Critical Current (I-Crit) Based Spice Model Extraction For Sram Cell

Critical currents (I-CRIT) extracted from the N-curves of a 6-T SRAM bit cell have been shown in recent research to be important and effective figures of merit for the cell's stability and write-ability. SPICE models of cell transistors, therefore, not only need to fit closely to individual transistor's I-V characteristics, but also faithfully reproduce I(CRIT)s' behavior of the cell as a whole. A branch current analysis is performed to reveal individual transistors' impact on I(CRIT)s' and their key bias regions. Based on the insight from the analysis, an efficient SPICE model extraction flow is proposed that enables decoupled fine tuning of the pass-gate, pull-down, and pull-up transistor models to achieve satisfactory fit to I(CRIT)s without model extraction iterations.