Critical current (ICRIT) 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_CRITs¿ behavior of the cell as a whole. A branch current analysis is performed to reveal individual transistors¿ impact on I_CRITs¿ 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_CRITs without model extraction iterations.