Variability Analysis of 6T and 7T SRAM Cell in Sub-45nm Technology

This paper analyses standard 6T and 7T SRAM (static random access memory) cell in light of process, voltage and temperature (PVT) variations to verify their functionality and robustness. The 7T SRAM cell consumes higher hold power due to its extra cell area required for its functionality constraint. It shows 60% improvement in static noise margin (SNM), 71.4% improvement in read static noise margin (RSNM) and 50% improvement in write static noise margin (WSNM). The 6T cell outperforms 7T cell in terms of read access time (TRA) by 13.1%. The write access time (TWA) of 7T cell for writing 1 is 16.6 x longer than that of 6T cell. The 6T cell proves it robustness against PVT variations by exhibiting narrower spread in TRA (by 1.2x ) and TWA (by 3.4x). The 7T cell offers 65.6% saving in read power (/?PWR) and 89% saving in write power (WPWR)- The APWR variability indicates that 6T cell is more robust against process variation by 3.9x. The 7T cell shows 1.3x wider write power (WpWR) variability indicating 6T cell s robustness against PVT variations. All the results are based on HSPICE simulation using 32 nm CMOS Berkeley Predictive Technology Model (BPTM).