fabrication process. In this article a new technique is presented for the analysis of SNM that is based on the solution of the complete set of transport equations that are solved self- consistently for the whole circuit. In this "mixed-mode" simulation the effects of the random doping fluctuations are analyzed by "perturbing" all transport equations with respect to the fluctuating quantities at each location inside the device. This technique overcomes the disadvantages of compact models and provides information that can be used in the design of SRAMs with low fluctuation of SNM.