A Sub-600-mV, Fluctuation Tolerant 65-nm CMOS SRAM Array With Dynamic Cell Biasing

Fluctuation limitations on scaling CMOS SRAM cell transistor dimensions and operating voltages are demonstrated by measuring local stochastic distributions of 65-nm PDSOI CMOS SRAM cell storage node voltages during read, write, and retention modes of operation. These measurements reveal insights into terminal voltage dependencies of cell margin distributions - observations that are engaged to increase cell immunity to random V_T fluctuations by several orders of magnitude by biasing the cell terminal voltages dynamically with a read-write asymmetry. Combinations of circuit techniques implementing these dynamic cell biasing schemes are demonstrated in a 9 kb times74 b PDSOI CMOS SRAM array with a conventional 65 nm SRAM cell and an ABIST. Measurements demonstrate these techniques to enable V_MIN reductions of over 200 mV - lowering measured V_MIN to 0.54 V and 0.38 V/0.50 V for single and dual V_DD implementations, respectively. The techniques consume a 10%-12% overhead in area, impact performance marginally (<5%) and also enable over 50% reduction in cell leakage.